Enhanced oxidative stress and impaired thioredoxin expression in spontaneously hypertensive rats

Basal and angiotensin II-inhibited neuronal delayed-rectifier K+ current are regulated by thioredoxin

In previous studies, we determined that macrophage migration inhibitory factor (MIF), acting intracellularly via its intrinsic thiol-protein oxidoreductase (TPOR) activity, stimulates basal neuronal delayed-rectifier K+ current ( IKv) and inhibits basal and angiotensin (ANG) II-induced increases in neuronal activity. These findings are the basis for our hypothesis that MIF is a negative regulator of ANG II actions in neurons. MIF has recently been recategorized as a member of the thioredoxin (Trx) superfamily of small proteins. In the present study we have examined whether Trx influences basal and ANG II-modulated IKv in an effort to determine whether the Trx superfamily can exert a general regulatory influence over neuronal activity and the actions of ANG II. Intracellular application of Trx (0.8–80 nM) into rat hypothalamic/brain stem neurons in culture increased neuronal IKv, as measured by voltage-clamp recordings. This effect of Trx was abolished in the presence of the TPOR inhibitor PMX 464 (800 nM). Furthermore, the mutant protein recombinant human C32S/C35S-Trx, which lacks TPOR activity, failed to alter neuronal IKv. Trx applied at a concentration (0.08 nM) that does not alter basal IKv abolished the inhibition of neuronal IKv produced by ANG II (100 nM). Given our observation that ANG II increases Trx levels in neuronal cultures, it is possible that Trx (like MIF) has a negative regulatory role over basal and ANG II-stimulated neuronal activity via modulation of IKv. Moreover, these data suggest that TPOR may be a general mechanism for negatively regulating neuronal activity.

Thioredoxin1 as a negative regulator of cardiac hypertrophy

Excessive reactive oxygen species (ROS) play an important role in the development of cardiac hypertrophy. In contrast, antioxidants scavenge ROS, thereby maintaining the reduced environment of cells and inhibiting hypertrophy in the heart. Thioredoxin1 (Trx1) not only functions as a major antioxidant in the heart but also interacts with important signaling molecules and transcription factors, thereby attenuating cardiac hypertrophy. This review will discuss the molecular mechanisms by which Trx1 exerts antihypertrophic effects in the heart.

Differential regulation of thioredoxin and NAD(P)H oxidase by angiotensin II in male and female mice

OBJECTIVE

We hypothesized that downregulation of the antioxidant thioredoxin system contributes to oxidative stress in angiotensin II-induced hypertension. As oestrogen may protect against oxidative stress, we also evaluated whether the thioredoxin system, particularly in the heart, is differentially regulated between females and males.

RESULTS

C57Bl/6 male and intact or ovariectomized female mice were infused with angiotensin II (400 ng/kg per minute for 2 weeks). Systolic blood pressure (SBP) was increased by angiotensin II in both groups week 1 and increased further in males versus females in week 2. Angiotensin II increased SBP from 112 +/- 6 to 143 +/- 9 mmHg in ovariectomized mice. Basal cardiac thioredoxin expression and reductase activity were significantly higher (two to threefold) in females versus males. Angiotensin II increased thioredoxin expression (approximately threefold), thioredoxin reductase activity, nicotinamide adenine dinucleotide phosphate, reduced form (NAD(P)H) oxidase activity and plasma thiobarbituric acid-reducing substances in males but not in females. Angiotensin II increased thioredoxin expression and NAD(P)H oxidase activity in ovariectomized versus control mice. Apurinic/apyrimidinic endonuclease/redox factor 1 (APE/Ref-1) activation, which interacts with thioredoxin to activate inflammatory transcription factors, was increased by angiotensin II only in males.

CONCLUSION

These results demonstrate sex dimorphism with respect to thioredoxin, oxidative stress and inflammation, and suggest the differential regulation of blood pressure, the cardiac thioredoxin system and NAD(P)H oxidase activity by angiotensin II in male and female mice. Whereas angiotensin II increases the activity of thioredoxin reductase and APE/Ref-1, enhances oxidative stress, and amplifies blood pressure elevation in males, it has little effect in females. Such differences may partly relate to the protective actions of oestrogens.

Discordant response of glutathione and thioredoxin systems in human hypertension?

