PD-1/PD-L1 Inhibition Enhances Chemotherapy-Induced Neuropathic Pain by Suppressing Neuroimmune Antinociceptive Signaling.

Cytotoxic agents synergize with immune checkpoint inhibitors and improve outcomes for patients with several cancer types. Nonetheless, a parallel increase in the incidence of dose-limiting side effects, such as peripheral neuropathy, is often observed. Here, we investigated the role of the programmed cell death-1 (PD-1)/programmed death-ligand 1 (PD-L1) axis in the modulation of paclitaxel-induced neuropathic pain. We found that human and mouse neural tissues, including the dorsal root ganglion (DRG), expressed basal levels of PD-1 and PD-L1. During the development of paclitaxel-induced neuropathy, an increase in PD-L1 expression was observed in macrophages from the DRG. This effect depended on Toll-like receptor 4 activation by paclitaxel. Furthermore, PD-L1 inhibited pain behavior triggered by paclitaxel or formalin in mice, suggesting that PD-1/PD-L1 signaling attenuates peripheral neuropathy development. Consistent with this, we observed that the combined use of anti-PD-L1 plus paclitaxel increased mechanical allodynia and chronic neuropathy development induced by single agents. This effect was associated with higher expression of inflammatory markers (Tnf, Il6, and Cx3cr1) in peripheral nervous tissue. Together, these results suggest that PD-1/PD-L1 inhibitors enhance paclitaxel-induced neuropathic pain by suppressing PD-1/PD-L1 antinociceptive signaling.

Sulfated polysaccharide from Gracilaria caudata reduces hypernociception and inflammatory response during arthritis in rodents.

Polysaccharide from marine alga Gracilaria caudata has potential health benefits, such as anti-inflammatory, gastroprotective and antidiarrheal effects. Here, we investigated the effect of a sulfated polysaccharide from G. caudata (SP-GC) on hypernociception and inflammatory response in arthritis models. The animals received SP-GC (3, 10 or 30 mg/kg) 1 h before tibio-tarsal injection of zymosan. Hypernociception, histopathology, edema, vascular permeability, myeloperoxidase (MPO) activity, cell influx, interleukin (IL)-1ß and nitric oxide (NO) levels were evaluated in acute phase. In another protocol, animals received SP-GC (30 mg/kg) 2 h post-complete Freund's adjuvant (CFA). Hypernociception, edema and arthritis index were determined in acute, sub-chronic and chronic phases. Rota-rod test measured the motor performance. SP-GC significantly reduced, in a dose-dependent manner, the zymosan-induced hypernociception with maximal effect at 30 mg/kg. The microscopic inflammation, joint edema, MPO activity, cell influx, IL-1ß and NO levels were also reduced by SP-GC. In the CFA-induced arthritis, SP-GC inhibits the hypernociception, edema and arthritic index in acute, sub-chronic and chronic phases. SP-GC did not alter the motor performance of animals. In conclusion, SP-GC exerts protective effect in models of arthritis due to the modulation of cell influx, IL-1ß and NO levels, culminating in the reduction of hypernociception and edema.

Clinical-like cryotherapy improves footprint patterns and reduces synovial inflammation in a rat model of post-traumatic knee osteoarthritis.

Cryotherapy is a non-pharmacological treatment commonly used to control inflammation and improve function after acute traumas. However, there are no definitive findings about its effects on chronic joint diseases such as knee osteoarthritis (KOA). The aim of this study was to investigate the effects of clinical-like cryotherapy on functional impairment and synovial inflammation in a rat model of KOA generated by anterior cruciate ligament transection (ACLT). Thirty-two male Wistar rats were randomly divided into four groups (n = 8/group): Control, KOA, KOA + Cryotherapy and KOA + Placebo. The last two groups were submitted to the relevant interventions twice a day for five days (61 to 65), with each session lasting 20 min. Gait test, skin temperature, thermal response threshold and joint swelling were assessed in all groups before ACLT surgery, and pre (60th day) and post (66th day) intervention protocols. On day 66, the animals were euthanized and exsanguinated to remove the synovial membrane for histopathological examination and synovial fluid to determine the leukocyte count and cytokine concentration. After the intervention period (66th day), footprint area only increased in the KOA + Cryotherapy group (P = 0.004; 14%) when compared to KOA and KOA + Placebo, but did not differ from controls. Cryotherapy lowered the synovial fluid leukocyte count (P < 0.0001; ≥95.0%) and cytokine concentration (P < 0.0001; ≥55%) when compared to the KOA and Placebo groups. Synovial score and synovial fibrosis did not differ in the KOA groups. In conclusion, footprint patterns improved in rats with ACLT-induced KOA as a result of clinical-like cryotherapy, which also lowered the synovial fluid leukocyte count and inflammatory cytokine concentration in these rats.

