465 Gen. Physiol. Biophys. (2017), 36, 465–470 doi: 10.4149/gpb_2017005 Efect of lipoic acid on paraoxonase-1 and paraoxonase-3 protein levels, mRNA expression and arylesterase activity in liver hepatoma cells Eray Ozgun 1 , Gulben Sayilan Ozgun 1 , Kiymet Tabakcioglu 2 , Selma Suer Gokmen 1 , Necdet Sut 3 and Sevgi Eskiocak 1 1 Department of Medical Biochemistry, Trakya University School of Medicine, 22030 Edirne, Turkey 2 Department of Medical Biology, Trakya University School of Medicine, 22030 Edirne, Turkey 3 Department of Biostatistics and Medical Informatics, Trakya University School of Medicine, 22030 Edirne, Turkey Abstract. Paraoxonase-1 (PON1) and paraoxonase-3 (PON3) are anti-atherosclerotic enzymes, synthesized primarily in liver and bound to HDL in circulation. Te aim of the present study was to investigate the efects of therapeutic doses of lipoic acid on PON1 and PON3 protein levels, mRNA expression and arylesterase activity in liver. We treated HepG2 cells with 10, 40 and 200 μM lipoic acid for 72 h. Cell viability was evaluated by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H- tetrazolium bromide assay. PON1 and PON3 protein levels were measured by Western blotting, their mRNA expression was measured by quantitative PCR and arylesterase activity was measured spectrophotometrically. 200 µM lipoic acid caused a signifcant increase on PON1 and PON3 protein levels and arylesterase activity as compared with control, 10 µM and 40 µM lipoic acid- treated cells. 200 µM lipoic acid also caused a signifcant decrease on PON1 mRNA expression whereas on a signifcant increase PON3 mRNA expression as compared with control, 10 µM and 40 µM lipoic acid-treated cells. Our study showed that although lipoic acid up-regulates PON3 but down-regulates PON1 mRNA expression, it increases both PON1 and PON3 protein levels and arylesterase activity in HepG2 cells. We can report that lipoic acid may be useful for preventing atherosclerosis at therapeutic doses. Key words: Lipoic acid — Paraoxonase-1 — Paraoxonase-3 — Arylesterase — Liver Correspondence to: Eray Ozgun, Department of Medical Biochem- istry, Trakya University School of Medicine, 22030 Edirne, Turkey E-mail: drozgune@hotmail.com Introduction Paraoxonase-1 (PON1) and paraoxonase-3 (PON3) are the members of paraoxonase enzyme family which consists of three genes: PON1, PON2 and PON3 and are mainly syn- thesized by the liver (Précourt et al. 2011). All three proteins have peroxidase, lactonase and arylesterase activity and are capable of hydrolyzing oxidized phospholipids. In circula- tion, both PON1 and PON3 enzymes are bound to high density lipoprotein (HDL) and shows antioxidant properties (Draganov et al. 2000; Rosenblat et al. 2003; Précourt et al. 2011). PON1 prevents the development of atherosclerosis by protecting LDL against to oxidation and reducing mac- rophage foam cell formation (Aviram and Rosenblat 2004). On the other hand, it is known that the formation of mildly oxidized low density lipoprotein (LDL) and therefore the induction of monocyte chemotactic activity is prevented by PON3 (Reddy et al. 2001). PON1 activities were shown to be regulated both genetically and by diet (Précourt et al. 2011). Lipoic acid is synthesized from octanoic acid and cysteine in mitochondria (Golbidi et al. 2011) and is primarily me- tabolized in the liver (Goraca et al. 2011). Lipoic acid shows direct and indirect antioxidant properties (Rochette et al. 2013) and has been proposed as a potent antioxidant espe- cially for diabetes mellitus, cardiovascular and autoimmune diseases and cancer treatment (Goraca et al. 2011). In our previous study, we reported that lipoic acid pre- vents an increase in lipid peroxidation of the liver; therefore it has protective efects against to hepatic ischemia/reperfu- sion injury in rats (Ozgun et al. 2014). In another study, we also reported that lipoic acid treatment causes an increase in serum PON1 and PON3 protein levels and enzyme activities