Intimal infiltration by monocytes and accumulation of lipids represent a critical step in the formation of fatty streaks during atherogenesis. Because elevated plasma levels of asymmetric dimethylarginine (ADMA), a potent nitric oxide (NO) synthase (NOS) inhibitor, are prevalent in diverse cardiovascular diseases, the goal of this study was to examine the contribution of NO deficiency to macrophage lipid accumulation. Inhibition of NO synthesis in PMA-primed human monocytic leukemia HL-60 cells resulted in a twofold increase in expression of the receptor for oxidized LDL (OxLDL), termed the lectin-like OxLDL receptor (LOX-1). Blockade of inducible NOS in activated macrophages resulted in 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI)-OxLDL accumulation and imparted macrophages with a foamy appearance as detected with oil-red O lipid staining. ADMA (15 microM) or N(G)-nitro-l-arginine methyl ester (l-NAME, 300 microM), both of which suppress inducible NOS activity, increased oil-red staining 1.9- and 2.8-fold, respectively. Macrophages treated with ADMA or l-NAME showed a 2.4-fold increase in accumulation of DiI-OxLDL. To examine the role of LOX-1 in this process, we used small interfering RNA (siRNA) duplex-mediated LOX-1 gene silencing. LOX-1 expression was suppressed twofold by siRNA as shown by Western blot analysis. This suppression was associated with a two- to fourfold decrease in DiI-OxLDL uptake as identified by fluorescence microscopy and decreased oil-red O staining by activated macrophages. In conclusion, accumulation of ADMA (a competitive inhibitor of NOS) in patients with chronic renal failure may be responsible for upregulation of LOX-1 receptor and increased OxLDL uptake, thus contributing to lipidosis and foam cell formation. The data illustrate an additional nonendothelial mode of antiatherogenic action of NO: prevention of LOX-1 induction and lipid accumulation by macrophages.

Endothelial cell dysfunction is emerging as the ultimate culprit for diverse cardiovascular diseases and cardiovascular complications in patients with chronic renal diseases, yet the definition of this new syndrome, its pathophysiology and therapy remain poorly defined. Here, we summarize some molecular mechanisms leading from hyperhomocysteinemia, elevated asymmetric dimethylarginine (ADMA) and advanced glycation end products (AGEs)-modified proteins to atherogenic endothelial phenotype and offer a model of endothelial dysfunction based on the interconnectedness of diverse functions.

Smirnova, I. V., T. Sawamura, and M. S. Goligorsky. Upregulation of lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) in endothelial cells by nitric oxide deficiency. Am J Physiol Renal Physiol 287: F25-F32, 2004. First published March 9, 2004 10.1152/ajprenal.00449.2003.-Endothelial cell dysfunction (ECD) is emerging as a common denominator for diverse cardiovascular abnormalities associated with inhibition of endothelial nitric oxide (NO) synthase (eNOS). Elevated levels of asymmetric dimethylarginine (ADMA), a potent eNOS inhibitor, are common in renal failure and may contribute to ECD. Through DNA microarray screening of genes modulated in human umbilical vein endothelial cells (HUVEC) by N G -nitro-L-arginine methyl ester (L-NAME), we found a 1.8-fold increase in low-density lipoprotein receptor-1 (LOX-1) expression. LOX-1 is a major endothelial receptor for oxidized low-density lipoproteins (OxLDL) and is assumed to play a role in the initiation and progression of atherosclerosis. Here, we confirmed the upregulation of LOX-1 mRNA and protein level by quantitative RT-PCR and Western blot analysis. Increased expression of LOX-1 was associated with the accumulation of DiI-labeled OxLDL (DiI-OxLDL) in ADMA-and L-NAME-pretreated HUVEC. To evaluate the contribution of LOX-1 in ADMA-induced accumulation of OxLDL by HUVEC, we used the competitive receptor inhibitor, soluble LOX-1. Treatment of HUVEC with soluble LOX-1 was associated with an approximately two-to threefold inhibition of DiI-OxLDL uptake in L-NAME-or ADMA-treated HUVEC. In conclusion, ADMA-or L-NAME-induced NO deficiency leads to the increased expression of LOX-1 mRNA and protein in HUVEC, which in turn results in the accumulation of OxLDL. Competition with LOX-1-soluble extracellular domain reduces OxLDL accumulation. In summary, elevated ADMA levels, i.e., in patients with renal failure, may be responsible for endothelial accumulation of OxLDL via upregulated LOX-1 receptor, thus contributing to endothelial lipidosis and dysfunction. asymmetric dimethylarginine; endothelial dysfunction; chronic renal failure ENDOTHELIAL DYSFUNCTION IS emerging as a common denominator for diverse cardiovascular abnormalities, such as atherosclerosis, diabetes, hypertension, and renal failure. Inhibition of endothelial nitric oxide (NO) synthase (eNOS) is one of the hallmarks of developing endothelial cell dysfunction (2, 9, 15, 37). Impaired endothelium-dependent vasorelaxation precedes the development of clinical manifestations of the disease and is detectable even before angiographic manifestations become apparent (2,9,14,20,36). One of the mechanisms leading to endothelial dysfunction is the accumulation of an endogenous inhibitor of eNOS, asymmetric dimethylarginine (ADMA) (1,8,13,31,43,46). Plasma levels of ADMA are elevated in patients with chronic renal failure (11,21,22,32,34,44,49), hypercholesterolemia (8, 9, 29, 47), occlusive vascular disease, and hypertension (1, 5, 14, 16 -18, 20, 42, 43, 48) and associated with reduced NO production an...

Protein carbonyl levels, a measure of protein oxidation, were found to be significantly elevated (p < 0.0005) in the sera of chronic fatigue syndrome (CFS) patients vs. controls. In contrast, the total protein levels in sera CFS patients were unchanged from those of controls. The elevated protein carbonyl levels confirm earlier reports suggesting that oxidative stress is associated with chronic fatigue syndrome and are consistent with a prediction of the elevated nitric oxide/peroxynitrite theory of chronic fatigue syndrome and related conditions.