Free fatty acids differently affect apoptosis of micro- versus macrovascular endothelial cells

Objective: Elevated plasma free fatty acids (FFAs), as seen in obesity and diabetes, represent risk factors for the development of vascular dysfunction. Since it is unclear, whether FFAs differently affect micro- versus macrovascular endothelial cells, this study evaluated FFAs' proapoptotic activity and the respective underlying mechanisms in cultured human aortic- (HAECs) versus retinal endothelial cells (HRECs).

Methods: After exposure (24–48h) of endothelial cells to FFAs (100–300µmol/l), apoptosis and membrane rigidity were determined by DNA fragmentation assays and fluorescence correlation spectroscopy, respectively.

Results: In HAECs (n=7), palmitic- and oleic acid did not affect apoptosis, whereas stearic acid concentration-dependently induced (p<0.05) apoptosis up to 4.4±0.57fold. Only at 300µmol/l, polyunsaturated FFAs (PUFAs) triggered programmed cell death (linoleic-: 2.5±0.34-fold; α-linolenic-: 2.8±0.34-fold; arachidonic acid: 3.8±0.92-fold), which correlated with the number of double bonds (r=0.97, p<0.05). In HRECs (n=9), however, stearic acid was the only FFA causing apoptosis (1.85±0.24-fold versus solvent control, p<0.01), even after 48h-exposure. FFA-induced apoptosis in HAECs and HRECs was completely abolished by the pan-caspase inhibitor z-VAD.fmk, whereas only PUFA-, but not stearic acid-triggered cell death was abrogated by z-IETD.fmk, a caspase-8 inhibitor. Eicosapentaenoic acid (EPA; 20µmol/l) counteracted both, pro-apoptotic activity and membrane rigidity (1.4±0.1-fold, p<0.001) induced by stearic acid, but had no effect on cell death, triggered by PUFAs, which did not increase membrane rigidity, anyway.

Conclusion: Whereas poly-unsaturated free fatty acids selectively induce caspase-8-dependent apoptosis in aortic endothelial cells, saturated stearic acid triggers apoptosis in both, human retinal- and aortic endothelial cells, probably by increasing the cells' membrane rigidity.