Laser-mediated rupture of chlamydial inclusions triggers pathogen egress and host cell necrosis

Remarkably little is known about how intracellular pathogens exit the host cell in order to infect new hosts. Pathogenic chlamydiae egress by first rupturing their replicative niche (the inclusion) before rapidly lysing the host cell. Here we apply a laser ablation strategy to specifically disrupt the chlamydial inclusion, thereby uncoupling inclusion rupture from the subsequent cell lysis and allowing us to dissect the molecular events involved in each step. Pharmacological inhibition of host cell calpains inhibits inclusion rupture, but not subsequent cell lysis. Further, we demonstrate that inclusion rupture triggers a rapid necrotic cell death pathway independent of BAK, BAX, RIP1 and caspases. Both processes work sequentially to efficiently liberate the pathogen from the host cytoplasm, promoting secondary infection. These results reconcile the pathogen's known capacity to promote host cell survival and induce cell death.

RIP3 induces apoptosis independent of pronecrotic kinase activity

Receptor-interacting protein kinase 3 (RIP3 or RIPK3) has emerged as a central player in necroptosis and a potential target to control inflammatory disease. Here, three selective small-molecule compounds are shown to inhibit RIP3 kinase-dependent necroptosis, although their therapeutic value is undermined by a surprising, concentration-dependent induction of apoptosis. These compounds interact with RIP3 to activate caspase 8 (Casp8) via RHIM-driven recruitment of RIP1 (RIPK1) to assemble a Casp8-FADD-cFLIP complex completely independent of pronecrotic kinase activities and MLKL. RIP3 kinase-dead D161N mutant induces spontaneous apoptosis independent of compound, whereas D161G, D143N, and K51A mutants, like wild-type, only trigger apoptosis when compound is present. Accordingly, RIP3-K51A mutant mice (Rip3(K51A/K51A)) are viable and fertile, in stark contrast to the perinatal lethality of Rip3(D161N/D161N) mice. RIP3 therefore holds both necroptosis and apoptosis in balance through a Ripoptosome-like platform. This work highlights a common mechanism unveiling RHIM-driven apoptosis by therapeutic or genetic perturbation of RIP3.

Accelerated recovery of mitochondrial membrane potential by GSK-3β inactivation affords cardiomyocytes protection from oxidant-induced necrosis

Loss of mitochondrial membrane potential (ΔΨ_m) is known to be closely linked to cell death by various insults. However, whether acceleration of the ΔΨ_m recovery process prevents cell necrosis remains unclear. Here we examined the hypothesis that facilitated recovery of ΔΨ_m contributes to cytoprotection afforded by activation of the mitochondrial ATP-sensitive K⁺ (mK_ATP) channel or inactivation of glycogen synthase kinase-3β (GSK-3β). ΔΨ_m of H9c2 cells was determined by tetramethylrhodamine ethyl ester (TMRE) before or after 1-h exposure to antimycin A (AA), an inducer of reactive oxygen species (ROS) production at complex III. Opening of the mitochondrial permeability transition pore (mPTP) was determined by mitochondrial loading of calcein. AA reduced ΔΨ_m to 15±1% of the baseline and induced calcein leak from mitochondria. ΔΨ_m was recovered to 51±3% of the baseline and calcein-loadable mitochondria was 6±1% of the control at 1 h after washout of AA. mK_ATP channel openers improved the ΔΨ_m recovery and mitochondrial calcein to 73±2% and 30±7%, respectively, without change in ΔΨ_m during AA treatment. Activation of the mK_ATP channel induced inhibitory phosphorylation of GSK-3β and suppressed ROS production, LDH release and apoptosis after AA washout. Knockdown of GSK-3β and pharmacological inhibition of GSK-3β mimicked the effects of mK_ATP channel activation. ROS scavengers administered at the time of AA removal also improved recovery of ΔΨ_m. These results indicate that inactivation of GSK-3β directly or indirectly by mK_ATP channel activation facilitates recovery of ΔΨ_m by suppressing ROS production and mPTP opening, leading to cytoprotection from oxidant stress-induced cell death.

AIF-Mediated Programmed Necrosis: A Highly Orchestrated Way to Die

Historically, two main forms of cell death have been distinguished: apoptosis and necrosis. Apoptosis was initially considered as the only physiological and programmed form of cell death. This type of death is recurrently associated with caspases, a family of cysteine proteases activated in apoptotic conditions. However, it is now widely recognized that programmed cell death (PCD) can also occur in the complete absence of caspase activation. The existence of non-caspase PCD pathways was corroborated by the discovery of caspase-independent executioners, such as the mitochondrial protein Apoptosis-Inducing Factor (AIF). Necrosis has often been viewed as an accidental and uncontrolled cell death process. Nevertheless, increasing evidence shows that, like apoptosis, necrosis could be a highly orchestrated type of PCD. Indeed, apoptosis and necrosis present more similarities than it has been originally thought. Here, we summarize the different classifications of PCD and the current knowledge of a necrotic PCD pathway mediated by AIF: alkylating DNA-damage mediated death. We also outline the molecular mechanisms controlling this form of PCD and discuss their potential relevance in physiological and pathological settings. These emerging data on the molecular mechanisms regulating programmed necrosis may certainly have potent therapeutic consequences in treating both apoptotic-resistant tumors and degenerating adult neurons.

Cyclin-dependent kinase inhibitor 2B regulates efferocytosis and atherosclerosis

Genetic variation at the chromosome 9p21 risk locus promotes cardiovascular disease; however, it is unclear how or which proteins encoded at this locus contribute to disease. We have previously demonstrated that loss of one candidate gene at this locus, cyclin-dependent kinase inhibitor 2B (Cdkn2b), in mice promotes vascular SMC apoptosis and aneurysm progression. Here, we investigated the role of Cdnk2b in atherogenesis and found that in a mouse model of atherosclerosis, deletion of Cdnk2b promoted advanced development of atherosclerotic plaques composed of large necrotic cores. Furthermore, human carriers of the 9p21 risk allele had reduced expression of CDKN2B in atherosclerotic plaques, which was associated with impaired expression of calreticulin, a ligand required for activation of engulfment receptors on phagocytic cells. As a result of decreased calreticulin, CDKN2B-deficient apoptotic bodies were resistant to efferocytosis and not efficiently cleared by neighboring macrophages. These uncleared SMCs elicited a series of proatherogenic juxtacrine responses associated with increased foam cell formation and inflammatory cytokine elaboration. The addition of exogenous calreticulin reversed defects associated with loss of Cdkn2b and normalized engulfment of Cdkn2b-deficient cells. Together, these data suggest that loss of CDKN2B promotes atherosclerosis by increasing the size and complexity of the lipid-laden necrotic core through impaired efferocytosis.

