Effects of the superoxide dismutase-mimetic compound tempol on endothelial dysfunction in streptozotocin-induced diabetic rats

Combination therapy is it in the future for successfully treating peripheral diabetic neuropathy?

In 2022, the Center for Disease Control and Prevention reported that 11.3% of the United States population, 37.3 million people, had diabetes and 38% of the population had prediabetes. A large American study conducted in 2021 and supported by many other studies, concluded that about 47% of diabetes patients have peripheral neuropathy and that diabetic neuropathy was present in 7.5% of patients at the time of diabetes diagnosis. In subjects deemed to be pre-diabetes and impaired glucose tolerance there was a wide range of prevalence estimates (interquartile range (IQR): 6%-34%), but most studies (72%) reported a prevalence of peripheral neuropathy ≥10%. There is no recognized treatment for diabetic peripheral neuropathy (DPN) other than good blood glucose control. Good glycemic control slows progression of DPN in patients with type 1 diabetes but for patients with type 2 diabetes it is less effective. With obesity and type 2 diabetes at epidemic levels the need of a treatment for DPN could not be more important. In this article I will first present background information on the "primary" mechanisms shown from pre-clinical studies to contribute to DPN and then discuss mono- and combination therapies that have demonstrated efficacy in animal studies and may have success when translated to human subjects. I like to compare the challenge of finding an effective treatment for DPN to the ongoing work being done to treat hypertension. Combination therapy is the recognized approach used to normalize blood pressure often requiring two, three or more drugs in addition to lifestyle modification to achieve the desired outcome. Hypertension, like DPN, is a progressive disease caused by multiple mechanisms. Therefore, it seems likely as well as logical that combination therapy combined with lifestyle adjustments will be required to successfully treat DPN.

Oxidative stress contributes to reductions in microvascular endothelial- and nitric oxide-dependent dilation in women with a history of gestational diabetes

Women with a history of gestational diabetes mellitus (GDM) are twice as likely to develop cardiovascular disease and ~7x as likely to develop type II diabetes as their age-matched counterparts. However, the mechanism(s) mediating these associations remain unclear. We hypothesized that endothelium- and NO-dependent dilation would be attenuated through oxidant stress mechanisms in the microvasculature of women with a history of GDM compared to control women with a history of uncomplicated pregnancy (HC). Ten HC (35±4yrs) and 10 GDM (34±4yrs) underwent a standard local heating protocol (42°C; 0.1°C·s^-1). Two intradermal microdialysis fibers were placed in the ventral forearm for local delivery of lactated Ringer's (control), or 5mM L-ascorbate. After full expression of the local heating response, 15mM N^G-nitro-L-arginine methyl ester NO synthase-inhibition) was perfused. Red cell flux was measured continuously by laser-Doppler flowmetry and cutaneous vascular conductance (CVC=flux/MAP) was standardized to maximum (%CVCmax; 28mM SNP + 43°C). Urine albumin:creatinine ratio (ACR) was measured. GDM had attenuated endothelium-dependent (GDM: 67±7 vs. HC: 90±4%CVCmax; p<0.001) and NO-dependent (GDM: 54±7 vs. HC: 71±3%; p=0.001) dilation at the control site and tended to have higher urine ACR (p=0.06). Both endothelium-dependent (r²=0.53, p=0.02) and NO-dependent (r²=0.56, p=0.01) dilation were related to urine ACR in GDM. L-ascorbate perfusion improved endothelium-dependent (82±5%CVCmax; p=0.03 vs. control) and NO-dependent (68±5%; p=0.02 vs. control) dilation in GDM but had no effect in HC (p>0.05). Otherwise healthy women with a history of GDM have attenuated microvascular endothelial function and this dysfunction is mediated, in part, by oxidative stress.

Vascular Dysfunction in Diabetes and Obesity: Focus on TRP Channels

Transient receptor potential (TRP) superfamily consists of a diverse group of non-selective cation channels that has a wide tissue distribution and is involved in many physiological processes including sensory perception, secretion of hormones, vasoconstriction/vasorelaxation, and cell cycle modulation. In the blood vessels, TRP channels are present in endothelial cells, vascular smooth muscle cells, perivascular adipose tissue (PVAT) and perivascular sensory nerves, and these channels have been implicated in the regulation of vascular tone, vascular cell proliferation, vascular wall permeability and angiogenesis. Additionally, dysfunction of TRP channels is associated with cardiometabolic diseases, such as diabetes and obesity. Unfortunately, the prevalence of diabetes and obesity is rising worldwide, becoming an important public health problems. These conditions have been associated, highlighting that obesity is a risk factor for type 2 diabetes. As well, both cardiometabolic diseases have been linked to a common disorder, vascular dysfunction. In this review, we briefly consider general aspects of TRP channels, and we focus the attention on TRPC (canonical or classical), TRPV (vanilloid), TRPM (melastatin), and TRPML (mucolipin), which were shown to be involved in vascular alterations of diabetes and obesity or are potentially linked to vascular dysfunction. Therefore, elucidation of the functional and molecular mechanisms underlying the role of TRP channels in vascular dysfunction in diabetes and obesity is important for the prevention of vascular complications and end-organ damage, providing a further therapeutic target in the treatment of these metabolic diseases.

Catalytic Antioxidants in the Kidney

Reactive oxygen species and reactive nitrogen species are highly implicated in kidney injuries that include acute kidney injury, chronic kidney disease, hypertensive nephropathy, and diabetic nephropathy. Therefore, antioxidant agents are promising therapeutic strategies for kidney diseases. Catalytic antioxidants are defined as small molecular mimics of antioxidant enzymes, such as superoxide dismutase, catalase, and glutathione peroxidase, and some of them function as potent detoxifiers of lipid peroxides and peroxynitrite. Several catalytic antioxidants have been demonstrated to be effective in a variety of in vitro and in vivo disease models that are associated with oxidative stress, including kidney diseases. This review summarizes the evidence for the role of antioxidant enzymes in kidney diseases, the classifications of catalytic antioxidants, and their current applications to kidney diseases.

Vascular Inflammation and Oxidative Stress: Major Triggers for Cardiovascular Disease

Cardiovascular disease is a leading cause of death and reduced quality of life, proven by the latest data of the Global Burden of Disease Study, and is only gaining in prevalence worldwide. Clinical trials have identified chronic inflammatory disorders as cardiovascular risks, and recent research has revealed a contribution by various inflammatory cells to vascular oxidative stress. Atherosclerosis and cardiovascular disease are closely associated with inflammation, probably due to the close interaction of inflammation with oxidative stress. Classical therapies for inflammatory disorders have demonstrated protective effects in various models of cardiovascular disease; especially established drugs with pleiotropic immunomodulatory properties have proven beneficial cardiovascular effects; normalization of oxidative stress seems to be a common feature of these therapies. The close link between inflammation and redox balance was also supported by reports on aggravated inflammatory phenotype in the absence of antioxidant defense proteins (e.g., superoxide dismutases, heme oxygenase-1, and glutathione peroxidases) or overexpression of reactive oxygen species producing enzymes (e.g., NADPH oxidases). The value of immunomodulation for the treatment of cardiovascular disease was recently supported by large-scale clinical trials demonstrating reduced cardiovascular mortality in patients with established atherosclerotic disease when treated by highly specific anti-inflammatory therapies (e.g., using monoclonal antibodies against cytokines). Modern antidiabetic cardiovascular drugs (e.g., SGLT2 inhibitors, DPP-4 inhibitors, and GLP-1 analogs) seem to share these immunomodulatory properties and display potent antioxidant effects, all of which may explain their successful lowering of cardiovascular risk.

Drug-Free ROS Sponge Polymeric Microspheres Reduce Tissue Damage from Ischemic and Mechanical Injury

The inherent antioxidant function of poly(propylene sulfide) (PPS) microspheres (MS) was dissected for different reactive oxygen species (ROS), and therapeutic benefits of PPS-MS were explored in models of diabetic peripheral arterial disease (PAD) and mechanically induced post-traumatic osteoarthritis (PTOA). PPS-MS (∼1 μm diameter) significantly scavenged hydrogen peroxide (H2O2), hypochlorite, and peroxynitrite but not superoxide in vitro in cell-free and cell-based assays. Elevated ROS levels (specifically H2O2) were confirmed in both a mouse model of diabetic PAD and in a mouse model of PTOA, with greater than 5- and 2-fold increases in H2O2, respectively. PPS-MS treatment functionally improved recovery from hind limb ischemia based on ∼15-25% increases in hemoglobin saturation and perfusion in the footpads as well as earlier remodeling of vessels in the proximal limb. In the PTOA model, PPS-MS reduced matrix metalloproteinase (MMP) activity by 30% and mitigated the resultant articular cartilage damage. These results suggest that local delivery of PPS-MS at sites of injury-induced inflammation improves the vascular response to ischemic injury in the setting of chronic hyperglycemia and reduces articular cartilage destruction following joint trauma. These results motivate further exploration of PPS as a stand-alone, locally sustained antioxidant therapy and as a material for microsphere-based, sustained local drug delivery to inflamed tissues at risk of ROS damage.

