PPARδ agonist prevents endothelial dysfunction via induction of dihydrofolate reductase gene and activation of tetrahydrobiopterin salvage pathway.

BACKGROUND AND PURPOSE: Impaired endothelium-dependent relaxation (EDR) is a hallmark of endothelial dysfunction. A deficiency of tetrahydrobiopterin (BH4 ) causes endothelial NOS to produce ROS rather than NO. PPARδ is an emerging target for pharmacological intervention of endothelial dysfunction. Thus, the present study examined the role of PPARδ in the regulation of dihydrofolate reductase (DHFR), a key enzyme in the BH4 salvage pathway. EXPERIMENTAL APPROACH: Gene expression was measured by using qRT-PCR and western blotting. Biopterins and ROS were determined by using HPLC. NO was measured with fluorescent dye and electron paramagnetic resonance spectroscopy. Vasorelaxation was measured by Multi Myograph System. KEY RESULTS: The PPARδ agonist GW501516 increased DHFR and BH4 levels in endothelial cells (ECs). The effect was blocked by PPARδ antagonist GSK0660. Chromatin immunoprecipitation identified PPAR-responsive elements within the 5'-flanking region of the human DHFR gene. The promoter activity was examined with luciferase assays using deletion reporters. Importantly, DHFR expression was suppressed by palmitic acid (PA, a saturated fatty acid) but increased by docosahexaenoic acid (DHA, a polyunsaturated fatty acid). GSK0660 prevented DHA-induced increased DHFR expression. Conversely, the suppressive effect of PA was mitigated by GW501516. In mouse aortae, GW501516 ameliorated the PA-impaired EDR. However, this vasoprotective effect was attenuated by DHFR siRNA or methotrexate. In EC-specific Ppard knockout mice, GW501516 failed to improve vasorelaxation. CONCLUSION AND IMPLICATIONS: PPARδ prevented endothelial dysfunction by increasing DHFR and activating the BH4 salvage pathway. These results provide a novel mechanism for the protective roles of PPARδ against vascular diseases.

miRNA-24 Gene Sequence, DHFR -829C-T Genotypes, and Methotrexate Response in Mexican Patients with Rheumatoid Arthritis.

AIM: The present study looked for variation in the miRNA-24 sequence, and evaluated the associations between the dihydrofolate reductase (DHFR) gene-829 C-T polymorphism and plasma DHFR concentrations with response to methotrexate (MTX) treatment in Mexican patients with rheumatoid arthritis (RA). METHODS: A total of 135 women with RA were classified as responders (disease activity score [DAS28] <3.2) or nonresponders to MTX (DAS28 > 3.2). We determined the genotype of the patients using the polymerase chain reaction-restriction fragment length polymorphism method. Plasma DHFR enzyme levels and mi-RNA24 sequences were assessed by enzyme-linked immunosorbent assay (ELISA) and Sanger sequencing, respectively. Allelic frequencies and the genotypic distribution of the polymorphism were analyzed by the chi-square test. RESULTS: The genotype frequencies of the DHFR -829C-T polymorphism among responders were 37.0% CC, 52.1% CT, and 10.9% TT and for nonresponders were 33.9% CC, 56.4% CT, and 9.7% TT. No significant differences in genotype frequencies were found between the groups (p = 0.88). The DHFR levels relative to genotype for responders were 6.8 ± 2.7, 6.1 ± 2.7, and 6.5 ± 1.5 ng/mL for CC, CT, and TT, respectively, and for nonresponders were 6.5 ± 2.0, 6.1 ± 3.1, and 7.4 ± 1.8 ng/mL for CC, CT, and TT, respectively. No significant differences were found between the two groups. Similarly, both groups showed no sequence variations in miRNA-24 gene. CONCLUSION: The -829C-T polymorphism of DHFR gene was not associated with response to MTX by RA patients, and no variations were found in the miRNA-24 sequence that might modify the response to treatment or DHFR enzyme levels in a Mexican population with RA.

Association of FOLH1, DHFR, and MTHFR gene polymorphisms with susceptibility of Neural Tube Defects: A case control study from Eastern India.

