Chemical properties of lipids strongly affect the kinetics of the membrane-induced aggregation of α-synuclein

Intracellular α-synuclein deposits, known as Lewy bodies, have been linked to a range of neurodegenerative disorders, including Parkinson’s disease. α-Synuclein binds to synthetic and biological lipids, and this interaction has been shown to play a crucial role for both α-synuclein’s native function, including synaptic plasticity, and the initiation of its aggregation. Here, we describe the interplay between the lipid properties and the lipid binding and aggregation propensity of α-synuclein. In particular, we have observed that the binding of α-synuclein to model membranes is much stronger when the latter is in the fluid rather than the gel phase, and that this binding induces a segregation of the lipids into protein-poor and protein-rich populations. In addition, α-synuclein was found to aggregate at detectable rates only when interacting with membranes composed of the most soluble lipids investigated here. Overall, our results show that the chemical properties of lipids determine whether or not the lipids can trigger the aggregation of α-synuclein, thus affecting the balance between functional and aberrant behavior of the protein.The protein α-synuclein is mainly found in the presynaptic termini of neurons (1). The protein has been shown to populate a highly unstructured form in its unbound state both in vitro and in vivo and to adopt an α-helical conformation when bound to membranes (2). The balance between these two states has been found to play a role both in the proposed biological function of the protein, including the regulation of synaptic plasticity, and in the kinetics of its pathogenic aggregation; the latter is the hallmark of a range of diseases, known as synucleinopathies, of which the most common is Parkinson’s disease (3, 4). α-Synuclein has been shown to have its highest affinity for membranes containing either anionic lipids or so-called ”packing defects” (5–7), where the latter are defined as low-density regions in bilayers with high exposure of the lipid hydrophobic chains attributable to a mismatch between lipid shape and bilayer curvature (6, 7).Biological membranes are highly heterogeneous and differ from one cell or organelle to another in terms of the physical and chemical properties of the membranes, including curvature, charge, fluidity, and packing of the hydrophobic chains (8–10). The variety of membrane structures in cells can be directly related to differences in lipid (and protein) composition, where properties such as length and saturation of the hydrocarbon chain as well as the charge and size of the polar head group are crucial in determining the properties of the membrane (8, 9). In particular, most chemical and thermotropic properties of a lipid molecule are known to vary almost linearly with the length of its hydrophobic chain. As some examples, the standard change in free energy of transfer of a lipid molecule from water into a bilayer (i.e., its solubility in water), the melting temperature, and the enthalpy of melting have all been found to be proportional to the number of aliphatic carbons in the hydrophobic chain, which ranges from 8 to 18 (11). In addition, the adsorption and partitioning of small molecules and proteins to membranes can also affect the structural and thermotropic properties of the latter, and the magnitude and characteristics of these changes depend on the nature of the molecular interactions (e.g., electrostatic, hydrophobic) (12, 13).The interactions between amphipathic proteins and membranes have been extensively studied over the last three decades (7, 14–22). In general, the amino acid sequences of these peripheral proteins are characterized by patterns of hydrophobic and polar residues such that the proteins fold into amphipathic α-helices upon binding to hydrophobic patches exposed at the membrane interface (16, 17). In particular, molecular dynamics simulations and neutron reflectometry studies of deposited bilayers have shown that the amphipathic helix in α-synuclein is primarily located in the vicinity of the lipid phosphate groups and the glycerol backbone (16, 23–25).Although the binding of α-synuclein to membranes has been well characterized for different lipid systems (26–28), the observed modulation of the kinetics of the conversion of monomeric α-synuclein into amyloid fibrils by different membranes is less well understood (29–32). Most studies of this phenomenon have been performed under conditions of mechanical agitation (32) and/or in the presence of catalyzing polymer surfaces (31), where α-synuclein aggregates also in the absence of lipids and where the mechanism of aggregation has not yet been elucidated. Here, we take a different approach using an experimental procedure with protein-repellant surfaces and under quiescent conditions (33) that enables the systematic study of the manner in which a change in lipid properties can affect the ability of a model membrane to initiate α-synuclein aggregation. Indeed, we have previously shown that the presence of model membranes composed of 1,2-dimyristoyl-sn-glycero-3-phospho-l-serine (DMPS) triggers the aggregation of α-synuclein by specifically enhancing the rate of primary nucleation (33). In addition, this study showed how the protein:lipid (P:L) ratio modulates the kinetics of α-synuclein aggregation in the presence of DMPS; at low P:L ratios, effectively all of the protein molecules are adsorbed onto the surface of the membrane in a thermodynamically stable α-helical state and no aggregation is observed. At high P:L ratios, however, the protein molecules populate both the free monomeric state and the membrane-bound state, leading to rapid amyloid formation (33).In the present study, we have applied this experimental procedure to probe how changes in the chemical (charge and solubility) and physical (thermotropic) properties of lipids affect the binding of α-synuclein and the magnitude by which model membranes can trigger α-synuclein aggregation. The results reveal that the efficiency of the binding of α-synuclein to model membranes is correlated with their fluidity and, conversely, that the self-assembly of the lipids is affected by their association with the protein. In addition, although α-synuclein has a high affinity for all of the fluid anionic model membranes investigated here, this interaction is not sufficient for the efficient induction of aggregation. Rather, the rate of amyloid fibril formation is shown to be inversely correlated with the free energy of transfer of the lipid molecule from water into the bilayer. These results indicate that the chemical properties of the lipids are likely to play an important role in perturbing the balance between functional and deleterious interactions of α-synuclein with membranes.     

