Caspases in apoptotic death

Caspase inhibitors as anti-inflammatory and antiapoptotic agents

The striking efficacy of Z-VAD-fmk in the various animal models presented above may reflect its ability to inhibit multiple enzymes including caspases. In accord with this, more selective, reversible inhibitors usually show low efficacy in multifactorial models such as ischaemia, but may offer some protection against NMDA-induced excitotoxicity and hepatitis. Importantly, caspase inhibitors may exhibit significant activity in vivo even when they are applied post insult. As far as the CNS is concerned, the first systemically active inhibitors have emerged. Functional recovery could be achieved in some ischaemia models, but long-term protection by caspase inhibitors is still being questioned. Recent developments in drug design enabled the first caspase inhibitors to enter the clinic. Although initially directed towards peripheral indications such as rheumatoid arthritis, caspase inhibitors will no doubt eventually be used to target CNS disorders. For this purpose the peptidic character of current inhibitors will have to be further reduced. Small molecule, nonpeptidic caspase inhibitors, which have appeared recently, indicate that this goal can be accomplished. Unfortunately, many fundamental questions still remain to be addressed. In particular, the necessary spectrum of inhibitory activity required to achieve the desired effect needs to be determined. There is also a safety aspect associated with prolonged administration. Therefore, the next therapeutic areas for broader-range caspase inhibitors are likely to involve acute treatment. Recent results with synergistic effects between MK-801 and caspase inhibitors in ischaemia suggest that caspase inhibitors may need to be used in conjunction with other drugs. It can be expected that, in the near future, research on caspases and their inhibitors will remain a rapidly developing area of biology and medicinal chemistry. More time, however, may be needed for the first caspase inhibitors to appear on the market.

Attenuation of increased myocardial ischaemia-reperfusion injury conferred by hypercholesterolaemia through pharmacological inhibition of the caspase-1 cascade

1. Hypercholesterolaemia has been shown to be associated with greater myocardial ischaemia-reperfusion injury, in which apoptosis and inflammation-mediated necrosis both play a key role. 2. Caspase-1 is involved in the activation of both apoptosis and inflammation, through the intermediate of interleukin-1beta (IL-1beta). We herein examined whether pharmacological inhibition of the caspase-1 cascade, using Ac-Tyr-Val-Ala-Asp-CH(2)Cl (Ac-YVAD.cmk), after myocardial ischaemia have greater protective effects on myocardial ischaemia-reperfusion injury in diet-induced hypercholesterolaemic rabbits. 3. Male rabbits fed with standard chow or chow supplemented with 0.5% cholesterol and 10% coconut oil for 8 weeks were subjected to 30 min of left circumflex artery occlusion followed by 4 h of reperfusion. An intravenous bolus of Ac-YVAD.cmk (1.6 mg kg(-1)) or vehicle was given 20 min after coronary occlusion. 4. Postischaemic administration of Ac-YVAD.cmk markedly decreased infarct size from 26+/-3% to 12+/-2% in normally fed rabbits (P=0.005) and from 41+/-6% to 14+/-2% in cholesterol-fed rabbits (P<0.001). 5. In the ischaemic non-necrotic area, treatment with Ac-YVAD.cmk markedly reduced the percentage of terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labelling (TUNEL)-positive cardiomyocytes from 15.5+/-0.8% to 2.2+/-0.1% in normally fed rabbits (P<0.001) and from 39.0+/-2.3% to 2.2+/-0.1% in cholesterol-fed rabbits (P<0.001). 6. Ac-YVAD.cmk treatment resulted in a reduction not only of IL-1beta and caspase-1, but also of caspase-3 in the ischaemic myocardium in both normally fed and cholesterol-fed rabbits. 7. No differences in infarct size, the percentage of TUNEL-positive cardiomyocytes, IL-1beta levels or activity of caspase-1 and caspase-3 were observed between Ac-YVAD.cmk-treated normally fed and cholesterol-fed rabbits. 8. This study demonstrates that injection of a selective caspase-1 inhibitor after myocardial ischaemia markedly reduced the detrimental effect conferred by hypercholesterolaemia on myocardial ischaemia-reperfusion injury by attenuating both necrotic as well as apoptotic cell death pathways through inhibition of IL-1beta production and activation of caspase-1 and caspase-3.

