Giuseppina Morini

The Histamine H3 Receptor

Histamine is widely distributed in the body, although with marked quantitative differences in the various species and tissues, and it produces a variety of biological effects by interacting with specific receptors on the surface of target cells.

Searching for new NO-donor Aspirin-like molecules: a new class of nitrooxy-acyl derivatives of salicylic acid

A new class of products in which the phenol group of salicylic acid is linked to alkanoyl moieties bearing nitrooxy functions has been synthesized and studied for their polyvalent actions. The products were stable in acid and neutral media, while they were hydrolyzed in human serum. Their half-lives were dependent upon the structure of alkanoyl moieties. The products showed anti-inflammatory activities similar to aspirin when tested in the carrageenan-induced paw edema assay in the rat. Interestingly, unlike aspirin, they showed reduced or no gastrotoxicity in a lesion model in rats at equimolar doses. A number of them were able to inhibit platelet aggregation induced by collagen in human platelet-rich plasma. All of the products were capable of relaxing rat aortic strips precontracted with phenylephrine in a concentration-dependent manner. Selected members of this new class of nonsteroidal anti-inflammatory drugs might represent possible safer alternatives to aspirin in different clinical settings.

(R)-Alpha-Methylhistamine Inhibits Ethanol-lnduced Gastric Lesions in the Rat: Involvement of Histamine H3 Receptors?

This study examined the gastroprotective effect of (R)-alpha-methylhistamine (MHA), a selective agonist of histamine H3 receptors. Gastric lesions were induced in the rat by administering absolute ethanol in a volume of 1 ml. Stomachs were removed 1 h later and lesions evaluated both macroscopically and histologically. MHA dose-dependently inhibited ethanol-induced lesions in the range 1-100 mg/kg both by the intragastric and intraperitoneal route. Histological findings indicated that the number of mucous granules in surface and neck cells was increased and the process of reepithelialization was rapidly promoted by MHA. Thioperamide, at 10 mg/kg, inhibited the protective effect of 10 but not of 100 mg/kg of MHA. Larger doses of thioperamide could not be tested because of an interaction with ethanol causing central nervous system effects. Famotidine and indomethacin pretreatment only partially counteracted the MHA effect. The results indicate that MHA is highly effective in preventing ethanol-induced lesions but the exact mechanism is still uncertain.

Nociceptin/orphanin FQ prevents ethanol-induced gastric lesions in the rat

Nociceptin/orphanin FQ (N/OFQ), the endogenous ligand of the NOP receptor, exerts a variety of effects on the gastrointestinal tract. The present study was aimed at evaluating the possible implication of N/OFQ in the maintenance of gastric mucosal integrity. N/OFQ was given either centrally or peripherally 30 min prior to intragastric administration (i.g.) of 1 ml/rat of ethanol (either 25% or 50%, v/v), which produces macroscopically visible gastric lesions. Intracerebroventricular (i.c.v.) injection of 2 microg/rat of N/OFQ significantly reduced lesions caused by 50% ethanol, while 1 microg/rat was enough to significantly reduce lesions caused by 25% ethanol. Intracerebroventricular injection of 5 microg/rat of the selective NOP receptor antagonist, UFP-101, completely reversed the protective effect of N/OFQ, 1 or 4 microg/rat against 25% or 50% ethanol, respectively. The intraperitoneal (i.p.) injection of N/OFQ produced a significant reduction of lesions induced by 50% ethanol, the peak effect being observed at 10 microg/kg. Intraperitoneal pretreatment with UFP-101, 120 microg/kg, completely abolished the protective effect of peripherally injected N/OFQ. Therefore, N/OFQ acts both centrally and peripherally as a protective agent against ethanol-induced gastric lesions, and its effect is mediated by NOP receptors.

Searching for new NO-donor aspirin-like molecules: Furoxanylacyl derivatives of salicylic acid and related furazans.

