Biophysics最新文献

Using methods of general and biochemical blood analysis and histological analysis of the lungs, liver, heart and kidneys of Syrian hamsters, it was determined whether aerosol treatment of these animals with binuclear dinitrosyl iron complexes with glutathione, alone or followed by similar treatment of the same animals with diethyldithiocarbamate, as well as aerosol treatment of Syrian hamsters with dinitrosyl iron complexes with mercaptosuccinate, leads to negative toxic effects at the level of the whole organism. The detected weak reversible toxic effect in the form of nephrotoxicity of such treatment allows us to assert that such an effect, which suppresses of covid infection in these animals, is due to the selective in vivo action of dinitrosyl iron complexes and diethyldithiocarbamate on the SARS-CoV-2 virus, without affecting other tissues and organs of the animal.

The radioprotective efficacy of granulocyte colony-stimulating factor in the form of pegfilgrastim at fractionated irradiation was evaluated on male ICR (CD-1) mice. Mice were exposed to five daily exposures to X-rays at a dose of 2.5 Gy. Three hours after each exposure, pegfilgrastim was injected subcutaneously into mice at a dosage of 0.5 μg/g. The drug was also administered daily 3–7 days after the last irradiation. The efficacy of this therapeutic regimen was evaluated on the basis of the degree of DNA damage in spleen cells 30 min after the last irradiation; hematologic parameters were evaluated after 30 min and 3 days; Schiff bases, trieno, and oxodiene conjugates in the liver were evaluated after 30 min; and thymus and spleen weight, the number of karyocytes in the femur, and the content of thiobarbiturate-reactive products in the liver were evaluated after 3 days, as well as on the basis of 30-day survival. The application of the therapeutic regimen contributed to a significant correction of irradiation-induced oxidative stress: according to the criteria of the content of Schiff bases, trieno and oxodieno conjugates, the group receiving pegfilgrastim corresponded to the intact mice, the content of thiobarbiturate-reactive products in the liver decreased relative to the irradiated control, but the parameters of intact mice were not reached. Pegfilgrastim administration did not compensate for the irradiation-induced bone marrow cell death 3 days after the last irradiation and could eventually ensure the survival of only 3 mice out of 14 individuals receiving the drug. Thus, for effective application of pegfilgrastim during fractionated irradiation at a total dose of 12.5 Gy it is necessary to increase the number of irradiation sessions with decreasing dose of each session, or to decrease the total radiation dose. Joint use of pegfilgrastim with other radioprotective drugs with other mechanisms of action is also promising.

Computer-based molecular dynamics studies of the interaction of the pharmacological pair “vector–receptor” have been carried out to simulate promising mechanisms and processes of specific drug delivery to the tumor. The purpose of computational calculations is the description of interaction processes and the determination of the spatial positions of the RGD peptide + integrin α_vβ₃ receptor system, solvated with water. The configuration positions of the RGD peptide + integrin α_vβ₃ system in 100 ns relaxed states were obtained from molecular dynamics modeling. Two RGD peptides located outside and inside the integrin α_vβ₃ receptor were modeled. One of them is a peptide of the original PDB file localized inside the integrin α_vβ₃ receptor. The other RGD peptide is located outside the receptor in its initial position, freely diffuses throughout the entire area of the modeling cell, and naturally comes into contact and binds to integrin α_vβ₃.

Changes in the levels of some markers of apoptosis (lipid asymmetry of plasma membranes, production of reactive oxygen species, nitric oxide, and the concentration of ionized calcium) of human blood lymphocytes modified by exposure to hydrogen peroxide (10^–5 mol/L) and UV light (254 nm, 1510 J/m²) in the presence of cycloastragenol (10^–8–10^–5 mol/L) were studied. The intensity of apoptotic lymphocyte death processes was found to decrease after UV-light exposure in the presence of cycloastragenol (10^–8 mol/L). The cytoprotective effect of cycloastragenol on lymphocytes was found to be due to a decrease in the level of intracellular reactive oxygen species and calcium ions and an increase in the activity of catalase and glutathione reductase and nitric oxide production. Possible mechanisms of cycloastragenol action as a regulator of apoptotic death of lymphocytes induced by UV radiation and hydrogen peroxide exposure are discussed.

