Shinji Sakuma

Design of nanoparticles composed of graft copolymers for oral peptide delivery

The development of a dosage form that improves the absorption of peptide and protein drugs via the gastrointestinal tract is one of the greatest challenges in the pharmaceutical field. Many researchers have taken up the challenge, using approaches including mucoadhesive drug delivery, colon delivery, particulate drug delivery such as nanoparticles, microcapsules, liposomes, emulsions, micelles, and so on. The objective of this article is to provide the reader with outlines of novel nanoparticle technologies for oral peptide delivery based on polymer chemistry. The physicochemical properties of nanoparticles and their behavior on exposure to physiological media are greatly dominated by their chemical structures and surface characteristics. We will especially focus on the design of nanoparticles composed of novel graft copolymers having a hydrophobic backbone and hydrophilic branches as drug carriers.

Mucoadhesion of polystyrene nanoparticles having surface hydrophilic polymeric chains in the gastrointestinal tract.

The mucoadhesion of polystyrene nanoparticles having surface hydrophilic polymeric chains in the gastrointestinal (GI) tract was investigated in rats. Radiolabeled nanoparticles were synthesized by adding hydrophobic 3-(trifluoromethyl)-3-(m-[125I]iodophenyl)diazirine in the final process of nanoparticle preparation. The radioiodonated diazirine seemed to be incorporated in the hydrophobic polystyrene core of nanoparticles. The incorporation rate was less than 10%, irrespective of nanoparticle type. The diazirine incorporated in nanoparticles exhibited little leakage from them even though they were mixed with a solution corresponding to GI juice. The change in blood ionized calcium concentration after oral administration of salmon calcitonin (sCT) with nanoparticles showed that the in vivo enhancement of sCT absorption by radiolabeled nanoparticles was the same as that by non-labeled nanoparticles. The GI transit rates of nanoparticles having surface poly(N-isopropylacrylamide), poly(vinylamine) and poly(methacrylic acid) chains, which can improve sCT absorption, were slower than that of nanoparticles covered by poly(N-vinylacetamide), which does not enhance sCT absorption at all. These slow transit rates were probably the result of mucoadhesion of nanoparticles. The strength of mucoadhesion depended on the structure of the hydrophilic polymeric chains on the nanoparticle surface. The mucoadhesion of poly(N-isopropylacrylamide) nanoparticles, which most strongly enhanced sCT absorption, was stronger than that of ionic nanoparticles, and poly(N-vinylacetamide) nanoparticles probably did not adhere to the GI mucosa. These findings demonstrated that there is a good correlation between mucoadhesion and enhancement of sCT absorption.

Biorecognizable HPMA copolymer-drug conjugates for colon-specific delivery of 9-aminocamptothecin.

N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer conjugates for colon-specific delivery of 9-aminocamptothecin (9-AC) were designed. They hold 9-AC bound via spacers containing amino acid residues and aromatic azo bonds. In vitro release profiles of 9-AC from HPMA copolymer conjugates were evaluated under artificial conditions that simulated large intestinal azoreductase and peptidase activities. The studies indicated that the azo bond was reduced first, followed by the release of unmodified 9-AC from the 9-AC containing fragment by peptidases. Release profiles depended on the chemical structure of the peptide part of the spacer. Conjugates containing leucylalanine showed high colon-specific release of 9-AC when compared to alanine containing conjugates. It appears that the studied conjugates are suitable as colon-specific drug delivery systems.

Oral peptide delivery using nanoparticles composed of novel graft copolymers having hydrophobic backbone and hydrophilic branches

