Switching Rat Resident Macrophages from M1 to M2 Phenotype by Iba1 Silencing Has Analgesic Effects in SNL-Induced Neuropathic Pain.

Resident macrophages from dorsal root ganglia are important for the development of traumatic-induced neuropathic pain. In the first 5-7 days after a traumatic sciatic nerve injury (i.e., spinal nerve ligation (SNL), spared nerve injury (SNI), sciatic nerve transection or sciatic nerve ligation and transection), Ionized binding adapter protein 1 (Iba1) (+) resident macrophages cluster around dorsal root ganglia neurons, possibly contributing to nerve injury-induced hypersensitivity. Since infiltrating macrophages gradually recruited to the lesion site peak at about 7 days, the first few days post-lesion offer a window of opportunity when the contribution of Iba1 (+) resident macrophages to neuropathic pain pathogenesis could be investigated. Iba1 is an actin cross-linking cytoskeleton protein, specifically located only in macrophages and microglia. In this study, we explored the contribution of rat Iba1 (+) macrophages in SNL-induced neuropathic pain by using intra-ganglionic injections of naked Iba1-siRNA, delivered at the time the lesion occurred. The results show that 5 days after Iba1 silencing, Iba1 (+) resident macrophages are switched from an M1 (pro-inflammatory) phenotype to an M2 (anti-inflammatory) phenotype, which was confirmed by a significant decrease of M1 markers (CD32 and CD86), a significant increase of M2 markers (CD163 and Arginase-1), a reduced secretion of pro-inflammatory cytokines (IL-6, TNF-α and IL-1ß) and an increased release of pro-regenerative factors (BDNF, NGF and NT-3) which initiated the regrowth of adult DRG neurites and reduced SNL-induced neuropathic pain. Our data show for the first time, that it is possible to induce macrophages towards an anti-inflammatory phenotype by interacting with their cytoskeleton.

Therapeutic potential of certain drug combinations on paclitaxel-induced peripheral neuropathy in rats.

BACKGROUND AND AIMS: Experimental research and clinical data support the potential combination therapy for the treatment of neuropathic pain. We aimed to investigate the analgesic effect of the following associations: gabapentin + etifoxine; tramadol + etifoxine; gabapentin + tramadol, in an experimental model of peripheral neuropathy induced by paclitaxel. MATERIALS AND METHODS: Neuropathy was induced in male Wistar rats by the daily administration of 2 mg÷kg body weight (bw) paclitaxel intraperitoneally, four days in a row. Analgesics were given concomitantly with paclitaxel, in the following doses: tramadol 15 mg÷kg bw, etifoxine 100 mg÷kg bw, gabapentin 300 mg÷kg bw. Tactile allodynia and mechanical hyperalgesia were assessed using the Dynamic Plantar Aesthesiometer apparatus (Ugo Basile). After 18 days of treatment, the brain and liver tissue susceptibility to lipid peroxidation was evaluated and the sciatic nerve histological examination of the effect on myelin fibers was performed. RESULTS AND CONCLUSIONS: Experimental data have shown a strong analgesic effect of these three tested combinations expressed mainly by the statistically significant increased maximum response time, both in the assessment of allodynia and hyperalgesia. The gabapentin + tramadol combination lead to the maximum analgesic effect, immediately after the discontinuation of paclitaxel (44.94%, p<0.0001) and throughout the study. The treatment associated with tramadol caused a reduction in lipid peroxidation in the brain as compared to paclitaxel group. Combination therapy showed reduced damage to myelinated fiber density in the sciatic nerve. The drug combinations used in the experiment showed therapeutic potential in the fight against neuropathic pain induced by the administration of taxanes.