Preferential vasoconstriction to cysteinyl leukotrienes in the human saphenous vein compared with the internal mammary artery. Implications for graft performance

Comparative study of coronary artery bypass graft materials: reduced contraction and ADMA levels in internal mammary artery versus saphenous vein

BACKGROUND

Vasospasm and atherosclerosis due to low endothelial capacity are the most important causes of coronary artery bypass graft failure observed in internal mammary artery (IMA) and saphenous vein (SV). Vasospasm can be mimicked in in vitro studies by inducing vasoconstriction of graft materials. In the present study, we aimed to compare the vascular contraction induced by several spasmogens including prostaglandin E2 (PGE2), prostaglandin F2 alpha (PGF2α), phenylephrine (PE), leukotriene C4 (LTC4), LTD4, potassium chloride (KCl), and arachidonic acid between IMA and SV preparations. Furthermore, endothelial capacity, nitrite and asymmetric dimethylarginine (ADMA) levels were compared between two grafts.

METHODS

By using organ bath, contractile responses induced by different spasmogens were compared between IMA and SV preparations derived from patients underwent coronary artery bypass surgery (n=35). The endothelial capacity was determined by acetylcholine (ACh) -induced relaxation in PE-precontracted vessels. Nitrite and ADMA levels were measured in organ culture supernatant of IMA and SV preparations.

RESULTS

Contractile responses induced by PGE2, PGF2α, PE, LTC4, LTD4, KCl and arachidonic acid were significantly lower in IMA preparations versus SV preparations. ACh-induced relaxation was significantly more prominent in IMA than SV preparations. Nitrite levels were greater and ADMA levels were lower in IMA versus SV preparations.

CONCLUSIONS

IMA has reduced capacity to constrict to several vasoconstrictor agents. Furthermore, IMA has greater endothelial capacity associated with higher nitrite levels and lower ADMA levels. Our results support the greater patency rate observed in IMA versus SV preparations.

In vitro effects of sodium nitroprusside and leptin on norepinephrine-induced vasoconstriction in human internal mammary artery

Aim

The biological and pharmacological properties of vessels used in coronary artery bypass graft (CABG) surgery are as important as their mechanical properties. The aim of this study was to investigate the possible role of protein kinase C (PKC)-dependent mechanisms in leptin-induced relaxation in the human internal mammary artery (IMA).

Methods

IMA rings, obtained from patients undergoing CABG surgery, were suspended in isolated tissue baths containing Krebs-Henseleit solution, which were continuously gassed with 95% O₂ and 5% CO₂ at 37°C.

Results

The IMA rings were pre-contracted with increasing concentrations of norepinephrine (NE 10^-9–10^-4 mol/l) and the relaxation responses to sodium nitroprusside (SNP), a nitrosovasodilator, and leptin were studied in the presence and absence of a PKC inhibitor. Leptin (1 μM) caused a dose-dependent relaxation in NE pre-contracted IMA rings. Pre-treatment with a PKC inhibitor significantly attenuated this vasorelaxatory response to leptin in human isolated IMA.

Conclusion

It was found that SNP and leptin caused significant relaxation of the NE pre-contracted human IMA rings, and PKC was probably the sub-cellular mediator for this effect. Our findings may have clinical or pharmacological importance as it could be hypothesised that obese subjects who have a left IMA bypass graft would have better myocardial perfusion.

Coronary artery bypass graft: why is the saphenous vein prone to intimal hyperplasia?

Proliferation and migration of smooth muscle cells and the resultant intimal hyperplasia cause coronary artery bypass graft failure. Both internal mammary artery and saphenous vein are the most commonly used bypass conduits. Although an internal mammary artery graft is immune to restenosis, a saphenous vein graft is prone to develop restenosis. We found significantly higher activity of phosphatase and tensin homolog (PTEN) in the smooth muscle cells of the internal mammary artery than in the saphenous vein. In this article, we critically review the pathophysiology of vein-graft failure with detailed discussion of the involvement of various factors, including PTEN, matrix metalloproteinases, and tissue inhibitor of metalloproteinases, in uncontrolled proliferation and migration of smooth muscle cells towards the lumen, and invasion of the graft conduit. We identified potential target sites that could be useful in preventing and (or) reversing unwanted consequences following coronary artery bypass graft using saphenous vein.

