concanavalin-a and arginyl-glycyl-aspartic-acid

In chronic viral hepatitis, autoimmune hepatitis, and some chronic cholestatic liver diseases, T lymphocytes serve as effector cells of the immunostimulatory processes. Cellular interactions of immune cells with extracellular matrix components are regulated primarily via the beta 1 subfamily of integrin receptors. The target epitope of several such integrin receptors is the Arg-Gly-Asp sequence, a cell adhesion motif shared by several matrix-associated adhesive glycoproteins. We review the use of synthetic non-peptidic analogs of RGD in the prevention of immune-mediated, concanavalin A-induced liver damage in mice and in inhibiting the development of liver cirrhosis in rats. The Con A-induced elevation of serum transaminases and tumor necrosis factor-alpha and the infiltration of liver tissue by inflammatory cells were inhibited by pretreatment of the mice with the synthetic RGD mimetics. In rats, the progression of thioacetamide-induced liver cirrhosis was markedly inhibited by the co-administration of the RGD mimetic SF-6,5. The compounds described here may be examined therapeutically for pathological conditions in the liver, manifested as necro-inflammation and fibrosis.

Topics: Animals; Carcinogens; Concanavalin A; Disease Progression; Guanidines; Hepatitis, Autoimmune; Liver Cirrhosis, Experimental; Mice; Mitogens; Oligopeptides; Rats; Receptors, Immunologic; T-Lymphocytes; Thioacetamide; Transaminases; Tumor Necrosis Factor-alpha; Valerates

Integrin occupation can alter the function of neutrophils (PMN), but the mechanism(s) involved is still unclear. This study demonstrated that the occupation of PMN integrins (especially those of the beta(3) subfamily) strongly enhances TNF stimulation of the respiratory burst but down-regulates that induced by PMA, fMLP, Con A, and serum treated zymosan. Treatment of PMN with genistein, staurosporine, and wortmannin, inhibitors of tyrosine kinases, protein kinase C, and phosphotidylinostol 3-kinase (PI 3-kinase) respectively, completely blocked the TNF-stimulated respiratory burst in PMN. Genistein and wortmannin enhanced the PMA-stimulated respiratory burst but only in cells adherent to RGD peptide. These findings suggest that PMN integrins (beta(3) subfamily) can generate signals that regulate the PMN agonist responses, probably through the activities of tyrosine kinases and PI 3-kinase.

Topics: Antibodies; Antigens, CD; Cells, Cultured; Concanavalin A; Cytochalasin B; Down-Regulation; Fibronectins; Humans; Integrin beta3; Integrins; N-Formylmethionine Leucyl-Phenylalanine; Neutrophils; Oligopeptides; Platelet Membrane Glycoproteins; Protein Kinase Inhibitors; Protein Kinases; Receptor Aggregation; Respiratory Burst; Superoxides; Tetradecanoylphorbol Acetate; Tumor Necrosis Factor-alpha; Zymosan

The etiology of T-cell-mediated liver injury involves the migration of immune cells, notably CD4+ T lymphocytes, into liver tissues. This process is mediated primarily by integrin-recognition of the sub-endothelium basement membranes and the extracellular matrix. The Arg-Gly-Asp-containing peptide, a major cell-adhesive ligand of extracellular matrix, is present in various plasma- and matrix-glycoproteins, such as fibronectin. Recently, we have described the design and usage of nonpeptide mimetics of Arg-Gly-Asp which bind specifically to integrins, and thereby, inhibit T cell immunity in vivo. We examined the efficacy of Arg-Gly-Asp-mimetics as potential therapeutic compounds for the treatment of experimental T-cell-mediated liver injury induced in mice by injection of Concanavalin-A. We now report that the Arg-Gly-Asp-mimetics specifically inhibited the binding of murine T cells to fibronectin, but did not affect the proliferative response of these cells in vitro. Intraperitoneal or oral administration of the Arg-Gly-Asp-mimetics but not the Arg-Gly-Asp-containing peptide, inhibited liver damage in mice if given before their inoculation with Con-A, as manifested by a lesser elevation in their serum levels of hepatic enzymes. The inhibitory effect of the Arg-Gly-Asp-mimetics was dose-dependent, the ED50 of the tested molecules being in the range of 100 micrograms per mouse and reaching maximal effect, e.g. approximately 95% inhibition, at 500 micrograms per mice. Thus, the Arg-Gly-Asp-mimetics described here may be used therapeutically to prevent immune-cell-mediated acute or chronic pathological reactions in the liver.

Topics: Animals; Cell Adhesion; Concanavalin A; Epitopes; Extracellular Matrix; Fibronectins; Guanidines; Immunity, Cellular; Laminin; Liver; Male; Mice; Mice, Inbred BALB C; Molecular Mimicry; Oligopeptides; Receptors, Immunologic; T-Lymphocytes; Valerates

Immunofluorescence analysis of HeLa cells incubated with human adenovirus serotype 2 (Ad2) inoculum suggested that Ad2 receptors co-localized with the receptors of fibronectin (FNR) and vitronectin (VNR) at the cell surface. Ad2 adsorption also resulted in the occurrence of intracytoplasmic actin cables with submembranal anchorage. The cell binding of Ad2 virions, pentons and fibres was found to be efficiently inhibited by concanavalin A, laminin, anti-FNR and anti-VNR antibodies. Arginine-glycine-aspartyl tripeptide (RGD) and other related peptides reproducing cellular attachment sequences of adhesion proteins also competed with Ad2 for cell adsorption, and drastically reduced the virus progeny yield at the end of the infectious cycle. Data from binding competition assays with Ad2 virions showed that the apparent affinity constants of RGD motif-containing peptides for Ad2 receptor ranged from 0.75 x 10(8) M-1 to 2.2 x 10(8) M-1, with a number of peptide recognizing sites varying from 1.5 x 10(4) to 9 x 10(4) per cell for the different peptides studied. Polypeptide analysis of labelled plasma membrane fractions isolated after cross-linking to unlabelled Ad2 virions showed three major protein species with apparent M(r) of 130K, 60K and 44K, respectively, reacting with anti-FNR and anti-VNR antibodies. These results suggested that Ad2 and extracellular matrix proteins recognize similar adhesion sequences at the surface of HeLa cells, or alternatively that integrins and Ad2 receptors have overlapping ligand specificity.

Topics: Adenoviruses, Human; Amino Acid Sequence; Antibodies; Cell Adhesion; Cell Adhesion Molecules; Concanavalin A; HeLa Cells; Humans; Molecular Sequence Data; Oligopeptides; Receptors, Cytoadhesin; Receptors, Virus; Virion