Patent Application
20110245180
Neuropathic pain is a sensory disorder that results from damage or dysfunction of peripheral and/or central neuronal pathways through injury, cancer, diabetes, or infection. It is characterized by spontaneous and/or abnormal stimulus-evoked pain, such as allodynia (pain sensation evoked by normally innocuous stimuli) and/or hyperalgesia (increased pain intensity evoked by normally painful stimuli). Millions of people worldwide suffer from this disorder. Unfortunately, many forms of neuropathic pain cannot be adequately treated using conventional analgesics. For decades, pain modulation have been viewed as being mediated solely by neurons. Increasing evidence strongly suggests active involvement of glial cells and an inflammatory reaction, including chemokine signaling in the pathogenesis. The hypersensitive state experienced by individuals suffering from neuropathic pain involves spinal microgliosis which is not just a property of those cells already existing in the spinal cord, but also those coming from chemokine mediated proliferation and recruitment of blood-born macrophages and myeloid stem cells in the bone marrow (Zhang, et al., J. of Neurosci., 2007). All D:TTNYT will undergo further testing as a potential therapeutic for neuropathic pain.
Chemokine receptors CCR2, CCR5 and their ligands have been found in glia and neurons, respectively, following nerve injury. Receptor antagonist, DAPTA, an octapeptide derived from HIV gp120, dramatically blocks neuroinflammation in three different rat models (Socci, Peptides, 1996; Rosi, Neuroscience 2005)
The mechanism probably includes its ability to block CCR5 and CCR2 receptor-mediated monocyte chemotaxis and transformation into intravascular macrophages en route to the brain, as well as recruitment and activation of microglial cells and other progenitor cells. In any case, of the hundreds of HIV gp120 derived pentapeptide analogs of DAPTA identified and synthesized in our lab, all of them have potent CCR2 and CCR5 antagonist activity. It is logical that the HIV virus has evolved many sequences to evade immune surveillance all of which bind tightly to receptors on rapidly expanding and/or readily activated cells like monocytic stem cells
DAPTA reduces microglial and astrocyte activation in an inflammatory rat model of Alzheimer's disease. In this application, we sought to investigate All D:TTNYT, an analog of DAPTA in which all five amino acid residues are the “D” stereo isomers rather than the naturally occurring “L” stereo isomers. The purpose of the investigation was to determine whether All D:TTNYT is efficient in preventing and/or relieving nerve injury induced chronic pain by targeting activated spinal microglia/astrocytes and related inflammatory response.
Large peptides called chemokines not only orchestrate chemotaxis in immune cells, but also are involved in neurodevelopment and neurophysiological signaling in brain. Chemokines have recently been recognized as essential elements in numerous neurodegenerative diseases and related neuroinflammation. In particular, recruitment of “activated” peripheral blood monocytes containing CCR5 chemokine receptors into atherosclerotic and other types of neuropathological plaques is pivotal to a number of diseases with neuroinflammatory etiologies including HIV and other dementias.
The CCR5 or R5 receptor became the focus of much attention when it was shown to be the essential receptor to which HIV must bind before it enters and infects cells; virtually all “founder” viruses, clones of the actual disease-transmitting virus, use CCR5 exclusively as an entry protein. The drug receptor for DAPTA (D-Ala-Peptide T-amide), the first HIV receptor blocker and entry inhibitor, has been proven to be CCR5 (Polianova, et al., Antiviral Research, 2005).
A number of short enzyme-resistant peptide analogs have been developed which also act as antagonists of CCR2 and CCR5, blocking binding of free HIV envelop proteins (gp120) and receptor signaling, now understood to be causes of immune and CNS inflammatory pathogenesis. Even when plasma HIV is undetectable, the viral “reservoir” of persistently infected cells, now identified as monocytes, continues to release highly potent, receptor active gp120 which drives pathogenesis.
Monomeric DAPTA (M-DAPTA or Adaptavir®) is a third generation HIV receptor blocker antiviral currently in Phase II studies in healthy patients with no detectable HIV-plasma virus as the result of being treated with and maintained on various cocktails of anti-retroviral therapeutics; m-DAPTA, which has been manufactured and formulated to avoid its tendency to form biologically inactive aggregates, has an extremely high (femtomolar range) affinity for R5. The primary endpoint of the ongoing trial is the previously observed (Polianova et al., Peptides, 2003) gradual reduction of infectious virus in white blood cells to undetectable levels in most patients by six months. The secondary endpoints include the serum levels of a number of inflammatory and anti-inflammatory cytokines to replicate a previous clinical study (Ruff, et al., Current HIV Research, 2003) which showed that DAPTA significantly reduced 4 inflammatory cytokines and increased 4 anti-inflammatory cytokines M-DAPTA, was previously shown to block activated microglial cells and NFkB activation in rats infused intraventricularly with endotoxin (Rosi, et al., Neuroscience, 2005), a model of inflammatory pathogenesis in Alzheimer's Disease.
