Study of the relationship between lipid binding properties of cyclodextrins and their effect on the integrity of liposomes

It is well known that cyclodextrins are able to extract lipids constituting membranes, increasing their fluidity and permeability. This behaviour towards biological membranes is directly linked to the toxicological effects of methylated cyclodextrins. However, confusion is currently made in the literature between the different methylated cyclodextrin derivatives. Moreover, a new methylated cyclodextrin derivative recently occurred in the market, the Crysmeb. We wanted to compare and understand the effect of the most currently used cyclodextrins on a model membrane. We studied the influence of natural cyclodextrins (betaCD and gammaCD), methylated derivatives (2,6-dimethyl-betaCD (Dimeb), 2,3,6-trimethyl-betaCD (Trimeb) and randomly methylated-betaCD (Rameb), as well as the new derivative Crysmeb), hydroxypropylated derivatives (HPbetaCD of different substitution degrees and HPgammaCD) and the sulfobutylated derivative (SBEbetaCD) on the release of a fluorescent marker encapsulated in the inner cavity of liposomes. It was shown that the observed effect on calcein release can be directly related to the affinity of cyclodextrins for both lipid components of liposomes, cholesterol and phosphatidylcholine. From this relationship, we were able to determine, for each cyclodextrin, a theoretical concentration giving rise to 50% or 100% calcein release. This theoretical concentration was confirmed experimentally. We have also showed that cyclodextrins which provoke calcein release also induce large structure modifications of liposomes.

[Comparative study of a slow-release quinidine preparation and flecainide administered in 2 daily doses for the treatment of extrasystole]

The new anti-arrhythmic agent flecainide was compared in a single-blind cross-over study to arabogalactane quinidine sulfate in the treatment of stable chronic extrasystole, using a fixed twice-daily dose protocol. Results were assessed by the Holter method. 12 patients (7 men and 5 women) with an average age of 56.5 were selected on the basis of stable and essentially ventricular extrasystole (VES) in 11 cases, and essentially atrial extrasystole (AES) in the remaining case. All patients however had some VES and 6 had some AES, and 5 patients had bursts of VES. The protocol provided for four sequences lasting one week each: one fixed, for selection, and the other three random, flecainide (375 mg), quinidine (660 mg), or placebo (2 doses). Data on each were recorded for Holter analysis. Statistical comparison of results was performed by studying variances on an equilibrated block. Comparison between the selection and placebo sequences showed the stability of the arrhythmia whatever its type. Against ectopic complexes as a whole, only flecainide had significant activity (p less than 0.01). Against AES, both compounds were active (p less than 0.05), quinidine more than flecainide (-73%/63%: a non-significant difference). Only flecainide was active against VES (-88.5%). Quinidine did not significantly reduce VES (-56%).(ABSTRACT TRUNCATED AT 250 WORDS)