Probable Involvement of the 5-Hydroxytryptamine 4 Receptor in Methotrexate-Induced Delayed Emesis in Dogs

ABSTRACT Delayed emesis in cancer patients undergoing chemotherapy remains a significant problem. The pathogenesis of delayed emesis is still obscure. It was recently demonstrated that methotrexate (MTX), an anticancer drug, evoked delayed emesis in dogs in a manner similar to its actions in humans. We evaluated the antiemetic activity of FK1052, a potent antagonist for both the 5-hydroxytryptamine (HT) 3 and 5-HT 4 receptors, on delayed emesis induced by MTX in beagle dogs. Animal behavior was recorded for 3 days using a video camera. Delayed emesis lasting up to 72 h was observed in dogs treated with MTX (2.5 mg/kg i.v.), but acute emesis did not occur. The following antiemetics, at the dose that prevents cisplatin-induced acute emesis in dogs, were administered i.v. as multiple injections every 12 h during days 2 to 3. FK1052 (1 and 3.2 mg/kg) significantly reduced the emetic episodes caused by MTX, whereas ondansetron (1 mg/kg), a selective 5-HT 3 receptor antagonist, was not effective. The emetic episodes induced by MTX were also inhibited by another 5-HT 3/4 receptor antagonist, tropisetron (1 mg/kg). CP-122,721 (0.1 mg/kg), a potent selective tachykinin NK 1 receptor antagonist, significantly reduced the emetic responses to MTX. Copper sulfate-induced emesis in dogs was also prevented by FK1052, tropisetron, and CP-122,721 but not by ondansetron. FK1052, tropisetron, and ondansetron had negligible affinity for the NK 1 receptor at 1 M. These results suggest that the 5-HT 4 receptor may be in part involved in the production of delayed emesis induced by MTX in dogs and that FK1052 may be a useful drug against both acute and delayed emesis induced by cancer chemotherapy

Calcineurin inhibitors exert rapid reduction of inflammatory pain in rat adjuvant-induced arthritis

1. FK506 and cyclosporin A (CsA) are immunosuppressive drugs, that specifically inhibit T-cell activation via calcineurin inhibition. This study was undertaken to investigate whether calcineurin inhibitors exert analgesic actions in rat adjuvant-induced arthritis (AIA), an animal model of rheumatoid arthritis (RA). 2. AIA was induced in female Lewis rats. Single doses of FK506 and CsA were orally administered to arthritic rats 17 days after arthritis induction. Intensity of hyperalgesia was assessed by measuring the pain threshold of hind paws. Tumor necrosis factor (TNF)-α, IL-1β and PGE(2) levels in paw extracts were determined by ELISA. TNF activity was measured by L929 cell cytotoxicity assay. IL-1β and cyclooxygenase (COX) mRNA expression in arthritic paws were measured by RT–PCR. 3. Single doses of FK506 and CsA markedly reduced joint hyperalgesia 24 h after drug administration, without affecting inflammation in an advanced stage of AIA. 4. The calcineurin inhibitors partially reduced the elevated level of TNF-α in arthritic paws, however, the analgesic effects of these drugs were not associated with the reduction in TNF-α level. 5. Moreover, treatment with anti-rat TNF-α antibody did not affect the hyperalgesia, when TNF-α activity was suppressed in arthritic paws by that treatment. 6. Both calcineurin inhibitors reduced the elevated level of IL-1β in arthritic paws to a normal level, 24 h after drug administration. 7. FK506 reduced IL-1β and COX-2 mRNA expression and PGE(2) level in arthritic paws. 8. In conclusion, calcineurin inhibitors rapidly reduce joint hyperalgesia probably by downregulating IL-1β, but not TNF-α, in AIA. Our findings may provide a new strategy for the treatment of pain in RA