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We have recently reported Catalytides (Catalytic peptides) JAL-TA9 (YKGSGFRMI) and ANA-TA9 (SKGQAYRMI), which are the first Catalytides found to cleave Aβ42. Although the Catalytides must be delivered to the brain parenchyma to treat Alzheimer’s disease, the blood–brain barrier (BBB) limits their entry into the brain from the systemic circulation. To avoid the BBB, the direct route from the nasal cavity to the brain was used in this study. The animal studies using rats and mice clarified that the plasma clearance of ANA-TA9 was more rapid than in vitro degradation in the plasma, whole blood, and the cerebrospinal fluid (CSF). The brain concentrations of ANA-TA9 were higher after nasal administration than those after intraperitoneal administration, despite a much lower plasma concentration after nasal administration, suggesting the direct delivery of ANA-TA9 to the brain from the nasal cavity. Similar findings were observed for its transport to CSF after nasal and intravenous administration. The concentration of ANA-TA9 in the olfactory bulb reached the peak at 5 min, whereas those in the frontal and occipital brains was 30 min, suggesting the sequential backward translocation of ANA-TA9 in the brain. In conclusion, ANA-TA9 was efficiently delivered to the brain by nasal application, as compared to other routes.

A well-developed lymphatic network is located under the nasal mucosa, and a few drugs that permeate the nasal mucosa are absorbed into the lymphatic capillaries. Lymph from the nasal cavity flows to the cervical lymph nodes (CLNs). In this study, we evaluated the pharmacokinetics of the direct transport of intranasally administered drugs to CLNs through the nasal mucosa of Wistar rats using methotrexate as a model drug. The drug targeting index, which was calculated based on the areas under the concentration–time curves after intravenous and intranasal administration, was 3.78, indicating the benefits of nasal delivery of methotrexate to target CLNs. The direct transport percentage, which was indicative of the contribution of the direct nose–CLN pathway of methotrexate after intranasal administration, was 74.3%. The rate constant of methotrexate from the nasal cavity to CLNs was 0.0047 ± 0.0013 min−1, while that from systemic circulation to CLNs was 0.0021 ± 0.0009 min−1. Through pharmacokinetic analysis, this study demonstrated that the direct nasal–CLN pathway contributed more to the transport of methotrexate to the CLNs than the direct blood–CLN pathway.

Based on structural data on the nasal cavity and brain of the cynomolgus monkey, species differences in the olfactory bulb and cribriform plate were discussed from the viewpoint of direct delivery from the nose to the brain. Structural 3D data on the cynomolgus monkey skull were obtained using X-ray computed tomography. The dimensions of the nasal cavity of the cynomolgus monkey were 5 mm width × 20 mm height × 60 mm depth. The nasal cavity was very narrow and the olfactory region was far from the nostrils, similar to rats and humans. The weight and size of the monkey brain were 70 g and 55 mm width × 40 mm height × 70 mm depth. The olfactory bulb of monkeys is plate-like, while that of humans and rats is bulbar, suggesting that the olfactory area connected with the brain of monkeys is narrow. Although the structure of the monkey nasal cavity is similar to that of humans, the size and shape of the olfactory bulb are different, which is likely to result in low estimation of direct delivery from the nose to the brain in monkeys.

Recently, various types of cultured cells have been used to research the mechanisms of transport and metabolism of drugs. Although many studies using cultured cell systems have been published, a comparison of different cultured cell systems has never been reported. In this study, Caco-2, Calu-3, Madin−Darby canine kidney (MDCK), EpiAirway and MucilAir were used as popular in vitro cell culture systems, and the permeability of model compounds across these cell systems was evaluated to compare barrier characteristics and to clarify their usefulness as an estimation system for nasal drug absorption in rats. MDCK unexpectedly showed the best correlation (r = 0.949) with the fractional absorption (Fn) in rats. Secondly, a high correlation was observed in Calu-3 (r = 0.898). Also, Caco-2 (r = 0.787) and MucilAir (r = 0.750) showed a relatively good correlation with Fn. The correlation between Fn and permeability to EpiAirway was the poorest (r = 0.550). Because EpiAirway forms leakier tight junctions than other cell culture systems, the paracellular permeability was likely overestimated with this system. On the other hand, because MDCK formed such tight cellular junctions that compounds of paracellular model were less likely permeated, the paracellular permeability could be underestimated. Calu-3, Caco-2 and MucilAir form suitable cellular junctions and barriers, indicating that those cell systems enable the precise estimation of nasal drug absorption.

Carbamazepine (CBZ), a widely used antiepileptic, is known to be sensitive to light. The aim of this study was to evaluate the photostabilities of three cocrystals of CBZ (CBZ−succinic acid (SUC), CBZ−saccharin (SAC) form I, and CBZ−SAC form II) illuminated with a D65 fluorescent lamp compared with those of the conventional solid forms: CBZ polymorphs (forms I, II, and III). The order of discoloration determined using a colorimetric measurement was almost consistent with that of the degradation rates estimated using Fourier-transform infrared reflection−absorption spectroscopy, and these parameters of CBZ polymorphs increased in the order of form III, form I, and form II. CBZ−SUC and CBZ−SAC form I significantly suppressed the discoloration and degradation of CBZ compared with the raw CBZ, while CBZ−SAC form II facilitated the discoloration and degradation of CBZ. These results were supported by the results from the low-frequency Raman spectroscopy. The molecular mobility estimated using solid-state nuclear magnetic resonance 1H spin−lattice relaxation time strongly correlated with the degradation rate constant, indicating that molecular mobility significantly decreased following the formation of CBZ−SUC and CBZ−SAC form I and resulted in higher photostability. Overall, CBZ−SUC and CBZ−SAC form I are photostable forms and cocrystallization was proven to be an effective approach to improving the photostability of a photolabile drug.

