Effect of heavy atoms in bioluminescent reactions

Marine Bacteria under Low-Intensity Radioactive Exposure: Model Experiments

Radioactive contaminants create problems all over world, involving marine ecosystems, with their ecological importance increasing in the future. The review focuses on bioeffects of a series of alpha and beta emitting radioisotopes (americium-241, uranium-(235 + 238), thorium-232, and tritium) and gamma radiation. Low-intensity exposures are under special consideration. Great attention has been paid to luminous marine bacteria as representatives of marine microorganisms and a conventional bioassay system. This bioassay uses bacterial bioluminescence intensity as the main testing physiological parameter; currently, it is widely applied due to its simplicity and sensitivity. Dependences of the bacterial luminescence response on the exposure time and irradiation intensity were reviewed, and applicability of hormetic or threshold models was discussed. A number of aspects of molecular intracellular processes under exposure to low-intensity radiation were analyzed: (a) changes in the rates of enzymatic processes in bacteria with the bioluminescent system of coupled enzymatic reactions of NADH:FMN-oxidoreductase and bacterial luciferase taken as an example; (b) consumption of an intracellular reducer, NADH; (c) active role of reactive oxygen species; (d) repairing of the DNA damage. The results presented confirm the function of humic substances as natural radioprotectors.

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

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.

Antioxidant Activity and Toxicity of Fullerenols via Bioluminescence Signaling: Role of Oxygen Substituents

Fullerenols are nanosized water-soluble polyhydroxylated derivatives of fullerenes, a specific allotropic form of carbon, bioactive compounds, and perspective basis for drug development. Our paper analyzes the antioxidant activity and toxicity of a series of fullerenols with different number of oxygen substituents. Two groups of fullerenols were under investigation: (1) C₆₀O_y(OH)_x, C_60,70O_y(OH)_x, where x+y = 24–28 and (2) C_60,70O_y(OH)_x, Fe_0,5C₆₀O_y(OH)_x, Gd@C₈₂O_y(OH)_x, where x+y = 40–42. Bioluminescent cellular and enzymatic assays (luminous marine bacteria and their enzymatic reactions, respectively) were applied to monitor toxicity in the model fullerenol solutions and bioluminescence was applied as a signaling physiological parameter. The inhibiting concentrations of the fullerenols were determined, revealing the fullerenols’ toxic effects. Antioxidant fullerenol’ ability was studied in solutions of model oxidizer, 1,4-benzoquinone, and detoxification coefficients of general and oxidative types (D_GT and D_OxT) were calculated. All fullerenols produced toxic effect at high concentrations (>0.01 g L⁻¹), while their antioxidant activity was demonstrated at low and ultralow concentrations (<0.001 g L⁻¹). Quantitative toxic and antioxidant characteristics of the fullerenols (effective concentrations, concentration ranges, D_GT, and D_OxT) were found to depend on the number of oxygen substituents. Lower toxicity and higher antioxidant activity were determined in solutions of fullerenols with fewer oxygen substituents (x+y = 24–28). The differences in fullerenol properties were attributed to their catalytic activity due to reversible electron acceptance, radical trapping, and balance of reactive oxygen species in aqueous solutions. The results provide pharmaceutical sciences with a basis for selection of carbon nanoparticles with appropriate toxic and antioxidant characteristics. Based on the results, we recommend, to reduce the toxicity of prospective endohedral gadolinium-fullerenol preparations Gd@C₈₂O_y(OH)_x, decreasing the number of oxygen groups to x+y = 24–28. The potential of bioluminescence methods to compare toxic and antioxidant characteristics of carbon nanostructures were demonstrated.

On mechanism of antioxidant effect of fullerenols

Fullerenols are nanosized water-soluble polyhydroxylated derivatives of fullerenes, specific allotropic form of carbon, bioactive compounds and perspective pharmaceutical agents. Antioxidant activity of fullerenols was studied in model solutions of organic and inorganic toxicants of oxidative type - 1,4-benzoquinone and potassium ferricyanide. Two fullerenol preparations were tested: С₆₀О_2-4(ОН)_20-24 and mixture of two types of fullerenols С₆₀О_2-4(ОН)_20-24+С₇₀О_2-4(ОН)_20-24. Bacteria-based and enzyme-based bioluminescent assays were used to evaluate a decrease in cellular and biochemical toxicities, respectively. Additionally, the enzyme-based assay was used for the direct monitoring of efficiency of the oxidative enzymatic processes. The bacteria-based and enzyme-based assays showed similar peculiarities of the detoxification processes: (1) ultralow concentrations of fullerenols were active (ca 10^-17-10^-4 and 10^-17-10^-5 g/L, respectively), (2) no monotonic dependence of detoxification efficiency on fullerenol concentrations was observed, and (3) detoxification of organic oxidizer solutions was more effective than that of the inorganic oxidizer. The antioxidant effect of highly diluted fullerenol solutions on bacterial cells was attributed to hormesis phenomenon; the detoxification was concerned with stimulation of adaptive cellular response under low-dose exposures. Sequence analysis of 16S ribosomal RNA was carried out; it did not reveal mutations in bacterial DNA. The suggestion was made that hydrophobic membrane-dependent processes are involved to the detoxifying mechanism. Catalytic activity of fullerenol (10^-8 g/L) in NADH-dependent enzymatic reactions was demonstrated and supposed to contribute to adaptive bacterial response.

