Intracellular GSH of Streptococcus thermophilus shows anti-oxidative activity against low-density lipoprotein oxidation in vitro and in a hyperlipidaemic hamster model

Abstract

Streptococcus thermophilus YIT 2001 (ST-1), a lactic acid bacterial strain, was shown to have inhibitory effects on the oxidation of low-density lipoprotein (LDL) and the development of aortic fatty lesions in an animal model, and lower the serum levels of malondialdehyde-modified LDL, an oxidative modification product of LDL, in a clinical trial. This study aimed to identify the intracellular active component of ST-1 associated with anti-oxidative activity against LDL oxidation. High-performance liquid chromatography-electrospray ionisation mass spectrometry analysis after fractionation of the cellular extract by reversed-phase chromatography demonstrated that the active fraction contained reduced glutathione (GSH). GSH showed anti-oxidative activity in a dose-dependent manner, while this activity disappeared following thiol derivatisation. ST-1 had the strongest anti-oxidative activity against LDL oxidation and the highest level of intracellular GSH among five strains of S. thermophilus. In addition, the anti-oxidative activity of ST-1 after thiol derivatisation decreased by about half, which was similar to that of three other strains containing poor or no intracellular GSH or thiol components. Moreover, anti-oxidative activity against LDL oxidation was observed in hyperlipidaemic hamsters fed with high GSH ST-1 cells but not in those given low GSH cells. These findings suggest that intracellular GSH in ST-1 may provide beneficial effects via anti-oxidative activity against LDL oxidation and excess oxidative stress in the blood.