Do Probiotics Protect Against the Deleterious Effects of a High-Fat Diet?
High-fat diets and obesity have been linked to unfavorable changes in gut bacteria and increased leakage of bacterially-derived lipopolysaccharide (endotoxin) from the intestinal tract into circulation, which is associated with low-grade inflammation, metabolic dysregulation and degradation of tight-junction proteins between intestinal cells. Probiotic supplementation is the practice of ingesting live strains of bacteria that are proposed to have a beneficial effect on the host by enriching the intestine with healthy bacteria. The purpose of this project was to determine if probiotic supplementation would prevent increased inflammatory tone, decreased oxidative capacity, and decreased tight-junction protein expression associated with high-fat feeding and elevated endogenous endotoxin. Male C57BL/6J mice were fed either a control (CD, 10% fat) or high-fat (HFD, 60% fat) diet for 4 weeks while receiving a daily oral gavage of water (C-VSL#3, HF-VSL#3) or probiotics (C+VSL#3, HF+VSL#3) equivalent to 1.2 billion live cultures. Changes in body weight, body composition, respiratory exchange ratio, energy expenditure, and glucose and insulin tolerance were measured in live mice. Markers of metabolic function were measured in whole muscle homgenates and mitochondria isolated from red and white skeletal muscle. Plasma endotoxin was measured in blood collected from fasted mice at the time of euthanization. The large and small intestines were collected and mRNA levels of tight-junction proteins and markers of nutrient sensing were measured. To determine a possible protective effect against endogenous LPS, a second cohort of mice were given an intraperitoneal injection of 0.1µg/kg LPS or saline to induce endotoxemia after four weeks of the aforementioned feeding protocol. Markers of metabolic function and inflammation were measured in mitochondria, skeletal muscle and liver. VSL#3 supplementation improved glucose homeostasis and markers of inflammation while enhancing nutrient sensing in the gut.