Edelfosine and miltefosine effects on lipid raft properties: membrane biophysics in cell death by antitumor lipids

Edelfosine (1-O-octadecyl-2-O-methyl-sn-glycero-phosphocholine) and miltefosine (hexadecylphosphocholine) are synthetic alkylphospholipids (ALPs) that are reported to selectively accumulate in tumor cell membranes, inducing Fas clustering and activation on lipid rafts, triggering apoptosis. However, the exact mechanism by which these lipids elicit these events is still not fully understood. Recent studies propose that their mode of action might be related with alterations of lipid rafts biophysical properties caused by these lipid drugs. To achieve a clear understanding of this mechanism, we studied the effects of pharmacologically relevant amounts of edelfosine and miltefosine in the properties of model and cellular membranes. The influence of these molecules on membrane order, lateral organization, and lipid rafts molar fraction and size were studied by steady-state and time-resolved fluorescence methods, Förster resonance energy transfer (FRET), confocal and fluorescence lifetime imaging microscopy (FLIM). We found that the global membrane and lipid rafts biophysical properties of both model and cellular membranes were not significantly affected by both the ALPs. Nonetheless, in model membranes, a mild increase in membrane fluidity induced by both alkyl lipids was detected, although this effect was more noticeable for edelfosine than miltefosine. This absence of drastic alterations shows for the first time that ALPs mode of action is unlikely to be directly linked to alterations of lipid rafts biophysical properties caused by these drugs. The biological implications of this result are discussed in the context of ALPs effects on lipid metabolism, mitochondria homeostasis modulation, and their relationship with tumor cell death.

Acute pancreas allograft rejection is associated with increased risk of graft failure in pancreas transplantation

The effect of acute allograft rejection (AR) on long-term pancreas allograft function is unclear. We retrospectively studied 227 consecutive pancreas transplants performed at our institution between January 1, 998 and December 31, 2009 including: 56 simultaneous pancreas and kidney (SPK), 69 pancreas transplantation alone (PTA); and 102 pancreas after kidney (PAK) transplants. With a median follow-up of 6.1 (IQR 3-9) years, 57 patients developed 79 episodes of AR, and 19 experienced more than one episode. The cumulative incidence for AR was 14.7%, 19.7%, 26.6% and 29.1% at 1, 2, 5 and 10 years. PTA transplant (hazards ratio [HR]=2.28, p=0.001) and donor age (per 10 years) (HR=1.34, p=0.006) were associated with higher risk for AR. The first AR episode after 3 months post PT was associated with increased risk for complete loss (CL) (HR 3.79, p<0.001), and the first AR episode occurring during 3- to 12-month and 12- to 24-month periods after PT were associated with significantly increased risk for at least partial loss (PL) (HR 2.84, p=0.014; and HR 6.25, p<0.001, respectively). We conclude that AR is associated with increased risk for CL and at least PL. The time that the first AR is observed may influence subsequent graft failure.

Decompressive craniectomy and brain death prevalence and mortality: 8-year retrospective review

Decompressive craniectomy (DC) is a surgical practice that has been used since the late 19th century. The cerebral blood flow increase after the performance of a DC can delay and even prevent the development of cerebral circulatory arrest and brain death (BD). We aimed to determine the prevalence of BD, the use of DC, and the evolution to BD with versus without DC. This retrospective, observational, cross-sectional study was performed in a single high-intensity center in Argentina from January 2003 to December 2010. Inclusion criteria were all patients with Glasgow Coma Score of at most 7 on admission or during their stay in the intensive care units. Exclusion criteria were patients with incomplete data. In cases of death, we assessed whether they fulfilled BD criteria or if the cause of death was a cardiac arrest (CA). The 698 patients considered for analysis showed a 60% (n = 418) global mortality rate. The causes were: CA (n = 270); BD (n = 108) and others considered to be "undefined," namely not assessed completely for the diagnosis of BD (n = 40). According to diagnosis category, traumatic brain injury (TBI) was largest (nearly 50%). The DC group (n = 206) showed significant differences regarding sex and diagnosis category versus no DC group. Mortality was significantly lower in this group (48% versus 65%, P < .001). No significant differences were observed comparing causes of death (CA, BD, or undefined). The use of DC did not influence the frequency of BD development (24% versus 26%, P = .72). The average DC rate was 30% and of BD 16%. The prevalence of DC and better survival were recorded compared with subjects without DC. The prevalence of BD was lower than expected in accordance with national registries; however, among our group, DC did not seem to modify the evolution to BD.

