Homocysteine impairs coronary microvascular dilator function in humans

OBJECTIVES: We sought to use positron emission tomography (PET) to test the hypothesis that hyperhomocysteinemia adversely effects coronary microvascular dilator function. BACKGROUND: Hyperhomocysteinemia is associated with abnormal endothelium-dependent vasodilation in peripheral human arteries. However, its effect on the coronary circulation is not known. METHODS: Eighteen healthy humans, age 24 to 56 years, were enrolled in a double-blind, crossover trial. Basal and adenosine-stimulated myocardial blood flow (MBF) was determined by PET: after ingestion of placebo and after methionine-induced hyperhomocysteinemia. Further, brachial ultrasonography was used to assess flow-mediated vasodilation. Additionally, to assess the role of nitric oxide (NO) in adenosine-mediated vasodilation, the MBF response to adenosine was measured in the presence and absence of the NO synthase antagonist NG-monomethyl-l-arginine (l-NMMA) (0.3 mg/kg/min intravenously). RESULTS: Hyperhomocysteinemia resulted in a reduction in the MBF dose-response curve to adenosine (p < 0.05). This was most apparent with low dose adenosine, where MBF augmentation was significantly blunted during hyperhomocysteinemia (1.06 +/- 1.00 ml/min/g vs. 0.58 +/- 0.78 ml/min/g, placebo vs. methionine, p < 0.05). Similarly, flow-mediated brachial artery vasodilation was impaired during hyperhomocysteinemia (4.4 +/- 2.6% vs. 2.6 +/- 2.3%, placebo vs. methionine, p < 0.05). In a separate series of experiments, MBF during adenosine was reduced in the presence of l-NMMA (p < 0.05 analysis of variance). This was most apparent at the low dose of adenosine, where MBF response to adenosine was blunted in the presence of l-NMMA (2.08 +/- 1.34 ml/min/g vs. 1.48 +/- 1.32 ml/min/g, placebo vs. l-NMMA, p < 0.05). CONCLUSION: The data, therefore, support the hypothesis that acute hyperhomocysteinemia impairs microvascular dilation in the human coronary circulation as a result of reduced NO bioavailability.     

Aprotinin impairs coronary endothelial function and down-regulates endothelial NOS in rat coronary microvascular endothelial cells

OBJECTIVE: The non-specific serine protease inhibitor aprotinin is currently used to reduce blood loss and the need for blood transfusion after cardiopulmonary bypass. We have recently reported that aprotinin impairs endothelium-dependent but not endothelium-independent relaxations in rat thoracic aortic rings due to its inhibitory effect on endothelial nitric oxide (NO) production. In light of these findings, the current study was designed to investigate the effects of aprotinin on coronary endothelial function in isolated rat hearts and on the expression of endothelial NO synthase (eNOS) in cultured rat coronary microvascular endothelial cells (CMEC). METHODS: Hearts obtained from Sprague-Dawley rats were perfused on a constant flow Langendorff isolated heart system and coronary perfusion pressure and cardiac parameters were recorded. The coronary relaxant responses to bolus infusions of bradykinin (BK) and sodium nitroprusside (SNP) were recorded in the absence and presence of aprotinin. Total RNA and protein samples were extracted from CMEC incubated with aprotinin or the vehicle, 0.9% NaCl. RT-PCR-Southern blotting and Western analyses were carried out to assess eNOS mRNA and protein levels, respectively. RESULTS: Aprotinin (125 and 250 kIU/ml) increased coronary perfusion pressure without changing the heart rate and cardiac contractility. Aprotinin inhibited BK-induced coronary vasodilatation at 250 kIU/ml, but not at 125 kIU/ml concentrations. The relaxant response to SNP did not change in response to either concentration of the drug. Incubation of CMEC with aprotinin down-regulated eNOS mRNA and protein at 250 kIU/ml, but not at 125 kIU/ml concentration. CONCLUSION: These data suggest that aprotinin selectively inhibits NO synthesis at higher doses (> or = 250 kIU/ml) and therefore impairs endothelium-dependent coronary vascular tone. This effect of the drug may contribute to its 'blood-sparing' action, but may also account for the increase in the incidence of postoperative graft thrombosis observed in clinical practice during aprotinin therapy.     

