Semicarbazide as potential source of formaldehyde and nitric oxide formation

Growing evidence that the potential carcinogen, semicarbazide, may get into the human body makes especially important of knowledge for its metabolic fate. While the general agreement that semicarbazide is aldehyde trapping agent and inhibitor of semicarbazide sensitive amine oxidase, which activity increases in blood and body tissues in pathological states, there is assumption that at least one clearans mechanism must operate in vivo. We supposed that semicarbazide may be metabolysed by the members of cytochrome P-450 (CYP-450) family in liver microsomes generating dangerous products. Using difference spectrometry we have found that semicarbazide-induced spectral changes reflect its binding to the active site of CYP-450. To identify the products of semicarbazide decomposition, 7.5 mM semicarbazide was incubated with rat liver microsomes. The concentrations of formaldehyde, nitric oxide on the basis of accumulation of nitrite in the medium, and ammonium were determined by microplate-based spectrophotometry and fluorometry, accordingly. There was net increase in the concentrations of the products during incubation in comparison with control to the extent of 22.04±7.1 for formaldehyde and 11.29±1.91 for nitric oxide μmol/mg protein within 15 min. Formaldehyde and nitric oxide formations were additionally confirmed by using their traps. Dimedone, formaldehyde trap, decreased its amount in the reaction mixture by 55%, whereas iron-dithiocarbamate complex, nitric oxide trap, by 52%. The results suggest that semicarbazide transformation is viewed as two important pathways: one, yielding formaldehyde, and other, producing nitric oxide and ammonium. These hazard products are the reasons for semicarbazide toxicity.