Regulation of caspases and XIAP in the brain after asphyxial cardiac arrest in rats

The aim of this study was to determine whether hypoxic-ischemia from asphyxial cardiac arrest activates brain caspases-1 and -3, and the anti-apoptotic protein, XIAP. Asphyxial cardiac arrest in rats was used to induce hypoxic-ischemia. A pan-caspase inhibitor (zVAD) was given in the treatment group. At 72 h after reperfusion, caspase-3 and XIAP expression were present in multiple vulnerable brain regions, whereas caspase-1 was predominantly found in the CA1 hippocampus. zVAD significantly reduced expression of caspases and XIAP and the number of ischemic neurons in the CA1 hippocampus while neurological deficit scores were improved. We conclude that hypoxic-ischemia increases caspases-1 and-3, and XIAP expression. Treatment with zVAD significantly decreases caspase and XIAP expression in these brain regions and improves neurological outcome.

Experimental and emerging therapies for sepsis and septic shock

The underlying principles of sepsis therapy have remained unchanged for decades. These include: prompt institution of antimicrobial agents aimed at the inciting pathogen, source control directed at removal of the infection nidus whenever possible, and support of organ dysfunction. Despite advances in antibiotics, surgical techniques and organ support technology, the morbidity and mortality from sepsis-related diseases have remained substantially unchanged (30 - 50%). Immunomodulation of the inflammatory cascade has been suggested as a crucial but inadequately addressed element in the treatment of sepsis. The list of potential therapeutic targets has been growing as more and more mediators are identified in the pathogenesis of sepsis. To date, numerous anti-inflammatory agents, found to have favourable effects in animal models of septic shock, have been tested in a number of clinical trials on thousands of patients. In this first of a three part series, we go through some of the background and current strategies in sepsis therapy. In this review, we include the two novel therapies that have shown clear survival benefit in large, randomised, placebo-controlled, multi-centre trials, low-dose steroids and recombinant activated protein C. Also included in this review are studies on antithrombin III, platelet-activating factor antagonists, complement modulators, nitric oxide synthase inhibitors and caspase inhibitors (apoptosis inhibitors).

[W206R]-procaspase 3: an inactivatable substrate for caspase 8

We report here the cloning and high-level expression of a soluble proform of human caspase 3 (Ser(24)-H(277)) engineered to contain a short stretch of N-terminal sequence (MTISDSPREQD) from the prosegment of procaspase 8 and a C-terminal heptahistidine tag. The precursor protein isolated from extracts of recombinant Escherichia coli by immobilized metal-ion affinity chromatography was predominantly unprocessed and migrated as a 32-kDa polypeptide on sodium dodecyl sulfate-polyacrylamide gels. Incubation of this protein with recombinant human caspase 8 produced fragments characteristic of the properly processed caspase 3, but the product was inactive. Amino-terminal sequence analysis of the caspase 3 polypeptides proved that caspase 8 had specifically cleaved the Asp(175)-Ser(176) bond to yield the expected p18 and p12 subunits, with partial cleavage at the Asp(28)-Ser(29) bond to release the prosegment. The lack of caspase 3 activity was found to be the result of a fortuitous mutation in which Trp(206) in the S4 subsite was replaced by arginine (W206R). This mutant procaspase 3, which we call m-pro3, serves as a useful reagent with which to test the efficacy of caspase 8 inhibitors in blocking processing of the natural polypeptide substrate of this enzyme and may be valuable as a source of "proenzyme" for crystallographic analysis.

Inhibition of caspase-1-like activity by Ac-Tyr-Val-Ala-Asp-chloromethyl ketone induces long-lasting neuroprotection in cerebral ischemia through apoptosis reduction and decrease of proinflammatory cytokines

Broad spectrum caspase inhibitors have been found to reduce neurodegeneration caused by cerebral ischemia. We studied whether blockade of group I caspases, mainly caspase-1, using the inhibitor Ac-YVAD.cmk reduced infarct volume and produced prolonged neuroprotection. Ac-YVAD.cmk (300 ng/rat) was injected intracerebroventricularly 10 min after permanent middle cerebral artery occlusion in the rat. Drug treatment induced a significant reduction of infarct volume not only 24 hr after ischemia (total damage, percentage of hemisphere volume: control, 41.1 +/- 2.3%; treated, 26.5 +/- 2.1%; p < 0.05) but also 6 d later (total damage: control, 30.6 +/- 2.2%; treated, 23.0 +/- 2.2%; p < 0.05). Ac-YVAD. cmk treatment resulted in a reduction not only of caspase-1 (control, 100 +/- 20.3%; treated, 3.4 +/- 10.4%; p < 0.01) but also of caspase-3 (control, 100 +/- 30.3%; treated, 13.2 +/- 9.5%; p < 0.05) activity at 24 hr and led to a parallel decrease of apoptosis as measured by nucleosome quantitation (control, 100 +/- 11.8%; treated, 47 +/- 5.9%; p < 0.05). Six days after treatment no differences in these parameters could be detected between control and treated animals. Likewise, brain levels of the proinflammatory cytokines IL-1beta and TNF-alpha were reduced at 24 hr (39.5 +/- 23.7 and 51.9 +/- 10.3% of control, respectively) but not at 6 d. Other cytokines, IL-10, MCP-1, MIP-2, and the gaseous mediator nitric oxide, were not modified by the treatment. These findings indicate that blockade of caspase-1-like activity induces a long-lasting neuroprotective effect that, in our experimental conditions, takes place in the early stages of damage progression. Finally, this effect is achieved by interfering with both apoptotic and inflammatory mechanisms.

