A Shared Prebiotic Formation of Neopterins and Guanine Nucleosides from Pyrimidine Bases

The prebiotic origins of biopolymers and metabolic co-factors are key questions in Origins of Life studies. In a simple warm-little-pond model, using a drying phase to produce a urea-enriched solution, we present a prebiotic synthetic path for the simultaneous formation of neopterins and tetrahydroneopterins, along with purine nucleosides. We show that, in the presence of ribose and in a formylating environment consisting of urea, ammonium formate, and water (UAFW), the formation of neopterins from pyrimidine precursors is robust, while the simultaneous formation of guanosine requires a significantly higher ribose concentration. Furthermore, these reactions provide a tetrahydropterin-pterin redox pair. This model suggests a prebiotic link in the origin of purine nucleosides and pterin cofactors that provides a possible deep prebiotic temporal connection for the emergence of nucleic acids and metabolic cofactors.

Effects of Neopterin on the Hematopoietic Microenvironment of Senescence-Accelerated Mice (SAM)

The pteridine neopterin (NP) is produced by monocytes and is known to be a useful marker of immunological activation, although, it remains elusive whether neopterin itself exhibits biological functions. Recently, we found that NP stimulates hematopoietic cell proliferation and differentiation by activating bone marrow stromal cell function. In order to elucidate the biological effect of NP on stromal cells, its effects on hematopoiesis was determined in the mouse model of age-related stromal impairment, senescence-accelerated mice (SAMs). An intraperitoneal administration of NP increased the number of peripheral leukocytes and CFU-GM in the bone marrow and spleen of young SAMs, however, no increase of CFU-GM in old SAMs (stromal impairment) was observed when compared with young SAMs. NP also increased the CFU-GM colony formation of bone marrow and spleen cells from young SAMs in a soft agar culture system, but it did not enhance CFU-GM colony formation of cells from old SAMs cultured in this system. Treatment with NP induced the production of hematopoietic stimulating factors, including IL-6 and GM-CSF, by bone marrow stromal cells from young SAMs but stromal cells from old SAMs did not respond to NP stimulation. Further studies will be required to clarify the mechanism by which NP stimulates the production of hematopoietic growth factors from stromal cells, the results of this study indicate that NP is a potent hematopoietic regulatory factor by activating stromal cell function(s).

Stimulatory effects of neopterin on hematopoiesis in vitro are mediated by activation of stromal cell function

The pteridine neopterin (NP) was shown to be produced by monocytes and is known to be a useful marker of immunological activation, although, its biological activity is still unclear. Recently, we found that intravenous administration of NP increased the numbers of blood leukocytes, and granulocyte-macrophage progenitor cells (CFU-GM) in the bone marrow and spleens of mice. In order to elucidate the mechanism whereby NP stimulates hematopoiesis, the effects of NP on hematopoietic stem cell proliferation and differentiation in vitro were studied using a long-term bone marrow culture (LTMC) system with cloned stromal cell line, MS-5. Adding NP to the LTMC increased the numbers of cells in total, CFU-GM and colony-forming unit in spleen (CFU-S). NP also increased the number of CFU-GM in a soft agar culture system, but it did not enhance CFU-GM colony formation when target bone marrow cells were semi-purified (T, B and adherent cell-depleted bone marrow cells) and cultured in this system, suggesting that NP did not directly affect the proliferation of hematopoietic progenitors. Conditioned medium obtained from NP-treated stromal cells had much greater colony-stimulating activity than that obtained from untreated stromal cells. Furthermore, NP treatment stimulated the production of IL-6 and GM-CSF by stromal cells. All these findings suggest that NP stimulates hematopoietic cell proliferation and differentiation in vitro by activating stromal cell function.

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.

