Mechanisms of liver adaptation to prolonged selective biliary obstruction (SBO) in the rat

Hepatic vein embolization after portal vein embolization to induce additional liver hypertrophy in patients with metastatic colorectal carcinoma

OBJECTIVES

To assess the effect of salvage hepatic vein embolization (HVE) on the volume of the future liver remnant (FLR) for patients with metastatic colorectal cancer (mCRC) and inadequate hypertrophy following initial portal vein embolization (PVE).

METHODS

From April 2011 to October 2018, 9 patients with mCRC underwent HVE following PVE. The right or middle hepatic vein was embolized with coils and/or vascular plugs. Liver volumes were calculated at baseline, following PVE, and following HVE, in order to assess the hypertrophic effect of PVE and HVE on the FLR.

RESULTS

Nine patients underwent HVE (n = 3, right HVE; n = 6, middle HVE) because of inadequate FLR hypertrophy following PVE. The standardized FLR increased from 0.16 (median, range 0.08-0.24) at baseline to 0.22 (median, range 0.13-0.29) following PVE (p = 0.0005) to 0.26 (median, range 0.19-0.37) following HVE (p = 0.0050). HVE was performed 40 days (median, range 19-128 days) following PVE, and assessment of FLR hypertrophy was performed 41 days (median, range 19-92 days) following HVE. Four of nine patients underwent hepatectomy; 5 patients failed to undergo hepatectomy (n = 3, inadequate hypertrophy; n = 1, disease progression; n = 1, portal hypertension). One patient required repeat HVE due to a patent accessory vein.

CONCLUSIONS

Salvage HVE is an effective technique to induce additional FLR hypertrophy in patients with mCRC and inadequate FLR after initial PVE.

KEY POINTS

• Hepatic vein embolization is effective to induce additional liver hypertrophy in surgical patients with metastatic colorectal carcinoma and inadequate hypertrophy after portal vein embolization. • Increases in future liver remnant volume are feasible in patients who receive hepatotoxic neoadjuvant systemic therapy for metastatic colorectal carcinoma. • Sequential portal vein embolization and hepatic vein embolization can be a viable technique to induce liver hypertrophy in patients with small baseline future liver remnant volumes (< 20%).

Liver regeneration and the atrophy-hypertrophy complex

The atrophy-hypertrophy complex (AHC) refers to the controlled restoration of liver parenchyma following hepatocyte loss. Different types of injury (e.g., toxins, ischemia/reperfusion, biliary obstruction, and resection) elicit the same hypertrophic response in the remnant liver. The AHC involves complex anatomical, histological, cellular, and molecular processes. The signals responsible for these processes are both intrinsic and extrinsic to the liver and involve both physical and molecular events. In patients in whom resection of large liver malignancies would result in an inadequate functional liver remnant, preoperative portal vein embolization may increase the remnant liver sufficiently to permit aggressive resections. Through continued basic science research, the cellular mechanisms of the AHC may be maximized to permit curative resections in patients with potentially prohibitive liver function.

Repetitive short-term bile duct obstruction and relief causes reproducible and reversible bile acid regurgitation

BACKGROUND

Long-term bile duct obstruction causes sinusoidal regurgitation of bile acids, a shift in bile acid metabolism, and alterations of liver histology. In this study we investigated the regurgitation of bile acids during short-term bile duct obstruction and its reversibility and reproducibility. In addition, the biotransformation of taurodeoxycholate and its appearance in bile and perfusate effluent were studied as well as liver histology.

METHODS

Rat livers (n = 5) were perfused in vitro with 32 nmol/min/g liver taurodeoxycholate over 85 min with the bile duct being intermittently closed for 30 and 20 min, respectively.

RESULTS

Within the first 5 min after bile duct obstruction bile acids started to regurgitate to the perfusate effluent amounting to approximately 15% of hepatic uptake until the end of the perfusion period. After relief of obstruction, bile flow and biliary bile acid excretion showed an overshoot phenomenon and were almost doubled compared to preobstruction. In contrast, sinusoidal bile acid regurgitation declined. The same phenomenon was observed during the second closure/opening cycle of the bile duct. Regurgitated bile acids consisted of significantly more taurodeoxycholate metabolites (approximately 70%) than did biliary bile acids (approximately 30%). Histology of liver parenchyma was preserved.

CONCLUSIONS

During repetitive short-term bile duct obstruction bile acid regurgitation is reversible and reproducible. The absence of altered mechanical barriers suggests that specific pathways are involved in the regurgitation process of bile acids.

