Introduction: Stress oxidative is a major problem for centuries and the origin of various disease from cataracts to cancer. Free radicals are atoms or molecules the have the single electron that re highly reactive and can be irreversible damage to vital molecules in organisms. Antioxidants are capable of biological systems to protect against this elements. zinc oxide nanoparticle have antimicrobial, anti-cancer and antioxidant properties. The purpose of this study was to assess the antioxidant effect of zinc oxide nanoparticle synthesized  by green method and catalase gene expression changes in human liver cancer cells (HepG2) in response to different concentration of nanoparticles.

Materials & methods: Antioxidant activity of zinc oxide nanoparticles synthesized by green method was measured using ABTS (2, 2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) radical absorbance. The human liver cancer cells (HepG2) cultured in the six well plates and then were treated with different concentrations of nanoparticles. After extraction of RNA and synthesis of cDNA, Real time PCR was carried out and catalase gene expression changes were assessed.

Findings: Antioxidant activity of zinc oxide nanoparticles synthesized  by green method was measured by ABTS (2, 2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) (IC₅₀= 1200µg) radical scavenging activity. Also, with the increasing concentration of zinc oxide nanoparticles synthesized  by green method , catalase gene expression compared to control gene GAPDH increased.

Discussion & conclusions: The results of this study showed that the concentration of zinc oxide nanoparticles synthesized  by green method had a strong antioxidant activity.