EP2306 and EP2302, Two Novel Squalene Synthase Inhibitors, Stimulate Endothelial Nitric Oxide Synthase Expression in Cultured Endothelial Cells

EP2306 and EP2302 are two novel squalene synthase inhibitors with hypolipidemic, antiatherosclerotic, and antioxidant properties. In the present study, the authors investigated their effect on the expression and activity of endothelial nitric oxide synthase (eNOS) in cultured bovine aortic endothelial (BAE) cells and calf pulmonary artery endothelial (CPAE) cells. eNOS concentration was determined by immunoassay and eNOS activity by measuring the conversion of [(3)H]arginine to [(3)H]citrulline. Basal levels of eNOS in untreated BAE cells were 13.3 +/-1.6 ng/mg protein. Stimulation for 4 h with 30 microM of EP2306 or EP2302 resulted in increased eNOS protein level to 40% +/- 10% (p<.05) or 165% +/- 15% (p < .05) of unstimulated levels, respectively. Basal levels of eNOS in untreated CPAE cells were 3.4 +/- 0.4 ng/mg protein. Stimulation of CPAE cells for 4 h with 30 microM of EP2306 or EP2302 resulted in increased eNOS protein level to 195% +/- 24% (p < .05) and 152% +/- 19% (p < .05) of unstimulated levels, respectively. Despite their stimulatory action on eNOS expression, EP2300 compounds failed to induce any significant changes on eNOS enzymatic activity in BAE and CPAE cells. The finding that EP2300 compounds significantly increase the accumulation of eNOS in cultured endothelial cells sheds some light into their mechanism of action and supports a possible protective role of these compounds in atherosclerosis-related diseases.