Coordinate secretion of acid hydrolases in rat bile

The P2X4 purinergic receptor impacts liver regeneration after partial hepatectomy in mice through the regulation of biliary homeostasis

Many regulatory pathways are involved in liver regeneration after partial hepatectomy (PH), to initiate growth, protect liver cells, and sustain remnant liver functions. Extracellular adenosine triphosphate rises in blood and bile after PH and contributes to liver regeneration, although purinergic receptors and mechanisms remain to be precisely explored. In this work we analyzed during regeneration after PH the involvement of P2X4 purinergic receptors, highly expressed in the liver. P2X4 receptor expression in the liver, liver histology, hepatocyte proliferation, plasma bile acid concentration, bile flow and composition, and lysosome distribution in hepatocytes were studied in wild-type and P2X4 knockout (KO) mice, before and after PH. P2X4 receptors were expressed in hepatocytes and Kupffer cells; in hepatocytes, P2X4 was concentrated in subcanalicular areas closely costained with lysosomal markers. After PH, delayed regeneration, hepatocyte necrosis, and cholestasis were observed in P2X4-KO mice. In P2X4-KO mice, post-PH biliary adaptation was impaired with a smaller increase in bile flow and HCO3 (-) biliary output, as well as altered biliary composition with reduced adenosine triphosphate and lysosomal enzyme release. In line with these data, lysosome distribution and biogenesis were altered in P2X4-KO compared with wild-type mice.

CONCLUSION

During liver regeneration after PH, P2X4 contributes to the complex control of biliary homeostasis through mechanisms involving pericanalicular lysosomes, with a resulting impact on hepatocyte protection and proliferation. (Hepatology 2016;64:941-953).

Demonstration of lanthanum in liver cells by energy-dispersive X-ray spectroscopy, electron energy loss spectroscopy and high-resolution transmission electron microscopy

The appearance of lanthanum in liver cells as a result of the injection of lanthanum chloride into rats is investigated by advanced transmission electron microscopy techniques, including electron energy loss spectroscopy and high-resolution transmission electron microscopy. It is demonstrated that the lysosomes contain large amounts of lanthanum appearing in a granular form with particle dimensions between 5 and 25 nm, whereas no lanthanum could be detected in other surrounding cellular components.

Output of liver fatty acid-binding protein (L-FABP) in bile

Liver fatty acid-binding protein (L-FABP) is a small cytoplasmic molecule highly expressed in the liver. Since L-FABP exhibits affinities for several biliary components, its presence in bile was explored by Western blotting and competitive ELISA in various mammalian species. A L-FABP-like immunoreactivity was consistently found in both hepatic and gallbladder bile. A close molecular identity between this 14 kDa biliary protein and the purified L-FABP was assessed by immunological analyses and high performance capillary electrophoresis. Pharmacological induction of hepatic L-FABP biosynthesis led to a similar increase in biliary L-FABP levels showing a close relationships between the cytosolic and biliary contents of this protein. Finally, a correlation between the presence of L-FABP in bile and both bile flow and bile acid release was found. These data suggest an output of L-FABP in bile in normal conditions which might be coupled with the physiological release of biliary components.

Decreased biliary secretion of proteins and phospholipids by rats with 1,1-dichloroethylene-induced bile canalicular injury

1,1-Dichloroethylene (DCE, 50 mg/kg) rapidly and selectively injures the bile canalicular membrane of zone 3 hepatocytes. Thus, DCE is of value as a tool to assess the consequences of alterations in canalicular membrane integrity on bile formation. Our objective was to characterize the effects of DCE on the biliary secretion of proteins and phospholipids in freely moving rats. DCE treatment caused a rapid and sustained decrease in total biliary protein output. In contrast, canalicular membrane-localized enzyme activities more slowly increased to 8- to 15-fold in bile from DCE-treated rats. Biliary output of lysosomal enzymes was altered in a biphasic manner. Specifically, there was a transient fivefold increase within 30 min of DCE treatment and then a progressive decrease to approximately 10% basal levels by 4 h. Secretion of phospholipids into bile decreased rapidly in a striking and sustained manner, after DCE. Our findings of diminished lysosomal protein and phospholipid secretion following DCE treatment are consistent with an important role for canalicular membrane integrity in their entry into bile.

Ursodeoxycholic acid may inhibit deoxycholic acid-induced apoptosis by modulating mitochondrial transmembrane potential and reactive oxygen species production

BACKGROUND

The hydrophilic bile salt ursodeoxycholate (UDCA) inhibits injury by hydrophobic bile acids and is used to treat cholestatic liver diseases. Interestingly, hepatocyte cell death from bile acid-induced toxicity occurs more frequently from apoptosis than from necrosis. However, both processes appear to involve the mitochondrial membrane permeability transition (MPT). In this study, we determined the inhibitory effect of UDCA on deoxycholic acid (DCA)-induced MPT in isolated mitochondria by measuring changes in transmembrane potential (delta psi m) and production of reactive oxygen species (ROS). In addition, we examined the expression of apoptosis-associated proteins in mitochondria isolated from livers of bile acid-fed animals.

MATERIALS AND METHODS

Adult male rats were maintained on standard diet supplemented with DCA and/or UDCA for 10 days. Mitochondria were isolated from livers by sucrose/percoll gradient centrifugation and MPT was measured using spectrophotometric and fluorimetric assays. delta psi m and ROS generation were determined by FACScan analysis. Cytoplasmic and mitochondrial protein abundance were determined by Western blot analysis.

RESULTS

DCA increased mitochondrial swelling 25-fold over controls (p < 0.001); UDCA reduced the swelling by > 40% (p < 0.001). Similarly, UDCA inhibited DCA-mediated release of calcein-loaded mitochondria by 50% (p < 0.001). delta psi m was significantly decreased in mitochondria incubated with DCA but not with UDCA. delta psi m disruption was followed closely by increased superoxide anion and peroxides production (p < 0.01). Coincubation of mitochondria with UDCA significantly inhibited the changes associated with DCA (p < 0.05). In vivo, DCA feeding was associated with a 4.5-fold increase in mitochondria-associated Bax protein levels (p < 0.001); combination feeding with UDCA almost totally inhibited this increase (p < 0.001).

CONCLUSION

UDCA significantly reduces DCA-induced disruption of delta psi m, ROS production, and Bax protein abundance in mitochondria, suggesting both short- and long-term mechanisms in preventing MPT. The results suggest a possible role for UDCA as a therapeutic agent in the treatment of both hepatic and nonhepatic diseases associated with high levels of apoptosis.

