Oxidative stress inhibits calpain activity in situ

Oxidative environments decrease tenderization of beef steaks through inactivation of μ-calpain1

This study was designed to test the hypothesis that oxidative conditions in postmortem (PM) tissue decrease calpain activity and proteolysis, subsequently minimizing the extent of tenderization. To achieve different levels of oxidation, the diets of beef cattle were supplemented with vitamin E for the last 126 d on feed, and beef steaks were irradiated early PM. Ten steers were fed a finishing diet with the inclusion of vitamin E at 1,000 IU per steer daily (VITE). Another 10 beef steers were fed the same finishing diet without added vitamin E (CON). At 22 to 24 h PM, strip loins from each carcass were cut into 2.54-cm-thick steaks and individually vacuum packaged. Within 26 h PM, steaks were irradiated at 0 or 6.4 kGy and then aged at 4 degrees C for 0, 1, 3, 7, and 14 d postirradiation. Steaks from each time point were used to determine Warner-Bratzler shear force (WBSF) and calpain activity, and for western blotting of sarcoplasmic proteins and myofibrillar proteins. Calpastatin activity was determined at 0, 3, and 14 d postirradiation. At 1, 3, 7, and 14 d postirradiation, WBSF values of irradiated steaks were higher (P < 0.03) than for nonirradiated steaks. Western blots of troponin-T and desmin showed decreased proteolysis in irradiated samples compared with nonirradiated samples. At 2 d PM, troponin-T degradation products were more evident (P < 0.03) in nonirradiated steaks supplemented with VITE than nonirradiated steaks from the CON diet. Similarly, VITE treatment resulted in steaks with lower (P < 0.05) calpastatin activity at 1 d PM than in steaks from steers fed the CON diet. Irradiation diminished the rate of calpastatin inactivation. Irradiated samples, regardless of diet, had no detectable levels of intact titin or nebulin. Irradiation decreased mu-calpain activity and autolysis, whereas mu-calpain activity was not affected by diet or irradiation. Inactivation of mu-calpain by oxidation during early times PM decreased the amount of myofibrillar proteolysis, thereby decreasing the extent of tenderization of beef steaks.

Oxidative stress inhibits ionomycin-mediated cell death in cortical neurons

Thiol-proteases play important roles in many cellular processes, including maintenance of protein homeostasis and execution of cell death. Therefore, determining how this family of enzymes is regulated is critical for our understanding of both physiological and pathological conditions. Because these proteases require a reduced cysteine residue for activity, the cellular redox state plays a crucial role in regulating the activity of thiol proteases. Importantly, increased oxidative stress can result in the direct modification of the active site cysteine, leading to enzyme inactivation. This would suggest that oxidative stress that occurs during pathological insults could prolong cell survival by preventing the execution of thiol-protease-dependent cell death pathways. To test this hypothesis, cultured rat cortical neurons were treated with the oxidizing agent diamide or doxorubicin in the presence or absence of the calcium ionophore ionomycin. Under normoxic conditions, ionomycin treatment resulted in approximately 70% cell death, which was prevented by addition of the calpain-selective inhibitor benyzloxycarbonyl-Leu-Leu-Tyr fluoromethylketone. Similarly, pretreatment of neurons with either oxidant was also protective. Protection resulting from oxidative stress was not due to new protein synthesis, insofar as cycloheximide did not affect oxidant-mediated protection. Interestingly, treatment with the antioxidant Trolox to reverse or prevent oxidative stress blocked the protective effects of both oxidants against ionomycin-induced cell death. We interpret these findings to suggest that, in diseases or conditions in which oxidative stress is increased, the ability of thiol-proteases to execute cell death pathways fully is decreased and may prolong cell survival.

