Iron-dependent formation of homocysteine from methionine and other thioethers

Potential Antioxidative Activity of Homocysteine in Erythrocytes under Oxidative Stress

Homocysteine is an amino acid containing a free sulfhydryl group, making it probably contribute to the antioxidative capacity in the body. We recently found that plasma total homocysteine (total-Hcy) concentration increased with time when whole blood samples were kept at room temperature. The present study was to elucidate how increased plasma total-Hcy is produced and explore the potential physiological role of homocysteine. Erythrocytes and leukocytes were separated and incubated in vitro; the amount of total-Hcy released by these two kinds of cells was then determined by HPLC-MS. The effects of homocysteine and methionine on reactive oxygen species (ROS) production, osmotic fragility, and methemoglobin formation in erythrocytes under oxidative stress were studied. The reducing activities of homocysteine and methionine were tested by ferryl hemoglobin (Hb) decay assay. As a result, it was discovered that erythrocytes metabolized methionine to homocysteine, which was then oxidized within the cells and released to the plasma. Homocysteine and its precursor methionine could significantly decrease Rosup-induced ROS production in erythrocytes and inhibit Rosup-induced erythrocyte's osmotic fragility increase and methemoglobin formation. Homocysteine (but not methionine) was demonstrated to enhance ferryl Hb reduction. In conclusion, erythrocytes metabolize methionine to homocysteine, which contributes to the antioxidative capability under oxidative stress and might be a supplementary protective factor for erythrocytes against ROS damage.

Impacts of dietary supplementation with nano-iron and methionine on growth, blood chemistry, liver biomarkers, and tissue histology of heat-stressed broiler chickens

A 28-day study was done to explore the impact of nano-iron alone or combined with methionine on growth, blood chemistry, liver biomarkers, and tissue histology of heat-stressed chicken. One-day-old Ross 308 chicks were randomly allocated to three groups. Each group was divided into three replicates (13 chicks/replicate). The first group was the control one that was fed a basal diet without supplementation (T0). The second group was fed a basal diet with nano-iron 4 mg kg^-1 diet (T1). The third group was fed a basal diet with nano-iron 4 mg kg^-1 diet plus methionine 4 g kg^-1 diet (T2). The results showed that the birds in the control group had significantly (p < 0.05) higher final weights. Also, a partial relief of heat stress adverse effects was observed on growth by T1 compared to T2. The T2 showed a significantly increased (p < 0.05) free iron (Fe) level and transferrin saturation index. Likewise, T2 significantly (p < 0.05) reduced total iron-binding capacity (TIBC) and transferrin level in comparison with T0 and T1. Also, hepatic impairment and inflammatory response were observed in the T2 group when compared to T0 and T1, besides a bad lipid profile. Further, T2 showed raised levels of Fe and ferritin in their hepatic tissues compared to those T1 and T0. A significant increment of thiobarbituric acid reactive and decrement of reduced glutathione levels in the hepatic tissues of T2 and T1 versus T0 levels were recorded. It is concluded that nano-iron at the level of 4 mg kg^-1 in this study is highly absorbed, leading to harmful effects. Further investigations are needed to detect the proper supplemental level.

Vitamin D Supplementation and Nordic Walking Training Decreases Serum Homocysteine and Ferritin in Elderly Women

The aim of the study was to verify if coupling 12 weeks of vitamin D supplementation and Nordic walking training favoured lowering the homocysteine (Hcy) level. Ninety-four elderly women were divided into three groups: Nordic walking (NW), supplemented (SG) and control (CG). The NW and SG groups received a weekly dose of 28,000 IU of vitamin D3. A blood analysis was performed at baseline, 1h after the first training session and at the end of the experiment. The amino acid profile (methionine and cysteine) and homocysteine concentration were determined. Additionally, the concentration of myokine was assessed. The first session of NW training reduced serum homocysteine, particularly among women with baseline homocysteine above 10 µmol·L⁻¹: 12.37 ± 2.75 vs. 10.95 ± 3.94 µmol·L⁻¹ (p = 0.05). These changes were accompanied by shifts in the cysteine (p = 0.09) and methionine (p = 0.01) concentration, regardless of the Hcy concentration. Twelve weeks of training significantly decreased the homocysteine (9.91 ± 2.78, vs. 8.90 ± 3.14 µmol·L⁻¹, p = 0.05) and ferritin (94.23 ± 62.49 vs. 73.15 ± 47.04 ng·mL⁻¹, p = 0.05) concentrations in whole NW group. Also, in the NW group, ferritin correlated with the glucose level (r = 0.51, p = 0.00). No changes in the myokine levels were observed after the intervention. Only the brain-derived neurotrophic factor dropped in the NW (42.74 ± 19.92 vs. 31.93 ± 15.91 ng·mL⁻¹, p = 0.01) and SG (37.75 ± 8.08 vs. 16.94 ± 12.78 ng·mL⁻¹, p = 0.00) groups. This study presents a parallel decrease of homocysteine and ferritin in response to regular training supported by vitamin D supplementation.

