S. Beken et al., 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-ALT L, 29(1), 2001, pp. 35-53
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.