Inflammation induced changes in adenosine 3',5'-cyclic monophosphate production by ciliary epithelial cell bilayers

QSAR of adenosine A3 receptor antagonist 1,2,4-triazolo[4,3-a]quinoxalin-1-one derivatives using chemometric tools

Considering the potential of selective adenosine A3 receptor subtype ligands in the development of prospective therapeutic agents, an attempt has been made to explore physicochemical requirements of 1,2,4-triazolo[4,3-a]quinoxalin-1-one derivatives for A3 receptor binding. In this study, lipophilicity (logP), physicochemical substituent constants (pi, MR, sigma p) of phenyl ring substituents, and Wang-Ford charges of common atoms of the quinoxaline nucleus (calculated from molecular electrostatic potential surface of energy-minimized geometry using AM1 technique) were used as independent variables along with suitable dummy parameters. The best multiple linear regression (MLR) equation obtained from factor analysis (FA-MLR) as the preprocessing step could explain and predict 72.6% and 65.3%, respectively, of the variance of the binding affinity. The same equation also emerged as the best equation in the population of 100 equations obtained from genetic function approximation (GFA-MLR). The results suggested that presence of an electron-withdrawing group at the para position of the phenyl ring would be favorable for the binding affinity. Again, the presence of a nitro group at position R1 increases the binding affinity. When factor scores were used as predictor variables in the principal component regression analysis, the resultant model showed 78.6% explained variance and 63.1% predicted variance. The best equation derived from G/PLS could explain and predict 74.4% and 64.8%, respectively. The results have suggested the importance of Wang-Ford charges of atoms C15 and C19, apart from positive contributions of electron-withdrawing para substituents of the variance of the phenyl ring and nitro group at the R1 position.

Inflammatory cytokines regulate function and expression of adenosine A(2A) receptors in human monocytic THP-1 cells

Adenosine, acting at its receptors, particularly A(2A) receptors, is a potent endogenous anti-inflammatory agent that modulates the functions and differentiation of inflammatory and immune cells. Because the inflammatory milieu abounds in proinflammatory cytokines, we investigated the effects of Th1-inflammatory cytokines on function and expression of adenosine A(2A) receptors in the human monocytic cell line THP-1. We found that, consistent with previous reports, adenosine and 2-[p-(2-carnonylethyl)phenylethylamino]-5'-N-ethylcarboxamidoadenosine (CGS-21680), a selective A(2A) receptor agonist, suppress IL-12 production but increase IL-10 production in LPS-activated THP-1 cells. These effects were blocked by the A(2A) receptor antagonist 4-(2-[7-amino-2-(2-furyl)[1,2,4-triazolo[2,3-a][1,3,5]triazin-5-ylamino]ethyl)phenol (ZM-241385). More importantly, the suppressive effect of adenosine and CGS-21680 on IL-12 production was significantly enhanced in cells pretreated with either IL-1 (10 U/ml) or TNF-alpha (100 U/ml) but markedly attenuated in cells pretreated with IFN-gamma (100 U/ml). Similarly, IL-1 and TNF-alpha treatment potentiated the stimulatory effect of adenosine and CGS-21680 on IL-10 production, whereas IFN-gamma treatment almost completely abolished this effect. CGS-21680 stimulated an increase in intracellular cAMP in a time- and dose-dependent manner in IL-1- and TNF-alpha-treated cells but not in control or IFN-gamma-treated cells. Both IL-1 and TNF-alpha increased A(2A) receptor mRNA and protein. In parallel with its effect on A(2A) receptor function, IFN-gamma down-regulated A(2A) receptor message and protein. Because adenosine mediates many of the antiinflammatory effects of drugs such as methotrexate, these observations suggest that local changes in the cytokine milieu may influence the therapeutic response to those drugs by altering the expression and function of adenosine receptors on inflammatory cells.

TGF-beta2 inhibits growth of uveal melanocytes at physiological concentrations

The effect of TGF-beta2 on growth of uveal melanocytes in vitro was studied and the dose-dependent inhibitory effect of TGF-beta2 was compared with the known concentration of TGF-beta2 in aqueous humor. Uveal melanocytes were isolated and cultured with medium supplemented with cAMP elevating agents and basic fibroblast growth factor. The uveal melanocytes were plated into multi-well plates. After 24 hr, TGF-beta2 was added to the medium in various concentrations. After 5 days, the cells were detached, counted and compared to the controls. The effect of TGF-beta2 on DNA synthesis (as evaluated by uptake of bromodeoxyuridine) were also tested. TGF-beta2 inhibited growth and DNA synthesis of cultured uveal melanocytes in a dose-dependent manner at concentrations from 0.03-10.0 ng ml-1. The growth-inhibition of TGF-beta2 was present even in serum-free medium. TGF-beta2 had little or no effect on melanogenesis of cultured uveal melanocytes. The serum used for cultivation did not contain active TGF-beta1 or TGF-beta2 as measured by immunoassay. The known amount of active TGF-beta2 in aqueous humor (0.2-0.4 ng ml-1) is sufficient to inhibit the growth of uveal melanocytes. It indicates that TGF-beta2 is a potent growth inhibit factor of uveal melanocytes and may play an important role in maintaining the non-proliferative, relatively quiescence status of uveal melanocytes in vivo.