The Catalytic Reaction of Nitroxides with Peroxyl Radicals and Its Relevance to Their Cytoprotective Properties

Sterically-hindered nitroxides such as 2,2,6,6-tetramethylpiperidin- N-oxyl (TEMPO) have long been ascribed antioxidant activity that is thought to underlie their chemopreventive and anti-aging properties. However, the most commonly invoked reactions in this context-combination with an alkyl radical to give a redox inactive alkoxyamine or catalysis of superoxide dismutation-are unlikely to be relevant under (most) physiological conditions. Herein, we characterize the kinetics and mechanisms of the reactions of TEMPO, as well as an N-arylnitroxide and an N, N-diarylnitroxide, with alkylperoxyl radicals, the propagating species in lipid peroxidation. In each of aqueous solution and lipid bilayers, they are found to be significantly more reactive than Vitamin E, Nature's premier radical-trapping antioxidant (RTA). Inhibited autoxidations of THF in aqueous buffers reveal that nitroxides reduce peroxyl radicals by electron transfer with rate constants ( k ≈ 10⁶ to >10⁷ M^-1 s^-1) that correlate with the standard potentials of the nitroxides ( E° ≈ 0.75-0.95 V vs NHE) and that this activity is catalytic in nitroxide. Regeneration of the nitroxide occurs by a two-step process involving hydride transfer from the substrate to the nitroxide-derived oxoammonium ion followed by H-atom transfer from the resultant hydroxylamine to a peroxyl radical. This reactivity extends from aqueous solution to phosphatidylcholine liposomes, where added NADPH can be used as a hydride donor to promote nitroxide recycling, as well as to cell culture, where the nitroxides are shown to be potent inhibitors of lipid peroxidation-associated cell death (ferroptosis). These insights have enabled the identification of the most potent nitroxide RTA and anti-ferroptotic agent yet described: phenoxazine- N-oxyl.

Endothelial dysfunction and vascular disease - a 30th anniversary update

The endothelium can evoke relaxations of the underlying vascular smooth muscle, by releasing vasodilator substances. The best-characterized endothelium-derived relaxing factor (EDRF) is nitric oxide (NO) which activates soluble guanylyl cyclase in the vascular smooth muscle cells, with the production of cyclic guanosine monophosphate (cGMP) initiating relaxation. The endothelial cells also evoke hyperpolarization of the cell membrane of vascular smooth muscle (endothelium-dependent hyperpolarizations, EDH-mediated responses). As regards the latter, hydrogen peroxide (H₂ O₂ ) now appears to play a dominant role. Endothelium-dependent relaxations involve both pertussis toxin-sensitive G_i (e.g. responses to α₂ -adrenergic agonists, serotonin, and thrombin) and pertussis toxin-insensitive G_q (e.g. adenosine diphosphate and bradykinin) coupling proteins. New stimulators (e.g. insulin, adiponectin) of the release of EDRFs have emerged. In recent years, evidence has also accumulated, confirming that the release of NO by the endothelial cell can chronically be upregulated (e.g. by oestrogens, exercise and dietary factors) and downregulated (e.g. oxidative stress, smoking, pollution and oxidized low-density lipoproteins) and that it is reduced with ageing and in the course of vascular disease (e.g. diabetes and hypertension). Arteries covered with regenerated endothelium (e.g. following angioplasty) selectively lose the pertussis toxin-sensitive pathway for NO release which favours vasospasm, thrombosis, penetration of macrophages, cellular growth and the inflammatory reaction leading to atherosclerosis. In addition to the release of NO (and EDH, in particular those due to H₂ O₂ ), endothelial cells also can evoke contraction of the underlying vascular smooth muscle cells by releasing endothelium-derived contracting factors. Recent evidence confirms that most endothelium-dependent acute increases in contractile force are due to the formation of vasoconstrictor prostanoids (endoperoxides and prostacyclin) which activate TP receptors of the vascular smooth muscle cells and that prostacyclin plays a key role in such responses. Endothelium-dependent contractions are exacerbated when the production of nitric oxide is impaired (e.g. by oxidative stress, ageing, spontaneous hypertension and diabetes). They contribute to the blunting of endothelium-dependent vasodilatations in aged subjects and essential hypertensive and diabetic patients. In addition, recent data confirm that the release of endothelin-1 can contribute to endothelial dysfunction and that the peptide appears to be an important contributor to vascular dysfunction. Finally, it has become clear that nitric oxide itself, under certain conditions (e.g. hypoxia), can cause biased activation of soluble guanylyl cyclase leading to the production of cyclic inosine monophosphate (cIMP) rather than cGMP and hence causes contraction rather than relaxation of the underlying vascular smooth muscle.

Effects of tempol on altered metabolism and renal vascular responsiveness in fructose-fed rats

This study investigated the effect of tempol (a superoxide dismutase mimetic) on renal vasoconstrictor responses to angiotensin II (Ang II) and adrenergic agonists in fructose-fed Sprague–Dawley rats (a model of metabolic syndrome). Rats were fed 20% fructose in drinking water (F) for 8 weeks. One fructose-fed group received tempol (FT) at 1 mmol·L–1 in drinking water for 8 weeks or as an infusion (1.5 mg·kg–1·min–1) intrarenally. At the end of the treatment regimen, the renal responses to noradrenaline, phenylephrine, methoxamine, and Ang II were determined. F rats exhibited hyperinsulinemia, hyperuricemia, hypertriglyceridemia, and hypertension. Tempol reduced blood glucose and insulin levels (all p < 0.05) in FT rats compared with their untreated counterparts. The vasoconstriction response to all agonists was lower in F rats than in control rats by about 35%–65% (all p < 0.05). Vasoconstrictor responses to noradrenaline, phenylephrine, and methoxamine but not Ang II were about 41%–75% higher in FT rats compared with F rats (all p < 0.05). Acute tempol infusion blunted responses to noradrenaline, methoxamine, and Ang II in control rats by 32%, 33%, and 62%, while it blunted responses to noradrenaline and Ang II in F rats by 26% and 32%, respectively (all p < 0.05), compared with their untreated counterparts. Superoxide radicals play a crucial role in controlling renal vascular responses to adrenergic agonists in insulin-resistant rats. Chronic but not acute tempol treatment enhances renal vascular responsiveness in fructose-fed rats.

Vascular Impairment of Epineurial Arterioles of the Sciatic Nerve: Implications for Diabetic Peripheral Neuropathy

This article reviews the impact of diabetes and its treatment on vascular function with a focus on the reactivity of epineurial arterioles, blood vessels that provide circulation to the sciatic nerve. Another focus is the relationship between the dysregulation of neurovascular function and diabetic peripheral neuropathy. Diabetic peripheral neuropathy is a debilitating disorder that occurs in more than 50 percent of patients with diabetes. The etiology involves metabolic, vascular, and immunologic pathways besides neurohormonal growth factor deficiency and extracellular matrix remodeling. In the light of this complex etiology, an effective treatment for diabetic peripheral neuropathy has not yet been identified. Current opinion postulates that any effective treatment for diabetic peripheral neuropathy will require a combination of life style and therapeutic interventions. However, a more comprehensive understanding of the factors contributing to neurovascular and neural dysfunction in diabetes is needed before such a treatment strategy can be developed. After reading this review, the reader should have gained insight into the complex regulation of vascular function and blood flow to the sciatic nerve, and the impact of diabetes on numerous elements of vascular reactivity of epineurial arterioles of the sciatic nerve.

Oxidative stress and epigenetic modifications in the pathogenesis of diabetic retinopathy

Diabetic retinopathy remains the major cause of blindness among working age adults. Although a number of metabolic abnormalities have been associated with its development, due to complex nature of this multi-factorial disease, a link between any specific abnormality and diabetic retinopathy remains largely speculative. Diabetes increases oxidative stress in the retina and its capillary cells, and overwhelming evidence suggests a bidirectional relationship between oxidative stress and other major metabolic abnormalities implicated in the development of diabetic retinopathy. Due to increased production of cytosolic reactive oxygen species, mitochondrial membranes are damaged and their membrane potentials are impaired, and complex III of the electron transport system is compromised. Suboptimal enzymatic and nonenzymatic antioxidant defense system further aids in the accumulation of free radicals. As the duration of the disease progresses, mitochondrial DNA (mtDNA) is damaged and the DNA repair system is compromised, and due to impaired transcription of mtDNA-encoded proteins, the integrity of the electron transport system is encumbered. Due to decreased mtDNA biogenesis and impaired transcription, superoxide accumulation is further increased, and the vicious cycle of free radicals continues to self-propagate. Diabetic milieu also alters enzymes responsible for DNA and histone modifications, and various genes important for mitochondrial homeostasis, including mitochondrial biosynthesis, damage and antioxidant defense, undergo epigenetic modifications. Although antioxidant administration in animal models has yielded encouraging results in preventing diabetic retinopathy, controlled longitudinal human studies remain to be conducted. Furthermore, the role of epigenetic in mitochondrial homeostasis suggests that regulation of such modifications also has potential to inhibit/retard the development of diabetic retinopathy.

