Molecular pharmacology and pathophysiological significance of endothelin

From waste to wonder: exploring the hypoglycemic and anti-oxidant properties of corn processing by-products

Introduction: The industrial processing of corn (Zeamays L.) generates by-products such as corn silk, straw peels, and straw core, which contribute to adverse environmental impacts. Our study aimed to investigate sustainable approaches for mitigating these effects by evaluating the hypoglycemic potential and mechanisms of ethyl acetate fractions derived from these corn derivatives. Methods: We employed glucose consumption assays, high glucose stress tests, UPLC-QE-Orbitrap-MS analysis, molecular docking, and simulations to assess their components and efficacy. Antioxidant capacities were evaluated using DPPH, FRAP, ABTS, and •OH scavenging assays. Results: Notably, the ethyl acetate fraction extracted from straw peels (SPE) exhibited a high concentration of flavonoids and phenolic compounds along with pronounced hypoglycemic activity and antioxidant capacity. SPE significantly enhanced glucose consumption in insulin-resistant HepG2 cells while protecting HUVECs against damage caused by high glucose levels. Molecular docking analyses confirmed the interaction between active compounds and α-glucosidase as well as α-amylase, while molecular dynamic simulations indicated stability at their binding sites. Discussion: In conclusion, the hypoglycemic and antioxidative properties observed in corn by-products such as straw peels, corn silk, and straw core can be attributed to the inhibition of α-glucosidase and α-amylase activities, coupled with their rich phenolic and flavonoid content. These findings highlight the potential of these by-products for applications in healthcare management and their sustainable utilization, demonstrating significant value in the use of agricultural residues.

O-Linked β-N-Acetylglucosamine Modification: Linking Hypertension and the Immune System

The O-linked β-N-acetylglucosamine modification (O-GlcNAcylation) of proteins dynamically regulates protein function, localization, stability, and interactions. This post-translational modification is intimately linked to cardiovascular disease, including hypertension. An increasing number of studies suggest that components of innate and adaptive immunity, active players in the pathophysiology of hypertension, are targets for O-GlcNAcylation. In this review, we highlight the potential roles of O-GlcNAcylation in the immune system and discuss how those immune targets of O-GlcNAcylation may contribute to arterial hypertension.

Dysregulation of Endothelin-1: Implications for Health Disparities in Alzheimer's Disease

Alzheimer's disease (AD) and related dementias disproportionately impact racial and ethnic minorities. The racial and ethnic disparities in AD could be explained by differences in cerebral vascular disease pathology. Endothelin-1 (ET-1) is a potent vasoconstrictive peptide that regulates smooth muscle, endothelial cell, and pericyte contractions that may result in cerebral vascular constriction, leading to cerebral hypoperfusion; over time, ET-1 may result in neuronal injury contributing to the pathology of AD. Upregulation of the ET-1 system has been observed in African Americans when compared with non-Hispanic Whites. The role of the ET-1 system as a driver of ethnic disparities in AD requires further investigation. Targeting of the ET-1 system as a therapeutic intervention that could impact AD progression also needs further study. Dysregulation of ET-1 in Hispanic/Latino populations largely have been unexplored. Genetics linking ET-1 dysregulation and racial disparities in AD also needs further investigation. In this review, I examine how AD effects underserved minority populations and how dysregulation of the ET-1 system specifically predisposes ethnic minorities to AD. In addition, I examine the molecular interactions of the ET-1 system and amyloid beta, the role the ET-1 system in neurodegeneration, potential therapeutics for ET-1 dysregulation, and the impact on AD progression.

Effects of Danhong Injection (丹红注射液) and its main components on anticoagulation and fibrinolysis in cultured vein endothelial cells

OBJECTIVE

To observe the effects of Danhong Injection (丹红注射液) and its main components, including daiclzein and hydroxysafflor yellow A (HSYA), on the anticoagulation, fibrinolysis, anti-apoptosis in hypoxia model of vein endothelial cells (VECs).

METHODS

VECs were prepared and were put in a hypoxia environment, which consisted of mixed gas of 95% N and 5% CO mixed gas, when reached confluent culture. Five groups used different treatments, including normal control group, hypoxia group, daiclzein group, HSYA group and Danhong Injection group. The VECs were identified by fluorescence double labeling methods. The morphology was observed by a phase contrast microscopy. The effects of Danhong Injection, daiclzein and HSYA on 6 keto prostaglandin F1α (6-keto-PGF1α) level was measured by the method of radioimmunoassay (RIA). Superoxide dismutase (SOD) activity was tested by water soluble tetrazolium salt. The content of malondialdehyde (MDA) was measured by thiobarbituric acid. The activities of tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor (PAI) were measured by the method of chromogenic substrate. The contents of endothelin (ET) and nitric oxide (NO) were detected by non-equilibrium RIA and enzymelinked immunosorbent assay. Cells apoptosis rate was determined by flow cytometry.

RESULTS

Compared with the normal control group, the floating cells number, PAI activity, ET and MDA contents, and cells apoptosis rate in the culture solution of hypoxia group were all significantly increased, whereas the 6-keto-PGF1α and NO contents, and t-PA and SOD activities were decreased significantly (P<0.01). Compared with the hypoxia group, Danhong Injection markedly increased the 6-keto-PGF1α content and SOD activity, regulated PAI and t-PA activities, ET and NO contents, and decreased MDA content and cells apoptosis rate (P<0.05 or P<0.01).

CONCLUSIONS

Danhong Injection and its main components played an important role in protecting primary VECs from hypoxic damage by regulating the secretion and vasomotor function of VECs. The function of Danhong Injection was most remarkable.

Endothelin-1 induces LIMK2-mediated programmed necrotic neuronal death independent of NOS activity

BACKGROUND

Recently, we have reported that LIM kinase 2 (LIMK2) involves programmed necrotic neuronal deaths induced by aberrant cyclin D1 expression following status epilepticus (SE). Up-regulation of LIMK2 expression induces neuronal necrosis by impairment of dynamin-related protein 1 (DRP1)-mediated mitochondrial fission. However, we could not elucidate the upstream effecter for LIMK2-mediated neuronal death. Thus, we investigated the role of endothelin-1 (ET-1) in LIMK2-mediated neuronal necrosis, since ET-1 involves neuronal death via various pathways.

RESULTS

Following SE, ET-1 concentration and its mRNA were significantly increased in the hippocampus with up-regulation of ETB receptor expression. BQ788 (an ETB receptor antagonist) effectively attenuated SE-induced neuronal damage as well as reduction in LIMK2 mRNA/protein expression. In addition, BQ788 alleviated up-regulation of Rho kinase 1 (ROCK1) expression and impairment of DRP1-mediated mitochondrial fission in CA1 neurons following SE. BQ788 also attenuated neuronal death and up-regulation of LIMK2 expression induced by exogenous ET-1 injection.

CONCLUSION

These findings suggest that ET-1 may be one of the upstream effectors for programmed neuronal necrosis through abnormal LIMK2 over-expression by ROCK1.

