Lack of association between carotid intima-media thickness and methylenetetrahydrofolate reductase gene polymorphism or serum homocysteine in non-insulin-dependent diabetes mellitus

Additive effect between homocysteine and low-density-lipoprotein cholesterol upon incidence of novel carotid plaque formation: data from a Chinese community-based cohort

OBJECTIVE

Homocysteine (HCY) has been associated with carotid plaque in cross-sectional studies, but the prospective relationship between HCY and incident carotid plaque has not been well established. The purpose of this study was to investigate the association between HCY and incidence of novel carotid plaque in a Chinese community-based population without pre-existing carotid atherosclerosis and to assess the additive effect of HCY and low-density lipoprotein cholesterol (LDL-C) on the incidence of novel plaque.

METHODS

At baseline, we measured HCY and other risk factors in subjects aged ≥ 40 years. All participants underwent carotid ultrasound examinations at baseline and after an average of 6.8 years of follow-up. Incidence of plaque was identified if plaque was absent at baseline, but plaque was detected at the end of follow-up. A total of 474 subjects were included in the analysis.

RESULTS

The incidence of novel carotid plaque was 24.47%. Multivariate regression analyses showed that HCY was independently associated with a 1.05-fold-higher likelihood for incident novel plaque (adjusted odds ratio [OR] = 1.05, 95% confidence interval [CI]: 1.01-1.09, P = 0.008). Using tertile 1 and tertile 2 for reference, the top HCY tertile (T3) showed a 2.28-fold-higher likelihood for incident plaque (adjusted OR = 2.28, 95%CI: 1.33-3.93, P = 0.002). The combination of HCY T3 and LDL-C ≥ 3.4 mmol/L had the highest risk for novel plaque formation (adjusted OR = 3.63, 95%CI: 1.67-7.85, P = 0.001) compared to those without either condition. In the LDL-C ≥ 3.4 mmol/L subgroup, HCY was significantly associated with incidence of plaque (adjusted OR = 1.16, 95%CI: 1.04-1.28, P = 0.005, P-interaction = 0.023).

CONCLUSION

In the Chinese community-based population, HCY was independently associated with the incidence of novel carotid plaque. There were additive effect between HCY and LDL-C on the incidence of plaque, the highest risk was observed in individuals with both high HCY levels and LDL-C ≥ 3.4 mmol/L. Our findings suggest that HCY may be a potential target for preventing the incidence of carotid plaque, particularly in individuals with elevated LDL-C levels.

The association between elevated fasting plasma glucose levels and carotid intima-media thickness in non-diabetic adults: a population-based cross-sectional study

We assessed the association between the mean carotid intima-media thickness (CIMT) and fasting plasma glucose (FPG) levels in a low-income population in rural China. Adults aged ≥45 years without a history of diabetes, stroke, or cardiovascular disease were recruited. All participants were categorized into four groups according to FPG level. A total of 3509 participants were analyzed in this study. In the univariate analysis, sex, age, education level, hypertension, central obesity, current smoking, alcohol consumption, and higher levels of FPG, total cholesterol (TC), triglycerides (TG), high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C) were associated with mean CIMT and frequency of increased CIMT. FPG levels were significantly associated with mean CIMT; each 1-mmol/L increase in FPG resulted in a 2.75-μm increase in mean CIMT when adjusted by age, sex, education level, current smoking status, alcohol consumption, hypertension, and the levels of TC, TG, HDL-C, and LDL-C (P = 0.044). However, the association between FPG and the frequency of increased CIMT disappeared after adjusting by covariates. These findings indicate that FPG is an independent determinant of mean CIMT in a non-diabetic population. Management and control of FPG levels is crucial for preventing atherosclerosis in populations with high stroke risks in China.

