Antioxidant treatment in peripheral artery disease: the rationale is there, but what about clinical results?

Oxidative stress and vascular dysfunction: Potential therapeutic targets and therapies in peripheral artery disease

Peripheral artery disease (PAD) is the manifestation of atherosclerosis characterized by the accumulation of plaques in the arteries of the lower limbs. Interestingly, growing evidence suggests that the pathology of PAD is multifaceted and encompasses both vascular and skeletal muscle dysfunctions, which contributes to blunted physical capabilities and diminished quality of life. Importantly, it has been suggested that many of these pathological impairments may stem from blunted reduction-oxidation (redox) handling. Of note, in those with PAD, excessive production of reactive oxygen species (ROS) outweighs antioxidant capabilities resulting in oxidative damage, which may have systemic consequences. It has been suggested that antioxidant supplementation may be able to assist in handling ROS. However, the activation of various ROS production sites makes it difficult to determine the efficacy of these antioxidant supplements. Therefore, this review focuses on the common cellular mechanisms that facilitate ROS production and discusses how excessive ROS may impair vascular and skeletal muscle function in PAD. Furthermore, we provide insight for current and potential antioxidant therapies, specifically highlighting activation of the Kelch-like ECH-associated protein 1 (Keap1) - Nuclear Factor Erythroid 2-related factor 2 (Nrf2) pathway as a potential pharmacological therapy to combat ROS accumulation and aid in vascular function, and physical performance in patients with PAD. Altogether, this review provides a better understanding of excessive ROS in the pathophysiology of PAD and enhances our perception of potential therapeutic targets that may improve vascular function, skeletal muscle function, walking capacity, and quality of life in patients with PAD.

Cocoa flavanols, Nrf2 activation, and oxidative stress in peripheral artery disease: mechanistic findings in muscle based on outcomes from a randomized trial

The pathophysiology of muscle damage in peripheral artery disease (PAD) includes increased oxidant production and impaired antioxidant defenses. Epicatechin (EPI), a naturally occurring flavanol, has antioxidant properties that may mediate the beneficial effects of natural products such as cocoa. In a phase II randomized trial, a cocoa-flavanol-rich beverage significantly improved walking performance compared with a placebo in people with PAD. In the present work, the molecular mechanisms underlying the therapeutic effect of cocoa flavanols were investigated by analyzing baseline and follow-up muscle biopsies from participants. Increases in nuclear factor erythroid 2-related factor 2 (Nrf2) target antioxidants heme oxygenase-1 (HO-1) and NAD(P)H dehydrogenase [quinone] 1 (NQO1) in the cocoa group were significantly associated with reduced accumulation of central nuclei, a myopathy indicator, in type II muscle fibers (P = 0.017 and P = 0.023, respectively). Protein levels of the mitochondrial respiratory complex III subunit, cytochrome b-c1 complex subunit 2 (UQCRC2), were significantly higher in the cocoa group than in the placebo group (P = 0.032), and increases in UQCRC2 were significantly associated with increased levels of Nrf2 target antioxidants HO-1 and NQO1 (P = 0.001 and P = 0.035, respectively). Exposure of non-PAD human myotubes to ex vivo serum from patients with PAD reduced Nrf2 phosphorylation, an indicator of activation, increased hydrogen peroxide production and oxidative stress, and reduced mitochondrial respiration. Treatment of myotubes with EPI in the presence of serum from patients with PAD increased Nrf2 phosphorylation and protected against PAD serum-induced oxidative stress and mitochondrial dysfunction. Overall, these findings suggest that cocoa flavanols may enhance antioxidant capacity in PAD via Nrf2 activation.NEW & NOTEWORTHY The current study supports the hypothesis that in people with PAD, cocoa flavanols activate Nrf2, thereby increasing antioxidant protein levels, protecting against skeletal muscle damage, and increasing mitochondrial protein abundance. These results suggest that Nrf2 activation may be an important therapeutic target for improving walking performance in people with PAD.

Redox Balance in Type 2 Diabetes: Therapeutic Potential and the Challenge of Antioxidant-Based Therapy

Oxidative stress is an important factor in the development of type 2 diabetes (T2D) and associated complications. Unfortunately, most clinical studies have failed to provide sufficient evidence regarding the benefits of antioxidants (AOXs) in treating this disease. Based on the known complexity of reactive oxygen species (ROS) functions in both the physiology and pathophysiology of glucose homeostasis, it is suggested that inappropriate dosing leads to the failure of AOXs in T2D treatment. To support this hypothesis, the role of oxidative stress in the pathophysiology of T2D is described, together with a summary of the evidence for the failure of AOXs in the management of diabetes. A comparison of preclinical and clinical studies indicates that suboptimal dosing of AOXs might explain the lack of benefits of AOXs. Conversely, the possibility that glycemic control might be adversely affected by excess AOXs is also considered, based on the role of ROS in insulin signaling. We suggest that AOX therapy should be given in a personalized manner according to the need, which is the presence and severity of oxidative stress. With the development of gold-standard biomarkers for oxidative stress, optimization of AOX therapy may be achieved to maximize the therapeutic potential of these agents.

