Fetal rat hepatocytes: isolation, characterization, and transplantation in the Nagase analbuminemic rats

BACKGROUND

In contrast to adult hepatocytes, fetal hepatocytes (FH) are thought to be highly proliferative, less immunogenic, and resistant to cryopreservation and ischemic injury. These qualities could enhance FH engraftment, proliferation, and gene transfer requiring active DNA synthesis.

METHODS

Rat FH were obtained using the nonperfusion collagenase/DNase digestion method. Free and cultured cells were studied using electron microscopy, fluorescence-activated cell sorting, and Northern analysis using alpha-fetoprotein and albumin as markers of hepatocyte lineage. DNA synthetic activity was measured in quiescent and mitogen-stimulated fetal and adult hepatocytes by [3H]thymidine incorporation. Susceptibility of cultured FH to retrovirally mediated gene transfer was studied using an amphotropic retroviral vector carrying the Escherichia coli lac-Z gene. Nagase analbuminemic rats were used as recipients to study the effects of intraportal FH transplantation. Analysis of serum albumin was carried out by enzyme-linked immunosorbent assay.

RESULTS

In fetal liver, 87+/-2% of the cells showed morphological and molecular features of hepatocytes. DNA synthetic activity in nonstimulated cultured FH was 10 times greater than the maximal hepatocyte growth factor-driven response in adult rat hepatocytes. A total of 5-15% FH stained positive for X-gal; results of transduction in adult hepatocyte cultures were negative. In Nagase analbuminemic rat recipients, FH produced significant amounts of albumin only when a hepatic regenerative stimulus was applied. Immunohistochemistry confirmed presence of albumin-positive hepatocytes.

CONCLUSIONS

Fetal rat liver from the late gestation period is highly enriched with hepatocyte progenitors. They are highly proliferative and susceptible to retroviral transduction and can engraft and function in the adult rat liver if transplanted under a hepatic regenerative stimulus.

Immunoregulation via Adhesion Molecules in Allogenic and Xenogenic Hepatocyte Transplantation to Nagase's Analbuminemic Rats

We investigated the effects of monoclonal antibodies (mAbs) against lymphocyte function-associated antigen-1 (LFA-1) and intercellular adhesion molecule-1 (ICAM-1) on intrasplenic allogenic and xenogenic hepatocyte transplantation (HCTx) to analbuminemic rats. Ten to 12-wk-old male Nagase's analbuminemic rats (RT1l) were used as recipients, Wistar/Shi rats (RTlk) were used as donors for allografts and BALB/C mice were used as donors for xenografts. The experimental groups were as follows: group 1, allo-HCTx (n = 7); group 2, allo-HCTx + antirat ICAM-1/antirat LFA-1 mAbs (1.0 mg/kg/day, for 7 days, respectively) (n = 6); group 3, xeno-HCTx (n = 5); group 4, xeno-HCTx + mAbs (antimouse LFA-1/antirat ICAM-1) (n = 5). group 5, xeno-HCTx + mAbs (antirat LFA-1/antimouse ICAM-1) (n = 5). Serum rat albumin levels were measured in groups 1 and 2, and serum mouse albumin levels were measured in groups 3, 4, and 5, as indicators of the function of grafted hepatocytes. In allotransplantation groups, the serum rat albumin levels in the mAbs-treated group were significantly higher than those in the control group for 6 wk after transplantation. In xenotransplantation groups, no increase in the serum mouse albumin levels was detected in any group.

Long-term effects of intrasplenically transplanted adult hepatocytes and fetal liver in hyperbilirubinemic Gunn rats

We performed adult hepatocyte transplantation (HCTx) and fetal liver transplantation (FLTx) into the spleens of hyperbilirubinemic Gunn rats in congenic combination and we compared the long-term effects of these procedures for as long as 12 months. Proliferative activity of intrasplenic hepatocytes was evaluated using antiproliferating cell nuclear antigen (PCNA) immunohistochemical staining. The serum total bilirubin levels (T. Bil) significantly decreased from 7.16 +/- 0.25 mg/dl to 4.38 +/- 0.60 mg/dl 2 months after HCTx and gradually decreased thereafter until 12 months after transplantation (3.23 +/- 0.37 mg/dl, P < 0.05 vs preoperative value). The T. Bil change after FLTx was similar to that of HCTx: 7.22 +/- 0.24 mg/dl before FLTx, and 4.92 +/- 0.24 and 3.06 +/- 0.47 mg/dl, 2 and 12 months after FLTx (P < 0.05), respectively. Bilirubin glucuronides, which were not detectable in the bile from untreated Gunn rats, appeared in considerable amounts 4 months after HCTx and FLTx (27.5% and 36.0% of total bile, respectively). PCNA labeling indices of intrasplenic hepatocytes (4.9% +/- 0.9% and 3.7% +/- 0.7%, 6 months after HCTx and FLTx, respectively) were slightly higher than those of normal hepatocytes (1.0% +/- 0.1%) in the host liver. In conclusion, both adult and fetal rat hepatocytes transplanted into the spleen in congenic combination functioned for at least a year in terms of bilirubin glucuronidation. The spleen is considered to be one of the optimal grafting sites for hepatocytes, with nearly lifelong significant function and proliferative activity.