Is there a causal role for homocysteine concentration in blood pressure? A Mendelian randomization study

Homocysteine, hyperhomocysteinemia, and H-type hypertension

Homocysteine (Hcy) is a sulphur-containing nonessential amino acid derived from the intermediate metabolites of methionine. Methionine is obtained from dietary proteins, such as poultry, meat, eggs, seafood, and dairy products. Abnormalities in Hcy metabolic pathways, deficiencies in dietary methionine, folate, and vitamins B12, B6, and B2 and genetic defects, polymorphisms, or mutations in Hcy metabolism-related enzymes may lead to an increase in plasma Hcy levels. Generally, a plasma Hcy level higher than 10 or 15 μmol/L has been defined as hyperhomocysteinemia (HHcy). An individual with essential hypertension complicated with HHcy is considered to have H-type hypertension (HTH). Currently, HHcy is considered a novel independent risk factor for various cardiovascular diseases. To provide a useful reference for clinicians, the research progress on Hcy, HHcy, and HTH in recent years was systematically reviewed here, with a focus on the source and metabolic pathways of Hcy, plasma Hcy levels and influencing factors, detection methods for plasma Hcy levels, relationship between Hcy concentration and hypertension, pathogenesis of HTH, cardiovascular complications of HTH, and treatment of HTH.

Association Between Plasma Homocysteine Level and Mortality: A Mendelian Randomization Study

BACKGROUND AND OBJECTIVES

In previous studies, high homocysteine levels were associated with high cardiovascular mortality. However, these results were inconsistent with those of randomized controlled trials. We aimed to evaluate the causal role of homocysteine on all-cause and cardiovascular mortality using Mendelian randomization (MR) analysis.

METHODS

This study included the 10,005 participants in the Namwon Study. In conventional observational analysis, age, sex, survey years, lifestyles, body mass index, comorbidities, and serum folate level were adjusted using multivariate Cox proportional regression. MR using 2-stage least squares regression was used to evaluate the association between genetically predicted plasma homocysteine levels and mortality. Age, sex, and survey years were adjusted for each stage. The methylenetetrahydrofolate reductase (MTHFR) polymorphism was used as an instrumental variable for predicting plasma homocysteine levels.

RESULTS

Observed homocysteine levels were positively associated with all-cause (hazard ratio [HR], 1.40; 95% confidence interval [CI], 1.26-1.54) and cardiovascular (HR, 1.62; 95% CI, 1.28-2.06) mortality when plasma homocysteine levels doubled. However, these associations were not significant in MR analysis. The HRs of doubling genetically predicted plasma homocysteine levels for all-cause and cardiovascular mortality were 0.99 (95% CI, 0.62-1.57) and 1.76 (95% CI, 0.54-5.77), respectively.

CONCLUSIONS

This MR analysis did not support a causal role for elevated plasma homocysteine concentrations in premature deaths.

Plasma homocysteine levels and risk of congestive heart failure or cardiomyopathy: A Mendelian randomization study

Background

Although observational studies have demonstrated associations between elevated plasma homocysteine levels and the risk of cardiovascular diseases, controversy remains.

Objective

This study investigated the causal association of plasma homocysteine levels with congestive heart failure and cardiomyopathy risk.

Methods

We performed a two-sample Mendelian randomization (MR) study of congestive heart failure (n = 218,792), cardiomyopathy (n = 159,811), and non-ischemic cardiomyopathy (n = 187,152). Genetic summary data on the association of single-nucleotide polymorphisms with homocysteine were extracted from the most extensive genome-wide association study of 44,147 individuals. MR analyses, including the random-effect inverse variance-weighted (IVW) meta-analysis, weighted median, simple median, maximum likelihood, penalized weighted median, MR-PRESSO, and MR-Egger regression, were used to estimate the associations between the selected single-nucleotide polymorphisms and congestive heart failure or cardiomyopathy.

Results

The MR analyses revealed no causal role of higher genetically predicted plasma homocysteine levels with congestive heart failure risk (random-effect IVW, odds ratio [OR] per standard deviation (SD) increase in homocysteine levels = 1.753, 95% confidence interval [CI] = 0.674-4.562, P = 0.250), cardiomyopathy (random-effect IVW, OR per SD increase in homocysteine levels = 0.805, 95% CI = 0.583 to 1.020, P = 0.189), or non-ischemic cardiomyopathy (random-effect IVW, OR per SD increase in homocysteine levels = 1.064, 95% CI = 0.927-1.222, P = 0.379). The results were consistent with other analytical methods and sensitivity analyses.

Conclusion

Genetically predicted homocysteine level was not associated with congestive heart failure or cardiomyopathy risk. It is unlikely that homocysteine-lowering therapy decreases the incidence or improves the outcomes of congestive heart failure and cardiomyopathy.

