Antioxidant improves smooth muscle sarco/endoplasmic reticulum Ca(2+)-ATPase function and lowers tyrosine nitration in hypercholesterolemia and improves nitric oxide-induced relaxation

Substitution of the SERCA2 Cys674 reactive thiol accelerates atherosclerosis by inducing endoplasmic reticulum stress and inflammation

BACKGROUND AND PURPOSE

The cysteine⁶⁷⁴ (C674) thiol of sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase 2 is easily and irreversibly oxidized under atherosclerotic conditions. However, the contribution of the C674 thiol redox status in the development of atherosclerosis remains unclear. Our goal was to elucidate the possible mechanism involved.

EXPERIMENTAL APPROACH

Heterozygous SERCA2 C674S knock-in mice in which half of the C674 was substituted by serine⁶⁷⁴ (S674) were used to mimic the removal of the reactive C674 thiol which occurs under pathological conditions. Bone marrow-derived macrophages (BMDMs) and cardiac endothelial cells (ECs) were used for intracellular Ca²⁺ , macrophage adhesion, and protein expression analysis. The whole aorta and aortic root were isolated for histological analysis.

KEY RESULTS

Cell culture studies suggest the partial substitution of SERCA2 C674 increased intracellular Ca²⁺ levels and induced ER stress in both BMDMs and ECs. The release of pro-inflammatory factors and macrophage adhesion increased in SKI BMDMs. In ECs, the overexpression of S674 induced endothelial inflammation and promoted macrophage recruitment. SKI mice developed more severe atherosclerotic plaque and macrophage accumulation. Additionally, 4-phenyl butyric acid (PBA), an ER stress inhibitor, suppressed ER stress and inflammatory responses in BMDMs and ECs, and alleviate atherosclerosis in SKI mice.

CONCLUSIONS AND IMPLICATIONS

The substitution of SERCA2 C674 thiol accelerates the development of atherosclerosis by inducing ER stress and inflammation. Our findings highlight the importance of SERCA2 C674 redox state in the context of atherosclerosis and open up a novel therapeutic strategy to combat atherosclerosis.

Roles of ATP and SERCA in the Regulation of Calcium Turnover in Unloaded Skeletal Muscles: Current View and Future Directions

A decrease in skeletal muscle contractile activity or its complete cessation (muscle unloading or disuse) leads to muscle fibers’ atrophy and to alterations in muscle performance. These changes negatively affect the quality of life of people who, for one reason or another, are forced to face a limitation of physical activity. One of the key regulatory events leading to the muscle disuse-induced changes is an impairment of calcium homeostasis, which leads to the excessive accumulation of calcium ions in the sarcoplasm. This review aimed to analyze the triggering mechanisms of calcium homeostasis impairment (including those associated with the accumulation of high-energy phosphates) under various types of muscle unloading. Here we proposed a hypothesis about the regulatory mechanisms of SERCA and IP3 receptors activity during muscle unloading, and about the contribution of these mechanisms to the excessive calcium ion myoplasmic accumulation and gene transcription regulation via excitation–transcription coupling.

The anti-diabetic drug trelagliptin induces vasodilation via activation of Kv channels and SERCA pumps

AIMS

In this study, we investigated the vasodilatory effects of trelagliptin (a dipeptidyl peptidase-4 inhibitor) and its related mechanisms using rabbit aortic rings.

MAIN METHODS

Arterial tone measurement was performed in rabbit thoracic aortic rings.

KEY FINDINGS

Trelagliptin induced vasodilation in a dose-dependent manner. Pretreatment with the ATP-sensitive K⁺ channel inhibitor glibenclamide, large-conductance Ca²⁺-activated K⁺ channel inhibitor paxilline, and inwardly rectifying K⁺ channel inhibitor Ba²⁺ did not affect the vasodilatory effect of trelagliptin. However, pretreatment with the voltage-dependent K⁺ (Kv) channel inhibitors 4-aminopyridine and tetraethylammonium significantly attenuated the vasodilatory effect of trelagliptin, suggesting that the vasodilatory effect of trelagliptin is associated with Kv channel activation. Although pretreatment with Kv1.5 and Kv2.1 subtype inhibitors did not affect the response to trelagliptin, pretreatment with a Kv7.X subtype inhibitor effectively reduced the vasodilatory effect of trelagliptin. Furthermore, sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) pump inhibitors also significantly attenuated the vasodilatory effect of trelagliptin. These effects, however, were not affected by pretreatment with Ca²⁺ channel inhibitors, adenylyl cyclase/PKA inhibitors, guanylyl cyclase/PKG inhibitors, or removal of the endothelium.

SIGNIFICANCE

From these results, we concluded that the vasodilatory effect of trelagliptin was associated with the activation of Kv channels (primary the Kv7.X subtype) and SERCA pump regardless of other K⁺ channels, Ca²⁺ channels, cAMP/PKA-related or cGMP/PKG-related signaling pathways, and the endothelium. Therefore, caution is required when prescribing trelagliptin to the patients with hypotension and diabetes.

Redox Regulation of the Microcirculation

The microcirculation maintains tissue homeostasis through local regulation of blood flow and oxygen delivery. Perturbations in microvascular function are characteristic of several diseases and may be early indicators of pathological changes in the cardiovascular system and in parenchymal tissue function. These changes are often mediated by various reactive oxygen species and linked to disruptions in pathways such as vasodilation or angiogenesis. This overview compiles recent advances relating to redox regulation of the microcirculation by adopting both cellular and functional perspectives. Findings from a variety of vascular beds and models are integrated to describe common effects of different reactive species on microvascular function. Gaps in understanding and areas for further research are outlined. © 2020 American Physiological Society. Compr Physiol 10:229-260, 2020.

Redox Regulation of Calpains: Consequences on Vascular Function

SIGNIFICANCE

Calpains (CAPNs) are a family of calcium-activated cysteine proteases. The ubiquitous isoforms CAPN1 and CAPN2 have been involved in the maintenance of vascular integrity, but uncontrolled CAPN activation plays a role in the pathogenesis of vascular diseases. Recent Advances: It is well accepted that chronic and acute overproduction of reactive oxygen species (ROS) is associated with the development of vascular diseases. There is increasing evidence that ROS can also affect the CAPN activity, suggesting CAPN as a potential link between oxidative stress and vascular disease.

CRITICAL ISSUES

The physiopathological relevance of ROS in regulating the CAPN activity is not fully understood but seems to involve direct effects on CAPNs, redox modifications of CAPN substrates, as well as indirect effect on CAPNs via changes in Ca²⁺ levels. Finally, CAPNs can also stimulate ROS production; however, data showing in which context ROS are the causes or the consequences of CAPN activation are missing.

FUTURE DIRECTIONS

Detailed characterization of the molecular mechanisms underlying the regulation of the different members of the CAPN system by specific ROS would help understanding the pathophysiological role of CAPN in the modulation of the vascular function. Moreover, given that CAPNs have been found in different cellular compartments such as mitochondria and nucleus as well as in the extracellular space, identification of new CAPN targets as well as their functional consequences would add new insights in the function of these enigmatic proteases.

