Functional properties of hepatocytes in vitro are correlated with cell polarity maintenance.

Exploring the cell biology of hepatocytes in vitro could be a powerful strategy to dissect the molecular mechanisms underlying the structure and function of the liver in vivo. However, this approach relies on appropriate in vitro cell culture systems that can recapitulate the cell biological and metabolic features of the hepatocytes in the liver whilst being accessible to experimental manipulations. Here, we adapted protocols for high-resolution fluorescence microscopy and quantitative image analysis to compare two primary hepatocyte culture systems, monolayer and collagen sandwich, with respect to the distribution of two distinct populations of early endosomes (APPL1 and EEA1-positive), endocytic capacity, metabolic and signaling activities. In addition to the re-acquisition of hepatocellular polarity, primary hepatocytes grown in collagen sandwich but not in monolayer culture recapitulated the apico-basal distribution of EEA1 endosomes observed in liver tissue. We found that such distribution correlated with the organization of the actin cytoskeleton in vitro and, surprisingly, was dependent on the nutritional state in vivo. Hepatocytes in collagen sandwich also exhibited faster kinetics of low-density lipoprotein (LDL) and epidermal growth factor (EGF) internalization, showed improved insulin sensitivity and preserved their ability for glucose production, compared to hepatocytes in monolayer cultures. Although no in vitro culture system can reproduce the exquisite structural features of liver tissue, our data nevertheless highlight the ability of the collagen sandwich system to recapitulate key structural and functional properties of the hepatocytes in the liver and, therefore, support the usage of this system to study aspects of hepatocellular biology in vitro.

Potency of individual bile acids to regulate bile acid synthesis and transport genes in primary human hepatocyte cultures.

Bile acids (BAs) are known to regulate their own homeostasis, but the potency of individual bile acids is not known. This study examined the effects of cholic acid (CA), chenodeoxycholic acid (CDCA), deoxycholic acid (DCA), lithocholic acid (LCA) and ursodeoxycholic acid (UDCA) on expression of BA synthesis and transport genes in human primary hepatocyte cultures. Hepatocytes were treated with the individual BAs at 10, 30, and 100µM for 48 h, and RNA was extracted for real-time PCR analysis. For the classic pathway of BA synthesis, BAs except for UDCA markedly suppressed CYP7A1 (70-95%), the rate-limiting enzyme of bile acid synthesis, but only moderately (35%) down-regulated CYP8B1 at a high concentration of 100µM. BAs had minimal effects on mRNA of two enzymes of the alternative pathway of BA synthesis, namely CYP27A1 and CYP7B1. BAs increased the two major target genes of the farnesoid X receptor (FXR), namely the small heterodimer partner (SHP) by fourfold, and markedly induced fibroblast growth factor 19 (FGF19) over 100-fold. The BA uptake transporter Na(+)-taurocholate co-transporting polypeptide was unaffected, whereas the efflux transporter bile salt export pump was increased 15-fold and OSTα/ß were increased 10-100-fold by BAs. The expression of the organic anion transporting polypeptide 1B3 (OATP1B3; sixfold), ATP-binding cassette (ABC) transporter G5 (ABCG5; sixfold), multidrug associated protein-2 (MRP2; twofold), and MRP3 (threefold) were also increased, albeit to lesser degrees. In general, CDCA was the most potent and effective BA in regulating these genes important for BA homeostasis, whereas DCA and CA were intermediate, LCA the least, and UDCA ineffective.

How useful are clinical liver function tests in in vitro human hepatotoxicity assays?

In preclinical hepatotoxicity testing cell based assays are frequently employed. However, prediction of clinical drug induced liver injury (DILI) remains a major challenge. Here we examined the usefulness of frequently employed markers of hepatocellular injury in cultures of primary human hepatocytes (PHH) in response to treatment with either paracetamol, rifampicin, petadolex and/or amiodarone. The changes in the metabolic competency (urea and albumin) and cellular injury (AST, ALT, ALP, LDH, γGT and succinate dehydrogenase) were determined at therapeutic and above drug concentrations as to evaluate the utility of these markers in in vitro systems. Initially, treatment of PHH with any of the drugs caused a statistically significant reduction in enzyme activities to suggest a switch from basic amino acid metabolism towards induced detoxification. However, treatment for prolonged periods of time caused cytolysis, as evidenced by the significant rise in extracellular LDH and the concomitant increase in ALT and AST activity. Notably, amongst the various endpoints studied, urea was best to demonstrate dose dependent metabolic stress, while other markers of hepatocellular injury were highly variable. Taken collectively, urea measurement proofed to be robust in predicting hepatocellular stress; therefore it should be included in preclinical testing strategies for an improved prediction of DILI.

Drug metabolizing enzyme and transporter protein profiles of hepatocytes derived from human embryonic and induced pluripotent stem cells.

