Tumor necrosis factor-alpha inhibits endothelium-dependent relaxation

Mechanistic, participant, and movement-related factors that contribute to low-flow-mediated constriction

Endothelial function is commonly determined via the ultrasound-based flow-mediated dilation (FMD) technique which assesses arterial dilation in response to a hyperemia response following distal cuff occlusion. However, the low-flow-mediated constriction (L-FMC) response during cuff-induced ischemia is often overlooked. L-FMC provides unique information regarding endothelial function, but vascular researchers may be unclear on what this metric adds. Therefore, the objective of this review was to examine the mechanistic determinants and participant-level factors of L-FMC. Existing mechanistic studies have demonstrated that vasoreactivity to low flow may be mediated via non-nitric oxide vasodilators (i.e., endothelial hyperpolarizing factors and/or prostaglandins), inflammatory markers, and enhancement of vasoconstriction via endothelin-1. In general, participant-level factors such as aging and presence of cardiovascular conditions generally are associated with attenuated L-FMC responses. However, the influence of sex on L-FMC is unclear with divergent results between L-FMC in upper versus lower limb vessels. The ability of aerobic exercise to augment L-FMC (i.e., make more negative) is well supported, but there is a major gap in the literature concerning the mechanistic underpinnings of this observation. This review summarizes that while larger L-FMC responses are generally healthy, the impact of interventions to augment/attenuate L-FMC has not included mechanistic measures that would provide insight into non-nitric oxide-based endothelial function. Clarifications to terminology and areas of further inquiry as it relates to the specific pharmacological, individual-level factors, and lifestyle behaviors that impact L-FMC are highlighted. A greater integration of mechanistic work alongside applied lifestyle interventions is required to better understand endothelial cell function to reductions in local blood flow.

Etanercept Prevents Endothelial Dysfunction in Cafeteria Diet-Fed Rats

Obesity is associated with endothelial dysfunction and this relationship is probably mediated in part by inflammation. Objective: The current study evaluated the effects of etanercept, a tumor necrosis factor-alpha (TNF-α) inhibitor, on endothelial and vascular reactivity, endothelial nitric oxide synthase (eNOS) immunoreactivity, and serum and aortic concentrations of TNF-α in a diet-induced rat model. Design and results: Male weanling Wistar rats were exposed to a standard diet and cafeteria diet (CD) for 12 weeks and etanercept was administered during CD treatment. Isolated aortas of the rats were used for isometric tension recording. Carbachol-induced relaxant responses were impaired in CD-fed rats, while etanercept treatment improved these endothelium-dependent relaxations. No significant change was observed in papaverine- and sodium nitroprusside (SNP)-induced relaxant responses. eNOS expression decreased in CD-fed rats, but no change was observed between etanercept-treated CD-fed rats and control rats. CD significantly increased both the serum and the aortic levels of TNF-α, while etanercept treatment suppressed these elevated levels. CD resulted in a significant increase in the body weight of the rats. Etanercept-treated (ETA) CD-fed rats gained less weight than both CD-fed and control rats.

Ecklonia Cava Extract Attenuates Endothelial Cell Dysfunction by Modulation of Inflammation and Brown Adipocyte Function in Perivascular Fat Tissue

It is well known that perivascular fat tissue (PVAT) dysfunction can induce endothelial cell (EC) dysfunction, an event which is related with various cardiovascular diseases. In this study, we evaluated whether Ecklonia cava extract (ECE) and pyrogallol-phloroglucinol-6,6-bieckol (PPB), one component of ECE, could attenuate EC dysfunction by modulating diet-induced PVAT dysfunction mediated by inflammation and ER stress. A high fat diet (HFD) led to an increase in the number and size of white adipocytes in PVAT; PPB and ECE attenuated those increases. Additionally, ECE and PPB attenuated: (i) an increase in the number of M1 macrophages and the expression level of monocyte chemoattractant protein-1 (MCP-1), both of which are related to increases in macrophage infiltration and induction of inflammation in PVAT, and (ii) the expression of pro-inflammatory cytokines (e.g., tumor necrosis factor-α (TNF-α) and interleukin (IL)-6, chemerin) in PVAT which led to vasoconstriction. Furthermore, ECE and PPB: (i) enhanced the expression of adiponectin and IL-10 which had anti-inflammatory and vasodilator effects, (ii) decreased HFD-induced endoplasmic reticulum (ER) stress and (iii) attenuated the ER stress mediated reduction in sirtuin type 1 (Sirt1) and peroxisome proliferator-activated receptor γ (PPARγ) expression. Protective effects against decreased Sirt1 and PPARγ expression led to the restoration of uncoupling protein -1 (UCP-1) expression and the browning process in PVAT. PPB or ECE attenuated endothelial dysfunction by enhancing the pAMPK-PI3K-peNOS pathway and reducing the expression of endothelin-1 (ET-1). In conclusion, PPB and ECE attenuated PVAT dysfunction and subsequent endothelial dysfunction by: (i) decreasing inflammation and ER stress, and (ii) modulating brown adipocyte function.

NADPH oxidase 2 inhibitors CPP11G and CPP11H attenuate endothelial cell inflammation & vessel dysfunction and restore mouse hind-limb flow

First described as essential to the phagocytic activity of leukocytes, Nox2-derived ROS have emerged as mediators of a range of cellular and tissue responses across species from salubrious to deleterious consequences. Knowledge of their role in inflammation is limited, however. We postulated that TNFα-induced endothelial reactive oxygen species (ROS) generation and pro-inflammatory signaling would be ameliorated by targeting Nox2. Herein, we in silico-modelled two first-in-class Nox2 inhibitors developed in our laboratory, explored their cellular mechanism of action and tested their efficacy in in vitro and mouse in vivo models of inflammation. Our data show that these inhibitors (CPP11G and CPP11H) disrupted canonical Nox2 organizing factor, p47^phox, translocation to Nox2 in the plasma membrane; and abolished ROS production, markedly attenuated stress-responsive MAPK signaling and downstream AP-1 and NFκB nuclear translocation in human cells. Consequently, cell adhesion molecule expression and monocyte adherence were significantly inhibited by both inhibitors. In vivo, TNFα-induced ROS and inflammation were ameliorated by targeted Nox2 inhibition, which, in turn, improved hind-limb blood flow. These studies identify a proximal role for Nox2 in propagated inflammatory signaling and support therapeutic value of Nox2 inhibitors in inflammatory disease.

Pro-contractile effects of perivascular fat in health and disease

Perivascular adipose tissue (PVAT) is now recognized as an active player in vascular homeostasis. The expansion of PVAT in obesity and its possible role in vascular dysfunction have attracted much interest. In terms of the regulation of vascular tone and blood pressure, PVAT has been shown to release vasoactive mediators, for instance, angiotensin peptides, reactive oxygen species, chemokines and cytokines. The secretory profile of PVAT is altered by obesity, hypertension and other cardiovascular diseases, leading to an imbalance between its pro-contractile and anti-contractile effects. PVAT adipocytes represent an important source of the mediators, but infiltrating immune cells may become more important under conditions of hypoxia and inflammation. This review describes recent advances in the effects of PVAT on the regulation of vascular tone, highlighting the evidence for a pro-contractile action in health and disease. The role of the endothelium, vascular smooth muscle, immune cells and probably perivascular nerves in PVAT function is also discussed.

LINKED ARTICLES

This article is part of a themed section on Molecular Mechanisms Regulating Perivascular Adipose Tissue - Potential Pharmacological Targets? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.20/issuetoc.

Protective vascular effects of quercitrin in acute TNBS-colitis in rats: the role of nitric oxide

Quercitrin (quercetin 3-rhamnoside) is a bioflavonoid with anti-inflammatory activity in experimental colitis.

Perivascular adipose tissue, vascular reactivity and hypertension

Most blood vessels are surrounded by a variable amount of adventitial adipose tissue, perivascular adipose tissue (PVAT), which was originally thought to provide mechanical support for the vessel. It is now known that PVAT secretes a number of bioactive substances including vascular endothelial growth factor, tumor necrosis factor-alpha (TNF-α), leptin, adiponectin, insulin-like growth factor, interleukin-6, plasminogen activator substance, resistin and angiotensinogen. Several studies have shown that PVAT significantly modulated vascular smooth muscle contractions induced by a variety of agonists and electrical stimulation by releasing adipocyte-derived relaxing (ADRF) and contracting factors. The identity of ADRF is not yet known. However, several vasodilators have been suggested including adiponectin, angiotensin 1-7, hydrogen sulfide and methyl palmitate. The anticontractile effect of PVAT is mediated through the activation of potassium channels since it is abrogated by inhibiting potassium channels. Hypertension is characterized by a reduction in the size and amount of PVAT and this is associated with the attenuated anticontractile effect of PVAT in hypertension. However, since a reduction in size and amount of PVAT and the attenuated anticontractile effect of PVAT were already evident in prehypertensive rats with no evidence of impaired release of ADRF, there is the possibility that the anticontractile effect of PVAT was not directly related to an altered function of the adipocytes per se. Hypertension is characterized by low-grade inflammation and infiltration of macrophages. One of the adipokines secreted by macrophages is TNF-α. It has been shown that exogenously administered TNF-α enhanced agonist-induced contraction of a variety of vascular smooth muscle preparations and reduced endothelium-dependent relaxation. Other procontractile factors released by the PVAT include angiotensin II and superoxide. It is therefore possible that the loss could be due to an increased amount of these proinflammatory and procontractile factors. More studies are definitely required to confirm this.

