Minute oxidative stress is sufficient to induce apoptotic death of NIT-1 insulinoma cells

2-(3',5'-Dimethoxybenzylidene) cyclopentanone, a novel synthetic small-molecule compound, provides neuroprotective effects against ischemic stroke

2-(3',5'-Dimethoxybenzylidene) cyclopentanone (DMBC) is a novel small-molecule compound synthesized by our group. Here, we found that in rat models of permanent middle cerebral artery occlusion (pMCAO), intraperitoneal injection (ip) of DMBC at 1h after ischemia reduced infarct volume, improved neurological deficits and increased the protein levels of microtubule-associated protein 2 (MAP 2) and glial fibrillary acid protein (GFAP) in the ischemic cortex. Post-treatment of DMBC still produced neuroprotective effects even when administered at 6h after ischemia. In the oxygen-glucose deprivation (OGD)-induced astrocytes or HT22 cell injury, DMBC treatment decreased the OGD-induced lactate dehydrogenase (LDH) leakage and increased the GFAP levels in astrocytes. In addition, Annexin-V-Fluos staining analysis revealed that DMBC treatment attenuated both OGD-induced apoptosis and necrosis in astrocytes. Western blotting analysis showed DMBC treatment inhibited the ischemia or OGD-induced increases in active cathepsin B in the ischemic cortex or in astrocytes or HT22 cells. Immunofluorescence analysis demonstrated that DMBC treatment blocked the ischemia or OGD-induced release of cathepsin B from the lysosomes into the cytoplasm in the ischemic cortex or in astrocytes or HT22 cells. Taken together, our results indicate that DMBC can offer neuroprotective effects against cerebral ischemia with an extended therapeutic window and its mechanism might be associated with inhibition of the cathepsin B activation.

Novel culture technique involving an histone deacetylase inhibitor reduces the marginal islet mass to correct streptozotocin-induced diabetes

Islet transplantation is limited by the difficulties in isolating the pancreatic islets from the cadaveric donor and maintaining them in culture. To increase islet viability and function after isolation, here we present a novel culture technique involving an histone deacetylase inhibitor (HDACi) to rejuvenate the isolated islets. Pancreatic islets were isolated from Sprague-Dawley (SD) rats and one group (FIs; freshly isolated islets) was used after overnight culture and the other group (RIs; rejuvenated islet) was subjected to rejuvenation culture procedure, which is composed of three discrete steps including degranulation, chromatin remodeling, and regranulation. FIs and RIs were compared with regard to intracellular insulin content, glucose-stimulated insulin secretion (GSIS) capacity, gene expression profile, viability and apoptosis rate under oxidative stresses, and the engraftment efficacy in the xenogeneic islet transplantation models. RIs have been shown to have 1.9 ± 0.28- and 1.7 ± 0.31-fold greater intracellular insulin content and GSIS capacity, respectively, than FIs. HDACi increased overall histone acetylation levels, with inducing increased expression of many genes including insulin 1, insulin 2, GLUT2, and Ogg1. This enhanced islet capacity resulted in more resistance against oxidative stresses and increase of the engraftment efficacy shown by reduction of twofold marginal mass of islets in xenogeneic transplantation model. In conclusion, a novel rejuvenating culture technique using HDACi as chromatin remodeling agents improved the function and viability of the freshly isolated islets, contributing to the reduction of islet mass for the control of hyperglycemia in islet transplantation.

