A hydroxyl radical-like species oxidizes cynomolgus monkey artery wall proteins in early diabetic vascular disease

Urinary Metabolites of Polycyclic Aromatic Hydrocarbons of Rural Population in Northwestern China: Oxidative Stress and Health Risk Assessment

Polycyclic aromatic hydrocarbon (PAH) exposure is suspected to be linked to oxidative damage. Herein, ten PAH human exposure biomarkers [hydroxylated PAH metabolites (OH-PAHs)] and five oxidative stress biomarkers (OSBs) were detected in urine samples collected from participants living in a rural area (n = 181) in Northwestern China. The median molar concentration of ΣOH-PAHs in urine was 47.0 pmol mL-1. The 2-hydroxynaphthalene (2-OHNap; median: 2.21 ng mL-1) was the dominant OH-PAH. The risk assessment of PAH exposure found that hazard index (HI) values were <1, indicating that the PAH exposure of rural people in Jingyuan would not generate significant cumulative risks. Smokers (median: 0.033) obtained higher HI values than nonsmokers (median: 0.015, p < 0.01), suggesting that smokers face a higher health risk from PAH exposure than nonsmokers. Pearson correlation and multivariate linear regression analysis revealed that ΣOH-PAH concentrations were significant factors in increasing the oxidative damage to deoxyribonucleic acid (DNA) (8-hydroxy-2'-deoxyguanosine, 8-OHdG), ribonucleic acid (RNA) (8-oxo-7,8-dihydroguanine, 8-oxoGua), and protein (o, o'-dityrosine, diY) (p < 0.05). Among all PAH metabolites, only 1-hydroxypyrene (1-OHPyr) could positively affect the expression of all five OSBs (p < 0.05), suggesting that urinary 1-OHPyr might be a reliable biomarker for PAH exposure and a useful indicator for assessing the impacts of PAH exposure on oxidative stress. This study is focused on the relation between PAH exposure and oxidative damage and lays a foundation for the study of the health effect mechanism of PAHs.

Reactive oxygen species in biological media are they friend or foe? Major In vivo and In vitro sensing challenges

The role of Reactive Oxygen Species (ROS) on biological media has been shifting over the years, as the knowledge on the complex mechanism that lies in underneath their production and overall results has been growing. It has been known for some time that these species are associated with a number of health conditions. However, they also participate in the immunoactivation cascade process, and can have an active role in theranostics. Macrophages, for example, react to the presence of pathogens through ROS production, potentially allowing the development of new therapeutic strategies. However, their short lifetime and limited spatial distribution of ROS have been limiting factors to the development and understanding of this phenomenon. Even though, ROS have shown successful theranostic applications, e.g., photodynamic therapy, their wide applicability has been hampered by the lack of effective tools for monitoring these processes in real time. Thus the development of innovative sensing strategies for in vivo monitoring of the balance between ROS concentration and the resultant immune response is of the utmost relevance. Such knowledge could lead to major breakthroughs towards the development of more effective treatments for neurodegenerative diseases. Within this review we will present the current understanding on the interaction mechanisms of ROS with biological systems and their overall effect. Additionally, the most promising sensing tools developed so far, for both in vivo and in vitro tracking will be presented along with their main limitations and advantages. This review focuses on the four main ROS that have been studied these are: singlet oxygen species, hydrogen peroxide, hydroxyl radical and superoxide anion.

Association of Vegetable and Fruit Consumption with Urinary Oxidative Biomarkers in Teenaged Girls: A School-Based Pilot Study in Japan

Hexanoyl-lysine (HEL), 8-hydroxy-2'deoxyguanosine (8-OHdG), and dityrosine (DT) have served as potential biomarkers for detecting oxidative modified lipids, DNA, and proteins in biological samples, respectively. Whether regular higher levels of consumption of vegetables/fruit (V/F) would decrease oxidative modification of these biomolecules in the body remain unelucidated. To examine the association of regular V/F consumption with the generation of these reactive oxygen species-induced biomarkers, this study evaluated V/F consumption in a school-based sample of teenaged girls (mean age 15.6 ± 1.7 years, n = 103), and quantified the formation of oxidative stress biomarkers in their urine. Only 19.4% and 23.3% of participants reported that they consumed the recommended daily amount of vegetables and fruits, respectively. Individuals who consumed lower levels of fruit (<100g/day) or vegetables (<250g/day) had significantly higher HEL excretion in their urine than those who consumed higher levels of fruit (≥100g/day) (p < 0.05) or vegetables (≥250g/day) (p = 0.057). The results of a multiple regression analysis showed that vegetable consumption was an important inhibiting factor of early lipid peroxidation measured as HEL in urine, independent of various confounders (β = - 0.332, p < 0.05). The findings suggest that relatively higher consumption of vegetables would help in the prevention of early lipid peroxidation in adolescents.

Incorporation of Oxidized Phenylalanine Derivatives into Insulin Signaling Relevant Proteins May Link Oxidative Stress to Signaling Conditions Underlying Chronic Insulin Resistance

A link between oxidative stress and insulin resistance has been suggested. Hydroxyl free radicals are known to be able to convert phenylalanine (Phe) into the non-physiological tyrosine isoforms ortho- and meta-tyrosine (o-Tyr, m-Tyr). The aim of our study was to examine the role of o-Tyr and m-Tyr in the development of insulin resistance. We found that insulin-induced uptake of glucose was blunted in cultures of 3T3-L1 grown on media containing o- or m-Tyr. We show that these modified amino acids are incorporated into cellular proteins. We focused on insulin receptor substrate 1 (IRS-1), which plays a role in insulin signaling. The activating phosphorylation of IRS-1 was increased by insulin, the effect of which was abolished in cells grown in m-Tyr or o-Tyr media. We found that phosphorylation of m- or o-Tyr containing IRS-1 segments by insulin receptor (IR) kinase was greatly reduced, PTP-1B phosphatase was incapable of dephosphorylating phosphorylated m- or o-Tyr IRS-1 peptides, and the SH2 domains of phosphoinositide 3-kinase (PI3K) bound the o-Tyr IRS-1 peptides with greatly reduced affinity. According to our data, m- or o-Tyr incorporation into IRS-1 modifies its protein–protein interactions with regulating enzymes and effectors, thus IRS-1 eventually loses its capacity to play its role in insulin signaling, leading to insulin resistance.

The multifaceted role of cytochrome P450-Derived arachidonic acid metabolites in diabetes and diabetic cardiomyopathy

Understanding lipid metabolism is a critical key to understanding the pathogenesis of Diabetes Mellitus (DM). It is known that 60-90% of DM patients are obese or used to be obese. The incidence of obesity is rising owing to the modern sedentary lifestyle that leads to insulin resistance and increased levels of free fatty acids, predisposing tissues to utilize more lipids with less glucose uptake. However, the exact mechanism is not yet fully elucidated. Diabetic cardiomyopathy seems to be associated with these alterations in lipid metabolism. Arachidonic acid (AA) is an important fatty acid that is metabolized to several bioactive compounds by cyclooxygenases, lipoxygenases, and the more recently discovered, cytochrome P450 (P450) enzymes. P450 metabolizes AA to either epoxy-AA (EETs) or hydroxy-AA (HETEs). Studies showed that EETs could have cardioprotective effects and beneficial effects in reversing abnormalities in glucose and insulin homeostasis. Conversely, HETEs, most importantly 12-HETE and 20-HETE, were found to interfere with normal glucose and insulin homeostasis and thus, might be involved in diabetic cardiomyopathy. In this review, we highlight the role of P450-derived AA metabolites in the context of DM and diabetic cardiomyopathy and their potential use as a target for developing new treatments for DM and diabetic cardiomyopathy.

Direct Actions of AT1 (Type 1 Angiotensin) Receptors in Cardiomyocytes Do Not Contribute to Cardiac Hypertrophy

Supplemental Digital Content is available in the text.

