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Objectives Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid mediator. Although the plasma S1P concentration is reportedly determined by cellular components, including erythrocytes, platelets, and vascular endothelial cells, the possible involvement of other factors, such as serum sphingomyelin (SM) and autotaxin (ATX), remains to be elucidated. Design and methods We measured S1P using high-performance liquid chromatography (HPLC), SM and lysophosphatidic acid (LPA) using enzymatic assays, ATX antigen using a two-site enzyme immunoassay, and ATX activity using a lysophospholipase D activity assay. To fractionate the lipoproteins, plasma samples were separated using fast protein liquid chromatography (FPLC) utilizing a Superose 6 column. Results The plasma S1P level was positively correlated with the levels of SM and lysophosphatidylcholine, but not with the level of phosphatidylcholine. Although SM was present in the very low-density lipoprotein (VLDL) fraction, neither the plasma S1P level nor the SM level was affected by feeding. The plasma S1P level was negatively correlated with the ATX activity. Although the incubation of 100 μmol/L of sphingosylphosphorylcholine (SPC) with the serum resulted in a significant increase in the S1P level because of the presence of ATX, the physiological concentration of SPC did not mimic this effect. Conclusion The plasma S1P level was affected by the serum SM level, while the possibility of ATX involvement in the increase in the plasma S1P level was considered to be remote at least in healthy human subjects.

Cholesteryl ester transfer protein (CETP) is one of the factors that regulate plasma levels of HDL-cholesterol. To identify the factors that may regulate CETP activity, and to determine to what extent CETP is correlated with physiologic concentrations of lipoprotein, we performed an epidemiologic study in 586 healthy volunteers (317 males and 269 females mean age 52.2 +/- 10.9 years). CETP activity in these subjects was 192.96 +/- 48.73 (mean +/- S.D.) nmol/ml/h and distributed to a wide range (60-450 nmol/ml/h). Using multiple regression analysis, we found significant positive correlations between CETP activity and LDL-cholesterol (P < 0.03), apolipoprotein (apo) E (P < 0.005) and LCAT activity (P < 0.001). CETP activities showed significant negative correlation with apo A-I (P < 0.03). However, CETP activity showed no significant correlation either with HDL cholesterol or with apo B. One-way layout analysis of variance showed that alcohol drinking and cigarette smoking significantly reduced CETP activity, but there was no significant association between CETP activity and body mass index. Although CETP activities were significantly higher in females than in males (P < 0.001), multiple regression analysis showed no correlation between CETP activity and age in either the males or the females. Our results suggest that CETP activity regulates the concentration of apo A-I and LDL-cholesterol, and that such activity may be influenced by gender, alcohol consumption and cigarette smoking.