DEVELOPMENTAL EXPRESSION OF CYTOCHROME-P450 ISOFORMS AFTER TRANSPLANTATION OF FETAL LIVER-TISSUE SUSPENSION INTO THE SPLEENS OF ADULT SYNGENIC RATS

In the present study, the developmental expression of three cytochrome P450 (P450) isoforms, 1A1, 2B1 and 3A2, and the ability to store glyc ogen was investigated in intrasplenic liver cell explants in compariso n to adult and fetal liver. Fetal liver tissue suspensions were transp lanted into the spleens of adult male syngenic Fisher inbred rats. Ani mals were sacrificed at 3 days, 1, 2, 4 weeks, 2, 4, 6 months and 1 ye ar after transplantation. Spleens and livers of transplant recipients were compared to those of sham operated and control rats. Three days a fter transplantation little bulks of hepatocytes and only few bile duc ts were seen in the red pulp of the transplant containing spleens. A m assive hypertrophy and proliferation of bile ducts and also an augment ation in the number of hepatocytes were observed 4 weeks after transpl antation. One month later, however, the bile ducts had become more and more atrophic, while instead the number of hepatocytes continuously i ncreased. One year after surgery large masses of hepatocytes with appa rent cord structure and only few but well preserved bile ducts were se en. Within the livers of adult rats, P450 1A1 was only slightly expres sed by some hepatocytes around the central veins. P450 2B1 and 3A2 iso forms expression was much stronger, but also predominantly located in the hepatocytes of the central zone of the liver lobule. Hepatocytes o f fetal livers displayed a moderate P450 1A1 expression. In some cells also a very mild staining for P450 2B1 and 3A2 was observed. Within t he hepatocytes of the intrasplenic liver cell explants P450 1A1 was st ill expressed 3 days after transplantation, disappeared at 1 week afte r surgery, but reappeared at 4 weeks after transplantation. After 2, 4 and 6 months no staining for P450 1A1 was detectable any more. One ye ar after transplantation again a slight P450 1A1 expression appeared. With P450 2B1 and 3A2 a mild to moderate expression was seen already a t 3 days after transplantation. Four weeks after surgery nearly all of the hepatocytes were stained for P450 2B1 and 3A2, but there were mar ked differences between the individual cells in the extent of the expr ession of these two P450 subtypes, like it was also the case with norm al adult liver. Within hepatocytes of the fetal livers strongly staine d glycogen granules were seen, which, in comparison to adult livers, w ere rather coarse-grained. Three days after transplantation the glycog en granules in the transplanted hepatocytes were still coarse-grained, but from 1 week after transplantation on, they became more and more f ine-grained. As it was also the case with normal adult liver cells, th ere were marked differences between the individual transplanted hepato cytes in their glycogen content. These results demonstrate that transp lanted liver cells originating from syngenic fetal liver tissue suspen sions can survive in host organs like the spleen for at least 1 year. They proliferate, differentiate, are able to store glycogen, and expre ss different P450 isoforms, like normal adult liver cells.