Effects of colchicine on the hepatocellular transport of indocyanine green in the rat

Molecular changes in hepatic metabolism and transport in cirrhosis and their functional importance

Liver cirrhosis is the common endpoint of many hepatic diseases and represents a relevant risk for liver failure and hepatocellular carcinoma. The progress of liver fibrosis and cirrhosis is accompanied by deteriorating liver function. This review summarizes the regulatory and functional changes in phase I and phase II metabolic enzymes as well as transport proteins and provides an overview regarding lipid and glucose metabolism in cirrhotic patients. Interestingly, phase I enzymes are generally downregulated transcriptionally, while phase II enzymes are mostly preserved transcriptionally but are reduced in their function. Transport proteins are regulated in a specific way that resembles the molecular changes observed in obstructive cholestasis. Lipid and glucose metabolism are characterized by insulin resistance and catabolism, leading to the disturbance of energy expenditure and wasting. Possible non-invasive tests, especially breath tests, for components of liver metabolism are discussed. The heterogeneity and complexity of changes in hepatic metabolism complicate the assessment of liver function in individual patients. Additionally, studies in humans are rare, and species differences preclude the transferability of data from rodents to humans. In clinical practice, some established global scores or criteria form the basis for the functional evaluation of patients with liver cirrhosis, but difficult treatment decisions such as selection for transplantation or resection require further research regarding the application of existing non-invasive tests and the development of more specific tests.

The emerging role of transport systems in liver function tests

Liver function tests are of critical importance for the management of patients with severe or terminal liver disease. They are also used as prognostic tools for planning liver resections. In recent years many transport systems have been identified that also transport substances employed in liver function tests. Such substances include endogenous bilirubin or exogenously administered indocyanine green, agents for magnetic resonance imaging, agents for single photon emission computed tomography or agents for breath tests. The increasing functional and molecular information on the respective transport systems should improve the management and as a result the outcome of patients scheduled for liver surgery or transplantation. To achieve the latter goal, clinical studies that assess individual patients' liver function over the course of their disease with liver function tests are needed to firmly establish and validate recently introduced and novel liver function markers.

Effects of colchicine on the maximum biliary excretion of cholephilic compounds in rats

BACKGROUND AND AIM

Colchicine, an inhibitor of intracellular vesicular transport, has been reported to inhibit the biliary excretion of bile acids and organic anions, but the previous findings are controversial. In order to systematically evaluate the effect of colchicine on the biliary excretion of cholephilic compounds, we studied the effect of colchicine on the biliary excretion of substrates of various canalicular transporters, which were administered at or above the excretory maximum in rats.

METHODS

Substrates of various canalicular adenosine triphosphate-binding-cassette transporters were infused at or above the rate of maximum excretion into rats, and the effect of colchicine (0.2 mg/100 g), which was intraperitoneally injected 3 h before, on the biliary excretion was studied. Furthermore, the effect of tauroursodeoxycholate (TUDC) co-infusion on the biliary excretion of taurocholate (TC) after colchicine treatment was also studied.

RESULTS

The biliary excretion of TC and cholate administered at the rate of 1 micro mol/min/100 g was markedly inhibited by colchicine, whereas that of TUDC was not inhibited even with the infusion rate of 2 micro mol/min/100 g. TUDC co-infusion at the rate of 1 micro mol/min/100 g increased the biliary excretion of TC (1 micro mol/min/100 g), which was decreased by the colchicine pretreatment. The biliary excretory maximum of taurolithocholate-sulfate and sulfobromophthalein, substrates of the multidrug resistance protein 2, of erythromycin, a substrate of the P-glycoprotein, and of indocyanine green were not affected by colchicine.

CONCLUSIONS

The different excretory maximums of TC and TUDC and the different effect of colchicine on the excretion of these bile acids are considered to be a result of different regulatory mechanisms of vesicular targeting of the bile salt export pump to the canalicular membrane by these bile acid conjugates. The vesicular targeting of the multidrug resistance protein 2 and the P-glycoprotein to the canalicular membrane is considered to be colchicine insensitive in the absence of bile acid coadministration.

