Patent Application
20120021421
The present invention relates to a method for predicting and/or diagnosing a cardiovascular or metabolic disease in a subject.
Metabolic diseases such as type 2 diabetes or obesity and their vascular complications are a major public health issue, the importance of which should increase with the spread of the obesity epidemic. The set-up of a low tonus but chronic metabolic-type inflammatory reaction is one of the cellular mechanisms that appear early during the development of these diseases. The active molecules which are released by the inflammatory process lower the insulin action and favour the development of fat tissue and atheroma plaques.
A growing body of evidence supports a link between digestive microflora, metabolic diseases and atherosclerosis. From an epidemiological point of view, large prospective observational studies showed that chronic infectious diseases involving Gram-negative bacteria such as periodontis predict the incidence of acute cardiovascular events (Howell et al. (2001) J. Am. Coll. Cardiol. 37:445-450, Dietrich et al. (2008) Circulation 117:1668-1674). Recently, a large population based study established the predictive value of periodontis on diabetes. Furthermore, many cross-sectional trials have reported the presence of various bacterial pathogens in the arterial vessel wall.
Accordingly, it has been hypothesized that the presence of bacteria could predict the occurrence of a metabolic and/or cardiovascular disease. Diagnosis methods of metabolic and cardiovascular diseases comprising the detection of bacteria have thus been proposed. Nevertheless, the only available methods need to investigate the presence of each bacterial strain potentially involved in the genesis of metabolic or cardiovascular diseases. Such methods are consequently costly and difficult to be performed in routine and in a large scale.
There is thus a need for new methods and new markers for predicting metabolic and/or cardiovascular diseases, which could be used routinely, in a large scale and at a low cost.
The present inventors have demonstrated that change in bacterial lipopolysaccharides (LPS) blood concentration, the main components of the outer wall of Gram-negative bacteria and the natural ligands of Toll-like receptor 4 which has been identified as central in the atherosclerosis process, was a causative triggering factor of weight intake and diabetes (Cani et al. (2007) Diabetes 56:1761-1772, Cani et al. (2008) Diabetes 57:1470-1481). From these results, they hypothesized that bacterial LPS could play a key role in humans on the atherosclerotic process and the development of metabolic diseases. Nevertheless, blood LPS concentration was not considered as a good candidate as marker of metabolic and/or cardiovascular diseases because 1) LPS was difficultly assayable in a blood sample; 2) its blood concentration could vary rapidly according to the feeding status and 3) no significant association between plasma LPS concentration and metabolic parameters of atherosclerotic plaques could be observed in a french population-based sample. Furthermore, no significant association between plasma LPS concentration in human and cardiovascular events has been reported so far.
The present invention arises from the unexpected finding, by the inventors, that the concentration of bacterial DNA in the blood of a subject is a reliable risk marker and a predictor of metabolic and/or cardiovascular diseases.
Thus, the present invention relates to an in vitro method for predicting and/or diagnosing a cardiovascular and/or metabolic disease in a subject, which method comprises determining the concentration of bacterial DNA in a biological sample of said subject.
In the context of the invention, a “cardiovascular disease” refers to a disease that involves the heart or blood vessels (arteries and veins). More particularly, a cardiovascular disease according to the invention denotes a disease, lesion or symptom associated with an atherogenesis process that affects the cardiovascular system. It includes especially the conditions in which an atheroma plaque develops as well as the complications due to the formation of an atheroma plaque (stenosis, ischemia) and/or due to its evolution toward an acute ischemic stroke (thrombosis, embolism, infarction, arterial rupture).
Cardiovascular diseases include coronary artery disease, coronary heart disease, hypertension, atherosclerosis, in particular iliac or femoral atherosclerosis, angina pectoris, thrombosis, heart failure, stroke, vascular aneurysm, vascular calcification, myocardial infarction, vascular stenosis and infarction, and vascular dementia. Preferably, the cardiovascular disease according to the invention is selected from the group consisting in coronary artery disease, hypertension, atherosclerosis, vascular aneurysm, vascular calcification, vascular dementia and heart failure. More preferably, the cardiovascular disease according to the invention is atherosclerosis. Most preferably, the cardiovascular disease according to the invention is atherosclerotic carotid plaques.
As used herein, a “coronary artery disease” denotes a disease corresponding to the end result of the accumulation of atheromatous plaques within the walls of the arteries that supply the myocardium with oxygen and nutrients. It is one of the most common causes of coronary heart disease.
As used herein, a “coronary heart disease” denotes a progressive disease, due to a bad irrigation of the heart muscle, consecutive to the narrowing (stenosis) or calcification (sclerosis) of a coronary artery. The complete obstruction of a coronary artery leads to myocardial infarction.
As used herein, “hypertension”, also referred to as “high blood pressure”, “HTN” or “HPN”, denotes a medical condition in which the blood pressure is chronically elevated.
As used herein, “atherosclerosis” denotes a disease affecting arterial blood vessels. Atherosclerosis can be characterized by a chronic inflammatory response in the walls of arteries, mainly due to the accumulation of macrophages and promoted by low density lipoproteins without adequate removal of fats and cholesterol from macrophages by functional high density lipoproteins.
As used herein, an “atheroma plaque” or “atherosclerotic plaque” refers to a lesion of vessel walls. Preferably, an “atherosclerotic plaque” comprises a lipid core and a fibrous cap, said cap being constituted by smooth muscle cells, collagens and an extracellular matrix and isolating the lipid core from the arterial lumen. Atherosclerotic plaques may be found for example in the aorta, the carotid, or in the coronary artery. When the plaque comprises a thin fibrous cap (about 65 to 150 μm thick) and a considerable lipid core, they are referred to as “vulnerable atherosclerotic plaques” or “vulnerable atheroma plaques” or “vulnerable plaques”. These plaques, which are prone to rupture, may be found in coronary arteries and in aorta and its branches.
As used herein, “angina pectoris” or “angina” denotes a severe chest pain due to ischemia of the heart muscle.
As used herein, “thrombosis” denotes the formation of a blood clot inside a blood vessel.
As used herein, “heart failure” denotes a condition in which a problem with the structure or function of the heart impairs its ability to supply sufficient blood flow to meet the body's needs.
As used herein, a “stroke” denotes the rapidly developing loss of brain functions due to a disturbance in the blood vessels supplying blood to the brain.
As used herein, a “vascular aneurysm” or “aneurysm” denotes a localized, blood-filled dilation of a blood vessel caused by a disease or weakening of the vessel wall. Aneurysms most commonly occur in arteries at the base of the brain and in the aorta.
As used herein, an “infarction” denotes the process resulting in a macroscopic area of necrotic tissue in some organ caused by loss of adequate blood supply. In particular, a “myocardial infarction” denotes the interruption of blood supply to part of the heart.
As used herein, a “vascular dementia” denotes a degenerative cerebrovascular disease that leads to a progressive decline in memory and cognitive functioning. It includes in particular multi-infarct dementia (multiple large and complete infarcts), post-hemorrhage dementia, subcortical vascular dementia (small vessel disease) and mixed demention (combination of Alzheimer disease and vascular dementia).
