Patent Application
20090239242
This invention relates to the early identification and prediction of kidney damage, including early identification and prediction of elevated blood creatinine levels resulting from a reduction in kidney function in a subject and, in particular, to biomarkers for the detection thereof.
There are many causes of a reduction in kidney function and it is essential that corrective action is taken as early as possible by appropriate medical intervention so as to minimise as far as possible the deleterious consequences, which include total renal failure and a need for dialysis and ultimately kidney transplant. For example, an abrupt reduction in kidney function occurs frequently following cardiothoracic (CT) surgery. Thus, Acute Kidney Injury (AKI) is common following CT surgery occurring in 7-42% of patients (Mora Mangano, C. et al (1998) Ann Intern Med 128:194-203; and Tuttle, K. R. et al (2003) Amer J. Kid Dis 41:76-83.) Small changes in serum creatinine have been shown to correlate with increased morbidity and mortality, following CT surgery (Lassnigg, A. et al (2004) J. Am Soc Nephrol 15; 1597-1605)
Measurement of creatinine is the standard test in the clinic for measuring kidney function. If kidney function is abnormal, creatinine levels will increase in the blood due to decreased excretion of creatinine in the urine. Creatinine levels vary according to a person's age, size and muscle mass. In acute conditions build up of creatinine in the blood may take up to 24-72 hours to occur.
Patients who develop severe AKI requiring Renal Replacement Therapy (RRT), after CT surgery have a greatly increased in-hospital mortality (63%) compared to those with non-dialyzed AKI (19%), or stable renal function (0.9%) (Mora Mangano, C. et al (1998) supra).
Koyner, J. L. et al (poster presentation at American Society of Nephrology, Renal Week 2007, Oct. 31-Nov. 5, 2007, Moscone Center, San Francisco, Calif.) have investigated urinary Cystatin C (CyC) and Neutrophil Gelatinase—Associated Lipocalin (NGAL) in patients with AKI following adult cardiac surgery. Koyner, J L et al found that urinary CyC excretion increases in the early post-operative period following adult CT surgery and concluded that urinary CyC may be a useful early biomarker for the development of AKI as it appears to correlate with the severity of AKI and thus the future need of RRT. Similarly, Koyner, J L et al found that urinary NGAL in the early post-operative period appears to predict the development of AKI and correlate strongly with the future need of RRT.
U.S. Publication 2004/0219603 discloses that urinary NGAL measured within two hours of cardiac surgery was predictive of Acute Renal Failure (ARF) as reflected by serum creatinine peak, which occurs several hours or even days later.
Koyner J. L. et al (2007) (supra) show that for both CyC and NGAL the main increase occurs in the ICU (Intensive Care Unit) phase post CT surgery.
Eijkenboom, J. J. A. et al (2005) Intensive Care Med 31:664-667 show that an increase in Glutathione S-Transferase (GST), excretion following cardiac surgery was not correlated with changes in plasma creatinine and is not associated with clinically relevant renal injury.
Davis, C. L. et al (1999) J Am Soc Nephrol 10: 2396-2402 disclose that urinary GST excretion increased in most patients after CPB, however, this increase was not associated with the development of clinically apparent ARF.
There is a need for a biomarker which predicts elevated blood creatinine levels resulting from an abrupt reduction in kidney function and thus the development of AKI at the earliest stage post CT surgery, ideally at zero hours in the recovery room and prior to transfer to ICU or earlier, namely intraoperatively, so as to enable corrective action to be taken as soon as possible for those patients who develop AKI with the attendant consequences.
Currently no drug therapy is available for counteracting the effects of a reduction in kidney function as seen, for example in post CT surgery. Accordingly, the surgeon and other attending medical professionals will endeavour to reduce the effects of renal ischemia or other causative effect by managing fluid levels and other physiological parameters. However, as indicated above, frequently, if such measures do not prove successful, the patient will require RRT, namely dialysis.
Accordingly, the invention provides in a first aspect a method for the early identification and prediction of elevated blood creatinine levels resulting from a reduction in kidney function in a subject, which method comprises contacting a urine sample from the subject with a capture molecule for a biomarker specific for the distal region of the renal tubule and which biomarker is released from said region when there is damage to said region indicative and predictive of elevated blood creatinine levels resulting from a reduction in kidney function.
The method according to the invention, provides a means of detecting damage to, and predicting the extent of damage to, the kidney within two hours or less of the damage occurring with the attendant advantages for the patient.
By “capture molecule” herein is meant any molecule or portion thereof which binds reversibly or irreversibly to said biomarker, so that said biomarker can be detected in the urine sample.