Beneficial effect of troxerutin on diabetes-induced vascular damages in rat aorta: histopathological alterations and antioxidation mechanism

BACKGROUND

Diabetes is associated with micro- and macro-vascular complications affecting several organs. Oxidative stress plays a crucial role in the etiology of vascular disease in diabetes.

OBJECTIVES

The present study aimed to investigate the beneficial effect of troxerutin on diabetes-induced histopathological damages in rat aorta with focusing on its antioxidative actions.

MATERIALS AND METHODS

Male Wistar rats were randomly divided into four groups (n = 8/each): control, control plus troxerutin, diabetic and diabetic plus troxerutin. Diabetes was induced in rats by a single intraperitoneal injection of streptozotocin (50 mg/kg) and lasted for 10 weeks. Troxerutin was administered orally in concentration of 150 mg/kg/daily for one month before killing rats. At the end of treatment period, thoracic aorta was isolated and divided into two parts; one part was immersed in 10% formalin for histopathological evaluations and the other was frozen by liquid nitrogen for assessment of malondialdehyde (MDA, the main product of lipid peroxidation), activity of antioxidant enzymes superoxide dismutase (SOD) and glutathione peroxidase (GPX).

RESULTS

Lipid deposition in tunica intimae and media, thickening and structural deformity of vascular tissues as well as the level of plasma glucose and aortic tissue levels of lipid peroxidation were significantly increased in diabetic rats compared to control ones (P < 0.05). Troxerutin significantly reduced the severity of all vascular histopathological damages in treated versus untreated diabetic rats. In addition, treatment of diabetic rats with troxerutin significantly decreased the levels of MDA (5.1 ± 0.3 vs. 9.3 ± 1.2 nmol/mL) (P < 0.01) and increased the activity of antioxidant enzyme GPX compared to untreated-diabetic groups.

CONCLUSIONS

Troxerutin may reduce the vascular complications and tissue injuries induced by chronic diabetes in rat aorta through increasing the activity of tissue antioxidant system and reducing the level of lipid peroxidation.

Tempol, a superoxide dismutase mimetic agent, ameliorates cisplatin-induced nephrotoxicity through alleviation of mitochondrial dysfunction in mice

Background

Mitochondrial dysfunction is a crucial mechanism by which cisplatin, a potent chemotherapeutic agent, causes nephrotoxicity where mitochondrial electron transport complexes are shifted mostly toward imbalanced reactive oxygen species versus energy production. In the present study, the protective role of tempol, a membrane-permeable superoxide dismutase mimetic agent, was evaluated on mitochondrial dysfunction and the subsequent damage induced by cisplatin nephrotoxicity in mice.

Methods and Findings

Nephrotoxicity was assessed 72 h after a single i.p. injection of cisplatin (25 mg/kg) with or without oral administration of tempol (100 mg/kg/day). Serum creatinine and urea as well as glucosuria and proteinuria were evaluated. Both kidneys were isolated for estimation of oxidative stress markers, adenosine triphosphate (ATP) content and caspase-3 activity. Moreover, mitochondrial oxidative phosphorylation capacity, complexes I–IV activities and mitochondrial nitric oxide synthase (mNOS) protein expression were measured along with histological examinations of renal tubular damage and mitochondrial ultrastructural changes. Tempol was effective against cisplatin-induced elevation of serum creatinine and urea as well as glucosuria and proteinuria. Moreover, pretreatment with tempol notably inhibited cisplatin-induced oxidative stress and disruption of mitochondrial function by restoring mitochondrial oxidative phosphorylation, complexes I and III activities, mNOS protein expression and ATP content. Tempol also provided significant protection against apoptosis, tubular damage and mitochondrial ultrastructural changes. Interestingly, tempol did not interfere with the cytotoxic effect of cisplatin against the growth of solid Ehrlich carcinoma.

Conclusion

This study highlights the potential role of tempol in inhibiting cisplatin-induced nephrotoxicity without affecting its antitumor activity via amelioration of oxidative stress and mitochondrial dysfunction.

Diabetic cardiomyopathy and its mechanisms: Role of oxidative stress and damage

Diabetic cardiomyopathy as an important threat to health occurs with or without coexistence of vascular diseases. The exact mechanisms underlying the disease remain incompletely clear. Although several pathological mechanisms responsible for diabetic cardiomyopathy have been proposed, oxidative stress is widely considered as one of the major causes for the pathogenesis of the disease. Hyperglycemia-, hyperlipidemia-, hypertension- and inflammation-induced oxidative stress are major risk factors for the development of microvascular pathogenesis in the diabetic myocardium, which results in abnormal gene expression, altered signal transduction and the activation of pathways leading to programmed myocardial cell deaths. In the present article, we aim to provide an extensive review of the role of oxidative stress and anti-oxidants in diabetic cardiomyopathy based on our own works and literature information available.

Microvascular complications and diabetic retinopathy: recent advances and future implications

Retinal microvascular alterations have been observed during diabetic retinopathy (DR) due to the retinal susceptibility towards subtle pathological alterations. Therefore, retinal microvascular pathology is essential to understand the nature of retinal degenerations during DR. In this review, the role of retinal microvasculature complications during progression of DR, along with recent efforts to normalize such alterations for better therapeutic outcome, will be underlined. In addition, current therapeutics and future directions for advancement of standard treatment for DR patients will be discussed.

Reduction of reactive oxygen species ameliorates metabolism-secretion coupling in islets of diabetic GK rats by suppressing lactate overproduction

We previously demonstrated that impaired glucose-induced insulin secretion (IS) and ATP elevation in islets of Goto-Kakizaki (GK) rats, a nonobese model of diabetes, were significantly restored by 30-60-min suppression of endogenous reactive oxygen species (ROS) overproduction. In this study, we investigated the effect of a longer (12 h) suppression of ROS on metabolism-secretion coupling in β-cells by exposure to tempol, a superoxide (O2(-)) dismutase mimic, plus ebselen, a glutathione peroxidase mimic (TE treatment). In GK islets, both H2O2 and O2(-) were sufficiently reduced and glucose-induced IS and ATP elevation were improved by TE treatment. Glucose oxidation, an indicator of Krebs cycle velocity, also was improved by TE treatment at high glucose, whereas glucokinase activity, which determines glycolytic velocity, was not affected. Lactate production was markedly increased in GK islets, and TE treatment reduced lactate production and protein expression of lactate dehydrogenase and hypoxia-inducible factor 1α (HIF1α). These results indicate that the Warburg-like effect, which is characteristic of aerobic metabolism in cancer cells by which lactate is overproduced with reduced linking to mitochondria metabolism, plays an important role in impaired metabolism-secretion coupling in diabetic β-cells and suggest that ROS reduction can improve mitochondrial metabolism by suppressing lactate overproduction through the inhibition of HIF1α stabilization.

Outcome of periapical lesions in a rat model of type 2 diabetes: refractoriness to systemic antioxidant therapy

INTRODUCTION

This study evaluated the development of periapical lesions in a rat model of type 2 diabetes and assessed the potential actions of the antioxidant agent tempol in this model.

METHODS

Male Wistar rats were used; they received tap water (N = 5) or a 20% glucose solution (N = 15) during a period of 9 weeks. At the sixth week, periapical lesions were induced on the first mandibular molars, and the animals were subdivided into 4 groups. The subgroup 1 was composed of nondiabetic rats orally receiving saline solution (10 mL/kg). Chronically glucose-fed rats were divided into the following subgroups: (2) saline-treated animals (10 mL/kg by oral route), and animals treated with tempol by gavage at doses of (3) 50 mg/kg or (4) 100 mg/kg. The body weight was monitored thoroughly. After 21 days of apical periodontitis induction, the animals were killed, and the mandibles were collected and submitted to radiographic and histologic analysis. The livers were collected to determine free radicals, and the blood plasma was used to measure insulin levels.

RESULTS

Type 2 diabetic rats displayed a significant decrease of body weight gain and a slight increase of insulin levels, which were allied to reduced levels of the antioxidant components catalase and reduced glutathione; these alterations were reversed by tempol. Concerning the periapical lesions, neither radiographic nor histologic analysis revealed any significant difference between control and type 2 diabetic rats. In diabetic rats, the apical periodontitis was refractory to tempol treatment.

CONCLUSIONS

The extent and cellularity of periapical lesions in glucose-fed type 2 diabetic rats were similar to those seen in control rats. Despite affecting other parameters related to diabetes, tempol failed to improve the outcome of endodontic lesions in type 2 diabetic animals.

