Arteriolovenular Shunting Critically Determines Shutdown of Microcirculation Upon Cryotherapy in Tumor-Bearing Rat Liver

Heterogeneity of the intrahepatic portal venous blood flow: impact on hepatocyte transplantation

BACKGROUND

The poor repopulation rate of the liver by transplanted hepatocytes markedly hampers liver cell therapy, which might be due to a limited sequestration of cells within the hepatic microvasculature. We therefore present intravital fluorescence microscopic data of transplanted hepatocytes immediately after portal venous injection demonstrating their intrahepatic distribution.

METHODS

Male Wistar rats were transplanted with freshly isolated, rhodamine 123 labelled, primary rat hepatocytes. Cells (10(6) in 0.5 ml) were slowly injected via a catheter in the V. lienalis over 2 min. Their distribution in the left lateral liver lobe was visualized simultaneously as well as over the following 30 min by intravital fluorescence microscopy. In a second set of animals green fluorescent microspheres exhibiting a size of 15 μm were injected and observed identically. For further analyses of portal venous blood flow distribution sodium fluorescein was injected via the V. lienalis as well as via the V. jugularis.

RESULTS

In vivo imaging allowed the clear detection and observation of hepatocytes flowing into the liver and forming microemboli, which are trapped particularly in small distal portal branches. To a minor extent they were trapped as solitary cells in the periportal zone of sinusoids. Most interestingly, the distribution of cells within the liver was highly heterogeneous, as wide areas of acini were found free of transplanted cells after portal venous injection, while neighbouring areas showed disproportionately high hepatocyte occurrence. To further investigate this phenomenon sodium fluorescein was injected via the V. lienalis instead and an identical heterogeneous distribution pattern with clear anatomical borders defining highly, semi, and non-portal venous perfused liver acini could be observed. In contrast, systemic injection of sodium fluorescein via the V. jugularis in the same animals resulted in a homogenous dispersion within the liver.

CONCLUSION

Using in vivo fluorescence microscopy and exclusive portal venous injection of a fluorescent dye, we provide evidence for the existence of liver areas, differentially supplied by portal venous blood. As a consequence, hepatocytes transplanted via the portal tract are very heterogeneously distributed within the liver. This observation forces us to reconsider our current knowledge on (i) monitoring engrafted cells, (ii) the optimal hepatocyte number to be transplanted, (iii) portal hypertension after cell injection, and last but not least (iv) the optimal transplantation route. Moreover, the established model for in vivo visualization of transplanted hepatocytes allows development of new therapeutic strategies facilitating an improved engraftment of cells.

Evidence for tumor cell spread during local hepatic ablation of colorectal liver metastases

INTRODUCTION

The aim of the present study was to analyze the impact of cryosurgery (CRYO) on liver metastases compared to other thermoablative techniques. In a rat liver metastases model, evidence for tumor cell spread was analyzed comparing CRYO, radiofrequency ablation (RFA), and laser-induced thermotherapy (LITT).

METHODS

In an experimental study, we compared cell spillage in the washout of isolated perfused rat livers undergoing thermal ablation. Within the same model, CC531-GFP rat liver tumors were treated with CRYO, RFA, or LITT and the number of vital tumor cells within the perfusate was measured. Matrix metalloproteinases (MMP-2, MMP-9) were analyzed after in vivo ablation of rat colorectal liver metastases in the third experimental model.

RESULTS

Our data showed pronounced washout of cells after CRYO with a higher amount of intravascular cells and cell detritus compared to RFA and LITT. Only the effluent fluid of cryosurgery-treated livers revealed GFP-stained tumor cells. MMP-2 and MMP-9 expression was significantly higher after cryosurgery than after RFA and LITT.

CONCLUSION

When using thermoablative techniques, intravascular metastatic cell spillage is highest in CRYO, and increased expression of matrix metalloproteinases may further facilitate tumor cell spread. Therefore, RFA and LITT may be preferable whenever surgical resection of liver tumors is impossible.