Effects of rabeprazole, a gastric proton pump inhibitor, on biliary and hepatic lysosomal enzymes in rats

The effects of rabeprazole (E3810), omeprazole and chloroquine on hepatic lysosomal function were studied. After chloroquine (50 mg/kg), rabeprazole (5 mg/kg) or omeprazole (5 mg/kg) was given intraperitoneally to rats for 6 days, the bile was collected via a bile duct cannula for 5 hr, and hepatic and biliary lysosomal enzyme (N-acetyl-beta-glucosaminidase and beta-galactosidase) activities were measured. The latency (an index for the hepatic lysosomal membrane integrity) was calculated from the N-acetyl-beta-glucosaminidase activity. The biliary constituents and plasma concentrations of lipids were also measured. The administration of chloroquine significantly increased hepatic and biliary lysosomal enzyme activities, but did not affect the lysosomal enzyme latency, hepatic and biliary protein content or bile flow. It significantly decreased the bile acid level. On the other hand, the administration of rabeprazole and omeprazole did not alter the lysosomal enzyme activities, lysosomal enzyme latency, protein content in liver or liver weight. Furthermore, no significant differences were observed in biliary lysosomal enzyme activity, protein content, bile flow, biliary constituents or in the plasma concentrations of lipids between the drug groups (rabeprazole or omeprazole) and the control group. The results of the present study indicate that rabeprazole, like omeprazole, does not influence hepatic lysosomal function.

Biliary secretion of anionic polypeptide fraction is not coupled to that of phospholipids and cholesterol in rats

Anionic polypeptide fraction (APF) is a phospholipid- and calcium-binding apoprotein present in animal and human bile, predominantly associated with cholesterol-phospholipid vesicles. In bile, the protein may play a physiological role in preventing precipitation of calcium salts. APF has also been suggested to be of regulatory importance in the process of biliary lipid secretion. The aim of the present study was to investigate whether the secretion rates of APF and that of biliary lipids are coupled, which would support a physiological role of APF in biliary lipid secretion. Biliary secretion rates of bile acids, phospholipids, and cholesterol were experimentally modulated in three different rat models. Secretion rates of APF were compared with that of bile acids, lipids, and with that of two other biliary proteins, the lysosomal protein beta-glucuronidase and apolipoprotein A-I (apo A-I). Model 1: diurnal variation in bile formation during chronic bile diversion; model 2: specific inhibition of biliary phospholipid and cholesterol, but not of bile acid secretion by infusion of the organic anion, sulfated lithocholyltaurine; model 3: acute interruption of the enterohepatic circulation in unanesthetized rats. The diurnal variation in bile formation involved a parallel increase of the biliary secretion rates of bile acids (+56 +/- 7%, mean +/- SD), phospholipids (+53 +/- 29%), cholesterol (+73 +/- 54%), and APF (+72 +/- 86%) during the night phase of the cycle. Infusion of sulfated lithocholyltaurine inhibited biliary phospholipid and cholesterol secretion (-78 +/- 15%, and -54 +/- 25%, respectively), but did not affect biliary bile acid or APF secretion rate (-19 +/- 14%, and +12 +/- 107%, respectively). Within 4 hours after interruption of the enterohepatic circulation, bile secretion rates for bile acids (-92 +/- 3%), phospholipids (-74 +/- 13%), cholesterol (-64 +/- 8%), and APF (-58 +/- 24%) rapidly declined to a new steady-state level. Correlation analysis using the data from the three experimental models indicated that the biliary secretion rate of APF was independent from that of phospholipids, cholesterol, beta-glucuronidase, and, presumably, apolipoprotein A-I, and positively correlated to bile acid secretion rate and bile flow. The data from three experimental models indicate that the biliary secretion rates of APF and of phospholipids/cholesterol are not coupled and, therefore, do not support a direct physiological role of APF secretion in biliary lipid secretion. APF secretion into bile may, at least partially, be controlled by biliary bile acid secretion.

Biliary electrolytes and enzymes in patients with and without gallstones

pH, osmolarity, various electrolytes, nine enzymes, and bile acid were determined in hepatic and gallbladder biles from 108 and 100 patients, respectively, relating to various types of gallstones. The pH, osmolarity, and electrolytes were essentially identical in all groups of patients except for slightly higher Ca and Mg in the hepatic bile in patients with muddy pigment stones. The gallbladder bile contained much higher inorganic cations yet remained isosmotic as a result of their sequestration into bile acid micelles. Excluding extremely high values, the activities of nine enzymes in the bile showed only minor differences among four groups of patients except for a high beta-glucuronidase activity in the hepatic bile in patients with muddy pigment stones. The biliary baseline activities of various enzymes and the relation to their serum levels were determined by their sources and subcellular localization in the hepatocytes. We concluded that biliary electrolytes and enzymes were basically similar in patients with and without gallstones except for higher levels of Ca, Mg, and beta-glucuronidase in hepatic bile in patients with muddy pigment stones.

Regulation of protein secretion into bile: studies in mice with a disrupted mdr2 p-glycoprotein gene

BACKGROUND & AIMS

Protein is secreted into bile via several independent pathways. The aim of this study was to investigate whether these pathways are influenced by secretion of biliary lipid.

METHODS

Protein secretion and biliary lipid output were studied in wild-type mice (+/+), heterozygotes (+/-), and homozygotes (-/-) for mdr2 gene disruption. Biliary lipid and protein output were varied by infusion with taurocholate (TC) and tauroursodeoxycholate (TUDC).

RESULTS

Exocytosis and transcytosis were unaltered in (-/-) mice. Infusion with TC strongly induced secretion of alkaline phosphatase in (-/-) mice but had little effect in (+/-) and (+/+) mice. Infusion with TUDC had little effect on alkaline phosphatase output. In contrast, both TUDC and TC strongly stimulated secretion of aminopeptidase N and lysosomal enzymes in (+/+) mice but had no effect in (-/-) animals. Aminopeptidase N secretion correlated with phospholipid output, but only at high flux. At low flux, aminopeptidase N was secreted independently from both phospholipid and bile salts.

CONCLUSIONS

The canalicular membrane enzymes alkaline phosphatase and aminopeptidase N are secreted via separate pathways. Part of alkaline phosphatase output is controlled by bile salt hydrophobicity, whereas at high lipid flux, aminopeptidase N secretion seems to be coupled to phospholipid output. Lysosomal enzymes follow the latter pathway.

