Co-incubation of native and oxidized low-density lipoproteins: potentiation of relaxation impairment

Selective effect of laparoscopic Roux-en-Y gastric bypass on lipid metabolism

INTRODUCTION

Bariatric surgery (BS) has shown to reduce cardiovascular morbidity and mortality in obesity. The BS has improved the dyslipidemia of the insulin resistant patient, our objective was to evaluate if there was a difference in the lipid profile between the laparoscopic roux-en-Y gastric bypass (RYGB) technique vs. the sleeve gastrectomy (SG) technique at 18 months of follow-up.

METHODS

An observational, open, prospective study of morbidly obese patients who underwent bariatric surgery at 18-month follow-up. Anthropometric analysis, body composition, energy expenditure at rest, glucose, insulin, HbA_1c, LDL, HDL, TG and CT were performed.

RESULTS

Absence baseline differences were found in the proportion of patients with hypertension, diabetes, steatosis, and sex between the RYGB vs SG groups. A reduction of TG was observed at 6 months in favor of RYGB vs SG: 108.60±34.86 vs. 124.59±44.58, P = 0.044), however, a decrease in both LDL levels was found at 12 and 18 months in favor of the RYGB vs. SG group: 96.23±24.33 vs. 107.83±28.88, P = 0.025; 90.98±20.62 vs 106.22±31.48, P = 0.003; the decrease in CT was observed only at 18 months in favor of the RYGB vs. SG group: 171.39±25.058 vs. 186.89±31.81, P = 0.005. CONCLUSIóN: RYBG has shown to be more effective in reducing LDL and CT levels compared to SG, which provides an additional benefit of RYGB in relation to the lipid profile of the patient.

Native low-density lipoprotein-induced superoxide anion contributes to proliferation of human aortic smooth muscle cells

BACKGROUND

Native low-density lipoprotein (nLDL) was one of the modifiable risk factors contributed directly to cardiovascular diseases development. We investigated that nLDL stimulation induced NADPH oxidase activation and superoxide production that was an important factor on human aortic smooth muscle cells (hAoSMC) proliferation.

METHODS

Superoxide generation was recorded with fluorescent-staining of dihydroethidine or by measuring lucigenin-induced chemiluminescence for 5 minutes. We examined cell proliferation with 4[-3-(4-iodophenyl)-2-(4-nitrophenyl)-2H-5-tetrazolio]-1,3-benzene disulfonate (WST-1) reagent and analyzed the change of gene expression by northern blot analysis.

RESULTS

nLDL stimulation increased superoxide anion production in hAoSMC that confirmed through dihydroethidine staining and lucigenin-induced chemiluminescence methods. nLDL-induced proliferation abolished with preincubation of superoxide scavengers or NADPH oxidase inhibitor. NADPH as a substrate of NADPH oxidase increased superoxide generation in both nLDL-stimulated and unstimulated cell homogenate, which was completely blocked at the diphenylene iodinium (DPI)- or apocynin-pretreated hAoSMC homogenates. Furthermore, superoxide generation was only observed at the fraction of cellular precipitate, but not in soluble fraction. Expression of p22phox in mRNA level increased with nLDL treatment as early as 30 minutes and transfection of anti-sense oligonucleotide of p22phox completely abolished nLDL-induced proliferation of hAoSMC.

CONCLUSIONS

The above results have shown that nLDL-induced proliferation in hAoSMC depends on superoxide production through NADPH oxidase activation.

