Olives and olive oil have long been known to confer salutary effects to the skin.1 Leaves and fruits of the olive plant (Olea europaea) have been used as external emollients to treat skin ulcers and inflammatory wounds.2 The phenolic compound oleuropein, the most abundant phenolic found in olive leaves and oil, has been shown to exhibit antioxidant and free radical–scavenging activities.3,4 Also present in the stems and flowers of the plant, oleuropein, an ester of elenolic acid and 3,4-dihydroxyphenyl ethanol and the primary glycoside in olives,5 is thought to be the major contributor to its antioxidant and antimelanogenesis activities.6 Notably, olive leaves, which contain a copious supply of oleuropein, are thought to exert significantly more antioxidant activity than olive fruit.7
Hydroxytyrosol is an ortho-diphenolic substance and essential constituent of oleuropein that has been shown in vitro to prevent apoptotic cell death caused by UVB in HaCaT cells.8,9 Both oleuropein and hydroxytyrosol impart various anticancer properties at the initiation, promotion, and metastasis stages and yield protection against multiple cancers, including skin tumors.10 The antioxidant activity of both compounds, which has been found to be more potent than that of vitamin E, is attributed to their phenolic content.11,12 In addition, oleuropein and lipophilic olive mill wastewater derivatives have been useful as active ingredients for stabilizing cosmetic formulations.13 This column revisits oleuropein after 10 years to focus on its dermatologic potential.
Protection against UV damage
A hairless mouse study by Kimura and Sumiyoshi in 2009 revealed that olive leaf extract and its primary constituent oleuropein exert a skin-protective effect against chronic UVB-induced skin damage and carcinogenesis, as well as tumor growth. This is likely caused by reducing cutaneous cyclooxygenase (COX)-2 levels, thus suppressing the expression of vascular endothelial growth factor (VEGF) and various matrix metalloproteinases, specifically MMP-2, MMP-9, and MMP-13.14
A year later, the same researchers examined the potential protective effects of olive leaf extract and oleuropein on acute damage induced by UVB exposure in C57BL/6J mice. Both oral extract (300 mg/kg or 1,000 mg/kg) and oral oleuropein (25mg/kg or 85 mg/kg) hindered skin thickness increases engendered by daily doses of UVB (120 mJ/cm2 for 5 days, then every other day for 9 days). Olive leaf extract and oleuropein also suppressed increases in Ki-67- and 8-hydroxy-2’-deoxyguanosine–positive cell numbers, melanin granule area, and MMP-13 expression, the investigators noted.15 Preinitiation with oleuropein also appears to have prevented skin tumor formation in a two-stage carcinogenesis model in mice, which the investigators ascribed to the antioxidant and antiapoptotic properties of the olive protein.16
The cosmetic characteristics of oleuropein against UVB-induced erythema in healthy volunteers were assessed by Perugini et al. in 2008. Using an emulsion and emulgel containing oleuropein and vitamin E as a reference compound, the investigators found that the botanical ingredient was responsible for decreases in erythema (22%), transepidermal water loss (35%), and blood flow (30%). They suggested that the use of oleuropein in cosmetic formulations warrants further investigation for its potential to help mitigate UV damage.3