Förster resonance energy transfer as a tool for quantification of protein-lipid selectivity

This chapter addresses the determination of protein-lipid selectivity, here described as the preference of a protein for having a specific type of lipid in its vicinity (annular lipids), from Förster resonance energy transfer methodologies. These allow a quantification of the effect, i.e., the determination of the biasing in distribution of the lipid under study around the protein, as compared to its bulk membrane distribution, with advantages over established approaches that have been used for the same purpose, such as electron spin resonance spectroscopy. The experiment can be carried out with steady-state instrumentation, the formalisms are described in detail, and the model can be applied to a membrane protein of any size.

Heterogeneity in resistance to food-related stresses and biofilm formation ability among verocytotoxigenic Escherichia coli strains

This study assessed the resistance of ten verocytotoxigenic Escherichia coli (VTEC) isolates of commonly encountered serogroups/-types and two non-pathogenic E. coli strains to various food-related stresses (acid, alkaline, heat and high hydrostatic pressure treatments) and their biofilm formation ability. In addition, the global changes in the cellular composition in response to the exposure to these adverse environments were monitored by Fourier Transform Infrared (FT-IR) spectroscopy for two of the strains. Large inter-strain variations in stress resistance were observed. The most tolerant strains belonged to serogroup O157 which included both the O157:H7 type strain EDL933 and a representative isolate of the sorbitol fermenting O157:H- VTEC clone (strain MF3582). Strain C-600, a non-pathogenic laboratory strain, was sensitive to multiple stresses. Although wide variation in biofilm-forming ability was observed among VTEC isolates, no consistent relationships between biofilm-forming ability and capacity to withstand stress exposures were found. Analysis of the allelic status of the rpoS gene, involved in the general stress response of stationary-phase cells, allowed detection of loss-of-function mutations for two strains, E218/02 and MF2411, both of them showing as common features a high sensitivity to alkaline and heat treatments and a poor ability to form mature biofilms. Evidences found in this study confirm rpoS as a highly mutable gene in nature, and suggest its relevance not only for the mount of an active stress response but also for the establishment of mature biofilm communities. Our findings contribute to increase the knowledge on the resistance of VTEC to environmental stresses commonly encountered in the food chain, which can lead to improved strategies for preventing VTEC infections.

The photophysics of a Rhodamine head labeled phospholipid in the identification and characterization of membrane lipid phases

The organization of lipids and proteins into domains in cell membranes is currently an established subject within biomembrane research. Fluorescent probes have been used to detect and characterize these membrane lateral heterogeneities. However, a comprehensive understanding of the link between the probes' fluorescence features and membrane lateral organization can only be achieved if their photophysical properties are thoroughly defined. In this work, a systematic characterization of N-(lyssamine Rhodamine B sulfonyl)-1,2-dioleoyl-sn-3-phosphatidylehanolamine (Rhod-DOPE) absorption and fluorescence behavior in gel, liquid-ordered (l(o)) and liquid-disordered (l(d)) model membranes was performed. In agreement with a previous study, it was found that Rhod-DOPE fluorescence lifetimes present a strong sensitivity to lipid phases, becoming significantly shorter in l(o) membranes as the probe membrane concentration increases. The sensitivity of Rhod-DOPE absorption and fluorescence properties to the membrane phase was further explored. In particular, the fluorescence lifetime sensitivity was shown to be a consequence of the enhanced Rhod-DOPE fluorescence dynamic self-quenching, due to the formation of probe-rich membrane domains in these condensed phases that cannot be considered as typical probe aggregates, as excitonic interaction is not observed. The highly efficient dynamic self-quenching was shown to be specific to l(o) phases, pointing to an important effect of membrane dipole potential in this process. Altogether, this work establishes how to use Rhod-DOPE fluorescence properties in the study of membrane lipid lateral heterogeneities, in particular cholesterol-enriched lipid rafts.

Organization and dynamics of Fas transmembrane domain in raft membranes and modulation by ceramide

To comprehend the molecular processes that lead to the Fas death receptor clustering in lipid rafts, a 21-mer peptide corresponding to its single transmembrane domain (TMD) was reconstituted into mammalian raft model membranes composed of an unsaturated glycerophospholipid, sphingomyelin, and cholesterol. The peptide membrane lateral organization and dynamics, and its influence on membrane properties, were studied by steady-state and time-resolved fluorescence techniques and by attenuated total reflection Fourier transformed infrared spectroscopy. Our results show that Fas TMD is preferentially localized in liquid-disordered membrane regions and undergoes a strong reorganization as the membrane composition is changed toward the liquid-ordered phase. This results from the strong hydrophobic mismatch between the length of the peptide hydrophobic stretch and the hydrophobic thickness of liquid-ordered membranes. The stability of nonclustered Fas TMD in liquid-disordered domains suggests that its sequence may have a protective function against nonligand-induced Fas clustering in lipid rafts. It has been reported that ceramide induces Fas oligomerization in lipid rafts. Here, it is shown that neither Fas TMD membrane organization nor its conformation is affected by ceramide. These results are discussed within the framework of Fas membrane signaling events.