Rat peritoneal macrophages express endothelin ET(B) but not endothelin ET(A) receptors

Evidence for the endothelin system as an emerging therapeutic target for the treatment of chronic pain

Many people worldwide suffer from pain and a portion of these sufferers are diagnosed with a chronic pain condition. The management of chronic pain continues to be a challenge, and despite taking prescribed medication for pain, patients continue to have pain of moderate severity. Current pain therapies are often inadequate, with side effects that limit medication adherence. There is a need to identify novel therapeutic targets for the management of chronic pain. One potential candidate for the treatment of chronic pain is therapies aimed at modulating the vasoactive peptide endothelin-1. In addition to vasoactive properties, endothelin-1 has been implicated in pain transmission in both humans and animal models of nociception. Endothelin-1 directly activates nociceptors and potentiates the effect of other algogens, including capsaicin, formalin, and arachidonic acid. In addition, endothelin-1 has been shown to be involved in inflammatory pain, cancer pain, neuropathic pain, diabetic neuropathy, and pain associated with sickle cell disease. Therefore, endothelin-1 may prove a novel therapeutic target for the relief of many types of chronic pain.

Spatial alterations in endothelin receptor expression are temporally associated with the altered microcirculation after brain trauma

OBJECTIVES

To study the cellular distribution of endothelin receptors A and B (ETrA and ETrB) in the post-traumatic sensorimotor cortex and hippocampus.

MATERIALS AND METHODS

We inflicted closed head trauma to male Sprague-Dawley rats and visualized ETrA and ETrB immunoreactivity with 3,3'-diaminobenzidine.

RESULTS

ETrA immunolabeling was the most prominent in pyramidal neurons 24 and 48 hours post-trauma, while it reached its peak in the microvasculature at hour 4. ETrB immunolabeling was observed in endothelial cells, perivascular neurons, smooth muscle cells (SM) and pericytes, the expression being the most pronounced 24 hours post-trauma.

DISCUSSION

The results suggest that the vasoconstrictor effect of endothelin-1 (ET-1) is mediated primarily by ETrA. The dual effects of ETrB are reflected in its vasoconstrictor role at the vascular bed and conversely, in the attenuation of ET-1 availability and synthesis. We conclude that both receptors play a role in the disturbed microvascular autoregulation and in the sustained reduction of blood flow following trauma to the brain.

Endothelin-1 production by the canine macrophage cell line DH82: enhanced production in response to microbial challenge

Endothelin-1 (ET-1) is a potent vasoconstrictive peptide which plays an important role in regulating mammalian cardiovascular development and homeostasis. Originally identified as a factor released by vascular endothelial cells, ET-1 is now recognized as a product of numerous cells and tissues with demonstrated involvement in an array of physiological and pathological processes. An area of great interest is the production of ET-1 by mononuclear cells (monocytes and macrophages) and its role in inflammation. We report that the canine macrophage cell line, DH82, constitutively secretes both ET-1 and its biologically inactive precursor big ET-1. The production of both peptides was increased following stimulation with lipopolysaccharide (endotoxin) from gram-negative bacteria. ET-1 production was also increased in response to stimulation with intact and viable gram-positive and gram-negative bacteria. In addition to producing ET-1, DH82 cells express transcripts encoding two receptors for the ET-1 peptide (ET(A) and ET(B) receptors) and an enzyme involved in the conversion of big ET-1 to ET-1. The constitutive secretion of ET-1 and the expression of ET(A) and ET(B) receptors may be related to the malignant origin of this cell line. Our results are the first report of ET-1 production by a canine cell line and provide the basis for further investigation into the role of ET-1 during infection and inflammation.