Impairment of endothelium-dependent aorta relaxation by phospholipid components of oxidized low-density lipoprotein

Oxidized low-density lipoprotein (LDL) is a major component in the pathophysiology of atherosclerosis and plays a role in the changes of vascular reactivity observed in this disease. Herein the authors investigate the potential involvement of platelet-activating factor (PAF)-like phospholipid components of oxidized LDL in rabbit aorta reactivity. Aortic rings were precontracted with noradrenaline (0.5 microM) and relaxation was induced by subsequent stimulation with sequential additions of acetylcholine (1 nM to 3 microM). High-performance liquid chromatography (HPLC) fractions (6- and 7-min) obtained from phospholipids extracted from oxidized LDL inhibited relaxation evoked by acetylcholine, but not the relaxation induced by sodium nitroprusside. This effect was not antagonized either by incubation of the fractions with PAF acetylhydrolase or by incubation of the aortic rings with a PAF receptor antagonist. Authentic PAF or C4-PAF, a PAF mimetic previously found in fractions 6 and 7 did not inhibit acetylcholine-induced relaxation. In contrast, lyso-PAF inhibited acetylcholine, but not sodium nitroprusside-induced relaxation. The authors conclude that phospholipids of oxidized LDL impair vascular reactivity to endothelium-dependent agonists. This effect is not due to oxidatively generated proinflammatory PAF mimetics, but rather to a metabolite of these phospholipids, lysoPAF.

Vitamin C protects low-density lipoprotein from homocysteine-mediated oxidation

Homocysteine, an atherogenic amino acid, promotes iron-dependent oxidation of low-density lipoprotein (LDL). We investigated whether vitamin C, a physiological antioxidant, could protect LDL from homocysteine-mediated oxidation. LDL (0.2 mg of protein/ml) was incubated at 37 degrees C with homocysteine (1000 microM) and ferric iron (10-100 microM) in either the absence (control) or presence of vitamin C (5-250 microM). Under these conditions, vitamin C protected LDL from oxidation as evidenced by an increased lag time preceding lipid diene formation (> or = 5 vs. 2.5 h for control), decreased thiobarbituric acid-reactive substances accumulation (< or = 19 +/- 1 nmol/mg when vitamin C > or = 10 microM vs. 32 +/- 3 nmol/mg for control, p <.01), and decreased lipoprotein anodic electrophoretic mobility. Near-maximal protection was observed at vitamin C concentrations similar to those in human blood (50-100 microM); also, some protection was observed even at low concentrations (5-10 microM). This effect resulted neither from altered iron redox chemistry nor enhanced recycling of vitamin E in LDL. Instead, similar to previous reports for copper-dependent LDL oxidation, we found that vitamin C protected LDL from homocysteine-mediated oxidation through covalent lipoprotein modification involving dehydroascorbic acid. Protection of LDL from homocysteine-mediated oxidation by vitamin C may have implications for the prevention of cardiovascular disease.

Native LDL induces proliferation of human vascular smooth muscle cells via redox-mediated activation of ERK 1/2 mitogen-activated protein kinases

This study investigated mechanisms underlying native low-density lipoprotein (LDL)-stimulated proliferation of human vascular smooth muscle cells (VSMC). Experiments were performed to determine whether native LDL affects reactive oxygen species (ROS) formation and activity of extracellular signal-regulated kinase 1/2 (ERK1/2), and whether redox-sensitive pathways contribute to LDL-induced cell proliferation. Native LDL (100 microg/mL, 24 hours) increased cell proliferation (to 303 to 388% of control, P<0.0001) as determined by [methyl-(3)H] thymidine incorporation. This effect was completely blocked either by the antioxidants N-acetylcysteine, Tiron, or nordihydroguaiaretic acid; the flavin-inhibitor diphenylene iodonium; or superoxide dismutase (all P<0.0001), and partly blocked by ERK-inhibitor PD98059 or meclofenamate (P<0.01). Exposure of VSMC to native LDL for 20 minutes stimulated ROS formation, measured by dichlorodihydrofluorescein oxidation, and increased ERK1/2 activity by 3.1-fold (P<0.001). The latter effect was sensitive to MEK1/2 inhibitor PD98059 and Tiron (P<0.001), and in part to N-acetylcysteine or diphenylene iodonium (P<0.05). These results demonstrate that native LDL induces acute formation of ROS and subsequent activation of redox-sensitive ERK 1/2 mitogen-activated protein kinases, pathways that appear to be important for mitogenic signaling of native LDL in human vascular smooth muscle cells.