Beta-hexosaminidase in bile and plasma from patients with cholestasis

beta-Hexosaminidase (Hex) activity was determined in bile from 18 patients with cholestasis, six patients without cholestasis and in ten normal liver biopsies. The difference in the mean activities in bile from patients with and without cholestasis was not significant. Only about 0.5 promille of total liver Hex activity was lost per day via the bile flow. Gel chromatography showed that enzyme forms present in bile had higher molecular weights than the forms present in liver tissue, indicating that the biliary enzyme was not routed through the lysosomes before release into the bile. In 32 patients with cholestasis, plasma Hex was increased compared to controls, and correlated to bilirubin. The activity was significantly higher in patients with severe cholestasis than in patients with less severe forms of cholestasis, but no significant difference in Hex activity was observed between patients with benign or malignant biliary obstruction. No significant difference was noted between patients with cholestasis for less than 1 week compared to those whose illness had lasted more than 1.5 weeks. The impact of biliary obstruction on plasma Hex is further illustrated by the observation that decompression lowered plasma Hex as well as bilirubin and alkaline phosphatase.

Measurement of apolipoprotein A1 in cholesterol gallstones and gallbladder bile of patients with gallstones

Biliary apolipoprotein A1 in bile inhibits the nucleation of cholesterol crystals from bile super-saturated with cholesterol. In the present study, using an enzyme-linked immunosorbent assay of apolipoprotein A1, we determined the content of apolipoprotein A1 in cholesterol gallstones and samples of gallbladder bile collected simultaneously from 23 patients during cholecystectomy. Protein content in cholesterol gallstones ranged from 50 to 5700 micrograms/g, with median, quartile, and three quartile values being 250, 111, and 740; apolipoprotein A1 content ranged from 9 to 9000 ng/g (200, 41, 647). The gallbladder bile samples contained protein at concentrations of 0.4-9.0 mg/ml (2.0, 1.1, 3.2), while apolipoprotein A1 was present at concentrations of 2.0-136.0 micrograms/ml (30.0, 10.0, 90.0). A notable finding was that the A1/total protein (TP) values for gallbladder bile, which ranged from 0.13% to 6.80% (1.62, 0.89, 3.34), were several times higher than those determined for gallstone samples, which ranged from 0.01% to 1.2%, 2% (0.06, 0.02, 0.25). The results of sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed that the protein profile in cholesterol gallstones was similar to that in gallbladder bile. It was concluded that: (1) the protein contained in gallstones may originate from bile, (2) the content of apolipoprotein A1 in cholesterol gallstones is only a trace amount, compared with that in gallbladder bile, and (3) biliary apolipoprotein A1 may be retained in a soluble phase in gallbladder bile, with minimal precipitation onto the surfaces of gallstones.

Ultrastructure of the intracellular membranous system of rat hepatocytes in intrahepatic cholestasis induced by phalloidin

To investigate the effect of a thickened pericanalicular ectoplasm in tubulovesicular transport and biliary excretion, we examined the ultrastructure of the intracellular membranous system in rat hepatocytes with and without phalloidin treatment, by transmission electron microscopy and scanning electron microscopy combined with the Aldehyde prefix Osmium-Dimethyl Sulfoxide-Osmium method. Hepatocytes possessed elaborate networks of tubules around bile canaliculi, and some of them extended to the bile canaliculi in control rats. Vesicles were also present around the bile canaliculus. Treatment of rats with phalloidin produced a thick pericanalicular ectoplasm around the bile canaliculus visualized by transmission electron microscopy, and the density of vesicles (p < 0.001) and tubules (p < 0.001) within 0.5 microns around the bile canaliculus significantly decreased in phalloidin-treated rats. The number of lysosomes in hepatocytes apparently increased in phalloidin-treated rats; however, they were rarely observed around the bile canaliculus. The Aldehyde prefix Osmium-Dimethyl Sulfoxide-Osmium method produced an organelle-free space around the bile canaliculus by removing the thick pericanalicular ectoplasm in scanning electron microscopic examination, and the thickened pericanalicular ectoplasm inhibited the approach of intracellular membranes to the canalicular membrane in the transmission electron microscopic examination. In some pathological cholestatic conditions, the thickened pericanalicular ectoplasm may inhibit not only bile canalicular contraction but also biliary excretion of substances, which is mediated by the tubulovesicular transport system.

Association of kinesin with the Golgi apparatus in rat hepatocytes

The Golgi apparatus is a dynamic membranous structure, which has been observed to alter its location and morphology during the cell cycle and after microtubule disruption. These dynamics are believed to be supported by a close structural interaction of the Golgi with the microtubule cytoskeleton and associated motor enzymes. One microtubule-dependent motor enzyme, kinesin, has been implicated in Golgi movement and function although direct evidence supporting this interaction is lacking. In this study, we utilized two well-characterized kinesin antibodies in conjunction with subcellular fractionation techniques, immunoblot analysis and immunofluorescence microscopy to conduct a detailed study on the association of kinesin with the Golgi and other membranous organelles in a polarized epithelial cell, the primary rat hepatocyte. We found that kinesin represents approximately 0.3% of total protein in rat liver homogenates, with approximately 30% membrane-associated and the remainder in the cytosol. Among membrane fractions, kinesin was concentrated markedly in Golgi-enriched fractions, which were prepared using two independent techniques. Kinesin was also abundant in fractions enriched in transcytotic carriers and secretory vesicles, with lower levels detected on fractions enriched in endosomes, endoplasmic reticulum, lysosomes and mitochondria. Immunofluorescence microscopy showed that kinesin is concentrated on Golgi-like structures in both primary cultured hepatocytes and rat hepatocyte-derived clone 9 cells. Double-label immunofluorescence demonstrated that kinesin staining colocalizes with the Golgi marker, alpha-mannosidase II, in both cell types. These results provide compelling evidence showing that kinesin is associated with the Golgi complex in cells and implicate this motor enzyme in Golgi structure, function and dynamics.

Urinary and biliary excretion of aluminoxamine and ferrioxamine in dogs with various renal function

We assessed the pharmacokinetics of aluminoxamine and ferrioxamine in dogs with sustained intermittent bile duct ligation and either normal renal function or stable chronic renal failure. A first group of male beagle dogs were given aluminoxamine and ferrioxamine, while a second group received desferrioxamine after loading them with iron and aluminum. Only minute amounts of ferrioxamine and aluminoxamine were found in the bile after administration of these compounds. The distribution volume of aluminoxamine and ferrioxamine appeared to be confined to the extracellular space and their renal excretion correlated with renal function. Administration of desferrioxamine to iron and aluminum-loaded dogs resulted in an increased biliary ferrioxamine but negligible aluminoxamine excretion. Renal clearance of the in vivo formed ferrioxamine and aluminoxamine in this group strongly correlated with renal function. Our observations indicate that biliary excretion of intravenously administered ferrioxamine and aluminoxamine is negligible even in renal failure. The data presented in this study provide indirect evidence that desferrioxamine administration to iron- and aluminum-loaded dogs results in the intra-hepatic formation of ferrioxamine which is partly excreted in the bile. Biliary excretion of aluminoxamine after desferrioxamine administration remained negligible.

