Pogostone Metabolic Pathway: Patchouli in Traditional Chinese Medicine

Pogostone is a chemical marker for the medicinal plant Pogostemon cablin, commonly known as patchouli.In traditional Chinese medicine, P. cablin‘s essential oil treats the common cold, fever, diarrhea and nausea. Pogostone itself demonstrates antibacterial, antifungal and pesticidal properties. For drug discovery relative to this compound, it is imperative to elucidate its pharmacokinetics, metabolic characteristics and, ultimately, its pharmacological mechanisms.

Recently, Li et al. used liquid chromatography–tandem mass spectrometry (LC-MS/MS) to characterize the pogostone metabolic pathway both in vivo and in vitro.¹ For in vivo analysis, they orally administered one 80 mg/kg dose of 99% pure pogostone to Sprague–Dawley laboratory rats and collected post-administration samples of urine (2 mL), feces (10 g), bile (2 mL) and blood plasma (500 μL). The researchers then subjected prepared samples to LC-MS/MS with a reversed-phase C18 column (2.1 mm × 100 mm, 3.5 μm) and electrospray ionization (ESI) source. The scanning mass range was m/z 100 to 600 in the negative ion mode. To acquire accurate mass values for pogostone and its metabolites, the research team used an LTQ Orbitrap hybrid ion trap-Orbitrap mass spectrometer and Xcalibur software (Thermo Scientific). For in vitro analysis, the researchers prepared rat liver microsomes (RLMs) incubated with pogostone in the presence of the reducing co-enzyme NADPH (nicotinamide adenine dinucleotide phosphate). They subjected the prepared samples to LC-MS/MS.

Using the biological samples, the researchers identified the peak at m/z 223 (14.1 minutes) as the deprotonated parent molecule (C₁₂H₁₅O₄), or non-metabolized pogostone, and proposed the following collision-induced dissociation pathway: loss of an H₂O molecule (mass shift -18 Da) at m/z 205; loss of a prop-1-ene moiety (mass shift -42 Da) at m/z 181; ring opening and loss of a CO₂ moiety (mass shift -44 Da) at m/z 179; ring opening and loss of both a CO₂ moiety and a prop-1-yne moiety (mass shift 84 Da) at m/z 139. The precise mass values for the main ions (m/z 179 and 139) were 179.1079 and 139.0766 Da, which indicate the following elemental compositions: C₁₁H₁₅O₂ and C₈H₁₁O₂. The researchers used these data for reference when characterizing the metabolic pathway.

Li et al. identified eight metabolites (M1–8) in the biological and in vitro samples (see table below). The proposed metabolic pathway and mechanisms are as follows: pogostone (M0) metabolizes into M1, M2 and M3 (via monohydroxylation) and M6 (via hydrolyzation); M1 and M2 metabolize into M4 (via dihydroxylation), then M5 (via hydroxylation and oxidation); M3 metabolizes into M7 (via oxidation) or M8 (via monohydroxylation and glucuronidation).

The researchers note that their previous research found a low half-life for pogostone in both mice (51–53 minutes) and rats (37–51 minutes), indicating that the intense metabolism proposed here may explain the rapid elimination they previously described. They call for further studies to define the precise pharmacological mechanisms of the eight metabolites in order to elucidate pogostone’s potential application in the development of antibiotic and pesticidal products.

 

Metabolite	m/z, minute	Sample source	Formula	Identification
M0	223, 14.09	RLM, plasma, urine, bile	C12H16O4	Pogostone
M1	239, 4.31	RLM, plasma	C12H16O5	monohydroxylation (+16 Da)
M2	239, 7.13	RLM, plasma, urine	C12H16O5	monohydroxylation (+16 Da)
M3	239, 11.93	RLM, plasma, urine, bile	C12H16O5	monohydroxylation (+16 Da)
M4	255, 4.41	RLM, plasma, urine	C12H16O6	dihydroxylation (+32 Da), metabolite of M1/M2
M5	253, 4.98	plasma, urine	C12H14O6	hydroxylation and oxidation (+30 Da), metabolite of M4
M6	241, 8.93	RLM, plasma, urine, bile	C12H18O5	Hydrolyzation (+18 Da)
M7	237, 10.47	plasma	C12H14O5	Oxidation (+14 Da), metabolite of M3
M8	415, 3.12	plasma, urine, feces	C18H24O11	Monohydroxylation and glucuronide conjugation (+192 Da), metabolite of M3

Reference

1. Li, Y., et al. (2014) “Characterisation of the Metabolism of Pogostone In Vitro and In Vivo Using Liquid Chromatography with Mass Spectrometry,” Phytochemical Analysis, 25 (pp. 97–105), doi: 10.1002/pca.2471.

 

Post Author: Melissa J. Mayer. Melissa is a freelance writer who specializes in science journalism. She possesses passion for and experience in the fields of proteomics, cellular/molecular biology, microbiology, biochemistry, and immunology. Melissa is also bilingual (Spanish) and holds a teaching certificate with a biology endorsement.