Therapeutic potential of sustained-release sodium nitrite for critical limb ischemia in the setting of metabolic syndrome

Structured Exercise Therapy Increases Endogenous Antioxidants to Repair Muscle Strength and Health in Porcine Ischemic Myopathy Model of Peripheral Artery Disease

Objective: The mechanisms of structured exercise therapy (SET) in peripheral artery disease (PAD) are not clear. We have developed an SET module for our large animal model of ischemic myopathy. We hypothesized that SET would increase muscle strength and walking distance in this model. The objective was to discover the SET-dependent mechanisms involved in this process. Approach: After induction of unilateral hind limb ischemia, three animals were exposed to standard environmental enrichment (sedentary or SED) and four animals underwent SET thrice weekly for 4 weeks postoperatively. Walking, hind limb pressure indices, and strength testing were performed weekly. Terminal muscle samples were used for skeletal muscle testing. Results: SET animals increased walking distance over time. SET increased muscle strength in both the ischemic and nonischemic limb. When comparing the ischemic SED hind limb muscle with that of ischemic + SET, the SET group has improved respiration and decreased oxidative stress. Markers of cell death and impaired functional regeneration were increased in SED ischemic muscles but returned toward baseline in the SET ischemic muscle. Innovation: This study uses a validated, large animal model of ischemic myopathy similar to that seen in humans with PAD. The effects of exercise on limb function, strength, and skeletal muscle health are reported in this model. Conclusion: SET increases muscle strength and regeneration by increasing endogenous antioxidants and mitochondrial respiration, resulting in favorable muscle health despite ongoing ischemia. This model may assist in preclinical testing of PAD therapies designed to improve muscle health. [Figure: see text].

New experimental model of hind limb ischemia in pot-bellied pigs

BACKGROUND

The simulation of limb ischemia in large laboratory animals is a complex and currently topical task in experimental medicine. Meanwhile, there is a demand for a reliable and effective model of limb ischemia for further testing of medicines to stimulate circulation and induce angiogenesis, gene medicines in particular. Aim of this study was to develop and experimentally test an effective method of simulation of hind limb ischemia.

METHODS

Female Vietnamese pot-bellied pigs were chosen as biological models. The reproduction of the pathology was evaluated using the following methods: laser doppler flowmetry, laboratory test of venous blood, immunohistochemical reaction with antibodies against CD31, a specific marker of endothelial cells, Van Gieson's staining of muscles for presence of connective tissue and clinical observation to detect the presence of lameness in pigs.

RESULTS

Laser doppler flowmetry recorded a significant decrease in the intensity of the blood circulation and a marked decrease in temperate in the operated limb. Increased lactate and creatine kinase were registered immediately after the surgery and were absent 3 or more days later. Clinical observation demonstrated presence of walking lameness. Histological and immunohistochemical methods revealed a credible increase in connective tissue area and a reduction in the number of blood vessels in the muscles, confirming the presence of ischemia.

CONCLUSIONS

An effective approach to modeling limb ischemia has been developed and experimentally tested. The proposed model may be used in cardiovascular surgery and will allow further testing of new medications designed to treat ischemia of hind limbs.

Human skeletal muscle nitrate and nitrite in individuals with peripheral arterial disease: Effect of inorganic nitrate supplementation and exercise

