The reduced folate carrier (RFC) is cytotoxic to cells under conditions of severe folate deprivation. RFC as a double edged sword in folate homeostasis

Folate as a potential treatment for lethal ventricular arrhythmias in TANGO2-deficiency disorder

TANGO2-deficiency disorder (TDD) is an autosomal-recessive genetic disease caused by biallelic loss-of-function variants in the TANGO2 gene. TDD-associated cardiac arrhythmias are recalcitrant to standard antiarrhythmic medications and constitute the leading cause of death. Disease modeling for TDD has been primarily carried out using human dermal fibroblast and, more recently, in Drosophila by multiple research groups. No human cardiomyocyte system has been reported, which greatly hinders the investigation and understanding of TDD-associated arrhythmias. Here, we established potentially novel patient-derived induced pluripotent stem cell differentiated cardiomyocyte (iPSC-CM) models that recapitulate key electrophysiological abnormalities in TDD. These electrophysiological abnormalities were rescued in iPSC-CMs with either adenoviral expression of WT-TANGO2 or correction of the pathogenic variant using CRISPR editing. Our natural history study in patients with TDD suggests that the intake of multivitamin/B complex greatly diminished the risk of cardiac crises in patients with TDD. In agreement with the clinical findings, we demonstrated that high-dose folate (vitamin B9) virtually abolishes arrhythmias in TDD iPSC-CMs and that folate's effect was blocked by the dihydrofolate reductase inhibitor methotrexate, supporting the need for intracellular folate to mediate antiarrhythmic effects. In summary, data from TDD iPSC-CM models together with clinical observations support the use of B vitamins to mitigate cardiac crises in patients with TDD, providing potentially life-saving treatment strategies during life-threatening events.

Unravelling the Influence of Host Genetic Factors on Malaria Susceptibility in Asian Populations

Malaria is a deadly blood-borne disease caused by a Plasmodium parasite. Infection results in various forms of malaria, including an asymptomatic state, uncomplicated disease, or severe disease. Severe malaria (SM) is particularly prevalent among young children and is a significant cause of mortality. SM is associated with the sequestration of parasitized erythrocytes in the microvasculature of vital host organs, disrupting the normal functioning of the immune system. Although the exact mechanisms of malaria pathogenesis are yet to be fully understood, researchers have been investigating the role of host genetics in determining the severity of the disease and the outcome of infection. The objective of this study is to identify specific host genes that have been examined for their association with malaria in Asian populations and pinpoint those most likely to influence susceptibility. Through an extensive screening process, a total of 982 articles were initially identified, and after careful review, 40 articles discussing 68 genes were included in this review. By constructing a network of protein-protein interactions (PPIs), we identified six key proteins (TNF, IL6, TLR4, IL1β, IL10, and IL8) that exhibited substantial interactions (more than 30 edges), suggesting their potential as significant targets for influencing malaria susceptibility. Notably, these six proteins have been previously identified as crucial components of the immune response, associated with malaria susceptibility, and capable of affecting different clinical forms of the disease. Identifying genes that contribute to malaria susceptibility or resistance holds the promise of enhancing the diagnosis and treatment of this debilitating illness. Such knowledge has the potential to pave the way for more targeted and effective strategies in combating malaria, particularly in Asian populations where controlling Plasmodium vivax is challenging, and India contributes the highest number of cases. By understanding the genetic factors underlying malaria vulnerability, we can develop interventions that are tailored to the specific needs of Asian populations, ultimately leading to better outcomes in the fight against this disease.

Immunodeficiency associated with a novel functionally defective variant of SLC19A1 benefits from folinic acid treatment

Insufficient dietary folate intake, hereditary malabsorption, or defects in folate transport may lead to combined immunodeficiency (CID). Although loss of function mutations in the major intestinal folate transporter PCFT/SLC46A1 was shown to be associated with CID, the evidence for pathogenic variants of RFC/SLC19A1 resulting in immunodeficiency was lacking. We report two cousins carrying a homozygous pathogenic variant c.1042 G > A, resulting in p.G348R substitution who showed symptoms of immunodeficiency associated with defects of folate transport. SLC19A1 expression by peripheral blood mononuclear cells (PBMC) was quantified by real-time qPCR and immunostaining. T cell proliferation, methotrexate resistance, NK cell cytotoxicity, Treg cells and cytokine production by T cells were examined by flow cytometric assays. Patients were treated with and benefited from folinic acid. Studies revealed normal NK cell cytotoxicity, Treg cell counts, and naive-memory T cell percentages. Although SLC19A1 mRNA and protein expression were unaltered, remarkably, mitogen induced-T cell proliferation was significantly reduced at suboptimal folic acid and supraoptimal folinic acid concentrations. In addition, patients' PBMCs were resistant to methotrexate-induced apoptosis supporting a functionally defective SLC19A1. This study presents the second pathogenic SLC19A1 variant in the literature, providing the first experimental evidence that functionally defective variants of SLC19A1 may present with symptoms of immunodeficiency.

Increasing Dosage of Leucovorin Results in Pharmacokinetic and Gene Expression Differences When Administered as Two-Hour Infusion or Bolus Injection to Patients with Colon Cancer

The combination of 5-fluorouracil (5-FU) and leucovorin (LV) forms the chemotherapy backbone for patients with colorectal cancer. However, the LV administration is often standardized and not based on robust scientific data. To address these issues, a randomized pharmacokinetics study was performed in patients with colon cancer. Thirty patients were enrolled, receiving 60, 200 or 500 mg/m² LV as a single two-hour infusion. Blood, tumor, mucosa, and resection margin biopsies were collected. Folate concentrations were analyzed with LC-MS/MS and gene expression with qPCR. Data from a previous study where patients received LV as bolus injections were used as comparison. Saturation of methylenetetrahydrofolate (MeTHF) and tetrahydrofolate (THF) levels was seen after two-hour infusion and polyglutamated MeTHF + THF levels in tumors decreased with increasing LV dosage. The decrease was associated with decreased FPGS and increased GGH expression, which was not observed after LV bolus injection. In the bolus group, results indicate activation of a metabolic switch possibly promoting TYMS inhibition in response to 5-FU. Different metabolic mechanisms appear to be induced when LV is administered as infusion and bolus injection. Since maximal inhibition of TYMS by the 5-FU metabolite 5-fluoro-2'-deoxyuridine 5'-monophosphate (FdUMP) requires excess polyglutamated MeTHF, the results point in favor of the bolus regimen.

