Bile salt hydrolase (BSH) is an enzyme primarily produced by gut bacteria. It plays an important role in modifying bile acids, liver-produced compounds that aid digestion. BSH activity is increasingly recognized for its broader implications in human health.
Understanding Bile Salt Hydrolase
BSH is an enzyme produced by various gut bacteria, including Firmicutes, Bacteroidetes, and Actinobacteria. It catalyzes the deconjugation of primary bile acids by removing a glycine or taurine molecule from conjugated bile salts.
The liver synthesizes primary bile acids, such as cholic acid (CA) and chenodeoxycholic acid (CDCA), and conjugates them with glycine or taurine to form more soluble bile salts. BSH transforms these conjugated bile salts into unconjugated bile acids. This deconjugation alters the solubility and reabsorption properties of bile acids in the small intestine.
BSH’s Role in Digestion and Cholesterol
BSH activity affects fat digestion and absorption. Conjugated bile salts are highly effective at emulsifying dietary fats, making them easier for enzymes to digest. When BSH deconjugates these, the resulting unconjugated bile acids become less soluble and less efficient at emulsifying fats, which can lead to reduced fat absorption.
Beyond fat digestion, BSH influences cholesterol metabolism. Unconjugated bile acids are less efficiently reabsorbed in the small intestine. This reduced reabsorption means more bile acids are excreted. To compensate, the liver increases its synthesis of new bile acids by converting cholesterol, which can contribute to lowering circulating blood cholesterol levels. Studies in mice suggest that increased BSH activity may lead to reduced weight gain, lower serum cholesterol, and decreased liver triglyceride levels.
Impact on Gut Microbiome and Overall Health
BSH activity influences the gut microbiome’s composition and balance. Bile acids act as signaling molecules and have antimicrobial properties, shaping the gut’s microbial community. By altering the bile acid pool through deconjugation, BSH influences which bacterial species thrive or are inhibited, impacting gut diversity and function.
The interaction between BSH, bile acids, and the gut microbiome has broader systemic health implications. Changes in bile acid profiles due to BSH can affect gut barrier function, the protective lining of the intestines. An altered barrier can contribute to inflammation. Imbalances in BSH activity and the bile acid pool have been linked to conditions such as obesity, metabolic syndrome, and liver diseases like non-alcoholic fatty liver disease (NAFLD). Reduced BSH gene abundance has been observed in patients with inflammatory bowel diseases and type 2 diabetes.
How Diet and Probiotics Affect BSH
Dietary factors shape the gut microbiome and the activity of BSH-producing bacteria. Dietary fiber, for example, is associated with increased bile acid deconjugation, likely through its interaction with gut microbiota BSHs. Whole food intake, often rich in fiber, correlates with increased BSH gene abundance and reduced conjugated bile acids in feces.
Probiotic supplementation, especially with BSH-active bacterial strains, can modulate bile acid metabolism. Strains from Lactobacillus and Bifidobacterium are often studied for their BSH activity. For instance, specific Lactobacillus plantarum strains have demonstrated high deconjugation activities and effects on cholesterol levels. The ability of probiotics to deconjugate bile salts may also contribute to their survival in the challenging environment of the duodenum.