N,N-Diethyl-3-toluamide Formulation Based on Ethanol Containing 0.1% 2-Hydroxypropyl-ß-cyclodextrin Attenuates the Drug's Skin Penetration and Prolongs the Repellent Effect without Stickiness.

N,N-diethyl-3-toluamide (DEET) is one of the most widely used insect repellents in the world. It was reported that a solution containing 6-30% cyclodextrin (CD) as a solvent instead of ethanol (EtOH) provided an enhancement of the repellent action time duration of the DEET formulation, although the high-dose CD caused stickiness. In order to overcome this shortcoming, we attempted to prepare a 10% DEET formulation using EtOH containing low-dose CDs (ß-CD, 2-hydroxypropyl-ß-CD (HPßCD), methyl-ß-CD, and sulfobutylether-ß-CD) as solvents (DEET/EtOH/CD formulations). We determined the CD concentration to be 0.1% in the DEET/EtOH/CD formulations, since the stickiness of 0.1% CDs was not felt (approximately 8 × 10-3 N). The DEET residue on the skin superficial layers was prolonged, and the drug penetration into the skin tissue was decreased by the addition of 0.1% CD. In particular, the retention time and attenuated penetration of DEET on the rat skin treated with the DEET/EtOH/HPßCD formulation was significantly higher in comparison with that of the DEET/EtOH formulation without CD. Moreover, the repellent effect of DEET was more sustained by the addition of 0.1% HPßCD in the study using Aedes albopictus. In conclusion, we found that the DEET/EtOH/HPßCD formulations reduced the skin penetration of DEET and prolonged the repellent action without stickiness.

Effect of inner physical properties on powder adhesion in inhalation capsules in case of a high resistance device.

The inhalation performance of a dry powder inhaler (DPI) depends on the inhalation patterns of patients, inhalation particle characteristics and inhalation devices. In capsule-based DPIs, the capsule plays an important role in the dispersion of inhalation particles. The present study investigated the effects of inner physical properties of capsules on drug release from capsules-based DPIs with high resistance device. Atomic force microscopy (AFM) was used to evaluate the capsule physical properties, such as the capsule inner structure and surface potential, of three capsules with different compositions (G-Cap, PEG/G-Cap, and HPMC-Cap). As a model dry powder for capsule-based DPIs, the dry powder in Spiriva® Inhalation Capsules containing tiotropium bromide was used. Inhalation performance was evaluated using a twin-stage liquid impinge and Handihaler® (flow rate 30 l/min). The results indicated that the capsule inner surface presented with numerous valleys and mountains, regardless of the capsule type. Furthermore, the valley and mountain areas on the capsule inner surface showed a significantly higher or lower surface potential. Following inhalation of capsule-based DPIs, the drug remained in the valleys on the capsule inner surface; however, no significant difference was observed in the drug release from capsule and lung drug delivery. Therefore, inhalation performance in capsule-based DPIs when a high resistance device, such as Handihaler®, is used at an appropriately flow rate is not markedly affected by the physical properties of the capsule inner surface due to capsule composition.

Balance of Drug Residence and Diffusion in Lacrimal Fluid Determine Ocular Bioavailability in In Situ Gels Incorporating Tranilast Nanoparticles.

We previously designed ophthalmic formulations (nTRA) containing tranilast nanoparticles (Tra-NPs) with high uptake into ocular tissues. In this study, we used in situ gel (ISG) bases comprising combinations of pluronic F127 (F127) and methylcellulose (MC/F127), pluronic F68 (F68/F127), and Carbopol (Car/F127), and we developed in situ gels incorporating Tra-NPs (Tra-NP-incorporated ISNGs) such as nTRA-F127, nTRA-MC/F127, nTRA-F68/F127, and nTRA-Car/F127. Moreover, we demonstrated the therapeutic effect on conjunctival inflammation using lipopolysaccharide-induced rats. Each Tra-NP-incorporated ISNG was prepared by the bead mill method, the particle size was 40-190 nm, and the tranilast release and diffusion from formulation were nTRA > nTRA-F127 > nTRA-F68/F127 > nTRA-Car/F127 > nTRA-MC/F127. In the Tra-NP-incorporated ISNGs, the tranilast residence time in the lacrimal fluid, cornea, and conjunctiva was prolonged, although the Cmax was attenuated in comparison with nTRA. On the other hand, no significant difference in conjunctival inflammation between non- and nTRA-F127-instilled rats was found; however, the nTRA-F68/F127, nTRA-Car/F127, and nTRA-MC/F127 (combination-ISG) attenuated the vessel leakage, nitric oxide, and tumor necrosis factor-α expression. In particular, nTRA-F68/F127 was significant in preventing the conjunctival inflammation. In conclusion, we found that the combination-ISG base prolonged the residence time of Tra-NPs; however, Tra-NP release from the formulation was attenuated, and the Tmax was delayed longer than that in nTRA. The balance of drug residence and diffusion in lacrimal fluid may be important in providing high ocular bioavailability in formulations containing solid nanoparticles.