Alterations in hepatocyte lysosomes in experimental hepatic copper overload in rats

BACKGROUND

Although Wilson's disease is characterized by an accumulation of copper within hepatocyte lysosomes, the effects of excess copper on hepatic lysosomes are unknown. We studied the effects of excess copper on the structure, physicochemical properties, and pH of hepatocyte lysosomes using a rodent model.

METHODS

Rats were copper loaded with 0.125% copper acetate in water for 6 weeks. Copper was measured by atomic absorption spectrophotometry. Morphology was studied by electron microscopy. Lysosomal membrane fluidity was studied by fluorescence polarization, and lipid composition was determined by gas chromatography. Hepatocyte lysosomal pH was determined by flow cytometry.

RESULTS

Copper overload resulted in a 10-fold increase in hepatic copper. Hepatocyte lysosomes were enlarged and abnormally shaped with a 27-fold increase in copper, increased in vitro fragility, and decreased lysosomal membrane fluidity. Thiobarbituric acid reactive substances, a measure of lipid peroxidation, doubled in isolated lysosomal membranes. Polyunsaturated fatty acids increased, saturated fatty acids decreased, and membrane content of selected fatty acids was modified after copper overload. Lysosomal pH increased from 4.67 +/- 0.02 to 4.87 +/- 0.02.

CONCLUSIONS

Copper overload causes alterations in lysosomal morphology, increases lysosomal fragility, decreases membrane fluidity, alters membrane fatty acid composition, and increases lysosomal pH. Copper catalyzed lipid peroxidation represents the likely mechanism for these alterations.

Tauroursodeoxycholic acid stimulates hepatocellular exocytosis and mobilizes extracellular Ca++ mechanisms defective in cholestasis

To assess the effects of tauroursodeoxycholic acid (TUDCA) on bile excretory function, we examined whether TUDCA modulates vesicular exocytosis in the isolated perfused liver of normal rats in the presence of high (1.9 mM) or low (0.19 mM) extracellular Ca++ and in cholestatic rats 24 h after bile duct ligation. In addition, the effects of TUDCA on Ca++ homeostasis were compared in normal and in cholestatic hepatocytes. In the isolated perfused rat liver, TUDCA (25 microM) stimulated a sustained increase in the biliary excretion of horseradish peroxidase, a marker of the vesicular pathway, in the presence of high, but not low extracellular Ca++ or in the cholestatic liver. In contrast, TUDCA stimulated bile flow to the same extent regardless of the concentration of extracellular Ca++ or the presence of cholestasis. In indo-1-loaded hepatocytes, basal cytosolic free Ca++ ([Ca++]i) levels were not different between normal and cholestatic cells. However, in cholestatic cells [Ca++]i increases induced by TUDCA (10 microM) and its 7 alpha-OH epimer taurochenodeoxycholic acid (50 microM) were reduced to 22% and 26%, respectively, compared to normal cells. The impairment of TUDCA-induced [Ca++]i increase in cholestatic cells could be mimicked by exposing normal cells to low extracellular Ca++ (21%) or to the Ca++ channel blocker NiCl2 (23%). These data indicate that (a) dihydroxy bile acid-induced Ca++ entry may be of functional importance in the regulation of hepatocellular vesicular exocytosis, and (b) this Ca++ entry mechanism across the plasma membrane is impaired in cholestatic hepatocytes. We speculate that the beneficial effect of ursodeoxycholic acid in cholestatic liver diseases may be related to the Ca+(+)-dependent stimulation of vesicular exocytosis by its conjugate.

Bile acid-dependent vesicular transport of lysosomal enzymes into bile in the rat

BACKGROUND

Bile acids may stimulate the movement of hepatocyte vesicles and enhance their fusion with the biliary canaliculus. The present study examined the effects of various bile acids on the exocytosis of the contents of hepatocyte lysosomes into the biliary canaliculus.

METHODS

The effects of various bile acids on hepatocyte lysosome movement and on exocytosis of the contents of hepatocyte lysosomes into the biliary canaliculus were determined from the distribution of fluorescein isothiocyanate-dextran--labeled lysosomes in hepatocyte couplets and by quantitating biliary lysosomal enzyme output in rats.

RESULTS

Hydrophobic as well as hydrophilic and nonmicellar bile acids were found to stimulate to a similar degree the output of lysosomal enzymes into bile, indicating that bile acid-induced change of canalicular or lysosomal membrane fluidity is not responsible for enhanced exocytosis. The taurocholate-dependent increase in lysosomal enzyme excretion was completely blocked by either microtubule or microfilament inhibition, suggesting that these subcellular structures are involved in bile acid-dependent vesicular transport. Fluorescent microscopy studies showed that taurocholate causes a microtubule-dependent translocation of lysosomes towards the canaliculus in hepatocyte couplets, which occurred at the same time as increased output of lysosomal enzymes into bile.

CONCLUSIONS

The results suggest that bile acids modulate vesicle traffic towards the canaliculus by a mechanism unrelated to bile acid interaction with the vesicle membrane.

Modification of reticuloendothelial function by muramyl dipeptide-encapsulated liposomes in jaundiced rats treated with biliary decompression

Rats with 2 weeks of biliary obstruction, with and without 1 week of concomitant biliary decompression relieving the jaundice, were treated with physiologic saline, free muramyl dipeptide (MDP), placebo liposomes, or liposome-encapsulated MDP. Reticuloendothelial system (RES) function was evaluated by blood clearance of intravenously injected 125I-labelled Escherichia coli. The corrected phagocytic index (alpha) after 1 week of biliary decompression returned to normal levels in animals treated with MDP liposomes, whereas RES function was impaired (P < 0.05) in all other jaundiced and biliary-decompressed groups. In the biliary-decompressed, MDP-liposome-treated group, hepatic uptake of radiolabelled bacteria was significantly higher (P < 0.05) and renal entrapment of bacteria was significantly lower (P < 0.05) than in all other jaundiced and biliary-decompressed groups. We conclude that treatment with MDP liposomes improves the otherwise impaired RES function in rats with biliary obstruction and biliary decompression.

The effect of copper and heliotrope on the composition of bile in sheep

The effects of interrupting the enterohepatic circulation (EHC) of bile salts for seven hours and of feeding copper and heliotrope alone and combined for 13 weeks, on bile flow and excretion of copper, zinc, iron and alpha-mannosidase were studied in sheep. Interruption of EHC reduced bile flow rate and increased the concentration of copper, zinc, iron and bile acids while alpha-mannosidase's activity remained stable. Changes in concentration were related to changes in bile volume for copper and zinc only. Total output per hour was not changed. Biliary concentration of copper correlated with alpha-mannosidase's activity in control sheep and those given copper or heliotrope, supporting the hypothesis that lysosomes are involved in biliary secretion of copper in sheep. Increasing the intake of copper increased the rate of excretion of copper in bile. Copper output was lower when heliotrope was fed alone.

