Tauroursodeoxycholic acid protects rat hepatocytes from bile acid-induced apoptosis via activation of survival pathways

Conjugated bile acids activate the sphingosine-1-phosphate receptor 2 in primary rodent hepatocytes

Bile acids have been shown to be important regulatory molecules for cells in the liver and gastrointestinal tract. They can activate various cell signaling pathways including extracellular regulated kinase (ERK)1/2 and protein kinase B (AKT) as well as the G-protein-coupled receptor (GPCR) membrane-type bile acid receptor (TGR5/M-BAR). Activation of the ERK1/2 and AKT signaling pathways by conjugated bile acids has been reported to be sensitive to pertussis toxin (PTX) and dominant-negative Gα(i) in primary rodent hepatocytes. However, the GPCRs responsible for activation of these pathways have not been identified. Screening GPCRs in the lipid-activated phylogenetic family (expressed in HEK293 cells) identified sphingosine-1-phosphate receptor 2 (S1P(2) ) as being activated by taurocholate (TCA). TCA, taurodeoxycholic acid (TDCA), tauroursodeoxycholic acid (TUDCA), glycocholic acid (GCA), glycodeoxycholic acid (GDCA), and S1P-induced activation of ERK1/2 and AKT were significantly inhibited by JTE-013, a S1P(2) antagonist, in primary rat hepatocytes. JTE-013 significantly inhibited hepatic ERK1/2 and AKT activation as well as short heterodimeric partner (SHP) mRNA induction by TCA in the chronic bile fistula rat. Knockdown of the expression of S1P(2) by a recombinant lentivirus encoding S1P(2) shRNA markedly inhibited the activation of ERK1/2 and AKT by TCA and S1P in rat primary hepatocytes. Primary hepatocytes prepared from S1P(2) knock out (S1P(2) (-/-) ) mice were significantly blunted in the activation of the ERK1/2 and AKT pathways by TCA. Structural modeling of the S1P receptors indicated that only S1P(2) can accommodate TCA binding. In summary, all these data support the hypothesis that conjugated bile acids activate the ERK1/2 and AKT signaling pathways primarily through S1P(2) in primary rodent hepatocytes.

Liver dysfunction and phosphatidylinositol-3-kinase signalling in early sepsis: experimental studies in rodent models of peritonitis

BACKGROUND

Hepatic dysfunction and jaundice are traditionally viewed as late features of sepsis and portend poor outcomes. We hypothesized that changes in liver function occur early in the onset of sepsis, yet pass undetected by standard laboratory tests.

METHODS AND FINDINGS

In a long-term rat model of faecal peritonitis, biotransformation and hepatobiliary transport were impaired, depending on subsequent disease severity, as early as 6 h after peritoneal contamination. Phosphatidylinositol-3-kinase (PI3K) signalling was simultaneously induced at this time point. At 15 h there was hepatocellular accumulation of bilirubin, bile acids, and xenobiotics, with disturbed bile acid conjugation and drug metabolism. Cholestasis was preceded by disruption of the bile acid and organic anion transport machinery at the canalicular pole. Inhibitors of PI3K partially prevented cytokine-induced loss of villi in cultured HepG2 cells. Notably, mice lacking the PI3Kγ gene were protected against cholestasis and impaired bile acid conjugation. This was partially confirmed by an increase in plasma bile acids (e.g., chenodeoxycholic acid [CDCA] and taurodeoxycholic acid [TDCA]) observed in 48 patients on the day severe sepsis was diagnosed; unlike bilirubin (area under the receiver-operating curve: 0.59), these bile acids predicted 28-d mortality with high sensitivity and specificity (area under the receiver-operating curve: CDCA: 0.77; TDCA: 0.72; CDCA+TDCA: 0.87).

CONCLUSIONS

Liver dysfunction is an early and commonplace event in the rat model of sepsis studied here; PI3K signalling seems to play a crucial role. All aspects of hepatic biotransformation are affected, with severity relating to subsequent prognosis. Detected changes significantly precede conventional markers and are reflected by early alterations in plasma bile acids. These observations carry important implications for the diagnosis of liver dysfunction and pharmacotherapy in the critically ill. Further clinical work is necessary to extend these concepts into clinical practice. Please see later in the article for the Editors' Summary.

Endoplasmic reticulum stress and lipid metabolism: mechanisms and therapeutic potential

The endoplasmic reticulum (ER) plays a crucial role in protein folding, assembly, and secretion. Disruption of ER homeostasis may lead to accumulation of misfolded or unfolded proteins in the ER lumen, a condition referred to as ER stress. In response to ER stress, a signal transduction pathway known as the unfolded protein response (UPR) is activated. UPR activation allows the cell to cope with an increased protein-folding demand on the ER. Recent studies have shown that ER stress/UPR activation plays a critical role in lipid metabolism and homeostasis. ER-stress-dependent dysregulation of lipid metabolism may lead to dyslipidemia, insulin resistance, cardiovascular disease, type 2 diabetes, and obesity. In this paper, we examine recent findings illustrating the important role ER stress/UPR signalling pathways play in regulation of lipid metabolism, and how they may lead to dysregulation of lipid homeostasis.

Ursodeoxycholic acid suppresses mitochondria-dependent programmed cell death induced by sodium nitroprusside in SH-SY5Y cells

Although ursodeoxycholic acid (UDCA) and its highly water-soluble formula (Yoo's solution; YS) have been shown to prevent neuronal damage, the effects of UDCA or YS against Parkinson's disease (PD)-related dopaminergic cell death has not been studied. This study investigated the protective effects of UDCA and YS on sodium nitroprusside (SNP)-induced cytotoxicity in human dopaminergic SH-SY5Y cells. Both UDCA (50-200 μM) and YS (100-200 μM) dose-dependently prevented SNP (1mM)-induced cell death. Results showed that both UDCA and YS effectively attenuated the production of total reactive oxygen species (ROS), peroxynitrite (ONOO(-)) and nitric oxide (NO), and markedly inhibited the mitochondrial membrane potential (MMP) loss and intracellular reduced glutathione (GSH) depletion. SNP-induced programmed cell death events, such as nuclear fragmentation, caspase-3/7 and -9 activation, Bcl-2/Bax ratio decrease, and cytochrome c release, were significantly attenuated by both UDCA and YS. Furthermore, selective inhibitor of phosphatidylinositiol-3-kinase (PI3K), LY294002, and Akt/PKB inhibitor, triciribine, reversed the preventive effects of UDCA on the SNP-induced cytotoxicity and Bax translocation. These results suggest that UDCA can protect SH-SY5Y cells under programmed cell death process by regulating PI3K-Akt/PKB pathways.

Ursodeoxycholic acid in cholestasis: linking action mechanisms to therapeutic applications

UDCA (ursodeoxycholic acid) is the therapeutic agent most widely used for the treatment of cholestatic hepatopathies. Its use has expanded to other kinds of hepatic diseases, and even to extrahepatic ones. Such versatility is the result of its multiple mechanisms of action. UDCA stabilizes plasma membranes against cytolysis by tensioactive bile acids accumulated in cholestasis. UDCA also halts apoptosis by preventing the formation of mitochondrial pores, membrane recruitment of death receptors and endoplasmic-reticulum stress. In addition, UDCA induces changes in the expression of metabolizing enzymes and transporters that reduce bile acid cytotoxicity and improve renal excretion. Its capability to positively modulate ductular bile flow helps to preserve the integrity of bile ducts. UDCA also prevents the endocytic internalization of canalicular transporters, a common feature in cholestasis. Finally, UDCA has immunomodulatory properties that limit the exacerbated immunological response occurring in autoimmune cholestatic diseases by counteracting the overexpression of MHC antigens and perhaps by limiting the production of cytokines by immunocompetent cells. Owing to this multi-functionality, it is difficult to envisage a substitute for UDCA that combines as many hepatoprotective effects with such efficacy. We predict a long-lasting use of UDCA as the therapeutic agent of choice in cholestasis.

Tauroursodeoxycholic acid (TUDCA) protects photoreceptors from cell death after experimental retinal detachment

BACKGROUND

Detachment of photoreceptors from the underlying retinal pigment epithelium is seen in various retinal disorders such as retinal detachment and age-related macular degeneration and leads to loss of photoreceptors and vision. Pharmacologic inhibition of photoreceptor cell death may prevent this outcome. This study tests whether systemic administration of tauroursodeoxycholic acid (TUDCA) can protect photoreceptors from cell death after experimental retinal detachment in rodents.

