2-Acetyl-5-tetrahydroxybutyl Imidazole

2-Acetyl-5-tetrahydroxybutyl imidazole (THI) is an inhibitor of sphingosine-1-phosphate (S1P) lyase in vivo.{13428} THI is not active at S1P lyase in cell-free or cell-based assays but is converted to A6770 in vivo, which is subsequently activated by phosphorylation.{45874} In mice, THI (50 µg/ml in drinking water) increases S1P levels by 100-fold in lymphoid tissue and reduces lymphocyte egress from thymus and peripheral lymphoid organs.{13428,17443} The resulting lymphopenia is reversible following cessation of THI treatment.{17442}