Adolescent Afghan Refugees Display a High Prevalence of Hyperhomocysteinemia and Associated Micronutrients Deficiencies Indicating an Enhanced Risk of Cardiovascular Disease in Later Life

A growing body of research evidence suggests that elevated homocysteine level (hyperhomocysteinemia) is an independent risk factor for cardiovascular diseases. The current study aimed to investigate the prevalence and associated risk factors for hyperhomocysteinemia among adolescent Afghan refugees aged 10−19 years. In total, 206 healthy adolescent boys and girls were randomly recruited from a refugee village in Peshawar, Pakistan, in 2020. Socio-demographic data, anthropometric assessment, and blood sample collection were performed following standard methods. Serum homocysteine was assessed using a chemiluminescent microparticle immunoassay, with hyperhomocysteinemia defined as levels ≥ 15 µmol/L. The overall prevalence of hyperhomocysteinemia was 25%, with mean homocysteine levels significantly (p = 0.004) higher among boys (14.1 µmol/L) than girls (11.8 µmol/L). Multivariate logistic regression analysis revealed a significant association between hyperhomocysteineimia and serum levels of vitamin B12 (OR 0.29; 95% CI of 0.14 to 0.62; p < 0.01) and folate (OR 0.1; 95% CI of 0.03 to 0.27; p < 0.001). Overall, our study findings indicate high prevalence of hyperhomocysteinemia among adolescent Afghan refugees who are potentially at high risk of developing cardiovascular diseases in future. There is a dire need to develop and implement nutritional and public health strategies to control hyperhomocysteinemia, protect against related diseases and complications in future, and ensure healthy lives and well-being among these vulnerable populations.

Homocysteine and female fertility, pregnancy loss and offspring birthweight: a two-sample Mendelian randomization study

BACKGROUND/OBJECTIVES

Observational studies link elevated homocysteine concentrations (Hcy) with female fertility, pregnancy loss, and low offspring birthweight. Maternal rs1801133, a functional variant in MTHFR strongly associated with lifelong elevated Hcy, is associated with recurrent pregnancy loss and offspring birthweight in Asian women. We investigated if genetically elevated Hcy is associated with fertility, pregnancy loss, and offspring birthweight in European women.

SUBJECTS/METHODS

We performed a two-sample Mendelian randomization (MR) study using publicly available data. We obtained 18 genetic variants (five involved in Hcy metabolism) explaining up to 5.9% of the variance in Hcy from a genome-wide association meta-analysis of 44,147 European individuals (82% women). We investigated fertility (including age at menopause), pregnancy loss, and offspring birthweight in the UK Biobank (N = 194,174), EGG (N = 190,406), and ReproGen (N = 69,360-252,514) consortia using summary statistics. We calculated inverse-variance weighted, and several sensitivity MR regression statistics.

RESULTS

rs1801133 was associated with a 7.45 months (95% CI: 4.09, 10.80) increase in age at menopause and 29.69 (12.87, 46.51) g decrease in offspring birthweight per SD increase in Hcy in the UK biobank, and confirmed in EGG and ReproGen. MR for Hcy metabolism alone (five variants in MTHFR, MTR, CBS) showed similar results for offspring birthweight across consortia. However, using all 18 variants resulted in no association for any of the outcomes across consortia.

CONCLUSION

Hcy and suggestively vitamin B variants are most likely the drug targets for folate supplementation in pregnant women on the offspring birthweight, while Hcy variants related to renal function or diabetes are not involved.

Prevalence and risk factors for hyperhomocysteinemia: a population-based cross-sectional study from Hunan, China

OBJECTIVES

Hyperhomocysteinemia is an independent risk factor for cardiovascular diseases. We aimed to investigate the prevalence and risk factors for hyperhomocysteinemia, especially modifiable lifestyle factors, such as smoking behaviour and dietary factors.

DESIGN

Population-based cross-sectional study.

SETTING

Hunan Province, China PARTICIPANTS: A total of 4012 participants completed the study, between July 2013 and March 2014. The median age is 55 (interquartile range: 45-63) years, with 1644 males (41%) and 2368 females (59%).

MAIN OUTCOME MEASURES

Homocysteine level were measured by the microplate enzyme immunoassay method. Hyperthomocysteinemia was defined as ≥15 µmol/L. Questionnaire was used to investigate potential risk factors of hyperhomocysteinemia. Crude odd ratio (OR) or adjusted OR with 95% CI were determined by using univariable or multivariable logistic regression models.

RESULTS

The prevalence of hyperhomocysteinemia is 35.4% (45.4% vs 28.5% for men, women, respectively). One-year increase in age is significantly associated with 2% higher risk of hyperhomocysteinemia (OR=1.02, 95% CI: 1.01 to 1.03). One unit increase of BMI is associated with 5% higher risk of hyperhomocysteinemia (OR=1.05, 95% CI: 1.03 to 1.07). Compared with the non-smoker, smoking participants have a 24% higher risk of hyperhomocysteinemia (OR=1.24, 95% CI: 1.006 to 1.53), while the risk for those quitting smoking are not significantly different (OR=1.14, 95% CI: 0.85 to 1.54). compared with those consuming fruit and vegetable at least once every day, those consuming less than once every day had a significantly higher risk of hyperhomocysteinemia (OR=1.29, 95% CI:1.11 to 1.50). In addition, we found there were significant sex interaction with education level or alcohol drinking on the risk of hyperhomocysteinemia (p_interaction <0.05).

CONCLUSIONS

Higher BMI and older age are potential risk factors for hyperhomocysteinemia. Current smoking but not quitting smoking is associated with higher risk of hyperhomocysteinemia. Fruit and vegetable consumption may have protective effect against hyperhomocysteinemia. Alcohol consumption or education level might interact to influence the risk of hyperhomocysteinemia.

