Potential role of histamine monochloramine in a rabbit model of ileitis

Betahistine dihydrochloride transdermal delivery via optimized thermosensitive gels: percutaneous absorption evaluation using rat growth as a biomarker

The aim of this study was to develop and optimize a betahistine dihydrochloride (BH) thermoreversible bioadhesive gel intended for transdermal delivery. The gels were obtained via cold method. A full factorial design was employed to investigate the joint effect of Poloxamer 407 concentration (18 and 20%), adhesive polymer type (Polyvinyl pyrolidone, Hydroxypropyl methylcellulose, and Carbopol 934), and adhesive polymer concentration (0.5 and 1.5%) on gelling temperature, viscosity at 37 °C, and adhesion strength. Data collected were analyzed using multiple linear regression. A desirability index approach with relative importance weight was used to choose the most desirable formulation. F4 (20% Poloxamer+1.5% Carbopol) was selected for further characterization. F4 released 96.97% drug in 12 h across hairless rat skin. F4 gelation temperature and time were 36 ± 0.35 °C, and 6 ± 0.7 min, respectively. F4 adhesive force was 8835.68 dyne/cm². F4 was tested for its appetite suppressing effect in a rat model and it was evaluated histopathologically. Rats' chow intake and weight gain was significantly decreased with no signs of inflammation or lipolysis when the optimized BH gel formulation, F4, was compared with untreated animals and animals treated with BH free gel. The results suggest that BH is percutaneously absorbed from the gel base and that the BH gel is tolerable. The desirability index approach with relative importance weight of responses was effective in determination of the optimum formulation. BH is systemically effective and well-tolerated when applied topically in hydrogel-based systems. The Carbopol-Poloxamer gel is a promising modality for transdermal delivery of BH.

Pathophysiological Mechanisms of Gastrointestinal Toxicity

Humans swallow a great variety and often large amounts of chemicals as nutrients, incidental food additives and contaminants, drugs, and inhaled particles and chemicals, thus exposing the gastrointestinal tract to many potentially toxic substances. It serves as a barrier in many cases to protect other components of the body from such substances and infections. Fortunately, the gastrointestinal tract is remarkably robust and generally is able to withstand multiple daily assaults by the chemicals to which it is exposed. Some chemicals, however, can affect one or more aspects of the gastrointestinal tract to produce abnormal events that reflect toxicity. It is the purpose of this chapter to evaluate the mechanisms by which toxic chemicals produce their deleterious effects and to determine the consequences of the toxicity on integrity of gastrointestinal structure and function. Probably because of the intrinsic ability of the gastrointestinal tract to resist toxic chemicals, there is a paucity of data regarding gastrointestinal toxicology. It is therefore necessary in many cases to extrapolate toxic mechanisms from infectious processes, inflammatory conditions, ischemia, and other insults in addition to more conventional chemical sources of toxicity.

Effect of γ-Aminobutyric Acid (GABA) Producing Bacteria on In vitro Rumen Fermentation, Biogenic Amine Production and Anti-oxidation Using Corn Meal as Substrate

The effects and significance of γ-amino butyric acid (GABA) producing bacteria (GPB) on in vitro rumen fermentation and reduction of biogenic amines (histamine, methylamine, ethylamine, and tyramine) using corn meal as a substrate were determined. Ruminal samples collected from ruminally fistulated Holstein cows served as inoculum and corn was used as substrate at 2% dry matter (DM). Different inclusion rates of GPB and GABA were evaluated. After incubation, addition of GPB had no significant effect on in vitro fermentation pH and total gas production, but significantly increased the ammonia nitrogen (NH3-N) concentration and reduced the total biogenic amines production (p<0.05). Furthermore, antioxidation activity was improved as indicated by the significantly higher concentration of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) among treated samples when compared to the control (p<0.05). Additionally, 0.2% GPB was established as the optimum inclusion level. Taken together, these results suggest the potential of utilizing GPB as feed additives to improve growth performance in ruminants by reducing biogenic amines and increasing anti-oxidation.