Lack of association between early atherosclerotic carotid artery wall lesions and serum level of homocysteine

The present study evaluated the possible association of high serum levels of homocysteine with ultrasonographic manifestations of carotid atherosclerosis in 65-year-old Finnish subjects drawn from a population-based cohort. Carotid ultrasonographic measurements were performed on 54 diabetic subjects, 97 subjects with impaired glucose tolerance and 57 normoglycaemic subjects. There were no statistically significant differences between the groups in the homocysteine levels. The median homocysteine level was higher in the subjects with a history of myocardial infarction (MI) (n=9) than in the subjects with no history of MI (14.8 [range 8.7—18.3] vs.12.3 [range 6.4—49.0] µmol/L, p=0.045). In the subjects without a history of MI or stroke, the maximal intima-media thickness (IMT) of the common carotid artery did not differ in the homocysteine quintiles. There was no association between the number of atheromatous plaques and the homocysteine level. In conclusion, although high levels of serum homocysteine were not associated with early atherosclerotic changes (i.e. increased carotid IMT or the number of plaques), high homocysteine concentrations were associated with advanced atherosclerosis (i.e. a history of MI).

Plasma total homocysteine and carotid intima-media thickness in type 1 diabetes: a prospective study

OBJECTIVE

Plasma total homocysteine (tHcy) has been positively associated with carotid intima-media thickness (IMT) in non-diabetic populations and in a few cross-sectional studies of diabetic patients. We investigated cross-sectional and prospective associations of a single measure of tHcy with common and internal carotid IMT over a 6-year period in type 1 diabetes.

RESEARCH DESIGN AND METHODS

tHcy levels were measured once, in plasma obtained in 1997-1999 from patients (n = 599) in the Epidemiology of Diabetes Interventions and Complications (EDIC) study, the observational follow-up of the Diabetes Control and Complications Trial (DCCT). Common and internal carotid IMT were determined twice, in EDIC "Year 6" (1998-2000) and "Year 12" (2004-2006), using B-mode ultra-sonography.

RESULTS

After adjustment, plasma tHcy [median (interquartile range): 6.2 (5.1, 7.5) μmol/L] was significantly correlated with age, diastolic blood pressure, renal dysfunction, and smoking (all p < 0.05). In an unadjusted model only, increasing quartiles of tHcy correlated with common and internal carotid IMT, again at both EDIC time-points (p < 0.01). However, multivariate logistic regression revealed no significant associations between increasing quartiles of tHcy and the 6-year change in common and internal carotid IMT (highest vs. lowest quintile) when adjusted for conventional risk factors.

CONCLUSIONS

In a type 1 diabetes cohort from the EDIC study, plasma tHcy measured in samples drawn in 1997-1999 was associated with measures of common and internal carotid IMT measured both one and seven years later, but not with IMT progression between the two time-points. The data do not support routine measurement of tHcy in people with Type 1 diabetes.

The genetics of vascular complications in diabetes mellitus

Prospective identification of which individuals with diabetes mellitus (DM) are at greatest risk for developing cardiovascular disease (CVD) complications would have considerable public health importance by allowing the allocation of limited resources to be focused on those individuals who would most benefit from aggressive intervention. Over the past 20 years genetic disease association studies have demonstrated that polymorphisms at specific genetic loci may identify those individuals at greatest risk for developing CVD in the setting of DM. This article reviews the evidence accumulated to date on four polymorphic loci with the aim of explaining how these polymorphisms modify the risk for CVD in DM by modifying the functional activity of a specific gene. Use of the knowledge of these genetic differences among individuals in targeting drug therapy (pharmacogenomics) is also discussed.

Methylentetrahydrofolate reductase and nitric oxide synthase polymorphism in patients with atherosclerosis and diabetes

The development of the atherosclerosis is based on multifactorial causes. In addition to the traditional risk factors, gene polymorphisms can play a role in the disease. Therefore in this study we investigated whether the eNOS and MTHFR gene polymorphisms is associated with myocardial infarction and stroke in patients with or without diabetes. We have identified polymorphisms in the NOS 3 gene and one of these polymorphisms, Glu(298-->)Asp, was found to be a major risk factor for carotid artery disease and myocardial infarction. Our results indicate that the MTHFR G677T allele is significantly associated with MI. MTHFR 677 G/T genotyping may be of clinical importance as a prognostic and therapeutic marker, although further studies are needed to substantiate this hypothesis.

