Mechanisms underlying lysophosphatidylcholine-induced potentiation of vascular contractions in the Otsuka Long-Evans Tokushima Fatty (OLETF) rat aorta

Metabolomics of Arterial Stiffness

Arterial stiffness (AS) is one of the earliest detectable signs of structural and functional alterations of the vessel wall and an independent predictor of cardiovascular events and death. The emerging field of metabolomics can be utilized to detect a wide spectrum of intermediates and products of metabolism in body fluids that can be involved in the pathogenesis of AS. Research over the past decade has reinforced this idea by linking AS to circulating acylcarnitines, glycerophospholipids, sphingolipids, and amino acids, among other metabolite species. Some of these metabolites influence AS through traditional cardiovascular risk factors (e.g., high blood pressure, high blood cholesterol, diabetes, smoking), while others seem to act independently through both known and unknown pathophysiological mechanisms. We propose the term 'arteriometabolomics' to indicate the research that applies metabolomics methods to study AS. The 'arteriometabolomics' approach has the potential to allow more personalized cardiovascular risk stratification, disease monitoring, and treatment selection. One of its major goals is to uncover the causal metabolic pathways of AS. Such pathways could represent valuable treatment targets in vascular ageing.

Mulberry leaf active components alleviate type 2 diabetes and its liver and kidney injury in db/db mice through insulin receptor and TGF-β/Smads signaling pathway

Mulberry leaf is one of the commonly used traditional Chinese medicines, has been shown to exert hypoglycemic effects against diabetes. The aim of this study is to investigate the effects and mechanism of mulberry leaf flavonoids (MF), polysaccharides (MP) and alkaloids (MA) on diabetic and its liver and kidney injury. The db/db mice was adopted and the results showed that the FBG (fasting blood glucose) of model group continued to increase and associated liver and kidney injury. After the intervention of MP and MA, the value of FBG exhibited the most obvious hypoglycemic effect. MF and MP have obvious improved effect on kidney injury, which reduced the content of mALB/Cre (microalbumin/creatinine) in urine and improved the tubular epithelial cells edematous and renal cystic epithelial thickening. While the MF and MA possessed a significant effect on liver damage, manifested in reducing the levels of ALT (alanine aminotransferase) and AST (aspartate aminotransferase) and pathological changes of liver on db/db mice. Through metabolomics analysis, 13 endogenous potential biomarkers were identified in serum. The three effective components of mulberry can regulate the 13 potential biomarkers and the corresponding metabolic pathway. Collectively, the components of mulberry leaf have clear hypoglycemic effect and protective effect on liver and kidney injury and the effects are related to insulin receptor and TGF-β/Smads signaling pathway.

Inverse relations of serum phosphatidylcholines and lysophosphatidylcholines with vascular damage and heart rate in patients with atherosclerosis

BACKGROUND AND AIMS

The rapidly growing discipline of lipidomics allows the study of a wide spectrum of lipid species in body fluids and provides new insights into the pathogenesis of cardiovascular disease. We investigated serum phosphatidylcholine (PC) and lysophosphatidylcholine (lysoPC) species in relation to arterial stiffness, hemodynamics, and endothelial dysfunction in symptomatic patients with atherosclerosis and in healthy controls.

METHODS AND RESULTS

Thirty-two patients with peripheral arterial disease (age 61.7 ± 9.0 years), 52 patients with coronary artery disease (age 63.2 ± 9.2 years), and 40 apparently healthy controls (age 60.3 ± 7.1 years) were studied. Serum levels of 90 glycerophospholipids were determined with the AbsoluteIDQ™ p180 kit (BIOCRATES Life Sciences AG, Innsbruck, Austria). The technique of applanation tonometry was used for non-invasive pulse wave analysis and carotid-femoral pulse wave velocity (cf-PWV) assessment. Decreased serum levels of several individual PC and lysoPC species (e.g., PC aa C28:1, PC aa C30:0, PC aa C32:2, PC ae C30:0 and PC ae C34:2, lysoPC a C18:2) were observed for the patient groups in comparison to the healthy subjects. In addition, a considerable number of PCs and lysoPCs were inversely related to either cf-PWV, heart rate, asymmetric dimethylarginine (ADMA) or ADMA/arginine for patients with symptomatic atherosclerosis but not for the controls.

CONCLUSION

We found altered relationships between PC and lysoPC profiles, inflammation, and arterial function in atherosclerotic patients, compared to healthy subjects.