The interleukin-1 receptor antagonist anakinra improves endothelial dysfunction in streptozotocin-induced diabetic rats

Background

Endothelial dysfunction is a crucial early phenomenon in vascular diseases linked to diabetes mellitus and associated to enhanced oxidative stress. There is increasing evidence about the role for pro-inflammatory cytokines, like interleukin-1β (IL-1β), in developing diabetic vasculopathy. We aimed to determine the possible involvement of this cytokine in the development of diabetic endothelial dysfunction, analysing whether anakinra, an antagonist of IL-1 receptors, could reduce this endothelial alteration by interfering with pro-oxidant and pro-inflammatory pathways into the vascular wall.

Results

In control and two weeks evolution streptozotocin-induced diabetic rats, either untreated or receiving anakinra, vascular reactivity and NADPH oxidase activity were measured, respectively, in isolated rings and homogenates from mesenteric microvessels, while nuclear factor (NF)-κB activation was determined in aortas. Plasma levels of IL-1β and tumor necrosis factor (TNF)-α were measured by ELISA. In isolated mesenteric microvessels from control rats, two hours incubation with IL-1β (1 to 10 ng/mL) produced a concentration-dependent impairment of endothelium-dependent relaxations, which were mediated by enhanced NADPH oxidase activity via IL-1 receptors. In diabetic rats treated with anakinra (100 or 160 mg/Kg/day for 3 or 7 days before sacrifice) a partial improvement of diabetic endothelial dysfunction occurred, together with a reduction of vascular NADPH oxidase and NF-κB activation. Endothelial dysfunction in diabetic animals was also associated to higher activities of the pro-inflammatory enzymes cyclooxygenase (COX) and the inducible isoform of nitric oxide synthase (iNOS), which were markedly reduced after anakinra treatment. Circulating IL-1β and TNF-α levels did not change in diabetic rats, but they were lowered by anakinra treatment.

Conclusions

In this short-term model of type 1 diabetes, endothelial dysfunction is associated to an IL-1 receptor-mediated activation of vascular NADPH oxidase and NF-κB, as well as to vascular inflammation. Moreover, endothelial dysfunction, vascular oxidative stress and inflammation were reduced after anakinra treatment. Whether this mechanism can be extrapolated to a chronic situation or whether it may apply to diabetic patients remain to be established. However, it may provide new insights to further investigate the therapeutic use of IL-1 receptor antagonists to obtain vascular benefits in patients with diabetes mellitus and/or atherosclerosis.

Soluble CD163 is associated with body mass index and blood pressure in hypertensive obese Saudi patients

BACKGROUND

The hallmark of vascular inflammation is the recruitment of circulating leucocytes, primarily monocytes, macrophages and T lymphocytes, into the vascular wall; however, the link between monocyte/macrophage activation and hypertension has not been established as yet. In this study, we determined how sCD163, a monocyte/macrophage soluble scavenger receptor and immunomodulator, relates to arterial blood pressure (BP) in hypertensive Saudi individuals.

MATERIALS AND METHODS

A total of 90 (30 non-hypertensive obese, 30 hypertensive obese and 30 lean normotensive controls) adult Saudi subjects, aged 40-60 years, participated in this cross-sectional study. Serum fasting blood glucose, triglycerides, total cholesterol, HDL-cholesterol (HDL-C), LDL-cholesterol (LDL-C), leptin, adiponectin, resistin, insulin, tumour necrosis factor-alpha (TNF-α), PAI-1, angiotensin II, high-sensitivity C-reactive protein (hsCRP) and sCD163 were measured in all subjects studied.

RESULTS

sCD163 concentrations were significantly increased in obese hypertensive patients compared to controls (P=0.016). Positive correlations between sCD163 and body mass index (BMI) (r=0.27, P=0.01), systolic BP (r=0.25, P=0.01), diastolic BP (r=0.33, P=0.001), LDL-C (r=0.21, P=0.04), TNF-α (r=0.23, P=0.02) and hsCRP (r=0.33, P=0.008) were observed. Positive correlations between sCD163 and diastolic BP (r=0.23, P=0.04) and LDL-C (r=0.22, P=0.03) remained significant after controlling for BMI.

CONCLUSIONS

Taken together, these data demonstrate that the monocyte/macrophage activation-related sCD163 is positively associated with BMI and increased arterial BP with the elevation in diastolic BP being independent of the BMI.

Soluble CD163 is associated with body mass index and blood pressure in hypertensive obese Saudi patients

Eur J Clin Invest 2012; 42 (11): 1221–1226

Abstract

Background  The hallmark of vascular inflammation is the recruitment of circulating leucocytes, primarily monocytes, macrophages and T lymphocytes, into the vascular wall; however, the link between monocyte/macrophage activation and hypertension has not been established as yet. In this study, we determined how sCD163, a monocyte/macrophage soluble scavenger receptor and immunomodulator, relates to arterial blood pressure (BP) in hypertensive Saudi individuals.

Materials and methods  A total of 90 (30 non‐hypertensive obese, 30 hypertensive obese and 30 lean normotensive controls) adult Saudi subjects, aged 40–60 years, participated in this cross‐sectional study. Serum fasting blood glucose, triglycerides, total cholesterol, HDL‐cholesterol (HDL‐C), LDL‐cholesterol (LDL‐C), leptin, adiponectin, resistin, insulin, tumour necrosis factor‐alpha (TNF‐α), PAI‐1, angiotensin II, high‐sensitivity C‐reactive protein (hsCRP) and sCD163 were measured in all subjects studied.

Results  sCD163 concentrations were significantly increased in obese hypertensive patients compared to controls (P = 0·016). Positive correlations between sCD163 and body mass index (BMI) (r = 0·27, P = 0·01), systolic BP (r = 0·25, P = 0·01), diastolic BP (r = 0·33, P = 0·001), LDL‐C (r = 0·21, P = 0·04), TNF‐α (r = 0·23, P = 0·02) and hsCRP (r = 0·33, P = 0·008) were observed. Positive correlations between sCD163 and diastolic BP (r = 0·23, P = 0·04) and LDL‐C (r = 0·22, P = 0·03) remained significant after controlling for BMI.

Conclusions  Taken together, these data demonstrate that the monocyte/macrophage activation‐related sCD163 is positively associated with BMI and increased arterial BP with the elevation in diastolic BP being independent of the BMI.

Ghrelin maintains the cardiovascular stability in severe sepsis

BACKGROUND

Cardiovascular dysfunction, characterized by reduced cardiac contractility and depressed endothelium-dependent vascular relaxation, is common in severe sepsis. Although it is known that ghrelin produces beneficial effects following various adverse circulatory conditions, it remains unknown whether ghrelin increases cardiac contractility and improves vascular responsiveness to vasoactive agents in severe sepsis.

METHODS

Male adult rats were subjected to sepsis by cecal ligation and puncture (CLP). At 5 h after CLP, a bolus intravenous injection of 2 nmol ghrelin was followed by a continuous infusion of 12 nmol ghrelin via a primed mini-pump over 15 h. At 20 h after CLP (i.e., severe sepsis), the maximal rates of ventricular pressure increase (+dP/dt(max)) and decrease (-dP/dt(max)) were determined in vivo. In additional groups of animals, the thoracic aortae were isolated at 20 h after CLP. The aortae were cut into rings, and placed in organ chambers. Norepinephrine (NE) was used to induce vascular contraction. Dose responses for an endothelium-dependent vasodilator, acetylcholine (ACh), and an endothelium-independent vasodilator, nitroglycerine (NTG) were carried out.

RESULTS

+dP/dt(max) and -dP/dt(max) decreased significantly at 20 h after CLP. Treatment with ghrelin significantly increased +dP/dt(max) and -dP/dt(max) by 36% (P < 0.05) and 35% (P < 0.05), respectively. Moreover, NE-induced vascular contraction and endothelium-dependent (ACh-induced) vascular relaxation decreased significantly at 20 h after CLP. Administration of ghrelin, however, increased NE-induced vascular contraction and ACh-induced vascular relaxation. In contrast, no significant reduction in NTG-induced vascular relaxation was seen in rats with severe sepsis irrespective of ghrelin treatment.

CONCLUSIONS

Ghrelin may be further developed as a useful agent for maintaining cardiovascular stability in severe sepsis.

