Metabolomic approach elucidated transformation of liver cells by 3-methylcholanthrene potentiates oxidative stress via down-regulation of glutathione synthesis

抄録

Polycyclic aromatic hydrocarbons (PAHs) are widespread contaminants resulting from the incomplete combustion of organic materials in the environment. The primary concern for the hazardous effect of PAHs is their ability to activate the pathway linked to the aryl hydrocarbon receptor (AhR) and lead to carcinogenesis. While previous research has demonstrated that oxidative stress plays a critical role in the AhR-dependent toxic response, the effect of PAHs on the biosynthesis of glutathione (GSH), which is a powerful endogenous antioxidant, has been paid only limited attention. In the present study, we utilized a global metabolomic approach, via high resolution magic angle spinning nuclear magnetic resonance spectroscopy, and found significant metabolome differences between non-tumorigenic liver cells (BNL CL.2; CL2) and transformed liver cells (BNL 1ME A. 7R.1; 1MEA) chronically exposed to 3-methylcholanthrene (3MC), a well-known carcinogenic PAH. One significant change identified was a lower GSH level for 1MEA cells as compared to CL2 cells. This was contrasted by increased levels of precursor metabolites to GSH synthesis, such as S-adenosylmethionine and cysteine. These changes were accompanied by a significantly reduced expression of γ-glutamylcysteine ligase (GCL), known to be the rate-limiting step of GSH synthesis. Furthermore, the protein level of cysteine dioxygenase was down-regulated; however, the concentration of taurine was unaltered. Taken together, this study demonstrated that transformed cells by chronic exposure of 3MC showed the inhibition of GSH biosynthesis by suppressing GCL protein expression and reducing cysteine availability, which could subsequently make cells vulnerable to oxidative stress.