Differential efficacy of caspase inhibitors on apoptosis markers during sepsis in rats and implication for fractional inhibition requirements for therapeutics

Liensinine alleviates sepsis-induced acute liver injury by inhibiting the NF-κB and MAPK pathways in an Nrf2-dependent manner

Sepsis remains a serious public health issue that needs to be addressed globally. Severe liver injury caused by sepsis increases the risk of death in patients with sepsis. Liensinine (Lie) is one of the primary active components in Plumula nelumbinis and has anti-inflammatory and antioxidant effects. Nevertheless, the effects of Lie on septic liver injury are unclear. This research investigated the protective effect of Lie (10, 20 and 40 mg/kg) on liver damage via intraperitoneal administration of LPS (10 mg/kg) to C57BL/6 mice. Lie was given through intraperitoneal injection once a day for five days. Mice were treated with LPS intraperitoneally for 6 h at 1 h after Lie administration on the last day. The results suggested that Lie could decrease AST and ALT levels in serum, ameliorate histopathological changes and inhibit cell apoptosis in mice with LPS-induced septic liver injury. In addition, Lie inhibited increases in the mRNA levels of TNF-α, IL-1β, iNOS and IL-6. Lie also increased the mRNA level of IL-10. Lie reduced the content of MDA, a marker of lipid peroxidation, and increased the activity of the antioxidant enzymes GSH-Px, CAT and SOD. Our results also showed that Lie could suppress the LPS-activated MAPK and NF-κB pathways and trigger the Nrf2 signaling pathway both in vitro and in vivo. Additionally, an Nrf2 inhibitor (ML385) weakened the suppressive effect of Lie on the MAPK and NF-κB pathways. Our results demonstrated that the suppressive effect of Lie on the MAPK and NF-κB pathways was partially reliant on activation of the Nrf2 pathway. In summary, these results indicate that Lie can improve inflammation and oxidative stress by activating Nrf2, which is a prospective therapeutic drug for alleviating septic liver injury.

Inhibition of Apoptosis in a Model of Ischemic Stroke Leads to Enhanced Cell Survival, Endogenous Neural Precursor Cell Activation and Improved Functional Outcomes

Stroke results in neuronal cell death, which causes long-term disabilities in adults. Treatment options are limited and rely on a narrow window of opportunity. Apoptosis inhibitors demonstrate efficacy in improving neuronal cell survival in animal models of stroke. However, many inhibitors non-specifically target apoptosis pathways and high doses are needed for treatment. We explored the use of a novel caspase-3/7 inhibitor, New World Laboratories (NWL) 283, with a lower IC50 than current caspase-3/7 inhibitors. We performed in vitro and in vivo assays to determine the efficacy of NWL283 in modulating cell death in a preclinical model of stroke. In vitro and in vivo assays show that NWL283 enhances cell survival of neural precursor cells. Delivery of NWL283 following stroke enhances endogenous NPC migration and leads to increased neurogenesis in the stroke-injured cortex. Furthermore, acute NWL283 administration is neuroprotective at the stroke injury site, decreasing neuronal cell death and reducing microglia activation. Coincident with NWL283 delivery for 8 days, stroke-injured mice exhibited improved functional outcomes that persisted following cessation of the drug. Therefore, we propose that NWL283 is a promising therapeutic warranting further investigation to enhance stroke recovery.

The roles of intracellular proteolysis in cardiac ischemia-reperfusion injury

Ischemic heart disease remains a leading cause of human mortality worldwide. One form of ischemic heart disease is ischemia-reperfusion injury caused by the reintroduction of blood supply to ischemic cardiac muscle. The short and long-term damage that occurs due to ischemia-reperfusion injury is partly due to the proteolysis of diverse protein substrates inside and outside of cardiomyocytes. Ischemia-reperfusion activates several diverse intracellular proteases, including, but not limited to, matrix metalloproteinases, calpains, cathepsins, and caspases. This review will focus on the biological roles, intracellular localization, proteolytic targets, and inhibitors of these proteases in cardiomyocytes following ischemia-reperfusion injury. Recognition of the intracellular function of each of these proteases includes defining their activation, proteolytic targets, and their inhibitors during myocardial ischemia-reperfusion injury. This review is a step toward a better understanding of protease activation and involvement in ischemic heart disease and developing new therapeutic strategies for its treatment.

Intracellular and Extracellular Lipopolysaccharide Signaling in Sepsis: Avenues for Novel Therapeutic Strategies

Sepsis is defined as organ dysfunction due to a dysregulated systemic host response to infection. During gram-negative bacterial infection and other acute illness such as absorption from the gut infection, lipopolysaccharide (LPS) is a major mediator in sepsis. LPS is able to trigger inflammation through both intracellular and extracellular pathways. Classical interactions between LPS and host cells first involve LPS binding to LPS binding protein (LBP), a carrier. The LPS-LBP complex then binds to a receptor complex including the CD14, MD2, and toll-like receptor 4 (TLR4) proteins, initiating a signal cascade which triggers the secretion of pro-inflammatory cytokines. However, it has been established that LPS is also internalized by macrophages and endothelial cells through TLR4-independent pathways. Once internalized, LPS is able to bind to the cytosolic receptors caspases-4/5 in humans and the homologous caspase-11 in mice. Bound caspases-4/5 oligomerize and trigger the assembly of the nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3 inflammasome followed by the activation of inflammatory caspase-1 resulting in subsequent release of interleukin-1β. Caspases-4/5 also activate the perforin gasdermin D and purinergic receptor P2X7, inducing cell lysis and pyroptosis. Pyroptosis is a notable source of inflammation and damage to the lung endothelial barrier during sepsis. Thus, inhibition of caspases-4/5/1 or downstream effectors to block intracellular LPS signaling may be a promising therapeutic approach in adjunction with neutralizing extracellular LPS for treatment of sepsis.

Dysregulated myelopoiesis and hematopoietic function following acute physiologic insult

PURPOSE OF REVIEW

The purpose of this review is to describe recent findings in the context of previous work regarding dysregulated myelopoiesis and hematopoietic function following an acute physiologic insult, focusing on the expansion and persistence of myeloid-deriver suppressor cells, the deterioration of lymphocyte number and function, and the inadequacy of stress erythropoiesis.

RECENT FINDINGS

Persistent myeloid-derived suppressor cell (MDSC) expansion among critically ill septic patients is associated with T-cell suppression, vulnerability to nosocomial infection, chronic critical illness, and poor long-term functional status. Multiple approaches targeting MDSC expansion and suppressor cell activity may serve as a primary or adjunctive therapeutic intervention. Traumatic injury and the neuroendocrine stress response suppress bone marrow erythropoietin receptor expression in a process that may be reversed by nonselective beta-adrenergic receptor blockade. Hepcidin-mediated iron-restricted anemia of critical illness requires further investigation of novel approaches involving erythropoiesis-stimulating agents, iron administration, and hepcidin modulation.