Stimulation of β-amyloid precursor protein α-processing by phorbol ester involves calcium and calpain activation

Normal processing of Alzheimer's beta-amyloid precursor protein (APP) is markedly stimulated by phorbol esters, but the underlying mechanisms have yet to be fully understood. In this study, we observed that: (a) Phorbol 12,13-dibutyrate (PDBu)-stimulated APP secretion in cultured SH-SY5Y neuroblastoma and fibroblast cells was blocked by EGTA and calpain inhibitors in a concentration-dependent manner, but not by other protease inhibitors. (b) Secretion of fibronectin, another secretory protein tested for comparison, was enhanced by PDBu, but insensitive to calpain inhibitors. (c) PDBu stimulated intracellular calpain activity as measured by the hydrolysis of a fluorogenic calpain substrate. (d) PDBu also induced rapid proteolysis of two endogenous substrates of calpains, i.e., tau and microtubule-associated protein-2 (MAP-2) and the proteolysis was blocked by EGTA and calpain inhibitors. Taken together, these results suggest that stimulation of APP alpha-processing by PDBu is through a mechanism that involves the activation of Ca(2+) and, most notably, calpain. The implications of the findings are discussed in relation to the regulatory mechanism of APP alpha-processing.

Calpain-dependent endoproteolytic cleavage of PrPSc modulates scrapie prion propagation

Previous studies using post-mortem human brain extracts demonstrated that PrP in Creutzfeldt-Jakob disease (CJD) brains is cleaved by a cellular protease to generate a C-terminal fragment, referred to as C2, which has the same molecular weight as PrP-(27-30), the protease-resistant core of PrP(Sc) (1). The role of this endoproteolytic cleavage of PrP in prion pathogenesis and the identity of the cellular protease responsible for production of the C2 cleavage product has not been explored. To address these issues we have taken a combination of pharmacological and genetic approaches using persistently infected scrapie mouse brain (SMB) cells. We confirm that production of C2 is the predominant cleavage event of PrP(Sc) in the brains of scrapie-infected mice and that SMB cells faithfully recapitulate the diverse intracellular proteolytic processing events of PrP(Sc) and PrP(C) observed in vivo. While increases in intracellular calcium (Ca(2+)) levels in prion-infected cell cultures stimulate the production of the PrP(Sc) cleavage product, pharmacological inhibitors of calpains and overexpression of the endogenous calpain inhibitor, calpastatin, prevent the production of C2. In contrast, inhibitors of lysosomal proteases, caspases, and the proteasome have no effect on C2 production in SMB cells. Calpain inhibition also prevents the accumulation of PrP(Sc) in SMB and persistently infected ScN2A cells, whereas bioassay of inhibitor-treated cell cultures demonstrates that calpain inhibition results in reduced prion titers compared with control-treated cultures assessed in parallel. Our observations suggest that calpain-mediated endoproteolytic cleavage of PrP(Sc) may be an important event in prion propagation.

Anthracyclines induce calpain-dependent titin proteolysis and necrosis in cardiomyocytes

Titin, the largest myofilament protein, serves as a template for sarcomere assembly and acts as a molecular spring to contribute to diastolic function. Titin is known to be extremely susceptible to calcium-dependent protease degradation in vitro. We hypothesized that titin degradation is an early event in doxorubicin-induced cardiac injury and that titin degradation occurs by activation of the calcium-dependent proteases, the calpains. Treatment of cultured adult rat cardiomyocytes with 1 or 3 micromol/liter doxorubicin for 24 h resulted in degradation of titin in myocyte lysates, which was confirmed by a reduction in immunostaining of an antibody to the spring-like (PEVK) domain of titin at the I-band of the sarcomere. The elastic domain of titin appears to be most susceptible to proteolysis because co-immunostaining with an antibody to titin at the M-line was preserved, suggesting targeted proteolysis of the spring-like domain of titin. Doxorubicin treatment for 1 h resulted in approximately 3-fold increase in calpain activity, which remained elevated at 48 h. Co-treatment with calpain inhibitors resulted in preservation of titin, reduction in myofibrillar disarray, and attenuation of cardiomyocyte necrosis but not apoptosis. Co-treatment with a caspase inhibitor did not prevent the degradation of titin, which precludes caspase-3 as an early mechanism of titin proteolysis. We conclude that calpain activation is an early event after doxorubicin treatment in cardiomyocytes and appears to target the degradation of titin. Proteolysis of the spring-like domain of titin may predispose cardiomyocytes to diastolic dysfunction, myofilament instability, and cell death by necrosis.

