Brendan M. McQuillan

Hyperhomocysteinemia but Not the C677T Mutation of Methylenetetrahydrofolate Reductase Is an Independent Risk Determinant of Carotid Wall Thickening The Perth Carotid Ultrasound Disease Assessment Study (CUDAS)

BACKGROUND Hyperhomocysteinemia has been identified as a potential risk factor for atherosclerosis. This study examined whether a modest elevation of plasma total homocysteine (tHcy) was an independent risk factor for increased carotid artery intimal-medial wall thickness (IMT) and focal plaque formation in a large, randomly selected community population. We also examined whether vitamin cofactors and the C677T genetic mutation of the methylenetetrahydrofolate reductase (MTHFR) enzyme were major contributors to elevated plasma tHcy and carotid vascular disease. METHODS AND RESULTS In 1111 subjects (558 men, 553 women) 52+/-13 years old (mean+/-SD; range, 27 to 77 years) recruited from a random electoral roll survey, we measured fasting tHcy and performed bilateral carotid B-mode ultrasound. For the total population, mean tHcy was 12.1+/-4.0 micromol/L. Plasma tHcy levels were correlated with IMT (Spearman rank rs=0.31, P=0.0001). After adjustment for age, sex, and other conventional risk factors, subjects in the highest versus the lowest quartile of tHcy had an odds ratio of 2.60 (95% CI, 1.51 to 4.45) for increased IMT and 1.76 (95% CI, 1.10 to 2.82) for plaque. Serum and dietary folate levels and the C677T mutation in MTHFR were independent determinants of tHcy (all P=0.0001). The mutant homozygotes (10% of the population) had higher mean tHcy than heterozygotes or those without the mutation (14.2 versus 12.3 versus 11.6 micromol/L, respectively, P=0.0001). The inverse association of folate levels with tHcy was steeper in the mutant homozygotes. Despite this, the C677T MTHFR mutation was not independently predictive of increased carotid IMT or plaque formation. CONCLUSIONS Mild hyperhomocysteinemia is an independent risk factor for increased carotid artery wall thickness and plaque formation in a general population. Lower levels of dietary folate intake and the C677T mutation in MTHFR are important causes of mild hyperhomocysteinemia and may therefore contribute to vascular disease in the community.

Elevated Interleukin-18 Levels Are Associated With the Metabolic Syndrome Independent of Obesity and Insulin Resistance

Objective—Activated innate immunity is thought to be involved in the pathogenesis of metabolic syndrome and type 2 diabetes. Interleukin-18 (IL-18) is a pleiotropic proinflammatory cytokine with important regulatory functions in the innate immune response. We sought to determine whether an elevated IL-18 concentration was a risk predictor for metabolic syndrome in a community population independent of obesity and hyperinsulinemia. Methods and Results—A representative general population, aged 27 to 77 years, without clinical diabetes was studied for clinical and biochemical risk factors for metabolic syndrome. Serum IL-18 concentration measured in 955 subjects correlated with metabolic syndrome traits including body mass index (BMI), waist circumference, triglyceride, high-density lipoprotein (inversely), and fasting glucose and insulin levels (all P<0.001). Mean IL-18 levels rose progressively with the increasing number of metabolic risk factors (ANOVA P<0.001). After adjusting for age, gender, BMI, and insulin levels, increasing IL-18 tertiles were associated with an odds ratio for metabolic syndrome of 1.0, 1.42, and 2.28, respectively (P trend=0.007). The graded risk relation was even stronger in nonobese subjects and not attenuated when adjusted for C-reactive protein and IL-6 levels. Conclusion—Our findings support the hypothesis that activation of IL-18 is involved in the pathogenesis of the metabolic syndrome.

Monocyte Count, But Not C-Reactive Protein or Interleukin-6, Is an Independent Risk Marker for Subclinical Carotid Atherosclerosis