SUMMARY

Emergency myelopoiesis is a dynamic process with unique phenotypes for different physiologic insults and host factors. Following an acute physiologic insult, critically ill patients are subject to persistent MDSC expansion, deterioration of lymphocyte number and function, and inadequate stress erythropoiesis. Better strategies are required to identify patients who are most likely to benefit from targeted therapies.

Nucleic-acid based gene therapy approaches for sepsis

Despite advances in overall medical care, sepsis and its sequelae continue to be an embarrassing clinical entity with an unacceptably high mortality rate. The central reason for high morbidity and high mortality of sepsis and its sequelae is the lack of an effective treatment. Previous clinical trials have largely failed to identify an effective therapeutic target to improve clinical outcomes in sepsis. Thus, the key goal favoring the outcome of septic patients is to devise innovative and evolutionary therapeutic strategies. Gene therapy can be considered as one of the most promising novel therapeutic approaches for nasty disorders. Since a number of transcription factors, such as nuclear factor-κB (NF-κB) and activator protein-1 (AP-1), play a pivotal role in the pathophysiology of sepsis that can be characterized by the induction of multiple genes and their products, sepsis may be regarded as a gene-related disorder and gene therapy may be considered a promising novel therapeutic approach for treatment of sepsis. In this review article, we provide an up-to-date summary of the gene-targeting approaches, which have been developed in animal models of sepsis. Our review sheds light on the molecular basis of sepsis pathology for the development of novel gene therapy approaches and leads to the conclusion that future research efforts may fully take into account gene therapy for the treatment of sepsis.

Caspase vinyl sulfone small molecule inhibitors prevent axonal degeneration in human neurons and reverse cognitive impairment in Caspase-6-overexpressing mice

BACKGROUND

The activation of the aspartate-specific cysteinyl protease, Caspase-6, is proposed as an early pathogenic event of Alzheimer disease (AD) and Huntington's disease. Caspase-6 inhibitors could be useful against these neurodegenerative diseases but most Caspase-6 inhibitors have been exclusively studied in vitro or show acute liver toxicity in humans. Here, we assessed vinyl sulfone small molecule peptide caspase inhibitors for potential use in vivo.

METHODS

The IC50 of NWL vinyl sulfone small molecule caspase inhibitors were determined on Caspase-1 to 10, and Caspase-6-transfected human colon carcinoma HCT116 cells. Inhibition of Caspase-6-mediated axonal degeneration was assessed in serum-deprived or amyloid precursor protein-transfected primary human CNS neurons. Cellular toxicity was measured by phase contrast microscopy, mitochondrial and lactate dehydrogenase colorimetric activity assays, or flow cytometry. Caspase inhibition was measured by fluorogenic activity assays, fluorescence microscopy, and western blot analyses. The effect of inhibitors on age-dependent cognitive deficits in Caspase-6 transgenic mice was assessed by the novel object recognition task. Liquid chromatography coupled to tandem mass spectrometry assessed the blood-brain barrier permeability of inhibitors in Caspase-6 mice.

RESULTS

Vinyl sulfone NWL-117 caspase inhibitor has a higher selectivity against Caspase-6, -4, -8, -9, and -10 whereas NWL-154 has higher selectivity against Caspase-6, -8, and -10. The half-maximal inhibitory concentrations (IC50) of NWL-117 and NWL-154 is 192 nM and 100 nM against Caspase-6 in vitro, and 4.82 μM and 3.63 μM in Caspase-6-transfected HCT116 cells, respectively. NWL inhibitors are not toxic to HCT116 cells or to human primary neurons. NWL-117 and NWL-154 inhibit serum deprivation-induced Caspase-6 activity and prevent amyloid precursor protein-mediated neurite degeneration in human primary CNS neurons. NWL-117 crosses the blood brain barrier and reverses age-dependent episodic memory deficits in Caspase-6 mice.

CONCLUSIONS

NWL peptidic vinyl methyl sulfone inhibitors are potent, non-toxic, blood-brain barrier permeable, and irreversible caspase inhibitors with neuroprotective effects in HCT116 cells, in primary human CNS neurons, and in Caspase-6 mice. These results highlight the therapeutic potential of vinyl sulfone inhibitors as caspase inhibitors against neurodegenerative diseases and sanction additional work to improve their selectivity against different caspases.

Clinical application: Restoration of immune homeostasis by autophagy as a potential therapeutic target in sepsis

Sepsis-induced lymphocyte and dendritic cell apoptosis contributes to immunosuppression, resulting in an inability to eradicate the primary infection and a propensity to acquire secondary infections. However, the inhibition of apoptosis may produce unexpected and undesirable consequences. Another cellular process, autophagy, is also activated in immune cells. There is increasing evidence to suggest that autophagy confers a protective effect in sepsis. The protective mechanisms underlying this effect include limiting apoptotic cell death and maintaining cellular homeostasis. Therefore, understanding the regulation of immune cell autophagy and apoptosis may provide insight into novel therapeutic strategies. The present review examined potential novel therapeutic strategies aimed at restoring immune homeostasis by inducing autophagy. The restoration of balance between apoptosis and autophagy may be a novel approach for improving sepsis-induced immunosuppression and decreasing susceptibility to sepsis.

Programmed cell death and its role in inflammation

Cell death plays an important role in the regulation of inflammation and may be the result of inflammation. The maintenance of tissue homeostasis necessitates both the recognition and removal of invading microbial pathogens as well as the clearance of dying cells. In the past few decades, emerging knowledge on cell death and inflammation has enriched our molecular understanding of the signaling pathways that mediate various programs of cell death and multiple types of inflammatory responses. This review provides an overview of the major types of cell death related to inflammation. Modification of cell death pathways is likely to be a logical therapeutic target for inflammatory diseases.

Revisiting caspases in sepsis

Sepsis is a life-threatening illness that occurs due to an abnormal host immune network which extends through the initial widespread and overwhelming inflammation, and culminates at the late stage of immunosupression. Recently, interest has been shifted toward therapies aimed at reversing the accompanying periods of immune suppression. Studies in experimental animals and critically ill patients have demonstrated that increased apoptosis of lymphoid organs and some parenchymal tissues contributes to this immune suppression, anergy and organ dysfunction. Immediate to the discoveries of the intracellular proteases, caspases for the induction of apoptosis and inflammation, and their striking roles in sepsis have been focused elaborately in a number of original and review articles. Here we revisited the different aspects of caspases in terms of apoptosis, pyroptosis, necroptosis and inflammation and focused their links in sepsis by reviewing several recent findings. In addition, we have documented striking perspectives which not only rewrite the pathophysiology, but also modernize our understanding for developing novel therapeutics against sepsis.

