Lack of role for nitric oxide (NO) in the selective destabilization of endothelial NO synthase mRNA by tumor necrosis factor-alpha

Effects of aurantiamide on a rat model of renovascular arterial hypertension

Asperglaucide (ASP) is an aurantiamide, an effective constituent of purslane (Portulaca oleracea L.), a safe to eat greenery. Effects of ASP on endothelial function, endothelial nitric oxide synthase (eNOS) expression, vascular fluidity, renal and vascular reactive oxygen, and nitrogen species (ROS/RNS) production was examined in the two-kidney one-clip (2 K-1C) rat model of renovascular arterial hypertension. ASP toxicity, dose dependent eNOS gene expression and protein levels were also analyzed in human umbilical vein endothelial cells (HUVEC). The 2 K-1C model of hypertension was created via surgery and mean blood pressure (MBP) was measured by tail-cuff method during four weeks of ASP treatment. Erythrocyte deformability was monitored by rotational ektacytometry, while vascular constrictor and dilator responses were determined in organ baths. eNOS gene expression and protein levels were assessed in thoracic aorta and HUVEC. MBP was significantly decreased in hypertensive rats treated with ASP. Endothelium dependent vascular dilator and constrictor responses were also considerably improved following ASP treatment. There was a notable increase in red blood cell deformability in hypertensive rats treated with ASP as compared to hypertensive rats alone. A significant increase was observed in eNOS gene expression and protein levels in both normotensive and hypertensive rats treated with ASP. Treatment of HUVEC with 3 µM ASP notably increased eNOS mRNA and protein levels. In conclusion, ASP lowered blood pressure, improved endothelium-mediated relaxation, decreased renovascular ROS/RNS production in hypertensive rats. ASP also increased eNOS protein expression in aorta and HUVEC at nontoxic doses. ASP may have future potential as an anti-hypertensive agent.

Beneficial effects of capsaicin and dihydrocapsaicin on endothelial inflammation, nitric oxide production and antioxidant activity

Capsaicin and dihydrocapsaicin (DHC) are major pungent capsaicinoids produced in chili peppers. Capsaicin has been previously shown to promote vascular health by increasing nitric oxide (NO) production and reducing inflammatory responses. While capsaicin has been extensively studied, whether DHC exerts cardiovascular benefits through similar mechanisms remains unclear. The current study aimed to investigate the direct effects of DHC on endothelial inflammation, NO release, and free radical scavenging properties. DHC at concentrations up to 50 µM did not affect cell viability, while concentrations of 100 and 500 µM of DHC led to endothelial cytotoxicity. Capsaicin decreased cell viability at concentration of 500 µM. To investigate the effects of capsaicinoids on endothelial activation, we first demonstrated that TNFα induced Ser536 phosphorylation of p65 NFκB, expressions of adhesion molecules, vascular cell adhesion molecule (VCAM)-1 and intercellular adhesion molecule (ICAM)-1, and IL-6 production in primary human endothelial cells. These effects were robustly abrogated by DHC. Consistently, DHC treatment led to a marked reduction in TNFα-mediated monocyte adhesion to endothelial cells. Additionally, NO production was significantly induced by DHC and capsaicin compared to vehicle control. Similar to capsaicin and vitamin C, DHC scavenged DPPH (1,1-diphenyl-2-picrylhydrazyl) free radicals in vitro. Our present study highlights the benefits of DHC and capsaicin treatment on human endothelial cells and provides evidence to support cardiovascular benefits from capsicum consumption.

[Type 2 Diabetes and Vascular Endothelial Dysfunction]

Vascular endothelial function is important for maintaining the homeostasis of the living body. Especially, nitric oxide (NO) produced in vascular endothelial cells regulates blood vessel tone and has an antiatherosclerotic effect. Type 2 diabetes is a typical disease that causes impaired vascular endothelial function, resulting in various vascular complications and damage to organs. Cardiovascular disease associated with type 2 diabetes is a chronic inflammatory disease that starts with endothelial dysfunction (ED), and vascular ED is important as an initial change in arteriosclerotic lesions. Vascular ED in type 2 diabetes is thought to be caused by hyperglycemia, hyperinsulinemia associated with insulin resistance, and hypoglycemia, in which elevated oxidative stress accompanying postprandial hyperglycemia and blood glucose fluctuation are involved. Vascular ED is also caused by postprandial metabolic abnormalities, so correcting postprandial metabolic abnormalities is also important. Meanwhile, Glucagon-like peptide-1 (GLP-1) receptor agonist, thiazolidine, biguanide and Dipeptidyl peptidase-4 (DPP-4) inhibitor have an effect of protecting vascular endothelial function beyond glycemic control. In order to promote a healthy lifestyle for diabetes patients, it is important not only to lower HbA1c but also to avoid postprandial hyperglycemia, blood glucose fluctuation, and hypoglycemia. It is also important to conduct treatment with a view to suppressing vascular complications, such as the selection of antiarteriosclerosis medications.

Periaortic Adipose Tissue Compared With Peribrachial Adipose Tissue Mass as Markers and Possible Modulators of Cardiometabolic Risk

Increased perivascular fat mass contributes to cardiometabolic risk (CMR). High peribrachial adipose tissue (PBAT) associates with insulin resistance independently of established CMR parameters. It is unknown to what extent periaortic adipose tissue (PAAT) may have a similar impact. In 95 participants, precise quantification of total adipose tissue, PBAT, PAAT, visceral adipose tissue (VAT), and liver fat (LF) content was performed by whole-body magnetic resonance imaging. Insulin sensitivity was determined by oral glucose tolerance test and carotid intima-media thickness (cIMT) by high-resolution ultrasound. In univariate analyses, PAAT correlated with PBAT (β = .65, P < .0001). A negative correlation of PAAT (β = -.35, P = .0002) and PBAT (β = -.43, P < .0001) with insulin sensitivity was observed. While in a stepwise forward regression analysis the relationship of PAAT with insulin sensitivity was no longer significant after adjustment for VAT, LF content, and other CMR factors ( P = 0.42), PBAT still correlated with insulin sensitivity ( r² = .35, P = .01). The association between PAAT and cIMT (β = .49, P < .0001) remained significant after adjustment for these variables ( r² = .42, P = .0001). Although PAAT and PBAT strongly correlate, PAAT is not associated with insulin resistance, but with cIMT. Therefore, PAAT and PBAT may act differently as possible modulators of insulin resistance and subclinical atherosclerosis.

The Protective Effect of Antioxidants Consumption on Diabetes and Vascular Complications

Obesity and diabetes is generally accompanied by a chronic state of oxidative stress, disequilibrium in the redox balance, implicated in the development and progression of complications such as micro- and macro-angiopathies. Disorders in the inner layer of blood vessels, the endothelium, play an early and critical role in the development of these complications. Blunted endothelium-dependent relaxation and/or contractions are quietly associated to oxidative stress. Thus, preserving endothelial function and oxidative stress seems to be an optimization strategy in the prevention of vascular complications associated with diabetes. Diet is a major lifestyle factor that can greatly influence the incidence and the progression of type 2 diabetes and cardiovascular complications. The notion that foods not only provide basic nutrition but can also prevent diseases and ensure good health and longevity is now attained greater prominence. Some dietary and lifestyle modifications associated to antioxidative supply could be an effective prophylactic means to fight against oxidative stress in diabesity and complications. A significant benefit of phytochemicals (polyphenols in wine, grape, teas), vitamins (ascorbate, tocopherol), minerals (selenium, magnesium), and fruits and vegetables in foods is thought to be capable of scavenging free radicals, lowering the incidence of chronic diseases. In this review, we discuss the role of oxidative stress in diabetes and complications, highlight the endothelial dysfunction, and examine the impact of antioxidant foods, plants, fruits, and vegetables, currently used medication with antioxidant properties, in relation to the development and progression of diabetes and cardiovascular complications.

Elevated C-reactive protein levels and enhanced high frequency vasomotion in patients with ischemic heart disease during brachial flow-mediated dilation

PURPOSE

The physiological role of vasomotion, rhythmic oscillations in vascular tone or diameter, and its underlying mechanisms are unknown. We investigated the characteristics of brachial artery vasomotion in patients with ischemic heart disease (IHD).

