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Biomedical subjects

John R Cockcroft

Publications and source records attributed to John R Cockcroft.

At least 19 recordsLinked to original sources
PubMed2007

Does arterial stiffness predict atherosclerotic coronary events?

Coronary heart disease is a major cause of death and morbidity. Due to the increased longevity of most developed societies, there is an increasing overlap between arteriosclerosis associated with normal vascular ageing and atherosclerosis associated with cardiovascular risk factors. There is therefore a need for improvements, both in the early identification of individuals at risk, and in cardiovascular risk stratification. Arterial stiffness is an important determinant of cardiovascular risk and can now be measured simply and noninvasively in large populations. This review will therefore focus on the current evidence as to the predictive value of arterial stiffness in relation to coronary events and also on the possible pathophysiological mechanisms linking arterial stiffness and atherosclerosis.

Blood Flow Velocity↗
PubMed2007

Cholesterol, lipids and arterial stiffness.

Arterial stiffness and pulse pressure are important determinants of cardiovascular risk. Patients with hypercholesterolaemia have a higher central pulse pressure and stiffer blood vessels than matched controls, despite similar peripheral blood pressures. These haemodynamic changes may contribute to the increased risk of cardiovascular disease associated with hypercholesterolaemia and their assessment may improve risk stratification. Lipid-lowering therapy, particularly with statins, generally leads to a reduction in arterial stiffness, re-enforcing the concept that stiffness is a modifiable parameter and risk factor. There are a number of potential mechanisms linking arterial stiffness and plasma lipids, including atherosclerosis, changes in the elastic elements of the arterial wall, endothelial dysfunction and inflammation. This review will focus on the current evidence linking cholesterol to larger artery stiffening, potential therapies and mechanisms.

Animals↗
PubMed2006

Endothelial function is associated with pulse pressure, pulse wave velocity, and augmentation index in healthy humans.

Arterial stiffness is an independent predictor of mortality and is regulated by a number of factors, including vascular smooth muscle tone. However, the relationship between endothelial function and definitive measures of arterial stiffness and wave reflections has not been described in healthy individuals. Therefore, we tested the hypothesis that endothelial function is inversely correlated with aortic pulse wave velocity (PWV), central pulse pressure, and augmentation index in healthy individuals. Peripheral and central pulse pressure and augmentation index were determined at rest, and global endothelial function was measured using pulse wave analysis and administration of sublingual nitroglycerin and inhaled albuterol. Aortic PWV was also determined at baseline in a subset of 89 subjects. In a separate group of subjects (n=89), aortic PWV was measured and brachial artery flow-mediated dilatation assessed as a measure of conduit artery endothelial function. Global endothelial function was significantly and inversely correlated with aortic PWV (r=-0.69; P<0.001), augmentation index (r=-0.59; P<0.001), and central (r=-0.34; P<0.001) and peripheral pulse pressure (r=-0.15; P=0.03). Moreover, there was a stronger correlation between central rather than peripheral pulse pressure. After adjusting for potential confounders, global endothelial function remained independently and inversely associated with aortic PWV and augmentation index. There was also a significant, inverse relationship between conduit artery endothelial function and aortic PWV (r=0.39, P<0.001), which remained independent after adjusting for confounding factors. In healthy individuals, a decline in endothelial function is associated with increased large artery stiffness, wave reflections, and central pulse pressure.

Administration, Inhalation↗
PubMed2006

Variation in the human matrix metalloproteinase-9 gene is associated with arterial stiffness in healthy individuals.

BACKGROUND: Arterial stiffness is an important determinant of cardiovascular risk. Elastin is the main elastic component of the arterial wall and can be degraded by a number of enzymes including serine proteases and matrix metalloproteinases (MMPs). Serum MMP-9 levels correlate with arterial stiffness and predict cardiovascular risk. Polymorphisms in the MMP-9 gene are also associated with large artery function in subjects with coronary artery disease. Therefore, we investigated the influence of known MMP-9 (-1562C>T, R279Q) polymorphisms on arterial stiffness in a large cohort of healthy individuals (n=865). METHODS AND RESULTS: Aortic pulse wave velocity (PWV) and augmentation index were assessed. Supine blood pressure, biochemical markers, MMP-9 levels, and serum elastase activity (SEA) were also determined. Genomic DNA was extracted and genotyping performed. Aortic PWV, serum MMP-9, and SEA were higher in carriers of the rare alleles for the -1562C>T and R279Q polymorphisms. These polymorphisms were also associated with aortic PWV after correction for other confounding factors. Stepwise regression models with known or likely determinants of arterial stiffness revealed that approximately 60% of the variability in aortic PWV was attributable to age, mean arterial pressure, and genetic variants (P<0.001). CONCLUSIONS: We have demonstrated for the first time that aortic stiffness and elastase activity are influenced by MMP-9 gene polymorphisms. This suggests that the genetic variation in this protein may be involved in the process of large artery stiffening.