Effect of glutamine on caspase-3 mRNA and protein expression in the myocardium of rats with sepsis

: Apoptosis and caspase-3 play an important role in the pathogenesis of sepsis. In this study, the authors monitored myocardial apoptosis and investigated caspase-3 protein expression change in rats with sepsis. In addition, we investigated the protective effect of glutamine (Gln) on myocardial injury in septic rats. A rat model of sepsis was established by intraperitoneal injection of lipopolysaccharide (LPS). Rats were divided into control group, endotoxin (LPS) group and LPS + Gln group, which were further divided into 4 subset groups (0, 6, 12 and 24 hour subgroups; n = 6). The rate of myocardial apoptosis, caspase-3 mRNA expression and caspase-3 protein expression were examined. Data were analyzed using the F-test or linear correlation test. The results revealed that the rate of myocardial apoptosis in the LPS group was significantly higher than that in the control group (P < 0.05). Compared with the control group, LPS group has an upregulated caspase-3 mRNA expression level. However, the caspase-3 protein was low expressed (P < 0.05). The LPS + Gln group has significant lower myocardial apoptosis rate compared with the LPS group (P < 0.05). In addition, caspase-3 mRNA expression levels and caspase-3 protein expression levels were lower in the LPS + Gln group (P < 0.05). We found that Gln reduces the extent of myocardial apoptotic cell death by decreasing the gene and protein expression of caspase-3. Therefore, Gln may be used to prevent the onset of sepsis at an early stage.

Cytoprotective effect of selective small-molecule caspase inhibitors against staurosporine-induced apoptosis

Caspases are currently known as the central executioners of the apoptotic pathways. Inhibition of apoptosis and promotion of normal cell survival by caspase inhibitors would be a tremendous benefit for reducing the side effects of cancer therapy and for control of neurodegenerative disorders such as Parkinson’s, Alzheimer’s, and Huntington’s diseases. The objective of this study was to discover small-molecule caspase inhibitors with which to achieve cytoprotective effect. We completed the high-throughput screening of Bionet’s 37,500-compound library (Key Organics Limited, Camelford, Cornwall, UK) against caspase-1, -3, and -9 and successfully identified 43 initial hit compounds. The 43 hit compounds were further tested for cytoprotective activity against staurosporine-induced cell death in NIH3T3 cells. Nineteen compounds were found to have significant cytoprotective effects in cell viability assays. One of the compounds, RBC1023, was demonstrated to protect NIH3T3 cells from staurosporine-induced caspase-3 cleavage and activation. RBC1023 was also shown to protect against staurosporine-induced impairment of mitochondrial membrane potential. DNA microarray analysis demonstrated that staurosporine treatment induced broad global gene expression alterations, and RBC1023 co-treatment significantly restored these changes, especially of the genes that are related to cell growth and survival signaling such as Egr1, Cdc25c, cdkn3, Rhob, Nek2, and Taok1. Collectively, RBC1023 protects NIH3T3 cells against staurosporine-induced apoptosis via inhibiting caspase activity, restoring mitochondrial membrane potential, and possibly upregulating some cell survival-related gene expressions and pathways.

Possible interventional therapies in severe sepsis or septic shock

For many years, basic research with relatively straightforward pathophysiologic approaches has driven clinical trials using molecules that supposedly interfere positively with inflammatory processes. However, most of these trials have failed to demonstrate any outcome benefit. Indeed, we need to revisit current paradigms and to think about the possibility that outcome may be predetermined in severe sepsis or septic shock. In addition, an early diagnosis of sepsis prior to the onset of clinical decline is also of particular interest to health practitioners because this information increases the possibilities for early and specific treatment of this life threatening condition. Indeed, the time to initiate therapy is thought to be crucial and the major determent factor in surviving sepsis. Despite substantial progress in sepsis therapy, the gap between the discovery of new effective medical molecules and their implementation in the daily clinical practice of the intensive care unit remains a major hurdle. Fortunately, ongoing research continues to provide new information on the management of sepsis, in particular, severe sepsis or septic shock. High quality and effective management tools are necessary to bring evidence-based therapy to the bedside. On this basis, new therapies could be tested to reduce mortality rates with respect to recently published studies.

The release of high mobility group box 1 in apoptosis is triggered by nucleosomal DNA fragmentation

High mobility group box 1 (HMGB1) initially identified as a non-histone chromosomal protein, which mainly functions as chromatin structure and transcriptional regulation, has been recently reported to be secreted into extracellular milieu in necrosis and apoptosis, and act as a proinflammatory mediator. However, the mechanism by which apoptotic cells release HMGB1 is not clear. In this study, we found that staurosporine (apoptosis-inducer)-induced HMGB1 release was associated with nucleosomal DNA fragmentation catalyzed by caspase-activated DNase (CAD) in WEHI-231 cells. Importantly, this event was effectively attenuated by the treatment of a pan-caspase inhibitor, Z-VAD-fmk, and by the inhibition of CAD-mediated DNA fragmentation by the expression of caspase-resistant inhibitor of CAD (ICAD-CR). In WEHI-231/ICAD-CR and WEHI-231/Puro cells, DNase γ-catalyzed nucleosomal DNA fragmentation occurred by anti-IgM antibody treatment was critical for HMGB1 release. Furthermore, in DNase γ stably-expressing HeLa S3 cells (HeLa S3/γ), the release of HMGB1 accompanied with nucleosomal DNA fragmentation was more apparent than that in parental HeLa S3 cells in which DNA fragmentation was scarcely observed. Taken together, these date suggest that nucleosomal DNA fragmentation catalyzed by CAD or DNase γ plays a pivotal role in HMGB1 release.

Insights into sepsis therapeutic design based on the apoptotic death pathway

Sepsis remains the leading cause of death in critically ill patients. A major problem contributing to sepsis-related high mortality is the lack of effective medical treatment. Thus, the key goal in critical care medicine is to develop novel therapeutic strategies that will impact favorably on septic patient outcome. While it is generally accepted that sepsis is an inflammatory state resulting from the systemic response to infection, apoptosis is implicated to be an important mechanism of the death of lymphocytes, gastrointestinal and lung epithelial cells, and vascular endothelial cells associated with the development of multiple organ failure in sepsis. The pivotal role of cell apoptosis is now highlighted by multiple studies demonstrating that prevention of cell apoptosis can improve survival in clinically relevant animal models of sepsis. In this review article, we address the scientific rationale for remedying apoptotic cell death in sepsis and propose that therapeutic efforts aimed at blocking cell signaling pathways leading to apoptosis may represent an attractive target for sepsis therapy.