BACKGROUND: Worldwide, Neural tube defects (NTDs) are considered as major clinical problems imposing a huge socio-economic burden for both affected individuals and their families. In India, the prevalence of Neural tube defects is significantly high. This study aims to evaluate the association between genetic defects in folate metabolism pathway genes, mainly: Folate hydrolase 1 (FOLH1), Dihydrofolate reductase (DHFR) and Methylenetetrahydrofolate reductase (MTHFR) and neural tube defects from eastern India. METHODS: We enrolled 62 consecutive mothers with NTDs foetuses as cases and their corresponding age matched 73 mothers with healthy babies as controls (genetic power has been calculated). Four single nucleotide polymorphisms (FOLH1: rs202676, DHFR: rs70991108, MTHFR: rs1801133 and rs1801131) have been amplified by polymerase chain reaction (PCR) and sequenced. Statistical analysis has been undertaken to find out association with NTDs. RESULTS: Genotype and allele frequency analysis of these SNPs revealed that, rs1801133 (p.Ala222Val) was significantly associated with NTDs risk (p value = 0.028; odds ratio-2.31; 95% CI 1.08-4.93), whereas rs202676 (p.Tyr60His) showed protective role (p value = 0.0066; odds ratio-0.11; 95% CI 0.01-0.86). Serum homocysteine (Hcy) concentration was respectively higher in subjects carrying 222Ala/Val and 222Val/Val alleles (p value = 0.009; p value ≤ 0.0001). CONCLUSION: In conclusion, it can be stated that, rs1801133 was associated with neural tube defects risk in patients from the eastern part of India and it might be counted as a molecular marker for evaluating the susceptibility of NTDs.

Antifolate agents: a patent review (2010 - 2013).

INTRODUCTION: The folate biosynthetic pathway, responsible for the de novo synthesis of thymidine and other key cellular components, is essential in all life forms and is especially critical in rapidly proliferating cells. As such, druggable targets along this pathway offer opportunities to impact many disease states such as cancer, infectious disease and autoimmune disease. In this article, recent progress on the development of antifolate compounds is reviewed. AREAS COVERED: The evaluation of the patent literature during the period 2010 - 2013 focused on any compounds inhibiting recognized targets on the folate biosynthetic pathway. EXPERT OPINION: The folate pathway constitutes a well-validated and well-characterized set of targets; this pathway continues to elicit considerable enthusiasm for new drug discovery from both academic and industrial pharmaceutical research groups. Within the pathway, the enzymes dihydrofolate reductase and thymidylate synthase persist as the most attractive targets for new drug discovery for the treatment of cancer and infectious disease. Importantly, new potential targets for antifolates such as those on the purine biosynthetic pathway have been recently explored. The use of structure-based drug design is a major aspect in modern approaches to these drug targets.

Defining the role of mutations in Plasmodium vivax dihydrofolate reductase-thymidylate synthase gene using an episomal Plasmodium falciparum transfection system.

Plasmodium vivax resistance to antifolates is prevalent throughout Australasia and is caused by point mutations within the parasite dihydrofolate reductase (DHFR)-thymidylate synthase. Several unique mutations have been reported in P. vivax DHFR, and their roles in resistance to classic and novel antifolates are not entirely clear due, in part, to the inability to culture P. vivax in vitro. In this study, we use a homologous system to episomally express both wild-type and various mutant P. vivax dhfr (pvdhfr) alleles in an antifolate-sensitive line of P. falciparum and to assess their influences on the susceptibility of the recipient P. falciparum line to commonly used and new antifolate drugs. Although the wild-type pvdhfr-transfected P. falciparum line was as susceptible to antifolate drugs as the P. falciparum parent line, the single (117N), double (57L/117T and 58R/117T), and quadruple (57L/58R/61M/117T) mutant pvdhfr alleles conferred a marked reduction in their susceptibilities to antifolates. The resistance index increased with the number of mutations in these alleles, indicating that these mutations contribute to antifolate resistance directly. In contrast, the triple mutant allele (58R/61M/117T) significantly reversed the resistance to all antifolates, indicating that 61M may be a compensatory mutation. These findings help elucidate the mechanism of antifolate resistance and the effect of existing mutations in the parasite population on the current and new generation of antifolate drugs. It also demonstrates that the episomal transfection system has the potential to provide a rapid screening system for drug development and for studying drug resistance mechanisms in P. vivax.