Adult↗
PubMed2006

Genetic variation at the growth hormone (GH1) and growth hormone receptor (GHR) loci as a risk factor for hypertension and stroke.

An increased prevalence of both hypertension and cerebrovascular stroke is apparent in growth hormone (GH) deficiency whilst hypertension is a frequent complication in acromegaly. This has suggested a possible link between GH, stature and arterial function. Since the risk of both hypertension and stroke also appears to be inversely correlated with adult height, we have instigated an exploratory study to assess whether inter-individual variation in the genes encoding human growth hormone (GH1) and the GH receptor (GHR) might be associated with an increased risk of hypertension and stroke. GH1 promoter haplotypes were found to differ significantly not only between hypertensive patients (n = 111) and controls (n = 121) but also between stroke patients (n = 155) and controls (n = 158). Intriguingly, the association between GH1 promoter haplotype and risk of hypertension was much greater in females than in males. An inverse correlation between height and central systolic blood pressure was apparent in both hypertensive patients and normal controls but was much stronger in individuals carrying at least one GH1 promoter risk haplotype. The GH1 genotype therefore constitutes a risk factor for hypertension that interacts with stature. A strong association was found between the presence of at least one GH1 risk haplotype and a family history of stroke at an early age (odds ratio: 9.07, 95% confidence interval: 1.14-72.22). Three novel GH variants (Arg16His, Phe176Cys, Cys189Arg) were identified during the course of this study. Although two exhibited markedly reduced biological activity in vitro, their clinical significance remains unclear. No association was found between GHR genotype and either hypertension or stroke, nor was any interaction noted between GHR and GH1 genotypes in terms of a disease association. However, an association between GHRd3 genotype and hypertension was observed among stroke patients, particularly females. Elevated HDL was found to be a risk factor for hypertension in individuals lacking a copy of the GHRd3 allele. Weak associations with GHR genotype were also noted for peripheral systolic and diastolic blood pressure in hypertensive patients. Although the underlying mechanisms are still unclear, our findings are consistent with a complex relationship between height, hypertension, GH1 promoter haplotype, GHR polymorphism and the risk of stroke.

Adult↗
PubMed2006

The latest generation of beta-blockers: new pharmacologic properties.

beta-Blockers have generally demonstrated smaller reductions in cardiovascular events, compared with other antihypertensive classes, despite similar reductions in blood pressure. This may be due to the ineffectiveness of traditional beta-blockers, such as atenolol, in reducing central aortic pressure, a strong, independent predictor of cardiovascular outcome. However, the beta-blocker class is heterogeneous, and some newer beta-blockers, which exhibit vasodilatory effects independent of beta-blockade, provide beneficial effects on arterial stiffness and endothelial dysfunction, which may lead to reductions in central aortic pressure and improvements in clinical outcomes. For example, the vasodilating beta-blocker nebivolol was shown to improve forearm blood flow and arterial stiffness and, in a large clinical study, to significantly reduce morbidity and mortality, independent of left ventricular ejection fraction, among patients with chronic heart failure. Further research is warranted to investigate any potential differences between traditional and newer vasodilating beta-blockers on cardiovascular outcomes.

Adrenergic beta-Antagonists↗
PubMed2006

Atenolol and eprosartan: differential effects on central blood pressure and aortic pulse wave velocity.

