Ischemia-Reperfusion Injury Reduces Kidney Folate Transporter Expression and Plasma Folate Levels

Acute or chronic kidney disease can cause micronutrient deficiency. Patients with end-stage renal disease, kidney transplantation or on dialysis have reduced circulating levels of folate, an essential B vitamin. However, the molecular mechanism is not well understood. Reabsorption of folate in renal proximal tubules through folate transporters is an important process to prevent urinary loss of folate. The present study investigated the impact of acute kidney injury (AKI) on folate transporter expression and the underlying mechanism. AKI was induced in Sprague-Dawley rats that were subjected to kidney ischemia (45 min)-reperfusion (24 h). Both male and female rats displayed kidney injury and low plasma folate levels compared with sham-operated rats. The plasma folate levels were inversely correlated to plasma creatinine levels. There was a significant increase in neutrophil gelatinase-associated lipocalin (NGAL) and IL-6 mRNA expression in the kidneys of rats with ischemia-reperfusion, indicating kidney injury and increased inflammatory cytokine expression. Ischemia-reperfusion decreased mRNA and protein expression of folate transporters including folate receptor 1 (FOLR1) and reduced folate carrier (RFC); and inhibited transcription factor Sp1/DNA binding activity in the kidneys. Simulated ischemia-reperfusion through hypoxia-reoxygenation or Sp1 siRNA transfection in human proximal tubular cells inhibited folate transporter expression and reduced intracellular folate levels. These results suggest that ischemia-reperfusion injury downregulates renal folate transporter expression and decreases folate uptake by tubular cells, which may contribute to low folate status in AKI. In conclusion, ischemia-reperfusion injury can downregulate Sp1 mediated-folate transporter expression in tubular cells, which may reduce folate reabsorption and lead to low folate status.

Folate Transporters Are Found Throughout the Colon of Humans and Their mRNA Expression Appears to Be Unaffected by Low Dose Folic Acid Supplementation

Objectives A large depot of folate resides in the colon and can exceed dietary intake. Little is known about the capacity of the colon to absorb folate. We aimed to determine the expression of key folate transporters, reduced folate carrier (RFC) and proton-coupled folate transporter (PCFT), throughout the colon of healthy adults and the impact of low dose folic acid (FA) supplementation. Methods In this 16 wk open-labelled randomized control trial, healthy adults (n = 25) from a colonoscopy waiting list were randomized to receive daily a multivitamin plus a 400 μg FA (400FA, n = 12) or no FA supplement (0FA, n = 13). Subjects were provided with low FA bread and pasta and instructions how to follow a low FA containing diet. Six 24-hr diet recalls were administered throughout the study and blood samples were collected at baseline, 8 and 16 wk. At colonoscopy (16 wk), 4 tissue biopsies were collected from the terminal ileum, cecum, ascending and descending colon. Blood folates were determined by microbial assay; mRNA levels of folate transporters were assessed using qPCR. Results One subject was removed from analysis due to missing data (0FA). No group differences in age, sex, BMI, dietary intake, vitamin B12, red blood cell (RBC) and plasma folate levels at baseline were observed. Mean ± SD FA supplement adherence was 92 ± 12% and 96 ± 9% at 8 and 16 wk, respectively. Subjects in the 400FA group had higher total folate intake (P < 0.05) and higher RBC and plasma folate levels (P < 0.01) at 8 and 16 wk compared to 0FA subjects. RBC values at 16 wk were 1764 ± 636 and 865 ± 190 nmol/L in the 400FA and 0FA group, respectively. RFC and PCFT were detected in terminal ileum and colon biopsies (n = 96) and their mRNA levels in each section did not differ between groups. However, expression of RFC was markedly higher than PCFT across all biopsy sections (P < 0.05) and highest in the terminal ileum, compared to the cecum, ascending and descending colon in both groups (P < 0.05). Conclusions We demonstrated expression of folate transporters, RFC and PCFT, throughout the human colon suggesting their potential contribution to overall folate absorption. mRNA expressions were not affected by a low dose FA supplement. A deeper understanding of how FA and folate status affect colonic transporter regulation may inform future revisions of folate intake recommendations. Funding Sources Natural Sciences and Engineering Research Council.