Cyclin-dependent kinase inhibitor 2B regulates efferocytosis and atherosclerosis

Genetic variation at the chromosome 9p21 risk locus promotes cardiovascular disease; however, it is unclear how or which proteins encoded at this locus contribute to disease. We have previously demonstrated that loss of one candidate gene at this locus, cyclin-dependent kinase inhibitor 2B (Cdkn2b), in mice promotes vascular SMC apoptosis and aneurysm progression. Here, we investigated the role of Cdnk2b in atherogenesis and found that in a mouse model of atherosclerosis, deletion of Cdnk2b promoted advanced development of atherosclerotic plaques composed of large necrotic cores. Furthermore, human carriers of the 9p21 risk allele had reduced expression of CDKN2B in atherosclerotic plaques, which was associated with impaired expression of calreticulin, a ligand required for activation of engulfment receptors on phagocytic cells. As a result of decreased calreticulin, CDKN2B-deficient apoptotic bodies were resistant to efferocytosis and not efficiently cleared by neighboring macrophages. These uncleared SMCs elicited a series of proatherogenic juxtacrine responses associated with increased foam cell formation and inflammatory cytokine elaboration. The addition of exogenous calreticulin reversed defects associated with loss of Cdkn2b and normalized engulfment of Cdkn2b-deficient cells. Together, these data suggest that loss of CDKN2B promotes atherosclerosis by increasing the size and complexity of the lipid-laden necrotic core through impaired efferocytosis.

SIRT2 activity is required for the survival of C6 glioma cells

SIRT2 is a tubulin deacetylase, which can play either detrimental or beneficial roles in cell survival under different conditions. While it has been suggested that reduced SIRT2 expression in human gliomas may contribute to development of gliomas, there has been no study that directly determines the effects of decreased SIRT2 activity on the survival of glioma cells. In this study we applied both pharmacological and molecular approaches to determine the roles of SIRT2 in the survival of glioma cells. Our studies, by conducting such assays as flow cytometry-based Annexin V assay and caspase-3 immunostaining, have indicated that decreased SIRT2 activity leads to apoptosis of C6 glioma cells by caspase-3-dependent pathway. Our experiments have further shown that reduced SIRT2 activity produces necrosis of C6 glioma cells. Moreover, our study applying SIRT2 siRNA has also shown that decreased SIRT2 leads to both necrosis and apoptotic changes of C6 glioma cells. Collectively, our study has provided novel evidence indicating that SIRT2 activity plays a key role in maintaining the survival of glioma cells, and that reduced SIRT2 activity can induce both necrosis and caspase-3-dependent apoptosis of C6 glioma cells. These results have also suggested that inhibition of SIRT2 might become a novel therapeutic strategy for gliomas.

c-Rel deficiency increases caspase-4 expression and leads to ER stress and necrosis in EBV-transformed cells

LMP1-mediated activation of nuclear factor of kappaB (NF-κB) is critical for the ligand independent proliferation and cell survival of in vitro EBV-transformed lymphoblastoid cell lines (LCLs). Previous experiments revealed that a majority of LMP1-dependent responses are regulated by NF-κB. However, the extent that individual NF-κB family members are required for these responses, in particular, c-Rel, whose expression is restricted to mature hematopoietic cells, remains unclear. Here we report that low c-Rel expression in LCLs derived from a patient with hyper-IgM syndrome (Pt1), resulted in defects in proliferation and cell survival. In contrast to studies that associated loss of NF-κB with increased apoptosis, Pt1 LCLs failed to initiate apoptosis and alternatively underwent autophagy and necrotic cell death. Whereas the proliferation defect appeared linked to a c-Rel-associated decrease in c-myc expression, identified pro-survival and pro-apoptotic targets were expressed at or near control levels consistent with the absence of apoptosis. Ultrastructural examination of Pt1 LCLs revealed a high level of cellular and ER stress that was further supported by gene expression profiling showing the upregulation of several genes involved in stress and inflammation. Apoptosis-independent cell death was accompanied by increased expression of the inflammatory marker, caspase-4. Using gene overexpression and siRNA knockdown we demonstrated that levels of c-Rel directly modulated expression of caspase-4 as well as other ER stress genes. Overall, these findings reveal the importance of c-Rel in maintaining LCL viability and that decreased expression results in ER stress and a default response leading to necrotic cell death.

Interactive toxicity of inorganic mercury and trichloroethylene in rat and human proximal tubules: effects on apoptosis, necrosis, and glutathione status

Simultaneous or prior exposure to one chemical may alter the concurrent or subsequent response to another chemical, often in unexpected ways. This is particularly true when the two chemicals share common mechanisms of action. The present study uses the paradigm of prior exposure to study the interactive toxicity between inorganic mercury (Hg(2+)) and trichloroethylene (TRI) or its metabolite S-(1,2-dichlorovinyl)-l-cysteine (DCVC) in rat and human proximal tubule. Pretreatment of rats with a subtoxic dose of Hg(2+) increased expression of glutathione S-transferase-alpha1 (GSTalpha1) but decreased expression of GSTalpha2, increased activities of several GSH-dependent enzymes, and increased GSH conjugation of TRI. Primary cultures of rat proximal tubular (rPT) cells exhibited both necrosis and apoptosis after incubation with Hg(2+). Pretreatment of human proximal tubular (hPT) cells with Hg(2+) caused little or no changes in GST expression or activities of GSH-dependent enzymes, decreased apoptosis induced by TRI or DCVC, but increased necrosis induced by DCVC. In contrast, pretreatment of hPT cells with TRI or DCVC protected from Hg(2+) by decreasing necrosis and increasing apoptosis. Thus, whereas pretreatment of hPT cells with Hg(2+) exacerbated cellular injury due to TRI or DCVC by shifting the response from apoptosis to necrosis, pretreatment of hPT cells with either TRI or DCVC protected from Hg(2+)-induced cytotoxicity by shifting the response from necrosis to apoptosis. These results demonstrate that by altering processes related to GSH status, susceptibilities of rPT and hPT cells to acute injury from Hg(2+), TRI, or DCVC are markedly altered by prior exposures.