The role of adrenomedullin in the renal NADPH oxidase and (pro)renin in diabetic mice

Adrenomedullin has an antioxidative action and protects organs in various diseases. To clarify the role of adrenomedullin in diabetic nephropathy, we investigated the NADPH oxidase expression, renin-secreting granular cell (GC) hyperplasia, and glomerular matrix expansion in the streptozotocin (STZ)-induced diabetic adrenomedullin gene knockout (AMKO) mice compared with the STZ-diabetic wild mice at 10 weeks. The NADPH oxidase p47phox expression and lipid peroxidation products were enhanced in the glomeruli of the diabetic mice compared with that observed in the controls in both wild and AMKO mice. These changes were more obvious in the AMKO mice than in the wild mice. Glomerular mesangial matrix expansion was more severe in the diabetic AMKO mice than in the diabetic wild mice and exhibited a positive correlation with the degree of lipid peroxidation products in the glomeruli. Proteinuria was significantly higher in the diabetic AMKO mice than in the diabetic wild mice. The GC hyperplasia score and the renal prorenin expression were significantly increased in the diabetic AMKO mice than in the diabetic wild mice, and a positive correlation was observed with the NADPH oxidase expression in the macula densa. The endogenous adrenomedullin gene exhibits an antioxidant action via the inhibition of NADPH oxidase probably by suppressing the local renin-angiotensin system.

Role of oxidative stress in diabetes-mediated vascular dysfunction: unifying hypothesis of diabetes revisited

Oxidative stress is recognized as a key participant in the development of diabetic complications in the vasculature. One of the seminal studies advancing the role of oxidative stress in vascular endothelial cells proposed that oxidative stress-mediated diversion of glycolytic intermediates into pathological pathways was a key underlying element in the development of diabetic complications. It is widely recognized that flux through glycolysis slows during diabetes. However, several bottlenecks develop in the glycolytic pathway, including glucose transport, phosphofructokinase, glyceraldehyde-3-phosphate dehydrogenase and pyruvate kinase. Of these limiting steps in glycolysis, glyceraldehyde-3-phosphate dehydrogenase is most sensitive to oxidative stress, leading to the hypothesis that glyceraldehyde-3-phosphate inactivation by ribosylation underlies the diversion of glycolytic intermediates into pathological pathways. However, recent studies question the mechanism underlying the effect of reactive oxygen species on key enzymes of the glycolytic pathway. The present review critiques the major premises of the hypothesis and concludes that further study of the role of oxidative stress in the development of diabetes-mediated vasculature dysfunction is warranted.

Beyond AREDS: is there a place for antioxidant therapy in the prevention/treatment of eye disease?

Age-related macular degeneration (AMD), the major cause of blindness in adults (65 years of age and older), and diabetic retinopathy, the major cause of blindness in working adults, are chronic, progressive diseases with multifaceted etiologies that are not fully understood. Progression and lack of treatment of both diseases may lead to the advanced stage with neovascularization. Although the detailed cellular mechanisms leading to the development of AMD and diabetic retinopathy remain elusive, oxidative damage to the retina and its pigment epithelium are considered to be involved. Clinical studies have shown that the progression of AMD can be slowed down by nutritional antioxidants, but trials with antioxidants for diabetic retinopathy (very limited in number) have been inconclusive. Long-term administration of the AREDS antioxidants, the same nutritional antioxidants that have been demonstrated to slow the progression of AMD, have yielded exciting results in preventing the pathogenesis of retinopathy in diabetic rodents. These results suggest the merit of testing the AREDS antioxidants in a clinical trial to prevent the development and/or progression of diabetic retinopathy, with the possibility of reducing the impact of this common vision-threatening disease.

Chronic resveratrol treatment restores vascular responsiveness of cerebral arterioles in type 1 diabetic rats

Decreased dilation of cerebral arterioles via an increase in oxidative stress may be a contributing factor in the pathogenesis of diabetes-induced complications leading to cognitive dysfunction and/or stroke. Our goal was to determine whether resveratrol, a polyphenolic compound present in red wine, has a protective effect on cerebral arterioles during type 1 diabetes (T1D). We measured the responses of cerebral arterioles in untreated and resveratrol-treated (10 mg·kg(-1)·day(-1)) nondiabetic and diabetic rats to endothelial (eNOS) and neuronal (nNOS) nitric oxide synthase (NOS)-dependent agonists and to a NOS-independent agonist. In addition, we harvested brain tissue from nondiabetic and diabetic rats to measure levels of superoxide under basal conditions. Furthermore, we used Western blot analysis to determine the protein expression of eNOS, nNOS, SOD-1, and SOD-2 in cerebral arterioles and/or brain tissue from untreated and resveratrol-treated nondiabetic and diabetic rats. We found that T1D impaired eNOS- and nNOS-dependent reactivity of cerebral arterioles but did not alter NOS-independent vasodilation. While resveratrol did not alter responses in nondiabetic rats, resveratrol prevented T1D-induced impairment in eNOS- and nNOS-dependent vasodilation. In addition, superoxide levels were higher in brain tissue from diabetic rats and resveratrol reversed this increase. Furthermore, eNOS and nNOS protein were increased in diabetic rats and resveratrol produced a further increased eNOS and nNOS proteins. SOD-1 and SOD-2 proteins were not altered by T1D, but resveratrol treatment produced a decrease in SOD-2 protein. Our findings suggest that resveratrol restores vascular function and oxidative stress in T1D. We suggest that our findings may implicate an important therapeutic potential for resveratrol in treating T1D-induced cerebrovascular dysfunction.

Emerging role for antioxidant therapy in protection against diabetic cardiac complications: experimental and clinical evidence for utilization of classic and new antioxidants

Diabetes mellitus (DM) markedly potentiates the risk of cardiovascular morbidity and mortality among individuals with diabetes as compared to the non-diabetic population. After myocardial infarction (MI), DM patients have a higher incidence of death than do non-diabetics. The excess mortality and poor prognosis of these patients results primarily from the development of recurrent MI and heart failure (HF). Although several lines of evidence support a role for increased oxidative stress in a range of cardiovascular diseases, clinical trials examining the therapeutic efficacy of antioxidants have yielded conflicting results. The reasons for these incongruous results is multifactorial. An underlying theme has been lack of patient inclusion based on elevated indices of oxidative stress which could have diluted the population susceptible to benefit in the clinical trials. Laboratory evidence has accumulated indicating that oxidative stress is dramatically accentuated in cardiac abnormalities inherent in DM. In this review, we provide the emergence of experimental and clinical evidence supporting antioxidant supplementation as a cardioprotective intervention in the setting of DM. Specifically, focus will be directed on preclinical animal studies and human clinical trials that have tested the effect of antioxidant supplements on MI and HF events in the presence of DM.

Cellular and molecular mechanisms of vascular injury in diabetes--part II: cellular mechanisms and therapeutic targets

Although the mechanisms by which insulin-resistance and hyperglycemia lead to cardiovascular disease are still incompletely understood, all mechanisms apparently converge on the vessel wall and the endothelium as a common disease target. Endothelial cells play a crucial role in vascular homeostasis, providing a functional barrier and modulating several signals involved in vasomotion, as well as antiplatelet, anti-inflammatory, anti-proliferative, and anti-oxidant properties of the vessel wall. Endothelial cell dysfunction occurs early in diabetes and insulin resistance states. Since atherosclerosis may result from an imbalance between the magnitude of vascular injury and the capacity of repair, a role has been recently postulated for a defective mobilization of vascular progenitors, including endothelial progenitor cells, in the pathogenesis of vascular disease. Here we summarize the evidence for such an occurrence. We also here highlight how new insights into pathways of vascular damage in diabetes may indicate new targets for preventive and treatment strategies.

Organic nitrates and nitrate resistance in diabetes: the role of vascular dysfunction and oxidative stress with emphasis on antioxidant properties of pentaerithrityl tetranitrate

Organic nitrates represent a class of drugs which are clinically used for treatment of ischemic symptoms of angina as well as for congestive heart failure based on the idea to overcome the impaired NO bioavailability by “NO” replacement therapy. The present paper is focused on parallels between diabetes mellitus and nitrate tolerance, and aims to discuss the mechanisms underlying nitrate resistance in the setting of diabetes. Since oxidative stress was identified as an important factor in the development of tolerance to organic nitrates, but also represents a hallmark of diabetic complications, this may represent a common principle for both disorders where therapeutic intervention should start. This paper examines the evidence supporting the hypothesis that pentaerithrityl tetranitrate may represent a nitrate for treatment of ischemia in diabetic patients. This evidence is based on the considerations of parallels between diabetes mellitus and nitrate tolerance as well as on preliminary data from experimental diabetes studies.

Inhibition of endothelin-1 receptors improves impaired nitric oxide synthase-dependent dilation of cerebral arterioles in type-1 diabetic rats

OBJECTIVE

Endothelin-1 has been implicated in the pathogenesis of many cardiovascular-related diseases, including diabetes. The goal of this study was to examine the influence of endothelin-1 receptors (ET(A)) in impaired responses of cerebral (pial) arterioles in type-1 diabetic rats.

