MBTPS1 and chronic kidney disease: Specifically, S1P has been demonstrated to enhance endothelial barrier function,38,39 induce vasodilator production,40,41 and inhibit endothelial inflammation.17 To investigate whether our observed associations of APOM with MACE in patients with CKD extend to S1P, we assessed S1P plasma levels in a subset of 421 patients by HPLC.