Endothelin-1 regulates parathyroid hormone expression of human parathyroid cells

Bosentan, a drug used in the treatment of pulmonary hypertension, can prevent development of osteoporosis

Objective(s):

We examined the antiosteoporotic effect of bosentan (Bose) by radiographic, histopathological, and molecular methods.

Materials and Methods:

Rats were divided into 4 groups of 8 rats each: one control (Sham), one osteoporosis only (OP), and two osteoporosis groups treated with Bose doses of 50 and 100 mg/kg (OP+Bose50, OP+Bose100). Six weeks later, Bose was administered for eight weeks to animals undergoing ovariectomy. The left femoral bone of the rats was evaluated in vitro after surgical removal. Bone mineral density (BMD) was analyzed by Dual-energy X-ray absorptiometry (DEXA). Endothelin 1 (ET-1), ET-A, and ET-B expressions were examined by real-time polymerase chain reaction (real time-PCR). In addition, bone tissue was evaluated histopathologically.

Results:

Compared with the osteoporosıs group, Bose significantly increased BMD values at both 50 and 100 mg/kg doses. ET-1 mRNA levels were significantly higher in the OP group than in the Sham group, while ET-1 mRNA levels were significantly lower in Bose treatment groups. ET-A mRNA levels were significantly lower in the OP group than in the Sham group, while ET-A mRNA levels were significantly higher in Bose treatment groups. Histopathological results supported the molecular results.

Conclusion:

Our study is the first to demonstrate the molecular, radiological, and histopathological effects of Bose in preventing osteoporosis in rats.

What is the role of bosentan in healing of femur fractures in a rat model?

The purpose of this study was to examine the effects bosentan (which is a strong vasoconstrictor) on bone fracture pathophysiology, and investigate the roles of the nonselective endothelin 1 receptor blocker bosentan on the bone fractures formed in rats through radiographic, histopathologic, and immunohistochemical methods. The rats were divided into three groups (six rats in each group): a femoral fracture control group, a femoral fracture plus bosentan at 50 mg/kg group, and a femoral fracture plus bosentan at 100 mg/kg group. The femoral fracture model was established by transversely cutting the femur at the midsection. After manual reduction, the fractured femur was fixed with intramedullary Kirschner wires. The radiographic healing scores of the bosentan 100 and 50 mg/kg groups were significantly better that those of the fracture control group. The fracture callus percent of new bone in the bosentan 100 mg/kg group was significantly greater than that in the control group. Also, semiquantitative analysis showed higher positive vascular endothelial growth factor and osteocalcin staining and lower positive endothelin receptor type A staining in the treatment groups than in the control group. Bosentan treatment also decreased tissue endothelin 1 expression relative to that in the fracture control group. As a result of our study, the protective effect of bosentan was shown in experimental femoral fracture healing in rats by radiographic, histopathologic, and molecular analyses.

Cross-talk between endothelin-1 and mineral metabolism in hemodialysis patients: a cross-sectional study

Background:

Endotheline-1 (ET-1), an endothelial mediator, influences on mineral metabolism; especially vascular calcification in uremic patients.

Objectives:

The aim of the present study was to evaluate of ET-1, high-sensitivity C-reactive protein (hs-CRP) and mineral metabolites as the main factors for vascular calcification and inflammation in hemodialysis (HD) patients.

Patients and Methods:

In this cross-sectional study, 46 chronic stable HD patients were selected from nephrology departments of Tabriz University of Medical Sciences affiliated hospitals and classified based on phosphorus (P), Ca-P product (Ca × P) and intact Parathyroid Hormone (iPTH) levels. We evaluated fasting serum ET-1and hs-CRP levels by the standard methods and compared with 46 healthy control subjects.

