The effect of colchicine on the development of lithocholic acid-induced cholestasis. A study of the role of microtubules in intracellular cholesterol transport

Bile acid bio-nanoencapsulation improved drug targeted-delivery and pharmacological effects via cellular flux: 6-months diabetes preclinical study

The antilipidemic drug, probucol (PB), has demonstrated potential applications in Type 2 diabetes (T2D) through its protective effects on pancreatic β-cells. PB has poor solubility and bioavailability, and despite attempts to improve its oral delivery, none has shown dramatic improvements in absorption or antidiabetic effects. Preliminary data has shown potential benefits from bile acid co-encapsulation with PB. One bile acid has shown best potential improvement of PB oral delivery (ursodeoxycholic acid, UDCA). This study aimed to examine PB and UDCA microcapsules (with UDCA microcapsules serving as control) in terms of the microcapsules’ morphology, biological effects ex vivo, and their hypoglycemic and antilipidemic and anti-inflammatory effects in vivo. PBUDCA and UDCA microcapsules were examined in vitro (formulation studies), ex vivo and in vivo. PBUDCA microcapsules exerted positive effects on β-cells viability at hyperglycemic state, and brought about hypoglycemic and anti-inflammatory effects on the prediabetic mice. In conclusion, PBUDCA co-encapsulation have showed beneficial therapeutic impact of dual antioxidant-bile acid effects in diabetes treatment.

Abcg5/Abcg8-independent pathways contribute to hepatobiliary cholesterol secretion in mice

The ATP-binding cassette (ABC) half-transporters ABCG5 and ABCG8 heterodimerize into a functional complex that mediates the secretion of plant sterols and cholesterol by hepatocytes into bile and their apical efflux from enterocytes. We addressed the putative rate-controlling role of Abcg5/Abcg8 in hepatobiliary cholesterol excretion in mice during (maximal) stimulation of this process. Despite similar bile salt (BS) excretion rates, basal total sterol and phospholipid (PL) output rates were reduced by 82% and 35%, respectively, in chow-fed Abcg5(-/-) mice compared with wild-type mice. When mice were infused with the hydrophilic BS tauroursodeoxycholate, similar relative increases in bile flow, BS output, PL output, and total sterol output were observed in wild-type, Abcg5(+/-), and Abcg5(-/-) mice. Maximal cholesterol and PL output rates in Abcg5(-/-) mice were only 15% and 69%, respectively, of wild-type values. An infusion of increasing amounts of the hydrophobic BS taurodeoxycholate increased cholesterol excretion by 3.0- and 2.4-fold in wild-type and Abcg5(-/-) mice but rapidly induced cholestasis in Abcg5(-/-) mice. Treatment with the liver X receptor (LXR) agonist T0901317 increased the maximal sterol excretion capacity in wild-type mice (fourfold), concomitant with the induction of Abcg5/Abcg8 expression, but not in Abcg5(-/-) mice. In a separate study, mice were fed chow containing 1% (wt/wt) cholesterol. As expected, hepatic expression of Abcg5 and Abcg8 was strongly induced (fivefold and fourfold) in wild-type but not LXR-alpha-deficient (Lxra(-/-)) mice. Surprisingly, hepatobiliary cholesterol excretion was increased to the same extent, i.e., 2.2-fold in wild-type mice and 2.0-fold in Lxra(-/-) mice, upon cholesterol feeding. Our data confirm that Abcg5, as part of the Abcg5/Abcg8 heterodimer, strongly controls hepatobiliary cholesterol secretion in mice. However, our data demonstrate that Abcg5/Abcg8 heterodimer-independent, inducible routes exist that can significantly contribute to total hepatobiliary cholesterol output.

