Combination therapy with olmesartan and azelnidipine improves EDHF-mediated responses in diabetic apolipoprotein E-deficient mice

Endothelium-Dependent Hyperpolarization (EDH) in Diabetes: Mechanistic Insights and Therapeutic Implications

Diabetes mellitus is one of the major risk factors for cardiovascular disease and is an important health issue worldwide. Long-term diabetes causes endothelial dysfunction, which in turn leads to diabetic vascular complications. Endothelium-derived nitric oxide is a major vasodilator in large-size vessels, and the hyperpolarization of vascular smooth muscle cells mediated by the endothelium plays a central role in agonist-mediated and flow-mediated vasodilation in resistance-size vessels. Although the mechanisms underlying diabetic vascular complications are multifactorial and complex, impairment of endothelium-dependent hyperpolarization (EDH) of vascular smooth muscle cells would contribute at least partly to the initiation and progression of microvascular complications of diabetes. In this review, we present the current knowledge about the pathophysiology and underlying mechanisms of impaired EDH in diabetes in animals and humans. We also discuss potential therapeutic approaches aimed at the prevention and restoration of EDH in diabetes.

Preservation of endothelium-dependent relaxation in atherosclerotic mice with endothelium-restricted endothelin-1 overexpression

In human atherosclerosis, which is associated with elevated plasma and coronary endothelin (ET)-1 levels, ETA receptor antagonists improve coronary endothelial function. Mice overexpressing ET-1 specifically in the endothelium (eET-1) crossed with atherosclerosis-prone apolipoprotein E knockout mice (Apoe(-/-)) exhibit exaggerated high-fat diet (HFD)-induced atherosclerosis. Since endothelial dysfunction often precedes atherosclerosis development, we hypothesized that mice overexpressing endothelial ET-1 on a genetic background deficient in apolipoprotein E (eET-1/Apoe(-/-)) would have severe endothelial dysfunction. To test this hypothesis, we investigated endothelium-dependent relaxation (EDR) to acetylcholine in eET-1/Apoe(-/-) mice. EDR in mesenteric resistance arteries from 8- and 16-week-old mice fed a normal diet or HFD was improved in eET-1/Apoe(-/-) compared with Apoe(-/-) mice. Nitric oxide synthase (NOS) inhibition abolished EDR in Apoe(-/-). EDR in eET-1/Apoe(-/-) mice was resistant to NOS inhibition irrespective of age or diet. Inhibition of cyclooxygenase, the cytochrome P450 pathway, and endothelium-dependent hyperpolarization (EDH) resulted in little or no inhibition of EDR in eET-1/Apoe(-/-) compared with wild-type (WT) mice. In eET-1/Apoe(-/-) mice, blocking of EDH or soluble guanylate cyclase (sGC), in addition to NOS inhibition, decreased EDR by 36 and 30%, respectively. The activation of 4-aminopyridine-sensitive voltage-dependent potassium channels (Kv) during EDR was increased in eET-1/Apoe(-/-) compared with WT mice. We conclude that increasing eET-1 in mice that develop atherosclerosis results in decreased mutual dependence of endothelial signaling pathways responsible for EDR, and that NOS-independent activation of sGC and increased activation of Kv are responsible for enhanced EDR in this model of atherosclerosis associated with elevated endothelial and circulating ET-1.

Anti-atherogenic effects of the combination therapy with olmesartan and azelnidipine in diabetic apolipoprotein E-deficient mice

Many studies have aimed to identify anti-atherogenic agents in cardiovascular medicine. We have recently demonstrated that the combination therapy with olmesartan (OLM), an angiotensin II receptor blocker, and azelnidipine (AZL), a dihydroprydine calcium-channel blocker, improves endothelial function in diabetic Apolipoprotein-deficient (ApoE(-/-)) mice. In the present study, we examined whether this combination therapy also inhibits atherosclerosis in mice. We used male control and streptozocin-induced diabetic ApoE(-/-) mice. Diabetic ApoE(-/-) mice were orally treated for 5 weeks with vehicle (Untreated), OLM (30 mg/kg/day), AZL (10 mg/kg/day), their combination (OLM+AZL), or hydralazine (HYD, 5 mg/kg/day) as an antihypertensive control. At 5 weeks, systolic blood pressure was significantly elevated in Untreated but was normalized in OLM+AZL and HYD. The atherosclerosis area in the thoracic aorta, perivascular fibrosis and medial thickness of the coronary arteries were increased in Untreated and were ameliorated in OLM+AZL but not in HYD. Staining with a fluorescent probe dihydroethidium showed that production of reactive oxygen species was increased in Untreated, and ameliorated in OLM+AZL. Consistent with these findings, macrophage infiltration in the kidney and the expression of receptor for advanced glycation end-products in the heart, kidney and liver were increased in Untreated and were all ameliorated in OLM+AZL, associated with up-regulation of endothelial NO syntheses (eNOS). In conclusion, the combination therapy with OLM and AZL exerts anti-atherogenic effect in diabetic ApoE(-/-) mice through suppression of oxidative stress and activation of eNOS, independent of its blood pressure-lowering effects. Clinically, this combination therapy may be useful for patients with hypertension, hyperlipidemia and diabetes.

