Abstract
Homocysteine (Hcy) is an intermediate non-diet amino acid connecting methionine and folate cycles. Elevated total Hcy level in blood, denoted as hyperhomocysteinemia, has emerged as a prevalent and strong risk factor for multiple diseases including atherosclerotic vascular disease in coronary, cerebral, and peripheral vessels. Its detrimental effect on vascular system implies the potential application as an inhibitor of angiogenesis. However, the detailed mechanism is unveiled. Inhibitory effect of Hcy was assessed on vascular endothelial growth factor (VEGF) induced cell proliferation and migration with endothelial cell (EC) culture system. Its effect on angiogenesis was further examined in vitro and in vivo. After Hcy treatment, key angiogenic factors were measured by RT-qPCR. Cellular skeletal structure was also evaluated by actin stress fiber staining. VEGF-induced human umbilical vein EC (HUVEC) proliferation and migration were dramatically down-regulated by Hcy in a dose-responsive manner. Hcy treatment significantly inhibited the VEGF-induced angiogenesis in vitro by tube formation assay and chick chorioallantoic membrane (CAM) vessel formation in vivo. Key angiogenic factors like VEGFR1/2 and angiopoietin (Ang)1/2 were substantially reduced by Hcy in HUVEC- and VEGF-induced actin stress fiber cytoskeletal structure was abolished. We demonstrated that Hcy could inhibit angiogenesis by targetting key angiogenic factor and disruption of actin cytoskeleton which is crucial for cell migration.
Highlights
Homocysteine (Hcy) is a sulphur-containing α-amino acid
We examined the function of Hcy as an inhibitor of angiogenesis in endothelial cell (EC) model and our results showed that Hcy could counteract the proliferative effect of vascular endothelial growth factor (VEGF) on EC to suppress the cell migration and tube formation ability in vitro
Using an established cell model human umbilical vein EC (HUVEC), we first examined the effect of Hcy on VEGF-driven cell proliferation assay, with dosage range based on literature and pilot study
Summary
Homocysteine (Hcy) is a sulphur-containing α-amino acid. It is not found in proteins and cannot be obtained from diet. In cells, it is biosynthesized from methionine via a cycle of chemical reactions. SAM is a ubiquitous methyl group donor which is required for a large family of SAM-dependent methyltransferases for methylation of DNA, RNA, proteins, and lipids. SAM is converted into S-adenosylhomocysteine (SAH) after the methyl group is transferred to acceptor molecules. SAH gives rise to Hcy via hydrolysis reaction to remove adenosine. Hcy can be recycled to form methionine by methylation or combined with serine to give rise to cysteine which is the precursor of an important antioxidant factor glutathione. Hcy transsulphuration pathway is critical for Hcy catabolism and is considered as a major source of glutathione in the liver [1,2,3]
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