MPC Polymer Promotes Recovery from Dry Eye via Stabilization of the Ocular Surface.

The polymer that includes 2-methacryloyloxy ethyl phosphorylcholine (MPC) is well-known as an effectively hydrating multifunction agent. In this study, we prepared an MPC polymer (MPCP) using radical polymerization with co-monomers-MPC/Stearyl Methacrylate/N,N-dimethylacrylamide-and evaluated the MPCP's usefulness for dry eye treatment using a rabbit model treated with N-acetylcysteine. The MPCP particle size was 50-250 nm, and the form was similar to that of micelles. The MPCP viscosity (approximately 0.95 mPa·s) was 1.17-fold that of purified water, and a decrease in the transepithelial electrical resistance value (corneal damage) was not observed in the immortalized human corneal epithelial cell line HCE-T cell (HCE-T cell layer). The MPCP enhanced the water maintenance on the cornea, and the instillation of MPCP increased the lacrimal fluid volume and prolonged the tear film breakup time without an increase in total mucin contents in the lacrimal fluid of the normal rabbits. The therapeutic potential of the MPCP for dry eye was evaluated using an N-acetylcysteine-treated rabbit model, and, in our investigation, we found that MPCP enhanced the volume of lacrimal fluid and promoted an improvement in the tear film breakup levels. These findings regarding the creation and characteristics of a novel MPCP will provide relevant information for designing further studies to develop a treatment for dry eyes.

Effects of the Ophthalmic Additive Mannitol on Antimicrobial Activity and Corneal Toxicity of Various Preservatives.

Ophthalmic preservatives are indispensable in eye drop formulations, but may be toxic to corneal structures. Corneal damage necessitates the discontinuation of treatment with ophthalmic solutions. Therefore, the development of a new and safe preservative system without corneal toxicity is needed. The present study investigated the effects of mannitol on the antimicrobial activities and corneal toxicities of various preservatives using Escherichia coli and a human corneal epithelial cell line (HCE-T cells). The following preservatives were examined: boric acid (BA), benzalkonium chloride (BAC), methyl parahydroxybenzoate (MP), propyl parahydroxybenzoate (PP), sodium chlorite (SC), and zinc chloride (ZC). The antimicrobial activities and HCE-T-cell toxicities of 50 µg/mL BA, MP, PP, SC, and ZC were reduced by a co-treatment with mannitol (0-300 µg/mL). The suppressed antimicrobial activities of BA, MP, PP, and SC by the co-treatment with mannitol were restored by the application of a mannitol content higher than 500 µg/mL. In contrast to these 5 preservatives, the addition of mannitol did not affect the antimicrobial activity of BAC and attenuated its HCE-T cell toxicity. Therefore, the balance between the contents of mannitol and preservatives is important in co-treatments. The present results will serve as a guide for the future development of eye drop formulations without corneal toxicity.

In Situ Gelling Systems Using Pluronic F127 Enhance Corneal Permeability of Indomethacin Nanocrystals.

We previously designed an ophthalmic dispersion containing indomethacin nanocrystals (IMC-NCs), showing that multiple energy-dependent endocytoses led to the enhanced absorption of drugs from ocular dosage forms. In this study, we attempted to prepare Pluronic F-127 (PLF-127)-based in situ gel (ISG) incorporating IMC-NCs, and we investigated whether the instillation of the newly developed ISG incorporating IMC-NCs prolonged the precorneal resident time of the drug and improved ocular bioavailability. The IMC-NC-incorporating ISG was prepared using the bead-mill method and PLF-127, which yielded a mean particle size of 50-150 nm. The viscosity of the IMC-NC-incorporating ISG was higher at 37 °C than at 10 °C, and the diffusion and release of IMC-NCs in the IMC-NC-incorporating ISG were decreased by PLF-127 at 37 °C. In experiments using rabbits, the retention time of IMC levels in the lacrimal fluid was enhanced with PLF-127 in the IMC-NC-incorporating ISG, whereby the IMC-NC-incorporating ISG with 5% and 10% PLF-127 increased the transcorneal penetration of the IMCs. In contrast to the results with optimal PLF-127 (5% and 10%), excessive PLF-127 (15%) decreased the uptake of IMC-NCs after instillation. In conclusion, we found that IMC-NC-incorporating ISG with an optimal amount of PLF-127 (5-10%) resulted in higher IMC corneal permeation after instillation than that with excessive PLF-127, probably because of the balance between higher residence time and faster diffusion of IMC-NCs on the ocular surface. These findings provide significant information for developing ophthalmic nanomedicines.

In Situ Gel Incorporating Disulfiram Nanoparticles Rescues the Retinal Dysfunction via ATP Collapse in Otsuka Long-Evans Tokushima Fatty Rats.

