Dietary inorganic nitrate attenuates hyperoxia-induced oxidative stress in obese type 2 diabetic male rats

Hyperoxia has beneficial metabolic effects in type 2 diabetes. However, hyperoxia exacerbates already existing oxidative stress in type 2 diabetes. Nitrate, a nitric oxide donor, is an effective new treatment in type 2 diabetes and also has antioxidant properties. The aim of this study was to determine whether nitrate administration can attenuate hyperoxia-induced oxidative stress in obese type 2 diabetic rats.

Fifty-six male Wistar rats (190-210 g) were divided into 8 groups: Controls (non-treated, nitrate-treated, O₂-treated, and nitrate + O₂-treated) and diabetes (non-treated, nitrate-treated, O₂-treated, and nitrate + O₂-treated). Diabetes was induced using high-fat diet and low-dose of streptozotocin (30 mg/kg). Rats in intervention groups, were exposed to 95% oxygen and consumed sodium nitrate (100 mg/L) in drinking water. Serum fasting glucose, oxidized (GSSG) and reduced (GSH) glutathiones, total oxidant status (TOS), catalase and superoxide dismutase (SOD) activities, and total antioxidant capacity (TAC) were measured after intervention. Oxidative stress index (OSI) was calculated as TOS/TAC ratio.

Diabetic rats had increased oxidative stress and hyperoxia exacerbated it. In O₂-diabetic rats, nitrate decreased GSSG (102.7 ± 2.1 vs. 236.0 ± 20.1 μM, P < 0.001), TOS (67.7 ± 7.3 vs. 104 ± 3.8 μM, P < 0.001), and OSI (0.44 ± 0.04 vs. 0.91 ± 0.07, P < 0.001) and increased catalase (2.8 ± 0.13 vs. 1.8 ± 0.21 KU/L, P = 0.014), SOD (53.4 ± 1.5 vs. 38.4 ± 1.2 U/mL, P < 0.001), GSH (43.7 ± 1.4 vs. 17.8 ± 0.5 mM, P = 0.003), TAC (152.5 ± 1.9 vs. 116.7 ± 5.0 mM, P < 0.001), and GSH/GSSG ratio (0.43 ± 0.01 vs. 0.08 ± 0.01, P = 0.005). Nitrate also potentiated effects of hyperoxia on decreasing fasting glucose.

Our results showed that dietary nitrate attenuates hyperoxia-induced oxidative stress in type 2 diabetic rats.