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.