Differential role of the Fas/Fas ligand apoptotic pathway in inflammation and lung fibrosis associated with reovirus 1/L-induced bronchiolitis obliterans organizing pneumonia and acute respiratory distress syndrome

Bronchiolitis obliterans organizing pneumonia (BOOP) and acute respiratory distress syndrome (ARDS) are two clinically and histologically distinct syndromes sharing the presence of an inflammatory and fibrotic component. Apoptosis via the Fas/Fas ligand (FasL) pathway plays an important role in the development of acute lung injury and fibrosis characteristic of these and other pulmonary inflammatory and fibrotic syndromes. We evaluated the role of apoptosis via the Fas/FasL pathway in the development of pulmonary inflammation and fibrosis in reovirus 1/L-induced BOOP and ARDS. CBA/J mice were intranasally inoculated with saline, 1 x 10(6) (BOOP), or 1 x 10(7) (ARDS) PFU reovirus 1/L, and evaluated at various days postinoculation for in situ apoptosis by TUNEL analysis and Fas/FasL expression. Our results demonstrate the presence of apoptotic cells and up-regulation of Fas/FasL expression in alveolar epithelium and in infiltrating cells during the inflammatory and fibrotic stages of both reovirus 1/L-induced ARDS and BOOP. Treatment of mice with the caspase 8 inhibitor, zIETD-fmk, inhibited apoptosis, inflammation, and fibrotic lesion development in reovirus 1/L-induced BOOP and ARDS. However, CBA/KlJms-Fas(lpr-cg)/J mice, which carry a point mutation in the Fas cytoplasmic region that abolishes the ability of Fas to transduce an apoptotic signal, do not develop pulmonary inflammation and fibrotic lesions associated with reovirus 1/L-induced BOOP, but still develop inflammation and fibrotic lesions associated with reovirus 1/L-induced ARDS. These results suggest a differential role for the Fas/FasL apoptotic pathway in the development of inflammation and fibrotic lesions associated with BOOP and ARDS.

VX-166: a novel potent small molecule caspase inhibitor as a potential therapy for sepsis

Introduction

Prevention of lymphocyte apoptosis by caspase inhibition has been proposed as a novel treatment approach in sepsis. However, it has not been clearly demonstrated that caspase inhibitors improve survival in sepsis models when dosed post-insult. Also, there are concerns that caspase inhibitors might suppress the immune response. Here we characterize VX-166, a broad caspase inhibitor, as a novel potential treatment for sepsis.

Methods

VX-166 was studied in a number of enzymatic and cellular assays. The compound was then tested in a murine model of endotoxic shock (lipopolysaccharide (LPS), 20 mg/kg IV) and a 10 d rat model of polymicrobial sepsis by caecal ligation and puncture (CLP).

Results

VX-166 showed potent anti-apoptotic activity in vitro and inhibited the release of interleukin (IL)-1beta and IL-18. In the LPS model, VX-166 administered 0, 4, 8 and 12 h post-LPS significantly improved survival in a dose-dependent fashion (P < 0.0028). In the CLP model, VX-166 continuously administered by mini-osmotic pump significantly improved survival when dosed 3 h after insult, (40% to 92%, P = 0.009). When dosed 8 h post-CLP, VX-166 improved survival from 40% to 66% (P = 0.19). Mode of action studies in the CLP model confirmed that VX-166 significantly inhibited thymic atrophy and lymphocyte apoptosis as determined by flow cytometry (P < 0.01). VX-166 reduced plasma endotoxin levels (P < 0.05), suggesting an improved clearance of bacteria from the bloodstream. Release of IL-1beta in vivo or T-cell activation in vitro were moderately affected.

Conclusions

Our studies enhance the case for the use of caspase inhibitors in sepsis. VX-166 itself has promise as a therapy for the treatment of sepsis in man.

Caspases as therapeutic targets

The development of small molecules to modulate caspase activity offers a novel therapeutic strategy in the treatment of apoptosis-related and inflammatory diseases. Caspases are key mediators of apoptosis and inflammation; deregulation of their activation or expression can lead to the development of conditions such as neurodegenerative and autoinflammatory disorders. This review details the different caspase-associated disorders while focusing on caspase-1 inhibition as a potential therapeutic strategy. Problems facing the development of effective and safe caspase therapeutics will also be addressed.

M867, a novel selective inhibitor of caspase-3 enhances cell death and extends tumor growth delay in irradiated lung cancer models

Background

Lung cancer remains the leading cause of cancer death worldwide. Radioresistance of lung cancer cells results in unacceptable rate of loco-regional failure. Although radiation is known to induce apoptosis, our recent study showed that knockdown of pro-apoptotic proteins Bak and Bax resulted in an increase in autophagic cell death and lung cancer radiosensitivity in vitro. To further explore the potential of apoptosis inhibition as a way to sensitize lung cancer for therapy, we tested M867, a novel chemical and reversible caspase-3 inhibitor, in combination with ionizing radiation in vivo and in vitro.

Methods and Findings

M867 reduced clonogenic survival in H460 lung cancer cells (DER = 1.27, p = 0.007) compared to the vehicle-treated treated cells. We found that administration of M867 with ionizing radiation in an in vivo mouse hind limb lung cancer model was well tolerated, and produced a significant tumor growth delay compared to radiation alone. A dramatic decrease in tumor vasculature was observed with M867 and radiation using von Willebrand factor staining. In addition, Ki67 index showed >5-fold reduction of tumor proliferation in the combination therapy group, despite the reduced levels of apoptosis observed with terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling staining. Radiosensitizing effect of M867 through inhibiting caspases was validated using caspase-3/-7 double-knockout (DKO) mouse embryonic fibroblasts (MEF) cell model. Consistent with our previous study, autophagy contributed to the mechanism of increased cell death, following inhibition of apoptosis. In addition, matrigel assay showed a decrease in in vitro endothelial tubule formation during the M867/radiation combination treatment.

Conclusions

M867 enhances the cytotoxic effects of radiation on lung cancer and its vasculature both in vitro and in vivo. M867 has the potential to prolong tumor growth delay by inhibiting tumor proliferation. Clinical trials are needed to determine the potential of this combination therapy in patients with locally advanced lung cancer.

Straw blood cell count, growth, inhibition and comparison to apoptotic bodies

Background

Mammalian cells transform into individual tubular straw cells naturally in tissues and in response to desiccation related stress in vitro. The transformation event is characterized by a dramatic cellular deformation process which includes: condensation of certain cellular materials into a much smaller tubular structure, synthesis of a tubular wall and growth of filamentous extensions. This study continues the characterization of straw cells in blood, as well as the mechanisms of tubular transformation in response to stress; with specific emphasis placed on investigating whether tubular transformation shares the same signaling pathway as apoptosis.

