Effects of a Western diet versus high glucose on endothelium-dependent relaxation in murine micro- and macro-vasculature

Sex, Endothelial Cell Functions, and Peripheral Artery Disease

Peripheral artery disease (PAD) is caused by blocked arteries due to atherosclerosis and/or thrombosis which reduce blood flow to the lower limbs. It results in major morbidity, including ischemic limb, claudication, and amputation, with patients also suffering a heightened risk of heart attack, stroke, and death. Recent studies suggest women have a higher prevalence of PAD than men, and with worse outcomes after intervention. In addition to a potential unconscious bias faced by women with PAD in the health system, with underdiagnosis, and lower rates of guideline-based therapy, fundamental biological differences between men and women may be important. In this review, we highlight sexual dimorphisms in endothelial cell functions and how they may impact PAD pathophysiology in women. Understanding sex-specific mechanisms in PAD is essential for the development of new therapies and personalized care for patients with PAD.

AFM-based nanoindentation indicates an impaired cortical stiffness in the AAV-PCSK9DY atherosclerosis mouse model

Investigating atherosclerosis and endothelial dysfunction has mainly become established in genetically modified ApoE^−/− or LDL-R^−/− mice transgenic models. A new AAV-PCSK9DY^DY mouse model with no genetic modification has now been reported as an alternative atherosclerosis model. Here, we aimed to employ this AAV-PCSK9^DY mouse model to quantify the mechanical stiffness of the endothelial surface, an accepted hallmark for endothelial dysfunction and forerunner for atherosclerosis. Ten-week-old male C57BL/6 N mice were injected with AAV-PCSK9^DY (0.5, 1 or 5 × 10¹¹ VG) or saline as controls and fed with Western diet (1.25% cholesterol) for 3 months. Total cholesterol (TC) and triglycerides (TG) were measured after 6 and 12 weeks. Aortic sections were used for atomic force microscopy (AFM) measurements or histological analysis using Oil-Red-O staining. Mechanical properties of in situ endothelial cells derived from ex vivo aorta preparations were quantified using AFM-based nanoindentation. Compared to controls, an increase in plasma TC and TG and extent of atherosclerosis was demonstrated in all groups of mice in a viral load-dependent manner. Cortical stiffness of controls was 1.305 pN/nm and increased (10%) in response to viral load (≥ 0.5 × 10¹¹ VG) and positively correlated with the aortic plaque content and plasma TC and TG. For the first time, we show changes in the mechanical properties of the endothelial surface and thus the development of endothelial dysfunction in the AAV-PCSK9^DY mouse model. Our results demonstrate that this model is highly suitable and represents a good alternative to the commonly used transgenic mouse models for studying atherosclerosis and other vascular pathologies.

Thioredoxin deficiency exacerbates vascular dysfunction during diet-induced obesity in small mesenteric artery in mice

OBJECTIVE

Thioredoxin (Trx) is a small cellular redox protein with established antioxidant and disulfide reductase properties. We hypothesized that Trx deficiency in mice would cause increased oxidative stress with consequent redox imbalance that would exacerbate obesity-induced vascular dysfunction.

METHODS

Non-transgenic (NT, C57BL/6) and dominant-negative Trx (dnTrx-Tg, low levels of redox-active protein) mice were either fed a normal diet (NC) or high fat diet plus sucrose (HFS) diet for 4 months (3-month HFD+ 1-month HFS). Weight gain, glucose tolerance test (GTT), insulin tolerance test (ITT), and other metabolic parameters were performed following NC or HFS diet. Arterial structural remodeling and functional parameters were assessed by myography.

RESULTS

Our study found that dnTrx mice with lower levels of active Trx exacerbated myogenic tone, inward arterial remodeling, arterial stiffening, phenylephrine-induced contraction, and endothelial dysfunction of MA. Additionally, FeTMPyP, a peroxynitrite decomposition catalyst, acutely decreased myogenic tone and contraction and normalized endothelial function in MA from dnTrx-Tg mice on HFS via increasing nitric oxide (NO)-mediated relaxation.

CONCLUSIONS

Our results indicate that deficiency of active Trx exacerbates MA contractile and relaxing properties during diet-induced obesity demonstrating that loss of redox balance in obesity is a key mechanism of vascular endothelial dysfunction.