According to one embodiment of the invention, the reduction in kidney function is caused by Acute Kidney Injury (AKI).
According to a further embodiment of the invention, the AKI is caused by a condition or disease selected from age, burns, pre-existing chronic kidney disease, reduced effective arterial volume, volume depletion, nephrotic syndrome, congestive heart failure, cirrhosis, sepsis, type I diabetes, type II diabetes, obesity, inflammation, surgery, solid organ transplant, allogenic bone marrow transplant, mechanical ventilation and/or trauma.
According to a still further embodiment of the invention, the AKI is caused by administration of a drug to the subject, including antibiotics.
Preferably, the drug is selected from aminoglycosides, non-steroidal anti-inflammatory drugs and radiocontrast drugs.
It will be appreciated that the AKI may be caused by a toxin.
According to a further embodiment of the invention, the AKI is caused by renal ischemia in a patient undergoing cardiothoracic (CT) surgery.
Preferably, the biomarker is detectable as early as intraoperatively, allowing for immediate corrective medical intervention.
The method according to the invention, by providing a means of detecting damage to, and predicting the extent of damage to, the kidney as early as intraoperatively represents a very significant advance in the management and treatment of patients undergoing CT surgery.
According to one embodiment of the invention, the biomarker is detectable in the recovery stage post CT surgery, allowing for immediate corrective medical intervention.
The method according to the invention, by providing a means of detecting damage to, and predicting the extent of damage to, the kidney in the recovery stage post CT surgery, allows for the appropriate medical intervention to be taken, dependent on the level of the biomarker detected during the recovery stage or earlier, namely intraoperatively.
Thus, the method according to the invention can indicate and/or predict a reduction in kidney function significantly earlier than the current standard creatinine test or other current methods hereinabove mentioned.
Preferably, the biomarker is detectable prior to transfer of the patient to the Intensive Care Unit (ICU).
When the abrupt reduction in kidney function is caused by AKI, the reduction in kidney function can be reversed by managing fluid levels and other physiological parameters.
The abrupt reduction in kidney function may result in a requirement for Renal Replacement Therapy (RRT).
In such a situation, the RRT will generally involve putting the patient on dialysis supplemented, as required, by managing fluid levels and other physiological parameters.
Thus, it will be appreciated that use of the method according to the invention can result in a significant reduction of the deleterious side effects of renal ischemia in a patient undergoing CT surgery.
Preferably, the biomarker is pi glutathione S transferase (πGST), also referred to hereinafter as pi GST.
According to one embodiment, the biomarker is detected by immunoassay.
When the biomarker is πGST, the capture molecule is preferably an antibody to πGST. The antibody may be a monoclonal or a polyclonal antibody which binds to πGST.
For example, the biomarker πGST can be detected using an enzyme immunoassay, more particularly an Enzyme Linked Immunosorbent Assay (ELISA). In this regard, the πGST can be assayed using a commercially available kit marketed by Biotrin International Limited, Dublin, Ireland as PI GST EIA, (Catalogue No. BIO 85) which is a 96 well EIA assay format kit. However, any other conventional assay for detecting πGST can be used.
It will be appreciated that when the biomarker is πGST, an enzyme, then the capture molecule therefor can also be a substrate or co-factor therefor.
Accordingly, according to a further embodiment of the invention, the biomarker can be detected enzymatically.
According to one embodiment of the invention the biomarker is detected by a point-of-care assay.
A point-of-care assay will typically be performed on a urine sample of less than 500 μl, typically 10 μl or less. In a point-of-care assay in accordance with the invention, the capture medium will be suitably a dip-stick or like device having the capture molecule affixed thereto.
The invention also provides πGST for use as a biomarker for the early identification and prediction of elevated blood creatinine levels resulting from a reduction in kidney function.
According to a further aspect of the invention, there is provided a method for predicting a need for renal replacement therapy (RRT) in a patient comprising:
determining a concentration of glutathione S transferase (GST) in a first urine sample from the patient; and
wherein a need for RRT is predicted when the GST concentration is determined to be elevated in comparison to a patient without kidney injury.
Without being bound by any theoretical explanation of the invention, it is believed that elevated urinary GST concentrations can be used to differentiate between patients with less severe acute kidney injury not likely to require RRT and those for whom RRT, for example peritoneal dialysis, hemofiltration, renal transplantation and the like, will be required.
According to this aspect of the invention, the method may further comprise contacting a urine sample from the patient with a capture molecule for a GST isozyme.
According to one embodiment of the invention, the GST is πGST.
The GST can be detected by immunoassay and the capture molecule can be an antibody to πGST.