METHODS

We performed a retrospective study of 37 patients with IHD. Endothelial function was assessed using flow-mediated dilation (FMD), and power spectral analysis of brachial artery diameter oscillations during FMD was performed. Frequency-domain components were calculated by integrating the power spectrums in three frequency bands (in ms2) using the MemCalc (GMS, Tokyo, Japan): very-low frequency (VLF), 0.003-0.04 Hz; low frequency (LF), 0.04-0.15 Hz; and high frequency (HF), 0.15-0.4 Hz. Total spectral power (TP) was calculated as the sum of all frequency bands, and each spectral component was normalized against TP.

RESULTS

Data revealed that HF/TP closely correlated with FMD (r = -0.33, p = 0.04), whereas VLF/TP and LF/TP did not. We also explored the relationship between elevated C-reactive protein (CRP) levels and vasomotion. HF/TP was significantly increased in subjects with high CRP levels (CRP;>0.08 mg/dL) compared with subjects with low CRP levels (0.052±0.026 versus 0.035±0.022, p<0.05). The HF/TP value closely correlated with CRP (r = 0.24, p = 0.04), whereas the value of FMD did not (r = 0.023, p = 0.84). In addition, elevated CRP levels significantly increased the value of HF/TP after adjustment for FMD and blood pressure (β = 0.33, p<0.05).

CONCLUSION

The HF component of brachial artery diameter oscillation during FMD measurement correlated well with FMD and increased in the presence of elevated CRP levels in subjects with IHD.

The effect of tumour necrosis factor-α and insulin on equine digital blood vessel function in vitro

OBJECTIVE AND DESIGN

Insulin and inflammatory cytokines may be involved in equine laminitis, which might be associated with digital vascular dysfunction. This study determined the effects of TNF-α and insulin on the endothelial-dependent relaxant responses of equine digital blood vessels and on equine digital vein endothelial cell (EDVEC) cGMP production.

MATERIAL

Isolated rings of equine digital arteries (EDAs) and veins (EDVs) were obtained and EDVECs were cultured from horses euthanized at an abattoir.

METHODS

The effect of incubation with TNF-α (10 ng/ml) and/or insulin (1,000 μIU/ml) for 1.5 h or overnight under hyperoxic and hypoxic conditions on carbachol (endothelium-dependent) induced relaxation was assessed. The time course and concentration dependency of the effect of TNF-α and the effect of insulin (1,000 μIU/ml) on EDVEC cGMP production was determined.

RESULTS

Incubation of EDAs overnight with TNF-α under hypoxic conditions resulted in endothelial-dependent vascular dysfunction. EDVs produced a more variable response. TNF-α increased EDVEC cGMP formation in a time- and concentration-dependent manner. Insulin had no significant effects.

CONCLUSIONS

There is a mismatch between the results obtained from isolated vessel rings and cultured endothelial cells suggesting TNF-α may reduce the biological effect of NO by reducing its bioavailability rather than its formation, leading to endothelial cell dysregulation.

Oxidative stress in diabetes: implications for vascular and other complications

In recent decades, oxidative stress has become a focus of interest in most biomedical disciplines and many types of clinical research. Increasing evidence shows that oxidative stress is associated with the pathogenesis of diabetes, obesity, cancer, ageing, inflammation, neurodegenerative disorders, hypertension, apoptosis, cardiovascular diseases, and heart failure. Based on these studies, an emerging concept is that oxidative stress is the “final common pathway” through which the risk factors for several diseases exert their deleterious effects. Oxidative stress causes a complex dysregulation of cell metabolism and cell–cell homeostasis; in particular, oxidative stress plays a key role in the pathogenesis of insulin resistance and β-cell dysfunction. These are the two most relevant mechanisms in the pathophysiology of type 2 diabetes and its vascular complications, the leading cause of death in diabetic patients.

Expression of endothelial nitric oxide synthase in the uterus of patients with leiomyoma or adenomyosis

AIM

To confirm the difference in the expression of endothelial nitric oxide synthase in the normal endometrium and myometrium of women who have leiomyoma or adenomyosis compared with controls, and its correlation with the pathogenesis of menorrhagia or dysmenorrhea in patients with uterine leiomyoma.

METHODS

Fifty-one hysterectomized patients were divided into three groups: (i) patients with leiomyoma (n=24); (ii) those with adenomyosis (n = 19); and (iii) the control group (n=8). The expression of endothelial nitric oxide synthase was confirmed on immunohistochemistry and analyzed using an evaluation nomogram.

RESULTS

The expression of endothelial nitric oxide synthase was significantly higher in the leiomyoma group and the adenomyosis group as compared with the control group. In the subgroup analysis of leiomyoma depending on symptoms (menorrhagia or dysmenorrhea or both), the expression of endothelial nitric oxide synthase was significantly higher in the symptomatic subgroup than the asymptomatic subgroup (endometrium P=0.0029, myometrium P=0.0276).

CONCLUSIONS

Based on the findings that the expression of endothelial nitric oxide synthase was significantly higher in the uterus with leiomyoma or adenomyosis, it can therefore be inferred that nitric oxide might have a pathological effect on the uterus with the above diseases. In particular, it is also presumed that endothelial nitric oxide synthase is closely associated with menorrhagia and dysmenorrhea.

Human obesity and endothelium-dependent responsiveness

Obesity is an ongoing worldwide epidemic. Besides being a medical condition in itself, obesity dramatically increases the risk of development of metabolic and cardiovascular disease. This risk appears to stem from multiple abnormalities in adipose tissue function leading to a chronic inflammatory state and to dysregulation of the endocrine and paracrine actions of adipocyte-derived factors. These, in turn, disrupt vascular homeostasis by causing an imbalance between the NO pathway and the endothelin 1 system, with impaired insulin-stimulated endothelium-dependent vasodilation. Importantly, emerging evidence suggests that the vascular dysfunction of obesity is not just limited to the endothelium, but also involves the other layers of the vessel wall. In particular, obesity-related changes in medial smooth muscle cells seem to disrupt the physiological facilitatory action of insulin on the responsiveness to vasodilator stimuli, whereas the adventitia and perivascular fat appear to be a source of pro-inflammatory and vasoactive factors that may contribute to endothelial and smooth muscle cell dysfunction, and to the pathogenesis of vascular disease. While obesity-induced vascular dysfunction appears to be reversible, at least in part, with weight control strategies, these have not proved sufficient to prevent the metabolic and cardiovascular complication of obesity on a large scale. While a number of currently available drugs have shown potentially beneficial vascular effects in patients with obesity and the metabolic syndrome, elucidation of the pathophysiological mechanisms underlying vascular damage in obese patients is necessary to identify additional pharmacologic targets to prevent the cardiovascular complications of obesity, and their human and economic costs.

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.

Tumor necrosis factor α decreases nitric oxide synthase type 3 expression primarily via Rho/Rho kinase in the thick ascending limb

Inappropriate Na(+) reabsorption by thick ascending limbs (THALs) induces hypertension. NO produced by NO synthase type 3 (NOS3) inhibits NaCl reabsorption by THALs. Tumor necrosis factor α (TNF-α) decreases NOS3 expression in endothelial cells and contributes to increases in blood pressure. However, the effects of TNF-α on THAL NOS3 and the signaling cascade are unknown. TNF-α activates several signaling pathways, including Rho/Rho kinase (ROCK), which is known to reduce NOS3 expression in endothelial cells. Therefore, we hypothesized that TNF-α decreases NOS3 expression via Rho/ROCK in rat THAL primary cultures. THAL cells were incubated with either vehicle or 1 nmol/L of TNF-α for 24 hours, and NOS3 expression was measured by Western blot. TNF-α decreased NOS3 expression by 51 ± 6% (P<0.002) and blunted stimulus-induced NO production. A 10-minute treatment with TNF-α stimulated RhoA activity by 60 ± 23% (P<0.04). Inhibition of Rho GTPase with 0.05 μg/mL of C3 exoenzyme blocked TNF-α-induced reductions in NOS3 expression by 30 ± 8% (P<0.02). Inhibition of ROCK with 10 μmol/L of H-1152 blocked TNF-α-induced decreases in NOS3 expression by 66 ± 15% (P<0.001). Simultaneous inhibition of Rho and ROCK had no additive effect. Myosin light chain kinase, NO, protein kinase C, mitogen-activated kinase kinase, c-Jun amino terminal kinases, and Rac-1 were also not involved in TNF-α-induced decreases in NOS3 expression. We conclude that TNF-α decreases NOS3 expression primarily via Rho/ROCK in rat THALs. These data suggest that some of the beneficial effects of ROCK inhibitors in hypertension could be attributed to the mitigation of TNF-α-induced reduction in NOS3 expression.

