B. Y. C. Wan

Effects of a selection of histone deacetylase inhibitors on mast cell activation and airway and colonic smooth muscle contraction

Studies of histone deacetylase (HDAC) inhibitors, novel anticancer drugs, in models of autoimmune diseases, asthma, and inflammatory bowel disease suggest that HDAC inhibitors may also have useful anti-inflammatory effects. Accordingly, in vitro studies relevant to asthma and inflammatory bowel disease were conducted using a selection of HDAC inhibitors: suberoylanilide hydroxamic acid (SAHA, Vorinostat), and a related branched hydroxamic acid, diamide (1), MGCD0103 and two short chain fatty acid derivatives: sodium butyrate (of use in inflammatory bowel disease) and sodium valproate. The ability of those HDAC inhibitors to modulate antigen- or agonist-induced contraction of isolated guinea pig tracheal rings and colon, agonist-induced contraction of rat colon, and histamine release from rat peritoneal mast cells was examined. Pre-incubation (up to 6 h) with 10-40 microM of SAHA, diamide (1), or MGCD0103 caused significant inhibition of the antigen-induced contraction of sensitised guinea pig tracheal rings as well as inhibition of the contraction induced by histamine, 5-hydroxytryptamine and carbachol (G-protein coupled receptor agonists), while sodium butyrate (1 mM) and sodium valproate (100 microM) were weak inhibitors. Contraction of tracheal rings by sodium fluoride (NaF, a non-selective G-protein activator), KCl and a peroxyl radical generator was blocked by MGCD0103. Additionally, MGCD0103 significantly inhibited antigen-induced histamine release from IgE antibody-sensitised rat peritoneal mast cells, and NaF-induced histamine release, as well as inhibiting NaF-induced colon contraction. Those various effects appear to involve modulation of cell signaling, probably involving G-protein coupled pathways, and further support the development of HDAC inhibitors as anti-inflammatory agents.

Inhibition of in vitro stimulated gastric acid secretion by a histamine H2-receptor antagonist, metiamide.

Abstract The effect of a specific histamine H 2 -receptor antagonist, metiamide, on gastric acid secretion induced by histamine or pentagastrin was studied in the isolated frog gastric mucosa and the isolated rat stomach. Histamine or pentagastrin approximately doubled acid secretion by the frog gastric mucosa; metiamide markedly inhibited acid secretion induced by these two stimulants. Consistent and significant stimulation of acid secretion by histamine and pentagastrin could be obtained in the isolated rat stomach provided that stomach preparations with initial low basal secretion were selected and that suitable concentrations of stimulants were used. Acid secretion induced by histamine or pentagastrin in these rat stomach preparations was strongly antagonised by metiamide. These results suggest that the basic effect of the H 2 -receptor antagonist is exerted directly on the acid secretory mechanisms in the gastric mucosa, although these in vitro findings do not rule out an additional in vivo effect of metiamide on gastric mucosal blood flow.

Role of nitric oxide in histamine release from human basophils and rat peritoneal mast cells

The effects of a range of nitric oxide (NO)-related compounds on histamine release from human basophils and rat peritoneal mast cells were studied. Basal and immunologic histamine releases from human basophils were not affected by N(omega)-nitro-L-arginine, N(omega)-nitro-L-arginine methyl ester, aminoguanidine or methylene blue (all inhibitors of NO production), sodium nitroprusside (an NO donor), L-arginine (a substrate for NO synthase) or D-arginine (the inactive enantiomer of L-arginine). In rat peritoneal mast cells, NO donors such as sodium nitroprusside, sodium nitrite and sodium nitrate, and lipopolysaccharide (an inducer of NO synthase) had little effect on basal histamine release, while 3-morpholino-sydnonimine (SIN-1, an NO donor), L-arginine and D-arginine increased this release by up to threefold. None of the inhibitors of NO production had any striking effect on histamine release induced by anti-rat immunoglobulin E (IgE), compound 48/80, sodium fluoride, phospholipase C, 1,2-dioctanoyl-sn-glycerol or ionophore A23187. However, haemoglobin was found to inhibit histamine release by anti-rat IgE or A23187 by ca. 40%. Alone of the NO donors, low concentrations of L-arginine produced a mild inhibition of histamine release induced by anti-IgE, compound 48/80 and A23187, but not other ligands, while sodium nitroprusside dose-dependently inhibited (by a maximum of ca. 30%) histamine release by anti-rat IgE, sodium fluoride or A23187. Stimulation with a variety of secretagogues or treatment with L-arginine, D-arginine, lipopolysaccharide, SIN-1 or sodium nitroprusside had no effect on NO production. Similarly, L-arginine, D-arginine or sodium nitroprusside did not change intracellular cGMP levels. On the basis of these results, it is suggested that NO does not play a significant role in the modulation of histamine release from human basophils or rat peritoneal mast cells. The effects of L-arginine, D-arginine and sodium nitroprusside may involve mechanisms unrelated to NO.

Effects of nitric oxide and hydrogen peroxide on histamine release from RBL-2H3 cells.