Bioluminescent Enzymatic Assay as a Tool for Studying Antioxidant Activity and Toxicity of Bioactive Compounds

A bioluminescent assay based on a system of coupled enzymatic reactions catalyzed by bacterial luciferase and NADH:FMN-oxidoreductase was developed to monitor toxicity and antioxidant activity of bioactive compounds. The assay enables studying toxic effects at the level of biomolecules and physicochemical processes, as well as determining the toxicity of general and oxidative types. Toxic and detoxifying effects of bioactive compounds were studied. Fullerenols, perspective pharmaceutical agents, nanosized particles, water-soluble polyhydroxylated fullerene-60 derivatives were chosen as bioactive compounds. Two homologous fullerenols with different number and type of substituents, C₆₀ O_2-4 (OH)_20-24 and Fe_0.5 C₆₀ (OH) _x O_y (x + y = 40-42), were used. They suppressed bioluminescent intensity at concentrations >0.01 g L^-1 and >0.001 g L^-1 for C₆₀ O_2-4 (OH)_20-24 and Fe_0.5 C₆₀ (OH)_x O_y , respectively; hence, a lower toxicity of C₆₀ O_2-4 (OH)_20-24 was demonstrated. Antioxidant activity of fullerenols was studied in model solutions of organic and inorganic oxidizers; changes in toxicities of general and oxidative type were determined; detoxification coefficients were calculated. Fullerenol C₆₀ O_2-4 (OH)_20-24 revealed higher antioxidant ability at concentrations 10^-17 -10^-5 g L^-1 . The difference in the toxicity and antioxidant activity of fullerenols was explained through their electron donor/acceptor properties and different catalytic activity. Principles of bioluminescent enzyme assay application for evaluating the toxic effect and antioxidant activity of bioactive compounds were summarized and the procedure steps were described.

Effect of low-dose ionizing radiation on luminous marine bacteria: radiation hormesis and toxicity

The paper summarizes studies of effects of alpha- and beta-emitting radionuclides (americium-241, uranium-235+238, and tritium) on marine microorganisms under conditions of chronic low-dose irradiation in aqueous media. Luminous marine bacteria were chosen as an example of these microorganisms; bioluminescent intensity was used as a tested physiological parameter. Non-linear dose-effect dependence was demonstrated. Three successive stages in the bioluminescent response to americium-241 and tritium were found: 1--absence of effects (stress recognition), 2--activation (adaptive response), and 3--inhibition (suppression of physiological function, i.e. radiation toxicity). The effects were attributed to radiation hormesis phenomenon. Biological role of reactive oxygen species, secondary products of the radioactive decay, is discussed. The study suggests an approach to evaluation of non-toxic and toxic stages under conditions of chronic radioactive exposure.

Antioxidant activity of humic substances via bioluminescent monitoring in vitro

This work considers antioxidant properties of natural detoxifying agents-humic substances (HS) in solutions of model inorganic and organic compounds of oxidative nature-complex salt K3[Fe(СN)6] and 1,4-benzoquinone. Bioluminescent system of coupled enzymatic reactions catalyzed by

NAD(P)H

FMN-oxidoreductase and bacterial luciferase was used as a bioassay in vitro to monitor toxicity of the oxidizer solutions. Toxicities of general and oxidative types were evaluated using bioluminescent kinetic parameters-bioluminescence intensity and induction period, respectively. Antioxidant activity of HS was attributed to their ability to decrease both general and oxidative toxicities; the HS antioxidant efficiency was characterized with detoxification coefficients D GT and D OxT, respectively. Dependencies of D GT and D OxT on HS concentration and time of preliminary incubation of the oxidizers with HS were demonstrated. The optimal conditions for detoxification of the oxidizers were >20-min incubation time and 0.5 × 10(-4) to 2 × 10(-4) M of HS concentration. The present study promotes application of the enzymatic luminescent bioassay to monitor toxicity of pollutants of oxidative nature in environmental and waste waters in remediation procedures.

Pollutant toxicity and detoxification by humic substances: mechanisms and quantitative assessment via luminescent biomonitoring

The paper considers mechanisms of detoxification of pollutant solutions by water-soluble humic substances (HSs), natural detoxifying agents. The problems and perspectives of bioassay application for toxicity monitoring of complex solutions are discussed from ecological point of view. Bioluminescence assays based on marine bacteria and their enzymes are of special attention here; they were shown to be convenient tools to study the detoxifying effects on cellular and biochemical levels. The advantages of bioluminescent enzymatic assay for monitoring both integral and oxidative toxicities in complex solutions of model pollutants and HS were demonstrated. The efficiencies of detoxification of the solutions of organic oxidizers and salts of metals (including radioactive ones) by HS were analyzed. The dependencies of detoxification efficiency on time of exposure to HS and HS concentrations were demonstrated. Antioxidant properties of HS were considered in detail. The detoxifying effects of HS were shown to be complex and regarded as 'external' (binding and redox processes in solutions outside the organisms) and/or 'internal' organismal processes. The paper demonstrates that the HS can stimulate a protective response of bacterial cells as a result of (1) changes of rates of biochemical reactions and (2) stabilization of mucous layers outside the cell walls. Acceleration of auto-oxidation of NADH, endogenous reducer, by HS was suggested as a reason for toxicity increase in the presence of HS due to abatement of reduction ability of intracellular media.