While disputed by most investigators, the inventors believe their observations make clear that neuroinflammation lies at the root of many diseases of unknown etiology and is initiated in one or more of three ways: 1) viral/microbial infection, 2) tissue trauma/injury or 3) environmental toxin exposure. The actual form the neuroinflammatory disease takes is a function of time and location. With respect to time, inflammation early in pregnancy, for example, can lead to autism; inflammation later in pregnancy, to schizophrenia; and inflammation after 65 years, to Alzheimer's. With respect to location, optic nerve inflammation can lead to demylination in multiple sclerosis; in spinal cord to Lou Gehrig' disease; in the substantia nigra of the brain to Parkinson's disease; in joints, to arthritis, etc.
Unilateral partial ligation of the sciatic nerve causing partial injury of somatosensory fibers with a rapid and long-lasting hypersensitivity (allodynia and hyperalgesia) is a rat model of human neuropathy. Before and one week following surgery, mechanical hypersensitivity was assessed using a series of calibrated von Frey monofilaments according to Chaplan; the 50% response threshold was calculated using Dixon's up-down method. Thermal hyperalgesia was measured using Hargreaves' paw withdrawal test with a focused high-intensity projector lamp.
For histological studies Rats and mice were deeply anaesthetized with ketamine/xylazine and then perfused transcardially with 0.9% saline followed by 4% paraformaldehyde (PFA) in 0.1 M sodium phosphate buffer (pH 7.4). The ipsi and contralateral L4-L6 DRGs from rats, as well as the corresponding levels of the spinal cords from both rats and mice were removed and placed in the same fixative overnight, then transferred to 30% sucrose for cryoprotection. Frozen spinal cords were cut transversely into 30 μm thick sections on a sliding microtome, collected in an antifreeze solution and stored at −20° C. until use. The DRG were embedded in OCT compound (Tissue Tek, Miles Laboratories, Elkhart, USA), cut longitudinally into 14 μm thickness in a cryostat (Microm, Heildeberg, Germany), mounted onto Superfrost Plus slides, and stored at −80° C. until use.
For real time PCR experiments Seven days after the nerve ligation, rats were deeply anaesthetized with isoflurane and decapitated. Lumbar (L4-L6) spinal cords and sciatic nerves were quickly removed and then snap frozen in liquid nitrogen and stored at −80° C. until use.
Reporter cells (GHOST R5) were allowed to attach in a 96 well plate for 3.5 hr then various concentrations of drugs (DAPTA and All D:TTNYT) were added in media replacement. A CCR5-specific virus (HIVBaL) was added 1 hr later. CCR5 receptor viral infectivity was tested on CCR5-containing cells with a Green Fluorescent Protein (GFP) reporter that responds to viral infection.
A partial ligation on the left sciatic nerve was conducted in adult male rats (Seltzer model).
Prevention: d0-d7 post-injury, 0.05, 0.1, 1 mg/kg daily p.o.
Reversal: d8-d12 post-injury, 0.1, 0.2, 1 mg/kg daily p.o.
Mechanical allodynia and of hind paw were measured with Von Frey Hairs (Chaplan et al., 1994)
Thermal hyperalgesia was measured in response to steady heat beam, by using Hargreaves
apparatus (Hargreaves et al., 1988)
Iba-1 and GFAP were used as markers for microglia and astrocyte respectively to monitor glial response to nerve injury and to All D:TTNYT treatment. Image analysis was performed with a fluorescence microscope equipped with a digital camera.
Quantitative real time-PCR was performed to detect changes of IL-1b and IL-6 mRNA within the spinal cord.
Statistical analyses of the results were made with Student's t-test or one-way ANOVA followed by Dunnett's case-comparison posthoc test.
Animals were acclimatized to standard laboratory conditions (14 h light, 10 h dark cycle) and given free access to rat chow and water. Adult male Sprague-Dawley rats (Charles River, Quebec, Canada) were used and weighed 250-275 g at the time of surgery. GFP+ chimeric mice were obtained from the CHUL Research Center, Laval University (Dr. S Rivest). Adult male CCR5 knock-out mice (B6.129p2-CCR5 tm1kuz/J) were purchased from Jackson lab (Bar Harbor, Me., USA). All protocols were performed in accordance with guidelines from the Canadian Council on Animal Care and were approved by the McGill University and Laval University Animal care Committees.
