Targeted retroviral gene transfer into the rat biliary tract

Delivery of non-viral naked DNA vectors to liver in small weaned pigs by hydrodynamic retrograde intrabiliary injection

Hepatic gene therapy by delivering non-integrating therapeutic vectors in newborns remains challenging due to the risk of dilution and loss of efficacy in the growing liver. Previously we reported on hepatocyte transfection in piglets by intraportal injection of naked DNA vectors. Here, we established delivery of naked DNA vectors to target periportal hepatocytes in weaned pigs by hydrodynamic retrograde intrabiliary injection (HRII). The surgical procedure involved laparotomy and transient isolation of the liver. For vector delivery, a catheter was placed within the common bile duct by enterotomy. Under optimal conditions, no histological abnormalities were observed in liver tissue upon pressurized injections. The transfection of hepatocytes in all tested liver samples was observed with vectors expressing luciferase from a liver-specific promoter. However, vector copy number and luciferase expression were low compared to hydrodynamic intraportal injection. A 10-fold higher number of vector genomes and luciferase expression was observed in pigs using a non-integrating naked DNA vector with the potential for replication. In summary, the HRII application was less efficient (i.e., lower luciferase activity and vector copy numbers) than the intraportal delivery method but was significantly less distressful for the piglets and has the potential for injection (or re-injection) of vector DNA by endoscopic retrograde cholangiopancreatography.

Identification and localization of sodium-phosphate cotransporters in hepatocytes and cholangiocytes of rat liver

Hepatocytes and cholangiocytes release ATP into bile, where it is rapidly degraded into adenosine and P(i). In rat, biliary P(i) concentration (0.01 mM) is approximately 100-fold and 200-fold lower than in hepatocytes and plasma, respectively, indicating active reabsorption of biliary P(i). We aimed to functionally characterize canalicular P(i) reabsorption in rat liver and to identify the involved P(i) transport system(s). P(i) transport was determined in isolated rat canalicular liver plasma membrane (LPM) vesicles using a rapid membrane filtration technique. Identification of putative P(i) transporters was performed with RT-PCR from liver mRNA. Phosphate transporter protein expression was confirmed by Western blotting in basolateral and canalicular LPM and by immunofluorescence in intact liver. Transport studies in canalicular LPM vesicles demonstrated sodium-dependent P(i) uptake. Initial P(i) uptake rates were saturable with increasing P(i) concentrations, exhibiting an apparent K(m) value of approximately 11 muM. P(i) transport was stimulated by an acidic extravesicular pH and by an intravesicular negative membrane potential. These data are compatible with transport characteristics of sodium-phosphate cotransporters NaPi-IIb, PiT-1, and PiT-2, of which the mRNAs were detected in rat liver. On the protein level, NaPi-IIb was detected at the canalicular membrane of hepatocytes and at the brush-border membrane of cholangiocytes. In contrast, PiT-1 and PiT-2 were detected at the basolateral membrane of hepatocytes. We conclude that NaPi-IIb is most probably involved in the reabsorption of P(i) from primary hepatic bile and thus might play an important role in the regulation of biliary P(i) concentration.

In vivo gene delivery via portal vein and bile duct to individual lobes of the rat liver using a polylysine-based nonviral DNA vector in combination with chloroquine

The objective of this study was to evaluate a bifunctional synthetic peptide as a DNA vector for regional gene delivery to the rat liver by the portal vein and bile duct routes. The 31-amino-acid peptide (polylysine-molossin) comprises an amino-terminal chain of 16 lysines for electrostatic binding of DNA, and the 15 amino acid integrin-binding domain of the venom of the American pit viper, Crotalus molossus molossus. Initial in vitro evaluation demonstrated that polylysine-molossin/DNA complexes were much smaller (approximately 50-100nm versus 500-1300nm), more positively charged, and more stable in isotonic dextrose in comparisons with salt-containing solutions. However, polylysine-molossin/DNA complexes in any solution other than complete culture medium were ineffective for gene delivery in vitro. Vector localization studies demonstrated that both the portal vein and bile duct routes provided excellent access of polylysine-molossin/DNA complexes to the liver. However, complexes delivered by the portal vein were rapidly lost (<15 min) following re-establishment of the portal circulation, whereas complexes delivered by the bile duct persisted much longer. Polylysine-molossin/DNA complexes in various isotonic solutions were delivered to the right lateral lobes either by perfusion through a branch of the portal vein or by infusion into appropriate branches of the bile duct. Two or three hours before gene delivery, rats were given a single injection of chloroquine. We report that the polylysine-molossin vector is much more effective (>10-fold) when delivered by the bile duct route with all isotonic solutions evaluated, and that polylysine-molossin/DNA complexes in isotonic dextrose are much more effective (>10-fold) than complexes in salt-containing solutions.

