Activation of a caspase-dependent oxidative damage response mediates TGFbeta1 apoptosis in rat hepatocytes

AT-MSCs Antifibrotic Activity is Improved by Eugenol through Modulation of TGF-β/Smad Signaling Pathway in Rats

For hepatic failure, stem cell transplantation has been chosen as an alternative therapy, especially for mesenchymal stem cells (MSCs). The aim of this study was to investigate the effect of eugenol (EUG) on the in vivo antifibrotic activity of adipose tissue-derived MSCs (AT-MSCs) and the underlying mechanism. After characterization of MSCs, rats were divided into five groups, Group 1 (normal control), Group 2 (CCl₄), Group 3 (CCl₄ + AT-MSCs), Group 4 (CCl₄ + EUG) and Group 5 (CCl₄ + AT-MSCs + EUG). Biochemical and histopathological investigations were performed. Furthermore, expression of type 1 collagen, α-SMA, TGF-β1, Smad3 and P-Smad3 was estimated. Compared to the single treatment with AT-MSCs, the combination treatment of the fibrotic rats with AT-MSCs and EUG significantly improved the plasma fibrinogen concentration, IL-10 level and proliferating cell nuclear antigen expression, and also significantly decreased the serum levels of liver enzymes, IL-6, IL-1β, TNF-α, type III collagen, hyaluronic acid, hydroxyproline and the TGF-β growth factor. Furthermore, the combination treatment significantly decreased the hepatic expression of fibrotic markers genes (Type 1 collagen and α-SMA) and proteins (α-SMA, TGF-β1 and phospho-Smad3) more than the treatment with AT-MSCs alone. We demonstrated that the combination treatment with EUG and AT-MSCs strongly inhibited the advancement of CCl₄-induced hepatic fibrosis, compared with AT-MSCs alone, through TGF-β/Smad pathway inhibition. This approach is completely novel, so more investigations are necessary to improve our perception of the underlying molecular mechanisms accountable for the effects of EUG on the antifibrotic potential of AT-MSCs.

A critical role of hepatitis B virus polymerase in cirrhosis, hepatocellular carcinoma, and steatosis

Hepatitis B is one of the most common infectious diseases in the world; more than 350 million people are carriers of hepatitis B virus (HBV). Chronic HBV infection (CHB) leads to liver diseases such as cirrhosis, hepatocellular carcinoma (HCC), and steatosis. Despite its seriousness in terms of public health, the pathogenic mechanism of how CHB leads to liver diseases, especially cirrhosis and steatosis, remains unclear. We studied the role of HBV polymerase (HBp) reverse transcriptase (RT) activity in association with the pathogenesis of liver diseases in CHB by developing transgenic mice expressing HBp or the RT domain of HBp. Thorough pathological, serological, and histological analyses of the transgenic mice, as well as mechanistic studies, were conducted. All of the transgenic mice expressing RT in their livers developed early cirrhosis with steatosis by 18 months of age, and 10% developed HCC. The RT activity of HBp stimulates coordinated proapoptotic and proinflammatory responses involving the caspase-9, caspase-3, and caspase-1 pathways that might lead to the development of cirrhosis, HCC, and steatosis. The animal model described here should prove useful for elucidating the molecular events in the CHB-induced liver diseases.

Glutathione Decreased Parenteral Nutrition–Induced Hepatocyte Injury in Infant Rabbits

BACKGROUND

This study was designed to explore the mechanisms in parenteral nutrition (PN)-associated hepatic dysfunction, and the possible effectiveness of glutathione (GSH) to alleviate this injury.

METHODS

Thirty 1-week-old New Zealand rabbits were divided into 3 groups: 10 in the control group (maternal fed); 10 in the PN group (PN for 10 days); and 10 in the GSH + PN group (PN plus glutathione for 10 days). At the end of the study, blood biochemistry analysis and liver histologic examination were performed by light and electronic microscope; malondialdehyde (MDA) content of liver tissues and apoptotic hepatocytes were also measured.

RESULTS

Direct bilirubin and bile acid in the PN group were significantly higher than that in the control group and in the GSH + PN group (p < .05, for both). In the PN group, there were some cholestatic or steatotic changes. In the GSH + PN group, histologic changes were reduced compared with the PN group. The electron microscopy appearances were in agreement with the histologic findings. MDA value was higher in the PN group than in the control group and in the GSH + PN group (p < .05, respectively). Terminal deoxynucleotidyl transferase mediated nick end labeling (TUNEL) assays showed that the rate of apoptotic hepatocytes in the PN group was the highest and the control group was the lowest among 3 groups (comparison between groups, p < .01, individually.)

