Comparison of immunomodulative effects of histamine-2 receptor antagonists in gastric cancer patients: Focus on the lymphoblastogenesis and cytotoxicity of peripheral blood mononuclear cells

A proposed mechanism of the immunomodulative effects of histamine-2 receptor antagonist (H2-RA) has been considered to be the inhibition of suppressor T-lymphocyte activity, an increase in interleukin-2 production of helper T-lymphocytes, and an enhancement of natural killer cell activity. Since there is a lack of comparative data about the immunomodulative effects of various H2-RAs, cimetidine, ranitidine and famotidine on peripheral blood mononuclear cells (PBMC), study of the comparison of the actions of H2-RA will be required. We compared the immunomodulative effect of each H2-RA on PBMC in patients with gastric cancer. DNA synthesis, cytotoxicity of PBMC against K562 cells and gastric cancer cell lines, and the levels of supernatant soluble interleukin-2 receptor (sIL-2R) were measured after the addition of each H2-RA, respectively. Increased suppressor cell activities were attenuated and restored to the levels of normal controls by the addition of cimetidine to H2-RA. Statistically significant lymphoblastogenesis and cytotoxicity against K562 cells were observed only in cimetidine-treated PBMC (P<0.05). Such effects were not observed in ranitidine- or famotidine-treated PBMC. Neither cimetidine- nor ranitidine-activated PBMC showed any significant cytotoxicity against gastric cancer cells. Significantly increased levels of sIL-2R were found in supernatants obtained from culture flasks treated with cimetidine or ranitidine and phytohemagglutinin (P<0.01). A significant correlation was found between the cytotoxicity of cimetidine- or ranitidine-treated PBMC and supernatant sIL-2R (P<0.05). In conclusion, the most strongly modulative substance among H2-RAs was cimetidine and the least modulative drug was famotidine. These results might be due to their structural differences. The immunological effects of H2-RA are unlikely to be mediated via specific interaction at the H2 receptor.     

Pharmacology of the novel H2 antagonist famotidine: In vitro studies

The novel antiulcer drug famotidine was found to be a potent and selective inhibitor of histamine H2 receptors. Its activity on different parameters involving H2 receptors was higher than that of other compounds of the family: pA₂ values were 8.33, 7.86 and 7.83 in the guinea pig atria, guinea pig papillary muscle and isolated rat gastric secretion, respectively. Apart from quantitative differences, famotidine differred from the other compounds, since it caused a competitive antagonism only at low concentrations and an unsurmountable antagonism at higher concentrations. The duration of the inhibitory action on the in vitro gastric secretion resembled that of cimetidine and ranitidine. Famotidine was highly effective (approximately 10 times as potent as ranitidine) also on the rat uterus (unsurmountable antagonism) and on the guinea pig gallbladder (pA₂value=7.71). Famotidine was apparently devoid of non-specific effects converning the gastrointestinal motility even at very high concentrations (10^–4 M). In this respect, famotidine appeared to be more selective than cimetidine and ranitidine at the H2 receptor level. The high potency, the peculiarity of the antagonism and the lack of side-effects on a number of isolated preparations, indicate this H2 antagonist as a very peculiar member of the group.     

Mechanism of action of H2-antagonists on histamine-or dimaprit-stimulated H2-receptors of spontaneously beating guinea-pig atrium

Cimetidine, ranitidine and famotidine are antagonists of the histamine H₂-receptors on the spontaneously beating right atrium of the guinea pig. When analyzed by the classical Schild method theirpA ₂-values are respectively: 6.3, 6.8 and 7.7 with dimaprit as agonist and 5.8, 6.5 and 7.7 with histamine as agonist. Radiolignad-displacement studies with [³H]-tiotidine as radioligand resulted inpK _d values for cimetidine, ranitidine and famotidine of 6.3; 6.9 and 8.2 respectively.In dimaprit-stimulated atria all antagonists added at concentrations above theirK _d values depressed the maximal increase in frequency. In the presence of histamine this effect was much less pronounced and only visible at concentrations of ranitidine and famotidine around 10 ·K _d.The rightward shift of the curves as well as the decrease inE _max are reversible but the dissociation constants of the antagonists are small (less than 10^–3 s^–1).The spontaneously beating right atrium showed receptor reserve for histamine and virtually no receptor reserve for dimaprit.The results have been interpreted in a model in which H₂-antagonists act mainly by competing with the agonist for the histamine receptor site but have in addition a distinct affinity for a secondary site on the receptor. Occupation of this site by the antagonist prevents building up of the stimulus elicited by the agonist and thus decreases theE _max. In systems with receptor reserve (histamine) the effect of antagonist binding to the secondary binding site is seen only at high concentration of antagonist while in absence of receptor reserve (dimaprit) the depression ofE _max is directly visible.Simulations of the model show that the affinity of this secondary binding site is 50- (famotidine) to 100-(cimetidine and ranitidine) fold lower than for the agonist binding site.     