METHODS

We measured responses of cerebral arterioles in non-diabetic rats to endothelial nitric oxide synthase (eNOS)-dependent (ADP), neuronal nitric oxide synthase (nNOS)-dependent (N-methyl-d-aspartic acid [NMDA]) and NOS-independent (nitroglycerin) agonists before and during application of BQ-123, an ET(A) receptor antagonist. In addition, we harvested brain tissue from non-diabetic and diabetic rats to measure the production of superoxide anion under basal conditions and during inhibition of ET(A) receptors.

RESULTS

We found that diabetes specifically impaired eNOS- and nNOS-dependent reactivity of cerebral arterioles, but did not alter NOS-independent vasodilation. In addition, while BQ-123 did not alter responses in non-diabetic rats, BQ-123 restored impaired eNOS- and nNOS-dependent vasodilation in diabetic rats. Further, superoxide production was higher in brain tissue from diabetic rats compared with non-diabetic rats under basal conditions and BQ-123 decreased basal production of superoxide in diabetic rats.

CONCLUSION

We suggest that activation of ET(A) receptors during type-1 diabetes mellitus plays an important role in impaired eNOS- and nNOS-dependent dilation of cerebral arterioles.

Effect of Agaricus blazei Murill on the pulmonary tissue of animals with streptozotocin-induced diabetes

The present study was designed to evaluate the oxidative stress as well as the therapeutic effect of Agaricus blazei Muril (A. Blazei) in rats with streptozotocin-induced diabetes. We used 25 Wistar rats, and DM was induced by injecting streptozotocin (70 mg/Kg i.p.). Agaricus blazei Muril was administered daily starting 40 days after disease onset. A. Blazei was tested as an aqueous extract for its phytochemical composition, and its antioxidant activity in vitro was also evaluated. Lipoperoxidation (LPO), and superoxide dismutase (SOD), catalase, and glutathione peroxidase activities were measured in the pulmonary tissue, as well as the presence of inducible nitric oxide synthase (iNOS), through immunohistochemistry. An anatomopathologic study was also performed. Phytochemical screening of A. Blazei detected the presence of alkaloids and saponins. The extract exhibited a significant antioxidant activity in the DPPH-scavenging and the hipoxanthine/xanthine oxidase assays. Pulmonary LPO increased in diabetic animals (0.43 ± 0.09; P < .001) as compared to the control group (0.18 ± 0.02), followed by a reduction in the A. Blazei-treated group (0.33 ± 0.04; P < .05). iNOS was found increased in the lung in diabetic rats and reduced in the A. Blazei-treated group. The pulmonary tissue in diabetic rats showed oxidative alterations related to the streptozotocin treatment. The A. Blazei treatment effectively reduced the oxidative stress and contributed to tissue recovery.

Mitochondrial dysfunction in diabetes: from molecular mechanisms to functional significance and therapeutic opportunities

Given their essential function in aerobic metabolism, mitochondria are intuitively of interest in regard to the pathophysiology of diabetes. Qualitative, quantitative, and functional perturbations in mitochondria have been identified and affect the cause and complications of diabetes. Moreover, as a consequence of fuel oxidation, mitochondria generate considerable reactive oxygen species (ROS). Evidence is accumulating that these radicals per se are important in the pathophysiology of diabetes and its complications. In this review, we first present basic concepts underlying mitochondrial physiology. We then address mitochondrial function and ROS as related to diabetes. We consider different forms of diabetes and address both insulin secretion and insulin sensitivity. We also address the role of mitochondrial uncoupling and coenzyme Q. Finally, we address the potential for targeting mitochondria in the therapy of diabetes.

Selective inhibition of protein kinase C beta(2) attenuates inducible nitric oxide synthase-mediated cardiovascular abnormalities in streptozotocin-induced diabetic rats

OBJECTIVE

Impaired cardiovascular function in diabetes is partially attributed to pathological overexpression of inducible nitric oxide synthase (iNOS) in cardiovascular tissues. We examined whether the hyperglycemia-induced increased expression of iNOS is protein kinase C-beta(2) (PKCbeta(2)) dependent and whether selective inhibition of PKCbeta reduces iNOS expression and corrects abnormal hemodynamic function in streptozotocin (STZ)-induced diabetic rats.

RESEARCH DESIGN AND METHODS

Cardiomyocytes and aortic vascular smooth muscle cells (VSMC) from nondiabetic rats were cultured in low (5.5 mmol/l) or high (25 mmol/l) glucose or mannitol (19.5 mmol/l mannitol + 5.5 mmol/l glucose) conditions in the presence of a selective PKCbeta inhibitor, LY333531 (20 nmol/l). Further, the in vivo effects of PKCbeta inhibition on iNOS-mediated cardiovascular abnormalities were tested in STZ-induced diabetic rats.

RESULTS

Exposure of cardiomyocytes to high glucose activated PKCbeta(2) and increased iNOS expression that was prevented by LY333531. Similarly, treatment of VSMC with LY333531 prevented high glucose-induced activation of nuclear factor kappaB, extracellular signal-related kinase, and iNOS overexpression. Suppression of PKCbeta(2) expression by small interference RNA decreased high-glucose-induced nuclear factor kappaB and extracellular signal-related kinase activation and iNOS expression in VSMC. Administration of LY333531 (1 mg/kg/day) decreased iNOS expression and formation of peroxynitrite in the heart and superior mesenteric arteries and corrected the cardiovascular abnormalities in STZ-induced diabetic rats, an action that was also observed with a selective iNOS inhibitor, L-NIL.

CONCLUSIONS

Collectively, these results suggest that inhibition of PKCbeta(2) may be a useful approach for correcting abnormal hemodynamics in diabetes by preventing iNOS mediated nitrosative stress.

High-cholesterol diet augments endothelial dysfunction via elevated oxidative stress and reduced tetrahydrobiopterin in Ins2(Akita) mice, an autosomal dominant mutant type 1 diabetic model

1. Oxidative stress contributes to endothelial dysfunction and atherogenesis in diabetes. The present study tested the hypothesis that a high-cholesterol diet accelerates endothelial dysfunction in Ins2(Akita) mice, a Type 1 diabetic model with a spontaneous autosomal preproinsulin gene (Ins2 gene) mutation, through further increase of superoxide production. 2. The Ins2(Akita) diabetic mice were fed a high-cholesterol diet (1.25% cholesterol) for 4 months. Some Ins2(Akita) mice were also treated for 4 months with the selective NADPH oxidase inhibitor apocynin (4 mg/kg per day in drinking water). Oxidative stress markers, tetrahydrobiopterin (BH4) levels, GTP cyclohydrolase I activity and endothelial function were determined in serum or arteries afterwards. 3. Serum lipid peroxidation and arterial superoxide levels were increased, whereas arterial BH(4) levels and GTP cyclohydrolase I activity were decreased, in Ins2(Akita) mice on a high-cholesterol diet, resulting in impaired endothelium-dependent nitric oxide-mediated relaxation in response to acetylcholine. 4. In vivo treatment with apocynin not only blunted serum lipid peroxidation and arterial superoxide levels, but also increased BH4 levels and GTP cyclohydrolase I activity, resulting in improved endothelium-dependent relaxation. 5. These results suggest that NADPH oxidase may play a potential role in oxidative stress-induced arterial BH4 and GTP cyclohydrolase I deficiency, resulting in endothelial dysfunction in Ins2(Akita) Type 1 diabetic mice fed a high-cholesterol diet.

Endothelial dysfunction and vascular disease

The endothelium can evoke relaxations (dilatations) of the underlying vascular smooth muscle, by releasing vasodilator substances. The best characterized endothelium-derived relaxing factor (EDRF) is nitric oxide (NO). The endothelial cells also evoke hyperpolarization of the cell membrane of vascular smooth muscle (endothelium-dependent hyperpolarizations, EDHF-mediated responses). Endothelium-dependent relaxations involve both pertussis toxin-sensitive G(i) (e.g. responses to serotonin and thrombin) and pertussis toxin-insensitive G(q) (e.g. adenosine diphosphate and bradykinin) coupling proteins. The release of NO by the endothelial cell can be up-regulated (e.g. by oestrogens, exercise and dietary factors) and down-regulated (e.g. oxidative stress, smoking and oxidized low-density lipoproteins). It is reduced in the course of vascular disease (e.g. diabetes and hypertension). Arteries covered with regenerated endothelium (e.g. following angioplasty) selectively loose the pertussis toxin-sensitive pathway for NO release which favours vasospasm, thrombosis, penetration of macrophages, cellular growth and the inflammatory reaction leading to atherosclerosis. In addition to the release of NO (and causing endothelium-dependent hyperpolarizations), endothelial cells also can evoke contraction (constriction) of the underlying vascular smooth muscle cells by releasing endothelium-derived contracting factor (EDCF). Most endothelium-dependent acute increases in contractile force are due to the formation of vasoconstrictor prostanoids (endoperoxides and prostacyclin) which activate TP receptors of the vascular smooth muscle cells. EDCF-mediated responses are exacerbated when the production of NO is impaired (e.g. by oxidative stress, ageing, spontaneous hypertension and diabetes). They contribute to the blunting of endothelium-dependent vasodilatations in aged subjects and essential hypertensive patients.