In the context of the invention, a “metabolic disease” denotes a disease that disrupts normal metabolism. Preferably, the metabolic disease according to the invention is a carbohydrate metabolism disorder.
As used herein a “carbohydrate metabolism disorder” denotes a disease wherein the metabolism of carbohydrate, for example of glucose, is disrupted. Carbohydrate metabolism disorders include diabetes, high fasting glycemia, overweight and obesity.
As used herein, “diabetes” denotes a syndrome of disordered metabolism, usually due to a combination of hereditary and environmental causes, resulting in abnormally high blood sugar levels.
As used herein, “high fasting glycemia” denotes a syndrome of disordered metabolism, resulting in a glycemia of more than 6.1 mmol/l.
As used herein, “overweight” denotes a condition in which excess body fat has accumulated to such an extent that health may be negatively affected. Overweight is commonly defined as a body mass index of 25 kg/m2 or higher.
As used herein, “obesity” denotes a condition in which excess body fat has accumulated to such an extent that health may be negatively affected. Obesity is commonly defined as a body mass index of 30 kg/m2 or higher.
In the context of the invention, “bacterial DNA” refers to a DNA belonging to any bacteria. In particular, a bacterial DNA according to the invention denotes a DNA sequence from the genome of a bacterium.
Preferably, the bacterial DNA is 16S DNA and/or LpxB DNA.
As used herein, “16S DNA” refers to the gene encoding the 16S ribosomal RNA (16S rRNA) constituted of about 1500 nucleotides, which is the main component of the small prokaryotic ribosomal subunit (30S). 16S DNA is highly conserved among bacteria. The reference Escherichia coli 16S rRNA gene sequence corresponds to SEQ ID NO: 1745 (called rrsA). In the context of the invention, 16S DNA refers to any sequence corresponding to SEQ ID NO: 1745 in other bacterial strains.
As used herein, “LpxB DNA” refers to the bacterial LpxB gene. The LpxB gene refers to a bacterial gene encoding the lipid A disaccharide synthase that catalyses the condensation of 2,3-bis(3-hydroxymyristol)-β-D-glucosaminyl 1-phosphate and UDP-2,3-bis(3-hydroxymyristoyl)glucosamine (lipid X) to form lipid A disaccharide. This reaction represents one of the first enzymatic reactions involved in lipid A biosynthesis. The reference Escherichia coli LpxB DNA sequence corresponds to SEQ ID NO: 1746. In the context of the invention, LpxB DNA refers to any sequence corresponding to SEQ ID NO: 1746 in other bacterial strains.
The present invention relates to an in vitro method for predicting and/or diagnosing a cardiovascular and/or metabolic disease in a subject, which method comprises determining the concentration of bacterial DNA in a biological sample of said subject.
As used herein, a “diagnosing method” or “diagnostic method” or “diagnosis” refers to a method for determining whether an individual suffers from a disease.
As used herein, a “predicting method” refers to a method for determining whether an individual is likely to develop a disease.
In the context of the present invention, a “subject” denotes a human or non-human mammal, such as a rodent (rat, mouse, rabbit), a primate (chimpanzee), a feline (cat), a canine (dog). Preferably, the subject is human.
As used herein, the term “biological sample” means a substance of biological origin. Examples of biological samples include, but are not limited to, blood and components thereof such as serum, plasma, platelets, subpopulations of blood cells such as leucocytes; urine, and tissues such as adipose tissues, hepatic tissues and the like. Preferably, a biological sample according to the present invention is a blood, serum, plasma, leucocytes, urine, adipose tissue or hepatic tissue sample.
In a particular embodiment, the method as defined above is for predicting and/or diagnosing a cardiovascular and metabolic disease in a subject and comprises determining the bacterial 16S DNA concentration and the LpxB DNA concentration in the biological sample of said subject.
In another particular embodiment, the method as defined above is for predicting and/or diagnosing a cardiovascular disease in a subject and comprises determining the LpxB DNA concentration in the biological sample of said subject.
In still another particular embodiment, the method as defined above is for predicting and/or diagnosing a metabolic disease in a subject and comprises determining the bacterial 16S DNA concentration in the biological sample of said subject. Preferably, this method further comprises determining LpxB DNA concentration in the biological sample of said subject.
Preferably, the bacterial DNA concentration is measured by polymerase chain reaction (PCR), more preferably by quantitative PCR (qPCR), most preferably by real-time quantitative PCR (RT-qPCR).
As used herein, “real-time quantitative PCR”, “real-time polymerase chain reaction”, or “kinetic polymerase chain reaction” refers to a laboratory technique based on the polymerase chain reaction, which is used to amplify and simultaneously quantify a targeted DNA molecule. It enables both detection and quantification (as absolute number of copies or relative amount when normalized to DNA input or additional normalizing genes) of a specific sequence in a sample. Two common methods of quantification are the use of fluorescent dyes that intercalate with double-stranded DNA, and modified DNA oligonucleotide probes that fluoresce when hybridized with a complementary DNA.
The present inventors specifically designed a method enabling the accurate determination of the bacterial 16S DNA concentration in a biological sample of a subject. In particular, this method enables discriminating bacterial 16S DNA and mitochondrial DNA.
The invention therefore also relates to an in vitro method for determining the bacterial 16S DNA concentration in a biological sample of a subject comprising the steps consisting of:
Y=Bottom+(Top−Bottom)/[1+10̂((Log EC50−X)*HillSlope)]
wherein
X=Log 10(mitochondrial DNA/bacterial 16S DNA), and
Y=−Rn′ read at the melting temperature of mitochondrial DNA/−Rn′ read at the melting temperature of bacterial 16S DNA;
As used herein, the term “amplifying” or “amplification” refers to the multiplication of a DNA template. Preferably, the amplification of step a) is performed by PCR, more preferably by quantitative PCR, most preferably by real-time quantitative PCR. Preferably, when the amplification is performed by PCR, a reporter that produces fluorescence, such as SYBR Green, is used.
In the context of the invention, the term “universal primers” refers to primers comprising a sequence which is able to hybridize to 16S DNA from essentially any origin. Preferably, the universal primers according to the invention are primers comprising a sequence selected from the group consisting of the sequence 5′-ACTCCTACGGGAGGCAGCAGT-3′ (SEQ ID NO: 1748) and the sequence 5′-GTATTACCGCGGCTGCTGGCAC-3′ (SEQ ID NO: 1749).
As used herein, the term “melting temperature” refers to the temperature wherein the DNA double strands dissociate. As known from the person skilled in the art, the melting temperature depends on the GC content of the DNA. The present inventors have demonstrated that the melting temperature of mitochondrial DNA was 75.5° C. whereas the melting temperature of bacterial 16S DNA was 82° C., which enables discriminating both types of DNA.
As used herein, the expression “standard curve” refers to a method of plotting assay data that is used to determine the concentration of a substance and which is first performed with various known concentrations of a substance similar to that being measured.
In the context of the invention, the term “Bottom” refers to the lower value of the standard curve.
As used herein, the term “Top” refers to the maximal value of the standard curve.