The significance of homocysteine in patients with hypertension

Cardiovascular disease is the most common cause of death in developed countries. Important factors leading to ischemic heart disease and strokes are hypertension and high levels of homocysteine in blood serum. The coexistence of these two factors significantly increases the risk of these diseases and premature deaths. Many studies indicate that patients with hypertension are significantly more likely to demonstrate increased blood serum homocysteine levels than those with normal blood pressure. This may be caused by a higher incidence of overweight, high intake of salt and increased uric acid levels. It has been shown that both these factors increase the prevalence of hypertension and lead to higher homocysteine levels. However, the results of some studies indicate that arterial hypertension and homocysteinemia are causally related. It was shown, among other things, that high homocysteine levels damage the endothelium and reduce nitric oxide synthesis, which may directly lead to hypertension. Serum homocysteine levels are slightly higher in patients with white coat hypertension than they are in healthy individuals and may therefore also increase the risk of cardiovascular diseases. Several authors have also shown that the levels of homocysteine in blood serum are higher in so-called non-dippers, i.e., patients with no night-time pressure drop. The lack of a 10%–20% decrease in blood pressure at night is associated with increased cardiovascular complications. Strokes occur especially frequently in older people with arterial hypertension and hyperhomocysteinemia. The administration of B vitamins and folic acid significantly reduces serum homocysteine levels. The administration of this acid also slightly, but statistically significantly, increases the effectiveness of hypotensive drugs. Large meta-analyses meta-analysis indicate that the increased supply of folic acid in patients with hypertension significantly reduces the risk of stroke. Such management is particularly effective in patients with hypertension and hyperhomocysteinemia.

Hypertension-Mediated Organ Damage Correlates With Serum Homocysteine Level in Community-Dwelling Elderly Chinese: The North Shanghai Study

Introduction: Serum homocysteine (Hcy) level is associated with cardiocerebrovascular disease. However, the relationship between Hcy and hypertension-mediated organ damage (HMOD) in non-hospitalized residents has not been elucidated. We aimed to investigate the association of HMOD with Hcy in elderly Chinese.

Methods: One thousand seven hundred and forty-four community-dwelling elderly Chinese (age ≥65 years) participated in the Northern Shanghai Study from Jun. 2014 to Aug. 2015. Hyperhomocysteinemia (HHcy) was defined as serum Hcy ≥15 mmol/L, and HMOD was estimated as arterial stiffness [carotid-femoral pulse wave velocity (CF-PWV) and ankle-brachial index (ABI)], cardiac impairment [left ventricular (LV) hypertrophy and LV diastolic dysfunction], and renal dysfunction [estimated glomerular filtration rate (eGFR) and urinary albumin/creatinine ratio]. Linear and logistic regression models were built to explore the associations of HMOD with Hcy.

Results: Among 1,744 participants, 632 (36.2%) were diagnosed as HHcy. HHcy group had more men (61.2 vs. 35.3%), with higher age (73.7 ± 6.7 vs. 70.4 ± 5.3 years) and BMI (24.2 ± 3.4 vs. 23.7 ± 3.5 kg/m²). Linear regression analysis showed that serum Hcy level was positively associated CF-PWV and negatively associated with ABI and eGFR. By logistic regression, HHcy was significantly associated with abnormal CF-PWV [odds ratio (OR) = 1.53, 95% confidence interval (CI) 1.08–2.16] and ABI (OR = 1.55, 95% CI 1.17–2.04), and decreased eGFR (OR = 7.09, 95% CI 4.03–12.47) after adjustment for covariates. Moreover, similar associations of serum Hcy level with CF-PWV and eGFR were observed in subgroups by gender and hypertensive state.

Conclusion: HMOD, particularly renal dysfunction and arterial stiffening, was significantly and independently associated with increased serum Hcy level in the elderly Chinese.

Clinical Trial Registration: [ClinicalTrial.gov], identifier [NCT02368938].

No causal association between plasma homocysteine levels and atrial fibrillation: A Mendelian randomization study

BACKGROUND AND AIMS

Although several studies have shown an association between plasma homocysteine (Hcy) levels and atrial fibrillation (AF), the causality remains unclear. We undertook a Mendelian randomization (MR) study to investigate the causal association between Hcy and AF.

METHODS AND RESULTS

Single-nucleotide polymorphisms (SNPs) which genome-wide significantly associated with plasma Hcy levels were obtained from a genome-wide meta-analysis (N = 44 147). MR analyses including the random-effect inverse variance-weighted (IVW) meta-analysis, weighted median analysis, and MR-Egger regression were used to estimate the associations between the selected SNPs and AF based on a meta-analysis of genome-wide association study for AF (N = 588 190). The MR analyses revealed no causal role of genetically elevated plasma Hcy levels with AF risk (random-effect IVW, odds ratio per 1 SD increase in Hcy levels = 0.972, 95% confidence interval = 0.919 to 1.027, P = 0.308). The results were consistent with the weighted median method, MR-Egger and the analysis after excluding the pleiotropic SNPs. No heterogeneity and directional pleiotropy were observed in sensitivity analyses.

CONCLUSION

The findings suggested that plasma Hcy levels were not causally associated with AF.

Exploration of the risk factors of essential hypertension with hyperhomocysteinemia: A hospital-based study and nomogram analysis

OBJECTIVES

To explore the risk factors of essential hypertension with hyperhomocysteinemia (H-type hypertension) and design a nomogram to predict this risk.

METHODS

A hospital-based study was conducted on 1,712 individuals, including 282 patients with H-type hypertension, 105 patients with simple hypertension, 645 individuals with hyperhomocysteinemia, and 680 healthy controls. Logistic regression and nomogram models were applied to evaluate the risk factors.

