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Characterization of Sandwich-Cultured Hepatocytes As an in Vitro Model to Assess the Hepatobiliary Disposition of Copper

Qualyst, Inc., Durham, North Carolina (J.H.A., R.L.S., R.W.H., H.A.G., K.R.B.); and Gilead Sciences, Foster City, California (M.R.W.)

Sandwich-cultured hepatocytes (SCH) from rats (SCRH), dogs (SCDH), and humans (SCHH) were used as an in vitro model to assess the hepatobiliary disposition of copper (Cu). The expression of Cu transporters, ceruloplasmin synthesis, Cu uptake, and biliary excretion and species differences in drug-induced alterations in Cu disposition were determined in SCH from all species. Western blot analysis verified basolateral Cu uptake transporter 1 (CTR1) and canalicular Cu efflux transporter (ATP7B) expression: enzyme-linked immunosorbent assay verified synthesis/secretion of ceruloplasmin (major Cu binding protein found in blood). Endogenous Cu in SCRH, SCDH, and SCHH were 17.2 ± 7.00, 490 ± 44.8, and 43.5 ± 15.8 ng/well, respectively. The hepatobiliary disposition of Cu as measured by uptake (increase in intracellular Cu in comparison to endogenous levels) and biliary excretion (increase in Cu in wash solutions obtained from hepatocytes exposed to calcium-free versus standard buffer) was determined as a function of Cu concentration and incubation time. In general, an increase in Cu concentration or incubation time resulted in an increase in Cu uptake and/or biliary excretion; however, the extent to which they affected Cu disposition was species dependent. 5-(1,1-Dioxido-1,2-thiazinan-2-yl)-N-(4-fluorobenzyl)-8-hydroxy-1,6-naphthyridine-7-carboxamide (L-000870810) (an anti-HIV compound, the development of which was halted due to an observed Cu-specific toxicity in the liver and kidneys of dogs after long-term exposure) showed no effect on Cu disposition in SCRH; however, it increased the biliary excretion of Cu in SCDH and SCHH. This is the first report to demonstrate the utility of SCH as a model to assess hepatobiliary disposition of Cu in an in vitro system.