The importance of inhibition of a catabolic pathway of methotrexate metabolism in its efficacy for rheumatoid arthritis.

Methotrexate (MTX), an antifolate, is the anchor drug for the treatment of rheumatoid arthritis (RA). It is inexpensive, effective, and generally safe. When clinical response is inadequate, biological therapies are commonly used in combination with MTX.

Folate-Dependent Purine Nucleotide Biosynthesis in Humans.

Purine nucleotide biosynthesis de novo (PNB) requires 2 folate-dependent transformylases-5'-phosphoribosyl-glycinamide (GAR) and 5'-phosphoribosyl-5-aminoimidazole-4-carboxamide (AICAR) transformylases-to introduce carbon 8 (C8) and carbon 2 (C2) into the purine ring. Both transformylases utilize 10-formyltetrahydrofolate (10-formyl-H4folate), where the formyl-carbon sources include ring-2-C of histidine, 3-C of serine, 2-C of glycine, and formate. Our findings in human studies indicate that glycine provides the carbon for GAR transformylase (exclusively C8), whereas histidine and formate are the predominant carbon sources for AICAR transformylase (C2).

Homocysteine, iron and cardiovascular disease: a hypothesis.

Elevated circulating total homocysteine (tHcy) concentrations (hyperhomocysteinemia) have been regarded as an independent risk factor for cardiovascular disease (CVD). However, several large clinical trials to correct hyperhomocysteinemia using B-vitamin supplements (particularly folic acid) have largely failed to reduce the risk of CVD. There is no doubt that a large segment of patients with CVD have hyperhomocysteinemia; therefore, it is reasonable to postulate that circulating tHcy concentrations are in part a surrogate marker for another, yet-to-be-identified risk factor(s) for CVD.

13C-enrichment of urinary uric acid after L-[Ring-2-13C]histidine dose in adult humans.

We determined whether ring-2 carbon of histidine is folate-dependently transferred to carbons 8 (C8) and/or 2 (C2) in urinary uric acid in humans. Two adults collected each urine void for four days. Aliquots of urine for the first day were used for baseline values; then the subjects ingested 0.

Meta-analysis of cancer risk in folic acid supplementation trials.

Several reports suggest that folate has a procarcinogenic effect. Folate has a unique role because its coenzymes are needed for de novo purine and thymine nucleotide biosynthesis. Antifolates, such as methotrexate, are used in cancer treatment.

Phenotypes and circadian rhythm in utilization of formate in purine nucleotide biosynthesis de novo in adult humans.

Aims: Folate coenzymes and dependent enzymes introduce one carbon units at positions 2 (C(2)) and 8 (C(8)) of the purine ring during de novo biosynthesis. Formate is one source of one-carbon units. Although much is known about lower organisms, little data exists describing formate utilization for purine biosynthesis in humans.

Measurement of erythrocyte methotrexate polyglutamate levels: ready for clinical use in rheumatoid arthritis?

Methotrexate (MTX) is one of the most commonly prescribed and most effective drugs for the treatment of rheumatoid arthritis (RA). Given the partial response of many patients and the side effect profile of the drug, there is considerable interest in identifying biomarkers to guide MTX therapy in RA. Upon entering cells, MTX is polyglutamated.

Evidence for the hypothesis that 10-formyldihydrofolate is the in vivo substrate for aminoimidazolecarboxamide ribotide transformylase.

We postulate that 10-formyl-7,8-dihydrofolate (10-HCO-H(2)folate), not 10-formyl-5,6,7,8-tetrahydrofolate (10-HCO-H(4)folate), is the predominant in vivo substrate for mammalian aminoimidazolecarboxamide ribotide (AICAR) transformylase, an enzyme in purine nucleotide biosynthesis de novo, which introduces carbon 2 (C(2)) into the purine ring. 10-HCO-H(2)folate exists in vivo as labeled 10-formyl-folic acid (10-HCO-folic acid: an oxidation product of 10-HCO-H(4)folate and 10-HCO-H(2)folate) and is found after doses of labeled folic acid in humans or laboratory animals. The bioactivity of the unnatural isomer, [6R]-5-formyltetrahydrofolate, in humans is explained by its in vivo conversion to 10-HCO-H(2)folate.

The safety of flavocoxid, a medical food, in the dietary management of knee osteoarthritis.

This study was designed to determine the safety of a medical food, flavocoxid, a proprietary blend of free-B ring flavonoids and flavans from the root of Scutellaria baicalensis (Chinese skullcap) and the bark of Acacia catechu in the dietary management of knee osteoarthritis. The 12-week, randomized, double-blind, placebo-controlled trial in an academic medical center enrolled 59 patients with moderate osteoarthritis of at least one knee who were recruited who were classified as having "below average" to "a moderately above average cardiovascular risk" with a Framingham-based scoring tool. Subjects were randomized to flavocoxid 250 mg twice a day versus identical placebo.

Methotrexate catabolism to 7-hydroxymethotrexate in rheumatoid arthritis alters drug efficacy and retention and is reduced by folic acid supplementation.

