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.