Experimental study of liver dysfunction evaluated by direct indocyanine green clearance using near infrared spectroscopy

BACKGROUND

Blood clearance of indocyanine green (ICG) is an objective test of liver function. Hepatic ICG clearance can now be measured directly using near infrared spectroscopy (NIRS). The aim of this study was to evaluate measurement of hepatic ICG clearance by NIRS in an animal model of acute hepatic dysfunction.

METHODS

New Zealand white rabbits (n = 36) underwent laparotomy for liver exposure. Hepatic blood flow and microcirculation were measured along with hepatic ICG concentration by NIRS. Hepatic ICG clearance was measured in groups of six animals after reduction of the hepatic blood flow by hepatic artery occlusion and portal vein partial occlusion, lobar ischaemia and reperfusion (I/R), colchicine administration and bile duct ligation. Hepatic ICG uptake and excretion rates were calculated by a non-linear least square curve fitting method from the ICG concentration-time curve.

RESULTS

There was a significant positive correlation between hepatic ICG rate of uptake and both hepatic blood flow and microcirculation (r = 0.79, P = 0.0001; r = 0.59, P = 0.005 respectively). I/R resulted in a significant reduction of both the rates of ICG uptake (mean(s.d.) 0. 85(0.59) min-1; P = 0.0002 versus control) and ICG excretion (0. 020(0.006) min-1; P = 0.02 versus control). Colchicine decreased the rate of hepatic ICG excretion (0.030(0.010) min-1; P = 0.02 versus control) as did bile duct ligation (0.002(0.001) min-1; P = 0.01 versus control).

CONCLUSION

Measurement of hepatic ICG clearance by NIRS is a promising technique for assessing hepatic parenchymal dysfunction and may have application in liver surgery and transplantation.

Effects of colchicine and phenothiazine on biliary excretion of organic anions in rats

Vesicular transport inhibitors have been reported to inhibit biliary excretion of some organic anions, suggesting that vesicular transport has a role in intracellular transport of these compounds. However, these inhibitors are substrates for P-glycoprotein. To examine whether P-glycoprotein has a role in canalicular transport of organic anions in addition to the canalicular multispecific organic anion transporter, we studied the effect of colchicine, a vesicular transport inhibitor, and phenothiazine to increase P-glycoprotein expression on biliary excretion of various organic anions in rats. Colchicine treatment slightly but significantly inhibited biliary excretion of indocyanine green, dinitrophenyl-glutathione and pravastatin, and had no effect on biliary excretion of sulphobromophthalein and dibromosulphophthalein. Phenothiazine treatment did not affect biliary excretion of indocyanine green and pravastatin, but it increased biliary sulphobromophthalein-glutathione excretion. In conclusion, the present findings suggest that P-glycoprotein plays an additive role on biliary excretion of some organic anions in addition to the canalicular multispecific organic anion transporter.

Role of bile salts in colchicine-induced hepatotoxicity. Implications for hepatocellular integrity and function

Colchicine, a microtubule-disrupting agent, induces hepatotoxicity in experimental animals at the doses commonly employed to explore vesicular transport in the liver. The effect of manipulations of the bile salt pool on colchicine-induced hepatotoxicity was studied in rats to determine the role of bile salts in this phenomenon. Leakage of enzyme markers of liver-cell damage into plasma and bile induced by colchicine pre-treatment displayed a sigmoidal log dose-effect curve, the half-maximal effect being reached at 0.12 micromol per 100 g body wt. Lumicolchicine, instead, showed no harmful effect. Maximal increment of biliary LDH discharge induced by colchicine was reduced from 950 +/- 124% to 216 +/- 29% by bile diversion leading to a marked reduction in bile salt output, and this parameter was further decreased to 100 +/- 13% and 157 +/- 39% by subsequent repletion of the bile salt pool with the hydrophilic bile salts taurodehydrocholate and tauroursodeoxycholate, respectively. Conversely, infusion of taurocholate into non-bile salt depleted, colchicine-treated rats led to cholestasis and massive discharge of enzymes into both blood and bile. Our data show conclusively that colchicine-induced hepatotoxicity depends on the magnitude and composition of the bile salt flux traversing the liver. They also support the view that functional integrity of vesicular mechanisms presumably involved in membrane repair are indispensable to protect the hepatocytes from the damaging effect of bile salts during normal bile formation.

