Kimiko Makino

Temperature- and ionic strength-induced conformational changes in the lipid head group region of liposomes as suggested by zeta potential data

Neutral liposomes composed of DMPC (dimyristoylphosphatidylcholine), DPPC (dipalmitoylphosphatidylcholine) or DSPC (distearoylphosphatidylcholine) are found to exhibit non-zero zeta potentials in an electric field even when they are dispersed in solution at pH 7.4. A model for the orientation of lipid head groups is proposed to explain the observed non-zero zeta potentials. The dependence of the zeta potential on temperature and ionic strength is analyzed via this model to obtain the information on the direction of the lipid head group in the liposome surface region. The direction of the lipid head group is found to be sensitive to the temperature and the ionic strength of the medium. At low ionic strengths, the phosphatidyl groups are located at the outer portion of the head group region. At constant temperature, as the ionic strength increases, the choline group approaches the outer region of the bilayer surface while the phosphatidyl group hides behind the surface. At the phase transition temperature of the lipid, the phosphatidyl group lies in the outer-most region of the surface and the choline group is in the inner-most region.

Inhaled drug therapy for treatment of tuberculosis

The lungs have received attention as a portal for drug delivery in tuberculosis (TB) from researchers addressing diverse objectives. These include: (a) targeting alveolar macrophages that harbour TB bacilli; (b) maintaining high drug concentrations in lung tissue; (c) systemic delivery of potent or second-line anti-TB agents; and (d) delivering agents that may change the host-pathogen dialectic. Formulation design considerations for each of the above objectives differ in slight, but important ways. As distinct from vaccine delivery formulations, inhalations intended for drug delivery are presumed to require chronic and repeated administration of larger amounts of material. This review seeks to summarize the consensus on the ways and means available or under development, to deliver different anti-TB agents as aerosols for inhalation. These agents include drugs in current clinical use, singly or in combination, experimental chemical entities, siRNA against host molecules, and finally, drugs in clinical use for unrelated pharmacological action, as modifiers of the host-pathogen dialectic. The pharmacokinetics of drug bioavailability in the lung, the blood and other tissues following lung deposition of inhaled therapies are also addressed. Finally, considerations on efficacy studies of drugs administered through aerosol delivery are discussed.

Mechanism of hydrolytic degradation of poly(L-lactide) microcapsules: effects of pH, ionic strength and buffer concentration

The hydrolytic degradation rate of poly(L-lactide) molecules constituting the microcapsule membrane was estimated at different pH, ionic strength and buffer concentration. Poly(L-lactide) microcapsules were observed to be hydrolytically degraded rapidly in a strongly alkaline solution to lactic acid as the final product. The degradation was accelerated when the poly(L-lactide) microcapsules were immersed in solutions of high ionic strength. The effect of pH and ionic strength of the bulk solution is interpreted in terms of the electric potential distribution in the membrane. It is suggested that the concentration of OH- in the membrane has an important role in the hydrolysis of poly(L-lactide) microcapsules, when the microcapsules are dispersed in solutions where the zeta potential of the microcapsules is negative. On the other hand, when the zeta potential is positive, the concentration of H+ in the membrane has a predominant effect on the degradation. The degradation was also found to be affected by the salt concentration in buffered solutions, suggesting that the cleavage reaction of the polymer ester bonds is accelerated by conversion of the acidic degradation products into neutral salts.

Phagocytic uptake of polystyrene microspheres by alveolar macrophages: effects of the size and surface properties of the microspheres

