Hepatozytäre, biliäre und endotheliale Leberrepopulation nach Bestrahlung und Leberzelltransplantation

Abstract

Introduction: The transplantation of isolated donor hepatocytes is considered a promising option to correct acute or chronic liver failure and for the correction of end-stage metabolic liver diseases through repopulation of the diseased organ [1]. The experimental design for transplantation of hepatocytes with the aim of repopulating the host liver has two fundamental requirements: Firstly, host liver repopulation by the means of transplanted hepatocytes needs a preparative regimen combining the failure of endogenous cell proliferation with a strong mitogenic stimulus. Secondly, donor cells need to be identified within the recipient tissue. The dipeptidylpeptidase IV (DPPIV, CD26) mutant Fischer 344 rat liver cell transplantation model implementing external beam radiotherapy and partial hepatectomy (PH) as selective stimulus fulfils both conditions. Recently, we could demonstrate that 25 Gy external beam liver irradiation to approximately 2/3 of the liver is sufficient to achieve partial repopulation of the host liver following hepatocyte transplantation, under the additional stimulus of 1/3 PH [2]: Transplanted DPPIV⁺-hepatocytes integrate rapidly into the irradiated liver tissue and proliferate extensively, finally repopulating the DPPIV-negative host liver. The aim of this study was to investigate whether transplanted non-parenchymal cells (biliary and endothelial cells) may also proliferate in the irradiated liver. Methods: Livers of DPPIV-deficient rats were pre-conditioned with percutaneous single dose irradiation (25 Gy) delivered to 2/3 of the liver. Four days later, a 1/3 PH was performed to resect the untreated liver lobule and 15 million wild-type (DPPIV⁺) liver cells (a mixture of hepatocytes and non-parenchymal cells) were transplanted via the spleen into the recipient livers. The degree of donor cell integration and growth was studied 8 and 16 weeks after transplantation. Tissue samples were immunostained for anti-connexin 32 (Cx32) [gap junction protein], anti-PECAM [endothelial cell marker], or anti-CD-49f [biliary cell marker]. Results: As expected, transplanted DPPIV⁺-hepatocytes integrated into the irradiated liver tissue and proliferated extensively, finally repopulating the DPPIV-negative host liver. Donor hepatocytes demonstrated an increasingly pronounced and distinct distribution of Cx32 as an indicator of their effective integration and intercellular communication within the recipient parenchyma. Furthermore, we could also detect DPPIV⁺ endothelial and biliary cells indicating additional repopulation of the host liver. Conclusion: Our data show that the combination of selective irradiation of 2/3 of the liver followed by 1/3 PH is a suitable preparative regimen for not only hepatocyte but also endothelial and biliary repopulation, thus enabling new perspectives concerning the therapy of liver failure. Furthermore, this >multi-repopulation< could be of special importance when considering high dose radiotherapy for the treatment of abdominal malignancies as the induced radiation damage could be compensated by the subsequent transplantation of liver cells. Similarly, it has been recently reported that local irradiation induces homing of human mesenchymal stem cells at exposed sites and also promotes their widespread engraftment to multiple organs [3]. The authors of this paper also conclude that repopulation may be one way to repair damaged normal tissue after radiotherapy.