Hypertension is frequently associated with oxidative stress caused by high production of reactive oxygen species and compromised antioxidant defenses. Humans with essential hypertension, with or without treatment, and controls were examined (35 hypertensive and 30 normotensive). We noted a discordant response of the glutathione and thioredoxin systems in essential hypertension and to antihypertensive treatment. Further studies examining the significance of these thiols in hypertension outcomes are warranted.

Hydroxyl radical mediates the augmented angiotensin II responses in thoracic aorta of spontaneously hypertensive rats

AIM

To investigate the role of hydroxyl radical in augmented angiotensin II (Ang II) responses in the thoracic aorta of spontaneously hypertensive rats (SHR).

METHODS

To elucidate the role of hydroxyl radical, we used edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one) as a tool for our study. The vascular responses to Ang II (10(-10) to 10(-6) mol/l), tert-butyl hydroperoxide (tBHP; 10(-6) to 10(-2) mol/l) and H(2)O(2) (10(-6) to 10(-2) mol/l) were constructed in aortic preparations obtained from control (WKY) and SHR in the absence and presence of edaravone.

RESULTS

The vascular responses to Ang II, tBHP and H(2)O(2) were found to be enhanced in aortic preparations from SHR as compared to control WKY rats. Edaravone selectively attenuated the augmented responses to Ang II but not to tBHP and H(2)O(2) suggesting that the .OH radical is involved in the augmented responses to Ang II. The elevated blood pressure in SHR was restored to a near normal value after 2 weeks of edaravone (10 mg kg(-1) i.p., b.i.d.) treatment.

CONCLUSION

From the results we infer that hydroxyl radical stress augments Ang II responses in the thoracic aorta of SHR and, by attenuating these enhanced vascular responses, edaravone could serve as an adjuvant antioxidant therapy for the vascular complications of hypertension.

Delay of photoreceptor degeneration intubbymouse by sulforaphane

In this study, the homozygous tubby (tub/tub) mutant mouse, with an early progressive hearing loss and photoreceptor degeneration, was used as a model system to examine the effects of systemic administration of a naturally occurring isothiocyanate, sulforaphane (SF), on photoreceptor degeneration. Several novel observations have been made: (i) the mRNA and protein expression of thioredoxin (Trx), thioredoxin reductase (TrxR) and NF-E2-related factor-2 (Nrf2) were significantly reduced even prior to photoreceptor cell degeneration in the retinas of tub/tub mice, suggesting that retinal expression of the Trx system is impaired and that Trx regulation is involved in the pathogenesis of retinal degeneration in this model, (ii) intraperitoneal injection with SF significantly up-regulated retinal levels of Trx, TrxR, and Nrf2, and effectively protected photoreceptor cells in tub/tub mice as evaluated functionally by electroretinography and morphologically by quantitative histology, and (iii) treatment with PD98059, an inhibitor of extracellular signal-regulated kinases (ERKs), blocked SF-mediated ERKs activation and up-regulation of Trx/TrxR/Nrf2 in the retinas of tub/tub mice. This suggests that ERKs and Nrf2 are involved in the mechanism of SF-mediated up-regulation of the Trx system to protect photoreceptor cells in this model. These novel findings are significant and could provide important information for the development of a unique strategy to prevent sensorineural deafness/retinal dystrophic syndromes and also other forms of inherited neurological disorders.

Sexual dimorphism in oxidant status in spontaneously hypertensive rats

Male spontaneously hypertensive rats (SHR) have a blunted pressure-natriuresis relationship and enhanced oxidative stress compared with female SHR. Furthermore, oxidative stress contributes to abnormal renal Na+ handling and renal damage in hypertension. The aim of this study was to determine whether a sex difference exists in renal inner medullary hydrogen peroxide (H2O2) levels and/or antioxidant systems in SHR and the influence of sex steroids on these systems. Thirteen-week-old intact and gonadectomized male and female SHR were placed in metabolic cages for 24-h urine collection. Renal inner medullas were isolated for antioxidant activity assays and Western blot analysis or for measurements of H2O2 using Amplex Red. Studies verified that male SHR had greater Na+ reabsorption compared with female SHR. Male SHR had enhanced urinary excretion of H2O2 compared with female SHR. Gonadectomy decreased H2O2 excretion in males and increased H2O2 excretion in females, suggesting that testosterone stimulates total body oxidative stress and estrogen suppresses levels of total body oxidative stress. There was not a sex difference in inner medullary H2O2 levels. Male SHR had a testosterone-dependent increase in inner medullary SOD activity, and both intact and gonadectomized males had high levels of inner medullary catalase activity compared with females. The results of this study showed that there was a sexual dimorphism in Na+ handling and oxidant status. We hypothesize that there is a testosterone-sensitive increase in whole body reactive oxygen species production that results in a compensatory increase in the inner medullary antioxidant capability possibly to normalize Na+ handling.

