Effect of glutathione peroxidase mimic ebselen (PZ51) on endothelium and vascular structure of stroke‐prone spontaneously hypertensive rats

Mechanisms of ebselen as a therapeutic and its pharmacology applications

Ebselen is a synthetic organoselenium radical scavenger compound that possesses glutathione peroxidase-like activity and its own unique bioactivity by reacting with thiols, hydroperoxides and peroxynitrites. Owing to its high affinity toward several essential reactions, ebselen protects cellular components from oxidative and free radical damage, and it has been employed as a useful tool for studying redox-related mechanisms. Based on numerous in vitro and in vivo research, mechanisms are proposed to understand the biomedical and molecular actions of ebselen in health and disease, and it is currently under clinical trials for the prevention and treatment of various human disorders. Based on these outstanding discoveries, this review summarizes the current understanding of the biochemical and molecular characteristics, pharmacological applications and future directions of ebselen.

Consequence of hyperhomocysteinaemia on α1-adrenoceptor-mediated contraction in the rat corpus cavernosum: the role of reactive oxygen species

OBJECTIVES

Our main objective was to investigate the mechanisms underlying the effects of hyperhomocysteinaemia (HHcy) on contractile response mediated by α1-adrenoceptors in the rat corpus cavernosum.

METHODS

Concentration-response curves for phenylephrine (PE) were obtained in strips of corpus cavernosum, in absence or after incubation with tiron, tempol or polyethylene glycol (PEG)-catalase combined or not with tempol. We also measured the superoxide anion (O2(-)) and hydrogen peroxide (H2O2) generation, superoxide dismutase (SOD) and catalase activity and α-actin expression in rat corpus cavernosum from both groups.

KEY FINDINGS

HHcy increased PE-induced contraction in cavernosal strips. Tiron, PEG-catalase or tempol increased PE-induced contraction in strips from control rats, but it was not altered by tiron or PEG-catalase in HHcy rats, whereas tempol reduced this response. The combination of PEG-catalase and tempol did not alter the contractile response to PE in both groups. HHcy increased O2(-) generation and SOD activity, whereas H2O2 concentration was reduced. Finally, HHcy did not alter catalase activity or expression of α-actin.

CONCLUSIONS

The major new finding from this study is that HHcy induced a marked increase in PE-induced contraction in rat corpus cavernosum by a mechanism that involves increased O2(-) generation and it could play a role in the pathogenesis of erectile dysfunction associated with HHcy.

No short-term effects of calorie-controlled Mediterranean or fast food dietary interventions on established biomarkers of vascular or metabolic risk in healthy individuals

BACKGROUND/OBJECTIVES

This study addressed the question whether the composition of supposedly 'healthy' or 'unhealthy' dietary regimes has a calorie-independent short-term effect on biomarkers of metabolic stress and vascular risk in healthy individuals.

SUBJECTS/METHODS

Healthy male volunteers (age 29.5 ± 5.9 years, n = 39) were given a standardized baseline diet for two weeks before randomization into three groups of different dietary regimes: fast food, Mediterranean and German cooking style. Importantly, the amount of calories consumed per day was identical in all three groups. Blood samples were analyzed for biomarkers of cardiovascular risk and metabolic stress after two weeks of the baseline diet and after two weeks of the assigned dietary regime.

RESULTS

No dietary intervention affected the metabolic or cardiovascular risk profile when compared in-between groups or compared to baseline. Subjects applied to the Mediterranean diet showed a statistically significant increase of uric acid compared to baseline and compared to the German diet group. Plasma concentrations of urea were significantly higher in both the fast food group and the Mediterranean group, when compared to baseline and compared to the German diet group. No significant differences were detected for the levels of vitamins, trace elements or metabolic stress markers (8-hydroxy-2-deoxyguanosine, malondialdehyde and methylglyoxal, a potent glycating agent). Established parameters of vascular risk (e.g. LDL-cholesterol, lipoprotein(a), homocysteine) were not significantly changed in-between groups or compared to baseline during the intervention period.

CONCLUSIONS

The calorie-controlled dietary intervention caused neither protective nor harmful short-term effects regarding established biomarkers of vascular or metabolic risk. When avoiding the noxious effects of overfeeding, healthy individuals can possess the metabolic capacity to compensate for a potentially disadvantageous composition of a certain diet.

