Bei‐Chia Guo

Hyperuricemia is closely associated with the mobility and mortality of patients with cardiovascular diseases. However, how hyperuricemia accelerates atherosclerosis progression is not well understood. The balance between asymmetric dimethylarginine (ADMA) and dimethylarginine dimethylaminotransferases (DDAHs) is crucial to regulate vascular homeostasis. Therefore, we investigated the role of the ADMA/DDAH pathway in hyperuricemia-induced endothelial dysfunction and atherosclerosis and the underlying molecular mechanisms in endothelial cells (ECs) and apolipoprotein E–knockout (apoe−/−) mice. Our results demonstrated that uric acid at pathological concentrations increased the intracellular levels of ADMA and downregulated DDAH-2 expression without affecting DDAH-1 expression. Excess uric acid also reduced NO bioavailability and increased monocyte adhesion to ECs, which were abolished by using the antioxidant N-acetylcysteine, the nicotinamide adenine dinucleotide phosphate oxidase inhibitor apocynin, or DDAH-2 overexpression. In apoe−/− mice, treatment with oxonic acid, a uricase inhibitor, increased the circulating level of uric acid, cholesterol, and lipid peroxidation; exacerbated systemic and aortic inflammation; and worsened atherosclerosis compared with vehicle-treated apoe−/− mice. Furthermore, oxonic acid–treated apoe−/− mice exhibited elevated ADMA plasma level and downregulated aortic expression of DDAH-2 protein. Notably, DDAH-2 overexpression in the ECs of apoe−/− mice prevented hyperuricemia-induced deleterious effects from influencing ADMA production, lipid peroxidation, inflammation, and atherosclerosis. Collectively, our findings suggest that hyperuricemia disturbs the balance of the ADMA/DDAH-2 axis, results in EC dysfunction, and, consequently, accelerates atherosclerosis.

We aimed to investigate the effect of bromelain, the extract from stems of pineapples on the high-fat diet (HFD)-induced deregulation of hepatic lipid metabolism and non-alcoholic fatty liver disease (NAFLD), and its underlying mechanism in mice. Mice were daily administrated with HFD with or without bromelain (20 mg/kg) for 12 weeks, and we found that bromelain decreased the HFD-induced increase in body weight by ~30%, organ weight by ~20% in liver weight and ~40% in white adipose tissue weight. Additionally, bromelain attenuated HFD-induced hyperlipidemia by decreasing the serum level of total cholesterol by ~15% and triglycerides level by ~25% in mice. Moreover, hepatic lipid accumulation, particularly that of total cholesterol, free cholesterol, triglycerides, fatty acids, and glycerol, was decreased by 15-30% with bromelain treatment. Mechanistically, these beneficial effects of bromelain on HFD-induced hyperlipidemia and hepatic lipid accumulation may be attributed to the decreased fatty acid uptake and cholesteryl ester synthesis and the increased lipoprotein internalization, bile acid metabolism, cholesterol clearance, the assembly and secretion of very low-density lipoprotein, and the β-oxidation of fatty acids by regulating the protein expression involved in the above mentioned hepatic metabolic pathways. Collectively, these findings suggest that bromelain has therapeutic value for treating NAFLD and metabolic diseases.

