Localization of nitric oxide synthase type III in the internal thoracic and radial arteries and the great saphenous vein: a comparative immunohistochemical study

Multi-Omics Profiling of Human Endothelial Cells from the Coronary Artery and Internal Thoracic Artery Reveals Molecular but Not Functional Heterogeneity

Major adverse cardiovascular events occurring upon coronary artery bypass graft surgery are typically accompanied by endothelial dysfunction. Total arterial revascularisation, which employs both left and right internal thoracic arteries instead of the saphenous vein to create a bypass, is associated with better mid- and long-term outcomes. We suggested that molecular profiles of human coronary artery endothelial cells (HCAECs) and human internal mammary artery endothelial cells (HITAECs) are coherent in terms of transcriptomic and proteomic signatures, which were then investigated by RNA sequencing and ultra-high performance liquid chromatography-mass spectrometry, respectively. Both HCAECs and HITAECs overexpressed molecules responsible for the synthesis of extracellular matrix (ECM) components, basement membrane assembly, cell-ECM adhesion, organisation of intercellular junctions, and secretion of extracellular vesicles. HCAECs were characterised by higher enrichment with molecular signatures of basement membrane construction, collagen biosynthesis and folding, and formation of intercellular junctions, whilst HITAECs were notable for augmented pro-inflammatory signaling, intensive synthesis of proteins and nitrogen compounds, and enhanced ribosome biogenesis. Despite HCAECs and HITAECs showing a certain degree of molecular heterogeneity, no specific markers at the protein level have been identified. Coherence of differentially expressed molecular categories in HCAECs and HITAECs suggests synergistic interactions between these ECs in a bypass surgery scenario.

Left Internal Mammary Artery as an Endocrine Organ: Insights Into Graft Biology and Long-term Impact Following Coronary Artery Bypass Grafting

The left internal mammary artery (LIMA) is considered the criterion standard vessel for use in coronary artery bypass grafting. In recent decades, countless studies have documented its superiority over other arterial and venous coronary artery bypass grafting conduits, although the full mechanisms for this superiority remain unknown. A growing body of literature has unveiled the importance of extracellular vesicles known as exosomes in cardiovascular signaling and various pathologic states. In this review, we briefly compare the clinical longevity of the LIMA relative to other conduits, explore the effects of varying grafting techniques on clinical and angiographic outcomes, and provide physiologic insights into graft function on a cellular and molecular level. Finally, we explore exosome signaling as it pertains to atherosclerosis in support of the LIMA as an "endocrine organ."

Effects of Remote Ischaemic Preconditioning on the Internal Thoracic Artery Nitric Oxide Synthase Isoforms in Patients Undergoing Coronary Artery Bypass Grafting

Remote ischaemic preconditioning (RIPC) is a medical procedure that consists of repeated brief periods of transient ischaemia and reperfusion of distant organs (limbs) with the ability to provide internal organ protection from ischaemia. Even though RIPC has been successfully applied in patients with myocardial infarction during coronary revascularization (surgery/percutaneous angioplasty), the underlying molecular mechanisms are yet to be clarified. Thus, our study aimed to determine the role of nitric oxide synthase (NOS) isoforms in RIPC-induced protection (3 × 5 min of forearm ischaemia with 5 min of reperfusion) of arterial graft in patients undergoing urgent coronary artery bypass grafting (CABG). We examined RIPC effects on specific expression and immunolocalization of three NOS isoforms — endothelial (eNOS), inducible (iNOS) and neuronal (nNOS) in patients’ internal thoracic artery (ITA) used as a graft. We found that the application of RIPC protocol leads to an increased protein expression of eNOS, which was further confirmed with strong eNOS immunopositivity, especially in the endothelium and smooth muscle cells of ITA. The same analysis of two other NOS isoforms, iNOS and nNOS, showed no significant differences between patients undergoing CABG with or without RIPC. Our results demonstrate RIPC-induced upregulation of eNOS in human ITA, pointing to its significance in achieving protective phenotype on a systemic level with important implications for graft patency.

The Growth Potential and Patency of Free Right Internal Thoracic Arteries Verified by Computed Tomography Angiography

BACKGROUND

The use of the left internal thoracic artery (LITA) is the gold standard in coronary artery bypass graft surgery (CABG). Multiarterial grafting for CABG is being increasingly emphasized. This study aimed to resolve the utility of the right internal thoracic artery (RITA) for multiple CABG as "free" RITA and described new evidence.

METHODS

One hundred sixty-three patients received solo CABG with bilateral internal thoracic arteries between 2005 and 2018. The RITA was used as in situ RITA, group A (n = 62), and the composite graft created with saphenous vein graft (SVG), group B (n = 101). The patency rate and graft size of the composite free RITA and SVG were examined by coronary computed tomography angiography.

RESULTS

The average number of distal anastomoses per patient was 3.4 ± 1.0 in group A, and 4.2 ± 1.1 in group B (P < .001). The sequential grafting with free RITA was in 86 patients. The patency rate of both LITA and RITA was similar in both groups. In group B, 40 patients received late computed tomography angiography at a mean of 46 months (range, 17 to 175). The late patency rate was 95.1% in LITA and 96.9% in free RITA. The diameter of free RITA increased from 2.06 ± 0.34 mm to 2.37 ± 0.23 mm (P = .036); that of in situ LITA increased from 2.08 ± 0.51 mm to 2.44 ± 0.49 mm (P = .047); and that of composite SVG decreased from 4.1 ± 0.9 mm to 2.6 ± 0.7 mm (P < .001).

CONCLUSIONS

Multiple bypass grafting can be sufficiently achieved with LITA and free RITA. The growth potential of free RITA and in situ LITA might play the important role of expected long-term patency.