Impact of long-term exposure to cigarette smoking on skin microvascular function

In order to evaluate the impact of cigarettes smoking and smokers' clinical characteristics on skin microvascular function, we measured the skin forearm blood flux, basally and during post-occlusive reactive hyperaemia, in 100 current smokers (mean age 51 ± 11 years; range: 18 to 86 years) and in 66 healthy never-smokers matched for age and sex, by using laser Doppler fluximetry (LDF). Basal and post-ischemic LDF tracings were analyzed in the frequency domain within 0.009–0.02 Hz, 0.021–0.06 Hz and 0.061–0.2 Hz ranges, related to endothelial-dependent, sympathetic-dependent and myogenic-dependent vasomotion, respectively, using an adapted version of the Fourier analysis. The post-ischemic percentage change from baseline of the area under the LDF curve (AUC%) was significantly lower in smokers than in never-smokers [162.5% (139.3–183.0) vs 190.1% (156.3–216.8); p = 0.00016]. Compared to controls, smokers also showed a reduced basal power spectral density (PSD) in the myogenic-dependent vasomotion (p = 0.0034) and a reduced post-ischemic percentage increase in PSD of the endothelial-dependent vasomotion (p = 0.0010) and sympathetic-dependent vasomotion (p = 0.0016). An inverse relationship was observed in smokers between AUC% and smoking exposure duration (r = 0.23, p = 0.018), pack-years (r = 0.33, p = 0.0007), age (r = 0.26, p = 0.008) and body mass index (r = 0.21, p = 0.037). In the multiple linear regression model, pack-years was the only variable independently associated with AUC% (r = 0.21, p = 0.03). This study confirms that smoking is associated with cutaneous microvascular dysfunction and shows that the severity of this impairment is independently related to the duration and intensity of the exposure to smoking.     

Ischemia-reperfusion impairs endothelium-dependent relaxation of coronary microvessels but does not affect large arteries

We examined the effects of ischemia with and without reperfusion on endothelium-dependent and -independent vascular relaxation in both conduit and resistance coronary arteries. Studies were performed on dogs under control conditions (n = 13) or after 1 hour of circumflex coronary artery occlusion with (n = 10) or without (n = 8) 1 hour of reperfusion. Rings of obtuse marginal branches of the left circumflex coronary artery (conduit arteries) were studied in organ chambers. Coronary microvessels (110-220-microns diameter) were studied in a pressurized state with an in vitro microvessel imaging apparatus. Relaxation was evaluated after preconstriction with prostaglandin F2 alpha and U46619 (a thromboxane A2 analogue) in conduit and resistance vessels, respectively. Conduit vessel function was not altered by ischemia with or without reperfusion. Endothelium-dependent microvascular relaxation was depressed in response to acetylcholine, ADP, and calcium ionophore A23187 after ischemia with reperfusion compared with control relaxation (ED50 as -log[M]: 6.0 +/- 0.2 [p less than 0.05], 5.1 +/- 0.4 [p less than 0.05], and 5.8 +/- 0.1 versus 6.8 +/- 0.2, 6.8 +/- 0.2, and 6.6 +/- 0.2, respectively). Ischemia without reperfusion modestly altered microvascular endothelium-dependent relaxation. Microvascular relaxation to nitroglycerin was not altered by ischemia with reperfusion. We conclude that 1) endothelium-dependent relaxation in large epicardial coronary arteries is relatively refractory to ischemia with or without reperfusion, 2) ischemia alone produces mild alterations of coronary microvascular reactivity, 3) ischemia followed by reperfusion produces a marked and selective impairment of endothelium-dependent responses in the coronary microcirculation.     

Evaluation of coronary microvascular function in patients with vasospastic angina

AIM: To investigate endothelium-dependent and independent coronary microvascular functions in patients with vasospastic angina (VSA). METHODS: Thirty-six patients with VSA (30 men and 6 women; mean age, 58 years) were enrolled in this study. VSA was defined as ≥ 90% narrowing of the epicardial coronary arteries on angiography performed during a spasm provocation test, presence of chest pain, and/or ST-segment deviation on an electrocardiogram (ECG). Patients (n = 36) with negative spasm provocation test results and those matched for age and sex were enrolled as a control group (nonVSA group). Low-dose acetylcholine (ACh; 3 μg/min) was infused into the left coronary ostium for 2 min during the spasm provocation test. Following the spasm provocation test, nitroglycerin (0.2 mg) was administered intracoronally. Coronary blood flow (was calculated from quantitativeangiography and Doppler flow velocity measurements, and the coronary flow reserve was calculated as the ratio of coronary flow velocity after injection of adenosine triphosphate (20 μg) to the baseline value. Changes in the coronary artery diameter in response to ACh and nitroglycerin infusion were expressed as percentage changes from baseline measurements. RESULTS: Body mass index was significantly lower in the VSA group than in the nonVSA group. The fre- quency of conventional coronary risk factors and the rate of statin use were similar between the 2 groups. The left ventricular ejection fraction as evaluated by echocardiography was similar between the 2 groups. The duration of angina was 9 ± 2 mo. The results of blood chemistry analysis were similar between the 2 groups. Low-dose ACh did not cause coronary spasms. The change in coronary artery diameter in response to ACh was lower in the VSA group (-1.4% ± 9.3%) than in the nonVSA group (3.1% ± 6.5%, P < 0.05), whereas nitroglycerin-induced coronary artery dilatation and coronary blood flow increase in response to ACh or coronary flow reserve did not differ significantly between the 2 groups. CONCLUSION: These findings suggest that microvascular coronary function may be preserved despite endothelial dysfunction of the epicardial coronary arteries in patients with VSA.     

