title: Toxic effects of imidazolium ionic liquids on the green seaweed Ulva lactuca: oxidative stress and DNA damage.
abstract: The green credentials of ionic liquids (ILs) are being increasingly questioned due to the growing evidence of their toxicity to aquatic ecosystems, although the mechanisms of toxicity are unknown. This study provides insights into the mechanism of toxicity and biological effects of 1-alkyl-3-methylimidazolium bromide [C(n)mim]Br (n = 4 to 16) on the marine macroalga Ulva lactuca. The cell viability of this alga during IL exposure was found to be negatively correlated to the chain length of the alkyl group. The IL ([C(12)mim]Br) exposure triggers the generation of reactive oxygen species (ROS viz. O(2)(•-), H(2)O(2), and OH(•)), damage of the membrane and DNA, and inhibition of antioxidant systems in the alga. The enhanced production of ROS and lipid peroxidation in the alga subjected to LC(50) concentration for 4 days was largely attributed to lipoxygenase (LOX) activity coupled with the induction of two LOX isoforms (~80 kDa and ~55 kDa). Pretreatment of the algal thallus with enzyme inhibitors such as diphenylene iodonium, sodium azide, cantharidin, and oxadiazoloquinoxalin-1-one, prior to [C(12)mim]Br exposure showed the regulation of ROS by the activation of membrane bound NADPH-oxidase and cytochrome oxidase. The IL exposure resulted in the accumulation of n-3 and n-6 fatty acids at 0.5 LC(50) concentration indicating the induction of desaturase enzymes. Furthermore, antioxidant enzyme activities such as superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR) were enhanced by 1.3-2.0-fold, while glutathione peroxidase (GSH-Px) diminished, together with a higher regeneration rate of reduced ascorbate and glutathione. The isoforms of antioxidant enzymes, namely, Mn-SOD (~85 kDa), APX (~125 and 45 kDa), and GR (~135 kDa) regulated differentially to IL exposure. The comet assay performed for the first time for seaweeds revealed the significant induction of DNA damage (>50-70% increase in % tail DNA over control) in alga exposed to ≥ LC(50) concentration.
authors.affiliation: Discipline of Marine Biotechnology and Ecology, Central Salt and Marine Chemicals Research Institute, Council of Scientific and Industrial Research (CSIR), Gijubhai Badheka Marg, Bhavnagar 364021, India.
authors.forename: Manoj
authors.initials: M
authors.lastname: Kumar
authors.forename: Nitin
authors.initials: N
authors.lastname: Trivedi
authors.forename: C R K
authors.initials: CR
authors.lastname: Reddy
authors.forename: Bhavanath
authors.initials: B
authors.lastname: Jha
mesh_terms: D060387:Ascorbate Peroxidases / Q000378:metabolism; D002374:Catalase / Q000378:metabolism; D020552:Comet Assay; D004249:DNA Damage; D004787:Environmental Pollution / Q000517:prevention & control*; D044943:Fatty Acid Desaturases / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism; D005979:Glutathione Peroxidase / Q000378:metabolism; D005980:Glutathione Reductase / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000378:metabolism; D007093:Imidazoles / Q000633:toxicity*; D020128:Inhibitory Concentration 50; D052578:Ionic Liquids / Q000633:toxicity*; D007527:Isoenzymes / Q000378:metabolism; D015227:Lipid Peroxidation / Q000187:drug effects; D058945:Lipoxygenases / Q000378:metabolism; D010084:Oxidation-Reduction / Q000187:drug effects; D018384:Oxidative Stress / Q000187:drug effects; D017382:Reactive Oxygen Species / Q000378:metabolism; D012624:Seaweed / Q000187:drug effects / Q000201:enzymology*; D013482:Superoxide Dismutase / Q000378:metabolism; D044445:Ulva / Q000187:drug effects / Q000201:enzymology*
chemical_list: D007093:Imidazoles; D052578:Ionic Liquids; D007527:Isoenzymes; D017382:Reactive Oxygen Species; D006861:Hydrogen Peroxide; D060387:Ascorbate Peroxidases; D002374:Catalase; D005979:Glutathione Peroxidase; D058945:Lipoxygenases; D044943:Fatty Acid Desaturases; D013482:Superoxide Dismutase; D005980:Glutathione Reductase; D005978:Glutathione