Diabetic Coronary Arteries Research Articles

Urocortin2 attenuates diabetic coronary microvascular dysfunction by regulating macrophage extracellular vesicles

Diabetic patients develop coronary microvascular dysfunction (CMD) and exhibit high mortality of coronary artery disease. Methylglyoxal (MGO) largely accumulates in the circulation due to diabetes. We addressed whether macrophages exposed to MGO exhibited damaging effect on the coronary artery and whether urocortin2 (UCN2) serve as protecting factors against such diabetes-associated complication. Type 2 diabetes was induced by high-fat diet and a single low-dose streptozotocin in mice. Small extracellular vesicles (sEV) derived from MGO-treated macrophages (MGO-sEV) were used to produce diabetes-like CMD. UCN2 was examined for a protective role against CMD. The involvement of arginase1 and IL-33 was tested by pharmacological inhibitor and IL-33-/- mice. MGO-sEV was capable of causing coronary artery endothelial dysfunction similar to that by diabetes. Immunocytochemistry studies of diabetic coronary arteries supported the transfer of arginase1 from macrophages to endothelial cells. Mechanism studies revealed arginase1 contributed to the impaired endothelium-dependent relaxation of coronary arteries in diabetic and MGO-sEV-treated mice. UCN2 significantly improved coronary artery endothelial function, and prevented MGO elevation in diabetic mice or enrichment of arginase1 in MGO-sEV. Diabetes caused a reduction of IL-33, which was also reversed by UCN2. IL-33-/- mice showed impaired endothelium-dependent relaxation of coronary arteries, which can be mitigated by arginase1 inhibition but can’t be improved by UCN2 anymore, indicating the importance of restoring IL-33 for the protection against diabetic CMD by UCN2. Our data suggest that MGO-sEV induces CMD via shuttling arginase1 to coronary arteries. UCN2 is able to protect against diabetic CMD via modulating MGO-altered macrophage sEV cargoes.

Quantitative evaluation and comparison of coronary artery characteristics by 3D coronary volume reconstruction

Non-atherosclerotic abnormalities of vessel calibre, aneurysm and ectasia, are challenging to quantify and are often overlooked in qualitative reporting. Utilising a novel 3-dimensional (3D) quantitative coronary angiography (QCA) application, we have evaluated the characteristics of normal, diabetic and aneurysmal or ectatic coronary arteries. We selected 131 individuals under 50 years-of-age, who had undergone coronary angiography for suspected myocardial ischaemia between 1st January 2011 and 31st December 2015, at the Bristol Heart Institute, Bristol, UK. This included 42 patients with angiographically normal coronary arteries, 36 diabetic patients with unobstructed coronaries, and 53 patients with abnormal coronary dilatation (aneurysm and ectasia). A total of 1105 coronary segments were analysed using QAngio XA 3D (Research Edition, Medis medical imaging systems, Leiden, The Netherlands). The combined volume of the major coronary arteries was significantly different between each group (1240 ± 476 mm3 diabetic group, 1646 ± 391 mm3 normal group, and 2072 ± 687 mm3 abnormal group). Moreover, the combined coronary artery volumes correlated with patient body surface area (r = 0.483, p < 0.01). Inter-observer variability was assessed and intraclass correlation coefficient of the total coronary artery volume demonstrated a low variability of 3D QCA (r = 0.996, p < 0.001). Dedicated 3D QCA facilitates reproducible coronary artery volume estimation and allows discrimination of normal and diseased vessels.

