Endothelin--biology and disease

Hypertension during vascular endothelial growth factor inhibition: focus on nitric oxide, endothelin-1, and oxidative stress

SIGNIFICANCE

Angiogenesis inhibition with humanized antibodies targeting vascular endothelial growth factor (VEGF) or orally active small tyrosine kinase inhibitors targeting VEGF receptors has become an established treatment modality for various forms of cancer. A common side effect of angiogenesis inhibition is the development of sometimes severe hypertension, which simultaneously appears to be predictive for a favorable antitumor response.

RECENT ADVANCES

Since VEGF increases the expression and activity of endothelial nitric oxide synthase, it has been assumed that the mean blood pressure (MAP) rise during angiogenesis inhibition is caused by a decrease in nitric oxide bioavailability. Yet, the results from experimental and clinical studies exploring this possibility are conflicting. Recent studies provided evidence that the MAP rise during angiogenesis inhibition rather is mediated by activation of the endothelin-1 (ET-1) axis, which, among others, induces oxidative stress. Nevertheless, conclusive evidence for the involvement of reactive oxygen species in the MAP rise could not be obtained so far.

CRITICAL ISSUES

The mechanism underlying activation of the ET-1 axis during angiogenesis inhibition is unclear, and this activation was not anticipated in view of studies showing that VEGF stimulates both the expression and production of ET-1 by endothelial cells.

FUTURE DIRECTIONS

In fact, this activation of the ET-1 axis may support the use of ET receptor antagonists for the treatment of angiogenesis inhibition-induced hypertension, especially because ET receptor stimulation in vascular smooth muscle cells results in VEGF production and mitogenesis in a mitogen-activated protein kinase pathway-dependent manner.

Avosentan is protective in hypertensive nephropathy at doses not causing fluid retention

Multiple studies indicate that endothelin antagonism may have a protective effect for chronic kidney disease. Despite that, clinical studies using avosentan have been halted due to adverse effects including fluid overload. Therefore, we aimed at investigating whether avosentan may have protective effects against hypertensive nephropathy at doses below those inducing fluid-retention. We used double transgenic rats (dTGR), overexpressing both the human renin and angiotensinogen gene, which develop malignant hypertension. Effects of avosentan alone or in combination with low-dose of valsartan (angiotensin AT1 receptor antagonist) on end-organ damage were studied. Avosentan induced a decrease of diuresis (18.3%) with a consequent decrease in hematocrit (8.3%) only at the highest dose investigated (100mg/kg). Treatment with the combination of avosentan and valsartan (10 and 0.1mg/kg, once daily by gavage, respectively) decreased albuminuria to a greater extent than each compound given alone (avosentan: 19.6mg/24h; valsartan: 12.9mg/24h; avosentan+valsartan: 1.7mg/24h, data are median values). Histological severity score also showed a drastic reduction of kidney damage. Furthermore, avosentan alone or in combination therapy dramatically decreased mortality compared to the 100% in untreated animals. These data support a therapeutic effect of avosentan at doses below those inducing fluid overload.

Metabolic actions of angiotensin II and insulin: a microvascular endothelial balancing act

Metabolic actions of insulin to promote glucose disposal are augmented by nitric oxide (NO)-dependent increases in microvascular blood flow to skeletal muscle. The balance between NO-dependent vasodilator actions and endothelin-1-dependent vasoconstrictor actions of insulin is regulated by phosphatidylinositol 3-kinase-dependent (PI3K)--and mitogen-activated protein kinase (MAPK)-dependent signaling in vascular endothelium, respectively. Angiotensin II acting on AT₂ receptor increases capillary blood flow to increase insulin-mediated glucose disposal. In contrast, AT₁ receptor activation leads to reduced NO bioavailability, impaired insulin signaling, vasoconstriction, and insulin resistance. Insulin-resistant states are characterized by dysregulated local renin-angiotensin-aldosterone system (RAAS). Under insulin-resistant conditions, pathway-specific impairment in PI3K-dependent signaling may cause imbalance between production of NO and secretion of endothelin-1, leading to decreased blood flow, which worsens insulin resistance. Similarly, excess AT₁ receptor activity in the microvasculature may selectively impair vasodilation while simultaneously potentiating the vasoconstrictor actions of insulin. Therapeutic interventions that target pathway-selective impairment in insulin signaling and the imbalance in AT₁ and AT₂ receptor signaling in microvascular endothelium may simultaneously ameliorate endothelial dysfunction and insulin resistance. In the present review, we discuss molecular mechanisms in the endothelium underlying microvascular and metabolic actions of insulin and Angiotensin II, the mechanistic basis for microvascular endothelial dysfunction and insulin resistance in RAAS dysregulated clinical states, and the rationale for therapeutic strategies that restore the balance in vasodilator and constrictor actions of insulin and Angiotensin II in the microvasculature.