Constitutive activation of a plasma membrane H(+)-ATPase prevents abscisic acid-mediated stomatal closure

Light activates proton (H(+))-ATPases in guard cells, to drive hyperpolarization of the plasma membrane to initiate stomatal opening, allowing diffusion of ambient CO(2) to photosynthetic tissues. Light to darkness transition, high CO(2) levels and the stress hormone abscisic acid (ABA) promote stomatal closing. The overall H(+)-ATPase activity is diminished by ABA treatments, but the significance of this phenomenon in relationship to stomatal closure is still debated. We report two dominant mutations in the OPEN STOMATA2 (OST2) locus of Arabidopsis that completely abolish stomatal response to ABA, but importantly, to a much lesser extent the responses to CO(2) and darkness. The OST2 gene encodes the major plasma membrane H(+)-ATPase AHA1, and both mutations cause constitutive activity of this pump, leading to necrotic lesions. H(+)-ATPases have been traditionally assumed to be general endpoints of all signaling pathways affecting membrane polarization and transport. Our results provide evidence that AHA1 is a distinct component of an ABA-directed signaling pathway, and that dynamic downregulation of this pump during drought is an essential step in membrane depolarization to initiate stomatal closure.

Aqueous peroxyl radical exposure to THP-1 cells causes glutathione loss followed by protein oxidation and cell death without increased caspase-3 activity

Protein oxidation within cells exposed to oxidative free radicals has been reported to occur in an uninhibited manner with both hydroxyl and peroxyl radicals. In contrast, THP-1 cells exposed to peroxyl radicals (ROO(*)) generated by thermo decomposition of the azo compound AAPH showed a distinct lag phase of at least 6 h, during which time no protein oxidation or cell death was observed. Glutathione appears to be the source of the lag phase as cellular levels were observed to rapidly decrease during this period. Removal of glutathione with buthionine sulfoxamine eliminated the lag phase. At the end of the lag phase there was a rapid loss of cellular MTT reducing activity and the appearance of large numbers of propidium iodide/annexin-V staining necrotic cells with only 10% of the cells appearing apoptotic (annexin-V staining only). Cytochrome c was released into the cytoplasm after 12 h of incubation but no increase in caspase-3 activity was found at any time points. We propose that the rapid loss of glutathione caused by the AAPH peroxyl radicals resulted in the loss of caspase activity and the initiation of protein oxidation. The lack of caspase-3 activity appears to have caused the cells to undergo necrosis in response to protein oxidation and other cellular damage.

Elemental selenium at nano size possesses lower toxicity without compromising the fundamental effect on selenoenzymes: comparison with selenomethionine in mice

Glutathione peroxidase and thioredoxin reductase are major selenoenzymes through which selenium exerts powerful antioxidant effects. Selenium also elicits pro-oxidant effects at toxic levels. The antioxidant and pro-oxidant effects, or bioavailability and toxicity, of selenium depend on its chemical form. Selenomethionine is considered to be the most appropriate supplemental form due to its excellent bioavailability and lower toxicity compared to various selenium compounds. The present studies reveal that, compared with selenomethionine, elemental selenium at nano size (Nano-Se) possesses equal efficacy in increasing the activities of glutathione peroxidase and thioredoxin reductase but has much lower toxicity as indicated by median lethal dose, acute liver injury, and short-term toxicity. Our results suggest that Nano-Se can serve as an antioxidant with reduced risk of selenium toxicity.

Modulation of p38 mitogen-activated protein kinase cascade and metalloproteinase activity in diaphragm muscle in response to free radical scavenger administration in dystrophin-deficient Mdx mice

Duchenne muscular dystrophy muscles undergo increased oxidative stress and altered calcium homeostasis, which contribute to myofiber loss by trigging both necrosis and apoptosis. Here, we asked whether treatment with free radical scavengers could improve the dystrophic pattern of mdx muscles. Five-week-old mdx mice were treated for 2 weeks with alpha-lipoic acid/l-carnitine. This treatment decreased the plasmatic creatine kinase level, the antioxidant enzyme activity, and lipid peroxidation products in mdx diaphragm. Free radical scavengers also modulated the phosphorylation/activity of some component of the mitogen-activated protein kinase (MAPK) cascades: p38 MAPK, the extracellular signal-related kinase, and the Jun kinase. beta-Dystroglycan (beta-DG), a multifunctional adaptor or scaffold capable of interacting with components of the extracellular signal-related kinase-MAP kinase cascade, was also affected after treatment. In the mdx muscles, beta-DG (43 kd) was cleaved by matrix metalloproteinases into a 30-kd form (beta-DG30). We show that the proinflammatory protein nuclear factor-kappaB activator decreased after the treatment, leading to a significant reduction of matrix metalloproteinase activity in the mdx diaphragm. Our data highlight the implication of oxidative stress and cell signaling defects in dystrophin-deficient muscle via the MAP kinase cascade-beta-DG interaction and nuclear factor-kappaB-mediated inflammation process.

Synergistic salubrious effect of ferulic acid and ascorbic acid on membrane-bound phosphatases and lysosomal hydrolases during experimental myocardial infarction in rats

Altered membrane integrity has been suggested as a major factor in the development of cellular injury during myocardial necrosis. The present study was designed to investigate the effect of the combination of ferulic acid (FA) and ascorbic acid (AA) on lysosomal hydrolases and membrane-bound phosphatases during isoproterenol (ISO) induced myocardial necrosis in rats. Induction of rats with 1SO (150 mg/kg b.wt, i.p.) for 2 days resulted in a significant increase in the activities of lysosomal hydrolases (beta-D-glucuronidase, beta-D-galactosidase, beta-D-N-acetylglucosaminidase, acid phosphatase and cathepsin-D) in the heart and serum. A significant increase in plasma lactate level, cardiac levels of sodium, calcium and a decrease in cardiac level of potassium was also observed, which was paralleled by abnormal activities of membrane-bound phosphatases (Na(+)-K(+) ATPase, Ca(2+) ATPase and Mg(2+) ATPase) in the heart of ISO-administered rats. Pre-co-treatment with the combination of FA (20 mg/kg b.wt) and AA (80 mg/kg b.wt) orally for 6 days significantly attenuated these abnormalities and restored the levels to near normalcy when compared to individual drug treated groups. The combination of FA and AA preserved the membrane integrity by mitigating the oxidative stress and associated cellular damage more effectively when compared to individual treatment groups. In our study, the protection conferred by FA and AA might be through the nitric oxide pathway and by their ability of quenching free radicals. In conclusion, these findings indicate the synergistic modulation of lysosomal hydrolases and membrane phosphatases by the combination of FA and AA.

