An Experimental Study On The Roles Of Ito Cells Involved In The Pathogenesis Of Total Parenteral Nutrition(TPN)-induced Liver Dysfunction In A Piglet Model

ObjectivesTo explore the morphological and functional changes of Ito cells and evaluate the possible roles of Ito cells involved in the pathogenesis of TPN-induced liver dysfunction.Methods16 piglets were randomly divided into TPN and control groups with 8 subjects each group. Piglets in TPN group were continuously administrated with 200Kcal/Kg.d hyperalimentation for 2 weeks; whereas piglets in control were allowed to have free access to laboratory chow. The amount of total calories between two groups were almost similar. Blood specimen were collected and liver biopsy specimen were harvested on starting day (day 0) and terminal day (day14) respectively for examination of biochemical function and histological changes. For liver biopsy specimen, besides the pathological analysis by light microscope, we also applied immunohistochemistry and transmission electron microscopy to discuss the significant changes of Ito cells in liver.ResultsAt the starting point, there was no significant changes in liver biochemical and histological examination between two groups. Although there was no changes for enzymic level except for significant increase in total bilirubin and bile acid concentration biochemicallly after two-week TPN administration, mild inflammation and extensive steatosis or hydropic degeneration accompanied by mild intrahepatic bile duct proliferation distinguished conspicuously from control group (P＜0.05). Besides, immunohistochemical examination revealed that the number of Ito cells positive expression toα-SMA dramatically increased compared with almost negative control specimen (P＜0.05). Furthermore, transmission electron microscopy showed that Ito cells located in space of Disse hypertrophied with extended cytoplasmic processes as well as loss of lipid droplet partially. The production of collagen bundles in space of Disse and subendothelial deposits of base membrane-like structure in sinusoid synergistically caused shrinkage of sinusoid. Abundant and well-developed RER were also pronounced in their cytoplasm indicating the transformation into MFB.Conclusions(1) After two-week TPN duration, great changes in liver tissue happened including mild inflammatory infiltration and intrahepatic canalicular proliferation as well as extensive steatosis or hydropic degeneration.(2) TPN administration as a direct or indirect contributing factor activated the quiescent Ito cell to transforme into myofibroblast cells characterized by abundant RER and myofilaments positively stained byα-SMA. Ito cells proliferation and hypertrophy followed by TPN, together with formation of collagen bundles resulted into stenosis of sinusoid through "squeeze-like" action.(3) Subendothelial deposits of base membrane-like structure and narrow of sinusoid caused disturbance of microcirculation reducing blood supply of hepatocytes suffered from ischemic injury, which could elucidate the biochemical "hysterisis" and pathologic insult of hepatocytes.(4) The loss of lipid droplets in some activated Ito cells suggests not only the possibility of "asynchronism", but also the presumption that the shift of lipid droplets from Ito ceils to hepatocytes contributing partially to steatosis.