The role of lysosomal rupture in neuronal death

Apoptosis research in the past two decades has provided an enormous insight into its role in regulating cell death. However, apoptosis is only part of the story, and inhibition of neuronal necrosis may have greater impact than apoptosis, on the treatment of stroke, traumatic brain injury, and neurodegenerative diseases. Since the "calpain-cathepsin hypothesis" was first formulated, the calpain- and cathepsin-mediated regulation of necrotic cascades observed in monkeys, has been demonstrated to be a common neuronal death mechanism occurring from simpler organisms to humans. However, the detailed mechanism inducing lysosomal destabilization still remains poorly understood. Heat-shock protein-70 (Hsp70) is known to stabilize lysosomal membrane and protect cells from oxidative stress and apoptotic stimuli in many cell death pathways. Recent proteomics approach comparing pre- and post-ischemic hippocampal CA1 neurons as well as normal and glaucoma-suffered retina of primates, suggested that the substrate protein upon which activated calpain acts at the lysosomal membrane of neurons might be Hsp70. Understanding the interaction between activated calpains and Hsp70 will help to unravel the mechanism that destabilizes the lysosomal membrane, and will provide new insights into clarifying the whole cascade of neuronal necrosis. Although available evidence is circumferential, it is hypothesized that activated calpain cleaves oxidative stress-induced carbonylated Hsp70.1 (a major human Hsp70) at the lysosomal membrane, which result in lysosomal rupture/permeabilization. This review aims at highlighting the possible mechanism of lysosomal rupture in neuronal death by a modified "calpain-cathepsin hypothesis". As the autophagy-lysosomal degradation pathway is a target of oxidative stress, the implication of autophagy is also discussed.

EFFECT OF COLLOIDAL SILVER AGAINST THE CYTOTOXICITY OF HYDROGEN PEROXIDE AND NAPHTHAZARIN ON PRIMARY CULTURED CORTICAL ASTROCYTES

One major pathogenesis in degenerative disorders of the central nervous system (CNS), including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and ischemia, is the oxidative stress induced by reactive oxygen species (ROS). The present study investigated the protective effect of colloidal silver, which is widely marketed as a dietary supplement for diseases like diabetes, AIDS, cancer, and various infections, upon the oxidative brain damage induced by H(2)O(2) or naphthazarin treatment. LDH release from primary cultured astrocytes was enhanced by naphthazarin treatment, and this elevation of the LDH concentration in medium was blocked by colloidal silver treatment. However, hydrogen peroxide was little affected by the colloidal silver. Fluorescence of DCF (peroxides) increased in astrocytes incubated with hydrogen peroxide or naphthazarin compared to the control. When exposed to naphthazarin-induced cells, ROS formation appeared to be reduced by colloidal silver. However, intracellular ROS formation in hydrogen peroxide-treated cells slightly reduced by colloidal silver. These results suggest that colloidal silver has a protective activity against the oxidative stress induced by naphthazarin, but not by hydrogen peroxide.

Involvement of calcium-mediated apoptotic signals in H2O2-induced MIN6N8a cell death

Reactive oxygen species are believed to be the central mediators of beta-cell destruction that leads to type 1 and 2 diabetes, and calcium has been reported to be an important mediator of beta cell death. In the present study, the authors investigated whether Ca(2+) plays a role in hydrogen peroxide (H(2)O(2))-induced MIN6N8a mouse beta cell death. Treatment with low concentration H(2)O(2) (50 microM) was found to be sufficient to reduce MIN6N8a cell viability by 55%, largely via apoptosis. However, this H(2)O(2)-induced cell death was near completely blocked by pretreatment with BAPTA/AM (5 microM), a chelator of intracellular Ca(2+). Moreover, the intracellular calcium store channel blockers, such as, xestospongin c and ryanodine, significant protected cells from 50 microM H(2)O(2)-induced cell death and under extracellular Ca(2+)-free conditions, 50 microM H(2)O(2) elicited transient [Ca(2+)](i) increases. In addition, pharmacologic inhibitors of calpain, calcineurin, and calcium/calmodulin-dependent protein kinase II were found to have a protective effect on H(2)O(2)-induced death. Moreover, H(2)O(2)-induced apoptotic signals, such as c-JUN N-terminal kinase activation, cytochrome c release, caspase 3 activation, and poly (ADP-ribose) polymerase cleavage were all down-regulated by the intracellular Ca(2+) chelation. These findings show that [Ca(2+)](i) elevation, possibly due to release from intracellular calcium stores and the subsequent activation of Ca(2+)-mediated apoptotic signals, critically mediates low concentration H(2)O(2)-induced MIN6N8a cell death. These findings suggest that a breakdown of calcium homeostasis by low level of reactive oxygen species may be involved in beta cell destruction during diabetes development.

