Role of transient receptor potential melastatin 8 activity in menthol-induced cold sensitivity and its qualitative perception in dry eye

Effects of a Long-Acting Diquafosol Ophthalmic Solution on the Ocular Surface, Tolerability, and Usability in Dry Eye Disease

INTRODUCTION

This study aimed to investigate the tolerability of high-viscosity diquafosol tetrasodium (DQS) ophthalmic solution (DIQUAS LX; DQSLX) and examine its usability and effect on clinical findings in patients with dry eye disease (DED).

METHODS

This interventional retrospective study included 66 eyes of 66 patients with DED who switched from conventional DQS to DQSLX ophthalmic solution. Tear function assessments (tear film breakup time [BUT], keratoconjunctival vital staining [VS] score), evaluations of DED symptom relief, and a four-item usability questionnaire ("comfort upon instillation," "irritation upon instillation," "eye mucus discharge," "convenience of instillation frequency") assessed using a visual analog scale from 0 (worst) to 10 (best) were administered 4 weeks after switching to DQSLX. Factors associated with drug tolerability were assessed using multiple regression analysis.

RESULTS

The symptoms improved by 64.2% after switching to DQSLX. The BUT value, VS score, and the questionnaire items "comfort upon instillation" and "convenience of instillation frequency" were significantly improved after switching to DQSLX. DQSLX tolerability was reported as acceptable in 56 (84.8%) and unacceptable in 10 (15.2%) patients. Overall, DQSLX tolerability was significantly associated with "comfort upon instillation" and "convenience of instillation frequency" and tended to be associated with a VS score ≥ 1. DQSLX tolerability depended on symptom and VS score improvements and absence of excessive "eye mucus discharge" in patients with a VS score ≥ 1 (39 patients), but on "comfort upon instillation" and absence of excessive "eye mucus discharge" in patients with a VS score = 0 (27 patients).

CONCLUSION

The high-viscosity DQSLX ophthalmic solution was generally considered acceptable in the study population. However, drug tolerability seemingly differed between patients with DED with and without epithelial damage. The former were affected by improvements in symptoms and clinical findings, whereas the latter were affected by comfort upon instillation.

TRIAL REGISTRATION

University Hospital Medical Information Network identifier, UMIN000051390.

Roles of Thermosensitive Transient Receptor Channels TRPV1 and TRPM8 in Paclitaxel-Induced Peripheral Neuropathic Pain

Paclitaxel, a microtubule-stabilizing chemotherapy drug, can cause severe paclitaxel-induced peripheral neuropathic pain (PIPNP). The roles of transient receptor potential (TRP) ion channel vanilloid 1 (TRPV1, a nociceptor and heat sensor) and melastatin 8 (TRPM8, a cold sensor) in PIPNP remain controversial. In this study, Western blotting, immunofluorescence staining, and calcium imaging revealed that the expression and functional activity of TRPV1 were upregulated in rat dorsal root ganglion (DRG) neurons in PIPNP. Behavioral assessments using the von Frey and brush tests demonstrated that mechanical hyperalgesia in PIPNP was significantly inhibited by intraperitoneal or intrathecal administration of the TRPV1 antagonist capsazepine, indicating that TRPV1 played a key role in PIPNP. Conversely, the expression of TRPM8 protein decreased and its channel activity was reduced in DRG neurons. Furthermore, activation of TRPM8 via topical application of menthol or intrathecal injection of WS-12 attenuated the mechanical pain. Mechanistically, the TRPV1 activity triggered by capsaicin (a TRPV1 agonist) was reduced after menthol application in cultured DRG neurons, especially in the paclitaxel-treated group. These findings showed that upregulation of TRPV1 and inhibition of TRPM8 are involved in the generation of PIPNP, and they suggested that inhibition of TRPV1 function in DRG neurons via activation of TRPM8 might underlie the analgesic effects of menthol.

Effectiveness and safety of Jiejing Runmu decoction in treatment of dry eye disease

OBJECTIVE

To investigate the effectiveness and safety of Jiejing Runmu decoction in relieving the clinical manifestations of dry eye disease (DED).

DESIGN AND INTERVENTIONS

This single-arm prospective intervention study was conducted at the Peking University Third Hospital and People's Hospital of Yongqing. Of the 211 patients recruited, 200 completing the follow-up were included in the analysis. Patients received Jiejing Runmu decoction once a day for 4 weeks continuously, without any change in eye care habits. Individuals were evaluated at four time points: pretreatment (baseline), 2 weeks, 1 month, and 3 months (2 months after completion of treatment), using the Ocular Surface Disease Index (OSDI), tear film breakup time (TBUT), corneal fluorescein staining, Schirmer test I and meibomian gland assessments. Adverse effects were evaluated at each follow-up visit and systematic examinations were performed during the first and last visits.

RESULTS

OSDI, TBUT, corneal fluorescein staining, Schirmer test I, meibomian gland expressibility, and quality of secretions improved at 2 weeks, 1 month and 3 months compared to baseline (P < 0.0001). No significant differences were found between the sexes. Patients above 45 years showed worse subjective symptoms and objective signs, and greater improvements in corneal fluorescein staining, meibomian gland expressibility, and quality of secretions were observed in this group. No obvious adverse effects were detected during any follow-up visit.

