Hydrogen peroxide inhibits exercise-induced increase of circulating stem cells with endothelial progenitor capacity

Selective impairment of blood pressure reduction by endothelial nitric oxide synthase dimer destabilization in mice

OBJECTIVES

Endothelial dysfunction and oxidative stress are associated with hypertension but whether endothelial superoxide may play a role in the early development of essential hypertension remains uncertain. We investigated whether endothelial nitric oxide synthase (eNOS)-derived endothelial oxidative stress is involved in the regulation of SBP.

METHODS

Wild-type eNOS [mice with endothelium-specific overexpression of bovine endothelial NO-synthase (eNOS-Tg)] or a novel dimer-destabilized eNOS-mutant harboring a partially disrupted zinc-finger [mice with endothelium-specific overexpression of destabilized bovine eNOS destabilized by replacement of Cys 101 to Ala (C101A-eNOS-Tg)] was introduced in C57BL/6 in an endothelial-specific manner. Mice were monitored for aortic endothelium-dependent relaxation, SBP, levels of superoxide and several posttranslational modifications indicating activity and/or increased vascular oxidative stress. Some groups of mice underwent voluntary exercise training for 4 weeks or treatment with the superoxide dismutase mimetic Tempol.

RESULTS

C101A-eNOS-Tg showed significantly increased superoxide generation, protein-tyrosine-nitration and eNOS-tyrosine-nitration, eNOS-S-glutathionylation, eNOS phosphorylation and AMP kinase-α phosphorylation at Thr172 in aorta, skeletal muscle, left ventricular myocardium and lung as compared with eNOS-Tg and wild-type controls. Exercise training increased phosphorylation of eNOS at Ser and AMP kinase-α in wild-type. These physiologic adaptations were absent in C101A-eNOS-Tg. Maximal aortic endothelium-dependent relaxation was similar in all strains. C101A-eNOS-Tg displayed normal SBP despite higher levels of eNOS, whereas eNOS-Tg showed significant hypotension. Tempol completely reversed the occurring protein modifications and significantly reduced SBP in C101A-eNOS-Tg but not in wild-type.

CONCLUSION

Oxidative stress generated by endothelial-specific expression of genetically destabilized C101A-eNOS selectively prevents SBP-reducing activity of vascular eNOS, while having no effect on aortic endothelium-dependent relaxation. These data suggest that oxidative stress in microvascular endothelium may play a role for the development of essential hypertension.

Modulation of Local and Systemic Heterocellular Communication by Mechanical Forces: A Role of Endothelial Nitric Oxide Synthase

In this review, we discuss the role of nitric oxide (NO) as a key physiological mechanotransducer modulating both local and systemic heterocellular communication and contributing to the integrated (patho)physiology of the cardiovascular system. A deeper understanding of mechanotransduction-mediated local and systemic nodes controlling heterocellular communication between the endothelium, blood cells, and other cell types (e.g., cardiomyocytes) may suggest novel therapeutic strategies for endothelial dysfunction and cardiovascular disease. Recent Advances: Mechanical forces acting on mechanoreceptors on endothelial cells activate the endothelial NO synthase (eNOS) to produce NO. NO participates in (i) abluminal heterocellular communication, inducing vasorelaxation, and thereby regulating vascular tone and blood pressure; (ii) luminal heterocellular communication, inhibiting platelet aggregation, and controlling hemostasis; and (iii) systemic heterocellular communication, contributing to adaptive physiological processes in response to exercise and remote ischemic preconditioning. Interestingly, shear-induced eNOS-dependent activation of vascular heterocellular communication constitutes the molecular basis of all methods applied in the clinical routine for evaluation of endothelial function. Critical Issues and Future Directions: The integrated physiology of heterocellular communication is still not fully understood. Dedicated experimental models are needed to analyze messengers and mechanisms underpinning heterocellular communication in response to physical forces in the cardiovascular system (and elsewhere). Antioxid. Redox Signal. 26, 917-935.

Mitochondria-specific antioxidant supplementation does not influence endurance exercise training-induced adaptations in circulating angiogenic cells, skeletal muscle oxidative capacity or maximal oxygen uptake

KEY POINTS

Reducing excessive oxidative stress, through chronic exercise or antioxidants, can decrease the negative effects induced by excessive amounts of oxidative stress. Transient increases in oxidative stress produced during acute exercise facilitate beneficial vascular training adaptations, but the effects of non-specific antioxidants on exercise training-induced vascular adaptations remain elusive. Circulating angiogenic cells (CACs) are an exercise-inducible subset of white blood cells that maintain vascular integrity. We investigated whether mitochondria-specific antioxidant (MitoQ) supplementation would affect the response to 3 weeks of endurance exercise training in CACs, muscle mitochondrial capacity and maximal oxygen uptake in young healthy men. We show that endurance exercise training increases multiple CAC types, an adaptation that is not altered by MitoQ supplementation. Additionally, MitoQ does not affect skeletal muscle or whole-body aerobic adaptations to exercise training. These results indicate that MitoQ supplementation neither enhances nor attenuates endurance training adaptations in young healthy men.