Succinylcholine--update

The action profile of succinylcholine is unmatched even 50 years after its introduction into anaesthestic practice. This is probably why succinylcholine, despite its many and partly life-threatening side-effects, is still considered to be indispensable by many anaesthetists and emergency doctors. The main indication for succinylcholine--the facilitation of endotracheal intubation in patients considered to be at an increased risk of aspiration of gastric fluid, e.g. patients undergoing a Caesarean section or presenting with an ileus--remains undisputed. Some of the side-effects of succinylcholine can be diminished by precurarisation. However, just like priming, this technique holds some considerable dangers (such as a clinically significant attenuation of the protective reflexes) and has become a matter of increasing controversy. Rocuronium (> or = 1 mg/kg) is currently the best alternative to succinylcholine for rapid sequence induction. The routine use of succinylcholine as a relaxant for intubation is questionable, mainly because there are a number of modern anaesthetic techniques (laryngeal mask airway) and new drugs (rocuronium, mivacurium, remifentanil) which make succinylcholine quite dispensable except for a few situations (e.g. re-positioning of fractures). In the case of an expected difficult airway no muscle relaxant should be given, because severe hypoxaemia in these patients probably can only be prevented by a professional airway management. Succinylcholine is no longer an option in elective paediatric anaesthesia. The drug, however, retains its value in critical situations where a rapid onset but a short duration of action is of prime importance.     

Modern CT diagnosis of acute thoracic and abdominal trauma

PURPOSE: To evaluate a modified algorithm in the diagnostic management of polytraumatized patients by using whole body multislice CT (MSCT) as primary diagnostic tool. MATERIAL AND METHODS: Between June 1999 and October 2000 532 polytraumatized patients were referred to the emergency department. 336 polytraumatized patients were primarily evaluated using whole body MSCT according to the "Innsbruck Emergency Algorithm." MSCT is performed immediately after cardiovascular stabilization of the patient. During the initial stabilization period free intraabdominal fluid is excluded or demonstrated by abdominal ultrasound. Time-consuming conventional radiographs are omitted with exception of an optimal chest X-ray. In patients with suspected or obvious arterial injuries or fractures the multislice-CT-dataset is used to perform 2D and 3D reconstructions in order to optimize visualization of additional skeletal and vascular injuries. RESULTS: By means of whole body MSCT it was possible to detect all injuries. The diagnostic advantage of whole body MSCT as compared to conventional X-ray was analyzed in 111 consecutive polytraumatized patients with an injury severity score (ISS) of 34.77. The early use of MSCT shortened the time for diagnostic work-up substantially (approximately 50%). CONCLUSION: Whole body multislice-CT used as primary diagnostic tool in the management of polytraumatized patients allows for a fast, accurate and comprehensive diagnostic work-up.     

