Investigating idebenone and idebenone linoleate metabolism: in vitro pig ear and mouse melanocyte studies.

Objective: The aim of this study was to investigate inherent in vitro permeability, metabolism, and cytotoxicity of idebenone - an active used to protect skin as an anti-aging agent - and compare it to idebenone linoleate.

Methods: Idebenone and idebenone linoleate were investigated in pig ear skin and melanoma (B16: F10 mouse) cells. Diffusion experiments were conducted at 37 degrees C (bath temperature) using Franz diffusion cells. Authentic metabolite samples were synthetically prepared. Samples were analyzed using liquid chromatography-mass spectrometry/mass spectrometry. Cell viability was determined via the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assay.

Results: Idebenone was shown to permeate across viable porcine ear tissue; there was no evidence that idebenone linoleate permeated across porcine ear tissue after 4 h. Idebenone was metabolized to idebenone acid in both pig ear and mouse melanocytes; only minor idebenone linoleate metabolism was observed. Idebenone displayed delayed in vitro toxicity (via MTT assay) in melanocytes, while idebenone linoleate displayed no such in vitro toxicity.

Conclusions: The in vitro metabolism and cytotoxicity results suggest that metabolic activation of idebenone is the likely culprit that activates the skin irritation mechanism via idebenone in vivo usage. An idebenone ester (e.g. idebenone linoleate) appears to provide a superior in vitro safety profile over idebenone.