Chlorine transfer between glycine, taurine, and histamine: reaction rates and impact on cellular reactivity

Hypochlorous acid formed by activated neutrophils reacts with amines to produce chloramines. Chloramines vary in stability, reactivity, and cell permeability. We have examined whether chloramine exchange occurs between physiologically important amines or amino acids and if this affects interactions of chloramines with cells. We have demonstrated transchlorination reactions between histamine, glycine, and taurine chloramines by measuring chloramine decay rates with mixtures as well as by mass spectrometry. Kinetic analysis suggested the formation of an intermediate complex with a high Km. Apparent second-order rate constants, determined for concentrations <Km, were 19.4, 23.8, 6.0, and 7.5 M(-1) min(-1) for glycine chloramine (Gly-Cl) and taurine, Gly-Cl and histamine, histamine chloramine and glycine, and taurine chloramine (Tau-Cl) and glycine, respectively. Thus with 10 mM amine concentrations, half-lives for chloramine exchange are of the order of a few minutes. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) activity in cells was measured as an indicator of permeability of the chloramines. When endothelial or Jurkat cells were treated in Hanks' buffer, Gly-Cl inhibited GAPDH, whereas Tau-Cl, which does not penetrate the cells, did not. Adding glycine to Tau-Cl brought about inhibition, whereas taurine mitigated the effect of Gly-Cl. For cells in full medium, high chloramine concentrations were needed to inhibit GAPDH because of scavenging by methionine and other constituents. In methionine-free medium, chlorine exchange resulted in GAPDH inhibition by Tau-Cl, whereas Gly-Cl was less effective than in Hanks' buffer. Thus interchange between chloramines occurs readily and modulates their cellular effects.

Chlorine transfer between glycine, taurine, and histamine: reaction rates and impact on cellular reactivity

Hypochlorous acid formed by activated neutrophils reacts with amines to produce chloramines. Chloramines vary in stability, reactivity, and cell permeability. We have examined whether chloramine exchange occurs between physiologically important amines or amino acids and if this affects interactions of chloramines with cells. We have demonstrated transchlorination reactions between histamine, glycine, and taurine chloramines by measuring chloramine decay rates with mixtures as well as by mass spectrometry. Kinetic analysis suggested the formation of an intermediate complex with a high K(m). Apparent second-order rate constants, determined for concentrations <K(m), were 19.4, 23.8, 6.0, and 7.5 M(-1) min(-1) for glycine chloramine (Gly-Cl) and taurine, Gly-Cl and histamine, histamine chloramine and glycine, and taurine chloramine (Tau-Cl) and glycine, respectively. Thus with 10 mM amine concentrations, half-lives for chloramine exchange are on the order of a few minutes. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) activity in cells was measured as an indicator of permeability of the chloramines. When endothelial or Jurkat cells were treated in Hanks' buffer, Gly-Cl inhibited GAPDH, whereas Tau-Cl, which does not penetrate the cells, did not. Adding glycine to Tau-Cl brought about inhibition, whereas taurine mitigated the effect of Gly-Cl. For cells in full medium, high chloramine concentrations were needed to inhibit GAPDH because of scavenging by methionine and other constituents. In methionine-free medium, chlorine exchange resulted in GAPDH inhibition by Tau-Cl, whereas Gly-Cl was less effective than in Hanks' buffer. Thus interchange between chloramines occurs readily and modulates their cellular effects.

Histamine chloramine reactivity with thiol compounds, ascorbate, and methionine and with intracellular glutathione

Histamine is stored in granules of mast cells and basophils and released by inflammatory mediators. It has the potential to intercept some of the HOCl generated by the neutrophil enzyme, myeloperoxidase, to produce histamine chloramine. We have measured rate constants for reactions of histamine chloramine with methionine, ascorbate, and GSH at pH 7.4, of 91 M(-1)s(-1), 195 M(-1)s(-1), and 721 M(-1)s(-1), respectively. With low molecular weight thiols, the reaction was with the thiolate and rates increased exponentially with decreasing thiol group pK(a). Comparing rate constants for different chloramines reacting with ascorbate or a particular thiol anion, these were higher when there was less negative charge in the vicinity of the chloramine group. Histamine chloramine was the most reactive among biologically relevant chloramines. Consumption of histamine chloramine and oxidation of intracellular GSH were examined for human fibroblasts. At nontoxic doses, GSH loss over 10 min was slightly greater than that with HOCl, but the cellular uptake of histamine chloramine was 5-10-fold less. With histamine chloramine, GSSG was a minor product and most of the GSH was converted to mixed disulfides with proteins. HOCl gave a different profile of GSH oxidation products, with significantly less GSSG and mixed disulfide formation. There was irreversible oxidation and losses to the medium, as observed with HOCl and other cell types. Thus, histamine chloramine shows high preference for thiols both in isolation and in cells, and in this respect is more selective than HOCl.