Nanoparticles composed of new graft copolymers having a hydrophobic backbone and hydrophilic branches were prepared by the dispersion copolymerization of hydrophilic polyvinyl macromonomers with styrene in a polar solvent. The potential of these nanoparticles as carriers for oral peptide delivery, was investigated using salmon calcitonin (sCT) in rats. The rate of sCT incorporated in nanoparticles was high and was affected by the macromonomer structure. Anionic nanoparticles having poly(methacrylic acid) macromonomer chains on their surfaces showed the highest incorporating activity. When the mixture of sCT and nanoparticles was administered orally, the decrease in the blood ionized calcium concentration was greater than that after oral administration of sCT aqueous solution. This hypocalcemic effect was also affected by the macromonomer structure, and the absorption of sCT was enhanced most strongly by nanoparticles having poly(N-isopropylacrylamide) macromonomer chains. However, the calcium concentration changed less when the nanoparticle concentration was low. On the other hand, the hypocalcemic effect was independent of the nanoparticle size and molecular weight of the macromonomers. The absorption enhancement of sCT by the nanoparticles probably results from both bioadhesion to the gastrointestinal (GI) mucosa and the increase of the stability of sCT in the GI tract. These nanoparticles were demonstrated to be useful carriers for incorporating highly water-soluble peptides and for enhancing peptide absorption via the GI tract.

Mechanisms of membrane transport of poorly soluble drugs: Role of micelles in oral absorption processes

Micelles formed in the GI tract by bile acid and lecithin play an important role in oral absorption of poorly soluble drugs. In this situation, the drug molecules are present in equilibrium between the free and micellar states. In this study, the relationship between the free drug concentration and the membrane permeability of poorly soluble drugs was examined. Permeability across a Caco-2 monolayer and a dialysis membrane were measured in a side-by-side chamber system. The concentrations of sodium taurocholate (NaTC) and lecithin were varied to allow measurement of membrane permeability at different concentrations of free drugs. For troglitazone, hexylparaben, and heptylparaben, an increase in the NaTC and lecithin concentrations caused the permeability across the Caco-2 monolayer to decrease slightly, whereas the permeability across the dialysis membrane decreased markedly. In contrast, the changes in permeability of griseofulvin with an increased micelle concentration were similar for the Caco-2 monolayer and the dialysis membrane. Assuming that the permeability for the dialysis membrane reflects the free drug concentration in the medium, these results suggest that troglitazone and alkylparabens, but not griseofulvin, can partition directly from micelles to Caco-2 monolayers. This mechanism may contribute to oral absorption of drugs that are poorly soluble in water.

Optimized chemical structure of nanoparticles as carriers for oral delivery of salmon calcitonin

Nanoparticles having two kinds of surface hydrophilic polymeric chains were prepared by the free radical copolymerization between styrene and hydrophilic macromonomers terminating in vinylbenzyl groups. Their potential as carriers for oral peptide delivery was investigated using salmon calcitonin (sCT) in rats. After oral administration of mixtures of sCT and nanoparticles, the ionized calcium concentration in blood was measured. The absorption of sCT was significantly enhanced by nanoparticles having poly-N-isopropylacrylamide (PNIPAAm) chains on their surfaces. This enhancement effect was considerably increased by introducing cationic poly-vinylamine (PVAm) groups to the surface of PNIPAAm nanoparticles. The absorption enhancement depended on the ratio of NIPAAm and VAm macromonomers to styrene in the nanoparticle preparation. In contrast, the introduction of nonionic poly-vinylacetamide (PNVA) groups eliminated completely the absorption-enhancing function of PNIPAAm nanoparticles. It was suggested that this disappearance was due to the shielding of PNIPAAm groups by PNVA groups. The enhancement effect of sCT absorption by nanoparticles was greatly dominated by their chemical structure that was closely related to surface characteristics. Optimization of the chemical structure on the basis of the mechanism of the absorption enhancement resulted in the further improvement of sCT absorption.

Coaxial Electrospray Formulations for Improving Oral Absorption of a Poorly Water-Soluble Drug

Development of oral dosage forms containing poorly water-soluble drugs is a major challenge in the pharmaceutical industry. This paper describes the use of coaxial electrospray deposition as a promising formulation technology for oral delivery of poorly water-soluble drugs. The technology produced core-shell particles composed of griseofulvin and poly(methacrylic acid-co-methyl methacrylate) (Eudragit L-100), with a diameter of around 1 μm. The drug phase was in an amorphous state when the griseofulvin core was coated with the Eudragit L-100 shell. The in vitro dissolution and in vivo oral absorption studies revealed that the core-shell formulation significantly improved dissolution and absorption behaviors, presumably because of a reduction in particle size, improvement in dispersity, and amorphization. Results demonstrated that coaxial electrospray deposition possesses great potential as novel formulation technology for enhancing oral absorption of poorly water-soluble drugs.

