Intestinal Absorption of Isoalantolactone and Alantolactone, Two Sesquiterpene Lactones from Radix Inulae, Using Caco-2 Cells

BACKGROUND

Isoalantolactone and alantolactone are the main sesquiterpene lactones in Radix Inulae (dried root of Inula helenium L. or I. racemosa Hook. F.), which is a frequently utilized herbal medicine. They also occur in several plants and have various pharmacologic effects. However, they have been found to have poor oral bioavailability in rats.

OBJECTIVES

To understand the intestinal absorptive characteristics of isoalantolactone and alantolactone as well specific influx and efflux transporters in their absorption.

METHODS

Bidirectional permeabilities of isoalantolactone and alantolactone were investigated across Caco-2 cell monolayers. Transport assays were performed using different concentrations of two lactones and specific inhibitors of ATP-binding cassette transporters and influx transporters.

RESULTS

The absorption permeability of isoalantolactone and alantolactone was high at the tested concentrations (5, 20 and 80 μmol/l), and the major permeation mechanism of both lactones was found to be passive diffusion with active efflux mediated by multidrug resistance-associated proteins (MRPs) and breast cancer resistance protein (BCRP).

CONCLUSION

Our results demonstrated that the absorption permeability of isoalantolactone and alantolactone was good in the Caco-2 cell model. The isoalantolactone and alantolactone absorption elucidated in this study provides useful information for further pharmacokinetics studies. Since low intestinal absorption can now be ruled out as a cause, further studies are needed to explain the low oral bioavailability of the two sesquiterpene lactones.

Metabolism Analysis of Alantolactone and Isoalantolactone in Rats by Oral Administration

Alantolactone and isoalantolactone are the major active ingredients of Inulae Radix. Their metabolism in vivo and in vitro was investigated by UPLC-Q-TOF-MS for the first time. As a result, nine metabolites in vivo including cysteine conjugates, oxidates, dehydrogenates, and hydrates were detected in rat bile after oral administration. The metabolites produced in vitro by incubation with rat liver microsomes were found to be substantially identical to those detected in vivo. However, no metabolites were detected in the samples of plasma, feces, and urine or in the incubates of gastric juice, intestinal juice, and intestinal bacteria. These results reveal that the liver is the main metabolic organ for alantolactone and isoalantolactone, and the first pass effect of the liver appears to be the reason for the low oral bioavailability of the two lactones.

倍半萜内酯类治疗肠易激综合征的应用前景

肠易激综合征(irritable bowel syndrome, IBS)是常见的功能性肠道疾病, 以腹痛或腹部不适、排便习惯异常为特征, 其发病机制尚不明确. 依照罗马Ⅲ标准可将其分为腹泻型、便秘型、混合型和未定型4种亚型. 目前临床治疗原则主要是对症治疗, 迄今尚无特效药物能够有效治疗所有类型IBS. 倍半萜内酯类成分是众多药用植物的生物活性成分, 具有广泛生物学活性, 包括抗肿瘤、抗炎镇痛、抗菌等. 本文就倍半萜内酯类成分可改善IBS症状的相关生物学活性, 及其在IBS治疗中的应用前景进行简要综述.