Macro- and microvascular endothelial dysfunction in diabetes

Endothelial cells, as well as their major products nitric oxide (NO) and prostacyclin, play a key role in the regulation of vascular homeostasis. Diabetes mellitus is an important risk factor for cardiovascular disease. Diabetes-induced endothelial dysfunction is a critical and initiating factor in the genesis of diabetic vascular complications. The present review focuses on both large blood vessels and the microvasculature. The endothelial dysfunction in diabetic macrovascular complications is characterized by reduced NO bioavailability, poorly compensated for by increased production of prostacyclin and/or endothelium-dependent hyperpolarizations, and increased production or action of endothelium-derived vasoconstrictors. The endothelial dysfunction of microvascular complications is primarily characterized by decreased release of NO, enhanced oxidative stress, increased production of inflammatory factors, abnormal angiogenesis, and impaired endothelial repair. In addition, non-coding RNAs (microRNAs) have emerged as participating in numerous cellular processes. Thus, this reviews pays special attention to microRNAs and their modulatory role in diabetes-induced vascular dysfunction. Some therapeutic strategies for preventing and restoring diabetic endothelial dysfunction are also highlighted.

Impaired endothelium-derived hyperpolarization-type relaxation in superior mesenteric arteries isolated from female Otsuka Long-Evans Tokushima Fatty rats

Endothelium-derived hyperpolarization (EDH) is an important signaling mechanism of endothelium-dependent vasorelaxation, and little attention has been paid to the EDH-type responses in female metabolic syndrome such as that observed with type-2 diabetes. We previously reported that EDH-type relaxation was impaired in superior mesenteric arteries from male Otsuka Long-Evans Tokushima Fatty (OLETF) rat, a model of type-2 diabetes, however, the response was unclear in female OLETF rat. Thus, the aim of this study was to examine if EDH-type relaxation was altered in superior mesenteric arteries isolated from female OLETF rats compared to age-matched, control female Long-Evans Tokushima Otsuka (LETO) rats at age 50-59 weeks. We investigated concentration-relaxation curves for acetylcholine (at age 50-53 weeks), NS309 (an activator of small- and intermediate-conductance calcium-activated potassium channels) (at age 50-53 weeks), and GSK1016790A (an agonist of transient receptor potential vanilloid type 4, TRPV4) (at age 58 or 59 weeks) in the presence of the nitric oxide synthase inhibitor N^G-nitro-L-arginine and the cyclooxygenase inhibitor indomethacin to investigate EDH-type responses in the superior mesenteric artery. Obesity, mild hyperglycemia, hyperinsulinemia, and hyperlipidemia (i.e., increased total cholesterol, triglyceride, and non-esterified fatty acids) were more frequent in OLETF rats than in age-matched LETO rats at age 50-53 weeks. Acetylcholine-, NS309-, and GSK1016790A-induced relaxations in arteries from OLETF rats were all significantly reduced compared to those in LETO rats. These results indicated that EDH-type relaxations were impaired in female OLETF rats. This novel experimental model may provide new insights into vascular dysfunction in metabolic syndrome in females.

β-Adrenoceptors differentially regulate vascular tone and angiogenesis of rat aorta via ERK1/2 and p38

β-Adrenoceptors (β-ARs) modulate ERK1/2 and p38 in different cells, but little is known about the contribution of these signaling pathways to the function of β-ARs in vascular tissue. Immunoblotting analysis of rat aortic rings, primary endothelial (ECs) and smooth muscle cells (SMCs) isolated from aorta showed that β-AR stimulation with isoprenaline activated p38 in aortic rings and in both cultured cell types, whereas it had a dual effect on ERK1/2 phosphorylation, decreasing it in ECs while increasing it in SMCs. These effects were reversed by propranolol, which by itself increased p-ERK1/2 in ECs. Isoprenaline β-AR mediated vasodilation of aortic rings was potentiated by the ERK1/2 inhibitor, U0126, in the presence or absence of endothelium or L-NAME, whereas inhibition of p38 had no impact. Isoprenaline moderately decreased sprouting from aorta rings in the Matrigel angiogenesis assay; conversely propranolol not only prevented isoprenaline inhibition, but stimulated angiogenesis. ERK1/2 inhibition decreased angiogenesis, while a dramatic stimulation was observed by p38 blockade. Our results suggest that ERK1/2 activation after β-ARs stimulation in the smooth muscle hinders the vasodilator effect of isoprenaline, but in the endothelium β-ARs decreases ERK1/2 and increases p38 activity reducing therefore angiogenesis.

