Alteration of vascular reactivity in diabetic human mammary artery and the effects of thiazolidinediones

Pioglitazone inhibits oxidative stress, MMP-mediated inflammation and vascular dysfunction in high glucose-induced human saphenous vein grafts

AIMS

The aim of this study was to investigate the effects of pioglitazone on reactive oxygen species (ROS), expressions/activities of MMPs and TIMP-2, and VSMC proliferation and vascular reactivity in high glucose (HG)-induced human saphenous vein (HSV) grafts.

METHODS

HSV grafts (n = 10) obtained from patients undergoing CABG were incubated with 30 mM glucose and/or 10 μM pioglitazone or 0.1 % DMSO for 24 h after endothelium removal. ROS levels were examined by chemiluminescence assay, MMP-2,-9,-14, TIMP-2, and α-SMA expression/activity was determined by gelatine zymography/immunohistochemistry. Vascular reactivity to potassium chloride, noradrenaline, serotonin, prostaglandin F_2α and papaverine was assessed in HSVs.

RESULTS

HG induced superoxide anion (SA) (123 %) and other ROS levels (159 %), up-regulated MMP-2 expression (180 %)/activity (79 %), MMP-14 expression (24 %) and MMP-9 activity while down-regulating TIMP-2 expression (27 %). HG elevated total MMP-2/TIMP-2 ratio (483 %) and MMP-14/TIMP-2 ratio (78 %). However, HG plus pioglitazone inhibited SA (30 %) and other ROS levels (29 %), down-regulated MMP-2 expression (76 %)/activity (83 %), MMP-14 expression (38 %) and MMP-9 activity, while reversing TIMP-2 expression (44 %). HG plus pioglitazone decreased total MMP-2/TIMP-2 ratio (91 %) and MMP-14/TIMP-2 ratio (59 %). HG impaired contractions to all agents but pioglitazone improved them.

CONCLUSIONS

Pioglitazone may contribute to the prevention of restenosis and maintaining vascular function in HSV grafts of DM patients undergoing CABG.

Lymphatic Collecting Vessel: New Perspectives on Mechanisms of Contractile Regulation and Potential Lymphatic Contractile Pathways to Target in Obesity and Metabolic Diseases

Obesity and metabolic syndrome pose a significant risk for developing cardiovascular disease and remain a critical healthcare challenge. Given the lymphatic system's role as a nexus for lipid absorption, immune cell trafficking, interstitial fluid and macromolecule homeostasis maintenance, the impact of obesity and metabolic disease on lymphatic function is a burgeoning field in lymphatic research. Work over the past decade has progressed from the association of an obese phenotype with Prox1 haploinsufficiency and the identification of obesity as a risk factor for lymphedema to consistent findings of lymphatic collecting vessel dysfunction across multiple metabolic disease models and organisms and characterization of obesity-induced lymphedema in the morbidly obese. Critically, recent findings have suggested that restoration of lymphatic function can also ameliorate obesity and insulin resistance, positing lymphatic targeted therapies as relevant pharmacological interventions. There remain, however, significant gaps in our understanding of lymphatic collecting vessel function, particularly the mechanisms that regulate the spontaneous contractile activity required for active lymph propulsion and lymph return in humans. In this article, we will review the current findings on lymphatic architecture and collecting vessel function, including recent advances in the ionic basis of lymphatic muscle contractile activity. We will then discuss lymphatic dysfunction observed with metabolic disruption and potential pathways to target with pharmacological approaches to improve lymphatic collecting vessel function.

Smooth Muscle Ion Channels and Regulation of Vascular Tone in Resistance Arteries and Arterioles