Thrombospondin-1 limits ischemic tissue survival by inhibiting nitric oxide-mediated vascular smooth muscle relaxation

The nitric oxide (NO)/cGMP pathway, by relaxing vascular smooth muscle cells, is a major physiologic regulator of tissue perfusion. We now identify thrombospondin-1 as a potent antagonist of NO for regulating F-actin assembly and myosin light chain phosphorylation in vascular smooth muscle cells. Thrombospondin-1 prevents NO-mediated relaxation of precontracted vascular smooth muscle cells in a collagen matrix. Functional magnetic resonance imaging demonstrated that an NO-mediated increase in skeletal muscle perfusion was enhanced in thrombospondin-1-null relative to wild-type mice, implicating endogenous thrombospondin-1 as a physiologic antagonist of NO-mediated vasodilation. Using a random myocutaneous flap model for ischemic injury, tissue survival was significantly enhanced in thrombospondin-1-null mice. Improved flap survival correlated with increased recovery of oxygen levels in the ischemic tissue of thrombospondin-1-null mice as measured by electron paramagnetic resonance oximetry. These findings demonstrate an important antagonistic relation between NO/cGMP signaling and thrombospondin-1 in vascular smooth muscle cells to regulate vascular tone and tissue perfusion.

Identification of factors contributing to hepatomegaly in severely burned children

Hepatomegaly is a common postmortem observation in severely burned children, with the liver often tripling in size when compared with normal livers for age, weight, and sex. Lesions identified at autopsy include deposition of large and small fat droplets in the hepatocyte, congestion, centrilobular necrosis, and cholestasis. The present study was designed to identify the primary causes of hepatomegaly in severely burned children postmortem. For this purpose, 41 autopsies were reviewed and, when available, blood and tissue samples were studied. Histopathologic findings showed that large intrahepatocytic fat droplets within hepatocytes and cholestasis were important contributors to hepatomegaly. Liver density and wet/dry weight ratios significantly decreased with increasing liver size. Hepatocyte volume increased with increasing liver size (P < 0.001) as did total fat content (P < 0.001). The liver enzymes, alanine aminotransferase and aspartate aminotransferase, remained normal except within 5 to 10 days of injury and 5 to 10 days of death. Triglycerides made up 4% to 70% of the total fat, with the percentage of triglycerides increasing with the severity of hepatomegaly. Saturated fatty acids represented about 85% of the total fatty acids in normal-sized livers, whereas in the largest livers (400% of predicted), only 25% of the fatty acids were saturated. This study provides evidence that 85% to 90% of the hepatomegaly observed in severely burned children postmortem is associated with hepatocyte enlargement, which includes up to 19% intracellular fat. Increases in extracellular protein, intracellular glycogen, and fluid accumulation may make a minor contribution to postburn hepatomegaly.

Direct evidence of secondary necrosis of neutrophils during intense lung inflammation

Several pulmonary inflammatory conditions are characterised by infiltration of neutrophils. Normally, neutrophils are silently removed by apoptosis, followed by phagocytosis. However, if phagocytosis fails, apoptotic cells undergo secondary necrosis. Recent findings of increased levels of the pan-necrosis marker lactate dehydrogenase in bronchoalveolar lavage from lipopolysaccharide-exposed mice implies potential involvement of secondary necrosis. Using a similar model, this study aimed to identify the source of lactate dehydrogenase and to search for direct histological evidence of secondary necrosis. Lipopolysaccharide (LPS) was administered to the lungs of BALB/c mice, and bronchoalveolar lavage and tissue samples were collected 4, 12, 24, 36, 48, 60 and 72 h after administration. LPS induced a patchy neutrophil-rich lung inflammation, where the numbers of terminal deoxynucleotide transferase-mediated dUTP nick-end labelling-positive neutrophils were increased at 12 h and onwards. Lavage levels of neutrophils and lactate dehydrogenase increased significantly at 4 and 24 h, respectively. Detailed electron microscopic assessment of neutrophil activation and death modes revealed that up to 14% of the neutrophils were undergoing secondary necrosis, whereas apoptotic or primary necrotic structural cells were rarely found. In summary, this study provides direct evidence that secondary necrosis of neutrophils is a common process during intense lung inflammation. This implies that neutrophil apoptosis may cause rather than resolve airway inflammation.

Caspase and calpain function in cell death: bridging the gap between apoptosis and necrosis

Calpain and caspase are families of cysteine proteases that have important roles in the initiation, regulation and execution of cell death. The function of both groups of proteases in the progression of apoptotic and necrotic pathways is presented here in the context of a concise overview of regulated cell death. Many of the morphological differences between apoptotic and necrotic processes are thought to be as a consequence of the action of cysteine proteases. Recent studies suggest that caspase and calpain cascades are tightly interrelated and an appreciation of how these proteases cross-talk should enable a greater understanding of how the boundaries between apoptotic and necrotic cell death have become blurred. Furthermore, an assessment of the contribution that caspase and calpain make to human physiology and pathology is provided, with a description of how these proteases can be detected and quantified. Lastly, an evaluation is made of how caspase and calpain activation might be exploited diagnostically.

The vacuolar H+ -ATPase mediates intracellular acidification required for neurodegeneration in C. elegans

Numerous studies implicate necrotic cell death in devastating human pathologies such as stroke and neurodegenerative diseases. Investigations in both nematodes and mammals converge to implicate specific calpain and aspartyl proteases in the execution of necrotic cell death. It is believed that these proteases become activated under conditions that inflict necrotic cell death. However, the factors that modulate necrosis and govern the erroneous activation of these otherwise benign enzymes are largely unknown. Here we show that the function of the vacuolar H(+)-ATPase, a pump that acidifies lysosomes and other intracellular organelles, is essential for necrotic cell death in C. elegans. Cytoplasmic pH drops in dying cells. Intracellular acidification requires the vacuolar H(+)-ATPase, whereas alkalization of endosomal and lysosomal compartments by weak bases protects against necrosis. In addition, we show that vacuolar H(+)-ATPase activity is required downstream of cytoplasmic calcium overload during necrosis. Thus, intracellular pH is an important modulator of necrosis in C. elegans. We propose that vacuolar H(+)-ATPase activity is required to establish necrosis-promoting, acidic intracellular conditions that augment the function of executioner aspartyl proteases in dying cells. Similar mechanisms may contribute to necrotic cell death that follows extreme acidosis-for example, during stroke-in humans.