Background and Purpose— Systemic inflammatory markers have been shown to predict future cardiovascular events, but whether they are associated with early atherosclerosis is uncertain. We investigated the relationship of inflammatory markers interleukin-6 (IL-6), high-sensitive C-reactive protein (hs-CRP), fibrinogen, monocyte count, and white cell count (WCC) with subclinical carotid atherosclerosis in a healthy community population. Methods— B-mode carotid ultrasound was performed on 1111 randomly selected male and female subjects aged 27 to 77 years. Serum IL-6, hs-CRP, plasma fibrinogen, monocyte count, and WCC were measured on all subjects, along with conventional cardiovascular risk factors. Results— Multivariate analysis showed that IL-6 (P <0.0001), fibrinogen (P =0.007), and monocyte count (P =0.001) were associated with carotid plaque formation in the whole population. Monocyte count remained associated independently with carotid plaque formation when adjusted further for conventional risk factors (odds ratio per SD increase in monocyte count 1.4; 95% CI, 1.13 to 1.73; P =0.002). IL-6 (P <0.0001), fibrinogen (P <0.0001), and monocyte count (P =0.04) were also associated with carotid intima-medial thickness (IMT) in the whole population. However, when adjusted further for conventional risk factors, none remained independently predictive of carotid IMT. Further analysis showed an age–monocyte interaction (P =0.03), with monocyte count being an independent predictor of carotid IMT in the older age group only (>53 years; P =0.003). Conclusion— In a healthy community population, monocyte count is a better independent predictor of common carotid IMT and plaque formation than IL-6, hs-CRP, fibrinogen, and WCC. Monocyte count may represent an inexpensive, easy-to-measure risk marker for subclinical carotid atherosclerosis.

Circulating adiponectin levels associate with inflammatory markers, insulin resistance and metabolic syndrome independent of obesity

Background:Adiponectin is an abundantly expressed adipocyte-specific protein, whose level is decreased in obesity, and which appears to be a key participant in developing inflammation, insulin resistance and metabolic syndrome (MetS). We examined whether the relationship between adiponectin and inflammatory markers, insulin resistance and MetS was independent of obesity.Methods and results:The study was performed in 1094 men and women, aged 27–77 years, from a representative community population. We measured serum inflammatory markers, homoeostasis model assessment of insulin resistance (HOMA-IR) and prevalent MetS using National Cholesterol Education Program ATPIII criteria. Sex- and age-adjusted plasma adiponectin concentration was inversely correlated with body mass index (BMI), waist–hip ratio, diastolic blood pressure, triglycerides, glucose and fasting insulin, and positively correlated with HDL cholesterol (all P<0.005). Log plasma adiponectin was a significant negative correlate of the levels of C-reactive protein, interleukin-6, interleukin-18, fibrinogen and white cell count independent of level of obesity. Log plasma adiponectin was also an inverse associate of log HOMA-IR (P<0.001) independent of obesity. Subjects in the top compared to bottom sex-specific plasma adiponectin quartile had a multivariate-adjusted odds ratio (OR) of 0.21 (95% CI, 0.11–0.42; P<0.001) for prevalent MetS, and the association was independent of age, sex, BMI, log insulin and log intereukin-18 levels.Conclusion:Our findings suggest that higher circulating adiponectin levels may mitigate against adipose-related inflammation, insulin resistance and MetS as much in lean as obese persons. At any rate circulating adiponectin level is a strong risk marker for MetS, which is independent of measures of adiposity, insulin resistance and inflammatory markers.

Antioxidant Vitamins and the Risk of Carotid Atherosclerosis. The Perth Carotid Ultrasound Disease Assessment Study (CUDAS)

OBJECTIVES This study examined whether dietary intake or plasma levels of antioxidant vitamins were independently associated with common carotid artery intima-media (wall) thickness (IMT) or focal plaque, or both, in a large, randomly selected community population. BACKGROUND Oxidation of low-density lipoprotein (LDL) cholesterol is thought to be important in early atherogenesis. Antioxidant micronutrients may therefore protect against lipid peroxidation and atherosclerotic vascular disease. METHODS We studied 1,111 subjects (558 men and 553 women; age 52 +/- 13 years [mean +/- SD], range 27 to 77). We measured dietary vitamin intake and fasting plasma levels of vitamins A, C and E, lycopene and alpha- and beta-carotene and performed bilateral carotid artery B-mode ultrasound imaging. RESULTS; After adjustment for age and conventional risk factors, there was a progressive decrease in mean IMT, with increasing quartiles of dietary vitamin E intake in men (p = 0.02) and a nonsignificant trend in women (p = 0.10). Dietary vitamin E levels accounted for 1% of the variance in measured IMT in men. For plasma antioxidant vitamins, there was an inverse association between carotid artery mean IMT and plasma lycopene in women (p = 0.047), but not in men. None of the other dietary or plasma antioxidant vitamins, nor antioxidant vitamin supplements, were associated with carotid artery IMT or focal carotid artery plaque. CONCLUSIONS This study provides limited support for the hypothesis that increased dietary intake of vitamin E and increased plasma lycopene may decrease the risk of atherosclerosis. No benefit was demonstrated for supplemental antioxidant vitamin use.

