Search

Uptake of oxidized LDL (ox-LDL) by vascular endothelial cells is a critical step in the initiation and development of atherosclerosis. Adhesion molecules are upregulated by ox-LDL and numerous inflammatory cytokines and play a pivotal role in atherogenesis. In this study, we examined whether diallyl sulfide (DAS), diallyl disulfide (DADS), and diallyl trisulfide (DATS), 3 major organosulfur compounds of garlic oil, reduce adhesion molecule expression induced by ox-LDL and, if so, through what mechanism. Human umbilical vein endothelial cells were preincubated with 1 mmol/L DAS, 200/[micro]mol/L DADS, or 100/[micro]mol/L DATS for 16 h and then with 40 mg/L ox-LDL for an additional 24 h. ox-LDL induction of cellular and cell surface expression of E-selectin and vascular cell adhesion molecule (VCAM)-I was suppressed by garlic allyl sulfides in the order DATS > DADS > DAS. The adhesion of HL-60 cells to endothelial cells was inhibited 27 and 33% and the production of cellular peroxides was inhibited 43 and 50% by DADS and DATS, respectively (P < 0.05). ox-LDL alone dephosphorylated protein kinase B (PKB) and cAMP responsive element binding protein (CREB); such deactivation was reversed by DADS and DATS. Electrophoretic mobility shift assay showed that the activation of CREB binding to DNA was consistent with changes in CREB phosphorylation. The protein kinase A (PKA) inhibitor H89 reversed the suppression of VCAM-1 by DADS and DATS, but the phosphoinositide 3-kinase (PI3K) inhibitor wortmannin had no effect. In contrast, wortmannin abolished DADS- and DATS-induced suppression of ox-LDL-induced E-selectin expression. These results suggest that the suppression of ox-LDL-induced E-selectin and VCAM-1 expression by DADS and DATS and, thus, monocyte adhesion to endothelial cells is likely dependent on the PI3K/PKB or PKA/CREB signaling pathway in an adhesion molecule-specific manner. To our knowledge, this is the first report that garlic modulates ox- LDL-mediated leukocyte adhesion to human endothelial cells through the PKB and PKA pathways.

Little is known about the immediate effects of dietary fat on the expression of genes involved in cholesterol metabolism in humans. We investigated the effects of a high-fat meal on circulating mononuclear cell messenger RNA (mRNA) for the LDL receptor (LDLR), LDLR-related protein (LRP), and 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) over 10 h. Selection of 12 C and 7 T homozygotes for the LRP exon 22 C200T polymorphism for the study also enabled us to examine the influence of this polymorphism on postprandial mRNA expression and lipoproteins, of relevance because of LRP's role in postprandial lipoprotein metabolism and association of the polymorphism with coronary artery disease. We found a postprandial decrease in LDLR mRNA abundance relative to the reference [beta]-actin (BA) mRNA. The decreased LDLR/BA mRNA value was apparent at 1 h (P < 0.005) and decreased to 25% of baseline at 6 h (P < 0.005). The LRP/BA mRNA value was also lower at 6 h (16% decrease, P < 0.05). HMGCR mRNA expression was unchanged. C homozygotes for the C200T polymorphism had higher LDLR/BA values than T homozygotes (P = 0.01) and although plasma LDL cholesterol (LDL-C) concentrations decreased in the postprandial period (P < 0.002), the decrease was less in C than in T homozygotes (P < 0.05). This study constitutes the first observation, to our knowledge, of postprandial changes in LDLR and LRP mRNA expression. It documents immediate effects of a fatty meal on these mRNA as well as an LRP genotype effect on LDLR mRNA and LDL-C.