Vascular tone of resistance arteries and arterioles determines peripheral vascular resistance, contributing to the regulation of blood pressure and blood flow to, and within the body's tissues and organs. Ion channels in the plasma membrane and endoplasmic reticulum of vascular smooth muscle cells (SMCs) in these blood vessels importantly contribute to the regulation of intracellular Ca2+ concentration, the primary determinant of SMC contractile activity and vascular tone. Ion channels provide the main source of activator Ca2+ that determines vascular tone, and strongly contribute to setting and regulating membrane potential, which, in turn, regulates the open-state-probability of voltage gated Ca2+ channels (VGCCs), the primary source of Ca2+ in resistance artery and arteriolar SMCs. Ion channel function is also modulated by vasoconstrictors and vasodilators, contributing to all aspects of the regulation of vascular tone. This review will focus on the physiology of VGCCs, voltage-gated K+ (KV) channels, large-conductance Ca2+-activated K+ (BKCa) channels, strong-inward-rectifier K+ (KIR) channels, ATP-sensitive K+ (KATP) channels, ryanodine receptors (RyRs), inositol 1,4,5-trisphosphate receptors (IP3Rs), and a variety of transient receptor potential (TRP) channels that contribute to pressure-induced myogenic tone in resistance arteries and arterioles, the modulation of the function of these ion channels by vasoconstrictors and vasodilators, their role in the functional regulation of tissue blood flow and their dysfunction in diseases such as hypertension, obesity, and diabetes. © 2017 American Physiological Society. Compr Physiol 7:485-581, 2017.

Potassium Channels in Regulation of Vascular Smooth Muscle Contraction and Growth

Potassium channels importantly contribute to the regulation of vascular smooth muscle (VSM) contraction and growth. They are the dominant ion conductance of the VSM cell membrane and importantly determine and regulate membrane potential. Membrane potential, in turn, regulates the open-state probability of voltage-gated Ca²⁺ channels (VGCC), Ca²⁺ influx through VGCC, intracellular Ca²⁺, and VSM contraction. Membrane potential also affects release of Ca²⁺ from internal stores and the Ca²⁺ sensitivity of the contractile machinery such that K⁺ channels participate in all aspects of regulation of VSM contraction. Potassium channels also regulate proliferation of VSM cells through membrane potential-dependent and membrane potential-independent mechanisms. VSM cells express multiple isoforms of at least five classes of K⁺ channels that contribute to the regulation of contraction and cell proliferation (growth). This review will examine the structure, expression, and function of large conductance, Ca²⁺-activated K⁺ (BK_Ca) channels, intermediate-conductance Ca²⁺-activated K⁺ (K_Ca3.1) channels, multiple isoforms of voltage-gated K⁺ (K_V) channels, ATP-sensitive K⁺ (K_ATP) channels, and inward-rectifier K⁺ (K_IR) channels in both contractile and proliferating VSM cells.

Soluble epoxide hydrolase inhibition and peroxisome proliferator activated receptor γ agonist improve vascular function and decrease renal injury in hypertensive obese rats

Cardiometabolic syndrome occurs with obesity and consists of pathophysiological factors that increase the risk for cardiovascular events. Soluble epoxide hydrolase inhibition (sEHi) is a novel therapeutic approach that exerts renal and cardiovascular protection. Although sEHi as a therapeutic approach is promising, it could be more effective for the treatment of cardiometabolic syndrome when combined with peroxisome proliferator activated receptor γ (PPARγ) agonists. We hypothesized that the PPARγ agonist, rosiglitazone in combination with a sEHi (tAUCB) will provide synergistic actions to decrease blood pressure, improve vascular function, decrease inflammation, and prevent renal damage in spontaneously hypertensive obese rats (SHROB). SHROB were treated with rosiglitazone, tAUCB or the combination of tAUCB and rosiglitazone for four-weeks and compared with spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. Blood pressure increased in SHROB (164 ± 7 mmHg) and decreased 10 mmHg when treated with rosiglitazone, tAUCB, or tAUCB and rosiglitazone. Mesenteric artery dilation to the K(ATP) channel opener pinacidil was attenuated in SHROB (E(Max) = 77 ± 7%), compared with WKY (E(Max) = 115 ± 19) and SHR (E(Max) = 93 ± 12%). Vasodilation to pinacidil was improved by rosiglitazone (E(Max) = 92 ± 14%) but not tAUCB. Renal macrophage infiltration increased in SHROB and significantly decreased with rosiglitazone or tAUCB and rosiglitazone treatment. Albuminuria was increased in SHROB (90 ± 20 mg/d) and was significantly decreased by the combination of tAUCB and rosiglitazone (37 ± 9 mg/d). Glomerular injury in SHROB was also significantly decreased by tAUCB and rosiglitazone. These results indicate that even though sEHi or PPARγ agonist have benefits when used individually, the combination is more beneficial for the multidisease features in cardiometabolic syndrome.

