Enhanced secretion of endothelin-1 by elevated glucose levels from cultured bovine aortic endothelial cells

Evaluating the impact of type 2 diabetes mellitus on pulmonary vascular function and the development of pulmonary fibrosis

The increasing prevalence of type 2 diabetes mellitus (T2DM) is a significant worldwide health concern caused by sedentary lifestyles and unhealthy diets. Beyond glycemic control, T2DM impacts multiple organ systems, leading to various complications. While traditionally associated with cardiovascular and microvascular complications, emerging evidence indicates significant effects on pulmonary health. Pulmonary vascular dysfunction and fibrosis, characterized by alterations in vascular tone and excessive extracellular matrix deposition, are increasingly recognized in individuals with T2DM. The onset of T2DM is often preceded by prediabetes, an intermediate hyperglycemic state that is associated with increased diabetes and cardiovascular disease risk. This review explores the relationship between T2DM, pulmonary vascular dysfunction and pulmonary fibrosis, with a focus on potential links with prediabetes. Pulmonary vascular function, including the roles of nitric oxide (NO), prostacyclin (PGI2), endothelin-1 (ET-1), thromboxane A2 (TxA2) and thrombospondin-1 (THBS1), is discussed in the context of T2DM and prediabetes. Mechanisms linking T2DM to pulmonary fibrosis, such as oxidative stress, dysregulated fibrotic signaling, and chronic inflammation, are explained. The impact of prediabetes on pulmonary health, including endothelial dysfunction, oxidative stress, and dysregulated vasoactive mediators, is highlighted. Early detection and intervention during the prediabetic stage may reduce respiratory complications associated with T2DM, emphasizing the importance of management strategies targeting blood glucose regulation and vascular health. More research that looks into the mechanisms underlying pulmonary complications in T2DM and prediabetes is needed.

Endothelin receptor antagonists in diabetic and non-diabetic chronic kidney disease

Chronic kidney disease (CKD) is one of the major causes of morbidity and mortality, affecting >800 million persons globally. While we still lack efficient, targeted therapies addressing the major underlying pathophysiologic processes in CKD, findings of several recent trials have brought about a shifting landscape of promising therapies. The endothelin system has been implicated in the pathophysiology of CKD and endothelin receptor antagonists are one class of drugs for which we have increasing evidence of efficacy in these patients. In this review we summarize the most recent findings on the safety and efficacy of endothelin receptor antagonists in diabetic and non-diabetic CKD, future directions of research and upcoming treatments.

Sodium glucose co-transporter 2 inhibition increases epidermal growth factor expression and improves outcomes in patients with type 2 diabetes

Underlying molecular mechanisms of the kidney protective effects of sodium glucose co-transporter 2 (SGLT2) inhibitors are not fully elucidated. Therefore, we studied the association between urinary epidermal growth factor (uEGF), a mitogenic factor involved in kidney repair, and kidney outcomes in patients with type 2 diabetes (T2D). The underlying molecular mechanisms of the SGLT2 inhibitor canagliflozin on EGF using single-cell RNA sequencing from kidney tissue were examined. Urinary EGF-to-creatinine ratio (uEGF/Cr) was measured in 3521 CANagliflozin cardioVascular Assessment Study (CANVAS) participants at baseline and week 52. Associations of uEGF/Cr with kidney outcome were assessed using multivariable-adjusted Cox regression models. Single-cell RNA sequencing was performed using protocol kidney biopsy tissue from ten young patients with T2D on SGLT2i, six patients with T2D on standard care only, and six healthy controls (HCs). In CANVAS, each doubling in baseline uEGF/Cr was associated with a 12% (95% confidence interval 1-22) decreased risk of kidney outcome. uEGF/Cr decreased after 52 weeks with placebo and remained stable with canagliflozin (between-group difference +7.3% (2.0-12.8). In young persons with T2D, EGF mRNA was primarily expressed in the thick ascending loop of Henle. Expression in biopsies from T2D without SGLT2i was significantly lower compared to HCs, whereas treatment with SGLT2i increased EGF levels closer to the healthy state. In young persons with T2D without SGLT2i, endothelin-1 emerged as a key regulator of the EGF co-expression network. SGLT2i treatment was associated with a shift towards normal EGF expression. Thus, decreased uEGF represents increased risk of kidney disease progression in patients with T2D. Canagliflozin increased kidney tissue expression of EGF and was associated with a downstream signaling cascade linked to tubular repair and reversal of tubular injury.

Endothelin-1 in Health and Disease

Discovered almost 40 years ago, the potent vasoconstrictor peptide endothelin-1 (ET-1) has a wide range of roles both physiologically and pathologically. In recent years, there has been a focus on the contribution of ET-1 to disease. This has led to the development of various ET receptor antagonists, some of which are approved for the treatment of pulmonary arterial hypertension, while clinical trials for other diseases have been numerous yet, for the most part, unsuccessful. However, given the vast physiological impact of ET-1, it is both surprising and disappointing that therapeutics targeting the ET-1 pathway remain limited. Strategies aimed at the pathways influencing the synthesis and release of ET-1 could provide new therapeutic avenues, yet research using cultured cells in vitro has had little follow up in intact ex vivo and in vivo preparations. This article summarises what is currently known about the synthesis, storage and release of ET-1 as well as the role of ET-1 in several diseases including cardiovascular diseases, COVID-19 and chronic pain. Unravelling the ET-1 pathway and identifying therapeutic targets has the potential to treat many diseases whether through disease prevention, slowing disease progression or reversing pathology.

Big Endothelin-1 and long-term all-cause death in patients with coronary artery disease and prediabetes or diabetes after percutaneous coronary intervention

BACKGROUND AND AIMS

The present study aimed to examine the association between big endothelin-1 (big ET-1) and long-term all-cause death in patients with coronary artery disease (CAD) and different glucose metabolism status.

METHODS AND RESULTS

We consecutively enrolled 8550 patients from January 2013 to December 2013. Patients were categorized according to both status of glucose metabolism status [Diabetes Mellitus (DM), Pre-Diabetes (Pre-DM), Normoglycemia (NG)] and big ET-1 levels. Primary endpoint was all-cause death. During a median of 5.1-year follow-up periods, 301 all-cause deaths occurred. Elevated big ET-1 was significantly associated with long-term all-cause death (adjusted HR: 2.230, 95%CI 1.629-3.051; p < 0.001). Similarly, patients with DM, but not Pre-DM, had increased risk of all-cause death compared with NG group (p < 0.05). When patients were categorized by both status of glucose metabolism and big ET-1 levels, high big ET-1 were associated with significantly higher risk of all-cause death in Pre-DM (adjusted HR: 2.442, 95% CI 1.039-5.740; p = 0.041) and DM (adjusted HR: 3.162, 95% CI 1.376-7.269; p = 0.007). The Kaplan-Meier curve indicated that DM patients with the highest big ET-1 levels were associated with the greatest risk of all-cause death (p < 0.05).

CONCLUSIONS

The present data indicate that baseline big ET-1 levels were independently associated with the long-term all-cause death in DM and Pre-DM patients with CAD undergoing PCI, suggesting that big ET-1 may be a valuable marker in patients with impaired glucose metabolism.

New insights into the role of melatonin in diabetic cardiomyopathy

Diabetic cardiovascular complications and impaired cardiac function are considered to be the main causes of death in diabetic patients worldwide, especially patients with type 2 diabetes mellitus (T2DM). An increasing number of studies have shown that melatonin, as the main product secreted by the pineal gland, plays a vital role in the occurrence and development of diabetes. Melatonin improves myocardial cell metabolism, reduces vascular endothelial cell death, reverses microcirculation disorders, reduces myocardial fibrosis, reduces oxidative and endoplasmic reticulum stress, regulates cell autophagy and apoptosis, and improves mitochondrial function, all of which are the characteristics of diabetic cardiomyopathy (DCM). This review focuses on the role of melatonin in DCM. We also discuss new molecular findings that might facilitate a better understanding of the underlying mechanism. Finally, we propose potential new therapeutic strategies for patients with T2DM.

Quantitative and Dynamic MRI Measures of Peripheral Vascular Function

The endothelium regulates and mediates vascular homeostasis, allowing for dynamic changes of blood flow in response to mechanical and chemical stimuli. Endothelial dysfunction underlies many diseases and is purported to be the earliest pathologic change in the progression of atherosclerotic disease. Peripheral vascular function can be interrogated by measuring the response kinetics following induced ischemia or exercise. In the presence of endothelial dysfunction, there is a blunting and delay of the hyperemic response, which can be measured non-invasively using a variety of quantitative magnetic resonance imaging (MRI) methods. In this review, we summarize recent developments in non-contrast, proton MRI for dynamic quantification of blood flow and oxygenation. Methodologic description is provided for: blood oxygenation-level dependent (BOLD) signal that reflect combined effect of blood flow and capillary bed oxygen content; arterial spin labeling (ASL) for quantification of regional perfusion; phase contrast (PC) to quantify arterial flow waveforms and macrovascular blood flow velocity and rate; high-resolution MRI for luminal flow-mediated dilation; and dynamic MR oximetry to quantify oxygen saturation. Overall, results suggest that these dynamic and quantitative MRI methods can detect endothelial dysfunction both in the presence of overt cardiovascular disease (such as in patients with peripheral artery disease), as well as in sub-clinical settings (i.e., in chronic smokers, non-smokers exposed to e-cigarette aerosol, and as a function of age). Thus far, these tools have been relegated to the realm of research, used as biomarkers of disease progression and therapeutic response. With proper validation, MRI-measures of vascular function may ultimately be used to complement the standard clinical workup, providing additional insight into the optimal treatment strategy and evaluation of treatment efficacy.

