Physico-chemical properties and metabolism of lissamine-rhodamine ceramides: effect of acyl chain length

The present report is a comparative study on physico-chemical properties and metabolism of three different Lissamine-Rhodamine (LRh) derivatives of ceramide (Cer), with twelve (C12–LRh–Cer), six (C6–LRh–Cer) acyl linker spacers or with the fluorescent probe directly linked to the sphingosine moiety (C0–LRh–Cer). Transfer kinetics of the LRh–ceramides from water dispersion, albumin complex and donor vesicles to acceptor liposomes followed a double-exponential curve. Among the three ceramides, C12–LRh–Cer showed the lowest mobility. All ceramides were taken up by human fibroblasts and, with the exception of C0–LRh–Cer which was not metabolised, fluorescent sphingomyelin (SM) was the only detectable metabolite. Despite its low incorporation, C12–LRh–Cer was converted to the corresponding C12–LRh–SM with an efficiency roughly three times higher than that of C6–LRh–Cer. ‘In vitro’ enzymatic assays using cell homogenate gave similar results. These data indicate that C12–LRh–Cer is the best mimic of the natural ceramide.