Results

There are approximately 100 billion, unconventional, tubular straw cells in human blood at any given time. The straw blood cell count (SBC) is 45 million/ml, which accounts for 6.9% of the bloods dry weight. Straw cells originating from the lungs, liver and lymphocytes have varying nodules, hairiness and dimensions. Lipid profiling reveals severe disruption of the plasma membrane in CACO cells during transformation. The growth rates for the elongation of filaments and enlargement of rabbit straw cells is 0.6~1.1 (μm/hr) and 3.8 (μm³/hr), respectively. Studies using apoptosis inhibitors and a tubular transformation inhibitor in CACO2 cells and in mice suggested apoptosis produced apoptotic bodies are mediated differently than tubular transformation produced straw cells. A single dose of 0.01 mg/kg/day of p38 MAPK inhibitor in wild type mice results in a 30% reduction in the SBC. In 9 domestic animals SBC appears to correlate inversely with an animal's average lifespan (R² = 0.7).

Conclusion

Straw cells are observed residing in the mammalian blood with large quantities. Production of SBC appears to be constant for a given animal and may involve a stress-inducible protein kinase (P38 MAPK). Tubular transformation is a programmed cell survival process that diverges from apoptosis. SBCs may be an important indicator of intrinsic aging-related stress.

Protection from brain damage and bacterial infection in murine stroke by the novel caspase-inhibitor Q-VD-OPH

Infarction size and infections are important determinants of stroke outcome in humans. Bacterial infections are promoted by stroke-induced immunodeficiency which in experimental stroke is mainly characterized by extensive lymphocyte apoptosis and dysfunction. Pharmacological inhibition of caspases may improve stroke outcome not only by reducing apoptotic brain damage but also by attenuating stroke-induced immunodeficiency. We investigated the effects of systemic administration of the novel, non-toxic caspase-inhibitor quinolyl-valyl-O-methylaspartyl-[-2,6-difluorophenoxy]-methyl ketone (Q-VD-OPH) on stroke-induced neuronal and lymphocyte apoptosis, susceptibility to infections, and mortality in a murine model of stroke induced by middle cerebral artery occlusion (MCAO). Q-VD-OPH reduced ischemic brain damage and stroke-induced programmed cell death in thymus and spleen, decreased susceptibility to post-stroke bacteremia, and improved survival. Therefore, Q-VD-OPH may be a promising therapeutic agent in stroke.

Prevention of lymphocyte apoptosis--a potential treatment of sepsis?

Sepsis is the leading cause of death in surgical intensive care units and is a major cause of morbidity and mortality in neonatal and medical intensive care units. The Centers for Disease Control and Prevention estimates that, in the United States alone, approximately 500,000 people develop sepsis and 175,000 people die each year. Sepsis is a growing problem; its incidence has tripled from 1972 to 1992. Recently, apoptosis has been identified as an important mechanism of cell death in animal models of sepsis and endotoxemia. During sepsis, there is extensive apoptotic death of lymphocytes and gastrointestinal epithelial cells. The extensive apoptotic death of lymphocytes is likely an important cause of the profound immunosuppression that is a hallmark of patients with sepsis. The apoptosis of gastrointestinal epithelial cells may compromise the integrity of the bowel wall, resulting in translocation of bacteria or endotoxins into the systemic circulation. The potential importance of apoptosis in the pathophysiology of sepsis is illustrated by results from animal models that demonstrate that blocking lymphocyte apoptosis improves survival in sepsis. A variety of strategies to inhibit apoptosis may ultimately provide an effective therapy for this highly lethal disorder.

Prevention of immune cell apoptosis as potential therapeutic strategy for severe infections

Some labile cell types whose numbers are normally controlled through programmed cell death are subject to markedly increased destruction during some severe infections. Lymphocytes, in particular, undergo massive and apparently unregulated apoptosis in human patients and laboratory animals with sepsis, potentially playing a major role in the severe immunosuppression that characterizes the terminal phase of fatal illness. Extensive lymphocyte apoptosis has also occurred in humans and animals infected with several exotic agents, including Bacillus anthracis, the cause of anthrax; Yersinia pestis, the cause of plague; and Ebola virus. Prevention of lymphocyte apoptosis, through either genetic modification of the host or treatment with specific inhibitors, markedly improves survival in murine sepsis models. These findings suggest that interventions aimed at reducing the extent of immune cell apoptosis could improve outcomes for a variety of severe human infections, including those caused by emerging pathogens and bioterrorism agents.

Programmed anuclear cell death delimits platelet life span

Platelets are anuclear cytoplasmic fragments essential for blood clotting and wound healing. Despite much speculation, the factors determining their life span in the circulation are unknown. We show here that an intrinsic program for apoptosis controls platelet survival and dictates their life span. Pro-survival Bcl-x(L) constrains the pro-apoptotic activity of Bak to maintain platelet survival, but as Bcl-x(L) degrades, aged platelets are primed for cell death. Genetic ablation or pharmacological inactivation of Bcl-x(L) reduces platelet half-life and causes thrombocytopenia in a dose-dependent manner. Deletion of Bak corrects these defects, and platelets from Bak-deficient mice live longer than normal. Thus, platelets are, by default, genetically programmed to die by apoptosis. The antagonistic balance between Bcl-x(L) and Bak constitutes a molecular clock that determines platelet life span: this represents an important paradigm for cellular homeostasis, and has profound implications for the diagnosis and treatment of disorders that affect platelet number and function.

Therapeutic targets in the mitochondrial apoptotic pathway

Every cell in the human body has most of the components of the apoptotic apparatus and is thus principally equipped to die by apoptosis. Situations of increased or decreased apoptosis contribute to many forms of human disease, making this pathway an attractive target of therapeutic intervention. The past few years have seen an enormous refinement in the understanding how apoptosis works on a molecular level and the role of mitochondria as a central element in apoptotic signal transduction has become obvious. Here, the authors consider the events that are critical in this mitochondrial pathway, in particular at mitochondria but also upstream and downstream. The authors' opinion is presented on the merits and feasibility of approaches that aim at treating disease by interfering with the mitochondrial apoptotic pathway.

