Calmodulin and cyclic ADP-ribose interaction in Ca2+ signaling related to cardiac sarcoplasmic reticulum: superoxide anion radical-triggered Ca2+ release

ROS-Influenced Regulatory Cross-Talk With Wnt Signaling Pathway During Perinatal Development

Over a century ago, it was found that a rapid burst of oxygen is needed and produced by the sea urchin oocyte to activate fertilization and block polyspermy. Since then, scientific research has taken strides to establish that Reactive Oxygen Species (ROS), besides being toxic effectors of cellular damage and death, also act as molecular messengers in important developmental signaling cascades, thereby modulating them. Wnt signaling pathway is one such developmental pathway, which has significant effects on growth, proliferation, and differentiation of cells at the earliest embryonic stages of an organism, apart from being significant role-players in the instances of cellular transformation and cancer when this tightly-regulated system encounters aberrations. In this review, we discuss more about the Wnt and ROS signaling pathways, how they function, what roles they play overall in animals, and mostly about how these two major signaling systems cross paths and interplay in mediating major cellular signals and executing the predestined changes during the perinatal condition, in a systematic manner.

CD38-NADase is a new major contributor to Duchenne muscular dystrophic phenotype

Duchenne muscular dystrophy (DMD) is characterized by progressive muscle degeneration. Two important deleterious features are a Ca²⁺ dysregulation linked to Ca²⁺ influxes associated with ryanodine receptor hyperactivation, and a muscular nicotinamide adenine dinucleotide (NAD⁺) deficit. Here, we identified that deletion in mdx mice of CD38, a NAD⁺ glycohydrolase‐producing modulators of Ca²⁺ signaling, led to a fully restored heart function and structure, with skeletal muscle performance improvements, associated with a reduction in inflammation and senescence markers. Muscle NAD⁺ levels were also fully restored, while the levels of the two main products of CD38, nicotinamide and ADP‐ribose, were reduced, in heart, diaphragm, and limb. In cardiomyocytes from mdx/CD38^−/− mice, the pathological spontaneous Ca²⁺ activity was reduced, as well as in myotubes from DMD patients treated with isatuximab (SARCLISA^®) a monoclonal anti‐CD38 antibody. Finally, treatment of mdx and utrophin–dystrophin‐deficient (mdx/utr^−/−) mice with CD38 inhibitors resulted in improved skeletal muscle performances. Thus, we demonstrate that CD38 actively contributes to DMD physiopathology. We propose that a selective anti‐CD38 therapeutic intervention could be highly relevant to develop for DMD patients.

Evidence Implicating Non-Dioxin-Like Congeners as the Key Mediators of Polychlorinated Biphenyl (PCB) Developmental Neurotoxicity

Despite being banned from production for decades, polychlorinated biphenyls (PCBs) continue to pose a significant risk to human health. This is due to not only the continued release of legacy PCBs from PCB-containing equipment and materials manufactured prior to the ban on PCB production, but also the inadvertent production of PCBs as byproducts of contemporary pigment and dye production. Evidence from human and animal studies clearly identifies developmental neurotoxicity as a primary endpoint of concern associated with PCB exposures. However, the relative role(s) of specific PCB congeners in mediating the adverse effects of PCBs on the developing nervous system, and the mechanism(s) by which PCBs disrupt typical neurodevelopment remain outstanding questions. New questions are also emerging regarding the potential developmental neurotoxicity of lower chlorinated PCBs that were not present in the legacy commercial PCB mixtures, but constitute a significant proportion of contemporary human PCB exposures. Here, we review behavioral and mechanistic data obtained from experimental models as well as recent epidemiological studies that suggest the non-dioxin-like (NDL) PCBs are primarily responsible for the developmental neurotoxicity associated with PCBs. We also discuss emerging data demonstrating the potential for non-legacy, lower chlorinated PCBs to cause adverse neurodevelopmental outcomes. Molecular targets, the relevance of PCB interactions with these targets to neurodevelopmental disorders, and critical data gaps are addressed as well.

Neurotoxicity of polychlorinated biphenyls and related organohalogens

Halogenated organic compounds are pervasive in natural and built environments. Despite restrictions on the production of many of these compounds in most parts of the world through the Stockholm Convention on Persistent Organic Pollutants (POPs), many "legacy" compounds, including polychlorinated biphenyls (PCBs), are routinely detected in human tissues where they continue to pose significant health risks to highly exposed and susceptible populations. A major concern is developmental neurotoxicity, although impacts on neurodegenerative outcomes have also been noted. Here, we review human studies of prenatal and adult exposures to PCBs and describe the state of knowledge regarding outcomes across domains related to cognition (e.g., IQ, language, memory, learning), attention, behavioral regulation and executive function, and social behavior, including traits related to attention-deficit hyperactivity disorder (ADHD) and autism spectrum disorders (ASD). We also review current understanding of molecular mechanisms underpinning these associations, with a focus on dopaminergic neurotransmission, thyroid hormone disruption, calcium dyshomeostasis, and oxidative stress. Finally, we briefly consider contemporary sources of organohalogens that may pose human health risks via mechanisms of neurotoxicity common to those ascribed to PCBs.

Atrial Infarction-Induced Spontaneous Focal Discharges and Atrial Fibrillation in Sheep: Role of Dantrolene-Sensitive Aberrant Ryanodine Receptor Calcium Release

BACKGROUND

The mechanisms underlying spontaneous atrial fibrillation (AF) associated with atrial ischemia/infarction are incompletely elucidated. Here, we investigate the mechanisms underlying spontaneous AF in an ovine model of left atrial myocardial infarction (LAMI).

