Noorafza Q. Khan

Health: Endothelin-1 synthesis reduced by red wine

Statistical evidence of reduced coronary heart disease in areas of high wine consumption has led to the widespread belief that wine affords a protective effect. Although moderate drinking of any alcohol helps to reduce the incidence of coronary heart disease, there is no clear evidence that red wine confers an additional benefit. Here we show that red wines strongly inhibit the synthesis of endothelin-1, a vasoactive peptide that is crucial in the development of coronary atherosclerosis. Our findings indicate that components specific to red wine may help to prevent coronary heart disease.

Metformin suppresses hepatic gluconeogenesis through induction of SIRT1 and GCN5

Abnormal elevation of hepatic gluconeogenesis is central to the onset of hyperglycaemia in patients with type 2 diabetes mellitus (T2DM). Metformin corrects hyperglycaemia through inhibition of gluconeogenesis, but its mechanism of action is yet to be fully described. SIRT1 and GCN5 (listed as KAT2A in the MGI Database) have recently been identified as regulators of gluconeogenic gene expression through modulation of levels and activity of the coactivators cAMP-response element binding protein-regulated transcription coactivator 2 (TORC2 or CRTC2 as listed in the MGI Database) and peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC1alpha or PPARGC1A as listed in the MGI Database). We report that in db/db mice, metformin (250 mg/kg per day; 7 days) increases hepatic levels of GCN5 protein and mRNA compared with the untreated db/db mice, as well as increases levels of SIRT1 protein and activity relative to controls and untreated db/db mice. These changes were associated with reduced TORC2 protein level and decreased gene expression and activation of the PGC1alpha gene target phosphoenolpyruvate carboxykinase, and lower plasma glucose and insulin. Inhibition of SIRT1 partially blocked the effects of metformin on gluconeogenesis. SIRT1 was increased through an AMP-activated protein kinase-mediated increase in gene expression of nicotinamide phosphoribosyltransferase, the rate-limiting enzyme of the salvage pathway for NAD(+). Moreover, levels of GCN5 were dramatically reduced in db/db mice compared with the controls. This indicates that loss of GCN5-mediated inhibition of gluconeogenesis appears to constitute a major mechanism for the onset of abnormally elevated hepatic glucose production in db/db mice. In conclusion, induction of GCN5 and SIRT1 potentially represents a critical mechanism of action of metformin. In addition, these data identify induction of hepatic GCN5 as a potential therapeutic strategy for treatment of T2DM.

Cytokine regulation of endothelin-1 release from bovine aortic endothelial cells

Summary: The action of cytokines on the endothelium is a pivotal event in a number of vascular pathologies and inflammatory conditions. Here we have tested the effect of tumor necrosis factor-α (TNF-α), interleukin (IL)-β, and IL-2 on endothelin-1 (ET-1) release from cultured bovine aortic endothelial cells. TNF-α and IL-1β caused concentration-dependent increases in ET-1 release. IL-2 up to concentrations of 100 ng/ml did not stimulate ET-1 release. The induction of ET-1 synthesis by cytokines may be of underlying importance in the endothelial cell dysfunction observed in a number of vascular diseases.

Red wine procyanidins and vascular health

Regular, moderate consumption of red wine is linked to a reduced risk of coronary heart disease and to lower overall mortality, but the relative contribution of wines alcohol and polyphenol components to these effects is unclear. Here we identify procyanidins as the principal vasoactive polyphenols in red wine and show that they are present at higher concentrations in wines from areas of southwestern France and Sardinia, where traditional production methods ensure that these compounds are efficiently extracted during vinification. These regions also happen to be associated with increased longevity in the population.

Comparison of red wine extract and polyphenol constituents on endothelin-1 synthesis by cultured endothelial cells.

Regular consumption of red wine reduces mortality from coronary heart disease. This observation has been attributed to the anti-thrombotic effects of ethanol and to the antioxidant properties of polyphenolic compounds present in red wine. Here we show that an extract of red wine polyphenols causes a concentration-dependent inhibition of endothelin-1 synthesis in cultured bovine aortic endothelial cells. This action was associated with modifications in phosphotyrosine staining, indicating that the active components of red wine cause specific modifications of tyrosine kinase signalling. Thus inhibition of endothelin-1 synthesis by red wine may reduce the development of atherosclerosis, and hence decrease coronary heart disease.