Polymorphisms of the methylenetetrahydrofolate reductase, vascular endothelial growth factor, endothelial nitric oxide synthase, monocyte chemoattractant protein-1 and apolipoprotein E genes are not associated with carotid intima-media thickness

BACKGROUND

Single nucleotide polymorphisms in the 5,10-methylenetetrahydrofolate reductase (MTHFR), vascular endothelial growth factor (VEGF), endothelial nitric oxide synthase (eNOS), monocyte chemoattractant protein-1 (MCP-1) and apolipoprotein E (ApoE) genes appear to be a genetic risk factor for atherosclerosis. Common carotid intima-media thickness (cIMT) provides information on the severity of atherosclerosis.

OBJECTIVE

To investigate the relationship between cIMT and gene polymorphisms associated with atherosclerosis in Turkish patients with coronary artery disease (CAD).

METHODS

Sixty-two patients with angiographically diagnosed stable CAD were divided into two groups according to their cIMT values (group 1: n=35, cIMT of 1 mm or greater; group 2: n=27, cIMT of less than 1 mm). MTHFR 677 C/T, VEGF --460 C/T, eNOS 894 G/T, MCP-1 --2518 A/G and ApoE (E2, E3 and E4) gene polymorphisms (where A is adenine, C is cytosine, G is guanine and T is thymine) were analyzed by polymerase chain reaction and restriction fragment length polymorphism. Evaluations of cardiovascular risk factors and coronary atherosclerotic lesions were performed in all patients. Serum homocysteine and high-sensitivity C-reactive protein were measured and compared between the two groups.

RESULTS

Serum high-sensitivity C-reactive protein (P=0.04) and homocysteine (P=0.006) levels were higher in group 1 than in group 2. The ratio of multivessel CAD and previous myocardial infarction was significantly higher in group 1 than in group 2 (P=0.014). In the study population, no significant difference in cIMT was observed according to the polymorphisms studied. Only hyperhomocysteinemia (OR 1.17 [95% CI 1.01 to 1.35], P=0.033) and previous myocardial infarction (OR 3.76 [95% CI 1.10 to 12.81], P=0.034) maintained a significant correlation with cIMT on multiple logistic regression analysis.

CONCLUSION

cIMT is increased in patients with hyperhomocysteinemia, inflammation and extended CAD. MTHFR 677 C/T, VEGF --460 C/T, eNOS 894 G/T, MCP-1 --2518 A/G and ApoE single nucleotide polymorphisms were not associated with increased cIMT.

Measuring subclinical atherosclerosis: is homocysteine relevant?

OBJECTIVES

We systematically reviewed published studies looking at the relationship between total serum homocysteine (tHcy) and subclinical markers of atherosclerosis, such as carotid intimal-medial thickness (C-IMT), coronary artery calcium (CAC) and ankle-brachial index (ABI) in asymptomatic individuals. We analyzed these studies to examine this relationship as well as to guide future avenues of investigation by identifying studies that will help in the inclusion of tHcy levels in current guidelines on atherosclerotic disease management.

BACKGROUND

tHcy has been known to be associated with clinically evident atherosclerotic disease. However, tHcy is not incorporated in current guidelines for diagnosis of subclinical disease in high-risk asymptomatic individuals.

METHODS

We searched online databases (e.g., PUBMED, MEDLINE) for published articles assessing the relationship between tHcy and C-IMT, CAC and ABI. We limited the studies to asymptomatic populations, and excluded any study including symptomatic patients or individuals with a history of coronary, peripheral or cerebrovascular disease.

RESULTS

A systemic review of 19 articles revealed a significant association between elevated levels of tHcy and subclinical markers of atherosclerosis in asymptomatic individuals in most studies. Mean tHcy levels were consistently found to be higher in men compared to women. A total of 12 studies showed a significant association between tHcy and other risk markers of atherosclerosis, even after adjusting for age, sex and conventional risk factors. There were seven studies in unique populations that showed no significant relationship. We also observed that studies lowering baseline tHcy levels did not lead to an improvement in C-IMT, CAC or ABI scores. This might indicate that tHcy has a stronger role as a marker of atherosclerotic disease than as a risk factor for the same.

CONCLUSIONS

Based on our review, we conclude that there is a significant association between the subclinical atherosclerotic process and tHcy, and it shows potential as a cheap marker for risk stratification of asymptomatic patients. However, future studies further elucidating this association and elaborating the exact role of tHcy in the atherosclerotic disease process are required. The results of these studies suggest the incorporation of plasma tHcy levels in future risk reduction protocols for identification of individuals at higher risk of atherosclerotic events, and thus to categorize them for more aggressive treatment with established preventive and therapeutic measures.