METHODS AND RESULTS

LAMI was created by ligating the atrial branch of the left anterior descending coronary artery. ECG loop recorders were implanted to monitor AF episodes. In 7 sheep, dantrolene-a ryanodine receptor blocker-was administered in vivo during the 8-day observation period (LAMI-D, 2.5 mg/kg, IV, BID). LAMI animals experienced numerous spontaneous AF episodes during the 8-day monitoring period that were suppressed by dantrolene (LAMI, 26.1±5.1; sham, 4.3±1.1; LAMI-D, 2.8±0.8; mean±SEM episodes per sheep, P<0.01). Optical mapping showed spontaneous focal discharges (SFDs) originating from the ischemic/normal-zone border. SFDs were calcium driven, rate dependent, and enhanced by isoproterenol (0.03 µmol/L, from 210±87 to 3816±1450, SFDs per sheep) but suppressed by dantrolene (to 55.8±32.8, SFDs per sheep, mean±SEM). SFDs initiated AF-maintaining reentrant rotors anchored by marked conduction delays at the ischemic/normal-zone border. NOS1 (NO synthase-1) protein expression decreased in ischemic zone myocytes, whereas NADPH (nicotinamide adenine dinucleotide phosphate, reduced form) oxidase and xanthine oxidase enzyme activities and reactive oxygen species (DCF [6-carboxy-2',7'-dichlorodihydrofluorescein diacetate]-fluorescence) increased. CaM (calmodulin) aberrantly increased [³H]ryanodine binding to cardiac RyR2 (ryanodine receptors) in the ischemic zone. Dantrolene restored the physiological binding of CaM to RyR2.

CONCLUSIONS

Atrial ischemia causes spontaneous AF episodes in sheep, caused by SFDs that initiate reentry. Nitroso-redox imbalance in the ischemic zone is associated with intense reactive oxygen species production and altered RyR2 responses to CaM. Dantrolene administration normalizes the CaM response, prevents LAMI-related SFDs, and AF initiation. These findings provide novel insights into the mechanisms underlying ischemia-related atrial arrhythmias.

Endoplasmic Reticulum Stress and Associated ROS

The endoplasmic reticulum (ER) is a fascinating network of tubules through which secretory and transmembrane proteins enter unfolded and exit as either folded or misfolded proteins, after which they are directed either toward other organelles or to degradation, respectively. The ER redox environment dictates the fate of entering proteins, and the level of redox signaling mediators modulates the level of reactive oxygen species (ROS). Accumulating evidence suggests the interrelation of ER stress and ROS with redox signaling mediators such as protein disulfide isomerase (PDI)-endoplasmic reticulum oxidoreductin (ERO)-1, glutathione (GSH)/glutathione disuphide (GSSG), NADPH oxidase 4 (Nox4), NADPH-P450 reductase (NPR), and calcium. Here, we reviewed persistent ER stress and protein misfolding-initiated ROS cascades and their significant roles in the pathogenesis of multiple human disorders, including neurodegenerative diseases, diabetes mellitus, atherosclerosis, inflammation, ischemia, and kidney and liver diseases.

Involvement of calpain in 4-hydroxynonenal-induced disruption of gap junction-mediated intercellular communication among fibrocytes in primary cultures derived from the cochlear spiral ligament

The endocochlear potential in the inner ear is essential for hearing ability, and maintained by various K(+) transport apparatuses including Na(+), K(+)-ATPase and gap junction-mediated intercellular communication (GJ-IC) in the lateral wall structures of the cochlea. Noise-induced hearing loss is known at least in part due to disruption of GJ-IC resulting from an oxidative stress-induced decrease in connexins (Cxs) level in the lateral wall structures. The purpose of this study was to investigate, using primary cultures of fibrocytes from the cochlear spiral ligament of mice, the mechanism underlying GJ-IC disruption induced by 4-hydroxynonenal (4-HNE), which is formed as a mediator of oxidative stress. An exposure to 4-HNE produced the following events: i.e., an increase in 4-HNE-adducted proteins; a decrease in the protein levels of Cx43, β-catenin, and Cx43/β-catenin complex along with intracellular translocation of this complex from the cell membrane to the cytoplasm; enhanced calpain-dependent degradation of endogenous α-fodrin; and disruption of GJ-IC. The 4-HNE-induced decrease in these protein levels and disruption of GJ-IC were most completely abolished by the calpain inhibitor PD150606. Taken together, our data suggest that 4-HNE disrupted GJ-IC through calpain-mediated degradation of Cx43 and β-catenin in primary cultures of fibrocytes derived from the cochlear spiral ligament.

CD38 mediates angiotensin II-induced intracellular Ca(2+) release in rat pulmonary arterial smooth muscle cells

CD38 is a multifunctional enzyme that catalyzes the formation of the endogenous Ca(2+)-mobilizing messengers cyclic ADP-ribose (cADPR) and nicotinic acid adenosine dinucleotide phosphate (NAADP) for the activation of ryanodine receptors (RyRs) of sarcoplasmic reticulum and NAADP-sensitive Ca(2+) release channels in endolysosomes, respectively. It plays important roles in systemic vascular functions, but there is little information on CD38 in pulmonary arterial smooth muscle cells (PASMCs). Earlier studies suggested a redox-sensing role of CD38 in hypoxic pulmonary vasoconstriction. This study sought to characterize its roles in angiotensin II (Ang II)-induced Ca(2+) release (AICR) in PASMCs. Examination of CD38 expression in various rat arteries found high levels of CD38 mRNA and protein in pulmonary arteries. The Ang II-elicited Ca(2+) response consisted of extracellular Ca(2+) influx and intracellular Ca(2+) release in PASMCs. AICR activated in the absence of extracellular Ca(2+) was reduced by pharmacological or siRNA inhibition of CD38, by the cADPR antagonist 8-bromo-cADPR or ryanodine, and by the NAADP antagonist Ned-19 or disruption of endolysosomal Ca(2+) stores with the vacuolar H(+)-ATPase inhibitor bafilomycin A1. Suppression of AICR by the inhibitions of cADPR- and NAADP-dependent pathways were nonadditive, indicating interdependence of RyR- and NAADP-gated Ca(2+) release. Furthermore, AICR was inhibited by the protein kinase C inhibitor staurosporine, the nonspecific NADPH oxidase (NOX) inhibitors apocynin and diphenyleneiodonium, the NOX2-specific inhibitor gp91ds-tat, and the scavenger of reactive oxygen species (ROS) tempol. These results provide the first evidence that Ang II activates CD38-dependent Ca(2+) release via the NOX2-ROS pathway in PASMCs.