Mouse models of atherosclerosis and their suitability for the study of myocardial infarction

Atherosclerotic plaques impair vascular function and can lead to arterial obstruction and tissue ischaemia. Rupture of an atherosclerotic plaque within a coronary artery can result in an acute myocardial infarction, which is responsible for significant morbidity and mortality worldwide. Prompt reperfusion can salvage some of the ischaemic territory, but ischaemia and reperfusion (IR) still causes substantial injury and is, therefore, a therapeutic target for further infarct limitation. Numerous cardioprotective strategies have been identified that can limit IR injury in animal models, but none have yet been translated effectively to patients. This disconnect prompts an urgent re-examination of the experimental models used to study IR. Since coronary atherosclerosis is the most prevalent morbidity in this patient population, and impairs coronary vessel function, it is potentially a major confounder in cardioprotective studies. Surprisingly, most studies suggest that atherosclerosis does not have a major impact on cardioprotection in mouse models. However, a major limitation of atherosclerotic animal models is that the plaques usually manifest in the aorta and proximal great vessels, and rarely in the coronary vessels. In this review, we examine the commonly used mouse models of atherosclerosis and their effect on coronary artery function and infarct size. We conclude that none of the commonly used strains of mice are ideal for this purpose; however, more recently developed mouse models of atherosclerosis fulfil the requirement for coronary artery lesions, plaque rupture and lipoprotein patterns resembling the human profile, and may enable the identification of therapeutic interventions more applicable in the clinical setting.

Targeting the Endothelial Ca2+ Toolkit to Rescue Endothelial Dysfunction in Obesity Associated-Hypertension

BACKGROUND

Obesity is a major cardiovascular risk factor which dramatically impairs endothelium- dependent vasodilation and leads to hypertension and vascular damage. The impairment of the vasomotor response to extracellular autacoids, e.g., acetylcholine, mainly depends on the reduced Nitric Oxide (NO) bioavailability, which hampers vasorelaxation in large conduit arteries. In addition, obesity may affect Endothelium-Dependent Hyperpolarization (EDH), which drives vasorelaxation in small resistance arteries and arterioles. Of note, endothelial Ca2+ signals drive NO release and trigger EDH.

METHODS

A structured search of bibliographic databases was carried out to retrieve the most influential, recent articles on the impairment of vasorelaxation in animal models of obesity, including obese Zucker rats, and on the remodeling of the endothelial Ca2+ toolkit under conditions that mimic obesity. Furthermore, we searched for articles discussing how dietary manipulation could be exploited to rescue Ca2+-dependent vasodilation.

RESULTS

We found evidence that the endothelial Ca2+ could be severely affected by obese vessels. This rearrangement could contribute to endothelial damage and is likely to be involved in the disruption of vasorelaxant mechanisms. However, several Ca2+-permeable channels, including Vanilloid Transient Receptor Potential (TRPV) 1, 3 and 4 could be stimulated by several food components to stimulate vasorelaxation in obese individuals.

CONCLUSION

The endothelial Ca2+ toolkit could be targeted to reduce vascular damage and rescue endothelium- dependent vasodilation in obese vessels. This hypothesis remains, however, to be probed on truly obese endothelial cells.

Decreased EDHF-mediated relaxation is a major mechanism in endothelial dysfunction in resistance arteries in aged mice on prolonged high-fat sucrose diet

