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

Acid-Suppressive Therapy and Risk of Infections: Pros and Cons

This narrative review summarises the benefits, risks and appropriate use of acid-suppressing drugs (ASDs), proton pump inhibitors and histamine-2 receptor antagonists, advocating a rationale balanced and individualised approach aimed to minimise any serious adverse consequences. It focuses on current controversies on the potential of ASDs to contribute to infections-bacterial, parasitic, fungal, protozoan and viral, particularly in the elderly, comprehensively and critically discusses the growing body of observational literature linking ASD use to a variety of enteric, respiratory, skin and systemic infectious diseases and complications (Clostridium difficile diarrhoea, pneumonia, spontaneous bacterial peritonitis, septicaemia and other). The proposed pathogenic mechanisms of ASD-associated infections (related and unrelated to the inhibition of gastric acid secretion, alterations of the gut microbiome and immunity), and drug-drug interactions are also described. Both probiotics use and correcting vitamin D status may have a significant protective effect decreasing the incidence of ASD-associated infections, especially in the elderly. Despite the limitations of the existing data, the importance of individualised therapy and caution in long-term ASD use considering the balance of benefits and potential harms, factors that may predispose to and actions that may prevent/attenuate adverse effects is evident. A six-step practical algorithm for ASD therapy based on the best available evidence is presented.

Histamine H2 Receptor in Blood Cells: A Suitable Target for the Treatment of Acute Myeloid Leukemia

Acute myeloid leukemia (AML) consists in a cancer of early hematopoietic cells arising in the bone marrow, most often of those cells that would turn into white blood cells (except lymphocytes). Chemotherapy is the treatment of choice for AML but one of the major complications is that current drugs are highly toxic and poorly tolerated. In general, treatment for AML consists of induction chemotherapy and post-remission therapy. If no further post-remission is given, almost all patients will eventually relapse. Histamine, acting at histamine type-2 (H₂) receptors on phagocytes and AML blast cells, helps prevent the production and release of oxygen-free radicals, thereby protecting NK and cytotoxic T cells. This protection allows immune-stimulating agents, such as interleukin-2 (IL-2), to activate cytotoxic cells more effectively, enhancing the killing of tumor cells. Based on this mechanism, post-remission therapy with histamine and IL-2 was found to significantly prevent relapse of AML. Alternatively, another potentially less toxic approach to treat AML employs drugs to induce differentiation of malignant cells. It is based on the assumption that many neoplastic cell types exhibit reversible defects in differentiation, which upon appropriate treatment results in tumor reprogramming and the induction of terminal differentiation. There are promissory results showing that an elevated and sustained signaling through H₂ receptors is able to differentiate leukemia-derived cell lines, opening the door for the use of H₂ agonists for specific differentiation therapies. In both situations, histamine acting through H₂ receptors constitutes an eligible treatment to induce leukemic cell differentiation, improving combined therapies.

Modulation of neutrophil oxidative burst via histamine receptors

Histamine has the ability to influence the activity of immune cells including neutrophils and plays a pivotal role in inflammatory processes, which are a complex network of cellular and humoral events. One of the main functions manifested by activated neutrophils is oxidative burst, which is linked to the production of reactive oxygen species; therefore, the effects of histamine receptor agonists and antagonists on the oxidative burst of neutrophils is reviewed. A role for the well-characterized histamine H1 and H2 receptors in this process is discussed and compared to that of the recently discovered H4 receptor.

Anti-inflammatory effects of low-intensity extremely high-frequency electromagnetic radiation: frequency and power dependence

Using a model of acute zymosan-induced footpad edema in NMRI mice, the frequency and power dependence of anti-inflammatory effect of low-intensity extremely high-frequency electromagnetic radiation (EHF EMR) was found. Single whole-body exposure of animals to EHF EMR at the intensity of 0.1 mW/cm(2) for 20 min at 1 h after zymosan injection reduced both the footpad edema and local hyperthermia on average by 20% at the frequencies of 42.2, 51.8, and 65 GHz. Some other frequencies from the frequency range of 37.5-70 GHz were less effective or not effective at all. At fixed frequency of 42.2 GHz and intensity of 0.1 mW/cm(2), the effect had bell-shaped dependence on exposure duration with a maximum at 20-40 min. Reduction of intensity to 0.01 mW/cm(2) resulted in a change of the effect dependence on exposure duration to a linear one. Combined action of cyclooxygenase inhibitor sodium diclofenac and EHF EMR exposure caused a partial additive effect of decrease in footpad edema. Combined action of antihistamine clemastine and EHF EMR exposure caused a dose-dependent abolishment of the anti-inflammatory effect of EHF EMR. The results obtained suggest that arachidonic acid metabolites and histamine are involved in realization of anti-inflammatory effects of low-intensity EHF EMR.

