Rotenone, deguelin, their metabolites, and the rat model of Parkinson's disease

Rotenone and deguelin are the major active ingredients and principal components of cube resin from Lonchocarpus utilis used as a botanical insecticide and piscicide. They are also potent complex I (NADH:ubiquinone oxidoreductase) inhibitors. Rotenone was known earlier, and deguelin is shown here to induce a Parkinson's disease (PD)-like syndrome after subcutaneous treatment of rats by osmotic minipump. Rotenone at 3 mg/kg/day or deguelin at 6 but not 3 mg/kg/day induces degeneration of the nigrostriatal dopaminergic pathway, as shown by reduced tyrosine hydroxylase immunoreactivity with treatments for 5 or 6 days. The neuropathological. lesions are associated with a brain level of parent rotenoid of 0.4-1.3 ppm but not with the much smaller brain level of 12abeta-hydroxyrotenoids or other metabolites analyzed by HPLC and LC/MS. We previously established that the hydroxylated metabolites and derivatives of rotenone and deguelin are all less active (i.e., detoxified) as complex I inhibitors relative to the parent rotenoids. The PD-like syndrome induced in rats by rotenone and deguelin is therefore due to the parent compounds rather than metabolites. Deguelin is about half as active as rotenone in inducing the PD-like syndrome in rats and in acute ip LD50 in mice. Rotenone and deguelin are metabolized by human recombinant 3A4 and 2C19 but not five other P450 enzymes. 2C19 is more selective than 3A4 in forming the 12abeta-hydroxyrotenoids. Identified sites of metabolic attack individually or in combination are as follows: 12abeta hydroxylation and 2-O-demethylation of both compounds, oxidation of the rotenone isopropenyl substituent to mono and diol derivatives, and probable oxidation of the deguelin dimethylehromene double bond. These toxicological features must be considered in using rotenone, deguelin, and their analogues as pesticides, candidate radioimaging and cancer chemopreventive agents, and models of PD.