Activation of AT₁ (type 1 Ang) receptors stimulates cardiomyocyte hypertrophy in vitro. Accordingly, it has been suggested that regression of cardiac hypertrophy associated with renin-Ang system blockade is due to inhibition of cellular actions of Ang II in the heart, above and beyond their effects to reduce pressure overload. We generated 2 distinct mouse lines with cell-specific deletion of AT_1A receptors, from cardiomyocytes. In the first line (C-SMKO), elimination of AT_1A receptors was achieved using a heterologous Cre recombinase transgene under control of the Sm22 promoter, which expresses in cells of smooth muscle lineage including cardiomyocytes and vascular smooth muscle cells of conduit but not resistance vessels. The second line (R-SMKO) utilized a Cre transgene knocked-in to the Sm22 locus, which drives expression in cardiac myocytes and vascular smooth muscle cells in both conduit and resistance arteries. Thus, although both groups lack AT₁ receptors in the cardiomyocytes, they are distinguished by presence (C-SMKO) or absence (R-SMKO) of peripheral vascular responses to Ang II. Similar to wild-types, chronic Ang II infusion caused hypertension and cardiac hypertrophy in C-SMKO mice, whereas both hypertension and cardiac hypertrophy were reduced in R-SMKOs. Thus, despite the absence of AT_1A receptors in cardiomyocytes, C-SMKOs develop robust cardiac hypertrophy. By contrast, R-SMKOs developed identical levels of hypertrophy in response to pressure overload–induced by transverse aortic banding. Our findings suggest that direct activation of AT₁ receptors in cardiac myocytes has minimal influence on cardiac hypertrophy induced by renin-Ang system activation or pressure overload.

Effects of a Forest Walk on Urinary Dityrosine and Hexanoyl-Lysine in Young People: A Pilot Study

A few studies indicate exposure to forests may alleviate oxidative stress in the body. However, more evidence is needed to support this potentiality. The purpose of the current study aimed at examining whether there is any difference in urinary levels of oxidatively modified proteins or lipids-dityrosine (DT) and hexanoyl-lysine (HEL), respectively, after a forest or urban walk. The study was performed on 29 university students who took part in forest walks (Shinjo Village) in Okayama Prefecture of Japan and on 42 university students who took part in urban walks in the downtown area of Okayama City. Urine samples before and after the walks were analyzed for DT and HEL excretion. Air phytoncides during the walks were also measured. We found a decreased tendency in urinary DT and HEL (p < 0.05) in most participants after the forest walks, but not after the urban walks. We further found the total levels of air phytoncides in the forest field were 1.50 times higher compared with those in the urban field. This study suggests the possibility that regular immersion in a forest environment might contribute toward weakening of the oxidative modifications of proteins or lipids in the body.

Role of 904 nm superpulsed laser-mediated photobiomodulation on nitroxidative stress and redox homeostasis in burn wound healing

BACKGROUND

Burn wound healing is delayed due to several critical factors such as sustained inflammation, vascular disorder, neuropathy, enhanced proteolysis, infection, and oxidative stress. Burn wounds have limited oxygen supply owing to compromised blood circulation. Hypoxic burn milieu leads to free radicals overproduction incurring oxidative injury, which impedes repair process causing damage to cell membranes, proteins, lipids, and DNA. Photobiomodulation (PBM) with 904 nm superpulsed laser had shown potent healing efficacy via attenuating inflammation while enhancing proliferation, angiogenesis, collagen accumulation, and bioenergetic activation in burn wounds.

METHODS

This study investigated the effects of 904 nm superpulsed laser at 0.4 mW/cm² average power density, 0.2 J/cm² total energy density, 100 Hz frequency, and 200 ns pulse width for 10 min daily for seven days postburn injury on nitroxidative stress, endogenous antioxidants status, and redox homeostasis.

RESULTS

Photobiomodulation treatment significantly decreased reactive oxygen species, nitric oxide, and lipid peroxidation levels as compared to non-irradiated control. Further, protective action of PBM against protein oxidative damage was evidenced by reduced protein carbonylation and advanced oxidation protein product levels along with significantly enhanced endogenous antioxidants levels of SOD, catalase, GPx, GST, reduced glutathione, and thiol (T-SH, Np-SH, P-SH). Biochemical changes aid in reduction of oxidative stress and maintenance of redox homeostasis, which further well corroborated by significantly up-regulated protein expression of Nrf 2, hemeoxygenase (HO-1), and thioredoxin reductase 2 (Txnrd2).

CONCLUSION

Photobiomodulation with 904 nm superpulsed laser led to reduction of nitroxidative stress, induction of endogenous antioxidants, and maintenance of redox homeostasis that could play a vital role in augmentation of burn wound healing.

A Highly Selective NIR Fluorescent Turn-on Probe for Hydroxyl Radical and Its Application in Living Cell Images

A highly selective NIR fluorescent turn-on probe for hydroxyl radical (·OH) has been built up using triphenylphosphine as a reactive-site for ·OH in an energy transfer cassette 2b consisting of 8-2'-(thiophen-2-yl) quinoline (TQ) as a donor and 3,5-diphenylphosphinostyryl-substituted BODIPY as an acceptor, which exhibits ca. 317 nm pseudo Stokes' shift due to efficient through-bond energy transfer (up to 169%). The triphenylphosphine substituent of 2b selectively oxidized by ·OH over the other reactive oxygen species (ROS) and the reactive nitrogen species (RNS) resulting in fluorescence enhancement in aqueous solution and in living cells.

Targeting Glucosylceramide Synthesis in the Treatment of Rare and Common Renal Disease

Sphingolipids, including ceramides, glycosphingolipids, sphingomyelin, and sphingosine-1-phosphate, have been recognized as important molecules that regulate critical cellular functions. Although originally studied in the context of lysosomal storage diseases, the roles of these compounds in more common disorders involving metabolism, vascular disease, and aberrant growth has been the focus of recent studies, including in disorders that affect the kidneys. These efforts have led to new insights into Fabry disease, a classic disorder of lysosomal function that results in renal failure as well as in more common renal diseases including diabetic nephropathy and polycystic kidney disease. Pathways for glycosphingolipid synthesis can be targeted with orally available small-molecule inhibitors, creating new opportunities for the treatment of both rare and common kidney diseases.

Asymmetrical flow field-flow fractionation for improved characterization of human plasma lipoproteins

High- and low-density lipoproteins (HDL and LDL) are attractive targets for biomarker discovery. However, ultracentrifugation (UC), the current methodology of choice for isolating HDL and LDL, is tedious, requires large sample volume, results in sample loss, and does not readily provide information on particle size. In this work, human plasma HDL and LDL are separated and collected using semi-preparative asymmetrical flow field-flow fractionation (SP-AF4) and UC. The SP-AF4 and UC separation conditions, sample throughput, and liquid chromatography/mass spectrometry (LC/MS) lipidomic results are compared. Over 600 μg of total proteins is recovered in a single SP-AF4 run, and Western blot results confirm apoA1 pure and apoB100 pure fractions, consistent with HDL and LDL, respectively. The SP-AF4 separation requires ~ 60 min per sample, thus providing a marked improvement over UC which can span hours to days. Lipidome analysis of SP-AF4-prepared HDL and LDL fractions is compared to UC-prepared HDL and LDL samples. Over 270 lipids in positive MS mode and over 140 lipids in negative MS mode are identified by both sample preparation techniques with over 98% overlap between the lipidome. Additionally, lipoprotein size distributions are determined using analytical scale AF4 coupled with multiangle light scattering (MALS) and dynamic light scattering (DLS) detectors. These developments position SP-AF4 as a sample preparation method of choice for lipoprotein biomarker characterization and identification. Graphical abstract ᅟ.

