We studied the mechanisms involved in the translocation of human calcitonin (hCT) through excised bovine nasal mucosa (net mucosal-to-serosal permeability approximately 10(-)5 cm s-1). To determine structural requirements for the suggested vesicular internalization two carboxyfluorescein-labeled (fl) hCT fragments, the C-terminal fragment [Nalpha-fl]hCT(9-32) and the N-terminal fragment [Lys(fl)18]hCT(1-24) were synthesized. In presence of the endocytosis inhibitor cytochalasin D mucosal-to-serosal and serosal-to-mucosal hCT permeabilities were equal. Pathway visualization by confocal laser scanning microscopy showed punctated fluorescence indicating vesicular internalization of both hCT and [Nalpha-fl]hCT(9-32). In contrast, the N-terminal fragment lacking the beta-sheet forming C-terminus (25-32) was not internalized. Circular dichroism showed that, when interacting with neutral and negatively charged liposomes, hCT adopts beta-sheet conformation. In a concentrated aqueous solution, beta-sheet formation induces hCT self-assembly and fibrillation. High partitioning of hCT into lipid bilayer membranes was reflected by an apparent partition coefficient log D(pH 7.4) = 2.5 (liposome-buffer equilibrium dialysis). We propose that the high lipid partitioning and beta-sheet formation result in C-terminus-restricted supramolecular self-assembly of hCT and [Nalpha-fl]hCT(9-32) in lipid membranes. Vesicular internalization is suggested to be associated with self-assembly induced perturbation of the lipid bilayer. Condensed hCT self-assemblies may explain the high capacity of net mucosal-to-serosal hCT permeation, which compares favorably with the low transport capacity of receptor-mediated endocytosis.
IntroductionOne in three Danish children under 3 years of age experience asthma-like symptoms, and one-third will later be diagnosed with asthma. Oral prednisolone is used in various formulations to treat acute asthma. However, the potential differences in bioequivalence between these formulations have never been examined in children despite interchangeable use in clinical practice.Methods and analysisAn open-label, randomised, two-treatment cross-over trial investigating the bioequivalence of different prednisolone formulations in children with airway disease.The included patients (6 months–11 years of age) are admitted to the Department of Paediatric and Adolescent Medicine Nordsjællands University Hospital, Hillerød, with asthma or asthma-like symptoms.The primary objective is to assess the bioequivalence between different prednisolone formulations herein area under the concentration time curve, Cmax and Tmax using saliva samples. The secondary objectives are to evaluate tolerability (five-point face scale), adverse events and severity of the disease. If the patient has an intravenous access for other purposes, the saliva samples will be validated with plasma samples.A total of 66 evaluable patients are needed according to European Medicines Agency Guideline on bioequivalence.Ethics and disseminationTraditional pharmacokinetic trials are burdensome due to the extent of blood samples necessary to capture the time-dependant drug profile. Saliva sampling is far more acceptable for paediatric patients. In addition, this trial adheres to standard dosing strategies. No additional venepunctures are performed, and no additional prednisolone doses are administered.Guidelines for paediatric bioequivalence trials are warranted.Trial registration numberThe Danish Medicines Agency EudraCT: 2017-003590-33, The Ethics Committee case no: H-17027252, and the Danish Data Protection Agency: BFH-2017–103, I-Suite no.: 05935.
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