Chronic inhibition of inducible nitric oxide synthase ameliorates cardiovascular abnormalities in streptozotocin diabetic rats

Previous studies from our lab have demonstrated cardiovascular abnormalities such as depressed mean arterial blood pressure and heart rate, endothelial dysfunction and attenuated pressor responses to vasoactive agents in streptozotocin diabetic rats. We investigated whether these abnormalities are due to diabetes-associated chronic activation of inducible nitric oxide synthase (iNOS). Control and streptozotocin (60 mg/kg, iv) diabetic rats were treated with either vehicle or N6-(1-Iminoethyl)-L-lysine dihydrochloride (L-NIL, 3 mg/kg/day, p.o), a specific inhibitor of iNOS for 8 weeks. At the end of treatment, the mean arterial blood pressure and heart rate were measured in freely moving conscious rats. Further, pressor responses to bolus doses of methoxamine were determined. Endothelial nitric oxide synthase (eNOS) and iNOS expression as well as nitrotyrosine (NT) levels were assessed in the heart and superior mesenteric arteries by western blot and immunohistochemistry. Untreated diabetic rats showed depressed mean arterial blood pressure and heart rate and exhibited vascular hyporeactivity that were significantly improved by treatment with L-NIL. Further, decreased eNOS expression and increased iNOS expression and activity were associated with increased NT levels in the heart and superior mesenteric arteries of untreated diabetic rats. L-NIL treatment of diabetic rats normalized the expression of eNOS and NT levels without any effect on iNOS expression in the heart and superior mesenteric arteries. The results of our study suggest that induction of iNOS in cardiovascular tissues contributes significantly to the depressed mean arterial blood pressure, heart rate and pressor responses to vasoactive agents. Chronic inhibition of iNOS in diabetes may prove beneficial in the treatment of cardiovascular abnormalities.

Effects of hyperglycemia on the modulation of vascular function by perivascular adipose tissue

OBJECTIVE

To study the acute and chronic effect of hyperglycemia on perivascular adipose tissue (PVAT) function in rat aorta.

METHOD

Alterations in PVAT function in rat aorta incubated with 22 mmol/l D-glucose for 30 min and in aorta from streptozotocin (STZ)-induced diabetic rats were studied.

RESULTS

Incubation with D-glucose caused an attenuation of contraction in response to phenylephrine, both in the presence and absence of endothelium, whereas removal of PVAT eliminated this attenuation effect. The presence of PVAT did not affect concentration-related relaxation response of the aorta to carbamylcholine in STZ rats. There was also no difference in the relaxation response of the aorta to carbamylcholine between STZ and control rats. The presence of PVAT, however, caused a higher attenuation of the concentration-dependent contraction to phenylephrine in aorta from STZ rats with intact endothelium as compared with that from control rats. Incubation of the aorta from control rats with Nomega-nitro-L-arginine or carboxy-2-phenyl-4,4,5,5-tetra-methyl-imidazoline-1-oxyl-3-oxide potentiated the contraction of the vessels to phenylephrine, and this potentiation effect was higher in the vessels from STZ rats than control rats when N-nitro-L-arginine was used. Removal of PVAT reduced this potentiation effect and eliminated the difference between the vessels from control and STZ rats.

CONCLUSION

Under both acute and chronic conditions, hyperglycemia enhanced the relaxation response of the vessels mediated by PVAT. These new findings provide important information on the mechanism underlying the postprandial effect of hyperglycemia on blood pressure control and the presence of hypotension under chronic hyperglycemia in a type-1 model of diabetes.

Early renal injury induced by caffeine consumption in obese, diabetic ZSF1 rats

Our previous studies indicate that prolonged caffeine consumption exacerbates renal failure in nephropathy associated with the metabolic syndrome. Reduced activity of the antioxidant defense system and beneficial effects of antioxidant therapy have been reported in diabetic rats and humans. The purpose of this study was to examine the early renal effects of caffeine consumption and the effects of concomitant antioxidant therapy in young obese, diabetic ZSF1 rats. Eleven-week-old male ZSF1 rats were randomized to drink tap water, caffeine (0.1%), tempol (1 mmol/L), or a solution containing caffeine and tempol for nine weeks. Caffeine significantly reduced body weight and glycosuria (weeks 2-9), improved glucose tolerance (week 9), had no effect on elevated plasma triglycerides, plasma cholesterol (week 9) and blood pressure (week 9), and significantly increased plasma cholesterol level (weeks 5 and 9). Yet, as early as after two weeks, caffeine greatly augmented proteinuria and increased renal vascular resistance (RVR) and heart rate (HR: week 9). Tempol had no effects on metabolic status and development of proteinuria, did not alter caffeine-induced metabolic changes and early proteinuria, and attenuated caffeine-induced increase in HR and RVR. Immunohistochemical analysis revealed significant glomerular and interstitial inflammation, proliferation, and fibrosis in control animals. Caffeine augmented the influx of glomerular and interstitial macrophages (ED1+ cells) influx, glomerular and tubular proliferative response, and glomerular collagen IV content. Tempol abolished the exacerbation of renal inflammation, proliferation, and fibrosis induced by caffeine. In conclusion, in nephropathy associated with the metabolic syndrome, caffeine--most likely through the interaction with adenosine receptors and interference with anti-inflammatory and/or glomerular hemodynamic effects of adenosine--augments proteinuria and stimulates some of the key proliferative mechanisms involved in glomerular remodeling and sclerosis. Tempol does not prevent early renal injury (i.e., proteinuria) induced by caffeine, yet abolishes late renal inflammatory, proliferative, and fibrotic change induced by chronic caffeine consumption in obese ZSF1 rats.

Hydroxyhydroquinone interferes with the chlorogenic acid-induced restoration of endothelial function in spontaneously hypertensive rats

BACKGROUND

Coffee is a rich source of antioxidative polyphenols, but epidemiological studies and interventional trials have failed to demonstrate any clear beneficial effects of coffee consumption on hypertension. The interaction between hydroxyhydroquinone (HHQ) and 5-caffeoylquinic acid (CQA) was examined, in an attempt to understand the controversial effects of coffee on hypertension.

METHODS

Male Wistar Kyoto (WKY) rats or spontaneously hypertensive rats (SHRs, 14 weeks old) were divided into the following four groups; those on a control diet, 0.005% HHQ diet, 0.5% CQA diet, and HHQ plus CQA diet. The rats were fed the above diets for 8 weeks, and the tail arterial blood pressure was monitored in conscious rats at 2-week intervals. Urinary nitric oxide (NO) metabolites and hydrogen peroxide (H(2)O(2)) excretion were measured 8 weeks after the start of the experiment. Endothelium-dependent and -independent vasorelaxant responses and immunohistochemical staining for nitrotyrosine were examined in aortas.

RESULTS

HHQ inhibited the CQA-induced improvement in hypertension, urinary NO metabolites or H(2)O(2) excretion, endothelial dysfunction, and nitrotyrosine deposits in aortas in SHR. However, the administration of HHQ alone had little effect on either strain.

CONCLUSIONS

Based on the content ratio of HHQ and chlorogenic acids in coffee, HHQ interfered with the CQA-induced improvement in blood pressure and endothelial function in SHR. The results explain, at least in part, the conflicting action of coffee drinking on hypertension and vascular reactivity.

Reduction of oxidative stress by a new low-molecular-weight antioxidant improves metabolic alterations in a nonobese mouse diabetes model

OBJECTIVES

We have previously established a nonobese diabetes mouse model characterized by moderate hyperglycemic levels, like those usually occurring in human type 2 diabetes. As oxidative stress is considered a major mechanism of progressive beta-cell damage in diabetes, we tested in this model the protective effects of a new low-molecular-weight antioxidant, namely, bis(1-hydroxy-2,2,6,6-tetramethyl-4-piperidinyl)decandioate dihydrochloride (IAC).

METHODS

Diabetes was induced in C57Bl/6J mice by streptozotocin (STZ) and nicotinamide (NA) administration. Two weeks later, STZ-NA mice were treated for 5 weeks with different doses of IAC (15 or 30 mg/kg per day intraperitoneally) and monitored for glycemia, insulinemia, glucose tolerance, and pancreatic insulin content.

RESULTS

Streptozotocin-NA mice showed moderate hyperglycemia, hypoinsulinemia, glucose intolerance, growth impairment, and markedly reduced pancreatic insulin content (22% of controls). IAC-treated STZ-NA mice showed clear-cut reduction of hyperglycemia and attenuation of glucose intolerance, associated to higher residual pancreatic insulin content with respect to untreated diabetic animals. Plasma nitrotyrosine levels (an index of oxidative stress), enhanced 3-fold in diabetic mice, were significantly reduced by IAC treatment. Significant correlations were found between plasma nitrotyrosine values and either blood glucose levels or pancreatic insulin content.