Prostaglandin E1 resuscitates hepatic organic anion transport independent of its hemodynamic effect after warm ischemia

Prostaglandin E1 (PGE1) is a promising agent against ischemic liver damage, but direct evidence of the benefit to intrinsic hepatocyte function has been lacking. We demonstrate here that organic anion transport can be supported by treatment with PGE1 even at a lower dose which does not affect hepatic microcirculation in rabbits with liver inflow occlusion. Near-infrared spectroscopy was applied to directly measure hepatic clearance of indocyanine green (ICG), an exogenous organic anion, and to estimate microcirculation as measured by oxygen saturation and the content of hemoglobin in the sinusoid. Also, morphological changes in microtubules, the cytoskeleton which is known to be associated with organic anion transport, and energy status, as measured by adenine nucleotide levels, were observed. ICG removal rate in hepatocytes decreased significantly from 0.100 +/- 0.018 to 0.027 +/- 0.019 min-1 (mean +/- SD, P < 0.01) by 60-min warm ischemia, whereas the value increased to 0.082 +/- 0.030 min-1 (P < 0.05) when PGE1 was given at a dose of 0.05 microgram/kg/min. The treated livers also showed early reorganization of microtubules, as well as amelioration of ATP resynthesis after reperfusion. However, there were no significant differences in intraoperative changes in oxygen saturation and the content of hemoglobin in the sinusoid between PGE1-treated and untreated groups, indicating that the influence of PGE1 at this dose on hemodynamic changes is not considerable. These results indicate that PGE1 resuscitates an inherent hepatocyte function of organic anion transport on reperfusion after warm ischemia and suggest that the benefit could be attributed solely to direct action on hepatocytes.

Disorganization of microtubular network in postischemic liver dysfunction: its functional and morphological changes

Microtubules in the hepatocytes have been implicated to serve as lines of cytoplasmic transport of secretory materials, but are highly labile structures sensitive to pathological conditions in the cytosol. We examined the role of ischemia/reperfusion-induced cytoskeletal alterations in postischemic liver dysfunction. Rabbit livers were subjected to 60-min warm ischemia followed by 1 h or 24 h of reperfusion. Liver function was assessed by directly measuring hepatic clearance of indocyanine green (ICG), an organic anion whose cytoplasmic transport is assumed to depend on intact microtubules, using near-infrared spectroscopy. Structural alterations of microtubules were observed immunohistochemically using tissue sections stained with monoclonal anti-beta-tubulin antibody. ICG removal from hepatocytes into bile canaliculi deteriorated 1 h but reversed 24 h after reperfusion. Immunohistochemistry showed fragmentation of microtubules at the end of liver ischemia. This cytoskeletal alteration was evident 1 h but was not observed 24 h after reperfusion. Treatment with prostaglandin E1 exerted its beneficial effect by preserving ICG clearance and microtubular network. These results demonstrate that liver ischemia and subsequent reperfusion both affect the organization of microtubular network and suggest that structural disruption of microtubules may be a cause of postischemic liver dysfunction.

Glutathione S-transferases as a cefpiramide binding protein in rat liver

To clarify the intrahepatical transport mechanism of cefpiramide, we investigated effects of various agents mainly excreted into the bile by several different mechanisms on the biliary excretion of cefpiramide in rats. Sulfobromophthalein, indocyanine green, bilirubin and probenecid, known to be bound to glutathione S-transferases (GST) (EC 2.5.1.18) in liver cytosol, reduced the biliary excretion of cefpiramide, while neither secretory IgA, which is transported via vesicles in the liver, nor colchicine, which inhibits movements of vesicles, had any effect on the excretion of cefpiramide. Propranolol and metoprolol, metabolized by mixed function oxidases, had no effect on the biliary excretion of cefpiramide. In the chromatography of liver cytosol, the amount of sulfobromophthalein or benzylpenicillin bound to the GST fraction decreased in the presence of cefpiramide or probenecid. The study showed that cefpiramide was transported in the liver without relation to mixed function oxidases or vesichle-mediated transporting system, but in relation to GST which binds cefpiramide, sulfobromophthalein, benzylpenicillin and probenecid, indicating an important role of GST in the cefpiramide excretion into the bile.