[PCBs cause necrosis of L6C5 myoblasts]

Polychlorinated biphenyls (PCBs) are structurally related to dioxins, widely used in the past in various industrial applications and daily used products. Although PCBs production was discontinued more than twenty years ago, their chemical stability and high lipophilicity make them persistent pollutants and dangerous occupational contaminants. Skeletal muscle is an important site of PCB accumulation. Our previous results about the effects of PCBs on L6C5 myoblasts, showed that "low concentrations" (< 10 microg/ml) of these compounds inhibit in vitro myogenic differentiation in a concentration-dependent fashion, while toxic effects only begin to be evident at PCB concentrations > or = 10 microg/ml. In the present paper we wondered if the observed cell mortality is due to necrosis or if it depends on the activation of programmed cell death mechanisms (apoptosis). Using different methods of analysis, we have observed that PCBs cause necrosis of myogenic cells and that such effect is related to the employed concentrations and to the time of exposure (EC50 approximately = 50 microg/ml). Our results may help to explain the creatin kinase elevation, observed in the blood of patients acutely exposed to high concentrations of PCBs, as the consequence of a necrotic damage of the skeletal muscle. It will be therefore interesting to evaluate the presence of muscular damages in the chronic exposures to PCBs.

Reactive Oxygen Species Promote TNFα-Induced Death and Sustained JNK Activation by Inhibiting MAP Kinase Phosphatases

TNFalpha is a pleiotropic cytokine that induces either cell proliferation or cell death. Inhibition of NF-kappaB activation increases susceptibility to TNFalpha-induced death, concurrent with sustained JNK activation, an important contributor to the death response. Sustained JNK activation in NF-kappaB-deficient cells was suggested to depend on reactive oxygen species (ROS), but how ROS affect JNK activation was unclear. We now show that TNFalpha-induced ROS, whose accumulation is suppressed by mitochondrial superoxide dismutase, cause oxidation and inhibition of JNK-inactivating phosphatases by converting their catalytic cysteine to sulfenic acid. This results in sustained JNK activation, which is required for cytochrome c release and caspase 3 cleavage, as well as necrotic cell death. Treatment of cells or experimental animals with an antioxidant prevents H(2)O(2) accumulation, JNK phosphatase oxidation, sustained JNK activity, and both forms of cell death. Antioxidant treatment also prevents TNFalpha-mediated fulminant liver failure without affecting liver regeneration.

Involvement of lysosomal cathepsins in the cleavage of DNA topoisomerase I during necrotic cell death

OBJECTIVE

Autoantibodies to DNA topoisomerase I (topo I) are associated with diffuse systemic sclerosis (SSc), appear to be antigen driven, and may be triggered by cryptic epitopes exposed during in vivo topo I fragmentation. These autoantibodies recognize topo I and fragments of this autoantigen generated during apoptosis and necrosis. We undertook this study to determine whether lysosomal cathepsins are involved in topo I fragmentation during necrosis.

METHODS

Topo I cleavage during necrosis was assessed by immunoblotting of lysates from L929 fibroblasts exposed to tumor necrosis factor alpha (TNFalpha) and the broad caspase inhibitor Z-VAD-FMK, and by immunoblotting of lysates from endothelial cells treated with HgCl2. Purified topo I and L929 nuclei were incubated with cathepsins B, D, G, H, and L, and topo I cleavage was detected by immunoblotting. The intracellular localization of cathepsin L activity and topo I in necrotic cells was examined using fluorescence microscopy.

RESULTS

Treatment of L929 cells with TNFalpha and Z-VAD-FMK induced caspase-independent cell death with necrotic morphology. This cell death involved topo I cleavage into fragments of approximately 70 kd and 45 kd. This cleavage profile was reproduced in vitro by cathepsins L and H and was inhibited by the cathepsin L inhibitor Z-FY-CHO. During necrosis, cathepsin L activity diffused from lysosomes into the cytoplasm and nucleus, whereas topo I partially relocalized to the cytoplasm. Z-FY-CHO delayed necrosis and partially blocked topo I cleavage. The topo I cleavage fragments were also detected in necrotic endothelial cells and recognized by SSc sera containing anti-topo I antibodies.

CONCLUSION

These results implicate cathepsins, particularly cathepsin L, in the cleavage of topo I during necrosis. This cleavage may generate potentially immunogenic fragments that could trigger anti-topo I immune responses in SSc.

Signaling modulation of bile salt-induced necrosis in isolated rat hepatocytes

Hydrophobic bile salts induce either necrosis or apoptosis depending on the severity of the injury caused by them. Since bile salt-induced apoptosis is influenced by Ca2+- and protein kinase-signaling pathways, and both necrosis and apoptosis share common initiating mechanisms, we analyzed whether these signaling cascades also influence bile salt-induced necrosis in isolated rat hepatocytes. Taurochenodeoxycholate (TCDC, 0.25-1.50 mM, 2 h) reduced, in a dose-dependent manner, the percentage of viable hepatocytes, and increased the release of the cytosolic enzyme, lactate dehydrogenase (LDH) and alanine aminotransferase (ALAT), and that of the plasma membrane enzyme, alkaline phosphatase (AP). The PKC inhibitors, H7 (100 microM) and chelerythrine (2.5 microM), both prevented significantly TCDC-induced necrosis. On the contrary, the PKA activator, dibutyryl-cAMP, exacerbated TCDC-induced cell damage in a dose-dependent manner; this effect was more likely due to cAMP-mediated PKA activation, as the PKA inhibitor, KT5720 (1 microM), counteracted this effect. Instead, the intracellular Ca2+ chelator, BAPTA/AM (20 microM), was without effect. TCDC (1 mM) increased lipid peroxidation from 0.7 +/- 0.2 to 7.5 +/- 0.9 nmol of malondialdehyde per mg of protein, p < 0.001; the addition of the free radical scavenger, diphenyl-p-phenylendiamine, completely blocked this increase and prevented significantly TCDC-induced necrosis. PKC inhibition induced only a slight attenuation of TCDC-induced lipid peroxidation. Possible mechanisms accounting for the modulatory effect of signal transduction pathways on TCDC-induced necrosis, including signaling influence on TCDC transport events and TCDC-induced oxidative stress, are discussed.

