Ethanol extract of Portulaca oleracea L. reverts the profile of cell death induced by acetic acid in Saccharomyces cerevisiae

Abstract

Saccharomyces cerevisiae exhibits stress response mechanisms that are in many cases identical to those of higher eukaryotes. Tests to evaluate the oxidant/antioxidant power of numerous chemicals including the detection of changes in cell growth and cell viability as well as enzymatic and non-enzyme antioxidant response, are increasingly being used, because their results are reproducible and, in many cases, easily applied to the man. Acetic acid, a by-product of alcoholic fermentation in several species of yeast is described as an oxidizing agent, able to induce oxidative stress and cell death. In Saccaromyces cerevisiae, the cell growth is often inhibited by weak acids such as acetic acid when is associated with high levels of ethanol and other toxic metabolites which, block fermentative metabolism by feedback mechanisms. To counteract the effects of acetic acid, S. cerevisae has metabolic resources that allow it to avoid its accumulation at high and potentially toxic levels inside the cell. Although in the absence of other carbon sources, acetic acid can be metabolized by gluconeogenesis, this preventive mechanism is repressed in the presence of glucose, so its accumulation becomes easier, behaving as an inducer of programmed cell death for exposure level of 20-80 mM acetic acid. Purslane (Portulaca oleracea L.) is a green leafy vegetable whose stems and leaves are edible and frequently used in culinary. The abundance and diversity of phytochemicals with biological activity detected in this plant contribute to its high functional value. Although nitrogen is the nutrient that most influences its production, it can decreases its functional value when applied in excess. This requires that the nitrogen fertilization of the plant is in the amount strictly necessary to ensure reasonable productivity without environmental impact. The main purpose of this work was to evaluate the biological effects of leaf-blade extracts of Portulaca oleracea L. var. sativa, fertilized with NH4NO3 (60 kg/ha) in S. cerevisiae UE-ME3 exposed to 25 mM acetic acid. The simultaneous exposure of S. cerevisiae UE-ME3 to 25 mM acetic acid and 12% ethanol extract of leaf-blade purslane, with high total phenols content and antioxidant power, during 200 min, maintained the biomass produced (dry weight), cell viability (cfu), cell damages levels (MDA), oxidative stress marker (GSH/GSSG ratio) and antioxidant enzyme activities ALP, GPx and CTA1 close to the control group, followed by an increase of the catalytic activities GR and SOD1. Ethanol extract of leaf-blade purslane seems to revert the cell death signature induced by 25 mM acetic acid.