Polyamines in rat hepatocyte cultures

Collagen sandwich culture affects intracellular polyamine levels of human hepatocytes

Extracellular matrices, like collagen layers, play an important role in preventing dedifferentiation of hepatocytes in long-term culture experiments. It has also been shown that polyamines are crucial for cell growth and liver differentiation - regeneration. Primary cultured hepatocytes with their low mitotic activity might be a valuable tool in studying the role of polyamines in differentiation. Here, our goal was to investigate whether an extracellular cell culture matrix can influence intracellular polyamine levels in human hepatocytes during long-term culture. Primary human hepatocytes were isolated from surgical tissue resections and were maintained either in single collagen (SG) or double collagen gel (DG) layer (sandwich) culture systems. Cell viability and function were examined and intracellular polyamine levels were measured using a highly sensitive high performance liquid chromatography (HPLC) method. Hepatocytes showed high viability in both culture systems used, but albumin secretion was diminished in SG cultured hepatocytes after 14 days. In general, total intracellular polyamine levels of hepatocytes decreased markedly in both SG and DG within the first days of culture, but remained constant until day 21 with a SG/DG ratio of about 1.4. Individual polyamines levels were dependent on the culture time and system, where spermine decreased and putrescine increased in both SG and DG over time (day 14), but spermidine increased only in DG. Our results suggest that polyamine levels, in particular putrescine, might be important regulators of hepatocyte specific function in vitro and therefore serve as a marker of differentiation for cultivated human hepatocytes.

Transport and metabolism of agmatine in rat hepatocyte cultures

Rat hepatocytes in culture take up [14C]-agmatine by both a high-affinity transport system [KM = 0.03 mM; Vmax = 30 pmol x min x (mg protein)-1] and a low-affinity system. The high-affinity system also transports putrescine, but not cationic amino acids such as arginine, and the polyamines spermidine and spermine. The rate of agmatine uptake is increased in cells deprived of polyamines with difluoromethylornithine. Of the agmatine taken up, 10% is transformed into polyamines and 50% is transformed into 4-guanidinobutyrate, as demonstrated by HPLC and MS. Inhibition by aminoguanidine and pargyline shows that this is due to diamine oxidase and an aldehyde dehydrogenase. 14C-4-aminobutyrate is also accumulated in the presence of an inhibitor of 4-aminobutyrate transaminase.

Effect of Berenil on polyamine metabolism in primary cultured rat hepatocytes

1. Putrescine and spermidine content increased in hepatocytes during culture. In the presence of 10 microM Berenil, putrescine content was further increased, while the increase of spermidine was prevented. 2. Ornithine decarboxylase activity was markedly reduced, and to a lesser extent also S-adenosylmethionine decarboxylase activity. 3. Berenil appears to promote an increase in the transformation of spermidine into putrescine, and to inhibit the polyamine efflux.