The effect of ranitidine on gastric acid secretory response curves to histamine,pentagastrin or bethanechol in the dog with a heidenhain pouch

The H₂-receptor antagonists ranitidine and cimetidine were tested against gastric secretory dose-response curves to histamine, pentagastrin and bethanechol in the Heidenhainpouch dog. Histamine-induced gastric secretion was antagonized in a competitive manner by both ranitidine and cimetidine, but ranitidine was approximately 8 times more potent than cimetidine. Pentagastrin-induced secretion was markedly reduced by ranitidine and cimetidine but this antagonism was not competitive in nature. Bethanechol-induced gastric secretion was slightly reduced by both drugs. These findings are discussed in relation to he physiological control of gastric secretion.     

Gastric mucosal cell proliferation in ethanol-induced chronic mucosal injury is related to oxidative stress and lipid peroxidation in rats

The oxygen free radicals-induced lipid peroxidation (LP) has been implicated in the pathogenesis of acute ethanol-induced gastric mucosal lesions. However, the role of LP in the generation of chronic gastric mucosal injury is unknown. We have developed a model of chronic mucosal injury induced by continuous ethanol ingestion for 5 days and characterized by marked alterations in plasma membranes from gastric mucosa. Therefore, LP was evaluated in this experimental model. Indicators of peroxidative activity, mucosal glutathione content, thymidine kinase activity (an index of cell proliferation), and histamine H2-receptor (H2R) binding constants were quantified in animals undergoing gastric mucosal damage. The effect of famotidine, a H2R antagonist that readily ameliorates the chronic mucosal injury, was also tested. Increased free radicals and LP levels were detected during gastritis; however, a second, higher peak of LP was noted in mucosal plasma membranes after ethanol withdrawal (recovery period). This further increase of LP coincided with active cell proliferation, decreased mucosal glutathione levels, and diminished specific cimetidine binding by H2R. Administration of famotidine accelerated the mucosal proliferative process, inducing the second lipoperoxidative episode sooner, and preserved the content of glutathione. In addition, LP correlated directly with cell proliferation and inversely with mucosal membrane cimetidine binding. In conclusion, LP seems to be involved in chronic ethanol-induced gastric mucosal injury. However, a further enhancement of plasma membrane LP occurred, associated with increased DNA synthesis and diminished cimetidine binding by membrane H2R. Therefore, increased LP could also participate in the compensatory mucosal proliferation initiated after ethanol withdrawal.     

Retinoic acid induces translocation of protein kinase C (PKC) and activation of nuclear PKC (nPKC) in rat splenocytes

Retinoic acid (RA), a vitamin A metabolite, has marked effects on growth of normal and malignant cells; however, the exact mechanism of action remains unclear. The effect of two RA analogs, 13-cis-RA and all-trans-RA, on transmembrane signalling processes was investigated in rat splenocytes. Treatment of rat splenic cells with these retinoic acid analogs resulted in translocation of protein kinase C (PKC) from the cytosol to the membrane. Previous studies have described nuclear RA receptors (RARs and RXRs) for several species and the biologic activity of RA has been shown to be mediated by specific interaction with these nuclear receptors. Thus, activation of nuclear pool(s) of protein kinase C (nPKC) by RA analogs was also studied. Rat splenocyte nuclei pure by enzymatic and electron microscope criteria demonstrated a biphasic pattern of bell-shaped curves for both cis- and trans-RA with maximum statistically significant peak of phosphate incorporation into endogenous substrates at 10⁻¹⁶ M cis-RA and 10⁻¹⁶-10⁻¹⁷ M trans-RA. A monoclonal antibody to PKC and the PKC inhibitors, H-7, sphingosine, and staurosporine, blocked the RA-stimulated nuclear phosphorylation. The ability of RA to activate cell membrane PKC resulting in an increase in particulate PKC activity correlates well with the activation of nPKC since the particulate fraction would include nuclear enzyme systems. This ability of RA to activate nPKC and possibly affect the growth status of a cell may provide a missing link to our understanding of the cellular sites of action for this vitamin.     