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)

Cytokine induction of neopterin production

The pteridine neopterin is a marker of immunological activation and has been shown to be a useful marker of graft-versus-host disease (GVHD) in bone marrow transplant patients. High levels of both neopterin and interferon-gamma (IFN-gamma) were produced in vitro during mixed lymphocyte responses, which may be considered to be a model of the primary events leading to GVHD. Neopterin was shown to be produced by monocytes in response to stimulation with IFN-gamma, but not other cytokines. However, the interleukins IL-1 alpha, IL-1 beta, IL-2, and tumour necrosis factor (TNF) alpha and beta, but not IL-6, stimulated neopterin production by unfractionated peripheral blood mononuclear cells (PBMC), and culture supernatants from PBMC stimulated with IL-1 alpha, IL-1 beta, IL-2 and IL-6, but not TNF-alpha or TNF-beta induced neopterin production following transfer to fresh monocyte cultures. It therefore appears that cytokines may generate neopterin by induction of IFN-gamma, by synergy with low levels of induced IFN-gamma, or by non-IFN-gamma-dependent mechanisms.

Immunological studies on the participation of 6-pyruvoyl tetrahydropterin (2'-oxo) reductase, an aldose reductase, in tetrahydrobiopterin biosynthesis

The NADPH-dependent reduction of the two carbonyl groups in the side chain of the first tetrahydropterin intermediate on the tetrahydrobiopterin biosynthetic pathway, 6-pyruvoyl tetrahydropterin, proceeds in a sequential manner whose order has not yet been resolved. Sepiapterin reductase can catalyze the reduction of both carbonyl groups starting with the 1'-oxo. 6-Pyruvoyl tetrahydropterin (2'-oxo) reductase, which has now been shown to be a member of the aldose reductase family, catalyzes the formation of only the 2'-hydroxy-1'-oxo intermediate which still requires sepiapterin reductase for final conversion to tetrahydrobiopterin. Inhibiting antibodies to the 2'-oxo reductase have been prepared and utilized to explore the distribution of this reductase in rat brain. The antiserum also maximally inhibited in vitro tetrahydrobiopterin synthesis in crude rat brain extracts by 60%, indicating that the majority of tetrahydrobiopterin biosynthesis in vivo may proceed via the 2'-hydroxy-1'-oxo intermediate. However, analogous experiments with rat liver extracts demonstrate that inhibition of the 2'-oxo reductase activity does not inhibit the conversion of 6-pyruvoyl tetrahydropterin to tetrahydrobiopterin, suggesting that tetrahydrobiopterin biosynthesis may proceed via different pathways in rat brain and liver.

Modulation of interleukin 2 high-affinity binding by lymphocyte-derived tetrahydrobiopterin: pterins as potential participants in the control of interleukin 2 receptor assembly

In this report, we have examined whether (6R)-tetrahydrobiopterin (H4biopterin) modulates the binding of interleukin 2 to high-affinity sites of the cloned mouse cytotoxic T-lymphocyte clone CTLL-2. Scatchard plot analysis of the equilibrium binding data reveals increased affinity when the cells are exposed simultaneously to interleukin 2 and to the pterin. The Kd values are statistically significantly reduced from 1.4 x 10(-11) M to 0.78 x 10(-11) M interleukin 2. The dissociation kinetics of the ligand were followed at 4 degrees C after equilibrium binding under high-affinity conditions (1.2 x 10(-10) M interleukin 2). In the presence of H4 biopterin, the dissociation rate constant (k-1) decreases from 6.2 x 10(-3) min-1 to 3.0 x 10(-3) min-1 and the half-time for dissociation increases from 106.8 min to 218.0 min. As a third approach interleukin 2 was bound to the surface of cells under high-affinity conditions by incubation in the cold and the internalization kinetics upon warming were determined. Sigmoidal-shaped kinetics of endocytosis in control cells indicate that the internalization rates increase only gradually. The presence of H4 biopterin causes an apparent immediate transition from higher-order kinetics to a linear response so that maximum internalization rates are reached immediately upon warming. The data show that lymphocyte-derived H4 biopterin in vitro at concentrations ranging from 2-8 x 10(-7) M modulates interleukin 2 high-affinity binding and that H4 biopterin potentially participates in the control of interleukin 2 receptor assembly.