Genetic Polymorphisms of Very Important Pharmacogene Variants in the Blang Population from Yunnan Province in China

Background

We aimed to enrich the pharmacogenomic information of a Blang population (BP) from Yunnan Province in China.

Methods

We genotyped 55 very important pharmacogene (VIP) variants from the PharmGKB database and compared their genotype distribution (GD) in a BP with that of 26 populations by the χ² test. The minor allele frequency (MAF) distribution of seven significantly different single-nucleotide polymorphisms (SNPs) was conducted to compare the difference between the BP and 26 other populations.

Results

Compared with the GD of 55 loci in the BP, among 26 studied populations, GWD, YRI, GIH, ESN, MSL, TSI, PJL, ACB, FIN and IBS were the top-10 populations, which showed a significantly different GD >35 loci. CHB, JPT, CDX, CHS, and KHV populations had a significantly different GD <20 loci. A GD difference of 27–34 loci was found between the BP and 11 populations (LWK, CEU, ITU, STU, PUR, CLM, GBR, ASW, BEB, MXL and PEL). The GD of five loci (rs750155 (SULT1A1), rs4291 (ACE), rs1051298 (SLC19A1), rs1131596 (SLC19A1) and rs1051296 (SLC19A1)) were the most significantly different in the BP as compared with that of the other 26 populations. The genotype frequency of rs1800764 (ACE) and rs1065852 (CYP2D6) was different in all populations except for PEL and LWK, respectively. MAFs of rs1065852 (CYP2D6) and rs750155 (SULT1A1) showed the largest fluctuation between the BP and SAS, EUR, AFR and AMR populations.

Conclusion

Our data can provide theoretical guidance for safe and efficacious personalized drug use in the Blang population.

The Concept of Folic Acid in Health and Disease

Folates have a pterine core structure and high metabolic activity due to their ability to accept electrons and react with O-, S-, N-, C-bounds. Folates play a role as cofactors in essential one-carbon pathways donating methyl-groups to choline phospholipids, creatine, epinephrine, DNA. Compounds similar to folates are ubiquitous and have been found in different animals, plants, and microorganisms. Folates enter the body from the diet and are also synthesized by intestinal bacteria with consequent adsorption from the colon. Three types of folate and antifolate cellular transporters have been found, differing in tissue localization, substrate affinity, type of transferring, and optimal pH for function. Laboratory criteria of folate deficiency are accepted by WHO. Severe folate deficiencies, manifesting in early life, are seen in hereditary folate malabsorption and cerebral folate deficiency. Acquired folate deficiency is quite common and is associated with poor diet and malabsorption, alcohol consumption, obesity, and kidney failure. Given the observational data that folates have a protective effect against neural tube defects, ischemic events, and cancer, food folic acid fortification was introduced in many countries. However, high physiological folate concentrations and folate overload may increase the risk of impaired brain development in embryogenesis and possess a growth advantage for precancerous altered cells.

Influence of RFC1 c.80A>G Polymorphism on Methotrexate-Mediated Toxicity and Therapeutic Efficacy in Rheumatoid Arthritis: A Meta-analysis

BACKGROUND

Methotrexate (MTX) is an antirheumatic drug, transported by reduced folate carrier-1 (RFC1). The most common RFC1 gene variant, c.80 A>G (rs1051266) is ambiguously linked to adverse effects of MTX therapy in some rheumatoid arthritis (RA) patients.

OBJECTIVE

The purpose of meta-analysis was to summarize all major published studies on c.80 A>G SNP to clarify this ambiguity in MTX therapy.

METHODS

A total of 18 studies representing 3592 RA patients comprising 699 men and 2893 women were included. Both fixed and random effect models were applied to study the data.

RESULTS

The RFC1 80A-allele showed null association with MTX-mediated toxicity in both fixed (odds ratio [OR] = 0.91; 95% CI = 0.80-1.03) and random effects (OR = 0.89; 95% CI: 0.71-1.11) models. Because heterogeneity was observed in this association (P = 0.0006), data were segregated based on use of folate therapy. In 7 studies (n = 1191) where folate was used along with MTX, RFC1 AA patients showed reduced risk for MTX-mediated toxicity (OR = 0.67; 95% CI: 0.50-0.89; P = 0.0006). The RFC1 80A-allele was found to increase the efficacy of MTX therapy by 1.53-fold (95% CI: 1.24-1.88), whereas the 80AA-genotype increased the efficacy by 1.85-fold (95% CI: 1.41-2.42). No publication bias was observed in these associations.

CONCLUSION AND RELEVANCE

RFC1 c.80 A>G is an important pharmacogenetic determinant of MTX therapy in RA. The RFC1 80A-allele robustly increased therapeutic efficacy and safety when folate was used along with MTX. Findings are relevant to decision-making in the clinical use of MTX as a treatment for RA patients harboring the RFC1 gene variant.

Folic Acid-Peptide Conjugates Combine Selective Cancer Cell Internalization with Thymidylate Synthase Dimer Interface Targeting

Drug-target interaction, cellular internalization, and target engagement should be addressed to design a lead with high chances of success in further optimization stages. Accordingly, we have designed conjugates of folic acid with anticancer peptides able to bind human thymidylate synthase (hTS) and enter cancer cells through folate receptor α (FRα) highly expressed by several cancer cells. Mechanistic analyses and molecular modeling simulations have shown that these conjugates bind the hTS monomer-monomer interface with affinities over 20 times larger than the enzyme active site. When tested on several cancer cell models, these conjugates exhibited FRα selectivity at nanomolar concentrations. A similar selectivity was observed when the conjugates were delivered in synergistic or additive combinations with anticancer agents. At variance with 5-fluorouracil and other anticancer drugs that target the hTS catalytic pocket, these conjugates do not induce overexpression of this protein and can thus help combating drug resistance associated with high hTS levels.

