Do bile acid sequestrants like colesevelam increase fecal excretion of bile acids by interrupting enterohepatic recirculation?

Bile acid sequestrants, such as colesevelam, are non-absorbable polymers that act primarily within the intestinal lumen. By exploiting electrostatic and hydrophobic interactions, these agents disrupt the highly efficient recycling process of bile acids, leading to significant metabolic shifts.

Clinical effectiveness and excretion

Research confirms that colesevelam effectively interrupts the enterohepatic circulation, a process that normally recovers approximately 95% of bile acids.

• Fecal Output: Clinical data, particularly in populations with bile acid diarrhea (BAD) and irritable bowel syndrome (IBS-D), show that colesevelam significantly increases the fecal excretion of bile acids by preventing their reabsorption in the terminal ileum.
• Lipid Management: By forcing the liver to convert endogenous cholesterol into new bile acids to replace those lost in the feces, colesevelam up-regulates hepatic LDL receptors. This mechanism typically results in a 15% to 18% reduction in LDL cholesterol levels.
• Glucose Regulation: In patients with type 2 diabetes, the interruption of bile acid recycling has the secondary effect of improving glycemic control (reducing HbA1c by approximately 0.5%) through the stimulation of the incretin hormone GLP-1.

Mechanistic explanations

The function of colesevelam is rooted in its chemical structure as a high-capacity, positively charged resin.

• Binding Affinity: At intestinal pH, colesevelam’s amino groups become protonated (positively charged), allowing them to bind strongly to the negatively charged molecules of glycocholic and taurocholic acids.
• Molecular Trapping: Once bound, these bile acids form large, insoluble complexes that are too bulky to be transported by the apical sodium-dependent bile acid transporter (ASBT).
• Bile-Carried Compounds: While primary evidence focuses on bile acids, the sequestration process naturally extends to other lipophilic compounds or drugs that utilize the enterohepatic cycle. These substances become trapped within the non-absorbable complex and are eliminated alongside the bile acids.

Bottom line

Colesevelam is scientifically proven to bind intestinal bile acids and interrupt their enterohepatic recirculation, significantly increasing fecal bile acid excretion. This process is a foundational mechanism for lowering LDL cholesterol and improving glycemic markers.