Abstract 5645: Novel Cross-Talk Between Oxidized LDL, Angiotensin II and Oxidative Stress After AT1 Blockade and AT1a/AT1b Double Knockout

Oxidized low-density-lipoprotein (oxLDL) and angiotensin II (Ang II) can increase formation of reactive oxygen species in endothelial cells. However, the potential cross-talk between both risk factors, the impact of Ang II receptor 1 (AT 1 ) blockade on lipoprotein-induced oxidative stress and endothelial function and of AT 1a /AT 1b double knockout on oxidative stress is not well understood. First, we studied the impact of native and oxidized LDL (nLDL, oxLDL) on Ang II receptor expression and formation of reactive oxygen species in primary cultures of human umbilical artery endothelial cells (HUAEC). Native and oxLDL (max. 100 μ g/mL) induced after 1 h AT 1 (3.3- and 3.7-fold) and AT 2 (1.8- and 2.8-fold) receptor mRNA expression in HUAEC. Increased AT 1 and AT 2 mRNA and protein expression could be observed for up to 24 h. Both lipoproteins increased intracellular AT 1 receptor immunofluorescence in HUAEC. Native LDL and oxLDL activated MEK/ERK and p38 MAPK pathways (ELISA, Western blot) in HUAEC. OxLDL induced oxLDL receptor LOX-1 expression in HUAEC (RT-PCR, Western blot). Induction of both Ang II receptors and of LOX-1 by oxLDL was reduced by AT 1 receptor antagonist candesartan. OxLDL induced in contrast to native LDL superoxide anion formation in HUAEC (chemiluminescence). AT 1 receptor blockade prevented lipoprotein-induced oxidative stress in HUAEC like SOD. Furthermore, AT 1 blockade prevented impaired endothelial function (increase of log EC 50 values and impaired max. relaxation by oxLDL in phenylephrine-preconstricted vessels). In aortic rings of wild-type mice, oxLDL-induced vascular superoxide anion formation was reduced by AT 1 blockade. Finally, deletion of AT 1 receptor subtypes 1a and 1b in AT 1a /AT 1b double knockout mice resulted in the aorta in significant downregulation of protein expression of LOX-1, Nox subunits Nox2, p47phox and p22phox, compared with wild-type mice. In conclusion, augmented vascular oxidative stress and endothelial dysfunction in response to lipoproteins involves induction of the AT 1 receptor. Double knockout of AT 1 receptors reduce LOX-1 and NAD(P)H oxidase expression. Our data suggest a cross-talk between oxidized LDL, angiotensin II and oxidative stress after AT 1 blockade and AT 1a /AT 1b double knockout.