Co-Culture of Primary Human Coronary Artery and Internal Thoracic Artery Endothelial Cells Results in Mutually Beneficial Paracrine Interactions

Although saphenous veins (SVs) are commonly used as conduits for coronary artery bypass grafting (CABG), internal thoracic artery (ITA) grafts have significantly higher long-term patency. As SVs and ITA endothelial cells (ECs) have a considerable level of heterogeneity, we suggested that synergistic paracrine interactions between CA and ITA ECs (HCAECs and HITAECs, respectively) may explain the increased resistance of ITA grafts and adjacent CAs to atherosclerosis and restenosis. In this study, we measured the gene and protein expression of the molecules responsible for endothelial homeostasis, pro-inflammatory response, and endothelial-to-mesenchymal transition in HCAECs co-cultured with either HITAECs or SV ECs (HSaVECs) for an ascending duration. Upon the co-culture, HCAECs and HITAECs showed augmented expression of endothelial nitric oxide synthase (eNOS) and reduced expression of endothelial-to-mesenchymal transition transcription factors Snail and Slug when compared to the HCAEC–HSaVEC model. HCAECs co-cultured with HITAECs demonstrated an upregulation of HES1, a master regulator of arterial specification, of which the expression was also exclusively induced in HSaVECs co-cultured with HCAECs, suggestive of their arterialisation. In addition, co-culture of HCAECs and HITAECs promoted the release of pro-angiogenic molecules. To conclude, co-culture of HCAECs and HITAECs results in reciprocal and beneficial paracrine interactions that might contribute to the better performance of ITA grafts upon CABG.

Preventing treatment failures in coronary artery disease: what can we learn from the biology of in-stent restenosis, vein graft failure, and internal thoracic arteries?

Coronary artery disease (CAD) remains one of the most important causes of morbidity and mortality worldwide, and the availability of percutaneous or surgical revascularization procedures significantly improves survival. However, both strategies are daunted by complications which limit long-term effectiveness. In-stent restenosis (ISR) is a major drawback for intracoronary stenting, while graft failure is the limiting factor for coronary artery bypass graft surgery (CABG), especially using veins. Conversely, internal thoracic artery (ITA) is known to maintain long-term patency in CABG. Understanding the biology and pathophysiology of ISR and vein graft failure (VGF) and mechanisms behind ITA resistance to failure is crucial to combat these complications in CAD treatment. This review intends to provide an overview of the biological mechanisms underlying stent and VGF and of the potential therapeutic strategy to prevent these complications. Interestingly, despite being different modalities of revascularization, mechanisms of failure of stent and saphenous vein grafts are very similar from the biological standpoint.

Does Bilateral Internal Mammary Artery Grafting Better Suit Patients With Diabetes? - Two Different Ways to Explore Outcomes

BACKGROUND

This analysis compared short-term mortality, sternal wound infection (SWI), and long-term survival outcomes in diabetic patients who underwent coronary artery bypass grafting (CABG) with bilateral (BIMA) vs. single (SIMA) internal mammary artery, as well as in diabetic vs. non-diabetic patients undergoing BIMA grafting.Methods and Results:Nineteen studies were included in the study, covering 21,143 different patients. Of these patients, 6,464 underwent CABG with BIMA, 10,264 underwent CAGB with SIMA, 11,584 had diabetes, and 6,717 did not. Compared with SIMA, BIMA had a significantly lower risk of in-hospital mortality (odds ratio [OR] 0.73, P=0.02), but a significantly higher risk of SWI (OR 1.30, P=0.04). However, compared with non-diabetic patients who underwent CABG with BIMA, diabetic patients with BIMA grafting did not have significantly higher risks of either mortality (OR 1.22, P=0.53) or SWI (OR 1.10, P=0.72). No significant differences were detected with different harvesting techniques. Longer term, BIMA was associated with a significantly higher rate of survival than SIMA (hazard ratio [HR] 0.76, P<0.001).

CONCLUSIONS

Results from the 2 types of comparisons indicate that BIMA is a preferable option for diabetic patients, even though it has a higher risk of infection. CABG with BIMA is also associated with a long-term survival benefit.

Saphenous vein versus right internal thoracic artery as a Y-composite graft: Five-year angiographic and clinical results of a randomized trial

OBJECTIVES

We compared the 5-year graft occlusion rates and midterm clinical outcomes of saphenous vein composite grafts with those of right internal thoracic artery composite grafts in patients who were enrolled in the SAphenous VEin versus Right Internal Thoracic Artery as a Y-Composite Graft trial.

METHODS

Of 224 eligible patients with multivessel coronary artery disease who were randomized to undergo off-pump revascularization using the saphenous vein (saphenous vein group, n = 112) or right internal thoracic artery (right internal thoracic artery group, n = 112) as Y-composite grafts based on the in situ left internal thoracic artery from September 2008 to October 2011, 219 patients (saphenous vein group, n = 109; right internal thoracic artery group, n = 110) entered the analysis. A third limb conduit to lengthen the graft limb for complete revascularization was used in 47 patients (saphenous vein group vs right internal thoracic artery group, 8 vs 39). Postoperative 5-year (61.7 ± 5.2 months) angiograms were performed in 186 patients (84.9%; saphenous vein group = 95; right internal thoracic artery group = 91). Follow-up was complete in 97.7% (214/219) of patients with a median follow-up of 80.7 months.

RESULTS

The overall graft occlusion rate was 3.6% at 5 years (3.5% in the saphenous vein group vs 3.7% in the right internal thoracic artery group, P = .910). The 5-year occlusion rate of the second limb conduits in the saphenous vein group was 4.3% and was noninferior to that of the right internal thoracic artery group (2.4%) within the 95% 2-sided confidence interval of -1.4% to 5.2% (P < .001 for noninferiority). No statistically significant differences were found in the overall survival (P = .439) and the freedom from major adverse cardiac and cerebrovascular event rates (P = .354) at 5 and 8 years between the 2 groups.

CONCLUSIONS

The saphenous vein composite grafts were noninferior to the right internal thoracic artery composite grafts in terms of 5-year graft occlusion rates and midterm clinical outcomes.

Coronary Artery Bypass Graft Versus Percutaneous Coronary Intervention

Background:

Multiple studies have compared coronary artery bypass graft (CABG) with percutaneous coronary interventions (PCI) for coronary revascularization. There is considerable evidence that adherence to medical therapy can affect the outcomes of therapeutic interventions. However, the long-term influence of compliance with recommended medical therapy on the comparative outcomes of CABG versus PCI remains to be defined.

