Synergy of genes and nutrients: the case of homocysteine

The evolution of human skin pigmentation: A changing medley of vitamins, genetic variability, and UV radiation during human expansion

This review examines putative, yet likely critical evolutionary pressures contributing to human skin pigmentation and subsequently, depigmentation phenotypes. To achieve this, it provides a synthesis of ideas that frame contemporary thinking, without limiting the narrative to pigmentation genes alone. It examines how geography and hence the quality and quantity of UV exposure, pigmentation genes, diet-related genes, vitamins, anti-oxidant nutrients, and cultural practices intersect and interact to facilitate the evolution of human skin color. The article has a strong focus on the vitamin D-folate evolutionary model, with updates on the latest biophysical research findings to support this paradigm. This model is examined within a broad canvas that takes human expansion out of Africa and genetic architecture into account. A thorough discourse on the biology of melanization is provided (includes relationship to BH4 and DNA damage repair), with the relevance of this to the UV sensitivity of folate and UV photosynthesis of vitamin D explained in detail, including the relevance of these vitamins to reproductive success. It explores whether we might be able to predict vitamin-related gene polymorphisms that pivot metabolism to the prevailing UVR exposome within the vitamin D-folate evolutionary hypothesis context. This is discussed in terms of a primary adaptive phenotype (pigmentation/depigmentation), a secondary adaptive phenotype (flexible metabolic phenotype based on vitamin-related gene polymorphism profile), and a tertiary adaptive strategy (dietary anti-oxidants to support the secondary adaptive phenotype). Finally, alternative evolutionary models for pigmentation are discussed, as are challenges to future research in this area.

Methylenetetrahydrofolate reductase gene polymorphisms are not associated with embryo chromosomal abnormalities and IVF outcomes

The aim of our study was to investigate the effect of maternal and embryo MTHFR C677T and A1298C polymorphisms on embryo aneuploidies and mosaicism and the correlation between these genetic variants in transferred euploid embryos and IVF outcomes. MTHFR genotype was analyzed in 77 women who performed an IVF/ICSI cycle with PGT-A. Moreover, to evaluate the effect of embryo MTHFR polymorphisms on embryo aneuploidies and mosaicism, the MTHFR genotype was analyzed in 191 biopsied embryos from the PGT-A cycles of these patients. Additionally, 218 DNA samples from trophectoderm biopsies belonging to a different group of patients were also genotyped. MTHFR polymorphisms were analyzed in a total amount of 409 trophectoderm samples. The main parameters analyzed were embryo aneuploidy and mosaicism rates. Finally, the IVF outcomes of 241 single euploid embryo transfers were assessed and compared between different MTHFR embryo genotypes. The aneuploidy rates were similar in embryos from homozygous normal women and women with at least one mutated allele (54.7% vs. 30.2% in 677C>T and 37.8% vs. 42.7% in 1298A>C). Furthermore, no differences were observed in the mosaicism rate (24.0% vs. 13.8% in 677C>T and 17.1% vs. 17.3% in 1298A>C). A similar analysis was performed, taking into account the embryo genotype results. No differences in aneuploidy rate were observed between the study groups. The only significant difference was the mosaicism rate among 677C>T genotype (13.5% in 677CC group vs. 5.4% in 677CT/TT; p = 0.019). Implantation rate, biochemical and clinical miscarriage rates, and ongoing pregnancy rate were compared between different embryo genotypes, and no statistically significant differences were found. In conclusion, the maternal MTHFR genotype did not influence embryo chromosomal abnormalities. Moreover, the embryo MTHFR genotype was not associated with embryo aneuploidy or IVF outcomes such as implantation, pregnancy loss, and ongoing pregnancy when euploid embryos were transferred.Abbreviations: MTHFR: methylenetetrahydrofolate reductase; IVF: in vitro fertilization; PGT-A: preimplantation genetic testing for aneuploidies; SAM: S-adenosyl methionine; SNP: single nucleotide polymorphism; SPSS: Statistical Package for Social Sciences; RIF: recurrent implantation failure; RPL: recurrent pregnancy loss; hCG: human chorionic gonadotropin; PBS: phosphate buffered saline; CGH: comparative genomic hybridization; NGS: next generation sequencing.

