The significance of apoptosis in the liver

Effect of tanshinone IIA on oxidative stress and apoptosis in a rat model of fatty liver

Oxidative stress is a crucial factor associated with fatty liver disease, which raises the possibility of using antioxidants to improve liver steatosis. Tanshinone IIA (TSIIA) is a traditional Chinese medicine that has been reported to have antioxidant effects in vitro. The present study aimed to investigate whether TSIIA possesses antioxidant effects in vivo and whether TSIIA was able to improve liver steatosis. Hence, the ability of TSIIA to protect rats from liver disease was explored, particularly in regard to antioxidant activity. Rats were fed a high-lipid diet for 90 days, causing severe liver steatosis, both morphologically and biochemically. An increase in reactive oxygen species (ROS) in the liver was exhibited in addition to significantly elevated serum lipids and malondialdehyde (MDA). Furthermore, hepatocyte apoptosis was measured by Hoechst staining, reverse transcription-quantitative polymerase chain reaction and western blot analysis and an increase in hepatocyte apoptosis rate was indicated in mice on a high-fat diet. Following intraperitoneal injection of TSIIA (10 mg/kg/day), liver steatosis was significantly inhibited. In rats receiving TSIIA treatment, less ROS were indicated in the liver and significantly decreased levels of MDA (P<0.05) in serum were exhibited, whereas significantly increased activities of total superoxide dismutase (T-SOD) and glutathione peroxidase (GSH-PX) were observed (P<0.05 and P<0.01, respectively). In addition, the rate of hepatocyte apoptosis was significantly decreased in the TSIIA group (P<0.01). However, TSIIA elicited no effect on serum lipid profiles. These results suggest that TSIIA attenuates oxidative stress by decreasing ROS and MDA production and enhancing the activity of T-SOD and GSH-PX, which may contribute to the inhibition of apoptosis and amelioration of liver steatosis.

Organ crosstalk: the role of the kidney

PURPOSE OF REVIEW

Acute kidney injury (AKI) continues to contribute significantly to morbidity and mortality in the ICU setting, especially when associated with distant organ dysfunction. There is increasing evidence that AKI directly contributes to organ dysfunction in lung, brain, liver, heart and other organs. This review will examine our current understanding of the deleterious organ crosstalk in the critically ill, which can provide a framework for developing novel therapeutics.

RECENT FINDINGS

The majority of studies correlating AKI with distant organ dysfunction have demonstrated the pathophysiological importance of proinflammatory and proapoptotic pathways as well as oxidative stress and reactive oxygen species (ROS) production. Leukocyte activation and infiltration, changes in levels of soluble factors such as cytokines and chemokines, and regulation of cell death in extra-renal organs are potentially important mechanisms by which AKI modulates multiorgan dysfunction.

SUMMARY

There is increasing knowledge of AKI and deleterious interorgan crosstalk that arises, at least in part, due to the imbalance of immune, inflammatory, and soluble mediator metabolism that attends severe insults to the kidney. Further studies can build on these new mechanistic observations to develop strategies to improve outcomes in the critically ill patient.

Pharmacokinetic-pharmacodynamic modeling of manganese after a single intravenous infusion of mangafodipir in patients with acute alcoholic hepatitis

To determine the pharmacokinetic (PK) profile of manganese (Mn) after a 2-hour intravenous infusion of mangafodipir at 5 micromol/kg body weight and to correlate Mn concentrations with oxidative stress, early decrease in serum total bilirubin concentration, and prothrombin time (PT) in chronic alcoholic patients with acute alcoholic hepatitis. In 7 patients, a total of 49 serum Mn concentrations were determined on day 1 (before the start of the infusion and 15, 30, and 45 minutes after the end of the infusion) and on days 2, 7, 14, and 21. Fifty-seven PTs, reflecting liver activity, were measured on days 1, 2, 7, 14, and 21 and at months 1, 2, and 3. A population PK-pharmacodynamic model was developed to describe the kinetics of serum Mn concentrations and PT, to estimate interpatient variability, and to test covariate influence. A 2-compartment model with zero-order absorption and first-order elimination best described the data, and a signal transduction model with 2 transit compartments best described PT. Mean PK estimates and the corresponding interindividual variabilities (%) were clearance 23.1 L/h (34%), central and peripheral volume of distribution 35.4 and 1090 L, respectively, intercompartmental clearance 27.3 L (34%), endogenous Mn concentrations 15.8 nmol/L, slope-relating effect to concentration 141 nmol x L(-1) x s(-1) (52%), and mean transit time (tau) 3.8 days (34%). When patients had an early decrease in bilirubin at day 7, tau increased to 28.2 days. Serum Mn concentrations could be related to a decrease in PT; the effect was longer in patients with an early decrease in total bilirubin serum concentrations.

