minocycline and Sciatica

Patients with unilateral sciatica have heightened responses to intradermal capsaicin compared to pain-free volunteers. No studies have investigated whether this pain model can screen for novel anti-neuropathic agents in patients with pre-existing neuropathic pain syndromes.. This study compared the effects of pregabalin (300 mg) and the tetracycline antibiotic and glial attenuator minocycline (400 mg) on capsaicin-induced spontaneous pain, flare, allodynia and hyperalgesia in patients with unilateral sciatica on both their affected and unaffected leg.. Eighteen patients with unilateral sciatica completed this randomised, double-blind, placebo-controlled, three-way cross-over study. Participants received a 10 µg dose of capsaicin into the middle section of their calf on both their affected and unaffected leg, separated by an interval of 75 min. Capsaicin-induced spontaneous pain, flare, allodynia and hyperalgesia were recorded pre-injection and at 5, 20, 40, 60 and 90 min post-injection. Minocycline tended to reduce pre-capsaicin injection values of hyperalgesia in the affected leg by 28% (95% CI 0% to 56%). The area under the effect time curves for capsaicin-induced spontaneous pain, flare, allodynia and hyperalgesia were not affected by either treatment compared to placebo. Significant limb differences were observed for flare (AUC) (-38% in affected leg, 95% CI for difference -19% to -52%). Both hand dominance and sex were significant covariates of response to capsaicin.. It cannot be concluded that minocycline is unsuitable for further evaluation as an anti-neuropathic pain drug as pregabalin, our positive control, failed to reduce capsaicin-induced neuropathic pain. However, the anti-hyperalgesic effect of minocycline observed pre-capsaicin injection is promising pilot information to support ongoing research into glial-mediated treatments for neuropathic pain. The differences in flare response between limbs may represent a useful biomarker to further investigate neuropathic pain. Inclusion of a positive control is imperative for the assessment of novel therapies for neuropathic pain.

Topics: Adult; Analysis of Variance; Capsaicin; Cross-Over Studies; Double-Blind Method; Drug Therapy, Combination; Female; gamma-Aminobutyric Acid; Humans; Hyperalgesia; Injections, Intradermal; Male; Middle Aged; Minocycline; Pain; Pregabalin; Sciatica; Time Factors; Treatment Outcome

The repeated administration of microglial inhibitor (minocycline) and CCR2 antagonist (RS504393) attenuated the neuropathic pain symptoms in rats following chronic constriction injury of the sciatic nerve, which was associated with decreased spinal microglia activation and the protein level of CCL2 and CCR2. Furthermore, in microglia primary cell cultures minocycline downregulated both CCL2 and CCR2 protein levels after lipopolysaccharide-stimulation. Additionally, in astroglia primary cell cultures minocycline decreased the expression of CCL2, but not CCR2. Our results provide new evidence that modulation of CCL2/CCR2 pathway by microglial inhibitor as well as CCR2 antagonist is effective for neuropathic pain development in rats.

Topics: Analgesics; Animals; Animals, Newborn; Benzodiazepines; Benzoxazines; Cells, Cultured; Chemokine CCL2; Disease Models, Animal; Gene Expression Regulation; Hyperalgesia; Male; Minocycline; Neuroglia; Pain Threshold; Physical Stimulation; Rats; Rats, Wistar; Receptors, CCR2; Sciatica; Signal Transduction; Spinal Cord; Spiro Compounds

The molecular mechanisms underlying neuropathic pain are constantly being studied to create new opportunities to prevent or alleviate neuropathic pain. The aim of our study was to determine the gene expression changes induced by sciatic nerve chronic constriction injury (CCI) that are modulated by minocycline, which can effectively diminish neuropathic pain in animal studies. The genes associated with minocycline efficacy in neuropathic pain should provide insight into the etiology of neuropathic pain and identify novel therapeutic targets.. We screened the ipsilateral dorsal part of the lumbar spinal cord of the rat CCI model for differentially expressed genes. Out of 22,500 studied transcripts, the abundance levels of 93 transcripts were altered following sciatic nerve ligation. Percentage analysis revealed that 54 transcripts were not affected by the repeated administration of minocycline (30 mg/kg, i.p.), but the levels of 39 transcripts were modulated following minocycline treatment. We then selected two gene expression patterns, B1 and B2. The first transcription pattern, B1, consisted of 10 mRNA transcripts that increased in abundance after injury, and minocycline treatment reversed or inhibited the effect of the injury; the B2 transcription pattern consisted of 7 mRNA transcripts whose abundance decreased following sciatic nerve ligation, and minocycline treatment reversed the effect of the injury. Based on the literature, we selected seven genes for further analysis: Cd40, Clec7a, Apobec3b, Slc7a7, and Fam22f from pattern B1 and Rwdd3 and Gimap5 from pattern B2. Additionally, these genes were analyzed using quantitative PCR to determine the transcriptional changes strongly related to the development of neuropathic pain; the ipsilateral DRGs (L4-L6) were also collected and analyzed in these rats using qPCR.. In this work, we confirmed gene expression alterations previously identified by microarray analysis in the spinal cord and analyzed the expression of selected genes in the DRG. Moreover, we reviewed the literature to illustrate the relevance of these findings for neuropathic pain development and therapy. Further studies are needed to elucidate the roles of the individual genes in neuropathic pain and to determine the therapeutic role of minocycline in the rat neuropathic pain model.