High‐fat sucrose (HFS) diet in aged individuals causes severe weight gain (obesity) with much higher risk of cardiovascular diseases such as hypertension or atherosclerosis. Endothelial dysfunction is a major contributor for these vascular disorders. We hypothesize that prolonged ingestion of HFS diet by aged mice would accentuate endothelial dysfunction in the small resistance arteries. Male C57BL/6J mice at 12 weeks of age were divided into four groups and fed either normal chow (NC) or high‐fat sucrose diet (HFS). Young group received NC for 4 months, and high‐fat diet (HFD) for 3 months and 1 month HFS + 10% Sucrose (HFS diet). Aged mice received NC for 12 months. Aged HFS group received HFD for 4 months + 1 month HFD + 10% sucrose + 8 months HFD. Total body weight, plasma blood glucose levels, and glucose tolerance were determined in all groups. Isolated mesenteric arteries were assessed for arterial remodeling, myogenic tone, and vasomotor responses using pressure and wire myography. Both young and aged HFS mice showed impaired glucose tolerance (Y‐NC, 137 ± 8.5 vs. Y‐NC HFS, 228 ± 11.71; A‐NC, 148 ± 6.42 vs. A‐HFS, 225 ± 10.99), as well as hypercholesterolemia (Y‐NC 99.50 ± 6.35 vs. Y‐HFS 220.40 ± 16.34 mg/dL; A‐NC 108.6 ± vs. A‐HFS 279 ± 21.64) and significant weight gain (Y‐NC 32.13 ± 0.8 g vs. Y‐HFS 47.87 ± 2.18 g; A‐NC 33.72 vs. A‐HFS 56.28 ± 3.47 g) compared to both groups of mice on NC. The mesenteric artery from mice with prolonged HFS diet resulted in outward hypertrophic remodeling, increased stiffness, reduced myogenic tone, impaired vasodilation, increased contractility and blunted nitric oxide (NO) and EDH‐mediated relaxations. Ebselen, a peroxinitrite scavenger rescued the endothelium derived relaxing factor (EDHF)‐mediated relaxations. Our findings suggest that prolonged diet‐induced obesity of aged mice can worsen small resistance artery endothelial dysfunction due to decrease in NO and EDHF‐mediated relaxation, but, EDHF‐mediated relaxation is a major contributor to overall endothelial dysfunction.

Apigenin and naringenin ameliorate PKCβII-associated endothelial dysfunction via regulating ROS/caspase-3 and NO pathway in endothelial cells exposed to high glucose

Endothelial dysfunction is a key event in the progression of atherosclerosis with diabetes. Increasing cell apoptosis may lead to endothelial dysfunction. Apigenin and naringenin are two kinds of widely used flavones. In the present study, we investigated whether and how apigenin and naringenin reduced endothelial dysfunction induced by high glucose in endothelial cells. We showed that apigenin and naringenin protected against endothelial dysfunction via inhibiting phosphorylation of protein kinase C βII (PKCβII) expression and downstream reactive oxygen species (ROS) production in endothelial cells exposed to high glucose. Furthermore, we demonstrated that apigenin and naringenin reduced high glucose-increased apoptosis, Bax expression, caspase-3 activity and phosphorylation of NF-κB in endothelial cells. Moreover, apigenin and naringenin effectively restored high glucose-reduced Bcl-2 expression and Akt phosphorylation. Importantly, apigenin and naringenin significantly increased NO production in endothelial cells subjected to high glucose challenge. Consistently, high glucose stimulation impaired acetylcholine (ACh)-mediated vasodilation in the rat aorta, apigenin and naringenin treatment restored the impaired endothelium-dependent vasodilation via dramatically increasing eNOS activity and nitric oxide (NO) level. Taken together, our results manifest that apigenin and naringenin can ameliorate endothelial dysfunction via regulating ROS/caspase-3 and NO pathway.

Protective effect of resveratrol and quercetin on in vitro-induced diabetic mouse corpus cavernosum

BACKGROUND

Hyperglycemia and increased levels of methylglyoxal (MGO) can trigger the development of vascular complications in diabetes. Resveratrol and quercetin are red wine polyphenols with known beneficial cardiovascular properties, including an antioxidant capacity. This study evaluated whether resveratrol and/or quercetin could prevent in vitro-induced diabetic changes in neurogenic and vascular relaxant responses of mouse arteries and corpora cavernosa.

METHODS

Isometric tension of isolated aorta, mesenteric arteries and corpora cavernosa was measured using organ bath systems. Diabetic conditions were mimicked in vitro by co-incubating the tissues for 2 h with high glucose (HG, 30 mM) and MGO (120 µM).

RESULTS

The presence of HG and MGO significantly blunted acetylcholine (Ach)-induced relaxations in corpora cavernosa and mesenteric arteries but not in aorta. Electrical field stimulated (EFS) responses of corpora cavernosa were also significantly inhibited by these diabetic conditions. In corpora cavernosa 2 h co-incubation with resveratrol (30 µM) or quercetin (30 µM) significantly attenuated HG and MGO-induced deficits in Ach- and EFS-responses.

CONCLUSIONS

Our study demonstrates that in mouse arteries, HG and MGO rather affect endothelium derived hyperpolarizing factor-mediated than nitric oxide (NO)-mediated relaxations. In corpora cavernosa HG and MGO interfere with NO release. Resveratrol and quercetin protect mouse corpora cavernosa from diabetic-induced damage to NO-mediated relaxant responses. This might rely on their antioxidant capacity.