Roles of proteolysis in regulation of GPCR function

The enzymatic activity of peptidases must be tightly regulated to prevent uncontrolled hydrolysis of peptide bonds, which could have devastating effects on biological systems. Peptidases are often generated as inactive propeptidases, secreted with endogenous inhibitors, or they are compartmentalized. Propeptidases become active after proteolytic removal of N-terminal activation peptides by other peptidases. Some peptidases only become active towards substrates only at certain pHs, thus confining activity to specific compartments or conditions. This review discusses the different roles proteolysis plays in regulating GPCRs. At the cell-surface, certain GPCRs are regulated by the hydrolytic inactivation of bioactive peptides by membrane-anchored peptidases, which prevent signalling. Conversely, cell-surface peptidases can also generate bioactive peptides, which directly activate GPCRs. Alternatively, cell-surface peptidases activated by GPCRs, can generate bioactive peptides to cause transactivation of receptor tyrosine kinases, thereby promoting signalling. Certain peptidases can signal directly to cells, by cleaving GPCR to initiate intracellular signalling cascades. Intracellular peptidases also regulate GPCRs; lysosomal peptidases destroy GPCRs in lysosomes to permanently terminate signalling and mediate down-regulation; endosomal peptidases cleave internalized peptide agonists to regulate GPCR recycling, resensitization and signalling; and soluble intracellular peptidases also participate in GPCR function by regulating the ubiquitination state of GPCRs, thereby altering GPCR signalling and fate. Although the use of peptidase inhibitors has already brought success in the treatment of diseases such as hypertension, the discovery of new regulatory mechanisms involving proteolysis that control GPCRs may provide additional targets to modulate dysregulated GPCR signalling in disease.

Pro-fibrotic processes in human lung fibroblasts are driven by an autocrine/paracrine endothelinergic system

BACKGROUND AND PURPOSE

Since endothelin (ET) may act as pro-fibrotic mediator, expression and release of ET isoforms, their receptors and potential pro-fibrotic ET effects were studied in human lung fibroblasts.

EXPERIMENTAL APPROACH

MRC-5 and primary human lung fibroblasts (phLFb) were cultured. Expression of prepro-ET isoforms was determined by qPCR and release of ET-1 by elisa. ET receptor function was analysed by real-time measurement of dynamic mass redistribution (DMR). Incorporation of [(3) H]-thymidine was determined as measure of proliferation and that of [(3) H]-proline for collagen synthesis. Phospho-p42/44 MAP kinase was determined by Western blot.

KEY RESULTS

ET-1 is the predominant ET in human lung fibroblasts (hLF), and TGF-β caused a further, selective and sustained up-regulation of ET-1 resulting in increased extracellular ET-1 accumulation. hLFb express mRNA encoding ET-A and ET-B receptors. Expression of both receptors was confirmed at protein level. ET-1 induced marked DMR signals, an effect that involved ET-A and ET-B receptors. Stimulatory effects of ET-1 on hLFb proliferation and collagen synthesis were mediated exclusively via ET-A receptors. ET-1, again via ET-A receptors, induced rapid activation of ERK MAPK, shown to be a crucial cellular signal in ET-1-induced collagen synthesis. ET-1-induced activation of ERK and collagen synthesis was, in contrast to corresponding effect of a muscarinic agonist, largely insensitive to pertussis toxin.

CONCLUSIONS AND IMPLICATIONS

hLFb are endowed with all elements necessary to build a functional autocrine/paracrine endothelinergic system, which appears to drive pro-fibrotic airway and lung remodelling processes, effects for which only ET-A, but not ET-B receptors appear to be of significance.

Role of nitric oxide and endothelin in endothelial maintenance of vasoconstrictor responses in aortas of diabetic female rats

BACKGROUND

Diabetes differentially affects the vascular system in males and females. Although various results have been reported, very few studies have focused on responses in females. In the present study, we investigated contractile responses to norepinephrine in aortas of alloxan-diabetic female rats and evaluated endothelial modulation of these responses.

METHODS

Concentration-response curves were constructed to norepinephrine in the absence or presence of N(G) -nitro-l-arginine methyl ester (l-NAME), indomethacin, losartan, tezosentan, and calphostin C; pre-pro-endothelin mRNA expression was evaluated; and norepinephrine-stimulated expression of phosphorylated (p-) Akt Ser(473) , p-endothelial nitric oxide synthase (eNOS) Ser(1177) , and p-eNOS Ser(633) was determined in endothelial cells incubated in the presence of low (5 mmol/L) or high (25 mmol/L) glucose concentrations.

RESULTS

Similar maximal responses (Rmax ) to norepinephrine were seen in control and diabetic endothelium-intact aortas; however, Rmax was reduced in diabetic endothelium-denuded aortas. Incubation of endothelium-intact aortas with 100 μmol/L l-NAME increased Rmax in the control group only. Inhibition of cyclo-oxygenase (10 μmol/L indomethacin) and blockade of angiotensin II receptors (10 μmol/L losartan) reduced Rmax in endothelium-intact aortas in both the control and diabetic groups. Blockade of endothelin receptors (0.1 μmol/L tezosentan) and inhibition of protein kinase C (PKC; 0.1 μmol/L calphostin C) reduced Rmax only in endothelium-intact aortas from diabetic rats. Pre-pro-endothelin mRNA expression was increased in aortas from diabetic female rats. Finally, p-Akt Ser(473) , p-eNOS Ser(1177) , and p-eNOS Ser(633) levels were enhanced after norepinephrine stimulation only in low glucose-treated endothelial cells.

CONCLUSIONS

In aortas of diabetic female rats, reductions in smooth muscle contractile responses to norepinephrine are counterbalanced by the endothelium via reduced eNOS activation and increased endothelin release and PKC activation.

