Vol 63, No 2 (2018)

Structural equation modeling (SEM) is a second-generation multivariate method to estimate the causal interactions in a set of variables and includes, as special cases, several statistical methods (regression analysis, path analysis, and confirmatory factor analysis). This review focuses on all of the main SEM models and various methods used to optimize the model parameters. Representative examples are discussed to illustrate SEM application in molecular biology, including modeling of biochemical processes, relationships between genetic markers and diseases, and interactions within gene networks.

The comparative characterization of thermal stability of human peroxiredoxins 1–6 (Prx1–Prx6) has been performed by physicochemical and biochemical methods and the role of disulfide bonds in stabilizing their structure has been shown. Prx1 and Prx2 among the tested peroxiredoxins exhibit the highest peroxidase activity and thermal stability. Prx1 and Prx2 are more than 2 times more active on average with H₂O₂ and tert-butyl hydroperoxide as substrates compared to other peroxiredoxins and retain at least 50% activity after 30 min heating at a temperature of 64°C, which is more than 10°C higher compared to Prx3–Prx6. The reduction of the disulfide bonds between Prx1 and Prx2 leads to a decrease of their thermal stability, comparable to the thermal stability of Prx3–Prx6, which confirms the important role of the intermolecular S–S bonds in stabilizing the structure of these proteins.

The hydrolytic degradation of polymer films of poly(3-hydroxybutyrate) of different molecular weights and its copolymers with 3-hydroxyvalerate (9 mol % 3-hydroxyvalerate in the poly(3-hydroxybutyrate) chain) of different molecular weights was studied in model conditions in vitro. The changes in the physicochemical properties of the polymers were investigated using different analytical techniques: viscometry, differential scanning calorimetry, gravimetrical method, and water contact angle measurement for polymers. The data showed that in a period of 6 months the weight of polymer films decreased insignificantly. The molecular weight of the samples was reduced significantly; the largest decline (up to 80% of the initial molecular weight of the polymer) was observed in the high-molecular-weight poly(3-hydroxybutyrate). The surface of all investigated polymers became more hydrophilic. In this work, we focus on a mathematical model that can be used for the analysis of the kinetics of hydrolytic degradation of poly(3-hydroxyaklannoate)s by noncatalytic and autocatalytic hydrolysis mechanisms. It was also shown that the degree of crystallinity of some polymers changes differently during degradation in vitro. Thus, the studied polymers can be used to develop biodegradable medical devices such that they can perform their functions for a long period of time.

A number of properties of isolated proto-mitochondria (small young animal cell organelles) were studied. Proto-mitochondria were obtained by filtration of the light fraction of rat-liver mitochondria through calibrated millipore filters with a pore diameter of 0.45 μm. It was found that proto-mitochondria have a decreased ability to synthesize ATP due to their much lower content of ATP synthetase. The level of cytochromes in proto-mitochondria and mitochondria differ little. It was found that proto-mitochondria have more flavoproteins than mitochondria. It was demonstrated that proto-mitochondria (unlike mitochondria) contain almost none of the lipofuscin “aging pigment.” These differences reflect the processes of intracellular maturation of proto-mitochondria to mitochondria and subsequent aging to post-mitochondria. The results are important for understanding the role of proto-mitochondria in the cellular metabolism of specialized animal cells.

A preliminary mild partial degassing of a neutrophil suspension at an atmospheric gas pressure of 640 mm Hg was accompanied by a decrease in oxygen to 412 ng-atom O/mL and was shown to cause a significant (fourfold) decrease in neutrophil priming index on exposure to combined weak magnetic fields (a static magnetic field of 42 μT and a low-frequency collinear alternating magnetic field of 860 nT; 1, 4.4, and 16.5 Hz) but did not affect the cell potential to generate a respiratory burst in response to an activator (the peptide N-formyl–Met–Leu–Phe) in the control. A partial replacement of the air mixture with carbogen, xenon, or sulfur hexafluoride reduced the intensity of luminol-dependent chemiluminescence of the samples.

The effects of the Thr–Ser–Lys–Tyr peptide, which was shown to display neuroprotective activity in cell cultures in vitro, were studied in the model of paired Mauthner cells of goldfish. It was found that intracerebral injections provided the peptide to be applied into the zone of the right Mauthner cell under the fourth ventricle of the hindbrain lead to a dose-dependent decrease in the number of spontaneous turns of the goldfish to the left. It was shown that this effect is not eliminated under long-lasting optokinetic stimulation when the fish instinctively follow stimuli with a low spatial frequency that are moving in the nasal-to-temporal direction. We used the method of three-dimensional reconstruction by serial histological sections to study the dendrite morphology of the Mauthner cells in control and experimental goldfish. It was found that optokinetic stimulation of control goldfish evokes the dystrophy of the ventral dendrite of the right Mauthner cell, which is the target of this type of stimulation. Conversely, the peptide stabilize the size of the ventral dendrite of the right Mauthner cell under stimulation. These data could be interpreted as evidence of the neuroprotective effect of the Thr–Ser–Lys–Tyr peptide in vivo.