Endothelial Cell Redox Regulation of Ischemic Angiogenesis

The endothelium produces and responds to reactive oxygen and nitrogen species (RONS), providing important redox regulation to the cardiovascular system in physiology and disease. In no other situation are RONS more critical than in the response to tissue ischemia. Here, tissue healing requires growth factor-mediated angiogenesis that is in part dependent on low levels of RONS, which paradoxically must overcome the damaging effects of high levels of RONS generated as a result of ischemia. Although the generation of endothelial cell RONS in hypoxia/reoxygenation is acknowledged, the mechanism for their role in angiogenesis is still poorly understood. During ischemia, the major low molecular weight thiol glutathione (GSH) reacts with RONS and protein cysteines, producing GSH-protein adducts. Recent data indicate that GSH adducts on certain proteins are essential to growth factor responses in endothelial cells. Genetic deletion of the enzyme glutaredoxin-1, which selectively removes GSH protein adducts, improves, whereas its overexpression impairs revascularization of the ischemic hindlimb of mice. Ischemia-induced GSH adducts on specific cysteine residues of several proteins, including p65 NF-kB and the sarcoplasmic reticulum calcium ATPase 2, evidently promote ischemic angiogenesis. Identifying the specific proteins in the redox response to ischemia has provided therapeutic opportunities to improve clinical outcomes of ischemia.

Kcnj11 Ablation Is Associated With Increased Nitro-Oxidative Stress During Ischemia-Reperfusion Injury: Implications for Human Ischemic Cardiomyopathy

BACKGROUND

Despite increased secondary cardiovascular events in patients with ischemic cardiomyopathy (ICM), the expression of innate cardiac protective molecules in the hearts of patients with ICM is incompletely characterized. Therefore, we used a nonbiased RNAseq approach to determine whether differences in cardiac protective molecules occur with ICM.

METHODS AND RESULTS

RNAseq analysis of human control and ICM left ventricular samples demonstrated a significant decrease in KCNJ11 expression with ICM. KCNJ11 encodes the Kir6.2 subunit of the cardioprotective K_ATP channel. Using wild-type mice and kcnj11-deficient (kcnj11-null) mice, we examined the effect of kcnj11 expression on cardiac function during ischemia-reperfusion injury. Reactive oxygen species generation increased in kcnj11-null hearts above that found in wild-type mice hearts after ischemia-reperfusion injury. Continuous left ventricular pressure measurement during ischemia and reperfusion demonstrated a more compromised diastolic function in kcnj11-null compared with wild-type mice during reperfusion. Analysis of key calcium-regulating proteins revealed significant differences in kcnj11-null mice. Despite impaired relaxation, kcnj11-null hearts increased phospholamban Ser16 phosphorylation, a modification that results in the dissociation of phospholamban from sarcoendoplasmic reticulum Ca²⁺, thereby increasing sarcoendoplasmic reticulum Ca²⁺-mediated calcium reuptake. However, kcnj11-null mice also had increased 3-nitrotyrosine modification of the sarcoendoplasmic reticulum Ca²⁺-ATPase, a modification that irreversibly impairs sarcoendoplasmic reticulum Ca²⁺ function, thereby contributing to diastolic dysfunction.

CONCLUSIONS

KCNJ11 expression is decreased in human ICM. Lack of kcnj11 expression increases peroxynitrite-mediated modification of the key calcium-handling protein sarcoendoplasmic reticulum Ca²⁺-ATPase after myocardial ischemia-reperfusion injury, contributing to impaired diastolic function. These data suggest a mechanism for ischemia-induced diastolic dysfunction in patients with ICM.

Early energy metabolism-related molecular events in skeletal muscle of diabetic rats: The effects of l-arginine and SOD mimic

Considering the vital role of skeletal muscle in control of whole-body metabolism and the severity of long-term diabetic complications, we aimed to reveal the molecular pattern of early diabetes-related skeletal muscle phenotype in terms of energy metabolism, focusing on regulatory mechanisms, and the possibility to improve it using two redox modulators, l-arginine and superoxide dismutase (SOD) mimic. Alloxan-induced diabetic rats (120 mg/kg) were treated with l-arginine or the highly specific SOD mimic, M40403, for 7 days. As appropriate controls, non-diabetic rats received the same treatments. We found that l-arginine and M40403 restored diabetes-induced impairment of phospho-5'-AMP-activated protein kinase α (AMPKα) signaling by upregulating AMPKα protein itself and its downstream effectors, peroxisome proliferator-activated receptor-γ coactivator-1α and nuclear respiratory factor 1. Also, there was a restitution of the protein levels of oxidative phosphorylation components (complex I, complex II and complex IV) and mitofusin 2. Furthermore, l-arginine and M40403 induced translocation of glucose transporter 4 to the membrane and upregulation of protein of phosphofructokinase and acyl coenzyme A dehydrogenase, diminishing negative diabetic effects on limiting factors of glucose and lipid metabolism. Both treatments abolished diabetes-induced downregulation of sarcoplasmic reticulum calcium-ATPase proteins (SERCA 1 and 2). Similar effects of l-arginine and SOD mimic treatments suggest that disturbances in the superoxide/nitric oxide ratio may be responsible for skeletal muscle mitochondrial and metabolic impairment in early diabetes. Our results provide evidence that l-arginine and SOD mimics have potential in preventing and treating metabolic disturbances accompanying this widespread metabolic disease.

Distinct Myocardial Mechanisms Underlie Cardiac Dysfunction in Endotoxemic Male and Female Mice

In male mice, sepsis-induced cardiomyopathy develops as a result of dysregulation of myocardial calcium (Ca) handling, leading to depressed cellular Ca transients (ΔCai). ΔCai depression is partially due to inhibition of sarcoplasmic reticulum Ca ATP-ase (SERCA) via oxidative modifications, which are partially opposed by cGMP generated by the enzyme soluble guanylyl cyclase (sGC). Whether similar mechanisms underlie sepsis-induced cardiomyopathy in female mice is unknown.Male and female C57Bl/6J mice (WT), and mice deficient in the sGC α1 subunit activity (sGCα1), were challenged with lipopolysaccharide (LPS, ip). LPS induced mouse death and cardiomyopathy (manifested as the depression of left ventricular ejection fraction by echocardiography) to a similar degree in WT male, WT female, and sGCα1 male mice, but significantly less in sGCα1 female mice. We measured sarcomere shortening and ΔCai in isolated, externally paced cardiomyocytes, at 37°C. LPS depressed sarcomere shortening in both WT male and female mice. Consistent with previous findings, in male mice, LPS induced a decrease in ΔCai (to 30 ± 2% of baseline) and SERCA inhibition (manifested as the prolongation of the time constant of Ca decay, τCa, to 150 ± 5% of baseline). In contrast, in female mice, the depression of sarcomere shortening induced by LPS occurred in the absence of any change in ΔCai, or SERCA activity. This suggested that, in female mice, the causative mechanism lies downstream of the Ca transients, such as a decrease in myofilament sensitivity for Ca. The depression of sarcomere shortening shortening after LPS was less severe in female sGCα1 mice than in WT female mice, indicating that cGMP partially mediates cardiomyocyte dysfunction.These results suggest, therefore, that LPS-induced cardiomyopathy develops through distinct sex-specific myocardial mechanisms. While in males LPS induces sGC-independent decrease in ΔCai, in female mice LPS acts downstream of ΔCai, possibly via sGC-dependent myofilament dysfunction.