Link between cancer and Alzheimer disease via oxidative stress induced by nitric oxide-dependent mitochondrial DNA overproliferation and deletion

Nitric oxide- (NO-) dependent oxidative stress results in mitochondrial ultrastructural alterations and DNA damage in cases of Alzheimer disease (AD). However, little is known about these pathways in human cancers, especially during the development as well as the progression of primary brain tumors and metastatic colorectal cancer. One of the key features of tumors is the deficiency in tissue energy that accompanies mitochondrial lesions and formation of the hypoxic smaller sized mitochondria with ultrastructural abnormalities. We speculate that mitochondrial involvement may play a significant role in the etiopathogenesis of cancer. Recent studies also demonstrate a potential link between AD and cancer, and anticancer drugs are being explored for the inhibition of AD-like pathology in transgenic mice. Severity of the cancer growth, metastasis, and brain pathology in AD (in animal models that mimic human AD) correlate with the degree of mitochondrial ultrastructural abnormalities. Recent advances in the cell-cycle reentry of the terminally differentiated neuronal cells indicate that NO-dependent mitochondrial abnormal activities and mitotic cell division are not the only important pathogenic factors in pathogenesis of cancer and AD, but open a new window for the development of novel treatment strategies for these devastating diseases.

Increased endothelin-1 responsiveness in human coronary artery smooth muscle cells exposed to 1,25-dihydroxyvitamin D3

Low blood concentrations of 25-hydroxyvitamin D3 are associated with increased mortality, while some studies suggest improved cardiovascular outcomes with vitamin D3 supplementation in chronic kidney disease. However, the physiological effects of vitamin D3 on the cardiovascular system remain poorly understood making it difficult to determine whether vitamin D3 supplementation might provide cardiovascular benefit or even cause harm. Thus here we investigated the effects of chronic 1,25-dihydroxyvitamin D3 treatment on intracellular signaling in human coronary artery smooth muscle cells (HCASMCs) and found that 1,25-dihydroxyvitamin D3 significantly potentiated endothelin (ET-1) signaling. Specifically, 1,25-dihydroxyvitamin D3 (24-h pretreatment) caused a more than threefold enhancement in both ET-1-induced intracellular calcium mobilization and extracellular signal-regulated kinase (ERK) activation. This 1,25-dihydroxyvitamin D3-elicited signaling enhancement was not observed for either vasopressin or carbachol. With the use of endothelin receptor (ETR) isoform-selective antagonists, ETRA was found to be primarily responsible for the 1,25-dihydroxyvitamin D3-induced ET-1 responsiveness and yet ETRA mRNA expression and protein abundance were unaltered following 1,25-dihydroxyvitamin D3 treatment. While there was an increase in ETRB mRNA expression in response to 1,25-dihydroxyvitamin D3, the protein abundance of ETRB was again unchanged. Finally, ETRA/ETRB heterodimerization was not detected in HCASMCs in either the absence or presence of 1,25-dihydroxyvitamin D3. Together, these data show for the first time that 1,25-dihydroxyvitamin D3 enhances endothelin responsiveness in HCASMCs and that the effect is mediated through ETRA.

Influence of block of NF-kappa B signaling pathway on oxidative stress in the liver homogenates

The aim of the present study was to assess whether BAY 11-7082, a nuclear factor-kappaB (NF-κB) inhibitor, influences the level of reactive oxygen species (ROS), tumor necrosis factor alpha (TNF-α), and NF-κB related signaling pathways in the liver. The animals were divided into 4 groups: I: saline; II: saline + endothelin-1 (ET-1) (1.25 μg/kg b.w., i.v.); III: saline + ET-1 (12.5 μg/kg b.w., i.v.); and IV: BAY 11-7082 (10 mg/kg b.w., i.v.) + ET-1 (12.5 μg/kg b.w., i.v.). Injection of ET-1 alone at a dose of 12.5 μg/kg b.w. showed a significant (P < 0.001) increase in thiobarbituric acid reactive substances (TBARS) and hydrogen peroxide (H₂O₂) level and decrease (P < 0.01) in GSH level (vs. control). ET-1 administration slightly downregulated gene expression of p65 of NF-κB but potently and in a dose-dependent way downregulated p21-cip gene expression in the liver. BAY 11-7082 significantly decreased TBARS (P < 0.001), H₂O₂ (P < 0.01) and improved the redox status (P < 0.05), compared to ET-1 group. The concentration of TNF-α was increased in the presence of ET-1 (P < 0.05), while BAY 11-7082 decreased TNF-α concentration (P < 0.01). Inhibition of IkBα before ET-1 administration downregulated gene expression of p21-cip but had no effect on p65.

Milano summer particulate matter (PM10) triggers lung inflammation and extra pulmonary adverse events in mice

