Tryptophan- and arginine-rich antimicrobial peptides: Structures and mechanisms of action

AbstractAntimicrobial peptides encompass a number of different classes, including those that are rich in a particular amino acid. An important subset are peptides rich in Arg and Trp residues, such as indolicidin and tritrpticin, that have broad and potent antimicrobial activity. The importance of these two amino acids for antimicrobial activity was highlighted through the screening of a complete combinatorial library of hexapeptides. These residues possess some crucial chemical properties that make them suitable components of antimicrobial peptides. Trp has a distinct preference for the interfacial region of lipid bilayers, while Arg residues endow the peptides with cationic charges and hydrogen bonding properties necessary for interaction with the abundant anionic components of bacterial membranes. In combination, these two residues are capable of participating in cation–π interactions, thereby facilitating enhanced peptide–membrane interactions. Trp sidechains are also implicated in peptide and protein folding in aqueous solution, where they contribute by maintaining native and nonnative hydrophobic contacts. This has been observed for the antimicrobial peptide from human lactoferrin, possibly restraining the peptide structure in a suitable conformation to interact with the bacterial membrane. These unique properties make the Arg- and Trp-rich antimicrobial peptides highly active even at very short peptide lengths. Moreover, they lead to structures for membrane-mimetic bound peptides that go far beyond regular α-helices and β-sheet structures. In this review, the structures of a number of different Trp- and Arg-rich antimicrobial peptides are examined and some of the major mechanistic studies are presented

Long-Term Incidence And Timing Of Intraocular Hypertension After Intravitreal Triamcinolone Acetonide Injection

Purpose: To describe the long-term incidence and timing of steroid-induced ocular hypertension after intravitreal triamcinolone acetonide (IVTA) therapy. Design: Retrospective case series of 929 eyes of 841 patients. Participants: Patients with a variety of posterior segment disorders in a single group practice. Intervention: Pars plana injection of IVTA. Main Outcome Measures: Intraocular pressure (IOP) and requirement for glaucoma surgery. Results: Overall, 929 eyes received ≥1 injections (mean, 1.6) of 4 mg of IVTA. During a mean follow-up period of 14±6.9 months, the Kaplan-Meier cumulative incidences of IOP elevations \u3e21 mmHg at 6, 12, 18, and 24 months post-injection were 28.2%, 34.6%, 41.2%, and 44.6%, respectively; similarly, the incidences of eyes with IOP measurements \u3e25 mmHg were 14.6%, 19.1%, 24.1%, and 28.2%, respectively. At the same time points, lOP-lowering medications were required byl3.0%, 16.9%, 20.7%, and 24.2% of eyes, respectively. Only 3 eyes (0.3%) required lOP-lowering surgery. Preexisting glaucoma, younger age, and a history of an IOP elevation after a previous IVTA injection were risk factors for IOP elevations after IVTA injection. The minimum and maximum follow-up were 3 weeks and 37 months. The mean rate of attrition in this study was 3% per month. Conclusions: Elevations in IOP after IVTA injection are common. Younger patients and eyes with preexisting glaucoma or a history of a steroid response should be monitored more closely for IOP elevations after IVTA therapy

Methyl-β-cyclodextrin restores the structure and function of pulmonary surfactant films impaired by cholesterol

AbstractPulmonary surfactant, a defined mixture of lipids and proteins, imparts very low surface tension to the lung–air interface by forming an incompressible film. In acute respiratory distress syndrome and other respiratory conditions, this function is impaired by a number of factors, among which is an increase of cholesterol in surfactant. The current study shows in vitro that cholesterol can be extracted from surfactant and function subsequently restored to dysfunctional surfactant films in a dose-dependent manner by methyl-β-cyclodextrin (MβCD). Bovine lipid extract surfactant was supplemented with cholesterol to serve as a model of dysfunctional surfactant. Likewise, when cholesterol in a complex with MβCD (“water-soluble cholesterol”) was added in aqueous solution, surfactant films were rendered dysfunctional. Atomic force microscopy showed recovery of function by MβCD is accompanied by the re-establishment of the native film structure of a lipid monolayer with scattered areas of lipid bilayer stacks, whereas dysfunctional films lacked bilayers. The current study expands upon a recent perspective of surfactant inactivation in disease and suggests a potential treatment