Relaxation of human pulmonary arteries by PPARγ agonists

It has been suggested that activation of nuclear peroxisome proliferator-activated receptors γ (PPARγ) may represent a new strategy for the treatment of pulmonary arterial hypertension. It has been demonstrated that PPARγ activation relaxed the isolated mouse pulmonary artery. The aims of the present study were to examine whether and to which extent the two PPARγ agonists rosiglitazone and pioglitazone relax the isolated human pulmonary artery and to investigate the underlying mechanism(s). Isolated human pulmonary arteries were obtained from patients without clinical evidence of pulmonary hypertension during resection of lung carcinoma. Vasodilatory effects of PPARγ agonists were examined on endothelium-intact or endothelium-denuded vessels preconstricted with the thromboxane prostanoid receptor agonist U-46619. Rosiglitazone and pioglitazone (0.01–100 μM) caused a concentration- and/or time-dependent full relaxation of U-46619-preconstricted vessels. The rosiglitazone-induced relaxation was attenuated by the PPARγ antagonist GW9662 1 μM, endothelium denudation, the nitric oxide synthase inhibitor L-NAME 300 μM, the cyclooxygenase inhibitor indomethacin 10 μM, and the K_ATP channel blocker glibenclamide 10 μM. The prostacyclin IP receptor antagonist RO1138452 1 μM shifted the concentration–response curve for rosiglitazone to the right. The PPARγ agonists pioglitazone and rosiglitazone relax human pulmonary arteries. The rosiglitazone-induced vasorelaxation is partially endothelium-dependent and involves PPARγ receptors, arachidonic acid degradation products, nitric oxide, and K_ATP channels. Thus, the relaxant effect of PPARγ agonists in human pulmonary arteries may represent a new therapeutic target in pulmonary arterial hypertension.

Rosiglitazone selectively inhibits K(ATP) channels by acting on the K(IR) 6 subunit

BACKGROUND AND PURPOSE

Rosiglitazone is an anti-diabetic drug acting as an insulin sensitizer. We recently found that rosiglitazone also inhibits the vascular isoform of ATP-sensitive K(+) channels and compromises vasodilatory effects of β-adrenoceptor activation and pinacidil. As its potency for the channel inhibition is in the micromolar range, rosiglitazone may be used as an effective K(ATP) channel inhibitor for research and therapeutic purposes. Therefore, we performed experiments to determine whether other isoforms of K(ATP) channels are also sensitive to rosiglitazone and what their sensitivities are.

EXPERIMENTAL APPROACH

K(IR) 6.1/SUR2B, K(IR) 6.2/SUR1, K(IR) 6.2/SUR2A, K(IR) 6.2/SUR2B and K(IR) 6.2ΔC36 channels were expressed in HEK293 cells and were studied using patch-clamp techniques.

KEY RESULTS

Rosiglitazone inhibited all isoforms of K(ATP) channels in excised patches and in the whole-cell configuration. Its IC(50) was 10 µmol·L(-1) for the K(IR) 6.1/SUR2B channel and ∼45 µmol·L(-1) for K(IR) 6.2/SURx channels. Rosiglitazone also inhibited K(IR) 6.2ΔC36 channels in the absence of the sulphonylurea receptor (SUR) subunit, with potency (IC(50) = 45 µmol·L(-1) ) almost identical to that for K(IR) 6.2/SURx channels. Single-channel kinetic analysis showed that the channel inhibition was mediated by augmentation of the long-lasting closures without affecting the channel open state and unitary conductance. In contrast, rosiglitazone had no effect on K(IR) 1.1, K(IR) 2.1 and K(IR) 4.1 channels, suggesting that the channel inhibitory effect is selective for K(IR) 6.x channels.

CONCLUSIONS AND IMPLICATIONS

These results suggest a novel K(ATP) channel inhibitor that acts on the pore-forming K(IR) 6.x subunit, affecting the channel gating.

