Differential leukotriene constrictor responses in human atherosclerotic coronary arteries

BACKGROUND

Leukotrienes are a class of biologically active lipids that have potent effects on the heart. To assess their role in coronary artery disease, we compared the contractile responses of leukotriene C4 (LTC4) and leukotriene D4 (LTD4) and their binding activity in both atherosclerotic and nonatherosclerotic human coronary arteries. We also studied expression of the enzymes that control their formation to understand how the 5-lipoxygenase (5-LO) pathway is activated in the coronary arteries.

METHODS AND RESULTS

The capacity of leukotrienes to affect coronary vessel tone and the influence of atherosclerosis was tested in organ baths. Leukotriene receptors were examined by autoradiography, and antibody binding to the various enzymes responsible for their formation was assessed by use of immunocytochemistry. Nonatherosclerotic coronary artery ring segments were unresponsive to LTC4 and LTD4. In contrast, LTC4 and LTD4 induced concentration-dependent contractions in atherosclerotic coronary arteries. Specific [3H]-LTC4 but not LTD4 binding to atherosclerotic coronary artery was evident, with no evidence of specific binding of [3H]-leukotrienes to nonatherosclerotic coronary artery. High-resolution autoradiography identified specific [3H]-LTC4 binding sites to smooth muscle cell and to regions of intimal proliferation and plaque. Cells showing positive antibody binding to 5-LO, FLAP (5-lipoxygenase activating protein), and leukotriene A4 hydrolase were also present in the coronary arteries and had a similar distribution to macrophages.

CONCLUSIONS

Atherosclerosis is associated with a specific leukotriene receptor(s) capable of inducing hyperreactivity of human epicardial coronary arteries in response to LTC4 and LTD4.

Endothelin--role in vascular disease

It is now two decades since it was demonstrated that ET-1 is one of the most powerful vasoconstrictors in biology. ET-1 mediates its effects through two membrane G-protein coupled receptors, ET(A) and ET(B), which exhibit a wide tissue distribution including the endothelial cells, vascular smooth muscle cells and adventitial fibroblasts. In recent years, ET-1 has been identified as a key player of endothelial dysfunction in various cardiovascular, autoimmune and CTDs. Endothelial dysfunction results from endothelial cell injury subsequently leading to the generation of an inflammatory process and endothelial cell activation. Thus, beyond its known 'classical' vasoactive effects, ET-1 is additionally considered to be an important mediator in vessel remodelling ultimately leading to major changes in cellular and tissue architecture; it also appears to function in conjunction with other growth factors and cytokines. Consequently, ET-1 receptor antagonists may be useful in ameliorating progression of vascular dysfunction and vascular disease due to their ability to negatively modulate vasoconstrictor pathways, cytokines and inflammatory markers production, and growth factor effects. This review briefly summarizes the current knowledge on the role of ETs in vascular dysfunction and vascular disease, with a particular emphasis on ET-1 in CTDs.

Endothelin is an important determinant of renal function in a rat model of acute liver and renal failure

BACKGROUND AND AIMS

Renal failure occurs in approximately 55% of patients with acute liver failure. We have previously shown that plasma endothelin 1 concentrations are elevated in patients with acute liver failure and the hepatorenal syndrome. There are few reported satisfactory animal models of liver failure together with functional renal failure. In this study, a rat model of acute liver failure induced by galactosamine that also develops renal failure was first characterised. This model was used to investigate the hypothesis that endothelin 1 is an important mediator involved in the pathogenesis of renal impairment that occurs in acute liver failure.

METHODS

Acute liver failure was induced in male Sprague-Dawley rats by intraperitoneal injection of galactosamine together with treatment with the endothelin receptor antagonist Bosentan. Twenty four hour urine collections were made using a metabolic cage. Renal blood flow was measured in anaesthetised animals.

RESULTS

This model developed renal failure and liver failure in the absence of any significant renal pathology, and with an accompanying fall in renal blood flow. Plasma concentrations of endothelin 1 were increased twofold following the onset of liver and renal failure (p<0.05), and there was significant upregulation of the endothelin receptor A (ET(A)) in the renal cortex (p<0.05). Administration of Bosentan prevented the development of renal failure when given before or 24 hours after the onset of liver injury (p<0.05) but had no effect on liver injury itself, or on renal blood flow.