Polymorphisms in the angiotensinogen gene are associated with carotid intimal–medial thickening in females from a community-based population

BACKGROUND Polymorphisms within genes of the renin-angiotensin system have been associated with an increased risk of cardiovascular disease. We investigated the association of polymorphisms in the angiotensinogen (AGT) and angiotensin II receptor type 1 (AGTR1) genes with increased intima-media thickness (IMT) and the presence of plaques in carotid arteries. METHODS Subjects (1111) from the Perth Carotid Ultrasound Disease Assessment Study (CUDAS) were genotyped for three polymorphisms: two in the promoter of the AGT gene, G-6A and A-20C; and one in the AGTR1 gene, A1166C. RESULTS Using multivariate generalised linear models, the AGT-6A allele (P<0.001) and the AGT-20C allele (P<0.03) were significantly associated with increased mean carotid IMT in females but not in males when adjusted for conventional risk factors. The AGTR1 A1166C polymorphism did not show any significant relationship to mean IMT. Results suggest that the I allele of the angiotensin converting enzyme insertion/deletion polymorphism may interact with the AGT-6G allele to increase mean carotid IMT in the population as a whole. None of the polymorphisms investigated were significantly associated with the presence of carotid plaques. CONCLUSION This study shows that polymorphisms in the angiotensinogen gene are associated with an increased risk of carotid intimal-medial wall thickening in females.

Angiotensin-Converting Enzyme Gene Polymorphism and Carotid Wall Thickening in a Community Population

The insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme (ACE) gene has been associated with an increased risk of coronary heart disease, but whether it is a risk factor for underlying atherosclerosis remains unclear. Therefore, we examined to see whether the ACE gene deletion polymorphism was associated with carotid wall thickening and atherosclerotic plaque formation in a large randomly selected community population. A total of 1111 subjects, aged 27 to 77 years, with an equal male:female ratio and equal numbers in each age decile, were randomly selected from the Perth community population. Mean common carotid intima-medial wall thickness (IMT) and focal plaque formation were assessed by high-resolution B-mode ultrasound. The ACE gene I/D polymorphism was detected by PCR. The distribution of the ACE genotypes conformed to the Hardy-Weinberg equilibrium (DD, 31.0%; ID, 48.4%; and II, 20.6%). The D allele was strongly correlated in a codominant fashion with plasma ACE activity (r(s)=0.53, P<0.0001), and accounted for 33% of the total variance in circulating ACE activity. No significant differences among the ACE genotypes were found with respect to age, sex, and conventional risk variables, including a history of hypertension and vascular disease. The average mean IMT and prevalence of increased IMT and focal plaque were not significantly different among genotypes in the overall population or in the subset (n=852) who were conventionally low risk by Framingham coronary heart disease risk score. Logistic regression analysis selected age, systolic blood pressure, pack-years of smoking, LDL cholesterol level, waist/hip ratio, and history of hypertension, but not the D allele, as multivariate predictors of increased IMT and carotid plaque formation. We conclude that, although the ACE I/D polymorphism is strongly related to ACE activity, it is not a risk predictor of carotid wall thickening or focal plaque formation when examined in a large randomly selected community population.

A comprehensive investigation of variants in genes encoding adiponectin ( ADIPOQ ) and its receptors ( ADIPOR1/R2 ), and their association with serum adiponectin, type 2 diabetes, insulin resistance and the metabolic syndrome

