Butyrate Supplementation Exacerbates Myocardial and Immune Cell Mitochondrial Dysfunction in a Rat Model of Faecal Peritonitis

SIMPLE SUMMARY: Sepsis is a major clinical problem with high incidence and mortality. While nutrition is routinely provided to critically ill patients, this essentially consists of a one-size-fits-all balanced protein-carbohydrate-fat diet given with little regard to the changing immunological, bioenergetic and metabolic status in sepsis. Besides being an important source of calories, nutrition also has a pharmacological impact. Fatty acids, such as butyrate, impact upon immune function, mitochondrial function and metabolism in different ways, and their individualised use may contribute to a personalised medicine approach depending on the patient’s immune and bioenergetic status. In this research, we combined immunomodulatory effects of butyrate with metabolism. We showed anti-inflammatory effects of butyrate in our ex vivo study on PBMCs isolated from healthy human volunteers. We took this forward in a clinically relevant faecal peritonitis rat model of sepsis with butyrate infusion, but rather demonstrated possible cardiometabolic stress with no impact on immune function. ABSTRACT: Mitochondrial dysfunction and immune cell dysfunction are commonplace in sepsis and are associated with increased mortality risk. The short chain fatty acid, butyrate, is known to have anti-inflammatory effects and promote mitochondrial biogenesis. We therefore explored the immunometabolic effects of butyrate in an animal model of sepsis. Isolated healthy human volunteer peripheral mononuclear cells were stimulated with LPS in the presence of absence of butyrate, and released cytokines measured. Male Wistar rats housed in metabolic cages received either intravenous butyrate infusion or placebo commencing 6 h following faecal peritonitis induction. At 24 h, splenocytes were isolated for high-resolution respirometry, and measurement of mitochondrial membrane potential (MMP), reactive oxygen species (mtROS), and intracellular cytokines (TNF alpha, IL-10) using flow cytometry. Isolated splenocytes from septic and septic butyrate treated rats were stimulated with LPS for 18 h and the effects of butyrate on cytokine release assessed. Ex vivo, butyrate (1.8 mM) reduced LPS-induced TNF alpha (p = 0.019) and IL-10 (p = 0.001) release by human PBMCs. In septic animals butyrate infusion reduced the respiratory exchange ratio (p < 0.001), consistent with increased fat metabolism. This was associated with a reduction in cardiac output (p = 0.001), and increased lactate (p = 0.031) compared to placebo-treated septic animals (p < 0.05). Butyrate treatment was associated with a reduction in splenocyte basal respiration (p = 0.077), proton leak (p = 0.022), and non-mitochondrial respiration (p = 0.055), and an increase in MMP (p = 0.007) and mtROS (p = 0.027) compared to untreated septic animals. Splenocyte intracellular cytokines were unaffected by butyrate, although LPS-induced IL-10 release was impaired (p = 0.039). In summary, butyrate supplementation exacerbates myocardial and immune cell mitochondrial dysfunction in a rat model of faecal peritonitis.