Role of microtubules in estradiol-17beta-D-glucuronide-induced alteration of canalicular Mrp2 localization and activity

Estradiol-17beta-D-glucuronide (E2-17G) induces a marked but reversible inhibition of bile flow in the rat together with endocytic retrieval of multidrug resistance-associated protein 2 (Mrp2) from the canalicular membrane to intracellular structures. We analyzed the effect of pretreatment (100 min) with the microtubule inhibitor colchicine or lumicholchicine, its inactive isomer (1 micromol/kg iv), on changes in bile flow and localization and function of Mrp2 induced by E2-17G (15 micromol/kg iv). Bile flow and biliary excretion of bilirubin, an endogenous Mrp2 substrate, were measured throughout, whereas Mrp2 localization was examined at 20 and 120 min after E2-17G by confocal immunofluorescence microscopy and Western analysis. Colchicine pretreatment alone did not affect bile flow or Mrp2 localization and activity over the short time scale examined (3-4 h). Administration of E2-17G to colchicine-pretreated rats induced a marked decrease (85%) in bile flow and biliary excretion of bilirubin as well as internalization of Mrp2 at 20 min. These alterations were of a similar magnitude as in rats pretreated with lumicolchicine followed by E2-17G. Bile flow and Mrp2 localization and activity were restored to control levels within 120 min of E2-17G in animals pretreated with lumicolchicine. In contrast, in colchicine-pretreated rats followed by E2-17G, bile flow and Mrp2 activity remained significantly inhibited by 60%, and confocal and Western studies revealed sustained internalization of Mrp2 120 min after E2-17G. We conclude that recovery from E2-17G cholestasis, associated with exocytic insertion of Mrp2 in the canalicular membrane, but not its initial E2-17G-induced endocytosis, is a microtubule-dependent process.

Taurolithocholate can inhibit the biliary discharge of lysosomes in the rat

The natural bile salt taurolithocholate (TLC) impairs the biliary excretion of lipids and proteins, which are known to reach the canaliculus via vesicles. In this study we examined whether these observations could be extended to the exocytic discharge of lysosomal contents into bile. The single intravenous injection of a cholestatic dose of TLC, 3 micromol/100 g body wt., markedly inhibited the biliary excretion of the lysosomal enzymes acid phosphatase and beta-glucuronidase, despite the excretion of bile salts being normalized after a transient diminution. Under such a condition, TLC did not affect the normal transport to and the processing in lysosomes of the exogenously administered [14C]sucrose-labeled horseradish peroxidase. However, the biliary excretion of the radioactive lysosomal metabolites of the protein was significantly reduced. The results indicate that TLC can inhibit the biliary discharge of lysosomes in the rat without altering the functional integrity of these organelles. Possible explanations for these findings are discussed.

Pathogenesis of lithocholate-induced intrahepatic cholestasis: role of glucuronidation and hydroxylation of lithocholate

It has been shown that lithocholic glucuronide is more cholestatic than lithocholic acid (LCA), as well as its taurine and glycine conjugates. Furthermore, LCA hydroxylation is thought to be a major detoxifying mechanism. Therefore, the role of LCA glucuronidation and hydroxylation was investigated during the development of LCA-induced cholestasis and recovery from it. Male rats received a bolus intravenous injection of [14C]LCA (12 mumol/100 g body weight) and bile samples were collected every 30 min for 5 h. Bile flow (BF) was reduced immediately after LCA injection, dropping to 40% of basal BF at 60 min. It then started to increase, reaching normal bile flow values at 3.5 h. Morphologically, canalicular lesions were dominant at 60 min and virtually absent at 2 h. At 60 min (maximal cholestasis), 30% of the LCA injected was secreted in bile, 20% was found in plasma while the other 50% was recovered in the liver and distributed mainly in plasma membranes, microsomes and cytosol. At the end of the experiment (normal BF), 20% of the LCA injected was still in the liver but was present mainly in the cytosol. In bile, within 30 min after injection, 46% of the LCA secreted was lithocholic glucuronide, 24% was conjugated with taurine and glycine, and 21% was in the form of hydroxylated bile acids. During the recovery period, lithocholic glucuronide secretion decreased to 18-25%. Taurine and glycine conjugate secretion increased to a maximum of 43% at 60 min, after which it was reduced to 21-28%. In contrast, hydroxylated metabolites were elevated during the recovery periods, reaching a maximum (45%) at 120 min and remaining constant thereafter. These results suggest that: (i) LCA binding to plasma membranes and microsomes appeared to correlate with the development of cholestasis; (ii) LCA glucuronidation may initiate and/or contribute to LCA-induced cholestasis; and (iii) hydroxylation predominates during recovery from cholestasis.

