Pteridine excretion from cells as indicator of cell proliferation

Nitric oxide synthases from photosynthetic organisms improve growth and confer nitrosative stress tolerance in E. coli. Insights on the pterin cofactor

Nitric oxide synthase (NOS) catalyzes NO formation from the substrate l-arginine (Arg). Previously, NOS with distinct biochemical properties were characterized from two photosynthetic microorganisms, the unicellular algae Ostreococcus tauri (OtNOS) and the cyanobacteria Synechococcus PCC 7335 (SyNOS). In this work we studied the effect of recombinant OtNOS and SyNOS expressed under IPTG-induced promoter in E. coli, a bacterium that lacks NOS. Results show that OtNOS and SyNOS expression promote E. coli growth in a nutrient replete medium and allow to better metabolize Arg as N source. In LB medium, OtNOS induces the expression of the NO dioxygenase hmp in E. coli, in accordance with high NO levels visualized with the probe DAF-FM DA. In contrast, SyNOS expression does not induce hmp and show a slight increase of NO production compared to OtNOS. NOS expression reduces ROS production and increases viability of E. coli cultures growing in LB. A strong nitrosative stress provoked by the addition of 1 mM of the NO donors sodium nitroprusside (SNP) and nitrosoglutathione (GSNO) inhibits bacterial growth rate. Under these conditions, the expression of OtNOS or SyNOS counteracts NO donor toxicity restoring bacterial growth. Finally, using bioinformatic tools and ligand docking analyses, we postulate that tetrahydromonapterin (MH4), an endogenous pterin found in E. coli, could act as cofactor required for NOS catalytic activity. Our findings could be useful for the development of biotechnological applications using NOS expression to improve growth in NOS-lacking bacteria.

FolX and FolM are essential for tetrahydromonapterin synthesis in Escherichia coli and Pseudomonas aeruginosa

Tetrahydromonapterin is a major pterin in Escherichia coli and is hypothesized to be the cofactor for phenylalanine hydroxylase (PhhA) in Pseudomonas aeruginosa, but neither its biosynthetic origin nor its cofactor role has been clearly demonstrated. A comparative genomics analysis implicated the enigmatic folX and folM genes in tetrahydromonapterin synthesis via their phyletic distribution and chromosomal clustering patterns. folX encodes dihydroneopterin triphosphate epimerase, which interconverts dihydroneopterin triphosphate and dihydromonapterin triphosphate. folM encodes an unusual short-chain dehydrogenase/reductase known to have dihydrofolate and dihydrobiopterin reductase activity. The roles of FolX and FolM were tested experimentally first in E. coli, which lacks PhhA and in which the expression of P. aeruginosa PhhA plus the recycling enzyme pterin 4a-carbinolamine dehydratase, PhhB, rescues tyrosine auxotrophy. This rescue was abrogated by deleting folX or folM and restored by expressing the deleted gene from a plasmid. The folX deletion selectively eliminated tetrahydromonapterin production, which far exceeded folate production. Purified FolM showed high, NADPH-dependent dihydromonapterin reductase activity. These results were substantiated in P. aeruginosa by deleting tyrA (making PhhA the sole source of tyrosine) and folX. The DeltatyrA strain was, as expected, prototrophic for tyrosine, whereas the DeltatyrA DeltafolX strain was auxotrophic. As in E. coli, the folX deletant lacked tetrahydromonapterin. Collectively, these data establish that tetrahydromonapterin formation requires both FolX and FolM, that tetrahydromonapterin is the physiological cofactor for PhhA, and that tetrahydromonapterin can outrank folate as an end product of pterin biosynthesis.

Escherichia coli abg genes enable uptake and cleavage of the folate catabolite p-aminobenzoyl-glutamate