Thioredoxin in the cardiovascular system

The thioredoxin (TRX) system (TRX, TRX reductase, and NADPH) is a ubiquitous thiol oxidoreductase system that regulates cellular reduction/oxidation (redox) status. The impairment of cell redox state alters multiple cell pathways, which may contribute to the pathogenesis of cardiovascular disorders including hypertension, atherosclerosis, and heart failure. In this manuscript, we review the essential roles that TRX plays by limiting oxidative stress directly via antioxidant effects and indirectly by protein-protein interactions with key signaling molecules such as thioredoxin interacting protein (TXNIP). TRX and its endogenous regulators may represent important future targets to develop clinical therapies for diseases associated with oxidative stress.

Endothelial progenitor cells: biology and therapeutic potential in hypertension

PURPOSE OF REVIEW

In this review, we summarize some of the recent advances in our understanding of the biology of endothelial progenitor cells, and discuss the potential relevance of these progenitor cells for endothelial function and associated microvascular abnormalities that can form the structural basis of essential hypertension.

RECENT FINDINGS

Both in experimental models of hypertension and in patients with hypertension, the function of endothelial progenitor cells is impaired. Also, some antihypertensive drugs that have been associated with reversal of endothelial function and microvascular rarefaction appear to correct endothelial progenitor cell dysfunction.

SUMMARY

While information on endothelial progenitor biology is still limited in patients with hypertension in comparison with, for example, patients with coronary artery disease, it is a topic that warrants the attention of researchers in the hypertension field, as it may have important implications for the development of organ damage, and potentially could be linked to the pathogenesis of hypertension itself.

Remodeling of the cardiac pacemaker L-type calcium current and its beta-adrenergic responsiveness in hypertension after neuronal NO synthase gene transfer

Hypertension is associated with abnormal neurohumoral activation. We tested the hypothesis that beta-adrenergic hyperresponsiveness in the sinoatrial node (SAN) of the spontaneously hypertensive rat occurs at the level of the L-type calcium current because of altered cyclic nucleotide-dependent signaling. Furthermore, we hypothesized that NO, a modulator of cGMP and cAMP, would normalize the beta-adrenergic phenotype in the hypertensive rat. Chronotropic responsiveness to norepinephrine (NE), together with production of cAMP and cGMP, was assessed in isolated atrial preparations from age-matched hypertensive and normotensive rats. Right atrial/SAN pacemaking tissue was injected with adenovirus encoding enhanced green fluorescent protein (control vector) or neuronal NO synthase (nNOS). In addition, L-type calcium current was measured in cells isolated from the SAN of transfected animals. Basal levels of cGMP were lower in hypertensive rat atria. These atria were hyperresponsive to NE at all of the concentrations tested, with elevated production of cAMP. This was accompanied by increased basal and norepinephrine-stimulated L-type calcium current. Using enhanced green fluorescent protein, we observed transgene expression within both tissue sections and isolated pacemaking cells. Adenoviral nNOS increased right atrial nNOS protein expression and cGMP content. NE-stimulated cAMP concentration and L-type calcium current were also attenuated by adenoviral nNOS, along with the chronotropic responsiveness to NE in hypertensive rat atria. Decreased calcium current after cardiac nNOS gene transfer contributes to the normalization of beta-adrenergic hyperresponsiveness in the SAN from hypertensive rats by modulating cyclic nucleotide signaling.

Thioredoxin: friend or foe in human disease?