ROS and intracellular ion channels

Oxidative stress is a well-known driver of numerous pathological processes involving protein and lipid peroxidation and DNA damage. The resulting increase of pro-apoptotic pressure drives tissue damage in a host of conditions, including ischemic stroke and reperfusion injury, diabetes, death in acute pancreatitis and neurodegenerative diseases. Somewhat less frequently discussed, but arguably as important, is the signaling function of oxidative stress stemming from the ability of oxidative stress to modulate ion channel activity. The evidence for the modulation of the intracellular ion channels and transporters by oxidative stress is constantly emerging and such evidence suggests new regulatory and pathological circuits that can be explored towards new treatments for diseases in which oxidative stress is an issue. In this review we summarize the current knowledge on the effects of oxidative stress on the intracellular ion channels and transporters and their role in cell function.

Atherosclerosis differentially affects calcium signalling in endothelial cells from aortic arch and thoracic aorta in Apolipoprotein E knockout mice

Apolipoprotein‐E knockout (ApoE^−/−) mice develop hypercholesterolemia and are a useful model of atherosclerosis. Hypercholesterolemia alters intracellular Ca²⁺ signalling in vascular endothelial cells but our understanding of these changes, especially in the early stages of the disease process, is limited. We therefore determined whether carbachol‐mediated endothelial Ca²⁺ signals differ in plaque‐prone aortic arch compared to plaque‐resistant thoracic aorta, of wild‐type and ApoE^−/− mice, and how this is affected by age and the presence of hypercholesterolemia. The extent of plaque development was determined using en‐face staining with Sudan IV. Tissues were obtained from wild‐type and ApoE^−/− mice at 10 weeks (pre‐plaques) and 24 weeks (established plaques). We found that even before development of plaques, significantly increased Ca²⁺ responses were observed in arch endothelial cells. Even with aging and plaque formation, ApoE^−/− thoracic responses were little changed, however a significantly enhanced Ca²⁺ response was observed in arch, both adjacent to and away from lesions. In wild‐type mice of any age, 1–2% of cells had oscillatory Ca²⁺ responses. In young ApoE^−/− and plaque‐free regions of older ApoE^−/−, this is unchanged. However a significant increase in oscillations (~13–15%) occurred in thoracic and arch cells adjacent to lesions in older mice. Our data suggest that Ca²⁺ signals in endothelial cells show specific changes both before and with plaque formation, that these changes are greatest in plaque‐prone aortic arch cells, and that these changes will contribute to the reported deterioration of endothelium in atherosclerosis.

We have investigated aortic endothelial cell calcium signalling changes in the Apolipoprotein E knockout mouse model of atherosclerosis. Our data show that calcium signals in endothelial cells undergo specific changes both before and with plaque formation, that these changes are greater in plaque‐prone aortic arch than in plaque‐resistant thoracic aorta, and that these changes will contribute to the reported deterioration of endothelium in atherosclerosis.

Cytosolic H2O2 mediates hypertrophy, apoptosis, and decreased SERCA activity in mice with chronic hemodynamic overload

Oxidative stress in the myocardium plays an important role in the pathophysiology of hemodynamic overload. The mechanism by which reactive oxygen species (ROS) in the cardiac myocyte mediate myocardial failure in hemodynamic overload is not known. Accordingly, our goals were to test whether myocyte-specific overexpression of peroxisomal catalase (pCAT) that localizes in the sarcoplasm protects mice from hemodynamic overload-induced failure and prevents oxidation and inhibition of sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA), an important sarcoplasmic protein. Chronic hemodynamic overload was caused by ascending aortic constriction (AAC) for 12 wk in mice with myocyte-specific transgenic expression of pCAT. AAC caused left ventricular hypertrophy and failure associated with a generalized increase in myocardial oxidative stress and specific oxidative modifications of SERCA at cysteine 674 and tyrosine 294/5. pCAT overexpression ameliorated myocardial hypertrophy and apoptosis, decreased pathological remodeling, and prevented the progression to heart failure. Likewise, pCAT prevented oxidative modifications of SERCA and increased SERCA activity without changing SERCA expression. Thus cardiac myocyte-restricted expression of pCAT effectively ameliorated the structural and functional consequences of chronic hemodynamic overload and increased SERCA activity via a post-translational mechanism, most likely by decreasing inhibitory oxidative modifications. In pressure overload-induced heart failure cardiac myocyte cytosolic ROS play a pivotal role in mediating key pathophysiologic events including hypertrophy, apoptosis, and decreased SERCA activity.

SERCA Cys674 sulphonylation and inhibition of L-type Ca2+ influx contribute to cardiac dysfunction in endotoxemic mice, independent of cGMP synthesis

The goal of this study was to identify the cellular mechanisms responsible for cardiac dysfunction in endotoxemic mice. We aimed to differentiate the roles of cGMP [produced by soluble guanylyl cyclase (sGC)] versus oxidative posttranslational modifications of Ca(2+) transporters. C57BL/6 mice [wild-type (WT) mice] were administered lipopolysaccharide (LPS; 25 μg/g ip) and euthanized 12 h later. Cardiomyocyte sarcomere shortening and Ca(2+) transients (ΔCai) were depressed in LPS-challenged mice versus baseline. The time constant of Ca(2+) decay (τCa) was prolonged, and sarcoplasmic reticulum Ca(2+) load (CaSR) was depressed in LPS-challenged mice (vs. baseline), indicating decreased activity of sarco(endo)plasmic Ca(2+)-ATPase (SERCA). L-type Ca(2+) channel current (ICa,L) was also decreased after LPS challenge, whereas Na(+)/Ca(2+) exchange activity, ryanodine receptors leak flux, or myofilament sensitivity for Ca(2+) were unchanged. All Ca(2+)-handling abnormalities induced by LPS (the decrease in sarcomere shortening, ΔCai, CaSR, ICa,L, and τCa prolongation) were more pronounced in mice deficient in the sGC main isoform (sGCα1(-/-) mice) versus WT mice. LPS did not alter the protein expression of SERCA and phospholamban in either genotype. After LPS, phospholamban phosphorylation at Ser(16) and Thr(17) was unchanged in WT mice and was increased in sGCα1(-/-) mice. LPS caused sulphonylation of SERCA Cys(674) (as measured immunohistochemically and supported by iodoacetamide labeling), which was greater in sGCα1(-/-) versus WT mice. Taken together, these results suggest that cardiac Ca(2+) dysregulation in endotoxemic mice is mediated by a decrease in L-type Ca(2+) channel function and oxidative posttranslational modifications of SERCA Cys(674), with the latter (at least) being opposed by sGC-released cGMP.