Mitochondrial involvement in Atuna racemosa induced toxicity

Our group has developed a system to extract information regarding potential novel pharmaceuticals from historic herbal texts. We have shown that one of the plants identified through this technique has the purported antibacterial properties suggested by the text. Here, the toxicity of this antibacterial extract was examined. Using a Jurkat cell model, a therapeutic window between the minimal inhibitory concentration for Gram-positive bacteria and the dose-dependent toxicity of the Atuna racemosa extract was established. Using cells with a mutated caspase 8, it was shown that the toxicity does not involve caspase 8. However, by transmission electron microscopy and a potentiometric dye, the toxicity was shown to involve the mitochondria. This toxicity also resulted in DNA cleavage and activation of caspase 3. This work suggests that the extract, originally reported as an antimicrobial therapeutic in a 400-year-old Dutch herbal text, may maintain a therapeutic window as an antibiotic. Furthermore, this work shows toxicity would occur in a mitochondrial dependent fashion.

Apoptosis and caspases regulate death and inflammation in sepsis

Although the prevailing concept has been that mortality in sepsis results from an unbridled hyper-inflammatory cytokine-mediated response, the failure of more than 30 clinical trials to treat sepsis by controlling this cytokine response requires a 'rethink' of the molecular mechanism underpinning the development of sepsis. As we discuss here, remarkable new studies indicate that most deaths from sepsis are actually the result of a substantially impaired immune response that is due to extensive death of immune effector cells. Rectification of this apoptotic-inflammatory imbalance using modulators of caspases and other components of the cell-death pathway have shown striking efficacy in stringent animal models of sepsis, indicating an entirely novel path forward for the clinical treatment of human sepsis.

Caspase inhibitors: viral, cellular and chemical

Caspases, key mediators of apoptosis, are a structurally related family of cysteine proteases that cleave their substrates at aspartic acid residues either to cause cell death or to activate cytokines as part of an immune response. They can be controlled upstream by the regulation of signals that lead to zymogen activation, or downstream by inhibitors that prevent them from reaching their substrates. This review specifically looks at caspase inhibitors as distinct from caspase regulators: those produced by the cell itself; those whose genes are carried by viruses; and artificial caspase inhibitors used for research and potentially as therapeutics.

Caspase independence of radio-induced cell death

Colon carcinoma cells subjected to gamma-irradiation (4 Gy) manifest signs of apoptosis (caspase activation, chromatin condensation, phosphatidylserine (PS) exposure on the cell surface, sub-diploid DNA content), correlating with their radiosensitivity, which is increased in cells lacking the 14-3-3sigma protein as compared to wild-type controls. Inhibition of caspases by addition of Z-Val-Ala-DL-Asp (OMe)-fluoromethylketone, by stable transfection with the Baculovirus gene coding for p35, or by Bax knockout reduced all signs of apoptosis, yet failed to suppress radio-induced micro- and multinucleation. Moreover, pharmacological caspase inhibition, p35 expression or Bax knockout had no effect on the clonogenic survival that was reduced by gamma-irradiation and caspase inhibition failed to abolish the increased radiosensitivity of 14-3-3sigma-deficient cells. Micro- and multinucleation was detectable among non-apoptotic cells lacking PS exposure, as well as among cells undergoing apoptosis. Moreover, a fraction of micro- or multinucleated cells manifested caspase activation, and videomicroscopic analyses revealed that such cells could succumb to caspase-dependent apoptosis. Altogether, these results suggest that genomic instability induced by gamma-irradiation can trigger apoptosis, although apoptosis is dispensable for radio-induced clonogenic death.

Hypoxia in presence of blockers of excitotoxicity induces a caspase-dependent neuronal necrosis

When excitotoxic mechanisms are blocked, severe or prolonged hypoxia and hypoxia-ischemia can still kill neurons, by a mechanism which is poorly understood. We studied this "non-excitotoxic hypoxic death" in primary cultures of rat dentate gyrus neurons. Many neurons subjected to hypoxia in the presence of blockers of ionotropic glutamate receptors developed the electron microscopic features of necrosis. They showed early mitochondrial swelling, loss of mitochondrial membrane potential and cytoplasmic release of cytochrome c, followed by activation of caspase-9, and by caspase-9-dependent activation of caspase-3. Caspase inhibitors were neuroprotective. These results suggest that "non-excitotoxic hypoxic neuronal death" requires the activation in many neurons of a cell death program originating in mitochondria and leading to necrosis.

Adenosine A2A receptor inactivation increases survival in polymicrobial sepsis

The mechanisms governing the impairment of bacterial clearance and immune function in sepsis are not known. Adenosine levels are elevated during tissue hypoxia and damage associated with sepsis. Adenosine has strong immunosuppressive effects, many of which are mediated by A(2A) receptors (A(2A)R) expressed on immune cells. We examined whether A(2A)R are involved in the regulation of immune function in cecal ligation and puncture-induced murine polymicrobial sepsis by genetically or pharmacologically inactivating A(2A)R. A(2A)R knockout (KO) mice were protected from the lethal effect of sepsis and had improved bacterial clearance compared with wild-type animals. cDNA microarray analysis and flow cytometry revealed increased MHC II expression in A(2A)-inactivated mice, suggesting improved Ag presentation as a mechanism of protection. Apoptosis was attenuated in the spleen of A(2A) KO mice indicating preserved lymphocyte function. Levels of the immunosuppressive cytokines IL-10 and IL-6 were markedly lower following A(2A)R blockade. Similar to observations with A(2A)R KO mice, an A(2A)R antagonist increased survival even when administered in a delayed fashion. These studies demonstrate that A(2A)R blockade may be useful in the treatment of infection and sepsis.

Correlating the fractional inhibition of caspase-3 in NT2 cells with apoptotic markers using an active-caspase-3 enzyme-linked immunosorbent assay

A rapid and quantitative method for measuring the activity and fractional inhibition of enzymes within their natural cellular environment remains an unmet need in drug discovery. We describe the use of a nonradioactive quantitative enzyme-linked immunosorbent assay (ELISA) for measuring intracellular caspase activity that is amenable to robotic automation. The ELISA specifically detects active-caspase-3 and was used to correlate the in-cell activity of caspase-3 with the progress of caspase-3-mediated events under varying concentrations of caspase-3 inhibitors in NT2 cells. We examined the cleavage of endogenous substrates (poly(ADP-ribose)polymerase and alphaII-spectrin), the extent of DNA fragmentation, and the autocatalytic removal of the caspase-3 prodomain as markers of caspase-3 activity. To impart inhibition of the downstream markers, a greater level of caspase-3 inhibition was required. Although the functional markers were found not to accurately predict intracellular caspase-3 activity, we found that the inhibition of intracellular caspase-3 was highly correlated (R(2) = 0.96) to the inhibition of DNA fragmentation. Also, by comparing the potency of the different inhibitors against the intracellular enzyme versus the purified enzyme, the effects of inhibitor functional groups on whole-cell activity were addressed.

