Evaluation of antioxidants: Scope, limitations and relevance of assays

Peroxidation of lipids, particularly polyunsaturated fatty acid residues (PUFA) of phospholipids and cholesterol esters, is a process of marked implications: it shortens the shelf-life of food and drugs, it causes fragmentation of DNA, it damages cellular membranes and it promotes the genesis of many human diseases. Much effort is therefore devoted to a search for "potent antioxidants", both synthetic and from natural sources, mostly plants. This, in turn, requires a reliable, simple, preferably high throughput assay of the activity of alleged antioxidants. The most commonly used assays are based on measurements of the total antioxidant capacity (TAC) of a solution, as evaluated either by determining the rate of oxidation of the antioxidant or by measuring the protection of an easily determined indicator against oxidation by the antioxidants. The commonly used assays utilized for ranking antioxidants share three common problems: (i) They usually evaluate the effects of those antioxidants that quench free radicals, which constitute only a part of the body's antioxidative network, in which enzymes play the central role. (ii) Both the capacity and potency of antioxidants, as obtained by various methods, do not necessarily correlate with each other. (iii) Most estimates are based on methods conducted in solution and are therefore not necessarily relevant to processes that occur at the lipid-water interfaces in both membranes and micro emulsions (e.g. lipoproteins). Given this "state of art", many researchers, including us, try to develop a method based on the formation of hydroperoxides (LOOH) upon peroxidation of PUFA in lipoproteins or in model membranes, such as liposomes. In these systems, as well as in lipoproteins, the most apparent effect of antioxidants is prolongation of the lag time preceding the propagation of a free radical chain reaction. In fact, under certain conditions both water soluble antioxidants (e.g. vitamin C and urate) and the lipid soluble antioxidant tocopherol (vitamin E), promote or even induce peroxidation. Based on the published data, including our results, we conclude that terms such as 'antioxidative capacity' or 'antioxidative potency' are context-dependent. Furthermore, criteria of the efficacy of antioxidants based on oxidation in solution are not necessarily relevant to the effects of antioxidants on peroxidation in biological systems or model lipid assemblies, because the latter processes occur at water/lipid interfaces. We think that evaluation of antioxidants requires kinetic studies of the biomarker used and that the most relevant characteristic of 'oxidative stress' in the biological context is the kinetics of ex vivo peroxidation of lipids. We therefore propose studying the kinetics of lipid-peroxidation in the absence of the studied antioxidant and in its presence at different antioxidant concentrations. These protocols mean that antioxidants are assayed by methods commonly used to evaluate oxidative stress. The advantage of such evaluation is that it enables quantization of the antioxidants' efficacy in a model of relevance to biological systems. In view of the sensitivity of the lag time preceding peroxidation, we propose studying how much antioxidant is required to double the lag observed prior to rapid peroxidation. The latter quantity (C(2lag)) can be used to express the strength of antioxidants in the relevant system (e.g. LDL, serum or liposomes).     

Synthesis of peptides containing α,β-didehydroamino acids. Scope and limitations

Summary α, β-Didehydroamino acids, which are key components of both natural andde novo peptides, are frequently encountered in naturally occurring peptides — mostly of microbial and fungal origin and/or from marine organisms. Herein, we report on a reappraisal of the use of the water-soluble carbodiimide/CuCl method for the preparation of this kind of peptide in both solution and solid-phase modes and describe some side reactions encountered during the process. Abbreviations: Alloc, allyloxycarbonyl; Barlos resin, 2-chlorotrityl chloride resin, Boc,tert-butoxycarbonyl; Boc₂O, di-tert-butyl dicarbonate; Bzl, benzyl; DABCO, 1,4-diazabicyclo[2.2.2]octane; DAST, (diethylamino)sulfur trifluoride; DBU, 1,8-diazabicyclo[5.4.0]undec-7-ene; DDAAs, α, β-didehydroarnino acids; DEAD, diethyl azodicarboxylate; Dha, Didehydroalanine, (Z)-Dhb, Z-Didebydroaminobutyric acid; (Z)-Dhp, Z-Didehydrophenylalanine; DSC, disuccinimidyl carbonate; DDP, α, β-didehydropeptides; EDC, WSC, 3-(3′-dimethylaminopropyl)-1-ethylearbodiimide; Fmoc, fiuorenylmethoxycarbonyl; HATU, N-{(dimethylamino)-1H-1,2,3-triazolo[4,5-b]pyridino-1-ylmethylene}-N-methylmethanaminium hexafluorophosphate; HOAt, 1-hydroxy-7-azabenzotriazole; (β-OH)Phe, phenylserine or β-hydroxyphenylalanine; Ph₃P, triphenylphosphine; PyAOP, (7-azabenzotriazol-1-yloxy)-tris(pyrrolidino)phosphonium hexafluorophosphate; TEA, triethylamine; TFA, trifluoroacetic acid. Amino acid symbols denote thel-configuration unless stated otherwise. All solvent ratios are volume/volume unless stated otherwise.     

Timelessness in Sleep: Multidimensional Scope

Sleep and Biological Rhythms -     

Conservation medicine and One Health in zoos: Scope,obstacles, and unrecognized potential

Zoo veterinarians and allied professionals have been contributing to conservation medicine (CM) and One Health (OH) activities for more than two decades. Although the Association of Zoos and Aquariums (AZA) considers conservation a key part of its mission, little published material exists about the extent of AZA work in CM/OH or the challenges and opportunities associated with these endeavors. To better understand the current scope of CM/OH in zoos, we surveyed 53 AZA‐accredited institutions from April through October of 2016. We obtained information on CM/OH infrastructure, support for expansion in this area, and strategies to overcome perceived obstacles hindering CM/OH from becoming a core AZA activity. Survey results revealed that while most zoos favor greater investment in CM/OH programs, awareness, and understanding of CM/OH across the broader zoo community and public is lacking. The majority of respondents stated that overcoming this challenge is paramount to attaining support for CM/OH initiatives. In spite of these obstacles, survey respondents highlighted many positive developments in CM/OH. We found that 84% of zoos surveyed are actively engaged in CM/OH activities, and 12% house formal CM/OH programs. Another 8% of respondents said their institutions were developing CM/OH programs. Perhaps most noteworthy, we found that zoo size did not have a significant bearing on the financial amount allocated toward an institution's CM/OH activities. This suggests that all zoos, regardless of size, can make meaningful contributions to the growing movement of CM/OH and help redefine the role of zoos within this movement.     

Interpreting Quantifier Scope Ambiguity: Evidence of Heuristic First,Algorithmic Second Processing

The present work suggests that sentence processing requires both heuristic and algorithmic processing streams, where the heuristic processing strategy precedes the algorithmic phase. This conclusion is based on three self-paced reading experiments in which the processing of two-sentence discourses was investigated, where context sentences exhibited quantifier scope ambiguity. Experiment 1 demonstrates that such sentences are processed in a shallow manner. Experiment 2 uses the same stimuli as Experiment 1 but adds questions to ensure deeper processing. Results indicate that reading times are consistent with a lexical-pragmatic interpretation of number associated with context sentences, but responses to questions are consistent with the algorithmic computation of quantifier scope. Experiment 3 shows the same pattern of results as Experiment 2, despite using stimuli with different lexical-pragmatic biases. These effects suggest that language processing can be superficial, and that deeper processing, which is sensitive to structure, only occurs if required. Implications for recent studies of quantifier scope ambiguity are discussed.