Inorganic Nitrate Alleviates Total Body Irradiation-Induced Systemic Damage by Decreasing Reactive Oxygen Species Levels.

Abstract

To evaluate the protective effect of inorganic nitrate against systemic damage in a mouse model of total body gamma irradiation (TBI). C57BL/6 mice in the irradiation (IR) + NaNO₃ group were pretreated with 2 mmol/L NaNO₃ in their drinking water for 1 week before receiving 5 Gy irradiation. Animals that received only 5 Gy irradiation were designated as the IR group. Survival and body weight were monitored. The peripheral blood lymphocytes, heart, liver, lung, and submandibular gland were harvested and assessed. Reactive oxygen species (ROS) were measured in the lung and submandibular gland. We examined phosphorylated histone H2AX (p-H2AX) and p53-binding protein 1 (53BP1) as markers of early-stage DNA damage and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) and Bax/caspase 3 mRNA expression as markers of apoptosis. No improvement of survival was observed in the IR + NaNO₃ group after TBI, but body weight loss after 5 Gy TBI was significantly attenuated in the IR + NaNO₃ group. The levels of peripheral blood erythrocytes, leukocytes, and platelets at 7 days postirradiation recovered with nitrate treatment; moreover, the p-H2AX level in the peripheral blood lymphocytes was much lower in the IR + NaNO₃ group at 2 and 4 hours post irradiation. In the lung and submandibular gland, the levels of p-H2AX, 53BP1 and ROS as well as TUNEL staining were significantly decreased in the IR + NaNO₃ group compared with those in the IR group. Gene expression of Bax and caspase 3 was decreased in both the lung and submandibular gland with nitrate treatment, indicating attenuation of apoptosis. Inorganic nitrate delivery could effectively prevent TBI-induced systemic damage. Nitrate-mediated decreases in ROS levels may contribute to this systemic protective effect.