Rosiglitazone inhibits vascular KATP channels and coronary vasodilation produced by isoprenaline

BACKGROUND AND PURPOSE

Rosiglitazone is an anti-diabetic drug improving insulin sensitivity and glucose uptake in skeletal muscle and adipose tissues. However, several recent clinical trials suggest that rosiglitazone can increase the risk of cardiovascular ischaemia, although other studies failed to show such risks. Therefore, the effects of rosiglitazone on the coronary circulation and any potential vascular targets need to be elucidated. Here, we show that the vascular isoform of the ATP-sensitive K(+) (K(ATP) ) channel is inhibited by rosiglitazone, impairing physiological regulation of the coronary circulation.

EXPERIMENTAL APPROACH

The K(IR) 6.1/SUR2B channel was expressed in HEK293 cells and studied in whole-cell and inside-out patch configurations. The Langendorff heart preparation was used to evaluate rosiglitazone in the coronary circulation of wild-type (WT) and K(IR) 6.1-null (Kcnj8(-/-) ) mice.

KEY RESULTS

K(IR) 6.1/SUR2B channels in HEK cells were inhibited by rosiglitazone in a membrane-delimited manner. This effect was markedly enhanced by sub-micromolar concentrations of glibenclamide and the IC(50) for rosiglitazone fell to 2µM, a therapeutically achievable concentration. In the Langendorff heart preparation rosiglitazone inhibited, concentration-dependently, the coronary vasodilation induced by isoprenaline, without affecting basal coronary tone. Effects of rosiglitazone on coronary perfusion were attenuated by more than 50% in the Kcnj8(-/-) mice, supporting the involvement of K(ATP) channels in this effect of rosiglitazone on the coronary circulation.

CONCLUSIONS AND IMPLICATIONS

These results indicate that the vascular K(ATP) channel is one of the targets of rosiglitazone action, through which this drug may compromise coronary responses to circulating vasodilators and perhaps also to metabolic stress.

A(2A) adenosine receptor-mediated increase in coronary flow in hyperlipidemic APOE-knockout mice

Adenosine-induced coronary vasodilation is predominantly A_2A adenosine receptor (AR)-mediated, whereas A₁ AR is known to negatively modulate the coronary flow (CF). However, the coronary responses to adenosine in hyperlipidemia and atherosclerosis are not well understood. Using hyperlipidemic/atherosclerotic apolipoprotein E (APOE)–knockout mice, CF responses to nonspecific adenosine agonist (5′-N-ethylcarboxamide adenosine, NECA) and specific adenosine agonists (2-chloro-N6-cyclopentyl-adenosine [CCPA, A₁ AR-specific] and CGS-21680, A_2A AR-specific) were assessed using isolated Langendorff hearts. Western blot analysis was performed in the aorta from APOE and their wild-type (WT) control (C57BL/6J). Baseline CF (expressed as mL/min/g heart weight) was not different among WT (13.23 ± 3.58), APOE (13.22 ± 2.78), and APOE on high-fat diet (HFD) for 12 weeks (APOE-HFD, 12.37 ± 4.76). Concentration response curves induced by CGS-21680 were significantly shifted to the left in APOE and APOE-HFD when compared with WT. CCPA induced an increase in CF only at 10⁻⁶ M in all groups and the effect was reversed by the addition of a selective A_2A AR antagonist, SCH-58261 (10⁻⁶ M), and a significant decrease in CF from baseline was observed. Western blot analysis showed a significant upregulation of A_2A AR in the aorta from APOE and APOE-HFD. This study provides the first evidence that CF responses to A_2A AR stimulation were upregulated in hyperlipidemic/atherosclerotic animals. The speculation is that the use of A_2A AR-specific agonist for myocardial perfusion imaging (such as regadenoson) could overestimate the coronary reserve in coronary artery disease patients.