Recent studies have suggested a link between particulate matter (PM) exposure and increased mortality and morbidity associated with pulmonary and cardiovascular diseases; accumulating evidences point to a new role for air pollution in CNS diseases. The purpose of our study is to investigate PM10sum effects on lungs and extra pulmonary tissues. Milano PM10sum has been intratracheally instilled into BALB/c mice. Broncho Alveolar Lavage fluid, lung parenchyma, heart and brain were screened for markers of inflammation (cell counts, cytokines, ET-1, HO-1, MPO, iNOS), cytotoxicity (LDH, ALP, Hsp70, Caspase8-p18, Caspase3-p17) for a putative pro-carcinogenic marker (Cyp1B1) and for TLR4 pathway activation. Brain was also investigated for CD68, TNF-α, GFAP. In blood, cell counts were performed while plasma was screened for endothelial activation (sP-selectin, ET-1) and for inflammation markers (TNF-α, MIP-2, IL-1β, MPO). Genes up-regulation (HMOX1, Cyp1B1, IL-1β, MIP-2, MPO) and miR-21 have been investigated in lungs and blood. Inflammation in the respiratory tract of PM10sum-treated mice has been confirmed in BALf and lung parenchyma by increased PMNs percentage, increased ET-1, MPO and cytokines levels. A systemic spreading of lung inflammation in PM10sum-treated mice has been related to the increased blood total cell count and neutrophils percentage, as well as to increased blood MPO. The blood-endothelium interface activation has been confirmed by significant increases of plasma ET-1 and sP-selectin. Furthermore PM10sum induced heart endothelial activation and PAHs metabolism, proved by increased ET-1 and Cyp1B1 levels. Moreover, PM10sum causes an increase in brain HO-1 and ET-1. These results state the translocation of inflammation mediators, ultrafine particles, LPS, metals associated to PM10sum, from lungs to bloodstream, thus triggering a systemic reaction, mainly involving heart and brain. Our results provided additional insight into the toxicity of PM10sum and could facilitate shedding light on mechanisms underlying the development of urban air pollution related diseases.

Refractoriness to the effect of endothelin-1 in porcine ciliary arteries

PURPOSE

Endothelin-1 (ET) is an important molecule in vascular physiology. After an acute stimulation with ET, vessels are to some extent temporarily refractory to further stimulation. However, few details are known about this phenomenon. The aim of our study was to verify the existence of refractoriness in ophthalmic ciliary arteries and, if present, to analyze its time course.

METHODS

Twenty freshly isolated porcine ciliary arteries were placed in a myograph system to measure isometric forces. Each vessel was stimulated with 10(-7) M ET twice. The experiment was performed in 5 groups of vessels, which differed in the time interval between the initial and the second stimulation with ET. The intervals were 15 min, 30 min, 1 h, 2 h, and 4 h, respectively.

RESULTS

The vasoconstrictive response to re-exposure to ET was time-dependently reduced. The response was lowest after 15 min (22% of baseline response), and then the sensitivity slowly recovered and was finally normal again after 4 h.

CONCLUSIONS

Our experiment with isolated porcine ophthalmic ciliary arteries revealed a refractoriness phase to ET after an acute stimulation with ET. This refractoriness was transient and disappeared after 4 h. The lowest response was observed in the group of vessels re-exposed 15 min after the first stimulation.

An assessment of the relationship between excess fluoride intake from drinking water and essential hypertension in adults residing in fluoride endemic areas

In this study, the relationships between high water fluoride exposure and essential hypertension as well as plasma ET-1 levels were investigated. A total of 487 residents aged 40 to 75 were randomly recruited from eight villages in Zhaozhou County from Heilongjiang Province in China and were divided into 4 groups according to the concentrations of fluoride in their water. Consumption levels of drinking water fluoride for normal, mild, moderate, and high exposure groups were 0.84±0.26 mg/L, 1.55±0.22 mg/L, 2.49±0.30 mg/L, and 4.06±1.15 mg/L, respectively. The prevalence of hypertension in each group was 20.16%, 24.54%, 32.30%, and 49.23%, respectively. There were significant differences between all the groups; namely, with the increase in water fluoride concentrations, the risk of essential hypertension in adults grows in a concentration-dependent manner. Significant differences were observed in the plasma ET-1 levels between the different groups (P<0.0001). In the multivariable logistic regression model, high water fluoride concentrations (F(-)≥3.01 mg/L, OR(4/1)=2.84), age (OR(3/1)=2.63), and BMI (OR(2/1)=2.40, OR(3/1)=6.03) were closely associated with essential hypertension. In other words, the study not only confirmed the relationship between excess fluoride intake and essential hypertension in adults, but it also demonstrated that high levels of fluoride exposure in drinking water could increase plasma ET-1 levels in subjects living in fluoride endemic areas.

Directly acting drugs prostacyclin or nitroglycerine and endothelin receptor blocker bosentan improve cell engraftment in rodent liver

To optimize strategies for liver-directed cell therapy, prevention of initial transplanted cell losses is particularly important for subsequent liver repopulation. After cell transplantation in hepatic sinusoids, perturbations in hepatic microcirculation along with changes in various liver cell types are among the earliest changes. Therefore, for advancing further concepts in cell engraftment we studied vascular and related events in the liver after transplanting syngeneic hepatocytes into dipeptidyl peptidase IV-deficient rats. We treated rats with vascular drugs to define whether deleterious cell transplantation-induced events could be controlled followed by improvements in transplanted cell engraftment and proliferation. We found cell transplantation altered liver gene expression related to vessel tone, inflammation, cell adhesion, thrombosis, or tissue damage/remodeling. This was due to hepatic ischemia, endothelial injury, and activation of neutrophils, Kupffer cells, and hepatic stellate cells. Treatment of rats before cell transplantation with the angiotensin converting enzyme blocker, lisinopril, or angiotensin II receptor blocker, losartan, did not improve cell engraftment. By contrast, direct-acting nitroglycerine or prostacyclin improved cell engraftment and also kinetics of liver repopulation. These drugs lowered hepatic ischemia and inflammation, whereas pretreatment of rats with the dual endothelin-1 receptor blocker, bosentan, improved cell engraftment independently of hepatic ischemia or inflammation, without improving liver repopulation. However, incubation of hepatocytes with bosentan protected cells from cytokine toxicity in vitro and produced superior cell engraftment and proliferation in vivo.