RESULTS

Logistic regression showed that advanced age, male sex, high body mass index (BMI), high total cholesterol levels, high glucose levels, and high creatinine levels were risk factors of H-type hypertension in the healthy population and were integrated into the nomogram model. Advanced age, male sex, high BMI, high total cholesterol levels, and high glucose levels were shown to be risk factors of H-type hypertension in the hyperhomocysteinemia population. Male sex and high creatinine levels were shown to be risk factors of H-type hypertension in the hypertension population. Nomogram analysis showed that the total factor score ranged from 106 to 206, and the corresponding risk rate ranged from 0.05 to 0.95.

CONCLUSIONS

Men are more likely to have H-type hypertension, and advanced age, high BMI, high total cholesterol levels, and high glucose levels are risk factors of H-type hypertension in healthy and hyperhomocysteinemia populations. Furthermore, high creatinine level is a risk factor of H-type hypertension in healthy and hypertension populations. Nomogram models may be used to intuitively evaluate H-type hypertension risk and provide a basis for personalized interventions.

Association between plasma levels of homocysteine, folate, and vitamin B12, and dietary folate intake and hypertension in a cross-sectional study

There are few studies examining the association between homocysteine (Hcy) level and the risk of hypertension with consideration for folate and vitamin B₁₂ as related to Hcy level. We simultaneously examined the associations of plasma levels of Hcy, folate, and vitamin B₁₂, and dietary folate intake with the prevalence of hypertension. Participants included 1046 men and 1033 women (mean age ± standard deviation: 56.0 ± 8.9 years) in the Japan Multi-Institutional Collaborative Cohort Study. Dietary folate intake was estimated using a validated food frequency questionnaire. Hypertension was defined based on measured blood pressure and use of antihypertensive medication. A total of 734 participants (35.3%) had hypertension. Multivariate-adjusted odds ratios of hypertension for the highest quartile group of Hcy were 2.36 (95% CI 1.41-3.96) in men and 1.86 (95% CI 1.11-3.11) in women, as compared with the lowest group (P for trend = 0.014 and 0.005, respectively). Dietary folate intake was not correlated with hypertension in both men and women (P for trend = 0.099 and 0.703, respectively). Plasma vitamin B₁₂ was positively associated with hypertension only in women (P for trend = 0.027). Plasma Hcy level was positively linked with hypertension after controlling for covariates, including folate and vitamin B₁₂.

Genetic Epidemiology in Latin America: Identifying Strong Genetic Proxies for Complex Disease Risk Factors

Epidemiology seeks to determine the causal effects of exposures on outcomes related to the health and wellbeing of populations. Observational studies, one of the most commonly used designs in epidemiology, can be biased due to confounding and reverse causation, which makes it difficult to establish causal relationships. In recent times, genetically informed methods, like Mendelian randomization (MR), have been developed in an attempt to overcome these disadvantages. MR relies on the association of genetic variants with outcomes of interest, where the genetic variants are proxies or instruments for modifiable exposures. Because genotypes are sorted independently and at random at the time of conception, they are less prone to confounding and reverse causation. Implementation of MR depends on, among other things, a strong association of the genetic variants with the exposure, which has usually been defined via genome-wide association studies (GWAS). Because GWAS have been most often carried out in European populations, the limited identification of strong instruments in other populations poses a major problem for the application of MR in Latin America. We suggest potential solutions that can be realized with the resources at hand and others that will have to wait for increased funding and access to technology.

Homocysteine, the methylenetetrahydrofolate reductase 677C>T polymorphism and hypertension: effect modifiers by lifestyle factors and population subgroups

Evidence linking fasting plasma total homocysteine (tHcy) and methylenetetrahydrofolate reductase (MTHFR) 677C>T genotype with hypertension is inconsistent. Differences in B vitamin status, other lifestyle factors or their consideration in analyses might explain this. We investigated these associations in the absence of mandatory fortification with folic acid and B vitamin supplement use. A cross-sectional study was conducted in 788 adults, aged 18-75 years, randomly selected from three Catalonian town population registers. Fasting plasma folate, cobalamin, tHcy, erythrocyte folate, erythrocyte glutathione reductase activation coefficient (EGRAC, functional riboflavin status indicator; increasing EGRAC indicates worsening riboflavin status), MTHFR 677C>T and solute carrier family 1 (SLC19A1) 80 G>A genotypes were determined. Medical history and lifestyle habits were recorded. Principal tHcy determinants differed between women (age, plasma folate, plasma cobalamin, cigarettes/d) and men (MTHFR 677TT genotype, plasma folate, plasma cobalamin and CT genotype). The MTHFR 677C>T polymorphism-tHcy association (β standardised regression coefficients) was stronger in male smokers (0·52, P < 0·001) compared with non-smokers (0·21, P = 0·001) and weaker in participants aged >50 years (0·19, P = 0·007) compared with ≤50 years (0·31, P < 0·001). Hypertension was more probable in the third tHcy tertile compared with other tertiles (OR 1·9; 95 % CI 1·2, 3·0), and in participants aged ≤50 years, for the MTHFR 677TT genotype compared with the CC genotype (OR 4·1; 95 % CI 1·0, 16·9). EGRAC was associated with increased probability of hypertension in participants aged >50 years (OR 6·2; 95 % CI 1·0, 38·7). In conclusion, moderately elevated tHcy and the MTHFR 677CT genotype were associated with hypertension. The MTHFR 677C>T genotype-hypertension association was confined to adults aged ≤50 years.

Homocysteine and IgA nephropathy: observational and Mendelian randomization analyses

BACKGROUND

High levels of plasma homocysteine occur almost uniformly in patients with end-stage renal disease (ESRD). IgA nephropathy (IgAN) is the most common form of primary glomerulonephritis and a common cause of ESRD in young adults. Here, we aimed to detect whether homocysteine was elevated and associated with clinical-pathologic manifestations of IgAN patients and tested its causal effects using a two-sample Mendelian randomization (MR) approach.