Permeation-enhancing effect of aloe-emodin anthrone on water-soluble and poorly permeable compounds in rat colonic mucosa

The aims of this study were to examine the enhancing effects of aloe-emodin anthrone (AEA) on the colonic membrane permeability of water-soluble and poorly permeable compounds and to clarify the mechanism of the permeation-enhancing activity of AEA. The permeation-enhancing activity of AEA was estimated from changes in the permeability coefficient of 5(6)-carboxyfluorescein (CF) in rat colonic mucosa using a Ussing-type chamber. Various inhibitors were used to investigate the mechanism of action of AEA. The structural change in the membrane and the cytotoxicity of AEA in the intestinal mucosa were evaluated by measuring the electrical resistance of the membrane (R(m)) and lactate dehydrogenase (LDH) activity, respectively. AEA significantly increased the permeation of CF in a dose-dependent manner. The enhanced permeability was significantly suppressed by a histamine H(1) receptor antagonist, pyrilamine, and a mast cell stabilizer, ketotifen, but not by a histamine H(2) receptor antagonist, cimetidine. The enhancing effect was also inhibited by an inhibitor of protein kinase C (PKC). Potential difference and short-circuit current values decreased, while R(m) values remained constant throughout the experiment. The addition of AEA to the mucosal solution decreased R(m) to 30%, but then remained constant. LDH activity with AEA was not significantly different from that of the control. In conclusion, AEA is a candidate for effective absorption enhancers without damage of the membrane and cytotoxicity. We propose that AEA stimulates mast cells within the colonic mucosa to release histamine, which probably bind to the H(1) receptor. The intracellular PKC route activated by H(1) receptor activation enhances the permeability of water-soluble and poorly permeable drugs via opening of tight junctions in rat colonic membrane.

Myeloperoxidase-catalyzed chlorination of histamine by stimulated neutrophils

To investigate neutrophil interactions with mediators released by mast cells at sites of inflammation, stimulated neutrophils were incubated with histamine. No accumulation of chlorinated histamine derivatives was detected in the medium. Instead, histamine inhibited the formation of chloramine derivatives of other amines. Incubation with radiolabeled histamine resulted in rapid uptake of label into the cells, and most of the label could be extracted and recovered as histamine. About 3% of the label taken up was incorporated into acid-precipitable forms. Uptake depended on myeloperoxidase (MPO)-catalyzed formation of chlorinating agents. Uptake was promoted by adding MPO and blocked by the MPO inhibitor dapsone, catalase, scavengers for hypochlorous acid and chloramines, or in a low-chloride medium, but not by histamine receptor antagonists. Incubation of histamine with MPO, hydrogen peroxide, and chloride resulted in formation of mono- and dichloramine derivatives of the primary amino group. Above pH 7.0, the chloramines were primarily in uncharged, lipophilic forms as indicated by partitioning into organic solvents. Histamine is a cation at neutral pH, but chlorination eliminated the charge on the amino group and shifted the pKa of the imidazole ring, resulting in formation of neutral histamine-chloramines. Incubation of neutrophils or other blood cells with radiolabeled histamine-chloramines resulted in rapid uptake of label, indicating membrane permeation by the uncharged, lipid-soluble forms. Incubation with labeled histamine-dichloramine also resulted in acid-precipitable incorporation. The results indicate that MPO-catalyzed chlorination of histamine could modulate histamine activity, tissue distribution, and metabolism at sites of inflammation.