Folylpoly-ɣ-glutamate synthetase association to the cytoskeleton: Implications to folate metabolon compartmentalization

Folates are essential for nucleotide biosynthesis, amino acid metabolism and cellular proliferation. Following carrier-mediated uptake, folates are polyglutamylated by folylpoly-ɣ-glutamate synthetase (FPGS), resulting in their intracellular retention. FPGS appears as a long isoform, directed to mitochondria via a leader sequence, and a short isoform reported as a soluble cytosolic protein (cFPGS). However, since folates are labile and folate metabolism is compartmentalized, we herein hypothesized that cFPGS is associated with the cytoskeleton, to couple folate uptake and polyglutamylation and channel folate polyglutamates to metabolon compartments. We show that cFPGS is a cytoskeleton-microtubule associated protein: Western blot analysis revealed that endogenous cFPGS is associated with the insoluble cellular fraction, i.e., cytoskeleton and membranes, but not with the cytosol. Mass spectrometry analysis identified the putative cFPGS interactome primarily consisting of microtubule subunits and cytoskeletal motor proteins. Consistently, immunofluorescence microscopy with cytosol-depleted cells demonstrated the association of cFPGS with the cytoskeleton and unconventional myosin-1c. Furthermore, since anti-microtubule, anti-actin cytoskeleton, and coatomer dissociation-inducing agents yielded perinuclear pausing of cFPGS, we propose an actin- and microtubule-dependent transport of cFPGS between the ER-Golgi and the plasma membrane. These novel findings support the coupling of folate transport with polyglutamylation and folate channeling to intracellular metabolon compartments. SIGNIFICANCE: FPGS, an essential enzyme catalyzing intracellular folate polyglutamylation and efficient retention, was described as a soluble cytosolic enzyme in the past 40 years. However, based on the lability of folates and the compartmentalization of folate metabolism and nucleotide biosynthesis, we herein hypothesized that cytoplasmic FPGS is associated with the cytoskeleton, to couple folate transport and polyglutamylation as well as channel folate polyglutamates to biosynthetic metabolon compartments. Indeed, using complementary techniques including Mass-spectrometry proteomics and fluorescence microscopy, we show that cytoplasmic FPGS is associated with the cytoskeleton and unconventional myosin-1c. This novel cytoskeletal localization of cytoplasmic FPGS supports the dynamic channeling of polyglutamylated folates to metabolon compartments to avoid oxidation and intracellular dilution of folates, while enhancing folate-dependent de novo biosynthesis of nucleotides and DNA/protein methylation.

Schedule-Dependent Synergy Between the Histone Deacetylase Inhibitor Belinostat and the Dihydrofolate Reductase Inhibitor Pralatrexate in T-and B-cell Lymphoma Cells in vitro

Pralatrexate (Folotyn; PLX) and belinostat (Beleodaq; BLS) are registered for the treatment of patients with peripheral T-cell lymphoma (PTCL) and are being considered for other lymphomas. In this study we investigated whether BLS had the ability to potentiate the cytotoxicity of PLX. A panel of lymphoma cell lines was used for the combination studies: the B-cell SUDHL-4, SUDHL-5, HT, Jeko-1 and T-cell Karpas-299 and Hut-78. Uptake of PLX was mediated by the reduced folate carrier (RFC). PLX showed a 6-fold better RFC substrate affinity compared to methotrexate, and 2-fold better than levoleucovorin (l-LV). Sensitivity expressed as the concentration that resulted in 50% growth inhibition (IC50) after 72 hr exposure to PLX varied from 2.8 to 20 nM and for BLS from 72 to 233 nM, independent of the background of the cell lines. The interaction between BLS and PLX was studied using the median-drug effect analysis. At a fixed molar ratio between the drugs based on the IC50 concentration the average combination index (CI) for all cell lines showed additivity (CI: around 1.0). In three selected cell lines (SUDHL-4, SUDHL-5, and HT) sequential exposure (24 h pretreatment with BLS, followed by 48 h to PLX + BLS), did not improve interaction (CI: 0.9–1.4). As an alternative approach a non-fixed ratio was used by exposing SUDHL-4, SUDHL-5, and HT cells to IC25 concentrations of either BLS or PLX in combination with the other drug. Exposure to IC25 of PLX did not decrease the IC50 for BLS (CI from 0.6–1.2), but exposure to IC25 of BLS markedly increased PLX sensitivity (low CIs from 0.40 to 0.66). Mechanistic studies focused on induction of apoptosis, and showed cleavage of predominantly caspase-9 in HT and SUDHL-4 cells for both drugs at their IC50s, being similar in the combination setting. Moreover, at these concentrations, the drugs were shown to confer an S-phase arrest. In conclusion, the combination of PLX and BLS showed additivity in various lymphoma cell lines, with a schedule-dependent synergism in B-cell lymphoma. Based on these data, proficient inhibition of HDAC activity by BLS holds promise in sensitization of tumor cells to PLX.

In silico analysis of the structural and functional implications of SLC19A1 R27H polymorphism

In view of the documented association of solute carrier family 19 member 1 (SLC19A1) G80A (R27H) polymorphism with the risk for different types of cancers and systemic lupus erythematosus (SLE), we have reanalysed the case-control study on breast cancer to ascertain the conditions in which this polymorphic variant exerts the risk of breast cancer. Association statistics have revealed that this polymorphism exerts the risk for breast cancer under the conditions of low folate intake, and in the absence of well-documented protective polymorphism in cytosolic serine hydroxymethyltransferase. To substantiate this observation, we have developed a homology model of SLC19A1 using glycerol-3-phosphate transporter (d1pw4a) as a template where 73% of the residues were modelled at 90% confidence while 162 residues were modelled ab initio. The wild and mutant proteins shared same topology in S3, S5, S6, S7, S11 and S12 transmembrane domains. The topology varied at S1 (28-43 residue vs 28-44 residue), S2 (66-87 residue vs 69-87 residue), S4 (117-140 residue vs 117-139 residue), S8 (305-325 residue vs 305-324 residue), S9 (336-356 residue vs 336-355residue), and S10 (361-386 residue vs 361-385 residue) transmembrane domains between wild versus mutant proteins. S2 domain is shortened by three amino acid residues in the mutant while in other domains the difference corresponds to one amino acid residue. The 3DLigandSite analysis revealed that the metallic-ligand-binding sites at 273Trp, 277Asn, 379Leu, 439Phe and 442Leu are although unaffected, there is a loss of active sites corresponding to nonmetallic ligand binding. Tetrahydrofolate and methotrexate have lesser affinity towards the mutant protein than the wild protein. To conclude, the R27H polymorphism affects the secondary and tertiary structures of SLC19A1 with the significant loss in ligand-binding sites.

