Assessment of mouse hind limb endothelial function by measuring femoral artery blood flow responses

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.

Pannexin 1 channels control the hemodynamic response to hypoxia by regulating O2-sensitive extracellular ATP in blood

Pannexin 1 (Panx1) channels export ATP and may contribute to increased concentration of the vasodilator ATP in plasma during hypoxia in vivo. We hypothesized that Panx1 channels and associated ATP export contribute to hypoxic vasodilation, a mechanism that facilitates the matching of oxygen delivery to metabolic demand of tissue. Male and female mice devoid of Panx1 (Panx1-/-) and wild-type controls (WT) were anesthetized, mechanically ventilated, and instrumented with a carotid artery catheter or femoral artery flow transducer for hemodynamic and plasma ATP monitoring during inhalation of 21% (normoxia) or 10% oxygen (hypoxia). ATP export from WT vs. Panx1-/-erythrocytes (RBC) was determined ex vivo via tonometer experimentation across progressive deoxygenation. Mean arterial pressure (MAP) was similar in Panx1-/- (n = 6) and WT (n = 6) mice in normoxia, but the decrease in MAP in hypoxia seen in WT was attenuated in Panx1-/- mice (-16 ± 9% vs. -2 ± 8%; P < 0.05). Hindlimb blood flow (HBF) was significantly lower in Panx1-/- (n = 6) vs. WT (n = 6) basally, and increased in WT but not Panx1-/- mice during hypoxia (8 ± 6% vs. -10 ± 13%; P < 0.05). Estimation of hindlimb vascular conductance using data from the MAP and HBF experiments showed an average response of 28% for WT vs. -9% for Panx1-/- mice. Mean venous plasma ATP during hypoxia was 57% lower in Panx1-/- (n = 6) vs. WT mice (n = 6; P < 0.05). Mean hypoxia-induced ATP export from RBCs from Panx1-/- mice (n = 8) was 82% lower than that from WT (n = 8; P < 0.05). Panx1 channels participate in hemodynamic responses consistent with hypoxic vasodilation by regulating hypoxia-sensitive extracellular ATP levels in blood.NEW & NOTEWORTHY Export of vasodilator ATP from red blood cells requires pannexin 1. Blood plasma ATP elevations in response to hypoxia in mice require pannexin 1. Hemodynamic responses to hypoxia are accompanied by increased plasma ATP in mice in vivo and require pannexin 1.

Reproducible hindlimb ischemia model based on photochemically induced thrombosis to evaluate angiogenic effects

Critical limb ischemia is one of the most common types of peripheral arterial disease. Preclinical development of ischemia therapeutics relies on the availability of a relevant and reproducible in vivo disease model. Thus, establishing appropriate animal disease models is essential for the development of new therapeutic strategies. Currently, the most commonly employed model of hindlimb ischemia is the surgical induction method with ligation of the femoral artery and its branches after skin incision. However, the efficiency of the method is highly variable depending on the availability of skilled technicians. In addition, after surgical procedures, animals can quickly and spontaneously recover from damage, limiting observations of the therapeutic effect of potential agents. The aim of this study was to develop a hindlimb ischemia mouse model with similarities to human ischemic disease. To that end, a photochemical reaction was used to induce thrombosis in the hindlimb. After the photochemical reaction was induced by light irradiation, thrombotic plugs and adjacent red blood cell stasis were observed in hindlimb vessels in the light-irradiated zone. Additionally, the photochemically induced thrombosis maintained the ischemic condition and did not cause notable side effects in mice.

Hierarchical organization of the hemostatic response to penetrating injuries in the mouse macrovasculature

Essentials Methods were developed to image the hemostatic response in mouse femoral arteries in real time. Penetrating injuries produced thrombi consisting primarily of platelets. Similar to arterioles, a core-shell architecture of platelet activation occurs in the femoral artery. Differences from arterioles included slower platelet activation and reduced thrombin dependence.

