Attenuation of 7-ketocholesterol- and 7β-hydroxycholesterol-induced oxiapoptophagy by nutrients, synthetic molecules and oils: Potential for the prevention of age-related diseases

Age-related diseases for which there are no effective treatments include cardiovascular diseases; neurodegenerative diseases such as Alzheimer's disease; eye disorders such as cataract and age-related macular degeneration; and, more recently, Severe Acute Respiratory Syndrome (SARS-CoV-2). These diseases are associated with plasma and/or tissue increases in cholesterol derivatives mainly formed by auto-oxidation: 7-ketocholesterol, also known as 7-oxo-cholesterol, and 7β-hydroxycholesterol. The formation of these oxysterols can be considered as a consequence of mitochondrial and peroxisomal dysfunction, leading to increased in oxidative stress, which is accentuated with age. 7-ketocholesterol and 7β-hydroxycholesterol cause a specific form of cytotoxic activity defined as oxiapoptophagy, including oxidative stress and induction of death by apoptosis associated with autophagic criteria. Oxiaptophagy is associated with organelle dysfunction and in particular with mitochondrial and peroxisomal alterations involved in the induction of cell death and in the rupture of redox balance. As the criteria characterizing 7-ketocholesterol- and 7β-hydroxycholesterol-induced cytotoxicity are often simultaneously observed in major age-related diseases (cardiovascular diseases, age-related macular degeneration, Alzheimer's disease) the involvement of these oxysterols in the pathophysiology of the latter seems increasingly likely. It is therefore important to better understand the signalling pathways associated with the toxicity of 7-ketocholesterol and 7β-hydroxycholesterol in order to identify pharmacological targets, nutrients and synthetic molecules attenuating or inhibiting the cytotoxic activities of these oxysterols. Numerous natural cytoprotective compounds have been identified: vitamins, fatty acids, polyphenols, terpenes, vegetal pigments, antioxidants, mixtures of compounds (oils, plant extracts) and bacterial enzymes. However, few synthetic molecules are able to prevent 7-ketocholesterol- and/or 7β-hydroxycholesterol-induced cytotoxicity: dimethyl fumarate, monomethyl fumarate, the tyrosine kinase inhibitor AG126, memantine, simvastatine, Trolox, dimethylsufoxide, mangafodipir and mitochondrial permeability transition pore (MPTP) inhibitors. The effectiveness of these compounds, several of which are already in use in humans, makes it possible to consider using them for the treatment of certain age-related diseases associated with increased plasma and/or tissue levels of 7-ketocholesterol and/or 7β-hydroxycholesterol.