Studies on the pathogenesis of vincristine-induced neuropathy

The pathogenesis of the peripheral neuropathy induced by vincristine is poorly understood, but interference of vinca alkaloids with microtubule assembly suggests that microtubule changes could be important. This possibility was studied by directly exposing the rat sciatic nerve to graded concentrations of vincristine sulfate. Microtubule length histograms prepared from randomly selected axons showed a unimodal distribution in vincristine and control axons. In vincristine-exposed axons, however, there was a shift to shorter length microtubules, and the mean measured length of microtubules (0.42 +/- 0.37 micron) was significantly (P less than 0.001) shorter than controls (0.67 +/- 0.55 micron). On cross-sections, the vincristine-exposed axons showed a decrease in the number of microtubules per square micrometer of axonal area compared to controls. These findings fit best with a loss of portion(s) of each microtubule and support the possibility that microtubules changes were associated with malorientation of microtubules and neurofilaments, accompanied by free vesicle accumulation and fragmentation of the smooth endoplasmic reticulum. These structural alterations would account for the previously observed abnormalities in axoplasmic transport and would also provide insight into the commonly observed peripheral neuropathy induced by vincristine treatment.