Colchicine inhibits lithocholate-3-O-glucuronide-induced cholestasis in rats

BACKGROUND/AIMS

It has been suggested that vesicular transport of bile acids in hepatocytes occurs, especially at high-dose loads.

METHODS

The effect was studied of colchicine, a vesicular transport inhibitor, on lithocholate-3-O-glucuronide-induced cholestasis in rats. Cholestasis was induced by an intravenous infusion of lithocholate-3-O-glucoronide at the rate of 0.1 mumol.min-1.100 g-1 for 40 min.

RESULTS

Colchicine treatment almost completely inhibited cholestasis and increased biliary excretion of lithocholate-3-O-glucoronide, whereas lumicolchicine had no effect. Treatment with vinblastine, another vesicular transport inhibitor, also reduced the cholestasis. Colchicine did not affect biliary excretion of taurocholate infused at the rate of 0.3 mumol.min-1.100 g-1 for 40 min, but markedly inhibited its biliary excretion when infused at the rate of 1.5 mumol.min-1.100 g-1 for 40 min. Colchicine had no effect on biliary excretion of tauroursodeoxycholate (1.5 mumol.min-1.100 g-1 for 40 min), lithocholate-3-sulfate (0.3 mumol.min-1.100 g-1 for 40 min), or a trace amount of lithocholate-3-O-glucuronide.

CONCLUSIONS

These findings indicate that lithocholate-3-O-glucoronide-induced cholestasis is caused by its increased access to the vesicular transport pathway, possibly beyond the capacity of the transport by the cytosolic binders, and that the transport of lithocholate-3-O-glucoronide via the vesicular pathway induces cholestasis. Furthermore, the contribution of the vesicular pathway to hepatic transport may be different among bile acids, and lithocholate-3-O-glucuronide seems to have higher accessibility to this transport system.

Effects of phalloidin and colchicine on diethylmaleate-induced choleresis and ultrastructural appearance of rat hepatocytes

Diethylmaleate is used as a model compound whose glutathione conjugates are secreted into bile, and which induce choleresis and the formation of Golgi-derived vesicles in hepatocytes. This study was performed to test the assumption that these vesicles are involved in the bile canalicular secretion of diethylmaleate. We reasoned that phalloidin and colchicine, two drugs acting on microfilaments and microtubules, respectively, can modify the movements of diethylmaleate-induced vesicles towards the bile canaliculus. Phalloidin induced the formation of a thick microfilamentous network around the bile canalicular plasma membrane domain. A significant decrease in diethylmaleate-stimulated choleresis was observed, associated with a striking accumulation of pericanalicular vesicles, which were confirmed by morphometric analysis. In contrast, in rats pretreated with colchicine, after diethylmaleate administration, only a few vesicles were observed around the bile canaliculus, while diethylmaleate-induced choleresis also decreased. These results suggest that: a) the thick microfilament network induced by phalloidin prevents diethylmaleate-associated vesicles reaching the bile canalicular plasma membrane; and b) colchicine produces a dispersion of these vesicles in the cytoplasm of hepatocytes by inhibiting the polymerization of microtubules. These observations support a role of vesicles in the transport of diethylmaleate by hepatocyte into bile, and are consistent with the existence of a vesicular pathway for the biliary secretion of diethylmaleate and possibly other organic anions.

The role of the canalicular multispecific organic anion transporter in the disposal of endo- and xenobiotics

Bile is an important excretory route for the elimination of amphiphilic organic anions, and hepatocytes are the primary secretory units of bile formation. The hepatocytic basolateral and canalicular membranes are equipped with various carrier proteins. Transport across the canalicular membrane represents a major concentrative step. Various ATP-dependent transporters have been identified, such as a multispecific organic anion transporter (canalicular multispecific organic ion transporter, cMOAT), a bile acid transporter and several P-glycoproteins. TR- rats, which lack cMOAT activity, have been valuable in defining the substrate specificity of cMOAT. A wide range of glucuronide-, glutathione- and sulfate-conjugates are transported by this system.

