Adenosine A1 receptors in neointimal hyperplasia and in-stent stenosis in Ossabaw miniature swine

Multiphasic changes in smooth muscle Ca2+ transporters during the progression of coronary atherosclerosis

Ischemic heart disease due to macrovascular atherosclerosis and microvascular dysfunction is the major cause of death worldwide and the unabated increase in metabolic syndrome is a major reason why this will continue. Intracellular free Ca²⁺ ([Ca²⁺]_i) regulates a variety of cellular functions including contraction, proliferation, migration, and transcription. It follows that studies of vascular Ca²⁺ regulation in reductionist models and translational animal models are vital to understanding vascular health and disease. Swine with metabolic syndrome (MetS) develop the full range of coronary atherosclerosis from mild to severe disease. Intravascular imaging enables quantitative measurement of atherosclerosis in vivo, so viable coronary smooth muscle (CSM) cells can be dispersed from the arteries to enable Ca²⁺ transport studies in native cells. Transition of CSM from the contractile phenotype in the healthy swine to the proliferative phenotype in mild atherosclerosis was associated with increases in SERCA activity, sarcoplasmic reticulum Ca²⁺, and voltage-gated Ca²⁺ channel function. In vitro organ culture confirmed that SERCA activation induces CSM proliferation. Transition from the proliferative to a more osteogenic phenotype was associated with decreases in all three Ca²⁺ transporters. Overall, there was a biphasic change in Ca²⁺ transporters over the progression of atherosclerosis in the swine model and this was confirmed in CSM from failing explanted hearts of humans. A major determinant of endolysosome content in human CSM is the severity of atherosclerosis. In swine CSM endolysosome Ca²⁺ release occurred through the TPC2 channel. We propose a multiphasic change in Ca²⁺ transporters over the progression of coronary atherosclerosis.

Recent advances in the role of the adenosinergic system in coronary artery disease

Adenosine is an endogenous nucleoside that plays a major role in the physiology and physiopathology of the coronary artery system, mainly by activating its A2A receptors (A2AR). Adenosine is released by myocardial, endothelial, and immune cells during hypoxia, ischaemia, or inflammation, each condition being present in coronary artery disease (CAD). While activation of A2AR improves coronary blood circulation and leads to anti-inflammatory effects, down-regulation of A2AR has many deleterious effects during CAD. A decrease in the level and/or activity of A2AR leads to: (i) lack of vasodilation, which decreases blood flow, leading to a decrease in myocardial oxygenation and tissue hypoxia; (ii) an increase in the immune response, favouring inflammation; and (iii) platelet aggregation, which therefore participates, in part, in the formation of a fibrin-platelet thrombus after the rupture or erosion of the plaque, leading to the occurrence of acute coronary syndrome. Inflammation contributes to the development of atherosclerosis, leading to myocardial ischaemia, which in turn leads to tissue hypoxia. Therefore, a vicious circle is created that maintains and aggravates CAD. In some cases, studying the adenosinergic profile can help assess the severity of CAD. In fact, inducible ischaemia in CAD patients, as assessed by exercise stress test or fractional flow reserve, is associated with the presence of a reserve of A2AR called spare receptors. The purpose of this review is to present emerging experimental evidence supporting the existence of this adaptive adenosinergic response to ischaemia or inflammation in CAD. We believe that we have achieved a breakthrough in the understanding and modelling of spare A2AR, based upon a new concept allowing for a new and non-invasive CAD management.

Guidelines for animal exercise and training protocols for cardiovascular studies

Whole body exercise tolerance is the consummate example of integrative physiological function among the metabolic, neuromuscular, cardiovascular, and respiratory systems. Depending on the animal selected, the energetic demands and flux through the oxygen transport system can increase two orders of magnitude from rest to maximal exercise. Thus, animal models in health and disease present the scientist with flexible, powerful, and, in some instances, purpose-built tools to explore the mechanistic bases for physiological function and help unveil the causes for pathological or age-related exercise intolerance. Elegant experimental designs and analyses of kinetic parameters and steady-state responses permit acute and chronic exercise paradigms to identify therapeutic targets for drug development in disease and also present the opportunity to test the efficacy of pharmacological and behavioral countermeasures during aging, for example. However, for this promise to be fully realized, the correct or optimal animal model must be selected in conjunction with reproducible tests of physiological function (e.g., exercise capacity and maximal oxygen uptake) that can be compared equitably across laboratories, clinics, and other proving grounds. Rigorously controlled animal exercise and training studies constitute the foundation of translational research. This review presents the most commonly selected animal models with guidelines for their use and obtaining reproducible results and, crucially, translates state-of-the-art techniques and procedures developed on humans to those animal models.

