Protective effects of milk thistle (Sylibum marianum) seed oil and α-tocopherol against 7β-hydroxycholesterol-induced peroxisomal alterations in murine C2C12 myoblasts: Nutritional insights associated with the concept of pexotherapy

Peroxisomes play an important role in regulating cell metabolism and RedOx homeostasis. Peroxisomal dysfunctions favor oxidative stress and cell death. The ability of 7β-hydroxycholesterol (7β-OHC; 50 μM, 24 h), known to be increased in patients with age-related diseases such as sarcopenia, to trigger oxidative stress, mitochondrial and peroxisomal dysfunction was studied in murine C2C12 myoblasts. The capacity of milk thistle seed oil (MTSO, 100 μg/mL) as well as α-tocopherol (400 µM; reference cytoprotective agent) to counteract the toxic effects of 7β-OHC, mainly at the peroxisomal level were evaluated. The impacts of 7β-OHC, in the presence or absence of MTSO or α-tocopherol, were studied with complementary methods: measurement of cell density and viability, quantification of reactive oxygen species (ROS) production and transmembrane mitochondrial potential (ΔΨm), evaluation of peroxisomal mass as well as topographic, morphologic and functional peroxisomal changes. Our results indicate that 7β-OHC induces a loss of cell viability and a decrease of cell adhesion associated with ROS overproduction, alterations of mitochondrial ultrastructure, a drop of ΔΨm, and several peroxisomal modifications. In the presence of 7β-OHC, comparatively to untreated cells, important quantitative and qualitative peroxisomal modifications were also identified: a) a reduced number of peroxisomes with abnormal sizes and shapes, mainly localized in cytoplasmic vacuoles, were observed; b) the peroxisomal mass was decreased as indicated by lower protein and mRNA levels of the peroxisomal ABCD3 transporter; c) lower mRNA level of Pex5 involved in peroxisomal biogenesis as well as higher mRNA levels of Pex13 and Pex14, involved in peroxisomal biogenesis and/or pexophagy, was found; d) lower levels of ACOX1 and MFP2 enzymes, implicated in peroxisomal β-oxidation, were detected; e) higher levels of very-long-chain fatty acids, which are substrates of peroxisomal β-oxidation, were found. These different cytotoxic effects were strongly attenuated by MTSO, in the same range of order as with α-tocopherol. These findings underline the interest of MTSO and α-tocopherol in the prevention of peroxisomal damages (pexotherapy).