In Vitro Free Radical Scavenging and Anti-Genotoxic Activities of Thunbergia Laurifolia Aqueous Leaf Extract

Abstract

Background: Lead (Pb) is a xenobiotic, which causes numerous health defects like neurological, metabolic, kidney disorders, as well as mutation including DNA damage. Thunbergia laurifolia (TL) is a renowned medicinal plant for its antidote properties in Thailand. These properties caused us to investigate its anti-genotoxic effects against Pb in human peripheral blood leukocytes.

Methods: The TL aqueous leaf extract was prepared and the 50% inhibition concentration (IC₅₀) on DPPH, superoxide, nitric oxide and hydroxyl radical scavenging activity determined. An in vitro, genotoxicity test was used to determine the magnitude of DNA damage of human peripheral blood leukocytes classified by a comet assay. TL extract at doses of 25, 50 and 100 µg/mL were used in combination with Pb at doses of 40 and 80 µg/mL, respectively, on in vitro human peripheral blood leukocytes and incubated at 37^oC for 1 hrs. H₂O₂ (40 mM) was used as a DNA damage positive control.

Results: Genotoxicity was induced by Pb and H₂O₂ exposure in human peripheral blood leukocytes leading to DNA damage. TL was found to be a potent free radical scavenger of superoxide, hydroxyl radical, DPPH, hydrogen peroxide and nitric oxide with IC₅₀ value of 0.298±0.004, 0.402±0.001, 0.869±0.030, 1.600±0.089 and 1.624±0.140 µg/mL, respectively. TL treatment ameliorated Pb induced genotoxicity in human peripheral blood leukocytes. Moreover, TL provided a protective effect on DNA damage against H₂O₂ in human peripheral blood leukocytes.

Conclusion: TL aqueous leaf extract possesses an anti-genotoxic effect, possibly due to its antioxidant capacity, and could prove useful as an antidote to lead toxicity.