Clozapine bioactivation induces dose-dependent, drug-specific toxicity of human bone marrow stromal cells: A potential in vitro system for the study of agranulocytosis

Clozapine, an atypical antipsychotic drug effective in treatment of refractory schizophrenia causes potentially life-threatening agranulocytosis. The drug undergoes bioactivation to a toxic, chemically reactive intermediate with capacity to target stromal cells, central components of the bone marrow microenvironment implicated in neutrophil development. To identify possible mechanisms underpinning disruption of stroma as a site of drug bioactivation, toxicity was induced in vitro. Therefore metabolite generation procedures utilizing HOCl or HRP-H(2)O(2) as primary components involved in clozapine metabolism were adapted for stromal culture and coupled with viability determinations. Drug oxidation by HOCl was less toxic to stromal cells than HRP-H(2)O(2) based methods. More specifically, clozapine bioactivation by HRP-H(2)O(2) caused dose-dependent inhibition of stromal viability at therapeutically relevant concentrations. Differences in susceptibility of HAS303 and LP101 cells to the clozapine nitrenium ion were also evident. Stromal cell death was attributed to clozapine in the presence of a complete metabolising system comprising HRP and H(2)O(2). In the absence of a complete metabolising system clozapine was not cytotoxic. For LP101 cells, drug plus HRP (minus H(2)O(2)) also induced toxicity. Importantly, other antipsychotic drugs including risperidone, olanzapine and haloperidol when bioactivated, were not cytotoxic, indicating system specificity for clozapine. Exogenous GSH, N-acetylcysteine, l-ascorbic acid, catalase, and sodium azide afforded protection to cells whereas S-methylGSH, GSSG, ketoprofen and proadifen did not. Thus functional data derived from the in vitro stromal system defined in these studies may enable further investigation of the mechanisms subserving stromal impairment in clozapine-induced agranulocytosis and direct attention to improved methods for its prevention.

Potential clozapine target sites on peripheral hematopoietic cells and stromal cells of the bone marrow

The antipsychotic drug clozapine, acts via interaction with selective neurotransmitter receptor systems. Its use however, is associated with life-threatening agranulocytosis. The mechanism by which this occurs and its possible relationship with the drug's atypicality remain unclear. As a first step in identifying mechanistic pathways involved, profiling of neurotransmitter receptors on human neutrophils, mononuclear and bone marrow stromal cells as putative targets for clozapine-mediated toxicity was undertaken. Expression of mRNA encoding dopaminergic d2, d3, d4; serotonergic 5ht2a, 5ht2c, 5ht3, 5ht6, 5ht7; adrenergic alpha1a, alpha2; histaminergic h1 and muscarinic m1, m2, m3, m4, m5 receptors was analyzed by reverse transcription-polymerase chain reaction methods. While 5ht2c, 5ht6, m1 and m2 mRNA were undetected, the presence of the other receptors indicates sites at which clozapine could bind and induce toxicity of neutrophils and stromal components which regulate granulopoiesis. The functional significance of differential receptor expression while unknown, may argue for neural regulation of hematopoiesis.

Protective effect of vasoactive intestinal peptide on testicular torsion-detorsion injury: association with heparin-containing mast cells

OBJECTIVES

To elucidate the action of vasoactive intestinal peptide (VIP) on detorsion injury and the heterogeneity of mast cells in the testes of rats.

METHODS

Prepubertal male Sprague-Dawley rats were used in six groups. Group 1 was the control group (sham operation); group 2 had 2 hours of torsion; group 3, 2 hours of torsion and 1 hour of detorsion after administration of saline; group 4 had 2 hours of torsion and 4 hours of detorsion after administration of saline; group 5, 2 hours of torsion and 1 hour of detorsion after administration of intraperitoneal VIP (25 ng/kg); and group 6, 2 hours of torsion and 4 hours of detorsion after intraperitoneal VIP. The 2 hours of torsion was created by rotating the right testis 720 degrees in a clockwise direction. VIP (25 ng/kg) was injected intraperitoneally 1 minute before the 1 and 4 hours of detorsion. At the end of the experiment, catalase enzyme activity was measured polarographically, and superoxide dismutase, malondialdehyde, and protein were measured spectrophotometrically. Nitric oxide was measured by capillary electrophoresis in the testicular tissue. Routine histologic examination of testicular mast cells was done under light microscopy; the histochemistry was also analyzed.

RESULTS

Torsion significantly induced oxidative stress, mast cell degranulation, and tissue damage. Detorsion attenuated oxidative stress without any diminution of the histologic damage to the tissue. VIP significantly protected the testicular tissue from detorsion injury. It also inhibited mast cell activity while increasing the heparin content.

CONCLUSIONS

VIP can protect testicular tissue from detorsion injury. Heparin-containing mast cells seem to be important mediator cells for this protection.