METHODS

For observational analysis, 108 IgAN patients, 30 lupus nephritis (LN) patients, 50 minimal change disease (MCD) patients, and 206 healthy controls were recruited from April 2014 to April 2015. Their plasma homocysteine was measured and clinical-pathologic manifestations were collected from medical records. For MR analysis, we further included 1686 IgAN patients. The missense variant methylenetetrahydrofolate reductase C677T (rs1801133) was selected as an instrument, which was genotyped by TaqMan allele discrimination assays.

RESULTS

Majority of IgAN patients (93.52%, 101/108) showed elevated levels of plasma homocysteine (>10 μmol/L). Plasma homocysteine in IgAN patients was significantly higher than that in MCD patients (median: 18.32 vs. 11.15 μmol/L, Z = -5.29, P < 0.01) and in healthy controls (median: 18.32 vs. 10.00 μmol/L, Z = -8.76, P < 0.01), but comparable with those in LN patients (median: 18.32 L vs. 14.50 μmol/L, Z = -1.32, P = 0.19). Significant differences were observed in sub-groups of IgAN patients according to quartiles of plasma homocysteine for male ratio (22.22% vs. 51.85% vs. 70.37% vs. 70.37%, χ = 14.29, P < 0.01), serum creatinine (median: 77.00 vs. 100.00 vs. 129.00 vs. 150.00 μmol/L, χ = 34.06, P < 0.01), estimated glomerular filtration rate (median: 100.52 vs. 74.23 vs. 52.68 vs. 42.67 mL·min·1.73 m, χ = 21.75, P < 0.01), systolic blood pressure (median: 120.00 vs. 120.00 vs. 125.00 vs. 130.00 mmHg, χ = 2.97, P = 0.05), diastolic blood pressure (median 80.00 vs. 75.00 vs. 80.00 vs. 81.00 mmHg, χ = 11.47, P < 0.01), and pathologic tubular atrophy and interstitial fibrosis (T) (T0/T1/T2: 62.96%/33.33%/3.70% vs. 29.63%/40.74%/29.63% vs. 24.00%/48.00%/28.00% vs. 14.81%/37.04%/48.15%, χ = 17.66, P < 0.01). The coefficient of each rs1801133-T allele on homocysteine levels after controlling age and sex was 7.12 (P < 0.01). MR estimates showed causal positive effects of homocysteine on serum creatine (β = 0.76, P = 0.02), systolic blood pressure (β = 0.26, P = 0.02), diastolic blood pressure (β = 0.20, P = 0.01), and pathologic T lesion (β = 0.01, P = 0.01) in IgAN.

CONCLUSIONS

By observational and MR analyses, consistent results were observed for associations of plasma homocysteine with serum creatinine, blood pressures, and pathologic T lesion in IgAN patients.

Discovery of potential plasma protein biomarkers for acute myocardial infarction via proteomics

Background

Acute myocardial infarction (AMI) is an acute disease with high mortality and seriously threatens human health. The identification of new effective biological markers for AMI is a prerequisite for treatment. Most proteomic studies have focused on atherosclerotic plaques, vascular cells, monocytes and platelets in the blood; however, the concentration of these factors in plasma is low, making it difficult to measure the complexity of plasma components. Moreover, some studies have examined the plasma protein of patients with acute coronary syndrome with histochemistry; however, the results are not consistent. Therefore, it is necessary to further investigate the differential proteins in the plasma of patients with AMI via proteomics to identify new biomarkers of AMI.

Methods

In this study, immunodepletion of high-abundance plasma proteins followed by an isobaric tagging for relative and absolute quantitation (iTRAQ)-based quantitative proteomic approach was used to analyze plasma samples from 5 control individuals and 10 AMI patients.

Results

Four hundred sixty-eight proteins were identified from two samples, and 33 proteins were differentially expressed in AMI patients compared to the controls. Among the 33 proteins, 12 proteins showed a ≥1.5-fold change between AMI and control samples. These proteins included fatty acid binding protein 3 (FABP3, ratio =6.36), creatine kinase-MB (CK-MB ratio =4.89), adenylate kinase1 (AK1 ratio =4.16), pro-platelet basic protein (PPBP ratio =3.29), creatine kinase (CK ratio =2.88), platelet factor 4 (PF4 ratio =2.62), peptidyl prolyl isomerase Cyclophilin A (PPIA ratio =2.05), Cofilin-1 (CFL1 ratio =1.81), coronin1A (CORO1A ratio =1.71), protein kinase M (PKM ratio =1.63), ribonuclease inhibitor (RNH1, ratio =1.67), and triose phosphate isomerase (TPI1 ratio =1.56). By contrast, there was a decrease of 19 proteins, such as adiponectin (ADIPOQ ratio =0.70), insulin-like growth factor binding protein6 (IGFBP6 ratio =0.70), Dickkopf-related protein 3 (DKK3 ratio =0.70) and complement 4B (C4B ratio =0.68). The most over-represented term was regulation of cell proliferation in the cellular component category of Gene Ontology (GO). The top 3 biological process terms were regulation of cell proliferation, response to wounding and wound healing. These proteins included immune proteins, blood coagulation proteins, lipid metabolism proteins, cytoskeleton proteins, energy metabolism proteins, gene regulation proteins, myocutaneous proteins, and myocardial remodeling proteins and were highly connected with each other, which indicates that the functional network of these processes contribute to the pathophysiology of AMI.

