Homocysteine (Hcy) has been identified as a primary risk factor for atherosclerosis as it induces endothelial cell (EC) activation/dysfunction and thus potentially initiating atherosclerotic plaque formation. There is accumulating evidence indicating a key role for oxidative stress in mediating Hcy atherogenic effects. The aim of this study was to evaluate the effects of chronic treatment with Hcy on EC activation and to explore the role of oxidative stress in these effects.
Human umbilical vein endothelial cells (HUVEC) were cultured and treated chronically with DL-Hcy for 5-9 days. An in vitro flow system was also used to characterize the different types of interactions between DL-Hcy-treated HUVEC and neutrophils under physiological flow conditions. EC activation was studied by characterizing the activation of the JNK pathway and the up-regulation of different cell adhesion molecules (CAM) and cytokines, using different techniques including western blot, immunohistochemical staining, enzyme-linked immunosorbent assay and polymerase chain reaction. The role of oxidative stress was investigated by measuring the production of ROS and evaluating the efficiency of antioxidants. Furthermore, the role of nitric oxide and nitric oxide synthase in modulating Hcy effects was investigated.
Chronic treatment with DL-Hcy did not kill the EC however, it inhibited cell proliferation. Furthermore, this treatment induced EC activation/dysfunction which was characterized by sustained activation of the JNK pathway, which in turn mediated up-regulation of E-selectin, ICAM-1 and to lesser extent P-selectin. Furthermore, DL-Hcy induced production of IL-8 protein. These CAM and chemokines collectively mediated different interactions between DL-Hcy-treated HUVEC and neutrophils under flow conditions including tethering, rolling, adherence and transmigration. DL-Hcy was also shown to induce significant ROS generation which mediated activation of the JNK pathway. Antioxidants restored DL-Hcy-induced interactions under flow to the basal level. DL-Hcy was shown to induce eNOS uncoupling which mediated, at least in part, the DL-Hcy-induced ROS production. Furthermore, short term treatment with NO inhibited DL-Hcy-induced HUVEC:neutrophil interactions in a cGMP-independent manner.
In summary, this research showed that DL-Hcy has several proatherogenic effects, mediated at least in part by the JNK pathway, and induces EC activation/dysfunction priming for atherosclerosis initiation. The data supports that oxidative stress mediates the majority of Hcy atherosclerotic effects. Antioxidants tested, JNK inhibitors and NO showed promising results in reversing all DL-Hcy effects and restoring EC normal status.