Impairment of calcium ATPases by high glucose and potential pharmacological protection

The review deals with impairment of Ca(2+)-ATPases by high glucose or its derivatives in vitro, as well as in human diabetes and experimental animal models. Acute increases in glucose level strongly correlate with oxidative stress. Dysfunction of Ca(2+)-ATPases in diabetic and in some cases even in nondiabetic conditions may result in nitration of and in irreversible modification of cysteine-674. Nonenyzmatic protein glycation might lead to alteration of Ca(2+)-ATPase structure and function contributing to Ca(2+) imbalance and thus may be involved in development of chronic complications of diabetes. The susceptibility to glycation is probably due to the relatively high percentage of lysine and arginine residues at the ATP binding and phosphorylation domains. Reversible glycation may develop into irreversible modifications (advanced glycation end products, AGEs). Sites of SERCA AGEs are depicted in this review. Finally, several mechanisms of prevention of Ca(2+)-pump glycation, and their advantages and disadvantages are discussed.

Hyperuricemia induces endothelial dysfunction via mitochondrial Na+/Ca2+ exchanger-mediated mitochondrial calcium overload

BACKGROUND

Uric acid (UA) has proven to be a causal agent in endothelial dysfunction in which ROS production plays an important role. Calcium overload in mitochondria can promote the mitochondrial production of ROS. We hypothesize that calcium transduction in mitochondria contributes to UA-induced endothelial dysfunction.

METHODS AND RESULTS

We first demonstrated that high concentrations of UA cause endothelial dysfunction, marked by a reduction in eNOS protein expression and NO release in vitro. We further found that a high concentration of UA increased levels of [Ca2+]mito, total intracellular ROS, H2O2, and mitochondrial O2·-, and Δψmito but not the [Ca2+]cyt level. When the mitochondrial calcium channels NCXmito and MCU were blocked by CGP-37157 and Ru360, respectively, the UA-induced increases in the levels of [Ca2+]mito and total intracellular ROS were significantly reduced. Mitochondrial levels of O2·- and Δψmito were reduced by inhibition of NCXmito but not of MCU. Moreover, inhibition of NCXmito, but not of MCU, blocked the UA-induced reductions in eNOS protein expression and NO release.

CONCLUSIONS

The increased generation of mitochondrial O2·- induced by a high concentration of UA is triggered by mitochondrial calcium overload and ultimately leads to endothelial dysfunction. In this process, the activation of NCXmito is the major cause of the influx of calcium into mitochondria. Our results provide a new pathophysiological mechanism for UA-induced endothelial dysfunction and may offer a new therapeutic target for clinicians.

Flavonoids in prevention of diseases with respect to modulation of Ca-pump function

Flavonoids, natural phenolic compounds, are known as agents with strong antioxidant properties. In many diseases associated with oxidative/nitrosative stress and aging they provide multiple biological health benefits. Ca²⁺-ATPases belong to the main calcium regulating proteins involved in the balance of calcium homeostasis, which is impaired in oxidative/nitrosative stress and related diseases or aging. The mechanisms of Ca²⁺-ATPases dysfunction are discussed, focusing on cystein oxidation and tyrosine nitration. Flavonoids act not only as antioxidants but are also able to bind directly to Ca²⁺-ATPases, thus changing their conformation, which results in modulation of enzyme activity.

Dysfunction of Ca²⁺-ATPases is summarized with respect to their posttranslational and conformational changes in diseases related to oxidative/nitrosative stress and aging. Ca²⁺-ATPases are discussed as a therapeutic tool and the possible role of flavonoids in this process is suggested.

High glucose induced rat aorta vascular smooth muscle cell oxidative injury: involvement of protein tyrosine nitration

The alteration and further damage of vascular smooth muscle function have been implicated in the development of vascular complications and diabetes. Little is known about protein tyrosine nitration in vascular smooth muscle cell injury induced by high glucose. In this article, vascular smooth muscle cell was exposed to 30 and 40 mM high glucose for 72 h, and then the cell injury in vascular smooth muscle cell induced by high glucose was studied. It was found that high glucose stimulated vascular smooth muscle cell injury in a dose-dependent manner, including decreasing intracellular and extracellular glutathione contents, increasing malondialdehyde and intracellular reactive oxygen species content, increasing the production of nitric oxide (increased nitrite content in cell and medium), as well as increasing protein tyrosine nitration. By comparing protein tyrosine nitration induced by high glucose conditions and extrinsic factors (hemin-nitrite-glucose oxidase system and 3-morpholinosydnonimine), it may be speculated that protein is nitrated selectively, and specific protein tyrosine nitration is involved in diabetic vascular complications.

Ca2+ regulatory mechanisms of exercise protection against coronary artery disease in metabolic syndrome and diabetes

Chronic exercise attenuates coronary artery disease (CAD) in humans largely independent of reductions in risk factors; thus major protective mechanisms of exercise are directly within the coronary vasculature. Further, tight control of diabetes, e.g., blood glucose, can be detrimental. Accordingly, knowledge of mechanisms by which exercise attenuates diabetic CAD could catalyze development of molecular therapies. Exercise attenuates CAD (atherosclerosis) and restenosis in miniature swine models, which enable precise control of exercise parameters (intensity, duration, and frequency) and characterization of the metabolic syndrome (MetS) and diabetic milieu. Intracellular Ca(2+) is a pivotal second messenger for coronary smooth muscle (CSM) excitation-contraction and excitation-transcription coupling that modulates CSM proliferation, migration, and calcification. CSM of diabetic dyslipidemic Yucatan swine have impaired Ca(2+) extrusion via the plasmalemma Ca(2+) ATPase (PMCA), downregulation of L-type voltage-gated Ca(2+) channels (VGCC), increased Ca(2+) sequestration by the sarcoplasmic reticulum (SR) Ca(2+) ATPase (SERCA), increased nuclear Ca(2+) localization, and greater activation of K channels by Ca(2+) release from the SR. Endurance exercise training prevents Ca(2+) transport changes with virtually no effect on the diabetic milieu (glucose, lipids). In MetS Ossabaw swine transient receptor potential canonical (TRPC) channels are upregulated and exercise training reverses expression and TRPC-mediated Ca(2+) influx with almost no change in the MetS milieu. Overall, exercise effects on Ca(2+) signaling modulate CSM phenotype. Future studies should 1) selectively target key Ca(2+) transporters to determine definitively their causal role in atherosclerosis and 2) combine mechanistic studies with clinical outcomes, e.g., reduction of myocardial infarction.

Pycnogenol and Ginkgo biloba extract: effect on peroxynitrite-oxidized sarcoplasmic reticulum Ca-ATPase

The effect of two natural standardized plant extracts, Pycnogenol(®) and EGb 761, on sarcoplasmic reticulum Ca(2+)-ATPase (SERCA) activity and posttranslational modifications induced by peroxynitrite was investigated to assess their possible protective role. EGb 761 was found to have a protective effect on SERCA activity in the concentration range of 5-40 µg/ml. On the other hand, Pycnogenol(®) caused a decrease of SERCA activity at concentrations of 25 µg/ml. EGb 761 did not prevent protein carbonyl formation upon oxidation with peroxynitrite. On the contrary, Pycnogenol(®) at the concentrations of 5 and 10 µg/ml significantly decreased the level of protein carbonyls by 44% and 54%, respectively. Neither Pycnogenol(®) nor EGb 761 exerted a protective effect against thiol group oxidation.The plant extracts studied modulated peroxynitrite-injured SERCA activity by different ways and failed to correlate with posttranslational modifications. Their effect seems to be associated with their ability to change SERCA conformation rather than by their antioxidant capacity.

