Liver cell death: patterns and mechanisms

Humanin Derivatives Inhibit Necrotic Cell Death in Neurons

Humanin and its derivatives are peptides known for their protective antiapoptotic effects against Alzheimer's disease. Herein, we identify a novel function of the humanin-derivative AGA(C8R)-HNG17 (namely, protection against cellular necrosis). Necrosis is one of the main modes of cell death, which was until recently considered an unmoderated process. However, recent findings suggest the opposite. We have found that AGA(C8R)-HNG17 confers protection against necrosis in the neuronal cell lines PC-12 and NSC-34, where necrosis is induced in a glucose-free medium by either chemohypoxia or by a shift from apoptosis to necrosis. Our studies in traumatic brain injury models in mice, where necrosis is the main mode of neuronal cell death, have shown that AGA(C8R)-HNG17 has a protective effect. This result is demonstrated by a decrease in a neuronal severity score and by a reduction in brain edema, as measured by magnetic resonance imaging (MRI). An insight into the peptide's antinecrotic mechanism was attained through measurements of cellular ATP levels in PC-12 cells under necrotic conditions, showing that the peptide mitigates a necrosis-associated decrease in ATP levels. Further, we demonstrate the peptide's direct enhancement of the activity of ATP synthase activity, isolated from rat-liver mitochondria, suggesting that AGA(C8R)-HNG17 targets the mitochondria and regulates cellular ATP levels. Thus, AGA(C8R)-HNG17 has potential use for the development of drug therapies for necrosis-related diseases, for example, traumatic brain injury, stroke, myocardial infarction, and other conditions for which no efficient drug-based treatment is currently available. Finally, this study provides new insight into the mechanisms underlying the antinecrotic mode of action of AGA(C8R)-HNG17.

Centrilobular necrosis in acute presentation of Japanese patients with type 1 autoimmune hepatitis

AIM

To compare clinicopathological features of acute presentation of type 1 autoimmune hepatitis (AIH) with or without centrilobular necrosis (CN).

METHODS

Our study comprised 41 patients with biopsy-proven acute presentation (acute exacerbation phase 36, acute hepatitis phase 5) of type 1 AIH at our hospital from 1975 to 2009. Elevated serum alanine aminotransferase (ALT) (> 5x upper limit of normal) identified acute presentation of the disease. We compared clinicopathological features of these AIH patients with or without CN. The data used for analysis included patient background (age, sex, type of disease, presence of complications with other autoimmune diseases, human leukocyte antigen, and International Autoimmune Hepatitis Group score), clinical parameters at presentation (ALT, alkaline phosphatase, IgG, anti-nuclear antibodies, and anti-smooth muscle antibodies), histology and therapy.

RESULTS

CN was found in 13 (31.7%) patients with acute presentation (acute exacerbation phase 10, acute hepatitis phase 3) of AIH. Serum IgG levels of patients with CN were significantly lower than those of patients without CN (mean: 2307 mg/dL vs 3126 mg/dL, P < 0.05), while antinuclear antibody-negative rates were significantly higher (30.7% vs 3.5%, P < 0.05). However, other clinical features were similar between the two groups. The frequency of advanced fibrosis in patients with CN was significantly lower than in patients without CN (F0-2: 84.6% vs 35.7%, F3-4: 15.4% vs 64.3%, P < 0.05). Other histological features were similar between the two groups. Although there was no significant difference between groups when evaluated using the revised original score (12 vs 14), the simplified AIH score of patients with CN was significantly lower (6 vs 7, P < 0.05). Frequency of DR4 was similar between patients with and without CN.

CONCLUSION

CN is observed in both Japanese patients with acute hepatitis phase and acute exacerbation phase of type 1 AIH, although AIH with CN often shows clinical features of the genuine acute form.

Impact of methylglyoxal and high glucose co-treatment on human mononuclear cells

Hyperglycemia and elevation of methylglyoxal (MG) are symptoms of diabetes mellitus (DM). In this report, we show that co-treatment of human mononuclear cells (HMNCs) with MG (5 μM) and high glucose (HG; 15 – 30 mM) induces apoptosis or necrosis. HG/MG co-treatment directly enhanced the reactive oxygen species (ROS) content in HMNCs, leading to decreased intracellular ATP levels, which control cell death via apoptosis or necrosis. Concentrations of 5 μM MG and 15 mM glucose significantly increased cytoplasmic free calcium and nitric oxide (NO) levels, loss of mitochondrial membrane potential (MMP), activation of caspases-9 and -3, and cell death. In contrast, no apoptotic biochemical changes were detected in HMNCs treated with 5 μM MG and 25 mM glucose, which appeared to undergo necrosis. Pretreatment with nitric oxide (NO) scavengers inhibited apoptotic biochemical changes induced by 5 μM MG/15 mM glucose, and increased the gene expression levels of p53 and p21 involved in apoptotic signaling. The results collectively suggest that the treatment dosage of MG and glucose determines the mode of cell death (apoptosis vs. necrosis) of HMNCs, and that both ROS and NO play important roles in MG/HG-induced apoptosis.