Cell death pathways in juvenile Batten disease

Apoptosis, Golgi fragmentation and elevated ceramide levels occur in Juvenile Neuronal Ceroid Lipofuscinosis (JNCL) neurons, lymphoblasts and fibroblasts. Our purpose was to examine whether apoptosis is the mechanism of cell death in JNCL. This was tested by analyzing caspase-dependent/independent pathways and autophagy, and caspase effects on ceramide and Golgi fragmentation. zVAD prevented caspase activation, but not all cell death. Inhibiting caspase-8 suppressed caspases more than inhibition of any other caspase. Inhibiting caspase-8/6 was synergistic. zVAD suppressed autophagy. 3-methyladenine suppressed caspase activation less than zVAD did. Blocking autophagy/caspase-8/or-6 was synergistic. Blocking autophagy/caspase-3/or-9 was not. Inhibiting caspase-9/3 suppressed autophagy. Golgi fragmentation was suppressed by zVAD, and blocked by CLN3. CLN3, not zVAD, prevented ceramide elevation.

IN CONCLUSION

caspase-dependent/independent apoptosis and autophagy occur caspase-dependent pathways initiate autophagy Golgi fragmentation results from apoptosis ceramide elevation is independent of caspases, and CLN3 blocks all cell death, prevents Golgi fragmentation and elevation of ceramide in JNCL.

The apoptotic and proliferative fate of cytokine-induced killer cells after redirection to tumor cells with bispecific Ab

BACKGROUND

Cytokine-induced killer (CIK) cells are ex vivo expanded T cells with co-expression of CD3 and CD56 and NK activity. They have recently been evaluated in a phase I/II clinical trial against malignant lymphoma. Bispecific Ab (bsAb) redirect CIK cells to tumor targets, thus enhancing their cytotoxicity. While bsAb may improve T-cell mediated anti-tumor activity, little is known about the fate of effector cells upon redirection to tumor targets using a bsAb.

METHODS

Using ex vivo-activated CIK cells, Her2/neu expressing breast and ovarian cell lines and a F(ab')2 Her2/neu x CD3 bsAb, we investigated the anti-tumor activity and the proliferative and apoptotic outcome of CIK cells.

RESULTS

When redirected to tumor targets with bsAb, there was a significant increase in anti-tumor activity as well as an increase in both CIK cell proliferation and apoptosis. The addition of agonistic Ab against CD28 did not significantly increase proliferation or apoptosis of CIK cells redirected to CD80- and CD86- tumor targets. To attempt to reduce T-cell apoptosis, we incubated CIK cells in the presence of the pan-caspase inhibitor z-VAD-fmk, which led to a partial reduction in T-cell apoptosis without increasing cellular cytotoxicity.

DISCUSSION

bsAb are effective in redirecting activated T cells to tumor targets and such redirection leads to both T-cell proliferation and apoptosis that are not altered by co-stimulation through CD28. Effector cell apoptosis can be reduced by using a caspase inhibitor but this does not increase CIK cell cytotoxicity.

Pharmacological manipulation of cell death: clinical applications in sight?

This series of Reviews on cell death explores the creation of new therapies for correcting excessive or deficient cell death in human disease. Signal transduction pathways controlling cell death and the molecular core machinery responsible for cellular self-destruction have been elucidated with unprecedented celerity during the last decade, leading to the design of novel strategies for blocking pathological cell loss or for killing unwanted cells. Thus, an increasing number of compounds targeting a diverse range of apoptosis-related molecules are being explored at the preclinical and clinical levels. Beyond the agents that are already FDA approved, a range of molecules targeting apoptosis-regulatory transcription factors, regulators of mitochondrial membrane permeabilization, and inhibitors or activators of cell death-related proteases are under close scrutiny for drug development.

Caspase-independent cell death

Caspase activation has been frequently viewed as synonymous with apoptotic cell death; however, caspases can also contribute to processes that do not culminate in cell demise. Moreover, inhibition of caspases can have cytoprotective effects. In a number of different models, caspase inhibition does not maintain cellular viability and instead shifts the morphology of death from apoptosis to nonapoptotic pathways. Here, we explore the contribution of caspases to cell death, either as upstream signals or as downstream effectors contributing to apoptotic morphology, as well as alternative strategies for cell death inhibition. Such alternative strategies may either target catabolic hydrolases or be aimed at preventing mitochondrial membrane permeabilization and its upstream triggers.

Balance between NF-κB and JNK/AP-1 activity controls dendritic cell life and death

The life cycle of dendritic cells (DCs) must be precisely regulated for proper functioning of adaptive immunity. However, signaling pathways actively mediating DC death remain enigmatic. Here we describe a novel mechanism of hierarchical transcriptional control of DC life and death. Ligation of tumor necrosis factor receptor superfamily (TNFR-SF) members on DCs and cognate contact with T cells resulted in quantitatively balanced nuclear factor-κB (NF-κB) and c-Jun N-terminal kinase (JNK)–mediated activator protein-1 (AP-1) induction and strongly enhanced DC longevity. Specific blockade of NF-κB in DCs induced strongly augmented JNK/AP-1 activity because of elevated levels of reactive oxygen species. In this scenario, DC activation by TNFR-SF members or T cells induced DC apoptosis. Specific inhibition of JNK/AP-1 rescued DCs from this activation-induced cell death program and restored TNFR-SF member- and T-cell–mediated survival. We conclude that JNK/AP-1 activity is under negative feedback control of NF-κB and can execute apoptosis in DCs. Thus, feedback-controlled signaling amplitudes of 2 transcriptional pathways decide the fate of a DC.

Novel pyrazinone mono-amides as potent and reversible caspase-3 inhibitors

The iterative process for the discovery of a series of pyrazinone mono-amides as potent, selective and reversible non-peptide caspase-3 inhibitors (e.g., M826 and M867) is reported. These compounds display potent anti apoptotic activities in a number of cell based systems in vitro as well as in several animal models in vivo.

Multiple death pathways in retina-derived 661W cells following growth factor deprivation: crosstalk between caspases and calpains

During development of the mammalian retina, neurons that do not succeed in establishing functional synaptic connections are eliminated by apoptosis, allowing the formation of a finely tuned network. Growth factors play a crucial role in controlling the balance between apoptosis and survival signals not only at developmental stages but also in long-term preservation of retinal functions. In the present work, we explore the apoptotic mechanisms triggered by growth factor deprivation of retina-derived 661W cells. Under serum starvation conditions, these cone photoreceptors underwent cell death with participation of caspase-9, -3 and -12. Interestingly, inhibition of caspases did not prevent apoptosis but only resulted in a temporary delay. We show m-calpain activation in parallel with caspases, indicating that more than one execution pathway is available to cone photoreceptors. Moreover, crosstalk of the caspase and calpain pathways was detected, suggesting a loop that may act to amplify the apoptotic cascade.