Role of peroxisome proliferators-activated receptor-gamma in advanced glycation end product-mediated functional loss of voltage-gated potassium channel in rat coronary arteries

BackgroundHigh blood glucose impairs voltage-gated K+ (Kv) channel-mediated vasodilation in rat coronary artery smooth muscle cells (CSMCs) via oxidative stress. Advanced glycation end product (AGE) and receptor for AGE (RAGE) axis has been found to impair coronary dilation by reducing Kv channel activity in diabetic rat small coronary arteries (RSCAs). However, its underlying mechanism remain unclear. Here, we used isolated arteries and primary CSMCs to investigate the effect of AGE incubation on Kv channel-mediated coronary dilation and the possible involvement of peroxisome proliferators-activated receptor (PPAR) -γ pathway.MethodsThe RSCAs and primary CSMCs were isolated, cultured, and treated with bovine serum albumin (BSA), AGE-BSA, alagrebrium (ALA, AGE cross-linking breaker), pioglitazone (PIO, PPAR-γ activator) and/or GW9662 (PPAR-γ inhibitor). The groups were accordingly divided as control, BSA, AGE, AGE + ALA, AGE + PIO, or AGE + PIO + GW9662. Kv channel-mediated dilation was analyzed using wire myograph. Histology and immunohistochemistry of RSCAs were performed. Western blot was used to detect the protein expression of RAGE, major Kv channel subunits expressed in CSMCs (Kv1.2 and Kv1.5), PPAR-γ, and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-2 (NOX-2).ResultsAGE markedly reduced Forskolin-induced Kv channel-mediated dilation of RSCAs by engaging with RAGE, and ALA or PIO significantly reversed the functional loss of Kv channel. In both RSCAs and CSMCs, AGE reduced Kv1.2/1.5 expression, increased RAGE and NOX-2 expression, and inhibited PPAR-γ expression, while ALA or PIO treatment partially reversed the inhibiting effects of AGE on Kv1.2/1.5 expression, accompanied by the downregulation of RAGE and decreased oxidative stress. Meanwhile, silencing of RAGE with siRNA remarkably alleviated the AGE-induced downregulation of Kv1.2/1.5 expression in CSMCs.ConclusionAGE reduces the Kv channel expression in CSMCs and further impairs the Kv channel-mediated dilation in RSCAs. The AGE/RAGE axis may enhance oxidative stress by inhibiting the downstream PPAR-γ pathway, thus playing a critical role in the dysfunction of Kv channels.

Chloroquine differentially modulates coronary vasodilation in control and diabetic mice.

Chloroquine is a traditional medicine to treat malaria. There is increasing evidence that chloroquine not only induces phagocytosis but regulates vascular tone. Few reports investigating the effect of chloroquine on vascular responsiveness of coronary arteries have been made. In this study, we examined how chloroquine affected endothelium-dependent relaxation in coronary arteries under normal and diabetic conditions. We isolated coronary arteries from mice and examined endothelium-dependent relaxation (EDR). Human coronary endothelial cells and mouse coronary endothelial cells isolated from control and diabetic mouse (TALLYHO/Jng [TH] mice, a spontaneous type 2 diabetic mouse model) were used for the molecular biological or cytosolic NO and Ca2+ measurements. Chloroquine inhibited endothelium-derived NO-dependent relaxation but had negligible effect on endothelium-derived hyperpolarization (EDH)-dependent relaxation in coronary arteries of control mice. Chloroquine significantly decreased NO production in control human coronary endothelial cells partly by phosphorylating eNOSThr495 (an inhibitory phosphorylation site of eNOS) and attenuating the rise of cytosolic Ca2+ concentration after stimulation. EDR was significantly inhibited in diabetic mice in comparison to control mice. Interestingly, chloroquine enhanced EDR in diabetic coronary arteries by, specifically, increasing EDH-dependent relaxation due partly to its augmenting effect on gap junction activity in diabetic mouse coronary endothelial cells. These data indicate that chloroquine affects vascular relaxation differently under normal and diabetic conditions. Therefore, the patients' health condition such as coronary macrovascular or microvascular disease, with or without diabetes, must be taken account into the consideration when selecting chloroquine for the treatment of malaria.

Tissue-specific up-regulation of arginase I and II induced by p38 MAPK mediates endothelial dysfunction in type 1 diabetes mellitus.

