The strong reaction of simple phenolic acids during oxidative stress caused by nickel, cadmium and copper in the microalga Scenedesmus quadricauda

Abstract

This work has analysed the influence of CdCl₂, NiCl₂ and CuCl₂ on simple phenolic acids, such as the 3PPP (phenylpyruvic, phenylacetic, and 4-hydroxyphenylpyruvic) and 2DR (3,4-dihydroxyphenylacetic and rosmarinic) phenolic acids for the first time and studied their interactions with antioxidant systems and the glutathione-ascorbate cycle in the freshwater green microalga Scenedesmus quadricauda. The compounds investigated are related to both the catabolic and anabolic pathways of l-phenylalanine and l-tyrosine, the main molecules in the biosynthesis of polyphenols. The concentrations of the simple phenolic acids responded significantly to NiCl₂, CdCl₂ and CuCl₂ at 5, 20 and 40 μM concentrations. The 3PPP phenolic acid concentrations after 24 h were always higher in metal-treated cells than in controls, while the 2DR concentrations were significantly lower in the metal-treated cells than the controls. The GSH/GSSG ratio was lower in all experimental groups treated with the selected metals (especially so at 40 μM). Pearson correlation analysis indicated a strong negative correlation between ascorbate and rosmarinic acid content (-0.670; p < 0.05) in NiCl₂-treated samples and reduced glutathione and 3,4-dihydroxyphenylacetic content (-0.700; p < 0.05) in CdCl₂-treated samples. The GSSG content in samples exposed to CuCl₂ was correlated with the concentrations of all of the investigated phenolic acids (4 negative, 1 positive).

Keywords: Ascorbate; Cadmium; Copper; Glutathione; Nickel; Oxidative stress; Scenedesmus quadricauda; Simple phenols.