Conclusions

In conclusion, the present quantitative proteomic study identified novel AMI biomarker candidates and might provide fundamental information for the development of an AMI biomarker.

Association between plasma homocysteine and hypertension: Results from a cross-sectional and longitudinal analysis in Beijing's adult population from 2012 to 2017

Plasma homocysteine (Hcy) levels are associated with elevated blood pressure. However, the causal association between Hcy levels and the risk of hypertension remains ambiguous. Taking the study design effect into consideration, this study aimed to investigate this issue through a cross-sectional and longitudinal analysis. Data were obtained from the Beijing Health Management Cohort study, which conducted routine health check-ups from 2012 to 2017. Multivariate logistic regression was used for the cross-sectional analysis, and a quadratic inference function approach was performed for the longitudinal analysis. A total of 30 376 subjects (mean age = 50.0 years) were included in the cross-sectional analysis, and a subgroup of 3913 subjects without hypertension at baseline was included in the longitudinal analysis. After adjusting for potential confounders, the risk of hypertension increased with Hcy levels in the cross-sectional analysis using the traditional definition of hypertension (OR = 1.262, 95% CI: 1.155-1.378, Q2 vs Q1; OR = 1.458, 95% CI: 1.335-1.593, Q3 vs Q1; OR = 1.520, 95% CI: 1.388-1.664, Q4 vs Q1) and the 2017 hypertension definition (OR = 1.159, 95% CI: 1.067-1.259, Q2 vs Q1; OR = 1.328, 95% CI: 1.221-1.445, Q3 vs Q1; OR = 1.328, 95% CI: 1.217-1.449, Q4 vs Q1). The longitudinal analysis showed that hypertension risk increased in the third quartile of Hcy (OR = 1.268, 95% CI: 1.030-1.560, Q3 vs Q1). Elevated total plasma Hcy may be used as a predictive biomarker for hypertension. Attention should be paid to gender-specific mechanisms when issuing precise precautions.

EPIGEN-Brazil Initiative resources: a Latin American imputation panel and the Scientific Workflow

EPIGEN-Brazil is one of the largest Latin American initiatives at the interface of human genomics, public health, and computational biology. Here, we present two resources to address two challenges to the global dissemination of precision medicine and the development of the bioinformatics know-how to support it. To address the underrepresentation of non-European individuals in human genome diversity studies, we present the EPIGEN-5M+1KGP imputation panel—the fusion of the public 1000 Genomes Project (1KGP) Phase 3 imputation panel with haplotypes derived from the EPIGEN-5M data set (a product of the genotyping of 4.3 million SNPs in 265 admixed individuals from the EPIGEN-Brazil Initiative). When we imputed a target SNPs data set (6487 admixed individuals genotyped for 2.2 million SNPs from the EPIGEN-Brazil project) with the EPIGEN-5M+1KGP panel, we gained 140,452 more SNPs in total than when using the 1KGP Phase 3 panel alone and 788,873 additional high confidence SNPs (info score ≥ 0.8). Thus, the major effect of the inclusion of the EPIGEN-5M data set in this new imputation panel is not only to gain more SNPs but also to improve the quality of imputation. To address the lack of transparency and reproducibility of bioinformatics protocols, we present a conceptual Scientific Workflow in the form of a website that models the scientific process (by including publications, flowcharts, masterscripts, documents, and bioinformatics protocols), making it accessible and interactive. Its applicability is shown in the context of the development of our EPIGEN-5M+1KGP imputation panel. The Scientific Workflow also serves as a repository of bioinformatics resources.

Serum homocysteine, arsenic methylation, and arsenic-induced skin lesion incidence in Bangladesh: A one-carbon metabolism candidate gene study

BACKGROUND

Inorganic arsenic (As) is methylated via one carbon metabolism (OCM) to mono- and dimethylated arsenicals (MMA and DMA), facilitating urinary excretion. Hyperhomocysteinemia (HHcys), a marker of impaired OCM, is a risk factor for As-induced skin lesions, but the influences of single nucleotide polymorphisms (SNPs) in OCM genes on Hcys, As metabolism and skin lesion risk is unclear.

OBJECTIVES

To (i) explore genetic sources of Hcys and the causal role of HHcys in As-induced skin lesion development using OCM genetic proxies for HHcys and (ii) identify OCM SNPs associated with urinary As metabolite proportions and/or skin lesion incidence.

METHODS

We conducted a case-control study nested in the Health Effects of Arsenic Longitudinal Study (HEALS) in Bangladesh which 876 incident skin lesion cases were matched to controls on sex, age, and follow-up time. We measured serum Hcys, urinary As metabolites, and 26 SNPs in 13 OCM genes.

RESULTS

Serum Hcys and urinary %DMA were independently associated with increased and decreased odds of skin lesions, respectively. The T allele of MTHFR 677 C ➔ T (rs1801133) was associated with HHcys, higher %MMA, and lower %DMA, but not with skin lesions. Interactions between SNPs and water As on skin lesion risk were suggestive for three variants: the G allele of MTRR rs1801394 and T allele of FOLR1 rs1540087 were associated with lower odds of skin lesions with lower As (≤50 μg/L), and the T allele of TYMS rs1001761 was associated with higher odds of skin lesions with higher As.