Emerging evidence suggests a selective up-regulation of arginase I in diabetes causing coronary artery disease; however, the mechanisms behind this up-regulation are still unknown. Activated p38 MAPK has been reported to increase arginase II in various cardiovascular diseases. We therefore tested the role of p38 MAPK in the regulation of arginase I and II expression and its effect on endothelial dysfunction in diabetes mellitus. Endothelial function was determined in septal coronary (SCA), left anterior descending coronary (LAD) and mesenteric (MA) arteries from healthy and streptozotocin-induced diabetic Wistar rats by wire myographs. Arginase activity and protein levels of arginase I, II, phospho-p38 MAPK and phospho-endothelial NOS (eNOS) (Ser(1177) ) were determined in these arteries from diabetic and healthy rats treated with a p38 MAPK inhibitor in vivo. Diabetic SCA and MA displayed impaired endothelium-dependent relaxation, which was prevented by arginase and p38 MAPK inhibition while LAD relaxation was not affected. Arginase I, phospho-p38 MAPK and eNOS protein expression was increased in diabetic coronary arteries. In diabetic MA, however, increased expression of arginase II and phospho-p38 MAPK, increased arginase activity and decreased expression of eNOS were observed. All these effects were reversed by p38 MAPK inhibition. Diabetes-induced activation of p38 MAPK causes endothelial dysfunction via selective up-regulation of arginase I expression in coronary arteries and arginase II expression in MA. Therefore, regional differences appear to exist in the arginase isoforms contributing to endothelial dysfunction in type 1 diabetes mellitus.

Regulation of vascular tension in diabetic coronary artery by large conductance Ca(2+)-activated K(+) channel in rats

to investigate the regulation in vascular tension of diabetic coronary artery by large conductance Ca(2+)-activated K(+) channel (BK channel) and to elucidate the mechanisms of coronary dysfunctions due to diabetes. regulation of vascular tension in normal coronary artery was evaluated by videomicroscopy system. Streptozotocin-induced rat diabetic animal model was established successfully by intraperitoneal injection. Coronary smooth muscle cells were isolated by enzyme digestion. The BK currents in control and diabetic groups were recorded by patch clamp technique in whole cell configuration. Changes of vascular tension in normal and diabetic coronary arteries were assayed by multi-wire myograph system. more than 50% was contracted in inner diameters of coronary arteries when 100 nmol/L IBTX, a specific BK channel blocker, was applied. In comparison with normal group, the BK current densities in diabetic group significantly decreased when test potentials were more than 60 mV (P < 0.05). The BK current densities at 150 mV in normal group and diabetic group were (275 ± 40) pA/pF and (70 ± 10) pA/pF respectively. When 100 mmol/L KCl was washed out, vascular tensions of normal and diabetic coronary artery were (398 ± 38) mg and (390 ± 35) mg respectively (P > 0.05); however, when 100 nmol/L IBTX was added, the vascular tensions of normal and diabetic coronary artery were (395 ± 40) mg and (50 ± 7) mg (P < 0.05). BK channels play an important role in the regulation of coronary vascular tension, whereas BK channels in diabetic coronary artery are dysfunction, BK currents decrease and vascular tensions increase.

O‐GlcNacase overexpression restores coronary endothelial dysfunction in type 1 diabetic mice (1076.1)

Cardiac ischemia is a leading cause of morbidity and mortality in diabetes, and endothelial cell (EC) dysfunction is implicated in coronary arterial disease. O‐linked N‐acetyglucosamine (O‐GlcNAcylation) is a post‐translational modification that is tightly controlled by two enzymes: O‐GlcNAc transferase (OGT, catalyzes the addition of an O‐GlcNAc to proteins) and O‐GlcNAcase (GCA, removes GlcNAc from proteins). In this study, we examine the role of GCA in coronary endothelial dysfunction in type 1 diabetic mice.We generated EC‐specific, inducible GCA transgenic mice and induced diabetes in these mice with streptozotocin. In diabetic mouse coronary endothelial cells (MCECs), GCA expression was significantly decreased and protein O‐GlcNAcylation was increased. GCA overexpression in diabetic mice decreased O‐GlcNAcylation in MCECs. Capillary density in the left ventricle was decreased in diabetes, while GCA overexpression significantly increased the density to the control level. Endothelium‐dependent relaxation was attenuated in diabetic coronary arteries (CAs) and restored by GCA overexpression. These data suggest that elevated protein O‐GlcNAcylation due to decreased GCA protein expression in MCECs contributes to coronary endothelial dysfunction in diabetes, whereas overexpression of GCA in ECs improves endothelial function and may have a beneficial effect on coronary vascular complications in diabetes.Grant Funding Source: supported by NIH/NHLBI(HL115578)