Cyclosporin A prevents calpain activation despite increased intracellular calcium concentrations, as well as translocation of apoptosis-inducing factor, cytochrome c and caspase-3 activation in neurons exposed to transient hypoglycemia

Blockade of mitochondrial permeability transition protects against hypoglycemic brain damage. To study the mechanisms downstream from mitochondria that may cause neuronal death, we investigated the effects of cyclosporin A on subcellular localization of apoptosis-inducing factor and cytochrome c, activation of the cysteine proteases calpain and caspase-3, as well as its effect on brain extracellular calcium concentrations. Redistribution of cytochrome c occurred at 30 min of iso-electricity, whereas translocation of apoptosis-inducing factor to nuclei occurred at 30 min of recovery following 30 min of iso-electricity. Active caspase-3 and calpain-induced fodrin breakdown products were barely detectable in the dentate gyrus and CA1 region of the hippocampus of rat brain exposed to 30 or 60 min of insulin-induced hypoglycemia. However, 30 min or 3 h after recovery of blood glucose levels, fodrin breakdown products and active caspase-3 markedly increased, concomitant with a twofold increase in caspase-3-like enzymatic activity. When rats were treated with neuroprotective doses of cyclosporin A, but not with FK 506, the redistribution of apoptosis-inducing factor and cytochrome c was reduced and fodrin breakdown products and active caspase-3 immuno-reactivity was diminished whereas the extracellular calcium concentration was unaffected. We conclude that hypoglycemia leads to mitochondrial permeability transition which, upon recovery of energy metabolism, mediates the activation of caspase-3 and calpains, promoting cell death.

Subcellular localization and in vivo subunit interactions of ubiquitous mu-calpain

Ubiquitously expressed calpains are Ca(2+)-dependent, intracellular cysteine proteases comprising a large catalytic subunit (domains DI-DIV) and a noncovalently bound small regulatory subunit (domains DV and DVI). It is unclear whether Ca(2+)-induced calpain activation is followed by subunit dissociation or not. Here, we have applied advanced fluorescence microscopy techniques to study calpain subunit interactions in living cells using recombinant calpain subunits or domains fused to enhanced cyan and enhanced yellow fluorescent reporter proteins. All of the overexpressed variants of the catalytic subunit (DI-IV, DI-III, and DI-IIb) were active and Ca(2+)-dependent. The intact large subunit, but not its truncated variants, associates with the small subunit under resting and ionomycin-activated conditions. All of the variants were localized in cytoplasm and nuclei, except DI-IIb, which accumulates in the nucleus and in nucleoli as shown by microscopy and cell fractionation. Localization studies with mutated and chimeric variants indicate that nuclear targeting of the DI-IIb variant is conferred by the two N-terminal helices of DI. Only those variants that contain DIII migrated to membranes upon the addition of ionomycin, suggesting that DIII is essential for membrane targeting. We propose that intracellular localization and in particular membrane targeting of activated calpain, but not dissociation of its intact subunits, contribute to regulate its proteolytic activity in vivo.

