Contents lists available at ScienceDirect Comparative Biochemistry and Physiology, Part C journal homepage: www.elsevier.com/locate/cbpc The possible role of microcystin (D-Leu 1 MC-LR) as an antioxidant on Microcystis aeruginosa (Cyanophyceae). In vitro and in vivo evidence G. Malanga a,b,1 , L. Giannuzzi c,d,1 , M. Hernando e, ⁎ a CONICET-Universidad de Buenos Aires, Instituto de Bioquímica y Medicina Molecular (IBIMOL), Buenos Aires, Argentina b Universidad de Buenos Aires, Facultad de Farmacia y Bioquímica, Fisicoquímica, Buenos Aires, Argentina c CONICET, Godoy Cruz 2290, Buenos Aires, Argentina d Área de Toxicología, Departamento de Ciencias Biológicas, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, Argentina e Departamento Radiobiología, Comisión Nacional de Energía Atómica, Buenos Aires, Argentina ARTICLE INFO Keywords: Microcystis aeruginosa Microcystins ROS Catalase Temperature ABSTRACT Microcystins constitute a serious threat to the quality of drinking water worldwide. However, the eco-physio- logical role of them is not completely known and it is suggested that toxins can play a role in the antioxidant protection. The objective of this study was to evaluate the microcystin antioxidant capacity in vitro by Electronic Paramagnetic Resonance, highly specific for the different reactive oxygen species and in vivo by 7 days exposure of Microcystis aeruginosa to high (29 °C) temperature in addition to a 26 °C control condition. An effective in vitro antioxidant activity was observed for [D-Leu 1 ]MC-LR against hydrosoluble radicals. As far as we know, this is the first in vitro record of the role of MC as antioxidant. In addition, a significant increase in cellular biomass was observed under 26 °C in cultures with [D-Leu 1 ]MC-LR supplementation in coincidence with a significant de- crease of reactive species. For cultures at 29 °C, the antioxidant role of toxins was inconclusive probably due to the presence of different reactive species generated during the experiment. Thus, MC could scavenge certain reactive species associated with the antioxidant role of CAT or the %OH content by SOD activity (not measured) and then CAT activity could be lower in the presence of MC. Reinforcing our hypothesis, the [D-Leu 1 ]MC-LR consumption after 7 days was significantly higher in cells with [D-Leu 1 ]MC-LR supplementation in both 26 °C and 29 °C.When the production of reactive species was controlled by the scavenger activity of antioxidants plus MC, cells avoided the potential oxidative damage and started with exponential growth. 1. Introduction When rivers and lakes become eutrophic, Microcystis spp. is one of the cyanobacteria genus that usually increases in relative abundance forming blooms (D'Angelo et al., 1998). Cyanobacteria may produce different types of secondary metabolites such as cyanotoxins (e.g. the microcystin, MC). Over 90 structural analogues of MC have been identified up to date, but only a few occur frequently at high MCs concentration. It consists of a general cyclic heptapeptide structure with variable amino acids (Qi et al., 2015). Qi et al. (2015) have shown seven new MC variants in the same strain of Microcystis aeruginosa used for the present study, which has been previously reported as a [D-Leu 1 ] MC-LR producer (Rosso et al., 2014). Such structural variants of MCs can be explained by the multispecificity of single domains of the MC biosynthesis complex. At this variable position, [D-Leu 1 ]MC-LR con- tains the amino acid leucine, whereas MC-LR (also present in our strain) contains alanine (Christiansen et al., 2003). There is an increasing concern that changes in climate (Stocker et al., 2013) will cause changes in phytoplankton community structure and composition. MCs are predominantly produced by freshwater cy- anobacteria of the genera Microcystis, Planktothrix and Anabaena (Dittmann et al., 2013), which would have adverse effects on humans and environment (Babica et al., 2006). Moreover, some studies found a direct influence of environmental factors on the MC production (e.g. Jähnichen et al., 2011; Giannuzzi et al., 2016). MC is known to irreversibly inhibit eukaryotic protein phosphatases of types 1 and 2A (Chorus and Bartram, 1999). However, the physio- logical role of MC is still unclear (Pflugmacher, 2002; Yoshida et al., 2007).For example, recent studies examining cyanotoxin production have found close links between these compounds and certain physio- logical functions that may be considered part of the primary metabo- lism of the cell, with a close connection to primary metabolism (Neilan https://doi.org/10.1016/j.cbpc.2019.108575 Received 11 April 2019; Received in revised form 18 June 2019; Accepted 16 July 2019 ⁎ Corresponding author. E-mail address: mhernando@cnea.gov.ar (M. Hernando). 1 Both authors contributed equally to this manuscript. Comparative Biochemistry and Physiology, Part C 225 (2019) 108575 Available online 18 July 2019 1532-0456/ © 2019 Elsevier Inc. All rights reserved. T