Endothelin-1 and cell proliferation in lung organ cultures. Implications for lung allografts

Gender-related differences in proliferative responses of vascular smooth muscle cells to endothelin-1

Endothelin-1 is an endothelium-derived factor which alters tone and proliferation of vascular smooth muscle and has been implicated in the development of atherosclerosis. Estrogen modulates production of and contractile responses to endothelin-1. Since atherosclerosis is less in estrogen-replete women compared to men, experiments were designed to determine whether or not there were gender-associated differences in proliferative responses to endothelin-1 and effect of estrogen status on those responses. Proliferation of smooth muscle cells derived from coronary arteries of sexually mature, gondally intact male and female and oophorectomized female pigs was determined by thymidine incorporation in the absence and presence of endothelin-1 with and without 17beta-estradiol. Endothelin-1 (10(-9) M to 10(-7) M) significantly inhibited proliferation only in coronary smooth muscle cells from intact female pigs. Addition of beta-estradiol inhibited proliferation of cells from intact females but there was not a synergistic effect with endothelin-1. Gender associated inhibition of smooth muscle proliferation by endothelin-1 may contribute, in part, to cardioprotection noted in estrogen-replete states.

Direct determination of endothelin receptor antagonist levels in plasma using a scintillation proximity assay

An assay using scintillation proximity bead technology has been developed suitable for the quantitation of endothelin (ET) receptor antagonists in preclinical and clinical samples of plasma. The assay measures the competitive inhibition of radiolabelled ET-1 binding to ET(A) receptor membranes bound to wheat germ agglutinin (WGA)-coated scintillation proximity assay (SPA) beads in the presence of plasma containing A-127722, a potent orally active, ET(A) selective ET antagonist. The assay requires as little as 50 microl plasma and no extraction procedure is needed. The SPA methodology eliminates the need for the separation of bound from free ligand. Using this method, A-127722 could be directly quantified in rat plasma with a detection limit of 1 ng/ml.

Endothelins and the lung

Since endothelins were discovered by Yanasigawa in 1988 it has been recognised that they may have an important role in lung pathophysiology. Despite their biological importance as vasoconstrictors the physiological role of endothelin has not yet been defined within the lungs. This review explores their role in acute and chronic disease. During acute inflammation and ischaemia-reperfusion injury cytokines may induce release of endothelin. This is important in the realm of acute lung injury and during surgical procedures such as cardiopulmonary operations including lung resections and transplantation. Complications of surgery including primary organ failure resulting in poor gas exchange as well as increased pulmonary vascular resistance have been linked to the presence of excessive endothelin. Endothelin may have an important role in transplantation biology. The complex process leading to successful lung transplantation includes optimising the donor with brain death, harvesting the lungs, managing acute and chronic rejection, and protecting the vital organs from toxic effects of immunosuppressants. During chronic disease processes, the mitotic action of endothelin may be important in vascular and airway remodelling by means of smooth muscle cell proliferation. We also explore recent advances in drug development, animal models and future directions for research.

Pulmonary vasoregulation by endothelin in conscious dogs after left lung transplantation

We tested the hypothesis that regulation of the pulmonary circulation by endogenous endothelin (ET) during normoxia and hypoxia was altered in conscious dogs 1 mo after left lung autotransplantation (LLA). Sham-operated control and post-LLA dogs were chronically instrumented to measure the left pulmonary vascular pressure-flow (LP-Q) relationship. LP-Q plots were generated on separate days during normoxia and hypoxia (arterial PO(2) approximately 50 Torr) in the intact condition, after selective ET(A)-receptor inhibition (BQ-485), and after combined ET(A+B)-receptor inhibition (bosentan). Although LLA resulted in a chronic increase in pulmonary vascular resistance, the ET-receptor antagonists had no effect on the LP-Q relationship during normoxia in either group. The magnitude of hypoxic pulmonary vasoconstriction (HPV) was flow dependent in both groups, and the HPV response was potentiated post-LLA compared with control. ET(A)-receptor inhibition attenuated the HPV response to the same extent in both groups. ET(A+B)-receptor inhibition attenuated the HPV response to a greater extent than did ET(A)-receptor inhibition alone, and this effect was greater post-LLA compared with control. Plasma ET-1 concentration only increased during hypoxia in the LLA group. These results indicate that ET does not regulate the baseline LP-Q relationship in either group. Both ET(A)- and ET(B)-receptor activation mediate a component of HPV in conscious dogs, and the vasoconstrictor influence of ET(B)-receptor activation is enhanced post-LLA.

Distribution of endothelin-1 in transplanted human lungs

BACKGROUND

This study was designed to assess which cells in transplanted lungs express endothelin-1 (ET-1) and if expression of the peptide can be used to discriminate between rejection and infection in transplanted lungs.

METHODS

Transbronchial biopsies (n=104) from 29 human lung transplant recipients were stained immunohistochemically for ET-1. Cells expressing ET-1 (pneumocytes, endothelial cells, airway epithelial cells, lymphocytes, and macrophages) were quantified and correlated with clinical histopathology findings.

RESULTS

ET-1 was expressed in airway epithelial cells (93% of the biopsies), infiltrating macrophages (86%), and lymphocytes (19%) but not in endothelial cells or pneumocytes. ET-1 expression did not vary with rejection, obliterative bronchiolitis, or infection. ET-1 expression did not correlate with age, grade of rejection, pulmonary function, or time after transplantation.

CONCLUSION

In transplanted human lungs, ET-1 is expressed in airway epithelial cells and infiltrating macrophages, and expression does not vary with pathological processes. Therefore, immunostaining for ET-1 probably cannot be used to discriminate between rejection and infection in transplanted lungs.