Discovery of Novel Biomarkers of Therapeutic Responses in Han Chinese Pemetrexed-Based Treated Advanced NSCLC Patients

Pemetrexed, one of the most commonly used drugs in advanced non–small cell lung cancer (NSCLC) therapies, often leads to various therapeutic responses in patients. These therapeutic responses to pemetrexed, including adverse drug reactions (ADRs) and its intended therapeutic effects, have been demonstrated to be highly individual-specific. Such difference in therapeutic responses across individuals may be caused by the unique genetic variations in each patient. However, only a few pemetrexed-based studies have been performed using Han Chinese patients. In this study, we aimed to identify genetic signatures of therapeutic responses of pemetrexed-based treatment using 203 Han Chinese patients with advanced NSCLC. All the participants received two different types of therapies: 1) treatment with only pemetrexed and 2) treatment with both pemetrexed and platinum (mainly cisplatin and carboplatin). We then performed a genetic association analysis on 16 selected single-nucleotide polymorphisms (SNPs) in 7 genes using these 2 groups. The analysis of patients receiving only pemetrexed suggests that the SNP rs1051298 on the SLC19A1 gene (c.*746C > T) increased the risk of all ADRs (collected all types of ADRs) in different cycles of pemetrexed therapy [1-2 cycles: P = 0.0059, odds ratio (OR) = 3.143; 1-4 cycles: P = 0.0072, OR = 2.340; 1-6 cycles: P = 0.0071, OR = 2.243]. This influence of rs1051298 is particularly significant in terms of liver injury (1-4 cycles: P = 0.0056, OR = 3.863; 1-6 cycles: P = 0.0071, OR = 3.466). In all the patients, including patients who received both pemetrexed and platinum, SNP rs1801133 on the MTHFR gene (665C > T) was found to be significantly associated with hematological ADRs in 1 to 2 cycles (P = 0.0079, OR = 3.566). Additionally, we discovered that SNP rs12995526 (c.815-102T > C) in the ATIC gene and SNP rs11545077 (c.91G > T) in the GGH gene were associated with both ADRs and therapeutic effects. In summary, our study identified several potential biomarkers that were significantly associated with ADRs and therapeutic effects of pemetrexed-related treatments using Han Chinese patients. Our discoveries will provide important clues for personalized pemetrexed-based treatment design for Han Chinese NSCLC patients in the future.

Folate and choline absorption and uptake: Their role in fetal development

SCOPE

In this review, we attempt to assess how choline and folate transporters affect fetal development. We focus on how the expression of these transporters in response to choline and folate intake affects transport effectiveness. We additionally describe allelic variants of the genes encoding these transporters and their phenotypic effects.

METHODS AND RESULTS

We made an extensive review of recent articles describing role of choline and folate - with particularly emphasize on their transporters - in fetal development. Folate and choline are necessary for the proper functioning of the cell and body. During pregnancy, the requirements of these nutrients increase because of elevated maternal demand and the rapid division of fetal cells. The concentrations of folate and choline in cells depend on food intake, the absorption of nutrients, and the cellular transport system, which is tissue-specific and developmentally regulated. Relatively few studies have investigated the role of choline transporters in fetal development.

CONCLUSIONS

In this review we show relations between functioning of folate and choline transporters and fetal development.

Neoadjuvant Therapy for Esophageal Adenocarcinoma in the Community Setting-Practice and Outcomes

There has been an alarming rise in the incidence of esophageal adenocarcinoma which continues to have poor survival rates primarily due to lack of effective chemotherapy and presentation at advanced stages. Over a dozen chemotherapeutic agents are FDA approved for esophageal cancer (EC), and a two or three-drug combination is typically prescribed as first-line therapy for the majority of EC patients, administered either pre or post-operatively with esophageal resection. We have noticed significant variability in adjuvant and neoadjuvant regimens used in the community setting. The aim of this study was to review the various drug regimens used in the neoadjuvant setting for EC patients with adenocarcinoma undergoing resection at a single tertiary referral center in the Midwest. A total of 123 patients (stage II–III) underwent esophageal resection after neoadjuvant treatment at the center. Overall, 18 distinct drug regimens were used in 123 patients including two patients who received targeted therapy. Median survival post-surgery for this group was 11.2 months with no single regimen offering a survival advantage. These results reveal an unclear algorithm of how accepted regimens are prescribed in the community setting as well as a dire need for agents that are more effective. Additionally, it was noted that although proteomic markers have been found to predict drug response to 92% of the FDA-approved drugs in EC (12 of 13), according to pathology reports, molecular diagnostic testing was not used to direct treatment in this cohort. We therefore propose potential strategies to improve clinical outcomes including the use of a robust molecular oncology diagnostic panel and discuss the potential role for targeted chemotherapy and/or immunotherapy in the management of EC patients.

Population-level diversity in the association of genetic polymorphisms of one-carbon metabolism with breast cancer risk

Aberrations in one-carbon metabolism were reported to increase breast cancer risk by influencing the DNA synthesis and methylation of DNA and catecholamines. However, the results of these association studies remain inconclusive. We have explored the contribution of eight genetic polymorphisms in modulating the susceptibility to breast cancer by performing a meta-analysis of worldwide studies. In total, 62 case-control studies representing 17 different populations involving 18,117 breast cancer cases and 23,573 healthy controls were included in this meta-analysis. Out of the eight polymorphisms analyzed, methylenetetrahydrofolate reductase (MTHFR) C677T exhibited positive association with the breast cancer risk in both fixed effects (OR 1.14, 95 % CI 1.10-1.17) and random effects (OR 1.10, 95 % CI 1.02-1.18) models. Solute carrier family 19 (folate transporter), member 1 (SLC19A1) G80A exhibited positive association (OR 1.16, 95 % CI 1.03-1.31) while MTR A2756G exhibited an inverse association (OR 0.78, 95 % CI 0.75-0.82) with the breast in fixed effect model alone. Significant heterogeneity was observed in the association of MTHFR C677T with breast cancer even between studies from the same geographical area, specifically among Chinese, Indians, and Turks. Subgroup analysis revealed MTHFR C677T-mediated breast cancer risk in post-menopausal women and women with low dietary intake of folate. Geographical area wise segregation of data revealed MTHFR-mediated increased breast cancer risk in populations who consume methionine-rich diet. Altitude-level variations were observed in the association of SHMT1 C1420T with breast cancer. India and Brazil of same altitude showed an inverse association with this polymorphism, while USA and China that share similar altitude showed a null association. MTHFR C677T and SLC19A1 G80A are the two polymorphisms of one-carbon metabolic pathway that increase breast cancer in the worldwide population. Dietary patterns and altitudinal variations are the likely risk modulators that are contributing toward ethnic- and population-level variations in genetic associations.

