PubMed · 8703590
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D Pullan. 1996-06-22. Migraine attacks.. https://doi.org/10.1038/sj.bdj.4809118
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As a novel temperature-sensitive drug delivery system, we have designed liposomes coated with poly(N-isopropylacrylamide), which exhibits a coil-globule transition at 32-35 degrees C. In a previous study [ K. Kono, H. Hayashi, T. Takagishi, J. Control. Release 30 (1994) 69-75], it was shown that the release of contents from the polymer-coated liposomes is enhanced above the transition temperature of the polymer but the release is not controlled completely by the conformational change of the polymer. In this study, to improve temperature-sensitivity of the poly(N-isopropylacrylamide)-modified liposomes, the influence of lipid composition on the temperature-sensitivity of the liposomes was investigated. A copolymer of N-isopropylacrylamide and N, N-didodecylacrylamide was synthesized by free radical copolymerization. While the copolymer was insoluble in water, it exhibited a coil-globule transition around 28 degrees C when incorporated into an egg yolk phosphatidylcholine membrane. The copolymer-modified egg yolk phosphatidylcholine/dioleoylphosphatidylethanolamine liposomes were prepared by sonication or reverse phase evaporation. Release of calcein from the copolymer-modified liposomes was very slow below the transition temperature of the copolymer, whereas the release was enhanced above the transition temperature. Incorporation of dioleoylphosphatidylethanolamine into liposome membranes enhanced release greatly above the transition temperature of the copolymer. Fluorometric measurements using 8-anilino-1-naphthalenesulfonate and 1,6-diphenyl-1,3,5-hexatriene suggested that the copolymer decreases membrane fluidity of the liposomes near and above the transition temperature of the copolymer and that interaction between the copolymer and the liposome membranes is enhanced by inclusion of dioleoylphosphatidylethanolamine.
The nuclear lamina protein, lamin A is produced by proteolytic cleavage of a 74 kDa precursor protein, prelamin A. The conversion of this precursor to mature lamin A is mediated by a specific endoprotease, prelamin A endoprotease. Subnuclear fractionation indicates that the prelamin A endoprotease is localized at the nuclear membrane. The enzyme appears to be an integral membrane protein, as it can only be removed from the nuclear envelope with detergent. It is effectively solubilized by the detergent n-octyl-beta-D-glucopyranoside and can be partially-purified (approximately 1200-fold) by size exclusion and cation exchange (Mono S) chromatography. Prelamin A endoprotease from HeLa cells was eluted from Mono S with 0.3 M sodium chloride as a single peak of activity. SDS-PAGE analysis of this prelamin A endoprotease preparation shows that it contains one major polypeptide at 65 kDa and smaller amounts of a second 68 kDa polypeptide. Inhibition of the enzyme activity in this preparation by specific serine protease inhibitors is consistent with the enzyme being a serine protease.
Lactose-based placebo tablets were coated using various combinations of two methacrylic acid copolymers, Eudragit L100-55 and Eudragit S100, by spraying from aqueous systems. The Eudragit L100-55-Eudragit S100 combinations (w/w) studied were 1:0, 4:1, 3:2, 1:1, 2:3, 1:4, 1:5 and 0:1. The coated tablets were tested in vitro for their suitability for pH dependent colon targeted oral drug delivery. The same coating formulations were then applied on tablets containing mesalazine as a model drug and evaluated for in vitro dissolution rates under various conditions. The disintegration data obtained from the placebo tablets demonstrate that disintegration rate of the studied tablets is dependent on: (i) the polymer combination used to coat the tablets, (ii) pH of the disintegration media, and (iii) the coating level of the tablets. Dissolution studies performed on the mesalazine tablets further confirmed that the release profiles of the drug could be manipulated by changing the Eudragit L100-55 and Eudragit S100 ratios within the pH range of 5.5 to 7.0 in which the individual polymers are soluble respectively, and a coating formulation consisting of a combination of the two copolymers can overcome the issue of high gastrointestinal (GI) pH variability among individuals. The results also demonstrated that a combination of Eudragit L100-55 and Eudragit S100 can be successfully used from aqueous system to coat tablets for colon targeted delivery of drugs and the formulation can be adjusted to deliver drug at any other desirable site of the intestinal region of the GI tract on the basis of pH-variability. For colon targeted delivery of drugs the proposed combination system is superior to tablets coated with either Eudragit L100-55 or Eudragit S100 alone.