Expression of DNase gamma during Fas-independent apoptotic DNA fragmentation in rodent hepatocytes

Endonuclease-induced DNA fragmentation is a hallmark of apoptosis. DNase gamma (DNase gamma) was recently identified as one of the endonucleases responsible for apoptotic DNA fragmentation. In this study, immunohistochemistry for DNase gamma was performed on paraffin sections of rodent liver in well-defined models of hepatocyte apoptosis induced by Fas antibody (Fas) or cycloheximide (CHX), and necrosis induced by lipopolysaccharide (LPS) or carbon tetrachloride (CCl4). DNase gamma immunoreactivity was compared with TdT-mediated dUTP nick-end labeling (TUNEL) reactivity. Our results showed TUNEL reactivity in both apoptotic and necrotic hepatocytes. DNase gamma immunoreactivity was not detected during LPS-induced or CCl4-induced hepatocyte necrosis. In contrast, it was evident during CHX-induced, but not Fas-induced, apoptotic DNA fragmentation. These findings suggest that DNase gamma plays an important role in Fas-independent apoptotic DNA fragmentation in hepatocytes.

Changes in arginase, aminotransferases and rhodanese in sera of domestic animals with experimentally induced liver necrosis

Changes in the serum concentrations of aspartic aminotransferase (AST), alanine aminotransferase (ALT), rhodanese and arginase were measured in dogs, sheep and cattle with hepatic necrosis induced by the oral administration of carbon tetrachloride. A new method for arginase assay was based on the determination of remaining arginine (after its conversion to urea and ornithine) by its reaction with p-nitrophenyl glyoxal (PNPG). In all species studied the serum arginase increased 6-12 h after liver damage, reached a peak value in 48 h and returned to normal thereafter. Rhodanese activity did not change in dogs but rose significantly in sheep and, to a lesser extent, in cattle. AST increased strikingly in sheep as compared with dogs and cattle and remained high for > 5 days. In dogs ALT rose sharply and remained elevated for > 10 days. No change in ALT was seen in sheep or cattle. The determination of arginase by a simple procedure such as the PNPG method, in conjunction with AST or ALT assay, may be of value in assessing the stage of liver necrosis.

Discrimination between periportal and pericentral necrosis of rat liver by determination of glutamine synthetase and other enzyme activities in serum

Periportal or pericentral necrosis of rat liver was produced by injection of allyl-alcohol or bromobenzene, respectively. Activities of predominantly periportal and perivenous enzymes were determined in serum during maximal necrosis. Aspartate aminotransferase, which is more or less homogeneously distributed in the liver acinus, exhibited similar activities in serum after periportal and pericentral injury. Serum activities of the mainly periportal enzymes alanine aminotransferase and fructose 1,6-bisphosphatase were 1.5- to 2-fold higher after periportal as compared to pericentral necrosis. Serum activity of the mainly pericentral glutamate dehydrogenase was 3-fold higher after pericentral than after periportal damage. However, due to individual variations necrosis could not be definitively localized in any case by measurement of these enzyme activities. Better discrimination between periportal and pericentral necrosis was achieved by the serum activity of the exclusively pericentral enzyme glutamine synthetase, which was 8-fold higher after pericentral as compared to periportal necrosis. Conclusive discrimination was obtained by the activity ratio fructose 1,6-bisphosphatase/glutamine synthetase in serum.

Increased endogenous N-nitrosamine and nitrate formation by induction of nitric oxide synthase in rats with acute hepatic injury caused by Propionibacterium acnes and lipopolysaccharide administration

In rats treated i.v. with heat-killed Propionibacterium acnes (100 mg/kg body wt), followed 5 days later by an i.v. dose of Escherichia coli lipopolysaccharide (LPS, 1 mg/kg body wt), acute hepatic cell necrosis was accompanied by significant induction of nitric oxide (NO) synthase activity in the liver. Endogenous nitrosation of thiazolidine 4-carboxylic acid (TCA, 50 mumol/rat) administered by three different routes (i.v., i.p. and p.o.) 5 h after LPS injection to the P. acnes-treated rats was assessed by analysing its nitrosated product (NTCA) excreted in 24 h urine. The amounts of NTCA formed in vivo after i.v., i.p. and p.o. administration of TCA were 4.07 +/- 1.00, 5.79 +/- 2.15 and 58.3 +/- 20.7 nmol/rat (n = 5-10) respectively, which were about 5-, 10- and 8-fold greater than those excreted by rats which had not been treated with P.acnes and LPS but received TCA by the same route. Nitrate concentration in plasma and NO synthase activity in the liver started to increase within 2.5 h after LPS injection, reached a maximum at 7.5 h and remained at high levels for several further hours. Levels of nitrite and nitrate in gastric contents were also increased significantly after LPS administration. The co-administration of N omega-nitro-L-arginine (an inhibitor of NO synthase) and LPS resulted in a marked reduction of urinary levels of nitrate and NTCA, indicating that nitrosation is mediated by NO synthase. These results together suggest that induction of NO synthase by infection with bacteria, parasite and viruses could result in increased endogenous nitrosation not only in the infected tissues but also in the stomach, where nitrosamines would be formed more rapidly under acidic conditions.

Selectivity of serum immunoreactive prolyl 4-hydroxylase as a marker for hepatic necrosis

To investigate the selectivity of serum immunoreactive prolyl 4-hydroxylase (S-IRPH) as a marker for hepatic necrosis, sera were taken from patients with hepatic inflammation and hepatic necrosis. The concentration of immunoreactive prolyl 4-hydroxylase in the sera was determined by radio-immunoassay, and S-IRPH and alanine aminotransferase (ALT) data were plotted. Patients with hepatic necrosis showed mainly prolyl 4-hydroxylase elevation while patients with inflammation had both prolyl 4-hydroxylase and alanine aminotransferase elevations. The addition of serum immunoreactive prolyl 4-hydroxylase to current serum markers would be useful in investigating the pathophysiology of hepatocellular damage, particularly in differentiating between hepatic necrosis and inflammation.