Folylpoly-γ-glutamate synthetase: A key determinant of folate homeostasis and antifolate resistance in cancer

Mammalians are devoid of autonomous biosynthesis of folates and hence must obtain them from the diet. Reduced folate cofactors are B9-vitamins which play a key role as donors of one-carbon units in the biosynthesis of purine nucleotides, thymidylate and amino acids as well as in a multitude of methylation reactions including DNA, RNA, histone and non-histone proteins, phospholipids, as well as intermediate metabolites. The products of these S-adenosylmethionine (SAM)-dependent methylations are involved in the regulation of key biological processes including transcription, translation and intracellular signaling. Folate-dependent one-carbon metabolism occurs in several subcellular compartments including the cytoplasm, mitochondria, and nucleus. Since folates are essential for DNA replication, intracellular folate cofactors play a central role in cancer biology and inflammatory autoimmune disorders. In this respect, various folate-dependent enzymes catalyzing nucleotide biosynthesis have been targeted by specific folate antagonists known as antifolates. Currently, antifolates are used in drug treatment of multiple human cancers, non-malignant chronic inflammatory disorders as well as bacterial and parasitic infections. An obligatory key component of intracellular folate retention and intracellular homeostasis is (anti)folate polyglutamylation, mediated by the unique enzyme folylpoly-γ-glutamate synthetase (FPGS), which resides in both the cytoplasm and mitochondria. Consistently, knockout of the FPGS gene in mice results in embryonic lethality. FPGS catalyzes the addition of a long polyglutamate chain to folates and antifolates, hence rendering them polyanions which are efficiently retained in the cell and are now bound with enhanced affinity by various folate-dependent enzymes. The current review highlights the crucial role that FPGS plays in maintenance of folate homeostasis under physiological conditions and delineates the plethora of the molecular mechanisms underlying loss of FPGS function and consequent antifolate resistance in cancer.

Possible selection of host folate pathway gene polymorphisms in patients with malaria from a malaria endemic region in North East India

BACKGROUND

Recent studies in experimental mice have shown that mild deficiency of methylenetetrahydrofolate reductase (MTHFR) enzyme confers protection against malaria, thus providing an important basis for the hypothesis that MTHFR polymorphism, i.e. C677T, might have been subjected to selection pressure against malaria. The present study was undertaken in a malaria endemic region in North East India to assess whether a similar selection advantage exists for other genes in folate metabolism pathway.

METHODS

A total of 401 subjects including 131 symptomatic malaria, 97 asymptomatic malaria and 173 normal healthy controls were analysed for nine polymorphisms (single-nucleotide polymorphisms [SNPs] in eight genes and insertion/deletion in one gene): MTHFR C677T, methionine synthase reductase (MTRR) A66G, glutamate carboxypeptidase II (GCPII) C1561T, cystathionine beta-synthase (CBS) 844ins68, reduced folate carrier-1 (RFC-1) G80A, serine hydroxymethyltransferase (SHMT) C1420T, methionine synthase (MTR) A2756G, MTHFR G1793A (D 919G), glycine N-methyltransferase (GNMT) 1289 by PCR-RFLP technique. Differences in frequencies of genotype distribution of each polymorphic marker between these groups were evaluated.

RESULTS

MTRR A2756G, SHMT C1420T, GCPII C1561T, MTRR A2756G and GNMT C1289T and RFC1 G80A polymorphisms showed significantly different prevalence between different groups analyzed. No significant differences were seen in the distribution of other polymorphisms.

CONCLUSIONS

The study gives a clue for the possible selection of specific polymorphisms in the genes involved in the folate metabolism pathway by malaria parasite.

Association Between RFC1 G80A Polymorphism and Acute Lymphoblastic Leukemia: a Review and Meta-Analysis of 10 Studies

BACKGROUND

Evidence indicates RFC1 G80A polymorphism as a risk factor for a number of cancers. Increasing studies have been conducted on the association of RFC1 G80A polymorphism with acute lymphoblastic leukemia (ALL) risk. However, the results were controversial. The aim of the present study was to derive a more precise estimation of the relationship.

MATERIALS AND METHOD

PubMed, Embase, Web of Science, Cochrane database, and Google Scholar were searched to get the genetic association studies between RFC1 G80A polymorphism and ALL. All eligible studies for the period up to February 2016 were identified. Subgroup analyses regarding ethnicity were also implemented. All statistical analyses were done with CMA 2.0.

RESULTS

A total of ten studies comprising of 2,168 ALL cases and 2,693 healthy controls were included in this meta-analysis. Overall, no significant association was detected for allelic model (OR = 1.029, 95 % CI 0.754- 1.405, P=0.000), Dominant model (OR = 1.619, 95 % CI 0.847-3.094, P=0.145), recessive model (OR = 1.169, 95 % CI 10.764-1.790, P=0.429), and homozygote model (OR = 1.288, 95 % CI 0.928-1.788, P=0.130). However, there was an obvious association under the heterozygote model (OR = 1.368, 95 % CI 1.056- 1.772, P=0.018). Also, in the stratified analysis by ethnicity, no significant association of this polymorphism with risk of OC was found in the Asian and Caucasian populations. However, there was not significant heterogeneity between heterozygote genetic model (P = 0.15, I(2) = 33%) in Caucasian. Therefore, we utilized the fixed-effect model to merge OR value.

CONCLUSION

Based on the available evidence, no association between RFC1 G80A Polymorphism and ALL risk was observed, even in the subanalysis by ethnicity. The direction of further research should focus not only on the simple relationship of RFC1 G80A Polymorphism and ALL risk, but also on gene-gene and gene-environment interaction.

