Albumin displacement at the air-water interface by Tween (Polysorbate) surfactants.

Tween (polysorbate) 20 and 80 are surfactants used for the development of parenteral protein drugs, due to their beneficial safety profile and stabilisation properties. To elucidate the mechanism by which Tween 20 and 80 stabilise proteins in aqueous solutions, either by a "direct" protein to surfactant interaction and/or by an interaction with the protein film at the air-water interface, we used spectroscopic (Infrared Reflection Absorption Spectroscopy, IRRAS) and microscopic techniques (Brewster Angle Microscopy, BAM) in combination with surface pressure measurements. To this end, the impact of both types of Tweens with regard to the displacement of the protein from the air-water interface was studied. As a model protein, human serum albumin (HSA) was used. The results for the displacement of the adsorbed HSA films by Tweens 20 and 80 can partially be understood on the basis of an orogenic displacement mechanism, which depends on the critical surface pressure of the adsorbed protein film. With increasing concentration of Tween in the sub-phase, BAM images showed the formation of different domain morphologies. IRRA-spectra supported the finding that at high protein concentration in the sub-phase, the protein film could not be completely displaced by the surfactants. Comparing the impact of both surfactants, we found that Tween 20 adsorbed faster to the protein film than Tween 80. The adsorption kinetics of both Tweens and the speed of protein displacement increased with rising surfactant concentration. Tween 80 reached significant lower surface pressures than Tween 20, which led to an incomplete displacement of the observed HSA film.

Effects of frequently used pharmaceutical excipients on the organic cation transporters 1-3 and peptide transporters 1/2 stably expressed in MDCKII cells.

There is ample evidence that pharmaceutical excipients, which are supposed to be pharmacologically inactive, have an impact on drug metabolism and efflux transport. So far, little is known whether they also modulate uptake transporter proteins. We have recently shown that commonly used solubilizing agents exert significant effects on the function of organic anion uptake transporting polypeptides. Therefore, we investigated in this study the influence of frequently used pharmaceutical excipients on the transport activity of organic cation transporters OCT1, OCT2 and OCT3 and the peptide transporters PEPT1 and PEPT2. Inhibition of the OCTs and PEPTs by the excipients polyethylene glycol 400 (PEG), hydroxypropyl-ß-cyclodextrin (HPCD), Solutol® HS15 (SOL), Cremophor® EL (CrEL), Tween® 20 (Tw20), Tween® 80 (Tw80), Kolliphor® P188 (P188) and Kolliphor® P407 (P407) was evaluated using stably transfected MDCKII cells with radio-labeled reference substrates and established inhibitors as controls. Intracellular accumulation of [3H]-1-methyl-4-phenylpyridinium (MPP+) for the OCTs and [3H]-glycyl-sarcosine (Gly-Sar) for the PEPTs was measured by liquid scintillation counting after cell lysis. Our studies revealed that PEG, HPCD, SOL, CrEL, Tw20 and Tw80 were potent inhibitors of OCT1-3 (e.g., Tw20 IC50 values<0.04%). Cellular uptake of Gly-Sar by PEPT1 and PEPT2 was strongly inhibited by both Tw20 and Tw80. SOL was also a strong inhibitor of PEPT1 and PEPT2 (e.g., SOL IC50 values<0.02%), while CrEL showed significantly inhibition of only PEPT2. The substantial inhibitory effects of certain solubilizing agents on OCTs and PEPTs should be considered if they are to be used in dosage forms for new chemical entities and registered drugs to avoid misinterpretation of pharmacokinetic data and undesired drug interactions.