Effect of methotrexate on the deoxyuridine suppression test: results with different cell preparations

The deoxyuridine suppression test in HIV-1 positive patients: the role of azydothymidine (AZT)

The deoxyuridine suppression test (dUST) was used to evaluate human immunodeficiency virus type 1 positive (HIV-1) patients with low serum levels of vitamin B12 and/or low red cell folate and to assess any possible interferences of azydothymidine (AZT) in this test. The dUST was studied in 29 HIV-1 positive patients, 18 without low serum vitamin B12 or low red cell folate and 11 with low serum vitamin B12 (6 patients), low red cell folate (4 patients) and 1 case with both. The role of AZT was studied using different concentrations (0.2, 2.5 and 10 microM/ml) in 2 groups: 1 group of 5 patients with vitamin B12 and/or folate deficiency and another group consisting of 13 healthy subjects. Methotrexate (MTX)(50 micrograms/ml) was added to induce a folate megaloblastic pattern in the latter group. Results of the dUST in the HIV-1 group without low levels of serum vitamin B12 fell within the health-related reference interval values. A vitamin B12 deficiency was only detected in 1 case in the HIV-1 group with low serum vitamin B12, although a folate deficiency pattern was observed in the 4 patients with low red cell folate. In the healthy subjects AZT induced a dose-dependent decrease of the MTX-induced folate megaloblastic pattern. The pattern was also observed in the group of patients with vitamin B12 or folate deficiency, although AZT did not entirely interfere with the dUST. The effect of AZT on the dUST was attributed to a decrease in the incorporation of the isotope in the absence of deoxyuridine. The dUST is useful in differentiating vitamin B12 deficient patients from HIV-1 infected patients with low levels of serum vitamin B12.

Cell kinetics of the rat corneal epithelium

In the rat corneal epithelium the mitotic rate (MR) is almost equal throughout the epithelium in the morning (Haaskjold et al. 1988). The labelling index (LI) shows a marked reduction in the central cornea, which could suggest a lack of uptake of tritiated thymidine via the salvage pathway (Haaskjold et al. 1989). In the present study we have used [3H]deoxycytidine, and [3H]thymidine after prior treatment with a methotrexate regimen to elucidate this discrepancy. Deoxycytidine is incorporated into DNA independent of thymidine kinase, while methotrexate, which depletes the cells of reduced folates, makes the cells completely dependent on the salvage pathway. With both techniques the same pattern of labelling was observed, confirming that in the morning the ratio between the MR and the LI differs throughout the cornea. Based on previous observations, an analysis of the MR/LI ratio during 24 h was performed, showing that these parameters were strongly correlated. This suggests that there may be different circadian variations in the cell proliferation parameters throughout the corneal epithelium. The methotrexate regimen may be a useful tool to investigate the salvage pathway.