Inhibition of differentiation of monocyte to macrophages in atherosclerosis by oligomeric proanthocyanidins -In-vivo and in-vitro study

Monocyte to macrophage differentiation is a key event in the progression of atherosclerosis. An understanding on the fundamental molecular mechanisms and the identification of regulatory mechanisms behind this differentiation may aid in the identification of new therapeutic strategies. Inhibition of this phenomenon will form first line of defense in the prevention and treatment of atherosclerosis. In the current study we explored hypercholesterolemia induced monocyte to macrophage differentiation in-vivo (Wistar rats) leading to atherosclerosis and OxyLDL, M-CSF induced monocyte differentiation in-vitro (U937 cells). Oligomeric proanthocyanidin (OPC) isolated from Crataegus oxyacantha was tested for its efficacy in downregulating this differentiation and in preventing atherogenic disturbances. Cholesterol cholic acid diet induced an increased monocyte to macrophage differentiation by upregulating MCP1 and VCAM1 which induced the inflammatory cytokines that further substantiated the monocyte conversion and infiltration into the vascular walls. On addition of OxyLDL and M-CSF to U937 cells, macrophage markers CD36 and CD 68, PPARγ, MMP2 and 9 were elevated, suggesting differentiation. OPC downregulated this differentiation and thus could prevent the initiation of atherosclerosis.

Upregulation of SK3 and IK1 channels contributes to the enhanced endothelial calcium signaling and the preserved coronary relaxation in obese Zucker rats

Background and Aims

Endothelial small- and intermediate-conductance K_Ca channels, SK3 and IK1, are key mediators in the endothelium-derived hyperpolarization and relaxation of vascular smooth muscle and also in the modulation of endothelial Ca²⁺ signaling and nitric oxide (NO) release. Obesity is associated with endothelial dysfunction and impaired relaxation, although how obesity influences endothelial SK3/IK1 function is unclear. Therefore we assessed whether the role of these channels in the coronary circulation is altered in obese animals.

Methods and Results

In coronary arteries mounted in microvascular myographs, selective blockade of SK3/IK1 channels unmasked an increased contribution of these channels to the ACh- and to the exogenous NO- induced relaxations in arteries of Obese Zucker Rats (OZR) compared to Lean Zucker Rats (LZR). Relaxant responses induced by the SK3/IK1 channel activator NS309 were enhanced in OZR and NO- endothelium-dependent in LZR, whereas an additional endothelium-independent relaxant component was found in OZR. Fura2-AM fluorescence revealed a larger ACh-induced intracellular Ca²⁺ mobilization in the endothelium of coronary arteries from OZR, which was inhibited by blockade of SK3/IK1 channels in both LZR and OZR. Western blot analysis showed an increased expression of SK3/IK1 channels in coronary arteries of OZR and immunohistochemistry suggested that it takes place predominantly in the endothelial layer.

Conclusions

Obesity may induce activation of adaptive vascular mechanisms to preserve the dilator function in coronary arteries. Increased function and expression of SK3/IK1 channels by influencing endothelial Ca²⁺ dynamics might contribute to the unaltered endothelium-dependent coronary relaxation in the early stages of obesity.

Body adiposity dictates different mechanisms of increased coronary reactivity related to improved in vivo cardiac function

BACKGROUND

Saturated fatty acid-rich high fat (HF) diets trigger abdominal adiposity, insulin resistance, type 2 diabetes and cardiac dysfunction. This study was aimed at evaluating the effects of nascent obesity on the cardiac function of animals fed a high-fat diet and at analyzing the mechanisms by which these alterations occurred at the level of coronary reserve.

MATERIALS AND METHODS

Rats were fed a control (C) or a HF diet containing high proportions of saturated fatty acids for 3 months. Thereafter, their cardiac function was evaluated in vivo using a pressure probe inserted into the cavity of the left ventricle. Their heart was isolated, perfused iso-volumetrically according to the Langendorff mode and the coronary reserve was evaluated by determining the endothelial-dependent (EDV) and endothelial-independent (EIV) vasodilatations in the absence and presence of endothelial nitric oxide synthase and cyclooxygenase inhibitors (L-NAME and indomethacin). The fatty acid composition of cardiac phospholipids was then evaluated.