Reversal of histamine-mediated immunosuppression by structurally diverse histamine type II (H2) receptor antagonists

The effect of a series of structurally-diverse histamine type II (H2)-receptor antagonists on histamine-mediated immunosuppression of human peripheral blood lymphocytes (HPBL) has been examined. This analysis of structure--activity relationships was undertaken to examine the validity of the recent proposal arising from clinical studies that H2-receptor antagonists containing a furan ring were devoid of the effects on lymphocyte function reported previously in studies using cimetidine and other H2-receptor antagonists containing an imidazole nucleus. Cimetidine and two furan-containing antagonists, ranitidine and SKF 93479, were found to be devoid of any effect on PHA-induced proliferation of human peripheral blood lymphocytes over a wide concentration range (10(-4) to 10(-10)M). At high drug concentrations (10(-3)M) significant suppression of mitogen stimulation was observed but this was accompanied by significant cytotoxicity. All three antagonists were effective in reversing the suppression of PHA-stimulation of HPBL induced by exogenous histamine. Reversal of histamine-induced immunosuppression was obtained at drug concentrations (2.0 X 10(-4) to 1.0 X 10(-6)M) which were non-toxic and did not affect PHA-induced proliferation in the absence of histamine. Ranitidine was the most potent antagonist in reversing histamine-mediated immunosuppression. The ability of structurally-diverse H2-receptor antagonists to modify the action of histamine on lymphocyte function lends support to the view that histamine exerts its effects via classical H2-receptors. The ability of ranitidine to alter lymphocyte responsiveness in analogous fashion to cimetidine indicates that the possibility of alterations in immune function should be considered in clinical studies using ranitidine and other furan-containing H2-receptor antagonists.     

Inhibitory effect of famotidine on cat gastric secretion

The inhibitory effect of the novel H2 receptor antagonist famotidine was studied in conscious gastric fistula cats against dimaprit-induced hypersecretion, in comparison with ranitidine. On the secretory plateau induced by dimaprit (2 mol kg^–1 h^–1) famotidine (0.05–0.2 mol kg^–1 i.v.) exerted a dose-dependent inhibitory effect, being approximately 4.5 times as potent as ranitidine (ID₅₀ values were 0.067±0.015 and 0.30±0.025 mol kg^–1 for famotidine and ranitidine, respectively). No significant differences were found between the two drugs, as for the time-course of the inhibitory effect. Famotidine (0.01–0.32 mol kg^–1 h^–1) caused a parallel displacement of the dose-response curve to dimaprit to the right, without reducing the maximum response to the stimulant, thus behaving as a competitive antagonist, like ranitidine. pA₂ values for famotidine and ranitidine were 7.95 and 6.92, respectively. In the same range of doses famotidine dose-dependently reduced also the secretory response to histamine. From these data it was concluded that famotidine is a potent histamine H2 receptor antagonist in the cat gastric mucosa; moreover, conversely from in vitro data, the antagonism was surmountable even at the highest doses tested. In vivo experiment, therefore, did not reveal any particular feature of this compound, apart from the undoubtedly high potency, in comparison with other members of the family.     