Pitavastatin ameliorates myocardial damage by preventing inflammation and collagen deposition via reduced free radical generation in isoproterenol-induced cardiomyopathy

Pitavastatin inhibits 3 hydroxy 3 methyl glutaryl coenzyme A (HMGCoA) reductase enzyme, preventing cholesterol synthesis along with elevating high density apolipoprotein A1 (Apo-A1). The present study was designed to evaluate cardioprotective potential of pitavastatin at 1 mg/kg/day and 3 mg/kg/day dose for 14 days in low dose isoproterenol (ISO) (5 mg/kg/day for 7 consecutive days) induced myocardial damage. ISO administration induced significant reduction in endogenous antioxidant enzymes like reduced glutathione (GSH), superoxide dismutase (SOD), catalase (CAT) and raised thiobarbituric acid reactive substances (TBARS) indicating activated lipid peroxidation. Along with this, a significant increase in level of cardiac injury biomarkers vie, creatine kinase (CK-MB), lactate dehydrogenase (LDH), aspartate amino transferase (AST), tumor necrosis factor (TNF-α) and transforming growth factor (TGF-β) as well as brain natriuretic peptide (BNP). Histological examination also revealed marked myocardial tissue damage in ISO treated rats. However, pretreatment with pitavastatin (3 mg/kg/day) significantly maintained nearly normal levels of cardiac biomarkers and oxidant antioxidant status as well as lipid peroxidation in ISO induced MI rats. Cardiac histological assessment and infarct size assessment also showed marked reduction in myocardial architecture alteration including infarct size as well as collagen deposition by pitavastatin that strongly supported biochemical findings. These observations strongly corroborate that pitavastatin prevents myocardial damages via up regulation of endogenous oxidants along with its hypocholesterolemic activity.

Myeloperoxidase-derived oxidants damage artery wall proteins in an animal model of chronic kidney disease-accelerated atherosclerosis

Increased myeloperoxidase (MPO) levels and activity are associated with increased cardiovascular risk among individuals with chronic kidney disease (CKD). However, a lack of good animal models for examining the presence and catalytic activity of MPO in vascular lesions has impeded mechanistic studies into CKD-associated cardiovascular diseases. Here, we show for the first time that exaggerated atherosclerosis in a pathophysiologically relevant CKD mouse model is associated with increased macrophage-derived MPO activity. Male 7-week-old LDL receptor-deficient mice underwent sham (control mice) or 5/6 nephrectomy and were fed either a low-fat or high-fat, high-cholesterol diet for 24 weeks, and the extents of atherosclerosis and vascular reactivity were assessed. MPO expression and oxidation products-protein-bound oxidized tyrosine moieties 3-chlorotyrosine, 3-nitrotyrosine, and o,o'-dityrosine-were examined with immunoassays and confirmed with mass spectrometry (MS). As anticipated, the CKD mice had significantly higher plasma creatinine, urea nitrogen, and intact parathyroid hormone along with lower hematocrit and body weight. On both the diet regimens, CKD mice did not have hypertension but had lower cholesterol and triglyceride levels than the control mice. Despite the lower cholesterol levels, CKD mice had increased aortic plaque areas, fibrosis, and luminal narrowing. They also exhibited increased MPO expression and activity (i.e. increased oxidized tyrosines) that co-localized with infiltrating lesional macrophages and diminished vascular reactivity. In summary, unlike non-CKD mouse models of atherosclerosis, CKD mice exhibit increased MPO expression and catalytic activity in atherosclerotic lesions, which co-localize with lesional macrophages. These results implicate macrophage-derived MPO in CKD-accelerated atherosclerosis.

EDTA Chelation Therapy to Reduce Cardiovascular Events in Persons with Diabetes

The Trial to Assess Chelation Therapy (TACT) was a randomized double-blind placebo-controlled trial enrolling patients age ≥50 years with prior myocardial infarction. TACT used a 2 × 2 factorial design to study ethylene diamine tetraacetic acid (EDTA) chelation and high-dose vitamin supplementation. Chelation provided a modest but significant reduction in cardiovascular endpoints. The benefit was stronger and significant among participants with diabetes but absent in those without diabetes. Mechanisms by which chelation might reduce cardiovascular risk in persons with diabetes include the effects of EDTA chelation on transition and toxic metals. Transition metals, particularly copper and iron, play important roles in oxidative stress pathways. Toxic metals, in particular cadmium and lead, are toxic for the cardiovascular system. This review discusses the epidemiologic evidence and animal and human studies supporting the role of these metals in the development of diabetes and ischemic heart disease and potential ways by which EDTA chelation could confer cardiovascular benefit.

Roles of the tyrosine isomers meta-tyrosine and ortho-tyrosine in oxidative stress

The damage to cellular components by reactive oxygen species, termed oxidative stress, both increases with age and likely contributes to age-related diseases including Alzheimer's disease, atherosclerosis, diabetes, and cataract formation. In the setting of oxidative stress, hydroxyl radicals can oxidize the benzyl ring of the amino acid phenylalanine, which then produces the abnormal tyrosine isomers meta-tyrosine or ortho-tyrosine. While elevations in m-tyrosine and o-tyrosine concentrations have been used as a biological marker of oxidative stress, there is emerging evidence from bacterial, plant, and mammalian studies demonstrating that these isomers, particularly m-tyrosine, directly produce adverse effects to cells and tissues. These new findings suggest that the abnormal tyrosine isomers could in fact represent mediators of the effects of oxidative stress. Consequently the accumulation of m- and o-tyrosine may disrupt cellular homeostasis and contribute to disease pathogenesis, and as result, effective defenses against oxidative stress can encompass not only the elimination of reactive oxygen species but also the metabolism and ultimately the removal of the abnormal tyrosine isomers from the cellular amino acid pool. Future research in this area is needed to clarify the biologic mechanisms by which the tyrosine isomers damage cells and disrupt the function of tissues and organs and to identify the metabolic pathways involved in removing the accumulated isomers after exposure to oxidative stress.

Role of Tyrosine Isomers in Acute and Chronic Diseases Leading to Oxidative Stress - A Review

Oxidative stress plays a major role in the pathogenesis of a variety of acute and chronic diseases. Measurement of the oxidative stress-related end products may be performed, e.g. that of structural isomers of the physiological para-tyrosine, namely meta- and ortho-tyrosine, that are oxidized derivatives of phenylalanine. Recent data suggest that in sepsis, serum level of meta-tyrosine increases, which peaks on the 2(nd) and 3(rd) days (p<0.05 vs. controls), and the kinetics follows the intensity of the systemic inflammation correlating with serum procalcitonin levels. In a similar study subset, urinary meta-tyrosine excretion correlated with both need of daily insulin dose and the insulin-glucose product in non-diabetic septic cases (p<0.01 for both). Using linear regression model, meta-tyrosine excretion, urinary meta-tyrosine/para-tyrosine, urinary ortho-tyrosine/para-tyrosine and urinary (meta- + orthotyrosine)/ para-tyrosine proved to be markers of carbohydrate homeostasis. In a chronic rodent model, we tried to compensate the abnormal tyrosine isomers using para-tyrosine, the physiological amino acid. Rats were fed a standard high cholesterol-diet, and were given para-tyrosine or vehicle orally. High-cholesterol feeding lead to a significant increase in aortic wall meta-tyrosine content and a decreased vasorelaxation of the aorta to insulin and the glucagon-like peptide-1 analogue, liraglutide, that both could be prevented by administration of para-tyrosine. Concluding, these data suggest that meta- and ortho-tyrosine are potential markers of oxidative stress in acute diseases related to oxidative stress, and may also interfere with insulin action in septic humans. Competition of meta- and ortho-tyrosine by supplementation of para-tyrosine may exert a protective role in oxidative stress-related diseases.

A sensitive fluorescent sensor for the detection of endogenous hydroxyl radicals in living cells and bacteria and direct imaging with respect to its ecotoxicity in living zebra fish

MPT-Cy2exhibited excellent selectivity and sensitivity toward ˙OH over other ROS and showed a high potential for the imaging of endogenous ˙OH in living cells and various types of bacteria.