Skeletal muscle may act as a reservoir for N-oxides following inorganic nitrate supplementation. This idea is most intriguing in individuals with peripheral artery disease (PAD) who are unable to endogenously upregulate nitric oxide. This study analyzed plasma and skeletal muscle nitrate and nitrite concentrations along with exercise performance, prior to and following 12-weeks of exercise training combined with oral inorganic nitrate supplementation (EX+BR) or placebo (EX+PL) in participants with PAD. Non-supplemented, at baseline, there were no differences in plasma and muscle nitrate. For nitrite, muscle concentration was higher than plasma (+0.10 nmol.g^-1 ). After 12 -weeks, acute oral nitrate increased both plasma and muscle nitrate (455.04 and 121.14 nmol.g^-1 , p < 0.01), which were correlated (r = 0.63, p < 0.01), plasma nitrate increase was greater than in muscle (p < 0.01). Nitrite increased in the plasma (1.01 nmol.g^-1 , p < 0.05) but not in the muscle (0.22 nmol.g^-1 ) (p < 0.05 between compartments). Peak walk time (PWT) increased in both groups (PL + 257.6 s;BR + 315.0 s). Six-minute walk (6 MW) distance increased only in the (EX+BR) group (BR + 75.4 m). We report no substantial gradient of nitrate (or nitrite) from skeletal muscle to plasma, suggesting a lack of reservoir-like function in participants with PAD. Oral nitrate supplementation produced increases in skeletal muscle nitrate, but not skeletal muscle nitrite. The related changes in nitrate concentration between plasma and muscle suggests a potential for inter-compartmental nitrate "communication". Skeletal muscle did not appear to play a role in within compartment nitrate reduction. Muscle nitrate and nitrite concentrations did not appear to contribute to exercise performance in patients with PAD.

Antioxidative and Angiogenic Hyaluronic Acid-Based Hydrogel for the Treatment of Peripheral Artery Disease

Peripheral arterial disease (PAD) is a progressive atherosclerotic disorder characterized by blockages of the arteries supplying the lower extremities. Ischemia initiates oxidative damage and mitochondrial dysfunction in the legs of PAD patients, causing injury to the tissues of the leg, significant decline in walking performance, leg pain while walking, and in the most severe cases, nonhealing ulcers and gangrene. Current clinical trials based on cells/stem cells, the trophic factor, or gene therapy systems have shown some promising results for the treatment of PAD. Biomaterial matrices have been explored in animal models of PAD to enhance these therapies. However, current biomaterial approaches have not fully met the essential requirements for minimally invasive intramuscular delivery to the leg. Ideally, a biomaterial should present properties to ameliorate oxidative stress/damage and failure of angiogenesis. Recently, we have created a thermosensitive hyaluronic acid (HA) hydrogel with antioxidant capacity and skeletal muscle-matching stiffness. Here, we further optimized HA hydrogels with the cell adhesion peptide RGD to facilitate the development of vascular-like structures in vitro. The optimized HA hydrogel reduced intracellular reactive oxygen species levels and preserved vascular-like structures against H₂O₂-induced damage in vitro. HA hydrogels also provided prolonged release of the vascular endothelial growth factor (VEGF). After injection into rat ischemic hindlimb muscles, this VEGF-releasing hydrogel reduced lipid oxidation, regulated oxidative-related genes, enhanced local blood flow in the muscle, and improved running capacity of the treated rats. Our HA hydrogel system holds great potential for the treatment of the ischemic legs of patients with PAD.

Phytochemicals as Therapeutic Interventions in Peripheral Artery Disease

Peripheral artery disease (PAD) affects over 200 million people worldwide, resulting in significant morbidity and mortality, yet treatment options remain limited. Among the manifestations of PAD is a severe functional disability and decline, which is thought to be the result of different pathophysiological mechanisms including oxidative stress, skeletal muscle pathology, and reduced nitric oxide bioavailability. Thus, compounds that target these mechanisms may have a therapeutic effect on walking performance in PAD patients. Phytochemicals produced by plants have been widely studied for their potential health effects and role in various diseases including cardiovascular disease and cancer. In this review, we focus on PAD and discuss the evidence related to the clinical utility of different phytochemicals. We discuss phytochemical research in preclinical models of PAD, and we highlight the results of the available clinical trials that have assessed the effects of these compounds on PAD patient functional outcomes.

