Mechanisms of vincristine-induced neurotoxicity: Possible reversal by erythropoietin

Vincristine (VCR) is a potent anticancer drug, but neurotoxicity is one of its most important dose-limiting toxicities. In this study, we investigated the neurotoxic effect of VCR, the possible mechanisms and the role of erythropoietin (EPO) in the protection against VCR-induced neurotoxicity in a rat model. The neurotoxicity of VCR and protective effect of EPO were examined using the tail flick test and by recording electrophysiological characteristics in isolated sciatic nerve. To elucidate the underlying mechanisms, mRNA expression of N-methyl-Daspartate (NMDA) receptor, an index of glutamate excitotoxicity, and calcitonin gene-related peptide (CGRP), an important regulator of vascular tone, were measured in both spinal cord and sciatic nerves using an RT-PCR method. After intraperitoneal injection at a dose of 150 mu g/kg three times weekly for five consecutive weeks, VCR significantly decreased the latency of tail withdrawal reflex, the amplitude of maximum compound action potential (MCAP) and chronaxie, and prolonged the duration of action potential (AP) and relative refractory period (RRP), but it had no effect on conduction velocity. VCR increased NMDA receptor expression and decreased CGRP expression. Forty mu g/kg of EPO improved all VCR-induced changes, except chronaxie, while a higher dose of 80 mu g/kg reversed all parameters and its effect was more prominent on tail flick test latency and NMDA receptor expression. These results suggested that VCR might cause increased nerve excitability and induce a state of glutamate excitotoxicity through enhancing NMDA receptor expression and diminishing CGRP expression, thus resulting in axonal degeneration. EPO had an obvious neuroprotective effect probably through decreasing NMDA receptor expression and increasing CGRP expression both centrally and peripherally.