Imaging the Proangiogenic Effects of Cardiovascular Drugs in a Diabetic Model of Limb Ischemia

The impact of statin therapy on the healing of diabetic foot ulcers: a case-control series

BACKGROUND

Diabetic foot ulcers (DFU) are a costly complication of diabetes mellitus (DM), with significant implications for the patient and the healthcare professionals that treat them. The primary objective of this study was to evaluate if there were improved healing rates in patients with a DFU that were taking a statin medication compared to those patients with a DFU who were not taking a statin medication. Secondary outcomes assessed were correlations with wound healing or statin use on data obtained from retrospective chart review.

METHODS

A case-control series was performed to obtain appropriate demographic information, comorbid conditions, laboratory values, and physical examination findings. From the time of presentation with DFU, these patients were followed for 12 weeks to evaluate for healing. Healing was defined as full epithelialization of the DFU with no further drainage. Wound healing and statin use correlation testing was then done for collected variables and each cohort. Chi square and Pearson correlation were then performed to identify any significant correlations. All p-values were two-sided, and findings were considered statistically significant at p < 0.05.

RESULTS

Our study identified 109 patients, 75 patients with a DFU on statin medication and 34 patients with a DFU not on statin medication. The statin cohort was more likely to be older, less than 5-year duration of diabetes, have more comorbidities, decreased low-density lipoprotein (LDL) cholesterol, and decreased total cholesterol (p < 0.05). Among those patients taking a statin medication, 48.0% (36/75) healed their DFU within 12 weeks. Among those patients not taking a statin medication, 44.1% (15/34) healed their DFU within 12 weeks. No correlation was noted between wound healing and statin use (p = 0.7). For wound healing, a negative correlation was noted for prior minor amputations (p < 0.05). For statin use, correlations were noted for age, duration of DM, LDL cholesterol level, total cholesterol level, HTN, CAD, and HLD (p < 0.05).

CONCLUSIONS

Statin medication use did not influence DFU healing rates between cohorts. There was a correlation noted between wound healing and prior minor amputations and between statin use and age, duration of DM, LDL cholesterol, total cholesterol, HTN, CAD and HLD. Additionally, we observed no correlation between DFU healing rates and use of a statin medication.

Multi-modality imaging for assessment of the microcirculation in peripheral artery disease: Bench to clinical practice

Peripheral artery disease (PAD) is a highly prevalent disorder with a high risk of mortality and amputation despite the introduction of novel medical and procedural treatments. Microvascular disease (MVD) is common among patients with PAD, and despite the established role as a predictor of amputations and mortality, MVD is not routinely assessed as part of current standard practice. Recent pre-clinical and clinical perfusion and molecular imaging studies have confirmed the important role of MVD in the pathogenesis and outcomes of PAD. The recent advancements in the imaging of the peripheral microcirculation could lead to a better understanding of the pathophysiology of PAD, and result in improved risk stratification, and our evaluation of response to therapies. In this review, we will discuss the current understanding of the anatomy and physiology of peripheral microcirculation, and the role of imaging for assessment of perfusion in PAD, and the latest advancements in molecular imaging. By highlighting the latest advancements in multi-modality imaging of the peripheral microcirculation, we aim to underscore the most promising imaging approaches and highlight potential research opportunities, with the goal of translating these approaches for improved and personalized management of PAD in the future.

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.

Molecular Imaging of Lower Extremity Peripheral Arterial Disease: An Emerging Field in Nuclear Medicine

Peripheral arterial disease (PAD) is an atherosclerotic disorder of non-coronary arteries that is associated with vascular stenosis and/or occlusion. PAD affecting the lower extremities is characterized by a variety of health-related consequences, including lifestyle-limiting intermittent claudication, ulceration of the limbs and/or feet, increased risk for lower extremity amputation, and increased mortality. The diagnosis of lower extremity PAD is typically established by using non-invasive tests such as the ankle-brachial index, toe-brachial index, duplex ultrasound, and/or angiography imaging studies. While these common diagnostic tools provide hemodynamic and anatomical vascular assessments, the potential for non-invasive physiological assessment of the lower extremities has more recently emerged through the use of magnetic resonance- and nuclear medicine-based approaches, which can provide insight into the functional consequences of PAD-related limb ischemia. This perspectives article specifically highlights and discusses the emerging applications of clinical nuclear medicine techniques for molecular imaging investigations in the setting of lower extremity PAD.

