Heat therapy improves body composition and muscle function but does not affect capillary or collateral growth in a model of obesity and hindlimb ischemia

The Efficacy of HGF/VEGF Gene Therapy for Limb Ischemia in Mice with Impaired Glucose Tolerance: Shift from Angiogenesis to Axonal Growth and Oxidative Potential in Skeletal Muscle

BACKGROUND

Combined non-viral gene therapy (GT) of ischemia and cardiovascular disease is a promising tool for potential clinical translation. In previous studies our group has developed combined gene therapy by vascular endothelial growth factor 165 (VEGF165) + hepatocyte growth factor (HGF). Our recent works have demonstrated that a bicistronic pDNA that carries both human HGF and VEGF165 coding sequences has a potential for clinical application in peripheral artery disease (PAD). The present study aimed to test HGF/VEGF combined plasmid efficacy in ischemic skeletal muscle comorbid with predominant complications of PAD-impaired glucose tolerance and type 2 diabetes mellitus (T2DM).

METHODS

Male C57BL mice were housed on low-fat (LFD) or high-fat diet (HFD) for 10 weeks and metabolic parameters including FBG level, ITT, and GTT were evaluated. Hindlimb ischemia induction and plasmid administration were performed at 10 weeks with 3 weeks for post-surgical follow-up. Limb blood flow was assessed by laser Doppler scanning at 7, 14, and 21 days after ischemia induction. The necrotic area of m.tibialis anterior, macrophage infiltration, angio- and neuritogenesis were evaluated in tissue sections. The mitochondrial status of skeletal muscle (total mitochondria content, ETC proteins content) was assessed by Western blotting of muscle lysates.

RESULTS

At 10 weeks, the HFD group demonstrated impaired glucose tolerance in comparison with the LFD group. HGF/VEGF plasmid injection aggravated glucose intolerance in HFD conditions. Blood flow recovery was not changed by HGF/VEGF plasmid injection either in LFD or HFD conditions. GT in LFD, but not in HFD conditions, enlarged the necrotic area and CD68+ cells infiltration. However, HGF/VEGF plasmid enhanced neuritogenesis and enlarged NF200+ area on muscle sections. In HFD conditions, HGF/VEGF plasmid injection significantly increased mitochondria content and ETC proteins content.

CONCLUSIONS

The current study demonstrated a significant role of dietary conditions in pre-clinical testing of non-viral GT drugs. HGF/VEGF combined plasmid demonstrated a novel aspect of potential participation in ischemic skeletal muscle regeneration, through regulation of innervation and bioenergetics of muscle. The obtained results made HGF/VEGF combined plasmid a very promising tool for PAD therapy in impaired glucose tolerance conditions.

Sympathetic Nerve Activity and Blood Pressure Response to Exercise in Peripheral Artery Disease: From Molecular Mechanisms, Human Studies, to Intervention Strategy Development

Sympathetic nerve activity (SNA) regulates the contraction of vascular smooth muscle and leads to a change in arterial blood pressure (BP). It was observed that SNA, vascular contractility, and BP are heightened in patients with peripheral artery disease (PAD) during exercise. The exercise pressor reflex (EPR), a neural mechanism responsible for BP response to activation of muscle afferent nerve, is a determinant of the exaggerated exercise-induced BP rise in PAD. Based on recent results obtained from a series of studies in PAD patients and a rat model of PAD, this review will shed light on SNA-driven BP response and the underlying mechanisms by which receptors and molecular mediators in muscle afferent nerves mediate the abnormalities in autonomic activities of PAD. Intervention strategies, particularly non-pharmacological strategies, improving the deleterious exercise-induced SNA and BP in PAD, and enhancing tolerance and performance during exercise will also be discussed.

Effects of home-based leg heat therapy on walking performance in patients with symptomatic peripheral artery disease: a pilot randomized trial