The Role of Protein Kinase C Activation in the Pathogenesis of Diabetic Vascular Complications

Many vascular diseases in diabetes are known to be associated with the activation of the diacylglycerol (OAG)protein kinase C (PKC) pathway. The major source of OAG that is elevated in diabetes is de novo synthesis from glycolytic intermediates. Among the various PKC isoforms, the β-isoform has been shown to be persistently activated in diabetic animals. Multiple lines of evidence have shown that many vascular alterations in diabetes such as a decrease in the activity of Na+-K+ -adenosine triphosphatase (Na+-K+-ATPase), and increases in extracellular matrix, cytokines, permeability, contractility, and cell proliferation -are caused by activation of PKC. Inhibition of PKC by two different kinds of PKC inhibitors, LY333531, a selective PKC-β-isoform inhibitor, and d-α-tocopherol, were able to prevent or reverse the various vascular dysfunctions in diabetic rats. These results have also provided in vivo evidence that OAG-PKC activation could be responsible for the hyperglycemia-induced vascular dysfunctions in diabetes. Clinical studies are now being performed to clarify the pathogenic roles of the OAG-PKC pathway in developing vascular complications in diabetic patients.

Influence of metabolic syndrome on cerebral perfusion and cognition

Vascular cognitive impairment (VCI) is associated with chronic cerebral hypoperfusion (CCH) and memory deficits, and often occurs concurrently with metabolic syndrome (MetS). Despite their common occurrence, it is unknown whether CCH and MetS act synergistically to exacerbate VCI-associated pathology. Here, using male Sprague-Dawley rats, we examined the effects of a clinically relevant model of adolescent-onset MetS and adult-onset CCH on neuro-vascular outcomes, combining a cafeteria diet with a 2-vessel occlusion (2VO) model. Using longitudinal imaging, histology, and behavioural assessments, we identified several features of MetS and CCH including reduced cerebral blood volume, white matter atrophy, alterations in hippocampal cell density, and memory impairment. Furthermore, we identified a number of significant associations, potentially predictive of MetS and pathophysiological outcomes. White matter volume was positively correlated to HDL cholesterol; hippocampal cell density was negatively correlated to fasted blood glucose; cerebral blood flow and volume was negatively predicted by the combination of 2VO surgery and increased fasted blood glucose. These results emphasize the importance of including comorbid conditions when modeling VCI, and they outline a highly translational preclinical model that could be used to investigate potential interventions to mitigate VCI-associated pathology and cognitive decline.

The Role of Endothelin and Endothelin Antagonists in Chronic Kidney Disease

Background

Endothelins (ET) are a family of peptides that act as potent vasoconstrictors and pro-fibrotic growth factors. ET-1 is integral to renal and cardiovascular pathophysiology and exerts effects via autocrine, paracrine and endocrine signaling pathways tied to regulation of aldosterone, catecholamines, and angiotensin. In the kidney, ET-1 is critical to maintaining renal perfusion and controls glomerular arteriole tone and hemodynamics. It is hypothesized that ET-1 influences the progression of chronic kidney disease (CKD), and the objective of this review is to discuss the pathophysiology, and role of ET and endothelin receptor antagonists (ERAs) in CKD.

Summary

The use of ERAs in hypertensive nephropathy has the potential to decrease proteinuria, and in diabetic nephropathy has the potential to restore glycocalyx thickness, also decreasing proteinuria. Focal segmental glomerular sclerosis has no specific Food and Drug Administration-approved therapy currently, however, ERAs show promise in decreasing proteinuria and slowing tissue damage. ET-1 is a potential biomarker for autosomal dominant polycystic kidney disease progression and so it is thought that ERAs may be of some therapeutic benefit.

Key Messages

Multiple studies have shown the utility of ERAs in CKD. These agents have shown to reduce blood pressure, proteinuria, and arterial stiffness. However, more clinical trials are needed, and the results of active or recently concluded studies are eagerly awaited.

Heme oxygenase-1 contributes to the protective effect of resveratrol against endothelial dysfunction in STZ-induced diabetes in rats

Endothelial dysfunction is a common complication of diabetes that mainly stems from increased reactive oxygen species, which makes antioxidants of great benefit. Resveratrol (RSV) is an antioxidant that shows protective effects in a variety of disease models where the ameliorative effect appears to be mediated, in part, via heme oxygenase-1 (HO-1) induction. However, the pathophysiological relevance of HO-1 in the ameliorative response of RSV in endothelial dysfunction is not clearly defined. The present study was conducted to investigate whether HO-1 plays a role in diabetes-induced vascular dysfunction. Streptozotocin-diabetic rats were treated with RSV (10 mg/kg) in presence or absence of an HO-1 blocker, Zinc protoporphyrin (ZnPP) to assess vascular function and indicators of disease status. We found that RSV treatment significantly abrogated diabetes induced vascular dysfunction. This improvement was associated with the ability of RSV to decrease oxidative stress markers alongside a reduction in the aortic TGF-β expression, elevation of NOS3 expression and aortic nitrite concentration as well as HO activity. These ameliorative effects were diminished when ZnPP was administered prior to RSV. Our results clearly demonstrate the protective effects of RSV in diabetes-associated endothelial dysfunction and verified a causal role of HO-1 in this setting.

Synergistic effect of renalase and chronic kidney disease on endothelin-1 in patients with coronary artery disease ‒ a cross-sectional study

Endothelin-1 (ET-1) is associated with endothelial dysfunction and vasoconstriction. Increased circulating ET-1 levels are associated with long-term cardiovascular mortality. Renalase, released from kidney, metabolizes catecholamines and regulates blood pressure. An increase in circulating renalase levels has been reported in patients with chronic kidney disease (CKD) and is associated with coronary artery disease (CAD). We hypothesized the existence of a synergistic effect of serum renalase levels and CKD on ET-1 levels in patients with CAD. We evaluated 342 non-diabetic patients with established CAD. ET-1 and renalase levels were measured in all patients after an overnight fast. Patients with CKD had higher ET-1 (1.95 ± 0.77 vs. 1.62 ± 0.76 pg/ml, P < 0.001) and renalase levels (46.8 ± 17.1 vs. 33.9 ± 9.9 ng/ml, P < 0.001) than patients without CKD. Patients with both CKD and high renalase levels (>the median of 36.2 ng/ml) exhibited the highest serum ET-1 (P value for the trend <0.001). According to multivariate linear regression analysis, the combination of high serum renalase levels with CKD was a significant risk factor for increased serum ET-1 levels (regression coefficient = 0.297, 95% confidence interval = 0.063‒0.531, P = 0.013). In conclusion, our data suggest a synergistic effect of high serum renalase levels and CKD on increases in ET-1 levels in patients with established CAD.

TRAF3IP2 mediates high glucose-induced endothelin-1 production as well as endothelin-1-induced inflammation in endothelial cells

Hyperglycemia-induced production of endothelin (ET)-1 is a hallmark of endothelial dysfunction in diabetes. Although the detrimental vascular effects of increased ET-1 are well known, the molecular mechanisms regulating endothelial synthesis of ET-1 in the setting of diabetes remain largely unidentified. Here, we show that adapter molecule TRAF3 interacting protein 2 (TRAF3IP2) mediates high glucose-induced ET-1 production in endothelial cells and ET-1-mediated endothelial cell inflammation. Specifically, we found that high glucose upregulated TRAF3IP2 in human aortic endothelial cells, which subsequently led to activation of JNK and IKKβ. shRNA-mediated silencing of TRAF3IP2, JNK1, or IKKβ abrogated high-glucose-induced ET-converting enzyme 1 expression and ET-1 production. Likewise, overexpression of TRAF3IP2, in the absence of high glucose, led to activation of JNK and IKKβ as well as increased ET-1 production. Furthermore, ET-1 transcriptionally upregulated TRAF3IP2, and this upregulation was prevented by pharmacological inhibition of ET-1 receptor B using BQ-788, or inhibition of NADPH oxidase-derived reactive oxygen species using gp91ds-tat and GKT137831. Notably, we found that knockdown of TRAF3IP2 abolished ET-1-induced proinflammatory and adhesion molecule (IL-1β, TNF-α, monocyte chemoattractant protein 1, ICAM-1, VCAM-1, and E-selectin) expression and monocyte adhesion to endothelial cells. Finally, we report that TRAF3IP2 is upregulated and colocalized with CD31, an endothelial marker, in the aorta of diabetic mice. Collectively, findings from the present study identify endothelial TRAF3IP2 as a potential new therapeutic target to suppress ET-1 production and associated vascular complications in diabetes. NEW & NOTEWORTHY This study provides the first evidence that the adapter molecule TRAF3 interacting protein 2 mediates high glucose-induced production of endothelin-1 by endothelial cells as well as endothelin-1-mediated endothelial cell inflammation. The findings presented herein suggest that TRAF3 interacting protein 2 may be an important therapeutic target in diabetic vasculopathy characterized by excess endothelin-1 production.