CONCLUSIONS

While HHcys and decreased %DMA were associated with increased risk for skin lesions, and MTHFR 677 C ➔ T was a strong predictor of HHcys, MTHFR 677 C ➔ T was not associated with skin lesion risk. Future studies should explore (i) non-OCM and non-genetic determinants of Hcys and (ii) if genetic findings are replicated in other As-exposed populations, mechanisms by which OCM SNPs may influence the dose-dependent effects of As on skin lesion risk.

Metabolic Profiling of Adiponectin Levels in Adults: Mendelian Randomization Analysis

BACKGROUND

Adiponectin, a circulating adipocyte-derived protein, has insulin-sensitizing, anti-inflammatory, antiatherogenic, and cardiomyocyte-protective properties in animal models. However, the systemic effects of adiponectin in humans are unknown. Our aims were to define the metabolic profile associated with higher blood adiponectin concentration and investigate whether variation in adiponectin concentration affects the systemic metabolic profile.

METHODS AND RESULTS

We applied multivariable regression in ≤5909 adults and Mendelian randomization (using cis-acting genetic variants in the vicinity of the adiponectin gene as instrumental variables) for analyzing the causal effect of adiponectin in the metabolic profile of ≤37 545 adults. Participants were largely European from 6 longitudinal studies and 1 genome-wide association consortium. In the multivariable regression analyses, higher circulating adiponectin was associated with higher high-density lipoprotein lipids and lower very-low-density lipoprotein lipids, glucose levels, branched-chain amino acids, and inflammatory markers. However, these findings were not supported by Mendelian randomization analyses for most metabolites. Findings were consistent between sexes and after excluding high-risk groups (defined by age and occurrence of previous cardiovascular event) and 1 study with admixed population.

CONCLUSIONS

Our findings indicate that blood adiponectin concentration is more likely to be an epiphenomenon in the context of metabolic disease than a key determinant.

Red cell distribution width and homocysteine act as independent risk factors for cardiovascular events in newly diagnostic essential hypertension

Hyperhomocysteinemia and increased red cell distribution width (RDW) are associated with a higher possibility of adverse clinical outcomes of hypertension. The study aims to validate the effect of homocysteine (Hcy) and RDW on cardiovascular events (CVE) and investigate whether RDW is independently associated with serum Hcy in patients with essential hypertension (EH). The study reviewed 804 patients with newly diagnosed EH in our hospital. The clinical characteristics and laboratory results of all subjects were grouped according to the presence/absence of CVE. Patients in the CVE group had higher RDW and Hcy, as compared to the patients in the no CVE group. Multiple Cox regression analysis demonstrated that both RDW (HR = 1.24, 95% CI =1.02-1.56, P = 0.002) and Hcy (HR = 1.37, 95% CI = 1.02-1.80, P < 0.001) resulted significantly related to the CVE. Subsequent analysis found that patients with high RDW had higher Hcy levels as compared with those with low RDW (P = 0.007). Although Pearson's correlation suggested that RDW was positively correlated with Hcy (r = 0.122, P = 0.028), no significant correlation was observed between RDW and Hcy (β = 0.15, p = 0.126) after adjusted for a series of potential confounders using multiple linear regression analysis. In conclusion, RDW is not correlated with Hcy in patients with EH. Both RDW and Hcy are independent risk factors for CVE in newly diagnostic EH and have the potential to improve risk stratification.

Genetically defined elevated homocysteine levels do not result in widespread changes of DNA methylation in leukocytes

BACKGROUND

DNA methylation is affected by the activities of the key enzymes and intermediate metabolites of the one-carbon pathway, one of which involves homocysteine. We investigated the effect of the well-known genetic variant associated with mildly elevated homocysteine: MTHFR 677C>T independently and in combination with other homocysteine-associated variants, on genome-wide leukocyte DNA-methylation.

METHODS

Methylation levels were assessed using Illumina 450k arrays on 9,894 individuals of European ancestry from 12 cohort studies. Linear-mixed-models were used to study the association of additive MTHFR 677C>T and genetic-risk score (GRS) based on 18 homocysteine-associated SNPs, with genome-wide methylation.

RESULTS

Meta-analysis revealed that the MTHFR 677C>T variant was associated with 35 CpG sites in cis, and the GRS showed association with 113 CpG sites near the homocysteine-associated variants. Genome-wide analysis revealed that the MTHFR 677C>T variant was associated with 1 trans-CpG (nearest gene ZNF184), while the GRS model showed association with 5 significant trans-CpGs annotated to nearest genes PTF1A, MRPL55, CTDSP2, CRYM and FKBP5.

CONCLUSIONS

Our results do not show widespread changes in DNA-methylation across the genome, and therefore do not support the hypothesis that mildly elevated homocysteine is associated with widespread methylation changes in leukocytes.

Homocysteine, visceral adiposity-related novel cardiometabolic risk factors, and exaggerated blood pressure response to the exercise treadmill test

OBJECTIVE

Exaggerated blood pressure response to exercise is a risk factor for the development of future hypertension. In this study, we aimed to investigate the association between homocysteine, epicardial fat thickness, nonalcoholic hepatic steatosis, and exaggerated blood pressure response to exercise.

PARTICIPANTS AND METHODS

We included 44 normotensive and 40 patients with exaggerated blood pressure response to exercise who have normal resting blood pressure and without a previous diagnosis of hypertension. All patients underwent treadmill exercise test and clinical, ultrasonographic, and echocardiographic evaluation. Exaggerated blood pressure response to exercise is defined as peak exercise systolic blood pressure of at least 210 mmHg in men and at least 190 mmHg in women. Homocysteine and other biochemical parameters were determined with standardized automated laboratory tests.