Homocysteine and vascular disease in diabetes: a double hit?

Cardiovascular disease is a major problem in diabetes, and risk factors presumably unrelated to diabetes, such as hyperhomocysteinaemia, may be related to the development of cardiovascular complications in diabetic individuals. Plasma homocysteine levels are usually normal in diabetes, although both lower and higher levels have been reported. Homocysteine levels in diabetes are modulated by hyperfiltration and renal dysfunction, as well as low folate status. Insulin resistance does not appear to be a major determinant of plasma homocysteine level. Hyperhomocysteinaemia has been associated with microalbuminuria and retinopathy in type 1 and type 2 diabetes. In patients with type 2 diabetes, plasma homocysteine concentration is a significant predictor of cardiovascular events and death. This relation seems to be stronger in subjects with diabetes than without. The underlying pathophysiological mechanism of this increased vascular risk remains unexplained, but may be related to worsening of endothelial dysfunction and/or structural vessel properties induced by oxidative stress. Because homocysteine and diabetes have apparent synergistic detrimental vascular effects, patients with diabetes are candidates for screening and treatment with folic acid until the results of ongoing clinical trials are available.

Association between uric acid and carotid atherosclerosis in elderly persons

OBJECTIVE

Several cohort studies have shown a link between serum uric acid (SUA) and subsequent cardiovascular disease. However, such an association did not remain significant after adjusting for concomitant risk factors for atherosclerosis in some studies. Thus, the role of SUA as an independent risk factor remains controversial. We therefore investigated the association between SUA and sclerotic lesions of common carotid atherosclerosis.

PATIENTS AND METHODS

We evaluated sclerotic lesions of the common carotid arterial intima-media thickness (IMT) by ultrasonography in 398 men aged 74+/-8 (range, 60-97) years and 521 women aged 75+/-8 (range, 60-104) years. To investigate the relation between SUA and various factors, all subjects were divided into three groups based on the tertile of SUA.

RESULTS

Stepwise multiple linear regression analysis using IMT as an objective variable, adjusted by various risk factors as explanatory variables showed that SUA [B, 0.0099; 95% confidence interval (CI), 0.0022-0.0175] was a significant independent contributing factor along with known risk factors such as age, sex, smoking status, systolic blood pressure, diastolic blood pressure, antihypertensive drug use, HDL-cholesterol, and LDL-cholesterol. Multiple logistic regression analysis for carotid IMT as a tertile of SUA and dependent variables showed that the adjusted odds ratio was 1.25 (95% CI, 0.87-1.78) for those in the middle tertile (4.2-5.5 mg/dl), and 1.66 (95% CI, 1.16-2.39) for those in the highest tertile (5.6-14.1 mg/dl) compared to that for subjects in the lowest tertile of SUA levels (0.51-4.1 mg/dl).

CONCLUSION

We suggest that SUA is a risk factor or marker for ultrasonographically determined IMT.

Homocysteine and carotid intima-media thickness: a critical appraisal of the evidence

This review examines the relationship between hyperhomocysteinemia, a risk factor for vascular disease, and carotid intima-media thickness (CIMT), a valid marker of generalized atherosclerosis and future vascular disease risk. The relationship between two important determinants of hyperhomocysteinemia in the general population-folate status and the 677C --> T methylenetetrahydrofolate reductase (MTHFR) polymorphism-and CIMT is also covered.

METHODS

We searched literature databases for articles examining homocysteine and CIMT published before September 2003.

RESULTS

We identified 54 studies. Observational studies generally failed to demonstrate a relationship between homocysteine and CIMT in homocystinuric, uremic, hypercholesterolemic or non-insulin-dependent diabetes mellitus patients or in subjects with insulin insensitivity. Weak associations, but usually only in certain sub-populations were found in vascular disease patients and in population-based studies. B vitamins reduce the progression of CIMT in renal transplant recipients and vascular disease patients as demonstrated by two trials. The majority of studies demonstrated increased CIMT in individuals with the MTHFR 677TT genotype. Folate status showed no relation to CIMT.