STIM1 Restores Coronary Endothelial Function in Type 1 Diabetic Mice

The endoplasmic reticulum (ER) is a major intracellular Ca(2+) store in endothelial cells (ECs). The Ca(2+) concentration in the ER greatly contributes to the generation of Ca(2+) signals that regulate endothelial functions. Many proteins, including stromal interaction molecule 1/2 (STIM1/2), Orai1/2/3, and sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase 3 (SERCA3), are involved in the ER Ca(2+) refilling after store depletion in ECs. This study is designed to examine the role of Ca(2+) in the ER in coronary endothelial dysfunction in diabetes. Mouse coronary ECs (MCECs) isolated from diabetic mice exhibited (1) a significant decrease in the Ca(2+) mobilization from the ER when the cells were treated by SERCA inhibitor, and (2) significant downregulation of STIM1 and SERCA3 protein expression in comparison to the controls. Overexpression of STIM1 restored (1) the increase in cytosolic Ca(2+) concentration due to Ca(2+) leak from the ER in diabetic MCECs, (2) the Ca(2+) concentration in the ER, and (3) endothelium-dependent relaxation that was attenuated in diabetic coronary arteries. Impaired ER Ca(2+) refilling in diabetic MCECs, due to the decrease in STIM1 protein expression, attenuates endothelium-dependent relaxation in diabetic coronary arteries, while STIM1 overexpression has a beneficial and therapeutic effect on coronary endothelial dysfunction in diabetes.

Role of superoxide anion in coronary endothelial dysfunction in type 2 diabetic mice

Coronary endothelial dysfunction leads to the increase in coronary blood flow and decrease in capillary density, and subsequently increases the incident of cardiac ischemia. Excess superoxide production (O2‐) has maladaptive effects on cellular functions in many tissues and organs. The objective of this study is to identify the role of O2‐ in coronary endothelial dysfunction in type 2 diabetic mice. Acetylcholine (ACh)‐induced relaxation (indicative of endothelium‐dependent relaxation) was significantly attenuated in diabetic coronary arteries (CAs) compared with control CAs. The pharmacological approach reveals that NO‐dependent relaxation, but not endothelial‐derived hyperpolarization‐dependent relaxation, is decreased in diabetic CAs. In the presence of Tempol (a O2‐scavenger), ACh‐induced relaxation in diabetic CAs is increased to the level seen in control CAs. In addition, mouse coronary endothelial cells (MCECs) isolated from diabetic mice exhibit significant increase in mitochondrial O2‐production and decrease in Mn‐SOD protein expression in comparison to those in control MCECs. These results suggest that the excess O2‐production in mitochondria attenuates the bioavailability of NO and subsequently decreases ACh‐induced relaxation in CAs in diabetic mice. This research was supported by grant DK083506.