Bioengineering strategies for the treatment of peripheral arterial disease

Peripheral arterial disease (PAD) is a progressive atherosclerotic disorder characterized by narrowing and occlusion of arteries supplying the lower extremities. Approximately 200 million people worldwide are affected by PAD. The current standard of operative care is open or endovascular revascularization in which blood flow restoration is the goal. However, many patients are not appropriate candidates for these treatments and are subject to continuous ischemia of their lower limbs. Current research in the therapy of PAD involves developing modalities that induce angiogenesis, but the results of simple cell transplantation or growth factor delivery have been found to be relatively poor mainly due to difficulties in stem cell retention and survival and rapid diffusion and enzymolysis of growth factors following injection of these agents in the affected tissues. Biomaterials, including hydrogels, have the capability to protect stem cells during injection and to support cell survival. Hydrogels can also provide a sustained release of growth factors at the injection site. This review will focus on biomaterial systems currently being investigated as carriers for cell and growth factor delivery, and will also discuss biomaterials as a potential stand-alone method for the treatment of PAD. Finally, the challenges of development and use of biomaterials systems for PAD treatment will be reviewed.

Collateral Development and Arteriogenesis in Hindlimbs of Swine After Ligation of Arterial Inflow

BACKGROUND

Development of collateral vasculature is key in compensating for arterial occlusions in patients with peripheral artery disease (PAD). We aimed to examine the development of collateral pathways after ligation of native vessels in a porcine model of PAD.

METHODS

Right hindlimb ischemia was induced in domestic swine (n = 11) using two versions of arterial ligation. Version 1 (n = 6) consisted of ligation with division of the right external iliac, profunda femoral, and superficial femoral arteries. Version 2 (n = 5) consisted of the ligation of version 1 with additional ligation with division of the right internal iliac artery. Development of collateral pathways was evaluated with standard angiography before arterial ligation and at termination (30 days later). Relative luminal diameter of the arteries supplying the ischemic right hind limb were determined by two-dimensional angiography.

RESULTS

The dominant collateral pathway that developed after version 1 ligation connected the right internal iliac artery to the right profunda femoral and then to the right superficial femoral and popliteal artery. Mean luminal diameter of the right internal iliac artery at termination increased by 38% compared with baseline. Two codominant collateral pathways developed in version 2 ligation: (i) from the left profunda femoral artery to the reconstituted right profunda femoral artery and (ii) from the common internal iliac trunk and the left internal iliac artery to the reconstituted right internal iliac artery, which then supplied the right profunda femoral and then the right superficial femoral and popliteal artery. The mean diameter of the left profunda and the left internal iliac artery increased at termination by 26% and 21%, respectively (P < 0.05).

CONCLUSIONS

Two versions of hindlimb ischemia induction (right ilio-femoral artery ligation with and without right internal iliac artery ligation) in swine produced differing collateral pathways, along with changes to the diameter of the inflow vessels (i.e., arteriogenesis).

Comparative effects of nitric oxide dependent and independent vasodilation on impaired hindlimb revascularization in eNOS−/− mice

Ischemia due to vascular occlusion induces vasodilation as an initial response, followed by arteriogenesis or angiogenesis. Vasodilation through nitric oxide (NO) independent and dependent mechanisms may be sufficient to restore the altered neovascularization in pathological situations where the NO is altered. Using a posterior limb claudication model to evaluate ischemia-induced revascularization in eNOS−/− mice, we compared the effects of sodium nitrite, a NO-dependent vasodilator, and prazocin, an alpha-adrenergic blocker and NO-independent vasodilator, on hindlimb revascularization. We evaluated the blood flow of the hindlimbs, NO and nitrites metabolites, the expression of tissue endothelial cell markers and proangiogenic factors, as well as the gait locomotion. Our results suggest that the use of a peripheral vasodilator can substitute the initial absence of NO as an endogenous vasodilator. However, final resolution of the ischemic process requires a NO-mediated pathway, which through changes in vascular hemodynamics, promotes the generation of angiogenic messengers facilitating the functional recovery of the damaged limb.