BackgroundLow levels of serum adiponectin have been linked to central obesity, insulin resistance, metabolic syndrome, and type 2 diabetes. Variants in ADIPOQ, the gene encoding adiponectin, have been shown to influence serum adiponectin concentration, and along with variants in the adiponectin receptors (ADIPOR1 and ADIPOR2) have been implicated in metabolic syndrome and type 2 diabetes. This study aimed to comprehensively investigate the association of common variants in ADIPOQ, ADIPOR1 and ADIPOR2 with serum adiponectin and insulin resistance syndromes in a large cohort of European-Australian individuals.MethodsSixty-four tagging single nucleotide polymorphisms in ADIPOQ, ADIPOR1 and ADIPOR2 were genotyped in two general population cohorts consisting of 2,355 subjects, and one cohort of 967 subjects with type 2 diabetes. The association of tagSNPs with outcomes were evaluated using linear or logistic modelling. Meta-analysis of the three cohorts was performed by random-effects modelling.ResultsMeta-analysis revealed nine genotyped tagSNPs in ADIPOQ significantly associated with serum adiponectin across all cohorts after adjustment for age, gender and BMI, including rs10937273, rs12637534, rs1648707, rs16861209, rs822395, rs17366568, rs3774261, rs6444175 and rs17373414. The results of haplotype-based analyses were also consistent. Overall, the variants in the ADIPOQ gene explained <5% of the variance in serum adiponectin concentration. None of the ADIPOR1/R2 tagSNPs were associated with serum adiponectin. There was no association between any of the genetic variants and insulin resistance or metabolic syndrome. A multi-SNP genotypic risk score for ADIPOQ alleles revealed an association with 3 independent SNPs, rs12637534, rs16861209, rs17366568 and type 2 diabetes after adjusting for adiponectin levels (OR=0.86, 95% CI=(0.75, 0.99), P=0.0134).ConclusionsGenetic variation in ADIPOQ, but not its receptors, was associated with altered serum adiponectin. However, genetic variation in ADIPOQ and its receptors does not appear to contribute to the risk of insulin resistance or metabolic syndrome but did for type 2 diabetes in a European-Australian population.

Lack of association between seropositivity to Chlamydia pneumoniae and carotid atherosclerosis

Since the Chlamydia pneumoniae (C. pneumoniae)-specific antibody was shown to be associated with acute myocardial infarction and chronic coronary heart disease, the role of C. pneumoniae in the etiology of cardiovascular disease has been studied by a number of groups. We investigated the association between the C. pneumoniae-specific antibody, measured by microimmunofluorescence, risk factors for cardiovascular disease, and atherosclerosis in a randomly selected urban population. Overall, immunoglobulin-G (IgG) seroprevalence to C. pneumoniae in this sample of 1,034 subjects was 58%, whereas IgA seroprevalence was 32%. There was a decline in seropositivity with age for IgG but not IgA. Men were more likely than women to be IgG (66% vs 51%, chi-square p = 0.001) and IgA seropositive (36% vs 28%, chi-square p = 0.005). Current smokers had higher IgA seropositivity than nonsmokers (43% vs 30%). Those patients with a family history of cerebrovascular disease were more likely to have IgG antibody than those without (75% vs 57%, chi-square p= 0.007). Neither IgG nor IgA seropositivity was associated with the standard risk factors of hypertension, hyperlipidemia, or family history of ischemic heart disease, nor was seropositivity associated with carotid intima medial thickening (IMT) or atherosclerotic plaque as measured by carotid B-mode ultrasound. There was no difference between those participants who were IgG or IgA seropositive and seronegative in measurements of mean IMT, prevalence of abnormal IMT, and percentage with atherosclerotic plaque. In conclusion, although C. pneumoniae was associated with several risk factors for cardiovascular disease in a large cross-sectional population, we found no independent association between seroprevalence to C. pneumoniae and carotid atherosclerosis as measured by carotid IMT.

Serum Ferritin and C282Y Mutation of the Hemochromatosis Gene as Predictors of Asymptomatic Carotid Atherosclerosis in a Community Population

Background and Purpose Serum ferritin and heterozygosity for the C282Y mutation of the hemochromatosis gene have both been associated with an increased risk of cardiovascular events. The purpose of the study was to test whether either is a risk predictor for asymptomatic carotid atherosclerosis. Methods We assessed carotid intima-media wall thickness (IMT) and focal plaque formation by high-resolution B-mode ultrasound, conventional risk factors, serum ferritin levels, and the C282Y mutation of the hemochromatosis gene in a randomly selected community population of 1098 subjects (545 women and 553 men) aged 27 to 77 years. Results After adjustment for conventional risk factors, serum ferritin was not associated with carotid mean IMT. Women with ferritin values over the first quartile (>34 &mgr;g/L) had an adjusted odds ratio of 2.1 (95% CI, 1.3 to 3.4;P =0.0016) for carotid plaque compared with the first quartile. Ferritin was not associated with carotid plaque in men. Subjects who were heterozygous for the C282Y mutation constituted 11.4% of the population, and there was no independent association of this genotype with either carotid IMT or focal plaque formation. Conclusions We conclude that in our community population, C282Y genotype status was not a risk predictor for either carotid mean IMT or plaque formation. Serum ferritin values in women were independently associated with carotid plaque.