Blocking Sodium‐Taurocholate Cotransporting Polypeptide Stimulates Biliary Cholesterol and Phospholipid Secretion in Mice

Abstract

Active secretion of bile salts into the canalicular lumen drives bile formation and promotes biliary cholesterol and phospholipid output. Disrupting hepatic bile salt uptake, by inhibition of sodium‐taurocholate cotransporting polypetide (NTCP; Slc10a1) with Myrcludex B, is expected to limit bile salt flux through the liver and thereby to decrease biliary lipid excretion. Here, we show that Myrcludex B–mediated NTCP inhibition actually causes an increase in biliary cholesterol and phospholipid excretion whereas biliary bile salt output and bile salt composition remains unchanged. Increased lysosomal discharge into bile was excluded as a potential contributor to increased biliary lipid secretion. Induction of cholesterol secretion was not a consequence of increased ATP‐binding cassette subfamily G member 5/8 activity given that NTCP inhibition still promoted cholesterol excretion in Abcg8−/− mice. Stimulatory effects of NTCP inhibition were maintained in Sr‐b1−/− mice, eliminating the possibility that the increase in biliary lipids was derived from enhanced uptake of high‐density lipoprotein–derived lipids. NTCP inhibition shifts bile salt uptake, which is generally more periportally restricted, toward pericentral hepatocytes, as was visualized using a fluorescently labeled conjugated bile salt. As a consequence, exposure of the canalicular membrane to bile salts was increased, allowing for more cholesterol and phospholipid molecules to be excreted per bile salt. Conclusion: NTCP inhibition increases biliary lipid secretion, which is independent of alterations in bile salt output, biliary bile salt hydrophobicity, or increased activity of dedicated cholesterol and phospholipid transporters. Instead, NTCP inhibition shifts hepatic bile salt uptake from mainly periportal hepatocytes toward pericentral hepatocytes, thereby increasing exposure of the canalicular membrane to bile salts linking to increased biliary cholesterol secretion. This process provides an additional level of control to biliary cholesterol and phospholipid secretion.

Reply

“…Not hampered by adaptations occurring during liver regeneration, we have directly investigated zonation‐related differences in bile formation using a very specific NTCP inhibitor combined with monitoring the distribution of a fluorescent bile salt. ( 1 ) The results are in line with a shift of hepatic bile salt uptake from predominantly periportal toward more pericentral hepatocytes, leading to increased canalicular exposure and more cholesterol and phospholipid excretion in bile while total biliary bile salts are not increased or are even decreased. It is not known to what extent such a shift occurs in the regenerating liver after PH, and given the complex adaptive changes after PH, this is difficult to predict without experimental data.…”

“…We sincerely thank Dr. Javitt for his interest in and perspective on our article. ( 1 ) He indicates that aspecific effects of Myrcludex B should be considered an explanation for increased biliary cholesterol and phospholipid secretion after Myrcludex B treatment as partial hepatectomy (PH) also leads to an increased contribution of pericentral hepatocytes to bile salt uptake and secretion, but biliary cholesterol and phospholipid secretion are not affected. In our opinion, nonspecific Myrcludex B–induced activation of canalicular or sinusoidal transporters seems unlikely given the absence of Na + ‐taurocholate cotransporting polypeptide (NTCP) homology with these transporters and our data from experiments with scavenger receptor class B member 1 or adenosine triphosphate binding cassette subfamily G member 8 null mice.…”

Inhibition of Hepatic Bile Acid Uptake by Myrcludex B Promotes Glucagon-Like Peptide-1 Release and Reduces Obesity

“… 18 , 20 , 54 , 55 In fact, the mice demonstrate lower plasma cholesterol levels, which is likely a consequence of increased biliary cholesterol secretion as NTCP inhibition shifts bile salt uptake from periportal to pericentral hepatocytes. 59 With the emerging interest of the virology field to treat hepatitis B and delta co-infected patients with the NTCP inhibitor Myrcludex B, its transition to clinical practice is accelerated. 18 , 20 , 54 , 60 , 61 Although clinical data on parameters such as body weight, fat mass, plasma glucose, GLP-1, and plasma TG still have to be elucidated, drug safety and the observed temporary increase in serum-conjugated bile acids, similar to our treated mice, makes Myrcludex B an interesting candidate drug to treat obesity and obesity-related metabolic dysfunctions in humans.…”

Letter to the Editor: Blocking Sodum‐Taurocholate Cotransporting Polypeptide Stimulates Biliary Cholesterol and Phospholipid Secretion in Mice

“…The recent report ( 1 ) that the increased cholesterol and lecithin content of hepatic bile after administration of the complex lipopeptide, myrcludex B, is attributable to its binding to the sodium taurocholate cotransporting polypeptide (NTCP), which causes a redistribution of canalicular bile transport to the pericentral zone, appears to conflict with a previous study. ( 2 ) After partial hepatectomy, NTCP expression significantly decreases in the remaining liver along with increased in hepatic bile flow and no change in cholesterol or lecithin output, findings that were also attributed to a shift in bile acid transport to the pericentral zone of the canaliculus.…”