Vascular reactivity of arterial coronary artery bypass grafts--implications for their performance

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.

The role of endothelin-1 in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a rare but debilitating disease, which if left untreated rapidly progresses to right ventricular failure and eventually death. In the quest to understand the pathogenesis of this disease differences in the profile, expression and action of vasoactive substances released by the endothelium have been identified in patients with PAH. Of these, endothelin-1 (ET-1) is of particular interest since it is known to be an extremely powerful vasoconstrictor and also involved in vascular remodelling. Identification of ET-1 as a target for pharmacological intervention has lead to the discovery of a number of compounds that can block the receptors via which ET-1 mediates its effects. This review sets out the evidence in support of a role for ET-1 in the onset and progression of the disease and reviews the data from the various clinical trials of ET-1 receptor antagonists for the treatment of PAH.

Differential in vitro response of the human radial artery versus left internal thoracic artery to cerivastatin: implications to bypass grafting

BACKGROUND

This study investigated acute (in vitro) and long-term (in vivo) effects of statins on the vascular function of human radial artery (RA) and left internal thoracic artery (LITA).

METHODS

RA and LITA specimens were divided into vascular rings, which were incubated in the absence or presence of 10(-6) mol/L Cerivastatin for 2 or 24 hours. In terms of preoperative statin treatment, four groups included: group 1 [preop statin(-)/in vitro cerivastatin(-)]; group 2 [preop(-)/in vitro(+)]; group 3 [preop(+)/in vitro(-)]; and group 4 [preop(+)/in vitro(+)]. Endothelial function was assessed with acetylcholine (10(-9) to 10(-5) mol/L) following contraction by 3 x 10(-8) mol/L endothelin-1.

RESULTS

Although endothelium-dependent vasodilatation was higher in RA (57.7% +/- 3.5%) than in LITA (46.5% +/- 3.8%, p = 0.046), there was no significant evidence that it depended on the preoperative use of statins or incubation period. In vitro incubation with cerivastatin significantly increased endothelium-dependent vasodilatation by 14.2% +/- 2.4% (p < 0.0001) independent of artery types (RA/LITA). There was no significant evidence that endothelium-dependent vasodilatation depended on the preoperative use of statins or incubation period.

CONCLUSIONS

In vitro incubation with cerivastatin preserved endothelial function more effectively than preoperative use of statins. This could have implications to perioperative use of statins for patients undergoing coronary surgery.

In vivo early and mid-term flow-mediated endothelial function of the radial artery used as a coronary bypass graft

OBJECTIVES

We sought to evaluate the in vivo endothelial function of the radial artery (RA) used as a coronary graft.

BACKGROUND

The RA is becoming a recognized alternative coronary bypass conduit. In vivo endothelial function is a possible predictor of long-term performance.

METHODS

Sixty consecutive patients underwent coronary artery bypass graft surgery (CABG); all received RA and left internal mammary artery (LIMA) grafts. Three weeks after CABG, 36 patients underwent angiography under basal conditions, during pacing and after intragraft injection of glyceryl trinitrate (GTN). Angiography was repeated at six months in 20 patients.

RESULTS

The estimated mean difference of 66 segments of the radial graft on the first QCA study was 0.170 mm (95% confidence interval [CI] 0.101 to 0.258, p < 0.001) between baseline and pacing, and 0.310 mm (CI 0.225 to 0.401, p < 0.001) between baseline and GTN. At six months, the differences between baseline and pacing and baseline and GTN were 0.112 mm (CI 0.062 to 0.162, p < 0.001) and 0.274 (CI 0.192 to 0.353, p < 0.001), respectively. The difference between baseline values at three weeks and six months was 0.416 mm (CI 0.236 to 0.603, p < 0.001). In the LIMA segments, the difference between baseline and pacing and baseline and GTN were 0.206 mm (CI 0.136 to 0.278, p < 0.001) and 0.304 mm (CI 0.213 to 0.396, p < 0.001), respectively. At six months, the differences between baseline and pacing and baseline and GTN were 0.098 mm (CI 0.014 to 0.173, p < 0.001) and 0.218 mm (CI 0.130 to 0.298, p < 0.001). The difference between baseline values at three weeks and six months was 0.061 mm (CI 0.064 to 0.176, p > 0.05).

CONCLUSIONS

In vivo flow-mediated dilation of the RA is comparable to that of pedicled LIMA. The increased dilation both at baseline and after pacing at six months represents a time-related improvement in the vasomotor function of the RA, which could have implications for its performance as a coronary conduit.

Delivery and expression of fluid shear stress-inducible promoters to the vessel wall: applications for cardiovascular gene therapy

In atherosclerosis, endothelial cells at sites of stenosis experience elevated levels of shear stress. We have constructed a series of shear stress-inducible transcription units (SITUs) expressing the luciferase reporter gene and determined their activation by fluid shear stress in transfected endothelial cells. Chimeric promoters were constructed that comprised basal transcription factor-binding sites coupled to a shear stress response element (SSRE). We have used consensus binding sites for transcription factors NF-kappaB, Ap1, Sp1, Oct1, and Egr-1/Sp1 in either the presence or absence of the previously defined "GAGACC" SSRE. The response of the promoters to shear stress was determined after transfection into human umbilical vein endothelial cells (HUVECs). After transient transfection into HUVECs, fluid shear stress activated the promoters by between two- and eightfold. The most responsive SITUs comprised an overlapping Sp1/Egr-1-binding site linked to a TATA box with (SP5) or without (SP7) the GAGACC SSRE. Instillation of SP5 DNA in vivo into the left carotid artery of rabbit and subsequent generation of a stenosis using a mechanical wire occluder caused a 10-fold upregulation of luciferase reporter gene expression at the site of vessel occlusion. These vectors show promise for therapeutic gene expression at sites of occlusive vascular disease.