Immune-mediated effects upon oral challenge of ovalbumin-sensitized Brown Norway rats: further characterization of a rat food allergy model

Although several in vivo antigenicity assays using parenteral immunization are operational, no full validated enteral models are available to study food allergy and allergenicity of food proteins. To further validate a developed enteral Brown Norway (BN) rat food allergy model, systemic and local immune-mediated reactions were studied upon oral challenges. The animals were exposed to ovalbumin (OVA) by daily gavage dosing (1 mg OVA/rat/day) for 6 weeks, without the use of an adjuvant, or by intraperitoneal injections with OVA together with AL(OH)3. Subsequently, effects on breathing frequency, blood pressure, and gastrointestinal permeability were investigated upon an oral challenge with 10 to 100 mg OVA in vivo. In both parenterally and orally sensitized rats, an increase in gut permeability (increased passage of beta-lactoglobulin as bystander protein) was determined between 0.5 and 1 h after an oral OVA challenge was given. An oral challenge with OVA did not induce a clear effect on the respiratory system or blood pressure in the majority of the animals. However, some animals demonstrated a temporary decrease in breathing frequency or systolic blood pressure. Upon oral challenge with OVA of orally and parenterally sensitized animals, local effects were observed in all animals whereas systemic effects were observed at a low frequency, which reflects the situation in food allergic patients after an oral challenge. These studies show that the BN rat provides a suitable animal model to study oral sensitization to food proteins as well as immune-mediated effects after oral challenge with food proteins.

Release of the mucosal mast cell granule chymase, rat mast cell protease-II, during anaphylaxis is associated with the rapid development of paracellular permeability to macromolecules in rat jejunum

The soluble granule chymase, rat mast cell protease-II (RMCP-II), is abundantly expressed in intestinal mucosal mast cells (MMC) but its function is not known. One hypothesis is that RMCP-II degrades the epithelial basement membrane and promotes the loss of enterocytes typically associated with type I hypersensitivity reactions in the rat. To test this hypothesis more directly, ex vivo perfusion of the cranial mesenteric artery and jejunal lumen was used to monitor the anaphylactic release of RMCP-II and its effects on mucosal permeability and epithelial integrity. Within 2 min of intravascular challenge with soluble adult Nippostrongylus brasiliensis worm antigen there was a 1,000-fold (P < 0.02) increase in the concentration of RMCP-II in the vascular perfusate from the jejunum of Nippostrongylus-sensitized rats but not the controls. Similarly, translocation of RMCP-II into the gut lumen increased 10-fold (P < 0.02) after 2 min only in worm antigen-challenged immune rats. Using an identical protocol, but incorporating Evans blue-labeled human serum albumin (EB-HSA) in the vascular perfusate, the timing of the release of RMCP-II into the two compartments was very similar to the first experiment and furthermore the translocation of EB-HSA increased 18-fold (P < 0.05) after 4 min in sensitized rats challenged with worm antigen. To examine the effects of RMCP-II more directly 1 mg of the highly purified chymase was introduced into the cranial mesenteric artery in ex vivo perfused normal rats. A significant (P < 0.05) 70-fold increase in concentration of RMCP-II in jejunal perfusate occurred after 6 min. In a repeat dose-response experiment, infusion of 0.375, 0.75, or 1.5 mg of RMCP-II, together with EB-HSA, established that the cumulative amounts of RMCP-II and EB-HSA translocated from the vasculature to the gut lumen in each perfusion (during the 10-min period of RMCP-II infusion) were significantly correlated. Analysis of intestinal perfusates by SDS-PAGE and by Western blotting using monoclonal anti-RMCP-II antibody confirmed that there was a concomitant translocation of both the protease and EB-HSA into the gut lumen. Histological evaluation of the mucosa failed to reveal any significant morphological change in any of the experiments. The rapid development of macromolecular leak, its association with the translocation of RMCP-II, and the absence of gross epithelial lesions, suggest for the first time that a mast cell granule chymase increases epithelial permeability via a paracellular route and implies that the substrate may be a protein, or proteins, in the epithelial junctional complex.