Effect of lysophosphatidylcholine on α-adrenoreactivity of rat aorta smooth muscles

In experiments on rat aortic ring segments, lysophosphatidylcholine in concentrations of 2×10(-6), 2×10(-5), and 2×10(-4) M did not suppress the tonotropic effect of phenylephrine (6×10(-6) and 6×10(-5) M) and in concentration of 2×10(-5) M even potentiated it, which was noted for phenylephrine at a concentration of 6×10(-6) M. It was concluded that the chemomodulating effect of lysophosphatidylcholine depends on the type of receptors and cells.

Enhanced estradiol-induced vasorelaxation in aortas from type 2 diabetic mice may reflect a compensatory role of p38 MAPK-mediated eNOS activation

Cardiovascular problems are a major cause of morbidity and mortality, mainly due to coronary artery disease and atherosclerosis, in type 2 diabetes mellitus. However, female gender is a protective factor in the development of, for example, atherosclerosis and hypertension. One of the female hormones, 17β-estradiol (E2), is known to protect against the cardiovascular injury resulting from endothelial dysfunction, but the mechanism by which it does so remains unknown. Our hypothesis was that E2-mediated activation of Akt and mitogen-activated protein kinase (MAPK), and the subsequent endothelial NO synthase (eNOS) phosphorylation, might protect the aorta in diabetic mellitus. The experimental type 2 diabetic model we employed to test that hypothesis (female mice given streptozotocin and nicotinamide) is here termed fDM. In fDM aortas, we examined the E2-induced relaxation response and the associated protein activities. In control (age-matched, nondiabetic) aortas, E2 induced a vascular relaxation response that was mediated via Akt/eNOS and mitogen-activated/ERK-activating kinase (MEK)/eNOS pathways. In fDM aortas (vs. control aortas), (a) the E2-induced relaxation was enhanced, (b) the mediation of the response was different (via Akt/eNOS and p38 MAPK/eNOS pathways), and (c) E2 stimulation increased p38 MAPK and eNOS phosphorylations, decreased MEK phosphorylation, but did not alter estrogen receptor activity. We infer that at least in fDM aortas, E2 has beneficial effects (enhanced vascular relaxation and protection) that are mediated through Akt activation and (compensating for reduced MEK activation) p38 MAPK activation, leading to enhanced eNOS phosphorylation.

Enhancement of mesenteric artery contraction to 5-HT depends on Rho kinase and Src kinase pathways in the ob/ob mouse model of type 2 diabetes

BACKGROUND AND PURPOSE

Arteries from hypertensive subjects are reportedly hyperresponsive to 5-hydroxytryptamine (5-HT), but it remains unclear whether this is true in chronic type 2 diabetes. We have assessed responses to 5-HT shown by mesenteric arteries from type 2 diabetic ob/ob mice (27-32 weeks old) and have identified the molecular mechanisms involved.

EXPERIMENTAL APPROACH

Contractions of mesenteric rings to 5-HT were examined in vitro. Activation of mesenteric RhoA, Rho kinase and Src was measured by Western blotting or by modified enzyme-linked immunosorbent assay.

KEY RESULTS

Concentration-dependent contractions to 5-HT were greater in mesenteric rings from the ob/ob than in those from the age-matched control ('Lean') group. In each group, there was no significant change in the 5-HT-induced contractions after inhibition of nitric oxide synthase (with N(G)-nitro-L-arginine), of cyclooxygenase (with indomethacin) or of protein kinase C (with chelerythrine). However inhibition of the MEK/ERK pathway (with PD98059) decreased the response to 5-HT. Although the diabetes-related enhancement of the 5-HT response was preserved with each of these inhibitors, enhancement was abolished by a Rho kinase inhibitor (Y27632) and by Src kinase inhibitors (PP1 analogue or Src kinase inhibitor I). 5-HT-induced activation of RhoA, Rho kinase and Src kinase in mesenteric arteries was greater in the ob/ob than in the Lean group, but the expression of RhoA, Rho kinase isoforms and Src did not differ between these groups.

CONCLUSIONS AND IMPLICATIONS

These results suggest that the enhancement of 5-HT-induced contraction in mesenteric arteries from ob/ob mice may be attributable to increased activation of RhoA/Rho kinase and Src kinase.