RESULTS

Although all the HF-fed rats increased their abdominal adiposity, some of them did not gain body weight (HF- group) compared to the C group whereas other ones had a higher body weight (HF+). All HF rats displayed a higher in vivo cardiac activity associated with an increased EDV. In the HF- group, the improved EDV was due to an increase in the endothelial cell vasodilatation activity whereas in the HF+ group, the enhanced EDV resulted from an improved sensitivity of coronary smooth muscle cells to nitric oxide. Furthermore, in the HF- group the main pathway implicated in the EDV was the NOS pathway while in the HF+ group the COX pathway.

CONCLUSIONS

Nascent obesity-induced improvement of cardiac function may be supported by an enhanced coronary reserve occurring via different mechanisms. These mechanisms implicate either the endothelial cells activity or the smooth muscle cells sensitivity depending on the body adiposity of the animals.

The microcirculation in adipose tissue inflammation

In most humans, obesity is associated with a chronic low-grade inflammatory reaction occurring in several organ tissues, including the adipose tissue. Infiltration of bone marrow derived leukocytes (granulocytes, monocytes, lymphocytes) into expanding adipose depots appears to be an integral component of inflammation in obesity. Circulating leukocytes invade organ tissues mainly through post-capillary venules in the microcirculation. The endothelium of the post-capillary venules acts as a gatekeeper to leukocyte adhesion and extravasation by displacing on its luminal surface adhesion molecules that bind the adhesive receptors expressed on circulating leukocytes. Several studies investigating the impact of obesity on the microcirculation have demonstrated the occurrence of microvascular dysfunction in experimental animal model of obesity, as well as in obese humans. To date though, working hypotheses and study designs have favored the view that microvascular alterations are secondary to adipose tissue dysfunction. Indeed, a significant amount of data exists in the scientific literature to support the concept that microvascular dysfunction may precede and cause adipose tissue inflammation in obesity. Through review of key published data, this article prospectively presents the concept that in response to nutrients overload the vascular endothelium of the microcirculation acutely activates inflammatory pathways that initiate infiltration of leukocytes in visceral adipose tissue, well before weight gain and overt obesity. The anatomical and physiological heterogeneity of different microcirculations is also discussed toward the understanding of how obesity induces different inflammatory phenotypes in visceral and subcutaneous fat depots.

Effects of glucose load and nateglinide intervention on endothelial function and oxidative stress

We analysed endothelial function and oxidative stress in patients with abnormal glucose metabolism, the effect of glucose load, and the impact of nateglinide. 109 participants were grouped into newly diagnosed diabetes, prediabetes, and control. Fasting plasma glucose (FPG), postprandial plasma glucose (PPG), glycosylated haemoglobin (HbA1c), and glycated albumin (GA) varied significantly among the study groups (P < 0.01). Nitric oxide (NO) and insulin resistance index (HOMA-IRI) levels were markedly different between the newly diagnosed diabetes and the control (P < 0.01). Glucose loading lowered flow-mediated endothelium-dependent dilation (FMEDD), NO, and superoxide dismutase (SOD) (P < 0.01). Fasting and glucose loading FMEDD, FPG, PPG, HbA1c, and GA were negatively correlated (r = -0.4573, -0.4602, -0.3895, -0.3897, and r = -0.4594, -0.4803, -0.4494, -0.3885; P < 0.01), whereas NO, SOD, and HOMA- β were positively correlated (r = 0.2983, 0.3211, 0.311, and r = 0.1954, 0.361, 0.2569; P < 0.05). After the treatment with nateglinide, significant decreases in FPG, PPG, GA, HbA1C, endothelin-1(ET-1), malondialdehyde (MDA), and HOMA-IRI were observed, whereas FMEDD, NO, and SOD increased (P < 0.01). Thus, the study demonstrated the adverse effect of glucose load on endothelial function and oxidative stress. Nateglinide lowers blood glucose, reduces insulin resistance and oxidative stress, and improves endothelial function in newly diagnosed diabetes.