CONCLUSIONS

In the STZ-NA diabetic mouse model, the new antioxidant, IAC, improves diabetic metabolic alterations, likely by counteracting beta-cell dysfunction and loss associated with oxidative stress.

Evidence for a role of superoxide generation in glucose-induced beta-cell dysfunction in vivo

OBJECTIVE

Prolonged elevation of glucose can adversely affect beta-cell function. In vitro studies have linked glucose-induced beta-cell dysfunction to oxidative stress; however, whether oxidative stress plays a role in vivo is unclear. Therefore, our objective was to investigate the role of oxidative stress in an in vivo model of glucose-induced beta-cell dysfunction.

RESEARCH DESIGN AND METHODS

Wistar rats were infused intravenously with glucose for 48 h to achieve 20 mmol/l hyperglycemia with/without co-infusion of one of the following antioxidants: taurine (2-amino ethanesulfonic acid) (TAU), an aldehyde scavenger; N-acetylcysteine (NAC), a precursor of glutathione; or tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl) (TPO), a superoxide dismutase mimetic. This was followed by islet isolation or hyperglycemic clamp.

RESULTS

A 48-h glucose infusion decreased glucose-stimulated insulin secretion (GSIS) and elevated reactive oxygen species (ROS), total superoxide, and mitochondrial superoxide in freshly isolated islets. TPO prevented the increase in total and mitochondrial superoxide and the beta-cell dysfunction induced by high glucose. However, TAU and NAC, despite completely normalizing H(2)DCF-DA (dihydro-dichlorofluorescein diacetate)-measured ROS, did not prevent the increase in superoxide and the decrease in beta-cell function induced by high glucose. TPO but not TAU also prevented beta-cell dysfunction induced by less extreme hyperglycemia (15 mmol/l) for a longer period of time (96 h). To further investigate whether TPO is effective in vivo, a hyperglycemic clamp was performed. Similar to the findings in isolated islets, prolonged glucose elevation (20 mmol/l for 48 h) decreased beta-cell function as assessed by the disposition index (insulin secretion adjusted for insulin sensitivity), and co-infusion of TPO with glucose completely restored beta-cell function.

CONCLUSIONS

These findings implicate superoxide generation in beta-cell dysfunction induced by prolonged hyperglycemia.

Adaptation to hypoxia in the diabetic rat kidney

Hypoxia of the kidney in diabetes could predispose it to develop acute and chronic renal failure. To examine the relationship between renal hypoxia and renal failure, we measured hypoxia (as a pimonidazole adducts), hypoxia-inducible factors (HIFs), and a hypoxia target gene heme oxygenase-1. The studies were performed in rats with streptozotocin (STZ)-induced diabetes, Cohen diabetes sensitive rats, and during short-term artificial hyperglycemia in rats induced by intravenous glucose and octreotide. STZ-treated rats received insulin, the superoxide dismutase mimetic tempol, or contrast medium. Radiocontrast media causes hypoxia and HIF induction. Hypoxia, HIFs, and heme oxygenase were undetectable in controls, but transiently activated in STZ-treated and the Cohen diabetes sensitive rats. Different patterns of HIFs and pimonidazole were observed between the three models. Insulin abolished pimonidazole and HIF induction, whereas tempol lead to increased HIFs and heme oxygenase induction at similar levels of pimonidazole. When compared with control rats, STZ-treated rats exhibited more intense and protracted renal pimonidazole, with augmented hypoxia inducible factor production and reduced GFR following contrast media. Our data suggest that both regional hypoxia and hypoxia adaptation transiently occur in early stages of experimental diabetes, largely dependent on hyperglycemia or after contrast media. Tempol may augment the HIF response in diabetes.

Acceleration of diabetic renal injury in the superoxide dismutase knockout mouse: effects of tempol

Indices of renal injury and oxidative stress were examined in mice with deficiency of cytosolic Cu(2+)/Zn(2+) superoxide dismutase (SOD1-/-, KO) and their wild-type (WT) littermates with streptozotocin-induced diabetes. After 5 weeks of diabetes, KO diabetic (D) but not WT-D mice developed marked albuminuria, increases in glomerular content of transforming growth factor beta, collagen alpha1(IV), and nitrotyrosine, and higher glomerular superoxide compared with corresponding values in nondiabetics. After 5 months of diabetes, increases in these parameters, mesangial matrix expansion, renal cortical malondialdehyde content, and severity of tubulointerstitial injury were all significantly greater, whereas cortical glutathione was lower, in KO-D than in WT-D. In contrast to WT-D, after 4 weeks of diabetes, KO-D mice did not develop the increase in inulin clearance (C(In)) characteristic of early diabetes. The nitric oxide synthase inhibitor N(omega)-nitro-l-arginine methylester suppressed C(In) in WT-D, but had no effect on C(In) in KO-D. Treatment of KO-D with the SOD mimetic tempol for 4 weeks suppressed albuminuria, increases in glomerular transforming growth factor beta, collagen alpha1(IV), nitrotyrosine, and glomerular superoxide, and concurrently increased C(In). The latter action of tempol in KO-D was blocked by the N(omega)-nitro-l-arginine methylester. The findings provide support for a role for superoxide and its metabolism by SOD1 in the pathogenesis of renal injury in diabetes in vivo, and implicate increased interaction of superoxide with nitric oxide as a pathogenetic factor.

The antioxidant tempol inhibits cardiac hypertrophy in the insulin-resistant GLUT4-deficient mouse in vivo

Reactive oxygen species such as superoxide are implicated in cardiac hypertrophy, but their contribution to the cardiac complications of insulin resistance is unresolved. We tested the hypothesis that the antioxidant tempol attenuates cardiac hypertrophy in insulin-resistant mice. Mice with cardiac GLUT4 deletion (GLUT4-knockout), superimposed on global GLUT4 suppression (GLUT4-knockdown) were administered tempol for 4 weeks. Age-matched GLUT4-knockdown littermates were used as controls (14 mice/group). GLUT4-knockout mice exhibited marked cardiac hypertrophy: heart to body weight ratio was increased 61+/-7% and expression of the hypertrophic genes beta-myosin heavy chain and B-type natriuretic peptide (BNP) were elevated 5.5+/-0.7- and 6.2+/-1.5-fold relative to control, respectively. Pro-fibrotic pro-collagen III expression was also higher (3.8+/-0.7-fold) in the GLUT4-knockout myocardium (all p<0.001). Both gp91(phox) and Nox1 subunits of NADPH oxidase were also upregulated, 4.9+/-1.2- and 9.3+/-2.8-fold (both p<0.01). Tempol treatment significantly attenuated all of these abnormalities in GLUT4-knockout mice. Heart to body weight ratio was decreased, as was fold expression of beta-myosin heavy chain (to 3.8+/-0.8), BNP (to 2.5+/-0.5), pro-collagen III (to 1.9+/-0.4), gp91(phox) (to 0.9+/-0.3) and Nox1 (to 2.3+/-0.1, all p<0.05 versus untreated GLUT4-knockout mice). In addition, tempol upregulated ventricular expression of both thioredoxin-2 (confirming an antioxidant action) and glycogen synthase kinase-3beta (GSK-3beta). Tempol did not elicit any other significant changes in control mice. Cardiac superoxide generation, however, was not altered by GLUT4-knockout or tempol. In conclusion, tempol treatment reduced morphological and molecular evidence of cardiac hypertrophy in the GLUT4-knockout insulin-resistant mouse in vivo, even at doses insufficient to lower cardiac superoxide. Parallel reductions in pro-collagen III and NADPH oxidase have important implications for our understanding of the molecular basis of cardiac hypertrophy in the setting of insulin resistance. Antioxidants may offer new alternatives in this disorder.

The effect of 2,3-dihydroxybenzoic acid and tempol in prevention of vancomycin-induced nephrotoxicity in rats

One of the major adverse effects of vancomycin (VAN) is nephrotoxicity, which the mechanism is not fully understood. However, there is some evidence that oxidative injury could be involved in its pathogenesis. In this study, we examined two antioxidants 4-hydroxyl-2,2,6,6-tetramethylpiperidine-1-oxyl (tempol) a superoxide dismutase mimetic and 2,3-dihydroxybenzoic acid (DHB) an iron chelator in VAN-induced nephrotoxicity in rats. DHB at doses of 50 and 100 mg/kg and tempol at doses of 7.5, 15 and 30 mg/kg were administered subcutaneously to rats 30 min prior to intraperitoneal injection of 200 mg/kg VAN. Drug administrations were done every 12 h for 7 days. In animals which received only VAN, the activity of urinary gamma-glutamyl-transferase (GGT) decreased and the activity of lactate dehydrogenase (LDH) in urine increased significantly compared to controls. Serum urea and creatinine (Cr) concentrations and the weight of animals' kidneys increased and body weights were decreased significantly in this group compared to controls. DHB at both doses normalized the GGT activity, but only at the higher dose restore the LDH activity. Both doses of DHB ameliorated the rise in serum urea and Cr concentrations and improved the changes in kidney and body weights significantly. Tempol did not show any beneficial effects at all. There were marked pathologic changes in tubules of kidneys of VAN treated animals. The tissue injury was prevented by both doses of DHB and there was almost no sign of tubular injury in 100 mg/kg treated group. Tempol in any doses could not prevent the tissue injury and there were significant differences in tissue injury in all tempol treated rats with controls. It seems that VAN-induced nephrotoxicity is at least partly due to free radical formation. Hydroxyl radicals might play a major role in VAN-induced nephrotoxicity, since an iron chelator (DHB) could reverse the adverse effects. However, production of other radicals such as superoxide is also probable.