Efficacy of administering an endothelin-receptor antagonist (SB209670) in ameliorating ischemia-reperfusion injury in lung allografts

The purpose of this study was to determine whether treatment with an endothelin-1 (ET-1)-receptor antagonist could prevent ET-1-mediated ischemia-reperfusion injury and early allograft dysfunction. Eleven dogs were subjected to left lung allotransplantation. Donor lungs were preserved with modified Eurocollins solution and stored at 4 degrees C for 18 to 20 h. Animals received an intravenous infusion of either the ET-receptor antagonist SB209670 (n = 6) (15 microg/kg/min) or saline (control, n = 5), in a blinded fashion. The infusion started 30 min before transplantation and continued for up to 6 h after transplantation. Hemodynamic measurements, blood gas tensions, and plasma samples were obtained with animals functioning solely on the transplanted lung. Open-lung biopsies were obtained for wet-to-dry-weight ratios and histologic and immunohistochemical analyses. Survival at 6 h after transplantation was 40% in the control group and 100% in the treatment group. Pulmonary vascular resistance and lung tissue wet-to-dry-weight ratio were significantly lower in treated animals at 3 and 6 h after transplantation. Histology of the transplanted lungs revealed more intense airway and interstitial inflammatory infiltration and edema in the control group. Arterial and venous plasma ET-1 concentrations increased after transplantation; however, they were significantly higher in the treatment group. Immunohistochemical analysis revealed more intense ET-1 immunostaining in the airways and parenchyma of the treatment group. We conclude that treatment of lung allografts with the mixed endothelin A/endothelin B (ETA/ETB) receptor antagonist SB209670 can ameliorate ischemia-reperfusion injury, resulting in improved graft function and survival after lung transplantation.

Immunohistochemical localization of endothelin-1 and endothelin-converting enzyme-1 in rat lung allografts

Chronic rejection is one of the principal factors that lead to development of obliterative bronchiolitis, which is the cause of death for 50% of lung allograft recipients. To more fully comprehend the pathogenesis of chronic rejection, we investigated the expression of endothelin-1 (ET-1) and endothelin-converting enzyme-1 (ECE-1) in inadequately immuno-suppressed rat lung allografts (n = 15) at monthly intervals after transplantation and compared these findings with those in normal rat lung (n = 5), using immunohistochemistry. Throughout the posttransplantation period, inflammatory cells expressed weak to moderate immunoexpression for both peptides. Constant weak to moderate immunoexpression for both peptides was also seen in the alveolar epithelium and neovascularized endothelium. Early after transplantation the vascular endothelium demonstrated strong immunostaining compared with control sections. This immunostaining, however, was reduced to control levels at later stages of rejection. As rejection progressed, staining in the airway epithelium diminished to weak levels as compared with that in controls. These findings suggest a causal role for ET-1 and ECE-1 in the inflammatory and proliferative damage associated with chronic rejection after lung transplantation.

Endothelin attenuates apoptosis in human smooth muscle cells

An imbalance between proliferation and apoptosis is an important causal factor for disorders involving abnormal cell accumulation. Endothelin (ET)-1, a 21-amino-acid peptide with mitogenic and vasoconstricting activities, not only acts as a mitogen, but also attenuates paclitaxel-induced apoptosis in smooth muscle cells. In both human pericardial and prostatic smooth muscle cells, addition of ET-1 reduced paclitaxel-induced DNA fragmentation and phosphatidylserine on the cell surface, two characteristics of apoptosis. By comparison, angiotensin II, another vasoactive peptide, did not have a significant effect on apoptosis. The effect of ET-1 was dose-dependent with an EC50 of 1 nM. These results suggest that ET is a potential survival factor for smooth muscle cells, and that altered activity of the ET system in disease states has potential to contribute to aberrant cell growth.

Characteristics of endothelin receptors in acutely rejecting transplanted lungs

Experiments were designed to characterize endothelin receptors in bronchi and parenchyma of transplanted lungs during acute rejection. Third-order bronchi from autografted or allografted lungs were either cut into rings and suspended in organ chambers for the measurement of isometric force or frozen for isolation of membrane proteins. Lung parenchyma was prepared for histology or isolation of membrane protein. The grade of rejection was 2.74+/-0.17 (n= 19) in allotransplanted lungs; evidence of infection was present in 58% of the transplanted lungs. In organ chamber experiments, endothelin 1 (which stimulates endothelin A receptors) caused comparable contraction of bronchi from autotransplanted and allotransplanted rejecting lungs. Endothelin 3 (which stimulates endothelin A and B receptors) caused contractions of bronchi from autotransplanted lungs which were not different from those caused by endothelin 1. In contrast, contractions caused by endothelin 3 were reduced in bronchi from rejecting allotransplanted lungs. The magnitude of contractions caused by endothelin 3 was reduced further when infection was present with rejection. Competitive inhibition of 125I-endothelin 1 by endothelin 3 was significant for a two-site binding model in membranes prepared from all bronchi and lung parenchyma. The total number of binding sites (Bmax) was reduced significantly in bronchi and parenchyma from rejecting lungs with or without infection. The relative proportions of high-affinity and low-affinity binding sites did not change. Affinities of both high- and low-affinity receptors were not altered with rejection. These results indicate that at least two subtypes of endothelin receptors are present on canine bronchial smooth muscle and parenchyma. The number of endothelin receptors associated with bronchial contractions is reduced with rejection of lung allografts.