CONCLUSIONS

This study demonstrates that this animal model has many of the features needed to be regarded as a model of renal failure that occurs in acute liver failure. The observation that plasma levels of endothelin 1 and ET(A) receptors are increased and upregulated, and that renal failure is prevented by an endothelin antagonist supports the hypothesis originally put forward that ET(A) is important in the pathogenesis of renal failure that occurs in patients with acute liver failure.

Stimulation of colorectal cancer cell line growth by ET-1 and its inhibition by ET(A) antagonists

BACKGROUND

The vasoactive peptide endothelin 1 (ET-1) acts via two receptors, endothelin receptors A (ET(A)) and B (ET(B)). ET-1 is overexpressed by human cancers in vivo and in vitro and may be mitogenic for cancer cells.

METHOD

To elucidate if ET-1 is a growth regulator the following were investigated in human colorectal cancer cell lines (LIM1215 and HT29): ET-1 production by ELISA; ET receptor expression using radioligand autoradiographic techniques; and responsiveness to ET-1, and to ET(A) and ET(B) antagonism by growth measurements.

RESULTS

ET-1 was produced by LIM1215 and HT29 cells (21.3 and 41.7 fmol/ml/10(6) cells (24 hours); 22.6 and 71.7 fmol/ml/10(6) cells (48 hours), respectively). ET(A) and ET(B) receptors were expressed by both cell lines. Addition of ET-1 resulted in a dose dependent increase in cell numbers which was significant at 10(-8)-10(-9) M for LIM1215, with the greatest increase at 10(-8) M (32.7% and 28.4% increase above controls at 48 hours and 72 hours; p<0.05) and at 10(-8)-10(-9) M for HT29, with the greatest increase at 10(-9) M (13.4% and 15.7% increase above controls at 48 hours and 72 hours; p<0.05). ET(A) antagonists BQ123 and BQ610, but not the ET(B) antagonist BQ788, inhibited ET-1 induced proliferation of both LIM1215 and HT29 (p<0.05).

CONCLUSION

ET-1 can stimulate the proliferation of colorectal cancer cell lines via the ET(A), but not the ET(B), receptor.

Endothelin receptor expression in colorectal cancer

The distribution of endothelin-A- and B- (ET(A), ET(B)) receptor subtypes was compared in colorectal cancer to that in normal colon and their expression in the colorectal cancer cell lines LIM1215. HT29, SKCO1, SKCO17 and LoVo was determined, using gross and high resolution autoradiography and quantified by densitometry. ET(A) and ET(B) binding sites were expressed by all the cell lines. There was significantly (p = 0.008) higher expression of ET(A)-receptors by cancers (205.95 dpm x 1000/mm2) compared normal colon (129.19 dpm x 1000/mm2). However, for ET(B)-receptors, this was reversed, with significantly (p = 0.008) higher expression of ET(B) binding in normal colon (207.00 dpm x 1000/mm2) than in tumours (122.35 dpm x 1000/mm2).

Acetylation of CCAR2 Establishes a BET/BRD9 Acetyl Switch in Response to Combined Deacetylase and Bromodomain Inhibition

There continues to be interest in targeting epigenetic "readers, writers, and erasers" for the treatment of cancer and other pathologies. However, a mechanistic understanding is frequently lacking for the synergy observed when combining deacetylase and bromodomain inhibitors. Here we identify cell cycle and apoptosis regulator 2 (CCAR2) as an early target for acetylation in colon cancer cells treated with sulforaphane. N-terminal acetylation of CCAR2 diminished its interactions with histone deacetylase 3 and β-catenin, interfering with Wnt coactivator functions of CCAR2, including in cells harboring genetically encoded CCAR2 acetylation. Protein domain arrays and pull-down assays identified acetyl "reader" proteins that recognized CCAR2 acetylation sites, including BRD9 and members of the bromodomain and extraterminal domain (BET) family. Treatment with the BET inhibitor JQ1 synergized with sulforaphane in colon cancer cells and suppressed tumor development effectively in a preclinical model of colorectal cancer. Studies with sulforaphane+JQ1 in combination implicated a BET/BRD9 acetyl switch and a shift in the pool of acetyl "reader" proteins in favor of BRD9-regulated target genes. SIGNIFICANCE: These results highlight the competition that exists among the "readers" of acetylated histone and nonhistone proteins and provide a mechanistic basis for potential new therapeutic avenues involving epigenetic combination treatments.

