Wallerian degeneration and hyperalgesia after peripheral nerve injury are glutathione-dependent

Experimental inflammatory compression injury to the sciatic nerve (chronic constriction injury, CCI) induces Wallerian degeneration of axons and damages non-neuronal cells at the injury site in association with the development of exaggerated pain-like behavior, or hyperalgesia, to noxious thermal stimuli in the affected anatomical area. We examined whether glutathione, one of whose many functions is an important endogenous antioxidant, influenced resulting neuropathology and hyperalgesia following CCI. Dietary supplementation of the amino acid N-acetyl-cysteine (NAC), a rate-limiting component of glutathione production, beginning 1 day prior to CCI significantly diminished both Wallerian degeneration, measured by quantitative morphometry of myelinated fibers, and thermal hyperalgesia. NAC treatment raised nerve glutathione levels compared to untreated nerves, as indicated using hemeoxygenase-1 (hsp32) immunoreactivity as a marker of glutathione depletion. Because NAC is also known to have antioxidant abilities, studies simultaneously inhibited glutathione synthesis, and results demonstrated no significant reduction in resulting neuropathology or hyperalgesia. Delaying NAC administration to post-injury times consistently decreased hyperalgesia, although not significantly. This study identifies glutathione levels, and presumably oxidative stress, as important determinants of the neuropathological and behavioral consequences of nerve injury, and suggests that dietary supplementation of NAC constitutes an effective pre-emptive therapeutic strategy for situations involving painful nerve injury, such as occurs during surgery.