Proteolysis of the N-methyl-d-aspartate receptor by calpain in situ

N-Methyl-D-aspartate (NMDA) receptors are calcium-permeable glutamate receptors that play putative roles in learning, memory, and excitotoxicity. NMDA receptor-mediated calcium entry can activate the calcium-dependent protease calpain, leading to substrate degradation. The major NMDA receptor 2 (NR2) subunits of the receptor are in vitro substrates for calpain at selected sites in the C-terminal region. In the present study, we assessed the ability of calpain-mediated proteolysis to modulate the NR1a/2A subtype in a heterologous expression system. Human embryonic kidney (HEK293t) cells, which endogenously express calpain, were cotransfected with NR1a/2A in addition to the calpain inhibitor calpastatin or empty vector as control. Receptor activation by glutamate and glycine as co-agonists led to calpain activation as measured by succinyl-L-leucyl-L-leucyl-L-valyl-L-tyrosyl-aminomethyl coumarin (Suc-LLVY-AMC). Calpain activation also resulted in the degradation of NR2A and decreased binding of (125)I-MK-801 ((125)I-dizocilpine) to NR1a/2A receptors. No stable N-terminal fragment of the NMDA receptor was formed after calpain activation, suggesting calpain regulation of NMDA receptor levels in ways distinct from that previously observed with in vitro cleavage. NR2 subunit constructs lacking the final 420 amino acids were not degraded by calpain. Agonist-stimulated NR1a/2A-transfected cells also had decreased calcium uptake and produced lower changes in agonist-stimulated intracellular calcium compared with cells cotransfected with calpastatin. Calpastatin had no effect on either calcium uptake or intracellular calcium levels when the NR2A subunit lacked the final 420 amino acids. These studies demonstrate that NR2A is a substrate for calpain in situ and that this proteolytic event can modulate NMDA receptor levels.

Screening the proteins that interact with calpain in a human heart cDNA library using a yeast two-hybrid system

Calpain, a cytosolic cysteine protease, requires calcium ions for activity. It has been reported that calpain is involved in the degradation of myofibrillar and neurofilament proteins, and the activation of phosphorylase b kinase and protein kinase C. More recently, calpain was shown to participate in apoptosis. In order to understand the calpain-related signal transduction pathway and its changes during hypertrophy, and especially in hypertension, we screened a human heart cDNA library to find proteins that interact with calpain. 1) Using PCR we amplified the full-length, domain II, domain III and domain IV cDNA of calpain (calcium-activated neutral protease, CANP) I large subunit respectively. 2) Then the fragments were cloned into pGBKT7 vector, resulting in 4 bait expression constructs (pGBKT7-CANP, pGBKT7-CANP II, pGBKT7-CANP III, and pG BKT7-CANP IV). 3) After 4 bait vectors were transformed into AH109 by the lithium acetate-mediated method, AH109/pGBKT7-CANP, AH109/pGBKT7-CANP II, AH109/pGBKT7-CANP III, and AH109/pGBKT7-CANP IV were obtained, respectively. 4) After the human heart cDNA library was sequentially transformed into AH109/ pGBKT7-CANP, 1000-1200 positive clones were grown on SD/Trp-Leu-Ade-His-. Only 150 positive clones were obtained through a colony-lift filter assay to detect beta-galactosidase activity. 5) Total 105 clones among above 150 positive clones were eliminated through that the duplicate, pseudopositive and autoactive detection, respectively. 6) Finally, sequencing eliminated clones with a wrong open reading frame (ORF). Eight clones were cancelled with wrong ORF. The remaining 37 positive clones were analyzed using BLAST software available on the Internet and classified as follows: 1. enzymes or proteins related to signal transduction in the cell; 2. contraction proteins 3. matrix proteins 4. unknown proteins. 7) In order to determine which domain of the calpain I large subunit was involved in the interaction with these real clones, the 37 clones were transformed into AH109/pGBKT7-CANP II, AH109/pGBKT7-CANP III or AH109/pGBKT7-CANP IV. Among these 37 clones, 29 clones could interact with domain II, 5 clones could interact with domain III and 6 clones could interact with domain IV. Thus, we successfully constructed 4 bait expression vectors, pGBKT7-CANP, pGBKT7-CANP II, pGBKT7-CANP III and pGBKT7-CANP IV, and obtained 37 real positive clones that interacted with the calpain I large subunit by screening a human heart cDNA library using pGBKT7-CANP as bait. Among them, 29 clones could interact with domain II of the calpain I large subunit, where the active site of calpain is located. Additional studies will be needed to clarify the calpain-related signal transduction pathway in greater detail.