Melatonin reduces oxidative stress and improves vascular function in pulmonary hypertensive newborn sheep

Pulmonary hypertension of the newborn (PHN) constitutes a critical condition with severe cardiovascular and neurological consequences. One of its main causes is hypoxia during gestation, and thus, it is a public health concern in populations living above 2500 m. Although some mechanisms are recognized, the pathophysiological facts that lead to PHN are not fully understood, which explains the lack of an effective treatment. Oxidative stress is one of the proposed mechanisms inducing pulmonary vascular dysfunction and PHN. Therefore, we assessed whether melatonin, a potent antioxidant, improves pulmonary vascular function. Twelve newborn sheep were gestated, born, and raised at 3600 meters. At 3 days old, lambs were catheterized and daily cardiovascular measurements were recorded. Lambs were divided into two groups, one received daily vehicle as control and another received daily melatonin (1 mg/kg/d), for 8 days. At 11 days old, lung tissue and small pulmonary arteries (SPA) were collected. Melatonin decreased pulmonary pressure and resistance for the first 3 days of treatment. Further, melatonin significantly improved the vasodilator function of SPA, enhancing the endothelial- and muscular-dependent pathways. This was associated with an enhanced nitric oxide-dependent and nitric oxide independent vasodilator components and with increased nitric oxide bioavailability in lung tissue. Further, melatonin reduced the pulmonary oxidative stress markers and increased enzymatic and nonenzymatic antioxidant capacity. Finally, these effects were associated with an increase of lumen diameter and a mild decrease in the wall of the pulmonary arteries. These outcomes support the use of melatonin as an adjuvant in the treatment for PHN.

Dose-dependent regulation of superoxide anion on the proliferation, differentiation, apoptosis and necrosis of human hepatoma cells: the role of intracellular Ca2+

Dose-dependent regulation of cellular processes is one important characteristic of signaling molecules. Although recent studies suggest that reactive oxygen species (ROS) may act as in vivo signaling molecules, the dose-dependent regulation of ROS on cellular processes together in one system needs to be evaluated. After treating cells with gradually increased O(2)(-), generated by the hypoxanthine-xanthine oxidase system, it was found that: (i) the proliferation of hepatoma cells firstly increased at 1-2 microM O(2)(-), then decreased markedly as the concentration increased; (2) at 8 or 16 microM O(2)(-), re-differentiation of hepatoma cells was induced, as indicated by the indices relating to cell malignancy or differentiation, such as cell surface charge, alpha-fetoprotein, gamma-glutamyltranspeptidase, tyrosine-alpha-ketoglutarate transaminase, cAMP, and the tumor's clonogenic potential; (iii) at 16 microM O(2)(-), accompanied by the re-differentiation of cells, cell apoptosis was also simultaneously induced as indicated by the appearance of apoptotic bodies, detached cells, and other apoptotic morphological features, as well as specific DNA fragmentation; (iv) at the highest concentration of O(2)(-) (32 microM) in this study, cell necrosis was dramatically induced as shown by Trypan blue exclusion; (v), an increase of intracellular Ca(2+) ([Ca(2+)](i)) was observed at all concentrations of O(2)(-) treatment, and this [Ca(2+)](i) increase was found to be involved in the regulation of O(2)(-) on the cellular processes. In conclusion, these results indicate that O(2)(-) could dose-dependently regulate the processes of cells, where Ca(2+) is one of its molecular targets, and hence provide a direct support for the hypothesis that ROS themselves are important signaling molecules.

ROS regulation of microdomain Ca(2+) signalling at the dyads

Reactive oxygen species (ROS) are emerging as centre-stage players in cardiac functional regulation. ROS and Ca(2+) signals converge at dyads, the structural and functional units of cardiac excitation-contraction coupling. These two prominent signalling systems are intertwined with ROS modulation of the entire Ca(2+)-signalling network, and vice versa. While constitutively generated homoeostatic ROS are important in setting the redox potential of the intracellular milieu, dynamic signalling ROS shape microdomain and global Ca(2+) signals on both the beat-to-beat and greater time scales. However, ROS effects are complex and subtle, characterized by multiphasic and bidirectional Ca(2+) responses; and sustained oxidative stress may lead to compromised contractility and arrhythmogenicity. These new understandings should be leveraged to harness ROS for their beneficial roles while avoiding deleterious effects in the heart.

An involvement of oxidative stress in endoplasmic reticulum stress and its associated diseases

The endoplasmic reticulum (ER) is the major site of calcium storage and protein folding. It has a unique oxidizing-folding environment due to the predominant disulfide bond formation during the process of protein folding. Alterations in the oxidative environment of the ER and also intra-ER Ca²⁺ cause the production of ER stress-induced reactive oxygen species (ROS). Protein disulfide isomerases, endoplasmic reticulum oxidoreductin-1, reduced glutathione and mitochondrial electron transport chain proteins also play crucial roles in ER stress-induced production of ROS. In this article, we discuss ER stress-associated ROS and related diseases, and the current understanding of the signaling transduction involved in ER stress.

