[Effect of xanthopterin on tumor metabolism].
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Animals↗
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[Therapeutic activity of combined xanthopterin-p-aminobenzoyl glutamic acid in experimental macrocytic anemia in rats].
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Anemia↗
The competitive inhibition of xanthine oxidation by xanthopterin.
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Biochemical Phenomena↗
[Fluorescent substances in the skin of Palomena prasina L. II. Identification of xanthopterin].
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Animals↗
Effect of pteridines on normal and neoplastic cell lines of Xiphophorus.
The effect of three pteridines namely biopterin, isoxanthopterin and xanthopterin on cell growth, viability and morphology of three embryo and one melanoma derived cell lines was studied. Pteridines were assayed in the range of 10(-6) M to 10(-4) M. Biopterin exerted no influence on all cell lines tested, whereas isoxanthopterin and xanthopterin caused a decrease in growth rate with increasing concentrations. The strongest decrease of cell growth was exerted by 10(-4) M xanthopterin. Furthermore at this concentration xanthopterin reduced the viability of normal cells and influenced the morphology of both normal and neoplastic cells. In general, normal cells were more sensitive to pteridines than neoplastic cells.
Animals↗
Altered pterin patterns in photobehavioral mutants of Phycomyces blakesleeanus.
Pterins were extracted with methanol from sporangiophores of the lower fungus Phycomyces blakesleeanus and separated and identified by high performance liquid chromatography (HPLC) with fluorescence detection. The following pterins were found and identified for the wild-type strain NRRL1555: carboxypterin (6.7 x 10(-6) M), neopterin (4.2 x 10(-7) M), xanthopterin (5.3 x 10(-6) M), biopterin (3.9 x 10(-7) M), pterin (9.1 x 10(-7) M), and 6,7-dimethylpterin (1.2 x 10(-6) M). The HPLC elution profiles of the wild type were compared to a set of phototropism mutants (genotype mad) with specific defects in the light-transduction pathway. The mutant profiles were qualitatively similar to those of the wild type. Quantitative differences were, however, discerned for madA, madC, and madH mutants. The madA mutation was associated with increased amounts of biopterin and 6,7-dimethylpterin and a reduction of neopterin, pterin, xanthopterin, and unidentified pterins eluting at 14-18 min. The stimulatory effect of the madA mutation on biopterin and 6,7-dimethylpterin appears to be compensated by a secondary mutation (pde) which is responsible for the loss of 75% of adenosine 3',5'-cyclic monophosphate (cAMP)-phosphodiesterase activity. In a madA pde double mutant the amounts of biopterin and 6,7-dimethylpterin fell below the wild-type level. These results suggest that an increased level of endogenous cAMP represses the biosynthesis of these pterins. The madC mutation increased the amounts of biopterin and xanthopterin and that of the unidentified pterins which could be derivatized to carboxypterin. Single madB mutations had, compared to the wild type, two times higher amounts of biopterin and two times lower amounts of neopterin.(ABSTRACT TRUNCATED AT 250 WORDS)
Flavins↗
Inter-relationships between pterins and cytokines produced during allogeneic immune reactions and possible use as early markers of immune activation.
The pterins neopterin and xanthopterin have been measured together with the cytokines IFN-gamma, TNF-alpha and TNF-beta in the supernatants of 20 allogeneic mixed lymphocyte reactions. We have calculated rank correlation coefficients between these analytes and the immune response. Our findings confirm that neopterin is a sensitive early marker of immune activation and show that another pterin, xanthopterin could be used likewise. Cytokine production was also proportional to immune activation but none could be used consistently as early markers of immune activation.
Biomarkers↗
Dihydroxanthopterinuria in phenylketonuria and lethal hyperphenylalaninemia patients.
7,8-Dihydroxanthopterin in identified in urine from phenylketonuria and lethal hyperphenylalaninemia patients. Because 7,8-dihyroxanthopterin is readily oxidised to xanthopterin, most of the characterisation was performed on xanthopterin. This finding indicates a gross disturbance of tetrahydrobiopterin metabolism in these patients. 7,8-dihydroxanthopterin or a related pterin may play a role in the pathogenesis of neurological symptoms in phenylketonuria and lethal hyperphenylalaninemia.
Amino Acid Metabolism, Inborn Errors↗
Participation of pterins in the control of lymphocyte stimulation and lymphoblast proliferation.