Malondialdehyde-acetaldehyde haptenated protein binds macrophage scavenger receptor(s) and induces lysosomal damage

There is evidence that the chemical modification of proteins (haptens) with malondialdehyde-acetaldehyde (MAA) and the immune response to these haptenated proteins is associated with the initiation and/or progression of alcohol liver disease. Experimentally, proteins modified with MAA induce antibody and T cell responses, which are mediated by scavenger receptor(s). Moreover, macrophages have been shown to play an important role in processing and presenting MAA-haptenated proteins in vitro. In vitro, MAA-modified proteins have been shown to induce both apoptosis and necrosis in a dose- and cell-type-dependent manner. Natural ligands modified by oxidative stress, such as oxidized LDL, similarly initiate not only antibody responses, but also cause cell death by disrupting lysosomes after binding to scavenger receptors and internalization. We therefore investigated the binding, internalization, and lysosomal integrity in a macrophage cell line to a MAA-haptenated protein. We demonstrate for the first time that MAA-haptenated proteins are preferentially bound by scavenger receptors on macrophages, which internalize the ligands and shuttle them to lysosomes. Moreover, MAA-haptenated proteins are demonstrated to be associated with a rapid dose-dependent disruption in lysosomal integrity, resulting in leakage and caspase activation. Similarly, as hen egg lysozyme (HEL)-MAA concentrations increased (>31.3 microg/ml), increased levels of apoptosis and a G1/S cell cycle checkpoint inhibition were identified. This study identifies mechanisms by which MAA-haptenated proteins are taken up by a representative antigen-presenting cell and may delineate steps by which MAA-haptenated proteins induce cell death and induce their immunogenicity to the carrier protein.

Broad-spectrum caspase inhibition paradoxically augments cell death in TNF-alpha -stimulated neutrophils

It is increasingly clear that there are caspase-dependent and -independent mechanisms for the execution of cell death and that the utilization of these mechanisms is stimulus- and cell type-dependent. Intriguingly, broad-spectrum caspase inhibition enhances death receptor agonist-induced cell death in a few transformed cell lines. Endogenously produced oxidants are causally linked to necroticlike cell death in these instances. We report here that broad-spectrum caspase inhibitors effectively attenuated apoptosis induced in human neutrophils by incubation with agonistic anti-Fas antibody or by coincubation with tumor necrosis factor-alpha (TNF-alpha) and cycloheximide ex vivo. In contrast, the same caspase inhibitors could augment cell death upon stimulation by TNF-alpha alone during the 6-hour time course examined. Caspase inhibitor-sensitized, TNF-alpha-stimulated, dying neutrophils exhibit apoptoticlike and necroticlike features. This occurred without apparent alteration in nuclear factor-kappaB (NF-kappaB) activation. Nevertheless, intracellular oxidant production was enhanced and sustained in caspase inhibitor-sensitized, TNF-alpha-stimulated neutrophils obtained from healthy subjects. However, despite reduced or absent intracellular oxidant production following TNF-alpha stimulation, cell death was also augmented in neutrophils isolated from patients with chronic granulomatous disease incubated with a caspase inhibitor and TNF-alpha. These results demonstrate that, in human neutrophils, TNF-alpha induces a caspase-independent but protein synthesis-dependent cell death signal. Furthermore, they suggest that TNF-alpha activates a caspase-dependent pathway that negatively regulates reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity.

