Differential signaling of sphingosine derivatives in U937 human monocytes depends on the degree of N-methylation

Previously, we studied N,N-dimethyl-d-erythro-sphingosine (DMS)-induced cell death and signaling in U937 human monocytes; we found that DMS-induced sphingosine kinase- and PKC-independent apoptosis. In the present study, we studied apoptotic responses by three N-methyl derivatives of sphingosine: N-monomethyl-d-erythro-sphingosine (MMS), N,N,N-trimethyl-d-erythro-sphingosine (TMS), and d-erythro-sphingosine (SPH). The potency order in the apoptotic response was DMS ≥ MMS > TMS > SPH. We compared cellular responses to the derivatives in terms of activities of MAPK signaling molecules, mitochondrial membrane potential (ΔΨm), and reactive oxygen species (ROS) generation. Our results suggest that the degree of N-methylation affects the apoptosis-inducing capacity and other related responses including MAPK modulation, ΔΨm, and ROS generation. Dimethylation and monomethylation on the C2 amine of sphingosine enhance the apoptotic response; however, trimethylation induces differential modulation of signaling molecules and less cytotoxicity. Our investigation will be useful for understanding the actions of sphingolipids in apoptosis and for developing chemotherapeutics based on DMS structure.