In our in vitro study, we analyzed the effects of incubation of J774A.1 macrophages with reduced glutathione (GSH) and quercetin on the extent of cellular cholesterol efflux by high-density lipoprotein (HDL) or apolipoprotein A1 (apoA1). This combination was the most potent one among other exogenous and endogenous antioxidant combinations, since it significantly increased the extent of HDL-mediated cholesterol efflux from macrophages by 47% versus control cells, whereas quercetin (20 μM) or GSH (200 μM) alone increased it by only 37% or 17%, respectively. Similarly, apoA1-mediated cholesterol efflux was increased by 11% or 22% in quercetin or quercetin + GSH-treated cells, respectively, versus control cells. These stimulatory effects were noted only after 20 h of cell incubation. The combination of quercetin + GSH demonstrated high scavenging capacity of free radicals versus quercetin or GSH alone. In addition, quercetin + GSH significantly decreased macrophage oxidative stress as measured by the scavenging capacity of free radicals in the cells, the formation of reactive oxygen species, and the levels of cellular glutathione and lipid peroxides. There was no significant effect of quercetin + GSH on cellular HDL binding, on ATP-binding cassette A1 (ABCA1) activity, or on ABCG1 messenger RNA (mRNA) levels. In contrast, mRNA levels for ABCA1 and peroxisome proliferator-activated receptor alpha (PPARα) were both significantly increased by 89% and 93%, respectively, in quercetin + GSH-treated cells versus control cells. Quercetin alone increased the mRNA levels for ABCA1 or PPARα by 42% or 77%, respectively, whereas GSH alone increased it by 22% or 28%, respectively. Mass spectra analysis revealed that oxidized quercetin reacts with GSH to form a new adduct product. We thus conclude that the stimulatory effects of quercetin + GSH on apoA1- or HDL-mediated macrophage cholesterol efflux are related to the ability of GSH to preserve quercetin in its reduced form.
Keywords: ABCA1; GSH; cholesterol efflux; macrophages; oxidative stress; quercetin.