Methylglyoxal and high glucose co-treatment induces apoptosis or necrosis in human umbilical vein endothelial cells

Hyperglycemia and elevation of methylglyoxal (MG) are symptoms of diabetes mellitus (DM). We previously showed that high glucose (HG; 30 mM) or MG (50-400 microM) could induce apoptosis in mammalian cells, but these doses are higher than the physiological concentrations of glucose and MG in the plasma of DM patients. The physiological concentration of MG and glucose in the normal blood circulation is about 1 microM and 5 mM, respectively. Here, we show that co-treatment with concentrations of MG and glucose comparable to those seen in the blood circulation of DM patients (5 microM and 15-30 mM, respectively) could cause cell apoptosis or necrosis in human umbilical vein endothelial cells (HUVECs) in vitro. HG/MG co-treatment directly increased the reactive oxygen species (ROS) content in HUVECs, leading to increases in intracellular ATP levels, which can control cell death through apoptosis or necrosis. Co-treatment of HUVECs with 5 microM MG and 20 mM glucose significantly increased cytoplasmic free calcium levels, activation of nitric oxide synthase (NOS), caspase-3 and -9, cytochrome c release, and apoptotic cell death. In contrast, these apoptotic biochemical changes were not detected in HUVECs treated with 5 microM MG and 30 mM glucose, which appeared to undergo necrosis. Pretreatment with nitric oxide (NO) scavengers could inhibit 5 microM MG/20 mM glucose-induced cytochrome c release, decrease activation of caspase-9 and caspase-3, and increase the gene expression and protein levels of p53 and p21, which are known to be involved in apoptotic signaling. Inhibition of p53 protein expression using small interfering RNA (siRNA) blocked the activation of p21 and the cell apoptosis induced by 5 microM MG/20 mM glucose. In contrast, inhibition of p21 protein expression by siRNA prevented apoptosis in HUVECs but had no effect on p53 expression. These results collectively suggest that the treatment dosage of MG and glucose could determine the mode of cell death (apoptosis vs. necrosis) in HUVECs, and both ROS and NO played important roles in MG/HG-induced apoptosis of these cells.

Epigallocatechin gallate dose-dependently induces apoptosis or necrosis in human MCF-7 cells

The catechins, a family of polyphenols found in tea, can evoke various responses, including cell death. However, the precise molecular mechanisms of these effects are unknown. Here, we demonstrate that treatment of human MCF-7 cells with 50 microM (-)-Epigallocatechin-3-gallate (EGCG), a catechin that is highly abundant in green tea, can induce apoptotic changes, including mitochondrial membrane potential changes and activation of c-Jun N-terminal kinase (JNK), caspase-9, and caspase-3. In contrast, higher concentrations of EGCG (100-400 microM) do not induce apoptosis, but rather trigger necrotic cell death in MCF-7 cells. Investigations of the possible mechanisms underlying these differences revealed that treatment with lower concentrations of EGCG (10-50 microM) directly increased intracellular oxidative stress, while higher concentrations (100-400 microM) did not. Immunoblotting revealed that treatment of MCF-7 cells with 10-50 microM EGCG caused increases in Bax protein levels and decreases in Bcl-2 protein levels, shifting the Bax-Bcl-2 ratio to favor apoptosis, while treatment with 100-400 microM EGCG had no such effect. Moreover, we observed a dose-dependent decrease in intracellular ATP levels in cells treated with high-dose EGCG. Blockade of reactive oxygen species (ROS) generation and ATP synthesis using antioxidants and ATP synthesis inhibitors revealed that ROS and ATP play important roles to switch cell death types with apoptosis or necrosis. Collectively, these results indicate for the first time that EGCG treatment has a dose-dependent effect on ROS generation and intracellular ATP levels in MCF-7 cells, leading to either apoptosis or necrosis, and that the apoptotic cascade involves JNK activation, Bax expression, mitochondrial membrane potential changes, and activation of caspase-9 and caspase-3.

Protective effect and mechanism of stronger neo-minophagen C against fulminant hepatic failure

AIM: To investigate the protective effect of stronger neo-minophafen C (SNMC) on fulminant hepatic failure (FHF) and its underlying mechanism.

METHODS: A mouse model of FHF was established by intraperitoneal injection of galactosamine (D-Gal N) and lipopolysaccharide (LPS). The survival rate, liver function, inflammatory factor and liver pathological change were obtained with and without SNMC treatment. Hepatocyte survival was estimated by observing the stained mitochondria structure with terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate fluorescence nick end labeling (TUNEL) method and antibodies against cytochrome C (Cyt-C) and caspase-3.

RESULTS: The levels of plasma tumor necrosis factor alpha (TNF-α), nitric oxide (NO), ET-1, interleukin-6 (IL-6), and the degree of hepatic tissue injury were decreased in the SNMC-treated groups compared with those in the model group (P < 0.01). However, there were no differences after different dosages administered at different time points. There was a significant difference in survival rates between the SNMC-treated groups and the model group (P < 0.01). The apoptosis index was 32.3% at 6 h after a low dose of SNMC, which was considerably decreased from 32.3% ± 4.7% vs 5% ± 2.83% (P < 0.05) to 5% on d 7. The expression of Cyt-C and caspase-3 decreased with the prolongation of therapeutic time. Typical hepatocyte apoptosis was obviously ameliorated under electron microscope with the prolongation of therapeutic time.

CONCLUSION: SNMC can effectively protect liver against FHF induced by LPS/D-Gal N. SNMC can prevent hepatocyte apoptosis by inhibiting inflammatory reaction and stabilizing mitochondria membrane to suppress the release of Cyt-C and sequent activation of caspase-3.

Centrilobular necrosis in autoimmune hepatitis: a histological feature associated with acute clinical presentation

AIMS

The characteristic histological feature of autoimmune hepatitis (AIH) is interface hepatitis with predominant portal lymphoplasmacytic necroinflammatory infiltration. Centrilobular necrosis (CN), reminiscent of toxic or circulatory liver injury, has been reported in AIH. The aim of this study was to assess the frequency of CN in patients with AIH and its correlation with laboratory and clinical data.