Proteolytic response to oxidative stress in mammalian cells

Oxidative stress in mammalian cells is an inevitable consequence of their aerobic metabolism. The production of reactive oxygen and nitric oxide species causes oxidative modifications of proteins often combined with a loss of their biological function. Like most partially denatured proteins, moderately oxidized proteins are more sensitive to proteolytic attack by proteases. The diverse cellular proteolytic systems are an important secondary defense against oxidative stress by degrading oxidized and damaged proteins, thereby preventing their intracellular accumulation. In mammalian cells, a range of proteases exists which are distributed throughout the cell. In this review we summarize the function of the cytosolic (proteasome and calpains), the lysosomal, the mitochondrial and the nuclear proteolytic pathways in response to oxidative stress. Particular emphasis is given to the proteasomal system, since this pathway appears to be the most important proteolytic system involved in the removal of oxidatively modified or damaged proteins.

Role of calcium and calcium-activated proteases in CYP2E1-dependent toxicity in HEPG2 cells

The objective of this work was to investigate whether CYP2E1- and oxidative stress-dependent toxicity in HepG2 cells is mediated by an increase of cytosolic Ca2+ and activation of Ca2+-modulated processes. HepG2 cells expressing CYP2E1 (E47 cells) or control cells not expressing CYP2E1 (C34 cells) were preloaded with arachidonic acid (AA, up to 10 microm) and, after washing, incubated with iron-nitrilotriacetic acid (up to 100 microm) for variable periods (up to 12 h). Toxicity was greater in E47 cells than in C34 cells at all times and combinations of iron/AA tested. Cytosolic calcium increased with incubation time in both cell lines, but the increase was higher in E47 cells than in C34 cells. The rise in calcium was an early event and preceded the developing toxicity. Toxicity in E47 cells and the increase in Ca2+ were inhibited by omission of Ca2+ from the extracellular medium, and toxicity was restored by reincorporation of Ca2+. An inhibitor of Ca2+ release from intracellular stores did not prevent the toxicity or the increase in Ca2+, reflecting a role for the influx of extracellular Ca2+ in the toxicity. Reactive oxygen production was similar in media with or without calcium, indicating that calcium was not modulating CYP2E1-dependent oxidative stress. Toxicity, lipid peroxidation, and the increase of Ca2+ in E47 cells exposed to iron-AA were inhibited by alpha-tocopherol. E47 cells (but not C34 cells) exposed to iron-AA showed increased calpain activity in situ (40-fold). The toxicity in E47 cells mirrored calpain activation and was inhibited by calpeptin, suggesting that calpain activation plays a causal role in toxicity. These results suggest that CYP2E1-dependent toxicity in this model depends on the activation of lipid peroxidation, followed by an increased influx of extracellular Ca2+ and activation of Ca2+-dependent proteases.

Inhibition of rat PC12 cell calpain activity by glutathione, oxidized glutathione and nitric oxide

Calpain, a calcium activated neutral protease, is involved in mediating neurotoxicity resulting from conditions of oxidative stress and free radical formation, such as hypoxia and ischemia. Nitric oxide (NO) may also be involved in modulating the cytotoxic effects of oxidative stress. We investigated the roles of reduced glutathione (GSH), oxidized glutathione (GSSG), and NO in modulating calpain activity in PC12 cells. Cell extracts were treated with GSSG, GSH, or the NO-donor S-nitroso-N-acetylpenicillamine. Calpain activity was determined by means of a fluorescent assay. Non-linear regression analysis was used to determine the type of inhibition (competitive, uncompetitive, or non-competitive). GSH displayed uncompetitive inhibition, with K(i)=7.0+/-2.0 mM (Mean+/-SEM) while GSSG exhibited competitive inhibition with K(i)=2.5+/-0.3 mM. NO was an irreversible inhibitor of calpain activity. These results suggest that both GSH and GSSG may be important physiological modulators of calpain activity.