Histamine chloramines have a persistent stimulating effect on histamine H2 receptors and gastric acid secretion

Histamine plays an important role in the control of gastric acid secretion. Recently, chlorinated derivatives of histamine have been identified as having multiple effects on the intestinal tract. The aim of this study was to investigate the role of histamine chloramines on gastric acid secretion. We compared the effects of histamine and histamine chloramines on the histamine H2 receptors in vitro using guinea pigs and on gastric acid secretion in rats. With respect to the effects on histamine H2 receptors, histamine monochloramine showed agonist effects similar to those seen with histamine, but the agonist effects of histamine dichloramine were about half those of histamine. Unlike histamine effects, the histamine H2 receptor agonist effects of histamine monochloramine and histamine dichloramine did not disappear after repeated washout. With respect to the stimulation of gastric acid secretion in vivo, histamine monochloramine was similar to histamine, while the effect of histamine dichloramine was 42.2-52.7% of that of histamine. The recovery time to the basal secretory level after completion of stimulation by histamine chloramines was significantly prolonged compared with histamine. These results suggest that histamine chloramines, which bind strongly with histamine H2 receptors, may delay the termination of gastric acid secretion and increase the burden on the gastric and duodenal mucosa.

Nitric oxide release in response to gut injury

We evaluated nitric oxide release in several models of intestinal inflammation through luminal nitrite concentrations. In anesthetized rabbits, piglets, and guinea pigs, luminal lavages were collected from loops of normal or injured small intestine. Lavages were analyzed spectrophotometrically for nitrite (Griess reagent) and protein. Myeloperoxidase (MPO) content of intestinal segments was used as an index of granulocyte infiltration and intestinal inflammation. Acute ileal inflammation was induced by luminal acetic acid + casein in rabbits and luminal deoxycholate in neonatal piglets and adult rabbits. Chronic ileitis was induced in guinea pigs by intraluminal trinitrobenzenesulfonic acid. In each model nitrite levels in ileal lavages were significantly greater than control loops/animals. Increased luminal protein and intestinal MPO activity paralleled the changes in nitrite levels. To determine whether nitric oxide production influenced mucosal repair, segments of ileum were perfused with the L-arginine antagonist NG-nitro-L-arginine methyl ester (L-NAME, 10 mg/ml) after acute acetic acid + casein exposure. L-NAME administration reversed the decline in epithelial permeability characteristic of epithelial restitution, causing an increase in epithelial permeability which was readily reversible. These results suggest that nitrite production is a useful index of gut injury and that nitric oxide may contribute to the functional repair of the epithelial barrier under acute conditions.

Rabbit gut permeability in response to histamine chloramines and chemotactic peptide

Granulocyte-derived chlorinated amines and bacterial formyl peptides are thought to enhance epithelial permeability. In the current study, gut permeability to [51Cr]ethylenediaminetetraacetic acid (EDTA) was monitored in response to luminal formyl-methionyl-leucyl-phenylalanine (fMLP) and histamine monochloramine and dichloramine. Responses were determined in rabbits during states of basal and elevated permeability. Luminal fMLP had minimal effects of gut permeability in control and injured states. Histamine monochloramine or dichloramine enhanced epithelial permeability under basal conditions; this effect was exaggerated by a pre-existing injury. Both histamine monochloramine and dichloramine retained full histamine agonist properties, and a combination of antioxidant and antihistamine therapy was required to block this increase in gut permeability. Whereas histamine chloramines caused a dose-dependent cytotoxicity in rat-cultured enterocytes, marked histological changes to the mucosa were not evident, nor were mucosal glutathione levels depleted. As histamine chloramines retain the histaminergic and oxidizing potential of their precursors, they represent a unique form of inflammatory mediator, although their highly reactive nature precludes in vivo confirmation of their formation.

Gastrointestinal food hypersensitivity: basic mechanisms of pathophysiology

Gastrointestinal symptoms occur in a large number of patients with food allergies. Immediate hypersensitivity mechanisms may give rise to the nausea, vomiting, abdominal pain, and diarrhea experienced by these patients. However, there are limited human data about the pathophysiological basis for these symptoms. Most of the available information comes from a variety of animal models. This article reviews the literature using models of intestinal food hypersensitivity, as well as human studies, that have contributed to our understanding of the pathophysiological mechanisms in gastrointestinal food hypersensitivity.