METHODS

Liver biopsies were obtained from 114 patients (90 women, 24 men, mean (SD) age 45.4 (19.4) years) with AIH and were evaluated under code by a single pathologist according to the modified Knodell score.

RESULTS

CN was found in 20 (17.5%) patients with virtually unaffected portal areas in four cases. Patients with AIH with CN had a higher total hepatic activity index (median (range) 11 (6 to 15) v 5 (2 to 10)) and presented less frequently with cirrhosis (10% v 38%). Patients with CN had a higher frequency of acute onset (87% v 32%), higher bilirubin (median (range) 12.0 (0.43 to 40.0) v 1.9 (0.36 to 46)) and higher ALT levels (median (range) 25.6 (2.7 to 63.9) v 7.2 (0.7 to 62.6)), than did patients with AIH without centrizonal injury.

CONCLUSION

CN with sparing of the portal areas represents a rare histological pattern in AIH. CN is associated with an acute clinical presentation and might reflect an early lesion preceding portal involvement. Recognition of this particular histological appearance enables early diagnosis of AIH and a timely initiation of immunosuppressive therapy.

Dosage effects of curcumin on cell death types in a human osteoblast cell line

Curcumin, the yellow pigment of Curcuma longa, is known to have antioxidant and anti-inflammatory properties, as well as their ability to either induce or prevent cell apoptosis. However, the precise molecular mechanisms of these effects are unknown. Here, we demonstrate that curcumin can induce apoptotic changes, including JNK activation, caspase-3 activation, and cleavage of PARP and PAK2, at treatment concentrations lower than 25 microM in human osteoblast cells. In contrast, treatment with 50-200 microM of curcumin does not induce apoptosis, but rather triggers necrotic cell death in human osteoblasts. Using the cell permeable dye 2',7'-dichlorofluorescin diacetate (DCF-DA) as an indicator of reactive oxygen species (ROS) generation, we found that while treatment with 12.5-25 microM curcumin directly increased intracellular oxidative stress, 50-200 microM curcumin had far less effect. Pretreatment of cells with N-acetyl cysteine or alpha-tocopherol, two well known ROS scavengers, attenuated the intracellular ROS levels increases and converted the apoptosis to necrosis induced by 12.5-25 microM curcumin. Moreover, we observed a dose-dependent decrease in intracellular ATP levels after treatment of osteoblast cells with curcumin and pretreatment of cells with antimycin or 2-deoxyglucose to cause ATP depletion significantly converted 12.5-25 microM curcumin-induced apoptosis to necrosis, indicating that ATP (a known mediator of apoptotic versus necrotic death) is most likely involved in the switching mechanism. Overall, our results signify that curcumin dosage treatment determines the possible effect on ROS generation, intracellular ATP levels, and cell apoptosis or necrosis in osteoblast cells.

Dosage effects of resveratrol on ethanol-induced cell death in the human K562 cell line

Previous studies have established that ethanol induces cell apoptosis and necrosis. However, the precise molecular mechanisms are currently unclear. Here, we show that higher concentrations of ethanol (250-400 mM) induced a shift from apoptotic to necrotic cell death in human K562 cells, and that resveratrol, a grape-derived phytoalexin with known antioxidant and anti-inflammatory properties, inhibited or enhanced ethanol-induced apoptosis/necrosis depending on the treatment dosage. Using the cell permeable dye 2',7'-dichlorofluorescin diacetate (DCF-DA) as an indicator of reactive oxygen species (ROS) generation, we showed that ethanol treatment directly increased intracellular oxidative stress. This intracellular oxidative stress increased in response to high concentrations (100-200 microM) of resveratrol, but remained unchanged following treatment with low concentrations (10-25 microM) of resveratrol. Further studies showed that resveratrol could attenuate or enhance ethanol-induced intracellular oxidative stress generation-dependent on treatment dosage, and that this effect could be correlated with cell apoptosis or necrosis. Importantly, ethanol-induced changes in intracellular ATP levels were also correlated with resveratrol dosage. Taken together, these results indicate that the treatment dosage may determine the effect of resveratrol on ethanol-induced ROS generation, intracellular ATP levels, and cell apoptosis or necrosis. Thus our findings support the possibility that appropriate dosage of resveratrol aids in decreasing the toxic effect of ethanol.

Necrotic cell death in response to oxidant stress involves the activation of the apoptogenic caspase-8/bid pathway

Human epithelial (A549) cells exposed to hyperoxia die by cellular necrosis. In the current study, we demonstrated the involvement of apoptogenic factors in epithelial cell necrosis in response to hyperoxia, including the formation of the Fas-related death-inducing signaling complex and initiation of mitochondria-dependent apoptotic pathways. We showed increased activation of both Bid and Bax in A549 cells subjected to hyperoxia. Bax activation involved a Bid-assisted conformational change. We discovered that the response to hyperoxia in vivo predominantly involved the activation of the Bid/caspase-8 pathway without apparent increases in Bax expression. Disruption of the Bid pathway by gene deletion protected against cell death in vivo and in vitro. Likewise, inhibition of caspase-8 by Flip also protected against cell death. Taken together, we have demonstrated the involvement of apoptogenic factors in epithelial cell responses to hyperoxia, despite a final outcome of cellular necrosis. We have, for the first time, identified a predominant role for the caspase-8/Bid pathway in signaling associated with hyperoxic lung injury and cell death in vivo and in vitro.