Few noninvasive therapies currently exist to improve functional capacity in people with lower extremity peripheral artery disease (PAD). The goal of the present study was to test the hypothesis that unsupervised, home-based leg heat therapy (HT) using water-circulating trousers perfused with warm water would improve walking performance in patients with PAD. Patients with symptomatic PAD were randomized into either leg HT (n = 18) or a sham treatment (n = 16). Patients were provided with water-circulating trousers and a portable pump and were asked to apply the therapy daily (7 days/wk, 90 min/session) for 8 wk. The primary study outcome was the change from baseline in 6-min walk distance at 8-wk follow-up. Secondary outcomes included the claudication onset-time, peak walking time, peak pulmonary oxygen consumption and peak blood pressure during a graded treadmill test, resting blood pressure, the ankle-brachial index, postocclusive reactive hyperemia in the calf, cutaneous microvascular reactivity, and perceived quality of life. Of the 34 participants randomized, 29 completed the 8-wk follow-up. The change in 6-min walk distance at the 8-wk follow-up was significantly higher (P = 0.029) in the group exposed to HT than in the sham-treated group (Sham: median: -0.9; 25%, 75% percentiles: -5.8, 14.3; HT: median: 21.3; 25%, 75% percentiles: 10.1, 42.4, P = 0.029). There were no significant differences in secondary outcomes between the HT and sham group at 8-wk follow-up. The results of this pilot study indicate that unsupervised, home-based leg HT is safe, well-tolerated, and elicits a clinically meaningful improvement in walking tolerance in patients with symptomatic PAD.NEW & NOTEWORTHY This is the first sham-controlled trial to examine the effects of home-based leg heat therapy (HT) on walking performance in patients with peripheral artery disease (PAD). We demonstrate that unsupervised HT using water-circulating trousers is safe, well-tolerated, and elicits meaningful changes in walking ability in patients with symptomatic PAD. This home-based treatment option is practical, painless, and may be a feasible adjunctive therapy to counteract the decline in lower extremity physical function in patients with PAD.

Microvascular Dysfunction in Peripheral Artery Disease: Is Heat Therapy a Viable Treatment?

Peripheral artery disease (PAD) is characterized by the development of atherosclerotic plaques in the lower-body conduit arteries. PAD is commonly accompanied by microvascular disease, which may result in poor wound healing, plantar ulcer development, and subsequent limb amputation. Understanding the mechanisms underlying the development of plantar ulcers is a critical step in the development of adequate treatment options for patients with PAD. Skin is classified into two major components: glabrous and non-glabrous. These skin types have unique microcirculation characteristics, making it important to differentiate between the two when investigating mechanisms for plantar ulcer development in PAD. There is evidence for a microcirculation compensatory mechanism in PAD. This is evident by the maintenance of basal microcirculation perfusion and capillary filling pressure despite a reduced pressure differential beyond an occlusion in non-critical limb ischemia PAD. The major mechanism for this compensatory system seems to be progressive vasodilation of the arterial network below an occlusion. Recently, heat therapies have emerged as novel treatment options for attenuating the progression of PAD. Heat therapies are capable of stimulating the cardiovascular system, which may lead to beneficial adaptations that may ultimately reduce fatigue during walking in PAD. Early work in this area has shown that full-body heating is capable of generating an acute cardiovascular response, similar to exercise, which has been suggested as the most efficient treatment modality and may generate adaptations with chronic exposure. Heat therapies may emerge as a conservative treatment option capable of attenuating the progression of PAD and ultimately impeding the development of plantar ulcers.

Skeletal Muscle Mitochondrial Dysfunction and Oxidative Stress in Peripheral Arterial Disease: A Unifying Mechanism and Therapeutic Target

Peripheral artery disease (PAD) is caused by atherosclerosis in the lower extremities, which leads to a spectrum of life-altering symptomatology, including claudication, ischemic rest pain, and gangrene requiring limb amputation. Current treatments for PAD are focused primarily on re-establishing blood flow to the ischemic tissue, implying that blood flow is the decisive factor that determines whether or not the tissue survives. Unfortunately, failure rates of endovascular and revascularization procedures remain unacceptably high and numerous cell- and gene-based vascular therapies have failed to demonstrate efficacy in clinical trials. The low success of vascular-focused therapies implies that non-vascular tissues, such as skeletal muscle and oxidative stress, may substantially contribute to PAD pathobiology. Clues toward the importance of skeletal muscle in PAD pathobiology stem from clinical observations that muscle function is a strong predictor of mortality. Mitochondrial impairments in muscle have been documented in PAD patients, although its potential role in clinical pathology is incompletely understood. In this review, we discuss the underlying mechanisms causing mitochondrial dysfunction in ischemic skeletal muscle, including causal evidence in rodent studies, and highlight emerging mitochondrial-targeted therapies that have potential to improve PAD outcomes. Particularly, we will analyze literature data on reactive oxygen species production and potential counteracting endogenous and exogenous antioxidants.