[Pterins: pigments, cofactors and signal connections in cell interactions]

Pteridines were originally described as pigments of insects and lower vertebrates. The electron-donating function of tetrahydrobiopterin for aromatic amino acid hydroxylation and thus, for neurotransmitter biosynthesis adduced the participation of unconjugated pterins in cellular metabolism. There has been increasing evidence moreover that they are signal molecules for intercellular recognition in primitive eucaryotes, as well as modifiers of signal polypeptides in higher vertebrates.

[Neopterin, a new biochemical marker for clinical assessment of cell-mediated immune response]

Activated T-lymphocytes represent crucial effector cells. They are pathogenetically involved into various disease states such as allograft rejection or viral infection. So far their assessment is laborious and rarely possible in clinical routine. In this review article we present the compount neopterin as a new biochemical marker for the in vivo and in vitro detection of activated T-lymphocytes. Our main finding was that in vitro as well as in vivo stimulation of T-lymphocytes with foreign and chemically or virally modified autologous cells in invariably associated with increased neopterin production. It thus appeared that neopterin might represent a potential marker for biochemical monitoring of diseases caused by or associated with T-lymphocyte activation. Our clinical experience with neopterin determination in allograft rejection and in infectious or autoimmune states strongly support this view. We conclude that evaluation of neopterin represents a useful and simple tool for the biochemical monitoring of immunological and/or malignant states.

Guanosine triphosphate cyclohydrolase I assay in human and rat liver using high-performance liquid chromatography of neopterin phosphates and guanine nucleotides

D-erythro-7,8-Dihydroneopterin triphosphate (NH2TP) formed from guanosine triphosphate (GTP) by GTP cyclohydrolase I (EC 3.5.4.16) in the presence of EDTA was oxidized to neopterin triphosphate (NTP) by iodine, separated from substrate and other compounds by ion-paired reverse-phase HPLC, and quantitated by fluorometric detection at 365/446 nm. Excess GTP at the end of reaction was controlled by simultaneous detection of guanine nucleotides at 254 nm. The method required only 15 mg of liver tissue for the measurement of GTP cyclohydrolase I and is suitable for activity measurement in liver biopsies. The detection limit was 4 pmol of NTP at a signal to noise ratio of 10:1. The activity of GTP-cyclohydrolase I in homogenates of human liver (n = 10) was 45 pmol NH2TP (range 32-60) formed per milligram protein per hour at 37 degrees C. Liver homogenates from Wistar rats (n = 8) formed 47 pmol NH2TP (range 35-61) per milligram protein per hour.

Urinary neopterine excretion in patient with genital cancer

Urinary neopterine values in 96 healthy women were compared with those in a group of 63 patients with cancer of the genitals who had not yet undergone treatment. Significantly higher median neopterine levels were found in the patients with carcinoma (p less than 0.001). In the 63 cancer patients who had not yet been treated, the diagnosis was made correctly in 65% of the cases by monitoring neopterine levels. In the follow-up of 72 patients with cancer of the genitals in 74% the neopterine values corresponded with the clinico-roentgenological findings. In 22%, false positive neopterine values (no recurrence of the tumor), and in 4% false negative values (recurrence, or progression of the carcinoma) were observed. These results confirm previous reports concerning the significance of pteridine excretion in patients with cancer. However, more investigations have to be performed to establish the value of neopterine sampling in monitoring patients with malignant tumors.

Enhanced urinary excretion of 7,8-dihydro-6-hydroxylumazine by mice bearing the Ehrlich ascites tumour

A fluorescent urinary metabolite, excreted by mice carrying the Ehrlich ascites tumour (EAT), has been identified as 7,8-dihydro-6-hydroxylumazine. This finding agrees with other data which show that a disorder in pteridine metabolism is commonly associated with the presence of malignant growth.