Reactive oxygen species in pulmonary vascular remodeling

The pathogenesis of pulmonary hypertension is a complex multifactorial process that involves the remodeling of pulmonary arteries. This remodeling process encompasses concentric medial thickening of small arterioles, neomuscularization of previously nonmuscular capillary-like vessels, and structural wall changes in larger pulmonary arteries. The pulmonary arterial muscularization is characterized by vascular smooth muscle cell hyperplasia and hypertrophy. In addition, in uncontrolled pulmonary hypertension, the clonal expansion of apoptosis-resistant endothelial cells leads to the formation of plexiform lesions. Based upon a large number of studies in animal models, the three major stimuli that drive the vascular remodeling process are inflammation, shear stress, and hypoxia. Although, the precise mechanisms by which these stimuli impair pulmonary vascular function and structure are unknown, reactive oxygen species (ROS)-mediated oxidative damage appears to play an important role. ROS are highly reactive due to their unpaired valence shell electron. Oxidative damage occurs when the production of ROS exceeds the quenching capacity of the antioxidant mechanisms of the cell. ROS can be produced from complexes in the cell membrane (nicotinamide adenine dinucleotide phosphate-oxidase), cellular organelles (peroxisomes and mitochondria), and in the cytoplasm (xanthine oxidase). Furthermore, low levels of tetrahydrobiopterin (BH4) and L-arginine the rate limiting cofactor and substrate for endothelial nitric oxide synthase (eNOS), can cause the uncoupling of eNOS, resulting in decreased NO production and increased ROS production. This review will focus on the ROS generation systems, scavenger antioxidants, and oxidative stress associated alterations in vascular remodeling in pulmonary hypertension.

Novel pathways and therapies in experimental diabetic atherosclerosis

Diabetic subjects are at a greater risk of developing major vascular complications due to abnormalities pertinent to the diabetic milieu. Current treatment options achieve significant improvements in glucose levels and blood pressure control, but do not necessarily prevent or retard diabetes-mediated macrovascular disease. In this review, we highlight several pathways that are increasingly being appreciated as playing a significant role in diabetic vascular injury. We focus particularly on the advanced glycation end product/receptor for advanced glycation end product (AGE/RAGE) axis and its interplay with the nuclear protein HMGB1. We discuss evidence implicating a significant role for the renin-angiotensin system, urotensin II and PPAR, as well as the importance of proinflammatory mediators and oxidative stress in cardiovascular complications. The specific targeting of these pathways may lead to novel therapies to reduce the burden of diabetic vascular complications.

Oxidative stress, Noxs, and hypertension: experimental evidence and clinical controversies

Reactive oxygen species (ROS) are signaling molecules that influence many physiological processes. Increased ROS bioavailability and altered redox signaling (oxidative stress) have been implicated in chronic diseases including hypertension. Although oxidative stress may not be the sole cause of hypertension, it amplifies blood pressure elevation in the presence of other prohypertensive factors (salt, renin-angiotensin system, sympathetic hyperactivity). A major source for cardiovascular ROS is a family of non-phagocytic NADPH oxidases (Nox1, Nox2, Nox4, Nox5). Other sources of ROS involve mitochondrial electron transport enzymes, xanthine oxidase, and uncoupled nitric oxide synthase. Although evidence from experimental and animal studies supports a role for oxidative stress in the pathogenesis of hypertension, there is still no convincing proof that oxidative stress is a cause of human hypertension. However, what is clear is that oxidative stress is important in the molecular mechanisms associated with cardiovascular and renal injury in hypertension and that hypertension itself can contribute to oxidative stress. The present review addresses the putative function of ROS in the pathogenesis of hypertension and focuses on the role of Noxs in ROS generation in vessels and the kidney. Implications of oxidative stress in human hypertension are discussed, and clinical uncertainties are highlighted.