Antioxidant network expression abrogates oxidative posttranslational modifications in mice

Antioxidant enzymatic pathways form a critical network that detoxifies ROS in response to myocardial stress or injury. Genetic alteration of the expression levels of individual enzymes has yielded mixed results with regard to attenuating in vivo myocardial ischemia-reperfusion injury, an extreme oxidative stress. We hypothesized that overexpression of an antioxidant network (AON) composed of SOD1, SOD3, and glutathione peroxidase (GSHPx)-1 would reduce myocardial ischemia-reperfusion injury by limiting ROS-mediated lipid peroxidation and oxidative posttranslational modification (OPTM) of proteins. Both ex vivo and in vivo myocardial ischemia models were used to evaluate the effect of AON expression. After ischemia-reperfusion injury, infarct size was significantly reduced both ex vivo and in vivo, ROS formation, measured by dihydroethidium staining, was markedly decreased, ROS-mediated lipid peroxidation, measured by malondialdehyde production, was significantly limited, and OPTM of total myocardial proteins, including fatty acid-binding protein and sarco(endo)plasmic reticulum Ca(²+)-ATPase (SERCA)2a, was markedly reduced in AON mice, which overexpress SOD1, SOD3, and GSHPx-1, compared with wild-type mice. These data demonstrate that concomitant SOD1, SOD3, and GSHPX-1 expression confers marked protection against myocardial ischemia-reperfusion injury, reducing ROS, ROS-mediated lipid peroxidation, and OPTM of critical cardiac proteins, including cardiac fatty acid-binding protein and SERCA2a.

Vascular oxidative stress: the common link in hypertensive and diabetic vascular disease

Vascular disease in hypertension and diabetes is associated with increased oxidants. The oxidants arise from NADPH oxidase, xanthine oxidase, and mitochondria. Superoxide anion and hydrogen peroxide are produced by both leukocytes and vascular cells. Nitric oxide is produced in excess by inducible nitric oxide synthase, and the potent oxidant, peroxynitrite, is formed from superoxide and nitric oxide. The damage to proteins caused by oxidants is selective, affecting specific oxidant-sensitive amino acid residues. With some important vascular proteins, for example, endothelial nitric oxide synthase, prostacycline synthase, and superoxide dismutase, oxidation of a single susceptible amino acid inactivates the enzyme. The beneficial effects of antioxidants, at least in animal models of hypertension and diabetes, can in part be ascribed to protection of these and other proteins. Mutant proteins lacking their reactive constituent can recapitulate some disease phenotypes suggesting a pathogenic role of the oxidation. Thus, many of the shared functional abnormalities of hypertensive and diabetic blood vessels may be caused by oxidants. Although studies using antioxidants have failed in patients, the successful treatment of vascular disease with HMG-CoA reductase inhibitors, thromboxane A2 antagonists, and polyphenols may depend on their anti-inflammatory effects and ability to decrease production of damaging oxidants.

Cardiac contractile dysfunction during acute hyperglycemia due to impairment of SERCA by polyol pathway-mediated oxidative stress

Hyperglycemia is an indication of poor outcome for heart attack patients, even for nondiabetic patients with stress-induced hyperglycemia. Previous studies showed that inhibition of aldose reductase, the first and rate-limiting enzyme of the polyol pathway, attenuated contractile dysfunction in diabetic animals, but the mechanism is unclear. We therefore wanted to find out whether the polyol pathway also contributes to acute hyperglycemia-induced cardiac contractile dysfunction, and determine the mechanism involved. Rat hearts were isolated and retrogradely perfused with Krebs buffer containing either normal or high concentrations of glucose for 2 h. Short exposure to high-glucose medium led to contractile dysfunction as indicated by decreased -dP/dt(max), as well as elevation in left ventricular end-diastolic pressure. Cardiomyocytes incubated in high-glucose medium showed abnormal Ca2+ signaling, most likely because of decreased activity of sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) inactivated by oxidative stress. Inhibition of aldose reductase or sorbitol dehydrogenase, the second enzyme in the polyol pathway, ameliorated contractile dysfunction, attenuated oxidative stress, and normalized Ca2+ signaling and SERCA activity caused by high glucose, indicating that the polyol pathway is the major contributor to acute hyperglycemia-induced oxidative stress leading to the inactivation of SERCA and contractile dysfunction.

Reduction of AMP-activated protein kinase alpha2 increases endoplasmic reticulum stress and atherosclerosis in vivo

BACKGROUND

Aberrant endoplasmic reticulum (ER) stress is associated with several cardiovascular diseases, including atherosclerosis. The mechanism by which aberrant ER stress develops is poorly understood. This study investigated whether dysfunction of AMP-activated protein kinase (AMPK) causes aberrant ER stress and atherosclerosis in vivo.

METHODS AND RESULTS

Human umbilical vein endothelial cells and mouse aortic endothelial cells from AMPK-deficient mice were used to assess the level of ER stress with Western blotting. Reduction of AMPKalpha2 expression significantly increased the level of ER stress in human umbilical vein endothelial cells. In addition, mouse aortic endothelial cells from AMPKalpha2 knockout (AMPKalpha2(-/-)) mice had higher expression of markers of ER stress and increased levels of intracellular Ca2+. These phenotypes were abolished by adenovirally overexpressing constitutively active AMPK mutants (Ad-AMPK-CA) or by transfecting sarcoendoplasmic reticulum calcium ATPase (SERCA). Inhibition of SERCA induced ER stress in endothelial cells. Furthermore, reduction of AMPKalpha expression suppressed SERCA activity. In addition, SERCA activity was significantly reduced concomitantly with increased oxidation of SERCA in mouse aortic endothelial cells from AMPKalpha2(-/-) mice. Both of these phenotypes were abolished by adenovirally overexpressing Ad-AMPK-CA. Furthermore, Tempol, which restored SERCA activity and decreased oxidized SERCA levels, markedly reduced the level of ER stress in mouse aortic endothelial cells from AMPKalpha2(-/-) mice. Finally, oral administration of tauroursodeoxycholic acid, a chemical chaperone that inhibits ER stress, significantly reduced both ER stress and aortic lesion development in low-density lipoprotein receptor- and AMPKalpha2-deficient mice.

CONCLUSIONS

These results suggest that AMPK functions as a physiological suppressor of ER stress by maintaining SERCA activity and intracellular Ca2+ homeostasis.

Targeting the redox regulation of SERCA in vascular physiology and disease

The sarco/endoplasmic reticulum calcium ATPase (SERCA) is essential for the control of intracellular free Ca(2+) levels. Although the importance for this enzyme in cardiac myocytes is well recognized, it is only recently that SERCA has been identified as an important effector of nitric oxide (NO) action in vascular cells. NO can stimulate the uptake of cytosolic Ca(2+) via SERCA by adducting glutathione to the reactive cysteine-674. Mutation of this single amino acid prevents the stimulation of Ca(2+) uptake by NO, as well as its ability to inhibit smooth muscle cell functions including migration. NO function is impaired in a variety of cardiovascular diseases, including diabetes, hypercholesterolemia, and atherosclerosis, which are all associated with SERCA dysfunction caused by the increased oxidants in these diseases. Targeting the oxidant sources in vascular diseases to prevent SERCA from being oxidized and/or increasing the expression of SERCA may improve vascular disease development.