SUMMARY

Background Intravital studies performed in the mouse microcirculation show that hemostatic thrombi formed after penetrating injuries develop a characteristic architecture in which a core of fully activated, densely packed platelets is overlaid with a shell of less activated platelets. Objective Large differences in hemodynamics and vessel wall biology distinguish arteries from arterioles. Here we asked whether these differences affect the hemostatic response and alter the impact of anticoagulants and antiplatelet agents. Methods Approaches previously developed for intravital imaging in the mouse microcirculation were adapted to the femoral artery, enabling real-time fluorescence imaging despite the markedly thicker vessel wall. Results Arterial thrombi initiated by penetrating injuries developed the core-and-shell architecture previously observed in the microcirculation. However, although platelet accumulation was greater in arterial thrombi, the kinetics of platelet activation were slower. Inhibiting platelet ADP P2Y12 receptors destabilized the shell and reduced thrombus size without affecting the core. Inhibiting thrombin with hirudin suppressed fibrin accumulation, but had little impact on thrombus size. Removing the platelet collagen receptor, glycoprotein VI, had no effect. Conclusions These results (i) demonstrate the feasibility of performing high-speed fluorescence imaging in larger vessels and (ii) highlight differences as well as similarities in the hemostatic response in the macro- and microcirculation. Similarities include the overall core-and-shell architecture. Differences include the slower kinetics of platelet activation and a smaller contribution from thrombin, which may be due in part to the greater thickness of the arterial wall and the correspondingly greater separation of tissue factor from the vessel lumen.

Evaluation of Endothelial Dysfunction In Vivo

Vascular endothelial cells play a major role in maintaining cardiovascular homeostasis. Impairment of physiological properties of the endothelium, such as the promotion of vasodilation and anti-aggregation, leads to a condition called endothelial dysfunction. Endothelial dysfunction is an important early event in the pathogenesis of atherosclerosis and has been shown to have prognostic value in predicting vascular events including stroke and myocardial infarction.Endothelial-dependent vasodilation is one of the most widely used methods for assessment of endothelial function in rodents. It includes pharmacological stimulation (for example by acetylcholine) of endothelial release of NO and other vasoactive compounds in comparison with vascular response to endothelium-independent dilators such as sodium nitroprusside. However, usually this technique is performed in anesthetized animals. Here we describe a method which allows evaluation of endothelial dysfunction in conscious, freely moving mice and rats.

In Vivo Anastomosis and Perfusion of a Three-Dimensionally-Printed Construct Containing Microchannel Networks

The field of tissue engineering has advanced the development of increasingly biocompatible materials to mimic the extracellular matrix of vascularized tissue. However, a majority of studies instead rely on a multiday inosculation between engineered vessels and host vasculature rather than the direct connection of engineered microvascular networks with host vasculature. We have previously demonstrated that the rapid casting of three-dimensionally-printed (3D) sacrificial carbohydrate glass is an expeditious and a reliable method of creating scaffolds with 3D microvessel networks. Here, we describe a new surgical technique to directly connect host femoral arteries to patterned microvessel networks. Vessel networks were connected in vivo in a rat femoral artery graft model. We utilized laser Doppler imaging to monitor hind limb ischemia for several hours after implantation and thus measured the vascular patency of implants that were anastomosed to the femoral artery. This study may provide a method to overcome the challenge of rapid oxygen and nutrient delivery to engineered vascularized tissues implanted in vivo.

Novel method to assess arterial insufficiency in rodent hind limb

BACKGROUND

Lack of techniques to assess maximal blood flow capacity thwarts the use of rodent models of arterial insufficiency to evaluate therapies for intermittent claudication. We evaluated femoral vein outflow (VO) in combination with stimulated muscle contraction as a potential method to assess functional hind limb arterial reserve and therapeutic efficacy in a rodent model of subcritical limb ischemia.

MATERIALS AND METHODS

VO was measured with perivascular flow probes at rest and during stimulated calf muscle contraction in young, healthy rats (Wistar Kyoto, WKY; lean Zucker rats, LZR) and rats with cardiovascular risk factors (spontaneously hypertensive [SHR]; obese Zucker rats [OZR]) with acute and/or chronic femoral arterial occlusion. Therapeutic efficacy was assessed by administration of Ramipril or Losartan to SHR after femoral artery excision.

RESULTS

VO measurement in WKY demonstrated the utility of this method to assess hind limb perfusion at rest and during calf muscle contraction. Although application to diseased models (OZR and SHR) demonstrated normal resting perfusion compared with contralateral limbs, a significant reduction in reserve capacity was uncovered with muscle stimulation. Administration of Ramipril and Losartan demonstrated significant improvement in functional arterial reserve.