Hepatic accumulation of lysosomes and defective transcytotic vesicular pathways in cirrhotic rat liver

To investigate the potential role of lysosomes in cirrhosis, we analyzed the activity of lysosomal enzymes in rats exposed long-term to phenobarbital and carbon tetrachloride. The activity of lysosomal enzymes was markedly increased in the homogenate of cirrhotic livers (e.g., arylsulfatase 9 +/- S.D.2 vs. 16 +/- 6 nmoles.min-1.mg-1 in control rats and cirrhotic rats, respectively; p less than 0.001). The corresponding plasma levels were also increased (7 +/- 1 vs. 12 +/- 3 nmoles.min-1.mg-1; p less than 0.01), whereas biliary excretion was diminished (16 +/- 7 vs. 7 +/- 2 pmol.min-1.gm liver-1; p less than 0.05) in cirrhotic rats. Stereological quantification of lysosomes visualized cytochemically revealed an increase of pericanalicular lysosomes averaging 1.5 +/- 0.4 around a canaliculus in controls and 3.7 +/- 1.0 in cirrhotic rats (p less than 0.01). Because this suggested a defect in the transcellular vesicular pathway, we investigated the biliary excretion of horseradish peroxidase and epidermal growth factor in perfused livers. Bile flow and total horseradish peroxidase excretion were similar in control rats and cirrhotic rats. However, the early peak of biliary horseradish peroxidase excretion--usually taken as evidence of paracellular transport--was increased in cirrhotic rats (13 +/- 7 vs. 57 +/- 22%; p less than 0.01), whereas the second peak--reflecting the transcellular vesicular pathway(s)--was markedly reduced (87 +/- 7 vs. 43 +/- 22%; p less than 0.001). A similar reduction in the biliary excretion of intact epidermal growth factor and of its degradation products was found. These results demonstrate an increased number of lysosomes in hepatocytes of cirrhotic livers; this appears to be the result of accumulation rather than proliferation, in view of the reduced transcellular vesicular movement of different markers into bile.

Inhibition of biliary lipid and protein secretion by cyclosporine A in the rat

We investigated the effect of cyclosporine A (CyA) administered as a single i.v. dose of 20 and 40 mg/kg body wt, on biliary secretion of cholesterol, phospholipid, bile acid, and lysosomal marker and canalicular plasma membrane marker enzymes in anaesthetized Wistar rats. CyA reduced the concentration and biliary secretion of cholesterol, phospholipid and bile acid to a considerable extent; the inhibitory effect of CyA on the biliary secretion of phospholipid and bile acid was greater than that on cholesterol. The biliary outputs of acid phosphatase (AcP) and gamma-glutamyltransferase (gamma-GT) were also diminished by the drug, all these effects being dose-dependent. Maximum decreases in bile acid secretion were observed 10 min after administration, whereas those of cholesterol and phospholipid were delayed. Bile acid concentrations and secretion returned to pretest values at 30-50 min after CyA injection whereas those of cholesterol and phospholipid remained significantly reduced at this time point. The greater inhibitory effect of CyA on the biliary outputs of phospholipid and bile acid relative to cholesterol secretion together with the asynchronous fall and recovery of bile acid, cholesterol and phospholipid concentrations and secretion alter the cholesterol/bile acid, phospholipid/bile acid and cholesterol/phospholipid molar ratios as well as the lithogenic index, thus suggesting that CyA would uncouple biliary lipid secretion from bile acid secretion. Since under physiological conditions biliary lipid and gamma-GT secretion is related to and dependent upon bile acid secretion, we propose that the CyA-induced inhibition on lipid and gamma-GT secretion is, at least partly, secondary to the fall in bile acid output caused by the drug. However, since CyA inhibits secretory processes independent of the hepatobiliary flux of bile acid, such as the exocytic discharge of AcP, and because it also uncouples biliary lipid from bile acid secretion, other mechanisms and factors involved in lipid and protein secretion (such as intracellular transport, canalicular membrane fluidity and/or intracanalicular events) might also be altered by this drug.

Indian childhood cirrhosis in an American child

Indian childhood cirrhosis is a fatal liver disease characterized by a striking accumulation of copper-containing granules within hepatocytes. A two-year-old American boy, the product of a third-cousin marriage, with clinical, biochemical, and histological signs of Indian childhood cirrhosis was studied. Liver biopsies at 22 and 30 months of age revealed a rapid progression from fibrosis to micronodular cirrhosis, with many of the remaining hepatocytes staining strongly for copper and copper-binding proteins. Electron microscopy showed characteristic dense granules containing copper and sulfur by electron probe analysis. Hepatic copper content was 1500 micrograms/g dry weight (normal, 20-50). Urinary copper was 3.6 mumol/d (229 micrograms/24 hours; normal, 15-20), and serum ceruloplasmin was 352 mg/L (normal, 150-320). The case suggests that both genetic and environmental components contribute to the manifestations of Indian childhood cirrhosis, and that the diagnosis of Indian childhood cirrhosis should be considered even in non-Indian infants with progressive liver disease.

Alterations in the structure, physicochemical properties, and pH of hepatocyte lysosomes in experimental iron overload

While hemochromatosis is characterized by sequestration of iron-protein complexes in hepatocyte lysosomes, little is known about the effects of excess iron on these organelles. Therefore, we studied the effects of experimental iron overload on hepatocyte lysosomal structure, physicochemical properties, and function in rats fed carbonyl iron. A sixfold increase (P less than 0.0001) in hepatic iron and a fivefold increase in lysosomal iron (P less than 0.01) was observed after iron loading; as a result, hepatocyte lysosomes became enlarged and misshapen. These lysosomes displayed increased (P less than 0.0001) fragility; moreover, the fluidity of lysosomal membranes isolated from livers of iron-loaded rats was decreased (P less than 0.0003) as measured by fluorescence polarization. Malondialdehyde, an end product of lipid peroxidation, was increased by 73% (P less than 0.008) in lysosomal membranes isolated from livers of iron-overloaded rats. While amounts of several individual fatty acids in isolated lysosomal membranes were altered after iron overload, cholesterol/phospholipid ratios, lipid/protein ratios, double-bond index, and total saturated and unsaturated fatty acids remained unchanged. The pH of lysosomes in hepatocytes isolated from livers of iron-loaded rats and measured by digitized video microscopy was increased (control, 4.70 +/- 0.05; iron overload, 5.21 +/- 0.10; P less than 0.01). Our results demonstrate that experimental iron overload causes marked alterations in hepatocyte lysosomal morphology, an increase in lysosomal membrane fragility, a decrease in lysosomal membrane fluidity, and an increase in intralysosomal pH. Iron-catalyzed lipid peroxidation is likely the mechanism of these structural, physicochemical, and functional disturbances.