A new group of derivatives of salicylic acid containing NO-donor furoxans, and the related des-NO-furazans, were synthesized and evaluated as new aspirin-like molecules. Their stability was assessed in acid (pH 1) and physiological solutions (pH 7.4), and in human serum. No compound exhibited COX-inhibitory activity against COX-1 and COX-2 isoforms, when tested up to 100μM, respectively, on isolated platelets and on monocytes. Phenylsulfonyl- and cyano-substituted furoxans inhibited platelet aggregation induced by collagen in human platelet-rich plasma, through a cGMP dependent mechanism. Furoxan derivatives displayed cGMP-dependent vasodilator activities, tested on rat aorta strips precontracted with phenylephrine. All products showed anti-inflammatory activity similar to that of ASA, tested on rats by the carrageenan-induced paw edema assay. Unlike ASA, all products showed markedly reduced gastrotoxicity in a rat lesion model.

Histamine H3 and H4 receptors are expressed on distinct endocrine cell types in the rat fundic mucosa.

The histamine H3 receptor (H3R) is expressed in the central nervous system of different mammalian species [1] and is also localized to the endocrine cells of rat gastric mucosa [2]. In this study, the expression and the distribution of histamine H4 receptor (H4R) within the rat gastric fundus and its possible coexistence with H3R have been explored by immunohistochemistry using our unique immunological probes [3, 4].

Ligands for histamine H3 receptors modulate cell proliferation and migration in rat oxyntic mucosa

(R)‐α‐methylhistamine, a selective agonist of histamine H3 receptors, promotes mucus secretion and increases the number and volume of mucus‐secreting cells. The hypothesis that the increased number of mucous cells could reside in an alteration of homeostasis in the gastric epithelium was investigated. (R)‐α‐methylhistamine was administered to rats 1 h (10–100 mg kg−1 by intragastric and by intraperitoneal route) and 24 h (100 mg kg−1 by intragastric route) prior to killing. The (S)‐isomer of α‐methylhistamine (55.4 mg kg−1), 100 times less potent than the (R)‐isomer at H3 receptors, and the H3‐receptor agonist FUB 407 (9.14–91.35 mg kg−1) were intragrastically administered 1 h prior to killing. The H1‐receptor antagonist mepyramine (30 mg kg−1), the H2‐receptor antagonist famotidine (3 mg kg−1), and the H3‐receptor antagonists ciproxifan (3 mg kg−1) and clobenpropit (30 mg kg−1) were intragastrically administered 30 min before (R)‐α‐methylhistamine. Gastric tissue was processed for histology and immunohistochemistry. Within 1 h, (R)‐α‐methylhistamine and FUB 407 dose‐dependently increased the number of BrdU‐positive cells and of apoptotic cells. (S)‐α‐methylhistamine failed to modify proliferation and apoptosis. The increase in proliferation by (R)‐α‐methylhistamine was reversed by ciproxifan and clobenpropit, but not by mepyramine and famotidine. (R)‐α‐methylhistamine accelerated the differentiation towards pit cells and their outward migration 24 h after its administration. These effects were counteracted by ciproxifan. The apoptosis rate was unaffected at 24 h. These findings reveal a primary role of histamine H3‐receptor ligands in modulating cell proliferation and migration in rat fundic mucosa.

Pharmacological profile of new thioperamide derivatives at histamine peripheral H1-, H2-, H3-receptors in guinea-pig

The recent availability of potent and selective ligands, namely R-(α)-methylhistamine and thioperamide, led to conclusive progresses as regards histamine H3-receptor knowledge. The aim of this work is to investigate byin vitro tests the pharmacological properties of new amino and methyl derivatives of the H3-antagonist thioperamide. Such original compounds, developed by the modulation of the thioperamide imidazolyl moiety, were assayed at guinea-pig ileal contractile H1-, atrial chronotropic H2- and enteric neuronal H3-receptors.None of the drugs exhibited interaction with H1 or H2 sites. On electrically stimulated ileum, two of the thioperamide methyl derivatives competitively antagonized the inhibitory effect of the H3-agonist R-(α)-methylhistamine. On the basis of the Schild analysis, the more active isomer (compound IV) displayed an affinity at H3-receptors only five times lower than thioperamide. These results could contribute to elucidate further the structural features required to develop potent and selective H3-antagonists. On the other hand, to prove the hypothesized apparent heterogeneity between peripheral and central H3-sites, as emerged by pharmacological and binding studies, autoradiographic investigations are in progress.