BACKGROUND: Recent data suggest that atenolol may be inferior to other antihypertensive drugs in reducing cardiovascular risk in older individuals with hypertension, despite lowering peripheral blood pressure (BP). We hypothesized that that atenolol fails to reduce central BP as much as other agents. The aim of the present study was to compare the hemodynamic effects of atenolol and eprosartan in a double-blind, randomized, cross-over study. METHODS: After a 2-week placebo run-in, 21 subjects with never-treated hypertension underwent 6 weeks of therapy with atenolol (50 mg) and eprosartan (600 mg). Central BP and augmentation index were assessed using pulse wave analysis, and aortic pulse wave velocity was measured, at baseline and at the end of each treatment. RESULTS: Both drugs reduced peripheral BP to the same degree. However, there was a significantly greater reduction in central systolic BP with eprosartan (means +/- SEM: 16 +/- 3 v 11 +/- 2 mm Hg; P = .03). Despite identical reductions in mean pressure, atenolol reduced aortic pulse wave velocity more than eprosartan (0.8 +/- 0.1 v 0.5 +/- 0.1 m/sec; P = .005). Conversely, augmentation index and N-terminal pro-brain natiuretic peptide levels were reduced significantly after eprosartan (6% +/- 2% and 11 +/- 5 pg/mL, respectively) but were increased after atenolol (7% +/- 2% and 67 +/- 24 pg/mL, respectively). CONCLUSIONS: These data indicate that despite similar effects on peripheral BP and a greater effect on aortic stiffness, atenolol had less impact on central systolic BP than eprosartan because it failed to reduce wave reflection. This provides one potential explanation for the failure of atenolol to improve outcome in older patients with essential hypertension.

Acrylates↗
PubMed2006

Genetic variation in fibrillin-1 gene is not associated with arterial stiffness in apparently healthy individuals.

OBJECTIVE: Arterial stiffness is an independent determinant of cardiovascular risk, and there is evidence that it has a strong genetic component. Fibrillin-1 (FBN-1) is the disease gene for Marfan's syndrome and an FBN-1 polymorphism has been associated with large artery stiffening and elevated pulse pressure (PP) in patients with cardiovascular disease. The aim of this study was to investigate the possible influence of the common FBN-1 genotypes on arterial stiffness in a large cohort of healthy individuals. SUBJECTS AND METHODS: A total of 742 individuals free from cardiovascular disease or risk factors were studied. Aortic pulse wave velocity (PWV) and augmentation index (AIx), blood pressure, lipids and glucose were assessed. Genomic DNA was extracted, and genotyping for the FBN-1 variable nucleotide tandem repeat (VNTR) was performed using a CEQ 8000 sequencer. RESULTS: The mean age (+/- SEM) of the cohort was 49 +/- 1 years. The three common VNTR genotypes accounted for 87.1% of the population frequency. Their frequencies were: 52.3%, 2-2; 16.3%, 2-3; 18.5% 2-4. There were no significant differences in the blood pressure, AIx, PWV, lipids or body mass index among the common genotypes. Moreover, the FBN-1 genotype was not associated with either aortic PWV or other measures of stiffness after correction for other confounding factors. CONCLUSION: These data do not support the hypothesis that aortic PWV or PP are influenced by the FBN-1 VNTR genotype. Although we cannot exclude small effects, this negative finding also suggests that there is not a major allele for stiffness or blood pressure in apparently healthy individuals linked to this VNTR.

Adolescent↗
PubMed2006

Targeting nitric oxide with drug therapy.

Increasing knowledge of the role of nitric oxide (NO) in physiology and disease has stimulated efforts to target the NO pathway pharmacologically. These therapeutic strategies include NO donors that directly or indirectly release NO and agents that increase NO bioactivity. Traditional organic nitrates such as nitroglycerin, which indirectly release NO, were believed to have limited long-term efficacy and tolerability, chiefly because of nitrate tolerance. Recent studies, however, suggest more effective ways of using these agents and new applications for them. Nicorandil, a hybrid organic nitrate that also activates potassium channels, has demonstrated significant benefits in acute coronary syndromes. Other nitrates are being investigated for use in neurodegenerative diseases. Direct NO donors include NO gas, which is useful in respiratory disorders, and the more recent classes of diazeniumdiolates, sydnonimines, and S-nitrosothiols. Preliminary data suggest that these agents may be effective as antiatherosclerotic agents as well as in other disease states. In addition, hybrid agents that consist of an NO donor coupled with a parent anti-inflammatory drug, including nonsteroidal anti-inflammatory drugs, have demonstrated enhanced efficacy and tolerability compared with the anti-inflammatory parent drug alone in diverse experimental models. Established drugs that enhance NO bioactivity include antihypertensive agents, particularly angiotensin-converting enzyme inhibitors, calcium channel blockers, and newer vasodilating beta-blockers. In addition, 3-methylglutaryl coenzyme A reductase inhibitors (statins) promote NO bioactivity, both through and independent of lipid lowering. The NO-promoting actions of these established drugs provide some insight into their known benefits and suggest possible therapeutic potential.