Induction of endothelial nitric oxide synthase expression by IL-17 in human vascular endothelial cells: implications for vascular remodeling in transplant vasculopathy

IL-17 is a signature cytokine of Th17 cells, a recently described subset of effector CD4 T cells implicated in the development of several pathologies. We have examined the role of IL-17 in regulating endothelial NO synthase (eNOS) expression in human vascular endothelial cells (ECs) because of the key role of eNOS in determining the pathological outcome of immune-mediated vascular diseases. In cultured ECs, IL-17 increased expression of eNOS, eNOS phosphorylation at Ser(1177), and NO production. The induction of eNOS expression by IL-17 was prevented by the pharmacological inhibition of NF-κB, MEK, and JNK, as well as by small interfering RNA-mediated gene silencing of these signaling pathways. The expression of IL-17 was then examined by immunohistochemistry in human arteries affected by transplant vasculopathy (TV), a vascular condition that is a leading reflection of chronic heart transplant rejection. IL-17 was expressed by infiltrating leukocytes in the intima of arteries with TV, and the majority of IL-17-positive cells were T cells. The number of IL-17-positive cells was not correlated with the intima/media ratio, but was negatively correlated with the amount of luminal occlusion. There was also a significant positive correlation between the number of IL-17-positive cells and the density of eNOS-expressing luminal ECs in arteries with TV. Altogether, these findings show that IL-17 induces the expression of eNOS in human ECs and that this may facilitate outward expansion of arteries afflicted with TV.

Obesity, blood vessels and metabolic syndrome

Obesity is rising worldwide at an alarming rate and so is the incidence of obesity-related disorders, such as the metabolic syndrome, type 2 diabetes and cardiovascular diseases. The obesity-dependent vascular damage appears to be derived from a variety of changes in the adipose tissue, leading to a chronic inflammatory state and dysregulation of adipocyte-derived factors. This, in turn, impairs vascular homeostasis by determining an unbalance between the protective effect of the nitric oxide pathway and the unfavourable action of the endothelin-1 system. In addition, hyperinsulinemia and insulin resistance contribute to vascular dysfunction because the opposing endothelium-dependent vasodilating and vasoconstrictor effects of insulin are shifted towards a predominant vasoconstriction in patients with obesity. Importantly, emerging evidence suggests that the vascular dysfunction of obesity is not only limited to the endothelium but also involves the other layers of the vessel wall. In particular, obesity-related changes in vascular smooth muscle seem to disrupt the physiological facilitatory action of insulin on the responsiveness to vasodilator stimuli, whereas the adventitia and the perivascular fat appear to be a source of proinflammatory and vasoactive factors that may contribute to endothelial and smooth muscle cell dysfunction and to the pathogenesis of vascular disease.

Macrovascular and microvascular dysfunction in the metabolic syndrome

The metabolic syndrome (MetS) is associated with increased risk of type-2 diabetes and cardiovascular disease (CVD). We hypothesized that both small and large arteries may be impaired in subjects with the MetS, even in the absence of known CVD or diabetes. We compared both skin capillary density (CD) and pulse-wave velocity (PWV) in 36 cases with the MetS with those from 108 age- and gender-matched controls from the SU.VIM.AX-2 cohort. Compared with controls, MetS subjects demonstrated increased PWV (12.2+/-2.8 vs. 10.7+/-1.9 m s(-1), P=0.005) and lower functional CD (83.1+/-15.7 vs. 89.4+/-14.2 capillaries per mm(2), P=0.03). Functional CD was inversely related to fasting glucose, triglycerides (TGs) and HOMA-IR (all P<0.05). On the other hand, no association was found between CD and BP or with PWV. In multivariate models, the odds ratios (95% confidence interval) for one standard deviation change, for having an impaired PWV (>or=12 m s(-1), n=44), were: 1.65 (1.11-2.45) for systolic BP and 1.93 (1.25-2.99) for TG only. For impaired CD (<or=80 capillaries per mm(2)), the odds ratios (95% confidence interval) were 1.45 (1.00-2.08) for TG and 1.65 (1.13-2.43) for fasting glucose, only. In conclusion, MetS subjects exhibited evidence of macro- and microcirculatory dysfunction, even in the absence of diabetes and CVD. The common mechanism linking MetS components to CVD risk through small- and large-artery dysfunctions may be mediated through metabolic factors related to insulin resistance, not to increased BP.

Visfatin activates eNOS via Akt and MAP kinases and improves endothelial cell function and angiogenesis in vitro and in vivo: translational implications for atherosclerosis

Improving endothelial nitric oxide synthase (eNOS) bioactivity and endothelial function is important to limit native, vein graft, and transplant atherosclerosis. Visfatin, a NAD biosynthetic enzyme, regulates the activity of the cellular survival factor, Sirt1. We hypothesized that visfatin may improve eNOS expression, endothelial function, and postnatal angiogenesis. In human umbilical vein (HUVEC) and coronary artery endothelial cells, we evaluated the effects of recombinant human visfatin on eNOS protein and transcript expression and mRNA stability, in the presence and absence of visfatin RNA silencing. We also assessed visfatin-induced protein kinase B (Akt) activation and its association with src-tyrosine kinases, phosphorylation of Ser(1177) within eNOS in the presence and absence of phosphatidylinositol 3-kinase (PI 3-kinase) inhibition with LY-294002, and evaluated the contributory role of extracellular signal-regulated kinase 1/2. Finally, we determined the impact of visfatin on HUVEC migration, proliferation, inflammation-induced permeability, and in vivo angiogenesis. Visfatin (100 ng/ml) upregulated and stabilized eNOS mRNA and increased the production of nitric oxide and cGMP. Visfatin-treated HUVEC demonstrated greater proliferation, migration, and capillary-like tube formation but less tumor necrosis factor-alpha-induced permeability; these effects were decreased in visfatin gene-silenced cells. Visfatin increased total Akt and Ser(473)-phospho-Akt expression with concomitant rises in eNOS phosphorylation at Ser(1177); these effects were blocked by LY-2940002. Studies with PP2 showed that the nonreceptor tyrosine kinase, src, is an upstream stimulator of the PI 3-kinase-Akt pathway. Visfatin also activated mitogen-activated protein (MAP) kinase through PI 3-kinase, and mitogen/extracellular signal-regulated kinase inhibition attenuated visfatin-elicited Akt and eNOS phosphorylation. Visfatin-filled Matrigel implants showed an elevated number of infiltrating vessels, and visfatin treatment produced significant recovery of limb perfusion following hindlimb ischemia. These results indicate a novel effect of visfatin to stimulate eNOS expression and function in endothelial cells, via a common upstream, src-mediated signaling cascade, which leads to activation of Akt and MAP kinases. Visfatin represents a translational target to limit endothelial dysfunction, native, vein graft and transplant atherosclerosis, and improve postnatal angiogenesis.

Getting the message across: mechanisms of physiological cross talk by adipose tissue

Obesity is associated with resistance of skeletal muscle to insulin-mediated glucose uptake, as well as resistance of different organs and tissues to other metabolic and vascular actions of insulin. In addition, the body is exquisitely sensitive to nutrient imbalance, with energy excess or a high-fat diet rapidly increasing insulin resistance, even before noticeable changes occur in fat mass. There is a growing acceptance of the fact that, as well as acting as a storage site for surplus energy, adipose tissue is an important source of signals relevant to, inter alia, energy homeostasis, fertility, and bone turnover. It has also been widely recognized that obesity is a state of low-grade inflammation, with adipose tissue generating substantial quantities of proinflammatory molecules. At a cellular level, the understanding of the signaling pathways responsible for such alterations has been intensively investigated. What is less clear, however, is how alterations of physiology, and of signaling, within one cell or one tissue are communicated to other parts of the body. The concepts of cell signals being disseminated systemically through a circulating "endocrine" signal have been complemented by the view that local signaling may similarly occur through autocrine or paracrine mechanisms. Yet, while much elegant work has focused on the alterations in signaling that are found in obesity or energy excess, there has been less attention paid to ways in which such signals may propagate to remote organs. This review of the integrative physiology of obesity critically appraises the data and outlines a series of hypotheses as to how interorgan cross talk takes place. The hypotheses presented include the "fatty acid hypothesis,", the "portal hypothesis,", the "endocrine hypothesis,", the "inflammatory hypothesis,", the "overflow hypothesis,", a novel "vasocrine hypothesis," and a "neural hypothesis," and the strengths and weaknesses of each hypothesis are discussed.