Demethylation of methionine and keratin damage in human hair

Growing human head hair contains a history of keratin and provides a unique model for studies of protein damage. Here, we examined mechanism of homocysteine (Hcy) accumulation and keratin damage in human hair. We found that the content of Hcy-keratin increased along the hair fiber, with levels 5-10-fold higher levels in older sections at the hair's tip than in younger sections at hair's base. The accumulation of Hcy led to a complete loss of keratin solubility in sodium dodecyl sulfate. The increase in Hcy-keratin was accompanied by a decrease in methionine-keratin. Levels of Hcy-keratin were correlated with hair copper and iron in older hair. These relationships were recapitulated in model experiments in vitro, in which Hcy generation from Met exhibited a similar dependence on copper or iron. Taken together, these findings suggest that Hcy-keratin accumulation is due to copper/iron-catalyzed demethylation of methionine residues and contributes to keratin damage in human hair.

Homocysteine Editing, Thioester Chemistry, Coenzyme A, and the Origin of Coded Peptide Synthesis †

Aminoacyl-tRNA synthetases (AARSs) have evolved “quality control” mechanisms which prevent tRNA aminoacylation with non-protein amino acids, such as homocysteine, homoserine, and ornithine, and thus their access to the Genetic Code. Of the ten AARSs that possess editing function, five edit homocysteine: Class I MetRS, ValRS, IleRS, LeuRS, and Class II LysRS. Studies of their editing function reveal that catalytic modules of these AARSs have a thiol-binding site that confers the ability to catalyze the aminoacylation of coenzyme A, pantetheine, and other thiols. Other AARSs also catalyze aminoacyl-thioester synthesis. Amino acid selectivity of AARSs in the aminoacyl thioesters formation reaction is relaxed, characteristic of primitive amino acid activation systems that may have originated in the Thioester World. With homocysteine and cysteine as thiol substrates, AARSs support peptide bond synthesis. Evolutionary origin of these activities is revealed by genomic comparisons, which show that AARSs are structurally related to proteins involved in coenzyme A/sulfur metabolism and non-coded peptide bond synthesis. These findings suggest that the extant AARSs descended from ancestral forms that were involved in non-coded Thioester-dependent peptide synthesis, functionally similar to the present-day non-ribosomal peptide synthetases.

Aminoacyl-tRNA synthetases and the evolution of coded peptide synthesis: the Thioester World

Coded peptide synthesis must have been preceded by a prebiotic stage, in which thioesters played key roles. Fossils of the Thioester World are found in extant aminoacyl-tRNA synthetases (AARSs). Indeed, studies of the editing function reveal that AARSs have a thiol-binding site in their catalytic modules. The thiol-binding site confers the ability to catalyze aminoacyl~coenzyme A thioester synthesis and peptide bond formation. Genomic comparisons show that AARSs are structurally related to proteins involved in sulfur and coenzyme A metabolisms and peptide bond synthesis. These findings point to the origin of the amino acid activation and peptide bond synthesis functions in the Thioester World and suggest that the present-day AARSs had originated from ancestral forms that were involved in noncoded thioester-dependent peptide synthesis.

Homocysteine, iron and cardiovascular disease: a hypothesis

Elevated circulating total homocysteine (tHcy) concentrations (hyperhomocysteinemia) have been regarded as an independent risk factor for cardiovascular disease (CVD). However, several large clinical trials to correct hyperhomocysteinemia using B-vitamin supplements (particularly folic acid) have largely failed to reduce the risk of CVD. There is no doubt that a large segment of patients with CVD have hyperhomocysteinemia; therefore, it is reasonable to postulate that circulating tHcy concentrations are in part a surrogate marker for another, yet-to-be-identified risk factor(s) for CVD. We found that iron catalyzes the formation of Hcy from methionine, S-adenosylhomocysteine and cystathionine. Based on these findings, we propose that an elevated amount of non-protein-bound iron (free Fe) increases circulating tHcy. Free Fe catalyzes the formation of oxygen free radicals, and oxidized low-density lipoprotein is a well-established risk factor for vascular damage. In this review, we discuss our findings on iron-catalyzed formation of Hcy from thioethers as well as recent findings by other investigators on this issue. Collectively, these support our hypothesis that circulating tHcy is in part a surrogate marker for free Fe, which is one of the independent risk factors for CVD.

Homocysteine is related to aortic mineralization in patients with ischemic heart disease

Homocysteine is implicated as an early atherosclerotic promoter, which enhances the smooth muscle cell proliferation and produces free radicals that induce cellular damage. These factors must have a role in the progression of atherosclerosis that subsequently leads to vascular mineralization.

AIM

Identify a correlation between the plasma concentration of total homocysteine and the amount of minerals that accumulate in the aorta of patients with atherosclerosis.

METHODS

We performed a cross-sectional study in 13 patients with three-vessel coronary artery disease, undergoing coronary artery bypass surgery. Aortic and mammary artery specimens were analyzed using a scanning electron microscope with an energy dispersive X-ray spectrometer. The homocysteine was determined using an immunonephelometry method.

RESULTS

The amount of minerals in the aorta was greater (300 ± 181.6 particles per 500 µm2 than that in the mammary artery (64 ± 45 particles per 500 µm2 (p < 0.01). The average tHcy was 9.5 ± 2.3 µmol/L. The Spearman's rank correlation coefficient was positive between tHcy, and aortic iron (p < 0.05).

CONCLUSIONS

Our study demonstrates that the aorta is dramatically affected by mineralization compared to the mammary artery. In addition, a direct correlation was identified between the levels of tHcy and the iron particles in the aortic wall.