Folate and thiamine transporters mediated by facilitative carriers (SLC19A1-3 and SLC46A1) and folate receptors

Biotin Homeostasis and Human Disorders: Recent Findings and Perspectives

Biotin (vitamin B7, or vitamin H) is a water-soluble B-vitamin that functions as a cofactor for carboxylases, i.e., enzymes involved in the cellular metabolism of fatty acids and amino acids and in gluconeogenesis; moreover, as reported, biotin may be involved in gene regulation. Biotin is not synthesized by human cells, but it is found in food and is also produced by intestinal bacteria. Biotin status/homeostasis in human individuals depends on several factors, including efficiency/deficiency of the enzymes involved in biotin recycling within the human organism (biotinidase, holocarboxylase synthetase), and/or effectiveness of intestinal uptake, which is mainly accomplished through the sodium-dependent multivitamin transporter. In the last years, administration of biotin at high/"pharmacological" doses has been proposed to treat specific defects/deficiencies and human disorders, exhibiting mainly neurological and/or dermatological symptoms and including biotinidase deficiency, holocarboxylase synthetase deficiency, and biotin-thiamine-responsive basal ganglia disease. On the other hand, according to warnings of the Food and Drug Administration, USA, high biotin levels can affect clinical biotin-(strept)avidin assays and thus lead to false results during quantification of critical biomarkers. In this review article, recent findings/advancements that may offer new insight in the abovementioned research fields concerning biotin will be presented and briefly discussed.

Folic Acid-Conjugated Brush Polymers Show Enhanced Blood-Brain Barrier Crossing in Static and Dynamic In Vitro Models Toward Brain Cancer Targeting Therapy

Over the past decades, evidence has consistently shown that treatment of central nervous system (CNS)-related disorders, including Alzheimer's disease, Parkinson's disease, stroke, multiple sclerosis, and brain cancer, is limited due to the presence of the blood-brain barrier (BBB). To assist with the development of new therapeutics, it is crucial to engineer a drug delivery system that can cross the BBB efficiently and reach target cells within the brain. In this study, we present a potentially efficient strategy for targeted brain delivery through utilization of folic acid (FA)-conjugated brush polymers, that specifically target the reduced folate carrier (RFC, SLC19A1) expressed on brain endothelial cells. Here, azide (N3)-decorated brush polymers were prepared in a straightforward manner coupling a heterotelechelic α-NH2, ω-N3-poly(2-ethyl-2-oxazoline) (NH2-PEtOx-N3) to N-acylated poly(amino ester) (NPAE)-based brushes. Strain-promoted azide-alkyne cycloaddition (SPAAC) 'click chemistry' with DBCO-folic acid (FA) yielded FA-brush polymers. Interestingly, while azide functionalization of the brush polymers dramatically reduced their association to brain microvascular endothelial cells (hCMEC/D3), the introduction of FA to azide led to a substantial accumulation of the brush polymers in hCMEC/D3 cells. The ability of the polymeric brush polymers to traverse the BBB was quantitatively assessed using different in vitro BBB models including static Transwell and microfluidic platforms. FA-brush polymers showed efficient transport across hCMEC/D3 cells in a manner dependent on FA composition, whereas nonfunctionalized brush polymers exhibited limited trafficking under the same conditions. Further, cellular uptake inhibition studies suggested that the interaction and transport pathway of FA-brush polymers across BBB relies on the RFC-mediated pathways. The potential application of the developed FA-brush polymers in brain cancer delivery was also investigated in a microfluidic model of BBB-glioblastoma. Brush polymers with more FA units successfully presented an enhanced accumulation into U-87 MG glioma cells following its BBB crossing, compared to controls. These results demonstrate that FA-modified brush polymers hold a great potential for more efficient delivery of future brain therapeutics.

Hypoxia leads to gill endoplasmic reticulum stress and disruption of mitochondrial homeostasis in grass carp (Ctenopharyngodon idella): Mitigation effect of thiamine

Hypoxia in water environment is one of the important problems faced by intensive aquaculture. Under hypoxia stress, the effects of dietary thiamine were investigated on grass carp gill tissue damage and their mechanisms. Six thiamine diets with different thiamine levels (0.22, 0.43, 0.73, 1.03, 1.33 and 1.63 mg/kg) were fed grass carp (Ctenopharyngodon idella) for 63 days. Then, 96-hour hypoxia stress test was conducted. This study described that thiamine enhanced the growth performance of adult grass carp and ameliorated nutritional status of thiamine (pyruvic acid, glucose, lactic acid and transketolase). Additionally, thiamine alleviated the deterioration of blood parameters [glutamic oxalacetic transaminase (GOT), glutamic pyruvic transaminase (GPT), glucose, cortisol, lactic dehydrogenase (LDH), erythrocyte fragility, and red blood cell count (RBC count)] caused by hypoxia stress, and reduced reactive oxygen species (ROS) content and oxidative damage to the gills. In addition, thiamine alleviated endoplasmic reticulum stress in the gills, which may be related to its inhibition of RNA-dependent protein kinase-like ER kinase (PERK)/eukaryotic translation initiation factor-2α (eIF2α)/activating transcription factor4 (ATF4), inositol-requiring enzyme 1 (IRE1)/X-Box binding protein 1 (XBP1) and activating transcription factor 6 (ATF6) pathways. Furthermore, thiamine maintaining mitochondrial dynamics balance was probably related to promoting mitochondrial fusion and inhibiting mitochondrial fission, and inhibiting mitophagy may involve PTEN induced putative kinase 1 (PINK1)/Parkin-dependent pathway and hypoxia-inducible factor (HIF)-Bcl-2 adenovirus E1B 19 kDa interacting protein 3 (BNIP3) pathway. In summary, thiamine alleviated hypoxia stress in fish gills, which may be related to reducing endoplasmic reticulum stress, regulating mitochondrial dynamics balance and reducing mitophagy. The thiamine requirement for optimum growth [percent weight gain (PWG)] of adult grass carp was estimated to be 0.81 mg/kg diet. Based on the index of anti-hypoxia stress (ROS content in gill), the thiamine requirement for adult grass carp was estimated to be 1.32 mg/kg diet.

Two maize homologs of mammalian proton-coupled folate transporter, ZmMFS_1-62 and ZmMFS_1-73, are essential to salt and drought tolerance

Folates are essential to the maintenance of normal life activities in almost all organisms. Proton-coupled folate transporter (PCFT), belonging to the major facilitator superfamily, is one of the three major folate transporter types widely studied in mammals. However, information about plant PCFTs is limited. Here, a genome-wide identification of maize PCFTs was performed, and two PCFTs, ZmMFS_1-62 and ZmMFS_1-73, were functionally investigated. Both proteins contained the typical 12 transmembrane helixes with N- and C-termini located in the cytoplasm, and were localized in the plasma membrane. Molecular docking analysis indicated their binding activity with folates via hydrogen bonding. Interference with ZmMFS_1-62 and ZmMFS_1-73 in maize seedlings through virus-induced gene silencing disrupted folate homeostasis, mainly in the roots, and reduced tolerance to drought and salt stresses. Moreover, a molecular chaperone protein, ZmHSP20, was found to interact with ZmMFS_1-62 and ZmMFS_1-73, and interference with ZmHSP20 in maize seedlings also led to folate disruption and increased sensitivity to drought and salt stresses. Overall, this is the first report of functional identification of maize PCFTs, which play essential roles in salt and drought stress tolerance, thereby linking folate metabolism with abiotic stress responses in maize.

In Vitro and In Silico Studies on Cytotoxic Properties of Oxythiamine and 2'-Methylthiamine

It is important to search for cytostatic compounds in order to fight cancer. One of them could be 2'-methylthiamine, which is a thiamine antimetabolite with an additional methyl group at the C-2 carbon of thiazole. So far, the cytostatic potential of 2'-methylthiamine has not been studied. We have come forward with a simplified method of synthesis using commercially available substrates and presented a comparison of its effects, as boosted by oxythiamine, on normal skin fibroblasts and HeLa cancer cells, having adopted in vitro culture techniques. Oxythiamine has been found to inhibit the growth and metabolism of cancer cells significantly better than 2'-methylthiamine (GI50 36 and 107 µM, respectively), while 2'-methylthiamine is more selective for cancer cells than oxythiamine (SI = 180 and 153, respectively). Docking analyses have revealed that 2'-methylthiamine (ΔG -8.2 kcal/mol) demonstrates a better affinity with thiamine pyrophosphokinase than thiamine (ΔG -7.5 kcal/mol ) and oxythiamine (ΔG -7.0 kcal/mol), which includes 2'-methylthiamine as a potential cytostatic. Our results suggest that the limited effect of 2'-methylthiamine on HeLa arises from the related arduous transport as compared to oxythiamine. Given that 2'-methylthiamine may possibly inhibit thiamine pyrophosphokinase, it could once again be considered a potential cytostatic. Thus, research should be carried out in order to find the best way to improve the transport of 2'-methylthiamine into cells, which may trigger its cytostatic properties.

