IN-VITRO HEMATOTOXIC EFFECTS OF 3 METHYLATED HYDROXYLAMINES

Hydroxylamine (HYAM, HONH2) and some of its derivatives are known to c ause erythrotoxic effects both in vitro and in vivo. Previous studies have shown that the primary in vitro effect of HYAM and O-ethyl hydrox ylamine (OEH) is methaemoglobin formation, leading to liberation of fr ee radicals which cause lipid peroxidation, enzyme inhibitions and glu tathione depletion. By contrast, N-substituted N,O-dimethyl hydroxylam ine (NODMH), primarily induces impairment of glucose 6-phosphate dehyd rogenase (G6PDH) and glutathione reductase (GR). The oxidative potency of HYAM and the O-derivative was larger than the potency of the N,O-d erivative. This seemed to indicate that attachment of an alkyl group t o the nitrogen atom of hydroxylamine leads to decreased reactivity. To achieve a better understanding of the structure activity relationship for hydroxylamines three methylated derivatives were tested: N-methyl hydroxylamine (NMH), N-dimethyl hydroxylamine (NDMH) and O-methyl hyd roxylamine (OMH). We were also interested in the erythrotoxic potency of OMH which recently entered industrial production. Methaemoglobin fo rmation, high release of lipid peroxidation products, inhibition of NA DPH methaemoglobin reductase and glutathione S-transferase (GST) and d epletion of total glutathione (GT) were seen for OMH. The reducing enz ymes G6PDH and GR were not impaired by OMH. These findings for OMH are consistent with the proposed mechanism for O-derivatives. Since both the effects caused by OMH and its potency are comparable to those of H YAM and OEH this indicates that possible occupational exposure to this compound may be approached similarly to HYAM and OEH. NMH only inhibi ted G6PDH and GR activity, which is fully in accord with the proposed mechanism for N-substituted derivatives of HYAM. However, NDMH a doubl e N-substituted compound, caused a strikingly different scheme of reac tivity: inhibition of G6PDH but not of GR, severe methaemoglobin forma tion, only little lipid peroxidation and some impairment of NADPH meth aemoglobin reductase. This study confirms that O-derivatives of HYAM a re potent haemoglobin oxidators, leading to other oxidative effects. T he main effect was confirmed for single N-derivatives as inhibition of the two protective enzymes G6PDH and GR. However, the results for NDM H indicate that this simple classification of O-derivatives and N-deri vatives has to be extended for double N-substituted compounds which gi ve a mixture of effects.