Application of Dissolution/Permeation System for Evaluation of Formulation Effect on Oral Absorption of Poorly Water-Soluble Drugs in Drug Development

ABSTRACTPurposeThe aim of the present study is to evaluate the formulation effect on the oral absorption of poorly water-soluble drugs using a dissolution/permeation system (D/P system).MethodsThis D/P system, consisting of apical and basal chambers and a Caco-2 cell monolayer mounted between chambers, can be used to perform simultaneous analysis of drug dissolution and permeation process of drugs applied as various dosage forms. Oral administration study with rats was also performed for both drugs as the same dosage forms.ResultsWhen danazol, a low-soluble and high-permeable drug, was applied to the D/P system as various formulations, dissolved and permeated amounts were significantly high compared with those from a suspension form. On the other hand, whereas the dissolved amount of pranlukast, a low-soluble and low-permeable drug, was significantly increased by formulations, there were no significant changes observed in the permeated amount between suspension and formulation. The oral availability of danazol was significantly increased by formulations but not pranlukast, which corresponded well to in vitro evaluations.ConclusionThese results indicated that the D/P system might be applicable for selection of formulation on the basis of physicochemical drug properties.

Behavior of mucoadhesive nanoparticles having hydrophilic polymeric chains in the intestine

The behavior of nanoparticles having surface hydrophilic poly(N-isopropylacrylamide), poly(N-vinylacetamide), poly(vinylamine) or poly(methacrylic acid) chains in the intestine was examined. The permeability of salmon calcitonin (sCT) from the mucosal to serosal side of the everted jejunum was enhanced in the presence of nanoparticles. This enhancement, which correlated with the amount of sCT incorporated in nanoparticles, disappeared completely after removal of the mucous layer. When fluorescein isothiocyanate-dextran (FD-4) was used instead of sCT, its permeability through the everted jejunum with and without mucous layer was not enhanced by any nanoparticles, because FD-4 was not incorporated in nanoparticles at all. These findings indicated that the accumulation of nanoparticles incorporating sCT in the mucous layer resulted in the enhancement of sCT permeability. Nanoparticles with poly(N-isopropylacrylamide) or poly(vinylamine) on their surfaces did not cause any damage to the intestinal mucosa. Also, none of the nanoparticles opened the tight junction of the intestinal membrane. It was concluded that mucoadhesion of nanoparticles incorporating sCT to the gastrointestinal mucosa contributed to the absorption enhancement of sCT.

Absorption enhancement of orally administered salmon calcitonin by polystyrene nanoparticles having poly(N-isopropylacrylamide) branches on their surfaces

Abstract Polystyrene nanoparticles having poly(N-isopropylacrylamide) branches on their surfaces (PNIPAAm nanoparticles) were synthesized and various attempts were made in rats to increase the absorption enhancement of orally administered salmon calcitonin (sCT) by these nanoparticles. The hypocalcemic effect after oral administration of a mixture of sCT and PNIPAAm nanoparticles depended greatly on the administration schedule. When one half of a dose of the mixture was given orally 40 min after the other half, sCT-induced hypocalcemic effect was markedly enhanced by PNIPAAm nanoparticles and the area of the reduction of the blood ionized calcium concentration was about 3 times that after administration of a single full dose of the same mixture. However, there was no further enhancement of the pharmacological activity of sCT when the half-doses were administered 120 min apart, sCT absorption was also affected by the hydrophobicity of the PNIPAAm nanoparticles. The hydrophobic PNIPAAm nanoparticles dispersed in hydrochloric acid-sodium chloride solution of pH 1.2, increased in sCT-induced hypocalcemic effect considerably. When two half-doses of the mixture containing these hydrophobic nanoparticles were given orally 40 min apart, the hypocalcemic effect remained strong, even though the dose was reduced to less than half. These changes probably depended on the bioadhesion of PNIPAAm nanoparticles to the gastric mucosa. It was demonstrated that PNIPAAm nanoparticles are good drug carriers that substantially enhance sCT absorption via the gastrointestinal tract.