Cardiovascular consequences when nitric oxide and lipid signaling converge

The identification of nitric oxide ((*)NO) as an endogenously produced free radical mediator of endothelial-dependent relaxation and host defense has fundamentally changed concepts of cell signal transduction. Ligand-receptor oriented paradigms of cell signaling were originally centered on the concept of a high affinity and specific interaction between a ligand and its receptor, resulting in the activation of secondary signaling events such as gene expression or modulation of catalytic protein function. While (*)NO ligation of the heme iron of soluble guanylate cyclase is consistent with this perspective, the readily diffusible and broadly reactive (*)NO is increasingly appreciated to react with a vast array of target molecules that mediate paracrine vasodilator actions, inhibition of thrombosis and neointimal proliferation, and both pro- and antiinflammatory signaling reactions that are not affected by inhibitors of soluble guanylate cyclase. There is an expanding array of functionally significant "off target" collateral reactions mediated by (*)NO that are guanylate cyclase-independent and rather are dictated by anatomic distribution and the formation of secondary (*)NO-derived species. These reactions are a critical element of redox-regulated signaling and are addressed herein in the context of the oxidation of unsaturated fatty acids to vascular and inflammatory signaling mediators. Because of their abundance and the intrinsic reactivity of unsaturated lipid intermediates and eicosanoid metabolism enzymes with (*)NO and other oxides of nitrogen, lipid signaling mechanisms are a significant target for regulation by (*)NO in the vascular compartment. This convergence of (*)NO and lipid signaling pathways thus adds another level of regulation to physiological responses such as vasodilation, thrombosis, and inflammation. Herein, interactions between (*)NO and lipid signaling events are placed in the context of cardiovascular regulation.

The 5 lipoxygenase system in the vasculature: emerging role in health and disease

Activation of the 5 lipoygenase (5LO) system within the vascular bed requires the presence of several cell types with distinct transcellular cross-talk mechanisms, resulting in the generation of 5LO produced metabolites and increased expression of receptors for these metabolites in vascular cells. The key products in this system, the leukotriens LTB4, LTC4 and LTD4, are potent mediators of vascular inflammation initiated by white blood cells and sustained or propagated thereafter through amplified metabolite generation and direct effects in endothelial and vascular smooth muscle cells. Leukotrienes act to enhance cell permeability and increase oxidative stress, vascular smooth muscle cell migration and arterial tone. 5LO activation is highly regulated, and is apparently both model/species-specific and region-specific. 5LO activation is also linked to plaque progression, plaque stability, activation of matrix metalloproteinases, propensity to coronary and cerebrovascular events and the evolution of aortic aneurysms. Genetic variants in the 5LO activating protein are strongly linked to increased cardiovascular risk and may serve as useful markers for future therapy targeting down regulation of 5LO expression and activity as a means to combat cardiovascular disease.

Leukotriene receptors in atherosclerosis

Leukotriene-forming enzymes are expressed within atherosclerotic lesions and locally produced leukotrienes exert pro-inflammatory actions within the vascular wall by means of cell surface receptors of the BLT and CysLT receptor subtypes. The migration and accumulation of inflammatory cells that follow leukotriene receptor activation have been implicated in atherosclerosis initiation and progression. Leukotriene receptors are in addition expressed on endothelial and vascular smooth muscle cells, associated with intimal hyperplasia in early atherosclerosis and restenotic lesions after angioplasty. Taken together, recent evidence suggests that leukotriene receptors may be a potential target in the treatment of atherosclerosis and in the prevention of restenosis after coronary interventions.

The quest for new cysteinyl-leukotriene and lipoxin receptors: recent clues

The metabolism of arachidonic acid via the 5-lipoxygenase enzymatic pathway leads to the formation of the cysteinyl-leukotrienes and lipoxins, which have been implicated in several inflammatory reactions. While these lipid mediators are responsible for a variety of effects, their actions occur through the activation of 3 specific types of cloned receptors (i.e., CysLT(1), CysLT(2), and ALX). Although receptor activation can explain several biological actions associated with the mediators, there is some evidence to suggest that not all responses fit the well-known characteristics of these cloned receptors. Other receptor subtypes may also exist. Interestingly, the indirect evidence for support of this observation is principally derived from work performed on either blood elements and/or vascular smooth muscle. Because the initiating events associated with inflammation are essentially of vascular origin, further work at the molecular level may be necessary to confirm the data, which do not fit the well-known CysLT and ALX receptor profiles.