Increased synthesis of folate transporters regulates folate transport in conditions of ethanol exposure and folate deficiency

Excessive alcohol consumption and dietary folate inadequacy are the main contributors leading to folate deficiency (FD). The present study was planned to study regulation of folate transport in conditions of FD and ethanol exposure in human embryonic kidney cell line. Also, the reversible nature of effects mediated by ethanol exposure and FD was determined by folate repletion and ethanol removal. For ethanol treatment, HEK293 cells were grown in medium containing 100 mM ethanol, and after treatment, one group of cells was shifted on medium that was free from ethanol. For FD treatment, cells were grown in folate-deficient medium followed by shifting of one group of cells on folate containing medium. FD as well as ethanol exposure resulted in an increase in folate uptake which was due to an increase in expression of folate transporters, i.e., reduced folate carrier, proton-coupled folate transporter, and folate receptor, both at the mRNA and protein level. The effects mediated by ethanol exposure and FD were reversible on removal of treatment. Promoter region methylation of folate transporters remained unaffected after FD and ethanol exposure. As far as transcription rate of folate transporters is concerned, an increase in rate of synthesis was observed in both ethanol exposure and FD conditions. Additionally, mRNA life of folate transporters was observed to be reduced by FD. An increased expression of folate transporters under ethanol exposure and FD conditions can be attributed to enhanced rate of synthesis of folate transporters.

Association of reduced folate carrier-1 (RFC-1) polymorphisms with ischemic stroke and silent brain infarction

Stroke is the second leading cause of death in the world and in South Korea. Ischemic stroke and silent brain infarction (SBI) are complex, multifactorial diseases influenced by multiple genetic and environmental factors. Moderately elevated plasma homocysteine levels are a major risk factor for vascular diseases, including stroke and SBI. Folate and vitamin B12 are important regulators of homocysteine metabolism. Reduced folate carrier (RFC), a bidirectional anion exchanger, mediates folate delivery to a variety of cells. We selected three known RFC-1 polymorphisms (-43C>T, 80A>G, 696T>C) and investigated their relationship to cerebral infarction in the Korean population. We used the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method to analyze associations between the three RFC-1 polymorphisms, disease status, and folate and homocysteine levels in 584 ischemic stroke patients, 353 SBI patients, and 505 control subjects. The frequencies of the RFC-1 -43TT, 80GG, and 696CC genotypes differed significantly between the stroke and control groups. The RFC-1 80A>G substitution was also associated with small artery occlusion and SBI. In a gene-environment analysis, the RFC-1 -43C>T, 80A>G, and 696T>C polymorphisms in the ischemic stroke group had combined effects with all environmental factors. In summary, we found that the RFC-1 -43C>T, 80A>G, and 696T>C polymorphisms may be risk factors for ischemic stroke.

Post-transcriptional regulation of the human reduced folate carrier as a novel adaptive mechanism in response to folate excess or deficiency

The RFC (reduced folate carrier) is the principal mechanism by which folates and clinically used antifolates are delivered to mammalian cells. hRFC (human RFC) is subject to complex transcriptional controls and exists as homo-oligomer. To explore the post-transcriptional regulation of hRFC by exogenous folates, hRFC-null HeLa cells were stably transfected with hRFC under control of a constitutive promoter. hRFC transcripts and the total membrane protein increased with increasing LCV [(6R,S)5-formyl tetrahydrofolate (leucovorin)] with a maximum at 20 nM LCV, attributable to reduced turnover of hRFC transcripts. hRFC homo-oligomerization was unaffected by increasing LCV. Cell surface hRFC paralleled [³H]methotrexate transport and increased from 0.5 to 2 nM LCV, and then decreased (~2-fold) with increasing LCV up to 20 nM. hRFC was localized to the cell surface at low LCV concentrations (0.5–1.5 nM). However, at higher LCV concentrations, significant intracellular hRFC was localized to the ER (endoplasmic reticulum), such that at 20 nM LCV, intracellular hRFC was predominated. Our results demonstrate a novel post-transcriptional regulation of hRFC involving: (i) increased hRFC transcripts and proteins, accompanying increased extracellular folates, attributable to differences in hRFC transcript stabilities; and (ii) increased retention of hRFC in the ER under conditions of folate excess, because of impaired intracellular trafficking and plasma membrane targeting.

A novel regulation of the physiologically/pharmacologically important human reduced folate carrier was demonstrated in response to increasing extracellular folates, involving: (i) increased transcripts and total protein, reflecting increased transcript stabilities; and (ii) increased endoplasmic reticulum trapping, due to impaired intracellular trafficking.

The major facilitative folate transporters solute carrier 19A1 and solute carrier 46A1: biology and role in antifolate chemotherapy of cancer

This review summarizes the biology of the major facilitative membrane transporters, the reduced folate carrier (RFC) (Solute Carrier 19A1) and the proton-coupled folate transporter (PCFT) (Solute Carrier 46A1). Folates are essential vitamins, and folate deficiency contributes to a variety of health disorders. RFC is ubiquitously expressed and is the major folate transporter in mammalian cells and tissues. PCFT mediates the intestinal absorption of dietary folates and appears to be important for transport of folates into the central nervous system. Clinically relevant antifolates for cancer, such as methotrexate and pralatrexate, are transported by RFC, and loss of RFC transport is an important mechanism of methotrexate resistance in cancer cell lines and in patients. PCFT is expressed in human tumors, and is active at pH conditions associated with the tumor microenvironment. Pemetrexed is an excellent substrate for both RFC and PCFT. Novel tumor-targeted antifolates related to pemetrexed with selective membrane transport by PCFT over RFC are being developed. In recent years, there have been major advances in understanding the structural and functional properties and the regulation of RFC and PCFT. The molecular bases for methotrexate resistance associated with loss of RFC transport and for hereditary folate malabsorption, attributable to mutant PCFT, were determined. Future studies should continue to translate molecular insights from basic studies of RFC and PCFT biology into new therapeutic strategies for cancer and other diseases.

