Inorganic nitrate alleviates irradiation-induced salivary gland damage by inhibiting pyroptosis

Over 80% of patients undergoing radiotherapy (RT) for head and neck cancer (HNC) suffer reduced saliva secretion and dry mouth symptoms due to salivary gland damage. Although therapeutic interventions to alleviate such RT-induced damage are available, long-term hypofunction remains a significant issue. Therefore, novel therapeutic solutions to prevent irradiation (IR)-induced salivary gland damage are required. This study explored the protective effect of inorganic nitrate in preventing IR-induced salivary gland injury via pyroptosis suppression, both in vivo and in vitro. In the treatment group, C57BL/6 mice were pretreated with 2 mmol/L NaNO3 supplied in drinking water one week before a single-dose of 15 Gy IR in the submandibular gland (SMG) region. Human vein endothelial cells (HUVECs) and mice SMG cells were treated with 10 μmol/L or 100 μmol/L NaNO3 2 h before a single-dose of 8 Gy IR. In vivo, IR-induced decreased saliva flow rate and body weight loss could be alleviated by nitrate supplementation. Nitrate prevented acinar and microvascular endothelial cell loss. Moreover, nitrate improved mitochondrial function and significantly decreased pyroptosis-related indexes. In vitro, nitrate supplementation reduced reactive oxygen species (ROS) generation by preserving mitochondrial homeostasis to inhibit NLPR3 inflammasome-mediated pyroptosis both in HUVECs and SMG cells. Nitrate showed potential as an oral protective agent to prevent IR-induced salivary gland damage; prospective insight into the underlying molecular mechanisms is presented.