Blockade of endothelin ETA/ETB receptors favors a role for endothelin during acute Trypanosoma cruzi infection in rats

Endothelin has been implicated in the pathogenesis of experimental and human Chagas' disease (American trypanosomiasis). In the present study, we tested the effect of bosentan, an antagonist of both ET(A) and ET(B) endothelin receptors, on parasitemia, histopathology (heart and diaphragm), heart levels of tumor necrosis factor (TNF)-alpha, interleukin (IL)-10, interferon (IFN)-gamma, CCL2, CCL3 and CCL5, and the serum levels of nitrate/nitrite (NOx). Bosentan treatment was accompanied by a significant increase in parasitemia and tissue parasitism or inflammation. In vehicle-treated rats, Trypanosoma cruzi infection increased the cardiac levels of TNF-alpha, IFN-gamma and IL-10, at day 9 post inoculation, and the TNF-alpha remained elevated until day 13. The infection also caused a significant increase in the cardiac levels of the chemokines CCL2 (9, 13 and 18 days) and CCL3 (13 and 18 days). Bosentan-treatment had no significant effect on the infection-associated increase in IFN-gamma and chemokine concentrations. There was a lower increase in IL-10 at day 9 and this was mirrored by a greater increase of TNF-alpha at day 13, in comparison with vehicle-treated rats. These latter findings correlated well with the enhanced inflammatory process in hearts of bosentan-treated infected rats. Bosentan treatment reduced the infection-associated increase in NOx serum concentration. Altogether, our data suggest that ET action on ET(A) and ET(B) receptors may play a role in the initial control of T. cruzi infection in rats probably by interfering in NO production.

The role of endothelin-1 in myocarditis and inflammatory cardiomyopathy: old lessons and new insights

Endothelin-1 has emerged as an important participant in the pathophysiology of a variety of cardiovascular diseases, where it may act on endocrine, paracrine and autocrine bases. Here we review its regulated biosynthesis, receptor-mediated signaling, and functional consequences in the heart, with particular emphasis on cardiac development and disease. Exploring published data employing molecular genetic mouse models of endothelin dysregulation, we highlight its heretofore underappreciated role as a pro-inflammatory cytokine. We also present novel micro-array data from one such mouse model, which implicate the specific downstream pathways that may mediate endothelin-1's effects.Key words: endothelin-1, cardiac development, inflammation, transgenic mice, gene expression profiling.

Endothelin and the tumorigenic component of bone cancer pain

Tumors including sarcomas and breast, prostate, and lung carcinomas frequently grow in or metastasize to the skeleton where they can induce significant bone remodeling and cancer pain. To define products that are released from tumors that are involved in the generation and maintenance of bone cancer pain, we focus here on endothelin-1 (ET-1) and endothelin receptors as several tumors including human prostate and breast have been shown to express high levels of ETs and the application of ETs to peripheral nerves can induce pain. Here we show that in a murine osteolytic 2472 sarcoma model of bone cancer pain, the 2472 sarcoma cells express high levels of ET-1, but express low or undetectable levels of endothelin A (ETAR) or B (ETBR) receptors whereas a subpopulation of sensory neurons express the ETAR and non-myelinating Schwann cells express the ETBR. Acute (10 mg/kg, i.p.) or chronic (10 mg/kg/day, p.o.) administration of the ETAR selective antagonist ABT-627 significantly attenuated ongoing and movement-evoked bone cancer pain and chronic administration of ABT-627 reduced several neurochemical indices of peripheral and central sensitization without influencing tumor growth or bone destruction. In contrast, acute treatment (30 mg/kg, i.p.) with the ETBR selective antagonist, A-192621 increased several measures of ongoing and movement evoked pain. As tumor expression and release of ET-1 has been shown to be regulated by the local environment, location specific expression and release of ET-1 by tumor cells may provide insight into the mechanisms that underlie the heterogeneity of bone cancer pain that is frequently observed in humans with multiple skeletal metastases.

Role of endothelin ETA and ETB receptors in the guinea-pig urinary bladder contraction

The distribution and function of endothelin receptors in the guinea-pig urinary bladder were examined. Specific [125I]endothelin-1 binding sites with both the endothelin ET(A) and ET(B) receptor subtypes were distributed in the muscle layer. Endothelin-1 elicited a tonic contraction which was inhibited by cyclo(D-Asp-Pro-D-Val-Leu-D-Trp) (BQ123) but not by N-cis-2,6-dimethylpiperidinocarbonyl-L-gamma-methylleucyl-D-1-methoxycarbonyltryptophanyl-D-norleucine (BQ788) and which was inhibited more strongly by a combination of BQ123 and BQ788. Sarafotoxin S6c elicited a contraction which was abolished by BQ788. The concentration of endothelin-1 in the muscle layer was 707.0+/-67.5 pg/g wet weight. Thus, endothelin-1 may regulate muscle tone via both subtypes of endothelin receptors in an autocrine manner in the guinea-pig urinary bladder.