Mycobacterium tuberculosis dihydrofolate reductase is not a target relevant to the antitubercular activity of isoniazid.

Mycobacterium tuberculosis enoyl-acyl-ACP reductase (InhA) has been demonstrated to be the primary target of isoniazid (INH). Recently, it was postulated that M. tuberculosis dihydrofolate reductase (DHFR) is also a target of INH, based on the findings that a 4R-INH-NADP adduct synthesized from INH by a nonenzymatic approach showed strong inhibition of DHFR in vitro, and overexpression of M. tuberculosis dfrA in M. smegmatis conferred a 2-fold increase of resistance to INH. In the present study, a plasmid expressing M. tuberculosis dfrA was transformed into M. smegmatis and M. tuberculosis strains, respectively. The transformant strains were tested for their resistance to INH. Compared to the wild-type strains, overexpression of dfrA in M. smegmatis and M. tuberculosis did not confer any resistance to INH based on the MIC values. Similar negative results were obtained with 14 other overexpressed proteins that have been proposed to bind some form of INH-NAD(P) adduct. An Escherichia coli cell-based system was designed that allowed coexpression of both M. tuberculosis katG and dfrA genes in the presence of INH. The DHFR protein isolated from the experimental sample was not found bound with any INH-NADP adduct by enzyme inhibition assay and mass spectroscopic analysis. We also used whole-genome sequencing to determine whether polymorphisms in dfrA could be detected in six INH-resistant clinical isolates known to lack mutations in inhA and katG, but no such mutations were found. The dfrA overexpression experiments, together with the biochemical and sequencing studies, conclusively demonstrate that DHFR is not a target relevant to the antitubercular activity of INH.

FolX and FolM are essential for tetrahydromonapterin synthesis in Escherichia coli and Pseudomonas aeruginosa.

Tetrahydromonapterin is a major pterin in Escherichia coli and is hypothesized to be the cofactor for phenylalanine hydroxylase (PhhA) in Pseudomonas aeruginosa, but neither its biosynthetic origin nor its cofactor role has been clearly demonstrated. A comparative genomics analysis implicated the enigmatic folX and folM genes in tetrahydromonapterin synthesis via their phyletic distribution and chromosomal clustering patterns. folX encodes dihydroneopterin triphosphate epimerase, which interconverts dihydroneopterin triphosphate and dihydromonapterin triphosphate. folM encodes an unusual short-chain dehydrogenase/reductase known to have dihydrofolate and dihydrobiopterin reductase activity. The roles of FolX and FolM were tested experimentally first in E. coli, which lacks PhhA and in which the expression of P. aeruginosa PhhA plus the recycling enzyme pterin 4a-carbinolamine dehydratase, PhhB, rescues tyrosine auxotrophy. This rescue was abrogated by deleting folX or folM and restored by expressing the deleted gene from a plasmid. The folX deletion selectively eliminated tetrahydromonapterin production, which far exceeded folate production. Purified FolM showed high, NADPH-dependent dihydromonapterin reductase activity. These results were substantiated in P. aeruginosa by deleting tyrA (making PhhA the sole source of tyrosine) and folX. The DeltatyrA strain was, as expected, prototrophic for tyrosine, whereas the DeltatyrA DeltafolX strain was auxotrophic. As in E. coli, the folX deletant lacked tetrahydromonapterin. Collectively, these data establish that tetrahydromonapterin formation requires both FolX and FolM, that tetrahydromonapterin is the physiological cofactor for PhhA, and that tetrahydromonapterin can outrank folate as an end product of pterin biosynthesis.