Characterization of cysteinyl leukotriene receptors on human saphenous veins: antagonist activity of montelukast and its metabolites

The aims of this study were to determine the cysteinyl leukotriene (CysLT) receptors expressed in the human saphenous vein, to examine contractile response to LTC4 and LTD4, to evaluate antagonist activity of montelukast, a specific CysLT1 receptor antagonist used in asthma, and to characterize the CysLT receptors involved in the contractile response. The analysis by reverse-transcriptase polymerase chain reaction indicated that CysLT1 and CysLT2 receptors are expressed by saphenous veins. In varicose vein rings, the potencies (pD2) of LTC4 and LTD4 were similar: 7.4 +/- 0.2 and 7.4 +/- 0.1, respectively. Pretreatment with acivicin, a gamma-glutamyl transpeptidase (gamma-GT) inhibitor, to prevent potential metabolism of LTC4 to LTD4, did not alter the response to LTC4. In nondistended vein rings from patients undergoing arterial bypass, the LTC4 pD2 was 7.8 +/- 0.1, and pretreatment with S-hexyl-GSH, a potent gamma-GT inhibitor, caused a fourfold rightward shift of the LTC4 concentration-response curve. In varicose and nondistended saphenous vein rings, montelukast (10(-8) and 10(-7) M) exerted a potent activity against LTD4 and LTC4, in the presence or absence of gamma-GT inhibitors. In varicose vein rings, the two active metabolites of montelukast also exerted antagonist activities with potencies similar to montelukast. BAY u9773 (CysLT2 agonist/dual CysLT1/CysLT2 antagonist) did not cause contraction and inhibited the LTC4- and LTD4-induced contractions. In conclusion, human saphenous veins express CysLT1 and CysLT2 receptors, but only CysLT1 receptors are implicated in the contraction.

Leukotriene B4 is an indirectly acting vasoconstrictor in guinea pig aorta via an inducible type of BLT receptor

Leukotriene B(4) (LTB(4)) is a potent leukocyte chemoattractant recently implicated in the pathogenesis of atherosclerosis. The aim of this study was to assess the effects of LTB(4) on isolated aortic preparations. Rings of guinea pig aorta were challenged with LTB(4) for recording mechanical responses and measurements of mediator release, and LTB(4) receptor (BLT(1)) expression was assessed by RT-PCR. Single concentrations of LTB(4) induced concentration-dependent contractions that were inhibited by treatment with antihistamines, indomethacin, or the thromboxane receptor antagonist BAYu3405 as well as by denudation of endothelium. In addition, LTB(4) increased the release of histamine and thromboxane in the bath. The contractions induced by LTB(4) were inhibited by either the unselective BLT receptor antagonist ONO-4057 or the selective BLT(1) receptor antagonist U-75302. Pretreatment with all-trans-retinoic acid enhanced the contractions and the release of histamine induced by LTB(4), without affecting either the contractions induced by histamine or the histamine release evoked by calcium ionophore A23187. Analysis by RT-PCR indicated the expression of a BLT(1) receptor in the guinea pig aorta and that BLT(1) receptor mRNA was upregulated after treatment with retinoic acid. These results suggest that LTB(4) contracts the guinea pig aorta via an indirect mechanism involving the release of histamine and thromboxane and that this BLT(1) receptor-mediated response can be upregulated by all-trans-retinoic acid.

International Union of Pharmacology XXXVII. Nomenclature for leukotriene and lipoxin receptors

The leukotrienes and lipoxins are biologically active metabolites derived from arachidonic acid. Their diverse and potent actions are associated with specific receptors. Recent molecular techniques have established the nucleotide and amino acid sequences and confirmed the evidence that suggested the existence of different G-protein-coupled receptors for these lipid mediators. The nomenclature for these receptors has now been established for the leukotrienes. BLT receptors are activated by leukotriene B(4) and related hydroxyacids and this class of receptors can be subdivided into BLT(1) and BLT(2). The cysteinyl-leukotrienes (LT) activate another group called CysLT receptors, which are referred to as CysLT(1) and CysLT(2). A provisional nomenclature for the lipoxin receptor has also been proposed. LXA(4) and LXB(4) activate the ALX receptor and LXB(4) may also activate another putative receptor. However this latter receptor has not been cloned. The aim of this review is to provide the molecular evidence as well as the properties and significance of the leukotriene and lipoxin receptors, which has lead to the present nomenclature.

Modulation of vascular tone and reactivity by nitric oxide in porcine pulmonary arteries and veins

Isolated porcine pulmonary vessels were studied in order to evaluate the role of nitric oxide in arteries and veins. Leukotriene C4 and noradrenaline contracted porcine pulmonary arteries but induced only negligible contractions of porcine pulmonary veins. After treatment with the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine (L-NOARG), significant contractions to leukotriene C4 and noradrenaline were uncovered in pulmonary veins. In arterial preparations, L-NOARG caused a less marked potentiation of noradrenaline-induced contractions and did not alter leukotriene C4-induced contractions. Endothelium-dependent relaxations to acetylcholine were greater in veins compared with arteries whereas the endothelium-independent relaxations to the nitric oxide donor sodium nitroprusside (SNP) and the cyclic nucleotide analogue 8-bromo-cGMP were similar in the two preparations. Taken together these data suggest that the apparent insensitivity of porcine pulmonary veins to leukotriene C4 and noradrenaline was because of release of nitric oxide. The effect of nitric oxide synthase inhibition was less pronounced in porcine pulmonary arteries, suggesting a preferential functional role of nitric oxide in porcine pulmonary veins, originating in a greater production of nitric oxide by veins as opposed to arteries.

