Simultaneous Analysis of Honokiol and Magnolol in Rat Serum by HPLC with Fluorescence Detection after Solidphase Extraction for Pharmacokinetic Studies

The author and co-workers previously reported an HPLC method coupled with fluorescence detection (FL) for determination of honokiol and magnolol, and showed that Hange-koboku-to dried extract granules (1.00 g) contained honokiol (3.30 mg) and magnolol (5.40 mg). In this study, the author modified the previous method to make it suitable for simultaneous HPLC-FL analysis of honokiol and magnolol in rat serum. Solid-phase extraction with a Bond Elut-C18 cartridge was carried out for pretreatment of rat serum. 1,1-Bis(4- hydroxyphenyl)cyclohexane was utilized as an internal standard. The mobile phase was prepared by the addition of methanol (750 mL) to a solution of trifluoroacetic acid (0.1 v/v%) in 250 mL of water. The regression equations for honokiol and magnolol in rat serum showed good linearity in the range of 0.1 to 2.5 Μg/mL with lower limits of detection (signal-to-noise ratio of 3) of 0.011 and 0.014 Μg/mL, respectively. The coefficient of variation of the assay and the extraction ratios of honokiol and magnolol by the pretreatment were satisfactory. Magnolol was determined in rat serum after a single p.o. administration of the granules (18 mg/kg as honokiol and 30 mg/kg as magnolol) to rats and its pharmacokinetic parameters were estimated. The level of honokiol in the serum was less than the lower limit of quantification.