An autoradiographic demonstration of prazosin binding to arterial vessels in the rat

Prazosin is believed to have an antihypertensive action due to a selective blockade of alpha-adrenoceptors on vascular smooth muscle. Using an in vitro autoradiographic technique specific binding of [3H]prazosin to the abdominal aorta and renal artery in the rat has been shown. The binding of [3H]prazosin to arterial vessels may provide some evidence for the site where prazosin exerts its antihypertensive action.

Autoradiographic localisation and contractile properties of prostatic endothelin receptors in patients with bladder outlet obstruction

OBJECTIVES

Previous studies have used endothelin (ET) receptor agonists and antagonists to localise ET receptor subtypes in prostatic tissue. We have utilised high affinity ET(A) ([(125)I]PD151242) and ET(B) ([(125)I]BQ3020) receptor-specific radioligands to determine the density and distribution of ET receptor subtypes in prostatic tissues obtained from patients with symptomatic benign prostatic hyperplasia (BPH). The contractile properties of the ET receptor subtypes as well as the effect of ET-1 on alpha(1)-adrenergic receptor-mediated prostatic smooth muscle contraction were assessed.

PATIENTS AND METHODS

Saturation binding and quantitative autoradiographic studies were performed using specific radioligands for ET(A) and ET(B) receptors on prostate sections obtained from patients with bladder outflow obstruction secondary to BPH. In vitro isometric tension studies were carried out to characterise the ET receptor subtypes in prostatic smooth muscle strips from the same group of patients. In addition, the effect of ET-1 on alpha(1)-adrenergic receptor-induced prostatic smooth muscle contraction was also investigated.

RESULTS

There were dense ET(A) and ET(B) receptor-binding sites in the prostatic stroma. ET(A) receptor-binding sites were also prominent on the prostatic epithelium. ET-1 and sarafotoxin 6 c (ET(B) receptor agonist) elicited prostatic smooth muscle contraction (-log EC(50) 8.31+/-0.15 and 8.22+/-0.22 M, respectively). Both BQ123 (ET(A) antagonist) and BQ788 (ET(B) antagonist) significantly inhibited ET-1- and S6c-mediated prostatic smooth muscle contractile responses, respectively. ET-1 at sub-threshold concentrations significantly enhanced alpha(1)-adrenergic receptor-mediated prostatic smooth muscle contractile responses.

CONCLUSIONS

ET(A) receptor-binding sites are prominent in both prostatic stroma and epithelium, whereas ET(B) receptor-binding sites were predominantly seen in the prostatic stroma in symptomatic BPH. Both ET(A) and ET(B) receptors mediate prostatic smooth muscle contraction. ET-1 enhances alpha(1)-adrenergic receptor-mediated contractile responses, suggesting that ET may play a pathophysiological role in bladder outlet obstruction associated with BPH.

Abstract B190: Efficacy of the specific ETA receptor antagonist zibotentan (ZD4054) in cancer cells and fibroblasts from colorectal cancer

Endothelin-1 (ET-1) contributes to growth and progression of solid cancers, mainly through endothelin receptor A (ETAR). Therefore endothelin receptor antagonism is emerging as a potential treatment for neoplasms. We evaluated the efficacy of the specific ETAR antagonist zibotentan (ZD4054) in blocking ET-driven cellular effects in colorectal cancer (CRC). CRC cell lines (HT29, SW620) and primary normal fibroblast strains isolated from human colorectal tissues (CF36, CF56, CF65, CF75) were incubated in ET-1 with/without BQ123, zibotentan (ETAR antagonists), BQ788 (ETBR antagonist). Resultant cell growth was measured by the colourimetric methylene blue assay; migration by a modified monolayer scratch assay; contraction in collagen gels; downstream effectors by western blotting. ET-1 driven growth (18%–45% above control) was significantly inhibited (p&lt;0.01) by ETAR (not ETBR) antagonism (BQ123=zibotentan CRC; fibroblasts). ET-1 driven fibroblast migration and contraction were blocked by ETAR and ETBR antagonism (zibotentan=BQ123). CRC cells did not migrate or contract. ET-1-stimulated expression of downstream effectors was driven by ETAR or ETBR, eg: (1) connective tissue growth factor (CTGF) was blocked by ETAR antagonism (zibotentan&gt;BQ123; CRC and fibroblasts); (2) collagen XI was blocked by ETAR&gt;ETBR antagonism (zibotentan&gt;BQ123; fibroblasts). The specific ETAR antagonist zibotentan is at least as efficacious as BQ123 in blocking ET-1 driven growth, migration and contraction both in CRC cells and colorectal fibroblasts, which form the supporting tumor stroma. Zibotentan is a strong candidate for adjuvant treatment in CRC.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B190.