Apolipoprotein-induced conversion of phosphatidylcholine bilayer vesicles into nanodisks

AbstractApolipoprotein mediated formation of nanodisks was studied in detail using apolipophorin III (apoLp-III), thereby providing insight in apolipoprotein–lipid binding interactions. The spontaneous solubilization of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) vesicles occured only in a very narrow temperature range at the gel–liquid–crystalline phase transition temperature, exhibiting a net exothermic interaction based on isothermal titration calorimetry analysis. The resulting nanodisks were protected from proteolysis by trypsin, endoproteinase Glu-C, chymotrypsin and elastase. DMPC solubilization and the simultaneous formation of nanodisks were promoted by increasing the vesicle diameter, protein to lipid ratio and concentration. Inclusion of cholesterol in DMPC dramatically enhanced the rate of nanodisk formation, presumably by stabilization of lattice defects which form the main insertion sites for apolipoprotein α-helices. The presence of fully saturated acyl chains with a length of 13 or 14 carbons in phosphatidylcholine allowed the spontaneous vesicle solubilization upon apolipoprotein addition. Nanodisks with C13:0-phosphatidylcholine were significantly smaller with a diameter of 11.7±3.1nm compared to 18.5±5.6nm for DMPC nanodisks determined by transmission electron microscopy. Nanodisk formation was not observed when the phosphatidylcholine vesicles contained acyl chains of 15 or 16 carbons. However, using very high concentrations of lipid and protein (>10mg/ml), 1,2,-dipalmitoyl-sn-glycero-3-phosphocholine nanodisks could be produced spontaneously although the efficiency remained low

Structure–activity relationships of the antimicrobial peptide gramicidin S and its analogs: Aqueous solubility, self-association, conformation, antimicrobial activity and interaction with model lipid membranes

AbstractGS10 [cyclo-(VKLdYPVKLdYP)] is a synthetic analog of the naturally occurring antimicrobial peptide gramicidin (GS) in which the two positively charged ornithine (Orn) residues are replaced by two positively charged lysine (Lys) residues and the two less polar aromatic phenylalanine (Phe) residues are replaced by the more polar tyrosine (Tyr) residues. In this study, we examine the effects of these seemingly conservative modifications to the parent GS molecule on the physical properties of the peptide, and on its interactions with lipid bilayer model and biological membranes, by a variety of biophysical techniques. We show that although GS10 retains the largely β-sheet conformation characteristic of GS, it is less structured in both water and membrane-mimetic solvents. GS10 is also more water soluble and less hydrophobic than GS, as predicted, and also exhibits a reduced tendency for self-association in aqueous solution. Surprisingly, GS10 associates more strongly with zwitterionic and anionic phospholipid bilayer model membranes than does GS, despite its greater water solubility, and the presence of anionic phospholipids and cholesterol (Chol) modestly reduces the association of both GS10 and GS to these model membranes. The strong partitioning of both peptides into lipid bilayers is driven by a large favorable entropy change opposed by a much smaller unfavorable enthalpy change. However, GS10 is also less potent than GS at inducing inverted cubic phases in phospholipid bilayer model membranes and at inhibiting the growth of the cell wall-less bacterium Acholeplasma laidlawii B. These results are discussed in terms of the comparative antibiotic and hemolytic activities of these peptides

Dams with head increaser effect: Harnessing potential and kinetic power from rivers with large head and flow variation