CONCLUSION

Cell transplantation-induced changes in hepatic microcirculation contributed to transplanted cell clearances from liver. Vascular drugs, such as nitroglycerine, prostacyclin, and bosentan, offer opportunities for improving cell therapy results through superior cell engraftment and liver repopulation. Ongoing clinical use of these drugs will permit rapid translation of the findings in people.

Generation and characterization of rendomab-B1, a monoclonal antibody displaying potent and specific antagonism of the human endothelin B receptor

Endothelin B receptor (ETBR) is a G protein-coupled receptor able to bind equally to the three identified human endothelin peptides. It is expressed primarily on vascular endothelial cells and involved in various physiological processes including vascular tone homeostasis, enteric nervous system development, melanogenesis and angiogenesis. Furthermore, overactivation or overexpression of ETBR have been associated with the development of various diseases such as cardiovascular disorders and cancers. Therefore, ETBR appears to be relevant target for the therapy or diagnosis of highly prevalent human diseases. In this study, we report the in vitro characterization of rendomab-B1, a monoclonal antibody (mAb) obtained by genetic immunization, which selectively recognizes the native form of human ETBR (hETBR). Rendomab-B1 is the first-reported mAb that behaves as a potent antagonist of hETBR. It recognizes an original extracellular conformational epitope on the receptor, distinct from the endothelin-1 (ET-1) binding site. Rendomab-B1 not only blocks ET-1-induced calcium signaling pathway and triggers rapid receptor internalization on recombinant hETBR-expressing cells, but also exerts pharmacological activities on human vascular endothelial cells, reducing both cell viability and ET-1-induced hETBR synthesis. In addition, binding experiments using rendomab-B1 on different melanoma cell lines reveal the structural and functional heterogeneity of hETBR expressed at the surface of these cancer cells, strongly suggesting the existence of tumor-specific receptors. Collectively, our results underscore the value of rendomab-B1 for research, therapeutic and diagnostic applications dealing with hETBR.

The endothelin axis in uterine leiomyomas: new insights

The endothelin axis, comprising endothelin-1 (ET-1) and its receptors (ETA and ETB), is involved in the pathophysiology of different human tumors. Here we review conventional approaches and gene expression profiling indicating the association of ET-1 and its cognate receptors with human and rat leiomyomas, the most common benign tumors of myometrium. Specifically, ET-1/ETA interactions affect human and rat leiomyoma cell proliferation through protein kinase C and mitogen-activated protein kinase-dependent signaling pathways. Recent experiments demonstrate that the ET-1 axis exerts a potent antiapoptotic effect involving sphingolipid metabolism and prostaglandin-endoperoxide synthase 2/prostaglandin system in the rat Eker leiomyoma tumor-derived ELT3 cell line. Evidence supports that steroid hormones, growth factors, and extracellular matrix are key regulators of the leiomyoma growth. Interestingly, the ET-1 axis is under steroid hormones and can cooperate with these growth factors. Therefore, ET-1 alone or in association with these factors could contribute to the complex regulation of uterine tumor growth, such as proliferation, survival, and extracellular matrix production. This review summarizes current knowledge and emerging data on ET-1 in uterine leiomyoma pathology.

Altered endothelin expression in granulosa-lutein cells of women with polycystic ovary syndrome

AIMS

To examine the levels of endothelin system components in granulosa lutein cells (GLCs) of women with PCOS and compare them to normally ovulating women undergoing In Vitro Fertilization (IVF). Polycystic ovary syndrome (PCOS) is one of the most common endocrine-metabolic disorders in women of reproductive age. Endothelins are locally produced by endothelial and granulosa cells of the preovulatory follicle. Abnormal expression or production of endothelins may be a contributing factor in PCOS pathogenesis.

MAIN METHODS

Follicular aspirates containing GLCs were obtained from PCOS and normally ovulating patients undergoing oocyte retrieval during the IVF cycle. RNA was extracted and endothelin system components were quantified using real-time PCR. GLCs were cultured in basal media for 7 days, and then challenged with various luteinizing agents (luteinizing hormone, hCG, or forskolin) for 24 h.

KEY FINDINGS

In GLCs from women with PCOS, Endothelin-1 mRNA expression was elevated (2.2-fold) as compared with normally ovulating women, whereas endothelin-2 mRNA was reduced (1.8-fold). ET receptors and endothelin-converting enzyme showed the same expression levels in the two groups. In vitro modeling showed that although the steroidogenic response was preserved in GLC, endothelin expression levels were not exhibited in vitro in their original pattern.

SIGNIFICANCE

Dysregulation of ovarian endothelin expression may induce a pathologic ovulation pattern characteristic of PCOS.

Effects of BQ-788 on amitriptyline-induced cardiovascular toxicity

Objective:

We investigated both the effects of the endothelin type B (ETB) receptor antagonist, BQ-788, on amitriptyline-induced cardiotoxicity and the role of ETB receptors on amitriptyline-induced cardiovascular depression.

Methods:

Male Wistar rats were anaesthetized with urethane/chloralose. Mean arterial pressure (MAP), heart rate (HR) and QRS duration were recorded. Toxicity was induced by amitriptyline infusion (0.94 mg/kg per min) until the 50% inhibition of MAP. In the first protocol, 5% dextrose or BQ-788 bolus was administered to control or experimental group animals, respectively. In the second protocol, after incubation with BQ-788 or 5% dextrose, amitriptyline was infused.