Thioredoxin (Trx), a small, ubiquitous thiol [sulfydryl (-SH)] protein, is one of the most important regulators of reduction-oxidation (redox) balance and, thus, redox-controlled cell functions. Although Trx was discovered 40 years ago in bacteria, the number and diversity of processes that Trx influences in human cells have only been appreciated recently. Processes influenced by Trx include the control of cellular redox balance, the promotion of cell growth, the inhibition of apoptosis and the modulation of inflammation. Not surprisingly, the role of Trx in a wide range of human diseases and conditions, including cancer, viral disease, ischaemia-reperfusion injury, cardiac conditions, aging, premature birth and newborn physiology, is subject to intense investigation. However, whether Trx contributes to or prevents the pathology of a particular condition is not always clear. In this article, we review the role of Trx in human disease and relate this to its redox activity and biological properties, and discuss the development and use of therapies that either inhibit or augment Trx activity.

Decreased blood pressure in NOX1-deficient mice

To understand the role of the superoxide-generating NADPH oxidase NOX1 in the vascular system, we have generated NOX1-deficient mice. NOX1-deficient mice had a moderately decreased basal blood pressure. In response to angiotensin II they showed an almost complete loss of the sustained blood pressure response, while the initial increase was conserved. NOX1-deficient mice showed a marked reduction in aortic media hypertrophy. Angiotensin II-induced smooth muscle cell proliferation was conserved, but there was a marked decrease in extracellular matrix accumulation. Our results establish a role for NOX1 in blood pressure regulation and vascular angiotensin II response.

Thioredoxin and its role in premature newborn biology

Thioredoxin (Trx) is a redox-active protein that has been shown to regulate various cellular processes due to its thiol-disulfide exchange reaction. It has antioxidant properties and also induces the expression of critical antioxidant enzymes such as manganese superoxide dismutase. Trx along with thioredoxin reductase and peroxiredoxins forms a complete system similar to the glutathione system, but with different and divergent functions. This review is a mini-update on key advances in the role of Trx in signal transduction and premature newborn biology. In addition, this mini-update also reviews recently reported prooxidant properties of Trx that relate to anthracycline redox cycling.

Endothelial progenitor cell senescence is accelerated in both experimental hypertensive rats and patients with essential hypertension

OBJECTIVES

Recent studies have revealed an association between coronary risk factors and both the number and function of bone marrow-derived endothelial progenitor cells (EPCs). Although hypertension is an important coronary risk factor, the influence to the EPCs is not fully understood. We investigated the effect of hypertension on EPC senescence.

METHODS

Experimental study We investigated the number and senescence of EPCs in spontaneously hypertensive rats (SHR/Izm) and deoxycorticosterone acetate (DOCA)-salt hypertensive rats. EPCs were isolated from peripheral blood of rats and were characterized. EPC senescence was detected by acidic beta-galactosidase staining. In addition, we measured the telomerase activity using polymerase chain reaction-enzyme-linked immunosorbent assay.

CLINICAL STUDY

EPCs were isolated from peripheral blood samples in 37 patients with essential hypertension. After ex-vivo cultivation, we detected senescence and measured the telomerase activity. The total severity index of hypertension-induced organ damage was calculated by the summation of each severity index in the classification of hypertension severity by Tokyo University (1984).

RESULTS

Experimental study The EPC senescence in SHR/Izm and DOCA-salt hypertensive rats was significantly increased compared with that of control rats. The telomerase activities in SHR/Izm and DOCA-salt hypertensive sensitive rats were also significantly lowered compared with those of control rats. Clinical study Compared with the control group, EPCs from hypertensive patients showed accelerated senescence and also showed reduced telomerase activity. In hypertensive patients, the degree of hypertension-induced organ damage was negatively correlated with telomerase activity, and was positively correlated with EPC senescence.

CONCLUSIONS

EPC senescence is accelerated in both experimental hypertensive rats and patients with essential hypertension, which may be related to telomerase inactivation. The hypertension-induced EPC senescence may affect the process of vascular remodeling.

