RESUMEN
Phenomenon: Internationally, efforts to produce an adequate supply of effective generalist physicians commonly encounter resistance. Achieving reform requires changes in educational and clinical practice cultures, and clinician educators play a central role in championing change. In Japan, training in generalist fields has historically been lacking, but for decades the government has advocated alignment with Western models. Meanwhile, some Japanese physicians have pursued U.S. training in generalist fields with intention to help change the clinical education and practice systems back in Japan. This study examines the endeavors of repatriated Japanese International Medical Graduates and provides a lens to understanding national challenges with reform and insights into strategizing next steps. Approach: Individual, semi-structured interviews were conducted with 19 purposively sampled Japanese IMGs who had repatriated across Japan after completing U.S. clinical residency in generalist fields. Iterative data collection and thematic analyses were performed using constant comparison. Findings: Participants identified Japanese medical universities and public sectors as steeped in traditions with systemic inertia. In turn, participants described well-informed career decision making involving connections and teammates, which commonly resulted in employment at new or smaller hospitals. Education-related efforts prioritized direct clinical work with physician trainees in the hope of building expansive lineages of educators. Main challenges were Japanese structural and cultural incongruences with Western generalist-based clinical practice. Participants described a competitive relationship with the long-standing ikyoku-based postgraduate education model and associated organ-based organization of clinical practice. Insights: Japanese IMG championing of clinical education and practice in generalist fields is largely marginalized within Japan's clinical education and practice landscape. National-level reform will require transforming or displacing the structurally and culturally rooted traditional infrastructure. Specific measures must be culturally nuanced but likely include those proven effective for similar reforms elsewhere. Based on Japan's national cultural characteristics, sustained leadership is anticipated to be particularly important.
Asunto(s)
Educación Médica , Médicos Graduados Extranjeros , Internado y Residencia , Innovación Organizacional , Femenino , Humanos , Entrevistas como Asunto , Japón , Masculino , Investigación Cualitativa , Estados UnidosRESUMEN
To overcome the mucus layer and cell membrane barrier, self-emulsifying drug delivery systems (SEDDS) exhibiting negative zeta potential, switching to positive values when having reached the cell membrane is a promising approach. Accordingly, a novel conjugate was synthesized by covalent attachment of phosphotyrosine to octadecylamine, which was incorporated into SEDDS. Generated system presented an average diameter of 32â¯nm and zeta potential of around -12â¯mV when being diluted 1:100 in 100â¯mM HEPES buffer pH 7.5 containing 5â¯mM MgCl2 and 0.2â¯mM ZnCl2. Incubation of SEDDS with isolated intestinal alkaline phosphatase (IAP) resulting in enzymatic cleavage of phosphate ester moiety caused a shift in zeta potential up to +5.3â¯mV. As non-toxicity of the developed SEDDS diluted 1:1000 in 25â¯mM HEPES buffer pH 7.5 containing 5% glucose was observed on Caco-2 cells by employing resazurin assay, this system may provide an inspiring strategy for future zeta potential changing drug delivery systems to master the mucus and membrane barrier.
Asunto(s)
Sistemas de Liberación de Medicamentos , Emulsionantes , Nanopartículas , Células CACO-2 , Química Farmacéutica , Emulsiones , HumanosRESUMEN
AIM: The aim of this study was to develop zeta-potential-changing nanoparticles (NPs) combining cell-penetrating peptides for gene delivery. METHODS & MATERIALS: NPs were formed using phosphorylated carboxymethyl cellulose-glucosamine 6-phosphate (CMC-G6P) and polyethylene imine-polyarginine conjugates. Phosphate release was evaluated using intestinal alkaline phosphatase and cell lines. Transfection studies with plasmid DNA were then performed. RESULTS: The zeta potential of CMC-G6P/branched PEI NPs was -3 mV and switched to +4 mV after intestinal alkaline phosphatase cleavage. The released phosphate in human colon adenocarcinoma cell line was more pronounced than human embryonic kidney cell line 293. Transfection studies demonstrated the greatest expression of plasmid DNA when being incorporated into CMC-G6P/polyethylene imine-polyarginine NPs. CONCLUSION: Novel zeta potential changing NPs combining cell-penetrating peptides are a promising tool to deliver DNA drugs to target cells.
