British Journal of Dermatology 2000; 143: 524±531. Nicotinamide increases biosynthesis of ceramides as well as other stratum corneum lipids to improve the epidermal permeability barrier O.TANNO, Y.OTA, N.KITAMURA, T.KATSUBE AND S.INOUE Basic Research Laboratory, Kanebo Ltd, 5-3-28 Kotobuki-cho, Odawara-shi, Kanagawa 250-0002, Japan Accepted for publication 3 April 2000 Summary Background Stratum corneum lipids, particularly ceramides, are important components of the epidermal permeability barrier that are decreased in atopic dermatitis and aged skin. Objectives We investigated the effects of nicotinamide, one of the B vitamins, on biosynthesis of sphingolipids, including ceramides and other stratum corneum lipids, in cultured normal human keratinocytes, and on the epidermal permeability barrier in vivo. Methods The rate of sphingolipid biosynthesis was measured by the incorporation of [ 14 C]-serine into sphingolipids. Results When the cells were incubated with 1±30 mmol L 21 nicotinamide for 6 days, the rate of ceramide biosynthesis was increased dose-dependently by 4´1±5´5-fold on the sixth day compared with control. Nicotinamide also increased the synthesis of glucosylceramide (7´4-fold) and sphingomyelin (3´1-fold) in the same concentration range effective for ceramide synthesis. Furthermore, the activity of serine palmitoyltransferase (SPT), the rate-limiting enzyme in sphingolipid synthesis, was increased in nicotinamide-treated cells. Nicotinamide increased the levels of human LCB1 and LCB2 mRNA, both of which encode subunits of SPT. This suggested that the increase in SPT activity was due to an increase in SPT mRNA. Nicotinamide increased not only ceramide synthesis but also free fatty acid (2´3-fold) and cholesterol synthesis (1´5-fold). Topical application of nicotinamide increased ceramide and free fatty acid levels in the stratum corneum, and decreased transepidermal water loss in dry skin. Conclusions Nicotinamide improved the permeability barrier by stimulating de novo synthesis of ceramides, with upregulation of SPT and other intercellular lipids. Key words: ceramide synthesis, epidermal permeability barrier, nicotinamide, serine palmitoyl- transferase, stratum corneum lipids Nicotinamide is one of the B vitamins, deficiency of which results in a clinical syndrome called pellagra that is characterized by dermatitis, diarrhoea and dementia. 1 Nicotinamide is necessary for the pro- duction of nicotinamide adenine dinucleotide (NAD) and NAD phosphate (NADP), which act as coenzymes in over 40 biochemical reactions. Although the mechanism responsible for pellagra is obscure, defi- ciency of NAD or NADP caused by nicotinamide deficit is thought to result in pellagra. The three symptoms appear frequently in pellagra, and it is rare to find a proven case without dermatitis. However, the role of nicotinamide in the epidermis and why nicotinamide deficit results in dermatitis have not been determined. Stratum corneum lipids, rich in sphingolipids, free fatty acids and cholesterol, are required for the epi- dermal permeability barrier. 2 In particular, sphingo- lipids such as ceramides play a crucial part in epidermal barrier homeostasis. 3,4 The level of ceramides in the stratum corneum is decreased in atopic dermatitis 5 and aged skin. 6 Moreover, a recent study showed that winter xerosis is related to compositional changes in stratum corneum lipids and marked reductions in ceramide levels. 7 Although nicotinamide has been applied in the treatment of cutaneous lesions of other forms of dermatitis because the symptoms are similar to those 524 q 2000 British Association of Dermatologists Correspondence: Shintaro Inoue. E-mail: inoshin@oda.cos.kanebo.co.jp