Demonstration of vesicular-dependent bile flow in the sucrose-loaded rat

The contribution of the hepatocyte vacuolar apparatus to bile fluid formation was assessed by studying the transcellular transport and biliary excretion of the fluid-phase marker sucrose. In rats sucrose-loaded by IP administration of sucrose, electron microscopy showed expansion of the vacuolar apparatus and numerous large lysosomelike structures in hepatocytes. Subcellular distribution studies showed that sucrose was sequestered in lysosomes. Compared with controls, sucrose-loaded rats had a 30% higher (P less than 0.01) bile flow with no change in biliary bile acid or electrolyte concentrations. Administration of colchicine ablated the sucrose-induced choleresis and resulted in parallel changes in biliary secretions of sucrose and lysosomal enzymes. Our data suggest that in the sucrose-loaded rat, the hepatocyte vacuolar apparatus may contribute significantly to bile formation by microtubule-dependent release of fluid into bile by exocytosis.

Clogging of biliary endoprostheses: a new perspective

Endoscopic palliation with biliary endoprostheses is now an established treatment for benign and malignant strictures of the biliary tree. These endoprostheses, however, tend to clog with time. We investigated this problem by undertaking in vitro studies on stents of different designs made of different polymer materials. The stent that performed best was then tested in an in vivo trial. There was a direct relation in vitro between the frictional coefficient of a polymer and the amount of encrusted material. Catheters perfused in bacterially contaminated bile, irrespective of material and design, accrued significantly more sludge than catheters perfused with sterilised bile. The presence of side holes significantly increased the amount of sludge in the stents, but eliminated any differences between the various materials. We therefore investigated the effect of omitting side holes in a clinical trial which consisted of two groups of 20 patients each. The group treated with conventional stents accrued significantly more sludge in the stents than the group treated with experimental stents without side holes (p less than 0.05). The absence of side holes did not cause incomplete drainage or increase morbidity. Side holes are detrimental to stent patency, which is adversely affected by other factors including bacteria and proteins.

Effects of bile acid depletion and of ursodeoxycholic and chenodeoxycholic acids on biliary protein secretion in the hamster

The effect of changes of both the rate of secretion and the composition of bile acids on biliary proteins was studied in a bile fistula hamster model. Biliary protein secretion as well as bile flow and bile acid secretion were studied in response to intravenous infusions of low, medium and high doses of ursodeoxycholic acid and chenodeoxycholic acid in comparison to the infusion of the normal saline carrier (control) solution. The control-infused animals showed a marked and statistically significant increase in both the concentration and total excretion of biliary proteins. All three doses of ursodeoxycholic acid either prevented the increase of protein concentration or led to its decrease. The low and medium doses of chenodeoxycholic acid had similar effects. However, the high dose of this bile acid was cholestatic and increased the biliary protein concentration. The results of the study indicate that decreases in bile acid secretion, as they occur after an interruption of the enterohepatic circulation, may lead to major increases in biliary protein concentration. The study also shows that these changes in protein secretion, which may promote nucleation, are reversed by the cholelitholytic bile acids, ursodeoxycholic acid and chenodeoxycholic acid.

Purification and immunological quantification of rat liver lysosomal glycosidases

Although lysosomal enzyme activities are known to vary in response to numerous physiological and pharmacological stimuli, the relationship between lysosomal enzyme activity and enzyme concentration has not been systematically studied. Therefore we developed radioimmunoassays for two lysosomal glycosidases in order to determine lysosomal enzyme concentration. beta-Galactosidase and beta-glucuronidase were purified from rat liver 2780-fold and 1280-fold respectively, by using differential centrifugation, affinity chromatography, ion-exchange chromatography and molecular-sieve chromatography. Polyclonal antibodies to these enzymes were raised in rabbits, and two radioimmunoassays were established. Antibody specificity was shown by: (i) selective immunoprecipitation of enzyme activity; (ii) identical bands of purified enzyme on SDS/polyacrylamide-gel electrophoresis and immunoelectrophoresis; (iii) single immunoreactive peaks in molecular-sieve chromatography experiments. Sensitivities of the assays were such that 15 ng of beta-galactosidase and 45 ng of beta-glucuronidase decreased the ratio of bound to free radiolabel by 50%; minimal detectable amounts of immunoreactive enzymes were 2 ng and 10 ng respectively. The assays were initially used to assess the effects of physiological perturbations (i.e. fasting and age) on enzyme concentrations in rat liver; these experiments showed that changes in enzyme concentrations do not always correlate with changes in enzyme activities. This represents the first report of radioimmunoassays for lysosomal glycosidases. The results suggest that these radioimmunoassays provide useful technology for the study of regulatory control mechanisms of the concentrations of lysosomal glycosidases in mammalian tissues.

Biliary excretion of iron and ferritin in idiopathic hemochromatosis

The role of biliary excretion of iron and ferritin in iron overload was studied and evaluated. Ten patients with idiopathic hemochromatosis and two groups of controls (14 gallstone patients and 16 healthy subjects) were included. Liver tissue (obtained by percutaneous or operative biopsy) was investigated with light microscopy and transmission electron microscopy in combination with x-ray microanalysis. Fasting bile samples were obtained through duodenal aspiration or at cholecystectomy. Iron was determined in liver tissue and bile using atomic absorption spectroscopy, and ferritin was determined in serum and bile with a radioimmunoassay technique. All patients with hemochromatosis had iron-positive staining as seen in light microscopy. Electron microscopy showed iron-containing proteins in the lysosomes and cytosol of liver parenchymal cells, and this observation was supported by x-ray microanalysis. Hepatic iron concentration was increased about eightfold in the patients with hemochromatosis (p less than 0.001). Biliary iron concentration, expressed per millimole of bile acid, was increased about twofold (p less than 0.05) and biliary ferritin concentration about fivefold (p less than 0.001) in hemochromatosis. Four of the patients with hemochromatosis were reexamined after completed treatment with venesection; this resulted in normalized biliary concentrations of iron and ferritin. We conclude that biliary secretion of ferritin occurs in humans and that both iron and ferritin excretion are enhanced in hepatic iron overload. The apparently limited capacity of biliary iron excretion may be of importance for the hepatic iron accumulation in hemochromatosis.