CONCLUSION

Jiejing Runmu decoction significantly improved both the subjective symptoms and objective signs of DED, with favorable tolerance.

Loss of TRPM8 Exacerbate Herpes Simplex Keratitis Infection in Mice by Promoting the Infiltration of CD11b+ Ly6G+ Cells and Increasing the Viral Load in the Cornea

Purpose

To reveal the role of transient receptor potential cation subfamily M member 8 (TRPM8) channels in herpes simplex keratitis (HSK).

Methods

HSK models were established using TRPM8 knockout (TRPM8-/-) mice and their wild-type (WT) littermates. The infected corneas were graded and harvested to evaluate the mRNA levels of inflammatory factors through quantitative real-time polymerase chain reaction (RT-PCR), as well as the infiltration of inflammatory cells through immunofluorescence staining and flow cytometry. Viral titers were determined by plaque assay and absolute quantitative method. RNA-sequencing was conducted to elucidate the transcriptome of corneal epithelium in response to TRPM8 knockout after infection. The anti-inflammatory effect of TRPM8 agonist menthol was documented via subconjunctival administration.

Results

Compared to their wild-type counterparts, TRPM8-deficient mice exhibited exacerbated infection symptoms and thicker corneas in HSK models. Infection in TRPM8-deficient mice resulted in significant lymphocyte infiltration, primarily consisting of Ly6G+ CD11b+ cells. Additionally, TRPM8-deficient mice displayed increased levels of corneal viral titers after infection, along with decreased expression of interferon-stimulated genes (ISGs). Subconjunctival administration of menthol effectively alleviated infection-induced symptoms and Ly6G+ CD11b+ cell infiltration in herpes simplex virus type 1 (HSV-1)-treated mice.

Conclusions

TRPM8 promoted host resistance to HSV-1 infection by suppressing the accumulation of Ly6G+ CD11b+ cells and virus replication. These findings suggest that targeting TRPM8 could be valuable for therapeutic interventions against HSV-1 infections.

Variability of autonomic nerve activity in dry eye with decreased tear stability

The autonomic nervous system plays a crucial role in the maintenance of homeostasis. Neurogenic inflammation due to decreased stability of tear film may induce changes in autonomic nerve activity, which could be associated with symptom expression.This study aimed to measure biological parameters that represent autonomic nerve activity in dry eye (DE)s caused by tear film dysfunction and investigate their relationship with symptom intensity. This prospective, cross-sectional, comparative study evaluated 34 eyes of 34 participants (mean age: 52.5 ± 13.4 years; range: 20–81 years) without keratoconjunctival damage. Nineteen eyes in the DE group showed DE symptoms and tear break-up time (TBUT) of ≤5 seconds (short TBUT DE); the 15 eyes in the non-DE group showed no DE symptoms. Autonomic nerve activity was measured for 10 minutes—starting and ending 5 minutes before and after instilling ophthalmic solution—and evaluated using the low-frequency component (LF) to the high-frequency component (HF) ratio of heart rate variability (autonomic balance). The pre-ophthalmic solution administration LF/HF ratio was not significantly different (P = 0.59) between the two groups, however, the standard deviation of the LF/HF ratio (LF/HF-SD) tended to be higher in the DE group than that in the non-DE group (P = 0.086). The DE symptom intensity was significantly related to LF/HF-SD (P = 0.005), which significantly decreased after ophthalmic solution administration in the DE group (P = 0.04). The large fluctuations in autonomic balance may be key for the understanding of the mechanism underlying DE symptoms.

Corneal nerves and their role in dry eye pathophysiology

As the cornea is densely innervated, its nerves are integral not only to its structure but also to its pathophysiology. Corneal integrity depends on a protective tear film that is maintained by corneal sensation and the reflex arcs that control tearing and blinking. Furthermore, corneal nerves promote epithelial growth and local immunoregulation. Thus, corneal nerves constitute pillars of ocular surface homeostasis. Conversely, the abnormal tear film in dry eye favors corneal epithelial and nerve damage. The ensuing corneal nerve dysfunction contributes to dry eye progression, ocular pain and discomfort, and other neuropathic symptoms. Recent evidence from clinical studies and animal models highlight the significant but often overlooked neural dimension of dry eye pathophysiology. Herein, we review the anatomy and physiology of corneal nerves before exploring their role in the mechanisms of dry eye disease.

Ocular Surface Ion-Channels Are Closely Related to Dry Eye: Key Research Focus on Innovative Drugs for Dry Eye

Abundant ion-channels, including various perceptual receptors, chloride channels, purinergic receptor channels, and water channels that exist on the ocular surface, play an important role in the pathogenesis of dry eye. Channel-targeting activators or inhibitor compounds, which have shown positive effects in in vivo and in vitro experiments, have become the focus of the dry eye drug research and development, and individual compounds have been applied in clinical experimental treatment. This review summarized various types of ion-channels on the ocular surface related to dry eye, their basic functions, and spatial distribution, and discussed basic and clinical research results of various channel receptor regulatory compounds. Therefore, further elucidating the relationship between ion-channels and dry eye will warrant research of dry eye targeted drug therapy.