Dietary nitrite reverses features of postmenopausal metabolic syndrome induced by high-fat diet and ovariectomy in mice.

Menopausal women are at greater risk of developing metabolic syndrome with reduced endothelial nitric oxide synthase (eNOS) activity. Hormone replacement therapy increases eNOS activity and normalizes some characteristics of metabolic syndrome. We hypothesized that nitric oxide (NO) supplementation should have a therapeutic effect on this syndrome. We examined the effect of dietary nitrite in a mouse model with postmenopausal metabolic syndrome induced by ovariectomy (OVX) and a high fat diet (HF). C57BL/6 female mice were divided into five groups, sham+normal fat diet (NF), sham+ HF, OVX+HF with or without sodium nitrite (50 mg and 150 mg/l) in the drinking water. Daily food intake and weekly body weight were monitored for 18 wk. OVX and HF significantly reduced plasma levels of nitrate/nitrite (NOx), and mice developed obesity with visceral hypertrophic adipocytes and increased transcriptional levels of monocyte chemoattractant protein-1, TNF-α, and IL-6 in visceral fat tissues. The proinflammatory state in the adipocytes provoked severe hepatosteatosis and insulin resistance in OVX+HF group compared with sham+NF group. However, dietary nitrite significantly suppressed adipocyte hypertrophy and transcriptions of proinflammatory cytokines in visceral fat in a dose-dependent manner. The improvement of visceral inflammatory state consequently reversed the hepatosteatosis and insulin resistance observed in OVX+HF mice. These results suggest that an endogenous NO defect might underlie postmenopausal metabolic syndrome and that dietary nitrite provides an alternative source of NO, subsequently compensating for metabolic impairments of this syndrome.

Dietary nitrite supplementation improves insulin resistance in type 2 diabetic KKA(y) mice.

BACKGROUND: Because insulin signaling is essential for endothelial nitric oxide synthase (eNOS)-derived nitric oxide (NO) production, the loss of bioavailable NO might be a common molecular mechanism underlying the development of insulin resistance and endothelial dysfunction. Although dietary nitrite acts as a substrate for systemic NO generation, thereby serving as a physiological alternative source of NO for signaling, it is not precisely known how dietary nitrite affects type 2 diabetes mellitus. Here we report the therapeutic effects of dietary nitrite on the metabolic and histological features of KKA(y) diabetic mice. METHODS: KKA(y) mice were divided into three groups (without nitrite, and with 50 mg/L and 150 mg/L nitrite in drinking water), and two groups of C57BL/6J mice served as controls (without nitrite and with 150 mg/L nitrite in drinking water). After 10 weeks, blood samples, visceral adipose tissues, and gastrocnemius muscles were collected after a 16-hour fast to assess the homeostasis model assessment of insulin resistance (HOMA-IR) levels, the histology of the adipose tissue, insulin-stimulated sequential signaling to glucose transporter 4 (GLUT4), and nitrite and nitrate contents in the muscle using an HPLC system. RESULTS: KKA(y) mice developed obesity with enhanced fasting plasma levels of glucose and insulin and exhibited increased HOMA-IR scores compared with the C57BL/6J control mice. Dietary nitrite dose-dependently reduced the size of the hypertrophic adipocytes and TNF-α transcription in the adipose tissue of KKA(y) diabetic mice, which also restored the insulin-mediated signal transduction, including p85 and Akt phosphorylation, and subsequently restored the GLUT4 expression in the skeletal muscles. CONCLUSIONS: These results suggest that dietary nitrite provides an alternative source of NO, and subsequently improves the insulin-mediated signaling and the metabolic and histological features in KKA(y) diabetic mice.

Acute lethal crush-injured rats can be successfully rescued by a single injection of high-dose dexamethasone through a pathway involving PI3K-Akt-eNOS signaling.

BACKGROUND: Crush syndrome (CS) is characterized by ischemia/reperfusion-induced rhabdomyolysis and the subsequent onset of systemic inflammation. CS is associated with a high mortality, even when patients are treated with conventional therapy. We hypothesized that treatment of lethal CS rat model with dexamethasone (DEX) have therapeutic effects on the laboratory findings and clinical course and outcome. METHODS: To create a CS model, anesthetized rats were subjected to bilateral hind limb compression with rubber tourniquets for 5 hours and randomly divided into three groups as follows: saline-treated CS group, CS groups treated with low (0.1 mg/kg) and high doses (5.0 mg/kg) of DEX. Saline for the CS group or DEX for the DEX-treated CS groups was intravenously administered immediately before reperfusion. Under continuous monitoring and recording of arterial blood pressures, blood and tissue samples were collected for histologic and biochemical analysis at designated period before and after reperfusion. RESULTS: Ischemic compression of rat hind limbs reduced the nitrite content in the crushed muscle, and the subsequent reperfusion induced reactive oxygen species-mediated circulatory collapse and systemic inflammation, finally resulting in a mortality rate of 76% by 48 hours after reperfusion. A single injection of high-dose DEX immediately before reperfusion activated endothelial nitric oxide synthase (eNOS) by sequential phosphorylation through the nongenomic phosphoinositide 3-kinase (PI3K)-Akt-eNOS signaling pathway. DEX also exhibited anti-inflammatory effects by modulating proinflammatory and anti-inflammatory mediators, consequently suppressing myeloperoxidase activities and subsequent systemic inflammation, showing a complete recovery of the rats from lethal CS. CONCLUSION: These results indicate that high-dose DEX reduces systemic inflammation and contributes to the improved survival rate in a rat CS model.

Nitrite reduces ischemia/reperfusion-induced muscle damage and improves survival rates in rat crush injury model.

BACKGROUND: Nitrite is an intrinsic signaling molecule with potential therapeutic implications in mammalian ischemia/reperfusion (I/R) injury of the heart, liver, and kidney. Although limb muscle compression and subsequent reperfusion are the causative factors in developing crush syndrome (CS), there has been no report evaluating the therapeutic effects of nitrite on CS. We therefore tested whether nitrite could be a therapeutic agent for the treatment of CS. METHODS: To create a CS model, anesthetized rats were subjected to bilateral hind limb compression with rubber tourniquets for 5 hours, followed by reperfusion for 0 hour to 6 hours while monitoring blood pressure. Saline for the CS group or sodium nitrite (NaNO(2)-100, 200, and 500 µmol/kg) for the nitrite-treated CS groups was intravenously administered immediately before reperfusion. Blood and tissue samples were collected for biochemical analysis. RESULTS: Tissue nitrite levels in injured muscles were significantly reduced in the CS group compared with the sham group during I/R injury. Nitrite administration to CS rats restored nitric oxide bioavailability by enhancing nitrite levels of the muscle, resulting in a reduction of rhabdomyolysis markers such as potassium, lactate dehydrogenase, and creatine phosphokinase. Nitrite treatment also reduced plasma levels of interleukin-6 and myeloperoxidase activities in muscle and lung tissues, finally resulting in a dose-dependent improvement of survival rate from 24% (CS group) to 36% (NaNO(2)-100 group) and 64% (NaNO(2)-200 and 500 groups). CONCLUSION: These results indicate that nitrite reduces I/R-induced muscle damage through its cytoprotective action and contributes to improved survival rate in a rat CS model.