Nemery B, Aldridge WN. Studies on the metabolism of the pneumotoxin O,S,S-trimethyl phosphorodithioate--II. Lung and liver slices.
Biochem Pharmacol 1988;
37:3717-22. [PMID:
3178883 DOI:
10.1016/0006-2952(88)90405-4]
[Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The metabolism of O,S,S-trimethyl phosphorodithioate (OSSMe), a pneumotoxic impurity in some organophosphorus insecticides, was investigated by incubating rat lung and liver slices with 1 mM OSSMe, labelled with 3H or 14C on one of its thiolo-methyl (CH3S-) groups. Protein bound radioactivity was higher in lung slices than in liver slices. In lung slices the predominant diester produced was O,S-dimethyl phosphorothioate (OSMeO-), whereas in liver slices it was S,S-dimethyl phosphorodithioate (SSMeO-). Other studies had shown binding of radioactivity and OSMeO- production to be cytochrome P-450-dependent processes in microsomes and SSMeO- production to result from the action of cytosolic glutathione-S-transferase on OSSMe. Preincubation of slices with 10(-5) M paraoxon did not influence the amount of protein-bound radioactivity, suggesting that binding of radioactivity did not simply result from protein phosphorylation. Pretreatments of the rats with O,O,O-trimethyl phosphorothioate [OOOMe(S) 0.5, 2.5 and 12.5 mg/kg p.o.], with p-xylene (1 g/kg, i.p.) or with bromophos (5.3 mg/kg, i.p.) which all protect against the lung toxicity of OSSMe probably by inhibiting pulmonary mixed-function oxidase, also led to significant decreases in both protein binding of radioactivity and OSMeO- production in lung slices, but not in liver slices. These results show that tissue slices are a convenient system for investigating xenobiotic metabolism in the lung and they suggest that the susceptibility of the lung to OSSMe probably results from a relatively high rate of activation, coupled with a relatively low rate of metabolism by non-toxic pathways and/or removal of reactive metabolites in some lung cells, possibly the alveolar type I cells.
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