PET Imaging of Adenosine Receptors in Diseases

Adenosine receptors (ARs) are a class of purinergic G-protein-coupled receptors (GPCRs). Extracellular adenosine is a pivotal regulation molecule that adjusts physiological function through the interaction with four ARs: A1R, A2AR, A2BR, and A3R. Alterations of ARs function and expression have been studied in neurological diseases (epilepsy, Alzheimer's disease, and Parkinson's disease), cardiovascular diseases, cancer, and inflammation and autoimmune diseases. A series of Positron Emission Tomography (PET) probes for imaging ARs have been developed. The PET imaging probes have provided valuable information for diagnosis and therapy of diseases related to alterations of ARs expression. This review presents a concise overview of various ARs-targeted radioligands for PET imaging in diseases. The most recent advances in PET imaging studies by using ARs-targeted probes are briefly summarized.

Adenosine as a Marker and Mediator of Cardiovascular Homeostasis: A Translational Perspective

Adenosine, a purine nucleoside, is produced broadly and implicated in the homeostasis of many cells and tissues. It signals predominantly via 4 purinergic adenosine receptors (ADORs) - ADORA1, ADORA2A, ADORA2B and ADOosine signaling, both through design as specific ADOR agonists and antagonists and as offtarget effects of existing anti-platelet medications. Despite this, adenosine has yet to be firmly established as either a therapeutic or a prognostic tool in clinical medicine to date. Herein, we provide a bench-to-bedside review of adenosine biology, highlighting the key considerations for further translational development of this proRA3 in addition to non-ADOR mediated effects. Through these signaling mechanisms, adenosine exerts effects on numerous cell types crucial to maintaining vascular homeostasis, especially following vascular injury. Both in vitro and in vivo models have provided considerable insights into adenosine signaling and identified targets for therapeutic intervention. Numerous pharmacologic agents have been developed that modulate adenmising molecule.

Pharmacology of Adenosine Receptors: The State of the Art

Adenosine is a ubiquitous endogenous autacoid whose effects are triggered through the enrollment of four G protein-coupled receptors: A₁, A_2A, A_2B, and A₃. Due to the rapid generation of adenosine from cellular metabolism, and the widespread distribution of its receptor subtypes in almost all organs and tissues, this nucleoside induces a multitude of physiopathological effects, regulating central nervous, cardiovascular, peripheral, and immune systems. It is becoming clear that the expression patterns of adenosine receptors vary among cell types, lending weight to the idea that they may be both markers of pathologies and useful targets for novel drugs. This review offers an overview of current knowledge on adenosine receptors, including their characteristic structural features, molecular interactions and cellular functions, as well as their essential roles in pain, cancer, and neurodegenerative, inflammatory, and autoimmune diseases. Finally, we highlight the latest findings on molecules capable of targeting adenosine receptors and report which stage of drug development they have reached.

Large animal models of cardiovascular disease

The human cardiovascular system is a complex arrangement of specialized structures with distinct functions. The molecular landscape, including the genome, transcriptome and proteome, is pivotal to the biological complexity of both normal and abnormal mammalian processes. Despite our advancing knowledge and understanding of cardiovascular disease (CVD) through the principal use of rodent models, this continues to be an increasing issue in today's world. For instance, as the ageing population increases, so does the incidence of heart valve dysfunction. This may be because of changes in molecular composition and structure of the extracellular matrix, or from the pathological process of vascular calcification in which bone-formation related factors cause ectopic mineralization. However, significant differences between mice and men exist in terms of cardiovascular anatomy, physiology and pathology. In contrast, large animal models can show considerably greater similarity to humans. Furthermore, precise and efficient genome editing techniques enable the generation of tailored models for translational research. These novel systems provide a huge potential for large animal models to investigate the regulatory factors and molecular pathways that contribute to CVD in vivo. In turn, this will help bridge the gap between basic science and clinical applications by facilitating the refinement of therapies for cardiovascular disease.