DISCUSSION

In non-patient populations, hyperhomocysteinemia is weakly associated with CIMT. The association of the 677 C--> T MTHFR polymorphism with CIMT further supports this finding. Lastly, folate levels may need to reach a critically low status before an association can be found between folate and CIMT. Larger trials in various population types are needed to determine whether folate alone or in combination with Vitamins B6 and B12 will slow down or even reverse atherosclerotic progression.

Glucose level is a major determinant of carotid intima???media thickness in patients with hypertension and hyperglycemia

BACKGROUND

A causal relationship has been established between hyperglycemia and cardiovascular diseases, but no threshold has been retained to determine a 'glycemia-associated' cardiovascular risk. Carotid intima-media thickness (CIMT) is an independent predictor for cardiovascular events. High blood pressure is a major determinant of CIMT.

OBJECTIVES

To determine the influence of fasting glycemia on CIMT in hypertensive patients with either normal fasting glucose, impaired fasting glucose (IFG) or type 2 diabetes (DM-2).

METHODS

We included 158 essential hypertensive patients with either normal fasting glucose (n=74), IFG (n=24) or DM-2 (n=60) in a cross-sectional study. Common carotid IMT was measured with a high resolution echotracking system.

RESULTS

CIMT of DM-2 patients was significantly higher than that of IFG and normal fasting glucose patients (809 +/- 180, 697 +/- 151 and 689 +/- 134 microm, respectively; analysis of variance (ANOVA) P <0.0001). In multivariate analysis in normal fasting glucose patients, local pulse pressure and age were the major determinants of CIMT, whereas glycemia was not. In IFG and DM-2 patients, fasting glycemia was strongly associated with CIMT, explaining 21 and 18% of its variance, respectively. Particularly, in IFG patients, an increase in 1 mmol/l glycemia was associated with a 165 microm increase in CIMT. In hyperglycemic patients, with either IFG or DM-2, age was an important determinant of CIMT, whereas local pulse pressure was not.

CONCLUSION

These data suggest that glycemia is a major independent determinant of CIMT in hypertensive hyperglycemic patients, not only in DM-2 patients but also at the earlier stage of IFG, offsetting the mechanical role of local pulse pressure.

Homocysteine levels are associated with the severity of peripheral arterial disease in Type 2 diabetic patients

BACKGROUND

Homocysteine levels are positively associated with the risk of cardiovascular disease. They might be determined by both MTHFR677C-->T polymorphisms and folate or B-vitamin status.

OBJECTIVES

To investigate the possible association between plasma homocysteine levels and its genetic or environmental determinants and either the presence or the severity of peripheral arterial disease (PAD), in Type 2 diabetic patients.

METHODS

From a cohort of 944 patients with Type 2 diabetes, 135 patients with PAD were selected, and frequency-matched for age and sex with 219 Type 2 diabetic control patients without macrovascular complications. According to the increasing severity of the disease, patients were divided into PAD1 (only diffuse calcifications of the arteries without any stenosis or occlusion), PAD2 (one or two stenosis or occlusions) and PAD3 (three or more).

RESULTS

Homocysteine levels were similar in control and case patients (10.3 micromol L-1 vs. 10.7 micromol L-1, P = 0.53); however, a significant increase was found in PAD3 patients: odds ratio = 2.77 (95% confidence interval 1.14, 6.72) for patients with homocysteine levels above the median vs. those under the median in multivariate analysis. Although all significantly associated with homocysteine levels, neither MTHFR genotype nor folic acid or vitamin B12 levels were associated with severity of PAD. A significant interaction (P < 0.05) was found between folic acid and MTHFR polymorphism in determining the levels of homocysteine.

CONCLUSIONS

In Type 2 diabetes, homocysteine was associated with the angiographic severity of PAD, but neither the genotypes nor vitamin levels contributed to this association.

Plasma homocysteine and S-adenosylmethionine in erythrocytes as determinants of carotid intima-media thickness: different effects in diabetic and non-diabetic individuals. The Hoorn Study

OBJECTIVE

Hyperhomocysteinemia is a risk factor for atherothrombosis. Through unknown mechanisms, individuals with type 2 diabetes appear particularly susceptible. We determined whether components of homocysteine metabolism are associated with intima-media thickness in individuals with and without type 2 diabetes.

