The Oral Absorption Mechanisms Of Puerarin O/W And W/O Microemulsions

OBJECTIVESPuerarin (Pue) which is extracted from the Puerarin Lobata Ohwi, is widely used in clinical treatment of cardiovascular and cerebrovascular diseases. However, its clinical application is limited due to the low solubility and low oral bioavailability of puerarin. Microemulsion (ME), which can significantly improve the oral bioavailability of water-insoluble drugs, is widely used as oral delivery systems followed by the development of liposomes and solid lipid nanoparticles. The microemulsions can be mainly divided into two types, oil-in-water (O/W) microemulsion and water-in-oil (W/O) microemulsion. Due to their small particle sizes, stability and resistance to degradation in the gastrointestinal, microemulsions have a good prospect of application. According to research reports, O/W-ME and W/O-ME have been shown to increase the oral bioavailabilities of drugs differently, while their oral absorption mechanisms have not been elucidated. In this paper, O/W-ME and W/O-ME of puerarin were developed to investigate the oral absorption and transportation channels of them by using a chylomicron flow block method. Rat in situ stomach perfusion and single-pass intestinal perfusion technique (SPIP) were employed to investigate the absorption of O/W-ME and W/O-ME in stomach and intestines and the oral absorption mechanism of miroemulsions were explained which will provide experimental basis for the design of oral miroemulsion delivery system.METHODS AND RESULTS1. Evaluation of the absorption of puerarin O/W and W/O microemulsions in lymphatic pathwayThe absorption of puerarin O/W, W/O microemulsions in lymphatic pathway was compared with puerarin suspension by using a chylomicron flow block method. The results showed that the Cmax of puerarin O/W-ME, W/O-ME and suspension in lymph blocking group and control group were0.486±0.098vs1.029±0.208,0.618±0.102vs1.966±0.362and 0.408±0.048vs0.740±0.099, the AUC0�'∞of puerarin O/W-ME, W/O-ME and suspension in lymph blocking group and control group were4.008±1.407vs6.998±0.683、4.373±0.326vs7.669±1.866and3.679±2.871vs3.939±0.980, respectively. The proportion of lymphatic transport of puerarin O/W-ME and W/O-ME were43.0%and42.7%, while the suspension was only6.6%(P＜0.05), calculated by the AUC0�'∞. The results showed that O/W-ME and W/O-ME can significantly improve the absorption of puerarin through the lymphatic transfer pathway. Transport through the lymphatic is one of the important reasons of microemulsions to improve the oral bioavailabilities of drugs.2. Study of puerarin O/W and W/O microemulsions in the stomach of ratsThe analytical method of puerarin in the gastric perfusate was set up and the results showed the method had a high specificity and good relationship which achieved the analysis requirements. The absorption of puerarin O/W-ME and W/O-ME in stomach were investigated in in situ stomach perfusion. The results showed that both of the O/W-ME and W/O-ME can promote the absorption of puerarin in the stomach compared with puerarin suspension (P＜0.05). What’s more, the W/O-ME tended to be more effective to enhance the absorption of puerarin which may due to the cosurfactant of W/O-ME was ethanol.3. Study of puerarin O/W and W/O microemulsions in intestines of ratsW/O microemulsion formulations with oil phases of different carbon chain lengths were studied by using pseudo-ternary phase diagrams. The W/O microemulsion formulations with three carbon chain lengths of the oil phase were screened out after preliminary evaluation of the microemulsion quality. L-W/O-ME, M-W/O-ME and S-W/O-ME with the oil phases were EO, IPM and ethyl acetate were selected. Rat single-pass intestinal technique (SPIP) was employed to investigate the difference of W/O-ME and O/W-ME on the absorption rate constant (Ka) and the intestinal apparent permeability coefficient (Papp)-The absorption mechanism of microemulsion was studied with the in vivo intestinal absorption features of puerarin W/O-ME with different oil phases and O/W-ME. The results showed that puerarin can be absorbed in whole intestinal segments. The Ka and Papp in the formulations showed W/O-ME>O/W-ME Suspension (P<0.05). Furthermore, the L-W/O-ME presented the highest absorption rate than that of M-W/O-ME and S-W/O-ME. The absorption of puerarin W/O-ME showed a good positive correlation between the absorption rate and the oil phase carbon chain length. Meanwhile, the results suggested that the W/O-ME seemed to be more effective to promote the intestinal absorption of puerarin than O/W-ME.CONCLUSIONSThese results illustrated that both puerarin O/W-ME and W/O-ME can improve the oral bioavailability of puerarin due to increasing the proportion of lymphatic transport of puerarin compared with suspension. The absorption of puerarin O/W-ME and W/O-ME in the stomach and the intestines were better than suspension. Furthermore, within a certain range, the longer the carbon chain the better its intestinal absorption. The study of the transport mechanism of oral microemulsion in the gastrointestinal tract provided a theoretical basis for the microemulsion formulation design. The release mechanism of the microemulsions in the gastrointestinal tract remains to be further studied.