Results:

Amitriptyline caused a significant decrease in MAP, prolonged QRS duration and decreased HR for both the groups. BQ-788 administration improved MAP (5, 10 and 15 min), shortened the prolonged QRS (5 and 10 minutes) and increased HR (5, 10 and 15 min) compared with dextrose group. While all the amitriptyline-infused rats survived in BQ-788 group, all the amitriptyline-infused rats died within 20 min in dextrose group. In the second protocol, BQ-788 incubation did not cause any statistically significant change in amitriptyline-induced cardiovascular depression.

Conclusion:

BQ-788 may have beneficial effects in amitriptyline-induced cardiovascular changes via a physiologic antagonism. ETB receptor antagonists may be the promising antidotes for the cardiovascular toxicity with hypotension and bradycardia.

Constriction of retinal arterioles to endothelin-1: requisite role of rho kinase independent of protein kinase C and L-type calcium channels

PURPOSE

Although endothelin-1 (ET-1) is a potent vasoconstrictor peptide implicated in several retinal pathologies, the underlying mechanism of vasoconstriction is understood incompletely. We addressed this issue by assessing the contributions of extracellular calcium (Ca²⁺), L-type voltage-operated calcium channels (L-VOCCs), Rho kinase (ROCK), and protein kinase C (PKC) to ET-1-induced constriction of porcine retinal arterioles, all of which have been implicated commonly in vascular smooth muscle contraction.

METHODS

Porcine retinal arterioles (~50-100 μm) were isolated for vasomotor study and molecular assessment of ROCK isoforms.

RESULTS

Isolated arterioles developed stable basal tone at 55 cmH₂O luminal pressure and constricted to ET-1 (0.1 nM) with a 40 ± 6% reduction in resting diameter in 20 minutes. In the absence of extraluminal Ca²⁺, arterioles lost basal tone and failed to constrict to ET-1. Although L-VOCC inhibitor nifedipine reduced basal tone and blocked vasoconstriction to PKC activator PDBu, vasoconstriction to ET-1 was unaffected. The broad-spectrum PKC inhibitor Gö-6983 abolished vasoconstriction to PDBu, but did not alter ET-1-induced vasoconstriction or basal tone. Incubation of arterioles with ROCK inhibitor H-1152 abolished basal tone and vasoconstrictions to ET-1 and PDBu. Both ROCK1 and ROCK2 isoforms were expressed in the retinal arteriolar wall.

CONCLUSIONS

Extracellular Ca²⁺ entry via L-VOCCs and basal ROCK activity play important roles in the maintenance of basal tones of porcine retinal arterioles. ET-1-induced constriction is mediated by extracellular Ca²⁺ entry independent of L-VOCCs and by ROCK activation without the involvement of PKC. However, direct PKC activation can cause vasoconstriction via L-VOCC and ROCK signaling.

Purification and characterization of recombinant human endothelin receptor type A

Human endothelin receptor type A (ET(A)) is a G-protein coupled receptor that mediates vasoconstriction of blood vessels. To determine the structural characteristics and signaling mechanism of ET(A), we have expressed recombinant ET(A) as a fusion protein with p9 envelope protein from phi6 bacteriophage. The His-tag-labeled p9-ET(A) fusion protein was highly expressed in the membrane fraction of Escherichia coli and purified to homogeneity by single affinity chromatography after solubilization with detergents. Purified p9-ET(A) appeared as an oligomer and presented mainly as an α-helical structure. The protein also showed specific binding to endothelin-1 (ET-1) and the alpha subunit of G(q) protein with apparent K(D) values of 17 and 20 nM, respectively. An antagonist of ET(A), bosentan, prevented the interaction between p9-ET(A) and ET-1 in a concentration-dependent manner. These results indicate that recombinant p9-ET(A) has a competent conformation for interactions with ET-1 and the alpha subunit of G(q) protein.

Distal airway stem cells yield alveoli in vitro and during lung regeneration following H1N1 influenza infection

The extent of lung regeneration following catastrophic damage and the potential role of adult stem cells in such a process remains obscure. Sublethal infection of mice with an H1N1 influenza virus related to that of the 1918 pandemic triggers massive airway damage followed by apparent regeneration. We show here that p63-expressing stem cells in the bronchiolar epithelium undergo rapid proliferation after infection and radiate to interbronchiolar regions of alveolar ablation. Once there, these cells assemble into discrete, Krt5+ pods and initiate expression of markers typical of alveoli. Gene expression profiles of these pods suggest that they are intermediates in the reconstitution of the alveolar-capillary network eradicated by viral infection. The dynamics of this p63-expressing stem cell in lung regeneration mirrors our parallel finding that defined pedigrees of human distal airway stem cells assemble alveoli-like structures in vitro and suggests new therapeutic avenues to acute and chronic airway disease.