Methods:

All non–ST-segment–elevation myocardial infarction patients undergoing coronary revascularization in an 8-hospital network were followed for up to 8 years to determine medication history and major adverse cardiac events: all-cause mortality, nonfatal myocardial infarction, and reintervention. All mortalities were checked against the Social Security Death Index. Survival curves were derived with Kaplan-Meier methods; hazard ratios were calculated with the Cox proportional hazard model; and propensity score matching was used to account for differences in patient selection.

Results:

Among the 973 CABG and 2255 PCI patients, Kaplan-Meier major adverse cardiac event–free survival curves demonstrated a significant benefit for antiplatelet, lipid-lowering, and β-blocker therapy in both the CABG and PCI groups ( P =0.001 for all 3 medications). Cox regression identified compliance with optimal medical therapy as a more powerful predictor of major adverse cardiac event–free survival than choice of therapy (hazard ratio for noncompliance=2.79; 95% confidence limits, 2.19–3.54; P <0.001; hazard ratio for PCI versus CABG=1.68, 95% confidence limits, 138–2.04; P <0.001). In propensity-matched patients, CABG outcomes were superior to PCI outcomes in patients nonadherent to optimal medical therapy ( P =0.001) but were not different in patients adherent to optimal medical therapy ( P =0.574).

Conclusions:

Regardless of coronary revascularization strategy, medication adherence has a dramatic effect on long-term outcome. Among comparable patients who adhere to optimal medical therapy, outcomes of PCI and CABG may not differ; however, among nonadherent patients, CABG affords better major adverse cardiac event–free survival. Therefore, patient compliance with medical therapy may inform clinical decision making and should be incorporated into all future comparative studies of comparative coronary revascularization strategies.

The Immunoquantification of Caveolin-1 and eNOS in Human and Rabbit Diseased Blood Vessels

In this study, caveolin-1 (cav-1), an inhibitor of endothelial nitric oxide synthase (eNOS), was semi-quantified in diseased human and rabbit blood vessels. New Zealand White rabbits were fed, for 12 weeks, a high methionine diet (to induce intimal hyperplasia), 0.5% cholesterol diet, a normal diet, or the combination of both experimental diets. Excess segments of human internal mammary arteries (IMA) and radial arteries (RA) were obtained from patients undergoing coronary artery bypass surgery. eNOS and cav-1 were localized throughout both human and rabbit vessels. In rabbit arteries, eNOS was significantly increased in the endothelium overlying intimal thickening and atherosclerotic plaques compared with the adjacent endothelium overlying normal media. Interestingly, the endothelial cav-1:eNOS ratio increased 5-fold only in endothelium overlying plaques but decreased in endothelium overlying vessels with neo-intimal thickening. In human tissue, there was no difference between RA and IMA eNOS immunoreactivity in endothelium, intima, or media; however, RA endothelial, intimal, and medial cav-1 immunoreactivity increased 4-fold ( p,<0.02), 8-fold ( p<0.001), and 4-fold ( p<0.004), respectively, compared with IMA. Furthermore, the cav-1:eNOS immunostaining ratio in the media correlated with intimal thickening (r2 = 0.5). Our results suggest a close relationship between increased cav-1 and diseased blood vessels.

Multiple arterial grafting for coronary revascularization: "A guide for the perplexed"

The surgical literature abounds with articles extolling the benefits of arterial grafting for patients with advanced coronary artery disease in need of surgical revascularization. However, examination of clinical performance demonstrates that extensive use of arterial grafting is highly selective and generally uncommon. Rather than to merely repeat multiple excellent recent literature reviews, the goal herein is to provide the reader with a guide to the evaluation of the current literature as well as to suggest fruitful areas for further research. More circumspect understanding of the strengths and weaknesses of our current knowledge base will not only help to explain the current apparent disparity between theory and practice but will hopefully inform future decision-making and patient care.

Comparison of perfusion and thickening between vein and right internal thoracic artery composite grafts from a randomized trial substudy

BACKGROUND

Improvements in myocardial perfusion and thickening were compared in coronary artery bypass grafting patients who received saphenous vein (SV) Y-composite grafts versus those who received right internal thoracic artery ([R]ITA) Y-composite grafts.

METHODS

Of the 224 patients enrolled in a randomized clinical trial, 116 patients (SV group, n = 65; RITA group, n = 51) in whom myocardial single-photon-emission computed tomography was performed preoperatively, and at 3 months and 1 year postoperatively, were retrospectively studied. A 20-segment model was adopted, and a total of 792 ischemic myocardial segments (SV group, n = 443; RITA group, n = 349) were analyzed. The reversibility score (rest minus stress perfusion value) as an indicator of ischemic myocardium, and Z-values for segmental myocardial thickening, were calculated.

RESULTS

Compared with preoperative values, both myocardial perfusion and segmental myocardial thickening had improved significantly at 3 months and 1 year postoperatively (reversibility scores [mean ± SD] were, respectively: 13.5 ± 8.0 vs 5.8 ± 6.2 and 5.1 ± 6.2, P < .001; Z-values were -1.13 ± 1.53 vs -0.62 ± 1.40 and -0.67 ± 1.35, P < .001). Mixed-effect model analyses showed no differences in improvements in myocardial perfusion and segmental myocardial thickening between the 2 groups 1 year after revascularization. Separate analysis demonstrated less improvement of myocardial perfusion in the right coronary artery territory of the RITA group than the SV group, with marginal significance (P = .056).

CONCLUSIONS

Improvements in myocardial perfusion and segmental myocardial thickening were similar between the 2 groups at 1 year after revascularization. The SV, versus the right ITA, composite graft may be more beneficial in perfusion improvement of the right coronary artery territory.

Graft pathology at the time of harvest: impact on long-term survival

Objective

This study aims to present the graft pathology at the time of harvest and its impact on long-term survival.

Methods

The remnants of the bypass grafts from 66 consecutive patients with coronary artery disease receiving a coronary artery bypass grafting were investigated pathologically, and pertinent predictive risk factors and survival were analyzed.

