Heike Langbein

NADPH oxidase 4 protects against development of endothelial dysfunction and atherosclerosis in LDL receptor deficient mice

Genetic deletion of the hydrogen peroxide producing NADPH oxidase 4 (Nox4), as shown in the present study, leads to endothelial dysfunction and increased atherosclerosis under pathological conditions. Consequently, endothelial activation of Nox4 may represent a promising novel strategy for preventing endothelial dysfunction and atherosclerosis and its severe clinical complications. This also suggests that in contrast to the deleterious effects of oxidative stress certain reactive oxygen species might mediate beneficial effects in the vessel wall.

Dehydroepiandrosterone-sulphate (DHEA-S) promotes neuroendocrine differentiation of chromaffin pheochromocytoma PC12 cells

The major source for dehydroepiandrosterone (DHEA) and its sulphate compound DHEA-S is the inner zone of the adrenal cortex, which is in direct contact to adrenomedullary chromaffin cells. Due to their close proximity, direct interactions of DHEA and DHEA-S with chromaffin cells during adrenal gland development and throughout the whole life span are hypothesized. A possible direct effect of DHEA-S and the cellular and molecular mechanisms of DHEA-S action on chromaffin cells remain unresolved. Therefore, in this study, we aimed at clarifying DHEA-S effects and mechanisms of action on rat chromaffin PC12 cells. DHEA-S (10(-6)mol/l) inhibited nerve growth factor (NGF, 20ng/ml)-induced cell proliferation by 66% (n=4, p<0.001). In NGF-stimulated cells, neuronal differentiation was inhibited by DHEA-S, as demonstrated by a 22% reduction (n=3; p<0.05) of neuronal differentiation marker expression, synaptosome-associated protein of 25kDa (SNAP-25), and a 59% (n=6; p<0.001) decrease in neurite outgrowth. Moreover, DHEA-S stimulated expression of endocrine marker chromogranin A (CgA) by 31% (n=4; p<0.05 vs. control) and catecholamine release from NGF-treated PC12 cells by 229% (n=3-5; p<0.001), indicating a DHEA-S-induced shift towards neuroendocrine differentiation. On a molecular level, DHEA-S diminished NGF-induced ERK1/2 phosphorylation. Taken together, DHEA-S inhibited NGF-induced proliferation and neuronal differentiation and shifted cells towards a more endocrine phenotype. Interference of DHEA-S with NGF-stimulated ERK1/2 activation might be involved in this effect. Our study provides support for the notion that adrenocortical-derived DHEA-S impacts adrenomedullary chromaffin cells during development and differentiation.

Impact of high-fat diet and voluntary running on body weight and endothelial function in LDL receptor knockout mice

OBJECTIVE Obesity and physical inactivity are important cardiovascular risk factors. Regular physical exercise has been shown to mediate beneficial effects in the prevention of cardiovascular diseases. However, the impact of physical exercise on endothelial function in proatherosclerotic low-density lipoprotein receptor deficient (LDLR(-/-)) mice has not been studied so far. METHODS Six-week-old male LDLR(-/-) mice were fed a standard diet or a high-fat diet (39 kcal% fat diet) for 20 weeks. The impact of high-fat diet and voluntary running on body weight and amount of white adipose tissue was monitored. Basal tone and endothelial function was investigated in aortic rings using a Mulvany myograph. RESULTS LDLR(-/-) mice on high-fat diet had increased cumulative food energy intake, but also higher physical activity compared to mice on control diet. Body weight and amount of visceral and retroperitoneal white adipose tissue of LDLR(-/-) mice were significantly increased by high-fat diet and partially reduced by voluntary running. Endothelial function in aortae of LDLR(-/-) mice was impaired after 20 weeks on standard and high-fat diet and could not be improved by voluntary running. Basal tone showed a trend to be increased by high-fat diet. CONCLUSION Voluntary running reduced body weight and amount of white adipose tissue in LDLR(-/-) mice. Endothelial dysfunction in LDLR(-/-) mice could not be improved by voluntary running. In a clinical context, physical exercise alone might not have an influence on functional parameters and LDL-C levels in patients with familial hypercholesterolemia. However, physical activity in these patients may be in general beneficial and should be performed.

Increased gene expression of the cardiac endothelin system in obese mice.

Obesity is a well-known risk factor of atherosclerosis and heart failure. In the human heart, a local endothelin system containing prepro-endothelin-1, endothelin-converting enzyme-1, and endothelin receptors A and B has been described. The endothelin system is activated in heart failure; however, the impact of obesity on the cardiac endothelin system is unknown. In this study, 18-week-old male C57BL/6 mice fed either a control diet or a high-fat diet for 10 weeks were analyzed. High-fat diet significantly increased the body weight of the animals and augmented low-density lipoprotein, high-density lipoprotein, and cholesterol plasma levels, compared to control. The animal groups showed no significant differences in left ventricular size or function (heart rate, ejection fraction, fractional shortening, left ventricular posterior wall thickness, cardiac output) after control or high-fat diet. We did not observe signs of cardiac hypertrophy or changes in markers of cardiac fibrosis in these heart samples. The cardiac expression of prepro-endothelin-1 mRNA, endothelin-converting enzyme-1 mRNA, and protein and endothelin receptors A and B mRNA was increased in 18-week-old obese C57BL/6 mice compared to animals with normal weight (p<0.05 vs. control). Furthermore, endothelin-1 plasma levels showed an increasing trend. In conclusion, an increased expression of genes of the endothelin system was observed in the hearts of 18-week-old mice after high-fat diet, possibly contributing to later cardiovascular complications of obesity.