Interleukin 6 underlies angiotensin II-induced hypertension and chronic renal damage

Chronic kidney disease (CKD) is a prevalent life-threatening disease frequently associated with hypertension, progression to renal fibrosis, and eventual renal failure. Although the pathogenesis of CKD remains largely unknown, an increased inflammatory response is known to be associated with the disease and has long been speculated to contribute to disease development. However, the causative factors, the exact role of the increased inflammatory cascade in CKD, and the underlying mechanisms for its progression remain unidentified. Here we report that interleukin 6 (IL-6) expression levels were significantly increased in the kidneys collected from CKD patients and further elevated in CKD patients characterized with hypertension. Functionally, we determined that angiotensin II is a causative factor responsible for IL-6 induction in the mouse kidney and that genetic deletion of IL-6 significantly reduced hypertension and key features of CKD, including renal injury and progression to renal fibrosis in angiotensin II-infused mice. Mechanistically, we provide both human and mouse evidence that IL-6 is a key cytokine functioning downstream of angiotensin II signaling to directly induce fibrotic gene expression and preproendothelin 1 mRNA expression in the kidney. Overall, both the mouse and human studies reported here provide evidence that angiotensin II induces IL-6 production in the kidney, and that, in addition to its role in hypertension, increased IL-6 may play an important pathogenic role in CKD by inducing fibrotic gene expression and ET-1 gene expression. These findings immediately suggest that the IL-6 signaling is a novel therapeutic target to manage this devastating disorder affecting millions worldwide.

Salivary endothelin-1 potential for detecting oral cancer in patients with oral lichen planus or oral cancer in remission

Endothelin-1 (ET-1) is a potent vasoconstrictor involved not only in vascular biology but also in carcinogenesis. Results of a study in 2007 suggested salivary ET-1 as a potential biomarker for oral squamous cell carcinoma (OSCC), but a later study showed conflicting results. The purpose of our pilot study was to investigate feasibility of using salivary ET-1 as a biomarker for OSCC in two groups: oral lichen planus (OLP) patients and patients with OSCC in remission. Saliva samples were collected from five groups of subjects: patients with newly diagnosed, active OSCC (Group A); patients with OSCC in remission (Group B); patients with active OLP lesions (Group C); patients with OLP in remission (Group D); and normal controls (Group E). Salivary ET-1 levels were determined by enzyme-linked immunosorbent assay, and the results were analyzed by the Mann-Whitney U test. The mean salivary ET-1 level in Group A was significantly higher than that found in Group C (p=0.001), Group D (p=0.015) or Group E (p=0.004). There were no significant differences (p>0.05) in the mean salivary ET-1 levels between Groups A and B; Groups B and C; Groups B and D; Groups B and E; Groups C and D; Groups C and E; or Groups D and E. Salivary ET-1 could be a good biomarker for OSCC development in OLP patients regardless of the degree of OLP disease activity. However, it appeared not to be a good biomarker for detecting recurrence of OSCC in patients in remission.

Brain endothelial barrier passage by monocytes is controlled by the endothelin system

Homeostasis of the brain is dependent on the blood-brain barrier (BBB). This barrier tightly regulates the exchange of essential nutrients and limits the free flow of immune cells into the CNS. Perturbations of BBB function and the loss of its immune quiescence are hallmarks of a variety of brain diseases, including multiple sclerosis (MS), vascular dementia, and stroke. In particular, diapedesis of monocytes and subsequent trafficking of monocyte-derived macrophages into the brain are key mediators of demyelination and axonal damage in MS. Endothelin-1 (ET-1) is considered as a potent pro-inflammatory peptide and has been implicated in the development of cardiovascular diseases. Here, we studied the role of different components of the endothelin system, i.e., ET-1, its type B receptor (ET(B)) and endothelin-converting enzyme-1 (ECE-1) in monocyte diapedesis of a human brain endothelial cell barrier. Our pharmacological inhibitory and specific gene knockdown studies point to a regulatory function of these proteins in transendothelial passage of monocytes. Results from this study suggest that the endothelin system is a putative target within the brain for anti-inflammatory treatment in neurological diseases.

Endothelin and hepatic wound healing

Liver wound healing is a coordinated response to injury caused by infections (hepatitis) or toxins (alcohol) or other processes where activation of hepatic stellate cells are a central component. During stellate cell activation, a major phenotypic transformation occurs which leads to increased production of increased extracellular matrix proteins and smooth muscle α-actin the results is organ dysfunction due to gross architectural disruption and impaired blood flow. Endothelin-1 (ET-1) is produced in increased amounts and the cellular source of ET-1 shifts from endothelial cells to stellate cells during liver injury thus setting a feedback loop which accentuates further activation, stellate cell proliferation, and production of extracellular matrix proteins. Therapy directed at intervening the ET-1 signaling pathway has significant therapeutic potential in patients with liver disease.

The interaction between endothelin-1 and nitric oxide in the vasculature: new perspectives

Nitric oxide (NO) and endothelin-1 (ET-1) are natural counterparts in vascular function, and it is becoming increasingly clear that an imbalance between these two mediators is a characteristic of endothelial dysfunction and is important in the progression of vascular disease. Here, we review classical and more recent data that suggest that ET-1 should be regarded as an essential component of NO signaling. In particular, we review evidence of the role of ET-1 in models of acute and chronic NO synthase blockade. Furthermore, we discuss the possible mechanisms by which NO modulates ET-1 activity. On the basis of these studies, we suggest that NO tonically inhibits ET-1 function, and in conditions of diminished NO bioavailability, the deleterious effects of unmitigated ET-1 actions result in vasoconstriction and eventually lead to vascular remodeling and dysfunction.

