Reduced activity of the electron transport chain in liver mitochondria isolated from rats with secondary biliary cirrhosis

Rats with Long-Term Cholestasis Have a Decreased Cytosolic but Maintained Mitochondrial Hepatic CoA Pool

Previous studies showed that rats with long-term bile duct ligation have reduced coenzyme A stores per g of liver but maintained mitochondrial CoA stores. Based on these observations, we determined the CoA pool in the liver homogenate, liver mitochondria, and liver cytosol of rats with bile duct ligation for 4 weeks (BDL rats, n = 9) and sham-operated control rats (CON rats, n = 5). In addition, we tested the cytosolic and mitochondrial CoA pools by assessing the metabolism of sulfamethoxazole and benzoate in vivo and of palmitate in vitro. The hepatic total CoA content was lower in BDL than CON rats (mean ± SEM; 128 ± 5 vs. 210 ± 9 nmol/g), affecting all subfractions equally (free CoA (CoASH), short- and long-chain acyl-CoA). In BDL rats, the hepatic mitochondrial CoA pool was maintained, and the cytosolic pool was reduced (23.0 ± 0.9 vs. 84.6 ± 3.7 nmol/g liver; CoA subfractions were affected equally). The urinary excretion of hippurate after i.p. benzoate administration (measuring mitochondrial benzoate activation) was reduced in BDL rats (23.0 ± 0.9 vs. 48.6 ± 3.7% of dose/24 h), whereas the urinary elimination of N-acetylsulfamethoxazole after i.p. sulfamethoxazole administration (measuring the cytosolic acetyl-CoA pool) was maintained (36.6 ± 3.0 vs. 35.1 ± 2.5% of dose/24 h BDL vs. CON rats). Palmitate activation was impaired in the liver homogenate of BDL rats but the cytosolic CoASH concentration was not limiting. In conclusion, BDL rats have reduced hepatocellular cytosolic CoA stores, but this reduction does not limit sulfamethoxazole N-acetylation or palmitate activation. The hepatocellular mitochondrial CoA pool is maintained in BDL rats. Impaired hippurate formation in BDL rats is explained best by mitochondrial dysfunction.

Sesamol Supplementation Mitigates Isoproterenol-Induced Cardiac Toxicity in Rats by Stabilizing Cardiac Mitochondrial and Lysosomal Enzymes

The current investigation was intended to evaluate the antimyocardial ischemic effects of sesamol on lactate dehydrogenase (LDH) isoenzymes, DNA damage, and mitochondrial and lysosomal enzyme activities in isoproterenol (ISO)-induced myocardial infarction (MI) in male albino Wistar strain rats. Rats that received ISO (85 mg/kg body weight (B.W) subcutaneously) for the first 2 consecutive days showed significant reduction in the activities of tricarboxylic acid (TCA) cycle enzymes (isocitrate dehydrogenase, α-ketoglutarate dehydrogenase, malate dehydrogenase, and succinate dehydrogenase) and respiratory chain enzymes (cytochrome c oxidase and nicotinamide adenine dinucleotide hydrogen (NADH) dehydrogenase) in the heart mitochondria. The activities of the lysosomal enzymes (α-and β-glucosidases, α and β-galactosidases, β-glucuronidase and β-N-acetyl glucosaminidase and cathepsin-B and cathepsin-D) were increased significantly in the heart homogenate of ISO-induced MI rats. ISO injection also increased the % of tail DNA, tail length, and tail moment and decreased the % of head DNA. Pretreatment with sesamol (50 mg/kg B.W) every day for a period of 9 days prevented the above abnormalities induced by ISO. In conclusion, it can be inferred that administration of sesamol has a potent beneficial role against ISO-induced damage to the mitochondria, lysosomes, and DNA, thereby preventing MI.

Single Cell Gene Expression Analysis in a 3D Microtissue Liver Model Reveals Cell Type-Specific Responses to Pro-Fibrotic TGF-β1 Stimulation

3D cell culture systems are widely used to study disease mechanisms and therapeutic interventions. Multicellular liver microtissues (MTs) comprising HepaRG, hTERT-HSC and THP-1 maintain multicellular interactions and physiological properties required to mimic liver fibrosis. However, the inherent complexity of multicellular 3D-systems often hinders the discrimination of cell type specific responses. Here, we aimed at applying single cell sequencing (scRNA-seq) to discern the molecular responses of cells involved in the development of fibrosis elicited by TGF-β1. To obtain single cell suspensions from the MTs, an enzymatic dissociation method was optimized. Isolated cells showed good viability, could be re-plated and cultured in 2D, and expressed specific markers determined by scRNA-seq, qRT-PCR, ELISA and immunostaining. The three cell populations were successfully clustered using supervised and unsupervised methods based on scRNA-seq data. TGF-β1 led to a fibrotic phenotype in the MTs, detected as decreased albumin and increased αSMA expression. Cell-type specific responses to the treatment were identified for each of the three cell types. They included HepaRG damage characterized by a decrease in cellular metabolism, prototypical inflammatory responses in THP-1s and extracellular matrix remodeling in hTERT-HSCs. Furthermore, we identified novel cell-specific putative fibrosis markers in hTERT-HSC (COL15A1), and THP-1 (ALOX5AP and LAPTM5).

Metabolic Shifts as the Hallmark of Most Common Diseases: The Quest for the Underlying Unity

A hyper-specialization characterizes modern medicine with the consequence of classifying the various diseases of the body into unrelated categories. Such a broad diversification of medicine goes in the opposite direction of physics, which eagerly looks for unification. We argue that unification should also apply to medicine. In accordance with the second principle of thermodynamics, the cell must release its entropy either in the form of heat (catabolism) or biomass (anabolism). There is a decreased flow of entropy outside the body due to an age-related reduction in mitochondrial entropy yield resulting in increased release of entropy in the form of biomass. This shift toward anabolism has been known in oncology as Warburg-effect. The shift toward anabolism has been reported in most diseases. This quest for a single framework is reinforced by the fact that inflammation (also called the immune response) is involved in nearly every disease. This strongly suggests that despite their apparent disparity, there is an underlying unity in the diseases. This also offers guidelines for the repurposing of old drugs.

Impact of Parenteral Lipid Emulsion Components on Cholestatic Liver Disease in Neonates

Total parenteral nutrition (TPN) is a life-saving intervention for infants that are unable to feed by mouth. Infants that remain on TPN for extended periods of time are at risk for the development of liver injury in the form of parenteral nutrition associated cholestasis (PNAC). Current research suggests the lipid component of TPN is a factor in the development of PNAC. Most notably, the fatty acid composition, vitamin E concentration, and presence of phytosterols are believed key mediators of lipid emulsion driven PNAC development. New emulsions comprised of fish oil and medium chain triglycerides show promise for reducing the incidence of PNAC in infants. In this review we will cover the current clinical studies on the benefit of fish oil and medium chain triglyceride containing lipid emulsions on the development of PNAC, the current constituents of lipid emulsions that may modulate the prevalence of PNAC, and potential new supplements to TPN to further reduce the incidence of PNAC.

Maternal and fetal serum levels of caspase-cleaved fragments of cytokeratin-18 in intrahepatic cholestasis of pregnancy

OBJECTIVE

We aimed to investigate the relationship between intrahepatic cholestasis of pregnancy (ICP) and caspase-cleaved fragments of cytokeratin-18, also referred to as M30, a marker of apoptosis.

METHODS

In this case-control study, maternal and umbilical cord blood venous samples were obtained from 21 pregnant women with ICP and 22 healthy pregnant women as a control group. M30 levels were compared among the groups.