All D TTNYT (synthesized by RAPID Laboratories) was purified to >95% homogeneity and verified by HPLC isolation, amino acid analysis, and mass spectroscopy. Peptides were dissolved in sterile water and stored as frozen (−20° C.) aliquots at 0.1 mM until use.
Chemotaxis was assayed in 96-well plates (NeuroProbe, Cabin John, Md.) with 5 μM pore size, PVP-free membranes. Purified human monocytes (>95%) prepared from healthy adult human donors by centrifugal elutriation (>95% pure, gift of L Wahl, NIDR, NIH) were resuspended in chemotaxis assay buffer (DMEM supplemented with 0.1% BSA) at a density of 2×106 cells/ml. Cells were labelled with 1.0 μM Calcein AM (Invitrogen) for 30 minutes at 37° C., 5% CO2. Following incubation, cells were washed once and resuspended in chemotaxis assay buffer (DMEM, 1 mg/ml BSA, 25 mM Hepes) at a density of 2×106 cells/ml. Cells were then further treated with the indicated concentrations of All D TTNYT for 30 minutes at 37° C. Lower wells were filled with either buffer, MCP-1 or MIP-1β (PeproTech) as test chemoattractants. The filter plate was snapped on and monocytes which had been treated with All D TTNYT or buffer only (30 min, 37° C.) were loaded onto the upper filter surface (50,000 cells in 25 μl). Chambers were then incubated at 37° C. for 90 minutes. At the conclusion of the test period, non-migrating cells were wiped off the upper filter surface and relative fluorescence units (RFUs) of the migrating cells from the lower surface determined by bottom reading in a spectrometer (M5 SpectraMax) at 485/530 nm (Ex/Em). Triplicate determinations were made and results are expressed as the mean Chemotactic Index, the ratio of cell migration of the indicated chemokine compared to cells that had been treated with the indicated dose of All D TTNYT, of two independent determinations.
The current project uses the well established rat neuropathic pain model described by Seltzer et al [27]. Under anesthesia of isoflurane, the left common sciatic nerve was exposed via blunt dissection through the biceps femoris muscle. The dorsum of the nerve was carefully freed from surrounding connective tissues at a site near the trochanter. A 6-0 suture was inserted into the nerve with a ⅜ curved, reversed-cutting mini-needle (Tyco Health Care, Ontario, Canada) and tightly ligated so that the dorsal one-third to one-half of the nerve thickness was trapped in the ligature. The muscle and skin layers were closed with two muscle sutures (4-0) and three to four skin sutures (4-0). Sham-operated rats underwent the same surgical procedure but the nerve was exposed and left intact. Survival times were 7 and 12 days post-surgery. A group of naive rats was included in the protocol to obtain basal levels of certain gene and protein expression.
The partial ligation was also performed on the left sciatic nerve of GFP+ chimeric mice (10 weeks after irradiation and bone marrow transplantation) and CCR5 knock-out mice, according to the method described by Malmberg and Basbaum [15]. All mice were kept for 14 days.
Prevention: To investigate whether blockade of both CCR2 and CCR5 can prevent the development of behavioral hypersensitivity following nerve injury, a set of rats were treated with saline or All D TTNYT (0.05, 0.1 or 1 mg/kg b.w., p.o.) administered immediately after surgery and continued once daily for 7 days following nerve injury (n=4 for saline and n=4 for All D TTNYT/each dose).
Reversal: To further ascertain whether blockade of both CCR2 and CCR5 could also reverse already established neuropathic hypersensitivity, saline or All D TTNYT (0.1, 0.2 or 1 mg/kg b.w., p.o.) was administered to separate groups of rats starting from day 8 post-injury, when both mechanical allodynia and thermal hyperalgesia had reached their lowest level. The treatment lasted for 4 days (day 8-12) (n=5 for saline and n=4-8 for All D TTNYT/each dose).