Endothelin systems in the brain: involvement in pathophysiological responses of damaged nerve tissues

In addition to their potent vasoconstriction effects, endothelins (ETs) show multiple actions in various tissues including the brain. The brain contains high levels of ETs, and their production is stimulated in many brain disorders. Accumulating evidence indicates that activation of brain ET receptors is involved in several pathophysiological responses in damaged brains. In this article, the roles of brain ET systems in relation to brain disorders are reviewed. In the acute phase of stroke, prolonged vasospasm of cerebral arteries and brain edema occur, both of which aggravate brain damage. Studies using ET antagonists show that activation of ETA receptors in the brain vascular smooth muscle induces vasospasm after stroke. Brain edema is induced by increased activity of vascular permeability factors, such as vascular endothelial growth factor and matrix metalloproteinases. Activation of ETB receptors stimulates astrocytic production of these permeability factors. Increases in reactive astrocytes are observed in neurodegenerative diseases and in the chronic phase of stroke, where they facilitate the repair of damaged nerve tissues by releasing neurotrophic factors. ETs promote the induction of reactive astrocytes through ETB receptors. ETs also stimulate the production of astrocytic neurotrophic factors. Recent studies have shown high expression of ETB receptors in neural progenitors. Activation of ETB receptors in neural progenitors promotes their proliferation and migration, suggesting roles for ETB receptors in neurogenesis. Much effort has been invested in the pursuit of novel drugs to induce protection or repair of damaged nerve tissues. From these studies, the pharmacological significance of brain ET systems as a possible target of neuroprotective drugs is anticipated.

Pathogenesis of brain edema and investigation into anti-edema drugs

Brain edema is a potentially fatal pathological state that occurs after brain injuries such as stroke and head trauma. In the edematous brain, excess accumulation of extracellular fluid results in elevation of intracranial pressure, leading to impaired nerve function. Despite the seriousness of brain edema, only symptomatic treatments to remove edema fluid are currently available. Thus, the development of novel anti-edema drugs is required. The pathogenesis of brain edema is classified as vasogenic or cytotoxic edema. Vasogenic edema is defined as extracellular accumulation of fluid resulting from disruption of the blood-brain barrier (BBB) and extravasations of serum proteins, while cytotoxic edema is characterized by cell swelling caused by intracellular accumulation of fluid. Various experimental animal models are often used to investigate mechanisms underlying brain edema. Many soluble factors and functional molecules have been confirmed to induce BBB disruption or cell swelling and drugs targeted to these factors are expected to have anti-edema effects. In this review, we discuss the mechanisms and involvement of factors that induce brain edema formation, and the possibility of anti-edema drugs targeting them.

Late dual endothelin receptor blockade with bosentan restores impaired cerebrovascular function in diabetes

AIMS

Up-regulation of the endothelin (ET) system in type-2 diabetes increases contraction and decreases relaxation in basilar artery. We showed that 1) ET-receptor antagonism prevents diabetes-mediated cerebrovascular dysfunction; and 2) glycemic control prevents activation of the ET-system in diabetes. Here, our goal is to determine whether and to what extent glycemic control or ET-receptor antagonism reverses established cerebrovascular dysfunction in diabetes.

MAIN METHODS

Non-obese type-2 diabetic Goto-Kakizaki rats were administered either vehicle, metformin (300 mg/kg/day) or dual ET-receptor antagonist bosentan (100mg/kg) for 4-weeks starting at 18-weeks after established cerebrovascular dysfunction (n=5-6/group). Control group included vehicle-treated aged-matched Wistar rats. Blood glucose and pressure were monitored weekly. At termination, basilar arteries were collected and cumulative dose-response curves to ET-1 (0.1-500 nM), 5-HT (1-1000 nM) and acetylcholine (Ach, 0.1 nM-5 μM) were studied by wire myograph. Middle cerebral artery (MCA) myogenic reactivity and tone were measured using pressurized arteriograph.

KEY FINDINGS

There was no difference in ET-1 and 5-HT-mediated constrictions. Endothelium-dependent relaxation was impaired in diabetes. Bosentan improved sensitivity to Ach as well as the maximum relaxation. Myogenic-tone is decreased over the course of the disease. Both treatments improved the ability of MCAs to develop tone at 80 mm Hg and only bosentan improved the tone at higher pressures.

SIGNIFICANCE

These results suggest that contractile response is not affected by glycemic control or ET-receptor antagonism. Meanwhile, dual ET-receptor blockade is effective in partially improving endothelium-dependent relaxation and myogenic response in a blood pressure-independent manner even after established cerebrovascular dysfunction and offers therapeutic potential.

Endothelin-1 stimulates cyclin D1 expression in rat cultured astrocytes via activation of Sp1

Endothelins (ETs), a family of vasoconstrictor peptides, are up-regulated in several pathological conditions in the brain, and induce astrocytic proliferation. We previously observed that ET-1 increased the expression of cyclin D1 protein. Thus, we confirmed the intracellular up-regulation of cyclin D1 by ET-1 in rat cultured astrocytes. Real-time PCR analysis indicated that ET-1 (100 nM) and Ala(1,3,11,15)-ET-1 (100 nM), a selective agonist of the ETB receptor, induced a time-dependent and transient increase in cyclin D1 mRNA. The effect of ET-1 was diminished by an ETB antagonist (1 μM BQ788) or inhibitors of Sp1 (500 nM mithramycin), ERK (50 μM PD98059), p38 (20 μM SB203580) and JNK (1 μM SP600125), but not inhibitors of NF-κB (10 μM SN50 and 100 μM pyrrolidine dithiocarbamate). The binding assay for Sp1 indicated that ET-1 increased the binding activity of Sp1 to consensus sequences, and two oligonucleotides of the cyclin D1 promoter including the Sp1-binding sites diminished the effect of ET-1. Western blot analysis showed that ET-1 induced time-dependent and transient phosphorylation of Sp1 on Thr453 and Thr739 via the ETB receptor. ET-1-induced phosphorylation of Sp1 was attenuated by PD98059 and SP600125. Additionally, ET-1 increased the incorporation of bromodeoxyuridine (BrdU) in cultured astrocytes and the number of BrdU-positive cells decreased in the presence of PD98059, SP600125 and mithramycin. These results suggest that ET-1 increases the expression of cyclin D1 via activation of Sp1 and induces astrocytic proliferation.

Pathological Importance of the Endothelin-1/ET(B) Receptor System on Vascular Diseases

Activation of the endothelin (ET)-1/ET receptor system is involved in the development of vascular diseases such as atherosclerosis, vascular hypertrophy, and restenosis. Some issues still remain unresolved including whether ET receptor antagonists are expected to become the new therapeutic tools for the treatment of vascular diseases. One of the unresolved critical points is the functional role of ET receptor subtypes on each vascular disease, in particular the pathophysiological roles of the ET_B receptor. We recently demonstrated that selective inhibition of the ET_B receptor system showed harmful effects in the development of neointimal formation after vascular injury. However, there was no apparent difference in the therapeutic effects between a nonselective ET_A/ET_B receptor antagonist and selective ET_A receptor antagonist. These findings indicate that antagonism of the ET_A receptor system is essential for suppressing vascular remodeling, irrespective of the presence of ET_B-receptor-mediated actions, although the selective ET_B receptor antagonist worsens vascular remodeling. In addition, we found that ET receptor systems contribute to sex differences in the severity of vascular disease, thereby suggesting that the efficacy of ET receptor antagonists for vascular diseases may differ between sexes. In this paper, we outline the roles of the ET-1/ET_B receptor system on vascular diseases and its sex differences.

