Diabetic LDL Triggers Apoptosis in Vascular Endothelial Cells

Diabetic LDL Triggers Apoptosis in Vascular Endothelial Cells Michaela Artwohl 1 , Wolfgang F. Graier 2 , Michael Roden 1 , Martin Bischof 1 , Angelika Freudenthaler 1 , Werner Waldhäusl 1 and Sabina M. Baumgartner-Parzer 1 1 Department of Internal Medicine III, Division of Clinical Endocrinology and Metabolism, University of Vienna, Vienna, Austria 2 Department of Medical Biochemistry and Medical Molecular Biology, University of Graz, Graz, Austria Abstract This study compares the effects of LDL glycated either in vitro (LDL iv ) or in vivo in diabetic patients (LDL D ) on apoptosis, proliferation, and associated protein expression in cultured human umbilical vein endothelial cells. At 100 mg/l, both LDL species considerably increase apoptosis (LDL iv 63%, LDL D 40%; P < 0.05) compared with intraindividual nonglycated LDL subfractions. Considering its lower degree of glycation (LDL D 5–10%, LDL iv 42%), LDL D ’s relative proapoptotic activity is 2.7-fold greater than that of LDL iv . Glycated LDL-induced apoptosis is associated with increased expression of apoptosis promotors (LDL iv : bak 88%, CPP-32 49%; LDL D : bak 18%, CPP-32 11%; P < 0.05) and is attenuated by caspase inhibitors. Glycated LDL’s antiproliferative activity (LDL iv −34%, LDL D −9%; P < 0.01) relates to reduction ( P < 0.05) of cyclin D3 (LDL iv −27%, LDL D −24%) and of hypo- (LDL iv −22%, LDL D −19%) and hyperphosphorylated (LDL iv −53%, LDL D −22%) retinoblastoma protein and is paralleled by reduced expression of endothelial nitric oxide synthase (LDL iv −30%, LDL D −23%). In response to lipoprotein lipase, LDL D more markedly triggers endothelial apoptosis (27.1-fold) compared with LDL iv , suggesting that LDL D owns a higher potential for endothelial cell damage than LDL iv . The observed behavior of LDL D versus LDL iv could be of clinical importance and well relate to differences in structure and cellular uptake of LDL D compared with LDL iv . Footnotes Address correspondence and reprint requests to Sabina M. Baumgartner-Parzer, Department of Internal Medicine III, Division of Clinical Endocrinology and Metabolism, University of Vienna, Währinger Gürtel 18-20, A-1090 Vienna, Austria. E-mail: sabina.baumgartner-parzer{at}akh-wien.ac.at . Received for publication 13 October 2002 and accepted in revised form 14 February 2003. eNOS, endothelial NO synthase; HUVEC, human umbilical vein endothelial cell; LPL, lipoprotein lipase; pRb, retinoblastoma protein; TNBSA, trinitro-benzenesulfoni