A group of GFP+ chimeric mice received All D TTNYT or saline treatment (day 0-day 14, 1 mg/kg b.w., p.o.) to examine the effects of All D TTNYT in monocyte trafficking into the spinal cord (n=4/group)
Both rats and mice subject for behavioral testing were habituated to the testing environment daily for at least two days before baseline testing. All animals were assessed for mechanical allodynia and thermal hyperalgesia of both hind paws before surgery and at specified time points after injury until they were sacrificed for histological studies. The behavioral tests started 3-4 hrs after the drug administration. The investigator was totally blinded to the treatments the rats received. Mechanical sensitivity was assessed using calibrated von Frey hairs as described by Chaplan et al [6]. Animals were placed in boxes on an elevated metal mesh floor and allowed 40 to 60 min for habituation before testing. A series of von Frey filaments with logarithmically incrementing stiffness (Stoelting) was applied perpendicular to the mid-plantar region of the hind paw. The 50% paw withdrawal threshold was determined using Dixon's up-down method as previously described [9]. Thermal hyperalgesia was measured using paw withdrawal test. Animals were placed on a glass floor within Plexiglass cubicles. After habituation, a focused high-intensity projector lamp was directed below onto the mid-plantar surface of the hind paw and reaction time (withdrawal latency of the hind paw) of the rat was recorded automatically [11]. The commercial device (IITC Model 336) was calibrated so that the pre-surgical baseline paw withdrawal latencies were approximately 10-12 sec. Twenty seconds was used as a cut-off time to avoid damage to the animal's skin. The measurements were repeated four times for rats and eight times for mice, at 3 min intervals on each paw. The initial pair of measurements was not used. The average of the three or seven remaining pairs of measurements was taken as data. Efficacy of All D TTNYT was determined according to the following formula: MeanAll D TTNYT−Meancontrol (saline)/Meannaive (baseline)−Meancontrol (saline)×100%.
Detection of mRNAs encoding CCR5 was performed on lumbar spinal cord and DRG sections using 35S-labeled riboprobes. Radiolabeled CCR5 probe was synthesized with a 702 bp-cDNA cloned into expression vector pCR-Blunt II-TOPO. Sequence chosen was verified by BLAST analysis in GenBank. Hybridization were performed as per a previously described protocol [30]. Briefly, plasmids were linearized and sense and anti-sense cRNA probes were synthesized with appropriate RNA polymerase. Sections were postfixed in 4% PFA and digested by proteinase K (10 μg/ml), after which spinal cord sections were rinsed in water and by a solution of 0.1 M triethanolamine (TEA, pH 8.0), acetylated in 0.25% acetic anhydride in 0.1 M TEA and then dehydrated. Hybridization of the sections by riboprobe involved 90 μl hybridization mixture containing 106 cpm/ml radioactivity and incubation at 55° C. overnight in a slide warmer. Slides were rinsed in standard saline citrate (1×SSC: 0.15 M NaCl, mM trisodium citrate buffer, pH 7.0) and digested by RNase A at 37° C. (20 μg/ml), rinsed in descending concentrations of SSC, and dehydrated through graded concentrations of ethanol. Sections were exposed to x-ray film (BioMax, Kodak, Rochester, N.Y.) for 2-3 days and dipped in NTB2 nuclear emulsion (Kodak). Slides were kept at 4° C. for 3-5 weeks safe from light and developed in D19 developer (Kodak) and counterstained with thionine.
Combination of Immunohistochemistry with ISH
Immunohistochemistry was combined with ISH to determine whether CCR5 is expressed on microglia. Spinal cord sections were processed by the avidin-biotin method using peroxidase as a substrate. Rabbit anti-ionized calcium-binding adaptor molecule 1(Iba-1) polyclonal antibody was used as a marker for microglia. Briefly, sections were incubated with rabbit Iba-1 polyclonal antibody (1:1000; Wako Chemicals, Richmond, Va.) at room temperature (21-23° C.) for 2 h, and followed by a 2 h incubation with a biotinylated secondary antibody (Vector Laboratories, Burlingham, Calif., USA), and before final incubation with an avidin-biotin-peroxidase complex (Vectostain ABC Elite Kit; Vector Laboratories). The staingings were visualized by reacting in 0.05% diaminobenzidine and 0.003% hydrogen peroxide. Thereafter, sections were mounted, dessicated, fixed in 4% PFA, and digested by proteinase K. Pre-hybridization, hybridization and post-hybridization steps were performed according to the above protocol, with shorter dehydration times in ascending alcohol to prevent decoloration of immunoreactive cells. The slides were dried, exposed and developed as described above.
Regular immunofluorescent staining was performed to characterize the spinal glial cell reaction to peripheral nerve injury and to All D TTNYT treatment. Free-floating sections were incubated overnight at 4° C. with the following antibodies: rabbit anti-Iba-1 polyclonal antibody (for microglia, 1:1000; Wako Chemicals, Richmond, Va.); and rabbit anti-glial fibrillary acid protein (GFAP) polyclonal antibody (for astrocytes, 1:1000; DakoCytomation, Carpinteria, Calif.); followed by 60-min incubation at room temperature in fluorochrome-conjugated goat secondary antibody.