Objective: To assess the catabolism of methotrexate (MTX) to 7-hydroxy-MTX (7-OH-MTX) in patients with rheumatoid arthritis as well as the effect of folic acid and folinic acid on this catabolism.

Methods: Urinary excretion of MTX and its catabolite, 7-OH-MTX, was measured in 2 24-hour urine specimens collected after MTX therapy. Urine samples were collected from patients after the sixth and seventh weekly doses of MTX.

13C-enrichment at carbons 8 and 2 of uric acid after 13C-labeled folate dose in man.

To evaluate folate-dependent carbon incorporation into the purine ring, we measured (13)C-enrichment independently at C(2) and C(8) of urinary uric acid (the final catabolite of purines) in a healthy male after an independent oral dose of [6RS]-5-[(13)C]-formyltetrahydrofolate ([6RS]-5-H(13)CO-H(4)folate) or 10-H(13)CO-7,8-dihydrofolate (10-H(13)CO-H(2)folate). The C(2) position was (13)C-enriched more than C(8) after [6RS]-5-H(13)CO-H(4)folate, and C(2) was exclusively enriched after 10-H(13)CO-H(2)folate. The enrichment of C(2) was greater from [6RS]-5-H(13)CO-H(4)folate than 10-H(13)CO-H(2)folate using equimolar bioactive doses.

13C enrichment of carbons 2 and 8 of purine by folate-dependent reactions after [13C]formate and [2-13C]glycine dosing in adult humans.

The 10-formyl moiety of 10-formyltetrahydrofolate is the source of carbons at the positions 8 (C(8)) and 2 (C(2)) of the purine ring, originating from formate and a few amino acids. Uric acid is the final catabolic product of purines. In adult humans, we independently measured the (13)C enrichment of the C(2) and C(8) positions of urinary uric acid after an oral dose of [(13)C]sodium formate and that of the C(2) and C(8) plus C(5) positions after [2-(13)C]glycine.

Methotrexate and erythro-9-(2-hydroxynon-3-yl) adenine therapy for rat adjuvant arthritis and the effect of methotrexate on in vivo purine metabolism.

The objectives were: (1) to test the association of methotrexate (MTX) efficacy in rat adjuvant arthritis (rat AA) with interference of purine biosynthesis and adenosine metabolism and (2) to test the efficacy of erythro-9-(2-hydroxynon-3-yl) adenine (EHNA), an inhibitor of adenosine deaminase, and the efficacy of aminoimidazolecarboxamide (AICA) riboside plus MTX in rat AA. Radiographic and histologic examinations of the hind limbs were measures of efficacy. Urinary excretions of AICA and adenosine were markers of AICA ribotide transformylase inhibition (i.

Medical foods: products for the management of chronic diseases.

Medical foods are a specific category of therapeutic agents created under the Orphan Drug Act of 1988, which separated medical foods from drugs for regulatory purposes. Products in this category share the requirements that they are intended for the nutritional management of a specific disease, are used under the guidance of a physician, and contain ingredients that are generally recognized as safe (GRAS). An example of medical foods are formulations intended to manage patients with inborn errors in amino acid metabolism.

The effect of folic acid and folinic acid supplements on purine metabolism in methotrexate-treated rheumatoid arthritis.

Objective: To determine if folinic acid supplementation during methotrexate (MTX) therapy for rheumatoid arthritis (RA) reduces both urinary 5-aminoimidazole-4-carboxamide (AICA) and urinary adenosine excretion more than does folic acid supplementation. AICA and adenosine are markers for MTX interference with purine metabolism.

Methods: Forty patients with RA who received MTX for 6 weeks were randomized to receive either daily folic acid or folinic acid supplements during an additional week of MTX therapy.

Effect of methotrexate therapy on bone mineral density and body composition in rat adjuvant arthritis.

Objective: To test whether methotrexate (MTX) therapy of rat adjuvant arthritis (AA) prevents loss of bone mineral density (BMD) and loss of adipose and lean body mass compared to pair-fed controls with untreated rat AA (positive controls) and rats without AA (negative controls).

Methods: AA was induced by a Mycobacterium butyricum injection at the base of the tail of 5-week-old female Lewis rats. The MTX-treated group was injected with adjuvant and then treated twice weekly with MTX (1.

The energy cost of adjuvant-induced arthritis in rats.

Objective: To test the hypothesis that rats with adjuvant-induced arthritis (AIA) need more metabolic energy to maintain body weight than healthy control rats or rats with AIA treated with methotrexate (MTX).

Methods: Rat AIA was induced by Mycobacterium butyricum injection at the base of the tail. The MTX-treated group was injected with MTX (1.

Mass spectrometric method for detecting carbon 13 enrichment introduced by folate coenzymes in uric acid.

Using [2-13C]uric acid as a test material, we developed a mass spectrometric procedure that detects and estimates the difference in 13C enrichment at the positions of carbons 2 and 8 of the purine ring. This method could replace radiochemical methods and could trace the incorporation of carbon fragments into the purine ring from 13C-labeled metabolites in humans.