Perivascular fatty tissue at the brachial artery is linked to insulin resistance but not to local endothelial dysfunction

AIMS/HYPOTHESIS

Different ectopic fat depots, such as visceral or hepatic fat, are known to affect whole body insulin sensitivity. It has recently been hypothesised that differences in perivascular adipose tissue (PVAT) mass around resistance vessels may also contribute to insulin resistance, possibly via direct vascular effects leading to reduced capillary cross-sectional area in the muscle, which in turn affects muscular blood flow and glucose uptake. Based on this, the aim of the present study was to test whether PVAT around conduit arteries (i.e. the brachial artery) influences NO bioavailability, expressed as flow-mediated dilation (FMD), or insulin sensitivity in humans in vivo.

METHODS

Insulin sensitivity was measured by OGTT in all 95 participants (59 women, 36 men; median age 47 years, range 19-66 years) and by the gold standard, a euglycaemic-hyperinsulinaemic clamp, in a randomly selected subgroup of 33 participants. Quantification of the different fat compartments, including PVAT around the brachial artery, was achieved by high-resolution magnetic resonance imaging (1.5 T). Blood flow and FMD were measured at the brachial artery using high-resolution (13 MHz) ultrasound, after 5 min of forearm occlusion.

RESULTS

PVAT was negatively correlated with insulin sensitivity and the post-ischaemic increase in blood flow. The association between PVAT and insulin sensitivity (r = -0.54, beta = -0.37, p = 0.009) was independent of age, sex, visceral adipose tissue, liver fat, BMI and further cardiovascular risk factors. No correlation could be detected between PVAT and local endothelial function. However, we observed an independent association between PVAT and post-ischaemic increase in blood flow (r = -0.241; beta = -1.69; p = 0.02).

CONCLUSIONS/INTERPRETATION

PVAT seems to play an independent role in the pathogenesis of insulin resistance. This may be due to direct vascular effects influencing muscular blood flow.

The association of interleukin-18 genotype and serum levels with metabolic risk factors for cardiovascular disease

OBJECTIVE

Circulating levels of interleukin (IL)-18 are associated with the metabolic syndrome and risk for the development of cardiovascular disease (CVD). This study investigated the association between the circulating IL-18 levels and the -137 G/C polymorphism within the IL-18 gene with metabolic risk factors for CVD in normal-weight and obese black South African women.

METHODS

Blood pressure (BP), body composition (dual-energy X-ray absorptiometer), visceral adiposity (computerized tomography), as well as fasting glucose, insulin, lipid profile, IL-18 levels, and IL-18 genotype were measured in 104 normal-weight (body mass index (BMI) < or = 25 kg/m2) and 124 obese (BMI > or = 30 kg/m2) black South African women.

RESULTS

Subjects with a GC genotype (23%) had a greater mean arterial pressure (MAP, 90.6+/-11.1 vs 85.5+/-10.3 mmHg, P<0.001) than the subjects with the GG genotype. Serum IL-18 levels were not associated with IL-18 genotype (P=0.985); however, they significantly correlated with percentage of body fat (r=0.25, P<0.001), visceral adiposity (r=0.32, P<0.001), MAP (r=0.22, P=0.001), HOMA-IR (r=0.33, P<0.001), fasting insulin (r=0.25, P<0.001), triglyceride (r=0.16, P<0.05), and high-density lipoprotein-cholesterol (r=-0.14, P<0.05) levels, after adjusting for age and body fatness.

CONCLUSIONS

We show for the first time that the GC genotype of the IL-18 -137 G/C polymorphism and the circulating IL-18 levels are independently associated with raised BP. Moreover, fasting IL-18 levels are associated with the other metabolic risk factors for CVD in normal-weight and obese black South African women.

Microvascular dysfunction in obesity: a potential mechanism in the pathogenesis of obesity-associated insulin resistance and hypertension

Obesity is an important risk factor for insulin resistance and hypertension and plays a central role in the metabolic syndrome. Insight into the pathophysiology of this syndrome may lead to new treatments. This paper has reviewed the evidence for an important role for the microcirculation as a possible link between obesity, insulin resistance and hypertension.

Insulin resistance and the metabolic syndrome--or the pitfalls of epidemiology

The clustering of dyslipidaemia, hypertension and glucose intolerance, predominantly in overweight individuals, has been ascribed many names, including syndrome X and the metabolic syndrome. In Reaven's original description of syndrome X, a central aetiological role was attributed to insulin resistance, and this assumption has remained as the dominant paradigm for the metabolic syndrome. There are a number of conceptual problems in such a model, particularly those arising from observations that several novel markers, including measures of endothelial dysfunction and of low-grade inflammation, are as closely related to insulin resistance as are the classic components of the syndrome. Because it is difficult to envisage how these traits might develop as a consequence of insulin resistance, such observations indicate the need for a new paradigm to explain the mechanisms of association better. It has been proposed that a state of low-grade inflammation, consequent upon the production of adipocytokines, particularly from truncal fat, explains the observed relationships between insulin resistance and endothelial dysfunction better than does a model revolving around insulin resistance. Furthermore, the inflammatory cytokines generated from adipose tissue may influence vessel endothelial function without elevations in circulating concentrations. This review alludes to several problems inherent in the epidemiological method in understanding disease mechanisms. These include crude biological measures, the use of venous systemic fasting samples, imprecision of assays, naive physiological models, simplistic statistical approaches and, without clinical trials, an inability to test causation. Integrated systems biology needs more complex approaches to investigate disease mechanisms, involving cell, organ, whole organism and population studies.

Tumor necrosis factor-α reduces argininosuccinate synthase expression and nitric oxide production in aortic endothelial cells

Endothelial dysfunction associated with elevated serum levels of TNF-α observed in diabetes, obesity, and congenital heart disease results, in part, from the impaired production of endothelial nitric oxide (NO). Cellular NO production depends absolutely on the availability of arginine, substrate of endothelial nitric oxide synthase (eNOS). In this report, evidence is provided demonstrating that treatment with TNF-α (10 ng/ml) suppresses not only eNOS expression but also the availability of arginine via the coordinate suppression of argininosuccinate synthase (AS) expression in aortic endothelial cells. Western blot and real-time RT-PCR demonstrated a significant and dose-dependent reduction of AS protein and mRNA when treated with TNF-α with a corresponding decrease in NO production. Reporter gene analysis demonstrated that TNF-α suppresses the AS proximal promoter, and EMSA analysis showed reduced binding to three essential Sp1 elements. Inhibitor studies suggested that the repression of AS expression by TNF-α may be mediated, in part, via the NF-κB signaling pathway. These findings demonstrate that TNF-α coordinately downregulates eNOS and AS expression, resulting in a severely impaired citrulline-NO cycle. The downregulation of AS by TNF-α is an added insult to endothelial function because of its important role in NO production and in endothelial viability.

TNF-alpha potentiates protein-tyrosine nitration through activation of NADPH oxidase and eNOS localized in membrane rafts and caveolae of bovine aortic endothelial cells

A major source of reactive oxygen species (ROS) in endothelial cells is the NADPH oxidase enzyme complex. The selective distributions of any enzyme within cells have important implications in regulating enzyme effectiveness through facilitation of access to local substrates and/or product targets. Because membrane rafts provide a spatially preferable environment for a variety of enzyme systems, we sought to determine whether NADPH oxidase is present and functional in this plasma membrane compartment in endothelial cells. We found that, in resting endothelial cells, NADPH oxidase subunits were preassembled and the enzyme functional in membrane rafts, specifically in caveolae. Stimulation with TNF-alpha induced additional recruitment of the p47(phox) regulatory subunit to raft-localized NADPH oxidase and enhanced ROS production within raft domains. TNF-alpha also induced nitric oxide production through activation of endothelial nitric oxide synthase (eNOS) present in the same membrane compartment. The dual activation of superoxide and nitric oxide-generating systems provided a spatially favorable environment for nitration of tyrosine-containing proteins localized to rafts. Perturbation of membrane raft structural integrity with cholesterol-sequestering compounds caused the delocalization of NADPH oxidase subunits and eNOS from the rafts and inhibited TNF-alpha-induced ROS production and protein tyrosine nitration. Together, these data provide evidence that membrane rafts and caveolae play a role in the spatial regulation of NADPH oxidase and subsequent ROS/reactive nitrogen species in endothelial cells.