METHODS AND RESULTS

In a cross-sectional design, we studied 231 Caucasian individuals, 60.6% having type 2 diabetes. We measured fasting homocysteine, vitamin B6 and vitamin B12 in plasma, and folate, S-adenosylmethionine and S-adenosylhomocysteine in plasma and erythrocytes. A homocysteine concentration >12 micromol/l was associated with a greater intima-media thickness of +0.07 mm (95% CI, +0.01 to +0.13; P=0.03) among diabetic individuals and of -0.004 mm (95%CI, -0.08 to +0.07; P=0.92) among non-diabetic individuals. An erythrocyte S-adenosylmethionine concentration above >4000 nmol/l was associated with a smaller intima-media thickness of -0.04 mm (95%CI, -0.10 to +0.02; P=0.17) for diabetic individuals versus -0.12 mm (95%CI, -0.20 to -0.36; P=0.005) for non-diabetic individuals.

CONCLUSIONS

With regard to carotid intima-media thickness, individuals with diabetes appear more susceptible to the detrimental effects of homocysteine than non-diabetic individuals. In addition, diabetic individuals may lack the protective effect on the vascular wall conferred by high concentrations of S-adenosylmethionine. These findings may help explain why hyperhomocysteinemia is an especially strong risk factor for atherothrombosis among individuals with type 2 diabetes.

Genetics of intima-media thickness

PURPOSE OF REVIEW

Increased carotid artery intima-media thickness is associated with an increased risk of coronary heart disease or cerebrovascular disease and is a powerful predictor of cardiovascular and cerebrovascular outcomes. Consequently, the measurement is now used in a number of case control, cohort and familial and linkage studies as an intermediate phenotype for the investigation of the genetic and environmental determinants of atherosclerosis. The aim of this paper is to review the most recent available data on the genetic determinants of carotid intima-media thickness.

RECENT FINDINGS

Genes could account for a significant amount of variation in carotid intima-media thickness: up to 30-66%. Carotid intima-media thickness progressed more rapidly with age in familial hypercholesterolemia patients than in patients without his condition. Familial hypercholesterolemia patients with a null LDL receptor allele tended to have higher carotid intima-media thickness than patients carrying the LDL receptor defective allele. Small association studies showing positive or negative results with the angiotensinogen gene variants as well as with the angiotensin converting enzyme I/D polymorphism add to the confusion in this largely controversial area. Differing results may depend on the vascular territory and genetic background. New associations have been described in small studies.

SUMMARY

Studies on the association of polymorphisms and intima-media thickness are frequently disappointing and lead occasionally to conflicting results. Among study limitations is the fact that mostly single gene effects are considered; longitudinal cohort studies may be more appropriate than case control studies. Ongoing large prospective population studies and clinical trials have integrated the measurements of intima-media thickness and genotype determination with a genomic approach. As a result, in the near future we may see more important and robust results with significant consequences on our understanding of genetic determinants of atherosclerotic cardiovascular disease.

Homocisteína y progresión de la aterosclerosis de la arteria carótida en pacientes con enfermedad coronaria

BACKGROUND AND OBJECTIVE

Carotid intima-media thickness (IMT) is a marker of generalized atherosclerosis. Sequential evaluation of carotid IMT has permitted to know the factors involved in its progression. However, there are few studies about the influence of homocysteine in such progression. The aim of this work was to know the effect of homocysteine values on the evolution of carotid IMT in patients with coronary disease.

PATIENTS AND METHOD

Carotid IMT (baseline and after 4 years of follow-up) was evaluated by a B-mode ultrasonography in 187 patients with coronary disease (166 males and 21 females; age: mean [standard deviation], 60 [7] years); 185 patients were treated with statins from the beginning of the study.