Endothelial integrity and nitric oxide synthase sources are better maintained in saphenous vein harvested by a ‘no-touch’ technique

Background

The saphenous vein (SV) is a commonly used conduit in bypass procedures. Early graft occlusion rates are greater than 20 per cent in both infrainguinal vein grafts and coronary artery bypass grafts (CABGs). Contributing factors include adventitial and endothelial damage, which may reduce nitric oxide availability in grafts. Nitric oxide has important vasorelaxant and thromboresistant properties beneficial to graft patency. Conventionally, during SV harvest, the perivascular tissue is stripped and the graft distended. A ‘no-touch’ technique has been described in which the SV is harvested together with a cushion of surrounding tissue without vein distension. This study compared endothelial integrity and the potential role of nitric oxide synthase (NOS) in segments of SV harvested by the two techniques.

Methods

SV was harvested from ten patients undergoing CABG. Distal and proximal ends of the SV were harvested using the no-touch technique, while the middle portion was stripped of the adventitia and distended. Sections of SV were cut and endothelial integrity was assessed with CD31 immunohistochemistry and quantified by morphometric analysis. Putative NOS was identified by reduced nicotinamide adenine dinucleotide phosphate (NADPH)–diaphorase histochemistry and autoradiographic localization of [3H]l-NG-nitroarginine binding.

Results

More dense CD31 staining was seen on the luminal aspect and vasa vasorum of vessels harvested by the no-touch technique. Morphometric analysis revealed a significant reduction in luminal CD31 staining in conventional compared with no-touch grafts (P &lt; 0·05, Student's t test). NADPH staining was almost continuous on the luminal aspect, and was also present in the adventitia of no-touch vessels, compared with poor staining of conventionally harvested vessels. The pattern of NADPH staining corresponded to endothelial cells lining the vessel lumen as well as vasa vasorum and paravascular nerves in the adventitia. Autoradiographic analysis of specific [3H]nitroarginine binding also showed greater binding in the no-touch vessels.

Conclusion

Endothelial integrity is better maintained by the no-touch technique. NOS sources on the endothelium and adventitia are preserved, suggesting that nitric oxide availability is retained by these grafts. This technique may therefore lead to improved early patency rates of SV grafts in bypass surgery.

Decreased endothelin binding and receptor density in varicose veins

Background

The primary cause of venodilatation and reduced contractility in varicose veins is unclear. Endothelin (ET) 1 acts on smooth muscle cell ET A/ET B receptors to induce contraction and growth, and on endothelial cells to induce production of the vasorelaxant and growth inhibitors nitric oxide and prostacyclin. These factors may be involved in the aetiology of varicose veins. This study investigated ET-1 binding and ET A/ET B receptor density in varicose and non-varicose veins.

Methods

Proximal long sapheous vein (LSV) sections from nine patients undergoing surgery for varicose veins were compared with normal LSV from nine patients undergoing coronary artery bypass surgery. Slide-mounted sections were incubated in [125I]-radiolabelled ET-1 and ET A/ET B binding sites were identified using subtype-selective radioligands. Receptor density and distribution was quantified on autoradiographs by densitometry and binding was localized at the cellular level by nuclear emulsion.

Results

ET-1 binding and ET B receptor density decreased significantly in the varicose group. There was no significant difference in ET A receptor density.

Conclusion

Decreased ET-1 binding may contribute to venodilatation and poor contractility in varicose veins. This may be due to decreased tunica media ET B receptor density.