Pentoxifylline Lowers Plasminogen Activator Inhibitor 1 Levels in Obese Individuals: A Pilot Study

Plasminogen activator inhibitor 1 (PAI-1), the primary inhibitor of fibrinolysis and C-reactive protein (CRP), is a predictor of myocardial infarction. Both are upregulated by tumor necrosis factor-alpha (TNF-α) within the obese population. This pilot study tested the hypothesis that TNF-α blockade with pentoxifylline lowers PAI-1 and high-sensitivity CRP (hsCRP) in obese individuals. Twenty participants were treated with pentoxifylline for 8 weeks. A proportional odds model was used to compare the change in PAI-1 and CRP in the pentoxifylline and placebo groups. Plasminogen activator inhibitor 1, but not hsCRP levels, decreased over the 8-week period of the study ( P = .025 and P = NS). There was significant dropout of participants due to drug tolerability. These findings suggest that these markers of cardiovascular risk are differentially regulated in obesity and that PAI-1 levels can be reduced by pentoxifylline in this population.

Role of adipokines in obesity-associated hypertension

It has been well documented that obesity is a major risk factor for the development of the hypertensive state. The correlation between body mass index and blood pressure level is well established. Nevertheless, the exact mechanisms which contribute to obesity-related hypertension remain poorly understood. In the last years, we have realized that the white adipose tissue is not just an inert organ for nutrient storage and isolation but rather depending on the body mass index the biggest endocrinological organ. Thus, the possible contribution of adipokines to the blood pressure elevation becomes an attractive hypothesis to explain the hypertensive state that often occurs in obesity. In this review, we consider direct and indirect effects of main adipokines on structural and functional changes in the cardiovascular system.

Assessment of activity of Crohn's disease by Doppler sonography of superior mesenteric artery flow

BACKGROUND

Evaluation of activity of Crohn's disease is based on CDAI. Several other tools have been studied to assess disease activity with more accuracy.

AIMS

To assess the correlation between Doppler parameters of superior mesenteric artery and disease activity and to assess the accuracy of these parameters in discriminating between active and quiescent Crohn's disease.

MATERIAL AND METHODS

We perform a prospective study including non-operated and non-complicated Crohn's disease patients involving terminal ileum and/or right colon and sex and age-matched controls. Doppler sonography of superior mesenteric artery was performed in all subjects.

RESULTS

We studied 41 patients and 15 controls. There was no statistical difference between patients and controls according to the studied US parameters. The difference in resistance index between the three groups using analysis of variance is not significant (p=0.064). Resistance index was significantly lower in patients with active disease compared to inactive disease patients (0.82 +/- 0.04 vs 0.85 +/- 0.03; p=0.01). Pulsatility index was also lower in patients with active disease compared to inactive disease patients (1.37 +/- 0.21 vs 1.53 +/- 0.15; p=0.01). A value of resistance index less than 0.79 predicted active disease with a sensitivity of 35.3% and specificity of 95.7%. A value of pulsatility index less than 1.56 predicted active disease with a sensitivity of 94.1% and specificity of 43.5%. In case of resistance index less than 0.79 and pulsatility index less than 1.56 in the same patient, the probability of active disease was 86%. However, in case of resistance index over than 0.79 and pulsatility index over than 1.56, this probability was only 9%. In Crohn's disease patients, correlation study showed that resistance index value was significantly correlated with CDAI (r=-0.46; p=0.003). Pulsatility index value was also correlated with CDAI (r=-0.39; p=0.01).

CONCLUSION

Doppler sonographic parameters of superior mesenteric artery are significantly correlated with disease activity in non-operated and non-complicated Crohn's disease.

Tumor necrosis factor-alpha as a therapeutic target for diabetic nephropathy

Activation of innate immunity with the subsequent development of a chronic low-grade inflammatory response is now recognized as a critical factor in the pathogenesis of diabetes mellitus and diabetic complications, including diabetic nephropathy. In the setting of diabetic nephropathy, there is now evidence of the relevant contribution of pro-inflammatory cytokines, with special participation of tumor necrosis factor-alpha (TNF-alpha). This new pathogenic perspective leads to new therapeutic implications derived from modulation of inflammation and inflammatory cytokines. Experimental studies have shown the beneficial renal actions derived from TNF-alpha inhibition with the use of soluble TNF-alpha receptor fusion proteins, chimeric monoclonal antibodies and pentoxifylline (PTF). Clinical application of this strategy is nowadays limited to PTF administration, which has demonstrated significant beneficial effects in patients with diabetic nephropathy. Overall, these studies indicate that inhibition of TNF-alpha might be an efficacious treatment for renal disease secondary to diabetes mellitus.

Role of TNF-alpha in vascular dysfunction

Healthy vascular function is primarily regulated by several factors including EDRF (endothelium-dependent relaxing factor), EDCF (endothelium-dependent contracting factor) and EDHF (endothelium-dependent hyperpolarizing factor). Vascular dysfunction or injury induced by aging, smoking, inflammation, trauma, hyperlipidaemia and hyperglycaemia are among a myriad of risk factors that may contribute to the pathogenesis of many cardiovascular diseases, such as hypertension, diabetes and atherosclerosis. However, the exact mechanisms underlying the impaired vascular activity remain unresolved and there is no current scientific consensus. Accumulating evidence suggests that the inflammatory cytokine TNF (tumour necrosis factor)-α plays a pivotal role in the disruption of macrovascular and microvascular circulation both in vivo and in vitro. AGEs (advanced glycation end-products)/RAGE (receptor for AGEs), LOX-1 [lectin-like oxidized low-density lipoprotein receptor-1) and NF-κB (nuclear factor κB) signalling play key roles in TNF-α expression through an increase in circulating and/or local vascular TNF-α production. The increase in TNF-α expression induces the production of ROS (reactive oxygen species), resulting in endothelial dysfunction in many pathophysiological conditions. Lipid metabolism, dietary supplements and physical activity affect TNF-α expression. The interaction between TNF-α and stem cells is also important in terms of vascular repair or regeneration. Careful scrutiny of these factors may help elucidate the mechanisms that induce vascular dysfunction. The focus of the present review is to summarize recent evidence showing the role of TNF-α in vascular dysfunction in cardiovascular disease. We believe these findings may prompt new directions for targeting inflammation in future therapies.

Role of Reactive Oxygen Species in Tumor Necrosis Factor-alpha Induced Endothelial Dysfunction

Endothelial cell injury and dysfunction are the major triggers of pathophysiological processes leading to cardiovascular disease. Endothelial dysfunction (ED) has been implicated in atherosclerosis, hypertension, coronary artery disease, vascular complications of diabetes, chronic renal failure, insulin resistance and hypercholesterolemia. Although now recognized as a class of physiological second messengers, reactive oxygen species (ROS) are important mediators in cellular injury, specifically, as a factor in endothelial cell damage. Uncontrolled ROS production and/or decreased antioxidant activity results in a deleterious state referred to as 'oxidative stress'. A candidate factor in causing ROS production in endothelial cells is tumor necrosis factor alpha (TNF-α), a pleiotropic inflammatory cytokine. TNF-α has been shown to both be secreted by endothelial cells and to induce intracellular ROS formation. These observations provide a potential mechanism by which TNF-α may activate and injure endothelial cells resulting in ED. In this review, we focus on the relationship between intracellular ROS formation and ED in endothelial cells or blood vessels exposed to TNF-α to provide insight into the role of this important cytokine in cardiovascular disease.

Impairment of NO-dependent relaxation in intralobar pulmonary arteries: comparison of urban particulate matter and manufactured nanoparticles

BACKGROUND AND OBJECTIVES

Because pulmonary circulation is the primary vascular target of inhaled particulate matter (PM), and nitric oxide is a major vasculoprotective agent, in this study we investigated the effect of various particles on the NO-cyclic guanosine monophosphate (cGMP) pathway in pulmonary arteries.

METHODS

We used intrapulmonary arteries and/or endothelial cells, either exposed in vitro to particles or removed from PM-instilled animals for assessment of vasomotricity, cGMP and reactive oxygen species (ROS) levels, and cytokine/chemokine release.

RESULTS

Endothelial NO-dependent relaxation and cGMP accumulation induced by acetylcholine (ACh) were both decreased after 24 hr exposure of rat intrapulmonary arteries to standard reference material 1648 (SRM1648; urban PM). Relaxation due to NO donors was also decreased by SRM1648, whereas responsiveness to cGMP analogue remained unaffected. Unlike SRM1648, ultrafine carbon black and ultrafine and fine titanium dioxide (TiO2) manufactured particles did not impair NO-mediated relaxation. SRM1648-induced decrease in relaxation response to ACh was prevented by dexamethasone (an anti-inflammatory agent) but not by antioxidants. Accordingly, SRM1648 increased the release of proinflammatory mediators (tumor necrosis factor-alpha, interleukin-8) from intrapulmonary arteries or pulmonary artery endothelial cells, but did not elevate ROS levels within intrapulmonary arteries. Decreased relaxation in response to ACh was also evidenced in intrapulmonary arteries removed from rats intratracheally instilled with SRM1648, but not with fine TiO2.