Progressive Coronary Artery Remodeling in Diabetic db/db Mice

Type 2 diabetes is associated with vascular dysfunction and remodeling. The aim of this study was to determine the progression of coronary artery remodeling in Type 2 diabetes. Septal coronary arteries from 12, 16, and 20‐wk‐old heterozygous Db/db and Type 2 diabetic db/db mice were isolated and mounted on a pressure myograph containing Ca2+‐free physiological saline solution, EGTA and sodium nitroprusside. Passive structural measurements across a range of pressures revealed no changes in coronary structure in 12‐wk db/db mice, a time at which endothelial dysfunction is reported. However, wall thickness in diabetic arteries at 16 and 20‐wks was augmented (Db/db‐16: 6.9±0.6 μm vs. db/db‐16: 9.7±0.5 μm and Db/db‐20 6.7±0.8 μm vs. db/db‐20 9.2±0.7 μm at 100 mmHg, p &lt; 0.05, respectively) while internal lumen diameters tended to be reduced (Db/db‐16: 117.6±4.6 μm vs. db/db‐16: 102.9±4.3 μm and Db/db‐20 112.3±9.1 μm vs. db/db‐20 106.2±6.7 μm at 100 mmHg). The wall/lumen ratio at the same ages was augmented in diabetic coronary arteries (Db/db‐16: 6.0±0.6 μm vs. db/db‐16: 9.5±0.4 μm and Db/db‐20 6.1±0.6 μm vs. db/db‐20 8.9±0.7 μm at 100 mmHg, p &lt; 0.01). Despite these structural changes, no change in compliance was observed between control and diabetic groups. These data indicate that diabetic coronary arteries undergo progressive inward remodeling that may lead to impaired cardiac perfusion and coronary flow reserve. Supported by NIH RO1‐HL056046 (PAL).

Peroxynitrite Mediates Diabetes-Induced Endothelial Dysfunction: Possible Role of Rho Kinase Activation

Endothelial dysfunction is characterized by reduced bioavailability of NO due to its inactivation to form peroxynitrite or reduced expression of eNOS. Here, we examine the causal role of peroxynitrite in mediating diabetes-induced endothelial dysfunction. Diabetes was induced by STZ-injection, and rats received the peroxynitrite decomposition catalyst (FeTTPs, 15 mg/Kg/day) for 4 weeks. Vasorelaxation to acetylcholine, oxidative-stress markers, RhoA activity, and eNOS expression were determined. Diabetic coronary arteries showed significant reduction in ACh-mediated maximal relaxation compared to controls. Diabetic vessels showed also significant increases in lipid-peroxides, nitrotyrosine, and active RhoA and 50% reduction in eNOS mRNA expression. Treatment of diabetic animals with FeTTPS blocked these effects. Studies in aortic endothelial cells show that high glucose or peroxynitrite increases the active RhoA kinase levels and decreases eNOS expression and NO levels, which were reversed with blocking peroxynitrite or Rho kinase. Together, peroxynitrite can suppress eNOS expression via activation of RhoA and hence cause vascular dysfunction.

Diabetes-associated changes and role of N ɛ-(carboxymethyl)lysine in big ET-1-induced coronary vasoconstriction

Using perfused hearts from streptozotocin-induced long-term diabetic rats, we studied the coronary vasoconstrictor effect of the endothelin-1 (ET-1) precursor big ET-1 and also whether this response was modulated by N ɛ-(carboxymethyl)lysine (CML; a representative advanced glycation end product that is implicated in the pathogenesis of diabetic vasculopathy). The big ET-1-induced vasoconstriction (a) developed more rapidly (i.e., was greater in the first 30 min) in the diabetic group than in the age-matched controls, and (b) in each group was largely suppressed by phosphoramidon [nonselective endothelin-converting enzyme (ECE)/neutral endopeptidase (NEP) inhibitor] or CGS35066 (selective ECE inhibitor), but not by thiorphan (selective NEP inhibitor). The ET-1 release occurring after treatment with big ET-1, which was greater in diabetic coronary arteries than in the controls, was reduced by CGS35066. The dose–response curve for ET-1 was shifted to the left in the diabetics, so that at some lower doses of ET-1 the vasoconstriction was greater than in the controls. CML enhanced big ET-1- or ET-1-induced vasoconstriction in the controls, but not in the diabetics. Finally, the plasma level of CML was higher in diabetic than in control rats. These findings suggest (a) that the increased responsiveness to big ET-1 shown by diabetic coronary arteries may be attributable both to a more rapid conversion of big ET-1 to ET-1 (by ECE), allowing it to exert its contractile activity, and to an increased vascular sensitivity to ET-1, and (b) that CML may be at least partly responsible for the diabetes-associated enhancement of big ET-1-mediated coronary vasoconstriction.

