Inhibition of inducible nitric oxide synthase by acetamidine derivatives of hetero-substituted lysine and homolysine.

The synthesis and in vitro evaluation of the acetamidine derivatives of hetero-substituted lysine and homolysine analogues have identified potent inhibitors of human nitric oxide synthase enzymes, including examples with marked selectivity for the inducible isoform.

Development of a novel series of trialkoxyaryl derivatives as specific and competitive antagonists of platelet activating factor.

The synthesis and structure-activity relationship (SAR) analysis of a novel series of trialkoxyaryl derivatives, as specific and competitive inhibitors of platelet activating factor (PAF), are described. Molecular modeling comparisons of PAF with the known antagonists Ginkgolide B and L-652731 led to the selection of N-[2-[(3,4,5-trimethoxybenzoyl)oxy]ethyl]-N,N,N-trimethylammonium iodide (1) from the Wellcome registry of compounds and to the synthesis of the lead compound N-[2-[[4-(hexyloxy)-3,5-dimethoxybenzoyl]oxy]ethyl]-N,N,N- trimethylammonium iodide (3, pKb 5.43). Further SAR considerations directed the design to 2-(hexyloxy)-1,3-dimethoxy-5-[4-(4-methylthiazol-5-yl)butyl] benzene (38) (pKb 7.14), a novel, specific, and competitive inhibitor of the PAF receptor in rabbit-washed platelets.

Comparative pharmacology of analogues of S-nitroso-N-acetyl-DL-penicillamine on human platelets.

1. The effects of two new analogues of S-nitroso-N-acetyl-DL-penicillamine (SNAP), S-nitroso-N-formyl-DL-penicillamine (SNFP) and S-nitroso-DL-penicillamine (SNPL), on platelet function were examined in vitro. 2. SNAP and its analogues were potent inhibitors of platelet aggregation and inducers of disaggregation. 3. All compounds inhibited fibrinogen binding to platelets. 4. They also decreased the release of P-selectin from platelets. 5. Both inhibition of fibrinogen binding and release of P-selectin correlated with an increase in intraplatelet cyclic GMP concentrations. 6. At concentrations sufficient to inhibit platelet function and induce cyclic GMP formation (0.01-3 microM), the release of NO could be detected from SNPL but not from SNAP and SNFP. 7. Release of NO from all compounds was detected at concentrations > or = 10 microM. 8. Thus, the spontaneous release of NO from SNPL explains the actions of this compound on platelet function; however, platelet-mediated mechanisms may be involved in the release of NO from SNAP and SNFP.

A quantitative investigation into the dependence of Ca2+ mobilisation on changes in inositol 1,4,5-trisphosphate levels in the stimulated neutrophil.

1. The coupling of N-formyl-methionyl-leucyl-phenylalanine (fMet-Leu-Phe) receptor stimulation to Ca2+ mobilisation has been investigated in the human neutrophil by measuring the concentration-effect curves for inositol 1,4,5-trisphosphate (IP3) formation and Ca2+ mobilisation. 2. fMet-Leu-Phe-dependent mobilisation of intracellular Ca2+ has been monitored in fluo-3-loaded human neutrophils by measuring increases in the cytoplasmic free Ca2+ concentration ([Ca2+]i) in the presence of extracellular EGTA. Fluo-3 was used in preference to fura-2 because it was found to be more sensitive to the high Ca2+ levels seen in stimulated neutrophils. 3. fMet-Leu-Phe induced a rapid mobilisation of intracellular Ca2+ (EC50 = 2.9 +/- 0.1 nM) and increased [Ca2+]i to a maximum of 1286 +/- 184 nM. 4. The amount of IP3 in fMet-Leu-Phe-stimulated neutrophils was determined by competition with [3H]-IP3 for a specific IP3 binding protein isolated from bovine adrenocortical microsomes. Basal IP3 levels of 13.3 +/- 2.0 pmol per 10(7) cells were increased nearly 4 fold by maximally effective concentrations of fMet-Leu-Phe. 5. The EC50 for the IP3 response (95 +/- 18 nM) was much higher than that for mobilisation of intracellular Ca2+, such that only a doubling in the concentration of IP3 was required to fully mobilise intracellular Ca2+. 6. As a result of this relationship IP3 production was more sensitive than Ca2+ mobilisation to inhibition by demethoxyviridin, an inhibitor of phospholipase activation.

Demethoxyviridin and wortmannin block phospholipase C and D activation in the human neutrophil.

