Biophysical interactions of flaxseed oil with tear lipids for improving tear stability in dry eye

Purpose : Dry eye is the most prevalent eye condition with multifactorial aetiology and loss of tear film homeostasis. Tear film instability is one of the causative mechanisms of dry eye. Tear lipids insufficiency contributes to excessive evaporation which leads to tear film instability. Lipids or oils in artificial tear solutions can help in maintaining integrity of the lipid layer of the tear film, reducing evaporation, and enhancing tear stability in dry eye. Flaxseed oil is one of the examples. This study aimed at studying interaction of flaxseed oil with various tear lipids to understand its biophysical mechanism of action in improving tear stability in topical application in dry eye disease.

Methods : Biophysical characteristics of flaxseed oil and model tear lipids (nonpolar: cholesterol oleate (CO), cholesterol (Chl), oleic acid (OA); and polar: dioleoyl phosphatidylcholine (DOPC)) were studied using Langmuir trough technology. Lipids were spread on an artificial tear (AT) solution containing salt composition of tears at the physiological pH (7.4) and temperature (35°C) of tears. The lipid films were compressed to record surface pressure-area (Π-A) isotherms of individual lipids. The lipids were mixed with flaxseed oil and Π-A isotherms of mixed films were obtained to determine the influence of flaxseed oil on tear lipids.

Results : The Π-A isotherm of flaxseed oil showed a maximum surface pressure of 24mN/m. In mixed films, flaxseed oil increased the surface pressure of CO by 22mN/m and expanded the lipid film substantially (by ~82cm2 at 5mN/m and by ~72cm2 at 10mN/m). Flaxseed oil did not increase the surface pressure of Chol and OA but expanded the lipid films (by 44cm2 and 43 cm2 at 10mN/m, respectively). Flaxseed oil did not increase the surface pressure of the polar lipid DOPC and expanded the lipid film (by ~25cm2 at 10mN/m).

Conclusions : Flaxseed oil expands the polar and non-polar lipids found in the lipid layer of the tear film. The biophysical mechanism of flaxseed oil to improve tear stability is mainly due to its capacity to expand the tear lipids allowing better spreading of the lipid layer of the tear film on the ocular surface which helps in improving tear stability.