Topical Mevalonic Acid Stimulates De Novo Cholesterol Synthesis and Epidermal Permeability Barrier Homeostasis in Aged Mice11The authors did not submit a completed declaration of conflict of interest form as requested by the JID’s ‘‘Information for authors’’.

Extracellular lipids of the stratum corneum, which are composed of cholesterol, fatty acid, and ceramides, are essential for the epidermal permeability barrier function. With damage to the barrier, a decreased capacity for epidermal lipid biosynthesis in aged epidermis results in an impaired repair response. Mevalonic acid is an intermediate after the rate-limiting step in cholesterol biosynthesis, which is catalyzed by 3-hydroxy-3-methylglutaryl coenzyme A reductase. In the present study, we investigated the effect of topical mevalonic acid on the murine epidermal permeability barrier function, comparing it with that of cholesterol. Topical treatment with acetone caused linear increases in transepidermal water loss, in proportion to the number of treatments more rapidly in aged mice than in young mice. Administration of mevalonic acid on aged murine epidermis enhanced its resistance against damage and the recovery rate of barrier function from acute barrier disruption. In contrast, although cholesterol also had the same effect, it required a much higher amount than mevalonic acid. In young mice, neither mevalonic acid nor cholesterol had any effect on resistance against acetone damage nor the recovery rate from acetone damage. In the skin of mice topically administered with mevalonic acid, stimulation of cholesterol synthesis and 3-hydroxy-3-methylglutaryl coenzyme A reductase activity were both observed, whereas none was seen with stimulation by equimolar cholesterol. These data indicate that a topical application of mevalonic acid enhances barrier recovery in aged mice, which is accompanied by not only acceleration of cholesterol synthesis from mevalonic acid but also stimulation of the whole cholesterol biosynthesis