Total RNA was extracted from spinal cords and sciatic nerves using RNeasy lipid tissue mini kit (QIAGEN). Synthesis of cDNA from total RNA was performed with SuperScript VILO cDNA synthesis kit (Invitrogen). Primers were produced by QIAGEN QuantiTect (IL-1-QT00181657, IL6-QT00182896, GAPDH-QT00199633). Spinal cords and sciatic nerves collected from the following groups were analyzed: 3 naive animals; 3 saline-treated animals and 4 All D TTNYT-treated animals. Experiments were performed in triplicate using the SYBR Green I Dye technology. Levels of target mRNAs were normalized to the housekeeping gene GAPDH. Fold changes versus naive animals in their respective ipsi and contralateral sides were analyzed using the comparative Ct (dCT) method [14].
Images were acquired using an Olympus BX51 (Tokyo, Japan) microscope equipped with a color digital camera (Olympus DP71) and Olympus confocal laser-scanning biological microscope (Fluoview 1000). Quantitative analysis of both Iba-1 and GFAP staining was performed on images digitized using a constant set of parameters (exposure time, gain, and postimage processing) with special attention to avoid signal saturation. Four areas of interest (AOI) defined as: 2 rectangles on the dorsal horn (DH) (lamina I-III) and 2 rectangles on the ventral horn (VH) (lamina IX), on both sides relative to the side of injury, were selected. Two thresholds of fluorescence intensity for Iba-1 and GFAP respectively were established according to the signals on naïve animals. All objects within the AOI having fluorescence intensity above the chosen threshold were considered as parts of Iba-1 or GFAP positive cells and were subject to the quantitative analysis (
All data are presented as mean±SEM. Statistic significance was determined using: 1) for behavioral analysis one way ANOVA followed by Dunnet's test for the changes of all time points vs. pre-surgery baseline; unpaired t-test for the difference between groups (All D TTNYT-treated vs. saline-treated at each time point); 2) unpaired t-test for the difference between groups in glial responses and in cytokine expression (CCR5 KO vs wild type, All D TTNYT-treated vs. saline-treated, injured saline treated vs naïve); 3) paired t-test for the difference between two sides (ipsi and contra) in cytokine expression. The criterion for statistical significance was p<0.05.
M-DAPTA attenuated pain in the paw of rats ipsilateral to experimentally inflicted nerve damage. All D:TTNYT, can be shown to be a CCR5 antagonist that blocks infection of a CCR5 using virus, comparable to m-DAPTA, in blocking HIV infectivity. It not only prevents the development of nerve-injury induced neuropathic pain in both behavioral tests, but also reverses already established hypersensitivity. The behavioral outcomes probably resulted from inhibition of the inflammatory response following nerve lesion: cytokine changes in spinal cord and relevant peripheral nerve will be described in light of the histopathology and All D:TTNYT's chemokine antagonist properties. Details and other results are reported below.
1. Relative antiviral in vitro potency of DAPTA & All D:TTNYT on CCR5 receptors
As illustrated in
2. The CCR5 receptor antagonist, All D:TTNYT, not only prevented the development of nerve injury induced chronic pain, but also reversed established hypersensitivity.
In a pilot study, we observed that 0.01 mg/kg of DAPTA inhibited neuropathic pain development (not shown). Our current experiments demonstrated that systemic administration of All D:TTNYT prevented the development of thermal hyperalgesia and mechanical allodynia following injury on the left sciatic nerve, which is effective at the dose of 0.1-1 mg/kg. All D:TTNYT also reversed already established mechanical and thermal hypersensitivity. The effect is more prominent with the dose of 0.2-1 mg/kg. N=4 per group, ##, p<0.01, injured vs baseline, *, P<0.05 All D:TTNYT vs saline; **p<0.01 All D:TTNYT vs saline.
3. All D:TTNYT, inhibited nerve injury induced spinal glial activation
A. Microglia Reaction (iba-1)
Nerve injury induced microglial activation in the ipsilateral side spinal cord, which was significantly reduced by the systemic administration of All D:TTNYT. Note the difference of microglial cell size, shape, cell density and iba-1 ir intensity between the group of saline and All D:TTNYT treated animals.
B. Astrocyte Reaction (GFAP)
All D:TTNYT slightly inhibited nerve injury induced spinal astrocyte activation. The effect of All D:TTNYT on astrocytes was less evident than that of microglia.
4. All D:TTNYT reduced local inflammatory response within the spinal cord.
Following peripheral nerve injury, IL-1b and IL-6 mRNA in the ipsilateral spinal cord is increased. The difference between ipsi and contralateral sides was reduced with the treatment of All D:TTNYT.
All D:TTNYT has been shown to prevent and reverse neuropathic pain and microglial activation after nerve injury fed to rats in a model where pathogenesis has been shown to be CCR2 dependent.
5. All D TTNYT blocked CCR2 and CCR5 mediated human monocyte chemotaxis
Where pathogenesis has been shown to be CCR2 dependent, All D:TTNYT has been shown to prevent and reverse neuropathic pain and microglial activation. The peptide was fed to rats in various nerve injury rat models as shown by the following sections.