Rapacuronium 2.0 or 2.5 mg kg-1 for rapid-sequence induction: comparison with succinylcholine 1.0 mg kg-1

The purpose of this nine-centre study in 602 patients was toshow that the frequency of acceptable intubating conditionsafter rapacuronium 2.0 or 2.5 mg kg^–1 is notmore than 10% lower than the frequency after succinylcholine1.0 mg kg^–1 during rapid-sequence inductionof anaesthesia with fentanyl 1–2 µg kg^–1and thiopental 2–7 mg kg^–1. Laryngoscopyand intubation were carried out 60 s after administrationof muscle relaxant by an anaesthetist blinded to its identity.Intubating conditions were clinically acceptable (excellentor good) in 91.8% of patients given succinylcholine and in 84.1and 87.6% of patients given rapacuronium 2.0 and 2.5 mg kg^–1respectively. With respect to the percentage of clinically acceptableintubating conditions, the estimated difference (and the upperlimit of the one-sided 97.5% confidence interval) between succinylcholineand rapacuronium 2.0 mg kg^–1 was 7.8 (14.4)%and between succinylcholine and rapacuronium 2.5 mg kg^–1it was 4.0 (10.2)%. For both comparisons, the upper limit ofthe one-sided confidence interval exceeded the predefined 10%difference. Hence, it could not be demonstrated that the intubatingconditions with either of the two doses of rapacuronium werenot inferior to those with succinylcholine 1.0 mg kg^–1.The increase in heart rate was significantly greater duringthe first 5 min in the rapacuronium groups, but the arterialpressure increased significantly only in the succinylcholinegroup (P<0.001). Respiratory side-effects were observed in4.0, 13.5 and 18.5% of patients after succinylcholine and rapacuronium2.0 and 2.5 mg kg^–1 respectively (P<0.05).As the non-inferiority of intubating conditions after rapacuronium2.0 and 2.5 mg kg^–1 could not be proven, succinylcholineshould be considered the neuromuscular blocking agent that providesbetter intubating conditions for rapid-sequence induction. Br J Anaesth 2000; 85: 724–31 ^* Corresponding author: Klinik für Anaesthesiologie der TechnischenUniversität München, Klinikum rechts der Isar, IsmaningerStr. 22, D-81675 München, Germany     

Post-traumatic stress disorder and memory: prescient medicolegal testimony at the International War Crimes Tribunal?

The nature of remembrance of traumatic events has been particularly controversial during the past decade as vigorous new research has reshaped thinking about trauma and memory. Memory alterations in traumatized individuals have been investigated within both theoretical and biological frameworks. There are different types of memory, and empirical studies have associated post-traumatic stress disorder (PTSD) with a simultaneous weakening and a strengthening of memory. Memory deficiencies in PTSD have been found to be related to problems in new learning (explicit memory), but other specific deficiencies are unvalidated. Recently, accuracy of memory has received particular scrutiny because considerable importance is attached to victims' recollections. In 1998, at the International War Crimes Tribunal in The Hague, The Netherlands, a Bosnian-Croatian soldier was tried for aiding and abetting the rape of a Muslim woman. The defendant's lawyers suggested that the woman's memory was inaccurate, having been adversely affected by her traumatic experiences, and that the defendant whom she identified was not present during her interrogation and abuse. The prosecution disagreed and argued that memories of traumatic experiences in individuals with PTSD are characteristically hyperaccessible. Expert witnesses on both sides were brought in to provide medicolegal testimony about the scientific parameters of stress and its long-term effects on brain regions associated with memory. With the expert witness discussion as background, this article reviews the most recent research about the nature of memory in the aftermath of trauma and the politics of psychological trauma and the law.     

Physician orders for life-sustaining treatment form: honoring end-of-life directives for nursing home residents

Physician Orders for Life-Sustaining Treatment (POLST) form provides choices about end-of-life care and gives these choices the power of physician orders. The POLST form assures end-of-life choices can be implemented in all settings, from the home through the health-care continuum. The use of the POLST form was evaluated in a pilot study in nursing homes in two eastern Washington counties. Chart reviews and template analysis of interviews revealed the POLST form accurately conveyed end-of-life wishes in 19 of 21 cases. An informed consent process was evidenced in 16 of 21 cases, and the POLST form was congruent with residents' existing advance directives for health care. The findings support the continued use, development, and evaluation of this promising tool for improving end-of-life care.