Endothelins and their receptors in cancer: identification of therapeutic targets

Endothelins and their receptors are important in normal physiology, but have been implicated in various pathophysiological conditions. Members of the so-called "endothelin axis" are dysregulated in a wide range of human cancers, opening the door for novel anticancer therapies. Established cancer chemotherapeutic agents and drugs that target specific components of the endothelin axis have been combined with promising results, but more work is needed in this area. The endothelin axis affects numerous signaling pathways, including Ras, mitogen activated protein kinases, β-catenin/T-cell factor/lymphoid enhancer factor, nuclear factor-κB (NFκB), SNAIL, and mammalian target of rapamycin (mTOR). There is much still to learn about optimizing drug specificity in this area, while minimizing off-target effects. Selective agonists and antagonists of endothelins, their receptors, and upstream processing enzymes, as well as knockdown strategies in vitro, are providing valuable leads for testing in the clinical setting. The endothelin axis continues to be an attractive avenue of scientific endeavor, both in the cancer arena and in other important health-related disciplines.

Tumor necrosis factor α stimulates endothelin-1 synthesis in rat hepatic stellate cells in hepatic wound healing through a novel IKK/JNK pathway

Endothelin-1 (ET-1), a potent vasoconstrictor peptide up-regulated during wound healing and fibrosis, induces myofibroblasts to contract tissue. Here we have used a liver injury model to test the hypothesis that TNFα may be an important stimulator of ET-1 production in hepatic wound healing. We examined primary rat hepatic stellate cells, isolated from either normal or injured livers and used standard methodology to measure preproET-1 mRNA and mature ET-1 peptide, specific kinases, and preproET-1 promoter activity. Chromatin immunoprecipitation analysis was used to determine basal binding of transcription factors to the preproET-1 promoter. TNFα induced preproET-1 expression in activated hepatic stellate cells in a c-Jun N-terminal kinase (JNK)/AP-1-dependent fashion. TNFα activated JNK through an IκB kinase (IKK) pathway, which activated the transcriptional factor, c-Jun, leading to preproET-1 promoter mediated ET-1 transcription. The TNFα mediated induction of ET-1 synthesis also had functional effects, specifically mediating autocrine induced stellate cell contraction. TNFα stimulated activated stellate cells to produce ET-1 via a novel IKK-JNK-dependent signaling pathway. The resulting autocrine functional effects of ET-1 are likely to be important in the wound-healing process.

Distinct modulation of microglial amyloid β phagocytosis and migration by neuropeptides (i)

Microglial activation plays an integral role in the development and course of neurodegeneration. Although neuropeptides such as bradykinin (BK), somatostatin (SST), and endothelin (ET) are known to be important mediators of inflammation in the periphery, evidence of a similar function in brain is scarce. Using immunocytochemistry, we demonstrate the expression of receptors for BK (B1, B2 subtypes), ET (ETA, ETB subtypes) and SST (SST 2, 3, 4 subtypes) in primary microglia and microglial cell lines. Exposure of BV2 and N9, as well as primary microglial cells to BK or SST increased Aβ uptake in a concentration-dependent manner, whereas endothelin decreased Aβ uptake. This was caused by increased phagocytosis of Aβ since the rate of intracellular Aβ degradation remained unaffected. All neuropeptides increased chemotactic activity of microglia. In addition, BK reduced Aβ-induced expression of proinflammatory genes including iNOS and COX-2. ET decreased the Aβ-induced expression of monocyte chemoattractant protein 1 and interleukin-6. These results suggest that neuropeptides play an important role in chemotaxis and Aβ clearance and modulate the brain's response to neuroinflammatory processes.

Zinc metalloproteinases and amyloid Beta-Peptide metabolism: the positive side of proteolysis in Alzheimer's disease

Alzheimer's disease is a neurodegenerative condition characterized by an accumulation of toxic amyloid beta- (Aβ-)peptides in the brain causing progressive neuronal death. Aβ-peptides are produced by aspartyl proteinase-mediated cleavage of the larger amyloid precursor protein (APP). In contrast to this detrimental "amyloidogenic" form of proteolysis, a range of zinc metalloproteinases can process APP via an alternative "nonamyloidogenic" pathway in which the protein is cleaved within its Aβ region thereby precluding the formation of intact Aβ-peptides. In addition, other members of the zinc metalloproteinase family can degrade preformed Aβ-peptides. As such, the zinc metalloproteinases, collectively, are key to downregulating Aβ generation and enhancing its degradation. It is the role of zinc metalloproteinases in this "positive side of proteolysis in Alzheimer's disease" that is discussed in the current paper.

Endothelin-1 gene regulation

Over two decades of research have demonstrated that the peptide hormone endothelin-1 (ET-1) plays multiple, complex roles in cardiovascular, neural, pulmonary, reproductive, and renal physiology. Differential and tissue-specific production of ET-1 must be tightly regulated in order to preserve these biologically diverse actions. The primary mechanism thought to control ET-1 bioavailability is the rate of transcription from the ET-1 gene (edn1). Studies conducted on a variety of cell types have identified key transcription factors that govern edn1 expression. With few exceptions, the cis-acting elements bound by these factors have been mapped in the edn1 regulatory region. Recent evidence has revealed new roles for some factors originally believed to regulate edn1 in a tissue or hormone-specific manner. In addition, other mechanisms involved in epigenetic regulation and mRNA stability have emerged as important processes for regulated edn1 expression. The goal of this review is to provide a comprehensive overview of the specific factors and signaling systems that govern edn1 activity at the molecular level.