Dihydropteridine reductase activity and neopterin levels in leukemias and lymphomas: is there any correlation between these two parameters?

Urinary neopterin levels, blood dihydropteridine reductase activity as well as other frequently used clinical parameters were evaluated in 110 patients suffering from various types of lymphomas and leukemias. Among them neopterin was detected as the most sensitive marker representing the severity of malignancy (p<0.00001). All patients with active diseases had significantly raised urinary neopterin levels compared to those in remission and healthy controls. Of 69 patients with active disease 66 (96%) were above the upper limit seen in healthy subjects. In addition, the highest neopterin excretion was found in patients with active chronic myeloid leukemia (1469+/-479 micromol/mol creatinine n=16). In contrast, only 1 of 41 patients in stable responsive disease and remission (2.4%) had increased urinary neopterin levels above the upper limit. Dihydropteridine reductase (DHPR) activities were also detected in all patients and control groups. In active disease slightly reduced (DHPR) activities were evident (3.42+/-0.37 for controls, 2.92+/-0.39 in active disease and 3.28+/-0.42 nmol red cytochrome C/min/5 mm diameter disc in remission patients). However in patients under medication this was strengthened. This data also suggest that DHPR activity can be effected by chemotherapy. The results of the present study support the fact that urinary neopterin levels may be an useful and reliable early prognostic marker for neoplasia when used together with other prognostic indicators. Our data also suggest that reductions in DHPR activities may also be an underlying cause for the neurological disorders that are commonly seen in patients with haematological malignancies.

Inhibition of xanthine oxidase by pterins.

The effect of a panel of pterins on xanthine oxidase was investigated by measuring formation of urate from xanthine as well as formazan production from nitroblue tetrazolium. The pterin derivatives, depending on their chemical structure, decreased urate as well as formazan generation: 200 microM neopterin and biopterin suppressed urate formation (90% from baseline) and formazan production (80% from baseline) as well. Their reduced forms, 7,8-dihydroneopterin and 5,6,7,8-tetrahydrobiopterin, showed a lesser but still strongly diminishing influence (40% from baseline). Another oxidized pterin namely leukopterin showed only a weak inhibitory effect. Xanthopterin, a known substrate of xanthine oxidase, had a strong effect on urate formation (80% inhibition), but a lesser effect on formazan production (30% reduction). When iron-(III)-EDTA complex was added to the reaction mixture all the effects were more pronounced. Superoxide dismutase, which removes superoxide anion by dismutation into oxygen, decreased formazan production in addition to pterin derivatives and had a small but enhancing effect on urate formation. Also the reductant N-acetylcysteine had an additive effect to pterins to diminish formazan production in a dose-dependent way. The results of our study suggest that depending on their chemical structure pterins reduce superoxide anion generation by xanthine oxidase.

Urinary neopterin excretion and dihydropteridine reductase activity in rheumatoid arthritis.

Neopterin and biopterin are two products of the pteridine pathway. Even though their roles and interrelationships have not been exactly clarified, neopterin is known as a biomarker of cell-mediated immunity. In this case, the highly elevated neopterin levels are parallel to the slightly elevated biopterin levels. On the other hand, the reduced form of biopterin-tetrahydrobiopterin is an essential cofactor of aromatic monoxygenases that leads to synthesis of tyrosine, tryptophan and dopamine neurotransmitters and its concentration in body fluids and tissues is maintained by the enzyme dihydropteridine reductase (DHPR). Increased numbers of activated lymphocytes can be found in peripheral blood, in the synovial fluid and synovial membranes or patients with rheumatoid arthritis (RA). Since the present study was undertaken to evaluate the role of the pteridine pathway in RA, we measured urine neopterin levels and dried blood DHPR activities in 36 patients with RA and in 20 healthy volunteers, in parallel with other clinical parameters. We found that neopterin excretion was significantly increased in RA patients compared with controls. The means were 433 +/- 216, 153 +/- 43 and 111 +/- 34 mumol/mol creatinine for patients in active stage, in remission and controls, respectively. Our results suggest that urine neopterin levels were strongly dependent on the stage and activity of RA. Either as an effect of the disease itself or of drug administration, slightly reduced DHPR activities were detected (3.484 +/- 0.304 for control, 2.974 +/- 0.255 in active stage RA, and 3.048 +/- 0.302 red cytochrome C/min/5 mm disc in remission).

Colchicine derivatives inhibit neopterin production in human peripheral blood mononuclear cells (PBMC).

Colchicine is a microtubule disrupting agent, mostly used as treatment in various kinds of inflammatory diseases such as acute familial Mediterranean fever and Behcet's disease, as well as gout. In patients with familial Mediterranean fever treatment with colchicine induces a decline of urinary neopterin concentrations which indicates a decrease of cell-mediated immune activation. In this study, we investigated a potential effect of colchicine on the T cell/macrophage system in vitro. The human myelomonocytic cell line THP-1 and PBMC were treated with colchicine or the colchicine derivative, colcemide, in the presence or absence of 250 U/ml interferon-gamma (IFN-gamma) or 10 microg/ml lipopolysaccharide (LPS) for 48 h or 96 h. Colchicine and colcemide increased neopterin/protein production in unstimulated THP-1 cells, but no such effect was apparent in cells stimulated with IFN-gamma. By contrast, when PBMC were treated with colchicine or colcemide a significant reduction in neopterin formation was evident in cells without and with prestimulation by IFN-gamma or LPS. In parallel, reduced production of IFN-gamma was observed in PBMC. These data suggest that colchicine and colcemide are able to inhibit T cell activation within the cellular immune response.

Tumor-associated antigen 90K activates myelomonocytic cell line THP-1.

90K is a tumor-associated antigen. Using myelomonocytic cell line THP-1 we determined neopterin production and tryptophan degradation after exposure of cells to 90K in the presence and the absence of interferon-gamma. Interferon-gamma is a well known stimulus for THP-1 cells inducing e.g. neopterin production and tryptophan degradation. Treatment of cells with 50 micrograms/ml 90K induced significant neopterin formation, and the exposure of cells to 90K in addition to 100 U/ml interferon-gamma amplified neopterin production compared to the sole effect of interferon-gamma. In parallel, a significant degradation of tryptophan was observed in culture supernatants leading to the formation of kynurenine. When the cells were treated with the combination of 90K and interferon-gamma the degradation of tryptophan was further enhanced. The data demonstrate that tumor-associated antigen 90K interferes with immunocompetent target cells and is able to induce a biochemical response in monocytic cells.