Methionine metabolism in the acute response to radiation in the gut - Abstract This research project focuses on investigating potential radiomitigating strategies for gastrointestinal (GI) acute radiation syndrome (GI-ARS), a severe condition resulting from high-dose ionizing radiation exposure to the GI tract. GI-ARS is characterized by impaired cell division in intestinal crypts, inflammation, loss of intestinal barrier integrity, and ultimately sepsis. Our study proposes two novel approaches to mitigate the effects of radiation exposure on the GI tract. The first approach centers on methionine restriction (MR). Methionine, an essential amino acid, plays a crucial role in normal tissue and tumor metabolic activity. It serves as a precursor for S-adenosylmethionine, a key methyl donor in various cellular processes. Previous data suggest that reducing dietary methionine improves intestinal barrier function and decreases inflammation. Preliminary studies have shown that MR preserves crypt depth and villous height in the jejunum following acute abdominal irradiation, indicating its potential as an intestinal radioprotector when initiated prior to irradiation. Aim 1 of the project seeks to assess the mitigating effects of dietary MR on GI-ARS following radiation exposure. We will use an animal model, employing total body irradiation, as well as partial body irradiation with 5% hindlimb protection. Twenty-four hours post-irradiation, animals will either continue on a control diet or transition to a diet with significantly reduced methionine content. We will evaluate survival rates after total and partial body irradiation, as well as examine various tissue markers at 3.5 and 7 days post-irradiation. These markers include crypt depth and villous height in the proximal jejunum, crypt survival, plasma citrulline levels, bacterial 16S RNA in the liver, and the expression of inflammation and tight junction genes in the proximal jejunum. The second approach, outlined in Aim 2, investigates the potential of 3-Deazaneplanocin A (DZNep), an inhibitor of methyltransferases, in mitigating GI-ARS. DZNep inhibits the enzyme S-adenosylhomocysteine hydrolase, resulting in reduced methyltransferase activity, similar to the effect of MR. Previous studies have shown that DZNep can decrease fibrosis, inflammation, and sepsis in animal models. Additionally, both MR and DZNep activate the amino acid stress response pathway (ATF4) and decrease the methylation ratio in normal human fibroblasts, suggesting a common mechanism of action. We will assess the mitigating effect of DZNep administration starting 24 hours after irradiation, using the same experimental setup and endpoints as in Aim 1. By exploring these two related but independent approaches, our project aims to identify effective strategies for mitigating the severe effects of GI-ARS. The findings from this study could potentially lead to the development of novel therapeutic interventions for radiation exposure, with implications for radiation emergency scenarios.