Pro-apoptotic effect of high concentrations of histamine on human neutrophils

Histamine receptors are expressed on neutrophils, and therefore, are likely to modulate neutrophil function. In this study, we investigated whether histamine modulates human neutrophil survival. Neutrophils were found to rapidly undergo spontaneous apoptosis upon culture in vitro and this was accelerated by high concentrations of histamine. Moreover, the percentage of apoptotic neutrophils was also markedly increased by treating with 10 mM histamine in the presence of inflammatory mediators, such as lipopolysaccharide (LPS), granulocyte macrophage-colony stimulating factor (GM-CSF), dibutyryl-cAMP (db-cAMP), or dexamethasone. Histamine-induced neutrophil apoptosis was inhibited by pyrilamine, a histamine receptor 1 antagonist, and by ranitidine, a selective histamine receptor 2 antagonist. In addition, diphenylene iodonium (DPI), an inhibitor of NADPH-oxidase, significantly blocked the apoptotic effect of histamine. Moreover, the induction of apoptosis by histamine was almost completely inhibited by zVAD-fmk, a pan-caspase inhibitor. In addition, immunoblotting showed that histamine induced the proteolytic activation of procaspase-3 in cell lysates treated with histamine. And, the protein kinase C (PKC)-delta inhibitor, rottlerin (5 microM) significantly blocked the apoptotic effect of histamine, though the cleavage of PKC-delta in 20 h cultured neutrophils was increased by histamine. However, an inhibitor of conventional PKC, Go6976 (100 nM) and a p38 mitogen-activated protein kinase inhibitor, SB203580 (10 microM), failed to block histamine-induced neutrophil apoptosis. These results suggest that high concentrations of histamine in local inflammatory and allergic lesions induce neutrophil apoptosis, and that this histamine-induced apoptosis is mediated by caspase activation and PKC-delta signaling.

Azithromycin modulates neutrophil function and circulating inflammatory mediators in healthy human subjects

Effects on human neutrophils and circulating inflammatory mediators were studied in 12 volunteers who received azithromycin (500 mg/day, p.o.) for 3 days. Blood was taken 1 h before treatment, 2.5, 24 h and 28 days after the last dose. An initial neutrophil degranulating effect of azithromycin was reflected in rapid decreases in azurophilic granule enzyme activities in cells and corresponding increases in serum. The oxidative response to a particulate stimulus was also acutely enhanced. These actions were associated with high plasma and neutrophil drug concentrations. A continuous fall in chemokine and interleukin-6 serum concentrations, within the non-pathological range, accompanied a delayed down-regulation of the oxidative burst and an increase in apoptosis of neutrophils up to 28 days after the last azithromycin dose. Neutrophils isolated from blood at this time point still contained detectable drug concentrations. Acute neutrophil stimulation could facilitate antibacterial effects of azithromycin, while delayed, potentially anti-inflammatory activity may curtail deleterious inflammation.

Vasoactive intestinal peptide inhibits degranulation and changes granular content of mast cells: a potential therapeutic strategy in controlling septic shock

Vasoactive intestinal peptide (VIP) has potent protective activity against sepsis and increases the survival rate of septic rats and mice. The present study was planned to evaluate the effect of VIP on mast cell activity, histamine and methylhistamine levels and oxidative stress in the liver and kidneys of septic rats. The effect of VIP was compared to that of nitric oxide synthesis inhibition, previously tested extensively in septic shock models, with doubtful benefit. The present study showed that endotoxic shock did not lead to oxidative stress in either liver or kidney of the rats. On the other hand, mast cells, based on their location, displayed functional heterogeneity to the septic insults. VIP possibly modulated the specific reactions of the tissues to mediators released from mast cells during septic shock. The most prominent effect of VIP as compared to nitric oxide synthesis inhibition was related to mast cells. In conclusion, the prevention of mast cell reactivity by VIP could be a potential therapeutic strategy in controlling septic shock.

Oxidative stress activates the human histidine decarboxylase promoter in AGS gastric cancer cells

Oxidant stress is thought to play a role in the pathogenesis of many gastric disorders. We have recently reported that histidine decarboxylase (HDC) promoter activity is stimulated by gastrin through a protein kinase C- and extracellular signal-regulating kinase (ERK)-dependent pathway in gastric cancer (AGS-B) cells, and this transcriptional response is mediated by a downstream cis-acting element, the gastrin response element (GAS-RE). To study the mechanism through which oxidant stress affects gastric cells, we examined the effects of hydrogen peroxide (H2O2) on HDC promoter activity and intracellular signaling in AGS-B cells. H2O2 (10 mM) specifically activated the HDC promoter 10-12-fold, and this activation was blocked by both mannitol and N-acetylcysteine. Hydrogen peroxide treatment of AGS-B cells increased the phosphorylation and kinase activity of ERK-1 and ERK-2, but did not affect Jun kinase tyrosine phosphorylation or kinase activity. In addition, treatment of AGS-B cells with H2O2 resulted in increased c-fos/c-jun mRNA expression and AP-1 activity, and also led to increased phosphorylation of epidermal growth factor receptor (EGFR) and Shc. H2O2-dependent stimulation of HDC promoter activity was completely inhibited by kinase-deficient ERKs, dominant-negative (N17 and N15) Ras, and dominant-negative Raf, and partially blocked by a dominant-negative EGFR mutant. In contrast, protein kinase C blockade did not inhibit H2O2-dependent induction of the HDC promoter. Finally, deletion analysis demonstrated that the H2O2 response element could be mapped to the GAS-RE (nucleotides 2 to 24) of the basal HDC promoter. Overall, these studies suggest that oxidant stress activates the HDC promoter through the GAS-RE, and through an Ras-, Raf-, and ERK-dependent pathway at least partially involving the EGFR.