Escherichia coli AbgT was first identified as a structural protein enabling the growth of p-aminobenzoate auxotrophs on exogenous p-aminobenzoyl-glutamate (M. J. Hussein, J. M. Green, and B. P. Nichols, J. Bacteriol. 180:6260-6268, 1998). The abg region includes abgA, abgB, abgT, and ogt; these genes may be regulated by AbgR, a divergently transcribed LysR-type protein. Wild-type cells transformed with a high-copy-number plasmid encoding abgT demonstrate saturable uptake of p-aminobenzoyl-glutamate (K(T)=123 microM); control cells expressing vector demonstrate negligible uptake. The addition of metabolic poisons inhibited uptake of p-aminobenzoyl-glutamate, consistent with this process requiring energy. p-Aminobenzoyl-glutamate taken in by cells expressing large amounts of AbgT alone is not rapidly metabolized to a form that is trapped in the cell, as the addition of nonradioactive p-aminobenzoyl-glutamate to these cells results in a rapid loss of intracellular label. The addition of nonradioactive p-aminobenzoate has no effect. The abgA, abgB, and abgAB genes were cloned into the medium-copy-number plasmid pACYC184; p-aminobenzoate auxotrophs transformed with the clone encoding abgAB demonstrated enhanced ability to grow on low levels of p-aminobenzoyl-glutamate. When transformed with complementary plasmids encoding high-copy levels of abgT and medium-copy levels of abgAB, p-aminobenzoate auxotrophs grew on 50 nM p-aminobenzoyl-glutamate. Our data are consistent with a model of p-aminobenzoyl-glutamate utilization in which AbgT catalyzes transport of p-aminobenzoyl-glutamate, followed by cleavage to p-aminobenzoate by a protein composed of subunits encoded by abgA and abgB. While endogenous expression of these genes is very low under the conditions in which we performed our experiments, these genes may be induced by AbgR bound to an unknown molecule. The true physiological role of this region may be related to some molecule similar to p-aminobenzoyl-glutamate, such as a dipeptide.

A research on the level of urine neopterin to see if it may provide a vital clue for a provisional diagnosis of breast cancer in menopausal women

OBJECTIVES

To search the relation between the level of neopterin in urine and breast cancer developed in menopause.

METHODS

In this study, urine samples were collected from randomly selected menopausal and post-menopausal women who attended hospital, and from a control group. The participants were classified into two representative sample groups and a control group; 1st group: 30 menopausal and post-menopausal women whose ages varied from 45 to 80 and who suffered from breast cancer but had no viral infections, chronic inflammatory diseases and smoking habit; 2nd group: 30 menopausal and post-menopausal women aged between 48 and 63 with no complaint of any type of tumors, viral infections or chronic inflammatory diseases and with no smoking habit; 3rd group: A control group with 20 women aged between 20 and 28, who did not take part in sexual activities yet, and had no complaint of any type of tumors, viral infections or chronic inflammatory diseases and had no smoking habit. Urinalysis was carried out for each sample in order to measure the level of neopterin.

RESULTS

The mathematical results of neopterin levels for the groups showed that group I was significantly higher than group II and III (P = 0.0001 ); group II was significantly higher than group III (P = 0.003 ).

CONCLUSIONS

If the results of this study were not confounded by another factor, then can we deduce that this relationship can be used as a risk factor that should warrent further investigation of breast cancer during the care and treatment of menopausal women.

Crystal structure of 7,8-dihydroneopterin triphosphate epimerase

BACKGROUND

Dihydroneopterin triphosphate (H2NTP) is the central substrate in the biosynthesis of folate and tetrahydrobiopterin. Folate serves as a cofactor in amino acid and purine biosynthesis and tetrahydrobiopterin is used as a cofactor in amino acid hydroxylation and nitric oxide synthesis. In bacteria, H2NTP enters the folate biosynthetic pathway after nonenzymatic dephosphorylation; in vertebrates, H2NTP is used to synthesize tetrahydrobiopterin. The dihydroneopterin triphosphate epimerase of Escherichia coli catalyzes the inversion of carbon 2' of H2NTP.

RESULTS

The crystal structure of the homo-octameric protein has been solved by a combination of multiple isomorphous replacement, Patterson search techniques and cyclic averaging and has been refined to a crystallographic R factor of 18.8% at 2.9 A resolution. The enzyme is a torus-shaped, D4 symmetric homo-octamer with approximate dimensions of 65 x 65 A. Four epimerase monomers form an unusual 16-stranded antiparallel beta barrel by tight association between the N- and C-terminal beta strands of two adjacent subunits. Two tetramers associate in a head-to-head fashion to form the active enzyme complex.

CONCLUSIONS

The folding topology, quaternary structure and amino acid sequence of epimerase is similar to that of the dihydroneopterin aldolase involved in the biosynthesis of the vitamin folic acid. The monomer fold of epimerase is also topologically similar to that of GTP cyclohydrolase I (GTP CH-1), 6-pyrovoyl tetrahydropterin synthase (PTPS) and uroate oxidase (UO). Despite a lack of significant sequence homology these proteins share a common subunit fold and oligomerize to form central beta barrel structures employing different cyclic symmetry elements, D4, D5, D3 and D2, respectively. Moreover, these enzymes have a topologically equivalent acceptor site for the 2-amino-4-oxo pyrimidine (2-oxo-4-oxo pyrimidine in uroate oxidase) moiety of their respective substrates.

