EPR characterization of the ROS-associated toxicity in gamma irradiated Lemna minor L

Objectives. The EPR-X-band e-scan (Bruker ER 116 DS) spectrometer was used for selective detection/ identification of paramagnetic (superoxide anions (O2−), hydroxyl (HO•), and peroxyl (RCOO•)) substances and as radiation-dosimeter on the kinetics and antioxidant activity of irradiated Lemna minor L. (LM) species of the Bulgarian flora. Lemna Minor L. (LM), an aquatic plant that belongs to the genus Lemna/ Lemnaceae, easily used in the treatment of asthma, vitiligo, glaucoma, allergies, rheumatism, possessed strong antioxidant activity. The chemical compound as phytol, campesterol, loliolide, dihydroactinidiolide, ascorbic acid, vanillic acid, 2,3-dihydroxybenzoic acid, caffeic acid, chlorogenic acid, and etc, exhibit LM antibacterial, anti-inflammatory, antihistamine, and anti-carcinogenic effects. Materials and methods. The dry/ ethanol solution LM samples were single irradiated by using a 60Co source at doses of 1, 2, 2.5, 3, 5, 10 Gy (Gamma cell 5001, India; 1.377 Gy/h). The spectrophotometric antioxidant activities of LM against superoxide (>81%), hydroxyl (>52.7%), DPPH (89.9%), ABTS (>55.5%), SOD-like (>50.9%), CAT-like (>56.2%), LP, and NO radicals (>56%) were maximally evaluated at a dose of 3 Gy. The reducing power in the aqueous phase was (>54.37%, R2 = 0.878). The LM ability to scavenge in vitro ROS production and associated toxicity after irradiation, the spin-trap BMPO• (5-tert-Butoxycarbonyl-5-methyl-1-pyrroline-N-oxide), and free –radicals TEMPOL (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl) and DPPH• (2,2-diphenyl-1-picrylhydrazyl) were expressed, at different time intervals (0h, 1h, 2h, 24, 48h). For the reference EPR-signal, the LM was replaced with 30 μL deionized water. Results. The maximal DPPH• (93%) and TEMPOL (79.7%) neutralization, was detected in about 1h, by the 3Gy irradiated LM sample. The antioxidant activity of LM in water solution was similar. The maximal spin-adduct formation (DMPO-OH•, 76%) and its neutralization to hydrogen atom were measured at 30 min for the 2.5Gy and 3Gy irradiated LM extracts. The EPR signal intensity in all analyzes sharply decrease at 1.2h. In conclusion, the LM sample from Bulgarian flora showed the highest ability to scavenge in vitro ROS production and to neutralize the associated radiation-toxicity, due to its high content of nutrients, and could be useful as a cosmetic ingredient. (author)