METHODOLOGY/PRINCIPAL FINDINGS

Retinal detachment was created in rats by subretinal injection of hyaluronic acid. The animals were treated daily with vehicle or TUDCA (500 mg/kg). TUNEL staining was used to evaluate cell death. Photoreceptor loss was evaluated by measuring the relative thickness of the outer nuclear layer (ONL). Macrophage recruitment, oxidative stress, cytokine levels, and caspase levels were also quantified. Three days after detachment, TUDCA decreased the number of TUNEL-positive cells compared to vehicle (651±68/mm(2) vs. 1314±68/mm(2), P = 0.001) and prevented the reduction of ONL thickness ratio (0.84±0.03 vs. 0.65±0.03, P = 0.002). Similar results were obtained after 5 days of retinal detachment. Macrophage recruitment and expression levels of TNF-a and MCP-1 after retinal detachment were not affected by TUDCA treatment, whereas increases in activity of caspases 3 and 9 as well as carbonyl-protein adducts were almost completely inhibited by TUDCA treatment.

CONCLUSIONS/SIGNIFICANCE

Systemic administration of TUDCA preserved photoreceptors after retinal detachment, and was associated with decreased oxidative stress and caspase activity. TUDCA may be used as a novel therapeutic agent for preventing vision loss in diseases that are characterized by photoreceptor detachment.

cAMP-guanine exchange factor protection from bile acid-induced hepatocyte apoptosis involves glycogen synthase kinase regulation of c-Jun NH2-terminal kinase

Cholestatic liver disorders are accompanied by the hepatic accumulation of cytotoxic bile acids that induce cell death. Increases in cAMP protect hepatocytes from bile acid-induced apoptosis by a cAMP-guanine exchange factor (cAMP-GEF)/phosphoinositide-3-kinase (PI3K)/Akt pathway. The aim of these studies was to identify the downstream substrate in this pathway and to determine at what level in the apoptotic cascade cytoprotection occurs. Since inhibitory phosphorylation of glycogen synthase kinase-3 (GSK) occurs downstream of PI3K/Akt and this phosphorylation has been implicated in cell survival, we conducted studies to determine whether GSK was downstream in cAMP-GEF/PI3K/Akt-mediated cytoprotection. Our results show that treatment of hepatocytes with the cAMP-GEF-specific analog, 4-(4-chlorophenylthio)-2'-O-methyladenosine-3',5'-cAMP, results in PI3K-dependent phosphorylation of GSK. Direct chemical inhibition of GSK in rat hepatocytes or human HUH7-NTCP cells with several structurally and functionally distinct inhibitors including bromoindirubin-3'-oxime (BIO), maleimides (SB216763, SB415286), thiadiazolidine derivatives, and LiCl attenuates apoptosis induced by glycochenodeoxycholate (GCDC). In addition, genetic silencing of the GSK β isoform with small interfering RNA attenuates GCDC apoptosis in HUH7-NTCP cells. Adenoviral inhibition of the Rap1 blocks both cAMP-GEF-mediated cytoprotection against GCDC-induced apoptosis and Akt/GSK3β phosphorylation. GCDC-induced phosphorylation of the proapoptotic kinase, c-Jun NH(2)-terminal kinase (JNK) is inhibited by GSK inhibition or cAMP-GEF activation. GCDC-induced apoptosis is accompanied by phosphorylation of the endoplasmic reticulum stress markers pIEF2α and IRE-1, and pretreatment with the cAMP-GEF analog or GSK inhibitors prevents this phosphorylation. Collectively, our results support the presence of a cAMP/cAMP-GEF/Rap1/PI3K/Akt/GSKβ survival pathway in hepatocytes that inhibits bile acid-induced JNK phosphorylation.

The chemical chaperones tauroursodeoxycholic and 4-phenylbutyric acid accelerate thyroid hormone activation and energy expenditure

Exposure of cell lines endogenously expressing the thyroid hormone activating enzyme type 2 deiodinase (D2) to the chemical chaperones tauroursodeoxycholic acid (TUDCA) or 4-phenylbutiric acid (4-PBA) increases D2 expression, activity and T3 production. In brown adipocytes, TUDCA or 4-PBA induced T3-dependent genes and oxygen consumption (∼2-fold), an effect partially lost in D2 knockout cells. In wild type, but not in D2 knockout mice, administration of TUDCA lowered the respiratory quotient, doubled brown adipose tissue D2 activity and normalized the glucose intolerance associated with high fat feeding. Thus, D2 plays a critical role in the metabolic effects of chemical chaperones.

Unconjugated bile salts shuttle through hepatocyte peroxisomes for taurine conjugation

Bile acid-CoA:amino acid N-acyltransferase (BAAT) conjugates bile salts to glycine or taurine, which is the final step in bile salt biosynthesis. In addition, BAAT is required for reconjugation of bile salts in the enterohepatic circulation. Recently, we showed that BAAT is a peroxisomal protein, implying shuttling of bile salts through peroxisomes for reconjugation. However, the subcellular location of BAAT remains a topic of debate. The aim of this study was to obtain direct proof for reconjugation of bile salts in peroxisomes. Primary rat hepatocytes were incubated with deuterium-labeled cholic acid (D(4)CA). Over time, media and cells were collected and the levels of D(4)CA, D(4)-tauro-CA (D(4)TCA), and D(4)-glyco-CA (D(4)GCA) were quantified by liquid chromatography-tandem mass spectrometry (LC/MS/MS). Subcellular accumulation of D(4)-labeled bile salts was analyzed by digitonin permeabilization assays and subcellular fractionation experiments. Within 24 hours, cultured rat hepatocytes efficiently (>90%) converted and secreted 100 μM D(4)CA to D(4)TCA and D(4)GCA. The relative amounts of D(4)TCA and D(4)GCA produced were dependent on the presence of glycine or taurine in the medium. Treatment of D(4)CA-exposed hepatocytes with 30-150 μg/mL digitonin led to the complete release of D(4)CA, D(4)GCA, and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) (cytosolic marker). Full release of D(4)TCA, catalase, and BAAT was only observed at 500 μg/mL digitonin, indicating the presence of D(4)TCA in membrane-enclosed organelles. D(4)TCA was detected in fractions of purified peroxisomes, which did not contain D(4)CA and D(4)GCA.

CONCLUSION

We established a novel assay to study conjugation and intra- and transcellular transport of bile salts. Using this assay, we show that cholic acid shuttles through peroxisomes for taurine-conjugation.

Conjugation is essential for the anticholestatic effect of NorUrsodeoxycholic acid in taurolithocholic acid-induced cholestasis in rat liver

NorUDCA (24-norursodeoxycholic acid), the C₂₃-homolog of ursodeoxycholic acid (UDCA), showed remarkable therapeutic effects in cholestatic Mdr2 (Abcb4) (multidrug resistance protein 2/ATP-binding cassette b4) knockout mice with sclerosing/fibrosing cholangitis. In contrast to UDCA, norUDCA is inefficiently conjugated in human and rodent liver, and conjugation has been discussed as a key step for the anticholestatic action of UDCA in cholestasis. We compared the choleretic, anticholestatic, and antiapoptotic properties of unconjugated and taurine-conjugated UDCA (C₂₄) and norUDCA (C₂₃) in isolated perfused rat liver (IPRL) and in natrium/taurocholate cotransporting polypeptide (Ntcp)-transfected human hepatoma (HepG2) cells. Taurolithocholic acid (TLCA) was used to induce a predominantly hepatocellular cholestasis in IPRL. Bile flow was determined gravimetrically; bile acids determined by gas chromatography and liquid chromatography/tandem mass spectrometry; the Mrp2 model substrate, 2,4-dinitrophenyl-S-glutathione (GS-DNP) was determined spectrophotometrically; and apoptosis was determined immunocytochemically. The choleretic effect of C₂₃-bile acids was comparable to their C₂₄-homologs in IPRL. In contrast, TnorUDCA, but not norUDCA antagonized the cholestatic effect of TLCA. Bile flow (percent of controls) was 8% with TLCA-induced cholestasis, and unchanged by coinfusion of norUDCA (14%). However, it was increased by TnorUDCA (83%), UDCA (73%) and TUDCA (136%). Secretion of GS-DNP was markedly reduced by TLCA (5%), unimproved by norUDCA (4%) or UDCA (17%), but was improved modestly by TnorUDCA (26%) or TUDCA (58%). No apoptosis was observed in IPRL exposed to low micromolar TLCA, but equivalent antiapoptotic effects of TUDCA and TnorUDCA were observed in Ntcp-HepG2 cells exposed to TLCA.

CONCLUSION

Conjugation is essential for the anticholestatic effect of norUDCA in a model of hepatocellular cholestasis. Combined therapy with UDCA and norUDCA may be superior to UDCA or norUDCA monotherapy in biliary disorders in which hepatocyte as well as cholangiocyte dysfunction contribute to disease progression.

Phosphatidylinositol-3-kinase p110γ contributes to bile salt-induced apoptosis in primary rat hepatocytes and human hepatoma cells

BACKGROUND & AIMS

Glycochenodeoxycholate (GCDC) and taurolithocholate (TLC) are hepatotoxic and cholestatic bile salts, whereas tauroursodeoxycholate (TUDC) is cytoprotective and anticholestatic. Yet they all act, in part, through phosphatidylinositol-3-kinase(PI3K)-dependent mechanisms ("PI3K-paradox"). Hepatocytes express three catalytic PI3K Class I isoforms (p110α/β/γ), specific functions of which, in liver, are unclear. In other cell types, p110γ is associated with detrimental effects. To shed light on the PI3K enigma, we determined whether hydrophobic and hydrophilic bile salts differentially activate distinct p110 isoforms in hepatocytes, and whether p110γ mediates bile salt-induced hepatocyte cell death.