Histaminwirkungen am Herzen unter besonderer Berücksichtigung kardialer Nebenwirkungen von H2-Rezeptor-Antagonisten

Summary The existence of cardiac h₁- and h₂-receptors is evidenced by pharmacologic studies. Despite of the relatively high content of cardiac histamine it is not clarified whether histamine actually plays a physiologic role — apart from pharmacologic effects — in the regulation of myocardial function and coronary blood flow. Under pathophysiologic conditions (during anaphylaxis, surgical procedures, accidents, stress etc.), however, when a local or systemic histamine release occurs both hemodynamic and arrhythmogenic effects are evident. Numerous studies in animal models conclusively demonstrated a role of cardiac histamine as a major mediator of serious arrhythmias. Consequently, a combination of h₁- and h₂-receptor antagonists (f.e. Dimetinden/Cimetidin) was recommended as a prophylactic treatment against severe anaphylaxis including life-threatening arrhythmias for cardiac patients at risk.There is pharmacologic evidence of both a positive inotropic and chronotropic effect in the human heart via h₂-receptor and stimulation of adenylate cyclase. Histamine-induced coronary effects such as vasoconstriction via h₁-receptor and coronary dilatation via h₂-receptor are not yet sufficiently validated. Studies on the human heart in vitro using coronary strips from explanted hearts and in vivo investigations on the intact coronary system yielded conflicting results.H₂-receptor blocking agents cimetidine, ranitidine and famotidine have qualitatively a different pharmocodynamic spectrum of side effects due to differences in chemical structure. Data on cardiac arrhythmias are mostly associated to cimetidine. Symptomatic bradycardia were reported for both ranitidine and cimetidine. A possible negative inotropic effect of famotidine, although presently not validated, requires further studies.— Causative and adverse side effects of cimetidine on the cardiovascular system, however, are to be expected extremely seldom due to easily reversible competetive h₂-receptor binding. For prophylaxis rapid intravenous injections of h₂-blockers, particularly in elder patients with cardiac diseases, should be avoided. Compared to cimetidine, a tendency of explainable difference seems to become apparent for ranitidine and famotidine due to higher receptor affinity.

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Abkürzungsverzeichnis A Atrium - AVN AV-Knoten - HF Herzfrequenz - V Ventrikel     

Pharmacological control of the histamine H2 receptor-adenylate cyclase system by famotidine and ranitidine in normal and cancerous human gastric epithelia

In human fundic glands, famotidine was about 17 times more potent than ranitidine as an inhibitor of histamine — stimulated cAMP generation. This H₂-receptor antagonist had no effect on the receptoradenylate cyclase systems sensitive to PGE₂, isoproterenol (₂), VIP and on forskolin-induced activation of the Gs/catalytic units of the membrane-bound enzyme prepared from human fundic glands. In the HGT-1 human gastric cancer cell line, famotidine and ranitidine showed long lasting, irreversible actions probably related to a slow rate of dissociation from the histamine H₂-receptor.     

Regulation of ERK2 phosphorylation by histamine in splenocytes

Histamine is implicated in allergic disease and asthma and ERK1/2 is involved in allergic inflammation including Th2 differentiation and proliferation. This study was designed to study the effects of histamine on ERK1/2 phosphorylation in splenocytes. C57/BL6 splenocytes were treated with different concentrations of histamine (10^?4 to 10^?11 M). Histamine (10^?4 M) increased ERK2 phosphorylation. There was, however, no significant effect seen at other concentrations (10^?11 to 10^?6 M). Surprisingly, H1 receptor agonist β-histine (10^?5 M), H2 agonist amthamine (10^?5 M), H3 agonist methimepip (10^?6 M), and H4 agonist 4-methyl histamine (10^?6 M), all increased ERK2 phosphorylation. H1R antagonist pyrilamine (10^?6 M), H2R antagonist ranitidine (10^?5 M), H3/H4R antagonist thioperamide (10^?6 M), and H3R antagonist clobenpropit (10^?5 M) inhibited histamine-mediated ERK2 phosphorylation suggesting that all four histamine receptor subtypes played some role in this phosphorylation. Because tumor necrosis factor-α (TNF-α) causes phosphorylation of ERK1/2, we investigated whether histamine acted via secretion of TNF-α to affect ERK1/2 phosphorylation. As a consequence, TNF-α knockout mice were used and we found that there was inhibition of ERK1 and ERK2 phosphorylation by H2, H3, and H4 agonists. This was in contrast to the wild-type splenocytes where histamine augmented the phosphorylation of ERK2 via H2, H3, and H4 receptors. In TNF-α knockout mice histamine did not affect the phosphorylation of ERK2 via H1 receptors. The results suggested that histamine indirectly caused the ERK2 phosphorylation via its effects on the secretion of TNF-α and these effects were mediated via H1, H2, H3, and H4 receptors.     

