N-Methylcanadine

Rationale: N-Methylcanadine and N-methylstylopine are two types of isoquinoline alkaloids which are considered to be the main medicinally active constituents of the genus Papaveraceae. However, to date, no metabolism studies of N-methylcanadine and N-methylstylopine have been reported. Therefore, the purpose of the present study was to investigate the in vitro metabolism of these two alkaloids in rat liver S9. Methods: N-Methylcanadine or N-methylstylopine was incubated with rat liver S9 for 1 h, and then the incubation mixture was processed with 15% trichloroacetic acid. High-performance liquid chromatography with quadrupole time-of-flight mass spectrometry (HPLC/QqTOF-MS) as a reliable analytical method was used. The structural characterization of these metabolites was performed by the combination of the accurate MS/MS spectra and the known elemental composition. Results: As a result, a total of four metabolites of N-methylcanadine and five metabolites of N-methylstylopine in rat liver S9 were tentatively identified. The cleavage of the methylenedioxy group of the drugs was the main metabolic pathway of N-methylcanadine and N-methylstylopine. Conclusions: The present study is the first in vitro metabolic investigation of N-methylcanadine and N-methylstylopine in rat liver S9 using a reliable HPLC/QqTOF-MS method. The metabolic pathways of N-methylcanadine and N-methylstylopine are tentatively proposed. This work lays the foundation for the in vivo metabolism of the two compounds in animals.

Noscapine is an antitumor alkaloid produced in opium poppy (Papaver somniferum) and some members of the Papaveraceae family. It has been primarily used for its antitussive effects; more recently, its anticancer properties were shown. Herein, we detected an SSR embedded in the promoter region of the CYP82Y1 gene, which was found to be the first committed-step enzyme in the noscapine biosynthesis pathway, using the MISA program. Some collected ecotypes of P. somniferum were investigated for understanding of SSRs role in the regulation of gene expression and metabolite content. Quantitative PCR showed that a variation in the motif repeat number (either a decrease or increase) down-regulated the expression of the CYP82Y1 gene. Furthermore, the analysis of noscapine content suggested that a variation in the promoter region influence noscapine amount. Moreover, P. bracteatum was analyzed in both transcript and metabolite levels, and illustrated much less expression and metabolite level in comparison to P. somniferum. By exploiting the transcriptome data from the eight genera of the Papaveraceae family, we found that noscapine biosynthesis genes are present in P. bracteatum and are not shared in other genera of the Papaveraceae family. This results may explain production of a confined metabolite within a genus.

Noscapine biosynthesis in opium poppy is thought to occur via N-methylcanadine, which would be produced through 9-O-methylation of (S)-scoulerine, methylenedioxy bridge formation on (S)-tetrahydrocolumbamine, and N-methylation of (S)-canadine. Only scoulerine 9-O-methyltransferase has been functionally characterized. We report the isolation and characterization of a cytochrome P450 (CYP719A21) from opium poppy that converts (S)-tetrahydrocolumbamine to (S)-canadine. Recombinant CYP719A21 displayed strict substrate specificity and high affinity (Km=4.63±0.71 μM) for (S)-tetrahydrocolumbamine. Virus-induced gene silencing of CYP719A21 caused a significant increase in (S)-tetrahydrocolumbamine accumulation and a corresponding decrease in the levels of putative downstream intermediates and noscapine in opium poppy plants.