Free radical scavenging decreases endothelin-1 excretion and glomerular albumin permeability during type 1 diabetes

Increased renal endothelin-1 (ET-1) production and an ET_A receptor-dependent increase in glomerular albumin permeability (P_alb) accompany type 1 diabetes mellitus (T1D). We hypothesized that T1D-induced oxidative stress contributes to renal ET-1 production and glomerular P_alb Male rats with streptozotocin-induced T1D were provided free access to drinking water without additives (T1D rats) or containing the free radical scavenger tempol (1 mmol/L; T1D+Tempol). After 3 weeks, T1D+Tempol rats displayed lower urinary excretion of thiobarbituric acid reactive substances and glomerular superoxide production (dihydroethidium staining) compared to T1D rats. Urinary ET-1 excretion and inner medullary (but not cortical or outer medullary) prepro-ET-1 mRNA expression were lower in the T1D+Tempol group than in the T1D group. P_alb, measured as the change in volume of isolated glomeruli upon exposure to oncotic gradients of albumin, was significantly lower in the T1D+Tempol group than in the T1D group. Tempol treatment did not alter protein excretion or creatinine clearance. These data support the postulate that oxidative stress contributes to glomerular P_alb and renal ET-1 production during the early phase of type 1 diabetes.

Endothelial dysfunction and vascular disease - a 30th anniversary update

The endothelium can evoke relaxations of the underlying vascular smooth muscle, by releasing vasodilator substances. The best-characterized endothelium-derived relaxing factor (EDRF) is nitric oxide (NO) which activates soluble guanylyl cyclase in the vascular smooth muscle cells, with the production of cyclic guanosine monophosphate (cGMP) initiating relaxation. The endothelial cells also evoke hyperpolarization of the cell membrane of vascular smooth muscle (endothelium-dependent hyperpolarizations, EDH-mediated responses). As regards the latter, hydrogen peroxide (H₂ O₂ ) now appears to play a dominant role. Endothelium-dependent relaxations involve both pertussis toxin-sensitive G_i (e.g. responses to α₂ -adrenergic agonists, serotonin, and thrombin) and pertussis toxin-insensitive G_q (e.g. adenosine diphosphate and bradykinin) coupling proteins. New stimulators (e.g. insulin, adiponectin) of the release of EDRFs have emerged. In recent years, evidence has also accumulated, confirming that the release of NO by the endothelial cell can chronically be upregulated (e.g. by oestrogens, exercise and dietary factors) and downregulated (e.g. oxidative stress, smoking, pollution and oxidized low-density lipoproteins) and that it is reduced with ageing and in the course of vascular disease (e.g. diabetes and hypertension). Arteries covered with regenerated endothelium (e.g. following angioplasty) selectively lose the pertussis toxin-sensitive pathway for NO release which favours vasospasm, thrombosis, penetration of macrophages, cellular growth and the inflammatory reaction leading to atherosclerosis. In addition to the release of NO (and EDH, in particular those due to H₂ O₂ ), endothelial cells also can evoke contraction of the underlying vascular smooth muscle cells by releasing endothelium-derived contracting factors. Recent evidence confirms that most endothelium-dependent acute increases in contractile force are due to the formation of vasoconstrictor prostanoids (endoperoxides and prostacyclin) which activate TP receptors of the vascular smooth muscle cells and that prostacyclin plays a key role in such responses. Endothelium-dependent contractions are exacerbated when the production of nitric oxide is impaired (e.g. by oxidative stress, ageing, spontaneous hypertension and diabetes). They contribute to the blunting of endothelium-dependent vasodilatations in aged subjects and essential hypertensive and diabetic patients. In addition, recent data confirm that the release of endothelin-1 can contribute to endothelial dysfunction and that the peptide appears to be an important contributor to vascular dysfunction. Finally, it has become clear that nitric oxide itself, under certain conditions (e.g. hypoxia), can cause biased activation of soluble guanylyl cyclase leading to the production of cyclic inosine monophosphate (cIMP) rather than cGMP and hence causes contraction rather than relaxation of the underlying vascular smooth muscle.

Obesity, type 2 diabetes, and impaired insulin-stimulated blood flow: role of skeletal muscle NO synthase and endothelin-1

Increased endothelin-1 (ET-1) and reduced endothelial nitric oxide phosphorylation (peNOS) are hypothesized to reduce insulin-stimulated blood flow in type 2 diabetes (T2D), but studies examining these links in humans are limited. We sought to assess basal and insulin-stimulated endothelial signaling proteins (ET-1 and peNOS) in skeletal muscle from T2D patients. Ten obese T2D [glucose disposal rate (GDR): 6.6 ± 1.6 mg·kg lean body mass (LBM)^-1·min^-1] and 11 lean insulin-sensitive subjects (Lean GDR: 12.9 ± 1.2 mg·kg LBM^-1·min^-1) underwent a hyperinsulinemic-euglycemic clamp with vastus lateralis biopsies taken before and 60 min into the clamp. Basal biopsies were also taken in 11 medication-naïve, obese, non-T2D subjects. ET-1, peNOS (Ser1177), and eNOS protein and mRNA were measured from skeletal muscle samples containing native microvessels. Femoral artery blood flow was assessed by duplex Doppler ultrasound. Insulin-stimulated blood flow was reduced in obese T2D (Lean: +50.7 ± 6.5% baseline, T2D: +20.8 ± 5.2% baseline, P < 0.05). peNOS/eNOS content was higher in Lean under basal conditions and, although not increased by insulin, remained higher in Lean during the insulin clamp than in obese T2D (P < 0.05). ET-1 mRNA and peptide were 2.25 ± 0.50- and 1.52 ± 0.11-fold higher in obese T2D compared with Lean at baseline, and ET-1 peptide remained 2.02 ± 1.9-fold elevated in obese T2D after insulin infusion (P < 0.05) but did not increase with insulin in either group (P > 0.05). Obese non-T2D subjects tended to also display elevated basal ET-1 (P = 0.06). In summary, higher basal skeletal muscle expression of ET-1 and reduced peNOS/eNOS may contribute to a reduced insulin-stimulated leg blood flow response in obese T2D patients.

NEW & NOTEWORTHY

Although impairments in endothelial signaling are hypothesized to reduce insulin-stimulated blood flow in type 2 diabetes (T2D), human studies examining these links are limited. We provide the first measures of nitric oxide synthase and endothelin-1 expression from skeletal muscle tissue containing native microvessels in individuals with and without T2D before and during insulin stimulation. Higher basal skeletal muscle expression of endothelin-1 and reduced endothelial nitric oxide phosphorylation (peNOS)/eNOS may contribute to reduced insulin-stimulated blood flow in obese T2D patients.

Et and diabetic nephropathy: preclinical and clinical studies

The incidence of progressive kidney disease associated with diabetes continues to increase worldwide. Only partial renoprotection is achieved by current standard therapy with angiotensin-converting enzyme inhibitors and/or angiotensin-receptor blockers, increasing the need for novel therapeutic approaches. Experimental studies have provided evidence of a pathogenic role for endothelin-1 (ET-1) and its cognate receptors in the development and progression of diabetic nephropathy. ET-1, mainly through the activation of ETA receptor, contributes to renal cell injury, inflammation, and fibrosis. In animal models of type 1 and type 2 diabetes, ETA-selective antagonists have been shown to provide renoprotective effects, supplying the rationale for clinical trials in patients with diabetic nephropathy with ETA-receptor antagonists administered in addition to renin-angiotensin system blockade.

