Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.5.1.3 (dihydrofolate reductase)
 5,819 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have previously demonstrated systemic resistance to methotrexate (MTX) in transgenic mice carrying a foreign, mutant dihydrofolate reductase (DHFR, E.C. 1.5.1.3) gene. The new gene was introduced as a cDNA cloned into an expression vector driven by the simian virus 40 (SV40) early promoter. Previous physiologic studies suggested that transgenic mice tolerated drug doses invariably lethal to controls on the basis of gastrointestinal (GI) resistance to MTX. In the present study we evaluated foreign gene expression at the RNA level in the three major sites of MTX toxicity: intestine, liver, and bone marrow. The transgene was transcriptionally active in small bowel, and levels of expression were high in animals tolerating the largest doses of MTX. The gene was also expressed in the liver in some pedigrees, but was not detected in hemopoietic tissues of any of the pedigrees tested. Our studies correlate the site of expression of a drug resistant dhfr gene with an altered physiologic response to MTX, and demonstrate that transgenic mice can be used as a test system for expression of genes considered for use in somatic gene therapy.
 ...
PMID:Expression of a methotrexate resistant dihydrofolate reductase gene in transgenic mice. 248 Aug 60

Synthesis of poly-gamma-glutamyl metabolites of methotrexate was demonstrated in mouse small intestine, liver, and bone marrow and in L1210 leukemia, Sarcoma 180, and Ehrlich tumor cells after s.c. injections of [3H]methotrexate to tumor-bearing mice. Ion-exchange chromatography of tissue extracts resolved six peaks of radioactivity believed to represent methotrexate and metabolites with up to five additional glutamyl residues. Polyglutamate formation in L1210 cells and small intestine was shown to be independent of dose at least to 400 mg/kg as long as intracellular levels of drug in excess of the dihydrofolate reductase-binding capacity (exchangeable) were maintained. Both the total amount of polyglutamates and the average length of the polyglutamyl chain increased with time as long as exchangeable level of drug was present intracellularly. The results also showed differences in the extent of metabolism of methotrexate polyglutamates among the tissues examined. Although these differences were at times very large, there was no consistent correlation between these differences and other pharmacological parameters or cytotoxicity. Tumor cells appeared to synthesize more polyglutamates than did the normal tissues examined. However, differences in total drug persistence and sensitivity to drug among tumor cells and among normal tissues did not reflect the relative extent of polyglutamate synthesis in each group. It is concluded that the extent of polyglutamate synthesis per se may not be a determinant of drug sensitivity in murine tissues. However, the accumulation of these metabolites may contribute in some way to overall therapeutic response or relative cytotoxicity.
 ...
PMID:Differential synthesis of methotrexate polyglutamates in normal proliferative and neoplastic mouse tissues in vivo. 617 39

Synthesis of poly-gamma-glutamyl metabolites of methotrexate was demonstrated in mouse small intestine, liver and bone marrow, and in L1210 leukemia, Sarcoma 180 and Ehrlich tumor cells after sc injections of [3H]methotrexate to tumor bearing mice. Ion exchange chromatography of tissue extracts resolved six peaks of radioactivity believed to represent methotrexate and metabolites with up to 4 additional glutamyl residues. Polyglutamate formation in L1210 cells and small intestine was shown to be independent of dose at least to 400 mg/kg as long as intracellular levels of drug in excess of the dihydrofolate reductase binding capacity (exchangeable) were maintained. Both the total amount of polyglutamates and the average length of the polyglutamyl chain increased with time as long as exchangeable level of drug were present intracellularily. The results also showed differences in the extent of metabolism of methotrexate polyglutamates among the tissues examined. Although, these differences were at times very large, there was no consistent correlation between these differences and other pharmacologic parameters or cytoxicity. Tumor cells appeared to synthesize more polyglutamates than the normal tissues examined. However, differences in total drug persistence and sensitivity to drug among tumor cells and among normal tissues did not reflect the relative extent of polyglutamate synthesis in each group. We observed no selective retention of polyglutamates as compared to methotrexate by L1210 cells in vitro as indicated by the extracellular accumulation during efflux of methotrexate and the polyglutamates. This could only be demonstrated by allowing efflux of intracellular drug in the presence of extracellular dihydrofolate reductase, which averted hydrolysis of the polyglutamates. It is concluded that the extent of polyglutamate synthesis per se may not be a determinant of drug sensitivity in murine tissues. However, the accumulation of these metabolites may contribute in some way to overall therapeutic response or relative cytotoxicity.
 ...
PMID:Studies on the in vivo synthesis of methotrexate polyglutamates and their efflux properties in normal, proliferative, and neoplastic mouse tissues. 619 89

Folate is a vitamin that plays a role as a cofactor and coenzyme in many essential reactions. These reactions are interrelated and any change in folate homeostasis could affect other reactions. With food fortified with folic acid, and use of multivitamin, unmetabolized folic acid (UMFA) has been detected in blood circulation, particularly among older adults. This has raised concern about the potential harmful effect of high folic acid intake and UMFA on health conditions such as cognitive dysfunction and cancer. To examine what is known about folate metabolism and the release of circulating UMFA, the Key Events Dose-Response Framework (KEDRF) was used to review each of the major key events, dose-response characteristics and homeostatic mechanisms of folate metabolism. The intestine, liver and kidneys each play essential roles in regulating body folate homeostasis. But the determining event in folate metabolism leading to the release of UMFA in circulation appears to be the saturation of dihydrofolate reductase in the liver. However, at each of the key events in folate metabolism, limited information is available on threshold, homeostatic regulation and intracellular effects of folic acid. More studies are needed to fill in the knowledge gaps for quantitatively characterizing the dose-effect relationship especially in light of the call for extending folate fortification to other foods.
...
PMID:Application of the Key Events Dose-response Framework to Folate Metabolism. 2567 17