Biopterin accumulation had been demonstrated as the result of normal and, especially, of malignant hemopoietic cell proliferation (Ziegler, I. et al. Blut, 44: 231-240, and 261-270, 1982). Among 13 major intermediates of pterin metabolism and two lumazines, xanthopterin (but not dihydroxanthopterin) was found to inhibit cell proliferation (half-maximum inhibition at 1.8 X 10(-5) M) during concanavalin A-induced lymphocyte activation in pre-stimulated lymphocytes and in a lymphoid cell line grown in continuous culture (LS-2). LS-2 cells exposed to maximum inhibitor concentrations largely maintained the initial thymidine incorporation rate for about 40 hr but failed to enter logarithmic growth. Isoxanthopterin inhibition was found only in serum-free medium, since it is trapped by the alpha-acid glycoprotein present in the serum. The reduced biopterin derivatives, sepiapterin, dihydrobiopterin, and tetrahydrobiopterin, are costimulators during concanavalin A-induced lymphocyte activation. Their costimulatory effect follows an optimum curve and peaks at 1.5 to 3 X 10(-5) M. It is highest at the suboptimal and supraoptimal concanavalin A concentration. The D-erythro isomer dihydroneopterin was inactive. The results indicate that the anabolic-reduced biopterin derivatives are not simply lymphocytic products, but, in combination with the catabolites xanthopterin and isoxanthopterin, they also participate in the regulation of lymphocyte activation. Hence, they fulfill the criteria for lymphokines.
Animals↗
Reflective organelles in the anterior pigment epithelium of the iris of the European starling Sturnus vulgaris.
The ultrastructure and chemical composition of reflective organelles in the anterior pigment epithelium of the iris of the European starling Sturnus vulgaris were examined. The reflective organelles produced a diffuse white reflectance at the iris mid-section which was visible only when the stroma was removed. The pigment granules were clear, angular, and birefringent under the light microscope. In electron micrographs the granules were irregular in shape and density, sometimes crystalline in appearance, but more often they were lost during sectioning or staining. Guanine was abundant in the modified pigment epithelium of the starling, but not in the pigment epithelia of other birds that lacked birefringent granules. Pteridines, such as xanthopterin and leucopterin, were present in small amounts. Pteridines were also present in the iris stroma which had no reflective organelles. The reflective organelles in the starling pigment epithelium resemble both the reflecting platelets of lower vertebrate chromatophores and the reflective granules in the tapeta of various vertebrates. Possible derivation of the organelles from these sources is discussed.
Animals↗
Urinary excretion levels of unconjugated pterins in cancer patients and normal individuals.
Urinary excretion levels of seven unconjugated pterins in healthy individuals and in cancer patients, most of whom were undergoing chemotherapy, were measured utilizing a newly developed high-pressure liquid chromatographic system. Excretion of pterins in the control group appears to be under strict metabolic control as the values obtained were confined within a small range. When the mean excretion levels in control subjects were compared with those in cancer patients, we found a significant increase in the excretion of xanthopterin, neopterin and pterin and a significant decrease in isoxanthopterin by cancer patients. Biopterin levels, on the other hand, were found only slightly but not significantly increased, whereas pterin-6-carboxylic acid and 6-hydroxymethylpterin were found to be excreted in approximately equal amounts in both groups. Urinary excretion levels of pterins were monitored for a period of nine months in a patient being treated with chemotherapy for metastatic ovarian carcinomatosis. We found that the excretion pattern of pterins appeared to correlate with the clinical status of the patient. These results indicate that a definite imbalance in pterin, and possibly folate metabolism, is associated with the presence of malignant diseases.
Adult↗
Stimulus-dependent production of cytokines and pterins by peripheral blood mononuclear cells.