Role of transmethylation reactions in alcoholic liver disease

Alcoholic liver disease is a major health care problem worldwide. Findings from many laboratories, including ours, have demonstrated that ethanol feeding impairs several of the many steps involved in methionine metabolism. Ethanol consumption predominantly results in a decrease in the hepatocyte level of S-adenosylmethionine and the increases in two toxic metabolites, homocysteine and S-adenosylhomocysteine. These changes, in turn, result in serious functional consequences which include decreases in essential methylation reactions via inhibition of various methyltransferases. Of particular interest to our laboratory is the inhibition of three important enzymes, phosphatidylethanolamine methyltransferase, isoprenylcysteine carboxyl methyltransferase and protein L-isoaspartate methyltransferase. Decreased activity of these enzymes results in increased fat deposition, increased apoptosis and increased accumulation of damaged proteins-all of which are hallmark features of alcoholic liver injury. Of all the therapeutic modalities available, betaine has been shown to be the safest, least expensive and most effective in attenuating ethanol-induced liver injury. Betaine, by virtue of aiding in the remethylation of homocysteine, removes both toxic metabolites (homocysteine and S-adenosylhomocysteine), restores S-adenosylmethionine level, and reverses steatosis, apoptosis and damaged proteins accumulation. In conclusion, betaine appears to be a promising therapeutic agent in relieving the methylation and other defects associated with alcoholic abuse.

Apoptotic and proliferating hepatocytes differ in prothymosin α expression and cell localization

Prothymosin alpha is an acidic protein, reported to be involved in cell proliferation and apoptosis, although its precise function in both processes are still unknown. Due to the importance of these processes in the pathogenesis of hepatic diseases and the need to understand the molecular mechanisms underlying these diseases we aimed to investigate the behavior of this protein in liver growth and apoptosis, in two models of hepatocytes in culture. Prothymosin alpha expression varied throughout the hepatocyte cell cycle, according to its progression. Proliferating hepatocytes showed increased expression of the protein, while apoptotic ones showed decreased levels. The subcellular location of prothymosin alpha differed according to the different phases of the cell cycle. Thus, it appeared with a stippled and widely dispersed pattern throughout the nucleus in quiescent and proliferating hepatocytes, while it became cytoplasmic in mitotic and late apoptotic cells. These results are in agreement with the idea that high levels of prothymosin alpha need to be present in the nucleus for proliferation, and programmed cell death requires low levels of prothymosin alpha outside of the nucleus. The differences in prothymosin alpha expression and localization during hepatocyte proliferation and apoptosis suggest that this protein may have a pleiotropic function that depends not only on its availability but also on its various localizations in different subcellular compartments.

Antisense oligonucleotide inhibition of Bcl-xL and Bid expression in liver regulates responses in a mouse model of Fas-induced fulminant hepatitis