Abstract Polystyrene microspheres with diameters of 0.2, 0.5, 1.0, 6.0 and 10 μm were added to alveolar macrophages, and their uptake was determined as the amount of superoxide generated from macrophages by the usage of chemiluminescence assay with luminol. The amount of superoxide generated was apparently higher with polystyrene microspheres with a diameter of 1 μm than those with diameters smaller than 1 μm (i.e. 0.2 or 0.5 μm) and with larger than 1 μm (6 or 10 μm). The effects of the functional groups located on the microsphere surfaces upon the uptake by alveolar macrophages were studied with polystyrene microspheres of 1 μm diameter having the primary amine, sulfate, hydroxyl, or carboxyl groups on their surfaces. We found that the macrophages most effectively trapped polystyrene microspheres with primary amine groups, those with carboxyl groups to a slightly lesser extent, and other microspheres much less amounts. The surface properties of these microspheres were determined by measuring their electrophoretic mobility in phosphate buffer solution (pH 7.4) with various ionic strengths. By the analysis of data with Ohshimas electrokinetic theory for soft particles, the surface charge density and the electrophoretic softness of the microsphere surfaces were determined. All the microsphere surfaces were found to be negatively charged, and those with primary amine groups and carboxyl groups were softer than other microspheres. From these findings, it is suggested that microspheres having soft surfaces are easily accessible to alveolar macrophages, and effectively trapped by macrophages.

Enhanced transdermal delivery of indomethacin-loaded PLGA nanoparticles by iontophoresis

Nanoparticles effectively deliver therapeutic agent by penetrating into the skin. Indomethacin (IM) and coumarin-6 were loaded in PLGA nanoparticles with an average diameter of 100 nm. IM and coumarin-6 were chosen as a model drug and as a fluorescent marker, respectively. The surfaces of the nanoparticles were negatively charged. Permeability of IM-loaded PLGA nanoparticles through rat skin was studied. Higher amount of IM was delivered through skin when IM was loaded in nanoparticles than IM was free molecules. Also, iontophoresis was applied to enhance the permeability of nanoparticles. When iontophoresis with 3 V/cm was applied, permeability of IM was much higher than that obtained by simple diffusion of nanoparticles through skin. The combination of charged nanoparticle system with iontophoresis is useful for effective transdermal delivery of therapeutic agents.

Enhanced transdermal delivery of indomethacin using combination of PLGA nanoparticles and iontophoresis in vivo

Nanoparticles effectively deliver therapeutic agent by penetrating into the rat skin in vivo. Indomethacin (IM) and coumarin-6 were loaded in PLGA nanoparticles with an average diameter of 100 nm. Indomethacin (IM) and coumarin-6 were chosen as a model drug and as a fluorescent marker, respectively. The surfaces of the nanoparticles were negatively charged. Permeability of IM-loaded PLGA nanoparticles through rat skin was studied in vivo. Higher amount of IM was delivered through skin when IM was loaded in nanoparticles than IM was free molecules. Also, iontophoresis was applied to enhance the permeability of nanoparticles. When iontophoresis was applied at 0.05 mA/cm(2), permeability of IM was much higher than that obtained by simple diffusion of nanoparticles through skin. The combination of charged nanoparticle system with iontophoresis is useful for effective transdermal systemic delivery of therapeutic agents.

Electrophoretic mobility of a colloidal particle with constant surface charge density.

When the electrophoretic mobility of a particle in an electrolyte solution is measured, the obtained electrophoretic mobility values are usually converted to the particle zeta potential with the help of a proper relationship between the electrophoretic mobility and the zeta potential. For a particle with constant surface charge density, however, the surface charge density should be a more characteristic quantity than the zeta potential because for such particles the zeta potential is not a constant quantity but depends on the electrolyte concentration. In this article, a systematic method that does not require numerical computer calculation is proposed to determine the surface charge density of a spherical colloidal particle on the basis of the particle electrophoretic mobility data. This method is based on two analytical equations, that is, the relationship between the electrophoretic mobility and zeta potential of the particle and the relationship between the zeta potential and surface charge density of the particle. The measured mobility values are analyzed with these two equations. As an example, the present method is applied to electrophoretic mobility data on gold nanoparticles (Agnihotri, S. M.; Ohshima, H.; Terada, H.; Tomoda, K.; Makino, K. Langmuir 2009, 25, 4804).

