Abstract
Background: Phyllanthus niruri, Thymus vulgaris, Centella asiatica, and Apium graveolens L. have been frequently used as medical herbs for various diseases. However, the use of the herbs is not based on any evidence of their contents.

Aims and Objective: To examine their potential activity of becoming antioxidant, using in vitro and in vivo models and isolate active compound.

Materials and Methods: The antioxidant activity of the samples was assessed using 1,1-diphenyl-2-picrylhydrazyl (DPPH) as radical compounds. The decrease of DPPH radical was measured using spectrophotometer at 517 nm, after an incubation for 30 min. The highest antioxidant activity of the sample was then continued with in vivo model using Sprague Dawley (SD) rats. Paracetamol was used as an inducer to increase the malondialdehyde (MDA) levels in plasma, with doses of 2.5 g/kg BW. The rats were divided into four groups: negative control, dose of 50 mg/kg BW, dose of 100 mg/kg BW, and dose of 200 mg/kg BW. Isolation method was guided by antioxidant activity by using fractionation and column chromatography. The obtained compound was then characterized by 1H-nuclear magnetic resonance (NMR) and compared with the earlier study.

Result: The IC50 value of these samples were 14.21 ± 0.73; 14.41 ± 1.13; 98.66 ± 9.59; and 237.33 ± 17.26 mg/mL, respectively, and the total phenolic contents were 81.59 ± 2.85; 154.09 ± 11.61; 6.36 ± 3.99; 2.03 ± 0.78 mg/g of sample extract, respectively. The in vivo study showed that P. niruri with dose of 100 mg/kg BW and 200 mg/kg BW were able to reduce MDA levels by 90.44% and 92.64%, respectively. Meanwhile, the proton and carbon NMR spectra showed that the isolate was quercetin. The IC50 value of the isolate, being 5.85 mg/mL, was lower than that of vitamin E, which was 6.85 mg/mL.

Conclusion: The extract shows a potential effect with antioxidant activity, both in in vitro and in vivo models. Quercetin is the active compound, the antioxidant activity of which is higher than that of vitamin E.