CONCLUSIONS

The study showed that PN can induce hepatic dysfunction in infant rabbits. GSH can effectively reduce this injury. The study implies that oxidative stress and apoptosis contribute to PN-associated hepatic dysfunction.

Estrogen promotes benzo[a]pyrene-induced lung carcinogenesis through oxidative stress damage and cytochrome c-mediated caspase-3 activation pathways in female mice

Estrogen may contribute to the development of smoking-induced lung cancer in women. To test this hypothesis, an mouse model was used to investigate the effects of 17 beta-estradiol (E2) on benzo[a]pyrene (B[a]P)-induced lung carcinogenesis. We found that B[a]P could cause oxidative stress damage, upregulate mitochondrial cytochrome-c and caspase-3 expression, induce lung carcinogenesis in female mice, E2 promoted these effects of B[a]P while tamoxifen (TAM) inhibited this effects of E2. We conclude that E2 can promote the tumorigenic effects of B[a]P in female mice, and oxidative stress damage and activation of cytochrome-c-mediated caspase-3 pathway may be involved in this process.

Constitutive activation of caspase-3 and Poly ADP ribose polymerase cleavage in fanconi anemia cells

Fanconi anemia (FA) is a rare syndrome characterized by developmental abnormalities, progressive bone marrow failure, and cancer predisposition. Cells from FA patients exhibit hypersensitivity to DNA cross-linking agents and oxidative stress that may trigger apoptosis. Damage-induced activation of caspases and poly ADP ribose polymerase (PARP) enzymes have been described for some of the FA complementation groups. Here, we show the constitutive activation of caspase-3 and PARP cleavage in the FA cells without exposure to exogenous DNA-damaging factors. These effects can be reversed in the presence of reactive oxygen species scavenger N-acetylcystein. We also show the accumulation of oxidized proteins in FA cells, which is accompanied by the tumor necrosis factor (TNF)-alpha oversecretion and the upregulation of early stress response kinases pERK1/2 and p-P38. Suppression of TNF-alpha secretion by the extracellular signal-regulated kinase inhibitor PD98059 results in reduction of caspase-3 cleavage, suggesting a possible mechanism of caspases-3 activation in FA cells. Thus, the current study is the first evidence demonstrating the damage-independent activation of caspase-3 and PARP in FA cells, which seems to occur through mitogen-activated protein kinase activation and TNF-alpha oversecretion.

Apoptosis and its suppression in hepatocytes culture

In order to achieve the goal of developing extracorporeal liver support devices, it is necessary to optimise bioprocess environment such that viability and function are maximised. Optimising culture medium composition and controlling the constitution of the cellular microenvironment within the bioreactor have for many years been considered vital to achieving these aims. Coupled to this is the need to understand apoptosis, the prime suspect in the demise of animal cultures, including those of hepatocytes. Results presented here show that absent nutrients including glucose and amino acids play a substantial part in the induction of apoptosis. The use of chemical apoptosis inhibitors was utilised to investigate key components of hepatic apoptosis where caspases, predominantly caspase 8, were implicated in staurosporine (STS)-induced HepZ apoptosis. Caspase 9 and 3 activation although recorded was of less significance. Interestingly, these results were not consistent with those of mitochondrial membrane depolarisation where inhibition of caspase activation appeared to drive depolarisation. Inhibition of mitochondrial permeability transition and use of anti-oxidants was unsuccessful in reducing apoptosis, caspase activation and mitochondrial membrane depolarisation. In further studies, the anti-apoptotic gene bcl-2 was over-expressed in HepZ, resulting in a cell line that was more robust and resistant to death induced by glucose and cystine deprivation and treatment with STS. Bcl-2 did not however show significant cytoprotectivity where apoptosis was stimulated by deprivation of glutamine and serum. Overall, results indicated that although apoptosis can be curbed by use of chemical inhibitors and genetic manipulation, their success is dependent on apoptotic stimuli.

