The cellular uptake of oxidized low density lipoprotein (LDL) is mediated through the oxidized LDL receptor-1, LOX-1. We investigated whether circulating factors link LOX-1 expression in endothelial cells and impaired endothelium-dependent vasoreactivity (EDVR) as functional indicator of atherogenesis. EDVR was measured as flow-mediated dilation (FMD) of the brachial artery in 27 patients with a known history of cardiovascular disease. Human umbilical vein endothelial cells (HUVEC) were incubated with bradykinin or prostacyclin in the presence of tumour necrosis factor-alpha (TNF-α) or with serum of each patient for four hours. Total mRNA and protein extracts were analysed for LOX-1 and eNOS expression relative to the expression in medium-treated cells and corrected for GAPDH expression.
Results: Prostacyclin and bradykinin did not modulate LOX-1 basal expression but were able to prevent significantly the up-regulation of LOX-1 expression by TNF-α, in HUVEC in vitro. Impaired EDVR was associated significantly with reduced endothelial nitric oxide synthase (eNOS) protein expression in HUVEC (r=0.788, P<0.001), diabetes (P=0.024), and smoking status (yes/no, P=0.047). In contrast, no such association was established with LOX-1 mRNA (r=0.292, P=0.138) or with LOX-1 protein expression in HUVEC (r=0.201, P=0.312).
Conclusions: Using a combination of in vitro experiments with in vivo measurements, we found no evidence that endothelial LOX-1 expression and EDVR mediated through circulating factors were associated.