RESULTS

Maternal serum M30 levels were significantly higher in the severe ICP group than in the control (p < 0.001) and mild ICP groups (p = 0.006). The values were comparable between the mild ICP and the control groups. The umbilical cord serum M30 levels were also significantly greater in the severe ICP group than in the control group (p = 0.001).

CONCLUSIONS

Changes in M30 levels, as an apoptosis marker, may shed light on the pathogenesis of ICP. Explaining the mechanisms of bile acid (BA)-induced hepatocyte injury may contribute further therapeutic strategies for the treatment of human cholestatic diseases.

A switch in the source of ATP production and a loss in capacity to perform glycolysis are hallmarks of hepatocyte failure in advance liver disease

BACKGROUND & AIMS

The cause of hepatic failure in the terminal stages of chronic injury is unknown. Cellular metabolic adaptations in response to the microenvironment have been implicated in cellular breakdown.

METHODS

To address the role of energy metabolism in this process we studied mitochondrial number, respiration, and functional reserve, as well as cellular adenosine-5'-triphosphate (ATP) production, glycolytic flux, and expression of glycolysis related genes in isolated hepatocytes from early and terminal stages of cirrhosis using a model that produces hepatic failure from irreversible cirrhosis in rats. To study the clinical relevance of energy metabolism in terminal stages of chronic liver failure, we analyzed glycolysis and energy metabolism related gene expression in liver tissue from patients at different stages of chronic liver failure according to Child-Pugh classification. Additionally, to determine whether the expression of these genes in early-stage cirrhosis (Child-Pugh Class A) is related to patient outcome, we performed network analysis of publicly available microarray data obtained from biopsies of 216 patients with hepatitis C-related Child-Pugh A cirrhosis who were prospectively followed up for a median of 10years.

RESULTS

In the early phase of cirrhosis, mitochondrial function and ATP generation are maintained by increasing energy production from glycolytic flux as production from oxidative phosphorylation falls. At the terminal stage of hepatic injury, mitochondria respiration and ATP production are significantly compromised, as the hepatocytes are unable to sustain the increased demand for high levels of ATP generation from glycolysis. This impairment corresponds to a decrease in glucose-6-phosphatase catalytic subunit and phosphoglucomutase 1. Similar decreased gene expression was observed in liver tissue from patients at different stages of chronic liver injury. Further, unbiased network analysis of microarray data revealed that expression of these genes was down regulated in the group of patients with poor outcome.

CONCLUSIONS

An adaptive metabolic shift, from generating energy predominantly from oxidative phosphorylation to glycolysis, allows maintenance of energy homeostasis during early stages of liver injury, but leads to hepatocyte dysfunction during terminal stages of chronic liver disease because hepatocytes are unable to sustain high levels of energy production from glycolysis.

Modulation of mitochondrial glutathione status and cellular energetics in primary cultures of proximal tubular cells from remnant kidney of uninephrectomized rats

Compensatory renal hypertrophy following reduction in renal mass leads to a hypermetabolic state and increases in basal mitochondrial oxidative stress and susceptibility to several nephrotoxicants. Previous studies provide conflicting data on whether renal mitochondria after reduction in renal mass undergo proliferation or hypertrophy or both. In the present study, our goal was to determine whether mitochondria of hypertrophied kidney undergo hypertrophy or proliferation after uninephrectomy using the uninephrectomized (NPX) rat model. Renal proximal tubular (PT) cells from NPX rats exhibited increased mitochondrial density, membrane potential and protein but no significant difference in mitochondrial DNA, as compared to PT cells from control rats. Our previous studies showed that overexpression of two mitochondrial anion transporters, the dicarboxylate (DIC, Slc25a10) and oxoglutarate (OGC, Slc25a11) carriers, in NRK-52E cells resulted in increased mitochondrial uptake of glutathione (GSH) and protection from chemically induced apoptosis. In the present study, we overexpressed DIC- and OGC-cDNA plasmids to assess their function in renal PT cells after compensatory renal hypertrophy. PT cells from NPX rats that were first preincubated with GSH were protected from cytotoxicity due to the mitochondrial inhibitor antimycin A by overexpression of either of the two mitochondrial GSH transporters. Our present results provide further evidence that compensatory renal hypertrophy is associated primarily with mitochondrial hypertrophy and hyperpolarization and that manipulation of mitochondrial GSH transporters in PT cells of hypertrophied kidney can alter susceptibility to chemically induced injury under appropriate conditions and may be a suitable therapeutic approach.

Influence of biliary anastomosis on recovery from secondary biliary cirrhosis

OBJECTIVE

The influence of choledochoduodenostomy and choledochojejunostomy on the repair of hepatic lesions secondary to biliary obstruction is not well known. The aim of the present study was to compare the effects of choledochoduodenostomy and choledochojejunostomy on the recovery of these lesions in rats with biliary obstruction.

METHODS

Rats subjected to 4 weeks of biliary obstruction underwent choledochoduodenostomy (n=10) or choledochojejunostomy (n=10). The following variables were measured: total bilirubin, alkaline phosphatase, aminotransferases, and albumin. Hepatic mitochondrial energy metabolism was evaluated by calculating the respiratory control ratio and the oxidative phosphorylation index. Hepatic morphometry was used to estimate the mass of the hepatocytes, bile ducts, and fibrosis, as well as the hepatic stellate cell count.

RESULTS

After choledochoduodenostomy and choledochojejunostomy, there was a regression in cholestasis and a reduction in the oxidative phosphorylation index. However, the total bilirubin, alkaline phosphatase, albumin, and respiratory control ratio values improved only after choledochojejunostomy. The mass of the liver, spleen, and fibrosis was reduced after both choledochoduodenostomy and choledochojejunostomy, but the number of hepatic stellate cells increased. After choledochojejunostomy, the hepatic mass recovered completely, and the spleen mass was significantly reduced compared with that after choledochoduodenostomy. After both choledochoduodenostomy and choledochojejunostomy, enterobiliary reflux, biliary contamination, and an exacerbation in hepatic inflammation developed.

CONCLUSION

Choledochojejunostomy was more effective than choledochoduodenostomy, but both techniques induced enterobiliary reflux and biliary contamination, which may explain the maintenance of hepatic alterations, especially after choledochoduodenostomy.

Mitochondrial roles and cytoprotection in chronic liver injury

The liver is one of the richest organs in terms of number and density of mitochondria. Most chronic liver diseases are associated with the accumulation of damaged mitochondria. Hepatic mitochondria have unique features compared to other organs' mitochondria, since they are the hub that integrates hepatic metabolism of carbohydrates, lipids and proteins. Mitochondria are also essential in hepatocyte survival as mediator of apoptosis and necrosis. Hepatocytes have developed different mechanisms to keep mitochondrial integrity or to prevent the effects of mitochondrial lesions, in particular regulating organelle biogenesis and degradation. In this paper, we will focus on the role of mitochondria in liver physiology, such as hepatic metabolism, reactive oxygen species homeostasis and cell survival. We will also focus on chronic liver pathologies, especially those linked to alcohol, virus, drugs or metabolic syndrome and we will discuss how mitochondria could provide a promising therapeutic target in these contexts.

Redox control of liver function in health and disease

Reactive oxygen species (ROS), a heterogeneous population of biologically active intermediates, are generated as by-products of the aerobic metabolism and exhibit a dual role in biology. When produced in controlled conditions and in limited quantities, ROS may function as signaling intermediates, contributing to critical cellular functions such as proliferation, differentiation, and cell survival. However, ROS overgeneration and, particularly, the formation of specific reactive species, inflicts cell death and tissue damage by targeting vital cellular components such as DNA, lipids, and proteins, thus arising as key players in disease pathogenesis. Given the predominant role of hepatocytes in biotransformation and metabolism of xenobiotics, ROS production constitutes an important burden in liver physiology and pathophysiology and hence in the progression of liver diseases. Despite the recognized role of ROS in disease pathogenesis, the efficacy of antioxidants as therapeutics has been limited. A better understanding of the mechanisms, nature, and location of ROS generation, as well as the optimization of cellular defense strategies, may pave the way for a brighter future for antioxidants and ROS scavengers in the therapy of liver diseases.