Hemodynamics in stented vertebral artery ostial stenosis based on computational fluid dynamics simulations

Hemodynamic factors may affect the potential occurrence of in-stent restenosis (ISR) after intervention procedure of vertebral artery ostial stenosis (VAOS). The purpose of the present study is to investigate the influence of stent protrusion length in implantation strategy on the local hemodynamics of the VAOS. CTA images of a 58-year-old female patient with posterior circulation transient ischemic attack were used to perform a 3D reconstruction of the vertebral artery. Five models of the vertebral artery before and after the stent implantation were established. Model 1 was without stent implantation, Model 2-5 was with stent protruding into the subclavian artery for 0, 1, 2, 3 mm, respectively. Computational fluid dynamics simulations based on finite element analysis were employed to mimic the blood flow in arteries and to assess hemodynamic conditions, particularly the blood flow velocity and wall shear stress (WSS). The WSS and the blood flow velocity at the vertebral artery ostium were reduced by 85.33 and 35.36% respectively after stents implantation. The phenomenon of helical flow disappeared. Hemodynamics comparison showed that stent struts that protruded 1 mm into the subclavian artery induced the least decrease in blood speed and WSS. The results suggest that stent implantation can improve the hemodynamics of VAOS, while stent struts that had protruded 1 mm into the subclavian artery would result in less thrombogenesis and neointimal hyperplasia and most likely decrease the risk of ISR.

CD73 regulates vascular smooth muscle cell functions and facilitates atherosclerotic plaque formation

Extracellular adenosine, generated by ecto-5'-nucleotidase (CD73) via enzymatic catalyzation, has been found to facilitate atherosclerosis (AS). Thus, suppressing CD73 may attenuate AS. In this study, we evaluated the role of CD73 during AS development and further explored cellular and molecular mechanism in smooth muscle cells (SMCs). In a mouse model of carotid artery ligation, inactivation of CD73 inhibited migration and proliferation of vascular SMCs. In in vitro experiments, RNA interference of CD73 inhibited migration, proliferation, and foam cell transformation of human umbilical artery smooth muscle cells. Further, we established an atherosclerotic model using ApoE-/- mice fed with a western diet for 16 weeks. Inactivation of CD73-attenuated AS and hyperlipidemia in ApoE-/- mice. In conclusion, our data suggest that CD73 facilitates AS by promoting migration, proliferation, and foam cell transformation of vascular SMCs and elevating serum lipid levels. Thus, inhibition of CD73 may be beneficial for prevention and treatment of AS.

Adenosine A1 modulators: a patent update (2008 to present)

INTRODUCTION

In 2008, we published our review titled 'Therapeutic potential of A1 adenosine receptor ligands - a survey of recent patent literature' that reported the compounds active on A1 adenosine receptors (ARs) and the applications of A1 AR ligands patented in the period 2005 - 2008.

AREAS COVERED

This article is a discussion of the patents about the same subjects, issued in the period 2008 to present. It is organized similarly to the first one, with a section about new compounds, subdivided on the basis of their functional activity (agonists, antagonists and allosteric modulators) and a section regarding new therapeutic applications.

EXPERT OPINION

The main novelty is represented by the patenting of A1 AR ligands with dual selectivity which may show, in some conditions, better efficacy and fewer side effects. Moreover, while the way to arrive into the market appears full of obstacles for selective A1 ligands that need systemic administration for long-term therapy, better chances are foreseen in applications requiring topical administration.

Ca2+ regulatory mechanisms of exercise protection against coronary artery disease in metabolic syndrome and diabetes

