Endothelin induces vasoconstriction in the bone vasculature in vitro: an effect mediated by a single receptor population

Evaluation of methylation status of the eNOS promoter at birth in relation to childhood bone mineral content

Our previous work has shown associations between childhood adiposity and perinatal methylation status of several genes in umbilical cord tissue, including endothelial nitric oxide synthase (eNOS). There is increasing evidence that eNOS is important in bone metabolism; we therefore related the methylation status of the eNOS gene promoter in stored umbilical cord to childhood bone size and density in a group of 9-year-old children. We used Sequenom MassARRAY to assess the methylation status of two CpGs in the eNOS promoter, identified from our previous study, in stored umbilical cords of 66 children who formed part of a Southampton birth cohort and who had measurements of bone size and density at age 9 years (Lunar DPXL DXA instrument). Percentage methylation varied greatly between subjects. For one of the two CpGs, eNOS chr7:150315553 + , after taking account of age and sex, there were strong positive associations between methylation status and the child's whole-body bone area (r = 0.28, P = 0.02), bone mineral content (r = 0.34, P = 0.005), and areal bone mineral density (r = 0.34, P = 0.005) at age 9 years. These associations were independent of previously documented maternal determinants of offspring bone mass. Our findings suggest an association between methylation status at birth of a specific CpG within the eNOS promoter and bone mineral content in childhood. This supports a role for eNOS in bone growth and metabolism and implies that its contribution may at least in part occur during early skeletal development.

Comparison of plasma endothelin levels between osteoporotic, osteopenic and normal subjects

Background

It has been demonstrated that endothelins (ET) have significant roles in bone remodeling, metabolism and physiopathology of several bone diseases. We aimed to investigate if there was any difference between the plasma ET levels of osteoporotic patients and normals.

Methods

86 patients (70 women and 16 men) with a mean age of 62.6 (ranges: 51–90) years were included in this study. Patients were divided into groups of osteoporosis, osteopenia and normal regarding reported T scores of DEXA evaluation according to the suggestions of World Health Organization. According to these criteria 19, 43 and 24 were normal, osteopenic and osteoporotic respectively. Then total plasma level of ET was measured in all patients with monoclonal antibody based sandwich immunoassay (EIA) method. One-way analysis of variance test was used to compare endothelin values between normals, osteopenics and osteoporotics.

Results

Endothelin total plasma level in patients was a mean of 98.36 ± 63.96, 100.92 ± 47.2 and 99.56 ± 56.6 pg/ml in osteoporotic, osteopenic and normal groups respectively. The difference between groups was not significant (p > 0.05).

Conclusion

No significant differences in plasma ET levels among three groups of study participants could be detected in this study.

Atrasentan, an endothelin-receptor antagonist for refractory adenocarcinomas: safety and pharmacokinetics

PURPOSE

Endothelin receptors, particularly the ET(A) receptor, have been shown to participate in the pathophysiology of prostate and other cancers. Atrasentan, an endothelin antagonist, binds selectively to the ET(A) receptor. This study evaluated the safety, pharmacokinetics, and maximum-tolerated dose of atrasentan in cancer patients.

PATIENTS AND METHODS

Patients who were 18 years or older and had histologically confirmed adenocarcinoma refractory to therapy enrolled in this 28-day, open-label, phase I study. Enrollment was planned for cohorts of three patients at doses escalating from 10 to 140 mg/d. When any patient had dose-limiting toxicity, that cohort was expanded. The primary outcome variable was safety; secondary outcome variables were pharmacokinetics, tumor response, and pain relief.

RESULTS

Thirty-one cancer patients (14 prostate) were treated at daily atrasentan doses of 10, 20, 30, 45, 60, and 75 mg (n = 3 to 8 per cohort). The most common adverse events, such as rhinitis, headache, asthenia, and peripheral edema, were reversible on drug discontinuation and responded to symptom-specific treatment. Reversible hemodilution was apparent in laboratory findings and weight gain. Clinically significant headache was the dose-limiting adverse event; the maximum-tolerated dose was 60 mg/d. Pharmacokinetics were dose-proportional across the 10- to 75-mg dose range. Atrasentan was rapidly absorbed; the time to maximum observed concentration was approximately 1.5 hours. The terminal elimination half-life was approximately 24 hours, and steady-state plasma concentrations were achieved within 7 days. Decreases in prostate-specific antigen and pain relief were noted in a patient subset.

CONCLUSION

Adverse events were consistent with atrasentan's pharmacologic vasodilatory effect. Linear, dose-proportional pharmacokinetics suggest that atrasentan can be easily and consistently dosed.