The cytokine profiles produced by peripheral blood mononuclear cell (PBMC) cultures were dependent upon the nature of the stimulus used. Powerful lymphocyte activators such as mitogens induced rapid cell proliferation together with the production of both inflammatory (IL-1 alpha, IL-1 beta, IL-6 and TNF alpha) and immune (IFN-gamma, TNF-alpha and TNF-beta) cytokines, and immune activation markers (soluble IL-2 receptor, neopterin and xanthopterin). Bacterial endotoxin failed to induce cell proliferation but resulted in the rapid production of inflammatory cytokines together with a short burst of IFN-gamma production, without the production of the other immune cytokines or activation markers. Alloantigen stimulation gave a typical immune cytokine and marker profile, with little or no production of inflammatory cytokines. Re-call antigens (candida and PPD) induced maximal cell proliferation at days 5 to 6, but induced little or no production of inflammatory cytokines. Markedly different immune cytokine profiles were obtained with these re-call antigens. Candida induced an early burst of IFN-gamma production on day 1 followed by later production of TNF-alpha. In cultures stimulated with PPD, both IFN-gamma and TNF-alpha were detected from day 2. With both re-call antigens, the levels of production of the activation markers were equivalent to the proliferative responses obtained.
Biopterins↗
Simultaneous determination of pteridines in multicomponent mixtures using derivative spectrophotometry and partial least-squares calibration.
Simple binary mixtures composed of very similar pteridines (neopterin and pterin) have been resolved by derivative spectrophotometry. Detection limits of 0.30 microgram ml-1 and 0.12 microgram ml-1 for pterin and neopterin, respectively, have been calculated. Also, different mixtures of pteridines considered as disease markers, such as pterin, neopterin, xanthopterin and isoxanthopterin, have been determined by using a partial least-squares (PLS-2) model. Calibration set containing 0-7 micrograms ml-1 for each component was used. The resolution of several mixtures and single determination was tested in artificial samples.
Drug Combinations↗
Characterization of the reflective materials and organelles in the bright irides of North American blackbirds (Icterinae).
The reflective materials in the iris stroma of bright-irised American blackbirds (Icterinae, Emberizidae) and the red-eyed vireo (vireo olivaceus) (Vireonidae) were characterized using high-performance liquid chromatography (HPLC) and diode-array detection. Two purines, guanine and hypoxanthine, and two pteridines, leucopterin and xanthopterin, were detected in large amounts in all bright irides. The brown iris of the red-winged blackbird (Agelaius phoeniceus) by comparison contained only small amounts of these and additional unidentified compounds. The absolute and relative amounts of light-absorbing compounds in the iris varied somewhat among species of blackbirds with bright irides, and markedly within one species (brewer's blackbird, Euphagus cyanocephalus) between sexes and age classes that very in eye color. Differences in the types, numbers, and sizes of pigment organelles in the irides appeared to underlie the differences in amounts of light-absorbing compounds. Guanine was the most abundant light-absorbing compound in all bright irides, accounting for about 90% of the total absorption at 250 nm. A wide range of concentrations of guanine, from 96 to 9 micrograms per iris, produced bright irides. The primary pigment organelles of pigment cells in bright irides were reflecting platelets, which typically appeared as open spaces on electron micrographs. In the red-eyed vireo there were in addition red pterinosome-like pigment organelles in the pigment cells on the anterior surface of the iris stroma. Guanine was present even in irides with no overt reflecting platelets.
Animals↗
Studies of the reductive half-reaction of milk xanthine dehydrogenase.
The reductive half-reaction of milk xanthine dehydrogenase (XDH) with NADH and with xanthine has been studied at pH 7.5, 25 degree C. NADH reduces XDH to the two-electron reduced form at a rate of 18 s-1, independent of NADH concentration over the range studied. Further reduction by NADH to the four-electron state is inhibited by excess NADH. Subsequent binding of NADH to the four-electron reduced form of the enzyme causes the redistribution of one electron from the flavin to the molybdenum center. The four-electron reduced species reached through reduction by NADH is the same as the species obtained upon reaction of NAD with fully reduced XDH. In contrast, xanthine rapidly reduces XDH to the four-electron level; further reduction is comparatively slow and is inhibited by excess xanthine. Studies using substoichiometric xanthine show that the reaction of XDH with 1 equivalent of xanthine involves rapid substrate binding and rapid reduction of the molybdenum center of the enzyme. Before the release of urate from the molybdenum active site, an electron is transferred at 15 s-1 from the reduced molybdenum center to one of the iron-sulfur centers of XDH. Urate is then released at a rate of 13 s-1, followed by a rapid electron redistribution within the protein. The reductive half-reaction of XDH with xanthine is rate-limiting in xanthine/NAD turnover, which appears to occur between the two- and four-electron reduced enzyme species. The reduction of XDH by substoichiometric amounts of the fluorescent substrate xanthopterin was also studied. This reaction, monitored by changes in both absorbance and fluorescence, was found to involve the formation of two molybdenum complexes (an Eox.S complex and an Ered.P complex) followed by the release of the product, leucopterin.