Microvascular responsiveness in obesity: implications for therapeutic intervention

Obesity has detrimental effects on the microcirculation. Functional changes in microvascular responsiveness may increase the risk of developing cardiovascular complications in obese patients. Emerging evidence indicates that selective therapeutic targeting of the microvessels may prevent life-threatening obesity-related vascular complications, such as ischaemic heart disease, heart failure and hypertension. It is also plausible that alterations in adipose tissue microcirculation contribute to the development of obesity. Therefore, targeting adipose tissue arterioles could represent a novel approach to reducing obesity. This review aims to examine recent studies that have been focused on vasomotor dysfunction of resistance arteries in obese humans and animal models of obesity. Particularly, findings in coronary resistance arteries are contrasted to those obtained in other vascular beds. We provide examples of therapeutic attempts, such as use of statins, ACE inhibitors and insulin sensitizers to prevent obesity-related microvascular complications. We further identify some of the important challenges and opportunities going forward.

LINKED ARTICLES

This article is part of a themed section on Fat and Vascular Responsiveness. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-3.

Postprandial hyperglycemia impairs vascular endothelial function in healthy men by inducing lipid peroxidation and increasing asymmetric dimethylarginine:arginine

Postprandial hyperglycemia induces vascular endothelial dysfunction (VED) and increases future cardiovascular disease risk. We hypothesized that postprandial hyperglycemia would decrease vascular function in healthy men by inducing oxidative stress and proinflammatory responses and increasing asymmetric dimethylarginine:arginine (ADMA:arginine), a biomarker that is predictive of reduced NO biosynthesis. In a randomized, cross-over design, healthy men (n = 16; 21.6 ± 0.8 y) ingested glucose or fructose (75 g) after an overnight fast. Brachial artery flow-mediated dilation (FMD), plasma glucose and insulin, antioxidants, malondialdehyde (MDA), inflammatory proteins, arginine, and ADMA were measured at regular intervals during the 3-h postprandial period. Baseline FMD did not differ between trials (P > 0.05). Postprandial FMD was reduced following the ingestion of glucose only. Postprandial MDA concentrations increased to a greater extent following the ingestion of glucose compared to fructose. Plasma arginine decreased and the ratio of ADMA:arginine increased to a greater extent following the ingestion of glucose. Inflammatory cytokines and cellular adhesion molecules were unaffected by the ingestion of either sugar. Postprandial AUC(0-3 h) for FMD and MDA were inversely related (r = -0.80; P < 0.05), suggesting that hyperglycemia-induced lipid peroxidation suppresses postprandial vascular function. Collectively, these findings suggest that postprandial hyperglycemia in healthy men reduces endothelium-dependent vasodilation by increasing lipid peroxidation independent of inflammation. Postprandial alterations in arginine and ADMA:arginine also suggest that acute hyperglycemia may induce VED by decreasing NO bioavailability through an oxidative stress-dependent mechanism. Additional work is warranted to define whether inhibiting lipid peroxidation and restoring arginine metabolism would mitigate hyperglycemia-mediated decreases in vascular function.

Role of arachidonic acid lipoxygenase metabolites in acetylcholine-induced relaxations of mouse arteries

Arachidonic acid (AA) metabolites function as EDHFs in arteries of many species. They mediate cyclooxygenase (COX)- and nitric oxide (NO)-independent relaxations to acetylcholine (ACh). However, the role of AA metabolites as relaxing factors in mouse arteries remains incompletely defined. ACh caused concentration-dependent relaxations of the mouse thoracic and abdominal aorta and carotid, femoral, and mesentery arteries (maximal relaxation: 57 ± 4%, 72 ± 4%, 82 ± 3%, 80 ± 3%, and 85 ± 3%, respectively). The NO synthase inhibitor nitro-L-arginine (L-NA; 30 μM) blocked relaxations in the thoracic aorta, and L-NA plus the COX inhibitor indomethacin (10 μM) inhibited relaxations in the abdominal aorta and carotid, femoral, and mesenteric arteries (maximal relaxation: 31 ± 10%, 33 ± 5%, 41 ± 8%, and 73 ± 3%, respectively). In mesenteric arteries, NO- and COX-independent relaxations to ACh were inhibited by the lipoxygenase (LO) inhibitors nordihydroguaiaretic acid (NDGA; 10 μM) and BW-755C (200 μM), the K(+) channel inhibitor apamin (1 μM), and 60 mM KCl and eliminated by endothelium removal. They were not altered by the cytochrome P-450 inhibitor N-methylsulfonyl-6-(2-propargyloxyphenyl)hexanamide (20 μM) or the epoxyeicosatrienoic acid antagonist 14,15-epoxyeicosa-5(Z)-enoic acid (10 μM). AA relaxations were attenuated by NDGA or apamin and eliminated by 60 mM KCl. Reverse-phase HPLC analysis revealed arterial [(14)C]AA metabolites that comigrated with prostaglandins, trihydroxyeicosatrienoic acids (THETAs), hydroxyepoxyeicosatrienoic acids (HEETAs), and hydroxyeicosatetraenoic acids (HETEs). Epoxyeicosatrienoic acids were not observed. Mass spectrometry confirmed the identity of 6-keto-PGF(1α), PGE(2), 12-HETE, 15-HETE, HEETAs, 11,12,15-THETA, and 11,14,15-THETA. AA metabolism was blocked by NDGA and endothelium removal. 11(R),12(S),15(S)-THETA relaxations (maximal relaxation: 73 ± 3%) were endothelium independent and blocked by 60 mM KCl. Western immunoblot analysis and RT-PCR of the aorta and mesenteric arteries demonstrated protein and mRNA expression of leukocyte-type 12/15-LO. Thus, in mouse resistance arteries, 12/15-LO AA metabolites mediate endothelium-dependent relaxations to ACh and AA.