As used herein, the term “Log EC50” refers to the Log 10 value of the quantity of mitochondrial DNA/quantity of bacterial 16S DNA ratio that gives a −Rn′ half way between bottom and top.
As used herein, the term “HillSlope” describes the steepness of the family of response curves.
The present invention also relates to an isolated nucleic acid which comprises a sequence that hybridizes specifically under high stringency conditions to LpxB DNA or bacterial 16S DNA and to the use, preferably in vitro, of at least one isolated nucleic acid which comprises a sequence that hybridizes specifically under high stringency conditions to LpxB DNA or bacterial 16S DNA for detecting the presence of bacteria in a biological sample of a subject.
As used herein, the term “isolated nucleic acid” refers to both RNA and DNA, including cDNA, genomic DNA, and synthetic DNA. Nucleic acids can have any three-dimensional structure. A nucleic acid can be double-stranded or single-stranded (i.e., a sense strand or an antisense strand). Non-limiting examples of nucleic acids include genes, gene fragments, exons, introns, messenger RNA (mRNA), transfer RNA (tRNA), ribosomal RNA, siRNA, micro-RNA, ribozymes, cDNA, recombinant nucleic acids, and branched nucleic acids. A nucleic acid may contain unconventional or modified nucleotides. Isolated nucleic acids according to the invention may be purified or recombinant.
In the context of the invention, the terms “hybridize” or “hybridization,” as is known to those skilled in the art, refer to the binding of a nucleic acid molecule to a particular nucleotide sequence under suitable conditions, namely under stringent conditions.
The term “stringent conditions” or “high stringency conditions” as used herein corresponds to conditions that are suitable to produce binding pairs between nucleic acids having a determined level of complementarity, while being unsuitable to the formation of binding pairs between nucleic acids displaying a complementarity inferior to said determined level. Stringent conditions are the combination of both hybridization and wash conditions and are sequence dependent. These conditions may be modified according to methods known from those skilled in the art (Tijssen, 1993, Laboratory Techniques in Biochemistry and Molecular Biology—Hybridization with Nucleic Acid Probes, Part I, Chapter 2 “Overview of principles of hybridization and the strategy of nucleic acid probe assays”, Elsevier, New York). Generally, high stringency conditions are selected to be about 5° C. lower than the thermal melting point (Tm), preferably at a temperature close to the Tm of perfectly base-paired duplexes (Andersen, Nucleic acid Hybridization, Springer, 1999, p. 54). Hybridization procedures are well known in the art and are described for example in Ausubel, F. M., Brent, R., Kingston, R. E., Moore, D. D., Seidman, J. G., Smith, J. A., Struhl, K. eds. (1998) Current protocols in molecular biology. V. B. Chanda, series ed. New York: John Wiley & Sons.
High stringency conditions typically involve hybridizing at about 50° C. to about 68° C. in 5×SSC/5× Denhardt's solution/1.0% SDS, and washing in 0.2×SSC/0.1% SDS at about 60° C. to about 68° C.
As used herein, the expression “hybridizes specifically” indicates that the nucleic acid of a determined sequence displays a sufficient degree of complementarity with a target sequence to form a stable binding between the nucleic acid and the target sequence and to avoid non-specific binding with a non-target sequence, under high stringency conditions. The degree of complementarity is calculated by comparing the sequence of said nucleic acid optimally aligned with the complementary target sequence, determining the number of positions at which the nucleic acid bases are complementary to yield the number of complementary positions, dividing the number of complementary positions by the total number of positions of the target sequence, and multiplying the result by 100 to yield the degree of complementarity. The degree of complementarity may be determined routinely using BLAST programs (basic local alignment search tools) and PowerBLAST programs known in the art (Altschul et al., (1990) J. Mol. Biol. 215: 403-410; Zhang and Madden (1997) Genome Res. 7:649-656).
In a particular embodiment, the at least one isolated nucleic acid as defined above is used, preferably in vitro, for predicting and/or diagnosing a metabolic and/or cardiovascular disease in a subject.
In a preferred embodiment, said nucleic acid is a probe or a primer.
As used herein, a “probe” refers to an oligonucleotide capable of binding in a base-specific manner to a complementary strand of nucleic acid. Probes according to the invention may be purified or recombinant. They may be labelled with a detectable moiety, i.e. a moiety capable of generating a detectable signal, such as radioactive, calorimetric, fluorescent, chemiluminescent or electrochemiluminescent signal. Numerous such detectable moieties are known in the art. By way of example, the moiety may be a radioactive compound or a detectable enzyme (e.g. horseradish peroxidase (HRP)). Preferably, the probe according to the invention comprises or is constituted of from about 10 to about 1000 nucleotides.
As used herein, the term “primer” refers to an oligonucleotide which is capable of annealing to a target sequence and serving as a point of initiation of DNA synthesis under conditions suitable for amplification of the primer extension product which is complementary to said target sequence. The primer is preferably single stranded for maximum efficiency in amplification. Preferably, the primer is an oligodeoxyribonucleotide. The length of the primer depends on several factors, including temperature and sequence of the primer, but must be long enough to initiate the synthesis of amplification products. Preferably the primer is from 10 to 35 nucleotides in length. More preferably, the primer is from 15 to 30 nucleotides in length. Most preferably, the primer is 22 or 29 nucleotides in length. A primer can further contain additional features which allow for detection, immobilization, or manipulation of the amplified product. The primer may furthermore comprise covalently-bound fluorescent dyes, which confer specific fluorescence properties to the hybrid consisting of the primer and the target sequence or non covalently-bound fluorescent dyes which can interact with the double-stranded DNA/RNA to change the fluorescence properties. Fluorescent dyes which can be used are for example SYBR-green or ethidium bromide.
The present inventors have designed degenerated primers able to amplify the LpxB gene in all bacterial genomes currently registered in NCBI database, in a region corresponding to nucleotides 154 to 299 in Escherichia coli. These primers border a region of 146 nucleotides which amplifies various DNA fragments corresponding to LpxB genes.
Accordingly, the present invention also relates to an isolated nucleic acid which comprises a sequence selected from the group consisting of the sequence 5′-GAAGCNTGGTANGANATGGAAG-3′ (SEQ ID NO: 1), wherein N in 6th position from 5′ is 90% C or 10% T, N in 12th position from 5′ is 60% C or 40% T and N in 15th position from 5′ is 60% A or 40% G, and the sequence 5′-GGNGCNTCNATNCCNACNAANACATCNGG-3′ (SEQ ID NO: 10), wherein N in 3rd position from 5′ is 50% C or 50% G, N in 6th position from 5′ is 70% C or 30% T, N in 9th position from 5′ is 90% A or 10% G, N in 12th position from 5′ is 50% A, 15% C or 35% T, N in 15th position from 5′ is 60% A, 10% C or 30% G, N in 18th position from 5′ is 90% A or 10% G, N in 21st position from 5′ is 45% A, 10% C or 45% G and N in 27th position from 5′ is 10% A, 10% C, 40% G or 40% T. In other words, when the isolated nucleic acid as defined above comprises the sequence 5′-GAAGCNTGGTANGANATGGAAG-3′ (SEQ ID NO: 1), wherein N in 6th position from 5′ is 90% C or 10% T, N in 12th position from 5′ is 60% C or 40% T and N in 15th position from 5′ is 60% A or 40% G, said isolated nucleic acid comprises a sequence selected from the group consisting of SEQ ID NO: 2 to SEQ ID NO: 9. Similarly, when the isolated nucleic acid as defined above comprises the sequence 5′-GGNGCNTCNATNCCNACNAANACATCNGG-3′ (SEQ ID NO: 10), wherein N in 3rd position from 5′ is 50% C or 50% G, N in 6th position from 5′ is 70% C or 30% T, N in 9th position from 5′ is 90% A or 10% G, N in 12th position from 5′ is 50% A, 15% C or 35% T, N in 15th position from 5′ is 60% A, 10% C or 30% G, N in 18th position from 5′ is 90% A or 10% G, N in 21st position from 5′ is 45% A, 10% C or 45% G and N in 27th position from 5′ is 10% A, 10% C, 40% G or 40% T, said isolated nucleic acid comprises a sequence selected from the group consisting of SEQ ID NO: 11 to SEQ ID NO: 1738.