Effect of resveratrol on metabolic and cardiovascular function in male and female adult offspring exposed to prenatal hypoxia and a high-fat diet

Prenatal hypoxia, a common outcome of pregnancy complications, predisposes offspring to the development of metabolic and cardiovascular disorders in later life. We have previously observed that resveratrol improved cardiovascular and metabolic health in adult male rat offspring exposed to prenatal hypoxia and a postnatal high-fat (HF) diet; however, the effects of resveratrol in female rat offspring are not known. Our aim was to identify the mechanism(s) by which resveratrol may prevent metabolic and cardiac dysfunction in both male and female rat offspring exposed to prenatal hypoxia and a postnatal HF diet. Offspring that experienced normoxia or hypoxia in utero were fed a HF diet or a HF diet supplemented with resveratrol for 9 weeks following weaning. Body composition, metabolic function, in vivo cardiac function and ex vivo cardiac susceptibility to ischaemia-reperfusion (I/R) injury were assessed at 12 weeks of age. Prenatal hypoxia impaired metabolic function in male, but not female, rat offspring fed a HF diet and this was improved by resveratrol supplementation. Prenatal hypoxia also led to reduced recovery from cardiac I/R injury in male, and to a lesser extent in female, rat offspring fed a HF diet. Indices of cardiac oxidative stress after I/R were enhanced in both male and female rat offspring exposed to prenatal hypoxia. Resveratrol improved cardiac recovery from I/R injury and attenuated superoxide levels in both male and female rat offspring. In conclusion, prenatal hypoxia impaired metabolic and cardiac function in a sex-specific manner. Resveratrol supplementation may improve metabolic and cardiovascular health in adult male and female rat offspring exposed to prenatal hypoxia.

The balance of powers: Redox regulation of fibrogenic pathways in kidney injury

Oxidative stress plays a central role in the pathogenesis of diverse chronic inflammatory disorders including diabetic complications, cardiovascular disease, aging, and chronic kidney disease (CKD). Patients with moderate to advanced CKD have markedly increased levels of oxidative stress and inflammation that likely contribute to the unacceptable high rates of morbidity and mortality in this patient population. Oxidative stress is defined as an imbalance of the generation of reactive oxygen species (ROS) in excess of the capacity of cells/tissues to detoxify or scavenge them. Such a state of oxidative stress may alter the structure/function of cellular macromolecules and tissues that eventually leads to organ dysfunction. The harmful effects of ROS have been largely attributed to its indiscriminate, stochastic effects on the oxidation of protein, lipids, or DNA but in many instances the oxidants target particular amino acid residues or lipid moieties. Oxidant mechanisms are intimately involved in cell signaling and are linked to several key redox-sensitive signaling pathways in fibrogenesis. Dysregulation of antioxidant mechanisms and overproduction of ROS not only promotes a fibrotic milieu but leads to mitochondrial dysfunction and further exacerbates kidney injury. Our studies support the hypothesis that unique reactive intermediates generated in localized microenvironments of vulnerable tissues such as the kidney activate fibrogenic pathways and promote end-organ damage. The ability to quantify these changes and assess response to therapies will be pivotal in understanding disease mechanisms and monitoring efficacy of therapy.

High fat diet exacerbates vascular endothelial dysfunction in rats exposed to continuous hypobaric hypoxia

Independently, a high fat diet and hypoxia are associated with vascular endothelial dysfunction (VED) and often occur concurrently in patients. Nevertheless, the effects of a high fat diet on vascular endothelial function combined with hypoxia, a situation occurring with increasing frequency in many parts of the world, remain largely unknown. We investigated the effects of a high fat diet on vascular endothelial function in rats exposed to continuous hypoxia for 4 weeks. Seventy two male Sprague-Dawley rats were randomly divided into 3 groups: a hypoxia group fed regular chow, a combined hypoxia and high fat diet (HFD) group, and for comparison, rats maintained in normoxia, regular chow conditions were set as baseline (BL) group. The experimental data of BL group were obtained at beginning of hypoxia given in the other groups. Continuous hypoxia was induced in a hypobaric chamber maintained at an altitude of 5000 m. Compared to hypoxic conditions alone, hypoxia plus a HFD prevented adaptive changes in plasma nitric oxide (NOx) levels and caused earlier and more severe changes in aortic endothelial structures. Functionally, hypoxia plus a HFD resulted in impaired endothelium-dependent vasorelaxation responses to acetylcholine and altered the bioavailability of the nitric oxide synthase (NOS) substrate L-Arginine. At the molecular level, hypoxia plus a HFD blunted increases in endothelial NOS (eNOS) mRNA and protein in aortic endothelial tissue. Taken together, our findings demonstrate that in the setting of hypoxia, a high fat diet leads to earlier and more severe VED than hypoxia alone. These data have important implications for populations residing at high-altitude, as dietary patterns shift towards increased fat intake.

Targets of protein carbonylation in spontaneously hypertensive obese Koletsky rats and healthy Wistar counterparts: a potential role on metabolic disorders

The study innovatively pinpoints target proteins of carbonylation, a key PTM induced by oxidative stress, in the SHROB (genetically obese spontaneously hypertensive) rat model of metabolic syndrome (MetS). Protein carbonylation was assessed by a fluorescence-labeling proteomics approach, and complemented with biometric and biochemical markers of MetS. SHROB and healthy Wistar rats were fed two diets, soybean and linseed oil supplementations, in order to distinguish intrinsic carbonylation of SHROB animals from diet-modulated carbonylation unrelated to MetS. First exploratory data showed similar carbonylation patterns and metabolic conditions in SHROB rats fed soybean and linseed, but different from Wistar animals. A total of 18 carbonylated spots in liver, and 12 in skeletal tissue, related to pathways of lipid (29.6%), carbohydrate (25.9%) and amino acid (18.5%) metabolisms, were identified. In particular, SHROB animals present higher carbonylation in four liver proteins belonging to lipid metabolism, redox regulation and chaperone activity (ALDH2, PDI, PDIA3, PECR), and in the skeletal muscle ALDOA that is involved in muscle dysfunction. Conversely, SHROB rats display lower carbonylation in liver albumin, AKR1C9, ADH1 and catalase. This investigation provides a novel perspective of carbonylation in the context of metabolic disorders, and may be a starting point to characterize new redox pathways exacerbating MetS.

BIOLOGICAL SIGNIFICANCE

Oxidative stress is a concomitant factor in the pathogenesis of MetS that induces oxidative PTM as carbonylation. Through the use of a redox proteomics approach, we have thoroughly mapped the occurrence of protein targets of carbonylation in the genetically-induced MetS model SHROB rat. The present research brings a new insight of MetS pathogenesis and it may provide valuable information to understand the biological impact of oxidative stress in patients with MetS.

Oxidation of cellular amino acid pools leads to cytotoxic mistranslation of the genetic code

Aminoacyl-tRNA synthetases use a variety of mechanisms to ensure fidelity of the genetic code and ultimately select the correct amino acids to be used in protein synthesis. The physiological necessity of these quality control mechanisms in different environments remains unclear, as the cost vs benefit of accurate protein synthesis is difficult to predict. We show that in Escherichia coli, a non-coded amino acid produced through oxidative damage is a significant threat to the accuracy of protein synthesis and must be cleared by phenylalanine-tRNA synthetase in order to prevent cellular toxicity caused by mis-synthesized proteins. These findings demonstrate how stress can lead to the accumulation of non-canonical amino acids that must be excluded from the proteome in order to maintain cellular viability.

DOI:http://dx.doi.org/10.7554/eLife.02501.001

Proteins are built from molecules called amino acids. The amino acids that make up a particular protein, and the order they appear in, are determined by the gene that encodes that protein. First, the gene is transcribed to produce a molecule of messenger RNA, which is then translated by a molecular machine called a ribosome. This involves other RNA molecules, called transfer RNAs (tRNAs), bringing the correct amino acids to the ribosome, which then joins the amino acids together to build the protein.

Amino acids are loaded onto their corresponding tRNA molecules by enzymes called tRNA synthetases. Occasionally, however, the wrong amino acid can be loaded onto a tRNA. If this amino acid ends up in a protein, the protein might not be able to function properly, or it might even be toxic to the cell, so cells need to be able to fix this problem. Some tRNA synthetases can check if a wrong amino acid has been loaded onto a tRNA, and remove it before it can cause harm. However, the importance of these ‘editing’ activities to living cells is unclear.

Here, Bullwinkle, Reynolds et al. show that, in the bacterium E. coli, a tRNA synthetase works to stop an incorrect amino acid—which accumulates in cells that are exposed to harmful chemicals—from being built into proteins. Without the enzyme’s editing activity, the build-up of this amino acid slows the growth of the bacteria. However, E. coli can thrive without this editing activity when it is grown under normal conditions in a laboratory. Yeast benefit slightly from this editing activity when exposed to the stress-produced amino acid. But, unlike E. coli, yeast strongly rely on this activity when grown in an excess of another amino acid, which is used to build proteins but is the wrong amino acid for this tRNA synthetase.