Endothelin Blockade in Diabetic Kidney Disease

Diabetic kidney disease (DKD) remains the most common cause of chronic kidney disease and multiple therapeutic agents, primarily targeted at the renin-angiotensin system, have been assessed. Their only partial effectiveness in slowing down progression to end-stage renal disease, points out an evident need for additional effective therapies. In the context of diabetes, endothelin-1 (ET-1) has been implicated in vasoconstriction, renal injury, mesangial proliferation, glomerulosclerosis, fibrosis and inflammation, largely through activation of its endothelin A (ET_A) receptor. Therefore, endothelin receptor antagonists have been proposed as potential drug targets. In experimental models of DKD, endothelin receptor antagonists have been described to improve renal injury and fibrosis, whereas clinical trials in DKD patients have shown an antiproteinuric effect. Currently, its renoprotective effect in a long-time clinical trial is being tested. This review focuses on the localization of endothelin receptors (ET_A and ET_B) within the kidney, as well as the ET-1 functions through them. In addition, we summarize the therapeutic benefit of endothelin receptor antagonists in experimental and human studies and the adverse effects that have been described.

Endothelin and endothelin antagonists in chronic kidney disease

The incidence and prevalence of chronic kidney disease (CKD), with diabetes and hypertension accounting for the majority of cases, is on the rise, with up to 160 million individuals worldwide predicted to be affected by 2020. Given that current treatment options, primarily targeted at the renin-angiotensin system, only modestly slow down progression to end-stage renal disease, the urgent need for additional effective therapeutics is evident. Endothelin-1 (ET-1), largely through activation of endothelin A receptors, has been strongly implicated in renal cell injury, proteinuria, inflammation, and fibrosis leading to CKD. Endothelin receptor antagonists (ERAs) have been demonstrated to ameliorate or even reverse renal injury and/or fibrosis in experimental models of CKD, whereas clinical trials indicate a substantial antiproteinuric effect of ERAs in diabetic and nondiabetic CKD patients even on top of maximal renin-angiotensin system blockade. This review summarizes the role of ET in CKD pathogenesis and discusses the potential therapeutic benefit of targeting the ET system in CKD, with attention to the risks and benefits of such an approach.

Role of microangiopathy in diabetic cardiomyopathy

Although heart disease due to diabetes is mainly associated with complications of the large vessels, microvascular abnormalities are also considered to be involved in altering cardiac structure and function. Three major defects, such as endothelial dysfunction, alteration in the production/release of hormones, and shift in metabolism of smooth muscle cells, have been suggested to produce damage to the small arteries and capillaries (microangiopathy) due to hyperglycemia, and promote the development of diabetic cardiomyopathy. These factors may either act alone or in combination to produce oxidative stress as well as changes in cellular signaling and gene transcription, which in turn cause vasoconstriction and structural remodeling of the coronary vessels. Such alterations in microvasculature produce hypoperfusion of the myocardium and thereby lower the energy status resulting in changes in Ca(2+)-handling, apoptosis, and decreased cardiac contractile force. This article discusses diabetes-induced mechanisms of microvascular damage leading to cardiac dysfunction that is characterized by myocardial dilatation, cardiac hypertrophy as well as early diastolic and late systolic defects. Metabolic defects and changes in neurohumoral system due to diabetes, which promote disturbances in vascular homeostasis, are highlighted. In addition, increase in the vulnerability of the diabetic heart to the development of heart failure and the signaling pathways integrating nuclear factor κB and protein kinase C in diabetic cardiomyopathy are also described for comparison.

Vitreous biomarkers in diabetic retinopathy: a systematic review and meta-analysis

The aim of this study was to perform a systematic meta-analysis of biomarkers investigated with diabetic retinopathy (DR) in the vitreous, and to explore the molecular pathway interactions of these markers found to be consistently associated with DR. Relevant databases [PubMed and ISI web of science] were searched for all published articles investigating molecular biomarkers of the vitreous associated with DR. Based on set exclusion/inclusion criteria available data from studies with human vitreous samples were extracted and used for our meta-analysis. The interactions of significant biomarkers in DR were investigated via STRING and KEGG pathway analysis. Our meta-analysis of DR identifies eleven biomarkers as potential therapeutic candidates alternate to current anti-VEGF therapy. Four of these are deemed viable therapeutic targets for PDR; ET receptors (ET A and ET B), anti-PDGF-BB, blocking TGF-β using cell therapy and PEDF. The identification of supplementary or synergistic therapeutic candidates to anti VEGF in the treatment of DR may aid in the development of future treatment trials.

Molecular interactions of serotonin (5-HT) and endothelin-1 in vascular smooth muscle cells: in vitro and ex vivo analyses

Elevated levels of serotonin (5-HT) and endothelin-1 (ET-1) may be involved in cardiovascular complications of diabetes mellitus. Data suggest supraphysiological concentrations of 5-HT (10(-6) M) potentiate the ability of ET-1 to stimulate DNA synthesis and vascular smooth muscle cell (VSMC) proliferation in vitro via activation of mitogen-activated protein kinase (p42/44 MAPK) and Janus kinase 2 (JAK2) pathways. Additionally, 5-HT enhances agonist-induced contractions via p42/44 MAPK and an unknown tyrosine kinase. However, the exact mechanisms of the 5-HT/ET-1 interactions and whether these effects occur at physiological levels (10(-9) M) are unknown. Therefore, we hypothesized that interactions between 5-HT and ET-1 at physiological concentrations in VSMC enhanced activation of both p42/44 MAPK and JAK2 pathways contributing to vascular growth and contractile responses. With the use of rat VSMC and Western blot analysis, our data suggest no effect of acute (30 min) preincubation with 5-HT (10(-9) M) and/or ET-1 (10(-9) M) on the activation of either pathway in normal or high glucose conditions. To determine if there was altered vascular reactivity in intact vessels we tested the effects of 5-HT and ET-1 interaction using myographs to measure isometric contractions of rat thoracic aortic rings. 5-HT (10(-9) M) and ET-1 (10(-12) M) stimulate enhanced contractile responses to each other that were inhibited by JAK2 and p42/44 MAPK antagonists. Our findings demonstrate that both 5-HT and ET-1 at physiological concentrations could interact with each other and activate p42/44 MAPK and JAK2 signaling pathways to cause an increase in smooth muscle contraction that could lead to altered vascular function.

High glucose-induced increased expression of endothelin-1 in human endothelial cells is mediated by activated CCAAT/enhancer-binding proteins

High glucose-induced endothelial dysfunction is partially mediated by the down-stream pathophysiological effects triggered by increased expression of endothelin-1 (ET-1). The molecular control mechanisms of ET-1 synthesis are yet to be discovered. Members of the CCAAT/enhancer-binding proteins (C/EBP) family are important regulators of key metabolic processes, cellular differentiation and proinflammatory genes. In this study, we aimed at elucidating the role of C/EBP in mediating the high glucose effect on ET-1 expression in human endothelial cells (EC). Human umbilical vein cells (EAhy926) and primary cultures of human aortic EC were exposed to high levels of glucose (16.5-25 mM). Real-time PCR, Western blot, enzyme-linked immunosorbent assay, ET-1 promoter-luciferase reporter analysis, and chromatin immunoprecipitation assays were employed to investigate ET-1 regulation. High glucose activated C/EBPα, C/EBPβ, and C/EBPδ in a dose-dependent manner. It also promoted significant increases in ET-1 gene and peptide expression. Chemical inhibition of JNK, p38MAPK and ERK1/2 diminished significantly the high glucose-induced nuclear translocation of C/EBP and ET-1 expression. Silencing of C/EBPα, C/EBPβ or C/EBPδ greatly reduced the high glucose-induced upregulation of ET-1 mRNA, pre-pro-ET-1, and ET-1 secretion. The expression of various C/EBP isoforms was selectively downregulated by siRNA-mediated gene silencing. In silico analysis indicated the existence of typical C/EBP elements within human ET-1 gene promoter. Transient overexpression of C/EBPα, C/EBPβ or C/EBPδ upregulated the luciferase level controlled by the ET-1 gene promoter. The direct interaction of C/EBPα, C/EBPβ or C/EBPδ proteins with the ET-1 promoter in high glucose-exposed EC was confirmed by chromatin immunoprecipitation assay. High glucose-induced ET-1 expression is mediated through multiple mechanisms. We present evidence that members of the C/EBP proinflammatory transcription factors are important regulators of ET-1 in high glucose-exposed human endothelial cells. High glucose-induced activation of C/EBP-related signaling pathways may induce excessive ET-1 synthesis, thus promoting vasoconstriction and dysfunction of the vascular wall cells in diabetes.

Role of endothelium in vasomotor responses to endothelin system and protein kinase C activation in porcine retinal arterioles

PURPOSE

Endothelial cells synthesize vasodilator nitric oxide (NO) and vasoconstrictor endothelin-1 (ET-1) from NO synthase (eNOS) and endothelin-converting enzyme-1 (ECE-1), respectively. Protein kinase C (PKC) and Rho kinase (ROCK) are major signaling molecules mediating vasoconstriction. Although endothelial cells express eNOS, ECE-1, endothelin B (ET(B)) receptors, PKC, and ROCK, their influences on ET-1-induced vasoconstriction remain elusive. We studied whether these endothelial signaling molecules modulate retinal arteriolar constriction to ET-1.