Involvement of Endothelin Receptors in Peripheral Sensory Neuropathy Induced by Oxaliplatin in Mice.

The aim of this study was to evaluate the participation of the endothelin ETA and ETB receptors and the effects of bosentan in oxaliplatin-induced peripheral sensory neuropathy (OIN) in mice. Adult male Swiss mice received 1 mg/kg of oxaliplatin intravenously, twice a week for 5 weeks. Dorsal root ganglia (DRG) and spinal cords were removed for evaluation of the endothelin ETA and ETB receptor expression. Afterwards, selective (BQ-123 and BQ-788; 10 nmol in 30 µL, intraplantarly) and non-selective (bosentan, 100 mg/kg, orally) antagonists were administered in order to evaluate the involvement of the endothelin receptors in OIN. Mechanical and thermal nociception tests were performed once a week for 56 days. Oxaliplatin induced mechanical and thermal hypersensitivity and increased the endothelin ETA receptor expression in both the DRG and spinal cord (P < 0.05). Endothelin ETB receptor expression was increased in the DRG (P < 0.05) but not in the spinal cord. Both endothelin ETA and ETB receptor selective antagonists partially prevented mechanical hyperalgesia in mice with OIN (P < 0.05). Moreover, bosentan prevented mechanical and thermal hypersensitivity in oxaliplatin-treated mice (P < 0.05). In conclusion, both endothelin ETA and ETB receptors seem to be involved in the OIN in mice and they should be considered possible targets for the management of this clinical feature.

Neurotoxic effect of oxaliplatin: Comparison with its oxalate-free analogue cis-[PtII(1R,2R-DACH)(3-acetoxy-1,1-cyclobutanedicarboxylato)] (LLC-1402) in mice.

Studies suggest that oxalate is involved in the development oxaliplatin-induced peripheral sensory neuropathy (OPSN). This study aimed to compare the neurotoxic effects of oxaliplatin with its oxalate-free cytotoxic analogue cis-[PtII(1R,2R-DACH)(3-acetoxy-1,1-cyclobutanedicarboxylato)] (LLC-1402) in mice. Oxaliplatin and LLC-1402 were intravenously injected in male Swiss mice with a total of nine injections. Oxalate was intraperitoneally injected in other animals. The development of OPSN was evaluated using mechanical and thermal sensitivity tests. Dorsal root ganglia of the mice were removed to evaluate c-Fos, ATF3 and iNOS expression and a sample of blood was collected for leukocyte count and hepatic and renal biochemical function tests. Oxaliplatin and LLC-1402 decreased the mechanical and thermal nociceptive threshold, whilst oxalate lead to a partial and later increase in the mechanical sensitivity (P<0.05). c-Fos, ATF3 and iNOS expressions were increased in neuronal cells during and after the end of the injections in animals treated with oxaliplatin and LLC-1402 (P<0.05), even though oxaliplatin lead to an earlier increase. Only c-Fos expression was elevated during the period of injections in the oxalate group (P<0.05), but this expression reduced after the end of the treatment. c-Fos expression was also shown in glial satellite cells only in the oxaliplatin-treated animals. Oxaliplatin and LLC-1402 reduced leukocyte count (P<0.05), but did not change renal and liver functions. In conclusion, oxalate may contribute to an earlier development of peripheral sensory neuropathy. However, the antitumor cytotoxic mechanism of oxaliplatin seems to be the main responsible by its neurotoxic effect.

Antinociceptive and anti-inflammatory effects of Caryocar coriaceum Wittm fruit pulp fixed ethyl acetate extract on zymosan-induced arthritis in rats.

The ethyl acetate extract from the fruit pulp of Caryocar coriaceum Wittm (Caryocaraceae), popularly known as pequi, has wide applications in popular medicine. Preclinical tests have demonstrated the therapeutic properties of the oil. We investigated the antinociceptive and anti-inflammatory effects of Pequi C. coriaceum Wittm ethyl acetate extract (PCCO) on zymosan-induced arthritis in rat knee joint. The animals were pretreated with PCCO for 7 consecutive days or with a single dose. Paw elevation time (PET), leukocyte infiltration, myeloperoxidase activity (MPO) and cytokine levels were assessed 4h after zymosan injection. Synovial tissue was harvested for immunohistochemical analysis, edema and vascular permeability. We observed a significant decrease in PET with PCCO pretreatment. PCCO showed a significant reduction of leukocyte migration and a decrease in MPO. Decreases were observed in cytokine release in the synovial fluid and TNF-α and cyclooxygenase-1 immunostaining in synovial tissue. Edema was inhibited by treatment with all doses of PCCO. The data suggest that PCCO exerts antinociceptive and anti-inflammatory effects on arthritis in rats.