Epigenetic modulation of RFC1, MHC2TA and HLA-DR in systemic lupus erythematosus: association with serological markers and six functional polymorphisms of one-carbon metabolic pathway

The current study was conducted to elucidate the effect of genetic variations in one-carbon metabolism on the epigenetic regulation of major histocompatibility complex II transactivator (MHC2TA), reduced folate carrier 1 (RFC1/SLC19A1) and human leukocyte antigen (HLA)-DR in systemic lupus erythematosus (SLE). PCR-RFLP/AFLP, bisulfite-sequencing and real-time PCR approaches were used for genetic, epigenetic and expression analysis respectively. SLE cases exhibited elevated plasma homocysteine levels compared to healthy controls (24.93 ± 1.3 vs. 11.67 ± 0.48 μmol/l), while plasma folate levels showed no association (7.10 ± 2.49 vs. 7.64 ± 2.09 ng/ml). The RFC1 80G>A polymorphism showed 1.32-fold risk (95% CI: 1.02-1.72) for SLE, while glutamate carboxypeptidase II (GCPII) 1561C>T showed reduced risk (OR: 0.47, 95% CI: 0.24-0.90). The expression of RFC1 (0.37 ± 0.09 vs. 0.60 ± 0.17) and HLA-DR (0.68 ± 0.17 vs. 0.98 ± 0.02) was down regulated in the SLE cases. The hypermethylation of RFC1 as observed in the current study may contribute for its down regulation. Plasma folate and thymidylate synthase (TYMS) 5'-UTR 28 bp tandem repeat showed an inverse association with methylation of RFC1 and MHC2TA. SLE cases with hypocomplementemia showed hypermethylation of RFC1, hypomethylation/up regulation of MHC2TA and down regulation of HLA-DR. The hypermethylation of MHC2TA and down regulation of RFC1, MHC2TA and HLA-DR were observed in anti-cardiolipin antibody positive SLE cases. The up regulation of RFC1 and HLA-DR was observed in anti-dsDNA antibody positive SLE cases. The hypomethylation/upregulation of RFC1 and MHC2TA was observed in anti-RNP antibody positive cases. To conclude, one-carbon genetic variants influence epigenetic of MHC2TA and RFC1, thus contributing to phenotypic heterogeneity of SLE.

Epigenetic alterations in folate transport genes in placental tissue from fetuses with neural tube defects and in leukocytes from subjects with hyperhomocysteinemia

The objectives of this study were to identify tissue-specific differentially methylated regions (T-DMR’s) in the folate transport genes in placental tissue compared with leukocytes, and from placental tissues obtained from normal infants or with neural tube defects (NTDs). Using pyrosequencing, we developed methylation assays for the CpG islands (CGIs) and the CGI shore regions of the folate receptor α (FOLR1), proton-coupled folate transporter (PCFT) and reduced folate carrier 1 (RFC1) genes. The T-DMRs differed in location for each gene and the difference in methylation ranged between 2 and 54%. A higher T-DMR methylated fraction was associated with a lower mRNA level of the FOLR1 and RFC1 genes. Methylation fractions differed according to RFC1 80G > A genotype in the NTD cases and in leukocytes from subjects with high total plasma homocysteine (tHcy). There were no differences in methylated fraction of folate transporter genes between NTD cases and controls. We suggest that T-DMRs participate in the regulation of expression of the FOLR1 and RFC1 genes, that the RFC1 80G > A polymorphism exerts a gene-nutrition interaction on DNA methylation in the RFC1 gene, and that this interaction appears to be most prominent in NTD-affected births and in subjects with high tHcy concentrations.

Gene-gene interactions in folate and adenosine biosynthesis pathways affect methotrexate efficacy and tolerability in rheumatoid arthritis

OBJECTIVE

As no single nucleotide polymorphism has emerged as pivotal to predict the lack of efficacy and dose-limiting toxicities to methotrexate (MTX), we evaluated the contribution of gene-gene interactions to the effects of this prodrug in rheumatoid arthritis.

METHODS

A total of 255 patients treated with MTX for at least 3 months were evaluated with efficacy assessed using the European League Against Rheumatism response criteria or a physician's assessment of patient's response to MTX visual analog scale. Gastrointestinal and neurological idiosyncrasies were recorded in 158 patients. Fourteen single nucleotide polymorphisms in folate and adenosine biosynthesis pathways were measured and detection of gene-gene interactions was performed using multifactor-dimensionality reduction, a method that reduces high-dimensional genetic data into a single dimension of predisposing or risk-genotype combinations.

RESULTS

Efficacy to MTX (53% responders) was associated with high-order epistasis among variants in inosine-triphosphate pyrophosphatase, aminoimidazole-carboxamide ribonucleotide transformylase, and reduced folate carrier genes. In the absence of predisposing genotype combinations, a 3.8-fold lower likelihood of efficacy was observed (vs. in their presence, 95% confidence interval: 2.2-6.4; P<0.001). Increasing MTX polyglutamate concentrations tended to partially overcome this selective disadvantage. Idiosyncrasies occurred in 29% of patients. In the presence of risk-genotype combinations among variants in methylene tetrahydrofolate reductase, γ-glutamyl-hydrolase, thymidylate synthase, serine hydroxymethyltransferase, and inosine-triphosphate pyrophosphatase genes, an 8.9-fold higher likelihood to exhibit toxicities was observed (vs. in their absence, 95% confidence interval: 3.6-21.9; P<0.001). False-positive report probabilities were below 0.2, thereby indicating that true signals were likely detected in this cohort.

CONCLUSION

These data indicate that gene-gene interactions impact MTX efficacy and tolerability in rheumatoid arthritis.

Patterns of interaction between genetic and nongenetic attributes and methotrexate efficacy in rheumatoid arthritis

OBJECTIVE

The contribution of low-penetrance single nucleotide polymorphisms to methotrexate efficacy in rheumatoid arthritis (RA) is inconsistent between studies. We sought to elucidate architecture of methotrexate response in three cohorts of patients with RA treated with methotrexate.

METHODS

Single nucleotide polymorphism frequencies in genes from folate, purine, and pyrimidine pathways were measured to develop a model of gene-gene interactions using multifactor dimensionality reduction in 439 patients who received methotrexate in the USA and The Netherlands. A third cohort of 530 patients with RA from Sweden was used to replicate the findings. Methotrexate efficacy was assessed using the European League Against Rheumatism criteria in the majority of patients.