Modulation of vascular sarco/endoplasmic reticulum calcium ATPase in cardiovascular pathophysiology

Endothelial dysfunction associated with decreased nitric oxide (NO) bioactivity is a major feature of vascular diseases such as atherosclerosis or diabetes. Sodium nitroprusside (SNP)-induced relaxation is entirely dependent on cyclic guanosine monophosphate (cGMP) and preserved in atherosclerosis, suggesting that smooth muscle response to NO donor is intact. However, NO gas activates both cGMP-dependent and -independent signal pathways in vascular smooth muscle cells, and oxidative stress associated with vascular diseases selectively impairs cGMP-independent relaxation to NO. Sarco/endoplasmic reticulum Ca(2+) ATPase (SERCA), which regulates intracellular Ca(2+) levels by pumping Ca(2+) into store, is a major cGMP-independent target for NO. Physiological levels of reactive nitrogen species (RNS) S-glutathiolate SERCA at Cys674 to increase its activity, and the augmentation of RNS in vascular diseases irreversibly oxidizes Cys674 or nitrates tyrosine residues at Tyr296-Tyr297, which are associated with loss of function. S-glutathiolation of various proteins by NO can explain redox-sensitive cGMP-independent actions, and oxidative inactivation of target proteins for NO can be associated with the pathogenesis of cardiovascular diseases. Oxidative inactivation of SERCA is also implicated with dysregulation of smooth muscle migration, promotion of platelet aggregation, and impairment of cardiac function, which can be implicated with restenosis, pathological angiogenesis, thrombosis, as well as heart failure. Analysis of posttranslational oxidative modifications of SERCA and the preservation of SERCA function can be novel strategies against cardiovascular diseases associated with oxidative stress.

Polyol pathway impairs the function of SERCA and RyR in ischemic-reperfused rat hearts by increasing oxidative modifications of these proteins

A number of studies have shown that the polyol pathway, consisting of aldose reductase (AR) and sorbitol dehydrogenase (SDH), contributes to ischemia-reperfusion (I/R)-induced myocardial infarction due to depletion of ATP. In this report we show that the polyol pathway in I/R heart also contributes to the impairment of sacro/endoplasmic reticulum Ca(2+)-ATPase (SERCA) and ryanodine receptor (RyR), two key players in Ca(2+) signaling that regulate cardiac contraction. Rat hearts were isolated and retrogradely perfused with either Krebs' buffer containing 1 microM AR inhibitor, zopolrestat, or 200 nM SDH inhibitor, CP-170,711, and challenged by 30 min of regional ischemia and 45 min of reperfusion. We found that post-ischemic contractile function of the isolated perfused hearts was improved by pharmacological inhibition of the polyol pathway. I/R-induced contractile dysfunction is most likely due to impairment in Ca(2+) signaling and the activities of SERCA and RyR. All these abnormalities were significantly ameliorated by treatment with ARI or SDI. We showed that the polyol pathway activities increase the level of peroxynitrite, which enhances the tyrosine nitration of SERCA and irreversibly modifies it to form SERCAC674-SO(3)H. This leads to reduced level of S-glutathiolated SERCA, contributing to its inactivation. The polyol pathway activities also deplete the level of GSH, leading to decreased active RyR, the S-glutathiolated RyR. Thus, in I/R heart, inhibition of polyol pathway improved the function of SERCA and RyR by protecting them from irreversible oxidation.

Redox modulation of Ca2+ signaling in human endothelial and smooth muscle cells in pre-eclampsia

Pre-eclampsia (PE) is a leading cause of maternal hypertension in pregnancy and is associated with fetal growth restriction, premature birth, and fetal and maternal mortality. Activation and dysfunction of the maternal and fetal endothelium in PE appears to be a consequence of increased oxidative stress, resulting from elevated levels of circulating lipid peroxides. Accumulating evidence implicates reactive oxygen species (ROS) in the pathogenesis of vascular dysfunction in PE, perhaps involving a disturbance in intracellular Ca(2+) signaling. Several ion-transport pathways are highly sensitive to oxidative stress, and the resulting modulation of ion transport by ROS will affect intracellular Ca(2+) homeostasis. We review the evidence that changes in ion transport induced by ROS may be linked with abnormalities in Ca(2+)-mediated signal transduction, leading to endothelial and smooth muscle dysfunction in maternal and fetal circulations in PE. As dysregulation of Ca(2+) signaling in fetal umbilical endothelial cells is maintained in culture and embryonic, fetal, and postnatal development is affected by the cellular redox state, we hypothesize that impaired redox signaling in PE may influence "programming" of the fetal cardiovascular system and endothelial function in adulthood.

Reactive nitrogen species: molecular mechanisms and potential significance in health and disease

Reactive nitrogen species (RNS) are various nitric oxide-derived compounds, including nitroxyl anion, nitrosonium cation, higher oxides of nitrogen, S-nitrosothiols, and dinitrosyl iron complexes. RNS have been recognized as playing a crucial role in the physiologic regulation of many, if not all, living cells, such as smooth muscle cells, cardiomyocytes, platelets, and nervous and juxtaglomerular cells. They possess pleiotropic properties on cellular targets after both posttranslational modifications and interactions with reactive oxygen species. Elevated levels of RNS have been implicated in cell injury and death by inducing nitrosative stress. The aim of this comprehensive review is to address the mechanisms of formation and removal of RNS, highlighting their potential cellular targets: lipids, DNA, and proteins. The specific importance of RNS and their paradoxic effects, depending on their local concentration under physiologic conditions, is underscored. An increasing number of compounds that modulate RNS processing or targets are being identified. Such compounds are now undergoing preclinical and clinical evaluations in the treatment of pathologies associated with RNS-induced cellular damage. Future research should help to elucidate the involvement of RNS in the therapeutic effect of drugs used to treat neurodegenerative, cardiovascular, metabolic, and inflammatory diseases and cancer.

Atherosclerosis: A Link between Lipid Intake and Protein Tyrosine Nitration

Atherosclerosis, a disease characterized by plaque formation in the arterial wall that can lead to heart attack and stroke, is a principal cause of death in the world. Since the 1990's, protein nitrotyrosine formation has been known to occur in the atherosclerotic plaque. This potentially damaging reaction occurs as a result of tyrosine modification by reactive nitrogen species, such as nitrogen dioxide radical, which forms upon peroxynitrite decomposition or nitrite oxidation by hydrogen peroxide-activated peroxidase enzymes. The presence of protein-bound nitrotyrosine can be considered an indicator of a loss in the natural balance of oxidants and antioxidants, and as such, there is an emerging view that protein-bound nitrotyrosine may be a risk factor for cardiovascular disease. This review brings together evidence that the accumulation of protein nitrotyrosine during atherogenesis is more widespread than initially thought (as its presence can be detected not only in the lesion but also in the blood stream and other organs) and is closely linked to lipid intake.