Regulation of Vascular Endothelial Function by Procyanidin-Rich Foods and Beverages†

Flavonoid-rich diets are associated with a lower mortality from cardiovascular disease. This has been linked to improvements in endothelial function. However, the specific flavonoids, or biologically active metabolites, conferring these beneficial effects have yet to be fully defined. In this experimental study of the effect of flavonoids on endothelial function cultured endothelial cells have been used as a bioassay with endothelin-1 (ET-1) synthesis being measured an index of the response. Evaluation of the relative effects of extracts of cranberry juice compared to apple, cocoa, red wine, and green tea showed inhibition of ET-1 synthesis was dependent primarily on their oligomeric procyanidin content. Procyanidin-rich extracts of cranberry juice triggered morphological changes in endothelial cells with reorganization of the actin cytoskeleton and increased immunostaining for phosphotyrosine residues. These actions were independent of antioxidant activity. Comparison of the effects of apple procyanidin monomers through heptamer showed a clear structure-activity relationship. Although monomer, dimer, and trimer had little effect on ET-1 synthesis, procyanidin tetramer, pentamer, hexamer, and heptamer produced concentration-dependent decreases with IC(50) values of 5.4, 1.6, 0.9, and 0.7 microM, respectively. Levels of ET-1 mRNA showed a similar pattern of decreases, which were inversely correlated with increased expression of Kruppel-like factor 2 (KLF2), a key endothelial transcription factor with a broad range of antiatherosclerotic actions including suppression of ET-1 synthesis. Future investigations of procyanidin-rich products should assess the role KLF2 induction plays in the beneficial vascular effects of high flavonoid consumption.

Fructose induces gluconeogenesis and lipogenesis through a SIRT1-dependent mechanism

Consumption of a fructose-rich diet leads to insulin resistance and dyslipidemia in part due to elevated gluconeogenesis and lipogenesis. SIRT1, an NAD(+)-dependent protein deacetylase, can induce gluconeogenesis and lipogenesis. The aim of this study was to determine whether fructose increased hepatic SIRT1, leading to induction of gluconeogenesis and lipogenesis. Rat hepatocytes were incubated with fructose (1-5 mM). SIRT1 protein, SIRT1 activity, and NAD(+)/NADH ratio were measured. The effects of SIRT1 inhibitors (EX-527 and nicotinamide) and activators (SIRT1 activator 3 and SRT1720) and the mitochondrial complex I inhibitor rotenone were examined on fructose-induced increases in gluconeogenesis and lipogenesis. Fructose increased SIRT1 protein, SIRT1 activity, and NAD(+)/NADH ratio. Fructose also induced gluconeogenesis, with increases in peroxisome proliferator-activated receptor coactivator 1-alpha (PGC1α) and phosphoenolpyruvate carboxykinase (PEPCK; gene code Pck1) gene expression, PEPCK activity, and hepatocyte glucose production. In addition, levels of 3-hydroxy-3-methylglutaryl coenzyme A reductase (Hmgcr) and acetyl-coA carboxylase (Acc) mRNA, and intracellular cholesterol were increased. Increases in gluconeogenesis, Hmgcr, Acc, and cholesterol were abolished by SIRT1 inhibitors and rotenone, while SIRT1 activators increased gluconeogenesis, Hmgcr, Acc, Pgc1β, and sterol regulatory element-binding protein 1c (Srebp1c) gene expression. In conclusion, fructose induces gluconeogenesis and lipogenesis through a SIRT1-dependent mechanism, suggesting that induction of hepatic SIRT1 could play a pivotal role in the metabolic changes observed in humans and animals consuming a fructose-rich diet. These results highlight the need for a greater understanding of the role of SIRT1 in metabolic regulation and indicate the potential for adverse effects of SIRT1 activators if used therapeutically.

The procyanidin-induced pseudo laminar shear stress response: a new concept for the reversal of endothelial dysfunction.