Apoptosis in organs of rats in early stage after polytrauma combined with shock

OBJECTIVE

Apoptosis in organs of rats in early stage after polytrauma combined with shock was researched.

METHODS

Sixty Sprague-Dawley rats were divided into six groups: normal control (A, n = 6), sham-operation (N, n = 6), single hemorrhagic shock (S, n = 6), two-site trauma/shock (B, n = 6), four-site trauma/shock (C, n = 6), and six-site trauma/shock (D, n = 30). Shock was kept 60 min by blood withdrawal. Polytrauma was performed by clamping different sites of limbs to make fractures according to different groups: B at both femurs; C at femurs and tibias; and D at femurs, tibias, and humeri. The animals of A were totally normal without any operation. The rats of N, S, B, and C were killed at 6 hours after resuscitation, and the rats of D were killed at 1, 3, 6, 12, and 24 hours, respectively. Then, DNA agarose gel electrophoresis, in situ end-labeling (ISEL), and light and electron microscopy were performed and the percentage of DNA fragmentation was detected to assess apoptosis.

RESULTS

In B, C, and D, the special ladder patterns for apoptosis were seen in thymus, spleen, liver, lung, and intestine, but not in heart, kidney, and brain. However, positive responses were observed in all these eight organs by ISEL. At 6 hours after resuscitation, the percentages of DNA fragmentation in thymus, spleen, liver, lung, and intestine all increased together with the severity of trauma. In D, the percentages of DNA fragmentation in these five organs all increased significantly at 1 hour after resuscitation. At 3 hours, the percentages in spleen, liver, lung, and intestine reached peak, and declined gradually afterward, whereas those in thymus continued increasing after 3 hours and kept stable from 6 hours to 24 hours. It was shown by morphologic examination that the majority of apoptotic cells lay in cortex of thymus, in growth center of white pulp of spleen, in border area of hepatic lobule and portal area of liver, and at the base of crypts of intestine. In lung, multiple kinds of cells, including alveolar epithelial cells, vascular endothelial cells, and polymorphonuclear neutrophils, induced apoptosis.

CONCLUSION

Apoptosis was induced in thymus, spleen, liver, lung, and intestine in early stage after polytrauma combined with shock, which may play partial roles in the development of multiple organ failure.

Involvement of apoptosis in the endotoxemic lesions of the liver and kidneys of piglets

The involvement of apoptosis was evaluated in lesions of endotoxemic piglets. A single injection with E. coli O111:B4 lipopolysaccharide (LPS) induced foci of coagulative necrosis in the liver and kidneys. No significant change was observed in these organs at 1.5 hr after LPS injection, but at 6 hr, epithelial cells with chromatin condensation or fragmentation and apoptotic bodies were visible. Foci of coagulative necrosis were formed within 24 hr after LPS inoculation. In and adjacent to the necrotic foci, dead hepatocytes with nuclear condensation or fragmentation were scattered. These dead cells were positively stained by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) methods. Electronmicroscopy revealed apoptotic cells with condensed or fragmented homogeneous nuclear chromatin, and necrotic cells with irregularly destroyed nuclei and cytoplasmic membranes. Apoptotic cell death were also observed in parietal cells of the stomach and lymphocytes in the lymphatic system. DNA ladders with approximately 200-bp multimers were observed in hepatic, renal and thymic samples prepared after 6 and 24 hr of LPS injection by agarose gel electrophoresis. These results suggest that apoptosis is involved in the pathology of swine endotoxemia.

Aponecrosis: morphological and biochemical exploration of a syncretic process of cell death sharing apoptosis and necrosis

A rat fibroblastic cell line (rat-1/myc-ERtrade mark) was treated with different concentration of Antimycin A, a metabolic poison that affects mitochondrial respiratory chain complex III. The modes of cell death were analyzed by time-lapse videomicroscopy, in situ end-labeling (ISEL) technique, and ultrastructural analysis. Intracellular ATP levels were also measured in order to detect whether the energetic stores were determinant for the type of cell death. It was found that while apoptosis was the prevalent cell death in the fibroblasts treated with low doses, 100 or 200 microM Antimycin A, a new type of cell demise that shared dynamic, molecular, and morphological features with both apoptosis and necrosis represents the most common cell death when the cells were exposed to high doses, 300 or 400 microM, of the hypoxic stimulus. This new type of cell death has been chimerically termed aponecrosis. The inhibition of caspase 3, an enzyme critical for the apoptotic DNA degradation, caused a clear shift from aponecrosis to necrosis in the cell culture, suggesting that this new type of cell death could account for an incomplete execution of the apoptotic program and the following degeneration in necrosis. After being treated with higher doses, i.e., 1000 microM Antimycin A, almost all of the cells died by true necrosis. The analysis of the cellular energetic stores showed that the levels of ATP were a primary determinant in directing toward active cell death (apoptosis), aponecrosis, or necrosis. We conclude that chemically induced hypoxia produces different types of cell death depending on the intensity of the insult and on the ATP availability of the cell, and that the classic apoptosis and necrosis may represent only two extremes of a continuum of intermediate forms of cell demise.