Human embryonic and induced pluripotent stem cell-derived hepatocytes (hESC-Hep and hiPSC-Hep) have the potential to provide relevant human in vitro model systems for toxicity testing and drug discovery studies. In this study, the expression and function of important drug metabolizing cytochrome P450 (CYP) enzymes and transporter proteins in hESC-Hep and hiPSC-Hep were compared to cryopreserved human primary hepatocytes (hphep) and HepG2 cells. Overall, CYP activities in hESC-Hep and hiPSC-Hep were much lower than in hphep cultured for 4 h, but CYP1A and 3A activities were comparable to levels in hphep cultured for 48h (CYP1A: 35% and 26% of 48 h hphep, respectively; CYP3A: 80% and 440% of 48 h hphep, respectively). Importantly, in hESC-Hep and hiPSC-Hep, CYP activities were stable or increasing for at least one week in culture which was in contrast to the rapid loss of CYP activities in cultured hphep between 4 and 48 h after plating. With regard to transporters, in hESC-Hep and hiPSC-Hep, pronounced NTCP activity (17% and 29% of 4 h hphep, respectively) and moderate BSEP activity (6% and 8% of 4 h hphep, respectively) were observed. Analyses of mRNA expression and immunocytochemistry supported the observed CYP and transporter activities and showed expression of additional CYPs and transporters. In conclusion, the stable expression and function of CYPs and transporters in hESC-Hep and hiPSC-Hep for at least one week opens up the possibility to reproducibly perform long term and extensive studies, e.g. chronic toxicity testing, in a stem cell-derived hepatic system.

Optimización de cultivos de hepatocitos humanos para estudios de citotoxicidad / Optimization of human hepatocyte cultures for citotoxicity studies

Los cultivos de hepatocitos entregan un valioso acercamiento al estudio de las funciones metabólicas específicas del hígado, evaluación de citotoxicidad. No existen líneas humanas inmortales con función normal. La inmortalización de hepatocitos humanos con el método UCHT1(medio de cultivo condicionado por células tumorales de tiroides) permitirá prolongar la sobrevida y función de estos, siendo útil para evaluar funcionalidad y citotoxicidad. Objetivo: Optimizar el cultivo de hepatocitos humanos. Metodología: En cultivos primarios de hepatocitos humanos, se agregó medio UCHT1 cultivando en superficies de colágeno, polilisina, gelatina y matrigel. Como control positivo, se utilizó línea Gherschenson (GER) para evaluar curva de crecimiento y producción de Glucógeno (PAS). Se evaluó citotoxicidad (LIVE/DEAD) en hepatocitos GER expuestos a Metotrexato (10, 100 y 1000 mM) a 24, 48 y 72 hrs. Resultados: Se realizó 3 cultivos primarios. Fue efectiva la utilización de Polilisina y Colágeno. Duración 8 meses. No se ha realizado la curva de crecimiento, ni evaluación de funcionalidad en hepatocitos humanos. La línea GER tiene un crecimiento exponencial (tiempo duplicación: 36 hrs). Se observó producción de glucógeno en condiciones de diferenciación hasta 120 hrs. La citotoxicidad por Metotrexato tiene una curva dosis dependiente, significativa en todas las concentraciones (p<0,001) (CL50 a 1000 mM a 24 hrs). Conclusiones: Se logró establecer una línea primaria de hepatocitos humanos. La polilisina y el colágeno han optimizado el establecimiento de cultivos primarios. El método PAS permitió evaluar producción de glucógeno (diferenciación). Los valores de citotoxicidad demostraron un efecto dosis dependiente en las condiciones experimentales. Logrando estandarizar el método para evaluación futura de líneas celulares humanas.

Background: Hepatocyte cultures are a valuable tool to study specific metabolic liver functions and cytoxicity. Human hepatocyte cell lines with normal function do not exist. Immortalization of human hepatocytes with a rat thyroid cell line (UCHT1) allows long-term survival and function of these cells, becoming useful to evaluate functionality and cytotoxicity. Aim: To optimize long-term culture of human hepatocytes. Material and Methods: UCHT1 media was added to primary cultures of human hepatocytes, seeding in collagen, gelatin, matrigel and polilisine surfaces. Gherschenson cell line (GER) was used as a positive control to evaluate the growth curve and Glycogen production (PAS). Cytotoxicity was evaluated (LIVE/ DEAD) in GER hepatocytes exposed to Metotrexate (10, 100 and 1000 µM) 24, 48 and 72 hrs. Results: Three primary cultures were made. The use of Polilisine and Collagen was effective. Cultures were kept for 8 months. Growth curves or evaluation of functionality in human hepatocytes, were not carried out. GER cell line had an exponential growth (duplication time: 36 hrs). Production of glycogen in differentiation conditions was observed up to 120 hrs. Cytotoxicity by Metotrexate had a dose dependent curve with a 50% lethal dose calculated as 1000 µM at 24 hrs. Conclusions: A primary line of human hepatocytes was obtained. Polilisine and collagen optimized the establishment of primary cultures. PAS method allowed the evaluation of glycogen production (differentiation). Cytotoxicity demonstrated a dose dependent effect in experimental conditions.