Activation of the cell-surface receptor Fas can lead to apoptosis in parenchymal cells in the liver, and if severe enough, result in fulminant hepatic failure and animal death. In the present study, we have examined the roles played by the Bcl-2 family members Bcl-xL and Bid in regulating this response. To do this, we have developed chemically modified 2'-O-(2-methoxy) ethyl antisense inhibitors of both Bid and Bcl-xL expression. In Balb/c mice, dosing with these antisense oligonucleotides reduced expression of the targeted mRNA by greater than 80% in the liver. This reduction was highly dependent upon oligonucleotide sequence and oligonucleotide dose. Reduction of Bcl-xL expression resulted in a potentiation of Fas-mediated apoptosis in liver and significant increase of the lethality of Fas-mediated fulminant hepatitis (p < 0.0001). In contrast, reduction of Bid expression protected the animals against Fas-mediated fulminant hepatitis and death (p < 0.0001). Simultaneous dosing of mice with Bcl-xL and Bid-targeting antisense oligonucleotides resulted in an inhibition of expression of both targeted proteins and protection of the animals from Fas-mediated apoptosis. These results demonstrate, for the first time, the role of Bcl-xL in regulating responses to proapoptotic Fas signaling in mouse liver. In addition, this is the first reported example demonstrating the ability of antisense inhibitors to reduce expression of multiple proteins in animals by simultaneous dosing.

Stress-induced disruption of colonic epithelial barrier: role of interferon-gamma and myosin light chain kinase in mice

BACKGROUND & AIMS

Stressful life events are supposed to be involved in various diseases such as inflammatory bowel diseases and irritable bowel syndrome. Impairment of the intestinal epithelial barrier function is a suspected consequence of stress, but the underlying mechanisms remain unclear. This study aimed to determine the mechanisms through which stress modulates the colonic epithelial barrier.

METHODS

Cytokine messenger RNA (mRNA) expression was evaluated in murine colon, liver, and spleen by competitive reverse-transcription polymerase chain reaction after 1-4 days of daily 2-hour stress sessions. Colonic paracellular permeability was measured as the in vivo lumen-to-blood ratio of (51)Cr-ethylenediaminetetraacetic acid. The effect of a myosin light chain (MLC) kinase inhibitor (ML-7) was assessed on stress-induced interferon (IFN)-gamma mRNA expression and colonic epithelial barrier impairment, and MLC phosphorylation was determined by immunoblot. Finally, the incidence of repeated stress sessions on bacterial translocation was determined.

RESULTS

Repeated stress induced an overexpression of colonic IFN-gamma. In the liver, higher levels of IFN-gamma, interleukin (IL)-4, and IL-10 mRNAs were detected and were associated with bacterial translocation, inflammation, and apoptosis. Stress increased colonic permeability of control mice, but not of SCID and IFN-gamma-deficient mice. ML-7 inhibited the stress-induced increased permeability, bacterial translocation, and cytokine overexpression in the liver and restored a normal histology. Larger amounts of phosphorylated MLC were detected in stressed animals.

CONCLUSIONS

Repeated stress sessions drive organ-specific cytokine expression patterns and alter colonic mucosal barrier functions associated with bacterial translocation. This effect depends on the presence of CD4(+) T cells and requires IFN-gamma production and MLC phosphorylation.

Bile acid regulation of C/EBPbeta, CREB, and c-Jun function, via the extracellular signal-regulated kinase and c-Jun NH2-terminal kinase pathways, modulates the apoptotic response of hepatocytes

Previously, we have demonstrated that deoxycholic acid (DCA)-induced signaling of extracellular signal-regulated kinases 1 and 2 (ERK1/2) in primary hepatocytes is a protective response. In the present study, we examined the roles of the ERK and c-Jun NH(2)-terminal kinase (JNK) pathways, and downstream transcription factors, in the survival response of hepatocytes. DCA caused activation of the ERK1/2 and JNK1/2 pathways. Inhibition of either DCA-induced ERK1/2 or DCA-induced JNK1/2 signaling enhanced the apoptotic response of hepatocytes. Further analyses demonstrated that DCA-induced JNK2 signaling was cytoprotective whereas DCA-induced JNK1 signaling was cytotoxic. DCA-induced ERK1/2 activation was responsible for increased DNA binding of C/EBPbeta, CREB, and c-Jun/AP-1. Inhibition of C/EBPbeta, CREB, and c-Jun function promoted apoptosis following DCA treatment, and the level of apoptosis was further increased in the case of CREB and c-Jun, but not C/EBPbeta, by inhibition of MEK1/2. The combined loss of CREB and c-Jun function or of C/EBPbeta and c-Jun function enhanced DCA-induced apoptosis above the levels resulting from the loss of either factor individually; however, these effects were less than additive. Loss of c-Jun or CREB function correlated with increased expression of FAS death receptor and PUMA and decreased expression of c-FLIP-(L) and c-FLIP-(S), proteins previously implicated in the modulation of the cellular apoptotic response. Collectively, these data demonstrate that multiple DCA-induced signaling pathways and transcription factors control hepatocyte survival.