Effects of a novel hydrogen sulfide prodrug in a porcine model of acute limb ischemia

OBJECTIVE

Previous studies have shown that hydrogen sulfide (H₂S) exerts potent proangiogenic properties under in vitro conditions and in rodent models. We sought to determine whether a novel H₂S prodrug promotes peripheral revascularization in a swine model of acute limb ischemia (ALI).

METHODS

ALI was induced in 17 female miniswine via intravascular occlusion of the external iliac. At day 7 after ALI induction, miniswine (n = 17) were randomized to received placebo or the H₂S prodrug, SG-1002 (800 mg per os twice a day), for 35 days. At day 35 SG-1002 increased circulating levels of H₂S (5.0 ± 1.2 μmol/L vs 1.8 ± 0.50 μmol/L; P < .05), sulfane sulfur (10.6 ± 2.3 μmol/L vs 2.6 ± 0.8 μmol/L; P < .05), and nitrite (0.5 ± 0.05 μmol/L vs 0.3 ± 0.03 μmol/L; P < .005) compared with placebo. SG-1002 therapy increased angiographic scoring in ischemic limb vessel number (27.6 ± 1.6 vs 22.2 ± 1.8; P < .05) compared with placebo. Treatment with SG-1002 preserved existing capillaries in ischemic limbs (128.3 ± 18.7 capillaries/mm² vs 79.0 ± 9.8 capillaries/mm²; P < .05) compared with placebo. Interestingly, treatment with SG-1002 also improved coronary vasorelaxation responses to bradykinin and substance P in miniswine with ALI.

CONCLUSIONS

Our results suggest that daily administration of the H₂S prodrug, SG-1002, leads to an increase in circulating H₂S and nitric oxide signaling and preserves vessel number and density in ischemic limbs. Furthermore, SG-1002 therapy improved endothelial-dependent coronary artery vasorelaxation in the setting of ALI. Our data demonstrate that SG-1002 preserves the vascular architecture in ischemic limbs and exerts vascular protective effects in the coronary vasculature in a model of peripheral vascular disease.

Blood Pressure–Lowering Effect of Orally Ingested Nitrite Is Abolished by a Proton Pump Inhibitor

Inorganic nitrate and nitrite from dietary and endogenous sources are metabolized to NO and other bioactive nitrogen oxides that affect blood pressure. The mechanisms for nitrite bioactivation are unclear, but recent studies in rodents suggest that gastric acidity may influence the systemic effects of this anion. In a randomized, double-blind, placebo-controlled crossover study, we tested the effects of a proton pump inhibitor on the acute cardiovascular effects of nitrite. Fifteen healthy nonsmoking, normotensive subjects, aged 19 to 39 years, were pretreated with placebo or esomeprazole (3×40 mg) before ingesting sodium nitrite (0.3 mg kg −1 ), followed by blood pressure monitoring. Nitrite reduced systolic blood pressure by a maximum of 6±1.3 mm Hg when taken after placebo, whereas pretreatment with esomeprazole blunted this effect. Peak plasma nitrite, nitrate, and nitroso species levels after nitrite ingestion were similar in both interventions. In 8 healthy volunteers, we then infused increasing doses of sodium nitrite (1, 10, and 30 nmol kg −1 min −1 ) intravenously. Interestingly, although plasma nitrite peaked at similar levels as with orally ingested nitrite (≈1.8 µmol/L), no changes in blood pressure were observed. In rodents, esomeprazole did not affect the blood pressure response to the NO donor, DEA NONOate, or vascular relaxation to nitroprusside and acetylcholine, demonstrating an intact downstream NO-signaling pathway. We conclude that the acute blood pressure–lowering effect of nitrite requires an acidic gastric environment. Future studies will reveal if the cardiovascular complications associated with the use of proton pump inhibitors are linked to interference with the nitrate–nitrite–NO pathway.

