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  • 1
    ISSN: 1573-904X
    Keywords: superoxide dismutase ; lipid membranes ; FT-IR ; conformation ; thermal stability ; curve-fitting
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. Superoxide dismutase (SOD), an antioxidant enzyme, converts peroxide radicals into hydrogen peroxide. Liposomes have been used as carriers for SOD to enhance its antioxidant effect. Our previous DSC study has suggested that SOD binding to dipalmitoylphosphatidylglycerol (DPPG) may protect lipid membranes against oxygen-mediated injury. We now present FT-IR studies on the effect of DPPG binding on the temperature-induced SOD folding-unfolding process. Methods. The FT-IR spectra of SOD in D2O or DPPG membranes are measured as temperatures increase from 28° to 121°C at a rate of 0.5°C/ min. From the quantitative determination of the changes in the amide I band components of the Fourier self-deconvoluted spectra, the DPPG-induced changes of SOD secondary structure could be detected as a function of temperature. Results. We observe that the relative intensity of the SOD bands from 28°C to 77°C show graduate loss of β-sheet “distorted” structure, loss of turns, and existence of an intermediate state around 50°C. Beginning at 80°C, changes are obtained in three temperature regions: (i) 80°C, (ii) 92°C, (iii) 109°C. The result suggests that SOD folding/unfolding transition involves mostly the relative changes within the regions of helix-like hydrogen bonding pattern, turn, twisted β-bend and irregular structures. When SOD is bound to DPPG, the conformational changes shift to lower temperatures, indicating a reduction of SOD thermal stability. In addition, the gel to liquid crystalline phase transition temperature of DPPG increases from 42°C to 43.5°C. Conclusions. These results suggest that the thermal stability of SOD is reduced by DPPG binding. However, DPPG bilayer is stabilized by the presence of SOD.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-904X
    Keywords: liposome ; cyclosporine ; acute toxicity ; pharmacokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The currently available intravenous dosage form of cyclosporine (CSA), Sandimmune I.V., contains the vehicle, Cremophor EL, which has been implicated in producing anaphylactic reactions in man and animals. This formulation also leaches through silicone tubing, an important component of some automatic drug delivery devices, causing pump dysfunction. In an attempt to develop a less toxic and pump-compatible formulation of CSA, suitable for intrarenal infusion in a canine transplant model, we compared the acute toxicity, pharmacokinetics, and pump compatibility of emulsified (CSA/emulsion) and liposomal (CSA/liposomes) CSA preparations with those of Sandimmune I.V. and CSA dissolved in ethanol vehicle (CSA/alcohol) in healthy, unoperated dogs. Animals receiving Sandimmune I.V. demonstrated marked acute toxicity despite progressive 10-fold dose reduction and 〉50-fold prolongation of infusion duration. One of two animals receiving CSA/emulsion and both dogs receiving emulsion vehicle alone exhibited a moderately severe reaction, while five of seven dogs receiving CSA/alcohol demonstrated immediate, mild reactions. No discernible adverse reactions occurred in any animal receiving CSA/liposomes. Systemic disposition of CSA/alcohol and CSA/liposomes was similar. In contrast to the liposomal vehicle, the emulsion vehicle produced a marked, early weight gain and substantial decrease in tensile strength of the pump tubing, both of which would adversely affect pump function. These results provide the first description of liposomal CSA toxicology and pharmacokinetics in a large animal model and may lead to the successful development of a less toxic parenteral CSA formulation for systemic and local pump-based administration.
    Type of Medium: Electronic Resource
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