A clinically applicable method for long-term salvage of postischemic skeletal muscle

The clinical significance and applicability of interventions aimed at reducing reperfusion injury in postischemic skeletal muscle remain unproven, since long-term muscle salvage has not been demonstrated by most treatment protocols that attenuate early reperfusion injury. We have shown that reperfusion of ischemic skeletal muscle results in an early and prolonged sequestration of white blood cells and activation of the alternative complement cascade. The purpose of this study was to determine if 40 minutes of reperfusion with blood depleted of white blood cells and complement proteins, followed by 2 days of normal perfusion, would reduce muscle necrosis after 5 hours of ischemia. The isolated paired canine gracilis muscle model was used. The treatment muscle was initially reperfused with arterial blood that had been spun, washed, passed through a leukocyte removal filter, and resuspended in hydroxyethyl starch (greater than 99.9% removal of white blood cells and the complement proteins factor B and C4). The contralateral control muscle was subjected to unaltered reperfusion. Blood flow (ml/min/100 gm) was measured by timed collection of gracilis venous blood. Myeloperoxidase activity (absorbance at 655 nm/min/mg tissue protein) in muscle biopsies was used to monitor white blood cell sequestration. After 48 hours of reperfusion in vivo, necrosis was quantified by nitroblue tetrazolium staining. Initial reperfusion with white blood cell and complement depleted blood significantly reduced muscle necrosis (53% +/- 3% vs 29% +/- 8%, p less than 0.0025, paired t test). Early blood flow was improved, (p = 0.0025, repeated measure-ANOVA), but subsequent white blood cell sequestration was not altered (p = 0.33, repeated measure-ANOVA). This suggests that a significant amount of white blood cell mediated injury occurs during the first 40 minutes of reperfusion. Preventing early complement activation and white blood cell mediated reperfusion injury is an intervention that is feasible during surgery and may result in clinically significant salvage of postischemic skeletal muscle.

Isoforms of creatine kinase MM and MB in acute myocardial infarction: a clinical evaluation

Serum creatine kinase (CK, EC 2.7.3.2) isoenzymes MM and MB were resolved, respectively, into three (MM1, MM2, MM3) and two (MB1, MB2) isoforms (subforms derived from the same isoenzyme) by electrophoresis and the isoform patterns were determined in multiple sequential serum samples, timed from the onset of chest pain, from 58 patients with acute myocardial infarction (AMI). During the first 3 h after the onset of chest pain, the serum isoform activity resembled the pattern seen in normal volunteers. Specimens obtained 6 h after AMI showed predominantly MM3 and MB2 (45% and 11% of the total CK activity, respectively). Between 10 and 72 h, there was a gradual shift in which MM3, MM2 and MB2 decreased, while MM1 and MB1 increased. MB2 and MB1 disappeared from the pattern for samples collected after 24-48 h, while MM1 was always the most prominent band at the end of the observation period (66%, range 41-77%, at 48 h). These data suggest that a single determination of CK isoform pattern, drawn between 6 and 48 h after AMI, may provide an effective means of predicting the time of onset of necrosis. There were no significant differences in the CK isoform patterns according to infarct location and functional status of patients.

Evaluation of the protection of rat gastric mucosa by a prostaglandin analogue using cellular enzyme marker and histologic techniques

Damage to the rat gastric mucosa after oral administration of ethanol and the effect of pretreatment with a prostaglandin analogue has been evaluated using histologic and enzyme-marker techniques. Rat whole stomachs were incubated in vitro and the intraluminal release of the cytoplasmic enzyme lactate dehydrogenase and the lysosomal enzymes acid phosphatase and beta-glucuronidase was determined by spectrophotometric techniques. Ethanol irrigation in vivo for 10 min significantly elevated the subsequent intraluminal release of both cytoplasmic and lysosomal enzymes in vitro. Pretreatment with 16,16-dimethyl prostaglandin E2 (0.1-1.25 microgram/kg p.o.) in doses that substantially inhibited the formation of macroscopically apparent necrotic lesions failed to prevent enzyme release. However, higher doses of the prostaglandin analogue (2.5-20 micrograms/kg) did significantly reduce the intraluminal release of the cellular enzymes, with the lysosomal enzymes being more readily inhibited. Histologic studies confirmed that the lower doses of the prostanoid prevented deep tissue necrosis and vasocongestion, yet did not protect surface epithelial cells from ethanol-induced damage. However, with the highest dose of 16,16-dimethyl prostaglandin E2 (20 micrograms/kg) a significant reduction in the extent of damage to the superficial epithelial cells was observed, suggesting a correlation with the findings using enzyme markers of cell damage. The apparent protective mechanisms of this prostanoid under the present conditions may involve mucus and fluid effusion that could allow restitution of the surface epithelial layer.

Influence of aging on the susceptibility of rats to hepatotoxic injury

The effects of allyl alcohol, galactosamine, bromobenzene, and corn oil administration were evaluated in male Fischer 344 rats at 4 to 5, 14 to 15, and 24 to 25 months of age to determine if susceptibility to hepatotoxic injury is modified as a consequence of aging. Parameters measured were (1) severity of hepatocellular necrosis as judged by light microscopy of liver sections, (2) activity of alanine aminotransferase and aspartate aminotransferase in serum, and (3) hepatic microsomal cytochrome P-450 content and NADPH-cytochrome P-450 reductase activity. Allyl alcohol toxicity was more severe in middle-aged and old rats than in young-adult rats. In contrast, galactosamine and bromobenzene toxicities were slightly decreased or unchanged in old rats. The results demonstrate that aging has effects on some types of chemically induced hepatotoxicity.

Dilazep-induced reduction of ischemic necrosis in rats with coronary artery occlusion

To assess whether dilazep reduces myocardial necrosis we assigned 72 rats that survived coronary artery occlusion to 3 groups. The first control group (n = 26) received coronary occlusion and was untreated. The second group (n = 21) received coronary occlusion and was treated with dilazep (150 micrograms/kg s.c.) every 8 hours for 48 hours. The third group (n = 25) was sham-operated. Forty-eight hours later the creatine-kinase activity of the left ventricle was measured. The calculated left ventricular fraction that survived the occlusion was larger in dilazep-treated rats (44.5 +/- 4.1% of left ventricle) than in controls (31.2 +/- 3.2%; P less than 0.05). Twenty-six more rats also underwent coronary occlusion; 12 were controls and the remaining 14 were treated with dilazep at the same time and dose as before and killed 21 days after occlusion. Infarct size was evaluated on histological sections of the hearts by planimetry. The amount of left ventricle preserved from necrosis was larger in dilazep-treated rats, 82.1 +/- 0.9%, compared to controls 69.5 +/- 1.4% (P less than 0.05). Dilazep seems effective in preserving myocardial tissue from ischemic necrosis, and its beneficial effects are long-lasting, producing permanent reduction of infarct size.

