Enhanced hydration of dipalmitoylphosphatidylcholine multibilayer by vinblastine sulphate.

Vinblastine sulphate, an antimitotic and anti-inflammatory agent, modifies the thermal behaviour of the model membranes: the dipalmitoylphosphatidylcholine DPPC bilayers. The mixed DPPC and vinblastine sulphate multibilayers in the range of DPPC mole fraction 0.4 to 1 display clearly the gel-liquid crystal (chain melting) transition on the thermograms obtained with a differential scanning microcalorimeter. The molar enthalpy of this transition is slightly depressed by vinblastine sulphate (less than 10%). The temperature-composition phase diagram corresponds to a total insolubility of vinblastine sulphate inside the frozen (gel) bilayers and to a solubility of 0.2 (mole fraction) of vinblastine sulphate inside the fluid (liquid crystalline) bilayers. The dissolved vinblastine sulphate depresses the cooperativity number of the frozen in equilibrium fluid transition of the bilayers very strongly (4- to 5-times). Up to its solubility concentration, vinblastine sulphate increases the amount of the structural water of the bilayers and modifies the thermal behaviour of this water. The 'expelled' vinblastine sulphate molecules are retained by the polar groups of DPPC molecules and screen their electrostatic interactions with the structural water molecules. Below 0 degree C, the amount of the structural water, which forms the aqueous separation between two bilayers, is enhanced by vinblastine sulphate. However, the drug reduces (screens) the bilayers interaction with the structural water molecules.

Tumor promoter 12-O-tetradecanoylphorbol 13-acetate alters state, fluidity and hydration of 1,2-diacyl-sn-glycero-3-phosphocholine bilayers.

Previous results (Castagna et al. (1979) FEBS Lett. 100, 62-66; Fisher et al. (1979) Biochem. Biophys. Res. Commun. 86, 1063-1068) indicated us that the active tumor promoter TPA (12-O-tetradecanoylphorbol 13-acetate) decreased fluorescence polarisation of diphenylhexatriene in lymphoblastoid and rat embryo cells. In the present study, experiments aimed at examining the molecular interactions of tumor promoters with cell membrane components are performed with fully hydrated multibilayers of 1,2-diacyl-sn-glycero-3-phosphocholine (DPPC) into which increasing amounts of TPA are inserted. The thermotropic behaviour of both the phospholipid bilayers and the interbilayer water was investigated using the differential scanning calorimetry (DSC) and the approach of Ter-Minassian-Saraga et al. ((1982) J. Colloïd Interface Sci. 81, 369-383). The major effects of the tumor promoter are confined to concentrations up to 20% mol fractions of TPA. In this range of concentrations the incorporation of TPA into liposomes decreases the phase-transition temperature but did not affect delta HDPPC. Furthermore TPA increases the hydration of the multibilayers. Above 20% mol fractions of TPA, a different thermal behaviour of the system which might suggest morphological rearrangements was observed. The lipid state in TPA-treated liposomes was monitored by fluorescence polarisation using diphenylhexatriene as a lipophilic fluorescent probe and the phase-transition temperature was calculated. The phase transition temperatures determined by both methods were in good agreement. The lowering of this temperature and the decay of fluorescence anisotropy of diphenylhexatriene were parallel. Those effects are consistent with the "fluidising' effect of TPA on DPPC.

The binding of the radioprotective agent cysteamine with the phospholipidic membrane headgroup-interface region.

The interaction of the aminothiol radioprotector cysteamine (beta-mercaptoethylamine) (CYST) with dipalmitoylphosphatidylcholine (DPPC) artificial membranes has been studied by differential scanning calorimetry (DSC), turbidimetry and spin labeling. This hydrophilic molecule displays a biphasic, concentration-dependent binding to the phospholipidic head groups at neutral pH. In the CYST/DPPC molar ratio 1:160-1:2 (mole/mole) an increasing ordering effect is observed. At high concentrations (over 3:1 ratio), this ordering effect decreases. With the symmetric disulfide dimer cystamine, the biphasic effect is not shown and the membrane rigidity decrease is obtained only at concentration ratio higher than 1:1. The charge repartition of the cysteamine molecule has been shown to be disymmetric, +0.52 e on the NH3 group and +0.19 e on the SH extremity, [38] whereas the cystamine molecule is electrostatically symmetrical. These properties could be related to their membrane effects. With cysteamine, at a low concentration, an electrostatic bridging between the negatively charged phosphate groups of the polar heads induces the increase in membrane stability: the molecules behave like a divalent cation. At high concentrations a displacement of the slightly charged SH extremity by the amine disrupts the bridges and induces the decrease in rigidity: the drug behaves like a monovalent cation. Due to its symmetric charge and its double length, such an effect is not observed with cystamine. This study could bring further information about the interactions between cysteamine and polyelectrolytic structures (ADN for example) and about the radioprotective properties of this drug.

