Homocysteine and cardiovascular disease: A review of current recommendations for screening and treatment

Homocysteine and Hyperhomocysteinaemia

Homocysteine (Hcy) is a thiol group containing the amino acid, which naturally occurs in all humans. Hcy is degraded in the body through two metabolic pathways, while a minor part is excreted through kidneys. The chemical reactions that are necessary for degradation of Hcy require the presence of folic acid, vitamins B6 and B12. Consequently, the level of the total Hcy in the serum is influenced by the presence or absence of these vitamins. An elevated level of the Hcy, hyperhomocysteinemia (HHcy) and homocystinuria is connected with occlusive artery disease, especially in the brain, the heart, and the kidney, in addition to venous thrombosis, chronic renal failure, megaloblastic anemia, osteoporosis, depression, Alzheimer's disease, pregnancy problems, and others. Elevated Hcy levels are connected with various pathologies both in adult and child population. Causes of HHcy include genetic mutations and enzyme deficiencies in 5, 10-methylenetetrahydrofolate reductase (MTHFR) methionine synthase (MS), and cystathionine β-synthase (CβS). HHcy can be caused by deficiencies in the folate, vitamin B12 and to a lesser extent, deficiency in B6 vitamin what influences methionine metabolism. Additionally, HHcy can be caused by the rich diet and renal impairment. This review presents literature data from recent research related to Hcy metabolism and the etiology of the Hcy blood level disorder. In addition, we also described various pathological mechanisms induced by hereditary disturbances or nutritional influences and their association with HHcy induced pathology in adults and children and treatment of these metabolic disorders.

Pyridoxal-5'-phosphate deficiency is associated with hyperhomocysteinemia regardless of antioxidant, thiamine, riboflavin, cobalamine, and folate status in critically ill patients

BACKGROUND & AIMS

Critically ill patients develop severe stress, inflammation and a clinical state that may raise the utilization and metabolic replacement of pyridoxal-5'-phosphate decreasing their body reserves. This study was designed to assess the nutritional pyridoxal-5'-phosphate status in critical care patients with systemic inflammatory response syndrome, comparing them with a group of healthy people, and studying it's association with factors involved in the pyridoxine and other B vitamins metabolism, as the total antioxidant capacity and Hcy as cardiovascular risk biomarker.

METHODS

Prospective, multicentre, comparative, observational and analytic study. One hundred and three critically ill patients from different hospitals, and eighty four healthy subjects from Granada, Spain, all with informed consent. Data from daily nutritional assessment, ICU severity scores, clinical and nutritional parameters, antioxidant status and homocysteine levels was taken at admission and at the seventh day of the ICU stay.

RESULTS

Thiamine, riboflavin, pyridoxine and folate status proved deficient in a large number of patients, being significantly lower in comparison with control group, and significantly decreased at 7th day of ICU stay. Higher homocysteine was observed in patients compared with control group (p < 0.05) where 31.5 and 26.8 percent of subjects presented hyperhomocysteinemia at initial and final of study, respectively. Antioxidant status was lower than control group in two periods analysed, and decreased at 7th day of ICU stay (p < 0.05) being associated with PLP deficiency. PLP deficiency was also correlated with hyperhomocysteinemia at two times measured (r. -0.73, p < 0.001; r. -0.69, p < 0.001, respectively), showing at day 7 an odds ratio of 6.62 in our multivariate model.

CONCLUSION

Critically ill patients with SIRS show deficient B vitamin and low antioxidant statuses. Despite association found between PLP deficiency and low antioxidant status in critically ill patients, PLP deficiency was only associated with hyperhomocysteinemia regardless of antioxidant, riboflavin, cobalamine, and folate statuses in critically ill patients with SIRS at seventh day of ICU stay. PLP deficient patients presented about six times more risk of cardiovascular disease than non deficients.

Mercury/homocysteine ligation-induced ON/OFF-switching of a T-T mismatch-based oligonucleotide molecular beacon

