Chamnan Patarapanich

Synthesis of glabridin derivatives as tyrosinase inhibitors

A novel 3″,4″-dihydroglabridin was successfully prepared for studying on tyrosinase inhibitory activity. The result demonstrated that 3″,4″-dihydroglabridin exhibited higher activity than glabridin (IC50 value = 11.40 μM), which is probably due to the 4-substituted resorcinol skeleton and the lacking of double bond between carbon atom 3″ and 4″ on its structure giving more conformational flexibily to interact with the enzyme more effectively. In addition, various acylated derivatives were synthesized as glabridin prodrugs. The chemical and enzymatic hydrolysis of prodrugs revealed that the diacetate ester was rapidly hydrolyzed by porcine liver esterase with the half-life of 2.36 minute, while those of the dihexanoate was 14.8 hour. Both of them were sufficiently stable in phosphate buffer, both pH 5.5 and 7.4, at 37°C with more than 15 days half-life.

In vitro inhibitory effects of asiaticoside and madecassoside on human cytochrome P450

The inhibitory effects and types of inhibition of asiaticoside and madecassoside on human CYPs were studied in vitro using recombinant human CYPs. The median inhibitory concentrations (IC50) of asiaticoside and madecassoside were determined for CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP2E1 and CYP3A4. Asiaticoside inhibited CYP2C19 (IC50 = 412.68 ± 15.44 μM) and CYP3A4 (IC50=343.35 ± 29.35 μM). Madecassoside also inhibited CYP2C19 (IC50 = 539.04 ± 14.18 μM) and CYP3A4 (IC50 = 453.32 ± 39.33 μM). Asiaticoside and madecassoside had no effect on the activities of CYP1A2, CYP2C9 and CYP2D6 and CYP2E1. Assessment of mechanism-based inhibition and the type of inhibition were performed for asiaticoside and madecassoside with CYP2C19 and CYP3A4. These results suggested that madecassoside is a mechanism-based inhibitor of CYP2C19 and CYP3A4. Assessment of mechanism-based inhibition by asiaticoside was limited by its low solubility. Asiaticoside exhibited non-competitive inhibition of CYP2C19 (Ki=385.24 ± 8.75 μM) and CYP3A4 (Ki = 535.93 ± 18.99 μM). Madecassoside also showed non-competitive inhibition of CYP2C19 (Ki = 109.62 ± 6.14 μM) and CYP3A4 (Ki = 456.84 ± 16.43 μM). These results suggest that asiaticoside and madecassoside could cause drug-drug interactions via inhibition of CYP2C19 and CYP3A4. An in vivo study is needed to examine this further.

Acute effects of N-(2-propylpentanoyl)urea on hippocampal amino acid neurotransmitters in pilocarpine-induced seizure in rats

The present study aimed to investigate the anticonvulsant activity as well as the effects on the level of hippocampal amino acid neurotransmitters (glutamate, aspartate, glycine and GABA) of N-(2-propylpentanoyl)urea (VPU) in comparison to its parent compound, valproic acid (VPA). VPU was more potent than VPA, exhibiting the median effective dose (ED(50)) of 49 mg/kg in protecting rats against pilocarpine-induced seizure whereas the corresponding value for VPA was 322 mg/kg. In vivo microdialysis demonstrated that an intraperitoneal administration of pilocarpine induced a pronounced increment of hippocampal glutamate and aspartate whereas no significant change was observed on the level of glycine and GABA. Pretreatment with either VPU (50 and 100 mg/kg) or VPA (300 and 600 mg/kg) completely abolished pilocarpine-evoked increases in extracellular glutamate and aspartate. In addition, a statistically significant reduction was also observed on the level of GABA and glycine but less than a drastic reduction of glutamate and aspartate level. Based on the finding that VPU and VPA could protect the animals against pilocarpine-induced seizure it is suggested that the reduction of inhibitory amino acid neurotransmitters was comparatively minor and offset by a pronounced reduction of glutamate and aspartate. Therefore, like VPA, the finding that VPU could drastically reduce pilocarpine-induced increases in glutamate and aspartate should account, at least partly, for its anticonvulsant activity observed in pilocarpine-induced seizure in experimental animals. Some other mechanism than those being reported herein should be further investigated.