Purification, cloning, and functional expression of dihydroneopterin triphosphate 2'-epimerase from Escherichia coli

Dihydroneopterin triphosphate (H2NTP) 2'-epimerase from Escherichia coli catalyzes the epimerization of H2NTP to dihydromonapterin triphosphate (H2MTP). The enzyme was purified 954-fold to apparent homogeneity by a combination of ammonium sulfate fractionation and column chromatography of Cibacron blue 3GA dye ligand, phenyl-Sepharose CL-4B, methotrexate-agarose, and Superdex 200 HR 10/30 FPLC column. The molecular mass of the epimerase determined on a Superdex column was 82.6 kDa, while the subunit molecular mass determined on SDS-polyacrylamide gel electrophoresis was 13.7 kDa. This implies that the epimerase most probably exists as homohexamer. The 20-amino acid sequence from the N terminus was determined (AQPAAIIRIKNLRLRTFIGI). Based on this sequence, the gene encoding the epimerase was cloned using a simple polymerase chain reaction approach. Translation of the nucleotide sequence of the cloned gene revealed the presence of an open reading frame containing 120 amino acids with a predicted molecular mass of 13,993 Da. The epimerase gene located in a 2.3-kilobase BamHI-EcoRI fragment from Kohara's clone 406 was overexpressed 300-fold, which was confirmed by the prominent increase in the 14-kDa protein band on SDS-polyacrylamide electrophoresis gels. It showed no homology with the sequences of isomerases or other enzymes in GenBank/EMBL data bases.

Control of 6-(D-threo-1',2'-dihydroxypropyl) pterin (dictyopterin) synthesis during aggregation of Dictyostelium discoideum. Involvement of the G-protein-linked signalling pathway in the regulation of GTP cyclohydrolase I activity

6-(D-threo-1',2'-Dihydroxypropylpterin (dictyopterin) has been identified in extracts of growing Dictyostelium dicoideum cells [Klein, Thiery and Tatischeff (1990) Eur. J. Biochem. 187, 665-669]. We demonstrate that it originates from GTP by de novo biosynthesis and that the first committed step is catalysed by GTP cyclohydrolase I, yielding dihydroneopterin triphosphate [neopterin is 6-(D-erythro-1',2',3'-trihydroxypropyl) pterin]. The GTP cyclohydrolase I activity is found in the cytosolic fraction and in a membrane-associated form. The level of a 0.9 kb mRNA coding for GTP cyclohydrolase I decreases to about 10% of its initial value within 2 h after Dictyostelium cells start development induced by starvation. In the cytosolic fraction, the specific activities of GTP cyclohydrolase I, as well as the concentrations of (6R/S)-5,6,7,8-tetrahydrodictyopterin (H4dictyopterin), follow this decline of the mRNA level. In the particulate fraction, however, the specific activities of GTP cyclohydrolase I and, in consequence, H4dictyopterin synthesis, transiently increase and reach a maximum after 4-5 h of development. The time-course of H4dictyopterin concentrations in the starvation medium closely correlates with its production in the membrane fraction. The activity of membrane-associated GTP cyclohydrolase I can be increased by pre-incubation of the cell lysate with guanosine 5'-[gamma-thio]triphosphate and Mg2+. This GTP analogue does not serve as a substrate and has no direct effect on the enzyme activity, indicating that a G-protein-linked signalling pathway is involved in the regulation of GTP cyclohydrolase I activity and thus in H4dictyopterin production during early development of D. discoideum.

Effects of pteridines on luminol-dependent chemiluminescence induced by chloramine-T

Pteridines are ubiquitous in living organisms, but little is known about their biological functions. Different pteridines were tested for their ability to modulate luminol-dependent chemiluminescence induced by chloramine-T at pH = 7.5 and at a concentration of 100 microM for each pteridine. We observed striking differences between the compounds; whereas reduced pteridine species were generally potent scavengers, aromatic pteridines were weak to strong enhancers of the chemiluminescence. Taking into account the detailed chemical structure of the molecules, by multiple linear regression analysis a simple index was constructed that allows prediction of the effects of the different pteridines with high accuracy (linear correlation coefficient between predicted and observed values r = 0.89). The effects of different pteridines on free radical-induced chemiluminescence might bear biological significance since, for example, certain pteridines take part in enzymic reactions involving free-radical intermediates, or are related to the activation of macrophages in close relationship with the oxidative burst.