The findings of Bullwinkle, Reynolds et al. will help to improve our understanding of which activities in a cell are most affected by mistakes in protein synthesis, and how these mistakes may relate to disease.

DOI:http://dx.doi.org/10.7554/eLife.02501.002

Oxidation of cellular amino acid pools leads to cytotoxic mistranslation of the genetic code

Aminoacyl-tRNA synthetases use a variety of mechanisms to ensure fidelity of the genetic code and ultimately select the correct amino acids to be used in protein synthesis. The physiological necessity of these quality control mechanisms in different environments remains unclear, as the cost vs benefit of accurate protein synthesis is difficult to predict. We show that in Escherichia coli, a non-coded amino acid produced through oxidative damage is a significant threat to the accuracy of protein synthesis and must be cleared by phenylalanine-tRNA synthetase in order to prevent cellular toxicity caused by mis-synthesized proteins. These findings demonstrate how stress can lead to the accumulation of non-canonical amino acids that must be excluded from the proteome in order to maintain cellular viability.

Increase in insulin-induced relaxation of consecutive arterial segments toward the periphery: Role of vascular oxidative state

RATIONALE

The oxidative state has been implicated in the signaling of various vasomotor functions, yet its role regarding the vasomotor action of insulin is less known.

OBJECTIVE

To investigate the insulin-evoked relaxations of consecutive arterial segments of different oxidative state and the role of extracellular signal-regulated kinase (ERK) pathway.

METHODS AND RESULTS

The oxidative state, as assessed by the level of ortho-tyrosine, was higher in the thoracic aorta of rats than in the abdominal aorta, and was the lowest in the femoral artery. The vasomotor function of vessels of same origin was studied using a small-vessel myograph. Insulin-induced relaxations increased toward the periphery (i.e., thoracic < abdominal < femoral). Aortic banding and hydrogen peroxide/aminotriazole increased the oxidative state of the thoracic aorta that was accompanied by ERK activation and decreased relaxation to insulin, and vice versa, acutely lowered oxidative state by superoxide dismutase/catalase improved relaxation. In contrast, insulin-induced relaxation of the femoral artery could be enhanced with a higher oxidative state, and reduced with a lower state.

CONCLUSIONS

Oxidative state of vessels modulates the magnitude of vasomotor responses to insulin, which appears to be mediated via the ERK signaling pathway.

Alterations in the ubiquitin proteasome system in persistent but not reversible proteinuric diseases

Podocytes are the key cells affected in nephrotic glomerular kidney diseases, and they respond uniformly to injury with cytoskeletal rearrangement. In nephrotic diseases, such as membranous nephropathy and FSGS, persistent injury often leads to irreversible structural damage, whereas in minimal change disease, structural alterations are mostly transient. The factors leading to persistent podocyte injury are currently unknown. Proteolysis is an irreversible process and could trigger persistent podocyte injury through degradation of podocyte-specific proteins. We, therefore, analyzed the expression and functional consequence of the two most prominent proteolytic systems, the ubiquitin proteasome system (UPS) and the autophagosomal/lysosomal system, in persistent and transient podocyte injuries. We show that differential upregulation of both proteolytic systems occurs in persistent human and rodent podocyte injury. The expression of specific UPS proteins in podocytes differentiated children with minimal change disease from children with FSGS and correlated with poor clinical outcome. Degradation of the podocyte-specific protein α-actinin-4 by the UPS depended on oxidative modification in membranous nephropathy. Notably, the UPS was overwhelmed in podocytes during experimental glomerular disease, resulting in abnormal protein accumulation and compensatory upregulation of the autophagosomal/lysosomal system. Accordingly, inhibition of both proteolytic systems enhanced proteinuria in persistent nephrotic disease. This study identifies altered proteolysis as a feature of persistent podocyte injury. In the future, specific UPS proteins may serve as new biomarkers or therapeutic targets in persistent nephrotic syndrome.

Pathogenesis of chronic hyperglycemia: from reductive stress to oxidative stress

Chronic overnutrition creates chronic hyperglycemia that can gradually induce insulin resistance and insulin secretion impairment. These disorders, if not intervened, will eventually be followed by appearance of frank diabetes. The mechanisms of this chronic pathogenic process are complex but have been suggested to involve production of reactive oxygen species (ROS) and oxidative stress. In this review, I highlight evidence that reductive stress imposed by overflux of NADH through the mitochondrial electron transport chain is the source of oxidative stress, which is based on establishments that more NADH recycling by mitochondrial complex I leads to more electron leakage and thus more ROS production. The elevated levels of both NADH and ROS can inhibit and inactivate glyceraldehyde 3-phosphate dehydrogenase (GAPDH), respectively, resulting in blockage of the glycolytic pathway and accumulation of glycerol 3-phospate and its prior metabolites along the pathway. This accumulation then initiates all those alternative glucose metabolic pathways such as the polyol pathway and the advanced glycation pathways that otherwise are minor and insignificant under euglycemic conditions. Importantly, all these alternative pathways lead to ROS production, thus aggravating cellular oxidative stress. Therefore, reductive stress followed by oxidative stress comprises a major mechanism of hyperglycemia-induced metabolic syndrome.

Diabetic nephropathy: are there new and potentially promising therapies targeting oxygen biology?

The multipronged drug approach targeting blood pressure and serum levels of glucose, insulin, and lipids fails to fully prevent diabetic nephropathy (DN). Recently, a broad range of anomalies associated with oxygen biology, such as hypoxia, oxidative stress (OS), and dyserythropoiesis, have been implicated in DN. This review delineates the cellular mechanisms of these anomalies to pinpoint novel therapeutic approaches. The PHD-HIF system mitigates hypoxia: HIF activates a broad range of reactions against hypoxia whereas PHD is an intracellular oxygen sensor negatively regulating HIF. The Keap1-Nrf2 system mitigates OS: Nrf2 activates cellular reactions against OS whereas Keap1 negatively regulates Nrf2. Clinical trials of PHD inhibitors to correct anemia in patients with CKD as well as of a Nrf2 activator, bardoxolone methyl, for DN are under way, even if the latter has been recently interrupted. A specific PHD1 inhibitor, a Keap1 inhibitor, and an allosteric effector of hemoglobin may offer alternative, novel therapies. Erythropoietin (EPO) is critical for the development of erythroid progenitors and thus for tissue oxygen supply. Renal EPO-producing (REP) cells, originating from neural crests, but not fibroblasts from injured tubular epithelial cells, transdifferentiate into myofibroblasts and contribute to renal fibrosis. Agents restoring the initial function of REP cells might retard renal fibrosis. These newer approaches targeting oxygen biology may offer new treatments not only for DN but also for several diseases in which hypoxia and/or OS is a final, common pathway.

The world pandemic of vitamin D deficiency could possibly be explained by cellular inflammatory response activity induced by the renin-angiotensin system

This review attempts to show that there may be a relationship between inflammatory processes induced by chronic overstimulation of the renin-angiotensin system (RAS) and the worldwide deficiency of vitamin D (VitD) and that both disorders are probably associated with environmental factors. Low VitD levels represent a risk factor for several apparently different diseases, such as infectious, autoimmune, neurodegenerative, and cardiovascular diseases, as well as diabetes, osteoporosis, and cancer. Moreover, VitD insufficiency seems to predispose to hypertension, metabolic syndrome, left ventricular hypertrophy, heart failure, and chronic vascular inflammation. On the other hand, inappropriate stimulation of the RAS has also been associated with the pathogenesis of hypertension, heart attack, stroke, and hypertrophy of the left ventricle and vascular smooth muscle cells. Because VitD receptors (VDRs) and RAS receptors are almost distributed in the same tissues, a possible link between VitD and the RAS is even more plausible. Furthermore, from an evolutionary point of view, both systems were developed simultaneously, actively participating in the regulation of inflammatory and immunological mechanisms. Changes in RAS activity and activation of the VDR seem to be inversely related; thus any changes in one of these systems would have a completely opposite effect on the other, making it possible to speculate that the two systems could have a feedback relationship. In fact, the pandemic of VitD deficiency could be the other face of increased RAS activity, which probably causes lower activity or lower levels of VitD. Finally, from a therapeutic point of view, the combination of RAS blockade and VDR stimulation appears to be more effective than either RAS blockade or VDR stimulation individually.