Potassium channels sensitive to combination of charybdotoxin and apamin regulate the tone of diabetic isolated canine coronary arteries

Functional roles of calcium-activated potassium channels on the mechanical activity of epicardial coronary arteries obtained from a canine model of diabetes were investigated. Coronary arteries were isolated from healthy, alloxan-diabetic and insulin-treated diabetic dogs. Basal tensions, contractions induced by the prostaglandin (PG) analogue, U46619, and endothelium-dependent relaxations to acetylcholine (ACh) were modified with charybdotoxin (CHTX) + apamin (APA), inhibitors of calcium-activated potassium channels, as well as with N(omega)-nitro-l-arginine (LNA) + indomethacin (INDO) to suppress the synthesis of nitric oxide (NO) and PGs. The relaxing effect of nitroprusside-sodium (SNP), an NO donor, was also determined. In diabetic coronary arteries, CHTX + APA did not change while LNA + INDO elevated the basal tension. PG-induced contractions were enhanced by CHTX + APA and by LNA + INDO in all the three groups of animals. CHTX + APA decreased the maximal relaxations to ACh in a partly insulin-dependent manner. LNA + INDO abolished the endothelium-dependent relaxations to ACh. In diabetic coronary arteries, the sensitivity to SNP-induced relaxation was enhanced, insulin independently, suggesting that NO could be partly responsible for maintaining intact ACh-induced vasorelaxation. In diabetic canine coronary artery, the vasomotor responses reflect up-regulation of calcium-activated potassium channels. This endothelial mechanism of the canine epicardial coronary artery may oppose vasoconstrictions in diabetic vascular tissue.

Diabetes-induced Coronary Vascular Dysfunction Involves Increased Arginase Activity

Increases in arginase activity have been reported in a variety of disease conditions characterized by vascular dysfunction. Arginase competes with NO synthase for their common substrate arginine, suggesting a cause and effect relationship. We tested this concept by experiments with streptozotocin diabetic rats and high glucose (HG)-treated bovine coronary endothelial cells (BCECs). Our studies showed that diabetes-induced impairment of vasorelaxation to acetylcholine was correlated with increases in reactive oxygen species and arginase activity and arginase I expression in aorta and liver. Treatment of diabetic rats with simvastatin (5 mg/kg per day, subcutaneously) or L-citrulline (50 mg/kg per day, orally) blunted these effects. Acute treatment of diabetic coronary arteries with arginase inhibitors also reversed the impaired vasodilation to acetylcholine. Treatment of BCECs with HG (25 mmol/L, 24 hours) also increased arginase activity. This effect was blocked by treatment with simvastatin (0.1 micromol/L), the Rho kinase inhibitor Y-27632 (10 micromol/L), or L-citrulline (1 mmol/L). Superoxide and active RhoA levels also were elevated in HG-treated BCECs. Furthermore, HG significantly diminished NO production in BCECs. Transfection of BCECs with arginase I small interfering RNA prevented the rise in arginase activity in HG-treated cells and normalized NO production, suggesting a role for arginase I in reduced NO production with HG. These results indicate that increased arginase activity in diabetes contributes to vascular endothelial dysfunction by decreasing L-arginine availability to NO synthase.