Targeting endothelial dysfunction in vascular complications associated with diabetes

Cardiovascular complications associated with diabetes remain a significant health issue in westernized societies. Overwhelming evidence from clinical and laboratory investigations have demonstrated that these cardiovascular complications are initiated by a dysfunctional vascular endothelium. Indeed, endothelial dysfunction is one of the key events that occur during diabetes, leading to the acceleration of cardiovascular mortality and morbidity. In a diabetic milieu, endothelial dysfunction occurs as a result of attenuated production of endothelial derived nitric oxide (EDNO) and augmented levels of reactive oxygen species (ROS). Thus, in this review, we discuss novel therapeutic targets that either upregulate EDNO production or increase antioxidant enzyme capacity in an effort to limit oxidative stress and restore endothelial function. In particular, endogenous signaling molecules that positively modulate EDNO synthesis and mimetics of endogenous antioxidant enzymes will be highlighted. Consequently, manipulation of these unique targets, either alone or in combination, may represent a novel strategy to confer vascular protection, with the ultimate goal of improved outcomes for diabetes-associated vascular complications.

Multiple aberrations in shared inflammatory and oxidative & nitrosative stress (IO&NS) pathways explain the co-association of depression and cardiovascular disorder (CVD), and the increased risk for CVD and due mortality in depressed patients

There is evidence that there is a bidirectional relationship between major depression and cardiovascular disorder (CVD): depressed patients are a population at risk for increased cardiac morbidity and mortality, and depression is more frequent in patients who suffer from CVD. There is also evidence that inflammatory and oxidative and nitrosative stress (IO&NS) pathways underpin the common pathophysiology of both CVD and major depression. Activation of these pathways may increase risk for both disorders and contribute to shared risk. The shared IO&NS pathways that may contribute to CVD and depression comprise the following: increased levels of pro-inflammatory cytokines, like interleukin-1β (IL-1β), IL-2, IL-6, IL-8, IL-12, tumor necrosis factor-α, and interferon-γ; T cell activation; increased acute phase proteins, like C-reactive protein, haptoglobin, fibrinogen and α1-antitrypsin; complement factors; increased LPS load through bacterial translocation and subsequent gut-derived inflammation; induction of indoleamine 2,3-dioxygenase with increased levels of tryptophan catabolites; decreased levels of antioxidants, like coenzyme Q10, zinc, vitamin E, glutathione and glutathione peroxidase; increased O&NS characterized by oxidative damage to low density lipoprotein (LDL) and phospholipid inositol, increased malondialdehyde, and damage to DNA and mitochondria; increased nitrosative stress; and decreased ω3 polyunsaturated fatty acids (PUFAs). The complex interplay between the abovementioned IO&NS pathways in depression results in pro-atherogenic effects and should be regarded as a risk factor to future clinical CVD and due mortality. We suggest that major depression should be added as a risk factor to the Charlson "comorbidity" index. It is advised that patients with (sub)chronic or recurrent major depression should routinely be assessed by serology tests to predict if they have an increased risk to cardiovascular disorders.

Antiatherosclerotic and renoprotective effects of ebselen in the diabetic apolipoprotein E/GPx1-double knockout mouse

OBJECTIVE

To investigate the effect of the GPx1-mimetic ebselen on diabetes-associated atherosclerosis and renal injury in a model of increased oxidative stress.

RESEARCH DESIGN AND METHODS

The study was performed using diabetic apolipoprotein E/GPx1 (ApoE(-/-)GPx1(-/-))-double knockout (dKO) mice, a model combining hyperlipidemia and hyperglycemia with increased oxidative stress. Mice were randomized into two groups, one injected with streptozotocin, the other with vehicle, at 8 weeks of age. Groups were further randomized to receive either ebselen or no treatment for 20 weeks.

RESULTS

Ebselen reduced diabetes-associated atherosclerosis in most aortic regions, with the exception of the aortic sinus, and protected dKO mice from renal structural and functional injury. The protective effects of ebselen were associated with a reduction in oxidative stress (hydroperoxides in plasma, 8-isoprostane in urine, nitrotyrosine in the kidney, and 4-hydroxynonenal in the aorta) as well as a reduction in VEGF, CTGF, VCAM-1, MCP-1, and Nox2 after 10 weeks of diabetes in the dKO aorta. Ebselen also significantly reduced the expression of proteins implicated in fibrosis and inflammation in the kidney as well as reducing related key intracellular signaling pathways.

