Background and Objective: Atheroma formation and progression of atherosclerosis are dependent on the expression of bone matrix proteins and regulatory factors such as osteonectin in the vessel walls. Studies have shown that consumption of Trans fatty acids increase risk of cardiovascular diseases. In this study, the effect of elaidic acid on osteonectin gene expression as one of the vascular calcification factors was investigated. Materials and Methods: Vascular smooth muscle cells were treated with concentrations of 5, 10 and 20 µM of elaidic acid for 48h and compared with control group. Total RNA was extracted and cDNA was synthesized and then the quantity of osteonectin gene expression was measured by real time PCR. Results: Overall 10 and 20µM concentrations of elaidic acid increased osteonectin gene expressions in vascular smooth muscle cells by 4.34 and 6.58 folds compared with the control group (p<0.05). 5µM concentration of elaidic acid had no effect on osteonectin gene expression. Conclusion: Elaidic acid increases osteonectin gene expression. Therefore this trans fatty acid could increase atheroma formation and the risk of cardiovascular diseases due to vascular calcification. References 1- Insull Jr W. The pathology of atherosclerosis: plaque development and plaque responses to medical treatment. Am J Med. 2009 122: S1-S64. 2- Wu M, Rementer C, Giachelli CM. Vascular calcification: an update on mechanisms and challenges in treatment. Calcif Tissue Int. 2013 93: 365-73. 3- Demer LL, Tintut Y. Vascular calcification pathobiology of a multifaceted disease. Circulation. 2008 117: 2938-48. 4- Zhu D, Mackenzie NC, Farquharson C, MacRae VE. 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