Chronic exercise attenuates coronary artery disease (CAD) in humans largely independent of reductions in risk factors; thus major protective mechanisms of exercise are directly within the coronary vasculature. Further, tight control of diabetes, e.g., blood glucose, can be detrimental. Accordingly, knowledge of mechanisms by which exercise attenuates diabetic CAD could catalyze development of molecular therapies. Exercise attenuates CAD (atherosclerosis) and restenosis in miniature swine models, which enable precise control of exercise parameters (intensity, duration, and frequency) and characterization of the metabolic syndrome (MetS) and diabetic milieu. Intracellular Ca(2+) is a pivotal second messenger for coronary smooth muscle (CSM) excitation-contraction and excitation-transcription coupling that modulates CSM proliferation, migration, and calcification. CSM of diabetic dyslipidemic Yucatan swine have impaired Ca(2+) extrusion via the plasmalemma Ca(2+) ATPase (PMCA), downregulation of L-type voltage-gated Ca(2+) channels (VGCC), increased Ca(2+) sequestration by the sarcoplasmic reticulum (SR) Ca(2+) ATPase (SERCA), increased nuclear Ca(2+) localization, and greater activation of K channels by Ca(2+) release from the SR. Endurance exercise training prevents Ca(2+) transport changes with virtually no effect on the diabetic milieu (glucose, lipids). In MetS Ossabaw swine transient receptor potential canonical (TRPC) channels are upregulated and exercise training reverses expression and TRPC-mediated Ca(2+) influx with almost no change in the MetS milieu. Overall, exercise effects on Ca(2+) signaling modulate CSM phenotype. Future studies should 1) selectively target key Ca(2+) transporters to determine definitively their causal role in atherosclerosis and 2) combine mechanistic studies with clinical outcomes, e.g., reduction of myocardial infarction.

Stent-induced coronary artery stenosis characterized by multimodal nonlinear optical microscopy

We demonstrate for the first time the applicability of multimodal nonlinear optical (NLO) microscopy to the interrogation of stented coronary arteries under different diet and stent deployment conditions. Bare metal stents and Taxus drug-eluting stents (DES) were placed in coronary arteries of Ossabaw pigs of control and atherogenic diet groups. Multimodal NLO imaging was performed to inspect changes in arterial structures and compositions after stenting. Sum frequency generation, one of the multimodalities, was used for the quantitative analysis of collagen content in the peristent and in-stent artery segments of both pig groups. Atherogenic diet increased lipid and collagen in peristent segments. In-stent segments showed decreased collagen expression in neointima compared to media. Deployment of DES in atheromatous arteries inhibited collagen expression in the arterial media.

Morbid obesity and metabolic syndrome in Ossabaw miniature swine are associated with increased platelet reactivity

BACKGROUND

Metabolic syndrome (MetS) and type 2 diabetes mellitus in humans are associated with increased platelet activation and hyperreactivity of platelets to various agonists. Ossabaw swine develop all the hallmarks of MetS including obesity, insulin resistance, hypertension, dyslipidemia, endothelial dysfunction, and coronary artery disease when being fed excess calorie atherogenic diet. We hypothesized that Ossabaw swine with MetS would exhibit increased platelet reactivity compared with lean pigs without MetS.

MATERIALS AND METHODS

Ossabaw swine were fed high caloric, atherogenic diet for 44 weeks to induce MetS (n = 10) and were compared with lean controls without MetS that had been fed normal calorie standard diet (n = 10). Light transmittance aggregometry was performed using adenosine diphosphate (ADP), collagen, thrombin, and arachidonic acid (AA) at different concentrations. Dose response curves and EC50 were calculated. Glucose tolerance testing and intravascular ultrasound study of coronary arteries were performed.

RESULTS

MetS pigs compared with lean controls were morbidly obese, showed evidence of arterial hypertension, elevated cholesterol, low-density lipoprotein/high-density lipoprotein, and triglycerides, and insulin resistance. Platelets from MetS pigs were more sensitive to ADP-induced platelet aggregation than leans (EC50: 1.83 ± 1.3 μM vs 3.64 ± 2.2 μM; P = 0.02). MetS pigs demonstrated higher platelet aggregation in response to collagen than lean pigs (area under the curve: 286 ± 74 vs 198 ± 123; P = 0.037) and a trend for heightened response to AA (AUC: 260 ± 151 vs 178 ± 145; P = 0.13). No significant difference was found for platelet aggregation in response to thrombin.

CONCLUSIONS

MetS in Ossabaw swine is associated with increased reactivity of platelets to ADP and collagen. The Ossabaw swine may be a practical, large animal model for the study of certain aspects of platelet pathophysiology and examine vascular devices in a metabolic environment comparable to humans with MetS.