An interaction of the pre- and post-weaning diets rich in omega-6 polyunsaturated fats alters plasma lipids, hepatic gene expression and aortic vascular reactivity in adult C57BL/6 mice

Aim:

To investigate the effects of diets rich in n-6 polyunsaturated fats (PUFA) fed during pre- and post-weaning time periods on the lipid metabolism and vascular reactivity in adult C57Bl/6 mice, in order to assess the impact of maternal nutrition and its interaction with the offspring diet on the metabolism of adult offspring.

Methods:

Female C57Bl/6 mice were fed a high-fat diet enriched with n-6 PUFA (P) or control diet (C) for 2-weeks before, during mating, gestation and lactation, while their pups received either P or C for 8-weeks post-weaning.

Results:

A significant interaction between the maternal and post-weaning diets was observed for the offspring body weight, food-, caloric-intake, plasma lipids, hepatic mRNA expression of lecithin cholesterol acyltransferase, aortic contractile and relaxation responses (P < 0.05).

Conclusion:

The overall metabolic and physiological outcome in the offspring is dependent upon the interaction between the pre- and post-weaning dietary environments.

Caveolin-1 limits the contribution of BK(Ca) channel to EDHF-mediated arteriolar dilation: implications in diet-induced obesity

AIMS

Caveolin-1 (Cav-1) interacts with large conductance Ca(2+)-activated potassium channels (BKCa) and likely exerts a negative regulatory effect on the channel activity. We investigated the role of Cav-1 in modulating BK(Ca) channel-mediated, endothelium-derived hyperpolarizing factor (EDHF)-dependent arteriolar dilation in normal condition and in an experimental model of obesity.

METHODS AND RESULTS

In isolated, pressurized (80 mmHg) gracilis muscle arterioles (approximately 100 microm) of Cav-1 knockout mice, acetylcholine (ACh)-induced, EDHF-mediated dilations were enhanced and were significantly reduced by the BK(Ca) channel inhibitor, iberiotoxin (IBTX), whereas IBTX had no effect on EDHF-mediated dilations in the wild-type mice. Dilations to the selective BK(Ca) channel opener, NS-1619 were augmented in the Cav-1 knockout mice. In high-fat diet-treated, obese rats ACh-induced coronary arteriolar dilations were preserved, whereas IBTX-sensitive, ACh-induced and also NS-1619-evoked vasodilations were augmented when compared with lean animals. In coronary arterioles of obese rats a reduced protein expression of Cav-1 was detected by western immunoblotting and immunohistochemistry. Moreover, in coronary arterioles of lean rats, disruption of caveolae with methyl-beta-cyclodextrin augmented IBTX-sensitive, ACh-induced, and also NS-1619-evoked dilations.

CONCLUSION

Thus, under normal conditions, Cav-1 limits the contribution of the BK(Ca) channel to EDHF-mediated arteriolar dilation. In obesity, a reduced expression of Cav-1 leads to greater contribution of the BK(Ca) channel to EDHF-mediated response, which seems essential for maintained coronary dilation.