An endovascular model of ischemic myopathy from peripheral arterial disease

OBJECTIVE

Peripheral arterial disease (PAD) is a significant age-related medical condition with limited pharmacologic options. Severe PAD, termed critical limb ischemia, can lead to amputation. Skeletal muscle is the end organ most affected by PAD, leading to ischemic myopathy and debility of the patient. Currently, there are not any therapeutics to treat ischemic myopathy, and proposed biologic agents have not been optimized owing to a lack of preclinical models of PAD. Because a large animal model of ischemic myopathy may be useful in defining the optimal dosing and delivery regimens, the objective was to create and to characterize a swine model of ischemic myopathy that mimics patients with severe PAD.

METHODS

Yorkshire swine (N = 8) underwent acute right hindlimb ischemia by endovascular occlusion of the external iliac artery. The effect of ischemia on limb function, perfusion, and degree of ischemic myopathy was quantified by weekly gait analysis, arteriography, hindlimb blood pressures, femoral artery duplex ultrasound scans, and histologic examination. Animals were terminated at 5 (n = 5) and 6 (n = 3) weeks postoperatively. Ossabaw swine (N = 8) fed a high-fat diet were used as a model of metabolic syndrome for comparison of arteriogenic recovery and validation of ischemic myopathy.

RESULTS

There was persistent ischemia in the right hindlimb, and occlusion pressures were significantly depressed compared with the untreated left hindlimb out to 6 weeks (systolic blood pressure, 31 ± 21 vs 83 ± 15 mm Hg, respectively; P = .0007). The blood pressure reduction resulted in a significant increase of ischemic myopathy in the gastrocnemius muscle in the treated limb. Gait analysis revealed a functional deficit of the right hindlimb immediately after occlusion that improved rapidly during the first 2 weeks. Peak systolic velocity values in the right common femoral artery were severely diminished throughout the entire study (P < .001), and the hemodynamic environment after occlusion was characterized by low and oscillatory wall shear stress. Finally, the internal iliac artery on the side of the ischemic limb underwent significant arteriogenic remodeling (1.8× baseline) in the Yorkshire but not in the Ossabaw swine model.

CONCLUSIONS

This model uses endovascular technology to produce the first durable large animal model of ischemic myopathy. Acutely (first 2 weeks), this model is associated with impaired gait but no tissue loss. Chronically (2-6 weeks), this model delivers persistent ischemia, resulting in ischemic myopathy similar to that seen in PAD patients. This model may be of use for testing novel therapeutics including biologic therapies for promoting neovascularization and arteriogenesis.

Radiofrequency Renal Denervation Protects the Ischemic Heart via Inhibition of GRK2 and Increased Nitric Oxide Signaling

Rationale:

Catheter-based renal denervation (RDN) is currently under development for the treatment of resistant hypertension and is thought to reduce blood pressure via interruption of sympathetic pathways that modulate cardiovascular function. The sympathetic nervous system also plays a critical role in the pathogenesis of acute myocardial infarction and heart failure.

Objective:

We examined whether treatment with radiofrequency (RF)-RDN would protect the heart against subsequent myocardial ischemia/reperfusion injury via direct effects on the myocardium.

Methods and Results:

Spontaneously hypertensive rats received either bilateral RF-RDN or sham-RDN. At 4 weeks after RF-RDN (n=14) or sham-RDN (n=14) treatment, spontaneously hypertensive rats were subjected to 30 minutes of transient coronary artery occlusion and 24 hours –7 days reperfusion. Four weeks after RF-RDN, myocardial oxidative stress was markedly attenuated, and transcription and translation of antioxidants, superoxide dismutase 1 and glutathione peroxidase-1, were significantly upregulated compared with sham-RDN spontaneously hypertensive rats. RF-RDN also inhibited myocardial G protein–coupled receptor kinase 2 pathological signaling and enhanced myocardial endothelial nitric oxide synthase function and nitric oxide signaling. RF-RDN therapy resulted in a significant reduction in myocardial infarct size per area at risk compared with sham-RDN (26.8 versus 43.9%; P<0.01) at 24 hours postreperfusion and significantly improved left ventricular function at 7 days after myocardial ischemia/reperfusion.