Results

Medial degenerative changes with or without intimal proliferation were present in 36.8%, 37.8% and 35.6% of left internal mammary artery (IMA), radial artery and saphenous vein grafts. There were 2 (3.0%) hospital deaths and 9 (14.1%) late deaths. Multinomial logistic regression revealed left IMA pathological changes, dyslipidemia, history of percutaneous transluminal coronary angioplasty/stent deployment and Y-graft were significant predictive risk factors negatively influencing the patients’ long-term survival. Kaplan-Meier survival analysis revealed that the long-term survival of patients with left IMA pathological changes were significantly reduced compared with those without (74.1% vs. 91.4%, P=0.002); whereas no differences were noted in long-term survivals between patients with and without pathological changes of the radial arterial or saphenous vein grafts.

Conclusion

Pathological changes may be seen in the bypass graft at the time of harvest. The subtle ultrastructural modifications and the expressions of vascular tone regulators might be responsible for late graft patency. The pathological changes of the left IMA at the time of harvest rather than those of the radial artery or saphenous vein graft affect significantly longterm survival. Non-traumatic maneuver of left IMA harvest, well-controlled dyslipidemia and avoidance of using composite grafts can be helpful in maintaining the architecture of the grafts.

Myocardial revascularization with both internal thoracic arteries 25 years after delayed repair for aortic coarctation

Aortic coarctation has been reported to cause alterations in the internal thoracic arteries that make these vessels unsuitable to be used as grafts for myocardial revascularization, especially if coarctation repair was performed in adulthood. This is the first reported bilateral internal thoracic grafting for myocardial revascularization in a patient who had undergone aortic coarctation repair 25 years earlier.

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.

Role of surgical revascularization in diabetic patients with coronary artery disease

Diabetes is a well-known risk factor for morbidity and mortality associated with coronary artery disease. Currently, diabetics represent approximately a quarter of patients requiring coronary revascularization in the USA. The purpose of this article is to review and analyze the available data in surgical revascularization of diabetic patients with coronary artery disease. The review will also examine new developments in myocardial revascularization and assess their probable impact on the long-term outcome of diabetic patients.

The effect of nebivolol on internal mammary artery blood flow during coronary artery bypass graft surgery

Background:

During coronary artery bypass grafting (CABG), one of the most important complications related to the internal mammary artery (IMA) is perioperative spasm. Nebivolol causes endothelium-dependent vascular relaxation by increasing nitric oxide (NO) release and prevents endothelial dysfunction in long-term use. In our study, we measured the effect of a third generation beta blocker, nebivolol, on the flow dynamics of IMA grafts.

Methods:

We recruited 90 hypertensive patients undergoing isolated CABG operation, who were divided into three groups and each group included 30 patients: Group 1 patients were under antihypertensive treatment other than beta-blockers (angiontensin-converting enzyme [ACE] inhibitors, calcium channel blockers or diuretics; monotherapy or combination therapy), Group 2 received metoprolol (50 mg/day) and Group 3 received nebivolol (5 mg/day). These antihypertensive therapies were given for at least one week before the operation and continued thereafter. IMA blood flow volume was measured for one minute just before cardiopulmonary bypass (measurement A) and before left internal mammary artery (LIMA)-left anterior descending (LAD) artery anastomosis (measurement B) in the three groups. Cardiac output measurements were also achieved simultaneously.

Results:

The measurement A results were 56.3 ± 36.2, 54.6 ± 28.1 and 66.8 ± 34.2 mL/min in Groups 1, 2 and 3, respectively (p<0.05). The measurement B results were 78.3 ± 29.6, 80 ± 28.8 and 91.1 ± 40.8 mL/min in Groups 1, 2 and 3 (p<0.05), respectively. There were no differences in cardiac outputs among the groups; 5.2 ± 1.4, 5.0 ± 1.6 and 5.3 ± 1.1 L/min (p>0.05). While the cardiac outputs were similar within the three groups, the IMA free flow volume was higher in the nebivolol group after local papaverine use.

Conclusion:

Nebivolol might represent a good choice in hypertensive patients undergoing cardiac surgery by preventing perioperative myocardial hypoperfusion which increases early morbidity and mortality.

Long-term morphofunctional remodeling of internal thoracic artery grafts: a frequency-domain optical coherence tomography study

BACKGROUND

Internal thoracic arteries (ITAs) are frequently anastomosed to the coronary circulation for bypass grafting. The purpose of this research was to investigate in vivo the long-term morphofunctional changes of ITAs after their use as coronary artery bypass conduits, by comparing the morphological features and vasoreactivity of the grafted left ITA (LITA) with the native, nonharvested right ITA (RITA) in the same patient.

METHODS AND RESULTS

At least 10 years after surgery, in 10 patients, LITA graft and nonharvested RITA were assessed by quantitative angiography and frequency-domain optical tomography. Endothelium-dependent and independent vasodilation was tested by selective infusion of acetylcholine and isosorbide dinitrate. Quantitative angiography showed that baseline mean diameter of LITA graft was significantly smaller than that of RITA (2.59 mm [2.29-3.04] versus 3.05 mm [2.75-3.32]; P=0.01). LITA showed a significant intimal thickening (P=0.05) and a nonsignificant medial thinning (P=0.22) compared with RITA, leading to an increased intima-media ratio (intima-media ratio, 0.72 [0.53-0.91] versus 0.23 [0.12-0.38]; P=0.02). The intima-media ratio correlated inversely with the vasodilatatory response in RITA (r=-0.68, P=0.03 for acetylcholine and r=-0.62, P=0.05 for isosorbide dinitrate) but not in LITA (r=-0.18, P=0.63 for acetylcholine and r=-0.11, P=0.75 for isosorbide dinitrate).

CONCLUSIONS

Ten years after implantation to the coronary circulation, LITA grafts show intimal thickening, increased intima/media ratio, and maintained endothelium-derived vasodilation. These changes are likely to be an adaptive answer to the different flow dynamics typical of coronary circulation.