Targeted cancer treatment using folate-conjugated sponge-like ZIF-8 nanoparticles: a review

ZIF-8 (zeolitic imidazolate framework-8) is a potential drug delivery system because of its unique properties, which include a large surface area, a large pore capacity, a large loading capacity, and outstanding stability under physiological conditions. ZIF-8 nanoparticles may be readily functionalized with targeting ligands for the identification and absorption of particular cancer cells, enhancing the efficacy of chemotherapeutic medicines and reducing adverse effects. ZIF-8 is also pH-responsive, allowing medication release in the acidic milieu of cancer cells. Because of its tunable structure, it can be easily functionalized to design cancer-specific targeted medicines. The delivery of ZIF-8 to cancer cells can be facilitated by folic acid-conjugation. Hence, it can bind to overexpressed folate receptors on the surface of cancer cells, which holds the promise of reducing unwanted deliveries. As a result of its importance in cancer treatment, the folate-conjugated ZIF-8 was the major focus of this review.

Identification and characterization of an endogenous biomarker of the renal vectorial transport (OCT2-MATE1)

The renal tubular organic cation transporter 2 (OCT2) and multidrug and toxin extrusion protein 1 (MATE1) mediate the vectorial elimination of many drugs and toxins from the kidney, and endogenous biomarkers for vectorial transport (OCT2-MATE1) would allow more accurate drug dosing and help to characterize drug-drug interactions and toxicity. Human serum uptake in OCT2-overexpressing cells and metabolomics analysis were carried out. Potential biomarkers were verified in vitro and in vivo. The specificity of biomarkers was validated in renal transporter overexpressing cells and the sensitivity was investigated by Km . The results showed that the uptake of thiamine, histamine, and 5-hydroxytryptamine was significantly increased in OCT2-overexpressing cells. In vitro assays confirmed that thiamine, histamine, and 5-hydroxytryptamine were substrates of both OCT2 and MATE1. In vivo measurements indicated that the serum thiamine level was increased significantly in the presence of the rOCT2 inhibitor cimetidine, and the level in renal tissue was increased significantly by the rMATE1 inhibitor pyrimethamine. There were no significant changes in the uptake or efflux of thiamine in cell lines overexpressed OAT1, OAT2, OAT3, MRP4, organic anion transporting polypeptide 4C1, P-gp, peptide transporter 2, urate transporter 1, and OAT4. The Km for thiamine with OCT2 and MATE1 were 71.2 and 10.8 μM, respectively. In addition, the cumulative excretion of thiamine at 2 and 4 h was strongly correlated with metformin excretion (R2  > 0.6). Thus, thiamine is preferentially secreted by the OCT2 and MATE1 in renal tubules and can provide a reference value for evaluating the function of the renal tubular OCT2-MATE1.

Pharmacokinetics of vitamin dosage forms: A complete overview

Vitamins are crucial for sustaining life because they play an essential role in numerous physiological processes. Vitamin deficiencies can lead to a wide range of severe health issues. In this context, there is a need to administer vitamin supplements through appropriate routes, such as the oral route, to ensure effective treatment. Therefore, understanding the pharmacokinetics of vitamins provides critical insights into absorption, distribution, and metabolism, all of which are essential for achieving the desired pharmacological response. In this review paper, we present information on vitamin deficiencies and emphasize the significance of understanding vitamin pharmacokinetics for improved clinical research. The pharmacokinetics of several vitamins face various challenges, and thus, this work briefly outlines the current issues and their potential solutions. We also discuss the feasibility of enhanced nanocarrier-based pharmaceutical formulations for delivering vitamins. Recent studies have shown a preference for nanoformulations, which can address major limitations such as stability, solubility, absorption, and toxicity. Ultimately, the pharmacokinetics of pharmaceutical dosage forms containing vitamins can impede the treatment of diseases and disorders related to vitamin deficiency.

A high-throughput single-cell RNA expression profiling method identifies human pericyte markers

AIMS

We sought to identify and optimise a universally available histological marker for pericytes in the human brain. Such a marker could be a useful tool for researchers. Further, identifying a gene expressed relatively specifically in human pericytes could provide new insights into the biological functions of this fascinating cell type.

METHODS

We analysed single-cell RNA expression profiles derived from different human and mouse brain regions using a high-throughput and low-cost single-cell transcriptome sequencing method called EasySci. Through this analysis, we were able to identify specific gene markers for pericytes, some of which had not been previously characterised. We then used commercially (and therefore universally) available antibodies to immunolabel the pericyte-specific gene products in formalin-fixed paraffin-embedded (FFPE) human brains and also performed immunoblots to determine whether appropriately sized proteins were recognised.

RESULTS

In the EasySci data sets, highly pericyte-enriched expression was notable for SLC6A12 and SLC19A1. Antibodies against these proteins recognised bands of approximately the correct size in immunoblots of human brain extracts. Following optimisation of the immunohistochemical technique, staining for both antibodies was strongly positive in small blood vessels and was far more effective than a PDGFRB antibody at staining pericyte-like cells in FFPE human brain sections. In an exploratory sample of other human organs (kidney, lung, liver, muscle), immunohistochemistry did not show the same pericyte-like pattern of staining.

CONCLUSIONS

The SLC6A12 antibody was well suited for labelling pericytes in human FFPE brain sections, based on the combined results of single-cell RNA-seq analyses, immunoblots and immunohistochemical studies.

A nutritional supplement during preconception and pregnancy increases human milk vitamin D but not B-vitamin concentrations

BACKGROUND & AIMS

Optimal maternal vitamin status during pregnancy and lactation is essential to support maternal and infant health. For instance, vitamin D3 is involved in infant bone development, and B-vitamins are involved in various metabolic processes, including energy production. Through a double-blind randomised controlled trial, we investigated the effects of maternal supplementation from preconception throughout pregnancy until birth on human milk (HM) concentrations of vitamin D3 and B-vitamins. In addition, we aimed to characterise longitudinal changes in milk concentrations of these vitamins.

METHODS

Both control and intervention supplements contained calcium, iodine, iron, β-carotene, and folic acid, while the intervention also contained zinc, vitamins B2, B6, B12, and D3, probiotics, and myo-inositol. HM samples were collected across 4 time points from 1 week to 3 months post-delivery from 158 mothers in Singapore, and 7 time points from 1 week to 12 months from 180 mothers in New Zealand. HM vitamin D was quantified using supercritical fluid chromatography and B-vitamins with mass spectrometry. Potential intervention effects on HM vitamins D3, B2, B6, and B9, as well as other B-vitamin (B1 and B3) concentrations were assessed using linear mixed models with a repeated measures design.

RESULTS

Over the first 3 months of lactation, HM 25-hydroxyvitamin D3 concentrations were 20% (95% CI 8%, 33%, P = 0.001) higher in the intervention group, with more marked effects in New Zealand. There were no observed intervention effects on HM concentrations of vitamins B1, B2, B3, B6, and B9. In New Zealand mothers, longitudinally, vitamin D3 concentrations gradually increased from early lactation up to 12 months, while vitamins B1 and B2 peaked at 6 weeks, B3 at 3 weeks, and B6 and B9 at 3 months.

CONCLUSIONS

Maternal supplementation during preconception and pregnancy increased HM vitamin D, but not B-vitamin concentrations in lactation. Further studies are required to examine the discrete benefits of vitamin D supplementation starting preconception vs during pregnancy, and to further characterise the effects of supplementation on later offspring health outcomes.

CLINICAL TRIAL REGISTRATION

Registered at ClinicalTrials.gov on the 16 July 2015 (identifier NCT02509988); Universal Trial Number U1111-1171-8056. This study was academic-led by the EpiGen Global Research Consortium.