Winning a won game: caffeine panacea for obesity syndemic

Over the past decades, chronic sleep reduction and a concurrent development of obesity have been recognized as a common problem in the industrialized world. Among its numerous untoward effects, there is a possibility that insomnia is also a major contributor to obesity. This attribution poses a problem for caffeine, an inexpensive, “natural” agent that is purported to improve a number of conditions and is often indicated in a long-term pharmacotherapy in the context of weight management. The present study used the “common target” approach by exploring the tentative shared molecular networks of insomnia and adiposity. It discusses caffeine targets beyond those associated with adenosine signaling machinery, phosphodiesterases, and calcium release channels. Here, we provide a view suggesting that caffeine could exert some of its effects by acting on several signaling complexes composed of HIF-1α/VEGF/IL-8 along with NO, TNF-α, IL1, and GHRH, among others. Although the relevance of these targets to the reported therapeutic effects of caffeine has remained difficult to assess, the utilization of caffeine efficacies and potencies recommend its repurposing for development of novel therapeutic approaches. Among indications mentioned, are neuroprotective, nootropic, antioxidant, proliferative, anti-fibrotic, and anti-angiogenic that appear under a variety of dissimilar diagnostic labels comorbid with obesity. In the absence of safe and efficacious antiobesity agents, caffeine remains an attractive adjuvant.

A₂B receptors mediate the induction of early genes and inhibition of arterial smooth muscle cell proliferation via Epac

AIMS

Extracellular adenosine and adenine nucleotides play important roles in the regulation of the blood vessel tonus and platelet aggregation. Less is known about the effects of these extracellular signalling molecules on gene expression in vascular smooth muscle cells involved in long-term vascular effects. In the present study, we therefore searched for adenosine-induced changes in the expression of early genes in cultured human coronary artery smooth muscle cells (HCASMCs).

METHODS AND RESULTS

Whole-genome DNA array hybridization revealed that adenosine induced a set of early genes including the nuclear receptor subfamily 4, group A, member 1 (NR4A1/Nur77/TR3). The pattern of the effects of adenosine on gene expression resembles the change in expression induced by the direct activator of adenylate cyclase forskolin. Real-time reverse-transcriptase PCR confirmed that adenosine and its analogue N-ethyl-carboxamidoadenosine elicited a strong induction of NR4A1. These effects were markedly attenuated by A(2B) receptor antagonists including 8-[4-(4-benzylpiperazide-1-sulfonyl)phenyl]-1-propylxanthine (PSB-601) and were mimicked by a cyclic AMP (cAMP) analogue [8-(4-chlorophenylthio)-2'-O-methyl-cAMP, 8CPT] acting on the exchange protein activated by cAMP (Epac). Long-term experiments over 5 days showed that 2-chloroadenosine decreased cell proliferation in the presence of platelet-derived growth factor. This effect of 2-chloroadenosine was also attenuated by PSB-601 and mimicked by 8CPT. Treatment with small interfering RNA directed against NR4A1 attenuated the inhibitory effect of 8CPT on proliferation.

CONCLUSIONS

In summary, our results demonstrate the operation of adenosine A₂(B) receptors mediating an early induction of NR4A1 and a decrease in cell proliferation via the cAMP/Epac pathway in HCASMCs.

Adenosine and its receptors in the heart: regulation, retaliation and adaptation

The purine nucleoside adenosine is an important regulator within the cardiovascular system, and throughout the body. Released in response to perturbations in energy state, among other stimuli, local adenosine interacts with 4 adenosine receptor sub-types on constituent cardiac and vascular cells: A(1), A(2A), A(2B), and A(3)ARs. These G-protein coupled receptors mediate varied responses, from modulation of coronary flow, heart rate and contraction, to cardioprotection, inflammatory regulation, and control of cell growth and tissue remodeling. Research also unveils an increasingly complex interplay between members of the adenosine receptor family, and with other receptor groups. Given generally favorable effects of adenosine receptor activity (e.g. improving the balance between myocardial energy utilization and supply, limiting injury and adverse remodeling, suppressing inflammation), the adenosine receptor system is an attractive target for therapeutic manipulation. Cardiovascular adenosine receptor-based therapies are already in place, and trials of new treatments underway. Although the complex interplay between adenosine receptors and other receptors, and their wide distribution and functions, pose challenges to implementation of site/target specific cardiovascular therapy, the potential of adenosinergic pharmacotherapy can be more fully realized with greater understanding of the roles of adenosine receptors under physiological and pathological conditions. This review addresses some of the major known and proposed actions of adenosine and adenosine receptors in the heart and vessels, focusing on the ability of the adenosine receptor system to regulate cell function, retaliate against injurious stressors, and mediate longer-term adaptive responses.