The technique for the preparation of biological tissue sections developed for Electron Probe Microanalysis has been adapted for ToF-SIMS analysis of mouse GV stage oocytes. GV-oocyte sample preparation involves the following steps: plunge freezing, freeze drying, impregnation in an embedding medium, and section cutting. Molecule-specific images of the distribution of molecules in a single oocyte have been obtained with the described technique and ToF-SIMS analysis. The ToF-SIMS analysis data show that the efficient lateral image resolution is approximately 1 μm. Hence, ToF-SIMS enables us to study the distribution of chemical substances in relation to the morphological data obtained by scanning electron microscopy or conventional light microscopy.

In hibernation season during torpor bouts, the spleen weight and the hemoglobin level, as well as the total and extracted protein contents in the spleen of the ground squirrel Spermophilus undulatus are increased when animals enter torpor and reach maximum values when the body temperature drops below 25°C. All these parameters return to the characteristic values of the euthermic animals during arousal, before the body temperature increases to 20°C. There were no significant differences in the numbers of splenocytes between ground squirrels in interbout euthermia and torpor. The minimum number of splenocytes was observed in animals that entered torpor when the core body temperature was approximately 18°C. The activity of ornithine decarboxylase, a key enzyme in polyamine synthesis, which is correlated with the functional and proliferative status of lymphoid tissue, was the same for the euthermic and summer ground squirrels and decreased monotonically during torpor. Upon arousal of the animals when body temperature was below 29°C, no resumption of the spleen ornithine decarboxylase activity was observed.

The influence of murine intestinal adenocarcinoma on the antioxidant status and hemoglobin content in the blood was analyzed. Murine adenocarcinoma was accompanied with a decrease of the nonprotein thiol concentration and an increase in ceruloplasmin. A conformational change in the globin molecule but not in the heme group was revealed in the hemoglobin molecule. The changes in the protein appear to be caused by nonspecific damage that results from the processes of peroxidation.

This paper presents a model of saccadic eye movements. Eye movements are considered as being ballistic, since saccades (rapid concurrent movements of both eyes) occur several hundred thousand times per day; visual perception of the environment is interrupted by a saccade. The optimal control was constructed for the motion considered in three consecutively refined assumptions. The controls included in the time-optimal problem were the resultant moment of force exerted by the extraocular muscles, individual moments of force exerted by either muscle of the agonist–antagonist pair, and finally, the rate of change of these moments. This approach is consistent with the view that is currently upheld by physiologists, who believe that a saccade is programmed by the central nervous system before the beginning of an eye movement and is scarcely adjusted during the movement itself. The solution of the optimal control problem and the results obtained by subsequent numerical modeling of saccadic trajectories were compared with the published experimental data. The saccadic trajectories were compared based on the main sequence, the known consistent relationship between saccade amplitude and duration, which is the most widely applied and commonly accepted way of describing saccade data. The main sequence of saccades obtained from the solution of the optimal control problem formulated in the most complete form agreed well with published experimental results.

This article is devoted to the development of a virtual coronary angiography method, a noninvasive method of evaluation of the state of the human coronary artery. Registration and processing of the signal of peripheral arterial blood pulsation against the background of a functional test with controlled respiration form the basis of the method. A mathematical model of the relationship between relative change in spectral evaluations of the variability of the cardiac rhythm and the degree of coronary-artery stenosis was developed. Clinical testing, which demonstrated the high efficiency of the proposed virtual coronary angiography method when examining patients with different states of coronary arteries, was conducted.

A differential scanning calorimetry study of the specific isobaric heat capacity, phase-transition enthalpy, moisture content, and cryoscopic temperature for samples of benign and malignant human prostate tumor tissues is reported. Empirical relationships have been obtained that describe the specific isobaric heat capacity of prostate-tissue samples in a wide temperature range and the effect of the moisture contents of the samples on the cryoscopic temperature and the heat of the phase transition, as well as a semi-empirical relationship that describes the effective specific-heat capacity in the subcryoscopic temperature range. The correlations and experimental data presented in this article can be used in mathematical modeling and optimization of heat-exchange processes in cryosurgery.

Variations of electrical conductivity of distilled water were continuously measured for 1 month. Long-period (up to 7 days or longer) variations were observed in electrical conductivity of water. The effect of temperature on the conductivity was minimized methodically and analytically. Temporal variations in distilled water conductivity were periodically observed to correlate with the intensity of solar radiation at a wavelength of 10.7 cm and variations in atmospheric pressure and global magnetic indices. Possible causes of the phenomena are discussed.

A differential evolution algorithm was used to detect the biotropic influence of geomagnetic activity on several parameters of human vascular tone. Studies of the characteristics of vascular tone in healthy volunteers showed that arterial stiffness and endothelial function, as well as blood pressure and heart rate, depend on the geomagnetic and, in most cases, weather conditions. The pulse wave velocity (PWV) was measured to characterize the arterial stiffness and was found to be the most sensitive to the effects of space weather parameters. The strength of the effect of geomagnetic activity was for the first time observed to depend on the configuration of terrestrial weather parameters. A linear correlation between the K index of geomagnetic activity and PWV was estimated at r =–0.44 (p = 0.0003), although the relationship was detectable exclusively in the case of certain terrestrial weather parameters. Endothelial dysfunction and the pulse-rate response to variations in geomagnetic activity implicated nitrogen monoxide in body adaptation to variations in geomagnetic activity.

A case study of hydrocephalus shows the vagueness of the concept of the “norm” as used in medicine. Self-organizing dynamic stability in biosystems can go far beyond the average statistical norm, while the body still retains its stability and functional performance.