CONCLUSION

In contrast to manufactured particles (including nanoparticles), urban PM impairs NO but not cGMP responsiveness in intrapulmonary arteries. We attribute this effect to oxidative-stress-independent inflammatory response, resulting in decreased guanylyl cyclase activation by NO. Such impairment of the NO pathway may contribute to urban-PM-induced cardiovascular dysfunction.

Influence of acute pancreatitis on the in vitro responsiveness of rat mesenteric and pulmonary arteries

Background

Acute pancreatitis is an inflammatory disease characterized by local tissue injury and systemic inflammatory response leading to massive nitric oxide (NO) production and haemodynamic disturbances. Therefore, the aim of this work was to evaluate the vascular reactivity of pulmonary and mesenteric artery rings from rats submitted to experimental pancreatitis.

Male Wistar rats were divided into three groups: saline (SAL); tauracholate (TAU) and phospholipase A₂ (PLA₂). Pancreatitis was induced by administration of TAU or PLA₂ from Naja mocambique mocambique into the common bile duct of rats, and after 4 h of duct injection the animals were sacrificed. Concentration-response curves to acetylcholine (ACh), sodium nitroprusside (SNP) and phenylephrine (PHE) in isolated mesenteric and pulmonary arteries were obtained. Potency (pEC₅₀) and maximal responses (E_MAX) were determined. Blood samples were collected for biochemical analysis.

Results

In mesenteric rings, the potency for ACh was significantly decreased from animals treated with TAU (about 4.2-fold) or PLA₂ (about 6.9-fold) compared to saline group without changes in the maximal responses. Neither pEC₅₀ nor E_MAX values for Ach were altered in pulmonary rings in any group. Similarly, the pEC₅₀ and the E_MAX values for SNP were not changed in both preparations in any group. The potency for PHE was significantly decreased in rat mesenteric and pulmonary rings from TAU group compared to SAL group (about 2.2- and 2.69-fold, for mesenteric and pulmonary rings, respectively). No changes were seen in the E_MAX for PHE. The nitrite/nitrate (NO_x^-) levels were markedly increased in animals submitted to acute pancreatitis as compared to SAL group, approximately 76 and 68% in TAU and PLA₂ protocol, respectively.

Conclusion

Acute pancreatitis provoked deleterious effects in endothelium-dependent relaxing response for ACh in mesenteric rings that were strongly associated with high plasma NO_x^- levels as consequence of intense inflammatory responses. Furthermore, the subsensitivity of contractile response to PHE in both mesenteric and pulmonary rings might be due to the complications of this pathological condition in the early stage of pancreatitis.

Testosterone augments endotoxin-mediated cerebrovascular inflammation in male rats

Activation of inflammatory mechanisms contributes to cerebrovascular pathophysiology. Male gender is associated with increased stroke risk, yet little is known about the effects of testosterone in the cerebral circulation. Therefore, we explored the impact of testosterone treatment on cerebrovascular inflammation with both in vivo and in vitro models of inflammation. We hypothesized that testosterone would augment the expression of two vascular markers of cellular inflammation, cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS). Using four groups of male rats [intact, orchiectomized (ORX), and ORX treated with either testosterone (ORXT) or the testosterone metabolite 17β-estradiol (ORXE)], we determined effects of the sex hormones on cerebrovascular inflammation after intraperitoneal LPS injection. Western blot analysis showed that induction of inflammatory markers was increased in cerebral blood vessels from ORXT rats compared with intact or ORX rats. In contrast, in cerebral blood vessels from ORXE rats, there was a significant decrease in endotoxin-induced COX-2 and iNOS protein levels. Confocal microscopy of cerebral blood vessels from ORXT rats showed increased COX-2 and iNOS immunoreactivity in both endothelial and smooth muscle cells after LPS treatment. In vitro incubation with LPS also induced COX-2 in pial vessels isolated from the four animal treatment groups, with the greatest induction observed in ORXT vessels compared with the ORX and ORXE groups. Production of PGE2, a principal COX-2-derived prostaglandin end product, was also greatest in cerebral vessels isolated from ORXT rats. In conclusion, testosterone increases cerebrovascular inflammation; this effect may contribute to stroke differences between men and women.

Effect of Acute Sublethal Endotoxaemia on In Vitro Digital Vascular Reactivity in Horses

Endotoxaemia is a syndrome linked to the development of equine laminitis; however, the relationship between them is uncertain. The aim of this experiment was to evaluate the effect of an experimental acute sublethal endotoxaemia model on in vitro equine palmar digital vascular reactivity. Rings of arteries and veins of each forelimb were obtained from 11 clinically healthy horses submitted to two surgical procedures, 3 weeks apart. Before the second surgery, 0.25 microg/kg of lipopolysaccharide from Escherichia coli O55:B5 in saline, was administered i.v. in 30 min. After 3 h, the vessels were harvested and submitted to in vitro vascular reactivity experiments and histopathology. The response to depolarizing Krebs solution (DKS, 40 mm), phenylephrine (PHE), acetylcholine (ACh) and sodium nitroprusside (SNP) were evaluated. All horses showed colic pain and watery diarrhoea, tachycardia, tachypnea, hyperthermia and leucopenia. Concentration-response curve (CRC) to PHE was shifted to the left in arteries rings from endotoxemic horses without any effect on vein rings. The CRC to ACh was shifted to the right with a reduction in the maximal response. The response to SNP and DKS was similar between groups. There was no evidence of histopathological effects. The increased response to PHE in digital arteries together with a reduction of the endothelium-dependent response to ACh in arteries and veins, confirm the existing reports where endotoxaemia was found to modify the digital vascular reactivity during the acute phase. As the digital endothelial function is impaired, there may be an increased potential to develop a digital prothrombotic state with a reduced vasodilatory capacity.

Modulation of cerebral vascular tone by activated glia: involvement of nitric oxide

The ability of activated glia to affect cerebral vascular tone has been evaluated using an in vitro experimental system in which basilar arteries were incubated with glial cultures activated by treatment with lipopolysaccharide (LPS). Vascular tone was measured with an isometric myograph. Contraction in response to high KCl and serotonin was reduced in arteries co-incubated for 24 h with LPS-activated glia, whereas the response to acetylcholine was not modified. The reduced contraction was prevented when the nitric oxide synthase (NOS) inhibitor L-N-nitro-arginine (L-NNA) was added throughout the whole incubation time (activation of glial cells with LPS + co-incubation of glial cells with cerebral arteries). Under these conditions, nitrite levels were drastically reduced. A reduced contraction to KCl was also observed after treatment of the cerebral vessel with sodium nitroprusside. In contrast, L-NNA added to the vessel did not modify the response to contracting stimuli and the expression of endothelial NOS was not modified in cerebral arteries pre-incubated with activated glia. These results suggest that activated glia, which finds an in vivo correlate in several neuropathological conditions, can contribute to changes of vascular tone by modifying the levels of nitric oxide (NO) to which the vessel is exposed.

Regulation of pulmonary venous tone in response to muscarinic receptor activation

We investigated cellular mechanisms that mediate or modulate the vascular response to muscarinic receptor activation (ACh) in pulmonary veins (PV). Isometric tension was measured in isolated canine PV rings with endothelium (E+) and without endothelium (E−). Tension and intracellular Ca2+concentration ([Ca2+]i) were measured simultaneously in fura-2-loaded E− PV strips. In the absence of preconstriction, ACh (0.01–10 μM) caused dose-dependent contraction in E+ and E− rings. ACh contraction was potentiated by removing the endothelium or by nitric oxide (NO) synthase inhibition ( N-nitro-l-arginine methyl ester, P = 0.001). Cyclooxygenase inhibition (indomethacin) reduced ACh contraction in both E+ and E− PV rings ( P = 0.013 and P = 0.037, respectively). ACh contraction was attenuated by inhibitors of voltage-operated Ca2+channels (nifedipine, P < 0.001), inositol-1,4,5-trisphosphate (IP3)-mediated Ca2+release (2-aminoethoxydiphenyl borate, P = 0.001), PKC (bisindolylmaleimide I, P = 0.001), Rho-kinase (Y-27632, P = 0.002), and tyrosine kinase (TK; tyrphostin 47, P = 0.015) in E− PV rings. ACh (1 μM) caused a leftward shift in the [Ca2+]i-tension relationship ( P = 0.015), i.e., ACh increased myofilament Ca2+sensitivity. Inhibition of PKC, Rho-kinase, and TK attenuated the ACh-induced increase in myofilament Ca2+sensitivity ( P < 0.001, P < 0.001, and P = 0.024, respectively). These findings indicate that in canine PV, ACh contraction is modulated by NO and partially mediated by metabolites of the cyclooxygenase pathway and involves Ca2+influx through voltage-operated Ca2+channels and IP3-mediated Ca2+release. In addition, ACh induces increased myofilament Ca2+sensitivity, which requires the PKC, Rho-kinase, and TK pathways.

