In vitro quantitative structure-activity relationship assessment of pyrrole adducts production by gamma-diketone-forming neurotoxic solvents.

Organic solvents that are metabolically transformable into gamma-diketones produce central- peripheral distal axonopathy. One of the mechanisms proposed to explain the development of this neuropathy has been the formation of pyrrole adducts between gamma-diketone metabolites and -amine groups of lysine residues on the neuronal cytoskeletal proteins. In vivo studies on the neurotoxic capability of different solvents, derivatives of n-hexane and n-heptane, have previously established the quantitative structure-activity sequence. An in vitro assay for the quantification of pyrrole adduct formation is reported here that allows prediction of neurotoxic potency, using an index of neurotoxic potential. The kinetics of pyrrole adduct formation was established by incubation of each solvent with a purified microsomal fraction of liver from rats preinduced with phenobarbital. The solvents assayed in the in vitro system were 2-hexanone, 3,4-dimethylhexane, 2,5-hexanedione, 3,4-dimethyl-2,5-hexanedione, 2-hexanol and 2,5-hex- anediol as derivatives of n-hexane; and 4-heptanone, 5-methyl-3-heptanone, 6-methyl-2,4-heptanedione and 4-heptanol as derivatives of n-heptane. The results indicate good correlation between neurotoxic potency in vivo and quantitative production of adducts in vitro with both n-hexane and n-heptane derivatives.