Protective effects of pyrroloquinoline quinone in brain folate deficiency

BACKGROUND

Folates (Vitamin B9) are critical for normal neurodevelopment and function, with transport mediated by three major pathways: folate receptor alpha (FRα), proton-coupled folate transporter (PCFT), and reduced folate carrier (RFC). Cerebral folate uptake primarily occurs at the blood-cerebrospinal fluid barrier (BCSFB) through concerted actions of FRα and PCFT, with impaired folate transport resulting in the neurological disorder cerebral folate deficiency (CFD). Increasing evidence suggests that disorders associated with CFD also present with neuroinflammation, oxidative stress, and mitochondrial dysfunction, however the role of brain folate deficiency in inducing these abnormalities is not well-understood. Our laboratory has identified the upregulation of RFC by nuclear respiratory factor 1 (NRF-1) at the blood-brain barrier (BBB) once indirectly activated by the natural compound pyrroloquinoline quinone (PQQ). PQQ is also of interest due to its anti-inflammatory, antioxidant, and mitochondrial biogenesis effects. In this study, we examined the effects of folate deficiency and PQQ treatment on inflammatory and oxidative stress responses, and changes in mitochondrial function.

METHODS

Primary cultures of mouse mixed glial cells exposed to folate-deficient (FD) conditions and treated with PQQ were analyzed for changes in gene expression of the folate transporters, inflammatory markers, oxidative stress markers, and mitochondrial DNA (mtDNA) content through qPCR analysis. Changes in cellular reactive oxygen species (ROS) levels were analyzed in vitro through a DCFDA assay. Wildtype (C57BL6/N) mice exposed to FD (0 mg/kg folate), or control (2 mg/kg folate) diets underwent a 10-day (20 mg/kg/day) PQQ treatment regimen and brain tissues were collected and analyzed.

RESULTS

Folate deficiency resulted in increased expression of inflammatory and oxidative stress markers in vitro and in vivo, with increased cellular ROS levels observed in mixed glial cells as well as a reduction of mitochondrial DNA (mtDNA) content observed in FD mixed glial cells. PQQ treatment was able to reverse these changes, while increasing RFC expression through activation of the PGC-1α/NRF-1 signaling pathway.

CONCLUSION

These results demonstrate the effects of brain folate deficiency, which may contribute to the neurological deficits commonly seen in disorders of CFD. PQQ may represent a novel treatment strategy for disorders associated with CFD, as it can increase folate uptake, while in parallel reversing many abnormalities that arise with brain folate deficiency.

Thiamine and benfotiamine: Focus on their therapeutic potential

Thiamine, also known as vitamin B1, is an essential nutrient that plays a crucial role in energy metabolism and overall health. It is a water-soluble vitamin that plays an important role in the conversion of carbohydrates into energy in the body. Thiamine is essential for the proper functioning of the nervous system, heart and muscles. Thiamine deficiency is a life-threatening disease that leads to various disorders and lesions in the nerves and brain, at least in vertebrates. Several thiamine precursors with higher bioavailability have been developed to compensate for thiamine deficiency, including benfotiamine. Benfotiamine is more bioavailable and has higher tissue penetration than thiamine. Studies have shown its antioxidant and anti-inflammatory potential in activated immune and glial cells. It also improves complications observed in type 2 diabetes and has beneficial effects in mouse models of neurodegenerative disease. Benfotiamine represents an off-the-shelf agent used to support nerve health, promote healthy aging and support glucose metabolism. Accordingly, the present review aimed to provide an overview of the neuroprotective effects of thiamine/benfotiamine in the context of inflammation and oxidative stress.

The importance of thiamine (vitamin B1) in humans

Thiamine (thiamin, B1) is a vitamin necessary for proper cell function. It exists in a free form as a thiamine, or as a mono-, di- or triphosphate. Thiamine plays a special role in the body as a coenzyme necessary for the metabolism of carbohydrates, fats and proteins. In addition, it participates in the cellular respiration and oxidation of fatty acids: in malnourished people, high doses of glucose result in acute thiamine deficiency. It also participates in energy production in the mitochondria and protein synthesis. In addition, it is also needed to ensure the proper functioning of the central and peripheral nervous system, where it is involved in neurotransmitter synthesis. Its deficiency leads to mitochondrial dysfunction, lactate and pyruvate accumulation, and consequently to focal thalamic degeneration, manifested as Wernicke's encephalopathy or Wernicke-Korsakoff syndrome. It can also lead to severe or even fatal neurologic and cardiovascular complications, including heart failure, neuropathy leading to ataxia and paralysis, confusion, or delirium. The most common risk factor for thiamine deficiency is alcohol abuse. This paper presents current knowledge of the biological functions of thiamine, its antioxidant properties, and the effects of its deficiency in the body.

Therapeutic strategies targeting folate receptor α for ovarian cancer

Epithelial ovarian cancer (EOC) is the deadliest gynecological cancer, and presents a major clinical challenge due to limited treatment options. Folate receptor alpha (FRα), encoded by the FOLR1 gene, is an attractive therapeutically target due to its prevalent and high expression in EOC cells. Recent basic and translational studies have explored several modalities, such as antibody-drug conjugate (ADC), monoclonal antibodies, small molecules, and folate-drug conjugate, to exploit FRα for EOC treatment. In this review, we summarize the function of FRα, and clinical efficacies of various FRα-based therapeutics. We highlight mirvetuximab soravtansine (MIRV), or Elahere (ImmunoGen), the first FRα-targeting ADC approved by the FDA to treat platinum-resistant ovarian cancer. We discuss potential mechanisms and management of ocular adverse events associated with MIRV administration.

Gender-specific association of SLC19A1 and MTHFR genetic polymorphism with oxidative stress biomarkers and plasma folate levels in older adults

BACKGROUND

Plasma folate levels are closely related to antioxidant capacity and are regulated by folate pathway gene polymorphism. However, few studies have explored the gender-specific association of folate pathway gene polymorphism with oxidative stress biomarkers. The present study was designed to explore the gender-specific independent and combined impacts of solute carrier family 19 member 1 (SLC19A1) and methylenetetrahydrofolate reductase (MTHFR) genetic polymorphisms on oxidative stress biomarkers in older adults.

METHODS

A total of 401 subjects were recruited, including 145 males and 256 females. Demographic characteristics of the participants were collected by using a self-administered questionnaire. Fasting venous blood samples were taken for folate pathway gene genotyping, circulating lipids parameters and erythrocyte oxidative stress biomarkers measurement. The difference of genotype distribution and the Hardy-Weinberg equilibrium was calculated by the Chi-square test. The general linear model was applied to compare the plasma folate levels and erythrocyte oxidative stress biomarkers. Multiple linear regression was used to explore the correlation between genetic risk scores and oxidative stress biomarkers. Logistic regression was used to explore the association of genetic risk scores of folate pathway gene with folate deficiency.

RESULTS

The male subjects have lower plasma folate and HDL-C levels than the female ones, and the male carrying MTHFR rs1801133 (CC) or MTHFR rs2274976 (GA) genotypes have higher erythrocyte SOD activity. The plasma folate levels, erythrocyte SOD and GSH-PX activities were negatively correlated with genetic risk scores in the male subjects. A positive correlation between the genetic risk scores and folate deficiency was observed in the male subjects.

CONCLUSIONS

There was association between folate pathway gene polymorphism of Solute Carrier Family 19 Member 1 (SLC19A1) and Methylenetetrahydrofolate Reductase (MTHFR) with erythrocyte SOD and GSH-PX activities, and folate levels in male but not in female aging subjects. Genetic variant of genes involved in folate metabolism has strong impact on plasma folate levels in the male aging subjects. Our data demonstrated that there was a potential interaction of gender and its genetic background in affecting the body's antioxidant capacity and the risk of folate deficiency in aging subjects.

cGAMP the travelling messenger

2'3'-cGAMP is a key molecule in the cGAS-STING pathway. This cyclic dinucleotide is produced by the cytosolic DNA sensor cGAS in response to the presence of aberrant dsDNA in the cytoplasm which is associated with microbial invasion or cellular damage. 2'3'-cGAMP acts as a second messenger and activates STING, the central hub of DNA sensing, to induce type-I interferons and pro-inflammatory cytokines necessary for responses against infection, cancer or cellular stress. Classically, detection of pathogens or danger by pattern recognition receptors (PRR) was thought to signal and induce the production of interferon and pro-inflammatory cytokines in the cell where sensing occurred. These interferon and cytokines then signal in both an autocrine and paracrine manner to induce responses in neighboring cells. Deviating from this dogma, recent studies have identified multiple mechanisms by which 2'3'-cGAMP can travel to neighboring cells where it activates STING independent of DNA sensing by cGAS. This observation is of great importance, as the cGAS-STING pathway is involved in immune responses against microbial invaders and cancer while its dysregulation drives the pathology of a wide range of inflammatory diseases to which antagonists have been elusive. In this review, we describe the fast-paced discoveries of the mechanisms by which 2'3'-cGAMP can be transported. We further highlight the diseases where they are important and detail how this change in perspective can be applied to vaccine design, cancer immunotherapies and treatment of cGAS-STING associated disease.