As used herein, the expression “wherein N is x % X or y % Y” means that the nucleotide N is X in x % of the cases and Y in y % of the cases.
The present invention also encompasses the use, preferably in vitro, of the isolated nucleic acid as defined above for predicting and/or diagnosing a metabolic and/or cardiovascular disease in a subject. It also relates to the isolated nucleic acid as defined above for use for predicting and/or diagnosing a metabolic and/or cardiovascular disease in a subject.
The present invention also relates to an in vitro method for predicting and/or diagnosing a metabolic and/or cardiovascular disease in a subject, wherein a nucleic acid as defined above is used.
The present invention also relates to an isolated primer comprising the nucleic acid as defined above.
Another object of the present invention relates to a pair of primers comprising a first and a second primer, wherein the first primer comprises a nucleic acid which consists of the sequence 5′-GAAGCNTGGTANGANATGGAAG-3′ (SEQ ID NO: 1), wherein N in 6th position from 5′ is 90% C or 10% T, N in 12th position from 5′ is 60% C or 40% T and N in 15th position from 5′ is 60% A or 40% G; and the second primer comprises a nucleic acid which consists of the sequence 5′-GGNGCNTCNATNCCNACNAANACATCNGG-3′ (SEQ ID NO: 10), wherein N in 3rd position from 5′ is 50% C or 50% G, N in 6th position from 5′ is 70% C or 30% T, N in 9th position from 5′ is 90% A or 10% G, N in 12th position from 5′ is 50% A, 15% C or 35% T, N in 15th position from 5′ is 60% A, 10% C or 30% G, N in 18th position from 5′ is 90% A or 10% G, N in 21′ position from 5′ is 45% A, 10% C or 45% G and N in 27th position from 5′ is 10% A, 10% C, 40% G or 40% T. In other words, the first primer of the pair of primers according to the invention comprises a nucleic acid which consists of a sequence selected from the group consisting of SEQ ID NO: 2 to SEQ ID NO: 9, and the second primer of the pair of primers according to the invention comprises a nucleic acid which consists of a sequence selected from the group consisting of SEQ ID NO: 11 to SEQ ID NO: 1738.
Another object of the present invention relates to the use, preferably in vitro, of at least one nucleic acid as defined above wherein said at least one nucleic acid is a primer of sequence as defined above or a primer from a pair of primers of sequences as defined above.
The present invention also relates to an in vitro method for predicting and/or diagnosing a metabolic and/or cardiovascular disease in a subject, wherein a primer or a pair of primers as defined above is used.
The present inventors have also designed primers which are specific for 16S DNA. In particular, these primers do not cross hybridize with mitochondrial DNA.
The present invention therefore also relates to an isolated nucleic acid which comprises a sequence selected from the group consisting of the sequence 5′-TCCTACGGGAGGCAGCAGT-3′ (SEQ ID NO: 1750) and the sequence 5′-GGACTACCAGGGTATCTAATCCTGTT-3′ (SEQ ID NO: 1751).
The present invention also encompasses the use, preferably in vitro, of the nucleic acid as defined above for predicting and/or diagnosing a metabolic and/or cardiovascular disease in a subject. It also relates to the isolated nucleic acid as defined above for use for predicting and/or diagnosing a metabolic and/or cardiovascular disease in a subject.
The present invention also relates to an in vitro method for predicting and/or diagnosing a metabolic and/or cardiovascular disease in a subject, wherein a nucleic acid as defined above is used.
The present invention also relates to an isolated primer comprising the nucleic acid as defined above.
Another object of the present invention relates to a pair of primers comprising a first and a second primer, wherein the first primer comprises a nucleic acid which consists of the sequence 5′-TCCTACGGGAGGCAGCAGT-3′ (SEQ ID NO: 1750) and the second primer comprises a nucleic acid which consists of the sequence 5′-GGACTACCAGGGTATCTAATCCTGTT-3′ (SEQ ID NO: 1751).
Another object of the present invention relates to the use, preferably in vitro, of at least one nucleic acid as defined above wherein said at least one nucleic acid is a primer of sequence as defined above or a primer from a pair of primers of sequences as defined above.
The present invention also relates to an in vitro method for predicting and/or diagnosing a metabolic and/or cardiovascular disease in a subject, wherein a primer or a pair of primers as defined above is used.
Another object of the present invention relates to a kit for predicting and/or diagnosing a metabolic and/or cardiovascular disease in a subject, wherein said kit comprises at least one nucleic acid that hybridizes specifically under high stringency conditions to LpxB DNA, and optionally instructions for use.
Preferably, said kit further comprises at least one nucleic acid that hybridizes under high stringency conditions to bacterial 16S DNA. Examples of suitable nucleic acids include in particular nucleic acids hybridizing to the conserved region of the gene coding for bacterial 16S rRNA and bordering the variable V3 region.
More preferably, said kit comprises at least one primer of sequence as defined above or at least one pair of primers of sequences as defined above. Most preferably, the kit comprises the primers of sequence SEQ ID NO: 2 to SEQ ID NO: 9 and SEQ ID NO: 11 to SEQ ID NO: 1738.
Preferably, said kit further comprises at least one nucleic acid which comprises a sequence selected from the group consisting of the sequence 5′-TCCTACGGGAGGCAGCAGT-3′ (SEQ ID NO: 1750) and the sequence 5′-GGACTACCAGGGTATCTAATCCTGTT-3′ (SEQ ID NO: 1751).
“Instructions for use” typically include a tangible expression describing the technique to be employed in using the components of the kit and explaining how to correlate detection of LpxB DNA, and optionally of bacterial 16S DNA, to the prediction or diagnosis of a metabolic and/or cardiovascular disease.
