Hyperhomocysteinemia and response of methionine cycle intermediates to vitamin treatment in renal patients

Identification of methylation-regulated genes modulating microglial phagocytosis in hyperhomocysteinemia-exacerbated Alzheimer's disease

BACKGROUND

Hyperhomocysteinemia (HHcy) has been linked to development of Alzheimer's disease (AD) neuropathologically characterized by the accumulation of amyloid β (Aβ). Microglia (MG) play a crucial role in uptake of Aβ fibrils, and its dysfunction worsens AD. However, the effect of HHcy on MG Aβ phagocytosis remains unstudied.

METHODS

We isolated MG from the cerebrum of HHcy mice with genetic cystathionine-β-synthase deficiency (Cbs-/-) and performed bulk RNA-seq. We performed meta-analysis over transcriptomes of Cbs-/- mouse MG, human and mouse AD MG, MG Aβ phagocytosis model, human AD methylome, and GWAS AD genes.

RESULTS

HHcy and hypomethylation conditions were identified in Cbs-/- mice. Through Cbs-/- MG transcriptome analysis, 353 MG DEGs were identified. Phagosome formation and integrin signaling pathways were found suppressed in Cbs-/- MG. By analyzing MG transcriptomes from 4 AD patient and 7 mouse AD datasets, 409 human and 777 mouse AD MG DEGs were identified, of which 37 were found common in both species. Through further combinatory analysis with transcriptome from MG Aβ phagocytosis model, we identified 130 functional-validated Aβ phagocytic AD MG DEGs (20 in human AD, 110 in mouse AD), which reflected a compensatory activation of Aβ phagocytosis. Interestingly, we identified 14 human Aβ phagocytic AD MG DEGs which represented impaired MG Aβ phagocytosis in human AD. Finally, through a cascade of meta-analysis of transcriptome of AD MG, functional phagocytosis, HHcy MG, and human AD brain methylome dataset, we identified 5 HHcy-suppressed phagocytic AD MG DEGs (Flt1, Calponin 3, Igf1, Cacna2d4, and Celsr) which were reported to regulate MG/MΦ migration and Aβ phagocytosis.

CONCLUSIONS

We established molecular signatures for a compensatory response of Aβ phagocytosis activation in human and mouse AD MG and impaired Aβ phagocytosis in human AD MG. Our discoveries suggested that hypomethylation may modulate HHcy-suppressed MG Aβ phagocytosis in AD.

Homocysteine metabolism as the target for predictive medical approach, disease prevention, prognosis, and treatments tailored to the person

Homocysteine (Hcy) metabolism is crucial for regulating methionine availability, protein homeostasis, and DNA-methylation presenting, therefore, key pathways in post-genomic and epigenetic regulation mechanisms. Consequently, impaired Hcy metabolism leading to elevated concentrations of Hcy in the blood plasma (hyperhomocysteinemia) is linked to the overproduction of free radicals, induced oxidative stress, mitochondrial impairments, systemic inflammation and increased risks of eye disorders, coronary artery diseases, atherosclerosis, myocardial infarction, ischemic stroke, thrombotic events, cancer development and progression, osteoporosis, neurodegenerative disorders, pregnancy complications, delayed healing processes, and poor COVID-19 outcomes, among others. This review focuses on the homocysteine metabolism impairments relevant for various pathological conditions. Innovative strategies in the framework of 3P medicine consider Hcy metabolic pathways as the specific target for in vitro diagnostics, predictive medical approaches, cost-effective preventive measures, and optimized treatments tailored to the individualized patient profiles in primary, secondary, and tertiary care.

The Importance of Telomere Shortening for Atherosclerosis and Mortality

Telomeres are the protective end caps of chromosomes and shorten with every cell division. Short telomeres are associated with older age and adverse lifestyle factors. Leucocyte telomere length (LTL) has been proposed as a biomarker of biological age. The shortening of LTL with age is the result of the end-replication problem, environmental, and lifestyle-related factors. Epidemiologic studies have shown that LTL predicts cardiovascular disease, all-cause mortality, and death from vascular causes. Age appears to be an important co-variate that explains a substantial fraction of this effect. Although it has been proposed that short telomeres promote atherosclerosis and impair the repair of vascular lesions, existing results are inconsistent. Oxidative stress and chronic inflammation can both accelerate telomere shortening. Multiple factors, including homocysteine (HCY), vitamin B6, and vitamin B12 modulate oxidative stress and inflammation through direct and indirect mechanisms. This review provides a compact overview of telomere physiology and the utility of LTL measurements in atherosclerosis and cardiovascular disease. In addition, it summarizes existing knowledge regarding the impact of oxidative stress, inflammation, HCY, and B-vitamins on telomere function.