Vitamin-related phenotypic adaptation to exposomal factors: The folate-vitamin D-exposome triad

The biological role of two key vitamins, folic acid and vitamin D is so fundamental to life processes, it follows that their UV sensitivity, dietary abundance (both key exposomal factors) and variability in dependent genes will modify their functional efficacy, particularly in the context of maintaining the integrity and function of genome and epigenome. This article therefore examines folate and vitamin D-related phenotypic adaptation to environmental factors which vary across the human life cycle as well as over an evolutionary time-scale. Molecular mechanisms, key nutrigenomic factors, phenotypic maladaptation and evolutionary models are discussed.

Methotrexate modulates folate phenotype and inflammatory profile in EA.hy 926 cells

EA.hy 926 cells grown under low folate conditions adopt a "pro-atherosclerotic" morphology and biochemical phenotype. Pharmacologically relevant doses of the antifolate drug methotrexate (MTX) were applied to EA.hy 926 cells maintained in normal (Hi) and low (Lo) folate culture media. Under both folate conditions, MTX caused inhibition of cell proliferation without significantly compromising metabolic activity. MTX treated Hi cells were depleted of folate derivatives, which were present in altered proportions relative to untreated cells. Transcript profiling using microarrays indicated that MTX treatment modified the transciptome in similar ways for both Hi and Lo cells. Many inflammation-related genes, most prominently those encoding C3 and IL-8, were up-regulated, whereas many genes involved in cell division were down-regulated. The results for C3 and IL-8 were confirmed by quantitative RT-PCR and ELISA. MTX appears to modify the inflammatory potential of EA.hy 926 cells such that its therapeutic properties may, at least under some conditions, be accompanied by the induction of a subset of gene products that promote and/or maintain comorbid pathologies.

Vitamin D, folate, and potential early lifecycle environmental origin of significant adult phenotypes

Solar radiation early in pregnancy interacts with light sensitive vitamins to influence an embryo's genetic profile. This influences both adult disease risk and may play a role in the evolution of skin colour.

Background and objectives: Vitamin D and folate are highly UV sensitive, and critical for maintaining health throughout the lifecycle. This study examines whether solar irradiance during the first trimester of pregnancy influences vitamin D receptor (VDR) and nuclear folate gene variant occurrence, and whether affected genes influence late-life biochemical/clinical phenotypes.

Methodology: 228 subjects were examined for periconceptional exposure to solar irradiance, variation in vitamin D/folate genes (polymerase chain reaction (PCR)), dietary intake (food frequency questionnaire (FFQ)) and important adult biochemical/clinical phenotypes.

Results: Periconceptional solar irradiance was associated with VDR-BsmI (P = 0.0008^wk7), TaqI (P = 0.0014^wk7) and EcoRV (P = 0.0030^wk6) variant occurrence between post-conceptional weeks 6–8, a period when ossification begins. Similar effects were detected for other VDR gene polymorphisms. Periconceptional solar irradiance was also associated with 19 bp del-DHFR (P = 0.0025^wk6), and to a lesser extent C1420T-SHMT (P = 0.0249^wk6), a folate-critical time during embryogenesis. These same genes were associated with several late-life phenotypes: VDR-BsmI, TaqI and ApaI determined the relationship between dietary vitamin D and both insulin (P < 0.0001/BB, 0.0007/tt and 0.0173/AA, respectively) and systolic blood pressure (P = 0.0290/Bb, 0.0299/Tt and 0.0412/AA, respectively), making them important early and late in the lifecycle. While these and other phenotype associations were found for the VDR variants, folate polymorphism associations in later-life were limited to C1420T-SHMT (P = 0.0037 and 0.0297 for fasting blood glucose and HbA1c levels, respectively). We additionally report nutrient–gene relationships with body mass index, thiol/folate metabolome, cognition, depression and hypertension. Furthermore, photoperiod at conception influenced occurrence of VDR-Tru9I and 2R3R-TS genotypes (P = 0.0120 and 0.0360, respectively).

Conclusions and implications: Findings identify environmental and nutritional agents that may interact to modify gene–phenotype relationships across the lifecycle, offering new insight into human ecology. This includes factors related to both disease aetiology and the evolution of skin pigmentation.

Diet and our genetic legacy in the recent anthropocene: a Darwinian perspective to nutritional health

Nutrient-gene research tends to focus on human disease, although such interactions are often a by-product of our evolutionary heritage. This review explores health in this context, reframing genetic variation/epigenetic phenomena linked to diet in the framework of our recent evolutionary past. This "Darwinian/evolutionary medicine" approach examines how diet helped us evolve among primates and to adapt (or fail to adapt) our metabolome to specific environmental conditions leading to major diseases of civilization. This review presents updated evidence from a diet-gene perspective, portraying discord that exists with respect to health and our overall nutritional, cultural, and activity patterns. While Darwinian theory goes beyond nutritional considerations, a significant component within this concept does relate to nutrition and the mismatch between genes, modern diet, obesogenic lifestyle, and health outcomes. The review argues that nutritional sciences should expand knowledge on the evolutionary connection between food and disease, assimilating it into clinical training with greater prominence.