Cysteine-674 oxidation and degradation of sarcoplasmic reticulum Ca(2+) ATPase in diabetic pig aorta

The sarcoplasmic reticulum Ca2+ ATPase (SERCA) is redox-regulated by posttranslational thiol modifications of cysteine-674 to regulate smooth muscle relaxation and migration. To detect oxidation of cysteine-674 that irreversibly prevents redox regulation, a polyclonal, sequence-specific antibody was developed toward a peptide containing cysteine-674 sulfonic acid. The antibody stained intact 110-kDa SERCA in pig cardiac SR that was oxidized in vitro by peroxynitrite in a sequence-specific manner, and histochemically stained atherosclerotic pig and rabbit aorta. Surprisingly, immunoblots of the pig aorta failed to stain intact 110-kDa SERCA protein, but rather, higher molecular mass aggregates and lower molecular mass bands. Of the latter bands at 70 and 60 kDa, the largest were observed in diabetic, hyperlipidemic pigs, and coincided with the most positive histochemical staining. The 70- and 60-kDa molecular mass bands also coincided with the majority of the protein detected by a monoclonal total anti-SERCA antibody, which detected the intact 110-kDa protein in normal pigs. Mass spectrometry identified SERCA in all the major bands detected by the sulfonic acid antibody as well as the oxidation of cysteine-674 in the 70-kDa band. These studies demonstrate a sequence-specific antibody that detects partial degradation products of SERCA, which represent the majority of the protein in some diabetic hypercholesterolemic pig aortae. In addition, the results suggest an association between irreversible oxidation of SERCA and its degradation, and that an important portion of the oxidized protein in tissue samples may be partially degraded.

The cardiac sarcoplasmic/endoplasmic reticulum calcium ATPase: a potent target for cardiovascular diseases

The cardiac isoform of the sarcoplasmic/endoplasmic reticulum calcium ATPase (SERCA2a) is a calcium ion (Ca(2+)) pump powered by ATP hydrolysis. SERCA2a transfers Ca(2+) from the cytosol of the cardiomyocyte to the lumen of the sarcoplasmic reticulum during muscle relaxation. As such, this transporter has a key role in cardiomyocyte Ca(2+) regulation. In both experimental models and human heart failure, SERCA2a expression is significantly decreased, which leads to abnormal Ca(2+) handling and a deficient contractile state. Following a long line of investigations in isolated cardiac myocytes and small and large animal models, a clinical trial is underway that is restoring SERCA2a expression in patients with heart failure by use of adeno-associated virus type 1. Beyond its role in contractile abnormalities in heart failure, SERCA2a overexpression has beneficial effects in a host of other cardiovascular diseases. Here we describe the mechanism of Ca(2+) regulation by SERCA2a, examine the beneficial effects as well as the failures, risks and complexities associated with SERCA2a overexpression, and discuss the potential of SERCA2a as a target for the treatment of cardiovascular disease.

Aorta remodeling responses to distinct atherogenic stimuli: hypertension, hypercholesterolemia and turbulent flow/low wall shear stress

This review is based on recently published data from our laboratory. We investigated the role of hypertension and laminar flow, hypercholesterolemia and laminar flow and turbulent blood flow/low wall shear stress, and turbulent blood flow/low wall shear stress associated with hypercholesterolemia on aorta remodeling of rats feeding normal diet or hypercholesterolemic diet. Our findings suggest that increased circumferential wall tension due to hypertension plays a key role in the remodeling through biomechanical effects on oxidative stress and increased TGF-beta expression; the remodeling observed in the presence of hypercholesterolemia could be initiated by oxidative stress that is involved in several processes of atherogenesis and this remodeling is more pronounced in the presence of turbulent blood flow/low wall shear stress.

Turbulent blood flow plays an essential localizing role in the development of atherosclerotic lesions in experimentally induced hypercholesterolaemia in rats

Taking into account that atherosclerosis is a focal disease and high levels of plasma cholesterol are closely correlated with its pathogenesis, it is a challenge to explain how equal concentrations of cholesterol bathing the endothelium can produce local, rather than global, effects on arteries. The focal distribution of atherosclerotic lesions has been considered to be dependent, at least in part, on hydrodynamic factors. The present study was carried out to further test the hypothesis that these forces are an important localizing factor in rats feeding a hypercholesterolaemic diet and submitted to infra-diaphragmatic aortic constriction. These animals develop a normotensive prestenotic region with laminar blood flow that serves as control for a normotensive poststenotic region with turbulent blood flow. Our findings clearly demonstrated that the combination of turbulent blood flow and low wall shear stress (WSS) in the presence of hypercholesterolaemia and oxidative stress creates conditions to the formation of focally distributed incipient atherosclerotic lesions observed in the poststenotic segment. In contrast, only diffuse fatty streaks could be observed in the normotensive prestenotic segment with laminar blood flow and normal WSS in the presence of hypercholesterolaemia and oxidative stress. Although haemodynamic forces are not by themselves responsible for the pathogenesis of atherosclerosis, they prime the local vascular wall in which the lesion develop. Further studies are required to establish how haemodynamic forces are detected and transduced into chemical signalling by the cells of the artery wall and then converted into pathophysiologically relevant phenotypic changes.

Paraoxonase 1 gene transfer lowers vascular oxidative stress and improves vasomotor function in apolipoprotein E-deficient mice with pre-existing atherosclerosis

BACKGROUND AND PURPOSE

Transgenesis of human paraoxonase 1 (PON1), a HDL-associated enzyme that destroys lipid peroxides, has been reported to reduce early atherogenesis in mice. The present study explored the therapeutic potential of human PON1 gene transfer in old apolipoprotein E-deficient (apoE(-/-)) mice with advanced atherosclerosis.

EXPERIMENTAL APPROACH

ApoE(-/-) mice (18 months, regular chow) were transfected with PON1 adenovirus (AdPON1, n=10) or control adenovirus (AdRR5, n=10). Non-transfected apoE(-/-) (n=9) and C57Bl/6J (WT, n=6) mice served as controls. Three weeks later, plaque size and composition, and endothelial cell (EC) and smooth muscle cell (SMC) function were assessed in the aorta.

KEY RESULTS

PON1 gene transfer raised total PON1 serum activity 13-15 fold during the 3-week study period, without affecting hypercholesterolaemia or lesion size. However, PON1 decreased the oxLDL content of the plaque. Plaque-free thoracic aorta rings from apoE(-/-) mice displayed, like rings from WT mice, complete relaxation to acetylcholine (ACh, 86+/-2%), ATP (90+/-2%) or UTP (83+/-3%). In contrast, in plaque-bearing segments amplitude (55+/-7%, 68+/-8%, 52+/-8% respectively) and sensitivity were decreased. EC function was completely (ATP, UTP) or largely (ACh) restored by AdPON1. Furthermore, apoE(-/-) SMCs released less intracellular calcium than WT upon sarco-endoplasmic reticulum calcium ATPase (SERCA) inhibition by cyclopiazonic acid. This defect was also restored by AdPON1 transfection.

