Do cardiac risk factors affect the homocysteine and asymmetric dimethylarginine relationship in patients with coronary artery diseases?

Advances in the role of epigenetics in homocysteine-related diseases

Homocysteine has a wide range of biological effects. However, the specific molecular mechanism of its pathogenicity is still unclear. The diseases induced by hyperhomocysteinemia (HHcy) are called homocysteine-related diseases. Clinical treatment of HHcy is mainly through folic acid and B-complex vitamins, which are not effective in reducing the associated end point events. Epigenetics is the alteration of heritable genes caused by DNA methylation, histone modification, noncoding RNAs and chromatin remodeling without altering the DNA sequence. In recent years the role of epigenetics in homocysteine-associated diseases has been gradually discovered. This article summarizes the latest evidence on the role of epigenetics in HHcy, providing new directions for its prevention and treatment.

MTRR rs326119 polymorphism is associated with plasma concentrations of homocysteine and cobalamin, but not with congenital heart disease or coronary atherosclerosis in Brazilian patients

Background

Differences in the distribution of the MTRR rs326119 polymorphism (c.56 + 781 A > C) between patients with congenital heart disease (CHD) and controls have been described in Chinese individuals. The association is thought to be due to deregulation of homocysteine-cobalamin pathways. This has not been replicated in other populations. The primary objective of this study was to assess the influence of the MTRR rs326119 polymorphism on biochemical parameters of vitamin B12 metabolism, coronary lesions, and congenital heart disease in Brazilian subjects.

Methods

We selected 722 patients with CHD, 1432 patients who underwent coronary angiography, and 156 blood donors. Genotyping for the MTRR polymorphism was evaluated by high-resolution melting analysis, and biochemical tests of vitamin B12 metabolism were measured.

Results

Subjects carrying the AC or CC genotypes had higher homocysteine concentrations (9.7 ± 0.4 μmol/L and 10.1 ± 0.6 μmol/L) and lower cobalamin concentrations (260.5 ± 13.3 pmol/L and 275.6 ± 19.9 pmol/L) compared with the subjects carrying the AA genotype (8.7 ± 0.5 μmol/L and 304.8 ± 14.7 pmol/L), respectively. A multiple linear regression model also identified a significant association between the number of C variant alleles with the concentrations of homocysteine and cobalamin. Nonetheless, the allelic and genotypic distributions for MTRR rs326119 were not associated with CHD or coronary atherosclerosis in the studied samples.

Conclusion

Our findings indicate that the MTRR rs326119 variant might be a genetic marker associated with homocysteine and cobalamin concentrations, but not a strong risk factor for CHD or coronary atherosclerosis in the Brazilian population.

Symmetric Dimethylarginine Is Not Associated with Cumulative Inflammatory Load or Classical Cardiovascular Risk Factors in Rheumatoid Arthritis: A 6-Year Follow-Up Study

Symmetric dimethylarginine (SDMA) indirectly inhibits nitric oxide (NO) synthesis and predicts cardiovascular and all-cause mortality in high-risk patients. The aim of our study was to investigate the associations of cumulative inflammatory burden (assessed by serial measurements of inflammatory markers) and classical cardiovascular (CV) disease risk factors with SDMA in RA patients. 201 RA patients (155 females, median age 67 (59–73)) were assessed at baseline (2006). Classical CV disease risk factors were recorded and systemic inflammation was determined by the measurement of C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR). At follow-up (2012) SDMA levels were measured by enzyme-linked immunosorbent assay. Mean SDMA levels in RA population were 0.40 (0.40–0.53) μmol/L. No significant association between SDMA and cumulative inflammatory load was established in the analysis. SDMA levels were not found to be significantly related to CV disease risk factors. We explored the potential relationship between SDMA and cumulative inflammatory burden in patients with RA and obtained negative results. SDMA did not relate to CV disease risk factors in our population and its clinical significance as a surrogate marker of endothelial dysfunction in patients with RA remains to be determined.

Cumulative inflammation associates with asymmetric dimethylarginine in rheumatoid arthritis: a 6 year follow-up study

OBJECTIVE

The aim of the present study was to investigate the associations of cumulative inflammatory burden (assessed by serial measurements of inflammatory markers) and classical cardiovascular disease (CVD) risk factors with asymmetric dimethylarginine (ADMA) in a large prospective cohort of patients with established RA.