Adrenergic alpha-Antagonists↗
PubMed2005

Normal vascular aging: differential effects on wave reflection and aortic pulse wave velocity: the Anglo-Cardiff Collaborative Trial (ACCT).

OBJECTIVES: The aim of the current investigation was to test the hypothesis that age-related changes in augmentation index (AIx) are more prominent in younger individuals (<50 years), whereas changes in aortic stiffness per se are more marked in older individuals (>50 years). BACKGROUND: Aging exerts a number of deleterious changes in the cardiovascular system, and, in particular, on the large arteries. Previous studies have suggested that AIx and pulse wave velocity (PWV) increase linearly with age, yet epidemiological data concerning pulse pressure suggest that large artery stiffening predominantly occurs later in life. METHODS: Peripheral and central blood pressure, augmentation pressure (AP), and AIx were determined in 4,001 healthy, normotensive individuals, aged 18 to 90 years. Aortic and brachial PWV were also determined in a subset of 998 subjects. RESULTS: Peripheral and central pulse pressure, AP, AIx, and aortic and brachial PWV all increased significantly with age; however, the age-related changes in AIx and aortic PWV were non-linear, with AIx increasing more in younger individuals, whereas the changes in PWV were more prominent in older individuals. CONCLUSIONS: These data suggest that AIx might be a more sensitive marker of arterial stiffening and risk in younger individuals but aortic PWV is likely to be a better measure in older individuals.

Adolescent↗
PubMed2005

In vivo aspirin supplementation inhibits nitric oxide consumption by human platelets.

Antiplatelet therapies improve endothelial function in atherosclerosis, suggesting that platelets regulate vascular nitric oxide (NO) bioactivity in vivo. Herein, washed platelets consumed NO on activation in an aspirin-sensitive manner, and aspirin enhanced platelet NO responses in vitro. To examine whether in vivo aspirin can inhibit platelet NO consumption, a double-blind placebo-controlled study was conducted. After a 2-week nonsteroidal anti-inflammatory drug (NSAID)-free period, healthy men were randomly assigned and administered aspirin (75 mg/d orally) or identical placebo for 14 days, then crossed over to the opposite arm. Following in vivo aspirin, NO consumption by platelets was inhibited 91%. Rate of onset and recovery following aspirin withdrawal was consistent with cyclooxygenase 1 (COX-1) inhibition. In a small substudy, NO consumption by platelets from postmenopausal women was faster in hypercholesterolemics and less sensitive to aspirin (ie, 39% versus 76% inhibition for hypercholesterolemics or normocholesterolemics, respectively). However, 150 mg aspirin/day increased inhibition of NO consumption by platelets of hypercholesterolemics to 80%. Comparisons of platelet COX-1 or -2 expression and urinary 11-dehydro-thromboxane B2 excretion suggested that aspirin was less able to block platelet activation in vivo in hypercholesterolemia. In conclusion, aspirin inhibits NO consumption by platelets from healthy subjects, but its beneficial effects on NO bioactivity may be compromised in some hypercholesterolemic patients.

Aspirin↗
PubMed2005

Basal NO locally modulates human iliac artery function in vivo.

We demonstrated previously that endogenous NO influences large-artery distensibility in the ovine hindlimb. However, the role of basal NO in larger human conduit arteries is controversial. The aim of this study was to investigate whether basal production of NO, acting locally, influences iliac artery distensibility in humans. Distensibility was assessed by intra-arterial measurement of the pulse wave velocity. Eighteen subjects, free of significant coronary or iliac artery disease, were studied after diagnostic cardiac catheterization. Simultaneous pressure waveforms were recorded with a high-fidelity dual-pressure sensing catheter, placed in the common iliac artery during intra-arterial infusion of saline (baseline), glyceryl trinitrate (4 nmol/min), or NG-monomethyl-L-arginine (8 and 16 micromol/min). Drugs were infused proximally, via the catheter to perfuse the segment of artery under study, or distally, via the sheath, to control for any reflex changes in flow or sympathetic activation. Velocity was calculated using the foot-to-foot methodology. Six subjects received glyceryl trinitrate and 12 NG-monomethyl-L-arginine. There was no change in velocity after infusion of glyceryl trinitrate or NG-monomethyl-L-arginine via the sheath. However, infusion of glyceryl trinitrate via the catheter significantly reduced velocity by 31.43+/-5.80% (mean+/-SEM; P<0.01; P=0.02 for comparison). Likewise, infusion of the highest dose of NG-monomethyl-L-arginine via the catheter significantly increased velocity by 27.25+/-8.20% (P=0.001; P=0.02 for comparison). Importantly, there was no change in mean arterial blood pressure throughout the studies. These data indicate that under resting conditions, local NO production modulates human iliac artery distensibility and that exogenous NO increases arterial distensibility.