METHODS

Porcine retinal arterioles were isolated and pressurized for vasomotor study, under conditions with intact or denuded endothelium, using videomicroscopic techniques.

RESULTS

Retinal arterioles developed similar resting tone (≈45% of maximum diameter) with or without endothelium. Endothelial denudation attenuated vasoconstriction to ET-1 precursor, big ET-1, by almost equal to 50%, but did not affect vasoconstrictions to ET-1, ET(B) agonist sarafotoxin S6c, or PKC activator phorbol-12, 13-dibutyrate (PDBu). The ROCK inhibitor H-1152 caused vasodilation, and abolished vasoconstrictions to ET-1 and PDBu independent of endothelium. With L-type voltage-operated calcium channel (L-VOCC) blocker nifedipine, PDBu-induced vasoconstriction was abolished and converted to NO-mediated vasodilation in the presence of endothelium. The ET-1-induced vasoconstriction was unaffected by NO released from endothelium during flow elevation.

CONCLUSIONS

Endothelial and smooth muscle ECE-1 contribute equally to synthesis of vasoactive ET-1 in retinal arterioles, with nominal role of endothelial ETB receptors in vasoconstriction to ET-1. The PKC activation leads to endothelium-dependent NO-mediated vasodilation when smooth muscle contraction is ablated by L-VOCC blockade. Endothelial cells and NO appear to have modest roles in modulating ROCK-dependent vasoconstriction, and are insufficient to counteract smooth muscle contractions to ET-1 and PKC activation.

Peroxynitrite decomposition with FeTMPyP improves plasma-induced vascular dysfunction and infarction during mild but not severe hyperglycemic stroke

We investigated mechanisms by which circulating factors during hyperglycemic (HG) stroke affect cerebrovascular function and the role of peroxynitrite in stroke outcome. Middle cerebral arteries (MCAs) were isolated from male Wistar rats and perfused with plasma from rats that were hyperglycemic for 5 to 6 days by streptozotocin and underwent either MCA occlusion (HG MCAO) or Sham surgery (HG Sham) compared with MCA perfused with physiologic saline (No plasma). Myogenic responses and endothelial function were compared in untreated MCA (n=8/group) or with inhibitors of NADPH oxidase (apocynin; n=8), peroxynitrite (FeTMPyP; n=8) or endothelin-1 (ET-1)(A) (BQ-123; n=8). Finally, animals were treated in vivo before reperfusion after mild (<68% cerebral blood flow (CBF) decrease) or severe (>68% CBF decrease) MCAO with FeTMPyP (n=12) or vehicle (n=12) and CBF and infarction measured. The HG MCAO plasma increased tone in MCA versus No plasma (P<0.05) that was reversed by FeTMPyP, but not by apocynin or BQ-123. The HG Sham plasma also increased tone in MCA (P<0.05) that was reversed by BQ-123 only. In vivo, FeTMPyP was neuroprotective during mild, but not severe ischemia. These results show that circulating factors in plasma can affect cerebrovascular function through peroxynitrite generation and ET-1. In addition, peroxynitrite decomposition improves stroke outcome acutely during mild, but not severe HG ischemia.

New options and perspectives for proteinuria management after kidney transplantation

Proteinuria has been strongly correlated with reduced function and graft survival in kidney-transplanted patients. Data regarding new strategies in proteinuria treatment and subsequent allograft survival are lacking. Similarities between chronic graft injury and chronic kidney disease (CKD) suggest that the same therapeutic antiproteinuric tools should be effective in kidney-transplanted patients. The classic strategies to decrease proteinuria such as blood pressure control, nicotine cessation, low-salt diet, and maintaining an ideal body weight seem to be not enough to achieve proteinuria control. Improvements in our understanding of the pathogenesis of CKD have led to the identification of several novel targets for proteinuria management. In this review, we discuss novel pharmacological approaches that aim to decrease proteinuria in CKD patients, including the use of direct renin inhibitors, vitamin D analogs, pentoxifylline, and endothelin receptor antagonists. We also discuss the promise of using antifibrotic agents to treat proteinuria. The identification of new biomarkers of CKD and its progression can help in the selection of the most effective treatment for decreasing proteinuria and maintaining kidney function.

Involvement of the endothelin and nitric oxide systems in the pathogenesis of renal ischemic damage in an experimental diabetic model

AIMS

Ischemic acute kidney injury (iAKI) in experimental diabetes mellitus (DM) is associated with a rapid kidney dysfunction more than in non-diabetic rats. We hypothesize that this vulnerability is due to excessive endothelin-1 (ET-1) expression along with dysregulation of nitric oxide synthase (NOS) isoforms. The aim of the present study was to assess the impact of ischemia on renal function in diabetic rats as compared with non-diabetic rats, and to investigate the involvement of ET-1 and NO systems in the susceptibility of diabetic kidney to ischemic damage.

MAIN METHODS

DM was induced by Streptozotocin. iAKI was induced by clamping of left renal artery for 30 min. Right intact kidney served as control. 48 h following ischemia, clearance protocols were applied to assess glomerular filtration rate (GFR), urinary flow (V) and sodium excretion (U(Na)V) in both kidneys. The renal effects of ABT-627, ET(A) antagonist; A192621.1, ET(B) antagonist; L-NAME, NOS non-selective inhibitor; 1400 W, inducible NOS (iNOS) inhibitor; and NPLA, neuronal NOS (nNOS) inhibitor, were assessed following ischemic renal injury in diabetic rats.

KEY FINDINGS

Induction of iAKI in diabetic and non-diabetic rats caused significant reductions in GFR, V, and U(Na)V, which were greater in diabetic than non-diabetic rats. While, treatment with ABT-627 decreased V and U(Na)V, and increased GFR, A192621.1 decreased all these parameters. L-NAME, 1400 W, and NPLA improved GFR in the ischemic diabetic kidney.

SIGNIFICANCE

Excessive vasoconstrictive effects of ET-1 via ET(A) and upregulation of iNOS, are partly responsible for the impaired recovery of renal function following ischemia in diabetic rats.

Renal and systemic effects of endothelin-1 in diabetic-hypertensive rats

The Cohen-Rosenthal Diabetic Hypertensive rat (CRDH) is a unique animal model in which genetic hypertension and diabetes developed after crossbreeding of Cohen diabetic rats sensitive substrain (CDR) and spontaneously hypertensive rats (SHR). The present study examined: 1) The acute effects of ET-1 on the systemic and renal hemodynamics in CRDH rats, CDR, and SHR; 2) The expression of ET-1 and its receptors in the renal tissue of CRDH rats. Intravenous injection of ET-1 (1.0 nmol/kg) into anesthetized SHR rats resulted in a significant immediate depressor response (mean arterial pressure (MAP) decreased from 165 ± 3 to 124 ± 12 mmHg, p < 0.0001) followed by a minor hypertensive phase (MAP increased to 170 ± 2 mmHg). Simultaneously, the administration of ET-1 caused a significant decrease in renal blood flow (RBF) from 5.8 ± 0.9 ml/min to 3.2 ± 0.5 ml/min (p = 0.026). These responses were blunted in CRDH rats and CDR. Analysis of intra-renal blood flow by laser-Doppler in CRDH rats revealed that ET-1 injection caused a decrease in cortical blood flow (Δ = -12 ± 2.9%). However, in contrast to its well-known renal medullary vasodilatory effect, ET-1 produced a significant decline in the medulla blood flow (Δ = -17.5 ± 3.4%) (p = 0.0125). These findings suggest that CDR and CRDH rats have reduced sensitivity to vascular and renal action of ET-1. Furthermore, in the CRDH rats, the expected ET-1-induced medullary vasodilatation was abolished and even reversed into prolonged vasoconstriction.

Distinct actions of endothelin A-selective versus combined endothelin A/B receptor antagonists in early diabetic kidney disease

Selective endothelin A (ET(A)) and combined ET(A) and ET(B) receptor antagonists are being investigated for use in treating diabetic nephropathy. However, the receptor-specific mechanisms responsible for producing the potential benefits have not been discerned. Thus, we determined the actions of ET(A) and ET(B) receptors on measures of glomerular function and renal inflammation in the early stages of diabetic renal injury in rats through the use of selective and combined antagonists. Six weeks after streptozotocin (STZ)-induced hyperglycemia, rats were given 2R-(4-methoxyphenyl)-4S-(1,3-benzodioxol-5-yl)-1-(N,N-di(n-butyl)aminocarbonyl-methyl)-pyrrolidine-3R-carboxylic acid (ABT-627) (5 mg/kg/day), a selective ET(A) antagonist; (2R,3R,4S)-4-(benzo[d][1,3]dioxol-5-yl)-2-(3-fluoro-4-methoxyphenyl)-1-(2-(N-propylpentylsulfonamido)ethyl)pyrrolidine-3-carboxylic acid hydrochloride (A-182086) (10 mg/kg/day), a combined ET(A/B) antagonist; or vehicle for 1 week. Sham controls received STZ vehicle (saline). Hyperglycemia led to significant proteinuria, increased glomerular permeability to albumin (P(alb)), nephrinuria, and an increase in total matrix metalloprotease (MMP) and transforming growth factor-β1 (TGF-β1) activities in glomeruli. Plasma and glomerular soluble intercellular adhesion molecule-1 (sICAM-1) and monocyte chemoattractant protein-1 (MCP-1) were elevated after 7 weeks of hyperglycemia. Daily administration of both ABT-627 and A-182086 for 1 week significantly attenuated proteinuria, the increase in P(alb), nephrinuria, and total MMP and TGF-β1 activity. However, glomerular sICAM-1 and MCP-1 expression was attenuated with ABT-627, but not A-182086, treatment. In summary, both selective ET(A) and combined ET(A/B) antagonists reduced proteinuria and glomerular permeability and restored glomerular filtration barrier component integrity, but only ET(A)-selective blockade had anti-inflammatory and antifibrotic effects. We conclude that selective ET(A) antagonists are more likely to be preferred for the treatment of diabetic kidney disease.