Hypoxic Pulmonary Vasoconstriction

It has been known for more than 60 years, and suspected for over 100, that alveolar hypoxia causes pulmonary vasoconstriction by means of mechanisms local to the lung. For the last 20 years, it has been clear that the essential sensor, transduction, and effector mechanisms responsible for hypoxic pulmonary vasoconstriction (HPV) reside in the pulmonary arterial smooth muscle cell. The main focus of this review is the cellular and molecular work performed to clarify these intrinsic mechanisms and to determine how they are facilitated and inhibited by the extrinsic influences of other cells. Because the interaction of intrinsic and extrinsic mechanisms is likely to shape expression of HPV in vivo, we relate results obtained in cells to HPV in more intact preparations, such as intact and isolated lungs and isolated pulmonary vessels. Finally, we evaluate evidence regarding the contribution of HPV to the physiological and pathophysiological processes involved in the transition from fetal to neonatal life, pulmonary gas exchange, high-altitude pulmonary edema, and pulmonary hypertension. Although understanding of HPV has advanced significantly, major areas of ignorance and uncertainty await resolution.

Neuroprotective effects of Tacrolimus (FK-506) and Cyclosporin (CsA) in oxidative injury

The detrimental effects of hypoxic damage to central nervous system lead to energy depletion, free radical formation, lipid peroxidation (LPO), and increased calcium. We hypothesized that in vitro tacrolimus (FK-506) and cyclosporine A (CsA) could be protective against hypoxic damage in spinal cord. Dorsal columns were isolated from the spinal cord of adult rats and injured by exposure to hypoxic condition for 1 h, and treated with FK-506 (0.1 μM) and CsA (0.1 μM). After injury, reperfusion was carried out for 2 h. Tissues were collected, processed for biochemical assays, and 2,3,5-triphenyltetrazolium chloride (TTC) staining. Spinal cord hypoxia caused a significant decrease (P < 0.001) in mitochondrial ATP (30.64%) and tissue reduced glutathione (GSH) (60.14%) content. Conversely, a significant increase (P < 0.001) in tissue LPO level (57.77%) and myeloperoxidase (MPO) activity (461.24%) was observed in hypoxic group. Mitochondrial swelling was also significantly increased in hypoxic group (90.0%). Treatment with either FK-506 or CsA showed that significant neuroprotective effects (P < 0.05-0.01) were measured in various parameters in hypoxic groups. FK-506 and CsA treatment showed increase in ATP by 11.19% and 16.14% while GSH content increased by 66.46% and 77.32%, respectively. Conversely, LPO content decreased by 18.97% and 24.06% and MPO level by 42.86% and 18.66% after FK-506 and CsA treatment. Calcium uptake was also decreased in mitochondria as exhibited by the increase in absorbance by 11.19% after FK-506 treatment. TTC staining also showed increased viability after FK-506 and CsA treatment. In conclusion, present study demonstrates the neuroprotective effect of FK-506 and CsA treatment against spinal cord hypoxia induced damage is mediated via their antioxidant actions.

Cyclic ADP-ribose and NAADP: fraternal twin messengers for calcium signaling

The concept advanced by Berridge and colleagues that intracellular Ca(2+)-stores can be mobilized in an agonist-dependent and messenger (IP(3))-mediated manner has put Ca(2+)-mobilization at the center stage of signal transduction mechanisms. During the late 1980s, we showed that Ca(2+)-stores can be mobilized by two other messengers unrelated to inositol trisphosphate (IP(3)) and identified them as cyclic ADP-ribose (cADPR), a novel cyclic nucleotide from NAD, and nicotinic acid adenine dinucleotide phosphate (NAADP), a linear metabolite of NADP. Their messenger functions have now been documented in a wide range of systems spanning three biological kingdoms. Accumulated evidence indicates that the target of cADPR is the ryanodine receptor in the sarco/endoplasmic reticulum, while that of NAADP is the two pore channel in endolysosomes.As cADPR and NAADP are structurally and functionally distinct, it is remarkable that they are synthesized by the same enzyme. They are thus fraternal twin messengers. We first identified the Aplysia ADP-ribosyl cyclase as one such enzyme and, through homology, found its mammalian homolog, CD38. Gene knockout in mice confirms the important roles of CD38 in diverse physiological functions from insulin secretion, susceptibility to bacterial infection, to social behavior of mice through modulating neuronal oxytocin secretion. We have elucidated the catalytic mechanisms of the Aplysia cyclase and CD38 to atomic resolution by crystallography and site-directed mutagenesis. This article gives a historical account of the cADPR/NAADP/CD38-signaling pathway and describes current efforts in elucidating the structure and function of its components.

Mouse embryonic fibroblasts from CD38 knockout mice are resistant to oxidative stresses through inhibition of reactive oxygen species production and Ca(2+) overload

CD38 is a multifunctional enzyme that has both ADP-ribosyl cyclase and cADPR hydrolase activities, being capable of cleaving NAD(+) to cyclic ADP ribose (cADPR) and hydrolyzing cADPR to ADPR. It has been reported that there is markedly a reduction of cADPR and elevation of NAD in many tissues from CD38 knockout (CD38(-/-)) mice. Cyclic ADPR is a potent second messenger for intracellular Ca(2+) mobilization, and NAD is a key cellular metabolite for cellular energetic and a crucial regulator for multiple signaling pathways in cells. We hypothesize that CD38 knockout may have a protective effect in oxidative stresses through elevating NAD and decreasing cADPR. In the present study, we observed that the mouse embryonic fibroblasts (MEFs) from CD38(-/-) mice were significantly resistant to oxidative stress such as H(2)O(2) injury and hypoxia/reoxygenation compared with wild type MEFs (WT MEFs). We further found that production of reactive oxygen species (ROS) and concentrations of intracellular Ca(2+) ([Ca(2+)](i)) in CD38(-/-) MEFs were markedly reduced compared with WT MEFs during hypoxia/reoxygenation. Coincidence with these results, a remarkably lower mRNA level of Nox1, one of the enzymes responsible for ROS generation, was observed in CD38(-/-) MEFs. Furthermore, we found that transcription of Nox1 mRNA in WT MEFs could be elevated by calcium ionophore ionomycin in a dose-dependent manner, indicating that the expression of Nox1 mRNA can be regulated by elevation of intracellular [Ca(2+)]. Therefore we concluded that CD38(-/-) MEFs are resistant to oxidative stresses through inhibiting intracellular Ca(2+) overload and ROS production which may be regulated by Ca(2+)-mediated inhibition of Nox1 expression. Our data should provide an insight for elucidating the roles of CD38 in oxidative stresses and a novel perspective of dealing with the ischemia/reperfusion-related diseases.