We attempted to design an ophthalmic in situ gel formulation incorporating disulfiram (DIS) nanoparticles (Dis-NPs/ISG) and demonstrated the therapeutic effect of Dis-NPs/ISG on retinal dysfunction in 15-month-old Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a rat model of diabetes. The DIS particles were crushed using a bead mill to prepare the nanoparticles, and the Dis-NPs/ISG was prepared using a combination of the DIS nanoparticles and an in situ gelling system based on methylcellulose (MC). The particle size of the Dis-NPs/ISG was 80-250 nm, and there was no detectable precipitation or aggregation for 1 month. Moreover, the Dis-NPs/ISG was gelled at 37 °C, and the drug was delivered into the retina by instillation. Only diethyldithiocarbamate (DDC) was detected in the retina (DIS was not detected) when the Dis-NPs/ISG was instilled in the right eye, and the DDC levels in the right retina were significantly higher than those in the left retina. In addition, the retinal residence time of the drug was prolonged by the application of the in situ gelling system, since the DDC levels in the retinas of rats instilled with Dis-NPs/ISG were higher than those in DIS nanoparticles without MC. Furthermore, repetitive instillation of the Dis-NPs/ISG attenuated the deterioration of electroretinograms (ERGs) in 15-month-old OLETF rats by preventing the collapse of ATP production via excessive nitric oxide and recovered the decrease in retinal function. These findings provide important information for the development of novel therapeutic approaches to diabetic retinopathy.

An in situ Gelling System Based on Methylcellulose and Tranilast Solid Nanoparticles Enhances Ocular Residence Time and Drug Absorption Into the Cornea and Conjunctiva.

We previously developed ophthalmic formulations containing tranilast nanopartaicles (ophthalmic TL-NPs formulations), and found them to show high uptake into ocular tissues. In this study, we aimed to design an in situ gel incorporating TL-NPs with 0.5-3% methylcellulose (MC, type SM-4) to ensure long residence time of the drug at the ocular surface. The ophthalmic TL-NPs formulations were prepared by the bead mill method, which yielded a mean particle size of ~93 nm with or without MC (0.5-3%). Although the dispersibility of TL particles in ophthalmic formulations increased with the MC content, the diffusion behavior of TL particles in the dispersion medium decreased with MC content. In an in vivo study using rats, the TL content in the lacrimal fluid was enhanced with MC content in the ophthalmic TL-NPs formulations, and the optimum amount of MC (0.5-1.5%) enhanced the TL content in the cornea and conjunctiva, and an anti-inflammatory effect of TL in rats instilled with ophthalmic TL-NPs formulations was observed. On the other hand, excessive MC (3%) prevented the corneal uptake of TL-NPs after instillation, and the anti-inflammation effect of TL was lower than that of ophthalmic TL-NPs formulations with optimum MC (0.5-1.5%). In conclusion, we found that gel formulations of TL-NPs with 0.5 and 1.5% MC provided a prolonged pre-corneal and pre-conjunctival contact time of TL, and resulted in higher TL contents in the cornea and conjunctiva following instillation in comparison with TL-NPs with or without 3% MC. This is probably due to the balance between the higher residence time and faster diffusion of TL-NPs on the ocular surface. These findings provide significant information that can be used to design further studies aimed at developing ophthalmic nanomedicines.

Development of Sustained-Release Ophthalmic Formulation Based on Tranilast Solid Nanoparticles.

Eye drops containing Tranilast (TL), N-(3,4-dimethoxycinnamoyl) anthramilic acid, are used as an anti-allergic conjunctivitis drug in the ophthalmic field. Traditional eye drops are very patient compliant, although the bioavailability (BA) of most eye drops is low since eye drops cannot be instilled beyond the capacity of the conjunctival sac due to its limited volume. Thus, traditional eye drops have low BA and a short duration of the drug on the ocular surface, so solutions to these problems are highly anticipated. In this study, we designed a sustained-release drug-delivery system (DDS) for TL nanoparticles. TL nanoparticles were prepared by bead mill treatment, and the gel formulations containing TL nanoparticles (TL-NPs-Gel, particle size 50 nm-100 nm) were provided by carboxypolymethylene. The crystal structure of TL with and without bead mill treatment is the same, but the TL solubility in formulations containing nanoparticles was 5.3-fold higher compared with gel formulations containing TL microparticles (TL-MPs-Gel). The photo and thermal stabilities of TL-NPs-Gel are also higher than those of dissolved TL. Moreover, when TL-NPs-Gel is applied to the upper eyelid skin (outside), the TL is released as nanoparticles, and delivered to the lacrimal fluid through the meibomian glands. In addition, the TL release profile for TL-NPs-Gel was sustained over 180 min after the treatment. These findings can be used to develop a sustained-release DDS in the ophthalmic field.