Alternatively, the GST can be detected enzymatically as in the case of the method hereinabove described.
Furthermore, the GST can be detected by a point-of-care assay, as hereinbefore described.
Elevated urinary GST concentrations can persist for days in a patient in need of RRT.
According to a still further aspect of the invention there is provided a method for predicting a need for RRT in a patient comprising;
determining a concentration of GST in two urine samples taken at least 24 hours apart from the patient; and
wherein a need for RRT is predicted when the GST concentration is determined to be elevated in the two urine samples.
The elevated GST concentration in the urine can, for example, be ≧30 ng/ml, ≧60 ng/ml, ≧70 ng/ml, ≧80 ng/ml, ≧ or 90 ng/ml or more.
According to this embodiment of the invention, the GST is preferably a πGST isozyme.
The cause of the underlying renal dysfunction in the patient for whom RRT is predicted can, for example, be such that the patient is affected by an age-related condition, burns, pre-existing chronic kidney disease, reduced effective arterial volume, volume depletion, nephrotic syndrome, congestive heart failure, cirrhosis, sepsis, type I diabetes, type II diabetes, obesity, inflammation, surgery, being a solid organ transplant recipient, being an allogenic bone marrow transplant recipient, mechanical ventilation and/or trauma or has taken or has been administered an antibiotic, drug and/or toxin.
The method according to this aspect of the invention can further comprises detecting for the presence of risk factors for RRT in the patient wherein the risk factor is selected from the group consisting of elevated serum creatinine concentration, type I diabetes, type II diabetes, hypertension, dyslipidemia, hyperglycaemia, proteinuria and hypoalbuminemia.
The invention will be described herein with reference to one cause of a reduction in kidney function, namely that which frequently occurs in a patient undergoing CT surgery.
Preferably, the biomarker is detected earlier than 2 hours post CT surgery or earlier than two hours post Cardio-Pulmonary Bypass (CPB).
Further, preferably, the biomarker is detected at zero hours post CT surgery or CPB.
It will be appreciated that individuals have different urinary biomarker reference baseline levels. Therefore, post-operative or post-treatment results should be considered in relation to the patient's pre-operative or pre-treatment reference baseline biomarker level, as appropriate.
The invention will be further illustrated by the following Examples
A retrospective study of 68 patients who had undergone elective CT surgery at the University of Chicago Hospital was carried out.
The patients were screened and approached for enrollment. The patients were excluded if they met any of the following criteria:
Age <18 years old.
Use of radiocontrast within 24 hours of surgery.
Change in thyroid hormone replacement dose in the last 2 weeks
Change in thyroid chronic corticosteroids dose in the last 2 weeks
Unstable renal function (Δ Serum Creatinine ≧0.2 mg/dl in the last 2 months of Oliguria defined as <400 ml/day).
Urine and blood samples were collected and stored.
The urine samples were tested for the presence of πGST using the aforementioned πGST EIA available from Biotrin International Limited (Catalogue Number BIO85).
Serum Creatinine (SCr) was measured using the Jaffe Method in a manner known per se on a Beckman Unicel DxC 600 autoanalyser (Beckman Coulter, Fullerton, Calif., USA).
AKI was determined by change in SCr as defined as:
An abrupt (within 48 hours) reduction in kidney function currently defined as
1) absolute increase in serum creatinine of more than or equal to 0.3 mg/dl (≧26.4 μmol/l); or
2) a percentage increase in serum creatinine of more than or equal to 50% (1.5-fold from baseline).
This definition is consistent with the usual definition used, for example, by Mehta, R. L., et al (2007) Critical Care; 11: R31
The results are shown in Table 1 and
Significantly elevated levels of πGST are detected post-op, namely at zero hours.
Analysis of the data shows that πGST is a good early indicator of patients that will develop AKI by day 2 post surgery.
A study was carried out on the 68 patients, the subject of Example 1, using the same methodology for the detection of SCr and πGST.
Seven patients out of the 68 patients tested required RRT. The results are shown in Table 2.
The time point at which patients requiring RRT would be first diagnosed is shown in Table 3.
Table 4 shows the sensitivity and specificity of πGST to detect RRT as summarised therein.
The results are also depicted in
From
The results show that πGST is a very good early indicator of patients that will require RRT undergoing and post CT surgery. * * * * *
The above Examples show that πGST can be used to detect elevated blood creatinine, AKI and a requirement for RRT earlier than with current biomarkers used to detect an abrupt reduction in kidney function due to renal ischemia intraoperatively or post CT surgery, with the attendant advantages.