METHODS

Two hundred and one RA patients [155 females, median age 67 years (range 59-73)] were assessed at baseline (2006) for the presence of classical CVD risk factors and determination of systemic inflammation by CRP and ESR. Global CVD risk was identified by the Framingham Risk Score and the Reynolds Risk Score. At follow-up (2012), ADMA levels were measured by ELISA. A quarterly measurement of CRP and ESR for each year the patient was in the study was used to produce an average area under the curve (AAUC) for ESR and CRP.

RESULTS

Regression analysis revealed that baseline ESR in 2006 and the AAUC of ESR and CRP all had significant positive relationships with current ADMA (P = 0.004, P < 0.001 and P = 0.002, respectively). Baseline CRP in 2006 was not a significant predictor of ADMA (P = 0.093), although this relationship was in the same direction as the other factors. These results remained consistent after adjustment for classical CVD risk factors.

CONCLUSION

Cumulative inflammatory burden is positively associated with ADMA levels, suggesting a potential pathogenic mechanism through which chronic systemic inflammation exerts deleterious effects on nitric oxide metabolism and endothelial homeostasis. This association is independent of classical CVD risk factors.

Differential associations of angiographic extent and severity of coronary artery disease with asymmetric dimethylarginine but not insulin resistance in non-diabetic men with stable angina: a cross-sectional study

Background

Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthesis inhibitor, and insulin resistance (IR) have been implicated in atherogenesis. Our aim was to estimate relations between ADMA, the magnitude of IR and angiographic indices of extent and severity of coronary atherosclerosis in non-diabetic men with stable coronary artery disease (CAD).

Methods

We studied 151 non-diabetic men (mean age 57 ± 11 years) with stable angina, obstructive CAD (at least 1 luminal diameter stenosis of ≥70% in major coronary segments) and without heart failure, and 34 age-matched controls free of ≥50% coronary narrowings. The following CAD indices were computed: the number of major epicardial vessels with ≥70% stenosis, Sullivan extent score representing a proportion of the visible coronary tree with vessel wall irregularities, and Gensini score which reflects both CAD severity and extent, yet assigning a heavier weight to proximal segments and to the more severe narrowings by a non-linear point system. An estimate of IR was derived by homeostasis model assessment (HOMA-IR) from fasting insulin and glucose.

Results

Among the CAD patients, the proportions of subjects with 1-vessel, 2- vessel and 3-vessel CAD were 26%, 25% and 49%, respectively. ADMA levels were higher in patients with obstructive CAD compared to the controls (0.51 ± 0.10 vs. 0.46 ± 0.09 μmol/L [SD], P = 0.01), whereas HOMA-IR was similar (median, 3.2 [interquartile range: 2.4–4.9] vs. 2.9 [2.3–4.7], P = 0.2). Within the CAD group, ADMA increased across ascending quartiles of Sullivan score (Spearman’s rho = 0.23, P = 0.004), but not with Gensini score (rho = 0.12, P = 0.15) or the number of vessels involved (rho = 0.08, P = 0.3). ADMA correlated to log-transformed Sullivan score (Pearson's r = 0.21, P = 0.008), which was only slightly attenuated upon multivariate adjustment (β = 0.19 ± 0.08 [SEM], P = 0.015). HOMA-IR did not differ according to any measure of angiographic CAD (P ≥ 0.2). ADMA and log (HOMA-IR) were mutually unrelated (r = 0.07, P = 0.4).

Conclusions

ADMA is associated with diffuse but not focal coronary atherosclerosis in non-diabetic men with stable CAD irrespectively of the degree of IR. The independent relationship between ADMA and coronary atherosclerotic burden may contribute to the well-recognized prognostic effect of ADMA in CAD.

Diagnostic value of the combined measurement of serum hcy, serum cys C, and urinary microalbumin in type 2 diabetes mellitus with early complicating diabetic nephropathy