Adenosine receptor regulation of coronary blood flow in Ossabaw miniature swine

Adenosine clearly regulates coronary blood flow (CBF); however, contributions of specific adenosine receptor (AR) subtypes (A(1), A(2A), A(2B), A(3)) to CBF in swine have not been determined. ARs generally decrease (A(1), A(3)) or increase (A(2A), A(2B)) cyclic adenosine monophosphate, a major mediator of vasodilation. We hypothesized that A(1) antagonism potentiates coronary vasodilation and coronary stent deployment in dyslipidemic Ossabaw swine elicits impaired vasodilation to adenosine that is associated with increased A(1)/A(2A) expression. The left main coronary artery was accessed with a guiding catheter allowing intracoronary infusions. After placement of a flow wire into the left circumflex coronary artery the responses to bolus infusions of adenosine were obtained. Steady-state infusion of AR-specific agents was achieved by using a small catheter fed over the flow wire in control pigs. CBF was increased by the A(2)-nonselective agonist 2-phenylaminoadenosine (CV1808) in a dose-dependent manner. Baseline CBF was increased by the highly A(1)-selective antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), but not changed by other AR-specific agents. The nonselective A(2) antagonist 3,7-dimethyl-1-propargylxanthine and A(2A)-selective antagonist 4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-ylamino]ethyl)phenol (ZM241385) abolished adenosine-induced CBF, whereas A(2B) and A(3) antagonism had no effect. Dyslipidemia and stenting decreased adenosine-induced CBF ∼70%, whereas A(1), A(2A), and A(2B) mRNA were up-regulated in dyslipidemic versus control >5-fold and there was no change in the ratio of A(1)/A(2A) protein in microvessels distal to the stent. In control Ossabaw swine A(1) antagonism by DPCPX positively regulated basal CBF. Impaired adenosine-induced CBF after stenting in dyslipidemia is most likely caused by the altered balance between A(1) and A(2A) signaling, not receptor expression.

Short-term exercise training prevents micro- and macrovascular disease following coronary stenting

The purpose of this study was to determine the effects of exercise on coronary blood flow and macrovascular atherosclerosis in response to stent deployment. Male Yucatan swine were placed on a control diet (C); on a high-fat/cholesterol diet (hypercholesterolemic; H); or on a high-fat/cholesterol diet and aerobically exercise trained (HX) starting after 36 wk on the diet. All pigs underwent coronary angiography and intravascular ultrasound (IVUS) guided placement of a bare metal stent in the circumflex coronary artery after 40 wk on diets and 3 wk later pigs underwent repeat angiography and IVUS and coronary blood flow (CBF) measurement. Average peak velocity (APV) was measured under basal conditions and in response to intracoronary application of the endothelium-independent vasodilator adenosine and the endothelium-dependent vasodilator bradykinin. There was a similar approximately 8-fold increase in total cholesterol in H and HX compared with control. Baseline CBF was increased above control and H in HX (P<0.05). At all doses adenosine-induced CBF was impaired in H, but preserved in HX. Similarly, bradykinin-induced CBF was impaired in H vs. control, yet was potentiated in HX. Microvessel density was decreased in H and preserved in HX vs. control. Native atheroma in HX was lower relative to H and control, while in-stent stenosis in HX was not different from H. Hyperlipidemia-induced microvascular dysfunction after stent deployment may be a result of reduction in microvessel density. This is the first report that short-term exercise training near the time of stenting prevents stent-induced microvascular dysfunction and attenuates native atheroma independent of changes in plasma cholesterol in this porcine model.

Exercise training decreases store-operated Ca2+entry associated with metabolic syndrome and coronary atherosclerosis

AIMS

Stenting attenuates restenosis, but accelerated coronary artery disease (CAD) adjacent to the stent (peri-stent CAD) remains a concern in metabolic syndrome (MetS). Smooth muscle cell proliferation, a major mechanism of CAD, is mediated partly by myoplasmic Ca2+ dysregulation and store-operated Ca2+ entry (SOCE) via canonical transient receptor potential 1 (TRPC1) channels is proposed to play a key role. Exercise is known to prevent Ca2+ dysregulation in CAD. We tested the hypothesis that MetS increases SOCE and peri-stent CAD and exercise attenuates these events.

