Olive Pomace Phenolic Compounds: From an Agro-Industrial By-Product to a Promising Ocular Surface Protection for Dry Eye Disease

Dry eye (DED) is a prevalent disease with immune-mediated inflammation as the principal pathophysiological etiology. Olive pomace, the major by-product of the olive oil industry, is rich in high-value polyphenols. Their anti-inflammatory and immunomodulatory activities were determined on human CD4+ T cells (hTCD4+) and in a DED animal model. The viability of hTCD4+ cells isolated from peripheral blood and activated with phytohemagglutinin-M was evaluated after treatment for 48 h with an olive pomace extract (OPT3, 0.10-0.40 mg/mL) and its major compound, hydroxytyrosol (25-100 mu M). Regarding the DED animal model, 100 mu M hydroxytyrosol, 0.20 mg/mL OPT3, or vehicle (borate buffer) were topically administered to 14 days-desiccating stress-exposed (constant airflow/scopolamine administration) C57BL/6 mice. Tear volume, corneal fluorescein staining (CFS), CD4+, and CD8+ T cell count in lymph nodes (flow cytometry), and IP-10 and TNF-alpha gene expression (qRT-PCR) in the cornea, conjunctiva, and lacrimal glands were evaluated. OPT3 (0.2-0.4 mg/mL) and hydroxytyrosol (100 mu M) significantly reduced hTCD4+ proliferation. In mice, both treatments reduced lacrimal gland IP-10 gene expression. OPT3 also decreased CFS, and conjunctival IP-10 and corneal TNF-alpha gene expression. In lymph nodes, hydroxytyrosol reduced CD3+, OPT3, and CD8+ count. Thus, a high-value application as a promising DED protection was proposed for olive pomace.