Keratoconjunctivitis sicca (KCS), or dry eye syndrome, is characterized by chronic inflammation of the cornea, conjunctiva, and lacrimal glands caused by quantitative and/or qualitative tear changes
. Recently, several studies have proven that essential fatty acids (EFAs), omega-3 (ω-3) and omega-6 (ω-6), administered orally are an alternative therapy for patients with various types of tear deficiency, including Sjögren's syndrome and KCS
[2–6]. Additionally, the topical use of ω-3 and ω-6 effectively controlled the signs of experimentally induced inflammation in rats with KCS
Eicosanoids are biologically active substances that regulate physiological processes and are lipid mediators of inflammation. From the ω-6 EFA-derived prostanoids, arachidonic acid, via cyclooxygenase 1 (COX1) pro-inflammatory mediators, is synthesized, including prostaglandin (PGE2), thromboxane (TXA2), prostacyclin (PGI2), and the leukotrienes (LTA4, LTB4, LTC4, and LTD4). However, non-inflammatory mediators (PGE1 and TXA1) are also synthesized from the EFA series of ω-6 by the action of COX1 on dihomo-γ-linoleic acid (DGLA) and from the EFA series of ω-3 by the action of COX1 on eicosapentaenoic acid (PGE3, PGI3, and TXA3) as well as by the actions of lipoxygenase (LTA5, LTB5, LTC5, and LTD5) and of docosahexaenoic acid
The ω-3 and ω-6 EFAs are found in many foods, such as nuts, cold-water fish, soybeans, rapeseed oil, and linseed oil. Linseed, Linum usitatissimum, is composed of 57% ω-3, 16% ω-6, 28% monounsaturated fatty acids, and only 9% unsaturated fatty acids, and the ω-3-to-ω-6 ratio of 1:3 is considered close to ideal. Linseed is considered to be a natural anti-inflammatory agent due its potential in synthesizing non-inflammatory mediators, such as PGE1 and TXA1
[8–10]. The objective of this study was to evaluate the effectiveness of various linseed oil (LO) preparations (oral, topical, oral and topical combined), which are rich in ω-3 and ω-6, in treating experimentally induced KCS in rabbits.