Impaired Vasorelaxation of Coronary Arteries in Cynomolgus Monkeys with Diabetes

Diabetes promotes enhanced cardiovascular morbidity and mortality. We investigated the coronary vascular function in cynomolgus monkeys which were shown to develop accelerated atherosclerosis with diabetes. Methods Monkeys on an atherogenic diet were randomized to control and diabetic groups. Diabetes was induced by streptozotocin injection and blood glucose was controlled with insulin. Following one month of diabetes, vasorelaxation to acetylcholine (ACh) or nitroprusside (SNP) was evaluated in vitro in coronary arteries (<300 μm). Superoxide (SO) production in carotid arteries was measured by chemiluminescence. Endothelial nitric oxide synthase (eNOS) and Cu/Zn superoxide dismutase (SOD) expression in homogenates of hearts was assessed with real time PCR and immunoblotting. Results Diabetic monkeys had elevated blood glucose and impaired glucose tolerance as compared to control. Vasorelaxation to ACh as well as the SNP was diminished in diabetic coronary arteries. SO production was elevated in diabetic arteries. Expression of eNOS was enhanced in diabetic arteries while Cu/Zn SOD expression was similar compared to control arteries. Conclusions Coronary arteries of diabetic monkeys manifest impaired endothelium and smooth muscle dependent vasorelaxation despite enhanced expression of eNOS. Elevated SO may mediate vascular dysfunction by decreasing NO bioavailability and by altering smooth muscle relaxation (Support: NIH grants HL-30260, HL-46558, HL-50587, DK-62372).

Morphological characteristics of coronary atherosclerosis in diabetes mellitus

The incidence of diabetes is increasing in the general population because of increasing obesity, and is likely to result in a higher incidence of coronary artery disease. It was recently reported that diabetics (types I and II) dying suddenly from coronary artery disease have greater macrophage and T lymphocyte infiltration in atherosclerotic plaques, as well as larger necrotic cores compared with nondiabetics. The inflammatory cell infiltrates showed human leukocyte antigen-DR expression, which was greater in diabetics. The receptors for advanced glycosylation end-products expression, demonstrated by immunohistochemistry, was greater in diabetics than in nondiabetics in macrophages, smooth muscle cells and endothelial cells, and was associated with apoptosis of macrophages and smooth muscle cells, but not of endothelial cells. There is also a higher incidence of healed plaque ruptures and healed myocardial infarct in type II diabetics. Plaque burden is higher in diabetics than in nondiabetics; however, distal plaque burden was only significantly different in type II diabetics compared with nondiabetics. There was greater positive remodelling in diabetic coronary arteries than in nondiabetic ones, which correlated with the per cent necrotic core. Further studies are needed to better understand the mechanisms that govern greater inflammation and plaque burden in diabetics.

Diabetes-induced oxidative stress and low-grade inflammation in porcine coronary arteries.

Multiple pathways contribute to accelerated coronary atherosclerosis in diabetics, including increased oxidative stress and inflammatory burden. Accordingly, the mechanisms of abnormal formation of reactive oxygen species and the changes in inflammatory gene expression were examined in diabetic coronary arteries. In pigs with streptozotocin-induced diabetes, superoxide formation was augmented in coronary media and adventitia because of increased NAD(P)H oxidase activity (3 months) accompanied by upregulated expression of its cytosolic subunit, p22phox. Diabetes-induced oxidative stress resulted in the inflammatory response in the adventitia (increased expression of interleukin-6, tumor necrosis factor-alpha, monocyte chemotactic protein-1, vascular cell adhesion molecule-1 [VCAM-1]) and in the media (VCAM-1). To examine the mechanisms of these changes, studies with isolated coronary fibroblasts were undertaken. Advanced glycation end products (AGEs), rather than glucose itself, upregulated expression of interleukin-6, VCAM-1, and monocyte chemotactic protein-1 mRNAs. These results were paralleled by increased interleukin-6 secretion (P<0.01) and augmented leukocyte adhesion to AGE-stimulated coronary cells (P<0.001). AGEs increased expression of phosphorylated forms of mitogen-activated protein kinases in coronary cells (ERK1/2 and JNK) and resulted in redox-sensitive expression of inflammatory genes that was inhibited by several inhibitors of oxidative pathways [NAD(P)H oxidase inhibitors, N-acetylcysteine, and pyrrolidine dithiocarbamate]. Diabetes increased NAD(P)H oxidase activity and oxidative stress, producing inflammatory responses in porcine coronary media and adventitia. AGEs activated ERK1/2 and JNK signaling pathways and induced the expression of several inflammatory genes in coronary cells in a redox-sensitive manner. These results suggest the involvement of AGEs in the development of accelerated coronary atherosclerosis in diabetes.