Functional differences of tau isoforms containing 3 or 4 C-terminal repeat regions and the influence of oxidative stress

We report functional differences between tau isoforms with 3 or 4 C-terminal repeats and a difference in susceptibility to oxidative conditions, with respect to the regulation of microtubule dynamics in vitro and tau-microtubule binding in cultured cells. In the presence of dithiothreitol in vitro, a 3-repeat tau isoform promotes microtubule nucleation, reduces the tubulin critical concentration for microtubule assembly, and suppresses dynamic instability. Under non-reducing conditions, threshold concentrations of 3-repeat tau and tubulin exist below which this isoform still promotes microtubule nucleation and assembly but fails to reduce the tubulin critical concentration or suppress dynamic instability; above these threshold concentrations, amorphous aggregates of 3-repeat tau and tubulin can be produced at the expense of microtubule formation. A 4-repeat tau isoform is less sensitive to the oxidative potential of the environment, behaving under oxidative conditions similarly to the 3-repeat isoform under reducing conditions. Under conditions of oxidative stress, in Chinese hamster ovary cells stably expressing either 3- or 4-repeat tau, 3-repeat tau disassociates from microtubules more readily than the 4-repeat isoform, and tau-containing high molecular weight aggregates are preferentially observed in lysates from the Chinese hamster ovary cells expressing 3-repeat tau, indicating greater susceptibility of 3-repeat tau to oxidative conditions, compared with 4-repeat tau in vivo.

Antioxidants J811 and 17beta-estradiol protect cerebellar granule cells from methylmercury-induced apoptotic cell death

Cerebellar granule cells (CGC) have provided a reliable model for studying the toxicity of methylmercury (MeHg), a well-known neurotoxicant contaminating the environment. In the present study we report that doses of MeHg ranging from 0.1 microM to 1.5 microM activated apoptosis, as shown by cell shrinkage, nuclear condensation, and formation of high-molecular-weight DNA fragments. Nevertheless, caspase-3-like activity was not significantly induced, and the broad caspase inhibitor Z-VAD-FMK was not capable of protecting the cells. This argues for a minor role of caspases in the intracellular pathways leading to MeHg-induced cell death in CGC. Instead, proteolytic fragments obtained by specific calpain cleavage of procaspase-3 and alpha-fodrin were increased consistently in samples exposed to MeHg, pointing to a substantial activation of calpain. Notably, two antioxidants, 17beta-estradiol (10 microM) and the Delta(8,9)-dehydro derivative of 17alpha-estradiol J811 (10 microM), protected from MeHg damage, preventing morphological alterations, chromatin fragmentation, and activation of calpain. These findings underscore the key role of oxidative stress in MeHg toxicity, placing it upstream of calpain activation. The shielding effect of the 17beta-estradiol and the radical scavenger J811 is potentially relevant for the development of therapeutic strategies for MeHg intoxication.

Nitric oxide inhibits calpain-mediated proteolysis of talin in skeletal muscle cells

We tested the hypothesis that nitric oxide can inhibit cytoskeletal breakdown in skeletal muscle cells by inhibiting calpain cleavage of talin. The nitric oxide donor sodium nitroprusside prevented many of the effects of calcium ionophore on C(2)C(12) muscle cells, including preventing talin proteolysis and release into the cytosol and reducing loss of vinculin, cell detachment, and loss of cellular protein. These results indicate that nitric oxide inhibition of calpain protected the cells from ionophore-induced proteolysis. Calpain inhibitor I and a cell-permeable calpastatin peptide also protected the cells from proteolysis, confirming that ionophore-induced proteolysis was primarily calpain mediated. The activity of m-calpain in a casein zymogram was inhibited by sodium nitroprusside, and this inhibition was reversed by dithiothreitol. Previous incubation with the active site-targeted calpain inhibitor I prevented most of the sodium nitroprusside-induced inhibition of m-calpain activity. These data suggest that nitric oxide inhibited m-calpain activity via S-nitrosylation of the active site cysteine. The results of this study indicate that nitric oxide produced endogenously by skeletal muscle and other cell types has the potential to inhibit m-calpain activity and cytoskeletal proteolysis.