Mitochondrial glutathione, a key survival antioxidant

Mitochondria are the primary intracellular site of oxygen consumption and the major source of reactive oxygen species (ROS), most of them originating from the mitochondrial respiratory chain. Among the arsenal of antioxidants and detoxifying enzymes existing in mitochondria, mitochondrial glutathione (mGSH) emerges as the main line of defense for the maintenance of the appropriate mitochondrial redox environment to avoid or repair oxidative modifications leading to mitochondrial dysfunction and cell death. mGSH importance is based not only on its abundance, but also on its versatility to counteract hydrogen peroxide, lipid hydroperoxides, or xenobiotics, mainly as a cofactor of enzymes such as glutathione peroxidase or glutathione-S-transferase (GST). Many death-inducing stimuli interact with mitochondria, causing oxidative stress; in addition, numerous pathologies are characterized by a consistent decrease in mGSH levels, which may sensitize to additional insults. From the evaluation of mGSH influence on different pathologic settings such as hypoxia, ischemia/reperfusion injury, aging, liver diseases, and neurologic disorders, it is becoming evident that it has an important role in the pathophysiology and biomedical strategies aimed to boost mGSH levels.

Characterization of enantiomeric bile acid-induced apoptosis in colon cancer cell lines

Bile acids are steroid detergents that are toxic to mammalian cells at high concentrations; increased exposure to these steroids is pertinent in the pathogenesis of cholestatic disease and colon cancer. Understanding the mechanisms of bile acid toxicity and apoptosis, which could include nonspecific detergent effects and/or specific receptor activation, has potential therapeutic significance. In this report we investigate the ability of synthetic enantiomers of lithocholic acid (ent-LCA), chenodeoxycholic acid (ent-CDCA), and deoxycholic acid (ent-DCA) to induce toxicity and apoptosis in HT-29 and HCT-116 cells. Natural bile acids were found to induce more apoptotic nuclear morphology, cause increased cellular detachment, and lead to greater capase-3 and -9 cleavage compared with enantiomeric bile acids in both cell lines. In contrast, natural and enantiomeric bile acids showed similar effects on cellular proliferation. These data show that bile acid-induced apoptosis in HT-29 and HCT-116 cells is enantiospecific, hence correlated with the absolute configuration of the bile steroid rather than its detergent properties. The mechanism of LCA- and ent-LCA-induced apoptosis was also investigated in HT-29 and HCT-116 cells. These bile acids differentially activate initiator caspases-2 and -8 and induce cleavage of full-length Bid. LCA and ent-LCA mediated apoptosis was inhibited by both pan-caspase and selective caspase-8 inhibitors, whereas a selective caspase-2 inhibitor provided no protection. LCA also induced increased CD95 localization to the plasma membrane and generated increased reactive oxygen species compared with ent-LCA. This suggests that LCA/ent-LCA induce apoptosis enantioselectively through CD95 activation, likely because of increased reactive oxygen species generation, with resulting procaspase-8 cleavage.

Role of mitochondria in drug-induced cholestatic injury

Mitochondria have multiple functions in eukaryotic cells and are organized into dynamic tubular networks that continuously undergo changes through coordinated fusion and fission and migration through the cytosol. Mitochondria integrate cell-signaling networks, especially those involving the intracellular messenger Ca(2+), into the regulation of metabolic pathways. Recently, it has become clear that mitochondria are central to the three main cell death pathways, namely necrosis, apoptosis, and autophagic cell death. This article discusses the role of mitochondria in drug-induced cholestatic injury to the liver. The role of mitochondria in the cellular adaptation against the toxic effects of bile acids is discussed also.

Mitochondrial perturbation attenuates bile acid-induced cytotoxicity

Hydrophobic bile acids such as deoxycholate (DOC) are known to damage liver cells during cholestasis and promote colon cancer. Cellular stresses induced by bile acids, which include mitochondrial and endoplasmic reticulum (ER) stresses, can result in apoptosis. We found that inhibition of mitochondrial complexes I-V with rotenone, thenoyltrifluoroacetone (TTFA), antimycin A, myxothiazol or oligomycin strongly protected against DOC-induced apoptosis of HCT-116 cells. To understand the mechanism of this protection, we explored the ability of these specific inhibitors to reduce DOC-induced mitochondrial and ER stresses. Different inhibitors markedly reduced DOC-induction of mitochondrial condensation, the DOC-induced decrease in mitochondrial membrane potential and the DOC-induced dilatation of the ER (evidence of ER stress). A dramatic induction of nucleolar segregation by antimycin A and myxothiazol, two distinct complex III inhibitors, was also observed. These findings strongly implicate mitochondrial crosstalk with apoptotic signaling pathways and mitochondrial-nucleolar crosstalk in the development of apoptosis resistance in the colon.

"Let there be bile"--understanding hepatic injury in cholestasis

Cholestatic liver disorders account for a large proportion of chronic liver ailments in adults, children and infants, and are among the leading indications for liver transplantation in all age groups. Recent studies have begun to characterize the cellular and molecular mechanisms of hepatocyte injury caused by the retention of hydrophobic bile acids in cholestasis. Steatocholestasis is the combined presence of hepatic steatosis and cholestasis, common in genetic causes of metabolic liver disease in childhood. Retention of hydrophobic bile acids promotes hepatocellular injury and subsequent portal fibrosis in these conditions. Investigations at the mechanistic level have revealed that activation of hepatocyte death receptors, induction of oxidative stress, mitochondrial perturbations and activation of caspases are intracellular pathways that mediate hepatocyte injury. Several compounds in licorice root have been shown to modulate bile acid-induced apoptosis and necrosis of hepatocytes. Further investigations will be needed to identify novel molecular and cellular targets for which pharmaceuticals might be developed, to reduce liver injury and fibrosis in cholestasis and steatocholestasis.

Mitochondrial glutathione transport: physiological, pathological and toxicological implications

Although most cellular glutathione (GSH) is in the cytoplasm, a distinctly regulated pool is present in mitochondria. Inasmuch as GSH synthesis is primarily restricted to the cytoplasm, the mitochondrial pool must derive from transport of cytoplasmic GSH across the mitochondrial inner membrane. Early studies in liver mitochondria primarily focused on the relationship between GSH status and membrane permeability and energetics. Because GSH is an anion at physiological pH, this suggested that some of the organic anion carriers present in the inner membrane could function in GSH transport. Indeed, studies by Lash and colleagues in isolated mitochondria from rat kidney showed that most of the transport (>80%) in that tissue could be accounted for by function of the dicarboxylate carrier (DIC, Slc25a10) and the oxoglutarate carrier (OGC, Slc25a11), which mediate electroneutral exchange of dicarboxylates for inorganic phosphate and 2-oxoglutarate for other dicarboxylates, respectively. The identity and function of specific carrier proteins in other tissues is less certain, although the OGC is expressed in heart, liver, and brain and the DIC is expressed in liver and kidney. An additional carrier that transports 2-oxoglutarate, the oxodicarboxylate or oxoadipate carrier (ODC; Slc25a21), has been described in rat and human liver and its expression has a wide tissue distribution, although its potential function in GSH transport has not been investigated. Overexpression of the cDNA for the DIC and OGC in a renal proximal tubule-derived cell line, NRK-52E cells, showed that enhanced carrier expression and activity protects against oxidative stress and chemically induced apoptosis. This has implications for development of novel therapeutic approaches for treatment of human diseases and pathological states. Several conditions, such as alcoholic liver disease, cirrhosis or other chronic biliary obstructive diseases, and diabetic nephropathy, are associated with depletion or oxidation of the mitochondrial GSH pool in liver or kidney.