METHODS

Isoform-specific PI3K activity assays were established to determine isoform activation by bile salts in rat hepatocytes. Activation of Akt and JNK was determined by immunoblotting. Following stimulation with hydrophobic bile salts, hepatocellular apoptosis was determined morphologically after Hoechst staining and by analysis of caspase-3/-7 activity or caspase-3 cleavage. Activity or expression of PI3K p110γ was inhibited pharmacologically (AS604850) or by knock-down using specific siRNA.

RESULTS

All bile salts tested activated p110β, while p110α was activated by TUDC and GCDC. Intriguingly, only hydrophobic bile salts activated p110γ. Inhibition of p110γ attenuated GCDC-induced Akt- and JNK-activation, but did not alter TUDC- or cAMP-induced Akt-signaling in rat hepatocytes. Inhibition or knock-down of p110γ markedly attenuated hydrophobic bile salt-induced apoptosis in rat hepatocytes and human hepatoma cell lines but did not alter Fas-, tumor necrosis factor α- and etoposide-induced apoptosis. Depletion of Ca(++) prevented GCDC-induced toxicity in rat hepatocytes but did not affect GCDC-induced Akt- and JNK-activation.

CONCLUSIONS

PI3K p110γ is activated by hydrophobic, but not hydrophilic bile salts. Bile salt-induced hepatocyte apoptosis is partly mediated via a PI3K p110γ dependent signaling pathway, potentially involving JNK.

Anti-oxidants do not prevent bile acid-induced cell death in rat hepatocytes

BACKGROUND

Bile acids, reactive oxygen species (ROS) and inflammatory cytokines are crucial regulators of cell death in acute and chronic liver diseases. The contribution of each factor to hepatocyte death, either apoptosis or necrosis, has not been clarified as yet. It has been suggested that the generation of oxidative stress by bile acids contributes to hepatocyte death during cholestasis and bile acid toxicity, although the beneficial role of ROS prevention in bile acid-mediated cell death is not fully understood.

AIM

Study the effects of anti-oxidants in bile acid-induced cell death in vitro.

METHODS

Primary rat hepatocytes were exposed to the bile acids glycochenodeoxycholic acid (GCDCA) or taurolithocholic acid-3 sulphate in the absence or presence of ROS scavengers or anti-oxidants. Haeme oxygenase (HO)-1 mRNA levels were analysed by quantitative polymerase chain reaction. Apoptosis was quantified by acridine orange staining and caspase-3 activity assay. Necrosis was detected by Sytox green staining.

RESULTS

Anti-oxidants do not attenuate bile acid-induced cell death. Furthermore, bile acid exposure does not enhance the mRNA expression of the oxidative stress-responsive gene HO-1. The Src-kinase inhibitor, SU6656, does reduce GCDCA-induced apoptosis and necrosis.

CONCLUSIONS

In hepatocytes, bile acid-induced toxicity is not prevented by scavengers of oxidative stress. The beneficial effects observed in patients might be because of the contribution of ROS and cytokines rather than bile acid-mediated oxidative stress. However, the use of specific Src kinase inhibitors might be a useful tool to prevent bile acid-induced injury in liver diseases.

Restoring endoplasmic reticulum function by chemical chaperones: an emerging therapeutic approach for metabolic diseases

The endoplasmic reticulum (ER) is a eukaryotic organelle that plays important roles in protein synthesis, folding and trafficking, calcium homoeostasis and lipid and steroid synthesis. It is the major protein synthesis compartment for secreted, plasma membrane and organelle proteins. Perturbations of ER homeostasis such as the accumulation of unfolded or misfolded proteins cause ER stress. To alleviate this stress, ER triggers an evolutionarily conserved signalling cascade called the unfolded protein response (UPR). As an initial response, the UPR aims at adapting and restoring ER function by translational attenuation, upregulation of ER chaperones and degradation of unfolded proteins. However, if the ER function is severely impaired because of excessive or prolonged exposure to stress, then the inflicted cells may undergo programmed cell death. During ER stress, unstable or partially folded mutant proteins are prevented from trafficking to their proper subcellular localizations and usually rapidly degraded. The small molecules named chemical chaperones help to stabilize these mutant proteins and facilitate their folding and proper trafficking from the ER to their final destinations. Because increasing number of studies suggest that ER stress is involved in a number of disease pathogenesis including neurodegenerative diseases, cancer, obesity, diabetes and atherosclerosis, promoting ER folding capacity through chemical chaperones emerges as a novel therapeutic approach. In this review, we provide insight into the many important functions of chemical chaperones during ER stress, their impact on the ER-stress-related pathologies and their potential as a new drug targets, especially in the context of metabolic disorders.

Enhanced hepatic Nrf2 activation after ursodeoxycholic acid treatment in patients with primary biliary cirrhosis

The cytoprotective mechanisms of ursodeoxycholic acid (UDCA) in primary biliary cirrhosis (PBC) have not been fully clarified. UDCA has some antioxidant properties. Nuclear factor-E2-related factor-2 (Nrf2) plays a critical role in protecting a variety of tissues against oxidative stress. Therefore, to investigate the potential antioxidant effects of UDCA in PBC, we determined the intracellular status of both oxidant stress and antioxidant defenses in paired pre- and posttreatment liver biopsies from 13 PBC patients by immunodetection of 8-hydroxydeoxyguanosine (8-OHdG), Nrf2-, and Nrf2-mediated antioxidant proteins. After UDCA treatment, the number of 8-OHdG-positive hepatocytes or bile duct cells decreased with improvement of hepatic injury. The hepatic levels of both total and phosphorylated Nrf2 protein were increased, along with upregulation of nuclear phosphorylated Nrf2 expression in bile duct cells. In addition, the levels of both thioredoxin (TRX) and thioredoxin reductase 1 (TrxR1) protein were increased in the liver after UDCA. The upregulation of hepatic TRX or TrxR1 protein expression positively correlated with that of total Nrf2 protein expression. In conclusion, UDCA treatment can enhance hepatic Nrf2 activation and upregulate hepatic TRX and TrxR1 protein expression. Hepatic Nrf2 activation may play a role in the therapeutic response to UDCA in PBC.

Microwave-Assisted Synthesis of New Steroidal Thiosemicarbazones Derived from methyl 3-Oxocholanate under Solvent-Free Conditions

A series of novel steroidal thiosemicarbazones derived from methyl 3-oxocholanate were synthesised in good yields via microwave irradiation under solvent-free conditions. The structures of the compounds were confirmed by spectroscopic data. Compared to the conventional method, microwave irradiation was a fast and simple method. These compounds were tested for antibacterial activity against S. aureus, S. pyogenes, and E. coli bacteria.

Tauroursodeoxycholic acid inhibits carbon tetrachloride-induced liver fibrosis in rats

AIM: To determine the inhibitory effects of tauroursodeoxycholic acid (TUDCA) on carbon tetrachloride-induced liver fibrosis in rats.

METHODS: A total of 75 healthy Sprague-Dawley rats were randomly divided into five groups: normal control group, model group, low-dose TUDCA group, high-dose TUDCA group and pentoxifylline (PTX) group. Hepatic fibrosis was induced in rats by hypodermic injection of carbon tetrachloride (40%). The low- and high-dose TUDCA groups were orally administered TUDCA at doses of 50 and 100 mg/(kg•d), respectively. The PTX group was orally administered PTX at a dose of 16 mg/(kg•d). The treatment lasted 8 wk for all the groups. Hematoxylin and eosin staining and Masson's trichrome staining of liver tissue was performed for histopathological evaluation of liver fibrosis. Serum parameters of liver fibrosis were detected by enzyme-linked immunosorbent assay. The expression of transforming growth factor-β1 (TGF-β1) and α-smooth muscle actin (α-SMA) in liver tissue was detected by immunohistochemistry.

RESULTS: Compared with the model group, the levels of serum hyaluronic acid (HA), laminin (LN) and type IV collagen (IV-C) significantly decreased in the low- and high-dose TUDCA groups and the PTX group (HA: 146.33 ± 35.13, 162.2 ± 24.80 and 137.14 ± 22.24 vs 252.83 ± 51.94; LN: 77.20 ± 11.84, 66.80 ± 16.78 and 82.00 ± 10.74 vs 108.00 ± 30.00; IV-C: 14.14 ± 2.59, 12.60 ± 3.17 and 10.09 ± 2.22 vs 25.08 ± 5.93, all P < 0.05). Compared with the model group and normal control group, fibrous septa became thinner and even disappeared, and the number of diffuse cirrhotic nodules and the area of collagen fiber decreased in the TUDCA and PTX intervention groups (all P < 0.05). The expression intensity of TGF-β1 and α-SMA proteins was significantly lower in the TUDCA and PTX intervention groups than in the model group (all P < 0.05), but showed no significant difference between the TUDCA and PTX treatment groups.