Inhibition by colchicine of biliary secretion of diethylmaleate in the rat: evidence for microtubule-dependent vesicular transport

It has been proposed that a microtubule-dependent transport of vesicles derived from the Golgi apparatus may play a role in biliary secretion of bile salts and other cholephilic anions. To test this hypothesis, we examined the influence of colchicine and vinblastine, two microtubule inhibitors, on diethylmaleate-induced bile flow and on the biliary secretion of diethylmaleate, an organic anion whose glutathione conjugates may be secreted into bile through the Golgi apparatus and Golgi-derived vesicles. Rats were pretreated with colchicine or vinblastine, and diethylmaleate was injected intraperitoneally at doses of 28 to 400 mumol/100 gm body wt. Basal bile flow was unaffected by colchicine or vinblastine. In contrast, diethylmaleate-induced bile flow and the secretion into bile of diethylmaleate conjugates (estimated by the cation-anion gap in bile) were significantly lower in colchicine-treated and vinblastine-treated animals than in controls. Diethylmaleate-induced bile flow was reduced in proportion to diethylmaleate conjugate secretion. A linear relationship was seen between bile flow and biliary output of diethylmaleate conjugates: this relationship was similar in colchicine-treated or vinblastine-treated animals and in controls. At electron microscopy, diethylmaleate had induced distension of the Golgi saccules of the hepatocytes. In conclusion, colchicine and vinblastine inhibited the secretion into bile of diethylmaleate conjugates and diethylmaleate-induced bile flow. These results support the view that microtubule-dependent transport of Golgi-derived vesicles is involved in the biliary secretion of diethylmaleate and, perhaps, other cholephilic organic anions.

Hepatocellular dysfunction occurs early after hemorrhage and persists despite fluid resuscitation

The liver is a major organ involved in multiple organ failure (MOF) following hemorrhage and trauma. However, it is not known if active hepatocellular membrane transport, measured by in vivo indocyanine green (ICG) clearance, is depressed after hemorrhage and if it persists after resuscitation. To study this, rats were bled to and maintained at a mean BP of 40 mm Hg until 40% of maximum bleedout (MB) volume was returned in the form of Ringer's lactate (RL). The rats were then resuscitated with 2X or 3X the volume of MB with RL and hepatocellular function was determined at various intervals. ICG, two to four doses (0.167-1.667 mg/kg BW), was given intravenously and [ICG] was continuously recorded without the need of blood sampling, using an in vivo hemoreflectometer with computer-assisted data acquisition. Initial velocity of clearance (V0) was calculated from [ICG] vs time (t) according to [ICG] = e (a + bt + ct 2), where eab is V0. Maximal velocity of clearance (Vmax) and Km, a kinetic constant representing the efficiency of the active transport process, were determined from the Lineweaver-Burk plot. The results indicate that Vmax decreased by 66% at MB and remained depressed despite fluid resuscitation. Km, decreased by 58% at MB, returned to prehemorrhage level after 3X RL but was not maintained and it decreased by 60% at 4 hr after resuscitation. This in vivo study demonstrates that active hepatocellular function is significantly depressed early after hemorrhage and persists despite resuscitation with RL and may form the basis of the MOF observed after severe and prolonged hemorrhage.

Role of intracellular organelles in the hepatic transport of bile acids

The intracellular events associated with the vectorial transport of bile acids by the hepatocytes from the sinusoidal pole to the canalicular pole are reviewed. Binding to cytosolic proteins occurs. The role of this binding is to prevent efflux from the cytosol back into the blood. There is evidence from electron microscopy, from autoradiography and from immunoperoxidase observations that bile acids interact with the endoplasmic reticulum and the Golgi apparatus. There is also evidence that a carrier system or taurocholate exists on the Golgi membrane. We propose that a vesicular pathway involving the Golgi apparatus and dependent on the integrity of microtubules may play a role in bile acid transport in the cell. Inhibition of bile acid transport by microtubule poisons is consistent with this hypothesis. Finally, monohydroxylated, cholestatic bile acids such as lithocholate and taurolithocholate interact with the endoplasmic reticulum. This interaction results in a depletion of the endoplasmic reticulum calcium stores and an increase in intracellular ionized calcium. The relationship of this novel effect of bile acids to their cholestatic properties remains to be elucidated.

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.