Zhou Wei, Di Liu-qing, Wang Juan, Shan Jin-jun, Liu Shi-jia, Ju Wen-zheng, Cai Bao-chang
College of Pharmacy, Nanjing University of Chinese Medicine, Nanjing 210046, China.
Acta Pharmacol Sin. 2012 Aug;33(8):1069-79. doi: 10.1038/aps.2012.58. Epub 2012 Jul 9.
To investigate the mechanisms underlying the intestinal absorption of the major bioactive component forsythoside A (FTA) extracted from Forsythiae fructus.
An in vitro Caco-2 cell model and a single-pass intestinal perfusion in situ model in SD rats were used.
In the in vitro Caco-2 cell model, the mean apparent permeability value (P(app)-value) was 4.15×10(-7) cm/s in the apical-to-basolateral (AP-BL) direction. At the concentrations of 2.6-10.4 μg/mL, the efflux ratio of FTA in the bi-directional transport experiments was approximately 1.00. After the transport, >96% of the apically loaded FTA was retained on the apical side, while >97% of the basolaterally loaded FTA was retained on the basolateral side. The P(app)-values of FTA were inversely correlated with the transepithelial electrical resistance. The paracellular permeability enhancers sodium caprate and EDTA, the P-gp inhibitor verapamil and the multidrug resistance related protein (MRP) inhibitors cyclosporine and MK571 could concentration-dependently increase the Papp-values, while the uptake (OATP) transporter inhibitors diclofenac sodium and indomethacin could concentration-dependently decrease the P(app)-values. The intake transporter SGLT1 inhibitor mannitol did not cause significant change in the P(app)-values. In the in situ intestinal perfusion model, both the absorption rate constant (K(a)) and the effective permeability (P(eff)-values) following perfusion of FTA 2.6, 5.2 and 10.4 μg/mL via the duodenum, jejunum and ileum had no significant difference, although the values were slightly higher for the duodenum as compared to those in the jejunum and ileum. The low, medium and high concentrations of verapamil caused the largest increase in the P(eff)-values for duodenum, jejunum and ileum, respectively. Sodium caprate, EDTA and cyclosporine resulted in concentration-dependent increase in the P(eff)-values. Diclofenac sodium and indomethacin caused concentration-dependent decrease in the Peff-values. Mannitol did not cause significant change in the P(app)-values for the duodenum, jejunum or ileum.
The results suggest that the intestinal absorption of FTA may occur through passive diffusion, and the predominant absorption site may be in the upper part of small intestine. Paracellular transport route is also involved. P-gp, MRPs and OATP may participate in the absorption of FTA in the intestine. The low permeability of FTA contributes to its low oral bioavailability.
研究从连翘中提取的主要生物活性成分连翘酯苷A（FTA）的肠道吸收机制。
采用体外Caco-2细胞模型和SD大鼠单通道肠道原位灌注模型。
在体外Caco-2细胞模型中，从顶侧向基底侧（AP-BL）方向的平均表观渗透率值（P(app)值）为4.15×10(-7) cm/s。在2.6 - 10.4 μg/mL浓度下，FTA在双向转运实验中的外排率约为1.00。转运后，顶侧加载的FTA中>96%保留在顶侧，而基底侧加载的FTA中>97%保留在基底侧。FTA的P(app)值与跨上皮电阻呈负相关。细胞旁通透性增强剂癸酸钠和乙二胺四乙酸（EDTA）、P-糖蛋白（P-gp）抑制剂维拉帕米以及多药耐药相关蛋白（MRP）抑制剂环孢素和MK571可浓度依赖性增加Papp值，而摄取（OATP）转运体抑制剂双氯芬酸钠和吲哚美辛可浓度依赖性降低P(app)值。摄取转运体SGLT1抑制剂甘露醇对P(app)值无显著影响。在原位肠道灌注模型中，通过十二指肠、空肠和回肠灌注2.6、5.2和l0.4 μg/mL的FTA后，吸收速率常数（K(a)）和有效渗透率（P(eff)值）虽在十二指肠的值略高于空肠和回肠，但无显著差异。低、中、高浓度的维拉帕米分别使十二指肠、空肠和回肠的P(eff)值增加最大。癸酸钠、EDTA和环孢素导致P(eff)值呈浓度依赖性增加。双氯芬酸钠和吲哚美辛导致P eff值呈浓度依赖性降低。甘露醇对十二指肠、空肠或回肠的P(app)值无显著影响。
结果表明，FTA的肠道吸收可能通过被动扩散发生，主要吸收部位可能在小肠上部。细胞旁转运途径也参与其中。P-gp、MRPs和OATP可能参与FTA在肠道的吸收。FTA的低通透性导致其口服生物利用度低。