Hepatic metabolism of colloidal gold-low-density lipoprotein complexes in the rat: evidence for bulk excretion of lysosomal contents into bile

Rats were treated with 17 alpha-ethinyl estradiol to induce high levels of low-density lipoprotein receptors in hepatocytes. When these rats were given intravenous injections of low-density lipoprotein-colloidal gold complexes, most of the gold (labeled with 195Au) appeared to be taken up by Kupffer cells, as were complexes of colloidal gold with albumin or polyvinylpyrrolidone. However, when these rats were also administered gadolinium chloride, which blocks Kupffer cell activity, most of the low-density lipoprotein-gold (but not gold complexed with albumin or polyvinylpyrrolidone) was taken up into hepatocytes by receptor-mediated endocytosis and concentrated in peribiliary lysosomes, as determined by electron microscopy. Colloidal gold taken up as a complex with low-density lipoprotein was excreted into the feces via the common bile duct at a maximal rate of about 5% daily, 4 to 12 days after injection. Thereafter, the rate of gold excretion fell off until reaching a plateau after 3 weeks. At this late time, most of the colloidal gold was shown by electron microscopy to be in Kupffer cells, whereas earlier (6 days after injection) it was contained mainly in older hepatocytic lysosomes, identified by lipofuscin granules. It is concluded that, in rats, hepatocytic lysosomes empty most of their contents into bile every week or two, apparently by exocytosis.

Perhexilene: effects on hepatic lysosomal function in rats

1. Perhexilene, a long-acting anti-anginal drug, can induce adverse effects on the liver which may be dose-dependent. At high concentrations, perhexilene causes marked morphological changes in hepatocyte lysosomes. The current study examined the effect of 'therapeutic' doses of perhexilene on hepatic lysosomal function, particularly the biliary release of lysosomal enzymes, using an isolated perfused rat liver (IPRL) model. 2. Pharmacokinetic studies demonstrated that clearance of single doses of perhexilene by the perfused rat liver was dose-dependent and established a 'therapeutic' dose of 0.6 mg using the IPRL. A 5 day pretreatment regimen of 20 mg/kg per day was shown to produce 'therapeutic' perhexilene concentrations of 150-210 ng/ml. 3. At perhexilene concentrations equating the 'therapeutic' range in man, the major effect of perhexilene was at the biliary pole of the hepatocyte. In 5 day pretreatment dose studies, lysosomal enzyme excretion into bile was markedly increased. In single dose studies, the increase in biliary lysosomal enzyme output partially reflected an increase in bile water production which was not seen with the 5 day pretreatment regimen. Hepatic and perfusate lysosomal enzyme activities were not affected. 4. This selective effect of perhexilene on hepatocyte-to-bile lysosomal excretion may reflect intracellular lysosomal drug localization.

Biliary copper excretion by hepatocyte lysosomes in the rat. Major excretory pathway in experimental copper overload

We investigated the hypothesis that lysosomes are the main source of biliary copper in conditions of hepatic copper overload. We used a rat model of oral copper loading and studied the relationship between the biliary output of copper and lysosomal hydrolases. Male Sprague-Dawley rats were given tap water with or without 0.125% copper acetate for up to 36 wk. Copper loading produced a 23-fold increase in the hepatic copper concentration and a 30-65% increase in hepatic lysosomal enzyme activity. Acid phosphatase histochemistry showed that copper-loaded livers contained an increased number of hepatocyte lysosomes; increased copper concentration of these organelles was confirmed directly by both x ray microanalysis and tissue fractionation. The copper-loaded rats showed a 16-fold increase in biliary copper output and a 50-300% increase in biliary lysosomal enzyme output. In the basal state, excretory profiles over time were similar for biliary outputs of lysosomal enzymes and copper in the copper-loaded animals but not in controls. After pharmacologic stimulation of lysosomal exocytosis, biliary outputs of copper and lysosomal hydrolases in the copper-loaded animals remained coupled: injection of colchicine or vinblastine produced an acute rise in the biliary output of both lysosomal enzymes and copper to 150-250% of baseline rates. After these same drugs, control animals showed only the expected increase in lysosomal enzyme output without a corresponding increase in copper output. We conclude that the hepatocyte responds to an increased copper load by sequestering excess copper in an increased number of lysosomes that then empty their contents directly into bile. The results provide direct evidence that exocytosis of lysosomal contents into biliary canaliculi is the major mechanism for biliary copper excretion in hepatic copper overload.

Hepatocytic lipoprotein receptors and intracellular lipoprotein catabolism

Hepatocytes, as the major site of synthesis and terminal catabolism of plasma lipoproteins, exert the major regulatory influence on the concentration of atherogenic lipoproteins in blood plasma and may thereby influence the rate of atherogenesis. The LDL receptor on the microvillous sinusoidal surface of hepatocytes mediates the catabolism of remnants of triglyceride-rich lipoproteins and LDL. Binding of VLDL remnants to the receptor, mediated by apo E, is of very high affinity and presumably multivalent, whereas binding of LDL, mediated by apo B-100, is monovalent and of lower affinity, accounting for the much longer residence time of the latter in the blood. The magnitude of the influx of lipoprotein particles into hepatocytic endosomal compartments dwarfs that of other macromolecules undergoing receptor-mediated endocytosis and terminal catabolism in lysosomes of these cells. The intracellular compartments and processing steps in hepatocytic lipoprotein uptake and degradation are essentially the same as those described for other ligands in the liver and other cells. Receptors with bound lipoproteins migrate into coated pits which become coated vesicles. These vesicles uncoat and fuse to form CURL vesicles and tubules near the cell surface where most receptors are recycled, presumably via receptor-rich appendages that become separated from the vesicles. CURL vesicles become mature MVBs as they migrate to the Golgi/bile canalicular pole of hepatocytes, where they fuse with putative Golgi-derived primary lysosomes and are transformed into heterophagic secondary lysosomes. MVBs also contain a receptor-rich appendage that may recycle some receptors directly to the cell surface or through adjacent Golgi compartments. Dilated ends of trans-Golgi cisternae contain nascent VLDL undergoing packaging for secretion following their synthesis and assembly in the endoplasmic reticulum. Because these "forming secretory vesicles" resemble remnant-filled MVBs, occur in a similar location in the Golgi area of hepatocytes and coisolate in centrifugal fractions of liver homogenates, there has been considerable confusion about the identity of these compartments. With the aid of specific endocytic and exocytic markers, highly purified and morphologically intact endosomal and Golgi compartments can now be obtained from rat liver homogenates. The availability of these and similar fractions of defined purity should facilitate investigation of the hepatocytic processing of endocytosed and secreted macromolecules. Although chylomicron remnants are also taken up by receptor-mediated endocytosis, the nature of the hepatocytic remnant receptor remains elusive.(ABSTRACT TRUNCATED AT 400 WORDS)

