Systematic characterization of metabolic profiles of ingenol in rats by UPLC-Q/TOF-MS and NMR in combination with microbial biotransformation

Abstract

Ingenol, as the precursor of the marketed drug ingenol mebutate, has been proven to have a variety of bioactivities. The purpose of this study was to identify the metabolites of ingenol using ultra-performance liquid chromatography-quadrupole time-of-flight-mass spectrometry (UPLC-Q/TOF-MS) combined with UNIFI software. Plasma, urine and fecal samples of rats were obtained and analyzed. A total of 18 metabolites were detected and identified in rat, including five phase II metabolites (M14-M18). Moreover, as microbial biotransformation is helpful to obtain sufficient reference standards of metabolites, the co-culture of ingenol with the fungus Cunninghamella elegans bio-110930 was also studied and yielded 4 phase I metabolites, in which reference standards of three metabolites were further obtained by preparative scale biotransformation. By matching their retention times, accurate masses, and fragment ions with metabolites in rat, the structures of three metabolites (M2, M3 and M4) were unambiguously confirmed by NMR technology. The results revealed that C. elegans bio-110930 functioned as an appropriate model to mimic and prepare phase I metabolism of ingenol in vivo to a certain extent. It also revealed that hydroxylation, oxygenation, sulfonation, and glucuronidation were the major metabolic pathways of ingenol. Furthermore, the first systematic metabolic study of ingenol is of great significance to elucidate the metabolites and metabolic pathways in vivo, which is helpful to predict metabolites of ingenol in humans, understand the elimination mechanism of ingenol, and clarify its effectiveness and toxicity.

Fig. 1. The chemical structure of ingenol.

Fig. 2. A comprehensive strategy to systematically analyze the metabolites in rat of ingenol.

Fig. 3. The Mass spectrum (a) and proposed fragmentation pathways (b) of ingenol.

Fig. 4. Extracted ion chromatograms of ingenol metabolites in rat.

Fig. 5. Product ion spectra of ingenol metabolites in rat.

Fig. 6. The proposed metabolic pathway of ingenol in rat plasma (A), rat urine (B), rat feces (C), and micro-organism (D).

Fig. 7. Extracted ion chromatograms of ingenol metabolites in rat and reference standard isolated and purified from microbial transformation samples.