Asunto(s)
Carboximetilcelulosa de Sodio/química , Péptidos de Penetración Celular/química , ADN/administración & dosificación , Glucosamina/análogos & derivados , Glucosa-6-Fosfato/análogos & derivados , Nanopartículas/química , Transfección/métodos , Células CACO-2 , ADN/genética , Glucosamina/química , Glucosa-6-Fosfato/química , Células HEK293 , Humanos , Péptidos/química , Plásmidos/administración & dosificación , Plásmidos/genética , Polietileneimina/químicaRESUMEN
The aim of this study was the development of zeta potential changing self-emulsifying drug delivery systems (SEDDS). Various cationic surfactants were incorporated into a formulation consisting of 30% Cremophor EL, 30% Capmul MCM, 30% Captex 355 and 10% propylene glycol (w/w). A substrate of intestinal alkaline phosphatase (IAP), 1,2-dipalmitoyl-sn-glycero-3-phosphatidic acid sodium (PA), was thereafter incorporated into SEDDS. Size, zeta potential and polydispersity index were determined. Phosphate release studies were performed using three different models, namely, isolated IAP, Caco-2 cell monolayer and rat intestinal mucosa and the amount of released phosphate was quantified by malachite green assay. Interaction of SEDDS and mucus was investigated regarding surface charges and mucus diffusion studies were performed using rotating tube technique. SEDDS were diluted 1:100 in 100mM HEPES buffer and a negative zeta potential was obtained. By addition of isolated IAP, 15% to 20% phosphate was liberated from SEDDS within 3h and a shift of zeta potential from negative to positive was observed. On Caco-2 cell monolayer and rat intestinal mucosa, 12% and 23% phosphate were released, respectively, from SEDDS diluted 1:1000 in glucose-HEPES buffer. Positively charged droplets were bound to negatively charged mucus resulting in a decrease of zeta potential, whereas negatively charged SEDDS showed no interaction. Furthermore, negatively charged SEDDS diffused faster through mucus layer as higher extent of incorporated Lumogen was present in deeper mucus segments in comparison to positively charged ones. Accordingly, zeta potential changing SEDDS provide an effective mucus permeation combined with higher cellular uptake when droplets reach absorptive epithelium membrane.
Asunto(s)
Sistemas de Liberación de Medicamentos/métodos , Emulsionantes/administración & dosificación , Emulsionantes/metabolismo , Moco/efectos de los fármacos , Moco/metabolismo , Animales , Células CACO-2 , Evaluación Preclínica de Medicamentos/métodos , Humanos , Mucosa Intestinal/efectos de los fármacos , Mucosa Intestinal/metabolismo , Masculino , Permeabilidad/efectos de los fármacos , Ratas , Ratas Sprague-Dawley , PorcinosRESUMEN
The objective of this study was to evaluate the suitability of a zeta potential changing system as gene delivery system. The phosphate ester bearing ligand 6-phosphogluconic acid (6-PGA) was attached to linear and branched polyethyleneimine (PEI) via a carbodiimide-mediated reaction whereby 287 µmol and 413 µmol 6-PGA could be coupled per gram polymer. Nanocomplexes of these modified polymers with pDNA showed a zeta potential of +12 mV for nanocomplexes with the linear PEI-6PGA and +16 mV in case of the branched derivative. By the addition of carboxymethylcellulose (CMC), zeta potentials of the complexes were reduced to +2.86 and +3.25, respectively. Phosphate release studies on Caco 2 cells and HEK-293 cells demonstrated the ability to cleave the phosphate ester. Compared to HEK-293 cells, enzymatic degradation of the phosphate ester in Caco 2 cells was 2.3-fold higher from nanocomplexes comprising linear PEI and 4.3-fold higher from those with branched PEI. Furthermore, incubation with alkaline phosphatase led to an increase in the zeta potential of nanocomplexes based on linear PEI-6PGA to +6.96mV and +8.26 mV in nanocomplexes comprising branched PEI-6PGA. Studying transfection efficiency in Caco 2 cells and HEK-293 cells, a higher expression of the green fluorescent protein (GFP) could be detected in HEK-293 cells. In presence of a phosphate inhibitor, transfection efficiencies were decreased in both cells lines, due to a lacking shift of the zeta potential of the tested pDNA complexes. According to these results, zeta potential changing systems seem to be a promising strategy for future gene delivery systems, as this concept allows the in situ generation of positive charges in close proximity to the cellular surface.
Asunto(s)
ADN/administración & dosificación , Técnicas de Transferencia de Gen , Gluconatos/química , Polietileneimina/química , Células CACO-2 , Supervivencia Celular/efectos de los fármacos , ADN/química , Proteínas Fluorescentes Verdes/genética , Células HEK293 , Humanos , Fosfatos/metabolismo , PlásmidosRESUMEN
The aim of the study was to develop nanoparticles with the ability to change their zeta potential. By covalent attachment of 6-phosphogluconic acid to polyethylene imine, a charged, enzymatically removable moiety was introduced into the polymer. The novel conjugate displayed 400 µmol phosphate per gram polymer, as determined by malachite green assay. Studies evaluating the cleavage by intestinal alkaline phosphatase revealed that 69 % of the coupled phosphate could be released from the polymer. Furthermore, nanoparticles generated by polyelectrolyte complexation technique using carboxymethyl cellulose as negatively charged component exhibited a zeta potential of -6 mV and an average particle size of 300 nm. Enzymatic cleavage of the phosphate ester moiety by isolated intestinal alkaline phosphatase on these nanoparticles caused shift of the zeta potential from negative to positive value of +3 mV whereby 58% of the total amount of phosphate were released. Studies on Caco-2 cells revealed the capability of a living system to hydrolyze the phosphate ester in the novel conjugate as well as on the nanoparticles via their intestinal alkaline phosphatase. Based on these results, polymeric nanoparticles comprising an enzymatically degradable phosphate ester moiety can provide a promising strategy for zeta potential changing systems.