Folate Supplementation during Oocyte Maturation Positively Impacts the Folate-Methionine Metabolism in Pre-Implantation Embryos

Folic acid is vital for DNA synthesis and methylations through one-carbon (C1) metabolism. Thus, it is essential for cell division during embryonic development. The present study investigated the effect of folic acid supplementation on oocyte maturation, blastocyst development and the expression of folate transporters as well as folate metabolism enzymes in oocytes and pre-implantation embryos of goat. Immature goat oocytes, matured in maturation medium comprising different folic acid concentrations (0, 10, 50, 100 and 150 µM), were in vitro fertilized and cultured. Cumulus expansion markers (Ptx3 and Ptgs2) in cumulus cells were highly upregulated after 50 µM folic acid supplementation indicating higher degree of maturation. Supplementation of 50 µM folic acid during oocyte maturation resulted in significantly higher blastocyst production rate, reduction in intracellular ROS levels as well as upregulation of the transcripts for folate transporters and key folate-methionine cycle enzymes in comparison to control. The present study demonstrates the existence of active folate-methionine cycle in oocytes and pre-implantation goat embryos. Supplementation of 50 µM folic acid in maturation medium increases the blastocyst production rate, improves oocyte maturation, reduces ROS production as well as upregulate the expression of Folr1 and folate metabolism enzyme, Mtr.

Folate transporter dynamics and therapy with classic and tumor-targeted antifolates

There are three major folate uptake systems in human tissues and tumors, including the reduced folate carrier (RFC), folate receptors (FRs) and proton-coupled folate transporter (PCFT). We studied the functional interrelationships among these systems for the novel tumor-targeted antifolates AGF94 (transported by PCFT and FRs but not RFC) and AGF102 (selective for FRs) versus the classic antifolates pemetrexed, methotrexate and PT523 (variously transported by FRs, PCFT and RFC). We engineered HeLa cell models to express FRα or RFC under control of a tetracycline-inducible promoter with or without constitutive PCFT. We showed that cellular accumulations of extracellular folates were determined by the type and levels of the major folate transporters, with PCFT and RFC prevailing over FRα, depending on expression levels and pH. Based on patterns of cell proliferation in the presence of the inhibitors, we established transport redundancy for RFC and PCFT in pemetrexed uptake, and for PCFT and FRα in AGF94 uptake; uptake by PCFT predominated for pemetrexed and FRα for AGF94. For methotrexate and PT523, uptake by RFC predominated even in the presence of PCFT or FRα. For both classic (methotrexate, PT523) and FRα-targeted (AGF102) antifolates, anti-proliferative activities were antagonized by PCFT, likely due to its robust activity in mediating folate accumulation. Collectively, our findings describe a previously unrecognized interplay among the major folate transport systems that depends on transporter levels and extracellular pH, and that determines their contributions to the uptake and anti-tumor efficacies of targeted and untargeted antifolates.

Diminazene resistance in Trypanosoma congolense is linked to reduced mitochondrial membrane potential and not to reduced transport capacity

Trypanosoma congolense is one of the principal agents causing livestock trypanosomiasis in sub-Saharan Africa. This wasting disease is costing these developing economies billions of dollars and undermining food security. Only two old drugs, the diamidine diminazene and the phenanthridine isometamidium are regularly used, and resistance is widespread but poorly understood. We induce diminazene resistance in T. congolense laboratory strain IL3000 in vitro. Resistance was stable and not deleterious to in vitro growth. There was no cross-resistance with the phenanthridine drugs, with melaminophenyl arsenicals, with two promising new oxaborole trypanocides, nor with other diamidine trypanocides such as pentamidine, except the close structural analogues DB829 and DB75. Fluorescence microscopy showed that accumulation of DB75 was inhibited by folate. Uptake of [3H]-diminazene was also partly inhibited by folate, as well as by competing diamidine drugs, albeit at quite high concentrations, and uptake of tritiated diminazene and pentamidine was slow and low affinity. Uptake of [3H]-folate was in turn partly inhibited by diminazene, and inhibition of diminazene uptake by folate and pentamidine appeared to be additive, indicating multiple low affinity transport mechanisms for the drug. Expression of the T. congolense folate transporters TcoFT1-3 in diminazene-resistant T. b. brucei significantly sensitized the cells to diminazene and DB829, but not to oxaborole AN7973. However, [3H]-diminazene uptake was not different in T. congolense IL3000 and its diminazene resistant clones and RNAseq and whole-genome sequencing of multiple resistant clones did not reveal major changes in folate transporter sequence or expression. Instead, flow cytometry revealed a strong and stable reduction in the mitochondrial membrane potential Ψm in all resistant clones. We conclude that diminazene uptake in T. congolense proceed via multiple low affinity mechanisms including folate transporters and that resistance is the result of a reduction in Ψm that limits mitochondrial accumulation of the drug.