CONCLUSIONS

Ebselen has an antiatherosclerotic and renoprotective effect in a model of accelerated diabetic complications in the setting of enhanced oxidative stress. Our data suggest that ebselen effectively repletes the lack of GPx1, and indicate that ebselen may be an effective therapeutic for the treatment of diabetes-related atherosclerosis and nephropathy. Furthermore, this study highlights the feasibility of addressing two diabetic complications with one treatment regimen through the unifying approach of targeted antioxidant therapy.

Catalase and glutathione peroxidase mimics

Overproduction of the reactive oxygen species (ROS) superoxide (O(2)(-)) and hydrogen peroxide (H(2)O(2)) are increasingly implicated in human disease and aging. ROS are also being explored as important modulating agents in a number of cell signaling pathways. Earlier work has focused on development of small catalytic scavengers of O(2)(-), commonly referred to as superoxide dismutase (SOD) mimetics. Many of these compounds also have substantial abilities to catalytically scavenge H(2)O(2) and peroxynitrite (ONOO(-)). Peroxides have been increasingly shown to disrupt cell signaling cascades associated with excessive inflammation associated with a wide variety of human diseases. Early studies with enzymatic scavengers like SOD frequently reported little or no beneficial effect in biologic models unless SOD was combined with catalase or a peroxidase. Increasing attention has been devoted to developing catalase or peroxidase mimetics as a way to treat overt inflammation associated with the pathophysiology of many human disorders. This review will focus on recent development of catalytic scavengers of peroxides and their potential use as therapeutic agents for pulmonary, cardiovascular, neurodegenerative and inflammatory disorders.

NADPH oxidases, reactive oxygen species, and hypertension: clinical implications and therapeutic possibilities

Reactive oxygen species (ROS) influence many physiological processes including host defense, hormone biosynthesis, fertilization, and cellular signaling. Increased ROS production (termed "oxidative stress") has been implicated in various pathologies, including hypertension, atherosclerosis, diabetes, and chronic kidney disease. A major source for vascular and renal ROS is a family of nonphagocytic NAD(P)H oxidases, including the prototypic Nox2 homolog-based NAD(P)H oxidase, as well as other NAD(P)H oxidases, such as Nox1 and Nox4. Other possible sources include mitochondrial electron transport enzymes, xanthine oxidase, cyclooxygenase, lipoxygenase, and uncoupled nitric oxide synthase. NAD(P)H oxidase-derived ROS plays a physiological role in the regulation of endothelial function and vascular tone and a pathophysiological role in endothelial dysfunction, inflammation, hypertrophy, apoptosis, migration, fibrosis, angiogenesis, and rarefaction, important processes underlying cardiovascular and renal remodeling in hypertension and diabetes. These findings have evoked considerable interest because of the possibilities that therapies against nonphagocytic NAD(P)H oxidase to decrease ROS generation and/or strategies to increase nitric oxide (NO) availability and antioxidants may be useful in minimizing vascular injury and renal dysfunction and thereby prevent or regress target organ damage associated with hypertension and diabetes. Here we highlight current developments in the field of reactive oxygen species and cardiovascular disease, focusing specifically on the recently identified novel Nox family of NAD(P)H oxidases in hypertension. We also discuss the potential role of targeting ROS as a therapeutic possibility in the management of hypertension and cardiovascular disease.

NADPH oxidase inhibitors: new antihypertensive agents?

NADPH oxidases have recently been shown to contribute to the pathogenesis of hypertension. The development of specific inhibitors of these enzymes has focused attention on their potential therapeutic use in hypertensive disease. Two of the most specific inhibitors, gp91ds-tat and apocynin, have been shown to decrease blood pressure in animal models of hypertension. Other inhibitors, including diphenylene iodonium, aminoethyl benzenesulfono fluoride, S17834, PR39, protein kinase C inhibitors, and VAS2870, have shown promise in vitro, but their in vivo specificity, pharmacokinetics, and effectiveness in hypertension remains to be determined. Of importance, the currently available antihypertensive agents angiotensin-converting enzyme inhibitors and angiotensin receptor blockers also effectively inhibit NADPH oxidase activation. Similarly, the cholesterol-lowering agents, statins, have been shown to attenuate NADPH oxidase activation. Although, antioxidants act to scavenge the reactive oxygen species produced by these enzymes, their effectiveness is limited. Targeting NADPH homologues may have a distinct advantage over current therapies because it would specifically prevent the pathophysiological formation of reactive oxygen species that contributes to hypertension.