Abstract
BACKGROUND: Suppression of the peroxisome proliferator-activated receptor alpha (PPARα) has been related to poor outcomes in sepsis and may compromise ketogenesis during critical illness. Infusion of 3-hydroxybutyrate (3HB) was shown to attenuate muscle weakness in septic mice. We hypothesise that endogenous ketogenesis induced by pharmacological PPARα activation, either alone or combined with ketogenic nutrition, is safe and can also mitigate muscle weakness in septic mice. METHODS: In a fluid-resuscitated, antibiotic-treated mouse model of prolonged sepsis, we first (Study 1) assessed the safety and effectiveness (impact on ketosis and muscle weakness) of the PPARα agonist pemafibrate (1 mg/kg/d, n = 16), versus placebo (n = 15) combined with standard balanced parenteral nutrition (PN), composed of glucose, amino acids and long-chain triglycerides (LCT) (balanced-TPN). We subsequently (Study 2) evaluated the impact of pemafibrate combined with four types of PN on ketosis and muscle weakness: balanced-TPN (n = 18), TPN with extra LCTs (TPN + LCT, n = 18), low-dose pure LCT emulsion (Low-LCT, n = 16) and high-dose pure LCT emulsion (High-LCT n = 18). Carbohydrates and amino acids were omitted in the pure LCT groups. Healthy control mice (HC, n = 19) served as controls. Ex vivo muscle force was measured as the primary outcome. Metabolic, inflammatory and microstructural parameters were assessed on plasma and in muscle and liver tissue by targeted metabolomics, gene expression analysis, biochemical and metabolite assays and histological assessment. RESULTS: Pemafibrate treatment with balanced-TPN upregulated hepatic gene expression of PPARα (Ppara) and its downstream genes (Cd36, Cpt1a, Atgl, Acadl, Hadha, Acox1, and Hmgcs2) (p < 0.0001) and was well tolerated. However, pemafibrate treatment with the use of balanced-TPN administration did not induce detectable ketosis or improve muscle weakness. In combination with pemafibrate, TPN + LCT also did not induce ketosis, nor did it affect muscle weakness. In contrast, 3-hydroxybutyrate plasma concentrations increased with High-LCT (95-fold) and Low-LCT (10-fold) (p < 0.0001) in combination with pemafibrate, yet muscle force declined further (High-LCT 25.0%, Low-LCT 10.7% of HC, p < 0.0001). Blood glucose was lowered with pure High-LCT and Low-LCT (High-LCT 86.9%, Low-LCT 55.1% of TPN, p < 0.05), while plasma lipids and LC-carnitines were increased (p < 0.0001). Markers of hepatic protein catabolism were upregulated with High-LCT and Low-LCT (p < 0.007), while muscle glycolytic intermediates (p < 0.0001) and ATP levels (p < 0.0001) were depleted. CONCLUSIONS: In septic mice, pemafibrate combined with balanced-TPN or lipid-rich TPN induced PPARα activation but did not result in ketosis nor affect muscle weakness. Pemafibrate combined with pure LCTs induced ketosis in sepsis but worsened muscle weakness, possibly explained by muscular bioenergetic failure.