Essential role of bone marrow for microvascular endothelial and metabolic functions in mice

RATIONALE

We have previously demonstrated that the importance of endothelium-derived hyperpolarizing factor (EDHF) increases as the vessel size decreases and that endothelium-derived hydrogen peroxide (H(2)O(2)) is an EDHF in animals and humans, for which endothelial nitric oxide synthase (eNOS) is the major source. Recent studies have suggested the important role of the bone marrow (BM) in modulating cardiovascular and metabolic functions.

OBJECTIVE

We aimed to examine whether BM plays a role in modulating microvascular endothelial and metabolic functions in mice, and if so, to elucidate the mechanisms involved.

METHODS AND RESULTS

Male eNOS(-/-) mice were transplanted with BM cells from wild-type (WT) or eNOS(-/-) mice and were maintained for 6 weeks. Endothelium-dependent relaxations and hyperpolarizations of mesenteric arteries to acetylcholine were reduced in eNOS(-/-) mice and were markedly improved when transplanted with WT-BM but not with eNOS(-/-)-BM. The enhanced component of endothelium-dependent relaxations was abolished by catalase, indicating that the improved responses were mediated by H(2)O(2). In contrast, no such beneficial effect was noted in the aorta. Reduced plasma adiponectin levels and impaired glucose tolerance in eNOS(-/-) mice were also improved by WT-BM transplantation. Neuronal nitric oxide synthase (nNOS) in mesenteric arteries of eNOS(-/-) mice was significantly upregulated only when transplanted with WT-BM. Importantly, the beneficial effects of WT-BM transplantation were absent in eNOS(-/-)/adiponectin(-/-) or eNOS(-/-)/nNOS(-/-) mice.

CONCLUSIONS

These results provide the first evidence that BM plays an important role in modulating microvascular endothelial and metabolic functions, for which adiponectin and nNOS may be involved.

Hydrogen peroxide enhances vasodilatation by increasing dimerization of cGMP-dependent protein kinase type Iα

BACKGROUND

cGMP-dependent protein kinase type I (PKG I) plays a key role in vasodilatation caused by cGMP-elevating agents. It is a homodimer in mammalian cells, existing as 2 isoforms, Iα and Iβ. The aim of the present study was both to determine whether PKG I dimerization and activity are modulated by hydrogen peroxide (H(2)O(2)) and its influence on vasodilatation.

METHODS AND RESULTS

The dimers and monomers of total PKG I and PKG Iβ were analyzed by Western blotting. PKG I activity was assayed by measuring the incorporation of (32)P into BPDEtide. Changes in vessels tension were determined by organ chamber technique. In isolated porcine coronary arteries, H(2)O(2) increased the dimers of total PKG I in a concentration-dependent manner, but had no effect on dimerization of PKG Iβ. The dimerization of PKG I caused by H(2)O(2) was prevented by catalase but not by deferoxamine and tiron. H(2)O(2) promoted the translocation of PKG I from cytoplasm to membrane. H(2)O(2) enhanced the activity of PKG I and relaxations of porcine coronary arteries to the nitric oxide donor and 8-Br-cGMP. Inhibition of catalase under in vivo conditions significantly decreased rat mean arterial pressure, which was associated with increased dimerization of PKG I.

CONCLUSIONS

The present study suggests that H(2)O(2) may enhance the activity of PKG Iα-and PKG I-dependent vasodilatation via increased dimerization of the enzyme.

Current therapeutic strategies to mitigate the eNOS dysfunction in ischaemic stroke

Impairment of endothelial nitric oxide synthase (eNOS) activity is implicated in the pathogenesis of endothelial dysfunction in many diseases including ischaemic stroke. The modulation of eNOS during and/or following ischaemic injury often represents a futile compensatory mechanism due to a significant decrease in nitric oxide (NO) bioavailability coupled with dramatic increases in the levels of reactive oxygen species that further neutralise NO. However, applications of a number of therapeutic agents alone or in combination have been shown to augment eNOS activity under a variety of pathological conditions by potentiating the expression and/or activity of Akt/eNOS/NO pathway components. The list of these therapeutic agents include NO donors, statins, angiotensin-converting enzyme inhibitors, calcium channel blockers, phosphodiesterase-3 inhibitors, aspirin, dipyridamole and ellagic acid. While most of these compounds exhibit anti-platelet properties and are able to up-regulate eNOS expression in endothelial cells and platelets, others suppress eNOS uncoupling and tetrahydrobiopterin (an eNOS stabiliser) oxidation. As the number of therapeutic molecules that modulate the expression and activity of eNOS increases, further detailed research is required to reveal their mode of action in preventing and/or reversing the endothelial dysfunction.