Hydrogen sulphide-related thiol metabolism and nutrigenetics in relation to hypertension in an elderly population

Hydrogen sulphide (H(2)S) is a gaseous signalling molecule that regulates blood flow and pressure. It is synthesised from cysteine via cystathionine β-synthase and cystathionine γ-lyase. We examined whether thiol precursors of H(2)S, transsulphuration pathway gene variants (CBS-844ins68 and CTH-G1364T) and key B-vitamin cofactors might be critical determinants of hypertension in an elderly Australian population. An elderly Australian retirement village population (n = 228; age 65-96 years, 91 males and 137 females) was assessed for the prevalence of two transsulphuration pathway-related variant genes associated with cysteine synthesis and hence H(2)S production. Thiols were determined by HPLC, genotypes by PCR and dietary intake by food frequency questionnaire. Homocysteine levels were statistically higher in the hypertensive phenotype (p = 0.0399), but there was no difference for cysteine or glutathione. Using nominal logistic regression, cysteine, CTH-G1364T genotype, dietary synthetic folate and vitamin B(6) predicted clinical phenotype (determined as above/below 140/90 mm Hg) and then only in female subjects (p = 0.0239, 0.0178, 0.0249 and 0.0371, respectively). Least-squares regression supports cysteine being highly inversely predictive of diastolic blood pressure: p and r (2) values <0.0001 and 0.082; 0.0409 and 0.046; and <0.0001 and 0.113 for all subjects, males and females, respectively. Additionally, CTH-G1364T genotype predicts diastolic blood pressure in males (p = 0.0217; r (2) = 0.083), but contrasts with observations for females. Overall, analyses, including stepwise regression, suggest cysteine, dietary natural and synthetic folate, vitamins B(6) and B(12), and both genetic variants (CTH-C1364T and CBS-844ins68) are all aetiologically relevant in the regulation of blood pressure. Hydrogen sulphide is a vasorelaxant gasotransmitter with characteristics similar to nitric oxide. Cysteine and the G1364T and 844ins68 variants of the cystathionine γ-lyase and cystathionine β-synthase genes, respectively, are the biological determinants of H(2)S synthesis, and all three are shown here to influence the hypertensive phenotype. Additionally, B-vitamin cofactors for these three enzymes may also be important determinants of blood pressure.

TAS2R38 bitter taste genetics, dietary vitamin C, and both natural and synthetic dietary folic acid predict folate status, a key micronutrient in the pathoaetiology of adenomatous polyps

Taste perception may influence dietary preferences and nutrient intakes contributing to diet-related disease susceptibility. This study examined bitter taste genetics and whether variation in the TAS2R38 gene at three polymorphic loci (A49P, V262A and I296V) could alter dietary and systemic folate levels and dietary vitamin C intake, and whether a nutrigenetic circuit existed that might link bitter taste, folate/antioxidant status and risk for a colonic adenomatous polyp. TAS2R38 diplotype predicted bitter taste (PROP) phenotype (p value <0.00001) and red cell folate status (p=0.0179) consistent with the diplotype that has the broadest range of bitter perception (AVI/PAV) also possessing the highest average red cell folate value. However, TAS2R38 diplotype did not predict dietary intake of methylfolic acid, pteroylmonoglutamic acid or total folic acid. Neither did it predict dietary intake of vitamin C. Despite this, intake of dietary folate predicts red cell folate with analysis pointing to a key nutrient-nutrient interaction between vitamin C intake and systemic folate status. Analysis of 38 patients with an adenomatous polyp and 164 controls showed that individually, dietary nutrient intake, nutrient status and taste diplotype did not influence polyp risk. However, red cell folate status (in individuals below the population median value) did interact with bitter taste diplotype (AVI/PAV) to predict polyp risk (p=0.0145). Furthermore, synthetic folic acid (below median intake) was statistically associated with adenoma occurrence (p=0.0215); individuals with adenomatous polyps had a 1.77× higher intake than controls. Additionally, stepwise regression taking account of all dietary nutrients showed a tight relationship between methylfolic acid (but not pteroylmonoglutamic acid) intake and red cell folate level in those with a low folate status and occurrence of an adenomatous polyp (p=0.0039). These findings point to a role for folate in the pathoaetiology of adenomatous polyps, with the natural and synthetic vitamers not necessarily having the same biological effect.

