The Mechanisms of L-Arginine Metabolism Disorder in Endothelial Cells.

L-arginine is a key metabolite for nitric oxide production by endothelial cells, as well as signaling molecule of the mTOR signaling pathway. mTOR supports endothelial cells homeostasis and regulates activity of L-arginine-metabolizing enzymes, endothelial nitric oxide synthase, and arginase II. Disruption of the L-arginine metabolism in endothelial cells leads to the development of endothelial dysfunction. Conflicting results of the use of L-arginine supplement to improve endothelial function reveals a controversial role of the amino acid in the endothelial cell biology. The review is aimed at analysis of the current data on the role of L-arginine metabolism in the development of endothelial dysfunction.

Biochemical and biological activity of arginine deiminase from Streptococcus pyogenes M22.

Streptococcus pyogenes (group A Streptococcus; GAS) is an important gram-positive extracellular bacterial pathogen responsible for a number of suppurative infections. This micro-organism has developed complex virulence mechanisms to avoid the host's defenses. We have previously reported that SDSC from GAS type M22 causes endothelial-cell dysfunction, and inhibits cell adhesion, migration, metabolism, and proliferation in a dose-dependent manner, without affecting cell viability. This work aimed to isolate and characterize a component from GAS type M22 supernatant that suppresses the proliferation of endothelial cells (EA.hy926). In the process of isolating a protein possessing antiproliferative activity we identified arginine deiminase (AD). Further study showed that this enzyme is most active at pH 6.8. Calculating Km and Vmax gave the values of 0.67 mmol·L(-1) and 42 s(-1), respectively. A distinctive feature of AD purified from GAS type M22 is that its optimum activity and the maximal rate of the catalytic process is close to neutral pH by comparison with enzymes from other micro-organisms. AD from GAS type M22 suppressed the proliferative activity of endothelial cells in a dose-dependent mode. At the same time, in the presence of AD, the proportion of cells in G0/G1 phase increased. When l-Arg was added at increasing concentrations to the culture medium containing AD (3 µg·mL(-1)), the enzyme's capacity to inhibit cell proliferation became partially depressed. The proportion of cells in phases S/G2 increased concomitantly, although the cells did not fully recover their proliferation activity. This suggests that AD from GAS type M22 has potential for the suppression of excessive cell proliferation.

Influence of Immune Complexes on Expression of CD54 and CD95 on the Surface of Endothelial Cells of ECV-304 Line.

The etiology of rheumatoid arthritis (RA) remains unknown; however, recent studies have suggested a central role of the vascular endothelium in RA pathogenesis. The immune complex (IC)-mediated vasculitis is typical for RA. The studies reported herein were undertaken to determine 1) whether IC isolated from plasma of patients with RA are capable of inducing expression of ICAM-1/CD54 and Fas antigen/CD95 on the endothelial cell (EC) in vitro, 2) whether the capacity to induce expression of this phenotypic markers of EC activation is determined by the size or by the composition of the IC. The concentrations of IC were chosen to be within the range for IC levels in plasma. We have shown that all IC-containing samples (n = 8) significantly and in a dose-dependent manner increased level of ICAM-1 expression on the EC. In selected experiments EC were incubated with IC in the presence of complement. The presence of serum containing active complement components resulted in further up-regulation of ICAM-1 expression only in 4 of 8 cases, independently on the ability of IC to fix complement. Additionally, we have found that all IC samples significantly and in a dose-dependent manner induced the marked increase in CD95 expression on the EC. Furthermore, the levels of augmented expression of CD95 correlated with the levels of CD54 expression stimulated by the same IC-containing samples. We have demonstrated that these levels of stimulated expression of ICAM-1 as well as levels of Fas antigen expression negatively correlated with percentage amounts of IgM in total protein concentration of IC and directly correlated with IgG content in comparison to IgM in the structure of this IC. Our results show that IC stimulate ECs to express ICAM-1 and CD95, all of which have been implicated in the pathogenesis of rheumatic disease. The studies reported herein provide further information regarding to inflammatory potential of IC in RA.

Cells of Immune System: Development, Activation, Effector Functions.

While understanding the role of certain cell populations and subpopulations is being more precisely identified, the pool of immunocompetent cells becomes continuously broader. It has rather recently been shown that hematopoietic precursors that express CD34 on their surface may be served as precursors of both monocytes/macrophages (Mn/Mf), and dendritic cells (DC) Huge experimental data obtained for recent years have shown that DC may just be comprehensive APC, capable to present both bacterial, and viral antigens in both primary, and secondary immune response for recognition by both T helpers (CD4(+)) and cytotoxic T lymphocytes (CD8(+)). Both Mf, and DC are producers of cytokines. After microbe phagocytosis by Mf or after DC infection, microbe components may induce production of IL-12 in these cells followed by IL-12 induction of IFNgamma production in NK and CD4(+) T lymphocytes. IFNgamma production is highly inducible: primary steps of IFNgamma production require, at least, two activation signals: from TCR, from adhesive or costimulatory molecules or from receptor for any additional cytokine, for example, IL-12. IFNgamma is synergistic agent for IL-12 that is providing costimulatory signal in induction of Th1 differentiation and is enhancing the sensitivity of naive T lymphocytes to stimulatory action of IL-12. Either Th1, and Th2 express beta1-chain of IL-12 receptor, but only Th1 express beta2-chain of this receptor. Incapability of Th2 to respond to IL-12 by activation is related to such a situation.