Results:

The levels of serum hs-CRP and ET-1 were significantly higher in the patient’s group compared with controls (4.40 ± 1.26 vs. 1.38 ± 1.61, P < 0.0001, and 2.31 ± 0.87 vs. 0.75 ± 0.48, P < 0.0001, respectively) and with regard to Ca × P product cut-off point (3.99 ± 0.78 vs. 5.33 ± 1.64, P < 0.0001, and 2 ± 0.73 vs. 3.04 ± 0.73, P < 0.0001 respectively). ET-1 was correlated significantly with hs-CRP level (r = 0.776, P < 0.0001). Serum P, Ca × P and iPTH levels directly and Ca indirectly were correlated with serum ET-1 in HD patients (r = 0.932, P < 0.0001, r = 0.766, P < 0.0001, r = 0.514, P < 0.0001, r = -0.538, P < 0.0001 respectively). Multiple regression analysis demonstrated that serum P were independently associated with ET-1 levels (β = 0.932, P < 0.0001).

Conclusions:

Serum P and iPTH levels were independently associated with ET-1 and those may play a role in development of endothelial dysfunction in chronic kidney disease.

Osteopenia and endothelin-1-mediated vasconstrictor tone in postmenopausal women

Low bone mineral density is highly prevalent in postmenopausal women. Osteopenia in postmenopausal women is a predictor of adverse cardiovascular events. A potential mechanism contributing to the increased cardiovascular risk in postmenopausal women with osteopenia is endothelial vasomotor dysfunction. Endothelin (ET)-1 is a potent vasoconstrictor peptide that is associated with endothelial vasomotor dysfunction and increased cardiovascular risk. Currently, there is no information on osteopenia and ET-1 vasoconstrictor activity in postmenopausal women. We tested the hypothesis that ET-1 mediated vasoconstrictor activity is greater in postmenopausal women with osteopenia compared with those without. Forearm blood flow responses to intra-arterial infusion of BQ-123 (100 nmol/min for 60 min), a selective ET(A) receptor antagonist, were determined in postmenopausal women: 10 with osteopenia (age: 56+/-1 yr, lumbar spine T-score between -1.5 and -2.5) and 12 without osteopenia (age: 60+/-2 yr, T-score>-1.5). In women with osteopenia, forearm blood flow increased approximately 25% (P<0.05) in response to BQ-123. However, in the women without osteopenia, resting forearm blood flow was not significantly changed. In conclusion, these results suggest that osteopenia is associated with greater ET-1-mediated vasoconstrictor tone. Increased ET-1 vasoconstrictor activity may contribute to the elevated cardiovascular risk in postmenopausal women with osteopenia.

Parathyroid hormone is inversely related to endothelin-1 in patients on haemodialysis

AIM

Parathyroid hormone secretion is mainly influenced by hypocalcaemia, hyperphosphataemia and vitamin D deficiency. However, previous in vitro and in vivo studies showed that endothelin-1 can influence parathyroid hormone secretion. This study was aimed at evaluating this relationship in vivo in uraemic patients.

METHODS

Parathyroid hormone and endothelin-1 plasma concentrations were measured in 67 haemodialysed patients. Patients with history of cardiovascular diseases and those with parathyroid adenoma were excluded.

RESULTS

Plasma levels of endothelin-1 were found to be inversely related to those of parathyroid hormone (P < 0.04) The multiple regression analysis, carried out considering parathyroid hormone as a dependent variable, and including age, sex, blood pressure, calcium x phosphorus product, and endothelin-1, demonstrated that the independent correlates of parathyroid hormone were endothelin-1 (beta = -0.276; P = 0.015), and calcium x phosphorus product (beta = 0.417; P < 0.0001).

CONCLUSION

For the first time in vivo, we demonstrated an inverse independent relationship between endothelin-1 and parathyroid hormone in haemodialysed patients. Because both endothelin-1 and parathyroid hormone are endowed with well-known harmful actions on cardiovascular apparatus, whether such inverse relation may really influence the natural history of cardiovascular damage due to secondary hyperparathyroidism remains to be elucidated.