Cardiovascular redox and ox stress proteomics

SIGNIFICANCE

Oxidative post-translational modifications (OPTMs) have been demonstrated as contributing to cardiovascular physiology and pathophysiology. These modifications have been identified using antibodies as well as advanced proteomic methods, and the functional importance of each is beginning to be understood using transgenic and gene deletion animal models. Given that OPTMs are involved in cardiovascular pathology, the use of these modifications as biomarkers and predictors of disease has significant therapeutic potential. Adequate understanding of the chemistry of the OPTMs is necessary to determine what may occur in vivo and which modifications would best serve as biomarkers.

RECENT ADVANCES

By using mass spectrometry, advanced labeling techniques, and antibody identification, OPTMs have become accessible to a larger proportion of the scientific community. Advancements in instrumentation, database search algorithms, and processing speed have allowed MS to fully expand on the proteome of OPTMs. In addition, the role of enzymatically reversible OPTMs has been further clarified in preclinical models.

CRITICAL ISSUES

The identification of OPTMs suffers from limitations in analytic detection based on the methodology, instrumentation, sample complexity, and bioinformatics. Currently, each type of OPTM requires a specific strategy for identification, and generalized approaches result in an incomplete assessment.

FUTURE DIRECTIONS

Novel types of highly sensitive MS instrumentation that allow for improved separation and detection of modified proteins and peptides have been crucial in the discovery of OPTMs and biomarkers. To further advance the identification of relevant OPTMs in advanced search algorithms, standardized methods for sample processing and depository of MS data will be required.

Effect of deferiprone, an oral iron chelator, in diabetic and non-diabetic glomerular disease

Compelling experimental evidence exists for the role of oxidants and iron in glomerular disease. In preliminary studies, we confirmed increased urinary catalytic iron in patients with glomerulonephritis and diabetic nephropathy. We conducted two separate single-center, prospective, single-armed, open-labeled, proof-of-concept studies to evaluate the safety and efficacy of an oral iron chelator in patients with glomerulonephritis and diabetic nephropathy. Study 1 comprised 15 patients with biopsy-proven glomerulonephritis who had persistent proteinuria despite treatment with steroids and/or cyclophosphamides. Study 2 comprised 38 adult patients with diabetic nephropathy. Patients in Study 1 were treated with deferiprone (50 mg/kg/day) in three divided doses for 6 months and Study 2 patients were treated for 9 months. In Study 1, two patients had severe gastrointestinal intolerance and withdrew from the study after one dose and are not included in the results. There was a significant reduction (47 ± 9% mean) in 24-h urinary protein (4.01 ± 1.61 to 2.21 ± 1.62 [p = 0.009]), with no significant changes in serum creatinine. In Study 2, treatment with deferiprone resulted in a marked, persistent drop in the mean albumin/creatinine ratio (187 ± 47 at baseline to 25 ± 7 mg/g, [p = 0.01]) and stable renal function over a 9-month period. No clinically significant adverse events were observed in either study. Although these are small, open-labeled, and non-randomized studies, our results suggest that future randomized, double-blind trials examining the utility of deferiprone to treat glomerular diseases appear warranted.

Superoxide reaction with tyrosyl radicals generates para-hydroperoxy and para-hydroxy derivatives of tyrosine

Tyrosine-derived hydroperoxides are formed in peptides and proteins exposed to enzymatic or cellular sources of superoxide and oxidizing species as a result of the nearly diffusion-limited reaction between tyrosyl radical and superoxide. However, the structure of these products, which informs their reactivity in biology, has not been unequivocally established. We report here the complete characterization of the products formed in the addition of superoxide, generated from xanthine oxidase, to several peptide-derived tyrosyl radicals, formed from horseradish peroxidase. RP-HPLC, LC-MS, and NMR experiments indicate that the primary stable products of superoxide addition to tyrosyl radical are para-hydroperoxide derivatives (para relative to the position of the OH in tyrosine) that can be reduced to the corresponding para-alcohol. In the case of glycyl-tyrosine, a stable 3-(1-hydroperoxy-4-oxocyclohexa-2,5-dien-1-yl)-L-alanine was formed. In tyrosyl-glycine and Leu-enkephalin, which have N-terminal tyrosines, bicyclic indolic para-hydroperoxide derivatives were formed ((2S,3aR,7aR)-3a-hydroperoxy-6-oxo-2,3,3a,6,7,7a-hexahydro-1H-indole-2-carboxylic acid) by the conjugate addition of the free amine to the cyclohexadienone. It was also found that significant amounts of the para-OH derivative were generated from the hydroxyl radical, formed on exposure of tyrosine-containing peptides to Fenton conditions. The para-OOH and para-OH derivatives are much more reactive than other tyrosine oxidation products and may play important roles in physiology and disease.

Short-term hyperglycemia increases arterial superoxide production and iron dysregulation in atherosclerotic monkeys

The incidence and severity of atherosclerotic vascular disease are increased in diabetic patients, in part because of increased production of reactive oxygen species (ROS). Previously, we found both increased atherosclerosis and arterial protein oxidation 6 months after streptozotocin-induced diabetes in monkeys fed an atherogenic diet, the pattern of which was indicative of redox-active transition metal involvement. The goal of this study was to determine if short-term (1 month) hyperglycemia increases oxidative stress and dysregulates iron metabolism before differences in atherosclerosis. Cynomolgus monkeys with preexisting atherosclerosis were stratified by dietary history and plasma lipids and received either streptozotocin (STZ-DM; n = 10) or vehicle (control; n = 10). One month after diabetes induction, blood and artery samples were collected. There were no differences in plasma lipoprotein cholesterol, arterial cholesterol, and atherosclerosis between control and STZ-DM. However, plasma lipid peroxides were elevated 137% (P < .01); arterial superoxide was increased 47% (P < .05); plasma ferritin, an indicator of whole-body iron stores, was 46% higher (P < .05); and iron deposition within aortic atherosclerotic lesions was more prevalent in STZ-DM compared with controls. Arterial levels of the antioxidant enzymes, superoxide dismutase, catalase, and heme oxygenase-1 were not higher in STZ-DM, although superoxide was higher, suggesting impaired antioxidant response. The increase in ROS before differences in atherosclerosis supports ROS as an initiating event in diabetic vascular disease. Further studies are needed to determine if increases in iron stores and arterial iron deposition promote hydroxyl radical formation from superoxide and accelerate diabetic vascular damage.

Pathogenetic role of eNOS uncoupling in cardiopulmonary disorders

The homodimeric flavohemeprotein endothelial nitric oxide synthase (eNOS) oxidizes l-arginine to l-citrulline and nitric oxide (NO), which acutely vasodilates blood vessels and inhibits platelet aggregation. Chronically, eNOS has a major role in the regulation of blood pressure and prevention of atherosclerosis by decreasing leukocyte adhesion and smooth muscle proliferation. However, a disturbed vascular redox balance results in eNOS damage and uncoupling of oxygen activation from l-arginine conversion. Uncoupled eNOS monomerizes and generates reactive oxygen species (ROS) rather than NO. Indeed, eNOS uncoupling has been suggested as one of the main pathomechanisms in a broad range of cardiovascular and pulmonary disorders such as atherosclerosis, ventricular remodeling, and pulmonary hypertension. Therefore, modulating uncoupled eNOS, in particular eNOS-dependent ROS generation, is an attractive therapeutic approach to preventing and/or treating cardiopulmonary disorders, including protective effects during cardiothoracic surgery. This review provides a comprehensive overview of the pathogenetic role of uncoupled eNOS in both cardiovascular and pulmonary disorders. In addition, the related therapeutic possibilities such as supplementation with the eNOS substrate l-arginine, volatile NO, and direct NO donors as well as eNOS modulators such as the eNOS cofactor tetrahydrobiopterin and folic acid are discussed in detail.