Experimental atrophy/hypertrophy complex (AHC) of the liver: portal vein, but not bile duct obstruction, is the main driving force for the development of AHC in the rat

BACKGROUND/AIMS

Patients with lobar or segmental impairment of bile flow or of portal venous blood flow frequently develop considerable atrophy of the area involved, followed by compensatory hypertrophy/hyperplasia of the non-affected parts. This configuration is termed atrophy/hypertrophy complex of the liver.

METHODS

In order to analyze the relative contributions of bile duct and portal vein obstruction in the pathogenesis of atrophy/hypertrophy complex, we developed a rat model with selective bile duct and/or portal vein ligation of the anterior liver lobes, representing about two thirds of the liver mass. Evolution of total body weights and weights of the different liver lobes were determined, and morphometry and functional scintigraphy (hepatoiodida scanning) were performed immediately after ligation and at 30 h, 4, 8 and 28 days postoperatively.

RESULTS

The major findings were: 28 days after biliary and/or portal ligation there was no difference between the body weights of all animals, all ligated animals having compensated an initial body weight loss. Total liver weight remained constant during the whole observation period, while atrophy of the anterior and hypertrophy/hyperplasia of the posterior lobes occurred. A significant atrophy/hypertrophy complex developed only after selective portal ligation, but not after selective biliary ligation. Morphometrically analyzed histologic changes after selective biliary ligation were reversible, whereas in portally ligated liver lobes a progressive parenchymal destruction and involution with subsequent impairment of hepatic function of the concerned lobe were observed.

CONCLUSIONS

The present findings indicate that impairment of portal venous flow is the major driving force for the development of lobar atrophy in the rat and that atrophy/hypertrophy complex can be produced in a rodent model.

Potential role of bile duct collaterals in the recovery of the biliary obstruction: experimental study in rats using microcholangiography, histology, serology and magnetic resonance imaging

Obstructive cholestasis induced in animals at the level of the lobar and common bile ducts is known to be reversible with time. This study was conducted not only to test the hypothesis that formation of bile duct collaterals is responsible for the recovery of biliary obstruction but also to assess the potential of hepatobiliary agent-enhanced magnetic resonance imaging for visualizing cholestasis. A total of 52 rats were divided into three groups with selective biliary obstruction, total biliary obstruction and sham surgery. We studied the evolution of cholestasis by correlating microcholangiographic, histological findings with the results of liver tests and hepatobiliary agent-enhanced magnetic resonance imaging. Lobar cholestasis undetected by liver tests but seen on magnetic resonance imaging as a difference between ligated and unligated lobes, occurred in 15 out of 20 rats subjected to selective biliary obstruction within 48 hr after ligation, and recovered later on as a result of the development of bile duct collaterals. Five rats failed to show local cholestasis as a result of the existence of interlobar accessory bile channels. All 18 total biliary obstruction-treated rats were cholestatic soon after ligation, as confirmed by high serum bilirubin and alkaline phosphatase levels and as documented by poor liver enhancement on magnetic resonance imaging. Cholestasis recovered within 4 wk with normalization of liver enhancement on magnetic resonance imaging as a result of the formation of bile duct collaterals (as demonstrated by microcholangiographic and histological study). Bile duct collateral formation is responsible for the recovery from obstructive cholestasis in rats. A similar mechanism might be present in conditions of bile duct obstruction without cholestasis. Hepatobiliary agent-enhanced magnetic resonance imaging is more sensitive than blood tests in detecting local cholestasis and can be used to monitor noninvasively the evolution of biliary obstruction.

Intrahepatic cholestasis: a review of biochemical-pathological mechanisms

Intrahepatic cholestasis involves impaired excretion of bile via the hepatobiliary system as a consequence of one or more lesions within the liver. In humans, intrahepatic cholestasis most often results as a side-effect of drug therapy and the clinical manifestation of this condition, jaundice, has been estimated to account for hospitalization in 2 to 5% of the cases for the general population and approaches as much as 20% in the elderly. With the aging of the population and the common occurrence of poly-drug therapy in geriatric patients, it is to be expected that jaundice due to drug-induced intrahepatic cholestasis will become even more prevalent, and accordingly the need to understand the basic mechanisms of this disease condition will become more urgent. The list of culprit agents implicated in the induction of intrahepatic cholestasis in humans is continually expanding. These include various steroid hormones, bile acids, drugs and other chemicals. Experimentally, a wide spectrum of agents has been shown to precipitate intrahepatic cholestasis. Over the years, a number of hypotheses on the biochemical and pathological mechanisms of intrahepatic cholestasis has emerged, including the following: impaired sinusoidal membrane function; interference with the distribution and binding of cytoplasmic endogenous carrier proteins; interference with mitochondrial energy supply; defects in the canalicular membrane including altered Na+/K+ -ATP-ase activity; impairment of microfilament and microtubule functions; interference with bile secretion involving bile acid dependent and independent fractions, and altered bile acid metabolism due to "hypoactive hypertrophic smooth endoplasmic reticulum". In partial agreement with the latter hypothesis, our studies indicated that impairment of the endoplasmic reticulum might represent one of the early stages in the development of intrahepatic cholestasis. Various experimental conditions that induce intrahepatic cholestasis to different degrees resulted in an interference of the synthesis of microsomal phospholipids and altered microsomal function. The conditions included the administration of various hepatotoxic compounds or steroids, pregnancy, delayed development of the endoplasmic reticulum in neonates, and dietary methyl donor or choline deficiency. This review reports the biochemical-pathological mechanisms postulated to be involved in the genesis of intrahepatic cholestasis with specific reference to experimental models of drug-induced intrahepatic cholestasis. The important practical implications of cholestasis are also briefly surveyed.

