Background: Peripheral cold neuropathic pain is a serious side effect of oxaliplatin treatment. However, the mechanism of oxaliplatin-induced cold hyperalgesia is unknown. In the present study, we investigated the effects of oxaliplatin on transient receptor potential ankyrin 1 (TRPA1) in dorsal root ganglion (DRG) neurons of rats. Results: Behavioral assessment using the acetone spray test showed that 3 and 6 mg/kg oxaliplatin (i.p.) induced acute cold hypersensitivity after 1, 2, 4, and 7 days. Real-time PCR showed that oxaliplatin (6 mg/kg) significantly increased TRPA1 mRNA expression in DRGs at days 1, 2, and 4. Western blotting revealed that oxaliplatin significantly increased TRPA1 protein expression in DRGs at days 2, 4, and 7. Moreover, in situ hybridization histochemistry revealed that most TRPA1 mRNA-labeled neurons in the DRGs were small in size. Oxaliplatin significantly increased co-localization of TRPA1 expression and isolectin B4 binding in DRG neurons. Oxaliplatin induced a significant increase in the percent of TRPA1 mRNA-positive small neurons in DRGs at days 1, 2, and 4. In addition, we found that intrathecal administration of TRPA1 antisense, but not TRPA1 mismatched oligodeoxynucleotides, knocked down TRPA1 expression and decreased oxaliplatin-induced cold hyperalgesia. Double labeling showed that p-p38 mitogen-activated protein kinase (MAPK) was co-expressed in TRPA1 mRNA-labeled neurons at day 2 after oxaliplatin administration. Intrathecal administration of the p38 MAPK inhibitor, SB203580, significantly decreased oxaliplatin-induced acute cold hypersensitivity. Conclusions: Together, these results demonstrate that TRPA1 expression via activation of p38 MAPK in DRG neurons, at least in part, contributes to the development of oxaliplatin-induced acute cold hyperalgesia.

The clinical anti-cancer efficacy of vincristine is limited by the development of dose-dependent peripheral neuropathy. Up-regulation of transient receptor potential vanilloid 1 (TRPV1) is correlated with peripheral neuropathy following anti-cancer drug treatment. To analyze the contribution of TRPV1 to the development of vincristine-induced mechanical allodynia/hyperalgesia, TRPV1 expression in the rat dorsal root ganglion (DRG) was analyzed after vincristine treatment. Mechanical allodynia/hyperalgesia was tested with von Frey filaments 14 days after intraperitoneal administration of 0.1 mg/kg vincristine in rats. TRPV1 expression in DRGs following vincristine treatment was assessed with western blot analysis and in situ hybridization histochemistry. Vincristine-induced mechanical allodynia/hyperalgesia after day 14 was significantly inhibited by the TRP antagonist ruthenium red (3 mg/kg, s.c.) and the TRPV1 antagonist capsazepine (30 mg/kg, s.c.). Vincristine treatment increased the expression of TRPV1 protein in DRG neurons. In situ hybridization histochemistry revealed that most of the TRPV1 mRNA-labeled neurons in the DRG were small in size. Immunohistochemistry showed that isolectin B4-positive small DRG neurons co-expressed TRPV1 protein 14 days after treatment. These results suggest that vincristine treatment increases TRPV1 expression in small DRG neurons. TRPV1 expression may contribute to the development of vincristine-induced painful peripheral neuropathy.

Painful peripheral neuropathy is a common adverse effect of paclitaxel (PTX) treatment. To analyze the contribution of transient receptor potential vanilloid 1 (TRPV1) in the development of PTX-induced mechanical allodynia/hyperalgesia and thermal hyperalgesia, TRPV1 expression in the rat spinal cord was analyzed after intraperitoneal administration of 2 and 4 mg/kg PTX. PTX treatment increased the expression of TRPV1 protein in the spinal cord. Immunohistochemistry showed that PTX (4 mg/kg) treatment increased TRPV1 protein expression in the superficial layers of the spinal dorsal horn 14 days after treatment. Behavioral assessment using the paw withdrawal response showed that PTX-induced mechanical allodynia/hyperalgesia and thermal hyperalgesia after 14 days was significantly inhibited by oral or intrathecal administration of the TRPV1 antagonist AMG9810. We found that intrathecal administration of small interfering RNA (siRNA) to knock down TRPV1 protein expression in the spinal cord significantly decreased PTX-induced mechanical allodynia/hyperalgesia and thermal hyperalgesia. Together, these results demonstrate that TRPV1 receptor expression in spinal cord contributes, at least in part, to the development of PTX-induced painful peripheral neuropathy. TRPV1 receptor antagonists may be useful in the prevention and treatment of PTX-induced peripheral neuropathic pain.

Oxaliplatin is a chemotherapeutic agent that is effective against various types of cancer including colorectal cancer. Acute cold hyperalgesia is a serious side effect of oxaliplatin treatment. Although the therapeutic drug pregabalin is beneficial for preventing peripheral neuropathic pain by targeting the voltage-dependent calcium channel α₂δ-1 (Ca_vα₂δ-1) subunit, the effect of oxaliplatin-induced acute cold hypersensitivity is uncertain. To analyze the contribution of the Ca_vα₂δ-1 subunit to the development of oxaliplatin-induced acute cold hypersensitivity, Ca_vα₂δ-1 subunit expression in the rat spinal cord was analyzed after oxaliplatin treatment. Behavioral assessment using the acetone spray test showed that 6 mg/kg oxaliplatin-induced cold hypersensitivity 2 and 4 days later. Oxaliplatin-induced acute cold hypersensitivity 4 days after treatment was significantly inhibited by pregabalin (50 mg/kg, p.o.). Oxaliplatin (6 mg/kg, i.p.) treatment increased the expression level of Ca_vα₂δ-1 subunit mRNA and protein in the spinal cord 2 and 4 days after treatment. Immunohistochemistry showed that oxaliplatin increased Ca_vα₂δ-1 subunit protein expression in superficial layers of the spinal dorsal horn 2 and 4 days after treatment. These results suggest that oxaliplatin treatment increases Ca_vα₂δ-1 subunit expression in the superficial layers of the spinal cord and may contribute to functional peripheral acute cold hypersensitivity.