Transcriptional and posttranscriptional regulation of endothelial nitric oxide synthase expression

The ability of the endothelium to produce nitric oxide is essential to maintenance of vascular homeostasis; disturbance of this ability is a major contributor to the pathogenesis of vascular disease. In vivo studies have demonstrated that expression of endothelial nitric oxide synthase (eNOS) is vital to endothelial function and have led to the understanding that eNOS expression is subject to modest but significant degrees of regulation. Subsequently, numerous physiological and pathophysiological stimuli have been identified that modulate eNOS expression via mechanisms that alter steady-state eNOS mRNA levels. These mechanisms involve changes in the rate of eNOS gene transcription (transcriptional regulation) and alteration of eNOS mRNA processing and stability (posttranscriptional regulation). In cultured endothelial cells, shear stress, transforming growth factor-beta1, lysophosphatidylcholine, cell growth, oxidized linoleic acid, 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, and hydrogen peroxide have been shown to increase eNOS expression. In contrast, tumor necrosis factor-alpha, hypoxia, lipopolysaccaride, thrombin, and oxidized LDL can decrease eNOS mRNA levels. For many of these stimuli, both transcriptional and posttranscriptional mechanisms contribute to regulation of eNOS expression. Recent studies have begun to further define signaling pathways responsible for changes in eNOS expression and have characterized cis- and trans-acting regulatory elements. In addition, a role has been identified for epigenetic control of eNOS mRNA levels. This review will discuss transcriptional and posttranscriptional regulation of eNOS with emphasis on the molecular mechanisms that have been identified for these processes.

Does microvascular dysfunction link obesity with insulin resistance and hypertension?

Obesity and obesity-associated clinical disorders are becoming an increasing public health burden. In this perspective, we postulate that impairment of microvascular function links obesity with insulin resistance and hypertension. Obesity is characterized by generalized microvascular dysfunction, which is associated with, and may precede, the development of insulin resistance and hypertension. Understanding of mechanisms involved in obesity-associated microvascular dysfunction may reveal new therapeutic targets. In obesity, cellular regulatory mechanisms of vasoreactivity are shifted towards vasoconstriction, with an increased role for endothelin-1 and a decreased role for nitric oxide. In addition, communicative pathways between adipose tissue and the microvasculature comprise increased release of adipokines and increased sympathetic activity. Although one mechanism may dominate, microvascular defects in obesity are probably caused by an integrated response consisting of endocrine, vasocrine and neurogenic mechanisms. This remains a fruitful area for future research.

Molecular mechanisms of tumor necrosis factor-alpha-mediated plasminogen activator inhibitor-1 expression in adipocytes

Increased expression of plasminogen activator inhibitor -1 (PAI-1) in adipose tissues is thought to contribute to both the cardiovascular and metabolic complications associated with obesity. Tumor necrosis factor alpha (TNF-alpha) is chronically elevated in adipose tissues of obese rodents and humans and has been directly implicated to induce PAI-1 in adipocytes. In this study, we used 3T3-L1 adipocytes to examine the mechanism by which TNF-alpha up-regulates PAI-1 in the adipocyte. Acute (3 h) and chronic (24 h) exposure of 3T3-L1 adipocytes to TNF-alpha induces PAI-1 mRNA by increasing the rate of transcription of the PAI-1 gene, and de novo protein synthesis is not required for this process. Although the p44/42 and PKC signaling pathways appear to be significant in the induction of PAI-1 mRNA in response to acute treatment with TNF-alpha, the more dramatic induction of PAI-1 mRNA observed in response to chronic exposure of adipocytes to TNF-alpha was mediated by these and additional signaling molecules, including p38, PI3-kinase, tyrosine kinases, and the transcription factor NF-kappaB. Moreover, the dramatic increase in PAI-1 observed after chronic exposure of adipocytes to TNF-alpha was accompanied by increased metabolic insulin resistance. Finally, we demonstrate that the PKC pathway is also central for PAI-1 induction in response to insulin and transforming growth factor-beta (TGF-beta), two additional molecules which are elevated in obesity and shown to directly induce PAI-1 in the adipocyte. The understanding of the mechanism of regulating PAI-1 expression in the adipocytes at the molecular level provides new insight to help identify novel targets in fighting the pathological complications of obesity.

"Vasocrine" signalling from perivascular fat: a mechanism linking insulin resistance to vascular disease

Adipose tissue expresses cytokines that inhibit insulin signalling pathways in liver and muscle. Obesity also results in impairment of endothelium-dependent vasodilatation in response to insulin. We propose a vasoregulatory role for local deposits of fat around the origin of arterioles supplying skeletal muscle. Isolated first-order arterioles from rat cremaster muscle are under dual regulation by insulin, which activates both endothelin-1 mediated vasoconstriction and nitric-oxide-mediated vasodilatation. In obese rat arterioles, insulin-stimulated NO synthesis is impaired, resulting in unopposed vasoconstriction. We propose that this vasoconstriction is the consequence of production of the adipocytokine tumour necrosis factor alpha from the cuff of fat seen surrounding the origin of the arteriole in obese rats--a depot to which we ascribe a specialist vasoregulatory role. We suggest that this cytokine accesses the nutritive vascular tree to inhibit insulin-mediated capillary recruitment--a mechanism we term "vasocrine" signalling. We also suggest a homology between this vasoactive periarteriolar fat and both periarterial and visceral fat, which may explain relations between visceral fat, insulin resistance, and vascular disease.

Tumor necrosis factor-alpha inhibits endothelial nitric-oxide synthase gene promoter activity in bovine aortic endothelial cells

Tumor necrosis factor-alpha (TNF-alpha) has been shown to reduce endothelial nitric-oxide synthase (eNOS) gene expression through post-transcriptional regulation of mRNA stability. The current study documented an independent effect of the cytokine on the eNOS gene promoter. TNF-alpha effected a time- and dose-dependent reduction in activity of a transiently transfected human -1197 eNOS-luciferase reporter. This reduction was inhibited by co-transfection of dominant negative IKKbeta as well as a nonphosphorylatable constitutively suppressive mutant of IkappaB implying involvement of the NFkappaB cascade in the inhibitory effect. The locus of the TNF-alpha-dependent inhibition was traced to two Sp1-binding sites positioned between -109 and -95 and -81 and -67 relative to the transcription start site. Electrophoretic mobility shift analysis and immunoperturbation studies showed evidence for Sp1 and Sp3 binding to each element. TNF-alpha treatment had no effect on the binding pattern to the downstream (-81 to -67) site but did suppress association of Sp1 and Sp3 to the upstream (-109 to -95) site. Collectively, these data indicate that TNF-alpha exerts transcriptional, as well as post-transcriptional, effects on eNOS gene expression and suggest a potential mechanism to account for the endothelial dysfunction that accompanies disorders such as diabetes mellitus and heart failure.

Aging-induced proinflammatory shift in cytokine expression profile in coronary arteries

The phenotypic and functional changes of coronary arteries with aging promote ischemic heart disease. We hypothesized that these alterations reflect an aging-induced proinflammatory shift in vascular regulatory mechanisms. Thus, in isolated coronary arteries of young (3-month-old) and aged (25-month-old) male Fischer 344 rats the expression of 96 cytokines, chemokines, and their receptors were screened by a cDNA-based microarray technique. In aged vessels expressions of tumor necrosis factor (TNF)-alpha (3.3x), interleukin (IL)-1beta (3.0x), IL-6 (2.9x), IL-6Ralpha (2.8x) and IL-17 (6.1x) genes were significantly increased over young vessels. Quantitative reverse transcriptase-polymerase chain reaction confirmed these results. Western blotting demonstrated that protein expressions of TNF-alpha, IL-1beta, IL-6, and IL-17 were also significantly increased in vessels of aged rats compared with those of young rats. Immunofluorescent double labeling showed that in aged vessels IL-1beta and IL-6 are predominantly localized in the endothelium, whereas TNF-alpha and IL-17 are localized in smooth muscle. Thus, a proinflammatory shift in the profile of vascular cytokine expression may contribute to the aging-induced phenotypic changes in coronary arteries, promoting the development of ischemic heart disease in the elderly.

[Cardiovascular syndrome X and endothelial dysfunction]

Up to 30% of patients with chest pain who undergo coronary arteriography, have completely normal coronary angiograms. The subgroup with typical angina and a positive response to stress testing is generally included under the diagnosis of cardiovascular syndrome X. Several causes and mechanisms have been investigated in the past twenty years, to explain both chest pain and ischemic angina-like ST segment depression that are commonly observed in these patients. Clinical and pathogenic heterogeneity appears to be the main features of the syndrome. Among the suggested pathophysiological mechanisms, endothelial dysfunction of the coronary microcirculation features prominently. In this review, we present the available evidence regarding endothelial dysfunction in cardiovascular syndrome X.