Bilateral internal mammary artery grafting enhances survival in diabetic patients: a 30-year follow-up of propensity score-matched cohorts

BACKGROUND

The prevalence of diabetes mellitus is increasing at an unprecedented rate, affecting nearly 8% of the population. Previous studies have demonstrated a potential benefit for surgical over interventional revascularization in this group of patients. Similarly, studies have shown the superiority of bilateral internal mammary artery (BIMA) grafting over single internal mammary artery (SIMA) grafting in select populations. However, concerns about sternal wound infection have discouraged the use of BIMA grafting in diabetics. Therefore, we studied the long-term results of BIMA versus SIMA grafting in a large population of diabetic patients in whom BIMA grafting was broadly applied.

METHODS AND RESULTS

Between February 1972 and May 1994, 1107 consecutive diabetic patients underwent coronary artery bypass grafting with either SIMA (n=646) or BIMA (n=461) grafting. Optimal matching with the propensity score was used to create matched SIMA (n=414) and BIMA (n=414) cohorts. Cross-sectional follow-up (6 weeks to 30.1 years; mean, 8.9 years) determined long-term survival. There was no difference in operative mortality, sternal wound infection, or total complications between matched SIMA and BIMA groups (operative mortality, 10 of 414 [2.4%] versus 13 of 414 [3.1%]; P=0.279; sternal wound infection, 7 of 414 [1.7%] versus 13 of 414 [3.1%]; P=0.179); total complications, 71 of 414 [17.1%] versus 71 of 414 [17.1%]; P=1.000). Late survival was significantly enhanced with the use of BIMA grafting (median survival: SIMA, 9.8 years versus BIMA, 13.1 years; P=0.001). Use of BIMA was found to be associated with late survival on Cox regression (P=0.003).

CONCLUSION

Compared with SIMA grafting, BIMA grafting in propensity score-matched patients provides diabetics with enhanced survival without any increase in perioperative morbidity or mortality.

Oxidative stress in hypertensive patients induces an increased contractility in vein grafts independent of endothelial function

Objective. To evaluate the impact of oxidative stress on vascular reactivity to vasoconstrictors and on nitric oxide (NO) bioavailability in saphenous vein (SV) graft with endothelial dysfunction from hypertensive patients (HT). Methods. Endothelial function, vascular reactivity, oxidative state, nitrites and NO release were studied in isolated SV rings from HT and normotensive patients (NT). Only rings with endothelial dysfunction were used. Results. HT rings presented a hyperreactivity to vasoconstrictors that was reverted by diphenylene iodonium (DPI). In NT, no effect of DPI was obtained, but Nω-nitro-_L-arginine methyl ester (L-NAME) increased the contractile response. NO was present in SV rings without endothelial function. Nitrites were higher in NT than in HT (1066.1 ± 86.3 pmol/mg; n = 11 versus 487.8 ± 51.6; n = 23; P < 0.01) and inhibited by nNOS inhibitor. L-arginine reversed this effect. Antioxidant agents increased nitrites and NO contents only in HT. The anti-nNOS-stained area by immunohistochemistry was higher in NT than HT. HT showed an elevation of oxidative state. Conclusions. Extraendothelial NO counter-regulates contractility in SV. However, this action could be altered in hypertensive situations by an increased oxidative stress or a decreased ability of nNOS to produce NO. Further studies should be performed to evaluate the implication of these results in graft patency rates.

Reactive oxygen species mediate functional differences in human radial and internal thoracic arteries from smokers

OBJECTIVE

Smoking not only increases the risk that coronary heart disease will develop but also morbidity and mortality in patients with known coronary atherosclerosis and after coronary artery bypass grafting. Excessive generation of reactive oxygen species (ROS) has been implicated as the final common pathway for the development of endothelial dysfunction in various cardiovascular risk factors. This study assessed the influence of smoking on two different human arteries routinely used as coronary artery bypass graft conduits.

METHODS

Isometric tension was recorded on discarded segments of human left internal thoracic artery (ITA) and the radial artery (RA) from smokers and nonsmokers.

RESULTS

The contractile response to endothelin-1 was significantly stronger in arteries from smokers than in those from nonsmokers. By contrast, endothelium-dependent relaxant responses to acetylcholine were attenuated in RA rings but enhanced in ITA rings from smokers. In additional experiments, 5-(&6)-chloromethyl-2'-7'-dichlorodihydro-fluorescein diacetate (DCDHF) was used to photochemically detect ROS by confocal imaging of intact ITA and RA. Enhanced production of ROS was induced by exposure of tissues to 28 degrees C. While during exposure to 28 degrees C, basal fluorescence emission was unchanged in ITA rings, it increased significantly in RA rings, indicating enhanced formation of ROS in this peripheral artery.

CONCLUSIONS

Data suggest that smoking induces endothelial dysfunction by increasing vascular ROS production. Different levels of endogenous antioxidant enzyme activities and the degree of atherosclerotic changes might modulate physiologic and pharmacologic vasoreactivity and be responsible for decreased graft patency of RA compared with ITA conduits, especially in active smokers.

Expression of inducible nitric oxide synthase in conduits used in patients with diabetes mellitus undergoing coronary revascularization

BACKGROUND

Expression of inducible nitric oxide synthase (iNOS) is a marker of vascular inflammation which can result in thrombosis and atherosclerosis. This study was undertaken to examine the difference in iNOS expression in the internal mammary artery (IMA) and saphenous veins (SVs) of patients with diabetes mellitus undergoing coronary artery bypass graft (CABG) surgery using both qualitative and quantitative methodology.

METHODS

Segments of IMA and SV harvested in 100 diabetic patients with diabetes mellitus undergoing CABG surgery were fixed in formalin and immunostained to detect the presence of iNOS. Sections were graded using a qualitative score (0 = absence of iNOS expression to 3 = extensive expression of iNOS) and a quantitative computer-aided image analysis (area of staining/area of endothelium). Linear regression analyses were performed to assess the association of the degree of iNOS expression in both the IMA and SV with the type of diabetes control (insulin, oral, diet), and the serum levels of HbAlc, glucose, free fatty acids (ffa), C-reactive protein (CRP), and low-density liproprotein (LDL) at the time of conduit harvest.