Conjugates of ursodeoxycholate protect against cytotoxicity of more hydrophobic bile salts: in vitro studies in rat hepatocytes and human erythrocytes

Intraduodenal infusion of hydrophobic bile salts to bile-fistula rats leads within hours to severe hepatocellular necrosis and cholestasis; simultaneous administration of conjugates of ursodeoxycholate, either intraduodenally or intravenously, reduces or prevents liver injury. To evaluate the short-term protective effects of ursodeoxycholate at the cellular level, we incubated primary monolayer cultures of adult rat hepatocytes or freshly isolated washed human erythrocytes for 1 to 240 min with varying defined concentrations of different bile salts in the presence or absence of ursodeoxycholate. Cytolysis was quantified by measuring the release into the medium of cytosolic lactate dehydrogenase (hepatocytes) or hemoglobin (erythrocytes). In both systems, cytolysis increased sigmoidally with increasing bile salt concentration, and the relative toxicity of different bile salts proceeded in the following order: tauroursodeoxycholate was less toxic than taurocholate, which was less toxic than taurodeoxycholate. Taurochenodeoxycholate was more toxic to erythrocytes than taurodeoxycholate; the two were equally toxic to rat hepatocytes. Unconjugated bile salts were more toxic than their conjugates. The addition of tauroursodeoxycholate to taurochenodeoxycholate or taurodeoxycholate led to time-dependent and concentration-dependent reduction or elimination of the toxicity of the more hydrophobic component. Protection was evident within minutes. With respect to hemolysis, at pH 8.5 glyco was less protective than tauroursodeoxycholate, and free ursodeoxycholate was only minimally protective. We conclude that the hepatocytotoxicity of hydrophobic bile salts at millimolar concentrations is markedly reduced in the presence of tauroursodeoxycholate. Conjugates of ursodeoxycholate also prevented disruption of erythrocytes by bile salts, suggesting that protection does not depend on liver-specific pathways of bile salt uptake, compartmentation, transport or metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)

Conjugates of ursodeoxycholate protect against cholestasis and hepatocellular necrosis caused by more hydrophobic bile salts. In vivo studies in the rat

The protective effect of ursodeoxycholate conjugates against bile salt hepatotoxicity was studied in chronic bile fistula rats. Taurochenodeoxycholate or taurodeoxycholate, infused intraduodenally at 24 or 16 mumols/100 g rat per hour, respectively, caused cholestasis and severe hepatocellular necrosis within 8 hours. In contrast, tauroursodeoxycholate or taurocholate at 48 mumols/100 g rat per hour were choleretic. Tauroursodeoxycholate was not hepatotoxic, whereas taurocholate produced moderate hepatocellular necrosis. Simultaneous infusion of tauroursodeoxycholate to rats receiving taurochenoxycholate or taurodeoxycholate preserved bile flow and ameliorated hepatic injury in a dose-dependent manner. Tauroursodeoxycholate protected equally by intravenous and intraduodenal routes. Intravenous glycoursodeoxycholate also was protective. The hydrophobicity index of infused bile salts correlated well with their toxicity. Concurrent administration of ursodeoxycholate conjugates did not reduce biliary recovery of intraduodenally infused [24-14C]-taurocholate. Biliary alkaline phosphatase secretion was stimulated by infusion of taurocholate, taurodeoxycholate, or taurochenodeoxycholate; simultaneous infusion of ursodeoxycholate conjugates failed to prevent this increase. We conclude that ursodeoxycholate counteracts hepatoxicity of more hydrophobic bile salts via a direct effect at the level of the liver.