S-allyl L-cysteine diminishes cerebral ischemia-induced mitochondrial dysfunctions in hippocampus

Ischemic brain is highly vulnerable to free radicals mediated secondary neuronal damage especially mitochondrial dysfunctions. Present study investigated the neuroprotective effect of S-allyl L-cysteine (SAC), a water soluble compound from garlic, against cerebral ischemia/reperfusion (I/R)-induced mitochondrial dysfunctions in hippocampus (HIP). We used transient rat middle cerebral artery occlusion (MCAO) model of brain ischemia. SAC (300 mg/kg) was given twice intraperitoneally: 15 min pre-occlusion and 2 h post-occlusion at the time of reperfusion. SAC significantly restored ATP content and the activity of mitochondrial respiratory complexes in SAC treated group which were severely altered in MCAO group. A marked decrease in calcium swelling was observed as a result of SAC treatment. Western blot analysis showed a marked decrease in cytochrome c release as a result of SAC treatment. The status of mitochondrial glutathione (GSH) and glucose 6-phosphate dehydrogenase (G6-PD) was restored by SAC treatment with a significant decrease in mitochondrial lipid peroxidation (LPO), protein carbonyl (PC) and H2O2 content. SAC significantly improved neurological deficits assessed by different scoring methods as compared to MCAO group. Also, the brain edema was significantly reduced. The findings of this study suggest the ability of SAC in functional preservation of ischemic neurovascular units and its therapeutic relevance in the treatment of ischemic stroke.

Oxidative stress and aberrant signaling in aging and cognitive decline

Brain aging is associated with a progressive imbalance between antioxidant defenses and intracellular concentrations of reactive oxygen species (ROS) as exemplified by increases in products of lipid peroxidation, protein oxidation, and DNA oxidation. Oxidative conditions cause not only structural damage but also changes in the set points of redox-sensitive signaling processes including the insulin receptor signaling pathway. In the absence of insulin, the otherwise low insulin receptor signaling is strongly enhanced by oxidative conditions. Autophagic proteolysis and sirtuin activity, in turn, are downregulated by the insulin signaling pathway, and impaired autophagic activity has been associated with neurodegeneration. In genetic studies, impairment of insulin receptor signaling causes spectacular lifespan extension in nematodes, fruit flies, and mice. The predicted effects of age-related oxidative stress on sirtuins and autophagic activity and the corresponding effects of antioxidants remain to be tested experimentally. However, several correlates of aging have been shown to be ameliorated by antioxidants. Oxidative damage to mitochondrial DNA and the electron transport chain, perturbations in brain iron and calcium homeostasis, and changes in plasma cysteine homeostasis may altogether represent causes and consequences of increased oxidative stress. Aging and cognitive decline thus appear to involve changes at multiple nodes within a complex regulatory network.

Temporal relationship of peroxynitrite-induced oxidative damage, calpain-mediated cytoskeletal degradation and neurodegeneration after traumatic brain injury

We assessed the temporal and spatial characteristics of PN-induced oxidative damage and its relationship to calpain-mediated cytoskeletal degradation and neurodegeneration in a severe unilateral controlled cortical impact (CCI) traumatic brain injury (TBI) model. Quantitative temporal time course studies were performed to measure two oxidative damage markers: 3-nitrotyrosine (3NT) and 4-hydroxynonenal (4HNE) at 30 min, 1, 3, 6, 12, 24, 48, 72 h and 7 days after injury in ipsilateral cortex of young adult male CF-1 mice. Secondly, the time course of Ca(++)-activated, calpain-mediated proteolysis was also analyzed using quantitative western-blot measurement of breakdown products of the cytoskeletal protein alpha-spectrin. Finally, the time course of neurodegeneration was examined using de Olmos silver staining. Both oxidative damage markers increased in cortical tissue immediately after injury (30 min) and elevated for the first 3-6 h before returning to baseline. In the immunostaining study, the PN-selective marker, 3NT, and the lipid peroxidation marker, 4HNE, were intense and overlapping in the injured cortical tissue. alpha-Spectrin breakdown products, which were used as biomarker for calpain-mediated cytoskeletal degradation, were also increased after injury, but the time course lagged behind the peak of oxidative damage and did not reach its maximum until 24 h post-injury. In turn, cytoskeletal degradation preceded the peak of neurodegeneration which occurred at 48 h post-injury. These studies have led us to the hypothesis that PN-mediated oxidative damage is an early event that contributes to a compromise of Ca(++) homeostatic mechanisms which causes a massive Ca(++) overload and calpain activation which is a final common pathway that results in post-traumatic neurodegeneration.

Redox control of calcium channels: from mechanisms to therapeutic opportunities

Calcium plays an integral role in cellular function. It is a well-recognized second messenger necessary for signaling cellular responses, but in excessive amounts can be deleterious to function, causing cell death. The main route by which calcium enters the cytoplasm is either from the extracellular compartment or internal addistores via calcium channels. There is good evidence that calcium channels can respond to pharmacological compounds that reduce or oxidize thiol groups on the channel protein. In addition, reactive oxygen species such as hydrogen peroxide and superoxide that can mediate oxidative pathology also mediate changes in channel function via alterations of thiol groups. This review looks at the structure and function of calcium channels, the evidence that changes in cellular redox state mediate changes in channel function, and the role of redox modification of channels in disease processes. Understanding how redox modification of the channel protein alters channel structure and function is providing leads for the design of therapeutic interventions that target oxidative stress responses.