Pharmacologic perturbation of rat liver lysosomes: effects on release of lysosomal enzymes and of lipids into bile

Hepatocyte lysosomes disassemble materials derived from intracellular sources, including lipid-containing membranes, by a process called autophagy. In addition, hepatocyte lysosomes can release their contents into bile by exocytosis. Therefore, using both in vivo and in vitro models, we tested the hypothesis that acute pharmacologic induction of autophagy would modify the biliary excretion of lysosomal protein and of lipids. We treated rats with a single dose of chloroquine (10 mg/kg), glucagon (1 mg/kg), or control solutions and collected bile via bile fistulas. Both chloroquine and glucagon immediately caused a marked and parallel decrease in biliary excretion of three lysosomal enzymes, N-acetyl-beta-glucosaminidase, beta-glucuronidase, and beta-galactosidase, to 25%-30% of baseline values (p less than 0.01). This decrease was sustained for 2 h after glucagon and 4 h after chloroquine administration. In contrast, biliary lipid changes were minor: a slight lowering of biliary cholesterol secretion after chloroquine (p less than 0.05), but no change in biliary bile acids, cholesterol, and phospholipid secretion after glucagon. Changes in biliary excretion of lysosomal enzymes accompanying chloroquine and glucagon administration were associated with morphologic evidence of autophagy as assessed by electron microscopy and by increased fragility of hepatic lysosomes as assessed by latency of N-acetyl-beta-glucosaminidase. These in vivo changes in biliary lysosomal enzyme excretion induced by chloroquine and glucagon were confirmed in vitro using the isolated perfused rat liver. Thus, acute induction of autophagy results in conservation of hepatic lysosomal protein and has virtually no effect on biliary lipid excretion.

Ileal excretion of bile acids: comparison with biliary bile composition and effect of ursodeoxycholic acid treatment

The amount of bile acid excreted via an ileostomy at the end of the ileum should give an estimate of the amount of bile acid transported to the colon. In the present study, 8 patients with ileostomies at the end of the ileum but without disease or resection of the small intestine excreted 1690 +/- 205 mumol/day (mean +/- SEM) of bile acids from the ileostomies. In comparison with duodenal bile, cholic acid was increased at the end of the ileum and chenodeoxycholic acid decreased; in addition, bile acid sulfates were increased and bile acid glucuronides were decreased. When ursodeoxycholic acid, a bile acid that decreases biliary cholesterol saturation and dissolves gallstones, was administered at a dose of 500 mg to each subject, 59% +/- 8% (mean +/- SEM) of this bile acid was excreted within 24 h from the ileostomies. It is apparent from these studies that absorption of ursodeoxycholic acid from the small intestine is slower than previously anticipated and involves the entire small intestine and probably also the colon.

Identification of a phosphatidylcholine active phospholipase C in human gallbladder bile

This study describes the identification of a phospholipase C activity against phosphatidylcholine in delipidated human gallbladder bile. All biles were obtained from cholesterol gallstone patients and were negative on bacterial culture. The biliary enzyme was inhibited by EDTA and had a pH optimum of between 7-8. All of the 15 gallbladders examined contained significant phospholipase C activity (32.85 +/- 8.37 nmol/h/mg delipidated protein). The finding of a phospholipase C in gallbladder bile of patients with cholesterol gallstones may be one of the factors responsible for or related to the rapid in vitro nucleation seen in these biles.

Effect of chloroquine on biliary lipid and lysosomal enzyme output in the isolated perfused rat liver at low bile salt output rates

Chloroquine, when introduced into isolated perfused rat livers, caused a substantial output of cholesterol into bile, occurring after 30 min and peaking at 60 min, whereas the biliary output of acid phosphatase and beta-glucuronidase increased only after 90 min. The origins of this bile-salt-independent cholesterol are discussed.

Hepatic processing of transforming growth factor beta in the rat. Uptake, metabolism, and biliary excretion

Transforming growth factor beta (TGF beta), a recently discovered polypeptide, modulates growth of normal and neoplastic cells. Since little is known concerning in vivo disposition of TGF beta, we performed studies to examine the hepatic processing of biologically active 125I-TGF beta in the rat. After intravenous injection, 125I-TGF beta disappeared from the plasma with an initial t1/2 of 2.2 min; partial hepatectomy delayed the plasma disappearance of 125I-TGF beta by 80%. 60 min after intrafemoral injection, 63% of the recovered label was present in liver and/or bile; by 90 min, most of the label removed by the liver (83%) had been slowly excreted into bile. Nearly all the label in bile (96%) was soluble in trichloracetic acid and not immunoprecipitable by specific antiserum. Colchicine and vinblastine inhibited cumulative biliary excretion of label by 28 and 37%, respectively; chloroquine and leupeptin each increased the amount of label in bile that was precipitable by trichloracetic acid and that coeluted with authentic 125I-TGF beta on molecular sieve chromatography. There was efficient first-pass hepatic extraction of 125I-TGF beta (36%) in the isolated perfused rat liver, which was inhibited by unlabeled TGF beta (but not by epidermal growth factor, EGF) and by lectins in a dose-dependent manner; prolonged fasting also decreased clearance (26%). After fractionation of liver by differential or isopycnic centrifugation, radiolabel codistributed with marker enzymes for lysosomes. The results indicate rapid, extensive, inhibitable, and organ-selective extraction of TGF beta by the liver. After extraction, TGF beta undergoes efficient transhepatic transport, extensive intracellular metabolism, and slow but complete biliary excretion of its metabolites. Liver fractionation studies and pharmacologic manipulations suggest that these processes are associated with organelles that include microtubules and lysosomes. The data suggest that the liver is a major target tissue or site of metabolism for biologically active TGF beta.

Output of lysosomal contents and cholesterol into bile can be stimulated by taurodehydrocholate

Although biliary secretion of phospholipids and cholesterol is principally dependent on bile-salt secretion, at low bile-salt output secretion of some lipids continues; also the amount of cholesterol secretion is more than that of phospholipid under these conditions, but the origin of this cholesterol is not known. Taurodehydrocholate was continuously infused in isolated perfused rat livers under recycling perfusion conditions and the biliary lysosomal output and lipid output measured. The rate of acid phosphatase and beta-glucuronidase output increased 30-60 and 60-90 min respectively after liver isolation under these conditions. The rate of output of cholesterol and phospholipid increased in all the samples collected from taurodehydrocholate-infused livers. The increase in cholesterol output was approximately twice that of phospholipid output, leading to an increase in the cholesterol/phospholipid ratio in the bile.