CCR2 and CCR5 control trafficking of monocyte/macrophages and mediate the inflammatory response during infectious disease and tissue injury. MCP-1 is a specific ligand for CCR2, while MIP-1β is specific for CCR5. In order to identify the receptor targets of All D TTNYT, we tested the ability of All D TTNYT to antagonize the function of chemokine receptors by blocking the chemotactic migration of human monocytes in the presence of specific ligand. Monocytes were treated for 30 minutes, 37° C. with All D TTNYT before testing. The results (
6. Oral administration of All D TTNYT potently attenuated nerve injury induced mechanical and thermal hypersensitivity
All D TTNYT prevented the development of neuropathic pain. To test the hypothesis that All D TTNYT alleviates behavioral signs of neuropathic pain, we first evaluated the effects of All D TTNYT on the development of mechanical allodynia and thermal hyperalgesia in rats following nerve injury. Rats started to receive All D TTNYT or saline on the day of the surgery and the drug was delivered orally, once per day and the treatment lasted for 7 days. Shortly after partial ligation of the left sciatic nerve, rats receiving saline showed an exaggerated bilateral decrease of paw withdrawal threshold in response to von Frey hair stimulation (
All D TTNYT reversed already established neuropathic pain. We also examined the effects of All D TTNYT on already established hypersensitivity following nerve lesion. All D TTNYT was given orally on day 8 post-injury, where both paw withdrawal threshold and latency in response to mechanical and thermal stimuli, respectively, had already reached their lowest level (
7. All D TTNYT inhibited nerve injury induced spinal microglial activation
In order to understand the potential underlying mechanisms in relieving pain behavior, we examined the effects of All D TTNYT on spinal microglia. In nerve-injured rats receiving saline treatment, there was a strong increase in Iba-1 immunoreactivity (ir) condensed at the ipsilateral side of spinal DH and VH at 7 days post-surgery. This pattern of microglial expression was no longer observed in rats treated with All D TTNYT (
8. The effect of All D TTNYT on nerve injury induced spinal astrocyte activation
As nerve injury induced microglia and astrocytes activation usually occurred together, we also examined the effects of All D TTNYT on astrocyte activation in the spinal cord following nerve injury. Spinal astrocytes were labelled with an antibody against glial fibrillary acid protein (GFAP). Changes in GFAP ir after peripheral nerve injury are depicted in
9. All D TTNYT reduced the increase of cytokines in the spinal cord following the lesion on the sciatic nerve
To explore whether All D TTNYT, a potent dual CCR2/CCR5 antagonist, could alter local inflammatory response and thereby explain its potential effect on hypersensitivity, we measured levels of pro-inflammatory cytokines IL-1β and IL-6 transcripts in the spinal cords and in sciatic nerves with quantitative real time-PCR. As depicted in
10. Nerve injury induced CCR5 expression in activated spinal microglia
As the expression of CCR2 in spinal microglia has been reported previously [2], whether CCR5 can be induced within the spinal cord by nerve injury is unclear, to gain insight into the site of action of All D TTNYT in this specific neuropathic pain condition, we examined the expression and the cellular localization of CCR5 in rat spinal cord. CCR5 mRNAs were not detected within the spinal cords of naïve rats by using in situ hybridization method (
11. CCR5 is required for the development of neuropathic pain and spinal microglial activation following nerve injury
The critical role of CCR2 in the pathogenesis of neuropathic pain has been very well established [2;31]. To further confirm that CCR5 is also necessary for the development of neuropathic pain, we made use of CCR5 knock-out mice. As depicted in
The CCR2 AND CCR5 antagonist, All D:TTNYT, not only prevents the development of mechanical and thermal hypersensitivity following nerve injury, but also reverses established neuropathic pain.
Without exception the natural L-amino acid forms of these pentapeptides can be made as all D-amino acid forms with no loss of bioactivity, while protecting against inactivating proteolytic enzymes and bestowing useful pharmacodynamic properties, e.g. making oral activity possible. The “lock and key” model of peptide-receptor interactions has now been displaced with a “vibratory resonance” model.
The biological outcomes of All D:TTNYT in this context may be attributed to its inhibition of spinal microglial/astrocyte activation and local inflammatory responses by targeting the CCR2 receptor or the CCR5 receptor.