Cholestyramine feeding lowers number of colonic apoptotic cells in rat

Secondary bile acids that are formed in the colon by bacterial action have the potential property of eliciting pathological conditions. Apoptosis of mucosal epithelial cells is recognized as an adaptation that may counteract such pathologies. Cholestyramine, an anion exchange resin that sequesters bile salts in the gut, could decrease levels of secondary bile salt stress and thus conserve the potency of the protective action. Two groups of rats were studied: those fed 4% cholestyramine and those fed regular rat food. Rats were fed cholestyramine for 7, 14, 21, or 28 d. All animals were evaluated for cell death (apoptosis) using in situ TUNEL staining, and confirmed with single-stranded DNA (ssDNA). The effect of cholestyramine on the proliferating cell nuclear antigen (PCNA) in colonic crypt cells was also examined. Our data shows that animals fed cholestyramine for 28 d show evidence of a significant decrease in the levels of apoptotic cells in their large intestines, particularly goblet cells, when compared with the control animals and no change in cell proliferation. Thus, cholestyramine may serve as an alternative in attenuating apoptosis associated with inflammatory disorders that can result in significant enterocyte and goblet-cell death.

Modulation of expression of rat mitochondrial 2-oxoglutarate carrier in NRK-52E cells alters mitochondrial transport and accumulation of glutathione and susceptibility to chemically induced apoptosis

We previously showed that two anion carriers of the mitochondrial inner membrane, the dicarboxylate carrier (DIC; Slc25a10) and oxoglutarate carrier (OGC; Slc25a11), transport glutathione (GSH) from cytoplasm into mitochondrial matrix. In the previous study, NRK-52E cells, derived from normal rat kidney proximal tubules, were transfected with the wild-type cDNA for the DIC expressed in rat kidney; DIC transfectants exhibited increased mitochondrial uptake and accumulation of GSH and were markedly protected from chemically induced apoptosis. In the present study, cDNAs for both wild-type (WT) and a double-cysteine mutant of rat OGC (rOGC and rOGC-C221,224S, respectively) were expressed in Escherichia coli, purified, and reconstituted into proteoliposomes to assess their function. Although both WT rOGC and rOGC-C221,224S exhibited transport properties for GSH and 2-oxoglutarate that were similar to those found in mitochondria of rat kidney proximal tubules, rates of transport and mitochondrial accumulation of substrates were reduced by >75% in rOGC-C221,224S compared with the WT carrier. NRK-52E cells were stably transfected with the cDNA for WT-rOGC and exhibited 10- to 20-fold higher GSH transport activity than nontransfected cells and were markedly protected from apoptosis induced by tert-butyl hydroperoxide (tBH) or S-(1,2-dichlorovinyl)-L-cysteine (DCVC). In contrast, cells stably transfected with the cDNA for rOGC-C221,224S were not protected from tBH- or DCVC-induced apoptosis. These results provide further evidence that genetic manipulation of mitochondrial GSH transporter expression alters mitochondrial and cellular GSH status, resulting in markedly altered susceptibility to chemically induced apoptosis.

Ursodeoxycholic acid and superoxide anion

AIM: To investigate the ability of ursodeoxycholic acid (UDCA) to scavenge superoxide anion (O2^-).

METHODS: We assessed the ability of UDCA to scavenge (O2^-) generated by xanthine-xanthine oxidase (X-XO) in a cell-free system and its effect on the rate of O2^--induced ascorbic acid (AA) oxidation in hepatic post-mitochondrial supernatants.

RESULTS: UDCA at a concentration as high as 1 mmol/L did not impair the ability of the X-XO system to generate O2^-, but could scavenge O2^- at concentrations of 0.5 and 1 mmol/L, and decrease the rate of AA oxidation at a concentration of 100 µmol/L.

CONCLUSION: UDCA can scavenge O2^-, an action that may be beneficial to patients with primary biliary cirrhosis.

Hepatic mitochondrial glutathione: transport and role in disease and toxicity

Synthesized in the cytosol of cells, a fraction of cytosolic glutathione (GSH) is then transported into the mitochondrial matrix where it reaches a high concentration and plays a critical role in defending mitochondria against oxidants and electrophiles. Evidence mainly from kidney and liver mitochondria indicated that the dicarboxylate and the 2-oxoglutarate carriers contribute to the transport of GSH across the mitochondrial inner membrane. However, differential features between kidney and liver mitochondrial GSH (mGSH) transport seem to suggest the existence of additional carriers the identity of which remains to be established. One of the characteristic features of the hepatic mitochondrial transport of GSH is its regulation by membrane fluidity. Conditions leading to increased cholesterol deposition in the mitochondrial inner membrane such as in alcohol-induced liver injury decrease membrane fluidity and impair the mitochondrial transport of GSH. Depletion of mitochondrial GSH by alcohol is believed to contribute to the sensitization of the liver to alcohol-induced injury through tumor necrosis factor (TNF)-mediated hepatocellular death. Through control of mitochondrial electron transport chain-generated oxidants, mitochondrial GSH modulates cell death and hence its regulation may be a key target to influence disease progression and drug-induced cell death.

Absence of peroxisomes in mouse hepatocytes causes mitochondrial and ER abnormalities

Peroxisome deficiency in men causes severe pathology in several organs, particularly in the brain and liver, but it is still unknown how metabolic abnormalities trigger these defects. In the present study, a mouse model with hepatocyte-selective elimination of peroxisomes was generated by inbreeding Pex5-loxP and albumin-Cre mice to investigate the consequences of peroxisome deletion on the functioning of hepatocytes. Besides the absence of catalase-positive peroxisomes, multiple ultrastructural alterations were noticed, including hepatocyte hypertrophy and hyperplasia, smooth endoplasmic reticulum proliferation, and accumulation of lipid droplets and lysosomes. Most prominent was the abnormal structure of the inner mitochondrial membrane, which bore some similarities with changes observed in Zellweger patients. This was accompanied by severely reduced activities of complex I, III, and V and a collapse of the mitochondrial inner membrane potential. Surprisingly, these abnormalities provoked no significant disturbances of adenosine triphosphate (ATP) levels and redox state of the liver. However, a compensatory increase of glycolysis as an alternative source of ATP and mitochondrial proliferation were observed. No evidence of oxidative damage to proteins or lipids nor elevation of oxidative stress defence mechanisms were found. Altered expression of peroxisome proliferator-activated receptor alpha (PPAR-alpha) regulated genes indicated that PPAR-alpha is activated in the peroxisome-deficient cells. In conclusion, the absence of peroxisomes from mouse hepatocytes has an impact on several other subcellular compartments and metabolic pathways but is not detrimental to the function of the liver parenchyma. Supplementary material for this article can be found on the HEPATOLOGY website (http://interscience.wiley.com/jpages/0270-9139/suppmat/index.html).

Transcriptional reprogramming in murine liver defines the physiologic consequences of biliary obstruction

BACKGROUND/AIMS

While the metabolic and histological responses to cholestasis are recognized, the consequences of impaired biliary flow on liver gene expression are largely undefined. We hypothesized that biliary obstruction results in transcriptional reprogramming that dictates the physiologic response.

METHODS

We determined global gene expression in murine livers 1-21 days following bile duct ligation. Total hepatic cRNA from experimental and sham mice was hybridized to Affymetrix gene chips. Gene expression data was analyzed by GeneSpring software and validated by Northern analysis.