First-degree atrioventricular block in a young duodenal ulcer patient treated with a standard oral dose of ranitidine

A 20-year-old male patient on oral treatment with ranitidine 300 mg/day in a single bedtime dose was admitted to hospital for a brief episode of syncope which had occurred 20 min earlier. All clinical, laboratory and instrumental examinations yielded negative findings, except for electrocardiographic evidence of first-degree atrioventricular block. Administration of atropine produced transient disappearance of the block, which disappeared altogether after discontinuing ranitidine treatment. Two separate rechallenges with ranitidine each produced recurrence of (asymptomatic) first-degree atrioventricular block at electrocardiographic examination, but oral treatment with cimetidine (400–800 mg/day) and famotidine (40–80 mg/day) induced no electrocardiographic abnormalities. The hypothesis that this patient may be abnormally susceptible to the cholinergic or cholinergic-like effect of ranitidine, a side effect unrelated to the drug's primary H₂-blocking action, would appear to be consistent with evidence of an increased vagal tone of the atrioventricular node as revealed by atrial pacing. However, the ability of ranitidine to release histamine in man and the potential dysrhythmia-inducing effect of histamine should also be taken into consideration.     

Comparison of antisecretory potency and duration of action of the H2-receptor antagonists AH 22216, cimetidine,ranitidine and SK & F 93479 in the dog

The antisecretory potency and duration of action of the new histamine H₂-receptor antagonist AH 22216 have been compared with those of cimetidine, ranitidine and SK & F 93479 against histamine-induced gastric acid secretion in the conscious Heidenhain pouch dog. Ranitidine was 4–6 times more potent than cimetidine, with a similar duration of action. SK & F 93479 was approximately twice as potent as ranitidine and had a slightly longer duration of action. AH 22216 was most potent of the four H₂-antagonists, some 20–30 times more active than cimetidine, and had an extremely prolonged duration of action.     

Inhibition of14C-Aminopyrine accumulation in isolated rabbit gastric glands by the H2-receptor antagonist HOE 760 (TZU-0460)

Acid secretion in isolated rabbit gastric glands was measured by means of the¹⁴C-aminopyrine accumulation technique. Hoe 760 (TZU-0460) and Hoe 062, the desacetylated compound of Hoe 760, caused a concentration-dependent reduction of histamine (100 M) induced aminopyrine-accumulation. The IC₅₀-values were 3.16±0.84 M (n=5) and 1.58±0.6 M (n=6) for Hoe 760 and Hoe 062, respectively. In comparison an IC₅₀ of 9.0±0.72 M (n=6) was obtained for cimetidine and 3.3±1.4 M (n=5) for ranitidine. The IC₅₀-values of ranitidine, Hoe 760 and Hoe 062 were significantly different (p<0.05) from cimetidine. The addition of increasing concentrations of Hoe 760 to the histamine concentration-response curve caused a parallel rightward shift. The transformation of these concentration-response curves according to Arunlakshana and Schild indicated that this inhibition was caused by a competitive antagonism of the histamine receptor on the parietal cell. In agreement with these findings the dbc-AMP stimulated aminopyrine accumulation remained unaffected by the H₂-receptor antagonists.     

The effect of histamine on the oxidative burst of HL60 cells before and after exposure to reactive oxygen species

During an inflammation neutrophils are stimulated to produce reactive oxygen species (ROS). These ROS induce the release of histamine from mast cells, which are also present at the inflammation site. In this study dibutyryl cAMP differentiated HL60 cells are used as a model for human neutrophils. The effect of histamine on formyl-methionyl-leucyl-phenylalanine (fmlp) stimulated cells is examined. Except for histamine also an accumulation of ROS takes place at the inflammation site and we investigated if ROS can influence the response of the stimulated HL60 cells. It is found that 10^–3 M histamine can inhibit the fmlp induced superoxide anion radical production. This occurs partly via an H₂ receptor because H₂ antagonists like famotidine, mifentidine and ranitidine could partially antagonize this effect of histamine. When HL60 cells are exposed to hydrogen peroxide or hypochlorous acid (20 min), an increased fmlp response is found while the inhibiting effect of histamine remains unchanged.     