Animals↗
Crystalline pteridines in the stromal pigment cells of the iris of the great horned owl.
The bright yellow color of the iris of the Great Horned Owl (Bubo virginianus) is due to unusual pigment cells in the iris stroma. These cells are spherical and contain numerous clear lipid droplets. Around the periphery of these cells are ovoid crystalline granules that are highly birefringent and vary in color from yellow to clear gray. Differential extraction of the lipid droplets and peripheral granules with lipid solvents and 2% KOH confirmed the localization of the yellow pigment in these granules. The color, solubility, fluorescence, chromatographic mobility and ultraviolet absorption of the extracted pigment suggest it is primarily xanthopterin. It is proposed that the peripheral granules are crystalline pterinosomes capable of reflecting light. Most of the cells contain yellow reflecting granules and can be considered reflecting xanthophores. Cells lying deeper in the stroma have colorless reflecting granules and can be considered pteridine containing leucophores.
Animals↗
Separation of pteridines from blood cells and plasma by reverse-phase high-performance liquid chromatography.
In order to determine free and conjugated pteridines, the pteridine-releasing procedure for biological materials (e.g., plasma, blood cells, bone marrow) was optimized and the parameters which influence pteridine releasing are discussed. Using reverse-phase high-performance liquid chromatography (rp-HPLC) on 5-micron ODS (C18; mobile phase, K2HPO4 buffer, pH 7.0-7.8), up to 10 pteridines (pterin-6-carboxylic acid, xanthopterin, neopterin, monapterin, isoxanthopterin, lumazine, biopterin, 6-hydroxymethylpterin, pterin) could be separated in the extracts of blood samples and determined fluorometrically (femtomolar range). In addition, three sepiapterins (sepiapterin, deoxysepiapterin, 3'-hydroxysepiapterin) could be separated with aqueous methanol as eluent (uv and fluorometric detection, respectively). The methods described are suited to compile pteridine patterns for plasma and individual cell fractions (erythrocytes, lymphocytes, buffy coat) from blood. Moreover, it was shown that the pteridine concentrations in dog blood (beagles) were in some cases substantially higher than in human blood, and that neopterin is lacking in the blood cell fractions of beagle dogs or occurs only in very low concentrations.
Animals↗
Radioimmunoassay for neopterin in body fluids and tissues.
Specific antibodies against D-erythroneopterin have been prepared in rabbits using a conjugate of D-erythroneopterin to bovine serum albumin (D-erythroneopterinylcaproyl-bovine serum albumin). The antiserum distinguished D-erythroneopterin from other pteridines, i.e., three stereoisomers of neopterin, L-erythrobiopterin, folic acid, xanthopterin, and four other synthetic pteridines. Using this specific antiserum, a radioimmunoassay for D-erythroneopterin has been developed to measure the neopterin concentrations in urine and tissues. The conjugate of D-erythroneopterin with tyramine (NP-Tyra) was synthesized and labeled with 125I as the labeled ligand NP-[125I]tyra for the radioimmunoassay. The minimal detectable amount of neopterin was about 0.1 pmol. The concentration of total neopterin (neopterin, 7,8-dihydroneopterin, quinonoid dihydroneopterin, and tetrahydroneopterin) in the biological samples was obtained by iodine oxidation under acidic conditions prior to the radioimmunoassay, and that of neopterin plus 7,8-dihydroneopterin by oxidation under alkaline conditions. Total neopterin values in human urine obtained by this new radioimmunoassay showed a good agreement with those obtained by high-performance liquid chromatography with fluorescence detection. With rat tissue samples which contained very low concentrations of neopterin as compared to biopterin, biopterin was simultaneously determined by our previously reported radioimmunoassay, and neopterin values were corrected for the cross-reactivity (0.1%). The neopterin concentrations obtained by this method agreed with the values obtained by the radioimmunoassays for neopterin and biopterin after their separation by high-performance liquid chromatography. This very small amount of neopterin, as compared with biopterin, in rat tissues could not be determined by high-performance liquid chromatography-fluorometry alone due to the masking of the neopterin peak by a large biopterin peak.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