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Inhibition of microsomal oxidation of alcohols and of hydroxyl-radical-scavenging agents by the iron-chelating agent desferrioxamine.

ABSTRACT: Rat liver microsomes (microsomal fractions) catalyse the oxidation of straight-chain aliphatic alcohols and of hydroxyl-radical-scavenging agents during NADPH-dependent electron transfer. The iron-chelating agent desferrioxamine, which blocks the generation of hydroxyl radicals in other systems, was found to inhibit the following microsomal reactions: production of formaldehyde from either dimethyl sulphoxide or 2-methylpropan-2-ol (t-butylalcohol); generation of ethylene from 4-oxothiomethylbutyric acid; release of 14CO2 from [I-14C]benzoate; production of acetaldehyde from ethanol or butanal (butyraldehyde) from butan-1-ol. Desferrioxamine also blocked the increase in the oxidation of all these substrates produced by the addition of iron-EDTA to the microsomes. Desferrioxamine had no effect on a typical mixed-function-oxidase activity, the N-demethylation of aminopyrine, nor on the peroxidatic activity of catalase/H2O2 with ethanol. H2O2 appears to be the precursor of the oxidizing radical responsible for the oxidation of the alcohols and the other hydroxyl-radical scavengers. Chelation of microsomal iron by desferrioxamine most likely decreases the generation of hydroxyl radicals, which results in an inhibition of the oxidation of the alcohols and the hydroxyl-radical scavengers. Whereas desferrioxamine inhibited the oxidation of 2-methylpropan-2-ol, dimethyl sulphoxide, 4-oxothiomethylbutyrate and benzoate by more than 90%, the oxidation of ethanol and butanol could not be decreased by more than 45-60%. Higher concentrations of desferrioxamine were required to block the metabolism of the primary alcohols than to inhibit the metabolism of the other substrates. The desferrioxamine-insensitive rate of oxidation of ethanol was not inhibited by competitive hydroxyl-radical scavengers. These results suggest that primary alcohols may be oxidized by two pathways in microsomes, one dependent on the interaction of the alcohols with hydroxyl radicals (desferrioxamine-sensitive), the other which appears to be independent of these radicals (desferrioxamine-insensitive).

SUBMITTER: Cederbaum AI

PROVIDER: S-EPMC1154195 | biostudies-other | 1983 Jan

REPOSITORIES: biostudies-other

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Project description:Advanced oxidation treatment processes used in various applications to treat contaminated soil, water, and groundwater involve powerful radical intermediates, including hydroxyl radicals (•OH). Inefficiency in •OH-driven treatment systems involves scavenging reactions where •OH react with non-target species in the aqueous and solid phases. Here, •OH were generated in iron (Fe)- and UV-activated hydrogen peroxide (Fe-AHP, UV-AHP) systems where the loss of rhodamine B served as a quantitative metric for •OH activity. Kinetic analysis methods were developed to estimate the specific •OH surface scavenging rate constant (k≡S). In the Fe-AHP system, k≡S for silica (2.85 × 106 1/m2 × s) and alumina (3.92 × 106 1/m2 × s) were similar. In the UV-AHP system, estimates of k≡S for silica (4.50 × 106 1/m2 × s) and alumina (7.45 × 106 1/m2 × s) were higher. k≡S for montmorillonite (MMT) in the UV-AHP system was ≤4.22 × 105 1/m2 × s. Overall, k≡S,silica ∼ k≡S, alumina > k≡S,MMT indicating k≡S is mineral specific. Radical scavenging was dominated by surface scavenging at 10-50 g/L silica, alumina, or MMT, in both Fe-AHP and UV-AHP systems. The experimentally-derived surface •OH scavenging rate constants were extended to in-situ chemical oxidation (ISCO) treatment conditions to contrast •OH reaction rates with contaminant and aqueous phase reactants found in aquifer systems. •OH reaction was dominated by solid surfaces comprised of silica, alumina, and montmorillonite minerals relative to •OH reaction with trichloroethylene, the target compound, and H2O2, a well-documented radical scavenger. These results indicate that solid mineral surfaces play a key role in limiting the degradation rate of contaminants found in soil and groundwater, and the overall treatment efficiency in ISCO systems. The aggressive •OH scavenging measured was partially attributed to the relative abundance of scavenging sites on mineral surfaces.

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Inhibition of microsomal oxidation of alcohols and of hydroxyl-radical-scavenging agents by the iron-chelating agent desferrioxamine.

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