Mechanisms underlying the losartan treatment-induced improvement in the endothelial dysfunction seen in mesenteric arteries from type 2 diabetic rats

It is well known that type 2 diabetes mellitus is frequently associated with vascular dysfunction and an elevated systemic blood pressure, yet the underlying mechanisms are not completely understood. We previously reported that in mesenteric arteries from established type 2 diabetic Otsuka Long-Evans Tokushima fatty (OLETF) rats, which exhibit endothelial dysfunction, there is an imbalance between endothelium-derived vasodilators [namely, nitric oxide (NO) and hyperpolarizing factor (EDHF)] and vasoconstrictors [contracting factors (EDCFs) such as cyclooxygenase (COX)-derived prostanoids]. Here, we investigated whether the angiotensin II receptor antagonist losartan might improve endothelial dysfunction in OLETF rats at the established stage of diabetes. In mesenteric arteries isolated from OLETF rats [vs. those from age-matched control Long-Evans Tokushima Otsuka (LETO) rats]: (1) the acetylcholine (ACh)-induced relaxation was impaired, (2) the NO- and EDHF-mediated relaxations were reduced, (3) the ACh-induced EDCF-mediated contraction and the production of prostanoids were increased, and (4) superoxide generation was increased. After such OLETF rats had received losartan (25 mg/kg/day p.o. for 4 weeks), their isolated mesenteric arteries exhibited: (1) improvements in ACh-induced NO- and EDHF-mediated relaxations, (2) reduced EDCF- and arachidonic acid-induced contractions, (3) suppressed production of prostanoids, (4) reduced PGE(2)-mediated contraction, and (5) reduced superoxide generation. Within the timescale studied here, losartan did not change the protein expressions of endothelial NO synthase, COX1, or COX2 in mesenteric arteries from either OLETF or LETO rats. Losartan thus normalizes vascular dysfunction in this type 2 diabetic model, and the above effects may contribute to the reduction of adverse cardiovascular events seen in diabetic patients treated with angiotensin II receptor blockers.

Effect of inhibition of extracellular signal-regulated kinase on relaxations to beta-adrenoceptor agonists in porcine isolated blood vessels

BACKGROUND AND PURPOSE

Stimulation of vascular beta-adrenoceptors causes vasodilatation through activation of adenylyl cyclase (AC) and plasma membrane potassium channels, and beta-adrenoceptors have been linked to activation of extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase in various cell lines. However, how these findings relate to functional responses in intact tissues is largely unknown. The aim of this study, therefore, was to investigate the role of ERK in beta-adrenoceptor-induced vasodilatation.

EXPERIMENTAL APPROACH

Segments of porcine coronary artery were mounted in a Mulvany wire myograph and bathed in Krebs-Henseleit buffer gassed with 95% O(2)/5% CO(2) and maintained at 37 degrees C. Tissues were pre-contracted with the thromboxane mimetic U46619, endothelin-1 or KCl. Cumulative concentration-response curves to beta-adrenoceptor agonists or forskolin were then carried out in the absence or presence of the mitogen-activated protein kinase kinase (MEK) inhibitors PD98059 (10 or 50 microM) or U0126 (10 microM).

KEY RESULTS

PD98059 caused a concentration-dependent leftward shift in response to isoprenaline (pEC(50) control, 7.5 +/- 0.1; 50 microM PD98059, 8.1 +/- 0.1: P < 0.05). Inhibition of MEK also enhanced the maximum relaxation seen with salbutamol, but not the responses to the beta(1)-adrenoceptor selective agonist xamoterol or the AC activator forskolin. There was no enhancement of the relaxations to beta-adrenoceptor agonists after inhibition of ERK activation in tissues pre-contracted with KCl or treated with the K(+) channel blocker tetraethylammonium.

CONCLUSIONS AND IMPLICATIONS

These data indicate that ERK inhibits beta(2)-adrenoceptor-mediated vasodilatation through a mechanism which may involve inactivation of plasma membrane potassium channels.