Hepatic apoptotic activity following transient normothermic inflow occlusion and reperfusion in the swine model

Accelerated hepatic apoptosis was first described in portal vein-ligated livers but has since been reported in a variety of liver injuries. Because porto-prival states can induce apoptosis we sought to determine whether transient ischemic periods followed by reperfusion would trigger such cell death. The cytokines TNF-alpha and TGF-beta are known to facilitate apoptosis and are released in response to a number of stimuli including ischemia. We also investigated alterations in plasma and tissue levels of these cytokines which might lend support to their role in increased apoptotic activity following ischemia/reperfusion. Female pigs were used as the experimental model. Inflow occlusion of portal and hepatic arterial blood was performed to a portion of the swine liver directing the entire splanchnic flow to the remaining hepatic lobes for a period of 2 h. The livers were then reperfused and plasma and tissue samples taken for determination of apoptotic activity utilizing cell death immunoperoxidase staining of 3'-OH DNA ends generated by fragmentation and ELISA assay of histone-associated DNA fragments. Plasma and tissue levels of TNF-alpha and plasma levels of TGF-beta were determined by ELISA assay. An increase in apoptotic activity following reperfusion was seen at Day 2 and Day 4 compared to preischemic values by the cell death stain. The ELISA cell death assay showed an increase in apoptotic activity at 60 min, Day 2, and Day 4. Moreover, the ELISA cell death assay showed enhanced apoptotic activity in "hyperperfused" hepatic lobes compared to preischemic, or resting, liver. This was also observed when compared to sham-operated animals. Surprisingly, there was no detectable increase in plasma TNF-alpha or TGF-beta levels following ischemia/reperfusion, although homogenized liver TNF-alpha levels were increased at 60 min and Day 2 following reperfusion. We conclude that transient hepatic inflow occlusion followed by reperfusion can induce increased apoptotic activity in the swine model. Furthermore, increased apoptotic activity also occurs in the hyperperfused liver raising the possibility of a locally active factor or global hepatic expression of receptor activity in response to ischemia/reperfusion. This period of ischemia/reperfusion did not produce a detectable increase in circulating cytokine levels, and accelerated apoptosis could not be linked to heightened TNF-alpha or TGF-beta plasma activity. Higher tissue levels of TNF-alpha could reflect enhanced binding to TNF cell surface receptors or amplified receptor expression.

Acquisition of resistance to apoptosis and necrosis by Bcl-xL over-expression in rat hepatoma McA-RH8994 cells

BACKGROUND

Bcl-xL is the predominant anti-apoptotic Bcl-2 family member in the liver. Suppression of cell death promotes carcinogenesis and contributes to resistance to radiation and chemotherapeutic agents.

METHODS

Direct effects of Bcl-xL protein on apoptosis and necrosis were investigated in rat hepatoma cells. Rat hepatoma cell line McA-RH8994 cells were transfected with expression plasmids containing a whole coding sequence of rat bcl-xL cDNA of sense orientation. Stable transfectant cell lines expressing bcl-xL cDNA (designated as RH8994/Bcl-xL-S), or control plasmid DNA (designated as RH8994/pT) were established.

RESULTS

Cellular amounts of Bcl-xL in RH8994/Bcl-xL-S cells were demonstrated to be more than 20-fold that of RH8994/pT and parental cells. Three independent clones of RH8994/Bcl-xL-S were isolated and their susceptibility to various cell death stimuli was compared with that of the control cells. Transforming growth factor-beta1 and tumour necrosis factor-alpha induced apoptosis dose dependently in these cells, but the 50% cytotoxicity concentrations of these factors in RH8994/Bcl-xL-S cells were more than 10-fold higher than those in RH8994/pT and parental cells. Similarly, RH8994/Bcl-xL-S cells were shown to be significantly less susceptible to necrotic cell death induced by a calcium ionophore, A23187; a mutagen, N-methyl-N'-nitro-N-nitrosoguanidine; and UV-irradiation when compared with the control cells.

CONCLUSIONS

Over-expression of Bcl-xL was shown to provide protection against apoptotic and necrotic cell death in rat hepatoma cells.

The effects of cell density, attachment substratum and dexamethasone on spontaneous apoptosis of rat hepatocytes in primary culture

The rates of spontaneous cell detachment, cell viability, and apoptosis in primary cultures of rat hepatocytes plated at high and low density were compared. Apoptosis was frequent in detached cells, and the rates of cell detachment and apoptosis were greater in high-density than in low-density cultures. Among attached cells, more cells had condensed or fragmented nuclei in high-density than in low-density cultures. Further, ladder-like DNA fragmentation was not seen in low-cell-density cultures but was clearly evident in high-density cultures. Bax was more highly expressed in cells cultured at high density, and on collagen vs. matrigel, whereas changes of Bcl-2 and Fas expression observed in culture appeared unrelated to the rate of apoptosis. The rate of hepatocyte apoptosis appeared to be identical in low-density cultures on collagen 1 and matrigel, but when cells were cultured at high density, matrigel suppressed apoptosis by more than 50% at 36 h. In hepatocytes cultured on collagen 1, dexamethasone (0.1 microM) suppressed apoptosis in both low- and high-density cultures; higher doses had no further effects. In high density cultures, aurintricarboxylic acid (10 microM) suppressed apoptosis and this improved cell attachment at 48 h. It is concluded that cell viability in primary cultures of rat hepatocytes grown on collagen I is dependent on optimal culture density and that the cell population is regulated, at least in part, by apoptosis. Corticosteroids suppress spontaneous apoptosis of cultured hepatocytes in a non-dose-dependent manner, whereas matrigel abolishes apoptosis induced by increasing cell density. Bax may be an important protein in the cell density and cell matrix-dependent regulation of apoptosis in cultured hepatocytes.