Vitamin B Supplementation and Nutritional Intake of Methyl Donors in Patients with Chronic Kidney Disease: A Critical Review of the Impact on Epigenetic Machinery

Cardiovascular morbidity and mortality are several-fold higher in patients with advanced chronic kidney disease (CKD) and end-stage renal disease (ESRD) than in the general population. Hyperhomocysteinemia has undoubtedly a central role in such a prominent cardiovascular burden. The levels of homocysteine are regulated by methyl donors (folate, methionine, choline, betaine), and cofactors (vitamin B6, vitamin B12,). Uremia-induced hyperhomocysteinemia has as its main targets DNA methyltransferases, and this leads to an altered epigenetic control of genes regulated through methylation. In renal patients, the epigenetic landscape is strictly correlated with the uremic phenotype and dependent on dietary intake of micronutrients, inflammation, gut microbiome, inflammatory status, oxidative stress, and lifestyle habits. All these factors are key contributors in methylome maintenance and in the modulation of gene transcription through DNA hypo- or hypermethylation in CKD. This is an overview of the epigenetic changes related to DNA methylation in patients with advanced CKD and ESRD. We explored the currently available data on the molecular dysregulations resulting from altered gene expression in uremia. Special attention was paid to the efficacy of B-vitamins supplementation and dietary intake of methyl donors on homocysteine lowering and cardiovascular protection.

Vitamin B₆ and Its Role in Cell Metabolism and Physiology

Vitamin B₆ is one of the most central molecules in cells of living organisms. It is a critical co-factor for a diverse range of biochemical reactions that regulate basic cellular metabolism, which impact overall physiology. In the last several years, major progress has been accomplished on various aspects of vitamin B₆ biology. Consequently, this review goes beyond the classical role of vitamin B₆ as a cofactor to highlight new structural and regulatory information that further defines how the vitamin is synthesized and controlled in the cell. We also discuss broader applications of the vitamin related to human health, pathogen resistance, and abiotic stress tolerance. Overall, the information assembled shall provide helpful insight on top of what is currently known about the vitamin, along with addressing currently open questions in the field to highlight possible approaches vitamin B₆ research may take in the future.

DNA methylation status of the methylenetetrahydrofolate reductase gene promoter in peripheral blood of end-stage renal disease patients

End-stage renal disease (ESRD) is one of the main causes of morbidity and mortality worldwide. DNA methylation is a major epigenetic modification of the genome that has the potential to silence gene expression. Methylenetetrahydrofolate reductase (MTHFR) gene inactivation was recognized as a predisposing factor of hyperhomocysteinemia in renal patients. The current study aimed to determine the methylation status within the MTHFR promoter region in DNA isolated from peripheral blood of ESRD patients and controls and the correlation of this methylation with the clinical and biochemical characteristics in ESRD patients. Ninety-six ESRD patients and 96 healthy ethnically, age and gender matched controls were included within the study. MTHFR promoter methylation was assessed using methylation specific polymerase chain reaction. The frequency of MTHFR methylation was significantly higher in ESRD patients than in controls (P = 0.003), additionally, MTHFR methylation was associated to a decrease in estimated glomerular filtration rate, serum high-density lipoprotein cholesterol level and an increase in both serum total cholesterol and low-density lipoprotein cholesterol levels. Data generated from this study suggest the possible involvement of MTHFR promoter methylation in the pathogenesis of ESRD and support a new dimension of MTHFR inactivation.

Acute effects of 5-methyltetrahydrofolate on endothelial function and asymmetric dimethylarginine in patients with chronic heart failure

BACKGROUND AND AIMS

Folic acid enhances endothelial function in vascular disease states but its effects in chronic heart failure (CHF) are largely unknown. We studied the acute effects of i.v. methyltetrahydrofolate (5MTHF), the active metabolite of folic acid, on endothelial function and asymmetric dimethylarginine (ADMA) in CHF patients.

