| Ginkgo seed poisoning sometimes occurs in Japan and China. The symptoms are mainly convulsions and loss of consciousness. 4-O-Methylpyridoxine, MPN, the causative substance has been identified. MPN toxicity shows species differences between guinea pig and rat. The LD50 of MPN in guinea pigs was 200 times lower than that of rats. We tried to clarify the species differences in metabolism of MPN.
Methods
After phenobarbital (PB) or beta-naphtoflavone (B-NF) was administered once a day for five days to each guinea pig and rat, the animals were killed and liver microsomes and brain S9 fractions were prepared. The demethylation of MPN activity was determined using Nash's method. Further, the P450 isozyme involved in the demethylation of MPN was identified using anti-rat P450 antibodies (CYP1A2, 2B1, 2C11, 3A2).
Results
- Demethylation of MPN in rat and guinea pigs liver microsomes was dependent on NADPH and significantly inhibited by octylamine. This activity was induced with PB and inhibited with B-NF in both rats and guinea pigs and differences between rats and guinea pig liver microsomes were not observed. The P450 isozyme which catalyzed the demethylation of MPN belongs to the CYP2B and 3A subfamily by inhibition experiments using anti-rat P450 antibodies.
- The demethylation of MPN in brain S9 from animals which were pretreated with PB was higher than that of B-NF or control in both rats and guinea pigs. A significant difference in MPN demethylation activity between rat and guinea pigs brain S9 was observed in which the demethylation activity of rat brain S9 was 10-50 fold higher than that of guinea pigs brain S9.
Therefore, we concluded that one of the factors in species toxicity differences might due to the gap of metabolism in brain. We also present the analytical method of MPN in biological fluids. We will report the elimination rate of MPN in rats and guinea pigs brain, and pharmacokinetics of MPN. |