The present invention also relates to a method, preferably in vitro, for screening probiotics, prebiotics or chemical or biological compounds suitable for preventing and/or treating metabolic and/or cardiovascular diseases, comprising determining the bacterial 16S DNA concentration and/or LpxB DNA concentration in a biological sample of a subject which has been treated with the candidate probiotic, prebiotic or chemical or biological compound, and comparing said concentrations with those of a control subject which has not been treated. Specifically, a higher bacterial 16S DNA concentration and/or a higher LpxB DNA concentration in the biological sample of the control subject than in the biological sample of the subject treated with the candidate probiotic, prebiotic or chemical or biological compound, indicates said candidate probiotic, prebiotic or chemical or biological compound is a probiotic, prebiotic or chemical or biological compound suitable for preventing and/or treating metabolic and/or cardiovascular diseases.
As used herein, the term “probiotics” denotes dietary supplements and live microorganisms containing potentially beneficial bacteria or yeasts. According to the currently adopted definition by FAO/WHO, probiotics correspond to live microorganisms which when administered in adequate amounts confer a health benefit on the host. Examples of probiotics according to the invention include bifidobacteria, lactobacillus, bacteroids and fusobacteria.
As used herein, the term “prebiotics” denotes a non-digestible food ingredient that beneficially affects the host by selectively stimulating as a substrate the growth and/or activity of one or a limited number of bacteria in the colon, and thus improves host health.
In the context of the invention, “prebiotics” encompass isolated or purified prebiotics as well as natural prebiotics present in dietary supplements.
In the context of the invention, “probiotics”, encompass isolated or purified probiotics as well as natural probiotics present in dietary supplements.
As used herein, the term “chemical or biological compound” encompasses chemically synthetized compounds and compounds of biological origin which have an effect on the growth, metabolism, the survival of bacteria and/or their passage through the intestinal barrier. In particular, chemical or biological compounds according to the invention include molecules which modify the bacterial flora of the digestive tract and/or which modify the migration of bacteria through the digestive tract and/or which modify the permeability of the intestinal epithelial barrier. Examples of chemical or biological compounds of the invention include bactericides, antibiotics, as well as compounds acting on epithelial intercellular tight junctions, microvillies, cell coat, and/or intestinal epithelial cells.
The control subject which has not been treated may be a subject unrelated to the subject receiving the candidate prebiotic, probiotic or chemical or biological compound, or the same subject before treatment with the candidate prebiotic, probiotic or chemical or biological compound.
The present invention also relates to an in vitro method for identifying predictive markers of a cardiovascular and/or metabolic disease, comprising
(i) detecting at least one sequence of bacterial DNA in a biological sample of an apparently healthy subject,
(ii) analyzing parameters that are indicative of a cardiovascular and/or metabolic disease in said subject and
(iii) identifying as predictive markers the sequences detected in the biological sample of said subject which are positively associated with the parameters that are indicative of a cardiovascular and/or metabolic disease.
As used herein, “apparently healthy” means subjects who have not previously had a cardiovascular event such as a myocardial infarction. Apparently healthy subjects also do not otherwise exhibit symptoms of disease. In other words, such subjects, if examined by a medical professional, would be characterized as healthy and free of symptoms of disease.
In the context of the invention, a “predictive marker of a cardiovascular and/or metabolic disease” refers to a marker that enables to make finding that a subject has a significantly enhanced probability of developing a cardiovascular and/or metabolic disease. As used herein, the marker is a sequence of bacterial DNA, preferably a gene.
Examples of parameters that are indicative of a cardiovascular and/or metabolic disease are well-known from those skilled in the art and include plasma total cholesterol, plasma total triglycerides, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, glycemia and C reactive protein (CRP).
As used herein, the expression “positively associated” means that there is a correlation between the predictive marker sequence and the parameters indicative of a cardiovascular and/or metabolic disease.
The term “correlation” indicates herein a statistical relationship between two random variables. The correlation between two variables may be determined by calculating the correlation coefficient between the variables. Statistical tests suitable to determine the correlation between two variables are well-known from those skilled in the art and include the Pearson product-moment correlation coefficient, which is obtained by dividing the covariance of the two variables by the product of their standard deviations, the Spearman's rank correlation coefficient or Spearman's rho, which is a special case of the Pearson product-moment coefficient in which two sets of data X, and Y, are converted to rankings x, and y, before calculating the coefficient.
The invention will be further illustrated by the following figures and examples.
The following example provides evidence showing that bacterial 16S DNA and LpxB DNA are potent markers of the presence of a metabolic and/or cardiovascular disease.
Among 1015 subjects, aged between 35 and 64 years, randomly selected from the polling lists by the Toulouse MONICA centre between 1995 and 1997, 311 men with complete data for all the measurements, were analysed. Authorization from the appropriate Ethics Committee (Comité Consultatif de Protection des Personnes dans la Recherche Biomédicale, Lille) was obtained and each subject signed an informed consent.
The examination was performed in the morning and a blood sample was drawn after an overnight fast. Helped by the medical staff, each subject filled in a questionnaire on his/her medical history, drug intake, smoking habits, and alcohol consumption. Height, weight, waist and hip circumferences were measured. Tobacco consumption was defined according to current and past consumption.
BP measurements were performed with a standard sphygmomanometer (Mercurex III, Spengler, Paris) using cuff size adapted to the subject's arm circumference. After a 5-min rest at least, carotid-femoral pulse wave velocity (PWV) was measured in supine position. Immediately after, heart rate and BP were measured twice in supine position. The average of the BP measurements was used for the statistical analysis.
Aortic stiffness was assessed by carotid-femoral PWV measurement with a semi-automatic device Complior (Garge les Gonesse, France). The two pressure waveforms were digitised. Time delay (t) between the two pressure upstrokes was automatically calculated. This procedure was repeated on 10 cardiac cycles and the mean value was used for the statistical analysis. The distance covered by the pulse wave was measured on the surface of the body and represented the distance between the 2 recording sites (D). PWV was automatically calculated as PWV=D/t. For the sub-sample (n=26) of subjects submitted to a second measurement, the intra-class coefficient for PWV was 0.80 (p<0.001).
High-resolution B-mode ultrasonography was used to detect atherosclerotic plaques in carotid arteries. An ATL UM9 system (Advanced Technology Laboratories Ultramark 9 High Definition Imaging) was used with a 7.4 MHz transducer. A plaque was defined as a distinct zone identified with either a focal area of hyperechogenicity relative to adjacent segments or a focal protrusion into the lumen of the vessel, composed of only calcified deposits or a combination of calcified and non calcified material. The presence of atherosclerotic plaques was investigated in the right and left common carotid arteries, internal and external carotid arteries (including carotid bulbs). The reproducibility of the plaque measurement was evaluated in a sample of randomly selected subjects submitted to a second ultrasound scan. The percentage of agreement and the kappa coefficient for the assessment of atherosclerotic plaques was 0.88 and 0.64 (p<0.001) respectively.
Plasma total cholesterol and triglycerides were measured by enzymatic methods (Boehringer Mannheim, Germany). High-density lipoprotein (HDL) cholesterol was measured in the supernatant after sodium phosphotungstate/magnesium chloride precipitation (Boehringer Mannheim). Low-density lipoprotein (LDL) cholesterol was determined by the Friedewald formula. C reactive protein was measured using an immuno-enzymatic method (IBL, GmbH, Hamburg, Germany).