Apoptosis modulators in the therapy of neurodegenerative diseases

Apoptosis is a prerequisite to model the developing nervous system. However, an increased rate of cell death in the adult nervous system underlies neurodegenerative disease and is a hallmark of multiple sclerosis (MS) Alzheimer's- (AD), Parkinson- (PD), or Huntington's disease (HD). Cell surface receptors (e.g., CD95/APO-1/Fas; TNF receptor) and their ligands (CD95-L; TNF) as well as evolutionarily conserved mechanisms involving proteases, mitochondrial factors (e.g. , Bcl-2-related proteins, reactive oxygen species, mitochondrial membrane potential, opening of the permeability transition pore) or p53 participate in the modulation and execution of cell death. Effectors comprise oxidative stress, inflammatory processes, calcium toxicity and survival factor deficiency. Therapeutic agents are being developed to interfere with these events, thus conferring the potential to be neuroprotective. In this context, drugs with anti-oxidative properties, e.g., flupirtine, N-acetylcysteine, idebenone, melatonin, but also novel dopamine agonists (ropinirole and pramipexole) have been shown to protect neuronal cells from apoptosis and thus have been suggested for treating neurodegenerative disorders like AD or PD. Other agents like non-steroidal anti-inflammatory drugs (NSAIDs) partly inhibit cyclooxygenase (COX) expression, as well as having a positive influence on the clinical expression of AD. Distinct cytokines, growth factors and related drug candidates, e.g., nerve growth factor (NGF), or members of the transforming growth factor-beta (TGF-beta ) superfamily, like growth and differentiation factor 5 (GDF-5), are shown to protect tyrosine hydroxylase or dopaminergic neurones from apoptosis. Furthermore, peptidergic cerebrolysin has been found to support the survival of neurones in vitro and in vivo. Treatment with protease inhibitors are suggested as potential targets to prevent DNA fragmentation in dopaminergic neurones of PD patients. Finally, CRIB (cellular replacement by immunoisolatory biocapsule) is an auspicious gene therapeutical approach for human NGF secretion, which has been shown to protect cholinergic neurones from cell death when implanted in the brain. This review summarises and evaluates novel aspects of anti-apoptotic concepts and pharmacological intervention including gene therapeutical approaches currently being proposed or utilised to treat neurodegenerative diseases.

The atomic-resolution structure of human caspase-8, a key activator of apoptosis

BACKGROUND

Caspases are a family of cysteine proteases that have important intracellular roles in inflammation and apoptosis. Caspase-8 activates downstream caspases which are unable to carry out autocatalytic processing and activation. Caspase-8 is designated as an initiator caspase and is believed to sit at the apex of the Fas- or TNF-mediated apoptotic cascade. In view of this role, the enzyme is an attractive target for the design of inhibitors aimed at blocking the undesirable cell death associated with a range of degenerative disorders.

RESULTS

The structure of recombinant human caspase-8, covalently modified with the inhibitor acetyl-Ile-Glu-Thr-Asp-aldehyde, has been determined by X-ray crystallography to 1.2 A resolution. The asymmetric unit contains the p18-p11 heterodimer; the biologically important molecule contains two dimers. The overall fold is very similar to that of caspase-1 and caspase-3, but significant differences exist in the substrate-binding region. The structure answers questions about the enzyme-inhibitor complex that could not be explained from earlier caspase structures solved at lower resolution.

CONCLUSIONS

The catalytic triad in caspase-8 comprises Cys360, His317 and the backbone carbonyl oxygen atom of Arg258, which points towards the Nepsilon atom of His317. The oxygen atom attached to the tetrahedral carbon in the thiohemiacetal group of the inhibitor is hydrogen bonded to Ndelta of His317, and is not in a region characteristic of a classical 'oxyanion hole'. The N-acetyl group of the inhibitor is in the trans configuration. The caspase-8-inhibitor structure provides the basis for understanding structure/function relationships in this important initiator of the proteolytic cascade that leads to programmed cell death.