METHODS AND RESULTS

Twenty two CHF patients and 22 controls received one of the following three-step infusions (1h per each step) in a randomized, parallel group, placebo-control study: (1) active treatment (saline, 5MTHF, and 5MTHF+the endothelial nitric oxide inhibitor N(G)-monomethyl l-arginine, LNMMA); or (2) placebo (salinex3). Endothelium-dependent vasodilatation was assessed by pulse-wave analysis (salbutamol-mediated changes in augmentation index, AIx). 5MTHF did not exert any significant effects on endothelium-dependent vasodilatation both in controls [DeltaAIx post-salbutamol baseline -7.6% (-24.8/-4.1) vs. 5MTHF -5.5% (-16.7/-3.6), medians and interquartile range, and CHF patients [-1.8% (-17.3/+1.3) vs. -2.4% (-3.8/-1.2)]. However, a significant reduction in ADMA concentrations was observed in both groups [controls baseline 0.68micromol/L (0.64/0.77) vs. 5MTHF 0.65 (0.57/0.74); CHF baseline 0.76 (0.63/0.82) vs. 5MTHF 0.69 (0.66/0.71), P=0.05 for both vs. baseline and placebo. These effects persisted during co-infusion with LNMMA.

CONCLUSION

5MTHF did not affect endothelial function but significantly reduced serum ADMA concentrations both in CHF patients and controls. This suggests a direct effect of 5MTHF on ADMA metabolism.

Experimental hyperhomocysteinaemia: differences in tissue metabolites between homocystine and methionine feeding in a rat model

AIM

Hyperhomocysteinaemia, diagnosed by serum levels, is regarded as an independent risk indicator for cardiovascular events and is associated with various diseases. The pathomechanisms seem to be partly due to concentrations of homocysteine metabolites and their effect on the cellular transmethylation processes.

METHODS

We compared two common models for experimental hyperhomocysteinaemia - high methionine diet and homocystine-enriched diet - regarding their effects on tissue concentrations of homocysteine metabolites.

RESULTS

Both diets induced hyperhomocysteinaemia without affecting renal function or vitamine status. However, the tissue contents of homocysteine and its precursors S-adenosyl-homocysteine (SAH) and S-adenosyl-methionine exhibited major differences between both models. Transmethylation potential was elevated 1.7-fold in liver of rats fed the methionine diet, whereas it was unaltered after homocystine-enriched diet. Kidneys of rats fed the methionine diet did not show any alterations in tissue content of homocysteine and its precursors, whereas in the homocystine group homocysteine and the transmethylation inhibitor SAH were elevated from 23.1 +/- 10.4 to 78.0 +/- 26.0 nmol g(-1) and from 106 +/- 4 to 170 +/- 22 nmol g(-1) respectively. Homocysteine tissue content was elevated in the homocystine, but not in the methionine group.

CONCLUSIONS

Alterations to homocysteine metabolism are distinct in both models. These findings may explain divergent results, which have been published for these models of hyperhomocysteinaemia and which have resulted in controversial discussions in the past.

Randomized placebo-controlled trial assessing a treatment strategy consisting of pravastatin, vitamin E, and homocysteine lowering on plasma asymmetric dimethylarginine concentration in mild to moderate CKD

BACKGROUND

Chronic kidney disease (CKD) is associated with an increased incidence of cardiovascular disease (CVD). The Anti-oxidant Therapy In Chronic Renal Insufficiency (ATIC) Study showed that a multistep treatment strategy improved carotid intima-media thickness, endothelial function, and microalbuminuria in patients with stages 2 to 4 CKD. Increased plasma concentrations of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, have been linked to greater CVD risk in patients with CKD. The aim of this study is to assess effects of the multistep intervention on plasma ADMA concentrations in the ATIC Study.

STUDY DESIGN

Secondary analysis of a randomized double-blind placebo-controlled trial.

SETTING & PARTICIPANTS

93 patients with creatinine clearance of 15 to 70 mL/min/1.73 m(2) (according to the Cockcroft-Gault equation) from 7 outpatient clinics in Amsterdam, The Netherlands.

INTERVENTION

The treatment group received sequential treatment consisting of pravastatin, 40 mg/d. After 6 months, vitamin E, 300 mg/d, was added, and after another 6 months, homocysteine-lowering therapy (folic acid, 5 mg/d; pyridoxine, 100 mg/d; and vitamin B(12), 1 mg/d, all in 1 tablet) were added and continued for another year. The control group received matching placebos.

