Antioxidant and antidiabetic effects of gallic and protocatechuic acids: a structure–function perspective

This study sought to investigate antioxidant and antidiabetic effects of gallic acid (GA) and protocatechuic acids (PCAs) based on their structure–function relationship. Twenty micromolar of phenolic acid (GA and PCA) solutions was prepared and their antioxidant properties determined. Then, interaction of the phenolic acids with key enzymes linked to type 2 diabetes (α-amylase, α-glucosidase) was subsequently assessed. The results showed that both phenolic acids significantly (P < 0.05) decreased Fe²⁺-elevated pancreas malondialdehyde (MDA) contents, chelated Fe²⁺, reduced Fe³⁺ to Fe²⁺, and scavenged 1,1-diphenyl-2-picrylhydrazyl, 2,2-azinobis(3-ethylbenzothiazoline-6-sulfonate), and hydroxyl radicals and furthermore inhibit α-amylase and α-glucosidase activities in a dose-dependent manner. However, GA (IC₅₀ = 1.22 μM) had significantly (P < 0.05) higher inhibitory effect on the α-glucosidase activity than PCA (IC₅₀ = 1.76 μM). Conclusively, both GA and PCA are rich sources of antioxidant and antidiabetic molecules. However, GA showed better antioxidant and antidiabetic effects than PCA. These effects may be due to additional hydroxyl group on its aromatic ring structure.