Pivotal role of dihydrofolate reductase knockdown in the anticancer activity of 2-hydroxyoleic acid.

alpha-Hydroxy-9-cis-octadecenoic acid, a synthetic fatty acid that modifies the composition and structure of lipid membranes. 2-Hydroxyoleic acid (HOA) generated interest due to its potent, yet nontoxic, anticancer activity. It induces cell cycle arrest in human lung cancer (A549) cells and apoptosis in human leukemia (Jurkat) cells. These two pathways may explain how HOA induces regression of a variety of cancers. We showed that HOA repressed the expression of dihydrofolate reductase (DHFR), the enzyme responsible for tetrahydrofolate (THF) synthesis. Folinic acid, which readily produces THF without the participation of DHFR, reverses the antitumor effects of HOA in A549 and Jurkat cells, as well as the inhibitory influence on cyclin D and cdk2 in A549 cells, and on DNA and PARP degradation in Jurkat cells. This effect was very specific, because either elaidic acid (an analog of HOA) or other lipids, failed to alter A549 or Jurkat cell growth. THF is a cofactor necessary for DNA synthesis. Thus, impairment of DNA synthesis appears to be a common mechanism involved in the different responses elicited by cancer cells following treatment with HOA, namely cell cycle arrest or apoptosis. Compared with other antifolates, such as methotrexate, HOA did not directly inhibit DHFR but rather, it repressed its expression, a mode of action that offers certain therapeutic advantages. These results not only demonstrate the effect of a fatty acid on the expression of DHFR, but also emphasize the potential of HOA to be used as a wide-spectrum drug against cancer.

[Folate metabolism dysfunction]. / Alterazioni del metabolismo dell'aciso folico.

This review examines the history of folate, its metabolism and its relationship to drugs and diseases. The scientific interest in folate has been increasing in recent years because of new findings related to its important role in many diseases like macrocytic anemia, congenital malformations, vascular thrombosis, atherosclerotic disease and cancer. The fascinating puzzle of folate is analyzed and the most recent news about folate treatment in patients with chronic renal failure is reported.

Detection of protein-protein interactions using a simple survival protein-fragment complementation assay based on the enzyme dihydrofolate reductase.

Biochemical 'pathways' are systems of dynamically assembling and disassembling protein complexes, and thus, much of modern biological research is concerned with how, when and where proteins interact with other proteins involved in biochemical processes. The demand for simple approaches to study protein-protein interactions, particularly on a large scale, has grown recently with the progress in genome projects, as the association of unknown with known gene products provides one crucial way of establishing the function of a gene. It was with this challenge in mind that our laboratory developed a simple survival protein-fragment complementation assay (PCA) based on the enzyme dihydrofolate reductase (DHFR). In the DHFR PCA strategy, two proteins of interest are fused to complementary fragments of DHFR. If the proteins of interest interact physically, the DHFR complementary fragments are brought together and fold into the native structure of the enzyme, reconstituting its activity, detectable by the survival of cells expressing the fusion proteins and growth in selective medium. Using the protocol described here, the survival selection can be completed in one to several days, depending on the cell type.

Effect of dihydrofolate reductase gene knock-down on the expression of heart and neural crest derivatives expressed transcript 2 in zebrafish cardiac development.

BACKGROUND: Folic acid is very important for embryonic development and dihydrofolate reductase is one of the key enzymes in the process of folic acid performing its biological function. Therefore, the dysfunction of dihydrofolate reductase can inhibit the function of folic acid and finally cause the developmental malformations. In this study, we observed the abnormal cardiac phenotypes in dihydrofolate reductase (DHFR) gene knock-down zebrafish embryos, investigated the effect of DHFR on the expression of heart and neural crest derivatives expressed transcript 2 (HAND2) and explored the possible mechanism of DHFR knock-down inducing zebrafish cardiac malformations. METHODS: Morpholino oligonucleotides were microinjected into fertilized eggs to knock down the functions of DHFR or HAND2. Full length of HAND2 mRNA which was transcribed in vitro was microinjected into fertilized eggs to overexpress HAND2. The cardiac morphologies, the heart rates and the ventricular shortening fraction were observed and recorded under the microscope at 48 hours post fertilization. Whole-mount in situ hybridization and real-time PCR were performed to detect HAND2 expression. RESULTS: DHFR or HAND2 knock-down caused the cardiac malformation in zebrafish. The expression of HAND2 was obviously reduced in DHFR knock-down embryos (P < 0.05). Microinjecting HAND2 mRNA into fertilized eggs can induce HAND2 overexpression. HAND2 overexpression rescued the cardiac malformation phenotypes of DHFR knock-down embryos. CONCLUSIONS: DHFR plays a crucial role in cardiac development. The down-regulation of HAND2 caused by DHFR knock-down is the possible mechanism of DHFR knock-down inducing the cardiac malformation.