84 Folate-methionine cycle and folate transport in developing buffalo embryos

Periconceptional folic acid is known to have a major role in the prevention of neural tube defects, leading to global recommendations for folic acid supplementation before and in early pregnancy. Maternal folate throughout pregnancy may have other roles in offspring health, including neurodevelopment and cognitive performance in childhood. Folate and folic acid (vitamin B9) act as a co-enzyme essential for single carbon metabolism, a network of pathways involved in several biological processes including nucleotide synthesis, DNA repair, and methylation reactions. In general, rapidly growing and multiplying cells require an adequate supply of folate. A primary deficiency of natural folate resulting in an increase of the total homocysteine concentration may be detrimental to the quality of the oocyte, subsequent fertilisation, embryogenesis, implantation, and fetal development. However, to date, folate-methionine metabolism and folate transport have not been studied in developing buffalo embryos. The present study details transcript expression for genes encoding key enzymes in the linked folate-methionine cycles in the ovary tissue, cumulus cells, immature oocytes, IVM oocytes, and pre-implantation embryos and also estimates the folate concentration in follicular fluid (FF) of buffalo. The FF was pooled and collected by aspiration of different sizes of surface follicles (2-8mm diameter). The total number of analysed samples was three, with different dilutions and estimation of folate in FF of buffalo done by chemiluminescence assay. Total RNA was extracted from oocytes, cumulus cells, ovarian tissue, and embryos produced from IVF. RT-PCR was performed to analyse the expression of folate-methionine cycle enzymes and folate transporters. Transcripts for all the enzymes of the folate-methionine cycle (i.e. SHMT, MTR, MTRR, MAT1A, MAT2B, GNMT, AHCY, CBS, and DHFR) and folate transporters (FOLR1, FOLR2) and reduced folate carrier (SLC19A1) were expressed in ovarian tissue, cumulus cells, oocytes, and pre-implantation embryos. Immunocytochemical analysis revealed FOLR2 and SLC19A1 protein expression on the plasma membrane and/or cytoplasm of the oocytes and embryos, and FOLR1 in the nucleus of pre-implantation embryos. The folate concentration in FF was 24ngmL−1. This is the first report to examine the concentration of folate in FF and revealed the identification of transcripts in different samples of buffalo species. The presence of these enzymes could have a profound effect on single-carbon metabolism within the ovary and pre-implantation embryo, therefore indicating that folate from FF is being disseminated through folate receptors within oocytes and embryos to participate in the folate pathway. This study advocates the necessity for examination of the result of folate supplementation throughout invitro embryo production for improving the quality and quantity of transferable blastocysts and subsequently live calf births in buffalo.

Rationale and preclinical development of LEAF-1401 and LEAF-1701: A novel class of potent next generation antifolates.

e14515 Background: Polyglutamation of antifolates by folylpolyglutamate synthase (FPGS) greatly enhances their activity, e.g. pentaglutamated pemetrexed is 80-fold more potent at inhibiting thymidylate synthase than pemetrexed. Polyglutamated antifolates however, do not readily cross the cell membrane, due to high negative charge and molecular mass. The resulting poor intracellular bioavailability greatly limits their therapeutic potential. Gamma glutamyl hydrolase (GGH) enzyme removes the glutamate residues from polyglutamates, which then are subject to efflux pumps. Resistance to pemetrexed has been linked to downregulation of both FPGS and folate transporters and upregulation of both GGH and the efflux pumps. We have been developing a novel class of nanoliposomal polyglutamated-antifolates including: LEAF-1401; nanoliposomal gamma-L pentaglutamated antifolate LEAF-1701; nanoliposomal alpha-L pentaglutamated antifolate These were designed to address key challenges of currently used antifolates namely: Bypassing the need for intracellular endogenous FPGS Direct delivery of the much more active polyglutamates through nanoliposome technology Minimizing toxicity to normal cells Mitigating against key antifolate resistance mechanisms such as downregulation of FPGS and folate transporters, and upregulation of GGH and efflux pumps Methods: In vitro testing in cell lines and in vivo testing in mice were performed using LEAF-1701 and LEAF-1401 in various tumor types. Results: Compared to pemetrexed: In vitro, LEAF-1701 and LEAF-1401 were more potent, in various cell lines while sparing normal neutrophils, colon and liver cells. In vivo, in H292 lung cancer xenografts, treatment with LEAF-1701 improved survival to 59 days vs 39 days for pemetrexed. In A549 lung cancer mouse orthotopic models, treatment with LEAF-1401 reduced metastatic tumor burden and prevented new metastases. In vivo, in mice doses of up to 80 mg/kg IV weekly were tolerated with little impact on blood counts and chemistry. Conclusions: LEAF-1701 and LEAF-1401 are innovative new chemical entities with promising preclinical activity and improved safety profiles and are now advancing to the clinic.