Impaired Function of Solute Carrier Family 19 Leads to Low Folate Levels and Lipid Droplet Accumulation in Hepatocytes

Low serum folate levels are inversely related to metabolic associated fatty liver disease (MAFLD). The role of the folate transporter gene (SLC19A1) was assessed to clarify its involvement in lipid accumulation during the onset of MAFLD in humans and in liver cells by genomic, transcriptomic, and metabolomic techniques. Genotypes of 3 SNPs in a case-control cohort were initially correlated to clinical and serum MAFLD markers. Subsequently, the expression of 84 key genes in response to the loss of SLC19A1 was evaluated with the aid of an RT² profiler-array. After shRNA-silencing of SLC19A1 in THLE2 cells, folate and lipid levels were measured by ELISA and staining techniques, respectively. In addition, up to 482 amino acids and lipid metabolites were semi-quantified in SLC19A1-knockdown (KD) cells through ultra-high-performance liquid chromatography coupled with mass spectrometry. SNPs, rs1051266 and rs3788200, were significantly associated with the development of fatty liver for the single-marker allelic test. The minor alleles of these SNPs were associated with a 0.6/-1.67-fold decreased risk of developing MAFLD. When SLC19A1 was KD in THLE2 cells, intracellular folate content was four times lower than in wild-type cells. The lack of functional SLC19A1 provoked significant changes in the regulation of genes associated with lipid droplet accumulation within the cell and the onset of NAFLD. Metabolomic analyses showed a highly altered profile, where most of the species that accumulated in SLC19A1-KD-cells belong to the chemical groups of triacylglycerols, diacylglycerols, polyunsaturated fatty acids, and long chain, highly unsaturated cholesterol esters. In conclusion, the lack of SLC19A1 gene expression in hepatocytes affects the regulation of key genes for normal liver function, reduces intracellular folate levels, and impairs lipid metabolism, which entails lipid droplet accumulation in hepatocytes.

The Role of Solute Carrier Transporters in Efficient Anticancer Drug Delivery and Therapy

Transporter-mediated drug resistance is a major obstacle in anticancer drug delivery and a key reason for cancer drug therapy failure. Membrane solute carrier (SLC) transporters play a crucial role in the cellular uptake of drugs. The expression and function of the SLC transporters can be down-regulated in cancer cells, which limits the uptake of drugs into the tumor cells, resulting in the inefficiency of the drug therapy. In this review, we summarize the current understanding of low-SLC-transporter-expression-mediated drug resistance in different types of cancers. Recent advances in SLC-transporter-targeting strategies include the development of transporter-utilizing prodrugs and nanocarriers and the modulation of SLC transporter expression in cancer cells. These strategies will play an important role in the future development of anticancer drug therapies by enabling the efficient delivery of drugs into cancer cells.

Transcriptomic profiling of hepatic tissues for drug metabolism genes in nonalcoholic fatty liver disease: A study of human and animals

Background

Drug metabolism genes are involved in the in vivo metabolic processing of drugs. In previous research, we found that a high-fat diet affected the transcript levels of mouse hepatic genes responsible for drug metabolism.

Aims

Our research intends to discover the drug metabolism genes that are dysregulated at the transcriptome level in nonalcoholic fatty liver disease (NAFLD).

Methods

We analyzed the transcriptome for drug metabolism genes of 35 human liver tissues obtained during laparoscopic cholecystectomy. Additionally, we imported transcriptome data from mice fed a high-fat diet in previous research and two open-access Gene Expression Omnibus (GEO) datasets (GSE63067 and GSE89632). Then, using quantitative real-time polymerase chain reaction (qRT-PCR), we cross-linked the differentially expressed genes (DEGs) in clinical and animal samples and validated the common genes.

Results

In this study, we identified 35 DEGs, of which 33 were up-regulated and two were down-regulated. Moreover, we found 71 DEGs (39 up- and 32 down-regulated), 276 DEGs (157 up- and 119 down-regulated), and 158 DEGs (117 up- and 41 down-regulated) in the GSE63067, GSE89632, and high-fat diet mice, respectively. Of the 35 DEGs, nine co-regulated DEGs were found in the Venn diagram (CYP20A1, CYP2U1, SLC9A6, SLC26A6, SLC31A1, SLC46A1, SLC46A3, SULT1B1, and UGT2A3).

Conclusion

Nine significant drug metabolism genes were identified in NAFLD. Future research should investigate the impacts of these genes on drug dose adjustment in patients with NAFLD.

Clinical Trial Registration

http://www.chictr.org.cn, identifier ChiCTR2100041714.

Bile duct ligation differently regulates protein expressions of organic cation transporters in intestine, liver and kidney of rats through activation of farnesoid X receptor by cholate and bilirubin

Body is equipped with organic cation transporters (OCTs). These OCTs mediate drug transport and are also involved in some disease process. We aimed to investigate whether liver failure alters intestinal, hepatic and renal Oct expressions using bile duct ligation (BDL) rats. Pharmacokinetic analysis demonstrates that BDL decreases plasma metformin exposure, associated with decreased intestinal absorption and increased urinary excretion. Western blot shows that BDL significantly downregulates intestinal Oct2 and hepatic Oct1 but upregulates renal and hepatic Oct2. In vitro cell experiments show that chenodeoxycholic acid (CDCA), bilirubin and farnesoid X receptor (FXR) agonist GW4064 increase OCT2/Oct2 but decrease OCT1/Oct1, which are remarkably attenuated by glycine-β-muricholic acid and silencing FXR. Significantly lowered intestinal CDCA and increased plasma bilirubin levels contribute to different Octs regulation by BDL, which are confirmed using CDCA-treated and bilirubin-treated rats. A disease-based physiologically based pharmacokinetic model characterizing intestinal, hepatic and renal Octs was successfully developed to predict metformin pharmacokinetics in rats. In conclusion, BDL remarkably downregulates expressions of intestinal Oct2 and hepatic Oct1 protein while upregulates expressions of renal and hepatic Oct2 protein in rats, finally, decreasing plasma exposure and impairing hypoglycemic effects of metformin. BDL differently regulates Oct expressions via Fxr activation by CDCA and bilirubin.

Molecular mechanism of substrate recognition by folate transporter SLC19A1

Folate (vitamin B₉) is the coenzyme involved in one-carbon transfer biochemical reactions essential for cell survival and proliferation, with its inadequacy causing developmental defects or severe diseases. Notably, mammalian cells lack the ability to de novo synthesize folate but instead rely on its intake from extracellular sources via specific transporters or receptors, among which SLC19A1 is the ubiquitously expressed one in tissues. However, the mechanism of substrate recognition by SLC19A1 remains unclear. Here we report the cryo-EM structures of human SLC19A1 and its complex with 5-methyltetrahydrofolate at 3.5-3.6 Å resolution and elucidate the critical residues for substrate recognition. In particular, we reveal that two variant residues among SLC19 subfamily members designate the specificity for folate. Moreover, we identify intracellular thiamine pyrophosphate as the favorite coupled substrate for folate transport by SLC19A1. Together, this work establishes the molecular basis of substrate recognition by this central folate transporter.

Novel localization of folate transport systems in the murine central nervous system

BACKGROUND

Folates are a family of B9 vitamins that serve as one-carbon donors critical to biosynthetic processes required for the development and function of the central nervous system (CNS) in mammals. Folate transport is mediated by three highly specific systems: (1) folate receptor alpha (FRα; FOLR1/Folr1), (2) the reduced folate-carrier (RFC; SLC19A1/Slc19a1) and (3) the proton-coupled folate transporter (PCFT; SLC46A1/Slc46a1). Folate transport into and out of the CNS occurs at the blood-cerebrospinal fluid barrier (BCSFB), mediated by FRα and PCFT. Impairment of folate transport at the BCSFB results in cerebral folate deficiency in infants characterized by severe neurological deficiencies and seizures. In contrast to the BCSFB, CNS folate transport at other brain barriers and brain parenchymal cells has not been extensively investigated. The aim of this study is to characterize folate transport systems in the murine CNS at several known barriers encompassing the BCSFB, arachnoid barrier (AB), blood-brain barrier (BBB) and parenchymal cells (astrocytes, microglia, neurons).

METHODS

Applying immunohistochemistry, localization of folate transport systems (RFC, PCFT, FRα) was examined at CNS barriers and parenchymal sites in wildtype (C57BL6/N) mice. Subcellular localization of the folate transport systems was further assessed in an in vitro model of the mouse AB. Gene and protein expression was analyzed in several in vitro models of brain barriers and parenchyma by qPCR and western blot analysis.