A new furoxan NO-donor rabeprazole derivative and related compounds.

The design of hybrid molecules by combining appropriate pharmacophoric groups with NO-releasing moieties is a promising approach to the production of new drugs with interesting potential for treating a variety of diseases. Our research group has been active in this field and we have designed several such products. These compounds include NO-donor nonsteroidal antiinflammatory drugs (NSAIDs) 5] and NO-donor H2-receptor antagonists. We pursued this line because nitric oxide (NO.) has protective effects on the gastric mucosa through a number of mechanisms, such as promotion of mucus secretion, increased mucosal blood flow and decreased adherence of neutrophils to the gastric vascular endothelium. In confirmation of this idea, we herein describe the new hybrid 12, obtained by joining the 4-alkoxy-3-phenylsulfonylfuroxan substructure to rabeprazole (1; Scheme 1). It is known that furoxans are able to release NO at physiological pH, in the presence of thiol cofactors. The mechanism of this release appears to be complex and may contributed to the dramatic T1 relaxivity changes. Gd±DTPA alone did not provide any meaningful enhancement of the signal, even when a 600-fold excess was used in the experiment. In conclusion, we have developed new types of imaging probes that have the potential to be used for in vivo imaging of blood coagulation. The specific peptide derived from 2AP labeled with various reporter groups can be covalently attached to fibrin by blood coagulation factor FX13 through transglutamination. Theoretically, the same approach could be applied to other transglutaminases, which are widely found in generic tissue stabilization and also contribute to a variety of diseases, such as cancer, neurodegenerative diseases, and celiac disease. 18]

Gastrosparing Effect of New Antiinflammatory Drug Amtolmetin Guacyl in the Rat (Involvement of Nitric Oxide)

The effect of the nonsteroidal antiinflammatorydrug (NSAID) amtolmetin guacyl (AMG) on the gastricmucosa was studied in the rat by means of histologicaland functional techniques. AMG administered at 50-300 mg/kg intragastrically was virtuallydevoid of gastrolesive properties after either acute orrepeated treatment. By contrast, its metabolite,tolmetin (TOL, 15-60 mg/kg, intragastrically) caused dose-dependent gastric damage after bothtreatments. Light and electron microscopy revealed thatAMG induced minimal changes in the surface epitheliumlayer, without signs of vasocongestion or leukocytes adherence. AMG (50 mg/kg intragastrically) didnot change basal gastric potential difference (PD),whereas acetylsalicylic acid and ibuprofen induced fallsin PD of 22 and 27 mV, respectively. AMG (50 mg/kg intragastrically) reduced by 60% the fall in PDinduced by 50% ethanol; this inhibition was dependent onthe incubation time, and was maximal when AMG was given4 hr before ethanol. AMG (100 mg/kg intragastrically) induced an increase in NO synthase type 2(NOS2) activity, which was significantly different fromcontrol values, when AMG was administered 4 hr beforethe test. The metabolites of AMG, tolmetin, MED 5, and guaiacol were ineffective. Pharmacokineticanalysis of the residence time of AMG in the differentareas of the gastrointestinal tract, revealed that AMGremains in the gastrointestinal tract at least for 4 hr, the time necessary for a maximalinduction of NOS2 and for maximal protection againstethanol-induced damage. In conclusion, these dataindicate that the nonsteroidal antiinflammatory drugamtolmetin guacyl is devoid of gastrolesive properties;this gastrosparing effect seems to involve theproduction of nitric oxide, which can counteract thedamaging effects due to prostaglandin inhibition. Thepresence in the stomach of the native molecule ofamtolmetin guacyl seems to be necessary for theprotective effect observed.