Generally, the use of absorption enhancers might be the most effective approaches to ameliorate the enteric absorption of poorly absorbed substances. Among numerous absorption enhancers, we already reported that a gemini surfactant, sodium dilauramidoglutamide lysine (SLG-30) with two hydrophobic and two hydrophilic moieties, is a novel and promising adjuvant with a high potency in improving the absorption safely. Here, we examined and elucidated the absorption-improving mechanisms of SLG-30 in the enteric absorption of substances. SLG-30 increased the intestinal absorption of 5(6)-carboxyfluorescein (CF) to a greater level than the typical absorption enhancers, including sodium glycocholate and sodium laurate, as evaluated by an in situ closed-loop method. Furthermore, SLG-30 significantly lowered the fluorescence anisotropy of dansyl chloride (DNS-Cl), suggesting that it might increase the fluidity of protein sections in the intestinal cell membranes. Moreover, SLG-30 significantly lowered the transepithelial-electrical resistance (TEER) values of Caco-2 cells, suggesting that it might open the tight junctions (TJs) between the enteric epithelial cells. Additionally, the levels of claudin-1 and claudin-4 expression decreased in the presence of SLG-30. These outcomes propose that SLG-30 might improve the enteric transport of poorly absorbed substances through both transcellular and paracellular routes.

l-cysteine (Cys)- and l-serine (Ser)-modified, third-generation polyamidoamine (PAMAM) dendrimer with multiple reduced thiols (Ser-PAMAM-Cys) was synthesized as a kidney-targeting reactive oxygen species (ROS) scavenger to help prevent renal ischemia/reperfusion injury. Ser-PAMAM-Cys effectively scavenged 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical and ROS (hydrogen peroxide and hydroxyl radical) in phosphate-buffered saline (PBS). In addition, ~64% of 111In-labeled Ser-PAMAM-Cys accumulated in mouse kidney 3 h after intravenous administration. An in vivo imaging system (IVIS) study indicated that near-infrared fluorescence dye (NIR)-labeled Ser-PAMAM-Cys specifically accumulated in the kidney. In a mouse renal ischemia/reperfusion injury model, increases in the kidney damage markers creatinine (Cre) and blood urea nitrogen (BUN) were significantly inhibited by intravenous Ser-PAMAM-Cys administration. In contrast, Cys injection had no statistically significant effect of preventing Cre or BUN elevation relative to the control. Ser-PAMAM-Cys also effectively downregulated the inflammatory factors NGAL, IL-18, ICAM-1, and VCAM-1 in the renal ischemia/reperfusion injury model. These results indicate that Ser-PAMAM-Cys is a promising kidney-targeting ROS scavenger which could prevent ischemia/reperfusion-induced renal failure.

Human parathyroid hormone (1-34) (PTH) has been widely used as the subcutaneous injection formulation for the treatment of osteoporosis. In the present study, we developed an efficient transdermal delivery system of PTH by using dissolving microneedle arrays (MNs) composed of hyaluronic acid (HA) for the treatment of osteoporosis. PTH-loaded MNs, with needle length 800 µm, were fabricated via a micro-molding method. The stability of PTH in MNs was found to be 6-fold higher than that of PTH solution when stored at room temperature (15⁻20 °C) for one month. Micron-scale pores were clearly visible in rat skin following application of PTH-loaded MNs. PTH-loaded MNs were completely dissolved by 60 min following application to rat skin. The bioavailability (BA) of PTH relative to subcutaneous injection was 100 ± 4% following application of PTH-loaded MNs in rats. In addition, PTH-loaded MNs were found to effectively suppress decreases in bone density in a rat model of osteoporosis. Furthermore, no skin irritation was observed at the site of application in rats. These findings indicate that our dissolving MNs have a potential use in formulations for the transdermal delivery of PTH and for the treatment of osteoporosis.

To improve the transdermal bioavailability and safety of alendronate (ALN), a nitrogen-containing bisphosphonate, we developed self-dissolving microneedle arrays (MNs), in which ALN is loaded only at the tip portion of micron-scale needles by a dip-coating method (ALN(TIP)–MN). We observed micron-scale pores in rat skin just after application of ALN(TIP)–MN, indicating that transdermal pathways for ALN were created by MN. ALN was rapidly released from the tip of MNs as observed in an in vitro release study. The tip portions of MNs completely dissolved in the rat skin within 5 min after application in vivo. After application of ALN(TIP)–MN in mice, the plasma concentration of ALN rapidly increased, and the bioavailability of ALN was approximately 96%. In addition, the decrease in growth plate was effectively suppressed by this efficient delivery of ALN in a rat model of osteoporosis. Furthermore, no skin irritation was observed after application of ALN(TIP)–MN and subcutaneous injection of ALN, while mild skin irritation was induced by whole-ALN-loaded MN (ALN–MN)—in which ALN is contained in the whole of the micron-scale needles fabricated from hyaluronic acid—and intradermal injection of ALN. These findings indicate that ALN(TIP)–MN is a promising transdermal formulation for the treatment of osteoporosis without skin irritation.