Protective effects of rilmenidine and AGN 192403 on oxidative cytotoxicity and mitochondrial inhibitor-induced cytotoxicity in astrocytes

Oxidative stress and mitochondrial dysfunction are important aspects of pathogenesis, particularly in the brain, which is highly dependent on oxygen, and the protection of astrocytes is essential for neuroprotection. In this context, imidazoline drugs have been reported to be neuroprotective. Our recent study showed that imidazoline drugs, including guanabenz, inhibit the naphthazarin-induced oxidative cytotoxicity associated with lysosomal destabilization. We now report on a study into the protective effects of rilmenidine and AGN 192403, which have affinity for imidazoline-1 receptors, on the cytotoxicity induced by naphthazarin and inhibitors of mitochondrial respiration in astrocytes. Cytotoxicity was measured grossly by LDH release and by measuring changes in lysosomal membrane stability and features of mitochondrial membrane permeabilization. Naphthazarin-induced cytotoxicity was evidenced by the ordered development of lysosomal acridine orange relocation, decrease in mitochondrial potential, cytochrome c release, and caspase-9 activation, and was inhibited by guanabenz, rilmenidine, and AGN 192403. Antimycin A and rotenone induced mitochondrial dysfunction primarily, and their cytotoxicities were inhibited only by AGN 192403. Rilmenidine and guanabenz may have a lysosomal stabilizing effect, which underlies their protective effects. AGN 192403 might affect the mitochondrial cell death cascades, and had a novel protective effect on the cytotoxicity associated with mitochondrial dysfunction.

Dose-dependent cysteine-mediated protection of insulin-producing cells from damage by hydrogen peroxide

AIMS/HYPOTHESIS

Oxidative damage is believed to play a key role in the process of pancreatic beta cell destruction leading to type 1 diabetes. The beta cells are sensitive to oxidative stress because their intracellular anti-oxidative defence mechanisms are weak. The defence mechanisms depend heavily on glutathione, the synthesis of which is dependent on the availability of cysteine. We investigated whether an increased amount of cysteine available could protect beta cells from oxidative damage.

METHODS

Rat insulinoma cells (RINm5F) were exposed to 50 or 100 microM hydrogen peroxide in the presence of three different cysteine concentrations (0.1, 1 and 5mM). Cell viability was analyzed by vital staining and the cellular metabolic status by C,N-diphenyl-N'-4,5-dimethyl thiazol-2-yl tetrazolium bromide (MTT) analysis. Intracellular insulin, DNA and glutathione contents were measured. The mechanism of death was further clarified by gel electrophoretic DNA fragmentation analysis.

RESULTS

Hydrogen peroxide decreased cell viability and induced functional impairment. Vital staining indicated that 1mM cysteine effectively protected the cells. The protective effect was confirmed by the MTT assay showing preserved metabolic integrity, and by measurements of intact intracellular insulin and DNA content. Cysteine increased intracellular glutathione. Gel electrophoretic analysis of DNA revealed hydrogen peroxide-induced apoptotic fragmentation. This was also abolished by 1mM cysteine. The therapeutic window of cysteine was narrow: 0.1mM cysteine provided inadequate protection, and 5mM cysteine was already toxic in this setting.

CONCLUSION

A proper dose of cysteine could provide a safe and effective means to protect beta cells from oxidative damage.

Imidazoline drugs stabilize lysosomes and inhibit oxidative cytotoxicity in astrocytes

Oxidative stress is a primary pathogenesis in the brain, which is particularly vulnerable to oxidative stress. Maintenance of astrocyte functions under oxidative stress is essential to prevent neuronal injuries and to recover neuronal functions in various pathologic conditions. Imidazoline drugs have affinities for imidazoline receptors, which are highly distributed in the brain, and have been shown to be neuroprotective. This study presented the protective effects of several imidazoline drugs against oxidative cytotoxicity, in primary cultures of astrocytes. Imidazoline drugs, such as idazoxan, guanabenz, guanfacine, BU224, and RS-45041-190, showed protective effects against naphthazarin-induced oxidative cytotoxicity, as evidenced by LDH release and Hoechst 33342/propidium iodide staining. The imidazoline drugs stabilized lysosomes and inhibited naphthazarin-induced lysosomal destabilization, as evidenced by acridine orange relocation. Guanabenz inhibited, the leakage of lysosomal cathepsin D to cytosol, the decreased mitochondrial potential, and the release of mitochondrial cytochrome c, which were induced by naphthazarin. The lysosomal destabilization by oxidative stress and other apoptotic signals and subsequent cathepsin D leakage to the cytosol can induce apoptotic changes of mitochondria and eventually cell death. Therefore, lysosomal stabilization by imidazoline drugs may be ascribed to their protective effects against oxidative cytotoxicity.