Endothelin-1 and diabetic complications: focus on the vasculature

Diabetes is not only an endocrine but also a vascular disease. Cardiovascular complications are the leading cause of morbidity and mortality associated with diabetes. Diabetes affects both large and small vessels and hence diabetic complications are broadly classified as microvascular (retinopathy, nephropathy and neuropathy) and macrovascular (heart disease, stroke and peripheral arterial disease) complications. Endothelial dysfunction, defined as an imbalance of endothelium-derived vasoconstrictor and vasodilator substances, is a common denominator in the pathogenesis and progression of both macro and microvascular complications. While the pathophysiology of diabetic complications is complex, endothelin-1 (ET-1), a potent vasoconstrictor with proliferative, profibrotic, and proinflammatory properties, may contribute to many facets of diabetic vascular disease. This review will focus on the effects of ET-1 on function and structure of microvessels (retina, skin and mesenteric arteries) and macrovessels (coronary and cerebral arteries) and also discuss the relative role(s) of endothelin A (ET(A)) and ET(B) receptors in mediating ET-1 actions.

Decreased contractile response to endothelin-1 of peripheral microvasculature from diabetic patients

BACKGROUND

We compared the contractile responses to endothelin-1 (ET-1) with and without the inhibition of ET-A receptors and protein kinase C-alpha (PKC-α) in the human peripheral microvasculature of diabetic and case-matched, nondiabetic patients.

METHODS

Chest wall skeletal muscle was harvested from patients with and without diabetics undergoing cardiac surgery. Peripheral arterioles (90-180 μm in diameter) were dissected from the harvested tissue. Microvascular constriction was assessed by videomicroscopy in response to ET-1 with and without an endothelin-A (ET-A) receptor antagonist, an endothelin B (ET-B) antagonist, or a PKC-α inhibitor.

RESULTS

ET-1 induced a dose-dependent contractile response of skeletal muscle arterioles from diabetic and nondiabetic patients. The contractile response of diabetic arterioles from both prebypass and postbypass to ET-1 (10(-9) mol/L) was decreased compared with those of nondiabetic patients (P < .05). The contractile responses of microvessels of both diabetics and nondiabetics to ET-1 were inhibited in the presence of either ET-A receptor antagonist BQ123 (10(-7) mol/L) or the PKC-α inhibitor safingol (2 × 10(-5) mol/L, P < .05, respectively). In contrast, the ET-1-induced vasoconstriction was not affected by the administration of the ET-B receptor antagonist BQ788 (10(-7) mol/L). There were no differences in skeletal muscle levels of the ET-A and ET-B receptors between diabetic and nondiabetic groups.

CONCLUSION

Diabetic patients demonstrated a decreased contractile response to ET-1 in human peripheral microvasculature. The contractile response of diabetic vessels to ET-1 occurs via activation of ET-A receptors and PKC-α. These results provide novel mechanisms of ET-1-induced contraction in vasomotor dysfunction in patients with diabetes.

Endothelin-1 response to glucose and insulin among African Americans

Endothelin-1 (ET-1) is implicated in the pathogenesis of hypertension. In vitro studies demonstrate that ET-1 is upregulated by insulin and glucose. The purpose of this study was to determine the effects of insulin and glucose on ET-1 levels in young adult African Americans, a population with a high burden of hypertension and diabetes. Plasma and urine ET-1 levels were measured before and after an oral glucose tolerance test (OGTT) and insulin clamp procedure in 288 participants. Subjects were classified according to glucose tolerance and blood pressure (BP) status. Plasma and urine ET-1 were not significantly different among the glucose tolerance groups. There was a trend toward increased plasma ET-1 among those with diabetes compared with impaired glucose tolerance and normal glucose tolerance; however, this was not statistically significant (P = .085). According to BP status, plasma ET-1 was highest among the high BP group compared with the normal BP group (P = .01). After glucose challenge, plasma ET-1 levels decreased and urine ET-1 increased in all three BP groups (P = .037). Our data show that plasma ET-1 is higher among young adult African Americans with hypertension compared with normotension. Urine ET-1 levels increased in response to glucose challenge, possibly indicating early renal injury.

Diabetes-associated changes and role of N epsilon-(carboxymethyl)lysine in big ET-1-induced coronary vasoconstriction

Using perfused hearts from streptozotocin-induced long-term diabetic rats, we studied the coronary vasoconstrictor effect of the endothelin-1 (ET-1) precursor big ET-1 and also whether this response was modulated by N(epsilon)-(carboxymethyl)lysine (CML; a representative advanced glycation end product that is implicated in the pathogenesis of diabetic vasculopathy). The big ET-1-induced vasoconstriction (a) developed more rapidly (i.e., was greater in the first 30 min) in the diabetic group than in the age-matched controls, and (b) in each group was largely suppressed by phosphoramidon [nonselective endothelin-converting enzyme (ECE)/neutral endopeptidase (NEP) inhibitor] or CGS35066 (selective ECE inhibitor), but not by thiorphan (selective NEP inhibitor). The ET-1 release occurring after treatment with big ET-1, which was greater in diabetic coronary arteries than in the controls, was reduced by CGS35066. The dose-response curve for ET-1 was shifted to the left in the diabetics, so that at some lower doses of ET-1 the vasoconstriction was greater than in the controls. CML enhanced big ET-1- or ET-1-induced vasoconstriction in the controls, but not in the diabetics. Finally, the plasma level of CML was higher in diabetic than in control rats. These findings suggest (a) that the increased responsiveness to big ET-1 shown by diabetic coronary arteries may be attributable both to a more rapid conversion of big ET-1 to ET-1 (by ECE), allowing it to exert its contractile activity, and to an increased vascular sensitivity to ET-1, and (b) that CML may be at least partly responsible for the diabetes-associated enhancement of big ET-1-mediated coronary vasoconstriction.

Role of protein kinase C in the expression of endothelin converting enzyme-1

Increased expression of endothelin converting enzyme-1 (ECE-1) is associated with diabetic nephropathy. The molecular mechanisms underlying this association, as yet unknown, possibly involve protein kinase C (PKC) pathways. In the present study, we examined the effects of high glucose and PKC activation on ECE-1 expression in primary human umbilical vein endothelial cells (HUVECs) and in HUVEC line (EA.hy926). Increasing glucose concentration, but not mannitol, from 5.5-22.2 mmol/liter for 3 d, enhanced prepro endothelin-1 (ET-1) mRNA expression, ET-1 levels, ECE-1 protein, and mRNA expressions by 7, 4, 20, and 2.6-fold, respectively. High glucose increased ECE-1 protein expression dose and time dependently. By Western blot analysis, PKC-beta1, -beta2, and -delta isoform levels were significantly increased relative to other isoforms when glucose level was increased. Treatment with Rottlerin, a PKC-delta isoform inhibitor, reduced significantly the glucose-induced ET-1 secretion, and ECE-1 protein expression, but (S)-13-[(dimethylamino)methyl]-10,11,14,15-tetrahydro-4,9:16,21-dimetheno 1H,1(3)H-dibenzo[e,k]pyrrolo[3,4-h] (1, 4, 3) oxadiaza-cyclohexadecene-1,3(2H)-dione or Gö6976, specific PKC-beta and -alpha inhibitors, respectively, did not. Overexpression of PKC-delta but not PKC-alpha or -beta1 isoforms by adenovirus vector containing the respective cDNA in HUVECs incubated with 5.5 mmol/liter glucose, increased in parallel PKC proteins, and glucose-induced endothein-1 and ECE-1 protein expression by 4- to 6-fold. These results show that enhanced ECE-1 expression induced by hyperglycemia is partly due to activation of the PKC-delta isoform. Thus, inhibition of this PKC isoform may prevent diabetes-related increase in ET-1.