These observations make clear that neuroinflammation lies at the root of many diseases of unknown etiology and is initiated in one or more of three ways: 1) viral/microbial infection, 2) tissue trauma/injury or 3) environmental toxin exposure. The actual form the neuroinflammatory disease takes is a function of when? [e.g., first trimester (autism), second trimester (schizophrenia), after 65 years (Alzheimer's), etc] and “where?” [eg, optic nerve demylination in multiple sclerosis, spinal cord in Lou Gehrig' disease, substantia nigra of brain (Parkinson's disease, joints (arthritis), etc.] The inventors also believe that cancers associated with inflammation will respond to this treatment. This is the first report showing a benefit of All D TTNYT in a model of neuropathic pain. While CCR2 has a well established role in the inflammation underlying chronic pain, some evidence for the involvement of CCR5 in development of neuropathic pain after injury is suggested by studies showing that injection of MIP1α and RANTES into peripheral nerve elicited pain behaviors [13;18]. Our results support such a view and, using genetically deficient animals, demonstrate that CCR5 is required for the development of neuropathic pain. Mice lacking CCR5 develop neither mechanical nor thermal hypersensitivity following injury on the nerve.
Our results further suggest that pharmacological blockade by All D TTNYT of either or both CCR2 and CCR5 have therapeutic potential in injury associated-neuropathic pain. All D TTNYT acts as a potent antagonist for both CCR5 and CCR2 mediated human monocyte chemotaxis. In vivo experiments revealed that this dual antagonist is orally active and exerts potent antiallodynic and antihyperalgesic effects in both preventive and reversal treatment paradigms in rats following peripheral nerve injury. All D TTNYT relieves neuropathic pain through reducing CCR2/CCR5 mediated inflammatory reaction, since in parallel with the behavioral outcomes, we observed that 1) pharmacological blockade of both CCR2/CCR5 by All D TTNYT reduced spinal microglial activation triggered by nerve injury, including the abolishment of blood born monocyte/macrophage recruitment into the spinal parenchyma; 2) All D TTNYT was able to prevent the increase of pro-inflammatory cytokines along the pain signaling pathway.
DAPTA, the parent compound from which All D TTNYT was derived, had previously been shown to have anti-inflammatory effects including inhibition of CCR5/MIP-1β chemotaxis on human monocytes [21], attenuation of neuroinflammation in an Alzheimer's disease model [25] and reduction of the inflammatory cytokines TNF-α, IL-1, and IL-6 in HIV patients [26]. In the current study, our in vitro experiments clearly demonstrated that All D TTNYT potently blocks MIP-1β and MCP-1 elicited monocyte chemotaxis with IC50s of 0.18 pM and 4.2 pM, respectively. The remarkably potent inhibitory effect of All D TTNYT on both CCR5 and CCR2 mediated monocyte trafficking suggests that dual antagonists of CCR2 and CCR5 may provide new tools for the study of chemokine signaling in different pathological conditions, and potentially therefore better treatment outcomes.
The roles of MCP-1/CCR2 signaling in chronic pain have been well documented. Over-expression of MCP-1 showed enhanced pain sensitivity [17]. Neutralizing MCP-1 prevented the development of nerve injury evoked hypersensitivity [10]. Drugs that block CCR2 receptors can reduce hypersensitivity in HIV [5] and focal nerve demyelination [4] associated peripheral neuropathy. Lack of CCR2 in mice impaired the development of mechanical allodynia following nerve injury [2;31]. Relative to CCR2, the function of CCR5 in chronic pain is less well defined. However, some recent evidence suggested the potential involvement of CCR5 in different aspects of pain modulation. Microinjection of RANTES, a natural ligand for CCR5, into the periaqueductal grey, a brain region critical to the processing of pain signals, induced hyperalgesia, which was prevented by pretreatment with antibodies against RANTES [3]. Partial sciatic nerve ligation induced expression of MIP-1α, another natural ligand for CCR5, on macrophages and Schwann cells in injured nerve. Tactile allodynia and thermal hyperalgesia developed following nerve lesion was prevented by perineural injection of neutralising anti-MIP-1α and CCR5 siRNA [13]. The results yielded from our current investigation using CCR5 KO mice clearly demonstrated that similar to CCR2, CCR5 is required for the development of neuropathic pain following nerve injury. Pharmacological intervention with All D TTNYT, a dual antagonist of both CCR2 and CCR5, delivered orally, not only prevented the initiation of mechanical and thermal hypersensitivity, but also reversed both mechanical and thermal hypersensitivity already established in rats having ligation on the sciatic nerve.
