Amino Acids as Regulators of Cell Metabolism.

In this review, we discuss the principles of regulation and synchronization of metabolic processes in mammalian cells using a two-component model of cell metabolism consisting of a controlling signaling system that regulates major enzymatic cascades and executive metabolic system that directly performs biosynthetic reactions. This approach has allowed us to distinguish two transitional metabolic states (from catabolism to anabolism and vice versa) accompanied by major rearrangements in the signaling system. The signaling system of natural amino acids was selected, because amino acids are involved in both signaling and executive metabolic subsystems of general cell metabolism. We have developed a graphical representation of metabolic events that allowed us to demonstrate the succession of processes occurring in both metabolic subsystems during complete metabolic cycle in a non-dividing cell. An important revealed feature of the amino acid signaling system is that the signaling properties of amino acid are determined not only by their molecular structure, but also by the location within the cell. Four major signaling groups of amino acids have been identified that localize to lysosomes, mitochondria, cytosol, and extracellular space adjacent to the plasma membrane. Although these amino acids groups are similar in the composition, they have different receptors. We also proposed a scheme for the metabolism regulation by amino acids signaling that can serve as a basis for developing more complete spatio-temporal picture of metabolic regulation involving a wide variety of intracellular signaling cascades.

Fundamental constraints of vessels network architecture properties revealed by reconstruction of a rat brain vasculature.

The studies of mammalian vasculature are an essential part of biomedical research, enabling the development of physiological understanding and forming the background of medical techniques and therapy. Despite the fact that the basic principles of vessel network description were established in the first quarter of the twentieth century, a digital model describing the vasculature in full accordance with experimental data has not yet been created. In the present study, we combine the determined structure design of basic arterial vessels with the stochastic creation of small vessel networks. By the example of rat brain arterial network model it was shown that the arterial blood volume and the magnitude of the blood flow impose a limitation on the network architecture. In particular, the bifurcation exponent (γ) should not be less than 2.7, and the optimal value of this parameter lies in the range of 2.9-3.0. Although the networks with a low γ appear as branched and complex, they do not fill out the phantom properly. Thus, the architecture of the vasculature is fundamentally determined by topological geometrical parameters.

Multiparametric topological analysis of reconstructed rat brain arterial system.

All metabolic processes in living tissues are provided by the vascular system, whose functionality largely depends on its structure and topology. The paper proposes an algorithm for constructing the circulatory system based on a combination of stochastic and deterministic approaches. Analyses of the topological characteristics of arterial tree models with different values of the bifurcation exponent ([Formula: see text]) and length coefficient ([Formula: see text]) show that the maximum agreement with experimental data can be achieved only with the optimal values of both parameters (3.0 and 0.90, respectively). Application of the multiparametric optimization in conjunction with topological analysis makes it possible to quantify the biological division of the distributing and delivering vessels of a tree with a high degree of branching. The proposed approach allows both the correct spatial localization of the main arteries and the complex topology of the complete arterial system down to the capillaries to be reproduced.

Mechanism underlying the protective effect of glycine in energetic disturbances in brain tissues under hypoxic conditions.

Glycine stabilizes energetics of brain mitochondria under conditions of brain hypoxia in vivo modeled by ligation of the common carotid artery in rats. Hypoxia reduced respiratory control in brain cortex mitochondria from 7.7 ± 0.5 to 4.5 ± 0.3. Preliminary oral administration of glycine almost completely prevented this decrease. In both in vitro models of hypoxia, similar phosphorylation disturbances were detected in both cortical slices and isolated brain mitochondria; they were effectively prevented by glycine. Hypoxia activates H(2)O(2) generation in mitochondrial suspension. The process is significantly reduced in the presence of 5 mM glycine. It is concluded that both in the model of hypoxia in vivo and during in vitro modeling of hypoxia in cortical slices and mitochondria, glycine acts as a protector inhibiting generation of reactive oxygen species in mitochondria and preventing energetics disturbances in brain mitochondria.

Effect of glycine on the microcirculation in rat mesenteric vessels.