METHODS AND RESULTS

Groups (n = 9 pigs each) were (i) healthy lean Ossabaw swine fed standard chow, (ii) excess calorie atherogenic diet fed (MetS), and (iii) aerobically exercise trained starting after 50 weeks of development of MetS (XMetS). Bare metal stents were placed after 54 weeks on diets, and CAD and SOCE were assessed 4 weeks later. Coronary cells were dispersed proximal to the stent (peri-stent) and from non-stent segments, and fura-2 fluorescence was used to assess SOCE, which was verified by Ni2+ blockade and insensitivity to nifedipine. XMetS pigs had increased physical work capacity and decreased LDL/HDL (P < 0.05), but no attenuation of robust insulin resistance, glucose intolerance, hypertriglyceridaemia, or hypertension. CAD was greater in peri-stented vs. non-stented artery segments. MetS had the greatest CAD, SOCE, and TRPC1 and STIM1 mRNA and protein expression, which were all attenuated in XMetS.

CONCLUSION

This is the first report of the protective effect of exercise on native CAD, peri-stent CAD, SOCE, and molecular expression of TRPC1, STIM1, and Orai1 in MetS.

Metabolic syndrome reduces the contribution of K+ channels to ischemic coronary vasodilation

This investigation tested the hypothesis that metabolic syndrome decreases the relative contribution of specific K(+) channels to coronary reactive hyperemia. Ca(2+)-activated (BK(Ca)), voltage-activated (K(V)), and ATP-dependent (K(ATP)) K(+) channels were investigated. Studies were conducted in anesthetized miniature Ossabaw swine fed a normal maintenance diet (11% kcal from fat) or an excess calorie atherogenic diet (43% kcal from fat, 2% cholesterol, 20% kcal from fructose) for 20 wk. The latter diet induces metabolic syndrome, increasing body weight, fasting glucose, total cholesterol, and triglyceride levels. Ischemic vasodilation was determined by the coronary flow response to a 15-s occlusion before and after cumulative administration of antagonists for BK(Ca) (penitrem A; 10 microg/kg iv), K(V) (4-aminopyridine; 0.3 mg/kg iv) and K(ATP) (glibenclamide; 1 mg/kg iv) channels. Coronary reactive hyperemia was diminished by metabolic syndrome as the repayment of flow debt was reduced approximately 30% compared with lean swine. Inhibition of BK(Ca) channels had no effect on reactive hyperemia in either lean or metabolic syndrome swine. Subsequent inhibition of K(V) channels significantly reduced the repayment of flow debt ( approximately 25%) in both lean and metabolic syndrome swine. Additional blockade of K(ATP) channels further diminished ( approximately 45%) the repayment of flow debt in lean but not metabolic syndrome swine. These data indicate that the metabolic syndrome impairs coronary vasodilation in response to cardiac ischemia via reductions in the contribution of K(+) channels to reactive hyperemia.

Contribution of BK(Ca) channels to local metabolic coronary vasodilation: Effects of metabolic syndrome

This investigation was designed to examine the hypothesis that impaired function of coronary microvascular large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels in metabolic syndrome (MetS) significantly attenuates the balance between myocardial oxygen delivery and metabolism at rest and during exercise-induced increases in myocardial oxygen consumption (MVo(2)). Studies were conducted in conscious, chronically instrumented Ossabaw swine fed a normal maintenance diet (11% kcal from fat) or an excess calorie atherogenic diet (43% kcal from fat, 2% cholesterol, 20% kcal from fructose) that induces many common features of MetS. Data were collected under baseline/resting conditions and during graded treadmill exercise before and after selective blockade of BK(Ca) channels with penitrem A (10 microg/kg iv). We found that the exercise-induced increases in blood pressure were significantly elevated in MetS swine. No differences in baseline cardiac function or heart rate were noted. Induction of MetS produced a parallel downward shift in the relationship between coronary venous Po(2) and MVo(2) (P < 0.001) that was accompanied by a marked release of lactate (negative lactate uptake) as MVo(2) was increased with exercise (P < 0.005). Inhibition of BK(Ca) channels with penitrem A did not significantly affect blood pressure, heart rate, or the relationship between coronary venous Po(2) and MVo(2) in lean or MetS swine. These data indicate that BK(Ca) channels are not required for local metabolic control of coronary blood flow under physiological (lean) or pathophysiological (MetS) conditions. Therefore, diminished function of BK(Ca) channels does not contribute to the impairment of myocardial oxygen-supply demand balance in MetS.