Inhibition of NAD(P)H oxidase alleviates impaired NOS-dependent responses of pial arterioles in type 1 diabetes mellitus

OBJECTIVE

The goal was to identify the role of NAD(P)H oxidase in cerebrovascular dysfunction in type 1 diabetes mellitus (T1D).

METHODS

In a first series of studies, rats were assigned to nondiabetic, diabetic (streptozotocin; 50 mg/kg IP), nondiabetic-apocynin (40 mg/kg/day in drinking water)-treated and diabetic-apocynin-treated groups. Two to three months later, the authors examined in vivo responses of pial arterioles to nitric oxide synthase (NOS)-dependent (acetylcholine and adenosine diphosphate (ADP)) and -independent (nitroglycerin) agonists. Next, they used Western blot analysis to examine protein levels for subunits of NAD(P)H oxidase in cerebral microvessels and parietal cortex tissue of nondiabetic and diabetic rats. Finally, they measured superoxide production by parietal cortex tissue in nondiabetic and diabetic rats.

RESULTS

Acetylcholine- and ADP-induced dilatation of pial arterioles was impaired in diabetic compared to nondiabetic rats. In addition, while apocynin did not alter responses in nondiabetic rats, apocynin alleviated T1D-induced impairment of NOS-dependent vasodilatation. In addition, p47phox and gp91phox proteins were elevated in cerebral microvessels and parietal cortex tissue, respectively, of diabetic compared to nondiabetic rats. Further, basal production of superoxide was increased in diabetic compared to nondiabetic rats and apocynin decreased this basal production.

CONCLUSIONS

The findings suggest that T1D impairs NOS-dependent reactivity of cerebral arterioles by a mechanism related to the formation of superoxide via activation of NAD(P)H oxidase.

Role of oxidative stress in defective renal dopamine D1 receptor-G protein coupling and function in old Fischer 344 rats

Aging is associated with an increase in oxidative stress. Previously, we have reported that dopamine failed to inhibit proximal tubular Na-K-ATPase and to promote sodium excretion in old rats (Beheray S, Kansra V, Hussain T, and Lokhandwala MF. Kidney Int 58: 712–720, 2000). This was due to uncoupling of dopamine D1 receptors from G proteins resulting from hyperphosphorylation of D1 receptors. The present study was designed to test the role of oxidative stress in the age-related decline in renal dopamine D1 receptor function. We observed that old animals had increased malondialdehyde (MDA) levels, a biomarker of oxidative stress, and decreased D1 receptor number and protein in the proximal tubules (PT) compared with adult rats. In old rats, there was increased G protein-coupled receptor kinase-2 (GRK-2) abundance, increased basal serine phosphorylation of D1 receptors, and defective D1 receptor-G protein coupling in PT membranes. Interestingly, supplementation with an antioxidant, tempol (1 mmol/l in drinking water for 15 days), lowered MDA levels and normalized D1 receptor number and protein in old rats to the level seen in adult rats. Furthermore, tempol decreased GRK-2 abundance and D1 receptor serine phosphorylation and restored D1 receptor-G protein coupling in PT of old rats. The functional consequence of these changes was the restoration of the natriuretic response to D1 receptor activation in tempol-supplemented old rats. Therefore, in old rats, tempol reduces oxidative stress and prevents GRK-2 membranous abundance and hyperphosphorylation of D1 receptors, resulting in restoration of D1 receptor-G protein coupling and the natriuretic response to SKF-38393. Thus tempol, by lowering oxidative stress, normalizes the age-related decline in dopamine receptor function.

N-acetylcysteine prevents nitrosative stress-associated depression of blood pressure and heart rate in streptozotocin diabetic rats

Previous studies have indicated that cardiovascular abnormalities such as depressed blood pressure and heart rate occur in streptozotocin (STZ) diabetic rats. Chronic diabetes, which is associated with increased expression of inducible nitric oxide synthase (iNOS) and oxidative stress, may produce peroxynitrite/nitrotyrosine and cause nitrosative stress. We hypothesized that nitrosative stress causes cardiovascular depression in STZ diabetic rats and therefore can be corrected by reducing its formation. Control and STZ diabetic rats were treated orally for 9 weeks with N-acetylcysteine (NAC), an antioxidant and inhibitor of iNOS. At termination, the mean arterial blood pressure (MABP) and heart rate (HR) were measured in conscious rats. Nitrotyrosine and endothelial nitric oxide synthase (eNOS) and iNOS expression were assessed in the heart and mesenteric arteries by immunohistochemistry and Western blot experiments. Untreated diabetic rats showed depressed MABP and HR that was prevented by treatment with NAC. In untreated diabetic rats, levels of 15-F(2t)-isoprostane, an indicator of lipid peroxidation increased, whereas plasma nitric oxide and antioxidant concentrations decreased. Furthermore, decreased eNOS and increased iNOS expression were associated with elevated nitrosative stress in blood vessel and heart tissue of untreated diabetic rats. N-acetylcysteine treatment of diabetic rats not only restored the antioxidant capacity but also reduced the expression of iNOS and nitrotyrosine and normalized the expression of eNOS to that of control rats in heart and superior mesenteric arteries. The results suggest that nitrosative stress depress MABP and HR following diabetes. Further studies are required to elucidate the mechanisms involved in nitrosative stress mediated depression of blood pressure and heart rate.

Oxidative Stress as the Leading Cause of Acute Myocardial Infarction in Diabetics

The risk factors, such as hypertension and metabolic syndrome, tend to promote heart pathology. These risk factors can aggravate concomitant heart insults as well. Diabetes mellitus represents one of the most important risk factors for the development of heart pathology. By itself it represents a source of vascular and heart dysfunction through formation of reactive oxygen species (ROS) and can compromise the recovery from cardiovascular diseases. This review focuses on the evidence that cellular oxidative stress is the leading cause of the worst outcome of myocardial infarction (MI) in diabetics. Hyperglycemia is viewed in this article as the primary mediator of a cascade of heart damaging events, starting from ROS formation and leading to myocardial ischemia, inflammation and death of myocytes. This article also provides insights into why diverse therapeutic interventions, which have in common the ability to reduce oxidative stress and inflammation, can impede or delay the onset of complications of myocardial infarction in diabetic patients.

Tempol reduces oxidative stress and restores renal dopamine D1-like receptor- G protein coupling and function in hyperglycemic rats

Dopamine via activation of renal D1-like receptors inhibits the activities of Na-K-ATPase and Na/H exchanger and subsequently increases sodium excretion. Decreased renal dopamine production and sodium excretion are associated with hyperglycemic conditions. We have earlier reported D1-like receptor-G protein uncoupling and reduced response to D1-like receptor activation in streptozotocin (STZ)-treated hyperglycemic rats (Marwaha A, Banday AA, and Lokhandwala MF. Am J Physiol Renal Physiol 286: F451-F457, 2004). The present study was designed to test the hypothesis that oxidative stress associated with hyperglycemia increases basal D1-like receptor serine phosphorylation via activation of the PKC-G protein receptor kinase (GRK) pathway, resulting in loss of D1-like receptor-G protein coupling and function. We observed that STZ-treated rats exhibited oxidative stress as evidenced by increased lipid peroxidation. Furthermore, PKC activity and expression of PKC-betaI- and -delta-isoforms were increased in STZ-treated rats. In addition, in STZ-treated rats there was increased GRK2 translocation to proximal tubular membrane and increased basal serine D1-like receptor phosphorylation. Supplementation with the antioxidant tempol lowered oxidative stress in STZ-treated rats, led to normalization of PKC activity, and prevented GRK2 translocation. Furthermore, tempol supplementation in STZ-treated rats restored D1-like receptor-G protein coupling and inhibition of Na-K-ATPase activity on D1-like receptor agonist stimulation. The functional consequence was the restoration of the natriuretic response to D1-like receptor activation. We conclude that oxidative stress associated with hyperglycemia causes an increase in activity and expression of PKC. This leads to translocation of GRK2, subsequent phosphorylation of the D1-like receptor, its uncoupling from G proteins and loss of responsiveness to agonist stimulation.