Pteridine biosynthesis and nitric oxide synthase in Physarum polycephalum

Physarum polycephalum, an acellular slime mould, serves as a model system to study cell-cycle-dependent events since nuclear division is naturally synchronous. This organism was shown to release isoxanthopterin which is structurally related to tetrahydrobiopterin, a cofactor of aromatic amino acid hydroxylases and of nitric oxide synthases (NOSs) (EC 1.14.13.39). Here, we studied Physarum pteridine biosynthesis in more detail and found that high amounts of tetrahydrobiopterin are produced and NOS activity is expressed. Physarum pteridine biosynthesis is peculiar in as much as 7,8-dihydroneopterin aldolase (EC 4.1.2.25), an enzyme of folic acid biosynthesis usually not found in organisms producing tetrahydrobiopterin, is detected in parallel. NOS purified from Physarum depends on NADPH, tetrahydrobiopterin and flavins. Enzyme activity is independent of exogenous Ca2+ and is inhibited by arginine analogues. The purified enzyme (with a molecular mass of 130 kDa) contains tightly bound tetrahydrobiopterin and flavins. During the synchronous cell cycle of Physarum, pteridine biosynthesis increases during S-phase whereas NOS activity peaks during mitosis, drops at telophase and peaks again during early S-phase. Our results characterize Physarum pteridine biosynthesis and NOS and suggest a possible link between NOS activity and mitosis.

The role of neopterin as a monitor of cellular immune activation in transplantation, inflammatory, infectious, and malignant diseases

The accumulated knowledge about the organization and function of the human immune system contributes to a better understanding of the pathogenesis of most diverse disorders and is opening new avenues for therapeutic regimens. To gain further insight into the complex interactions within the components of the immune system, it has become increasingly necessary to develop rapid and simple methods to monitor the status of the immune system in patients. The determination of neopterin concentrations in human body fluids allows to investigate sensitively the cell-mediated immune status to be investigated with considerable sensitivity. In recent years it was shown that production and release of neopterin is inducible in human monocytes/macrophages by interferon gamma. Increased neopterin levels indicate endogenous formation of gamma interferon, and monitoring of neopterin levels therefore permits the activation status of the cell-mediated immune system to be examined. Neopterin concentrations in serum and in urine increase in parallel to the clinical course of infections with viruses, intracellular bacteria, and parasites. In patients with human immunodeficiency virus infection neopterin concentration in serum and urine is a significant predictor of disease progression, the statistical power being similar to CD4+ T-cell numbers. In patients with autoimmune disorders, neopterin levels correlate with the extent and the activity of the disease. Neopterin concentrations are also sensitive indicators of immunological complications in allograft recipients. In certain malignant diseases neopterin concentrations correlate with the stage of the disease and bear prognostic information. Results of neopterin measurements agree with the important role that the cellular immune system plays in these disorders.

Structure of solfapterin (erythro-neopterin-3'-D-2-deoxy-2-aminoglucopyranoside) isolated from the thermophilic archaebacterium Sulfolobus solfataricus

The structure of the major fluorescent pterin present in thermophilic archaebacterium Sulfolobus solfataricus has been assigned, by analysis of the intact molecule and its hydrolytic and periodate cleavage products, as erythro-neopterin-3'-D-2-deoxy-2-aminoglucopyranoside. The trivial name solfapterin is proposed for this compound.

Significance of urinary neopterin in patients with malignant tumors of the genitourinary tract

The urinary neopterin excretion was measured by high-performance liquid chromatography in 417 healthy subjects and in 76 patients with clinically and pathohistologically verified neoplasias of the urinary tract (bladder tumor, carcinoma of the prostate, and renal cell carcinoma). The patients with early tumor stages both with bladder tumor and carcinoma of the prostate had normal urinary neopterin levels, except one patient with bladder tumor who had a value at the upper confidence limit. Of 40 patients with higher stages of bladder tumor and carcinoma of the prostate, 35 had elevated urinary neopterin levels. Two of 10 patients with bladder tumor in stage T3, 1 of 4 patients with carcinoma of the prostate Stage C, and 2 of 15 patients with prostatic cancer Stage D showed normal neopterin levels. The patients with renal cell carcinoma did not demonstrate any definite correlation between tumor stage and urinary neopterin excretion. The current study suggests that the neopterin assay may supplement laboratory measurements in tumors of the urinary tract, providing helpful information regarding case selection for the most convenient therapeutic management and postoperative follow-up.

[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.