Comparison of selective versus dual endothelin receptor antagonism on cerebrovascular dysfunction in diabetes

OBJECTIVES

Cerebrovascular tone plays a key role in controlling cerebral blood flow. Our studies have demonstrated that the endothelin system is upregulated in type 2 diabetes leading to increased sensitivity to endothelin-1 and decreased relaxation in basilar artery. While chronic endothelin A receptor blockade restored relaxation, selective endothelin B receptor blockade caused paradoxical constriction in diabetes. Whether this effect was due to activation of endothelin A receptors in the presence of endothelin B receptor blockade or due to the loss of vasculoprotective effects of endothelin B receptors remained unknown. The current study hypothesizes that due to the antagonism of the vasculoprotective endothelin receptor B, dual blockade will not be as effective as selective endothelin receptor A antagonism in improving cerebrovascular dysfunction in type 2 diabetes.

METHODS

These studies were done in non-obese, type 2 diabetic Goto-Kakizaki rats administered either vehicle, selective endothelin receptor A antagonist Atrasentan (5 mg/kg) or dual endothelin antagonist Bosentan (100 mg/kg) for 4 weeks. At termination, basilar arteries were collected and mounted on a wire myograph and cumulative dose-response curves to endothelin-1 (1-500 nM) and acetylcholine (1 nM-5 μm) were studied.

RESULTS

Basilar artery was highly sensitive to endothelin-1-mediated constriction in diabetic animals. While neither Atrasentan nor Bosentan affected endothelium-dependent vascular relaxation in control animals, both treatments improved the maximum dilatation in diabetes and Atrasentan also improved sensitivity to acetylcholine.

CONCLUSION

In light of our previous data which showed that endothelin B receptors are vasculoprotective and blockade of this receptor worsens relaxation, current findings suggest that when blocked simultaneously with the endothelin receptor A, the endothelin receptor B antagonism is protective by reducing the hyperreactivity and improving cerebrovascular function in diabetes.

Aminoguanidine normalizes ET-1-induced aortic contraction in type 2 diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats by suppressing Jab1-mediated increase in ET(A)-receptor expression

Circulating levels of endothelin (ET)-1 are increased in the diabetic state, as is endogenous ET(A)-receptor-mediated vasoconstriction. However, the responsible mechanisms remain unknown. We hypothesized that ET-1-induced vasoconstriction is augmented in type 2 diabetes with hyperglycemia through an increment in advanced glycation end-products (AGEs). So, we investigated whether treatment with aminoguanidine (AG), an inhibitor of AGEs, would normalize the ET-1-induced contraction induced by ET-1 in strips of thoracic aortas isolated from OLETF rats at the chronic stage of diabetes. In such aortas (vs. those from age-matched genetic control LETO rats): (1) the ET-1-induced contraction was enhanced, (2) the levels of HIF1α/ECE1/plasma ET-1 and plasma CML-AGEs were increased, (3) the ET-1-stimulated ERK phosphorylation mediated by ET(A)-R was increased, (4) the expression level of Jab1-modified ET(A)-R protein was reduced, and (5) the expression level of O-GlcNAcylated ET(A)-R protein was increased. Aortas isolated from such OLETF rats that had been treated with AG (50mg/kg/day for 10 weeks) exhibited reduced ET-1-induced contraction, suppressed ET-1-stimulated ERK phosphorylation accompanied by down-regulation of ET(A)-R, and increased modification of ET(A)-R by Jab1. Such AG-treated rats exhibited normalized plasma ET-1 and CML-AGE levels, and their aortas exhibited decreased HIF1α/ECE1 expression. However, such AG treatment did not alter the elevated levels of plasma glucose or insulin, or systolic blood pressure seen in OLETF rats. These data from the OLETF model suggest that within the timescale studied here, AG normalizes ET-1-induced aortic contraction by suppressing ET(A)-R/ERK activities and/or by normalizing the imbalance between Jab1 and O-GlcNAc in type 2 diabetes.

Mechanisms involved in the effects of endothelin-1 in pig prostatic small arteries

Since endothelin-1 (ET-1) is involved in prostatic disorders, the current study investigated the mechanisms underlying the ET-1-induced effects in pig prostatic small arteries. The experiments were performed in rings mounted in microvascular myographs containing physiological saline solution at 37oC for isometric force recordings. On basal tension, ET-1 (0.1-30 nM) evoked concentration-dependent contractions, which were enhanced by endothelium removal. ET-1 contractions were inhibited by blockade of endothelin ETA and ETB receptors, extracellular Ca2+ removal and blockade of voltage-dependent (L-type)- and non-voltage-dependent-Ca2+ channels. On endothelium intact rings precontracted with noradrenaline, the ETB endothelin receptor agonist BQ3020 promoted a concentration-dependent relaxation which was reduced by blockade of ETB receptors, nitric oxide synthase, guanylyl cyclase and prostanoids synthesis. Endothelium removal abolished its relaxant response and unmasked a BQ3020-induced contraction. Tetraethylammonium and 4-aminopyridine, blockers of non-selective K+ channels and voltage-dependent K+ (Kv) channels, respectively, inhibited the relaxations to BQ3020. Iberiotoxin, apamin and glibenclamide, blockers of large and small Ca2+-activated- and ATP-dependent- K+ channels, respectively, failed to modify these responses. These data suggest that ET-1 promotes contraction of pig prostatic small arteries by activating vascular smooth muscle contractile endothelin ETA and ETB receptors coupled to extracellular Ca2+ entry, via voltage-dependent (L-type)- and non-voltage-dependent Ca2+ channels, also being due to intracellular Ca2+ mobilization. In addition, a population of endothelial ETB receptors mediates vasorelaxation via NO-cGMP pathway, vasodilator cyclooxygenase product(s) and Kv channels.

Short-term angiotensin-1 receptor antagonism in type 2 diabetic Goto-Kakizaki rats normalizes endothelin-1-induced mesenteric artery contraction

Endothelin (ET)-1 and angiotensin II (Ang II) are likely candidates for a key role in diabetic vascular complications. We demonstrated previously that an enhanced ET-1-induced contraction is present in mesenteric arteries from Goto-Kakizaki (GK) rats at the chronic stage of type 2 diabetes. Here, we investigated whether short-term treatment of such rats with losartan, an angiotensin type 1 receptor antagonist, might normalize the ET-1-induced contraction. In mesenteric arteries from GK rats at the chronic stage (34-38 weeks) (vs. those from age-matched control Wistar rats): (1) the ET-1-induced contraction was enhanced, (2) the levels of ET-1 and Ang II were increased, (3) ET-1-stimulated ERK2 phosphorylation was increased, and (4) the ACh-induced endothelium-dependent relaxation was reduced. Mesenteric arteries isolated from such GK rats following treatment with losartan (25mg/kg/day for 2 weeks) exhibited reduced ET-1- and Ang II-induced contractions, suppressed ET-1-stimulated ERK phosphorylation, and increased ACh-induced relaxation, while the rats exhibited normalized plasma NO metabolism and their mesenteric arteries exhibited increased basal NO formation. However, such losartan treatment did not alter the increased levels of ET-1 and Ang II seen in GK mesenteric arteries. Our data suggest that within the timescale studied here, losartan normalizes ET-1-induced mesenteric artery contraction through a suppression of ERK activities and/or by normalizing endothelial function.