Role of vascular adrenergic mechanisms in the haemodynamic and PGI2 stimulating effects of angiotensin in diabetic dogs.

In aware of the well-known altered vascular responsiveness in the diabetic vasculature, this study aimed to compare the haemodynamic and PGI2 releasing effects of angiotensin in metabolically healthy (12) and alloxan-(560 umol/kg) diabetic (12) dogs as well as to analyze the role of vascular adrenoceptors in this. In vivo the effect of intracoronarially administered angiotensin (63-125-250-500-1000 pmol/kg/min) on coronary blood flow, mean arterial blood pressure, myocardial contractile force and heart rate was investigated without and with pretreatment of 2 umol/kg phentolamine. In vitro PGI2 release by isolated coronary rings was induced by 50 nmol/l angiotensin before and after pretreatment with 5 umol/l phentolamine and measured by radioimmunoassay. Angiotensin enhances dose-dependently both the mean arterial blood pressure and coronary blood flow, while it provokes a considerable (p < 0.05) increase of PGI2 formation by isolated coronary arterial rings. These alterations could be prevented by phentolamine administration both in vivo and in vitro, while this drug did not affect the angiotensin-induced enhancement of diabetic coronary blood flow. On the other hand the increase of blood pressure by angiotensin was found to be more (p < 0.05) expressed in diabetes and it could be further potentiated by phentolamine. PGI2 synthesis by isolated diabetic coronary rings could not be modified either by angiotensin alone or in combination with phentolamine. On the basis of above data, the lack of stimulated vascular PGI2 formation mediated by alpha-adrenergic mechanisms is supposed to causatively contribute to the diminished sensitivity of diabetic coronary arteries to vasodilation.

Does substrate inavailability explain the disturbed prostaglandin synthesis by the diabetic coronary arteries?

Does substrate inavailability explain the disturbed prostaglandin synthesis by the diabetic coronary arteries?

Vasomotor changes in isolated coronary arteries from diabetic rats.

Contractile responses to prostaglandin F2 alpha, serotonin, noradrenaline, and potassium were examined in isolated intramyocardial arteries of Wistar rats 8 weeks after the induction of diabetes mellitus by administration of streptozotocin (STZ). The concentration-response curves obtained were compared with those noted in vessels both from age- and from weight-matched control rats. Light and electron microscopy did not reveal any major change in coronary artery wall thickness or morphology. There was no difference in the pattern of vasomotor responses between the two control groups. Contractile responses to prostaglandin F2 alpha, and potassium were significantly reduced, while contractile responses to serotonin and noradrenaline were unaltered in coronary arteries from diabetic rats. The vasomotor responses to noradrenaline and potassium showed a biphasic pattern in control vessels, i.e. contraction noted at high agonist concentrations was preceded by slight, but reproducible relaxation at lower concentrations. In diabetic vessels these relaxant responses were absent. The contraction produced by noradrenaline was markedly enhanced by the presence of propranolol in both diabetic and control vessels. Dilator responses to verapamil, diltiazem, nifedipine, papaverine and magnesium were studied in serotonin-precontracted coronary arteries; the concentration-response curves obtained by verapamil and diltiazem were shifted to the right in diabetic vessels. It appears justified to use vessels from age-matched rats as controls when vasomotor reactivity in coronary arteries from STZ-diabetic rats is investigated. The reduction in contractile responses to prostaglandin F2 alpha and potassium, and the reduction or lack of relaxant responses to noradrenaline, potassium, verapamil and diltiazem, in diabetic coronary arteries, indicate a selective modification of the coronary circulation by the diabetic disease.