Topics: Amino Acid Transport System y+; Analgesics, Non-Narcotic; Animals; CD40 Antigens; Cytidine Deaminase; Disease Models, Animal; Functional Laterality; Gene Expression Profiling; Gene Expression Regulation; Lectins, C-Type; Male; Membrane Glycoproteins; Minocycline; Oligonucleotide Array Sequence Analysis; Pain Measurement; Pain Threshold; Rats; Rats, Wistar; Sciatica; Spinal Cord

In neuropathic pain the repeated minocycline treatment inhibited the mRNA and protein expression of the microglial markers and metalloproteinase-9 (MMP-9). The minocycline diminished the pronociceptive (IL-6, IL-18), but not antinociceptive (IL-1alpha, IL-4, IL-10) cytokines at the spinal cord level. In vitro primary cell culture studies have shown that MMP-9, TIMP-1, IL-1beta, IL-1alpha, IL-6, IL-10, and IL-18 are of microglial origin. Minocycline reduces the production of pronociceptive factors, resulting in a more potent antinociceptive effect. This change in the ratio between pro- and antinociceptive factors, in favour of the latter may be the mechanism of minocycline analgesia in neuropathy.

Topics: Analgesics; Animals; Animals, Newborn; Anti-Inflammatory Agents, Non-Steroidal; Cells, Cultured; Cytokines; Disease Models, Animal; Ganglia, Spinal; Gene Expression Regulation; Hyperalgesia; Male; Matrix Metalloproteinase 2; Matrix Metalloproteinase 9; Microglia; Minocycline; Neurons; Pain Measurement; Pain Threshold; Rats; Rats, Wistar; Sciatica; Spinal Cord; Tissue Inhibitor of Metalloproteinase-1

Metabotropic glutamate (mGlu) receptors, which are present on neurons and glial cells, have been shown to play a role in neuropathic pain. The present study sought to investigate how the glial inhibitors minocycline and pentoxifylline alter the effect that chronic constriction injury (CCI) has on the expression of mGlu receptors and on their associated ligands. RT-PCR analysis revealed that seven days after CCI, the mRNA levels of glial markers C1q and GFAP, as well as those of mGlu5 and mGlu3, but not mGlu7, were elevated in the lumbar spinal cord - ipsilateral to the injury. The protein levels of the microglial marker OX42, the astroglial marker GFAP, and mGlu5 receptor protein were increased, whereas the levels of mGlu2/3 and mGlu7 receptor proteins were reduced. Preemptive and repeated intraperitoneal (i.p.) administration (16 and 1h before nerve injury and then twice daily for seven days) of minocycline (30mg/kg) and pentoxifylline (20mg/kg) prevented the injury-induced changes in the levels of mGlu3 and mGlu5 receptor mRNAs and the injury-induced changes in the protein levels of all the receptors. Repeated administration of minocycline and pentoxifylline significantly attenuated CCI-induced allodynia (von Frey test) and hyperalgesia (cold plate test) measured on day seven after injury and potentiated the antiallodynic and antihyperalgesic effects of single i.p. and intrathecal (i.t.) injections of mGlu receptor ligands: MPEP, LY379268 or AMN082. We conclude that attenuation of injury-induced glial activation can reduce glutamatergic activity, thereby contributing to regulation of pain sensation.

Topics: Amino Acids; Analysis of Variance; Animals; Benzhydryl Compounds; Bridged Bicyclo Compounds, Heterocyclic; CD11b Antigen; Complement C1q; Disease Models, Animal; Drug Administration Schedule; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; Functional Laterality; Gene Expression Regulation; Glial Fibrillary Acidic Protein; Hyperalgesia; Male; Mice; Minocycline; Pain Measurement; Pain Threshold; Pentoxifylline; Pyridines; Receptors, Metabotropic Glutamate; RNA, Messenger; Sciatica; Spinal Cord

Substance P (SP), a representative member of the tachykinin family, is involved in nociception under physiological and pathological conditions. Recently, hemokinin-1 (HK-1) was identified as a new member of this family. Although HK-1 acts on NK(1) tachykinin receptors that are thought to be innate for SP, the roles of HK-1 in neuropathic pain are still unknown.. Using rats that had been subjected to chronic constrictive injury (CCI) of the sciatic nerve as a neuropathic pain model, we examined the changes in expression of SP- and HK-1-encoding genes (TAC1 and TAC4, respectively) in the L4/L5 spinal cord and L4/L5 dorsal root ganglia (DRGs) in association with changes in pain-related behaviours in this neuropathic pain state.. The TAC4 mRNA level was increased on the ipsilateral side of the dorsal spinal cord, but not in DRGs, at day 3 after CCI. In contrast, the TAC1 mRNA level was significantly increased in the DRGs at day 3 after CCI without any changes in the dorsal spinal cord. Analysis of a cultured microglial cell line revealed the presence of TAC4 mRNA in microglial cells. Minocycline, an inhibitor of microglial activation, blocked the increased expression of TAC4 mRNA after CCI and inhibited the associated pain-related behaviours and microglial activation in the spinal cord.. The present results suggest that HK-1 expression is increased at least partly in activated microglial cells after nerve injury and is clearly involved in the early phase of neuropathic pain.

Topics: Animals; Cell Line; Disease Models, Animal; Gene Expression; Immunohistochemistry; Lumbosacral Region; Male; Microglia; Minocycline; Pain Threshold; Rats; Rats, Sprague-Dawley; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Sciatica; Spinal Cord; Tachykinins