Stress-induced bystander signaling as a possible factor contributing to neuronal excitability and seizure generation/epileptogenesis

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.

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

Thorium is one of the most widespread radioactive elements in natural ecosystems, along with uranium, it is the most important source of nuclear energy. However, the effects of thorium on living organisms have not been thoroughly studied. Marine luminescent bacteria and their enzymes are optimal bioassays for studying low-dose thorium exposures. Luminescent bioassays provide a quantitative measure of toxicity and are characterized by high rates, sensitivity, and simplicity. It is known that the metabolic activity of bacteria is associated with the production of reactive oxygen species (ROS). We studied the effects of thorium-232 (10-11-10-3 M) on Photobacterium phosphoreum and bacterial enzymatic reactions; kinetics of bacterial bioluminescence and ROS content were investigated in both systems. Bioluminescence activation was revealed under low-dose exposures (<0.1 Gy) and discussed in terms of "radiation hormesis". The activation was accompanied by an intensification of the oxidation of a low-molecular reducer, NADH, during the enzymatic processes. Negative correlations were found between the intensity of bioluminescence and the content of ROS in bacteria and enzyme systems; an active role of ROS in the low-dose activation by thorium was discussed. The results contribute to radioecological potential of bioluminescence techniques adapted to study low-intensity radioactive exposures.

Humic Substances Mitigate the Impact of Tritium on Luminous Marine Bacteria. Involvement of Reactive Oxygen Species

The paper studies the combined effects of beta-emitting radionuclide tritium and Humic Substances (HS) on the marine unicellular microorganism—luminous bacteria—under conditions of low-dose radiation exposures (<0.04 Gy). Tritium was used as a component of tritiated water. Bacterial luminescence intensity was considered as a tested physiological parameter. The bioluminescence response of the marine bacteria to tritium corresponded to the “hormesis” model: it included stages of bioluminescence inhibition and activation, as well as the absence of the effect. HS were shown to decrease the inhibition and activation effects of tritium, similar to those of americium-241, alpha-emitting radionuclide, studied earlier. Correlations between the bioluminescence intensity and the content of Reactive Oxygen Species (ROS) were found in the radioactive bacterial suspensions. The results demonstrate an important role of HS in natural processes in the regions of low radioactive contamination: HS can mitigate radiotoxic effects and adaptive response of microorganisms to low-dose radioactive exposures. The involvement of ROS in these processes was demonstrated.

A nomogram to predict symptomatic epilepsy in patients with radiation-induced brain necrosis

OBJECTIVE

To develop and validate a nomogram to predict epilepsy in patients with radiation-induced brain necrosis (RN).

METHODS

The nomogram was based on a retrospective analysis of 302 patients who were diagnosed with symptomatic RN from January 2005 to January 2016 in Sun Yat-sen Memorial Hospital using the Cox proportional hazards model. Discrimination of the nomogram was assessed by the concordance index (C index) and the calibration curve. The results were internally validated using bootstrap resampling and externally validated using 128 patients with RN from 2 additional hospitals.

RESULTS

A total of 302 patients with RN with a median follow-up of 3.43 years (interquartile range 2.54-5.45) were included in the training cohort; 65 (21.5%) developed symptomatic epilepsy during follow-up. Seven variables remained significant predictors of epilepsy after multivariable analyses: MRI lesion volume, creatine phosphokinase, the maximum radiation dose to the temporal lobe, RN treatment, history of hypertension and/or diabetes, sex, and total cholesterol level. In the validation cohort, 28 out of 128 (21.9%) patients had epilepsy after RN within a median follow-up of 3.2 years. The nomogram showed comparable discrimination between the training and validation cohort (corrected C index 0.76 [training] vs 0.72 [95% confidence interval 0.62-0.81; validation]).

CONCLUSION

Our study developed an easily applied nomogram for the prediction of RN-related epilepsy in a large RN cohort.

CLASSIFICATION OF EVIDENCE

This study provides Class III evidence that a nomogram predicts post-RN epilepsy.

Tidal variations of background ionizing radiation and circadian timing of the suprachiasmatic nucleus clock

Recently, correlations of different physiological processes in humans with variations in the local lunisolar gravitational tide force have been observed under highly controlled laboratory conditions. Understanding of the physical nature of this phenomenon needs a comprehensive study of its possible molecular mechanisms. One of the possible timing cues is the strong periodic variation of the emanation fields of radon-222 and its progeny produced by tidal deformations of geological environment. In the present work, we argue that this variation could induce temporal modulation of radiation-induced bystander signaling pathways associated with fundamental regulators of gene expression in the suprachiasmatic nucleus clock.

Reactive Oxygen Species and low-dose effects of tritium on bacterial cells

The paper continues study of exposures of luminous marine bacteria to low-dose radiation of tritium; tritiated water (HTO) was applied as a source of the irradiation. Hypothesis on involvement of Reactive Oxygen Species (ROS) to signaling mechanism of bacterial cells under exposure to low-intensity tritium radiation was verified. Bacterial bioluminescence intensity was considered as a tested physiological parameter; it was compared to the ROS production in the bacterial environment of different activity concentrations: 0.03, 4.0, and 500 MBq/L. Exposure of the bacteria to chronic low-dose tritium irradiation (<0.08 Gy) increased bioluminescence intensity and ROS production considerably (up to 300%). Spearman rank correlation coefficients were calculated and confirmed relations between the bioluminescence intensity and ROS production. Additional peculiarities of HTO effect were: independence of the bioluminescence intensity and ROS content on HTO activity concentration; low ROS content in bacteria-free aquatic environment. Effects of HTO on bacterial bioluminescence were attributed to: (1) trigger function of tritium decay products in the bacterial metabolic oxygen-dependent processes, with bioluminescence involved; (2) signaling role of ROS as intercellular messengers in "bystander effect"; (3) fixed amount of bacterial cells (3•10⁷ cells/mL) provided the upper limits of the bioluminescence intensity and ROS content. As an outlook, in spite of low energy of tritium decay, its influence on aquatic biota via ROS production by microorganisms should be taken into consideration.

A novel technology to model pressure-induced cellular injuries in the brain

BACKGROUND

Elevated intracranial pressure (ICP) accompanying a number of neurological emergencies is poorly understood, and lacks a model to determine cellular pathophysiology. This limits our ability to identify cellular and molecular biomarkers associated with the pathological progression from physiologic to pathologic ICP.

NEW METHOD

We developed an ex vivo model of pressure-induced brain injury, which combines 3D neural cell cultures and a newly developed Pressure Controlled Cell Culture Incubator (PC³I). Human astrocytes and neurons maintained in 3D peptide-conjugated alginate hydrogels were subjected to pressures that mimic both physiologic and pathologic levels of ICP for up to 48h to evaluate the earliest impacts of isolated pressure on cellular viability and quantify early indicators of pressure-induced cellular injury.

RESULTS

Compared to control cell cultures grown under physiologic pressure, sustained pathologic pressure exposure increased the release of intracellular ATP in a cell-specific manner. Eighteen hours of sustained pressure resulted in increased ATP release from neurons but not astrocytes.

COMPARISON WITH EXISTING METHODS

Cell culture incubators maintain cultures at normal atmospheric pressure. Based on multiple literature searches, we are not aware of any other cell culture incubator systems that modify the pressure at which primary CNS cells are maintained.

CONCLUSION

This model simulates the clinical features of elevated ICP encountered in patients with hydrocephalus, and provides a first estimate of the pathological signaling encountered during the earliest perid of progression in neonatal hydrocephalus. This model should provide a means to better understand the pathological biomarkers associated with the earliest stages of elevated ICP.