ATLA::Alternatives to Laboratory Animals

Volume 29, Number 1

Effects of L-proline on phase I and phase II xenobiotic biotransformation capacities of rat and human hepatocytes in long-term collagen gel cultures.

ATLA 29, 35-53, January/February 2001

Sonja Beken,¹ Karen De Smet,¹ Marianne Depreter,² Frank Roels,² Antoine Vercruysse¹ and Vera Rogiers¹

¹Department of Toxicology, (FAFY), Vrije Universiteit Brussel, Laarbeeklaan 103, 1090 Brussels, Belgium; ²Department of Human Anatomy, Embryology and Histology, Universiteit Gent, Godshuizenlaan 4, 9000 Ghent, Belgium

SUMMARY

L-Proline supplementation of the medium for collagen gel cultures of hepatocytes has been shown to improve albumin secretion. A study was made as to whether L-proline is also essential for the maintenance of xenobiotic biotransformation capacities in collagen gel sandwich and immobilisation cultures of rat and human hepatocytes. Key phase I (cytochrome P450-dependent monooxygenase [CYPI and microsomal epoxide hydrase [mEH]) and phase II (glutathione S-transferase [GSTI]) biotransformation enzyme activities and the secretion of albumin in the culture medium were assessed in the absence and presence of L-proline. CYP and mEH activities were not affected by the addition of L-proline. whereas phase II a-Class GST activity of rat hepatocytes in collagen cultures was decreased. Species differences were demonstrated, as human hepatocytes showed a better maintenance of GST activities than their rat counterparts in the presence of L-proline. Albumin secretion, often considered to be a marker for differentiated cell function, does not parallel the biotransformation capacities of the hepatocytes in culture. Additional results demonstrated an L-proline-mediated enhancement of the proliferation rate of contaminating stellate cells in conventional monolayer culture. Transdifferentiation of stellate cells to proliferating myofibroblasts, along with an increased albumin secretion and collagen synthesis, are characteristic of fibrotic liver. Since the last two phenomena have been observed in L-proline-supplemented collagen gel cultures, it can be concluded that when stable collagen gel cultures of rat hepatocytes are needed for long-term pharmacotoxicological studies, it is preferable to use an L-proline-free culture medium. Further studies on medium optimisation are required for hepatocytes from species other than rat.

Keywords: cytochrorne P450-dependent enzymes, microsomal epoxide hydrase, glutathione S-transferases, albumin secretion, collagen gel sandwich, collagen gel immobilisation