Angiotensin II type 1A receptors in vascular smooth muscle cells do not influence aortic remodeling in hypertension

Vascular injury and remodeling are common pathological sequelae of hypertension. Previous studies have suggested that the renin-angiotensin system acting through the type 1 angiotensin II (AT(1)) receptor promotes vascular pathology in hypertension. To study the role of AT(1) receptors in this process, we generated mice with cell-specific deletion of AT(1) receptors in vascular smooth muscle cells using Cre/Loxp technology. We crossed the SM22α-Cre transgenic mouse line expressing Cre recombinase in smooth muscle cells with a mouse line bearing a conditional allele of the Agtr1a gene (Agtr1a (flox)), encoding the major murine AT(1) receptor isoform (AT(1A)). In SM22α-Cre(+)Agtr1a (flox/flox) (SMKO) mice, AT(1A) receptors were efficiently deleted from vascular smooth muscle cells in larger vessels but not from resistance vessels such as preglomerular arterioles. Thus, vasoconstrictor responses to angiotensin II were preserved in SMKO mice. To induce hypertensive vascular remodeling, mice were continuously infused with angiotensin II for 4 weeks. During infusion of angiotensin II, blood pressures increased significantly and to a similar extent in SMKO and control mice. In control mice, there was evidence of vascular oxidative stress indicated by enhanced nitrated tyrosine residues in segments of aorta; this was significantly attenuated in SMKO mice. Despite these differences in oxidative stress, the extent of aortic medial expansion induced by angiotensin II infusion was virtually identical in both groups. Thus, vascular AT(1A) receptors promote oxidative stress in the aortic wall but are not required for remodeling in angiotensin II-dependent hypertension.

Quantitative analysis of amino Acid oxidation markers by tandem mass spectrometry

Oxidative stress plays a central role in the pathogenesis of diverse chronic inflammatory disorders including diabetic complications, cardiovascular disease, aging, neurodegenerative disease, autoimmune disorders, and pulmonary fibrosis. Protein misfolding can lead to chronic endoplasmic reticulum (ER) stress which can exacerbate oxidative stress. This can trigger apoptotic cascades resulting in chronic inflammatory disorders. Despite intense interest in origins and magnitude of oxidative stress, ability to quantify oxidants has been limited because they are short lived. We have developed quantitative mass spectrometry (MS)-based analytical strategies to analyze stable end products of protein oxidation. These molecules provide quantitative and mechanistic assessment of degree of oxidative stress in cell cultures, tissues, and biofluids of animal models of disease and human samples. Our studies support the hypothesis that unique reactive intermediates generated in localized microenvironments of vulnerable tissues promote end-organ damage. The ability to quantify these changes and assess response to therapies will be pivotal in understanding disease mechanisms and monitoring efficacy of therapy.

Diabetic nephropathy: a disorder of oxygen metabolism?

Chronic hypoxia induces sequential abnormalities in oxygen metabolism (for example, oxidative stress, nitrosative stress, advanced glycation, carbonyl stress, endoplasmic reticulum stress) in the kidneys of individuals with diabetes. Identification of these abnormalities improves our understanding of therapeutic benefits that can be achieved with antihypertensive agents, the control of hyperglycemia and/or hyperinsulinemia and the dietary correction of obesity. Key to the body's defense against hypoxia is hypoxia-inducible factor, the activity of which is modulated by prolyl hydroxylases (PHDs)-oxygen sensors whose inhibition may prove therapeutic. Renal benefits of small-molecule PHD inhibitors have been documented in several animal models, including those of diabetic nephropathy. Three different PHD isoforms have been identified (PHD1, PHD2 and PHD3) and their respective roles have been delineated in knockout mouse studies. Unfortunately, none of the current inhibitors is specific for a distinct PHD isoform. Nonspecific inhibition of PHDs might induce adverse effects, such as those associated with PHD2 inhibition. Specific disruption of PHD1 induces hypoxic tolerance, without angiogenesis and erythrocytosis, through the reprogramming of basal oxygen metabolism and decreased generation of oxidative stress in hypoxic mitochondria. A specific PHD1 inhibitor might, therefore, offer a novel therapy for abnormal oxygen metabolism not only in the diabetic kidney, but also in other diseases for which hypoxia is a final, common pathway.

Erythritol is a sweet antioxidant

OBJECTIVE

Hyperglycemia, oxidative stress, and the onset and progression of diabetic complications are strongly linked. Reduction of oxidative stress could be of utmost importance in the long-term treatment of diabetic patients. The chronic nature of the disease calls for a mode of antioxidant intake that can be sustained easily, e.g., by the diet. Erythritol, a simple polyol, could be such a compound. It is orally available, well tolerated, and its chemical structure resembles that of mannitol, a well-known hydroxyl radical (HO*) scavenger.

METHODS

We studied the antioxidant properties of erythritol in vitro and subsequently determined its antioxidant activity and its vasoprotective effect in the streptozotocin diabetic rat.

RESULTS

Erythritol was shown to be an excellent HO* radical scavenger and an inhibitor of 2,2'-azobis-2-amidinopropane dihydrochloride-induced hemolysis but inert toward superoxide radicals. High-performance liquid chromatographic and electron spin resonance spectroscopy studies showed that the reaction of erythritol with hydroxyl radicals resulted in the formation of erythrose and erythrulose by abstraction of a carbon-bound hydrogen atom. In the streptozotocin diabetic rat, erythritol displayed an endothelium-protective effect and, in accordance with the in vitro experiments, erythrose was found in the urine of erythritol-consuming rats.

CONCLUSION

Erythritol acts as an antioxidant in vivo and may help protect against hyperglycemia-induced vascular damage.

Decreased nitric oxide bioavailability in a mouse model of Fabry disease

Fabry disease is a lysosomal storage disorder that results in an accumulation of globotriaosylceramide in vascular tissue secondary to a deficiency in alpha-galactosidase A. The glycolipid-associated vasculopathy results in strokes and cardiac disease, but the basis for these complications is poorly understood. Recent studies in the alpha-galactosidase A-knockout mouse suggested that a decrease in nitric oxide (NO) bioavailability may play a role in the abnormal thrombosis, atherogenesis, and vasorelaxation that are characteristic of these mice. To understand better the association between impaired NO bioavailability and glycolipid accumulation, we studied alpha-galactosidase A-knockout mice or primary cultures of their aortic endothelial cells. Treatment of knockout mice with a potent inhibitor of glucosylceramide synthase reversed accumulation of globotriaosylceramide but failed to normalize the defect in vasorelaxation. Basal and insulin-stimulated endothelial NO synthase (eNOS) activities in endothelial cells derived from knockout mice were lower than those observed from wild-type mice; normalization of glycolipid only partially reversed this reduction in eNOS activity. The loss of eNOS activity associated with a decrease in high molecular weight caveolin oligomers in endothelial cells and isolated caveolae, suggesting a role for glycolipids in caveolin assembly. Finally, concentrations of ortho-tyrosine and nitrotyrosine in knockout endothelial cells were markedly elevated compared with wild-type endothelial cells. These findings are consistent with a loss of NO bioavailability, associated with eNOS uncoupling, in the alpha-galactosidase A-knockout mouse.

Postprandial hyperglycemia as an etiological factor in vascular failure

Postprandial hyperglycemia is characterized by hyperglycemic spikes that induce endothelial dysfunction, inflammatory reactions and oxidative stress, which may lead to progression of atherosclerosis and occurrence of cardiovascular events. Emerging data indicate that postprandial hyperglycemia or even impaired glucose tolerance may predispose to progression of atherosclerosis and cardiovascular events. There is evidence that postprandial hyperglycemia, but not fasting hyperglycemia, independently predicts the occurrence of cardiovascular events. We proposed a concept of 'vascular failure' as a comprehensive syndrome of vascular dysfunction extending from risk factors to advanced atherosclerotic disease. Postprandial hyperglycemia is therefore one of the very important pathophysiological states contributing to vascular failure. Accordingly, controlling postprandial hyperglycemia should be the focus of future clinical investigation as a potential target for preventing vascular failure.

