Hemodynamic flow improves rat hepatocyte morphology, function, and metabolic activity in vitro
AMERICAN JOURNAL OF PHYSIOLOGY-CELL PHYSIOLOGY
Authors: Dash, A.; Simmers, M. B.; Deering, T. G.; Berry, D. J.; Feaver, R. E.; Hastings, N. E.; Pruett, T. L.; LeCluyse, E. L.; Blackman, B. R.; Wamhoff, B. R.
In vitro primary hepatocyte systems typically elicit drug induction and toxicity responses at concentrations much higher than corresponding in vivo or clinical plasma C-max levels, contributing to poor in vitro-in vivo correlations. This may be partly due to the absence of physiological parameters that maintain metabolic phenotype in vivo. We hypothesized that restoring hemodynamics and media transport would improve hepatocyte architecture and metabolic function in vitro compared with nonflow cultures. Rat hepatocytes were cultured for 2 wk either in nonflow collagen gel sandwiches with 48-h media changes or under controlled hemodynamics mimicking sinusoidal circulation within a perfused Transwell device. Phenotypic, functional, and metabolic parameters were assessed at multiple times. Hepatocytes in the devices exhibited polarized morphology, retention of differentiation markers [E-cadherin and hepatocyte nuclear factor-4 alpha (HNF-4 alpha)], the canalicular transporter [multidrug-resistant protein-2 (Mrp-2)], and significantly higher levels of liver function compared with nonflow cultures over 2 wk (albumin similar to 4-fold and urea similar to 5-fold). Gene expression of cytochrome P450 (CYP) enzymes was significantly higher (fold increase over nonflow: CYP1A1: 53.5 +/- 10.3; CYP1A2: 64.0 +/- 15.1; CYP2B1: 15.2 +/- 2.9; CYP2B2: 2.7 +/- 0.8; CYP3A2: 4.0 +/- 1.4) and translated to significantly higher basal enzyme activity (device vs. nonflow: CYP1A: 6.26 +/- 2.41 vs. 0.42 +/- 0.015; CYP1B: 3.47 +/- 1.66 vs. 0.4 +/- 0.09; CYP3A: 11.65 +/- 4.70 vs. 2.43 +/- 0.56) while retaining inducibility by 3-methylcholanthrene and dexamethasone (fold increase over DMSO: CYP1A = 27.33 and CYP3A = 4.94). These responses were observed at concentrations closer to plasma levels documented in vivo in rats. The retention of in vivo-like hepatocyte phenotype and metabolic function coupled with drug response at more physiological concentrations emphasizes the importance of restoring in vivo physiological transport parameters in vitro.
A novel cytochrome P450 3A isoenzyme in rat intestinal microsomes
BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS
Authors: Gushchin, GV; Gushchin, MI; Gerber, N; Boyd, RT
PCR with several pairs of primers facilitates screening for new isoenzymes among highly homologous cytochrome P450s (CYPs). Combinations of two pairs of primers, which amplify N- and C-terminal coding sequences of either CYP3A1/CYP3A23 or CYP3A2 detected the presence of a previously unrecognized CYP3A in enterocyte microsomes isolated from rats. PCR, Northern blot, and immunoblotting with specific antibodies indicated that this isoenzyme is clearly distinguishable from CYP3A1, 3A23 or 3A2. Sequencing of a 285 bp coding fragment of this gene revealed 97% similarity with rat olfactory CYP3A9 (P450olf3). (C) 1999 Academic Press.