ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Use of standardized units for a correct interpretation of IC50 values obtained from the inhibition of the DPPH radical by natural antioxidants

Flavio Martinez-Morales, Angel J. Alonso-Castro, Juan R. Zapata-Morales, Candy Carranza-Álvarez, and Othoniel H. Aragon-Martinez

Department of Pharmacology, School of Medicine, Autonomous University of San Luis Potosi, San Luis Potosí, Mexico

E-mail: hugo.aragon@uaslp.mx

Received: 11 December 2019  Accepted: 9 April 2020

Abstract:

Abstract

The 2,2′-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay is a valid and commonly test used to measure the total antioxidant capacity in natural extracts. The results of this assay are frequently expressed as IC₅₀ values. Nevertheless, the reported IC₅₀ value is influenced by the concentration of the DPPH solution used in the methodology. Consequently, the aim of this study was to determine an IC₅₀ value free of the influence of the DPPH concentration to evaluate correctly the antioxidant capacity of natural compounds. We have established a standardized unit for the antioxidant concentration (ng antioxidant agent/ nmol DPPH) in the concentration–response curves. Then, these curves were used to calculate the IC₅₀ values. The natural antioxidants assessed in this study were ascorbic acid, quercetin and an ethanolic extract of Justicia spicigera. The IC₅₀ values were estimated from nonlinear and linear regression analyses. The use of standardized units resulted in similar curves and IC₅₀ values for the same natural antioxidant (P values from 0.0931 to 0.5512), under different concentrations of the DPPH radical. The lack of usage of standardized units resulted in different curves and IC₅₀ values (P values from 0.0002 to 0.0022). In conclusion, our practical standardization provides a correct interpretation of the antioxidant capacities of natural products under the DPPH scavenging assay.

Graphic abstract

Keywords: IC50 value; Antioxidant measurement; Standardized unit; DPPH radical; Natural product

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-020-01161-x

Chemical Papers 74 (10) 3325–3334 (2020)