One of the solutions to increase the bioavailability of poorly water-soluble active pharmaceutical ingredients is their incorporation into lipid-based drug delivery system. After oral administration lipid-based drug delivery systems are digested in complex processes that cannot be simulated by conventional tests to evaluate the release of active ingredients. New tests based on in vitro lipolysis are being developed that take greater account of the conditions that affect digestion of lipid-based delivery systems. One of the important influences are digestive lipases, which hydrolyse lipid ester bonds and thus convert them into forms that are more easily absorbed. The aim of this thesis was to analyse physiological data on the activity of digestive lipases from literature and to optimize the in vitro lipolysis method using medium exchange process.
In the first part, we systematically searched the Pubmed database for articles with data on fasted and fed gastric and pancreatic lipase activity determined in healthy volunteers. We found 17 relevant articles, analysed them and graphically presented the obtained data. In the analysis of the articles, we found the values of gastric and pancreatic lipase activity are highly dependent on activity determination parameters such as structure of solid or liquid meal and lipase activity determination method (choice of method, substrate used). However, pancreatic lipase activities do not depend on the sampling site in duodenum.
The idea of the in vitro lipolysis method using medium exchange process is to disperse lipid-based delivery systems in 0.01 M HCl, which illustrates acidic gastric conditions, and then by adding digestive medium we demonstrate the passage of gastric contents into the small intestine. We tested several mixtures of 0,01 M HCl and maleate buffer in different ratios and with different concentrations of components and pH values of maleate buffer. We selected mixtures that had a pH of 7.5 or 6.5. Sodium deoxycholate and phosphatidylcholine were then added to the maleate buffer to prepare the digestive medium. We optimized the process of preparation of the digestive medium. The in vitro lipolysis method was successfully upgraded with a developed medium exchange process: 0.01 M HCl solution to which digestive medium prepared from 100 mM maleate buffer pH 7.8 is added with an optimized process of preparation.
The effect of pancreatic activity on the release of dipyridamole from the self-microemulsifying system (SMES) was evaluated with the in vitro lipolysis method using medium exchange process, comparing three activities of pancreatin (250, 600 in 1000 TBU/mL) selected based on literature analysis. We determined the concentration of released dipyridamole in the whole samples, in the samples of aqueous phase and in the residue. For some unknown reason, the results in the whole samples and the total amount of dipyridamole (sum of dipyridamole in the residue and mass of dipyridamole in the samples taken) were lower than 100 %. From the aqueous phase samples, we observed that the proportions of dipyridamole released were highest at the lowest pancreatic lipase activity and lowest at the highest pancreatic lipase activity, which was not within our expectations.