Novel cerebrovascular pathology in mice fed a high cholesterol diet

Background

Hypercholesterolemia causes atherosclerosis in medium to large sized arteries. Cholesterol is less known for affecting the microvasculature and has not been previously reported to induce microvascular pathology in the central nervous system (CNS).

Results

Mice with a null mutation in the low-density lipoprotein receptor (LDLR) gene as well as C57BL/6J mice fed a high cholesterol diet developed a distinct microvascular pathology in the CNS that differs from cholesterol-induced atherosclerotic disease. Microvessel diameter was increased but microvascular density and length were not consistently affected. Degenerative changes and thickened vascular basement membranes were present ultrastructurally. The observed pathology shares features with the microvascular pathology of Alzheimer's disease (AD), including the presence of string-like vessels. Brain apolipoprotein E levels which have been previously found to be elevated in LDLR-/- mice were also increased in C57BL/6J mice fed a high cholesterol diet.

Conclusion

In addition to its effects as an inducer of atherosclerosis in medium to large sized arteries, hypercholesterolemia also induces a microvascular pathology in the CNS that shares features of the vascular pathology found in AD. These observations suggest that high cholesterol may induce microvascular disease in a range of CNS disorders including AD.

Mechanisms of coronary microvascular adaptation to obesity

The metabolic syndrome (MetS) is associated with clustering of cardiovascular risk factors in individuals that may greatly increase their risk of developing coronary artery disease. Obesity and related metabolic dysfunction are the driving forces in the prevalence of MetS. It is believed that obesity has detrimental effects on cardiovascular function, but its overall impact on the vasomotor regulation of small coronary arteries is still debated. Emerging evidence indicates that in obesity coronary arteries adapt to hemodynamic changes via maintaining and/or upregulating cellular mechanism(s) intrinsic to the vascular wall. Among other factors, endothelial production of cyclooxygenase-2-derived prostacyclin and reactive oxygen species, as well as increased nitric oxide sensitivity and potassium channel activation in smooth muscle cells, have been implicated in maintaining coronary vasodilator function. This review aims to examine studies that have been primarily focused on alterations in coronary vasodilator function in obesity. A better understanding of cellular mechanisms that may contribute to coronary microvascular adaptation may provide insight into the sequence of pathological events in obesity and may allow the harnessing of these effects for therapeutic purposes.

Current concepts in diabetic gastroparesis

Diabetic gastroparesis is a common and debilitating condition affecting millions of patients with diabetes mellitus worldwide. Although gastroparesis in diabetes has been known clinically for more than 50 years, treatment options remain very limited. Until recently, the scientific literature has offered few clues regarding the precise aetiology of gastric dysfunction in diabetes.Up to 50% of patients with diabetes may experience postprandial abdominal pain, nausea, vomiting and bloating secondary to gastric dysfunction. There is no clear association between length of disease and the onset of delayed gastric emptying. Gastroparesis affects both type 1 (insulin dependent) and type 2 (non- insulin dependent) forms of diabetes. Diagnosis requires identifying the proper symptom complex, while excluding other entities (peptic ulcer disease, rheumatological diseases, medication effects). The diagnosis of gastroparesis may be confirmed by demonstrating gastric emptying delay during a 4-hour scintigraphic study. Treatment options are limited and rely on dietary modifications, judicious use of available pharmacological agents, and occasionally surgical or endoscopic placement of gastrostomies or jejunostomies. Gastric pacing offers promise for patients with medically refractory gastroparesis but awaits further investigation. Current pharmacological agents for treating gastroparesis include metoclopramide, erythromycin, cisapride (only available via a company-sponsored programme) and domperidone (not US FDA approved). All of these drugs act as promotility agents that increase the number or the intensity of gastric contractions. These medications are not uniformly effective and all have adverse effects that limit their use. Cisapride has been removed from the open market as a result of over 200 reported cases of cardiac toxicity attributed to its use. Unfortunately, there is a paucity of clinical studies that clearly define the efficacy of these agents in diabetic gastroparesis and there are no studies that compare these drugs to each other. The molecular pathophysiology of diabetic gastroparesis is unknown, limiting the development of rational therapies. New studies, primarily in animals, point to a defect in the enteric nervous system as a major molecular cause of abnormal gastric motility in diabetes. This defect is characterised by a loss of nitric oxide signals from nerves to muscles in the gut resulting in delayed gastric emptying. Novel therapies designed to augment nitric oxide signalling are being studied.