Diabetic nephropathy (DN) is a major cause of end-stage kidney disease, and therefore early diagnosis and intervention may help reverse renal damage. One hundred and sixty-eight patients with T2DM and 56 healthy volunteers (control group) were enrolled at Shandong University Qilu Hospital between April 2010 and October 2012. All subjects underwent blood sampling for sera homocysteine (Hcy) and cystatin C (Cys C) assays and a urine microalbumin test. The patients were divided into three groups according to the urine microalbumin excretion rate (UMAER): the simple DM group (SDM group, n = 51), the early-stage DN group (EDN group, n = 60), and the clinical DN and renal failure group (CDN group, n = 57). Correlation analysis was performed to examine the association between sera Hcy and Cys C levels with UMAER. Our findings showed that sera Hcy level, Cys C level, and UMAER increased significantly in the SDM group (P < 0.05, P < 0.01), the EDN group (P < 0.01), and the CDN group (P < 0.01) as compared with the control group. These three biochemical markers also increased significantly with DN progression (P < 0.01). Correlation analysis showed that sera Hcy and Cys C levels were positively correlated with UMAER (r = 0.702, P < 0.01; r = 0.873, P < 0.01). In conclusion, our results showed that sera Hcy and Cys C levels increased consistently with the development and progression of DN as indicated by UMAER. Sera Hcy and Cys C are sensitive biomarkers for the detection of early-stage DN and monitoring its progression.

Homocysteine induces energy imbalance in rat skeletal muscle: is creatine a protector?

Homocystinuria is a neurometabolic disease caused by a severe deficiency of cystathionine beta-synthase activity, resulting in severe hyperhomocysteinemia. Affected patients present several symptoms including a variable degree of motor dysfunction. In this study, we investigated the effect of chronic hyperhomocysteinemia on the cell viability of the mitochondrion, as well as on some parameters of energy metabolism, such as glucose oxidation and activities of pyruvate kinase, citrate synthase, isocitrate dehydrogenase, malate dehydrogenase, respiratory chain complexes and creatine kinase in gastrocnemius rat skeletal muscle. We also evaluated the effect of creatine on biochemical alterations elicited by hyperhomocysteinemia. Wistar rats received daily subcutaneous injections of homocysteine (0.3-0.6 µmol/g body weight) and/or creatine (50 mg/kg body weight) from the 6th to the 28th days of age. The animals were decapitated 12 h after the last injection. Homocysteine decreased the cell viability of the mitochondrion and the activities of pyruvate kinase and creatine kinase. Succinate dehydrogenase was increased other evaluated parameters were not changed by this amino acid. Creatine, when combined with homocysteine, prevented or caused a synergistic effect on some changes provoked by this amino acid. Creatine per se or creatine plus homocysteine altered glucose oxidation. These findings provide insights into the mechanisms by which homocysteine exerts its effects on skeletal muscle function, more studies are needed to elucidate them. Although creatine prevents some alterations caused by homocysteine, it should be used with caution, mainly in healthy individuals because it could change the homeostasis of normal physiological functions.

Protection of DDAH2 overexpression against homocysteine-induced impairments of DDAH/ADMA/NOS/NO pathway in endothelial cells

BACKGROUND/AIMS

Homocysteine-induced endothelial dysfunction favors the development of cardiovascular diseases through accumulation of endogenous nitric oxide (NO) synthase (NOS) inhibitor asymmetric dimethylarginine (ADMA). Dimethylarginine dimethylaminohydrolase 2 (DDAH2) is the major enzyme for the degradation of ADMA in endothelial cells. The purpose of this study was to determine whether suppressed DDAH2 expression contributed to impairments of DDAH/ADMA/NOS/NO pathway induced by homocysteine in endothelial cells and whether DDAH2 overexpression could prevent endothelial cell dysfunction caused by homocysteine.

METHODS

Liposome-mediated transfection of endothelial cells was performed to establish the cell line of DDAH2 overexpression. After treatment of cells with 1 mmol/L homocysteine for 24 h, the transcription and expression of DDAH1 and DDAH2, DDAH and NOS activities as well as ADMA and NO concentrations were measured.

RESULTS

Treatment of endothelial cells with homocysteine significantly suppressed the transcription and expression of DDAH2 but not DDAH1. This suppression was associated with the declined DDAH activity, increased ADMA accumulation, inhibited NOS activity and decreased NO production in endothelial cells. DDAH2 overexpression not only resisted homocysteine-induced decline of DDAH activity, but also decreased the accumulation of endogenous ADMA, subsequently attenuated the reductions of NOS activity and NO production induced by homocysteine.

CONCLUSIONS

These results indicate that suppression of DDAH2 expression is a culprit for homocysteine-induced impairments of DDAH/ADMA/NOS/NO pathway in endothelial cells, and therapeutic manipulation of DDAH2 expression may be a promising strategy for preventing endothelial dysfunction and cardiovascular diseases associated with hyperhomocysteinemia.