Monitoring of Low-Intensity Exposures via Luminescent Bioassays of Different Complexity: Cells, Enzyme Reactions, and Fluorescent Proteins

Abstract

The current paper reviews the applications of luminescence bioassays for monitoring the results of low-intensity exposures which produce a stimulative effect. The impacts of radioactivity of different types (alpha, beta, and gamma) and bioactive compounds (humic substances and fullerenols) are under consideration. Bioassays based on luminous marine bacteria, their enzymes, and fluorescent coelenteramide-containing proteins were used to compare the results of the low-intensity exposures at the cellular, biochemical, and physicochemical levels, respectively. High rates of luminescence response can provide (1) a proper number of experimental results under comparable conditions and, therefore, proper statistical processing, with this being highly important for "noisy" low-intensity exposures; and (2) non-genetic, i.e., biochemical and physicochemical mechanisms of cellular response for short-term exposures. The results of cellular exposures were discussed in terms of the hormesis concept, which implies low-dose stimulation and high-dose inhibition of physiological functions. Dependencies of the luminescence response on the exposure time or intensity (radionuclide concentration/gamma radiation dose rate, concentration of the bioactive compounds) were analyzed and compared for bioassays of different organization levels.

Keywords: antioxidant activity; bacterial cells, enzymes; bioactive compounds; fluorescent protein; hormesis; low-intensity factors; luminescence bioassays; radiation.

Figure 1

Scheme of dose–effect models: 1, hormesis; 2, threshold; 3, linear.

Figure 2

Chemical structure of the coelenteramide (CLM) molecule (neutral and ionized forms) and scheme of the photophysical and photochemical processes in CLM-containing fluorescent proteins.

Figure 3

Change of the fluorescence spectra of CLM-containing fluorescence proteins exposed to chemical agents or radiation.

Figure 4

Contributions of spectral components to the fluorescence spectra of CLM-containing protein at different concentrations of glycerol, C.

Figure 5

Bioluminescence kinetics of bacteria in a solution of americium-241, 3 kBq/L.

Figure 6

Effect of tritiated water on the bioluminescence of bacteria. (A) Bioluminescence kinetics of bacteria in tritiated water, 2 MBq/L; (B) bioluminescence intensity vs. activity concentration of tritiated water, A, at 20 and 50 h exposures.

Figure 7

Kinetics of bioluminescence intensity (I^rel) of Photobacterium phosphoreum under exposure to gamma radiation, ¹³⁷ Cs, 20 °C. The error for I^rel was 10%. (Dose rates: ■−4100; ◆−1040, •−460, ▲−150 µGy/h.

Figure 8

Bioluminescent intensity of an enzyme system, I^rel, vs. the specific radioactivity of tritiated water, A.

Figure 9

Relative contributions of spectral components to the fluorescence spectra of CLM-containing protein (“discharged obelin” from Obelia longissima) exposed to (A) tritiated water, 200 MBq/L [87]; or (B) gamma radiation, ¹³⁷ Cs, 2 mGy/h, 20 °C.

Figure 10

Hypothetical structure of bioactive compounds: (A) fragment of humic substances, (B) fullerenol C-60.

Figure 11

Principle of antioxidant efficiency evaluation using bacteria-based (upper path) and enzyme-based (lower path) bioluminescent assays.

Figure 12

Antioxidant coefficients D_OxT of F (A) and HS (B) in a model solution of organic oxidizer (1,4-benziquinone) [100]. The time of incubation of HS with the oxidizer (0 min and 50 min) is indicated in (B). Enzymatic assay.