Inhibition of phosphoinositide 3-kinase potentiates relaxation of porcine coronary arteries induced by nitroglycerin by decreasing phosphodiesterase type 5 activity

BACKGROUND

Vessel tension can be modulated by phosphoinositide 3-kinase (PI3K) acting on l-type calcium channel, rho kinase and phosphodiesterase (PDE) type 3 in smooth muscle cells. Inhibition of PI3K could increase the relaxation of porcine coronary arteries to nitroglycerin independent of this pathway, and the aim of the present study was therefore to determine the underlying mechanisms.

METHODS AND RESULTS

Isolated porcine coronary arteries were dissected from the heart and cut into rings in ice-cold modified Krebs-Ringer bicarbonate buffer. The response of these vessels was studied by using the organ chamber technique; the content of cyclic guanosine monophosphate (cGMP) was determined by using enzyme-linked immunosorbent assay kit; and PI3K and Akt activity were determined by measuring the phosphorylation level of their downstream signaling molecule on Western blot. Inhibition of PI3K with 2-(4-morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one hydrochloride (LY294002) potentiated the relaxation of porcine coronary arteries to nitroglycerin and nitric oxide (NO), but not to 8-bromo-guanosine 3'5'-cyclic monophosphate, isoproterenol or (R)-(+)-trans-4-(1-Aminoethyl)-N-(4-Pyridyl)cyclohexanecarboxamide dihydrochloride monohydrate (Y27632). Increased relaxation induced by LY294002 was eliminated by Akt1/2 kinase inhibitor (Akt-I: 1,3-dihydro-1-(1-((4-(6-phenyl-1H-imidazo(4,5-g)quinoxalin-7-yl)phenyl)methyl)-4-piperidinyl)-2H-benzimidazol-2-one trifluoroacetate salt hydrate) or zaprinast, but was not affected by 1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one, nifedipine or milrinone. Inhibition of Akt caused similar effects as LY294002. Incubation with LY294002 or Akt-I decreased the activity of PI3K and Akt but augmented the elevation of cGMP caused by NO. Enhanced cGMP elevation induced by LY294002 or Akt-I was also eliminated by zaprinast.

CONCLUSIONS

PI3K-Akt signaling may affect vascular tone through a stimulatory effect on PDE type 5.

Endothelium-derived hyperpolarizing factor and diabetes

In addition to its role as a barrier between blood and tissues, the vascular endothelium is responsible for the synthesis and released of a number of vasodilators including prostaglandins, nitric oxide and endothelium-derived hyperpolarizing factor (EDHF). As one of these vasodilators, the specific nature of EDHF has not been fully elucidated, although a number of roles have been proposed. Importantly, many conditions, such as hypertension, hyperlipidemia, heart failure, ischemia-reperfusion and diabetes mellitus comprise vascular endothelial dysfunction with EDHF dysregulation. This article reviews reports on the role of EDHF in diabetes-related endothelial dysfunction.

Synergistic effects of calcium-channel and angiotensin-receptor blockers on endothelial function and inflammatory responses in a porcine drug-eluting stent model

BACKGROUND

The rate of stent thrombosis is increased in association with drug-eluting stents (DES) due to delayed endothelialization and prolonged inflammation. Clinical studies have shown that either an angiotensin-receptor blocker (ARB) or a calcium-channel blocker (CCB) can improve endothelial dysfunction and inhibit inflammatory reactions in patients with hypertension. The effects of co-administered CCB and ARB on vascular protection after DES implantation, however, remain unknown.

METHODS AND RESULTS

Pigs (n=24) were implanted with coronary stents and randomly assigned to control, CCB, ARB or CCB + ARB groups. Endothelium-mediated vasodilation at the distal edge was significantly impaired compared to the intact site in the control group (P<0.05), but the difference between two sites in the CCB + ARB group was not significant. The combination produced a synergistic effect at the distal edge compared to the ARB, CCB and control groups (P<0.05). The expression of tumor necrosis factor-alpha and inflammatory cell adhesion were significantly inhibited in the CCB or ARB monotherapy groups compared with the control (P<0.05). The combination of CCB + ARB also improved inflammation.

CONCLUSIONS

Implanted DES exert adverse effects such as endothelial dysfunction and inflammatory reactions. The administration of either a CCB or an ARB reversed this adverse effect. Furthermore, recovery was synergistically enhanced by a CCB combined with an ARB.