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In this work we studied the particle size distribution of three liposomal preparations by quasi-elastic light scattering spectroscopy. Sized unilamellar vesicles of small diameter (s-SUV) were prepared by ultrasonication and subsequent centrifugation followed by extrusion through polycarbonate membranes of 0.2-micron pore size. Large unilamellar vesicles were obtained by reversed-phase evaporation (REV) and extrusion through polycarbonate filters with or without preliminary freezing-thawing cycles (VETI and VETII, respectively). After preparation, REV were sized to small diameter REV (s-REV) by extrusion through 0.4- and 0.2-micron polycarbonate membranes. According to the results, the s-SUV preparations were made up of two subpopulations, the major of which consisted of vesicles that were 26 nm in mean diameter and accounted for 95% of the overall s-SUV population. The s-REV dispersions always resolved into two populations centered at 120 and 380 nm, the relative proportions of which depended on the pore size of the filters used. VET structures were composed of a single population of vesicles that were approximately 100 nm in mean diameter. Cholesterol inclusion into the bilayer composition extended the distribution without altering its mean value. On the other hand, the internal volumes calculated from mean diameters or assuming a Gaussian distribution were inconsistent with experimental data obtained by usual techniques.

Liposomes can be produced by using various techniques such as mechanical agitation, ultrasonication, ether injection, detergent dialysis, reversed-phase evaporation, extrusion through polycarbonate filters of appropriate pore size, etc. Each procedure provides liposomes with their own perculiar features so the choice of a given one to obtain suitable vesicles for use as drug delivery systems should be based on careful experimentation. In this work we tested three liposome preparation methods that provide unilamellar structures with high yields. In fact, unilamellar vesicles of small diameters (SUV) were prepared by ultrasonication and large unilamellar vesicles (LUV) were obtained by (a) reversed-phase evaporation (REV) and (b) extrusion through polycarbonate filters--with or without preliminary freezing-thawing (VETI and VETII, respectively). According to the results obtained, subsequent filtration of the SUV and REV liposomal preparations results in dramatically decreased average diameters and polydispersity indices, as well as in marked changes in their encapsulation parameters and in lipid losses. Among extruded liposomes, those obtained with preliminary freezing-thawing (VETII) resulted in a higher lipid recovery, even though their average hydrodynamic diameter and polydispersity index as measured by quasi-elastic light-scattering spectroscopy (QELSS) were quite similar to those of the VETI counterparts.

Phenylbutazone (PhB), a powerful anti-inflammatory drug, is able to modify the phase transition of phospholipid bilayers without changing its calorimetric enthalpy (delta Hcal), as can be shown by differential scanning calorimetry (DSC) experiments. Under PhB interaction, dimiristoyl phosphatidylcholine (DMPC) multilamellar liposomes (MLV) undergo lateral phase separation as a result of immiscibility in the bilayer plane. On the other hand, the binding of the anionic fluorescent probe 8-anilino-1-naphthalene sulfonate (ANS) to the surface of DMPC liposomes is altered by PhB. Even though the quantum efficacy of the probe fluorescence emission remains unaffected, the negative cooperativity of the binding process disappears, with the intrinsic dissociation constant showing only a minor variation. From these results it is concluded that PhB would be most likely located close to the lipid:water interface.

Allogeneic bone marrow transplantation (BMT) was carried out on a 5-year-old boy with congenital hypoplastic anemia (CHA), who did not respond to corticosteroids and who was displaying signs of progressive hemosiderosis. Pretransplant preparation had to be modified because respiratory failure and cerebral edema supervened. This preparatory regimen consisted of busulfan (2 mg/kg for four days), cyclophosphamide (50 mg/kg for one day), and total body irradiation (750 rad). Hemopoiesis was completely restored and is still maintained 650 days after transplantation. This is the second published report on the use of BMT to treat a patient with CHA, and it is the first time it has resulted in long-term survival. BMT should be considered for patients with CHA who do not respond to corticosteroids.