Manometric changes during retrograde biliary infusion in mice

The manometric, ultrastructural, radiographic, and physiological consequences of retrograde biliary infusion were determined in normostatic and cholestatic mice. Intraluminal biliary pressure changed as a function of infusion volume, rate, and viscosity. Higher rates of constant infusion resulted in higher peak intraluminal biliary pressures. The pattern of pressure changes observed was consistent with biliary ductular and/or canalicular filling followed by leakage at a threshold pressure. Retrograde infusion with significant elevations in pressure led to paracellular leakage of lanthanum chloride, radiopaque dye, and [(14)C]sucrose with rapid systemic redistribution via sinusoidal and subsequent hepatic venous drainage. Chronic extrahepatic bile duct obstruction resulted in significantly smaller peak intrabiliary pressures and lower levels of paracellular leakage. These findings indicate that under both normostatic and cholestatic conditions elevated intrabiliary volumes/pressures result in an acute pressure-dependent physical opening of tight junctions, permitting the movement of infusate from the intrabiliary space into the subepithelial tissue compartment. Control of intraluminal pressure may potentially permit the selective delivery of macromolecules >18-20 A in diameter to specific histological compartments.

Gene transfer to the rat biliary tract with the HVJ-cationic liposome method

BACKGROUND/AIMS

The ability to transfer foreign genes into the biliary tract would be useful for the treatment of biliary tract diseases, including cancer, cystic fibrosis and other genetic diseases. To introduce a foreign gene precisely into the rat biliary epithelial cells, we developed a new technique, inserting a polyethylene catheter into the common bile duct through the papilla of Vater by use of a fusigenic cationic liposome with hemagglutinating virus of Japan (HVJ-cationic liposome).

METHODS

Transfection efficiency was estimated with the use of FITC-oligonucleotides (FITC-ODNs) and cDNA of beta-galactosidase (pCAG-lacZ).

RESULTS

FITC-ODNs encapsulated in HVJ-cationic liposome were effectively transfected into cell nuclei of human cholangiocellular carcinoma in vitro after a 30-min incubation as compared with the simple application of naked FITC-ODNs. After in vivo injection of FITC-ODNs using the HVJ-cationic liposome method through the papilla of Vater, fluorescence accumulation was observed only in the epithelial cells of the biliary tract, but not in the parenchymal cells of the liver. Beta-galactosidase expression was observed in the biliary epithelial cells 3 days after the transfection of pCAG-lacZ and was also detected at 14 days, but not at 28 days, without obvious cytotoxicity.

CONCLUSIONS

HVJ-cationic liposome-mediated gene transfer to the biliary tract via the papilla of Vater is a minimally-invasive and an effective gene-delivery method for site-specific targeting to the epithelial cells of the biliary tract, which could be applied to the treatment of human biliary tract diseases.

Wound healing in the liver with particular reference to stem cells

The efficiency of liver regeneration in response to the loss of hepatocytes is widely acknowledged, and this is usually accomplished by the triggering of normally proliferatively quiescent hepatocytes into the cell cycle. However, when regeneration is defective, tortuous ductular structures, initially continuous with the biliary tree, proliferate and migrate into the surrounding hepatocyte parenchyma. In humans, these biliary cells have variously been referred to as ductular structures, neoductules and neocholangioles, and have been observed in many forms of chronic liver disease, including cancer. In experimental animals, similar ductal cells are usually called oval cells, and their association with impaired regeneration has led to the conclusion that they are the progeny of facultative stem cells. Oval cells are of considerable biological interest as they may represent a target population for hepatic carcinogens, and they may also be useful vehicles for ex vivo gene therapy for the correction of inborn errors of metabolism. This review proposes that the liver harbours stem cells that are located in the biliary epithelium, that oval cells are the progeny of these stem cells, and that these cells can undergo massive expansion in their numbers before differentiating into hepatocytes. This is a conditional process that only occurs when the regenerative capacity of hepatocytes is overwhelmed, and thus, unlike the intestinal epithelium, the liver is not behaving as a classical, continually renewing, stem cell-fed lineage. We focus on the biliary network, not merely as a conduit for bile, but also as a cell compartment with the ability to proliferate under appropriate conditions and give rise to fully differentiated hepatocytes and other cell types.