Role of peroxynitrite in secondary oxidative damage after spinal cord injury

Peroxynitrite (PON, ONOO(-)), formed by nitric oxide synthase-generated nitric oxide radical ( NO) and superoxide radical (O(2) (-)), is a crucial player in post-traumatic oxidative damage. In the present study, we determined the spatial and temporal characteristics of PON-derived oxidative damage after a moderate contusion injury in rats. Our results showed that 3-nitrotyrosine (3-NT), a specific marker for PON, rapidly accumulated at early time points (1 and 3 h) and a significant increase compared with sham rats was sustained to 1 week after injury. Additionally, there was a coincident and maintained increase in the levels of protein oxidation-related protein carbonyl and lipid peroxidation-derived 4-hydroxynonenal (4-HNE). The peak increases of 3-NT and 4-HNE were observed at 24 h post-injury. In our immunohistochemical results, the co-localization of 3-NT and 4-HNE results indicates that PON is involved in lipid peroxidative as well as protein nitrative damage. One of the consequences of oxidative damage is an exacerbation of intracellular calcium overload, which activates the cysteine protease calpain leading to the degradation of several cellular targets including cytoskeletal protein (alpha-spectrin). Western blot analysis of alpha-spectrin breakdown products showed that the 145-kDa fragments of alpha-spectrin, which are specifically generated by calpain, were significantly increased as soon as 1 h following injury although the peak increase did not occur until 72 h post-injury. The later activation of calpain is most likely linked to PON-mediated secondary oxidative impairment of calcium homeostasis. Scavengers of PON, or its derived free radical species, may provide an improved antioxidant neuroprotective approach for the treatment of post-traumatic oxidative damage in the injured spinal cord.

The endoplasmic reticulum: folding, calcium homeostasis, signaling, and redox control

The endoplasmic reticulum (ER) plays a major role in regulating synthesis, folding, and orderly transport of proteins. It is also essentially involved in various cellular signaling processes, primarily by its function as a dynamic Ca(2+) store. Compared to the cytosol, oxidizing conditions are found in the ER that allow oxidation of cysteine residues in nascent polypeptide chains to form intramolecular disulfide bonds. However, compounds and enzymes such as PDI that catalyze disulfide bonds become reduced and have to be reoxidized for further catalytic cycles. A number of enzymes, among them products of the ERO1 gene, appear to provide oxidizing equivalents, and oxygen appears to be the final oxidant in aerobic living organisms. Thus, protein oxidation in the ER is connected with generation of reactive oxygen species (ROS). Changes in the redox state and the presence of ROS also affect the Ca(2+) homeostasis by modulating the functionality of ER-based channels and buffering chaperones. In addition, a close relationship exists between oxidative stress and ER stress, which both may activate signaling events leading to a rebalance of folding capacity and folding demand or to cell death. Thus, redox homeostasis appears to be a prerequisite for proper functioning of the ER.

Mitochondrial reactive oxygen species and Ca2+ signaling

Mitochondria are an important source of reactive oxygen species (ROS) formed as a side product of oxidative phosphorylation. The main sites of oxidant production are complex I and complex III, where electrons flowing from reduced substrates are occasionally transferred to oxygen to form superoxide anion and derived products. These highly reactive compounds have a well-known role in pathological states and in some cellular responses. However, although their link with Ca(2+) is well studied in cell death, it has been hardly investigated in normal cytosolic calcium concentration ([Ca(2+)](i)) signals. Several Ca(2+) transport systems are modulated by oxidation. Oxidation increases the activity of inositol 1,4,5-trisphosphate and ryanodine receptors, the main channels releasing Ca(2+) from intracellular stores in response to cellular stimulation. On the other hand, mitochondria are known to control [Ca(2+)](i) signals by Ca(2+) uptake and release during cytosolic calcium mobilization, specially in mitochondria situated close to Ca(2+) release channels. Mitochondrial inhibitors modify calcium signals in numerous cell types, including oscillations evoked by physiological stimulus. Although these inhibitors reduce mitochondrial Ca(2+) uptake, they also impair ROS production in several systems. In keeping with this effect, recent reports show that antioxidants or oxidant scavengers also inhibit physiological calcium signals. Furthermore, there is evidence that mitochondria generate ROS in response to cell stimulation, an effect suppressed by mitochondrial inhibitors that simultaneously block [Ca(2+)](i) signals. Together, the data reviewed here indicate that Ca(2+)-mobilizing stimulus generates mitochondrial ROS, which, in turn, facilitate [Ca(2+)](i) signals, a new aspect in the biology of mitochondria. Finally, the potential implications for biological modeling are discussed.

Angiotensin II, reactive oxygen species, and Ca2+signaling in afferent arterioles

