Olive Pomace Phenolic Compounds and Extracts Can Inhibit Inflammatory- and Oxidative-Related Diseases of Human Ocular Surface Epithelium.

Nikolaos Katsinas,Soraya Rodríguez-Rojo,Amalia Enríquez-De-Salamanca

doi:10.3390/antiox10071150

Abstract

Oxidative- and inflammatory-related ocular surface diseases have high prevalence and are an emerging issue in ophthalmology. Olive pomace (OP) is the olive oil’s industry main by-product, and is potentially environmentally hazardous. Nevertheless, it contains phenolic compounds with important bioactivities, like oleuropein (OL) and hydroxytyrosol (HT). The antioxidant and anti-inflammatory effects of four OP extracts (CONV, OPT(1–3)), pure OL and HT, and mixtures thereof were screened on human corneal (HCE) and conjunctival epithelial (IM-ConjEpi) cells. CONV was conventionally extracted, while OPT(1–3) were produced by pressurized liquid extraction. Thanks to their improved activity, CONV and OPT3 (HT-enriched) were selected for dose-dependent studies. Cells were stimulated with tumor necrosis factor-α or ultraviolet-B radiation, measuring interleukin (IL)-1β, IL-6, IL-8, and IL-17A as well as interferon γ-induced protein [IP]-10 secretion or intracellular ROS production, respectively. On HCE, both extracts and HT inhibited the secretion of most measured ILs, demonstrating a strong anti-inflammatory effect; while in IM-ConjEpi, all samples decreased IP-10 secretion. Moreover, HT, OL, and both extracts showed strong dose-dependent antioxidant activity in both cell lines. Compared with CONV, OPT3 was active at lower concentrations, demonstrating that intensified extraction techniques are selective towards targeted biomarkers. Hence, a high-value application as potential ocular surface therapy was proposed for the OP valorization.

Highlights

Ocular inflammation can occur in many different parts of the eye and represents an emerging issue in ophthalmology [1]
For the cell-based assays, plastic culture flasks, plates, tips and pipettes, Dulbecco’s modified Eagle’s medium/Nutrient Mixture F-12 (DMEM/F-12) + GlutaMax, DMEM/F12 without phenol red, Dulbecco’s phosphate buffered saline (DPBS), fetal bovine serum (FBS), human epithelial growth factor (EGF), human insulin, penicillin, streptomycin, and bicinchoninic acid (BCA) assay kit were purchased from Thermo Fisher Scientific (Rockford, IL, USA); cytokine tumor necrosis factor (TNF)-α from bioNova scientific (Fremont, CA, US); bovine insulin, 20,70-dichlorodihydrofluorescein diacetate (H2DCF-DA), 2,3-Bis-(2-Methoxy-4Nitro-5-Sulfophenyl)-2H-Tetrazolium-5-Carboxanilide (XTT) and 5-methylphenazinium methyl sulfate (PMS) reagents, dimethyl sulfoxide (DMSO), and Milliplex Human Cytokine/Chemokine HCYTOMAG-60K-5 plex Magnetic Kit (IL-1beta, IL-6, IL-8/CXCL8, IL-17A, and IP-10) from Merck Life Science
As already described [38], all selected olive pomace (OP) extracts were characterized in terms of extraction yield (EY), total phenolic content (TPC), and oxygen radical absorbance capacity (ORAC)-AA, as well as extract richness in OL, HT, and TY

Summary

Introduction

Ocular inflammation can occur in many different parts of the eye and represents an emerging issue in ophthalmology [1] It is involved in several ocular diseases, such as age-related macular degeneration, macular edema, and retinal vein occlusion [1]. Oxidative stress is involved in the pathophysiology of many ocular diseases [2], like age-related macular degeneration [3,4], cataract [5], conjunctivochalasis [6], or ocular allergy [7]. LFU dysfunction can lead to an abnormal tear film composition, and to an unstable precorneal film layer [7,8,9]. It appears with a high prevalence, ranging from 5 to 50% depending on the population [10], and considerably affects the patients’

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