RESULTS

We found 92 genes over-expressed > or =2-fold at one or more time points following bile duct ligation. Functional classification of these genes revealed the activation of three main biological processes in a sequential and time-restricted fashion. At day 1, genes involved in sterol metabolism were uniquely over-expressed, including HMG-CoA reductase, the rate-limiting enzyme of cholesterol biosynthesis. This was followed by an increased expression of growth-promoting genes at day 7, the time point coinciding with peak cholangiocyte proliferation. In later phases (days 14-21), the liver over-expressed genes encoding structural proteins and proteases.

CONCLUSIONS

Transcriptional reprogramming in the liver following biliary obstruction favors the activation of genes regulating metabolism, cell proliferation, and matrix remodeling in a time-restricted and sequential fashion.

Gastrointestinal manifestations of mitochondrial disease

Although non-specific gastrointestinal and hepatic symptoms are commonly found in most mitochondrial disorders, they are among the cardinal manifestations of several primary mitochondrial diseases, such as: mitochondrial neurogastrointestinal encephalomyopathy; mitochondrial DNA depletion syndrome; Alpers syndrome; and Pearson syndrome. Management of these heterogeneous disorders includes the empiric supplementation with various "mitochondrial cocktails," supportive therapies, and avoidance of drugs and conditions known to have a detrimental effect on the respiratory chain. There is a great need for improved methods of treatment and controlled clinical trials of existing therapies. Liver transplantation is successful in acquired cases; however neuromuscular involvement in primary mitochondrial disorders should be a contraindication for liver transplantation.

Oxidative-stress-related changes in the livers of bile-duct-ligated rats

The role of reactive oxygen species in liver fibrogenesis is not yet clarified. The aim of this study was to investigate oxidative-stress-related changes in cirrhotic rats. Cirrhosis was induced by bile duct ligation in Sprague-Dawley rats. Plasma malondialdehyde (MDA), hepatic 8-hydroxy-2'-deoxyguanosine (8-OHdG), hepatic mitochondrial respiratory functions and gene transcripts were measured at 2 and 4 weeks after surgery in bile-duct-ligated (BDL) and sham-operated-operated rats. The results showed progressive increases in the levels of plasma MDA, hepatic 8-OHdG and procollagen I and III mRNA expression, and progressive impairment of hepatic mitochondrial respiratory function in BDL rats at 2 and 4 weeks after ligation compared with sham-operated rats. Moreover, at 4 weeks after ligation, BDL rats exhibited reduced plasma glutathione and vitamin E levels, impaired hepatic mitochondrial electron transport enzyme activities and oxidative phosphorylation function. In addition, hepatic mRNA expression of transforming growth factor-beta1 was increased. Hepatomegaly, abnormal plasma alanine transaminase and aspartate transaminase levels, and portal hypertension were noted in BDL rats. Our results suggest that bile duct ligation in the rat induces mitochondrial dysfunction and biochemical and molecular changes related to oxidative stress in the liver.

Chenodeoxycholate induction of mitochondrial permeability transition pore is associated with increased membrane fluidity and cytochrome c release: protective role of carvedilol

Chenodeoxycholate (CDCA) is a primary bile acid mostly implicated in cholestatic liver injury. In this study, we have investigated the involvement of membrane fluidity and cytochrome c release in CDCA-induced mitochondrial permeability transition (MPT), and the preventive role of carvedilol. Treatment of calcium-loaded hepatic mitochondria with CDCA was found to cause osmotic swelling and release of cytochrome c, associated with an increase in membrane fluidity, in both protein and lipid regions. Carvedilol and cyclosporine A (CyA) reduced both cytochrome c release and alterations in membrane fluidity induced by CDCA. The hydroxylated metabolite of carvedilol, BM-910228, had no effect. Thus, modulation of membrane fluidity, plays an important role in MPT pore opening promoted by CDCA. As a result, we have delineated a pathway for the preventive role of carvedilol in mitochondrial dysfunction induced by CDCA.

Mitochondrially mediated synergistic cell killing by bile acids

The accumulation of endogenous bile acids contributes to hepatocellular damage during cholestatic liver disease. To examine the controversy regarding the therapeutic use of ursodeoxycholate (UDCA) in cholestatic patients, we investigated the possible cytoprotection or synergistic effects of UDCA against chenodeoxycholate (CDCA)-induced injury to isolated rat hepatocytes. Our aim was to investigate the role of the mitochondrial permeability transition (MPT) in the mechanism of cytotoxicity caused by UDCA plus CDCA. Although not toxic by itself, UDCA potentiated the mitochondrial depolarization, ATP depletion and cell killing caused by CDCA. Fructose maintained ATP levels and prevented bile acid-induced cell killing. Cyclosporine A (CyA), a potent inhibitor of the MPT, substantially reduced mitochondrial depolarization, ATP depletion and cell killing caused by CDCA. Our results demonstrate that the synergistic cytotoxicity by UDCA plus CDCA is mediated by impairment of mitochondrial function, an event that is expressed via induction of the MPT.

Mechanisms of liver steatosis in rats with systemic carnitine deficiency due to treatment with trimethylhydraziniumpropionate

Rats with systemic carnitine deficiency induced by treatment with trimethylhydraziniumpropionate (THP) develop liver steatosis. This study aims to investigate the mechanisms leading to steatosis in THP-induced carnitine deficiency. Rats were treated with THP (20 mg/100 g) for 3 or 6 weeks and were studied after starvation for 24 h. Rats treated with THP had reduced in vivo palmitate metabolism and developed mixed liver steatosis at both time points. The hepatic carnitine pool was reduced in THP-treated rats by 65% to 75% at both time points. Liver mitochondria from THP-treated rats had increased oxidative metabolism of various substrates and of beta-oxidation at 3 weeks, but reduced activities at 6 weeks of THP treatment. Ketogenesis was not affected. The hepatic content of CoA was increased by 23% at 3 weeks and by 40% at 6 weeks in THP treated rats. The cytosolic content of long-chain acyl-CoAs was increased and the mitochondrial content decreased in hepatocytes of THP treated rats, compatible with decreased activity of carnitine palmitoyltransferase I in vivo. THP-treated rats showed hepatic peroxisomal proliferation and increased plasma VLDL triglyceride and phospholipid concentrations at both time points. A reduction in the hepatic carnitine pool is the principle mechanism leading to impaired hepatic fatty acid metabolism and liver steatosis in THP-treated rats. Cytosolic accumulation of long-chain acyl-CoAs is associated with increased plasma VLDL triglyceride, phospholipid concentrations, and peroxisomal proliferation.

Cholestasis increases tumor necrosis factor-related apoptotis-inducing ligand (TRAIL)-R2/DR5 expression and sensitizes the liver to TRAIL-mediated cytotoxicity

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a potential chemotherapeutic agent for cancer, is not thought to be hepatotoxic. We have recently demonstrated, however, that bile acids increase TRAIL-R2/DR5 expression in a human liver cell line and render these cells susceptible to TRAIL-mediated apoptosis. These data suggest TRAIL may be hepatotoxic in cholestasis. The aim of this study was to directly assess TRAIL hepatotoxicity in bile duct-ligated mice, a model of extrahepatic cholestasis. Bile duct-ligated mice (3 days) were used for these studies. TRAIL-R2/DR5 expression was assessed by real-time and immunoblot analysis. The TRAIL death-inducing signaling complex (DISC) was evaluated by immunoprecipitation and immunoblot techniques. Bile duct ligation increased both liver TRAIL-R2/DR5 mRNA and protein expression (>10-fold). Following TRAIL administration (60 microg/mouse, i.v.) to bile duct ligation (BDL) mice, terminal deoxynucleotidyl transferase dUTP nick-end labeling-positive hepatocytes, liver tissue caspase 3-like activity, and serum alanine aminotransferase values increased significantly compared with vehicle-treated BDL mice. The effect of TRAIL on the liver was direct, as the TRAIL DISC (Fas-associated death domain and procaspase 8 protein) was detected in liver tissue. TRAIL-mediated hepatocyte apoptosis in bile duct-ligated mice was associated with significant hepatotoxicity, as assessed by histopathology, although there was no animal mortality. In conclusion, these data define conditions under which TRAIL is hepatotoxic.