RESULTS

Carotid IMT progression was confirmed in 59 patients (31.6%; 95% confidence interval [CI], 25.0-38.7%). Cardiovascular risk factors, basal biochemical parameters and methylenetetrahydrofolate reductase-C677T polymorphism were similar in patients with and without progression except for homocysteine values which were higher in the former (13.3 [5.3]; 95% CI, 12.0-14.6 vs 11.1 [3.5]; 95% CI, 10.5-11.7 (mol/l; p = 0.001). Biochemical changes at the end of the study were similar in both groups. In the multivariate analysis, IMT progression was associated with basal values of homocysteine (odds ratio [OR] 1.19; 95% CI, 1.07-1.31; p = 0.0008), female gender (OR 3.50; 95% CI, 1.17-10.50; p = 0.02), hypertension (OR 2.52; 95% CI, 1.14-5.59; p = 0.02) and basal high-density lipoprotein (HDL)-cholesterol values (OR, 0.94; 95% CI, 0.90-0.98; p = 0.009).

CONCLUSIONS

The concentration of homocysteine is associated with the progression of carotid atherosclerosis in patients with coronary heart disease treated with statins.

Heritability of carotid artery intima-medial thickness in type 2 diabetes

BACKGROUND AND PURPOSE

Carotid artery intima-medial thickness (IMT), a marker of subclinical atherosclerosis, is a strong predictor of subsequent cardiovascular morbidity. The role of genetic factors in thickening of the carotid wall remains largely unknown. We hypothesize that in families with multiple members having diabetes, carotid IMT is likely to be associated with both inherited and environmental factors.

METHODS

To determine the extent of the familial aggregation of carotid IMT in the presence of type 2 diabetes, we studied 252 individuals with type 2 diabetes (mean age 60.6 years) from 122 families. Common carotid artery IMT was measured by high-resolution B-mode ultrasonography. Other measured factors included lipid levels, body mass index, fasting glucose, hemoglobin A1c, albumin/creatinine ratio, and self-reported medical history. Heritability estimates were obtained by using variance component methodology, as implemented in the SOLAR software package. Tests for association between carotid IMT and variables were performed by using mixed model analysis while accounting for the correlation due to family structure.

RESULTS

The age-, sex-, and race-adjusted heritability estimate for carotid IMT was 0.32 (SE 0.17, P=0.02). Further adjustment for total cholesterol, hypertension status, and current smoking status resulted in a heritability estimate of 0.41 (SE 0.16, P=0.004). The strongest predictors of carotid IMT, after adjusting for age and sex, were ethnicity (African American versus white), total cholesterol, and smoking status.

CONCLUSIONS

These data provide empirical evidence that subclinical cardiovascular disease has a significant genetic component and merits a search for the genes involved in susceptibility to the atherosclerotic complications of diabetes.

The 807T allele in alpha2 integrin is protective against atherosclerotic arterial wall thickening and the occurrence of plaque in patients with type 2 diabetes

Polymorphism of alpha2 integrin (C807T) is shown to be associated with an increased incidence of thrombotic cardiovascular events. However, it is not clear whether this polymorphism is associated with atherosclerotic arterial wall thickening. In this study, we examined the association of C807T polymorphism with arterial wall thickness in 265 control subjects and 272 patients with type 2 diabetes. In all subjects, intima-media thickness of the right carotid artery in the 807TT group (0.649 +/- 0.028 mm [SE]) was significantly (P = 0.0228, Scheffe's F test) less than in the 807CC group (0.767 +/- 0.033). This effect of polymorphism is gene dose dependent (P = 0.0227, ANOVA). The similar association was also observed in patients with diabetes but not in control subjects. Multiple regression analysis in all subjects revealed that the T allele was inversely (beta = -0.095, P = 0.021) associated with intima-media thickness independent of age, HbA(1c), and HDL cholesterol. Finally, an inverse relation between the occurrence of carotid plaque and the T allele was observed in patients with diabetes with an adjusted odds ratio of 0.487 (P = 0.031) in multiple logistic regression analyses. These results suggest that the number of 807T alleles in alpha2 integrin is protective against atherosclerotic arterial wall thickening and the occurrence of plaque in patients with type 2 diabetes.

Plasma homocysteine, methylenetetrahydrofolate reductase gene polymorphism and carotid intima-media thickness in Italian type 2 diabetic patients

BACKGROUND

Moderately elevated levels of homocysteine have been associated with an increased cardiovascular risk in type 2 diabetic patients. The role of methylenetetrahydrofolate reductase gene polymorphism is less clear.