RESULTS

Nonlinear patterns of gene-gene interactions between variants in aminoimidazole carboxamide ribonucleotide transformylase (C347G), reduced-folate carrier (G80A) and inosine-triphosphate pyrophosphatase (C94A) revealed a predisposing genetic attribute significantly associated with methotrexate response in the USA and Dutch cohorts [odds ratio (OR)=2.9, 95% confidence interval (CI): 1.9-4.2; P<0.001]. Although the finding was not replicated in the Swedish cohort (OR=0.9; 95% CI: 0.64-1.37; P=0.74) a multifactor dimensionality reduction analysis superimposing the predisposing genetic attribute with patient's age, sex, and anticitrullinated peptide antibodies positivity (ACPA) revealed a pattern of interaction significant in all three cohorts (OR=2.2, 95% CI: 1.6-2.9; P<0.01). The selective advantage toward response in the presence of the predisposing genetic attribute was lost in females and ACPA-positive patients, whereas older and male ACPA-negative patients tended to exhibit a greater likelihood of response in the absence of the predisposing genetic attribute.

CONCLUSION

Gene-gene interactions together with nongenetic attributes may contribute to methotrexate efficacy in RA.

Association of aberrations in one-carbon metabolism with molecular phenotype and grade of breast cancer

We have earlier demonstrated the role of aberrant one-carbon metabolism in the etiology of breast cancer. In the current study, we examine the clinical utility of these factors in predicting the subtype of breast cancer and as indicators of disease progression. Polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) and PCR-amplified fragment length polymorphism (AFLP) approaches were used for genetic analysis. Plasma folate and homocysteine were measured using Axsym folate kit and reverse phase HPLC, respectively. Multiple linear regression models were used to test the predictability of disease progression. Luminal A subtype was associated with late age of onset, higher body mass index and lack of family history of breast cancer. Thymidylate synthase (TYMS) 5'-UTR 28 bp tandem repeat (OR: 2.09, 95% CI: 1.05-4.16) and methylene tetrahydrofolate reductase (MTHFR) C677T (OR: 4.10, 95% CI: 1.40-11.95) were strongly associated with Luminal B. Reduced folate carrier (RFC1) G80A (OR: 2.92, 95% CI: 1.22-6.97) and methionine synthase (MTR) A2756G (OR: 4.71, 95% CI: 1.66-13.31) polymorphisms were associated with LuminA-HH subtype while MTHFR C677T showed association with HER-enriched (OR: 30.41, 95% CI: 6.47-142.91). Cytosolic serine hydroxymethyltransferase (cSHMT) conferred protection against basal-like breast cancer (OR: 0.47, 95% CI: 0.22-0.98). HER-enriched and basal-like subtypes showed positive association with familial breast cancer and inverse association with plasma folate. Hyperhomocysteinemia was observed in Luminal B and basal-like subtypes. Multiple linear regression models of aberrant one-carbon metabolism were found to be moderate predictors of breast cancer grade (area under the receiver operating characteristic curve, C = 0.72, 95% CI: 0.58-0.87, P = 0.008). To conclude, aberrations in one-carbon metabolism predict the subtype of breast cancer and disease progression.

Epistatic interactions between loci of one-carbon metabolism modulate susceptibility to breast cancer

In view of growing body of evidence substantiating the role of aberrations in one-carbon metabolism in the pathophysiology of breast cancer and lack of studies on gene-gene interactions, we investigated the role of dietary micronutrients and eight functional polymorphisms of one-carbon metabolism in modulating the breast cancer risk in 244 case-control pairs of Indian women and explored possible gene-gene interactions using Multifactor dimensionality reduction analysis (MDR). Dietary micronutrient status was assessed using the validated Food Frequency Questionnaire. Genotyping was done for glutamate carboxypeptidase II (GCPII) C1561T, reduced folate carrier (RFC)1 G80A, cytosolic serine hydroxymethyltransferase (cSHMT) C1420T, thymidylate synthase (TYMS) 5'-UTR tandem repeat, TYMS 3'-UTR ins6/del6, methylenetetrahydrofolate reductase (MTHFR) C677T, methyltetrahydrofolate-homocysteine methyltransferase (MTR) A2756G, methyltetrahydrofolate-homocysteine methyltransferase reductase (MTRR) A66G polymorphisms by using the PCR-RFLP/AFLP methods. Low dietary folate intake (P < 0.001), RFC1 G80A (OR: 1.38, 95% CI 1.06-1.81) and MTHFR C677T (OR: 1.74 (1.11-2.73) were independently associated with the breast cancer risk whereas cSHMT C1420T conferred protection (OR: 0.72, 95% CI 0.55-0.94). MDR analysis demonstrated a significant tri-variate interaction among RFC1 80, MTHFR 677 and TYMS 5'-UTR loci (P (trend) < 0.02) with high-risk genotype combination showing inflated risk for breast cancer (OR 4.65, 95% CI 1.77-12.24). To conclude, dietary as well as genetic factors were found to influence susceptibility to breast cancer. Further, the current study highlighted the importance of multi-loci analyses over the single-locus analysis towards establishing the epistatic interactions between loci of one-carbon metabolism modulate susceptibility to the breast cancer.

Knockout of the folate transporter folt-1 causes germline and somatic defects in C. elegans

BACKGROUND

The C. elegans gene folt-1 is an ortholog of the human reduced folate carrier gene. The FOLT-1 protein has been shown to transport folate and to be involved in uptake of exogenous folate by worms. A knockout mutation of the gene, folt-1(ok1460), was shown to cause sterility, and here we investigate the source of the sterility and the effect of the folt-1 knockout on somatic function.

RESULTS

Our results show that folt-1(ok1460) knockout hermaphrodites have a substantially reduced germline, generate a small number of functional sperm, and only rarely produce a functional oocyte. We found no evidence of increased apoptosis in the germline of folt-1 knockout mutants, suggesting that germline proliferation is defective. While folt-1 knockout males are fertile, their rate of spermatogenesis was severely diminished, and the males were very poor maters. The mating defect is likely due to compromised metabolism and/or other somatic functions, as folt-1 knockout hermaphrodites displayed a shortened lifespan and elongated defecation intervals.

CONCLUSIONS

The FOLT-1 protein function affects both the soma and the germline. folt-1(ok1460) hermaphrodites suffer severely diminished lifespan and germline defects that result in sterility. Germline defects associated with folate deficiency appear widespread in animals, being found in humans, mice, fruit flies, and here, nematodes.