Characterization of non-oxidized and oxidized Ricinodendron heudelotii oil effects on human skin by using in vitro models

Details

Supervisors

Larondelle, Yvan

Faculty

Faculté des bioingénieurs

Degree label

Master [120] : bioingénieur en sciences agronomiques, à finalité spécialisée

Abstract

Ricinodendron heudelotii is a wild tree native to sub-Saharan Africa that produces kernels from which oil is extracted for topical use. This Ricinodendron heudelotii oil (RHO) is rich in alpha-eleostearic acid (-ESA), a conjugated linolenic acid (CLnA), accounting for approximately 45% of total fatty acids. CLnAs are isomers of alpha-linolenic acid (ALA) characterized by three double bonds among which at least two are conjugated. Since the early 2000s, CLnAs have been shown to exert strong anti-tumoral effects. Only recently has it become clear that the mechanism responsible for this anti-tumor effect is ferroptosis. Ferroptosis is an iron-dependent form of cell death triggered by the accumulation of lipid peroxides in membrane phospholipids. CLnAs trigger ferroptosis by inserting, under the action of enzymes, into membrane phospholipids before being oxidized and generating lipid peroxides. The accumulation of lipid peroxides within cell membranes leads to a loss of membrane integrity, subsequently triggering cell death. It has recently been reported that the most abundant by-product of the oxidation of an -ESA-rich oil is 2,4-tt-nonadienal. This highly electrophilic aldehyde could not only occur during the oxidation of -ESA present in cell membrane phospholipids but could also occur during oxidation caused by traditional RHO production processes. Indeed, the traditional processing methods employed involve a boiling and a drying phase subjecting kernels to prooxidative factors which may lead to the formation of harmful compounds, such as 2,4-tt-nonadienal. Highly electrophilic aldehydes are known to have mutagenic, carcinogenic, atherosclerotic, and cytotoxic properties. However, the effects on skin are unknown. The present work constitutes a first step in evaluating the effects of oxidized and non-oxidized CLnA-rich RHO in a topical application and was divided into three main objectives. For the first objective, the cytotoxic effects of -ESA and various autoxidation-derived aldehydes on the viability of keratinocytes (HEKa) and squamous carcinoma cells (A431) was evaluated. Unexpectedly the results showed cytotoxicity in both cell lines, which was explained by their proliferative state. For the second objective, the cell death pathway processes induced either by -ESA or 2,4-tt-nonadienal were evaluated in HEKa and A431 cells. The results showed that -ESA triggered ferroptosis in both cell lines, whereas this was not the case for 2,4-tt-nonadienal. For the last objective, the effects of -ESA were assessed on an in vitro reconstructed human epidermis (RHE) model. The effects of -ESA were both evaluated along and after differentiation of HEKa cells in RHE. Results showed that keratinocytes became resistant to ferroptosis once differentiated, but not at an expected level.