125,208 research outputs found
Further studies on the antioxidant role of pyrophosphate in model membranes
No full textOur previous studies (G. Cervato et al., Chem. Phys. Lipids 56 (1990), 91-99) demonstrated that 100 muM pyrophosphate (PPi) inhibits Fe2+/ascorbate-induced peroxidation of arachidonic acid (AA) inserted in unilamellar liposomes (SUVs) of dipalmitoylphosphatidylcholine (DPPC), by chelating ferrous ions in the aqueous phase. In this work we demonstrate that the kinetics of AA peroxidation in DPPC SUVs are strongly affected by PPi, also at very low concentration (1 muM). In fact at low PPi concentration there is a longer lag-phase, while the maximum of thiobarbituric acid reactive substances (TBARS) is similar in both the presence and absence of 1 muM PPi. The lag-phase of peroxidation of AA in lysophosphatidylcholine (palmitoyl) (LysoPC) micelles is also prolonged. The AA peroxidation in membrane models without choline as the polar headgroup (dipalmitoylphosphatidylethanolamine (DPPE) SUVs, or Triton X-100 micelles), or in which AA is not free but esterified with glycerol (stearoylarachidonylphosphatidylcholine (SAPC)), is unaffected by the presence of 1 muM PPi
Variability in alpha-tocopherol antioxidant activity in the core and surface layers of low- and high-density lipoproteins
No full textThe effect of alpha-tocopherol enrichment of low- and high-density lipoproteins on Cu(2+)-catalyzed lipid peroxidation in the hydrophobic core and in the hydrophilic envelope of lipoproteins was investigated by using two pyrene derivatives, namely, cholesteryl pyrenyl hexanoate (P6Chol) and pyrene dodecanoyl sulfatide (P12CS). The progressive decrease in fluorescence of P6Chol was used to monitor lipid peroxidation in the core of LDL and HDL, whereas that of P12CS was used to follow lipid peroxidation in the envelope of both lipoproteins. alpha-Tocopherol enrichment of LDL and HDL was obtained by incubating blood plasma at 37 degrees C with different concentrations of the vitamin (25-500 microM) before lipoprotein separation. The incorporation of alpha-tocopherol in LDL and HDL presents a progressive, time-dependent increase up to 200 microM alpha-tocopherol, then a plateau up to 500 microM. In the envelopes, the added tocopherol causes a great decrease in the rate of peroxidation and a dramatic increase in the latency phase in both lipoproteins. In the cores the lengthening of latency phase resulting from alpha-tocopherol enrichment was by far greater in LDL than in HDL, and the decrease in the rate of peroxidation in both lipoproteins was less than in the envelopes
Studies on the antioxidant activity of milk caseins
No full textThe antioxidant properties of milk casein subunits (alpha-casein, beta-casein and kappa-casein) were evaluated in liposomal models. All the subunits of casein are able to inhibit Fe-induced peroxidation of arachidonic acid inserted into multilamellar liposomes of dipalmitoylphosphatidylcholine (0.2 mM and 0.8 mM, respectively). The peroxidation was monitored as thiobarbituric acid reactive substances, and the strongest inhibitory effect occurred when 500 micrograms of alpha-casein were added to 0.5 ml of liposomal suspension. At this concentration, peroxidation was completely inhibited in our experimental conditions (incubation for 2 h at room temperature, with a mixture of ferrous sulfate and ascorbate, 50 and 500 microM final concentration, respectively). The mechanisms of antioxidant action are complex, but the strongest effect is achieved by modifying the Fe2+/Fe3+ equilibrium; in fact, caseins seem to favour the autoxidation of iron, and thus inhibit lipid peroxidation
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
A fluorescence method for the determination of plasma susceptibility to lipid peroxidation
No full textObjective: We propose a fluorescence kinetics method for monitoring plasma susceptibility to peroxidation.
Design and Method: Plasmatic peroxidation was induced by CuSO4 (500 mu M), and fluorescence was measured every 30 min. Kinetics were represented by a sigmoidal curve from which it was possible to calculate the latency time (lag-time) and the propagation velocity (slope) of plasma peroxidation.
Results: The lag-time monitored by the fluorescence kinetics method corresponded to the formation of thiobarbituric acid reactive substances, and to progressive depletion of polyunsaturated fatty acids and alpha-tocopherol. The mechanism of reaction appeared to be dependent upon plasmatic hydroperoxides, and independent of oxygen radicals. Plasma storage is possible for at least two months at -80 degrees C, and reproducibility of the method is very good.
Conclusions: Fluorescence kinetics provide a highly comprehensive picture of plasma susceptibility to peroxidation in comparison with the conventional measurements of anti- and prooxidant ratio
THERMODYNAMIC STATISTICAL EVALUATION OF S AND F FROM ELECTRON-SPIN-RESONANCE EXPERIMENTAL ORDER PARAMETERS
No full textA statistical analytical procedure for calculating entropy (S) and Helmholtz free energy (F) from the order parameters {Mathematical expression} obtained from ESR spectra of spin-labelled membranes is described. The method is here applied to some literature data. A brief discussion on the results is also reported
N-PYRENE DODECANOYL SULFATIDE AS MEMBRANE PROBE - A STUDY OF GLYCOLIPID DYNAMIC BEHAVIOR IN MODEL MEMBRANES
No full textAn N-linked pyrene-dodecanoyl sulfatide was employed to measure the ratio of excimer fluorescence to monomer fluoresence intensities (E/M). The E/M values provided information about both the dynamic behavior and the structural distribution of the labelled glycolipid in note dispersion of micellar sulfatides and multilamellar vesicles of different phospholipids. Most of the labelled sulfatide seems to be located in domains sequestered from the surrounding phospholipids still above the phase transition temperature of the vesicles. The glycolipids sequestered in these domain environment are less sensitive to the structural changes that the addition of cholesterol or Ca2+ can induce in the phospholipid regions during the phase transition
- …
