1 September 2019 | Volume 10 | Article 1033 ORIGINAL RESEARCH doi: 10.3389/fphar.2019.01033 published: 17 September 2019 Frontiers in Pharmacology | www.frontiersin.org Piper sarmentosum Promotes Endothelial Nitric Oxide Production by Reducing Asymmetric Dimethylarginine in Tumor Necrosis Factor-α-Induced Human Umbilical Vein Endothelial Cells Uma Mahgesswary Sundar 1 , Azizah Ugusman 1 *, Hui Kien Chua 1 , Jalifah Latip 2 and Amilia Aminuddin 1 1 Department of Physiology, Faculty of Medicine, Universiti Kebangsaan Malaysia Medical Centre, Kuala Lumpur, Malaysia, 2 Department of Pharmaceutical Chemistry, School of Chemical Sciences & Food Technology, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, Bangi, Malaysia Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of endothelial nitric oxide synthase (eNOS). ADMA is degraded by dimethylarginine dimethylaminohydrolase (DDAH). Elevated levels of ADMA lead to reduction in nitric oxide (NO) production, which is linked to endothelial dysfunction and atherosclerosis. Piper sarmentosum is an herb that has shown stimulation on endothelial NO production by increasing both expression and activity of eNOS. Thus, this study determined whether the positive effect of P. sarmentosum on NO production is related to its modulation on the DDAH–ADMA pathway in cultured human umbilical vein endothelial cells (HUVEC) exposed to tumor necrosis factor-α (TNF-α). HUVEC were divided into four groups: control, treatment with 250 µg/ml of aqueous extract of P. sarmentosum leaves (AEPS), treatment with 30 ng/ml of TNF-α, and concomitant treatment with AEPS and TNF-α for 24 h. After treatments, HUVEC were collected to measure DDAH1 messenger RNA (mRNA) expression using quantitative real-time polymerase chain reaction. DDAH1 protein level was measured using enzyme-linked immunosorbent assay (ELISA), and DDAH enzyme activity was measured using colorimetric assay. ADMA concentration was measured using ELISA, and NO level was measured using Griess assay. Compared to control, TNF-α- treated HUVEC showed reduction in DDAH1 mRNA expression (P < 0.05), DDAH1 protein level (P < 0.01), and DDAH activity (P < 0.05). Treatment with AEPS successfully increased DDAH1 mRNA expression (P < 0.05), DDAH1 protein level (P < 0.01), and DDAH activity (P < 0.05) in TNF-α-treated HUVEC. Treatment with TNF-α caused an increase in ADMA level (P < 0.01) and a decrease in endothelial NO production (P < 0.001). Whereas treatment with AEPS was able to reduce ADMA level (P < 0.01) and restore NO (P < 0.001) in TNF-α- treated HUVEC. The results suggested that AEPS promotes endothelial NO production by stimulating DDAH activity and thus reducing ADMA level in TNF-α-treated HUVEC. Keywords: Piper sarmentosum, asymmetric dimethylarginine, dimethylarginine dimethylaminohydrolase, human umbilical vein endothelial cells, tumor necrosis factor-α, endothelial dysfunction Edited by: Steyner F. Cortes, Federal University of Minas Gerais, Brazil Reviewed by: Juliana Montani Raimundo, Federal University of Rio de Janeiro, Brazil Roger Lyrio Santos, Federal University of Espirito Santo, Brazil *Correspondence: Azizah Ugusman dr.azizah@ppukm.ukm.edu.my Specialty section: This article was submitted to Ethnopharmacology, a section of the journal Frontiers in Pharmacology Received: 28 May 2019 Accepted: 14 August 2019 Published: 17 September 2019 Citation: Sundar UM, Ugusman A, Chua HK, Latip J and Aminuddin A (2019) Piper sarmentosum Promotes Endothelial Nitric Oxide Production by Reducing Asymmetric Dimethylarginine in Tumor Necrosis Factor-α-Induced Human Umbilical Vein Endothelial Cells. Front. Pharmacol. 10:1033. doi: 10.3389/fphar.2019.01033