Folic Acid: Beyond Metabolism

Mandatory and discretionary fortification with folic acid is eliminating deficiency of this vitamin. Blood levels of the vitamin have never been higher, with hematologic folate values commonly exceeding the upper range of calibration. The synthetic analog (pteroylmonoglutamic acid) prevents neural tube defects and lowers homocysteine, both positive attributes, yet negative correlates of pteroylmonoglutamic acid are increasingly reported. These involve increased risk for common cancers (ie, colon, breast, prostate) and antimetabolite effects on natural killer cells and at dihydrofolate reductase, a critical gatekeeper enzyme. This review, however, takes a different, human ecological perspective, examining novel folate-related phenomena distinct from the classic metabolic role of the vitamin in maintaining health and well-being. An argument is developed that at molecular, cellular, and organism levels, folate is crucial to some important events that link light to life.

The folic acid endophenotype and depression in an elderly population

OBJECTIVES

Folate status and/or genes have been linked to depression in a number of studies. This may be via a direct action (or actions) on neuronal membranes or indirect effects through the metabolism of methyl groups involved in neurotransmitter synthesis. This study examines folate and related thiol metabolism that might underpin either phenomenon.

DESIGN

Cohort study describing the relationship between several genetic and nutritional aspects of folic acid homeostasis and depression assessed by the HADS psychometric index in an elderly cohort.

SETTING

New South Wales (Australia) retirement village.

PARTICIPANTS

118 elderly participants (age 65-90 years).

RESULTS

Stepwise multiple regression was used to determine the best statistical model to predict depression; C677T-MTHFR (p=0.0103) was found to be positively associated with depression, while the thiol dipeptide Cys-Gly was negatively associated (p=0.0403). The statistical models used accounted for the major folate related indices (genetic and biochemical) that are most often evaluated in the context of health and disease. When only genetic data were examined for interactions, C677T-MTHFR was found to be negatively associated with the HADS Depression Index Score (p=0.0191).

CONCLUSION

The potential influence of Cys-Gly on this phenotype is novel, and of considerable interest given that it has been linked to altered spontaneous activity and sedation in an animal model. Cys-Gly is a recognised ligand at the N-methyl-D-aspartatic acid (NMDA) subclass of glutamate receptor, a system associated with depression. In addition, the C677T-MTHFR association adds further support to existing findings underscoring the potential role of folate in depression.

Serum adiponectin, leptin, C-peptide, homocysteine, and colorectal adenoma recurrence in the Polyp Prevention Trial

BACKGROUND

Serum adiponectin, leptin, C-peptide, and homocysteine are indicators for obesity, hyperinsulinemia, and chronic inflammation, which have all been associated with colorectal cancer.

AIMS

To determine whether serum adiponectin, leptin, C-peptide, and homocysteine are associated with fat, fiber, fruit and vegetable, flavonol, or dry bean intake and colorectal adenoma recurrence.

METHODS

Using logistic regression, we estimated odds ratios (OR) and 95% confidence intervals (95% CI) for adenoma recurrence in 627 participants from the control arm of the Polyp Prevention Trial, a 4-year trial that examined the effectiveness of a low-fat, high-fiber, high-fruit and vegetable diet on adenoma recurrence.

RESULTS

Serum concentrations of C-peptide and homocysteine were inversely related to fiber, fruit and vegetable, and flavonol intake and positively related to percentage of calories from fat (all P(trend) < or = 0.01). High homocysteine concentrations were associated with any (4th versus 1st quartile: OR, 2.26; 95% CI, 1.30-3.94) and more than one adenoma recurrence (OR, 2.11; 95% CI, 1.01-4.40). Individuals in the highest, versus lowest, tertile of serum leptin concentration had a decreased risk of advanced adenoma recurrence (OR, 0.22; 95% CI, 0.06-0.79).

CONCLUSION

Our results suggest that serum homocysteine may serve as an indicator of dietary exposure, including a low-fat and high-fiber, high-fruit and vegetable, and high-flavonol diet, as well as colorectal adenoma recurrence.

IMPACT

Discovering biomarkers that are both modifiable and can predict cancer risk is critical. We identified serum homocysteine as a novel indicator that is modified by diet and predicts risk of adenoma recurrence.

Folic acid fortification: a double-edged sword

PURPOSE OF REVIEW

To examine the impact of folic acid fortification, including its use as a functional food component, on human health.

