DPPIV activity and expression in the biliary tree of fatty livers are better preserved by subnormothermic machine perfusion respect to conventional cold storage

Background: Biliary complications often lead to acute and chronic liver injury after liver transplantation. Fatty livers, vulnerable to conventional cold storage preservation (CS), are being increasingly used as grafts due to the scarcity of donors. We developed a subnormothermic machine perfusion system (20°C; MP20) allowing a better preservation of hepatocytes and sinusoidal cells of fatty and even of normal rat livers as compared with CS (Vairetti et al., Liver Transpl 15:20-29,2009; Boncompagni et al., Eur J Histochem 55:221-228,2011). Here we report the response of the biliary tree to CS or MP20 in lean and obese Zucker rat livers, using as marker Dipeptidylpeptidase-IV (E.C. 3.4.14.5). DPPIV is crucial for the regulation of incretins and neuropeptides involved in glucose metabolism and the functionality of the enterohepatic axis (Gorrell, Clin Sci. 108:277-292, 2005 ).Methods: MP20: livers perfused for 6h with oxygenated Krebs-Henseleit solution (KH) pH 7.4 at 20°C. CS: livers perfused in situ and preserved with UW solution at 4°C for 6h. Reperfusion in both cases with oxygenated KH (2h @ 37°C). DPPIV activity investigated with an azocoupling method and protein expression by immunofluorescence. Results : In lean animals, CS and MP20 caused a slight decrease of enzyme activity/expression and preserved equally the parenchyma. Obese liver: “Chicken-wire” canalicular DPPIV in periportal and pericentral regions, distorted by lipid droplets in the midzone; DPPIV patterns similar to those of lean animals in Hering canals and bile ducts. Obese CS: Highly damaged parenchyma in the midzone; DPPIV almost absent in the midzone and decreased respect to controls in canaliculi of PP and PC hepatocytes and in bile ducts, whereas in Hering canals it was similar to the controls. Obese MP20: good preservation of the parenchyma, DPPIV present but less intense in bile canaliculi of the whole parenchyma and in the remaining segments of the biliary tree. Conclusions: in lean rat liver CS and MP20 have similar effects on DPPIV and thus presumably on bile tree function. By contrast, in obese rat liver, MP20 preserves DPPIV function much better than CS especially in the canalicular network, where the primary bile is formed. These new data confirm the potentiality of MP20 for the preservation and resume of functionality of steatotic liver grafts. Hering canals, the presumed niche of liver progenitor cells (Gaudio et al., Dig Liver Dis 41:455-462,2009), appear unharmed by CS in fatty liver, suggesting that its transitional cells are constitutively resistant to stresses that normally injury hepatocytes and/or cholangiocytes. Acknowledgements: Uni Pavia FAR 2010-11; Fondazione CARIPLO, Research Project "Real time monitoring of liver oxidative stress injuries by means of innovative methodology based on integrated autofluorescence optical biopsy. Application to transplantation procedure” (ref 2011-0439)