Cyclosporin A protects Balb/c mice from liver damage induced by superan tigen SEB and D-GalN

AIM: To investigate the pathogenic effect of SEB and D-GalN on liver and the protection of cyclosporin A, the relationship between hepatic apoptosis and necrosis and the possible mechanism of acute hepatic necrosis.

METHODS: After staphylococcal enterotoxin B (SEB) mixed with D-galactosamine (D-GalN) were injected intraperitoneally into Balb/c mice and those previously treated with cyclosporin A, blood samples were collected and livers were isolated at 2, 6, 12, 24h. Patterns of hepatocellular death were studied morphologically and biochemically, circulating cytokines (TNF-α, IFN-γ) and mice mortality within 24h was assessed.

RESULTS: The SEB could induce the typical apoptotic changes of hepatocytes, the D-GalN could induce hepatocytes apoptosis and degeneration at the same time, and the mice having received the SEB + D-GalN injections developed apoptosis at 2 and 6h, but after 12h hepatocytes were characterized by severe injury, whereas all the examinations in the cyclosporin A treated mice were normal.

CONCLUSION: Hepatic cell apoptosis might be related to necrosis, and massive hepatocyte apoptosis is likely the initiating step of acute hepatic necrosis in mice. The effects induced by SEB and D-GalN on hepatocytes might be mediated by T cells, and could be prevented by cyclosporin A.

Alterations of cell volume regulation in the development of hepatocyte necrosis

Intracellular Na+ accumulation has been shown to contribute to hepatocyte death caused by anoxia or oxidative stress. In this study we have investigated the mechanism by which Na+ overload can contribute to the development of cytotoxicity. ATP depletion in isolated hepatocytes exposed to menadione-induced oxidative stress or to KCN was followed by Na+ accumulation, loss of intracellular K+, and cell swelling. Hepatocyte swelling occurred in two phases: a small amplitude swelling (about 15% of the initial size) with preservation of plasma membrane integrity and a terminal large amplitude swelling associated with cell death. Inhibition of Na+ accumulation by the use of a Na+-free medium prevented K+ loss, cell swelling, and cytotoxicity. Conversely, blocking K+ efflux by the addition of BaCl2 did not influence Na+ increase and small amplitude swelling, but greatly stimulated large amplitude swelling and cytotoxicity. Menadione or KCN killing of hepatocytes was also enhanced by inducing cell swelling in an hypotonic medium. However, increasing the osmolarity of the incubation medium did not protect against large amplitude swelling and cytotoxicity, since stimulated Na+ accumulation and K+ efflux. Altogether these results indicate that the impairment of volume regulation in response to the osmotic load caused by Na+ accumulation is critical for the development of cell necrosis induced by mitochondrial inhibition or oxidative stress.

Histomorphological and immunohistochemical studies of chronic active hepatitis in Doberman Pinschers

Liver tissue samples were reviewed from 35 Doberman Pinschers with chronic active hepatitis in the precirrhotic stage. Thirty dogs had elevated hepatic copper concentrations, and five had normal liver copper concentrations. The earliest changes were inflammation and scar tissue deposition around the small hepatic vein branches. There was also apoptosis of scattered hepatocytes in zone 3. Inflammation consisted of macrophages, lymphocytes, and plasma cells. As the disease progressed, collagen deposition increased around the hepatic veins; in some liver specimens, thin scar tissue septa radiated from the hepatic vein branches, and inflammation spread to include the portal tracts. The sinusoids adjacent to the scar tissue were converted to endothelial-lined, thin-walled vessels. Chronic active hepatitis (commonly referred to as Doberman hepatitis or chronic active hepatitis of Dobermans) is a progressive fibrosis, inflammation and hepatocyte loss beginning among zone 3 hepatocytes around the terminal hepatic vein branches. The histomorphologic changes were the same among those Dobermans with elevated hepatic copper and those with normal hepatic copper. The cause was not determined, but these morphologic studies support the idea of immune-mediated disease.

Evidence of hepatocyte apoptosis in rat liver after the administration of carbon tetrachloride

In acute liver injury induced by the injection of CCl4, cell death has been attributed to the necrosis of hepatocytes in the centrilobular area. In the present study, we re-examined the hepatic injury evoked by CCl4 in rats and explored the possibility that apoptosis may also contribute to its pathogenesis. Apoptotic hepatocytes were identified and quantified by light and electron microscopy, the in situ immunohistochemical labeling of nuclear DNA fragmentation, flow cytometry, and DNA gel electrophoresis. We found that a substantial number of hepatocytes underwent apoptosis. Apoptotic changes were also observed in ballooned hepatocytes. Apoptotic hepatocytes increased in number at 3 hours and peaked at 6 hours after the CCl4 injection. Apoptotic bodies were sequestrated in the adjacent hepatocytes and sinusoidal cells. Double staining of the cells with immunostaining for phagocytes and terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling staining for labeling of DNA fragmentation showed that the majority of apoptotic hepatocytes were phagocytosed by Kupffer cells and macrophages. The results indicated that apoptosis occurs in the ballooned and injured hepatocytes of the centrilobular area. What occurs after CCl4 administration may be important in reducing inflammation, shortening the course of acute hepatic injury, and preventing the development of fibrosis.