Abundant apoptosis in nutmeg liver of cardiomyopathic hamsters. Apoptotic cell death as a possible mechanism of hepatic remodeling by congestion

Chronic congestive heart failure (CHF) causes structural remodeling of the liver, generally leading to nutmeg liver. Male UM-X7.1 hamsters, a strain developing cardiomyopathy, had no CHF and decompensated CHF (n = 6 each) at the age of 10 and 30 weeks, respectively. We used age-matched, male Syrian hamsters without CHF (n = 6 each) as controls. All the 30-week-old UM-X7.1 hamsters had a typical nutmeg liver in which the population of hepatocytes was decreased. Positive in situ nick end labeling (TUNEL) was found in 2.2 +/- 0.74% of hepatocytes in congestive livers, being significantly higher compared with the other groups without CHF (< 0.5%). DNA ladder pattern was also evident in the congestive livers. Electron microscopy revealed a typical apoptotic ultrastructure in the hepatocytes of the 30-week-old UM-X7.1 hamsters. However, many showed secondary necrotic changes. Although hepatocytes undergoing oncosis (primary necrosis) are rare, they were also found. The level of soluble Fas ligand in the plasma was increased, and Fas receptor in the liver was overexpressed in the CHF animals. In addition, both the Bax/Bcl-2 ratio and the Bad/Bcl-xL ratio were increased, and caspase-3 was activated in them. Our findings suggest that hepatocyte apoptosis contributes to hepatic remodeling under conditions of CHF.

Relationship between apoptosis, tumour necrosis factor, and cell proliferation in chronic cholestasis

BACKGROUND

Target of the immune response in chronic autoimmune cholestasis, is the bile duct epithelium. Lymphocytic infiltration and apoptosis have both been suggested to mediate the destruction of hepatocytes and biliary epithelium in primary biliary cirrhosis.

AIMS

To further address this issue in two cholestatic liver diseases characterized by an autoimmune pathogenesis and, furthermore, evaluate the relationship between apoptosis and both tumour necrosis factor alpha and cell proliferation.

METHODS

Liver tissue specimens from 16 patients with primary biliary cirrhosis, 15 with primary sclerosing cholangitis, and 16 with chronic hepatitis C (controls) were evaluated. DNA-fragmentation of apoptotic cells was ascertained by the TdT-mediated deoxyuridine triphosphate nick-end labelling method. Tumour necrosis factor alpha expression and cell proliferation (Ki-67 antigen) were assayed by immunohistochemistry.

RESULTS

Hepatocytes with DNA fragmentation were observed in 75% of patients with primary biliary cirrhosis, in 66.6% with primary sclerosing cholangitis, and in 43.7% with chronic hepatitis C. Biliocytes showed apoptosis in only 3 cases of primary biliary cirrhosis. Biliocytes showed a strong cytoplasmic expression in 4 cases (1 primary biliary cirrhosis, 2 primary sclerosing cholangitis and 1 chronic hepatitis C). A few intralobular and portal inflammatory mononuclear cells expressing tumour necrosis factor alpha were observed in 62.5% of patients with primary biliary cirrhosis, 46.1% with primary sclerosing cholangitis, and 56.2% with hepatitis C virus chronic hepatitis. The amount of intraportal mononuclear cells expressing Ki-67 antigen was significantly higher in primary biliary cirrhosis specimens than in primary sclerosing cholangitis (p<0.001) or hepatitis C virus-related chronic hepatitis (p<0.03). No correlation was found within the 3 groups of patients between the Ki-67 histological score and the severity of liver disease. Moreover, no relationship was found between TdT-mediated deoxyuridine triphosphate nick-end labelling and either tumour necrosis factor alpha or Ki-67 staining.