Genomic DNA was previously isolated from peripheral blood cells (CHU Lille France). Total DNA concentration was then assessed using NanoDrop ND-1000 UV/Vis Spectrophotometer (NanoDrop Technologies, Wilmington, Del., USA). For quantification of total bacterial DNA, conserved region of the gene coding for 16S rRNA and bordering the variable V3 region was amplified by real-time quantitative polymerase chain reaction (RT-qPCR) with primers of the following nucleotide sequences: HDA1-forward, 5′-CCTACGGGAGGCAGCAG-3′ (SEQ ID NO: 1739); HDA2-reverse, 5′-ATTACCGCGGCTGCTGG-3′(SEQ ID NO: 1740). The 16S rDNA region amplified with these primers in the different bacterial species was from nucleotide 341 to 534 in Escherichia coli. RT-qPCR was performed with Stepone Plus Real-Time PCR System on Microamp Fast Optical 96-wells reaction plates (Applied Biosystems, Foster City, Calif., USA) as follows: 1 μL of plasma DNA, 1 μL of standard DNA (E. coli DNA) or 1 μl or sterile TE (10 mM Tris-HCl pH 8.0, 1 mM EDTA) as negative control, was added to PCR mix containing 300 nM of each primer, 10 μl of sterile DEPC-treated water and 12.5 μL of Power SYBR Green PCR Master Mix (Applied Biosystems, Foster City, Calif., USA) per well in 25 μL total volume. Thermal cycling conditions were as follows: 10 min at 95° C. and 40 cycles with 15 sec at 95° C., 1 min at 55° C. and 30 sec at 72° C. In order to generate comparable data for all subjects, quantification using E. coli DNA as standard was independently performed on each plate and plasma 16S rRNA-DNA concentration was expressed as pg of 16S rRNA-DNA/ng of total DNA, representing the amount of bacterial DNA (from 16S rRNA gene) normalized by the total DNA extracted from blood cells.
Lipid A disaccharide synthase (LpxB) catalyzes the condensation of 2,3-bis(3-hydroxymyristoyl)-β-D-glucosaminyl 1-phosphate and UDP-2,3-bis(3-hydroxymyristoyl)glucosamine (lipid X) to form lipid A disaccharide. Primers used for detection of LpxB DNA by RT-qPCR were designed to amplify the LpxB gene in all bacterial genomes currently registered in NBCI database, in a region corresponding from nucleotide 154 to 299 in E. coli. Briefly, out of 1097 bacteria genomes 41 hits correspond to LpxB genomes. The alignments of the latter genomes allowed the inventors to define two regions of high homology nucleotides separating one region of low homology on the LpxB gene. These two regions were used to define primers with some degree of non-homology. The inventors ensured that at least one of the 3′ end nucleotides of each primer was C or G and absolutely conserved between all genomes. This set of primers borders a region of 146 nucleotides which amplifies various DNA fragments corresponding to LpxB genes (known and unknown sequences). The nucleotide sequences of these primers named “LpxB universal” are as follows: LPXB-forward, 5′-GAAGCNTGGTANGANATGGAAG-3′ (SEQ ID NO: 1) with N6 (degenerated nucleotide in 6th position from 5′)=90% C+10% T, N12=60% C+40% T and N15=60% A+40% G; LPXB-reverse, 5′-GGNGCNTCNATNCCNACNAANACATCNGG-3′ (SEQ ID NO: 10) with N3=50% C+50% G, N6=70% C+30% T, N9=90% A+10% G, N12=50% A+15%C+35% T, N15=60% A+10% C+30% G, N18=90% A+10% G, N21=45% A+10% C+45% G and N27=10% A+10% C+40% G+40% T. Before performing RT-qPCR with these primers, the inventors tested if the expected 146 by PCR product could be obtained after final point PCR from E. coli DNA with primers specific of this strain, which nucleotide sequences are as follows: E. coli LPXB-forward, 5′-GAAGCCTGGTACGAAATGGAAG-3′ (SEQ ID NO: 2); E. coli LPXB-reverse, 5′-GGCGCATCAATACCAACAAAAACATCTGG-3′ (SEQ ID NO: 1747). Final point PCR was performed with a VWR Unocycler (VWR International bvba, Leuven, Belgium) as follows: in 25 μL total volume, 14 ng of E. coli DNA, 300 nM of each primer, 200 μM of each deoxyribonucleotide triphosphate (Sigma ref. D7295), PCR buffer (10 mM Tris-HCl pH 8.3, 50 mM KCl) (Sigma ref. P2317), 1.5 mM MgCl2 (Sigma ref. M8787) and 16 μL of sterile DEPC-treated water, were first incubated for 5 min at 94° C. and subsequently cooled to 83° C., at which point 0.35 U of Taq DNA polymerase (Sigma ref. D4545) was added. PCR was then achieved during 28 cycles (30 sec at 94° C., 30 sec at 60° C., 1 min at 72° C.) followed by a final elongation of 10 min at 72° C. Amplification product was then analyzed by electrophoresis in 6% acrylamide gel and ethidium bromide staining.
RT-qPCR of LpxB DNA with “LpxB universal” primers from human DNA samples was then performed with Stepone Plus Real-Time PCR System on Microamp Fast Optical 96-wells reaction plates (Applied Biosystems, Foster City, Calif., USA) as follows: 1 μL of plasma DNA, 1 μL of standard DNA (E. coli DNA) or 1 μL of sterile TE (10 mM Tris-HCl pH 8.0, 1 mM EDTA) as negative control, was added to PCR mix containing per well in 25 μL total volume, 600 nM of each primer, 8.5 μL of sterile DEPC-treated water and 12.5 μL of Power SYBR Green PCR Master Mix (Applied Biosystems, Foster City, Calif., USA). Thermal cycling conditions were as follows: 10 min at 95° C. and 50 cycles with 15 sec at 95° C., 1 min at 60° C. and 30 sec at 72° C. In order to generate data comparable for all the subjects, quantification using E. coli DNA as standard was independently performed on each plate. Plasma LpxB DNA concentration was first expressed in pg LpxB DNA/ng of total DNA, representing total LpxB DNA normalized by the total DNA extracted from peripheral blood cells, as an index of peripheral blood Gram-negative specific bacteria. Plasma LpxB DNA was also normalized by performing the ratio between the concentration of LpxB DNA and 16S rRNA-DNA and expressed in % of total DNA. LpxA (UDP-N-acetylglucosamine acyltransferase) catalyzes the first reaction of lipid A biosynthesis. Similarly, primers were designed and the corresponding PCR product quantified. Briefly, “LpxA universal” primers were designed to amplify the LpxA gene in all bacterial genomes, in a region from nucleotide 1 to 224 in E. coli. The nucleotide sequences of these primers were as follows: LPXA-forward, 5′-GTGATTGANAAANCCGCCTTTNTNCATCC-3′ (SEQ ID NO: 1741) with N9=30% C+70% T, N13=40% A+60% T, N22=60% A+40% G and N24=30% C+40% G+30% T; LPXA-reverse, 5′-ANATCNTGNTTNNCTTCNCC-3′ (SEQ ID NO: 1742) with N2=10% C+90% G, N6=80% C+20% T, N9=10% A+90% G, N12=45% A+45% C+10% T, N13=75% A+25% G and N18=50% A+50% G. The expected 224 by PCR product was first amplified by final point PCR from E. coli DNA with specific primers. The specific sequences were as follows: E. coli LPXA-forward, 5′-GTGATTGATAAATCCGCCTTTGTGCATCC-3′ (SEQ ID NO: 1743); E. coli LPXA-reverse, 5′-AGATCCTGGTTAACTTCGCC-3′ (SEQ ID NO: 1744). Final point PCR was performed with the same protocol used for E. coli LpxB and final product visualized after electrophoresis on acrylamide gel and ethidium bromide staining.