ABSTRACT

Antioxidants have been shown to improve endothelial function and cardiovascular outcomes. However, the effects of antioxidants on exercise training-induced vascular adaptations remain elusive. General acting antioxidants combined with exercise have not impacted circulating angiogenic cells (CACs). We investigated whether mitochondria-specific antioxidant (MitoQ) supplementation would affect the response to 3 weeks of endurance exercise training on CD3+ , CD3+ /CD31+ , CD14+ /CD31+ , CD31+ , CD34+ /VEGFR2+ and CD62E+ peripheral blood mononuclear cells (PBMCs), muscle mitochondrial capacity, and maximal oxygen uptake (VO2 max ) in healthy men aged 22.1 ± 0.7 years, with a body mass index of 26.9 ± 0.9 kg m-2 , and 24.8 ± 1.3% body fat. Analysis of main effects revealed that training induced 33, 105 and 285% increases in CD14+ /CD31+ , CD62E+ and CD34+ /VEGFR2+ CACs, respectively, and reduced CD3+ /CD31- PBMCs by 14%. There was no effect of MitoQ on CAC levels. Also independent of MitoQ supplementation, exercise training significantly increased quadriceps muscle mitochondrial capacity by 24% and VO2 max by roughly 7%. In conclusion, endurance exercise training induced increases in multiple CAC types, and this adaptation is not modified by MitoQ supplementation. Furthermore, we demonstrate that a mitochondrial-targeted antioxidant does not influence skeletal muscle or whole-body aerobic adaptations to exercise training.

Nitric oxide up-regulates endothelial expression of angiotensin II type 2 receptors

Increasing vascular NO levels following up-regulation of endothelial nitric oxide synthase (eNOS) is considered beneficial in cardiovascular disease. Whether such beneficial effects exerted by increased NO-levels include the vascular renin-angiotensin system remains elucidated. Exposure of endothelial cells originated from porcine aorta, mouse brain and human umbilical veins to different NO-donors showed that expression of the angiotensin-II-type-2-receptor (AT2) mRNA and protein is up-regulated by activation of soluble guanylyl cyclase, protein kinase G and p38 mitogen-activated protein kinase without changing AT2 mRNA stability. In mice, endothelial-specific overexpression of eNOS stimulated, while chronic treatment with the NOS-blocker l-nitroarginine inhibited AT2 expression. The NO-induced AT2 up-regulation was associated with a profound inhibition of angiotensin-converting enzyme (ACE)-activity. In endothelial cells this reduction of ACE-activity was reversed by either the AT2 antagonist PD 123119 or by inhibition of transcription with actinomycin D. Furthermore, in C57Bl/6 mice an acute i.v. bolus of l-nitroarginine did not change AT2-expression and ACE-activity suggesting that inhibition of ACE-activity by endogenous NO is crucially dependent on AT2 protein level. Likewise, three weeks of either voluntary or forced exercise training increased AT2 expression and reduced ACE-activity in C57Bl/6 but not in mice lacking eNOS suggesting significance of this signaling interaction for vascular physiology. Finally, aortic AT2 expression is about 5 times greater in female as compared to male C57Bl/6 and at the same time aortic ACE activity is reduced in females by more than 50%. Together these findings imply that endothelial NO regulates AT2 expression and that AT2 may regulate ACE-activity.

Sustained hypertension despite endothelial-specific eNOS rescue in eNOS-deficient mice

The aim of the study was to evaluate the possible contribution of non-endothelial eNOS to the regulation of blood pressure (BP). To accomplish this, a double transgenic strain expressing eNOS exclusively in the vascular endothelium (eNOS-Tg/KO) has been generated by endothelial-specific targeting of bovine eNOS in eNOS-deficient mice (eNOS-KO). Expression of eNOS was evaluated in aorta, myocardium, kidney, brain stem and skeletal muscle. Organ bath studies revealed a complete normalization of aortic reactivity to acetylcholine, phenylephrine and the NO-donors in eNOS-Tg/KO. Function of eNOS in resistance arteries was demonstrated by acute i.v. infusion of acetylcholine and the NOS-inhibitor L-NAME. Acetylcholine decreased mean arterial pressure in all strains but eNOS-KO responded significantly less sensitive as compared eNOS-Tg/KO and C57BL/6. Likewise, acute i.v. L-NAME application elevated mean arterial pressure in C57BL/6 and eNOS-Tg/KO, but not in eNOS-KO. In striking contrast to these findings, mean, systolic and diastolic BP in eNOS-Tg/KO remained significantly elevated and was similar to values of eNOS-KO. Chronic oral treatment with L-NAME increased BP to the level of eNOS-KO only in C57BL/6, but had no effect on hypertension in eNOS-KO and eNOS-Tg/KO. Taken together, functional reconstitution of eNOS in the vasculature of eNOS-KO not even partially lowered BP. These data suggest that the activity of eNOS expressed in non-vascular tissue might play a role in physiologic BP regulation.

