Effect of nitrous oxide on folate coenzyme distribution and de novo synthesis of thymidylate in human bone marrow cells

Abstract The effect of nitrous oxide on intracellular folate metabolism of the human bone marrow was studied in vitro. Bone marrow cells, obtained from healthy volunteers, were incubated with 5 × 10−8m-[3H]5-formyltetrahydrofolate (5-formylTHF) for 18 hr to label intracellular folate pools. Subsequently the cells were exposed to nitrous oxide for up to 10 hr, and the intracellular folate coenzyme levels were quantitated by HPLC. The dU suppression test was carried out on part of the bone marrow samples in order to measure folate-dependent synthesis of the DNA precursor thymidylate (dTMP). After 5 hr exposure to nitrous oxide the de novo dTMP synthesis of the bone marrow cells was significantly decreased (P < 0.05), and this reduced synthesis persisted at 10 hr. After both 5 and 10 hr of exposure to nitrous oxide the amount of 10-formylTHF was reduced (P < 0.05) while that of 5-methylTHF was increased (P < 0.05). At 10 hr the level of THF was also decreased (P < 0.05). This study shows that nitrous oxide exposure of human bone marrow cells causes a redistribution of the various folate coenzymes which supports the idea of ‘functional cobalamin deficiency’. Moreover it seems probable that following prolonged exposure to nitrous oxide, not only folate-dependent dTMP synthesis but also de novo purine synthesis is reduced

Anti-leukemic potential of methyl-cobalamin inactivation by nitrous oxide

Myelo‐cytotoxicity of extended nitrous oxide (N2O) inhalation was described almost forty years ago and then incidentally applied already with temporary success for suppressing leukemia. In 1948 the accompanying megaloblastic maturation arrest was explained by inactivation of the methylcobalamin coenzyme and subsequent folate deficiency. We studied the anti‐leukemic effect of N2O on a transplantable acute leukemia in B(rown) N(orway) rats. Progression of this B,N,M(yelocytic)L(eukemia) was measured as spleen and liver weights, and leukemic blood cell counts. The deoxyuridine (dU)‐suppression test provided in vitro indication of the functional folate activity of leukemic cells. Breathing of N2O‐oxygen considerably reduced but did not eradicate, BNML‐proliferation. Addition of anti‐metabolites, interfering with some enzyme in the folate metabolism beyond the methylcobalamin co‐enzyme dependent methionine synthase step, acted at least synergistically. The anti‐leukemic effect of cycloleucine, which reduces S‐adenosyl‐methionine synthesis by inactivation of methionine adenosyltransferase, was moderate but became much stronger with N2O inhalation. Methotrexate, a potent anti‐leukemic agent by inhibiting tetrahydrofolate (THF) generation through inactivation of di‐HF reductase, became highly anti‐BNML, even in low dosage when combined with or preceded by N2O. 5‐Fluorouracil, which inhibits methylene‐THF dependent thymidilate synthase, itself was surprisingly anti‐BNML, but also became much more potent with previous or concomittant N2O exposure. Preliminary dU‐suppression test results with human acute leukemia cells, exposed to N2O and/or folate antagonists in vitro, correlated well with the in vivo BNML‐experiments. Combining the anticobalamin activity of N2O with an anti‐folate therefore seems to be a promising chemotherapeutic approach. Copyrigh

The effect of individualized iron supplementation on iron status in Dutch preterm infants born between 32 and 35 weeks of gestational age: evaluation of a local guideline

Objective: Iron deficiency (ID) and iron deficiency anemia (IDA) in early life are associated with adverse effects. Preterm infants are at risk for developing ID(A). Considering that not every preterm infant develops ID(A) and the potential risk of iron overload, indiscriminate iron supplementation in late preterm infants is debatable. This study aimed to evaluate the effect of a locally implemented guideline regarding individualized iron supplementation on the prevalence of ID(A) at the postnatal age of 4–6 months in Dutch preterm infants born between 32 and 35 weeks of gestational age (GA). Methods: An observational study comparing the prevalence of ID(A) at the postnatal age of 4–6 months in Dutch preterm infants born between 32 and 35 weeks of GA before (i.e. PRE-guideline group) and after (i.e. POST-guideline group) implementation of the local guideline. Results: Out of 372 eligible preterm infants, 110 were included (i.e. 72 and 38 in the PRE- and POST-guideline group, respectively). ID- and IDA-prevalence rates at 4–6 months of age in the PRE-guideline group were 36.1% and 13.9%, respectively, and in the POST-guideline group, 21.1% and 7.9%, respectively, resulting in a significant decrease in ID-prevalence of 15% and IDA-prevalence of 6%. No indication of iron overload was found. Conclusion: An individualized iron supplementation guideline for preterm infants born between 32 and 35 weeks GA reduces ID(A) at the postnatal age of 4–6 months without indication of iron overload