Blood Flow Velocity↗
PubMed2005

Pulse pressure predicts cardiovascular risk in patients with type 2 diabetes mellitus.

BACKGROUND: Pulse pressure (PP), a marker of arterial stiffness, is a better predictor of coronary heart disease (CHD) risk than systolic blood pressure (SBP) or diastolic blood pressure (DBP) in older adults. Whether this is also true in subjects with type 2 diabetes, who are at increased risk for cardiovascular disease, is unknown. METHODS: Data on 2911 type 2 diabetic subjects relating to blood pressure (BP), other risk factors, and cardiovascular events were abstracted from The Cardiff Diabetes Database. Logistic regression was used to assess the relationship among BP components and the risk of CHD, cerebrovascular (CVD), and peripheral vascular (PVD) events after correction for age, gender, cholesterol, and smoking status. RESULTS: In the 4-year follow-up period there were 574 CHD, 168 CVD, and 157 PVD events. Both PP and SBP, but not DBP, were positively associated with the risk of all event types. However, PP emerged as the best predictor of CHD events, and SBP as the best predictor of CVD and PVD events. Total and HDL-cholesterol were the most important variables associated with PP after age. CONCLUSIONS: In summary, PP is a better predictor of CHD events than SBP in persons with type 2 diabetes, but the converse is true for CVD and PVD.

Aged↗
PubMed2005

Exploring vascular benefits of endothelium-derived nitric oxide.

Although the regulation of arterial blood flow has been a subject of intensive medical research, the precise circulatory mechanisms involved are still not fully understood. It has been increasingly recognized that the endothelium plays a vital role in regulating vascular tone, structure, and function. A seminal discovery was made with the identification of endothelium-derived relaxing factor, a key mediator of vasodilation, which was later identified as nitric oxide (NO). Nitric oxide is synthesized from the amino acid L-arginine in the endothelium. Decreased bioavailability of NO is associated with arterial stiffness, hypertension, atherosclerosis, and cardiovascular disease (CVD). Nebivolol is a novel beta-blocker that is highly selective for beta1-adrenergic receptors. Nebivolol also causes vasodilation through a mechanism involving endothelium-derived NO. In clinical studies in hypertensive subjects, nebivolol significantly improves vasodilator responses to endothelium-dependent agonists such as acetylcholine. In addition, nebivolol significantly reduces pulse wave velocity (PWV), a measure of arterial stiffness, whereas the beta-blocker atenolol has no effect on PWV. Because endothelial dysfunction and arterial stiffness play an integral part in the early atherosclerotic process and are associated with poor outcomes and increased mortality, independent of blood pressure, the ability of nebivolol to enhance release of endothelium-derived NO may have significant clinical implications for the use of this agent in the treatment of hypertension and CVD.

Acetylcholine↗
PubMed2005

Endothelial function and dysfunction. Part II: Association with cardiovascular risk factors and diseases. A statement by the Working Group on Endothelins and Endothelial Factors of the European Society of Hypertension.

Dysfunction of the vascular endothelium is a hallmark of most conditions that are associated with atherosclerosis and is therefore held to be an early feature in atherogenesis. However, the mechanisms by which endothelial dysfunction occurs in smoking, dyslipidaemia, hyperhomocysteinaemia, diabetes mellitus, arterial hypertension, cerebrovascular diseases, coronary artery disease and heart failure are complex and heterogeneous. Recent data indicate that endothelial dysfunction is often associated with erectile dysfunction, which can precede and predict cardiovascular disease in men. This paper will provide a concise overview of the mechanisms causing endothelial dysfunction in the different cardiovascular risk factors and disease conditions, and of the impact of the intervention measures and treatments.

Cardiovascular Diseases↗