DL-threo PDMP is a mixture of ceramide analogs that contains two of the four possible stereoisomers of PDMP : D-threo (1R,2R) and L-threo (1S,2S) PDMP. DL-threo-PDMP inhibits glucosylceramide synthase by 33 and 48% in MDCK cell homogenates when used at concentrations of 5 and 10 µM. It reduces the synthesis of glucosylceramide, increases cellular ceramide, and induces cell cycle arrest in vitro. The ability to inhibit glucosylceramide synthase has been found to reside in the D-threo (1R,2R) enantiomer. The D-threo PDMP enantiomer is also responsible for inhibition of β-1,4-galactosyltransferase 6 and prevention of lactosylceramide synthesis, which is a promotor of neuroinflammation in mice during chronic experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis. DL-threo-PDMP increases amyloid-β (1-42) (Aβ42) and Aβ39 production independent of ceramide metabolism via modulation of γ-secretase activity in HEK293 cells expressing the γ-secretase substrate SC100.