ABSTRACT
The aim of this study was to find a lipase suitable as a surrogate for Human Gastric Lipase (HGL), since the development of predictive gastrointestinal lipolysis models are hampered by the lack of a lipase with similar digestive properties as HGL. Three potential surrogates for HGL; Rhizopus Oryzae Lipase (ROL), Rabbit Gastric Lipase (RGL) and recombinant HGL (rHGL), were used to catalyze the in vitro digestion of two infant formulas (a medium-chain triacylglyceride enriched formula (MC-IF) and a predominantly long-chain triacylglyceride formula (LC-IF)). Digesta were withdrawn after 0, 5, 15, 30, 60 min of gastric digestion and after 90 or 180 min of intestinal digestion with or without the presence of pancreatic enzymes, respectively. The digesta were analyzed by scanning electron microscopy and gas chromatography to quantify the release of fatty acids (FAs). Digestions of both formulas, catalyzed by ROL, showed that the extent of gastric digestion was higher than expected from previously published in vivo data. ROL was furthermore insensitive to FA chain length and all FAs were released at the same pace. RGL and rHGL favoured the release of MC-FAs in both formulas, but rHGL did also release some LC-FAs during digestion of MC-IF, whereas RGL only released MC-FAs. Digestion of a MC-IF by HGL in vivo showed that MC-FAs are preferentially released, but some LC-FAs are also released. Thus of the tested lipase rHGL replicated the digestive properties of HGL the best and is a suitable surrogate for HGL for use in in vitro gastrointestinal lipolysis models.
Subject(s)
Digestion , Gastric Juice/enzymology , Infant Formula , Lipase/metabolism , Models, Biological , Animals , Fungal Proteins/metabolism , Gastric Juice/metabolism , Humans , Infant , Kinetics , Lipase/genetics , Lipolysis , Liposomes , Microscopy, Electron, Scanning , Molecular Weight , Particle Size , Rabbits , Recombinant Proteins/metabolism , Rhizopus/enzymology , Substrate Specificity , Triglycerides/chemistry , Triglycerides/metabolismABSTRACT
Precipitation of poorly water-soluble drugs from lipid-based drug delivery systems (LbDDS) has been studied extensively during in vitro lipolysis but has never been shown in vivo. The aim of this study was therefore to investigate if drug precipitation can occur from LbDDS during transit of the gastrointestinal tract in vivo. Rats were administered 300 µL of either of two LbDDS (LbDDS I and LbDDS II) loaded with danazol or fenofibrate (or paracetamol to assess gastric emptying). The rats were euthanized at various time points after administration of both LbDDS containing either drug, and the contents of the stomach and proximal part of the small intestine were harvested. The contents were analyzed for crystalline drug by X-ray powder diffraction and polarized light microscopy. No drug precipitation was evident in the stomach or the intestine after administration of LbDDS I containing danazol at the tested time points. Fenofibrate precipitation was absent in the stomach initially after administration of LbDDS I, but was evident in the stomach 90 min after dosing. No crystalline fenofibrate was observed in the intestine. Danazol and fenofibrate precipitation was evident in the stomach following administration of LbDDS II containing either drug, but not in the intestine at the tested time point. Drug precipitation from LbDDS was observed in the stomach, but not in the intestine, which is contrary to what in vitro lipolysis data (obtained under human GI conditions) suggests. Thus, precipitation of drugs from LbDDS in vivo in rats is much lower than might be anticipated from in vitro lipolysis data.
