Cytokine Study of the Denervated Rat Model of the Dry Eye

Abstract

Purpose: : Dry eye results from the lack of tear production or abnormal tear contents and/or distribution that may lead to immunological responses and irritation of the cornea. These immunological responses, both innate and adaptive, are mediated by pro-inflammatory cytokines. In a previous study, we were able to create a dry eye rat model through radiofrequency trigeminal nerve ablation that showed accurate physical signs of dry eye. In this study, the tears produced by the dry eye animal model were analyzed for biochemical markers.

Methods: : The dry eye animal model was created by inserting a radiofrequency probe into the V1-V2 junction of the trigeminal nerve via stereotaxic surgery. The nerve was lesioned at 75 degrees Celsius for a duration of one minute. Tears were collected from the experimental left eye and the control right eye of 12 dry-eye animals one day prior to surgery and on the third post-operative day using micropipettes. The tears were then analyzed for the presence and concentration of 10 different cytokines implicated in the cause of dry eye: IL-1a, IL-1b, IL-2, IL-4, IL-6, IL-10, IL-12, IFN-g, RANTES, and TNF-a.

Results: : Four of the 10 cytokines (IL-1a, IL-2, IL-6, and IL-10) demonstrated a significant increase in concentration after trigeminal nerve ablation compared to that of the control and that of the pre-surgical baseline level. The concentration of IL-1a after trigeminal nerve ablation was 53 times the concentration in the control (P=.019) after a 5-fold increase from the pre-surgical baseline level (P=.021). IL-2 concentration was 5 times that of the control (P=.048) and was 6 times the baseline level (P=.030). Similarly, the mean IL-6 concentration in the experimental eye was 5423.3 ± 1571.2 pg/mL compared to 0 pg/mL in the control eye (P=.004) and the pre-surgical baseline level (P=.004). Lastly, IL-10 was 5 times higher in the ablated eye than the control eye (P=.031) following a 7-fold increase from the baseline (P=.030).

Conclusions: : This study supports the efficacy of our new dry eye model, and it may help to better understand the pathophysiology of the dry eye.

Keywords: cornea: tears/tear film/dry eye • cytokines/chemokines