MATERIALS AND METHODS

We investigated the contribution of plasma homocysteine levels and the methylenetetrahydrofolate reductase gene polymorphism to the variability of carotid intima-media thickness in 124 consecutive Italian patients with type 2 diabetes mellitus. Fasting plasma homocysteine was measured by high-pressure liquid chromatography with an electrochemical detector; methylenetetrahydrofolate reductase genotypes were determined by polymerase chain reaction and restriction enzyme digestion. The carotid intima-media thickness was evaluated with high-resolution B-mode ultrasonography.

RESULTS

Age, creatinine and plasma homocysteine levels showed a positive correlation with mean carotid intima-media thickness values, but only age and creatinine levels were still associated with mean carotid intima-media thickness values in the multivariate analysis. Plasma homocysteine levels were significantly higher in the patients bearing the 677T/677T genotype of the methylenetetrahydrofolate reductase polymorphism; mean carotid intima-media thickness values were not different in the three different methylenetetrahydrofolate reductase genotypes.

CONCLUSION

In 124 Italian patients with type 2 diabetes mellitus, basal levels of plasma homocysteine, as well as methylenetetrahydrofolate reductase gene polymorphism, did not explain the variability of mean carotid intima-media thickness.

Heterogeneity of the association between plasma homocysteine and atherothrombotic disease: insights from studies of vascular structure and function

Among individuals with severe hyperhomocysteinaemia, there is a striking heterogeneity in the severity of the clinical features. This observation demonstrates that factors must exist that modulate the relationship between hyperhomocysteinaemia and clinical disease. Investigations of the association between mild-to-moderate hyperhomocysteinaemia and atherothrombotic disease also suggest heterogeneity in the association between plasma homocysteine levels and 1) clinical disease; 2) angiographic and echographic estimates of the extent of atherosclerosis; 3) arterial stiffness; 4) endothelial function; and 5) procoagulant status. The commonly held view that homocysteine is a vasculotoxic substance that promotes atherogenesis by causing endothelial damage is incomplete, because it cannot explain this heterogeneity. I suggest that homocysteine may have both prothrombotic and proatherogenic properties, but that there are strong, as yet unidentified enhancing and protective factors, the prevalence of which may differ among populations. This concept could account for some of the observed heterogeneity. Identifying these factors would be of major clinical importance and would provide crucial mechanistic insights.

Antiatherogenic mitochondrial genotype in patients with type 2 diabetes

OBJECTIVE

To evaluate the significance of a longevity-associated mitochondrial genotype (Mt5178A) derived from a C --> A transversion at nucleotide position 5178 of mitochondrial DNA, which causes a Leu-to-Met substitution within the NADH dehydrogenase subunit 2 gene, in type 2 diabetic subjects.

RESEARCH DESIGN AND METHODS

Mt5178 typing was done by polymerase chain reaction-restriction fragment-length polymorphism with the restriction enzyme AluI in 1,148 type 2 diabetic Japanese subjects, and the results were compared with the clinical characteristics. Then, the association of Mt5178 type with early atherosclerotic changes of the bilateral carotid arteries on ultrasonography was assessed in 412 diabetic subjects randomly selected from the original 1,148 type 2 diabetic subjects, while maintaining the same frequency of Mt5178A and Mt5178C.

RESULTS

The frequency of Mt5178A in the type 2 diabetic subjects (454 of 1,148; 40%) was not different from that previously found in healthy blood donors (114 of 252; 45%). Clinical characteristics regarding diabetes were not significantly different between the Mt5178A group (n = 454) and the Mt5178C group (n = 694). However, the mean intima-media thickness (IMT) at six sites in the bilateral carotid arteries was significantly smaller in the Mrt5178A group than in the Mt5178C group (0.906 +/- 0.018 vs. 0.995 +/- 0.021 mm, mean +/- SEM, P = 0.022), and the Mt5178 type was significantly correlated with both the mean IMT and the presence of plaque on multiple regression analysis and discriminant analysis.

CONCLUSIONS

The Mt5178A genotype may be unrelated to the etiology of type 2 diabetes. However, Mt5178A seems to have an antiatherogenic effect, at least in type 2 diabetic individuals.