Adiponectin inhibits insulin-like growth factor-1-induced cell migration by the suppression of extracellular signal-regulated kinase 1/2 activation, but not Akt in vascular smooth muscle cells.

Adiponectin, an adipocyte-derived hormone, has been proposed to show antiatherogenic properties through the inhibitory effects against various growth factors. Insulin-like growth factor-1 (IGF-1) is one of the potent mitogens, which has been considered to play important roles in both atherogenesis and plaque stabilization in accordance to the phase of atherosclerosis. The aim of this study is to elucidate the adiponectin effects on IGF-1-induced cell migration and its intracellular signaling pathways in vascular smooth muscle cells (VSMCs). In this study, we assessed cell migration and several kinase activities in cultured rat aortic smooth muscle cells (RASMCs). Adiponectin pretreatment suppressed IGF-1-induced cell migration and extracellular signal-regulated kinase (ERK)1/2 activation, which is one of the major mediators for IGF-1-induced cell migration. In RASMCs, adiponectin and 5-aminoimidazole-4-carboxamide riboside (AICAR), a 5'-AMP-activated protein kinase (AMPK) activator, stimulated AMPK activation. AMPK activation by AICAR inhibited IGF-1-induced ERK1/2 activation and cell migration in RASMCs. On the other hand, phosphorylation of Akt and Bad, proapoptotic molecules of the Bcl-2 family, which were increased by IGF-1 stimulation, was not diminished by the pretreatment with adiponectin. It was shown that adiponectin inhibited IGF-1-induced VSMC migration through suppression of ERK1/2 activation, which might be implicated in AMPK activation. Furthermore, adiponectin selectively inhibited ERK1/2 pathway, not Akt-Bad pathway, stimulated by IGF-1. From these findings, it was implied that adiponectin suppressed IGF-1-induced VSMC migration and its signaling selectivity.

Quercetin glucuronide inhibits cell migration and proliferation by platelet-derived growth factor in vascular smooth muscle cells.

Many epidemiologic studies have reported that dietary flavonoids provide protection against cardiovascular disease. Quercetin, a member of the bioflavonoids family, has been proposed to have anti-inflammatory, anti-atherogenic, and anti-hypertensive properties leading to the beneficial effects against cardiovascular diseases. Recent studies demonstrated that orally administered quercetin appeared in plasma as glucuronide-conjugated forms in rats and humans. Therefore, we examined the effect of chemically synthesized quercetin glucuronide on platelet-derived growth factor (PDGF)-induced cell migration and kinase activation in cultured rat aortic smooth muscle cells (RASMCs). PDGF-induced RASMC migration was inhibited by quercetin 3-O-beta-D-glucuronide (Q3GA). Q3GA also attenuated PDGF-induced cell proliferation in RASMCs. PDGF activated extracellular-signal regulated kinase (ERK) 1/2, c-Jun N-terminal kinase (JNK), p38 mitogen-activated protein (MAP) kinase, and Akt in RASMCs. PDGF-induced JNK and Akt activations were suppressed by Q3GA, whereas ERK1/2 and p38 MAP kinase activations were not affected. We also confirmed that PDGF-induced JNK and Akt activations were inhibited by antioxidants, N-acetylcysteine and diphenyleneiodonium chloride, in RASMCs. These findings suggest Q3GA would be an active metabolite of quercetin in plasma and may possess preventing effects for cardiovascular diseases relevant to vascular smooth muscle cell disorders.

Dietary doses of nitrite restore circulating nitric oxide level and improve renal injury in L-NAME-induced hypertensive rats.