Redox control of caspases

Caspases are critical mediators of apoptotic cell death. All members of the caspase family contain the sequence QACXG which contains the active site cysteine. The putative active site of caspase 3 contains a cysteine residue that is subject to redox control. Both thioredoxin and glutathione have been shown to be required for caspase-3 activity to induce apoptosis. The regulation of inducible caspase 3 activity by oxidation-reduction (redox) dependent mechanisms is reviewed. Up until a few years ago, reactive oxygen species (ROS) research mostly focussed on oxidative damage and ROS were thought to be a key trigger for cell death. This view has been refined, leading to the understanding that the biological function of ROS is determined by numerous variables such as concentration, chemical type and cellular localization. For example, ROS and reactive nitrogen species may intercept inducible cell death under certain circumstances via the redox regulation of inducible caspase activity and/or by depleting cellular energy stores. Likewise, death of unwanted diseased or degenerative cells may be facilitated by pharmacologically enhancing the thiol status of such cells using redox-active α-lipoic acid.

Methylmercury and H(2)O(2) provoke lysosomal damage in human astrocytoma D384 cells followed by apoptosis

Methylmercury (MeHg) is a neurotoxic agent acting via diverse mechanisms, including oxidative stress. MeHg also induces astrocytic dysfunction, which can contribute to neuronal damage. The cellular effects of MeHg were investigated in human astrocytoma D384 cells, with special reference to the induction of oxidative-stress-related events. Lysosomal rupture was detected after short MeHg-exposure (1 microM, 1 h) in cells maintaining plasma membrane integrity. Disruption of lysosomes was also observed after hydrogen peroxide (H(2)O(2)) exposure (100 microM, 1 h), supporting the hypothesis that lysosomal membranes represent a possible target of agents causing oxidative stress. The lysosomal alterations induced by MeHg and H(2)O(2) preceded a decrease of the mitochondrial potential. At later time points, both toxic agents caused the appearance of cells with apoptotic morphology, chromatin condensation, and regular DNA fragmentation. However, MeHg and H(2)O(2) stimulated divergent pathways, with caspases being activated only by H(2)O(2). The caspase inhibitor z-VAD-fmk did not prevent DNA fragmentation induced by H(2)O(2), suggesting that the formation of high-molecular-weight DNA fragments was caspase independent with both MeHg and H(2)O(2). The data point to the possibility that lysosomal hydrolytic enzymes act as executor factors in D384 cell death induced by oxidative stress.

The autophagosomal-lysosomal compartment in programmed cell death

In the last decade a tremendous progress has been achieved in understanding the control of apoptosis by survival and death factors as well as the molecular mechanisms of preparation and execution of the cell's suicide. However, accumulating evidence suggests that programmed cell death (PCD) is not confined to apoptosis but that cells use different pathways for active self-destruction as reflected by different morphology: condensation prominent, type I or apoptosis; autophagy prominent, type II; etc. Autophagic PCD appears to be a phylogenetically old phenomenon, it may occur in physiological and disease states. Recently, distinct biochemical and molecular features have been be assigned to this type of PCD. However, autophagic and apoptotic PCD should not be considered as mutually exclusive phenomena. Rather, they appear to reflect a high degree of flexibility in a cell's response to changes of environmental conditions, both physiological or pathological. Furthermore, recent data suggest that diverse or relatively unspecific signals such as photodamage or lysosomotropic agents may be mediated by lysosomal cysteine proteases (cathepsins) to caspases and thus, apoptosis. The present paper reviews morphological, functional and biochemical/molecular data suggesting the participation of the autophagosomal-lysosomal compartment in programmed cell death.

Oxidative markers in diabetic ketoacidosis

Oxidative stress has been implicated in the pathogenesis of the chronic complications of diabetes mellitus but little is known in diabetic ketoacidosis (DKA). The aim of this work was to determine whether lipid peroxidation, as assessed by measuring malondialdehyde (MDA, a prooxidant) and antioxidant status (TAS, an index of antioxidant defenses), is modified in DKA, and also whether any observed abnormalities were related to metabolic disturbances.