The pioneer SOX2 transcription factor plays an important role in the regulation of gene expression by binding to condensed chromatin and inducing its decondensation. Experimental data on the preferred positions of SOX2 binding to DNA in the context of the nucleosome are contradictory: in some studies, binding to the inner segments of nucleosomal DNA is preferred, in others it binds to the edge segments. In the framework of this work, all possible variants of SOX2 binding to nucleosomal DNA at different distances from the nucleosome center (determined by the superhelix position parameter, SHL) and different orientations of the binding site relative to the nucleosome center (determined by the SHL sign) were analyzed by molecular modeling. It was shown that on an intact nucleosome binding is possible at positions SHL +2, SHL ±4, and SHL ±5, but if we assume a shift of nucleosomal DNA by one pair of nucleotides, binding becomes possible at positions corresponding to all integer values of the SHL. This observation helps to explain some of the contradictions between the experimental data.

During artificial incubation of slices of the sensorimotor cortex of guinea pigs and the telencephalon of turtles, microiontophoretic application of acetylcholine to neurons revealed a significantly lower frequency of spike responses in the nerve cells of turtles compared with guinea pig cells. This difference was attributed to the different rate of the M-cholinergic response in the temperature ranges of 27–29 and 34–36°C, as found previously in hypothermic experiments. Although experiments on guinea pig and turtle neurons were performed in the same temperature range (32–34°C), the genetically determined structure of neuronal membranes reflects the natural temperature dependence of both species: guinea pig membranes with a constant habitat temperature of 38°C have a higher density of K⁺ channels than turtles with a preferred temperature of 28–32°C. The difference in K⁺ channel representation was determined by a significantly longer activation after-effect in turtle neurons in response to glutamate-induced spike activation. The low density of K⁺ channels on membranes and the low rate of the M-cholinergic response, which closes them at the onset of any adaptive act, prevent neurons from forming high-frequency and long-lasting impulse sequences to regulate behavior over a wide range in turtles with a preferred temperature of 28–32°C.

The temperature dependence of the duration of tryptophan fluorescence in human and bovine serum albumin in an aqueous solution and glycerol in the temperature range of –170 to 20°C has been studied. A model of forward and reverse electronic transitions in the tryptophan molecule from the excited state to the ground state and to the charge transfer state has been constructed. Three main spectral regions of tryptophan fluorescence with different behaviors of the temperature dependences of transition rates from the excited state of tryptophan to the state with charge transfer were determined. It was found that the dynamics of the hydrogen bonding system in the selected spectral regions had a determining influence on the character of the changes in the duration of tryptophan fluorescence. The nonlinear dependence of intramolecular transition rates on temperature found in this work is determined by the interaction of tryptophan molecules with the microenvironment. The rearrangements in the hydrogen bonding system of albumin protein containing tryptophan molecule have a determining influence on the processes of excitation deactivation in tryptophan.

Bacteriophage endolysins are part of a complex of lytic enzymes responsible for the destruction of peptidoglycan in the bacterial cell wall. The dynamic features of single-domain endolysin of bacteriophage T5 and multi-domain endolysin PlyG of gamma phage have been studied by methods of molecular dynamics and normal mode analysis. The nature of activation of bacteriophage T5 endolysins by calcium and a discovered fundamental difference in the dynamic features of single-domain and multi-domain endolysins are explained.

The skeletal muscle contraction model as a complex of active motor units (sarcomeres) is discussed. The sarcomere model takes the fact into account that forces are generated by myosin bridges interacting with actin filaments in muscle myofibrils. The input of the model is the rate of calcium ion influx into muscle cells, which is assumed to be proportional to the motor neuron potential. The description of the muscle force as a whole uses averaging over an ensemble of motor units. The parameters of the model are adapted to describe contraction of a skeletal muscle sacromere. The transition from contraction of a single sarcomere to slow contraction of the whole muscle is constructed using motion separation methods. The model of “slow” contraction of a single muscle fiber excited by a single nerve impulse has no independent value because the characteristic time of change of the impulse potential is short. Nevertheless, for description of tetanic muscle contraction, when the change in the total action on the muscle is smooth enough, it seems acceptable to use such an approximate model. Approximate numerical estimates of the error of the constructed model for a simplified example are given.