Cyclooxygenase-2 Inhibition Improves Vascular Endothelial Dysfunction in a Rat Model of Endotoxic Shock: Role of Inducible Nitric-Oxide Synthase and Oxidative Stress

We investigated whether cyclooxygenase (COX) isoforms (COX-1 and COX-2) and decreased NO availability contribute to endothelial dysfunction in endotoxemic rats. The involvement of reactive oxygen species (ROS) was also evaluated. Rats were injected with Salmonella-derived lipopolysaccharide or saline. After 6 h, endothelial function of mesenteric resistance arteries was evaluated. In controls, acetylcholine (ACh)-induced relaxation was inhibited by the nitric-oxide synthase inhibitor N(G)-monomethyl-l-arginine (l-NMMA) and unaffected by 5,5-dimethyl-3-(3-fluorophenyl)-4-(4-methylsulphonyl)-phenyl-2(5H)-furanone (DFU) (COX-2 inhibitor). In lipopolysaccharide (LPS)-treated rats, the response to ACh was blunted compared with controls, less sensitive to l-NMMA, and enhanced by DFU. COX-2 blockade also improved the inhibitory effect of l-NMMA on cholinergic relaxation. SC-560 [5-(4-clorophenyl)-1-(4-metoxyphenyl)-3-trifluoromethylpirazole] (COX-1 inhibitor) did not modify the response to ACh in both groups. LPS-induced endothelial dysfunction was unaffected by the thromboxane A(2) (TxA(2)) receptor antagonist SQ-29548 (7-[3-[[2-[(phenylamino)carbonyl]hydrazino]methyl]-7-oxabicyclo[2.2.1] hept-2-yl]-[1S(1alpha,2alpha(Z),3alpha,4alpha)]-5-heptenoic acid). In vivo inducible nitric-oxide synthase (iNOS) inhibition by S-methylisothiourea partly attenuated LPS-induced endothelial dysfunction. The antioxidants ascorbic acid and superoxide dismutase normalized endothelium-dependent relaxation and restored the inhibitory action of l-NMMA on ACh. Responses to sodium nitroprusside were similar in both groups. In LPS-treated rats, reverse transcription-polymerase chain reaction showed a marked increase in mesenteric iNOS and COX-2 expressions, whereas endothelial nitric-oxide synthase and COX-1 were unchanged. LPS-induced COX-2 overexpression was reduced but not abrogated by S-methylisothiourea. LPS-induced COX-2 up-regulation was also documented by immunohistochemistry. In conclusion, mesenteric resistance vessels from endotoxemic rats show impaired endothelial function due to reduced NO availability, a condition that is partly ascribable to an iNOS-dependent enhanced COX-2 expression, whereas TxA(2) does not seem to be involved. Oxidative stress is the main mechanism responsible for reduced NO availability, and COX-2 might act as a source of ROS.

Interleukin-6 impairs endothelium-dependent NO-cGMP-mediated relaxation and enhances contraction in systemic vessels of pregnant rats

IL-6 is elevated in plasma of preeclamptic women, and twofold elevation of plasma IL-6 increases vascular resistance and arterial pressure in pregnant rats, suggesting a role of the cytokine in hypertension of pregnancy. However, whether the hemodynamic effects of IL-6 reflect direct effects of the cytokine on the mechanisms of vascular contraction/relaxation is unclear. The purpose of this study was to test the hypothesis that IL-6 directly impairs endothelium-dependent relaxation and enhances vascular contraction in systemic vessels of pregnant rats. Active stress was measured in aortic strips isolated from virgin and late pregnant Sprague-Dawley rats and then nontreated or treated for 1 h with IL-6 (10 pg/ml to 10 ng/ml). In endothelium-intact vascular strips, phenylephrine (Phe, 10(-5) M) caused an increase in active stress that was smaller in pregnant (4.2 +/- 0.3) than virgin rats (5.1 +/- 0.3 x 10(4) N/m(2)). IL-6 (1,000 pg/ml) caused enhancement of Phe contraction that was greater in pregnant (10.6 +/- 0.7) than virgin rats (7.5 +/- 0.4 x 10(4) N/m(2)). ACh and bradykinin caused relaxation of Phe contraction and increases in vascular nitrite production that were greater in pregnant than virgin rats. IL-6 caused reductions in ACh- and bradykinin-induced vascular relaxation and nitrite production that were more prominent in pregnant than virgin rats. Incubation of endothelium-intact strips in the presence of N(omega)-nitro-L-arginine methyl ester (10(-4) M) to inhibit nitric oxide (NO) synthase, or 1H-[1,2,4]oxadiazolo[4,3]-quinoxalin-1-one (ODQ, 10(-5) M) to inhibit cGMP production in smooth muscle, inhibited ACh-induced relaxation and enhanced Phe-induced stress in nontreated but to a lesser extent in IL-6-treated vessels, particularly those of pregnant rats. Removal of the endothelium enhanced Phe-induced stress in nontreated but not IL-6-treated vessels, particularly those of pregnant rats. In endothelium-denuded strips, relaxation of Phe contraction with sodium nitroprusside, an exogenous NO donor, was not different between nontreated and IL-6-treated vessels of virgin or pregnant rats. Thus IL-6 inhibits endothelium-dependent NO-cGMP-mediated relaxation and enhances contraction in systemic vessels of virgin and pregnant rats. The greater IL-6-induced inhibition of vascular relaxation and enhancement of contraction in systemic vessels of pregnant rats supports a direct role for IL-6 as one possible mediator of the increased vascular resistance associated with hypertension of pregnancy.

Effect of tumour necrosis factor-alpha and interleukin 1beta on endothelium-dependent relaxation in rat mesenteric resistance arteries in vitro

1. Pre-eclampsia is associated with elevated proinflammatory cytokine levels and endothelial dysfunction. This study examined the effect of two cytokines, tumour necrosis factor-alpha (TNF) and interleukin-1beta (IL-1) on endothelium-dependent relaxation in response to acetylcholine (ACH), bradykinin (BK) and histamine (HIS) in rat mesenteric small arteries in vitro. 2. Rat mesenteric arteries were mounted in an isometric myograph. Tone was induced with phenylephrine (PE) or a depolarizing solution containing 80 mM KCl (K(80)). Relaxation was measured in response to ACH, BK, HIS and sodium nitroprusside (SNP), an endothelium-independent relaxant. Inhibition of NO synthase by a combination of N(omega)-monomethyl-L-arginine (L-NMMA) and N(omega)-nitro-L-arginine methyl ester (L-NAME) significantly inhibited relaxation in response to ACH and BK. Addition of an inhibitor of cyclooxygenase, indomethacin, had no additional effect when added to L-NMMA and L-NAME. Inhibition of endothelium-derived hyperpolarizing factor (EDHF) by K(80) partially reduced responses to ACH and BK. Inhibition of HIS-induced relaxation was more marked with K(80). L-NMMA and L-NAME largely abolished the remaining relaxation to ACH, BK and HIS in arteries contracted with K(80). 3. Preincubation with TNF for 30 min caused an inhibition of relaxation in response to ACH and BK in arteries contracted with PE. Responses to HIS and SNP were not affected by TNF under these conditions. TNF also inhibited ACH-induced relaxation in arteries contracted with K(80). IL-1 had no effect on responses to ACH and the combination of TNF and IL-1 was not more effective than TNF alone. 4. The inhibitory effect of TNF on ACH-induced relaxation was abolished by coincubation with superoxide dismutase (SOD) and was not seen if NO synthase was inhibited by L-NMMA and L-NAME. 5. TNF inhibits the NO-dependent component of endothelium-dependent relaxation in response to ACH and BK, but does not inhibit the EDHF-dependent component. This effect may be attributable to the ability of TNF to increase levels of superoxide anions (O(2)(-)) and the ability of O(2)(-) to inactivate NO. This mechanism could contribute to the endothelial dysfunction seen in situations where TNF is elevated, such as pre-eclampsia.

Cyclooxygenase-2 expression and role of vasoconstrictor prostanoids in small mesenteric arteries from patients with Crohn's disease

BACKGROUND

The present study investigates the vascular reactivity and the involvement of nitric oxide and prostanoids in regulating vasoconstriction of small mesenteric arteries from patients with Crohn's disease (CD) to understand the vascular component of this pathology.

METHODS AND RESULTS

An increased production of proinflammatory cytokines (tumor necrosis factor-alpha and interleukins 1beta, 6, and 8) has been observed in biopsy specimens of inflammatory intestinal mucosa. However, contractile responses of small mesenteric arteries from CD patients in response to norepinephrine were not changed ex vivo when compared with controls. Exposure to either the nitric oxide synthase inhibitor N(G)-nitro-L-arginine or the cyclooxygenase (COX) inhibitor indomethacin did not modify contractions induced by norepinephrine in either control or CD patients. However, in the latter, the specific COX-2 inhibitor N-(2-cyclohexyloxy-4-nitrophenyl) methanesulfonamide significantly attenuated norepinephrine-induced vasoconstriction. Furthermore, immunohistochemical analysis showed marked COX-2 expression in the whole arterial wall of vessels from CD patients. Vessels from control patients exhibited weak COX-2 staining in the adventitial and endothelial layers only.