Expression of apoptosis regulatory factors during myocardial dysfunction in endotoxemic rats*

OBJECTIVES

To document the time course of apoptosis pathway activation in sepsis and to determine whether Bcl-2 overexpression would improve endotoxin-induced myocardial dysfunction and mortality rate.

DESIGN

Randomized, controlled trial.

SETTING

Experimental laboratory.

SUBJECTS

Male Sprague Dawley rats, wild-type C57BL/6 female mice, C57BL/6 female mice overexpressing Bcl-2.

INTERVENTIONS

Hearts were isolated from rats treated with endotoxin (10 mg/kg, intravenously) to perform heart function, immunohistochemistry (terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick 3'-end labeling, caspase 3), RNase protection assay, reverse transcriptase polymerase chain reaction, Western blotting (caspase 3), and radiolabeled annexin V studies. Twenty-four hours before endotoxin challenge (10 mg/kg, intravenously), rats were pretreated with saline or endotoxin (0.5 mg/kg, intraperitoneally), with or without parthenolide (1 mg/kg, intraperitoneally). Isolated hearts were used to test myocardial function. Mortality induced by endotoxin (10 mg/kg, intraperitoneally) was tested on wild-type or mice overexpressing Bcl-2.

MEASUREMENTS AND MAIN RESULTS

Endotoxin-induced heart dysfunction was maximal at 4 and 8 hrs postinjection, started to improve, and was fully restored at 24 hrs after endotoxin treatment. Endotoxin also induced phosphatidylserine outer leaflet membrane exposure, caspase 3 activation, nuclear apoptosis, and changes in apoptosis gene expression. Bcl-2 overexpression induced by endotoxin pretreatment prevented endotoxin-induced myocardial dysfunction. Mice overexpressing Bcl-2 had dramatic improvement in survival rate compared with wild-type mice.

CONCLUSIONS

These observations suggest that both death receptor and caspase-mediated apoptosis processes are activated in this sepsis model. Bcl-2 overexpression before endotoxin challenge prevents myocardial dysfunction in rats and improves survival rate in mice.

Prostaglandin F2alpha-mediated activation of apoptotic signaling cascades in the corpus luteum during apoptosis: involvement of caspase-activated DNase

Prostaglandin F(2alpha) (PGF(2alpha)) acting via a G protein-coupled receptor has been shown to induce apoptosis in the corpus luteum of many species. Studies were carried out to characterize changes in the apoptotic signaling cascade(s) culminating in luteal tissue apoptosis during PGF(2alpha)-induced luteolysis in the bovine species in which initiation of apoptosis was demonstrable at 18 h after exogenous PGF(2alpha) treatment. An analysis of intrinsic arm of apoptotic signaling cascade elements revealed that PGF(2alpha) injection triggered increased ratio of Bax to Bcl-2 in the luteal tissue as early as 4 h posttreatment that remained elevated until 18 h. This increase was associated with the elevation in the active caspase-9 and -3 protein levels and activity (p < 0.05) at 4-12 h, but a spurt in the activity was seen only at 18 h posttreatment that could not be accounted for by the changes in the Bax/Bcl-2 ratio or changes in translocation of Bax to mitochondria. Examination of luteal tissue for FasL/Fas death receptor cascade revealed increased expression of FasL and Fas at 18 h accompanied by a significant (p < 0.05) induction in the caspase-8 activity and truncated Bid levels. Furthermore, intrabursal administration of specific caspase inhibitors, downstream to the extrinsic and intrinsic apoptotic signaling cascades, in a pseudopregnant rat model revealed a greater importance of extrinsic apoptotic signaling cascade in mediating luteal tissue apoptosis during PGF(2alpha) treatment. The DNase responsible for PGF(2alpha)-induced apoptotic DNA fragmentation was found to be Ca(2+)/Mg(2+)-dependent, temperature-sensitive DNase, and optimally active at neutral pH conditions. This putative DNase was inhibited by the recombinant inhibitor of caspase-activated DNase, and immunodepletion of caspase-activated DNase from luteal lysates abolished the observed DNA fragmentation activity. Together, these data demonstrate for the first time temporal and spatial changes in the apoptotic signaling cascades during PGF(2alpha)-in-duced apoptosis in the corpus luteum.

Bcl-2-regulated apoptosis and cytochrome c release can occur independently of both caspase-2 and caspase-9

Apoptosis in response to developmental cues and stress stimuli is mediated by caspases that are regulated by the Bcl-2 protein family. Although caspases 2 and 9 have each been proposed as the apical caspase in that pathway, neither is indispensable for the apoptosis of leukocytes or fibroblasts. To investigate whether these caspases share a redundant role in apoptosis initiation, we generated caspase-2(-/-)9(-/-) mice. Their overt phenotype, embryonic brain malformation and perinatal lethality mirrored that of caspase-9(-/-) mice but were not exacerbated. Analysis of adult mice reconstituted with caspase-2(-/-)9(-/-) hematopoietic cells revealed that the absence of both caspases did not influence hematopoietic development. Furthermore, lymphocytes and fibroblasts lacking both remained sensitive to diverse apoptotic stimuli. Dying caspase-2(-/-)9(-/-) lymphocytes displayed multiple hallmarks of caspase-dependent apoptosis, including the release of cytochrome c from mitochondria, and their demise was antagonized by several caspase inhibitors. These findings suggest that caspases other than caspases 2 and 9 can promote cytochrome c release and initiate Bcl-2-regulated apoptosis.

A caspase active site probe reveals high fractional inhibition needed to block DNA fragmentation

Apoptotic markers consist of either caspase substrate cleavage products or phenotypic changes that manifest themselves as a consequence of caspase-mediated substrate cleavage. We have shown recently that pharmacological inhibitors of caspase activity prevent the appearance of two such apoptotic manifestations, alphaII-spectrin cleavage and DNA fragmentation, but that blockade of the latter required a significantly higher concentration of inhibitor. We investigated this phenomenon through the use of a novel radiolabeled caspase inhibitor, [(125)I]M808, which acts as a caspase active site probe. [(125)I]M808 bound to active caspases irreversibly and with high sensitivity in apoptotic cell extracts, in tissue extracts from several commonly used animal models of cellular injury, and in living cells. Moreover, [(125)I]M808 detected active caspases in septic mice when injected intravenously. Using this caspase probe, an active site occupancy assay was developed and used to measure the fractional inhibition required to block apoptosis-induced DNA fragmentation. In thymocytes, occupancy of up to 40% of caspase active sites had no effect on DNA fragmentation, whereas inhibition of half of the DNA cleaving activity required between 65 and 75% of active site occupancy. These results suggest that a high and persistent fractional inhibition will be required for successful caspase inhibition-based therapies.