Plasma big-endothelin levels, cardiac autonomic neuropathy, and cardiac functions in patients with insulin-dependent diabetes mellitus

BACKGROUND

The alteration of endothelin (ET) levels in diabetic patients with cardiac autonomic neuropathy (CAN) has not been studied extensively and its correlation with cardiac function parameters has not been discussed.

HYPOTHESIS

The aim of the present study was to discuss the correlation between the degree of cardiac autonomic neuropathy, plasma big-ET levels, and cardiac functions in diabetic patients who were clinically free of cardiovascular disease.

METHODS

Twenty subjects (32.1 +/- 7.8 years, 11 men, 9 women) with insulin-dependent diabetes mellitus (IDDM) were studied to evaluate the relationship between circulating big-endothelin (big-ET1) levels, CAN, and cardiac functions. The severity of CAN was scored according to Ewing's criteria. Cardiac functions were assessed using Doppler echocardiography.

RESULTS

Left ventricular systolic function in the patient group was within normal limits and comparable with the values of the control group (n = 10). The mean E/A values of diabetics with CAN (1.15 +/- 0.33, p = 0.004) and without CAN (1.34 +/- 0.17) were significantly lower than those of controls (1.57 +/- 0.27). Diabetics with CAN had significantly higher big-ET1 values (81.1 +/- 94 pg/ml) compared with others (12.4 +/- 5.9 and 21.1 +/- 17.7 pg/ml, p = 0.04). Circulating big-ET1 levels showed a significant correlation with E/A values in the control group (p = 0.01, r = -0.7) and with peak A values (p = 0.003, r = 0.64) in diabetics. The CAN score correlated negatively with E/A values (p = 0.01, r = 0.54).

CONCLUSIONS

High big-ET levels might have an important role in the pathogenesis or consequences of diastolic dysfunction in diabetics with CAN. Their role in cardiac autonomic neuropathy and diastolic dysfunction should be investigated further.

Method for diagnosis of a disease involving an anti-endothelin receptor antibody

BACKGROUND

Endothelin (ET) is a potent vasoconstrictor peptide with profibrotic, promitotic, and proinflammatory effects. Elevated levels of ET or inappropriate activation of ET receptors are believed to contribute to the pathogenesis of various disorders, including cardiovascular and autoimmune diseases and allograft rejection.

OBJECTIVE

The pathogenetic significance of activating anti-ET receptor autoantibodies and their diagnostic usefulness are addressed.

METHODS

PubMed and EMBASE searches were performed for '(activating) endothelin receptor (auto)antibodies' and '(activating) angiotensin receptor (auto)antibodies'.

RESULTS/CONCLUSION

While activating angiotensin receptor autoantibodies have been detected in several acute and chronic disorders, published data for a corresponding role of ET receptor antibodies are currently lacking. Thus, their diagnostic and prognostic value needs to be confirmed.

The role of endothelin in the cerebrovascular response following intracerebral haemorrhage: experimental studies using the endothelin antagonist SB209670

Primary intracerebral haemorrhage (ICH) is associated with considerable morbidity and mortality. Local endothelin release following ICH may contribute to the pathophysiology of perilesional ischaemia. In diabetics, endothelin release can be enhanced by hyperglycaemia and cerebrovascular dilation may be inhibited by vascular endothelial dysfunction. To examine the effects of endothelin-mediated vasoconstriction after spontaneous ICH in the normal and diabetic brain, regional cerebral blood flow (rCBF) was examined in insulin dependent BB-rats and non-diabetic BB control rats. These experiments were performed 24 h following experimental ICH in both groups of animals that were either given the endothelin antagonist SB209670 or saline. Perilesional oligaemia was similar in control and SB209670 treated diabetic rats, but SB209670 reduced perilesional oligaemia in normal rats. In brain contralateral to the experimental ICH, rCBF was increased by SB209670 in diabetic rats, but not in non-diabetic rats. These studies show that there are differences in the cerebrovascular effects of endothelin in perilesional and contralateral brain in non-diabetic and diabetic rats following ICH.

The serum endothelin-1 level in steatosis and NASH, and its relation with severity of liver fibrosis

Endothelin-1 (ET-1) is known to play an important role in hepatic fibrosis. ET-1 is also a mediator that is elevated in conditions such as insulin resistance, hyperglycemia, oxidative stress, and endothelial cell dysfunction. In this study, we investigated whether ET-1 has a role in determining the severity of liver fibrosis in NASH. Also, the relation between ALT levels, obesity, diabetes, and AST/ALT ratio and fibrosis and ET-1 level was sought. A total of 92 patients were enrolled in the study. The patients were categorized into three groups: group 1, patients with elevated transaminase levels who were diagnosed as NASH by liver biopsy (n=40); group II, patients with only hepatosteatosis determined by biopsy but having elevated transaminase levels (n=12); and group III, patients with hepatosteatosis observed by ultrasonography, having normal transaminase levels (n=40). The serum ET-1 level was measured by an appropriate ELISA kit for all patients. Mean serum ET-1 level was statistically significantly higher in the NASH group compared to the other two groups (15.56+/-4.63 vs 6.75+/-2.46 and 5.74+/-2.34 micromol/L; P < 0.01). Mean serum ET-1 levels in NASH patients with grade I, grade II, and grade IV fibrosis were 14.06+/-0.92, 17.70+/-2.32, and 20.40+/-1.40 micromol/L, respectively. None of the patients were identified as grade III fibrosis. It was found that the serum ET-1 level showed a statistically significant increase as fibrosis severity increased in NASH patients (P < 0.05). In conclusion, the serum ET-1 level is higher in NASH patients compared to patients having only steatosis. There appears to be a correlation between severity of fibrosis and serum ET-1 level in NASH patients. It has been found that NASH patients having a twofold increase in their ALT levels had higher ET-1 levels and a more severe grade of fibrosis.

Diabetes modulates differentially creatine kinase-specific activity responsiveness to estradiol-17beta and to raloxifene in rat organs

Diabetes mellitus increases the risk for CVD in women. While there is considerable evidence suggesting beneficial effects of estrogen on decreasing lipid peroxidation, atherosclerotic processes, and cardiovascular diseases, diabetes negates most estrogen protective effects as well as the skeletal protective effects of estrogens, which are not discernable in diabetic women. In the present study, we examined the in vivo effects of estradiol-17beta (E2), on creatine kinase (CK)-specific activity, in estrogen-responsive organs from healthy and diabetic rats. Healthy or diabetic (streptozotocin-induced) female rats were injected with either E2 (10-50 microg/rat) or raloxifene (Ral; 500-1,000 microg/rat). Twenty-four hours following the injection, animals were sacrificed; their organs removed and assayed for CK-specific activity. CK-specific activity in different organs [Left ventricle of heart (Lv), uterus (Ut), aorta (Ao), para uterine adipose tissue (Ad), epiphyseal cartilage (Ep), and diaphyseal bone (Di)] from healthy animals, was stimulated with increased doses of E2, with maximum at 20 microg/rat. Age-matched diabetic female rats exhibited a remarkable decreased response to E2 in all organs except Ut. In contrast, the response to Ral was not altered in diabetic rats. Similar results were observed in organs from ovariectomized female rats (Ovx), healthy or diabetic. These results support our previous in vitro findings, demonstrating that hyperglycemia decreases CK response to E2 but not to Ral in cultured human vascular and bone cells. In summary, diabetes mellitus decreases CK response to E2 but not that of Ral in skeletal and vascular tissues. The decreased response to E2 detected in organs derived from diabetic rats might be due to changes in nuclear and/or membrane estrogen receptors and/or other genomic and non-genomic pathways, as was shown in in vitro cellular models.

Transcriptional regulation of vascular bone morphogenetic protein by endothelin receptors in early autoimmune diabetes mellitus

Endothelin (ET) and bone morphogenic proteins (BMP) have been implicated in the development of micro- and macrovascular complications of type 2 diabetes mellitus due to atherosclerosis. This study investigated vascular BMP-expression during early development of experimental autoimmune diabetes mellitus and whether ET(A) receptors are involved in its regulation, using the selective ET(A) receptor antagonist BSF461314. Specificity of BSF461314 was confirmed through ET-mediated p44/42 mitogen-activated protein kinase (ERK1/2) phosphorylation experiments. For animal studies, non-obese diabetic (NOD) and control mice at 16 weeks of age were treated with BSF461314 for 6 weeks. Plasma glucose levels were measured before and after treatment and vascular gene expression of BMP-2, BMP-7, and BMP-type II receptor was determined in the aorta by quantitative real-time polymerase chain reaction analysis. At the beginning of the study in all animals, plasma glucose levels were within the normal range. After 6 weeks gene expression of vascular BMP-2, BMP-7 and BMP-type II receptor was almost doubled in NOD mice compared with non-diabetic controls (p < 0.05). Concomitant treatment with BSF461314 significantly reduced expression of all BMPs and lowered plasma glucose levels in NOD mice close to controls (all p < 0.05 versus untreated). In conclusion, vascular BMP-2, BMP-7, and BMP-type II receptor expression is upregulated in early stages of autoimmune diabetes mellitus. The data further indicate that ET(A) receptors inhibit diabetes-associated activation of vascular BMPs and regulate plasma glucose levels suggesting that ET(A) receptors might provide a new therapeutic target to interfere with the early development of atherosclerosis in patients with type 1 diabetes mellitus.