Measurement of urinary neopterin in normal pregnant and non-pregnant women and in women with benign and malignant genital tract neoplasms

Urinary neopterin was measured in healthy women (n = 209) and men (n = 208), in patients with benign gynecological tumors (n = 53), in women with precancerous lesions of the cervix and the endometrium (n = 24) and in women with cancer of the genital tract (n = 108). In addition urinary neopterin measurements were made in 109 pregnant women and 20 women in the puerperium. No significant difference was found between mean neopterin values in patients with benign gynecological tumors, in women with precancerous lesions and in healthy women. Patients with cancer had significantly higher mean urinary neopterin levels than the control group. Raised neopterin levels were found in 56% of patients with genital tract cancer, the figures varying between 93% for ovarian cancer and 47% for cancer of the cervix. Some of the cancer patients had serial urinary neopterin measurements and in about 80% there was some relation between urinary neopterin values and clinical progress as judged clinically and radiologically, the best agreement existing in patients with ovarian cancer. Significantly higher mean neopterin values were found during normal pregnancy and in the early puerperium than in non-pregnant healthy controls. Raised urinary neopterin excretion may be due to enhanced cell proliferation and alloantigenic activation of T-lymphocytes.

Urinary neopterine in the assessment of lymphoid and myeloid neoplasia, and neopterine levels in haemolytic anaemia and benign monoclonal gammopathy

The urinary neopterine levels were measured by HPLC in 417 normal subjects and in 216 patients with haematological diseases. All patients with active malignancies (multiple myeloma, polycythaemia vera. Hodgkin's lymphoma, non-Hodgkin's lymphoma, chronic myelocytic and chronic lymphocytic leukaemia) showed highly elevated mean and median values compared to the control groups. Those of patients with multiple myeloma stage I were only raised to near the upper limit of healthy subjects. Of 123 patients with active disease 105 (85%) were above the upper limit. In contrast, the mean and median values of 56 patients with neoplasias in remission (Hodgkin's and non-Hodgkin's lymphoma, acute leukemia and multiple myeloma) were not different from those of healthy subjects, and only 7 (12.5%) of these patients had levels above the upper limit. In patients with non-malignant diseases (haemolytic anaemia and benign monoclonal paraproteinaemia) the mean and median values were not raised. In patients with non-Hodgkin's lymphoma and with chronic lymphocytic leukemia, the neopterine levels corresponded with the tumor stage. The present data suggest tht neopterine assay may supplement laboratory measurements in haematological diseases, providing helpful information.

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.

Determination of neopterine in human urine by reversed-phase high-performance liquid chromatography

Since the analysis of urinary neopterine is important in diagnosing malignancy, a method has been developed for its rapid and sensitive separation and quantitation using high-performance liquid chromatography (HPLC) on reversed phase. Eluted neopterine is monitored by fluorescence at a excitation wavelength of 353 nm and measured at 438 nm. Separation was optimized by elution with 15 mmol/l potassium phosphate (pH 6.4) at a flow-rate of 0.8 ml/min. Urinary neopterine was related to creatinine with the aim of reducing variations due to fluctuating urinary concentrations. The proposed method has good performance characteristics and is not influenced by the presence of reduced neopterine in urine. Using this HPLC method, urinary neopterine related to creatinine was determined for 148 healthy male adults (mean neopterine/creatinine 113 mumol/mol), 146 healthy female adults (mean neopterine/creatinine 140 mumol/mol) 60 healthy children (mean neopterine/creatinine 163 mumol/mol). The neopterine levels for four healthy individuals were measured daily over a period of one month.

Urinary neopterine as marker for haematological neoplasias

Urinary neopterine levels were studied in 79 normal subjects and in 112 patients with haematological neoplasias. The mean values in 79 patients with active disease were significantly raised compared to the control group. Results obtained in 79 patients with active disease indicate that 91% had neopterine levels higher than the mean value of 79 normal individuals +3 SD. There is only a little overlap between the range of neopterine levels in cancer patients and the range in healthy subjects. No significant difference was found between the mean urinary neopterine levels of 33 patients with non-Hodgkin's or with Hodgkin's lymphoma in remission and the healthy group. Only 15% of these patients had elevated neopterine levels. The mean urinary neopterine levels correlated well with the tumor stage in patients with chronic lymphocytic leukaemia and with non-Hodgkin's disease. In patients with chronic leukaemia those without hepatosplenomegaly excreted significantly more neopterine than controls, and patients with hepatosplenomegaly significantly more than those without hepatosplenomegaly. It is concluded that urinary neopterine levels are of value for following the progression of haematological neoplasias.