In afferent arteriolar vascular smooth muscle cells, ANG II induces a rise in cytosolic Ca2+([Ca2+]i) via inositol trisphosphate receptor (IP3R) stimulation and by activation of the adenine diphosphate ribose (ADPR) cyclase to form cyclic ADPR, which sensitizes the ryanodine receptor (RyR) to Ca2+. We hypothesize that ANG II stimulation of NAD(P)H oxidases leads to the formation of superoxide anion (O2−·), which, in turn, activates ADPR cyclase. Afferent arterioles were isolated from rat kidney with the magnetized microsphere and sieving technique and loaded with fura-2 to measure [Ca2+]i. ANG II rapidly increased [Ca2+]iby 124 ± 12 nM. In the presence of apocynin, a specific inhibitor of NAD(P)H oxidase assembly, the [Ca2+]iresponse was reduced to 35 ± 5 nM ( P < 0.01). Tempol, a superoxide dismutase mimetic, did not alter the [Ca2+]iresponse to ANG II at a concentration of 10−4M (99 ± 12 nM), but 10−3M tempol reduced the response to 32 ± 3 nM ( P < 0.01). The addition of nicotinamide, an inhibitor of ADPR cyclase, to apocynin or tempol (10−3M) resulted in no further inhibition. Measurement of superoxide production with the fluorescent probe tempo 9-AC showed that ANG II caused an increase of 48 ± 20 arbitrary units; apocynin or diphenyl iodonium (an inhibitor of flavoprotein oxidases) inhibited the response by 94%. Hydrogen peroxide (H2O2) was studied at physiological (10−7M) and higher concentrations. In the presence of H2O2(10−7M), neither baseline [Ca2+]inor the response to ANG II was altered (125 ± 15 nM), whereas H2O2(10−6and 10−5M) inhibited the [Ca2+]iresponse to ANG II by 35 and 46%, respectively. We conclude that ANG II rapidly activates NAD(P)H oxidases of afferent arterioles, leading to the formation of O2−·, which then stimulates ADPR cyclase to form cADPR. cADPR, by sensitizing the RyR to Ca2+, augments the Ca2+response (calcium-induced calcium release) initiated by activation of the IP3R.

Hypoxic pulmonary vasoconstriction

Humans encounter hypoxia throughout their lives. This occurs by destiny in utero, through disease, and by desire, in our quest for altitude. Hypoxic pulmonary vasoconstriction (HPV) is a widely conserved, homeostatic, vasomotor response of resistance pulmonary arteries to alveolar hypoxia. HPV mediates ventilation-perfusion matching and, by reducing shunt fraction, optimizes systemic Po(2). HPV is intrinsic to the lung, and, although modulated by the endothelium, the core mechanism is in the smooth muscle cell (SMC). The Redox Theory for the mechanism of HPV proposes the coordinated action of a redox sensor (the proximal mitochondrial electron transport chain) that generates a diffusible mediator [a reactive O(2) species (ROS)] that regulates an effector protein [voltage-gated potassium (K(v)) and calcium channels]. A similar mechanism for regulating O(2) uptake/distribution is partially recapitulated in simpler organisms and in the other specialized mammalian O(2)-sensitive tissues, including the carotid body and ductus arteriosus. Inhibition of O(2)-sensitive K(v) channels, particularly K(v)1.5 and K(v)2.1, depolarizes pulmonary artery SMCs, activating voltage-gated Ca(2+) channels and causing Ca(2+) influx and vasoconstriction. Downstream of this pathway, there is important regulation of the contractile apparatus' sensitivity to calcium by rho kinase. Controversy remains as to whether hypoxia decreases or increases ROS and which electron transport chain complex generates the ROS (I and/or III). Possible roles for cyclic adenosine diphosphate ribose and an unidentified endothelial constricting factor are also proposed by some groups. Modulation of HPV has therapeutic relevance to cor pulmonale, high-altitude pulmonary edema, and sleep apnea. HPV is clinically exploited in single-lung anesthesia, and its mechanisms intersect with those of pulmonary arterial hypertension.

Endothelin-1, superoxide and adeninediphosphate ribose cyclase in shark vascular smooth muscle

In vascular smooth muscle (VSM) of Squalus acanthias, endothelin-1(ET-1) signals via the ETB receptor. In both shark and mammalian VSM, ET-1 induces a rise in cytosolic Ca2+ concentration([Ca2+]i) via activation of the inositol trisphosphate (IP3) receptor (IP3R) and subsequent release of Ca2+ from the sarcoplasmic reticulum (SR). IP3R-mediated release of SR Ca2+ causes calcium-induced calcium release (CICR) via the ryanodine receptor (RyR), which can be sensitized by cyclic adeninediphosphate ribose (cADPR). cADPR is synthesized from NAD+ by a membrane-bound bifunctional enzyme, ADPR cyclase. We have previously shown that the antagonists of the RyR, Ruthenium Red, high concentrations of ryanodine and 8-Br cADPR, diminish the[Ca2+]i response to ET-1 in shark VSM. To investigate how ET-1 might influence the activity of the ADPR cyclase, we employed inhibitors of the cyclase. To explore the possibility that ET-1-induced production of superoxide (O2.-) might activate the cyclase, we used an inhibitor of NAD(P)H oxidase (NOX), DPI and a scavenger of O2.-, TEMPOL. Anterior mesenteric artery VSM was loaded with fura-2AM to measure [Ca2+]i. In Ca2+-free shark Ringers, ET-1 increased[Ca2+]i by 104±8 nmol l-1. The VSM ADPR cyclase inhibitors, nicotinamide and Zn2+, diminished the response by 62% and 72%, respectively. Both DPI and TEMPOL reduced the response by 63%. The combination of the IP3R antagonists, 2-APB or TMB-8, with DPI or TEMPOL further reduced the response by 83%. We show for the first time that in shark VSM, inhibition of the ADPR cyclase reduces the[Ca2+]i response to ET-1 and that superoxide may be involved in the activation of the cyclase.

Mitochondrial production of oxidants is necessary for physiological calcium oscillations

Mitochondrial involvement in Ca2+ signaling is thought to be due to the effect of mitochondrial Ca2+ removal from and Ca2+ release to cytosolic domains close to ryanodine and IP3 Ca2+ channels. However, mitochondria are a source of low levels of endogenous reactive oxygen species, and Ca2+ release channels are known to be redox-sensitive. In the present work, we studied the role of mitochondrial production of oxygen species in Ca2+ oscillations during physiological stimulation. Mitochondria-targeted antioxidants and mitochondrial inhibitors quickly inhibited calcium oscillations in pancreatic acinar cells stimulated by postprandial levels of the gut hormone cholecystokinin. Confocal microscopy using different redox-sensitive dyes showed that cholecystokinin-induced oscillations are associated with mitochondrial production of reactive oxygen species. This production is inhibited by application of mitochondria-targeted antioxidants and mitochondrial inhibitors. In addition, we found no correlation between inhibition of oscillations and mitochondrial depolarization. We conclude that low level production of reactive oxygen species by mitochondria is a necessary element in the development of Ca2+ oscillations during physiological stimulation. This study unveils a new and unexplored aspect of the participation of mitochondria in calcium signals.