CONCLUSIONS

The above results provide direct evidence for COX-2 expression in small mesenteric arteries from CD patients. They also shed new light on the involvement of vasoconstrictor metabolites of COX in regulating contraction of these arteries. Of particular interest is the balance between vasoconstrictor products from COX-2 and unidentified vasodilatory products that maintained vascular reactivity in a physiological range despite an increase of circulatory cytokines in patients with CD.

TNF-alpha enhances contraction and inhibits endothelial NO-cGMP relaxation in systemic vessels of pregnant rats

Tumor necrosis factor-alpha (TNF-alpha) is elevated in the plasma of preeclamptic women and may have a role in pregnancy-induced hypertension. However, whether the hemodynamic effects of TNF-alpha reflect the direct effects on vascular reactivity is unclear. We tested the hypothesis that TNF-alpha impairs endothelium-dependent relaxation and enhances vascular contraction in systemic vessels of pregnant rats. We measured isometric contraction in aortic strips isolated from virgin and pregnant Sprague-Dawley rats (nontreated vs. treated for 2 h with 10-1,000 pg/ml TNF-alpha). In endothelium-intact vascular strips, TNF-alpha caused greater enhancement of phenylephrine (Phe) contraction in pregnant than virgin rats. TNF-alpha caused significant inhibition of ACh- and bradykinin-induced vascular relaxation and nitrite/nitrate production that were more prominent in pregnant than virgin rats. N(G)-nitro-L-arginine methyl ester [L-NAME, 100 microM, an inhibitor of nitric oxide (NO) synthase] or 1H-[1,2,4]oxadiazolo[4,3]-quinoxalin-1-one (ODQ, 1 microM, an inhibitor of cGMP production in smooth muscle) inhibited ACh relaxation and enhanced Phe contraction in nontreated but to a lesser extent in TNF-alpha-treated vessels, particularly those of pregnant rats. Endothelium removal enhanced Phe contraction in nontreated but not TNF-alpha-treated vessels, especially those of pregnant rats. Relaxation of Phe contraction with the NO donor sodium nitroprusside was not different between nontreated and TNF-alpha-treated vessels. Thus TNF-alpha enhances vascular contraction and inhibits endothelium-dependent NO-cGMP-mediated vascular relaxation in systemic vessels, particularly those of pregnant rats. The results support a direct role for TNF-alpha as a possible mediator of increased vascular resistance associated with pregnancy-induced hypertension.

Impaired contractile response of mesenteric arteries in Crohn's disease

BACKGROUND

Crohn's disease is associated with vascular injury and dysregulation of the intestinal immune system which together can provide disturbance of mesenteric circulation functional properties.

AIM

To evaluate the vascular reactivity of mesenteric arteries from patients with Crohn's disease.

METHODS

Phenylephrine-induced contractions were assessed from 10 patients with Crohn's disease and 8 control organ donors. NG-nitro-L-arginine-methyl-ester (L-NAME) was used to test the presence of inducible NO synthase. Endothelium dependent and independent relaxation was assessed using acetylcholine, bradykinin, calcium ionophore A23187 and sodium nitroprusside.

RESULTS

The contractile response to phenylephrine was significantly decreased in arteries without endothelium from patients with Crohn's disease. Exposure to the NO synthase inhibitor L-NAME restored the contractile response to phenylephrine. Relaxation remained unaltered in both groups.

CONCLUSION

These data provide direct evidence for fading of contraction caused by phenylephrine in Crohn's disease. The restored mesenteric artery tone by a specific NO synthase inhibitor suggests that an increased production for NO in vascular smooth muscle might be responsible of this altered vascular reactivity.

Impaired vascular sensitivity to nitric oxide in the coronary microvasculature after endotoxaemia

1. The effects of endotoxaemia on coronary vasodilator responses to bradykinin (BK), sodium nitroprusside (SNP) and nicardipine were investigated in the rat isolated heart perfused at constant flow ex vivo. 2. Dose-dependent reductions in coronary perfusion pressure reaching a maximum of 56+/-3 and 57+/-5 mmHg were observed for BK and SNP respectively. The BK response was biphasic, consisting of a rapid dilator response that was insensitive to N(G)nitro-L-arginine methyl ester (L-NAME, 0.1 mM) and a second slower component whose duration was attenuated by L-NAME. 3. Hearts obtained from rats treated with endotoxin (2.5 mg kg(-1), i.p.) for 2 or 6 h had increased basal coronary perfusion pressure and reduced vasodilator responses to BK or SNP. Dilator responses to nicardipine were not affected by endotoxin treatment. In vitro perfusion of hearts from endotoxin-treated rats with L-NAME (0.1 mM) restored SNP responses to control values. 4. Treatment with dexamethasone (1 mg kg(-1)), 1 h before endotoxin did not alter the endotoxin-induced impairment of dilator responses to BK or SNP. 5. These results show that coronary microvascular responses are altered following endotoxin exposure. Endotoxin results in increased coronary microvascular tone despite induction of NO synthase and inhibits the dilator response to BK and SNP, vasodilators that act via the release of NO. Responses to SNP in endotoxin-treated hearts were restored to control values in the presence of L-NAME suggesting that enhanced endogenous NO synthesis might saturate guanylate cyclase resulting in reduced response to NO donors. The reduced response to vasodilators and increased coronary resistance might be important in determining the response of the coronary circulation to systemic inflammation and infection.

The role of nitric oxide in the responses of the ovine digital artery to vasoactive agents and modification of these responses by endotoxin and cytokines

1. Laminitis, an important cause of lameness in domestic ungulates, occurs as a result of altered digital perfusion. Endotoxin and cytokines may mediate the vascular derangements observed through alterations in nitric oxide production. In this study, the vascular responses of the isolated ovine digital artery were examined and the influence of endotoxin and cytokines investigated. 2. Neither removal of the endothelium nor incubation with N(G)-nitro-L-arginine methyl ester (L-NAME, 300 microM) altered the response to phenylephrine (PE, 1 nM to 300 microM). Indomethacin (10 microM) decreased PE log EC(50) from -6.22+/-0.08 to -6.55+/-0.07. Acetylcholine (1 nM to 1 mM) and bradykinin (BK, 100 pM to 3 microM) induced endothelium-dependent relaxation. Bradykinin-induced relaxation was reduced by L-NAME, E(max) falling from -61.7+/-7.4 to -34.0+/-2.1%. Addition of indomethacin further reduced BK E(max) to -9.6+/-2.8%. Sodium nitroprusside (1 nM to 300 microM) produced endothelium-independent relaxation that was unaffected by L-NAME or indomethacin. 3. Following a 6 h incubation with endotoxin (3 microml(-1)), arterial responses to PE and BK did not differ from polymyxin B-treated controls (10 microg ml(-1)). Arteries incubated for 6 h with interferon-gamma (IFN-gamma, 10 ng ml(-1)) and tumour necrosis factor-alpha (TNF-alpha, 5 ng ml(-1)) exhibited greater relaxation to BK (E(max)-50.0+/-5.1%) than polymyxin B-treated controls (E(max)-33.1+/-4.0%), but did not differ in their response to PE. 4. Prolonged incubation (16 h) with endotoxin (3 microg ml(-1)) did not alter the response to PE, however incubation with IFN-gamma (10 ng ml(-1)), TNF-alpha (5 ng ml(-1)) and interleukin-1beta (20 ng ml(-1)) for 16 h increased PE log EC(50) from -6.44+/-0.09 to -6. 10+/-0.11. 5. Nitric oxide is an important mediator of endothelium-dependent relaxation in ovine digital arteries but does not modulate PE-induced vasoconstriction. Incubation with cytokines decreased the sensitivity of digital arteries to PE.

Salutary effects of ATP-MgCl2 on the depressed endothelium-dependent relaxation during hyperdynamic sepsis

OBJECTIVES

Studies have shown that endothelium-dependent relaxation (mediated by endothelium-derived nitric oxide) is depressed during the early, hyperdynamic stage of sepsis. Although it is known that ATP-MgCl2 produces beneficial effects following various adverse circulatory conditions, it remains unknown whether this agent attenuates the depressed endothelium-dependent relaxation during early sepsis. The aim of this study, therefore, was to determine whether or not the administration of ATP-MgCl2 early after the onset of sepsis improves or maintains endothelium-dependent relaxation.

DESIGN

Prospective, controlled animals study.

SETTING

A university research laboratory.

SUBJECTS

Adult male Sprague-Dawley rats were subjected to polymicrobial sepsis by cecal ligation and puncture (CLP), followed by administration of 3 mL/100 g body weight normal saline to these and sham-operated rats.