Taurolithocholate-induced inhibition of biliary lipid and protein excretion in the rat

Taurolithocholate (TLC), a natural bile salt, induces selective impairment on canalicular membrane of the hepatocyte, which seems to be a major determinant of its cholestatic effect in experimental animals. In order to extend existing studies about the effects of TLC on bile secretion, we examined in TLC-treated rats the biliary excretion of compounds that are transported to canalicular membrane via vesicles, such as lipids and proteins. The single intravenous injection of TLC (3 mumol/100 g body wt.) inhibited transiently the biliary bile salt excretion, while the biliary excretion of lipids (i.e., cholesterol and phospholipids) and proteins remained inhibited even though the biliary excretion and composition of bile salts were normalized. Under such a condition, TLC also inhibited the transcellular vesicular pathway to the exogenous protein horseradish peroxidase entry into bile, without altering the paracellular biliary access of the protein. The hepatic uptake of horseradish peroxidase was unaffected by TLC-treatment. The results indicate that TLC can inhibit the biliary excretion of compounds that reach the canaliculus via a vesicular pathway, such as lipids and proteins, by a mechanism not related to a defective bile salt excretion. Possible explanations for these findings are discussed.

Effects of partial hepatectomy on microtubules and hepatocellular transport of indocyanine green in rats

The effects of partial hepatectomy on plasma disappearance and biliary excretion of indocyanine green (ICG) have been studied in rats and correlated with morphometric changes of hepatocellular microtubules. The plasma disappearance rate of ICG was in good accord with recovery of liver weight after partial hepatectomy. Biliary excretion of ICG per 100 g liver significantly increased between 3 h and 7 days postoperatively. Colchicine significantly reduced plasma disappearance and biliary excretion of ICG, with no reduction in bile flow, in both intact and hepatectomized rats. Morphometrically, microtubules significantly increased from 3 h following partial hepatectomy and reached a maximum at 24 h with a gradual return to preoperative values at 5 days. These observations suggest that the increased hepatocellular transport of ICG after partial hepatectomy is related to an increase in the number of microtubules.

Colchicine blocks the action of parathyroid hormone but not nicotinamide on renal phosphate transport

Nicotinamide, like parathyroid hormone, is a rapidly acting specific inhibitor of Na+-dependent transport of phosphate (Pi) across the brush-border membrane of the proximal tubule of the mammalian kidney. Pretreatment of rats with colchicine (0.7 mg/kg body weight) for 1 h led to a significantly diminished phosphaturic response to parathyroid hormone (synthetic 1-34 fragment, 4 micrograms/kg). In contrast, the same dose of colchicine had no effect on the renal response to nicotinamide (1.0 g/kg), measured both as the change in urinary Pi excretion and as Na+-dependent Pi uptake by isolated brush-border membrane vesicles. These data suggest indirectly that the intracellular mechanism that mediates the inhibitory effects of nicotinamide on renal Pi transport does not require intact microtubules.

Dietary restriction influence bile formation in aging rats

Food restriction is one of the most effective interventions which increases the survival of rodents and influences a variety of physiologic and pathologic processes. Thus, we examined whether life-long caloric restriction would influence bile formation, one of the important hepatic functions. Female Sprague Dawley rats were subjected soon after weaning to a restricted diet (60% of the diet consumed by the rats fed ad libitum) and bile formation determined at 3.5, 12 and 24 months of age. Rats had their bile ducts cannulated under nembutal anesthesia and bile collected at 10 min. intervals. Bile flow rate decreased 35% between 3.5 and 24 months of age. This decrease was associated with a reduction of the bile acid dependent fraction of bile flow (BADF) up to 12 months of age, thereafter the bile acid independent fraction (BAIF) also decreased. Phospholipid and cholesterol secretion rates increased with age, but did not correlate with bile acid secretion. In rats fed the restricted diet, bile flow was about 20% higher at 3-5 months of age when compared with the ad libitum fed group. This bile flow rate remained constant until 24 months of age. The increased bile flow was attributed to higher BADF and BAIF. The phospholipid and cholesterol secretion followed that of bile acids. It thus appears that dietary restriction exerts a beneficial effect on the age related decline in bile formation.