CONCLUSION: TUDCA can prevent carbon tetrachloride-induced liver fibrosis in rats by reducing TGF-β1 synthesis, inhibiting hepatic stellate cell activation and decreasing extracellular matrix synthesis.

Bile salts and cholestasis

Bile salts have a crucial role in hepatobiliary and intestinal homeostasis and digestion. Primary bile salts are synthesized by the liver from cholesterol, and may be modified by the intestinal flora to form secondary and tertiary bile salts. Bile salts are efficiently reabsorbed from the intestinal lumen to undergo enterohepatic circulation. In addition to their function as a surfactant involved in the absorption of dietary lipids and fat-soluble vitamins bile salts are potent signaling molecules in both the liver and intestine. Under physiological conditions the bile salt pool is tightly regulated, but the adaptive capacity may fall short under cholestatic conditions. Elevated serum and tissue levels of potentially toxic hydrophobic bile salts during cholestasis may cause mitochondrial damage, apoptosis or necrosis in susceptible cell types. Therapeutic nontoxic bile salts may restore impaired hepatobiliary secretion in cholestatic disorders. The hydrophilic bile salt ursodeoxycholate is today regarded as the effective standard treatment of primary biliary cirrhosis and intrahepatic cholestasis of pregnancy, and is implicated for use in various other cholestatic conditions. Novel therapeutic bile salts that are currently under evaluation may also prove valuable in the treatment of these diseases.

Pharmacological strategies against cold ischemia reperfusion injury

IMPORTANCE OF THE FIELD

Good organ preservation is a determinant of graft outcome after revascularization. The necessity of increasing the quality of organ preservation, as well as of extending cold storage time, has made it necessary to consider the use of pharmacological additives.

AREAS COVERED IN THIS REVIEW

The complex physiopathology of cold-ischemia-reperfusion (I/R) injury--and in particular cell death, mitochondrial injury and endoplasmic reticulum stress--are reviewed. Basic principles of the formulation of the different preservation solutions are discussed.

WHAT THE READER WILL GAIN

Current strategies and new trends in static organ preservation using additives such as trimetazidine, polyethylene glycols, melatonin, trophic factors and endothelin antagonists in solution are presented and discussed. The benefits and mechanisms responsible for enhancing organ protection against I/R injury are also discussed. Graft preservation was substantially improved when additives were added to the preservation solutions.

TAKE HOME MESSAGE

Enrichment of preservation solutions by additives is clinically useful only for short periods. For longer periods of cold ischemia, the use of such additives becomes insufficient because graft function deteriorates as a result of ischemia. In such conditions, the preservation strategy should be changed by the use of machine perfusion in normothermic conditions.

Cyclic AMP stimulates Mrp2 translocation by activating p38{alpha} MAPK in hepatic cells

Cyclic AMP (cAMP) induces translocation of multidrug resistant protein 2 (Mrp2) to the canalicular membrane and activates p38 MAPK in rat hepatocytes. In this study, we tested the hypothesis that cAMP-induced Mrp2 translocation may be mediated via p38 MAPK. Studies were conducted in rat hepatocytes and in a human hepatoma cell line, HuH-7. In rat hepatocytes, cAMP increased Mrp2 translocation and p38 MAPK activity. These effects of cAMP were inhibited by SB203580, an inhibitor of p38 MAPK. Wortmannin, a specific inhibitor of phosphoinositide-3-kinase (PI3K), did not inhibit cAMP induced activation of p38 MAPK, indicating PI3K-independent activation of p38 MAPK by cAMP. To further define the role of p38 MAPK, molecular approaches were used to up- or downregulate p38 MAPK activity in HuH-7 cells using constitutively active (CA) and dominant-negative (DN) MAPK kinase 3 and 6 (MKK3/6). MKK3/6 are upstream kinases responsible for the activation of p38 MAPK. Cells transfected with CAMKK6 showed increased p38 MAPK activity and MRP2 translocation compared with empty vector. cAMP-induced activation of p38 MAPK was inhibited in cells transfected with DNMKK3/6 and DNMKK3, but not with DNMKK6. DNMKK3/6 and DNMKK3 also inhibited cAMP-induced MRP2 translocation. cAMP selectively activated p38alpha MAPK in HuH-7 cells. Knockdown of p38alpha MAPK by short heterodimer RNA resulted in decreased level of p38 MAPK and failure of cAMP to stimulate MRP2 translocation. Taken together, these results suggest that cAMP-induced MRP2 translocation in hepatic cells is mediated via PI3K-independent and MKK3-mediated activation of p38alpha MAPK.

p53 and the regulation of hepatocyte apoptosis: implications for disease pathogenesis

The interplay between p53 and apoptosis in diseases such as cancer, neurodegeneration, ischemia and atherosclerosis underscores the need to understand the complexity of p53 networks. Here, we highlight recent studies of p53-induced apoptosis in human diseases, with a focus on the modulation of liver cell apoptosis. In addition, recent work has provided new insights into mechanisms underlying the antiapoptotic functions of the endogenous bile acid ursodeoxycholic acid (UDCA), suggesting that the finely tuned, complex control of p53 by Mdm2 is a key step in the UDCA modulation of deregulated, p53-triggered apoptosis. The effect of targeting cell death signaling proteins has been established in preclinical models of human diseases. Finally, we review recent therapeutic strategies and clinical applications of targeted agents, with a particular emphasis on the potential use of UDCA.

Prevention of Clostridium sordellii lethal toxin-induced apoptotic cell death by tauroursodeoxycholic acid

Virulent strains of Clostridium sordellii cause gangrenous myonecrosis in humans. The released lethal toxin (TcsL) and hemorrhagic toxin (TcsH) are regarded as the major virulence factors. TcsL inactivates low molecular weight GTP-binding proteins of the Rho/Ras subfamilies by monoglucosylation. In cultured cell lines, glucosylation, i.e., inactivation of Rho/Ras proteins, results in actin reorganization ("cytopathic effect") and apoptotic cell death ("cytotoxic effect"). Apoptotic cell death induced by TcsL is suggested to be based on inhibition of the phosphoinositide 3-kinase (PI3K)/Akt-survival pathway. In this study, we analyze the critical role of PI3K/Akt signaling in TcsL-induced apoptosis using the antiapoptotic bile acid tauroursodeoxycholic acid (TUDCA) as the pharmacological tool. TUDCA preserved the TcsL-induced decrease of the cellular level of phospho-Akt, suggesting that TUDCA activated PI3K/Akt signaling downstream of inhibited Ras signaling. TcsL-induced apoptosis was prevented by TUDCA treatment. The antiapoptotic effect of TUDCA was abolished by the PI3K inhibitor LY294002 and the Akt inhibitor, showing that the antiapoptotic effect depends on PI3K/Akt signaling. Inhibition of Ras/Rho signaling by TcsL resulted in activation of p38 MAP kinase. Inhibition of p38 MAP kinase by SB203580 protected cells from TcsL-induced apoptosis. TUDCA induced activation of p38 MAP kinase as well, an aspect of the TUDCA effects that most likely did not contribute to its antiapoptotic activity. Due to its antiapoptotic activity, TUDCA is under investigation for its potential application as a therapeutic modulator of apoptosis-related diseases. TUDCA may represent a new concept for the treatment of disease associated with toxigenic C. sordellii.

Primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is an immune-mediated chronic cholestatic liver disease with a slowly progressive course. Without treatment, most patients eventually develop fibrosis and cirrhosis of the liver and may need liver transplantation in the late stage of disease. PBC primarily affects women (female preponderance 9–10:1) with a prevalence of up to 1 in 1,000 women over 40 years of age. Common symptoms of the disease are fatigue and pruritus, but most patients are asymptomatic at first presentation. The diagnosis is based on sustained elevation of serum markers of cholestasis, i.e., alkaline phosphatase and gamma-glutamyl transferase, and the presence of serum antimitochondrial antibodies directed against the E2 subunit of the pyruvate dehydrogenase complex. Histologically, PBC is characterized by florid bile duct lesions with damage to biliary epithelial cells, an often dense portal inflammatory infiltrate and progressive loss of small intrahepatic bile ducts. Although the insight into pathogenetic aspects of PBC has grown enormously during the recent decade and numerous genetic, environmental, and infectious factors have been disclosed which may contribute to the development of PBC, the precise pathogenesis remains enigmatic. Ursodeoxycholic acid (UDCA) is currently the only FDA-approved medical treatment for PBC. When administered at adequate doses of 13–15 mg/kg/day, up to two out of three patients with PBC may have a normal life expectancy without additional therapeutic measures. The mode of action of UDCA is still under discussion, but stimulation of impaired hepatocellular and cholangiocellular secretion, detoxification of bile, and antiapoptotic effects may represent key mechanisms. One out of three patients does not adequately respond to UDCA therapy and may need additional medical therapy and/or liver transplantation. This review summarizes current knowledge on the clinical, diagnostic, pathogenetic, and therapeutic aspects of PBC.