RESULTS

Mean age of all participants is 47.9±8.5 years, and 36 of 84 participants were female. The frequency of diabetes mellitus in both groups was similar (P=0.250). Homeostasis model assessment index-insulin resistance had a statistically insignificant trend to be higher in a patient with exercise hypertension (P=0.058). The nonalcoholic fatty liver was more frequent in patients with exercise hypertension (13.6 vs. 47.5%, P=0.002). Epicardial fat thickness was increased in patients with exercise hypertension (5.5±1.5 vs. 7.3±1.1 mm; P=0.001). However, homocysteine levels did not significantly differ between normotensive and exercise hypertensive patients [12.3 μmol/l (5.7-16.9 μmol/l) vs. 13 μmol/l (5.9-28.3 μmol/l); P=0.883].

CONCLUSION

In our study, homocysteine levels were not associated with exaggerated blood pressure response to exercise; however, fatty liver and epicardial fat thickness as visceral adiposity-related cardiometabolic risk factors were significantly related with exaggerated blood pressure response to exercise in patients without a previous diagnosis of hypertension.

Hyperhomocysteinaemia and vascular injury: advances in mechanisms and drug targets

Homocysteine is a sulphur-containing non-proteinogenic amino acid. Hyperhomocysteinaemia (HHcy), the pathogenic elevation of plasma homocysteine as a result of an imbalance of its metabolism, is an independent risk factor for various vascular diseases, such as atherosclerosis, hypertension, vascular calcification and aneurysm. Treatments aimed at lowering plasma homocysteine via dietary supplementation with folic acids and vitamin B are more effective in preventing vascular disease where the population has a normally low folate consumption than in areas with higher dietary folate. To date, the mechanisms of HHcy-induced vascular injury are not fully understood. HHcy increases oxidative stress and its downstream signalling pathways, resulting in vascular inflammation. HHcy also causes vascular injury via endoplasmic reticulum stress. Moreover, HHcy up-regulates pathogenic genes and down-regulates protective genes via DNA demethylation and methylation respectively. Homocysteinylation of proteins induced by homocysteine also contributes to vascular injury by modulating intracellular redox state and altering protein function. Furthermore, HHcy-induced vascular injury leads to neuronal damage and disease. Also, an HHcy-activated sympathetic system and HHcy-injured adipose tissue also cause vascular injury, thus demonstrating the interactions between the organs injured by HHcy. Here, we have summarized the recent developments in the mechanisms of HHcy-induced vascular injury, which are further considered as potential therapeutic targets in this condition.

LINKED ARTICLES

This article is part of a themed section on Spotlight on Small Molecules in Cardiovascular Diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.8/issuetoc.

Associations of plasma homocysteine levels with peripheral systolic blood pressure and noninvasive central systolic blood pressure in a community-based Chinese population

Previous studies indicated that homocysteine (Hcy) is associated with higher peripheral systolic blood pressure (pSBP). There have been few data on the relationship between Hcy and central SBP (cSBP). A total of 4,364 Chinese subjects from the Shijingshan community in Beijing were included. cSBP and pSBP were measured with an Omron HEM-9000AI device. Subjects were 57.20 ± 8.9 years old, 37.9% were male. The median of Hcy was 11.96 μmol/L. The mean of cSBP and pSBP was 129.94 ± 18.03 mmHg and 133.25 ± 18.58 mmHg. lnHcy was associated with cSBP (adjusted β = 2.17, SE = 0.80, P = 0.007) and pSBP (adjusted β = 2.42, SE = 0.75, P = 0.001). With increasing Hcy, there were enhanced correlations of Hcy with pSBP and cSBP (p for trend between quartiles <0.01). Using Q1 for reference, the Q4 was associated with cSBP (adjusted β = 1.77, SE = 0.89, P = 0.047) and pSBP (adjusted β = 2.15, SE = 0.84, P = 0.011). The correlations were more significant in non-obese subjects than in obese subjects (cSBP: β = 4.30 vs 0.46, pSBP: β = 5.04 vs 1.18, P for interaction <0.001). Our study showed that Hcy was associated with higher cSBP and pSBP, especially in non-obese subjects.

Homocysteine levels and risk of essential hypertension: A meta-analysis of published epidemiological studies

BACKGROUND

Plasma homocysteine (Hcy) levels may be associated with essential hypertension (EH). However, the results of previous studies on this association are inconsistent.

METHODS

In this meta-analysis, we performed a systematic literature search of the Embase, PubMed, Cochrane Library, and Web of Science for the relevant articles dated up to March 2016. Pooled odds ratios (ORs) and corresponding 95% confidence intervals (CIs) were used to evaluate the estimates.

RESULTS

We included 11 studies with a total of 16,571 participants (4,830 EH cases). We found that elevated Hcy levels were associated with the risk of EH (pooled OR: 1.36, 95% CI: 1.02-1.80 in the random-effects model). However, subsequent subgroup analyses showed that elevated Hcy levels increased the EH risk in retrospective studies (OR: 1.82, 95% CI: 1.53-2.16; p < 0.001) and unadjusted studies (OR: 1.72, 95% CI: 1.43-2.07; p < 0.001), but not in perspective studies (OR: 0.99, 95% CI: 0.73-1.28; p = 0.939) and adjusted studies (OR: 1.21, 95% CI: 0.85-1.72; p = 0.297). No significant publication bias was found (p = 0.876 for Begg's test, p = 0.144 for Egger's test).

CONCLUSION

Plasma Hcy levels are associated with EH risk. However, our findings do not support a causal association between Hcy levels and EH.