Enterohepatic circulation: physiological, pharmacokinetic and clinical implications

Enterohepatic recycling occurs by biliary excretion and intestinal reabsorption of a solute, sometimes with hepatic conjugation and intestinal deconjugation. Cycling is often associated with multiple peaks and a longer apparent half-life in a plasma concentration-time profile. Factors affecting biliary excretion include drug characteristics (chemical structure, polarity and molecular size), transport across sinusoidal plasma membrane and canniculae membranes, biotransformation and possible reabsorption from intrahepatic bile ductules. Intestinal reabsorption to complete the enterohepatic cycle may depend on hydrolysis of a drug conjugate by gut bacteria. Bioavailability is also affected by the extent of intestinal absorption, gut-wall P-glycoprotein efflux and gut-wall metabolism. Recently, there has been a considerable increase in our understanding of the role of transporters, of gene expression of intestinal and hepatic enzymes, and of hepatic zonation. Drugs, disease and genetics may result in induced or inhibited activity of transporters and metabolising enzymes. Reduced expression of one transporter, for example hepatic canalicular multidrug resistance-associated protein (MRP) 2, is often associated with enhanced expression of others, for example the usually quiescent basolateral efflux MRP3, to limit hepatic toxicity. In addition, physiologically relevant pharmacokinetic models, which describe enterohepatic recirculation in terms of its determinants (such as sporadic gall bladder emptying), have been developed. In general, enterohepatic recirculation may prolong the pharmacological effect of certain drugs and drug metabolites. Of particular importance is the potential amplifying effect of enterohepatic variability in defining differences in the bioavailability, apparent volume of distribution and clearance of a given compound. Genetic abnormalities, disease states, orally administered adsorbents and certain coadministered drugs all affect enterohepatic recycling.

Improved efficiency of hepatic mitochondrial function in rats with cholestasis induced by an acute dose of alpha-naphthylisothiocyanate

Cholestasis is a feature of many chronic human liver diseases. Previous studies pointed out an impairment of mitochondrial function as a cause of hepatocyte dysfunction leading to cholestatic liver injury. This study was aimed to evaluate liver mitochondrial bioenergetics of alpha-naphthylisothiocyanate-treated Wistar rats, an experimental model of cholestasis. Serum markers of liver injury and endogenous adenine nucleotides were measured. Changes in membrane potential, mitochondrial respiration, and alterations in mitochondrial permeability transition pore induction were monitored. In rats injected with alpha-naphthylisothiocyanate, liver injury with cholestasis developed within 48 h, as indicated by both serum enzyme activities and total bilirubin concentration. Liver mitochondria isolated from alpha-naphthylisothiocyanate-treated rats had a higher state 3 respiration, respiratory control ratio, ADP/O, and endogenous ATP/ADP ratio compared to controls. No change in state 4 respiration was observed. Associated with these parameters, cholestatic mitochondria exhibited an increased resistance to disruption of mitochondrial calcium homeostasis due to permeability transition pore induction. Hepatic mitochondria isolated from alpha-naphthylisothiocyanate-treated rats exhibited an improved efficiency. These data indicate that an adaptive response to resist cell death occurs during alpha-naphthylisothiocyanate-induced acute cholestasis.

Acetaminophen-induced suppression of hepatic AdoMet synthetase activity is attenuated by prodrugs of L-cysteine

Administration of acetaminophen (ACP, 400 mg/kg, i.p.) to fasted, male Swiss-Webster mice caused a rapid 90% decrease in total hepatic glutathione (GSH) and a 58% decrease in mitochondrial GSH by 2 h post ACP. This was followed by a time-dependent decrease (72%) in hepatic AdoMet synthetase activity and rise in plasma ALT levels (>10000 U/l) at 24 h post ACP treatment. AdoMet synthetase activity was maintained at 82, 78 and 60% of controls, respectively, by the cysteine prodrugs PTCA, CySSME and NAC. Total hepatic and mitochondrial GSH levels were also protected from severe ACP-induced depletion by CySSME and MTCA. These results suggest that the maintenance of GSH homeostasis by cysteine prodrugs can protect mouse hepatic AdoMet synthetase, a sulfhydryl enzyme whose integrity is dependent on GSH, as well as the liver itself from the consequences of oxidative stress elicited by toxic metabolites of xenobiotics.

Disruption of mitochondrial calcium homeostasis after chronic alpha-naphthylisothiocyanate administration: relevance for cholestasis

BACKGROUND

Hepatocyte dysfunction caused by impaired mitochondrial function has been pointed out as a probable leading cause of cholestatic liver injury. The aim of this study was to evaluate liver mitochondrial bioenergetics that followed repeated in vivo administration of alpha-naphthylisothiocyanate, a known cholestatic agent.

METHODS

Serum markers of liver injury and endogenous adenine nucleotides were measured in alpha-naphthylisothiocyanate-treated rats (intraperitoneally, 100 mg/Kg/wk x 6 wk). Changes in membrane potential, mitochondrial respiration, as well as alterations in mitochondrial calcium homeostasis were monitored.

RESULTS

In rats injected with alpha-naphthylisothiocyanate, liver injury with cholestasis developed within 48 hours, as indicated by both serum enzyme activities and total bilirubin concentration. However, 1 week after the last injection, serum enzyme activity returned to control levels. In addition, after chronic alpha-naphthylisothiocyanate administration, no alterations in mitochondrial respiratory function and membrane potential were observed. Associated with these parameters, mitochondria from treated animals exhibited increased susceptibility to disruption of mitochondrial calcium homeostasis by calcium phosphate and by bile acids, which was probably caused by induction of permeability transition pore.

CONCLUSIONS

Our data suggest that chronic cholestasis in rats leads to impaired mitochondrial function due to the disruption of mitochondrial calcium homeostasis. The initiating event is the induction of a cyclosporine A-sensitive release of calcium. This event may be an important determinant of the progression of cholestatic liver injury and associated liver cirrhosis. In addition, in the present study we observed that impairment of mitochondrial function is potentiated by chenodeoxycholate, a bile acid that is known to be toxic. Ursodeoxycholate (the beta- epimer of chenodeoxycholate) is approved for the treatment of chronic cholestatic liver disease. Interestingly, we show that the susceptibility to the cyclosporine A-sensitive release of calcium was increased by the combination of both bile acids. These results indicate that the reported improvement of biochemical parameters in cholestatic patients treated with ursodeoxycholate would not prevent the associated mitochondrial dysfunction. This may explain the progression of the histological stage and the maintenance of symptoms during cholestasis.

