Irradiation as preparative regimen for hepatocyte transplantation causes prolonged cell cycle block.
OBJECTIVE
Hepatocyte transplantation following liver irradiation (IR) and partial hepatectomy (PH) leads to extensive liver repopulation. We investigated the changes in the liver induced by IR explaining the loss of reproductive integrity in endogenous hepatocytes.


METHODS
Right lobules of rat liver underwent external beam IR (25 Gy). A second group was subjected to additional 33% PH of the untreated left liver lobule. Liver specimens and controls were analyzed for DNA damage, apoptosis, proliferation and cell cycle related genes (1 hour to up to 12 weeks).


RESULTS
Double strand breaks (phosphorylated histone H2AX) induced by IR rapidly declined within hours and were no longer detectable after 4 days. No significant apoptosis was noted and steady mRNA levels (B-cell lymphoma 2-associated X protein (BAX), caspase 3 and 9) were in line with the lack of DNA fragmentation. However, gene expression of p53 and p21 in irradiated liver tissue increased. Transcripts of cyclin D1, proliferating cell nuclear antigen (PCNA), and cyclin B augmented progressively, whereas cyclin E was only affected moderately. Following PH, irradiated livers displayed persistently high protein levels of p21 and cyclin D1. However, cell divisions were infrequent, as reflected by low PCNA levels up to four weeks.


CONCLUSIONS
IR leads to a major arrest in the G(1)/S phase and to a lesser extent in the G(2)/M transition of the cell cycle, resulting in reduced regenerative response following PH. The persistent block of at least four weeks may promote preferential proliferation of transplanted hepatocytes in this milieu.
Koenig
Sarah
S
University Hospital Goettingen, Department of General and Visceral Surgery, Robert-Koch-Strasse 40, 37099 Goettingen, Germany. skoenig1@gwdg.de
Krause
Petra
P
Schmidt
Thordis-Karen
TK
Rave-Fraenk
Margret
M
Rothe
Hilka
H
Hermann
Robert Michael
RM
Becker
Heinz
H
Hess
Clemens Friedrich
CF
Christiansen
Hans
H
D000818:Animals; D002453:Cell Cycle / Q000502:physiology* / Q000528:radiation effects*; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D004307:Dose-Response Relationship, Radiation; D022781:Hepatocytes / Q000166:cytology* / Q000378:metabolism / Q000528:radiation effects* / Q000637:transplantation; D008099:Liver / Q000166:cytology* / Q000378:metabolism / Q000528:radiation effects*; D008297:Male; D011300:Preoperative Care / Q000379:methods; D011829:Radiation Dosage; D051381:Rats; D011916:Rats, Inbred F344
D018797:Cell Cycle Proteins