Takatoshi Ogami

Koji, which is used for manufacturing Japanese traditional fermented foods, has long been safely used as a cosmetic product. Although its cosmetic effect has been empirically established, the underlying mechanism has not been reported. We and other groups have previously elucidated that koji contains glycosylceramides, including N-2′-hydroxyoctadecanoyl-1-O-β-d-glucosyl-9-methyl-4,8-sphingadienine and N-2′-hydroxyoctadecanoyl-1-O-β-d-galactosyl-9-methyl-4,8-sphingadienine. This led us to hypothesise that koji exerts its cosmetic effect by acting on the keratinocytes through glycosylceramides on the gene level. Therefore, in this study, we investigated the effects of glycosylceramides from various sources on gene expression in normal human epidermal keratinocytes. The results revealed that glycosylceramides purified from white koji and the white koji-producing non-pathogenic fungus Aspergillus luchuensis and A. oryzae increased the expression of occludin (OCLN, an epidermal tight junction protein) and ATP-binding cassette sub-family A member 12 (ABCA12, a cellular membrane transporter), albeit the effect was modest relative to that of ceramides. Indeed, ceramide was increased in the keratinocytes upon koji lipid extract addition. These results indicate that glycosylceramides, which are the major sphingolipids of most natural materials, have an effect of increasing ABCA12 and OCLN expression, and suggest that koji exerts its cosmetic effect by increasing ceramide and tight junctions via glycosylceramides.

Koji, rice fermented with Aspergillus, is used for saccharification of starch contained in crops during the manufacturing of many of Japanese traditional foods and drinks. Japanese people have long eaten koji, and many beneficial substances have been reported to be contained in koji. However, there has been no report on the existence or content of galactosylceramide in koji. To address this issue, we analyzed the chemical composition of the sugar moiety of monohexosylceramide contained in koji, and elucidate that 30.3% of yellow koji is galactosylceramide, 69.7% of that is glucosylceramide, 19.2% of white koji is galactosylceramide, and 80.8% of that is glucosylceramide. This is the first report of the existence and content of galactosylceramide in koji.