RESULTS

RFC, PCFT, and FRα expression was localized within the BCSFB and BBB consistent with previous reports. Only RFC and PCFT expression was detected at the AB. Varied levels of RFC and PCFT expression were detected in neuronal and glial cells.

CONCLUSIONS

Localization of RFC and PCFT within the AB, described here for the first time, suggest that AB may contribute to folate transport between the peripheral circulation and the CSF. RFC and PCFT expression observed in astrocytes and microglia is consistent with the role that one or both of these transporters may play in delivering folates into cells within brain parenchyma. These studies provide insights into mechanisms of folate transport in the CNS and may enhance our understanding of the critical role folates play in neurodevelopment and in the development of novel treatment strategies for disorders of brain folate deficiency due to impaired transporter function.

Thiamine metabolism genes in diatoms are not regulated by thiamine despite the presence of predicted riboswitches

Thiamine pyrophosphate (TPP), an essential co-factor for all species, is biosynthesised through a metabolically expensive pathway regulated by TPP riboswitches in bacteria, fungi, plants and green algae. Diatoms are microalgae responsible for c. 20% of global primary production. They have been predicted to contain TPP aptamers in the 3'UTR of some thiamine metabolism-related genes, but little information is known about their function and regulation. We used bioinformatics, antimetabolite growth assays, RT-qPCR, targeted mutagenesis and reporter constructs to test whether the predicted TPP riboswitches respond to thiamine supplementation in diatoms. Gene editing was used to investigate the functions of the genes with associated TPP riboswitches in Phaeodactylum tricornutum. We found that thiamine-related genes with putative TPP aptamers are not responsive to supplementation with thiamine or its precursor 4-amino-5-hydroxymethyl-2-methylpyrimidine (HMP), and targeted mutation of the TPP aptamer in the THIC gene encoding HMP-P synthase does not deregulate thiamine biosynthesis in P. tricornutum. Through genome editing we established that PtTHIC is essential for thiamine biosynthesis and another gene, PtSSSP, is necessary for thiamine uptake. Our results highlight the importance of experimentally testing bioinformatic aptamer predictions and provide new insights into the thiamine metabolism shaping the structure of marine microbial communities with global biogeochemical importance.

Hypoxia–Immune-Related Gene SLC19A1 Serves as a Potential Biomarker for Prognosis in Multiple Myeloma

Background

Multiple myeloma (MM) remains an incurable malignant tumor of plasma cells. Increasing evidence has reported that hypoxia and immune status contribute to the progression of MM. In this research, the prognostic value of the hypoxia–immune-related gene SLC19A1 in MM was evaluated by bioinformatics analysis.

Method

RNA-sequencing (RNA-seq) data along with clinical information on MM were downloaded from the Gene Expression Omnibus (GEO) database. Consistent clustering analysis and ESTIMATE algorithms were performed to establish the MM sample subgroups related to hypoxia and immune status, respectively, based on the GSE24080 dataset. The differentially expressed analysis was performed to identify the hypoxia–immune-related genes. Subsequently, a hypoxia–immune-gene risk signature for MM patients was constructed by univariate and multivariate Cox regression analyses, which was also verified in the GSE4581 dataset. Furthermore, the mRNA expression of SLC19A1 was determined using qRT-PCR in 19 MM patients, and the correlations between the genetic expression of SLC19A1 and clinical features were further analyzed.

Result

A total of 47 genes were identified as hypoxia–immune-related genes for MM. Among these genes, SLC19A1 was screened to construct a risk score model that had better predictive power for MM. The constructed prognostic signature based on SLC19A1 was verified in the GSE4581 dataset. All independent prognostic factors (age, β₂-microglobulin, LDH, albumin, MRI, and gene risk score) were used to develop a nomogram that showed a better performance for predicting the survival probability of MM patients for 1–5 years. Furthermore, SLC19A1 was highly expressed in newly diagnosed and relapsed MM patients, and high expression of SLC19A1 is correlated with higher bone marrow aspiration plasma cells and β₂-microglobulin levels in MM patients.

Conclusion

In conclusion, our results suggest that SLC19A1 is aberrantly expressed in MM and highly expressed SLC19A1 might be a biomarker correlated with inferior prognosis. More importantly, we identified SLC19A1 as a hypoxia–immune-related gene in MM. Future functional and mechanistic studies will further clarify the roles of SLC19A1 in MM.

Identification of the amino acid residues involved in the species-dependent differences in the pyridoxine transport function of SLC19A3

Recent studies have shown that human solute carrier SLC19A3 (hSLC19A3) can transport pyridoxine (vitamin B6) in addition to thiamine (vitamin B1), its originally identified substrate, whereas rat and mouse orthologs of hSLC19A3 can transport thiamine but not pyridoxine. This finding implies that some amino acid residues required for pyridoxine transport, but not for thiamine transport, are specific to hSLC19A3. Here, we sought to identify these residues to help clarify the unique operational mechanism of SLC19A3 through analyses comparing hSLC19A3 and mouse Slc19a3 (mSlc19a3). For our analyses, hSLC19A3 mutants were prepared by replacing selected amino acid residues with their counterparts in mSlc19a3, and mSlc19a3 mutants were prepared by substituting selected residues with their hSLC19A3 counterparts. We assessed pyridoxine and thiamine transport by these mutants in transiently transfected HEK293 cells. Our analyses indicated that the hSLC19A3-specific amino acid residues of Gln⁸⁶, Gly⁸⁷, Ile⁹¹, Thr⁹³, Trp⁹⁴, Ser¹⁶⁸, and Asn¹⁷³ are critical for pyridoxine transport. These seven amino acid residues were found to be mostly conserved in the SLC19A3 orthologs that can transport pyridoxine, but not in orthologs that are unable to transport pyridoxine. In addition, these residues were also found to be conserved in several SLC19A2 orthologs, including rat, mouse, and human orthologs, which were all found to effectively transport both pyridoxine and thiamine, exhibiting no species-dependent differences. Together, these findings provide a molecular basis for the unique functional characteristics of SLC19A3 and also of SLC19A2.

nMOWChIP-seq: low-input genome-wide mapping of non-histone targets

Genome-wide profiling of interactions between genome and various functional proteins is critical for understanding regulatory processes involved in development and diseases. Conventional assays require a large number of cells and high-quality data on tissue samples are scarce. Here we optimized a low-input chromatin immunoprecipitation followed by sequencing (ChIP-seq) technology for profiling RNA polymerase II (Pol II), transcription factor (TF), and enzyme binding at the genome scale. The new approach produces high-quality binding profiles using 1,000-50,000 cells. We used the approach to examine the binding of Pol II and two TFs (EGR1 and MEF2C) in cerebellum and prefrontal cortex of mouse brain and found that their binding profiles are highly reflective of the functional differences between the two brain regions. Our analysis reveals the potential for linking genome-wide TF or Pol II profiles with neuroanatomical origins of brain cells.

SLC46A3 is a lysosomal proton-coupled steroid conjugate and bile acid transporter involved in transport of active catabolites of T-DM1

Antibody-drug conjugates (ADCs) represent a new class of cancer therapeutics that enable targeted delivery of cytotoxic drugs to cancer cells. Although clinical efficacy has been demonstrated for ADC therapies, resistance to these conjugates may occur. Recently, SLC46A3, a lysosomal membrane protein, was revealed to regulate the efficacy of trastuzumab emtansine (T-DM1), a noncleavable ADC that has been widely used for treating breast cancer. However, the role of SLC46A3 in mediating T-DM1 cytotoxicity remains unclear. In this study, we discovered the function of SLC46A3 as a novel proton-coupled steroid conjugate and bile acid transporter. SLC46A3 preferentially recognized lipophilic steroid conjugates and bile acids as endogenous substrates. In addition, we found that SLC46A3 directly transports Lys-SMCC-DM1, a major catabolite of T-DM1, and potent SLC46A3 inhibitors attenuate the cytotoxic effects of T-DM1, suggesting a role in the escape of Lys-SMCC-DM1 from the lysosome into the cytoplasm. Our findings reveal the molecular mechanism by which T-DM1 kills cancer cells and may contribute to the rational development of ADCs that target SLC46A3.

Targeting Transporters for Drug Delivery to the Brain: Can We Do Better?