Interactions of combined bile acids on hepatocyte viability: cytoprotection or synergism

Cholestasis results from hepatocyte dysfunction due to the accumulation of bile acids in the cell, many of which are known to be cytotoxic. Recent evidence implicates competitive antagonism of key cytotoxic responses as the mechanism by which certain therapeutic bile acids might afford cytoprotection against cholestasis. In this work, we compare the relative cytotoxicity of bile acids in terms of dose- and time-dependence. To better elucidate the controversy related to the therapeutic use of ursodeoxycholate (UDCA) in cholestatic patients, we also evaluated the effects of bile acid combinations. Viability of Wistar rat hepatocytes in primary culture was measured by LDH leakage after 12 and 24 h exposure of cells to the various bile acids. All unconjugated bile acids caused a dose-dependent decrease in cell viability. The tauro- and glyco-conjugates of chenodeoxycholate (CDCA) and UDCA were all less toxic than the corresponding unconjugated form. Although relatively non-toxic, UDCA caused synergistic cell killing by lithocholate (LCA), CDCA, glyco-CDCA (GCDC) and tauro-CDCA (TCDC). Glycoursodeoxycholate decreased the toxicity of GCDC, but potentiated the toxicity of unconjugated CDCA and LCA. The tauro-conjugate of UDCA had no significant effect. These data suggest that at cholestatic concentrations, bile acid-induced cell death correlates with the degree of lipophilicity of individual bile acids. However, these results indicate that the reported improvement of biochemical parameters in cholestatic patients treated with UDCA is not due to a direct effect of UDCA on hepatocyte viability. Therefore, any therapeutic effect of UDCA must be secondary to some other process, such as altered membrane transport or nonparenchymal cell function.

The therapeutic effects of ursodeoxycholic acid as an anti-apoptotic agent

The dihydroxy bile acid, ursodeoxycholic acid (UDCA), has been in widespread clinical use in the Western world since the mid 1980s, when it was initially used for gallstone dissolution [1,2] and subsequently for the treatment of chronic cholestatic liver diseases [3,4]. Many clinical trials of UDCA in a variety of cholestatic disorders established biochemical and clinical improvements, and most importantly showed a significant prolongation of transplant-free survival after four years of treatment with UDCA in patients with primary biliary cirrhosis [5]. Despite its clinical efficacy, the precise mechanism(s) by which UDCA improves liver function during cholestasis is still a matter of debate [6]. It was initially considered that the choleretic effect of UDCA, coupled with its ability to cause a marked shift in the composition of the bile acid pool towards hydrophilicity, accounted for its mechanism of action. In recent years, however, it has become evident that UDCA and its conjugated derivatives are capable of exerting direct effects at the cellular, subcellular, and molecular levels by stabilising cell membranes, affecting signal transduction pathways, and regulating immune responses. In addition, we have shown that UDCA plays a unique role in modulating the apoptotic threshold in both hepatic and non-hepatic cells [7-10]. The purpose of this article is to examine the mechanism(s) by which UDCA prevents apoptotic cell death associated with cholestasis. In addition, we will also review a potentially novel and, heretofore, unrecognised role of UDCA as a therapeutic agent in the treatment of non-liver diseases associated with increased levels of apoptosis as a pathogenesis of the disorder.

Protective effect of carvedilol on chenodeoxycholate induction of the permeability transition pore

Intracellular accumulation of toxic, hydrophobic bile acids has been proposed as one of the putative final common pathways leading to cholestatic liver injury. Furthermore, bile acids have been proposed as a causative factor for hepatic cardiomyopathy. Hepatic tissue concentrations of chenodeoxycholic acid (CDCA) during cholestasis are greater than those of other toxic bile acids. In the presence of calcium and phosphate, CDCA induced the permeability transition pore (PTP) in freshly isolated rat liver mitochondria. In this study, we evaluated the effects of carvedilol, a multirole cardioprotective compound, on CDCA-induced PTP. Mitochondrial membrane potential, osmotic swelling, and calcium fluxes were monitored. CDCA-induced PTP, characterized by membrane depolarization, release of matrix calcium, and osmotic swelling, was prevented by carvedilol. Under the same conditions, its hydroxylated analog BM-910228 did not reveal any protective effect. This finding reinforces carvedilol's therapeutic interest, because it may potentially prevent mitochondrial dysfunction associated with cardiomyopathy in the pathophysiology of cholestatic liver disease

Bilirubin-induced apoptosis in cultured rat neural cells is aggravated by chenodeoxycholic acid but prevented by ursodeoxycholic acid

BACKGROUND/AIMS

Unconjugated bilirubin (UCB) can be neurotoxic in jaundiced neonates and in patients with Crigler-Najjar syndrome. UCB toxicity may culminate in cell death, however, the occurrence of apoptosis has never been investigated. Ursodeoxycholic acid (UDCA) is a strong modulator of the apoptotic threshold in both hepatic and nonhepatic cells. The aims of this study were to determine whether apoptosis plays a role in neural cell death induced by UCB, and to investigate the ability of UDCA to prevent cell death.

METHODS

Cultured rat astrocytes were incubated with UCB (17 and 86 microM) plus albumin (5.7 and 28.7 microM) for 4-22 h. In addition, astrocytes and neurones were treated with either UCB, 50 microM UDCA, or their combination for 4 h. Cultures were scored for nonviable cells by trypan blue dye exclusion. Apoptosis was assessed by Hoechst staining and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labelling assay.

RESULTS

UCB induced a concentration- and time-dependent decrease in astrocyte viability. Apoptosis was 4- and 7-fold increased after 4 h exposure to 17 and 86 microM UCB, respectively (P < 0.01). UDCA reduced apoptosis to <7%, which represents a appoximately 60% protection (P < 0.01). Cholic acid was not protective, and chenodeoxyholic acid aggravated UCB toxicity (P < 0.05). Finally, neurones showed a 1.5-fold greater sensitivity than astrocytes to UCB, while UDCA was still protective.

CONCLUSIONS

UCB is toxic to both astrocytes and neurones, causing cell death through an apoptotic process. Moreover, UDCA inhibits UCB-induced apoptosis in neural cells and this could not be mimicked by other bile acids.

The effect of bile salts and calcium on isolated rat liver mitochondria

Intact mitochondria were incubated with and without calcium in solutions of chenodeoxycholate, ursodeoxycholate, or their conjugates. Glutamate dehydrogenase, protein and phospholipid release were measured. Alterations in membrane and organelle structure were investigated by electron paramagnetic resonance spectroscopy. Chenodeoxycholate enhanced enzyme liberation, solubilized protein and phospholipid, and increased protein spin label mobility and the polarity of the hydrophobic membrane interior, whereas ursodeoxycholate and its conjugates did not damage mitochondria. Preincubation with ursodeoxycholate or its conjugate tauroursodeoxycholate for 20 min partially prevented damage by chenodeoxycholate. Extended preincubation even with 1 mM ursodeoxycholate could no longer prevent structural damage. Calcium (from 0.01 mM upward) augmented the damaging effect of chenodeoxycholate (0.15-0.5 mM). The combined action of 0.01 mM calcium and 0.15 mM chenodeoxycholate was reversed by ursodeoxycholate only, not by its conjugates tauroursodeoxycholate and glycoursodeoxycholate. In conclusion, ursodeoxycholate partially prevents chenodeoxycholate-induced glutamate dehydrogenase release from liver cell mitochondria by membrane stabilization. This holds for shorter times and at concentrations below 0.5 mM only, indicating that the different constitution of protein-rich mitochondrial membranes does not allow optimal stabilization such as has been seen in phospholipid- and cholesterol-rich hepatocyte cell membranes, investigated previously.

Altered transmembrane ionic flux in hepatocytes isolated from cirrhotic rats

BACKGROUND/AIMS

Although cirrhosis is known to be associated with many hepatocyte abnormalities, there is no well-established model to study the cellular drug uptake process independent of hemodynamic effects. The purpose of the present study was to test the following hypothesis: hepatocytes isolated from cirrhotic animals may be used as a model to study the cellular abnormalities associated with cirrhosis. Our hypothesis was tested by comparing the membrane potential (PD) of hepatocytes in anesthetized healthy and cirrhotic animals, and the PD and [3H]palmitic acid clearance rate of hepatocytes isolated from healthy and cirrhotic animals.

