INDUCTION OF APOPTOSIS BY SYNTHETIC CERAMIDE ANALOGS IN THE HUMAN KERATINOCYTE CELL-LINE HACAT

In contrast to extracellular, long chain ceramides which comprise a st ructural component of the epidermal water barrier, intracellular ceram ides originating from sphingomyelin hydrolysis have been shown to inhi bit proliferation and to induce apoptosis in different cell population s. To further elucidate the possible role of intracellular ceramides i n human epidermis, two new cell-permeable ceramide analogues, N-thioac etylsphingosine (C-2-Cer=S) and 4-dodecanoylamino-decan-5-ol (FS-5), w ere synthesized and tested for their ability to suppress cell growth a nd to induce apoptosis in immortalized human keratinocytes. It was sho wn that the well-investigated ceramide analogue N-acetylsphingosine (C -2-Cer= O), as well as the new compound C-2-Cer=S inhibited proliferat ion of HaCaT cells with half-inhibitory concentrations (IC50) Of 20 mu g/ml and 10 mu g/ml, respectively, whereas FS-5 has been potent with an IC50>40 mu g/ mi. Overall, all three ceramide analogues induced apo ptosis in HaCaT cells as assessed by DNA-fragmentation using ELISA tec hnique and in situ nick end labelling, thereby confirming the importan ce of ceramide signalling in keratinocytes.