On the mechanism of histamine induced enhancement of the cardiac Ca2+ current

In guinea pig ventricular myocytes, the effect of histamine on the slow Ca²⁺ current (I_Ca) was studied and the following results were obtained: (1) Superfusion of cells with histamine resulted in a dose-dependent enhancement of the amplitude of I_Ca. The threshold concentration of histamine was 10^–8 M, half maximal increase occurred at 3×10^–7 M and maximal enhancement (about 3–4-fold) at 5×10^–6 M. (2) The histamine effect was greatly reduced by the H₂ antagonist cimetidine (10^–5 M) but only slightly by the H₁ antagonist diphenhydramine (10^–5M). (3) Effects of isoprenaline (ISP) and histamine at maximal effective concentrations on I_Ca were not additive, suggesting that both agents use the same intracellular pathway. Intracellular infusion of a blocker of the cAMP-dependent protein kinase, R_p-cAMPS (10^–4 M), prevented the histamine effect. (4) The involvement of GTP-dependent transducer proteins was studied by cell dialysis with several GTP derivatives. Intracellular application of the stable GDP-analogue, GDP--S, reduced the histamine effect on I_Ca, whereas the stable GTP analogue, GTP--S, mimicked the histamine effect.     

Desensitization by histamine of H2 receptor activity in HGT-1 human cancerous gastric cells

Histamine produced a time-dependent (half-life: 20 min at 37°C), temperature-dependent (no effect at 20°C) and homologous desensitization of histamine H₂ receptor activity (H₂ R) in HGT-1 cells. Maximal and half-maximal desensitization were respectively observed at 10^–5 and 2×10^–7 M histamine. Decline of responsiveness in intact cells was related to a remarkable loss in histamine efficacy (from 15- to 2-fold stimulation in control and treated cells). The affinity of the H₂R for histamine (EC₅₀=10^–5 M) did not change during desensitization. Paradoxically, histamine treatment is associated with increased [³H] histamine binding capacity in intact HGT-1 cells, and no change in H₂ receptor antagonist binding ([³H]-tiodine and [³H]-SKF 93479). Desensitization process was preferentially mimicked by H₂ receptor agonists (impromidine > histamine > AET > PEA) and preferentially reversed by simultaneous addition of H₂ receptor antagonists (cimetidine > DPH). We suggest that the desensitization of H₂R activity by histamine presented here may be involved in the pathophysiological regulation and pharmacological control of gastric cell function in man.     

Increased parietal cell sensitivity after chronic treatment with ranitidine in the conscious cat

The sensitivity of histamine H₂ receptors of the gastric mucosa after one month treatment with ranitidine, administered daily (5 mg/kg i.m.), was checked in 5 conscious cats provided with gastric fistula. Basal acid secretion as well as the acid response to the H₂ agonist dimaprit (60 μg/kg/hr) were studied before and at different periods after cessation of ranitidine treatment (1, 3, 7 and 14 days). Control experiments were carried out in 5 gastric fistula cats which received daily physiological saline for one month. Basal acid secretion in treated animals increased significantly (P<0.05) from 0.04±0.002 to 0.24±0.05 mEq H⁺/10 min. Also the response to dimaprit increased significantly (p<0.05) from 0.49±0.08 to 0.86±0.12 mEq H⁺/10 min. Seven days after cessation of treatment, both basal and stimulated secretion returned to pretreatment levels. In control cats no significant difference was noticed in basal and stimulated secretion at the beginning and at the end of the study.     

Indomethacin induced changes in mucosal lysosomal enzyme activity: Effect of H2 antagonists

Indomethacin induced gastric damage in rats was accompanied by a decrease in mucosal activities of three lysosomal enzymes tested, with serum levels remaining unchanged. Petreatments with cimetidine (100 mg/kg b.w.) and ranitidine (30 mg/kg b.w.) were found partially to prevent the decrease ofN-acetylglucosaminidase and acid phosphatase, as well as of beta-glucuronidase, while the latter was also prevented by famotidine (10 mg/kg b.w.). All the H₂ antagonists tested reduced dose-dependently the extent of gastric injury induced by indomethacin and reversed the changes in protein levels. The stabilisation of lysosomal membranes and thus the prevention of lysosomal leakage may be one of the favourable additional mechanisms of antiulcer activity of H₂ antagonists.