Promoter methylation in prostate cancer and its application for the early detection of prostate cancer using serum and urine samples

Prostate cancer is the second most common cancer and the second leading cause of cancer death in men. However, prostate cancer can be effectively treated and cured, if it is diagnosed in its early stages when the tumor is still confined to the prostate. Combined with the digital rectal examination, the PSA test has been widely used to detect prostate cancer. But, the PSA screening method for early detection of prostate cancer is not reliable due to the high prevalence of false positive and false negative results. Epigenetic alterations including hypermethylation of gene promoters are believed to be the early events in neoplastic progression and thus these methylated genes can serve as biomarkers for the detection of cancer from clinical specimens. This review discusses DNA methylation of several gene promoters during prostate carcinogenesis and evaluates the usefulness of monitoring methylated DNA sequences, such as GSTP1, RASSF1A, RARβ2 and galectin-3, for early detection of prostate cancer in tissue biopsies, serum and urine.

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.

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

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

Drug discovery for overcoming chronic kidney disease (CKD): the endothelin ET B receptor/nitric oxide system functions as a protective factor in CKD

Accelerated cardiovascular disease (CVD) is a frequent complication of renal disease. Chronic kidney disease (CKD) develops hypertension and dyslipidemia, which in turn can contribute to the progression of renal failure. There is general agreement that endothelin-1 (ET-1), which acts through the two subtypes of receptor ET(A) and ET(B), plays important physiological roles in the regulation of normal cardiovascular function and that excessive ET-1 production is linked to CVD and CKD. Although selective ET(A) or nonselective ET(A)/ET(B) receptor antagonisms have been recognized as a potential strategy for treatment of several cardiovascular disease, it remains unclear which of the antagonisms is suitable for the individuals with CKD because upregulation of the nitric oxide (NO) system via ET(B) receptor is responsible for renal function such as natriuresis, diuresis, and glomerular hemodynamics. Our findings clearly indicate that the blockade of ET receptors, in particular ET(A)-receptor antagonism, not only produces a potential renoprotective effect in CKD but also reduces the risk of CVD. In contrast, pharmacological blockade or genetic deficiency of ET(B) receptor seems to aggravate CKD and CVD in several experimental models of rats. Moreover, preliminary evidence in patients with CKD also suggests that both selective ET(A)- and nonselective ET(A)/ET(B)-receptor blockade decreases blood pressure but that selective ET(A) blockade has additional desirable effects on renal hemodynamics. Thus, at least in CKD, these findings support the notion that ET(B) receptor-mediated actions produce a renoprotective effect and that nonselective ET(A)/ET(B)-receptors blockade seem to offer no advantage over selective ET(A) antagonism, and if anything may potentially reduce the benefits.

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

BACKGROUND AND PURPOSE

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

EXPERIMENTAL APPROACH

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

KEY RESULTS

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

CONCLUSIONS AND IMPLICATIONS

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

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

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

Endothelin-positive mast cells in porcine renal artery and vein

For a first time the endothelin (ET)-positive mast cells were examined in the wall of kidney renal artery and vein. The specimen's were collected from six 8-month-old Danmark Landrace pigs, immediately after slaughtering. Mast cells immunopositive to ET granules were observed in the wall of both artery and vein. In the renal artery, they were found mostly between the media and the adventitia. Some mast cells were found in the media, next to smooth muscle cells. Relatively few mast cells were found in the intima and between intima and tunica media. In the renal vein a smaller number of mast cells were observed. They showed similar localization as in the renal artery. Immunopositive mast cells were established also close to endothelial cells - mostly between internal elastic membrane and basal membrane of the endothelium. In conclusion, on the basis of obtained results, presumptions for active participation of ET (most probably mainly ET-1) in the motility of the vessels' smooth muscle and for stimulation of nitric oxide release from the intimal endothelial cells were made.

Effect of chronic and selective endothelin receptor antagonism on microvascular function in type 2 diabetes

Vascular dysfunction, which presents either as an increased response to vasoconstrictors or an impaired relaxation to dilator agents, results in worsened cardiovascular outcomes in diabetes. We have established that the mesenteric circulation in Type 2 diabetes is hyperreactive to the potent vasoconstrictor endothelin-1 (ET-1) and displays increased nitric oxide-dependent vasodilation. The current study examined the individual and/or the relative roles of the ET receptors governing vascular function in the Goto-Kakizaki rat, a mildly hyperglycemic, normotensive, and nonobese model of Type 2 diabetes. Diabetic and control rats received an antagonist to either the ET type A (ETA; atrasentan; 5 mg x kg(-1) x day(-1)) or type B (ET(B); A-192621; 15 or 30 mg x kg(-1) x day(-1)) receptors for 4 wk. Third-order mesenteric arteries were isolated, and vascular function was assessed with a wire myograph. Maximum response to ET-1 was increased in diabetes and attenuated by ETA antagonism. ETB blockade with 15 mg/kg A-192621 augmented vasoconstriction in controls, whereas it had no further effect on ET-1 hyperreactivity in diabetes. The higher dose of A-192621 showed an ETA-like effect and decreased vasoconstriction in diabetes. Maximum relaxation to acetylcholine (ACh) was similar across groups and treatments. ETB antagonism at either dose had no effect on vasorelaxation in control rats, whereas in diabetes the dose-response curve to ACh was shifted to the right, indicating a decreased relaxation at 15 mg/kg A-192621. These results suggest that ETA receptor blockade attenuates vascular dysfunction and that ETB receptor antagonism exhibits differential effects depending on the dose of the antagonists and the disease state.

Effect of chronic endothelin receptor antagonism on cerebrovascular function in type 2 diabetes

Diabetes increases the risk of stroke and contributes to poor clinical outcomes in this patient population. Myogenic tone of the cerebral vasculature, including basilar arteries, plays a key role in controlling cerebral blood flow. Increased myogenic tone is ameliorated with ET receptor antagonism in Type 1 diabetes. However, the role of endothelin-1 (ET-1) and its receptors in cerebrovascular dysfunction in Type 2 diabetes, a common comorbidity in stroke patients, remains poorly elucidated. Therefore, we hypothesized that 1) cerebrovascular dysfunction occurs in the Goto-Kakizaki (GK) model of Type 2 diabetes, and 2) pharmacological antagonism of ETA receptors ameliorates, while ETB receptor blockade augments vascular dysfunction. GK or control rats were treated with antagonists to either ETA (atrasentan, 5 mg.kg(-1).day(-1)) or ETB (A-192621, 15 or 30 mg.kg(-1).day(-1)) receptors for 4 wk and vascular function of basilar arteries was assessed using a wire myograph. GK rats exhibited increased sensitivity to ET-1. ET(A) receptor antagonism caused a rightward shift, indicating decreased sensitivity in diabetes, while it increased sensitivity to ET-1 in control rats. Endothelium-dependent relaxation was impaired in diabetes. ETA receptor blockade restored relaxation to control values in the GK animals with no significant effect in Wistar rats and ETB blockade with 30 mg.kg(-1).day(-1) A-192621 caused paradoxical constriction in diabetes. These studies demonstrate that cerebrovascular dysfunction occurs and may contribute to altered regulation of myogenic tone and cerebral blood flow in diabetes. While ETA receptors mediate vascular dysfunction, ETB receptors display differential effects. These results underscore the importance of ETA/ETB receptor balance and interactions in cerebrovascular dysfunction in diabetes.