CONCLUSIONS

Apoptosis is a phenomenon which frequently involves hepatocytes in chronic autoimmune cholestasis. This process is apparently parallel, but unrelated to cell proliferation. Cell proliferation mainly involves mononuclear cells in portal tracts of primary biliary cirrhosis specimens. The finding of tumour necrosis factor alpha expression in biliocytes deserves further study to establish whether this cytokine is involved in triggering bile duct lesions.

Deoxycholic acid (DCA) causes ligand-independent activation of epidermal growth factor receptor (EGFR) and FAS receptor in primary hepatocytes: inhibition of EGFR/mitogen-activated protein kinase-signaling module enhances DCA-induced apoptosis

Previous studies have argued that enhanced activity of the epidermal growth factor receptor (EGFR) and the mitogen-activated protein kinase (MAPK) pathway can promote tumor cell survival in response to cytotoxic insults. In this study, we examined the impact of MAPK signaling on the survival of primary hepatocytes exposed to low concentrations of deoxycholic acid (DCA, 50 microM). Treatment of hepatocytes with DCA caused MAPK activation, which was dependent upon ligand independent activation of EGFR, and downstream signaling through Ras and PI(3) kinase. Neither inhibition of MAPK signaling alone by MEK1/2 inhibitors, nor exposure to DCA alone, enhanced basal hepatocyte apoptosis, whereas inhibition of DCA-induced MAPK activation caused approximately 25% apoptosis within 6 h. Similar data were also obtained when either dominant negative EGFR-CD533 or dominant negative Ras N17 were used to block MAPK activation. DCA-induced apoptosis correlated with sequential cleavage of procaspase 8, BID, procaspase 9, and procaspase 3. Inhibition of MAPK potentiated bile acid-induced apoptosis in hepatocytes with mutant FAS-ligand, but did not enhance in hepatocytes that were null for FAS receptor expression. These data argues that DCA is causing ligand independent activation of the FAS receptor to stimulate an apoptotic response, which is counteracted by enhanced ligand-independent EGFR/MAPK signaling. In agreement with FAS-mediated cell killing, inhibition of caspase function with the use of dominant negative Fas-associated protein with death domain, a caspase 8 inhibitor (Ile-Glu-Thr-Asp-p-nitroanilide [IETD]) or dominant negative procaspase 8 blocked the potentiation of bile acid-induced apoptosis. Inhibition of bile acid-induced MAPK signaling enhanced the cleavage of BID and release of cytochrome c from mitochondria, which were all blocked by IETD. Despite activation of caspase 8, expression of dominant negative procaspase 9 blocked procaspase 3 cleavage and the potentiation of DCA-induced apoptosis. Treatment of hepatocytes with DCA transiently increased expression of the caspase 8 inhibitor proteins c-FLIP-(S) and c-FLIP-(L) that were reduced by inhibition of MAPK or PI(3) kinase. Constitutive overexpression of c-FLIP-(s) abolished the potentiation of bile acid-induced apoptosis. Collectively, our data argue that loss of DCA-induced EGFR/Ras/MAPK pathway function potentiates DCA-stimulated FAS-induced hepatocyte cell death via a reduction in the expression of c-FLIP isoforms.

Pathology of the liver

Traditional anatomic pathology studies and molecular investigations both contributed to the breadth of current information in the field of liver pathology this year. Techniques such as reverse transcription polymerase chain reaction can identify recurrence of hepatitis C virus infection in the liver as early as 5 days after transplantation. Chronic rejection after transplantation may be characterized not only by ductopenia but also by loss of portal tract hepatic artery branches. There are many diseases of small bile ducts in adults, and idiopathic adulthood ductopenia has been identified in extended family members. Adverse reactions to drugs may precipitate their removal from the pharmacopoeia, such as the many cases reported of severe bridging and submassive necrosis due to troglitazone (a thiazolidinedione antidiabetic agent). Several publications highlighted the association of hepatitis C virus infection with lymphoproliferative diseases and, newly, with cholangiocarcinoma.