RECENT FINDINGS

There is a consensus view that folic acid supplementation has numerous health benefits, many of which are significant in their impact. However, emerging evidence suggests that increased population exposure to folic acid may also have a negative impact with respect to certain developmental and degenerative disorders. As examples, presently much attention is focused on the role of folic acid fortification augmenting colon cancer risk, whereas earlier in the life cycle, the vitamin may additionally influence insulin resistance. Without question, conditions that are influenced by folic acid are both diverse and many - from concerns relating to cognitive decline, breast cancer and vascular disease through to preconceptional issues where maternal folate levels might conceivably alter the phenotype of offspring via epimutations.

SUMMARY

The highly complex and critical biological importance of folic acid-related molecular nutrition makes it a difficult micronutrient to deploy as a simple intervention at a population level - it has far too many biochemical spheres of influence to predict effects in a generalized way. Additionally, several gene variants and other nutrients are interactive factors. It is, therefore, hardly surprising that the scientific community does not have a true consensus view on whether mandatory fortification is appropriate as a population measure. This latter point not withstanding, any ultimate decisions on fortification should be well rooted in scientific fact rather than political expediency.

Folate and homocysteine phenotypes: Comparative findings using research and clinical laboratory data

OBJECTIVES

A low folate/high homocysteine phenotype is associated with several pathologies, including spina bifida and cardiovascular disease. Folate and total homocysteine (tHcy) measurements are used clinically to assess risk and the need for folic acid supplementation and in research to investigate the metabolic basis of disease. Red blood cell (RBC) folate, the best indicator of long-term folate status, is usually measured as "total" folate. However, different folate derivatives support distinct biochemical functions, suggesting a need to develop more precise methods. This study was designed to evaluate a method based on stable isotope dilution liquid chromatography-multiple reaction monitoring/mass spectrometry (LC-MRM/MS).

DESIGN AND METHODS

We used LC-MRM/MS to quantify the RBC folate derivatives 5-methyltetrahydrofolate (5-CH(3)-THF), tetrahydrofolate (THF), and 5,10-methenyltetrahydrofolate (5,10-methenylTHF) in pre-menopausal women. The concentration of each folate derivative was assessed for utility in predicting tHcy levels, and compared to folate and tHcy measurements derived by routine clinical laboratory methods.

RESULTS

LC-MRM/MS was qualitatively and quantitatively superior to routine clinical laboratory methods for determining folate and tHcy concentrations. RBC 5-CH(3)-THF had a reciprocal relationship with tHcy (p=0.0003), whereas RBC THF and RBC 5,10-methenylTHF had direct relationships (p=0.01, 0.04 respectively). In combination, these three variables accounted for 42% of the variation in tHcy.

CONCLUSIONS

Robust methods for measuring RBC 5-CH(3)-THF would improve the utility of folate/homocysteine phenotyping in patient management. The use of LC-MRM/MS would allow studies of hyperhomocysteinemia and diseases associated with a low folate/high homocysteine phenotype to be performed with less measurement error and greater statistical power to generate data with the potential to elucidate the etiologic mechanisms of complex diseases and traits.

Does the MTHFR 677C-->T variant affect the Recommended Dietary Allowance for folate in the US population?

BACKGROUND

The MTHFR 677C-->T variant is associated with reduced enzyme activity, abnormalities of folate metabolism, and potential increase in folate requirement. The effect of this variant on the Recommended Dietary Allowance (RDA) for folate is unclear.

OBJECTIVE

The aim of this study was to assess the effect of the MTHFR 677C-->T polymorphism on the current folate RDA for US adults aged > or =19 y (400 microg/d) by race and ethnicity.

DESIGN

We calculated the projected RDA for folate for each racial and ethnic group according to the methods of the Institute of Medicine. We modeled the projected RDA with different hypothetical effect sizes ranging from 5% to 50%. The RDA value was then weighted according to the US prevalence of the TT (or the combined CT/TT) genotype in each racial and ethnic group.

RESULTS

The projected RDA ranges were based on TT genotype frequencies and on different effect sizes (5-50%) that ranged from 400 to 421 microg/d for non-Hispanic whites, 401-436 microg/d for Mexican Americans, and 400-402 microg/d for non-Hispanic blacks.

CONCLUSIONS

Our findings suggest that the current RDA for folate differs little for non-Hispanic whites, non-Hispanic blacks, and Mexican Americans irrespective of the MTHFR TT genotype, and, from a population perspective, the MTHFR 677C-->T variant does not warrant modifications to the current RDA for dietary folate at this time.