Superoxide anions and hydrogen peroxide inhibit proliferation of activated rat stellate cells and induce different modes of cell death

BACKGROUND

In chronic liver injury, hepatic stellate cells (HSCs) proliferate and produce excessive amounts of connective tissue causing liver fibrosis and cirrhosis. Oxidative stress has been implicated as a driving force of HSC activation and proliferation, although contradictory results have been described.

AIM

To determine the effects of oxidative stress on activated HSC proliferation, survival and signalling pathways.

METHODS

Serum-starved culture-activated rat HSCs were exposed to the superoxide anion donor menadione (5-25 micromol/L) or hydrogen peroxide (0.2-5 mmol/L). Haem oxygenase-1 mRNA expression, glutathione status, cell death, phosphorylation of mitogen-activated protein (MAP) kinases and proliferation were investigated.

RESULTS

Menadione induced apoptosis in a dose- and time-dependent, but caspase-independent manner. Hydrogen peroxide induced necrosis only at extremely high concentrations. Both menadione and hydrogen peroxide activated Jun N-terminal kinase (JNK) and p38. Hydrogen peroxide also activated extracellular signal-regulated protein. Menadione, but not hydrogen peroxide, reduced cellular glutathione levels. Inhibition of JNK or supplementation of glutathione reduced menadione-induced apoptosis. Non-toxic concentrations of menadione or hydrogen peroxide inhibited platelet-derived growth factor- or/and serum-induced proliferation.

CONCLUSION

Reactive oxygen species (ROS) inhibit HSC proliferation and promote HSC cell death in vitro. Different ROS induce different modes of cell death. Superoxide anion-induced HSC apoptosis is dependent on JNK activation and glutathione status.

Bile acids: regulation of apoptosis by ursodeoxycholic acid

Bile acids are a group of molecular species of acidic steroids with peculiar physical-chemical and biological characteristics. At high concentrations they become toxic to mammalian cells, and their presence is pertinent in the pathogenesis of several liver diseases and colon cancer. Bile acid cytoxicity has been related to membrane damage, but also to nondetergent effects, such as oxidative stress and apoptosis. Strikingly, hydrophilic ursodeoxycholic acid (UDCA), and its taurine-conjugated form (TUDCA), show profound cytoprotective properties. Indeed, these molecules have been described as potent inhibitors of classic pathways of apoptosis, although their precise mode of action remains to be clarified. UDCA, originally used for cholesterol gallstone dissolution, is currently considered the first choice therapy for several forms of cholestatic syndromes. However, the beneficial effects of both UDCA and TUDCA have been tested in other experimental pathological conditions with deregulated levels of apoptosis, including neurological disorders, such as Alzheimer's, Parkinson's, and Huntington's diseases. Here, we review the role of bile acids in modulating the apoptosis process, emphasizing the anti-apoptotic effects of UDCA and TUDCA, as well as their potential use as novel and alternate therapeutic agents for the treatment of apoptosis-related diseases.

Hemochromatosis: as a conformational disorder

Hereditary hemochromatosis (HH) refers to a unique clinicopathologic subset of iron overload syndromes that includes the disorder related to C282Y homozygous mutation of the hemochromatosis protein (HFE), the most common form of hereditary hemochromatosis. Recent reports have highlighted analogies with the class of disorders, known as the conformational diseases whereby HFE C282Y mutant protein forms aggregates and is subsequently retained in the endoplasmic reticulum (ER). In conformational disorders, accumulation of unfolded or misfolded proteins in the ER can activate a complex cascade linked to the regulation of diverse physiologic processes, disease onset and progression. To-date, reviews on HFE C282Y HH have largely dealt with the end-stage consequence of this disorder (iron overload). However, our review focuses on upstream molecular events resulting from the mislocalization of the aggregation-prone HFE C282Y protein leading to potential advances in treatment and diagnosis.

Bile-acid-induced cell injury and protection

Several studies have characterized the cellular and molecular mechanisms of hepatocyte injury caused by the retention of hydrophobic bile acids (BAs) in cholestatic diseases. BAs may disrupt cell membranes through their detergent action on lipid components and can promote the generation of reactive oxygen species that, in turn, oxidatively modify lipids, proteins, and nucleic acids, and eventually cause hepatocyte necrosis and apoptosis. Several pathways are involved in triggering hepatocyte apoptosis. Toxic BAs can activate hepatocyte death receptors directly and induce oxidative damage, thereby causing mitochondrial dysfunction, and induce endoplasmic reticulum stress. When these compounds are taken up and accumulate inside biliary cells, they can also cause apoptosis. Regarding extrahepatic tissues, the accumulation of BAs in the systemic circulation may contribute to endothelial injury in the kidney and lungs. In gastrointestinal cells, BAs may behave as cancer promoters through an indirect mechanism involving oxidative stress and DNA damage, as well as acting as selection agents for apoptosis-resistant cells. The accumulation of BAs may have also deleterious effects on placental and fetal cells. However, other BAs, such as ursodeoxycholic acid, have been shown to modulate BA-induced injury in hepatocytes. The major beneficial effects of treatment with ursodeoxycholic acid are protection against cytotoxicity due to more toxic BAs; the stimulation of hepatobiliary secretion; antioxidant activity, due in part to an enhancement in glutathione levels; and the inhibition of liver cell apoptosis. Other natural BAs or their derivatives, such as cholyl-N-methylglycine or cholylsarcosine, have also aroused pharmacological interest owing to their protective properties.

cAMP-GEF cytoprotection by Src tyrosine kinase activation of phosphoinositide-3-kinase p110 beta/alpha in rat hepatocytes

Cyclic AMP protects against hepatocyte apoptosis by a protein kinase A-independent cAMP-GEF/phosphoinositide-3-kinase (PI3K)/Akt signaling pathway. However, the signaling pathway coupling cAMP-GEF with PI3K is unknown. The aim of this study was to investigate the role of Src tyrosine kinases (Src-TYK) and PI3K-p110 isoforms in this pathway. Studies were done in rat hepatocytes using the hydrophobic bile acid glycochenodeoxycholic acid (GCDC) to induce apoptosis. cAMP-binding guanine nucleotide exchange factors (cAMP-GEFs) were selectively activated by using 4-(4-chloro-phenylthio)-2'-O-methyladenosine-3'-5'-cyclic monophosphate (CPT-2-Me-cAMP), which sequentially phosphorylated Src-TYK (within 1 min) followed by Akt (within 5 min). The Src inhibitors PP2 and SU6656 inhibited basal and CPT-2-Me-cAMP-mediated Src and Akt phosphorylation. These inhibitors had no effect on CPT-2-Me-cAMP-mediated activation of Rap GTPases. CPT-2-Me-cAMP induced transient Src dependent autophosphorylation of the epidermal growth factor receptor (EGFR). Inhibition of the EGFR with AG 1478 partially inhibited the ability of CPT-2-Me to phosphorylate Akt. Whereas PP2 completely abolished the protective effect of CPT-2-Me-cAMP in GCDC induced apoptosis, AG 1478 partially inhibited the cytoprotective effect. CPT-2-Me-cAMP treatment resulted in Src-dependent activation of the p110 beta and alpha subunits of PI3K, but only the latter was sensitive to inhibition with AG 1478. In conclusion, activation of cAMP-GEFs results in phosphorylation of Src-TYK and Akt and activation of the p110 beta/alpha subunits of PI3K. Maximal cAMP-GEF-mediated Akt phosphorylation as well as protection from bile acid-induced apoptosis requires activation of Src-TYK and the EGFR. These studies support the existence of two pathways: cAMP-GEF/Rap/Src/PI3Kbeta/Akt and cAMP-GEF/Rap/Src/EGFR/PI3Kalpha/Akt, both of which are necessary for maximal cytoprotective effect of cAMP-GEFs in hepatocytes.

Ursodeoxycholic acid induces glutathione synthesis through activation of PI3K/Akt pathway in HepG2 cells

Ursodeoxycholic acid (UDCA) is widely recognized as an effective compound in the treatment of chronic hepatitis and is known to modulate the redox state of the liver accompanied by an increase of GSH. In the present study, to access the antioxidative effect of UDCA and to clarify the molecular basis of the action on GSH level, we evaluated its effects in HepG2 cells exposed to excessive iron. UDCA inhibited both a decrease in the GSH level and an increase in the reactive oxygen species caused by excessive iron in the cells. UDCA increased the gene expression of the catalytic- and modifier-units of glutamine-cysteine ligase (GCL), which is a key enzyme in GSH synthesis. We further investigated the effect of UDCA on the phosphatidylinositol 3-kinase (PI3K)/Akt pathway, and obtained results showing that UDCA-induced increase in the GSH level was prevented by LY294002, a PI3K inhibitor. In addition, Western blot analysis of Akt showed that, while the total Akt level remained unchanged, the phosphorylated Akt level was increased by UDCA, and this increase was also prevented by LY294002. Moreover, UDCA promoted the translocation of a transcription factor, nuclear factor-E2-related factor-2 (Nrf2), into the nucleus, and this action was inhibited by LY294002. From these results, it was indicated that UDCA increased the GSH synthesis through an activation of the PI3K/Akt/Nrf2 pathway. This may be a primary mechanism of antioxidative action of UDCA concerned with its therapeutic effectiveness in chronic hepatitis.