A molecular beacon (MB) with stem-loop (hairpin) DNA structure and with attached fluorophore-quencher pair at the ends of the strand has been applied to study the interactions of Hg(2+) ions with a thymine-thymine (T-T) mismatch in Watson-Crick base-pairs and the ligative disassembly of MB·Hg(2+) complex by Hg(2+) sequestration with small biomolecule ligands. In this work, a five base-pair stem with configuration 5'-GGTGG...CCTCC-3' for self-hybridization of MB has been utilized. In this configuration, the four GC base-pair binding energy is not sufficient to hybridize fully at intermediate temperatures and to form a hairpin MB conformation. The T-T mismatch built-in into the stem area can effectively bind Hg(2+) ions creating a bridge, T-Hg-T. We have found that the T-Hg-T bridge strongly enhances the ability of MB to hybridize, as evidenced by an unusually large MB melting temperature shift observed on bridge formation, ΔT(m) = +15.1 ± 0.5 °C, for 100 nM MB in MOPS buffer. The observed ΔT(m) is the largest of the ΔT(m) found for other MBs and dsDNA structures. By fitting the parameters of the proposed model of reversible MB interactions to the experimental data, we have determined the T-Hg-T bridge formation constant at 25 °C, K(1) = 8.92 ± 0.42 × 10(17) M(-1) from mercury(II) titration data and K(1) = 1.04 ± 0.51 × 10(18) M(-1) from the bridge disassembly data; ΔG° = -24.53 ± 0.13 kcal/mol. We have found that the biomarker of oxidative stress and cardiovascular disease, homocysteine (Hcys), can sequester Hg(2+) ions from the T-Hg-T complex and withdraw Hg(2+) ions from MB in the form of stable Hg(Hcys)(2)H(2) complexes. Both the model fitting and independent (1)H NMR results on the thymidine-Hg-Hcys system indicate also the high importance of 1:1 complexes. The high value of K(1) for T-Hg-T bridge formation enables analytical determinations of low concentrations of Hg(2+) (limit of detection LOD = 19 nM or 3.8 ppb, based on 3σ method) and Hcys (LOD = 23 nM, 3σ method). The conditional stability constants for Hg(Hcys)H(2)(2+) and Hg(Hcys)(2)H(2) at 52 °C have been determined, β(112) = 5.37 ± 0.3 × 10(46) M(-3), β(122) = 3.80 ± 0.6 × 10(68) M(-4), respectively.

Differences in Mexican American and Non-Hispanic White veterans' homocysteine levels

PURPOSE

To compare homocysteine (Hcy) levels and possible modulatory factors, such as nutrient or supplement intake, between Mexican American and Non-Hispanic White (NHW) male military veterans scoring at high- versus low-risk for stroke.

DESIGN

A cross-sectional survey with a high and low stroke risk biomarkers substudy.

METHODS

Voluntary participants were Mexican American (n=109) and NHW (n=120) veteran outpatients 54 to 85 years of age at a Southwestern Veterans Administration (VA) medical center. Measures included food frequency, health history, and stroke risk scale derived from the Framingham Study. Biomarker subgroups, 30 Mexican American and 30 NHW, half of each group scoring high or low on stroke risk, who were tested for morning fasting blood levels of Hcy, B12, and folate.

FINDINGS

In the cross-sectional study (n=229), nutrient intake was comparable between ethnic groups. In the substudy, Mexican Americans (n=30) with high or low stroke risk scores and NHW (n=30) with high stroke risk scores had elevated Hcy levels (12.5; 11.9; 11.4 micromol/L respectively) compared to NHW veterans with low stroke risk scores (7.8 micromol/L) even after controlling for age, education, folate, diabetes, and smoking pack-years (p=.001). Mexican Americans compared to NHW were significantly more likely to be in the preclinical (17% versus 3% >10 micromol/L) and clinical ranges (69% versus 35% >15 micromol/L) for Hcy.

CONCLUSIONS

Mexican Americans showed higher levels of Hcy whether they scored high or low for stroke, and greater representation in clinical and preclinical Hcy ranges compared to NHW veterans. The Framingham-derived, predominantly NHW population-based stroke risk measure might require ethnically relevant stroke risk factors for Mexican Americans.

Homocysteine-lowering action is another potential cardiovascular protective factor of aged garlic extract

We investigated hypohomocysteinemic action as a cardiovascular protective property of aged garlic extract (AGE). Hyperhomocysteinemia was induced in rats by feeding folate-depleted diets. Plasma folate concentrations of 5, 24, and 202 nmol/L were detected in rats fed a folate-deficient L-amino acid diet containing succinyl sulfathiazole, an AIN-93G folate-deficient diet, and an AIN-93G folate-sufficient diet, respectively. Plasma concentrations of total homocysteine were elevated to the highest level (32 micromol/L) by severe folate deficiency and to a moderate level (9 micromol/L) by mild folate deficiency, compared with the lowest level of (5 micromol/L), noted for the folate-sufficient group. The addition of AGE to the severely folate-deficient diet decreased plasma total homocysteine concentration by 30%. Hyperhomocysteinemia caused by mild folate deficiency remained unaltered by AGE supplementation. The reduction in total homocysteine of the severely folate-deficient rats was accompanied by a proportional decrease in protein-bound and free homocysteine, resulting in an unchanged protein-bound:free homocysteine ratio. AGE added to the diet did not alter plasma concentrations of other aminothiol compounds: cysteine, glutathione, and cysteinylglycine. These data, together with increased S-adenosylmethionine and decreased S-adenosylhomocysteine concentrations in the liver, suggest that the hypohomocysteinemic effect of AGE most likely stems from impaired remethylation of homocysteine to methionine and enhanced transsulfuration of homocysteine to cystathionine. More importantly, in addition to its cholesterol-lowering potential, blood pressure-lowering effect, and antioxidant property, a hypohomocysteinemic action may be another important cardiovascular protective factor of AGE.