Increased oxidative protein and DNA damage but decreased stress response in the aged brain following experimental stroke

Aged individuals experience the highest rate of stroke and have less functional recovery, but do not have larger infarcts. We hypothesized that aged individuals experience greater sublethal damage in peri-infarct cortex. Focal cortical stroke was produced in aged and young adult animals. After 30 min, 1, 3 and 5 days brain sections and Western blot were used to analyze markers of apoptotic cell death, oxidative DNA and protein damage, heat shock protein (HSP) 70 induction, total neuronal number and infarct size. Focal stroke produces significantly more oxidative DNA and protein damage and fewer cells with HSP70 induction in peri-infarct cortex of aged animals. There is no difference in infarct size or the number of cells undergoing apoptosis between aged and young adults. Stroke in the aged brain is associated with a greater degree of DNA and protein damage and a reduced stress response in intact, surviving tissue that surrounds the infarct.

Thioredoxin and its related molecules: update 2005

Studies on thioredoxin (Trx) and its related molecules have expanded dramatically recently. Proteins that share the similar active-site sequence, -Cys-Xxx-Yyy-Cys-, are called the Trx family, and the number of Trx family members is increasing. Trx reductase, which reduces oxidized Trx in cooperation with NADPH, has three isoforms, and peroxiredoxin, which is Trx-dependent peroxidase, has six isoforms. In addition to a role as an antioxidant, Trx and its related molecules play crucial roles in the redox regulation of signal transduction. The classical cytosolic Trx1 and truncated Trx80 are released from cells. Plasma/serum levels of Trx1 are good markers for oxidative stress. Exogenous Trx1 shows cytoprotective and antiinflammatory effects and has a good potential for clinical application. This is an update review on Trx and its related molecules.

Thioredoxin: a multifunctional antioxidant enzyme in kidney, heart and vessels

PURPOSE OF REVIEW

Recent studies indicate that an imbalance in cell redox state alters multiple cell pathways that may contribute to the pathogenesis of cardiovascular disorders including hypertension and renal failure.

RECENT FINDINGS

The thioredoxin system (thioredoxin, thioredoxin reductase, and NADPH) is a ubiquitous thiol oxidoreductase system that regulates cellular reduction/oxidation (redox) status. Thioredoxin plays an essential role in cell function by limiting oxidative stress directly via antioxidant effects and indirectly by protein-protein interactions with key signaling molecules such as thioredoxin-interacting protein (TXNIP). Examples include the findings that hyperglycemia and diabetes induce TXNIP and decrease thioredoxin activity, while steady blood flow decreases TXNIP and increases thioredoxin activity.

SUMMARY

Based on these findings we propose that thioredoxin and its endogenous regulators represent important future targets to develop clinical therapies for diseases associated with oxidative stress.

Low doses of reactive oxygen species protect endothelial cells from apoptosis by increasing thioredoxin-1 expression

The redox regulator thioredoxin-1 (Trx-1) is required for the redox potential of the cell and exerts important functions in cell growth and apoptosis. Severe oxidative stress has been implicated in the oxidation of proteins and cell death. However, the role of low doses of reactive oxygen species (ROS) is poorly understood. Here, we show that 10 and 50 microM H2O2 and short-term exposure to shear stress significantly increased Trx-1 mRNA and protein levels in endothelial cells. Since it is known that Trx-1 exerts anti-apoptotic functions, we next investigated whether low doses of ROS can inhibit basal and serum-depletion induced endothelial cell apoptosis. Indeed, treatment of endothelial cells with 10 and 50 microM H2O2 significantly reduced apoptosis induction. Reduction of Trx-1 expression using an antisense oligonucleotide approach resulted in the induction of apoptosis and abolished the inhibitory effect of low doses of H2O2. Taken together, our results demonstrate that low doses of ROS act as signaling molecules and exert anti-apoptotic functions in endothelial cells via upregulation of the redox-regulator Trx-1.