The Impact of Lower Extremity Skeletal Muscle Atrophy and Myosteatosis on Revascularization Outcomes in Patients with Peripheral Arterial Disease

Background: This study investigated whether lower extremity muscle atrophy and myosteatosis in patients with peripheral arterial disease (PAD) are correlated to postoperative outcomes, such as reintervention or amputation-free survival. Methods: In this single-center retrospective cohort study of 462 patients treated for peripheral arterial disease scheduled for intervention, muscle mass and the presence of fattening of the lower extremity muscles were measured semiautomatically in a single computed tomography slice of the treated leg. Binary logistic regression models and Cox proportional hazards models were used to determine the effect of muscle atrophy and myosteatosis on reintervention and amputation. Results: Muscle atrophy and myosteatosis increased in PAD patients with Fontaine class IV compared with Fontaine class IIa. In PAD patients with muscle atrophy or myosteatosis, no association was found with the reintervention rate or reintervention-free survival, but an association was found with amputation-free survival, even after adjustment for patient-related, disease-severity, and comorbidities-related factors. Conclusion: Muscle atrophy and mysosteatosis increased in PAD patients with increasing disease severity. Lower extremity muscle atrophy and myosteatosis are associated with amputation rate and amputation-free survival in PAD patients. No association with reintervention rate or reintervention-free survival was found. Muscle atrophy and myosteatosis may serve as additional risk factors in decision making in the often frail vascular patient.

Injectable thermosensitive chitosan-based hydrogel containing ferulic acid for treating peripheral arterial disease

Peripheral arterial disease (PAD) affects more than 200 million people worldwide. Recent studies suggest that oxidative stress-related inflammation can lead to the initiation and progression of PAD. Ferulic acid (FA) is a natural phenolic compound and has been proven to have antioxidant and angiogenesis effects. In this study, thermosensitive chitosan-gelatin-based hydrogel was used as a delivery vehicle of FA. The effects of hydrogel encapsulating FA (FA-gel) have been demonstrated in vitro and in vivo. The results revealed that the developed hydrogel with porous structure could provide a sustained release of FA. Post-treatment of FA-gel effectively decreased the oxidative stress-induced damage in human umbilical vein endothelial cells via decreasing endogenous reactive oxygen species production, inflammation-related gene expression and apoptosis level. In the mouse hindlimb ischemia model, the results revealed that FA-gel could improve blood flow, muscle regeneration and decreases inflammation in veins. These results suggested that FA-gel may have a therapeutic potential in PAD.

Critical Limb Ischaemia Exacerbates Mitochondrial Dysfunction in ApoE-/- Mice Compared with ApoE+/+ Mice, but N-acetyl Cysteine still Confers Protection

OBJECTIVES

The current study was performed in order to determine the influence of hypercholesterolaemia on critical limb ischaemia (CLI) and whether targeting oxidative stress by antioxidant therapies such as N-acetyl cysteine (NAC), considered to be a direct scavenger of reactive oxygen species, could confer muscle protection.

METHODS

Apolipoprotein E (ApoE)-/- mice (n = 9, 29 weeks old) and their genetic controls ApoE+/+ mice (n = 9, 29 weeks old) were submitted to sequential right femoral and iliac ligations; the left limb served as control. ApoE+/+ mice were divided into two groups: Group 1 (n = 4) and Group 2 (n = 5); as well as ApoE-/- mice: Group 3 (n = 3), and Group 4 (n = 6). NAC treatment was administered to Groups 2 and 4 in drinking water. Mice were sacrificed on Day 40 and gastrocnemius muscles were harvested to study mitochondrial respiration by oxygraphy, calcium retention capacity by spectrofluorometry, and production of reactive oxygen species by electron paramagnetic resonance.

RESULTS

CLI associated with ApoE deficiency resulted in more severe mitochondrial dysfunction: maximum oxidative capacity and calcium retention capacity were decreased (-42.9% vs. -25.1%, p = .010; and -73.1% vs. -40.3%, p = .003 respectively) and production of reactive oxygen species was enhanced (+63.6% vs. +41.4%, p = .03) in ApoE-/- mice compared with ApoE+/+ mice respectively. Antioxidant treatment restored oxidative capacity, calcium retention capacity and decreased production of reactive oxygen species in both mice strands.

CONCLUSIONS

In this small murine study, hypercholesterolaemia exacerbated mitochondrial dysfunction, as clinically expected; but antioxidant therapy appeared protective, which is counter to clinical experience. Further work is clearly needed.

Catalytic antioxidants for therapeutic medicine

In this Review, we focus on catalytic antioxidant study based on transition metal complexes, organoselenium compounds, supramolecules and protein scaffolds.

Oxidative Stress and Arterial Dysfunction in Peripheral Artery Disease

Peripheral artery disease (PAD) is an atherosclerotic disease characterized by a narrowing of the arteries in the lower extremities. Disease manifestations are the result of more than just reduced blood flow, and include endothelial dysfunction, arterial stiffness, and inflammation. Growing evidence suggests that these factors lead to functional impairment and decline in PAD patients. Oxidative stress also plays an important role in the disease, and a growing amount of data suggest a link between arterial dysfunction and oxidative stress. In this review, we present the current evidence for the involvement of endothelial dysfunction, arterial stiffness, and inflammation in the pathophysiology of PAD. We also discuss the links between these factors and oxidative stress, with a focus on nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 2 (NOX2)-derived reactive oxygen species (ROS) and decreased nitric oxide (NO) bioavailability. Finally, the potential therapeutic role of NOX2 antioxidants for improving arterial function and functional status in PAD patients is explored.