Conclusions:

RF-RDN reduced oxidative stress, inhibited G protein–coupled receptor kinase 2 signaling, increased nitric oxide bioavailability, and ameliorated myocardial reperfusion injury in the setting of severe hypertension. These findings provide new insights into the remote cardioprotective effects of RF-RDN acting directly on cardiac myocytes to attenuate cell death and protect against ischemic injury.

Nitrite Confers Preconditioning and Cytoprotection After Ischemia/Reperfusion Injury Through the Modulation of Mitochondrial Function

SIGNIFICANCE

Nitrite is now recognized as an intrinsic signaling molecule that mediates a number of biological processes. One of the most reproducible effects of nitrite is its ability to mediate cytoprotection after ischemia/reperfusion (I/R). This robust phenomenon has been reproduced by a number of investigators in varying animal models focusing on different target organs. Furthermore, nitrite's cytoprotective versatility is highlighted by its ability to mediate delayed preconditioning and remote conditioning in addition to acute protection.

RECENT ADVANCES

In the last 10 years, significant progress has been made in elucidating the mechanisms underlying nitrite-mediated ischemic tolerance.

CRITICAL ISSUES

The mitochondrion, which is essential to both the progression of I/R injury and the protection afforded by preconditioning, has emerged as a major subcellular target for nitrite. This review will outline the role of the mitochondrion in I/R injury and preconditioning, review the accumulated preclinical studies demonstrating nitrite-mediated cytoprotection, and finally focus on the known interactions of nitrite with mitochondria and their role in the mechanism of nitrite-mediated ischemic tolerance.

FUTURE DIRECTIONS

These studies set the stage for current clinical trials testing the efficacy of nitrite to prevent warm and cold I/R injury.

Sustained release nitrite therapy results in myocardial protection in a porcine model of metabolic syndrome with peripheral vascular disease

Metabolic syndrome (MetS) reduces endothelial nitric oxide (NO) bioavailability and exacerbates vascular dysfunction in patients with preexisting vascular diseases. Nitrite, a storage form of NO, can mediate vascular function during pathological conditions when endogenous NO is reduced. The aims of the present study were to characterize the effects of severe MetS and obesity on dyslipidemia, myocardial oxidative stress, and endothelial NO synthase (eNOS) regulation in the obese Ossabaw swine (OS) model and to examine the effects of a novel, sustained-release formulation of sodium nitrite (SR-nitrite) on coronary vascular reactivity and myocardial redox status in obese OS subjected to critical limb ischemia (CLI). After 6 mo of an atherogenic diet, obese OS displayed a MetS phenotype. Obese OS had decreased eNOS functionality and NO bioavailability. In addition, obese OS exhibited increased oxidative stress and a significant reduction in antioxidant enzymes. The efficacy of SR-nitrite therapy was examined in obese OS subjected to CLI. After 3 wk of treatment, SR-nitrite (80 mg · kg(-1) · day(-1) bid po) increased myocardial nitrite levels and eNOS function. Treatment with SR-nitrite reduced myocardial oxidative stress while increasing myocardial antioxidant capacity. Ex vivo assessment of vascular reactivity of left anterior descending coronary artery segments demonstrated marked improvement in vasoreactivity to sodium nitroprusside but not to substance P and bradykinin in SR-nitrite-treated animals compared with placebo-treated animals. In conclusion, in a clinically relevant, large-animal model of MetS and CLI, treatment with SR-nitrite enhanced myocardial NO bioavailability, attenuated oxidative stress, and improved ex vivo coronary artery vasorelaxation.