Arginine and S-adenosylmethionine may contribute to nerve regeneration.

Abstract

INTRODUCTION--Axon growth and axon regeneration are complex processes requiring an adequate supply of certain metabolic precursors and nutrients. MATERIAL AND METHODS--This article reviews the studies examining some of the processes of protein modification fundamental to both nerve regeneration and to the continuous and adequate supply of specific factors such as arginine, S-adenosylmethionine and polyamines. RESULTS--The process of arginylation notably increases following nerve injury and during subsequent regeneration of the nerve, with the most likely function of arginine-modification of nerve proteins being the degradation of proteins damaged through injury. It appears that defective methyl group metabolism may be one of the leading causes of demyelination, as suggested by the observation of reduced cerebrospinal fluid concentrations of s-adenosylmethionine (SAMe) and 5-methyltetrahydrofolate, the key metabolites in methylation processes, in patients with a reduction in myelination of corticospinal tracts. Polyamine synthesis, which depends strongly on the availability of both SAMe and arginine, markedly increases in neurons soon after an injury. This "polyamine-response" has been found to be essential for the survival of the parent neurons after injury to their axons. Polyamines probably exert their effects through involvement in DNA, RNA and protein synthesis, or through post-translational modifications that are indicated as the most relevant events of the "axon reaction." CONCLUSIONS--Nerve regeneration requires the presence of arginine, s-adenosylmethionine, and polyamines. Further studies are needed to explore the mechanisms involved in these processes.