Tissue transglutaminase: a possible role in neurodegenerative diseases

Tissue transglutaminase is a multifunctional protein that is likely to play a role in numerous processes in the nervous system. Tissue transglutaminase posttranslationally modifies proteins by transamidation of specific polypeptide bound glutamines. This action results in the formation of protein crosslinks or the incorporation of polyamines into substrate proteins, modifications that likely have significant effects on neural function. Tissue transglutaminase is a unique member of the transglutaminase family as in addition to catalyzing the calcium-dependent transamidation reaction, it also binds and hydrolyzes ATP and Guanosine 5'-triphosphate and may play a role in signal transduction. Tissue transglutaminase is a highly regulated and inducible enzyme that is developmentally regulated in the nervous system. In vitro, numerous substrates of tissue transglutaminase have been identified, and several of these proteins have been shown to be in situ substrates as well. Several specific roles for tissue transglutaminase have been described and there is evidence that tissue transglutaminase may also play a role in apoptosis. Recent findings have provided evidence that dysregulation of tissue transglutaminase may contribute to the pathology of several neurodegenerative conditions including Alzheimer's disease and Huntington's disease. In both of these diseases tissue transglutaminase and transglutaminase activity are elevated compared to age-matched controls. Further, immunohistochemical studies have demonstrated that there is an increase in tissue transglutaminase reactivity in affected neurons in both Alzheimer's and Huntington's disease. Although intriguing, many issues remain to be addressed to definitively establish a role for tissue transglutaminase in these neurodegenerative diseases.

Calpain inhibitors protect auditory sensory cells from hypoxia and neurotrophin-withdrawal induced apoptosis

Inhibitors of calpain have been shown to protect nerve growth factor (NGF)-deprived ciliary ganglion neurons and hypoxic cortical neurons. Calpains have been identified in the cochlea and are active during ischemic injury. Since apoptosis can be initiated by loss of neurotrophic support, hypoxia, and ototoxins (e.g., cisplatin, CDDP), the role of calpain inhibitors under these conditions was examined in auditory hair cells and neurons. Dissociated spiral ganglion neuron (SGN) cell cultures and organ of Corti explants from P3 rats were used to test the efficacy of calpain inhibitors as otoprotective molecules. Our results indicate that calpain inhibitor I, calpain inhibitor II, and leupeptin all provided significant protection of SGNs against neurotrophin-withdrawal and hypoxia-induced apoptosis. The increase in neuronal survival ranged from 2.16 to 2.31 times greater than in untreated neurotrophin-withdrawn SGN cell cultures. BOC-Asp(Ome)-Fluoromethyl Ketone (B-D-FMK), a general caspase inhibitor, increased neuronal survival 2.16 times more. Neuronal survival rates were from 1.88 to 2.27 times greater than in untreated, hypoxic neurons and hair cell survival rates were from 1.98 to 2.03 times greater than untreated, hypoxic organ of Corti explants. However, protection of auditory hair cells and neurons from CDDP-induced damage (10 and 6 micrograms/ml, respectively) was limited with any of these calpain inhibitors. Apoptotic pathways initiated by neurotrophin-deprivation and ototoxic stress (e.g., CDDP) have been shown to be different. Our results agree with this finding, with neurotrophin-withdrawal and hypoxia, but not CDDP damage-induced apoptosis being calpain-dependent.

Antioxidant enzymes and human diseases

OBJECTIVES

To describe the importance of the antioxidant enzymes superoxide dismutase, glutathione peroxidase, and catalase working together in human cells against toxic reactive oxygen species, their relationship with several pathophysiologic processes and their possible therapeutic implications.

CONCLUSIONS

Reactive oxygen species (ROS) are involved in the cell growth, differentiation, progression, and death. Low concentrations of ROS may be beneficial or even indispensable in processes such as intracellular signaling and defense against micro-organisms. Nevertheless, higher amounts of ROS play a role in the aging process as well as in a number of human disease states, including cancer, ischemia, and failures in immunity and endocrine functions. As a safeguard against the accumulation of ROS, several nonenzymatic and enzymatic antioxidant activities exist. Therefore, when oxidative stress arises as a consequence of a pathologic event, a defense system promotes the regulation and expression of these enzymes.