Effect of trehalose in low concentration on the binding and transport of porphyrins in liposome-human serum albumin system.

The influence of trehalose on the interaction of liposomes with porphyrins and with human serum albumin (HSA) was studied. Small unilamellar liposomes were prepared from 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) and from DMPC/1,2-dimyristoyl-sn-glycero-3-phosphatidylglycerol (DMPG) 19:1 w/w% and incorporated with mesoporphyrin IX (MP) or magnesium mesoporphyrin (MgMP). The fluorescence intensity and anisotropy of porphyrins were measured within the temperature range of 15-33 degrees C, in the presence and in the absence of 3x10(-2) M trehalose, to study the location of the porphyrins inside the liposomes and their partition between the liposomes and HSA. Based on the presented data and our earlier results (I. Bárdos-Nagy, R. Galántai, A.D. Kaposi, J. Fidy, Int. J. Pharm. 175 (1998) 255-267) we conclude that trehalose - even at this relatively low concentration - interacts with the head groups of the liposomes and that the presence of DMPG enhances the effect. This effect seems to hinder the binding of HSA to the liposome surface and influences the location of MgMP within the liposomes. In the case of MP, the porphyrin partition between the liposomes and HSA was affected by trehalose, while for MgMP, trehalose changed the structural conditions of porphyrin binding to the liposomes. The amount of trehalose used did not have a general trend to modify the association constants of porphyrin derivatives either to liposomes or to HSA.

The interaction of human serum albumin and model membranes.

It is frequently observed that the interaction of human serum albumin (HSA) with different lipid membranes may affect molecular transport both in vivo and in vitro experiments. There was a lack of consensus however in the interpretation of results. Earlier studies on the serum albumin membrane association had different conclusions depending on the source of protein, the preparation and the composition of the membranes applied. In this work the change of heat capacity, a sensitive parameter of the interacting system, is compared for uni- and multilamellar liposomes (dimyristoyl-phosphatidylcoline/dimyristoyl-phosphatidylglycerol) at 0, 1x10(-3), 8x10(-3), 1.2x10(-2) and 3.3x10(-2) HSA-lipid ratios. The thermal properties of the sonicated and vortexed liposomes show remarkable differences. The presence of HSA in both types of liposomes also modified their thermal properties, providing clear evidence for protein-vesicle interaction, different in the uni- and multilamellar liposomes. In the case of unilamellar liposomes, two additional transitions were observed at lower temperature, independently of the HSA-lipid ratio, and the protein binding mode to smaller or larger sized liposomes was also distinguishable. The addition of HSA to the multilamellar liposomes resulted in an increase of the pretransition temperature only at the higher HSA-lipid ratio, but the main transition temperature was not affected.

Serum albumin-lipid membrane interaction influencing the uptake of porphyrins.

It is frequently observed in pharmaceutical practice that entrapped substances are lost rapidly when liposomes are used as carriers to introduce substances into cells. The reason for the loss is the interaction of serum components with liposomes. To elucidate the mechanism of this phenomenon the partition of mesoporphyrin (MP) was systematically studied in model systems composed of various lipids and human serum albumin (HSA). As surface charge is an important factor in the interaction, neutral (1, 2-dimyristoyl-sn-glycero-3-phosphatidylcoline, DMPC) and negatively charged (1,2-dimyristoyl-sn-glycero-3-phosphatidylcoline/1, 2-dimyristoyl-sn-glycero-3-phosphatidylglycerol, DMPC/DMPG = 19/1 w/w) lipids were compared. The liposome/apomyoglobin system was the negative control. The size distribution of sonicated samples was carefully analyzed by dynamic light scattering. Constants of association of MP to the proteins and to the liposomes were determined: K(p,1) = (2.5 +/- 0.7) x 10(7) M(-1), K(p,2) = (1.0 +/- 0.7) x 10(8) M(-1), K(L,1) = (1.3 +/- 0.3) x 10(5) M(-1), and K(L,2) = (3.2 +/- 0.6) x 10(4) M(-1) for HSA, apomyoglobin, DMPC, and DMPC/DMPG liposomes, respectively. These data were used to evaluate the partition experiments. The transfer of MP from the liposomes to the proteins was followed by fluorescence spectroscopy. In the case of apomyoglobin, the experimental points could be interpreted by ruling out the protein-liposome interaction. In the case of HSA, the efflux of MP from the liposomes was strongly inhibited above a critical HSA concentration range for negatively charged vesicles. This effect was interpreted as the result of HSA coat formation on the liposome surface. This direct interaction is significant for small liposomes. The interpretation is fully supported by differential scanning calorimetry experiments.