Roles of Simvastatin and Sildenafil in Modulation of Cranial Irradiation-Induced Bystander Multiple Organs Injury in Rats

In radiobiology and radiation oncology fields, the observation of a phenomenon called radiation-induced bystander effect (RIBE) has introduced the prospect of remotely located tissues' affection. This phenomenon has been broadly developed to involve the concept of RIBE, which are relevant to the radiation-induced response of a distant tissue other than the irradiated one. The current study aimed at investigating each of the RIBE of cranial irradiation on oxidative and inflammatory status in different organs such as liver, kidney, heart, lung, and spleen. Being a vital target of the cholinergic anti-inflammatory response to an inflammatory stimulus, the splenic alpha-7-nicotinic acetylcholine receptor (alpha-7nAchR) was evaluated and the hepatic contents of thioredoxin, peroxisome proliferator-activated receptor-alpha and paraoxinase-1 (Trx/PPAR-a/PON) were also assessed as indicators for the liver oxidative stress and inflammatory responses. Being reported to act as antioxidant and anti-inflammatory agents, simvastatin (SV) and/ or sildenafil (SD) were investigated for their effects against RIBE on these organs. These objectives were achieved via the biochemical assessments and the histopathological tissues examinations. Five experimental groups, one sham irradiated and four irradiated groups, were exposed to cranial irradiation at dose level of 25 Gy using an experimental irradiator with a Cobalt (Co-60) source, RIBE, RIBE + SV (20 mg.(kg.bw) -1 day(-1)), RIBE+ SD (75 mg.(kg.bw)(-1) day(-1)), and RIBE+ SV + SD. Cranial irradiation induced structural, biochemical, and functional dys-regulations in non-targeted organs. RIBE-induced organs' injuries have been significantly corrected by the administration of SV and/or SD. Our results suggest the possibility of a potentiated interaction between SV and SD in the modulation of the RIBE associated with head and neck radiotherapy.