Prostate cancer epigenetics: a review on gene regulation

Prostate cancer is the most common cancer in men in western countries, and its incidence is increasing steadily worldwide. Molecular changes including both genetic and epigenetic events underlying the development and progression of this disease are still not well understood. Epigenetic events are involved in gene regulation and occur through different mechanisms such as DNA methylation and histone modifications. Both DNA methylation and histone modifications affect gene regulation and play important roles either independently or by interaction in tumor initiation and progression. This review will discuss the genes associated with epigenetic alterations in prostate cancer progression: their regulation and importance as possible markers for the disease.

[Endothelin-1 production and its involvement in cardiovascular diseases]

Endothelin (ET) has been implicated in the pathogenesis of several cardiovascular disorders because of its powerful vasoconstrictor and growth-promoting properties. The ET family consists of three isoforms, ET-1, ET-2 and ET-3. ET-1 appears to be the predominant member of the family generated by vascular endothelial cells. In view of the multiple cardiovascular actions of ET-1, there has been much interest in its contribution to the pathophysiology of hypertension and arteriosclerosis. We have been investigating the roles of ET(A) and ET(B) receptors in ET-1-related cardiovascular diseases using subtype-selective ET receptor antagonists and ET(B) receptor-deficient animals. Our studies have demonstrated that ET-1 overproduction and ET(A)-mediated ET-1 actions seem to play a crucial role in the development of several types of hypertensive and post-ischemic diseases. On the other hand, ET-1 biosynthesis and release are regulated at the transcriptional level, and various endogenous substances are known to stimulate ET-1 gene expression by DNA binding of transcription factors. We and others have recently demonstrated that nuclear factor-kappaB (NF-kappaB), a transcription factor with a pivotal role in inducing genes involved in immune, inflammatory and stress responses, is responsible for endothelial ET-1 production. In in vivo studies, agents that can inhibit the NF-kappaB activation improved the development of ET-1-related cardiovascular diseases. Thus, NF-kappaB inhibition may be a pertinent treatment for ET-1 related diseases.

Regional differences in the functional and biochemical properties of endothelin receptor subtypes in the rabbit prostatic urethra

OBJECTIVE

To examine the regional differences in the functional (pharmacological) and biochemical properties of endothelin (ET) receptors in the rabbit prostatic urethra.

MATERIALS AND METHODS

The properties of ET receptors in 6-month-old male rabbit prostatic urethras were examined using isolated muscle-bath and radioligand receptor-binding techniques. Using plasma membrane suspensions, saturation and inhibition experiments with [(125)I]ET-1 and unlabelled agonists and antagonists (ET(A)-selective antagonist BQ123, and ET(B)-selective agonist sarafotoxin 6c, STX6c) were done to determine the ET receptor densities and their subtype specificities in the different regions of the urethra.

RESULTS

The ETs (ET-1 and ET-3) produced significant concentration-dependent contractile responses in the smooth muscle strips from the different regions of the urethra. Although the maximum contractile responses induced by ET-1 were similar in the different regions, the maximum contractile responses induced by ET-3 were greater in the distal region than in the proximal or middle regions, suggesting that the contractile response to ET-1 is more potent than that to ET-3 in all regions, and that there are region-specific differences in the responses to ET-3 but not ET-1. Moreover, the ET-3-induced contractile response was suppressed by BQ788 (a selective antagonist of the ET(B) receptor) suggesting that the ET(B) receptor subtype contributes to the contractile responses mediated by ET-3. The ET receptors were expressed in higher concentrations in the distal than in the proximal or middle regions. BQ123 and STX6c inhibited [(125)I]ET-1 binding in all regions with high and low affinity constants, indicating the presence of both ET(A) and ET(B) receptor subtypes. The proportions of high-affinity binding sites for BQ123, representing ET(A) receptors, were approximately 68%, 63% and 42% in the proximal, middle and distal regions, respectively. By contrast, the proportions of high-affinity binding sites for STX6c, representing ET(B) receptors, were approximately 27%, 35% and 52% in the proximal, middle, and distal regions, respectively. These data indicate the presence of regional differences in the densities and subtype specificities of ET receptor subtypes, and the existence of regional differences in the rabbit prostatic urethra.

CONCLUSION

The results suggest regional differences in ET(B) receptor subtypes that mediate contractile responses to ET-3, reflecting differences in the densities and specificities of the ET receptor subtypes in the rabbit prostatic urethra.

Involvement of the endothelin ET(B) receptor in gender differences in deoxycorticosterone acetate-salt-induced hypertension

1. In the present study, we investigated the role of endothelin ET(B) receptors in gender differences in the development of deoxycorticosterone acetate (DOCA)-salt-induced hypertension by using the spotting-lethal (sl) rat, which carries a naturally occurring deletion in the ET(B) receptor gene. 2. In wild-type rats, the elevation of systolic blood pressure (SBP) by DOCA-salt treatment for 4 weeks was extremely lower in females than in males, but this gender difference was partially attenuated in ovariectomized (OVX) animals. These alterations of SBP corresponded with vascular superoxide () production. 3. In homozygous (sl/sl) group, the SBP of male, intact female and OVX rats was markedly elevated by DOCA-salt treatment to the same extent, indicating that the gender difference in DOCA-salt-induced hypertension was abolished by the genetic ET(B) receptor deficiency. There were similar increases in the vascular endothelin (ET)-1 content in the three DOCA-salt-treated animal groups, but vascular production in male and OVX rats was much higher than that in intact females. 4. Daily oral administration of ABT-627, an ET(A) receptor antagonist, to sl/sl rats for 2 weeks suppressed the DOCA-salt-induced hypertension more efficiently in intact female rats than in male animals. 5. Thus, vascular oxidative stress is related, at least in part, to differences in the development of DOCA-salt-induced hypertension between male and female rats, but this gender difference is abolished by the genetic ET(B) receptor deficiency, suggesting that ET(B) receptor-mediated vasoprotective actions contribute to the gender differences seen. In addition, in both sexes, vascular ET-1 overproduction and the ET(A) receptor-mediated action seem to be responsible for the enhanced susceptibility to DOCA-salt hypertension in genetic ET(B) receptor deficiency.