The active metabolite of leflunomide, A77 1726, protects rat hepatocytes against bile acid-induced apoptosis

BACKGROUND/AIMS

Leflunomide is used in the treatment of autoimmune diseases as an anti-inflammatory agent. Leflunomide and its active metabolite A77 1726 modulate mitogen-activated protein kinases (MAPK), Src kinases, the phosphoinositide-3 kinase (PI3K)/Akt-pathway and nuclear factor (NF)-kappaB activation. Both cell protective and cytotoxic effects of leflunomide have been described. Since leflunomide affects pathways involved in hepatocyte cell survival, we examined the effects of A77 1726 on hepatocyte cell death.

METHODS

Primary rat hepatocytes were exposed to the bile acid glycochenodeoxycholic acid (GCDCA), the superoxide anion donor menadione, or tumor necrosis factor (TNF) alpha in combination with actinomycin D. Activation of MAP-kinases was determined by Western blot analysis. Apoptosis and necrosis were analyzed by acridine orange staining and caspase activity and Sytox Green staining, respectively.

RESULTS

A77 1726 dose-dependently reduces GCDCA-induced apoptosis and necrosis, but not menadione- or TNFalpha/ActD-induced apoptosis. The hepatoprotective effect of A77 1726 does not involve ERK1/2, p38 or PI3K/Akt activation. A77 1726 does not inhibit NF-kappaB activation in hepatocytes.

CONCLUSIONS

Since A77 1726 inhibits bile acid-induced apoptosis and does not sensitize hepatocytes to TNFalpha, our results suggest that A77 1726 could be considered for the treatment of chronic liver diseases accompanied by elevated bile acid levels and inflammation.

Treatment with taurine attenuates hepatic apoptosis in NZB/W F1 mice fed with a high-cholesterol diet

Cholesterol-rich diets are known to cause hepatic apoptosis, which has been associated with the pathogenesis of systemic lupus erythematosus (SLE). However, the mechanisms and treatments for hepatic apoptosis in SLE are poorly understood. To clarify the effects of taurine on hepatic apoptosis in SLE, NZB/W F1 mice received control, cholesterol, and cholesterol/taurine diets. Significant reductions of caspase-3 activity, TUNEL-positive cells, and Fas- and mitochondrial- dependent apoptosis were detected in liver from the cholesterol/taurine group as compared to the cholesterol group. Moreover, significant increases of phosphorylated AKT, NF-kappaB (p65), and ERK1/2 proteins were detected in liver from the cholesterol/taurine group as compared to the cholesterol group. In contrast, a significant reduction of phosphorylated p38 protein was observed in the cholesterol/taurine group. These experimental results demonstrated positive effects of taurine against hepatic apoptosis in NZB/W F1 mice fed a high-cholesterol diet and suggested the therapeutic potential of taurine in SLE.

Activation of focal adhesion kinase and JNK contributes to the extracellular matrix and cAMP-GEF mediated survival from bile acid induced apoptosis in rat hepatocytes

BACKGROUND/AIMS

Adherence to an extracellular matrix (ECM) rescues hepatocytes from apoptosis, but how hepatocytes adhered to different ECM and respond to apoptotic and cytoprotective stimuli is unknown.

METHODS

Rat hepatocytes were plated on type 1 collagen (CI), laminin (LM) or polylysine (PL) and the amount of apoptosis induced by glycochenodeoxycholate (GCDC), deoxycholate (DCA), Fas ligand or serum withdrawal was determined by Hoechst staining. The response to cytoprotection by cAMP-guanine exchange factor (cAMP-GEF) activation was determined. Kinase activation was determined by immunoblotting with phosphospecific antibodies.

RESULTS

Hepatocytes on LM and PL had more apoptosis in response to all apoptotic stimuli. GCDC increased c-jun-N-terminal kinase (JNK) phosphorylation 2-fold in hepatocytes on CI, but 15- and 30-fold in hepatocytes on PL or LM. SP-600125, a JNK inhibitor, prevented LM and PL potentiation of bile acid apoptosis. GCDC induced dephosphorylation of focal adhesion kinase (FAK) was prevented by cAMP-GEF activation. Cytochalasin B which decreased FAK phosphorylation prevented cAMP-GEF cytoprotection.

CONCLUSIONS

JNK activation augments apoptosis in hepatocytes plated on PL and LM. Decreased FAK phosphorylation as seen in cells treated with bile acids or attached to PL and LM promotes hepatocyte apoptosis.

High dose ursodeoxycholic acid for the treatment of primary sclerosing cholangitis is safe and effective

BACKGROUND/AIMS

Ursodeoxycholic acid (UDCA) has been shown to improve serum liver tests in primary sclerosing cholangitis (PSC), but controlled trials have shown inconsistent effects on liver histology, and did not reveal a survival benefit. This pilot, randomised dose-ranging trial attempted to determine whether further enrichment of the bile acid pool with UDCA would lead to an improvement in outcome for PSC patients.

METHODS

Thirty-one patients with PSC were randomised to treatment with either 10 mg/kg (low dose), 20 mg/kg (standard dose) or 30 mg/kg (high dose) daily of UDCA for 2 years. Patients were assessed every 12 weeks and underwent liver biopsy at the beginning and end of the trial.

RESULTS

Serum liver tests improved in all groups taking UDCA. Survival probability at 1-4 years as evaluated by the Mayo risk score tended to improve for all patients and significantly improved for the high dose group (p<0.02). Only 3 (10%) of all patients had a Ludwig score showing histological deterioration over the trial period.

CONCLUSIONS

High dose UDCA is well-tolerated and is associated with an improvement in survival probability. A trend towards stability/improvement in histological stage was also observed. This treatment appears to be effective for PSC and deserves further evaluation.

Farnesoid X receptor protects liver cells from apoptosis induced by serum deprivation in vitro and fasting in vivo

The farnesoid X receptor (FXR) is a key metabolic regulator in the liver by maintaining the homeostasis of liver metabolites. Recent findings suggest that FXR may have a much broader function in liver physiology and pathology. In the present work, we identify a novel role of FXR in protecting liver cell from apoptosis induced by nutritional withdrawal including serum deprivation in vitro or starvation in vivo. Two FXR ligands, chenodeoxycholic acid (CDCA) and GW4064, rescued HepG2 cells from serum deprivation-induced apoptosis in a dose-dependent manner. This effect of FXR on apoptotic suppression was compromised when FXR was knocked down by short interfering RNA. Similarly, the effects of both CDCA and GW4064 were abolished after inhibition of the MAPK pathway by a specific inhibitor of MAPK kinase 1/2. Immunoblotting results indicated that FXR activation by CDCA and GW4064 induced ERK1/2 phosphorylation, which was attenuated by serum deprivation. In vivo, FXR(-/-) mice exhibited an exacerbated liver apoptosis and lower levels of phosphorylated-ERK1/2 compared to wild-type mice after starvation. In conclusion, our results suggest a novel role of FXR in modulating liver cell apoptosis.

Carbon monoxide blocks oxidative stress-induced hepatocyte apoptosis via inhibition of the p54 JNK isoform

Most chronic liver diseases are accompanied by oxidative stress, which may induce apoptosis in hepatocytes and liver injury. Oxidative stress induces heme oxygenase-1 (HO-1) expression. This stress-responsive cytoprotective protein is responsible for heme degradation into carbon monoxide (CO), free iron, and biliverdin. CO is an important intracellular messenger; however, the exact mechanisms responsible for its cytoprotective effect are not yet elucidated. Thus, we investigated whether HO-1 and CO protect primary hepatocytes against oxidative-stress-induced apoptosis. In vivo, bile duct ligation was used as model of chronic liver disease. In vitro, primary hepatocytes were exposed to the superoxide anion donor menadione in a normal and in a CO-- containing atmosphere. Apoptosis was determined by measuring caspase-9, -6, -3 activity and poly(ADP-ribose) polymerase cleavage, and necrosis was determined by Sytox green staining. The results showed that (1) HO-1 is induced in chronic cholestatic liver disease, (2) superoxide anions time- and dose-dependently induce HO-1 activity, (3) HO-1 overexpression inhibits superoxide-anions-induced apoptosis, and (4) CO blocks superoxide-anions-induced JNK phosphorylation and caspase-9, -6, -3 activation and abolishes apoptosis but does not increase necrosis. We conclude that HO-1 and CO protect primary hepatocytes against superoxide-anions-induced apoptosis partially via inhibition of JNK activity. CO could represent an important candidate for the treatment of liver diseases.