Endothelin-1 expression in long-term cultures of fetal rat calvarial osteoblasts: regulation by BMP-7

Endothelin-1 (ET-1) is a vasoactive peptide that modulates bone metabolism via regulatory effects on osteoblasts, chondrocytes, and osteoclasts. While ET-1 may circulate in the blood stream, tissue-specific expression of this peptide is more physiologically relevant. In the present study we measured ET-1 synthesis in sections of fetal rat calvaria (FRC) and in cultured FRC osteoblasts. Regulation of ET-1 synthesis in FRC osteoblasts by bone morphogenetic protein-7 (BMP-7) and transforming growth factor-beta1 (TGF-beta1) also was examined. Immunohistochemical analysis revealed ET-1 staining in calvarial osteoblasts, endothelial cells, and osteocytes. ET-1 mRNA expression was detected in cultured FRC cells and ET-1 peptide was present in conditioned media. During long-term culture of FRC cells (26 days) ET-1 peptide production rose sharply and peaked during the time of cellular proliferation (Days 0-3) then returned to baseline levels by Day 18, when mineralized nodules were forming. Treatment of FRC cells with BMP-7 enhanced ET-1 levels by three-fold on Day 3 and enhanced nodule formation by 15-fold on Day 26. To determine whether ET-1 was involved in an autocrine manner in BMP-7-induced nodule formation, cells were cultured in the presence of BMP-7 and BQ-123, an ET(A) receptor antagonist. BQ-123 had no effect on nodule formation in control or BMP-7-treated cells, indicating that osteoblast-derived ET-1 regulates other cell types in vivo during the bone formation process.

Glucocorticoids regulate the expression of the human osteoblastic endothelin A receptor gene

The endothelial cell-derived peptide endothelin 1 (ET1) stimulates cell proliferation and differentiated functions of human osteoblastic cells (HOC), and HOC constitutively express the endothelin A receptor (ETRA). Therefore, ET1 may play an important role in the regulation of bone cell metabolism. As glucocorticoids (GC) exert a profound influence on bone metabolism and increase the effects of ET1 on bone cell metabolism in vitro, the effects of GC on ETRA expression in HOC were investigated. Dexamethasone (DEX) increased ETRA mRNA levels in a dose- and time-dependent fashion. The effects of dexamethasone, prednisolone, and deflazacort on the increase of ETRA mRNA levels correlate positively with their binding affinity to the GC receptor. Scatchard analysis of ET1 binding data to HOC revealed that DEX increased the binding capacity for ET1 from 25,300 to 62,800 binding sites per osteoblastic cell, leading to an enhanced mitogenic effect of ET1 on HOC after preincubation with DEX. Transiently transfected primary HOC with a reporter gene construct, containing the 5'-flanking region of the ETRA gene fused to luciferase gene, showed a promoter-dependent expression of the reporter gene and the induction of reporter gene expression by DEX treatment. Total RNA extracts of femoral head biopsies with osteonecrotic lesions from GC-treated patients showed threefold higher ETRA mRNA levels compared with extracts of bone biopsies from patients with traumatically induced osteonecrosis and coxarthrosis. Furthermore, GC treatment increased plasma ET1 levels by 50% compared with pretreatment values. These findings suggest that GC induced upregulation of ETRA, and ET1 plasma levels enhance ET1's anabolic action on bone cell metabolism. Increased ET1 concentrations may also impair bone perfusion by vasoconstriction in a metabolically activated skeletal region.

Endothelin-A receptors mediate vascular smooth-muscle response to moderate acidosis in the canine tibial nutrient artery

Perfusate pH may influence the tone of vascular smooth muscle by affecting the release of endothelium-derived vasoactive factors or by directly modulating function of the smooth muscle. This study was designed to investigate the role of endothelium-derived factors on acidosis-induced responses of isolated canine tibial nutrient artery suspended in an organ chamber for the measurement of isometric contractile force. To investigate the specific role of the endothelium in half the rings, the endothelium was removed mechanically. Concentration-response curves to KCl were obtained in the absence or presence of inhibition of two important endothelium-derived relaxing factors, nitric oxide and prostacyclin, and an inhibitor of receptors for the endothelium-derived contracting factor, endothelin-1. Acidification of the perfusate from pH 7.45 to 7.0 significantly attenuated the contractions to KCl in arterial rings with endothelium (the mean of the effective concentration causing 50% of the maximal response for KCl at pH 7.45 and 7.0 was 12.31 +/- 0.40 nM and 14.60 +/- 0.55 nM, respectively). This difference was abolished by mechanical removal of the endothelium. In rings with endothelium, inhibition of nitric oxide or prostacyclin did not abolish the attenuation of KCl-induced contractions occurring with acidosis (the mean of the effective concentration causing 50% of the maximal response for KCl at pH 7.45 and 7.0 was 11.18 +/- 0.60 nM and 13.60 +/- 0.60 nM, respectively). Inhibition of endothelin-A receptors did not alter contractions to KCl at pH 7.45. However, the acidosis-induced attenuation of contractions with KCl was abolished by the endothelin-A-receptor antagonist BQ-123 (the mean of the effective concentration causing 50% of the maximal response at pH 7.45 and 7.0 was 13.8 +/- 1.34 nM and 13.2 +/- 1.34 nM, respectively). These results suggest that acidosis-induced relaxation of canine tibial nutrient artery is endothelium dependent and that activation of endothelin-A receptors during acidosis is coupled to a release of an endothelium-derived relaxing factor.