Substrate and inhibitor specificity of Mycobacterium avium dihydrofolate reductase.

Dihydrofolate reductase (EC 1.5.1.3) is a key enzyme in the folate biosynthetic pathway. Information regarding key residues in the dihydrofolate-binding site of Mycobacterium avium dihydrofolate reductase is lacking. On the basis of previous information, Asp31 and Leu32 were selected as residues that are potentially important in interactions with dihydrofolate and antifolates (e.g. trimethoprim), respectively. Asp31 and Leu32 were modified by site-directed mutagenesis, giving the mutants D31A, D31E, D31Q, D31N and D31L, and L32A, L32F and L32D. Mutated proteins were expressed in Escherichia coli BL21(DE3)pLysS and purified using His-Bind resin; functionality was assessed in comparison with the recombinant wild type by a standard enzyme assay, and growth complementation and kinetic parameters were evaluated. All Asp31 substitutions affected enzyme function; D31E, D31Q and D31N reduced activity by 80-90%, and D31A and D31L by > 90%. All D31 mutants had modified kinetics, ranging from three-fold (D31N) to 283-fold (D31L) increases in K(m) for dihydrofolate, and 12-fold (D31N) to 223 077-fold (D31L) decreases in k(cat)/K(m). Of the Leu32 substitutions, only L32D caused reduced enzyme activity (67%) and kinetic differences from the wild type (seven-fold increase in K(m); 21-fold decrease in k(cat)/K(m)). Only minor variations in the K(m) for NADPH were observed for all substitutions. Whereas the L32F mutant retained similar trimethoprim affinity as the wild type, the L32A mutation resulted in a 12-fold decrease in affinity and the L32D mutation resulted in a seven-fold increase in affinity for trimethoprim. These findings support the hypotheses that Asp31 plays a functional role in binding of the substrate and Leu32 plays a functional role in binding of trimethoprim.

Cyclin D1 antisense oligodexoyneucleotides inhibits growth and enhances chemosensitivity in gastric carcinoma cells.

AIM: To examine the effects of cyclin D1 antisense oligodexoyneucleotides (ASODN) on growth and chemosensitivity of gastric carcinoma cell lines SGC7901 and its mechanism. METHODS: Phosphorothioate modified cyclin D1 ASODN was encapsulated by LipofectAMINE2000 (LF2000) and transfected into cells, the dose-effect curves and growth curves were observed. 5-FU, MTX, CDDP of different concentrations were given after transfecting cells with cyclin D1 ASODN for 24 h the dose-effect responses were observed and IC50s were calculated. The mRNA expression of cyclin D1, thymidylate synthase (TS), thymidine phosphorylase (TP) and dihydrofolate reductase (DHFR) was detected by reverse transcription-PCR (RT-PCR) at 24 h and 48 h after transfection. RESULTS: Dose-dependent inhibitory effect was caused by cyclin D1 ASODN in SGC7901 cells. Transfecting gastric carcinoma cells with 0.2 micromol/L cyclin D1 ASODN for 24 h could inhibit growth significantly and reduce expression of cyclin D1 mRNA. Cyclin D1 ASODN could increase the chemosensitivity to 5-FU, MTX, CDDP in cells. The IC50s of different chemotherapeutic agents in ASODN plus chemotherapy groups were significantly lower than those in controls. Transfection with cyclin D1 ASODN leaded to an increase in TS and DHFR mRNA and a decrease in TP mRNA as determined by RT-PCR at 24 h, the alterations were more significant at 48 h. CONCLUSIONS: Cyclin D1 ASODN can decrease mRNA expression of cyclin D1, inhibit growth and enhance the chemosensitivity by changing the expression of enzymes related to metabolism of chemotherapeutic agents in SGC7901 gastric carcinoma cells.