Glycoxidative stress and cardiovascular complications in experimentally-induced diabetes: effects of antioxidant treatment

Diabetes mellitus (DM) is a common metabolic disease, representing a serious risk factor for the development of cardiovascular complications, such as coronary heart disease, peripheral arterial disease and hypertension. Oxidative stress (OS), a feature of DM, is defined as an increase in the steady-state levels of reactive oxygen species (ROS) and may occur as a result of increased free radical generation and/or decreased anti-oxidant defense mechanisms. Increasing evidence indicates that hyperglycemia is the initiating cause of the tissue damage in DM, either through repeated acute changes in cellular glucose metabolism, or through long-term accumulation of glycated biomolecules and advanced glycation end products (AGEs). AGEs are formed by the Maillard process, a non-enzymatic reaction between ketone group of the glucose molecule or aldehydes and the amino groups of proteins that contributes to the aging of proteins and to the pathological complications of DM. In the presence of uncontrolled hyperglycemia, the increased formation of AGEs and lipid peroxidation products exacerbate intracellular OS and results in a loss of molecular integrity, disruption in cellular signaling and homeostasis, followed by inflammation and tissue injury such as endothelium dysfunction, arterial stiffening and microvascular complications. In addition to increased AGE production, there is also evidence of multiple pathways elevating ROS generation in DM, including; enhanced glucose auto-oxidation, increased mitochondrial superoxide production, protein kinase C-dependent activation of NADPH oxidase, uncoupled endothelial nitric oxide synthase (eNOS) activity, increased substrate flux through the polyol pathway and stimulation of eicosanoid metabolism. It is, therefore, not surprising that the correction of these variables can result in amelioration of diabetic cardiovascular abnormalities. A linking element between these phenomena is cellular redox imbalance due to glycoxidative stress (GOS). Thus, recent interest has focused on strategies to prevent, reverse or retard GOS in order to modify the natural history of diabetic cardiovascular abnormalities. This review will discuss the links between GOS and diabetes-induced cardiovascular disorders and the effect of antioxidant therapy on altering the development of cardiovascular complications in diabetic animal models.

Oral glyburide, but not glimepiride, blocks the infarct-size limiting effects of pioglitazone

BACKGROUND

Many patients with type 2 diabetes mellitus receive several oral hypoglycemic agents, including sulfonylurea drugs. Intravenous glyburide (Glyb), a sulfonylurea agent, blocks the protective effects of "ischemic" and pharmacologic preconditioning in various animal models without affecting myocardial infarct size when administered alone. However, there are conflicting results when other sulfonylurea drugs are used. Pioglitazone (PIO) reduces infarct size in the rat. We asked whether oral Glyb and glimepiride (Glim) affect the infarct size-limiting effects of PIO.

METHODS

Sprague-Dawley rats received 3-day oral treatment with: PIO (5 mg/kg/day); PIO + Glyb (10 mg/kg/day); PIO + Glim (4 mg/kg/day) or water alone (experiment 1) or PIO (5 mg/kg/day) with or without 5-hydroxydecanoate (5HD, 10 mg/kg), a specific mitochondrial ATP-sensitive K+ channels inhibitor, administered intravenously 30 min before coronary artery ligation. PIO, Glyb and Glim were administered by oral gavage. Sugar 5% was added to water to prevent hypoglycemia. Rats underwent 30 min coronary artery occlusion and 4 h reperfusion (n = 6 in each group). Ischemic area at risk was assessed by blue dye and infarct size by triphenyl-tetrazolium-chloride.

RESULTS

Body weight and the size of the area at risk were comparable among groups. Infarct size (% of the area at risk) was significantly smaller in the PIO (14.3 +/- 1.1%; p < 0.001) and PIO + Glim (13.2 +/- 0.8%; p < 0.001) groups than in the control group (37.7 +/- 1.2%). Glyb completely blocked the effect of PIO (43.0 +/- 1.7%; p < 0.001). Glim did not affect the protective effect of PIO (p = 0.993). 5HD blocked the protective effect of PIO (infarct size 48.5 +/- 0.8% versus 14.8 +/- 0.6%, respectively; p < 0.0001). In conclusion, the infarct size limiting effects of PIO are dependent on activation of mitochondrial ATP-sensitive K+ channels. Oral Glyb, but not Glim, blocks the infarct size limiting effects of PIO. It is plausible that Glyb affects other pleiotropic effects of PIO and thus may attenuate favorable effects on cardiovascular outcomes. In contrast, Glim does not attenuate the protective effect of PIO.