BACKGROUND: Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of endothelial nitric oxide synthase (eNOS), is considered a risk factor for the pathogenesis of cardiovascular diseases. Simvastatin, a lipid-lowering drug with other pleiotropic effects, has been widely used for treatment of cardiovascular diseases. However, little is known about the effect and underlying molecular mechanisms of ADMA on the effectiveness of simvastatin in the vascular system. METHODS AND RESULTS: We conducted a prospective cohort study to enroll 648 consecutive patients with coronary artery disease for a follow-up period of 8 years. In patients with plasma ADMA level ≥0.49 μmol/L (a cut-off value from receiver operating characteristic curve), statin treatment had no significant effect on cardiovascular events. We also conducted randomized, controlled studies using in vitro and in vivo models. In endothelial cells, treatment with ADMA (≥0.5 μmol/L) impaired simvastatin-induced nitric oxide (NO) production, endothelial NO synthase (eNOS) phosphorylation, and angiogenesis. In parallel, ADMA markedly increased the activity of NADPH oxidase (NOX) and production of reactive oxygen species (ROS). The detrimental effects of ADMA on simvastatin-induced NO production and angiogenesis were abolished by the antioxidant, N-acetylcysteine, NOX inhibitor, or apocynin or overexpression of dimethylarginine dimethylaminohydrolase 2 (DDAH-2). Moreover, in vivo, ADMA administration reduced Matrigel plug angiogenesis in wild-type mice and decreased simvastatin-induced eNOS phosphorylation in aortas of apolipoprotein E-deficient mice, but not endothelial DDAH-2-overexpressed aortas. CONCLUSIONS: We conclude that ADMA may trigger NOX-ROS signaling, which leads to restricting the simvastatin-conferred protection of eNOS activation, NO production, and angiogenesis as well as the clinical outcome of cardiovascular events.

SCOPE: Epigallocatechin-3-gallate (EGCG), the most abundant catechin of green tea, has beneficial effects on physiological functions of endothelial cells (ECs), yet the detailed mechanisms are not fully understood. In this study, we investigated the role of transient receptor potential vanilloid type 1 (TRPV1), a ligand-gated nonselective calcium channel, in EGCG-mediated endothelial nitric oxide (NO) synthase (eNOS) activation and angiogenesis. METHODS AND RESULTS: In ECs, treatment with EGCG time-dependently increased the intracellular level of Ca(2+) . Removal of extracellular calcium (Ca(2+) ) by EGTA or EDTA or inhibition of TRPV1 by capsazepine or SB366791 abrogated EGCG-increased intracellular Ca(2+) level in ECs or TRPV1-transfected HEK293 cells. Additionally, EGCG increased the phsophorylation of eNOS at Ser635 and Ser1179, Akt at Ser473, calmodulin-dependent protein kinase II (CaMKII) at Thr286 and AMP-activated protein kinase (AMPK) at Thr172, all abolished by the TRPV1 antagonist capsazepine. EGCG-induced NO production was diminished by pretreatment with LY294002 (an Akt inhibitor), KN62 (a CaMKII inhibitor), and compound C (an AMPK inhibitor). Moreover, blocking TRPV1 activation prevented EGCG-induced EC proliferation, migration, and tube formation, as well as angiogenesis in Matrigel plugs in mice. CONCLUSION: EGCG may trigger activation of TRPV1-Ca(2+) signaling, which leads to phosphorylation of Akt, AMPK, and CaMKII; eNOS activation; NO production; and, ultimately, angiogenesis in ECs.

Fetuin-A, a hepatokine secreted by hepatocytes, binds to insulin receptors and consequently impairs the activation of the insulin signaling pathway, leading to insulin resistance. Apigenin, a flavonoid isolated from plants, has beneficial effects on insulin resistance; however, its regulatory mechanisms are not fully understood. In the present study, we investigated the molecular mechanisms underlying the protective effects of apigenin on insulin resistance. In Huh7 cells, treatment with apigenin decreased the mRNA expression of fetuin-A by decreasing reactive oxygen species-mediated casein kinase 2α (CK2α)-nuclear factor kappa-light-chain-enhancer of activated B activation; besides, apigenin decreased the levels of CK2α-dependent fetuin-A phosphorylation and thus promoted fetuin-A degradation through the autophagic pathway, resulting in a decrease in the protein levels of fetuin-A. Moreover, apigenin prevented the formation of the fetuin-A-insulin receptor (IR) complex and thereby rescued the PA-induced impairment of the insulin signaling pathway, as evidenced by increased phosphorylation of IR substrate-1 and Akt, and translocation of glucose transporter 2 from the cytosol to the plasma membrane. Similar results were observed in the liver of HFD-fed mice treated with apigenin. Collectively, our findings revealed that apigenin ameliorates obesity-induced insulin resistance in the liver by targeting fetuin-A.