Concentrations of lipids in plasma and lipoproteins and oxidative susceptibility of low-density lipoproteins in zinc-deficient rats fed linseed oil or olive oil

Interaction between marginal zinc and high fat supply on lipid metabolism and growth of weanling rats

The impact of a moderate Zn deficiency on growth and plasma and liver lipids was investigated in two 4-week experiments with male weanling rats fed fat-enriched diets. Semisynthetic, approximately isocaloric diets containing 3% soybean oil were supplemented with either 7 or 100 mg Zn/kg diet and with 22% beef tallow (BT) or sunflower oil (SF). In Experiment 1, which compared the dietary fat level and the fat source in a factorial design of treatments, all diets were fed ad libitum to 6 × 8 animals, whereas intake of the high-Zn BT and SF diets was restricted in Experiment 2 (5 × 6 rats) to the level of intake of the respective low-Zn diets. The low-Zn SF diet consistently depressed food intake and final live weights of the animals to a greater extent than the other low-Zn diets, while intake and growth were comparable among the animals fed the high-Zn diets. The marginal Zn deficit per se did not alter plasma triglyceride and cholesterol concentrations nor hepatic concentrations of triglyceride, cholesterol and phospholipids. The fatty acid pattern of liver phospholipids did not indicate that chain elongation and desaturation of fatty acids was impaired by a lack of zinc. It was concluded that dietary energy and fat intake, and fat source have a greater effect on plasma and liver lipids than a moderate Zn deficiency. Marginally Zn-deficient diets enriched with sunflower oil as a major energy source cause a greater growth retardation than diets rich in carbohydrates or beef tallow.

Zinc Modulates PPARγ Signaling and Activation of Porcine Endothelial Cells

Dietary zinc has potent antioxidant and anti-inflammatory properties and is a critical component of peroxisome proliferator-activated receptor (PPAR) gene expression and regulation. To assess the protective mechanisms of PPARgamma in endothelial cell dysfunction and the role of zinc in the modulation of PPARgamma signaling, cultured porcine pulmonary artery endothelial cells were exposed to the membrane-permeable zinc chelator N,N,N'N'-tetrakis (2-pyridylmethyl)-ethylene diamine (TPEN), thiazolidinedione (TZD; PPARgamma agonist) or bisphenol A diglycidyl ether (BADGE; PPARgamma antagonist). Subsequently, endothelial cells were activated by treatment with linoleic acid (90 micro mol/L) for 6 h. Zinc chelation by TPEN increased the DNA binding activity of nuclear factor (NF)-kappaB and activator protein (AP)-1, decreased PPARgamma expression and activation as well as up-regulated interleukin (IL)-6 expression and production. These effects were fully reversed by zinc supplementation. In addition, exposure to TZD down-regulated linoleic acid-induced DNA binding activity of NF-kappaB and AP-1, whereas BADGE further induced activation of these oxidative stress-sensitive transcription factors. Most importantly, the TZD-mediated down-regulation of NF-kappaB and AP-1 and reduced inflammatory response were impaired during zinc chelation. These data suggest that zinc plays a critical role in PPARgamma signaling in linoleic acid-induced endothelial cell activation and indicate that PPARgamma signaling is impaired during zinc deficiency.

High-Energy Diets, Fatty Acids and Endothelial Cell Function: Implications for Atherosclerosis

Diets high in fat and/or calories can lead to hypertriglyceridemia and postprandial lipemia and thus are considered a risk factor for the development of atherosclerosis. Plasma chylomicron levels are elevated in humans after consuming a high-fat meal, and hepatic synthesis of VLDL is increased when caloric intake is in excess of body needs. High lipoprotein lipase activity and subsequent hydrolysis of triglyceride-rich lipoproteins may be an important source of elevated concentrations of fatty acid anions in the proximity to the endothelium and hence a major risk factor for atherosclerosis. We have shown that selected fatty acids, as well as lipoprotein lipase-derived remnants of lipoproteins isolated from hypertriglyceridemic subjects, can activate vascular endothelial cells and disrupt endothelial integrity. Our studies suggest that omega-6 fatty acids, and especially linoleic acid, cause endothelial cell dysfunction most markedly as well as can potentiate TNF-mediated endothelial cell injury. We propose that high-energy diets, and especially diets rich in linoleic acid, are atherogenic by contributing to an imbalance in cellular oxidative stress/antioxidant status of the endothelium, which can lead to activation of oxidative stress-responsive transcription factors, inflammatory cytokine production and the expression of adhesion molecules. Our data also suggest that nutrients, which have antioxidant and/or membrane stabilizing properties, can protect endothelial cells. These findings contribute to the understanding of the interactive role of high fat/calorie diets and subsequent hypertriglyceridemia with inflammatory components and nutrients that exhibit antiatherogenic properties in the development of atherosclerosis. Moreover, results from our research further support the concept that high-fat/calorie diets and associated postprandial hypertriglyceridemia are significant risk factors for atherosclerosis.

Antioxidant-like properties of zinc in activated endothelial cells

OBJECTIVE

The objective of this study was to test the hypothesis that zinc deficiency in endothelial cells may potentiate the inflammatory response mediated by certain lipids and cytokines, possibly via mechanisms associated with increased cellular oxidative stress. Our experimental approach was to compare conditions of cellular zinc deficiency and zinc supplementation with oxidative stress-mediated molecular and biochemical changes in vascular endothelial cells.

METHODS

To investigate our hypothesis, porcine pulmonary artery-derived endothelial cells were depleted of zinc by culture in media containing 1% fetal bovine serum for eight days. Subsequently, endothelial cells were exposed to media enriched with or without zinc (10 microM) for two days, followed by exposure to either tumor necrosis factor-alpha (TNF, 500 U/mL) or linoleic acid (90 microM), before measurement of oxidative stress (DCF fluorescence), activation of nuclear factor kappaB (NF-kappaB) or activator protein-1 (AP-1) and production of the inflammatory cytokine interleukin 6 (IL-6).

RESULTS

Oxidative stress was increased markedly in zinc-deficient endothelial cells following treatment with fatty acid or TNF. This increase in oxidative stress was partially blocked by prior zinc supplementation. The oxidative stress-sensitive transcription factor NF-kappaB was up-regulated by zinc deficiency and fatty acid treatment. The up-regulation mediated by fatty acids was markedly reduced by zinc supplementation. Similar results were obtained with AP-1. Furthermore, endothelial cell production of IL-6 was increased in zinc-deficient endothelial cells following treatment with fatty acids or TNF. This increase in production of inflammatory cytokines was partially blocked by zinc supplementation.

DISCUSSION

Our previous data clearly show that zinc is a protective and critical nutrient for maintenance of endothelial integrity. The present data suggest that zinc may in part be antiatherogenic by inhibiting oxidative stress-responsive events in endothelial cell dysfunction. This may have implications in understanding mechanisms of atherosclerosis.