Galactosamine-induced apoptosis in the primary mouse hepatocyte cultures

Galactosamine (GalN)-induced apoptosis was investigated in cultured hepatocytes from mice. The percentage of fragmented DNA measured by the ELISA method increased in a concentration-dependent manner from the very early stage, i.e. 0.5 hrs, after GalN-exposure. In addition, a ladder-like fragmentation pattern by agarose gel electrophoresis appeared first at 3 hr-exposure to 20 mM GalN, at 6 hr-exposure to 10 mM GalN and at 12 hr-exposure to 5 mM GalN, respectively. On the other hand, cytotoxicity indicated by leakage of lactate dehydrogenase from cultured hepatocytes to culture medium was first detected at 24 hrs after GalN-treatment. Morphologically, formation of blebs and apoptotic bodies was observed from 12 hr-exposure to 20 mM GalN and from 24 hr-exposure to 10 mM GalN, respectively. Thus GalN could induce apoptosis in primary hepatocyte cultures from mice.

Induction of mitochondrial dysfunction and apoptosis in HeLa cells by bis-pyridinium oximes, a newly synthesized family of lipophilic biscations

When tested on HeLa cells, bis-pyridinium oximes (BPO), a family of newly synthesized molecules whose charged pyridinium moieties are linked by a linear polymethylene chain of variable length (N = 3 to 12) have been shown to possess an inhibitory effect on cell growth and finally to provoke cell death. BPO-affected cells displayed reduced mitochondrial oxygen consumption and ATP stores and were blocked in the G1 phase of the cell cycle. Mitochondrial membrane potential, as assayed with the dye 3,3'-diexyloxacarbocyanine iodide [DiOC6(3)], increased in BPO-treated cells with time of exposure. Cell growth inhibition as well mitochondrial dysfunction were observed only with derivatives having a long polymethylene linking chain (N > or = 6). Furthermore, the concentration of the compound eliciting such effects was inversely related to the number of methylene groups in the linking chain. None of the BPO with N = 6 to 12 modified the mitochondrial DNA content, relative to the nuclear DNA content. In BPO (N = 8 and N = 12)-treated cells, chromatin fragmentation and internucleosomal DNA cleavage occurred massively, indicating that the death mode induced by these compounds is apoptosis. The possible pathway of action and the potential pharmacological interest of these compounds are discussed.

Apoptosis in human hepatocellular carcinoma and in liver cell dysplasia is correlated with p53 protein immunoreactivity

AIMS

To investigate the prevalence of apoptosis in human hepatocellular carcinomas (HCC) of different types and grades and in liver cell dysplasia, and to test whether the apoptotic rate is correlated with the p53 protein status.

METHODS

37 HCC and 66 six liver samples with liver cell dysplasia were analysed for apoptosis using in situ DNA end labelling (ISEL), and for p53 protein expression by immunohistochemistry. In HCCs, proliferative activity was quantitatively assessed using proliferating cell nuclear antigen labelling.

RESULTS

The apoptotic index in HCC as based on ISEL ranged from 0.1 to 13.5 per 1000 cells analysed and was not related to type or grade. No nuclear staining was observed in multinuclear tumour cells. There was a significant correlation between the apoptotic rate and both the proliferative activity and p53 protein reactivity. In liver samples containing p53 protein positive liver cell dysplasia cells, there was a significantly higher apoptotic rate of these cells.

CONCLUSIONS

Apoptosis is detectable in HCC, and is not related to type and grade. There is a highly significant positive correlation between the apoptotic rate in HCC and both the proliferative activity and p53 protein expression. A similar phenomenon occurs for putative cancer precursors. The findings support the role of p53 in regulating apoptosis in preneoplastic and neoplastic liver lesions.

TGF-beta-mediated hepatocellular apoptosis by rat and human hepatoma cells and primary rat hepatocytes

BACKGROUND/AIMS

Primary cultures of rat hepatocytes, rat (FAO) and human (HepG2) hepatoma cells were studied by immunocytochemistry for expression of transforming growth factor (TGF)-beta, for the release of TGF-beta into the medium, and generation of hepatocellular apoptosis by the respective cell-conditioned media.

METHODS/RESULTS

Using the alkaline-phosphatase anti-alkaline-phosphatase technique, intense TGF-beta immunostaining was shown in all cell types. The cytokine is released almost entirely in the latent form into the culture medium; only the FAO-cells had a substantial fraction of bioactive TGF-beta in the native (unacidified) culture fluid. Exposure of hepatocytes with the respective cell-conditioned media in the activated, but not in the native form (except for FAO-cell media), induced severe detrimental effects as evidenced by: (i) gross morphological alterations, (ii) functional impairment (reduction of WST-1 test, detachment of cells, lactate dehydrogenase increase in the medium), and (iii) generation of apoptosis. The latter phenomenon was confirmed by an increase of internucleosomal DNA fragments, positive TUNEL reaction, and intense binding of the fluorochrome Hoechst 33342 to fragmented nuclei. All these effects, which were mimicked by addition of recombinant human TGF-beta 1, were almost entirely antagonized by pre-incubation of the conditioned media with latency associated peptide. In contrast to hepatocytes, both types of hepatoma cells were completely resistant to the multiple actions of TGF-beta and activated conditioned media.

CONCLUSIONS

It is concluded that hepatocytes might have the ability to induce autocrine, TGF-beta-mediated apoptosis, whereas hepatoma cells, because of their TGF-beta resistance, might generate TGF-beta-mediated peritumorous apoptosis of hepatocytes in a paracrine way, which could facilitate their expansion in situ. Both mechanisms, however, are critically dependent on extracellular TGF-beta activation.