METHODS

Mild to moderate cirrhosis was induced in female Sprague-Dawley rats by CCl4 administration. PD was recorded in anesthetized animals using intracellular microelectrodes. Hepatocytes from those livers were subsequently isolated by collagenase perfusion for further determinations of PD and [3H]palmitic acid uptake.

RESULTS

The mean (+/-SEM) hepatocyte PD from intact rat livers was 38+/-1 mV (control) and -32+/-1 mV (cirrhosis; n=6/group, p<0.01). The PD (mean+/-SEM) in isolated hepatocytes was -21+/-1 mV (control) and -15+/-1 mV (cirrhosis, n=13/group, p<0.01). The clearance rate of [3H]palmitic acid was lower in hepatocytes isolated from cirrhotic animals (26%) than in those isolated from healthy control animals (p<0.01).

CONCLUSION

The results of this study indicate that hepatocytes isolated from cirrhotic animals may be used to study the cellular abnormalities associated with cirrhosis.

Mitochondria and childhood liver diseases

The newly recognized mitochondrial hepatopathies should be considered in the differential diagnosis of acute and chronic liver disease in childhood. It may appear as neonatal liver failure, delayed onset liver failure in early childhood or as a multisystemic process. Comparison of features of several of the known primary mitochondrial hepatopathies is provided in Table 5. Secondary mitochondrial hepatopathies are examples of the critical importance of mitochondrial function in the pathogenesis of liver injury. Our improved understanding of the role of the mitochondria in cellular necrosis and apoptosis opens the way for development of new therapeutic approaches to several hepatic disorders. Primary mitochondrial hepatopathies (especially the respiratory chain defects) should be considered in any child with liver disease and neuromuscular involvement, multisystemic disease, lactic acidosis or rapidly progressive disease, and when hepatic steatosis is the dominant histologic finding on examination of a liver specimen. Current therapies are inadequate; improved therapeutic strategies are needed for these disorders. Some patients with respiratory chain defects limited to the liver have had successful liver transplantation. This field is in evolution and will undoubtedly provide new and important developments as the next millennium begins.

The effect of idebenone, a coenzyme Q analogue, on hydrophobic bile acid toxicity to isolated rat hepatocytes and hepatic mitochondria

Oxidant stress induced by hydrophobic bile acids has been implicated in the pathogenesis of liver injury in cholestatic liver disorders. We evaluated the effect of idebenone, a coenzyme Q analogue, on taurochenodeoxycholic acid (TCDC)-induced cell injury and oxidant stress in isolated rat hepatocytes and on glycochenodeoxycholic acid (GCDC)-induced generation of hydroperoxides in fresh hepatic mitochondria. Isolated rat hepatocytes in suspension under 9% oxygen atmosphere were preincubated with 0, 50, and 100 micromol/l idebenone for 30 min and then exposed to 1000 micromol/l TCDC for 4 h. LDH release (cell injury) and thiobarbituric acid reactive substances (measure of lipid peroxidation) increased after TCDC exposure but were markedly suppressed by idebenone pretreatment. In a second set of experiments, the addition of 100 micromol/l idebenone up to 3 h after hepatocytes were exposed to 1000 micromol/l TCDC resulted in abrogation of subsequent cell injury and markedly reduced oxidant damage to hepatocytes. Chenodeoxycholic acid concentrations increased to 5.15 nmol/10(6) cells after 2 h and to 7.05 after 4 h of incubation of hepatocytes with 1000 micromol/l TCDC, and did not differ in the presence of idebenone. In freshly isolated rat hepatic mitochondria, when respiration was stimulated by succinate, 10 micromol/l idebenone abrogated the generation of hydroperoxides during a 90-minute exposure to 400 micromol/l GCDC. These data demonstrate that idebenone functions as a potent protective hepatocyte antioxidant during hydrophobic bile acid toxicity, perhaps by reducing generation of oxygen free radicals in mitochondria.

Induction of the mitochondrial permeability transition as a mechanism of liver injury during cholestasis: a potential role for mitochondrial proteases

As part of this thematic series on mitochondria in cell death, we would like to review our data on: (1) the role of the mitochondrial permeability transition (MPT) in hepatocyte necrosis during cholestasis; and (2) the concept that endogenous mitochondrial protease activity may lead to the MPT. Many chronic human liver diseases are characterized by cholestasis, an impairment in bile flow. During cholestasis an accumulation of toxic hydrophobic bile salts in the hepatocyte causes necrosis. We tested the hypothesis that toxic hydrophobic bile salt, glycochenodeoxycholate (GCDC), causes hepatocyte necrosis by inducing the MPT. GCDC induces a rapid, cyclosporin A-sensitive MPT. The hydrophilic bile salt, ursodeoxycholate (UDCA), prevents the GCDC-induced MPT and hepatocyte necrosis providing an explanation for its beneficial effect in human liver disease. We have also demonstrated that the calcium-dependent MPT is associated with an increase in calpain-like protease activity and inhibited by calpain inhibitors. In an experimental model of cholestasis, mitochondrial calpain-like protease activity increases 1.6-fold. We propose for the first time that activation of mitochondrial proteases may initiate the MPT and cell necrosis during cholestasis.

Reversibility of hepatic mitochondrial damage in rats with long-term cholestasis

BACKGROUND/AIMS

Long-term bile duct ligation in rats is associated with secondary biliary cirrhosis and metabolic alterations, e.g. mitochondrial dysfunction. We performed the current studies to characterize the reversibility of hepatic mitochondrial dysfunction after reversing biliary obstruction by Roux-en-Y anastomosis.

METHODS

Rats were studied after 4 weeks of bile duct ligation, and after 5 or 14 days of reanastomosis. Control rats were pair-fed to treated rats and all rats were studied after starvation for 24 h. Mitochondria were isolated by differential centrifugation and enzyme activities determined by spectrophotometric methods.

RESULTS

In comparison to controls, plasma beta-hydroxybutyrate concentrations were decreased in bile duct ligated rats (200+/-70 vs. 790+/-200 micromol/l) and remained decreased after relief of biliary obstruction. In contrast, plasma free fatty acids were not different between controls and treated rats. Oxidative metabolism of L-glutamate, succinate and duroquinol was decreased in liver mitochondria from bile duct ligated rats. After relief of biliary obstruction, the metabolism of L-glutamate and duroquinol normalized quickly, whereas succinate metabolism remained impaired. Similar results were obtained for the mitochondrial oxidases in disrupted mitochondria. The activities of complex I, II, III and V of the respiratory chain were reduced in bile duct ligated rats. After relief of biliary obstruction, complex I and III normalized quickly, whereas complex II and V remained impaired. Oxidative metabolism of long-chain fatty acids by isolated liver mitochondria was decreased in bile duct ligated rats and did not recover after relief of biliary obstruction.

CONCLUSIONS

Long-term cholestasis in the rat is associated with a decrease in specific functions of liver mitochondria which recover only partially after Roux-en-Y anastomosis. The persistence of decreased mitochondrial fatty acid metabolism cannot be explained by impaired activity of the respiratory chain, but is more likely due to alterations in mitochondrial beta-oxidation.

Antioxidants in pediatric gastrointestinal disease

Oxidant stress seems to be involved in the pathogenesis of several important gastroenterologic disorders in infants and children. The question can still be asked, in most circumstances, whether the oxidant stress precedes, and therefore is involved in, tissue or cellular injury or is a result of injury and not of clinical importance. The data favor the former situation in several inflammatory conditions of the bowel and in a variety of liver diseases. Experimental and clinical testing of this possible basic mechanism of tissue injury over the next few years will shed light on the role of antioxidants in treating gastrointestinal disorders.