Together with its analgesic effect, we also observed that All D TTNYT efficiently inhibited spinal microglial activation, including changes in cell number, cell size and cell shape. In addition, All D TTNYT successfully blocked the entrance of blood born monocytes/macrophages into the spinal cord parenchyma. All these most likely occurred through the interaction of All D TTNYT with both CCR2 and CCR5 receptors present on circulating monocytes, macrophages and activated spinal microglia. Both CCR2 [31] and CCR5 KO (current study) mice exhibited an impaired microglial response following an injury on the nerve. In coincidence with the inhibition of microglial activation, the levels of some pro-inflammatory cytokines, such as IL-1β and IL-6, most likely released by activated spinal glial cells and peripheral immune cells, were also reduced with the treatment of All D TTNYT. The roles of these pro-inflammatory mediators in the pathophysiology of neuropathic pain has been extensively studied [23]. They contribute significantly to enhance excitability of sensory neurons and to maintain pathological pain states. Therefore, we assume that All D TTNYT attenuate mechanical and thermal hypersensitive response, at least partially, through modulation of nerve injury induced glial activation and subsequent inflammatory reaction.
Because of their key roles in inflammation related diseases, CCR2 and CCR5 constitute attractive therapeutic targets. However, it should be noted that the chemokine network is notorious for its redundancy and receptor promiscuity. Apparent redundancy in the chemokine system, such as CCR2 and CCR5, might exist to confer robustness to the control of inflammation [7;8;12]. Moreover, the fact that chemokine receptors form hetero-oligomeric complexes composed of at least three chemokine receptors CCR2, CCR5, and CXCR4, bring an additional layer of complexity to this system [29]. Specific antagonism of one chemokine receptor can lead to functional cross-inhibition of the others [29]. It is perhaps more correct to consider that the functional and biologically relevant therapeutic targets are the naturally occurring mixed receptor complexes. Heterologous desensitization of CCR2-mediated responses may provide an explanation for the functional action of All D TTNYT, which is derived from the CCR5 antagonist DAPTA [19]. CCR5 expression is low on resting cells and its up-regulation after injury, in the context of likely hetero-dimer formation may serve to attenuate or limit further CCR2 driven inflammation. CCR2 may be more important for early migration responses into injured spinal cord, as CCR5 is low. As CCR5 becomes expressed, and R5 ligands are locally released, the CCR5 pathways also contribute to spinal microglial reactions.
The action of All D TTNYT to limit CCR2 responses causing chronic pain may or may not occur directly via CCR2, but rather as a consequence of CCR5-mediated desensitization of CCR2 [29]. This model of joint CCR2/CCR5 interaction could help explain why selective or “pure” receptor-targeted therapeutic compounds that antagonize single chemokine receptors afford little efficacy in clinical use [32]. Useful antagonists might block multiple receptors, or could target a functional receptor complex, rather than constituent single receptors. Receptor oligomeration represents a regulatory mechanism for a more nuanced control of CCR2 and CCR5 driven inflammatory activation that might be exploited clinically. Drugs that block more than one component of the chemokine system may overcome the functional redundancy and cross-regulation in the chemokine system that presumably limits effectiveness of CCR2 antagonists and might be a more efficacious strategy than targeting either receptor alone. Our results support these hypotheses since a novel and potent, orally active dual CCR2/CCR5 antagonist, All D TTNYT, has multiple benefits in injury induced-neuropathic pain.
In conclusion, we provided evidence that in addition to chemokine receptor CCR2, CCR5 is equally necessary for the development of neuropathic pain. Based on the structural similarity and functional redundancy in controlling monocytes/macrophages trafficking and spinal microglial reaction, we suggest that dual targeting CCR2/CCR5 should provide greater efficacy than targeting CCR2 or CCR5 alone and All D TTNYT has the potential for broad clinical use in neuropathic pain treatment.
All D TTNYT has the ability to block monocyte chemotaxis mediated by other chemokine receptors, for example CX3CR1, the receptor for fractalkine, at similar highly potent concentrations. (data not shown). This receptor is almost as well established in mediating painful neuropathy as CCR2. The HIV envelope (gp120) has affinity for binding to many other chemokine receptors (see review by Lokesh, Agrawal) which are not well established as mediating painful neuropathy. Thus, the ability to block many chemokine receptors, which the HIV virus has evolved, can be exploited if, as this paper suggests, duel, triple, quadruple and multiple chemokine receptor blockades, can lead to more efficacious anti-neuropathic pain activities. Thus other gp120 derived modified peptide analogs would be predicted to be highly effective.
A gp120 derived peptide is a contiguous sequence of amino acids from a gp120 envelope protein found to have the proper chemokine antagonist activity. The peptide has a length between one hundred (100) amino acids and four (4) amino acids, including each and every range and each and every length between 100 and 4. Modifications include all common peptide stabilizing modifications, including, but not limited to the use of amino acid D stereo isomers.
This application claims the benefit of U.S. Provisional Application No. 61/302,933, filed Feb. 9, 2010.
| Number | Date | Country | |
|---|---|---|---|
| 61302933 | Feb 2010 | US |