Properties and Mechanism of the Mechanosensitive Ion Channel Inhibitor GsMTx4, a Therapeutic Peptide Derived from Tarantula Venom

Mechanosensitive ion channels (MSCs) are found in all types of cells ranging from Escherichia coli to morning glories to humans. They seem to fall into two families: those in specialized receptors, such as the hair cells of the cochlea, and those in cells not clearly differentiated for sensory duty. The physiological function of the channels in nonspecialized cells has not been demonstrated, although their activity has been demonstrated innumerable times in vitro. The only specific reagent to block MSCs isGsMTx4, a 4-kDa peptide isolated from tarantula venom. Despite being isolated from venom, it is nontoxic to mice. GsMTx4 is specific for an MSC subtype, the nonselective cation channels that may be members of the transient receptor potential (TRP) family. GsMTx4 acts as a gating modifier, increasing the energy of the open state relative to the closed state. The mirror image D enantiomer of GsMTx4 is equally active, so mode of action is not via the traditional lock and key model. GsMTx4 probably acts in the boundary lipid of the channel by changing local curvature and mechanically stressing the channel toward the closed state. Despite the lack of definitive physiological data on the function of the cationic MSCs, GsMTx4 may prove useful as a drug or lead compound that can affect physiological processes. These processes would be those driven by mechanical stress, such as blood vessel autoregulation, stress-induced contraction of smooth muscle, and Ca(2+) loading in muscular dystrophy.

Mechanisms underlying the chronic pioglitazone treatment-induced improvement in the impaired endothelium-dependent relaxation seen in aortas from diabetic rats

The objectives of this study were to determine the effects of chronic treatment with pioglitazone, a peroxisome proliferator-activated receptor gamma agonist, on the impaired endothelium-dependent relaxation seen in aortas from established streptozotocin (STZ)-induced diabetic rats, and to identify some of the molecular mechanisms involved. Starting at 8 weeks of diabetes, pioglitazone (10 mg/kg) was administered to STZ-induced diabetic rats for 4 weeks. In untreated STZ rats (vs age-matched control rats): (1) ACh-induced relaxation, cGMP accumulation, phosphorylation of the cGMP-dependent protein kinase substrate vasodilator-stimulated phosphoprotein at Ser-239 [an established biochemical end-point of nitric oxide (NO)/cGMP signaling], and Cu/Zn-superoxide dismutase (SOD) expression and SOD activity were all reduced; (2) aortic superoxide generation, nitrotyrosine expression, and NAD(P)H oxidase activity were increased; (3) plasma endothelin-1 (ET-1) and aortic c-Jun (AP-1 component) protein expressions were increased. Pioglitazone treatment markedly corrected the above abnormalities. Collectively, these results suggest that pioglitazone treatment improves endothelium-dependent relaxation by reducing oxidative stress via increased SOD activity, decreased NAD(P)H oxidase activity, and a decreased ET-1 level, and that this decreased ET-1 level may be attributable to an inhibition of the AP-1 signaling pathway.

Endothelin-converting enzyme inhibitors for the treatment of subarachnoid hemorrhage-induced vasospasm

A burgeoning body of evidence suggests that endothelin-1 (ET-1), the most potent endogenous vasoconstrictor yet identified, may be critical in the pathophysiology of various cardiovascular diseases. The ET system may also be implicated in the pathogenesis of cerebral vasospasm after aneurysmal subarachnoid hemorrhage (SAH). Clinical studies have shown that the levels of ET-1 are increased in the cerebrospinal fluid (CSF) of patients following SAH, suggesting that ET-1-mediated vasoconstriction plays a major role in the development of vasospasm after SAH. The potential involvement of ETs in SAH-induced vasospasm has triggered considerable interest in developing therapeutic strategies that inhibit the biologic effects of ET. One promising approach to block the biosynthesis of ETs is suppressing the proteolytic conversion of the precursor peptide (big ET-1) to its vasoactive form (ET-1) using metalloprotease as endothelin-converting enzyme (ECE) inhibitor. To date, three types of ECE-1 inhibitors have been synthesized: dual ECE-1/neutral endopeptidase 24.11 (NEP) inhibitors, triple ECE-1/NEP/angiotensin-converting enzyme (ACE) inhibitors and selective ECE-1 inhibitors. The therapeutic effects of ECE-1 inhibitors on the prevention and reversal of SAH-induced vasospasm in animal studies are reviewed and discussed.

Pharmacologic treatment of acute kidney injury: why drugs haven't worked and what is on the horizon

Current strategies to limit the extent of injury in acute renal failure are based on extensive studies that identified cellular and molecular mechanisms of acute kidney injury. Despite successes in various animal models, translation to human studies has failed or studies are inconclusive. This review describes past failures and barriers to successful clinical trials. It also focuses on promising preclinical studies using novel compounds that currently are in or close to human investigation. Implementation of previous or novel compounds in well-designed clinical trials provides hope for the successful treatment of this devastating disorder.

Design and Synthesis of Diversely Substituted Azacyclic Inhibitors of Endothelin Converting Enzyme

A series of azacyclic phosphonic acids were synthesized from L-pyroglutamic acid, 6-oxo-L-pipecolic acid, and their enantiomers. The objective was to study the effect of constraining acyclic inhibitors of endothelin converting enzyme on inhibitory activity. Potential pharmacophoric tethers were introduced by stereocontrolled reactions to give highly substituted pyrrolidine- and piperidine-alpha-phosphonic acids. Weak inhibitory activity was observed for one diastereomer in each series having the same relative orientation of substituents.

Blood pressure regulation by ETA and ETB receptors in conscious, telemetry-instrumented mice and role of ETA in hypertension produced by selective ETB blockade

The net contribution of endothelin type A (ET(A)) and type B (ET(B)) receptors in blood pressure regulation in humans and experimental animals, including the conscious mouse, remains undefined. Thus we assessed the role of ET(A) and ET(B) receptors in the control of basal blood pressure and also the role of ET(A) receptors in maintaining the hypertensive effects of systemic ET(B) blockade in telemetry-instrumented mice. Mean arterial pressure (MAP) and heart rate were recorded continuously from the carotid artery and daily (24 h) values determined. At baseline, MAP ranged from 99 +/- 1 to 101 +/- 1 mmHg and heart rate ranged between 547 +/- 15 and 567 +/- 19 beats/min (n = 6). Daily oral administration of the ET(B) selective antagonist A-192621 [10 mg/kg twice daily] increased MAP to 108 +/- 1 and 112 +/- 2 mmHg on days 1 and 5, respectively. Subsequent coadministration of the ET(A) selective antagonist atrasentan (5 mg/kg twice daily) in conjunction with A-192621 (10 mg/kg twice daily) decreased MAP to baseline values on day 6 (99 +/- 2 mmHg) and to below baseline on day 8 (89 +/- 3 mmHg). In a separate group of mice (n = 6) in which the treatment was reversed, systemic blockade of ET(B) receptors produced no hypertension in animals pretreated with atrasentan, underscoring the importance of ET(A) receptors to maintain the hypertension produced by ET(B) blockade. In a third group of mice (n = 10), ET(A) blockade alone (atrasentan; 5 mg/kg twice daily) produced an immediate and sustained decrease in MAP to values below baseline (baseline values = 101 +/- 2 to 103 +/- 2 mmHg; atrasentan decreased pressure to 95 +/- 2 mmHg). Thus these data suggest that ET(A) and ET(B) receptors play a physiologically relevant role in the regulation of basal blood pressure in normal, conscious mice. Furthermore, systemic ET(B) receptor blockade produces sustained hypertension in conscious telemetry-instrumented mice that is absent in mice pretreated with an ET(A) antagonist, suggesting that ET(A) receptors maintain the hypertension produced by ET(B) blockade.