METHODS

four groups of patients were studied, comprising 19 patients with DKA, massive ketonuria and plasma standard bicarbonate levels below 16 mmol/l (group 1); 20 patients with poorly controlled diabetes, glycated hemoglobin (HbA1c) above 8% and plasma bicarbonate levels above 16 mmol/l (group 2); 11 patients with well-controlled diabetes and HbA1c below 8% (group 3); and 10 non-diabetic, non-obese control subjects (group 4). Metabolic parameters, MDA levels and TAS were assessed in the plasma of the four groups of subjects.

RESULTS

mean plasma MDA and TAS values were significantly different among the four groups (respectively p < 0.001 and p < 0.01). Mean plasma MDA value was significantly higher in group 1 than in group 3 (p < 0.02) and group 4 (p < 0.001) but was not different from that in group 2. Mean plasma MDA value in group 2 was significantly lower than that in group 4 (p = 0.002). Mean plasma TAS value in group 1 was significantly lower than in groups 3 (p < 0.002) and 4 (p < 0.05). Mean plasma TAS value was significantly lower in group 2 than in group 4 (p<0.05). Plasma MDA values in the diabetic patients (groups 1+2+3) were not related to any clinical characteristics (BMI, age, duration of the disease) or metabolic parameters (glycemia, HbA1c bicarbonates, blood urea nitrogen, phosphatemia, lipids), while plasma TAS values correlated negatively with glycemia, osmolality and HbA1c. A significant relationship was also found between TAS and HbA1c in group 1 (p < 0.05) and between MDA and HbA1c in group 3 (p < 0.05). Correlations were also found between TAS and phosphatemia in group 1 (p < 0.01) and between MDA and phosphatemia in group 2 (p < 0.01). A positive relationship between MDA and cholesterol levels was found in group 1 (p < 0.01). In conclusion, MDA values are increased and TAS values decreased in DKA and poorly controlled diabetes, and tend to correlate more with markers of diabetic imbalance than with markers of acute metabolic disturbances of DKA.

Protection against oxidant-mediated lysosomal rupture: a new anti-apoptotic activity of Bcl-2?

Bcl-2 antagonizes apoptosis through mechanisms which are not completely understood. We have proposed that apoptosis is initiated by minor lysosomal destabilization followed some time later by secondary massive lysosomal rupture. In J774 cells over-expressing Bcl-2, early oxidant-induced lysosomal destabilization is unaffected but secondary lysosomal rupture and apoptosis are suppressed, despite the fact that wild-type and Bcl-2 over-expressing cells degrade hydrogen peroxide at similar rates. It may be that Bcl-2 directly blocks the effects of released lysosomal enzymes and/or prevents downstream activation of unknown cytosolic pro-enzymes by released lysosomal hydrolases, suggesting a new and heretofore unknown activity of Bcl-2.

Clustering of apoptotic cells via bystander killing by peroxides

Clustering of apoptotic cells is a characteristic of many developing or renewing systems, suggesting that apoptotic cells kill bystanders. Bystander killing can be triggered experimentally by inducing apoptosis in single cells and may be based on the exchange of as yet unidentified chemical cell death signals between nearby cells without the need for cell-to-cell communication via gap junctions. Here we demonstrate that apoptotic cell clusters occurred spontaneously, after serum deprivation or p53 transfection in cell monolayers in vitro. Clustering was apparently induced through bystander killing by primary apoptotic cells. Catalase, a peroxide scavenger, suppressed bystander killing, suggesting that hydrogen peroxide generated by apoptotic cells is the death signal. Although p53 expression increased the number of apoptoses, clustering was found to be similar around apoptotic cells whether or not p53 was expressed, indicating that there is no specific p53 contribution to bystander killing. Bystander killing through peroxides emitted by apoptotic cells may propagate tissue injury in different pathological situations and be relevant in chemo-, gamma-ray, and gene therapy of cancer.