Effects of eye rubbing on the levels of protease, protease activity and cytokines in tears: relevance in keratoconus

Abstract

Background: Proteases, protease activity and inflammatory molecules in tears have been found to be relevant in the pathogenesis of keratoconus. We sought to determine the influence of eye rubbing on protease expression, protease activity and concentration of inflammatory molecules in tears. Methods: Basal tears were collected from normal volunteers before and after 60 seconds of experimental eye rubbing. The total amount of matrix metalloproteinase (MMP)-13 and inflammatory molecules interleukin (IL)-6 and tumour necrosis factor (TNF)-a in the tear samples were measured using specific enzyme-linked immunosorbent assays (ELISA). Tear collagenase activity was investigated using a specific activity assay. Results: The concentrations of MMP-13 (51.9 Ϯ 34.3 versus 63 Ϯ 36.8 pg/ml, p = 0.006), IL-6 (1.24 Ϯ 0.98 versus 2.02 Ϯ 1.52 pg/ml, p = 0.004) and TNF-a (1.16 Ϯ 0.74 versus 1.44 Ϯ 0.66 pg/ml, p = 0.003) were significantly increased in normal subjects after eye rubbing. The experimental eye rub did not alter significantly the collagenase activity (5.02 Ϯ 3 versus 7.50 Ϯ 3.90 fluorescent intensity units, p = 0.14) of tears. Conclusion: Eye rubbing for 60 seconds increased the level of tear MMP-13, IL-6 and TNF-a in normal study subjects. This increase in protease, protease activity and inflammatory mediators in tears after eye rubbing may be exacerbated even further during persistent and forceful eye rubbing seen in people with keratoconus and this in turn may contribute to the progression of the disease.

Keratoconus: an inflammatory disorder?

“…Eye rubbing is a proven factor that triggers the onset and progression of the disease, through several effects including stimulation of inflammation. 112,113,119,120 Increasing evidence supports the fact that thinning and ectasia of the cornea are related to a degraded extracellular matrix involving inflammatory events (mainly increased levels of MMP-9, IL-6, and TNF-α) 10,[12][13][14]67,91 and increased oxidative stress. [143][144][145][146] However, the precise role of each of the identified molecular factors still needs to be defined in further studies.…”

“…All of these could probably be the result of a complex interaction of both genetic predisposition and environmental triggering factors, such as eye rubbing and contact lenses wear (the 'two-hit hypothesis') in keratoconus. 42,52,100,113,119,120 conditions in the cornea, will contribute to elucidate these questions and ultimately help to unravel the etiological mysteries of keratoconus. The tear film proteome has become and will stay as an area of high interest for the identification of potential targets for early diagnosis and therapy in these patients, due to its non-invasive nature.…”

Influence of the Corneal Collagen Cross-linking on Levels of Il- 1b, Il-6, Il-10 and MMP-2 in the Tear film of Patients with Keratoconus.

“…Mechanical damage caused by microtraumas may affect Il-6 levels, increasing the risk of development of keratoconus. Balasubramanian et al [19] revealed a significant elevation in Il-6 concentrations after 60 seconds of eye rubbing by healthy volunteers. Confirmation of an aforementioned hypothesis may also be found in outcomes of a study conducted by Wilson et al [20] who revealed 2-40 times higher concentrations of proinflammatory cytokines, such as Il-6, in people using contact lenses.…”

Eye Rubbing and Keratoconus: A Literature Review

“…Balasubramanian et al used specific enzymelinked immunosorbent assays to measure the amount of inflammatory markers 60 seconds after eye-rubbing in normal subjects. 51 They found an increased expression in tear matrix metalloproteinase-13, interleukin-6 and tumour necrosis factor-α in normal subjects. There was no significant change in collagenase activity.…”

“…There was no significant change in collagenase activity. 51 These inflammatory changes after rubbing are thought to contribute to the pathogenesis.…”