1. The fungal metabolite, wortmannin, has recently been shown to inhibit fMet-Leu-Phe-stimulated superoxide production and phospholipase D (PLD) activation in the human neutrophil. 2. We have found that a close structural analogue of wortmannin, demethoxyviridin, has a similar inhibitory profile but in addition blocks phosphatidylinositol 4,5-bisphosphate-specific phospholipase C and hence inositol 1,4,5-trisphosphate (IP3) formation. 3. Inhibition of fMet-Leu-Phe-stimulated PLD by demethoxyviridin was characteristically non-competitive (IC50 = 31 +/- 10 nM). 4. Inhibition of fMet-Leu-Phe-stimulation IP3 formation required concentrations almost 10 times higher (IC50 = 250 +/- 130 nM). 5. Surprisingly, demethoxyviridin only inhibited fMet-Leu-Phe-induced intracellular calcium mobilization at concentrations 100 times greater than those needed to block IP3 formation. 6. Demethoxyviridin also inhibited PLD activation induced by sodium fluoride or phorbol myristate acetate (PMA) but the concentrations required were 100 times those needed to block fMet-Leu-Phe-stimulated PLD. 7. These observations support the contention that PLD plays an important role in signal transduction in the human neutrophil and indicate that wortmannin and demethoxyviridin inhibit PLD activation at a common step in the signalling pathway. 8. Furthermore, these results suggest that demethoxyviridin may block the interaction between the chemotactic peptide receptor and a GTP-binding protein that is intimately involved in PLD activation.

Characterization of three inhibitors of endothelial nitric oxide synthase in vitro and in vivo.

1. Three analogues of L-arginine were characterized as inhibitors of endothelial nitric oxide (NO) synthase by measuring their effect on the endothelial NO synthase from porcine aortae, on the vascular tone of rings of rat aorta and on the blood pressure of the anaesthetized rat. 2. NG-monomethyl-L-arginine (L-NMMA), N-iminoethyl-L-ornithine (L-NIO) and NG-nitro-L-arginine methyl ester (L-NAME; all at 0.1-100 microM) caused concentration-dependent inhibition of the Ca2(+)-dependent endothelial NO synthase from porcine aortae. 3. L-NMMA, L-NIO and L-NAME caused an endothelium-dependent contraction and an inhibition of the endothelium-dependent relaxation induced by acetylcholine (ACh) in aortic rings. 4. L-NMMA, L-NIO and L-NAME (0.03-300 mg kg-1, i.v.) induced a dose-dependent increase in mean systemic arterial blood pressure accompanied by bradycardia. 5. L-NMMA, L-NIO and L-NAME (100 mg kg-1, i.v.) inhibited significantly the hypotensive responses to ACh and bradykinin. 6. The increase in blood pressure and bradycardia produced by these compounds were reversed by L-arginine (30-100 mg kg-1, i.v.) in a dose-dependent manner. 7. All of these effects were enantiomer specific. 8. These results indicate that L-NMMA, L-NIO and L-NAME are inhibitors of NO synthase in the vascular endothelium and confirm the important role of NO synthesis in the maintenance of vascular tone and blood pressure.

A specific inhibitor of nitric oxide formation from L-arginine attenuates endothelium-dependent relaxation.

1. The role of L-arginine in the basal and stimulated generation of nitric oxide (NO) for endothelium-dependent relaxation was studied by use of NG-monomethyl L-arginine (L-NMMA), a specific inhibitor of this pathway. 2. L-Arginine (10-100 microM), but not D-arginine (100 microM), induced small but significant endothelium-dependent relaxations of rings of rabbit aorta. In contrast, L-NMMA (1-300 microM) produced small, endothelium-dependent contractions, while its enantiomer NG-monomethyl-D-arginine (D-NMMA; 100 microM) had no effect. 3. L-NMMA (1-300 microM) inhibited endothelium-dependent relaxations induced by acetylcholine (ACh), the calcium ionophore A23187, substance P or L-arginine without affecting the endothelium-independent relaxations induced by glyceryl trinitrate or sodium nitroprusside. 4. The inhibition of endothelium-dependent relaxation by L-NMMA (30 microM) was reversed by L-arginine (3-300 microM) but not by D-arginine (300 microM) or a number of close analogues (100 microM). 5. The release of NO induced by ACh from perfused segments of rabbit aorta was also inhibited by L-NMMA (3-300 microM), but not by D-NMMA (100 microM) and this effect of L-NMMA was reversed by L-arginine (3-300 microM). 6. These results support the proposal that L-arginine is the physiological precursor for the basal and stimulated generation of NO for endothelium-dependent relaxation.

Ca2+-independent binding of [3H]phorbol dibutyrate to protein kinase C is supported by protamine and other polycations.