Pyrrolidine dithiocarbamate reduces vascular prostanoid-induced responses in aged type 2 diabetic rat model

It has been shown that enhancement of vasoconstrictor prostanoids plays an important role in the development of cardiovascular diseases. The aim of the present study was to examine the effects of pyrrolidine dithiocarbamate (PDTC), a low-molecular-weight thiol antioxidant and a potent inhibitor of nuclear factor-kappaB (NF-kappaB), on both the response to and production of prostanoids in arterial vessels isolated from rats at the chronic stage of type 2 diabetes. Using aortas from type 2 diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats, control Long-Evans Tokushima Otsuka (LETO) rats, and LETO and OLETF rats treated with PDTC (30 mg/kg, s.c., daily, for 1 week), we measured the production of prostanoids and NF-kappaB activity. The arachidonic acid-induced contraction and the acetylcholine-induced endothelium-derived contracting factor (EDCF)-mediated contraction in mesenteric arteries were also compared among these groups. OLETF rats exhibited (vs. age-matched LETO rats) the following: increased responses to both arachidonic acid and EDCF and greater productions of PGE(2) and TXA(2). Treatment with PDTC resulted in the following: 1) reduced arachidonic acid- and EDCF-mediated contractions, 2) suppressed the production of prostanoids, and 3) normalized NF-kappaB activity. These results suggest that PDTC has beneficial effects against the abnormal vasoconstrictor prostanoid signaling present in rats at the chronic stage of type 2 diabetes.

Involvement of NO and MEK/ERK pathway in enhancement of endothelin-1-induced mesenteric artery contraction in later-stage type 2 diabetic Goto-Kakizaki rat

Endothelin (ET)-1 is a likely candidate for a key role in diabetic vascular complications. However, no abnormalities in the vascular responsiveness to ET-1 have been identified in the chronic stage of type 2 diabetes. Our goal was to look for abnormalities in the roles played by ET receptors (ETA and ETB) in the mesenteric artery of the type 2 diabetic Goto-Kakizaki (GK) rat and to identify the molecular mechanisms involved. Using mesenteric arteries from later-stage (32–38 wk old) individuals, we compared the ET-1-induced contraction and the relaxation induced by the selective ETB receptor agonist IRL1620 between GK rats and control Wistar rats. Mesenteric artery ERK activity and the protein expressions for ET receptors and MEK were also measured. In GK rats (vs. age-matched Wistar rats), we found as follows. 1) The ET-1-induced contraction was greater and was attenuated by BQ-123 (ETA antagonist) but not by BQ-788 (ETB antagonist). In the controls, BQ-788 augmented this contraction. 2) Both the relaxation and nitric oxide (NO) production induced by IRL1620 were reduced. 3) ET-1-induced contraction was enhanced by NG-nitro-l-arginine (l-NNA; NO synthase inhibitor) but suppressed by sodium nitroprusside (NO donor). 4) The enhanced ET-1-induced contraction was reduced by MEK/ERK pathway inhibitors (PD-98059 or U0126). 5) ET-1-stimulated ERK activation was increased, as were the ETA and MEK1/2 protein expressions. 6) Mesenteric ET-1 content was increased. These results suggest that upregulation of ETA, a defect in ETB-mediated NO signaling, and activation of the MEK/ERK pathway together represent a likely mechanism mediating the hyperreactivity to ET-1 examined in this study.

The ischemic metabolite lysophosphatidylcholine increases rat coronary arterial tone by endothelium-dependent mechanisms

Lysophosphatidylcholine (LPC), a hydrolysis product of phospholipid degradation, accumulates in the ischemic myocardium. Using isolated hearts or rat coronary septal arteries, we tested the impact of LPC in modulating basal function or the responses to vasoactive agents. Sustained perfusion of hearts with LPC augmented coronary perfusion pressure (CPP) and reduced left ventricular developed pressure (LVDP). By mechanisms that have yet to be identified, these effects on CPP and LVDP were exaggerated when LPC was removed from the perfusate. Although LPC (or its washout) had no direct effect on vascular tone in the isolated coronary artery, it selectively potentiated the receptor-coupled vasoconstrictor response to U-46619, a thromboxane A(2) mimetic. Interestingly, when LPC was washed out, the potentiation to U-46619 was even more pronounced. Both the immediate and residual effects of LPC were endothelium-dependent. EDHF was likely the sole mediator responsible for the direct effects of LPC on U-46619-vasoconstriction, whereas the augmented vasoconstrictor responses following LPC washout may in part be related to an increase in ET-1, and a striking reduction in the bioavailability of NO. Our data suggest that in addition to reducing the accumulation of LPC to prevent ischemia-reperfusion (I/R) damage, efforts targeting an improved endothelium-dependent regulation of vascular tone could be an attractive approach to limit the cardiac damage induced by I/R.