Limited drug delivery to the brain is one of the major reasons for high failure rates of central nervous system (CNS) drug candidates. The blood–brain barrier (BBB) with its tight junctions, membrane transporters, receptors and metabolizing enzymes is a main player in drug delivery to the brain, restricting the entrance of the drugs and other xenobiotics. Current knowledge about the uptake transporters expressed at the BBB and brain parenchymal cells has been used for delivery of CNS drugs to the brain via targeting transporters. Although many transporter-utilizing (pro)drugs and nanocarriers have been developed to improve the uptake of drugs to the brain, their success rate of translation from preclinical development to humans is negligible. In the present review, we provide a systematic summary of the current progress in development of transporter-utilizing (pro)drugs and nanocarriers for delivery of drugs to the brain. In addition, we applied CNS pharmacokinetic concepts for evaluation of the limitations and gaps in investigation of the developed transporter-utilizing (pro)drugs and nanocarriers. Finally, we give recommendations for a rational development of transporter-utilizing drug delivery systems targeting the brain based on CNS pharmacokinetic principles.

Trophoblast Differentiation Affects Crucial Nutritive Functions of Placental Membrane Transporters

Cytotrophoblasts are progenitor cells that proliferate and fuse to form the multinucleated syncytiotrophoblast layer, implicated in placental endocrine and transport functions. While membrane transporters play a critical role in the distribution of nutrients, hormones, and xenobiotics at the maternal-fetal interface, their selectivity to the syncytiotrophoblast layer is poorly characterized. We aimed to evaluate the regulation of placental transporters in response to trophoblast differentiation in vitro. Experiments were carried out in isolated primary human trophoblast cells before and after syncytialization. Gene expression of six molecular markers and thirty membrane transporters was investigated by qPCR analysis. Subsequently, functional expression was evaluated for proteins involved in the transplacental transfer of essential nutrients i.e., cholesterol (ABCA1, ABCG1), glucose (SLC2A1), leucine (SLC3A2, SLC7A5), and iron (transferrin receptor, TfR1). We identified that human chorionic gonadotropin, placental lactogen, endoglin, and cadherin-11 serve as optimal gene markers for the syncytialization process. We showed that trophoblast differentiation was associated with differential gene expression (mostly up-regulation) of several nutrient and drug transporters. Further, we revealed enhanced protein expression and activity of ABCG1, SLC3A2, SLC7A5, and TfR1 in syncytialized cells, with ABCA1 and GLUT1 displaying no change. Taken together, these results indicate that the syncytiotrophoblast has a dominant role in transporting essential nutrients cholesterol, leucine, and iron. Nonetheless, we present evidence that the cytotrophoblast cells may also be linked to transport functions that could be critical for the cell fusion processes. Our findings collectively yield new insights into the cellular functions associated with or altered by the trophoblast fusion. Importantly, defective syncytialization could lead to nutrient transfer imbalance, ultimately compromising fetal development and programming.

The Roles of Solute Carriers in Auditory Function

Solute carriers (SLCs) are important transmembrane transporters with members organized into 65 families. They play crucial roles in transporting many important molecules, such as ions and some metabolites, across the membrane, maintaining cellular homeostasis. SLCs also play important roles in hearing. It has been found that mutations in some SLC members are associated with hearing loss. In this review, we summarize SLC family genes related with hearing dysfunction to reveal the vital roles of these transporters in auditory function. This summary could help us understand the auditory physiology and the mechanisms of hearing loss and further guide future studies of deafness gene identification.

Dietary supplementation of thiamine enhances colonic integrity and modulates mucosal inflammation injury in goats challenged by lipopolysaccharide and low pH

The current study aimed to investigate the protective effects of dietary thiamine supplementation on the regulation of colonic integrity and mucosal inflammation in goats fed a high-concentrate (HC) diet. Twenty-four Boer goats (live weight of 35·62 (sem 2·4) kg) were allocated to three groups (CON: concentrate/forage = 30:70; HC; concentrate/forage = 70:30 and HCT: concentrate/forage = 70:30 with 200 mg thiamine/kg DMI) for 12 weeks. Results showed that compared with the HC treatment, the HCT group had a significantly higher ruminal pH value from 0 to 12 h after the feeding. The haematoxylin-eosin staining showed that desquamation and severe cellular damage were observed in the colon epithelium of the HC group, whereas the HCT group exhibited more structural integrity of the epithelial cell morphology. Compared with the HC treatment, the HCT group showed a markedly increase in pyruvate dehydrogenase and α-ketoglutarate dehydrogenase enzymes activity. The mRNA expressions in the colonic epithelium of SLC19A2, SLC19A3, SLC25A19, Bcl-2, occludin, claudin-1, claudin-4 and ZO-1 in the HCT group were significantly increased in comparison with the HC diet treatment. Compared with the HC treatment, the HCT diet significantly increased the protein expression of claudin-1 and significantly decreased the protein expression of NF-κB-related proteins p65. The results show that dietary thiamine supplementation could improve the colon epithelial barrier function and alleviate mucosal inflammation injury in goats after lipopolysaccharide and low pH challenge.

Hiding in Plain Sight: Modern Thiamine Deficiency

Thiamine or vitamin B1 is an essential, water-soluble vitamin required for mitochondrial energetics—the production of adenosine triphosphate (ATP). It is a critical and rate-limiting cofactor to multiple enzymes involved in this process, including those at the entry points and at critical junctures for the glucose, fatty acid, and amino acid pathways. It has a very short half-life, limited storage capacity, and is susceptible to degradation and depletion by a number of products that epitomize modern life, including environmental and pharmaceutical chemicals. The RDA for thiamine is 1.1–1.2 mg for adult females and males, respectively. With an average diet, even a poor one, it is not difficult to meet that daily requirement, and yet, measurable thiamine deficiency has been observed across multiple patient populations with incidence rates ranging from 20% to over 90% depending upon the study. This suggests that the RDA requirement may be insufficient to meet the demands of modern living. Inasmuch as thiamine deficiency syndromes pose great risk of chronic morbidity, and if left untreated, mortality, a more comprehensive understanding thiamine chemistry, relative to energy production, modern living, and disease, may prove useful.

Structural basis of antifolate recognition and transport by PCFT

Folates (also known as vitamin B9) have a critical role in cellular metabolism as the starting point in the synthesis of nucleic acids, amino acids and the universal methylating agent S-adenylsmethionine1,2. Folate deficiency is associated with a number of developmental, immune and neurological disorders3-5. Mammals cannot synthesize folates de novo; several systems have therefore evolved to take up folates from the diet and distribute them within the body3,6. The proton-coupled folate transporter (PCFT) (also known as SLC46A1) mediates folate uptake across the intestinal brush border membrane and the choroid plexus4,7, and is an important route for the delivery of antifolate drugs in cancer chemotherapy8-10. How PCFT recognizes folates or antifolate agents is currently unclear. Here we present cryo-electron microscopy structures of PCFT in a substrate-free state and in complex with a new-generation antifolate drug (pemetrexed). Our results provide a structural basis for understanding antifolate recognition and provide insights into the pH-regulated mechanism of folate transport mediated by PCFT.

Potential protective effects of thiamine supplementation on the ruminal epithelium damage during subacute ruminal acidosis

In ruminants, the ruminal epithelium not only has the function of absorbing nutrients but also is an important tissue to prevent harmful substances in the rumen from entering the blood circulation. Thus, the normal function of ruminal epithelium is critical for ruminants. However, subacute ruminal acidosis induced by high-concentrate diets often damages the barrier function of ruminal epithelium in ruminants. Recently, many studies have shown that dietary supplementation with thiamine is an effective method to alleviate subacute ruminal acidosis. In order to provide theoretical reference for the in-depth study of subacute ruminal acidosis and the application of thiamine in the future, this review introduces the effects of subacute ruminal acidosis on morphological structure, inflammatory response, and tight junction of ruminal epithelium. In addition, this paper summarizes the role of thiamine in maintaining ruminal epithelial function of ruminants during subacute ruminal acidosis challenge.

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.

A guide to plasma membrane solute carrier proteins

This review aims to serve as an introduction to the solute carrier proteins (SLC) superfamily of transporter proteins and their roles in human cells. The SLC superfamily currently includes 458 transport proteins in 65 families that carry a wide variety of substances across cellular membranes. While members of this superfamily are found throughout cellular organelles, this review focuses on transporters expressed at the plasma membrane. At the cell surface, SLC proteins may be viewed as gatekeepers of the cellular milieu, dynamically responding to different metabolic states. With altered metabolism being one of the hallmarks of cancer, we also briefly review the roles that surface SLC proteins play in the development and progression of cancer through their influence on regulating metabolism and environmental conditions.