Delivery of natural polyphenols by polymeric nanoparticles improves the resistance of endothelial progenitor cells to oxidative stress

PURPOSE

Bone marrow-derived endothelial progenitor cells (EPCs) circulate into peripheral blood and significantly contribute to neo-vascularisation and re-endothelialisation as part of the process of vascular repair. Several studies have reported decreased EPC number in the presence of oxidative stress. Aim of this study was to evaluate the validity of mucoadhesive polymeric nanoparticles as a delivery system of natural products able to protect EPCs from oxidative stress.

METHODS

The total polyphenol content and antioxidant capacity of red grape seed extract (GSE) either pre-veraison (p-GSE) or ripe (r-GSE) were measured. Cell viability was evaluated by WST-1 assay. Nanoparticles were prepared by ionotropic crosslinking of two structurally different thiolated quaternary ammonium-chitosan conjugates. A hyaluronic acid solution, containing p-GSE or r-GSE, was added to a stirred solution of each of the two chitosan derivatives to obtain p- or r-GSE loaded nanoparticles (NP) of two types.

RESULTS

Both GSE types demonstrated strong antioxidant capacity. p-GSE showed a higher content in total polyphenols compared to r-GSE. NP size was in the 310-340 nm range, with 24 h stability, and nearly 100% encapsulation efficiency for both GSE types. NP were internalized by cells to an extent related directly with their surface charge intensity. GSE-NP uptake significantly improved cell viability and resistance to oxidation.

CONCLUSIONS

Nanotechnology has a great potential in nutraceutical delivery. The present results suggest that NP is a highly promising polyphenol carrier system particularly useful to protect EPCs from oxidative stress, thus improving their survival.

Effects of chronic swimming training and oestrogen therapy on coronary vascular reactivity and expression of antioxidant enzymes in ovariectomized rats

The aim of this study was to evaluate the effects of swimming training (SW) and oestrogen replacement therapy (ERT) on coronary vascular reactivity and the expression of antioxidant enzymes in ovariectomized rats. Animals were randomly assigned to one of five groups: sham (SH), ovariectomized (OVX), ovariectomized with E2 (OE2), ovariectomized with exercise (OSW), and ovariectomized with E2 plus exercise (OE2+SW). The SW protocol (5×/week, 60 min/day) and/or ERT were conducted for 8 weeks; the vasodilator response to bradykinin was analysed (Langendorff Method), and the expression of antioxidant enzymes (SOD-1 and 2, catalase) and eNOS and iNOS were evaluated by Western blotting. SW and ERT improved the vasodilator response to the highest dose of bradykinin (1000 ng). However, in the OSW group, this response was improved at 100, 300 and 1000 ng when compared to OVX (p<0,05). The SOD-1 expression was increased in all treated/trained groups compared to the OVX group (p<0,05), and catalase expression increased in the OSW group only. In the trained group, eNOS increased vs. OE2, and iNOS decreased vs. SHAM (p<0,05). SW may represent an alternative to ERT by improving coronary vasodilation, most likely by increasing antioxidant enzyme and eNOS expression and augmenting NO bioavailability.

Critical role of endothelial hydrogen peroxide in post-ischemic neovascularization

Background

Reactive oxygen species (ROS) play an important role in angiogenesis in endothelial cells (ECs) in vitro and neovascularization in vivo. However, little is known about the role of endogenous vascular hydrogen peroxide (H₂O₂) in postnatal neovascularization.