Eicosapentaenoic acid improves imbalance between vasodilator and vasoconstrictor actions of endothelium-derived factors in mesenteric arteries from rats at chronic stage of type 2 diabetes

Accumulating evidence demonstrates that dietary intake of n-3 polyunsaturated fatty acids (PUFAs) is associated with a reduced incidence of several cardiovascular diseases that involve endothelial dysfunction. However, the molecular mechanism remains unclear. We previously reported that mesenteric arteries from type 2 diabetic Otsuka Long-Evans Tokushima fatty (OLETF) rats exhibit endothelial dysfunction, leading to an imbalance between endothelium-derived vasodilators [namely, nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF)] and vasoconstrictors [endothelium-derived contracting factors (EDCFs)] [namely cyclooxygenase (COX)-derived prostanoids] (Am J Physiol Heart Circ Physiol 293:H1480-H1490, 2007). We hypothesized that treating OLETF rats with eicosapentaenoic acid (EPA), a major n-3 PUFA, may improve endothelial dysfunction by correcting this imbalance. In OLETF rats [compared with age-matched control Long-Evans Tokushima Otsuka (LETO) rats]: 1) acetylcholine (ACh)-induced (endothelium-dependent) relaxation was impaired, 2) NO- and EDHF-mediated relaxations and nitrite production were reduced, and 3) ACh-induced EDCF-mediated contraction, production of prostanoids, and the protein expressions of COX-1 and COX-2 were all increased. When OLETF rats received chronic EPA treatment long-term (300 mg/kg/day p.o. for 4 weeks), their isolated mesenteric arteries exhibited: 1) improvements in ACh-induced NO- and EDHF-mediated relaxations and COX-mediated contraction, 2) reduced EDCF- and arachidonic acid-induced contractions, 3) normalized NO metabolism, 4) suppressed production of prostanoids, 5) reduced COX-2 expression, and 6) reduced phosphoextracellular signal-regulated kinase (ERK) expression. Moreover, EPA treatment reduced both ERK2 and nuclear factor (NF)-kappaB activities in isolated OLETF aortas. We propose that EPA ameliorates endothelial dysfunction in OLETF rats by correcting the imbalance between endothelium-derived factors, at least partly, by inhibiting ERK, decreasing NF-kappaB activation, and reducing COX-2 expression.

Glucose-dependent enhancement of diabetic bladder contraction is associated with a rho kinase-regulated protein kinase C pathway

Urinary bladder dysfunction, which is one of the most common diabetic complications, is associated with alteration of bladder smooth muscle contraction. However, details regarding the responses under high-glucose (HG) conditions in diabetes are poorly understood. The objective of this study was to identify a relationship between extracellular glucose level and bladder smooth muscle contraction in diabetes. Bladder smooth muscle tissues were isolated from spontaneously type II diabetic (ob/ob mouse; 16-20 weeks of age, male) and age-matched control (C57BL mouse) mice. Carbachol (CCh) induced time- and dose-dependent contractions in ob/ob and C57BL mice; however, maximal responses differed significantly (14.34 +/- 0.32 and 12.69 +/- 0.22 mN/mm(2) after 30 microM CCh treatment, respectively; n = 5-8). Pretreatment of bladders under HG conditions (22.2 mM glucose; concentration is twice that of normal glucose for 30 min) led to enhancement of CCh-induced contraction solely in diabetic mice (15.9 +/- 0.26 mN/mm(2); n = 5). Basal extracellular glucose-dependent enhancement of bladder contraction in diabetes was documented initially in this study. The correlation between intracellular calcium concentration and contraction was enhanced only in the ob/ob mouse. This enhancement of contraction and total protein kinase C (PKC) activity were inhibited by pretreatment with not only a PKC inhibitor (rottlerin) but also with a rho kinase inhibitor, fasudil [1-(5-isoquinolinesulfonyl)homopiperazine HCl]. These reagents also suppressed the differences between ob/ob and C57BL mouse bladder contractions under HG conditions. The data indicated that glucose-dependent enhancement of contraction in diabetic bladder is involved in the activation of the rho kinase and calcium-independent PKC pathways. This dysfunction may contribute to bladder complications such as detrusor overactivity and reduced bladder capacity in diabetes.

