Teruo Jojima

RETRACTED ARTICLE: A glucagon-like peptide-1 (GLP-1) analogue, liraglutide, upregulates nitric oxide production and exerts anti-inflammatory action in endothelial cells

Aims/hypothesisGlucagon-like peptide-1 (GLP-1), a member of the proglucagon-derived peptide family, was seen to exert favourable actions on cardiovascular function in preclinical and clinical studies. The mechanisms through which GLP-1 modulates cardiovascular function are complex and incompletely understood. We thus investigated whether the GLP-1 analogue, liraglutide, which is an acylated GLP-1, has protective effects on vascular endothelial cells.MethodsNitrite and nitrate were measured in medium with an automated nitric oxide detector. Endothelial nitric oxide synthase (eNOS) activation was assessed by evaluating the phosphorylation status of the enzyme and evaluating eNOS activity by citrulline synthesis. Nuclear factor κB (NF-κB) activation was assessed by reporter gene assay.ResultsLiraglutide dose-dependently increased nitric oxide production in HUVECs. It also caused eNOS phosphorylation, potentiated eNOS activity and restored the cytokine-induced downregulation of eNOS (also known as NOS3) mRNA levels, which is dependent on NF-κB activation. We therefore examined the effect of liraglutide on TNFα-induced NF-κB activation and NF-κB-dependent expression of proinflammatory genes. Liraglutide dose-dependently inhibited NF-κB activation and TNFα-induced IκB degradation. It also reduced TNFα-induced MCP-1 (also known as CCL2), VCAM1, ICAM1 and E-selectin mRNA expression. Liraglutide-induced enhancement of nitric oxide production and suppression of NF-κB activation were attenuated by the AMP-activated protein kinase (AMPK) inhibitor compound C or AMPK (also known as PRKAA1) small interfering RNA. Indeed, liraglutide induced phosphorylation of AMPK, which occurs through a signalling pathway independent of cyclic AMP.Conclusions/interpretationLiraglutide exerts an anti-inflammatory effect on vascular endothelial cells by increasing nitric oxide production and suppressing NF-κB activation, partly at least through AMPK activation. These effects may explain some of the observed vasoprotective properties of liraglutide, as well as its beneficial effects on the cardiovascular system.

Aldosterone impairs vascular endothelial cell function.

Aldosterone is a mineralocorticoid hormone that plays an important role in regulating electrolyte balance and blood pressure and also participates in endothelial dysfunction. We evaluated the direct effect of aldosterone on human umbilical vein cells (HUVEC). Levels of eNOS phosphorylation by vascular endothelial growth factor were diminished, and the amount of NO produced in response to vascular endothelial growth factor measured as NO2−+NO3− was significantly decreased in cells previously incubated with aldosterone. Incubation with aldosterone for 24 h dose-dependently increased Nox4 mRNA expression in HUVEC. Although NF-κB was not apparently activated by aldosterone, mRNA levels of vascular cell adhesion molecule-1, E-selectin, monocyte chemotactic protein-1, and intercellular adhesion molecule-1 in HUVEC were significantly increased after incubation with aldosterone. Thus, aldosterone directly causes the dysregulation of endothelial cell function, which may be partly responsible for high blood pressure and atherosclerosis.

Telmisartan inhibits cytokine-induced nuclear factor-κB activation independently of the peroxisome proliferator-activated receptor-γ