CONCLUSIONS AND IMPLICATIONS

These data indicate that AdPON1 gene transfer improved vascular wall oxidative stress, EC function, and SMC Ca(2+) homeostasis in segments with pre-existing atherosclerosis, independently of an effect on plaque size.

Insulin-induced impairment via peroxynitrite production of endothelium-dependent relaxation and sarco/endoplasmic reticulum Ca(2+)-ATPase function in aortas from diabetic rats

We designed this study to determine whether a high insulin level and a diabetic state need to exist together to cause an impairment of endothelium-dependent relaxation. In diabetic rat aortas organ-cultured with insulin [vs both control rat aortas cultured with insulin and diabetic rat aortas cultured in serum-free medium]: (1) the relaxation responses to both acetylcholine (endothelium-dependent relaxation) and Angeli's salt (nitric oxide donor) were significantly weaker, (2) acetylcholine-stimulated nitric oxide production was significantly smaller, (3) superoxide and nitric oxide production into the culture medium was greater, and (4) the levels of both nitrotyrosine and tyrosine-nitrated sarco/endoplasmic reticulum calcium ATPase (SERCA) protein were greater. The insulin-induced effects were prevented by cotreatment with either a superoxide scavenger or a peroxynitrite scavenger. After preincubation with an irreversible SERCA inhibitor, the relaxation induced by the nitric oxide donor was significantly impaired in control aortas cultured with or without insulin and in diabetic aortas cultured without insulin, but not in diabetic aortas cultured with insulin. These results suggest that the coexistence of a high insulin level and an established diabetic state may lead to an excessive generation of peroxynitrite, and that this may in turn trigger an impairment of endothelium-dependent relaxation via a decrease in SERCA function.

Black Tea Improves Endothelial Function in Renal Transplant Recipients

BACKGROUND

Endothelial damage and dysfunction are commonplace in renal transplant recipients. Impaired endothelial function is an important contributor to cardiovascular diseases. We hypothesized that short-term black tea consumption may improve endothelium-dependent arterial dilation in kidney recipients.

METHODS

Fifteen recipients were studied on an outpatient basis in a single, university-affiliated clinic. Inclusion criteria were stable and good allograft function. The main exclusion criteria were uncontrolled hypertension, smoking, alcohol consumption, coffee drinking, diabetes mellitus, and coronary artery disease, or a history of upper limb vascular manipulations. After overnight fasting, the brachial artery diameter (BAD) was measured at the end of diastole using an ultrasound machine before (basal BAD) and 1 minute after temporary ( approximately 3 minutes) external occlusion (posthyperemia BAD). Flow-mediated vasodilation (FMV) and percent of FMV (FMV%) were calculated by appropriate formula. FMV and FMV% were determined at baseline and 2 hours after consuming 0.5 L freshly brewed black tea. For control, the study was repeated for each patient the next day and FMV and FMV% were determined before and 2 hours after consuming 0.5 L of water.

RESULTS

The men age of patients was 37.2 +/- 9.7 years (range, 25 to 50) with a male:female ratio of 3:2. Patients were 26.8 +/- 10.6 months postrenal transplantation. Black tea consumption significantly increased posthyperemia BAD, FMV, and FMV% (P<.05). However, water consumption did not alter the basal or posthyperemia BAD, FMV, or FMV% (P>.05).

CONCLUSION

Based on our study, short-term consumption of black tea may improve endothelial function and endothelium-dependent arterial vasodilation in renal transplant recipients.

Proteomic analysis of protein nitration in rat cerebellum: effect of biological aging

3-Nitrotyrosine (3-NT) is a useful biomarker of increasing oxidative stress and protein nitration during biological aging. The proteomic analysis of cerebellar homogenate from Fisher 344/Brown Norway (BN/F1) rats shows an age-dependent increase in protein nitration, monitored by western-blot analysis after two-dimensional gel electrophoresis (2DE), mainly in the acidic region. Analysis of in-gel digests by nanoelectrospray (NSI)-MS/MS resulted in the identification of 16 putatively nitrated proteins. The selective isolation of nitrated proteins using immunoprecipitation, followed by SDS-PAGE and in-gel digest/NSI-MS/MS analysis led to the identification of 22 putatively nitrated proteins, of which 7 were identical to those detected after 2DE. When proteins were separated by solution isoelectrofocusing and analyzed by NSI MS/MS, we obtained MS/MS spectra of 3-NT containing peptides of four proteins - similar to ryanodine receptor 3, low density lipoprotein related receptor 2, similar to nebulin-related anchoring protein isoform C and 2,3 cyclic nucleotide 3-phosphodiesterase. Although the functional consequences of protein nitration for these targets are not yet known, our proteomic experiments serve as a first screen for the more targeted analysis of nitrated proteins from aging cerebellum for functional characterization.

Enalapril improves impairment of SERCA-derived relaxation and enhancement of tyrosine nitration in diabetic rat aorta

We investigated the involvement of angiotensin II and vascular smooth muscle sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) function in the impaired NO-induced relaxation seen in established streptozotocin-induced diabetes. Plasma angiotensin II levels, which were elevated in untreated diabetic rats (vs age-matched controls), were improved by treatment with the angiotensin-converting enzyme inhibitor enalapril. Systolic blood pressure was significantly decreased in chronic enalapril-treated diabetics (vs the other two groups). Intact aortae from diabetic rats and chronic angiotensin II-infused control rats, but not those from diabetic rats treated with enalapril, showed impaired endothelium-dependent relaxations to acetylcholine (vs controls). The relaxation induced by Angeli's Salt (a NO donor) was significantly impaired in endothelium-denuded aortae from diabetic rats (vs controls) but it was normalised by enalapril treatment. After preincubation with the irreversible SERCA inhibitor, thapsigargin, the relaxation induced by Angeli's Salt was significantly impaired in endothelium-denuded aortae from the controls, but not from the diabetics, and there was no significant difference between the thapsigargin-treated groups. Nitrotyrosine, an indirect marker of peroxynitrite, was markedly increased in aortic smooth muscle from diabetic rats, while chronic enalapril administration reduced this increase. These results suggest that in streptozotocin-induced diabetic rats, excessive angiotensin II production may lead to the generation of peroxynitrite and that this may in turn trigger a dysfunction of vascular smooth muscle SERCA. Enalapril improved the diabetes-related impairments.

Mass spectrometry of protein modifications by reactive oxygen and nitrogen species

The modification of proteins by reactive oxygen and nitrogen species plays an important role in various biologic processes involving protein activation and inactivation, protein translocation and turnover during signal transduction, stress response, proliferation, and apoptosis. Recent advances in protein and peptide separation and mass spectrometry provide increasingly sophisticated tools for the quantitative analysis of such protein modifications, which are absolutely necessary for their correlation with biologic phenomena. The present review focuses specifically on the qualitative and quantitative mass spectrometric analysis of the most common protein modifications caused by reactive oxygen and nitrogen species in vivo and in vitro and details a case study on a membrane protein the sarco/endoplasmic reticulum Ca-ATPase (SERCA).