BackgroundOxaliplatin is an important drug used in the treatment of colorectal cancer. However, it frequently causes severe acute and chronic peripheral neuropathies. We recently reported that repeated administration of oxaliplatin induced cold hyperalgesia in the early phase and mechanical allodynia in the late phase in rats, and that oxalate derived from oxaliplatin is involved in the cold hyperalgesia. In the present study, we examined the effects of Ca2+ channel blockers on oxaliplatin-induced cold hyperalgesia in rats.MethodsCold hyperalgesia was assessed by the acetone test. Oxaliplatin (4 mg/kg), sodium oxalate (1.3 mg/kg) or vehicle was injected i.p. on days 1 and 2. Ca2+ (diltiazem, nifedipine and ethosuximide) and Na+ (mexiletine) channel blockers were administered p.o. simultaneously with oxaliplatin or oxalate on days 1 and 2.ResultsOxaliplatin (4 mg/kg) induced cold hyperalgesia and increased in the transient receptor potential melastatin 8 (TRPM8) mRNA levels in the dorsal root ganglia (DRG). Furthermore, oxalate (1.3 mg/kg) significantly induced the increase in TRPM8 protein in the DRG. Treatment with oxaliplatin and oxalate (500 μM for each) also increased the TRPM8 mRNA levels and induced Ca2+ influx and nuclear factor of activated T-cell (NFAT) nuclear translocation in cultured DRG cells. These changes induced by oxalate were inhibited by nifedipine, diltiazem and mexiletine. Interestingly, co-administration with nifedipine, diltiazem or mexiletine prevented the oxaliplatin-induced cold hyperalgesia and increase in the TRPM8 mRNA levels in the DRG.ConclusionsThese data suggest that the L type Ca2+ channels/NFAT/TRPM8 pathway is a downstream mediator for oxaliplatin-induced cold hyperalgesia, and that Ca2+ channel blockers have prophylactic potential for acute neuropathy.

Bortezomib, an effective anticancer drug for multiple myeloma, often causes peripheral neuropathy which is mainly characterized by numbness and painful paresthesia. Nevertheless, there is no effective strategy to escape or treat bortezomib-induced peripheral neuropathy (BIPN), because we have understood few mechanism of this side effect. In this study, we evaluated behavioral and pathological characteristics of BIPN, and investigated pharmacological efficacy of various analgesic drugs and adjuvants on mechanical allodynia induced by bortezomib treatment in rats. The repeated administration of bortezomib induced mechanical and cold allodynia. There was axonal degeneration of sciatic nerve behind these neuropathic symptoms. Furthermore, the exposure to bortezomib shortened neurite length in PC12 cells. Finally, the result of evaluation of anti-allodynic potency, oral administration of tramadol (10 mg/kg), pregabalin (3 mg/kg), duloxetine (30 mg/kg) or mexiletine (100 mg/kg), but not amitriptyline or diclofenac, transiently relieved the mechanical allodynia induced by bortezomib. These results suggest that axonal degeneration of the sciatic nerve is involved in BIPN and that some analgesic drugs and adjuvants are effective in the relief of painful neuropathy.

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Paclitaxel, an anticancer drug, frequently causes painful peripheral neuropathy. In this study, we investigated the preventive effect of polaprezinc on paclitaxel-induced peripheral neuropathy in rats. Polaprezinc (3 mg/kg, p.o., once daily) inhibited the development of mechanical allodynia induced by paclitaxel (4 mg/kg, i.p., on days 1, 3, 5 and 7) and suppressed the paclitaxel-induced increase in macrophage migration in dorsal root ganglion cells. In addition, polaprezinc did not affect the anti-tumor activity of paclitaxel in cultured cell lines or tumor-bearing mice. These results suggest a clinical indication for polaprezinc in the prevention of paclitaxel-induced neuropathy.

Although oxaliplatin (L‐OHP) is an important anticancer agent against colorectal cancer, severe acute and chronic peripheral neuropathies are frequently occurred. We peviously reported that oxalate derived from L‐OHP is involved in acute cold hyperalgesia. In the present study, the mechanism of L‐OHP‐induced acute neuropathy was examined with the effects of calcium channel blockers in the rat model and primary cultured dorsal root ganglia (DRG). Administration of L‐OHP or oxalate to rats induced cold hyperalgesia, and increased in transient receptor potential melastatin 8 (TRPM8) mRNA levels in DRG. In addition, the treatment of L‐OHP or oxalate induced Ca²⁺ influx and nuclear factor of activated T‐cell (NFAT) nuclear translocation as well as up‐regulation of the TRPM8 mRNA levels in cultured DRG. These oxalate‐induced changes were inhibited by nifedipine, diltiazem and mexiletine. Comparable to the in vitro results, administration of these calcium channel blockers prevented the L‐OHP‐induced cold hyperalgesia in rats. These results suggest that the L type calcium channels/NFAT/TRPM8 pathway is a downstream mediator for L‐OHP‐induced cold hyperalgesia, and that calcium channel blockers may have prophylactic potential against L‐OHP‐induced acute neuropathy.