Enzymatic Responses to Low-Intensity Radiation of Tritium

Abstract

The present study considers a possible role of enzymatic reactions in the adaptive response of cells to the beta-emitting radionuclide tritium under conditions of low-dose exposures. Effects of tritiated water (HTO) on the reactions of bacterial luciferase and NAD(P)H:FMN-oxidoreductase, as well as a coupled system of these two reactions, were studied at radioactivity concentrations ≤ 200 MBq/L. Additionally, one of the simplest enzymatic reactions, photobiochemical proton transfer in Coelenteramide-containing Fluorescent Protein (CLM-FP), was also investigated. We found that HTO increased the activity of NAD(P)H:FMN-oxidoreductase at the initial stage of its reaction (by up to 230%); however, a rise of luciferase activity was moderate (<20%). The CLM-FP samples did not show any increase in the rate of the photobiochemical proton transfer under the exposure to HTO. The responses of the enzyme systems were compared to the ‘hormetic’ response of luminous marine bacterial cells studied earlier. We conclude that (1) the oxidoreductase reaction contributes significantly to the activation of the coupled enzyme system and bacterial cells by tritium, and (2) an increase in the organization level of biological systems promotes the hormesis phenomenon.

Development of Cellular and Enzymatic Bioluminescent Assay Systems to Study Low-Dose Effects of Thorium

“…Previously [ 6 , 16 , 17 ], we found correlations between the ROS content and bacterial bioluminescence intensity in tritiated water and thus suggested the involvement of ROS in the activation of bacterial physiological functions under exposure to the beta-emitting radionuclide tritium. A question of special interest is: are ROS effects responsible for the bioeffects of other radionuclides with differing characteristics of radioactive decay?…”

“…In our previous studies, we demonstrated the advantages of the bacteria-based and enzyme-based bioluminescent bioassays to monitor low-dose effects of radionuclide solutions [ 12 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 ] and gamma radiation [ 22 ]. It can be noted that in 2003 the luminous marine bacteria were applied to study the toxicity of radiation for the first time [ 23 ].…”

“…Our previous works showed that the responses of luminous marine bacteria to the low-dose radiation of alpha and beta types [ 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 27 , 28 ] correspond to the conventional “hormesis” model [ 29 , 30 , 31 , 32 ]. This model includes, in the broadest case, three stages of the biological dose-dependent response—stress recognition, activation, and inhibition of organismal functions.…”

“…On the other hand, ROS are native products of metabolic oxidative processes in living organisms [ 38 , 39 , 40 ]. Our previous results [ 6 , 16 , 17 ] have demonstrated that luminous marine bacteria naturally increase ROS content in aquatic media and intensify the ROS production in the presence of the radionuclide tritium.…”

Hormetic Responses of Photosystem II in Tomato to Botrytis cinerea

“…Photosystem II responses of tomato leaflets to B. cinerea inoculation can be described as a time-dependent hormetic response ( Figure 8 ) in terms of “stress defense response” and “toxicity” [ 76 , 80 ]. Activation by a low-dose effect or short-time exposure is a common phenomenon that is associated with the term “hormesis”, typically indicating a positive biological response [ 13 , 44 , 55 , 81 , 82 , 83 , 84 , 85 , 86 ]. There are published studies reporting a time-dependent hormesis [ 55 , 82 ], but it is only recently that analysis has been made regarding the features of hormesis as a function of time [ 13 , 81 , 82 ], and according to our data, under biotic stress.…”