Effect of N-acetyl-L-cysteine on scavenging long-lived radicals in mammalian cells by adding AFTER irradiation

Abstract

We report that NAC (N-Acetyl-L-cysteine) scavenges long-lived radicals (LLRs), mainly in proteins assigned recently as sulfinyl radicals (R-CH₂SO). LLRs levels in gamma-ray irradiated (5 kGy) Syrian Golden Hamster embryo (SHE) cells at room temperature were directly measured by electron spin resonance (ESR) spectroscopy at 77 K. NAC (100 mM) was added to the cells at 2 h after irradiation. The rate constant between LLRs and NAC was estimated as 9.3*10^-3M^-1s^-1, which is almost the same as that of Vitamin C. The rate constant between LLRs and RibCys (Ribose Cysteine, which act as a cysteine after hydrolysis) was estimated as 2.9*10^-4M^-1s^-1, and L-cysteine, which doesn't seem to go through membrane, did not scavenge LLRs. In mutation experiments, RibCys (4 mM), added after radiation with carbon ions (3 Gy), decreased levels of CD59^- mutants in A_L hybrid cells by about 50%. These results indicate that NAC could decrease mutation frequency by scavenging LLRs as same as Vitamin C.