INTERVENTIONS

At 1 hr after CLP, ATP-MgCl2 (50 micromol/kg body weight) or an equivalent volume of normal saline was infused intravenously over 90 mins.

MEASUREMENTS AND MAIN RESULTS

At 5 hrs or 10 hrs after CLP (i.e., the early, hyperdynamic stage of sepsis), the thoracic aorta was isolated, cut into rings, and placed in organ chambers. Norepinephrine was used to preconstrict vessel rings. Dose responses for an endothelium-dependent vasodilator, acetylcholine (ACh, via endothelium-dependent nitric oxide), and an endothelium-independent vasodilator, nitroglycerin, were determined. These results indicate that endothelium-dependent relaxation induced by ACh was significantly depressed at 5 and 10 hrs after CLP. Administration of ATP-MgCl2 after the onset of sepsis, however, maintained ACh-induced vascular relaxation. In contrast, no significant difference in nitroglycerin-induced vascular relaxation as well as norepinephrine-induced contraction was observed, irrespective of administration of ATP-MgCl2.

CONCLUSION

Since administration of ATP-MgCl2 prevents the impaired vascular relaxation to the endothelium-dependent vasodilator ACh, this agent may be a useful adjunct for maintaining endothelial cell function during the hyperdynamic stage of sepsis.

Inhibition of inducible nitric oxide synthase restores endothelium-dependent relaxations in proinflammatory mediator-induced blood vessels

Endothelium-dependent relaxations mediated by nitric oxide (NO) are attenuated in arteries exposed to proinflammatory mediators. Because proinflammatory mediators stimulate the expression of the inducible NO synthase (iNOS) in vascular cells, the role of iNOS-derived NO in the impaired endothelium-dependent relaxation was examined in arterial ring preparations. Exposure of rabbit carotid arteries to interleukin-1 beta (IL-1 beta; 100 U/mL for 7 hours) and porcine coronary arteries to a combination of tumor necrosis factor-alpha (1000 U/mL), interferon-gamma (500 U/mL), and lipopolysaccharide (10 micrograms/mL) for 15 hours (conditions that are associated with iNOS expression) markedly attenuated relaxations to receptor-dependent agonists, whereas those to the calcium ionophore A23187 and sodium nitroprusside were virtually unchanged. The impaired relaxation was not associated with a reduced level of the constitutive endothelial NOS (cNOS) but was accompanied by a reduced formation of biologically active NO as assessed in a bioassay system. The attenuated relaxation of carotid arteries to acetylcholine was not affected by superoxide dismutase and was neither found in arteries exposed to IL-1 beta for only 15 minutes nor in IL-1 beta-treated arteries for 7 hours followed by a 17-hour incubation period without the cytokine. Furthermore, no impaired relaxation was found in rings exposed to IL-1 beta in combination with either cycloheximide or N-alpha-tosyl-L-lysine chloromethyl ketone or pyrrolidine dithiocarbamate, treatments that prevent iNOS expression. In addition, selective inhibition of iNOS with S-methylisothiourea (10 mumol/L) completely restored acetylcholine-induced relaxations. These findings indicate that the continuous generation of NO induced by proinflammatory mediators plays a major role in the inhibition of endothelium-dependent relaxation, most likely by impairing a step in the signal transduction cascade that links activation of endothelial receptors to the calcium-calmodulin-dependent activation of NOS.

Pentoxifylline treatment attenuates pulmonary vasomotor dysfunction in acute lung injury

Acute lung injury (ALI) is characterized by pulmonary hypertension. Although the pathophysiology of ALI is complex, cytokine production, especially tumor necrosis factor-alpha (TNF-alpha), is known to mediate histologic lung injury. Pentoxifylline (PTX) is known to inhibit the expression of many cytokines, including TNF-alpha. The purpose of this study was to determine the effect of PTX treatment on endotoxin-induced impairment of endothelium-dependent mechanisms of pulmonary vasorelaxation. Mechanisms of endothelium-dependent relaxation were studied with the muscarinic receptor agonist, acetylcholine (ACh), and the receptor-independent calcium ionophore, A23187. Endothelium-independent pulmonary vasorelaxation was examined by direct stimulation of smooth muscle guanylate cyclase with the nitric oxide donor, sodium nitroprusside (SNP). Five rats received PTX (50 mg/kg) and endotoxin (20 mg/kg), endotoxin alone, or saline ip. After 6 hr, dose-response curves to ACh, A23187, and SNP were determined in isolated pulmonary artery rings preconstricted with phenylephrine (PE). PTX attenuated but did not eliminate endotoxin-induced impairment of endothelium-dependent and -independent pulmonary vasorelaxation. These data suggest that PTX may offer a therapeutic modality for the treatment of pulmonary hypertension in ALI.

Attenuation of endothelium-dependent hyperpolarizing factor by bacterial lipopolysaccharides

Endothelium-dependent hyperpolarizing factor (EDHF) is an important contributor to agonist-induced vascular dilation. Recent studies suggest that bacterial lipopolysaccharides attenuate endothelium-dependent dilation. Whether or not this effect is mediated through inhibition of EDHF is not known. We studied the in vitro influence of Escherichia coli lipopolysaccharides on endothelium-dependent smooth muscle dilation and hyperpolarization in porcine coronary arteries. Endothelium-intact porcine coronary arterial rings were examined after 20 h of incubation with either saline or E. coli lipopolysaccharides (100 microg/ml). Endothelium-dependent dilation elicited by increasing concentrations of bradykinin was significantly attenuated by lipopolysaccharides. Baseline values of smooth muscle membrane potential were not influenced by lipopolysaccharides. However, lipopolysaccharides significantly attenuated bradykinin-induced smooth muscle membrane hyperpolarization. Our results suggest that attenuation of EDHF is an important mechanism through which lipopolysaccharides influence vascular dilation in severe sepsis.

Inhaled nitric oxide and pentoxifylline in rat lung transplantation from non-heart-beating donors. The Paris-Sud University Lung Transplantation Group

BACKGROUND

In non-heart-beating donor lung transplantation, postmortem warm ischemia poses a special challenge. Inhaled nitric oxide and pentoxifylline have been shown to attenuate ischemia-reperfusion injury after lung transplantation. We hypothesized that concomitant administration of inhaled nitric oxide and pentoxifylline would result in a synergistic effect on ischemia-reperfusion lung injury.

METHODS

Lungs were harvested from non-heart-beating donors after 30 minutes of in situ warm ischemia, flushed, and stored for 2 hours at 4 degrees C before left lung transplantation in rats. Inhaled nitric oxide (30 ppm) was added during cadaver ventilation and reperfusion; pentoxifylline was given intravenously throughout reperfusion. The following groups were studied (n = 8 each): control, pentoxifylline, nitric oxide, and nitric oxide+pentoxifylline. Hemodynamic indices and arterial blood gases were obtained after ligation of the right pulmonary artery. Lung myeloperoxidase and wet/dry ratio were measured after death.

RESULTS

All rats that did not receive nitric oxide died within 10 minutes after ligation. Inhaled nitric oxide significantly decreased pulmonary vascular resistance and improved recipient survival. Nitric oxide + pentoxifylline improved pulmonary vascular resistance, arterial oxygen tension, and survival even further and reduced lung myeloperoxidase as compared with the group that received nitric oxide only. Preservation solution flush time was significantly decreased in both groups receiving nitric oxide, suggesting that inhaled nitric oxide used during cadaver ventilation allows for a more even distribution of the preservation solution.

CONCLUSIONS

We conclude that treatment with inhaled nitric oxide + pentoxifylline results in a synergistic protection from ischemia-reperfusion injury after non-heart-beating donor lung transplantation. This is likely the result of a dual action on the graft vasculature and neutrophil sequestration.

Pentoxifylline maintains vascular endothelial cell function during hyperdynamic and hypodynamic sepsis

BACKGROUND

Although pentoxifylline produces various beneficial effects after endotoxemia or sepsis occurs, it is not known whether this agent attenuates the depressed endothelial cell function during sepsis. Therefore the aim of this study was to determine whether pentoxifylline maintains vascular endothelial cell function (i.e., improves the release of endothelium-derived nitric oxide) during hyperdynamic and hypodynamic stages of polymicrobial sepsis.

METHODS

Rats were subjected to sepsis by cecal ligation and puncture (CLP), after which 3 ml/100 gm body wt normal saline solution was injected subcutaneously in these and rats in a sham-operated group. At 1 hour after the onset of sepsis, pentoxifylline (50 mg/kg body wt) or an equal volume of normal saline solution was infused intravenously during a 30 minute period. At 10 and 20 hours after CLP was performed (10-hour CLP, hyperdynamic sepsis; 20-hour CLP, hypodynamic sepsis), the thoracic aorta was isolated, cut into rings, and placed in organ chambers. Norepinephrine (2 x 10(-7) mol/L) was used to achieve near maximal tension. Dose responses for an endothelium-dependent vasodilator, acetylcholine, and an endothelium-independent vasodilator, nitroglycerine, were carried out. The changes in percentage relaxation in the aortic rings by these agonists were then determined.

