In vitro lipolysis tests on lipid nanoparticles: comparison between lipase/co-lipase and pancreatic extract.

Solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLC) are lipid nanocarriers aimed to the delivery of drugs characterized by a low bioavailability, such as poorly water-soluble drugs and peptides or proteins. The oral administration of these lipid nanocarriers implies the study of their lipolysis in presence of enzymes that are commonly involved in dietary lipid digestion in the gastrointestinal tract. In this study, a comparison between two methods was performed: on one hand, the lipase/co-lipase assay, commonly described in the literature to study the digestion of lipid nanocarriers, and on the other hand, the lipolysis test using porcine pancreatic extract and the pH-stat apparatus. This pancreatic extract contains both the pancreatic lipase and carboxyl ester hydrolase (CEH) that permit to mimic in a biorelevant manner the duodenal digestive lipolysis. The test was performed by means of a pH-stat apparatus to work at constant pH, 5.5 or 6.25, representing respectively the fasted or fed state pH conditions. The evolution of all acylglycerol entities was monitored during the digestion by sampling the reaction vessel at different time points, until 60 min, and the lipid composition of the digest was analyzed by gas chromatography. SLN and NLC systems obtained with long-chain saturated acylglycerols were rapidly and completely digested by pancreatic enzymes. The pH-stat titration method appears to be a powerful technique to follow the digestibility of these solid lipid-based nanoparticles.

In vitro digestion of the self-emulsifying lipid excipient Labrasol(®) by gastrointestinal lipases and influence of its colloidal structure on lipolysis rate.

PURPOSE: Labrasol(®) is a self-emulsifying excipient used to improve the oral bioavailability of poorly water-soluble drugs. It is a mixture of acylglycerols and PEG esters, these compounds being substrates for digestive lipases. The characterization of Labrasol(®) gastrointestinal lipolysis is essential for understanding its mode of action. METHODS: Labrasol(®) lipolysis was investigated using either individual enzymes (gastric lipase, pancreatic lipase-related protein 2, pancreatic carboxyl ester hydrolase) or a combination of enzymes under in vitro conditions mimicking first the gastric phase of lipolysis and second the duodenal one. Specific methods for quantifying lipolysis products were established in order to determine which compounds in Labrasol(®) were preferentially hydrolyzed. RESULTS: Gastric lipase showed a preference for di- and triacylglycerols and the main acylglycerols remaining after gastric lipolysis were monoacylglycerols. PEG-8 diesters were also hydrolyzed to a large extent by gastric lipase. Most of the compounds initially present in Labrasol(®) were found to be totally hydrolyzed after the duodenal phase of lipolysis. The rate of Labrasol(®) hydrolysis by individual lipases was found to vary significantly with the dilution of the excipient in water and the resulting colloidal structures (translucent dispersion; opaque emulsion; transparent microemulsion), each lipase displaying a distinct pattern depending on the particle size. CONCLUSIONS: The lipases with distinct substrate specificities used in this study were found to be sensitive probes of phase transitions occurring upon Labrasol(®) dilution. In addition to their use for developing in vitro digestion models, these enzymes are interesting tools for the characterization of self-emulsifying lipid-based formulations.

Labrasol® is an efficacious intestinal permeation enhancer across rat intestine: Ex vivo and in vivo rat studies.

Labrasol® ALF (Labrasol®), is a non-ionic surfactant excipient primarily used as a solubilising agent. It was investigated here as an intestinal permeation enhancer in isolated rat colonic mucosae in Ussing chamber and in rat in situ intestinal instillations. Labrasol® comprises mono-, di- and triglycerides and mono- and di- fatty acid esters of polyethylene glycol (PEG)-8 and free PEG-8, with caprylic (C8)- and capric acid (C10) as the main fatty acids. Source components of Labrasol® as well as Labrasol® modified with either C8 or C10 as the sole fatty acid components were also tested to determine which element of Labrasol® was responsible for its permeability-enhancing properties. Labrasol® (4, 8 mg/mL) enhanced the transport of the paracellular markers, [14C] mannitol, FITC-dextran 4000, and FITC-insulin across colonic mucosae. The enhancement was non-damaging, transient, and molecular weight-dependent. The PEG ester fraction of Labrasol® also had enhancing properties. When insulin was administered with Labrasol® in instillations, it had a relative bioavailability of 7% in jejunum and 12% in colon. C8- and C10 versions of Labrasol® and the PEG ester fraction also induced similar bioavailability values in jejunal instillations: 6, 5 and 7% respectively. Inhibition of lipases in instillations did not reduce the efficacy of Labrasol®, suggesting that its mechanism as a PE is not simply due to liberated medium chain fatty acids. Labrasol® acts as an efficacious intestinal permeation enhancer and has potential for use in oral formulations of macromolecules and BCS Class III molecules.

Development of self emulsifying lipid formulations of BCS class II drugs with low to medium lipophilicity.

Lipid-based formulations can be effective drug delivery systems for poorly water-soluble chemical entities, provided they are designed with careful selection of the excipients, based on their role in the delivery system and in relation to drug properties. The primary factor leading to increased bioavailability is the administration of the drug in a pre-dissolved state thereby avoiding the dissolution limiting step. All model drugs tested (piroxicam, curcumin and nifedipine) belong to the same chemical space--small BCS class II molecules with logP ranging from 2 to 3. These drugs, exhibiting low to medium logP, are not soluble in lipophilic lipid-based excipients (e.g., vegetable oils). Water-soluble and water-dispersible surfactants are able to dissolve the target dose of each drug in the dosage form and efficiently keep it in solution during dispersion. In vitro digestion testing was necessary to discriminate formulations and enable selection of the most robust one. For each molecule, the system with the best performance during dispersion/digestion tests did not comprise the surfactant which delivered the highest solvent capacity for the drug. This study demonstrates the potential of surfactant-based formulations - i.e., Type IV systems from the lipid formulation classification system - for this type of hydrophobic drug.