Advancements in folate receptor targeting for anti-cancer therapy: A small molecule-drug conjugate approach

Targeted delivery combined with controlled release of drugs has a crucial role in future of personalized medicine. The majority of cancer drugs are intended to interfere with one or more cellular events. Anticancer agents can also be toxic to healthy cells, as healthy cells may also need to proliferate and avoid apoptosis. The focus of this review covers the principles, advantages, drawbacks and summarize criteria that must be met for design of small molecule-drug conjugates (SMDCs) to achieve the desired therapeutic potency with minimal toxicity. SMDCs are composed of a targeting ligand, a releasable bridge, a spacer, and a therapeutic payload. We summarize the criteria for the effective design that influences the selection of tumor specific receptor and optimum elements in the design of SMDCs. We also discuss the criteria for selecting the optimal therapeutic drug payload, spacer and linker. The linker chemistries and cleavage strategies are also discussed. Finally, we review the folate receptor targeting SMDCs that are in preclinical development and in clinical trials.

Interplay Between Thiamine and p53/p21 Axes Affects Antiproliferative Action of Cisplatin in Lung Adenocarcinoma Cells by Changing Metabolism of 2-Oxoglutarate/Glutamate

Thiamine (vitamin B1) is often deficient in oncopatients, particularly those undergoing chemotherapy. However, interaction between the thiamine deficiency and anticancer action of drugs has not been characterized. A major natural thiamine derivative, thiamine diphosphate (ThDP), is a coenzyme of central metabolism, also known to affect transcriptional activity of the master metabolic regulator and genome guardian p53. A direct transcriptional target of p53, p21, regulates cell cycle dynamics and DNA damage response. Our work focuses on dependence of the action of the DNA damaging anticancer drug cisplatin on metabolic regulation through p53/p21 axes and cellular thiamine status in human lung adenocarcinoma cells A549. These cells are used as a model of a hardly curable cancer, known to develop chemoresistance to platinum drugs, such as cisplatin. Compared to wild type (A549WT), a stable line with a 60% knockdown of p21 (A549p21-) is less sensitive to antiproliferative action of cisplatin. In contrast, in the thiamine-deficient medium, cisplatin impairs the viability of A549p21- cells more than that of A549WT cells. Analysis of the associated metabolic changes in the cells indicates that (i) p21 knockdown restricts the production of 2-oxoglutarate via glutamate oxidation, stimulating that within the tricarboxylic acid (TCA) cycle; (ii) cellular cisplatin sensitivity is associated with a 4-fold upregulation of glutamic-oxaloacetic transaminase (GOT2) by cisplatin; (iii) cellular cisplatin resistance is associated with a 2-fold upregulation of p53 by cisplatin. Correlation analysis of the p53 expression and enzymatic activities upon variations in cellular thiamine/ThDP levels indicates that p21 knockdown substitutes positive correlation of the p53 expression with the activity of 2-oxoglutarate dehydrogenase complex (OGDHC) for that with the activity of glutamate dehydrogenase (GDH). The knockdown also changes correlations of the levels of OGDHC, GDH and GOT2 with those of the malate and isocitrate dehydrogenases. Thus, a p53/p21-dependent change in partitioning of the glutamate conversion to 2-oxoglutarate through GOT2 or GDH, linked to NAD(P)-dependent metabolism of 2-oxoglutarate in affiliated pathways, adapts A549 cells to thiamine deficiency or cisplatin treatment. Cellular thiamine deficiency may interfere with antiproliferative action of cisplatin due to their common modulation of the p53/p21-dependent metabolic switch between the glutamate oxidation and transamination.

Effectiveness of B Vitamins and Their Interactions with Aspirin in Improving Cognitive Functioning in Older People with Mild Cognitive Impairment: Pooled Post-Hoc Analyses of Two Randomized Trials

BACKGROUND AND OBJECTIVES

A randomized placebo-controlled trial found a significant negative interaction between aspirin and B vitamins in cognitive functioning in older people with mild cognitive impairment (MCI). To validate this finding, we pooled data of this trial with that of a similar B-vitamin trial (VITACOG) to examine the effectiveness of B vitamins and their interactions with aspirin in improving global cognitive functioning and slowing brain atrophy in older people with MCI.

DESIGN

Pooled post-hoc analyses of two randomized placebo-controlled trials.

PARTICIPANTS

In total, 545 older people with MCI were included in the study.

INTERVENTION

Placebo or B-vitamin supplements (vitamin B12, folic acid with or without vitamin B6) for 24 months.

MEASUREMENTS

The primary outcome was the Clinical Dementia Rating scale-global score (CDR-global). The secondary outcomes were CDR-sum of box score (CDR-SOB), memory Z-score, executive function Z-score, and whole brain atrophy rate.

RESULTS

71 (26.2%) and 83 (30.3%) subjects in the active and placebo group respectively were aspirin users. Overall, B vitamins reduced whole brain atrophy rate significantly (P = 0.003), but did not have significant effect on CDR-global, CDR-SOB, memory and executive function. Aspirin use had significant negative interaction effects on B vitamins in CDR-global and CDR-SOB (Beta = 0.993, P = 0.038, and Beta = 0.583, P = 0.009, respectively), but not in memory or executive function Z-scores. Among aspirin non-users, B-vitamin group subjects had more favourable changes in CDR-global and CDR-SOB (P = 0.019 and 0.057, respectively). B vitamins significantly slowed brain atrophy in aspirin non-users (P = 0.001), but not in aspirin users, though the interaction term was not significant (Beta = 0.192, P = 0.276).

CONCLUSION

In older people with MCI, B vitamins had significantly favourable effects on global cognitive functioning and whole brain atrophy rate in those who were not taking aspirin, but not in aspirin users.

pH-dependent pyridoxine transport by SLC19A2 and SLC19A3: Implications for absorption in acidic microclimates

SLC19A2 and SLC19A3, also known as thiamine transporters (THTR) 1 and 2, respectively, transport the positively charged thiamine (vitamin B1) into cells to enable its efficient utilization. SLC19A2 and SLC19A3 are also known to transport structurally unrelated cationic drugs, such as metformin, but whether this charge selectivity extends to other molecules, such as pyridoxine (vitamin B6), is unknown. We tested this possibility using Madin-Darby canine kidney II (MDCKII) cells and human embryonic kidney 293 (HEK293) cells for transfection experiments, and also using Caco-2 cells as human intestinal epithelial model cells. The stable expression of SLC19A2 and SLC19A3 in MDCKII cells (as well as their transient expression in HEK293 cells) led to a significant induction in pyridoxine uptake at pH 5.5 compared with control cells. The induced uptake was pH-dependent, favoring acidic conditions over neutral to basic conditions, and protonophore-sensitive. It was saturable as a function of pyridoxine concentration, with an apparent Km of 37.8 and 18.5 μm, for SLC19A2 and SLC19A3, respectively, and inhibited by the pyridoxine analogs pyridoxal and pyridoxamine as well as thiamine. We also found that silencing the endogenous SLC19A3, but not SLC19A2, of Caco-2 cells with gene-specific siRNAs lead to a significant reduction in carrier-mediated pyridoxine uptake. These results show that SLC19A2 and SLC19A3 are capable of recognizing/transporting pyridoxine, favoring acidic conditions for operation, and suggest a possible role for these transporters in pyridoxine transport mainly in tissues with an acidic environment like the small intestine, which has an acidic surface microclimate.

Perspectives of Methotrexate-Based Radioagents for Application in Nuclear Medicine

Methotrexate is a gold standard among disease modifying antirheumatic drugs and is also extensively used clinically in combination with oncological therapies. Thus, it is not surprising that nuclear medicine found an interest in methotrexate in the search for diagnostic and therapeutic solutions. Numerous folate-related radiopharmaceuticals have been proposed for nuclear medicine purposes; however, methotrexate radioagents represent only a minority. This imbalance results from the fact that methotrexate has significantly weaker affinity for folate receptors than folic acid. Nevertheless, radiolabeled methotrexate agents utilized as a tool for early detection and imaging of inflammation in rheumatoid arthritis patients gave promising results. Similarly, the use of multimodal MTX-release nanosystems may find potential applications in radiosynovectomy and theranostic approaches in folate receptor positive cancers.

Environmental mechanisms of orofacial clefts

Orofacial clefts (OFCs) are among the most common birth defects and impart a significant burden on afflicted individuals and their families. It is increasingly understood that many nonsyndromic OFCs are a consequence of extrinsic factors, genetic susceptibilities, and interactions of the two. Therefore, understanding the environmental mechanisms of OFCs is important in the prevention of future cases. This review examines the molecular mechanisms associated with environmental factors that either protect against or increase the risk of OFCs. We focus on essential metabolic pathways, environmental signaling mechanisms, detoxification pathways, behavioral risk factors, and biological hazards that may disrupt orofacial development.

Periconceptional use of cod liver oil, a vitamin D source, could decrease the risk of CHD in offspring

OBJECTIVE

To explore if there is association between vitamin D supplementation through cod liver oil ingestion around the periconceptional period and the risk of developing severe CHD in offspring. Furthermore, we would examine the interaction between vitamin D and folic acid supplementation in the association.