A Thermoresponsive Chitosan/β-Glycerophosphate Hydrogel for Minimally Invasive Treatment of Critical Limb Ischaemia

A reduction in blood supply to any limb causes ischaemia, pain and morbidity. Critical limb ischaemia is the most serious presentation of peripheral vascular disease. One in five patients with critical limb ischaemia will die within six months of diagnosis and one in three will require amputation in this time. Improving blood flow to the limb, via the administration of angiogenic agents, could relieve pain and avoid amputation. Herein, chitosan is combined with β-glycerophosphate to form a thermoresponsive formulation (chitosan/β-GP) that will flow through a syringe and needle at room temperature but will form a gel at body temperature. The chitosan/β-GP hydrogel, with or without the angiogenic molecule desferrioxamine (DFO), was injected into the mouse hind limb, following vessel ligation, to test the ability of the formulations to induce angiogenesis. The effects of the formulations were measured using laser Doppler imaging to determine limb perfusion and CD31 staining to quantify the number of blood vessels. Twenty-eight days following induction of ischaemia, the chitosan/β-GP and chitosan/β-GP + 100 µM DFO formulations had significantly (p < 0.001 and p < 0.05, respectively) improved blood flow in the ischaemic limb compared with an untreated control. Chitosan/β-GP increased vessel number by 1.7-fold in the thigh of the ischaemic limb compared with an untreated control, while chitosan/β-GP + 100 µM DFO increased vessel number 1.8-fold. Chitosan/β-GP represents a potential minimally invasive treatment for critical limb ischaemia.

Metformin Reduces Vascular Assembly in High Glucose-Treated Human Microvascular Endothelial Cells in An AMPK-Independent Manner

Objective

The aim is to examine the effect of metformin in human microvascular endothelial cells exposed to high glucose (HG) concentration and compare them with the effects of other 5' adenosine monophosphate-activated protein kinase (AMPK) modulators under the same condition.

Materials and Methods

In this experimental study, human microvascular endothelial cells (HMECs) were treated with 15 mM metformin, 1 mM 5-aminoimidazol-4-carboxamideribonucleotide (AICAR) and 10 mM compound C in the presence of 20 mM glucose (hyperglycemic condition). Migration, invasion and proliferation were evaluated as well as the capillary-like structures formation. Moreover, the expression of angiogenic genes was assessed.

Results

Metformin significantly inhibited vessel formation and migration, although it did not change HMECs proliferation and invasion. In addition, metformin significantly reduced collagen formation as evidenced by histological staining. Concomitantly, expression of several genes implicated in angiogenesis and fibrosis, namely TGFß2, VEGFR2, ALK1, JAG1, TIMP2, SMAD5, SMAD6 and SMAD7, was slightly upregulated. Immunostaining for proteins involved in ALK5 receptor signaling, the alternative TGFß signaling pathway, revealed significant differences in SMAD2/3 expression.

Conclusion

Our data showed that metformin prevents vessel assembly in HMECs, probably through an AMPK- independent mechanism. Understanding the molecular mechanisms by which this pharmacological agent affects endothelial dysfunction is of paramount importance and paves the way to its particular use in preventing development of diabetic retinopathy and nephropathy, two processes where angiogenesis is exacerbated.

Metformin: The next angiogenesis panacea?

Angiogenesis, the development of new blood vessels from existing ones, is a critical process in wound healing and skeletal muscle hypertrophy. It also leads to pathological conditions such as retinopathy and tumor genesis. Metformin, the first-line treatment for type 2 diabetic mellitus, has a specific regulatory effect on the process of angiogenesis. Anti-angiogenesis can inhibit the occurrence and metastasis of tumors and alleviate patients’ symptoms with polycystic ovary syndrome. Moreover, promoting angiogenesis effect can accelerate wound healing and promote stroke recovery and limb ischemia reconstruction. This review reorganizes metformin in angiogenesis, and the underlying mechanism in alleviating disease to bring some inspiration to relevant researchers.

Sympathetic Nerve Control of Blood Pressure Response during Exercise in Peripheral Artery Disease and Current Application of Experimental Disease Models

In patients with peripheral artery disease (PAD), the blood supply directed to the lower limbs is reduced. This results in severe limb ischemia and thereby intermittent claudicating which is characterized by pain in lower limbs that occurs with walking and is relieved by rest. Of note, PAD can extremely affect the quality of living of patients and increase high risk of coronary and cerebral vascular accidents. However, effective treatments of PAD are still challenging in clinics. A number of reports have demonstrated the beneficial effects of supervised exercise on symptoms of PAD patients. This review will summarize results obtained from recent human and animal studies, which include the abnormalities in sympathetic control of blood pressure response during exercise in PAD, and rationality of animal models used for study human PAD. Nonetheless, additional in-depth studies are necessary to better explore the underlying mechanisms of the exaggerated responses of sympathetic nerve and blood pressure in PAD at molecular and cellular levels.

Mechanisms of action of metformin and its regulatory effect on microRNAs related to angiogenesis

Angiogenesis is rapidly initiated in response to pathological conditions and is a key target for pharmaceutical intervention in various malignancies. Anti-angiogenic therapy has emerged as a potential and effective therapeutic strategy for treating cancer and cardiovascular-related diseases. Metformin, a first-line oral antidiabetic agent for type 2 diabetes mellitus (T2DM), not only reduces blood glucose levels and improves insulin sensitivity and exerts cardioprotective effects but also shows benefits against cancers, cardiovascular diseases, and other diverse diseases and regulates angiogenesis. MicroRNAs (miRNAs) are endogenous noncoding RNA molecules with a length of approximately 19-25 bases that are widely involved in controlling various human biological processes. A large number of miRNAs are involved in the regulation of cardiovascular cell function and angiogenesis, of which miR-21 not only regulates vascular cell proliferation, migration and apoptosis but also plays an important role in angiogenesis. The relationship between metformin and abnormal miRNA expression has gradually been revealed in the context of numerous diseases and has received increasing attention. This paper reviews the drug-target interactions and drug repositioning events of metformin that influences vascular cells and has benefits on angiogenesis-mediated effects. Furthermore, we use miR-21 as an example to explain the specific molecular mechanism underlying metformin-mediated regulation of the miRNA signaling pathway controlling angiogenesis and vascular protective effects. These findings may provide a new therapeutic target and theoretical basis for the clinical prevention and treatment of cardiovascular diseases.