Effects of stent sizing on endothelial and vessel wall stress: potential mechanisms for in-stent restenosis

Stent sizing and apposition have been shown to be important determinants of clinical outcome. This study evaluates the mechanical effects of undersizing and oversizing of stents on endothelial wall shear stress (WSS) and vessel wall stress to determine a possible biomechanical mechanism of in-stent restenosis and thrombosis. Three-dimensional computational models of stents, artery, and internal fluid were created in a computer-assisted design package, meshed, and solved in finite element and computational fluid dynamic packages. The simulation results show that the effects of various degrees of undersizing on WSS, WSS gradient, and oscillatory shear index were highly nonlinear. As the degree of undersizing increased, the heterogeneity of WSS became smaller. The WSS distribution for the 20% undersizing was smooth and uniform, whereas the 5% case was very heterogeneous. The combination of lower WSS and higher WSS gradient and oscillatory shear index in the 5% undersized case may induce neointimal hyperplasia or thrombosis. Additionally, the oversizing simulation results show that the maximum intramural wall stress of the 20% oversizing case is significantly larger than the maximum stress for the 10% and zero oversizing cases. Edge stress concentration was observed, consistent with the restenosis typically observed in this region. This study demonstrates that proper sizing of stent is important for reducing the hemodynamic and mechanical disturbances to the vessel wall. Furthermore, the present findings may be used to improve stent design to reduce endothelial flow disturbances and intramural wall stress concentrations.

Adenosine receptors in wound healing, fibrosis and angiogenesis

Wound healing and tissue repair are critical processes, and adenosine, released from injured or ischemic tissues, plays an important role in promoting wound healing and tissue repair. Recent studies in genetically manipulated mice demonstrate that adenosine receptors are required for appropriate granulation tissue formation and in adequate wound healing. A(2A) and A(2B) adenosine receptors stimulate both of the critical functions in granulation tissue formation (i.e., new matrix production and angiogenesis), and the A(1) adenosine receptor (AR) may also contribute to new vessel formation. The effects of adenosine acting on these receptors is both direct and indirect, as AR activation suppresses antiangiogenic factor production by endothelial cells, promotes endothelial cell proliferation, and stimulates angiogenic factor production by endothelial cells and other cells present in the wound. Similarly, adenosine, acting at its receptors, stimulates collagen matrix formation directly. Like many other biological processes, AR-mediated promotion of tissue repair is critical for appropriate wound healing but may also contribute to pathogenic processes. Excessive tissue repair can lead to problems such as scarring and organ fibrosis and adenosine, and its receptors play a role in pathologic fibrosis as well. Here we review the evidence for the involvement of adenosine and its receptors in wound healing, tissue repair and fibrosis.

Leukemia inhibitory factor is upregulated in coronary arteries of Ossabaw miniature swine after stent placement

Leukemia inhibitory factor (LIF), an IL-6 class cytokine, is reported to be antiatherosclerotic. Thus, we hypothesized that LIF expression might be altered during in-stent neointimal hyperplasia. Ossabaw miniature swine, a unique large-animal model of metabolic syndrome and cardiovascular disease, were used for these studies. Bare-metal stents were deployed in the left anterior descending and left circumflex coronary arteries. Stents were expanded to either 1.0 x luminal diameter (in accordance with current clinical practice) or 1.3 x (overexpansion). The development of in-stent neointimal hyperplasia was assessed 28-day postimplantation using intravascular ultrasound. The atherosclerotic coverage of the vessel wall was approximately five-fold higher in 1.0 x stents and approximately nine-fold higher in 1.3 x stents 4 weeks after deployment, compared with the same segments before stenting. LIF mRNA was elevated approximately 11-fold in stented segments, relative to unstented epicardial coronary arteries. LIF expression and the intima : media ratio were strongly correlated in 1.0 x stented vessels. Further studies to investigate the nature of the association between LIF and neointimal hyperplasia revealed that vascular smooth muscle cell proliferation was inhibited by LIF treatment in an in-vitro model of atherosclerosis (coronary artery organ culture). These novel and clinically relevant studies show that elevated LIF gene expression is predictive for in-stent neointimal hyperplasia, and suggest that LIF upregulation may be a compensatory mechanism in this setting.