Inhibition of Autophagy by Chloroquine Stimulates Nitric Oxide Production and Protects Endothelial Function during Serum Deprivation

Abstract

Background/Aims: Autophagy plays a fundamental role in cell survival under stress conditions such as nutrient deprivation. Decreased nitric oxide (NO) production, which may contribute to vascular dysfunction, is one of the consequences of autophagy in endothelial cells. The antimalarial drug chloroquine (CLQ) inhibits autophagy by blocking autophagosome formation and has been proposed as adjuvant chemotherapy in other diseases. Methods: Autophagy was induced by serum deprivation in Human Umbilical Vascular Endothelial Cells (HUVEC) as demonstrated by formation of Acidic Vesicular Organelles (AVOs), conversion of Microtubule-associated protein 1 light chain (LC3), and Sequestosome-1 (SQTM1/p62) degradation. Using endothelium-dependent vasorelaxation assays, intracellular NO production in an ex vivo rat aortic ring model pre-constricted with phenylephrine was estimated along with DAF-2 DA cell membrane-permeable NO sensitive fluorescent dye. Results: The inhibition of autophagy by CLQ restored NO levels, protected against superoxide generation and preserved morphology as well as proliferation of HUVEC under serum deprivation. Interestingly, the incubation of rat aortic rings with CLQ resulted in endothelium-dependent relaxation mediated by the increase of NO. Conclusion: These findings emphasize the importance of autophagy in endothelial function and demonstrate the potential use of autophagy inhibitors to protect vascular function during nutrient deprivation.

Autoimmune therapeutic chloroquine lowers blood pressure and improves endothelial function in spontaneously hypertensive rats

“…Interestingly, the improvements in endothelial function we observed after chloroquine treatment in SHR could be attributed to improvements in both eNOS activity (even though there were no differences in basal phospho-eNOS Ser1177 expression) and decreases in ROS. Overall, our results are very much in agreement with others whom have reported that chloroquine and hydroxychloroquine are able to improve endothelium relaxation via increased NO bioavailability and decreased ROS in arteries from healthy [51] and diseased [15] rodents. Nonetheless, the underlying mechanisms for these improvements in endothelial function have been attributed to other sources of ROS, including NADPH-oxidase [15], and stimulation of NOS by chloroquine directly [51].…”

Ox-LDL-Induced MicroRNA-155 Promotes Autophagy in Human Endothelial Cells via Repressing the Rheb/ mTOR Pathway

“…On the contrary, several lines of evidence indicated that autophagy plays a harmful role in atherosclerosis. Inhibition of autophagy stimulates nitric oxide production and protects endothelial function [47]. Autophagic death of SMCs results in plaque destabilization owing to the reduced synthesis of collagen and thinning of the fibrous cap [48].…”

Chloroquine exacerbates serum withdrawal-induced G1 phase arrest via an autophagy-independent mechanism

“…35 Although several recent studies have reported the promising effect of CQ on the endothelialdependent vascular relaxation via increasing the release of nitric oxide in endothelial cells, 21,36 the efficiency of CQ application over the ischemic diseases is still largely controversial. [13][14][15] The effect of CQ on the cell cycle arrest caused by nutrient deciency in endothelial cells and the underlying mechanisms have not been fully characterized.…”