Endothelin inhibition delays onset of hyperglycemia and associated vascular injury in type I diabetes: evidence for endothelin release by pancreatic islet beta-cells

This study investigated the role of endothelin-1 for hyperglycemia, vascular, and pancreatic injury in early type I diabetes in non-obese-diabetic (NOD) mice. Endothelium dependent relaxation to acetylcholine and vascular gene expression of endothelin converting enzyme (ECE) isoforms 1 and 2 were studied as indicators of vascular injury. Endothelial NO bioactivity in the aorta was reduced in diabetic NOD mice while vascular expression of ECE-1 and ECE-2 mRNA was increased compared with controls (all p<0.05). Vascular histology was normal in all animals. Unexpectedly, treatment of prediabetic NOD mice for 6 weeks with the orally active ET(A) receptor antagonist BSF461314 prevented onset of diabetes without affecting insulitis severity. ET(A) receptor blockade also restored abnormal endothelial NO bioactivity and reduced ECE-1 and ECE-2 gene expression in NOD mice to levels comparable with healthy controls (p<0.05). Moreover, secretion of endothelin-1 in a time-dependent fashion was observed by pancreatic islet beta-cells cultured in vitro. These data suggest a critical role for ET(A) receptor signaling in the development of autoimmune forms of diabetes and the early vascular injury associated with it.

High glucose blocks the effects of estradiol on human vascular cell growth: differential interaction with estradiol and raloxifene

Because diabetic women appear not to be protected by estrogen in terms of propensity to cardiovascular disease, we tested the possibility that chronic hyperglycemia modulates the effects of E(2) on vascular cell growth in vitro. Human endothelial cells (E304) and vascular smooth muscle cells (VSMC) were grown in normal glucose (5.5 mmol/l), high glucose (22 mmol/l) or high manitol (22 nmol/l; an osmotic control) for 7 days. In endothelial cells glucose per se stimulated DNA synthesis. However E(2)- (but not RAL-) stimulated [3H] thymidine incorporation was attenuated in the presence of high glucose. In parallel, E(2)-dependent MAP-kinase-kinase activity was blocked in the presence of high glucose. High glucose increased basal creatine kinase (CK) specific activity, but E(2)-stimulated CK was not significantly impaired in the presence of high glucose. In VSMC, high glucose prevented the inhibitory effect of high E(2) (but not of high RAL) concentrations on DNA synthesis. High glucose also prevented E(2)-induced MAP-kinase-kinase activity. In contrast, while high glucose augmented basal CK, the relative E(2)-induced changes were roughly equal in normal and high high glucose media. Hence, high glucose blocks several effects of E(2) on vascular cell growth, which are mediated, in part, via the MAP-kinase system and are likely contributors to E(2)'s anti-atherosclerotic properties. Since RAL's estrogen-mimetic effects on human vascular cell growth were independent of MAP-kinase activation and were not affected by hyperglycemia, the potential use of RAL to circumvent the loss of estrogen function induced by hyperglycemia and diabetes in the human vasculature should be further explored.

Combined ETA/ETB receptor blockade of human peritoneal mesothelial cells inhibits collagen I RNA synthesis

BACKGROUND

Peritoneal fibrosis is a serious complication of peritoneal dialysis; however, the mechanisms are poorly understood. We studied osmolarity and physical stress-induced effects on collagen I RNA synthesis in human peritoneal mesothelial cells (HPMCs) and focused on endothelin as a possible mediator.

METHODS

HPMCs were grown in a medium containing either d-glucose or glycerol to analyze the impact of osmolarity on mesothelial endothelin-1 (ET-1) release and on collagen I RNA synthesis [reverse transcription-polymerase chain reaction (RT-PCR)]. A cellular model of nonlaminar fluid shear stress and cellular stretch was used to analyze the effects of physical forces. To neutralize the endothelin effects, a combined ETA/ETB receptor antagonist (LU 302 872) was chosen.

RESULTS

Glucose, but not glycerol, increased mesothelial ET-1 release in a concentration and time-dependent manner (P < 0.05 vs. controls). Collagen I RNA synthesis was significantly higher in glucose-challenged cell cultures (P < 0.05 vs. controls). The glucose-mediated collagen I RNA synthesis was completely inhibited by adding the combined ETA/ETB receptor antagonist to the medium. Fluid shear stress, but not cellular stretch, led to a significant increase in the mesothelial ET-1 release (P < 0.005 vs. controls) and collagen I RNA synthesis (P < 0.05 vs. controls). LU 302 872 completely inhibited these effects.

CONCLUSION

We found that glucose and fluid shear stress are potent stimuli for ET-1 release and collagen I RNA synthesis in a model cellular system. Although our system is highly artificial, our findings raise the hypothesis that similar effects may occur in the peritoneal membranes of peritoneal dialysis patients and suggest that endothelin might be involved.

Endothelin receptor blockers in cardiovascular disease

The endothelin (ET) system is comprised of 4 active ETs, with ET-1 being the predominant isoform in the cardiovascular system. Because of the potent vasoconstricting and mitogenic effects of ET-1 and its involvement in various cardiovascular diseases, blockade of the ET receptor has received considerable attention. ET receptor antagonism has been demonstrated to be beneficial in patients with pulmonary hypertension. The nonselective ET receptor antagonist bosentan improves exercise capacity and increases time to clinical worsening in patients with pulmonary arterial hypertension. The selective ET A receptor antagonist sitaxsentan also improves hemodynamics and exercise capacity in patients with pulmonary arterial hypertension. Results with ET receptor antagonists in congestive heart failure have been disappointing. Although some studies have suggested benefit, larger studies have been neutral. The use of ET receptor antagonists for other conditions has not been fully explored. Future studies with the use of ET receptor antagonists as part of a multidrug regimen are also needed.

Endothelins in chronic diabetic complications

Endothelins are widely distributed in the body and perform several vascular and nonvascular functions. Experimental data indicate abnormalities of the endothelin system in several organs affected in chronic diabetic complications. In support of this notion, it has been shown that endothelin-receptor antagonists prevent structural and functional abnormalities in target organs of diabetic complications in animal models. Alterations of plasma endothelin levels have also been demonstrated in human diabetes. This review discusses the role of endothelins in the pathogenesis of chronic diabetic complications. The current experimental evidence suggests that endothelin-receptor antagonism may potentially be an adjuvant therapeutic tool in the treatment of chronic diabetic complications.

Chronic endothelin antagonism restores cerebrovascular function in diabetes

OBJECTIVE

Diabetes profoundly alters vascular function and is a risk factor for cerebrovascular disease. Diabetes increases myogenic tone and decreases responsiveness to adenosine triphosphatase (ATP)-sensitive K(+) (K(ATP)) channel openers and endothelium-dependent vasodilators. The mechanism(s) by which diabetes impairs cerebrovascular function remain obscure. In the present study, the effects of the potent vasoactive peptide endothelin-1 on myogenic tone and endothelium-dependent and potassium channel-mediated vasodilation in middle cerebral arteries from diabetic and nondiabetic rats were investigated.

METHODS

Twenty-eight Wistar rats were divided into four experimental groups (n = 7 per group): control (C), control treated with bosentan (an endothelin A/B receptor antagonist) (CB), diabetic (D), and diabetic bosentan-treated (DB). Diabetes was induced with streptozotocin (D and DB groups), after which chronic bosentan treatment was initiated (CB and DB groups). Middle cerebral arteries were mounted in a pressure myograph, and myogenic responses were recorded. In addition, endothelium-dependent and -independent responses and the effects of the K(ATP) channel opener pinacidil were examined.

RESULTS

Cerebral arteries from the diabetic and nondiabetic rats constricted in response to graded pressure increases. Maximum myogenic responses (percent constriction at 60 mm Hg) were significantly greater in the D group (38 +/- 3% versus 25 +/- 3% in C; P < 0.02). The enhanced myogenic tone in the D group was completely prevented by bosentan treatment (DB, 23 +/- 5% versus D; P < 0.003) without an effect on the CB group. In addition, bosentan treatment improved endothelium-dependent vasomotion and improved K(ATP)-mediated vasodilation in the DB group (P < 0.001).

CONCLUSION

These data describe, for the first time, the interaction between endothelin-1, myogenic tone, and endothelial function in diabetes. Chronic endothelin antagonism restores cerebrovascular function in this model of diabetes and has global implications for the management of cerebrovascular disease in diabetes.