OUTCOME & MEASURES

Plasma ADMA levels.

RESULTS

36 participants (77%) in the treatment group and 38 (83%) in the placebo group completed the study. Mean ADMA and symmetric dimethylarginine concentrations in the total study population were 0.53 +/- 0.07 (SD) and 1.14 +/- 0.46 mumol/L, respectively. After 24 months, there was no overall effect of the treatment strategy on ADMA concentrations (beta = -0.006; P = 0.27). Analysis of separate treatment effects suggested that vitamin E significantly decreased ADMA levels by 4% in the treatment group compared with the placebo group (multiple adjusted P = 0.02).

LIMITATIONS

The study was a secondary analysis, power calculation was based on the primary end point of carotid intima-media thickness, mean plasma ADMA levels were relatively low.

CONCLUSION

Overall, a multistep treatment strategy consisting of pravastatin, vitamin E, and B vitamins had no effect on plasma ADMA levels in a stage 2 to 4 CKD population. This suggests that the beneficial effects of the intervention were not mediated by changes in ADMA levels. Possible ADMA-lowering effects of vitamin E deserve further attention.

Effects of moderate hyperhomocysteinaemia induced by 4 weeks methionine-enriched diet on metabolite profile and mesenteric artery function in rats

Methionine is an essential amino acid and methyl donor for most transmethylation reactions in mammals. The product of transmethylation reactions is homocysteine, which is associated with enhanced risk for CVD. The aim of this study was to analyse metabolic and vascular functional consequences of a methionine-enriched diet in rats. The dose of methionine was chosen to reflect the range of over-nutrition in man. We quantified plasma levels of homocysteine, asymmetrical dimethylarginine and adenosine, determined methionine and its metabolites in tissues and blood plasma and assessed relaxation of mesenteric arteries toward acetylcholine and sodium nitroprusside. A methionine-enriched diet for 4 weeks elevated homocysteine levels in plasma 2-fold and in spleen by 70 %. The level of S-adenosylhomocysteine was increased in liver only, while methionine and S-adenosylmethionine were unchanged in all organs studied. Plasma adenosine and asymmetrical dimethylarginine levels were unchanged, as were vessel relaxations. A 2-fold elevation of plasma homocysteine, which is assigned a risk indicator for cardiovascular events, did not impair mesenteric artery vasodilatation during 4 weeks of a methionine-rich diet. Furthermore, asymmetrical dimethylarginine and adenosine, which have been shown to be changed in more severe degrees of hyperhomocysteinaemia, remained unaltered.

Decreased p66Shc promoter methylation in patients with end-stage renal disease

BACKGROUND

p66Shc is a stress response protein and partially regulated by epigenetic modifications. Mice lacking p66Shc have reduced atherosclerosis, increased resistance to oxidative stress and a prolonged life time. The aim of the present study was to compare promoter methylation of the p66Shc gene between healthy controls and patients with end-stage renal disease (ESRD). There are two reasons for studying patients with ESRD. First, patients with ESRD have a disturbed homocysteine metabolism, and second an increased risk of morbidity and mortality from cardiovascular disease is a constant finding in these patients.

METHODS

In our study, we measured fasting levels of homocysteine, S-adenosylmethionine (SAM), S-adenosylhomocysteine (SAH) and 8-isoprostane in 22 patients and in 26 healthy, age- and sex-matched controls. The methylation of the p66Shc promoter and Line-1, as surrogate marker of whole genome methylation was quantified in peripheral blood mononuclear cells.

RESULTS

In comparison to the control group, homocysteine, SAM, SAH, 8-isoprostane and whole genome methylation were significantly elevated in ESRD patients, while the p66Shc promoter methylation was significantly reduced. A significant correlation was found between SAH and p66Shc promoter methylation in the patient group. This observation underlines the role of SAH as a potent inhibitor of methyltransferases. Using backward regression analysis, we demonstrated that 8-isoprostane has a significant influence on p66Shc promoter methylation. In the control group and in patients with ESRD, increasing 8-isoprostane levels were linked to an elevated promoter methylation.

CONCLUSIONS

Under physiological conditions, based on the results of the control group, the p66Shc expression is more silenced through epigenetic modifications. The atherosclerotic risk is dramatically increased in ESRD patients; therefore, our experimental results of methylation are in accordance with the clinical situation.