Effect of ethanol on pro-apoptotic mechanisms in polarized hepatic cells

Chronic ethanol consumption is associated with serious and potentially fatal alcohol-related liver injuries such as hepatomegaly, alcoholic hepatitis and cirrhosis. Moreover, it has been documented that the clinical progression of alcohol-induced liver damage may be associated with an increase in hepatocellular death that involves apoptotic mechanisms. Although much information has been learned about the clinical manifestations associated with alcohol-related diseases, the search continues for a better understanding of the molecular and/or cellular mechanisms by which ethanol exerts its deleterious effects such as the induction of pro-apoptotic mechanisms and related cell damaging events. As part of the effort to enhance our understanding of those particular cellular pathways and mechanisms associated with ethanol toxicity, researchers over the years have utilized a variety of model systems. Recently, work has come forth demonstrating the utility of a hybrid cell line (WIF-B) as a cell culture model system for the study of alcohol-associated alterations in hepatocellular mechanisms. Success with such emerging model systems could aid in the development of potential therapeutic treatments for the prevention of alcohol-induced apoptotic cell death that may ultimately serve as a significant target in delaying the onset and/or progression of clinical symptoms of alcohol-mediated liver disease. This review article summarizes the current understanding of ethanol-mediated modifications in cell survival and thus the promotion of pro-apoptotic events with emphasis on analyses made in various experimental model systems, particularly the more recently characterized WIF-B cell system.

Oxidative injury and hepatocyte apoptosis in total parenteral nutrition-associated liver dysfunction

PURPOSE

The aim of this study was to investigate the impact of oxidative injury and apoptosis on total parenteral nutrition (TPN)-associated hepatic dysfunction.

METHODS

Fifty-nine New Zealand rabbits (6-8 days old) were divided into 4 groups: 12 in the control group (maternal fed), 15 in the PN-3 group (TPN for 3 days), 14 in the PN-7 group (TPN for 7 days), and 18 in the PN-10 group (TPN for 10 days). At the end of the experiment, blood biochemistry analysis and histologic examination of the liver were performed; the malondialdehyde content of liver tissues was determined and hepatocyte apoptosis was evaluated by terminal deoxynucleotidyl transferase-mediated nick-end labeling assay.

RESULTS

We found that the serum level of direct bilirubin became higher as PN duration was extended. The light microscopy features in the PN-3 and PN-7 groups included inflammatory cells infiltrated in portal areas and some degeneration changes, whereas in the PN-10 group, cholestasis (proliferation of bile ducts and bile pigments in hepatocytes) or diffuse steatosis was shown. Electron microscopic manifestation in PN groups included reduced numbers of microvilli and some preapoptosis changes. Both the malondialdehyde content and apoptosis index were the highest in the PN-10 group; there were more apoptotic hepatocytes in the groups with longer PN duration.

CONCLUSIONS

The longer the TPN duration, the more severe the liver injury. Both oxidative injury and apoptosis may play important roles in the mechanism of TPN-associated hepatic dysfunction.

Maternal dietary choline availability alters the balance of netrin-1 and DCC neuronal migration proteins in fetal mouse brain hippocampus

Alterations in maternal dietary choline availability during days 12-17 of pregnancy led to an increase in the level of immunoreactive netrin-1 and a decrease in the level of DCC protein in the developing fetal mouse brain hippocampus compared with controls. Changes in the expression of cell migration cues during development could account for some of the lifelong consequences of maternal dietary choline availability for cognitive and memory processes.

Regulation of choline deficiency apoptosis by epidermal growth factor in CWSV-1 rat hepatocytes

Previous studies show that acute choline deficiency (CD) triggers apoptosis in cultured rat hepatocytes (CWSV-1 cells). We demonstrate that prolonged EGF stimulation (10 ng/mL x 48 hrs) restores cell proliferation, as assessed by BrdU labeling, and protects cells from CD-induced apoptosis, as assessed by TUNEL labeling and cleavage of poly(ADP-ribose) polymerase. However, EGF rescue was not accompanied by restoration of depleted intracellular concentrations of choline, glycerphosphocholine, phosphocholine, or phosphatidylcholine. In contrast, we show that EGF stimulation blocks apoptosis by restoring mitochondrial membrane potential (Delta Psi(m)), as determined using the potential-sensitive dye chloromethyl-X-rosamine, and by preventing the release and nuclear localization of cytochrome c. We investigated whether EGF rescue involves EGF receptor phosphorylation and activation of the down-stream cell survival factor Akt. Compared to cells in control medium (CT, 70 micromol choline x 48 hrs), cells in CD medium (5 micromol choline) were less sensitive to EGF-induced (0-300 ng/mL x 5 min) receptor tyrosine phosphorylation. Compared to cells in CT medium, cells in CD medium treated with EGF (10 ng/mL x 5 min) exhibited higher levels of phosphatidylinositol 3-kinase (PI3K)-dependent phosphorylation of AktSer473. Inactivation of PI3K was sufficient to block EGF-stimulated activation of Akt, restoration of mitochondrial Delta Psi(m), and prevention of cytochrome c release. These studies indicate that stimulation with EGF activates a cell survival response against CD-apoptosis by restoring mitochondrial membrane potential and preventing cytochrome c release and nuclear translocation which are mediated by activation of Akt in hepatocytes.

