Chemodynamics underlying N-acetyl cysteine-mediated bone cement monomer detoxification

Methyl methacrylate (MMA)-based bone cement monomer is cytotoxic. N-Acetyl cysteine (NAC), a cysteine derivative, may alleviate this toxicity by inactivating the monomer components with its sulfhydryl moiety. This study examined the chemical interaction dynamics between bone cement monomer and NAC resulting in detoxification of the monomer. A monomer/NAC mixture was prepared by mixing and incubating a commercially available MMA-based bone cement monomer with NAC for various time periods of 1 min, 1h, 6h and 24h. Rat bone marrow-derived osteoblastic cells were cultured with either the monomer/NAC mixture or the monomer alone. Only 17% of the cells were viable 24h after seeding in the culture containing the monomer alone. The proliferation rate and alkaline phosphatase activity of the cells were substantially reduced under this condition. In contrast, when cultured with the monomer/NAC mixture, the viability and function of the cells were improved with increasing time of monomer/NAC incubation. For instance, the monomer/NAC mixture that was pre-reacted for 1 min increased cell viability from 17% to 55%. The monomer/NAC mixture that was pre-reacted for 24h nearly completely restored cell viability, proliferation and ALP activity to the level of an untreated control culture. The DPPH radical-scavenging capacity of monomer/NAC mixture decreased with an increase in their reaction time, indicating time-dependent depletion of the NAC anti-oxidant moiety. Within the limit of this experimental condition, these data demonstrate the immediate initiation and rapid completion of bone cement monomer/NAC interaction, resulting in abrogation of the monomer's cytotoxicity.