CHOP deficiency attenuates cholestasis-induced liver fibrosis by reduction of hepatocyte injury

CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP) is a key component in endoplasmic reticulum (ER) stress-mediated apoptosis. The goal of the study was to investigate the role of CHOP in cholestatic liver injury. Acute liver injury and liver fibrosis were assessed in wild-type (WT) and CHOP-deficient mice following bile duct ligation (BDL). In WT livers, BDL induced overexpression of CHOP and Bax, a downstream target in the CHOP-mediated ER stress pathway. Liver fibrosis was attenuated in CHOP-knockout mice. Expression levels of alpha-smooth muscle actin and transforming growth factor-beta1 were reduced, and apoptotic and necrotic hepatocyte death were both attenuated in CHOP-deficient mice. Hepatocytes were isolated from WT and CHOP-deficient mice and treated with 400 microM glycochenodeoxycholic acid (GCDCA) for 8 h to examine bile acid-induced apoptosis and necrosis. GCDCA induced overexpression of CHOP and Bax in isolated WT hepatocytes, whereas CHOP-deficient hepatocytes had reduced cleaved caspase-3 expression and a lower propidium iodide index after GCDCA treatment. In conclusion, cholestasis induces CHOP-mediated ER stress and triggers hepatocyte cell death, and CHOP deficiency attenuates this cell death and subsequent liver fibrosis. The results demonstrate an essential role of CHOP in development of liver fibrosis due to cholestatic liver damage.

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.

Taurolithocholic acid-3 sulfate impairs insulin signaling in cultured rat hepatocytes and perfused rat liver

BACKGROUND/AIMS

The role of bile acids for insulin resistance in cholestatic liver disease is unknown.

METHODS

The effect of taurolithocholic acid-3 sulfate (TLCS) on insulin signaling was studied in cultured rat hepatocytes and perfused rat liver.

RESULTS

TLCS induced insulin resistance at the level of insulin receptor (IR) beta Tyr(1158) phosphorylation, phosphoinositide (PI) 3-kinase activity and protein kinase (PK)B Ser(473) phosphorylation in cultured hepatocytes. Consistently, the insulin stimulation of the PI 3-kinase-dependent K(+) uptake, hepatocyte swelling and proteolysis inhibition was blunted by TLCS in perfused rat liver. The PKC inhibitor Go6850 and tauroursodeoxycholate (TUDC) counteracted the suppression of insulin-induced IRbeta and PKB phosphorylation by TLCS. Rapamycin and dibutyryl-cAMP, which inhibited basal signaling via mammalian target of rapamycin (mTOR), restored insulin-induced PKB- but not IRbeta phosphorylation. In livers from 7 day bile duct-ligated rats PKB Ser(473) phosphorylation was decreased by about 50%.

CONCLUSION

TLCS induces insulin resistance by a PKC-dependent suppression of insulin-induced IRbeta phosphorylation and the PI 3-kinase/PKB path. This can in part be compensated by a decrease of mTOR activity, which may release insulin-sensitive components downstream of the insulin receptor from tonic inhibition. The data suggest that retention of hydrophobic bile acids confers insulin resistance on the cholestatic liver.

Tauroursodeoxycholic acid reduces bile acid-induced apoptosis by modulation of AP-1

Ursodeoxycholic acid (UDCA) is used in the therapy of cholestatic liver diseases. Apoptosis induced by toxic bile acids plays an important role in the pathogenesis of liver injury during cholestasis and appears to be mediated by the human transcription factor AP-1. We aimed to study if TUDCA can decrease taurolitholic acid (TLCA)-induced apoptosis by modulating AP-1. TLCA (20 microM) upregulated AP-1 proteins cFos (26-fold) and JunB (11-fold) as determined by quantitative real-time PCR in HepG2-Ntcp hepatoma cells. AP-1 transcriptional activity increased by 300% after exposure to TLCA. cFos and JunB expression as well as AP-1 transcriptional activity were unaffected by TUDCA (75 microM). However, TUDCA significantly decreased TLCA-induced upregulation of cFos and JunB. Furthermore, TUDCA inhibited TLCA-induced AP-1 transcriptional activity and reduced TLCA-induced apoptosis. These data suggest that reversal of bile acid-induced AP-1 activation may be relevant for the antiapoptotic effect of TUDCA in liver cells.

Ursodeoxycholic acid: Mechanism of action and novel clinical applications

Ursodeoxycholic acid (UDCA) is used in the treatment of cholestatic liver diseases, gallstone dissolution, and for patients with hepatitis C virus infection to ameliorate elevated alanine aminotransferase levels. The efficacy of UDCA treatment has been debated and the mechanisms of action in humans have still not defined. Suggested mechanisms include the improvement of bile acid transport and/or detoxification, cytoprotection, and anti-apoptotic effects. In this review, we summarize the proposed molecular mechanisms for the action of UDCA, especially in hepatocytes, and also discuss the putative future clinical usage of this unique drug.

PF2401-SF, standardized fraction of Salvia miltiorrhiza and its constituents, tanshinone I, tanshinone IIA, and cryptotanshinone, protect primary cultured rat hepatocytes from bile acid-induced apoptosis by inhibiting JNK phosphorylation

Bile acid-induced hepatocyte apoptosis plays an important role in cholestatic liver disease, and the role of apoptosis may be of therapeutic interest in preventing liver disease. The dried root of Salvia miltiorrhiza Bunge (Labiatae) has been used traditionally to treat liver diseases. We investigated the antiapoptotic effects of a standardized fraction of S. miltiorrhiza (PF2401-SF) and its components, tanshinone I, tanshinone IIA, and cryptotanshinone, in primary cultured rat hepatocytes. PF2401-SF was enriched with tanshinone I (11.5%), tanshinone IIA (41.0%), and cryptotanshinone (19.1%). Glycochenodeoxycholic acid (GCDC)-induced apoptosis, as shown by DNA fragmentation, poly(ADP-ribose) polymerase cleavage, and activation of caspases-8, -9, and -3. PF2401-SF and its components, tanshinone I, tanshinone IIA, and cryptotanshinone showed antiapoptotic activity. Treatment with PF2401-SF or with its components significantly inhibited the generation of intracellular reactive oxygen species. Hydrophobic bile acids activate c-Jun-NH(2)-terminal kinase (JNK), p38 mitogen-activated protein kinases (MAPK), and extracellular signal-regulated kinase 1/2, and PF2401-SF inhibited the phosphorylation of JNK and p38. All three components of PF2401-SF inhibited JNK phosphorylation. Addition of inhibitors of MAPK showed that inhibition of JNK decreased apoptosis. These data indicate that PF2401-SF and its components protect hepatocytes from GCDC-induced apoptosis in vitro by inhibiting JNK.

Effects of bile acids on expression of the human apical sodium dependent bile acid transporter gene

Using a luciferase reporter assay in both LMH cells and Caco2 cells we found that certain bile acids including unconjugated deoxycholic and others transactivated the ileal apical sodium-dependent bile acid transporter (ASBT) at concentrations ranging from 20 to 300 microM. Confirming this effect, addition of deoxycholic acid to fresh human ileal biopsies caused an approximate 40% increase in endogenous ASBT mRNA production. Promoter deletion analysis indicated the effect of bile acids was mediated by a response element located in the downstream half of the 5'-UTR, a region known to contain a retinoic acid (RXR/RAR) response element and an activated protein-1 (AP-1) response element. Site-directed mutagenesis of the RAR/RXR response element actually enhanced response to deoxycholic acid. Site-directed mutagenesis of the downstream AP-1 response element reduced activation by deoxycholic acid while deletion of this response element completely eliminated this response. The epidermal growth factor (EGF) receptor inhibitor, AG1478, completely eliminated the response to bile acid while the mitogen-activated protein extracellular signal-regulated kinase cascade (MEK) inhibitor, U0126, partially inhibited the response to bile acid. These studies demonstrate that certain bile acids stimulate ASBT gene expression acting on the down-stream AP-1 response element via the EGF receptor and MEK cascade.

