A mechanism for the loss of cytochrome P-450 in primary mouse hepatocytes

Mechanistic evaluation of primary human hepatocyte culture using global proteomic analysis reveals a selective dedifferentiation profile

The application of primary human hepatocytes following isolation from human tissue is well accepted to be compromised by the process of dedifferentiation. This phenomenon reduces many unique hepatocyte functions, limiting their use in drug disposition and toxicity assessment. The aetiology of dedifferentiation has not been well defined, and further understanding of the process would allow the development of novel strategies for sustaining the hepatocyte phenotype in culture or for improving protocols for maturation of hepatocytes generated from stem cells. We have therefore carried out the first proteomic comparison of primary human hepatocyte differentiation. Cells were cultured for 0, 24, 72 and 168 h as a monolayer in order to permit unrestricted hepatocyte dedifferentiation, so as to reveal the causative signalling pathways and factors in this process, by pathway analysis. A total of 3430 proteins were identified with a false detection rate of <1 %, of which 1117 were quantified at every time point. Increasing numbers of significantly differentially expressed proteins compared with the freshly isolated cells were observed at 24 h (40 proteins), 72 h (118 proteins) and 168 h (272 proteins) (p < 0.05). In particular, cytochromes P450 and mitochondrial proteins underwent major changes, confirmed by functional studies and investigated by pathway analysis. We report the key factors and pathways which underlie the loss of hepatic phenotype in vitro, particularly those driving the large-scale and selective remodelling of the mitochondrial and metabolic proteomes. In summary, these findings expand the current understanding of dedifferentiation should facilitate further development of simple and complex hepatic culture systems.

In vitro model of the human liver parenchyma to study hepatotoxic side effects by Dy-EOB-DTPA

RATIONALE AND OBJECTIVES

In vivo studies have shown species-specific toxicity after application of the liver-specific contrast agent Dy-ethoxybenzyl (EOB)-DTPA. To predict species differences in the laboratory, an in vitro model of the liver was used to examine the divergent results.

METHODS

Rat, canine, porcine, and human hepatocytes were isolated and embedded between layers of collagen. During and after 48 hours of incubation with different concentrations of Dy-EOB-DTPA (maximum concentration 50 mmol/L), morphological changes and enzyme leakage were determined.

RESULTS

The response to the contrast agent varied for hepatocytes from different species. For canine cells, morphological changes and cell death were evident with as little as 5 mmol/L Dy-EOB-DTPA. Rat hepatocytes tolerated up to 50 mmol/L Dy-EOB-DTPA, and enzyme leakage was transient. Only after incubation with 50 mmol/L Dy-EOB-DTPA was the formation of intracellular vacuoles evident. In contrast, even the highest concentration of Dy-EOB-DTPA did not cause an enzyme leakage of porcine or human hepatocytes, although similar vacuoles were seen.

CONCLUSIONS

These data demonstrate a species-dependent toxicity for Dy-EOB-DTPA in vitro, with similar responses in porcine and human hepatocytes.

An organotypical in vitro model of the liver parenchyma for uptake studies of diagnostic MR receptor agents

Testing of receptor-specific MR contrast agents targeted to the liver is hampered by a shortage of viable in vitro models with in vivo-like hepatocellular morphology. Coated pits are ultrastructural signs of an active receptor mediated endocytosis in hepatocytes. Expression of coated pits by matrix overlaid hepatocytes was studied by transmission electron microscopy. Binding of a rhodaminated asialoglycoprotein receptor agent (MION-ASF-rh) was assessed by fluorescence microscopy. Fluorescence of cells exposed to MION-ASF-rh with D(+)-galactose reduced fluorescent light emission to a level of 58% of MION-ASF-rh-induced fluorescence. After preincubation with the hepatotoxin CCl4 a dose-dependent decrease in fluorescent light emission resulted. Hepatocytes maintained a homogeneous cell surface expression, with microprojections, coated pits, and vesicles on both sinusoidal surfaces. Matrix overlaid primary hepatocytes constitute a viable, morphologically and functionally differentiated model. This model can be used to study receptor binding, uptake, and blockage of diagnostic magnetopharmaceuticals under controlled conditions.