T1869 Bile Acid Uptake Capacity in Ileal Mucosa Correlates With the Expression of Apical but Not Intracellular Bile Acid Transporter

Identification of Na+/taurocholate co-transporting polypeptide (NTCP) as high-affinity hepatic entry receptor for the Hepatitis B and D viruses (HBV/HDV) opened the field for target-based development of cell-entry inhibitors. However, most of the HBV/HDV entry inhibitors identified so far also interfere with the physiological bile acid transporter function of NTCP. The present study aimed to identify more virus-selective inhibitors of NTCP by screening of 87 propanolamine derivatives from the former development of intestinal bile acid reabsorption inhibitors (BARIs), which interact with the NTCP-homologous intestinal apical sodium-dependent bile acid transporter (ASBT). In NTCP-HEK293 cells, the ability of these compounds to block the HBV/HDV-derived preS1-peptide binding to NTCP (virus receptor function) as well as the taurocholic acid transport via NTCP (bile acid transporter function) were analyzed in parallel. Hits were subsequently validated by performing in vitro HDV infection experiments in NTCP-HepG2 cells. The most potent compounds S985852, A000295231, and S973509 showed in vitro anti-HDV activities with IC50 values of 15, 40, and 70 µM, respectively, while the taurocholic acid uptake inhibition occurred at much higher IC50 values of 24, 780, and 490 µM, respectively. In conclusion, repurposing of compounds from the BARI class as novel HBV/HDV entry inhibitors seems possible and even enables certain virus selectivity based on structure-activity relationships.

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Modulation of ileal apical Na+-dependent bile acid transporter ASBT by protein kinase C

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.00052.2009 ◽

2009 ◽

Vol 297 (3) ◽

pp. G532-G538 ◽

Cited By ~ 21

Author(s):

Zaheer Sarwar ◽

Fadi Annaba ◽

Alka Dwivedi ◽

Seema Saksena ◽

Ravinder K. Gill ◽

...

Keyword(s):

Protein Kinase C ◽

Bile Acid ◽

Protein Kinase ◽

Intestinal Lumen ◽

Acid Uptake ◽

Maximal Velocity ◽

Kinase C ◽

Bile Acid Transporter ◽

Acid Transporter ◽

Dependent Pathway

Ileal apical Na+-dependent bile acid transporter (ASBT) is responsible for reabsorbing the majority of bile acids from the intestinal lumen. Rapid adaptation of ASBT function in response to physiological and pathophysiological stimuli is essential for the maintenance of bile acid homeostasis. However, not much is known about molecular mechanisms responsible for acute posttranscriptional regulation of ileal ASBT. The protein kinase C (PKC)-dependent pathway represents a major cell signaling mechanism influencing intestinal epithelial functions. The present studies were, therefore, undertaken to investigate ASBT regulation in intestinal Caco-2 monolayers by the well-known PKC activator phorbol 12-myristate 13-acetate (PMA). Our results showed that Na+-dependent [3H]taurocholic acid uptake in Caco-2 cells was significantly inhibited in response to 2 h incubation with 100 nM PMA compared with incubation with 4α-PMA (inactive form). The inhibitory effect of PMA was blocked in the presence of 5 μM bisindolylmaleimide I (PKC inhibitor) but not 1,2-bis(2-aminophenoxy)ethane- N,N,N′,N′-tetraacetic acid-AM (Ca2+ chelator) or LY-294002 (phosphatidylinositol 3-kinase inhibitor). PMA inhibition of ASBT function was also abrogated in the presence of myristoylated PKCζ pseudosubstrate peptide, indicating involvement of the atypical PKCζ isoform. The inhibition by PMA was associated with a significant decrease in the maximal velocity of the transporter and a reduction in ASBT plasma membrane content, suggesting a modulation by vesicular recycling. Our novel findings demonstrate a posttranscriptional modulation of ileal ASBT function and membrane expression by phorbol ester via a PKCζ-dependent pathway.

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