Glycoursodeoxycholic Acid and Interleukin-10 Modulate the Reactivity of Rat Cortical Astrocytes to Unconjugated Bilirubin

The pathogenesis of bilirubin encephalopathy seems to result from accumulation of unconjugated bilirubin (UCB) within the brain. We have recently demonstrated that UCB causes astroglial release of proinflammatory cytokines and glutamate, as well as cell death. The bile acid glycoursodeoxycholic acid (GUDCA) and the anti-inflammatory cytokine interleukin (IL)-10 have been reported to modulate inflammation and cell survival. In this study we investigated the effect of these therapeutic agents on the astroglial response to UCB. Only GUDCA prevented UCB-induced astroglial death. The secretion of tumor necrosis factor-alpha (TNF-alpha) and IL-1beta elicited by UCB in astrocytes was reduced in the presence of GUDCA and IL-10, whereas the suppression of IL-6 was only counteracted by GUDCA. Neither GUDCA nor IL-10 modulated the accumulation of extracellular glutamate. Additionally, IL-10 markedly inhibited UCB-induced nuclear factor-kappaB nuclear translocation and cytokine mRNA expression, whereas GUDCA only prevented TNF-alpha mRNA expression. Moreover, GUDCA inhibited TNF-alpha- and IL-1beta-converting enzymes, preventing the maturation of these cytokines and their consequent release. Collectively, this study shows that IL-10 action is restricted to UCB-induced release of TNF-alpha and IL-1beta from the astrocytes, whereas GUDCA presents a more ubiquitous action on the astroglial reactivity to UCB. Hence, GUDCA may have potential benefits over an IL-10 therapeutic approach in reducing UCB-induced astrocyte immunostimulation and death.

Intestinal capacity to digest and absorb carbohydrates is maintained in a rat model of cholestasis

Cholestasis is associated with systemic accumulation of bile salts and with deficiency of bile in the intestinal lumen. During the past years bile salts have been identified as signaling molecules that regulate lipid, glucose, and energy metabolism. Bile salts have also been shown to activate signaling routes leading to proliferation, apoptosis, or differentiation. It is unclear, however, whether cholestasis affects the constitution and absorptive capacity of the intestinal epithelium in vivo. We studied small intestinal morphology, proliferation, apoptosis, expression of intestine-specific genes, and carbohydrate absorption in cholestatic (1 wk bile duct ligation), bile-deficient (1 wk bile diversion), and control (sham) rats. Absorptive capacity was assessed by determination of plasma [(2)H]- and [(13)C]glucose concentrations after intraduodenal administration of [(2)H]glucose and naturally enriched [(13)C]sucrose, respectively. Small intestinal morphology, proliferation, apoptosis, and gene expression of intestinal transcription factors (mRNA levels of Cdx-2, Gata-4, and Hnf-1alpha, and Cdx-2 protein levels) were similar in cholestatic, bile-deficient, and control rats. The (unlabeled) blood glucose response after intraduodenal administration was delayed in cholestatic animals, but the absorption over 180 min was quantitatively similar between the groups. Plasma concentrations of [(2)H]glucose and [(13)C]glucose peaked to similar extents in all groups within 7.5 and 30 min, respectively. Absorption of [(2)H]glucose and [(13)C]glucose in plasma was similar in all groups. The present data indicate that neither accumulation of bile salts in the body, nor their intestinal deficiency, two characteristic features of cholestasis, affect rat small intestinal proliferation, differentiation, apoptosis, or its capacity to digest and absorb carbohydrates.

Tauroursodeoxycholic acid inhibits apoptosis induced by Z alpha-1 antitrypsin via inhibition of Bad

Z alpha-1 antitrypsin (AAT) deficiency is a genetic disease associated with accumulation of misfolded AAT in the endoplasmic reticulum (ER) of hepatocytes. ZAAT-expressing cells display ER stress responses including nuclear factor kappaB activation and apoptosis. Using an in vitro model of ZAAT ER accumulation, we investigated the mechanism of ZAAT-mediated ER-induced apoptosis and evaluated methods to inhibit this process. Here we demonstrate that expression of ZAAT, but not normal MAAT, in HEK293 cells leads to cleavage and activation of caspase-4 and induces apoptosis that is characterized by activation of caspase-3 and caspase-7 and DNA fragmentation. Similar effects are also induced using the ER agonist thapsigargin. A caspase-4-specific short interfering RNA (siRNA) does not impair ZAAT-induced caspase-3/7 activation or cell death in these cells. However, inhibition studies performed using tauroursodeoxycholic acid (TUDCA) demonstrate its ability to inhibit caspase-4 and caspase-3/7 activation, mitochondrial cytochrome c release, and caspase-3 cleavage induced by ZAAT and to promote cell survival. The mechanism by which TUDCA (tauroursodeoxycholic acid) promotes cell survival in ZAAT-expressing cells involves phosphorylation and inactivation of the proapoptotic factor Bad. TUDCA is unable to rescue cells from apoptosis or phosphorylate Bad in the presence of LY294002, a selective P-I-3-kinase inhibitor.

CONCLUSION

These data show that caspase-4 is not essential for ZAAT-induced apoptosis in HEK293 cells and implicates P-I-3-kinase and Bad as potential therapeutic targets for the liver disease associated with ZAAT deficiency.

Expression of hereditary hemochromatosis C282Y HFE protein in HEK293 cells activates specific endoplasmic reticulum stress responses

BACKGROUND

Hereditary Hemochromatosis (HH) is a genetic disease associated with iron overload, in which individuals homozygous for the mutant C282Y HFE associated allele are at risk for the development of a range of disorders particularly liver disease. Conformational diseases are a class of disorders associated with the expression of misfolded protein. HFE C282Y is a mutant protein that does not fold correctly and consequently is retained in the Endoplasmic Reticulum (ER). In this context, we sought to identify ER stress signals associated with mutant C282Y HFE protein expression, which may have a role in the molecular pathogenesis of HH.

RESULTS

Vector constructs of Wild type HFE and Mutant C282Y HFE were made and transfected into HEK293 cell lines. We have shown that expression of C282Y HFE protein triggers both an unfolded protein response (UPR), as revealed by the increased GRP78, ATF6 and CHOP expression, and an ER overload response (EOR), as indicated by NF-kappaB activation. Furthermore, C282Y HFE protein induced apoptotic responses associated with activation of ER stress. Inhibition studies demonstrated that tauroursodeoxycholic acid, an endogenous bile acid, downregulates these events. Finally, we found that the co-existence of both C282Y HFE and Z alpha 1-antitrypsin protein (the protein associated with the liver disease of Z alpha 1-antitrypsin deficiency) expression on ER stress responses acted as potential disease modifiers with respect to each other.

CONCLUSION

Our novel observations suggest that both the ER overload response (EOR) and the unfolded protein response (UPR) are activated by mutant C282Y HFE protein.

Function of nuclear steroid receptors in apoptosis: role of ursodeoxycholic acid

Nuclear steroid receptors such as the glucocorticoid and the mineralocorticoid receptors modulate apoptosis in different cell types through transactivation-dependent and -independent mechanisms. They are involved in both the induction and prevention of apoptosis depending on cell type. However, it is unclear how nuclear steroid receptors can affect expression of the same gene in opposing ways for different cells. In addition to their function as modulators of gene expression, nuclear steroid receptors often act as nuclear transporters of other regulatory molecules, thus indirectly regulating several apoptosis-related genes. Curiously, nuclear steroid receptors are thought to cooperate with the antiapoptotic endogenous bile acid, ursodeoxycholic acid, to prevent programmed cell death. The next decade will almost certainly unveil the remarkable role of nuclear steroid receptors in modulating the life and death struggle of cells and organ systems in human development and function.

Bile salts regulate proliferation and apoptosis of liver cells by modulating the IGF1 system

BACKGROUND

In different cell types, the insulin-like growth factor 1 and its receptor modulate growth, apoptosis and damage repair in cooperation with estrogen receptors.

AIM

To evaluate the involvement of the insulin-like growth factor 1 system and estrogen receptors in bile salts modulation of apoptosis/proliferation of hepatocytes and cholangiocytes. Primary cultures of rat hepatocytes and cholangiocytes were exposed to glycochenodeoxycholate or tauro-CDC in the presence or absence of insulin-like growth factor 1 receptor blocking antibody (alphaIR3), small interfering RNA for insulin-like growth factor 1, 17beta-estradiol or estrogen receptor antagonist (ICI 182,780). Proliferation was evaluated by proliferating cell nuclear antigen Western blot and apoptosis by measuring caspase-3 activity or annexin-V.

RESULTS

In hepatocytes, the insulin-like growth factor 1 receptor blocker enhanced glycochenodeoxycholate-induced apoptosis and caused tauro-CDC to promote apoptosis. 17Beta-estradiol or the estrogen receptor antagonist (ICI 182,780) did not influence the apoptotic effect of glycochenodeoxycholate. In cholangiocytes, both glycochenodeoxycholate and tauro-CDC induced proliferation at 100microM, while they induced apoptosis at 1mM with a more pronounced effect of glycochenodeoxycholate. Apoptosis induced by 1mM glycochenodeoxycholate or tauro-CDC in cholangiocytes was enhanced by blocking insulin-like growth factor 1 receptor or by silencing insulin-like growth factor 1. 17Beta-estradiol counteracts glycochenodeoxycholate-induced cholangiocyte apoptosis by enhancing insulin-like growth factor 1 secretion and activating the insulin-like growth factor 1 system.

CONCLUSIONS

Modulation of the IGF1 system could represent a potential strategy for the management of bile salts-induced liver injury.