Telmisartan is an angiotensin-II type 1 receptor (AT1R) blocker, currently used to treat patients with hypertension. Telmisartan, in addition to its effect on AT1R, is thought to activate the nuclear transcription factor, peroxisome proliferator-activated receptor-γ (PPAR γ), thereby acting as a partial PPARγ agonist. This study was conducted to examine whether telmisartan might suppress cytokine-induced inflammatory signaling in vascular endothelial cells, thereby attenuating cellular inflammation possibly by PPARγ activation. Telmisartan caused a dose-dependent suppression of the tumor necrosis factor-α (TNFα)-induced activation of nuclear factor (NF)-κB in vascular endothelial cells in this study. The PPARγ antagonist, GW9662, did not influence the inhibitory effect of telmisartan on NF-κB activation. The thiazolidinediones neither influenced TNFα-induced NF-κB activation nor influenced the inhibitory effect of telmisartan in this process. Telmisartan dose dependently diminished the TNFα-induced gene expression of VCAM-1, and GW9662 did not attenuate this effect. Thus, telmisartan inhibits the cytokine-induced expression of the VCAM-1 gene by blocking NF-κB activation independently of PPARγ activation. Although the mechanism by which this occurs remains unclear, our findings suggest that telmisartan-induced anti-inflammatory effects might have favorable effects on vasculature in hypertensive patients.

Glimepiride upregulates eNOS activity and inhibits cytokine‐induced NF‐κB activation through a phosphoinoside 3‐kinase–Akt‐dependent pathway

Aims:  Several studies suggest increased mortality postcoronary angioplasty in patients on sulphonylureas. However, a theoretical reduction in cardiac risk has been suggested with the newer sulphonylurea agents, which differ from the first‐generation agents. In the present study, we investigated whether a third generation of sulphonylurea, glimepiride, might stimulate nitric oxide (NO) production and thereby inhibit cytokine‐induced nuclear factor (NF)‐κB activation in endothelial cells compared with the classical sulphonylurea glibenclamide.

Fluvastatin upregulates endothelial nitric oxide synthase activity via enhancement of its phosphorylation and expression and via an increase in tetrahydrobiopterin in vascular endothelial cells.

BACKGROUND An HMG-CoA reductase inhibitor, fluvastatin, appears to act directly on the blood vessel wall to stabilize plaques in situ, agents that share this property have been termed vascular statins. METHODS We investigated the effects of fluvastatin on endothelial nitric oxide synthase (eNOS) phosphorylation and expression, as well as terahydrobiopterin (BH4) metabolism, in human umbilical vein endothelial cells (HUVEC). RESULTS Fluvastatin was observed to enhance eNOS phosphorylation at Ser-1177 and Ser-633 through the PI3-kinase/Akt and PKA pathways, respectively. Inhibition of eNOS phosphorylation using inhibitors of these pathways attenuated acute NO release in response to fluvastatin. The mRNA of GTP cyclohydrolase I (GTPCH), the rate-limiting enzyme of the first step of de novo BH4 synthesis, as well as eNOS, was upregulated in HUVEC treated with fluvastatin. In parallel with this observation, fluvastatin increased intracellular BH4. Pre-treatment of HUVEC with the selective GTPCH inhibitor, 2,4-diamino-6-hydroxypyrimidine, reduced intracellular BH4 and decreased citrulline formation following stimulation with ionomycin. Furthermore, the potentiating effect of fluvastatin was reduced by limiting the cellular availability of BH4. CONCLUSIONS Our data demonstrate that fluvastatin phosphorylates and activates eNOS, and increases eNOS expression in vascular endothelial cells. In addition to modulating eNOS, fluvastatin potentiates GTPCH gene expression and BH4 synthesis, thereby increasing NO production and preventing relative shortages of BH4.

Tetrahydrobiopterin Slows the Progression of Atherosclerosis

Abstract We investigated whether oral tetrahydrobiopterin (BH4) treatment might slow the progression of atherosclerosis using hypercholesterolemic ApoE-knockout (KO) mice. We report that ingesting BH4 in drinking water is effective to inhibit atherogenesis in mice. Furthermore, we report that BH4 treatment improves endothelial dysfunction and attenuates increased mRNA expression of NADPH oxidase components, as well as a number of inflammatory factors, such as LOX-1 and MCP-1, in the aortas of ApoE-KO mice. Strategies such as oral administration of BH4 to ensure continuous BH4 availability may be effective in restoring NO-mediated endothelial function and limiting vascular disease and the progression of atherosclerosis.