Reduced endothelium-dependent vasodilator responses with increased synthesis of ET-1 (endothelin-1) are characteristics of endothelial dysfunction in heart failure and are predictive of mortality. Identification of treatments that correct these abnormalities may have particular benefit for patients who become refractory to current regimens. Hawthorn preparations have a long history in the treatment of heart failure. Therefore we tested their inhibitory effects on ET-1 synthesis by cultured endothelial cells. These actions were compared with that of GSE (grape seed extract), as the vasoactive components of both these herbal remedies are mainly oligomeric flavan-3-ols called procyanidins. This showed extracts of hawthorn and grape seed were equipotent as inhibitors of ET-1 synthesis. GSE also produced a potent endothelium-dependent vasodilator response on preparations of isolated aorta. Suppression of ET-1 synthesis at the same time as induction of endothelium-dependent vasodilation is a similar response to that triggered by laminar shear stress. Based on these results and previous findings, we hypothesize that through their pharmacological properties procyanidins stimulate a pseudo laminar shear stress response in endothelial cells, which helps restore endothelial function and underlies the benefit from treatment with hawthorn extract in heart failure.

Effects of Phosphoramidon in Endothelial Cell Cultures on the Endogenous Synthesis of Endothelin-1 and on Conversion of Exogenous Big Endothelin-1 to Endothelin-1

Several studies have shown that phosphoramidon (PHOS) reduces the release of endothelin-1 (ET-1) from cultured endothelial cells. Moreover, the main endothelin-converting enzyme (ECE) activity in these cells is a membrane-bound metallopeptidase that is also inhibited by PHOS. We have investigated further the role of the PHOS-sensitive ECE in the conversion of big ET-1 to ET-1. ET-1 was measured using a radioimmunoassay specific for the C-terminal ET[16-21] sequence. The effect of PHOS on the production of ET-1 from endogenous precursors was determined using cultured bovine aortic endothelial cells (BAECs) and the human endothelial cell line (EA.hy 926). The concentrations of ET-1 accumulating in the medium over 24 h from BAECs were lowered by PHOS (-27% 10 microM, -76% 100 microM). In contrast, with EA.hy 926 cells, the same concentrations of PHOS increased by five- to sixfold the amount of ET-1 present in the medium after 24-h incubation. In other experiments, incubation of big ET-1 (1 microM) with intact BAECs or EA.hy 926 cells resulted in the generation of ET-1, and with both cell types this was inhibited by PHOS (IC50: BAECs = 6.4 microM; EA.hy 926 = 0.26 microM). These results are consistent with both cell types having a PHOS-sensitive ECE that is readily accessible to exogenous big ET-1 and is therefore probably located on the plasma membrane. Furthermore, another intracellular ECE may play a part in the endogenous intracellular formation of ET-1 in EA.hy 926 cells.

Calcium ionophores inhibit the release of endothelin-1 from endothelial cells.

We have determined the effect on endothelin-1 (ET-1) release of stimulating cultured endothelial cells for 24 h with Ca2+ ionophores. The results obtained using cultured bovine aortic endothelial cells (BAECs) were compared with those using the human endothelial cell line (EA.hy 926). ET-1 was measured using a radioimmunoassay specific for the C-terminal ET[16-21] sequence. Ionomycin (1 microM) lessened ET-1 accumulation over 24 h in the conditioned medium from BAECs (-37%) and EA.hy 926 (-25%). A23187 was a more potent inhibitor of ET-1 release. With BAECs, ET-1 release was inhibited by 28% and 77% at 0.1 microM and 1 microM A23187, respectively. The corresponding decreases for EA.hy 926 were 20% and 98%. A23187 at 0.2 microM lowered ET-1 concentrations in the medium after 24 h by 44% and 24% for BAECs and EA.hy 926, respectively. Neither NG-monomethyl-L-arginine (0.2 mM) nor indomethacin (10 microM), either alone or in combination, affected the inhibition by A23187. Thus, this inhibitory effect is not dependent on the stimulation of nitric oxide or prostacyclin synthesis. Additional factors in endothelial cells, activated by elevated Ca2+ levels, may be important in exerting an inhibitory influence on ET-1 formation.