Molecular mechanisms involved in the regulation of the endothelial nitric oxide synthase

The endothelial nitric oxide synthase (eNOS), the expression of which is regulated by a range of transcriptional and posttranscriptional mechanisms, generates nitric oxide (NO) in response to a number of stimuli. The physiologically most important determinants for the continuous generation of NO and thus the regulation of local blood flow are fluid shear stress and pulsatile stretch. Although eNOS activity is coupled to changes in endothelial cell Ca(2+) levels, an increase in Ca(2+) alone is not sufficient to affect enzyme activity because the binding of calmodulin (CaM) and the flow of electrons from the reductase to the oxygenase domain of the enzyme is dependent on protein phosphorylation and dephosphorylation. Two amino acids seem to be particularly important in regulating eNOS activity and these are a serine residue in the reductase domain (Ser(1177)) and a threonine residue (Thr(495)) located within the CaM-binding domain. Simultaneous alterations in the phosphorylation of Ser(1177) and Thr(495) in response to a variety of stimuli are regulated by a number of kinases and phosphatases that continuously associate with and dissociate from the eNOS signaling complex. eNOS associated proteins, such as caveolin, heat shock protein 90, eNOS interacting protein, and possibly also motor proteins provide the scaffold for the formation of the protein complex as well as its intracellular localization.

A low-calorie diet improves endothelium-dependent vasodilation in obese patients with essential hypertension

BACKGROUND

Both obesity and hypertension are associated with endothelial dysfunction. The purpose of this study was to investigate the effects of a low-calorie diet on endothelial function in obese patients with essential hypertension.

METHODS

We measured forearm blood flow (FBF) during intra-arterial infusion of acetylcholine (ACh; 7.5, 15, 30 microg/min), an index of endothelium-dependent vasodilation, and isosorbide dinitrate (ISDN; 0.75, 1.5, 3.0 microg/min), an index of endothelium-independent vasodilation, in obese patients with essential hypertension before and after 2 weeks on a low-calorie diet (800 kcal/d). The study included 11 obese hypertensive Japanese patients (mean body mass index, 30.8 +/- 3.6 kg/m2). Fifteen healthy Japanese normotensive individuals were recruited as a control group.

RESULTS

In obese patients with hypertension, the response of FBF to ACh was attenuated compared to healthy individuals (P < .001). Caloric restriction reduced body weight from 77.5 +/- 15.0 to 73.2 +/- 13.5 kg (P < .01), the mean blood pressure from 118.4 +/- 8.7 to 105.7 +/- 8.5 mm Hg (P < .01), fasting plasma insulin from 85.8 +/- 22.8 to 64.8 +/- 27.0 pmol/L (P < .05), serum total cholesterol from 5.30 +/- 0.76 to 4.67 +/- 0.58 mmol/L (P < .05), and low density lipoprotein cholesterol from 3.80 +/- 0.48 to 3.29 +/- 0.44 mmol/L (P < .05). Basal FBF was similar before and after weight reduction. Caloric restriction enhanced the response of FBF to ACh (P < .05), but did not alter the response to ISDN. The intra-arterial infusion of NG-monomethyl-L-arginine (8 micromol/min), a nitric oxide synthase inhibitor, decreased the enhanced ACh-induced blood flow response induced by caloric restriction.

CONCLUSIONS

The present findings suggest that the caloric restriction improves endothelial-dependent vasodilation through an increased release of nitric oxide in obese hypertensive patients.

Tumor necrosis factor alpha negatively regulates the expression of the carcinoma-associated antigen epithelial cell adhesion molecule

BACKGROUND

The epithelial cell adhesion molecule (EpCAM) is a homophilic and Ca2+ independent adhesion molecule that is expressed de novo in squamous cell carcinoma (SCC) but is absent in the majority of healthy squamous epithelia. EpCAM expression correlates with cell proliferation and dedifferentiation along with a progression in tumorigenicity. To date, nothing is known about the molecular mechanisms responsible for the regulation of the EpCAM gene.

METHODS

The authors analyzed the regulation of a fragment of the EpCAM promoter.

RESULTS

The analyzed fragment has significant activity in EpCAM positive cells, and it is regulated negatively by tumor necrosis factor alpha (TNFalpha). This negative regulation results in diminished mRNA expression and in the down-regulation of EpCAM protein at the cell surface in SCC cells. Both effects can be mimicked by the treatment of cells with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA). TNFalpha-induced inhibition of the EpCAM expression is mediated by TNF receptor 1 through the TNF receptor-associated death domain protein (TRADD) and by the activation of nuclear factor kappaB (NF-kappaB), and it can be blocked by dominant-negative variants of TRADD and the NF-kappaB inhibitor, IkappaB. The authors provide further evidence that NF-kappaB represses EpCAM expression by competing for the transcriptional coactivator p300/CREB binding protein (p300/CBP).

CONCLUSIONS

The current results provide the first insights into the regulation of EpCAM expression, which is regulated negatively by TNFalpha and TPA through the activation of NF-kappaB. The repression may rely on the competition of NF-kappaB for p300/CBP histone acetyl transferase activity, because the overexpression of p300 reverts TNFalpha effects.

Cerivastatin prevents tumor necrosis factor-alpha-induced downregulation of endothelial nitric oxide synthase: role of endothelial cytosolic proteins

Cardiovascular disease is accompanied by an impaired endothelium-dependent vasodilatory response. Loss of endothelial nitric oxide synthase (eNOS) expression may contribute to endothelial dysfunction. The aim of the present study was to analyze the effect of cerivastatin, a novel HMG CoA reductase inhibitor, on tumor necrosis factor-alpha (TNF-alpha)-induced downregulation of eNOS protein expression in bovine aortic endothelial cells (BAEC). TNF-alpha (10 ng/ml)- incubated BAEC showed a reduced expression of eNOS protein and decreased eNOS mRNA stabilization. This effect was associated with an increased binding activity of BAEC cytosolic proteins to the 3'-untranslated region (3'UTR) of eNOS mRNA. Cerivastatin prevented TNF-alpha-induced downregulation of eNOS protein expression in a concentration-dependent manner (10(-8) to 10(-5) M). Cerivastatin also prevented the binding of the cytosolic proteins to 3'-UTR of eNOS mRNA and was associated with eNOS mRNA stabilization. The reduced expression of eNOS protein by TNF-alpha was also prevented by coincubation with cycloheximide. In addition cycloheximide inhibited the binding activity of the cytosolic proteins to 3'-UTR of eNOS mRNA, suggesting the inducible character of the mentioned-cytosolic proteins. TNF-alpha stimulated the translocation of nuclear factor-kappaB (NF-kappaB), an effect that was not modified by cerivastatin. Furthermore, an inhibitor of NF-kappaB translocation, pyrrolidine dithiocarbamate failed to modify both the downregulation of eNOS expression and the increased binding activity of the cytosolic proteins to 3'-UTR of eNOS mRNA by TNF-alpha. The effect of cerivastatin on eNOS expression and the binding activity of the cytosolic proteins were reversed by coincubation with L-mevalonate. In conclusion, cerivastatin stabilized eNOS mRNA and upregulated eNOS expression in the endothelium, and this was associated with a decreased binding activity of cytosolic proteins to 3'-UTR of eNOS mRNA. The effect of cerivastatin on the regulation of eNOS expression was independent of NF-kappaB mobilization by TNF-alpha. These findings suggest that cerivastatin may have beneficial effects on the endothelial dysfunction associated with cardiovascular diseases beyond its effect on lowering cholesterol.

Expression of an endothelial-type nitric oxide synthase isoform in human neutrophils: modification by tumor necrosis factor-alpha and during acute myocardial infarction

OBJECTIVES

The purpose of this study was to determine whether human neutrophils express an endothelial-type nitric oxide synthase (eNOS), and to study the effect of tumor necrosis factor-alpha (TNF-alpha) on its expression.

BACKGROUND

Several studies have demonstrated the presence of a constitutively expressed nitric oxide svnthase (NOS) in neutrophils. Cardiovascular disease is characterized by increased levels of plasma TNF-alpha, a cytokine that has demonstrated eNOS messenger ribonucleic acid (mRNA) destabilization in cultured endothelial cells.

METHODS

Neutrophils were obtained from healthy volunteers and from patients with acute myocardial infarction (AMI).