RT-qPCR of LpxA DNA from human DNA samples with “LpxA universal” primers was then performed with the same protocol used for LpxB DNA RT-qPCR. Plasma LpxA DNA concentration was expressed in pg LpxA DNA/ng total DNA and as a ratio between the concentration of LpxA DNA and 16S rRNA-DNA and expressed in % of total DNA.
Statistical analyses were performed with SAS statistical software release 8.2 (SAS Institute Inc, Cary, N.C., USA). The distribution of bacterial DNA values was highly skewed, with about 40% of values below the level of detection. Thus, the inventors analyzed bacterial DNA concentration as a dichotomous outcome according to the median. Also they defined as glucose metabolism abnormality patients with fasting glycemia>6.1 mmol/l and/or treated diabetes. A bivariate analysis between bacterial DNA concentration and clinical and biological variables was made using Spearman rank correlation. The relationships between the number of carotid plaques and LpxB concentration was assessed using a general linear model. The relationships between glucose metabolism abnormality and LpxB were assessed using multivariate logistic regression. P<0.05 was considered as statistically significant.
311 subjects were analyzed. Weight, waist, fasting glycemia, prevalence of treated diabetes and glucose metabolism abnormality, pulse wave velocity and the number of carotid plaques were found significantly higher in patients with LpxB above the median value (Table 1).
$ the analysis was performed in 290 subjects only.
Using Spearman rank test, the inventors found that plasma LpxB DNA concentration correlated with weight, waist, fasting glycemia, prevalence of treated diabetes and glucose metabolism abnormality and number of carotid plaques whereas bacterial DNA correlates with metabolic parameters but not with carotid plaques (Table 2).
In multivariate logistic regression, LpxB was independently associated with glucose metabolism abnormality after adjustment for traditional risk factors (Table 3).
However this association was no more statistically significant when 16S rRNA-DNA was added in the model (Table 4).
Conversely, 16S rRNA-DNA remained independently correlated with glucose metabolism abnormality. Finally, LpxB was independently associated with the number of carotid plaques (Table 5).
§ log(1 + x) transformed
$ current smokers = 1 and no smokers = 0;
Importantly no correlation was observed with LpxA showing the specificity of LpxB and total 16S rRNA-DNA for the correlated parameters.
Accordingly, the inventors demonstrated that 1) bacterial DNA could be detected in blood of apparently healthy men, 2) the concentration of 16S rRNA-DNA correlated with glucose metabolism abnormality, and 3) the concentration of LpxB DNA correlated with the number of atherosclerotic carotid plaques.
In the present study, the inventors found an independent correlation between LpxB and glucose metabolism abnormality. However, global bacteria burden in blood as assessed by 16S rRNA-DNA appeared as a better predictor of metabolic diseases than LpxB. These results demonstrate that bacteria distinct from those recognized by the primer used by the inventors contribute to metabolic diseases. However, with respect to the cross sectional nature of the present data, these results do not rule out the triggering role on the onset of metabolic diseases of bacteria coding for LPS as previously found in animal models. It is of note that odds ratio of having metabolic diseases was of 7 in patients in the top of distribution of 16S rRNA-DNA and this relation is independent from traditional risk factors such as waist. Furthermore, this relation is independent of inflammatory markers such as C reactive protein and interleukin 6. These data thus confirmed that 16S rRNA-DNA could be an innovative and potent marker to predict the occurrence of metabolic diseases in subjects at risk. Also, it could be speculated from these results that changes in microbiota could be a therapeutic target to prevent diabetes.
The inventors found an independent correlation between the concentration of LpxB DNA and plaques. They demonstrated that LpxB DNA blood concentration was connected with atherosclerosis process. Importantly, their results suggest that among microbiota, specifically, bacteria carrying the LpxB gene have a deleterious impact on atherosclerosis process. It is likely that a specific component of LPS could play a key role on atherosclerosis process. Importantly this correlation is independent from CRP, interleukin 6 and leucocyte count suggesting first that interleukin 6 and CRP are not involved in this relation. Additionally, the inventors did not find any significant association in a sub-sample of patients between plasma LPS concentration and LpxB DNA and between plasma LPS concentration and plaques. In this respect, LpxB DNA is a more reliable marker of atherosclerotic disease than endotoxin.
The following example shows the role of 16S DNA blood concentration as a marker of bacterial translocation on the onset of metabolic disease in a large sample of the general population.
D.E.S.I.R. is a longitudinal cohort study of 5,212 adults aged 30-64 years at baseline with the primary aim of describing the natural history of the metabolic syndrome (Cauchy et aL (2006) Diabetes 55:3189-3192). Subjects were recruited from 1994 to 1996 from 10 different Social Security Health Examination centres in western-central France among volunteers insured by the French national social security system (80% of the French population, any employed or retired person and their dependents which offers free periodic health examinations). As part of the recruitment design, men and women were recruited equally among five-year age groups. All subjects gave written informed consent, and the study protocol was approved by the Comité Consultatif de Protection des Personnes pour la Recherche Biomédicale of Bicêtre hospital (Paris, France). Participants were clinically and biologically evaluated at inclusion and at 3-, 6- and 9-year follow-up visits.
The inventors assessed the relation between 16S DNA blood concentration in subjects free of diabetes at inclusion and the onset of diabetes at different times of follow-up. Then, in order to test the predictive value of bacterial 16S DNA in subjects at low risk of diabetes according to established risk factors, they performed a subgroup analysis in subjects free of metabolic syndrome according to NCEP-ATP (National Cholesterol Education Program—Adult Treatment Panel) criteria at inclusion (National Institutes of Health: Third Report of the National Cholesterol Education Program Expert Panel on Detection, Evaluation and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III). Executive Summary. Bethesda, Md., National Institutes of Health, National Heart, Lung and Blood Institute, 2001 (NIH publ. no. 01-3670)) or in subjects with waist perimeter below the median of waist perimeter according to the sex.
According to NCEP-ATP criteria, a participant has the metabolic syndrome if he or she has three or more of the following criteria:
1) Abdominal obesity: waist circumference>102 cm in men and >88 cm in women.
2) Hypertriglyceridemia: ≧1.7 mmol/l
3) Low HDL cholesterol: <1.03 mmol/l in men and <1.29 mmol/l in women
4) High blood pressure: ≧130/85 mmHg
5) High fasting glucose: ≧6.1 mmol/l
The inventors assessed the relation between 16S DNA concentration in the whole DESIR cohort with available data except patients with diabetes at baseline.
