Simple separation of adenine and adenosyl-sulfur compounds by high-performance liquid chromatography

Selection of a Mimotope Peptide of S-adenosyl-l-homocysteine and Its Application in Immunoassays

A competitive immunoassay for S-adenosyl-l-homocysteine (SAH) has been used in the clinical test for homocysteine via an enzymatic conversion reaction. Since S-adenosyl-l-homocysteine is a relatively unstable compound, we have used peptide library phage display to select a new mimotope peptide that interacts with the anti-SAH antibody. By immobilizing the synthetic peptide on solid phase as a competitive surrogate for SAH, we demonstrate its utility in a competitive ELISA assay. The linear range of the assay for SAH was 0.4–6.4 µM, in good correlation to the conventional assay using an SAH-conjugated plate. Our results show that the mimotope peptide has potential to substitute for SAH in immunoassays.

Inhibition of catechol O-methyltransferase-catalyzed O-methylation of 2- and 4-hydroxyestradiol by quercetin. Possible role in estradiol-induced tumorigenesis

Catecholestrogens have been postulated to mediate the induction of kidney tumors by estradiol in male Syrian hamsters. In this study, we examined the mechanism of inhibition by quercetin of the catechol O-methyltransferase-catalyzed O-methylation of catecholestrogens as a basis for the previously reported enhancement of estradiol-induced tumorigenesis by this flavonoid. In hamsters treated with 50 micrograms of [6,7-3H]estradiol, quercetin increased concentrations of 2- and 4-hydroxyestradiol in kidney by 80 and 59%, respectively. In animals treated with two 10-mg estradiol implants, quercetin also decreased by 63-65% the urinary excretion of 2- and 4-hydroxyestradiol monomethyl ethers. Taken together, these results demonstrate the in vivo inhibition of the O-methylation of catecholestrogens by quercetin. S-Adenosyl-L-homocysteine, produced by the methylation of catecholestrogens, noncompetitively inhibited the O-methylation of 2- and 4-hydroxyestradiol by hamster kidney cytosolic catechol O-methyltransferase (IC50 approximately 10-14 microM). Due to the rapid O-methylation of quercetin itself, quercetin decreased renal concentrations of S-adenosyl-L-methionine by approximately 25% in control or estradiol-treated hamsters and increased concentrations of S-adenosyl-L-homocysteine by 5-15 nmol/g of wet tissue, which was estimated to cause a 30-70% inhibition of the enzymatic O-methylation of catecholestrogens. Quercetin or fisetin (a structural analog) inhibited the O-methylation of 2- and 4-hydroxyestradiol by a competitive plus noncompetitive mechanism (IC50 approximately 2-5 microM). These results suggest that the in vivo O-methylation of catecholestrogens is inhibited more by S-adenosyl-L-homocysteine than by quercetin. The accumulation of 2- and 4-hydroxyestradiol during co-administration of estradiol and quercetin may enhance metabolic redox cycling of catecholestrogens and thus estradiol-induced kidney tumorigenesis.

Two-dimensional high-performance liquid chromatographic method for assaying S-adenosyl-L-methionine and its related metabolites in tissues

S-Adenosyl-L-methionine (SAM) is a methyl-donor compound which is actively involved in a variety of biochemical reactions. An assay has been developed permitting the quantitative measurement of SAM and its related metabolites (S-adenosylhomocysteine, decarboxylated SAM, methylthioadenosine, adenosine and adenine) in liver and cell cultures. As gradient reversed-phase chromatographic or cation-exchange chromatographic methods often resulted in overlapping peaks, a two-dimensional high-performance liquid chromatographic (HPLC) procedure was developed involving gradient reversed-phase chromatographic separation followed by ion-exchange chromatography. After precipitating large molecules in the sample by perchloric acid, gel permeation was carried out on a Sephadex G 25 column to separate small water-soluble metabolites from proteins and membrane fragments. The freeze-dried sample was injected onto an ODS column and a 0-10% acetonitrile gradient in 10 mM ammonium formate buffer (pH 2.9) (20 min, linear) was applied. The relevant fractions were collected and injected onto a cation-exchange column (Partisil SCX, 10 microns, 250 mm x 4.6 mm I.D.). Elution and quantification were carried out using ammonium formate buffers of various concentration (15-400 mM), pH 2.9. The detector response (254 nm) as a function of concentration was linear over the concentration range 30-500 pmol. The detection limits of the compounds after the two-dimensional chromatographic procedure ranged from 10 to 60 pmol and the recovery was higher than 70%. The reproducibility of the results obtained from given samples was within 9-22% for rat liver and 6-24% for mast cells.