We have reported that pharmacological doses of oral nitrite increase circulating nitric oxide (NO) and exert hypotensive effects in Nomega-nitro-L-arginine methyl ester (L-NAME)-induced hypertensive rats. In this study, we examined the effect of a chronic dietary dose of nitrite on the hypertension and renal damage induced by chronic L-NAME administration in rats. The animals were administered tap water containing L-NAME (1 g/l) or L-NAME + nitrite (low dose: 0.1 mg/l, medium dose: 1 mg/l, high dose: 10 mg/l) for 8 wk. We evaluated blood NO levels as hemoglobin-NO adducts (iron-nitrosyl-hemoglobin), using an electron paramagnetic resonance method. Chronic administration of L-NAME for 8 wk induced hypertension and renal injury and reduced the blood iron-nitrosyl-hemoglobin level (control 38.8 +/- 8.9 vs. L-NAME 6.0 +/- 3.1 arbitrary units). Coadministration of a low dose of nitrite with L-NAME did not change the reduced iron-nitrosyl-hemoglobin signal and did not improve the L-NAME-induced renal injury. The blood iron-nitrosyl-hemoglobin signals of the medium dose and high dose of nitrite were significantly higher than that of L-NAME alone. Chronic administration of a medium dose of nitrite attenuated L-NAME-induced renal histological changes and proteinuria. A high dose of nitrite also attenuated L-NAME-induced renal injury. These findings suggest that dietary doses of nitrite that protect the kidney are associated with significant increase in iron-nitrosyl-hemoglobin levels. We conclude that dietary nitrite-derived NO generation may serve as a backup system when the nitric oxide synthase/L-arginine-dependent NO generation system is compromised.

Effects of angiotensin II type 1 receptor blockade on the systemic blood nitric oxide dynamics in Nomega-nitro-L-arginine methyl ester-treated rats.

We previously succeeded in measuring the nitrosylhemoglobin (HbNO) level as an index of blood nitric oxide (NO) by the electron paramagnetic resonance (EPR) HbNO signal subtraction method. In this study, we examined the effects of olmesartan, an angiotensin II type 1 receptor blocker (ARB), on NO dynamics in N(omega)-nitro-L-arginine methyl ester (L-NAME)-treated rats by the EPR-subtraction method. Oral administration of L-NAME for 2 weeks induced serious hypertension, and the HbNO concentration was reduced to 37.6% of the level in controls. Coadministration of olmesartan improved hypertension and increased the blood HbNO concentration of L-NAME-treated rats. In contrast, coadministration of hydralazine improved hypertension but did not affect the blood HbNO concentration. In conclusion, our findings suggested that chronic administration of olmesartan ameliorated the endothelial dysfunction in L-NAME-treated rats.

Evaluation of systemic blood NO dynamics by EPR spectroscopy: HbNO as an endogenous index of NO.

The measurement of hemoglobin-nitric oxide (NO) adduct (HbNO) in whole blood by the electron paramagnetic resonance (EPR) method seems relevant for the assessment of systemic NO levels. However, ceruloplasmin and unknown radical species overlap the same magnetic field as that of HbNO. To reveal the EPR spectrum of HbNO, we then introduced the EPR signal subtraction method, which is based on the computer-assisted subtraction of the digitized EPR spectrum of HbNO-depleted blood from that of sample blood using the software. Rats were treated with N(omega)-nitro-L-arginine methyl ester (L-NAME; 120 mg. kg-1. day-1) for 1 wk to obtain HbNO-depleted blood. When this method was applied to the analysis of untreated fresh whole blood, the five-coordinate state of HbNO was observed. HbNO concentration in pentobarbital-anesthetized rats was augmented (change in [HbNO] = 1.6-5.5 microM) by infusion of L-arginine (0.2-0.6 g/kg) but not D-arginine. Using this method, we attempted to evaluate the effects of temocapril on HbNO dynamics in an L-NAME-induced rat endothelial dysfunction model. The oral administration of L-NAME for 2 wk induced a serious hypertension, and the HbNO concentration was reduced (change in [HbNO] = 5.7 microM). Coadministration of temocapril dose dependently improved both changes in blood pressure and the systemic HbNO concentration. In this study, we succeeded in measuring the blood HbNO level as an index of NO by the EPR HbNO signal subtraction method. We also demonstrated that temocapril improves abnormalities of NO dynamics in L-NAME-induced endothelial dysfunction rats using the EPR HbNO signal subtraction method.