Characterization of fasted human gastric fluid for relevant rheological parameters and gastric lipase activities

Purpose: To characterize human gastric fluid with regard to rheological properties and gastric lipase activity. In addition, traditional physicochemical properties were determined. Methods: Fasted HGA were collected from 19 healthy volunteers during a gastroscopic examination. Rheological characterization of the aspirates was conducted on a TA AR-G2 rheometer, using cone and plate geometry. Lipase activity was measured by continuous titration of released free fatty acid from tributyrate. Further, pH, osmolality, buffer capacity, and surface tension were measured and the total protein content and bile salt level were determined using assay kits. Results: Rheological examination of HGA showed non-Newtonian shear-thinning behavior with predominant elastic behavior in the linear range. The apparent viscosity was measured to be in the range of 1.7-9.3 mPa s at a shear rate of 50 s(-1). The FaSSGF and HCl pH 1.2 have no shear-thinning properties and showed lower viscosity (1.1 mPa s at 50 s(-1)). The observed viscosity of the HGA will decrease the intrinsic dissolution rate of drugs. The activity of the gastric lipase was 7.4 +/- 4.0 U/mL (N = 6, n = 3) and 99.0 +/- 45.3 U/mL (N = 19, n = 3) at pH 2.8 and 5.4, respectively. pH, surface tension, buffer capacity, bile salt concentration, and osmolality were measured and compared with literature data. Conclusion: The rheological behavior and the mean apparent viscosity of HGA are significantly different from that of water and should therefore be considered important during development of gastric simulated media. Further, the activity of the HGL is active even under fasted gastric conditions and might contribute to the digestion and emulsification of lipid-based drug delivery systems in the entire gastrointestinal tract. HGL should therefore be considered in gastric evaluation of lipid-based drug delivery systems. (C) 2013 Published by Elsevier B.V.