Bending elasticities of model membranes: influences of temperature and sterol content.

Giant liposomes obtained by electroformation and observed by phase-contrast video microscopy show spontaneous deformations originating from Brownian motion that are characterized, in the case of quasispherical vesicles, by two parameters only, the membrane tension sigma and the bending elasticity k(c). For liposomes containing dimyristoyl phosphatidylcholine (DMPC) or a 10 mol% cholesterol/DMPC mixture, the mechanical property of the membrane, k(c), is shown to be temperature dependent on approaching the main (thermotropic) phase transition temperature T(m). In the case of DMPC/cholesterol bilayers, we also obtained evidence for a relation between the bending elasticity and the corresponding temperature/cholesterol molecular ratio phase diagram. Comparison of DMPC/cholesterol with DMPC/cholesterol sulfate bilayers at 30 degrees C containing 30% sterol ratio shows that k(c) is independent of the surface charge density of the bilayer. Finally, bending elasticities of red blood cell (RBC) total lipid extracts lead to a very low k(c) at 37 degrees C if we refer to DMPC/cholesterol bilayers. At 25 degrees C, the very low bending elasticity of a cholesterol-free RBC lipid extract seems to be related to a phase coexistence, as it can be observed by solid-state (31)P-NMR. At the same temperature, the cholesterol-containing RBC lipid extract membrane shows an increase in the bending constant comparable to the one observed for a high cholesterol ratio in DMPC membranes.

[Diagnosis and treatment of cervical dysplasia. Report of 42 cases]. / Diagnostic et traitement des dysplasies cervicales. A propos de 42 cas.

The authors present a retrospective study of 42 cases of conization carried out between January 1987 and October 1989 in the Department of Gynaecology 1 of Dupuytren University Hospital in Limoges. The average age of the population was 42 years and 7 months, with an average parity of 1.9 children per woman. Conization was carried out using either a cold knife (37 cases) or an electric knife (5 cases). Complications consisted of 4 stenoses, 2 secondary haemorrhages and 1 perineal burn. 4 microinvasive cancers, 7 CIN III, 10 CIN II, 4 CIN I and 3 pieces of tissue free from any dysplastic lesion were found on histological examination of the conization tissue. 17 patients (40.4%) had flat condylomas. There was perfect agreement between the diagnoses from the smears and biopsies in 82.1 p. cent of cases; there was 57.1 p. cent agreement when the smear result was compared with the histological study of the conization tissue, and 39.2 p. cent agreement when the latter was compared with biopsy results. On the other hand, false diagnosis due to overevaluation of the severity of the dysplasia was predominant using the least invasive examination (42.8 p. cent when comparing the smear results with those from the study of conization tissue, and 39.2% for biopsies with respect to the conizations). According to the authors, the therapeutic strategy to be used in treating dysplasia must take the severity of the dysplasia, the presence of infection due to HPV and its serotyping, the location and size of the dysplasia, the visibility of the endo-exocol junction line and the psychological context of the patient into consideration.

Comparison of the experimental antitumor activities of three nitrosourea derivatives chlorozotocin, RFCNU and CNCC encapsulated in liposomes with those in the free state.

L1210 leukemia was used to compare the antitumor activities of three nitrosoureas (chlorozotocin, RFCNU and CNCC) encapsulated in liposomes with those in the free state. The results obtained varied according to the chemical structure of the compound, its solubility in oil or water, the route of administration into the body, and the treatment dose. The application of liposomes in the chemotherapy of malignant disease deserves further investigations.

Theoretical conformational analysis of phospholipids. I. Study of the interactions between phospholipid molecules by use of semi-empirical methods with the explicit introduction of polar headgroup interactions.

We present a theoretical conformational analysis of a system composed of seven dipalmitoylphosphatidylethanolamine molecules in interaction. The combined use of classical semi-empirical methods for the polar headgroup region with mechanical statistical calculations for the aliphatic chains permits the evaluation of the free energy for a phospholipids molecule. The free energy variation in function of the mean intermolecular interchain distance gives information about the main lipid bilayer phase transition. It appears, however, necessary to take into account the hydration of the polar headgroups.

Theoretical conformational analysis of phospholipids. II. Role of hydration in the gel to liquid crystal transition of phospholipids.

To obtain a satisfactory agreement between computed transition temperatures and those determined experimentally, we introduce explicitly water molecules which hydrate the polar headgroup of dipalmitoylphosphatidylethanolamine molecules. The calculated free energy curves as a function of the intermolecular interchain distance and the degree of hydration of the polar groups permit the determination of the transition of the phospholipid system from the gel to the liquid crystalline phase. The detailed structure of the hydration shell is defined using the supermolecular approach.