PT  - JOURNAL ARTICLE
AU  - Paresh P. Chothe
AU  - Rachel Pemberton
AU  - Niresh Hariparsad
TI  - <strong>Function and Expression of Bile Salt Export Pump in Suspension Human Hepatocytes</strong>
AID  - 10.1124/dmd.120.000057
DP  - 2021 Jan 01
TA  - Drug Metabolism and Disposition
PG  - DMD-AR-2020-000057
4099  - http://dmd.aspetjournals.org/content/early/2021/01/20/dmd.120.000057.short
4100  - http://dmd.aspetjournals.org/content/early/2021/01/20/dmd.120.000057.full
AB  - The mechanistic understanding of bile salt disposition is not well established in suspension human hepatocytes (SHH) due to limited information on the expression and function of bile salt export protein (BSEP) in this system. We investigated the transport function of BSEP in SHH using a method involving in situ biosynthesis of bile salts from their precursor bile acids, cholic acid (CA) and chenodeoxycholic acid (CDCA). Our data indicated that glycine and taurine-conjugated CA and CDCA were generated efficiently and transported out of hepatocytes in a concentration-and time-dependent manner. We also observed that the membrane protein abundance of BSEP was similar between SHH and sandwich cultured human hepatocytes. Furthermore, known cholestatic agents significantly inhibited G-CA and G-CDCA efflux in SHH. Interestingly, cyclosporine A, troglitazone, itraconazole, loratadine and lovastatin inhibited G-CA efflux more potently than G-CDCA efflux (3-5-fold). Due to these significant differential effects on G-CA and G-CDCA efflux inhibition, we determined the IC50 values of troglitazone for G-CA (9.9 µM) and for G-CDCA (43.1 µM) efflux. The observed discrepancy in the IC50 was attributed to the fact that troglitazone also inhibits organic anion transporting polypeptide (OATP)s and Na+/ taurocholate co-transporting polypeptide (NTCP) in addition to BSEP. The hepatocyte uptake study suggested that both active uptake and passive diffusion contribute to the liver uptake of CA while CDCA primarily undergoes passive diffusion into the liver. In summary, these data demonstrated the expression and function of BSEP and its major role in transport of bile salts in cryopreserved SHH. Significance Statement BSEP transport function and protein abundance was evident in SHH in the present study. The membrane abundance of BSEP protein was similar between SHH and SCHH. The study also illustrated the major role of BSEP relative to basolateral MRP3 and MRP4 in transport of bile salts in SHH. Understanding of BSEP function in SHH may bolster the utility of this platform in mechanistic understanding of bile salt disposition and potentially in the assessment of drugs for BSEP inhibition.