J. E. Casida

Hydroxylation and cyclization reactions involved in the metabolism of tri-O-cresyl phosphate

Abstract Tri- o -cresyl phosphate is metabolized in rats by hydroxylation and cyclization of the hydroxymethyl derivatives. Indirect evidence was obtained for two intermediates, di-( o -cresyl) mono- o -hydroxymethylphenyl phosphate and di-( o -hydroxymethyl-phenyl)mono- o -cresyl phosphate. These intermediates cyclize spontaneously. The principal cyclic phosphate formed was 2-( o -cresyl)-4H-1:3:2-benzodioxaphosphoran-2-one, as ascertained by isolation and synthesis. Evidence is also presented for 2-( o -hydroxymethylphenyl)-4H-1:3:2-benzodioxaphosphoran-2-one and 2-( o -hydroxy-benzyl)-4H-1:3:2-benzodioxaphosphoran-2-one, as either metabolites or products formed on spontaneous cyclization. The primary cyclic metabolite (see above) hydrolyses in mild alkali or reacts with chymotrypsin by cleavage of the cyclic phosphate at the P—O-aryl bond. The deleterious biological activity of tri - o -cresyl phosphate appears to result from esterase inhibition by these cyclic phosphate metabolites.

Potentiation and neurotoxicity induced by certain organophosphates

Abstract The following types of phosphorus compounds were found to be active in potentiating the toxicity of malathion to mice: triphenyl phosphates and phosphonates containing o- and p-, methyl and ethyl substitutents; certain di-(substituted-phenyl) phenylphosphonates and N-methylphosphoramidates; S,S,S-trialkyl phosphorotrithioites and phosphorotrithioates; and certain saligenin cyclic phosphorus esters. Some compounds in the latter two groups also produced ataxia in hens. Certain of the saligenin cyclic phosphorus esters were as potent in effecting ataxia as the dialkyl phosphorofluoridates, but required much larger doses to produce parasympathomimetic effects. Also considered are the activity of the 112 phosphorus esters investigated for inhibition in vitro of mouse plasma esterases hydrolyzing malathion and propionylcholine, and the stability of the saligenin cyclic phosphorus esters to enzymatic and nonenzymatic hydrolysis.

Metabolism of N:N-dialkyl carbamates and related compounds by rat liver

Abstract N:N-Dimethyl- p -nitrophenyl carbamate is metabolized by an enzyme or enzyme system of rat liver microsomes which requires TPNH and oxygen. The resulting product can be extracted into organic solvents and decomposes in strong acid to yield formaldehyde. Its stability in alkali is intermediate between that of the substrate and N-methyl- p -nitrophenylcarbamate. It is formed in vivo by rats and probably by certain insects. The rate at which this or similar systems, in vitro , will attack analogs of N:N-dimethyl- p -nitrophenyl carbamate with different alkyl groups is considerably reduced when the alkyl groups are longer than ethyl. These enzyme systems are inhibited by β-diethylaminoethyl diphenylpropyl acetate (SKF 525-A), by the methylene dioxyphenyl compounds, piperonyl butoxide and sesamex, and by N-octyl bi cyclo heptane dicarboximide. The metabolism of twenty-five N:N-dimethyl carbamates and twenty-three related compounds was investigated. Isolan metabolism was evident when followed both by the formation of formaldehyde-yielding material and reduction in the ability to inhibit cholinesterase in vitro . Metabolism of certain other carbamates gave formaldehyde-yielding materials without loss in cholinesterase-inhibiting activity.

Nicotinic acid analogs: effects on response of chick embryos and hens to organophosphate toxicants.

Embryonic abnormalities are known to be induced in chick embryos when they are injected with certain organophosphate insecticides prior to incubation. The marked teratogenic effects of Bidrin [3-(dimethoxyphosphinyloxy) N, N-dimethyl-cis-crotonamide] can be alleviated by many analogs of nicotinamide and nicotinamide adenine dinucleotide. Successive hydroxylation and N-dealkylation of Bidrin in the egg are not greatly altered by injection of nicotinamide. The delayed neurotoxicity in adult hens after administering tri-o-cresyl phosphate is also partially relieved by administering certain nicotinamide analogs.

Specificity of substituted phenyl phosphorus compounds for esterase inhibition in mice

Abstract Forty-three substituted phenyl phosphorus compounds were studied in relation to selective esterase inhibition in mice, ability to potentiate the toxicity of malathion, and metabolic conversion to more active antiestsrase agents. The malathion potentiation and the degree of in vivo inhibition of the aliphatic esterases hydrolyzing malathion were generally related. A similarity appeared among compounds containing the o -methyl-, o -ethyl- and p -ethylphenyl groupings in their activity for producing neurtotoxicity in hens (activity as recorded in the literature) and for potentiation of malathion in mice. However, several compounds lacking the o -methyl- and o -ethyphenyl groupings were quite selective aliphatic esterase inhibitors and were active in malathion potentiation in mice but did not yield a neurotoxicity with hens. The most active potentiator of malathion by the assay method used was di- o -tolyl mono- p -tolyl phosphate. Metabolic activation to more potent esterase inhibitors was demonstrated for many aryl phosphates containing alkyl substituents in several positions on the phenyl group.

Nonhydrolytic Pathway in Metabolism of N-Methylcarbamate Insecticides.

Sevin (1-naphthyl N-methylcarbamate), when metabolized by rat liver microsomes and insects, yielded at least five carbamate metabolites involving modification of both the methyl group and ring. Certain of these metabolites appeared in milk when Sevin was fed to a goat. The metabolism of o-isopropoxyphenyl N-methylcarbamate by liver microsomes, insects, and plants was compared to that of Sevin.

Enzymatic and antidotal studies on the neurotoxic effect of certain organophosphates

The antiesterase activity of tri-o-cresyl phosphate (TOCP) and its cyclic phosphate metabolite (SM-1) was examined. Administration of TOCP and SM-1 to hens in ataxia-inducing doses resulted in selective rather than prolonged inhibition of the nerve esterases hydrolyzing butyryl esters of choline, glycerol, and phenols. Nerve esterase inhibition was more persistent with TOCP than with SM-1. Selective inhibition of esterases hydrolyzing butyryl esters was also evident in studies in vitro with spinal cord homogenates and SM-1 or diisopropyl fluorophosphate (DFP). TOCP and SM-1 did not affect succinate, α-ketoglutarate, or pyruvate oxidation by preparations of nerve and liver from treated birds, nor was the response of the pyruvate oxidation by brain homogenates to thiamine pyrophosphate affected by TOCP. Many compounds tested as possible antidotes for the neurotoxicity induced by TOCP, SM-1, and DFP proved ineffective. Cortisone acetate gave limited improvement in the condition of the birds, thiamine and oxythiamine appeared to be detrimental, and many potential cholinesterase reactivators and other materials were without effect on the neurotoxicity.