Pentoxifylline prevents spontaneous brain ischemia in stroke-prone rats

Anti-inflammatory properties of pentoxifylline (PTX) have recently been described. Spontaneously hypertensive stroke-prone rats (SHRSP) constitute an animal model that develops an inflammatory condition that precedes the appearance of brain abnormalities. The aim of the present investigation was to assess: 1) the efficacy of PTX treatment in protecting the neural system in SHRSP, and 2) how its anti-inflammatory properties might be involved in this effect. Male SHRSP fed with a permissive diet received no drug or PTX (100 or 200 mg/kg/day). Brain abnormalities detected by magnetic resonance imaging developed spontaneously in control rats after 42 +/- 3 days, whereas in rats treated with 100 mg/kg/day PTX, abnormalities developed in only 80% of the animals and only after 70 to 80 days. Treatment with a higher dose of PTX (200 mg/kg/day) completely protected the brain from abnormal development. The drug treatment prevented the accumulation of macrophages or CD4+ positive cells, the activation of glia in brain tissues, and the appearance of inflammatory proteins and thiobarbituric acid-reactive substances in body fluids. PTX treatment did induce a greater increase of serum tumor necrosis factor-alpha (TNF-alpha), but not of interleukin (IL)-1beta and IL-6 induced by in vivo administration of lipopolysaccharide (LPS), which suggests a protective role for TNF-alpha. PTX also exerted protective effects when it was administered after the first occurrence of proteinuria (>40 mg/day). These data indicate that PTX treatment dose-dependently prevents the occurrence of spontaneous brain damage by reducing inflammatory events. We also hypothesize that the increase of TNF-alpha by PTX treatment represents a protective mechanism in SHRSP.

Reactive oxygen species in vascular biology: implications in hypertension

Reactive oxygen species (ROS), including superoxide (*O2-), hydrogen peroxide (H2O2), and hydroxyl anion (OH-), and reactive nitrogen species, such as nitric oxide (NO) and peroxynitrite (ONOO-), are biologically important O2 derivatives that are increasingly recognized to be important in vascular biology through their oxidation/reduction (redox) potential. All vascular cell types (endothelial cells, vascular smooth muscle cells, and adventitial fibroblasts) produce ROS, primarily via cell membrane-associated NAD(P)H oxidase. Reactive oxygen species regulate vascular function by modulating cell growth, apoptosis/anoikis, migration, inflammation, secretion, and extracellular matrix protein production. An imbalance in redox state where pro-oxidants overwhelm anti-oxidant capacity results in oxidative stress. Oxidative stress and associated oxidative damage are mediators of vascular injury and inflammation in many cardiovascular diseases, including hypertension, hyperlipidemia, and diabetes. Increased generation of ROS has been demonstrated in experimental and human hypertension. Anti-oxidants and agents that interrupt NAD(P)H oxidase-driven *O2- production regress vascular remodeling, improve endothelial function, reduce inflammation, and decrease blood pressure in hypertensive models. This experimental evidence has evoked considerable interest because of the possibilities that therapies targeted against reactive oxygen intermediates, by decreasing generation of ROS and/or by increasing availability of antioxidants, may be useful in minimizing vascular injury and hypertensive end organ damage. The present chapter focuses on the importance of ROS in vascular biology and discusses the role of oxidative stress in vascular damage in hypertension.

Reactive oxygen species, vascular oxidative stress, and redox signaling in hypertension: what is the clinical significance?

Metabolism of oxygen by cells generates potentially deleterious reactive oxygen species (ROS). Under normal conditions the rate and magnitude of oxidant formation is balanced by the rate of oxidant elimination. However, an imbalance between prooxidants and antioxidants results in oxidative stress, which is the pathogenic outcome of oxidant overproduction that overwhelms the cellular antioxidant capacity. The kidney and vasculature are rich sources of NADPH oxidase-derived ROS, which under pathological conditions play an important role in renal dysfunction and vascular damage. Strong experimental evidence indicates that increased oxidative stress and associated oxidative damage are mediators of renovascular injury in cardiovascular pathologies. Increased production of superoxide anion and hydrogen peroxide, reduced nitric oxide synthesis, and decreased bioavailability of antioxidants have been demonstrated in experimental and human hypertension. These findings have evoked considerable interest because of the possibilities that therapies targeted against free radicals by decreasing ROS generation or by increasing nitric oxide availability and antioxidants may be useful in minimizing vascular injury and renal dysfunction and thereby prevent or regress hypertensive end-organ damage. This article highlights current developments in the field of ROS and hypertension, focusing specifically on the role of oxidative stress in hypertension-associated vascular damage. In addition, recent clinical trials investigating cardiovascular benefits of antioxidants are discussed, and some explanations for the rather disappointing results from these studies are addressed. Finally, important avenues for future research in the field of ROS, oxidative stress, and redox signaling in hypertension are considered.