Mechanisms of resistance of malaria parasites to antifolates.

Antifolate antimalarial drugs interfere with folate metabolism, a pathway essential to malaria parasite survival. This class of drugs includes effective causal prophylactic and therapeutic agents, some of which act synergistically when used in combination. Unfortunately, the antifolates have proven susceptible to resistance in the malaria parasite. Resistance is caused by point mutations in dihydrofolate reductase and dihydropteroate synthase, the two key enzymes in the folate biosynthetic pathway that are targeted by the antifolates. Resistance to these drugs arises relatively rapidly in response to drug pressure and is now common worldwide. Nevertheless, antifolate drugs remain first-line agents in several sub-Saharan African countries where chloroquine resistance is widespread, at least partially because they remain the only affordable, effective alternative. New antifolate combinations that are more effective against resistant parasites are being developed and in one case, recently introduced into use. Combining these antifolates with drugs that act on different targets in the parasite should greatly enhance their effectiveness as well as deter the development of resistance. Molecular epidemiological techniques for monitoring parasite drug resistance may contribute to development of strategies for prolonging the useful therapeutic life of this important class of drugs.

Multicopy suppressors for novel antibacterial compounds reveal targets and drug efflux susceptibility.

Gene dosage has frequently been exploited to select for genetic interactions between a particular mutant and clones from a random genomic library at high copy. We report here the first use of multicopy suppression as a forward genetic method to determine cellular targets and potential resistance mechanisms for novel antibacterial compounds identified through high-throughput screening. A screen of 8640 small molecules for growth inhibition of a hyperpermeable strain of Escherichia coli led to the identification of 49 leads for suppressor selection from clones harboring an E. coli genomic library. The majority of suppressors were found to encode the multidrug efflux pump AcrB, indicating that those compounds were substrates for efflux. Two leads, which produced clones containing the gene folA, encoding dihydrofolate reductase (DHFR), proved to target DHFR in vivo and were competitive inhibitors in vitro.

Protection and selection for gene therapy in the hematopoietic system.

Hematopoietic stem cell gene therapy is potentially curative for a number of inherited and acquired disorders. However, poor gene transfer and expression in repopulating hematopoietic stem cells attenuate this potential. Here we review potential means of conferring a selective advantage to hematopoietic stem cells and their progeny, and discuss the issues that surround the use of selective advantages in vivo.

Dihydropteridine reductase as an alternative to dihydrofolate reductase for synthesis of tetrahydrofolate in Thermus thermophilus.

A strategy devised to isolate a gene coding for a dihydrofolate reductase from Thermus thermophilus DNA delivered only clones harboring instead a gene (the T. thermophilus dehydrogenase [DH(Tt)] gene) coding for a dihydropteridine reductase which displays considerable dihydrofolate reductase activity (about 20% of the activity detected with 6,7-dimethyl-7,8-dihydropterine in the quinonoid form as a substrate). DH(Tt) appears to account for the synthesis of tetrahydrofolate in this bacterium, since a classical dihydrofolate reductase gene could not be found in the recently determined genome nucleotide sequence (A. Henne, personal communication). The derived amino acid sequence displays most of the highly conserved cofactor and active-site residues present in enzymes of the short-chain dehydrogenase/reductase family. The enzyme has no pteridine-independent oxidoreductase activity, in contrast to Escherichia coli dihydropteridine reductase, and thus appears more similar to mammalian dihydropteridine reductases, which do not contain a flavin prosthetic group. We suggest that bifunctional dihydropteridine reductases may be responsible for the synthesis of tetrahydrofolate in other bacteria, as well as archaea, that have been reported to lack a classical dihydrofolate reductase but for which possible substitutes have not yet been identified.