Biomedical subjects

Toyohiko Yokoi

Publications and source records attributed to Toyohiko Yokoi.

5 recordsLinked to original sources

PubMed2006

Fas ligand mRNA levels of circulating leukocytes reflect endothelial dysfunction in hyperlipidemic but not in non-hyperlipidemic patients.

To find a novel marker for identifying patients at high-risk for endothelial dysfunction among patients with atherosclerosis, we examined the correlation between mRNA levels of Fas ligand (FasL), an apoptosis-inducing factor, in circulating leukocytes and clinical parameters in these patients. FasL mRNA levels of circulating leukocytes were measured with the TaqMan-PCR method. A negative correlation was observed between brachial artery flow-mediated dilatation (%FMD) and FasL mRNA levels of leukocytes in hyperlipidemic but not in non-hyperlipidemic patients. %FMD was more impaired in patients with a high level of FasL mRNA than in those with a low level of FasL mRNA. Interestingly, the improvement of %FMD by treatment with a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor (simvastatin) was greater in the group showing a decrease in FasL mRNA than in the group with no such decrease. Additionally, simvastatin suppressed the FasL mRNA expression in leukocytes and decreased plasma oxidized low-density lipoprotein (OxLDL) levels. Furthermore, the supernatant of cultured leukocytes from hyperlipidemic patients induced cell death in Jurkat T cells, which was neutralized by an antibody against FasL. These findings suggest that high FasL mRNA expression in circulating leukocytes may be a marker of high-risk for endothelial dysfunction in hyperlipidemic but not in non-hyperlipidemic patients. This information may provide a novel basis for targeting of statin therapy in patients with vulnerable plaques.

Aged↗

PubMed2006

Apoptosis signal-regulating kinase 1 mediates cellular senescence induced by high glucose in endothelial cells.

Vascular ageing is accelerated in patients with diabetes. However, the underlying mechanism remains unclear. Here, we show that high glucose induces activation of apoptosis signal-regulating kinase 1 (ASK1), an apoptosis-inducing signal that mediates endothelial cell senescence induced by hyperglycemia. High glucose induced a time-dependent increase in the levels of ASK1 expression and its activity in human umbilical vein endothelial cells (HUVECs). Incubation of endothelial cells with high glucose increased the proportion of cells expressing senescence-associated beta-galactosidase (SA-beta-gal) activity. However, transfection with an adenoviral construct including a dominant negative form of ASK1 gene significantly inhibited SA-beta-gal activity induced by high glucose. In addition, infection with an adenoviral construct expressing the constitutively active ASK1 gene directly induced an increase in the levels of SA-beta-gal activity. Activation of the ASK1 signal also enhanced plasminogen activator inhibitor-1 (PAI-1) expression in HUVECs. Induction of senescent endothelial cells in aortas and elevation of plasma PAI-1 levels were observed in streptozotocin (STZ) diabetic mice, whereas these changes induced by STZ were attenuated in ASK1-knockout mice. Our results suggest that hyperglycemia accelerates endothelial cell senescence and upregulation of PAI-1 expression through activation of the ASK1 signal. Thus, ASK1 may be a new therapeutic target to prevent vascular ageing and thrombosis in diabetic patients.

Adenoviridae↗

PubMed2005

[Calcium antagonists and endothelial function].

Endothelial dysfunction is an early sign of atherosclerosis. Patients with risk factors for atherosclerosis (e.g., hypertension, hyperlipidemia and diabetes mellitus) often show endothelial dysfunction at early stages of atherosclerosis before cardiovascular complications develop. Clinical studies and basic researches are revealing that calcium antagonists not only protect the endothelium through their hypotensive action but also improve the endothelial function through the stimulation of NO production. Regarding the mechanism for this kind of action by nifedipine (a calcium antagonist), it seems likely that the drug stimulates SOD expression in endothelial cells through enhanced VEGF expression by vascular smooth muscle cells, and thus reduces oxidative stress, leading to increased NO production.

Antihypertensive Agents↗

PubMed2004

Homocysteine enhances endothelial apoptosis via upregulation of Fas-mediated pathways.

Hyperhomocysteinemia is an independent risk factor for the development of atherosclerosis. However, the underlying mechanism of endothelial cell injury in hyperhomocysteinemia has not been elucidated. In this study, we examined the effect of homocysteine (Hcy) on Fas-mediated apoptosis in endothelial cells. Hcy-induced upregulation of Fas in endothelial cells (ECs) in a dose-dependent manner. At the same time, Hcy increased intracellular peroxide in ECs. Hcy-induced Fas expression was inhibited by the treatment with catalase. Hcy increased NF-kappaB DNA binding activity, and adenovirus-mediated transfection of a Ikappa-B mutant (Ikappa-B mt) gene inhibited Hcy-induced Fas expression. ECs were sensitive to Fas-mediated apoptosis when exposed to Hcy. Under these condition, Ikappa-B mt protected ECs from Fas-mediated apoptosis. In addition, Hcy inhibited expression of the caspase-8 inhibitor FLICE-inhibitory protein (FLIP). Adenovirus-mediated transfection of constitutively active Akt gene abolished the Hcy-mediated downregulation of FLIP. These data suggest that upregulation of Fas expression and downregulation of FLIP is a mechanism through which Hcy induces EC apoptosis.

Animals↗

PubMed2004

Fas signaling induces Akt activation and upregulation of endothelial nitric oxide synthase expression.

A growing body of evidence has shown that Fas, a death receptor, mediates apoptosis-unrelated biological effects. Here, we report that Fas engagement with Fas ligand induced activation of Akt and upregulation of endothelial nitric oxide synthase expression without induction of apoptosis. In the presence of the phosphatidylinositol 3-kinase inhibitor wortmannin, Fas ligand, however, induced apoptosis instead of upregulation of endothelial nitric oxide synthase expression. In vivo, systolic blood pressure was slightly higher in mutant mice with decreased cell surface Fas expression (lpr mice) compared with wild-type mice. In addition, chronic inhibition of nitric oxide synthesis by N(G)-nitro-l-arginine induced a progressive increase in the levels of blood pressure in wild-type mice, whereas no further increase in the levels of blood pressure was observed in lpr mice. Furthermore, acetylcholine caused a lesser endothelium-dependent relaxation of the strips from lpr mice compared with wild-type mice, although the vasoconstrictor potency of phenylephrine was not different between the two groups. These findings indicate that Fas signaling may have a role in the regulation of endothelial function and blood pressure through modulating endothelial nitric oxide synthase expression in the Akt signal-dependent manner.

Acetylcholine↗