RESULTS

The degree of iNOS expression was significantly lower in the IMA compared to the SV by both qualitative (0.88 +/- 0.74 SD IMA vs. 1.38 +/- 0.68 SV; p < 0.0001) and quantitative (11.76 +/- 3.34% IMA vs. 17.10 +/- 2.54% SV; p = 0.01) methods. The Spearman rank correlation analysis showed a highly statistically significant association between the two methodologies (p < 0.0001). There was no correlation between iNOS expression in either the IMA or SV and the type of diabetes control, or levels of HA1c, glucose, ffa, and CRP. However, there was a significant (p = 0.04) correlation between LDL and iNOS expression in the SV graft, but not the IMA.

CONCLUSIONS

iNOS expression is significantly decreased in the IMA compared to the SV in patients with diabetes mellitus undergoing CABG surgery. The degree of iNOS expression is unrelated to the level of glycemic control at the time of conduit harvest, but is associated with serum LDL levels in the SV, but not in the IMA grafts.

IMMUNOHISTOCHEMICAL LOCALIZATION OF ENDOTHELIAL ISOFORM (eNOS) IN HUMAN CEREBRAL ARTERIES AND THE AORTA

The common carotid, vertebral, posterior cerebral arteries, and the aorta were studied in the human in terms of its eNOS expression. In around 10 weeks of gestation, the developing intima began to express notable eNOS. In the adult, the positive eNOS sites were in the endothelial cells and the tunica media where the smooth muscles were. In the vessels with athrosclerotic changes, eNOS was down regulated in the endothelial layer and most of the tunica media but was significantly upregulated in the tunica media around the lesion. The protein changes are related to the onset of the athrosclerotic diseases.

Internal Mammary Artery Grafts Reactivity in Hypertensive Patients: Role of Stretching in Extraendothelial Nitric Oxide

BACKGROUND

The internal mammary artery (IMA) used in bypass coronary surgery remains efficient for a longer time than other grafts, such as saphenous veins; however, its biological characteristics are incompletely defined.

OBJECTIVE

To compare in IMA grafts from hypertensive (HT) and normotensive (NT) patients the presence of endothelium and their functionability, the response to passive stretching and basal tone, the reactivity to exogenous vasoconstrictors, the role of stretching in NO release, and the possible extraendothelial NO source.

METHODS AND RESULTS

IMA rings contractility, presence of endothelium, and nitrite release were studied. An endothelial dysfunction associated with hypertension was found. IMA rings from HT had an impaired response to passive stretching, resulting in a decreased relaxation. All IMA grafts had an increased basal tone demonstrated by relaxation to SNP; however, a lesser response was found in HT. Interestingly, it was demonstrated that NO release was present in IMA grafts, despite an endothelial dysfunction and that stretching increased NO release. This effect was inhibited by Ca2+ -free media, L-NAME and a specific neuronal NO synthase (nNOS) inhibitor. Furthermore, the demonstration of the presence of nNOS in smooth muscle cells by immunohistochemistry supports a role of extraendothelial NO.

CONCLUSION

We demonstrate the impact of hypertension in IMA grafts producing increased endothelial dysfunction, reduced response to passive stretching, increased basal tone, and impaired responsiveness to exogenous vasoconstrictors and NO release. A specific role of stretching in extraendothelial NO release was demonstrated, which may have an important role in the outcome of IMA grafts due to the protective actions of NO, even in the absence of the endothelium.

Cardiovascular actions of insulin

Insulin has important vascular actions to stimulate production of nitric oxide from endothelium. This leads to capillary recruitment, vasodilation, increased blood flow, and subsequent augmentation of glucose disposal in classical insulin target tissues (e.g., skeletal muscle). Phosphatidylinositol 3-kinase-dependent insulin-signaling pathways regulating endothelial production of nitric oxide share striking parallels with metabolic insulin-signaling pathways. Distinct MAPK-dependent insulin-signaling pathways (largely unrelated to metabolic actions of insulin) regulate secretion of the vasoconstrictor endothelin-1 from endothelium. These and other cardiovascular actions of insulin contribute to coupling metabolic and hemodynamic homeostasis under healthy conditions. Cardiovascular diseases are the leading cause of morbidity and mortality in insulin-resistant individuals. Insulin resistance is typically defined as decreased sensitivity and/or responsiveness to metabolic actions of insulin. This cardinal feature of diabetes, obesity, and dyslipidemia is also a prominent component of hypertension, coronary heart disease, and atherosclerosis that are all characterized by endothelial dysfunction. Conversely, endothelial dysfunction is often present in metabolic diseases. Insulin resistance is characterized by pathway-specific impairment in phosphatidylinositol 3-kinase-dependent signaling that in vascular endothelium contributes to a reciprocal relationship between insulin resistance and endothelial dysfunction. The clinical relevance of this coupling is highlighted by the findings that specific therapeutic interventions targeting insulin resistance often also ameliorate endothelial dysfunction (and vice versa). In this review, we discuss molecular mechanisms underlying cardiovascular actions of insulin, the reciprocal relationships between insulin resistance and endothelial dysfunction, and implications for developing beneficial therapeutic strategies that simultaneously target metabolic and cardiovascular diseases.

Functional effects of nitric oxide-releasing aspirin on vein conduits of diabetic patients undergoing CABG

BACKGROUND

Type 2 diabetes mellitus (DM) is known to negatively affect biological properties of venous vasculature, and, particularly, to reduce endothelium-derived nitric oxide release. This condition might influence venous graft function following coronary artery bypass surgery (CABG). The aim of this study was to evaluate the functional effects of a NO-releasing aspirin (NORA) on vein grafts (VG) of diabetics and control patients undergoing elective CABG.

METHODS

In 40 consecutive ischemic heart disease patients, the effects of NORA were tested on segments of saphenous vein conduits harvested during elective CABG. Twenty patients had type-2 DM (mean age 69+/-2), whereas 20 patients had no DM (NDM) and represented the control group (mean age 67+/-4). Functional responses were tested by exposing VGs to NORA and to standard vasoactive agents in an organ-bath preparation. Histological features of VGs were also assessed by light and electronic microscopy.