Subdepressor dose of benidipine ameliorates diabetic cardiac remodeling accompanied by normalization of upregulated endothelin system in rats

We investigated whether benidipine, a long-acting calcium channel blocker (CCB), can normalize cardiac expression profiles of the endothelin (ET)-1 system in insulin-resistant diabetes. Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a model of human Type 2 diabetes, were treated for 12 wk with vehicle or benidipine (3 mg.kg(-1).day(-1)). OLETF rats exhibited a significant increase in ET-1 in plasma and left ventricular (LV) tissues compared with nondiabetic controls. Expression of prepro-ET-1, ET-converting enzyme, and ET(A) and ET(B) receptors in LV tissues was also significantly higher in OLETF rats. The two MAPKs, JNK and p38MAPK, both of which are activated by ET-1, were more abundantly expressed in OLETF rat LV tissues. All these alterations were reversed to nondiabetic levels when OLETF rats were treated with the subdepressor dose of benidipine. Furthermore, benidipine therapy resulted in hindering cardiomyocyte hypertrophy and cardiac perivascular fibrosis in OLETF rats. The beneficial actions of benidipine at the subdepressor dose on cardiac remodeling in insulin-resistant diabetes may involve normalization of the upregulated ET-1 system.

Differential inhibition by TAK-044 of the inotropic effects of endothelin-1 and endothelin-3

The influence of a nonselective antagonist of endothelin receptors, TAK-044 (cyclo-[d-alpha-aspartyl-3-[(4-phenylpiperazin-1-yl)carbonyl]-l-alanyl-l-alpha-aspartyl-d-2-(2-thienyl)glycyl-l-leucyl-d-tryptophyl] disodium), on the positive inotropic effect of endothelin-1 and endothelin-3 was investigated in isolated rabbit myocardium. While TAK-044 produced a concentration-dependent rightward shift of the concentration-response curve for endothelin-1 and endothelin-3, the effect of endothelin-3 was hundred times more sensitive to TAK-044 than that of endothelin-1. The combination of FR139317 ([2-(R)-[2(R)-[2(S)-[[1-(hexahydro-1H-azepinyl)]carbonyl]amino-4-methylpentanoyl]amino-3-[3-(1-methyl-1H-indolyl)]propionyl] amino-3-(2-pyridyl)propionic acid]) and BQ-788 (N-cis-2,6-dimethylpiperidinocarbonyl-l-gamma-methylleucyl-d-1-methoxycarbonyltryptophanyl-d-norleucine) mimicked the inhibitory action of TAK-044 on the positive inotropic effect of endothelin-3 but enhanced the effect of endothelin-1. In a receptor-binding assay, TAK-044 was four times more potent in antagonizing the specific binding of endothelin-1 than that of endothelin-3. Endothelin-1 may activate receptor subtypes that trigger both positive and negative inotropic effects, the latter being more susceptible to the antagonistic action of TAK-044, which may explain in part the differential antagonistic action of TAK-044 on the inotropic effect of endothelin-1 and endothelin-3.

Receptor subtypes mediating the inotropic effects and Ca(2+) signaling induced by endothelin-1 through crosstalk with norepinephrine in canine ventricular myocardium

In canine ventricular myocardium, endothelin-1 (ET-1) alone induced only a weak transient negative inotropic effect (NIE). However, ET-1 induced a marked sustained positive inotropic effect (PIE) subsequent to a transient NIE in the presence of norepinephrine (NE) at low concentrations (0.1 - 1 nM) and elicited a pronounced sustained NIE in the presence of NE at high concentrations (around 100 nM). Thus, the extent of beta-adrenoceptor stimulation induced by NE played a crucial role in determining the characteristics of the inotropic effects of ET-1. The characteristics of ET receptor subtypes involved in contractile regulation and Ca(2+) signaling induced by ET-1 were determined. The ET-1-induced transient NIE and decrease in Ca(2+) transients were abolished by the selective ET(A)-receptor antagonist FR319317, but not by the selective ET(B)-receptor antagonist BQ-788. The sustained PIE and the increase in Ca(2+) transients induced by ET-1 were abolished by FR319317, but not inhibited by BQ-788. In contrast, the sustained NIE of ET-1 was abolished by the non-selective ET antagonist TAK-044, markedly attenuated by FR319317, and partially inhibited by BQ-788. ET-1 alone elicited a PIE in the presence of BQ-788, which indicates that the activation of ET(B)-receptors counteracts the development of the PIE of ET-1. The current findings indicate that both ET(A) and ET(B) receptors are involved in the regulation of Ca(2+) signaling and contractility in canine ventricular myocardium.

Sesamin induces nitric oxide and decreases endothelin-1 production in HUVECs: possible implications for its antihypertensive effect

OBJECTIVE

Sesamin has been proved to be antihypertensive. Nitric oxide (NO) is the most important vascular relaxing factor that is regulated in endothelium. Endothelin-1 (ET-1) is characterized as a potent vasoconstrictor and is also regulated in endothelium. Alterations in the endothelial production of NO and ET-1 are known to correlate with hypertension. This study investigated the effect of sesamin on NO and ET-1 in the human umbilical vein endothelial cells (HUVECs).

DESIGN

The concentrations of NO and ET-1 in the medium of HUVECs treated by sesamin were measured. The mRNA and protein expressions of nitric oxide synthase (NOS), endothelin converting enzyme-1 (ECE-1), and endothelin-1 (ET-1) were also investigated. Other than the mRNA and protein expression, NOS activity and cyclic GMP (cGMP) were detected.

METHODS

The NO concentration was detected by colorimetric assay. The cGMP and ET-1 were analyzed by EIA. The eNOS, ECE-1, and ET-1 mRNA expressions were assayed by Northern blot. The eNOS and ECE-1 protein expressions were analyzed by Western blot. The NOS activity was assayed by detecting the level of [H]-1-citrullin transformed from [H]-1-arginine.

RESULTS

Sesamin not only increased the NO concentration in the medium of HUVECs in a dose-dependent manner after 24 h, but also induced eNOS mRNA and protein expressions. NOS activity in the HUVECs was also induced by sesamin. The content of cGMP was induced by sesamin through NO signaling. On the other hand, the ET-1 concentration in the medium of HUVECs treated by sesamin was suppressed in a dose-dependent manner after 24 h. The ECE-1 protein and mRNA expressions were also inhibited by sesamin. However, the mRNA expression of prepro ET-1 was not influenced by sesamin.

CONCLUSION

From the above results, it is suggested that sesamin may improve hypertension by its ability to induce NO and inhibit ET-1 production from endothelial cells. The increase of NO by sesamin is through the induction of eNOS gene expression. The decrease of ET-1 by sesamin is through the inhibition of ECE gene expression, but is not through the inhibition of prepro ET-1 gene expression.