RESULTS

Human neutrophils express eNOS mRNA and eNOS protein. Stimulation of neutrophils with TNF-alpha decreased eNOS protein expression by reducing eNOS mRNA stabilization. In the present study, we also show that the cytosol of human neutrophils contains proteins that bind to a specific region within the 3'-untranslated region (3'-UTR) of eNOS mRNA. Tumor necrosis factor-alpha increased the binding of the cytosolic proteins to the 3'-UTR of eNOS mRNA. Simvastatin reduced the TNF-alpha-related binding activity of neutrophil cytosolic proteins to eNOS mRNA, which was associated with its protective effect on eNOS protein expression. The in vivo reproduction of the in vitro findings was performed in neutrophils obtained from patients with AMI and showed a diminished expression of eNOS protein, which was associated with increased binding of the cytosolic proteins.

CONCLUSIONS

These observations demonstrate that human neutrophils express eNOS, which is downregulated by TNF-alpha and during AMI. This effect is associated with increased binding of neutrophil cytosolic proteins to the 3'-UTR of eNOS mRNA.

Expression of endothelial nitric oxide synthase in human peritoneal tissue: regulation by Escherichia coli lipopolysaccharide

Changes in the expression of endothelial nitric oxide synthase (eNOS) in the peritoneum could be involved in the peritoneal dysfunction associated with peritoneal inflammation. Demonstrated recently in bovine endothelial cells was the existence of cytosolic proteins that bind to the 3'-untranslated region (3'-UTR) of eNOS mRNA and could be implicated in eNOS mRNA stabilization. The present work demonstrates that eNOS protein is expressed in human endothelial and mesothelial peritoneal cells. Escherichia coli lipopolysaccharide shortened the half-life of eNOS message, reducing eNOS protein expression in peritoneal mesothelial and endothelial cells. Moreover, under basal conditions, human peritoneal samples expressed cytosolic proteins that bind to the 3'-UTR of eNOS mRNA. The cytosolic proteins that directly bind to 3'-UTR were identified as a 60-kD protein. After incubation of human peritoneal samples with lipopolysaccharide, the binding activity of the cytosolic 60-kD protein increased in a time-dependent manner. Studies are now necessary to determine the involvement of this 60-kD protein in the regulation of eNOS expression in peritoneal cells and particularly its involvement in the peritoneal dysfunction associated with inflammatory reactions.

Insulin inhibits the expression of intercellular adhesion molecule-1 by human aortic endothelial cells through stimulation of nitric oxide

Intercellular adhesion molecule-1 (ICAM-1) is expressed by endothelial and other cell types and participates in inflammation and atherosclerosis. It serves as a ligand for leukocyte function-associated antigen-1 on leukocytes and is partially responsible for the adhesion of lymphocytes, granulocytes, and monocytes to cytokine-stimulated endothelial cells and the subsequent transendothelial migration. Its expression on endothelial cells is increased in inflammation and atherosclerosis. As it has been suggested that insulin and hyperinsulinemia may have a role in atherogenesis, we have now investigated whether insulin has an effect on the expression of ICAM-1 on human aortic endothelial cells (HAEC). HAEC were prepared from human aortas by collagenase digestion and were grown in culture. Insulin (100 and 1000 microU/mL) caused a decrease in the expression of ICAM-1 (messenger ribonucleic acid and protein) by these cells in a dose-dependent manner after incubation for 2 days. This decrease was associated with a concomitant increase in endothelial nitric oxide synthase (NOS) expression also induced by insulin. To examine whether the insulin-induced inhibition of ICAM-1 was mediated by nitric oxide (NO) from increased endothelial NOS, HAEC were treated with N(omega)-nitro-L-arginine, a NOS inhibitor. N(omega)-Nitro-L-arginine inhibited the insulin-induced decrease in ICAM-1 expression in HAEC at the messenger ribonucleic acid and protein levels. Thus, the inhibitory effect of insulin on ICAM-1 expression is mediated by NO. We conclude that insulin reduces the expression of the proinflammatory adhesion molecule ICAM-1 through an increase in the expression of NOS and NO generation and that insulin may have a potential antiinflammatory and antiatherosclerotic effect rather than a proatherosclerotic effect.

Dual regulatory effects of nitric oxide on plasminogen activator inhibitor type 1 expression in endothelial cells

In this report we compared the mechanism by which nitric oxide (NO), generated exogenously and endogenously, affects the plasminogen activator inhibitor type 1 (PAI-1) expression in endothelial cells. For this purpose, we stimulated the endothelial cell line EA.hy 926 with tumour necrosis factor alpha (TNFalpha) in the presence of the exogenously NO-releasing donors, sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine, or regulators of nitric oxide synthase (NOS) inhibitor N-nitro-L-arginine-methyl ester hydrochloride and substrate L-Arg. Expression of PAI-1 in EA.hy 926 cells was determined by measuring the level of mRNA, using relative quantitative reverse transcriptase PCR, and protein, using ELISA. In addition, we estimated the level of activation of two mitogen-activated protein kinases (MAPKs), extracellular signal-regulated kinase (ERK1/2) and c-Jun N-terminal kinase (JNK1/2), in the cells before and after treatment with TNFalpha, in the presence or absence of NO donors and inhibitors. In contrast to exogenously released NO that significantly reduced mostly basal PAI-1 expression, endogenously generated NO by NOS potentiated TNFalpha-induced upregulation of PAI-1 expression. Exogenously and endogenously generated NO causes different effects on activation of the MAPKs ERK1/2 and JNK1/2. Specifically, the SNP-released NO activates only ERK1/2, while endogenously generated NO in a pathway induced by TNFalpha activates both MAPKs. Thus our data indicate that due to different cellular locations and mechanisms of generation, NO may participate in various signalling pathways leading to opposite effects on PAI-1 expression in endothelial cells.

Role of nitric oxide in the angiogenic response in vitro to basic fibroblast growth factor

Angiogenesis is a complex process that involves the activation of quiescent endothelial cells (ECs) to a proliferative and migratory phenotype and, subsequently, their redifferentiation to form vascular tubes. We hypothesized that NO contributes to angiogenesis by terminating the proliferative action of angiogenic growth factors and initiating a genetic program of EC differentiation. Human umbilical vein ECs (HUVECs) and calf pulmonary artery ECs (CPAECs) were grown directly on plastic dishes or on three-dimensional fibrin matrices. In the absence of fibrin, treatment with NO-donor compounds, such as S-nitroso-N-acetylpenicillamine (SNAP, 0.1 and 0.4 mmol/L), produced a dose-dependent inhibition of proliferation in both cell lines, whereas the inhibition of endogenous NO production using NG-nitro-L-arginine methyl ester (L-NAME, 1 mmol/L) or NG-monomethyl-L-arginine (L-NMMA, 1 mmol/L) significantly increased proliferation of the CPAECs. The addition of basic fibroblast growth factor (bFGF, 30 ng/mL) increased the expression of endothelial NO synthase mRNA and the production of NO in both cell types when cultured on three-dimensional fibrin gels and produced profound morphological changes characterized by the appearance of extensive capillary-like vascular structures and the loss of EC monolayers. These changes were quantified by measuring total tube length per low-power field (x100), and a differentiation index was derived using the ratio of tube length over area covered by residual EC monolayer. In the absence of additional angiogenic factors, the differentiation index was low for both HUVECs and CPAECs (control, 1.16+/-0.19 and 2.07+/-0.87, respectively). Treatment with bFGF increased the differentiation index significantly in both cell types (10.59+/-2.03 and 20.02+/-5.01 for HUVECs and CPAECs, respectively; P<.05 versus control), and the addition of SNAP (0.4 mmol/L) mimicked the angiogenic response to bFGF (8.57+/-1.34 and 12.20+/-3.49 for HUVECs and CPAECs, respectively; P<.05 versus control). Moreover, L-NAME inhibited EC tube formation in response to bFGF in a dose-response manner, consistent with a role of endogenous NO production in EC differentiation in this angiogenic model. These findings suggest that NO may act as a crucial signal in the angiogenic response to bFGF, terminating the proliferative actions of angiogenic growth factors and promoting EC differentiation into vascular tubes.

Endothelial nitric oxide synthase in the endometrium during the menstrual cycle in patients with endometriosis and adenomyosis

OBJECTIVE

To determine the expression of endothelial nitric oxide synthase in the endometrium during the menstrual cycle in endometriosis and adenomyosis.

DESIGN

Immunohistochemical identification of endothelial nitric oxide in endometrial tissues using the monoclonal antibody.

SETTING

Department of obstetrics and gynecology in a university hospital.