An univariate analysis was first performed to explore the relation between the onset of diabetes and 16S DNA concentration at different times of follow-up. The inventors analysed separately the early onset of diabetes (between inclusion and year 3 [0-3 years] follow-up period) and a late onset of diabetes (after year 3 until the end of follow-up ]3-9 years follow-up]). A multivariate logistic regression was then conducted with diabetes as dependent variable and 16S DNA blood concentration. The model was adjusted on age and sex and major risk factors for diabetes. Then subgroup analyses were performed.
Since the distribution of 16S DNA blood concentration was highly skewed, this quantitative variable was transformed into a dichotomous variable according to the median of the distribution.
The characteristics of the study population are shown in Table 6.
In univariate analysis (Table 7) the incidence of late onset of diabetes was higher in subjects in the top of the distribution of bacterial 16S DNA (median).
The comparisons were performed between subjects who experienced diabetes at different times and subjects free of diabetes during the whole follow-up.
This relation remained significant after adjustment for confounder (Tables 8 and 9). Then a subgroup analysis was performed in subjects at low risk for diabetes. In subjects in the bottom of the distribution of waist perimeter according to sex (≦89 cm in men and ≦72 cm in women) and in subjects free of metabolic syndrome at inclusion, 27 and 102 diabetes respectively occurred after year 3. In both these subgroups, bacterial 16S DNA remained positively and independently associated with the late onset of diabetes.
With respect to the number of diabetes, this model was adjusted for smoking status and fasting glucose only.
In conclusion, the inventors here confirmed that 16S DNA blood concentration is an independent predictive marker of the onset of diabetes. Furthermore they demonstrated that bacterial 16S DNA predicted the risk of diabetes in subjects free of central adiposity and metabolic syndrome. They also demonstrated that 16S DNA blood concentration was an independent predictive marker of the late onset of diabetes.
The following example describes the way the inventors improved a method for the determination of 16S DNA in tissues by discriminating between bacterial 16S DNA and mitochondrial DNA.
The mitochondrial and the bacterial DNA have a similar origin and primers usually used in the literature cross react with both types of DNA. Therefore, PCR techniques cannot discriminate between both DNA origin since they amplify altogether. The solution proposed by the inventors is based on the fact that bacterial DNA and mitochondrial DNA do not have the same GC content and hence the temperatures required to dissociate the double strand DNA sequences are different. The inventors have standardized the PCR procedure and the dissociation curves and identified the best fit formulation which allows discrimination between both DNA origins.
DNA from a fresh culture of Escherichia coli BL21 (prokaryotic 16S DNA) or from axenic (germ free, no bacterial DNA) mouse liver (eukaryotic mitochondrial DNA) were extracted using TriPure Isolation Reagent (Roche Applied Science, Germany) according to manufacturer's instructions. Standard DNA samples were obtained by mixing increasing quantities of prokaryotic DNA (ranging from 0.001 to 1000 ng) with a fixed quantity of eukaryotic DNA (100 ng). A PCR reaction was then performed as follows.
Amplification and detection of DNA by real time PCR was performed using Stepone Plus Real-Time PCR System and Microamp Fast Optical 96-wells reaction plates (Applied Biosystems, California, USA).
Duplicate samples were used for the determination of DNA by real time PCR. The PCR reaction was performed in a total volume of 25 μL using the Power SYBR® Green PCR master mix (Applied Biosystems, California, USA) and 300 nM of each of the universal forward and reverse primers HDA1 and HDA2. Thermal cycling conditions for amplification of DNA were 95° C. for 10 min followed by 42 cycles each comprising 95° C. for 15 s, 55° C. for 1 min and 72° C. for 30 s. The amplification stage was followed by a melting curve stage (dissociation curve) according to the manufacturer's instructions (from 55° C. to 90° C.) to determine the specificity of the amplification.
Four dose response curves were determined with fixed quantities of eukaryotic DNA (0.1; 1; 10 or 100 ng) and increasing quantities of prokaryotic DNA from 0.001 to 1000 ng for each fixed eukaryotic DNA quantity (
Melting curve data allowed discriminating amplification of either prokaryotic or eukaryotic DNA as follows. The 75.5° C. temperature and 82° C. temperature corresponded to the melting (dissociation) temperature of the eukaryotic mitochondrial DNA and the 16S DNA respectively. The negative first-derivative of the normalized fluorescence (−Rn′) generated by the reporter (SYBR Green) during PCR amplification was used.
The ratio between derivative reporter value read at 75.5° C. and 82° C. was calculated and plotted against the Log 10 of ng eukaryotic DNA/ng prokaryotic DNA to establish a dose response curve.
The calculation of the best fit formulation (
The following equation was established to calculate the ratio between eukaryotic and prokaryotic DNA:
Y=bottom+(top−bottom)/[1+10̂((Log EC50−X)*HillSlope)]
with
X=Log 10(eukaryotic DNA/prokaryotic DNA),
Y=−Rn′ read at 77.5° C./−Rn′ read at 82° C.,
bottom=0.1903,
top=81.94,
Log EC50=3.673,
HillSlope=1.39, and
EC50=4709.
Therefore, in an unknown sample the plotting of the ratio between both DNA species allowed the quantification of each specie.
For comparison, a dose response curve of threshold cycle values (Ct) according to Log 10 ng prokaryotic DNA was established by incubating increasing quantities of prokaryotic DNA with a fixed quantity of eukaryotic DNA (0.1 ng) (
Importantly, the method using the melting temperatures was ten times more sensitive that the Ct technique since it allowed the quantification of 0.001 ng of DNA.
In conclusion, the method designed by the inventors is summarized as follows:
The following example describes primers specific of 16S DNA usable in the methods of the invention.
The inventors designed primers which did not cross react with the mitochondrial DNA and which were specific for 16S DNA to quantify the amount of bacterial DNA present in a tissue and which would define a prediabetic state.
The inventors used the following primers: EUBAC-F, 5′-TCCTACGGGAGGCAGCAGT-3′ (SEQ ID NO: 1750); EUBAC-R, 5′-GGACTACCAGGGTATCTAATCCTGTT-3′ (SEQ ID NO: 1751).
Amplification and detection of 16S DNA by real time PCR was performed with
Stepone Plus Real-Time PCR System on Microamp Fast Optical 96-wells reaction plates (Applied Biosystems, California, USA) as follows: 2 μL of DNA were added to PCR mix comprising per well (25 μL total volume), 300 nM of each primer, 9 μL of sterile DEPC-treated water and 12.5 μL of Power SYBR® Green PCR Master Mix (Applied Biosystems, California, USA).
Thermal cycling conditions were as follows: 95° C. for 10 min and 42 cycles each involving 95° C. for 15 s, 60° C. for 1 min and 72° C. for 30 s.
These primers allowed the amplification of a DNA product which was unique and coded for a fraction of the 16S DNA gene.
In conclusion, these primers can be used directly to quantify the bacterial DNA by PCR and establish the prediagnosis.
| Number | Date | Country | Kind |
|---|---|---|---|
| 09305138.1 | Feb 2009 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2010/051820 | 2/12/2010 | WO | 00 | 10/6/2011 |
