Flow cytometric analysis of supravesicular structures in doxorubicin-containing pegylated liposomes

In an attempt to develop a quantitative assay for supravesicular structures (SVS) - such as aggregates, fused liposomes or solid lipid particles - in liposome preparations, forward vs. side scattering of liposomal doxorubicin (Doxil/Caelyx) was analyzed by flow cytometry. Based on calibration with fluorescent latex beads, the size resolution was between about 500 and 1000nm. Caelyx, just as structurally matched empty liposomes (Doxebo) produced dot plots clearly distinguishable from background, suggesting the presence of SVS in the above size region. A comparison of gated areas on the scattergrams obtained for different Caelyx preparations showed differences between current and expired samples, implying that SVS formation may be storage-time-dependent. Incubation of doxorubicin with Doxebo in a free drug and lipid concentration range that corresponds to that in Caelyx also led to varying SVS patterns, raising the possibility that free doxorubicin in Caelyx might contribute to SVS formation. Dynamic light scattering and transmission electron microscopic analysis of liposomes following gaiting and sorting of >500nm particles from Caelyx confirmed the presence of SVS, providing independent evidence for their stable existence. Based on a rough estimation, the amount of SVS in Caelyx is some 60 billionth part of all liposomes. These observations raise the possibility that the presence of an exceedingly small fraction of >500nm particles may be an intrinsic property of PEGylated small unilamellar liposomes, and that the described FACS analysis may be developed further as a quality assay for liposomal homogeneity

Role of complement activation in hypersensitivity reactions to doxil and hynic PEG liposomes: experimental and clinical studies.

Item does not contain fulltextPegylated liposomal doxorubicin (Doxil) and 99mTc-HYNIC PEG liposomes (HPL) were reported earlier to cause hypersensitivity reactions (HSRs) in a substantial percentage of patients treated i.v. with these formulations. Here we report that (1) Doxil, HPL, pegylated phosphatidylethanolamine (PEG-PE)-containing empty liposomes matched with Doxil and HPL in size and lipid composition, and phosphatidylglycerol (PG)-containing negatively charged vesicles were potent C activators in human serum in vitro, whereas small neutral liposomes caused no C activation. (2) Doxil and other size-matched PEG-PE and/or PG-containing liposomes also caused massive cardiopulmonary distress with anaphylactoid shock in pigs via C activation, whereas equivalent neutral liposomes caused no hemodynamic changes. (3) A clinical study showed more frequent and greater C activation in patients displaying HSR than in non-reactive patients. These data suggest that liposome-induced HSRs in susceptible individuals may be due to C activation, which, in turn, is due to the presence of negatively charged PEG-PE in these vesicles

Spontaneous labour at term is associated with fetal monocyte activation

The aetiology of both term and preterm labour remains incompletely understood. Maternal infectious diseases as well as intra-uterine infections were shown to be a well established cause of uncontrollable preterm delivery, indicating that inflammatory reactions, regulated by maternal immunecompetent cells, are implicated in labour-promoting mechanisms. To investigate the possibility that the activation of the fetal immune system may be involved in labour induction, we examined cytokine production patterns of different cord blood cell populations obtained from neonates after spontaneous onset of normal term labour and vaginal delivery (n = 25), vaginal delivery but induced term labour (n = 17), and preterm delivery because of uncontrollable labour (n = 27, 20 patients received corticoid treatment for fetal lung maturation), in comparison with cells obtained from neonates after elective term caesarean delivery in the absence of labour (n = 15). Our results demonstrate that spontaneous term labour, but not induced term labour, was associated with significantly increased IL-6 production by myelomonocytic cell populations. Preterm delivery due to uncontrollable labour with resistance to tocolysis was not associated with increased IL-6 production by fetal myelomonocytic cells. Two-colour flow cytometry combined with intracellular cytokine staining was used to identify fetal monocytes as sources of labour-associated IL-6 release at term. We did not find any activation of cord blood T cells in association with spontaneous term or uncontrollable preterm labour. Therefore, fetal T cell responses may not cause monocyte activation. Our results suggest that increased release of IL-6 from fetal monocytes is involved in mechanisms promoting normal term, but not preterm labour, and that mechanisms inducing term and preterm labour are completely different