Interaction of vinblastine sulfate with artificial phospholipid membranes. A study by differential scanning calorimetry and spin labeling.

The effect of the antimitotic drug vinblastine sulfate has been studied on fully hydrated dipalmitoylphosphatidylcholine (DPPC) liposomes in the temperature range 0 degrees to 60 degrees using differential scanning calorimetry and electron spin resonance spectroscopy with two fatty acid spin labels. In the gel phase, vinblastine interacts essentially with the DPPC polar heads and induces an important disorganization of the phospholipidic bilayer. The co-operativity of the main thermal transition is decreased. In the crystal-liquid phase, the drug penetrates inside the artificial membrane and induces the formation of domains which increased thermal stability. These effects are opposite to those observed with the drug isaxonine which is used to reduce the axonal degenerating effects due to vinblastine.

Isaxonine base is a strong perturber of phospholipid bilayer order and fluidity--a differential scanning calorimetry and spin labeling study.

The effects of the neurotropic drug isaxonine on fully hydrated dipalmitoyl-phosphatidyl-choline (DPPC) bilayers has been studied in the temperature range 0 degree-60 degrees, using differential scanning calorimetry and electron spin resonance spectroscopy, with two stearic acid spin labels. At low concentration (1% mol/mol), isaxonine is trapped in the polar interface and enhances the phospholipid multibilayers organization in the gel state. In contrast, at high concentration (30% mol/mol), the drug disorganizes the phospholipidic structures and may induce domain formation by phase separation. The strong interactions of isaxonine at the lipid-water interface change the ionization state of the stearic acid spin labels which become totally ionized. Then isaxonine acts as a modifier of the surface pH of the bilayer. The strong membrane effects of isaxonine may explain in part its pharmacological properties in vivo.

Physical aging of progesterone-loaded poly(D,L,-lactide-co-glycolide) microspheres.

PURPOSE: To study the interactions between a polymeric matrix and a drug during storage at a temperature lower than the glass transition temperature of the polymers. METHODS: Poly(lactide-co-glycolide) microspheres loaded with different progesterone ratios were stored at 4. 20 and 40 degrees C. DSC-scans were recorded at regular intervals, depending on the storage temperature. RESULTS: The physical aging of the polymeric matrix, as monitored by the amplitude of the endotherm associated with the glass transition, is slowed down by crystalline progesterone. The development of the progesterone polymorphic depends on the interface/volume ratio of the crystals. CONCLUSIONS: For polymeric drug delivery systems, the determination of all studies parameters must take into account an effect of dispersed drugs which are more sensitive as the storage temperature is lower than the glass transition temperature of the matrix.

A physicochemical study of the morphology of progesterone-loaded microspheres fabricated from poly(D,L-lactide-co-glycolide).

Progesterone-loaded microspheres are fabricated by a solvent evaporation process from a poly(D,L-lactide-co-glycolide) (85/15 PLG) and from alpha-progesterone. Methylene chloride is used as solvent and polyvinyl alcohol and methylcellulose are used as surfactants. The microspheres are characterized by scanning electron microscopy, differential scanning calorimetry, and x-ray powder diagrams. Our study shows that the morphology and the thermal behavior of PLG microspheres can vary significantly with progesterone loading and sample thermal history. Below and at 16.5% loading the microspheres exhibit a smooth outer surface. Above 23% loading, the surface becomes rough, embedded by copolymer particles or well-defined crystals. Pores and cracks can also be observed. Below 35% the progesterone is molecularly dispersed. At 35% and above crystal domains of the steroid appear and two crystalline forms are found: alpha- and beta-progesterone. The physical state of progesterone and the nature of its crystal domains dispersed in the PLG matrix can change during storage. Also a progressive development of an endothermic peak at the Tg event of the copolymer is observed during storage. No well defined relationship of peak size to progesterone loading can be shown.