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

L-Proline supplementation of the medium for collagen gel cultures of hepato cytes has been shown to improve albumin secretion. A study was made as to w hether L-proline is also essential for the maintenance of xenobiotic biotra nsformation capacities in collagen gel sandwich and immobilisation cultures of rat and human hepatocytes, Key phase I (cytochrome P450-dependent monoo xygenase [CYP] and microsoma) epoxide hydrase [mEH]) and phase II (glutathi one S-transferase [GST]) biotransformation enzyme activities and the secret ion of albumin in the culture medium were assessed in the absence and prese nce of L-proline. CYP and mEH activities were not affected by the addition of L-proline, whereas phase II alpha -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 th eir rat counterparts in the presence of L-proline. Albumin secretion, often considered to be a marker for differentiated cell function, does not paral lel the biotransformation capacities of the hepatocytes in culture. Additio nal results demonstrated an L-proline-mediated enhancement of the prolifera tion rate of contaminating stellate cells in conventional monolayer culture . Transdifferentiation of stellate cells to proliferating myofibroblasts, a long with an increased albumin secretion and collagen synthesis, are charac teristic 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-te rm pharmacotoxicological studies, it is preferable to use an L-proline-free culture medium. Further studies on medium optimisation are required For he patocytes from species other than rat.