The pharmacology of bosentan

This article describes the pharmacological properties and the overall preclinical and clinical profiling of bosentan (Ro 47-0203), a non-peptide endothelin receptor antagonist with oral activity. Bosentan is a combined and competitive antagonist of both ETA and ETB receptors that is selective for the endothelin system. In vitro and in vivo, bosentan potently antagonises the vascular response elicited by the endothelins. Preclinical efficacy is demonstrated in a variety of pathological models including pulmonary and essential hypertension, renal failure of ischaemic and nephrotic origin and cerebral vasospasm following subarachnoid haemorrhage. Effects are particularly marked in experimental models of heart failure (HF) where bosentan acts as a potent vasodilator that improves overall left ventricular performance. After chronic treatment, bosentan also improves survival in rats with HF. As a result of the first encouraging clinical results that show pulmonary and systemic vasodilation, long-term studies are ongoing in the treatment of congestive heart failure (CHF).

Endothelin ETB receptors inhibit articular nociception and priming induced by carrageenan in the rat knee-joint

The participation of the endothelin system on nociception and priming induced by carrageenan in the knee-joint was investigated. Intra-articular (i.a.) carrageenan (300 microg) caused long-lasting nociceptive effects (i.e., increases in paw elevation time [PET]), which were potentiated by endothelin-1 (dual endothelin ETA/ETB receptor agonist) and inhibited by sarafotoxin S6c (endothelin ETB receptor agonist; both at 30 pmol, i.a., 24 h beforehand). Priming the naive joint with carrageenan augmented nociceptive responses to a second carrageenan challenge, 72 h later. Carrageenan-induced priming, but not nociception, was potentiated by local BQ-788 (10 nmol, i.a., 15 min before priming; endothelin ETB receptor antagonist; N-cis-2,6-dimethylpiperidinocarbonyl-L-gamma-methylleucyl-D-1-methoxycarbonyl-tryptophanil-D-norleucine), but BQ-123 (endothelin ETA receptor antagonist; cyclo [D-Asp-Pro-D-Val-Leu]) was ineffective. Sarafotoxin S6c markedly suppressed carrageenan-induced priming to nociception triggered by carrageenan, endothelin-1 or sarafotoxin S6c, and BQ-788 prevented this action. Thus, selective endothelin ETB receptor agonists inhibit carrageenan-induced nociception and priming in the naive joint. This priming effect of carrageenan to nociception evoked by subsequent inflammatory insults is limited by an endothelin ETB receptor-operated mechanism.

Diabetes-related changes in contractile responses of stomach fundus to endothelin-1 in streptozotocin-induced diabetic rats

The contractile response of the stomach fundus to endothelin-1 (ET-1) was examined in streptozotocin (STZ)-induced diabetic rats. In STZ-diabetic rats (versus age-matched control rats) (a) ET-1 caused a longer-lasting contraction of stomach fundus strips, and (b) in the dose-response curve, the ET-1-induced contraction was significantly greater for a given concentration (3 x 10(-7) to 10(-7) M). Although repeated application of ET-1 led to desensitization, the desensitization was less pronounced in STZ-diabetic rats than in the controls. The density of the binding sites for [(125)I]-ET-1 was increased in the diabetic stomach fundus (versus the controls), but Kd values were similar between the two groups. The ET(B) receptor mRNA expression level was significantly increased in the diabetic stomach fundus. These results suggest that the diabetes-related enhancement of the ET-1-induced contraction of the stomach fundus may be due to an increase in the ET(B) receptor population.

The PI3-K/Akt pathway: roles related to alterations in vasomotor responses in diabetic models

Macro- and microvascular disease states currently represent the principal causes of morbidity and mortality in patients with type I or type II diabetes mellitus. Abnormal vasomotor responses and impaired endothelium-dependent vasodilation have been demonstrated in various beds in different animal models of diabetes and in humans with type I or type II diabetes. Several mechanisms leading to endothelial dysfunction have been reported, including changes in substrate avail ability, impaired release of NO, and increased destruction of NO. The principal mediators of diabetes-associated endothelial dysfunction are (a) increases in oxidized low density lipoprotein, endothelin-1, angiotensin II, oxidative stress, and (b) decreases in the actions of insulin or growth factors in endothelial cells. An accumulating body of evidence indicates that abnormal regulation of the phosphatidylinositol 3-kinase (PI3-K)/Akt pathway may be one of several factors contributing to vascular dysfunction in diabetes. The PI3-K pathway, which activates serine/threonine protein kinase Akt, enhances NO synthase phosphorylation and NO production. Several studies suggest that in diabetes the relative ineffectiveness of insulin and the hyperglycemia act together to reduce activity in the insulin-receptor substrates (IRS)/PI3-K/Akt pathway, resulting in impairments of both IRS/PI3-K/Akt-mediated endothelial function and NO production. This article summarizes the PI3-K/Akt pathway-mediated contraction and relaxation responses induced by various agents in the blood vessels of diabetic animals.

Mechanisms underlying enhanced contractile response to endothelin-1 in diabetic rat basilar artery

We investigated the influence of streptozotocin-induced diabetes on the responsiveness of the rat basilar artery to endothelin-1 (ET-1) and nitric oxide (NO), which is known to counteract ET-1. In basilar arteries isolated from diabetic rats: (a) the ET-1-induced contraction was enhanced, (b) the contraction induced by N(G)-nitro-l-arginine [a nitric oxide synthase (NOS) inhibitor] was weaker, and (c) the levels of the mRNAs for ET(A)/ET(B) receptors and prepro-ET-1, but not for NOS, were significantly elevated (all versus age-matched controls). These data indicate that ET-1-induced vasoconstriction may be increased in the diabetic rat basilar artery, and that this hyper-reactivity to ET-1 may be due to an overproduction of ET-1, an up-regulation of ET(A)/ET(B) receptors, and a defect in the bioavailability of NO.

Mechanosensation and endothelin in astrocytes--hypothetical roles in CNS pathophysiology

Endothelin (ET) is a potent autocrine mitogen produced by reactive and neoplastic astrocytes. ET has been implicated in the induction of astrocyte proliferation and other transformations engendered by brain pathology, and in promoting the malignant behavior of astrocytomas. Reactive astrocytes containing ET are found in the periphery/penumbra of a wide array of CNS pathologies. Virtually all brain pathology deforms the surrounding parenchyma, either by direct mass effect or edema. Mechanical stress is a well established stimulus for ET production and release by other cell types, but has not been well studied in the brain. However, numerous studies have illustrated that astrocytes can sense mechanical stress and translate it into chemical messages. Furthermore, the ubiquitous reticular meshwork formed by interconnected astrocytes provides an ideal morphology for sensing and responding to mechanical disturbances. We have recently demonstrated stretch-induced ET production by astrocytes in vitro. Inspired by this finding, the purpose of this article is to review the literature on (1) astrocyte mechanosensation, and (2) the endothelin system in astrocytes, and to consider the hypothesis that mechanical induction of the ET system may influence astrocyte functioning in CNS pathophysiology. We conclude by discussing evidence supporting future investigations to determine whether specific inhibition of stretch-activated ion channels may represent a novel strategy for treating or preventing CNS disturbances, as well as the relevance to astrocyte-derived tumors.