Deoxyuridine suppression studies in bone marrow in primary refractory sideroblastic anemia

Cobalamin-dependent metabolism in chronic myelogenous leukemia determined by deoxyuridine suppression test and the formiminoglutamic acid and methylmalonate excretion in urine

The cobalamin metabolism in chronic myelogenous leukemia (CML) was evaluated in 18 newly diagnosed and untreated patients by formiminoglutamic acid (FiGlu) and methyl malonic acid excretion (MMA) tests. A deoxyuridine (dU) suppression test of bone marrow cells was compared in patients with acute myelogenous leukemia (N = 5), myelodysplastic disease (N = 3), untreated pernicious anemia (N = 16), folate deficiency (N = 7), and a hospital reference group without signs of cobalamin or folate deficiency (N = 22). All had normal MMA excretion but 3 of 15 patients had increased FiGlu excretion. In vitro thymidine uptake in bone marrow cells of CML patients were lower (mean 40 fmol/106 cells) than pernicious anemia patients (115 fmol/106 cells). Methotrexate (MTX) increased the uptake in all cases. Addition of formyl-THF, methyltetrahydrofolate (methyl-THF), and pteroylglutamic acid (PGA) tended to normalize the effect of MTX. In pernicious anemia methyl-THF only decreased the uptake in combination with CN-Cbl. dU suppression values were significantly higher (6.3%) in CML than in the reference group (4.4%), but significantly lower than in pernicious anemia (41.6%) and folate deficiency (28.5%). The dU suppression values in bone marrow cells of CML patients correlated significantly with the transferrin saturation. In buffy coat cells dU suppression values were even higher (9.3%) than in bone marrow cells of the same CML patients. Addition of folate forms and CN-Cbl did not change the dU suppression values in CML, as it did in pernicious anemia. MTX increased dU suppression values significantly in all patients, but more in CML (64.5%) than in pernicious anemia (48.6%) and controls (49.8%). The MTX effect was to some extent neutralized by folate analogues with formyl-THF as the most effective followed by methyl-THF and lastly PGA. Methyl-THF also neutralized MTX in pernicious anemia, but its effect was certainly enhanced by addition of CN-Cbl. Thymidine uptake and dU suppression patterns were not significantly changed in CML after treatment with busulfan for 1 week or in accelerated phase. We concluded that signs of cobalamin or folate deficiency (apart from one patient) cannot be demonstrated in untreated CML. However, dU suppression was significantly increased and more so in circulating myeloid cells than in bone marrow. This indicates a deranged metabolism of deoxynucleotides which is independent of cobalamin and folates, and a difference between bone marrow cells and circulating cells. dU suppression is a valuable indicator of cobalamin deficiency.(ABSTRACT TRUNCATED AT 400 WORDS)

Deoxyuridine suppression: biochemical basis and diagnostic applications

The deoxyuridine (dU) suppression test evolved out of investigations into the biochemical basis of the megaloblastic changes seen in vitamin B12 and folate deficiency. Although the abnormality in dU suppression which occurs in vitamin B12- or folate-deficient states is assumed to reflect impaired methylation of deoxyuridylate, there is still no direct demonstration that this is so. Furthermore, there is evidence that reactions other than the methylation of deoxyuridylate are involved in the phenomenon of dU suppression. Nevertheless, in clinical practice abnormal dU suppression serves as a sensitive index of the presence of megaloblastosis due to vitamin B12 or folate deficiency. dU suppression is also abnormal in a number of conditions other than vitamin B12 or folate deficiency, but its overall specificity in detecting tissue dysfunction due to these two deficiency states is considerably higher than that of the serum vitamin B12 or red cell folate levels. Consequently, the test enables us simply and rapidly to define those patients in whom macrocytosis is unrelated to a deficiency of vitamin B12 or folate. For these reasons, the dU suppression test has been adopted by several laboratories across the world for investigating patients with (a) possible vitamin B12 or folate deficiency, (b) macrocytosis, and (c) megaloblastic erythropoiesis. Since the dU suppression test is abnormal in transcobalamin II deficiency and in some congenital disorders of vitamin B12 and folate metabolism, it is very useful in the investigation of obscure anaemias in infancy and childhood. In addition, it has contributed to our understanding of the mechanisms underlying the myelotoxicity of certain drugs, and particularly of nitrous oxide.

The deoxyuridine suppression test

The deoxyuridine suppression (dU) test, first described in 1964, has gained an important place both in the diagnosis of megaloblastic anemias and in the study of vitamin B12 folate interrelationships in the pathogenesis of megaloblastic anemia. The test measures the integrity of the de novo synthetic pathway of DNA synthesis, in which vitamin B12 and folate play an essential role. The exact mechanism of the test is still largely unknown. However, it is probably the most sensitive and specific functional test for the establishment of vitamin B12 and/or folate deficiency. As such, it is an important diagnostic tool in the investigation of patients suspected of suffering from deficiency of either or both of these vitamins. The test may also have applications towards the study of other factors required for the de novo synthesis of DNA.