Targeting the Meta-organismal Butyrate Pathway to Prevent Arterial Restenosis after Vascular Surgery

PROJECT SUMMARY/ABSTRACT Cardiovascular disease is a leading cause of death globally. Despite advancements in surgical approaches for cardiovascular disease, up to 50% of vascular procedures such as balloon angioplasty, stenting, and surgical bypass fail due to restenosis from neointimal hyperplasia in the treated artery, a cell proliferative process potentiated by inflammation. New therapies for prevention and treatment of neointimal hyperplasia are urgently needed. However, there are major knowledge gaps in understanding the complex contribution of environmental effectors in this process. Compelling preliminary work by the PI using germ-free (GF) and antibiotic-treated mouse models has demonstrated a novel meta-organismal pathway for neointimal hyperplasia susceptibility. We have shown that GF mice have attenuated neointimal hyperplasia compared to conventionally-raised mice, which is restored by fecal transplantation. Furthermore, antibiotic treatment to deplete gut microbiota results in reduced levels of butyrate, a short chain fatty acid produced exclusively by microbial fermentation of dietary fiber, which is accompanied by exacerbated neointimal hyperplasia susceptibility; these effects are reversed by butyrate supplementation. Arterial expression of the butyrate receptor, free fatty acid receptor 3 (FFAR3), is increased by injury, and stimulation of FFAR3 modulates endothelial (EC), vascular smooth muscle cell (VSMC), and inflammatory responses. Taken together, we now hypothesize that a meta-organismal microbe-host interaction impacts neointimal hyperplasia following vascular surgery: prebiotic fiber augments gut microbial production of butyrate; and butyrate, in turn, attenuates arterial injury-induced neointimal hyperplasia by direct effects on EC and inflammation that are mediated by FFAR3. We will test this innovative hypothesis in a comprehensive series of studies employing GF and transgenic mice, butyrogenic bacteria, and spatial and dynamic profiling of the inflammatory response. We will also test the translational application of this pathway using a novel formulation of encapsulated tributyrin, a butyrate precursor, in a pig model of arterial injury. Collectively, these studies will test phenomenological, mechanistic, and translational facets of this pathway, thus having a potentially transformative impact on patients undergoing vascular surgery.