A survey of some active sheep pineal fractions and a discussion on the possible significance of pteridines in those fractions in in vitro and in vivo assays

Aqueous extracts of sheep pineals are separated on Sephadex G-25 fraction with antigonadotropic activity are ultrafiltered through the membrane UM 2. The UM 2 filtrate is subsequently filtered through the membrane UM 05. The actions of the different fractions on the anterior hypophysis and hypothalamus are discussed. The fractions which show an activity are further separated on Sephadex G-10. The active Sephadex G-10 fractions of the UM 05 filtrate acting on the anterior hypophysis in vitro are purified by electrophoresis and paper chromatography. After elution of different fluorescence bands the main inhibitory activity is found in a region, with the same Rf value as synthetic 6-biopterin. Gas liquid chromatography and mass spectrometry studies of the isolated fractions are carried out. The mass spectrum of an isolated compound from that fraction is identical with that of synthetic 6-biopterin. Thinlayer chromatography and the results of the Crithidia fasciculata test reveal that the isolated compound is probably identical with 6-L-erythrobiopterin. The activity of the active paper chromatography fraction (C4) is compared with the activity of three synthetic biopterin-preparations in vitro and in vivo.

Specificity and binding capacity of human blood serum for tetrahydropterins

Binding behaviour of labelled biopterin, 6,7-dimethylpterin, 2,4-diamino-6,7-dimethylpteridin, and of their 5,6,7,8-tetrahydro derivatives was studied with human serum proteins. Binding capacity of serum proteins is in the range of 5 x 10-10--10-3 M without saturation for all these pteridines. Preincubation or competition with tetrahydrobiopterin does not influence binding of tetrahydro-6,7-dimethylpterin in these concentrations. The bulk of pteridines is bound through unspecific adsorption. Only at concentrations of less than 0.8 x 10-8 M does high affinity binding seem to be possible, corresponding to about 300 pmol/g protein, whereas physiological biopterin concentration is near 2 x 10-8 M. The binding proteins are very sensitive to ageing and lose their capacity during purification, whereas unspecific binding to serum proteins is only weakly influenced by alteration of salt concentration, pH, or temperature. Attempts to partially purify the binding proteins by ion exchange, dextran gel (Sephadex G-200), or affinity chromatography, demonstrate a specificity of tetrahydropterins for the alpha2-macroglobulin fraction. Due to the high lability of this protein fraction and of pteridine binding, purification of a protein which specifically binds tetrahydrobiopterin was not achieved.

Separation of pineal extracts by gelfiltration. VI. Isolation and identification from sheep pineals of biopterin; comparison of the isolated compound with some synthetic pteridines and the biological activity in in vitro and in vivo bioassays

Aqueous extracts of sheep pineal bodies were separated on Sephadex G-25. Two low molecular weight Sephadex G-25 fractions, F2 and F3, were ultrafiltrated through the Amicon membrane UM-2. The UM-2 filtrate was subsequently filtrated through the ultramembrane UM-05 and the UM-05 filtrate was separated on Sephadex G-10 columns. After paper electrophoresis, preparative paper chromatography was carried out. The fluorescent band showing a Rf value identical with synthetic 6-biopterin was eluted; gas liquid chromatography and mass spectrometry of the isolated compound were carried out. The mass spectra of the isolated compound were shown to be identical with synthetic 6-biopterin. The results of the Crithidia fasciculata test and thinlayer chromatography study revealed that the isolated compound is identical with 6-L-erythro-biopterin. The activities of the isolated compound and of synthetic biopterin in in vitro and in vivo bioassays are demonstrated.

Quantitative determination of unconjugated pterins in urine by gas chromatography/mass fragmentography

A gas chromatographic/mass fragmentographic method is described which permits the determination of unconjugated pterins in urine. After the addition of 6,7-dimethylpterin as an internal standard, the acidified urine samples are purified by liquid chromatography on Dowex-50 and Dowex-1 columns. The pterins are then converted to their corresponding trimethylsilyl derivatives and the base peaks of biopterin (m/e 409), neopterin (m/e 409) and 6,7-dimethylpterin (m/e 320) are determined. The method is sensitive and specific and permits the processing of large numbers of samples. By means of this method, the urinary excretion of biopterin and neopterin from 9 healthy subjects has been determined.