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      In situ monitoring of the structural change of microemulsions in simulated gastrointestinal conditions by SAXS and FRET

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          Abstract

          Microemulsions are promising drug delivery systems for the oral administration of poorly water-soluble drugs. However, the evolution of microemulsions in the gastrointestinal tract is still poorly characterized, especially the structural change of microemulsions under the effect of lipase and mucus. To better understand the fate of microemulsions in the gastrointestinal tract, we applied small-angle X-ray scattering (SAXS) and fluorescence resonance energy transfer (FRET) to monitor the structural change of microemulsions under the effect of lipolysis and mucus. First, the effect of lipolysis on microemulsions was studied by SAXS, which found the generation of liquid crystalline phases. Meanwhile, FRET spectra indicated micelles with smaller particle sizes were generated during lipolysis, which could be affected by CaCl 2, bile salts and lecithin. Then, the effect of mucus on the structural change of lipolysed microemulsions was studied. The results of SAXS and FRET indicated that the liquid crystalline phases disappeared, and more micelles were generated. In summary, we studied the structural change of microemulsions in simulated gastrointestinal conditions by SAXS and FRET, and successfully monitored the appearance and disappearance of the liquid crystalline phases and micelles.

          Graphical abstract

          Small-angle X-ray scattering (SAXS) and fluorescence resonance energy transfer (FRET) methods were applied to monitor the structural change of microemulsions under the effect of lipolysis and mucus in this work. We found that liquid crystalline phases and micelles were appeared under lipolysis, and liquid crystalline phases were disappeared in mucus.

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          Most cited references 43

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          Barrier properties of mucus.

           Richard Cone (2009)
          Mucus is tenacious. It sticks to most particles, preventing their penetration to the epithelial surface. Multiple low-affinity hydrophobic interactions play a major role in these adhesive interactions. Mucus gel is also shear-thinning, making it an excellent lubricant that ensures an unstirred layer of mucus remains adherent to the epithelial surface. Thus nanoparticles (NP) must diffuse readily through the unstirred adherent layer if they are to contact epithelial cells efficiently. This article reviews some of the physiological and biochemical properties that form the mucus barrier. Capsid viruses can diffuse through mucus as rapidly as through water and thereby penetrate to the epithelium even though they have to diffuse 'upstream' through mucus that is being continuously secreted. These viruses are smaller than the mucus mesh spacing, and have surfaces that do not stick to mucus. They form a useful model for developing NP for mucosal drug delivery.
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            Nanoparticle diffusion in respiratory mucus from humans without lung disease.

            A major role of respiratory mucus is to trap inhaled particles, including pathogens and environmental particulates, to limit body exposure. Despite the tremendous health implications, how particle size and surface chemistry affect mobility in respiratory mucus from humans without lung disease is not known. We prepared polymeric nanoparticles densely coated with low molecular weight polyethylene glycol (PEG) to minimize muco-adhesion, and compared their transport to that of uncoated particles in human respiratory mucus, which we collected from the endotracheal tubes of surgical patients with no respiratory comorbidities. We found that 100 and 200 nm diameter PEG-coated particles rapidly penetrated respiratory mucus, at rates exceeding their uncoated counterparts by approximately 15- and 35-fold, respectively. In contrast, PEG-coated particles ≥500 nm in diameter were sterically immobilized by the mucus mesh. Thus, even though respiratory mucus is a viscoelastic solid at the macroscopic level (as measured using a bulk rheometer), nanoparticles that are sufficiently small and muco-inert can penetrate the mucus as if it were primarily a viscous liquid. These findings help elucidate the barrier properties of respiratory mucus and provide design criteria for therapeutic nanoparticles capable of penetrating mucus to approach the underlying airway epithelium. Copyright © 2013 Elsevier Ltd. All rights reserved.
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              Lipid-based formulations for intestinal lymphatic delivery.

              The current state of the art of intestinal lymphatic transport is given by reviewing the more recent publications, which have utilized lipid-based vehicles. The results published often show variable trends depending on, the design of the vehicle, the components used, the physicochemical properties of the drug, the animal model and experimental techniques, these variables often make direct comparisons difficult. Traditionally intestinal lymphatic delivery has been expressed as a percentage of the dose transported in the lymph. Using this parameter results obtained to date, with lipid-based vehicles, are somewhat disappointing maximising at approximately 20-30%, for highly lipophilic compounds including DDT and halofantrine (Hf). Recent data, monitoring Hf, in a fed versus fasted dog study, have shown that a higher degree of lymphatic transport is possible (>50% dose) in the postprandial state, this study should result in stimulating renewed interest in the potential of achieving significant levels of lymphatic targeting. Although some relevant features controlling lymphatic transport have been identified over the years a deeper appreciation of all the mechanisms, which is vital for therapeutic exploitation of lymphatic transport, is still unrealized. This review analyses the success and limitations of a formulation approach using lipid-based vehicles and highlights potential areas for further research.
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                Author and article information

                Contributors
                Journal
                Acta Pharm Sin B
                Acta Pharm Sin B
                Acta Pharmaceutica Sinica. B
                Elsevier
                2211-3835
                2211-3843
                23 May 2018
                July 2018
                23 May 2018
                : 8
                : 4
                : 655-665
                Affiliations
                [a ]College of Pharmacy, Dalian Medical University, Dalian 116044, China
                [b ]College of Life Science, Dalian Minzu University, Dalian 116600, China
                [c ]Xinglin College, Liaoning University of Traditional Chinese Medicine, Shenyang 110167, China
                [d ]College of Medical Laboratory, Dalian Medical University, Dalian 116044, China
                Author notes
                [* ]Corresponding author. zhangjb@ 123456dmu.edu.cn
                [†]

                These authors made equal contributions to this work.

                Article
                S2211-3835(17)30684-6
                10.1016/j.apsb.2018.05.008
                6089861
                © 2018 Chinese Pharmaceutical Association and Institute of Materia Medica, Chinese Academy of Medical Sciences. Production and hosting by Elsevier B.V.

                This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

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