METHODS

A case-control study was conducted in Shanghai Children's Medical Center, in which, a total of 262 severe CHD cases versus 262 controls were recruited through June 2016 to December 2017. All children were younger than 2 years. To reduce potential selection bias and to minimise confounding effects, propensity score matching was applied.

RESULTS

After propensity score matching, vitamin D supplementation seemed to be associated with decreased odds ratio of severe CHD (odds ratio = 0.666; 95% confidence intervals: 0.449-0.990) in the multivariable conditional logistic analysis. Furthermore, we found an additive interaction between vitamin D and folic acid supplementation (relative excess risk due to interaction = 0.810, 95% confidence intervals: 0.386-1.235) in the association.

CONCLUSION

The results suggested that maternal vitamin D supplementation could decrease the risk of offspring severe CHD; moreover, it could strengthen the protective effect of folic acid. The significance of this study lies in providing epidemiological evidence that vitamin D supplementation around the periconceptional period could be a potential nutritional intervention strategy to meet the challenge of increasing CHD.

Plasma Homocysteine Concentration is Associated with the Expression Level of Folate Receptor 3

Folic acid and folate receptors (FOLRs) play an important role in the downregulation of homocysteine (Hcy), a risk factor of Alzheimer's disease, thrombosis, neuropsychiatric illness and fractures. While several studies have reported that FOLR1 and FOLR2 import folic acid into cells, the role of FOLR3 remains unknown. In this study, we evaluated the impact of FOLR3 on the metabolism of Hcy alongside its protective effect against homocysteine-induced neurotoxicity. To reveal the role of FOLR3, we constructed FOLR3-overexpressed HEK293 cells (FOLR3+ cells) and evaluated cell growth, folic acid intake and Hcy-induced neurotoxicity. Subjects with a high expression of FOLR3 exhibited low levels of plasma homocysteine. The ectopic expression of FOLR3 enhanced cell growth, and the enhanced effect was neutralised by folic acid-deficient media. The Western blot analysis revealed that FOLR3 is secreted into cell supernatant. The folic acid intake of FOLR3+ cells was higher than that of wild-type cells. Supernatant from FOLR3+ cells showed a protective effect on Hcy-induced cytotoxicity. FOLR3 expression in plasma is negatively correlated with plasma homocysteine. Our study emphasizes the role of FOLR3 in the intake of folic acid into cells on the one hand and its protective role in Hcy-induced cytotoxicity on the other.

Personalized Nutrition for Management of Micronutrient Deficiency-Literature Review in Non-bariatric Populations and Possible Utility in Bariatric Cohort

Background

Bariatric surgery can effectively treat morbid obesity; however, micronutrient deficiencies are common despite recommendations for high-dose supplements. Genetic predisposition to deficiencies underscores necessary identification of high-risk candidates. Personalized nutrition (PN) can be a tool to manage these deficiencies.

Methods

Medline, PubMed, and Google Scholar were searched. Articles involving genetic testing, micronutrient metabolism, and bariatric surgery were included.

Results

Studies show associations between genetic variants and micronutrient metabolism. Research demonstrates genetic testing to be a predictor for outcomes among obesity and bariatric surgery populations. There is limited research in bariatric surgery and micronutrient genetic variants.

Conclusion

Genotype-based PN is becoming feasible to provide an effective treatment of micronutrient deficiencies associated with bariatric surgery. The role of genomic technology in micronutrient recommendations needs further investigation.

Nuclear respiratory factor 1 (NRF-1) upregulates the expression and function of reduced folate carrier (RFC) at the blood-brain barrier

Folates are important for neurodevelopment and cognitive function. Folate transport across biological membranes is mediated by three major pathways: folate receptor alpha (FRα), proton-coupled folate transporter (PCFT), and reduced folate carrier (RFC). Brain folate transport primarily occurs at the choroid plexus through FRα and PCFT; inactivation of these transport systems results in suboptimal folate levels in the cerebrospinal fluid (CSF) causing childhood neurological disorders. Our group has reported that upregulation of RFC at the blood-brain barrier (BBB) through interactions with specific transcription factors, that is, vitamin D receptor (VDR) could increase brain folate delivery. This study investigates the role of nuclear respiratory factor 1 (NRF-1) in the regulation of RFC at the BBB. Activation of NRF-1/PGC-1α signaling through treatment with its specific ligand, pyrroloquinoline quinone (PQQ), significantly induced RFC expression and transport activity in hCMEC/D3 cells. In contrast, transfection with NRF-1 or PGC-1α targeting siRNA downregulated RFC functional expression in the same cell system. Applying chromatin immunoprecipitation (ChIP) assay, we further demonstrated that PQQ treatment increased NRF-1 binding to putative NRF-1 binding sites within the SLC19A1 promoter, which encodes for RFC. Additionally, in vivo treatment of wild type mice with PQQ-induced RFC expression in isolated mouse brain capillaries. Together, these findings demonstrate that NRF-1/PGC-1α activation by PQQ upregulates RFC functional expression at the BBB and could potentially enhance brain folate uptake.

Acid-Base Basics

Although students initially learn of ionic buffering in basic chemistry, buffering and acid-base transport in biology often is relegated to specialized classes, discussions, or situations. That said, for physiology, nephrology, pulmonology, and anesthesiology, these basic principles often are critically important for mechanistic understanding, medical treatments, and assessing therapy effectiveness. This short introductory perspective focuses on basic chemistry and transport of buffers and acid-base equivalents, provides an outline of basic science acid-base concepts, tools used to monitor intracellular pH, model cellular responses to pH buffer changes, and the more recent development and use of genetically encoded pH-indicators. Examples of newer genetically encoded pH-indicators (pHerry and pHire) are provided, and their use for in vitro, ex vivo, and in vivo experiments are described. The continued use and development of these basic tools provide increasing opportunities for both basic and potentially clinical investigations.

Clinical Implications of Folate Transport in the Central Nervous System

Folates are essential for key biosynthetic processes in mammalian cells and play a crucial role in the maintenance of central nervous system homeostasis. Mammals lack the metabolic capacity for folate biosynthesis; hence, folate requirements are largely met through dietary sources. To date, three major folate transport pathways have been characterized: the folate receptors (FRs), reduced folate carrier (RFC), and proton-coupled folate transporter (PCFT). This article reviews current knowledge on the role of folate transport systems in mediating folate delivery to vital tissues, particularly the brain, and how these pathways are modulated by various regulatory mechanisms. We will also briefly highlight the clinical significance of cerebral folate transport in relation to neurodevelopmental disorders associated with folate deficiency.

Microbial Metabolic Capacity for Intestinal Folate Production and Modulation of Host Folate Receptors

Microbial metabolites, including B complex vitamins contribute to diverse aspects of human health. Folate, or vitamin B9, refers to a broad category of biomolecules that include pterin, para-aminobenzoic acid (pABA), and glutamate subunits. Folates are required for DNA synthesis and epigenetic regulation. In addition to dietary nutrients, the gut microbiota has been recognized as a source of B complex vitamins, including folate. This study evaluated the predicted folate synthesis capabilities in the genomes of human commensal microbes identified in the Human Microbiome Project and folate production by representative strains of six human intestinal bacterial phyla. Bacterial folate synthesis genes were ubiquitous across 512 gastrointestinal reference genomes with 13% of the genomes containing all genes required for complete de novo folate synthesis. An additional 39% of the genomes had the genetic capacity to synthesize folates in the presence of pABA, an upstream intermediate that can be obtained through diet or from other intestinal microbes. Bacterial folate synthesis was assessed during exponential and stationary phase growth through the evaluation of expression of select folate synthesis genes, quantification of total folate production, and analysis of folate polyglutamylation. Increased expression of key folate synthesis genes was apparent in exponential phase, and increased folate polyglutamylation occurred during late stationary phase. Of the folate producers, we focused on the commensal Lactobacillus reuteri to examine host-microbe interactions in relation to folate and examined folate receptors in the physiologically relevant human enteroid model. RNAseq data revealed segment-specific folate receptor distribution. Treatment of human colonoid monolayers with conditioned media (CM) from wild-type L. reuteri did not influence the expression of key folate transporters proton-coupled folate transporter (PCFT) or reduced folate carrier (RFC). However, CM from L. reuteri containing a site-specific inactivation of the folC gene, which prevents the bacteria from synthesizing a polyglutamate tail on folate, significantly upregulated RFC expression. No effects were observed using L. reuteri with a site inactivation of folC2, which results in no folate production. This work sheds light on the contributions of microbial folate to overall folate status and mammalian host metabolism.