Corresponding distributions of increased endothelin-B receptor expression and increased endothelin-1 expression in the aorta of apolipoprotein E-deficient mice with advanced atherosclerosis

Endothelin (ET)-1 causes proliferation of vascular smooth muscle cells (VSMC). Although it has been reported that stimulation of ET(B) receptors as well as ET(A) receptors promote proliferation of VSMC, the precise distribution of each receptor subtype in atherosclerotic vessels is unknown. Previous studies demonstrated that apolipoprotein E (apoE)-deficient mice have hypercholesterolaemia and develop severe atherosclerosis. To investigate the pathophysiological roles of vascular ET system in atherosclerosis, we examined preproET-1 messenger ribonucleic acid expression in the aorta of apoE-deficient mice, and performed immunohistochemical staining for ET-1 and each ET receptor subtype (ET(A) and ET(B) receptors) in the atherosclerotic lesions of these mice. The level of preproET-1 mRNA in the aorta was significantly higher in the apoE-deficient mice than in the control mice. Strong ET-1 staining was observed in the macrophage-foam cells, intimal and medial VSMC in the atherosclerotic lesions of the apoE-deficient mice. In addition, in the atherosclerotic lesions, strong ET(B) receptor staining was observed in the macrophage-foam cells, intimal and medial VSMC, which distribution corresponded closely to that of ET-1. ET(A) receptor staining was observed in the medial VSMC of both groups, but not in the macrophage-foam cells of the apoE-deficient mice. ET(A) receptor staining in the medial VSMC was stronger in the apoE-deficient mice than in the control mice. These results suggest that the vascular ET system, including ET-1 and ET receptors, is activated in the atherosclerotic lesions of apoE-deficient mice. Since the distribution of strong ET(B) receptor staining corresponded closely to that of ET-1, it is suggested that the ET system, mediated by ET(B) receptors, has an important role in the pathophysiology of the atherosclerotic lesions of apoE-deficient mice.

Effects on haemodynamics by selective endothelin ET(B) receptor and combined endothelin ET(A)/ET(B) receptor antagonism during endotoxin shock

The endothelin system is highly activated during endotoxin and septic shock. To investigate this matter the selective non-peptide endothelin ET(B) receptor antagonist A-192621 ([2R-(2alpha,3beta, 4alpha)]-4-(1,3-benzodioxol-5-yl)-1-[2-[2, 6-diethylphenyl)amino]-2-oxoethyl]-2-(4-propoxy-phenyl)-3-py rrolidine carboxylic acid) was administered alone and in combination with the selective non-peptide endothelin ET(A) receptor antagonist PD 155080 (sodium 2-benzo[1, 3]dioxol-5-yl-3-benzyl-4-(4-methoxy-phenyl)-4-oxobut-2-enoat e) during established porcine endotoxin shock. Cardiopulmonary vascular function, metabolic parameters and plasma endothelin-1-like immunoreactivity levels were compared to a control group only receiving endotoxin. Administration of A-192621 alone resulted in cardiovascular collapse and death whereas combining A-192621 with PD 155080 abolished endotoxin induced pulmonary hypertension, enhanced cardiac performance and improved systemic oxygen delivery and acid-base balance. The beneficial effects of mixed endothelin ET(A)/ET(B) receptor antagonisms on the pulmonary and cardiovascular systems may result from blockage of constrictive endothelin receptors in and pulmonary circulation, reduced afterload and a direct inotropic effect. Possible mechanisms for the devastating effects by selective endothelin ET(B) receptor antagonism include increased endothelin ET(A) receptor-mediated vasoconstriction due to lack of endothelin ET(B) receptormediated vasodilation and decreased endothelin clearance from endothelin ET(B) receptor blockade. In conclusion, selective endothelin ET(B) receptor antagonism is deleterious whereas combined endothelin ET(A) and ET(B) receptor antagonism has favourable effects on haemodynamics, suggesting participation of the endothelin system in cardiopulmonary dysfunction during endotoxin shock.