RESULTS

Significant impairment of endothelial-dependent vasodilation (acetylcholine induced) was documented in VGs of DM subjects. NORA induced a significant and comparable vascular relaxation in all venous segments of NDM and DM patients (56+/-12% of maximal relaxation vs 61+/-11% in the control group, respectively). Histology showed variable extent of vascular layer and cellular abnormalities in VGs of diabetics (intimal hyperplasia, calcific deposition, endothelial cell degeneration) likely responsible of the endothelial functional impairment, whereas control group VG showed preserved structures.

CONCLUSIONS

This preliminary study confirms the impairment of endothelium-dependent vasodilative property of VGs in DM patients. It also indicates that NORA effectively induces vasodilation of VGs which was effective also in DM patients thereby representing a promising therapy for diabetics undergoing CABG with the use of VGs, although further studies are mandatory to conclusively assess the safety and benefits of this pharmacological agent.

Intraoperative and Histochemical Comparison of the Skeletonized and Pedicled Internal Thoracic Artery

BACKGROUND

Skeletonization of the internal thoracic artery (ITA) has advantages, but the variation of ITA preparation may be traumatic for the arterial wall. We sought to compare intraoperative results and endothelial nitric oxide synthase (e-NOS) expression on the vessel wall after left ITA harvesting with skeletonization and the conventional technique.

METHODS

A prospective evaluation of 84 consecutive patients undergoing coronary artery bypass grafting was performed: 40 patients with skeletonized and 44 patients with pedicled left ITA. The lengths of ITA and free ITA blood flow were measured. Distal ITA segments were analyzed histopathologically and stained by antibodies against e-NOS.

RESULTS

In the skeletonized group, the length of the ITA were significantly longer than in the pedicled group (15.7 +/- 0.4 cm versus 19.0 +/- 0.6 cm; P = .001). Also, the free-flow capacity of the ITA was significantly higher than in the pedicled group (62.4 +/- 4.8 mL/min versus 88.6 +/- 6.9 mL/min; P = .001). e-NOS expressions on endothelial cells were similar between the groups. Dense e-NOS immunostaining was observed in vaso vasorum of the adventitia in the pedicled group. However, there was not any e-NOS immunostaining in vaso vasorum of the adventitia in the skeletonized group.

CONCLUSIONS

Although skeletonization of the ITA is a more technically demanding procedure, it provides some advantages such as increased available graft length and reduced sternal devascularization. This technique did not have any detrimental effects on the endothelial cell lining and e-NOS expressions on the endothelial layer. To reach a definitive judgment for using skeletonized ITA, we need information about the long-term angiographic patency rates.

Expression of neuronal nitric oxide synthase in the internal thoracic artery and saphenous vein

OBJECTIVES

Endothelial nitric oxide synthase (type III) generates nitric oxide, which dilates blood vessels. Recently, it was discovered that arterial smooth muscle cells express neuronal nitric oxide synthase (type I). The purpose of this study was to determine the relative amounts of neuronal nitric oxide synthase in the human internal thoracic artery and saphenous vein.

METHODS

Remainder segments of internal thoracic arteries and saphenous veins were obtained from 45 patients during coronary artery bypass grafting. Western blotting used specific antibodies against the 3 isoforms of human nitric oxide synthase and beta-actin (for normalization) to measure the relative amounts of the 3 isoforms of nitric oxide synthase proteins in vessel specimens. Immunohistochemistry was used to localize the 3 proteins in specific cells.

RESULTS

Western blotting detected all 3 isoforms of nitric oxide synthase in the human internal thoracic artery. The band density (normalized to beta-actin) of neuronal nitric oxide synthase was not significantly different from the band density of endothelial nitric oxide synthase. The amounts of neuronal nitric oxide synthase in arteries and veins were equal. Immunohistochemistry showed that the highest expression of endothelial nitric oxide synthase was in endothelial cells, but some expression was also seen in smooth muscle cells. Most of the neuronal nitric oxide synthase was in smooth muscle cells. The location and relative amounts of inducible nitric oxide synthase were variable.

CONCLUSIONS

Neuronal nitric oxide synthase is expressed in the vascular smooth muscle of patients undergoing bypass, and the amount in the internal thoracic artery is the same as in the saphenous vein.

Harvesting the saphenous vein with surrounding tissue for CABG provides long-term graft patency comparable to the left internal thoracic artery: results of a randomized longitudinal trial

OBJECTIVE

Conventional harvesting of the saphenous vein in coronary artery bypass surgery produces vessel damage that contributes to graft failure. A novel "no touch" technique provides high short- and long-term patency rates.

METHOD

This randomized longitudinal trial compares graft patency of two patient groups undergoing coronary artery bypass surgery. Conventional: 52 patients had their veins stripped, distended, and stored in saline solution. No-touch: 52 patients had veins removed with surrounding tissue, not distended, and stored in heparinized blood. Angiographic assessment was performed at mean time 18 months after the operation in 46 patients in the conventional group and 45 patients in the no-touch group and repeated at mean time 8.5 years in 37 patients from both groups.

RESULTS

The distribution of the grafts to the recipient coronary arteries regarding their size and quality was similar in both groups. The angiographic assessment at 18 months postoperatively showed 89% conventional versus 95% no-touch grafts were patent. Repeated angiography at 8.5 years showed a patency rate for the conventional group of 76% and 90% for the no-touch group (P = .01). The multivariate analysis showed that the most important surgical factors for graft patency were the technique of harvesting (odds ratio= 3.7, P = .007) for the no-touch versus the conventional technique and the vein quality before implantation (odds ratio = 3.2, P = .007) for veins that were of good quality. By comparison the patency of the thoracic artery grafts was 90%.

CONCLUSION

Harvesting the saphenous vein with surrounding tissue provides high short- and long-term patency rates comparable to the left internal thoracic artery.