Enhanced production and action of cyclic ADP-ribose during oxidative stress in small bovine coronary arterial smooth muscle

Recent studies in our lab and by others have indicated that cyclic ADP-ribose (cADPR) as a novel second messenger is importantly involved in vasomotor response in various vascular beds. However, the mechanism regulating cADPR production and actions remains poorly understood. The present study determined whether changes in redox status influence the production and action of cADPR in coronary arterial smooth muscle cells (CASMCs) and thereby alters vascular tone in these arteries. HPLC analyses demonstrated that xanthine (X, 40 microM)/xanthine oxidase (XO, 0.1 U/ml), a superoxide-generating system, increased the ADP-ribosyl cyclase activity by 59% in freshly isolated bovine CASMCs. However, hydrogen peroxide (H2O2, 1-100 microM) had no significant effect on ADP-ribosyl cyclase activity. In these CASMCs, X/XO produced a rapid increase in [Ca2+]i (Delta[Ca2+]i=201 nM), which was significantly attenuated by a cADPR antagonist, 8-Br-cADPR. Both inhibition of cADPR production by nicotinamide (Nicot) and blockade of Ca2+-induced Ca2+ release (CICR) by tetracaine (TC) and ryanodine (Rya) significantly reduced X/XO-induced rapid Ca2+ responses. In isolated, perfused, and pressurized small bovine coronary arteries, X at 2.5-80 microM with a fixed XO level produced a concentration-dependent vasoconstriction with a maximal decrease in arterial diameter of 45%. This X/XO-induced vasoconstriction was significantly attenuated by 8-Br-cADPR, Nicot, TC, or Rya. We conclude that superoxide activates cADPR production, and thereby mobilizes intracellular Ca2+ from the SR and produces vasoconstriction in coronary arteries.

Heart resistance to oxidative stress in rats of different genetic strains

In August rats reperfusion after regional myocardial ischemia in situ or intracoronary administration of hydrogen peroxide less significantly suppressed contractile activity of the heart compared to Wistar rats. Activities of catalase and superoxide dismutase in the myocardium during reperfusion remained unchanged in August rats. In Wistar rats a profound inhibition of cardiac function was accompanied by a decrease in enzyme activity.

How does glucose generate oxidative stress in peripheral nerve?

Diabetes-associated oxidative stress is clearly manifest in peripheral nerve, dorsal root, and sympathetic ganglia of the peripheral nervous system and endothelial cells and is implicated in nerve blood flow and conduction deficits, impaired neurotrophic support, changes in signal transduction and metabolism, and morphological abnormalities characteristic of peripheral diabetic neuropathy (diabetic peripheral neuropathy). Hyperglycemia has a key role in oxidative stress in diabetic nerve, whereas the contribution of other factors, such as endoneurial hypoxia, transition metal imbalance, and hyperlipidemia, has not been rigorously proven. It has been suggested that oxidative stress, particularly mitochondrial superoxide production, is responsible for sorbitol pathway hyperactivity, nonenzymatic glycation/glycooxidation, and activation of protein kinase C. However, this concept is not supported by in vivo studies demonstrating the lack of any inhibition of the sorbitol pathway activity in peripheral nerve, retina, and lens by antioxidants, including potent superoxide scavengers. Its has been also hypothesized that aldose reductase (AR) detoxifies lipid peroxidation products, and therefore, the enzyme inhibition in diabetes is detrimental rather than benefical. However, the role for AR in lipid peroxdation product metabolism has never been demonstrated in vivo, and the effects of aldose reductase inhibitors and antioxidants on diabetic peripheral neuropathy are unidirectional, i.e., both classes of agents prevent and correct functional, metabolic, neurotrophic, and morphological changes in diabetic nerve. Growing evidence indicates that AR has a key role in oxidative stress in the peripheral nerve and contributes to superoxide production by the vascular endothelium. The potential mechanisms of this phenonmenon are discussed.

Early cell signaling by the cytotoxic enterotoxin of Aeromonas hydrophila in macrophages

A cytotoxic enterotoxin (Act) of Aeromonas hydrophila is an important virulence factor with hemolytic, cytotoxic and enterotoxic activities. In this report, we demonstrated Act rapidly mobilized calcium from intracellular stores and evoked influx of calcium from the extracellular milieu in macrophages. A direct role of calcium in Act-induced prostaglandin (e.g. PGE(2)) and tumor necrosis factor alpha (TNF alpha) production was demonstrated in macrophages using a cell-permeable calcium chelator BAPTA-AM, which also down-regulated activation of transcription factor NF-kappa B. We showed that Act's capacity to increase PGE(2) and TNF alpha production could be blocked by inhibitors of tyrosine kinases and protein kinase A. In addition, Act caused up-regulation of the DNA repair enzyme redox factor-1 (Ref-1), which potentially could promote DNA binding of the transcription factors allowing modulation of various genes involved in the inflammatory response. Taken together, a link between Act-induced calcium release, regulation of downstream kinase cascades and Ref-1, and activation of NF-kappa B leading to PGE(2) and TNF alpha production was established. Since Act also caused extensive tissue damage, we showed that Act increased reactive oxygen species, and the antioxidant N-acetyl cysteine, blocked Act-induced PGE(2) and TNF alpha production, as well as NF-kappa B nuclear translocation in macrophages. We have demonstrated for the first time early cell signaling initiated in eukaryotic cells by Act, which leads to various biological effects associated with this toxin.