The senomorphic impact of astaxanthin on irradiated rat spleen: STING, TLR4 and mTOR contributed pathway.

Objectives: Exposure of spleen tissues to ionizing radiation during radiotherapy can induce cellular stress and immune-dysfunction leading to cellular senescence.

Introduction: The process of a cancerous development is facilitated by the accumulation of senescent cells. This justifies the incorporation of anti-senescent medications during splenic irradiation (SI).

Methods: In this study senescence was induced in the spleen of male albino rats by radiation exposure (5Gy-single whole body gamma-irradiation) then after 2 weeks, oral astaxanthin regimen was started once daily in a dose of 25 mg/kg for 7 consecutive days. Concurrent control groups were carried out.

Results: the present data reflected that irradiation provoked an increase in the oxidative stress biomarkers (nitric oxide, lipid peroxidation and total reactive oxygen species levels)and the inflammatory biomarkers (Myeloperoxidase and interleukin-6). In addition irradiation led to the over expression of stimulator of interferon genes (cGAS-STING), mammalian target of rapamycin (mTOR) and Toll-like receptor 4 (TLR4) along with the lactate dehydrogenase (LDH), cyclin-dependent kinase inhibitor 1 (p21) cyclin-dependent kinase inhibitor 2A (p16) increment with elevation of tumor suppressor protein (p53) level. However, reduced glutathione contents and catalase activity were reduced post irradiation in spleen tissues, all these changes reflecting induction of cellular senescence. Astaxanthin treatment showed an improvement in the antioxidant/oxidative stress balance, inflammatory biomarkers, histopathological examination and immunohistochemical expressions of the tested proteins in the irradiated rats.

Conclusion: the current findings offer a new insight into the senomorphic effect of astaxanthin following radiation-induced spleen senescence via STING, mTOR, and TLR4 signalling pathways.