RESULTS

Endothelium-dependent (acetylcholine-induced) vascular relaxation decreased significantly at 10 and 20 hours after CLP. Administration of pentoxifylline, however, maintained acetylcholine-induced vascular relaxation at both time points. In contrast, no significant reduction in nitroglycerine-induced vascular relaxation was seen in rats with sepsis irrespective of pentoxifylline treatment.

CONCLUSIONS

Because pentoxifylline prevented endothelial cell dysfunction at 10 and 20 hours after CLP occurred, this agent appears to be a useful agent for maintaining vascular endothelial function during the hyperdynamic and hypodynamic stages of polymicrobial sepsis.

Tumor necrosis factor-alpha prevents interleukin-1 beta from augmenting capsaicin-induced vasodilatation in the rat skin

The effect of tumor necrosis factor-alpha (TNF alpha) and tumor necrosis factor-beta (TNF beta) on the capsaicin-induced increase in cutaneous blood flow was investigated in anaesthetized rats. Skin blood flow was measured by laser-Doppler flowmetry. Intraplantar subcutaneous injections of 5-500 pg TNF alpha and 50-5000 pg TNF beta had no effect on local blood flow, whereas 5000 pg TNF alpha induced a transient hyperaemia. However, neither the pretreatment with TNF alpha (5-5000 pg) nor that with TNF beta (50-5000 pg) enhanced the vasodilatator response to intraplantar capsaicin (0.03 micrograms; 0.1 microgram), whereas 50 pg interleukin-1 beta augmented the capsaicin-induced hyperaemia (P < 0.05). This enhancement of the cutaneous hyperaemic response to capsaicin was absent when interleukin-1 beta (50 pg) was co-injected with TNF alpha (500 pg or 5000 pg). The vasodilatation caused by calcitonin gene-related peptide or bradykinin was not altered by 500 pg or 5000 pg TNF alpha. These data indicate that TNFs, in contrast to interleukin-1 beta, do not amplify the hyperaemic response to afferent nerve stimulation with capsaicin but reverse the augmentation mediated by interleukin-1 beta.

L-arginine and pentoxifylline attenuate endothelial dysfunction after lung reperfusion injury in the rabbit. The Paris-Sud University Lung Transplant Group

BACKGROUND

Among the factors involved in the early complications of lung transplantation is the ischemia-reperfusion syndrome related to a warm reperfusion in ischemic lungs.

METHODS

Using an isolated rabbit lung preparation perfused with whole blood, we studied the effects of cold ischemia followed by a warm reperfusion on pulmonary vascular responses to reproduce experimentally the conditions encountered during lung transplantation.

RESULTS

Pulmonary vascular responses to acetylcholine were rapidly altered by warm ischemia (relaxation of 7% versus 60% in controls). Conversely, relaxation was maintained even after a prolonged cold ischemic storage (maximal relaxation of 57% at 48 hours). Warm reperfusion in ischemic lungs induced major alteration of endothelium-dependent relaxation (maximal relaxation of 13% at 4 hours). The addition of L-arginine or pentoxifylline during reperfusion prevented the pulmonary endothelial alteration resulting from warm reperfusion.

CONCLUSION

These data suggest that treatments aimed at maintaining intact functional endothelium reduce ischemia-reperfusion injury in transplanted lungs.

Pentoxifylline attenuates the depressed endothelial cell function and vascular muscle contractility following trauma and hemorrhagic shock

Although pentoxifylline (PTX) produces various beneficial effects following adverse circulatory conditions, it is not known whether this agent attenuates the depressed vascular endothelial cell function [i.e., the reduced release of endothelium-derived nitric oxide (EDNO)] and smooth muscle contractility after trauma and hemorrhage. To study this, rats underwent a midline laparotomy (i.e., trauma induced) and were bled to and maintained at a mean arterial pressure of 40 mm Hg until 40% of maximal shed volume was returned in the form of lactated Ringer's solution. The animals were then resuscitated with 4 times the volume of maximal bleedout with lactated Ringer's solution, following which PTX (50 mg/kg body weight), or an equivalent volume of normal saline, was infused intravenously over 95 minutes. At 1.5 hours after resuscitation, the aorta was isolated and studied in vitro. Norepinephrine-induced vascular contraction and dose responses for acetylcholine (ACh), an endothelium-dependent vasodilator, were then determined. The results indicate that the decreased ACh-induced relaxation in hemorrhaged animals was restored with PTX treatment. Moreover, the increased ACh IC50 values (ACh concentration that causes half-maximum relaxation) after hemorrhage were reduced by PTX. In contrast, there was no significant difference in the relaxation induced by an endothelium-independent vasodilator, nitroglycerine, in the tested groups. Thus, PTX restores a hemorrhage-induced decrease in endothelium-derived nitricoxide production. In addition, the depressed smooth muscle contractile function was also attenuated by PTX treatment. Because PTX restored the depressed endothelial cell function and smooth muscle contractility, this agent appears to be a useful adjunct to fluid resuscitation for the management of trauma and hemorrhage.

Ethanol suppresses LPS-induced mRNA for nitric oxide synthase II in alveolar macrophages in vivo and in vitro

Alcohol abuse increases the incidence and severity of opportunistic lung infections and pneumonias. Inducible nitric oxide (NO) synthase (iNOS II) and NO may be a pivotal system in the intracellular bactericidal activity of macrophages. We tested the hypothesis that acute administration of ethanol (ETOH) suppressed Escherichia coli endotoxin lipopolysaccharide (LPS) mediated upregulation of the iNOS II system in the lung of the rat, in vivo. We also tested the effect of ETOH on alveolar macrophage (AM) production of free NO using microelectrodes. Male Sprague-Dawley rats were given ETOH (5.5 g/kg, IP) 30 min. before giving intratracheal sterile phosphate buffered saline solution (PBS, 0.5 ml) or LPS (1 mg/kg in a total volume of 0.5 ml PBS). The isolated lungs were subjected to bronchoalveolar lavage (BAL) 3.5 hr. later. Aliquots of the BAL fluid were assayed for tumor necrosis factor alpha TNF alpha and reactive nitrogen intermediates (nitrate and nitrite) (RNI) with chemiluminescence. Aliquots of AM were incubated 1 hr ex vivo for spontaneous production of RNI or frozen and assayed for iNOS II mRNA with competitor exchange reverse transcriptase polymerase chain reaction (cERT-PCR). The lung was homogenized and assayed for RNI. LPS increased BAL fluid TNF alpha and RNI, lung RNI, and the spontaneous production of RNI by AM, ex vivo. These effects were inhibited by in vivo administration of inhibitors of iNOS II. LPS increased iNOS mRNA in AM. This was unaffected by iNOS inhibitors. ETOH suppressed LPS-induced BAL fluid TNF, iNOS mRNA and RNI production by AM and the lung.(ABSTRACT TRUNCATED AT 250 WORDS)

Escherichia coli-induced inhibition of endothelium-dependent relaxation and gene expression and release of nitric oxide is attenuated by chronic alcohol ingestion

We examined the effect of chronic administration of ETOH on Escherichia coli-mediated suppression of relaxation and nitric oxide (NO) production by the rat thoracic aorta (RTA) and gene expression for constitutive NO synthase (cNOS) by the adrenal gland. Chronic alcoholic rats ("alcoholic") were fed a diet containing ETOH as 36% of the caloric intake for 8-10 weeks. Nonalcoholic control rats ("control") were fed an isocaloric equivalent diet containing 36% dextrin. Alcoholic rats were given an injection of approximately approximately 10(10) live E. coli through a dorsal SC catheter 24 and 19 h before experimentation ("alcoholic-septic"), and control rats were treated in an identical manner ("septic"). The next day the rats were anesthetized with ketamine-xylazine (0.1 ml/100 g rat) and rings of RTA were mounted in muscle chambers for isometric recording of force development. Rings of RTA were precontracted with an EC50 concentration of phenylephrine, and relaxation to acetylcholine (ACh), A23187, and nitroglycerin were obtained. A23187- and ACh-induced relaxation was attenuated in RTA obtained from septic rats, whereas the relaxation to nitroglycerin was slightly enhanced. Chronic administration of ETOH attenuated the effects of E. coli on endothelium-dependent relaxation in alcoholic-septic rats. NO was measured with ozone chemiluminescence. Basal and stimulated NO production was attenuated in RTA obtained from septic rats and unaffected in RTA obtained from alcoholic or alcoholic-septic rats. cNOS was unmeasurable in adrenals from septic rats. ETOH increased mRNA for cNOS, an effect amplified in alcoholic-septic rats. Thus, E. coli inhibits endothelium-dependent relaxation and NO production, and ETOH attenuates these effects of E. coli on the endothelium-NO system, possibly by upregulating gene expression for cNOS.