Model experiments on biomicroscopy of mesenteric microvessels in laboratory rats were performed to evaluate the effect of natural metabolites (e.g., amino acid glycine) on the microcirculation. The effect of glycine was determined from a change in the diameter of arterioles. Application of glycine (0.1 ml, 1 M) to the mesenteric surface was followed by arteriolar dilation (by 50-80%). Histamine-induced disturbances in the microcirculation were not observed after preapplication of glycine. Under these conditions, pretreatment with histamine was accompanied by reversible changes. Our results suggest that the natural metabolite glycine has a prophylactic and therapeutic effect on microcirculatory disturbances, which are induced by inflammatory-and-allergic mediator histamine.

Effect of the inhibitory neurotransmitter glycine on slow destructive processes in brain cortex slices under anoxic conditions.

Slow destructive processes in brain cortex were studied under deep hypoxia (anoxia). Study of the character and dynamics of DNA destruction showed that apoptosis and necrosis run in parallel under the experimental conditions. These processes typically develop in tens of hours. A similar conclusion was reached from electron microscopic study of the tissue ultrastructure. More detailed study revealed that a relatively rare type of apoptosis not involving cytochrome c release from the intermembrane space of mitochondria and not associated with opening of the mitochondrial nonspecific pore occurs under the experimental conditions. As this is occurring, the process can be slowed by high concentrations of glycine, an inhibitory neurotransmitter. The study of DNA destruction demonstrated that high concentrations of glycine selectively slow apoptosis but have almost no effect on necrosis. Glycine also drastically decreases changes in the tissue ultrastructure, particularly of mitochondria, arising under anoxia. Glycine does not notably influence the mitochondrial oxidative phosphorylation system. Study of impairment of mitochondrial function demonstrated that the oxidative phosphorylation system is not disturbed for 1 h, which is several times longer than the inhibition time of brain function under deep hypoxia. The mitochondrial respiratory system is preserved for a relatively long time (24 h). Malate oxidase activity is deactivated after 48 h. The succinate oxidase fragment of the mitochondrial respiratory chain proved especially resistant; it retains activity under anoxia for more than 72 h. A possible mechanism of the effect of high glycine concentrations is discussed.

Brownian dynamic model of the glycine receptor chloride channel: effect of the position of charged amino acids on ion membrane currents.

Glycine is the major inhibitory neurotransmitter in the brainstem and spinal cord, where it participates in a variety of motor and sensory functions. It activates a special type of ligand-gated membrane receptor, which provides for Cl- ion conductance of the neuronal membrane. Computer simulations of a single-channel current through this receptor have been carried out on the basis of Brownian (Langevin) dynamics. The dependence of the currents on pore diameter and the location of the charged amino acid residues have been obtained. It has been shown that the presence and the symmetry of the filter-forming residues determined not only the ion-selectivity of the channel but also increased transmembrane anion current.

Effect of glycine on microcirculation in pial vessels of rat brain.

Single application of glycine in a final dose of 40 mg/kg to the surface of the parietal area of rat brain produced a potent vasodilatory effect. The diameter of arterioles increased to 250% from the baseline level 1-3 min after treatment. These changes persisted for 5-10 min. In the follow-up period the diameter of vessels progressively decreased to the baseline level. Repeated application of glycine in the same dose also induced dilation of arterioles. Application of physiological saline under similar conditions did not produce these changes.

Theoretical approach to description of time-dependent nitric oxide effects in the vasculature.

Nitric oxide (NO) is one of the most important signal compounds in a living cell. As a typical free radical it has both toxic and physiological effects and their balance is determined by a spatial distribution of NO concentration. Moreover, some biological functions, especially NO-mediated relaxation of blood vessels, have to be time-limited. In order to circumscribe this phenomenon non steady-state mathematical model has been used for description of nitric oxide diffusion in vascular smooth muscle. It was shown that the microvascular relaxation could be observed even after a short time of NO production in the endothelium. This time is up to 3 times below that needed to reach the steady-state spatial NO gradient. However, the effect of nitric oxide essentially depends on the rate of NO production and blood vessel diameter. Furthermore, non steady-state nitric oxide concentration gradient was represented as an analytical function of time and coordinate. It is essential that this function describes a common case of one-dimensional diffusion of uncharged low-mass molecules. Thus, the results can be used for calculation of an upper estimation of experimental data.