Effect of total hepatic vascular exclusion during liver resection on hepatic ultrastructure

The aim of this investigation was to observe ultrastructural changes in the liver in response to warm ischemia during liver surgery. In 11 noncirrhotic patients, hepatic resection was performed under total vascular exclusion (TVE). The mean duration of warm ischemia was 28 minutes (range 16-48 minutes). Three specimens were taken from each patient: before clamping, at the end of TVE, and after reperfusion. Biopsy specimens were studied by light microscopy and by transmission electron microscopy (EM). At the end of the ischemic phase sinusoids were collapsed with resultant loss of normal hepatic architecture. Morphological changes to hepatocytes included focal chromatin condensation at the nuclear margins, distended nuclear envelope, and swelling of both mitochondria and endoplasmic reticulum. After reperfusion these changes reversed. The phenomenon of sinusoidal and hepatocellular recovery after TVE was seen in all the cases of this study, irrespective of age, sex, disease, type and severity of surgical intervention, and duration of TVE. It can be concluded that TVE over a period of 48 minutes has no irreversible deleterious effects on the ultrastructure of the noncirrhotic liver.

Apoptosis induced by tumor necrosis factor-alpha in rat hepatocyte cell lines expressing hepatitis B virus

Three well differentiated SV40-immortalized rat hepatocyte cell lines, CWSV1, CWSV2, and CWSV14, and Hepatitis B Virus (HBV)-producing cell lines derived from them were examined for sensitivity to tumor necrosis factor (TNF)-alpha. CWSV1, CWSV2, and CWSV14 cells were co-transfected with a DNA construct containing a dimer of the HBV genome and the neo gene and selected in G418 to generate stable cell lines. Characterization of these cell lines indicated that they contain integrated HBV DNA, contain low molecular weight HBV DNA compatible with the presence of HBV replication intermediates, express HBV transcripts, and produce HBV proteins. The viability of CWSV1, CWSV2, and CWSV2 cells was not significantly altered when they were treated with TNF-alpha at concentrations as high as 20,000 U/ml. The HBV-expressing CWSV1 cell line, SV1di36, and the HBV-expressing CWSV14 cell line, SV14di208, were also not killed when treated with TNF-alpha. However, the HBV-expressing CWSV2 cell line, SV2di366, was extensively killed when treated with TNF-alpha at concentrations ranging from 200 to 20,000 U/ml. Analysis of several different HBV-producing CWSV2 cell lines indicated that TNF-alpha killing depended upon the level of HBV expression. The TNF-alpha-induced cell killing in high HBV-producing CWSV2 cell lines was accompanied by the presence of an oligonucleosomal DNA ladder characteristic of apoptosis.

Tumor necrosis factor-alpha-induced apoptosis in hepatocytes in long-term culture

Apoptosis occurs naturally in the liver and increases in specific pathogenic processes. We previously described the use of a chemically defined medium supplemented with epidermal growth factor and dimethylsulfoxide to maintain rat hepatocytes in a highly differentiated state for more than 30 days (long-term culture). In this study, we showed that hepatocytes in long-term dimethylsulfoxide culture have definite advantages over using cells in short-term culture (cells in culture for 2 to 4 days) to study apoptosis. We demonstrated that treatment with tumor necrosis factor (TNF)-alpha induced apoptosis (detected morphologically and by formation of an oligonucleosomal DNA ladder) only in hepatocytes that had been subjected to dimethylsulfoxide removal. Neither treatment with TNF-alpha alone or dimethylsulfoxide removal alone induced apoptosis. Apoptosis could be induced by concentrations as low as 500 U of TNF-alpha/ml. Although a DNA ladder was not detected by 12 hours after TNF-alpha treatment, it was easily identified by 24 hours. We conclude that this system can be used 1) to examine the underlying mechanism by which TNF-alpha causes apoptosis in hepatocytes and 2) to study induction of apoptosis in hepatocytes by other agents.

In situ detection of fragmented DNA (TUNEL assay) fails to discriminate among apoptosis, necrosis, and autolytic cell death: a cautionary note

Detection of DNA fragments in situ using the terminal deoxyribonucleotidyl transferase (TDT)-mediated dUTP-digoxigenin nick end labeling (TUNEL) assay is increasingly applied to investigate active cell death (apoptosis). We studied the specificity of the assay in well-defined models of apoptosis and necrosis as well as in postmortem autolysis in rat liver. During involution of liver hyperplasia, which follows stopping treatment with the hepatomitogens cyproterone acetate (CPA) or nafenopin (NAF), numerous apoptotic hepatocytes could be observed with TUNEL-positive chromatin residues. A similar TUNEL-positive reaction appeared in necrotic hepatocytes after a cytotoxic dose of carbon tetrachloride (CCl4) or N-nitrosomorpholine (NNM). Also, in insufficiently fixed, autolytic livers TUNEL-positive nuclei were observed. Thus, DNA fragmentation is common to different kinds of cell death; its detection in situ should not be considered a specific marker of apoptosis.

Apoptosis: regulation and relevance to toxicology

1. Apoptosis is a remarkably stereotyped morphological event across all tissues in response to a vast array of damaging agents. 2. Our very existence depends upon a willing exchange of old life for new: apoptotic cell death is our guardian and saviour from genetic damage. 3. There is a close link between cell proliferation and apoptosis: When a cell picks up the machinery to proliferate it also acquires an abort pathway--'better dead than wrong'. 4. A wide variety of highly conserved genes have been implicated in triggering apoptosis. 5. The release of DNA loops from the nuclear scaffold is a more crucial intracellular event than DNA 'laddering' in apoptotic cells. 6. The manipulation of apoptotic rates in many of the common diseases in man will be a major therapeutic strategy in the future.