A comparative study of the reversed-phase HPLC retention behaviour of S-adenosyl-L-methionine and its related metabolites on Hypersil ODS and Supelcosil LC-ABZ stationary phases

S-Adenosyl-L-methionine (SAM) and its metabolites S-adenosyl-L-homocysteine (SAH) and methyl-thioadenosine (MTA) are endogenous compounds that are heavily involved in a variety of biochemical processes, and have therefore been the target for several assays in body fluids and tissues. Reversed-phase chromatographic behaviour of SAM and its metabolites has been studied by using Supelcosil LC-ABZ column, specially designed for analysis of acidic, basic, zwitterionic and neutral compounds, and on a Hypersil ODS column as a function of mobile phase pH. The retentions of the compounds, expressed by the capacity ratio (k'), are measured on both column with mobile phases comprised of 10% acetonitrile and 10 mM ammonium formate buffer with pH values ranging from 2 to 9. Higher selectivity is observed on Supelcosil LC-ABZ within pH range 4-6. Different retention properties are observed at very low pH and seemed as if the Supelcosil LC-ABZ column reduced the effect of the mobile phase pH by about 1 pH unit. Whilst the Supelcosil column can be recommended for the routine analysis of SAM and its related metabolites in biological fluids by using mobile phase pH 5, the Hypersil ODS column may be suggested for use with mobile phase pH values of 3-4.

Quantification of erythrocyte S-adenosyl-L-methionine levels and its application in enzyme studies

A highly selective high-performance liquid chromatographic method for the quantification of human erythrocyte S-adenosyl-L-methionine levels is described. A strong cation-exchange sorbent with propylsulphonic acid functional groups was used to extract S-adenosyl-L-methionine and S-adenosylethionine (internal standard) from erythrocytes. Quantification of erythrocyte S-adenosyl-L-methionine levels was achieved by using reversed-phase high-performance liquid chromatography and ultraviolet detection at 254 nm. This method was adapted to measure methionine-adenosyltransferase activity in erythrocytes, which enables us to study the possible role of altered methylation in different diseases.

Cerebrospinal fluid concentrations of S-adenosylmethionine, methionine, and 5-methyltetrahydrofolate in a reference population: cerebrospinal fluid S-adenosylmethionine declines with age in humans

Cerebrospinal fluid concentrations of S-adenosylmethionine, methionine, and 5-methyltetrahydrofolate were measured in 80 children and young adults in whom there was no disturbance of the methyl transfer pathway. Cerebrospinal fluid was collected under standardized conditions and analyzed by high-performance liquid chromatography. S-Adenosylmethionine, but not methionine nor 5-methyltetrahydrofolate, concentrations declined sharply during the first year of life. There was no correlation between concentrations of S-adenosylmethionine and methionine or 5-methyltetrahydrofolate. Reference ranges for the three metabolites are given.

A method for the measurement of S-adenosylmethionine in small volume samples of cerebrospinal fluid or brain using high-performance liquid chromatography-electrochemistry

A method for the measurement of S-adenosylmethionine in cerebrospinal fluid and brain using high-performance liquid chromatography with electrochemical detection is described. The method is based upon the catechol O-methyltransferase-catalyzed methylation of dihydroxybenzylamine to its 3- and 4-methoxy derivatives and measurement of the latter. Detection limits are 0.1 pmol for 3- and 4-methoxyhydroxybenzylamine, recovery is 100%, and variability is less than 8%. HPLC measurement of 3- and 4-methoxyhydroxybenzylamine is linear up to at least 100 pmol injected. The use of a nonbiological catechol in the assay minimizes interference from endogenous and exogenous catechols and the wide limits of linearity allows the assay of small volumes of cerebrospinal fluid or brain extract without further concentration or dilution.

Metabolism of S-adenosyl-L-methionine in intact human erythrocytes

Freshly isolated human erythrocytes contain S-adenosyl-L-methionine (AdoMet) at a concentration of about 3.5 mumol/l cells. When such cells are incubated in a medium containing 30 microM L-methionine, 18 mM D-glucose and 118 mM sodium phosphate (pH 7.4), intracellular AdoMet levels continuously decrease to a value of about 0.1 microM after 24 h. This occurs in spite of the fact that the cellular concentrations of the substrates for the AdoMet synthetase reaction, ATP and L-methionine, remain relatively constant. In a search for incubation conditions that lead to stable levels of AdoMet in incubated cells, we have developed a sodium-Hepes-buffered medium which includes 1 mM adenine and a stoichiometric excess of MgCl2 over its ligand, phosphate. The inclusion of magnesium ion (and a reduction in phosphate) appears to increase intracellular free Mg2+, which is required for full activity of the erythrocyte AdoMet synthetase. Even in the presence of MgCl2, however, the AdoMet pool level can drop 4-6-fold within the first 2 h of incubation. We present evidence that suggests that this initial fall in the cellular AdoMet level may be due to the activation of AdoMet-dependent protein carboxyl methyltransferase, an enzyme which accounts for a large fraction of the total cellular AdoMet utilization. Adenine, or related compounds in the medium may prevent this activation, although the mechanism of this action is not clear at present.