We have studied the effect of nitric oxide (NO) and hydrogen peroxide (H(2)O(2)), two reactive oxygen species (ROS) on histamine release (HR) from RBL-2H3 cells, a rat mucosal-type mast cell line. Marked HR was elicited by antigen (DNP-HSA), calcium ionophore A23187, sodium fluoride or phospholipase C, but not with compound 48/80 or 1,2-dioctanoyl-sn-glycerol. The NO-synthase substrate L-arginine and its inactive enantiomer (D-arginine), each on its own, induced a small but significant increase in HR above the basal level. However, the NO-donors (sodium nitroprusside or NaNO(3)) or the NO-synthase inducer lipopolysaccharide did not induce HR. Moreover, methylene blue (MB), which inhibits guanylate cyclase and N(omega)-nitro-L-arginine (L-NA), an inhibitor of NO synthase, were also without effect on either the basal HR or the L-arginine-induced HR. HR induced by A23187, DNP-HSA, sodium fluoride or phospholipase C was markedly reduced by MB, but mildly by L-NA (both at 1-100 microM). H(2)O(2) (0.01-1.0 mM) on its own did not induce HR, but it had a potent inhibitory effect on DNP-HSA- or A23187-induced HR, which was not reversed by L-NA (1-100 microM). Taken together, it seems that neither the stimulatory nor the inhibitory effects of the NO-related compounds on HR can be attributed to NO, but rather to other mechanisms. The inhibition of HR by H(2)O(2) also does not involve NO and suggests a negative feedback regulatory role for the peroxide in the allergic inflammation.

Characteristics of deoxycholic acid-induced histamine release from mast cells of guinea-pig rectocolonic mucosa and rat peritoneal cavity.

Deoxycholic acid (DA) caused a dose-related release of histamine (HR) from mast cells of rat peritoneum (RPMC) and mucosal cells of guinea pig rectocolon (RCMC). In both cell populations, DA-induced HR was: (1) accompared by a parallel release of lactate dehydrogenase (LDH), (2) not affected by metabolic inhibitors, (3) dependent on time of incubation, temperature and pH, and affected by Ca++ concentration in RPMC but not in RCMC. DA-induced HR from RCMC may be involved in certain functional disorders of the colon.

Effect of genistein on agonist-induced airway smooth muscle contraction

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Mode of action of histone deacetylase inhibitors on mast cell histamine release and colon muscle contraction

Among histone deacetylase inhibitors (HDACis) are found novel anticancer drugs, and compounds that exhibit anti-inflammatory effects[1], although detailed mode of action of the latter is unknown. Accordingly, we have studied the effects of suberoylanilide hydroxamic acid (SAHA), a related branched hydroxamic acid, 2-phenylcarbamoyloctanedioic acid 8-hydroxyamide 1-phenylamide, (referred to as diamide 1), MGCD0103 and sodium butyrate (SB), on histamine release from rat peritoneal mast cells (RPMC) and colon (rat and guineapig) smooth muscle contraction, effects that may also be relevant to inflammatory bowel disease [2]. Here we describe the inhibitory effect of HDACis on RPMC activation and smooth muscle contraction, and preliminary studies on their mode of action. The effect of propranolol, which blocks the vasoconstrictor effect of noradrenaline and inhibits agonist-induced cAMP accumulation [3], on the action of HDACi on NaF-induced guinea-pig colon (GPC) muscle contraction is described. Aminoguanidine (AMG, an inhibitor of nitric oxide [NO] synthesis) and methylene blue (MB, an inhibitor of cyclic GMP synthesis and blocker of the vascular smooth muscle relaxing effect of NO) were used to investigate whether the action of HDACis on GPC involved NO [4].

Effect of cyclosporin—A on histamine release from tracheal strips of sensitized guinea pigs

Our previous work [1, 2] has drawn attention to a sharp contrast between the effects of cyclosporin-A (CsA) in two models of allergy: 1) antigen-induced media tor release from isolated mast cells and basophil leucocytes, which CsA potently and consistently inhibits [3-5] and 2) antigen-induced contractile response of smooth musclecontaining tissues (Schultz-Dale reaction, SDR), in which CsA has little if any inhibitory effect [1, 2]. In the present work, we report the effect of CsA on antigen-induced mediator release from the isolated trachea of albuminsensitized guinea-pigs (a model for asthma) and compare it with the drugs effect on simultaneously measured contraction (SDR).

Lack of inhibition by cyclosporin in the Schultz-Dale reaction

Several research groups, including ours, have shown that cyclosporin A (CsA) has a potent inhibitory effect on mediator release from isolated mast cells and basophils [1-4]. This led to speculation that the drug might be of some value to patients with severe asthma. As a step in testing this hypothesis, we investigated the effect of CsA in the Schultz-Dale reaction in the trachea, lung parenchyma and ileum and here report the disparity between the results in this model and the effect of CsA on mast cell secretion.

Effect of cyclosporin analogues on histamine release from rat peritoneal mast cells and rat basophilic leukaemia cells

Cyclosporin A (CsA), commonly used in graft rejection prevention, is also used in the treatment of psoriasis and has undergone a clinical trial for asthma in the U.K. CsA inhibits both T-lymphocyte IL-2 secretion [1], and mast cell histamine release [2]. However, CsAs immunosuppressive and nephrotoxic effects limit its use as an antiallergic drug. The aim of this study was to compare the effects of four cyclosporin analogues on rat peritoneal mast cells (RPMC) and rat basophilic leukaemia (RBL) cells. The test compounds included the known immunosuppressants CsA, CsC and CsD [3] together with CsH. CsH is non immunosuppressive but has a greater inhibitory action on neutrophil superoxide production than the other analogues [4].