Impaired coronary microvascular endothelial function in men with metabolic syndrome

AIM: To assess coronary endothelial function of conduit and resistance vessels in patients with metabolic syndrome (MS).METHODS: Seventy-eight men (mean age, 57 years) with chest pain and angiographically normal coronary arteries were included in the study. Patients with coronary spastic angina were excluded. Changes in coronary artery diameter and coronary blood flow (CBF) in response to acetylcholine (ACh) were determined using quantitative coronary angiography and Doppler velocity measurements. Coronary flow reserve was calculated as the ratio of coronary blood velocity after adenosine triphosphate infusion relative to baseline values. Patients were divided into two groups based on the presence or absence of MS.RESULTS: There were 24 patients in the MS group (31%). The increase in CBF in response to ACh infusion was impaired in the MS group (P < 0.0001) compared to the non-MS group, whereas changes in coronary artery diameter in response to ACh infusion did not differ between the two groups. Multivariate regression analysis revealed that MS was a significant factor associated with the lesser change in CBF induced by ACh infusion at 30 μg/min (P < 0.0001, r² = 0.46).CONCLUSION: Coronary endothelial dysfunction was present at the level of resistance vessels but not conduit vessels in the MS patients included in our study.     

Smoking status of step-parents as a risk factor for smoking in adolescence

AIM: To examine the extent to which smoking by step-parents and biological parents predicts adolescent smoking. DESIGN Five-year cohort study. SETTING Thirty-six schools in South London, England. Participants A subset of 650 students participating in the Health and Behaviour In Teenagers Study (HABITS), who reported living in step-families, were assessed annually from age 11-12 to age 15-16 years. MEASUREMENTS: Students reported their smoking status, which was cotinine-verified, as well as whether their parents smoked and, if they lived with a step-parent, whether that step-parent smoked. Analyses also controlled for gender, ethnicity and deprivation. FINDINGS: Students who reported that just their step-parent smoked at age 11-12 were significantly more likely to report current smoking at any time-point from age 11-16 than those who reported having neither biological parents nor a step-parent who smoked [odds ratio (OR) 2.72, 95% confidence interval (CI) = 1.36-5.47], as were those with both a parent and a step-parent who smoked (OR 2.23, 95% CI = 1.46-3.41). While the association between smoking in students and smoking in biological parents in this subsample did not reach statistical significance (OR 1.39, 95% CI = 0.88-2.19), these students were no more or less likely to smoke than those with just a step-parent who smoked. CONCLUSION: Smoking by a non-biological parent appears at least as influential as smoking by biological parents. This confirms the importance of social influence on smoking initiation and suggests that attempts to work with parents in smoking prevention should involve, and perhaps pay particular attention to, step-parents who smoke.     

Impact of obesity on coronary microvascular function in the Zucker rat

OBJECTIVE: To test the hypothesis that vasomotor control is impaired in the coronary circulation of prediabetic obese (OZR) relative to lean Zucker rats (LZR). METHODS: Cardiac function was assessed with in vivo measures of cardiac output and microvascular structure and function was assessed in vitro using videomicroscopic techniques. RESULTS: OZR showed a marked hyperdynamic circulation with an increased cardiac output and elevated stroke volume. Contrary to the stated hypothesis, the authors found no diminution of vasodilator function and no augmentation of vasoconstriction. Indeed, dilation to acetylcholine was potentiated and vasoconstriction to endothelin was reduced in OZR compared to LZR. Structural characteristics of small coronary arteries were similar between LZR and OZR. CONCLUSIONS: Taken together, these results indicate that obesity, as manifested in the prediabetic OZR, does not impair coronary vasomotor control. This lack of dysfunction in the presence of the same risk factors that affect other beds may reflect a reversal of vascular injury by the increased metabolism and coronary blood flow caused by hyperdynamic cardiac function early in obesity.     

Relation between C reactive protein concentrations and coronary microvascular endothelial function

Objective: To determine how C reactive protein (CRP), a sensitive marker of inflammation, is related to coronary endothelial function.