Methodology/Principal Findings

We used Tie2-driven endothelial specific catalase transgenic mice (Cat-Tg mice) and hindlimb ischemia model to address the role of endogenous H₂O₂ in ECs in post-ischemic neovascularization in vivo. Here we show that Cat-Tg mice exhibit significant reduction in intracellular H₂O₂ in ECs, blood flow recovery, capillary formation, collateral remodeling with larger extent of tissue damage after hindlimb ischemia, as compared to wild-type (WT) littermates. In the early stage of ischemia-induced angiogenesis, Cat-Tg mice show a morphologically disorganized microvasculature. Vascular sprouting and tube elongation are significantly impaired in isolated aorta from Cat-Tg mice. Furthermore, Cat-Tg mice show a decrease in myeloid cell recruitment after hindlimb ischemia. Mechanistically, Cat-Tg mice show significant decrease in eNOS phosphorylation at Ser1177 as well as expression of redox-sensitive vascular cell adhesion molecule-1 (VCAM-1) and monocyte chemotactic protein-1 (MCP-1) in ischemic muscles, which is required for inflammatory cell recruitment to the ischemic tissues. We also observed impaired endothelium-dependent relaxation in resistant vessels from Cat-Tg mice.

Conclusions/Significance

Endogenous ECs-derived H₂O₂ plays a critical role in reparative neovascularization in response to ischemia by upregulating adhesion molecules and activating eNOS in ECs. Redox-regulation in ECs is a potential therapeutic strategy for angiogenesis-dependent cardiovascular diseases.

Exercise-induced Signals for Vascular Endothelial Adaptations: Implications for Cardiovascular Disease

This article reviews recent advances in our understanding of hemodynamic signals, external/compressive forces, and circulating factors that mediate exercise training-induced vascular adaptations, with particular attention to the roles of these signals in prevention and treatment of endothelial dysfunction and cardiovascular (CV) diseases.

Catalase activity prevents exercise-induced up-regulation of vasoprotective proteins in venous tissue

Physical activity induces favourable changes of arterial gene expression and protein activity, although little is known about its effect in venous tissue. Although our understanding of the initiating molecular signals is still incomplete, increased expression of endothelial nitric oxide synthase (eNOS) is considered a key event. This study sought to investigate the effects of two different training protocols on the expression of eNOS and extracellular superoxide dismutase (ecSOD) in venous and lung tissue and to evaluate the underlying molecular mechanisms. C57Bl/6 mice underwent voluntary exercise or forced physical activity. Changes of vascular mRNA and protein levels and activity of eNOS, ecSOD and catalase were determined in aorta, heart, lung and vena cava. Both training protocols similarly increased relative heart weight and resulted in up-regulation of aortic and myocardial eNOS. In striking contrast, eNOS expression in vena cava and lung remained unchanged. Likewise, exercise up-regulated ecSOD in the aorta and in left ventricular tissue but remained unchanged in lung tissue. Catalase expression in lung tissue and vena cava of exercised mice exceeded that in aorta by 6.9- and 10-fold, respectively, suggesting a lack of stimulatory effects of hydrogen peroxide. In accordance, treatment of mice with the catalase inhibitor aminotriazole for 6 weeks resulted in significant up-regulation of eNOS and ecSOD in vena cava. These data suggest that physiological venous catalase activity prevents exercise-induced up-regulation of eNOS and ecSOD. Furthermore, therapeutic inhibition of vascular catalase might improve pulmonary rehabilitation.

Endothelial progenitor cells and exercise-induced redox regulation

Endothelial progenitor cells (EPCs) are thought to participate in endothelial cell regeneration and neovascularization in either a direct or an indirect way. The number of circulating EPCs is influenced by many factors like disease status, medication, age, and fitness level and is an independent predictor of disease progression and cardiovascular events. Experimental as well as clinical studies during the last 10 years clearly demonstrated that physical exercise training has a beneficial effect on endothelial function, which is a clear predictive value for cardiovascular mortality. Over the last years mainly clinical studies provided solid evidence for an exercise training induced mobilization of EPCs from the bone marrow, thereby possibly influencing the regeneration of the endothelial cell layer. This review will discuss the mechanisms how exercise induces mobilization of EPCs from the bone marrow with a focus on the influence on the redox balance.

Role of endothelial progenitor cells in the beneficial effects of physical exercise on atherosclerosis and coronary artery disease

In clinical trials as well as in several animal experiments it is evident that physical exercise is a powerful tool to positively influence the development and/or progression of atherosclerosis and coronary artery disease (CAD). The main target of physical exercise seems to be the maintenance of an intact endothelial cell layer. Since the discovery that endothelial progenitor cells (EPCs) are present in the circulation and the knowledge that exercise, either as a single exercise bout or an exercise training program, have the potency to mobilize EPCs from the bone marrow, the contribution of the EPCs for the preservation or repair of the endothelial cell layer is still under debate. Either the EPCs differentiate into mature endothelial cells, or they stimulate via a paracrine mechanism mature endothelial cells to proliferate. It is still unclear, if the exercise-induced mobilization of EPCs is casually related to the improvement of endothelial function. This review will discuss the role of endothelial progenitor cells in the beneficial effects of physical exercise on atherosclerosis and coronary artery disease.