Cilostazol improves endothelial dysfunction by increasing endothelium-derived hyperpolarizing factor response in mesenteric arteries from Type 2 diabetic rats

Diabetes mellitus impairs endothelial function, an effect that can be considered a hallmark of the development of cardiovascular diseases in diabetics. Cilostazol, a selective phosphodiesterase 3 inhibitor, is currently used to treat patients with diabetic vascular complications. However, the effects of cilostazol on responses mediated by endothelium-derived relaxing [in particular, nitric oxide (NO) and hyperpolarizing factors (EDHF)] and contracting factors remain unclear. Here, we hypothesized that cilostazol could improve endothelial dysfunctions in mesenteric arteries isolated from type 2 diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats. Using cilostazol-treated (100 mg/kg/day for 4 weeks) or -untreated OLETF and control (Long Evans Tokushima Otsuka) rats, we examined the acetylcholine-induced endothelium-dependent responses and the cell-permeant cyclic adenosine monophosphate (cAMP) analog-induced relaxations in the superior mesenteric artery. We also determined blood parameters in these animals. In OLETF rats, chronic treatment with cilostazol reduced the blood levels of triglyceride, non-esterified fatty acids, and leptin, and increased antioxidant capacity, but did not alter the blood glucose or insulin levels. In studies on mesenteric arteries from cilostazol-treated OLETF animals, the cilostazol treatment improved: (a) the acetylcholine-induced EDHF-mediated relaxation and (b) the cAMP-mediated relaxation. However, cilostazol did not alter the NO-mediated relaxation or the endothelium-derived contracting factor-mediated contraction. These results suggest that cilostazol improves endothelial functions in OLETF mesenteric arteries by increasing EDHF signaling, and that it normalizes some metabolic abnormalities in OLETF rats. On that basis, cilostazol may prove to be a potent drug for the clinical treatment of diabetic vasculopathy.

Diabetic state, high plasma insulin and angiotensin II combine to augment endothelin-1-induced vasoconstriction via ETA receptors and ERK

BACKGROUND AND PURPOSE

Mechanisms associated with the enhanced contractile response to endothelin-1 in hyperinsulinaemic diabetes have been examined using the rat aorta. Functions for angiotensin II, endothelin-1 receptor expression and extracellular signal-regulated kinase (ERK) have been investigated.

EXPERIMENTAL APPROACH

Streptozotocin-induced diabetic rats were infused with angiotensin II or, following insulin treatment, were treated with losartan, an angiotensin II receptor antagonist. Contractions of aortic strips with or without endothelium, in response to endothelin-1 and angiotensin II, were examined in vitro. Aortic ET(A) receptors and ERK/MEK expression were measured by western blotting.

KEY RESULTS

Insulin-treated diabetic rats exhibited increases in plasma insulin, angiotensin II and endothelin-1. The systolic blood pressure and endothelin-1-induced contractile responses in aortae in vitro were enhanced in insulin-treated diabetic rats and blunted by chronic losartan administration. LY294002 (phosphatidylinositol 3-kinase inhibitor) and/or PD98059 (MEK inhibitor) diminished the enhanced contractile response to endothelin-1 in aortae from insulin-treated diabetic rats. ET(A) and ET(B) receptors, ERK-1/2 and MEK-1/2 protein expression and endothelin-1-stimulated ERK phosphorylation were all increased in aortae from insulin-treated diabetic rats. Such increases were blunted by chronic losartan administration. Endothelin-1-induced contraction was significantly higher in aortae from angiotensin II-infused diabetic rats. angiotensin II-infusion increased ERK phosphorylation, but the expression of endothelin receptors and ERK/MEK proteins remained unchanged.

CONCLUSIONS AND IMPLICATIONS

These results suggest that the combination of high plasma angiotensin II and insulin with a diabetic state induced enhancement of endothelin-1-induced vasoconstriction, ET(A) receptor expression and ERK expression/activity in the aorta. Losartan improved both the diabetes-related abnormalities and the diabetic hypertension.

Gender differences in vascular reactivity to endothelin-1 (1-31) in mesenteric arteries from diabetic mice

Endothelin-1 (1-31) [ET-1 (1-31)], a novel member of the ET family, comprises 31 amino acids and is derived from the selective hydrolysis of big ET-1 by chymase. Although ET-1 (1-31) reportedly exerts biological effects by direct or indirect [via its conversion to ET-1 (1-21)] mechanisms, it is unclear whether in diabetes the vascular effects of ET-1 (1-31) display gender differences. We investigated this question by exposing mesenteric artery rings to ET-1 (1-31), using arteries from mice in the early or chronic phase of diabetes. In the early stage of diabetes, the ET-1 (1-31)-induced contraction was similar between age- and sex-matched control and streptozotocin (STZ)-induced diabetic mice. In the chronic stage of diabetes, the ET-1 (1-31)-induced contraction was enhanced in diabetic female mice, but not in diabetic male mice (vs. both age-matched control and early-stage diabetic mice). This enhancement was largely prevented by Y27632 (Rho kinase inhibitor), PD98059 [inhibitor of extracellular signal related kinases 1 and 2 (ERK1/2)], or SP600125 [C-jun terminal kinase (JNK) inhibitor]. These data indicate that the ET-1 (1-31)-induced vasoconstriction in the mesenteric artery may be specifically enhanced in established diabetic female mice, and that this enhancement may be due to alterations in the activities of Rho/Rho kinase or mitogen-activated protein kinase.