Kinetics of swelling and shrinking of poly (N-isopropylacrylamide) hydrogels at different temperatures

Abstract The swelling ratio of dried poly(N-isopropylacrylamide) hydrogels in distilled water was kinetically studied at different temperatures. The water content in the gel little increases after 30 min at higher temperatures than 33°C (LCST), while it increases for the initial 30 min with time. Between 25 and 33°C, the water content continues to increase for 8 hours, keeping the higher increase ratio at lower temperature. On the other hand, the hydrogel swollen in distilled water at 4°C starts to shrink after the hydrogel being moved into the distilled water kept at different temperatures between 25 and 40°C. There observed two types of shrinking behavior above and below LCST. In the initial 30 min of the shrinking process of the hydrogel, the water content decreases more obviously at higher temperatures. Over 3 h later, however, the water content kept in the hydrogel little decreases at 40°C, and the decreasing ratio during a unit time is highest at 35°C. At 37°C, the decreasing ratio of the water amount during a unit time gradually decreases with time after 1 h. Therefore, the water content kept in the hydrogel after the shrinking process of the swollen hydrogel for 24 h is lowest at 35°C, while that after the swelling process of dried hydrogel for 24 h is lowest at 37 and 40°C. From these findings, it is considered that there are at least three types of water molecules in the hydrogels, as follows: (i) water molecules adsorbed on the hydrophobic polymer chains in the tight skin phase formed by the shrinkage of the hydrogel at 37 and 40°C; (ii) water molecules movable in the looser polymer network in the skin phase formed around LCST and those adsorbed on the polymer chains; (iii) water molecules connected to each other with hydrogen bonds, adsorbed on the hydrophilic polymer chains, and movable in the polymer matrices.

Enhanced transdermal permeability of estradiol using combination of PLGA nanoparticles system and iontophoresis

Estradiol is a therapeutic agent for treatment of perimenopausal symptoms and osteoporosis. Conventional oral or intravenous administration of estradiol has many problems, such as, metabolization in gastrointestinal tract and liver, pain by using an injection needle, rapid increase of drug levels in blood and fast clearance with unwanted side effects including thrombosis, endometriosis and uterus carcinoma. The use of nanocarriers for transdermal delivery has been studied because of their ability to deliver therapeutic agents for long time with a controlled ratio, escaping from the first pass effect by liver. In this study, permeability of estradiol-loaded PLGA nanoparticles through rat skin was studied. Higher amount of estradiol was delivered through skin when estradiol was loaded in nanoparticles than estradiol was free molecules. Also, iontophoresis was applied to enhance the permeability of nanoparticles. When iontophoresis was applied, permeability of estradiol-loaded PLGA nanoparticles was much higher than that obtained by simple diffusion of them through skin, since they have negative surface charges. They were found to penetrate through follicles mainly. Also, enhanced permeability effect of estradiol by using nanoparticle system and iontophoresis were observed in vivo. The combination of charged nanoparticle system with iontophoresis is useful for effective transdermal delivery of therapeutic agents.

Pulsatile drug release from poly (lactide-co-glycolide) microspheres: how does the composition of the polymer matrices affect the time interval between the initial burst and the pulsatile release of drugs?

Abstract Pulsatile release of estradiol was observed from poly (lactide-co-glycolide) microspheres, of which the monomer composition was 75% lactide and 25% glycolide. Estradiol was monolithically dissolved in the polymer matrices. The microspheres were immersed in a pH 7.4 phosphate buffer saline at 37°C. When estradiol was loaded in microspheres consisting of poly (lactide-co-glycolide) of average molecular weight ( M w ) of 74 000 before degradation, the pulse of estradiol release was observed almost 50 days after the initial burst. On the other hand, if poly (lactide-co-glycolide) of M w 44 000 before degradation was used as a material to prepare the microspheres, then estradiol was released in a pulsatile manner almost 20 days after the initial burst effect. It was found that the time interval between the initial burst and the pulsatile release can be regulated by mixing the above two types of poly (lactide-co-glycolide) with different M w to prepare microspheres. For example, the pulsatile release of estradiol was observed 30 days after the degradation starts when the microspheres were composed of 50% poly (lactide-co-glycolide) of M w 74 000 and 50% poly (lactide-co-glycolide) of M w 44 000. In another case where the microspheres were composed of 75% poly (lactide-co-glycolide) of M w 74 000 and 25% poly (lactide-co-glycolide) of M w 44 000, the pulsatile release was observed 38 days after the degradation starts.