Relationship of metabolic syndrome with incident aortic valve calcium and aortic valve calcium progression: the Multi-Ethnic Study of Atherosclerosis (MESA)

OBJECTIVE

Metabolic syndrome (MetS) has been associated with increased prevalence of aortic valve calcium (AVC) and with increased progression of aortic stenosis. The purpose of this study was to determine whether MetS is associated with increased risks for the development of new ("incident") AVC or for progression of established AVC as assessed by CT.

RESEARCH DESIGN AND METHODS

The relationships of MetS or its components as well as of diabetes to risks for incident AVC or AVC progression were studied among participants with CT scans performed at baseline and at either year 2 or year 3 examinations in the Multi-Ethnic Study of Atherosclerosis (MESA).

RESULTS

Of 5,723 MESA participants meeting criteria for inclusion, 1,674 had MetS by Adult Treatment Panel III criteria, whereas 761 had diabetes. Among the 5,123 participants without baseline AVC, risks for incident AVC, adjusted for time between scans, age, sex, race/ethnicity, LDL cholesterol, lipid-lowering medications, and smoking, were increased significantly for MetS (odds ratio [OR] 1.67 [95% CI 1.21-2.31]) or diabetes (2.06 [1.39-3.06]). In addition, there was an increase in incident AVC risk with increasing number of MetS components. Similar results were found using the International Diabetes Federation MetS criteria. Among the 600 participants (10.5%) with baseline AVC, neither MetS nor diabetes was associated with AVC progression.

CONCLUSIONS

In the MESA cohort, MetS was associated with a significant increase in incident ("new") AVC, raising the possibility that MetS may be a potential therapeutic target to prevent AVC development.

Lipids versus glucose in inflammation and the pathogenesis of macrovascular disease in diabetes

Type 1 and type 2 diabetes both accelerate cardiovascular disease, yet the triggers are likely different for the two types of diabetes. Results from large-scale clinical trials suggest that intense blood glucose control can reduce cardiovascular events many years later in patients with type 1 diabetes. In type 2 diabetes, mechanisms related to insulin resistance and obesity may be more prominent in promoting atherosclerosis. In this article, we discuss the potential effects of hyperglycemia and diabetes-induced lipid abnormalities on atherosclerosis, particularly focusing on advanced stages of atherosclerosis and evidence from mouse models. In addition, we discuss new research findings in monocyte/macrophage biology that may present intriguing new areas of research related to diabetes and atherosclerosis.

Diabetic cardiomyopathy-associated dysfunction in spatially distinct mitochondrial subpopulations

Diabetic cardiomyopathy is the leading cause of heart failure among diabetic patients, and mitochondrial dysfunction has been implicated as an underlying cause in the pathogenesis. Cardiac mitochondria consist of two spatially, functionally, and morphologically distinct subpopulations, termed subsarcolemmal mitochondria (SSM) and interfibrillar mitochondria (IFM). SSM are situated beneath the plasma membrane, whereas IFM are embedded between myofibrils. The goal of this study was to determine whether spatially distinct cardiac mitochondrial subpopulations respond differently to a diabetic phenotype. Swiss-Webster mice were subjected to intraperitoneal injections of streptozotocin or citrate saline vehicle. Five weeks after injections, diabetic hearts displayed decreased rates of contraction, relaxation, and left ventricular developed pressures (P < 0.05 for all three). Both mitochondrial size (forward scatter, P < 0.01) and complexity (side scatter, P < 0.01) were decreased in diabetic IFM but not diabetic SSM. Electron transport chain complex II respiration was decreased in diabetic SSM (P < 0.05) and diabetic IFM (P < 0.01), with the decrease being greater in IFM. Furthermore, IFM complex I respiration and complex III activity were decreased with diabetes (P < 0.01) but were unchanged in SSM. Superoxide production was increased only in diabetic IFM (P < 0.01). Oxidative damage to proteins and lipids, indexed through nitrotyrosine residues and lipid peroxidation, were higher in diabetic IFM (P < 0.05 and P < 0.01, respectively). The mitochondria-specific phospholipid cardiolipin was decreased in diabetic IFM (P < 0.01) but not SSM. These results indicate that diabetes mellitus imposes a greater stress on the IFM subpopulation, which is associated, in part, with increased superoxide generation and oxidative damage, resulting in morphological and functional abnormalities that may contribute to the pathogenesis of diabetic cardiomyopathy.

Mass spectrometric quantification of amino acid oxidation products identifies oxidative mechanisms of diabetic end-organ damage

Diabetes mellitus is increasingly prevalent worldwide. Diabetic individuals are at markedly increased risk for premature death due to cardiovascular disease. Furthermore, substantial morbidity results from microvascular complications which include retinopathy, nephropathy, and neuropathy. Clinical studies involving diabetic patients have suggested that degree of diabetic hyperglycemia correlates with risk of complications. Recent evidence implicates a central role for oxidative stress and vascular inflammation in all forms of insulin resistance, obesity, diabetes and its complications. Although, glucose promotes glycoxidation reactions in vitro and products of glycoxidation and lipoxidation are elevated in plasma and tissue in diabetics, the exact relationships among hyperglycemia, the diabetic state, and oxidative stress are not well-understood. Using a combination of in vitro and in vivo experiments, we have identified amino acid oxidation markers that serve as molecular fingerprints of specific oxidative pathways. Quantification of these products utilizing highly sensitive and specific gas chromatography/mass spectrometry in animal models of diabetic complications and in humans has provided insights in oxidative pathways that result in diabetic complications. Our studies strongly support the hypothesis that unique oxidants are generated in the microenvironment of tissues vulnerable to diabetic damage. Potential therapies interrupting these reactive pathways in target tissue are likely to be beneficial in preventing diabetic complications.

Cardiovascular disease risk in type 2 diabetes mellitus: insights from mechanistic studies

Individuals with type 2 diabetes mellitus have increased cardiovascular disease risk compared with those without diabetes. Treatment of the residual risk, other than blood pressure and LDL-cholesterol control, remains important as the rate of diabetes increases worldwide. The accelerated atherosclerosis and cardiovascular disease in diabetes is likely to be multifactorial and therefore several therapeutic approaches can be considered. Results of mechanistic studies done in vitro and in vivo--animals and people--can provide important insights with the potential to improve clinical management decisions and outcomes. In this Review, we focus on three areas in which pathophysiological considerations could be particularly informative--ie, the roles of hyperglycaemia, diabetic dyslipidaemia (other than the control of LDL-cholesterol concentrations), and inflammation (including that in adipose tissue) in the acceleration of vascular injury.

Role of oxidative stress in high glucose-induced decreased expression of Gialpha proteins and adenylyl cyclase signaling in vascular smooth muscle cells

We have recently shown that aorta from streptozotocin (STZ)-induced diabetic rats and A10 vascular smooth muscle cells (VSMCs) exposed to high glucose exhibited decreased levels of inhibitory guanine nucleotide regulatory protein (Gi)alpha proteins. In the present studies, we investigated the implication of oxidative stress in the hyperglycemia/diabetes-induced decreased expression of the Gialpha protein and adenylyl cyclase signaling in VSMCs by using antioxidants. The levels of Gialpha proteins were significantly decreased in A10 VSMCs exposed to high glucose and in aortic VSMCs from STZ-diabetic rats compared with control cells and were restored to control levels by antioxidants. In addition, (111)Mn-tetralis(benzoic acid porphyrin) and uric acid, scavengers of peroxynitrite, and NG-nitro-L-arginine methyl ester, an inhibitor of nitric oxide synthase but not catalase, also restored the high glucose-induced decreased expression of Gialpha proteins to the control levels in A10 VSMCs. Furthermore, the enhanced production of superoxide anion (O2-) and increased activity of NADPH oxidase in these cells were also restored to control levels by diphenyleneiodonium, an inhibitor of NADPH oxidase. In addition, the diminished inhibition of adenylyl cyclase activity by inhibitory hormones and forskolin-stimulated adenylyl cyclase activity by low concentrations of GTPgammaS as well as the enhanced stimulation of adenylyl cyclase by stimulatory agonists in hyperglycemic cells were restored to control levels by antioxidant treatments. These results suggest that high glucose-induced decreased levels of Gialpha proteins and associated signaling in A10 VSMCs may be attributed to the enhanced oxidative stress due to augmented levels of peroxynitrite and not to H2O2.