LDL and UV-oxidized LDL induce upregulation of iNOS and NO in unstimulated J774 macrophages and HUVEC.

Oxidized low-density lipoprotein (LDL) diminishes NO production from activated macrophages. The interaction between LDL and inactivated macrophages is neglected and controversial. This study examines the effect of LDL, 7-oxysterols and iron compounds on NO production in unstimulated J774 macrophages. J774 cells and human umbilical vein endothelial cells (HUVEC) were either incubated for 24 h with native LDL (LDL) or ultraviolet (UV)-oxidized LDL (UVoxLDL), in the absence or presence of an inducible nitric oxide synthase (iNOS)- or an endothelial constitutive nitric oxide synthase (eNOS)-inhibitor. J774 cells were also incubated with lipopolysaccharide (LPS), in the absence or presence of an iNOS- or an eNOS-inhibitor. Nitrite was analysed as a marker of NO production. The mRNA levels of iNOS were evaluated by reverse transcriptase polymerase chain reaction. LDL and UVoxLDL significantly increased NO production from unstimulated J774 macrophages. This increase in NO was accompanied by enhanced expression of iNOS mRNA, and was inhibited by the iNOS inhibitor. Furthermore, NO production was elevated and angiotensin-converting enzyme (ACE) activity was reduced in HUVEC following the exposure to LDL and UVoxLDL. In conclusion, LDL may serve as an important inflammatory activator of macrophages and HUVEC, inducing inducible nitric oxide production but diminishing ACE. After its oxidation, this function of LDL may be further enhanced and may contribute to the regulation and progression of atheroma formation.