PATIENT(S)

The subjects were divided into three groups: 35 patients with endometriosis, 33 patients with adenomyosis proven histologically, and 46 fertile controls.

MAIN OUTCOME MEASURE(S)

Semiquantitative immunostaining (evaluation nomogram) score in endometrial cells.

RESULT(S)

The analyses revealed phase-dependent changes in the expression of endothelial nitric oxide synthase in the surface and glandular epithelia during the menstrual cycle in the fertile controls. The expression was weakest in the early proliferative phase, gradually increased, was most marked in the midsecretory phase, and decreased thereafter. In contrast, stromal cells did not change throughout the cycle. Contrary to expectations, the expression of endothelial nitric oxide synthase in endometriosis and adenomyosis was persistently greater than the control levels throughout the menstrual cycle.

CONCLUSION(S)

This study has shown that endothelial nitric oxide synthase is changed in a phase-dependent manner during the menstrual cycle. The exaggerated expression of endothelial nitric oxide synthase in the endometrium throughout the cycle suggests some pathologic role in endometriosis and adenomyosis.

Expression of endothelial constitutive nitric oxide synthase mRNA in gastrointestinal mucosa and its downregulation by endotoxin

Endothelial nitric oxide exerts local vasodilatory actions in the gastrointestinal (GI) microvasculature and is proposed to play a role in enteric vasomotor regulation. The aims of this study were to characterize the tissue distribution of mRNA for endothelial nitric oxide synthase (NOS-III) and to examine its response to endotoxin challenge in vivo. We demonstrate the expression of NOS-III mRNA and protein in mucosa throughout the gastrointestinal tract and show for the first time that NOS-III mRNA expression in the GI mucosa was down-regulated in the rats treated with endotoxin. The ubiquitous expression of NOS-III mRNA in digestive tissues is consistent with the proposed role of NOS-III in the physiology of the gastrointestinal tract. The decreased NOS-III mRNA, in parallel to induction of inducible NOS (NOS-II) mRNA, may contribute to the impaired endothelium-dependent relaxation and damaged mucosal integrity during sepsis.

Endothelial cytosolic proteins bind to the 3' untranslated region of endothelial nitric oxide synthase mRNA: regulation by tumor necrosis factor alpha

Changes in endothelial nitric oxide synthase (eNOS) expression may be involved in the endothelium-dependent vasorelaxation dysfunction associated with several vascular diseases. In the present work, we demonstrate that eNOS mRNA contains a previously undescribed cis element in the 3' untranslated region (3' UTR). A U+C-rich segment in the 3' UTR is critical in complex formation with bovine aortic endothelial cell cytosolic proteins. Tumor necrosis factor alpha (TNF-alpha), which destabilizes eNOS mRNA, increased the binding activity of the cytosolic proteins in a time-dependent manner. These data suggest that endothelial cytosolic proteins bind to the 3' UTR of eNOS mRNA. These proteins may play a role in TNF-alpha-induced eNOS mRNA destabilization.

Stimulation of endothelial nitric oxide production by homocyst(e)ine

Hyperhomocyst(e)inemia, characterized by accelerated atherosclerosis, is believed to induce endothelial cell injury and promote atherothrombosis by supporting the generation of hydrogen peroxide. Earlier observations in our laboratory demonstrated that in vitro nitrosation of homocyst(e)ine (HCY) prevents the generation of hydrogen peroxide. We, therefore, hypothesized that stimulating the production of nitric oxide (NO) by endothelial cells would detoxify HCY by forming the corresponding S-nitrosothiol, S-nitroso-homocysteine. In an attempt to prove this hypothesis, media containing 1 mM L-arginine, 1 microM bradykinin, a known NO agonist, and one of the biologically relevant thiols (HCY, cysteine, or glutathione) at concentrations of 0, 0.05, 0.5 and 5.0 mM were incubated with bovine aortic endothelial cells (BAEC) for 0.5, 1 and 4 h. S-nitrosothiol (RSNO) concentrations were measured by photolysis-chemiluminescence. Nitric oxide synthase (eNOS or isoform 3) activity and Nos 3 steady-state mRNA levels were determined by the conversion of [3H]L-arginine to [3H]L-citrulline and Northern analysis, respectively. Results demonstrate that increasing concentrations of HCY, and not cysteine or glutathione, in the presence of bradykinin at 0.5, 1, and 4 h led to significant (P < 0.05 by ANOVA) time- and dose-dependent increases in RSNO produced by BAEC. Cells exposed to 1 microM calcium ionophore A23187 in the presence of 5.0 mM HCY also produced a time-dependent increase in RSNO compared to control (P < 0.05 by ANOVA). In an attempt to determine if de novo synthesis was occurring, BAEC were treated with bradykinin following a 4 h pretreatment with HCY. Pretreatment with HCY followed by stimulation also led to a time- and dose-dependent increase in RSNO production (P < 0.05 by ANOVA). Using high performance liquid chromatography with electrochemical detection, S-nitroso-homocysteine was identified following treatment of BAEC with HCY and bradykinin. The increase in RSNO production in the presence of bradykinin and HCY at 4 h occurred concomitantly with a 78% increase in eNOS activity and a 58% increase in steady-state Nos 3 mRNA, with no change in Nos 3 mRNA half-life, compared to control. A partial explanation for HCY's unique ability to support an increase in NO production was demonstrated by showing that the t1/2 of HCY in media was greater than that of cysteine or glutathione. These data show that, in the presence of an NO agonist, HCY increases RSNO production in a time- and dose-dependent fashion that is reflected by an increase in eNOS activity and Nos 3 transcription. These results suggest that stimulation of endogenous NO, or provision of an exogenous NO donor, may ameliorate endothelial cell injury and thereby decrease the atherothrombotic risk of hyperhomocyst(e)inemic states.

Quantitative measurement for endothelial constitutive nitric oxide synthase in cultured human endothelial cells

Constitutively expressed endothelial nitric oxide synthase (ecNOS) produces nitric oxide (NO) from L-arginine and is important for the maintenance of cardiovascular homeostasis. We report the development of a capture ELISA which is specific for ecNOS. The assay detection limit is 0.5 ng/ml ecNOS protein, allowing the measurement of ecNOS from as few as 6000 human endothelial cells cultured in 96-well microtiter plates. This ELISA has been used to measure a downregulation of ecNOS with 24-h TNFalpha treatment, consistent with results obtained by Western blot analysis. Quantitation of ecNOS in human endothelial cells showed a higher expression of ecNOS in human aortic endothelial cells (18.3+/-1.35 ng ecNOS per 10(6) cells, n = 3 donors) than in human umbilical vein endothelial cells (10.4+/-0.48 ng ecNOS per 10(6) cells, n = 3 donors). These studies demonstrate that this convenient, quantitative assay is currently the most sensitive method for investigating ecNOS protein regulation.

Inhibition of macrophage scavenger receptor activity by tumor necrosis factor-alpha is transcriptionally and post-transcriptionally regulated

Regulation of expression of the scavenger receptor is thought to play a critical role in the accumulation of lipid by macrophages in atherosclerosis. Tumor necrosis factor-alpha (TNF-alpha) has been shown to suppress macrophage scavenger receptor function (van Lenten, B.J., and Fogelman, A.M. (1992) J. Immunol. 148, 112-6). However, the mechanism by which it does so is unknown. We evaluated the mechanism by which TNF-alpha inhibited macrophage scavenger receptor surface expression and binding of acetylated low density lipoprotein (aLDL). Binding of aLDL to phorbol 12-myristate 13-acetate (PMA)-differentiated THP-1 macrophages was suppressed by TNF-alpha in a dose-dependent manner. Inhibition of aLDL binding was paralleled by a reduction of macrophage scavenger receptor protein as detected by the Western blot. TNF-alpha partially decreased macrophage scavenger receptor mRNA steady state levels in PMA-differentiated THP-1 macrophages, a result that was confirmed by reverse transcription-polymerase chain reaction. PMA increased the luciferase activity driven by the macrophage scavenger receptor promoter in the transfected cells, whereas TNF-alpha partially reduced luciferase activity. However, macrophage scavenger receptor mRNA half-life was dramatically reduced in cells treated with TNF-alpha relative to untreated cells. Reduction in macrophage scavenger receptor message in response to TNF-alpha was dependent on new protein synthesis because it was blocked by cycloheximide. These results indicate that TNF-alpha regulates macrophage scavenger receptor expression in PMA-differentiated THP-1 macrophages by transcriptional and post-transcriptional mechanisms but principally by destabilization of macrophage scavenger receptor mRNA.