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The aim of the present study was to investigate the effect of streptozotocin-induced diabetes mellitus and lipoic acid treatment on serum paraoxonase-1 and paraoxonase-3 protein levels and paraoxonase, arylesterase and lactonase activities.36 rats were equally and randomly divided into 4 groups as control, lipoic acid, diabetes and diabetes+lipoic acid. To induce diabetes, a single dose of streptozotocin (40 mg/kg) was injected intraperitoneally to diabetes and diabetes+lipoic acid groups. Lipoic acid (10 mg/kg/day) was injected intraperitoneally for 14 days to lipoic acid and diabetes+lipoic acid groups. Serum PON1 and PON3 protein levels were measured by western blotting. Serum paraoxonase, arylesterase and lactonase activities were determined by the measuring initial rate of substrate (paraoxon, phenylacetate and dihydrocoumarin) hydrolysis.Streptozotocin-induced diabetes mellitus caused a significant decrease whereas lipoic acid treatment caused a significant increase in serum PON1 and PON3 protein levels and paraoxonase, arylesterase and lactonase activities. The increase percent of serum PON3 protein was higher than that of serum PON1 protein and the increase percent of serum lactonase activity was higher than that of serum paraoxonase and arylesterase activities in diabetes+lipoic acid group.We can report that, like PON1 protein, PON3 protein and actually its lactonase activity may also have a role as an antioxidant in diabetes mellitus and lipoic acid treatment may be useful for the prevention of the atherosclerotic complications of diabetes by increasing serum PON1 and PON3 protein levels and serum enzyme activities., Competing Interests: The authors declare no conflict of interest., (© Georg Thieme Verlag KG Stuttgart · New York.)

Objectives: We aimed to investigate the effect of lipoic acid in the prevention of myocardial infarction in diabetic rats., Methods: Rats were divided into five groups as control, ISO, LA+ISO, STZ+ISO and STZ+LA+ISO. To induce diabetes, single dose of streptozotocin was injected to STZ+ISO and STZ+LA+ISO groups. Lipoic acid (10 mg/kg/day) was injected for 14 days to LA+ISO and STZ+LA+ISO groups. To induce myocardial infarction, isoproterenol was injected to ISO, LA+ISO, STZ+ISO and STZ+LA+ISO groups on the days 13 and 14 of lipoic acid treatment. Cardiac necrosis and leucocyte infiltration were investigated histopathologically. Serum malondialdehyde levels, paraoxonase and lactonase activities were measured spectrophotometrically., Results: Isoproterenol caused a significant increase in cardiac necrosis, leucocyte infiltration and serum lipid peroxidation whereas a significant decrease in serum paraoxonase and lactonase activities. In myocardial infarcted non-diabetic rats, while lipoic acid caused a significant decrease in cardiac necrosis, leucocyte infiltration and serum lipid peroxidation and a significant increase in serum paraoxonase and lactonase activities, it did not change these histopathologic or biochemical parameters in myocardial infarcted diabetic rats., Conclusion: Lipoic acid, at the dose of 10 mg/kg, is effective to prevent myocardial infarction in non-diabetic rats but it is insufficient in diabetic rats (Tab. 1, Fig. 2, Ref. 35).

Paraoxonase-1 (PON1) and PON3 (PON3) are anti-atherosclerotic enzymes, synthesized primarily in liver and bound to HDL in circulation. The aim of the present study was to investigate the effects 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 significant 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 significant decrease on PON1 mRNA expression whereas on a significant 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.