Hepatic progenitor cell resistance to TGF-beta1's proliferative and apoptotic effects

The success of hepatocellular therapies using stem or progenitor cell populations is dependent upon multiple factors including the donor cell, microenvironment, and etiology of the liver injury. The following experiments investigated the impact of TGF-beta1 on a previously described population of hepatic progenitor cells (HPC). The majority of the hepatic progenitor cells were resistant to endogenously produced TGF-beta1's proapoptotic and anti-proliferative effects unlike more well-differentiated cellular populations (e.g., mature hepatocytes). Surprisingly, in vitro TGF-beta1 supplementation significantly inhibited de novo hepatic progenitor cell colony formation possibly via an indirect mechanism(s). Therefore despite the HPC's direct resistance to supplemental TGF-beta1, this cytokine's inhibitory effect on colony formation could have a potential negative impact on the use of these cells as a therapy for patients with liver disease.

Reversibility of caspase activation and its role during glycochenodeoxycholate-induced hepatocyte apoptosis

The accumulation of glycochenodeoxycholate (GCDC) induced hepatocyte apoptosis in cholestasis. However, many hepatocytes still survived GCDC-induced apoptosis. The molecular mechanism for the survival of hepatocytes remains unclear. In the present study, isolated rat hepatocytes were cultured in William's E medium and treated with 50 microM GCDC. DNA, RNA, cell lysate, and nuclear proteins were collected at different intervals for DNA fragmentation assay, reverse transcription PCR, Western blotting, and gel mobility shift assay, respectively. GCDC-induced active caspases were detected as early as 2 h by Western blotting and kinetic caspase assay, whereas hepatocyte apoptosis was found at 4 h by DNA fragmentation and terminal deoxynucleotidyl transferase-mediated dUPT nick-end labeling assay. When GCDC was removed, the increased caspases as well as NF-kappaB could be restored to control level. A1/Bfl-1 and inducible nitric oxide synthase (iNOS) were up-regulated in 2 h of GCDC stimulation. After GCDC was removed, hepatocytes decreased expression of A1/Bfl-1, but not iNOS, to the control level. NF-kappaB activation coincided with the change of A1/Bfl-1. Survivin, cIAP1, cIAP2, XIAP, and A1/Bfl-1, but not iNOS, were down-regulated by pan-caspase inhibitor benzyloxycarbonyl-VAD-fluoromethyl ketone. In addition, benzyloxycarbonyl-VAD-fluoromethyl ketone inhibited release of cytochrome c and suppressed NF-kappaB activation. Our data suggested that caspase pathway is an important regulatory factor during hepatocyte apoptosis. GCDC-induced caspase response is reversible, which may activate anti-apoptotic genes to protect hepatocytes from apoptosis.

Effect of selective PKC isoform activation and inhibition on TNF-alpha-induced injury and apoptosis in human intestinal epithelial cells

(1) We have investigated the effects of specific PKC isoforms in TNF-alpha mediated cellular damage using a human intestinal cell line (SCBN). (2) TNF-alpha treatment induced a decrease in the extent of intestinal cellular viability as determined by a formazan-based assay and an increase in the apoptotic index as assessed by immunohistology. These changes in cellular integrity were found to be related to the degradation of I-kappaBalpha, mobilization of NF-kappaB and release of mitochondrial cytochrome c. (3) TNF-alpha treatment also induced the activation of selective PKC isoforms which were associated with the decrease in cellular viability and an increase of cellular apoptosis. (4) Nonselective PKC antagonists, such as GF109203X and Gö6976 as well as isoform-selective PKC-inhibiting peptides would reverse the cellular injury as well as reduce the degradation of I-kappaBalpha and mitochondrial cytochrome c release. These effects were most highly correlated with changes in PKCdelta and epsilon primarily. (5) Intestinal cellular injury could be induced by treating cells with agonists selective for PKCdelta and epsilon mainly. (6) In conclusion, this study has shown that TNF-alpha treatment can induce the activation of PKCdelta and epsilon in the human intestinal cell line, SCBN, and this response is closely associated with an increase in cellular damage and apoptosis. PKCdelta and epsilon primarily mediate the release of mitochondrial cytochrome c and degradation of I-kappaBalpha and hence mobilization of NF-kappaB, which are responsible for the pathway leading to cell injury.