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Ionizing radiation induces radiolysis of water, generates free radicals,  and causes oxidative stress in living organisms which may result in DNA breaks. Free radicals may leave from the region exposed to radiation, reach into distant tissues/organs by systemic circulation, and generate oxidative stress in the route of way. Protection of vital organs from oxidative damage by natural products became important in  preventive medicine. The aim of the study was to investigate radioprotective effects of propolis, and its active component, caffeic acid phenethyl ester (CAPE) against ionizing radiation-induced oxidative stress in kidney tissue of rats exposed to cranial radiation.

Forty-eight male albino Sprague-Dawley rats were divided into six groups. Irradiation (IR) group: total cranial IR with a single dose of 5 Gray (Gy) was administered to the rats. CAPE plus IR group: rats in this group received total cranial IR with a single dose of 5 Gy and intraperitoneal (IP) injection of CAPE (10 μmol kg-1day-1) 30 minutes before IR . Propolis plus IR group: rats received total cranial IR with a single dose of 5 Gy and propolis (80 mg kg-1day-1) via an orogastric tube one hour before IR. Control group of propolis: rats in this group received 1-ml of saline via an orogastric tube. Control group of CAPE: rats in this group received DMSO by IP injections equal to the volume of CAPE in the CAPE group. Sham group: rats in this group did not receive IR, propolis, or CAPE. Oxidative and antioxidant status parameters were examined in the kidney tissue of rats. Oxidative parameters; lipid hydroperoxide (LOOH) levels, total oxidant status (TOS), and oxidative stress index (OSI), and antioxidant parameters; total antioxidant status (TAS), total sulfhydryl (–SH) levels, paraoxonase, ceruloplasmin, and arylesterase activities were determined. ANOVA test was used to analyze the differences between groups in normally distributed variables. Kruskal Wallis H test was used for abnormal distributed data.

Kidney TOS, OSI, and LOOH levels were found significantly higher in the IR group than all other groups (P <0.001). TAS and –SH levels in the IR group were significantly lower compared to propolis plus IR, CAPE plus IR, and sham group (P <0.001). Total –SH levels in the propolis plus IR group were found higher than CAPE plus IR group (P <0.001). Furthermore –SH levels were increased in CAPE plus IR group compared to the sham group (P <0.001). Statistically significant changes were not detected between groups in terms of paraoxonase, arylesterase, and ceruloplasmin activities.

Cranial ionizing radiation exposure leads formation of free radicals. These free radicals may be released to the systemic circulation and cause oxidative stress in kidneys. Propolis and CAPE may enhance antioxidant capacity and prevent kidney tissue from radiation-induced oxidative damage in rats.