CONCLUSIONS

The results demonstrate that this novel method to assess distal limb perfusion in small rodents with subcritical limb ischemia is sufficient to unmask perfusion deficits not apparent at rest, detect impaired compensation in diseased animal models with risk factors, and assess therapeutic efficacy. The approach provides a significant advance in methods to investigate potential mechanisms and novel therapies for subcritical limb ischemia in preclinical rodent models.

Treadmill running improves hindlimb arteriolar endothelial function in type 1 diabetic mice as visualized by X-ray microangiography

BACKGROUND

Vascular function is impaired in patients with diabetes, however diabetic vascular dysfunction is ameliorated by exercise training. We aimed to clarify which hindlimb arterial segments are affected by treadmill running in the hindlimbs of streptozocin-induced type 1 diabetic mice in vivo.

METHODS

Mice were divided into 3 groups; healthy control, diabetic control, and diabetic-running groups. The exercise regimen was performed by treadmill level running mice for 60 min/day, for 4 weeks. Thereafter, we examined the vascular response to systemic acetylcholine administration in the left hindlimb of anesthetized-ventilated mice using either 1) X-ray microangiography to visualize the arteries or 2) ultrasonic flowmetry to record the femoral arterial blood flow.

RESULTS

X-ray imaging clearly visualized the hindlimb arterial network (~70-250 μm diameter). The vasodilator response to acetylcholine was significantly attenuated locally in the arterioles <100 μm diameter in the diabetic group of mice compared to the control group of mice. Post-acetylcholine administration, all groups showed an increase in hindlimb vascular conductance, but the diabetic mice showed the smallest increase. Overall, compared to the diabetic mice, the treadmill-running mice exhibited a significant enhancement of the vasodilator response within the arterioles with diabetes-induced vasodilator dysfunction.

CONCLUSIONS

Diabetes impaired acetylcholine-induced vasodilator function locally in the arteries <100 μm diameter and decreased hindlimb vascular conductance responded to acetylcholine, while regular treadmill running significantly ameliorated the impaired vasodilator function, and enhanced the decreased conductance in the diabetic mice.

Measurement of Endothelium-Dependent Vasodilation in Mice—Brief Report

Objective—

Endothelium-dependent, flow-mediated vasodilation after an increase in shear stress at the endothelial lining of conduit arteries during reactive hyperemia after ischemia is a fundamental principle of vascular physiology adapting blood flow to demand of supplied tissue. Flow-mediated vasodilation measurements have been performed in human studies and are of diagnostic and prognostic importance, but have been impossible because of technical limitations in transgenic mice to date, although these represent the most frequently used animal model in cardiovascular research.

Approach and Results—

Using high-frequency ultrasound, we visualized, quantified, and characterized for the first time endothelium-dependent dilation of the femoral artery after temporal ischemia of the lower part of the hindlimb and demonstrated that the signaling was almost exclusively dependent on stimulation of endothelial nitric oxide synthase, similar to acetylcholine, completely abolished after pharmacological or genetic inhibition of endothelial nitric oxide synthase and endothelial denudation, substantially impaired in mice of increasing age and cholesterol-fed ApoE knock outs and increased by the dietary polyphenol (−)-epicatechin. Intra- and interindividual variability were similar to the human methodology.

Conclusions—

The physiology of flow-mediated vasodilation in mice resembles that in humans underscoring the significance of this novel technology to noninvasively, serially, and reliably quantify flow-mediated vasodilation in transgenic mice.

Multifunctional in vivo vascular imaging using near-infrared II fluorescence

In vivo real-time epifluorescence imaging of mouse hind limb vasculatures in the second near-infrared region (NIR-II) is performed using single-walled carbon nanotubes as fluorophores. Both high spatial (∼30 μm) and temporal (<200 ms per frame) resolution for small-vessel imaging are achieved at 1-3 mm deep in the hind limb owing to the beneficial NIR-II optical window that affords deep anatomical penetration and low scattering. This spatial resolution is unattainable by traditional NIR imaging (NIR-I) or microscopic computed tomography, and the temporal resolution far exceeds scanning microscopic imaging techniques. Arterial and venous vessels are unambiguously differentiated using a dynamic contrast-enhanced NIR-II imaging technique on the basis of their distinct hemodynamics. Further, the deep tissue penetration and high spatial and temporal resolution of NIR-II imaging allow for precise quantifications of blood velocity in both normal and ischemic femoral arteries, which are beyond the capabilities of ultrasonography at lower blood velocities.