There is an enormous untapped potential for hydropower generation in rivers with large head and high flow variation, currently not feasible for conventional hydropower dams. Conventional dams make use of the potential energy, but waste kinetic energy from spillage during periods of high flows. This article studies the possibility of harnessing energy from potential and kinetic energy from hydropower dams with large head and flow variation, analyses its potential, and shows possible technologies. Focus is given to a Moveable Hydro-Electric Power Plant (HEPP) system in which the turbine module can be adjusted according to the flow and water level in the river. During floods the exceeding flows can pass above and below the Moveable HEPP results in a sub-pressure environment after the turbine module, thereby reducing the dam’s downstream head, increasing the pressure difference between the turbine inlet and outlet and the flow through the turbine, which increases the electricity generation of the dam. Dams with head increaser arrangement have been implemented in several dams in the 1930–1950s and now are regaining attention in Middle Europe. The main intention for its implementation is harnessing hydropower generation at run-of-river plants, with low-head, with a 20%–30% cost reduction, lower flooded area at the dam site, the resulting evaporation and the impact on the aquatic fauna. A case study was performed with the proposal of the Aripuanã Moveable HEPP in the Madeira River with a 26 ms height dam and a generation capacity of 1400 MW. The increase in generation with the head increaser effect is as high as 21%. The estimated potential for this technology in the Amazon region is 20 GW. Other potential locations are discussed in the article. Dams with head increaser effect have been successfully implemented and have the potential to become a major alternative for base load renewable energy in the future

A limited and customized follow-up seems justified after endovascular abdominal aneurysm repair in octogenarians

ObjectiveThe objective of this study was to determine whether long-term follow-up after endovascular aneurysm repair (EVAR) is justified in octogenarians.MethodsBetween September 1996 and October 2011, all patients, including octogenarians, treated for an abdominal aortic aneurysm (AAA) by EVAR were included in a prospective database. Patients older than 80 years and with a nonruptured infrarenal aneurysm treated electively or urgently were included in the study (study group [SG]). Patients with ruptured aneurysms and patients who died during surgery or within the first postoperative month were excluded from further analysis. The control group (CG) consisted of patients younger than 80 years, matched for gender and AAA diameter. All patients were evaluated 4 to 8 weeks after EVAR and then annually thereafter. Follow-up data were complemented by review of the computerized hospital registry and charts and by contact of the patient's general practitioner or referring hospital. Primary outcomes were stent- or aneurysm-related complications and interventions. Secondary outcomes were additional surgical complications and patient survival.ResultsA total number of 193 patients (SG, n = 97; CG, n = 96) were included for analysis. Median age was 80 years, and 88.6% were male. Median follow-up time was 33.6 months (interquartile range [IQR], 12.9-68.3). Stent- and procedure-related postoperative complications were comparable between groups (SG, 41.2%; CG, 39.6%; P = .82). Median time to complication was 2.3 months (IQR, 0.2-19.4) in the SG compared with 18.1 months (IQR, 6.8-50.5) in the CG. The 2-year complication-free survival rates were 58% (SG) and 60% (CG). Interventions were performed significantly less frequently in octogenarians (SG, 8.2%; CG, 19.8%; P < .05). Median time to intervention was 11.1 months (IQR, 2.0-31.0) in the SG compared with 54.3 months (IQR, 15.0-93.2) in the CG. The 2-year intervention-free survival rates were 90% (SG) and 92% (CG). During follow-up, 98 patients died (SG, n = 54; CG, n = 44); median time to death was 31.8 months (IQR, 13.3-66.0) in the SG compared with 44.4 months (IQR, 15.0-77.7) in the CG. One aneurysm-related death occurred in the CG. The 2- and 5-year survival rates were 71% and 32% for the SG compared with 77% and 66% for the CG (P < .05).ConclusionsBecause of the low incidence of secondary procedures and AAA-related deaths in octogenarians, long-term and frequent follow-up after EVAR seems questionable. An adapted and shortened follow-up seems warranted in this patient group