Cysteinyl leukotrienes mediate enhanced vasoconstriction to angiotensin II but not endothelin-1 in SHR

We assessed whether cysteinyl leukotrienes mediate the vasoconstrictor responses to angiotensin II and endothelin-1 in the mesenteric vascular bed of Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) perfused ex vivo at a constant flow rate of 5 ml/min with Krebs buffer. Maximal perfusion pressure response (E(max)) but not EC(50) values to angiotensin II (P < 0.001) and endothelin-1 (P < 0.01) were significantly higher in the SHR, whereas the responses to potassium chloride remained unchanged. Inclusion of the selective 5-lipoxygenase inhibitor AA-861 or the cysteinyl leukotriene receptor antagonist MK-571 significantly reduced the vasoconstrictor responses to angiotensin II but not to endothelin-1 and potassium chloride. The reduction in E(max) to angiotensin II was more pronounced in SHR (P < 0.001) than in WKY (P < 0.05) rats. Cysteinyl leukotrienes LTC(4)-, LTD(4)-, and LTE(4) (1 microM)-evoked vasoconstrictor responses were significantly higher in SHR (P < 0.05), whereas LTB(4) failed to evoke any response in either strain. These data suggest that 5-lipoxygenase metabolites, particularly cysteinyl leukotrienes, contribute to the exaggerated vasoconstrictor responses to angiotensin II but not to endothelin-1.

Reactivity of the Human Internal Mammary Artery and the Gastroepiploic Artery to Constrictor Substances

The internal mammary artery (IMA) and the gastroepiploic artery (GEA) are frequently used to construct coronary artery bypass grafts. In order to determine and to compare their contractile properties, we studied the effects of constricting agents which are liberated or infused during coronary bypass surgery. IMA and GEA were arranged as ring segments and suspended in organ baths at optimal stretch using a normalization procedure. Concentration-contraction curves to angiotensin II, norepinephrine, U-46619, endothelin-1, leukotriene C(4) and KCl were performed. The sensitivity (pD(2)) of GEA and IMA to all the agents did not differ. However, GEA developed stronger maximal contraction force than IMA to angiotensin II (P < 0.001), norepinephrine (P < 0.05), U-46619 (P = 0.06), endothelin-1 (P < 0.01), and KCl (P < 0.01), whereas leukotriene C(4) did not induce a significant contraction on GEA and IMA. The higher contractility of GEA may explain that it is more prone to spasm than IMA in the clinical setting. This study reinforces IMA as a first-choice conduit for coronary artery bypass and emphasizes the need for antispastic drugs particularly when GEA is used as bypass vessel.http://link.springer-ny.com/link/service/journals/00547/bibs/8n4p187.html</hea

Functional comparison of the human isolated femoral artery, internal mammary artery, gastroepiploic artery, and saphenous vein

Human femoral, internal mammary, and gastroepiploic arteries and saphenous veins are used as bypass grafts for coronary surgery or for reconstruction in arterial occlusive disease. We have characterized the contractile responses of these vessels to various agents that are liberated during cardiac or vascular surgery. In organ baths, U46619 (a stable thromboxane A2 mimetic), norepinephrine, endothelin-1, angiotensin II, and KCl caused concentration-dependent contractions in all vessels tested. Leukotriene C4 did not induce any contraction in the arteries, whereas a contraction was obtained in the saphenous vein rings. U46619 induced the most powerful contraction in all vessels tested. The pD2 values for each agent did not differ among the different vessels. When responses were expressed as a percentage of KCl-induced contraction, the contraction of endothelin-1 (151 ± 5%) and leukotriene C4 (43 ± 5%) was more significant on saphenous veins than on arteries. In conclusion, thromboxane A2 appears to be the most potent endogenous constricting agent on different human vascular beds. Our second finding is that saphenous veins are more sensitive to contract to leukotriene C4 and endothelin-1 than arteries. These properties may influence early and (or) long-term vein graft patency.Key words: femoral arteries, vascular reactivity, thromboxane A2, endothelin-1, leukotrienes.