Blocking Sodium-Taurocholate Cotransporting Polypeptide Stimulates Biliary Cholesterol and Phospholipid Secretion in...

Area of Science:

• Hepatology
• Biliary Physiology
• Lipid Metabolism

Background:

• Bile salt secretion drives bile formation and biliary lipid output.
• Hepatic bile salt uptake, primarily via sodium-taurocholate cotransporting polypeptide (NTCP), regulates bile salt flux.
• Inhibiting NTCP was hypothesized to reduce biliary lipid excretion.

Purpose of the Study:

• To investigate the effect of NTCP inhibition on biliary cholesterol and phospholipid secretion.
• To elucidate the mechanisms underlying changes in biliary lipid excretion following NTCP inhibition.

Main Methods:

• Treatment with Myrcludex B to inhibit NTCP in mice.
• Analysis of biliary bile salt, cholesterol, and phospholipid output.
• Experiments in Abcg8^-/- and Sr-b1^-/- mice to assess transporter involvement.
• Visualization of bile salt uptake distribution using fluorescently labeled bile salts.

Main Results:

• Myrcludex B-mediated NTCP inhibition increased biliary cholesterol and phospholipid excretion.
• Biliary bile salt output and composition remained unchanged.
• The increase in biliary lipids was independent of lysosomal discharge, ABCG5/8, or SR-B1 activity.
• NTCP inhibition shifted bile salt uptake from periportal to pericentral hepatocytes.

Conclusions:

• NTCP inhibition enhances biliary lipid secretion independently of bile salt output or transporter activity.
• The shift in bile salt uptake distribution increases canalicular membrane exposure to bile salts.
• This mechanism provides a novel regulatory pathway for biliary cholesterol and phospholipid secretion.