The influence of dibenzocyclooctadiene lignans on macrophage glutathione and lipid metabolism associated with Chlamydia pneumoniae-induced foam cell formation

Abstract

Triggered by changes in macrophage redox status and lipid metabolism, foam cells represent a hallmark of atherosclerosis. Induction of macrophage foam cell formation by Chlamydia pneumoniae, a gram-negative human pathogen, has been established in various earlier studies in vitro and in vivo. Oxidation of low-density lipoprotein (LDL) by C. pneumoniae and alterations in macrophage lipid metabolism do not require chlamydial replication, making conventional antibiotics useless in the intervention of the process. In this work, we report on the ability of schisandrin B and schisandrin C, two dibenzocyclooctadiene lignans, to suppress the C. pneumoniae -induced foam cell formation in RAW264.7 macrophages. This effect was accompanied with the upregulation of PPARγ, a nuclear receptor acting as a major transcriptional regulator of lipid metabolism and inflammatory responses. Schisandrin B and schisandrin C also increased the total intracellular glutathione content of the macrophages. In the case of schisandrin B, this was accompanied with the upregulation of GSH biosynthetic genes glutamate cysteine ligase (both the catalytic and the modifier subunits GCLc and GCLm) as well as gamma-glutamyl transpeptidase GGT1. In addition, schisandrin B and schisandrin C upregulated the expression of a lipid transport protein ABCA1 gene mediating cholesterol efflux from macrophages translating into a reduction in total cholesterol concentration in the schisandrin B -treated cells. Collectively, these data indicate that both schisandrin B and schisandrin C are able to alleviate the pathogenic consequences of C. pneumoniae infection in macrophages by altering the cellular redox balance and lipid trafficking.