Metformin upregulates the expression of Gli1 in vascular endothelial cells in hyperoxia-exposed neonatal mice

Bronchopulmonary dysplasia (BPD) is characterized by arrested alveolar and vascular development in premature infants. Metformin protects against the cardiovascular impairment induced by diabetes. The aim of this study was to investigate whether metformin could also enhance pulmonary vascular development in hyperoxic neonatal mice and investigate possible mechanisms involved. C57BL/6J newborn mice were randomly assigned to either of two groups - the room air group or the hyperoxia group - within 12 h postnatally. The mice were subcutaneously injected with metformin (100 mg/kg) or saline for 14 days. Lung morphology and PECAM-1 (CD31) expression in the lung were evaluated at postnatal days 7 and 14. Ki-67 and Gli1 expression in vascular endothelial cells was evaluated at postnatal day 14 by immunofluorescence staining. Flow cytometry (FCM) was also used to analyze Gli1 expression. Human umbilical vein endothelial cell (HUVECs) were used to investigate the role of metformin in vascular proliferation and tubular formation under 90% oxygen in vitro by cell counting Kti-8 (CCK8) assays and tube formation assays. Exposure to hyperoxia resulted in impaired lung development in newborn mice. Metformin enhanced the terminal airspace and radial alveolar count in newborn mice thus exposed. Immunohistochemistry staining and western blot assays revealed that metformin enhanced the expression of CD31 in hyperoxia-exposed newborn mice. Immunofluorescence staining showed that metformin enhanced the expression of Ki-67 in vascular endothelial cells. Furthermore, both immunofluorescence staining and FCM demonstrated that metformin increased Gli1 expression in vascular endothelial cells. Additionally, cell counting Kit-8 (CCK8) and viability assays of HUVECs in vitro both indicated that metformin improved the vascular proliferation and tube formation of HUVECs under 90% oxygen. These results indicated that metformin enhanced lung vascular development and upregulated the expression of Gli1 in the pulmonary vascular endothelial cells in hyperoxic neonatal mice.

Imaging Fibrogenesis in a Diet-Induced Model of Nonalcoholic Steatohepatitis (NASH)

Purpose

Liver fibrosis is the hallmark of chronic nonalcoholic steatohepatitis (NASH) and is characterised by the excessive deposition of extracellular matrix proteins. Early detection and accurate staging of liver fibrosis is critically important for patient management. One of the earliest pathological markers in NASH is the activation of hepatic stellate cells (HSCs) which may be exploited as a marker of fibrogenesis. Activated HSCs secreting factors such as integrin α_vβ₃ propagate fibrosis. The purpose of the current study was to assess the utility of the integrin α_vβ₃ imaging agent [¹⁸F]FtRGD for the early detection of fibrosis in a diet-induced model of NASH longitudinally using PET imaging.

Procedures

Mice were fed with either standard chow diet (SD), high-fat diet (HFD), or a choline-deficient, L-amino acid-defined high-fat fibrogenic diet (CDAHFD) to mimic the clinical pathology of liver disease and followed longitudinally for 10 weeks to assess the development of liver fibrosis using [¹⁸F]FtRGD positron emission tomography (PET) imaging. Standard blood biochemistry, histological measures, and qPCR were used to quantify integrin α_vβ₃, smooth muscle actin, and collagen types 1 and 6 to assess the extent of NASH pathology and accurately stage liver fibrosis.

Results

The CDAHFD fibrogenic diet predictably developed hepatic inflammation and steatosis over the 10 weeks studied with little NASH pathology detected in high fat diet-treated animals. Stage 1 fibrosis was detected early by histology at day 21 and progressed to stage 2 by day 35 and stage 3 by day 56 in mice fed with CDAHFD diet only. Noninvasive imaging with [¹⁸F]FtRGD correlated well with integrin α_vβ₃ and was able to distinguish early mild stage 2 fibrosis in CDAHFD animals compared with standard chow diet-fed animals at day 35. When compared with high fat diet-fed animals, [¹⁸F]FtRGD was only able to distinguish later moderate stage 2 fibrosis in CDAHFD animals at day 49.

Conclusions

The diet-induced progression of liver fibrosis was confirmed using histology and correlated well with the mRNA of integrin α_vβ₃ and extracellular matrix protein expression. [¹⁸F]FtRGD showed very good correlation between liver uptake and integrin α_vβ₃ expression and similar detection sensitivity to the current clinical gold standard modalities for staging of liver fibrosis.