The activity of the Ca2+- and phospholipid-dependent protein kinase, protein kinase C (PKC), can be modulated by diacylglycerols and phorbol esters. The association of these agents with PKC is, in turn, generally understood to be dependent on Ca2+ and phospholipids. Certain substrates, e.g. protamine sulphate, are known to undergo cofactor-independent phosphorylation by PKC. We report here that, in the presence of such substrates, PKC bound 1,2-dihexanoylglycerol and phorbol dibutyrate in a Ca2+-independent manner. Histone IIIs, which is phosphorylated by PKC only in the presence of Ca2+ and phospholipid, also supported Ca2+-independent binding of 1,2-dihexanoylglycerol and phorbol dibutyrate to PKC, but to a lesser extent than did protamine. Support for Ca2+-independent binding was also exhibited by non-peptide polycations (e.g. DEAE-cellulose DE52), indicating that recognition of the catalytic site is not a prerequisite for this effect. The natural polyamines spermine and putrescine did not have this property, however. The affinity of PKC for phorbol dibutyrate and 1,2-dihexanoylglycerol was found to be unchanged by the presence of substrates or DE52. It is proposed that, in the absence of Ca2+, certain polycations favour expression of the diacylglycerol/phorbol ester binding site by stabilizing the active conformation of PKC.

Evidence that a second stereochemical centre in diacylglycerols defines interaction at the recognition site on protein kinase C.

The interaction of novel diacylglycerol analogues at the recognition site on protein kinase C has been evaluated using a modified [3H]phorbol dibutyrate binding assay and an established kinase activation assay. Studies with the 3-methyl analogues of 1,2-dihexanoyl-sn-glycerol have revealed a preferred stereochemical configuration at the C-3 position. Other chemical modifications have extended existing structure/activity relationships by showing that carbamates and sulphonyl esters cannot substitute for carboxylate esters and that cyclic acyl groups are active. Thus, most, if not all of the functionalities in the diacylglycerol molecule are required for interaction at the receptor on protein kinase C. Stereochemical specificity is required at C2 and C3.

The effects of a novel series of selective inhibitors of arachidonate 5-lipoxygenase on anaphylactic and inflammatory responses.

In conclusion, we have described a novel series of acetohydroxamic acids that are potent and selective inhibitors of arachidonate 5-lipoxygenase in vitro and in vivo. In addition, we have shown that these compounds attenuate "leukotriene-dependent" anaphylactic bronchospasm, the accumulation of inflammatory leukocytes, and the development of fever in experimental models. It now remains to be determined if these compounds have any therapeutic value in man.

Decrease of cellular ATP by dihexanoylglycerol may limit responses to protein kinase C activation.

1,2-sn-Dihexanoylglycerol (HHG) reduced the ATP content of HL-60 cells. This concentration-related (10-100 microM) effect reached a maximum of over 90%, was enantiomerically specific and not accompanied by release of lactate dehydrogenase. Oleoylacetylglycerols (3-100 microM) had no effect on ATP levels while phorbol dibutyrate (PDBu, 0.01-1 microM) decreased ATP content of HL-60 cells by up to 40%. Responses stimulated by HHG became limited as the concentration was increased above 10 microM, this being manifest as either a low maximum response compared to PDBu (superoxide release) or a bell-shaped concentration-effect curve (degranulation). HHG (30-100 microM) inhibited PDBu-stimulated superoxide release, this inhibition being enantiomerically specific. It is probable that the effect of HHG on ATP content impairs cellular responses mediated through protein kinase C activation.

Inhibition of phorbol ester stimulated superoxide production by 1-oleoyl-2-acetyl-sn-glycerol (OAG); fact or artefact?

OAG-stimulated superoxide (O2) production by HL-60 granulocytes showed enantiomeric specificity but reached a maximum of only 5% of that produced by either phorbol myristate acetate (PMA) or phorbol dibutyrate (PDBu). At 10-100 microM, OAG displaced specifically-bound [3H]PDBu from intact HL-60 cells by only 25%, suggesting limited cell penetration. OAG (10-100 microM) also inhibited PDBu-stimulated O2 production by 25%; this inhibition was enantiomerically specific. However, at a lower concentration (3 microM), both enantiomers of OAG fully blocked O2 production stimulated by PMA (0.5 microM). This inhibition is probably artefactual, due to the hydrophobic PMA physically associating with OAG in the extracellular fluid.

Doxantrazole, an antiallergic agent orally effective in man.

In-vivo studies have demonstrated antiallergic properties in doxantrazole when given orally to rats. These properties were confirmed in work with in-vitro preparations. No significant animal toxicity has been detected. 200 mg. given by mouth inhibited the immediate-type asthmatic response in volunteer patients challenged with specific antigen.