Mitigative effects of apigenin against gastrointestinal acute radiation syndrome (GI-ARS) in mice

Currently, there are no approved countermeasures for GI-ARS, a condition that can arise following exposure to high doses of radiation. To address this critical gap, our study will use a specialized partial-body irradiation technique known as the BM2.5-PBI format. This method is designed to shield 2.5% of bone marrow (BM) from radiation damage. Our research will focus on evaluating the efficacy of apigenin (AP), a naturally occurring flavonoid with potent anti-oxidative stress and anti-inflammatory properties, as a potential therapeutic countermeasure against GI-ARS given to mice after radiation exposure. We will also determine the most effective route of AP administration for counteracting radiation-induced intestinal damage. Recently, we discovered that AP significantly enhances stem cell growth and facilitates the restoration of a healthy gut microbiome following radiation-induced dysbiosis. Our findings strongly indicate that AP plays a crucial role in mitigating radiation- induced injuries in the hematopoietic and GI tissues. While it has been reported that administering AP to mice before radiation exposure increases their survival rate from GI-ARS, its effectiveness in improving survival rates when given after irradiation has not yet been investigated. This study aims to address that knowledge gap. The focus of our research is on the 30-day survival of irradiated mice (BM2.5-PBI) receiving AP at 24 hr post- exposure. We will expose male and female C57BL/6 mice to various radiation doses, i.e., 0, or 13.75, or 14, or 14.5 Gy of X rays using the BM2.5-PBI format (from Xstrahl Small Animal Radiation Research Platform). We will give AP at the concentrations of 0 (AP 0), 200 (AP 200), or 300 (AP 300) mg/kg body weight twice daily, with a 12-hour interval, to mice via either the oral route or subcutaneous injection. This AP treatment will begin 24 hours after exposing the mice to radiation, and continue for 3 d. The control group will receive neither radiation nor apigenin (AP 0), but only the vehicle solution. Mice exposed to radiation only will receive vehicle solutions on the same schedule as those treated with AP. To evaluate tissue damage and recovery following AP treatment, we will conduct a series of tests on blood and tissues (including bone marrow cells, sternum, duodenum, jejunum, and liver) collected from six mice in each treatment group on day 4 post-irradiation. This time point is standard for studying the effects of radiation on gastrointestinal crypts. We will measure hematological parameters and assess citrulline plasma levels. Additionally, histopathological evaluations will be performed on the collected tissues. The remaining mice will be used to evaluate the effectiveness of AP on 30-day survival. Throughout this observation period, any mouse that becomes critically ill or shows significant signs of poor health will be euthanized. All remaining mice that survive the 30 days post-irradiation will also undergo euthanasia. Blood samples and the GI tissues will be collected from both the moribund mice and those that survive the full 30-day period at the time of euthanasia for future analysis.