Metformin normalizes endothelial function by suppressing vasoconstrictor prostanoids in mesenteric arteries from OLETF rats, a model of type 2 diabetes

We previously reported that in mesenteric arteries from aged Otsuka Long-Evans Tokushima fatty (OLETF) rats (a type 2 diabetes model) endothelium-derived hyperpolarizing factor (EDHF)-type relaxation is impaired while endothelium-derived contracting factor (EDCF)-mediated contraction is enhanced (Matsumoto T, Kakami M, Noguchi E, Kobayashi T, Kamata K. Am J Physiol Heart Circ Physiol 293: H1480-H1490, 2007). Here we investigated whether acute and/or chronic treatment with metformin might improve this imbalance between the effects of the above endothelium-derived factors in mesenteric arteries isolated from OLETF rats. In acute studies on OLETF mesenteric arteries, ACh-induced relaxation was impaired and the relaxation became weaker at high ACh concentrations. Both metformin and 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside [AICAR, an AMP-activated protein kinase (AMPK) activator that is also activated by metformin] 1) diminished the tendency for the relaxation to reverse at high ACh concentrations and 2) suppressed both ACh-induced EDCF-mediated contraction and ACh-stimulated production of prostanoids (thromboxane A2 and PGE2). In studies on OLETF arteries from chronically treated animals, metformin treatment (300 mg.kg(-1).day(-1) for 4 wk) 1) improved ACh-induced nitric oxide- or EDHF-mediated relaxation and cyclooxygenase (COX)-mediated contraction, 2) reduced EDCF-mediated contraction, 3) suppressed production of prostanoids, and 4) reduced superoxide generation. Metformin did not alter the protein expressions of endothelial nitric oxide synthase (eNOS), phospho-eNOS (Ser1177), or COX-1, but it increased COX-2 protein. These results suggest that metformin improves endothelial functions in OLETF mesenteric arteries by suppressing vasoconstrictor prostanoids and by reducing oxidative stress. Our data suggest that within the timescale studied here, metformin improves endothelial function through this direct mechanism, rather than by improving metabolic abnormalities.

Imbalance between endothelium-derived relaxing and contracting factors in mesenteric arteries from aged OLETF rats, a model of Type 2 diabetes

We investigated whether the balance between endothelium-derived relaxing factors (EDRFs) and endothelium-derived contracting factors (EDCFs) might be altered in mesenteric arteries from aged Otsuka Long-Evans Tokushima Fatty (OLETF) rats (a Type 2 diabetic model) [vs. age-matched control Long-Evans Tokushima Otsuka (LETO) rats]. ACh-induced relaxation was impaired in the OLETF group, and a tendency for the relaxation to reverse at high ACh concentrations was observed in both groups. This tendency was abolished by indomethacin. Nitric oxide- and/or endothelium-derived hypolarizing factor-mediated relaxation and the protein expressions of phospho-endothelial nitric oxide synthase (Ser1177) and extracellular superoxide dismutase were also reduced in OLETF. An ACh-induced contraction was observed at higher ACh concentrations in the presence of NG-nitro-l-arginine (l-NNA) but was greater in OLETF rats. This contraction in OLETF rats was reduced by cyclooxygenase (COX) inhibitors and by prostanoid-receptor antagonists. The ACh-induced productions of thromboxane A2 and PGE2 were greater in OLETF than LETO rats, as were the mesenteric artery COX-1 and COX-2 protein expressions. Moreover, tert-butyl hydroperoxide ( t-BOOH) (membrane-permeant oxidant) induced a concentration-dependent contraction that was greater in OLETF rats. The t-BOOH-mediated contraction was increased both by l-NNA and by endothelium removal in LETO but not OLETF rats, suggesting that a negative modulatory role of the endothelium was lost in OLETF rats. These results suggest that an imbalance between EDRFs and EDCFs may be implicated in the endothelial dysfunction seen in aged OLETF mesenteric arteries, and may be attributable to increased oxidative stress.