Acute hemorrhagic pancreatic necrosis in mice: the activity of lysosomal enzymes in the pancreas and the liver

The activity of lysosomal enzymes of the pancreas and the liver has been studied during induction and onset of acute hemorrhagic pancreatic necrosis with fat necrosis (AHPN) in mice. We induced AHPN by feeding the animals a choline-deficient (CD) diet containing 0.5% DL-ethionine (CDE). Control animals were fed either laboratory chow or a plain CD DIET. Increased total activities of cathespin B1, beta-galactosidase, and acid phosphatase were found to occur in pancreas homogenates of mice fed the CDE diet for 2 and 3 days. Release of cathespin B1 into pancreas cytosol was observed after 1 day of feeding. beta-galactosidase and acid phosphatase were increased in pancreas cytosol after 2 and 3 days of feeding. Changes in total activity and location of the lysosomal enzymes did not occur in the liver. Feeding the CD and CDE diets resulted in an increase in the free activity of lysosomal enzymes of both the pancreas and the liver, suggesting the existence of alterations in the lysosomal membrane. Pancreas and liver homogenates were stored on ice up to 3 hours, and the free activity of acid phosphatase and beta-galactosidase were determined at various time intervals. The free activity of both enzymes increased progressively for 3 hours in the pancreas but not in the liver. It is concluded that: 1) induction of AHPN in mice is accompanied by an increase in the activity of lysosomal enzymes of the acinar cells of the pancreas; 2) cathepsin B1 may be responsible for triggering an intraparenchymal activation of zymogens, and 3) pancreatic lysosomes are labilized more easily than liver lysosomes.

Glutamate dehydrogenase: a reliable marker of liver cell necrosis in the alcoholic

The usefulness of blood enzyme determinations as markers of liver necrosis was tested in 100 alcoholics who underwent biopsy during clinical investigation. Mean values of glutamate dehydrogenase (GDH), serum aspartate and alanine transferase (SGOT and SGPT), ornithine carbamoyltransferase (OCT), and gamma-glutamyltranspeptidase (gamma-GTP) tended to rise with increasing liver cell necrosis, though values of SGOT, SGPT, OCT, and gamma-GTP showed considerable overlap between the 32 patients with histologically proved hepatitis and the 68 without. By contrast, GDH values showed virtually no overlap between patients with and without hepatitis, and a value of two and a half times the normal value discriminated between the two groups. Because of its easy determination and its reliable reflection of liver cell necrosis the GDH concentration should be estimated routinely in alcoholic patients.

Clinical significance of the isomorphic pattern of the isoenzymes of serum lactate dehydrogenase

Five hundred patients with the isomorphic pattern of the isoenzymes of serum lactate dehydrogenase (LDH) were surveyed. The isomorphic pattern of LDH isoenzymes is defined as a significant increase of total LDH with normal or low percentage of individual fractions, but with the LDH1:2 ratio less than unity. Diagnoses were, in descending order of frequency, cardiorespiratory diseases, malignancy, fracture, diseases of the central nervous system, infection/inflammation, hepatic cirrhosis and/or alcoholism, trauma without fracture, infectious mononucleosis, hypothyroidism, uremia, necrosis, pseudomononucleosis, viremia and intestinal obstruction. Incidence of increased serum activity in individuals without evidence of disease or drug explanation was 3 percent. Low PaO2 was observed in 88 percent of the 67 patients in whom it was measured.

[Inhibition of cell viability by cellular debris. Model experiments to study tissue damage (author's transl)]

Some aspects of tissue damage as it may accompany shock are investigated in an in vitro model system. Some effects of cell debris obtained by sonication of BHK 21 cells on viable cultures of freshly dissociated cells of the same line are evaluated. After 24 h incubation on a coverglass, the area covered by cell nuclei per square millimeter was determined. Spreading of viable cells is inhibited by the cell debris. In this way, growth and viability are also impeded. After 24 h the mitotic index in controls and treated cell-cultures is the same. The inhibition is exhibited as well by the supernatant as the pellet of a centrifuged suspension of sonicated cells. The growth retardation is counteracted by the polyvalent protease inhibitor Trasylol (50 KIE/ml), when the whole suspension or its pellet are added to the culture, but not when the supernatant affects the cells. These results indicate that the injurious substance is not a protease. The protective action of Trasylol may be due to a stabilisation of lysosomes. Tissue injury is often accompanied by alterations in cellular adhesiveness to substrate and in growth rate. The system used here offers a simple model to study the influence of necrotic tissue on cell viability as well as its pharmacological susceptibility.

The association of increased plasma MB CPK activity and irreversible ischemic myocardial injury in the dog

To evaluate the concordance between elevated plasma MB CPK and irreversible myocardial ischemic injury, coronary occlusion was induced for 10 minutes to 48 hours in 21 open chest dogs and 13 conscious animals. Results of plasma CPK and MB CPK assayed in samples obtained serially ofr 24 hours were compared to microscopic changes in hearts from the same animals examined 48 hours after occlusion. Twelve of the 34 dogs died within two hours after coronary occlusion. Among the surviving 22 dogs, one failed to exhibit gross of electrocardiographic evidence of ischemia and was therefore excluded. Twelve had coronary occlusion maintained for 30 minutes or longer and in 11 of these peak plasma MB CPK activity exceeded thenormal range (mean +/- 2 SD) and baseline values by at least 100%. Necrosis was present in the hearts from each manifested by nuclear pyknosis, eosinophilia, shrinkage of cytoplasm, and leukocytic infiltration. In the remaining nine dogs with occlusion for less than 30 minutes, peak plasma MB CPK activity was not elevated and necrosis was not detected. The close concordance between plasma MB CPK elevations and myocardial necrosis was significant (chi2 = 14.5, P less than 0.001), and thus, increased plasma MB CPK activity reflected irreversible myocardial ischemic injury.

The diagnostic significance of liver cell inhomogeneity: serum enzymes in patients with central liver necrosis and the distribution of glutamate dehydrogenase in normal human liver

16 Patients with acute right-sided cardiac failure associated with a high pressure of the central venous system, exhibited a marked increase in glutamate dehydrogenase activity in serum. This increase was 40-fold higher than in patients with acute viral hepatitis. Histological examination of seven deceased patients revealed central necrosis within the liver lobule. This observation led us to determine glutamate dehydrogenase activity in microdissected peripheral and central portions from the unchanged liver lobule. A 1.7-fold higher glutamate dehydrogenase activity was found in the central part of the liver lobule than in the peripheral portion. The diagnostic significance of the glutamate dehydrogenase activity distribution along the cords of liver cells is discussed in view of liver diseases with central necrosis.