Yoshihisa Koyama

Background: Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by persistent joint inflammation and progressive disability. Although current therapies have improved clinical outcomes, safer and more effective therapeutic approaches remain needed. Silicon (Si)-based agents have antioxidant and anti-inflammatory properties and have shown beneficial effects in several inflammatory disease models. Methods: We evaluated the effects of oral administration of a Si-based agent in a type II collagen-induced arthritis mouse model. Arthritis severity was assessed using an arthritis index, hindlimb oedema, and the hindlimb extension reflex test. Serum type II collagen-specific autoantibody levels were also measured. Vestibular function was evaluated using the vestibulo-ocular reflex (VOR), and inner-ear structural changes were assessed by magnetic resonance imaging and histological analysis. Results: The Si-based agent reduced arthritis-related outcomes, including the arthritis index, hindlimb oedema, and joint movement restriction, and reduced serum type II collagen-specific autoantibody levels. In contrast, no significant differences between the Si-based agent and control groups were detected in VOR-related outcomes, endolymphatic space measurements, or inner-ear histological findings. Conclusions: These findings suggest that the Si-based agent may have beneficial effects on arthritis-related manifestations. However, its effects on the vestibular function-related outcomes examined in this study were not evident. Further studies are needed to clarify the relationship between RA and vestibular dysfunction and to determine the potential therapeutic effects of Si-based agent on these complications.

Aversion can arise from a combination of unconditioned stimuli that induce physical discomfort, such as pain and nausea. Chemotherapy-induced side effects, including taste and olfactory aversion, can persist even after treatment has ended, thereby reducing the quality of life. Currently, however, no effective pharmacological interventions exist for treating chemotherapy-induced conditioned aversion learning. Therefore, elucidating its underlying mechanisms is of great importance. In this study, we investigated cisplatin-induced olfactory aversion learning using the two-bottle choice test. Cisplatin was found to induce aversive responses to neutral odorants, namely isoamyl acetate and benzaldehyde. Notably, we obtained two key findings. First, an odor solution that was not aversive in the two-bottle choice test (i.e., distilled water) became aversive to mice when compared with a third novel odor solution that had not been presented in the test. Second, when pairs of three odorants were alternated over an extended period, the mice occasionally shifted their aversive responses as the pairings changed. In clinical practice, patients are exposed to a variety of odors. Thus, the new insights gained from this study on olfactory aversion may help inform the development of novel treatments for chemotherapy-related side effects. (PsycInfo Database Record (c) 2026 APA, all rights reserved).

Postoperative delirium (POD) is a postoperative complication characterized by acute-onset attention deficits and cognitive impairment following surgery. Recently, oxidative stress has been increasingly recognized in its pathogenesis. This study investigated the relationship between postoperative behavioral changes and systemic oxidative stress responses under graded levels of surgical stress. Male C57BL/6J mice were divided into three groups: anesthesia alone, standard laparotomy, and open surgery with added localized thermal injury (OPT). The buried food test was performed 24 h after anesthesia induction to evaluate search latency. Serum was collected after the behavioral test to measure derivatives of reactive oxygen metabolites (d-ROMs), biological antioxidant potential (BAP), and the BAP/d-ROMs ratio. Search latency became more prolonged under conditions of increased surgical invasiveness. The d-ROMs values increased progressively with increasing surgical stress, whereas the BAP/d-ROMs ratio progressively decreased. Group-stratified and interaction analyses suggested that the relationship between postoperative behavioral changes and systemic oxidative stress responses differed according to the degree of surgical invasiveness, particularly regarding the BAP/d-ROMs ratio. These findings suggest that oxidative stress responses may contribute differently to postoperative behavioral changes under different levels of graded surgical stress.