Hypoxia induces a functionally significant and translationally efficient neuronal NO synthase mRNA variant

We tested the hypothesis that induction of neuronal NO synthase (nNOS) impairs vascular smooth muscle contractility after hypoxia. nNOS protein was increased in aorta, mesenteric arterioles, pulmonary arteries, brain, and diaphragm from rats exposed to 8% O2 for 48 hours and in human aortic SMCs after hypoxic incubation (1% O2). Ca-dependent NO synthase activity was increased in endothelium-denuded aortic segments from hypoxia-exposed rats. N-nitro-L-arginine methyl ester enhanced the contractile responses of endothelium-denuded aortic rings and mesenteric arterioles from hypoxia-exposed but not normoxic rats (P < 0.05). The hypoxia-inducible mRNA transcript expressed by human cells was found to contain a novel 5'-untranslated region, consistent with activation of transcription in the genomic region contiguous with exon 2. Translational efficiency of this transcript is markedly increased compared with previously described human nNOS mRNAs. Transgenic mice possessing a lacZ reporter construct under control of these genomic sequences demonstrated expression of the construct after exposure to hypoxia (8% O2, 48 hours) in the aorta, mesenteric arterioles, renal papilla, and brain. These results reveal a novel human nNOS promoter that confers the ability to rapidly upregulate nNOS expression in response to hypoxia with a functionally significant effect on vascular smooth muscle contraction.

Radial artery grafting

After its recent reintroduction in coronary surgery the radial artery is gaining wide acceptance as complementary arterial conduits for surgical myocardial revascularization. The main technical aspects of radial artery harvesting, the biological and vasoactive characteristics of radial artery grafts as well as the mid- to long-term angiographic results and the role of the antispatic therapy are reviewed.

The induction of heme oxygenase 1 decreases contractility in human internal thoracic artery and radial artery grafts

OBJECTIVE

Spasm remains a potential problem encountered during the use of arterial grafts in coronary artery bypass surgery. Heme oxygenase plays a role in the control of arterial vasoreactivity. Heme oxygenase exists in 2 constitutive isoforms (heme oxygenase 2 and 3) and an inducible isoform (heme oxygenase 1). The aim of our study was to induce heme oxygenase 1 by using hemin in human internal thoracic and radial arteries and to evaluate the effect of this induction on the contractility of these arterial grafts.

METHODS

Segments of human arterial grafts obtained from patients undergoing isolated coronary artery bypass surgery were incubated in organ chambers for 4 hours in the presence of 10(-4) mol/L hemin. Concentration-response curves to norepinephrine were obtained in control and hemin-treated arterial rings. Heme oxygenase 1 expression was evaluated by using enzyme-linked immunosorbent assays and immunohistochemical staining.

RESULTS

The contractility of the arterial rings to norepinephrine was significantly reduced after incubation with hemin. Zinc protoporphyrin (an inhibitor of heme oxygenase) reversed the effect of hemin, whereas the inhibitor of nitric oxide synthase had no effect. The inhibitor of soluble guanylate cyclase blocked the decrease in contractility induced by hemin. Immunohistochemical staining revealed a large expression of heme oxygenase 1 in all vascular layers of hemin-treated internal thoracic artery and radial artery rings. Enzyme-linked immunosorbent assay studies showed a significant increase in heme oxygenase 1 levels in hemin-treated internal thoracic artery and radial artery rings.

CONCLUSION

Hemin caused in vitro induction of heme oxygenase 1 in human internal thoracic artery and radial artery grafts. This induction resulted in a reduced contractility to norepinephrine, partially through the cyclic guanosine monophosphate-dependent pathway. This effect was independent from nitric oxide synthesis.

An in situ evidence for autocrine function of NO in the vasculature

The concept of endothelium derived relaxing factor (EDRF) implies that nitric oxide (NO) generated by NO synthase in the endothelium diffuses to the underlying vascular smooth muscle cells (VSMC) modulating thereby vascular tone. VSMC were regarded as passive recipients of NO from endothelial cells. However, this paradigm of a paracrine function of NO became currently subject to considerable debate. To address this issue, we examined the localization of enzymes engaged in l-arginine-NO-cGMP signaling in the rat blood vessels. Employing multiple immunocytochemical labeling complemented with signal amplification, electron microscopy, Western blotting, and RT-PCR, we found that NO synthase was differentially expressed in blood vessels depending on the blood vessel type. Moreover, the expression pattern of NO synthase in VSMC showed striking parallels with arginase and soluble guanylyl cyclase. Our findings challenge the commonly accepted view that the expression of NO synthase is restricted to vascular endothelial cells and lends further support to an alternative mechanism, by which constitutive local NOS expression in VSMC may modulate vascular functions in an endothelium-independent manner. Moreover, the co-expression of enzymes engaged in l-arginine-NO-cGMP signaling (NO synthase, arginase, and soluble guanylyl cyclase) in VSMC is indicative of an autocrine fashion of NO signaling in the vasculature in addition to the paracrine role of NO generated in the endothelium.

Histamine H1 and H2 receptor–mediated vasoreactivity of human internal thoracic and radial arteries

BACKGROUND

Although internal thoracic arteries (ITAs) and radial arteries (RAs) have been shown to have similar patency, RAs tend to be more vasospastic postoperatively compared with ITAs. Therefore, the purpose of this study was to examine the effect of histamine subclass 1 (H1) receptors and histamine subclass 2 (H2) receptors on vasoreactivity in human ITAs and RAs.

METHODS

Vessels were obtained from coronary artery bypass grafting patients. Human arterial rings (2 mm) were mounted in tissue baths, and baseline contractility was determined. Histamine concentration response curves (10(-9)-10(-3) mol/L) were performed in the absence or presence of diphenhydramine (H1 antagonist, 10(-4) mol/L) or famotidine (H2 antagonist, 10(-4) mol/L). Comparison of curves was performed by 2-way analysis of variance with repeated measures and a Bonferroni post-t test.

RESULTS

Maximal contraction to histamine was significantly greater in RA (8.3 +/- 0.8 g, n = 6) than in ITA (2.9 +/- 0.3, n = 6), (P < .05). However, there was no difference in sensitivity. Histamine-mediated responses of both RA and ITA were blocked by pre-exposure to H1 antagonist, whereas an H2 antagonist only partially inhibited RA responses while blocking most of the ITA response to histamine.

CONCLUSION

These studies suggest that H1 receptors alone cause contraction in RA but not in ITA, which may have potential linkage to patency and vasospasm. Further studies are necessary to identify the exact role of H2 receptors in ITA.