Netazepide, a gastrin/cholecystokinin-2 receptor antagonist, can eradicate gastric neuroendocrine tumours in patients with autoimmune chronic atrophic gastritis.

AIMS: Netazepide, a gastrin/cholecystokinin 2 receptor antagonist, once daily for 12 weeks reduced the number of tumours and size of the largest one in 16 patients with autoimmune chronic atrophic gastritis (CAG), achlorhydria, hypergastrinaemia and multiple gastric neuroendocrine tumours (type 1 gastric NETs), and normalized circulating chromogranin A (CgA) produced by enterochromaffin-like cells, the source of the tumours. The aim was to assess whether longer-term netazepide treatment can eradicate type 1 gastric NETs. METHODS: After a mean 14 months off netazepide, 13 of the 16 patients took it for another 52 weeks. Assessments were: gastroscopy; gene-transcript expression in corpus biopsies using quantitative polymerase chain reaction; blood CgA and gastrin concentrations; and safety assessments. RESULTS: While off-treatment, the number of tumours, the size of the largest one, and CgA all increased again. Netazepide for 52 weeks: cleared all tumours in 5 patients; cleared all but one tumour in one patient; reduced the number of tumours and size of the largest one in the other patients; normalized CgA in all patients; and reduced mRNA abundances of CgA and histidine decarboxylase in biopsies. Gastrin did not increase further, confirming that the patients had achlorhydria. Netazepide was safe and well tolerated. CONCLUSIONS: A gastrin/cholecystokinin 2 receptor antagonist is a potential medical and targeted treatment for type 1 gastric NETs, and an alternative to regular gastroscopy or surgery. Treatment should be continuous because the tumours will regrow if it is stopped. Progress can be monitored by CgA in blood or biomarkers in mucosal biopsies.

Surfactant-induced chronic pruritus: Role of L-histidine decarboxylase expression and histamine production in epidermis.

Shampoo and cleansers containing anionic surfactants including sodium dodecyl sulphate (SDS) often cause pruritus in humans. Daily application of 1-10% SDS for 4 days induced hind-paw scratching (an itch-related behaviour) in a concentration-dependent manner, and 10% SDS also caused dermatitis, skin dryness, barrier disruption, and an increase in skin surface pH in mice. SDS-induced scratching was inhibited by the opioid receptor antagonist naloxone and the H histamine receptor antagonist terfenadine. Mast-cell deficiency did not inhibit SDS-induced scratching, although it almost completely depleted histamine in the dermis. Treatment with SDS increased the histamine content of the epidermis, but not that of the dermis. SDS treatment increased the gene expression and post-translation processing of L-histidine decarboxylase in the epidermis. The present results suggest that repeated application of SDS induces itch through increased production of epidermal histamine, which results from an increase in the gene expression and post-translation processing of L-histidine decarboxylase.

Sequencing, characterization, and gene expression analysis of the histidine decarboxylase gene cluster of Morganella morganii.

The histidine decarboxylase gene cluster of Morganella morganii DSM30146(T) was sequenced, and four open reading frames, named hdcT1, hdc, hdcT2, and hisRS were identified. Two putative histidine/histamine antiporters (hdcT1 and hdcT2) were located upstream and downstream the hdc gene, codifying a pyridoxal-P dependent histidine decarboxylase, and followed by hisRS gene encoding a histidyl-tRNA synthetase. This organization was comparable with the gene cluster of other known Gram negative bacteria, particularly with that of Klebsiella oxytoca. Recombinant Escherichia coli strains harboring plasmids carrying the M. morganii hdc gene were shown to overproduce histidine decarboxylase, after IPTG induction at 37 °C for 4 h. Quantitative RT-PCR experiments revealed the hdc and hisRS genes were highly induced under acidic and histidine-rich conditions. This work represents the first description and identification of the hdc-related genes in M. morganii. Results support the hypothesis that the histidine decarboxylation reaction in this prolific histamine producing species may play a role in acid survival. The knowledge of the role and the regulation of genes involved in histidine decarboxylation should improve the design of rational strategies to avoid toxic histamine production in foods.

Proliferative effect of histamine on MA-10 Leydig tumor cells mediated through HRH2 activation, transient elevation in cAMP production, and increased extracellular signal-regulated kinase phosphorylation levels.

Mast cells (MC) occur normally in the testis with a species-specific distribution, yet their precise role remains unclear. Testicular MC express histidine decarboxylase (HDC), the unique enzyme responsible for histamine (HA) generation. Evidence to date supports a role for HA as a local regulator of steroidogenesis via functional H1 and H2 receptor subtypes (HRH1 and HRH2, respectively) present in Leydig cells. Given that HA is a well-known modulator of physiological and pathological proliferation in many different cell types, we aimed in the present study to evaluate whether HA might contribute to the regulation of Leydig cell number as well as to the control of androgen production. Herein, we demonstrate, to our knowledge for the first time, that MA-10 Leydig tumor cells, but not normal immature Leydig cells (ILC), exhibit a proliferative response upon stimulation with HA that involves HRH2 activation, transient elevation of cAMP levels, and increased extracellular signal-regulated kinase (ERK) phosphorylation. Our results also reveal that MA-10 cells show significantly heightened HDC expression compared to normal ILC or whole-testicular lysate and that inhibition of HDC activity decreases MA-10 cell proliferation, suggesting a possible correlation between autocrine overproduction of HA and abnormally increased proliferation in Leydig cells. The facts that germ cells are also both source and target of HA and that multiple testicular cells are susceptible to HA action underline the importance of the present study, which we hope will serve as a first step for further research into regulation of non-MC-related HDC expression within the testis and its significance for testicular function.

Histidine decarboxylase deficiency inhibits NBP-induced extramedullary hematopoiesis by modifying bone marrow and spleen microenvironments.

Histidine decarboxylase (HDC), a histamine synthase, is expressed in various hematopoietic cells and is induced by hematopoietic cytokines such as granulocyte colony-stimulating factor (G-CSF). We previously showed that nitrogen-containing bisphosphonate (NBP)-treatment induces extramedullary hematopoiesis via G-CSF stimulation. However, the function of HDC in NBP-induced medullary and extramedullary hematopoiesis remains unclear. Here, we investigated changes in hematopoiesis in wild-type and HDC-deficient (HDC-KO) mice. NBP treatment did not induce anemia in wild-type or HDC-KO mice, but did produce a gradual increase in serum G-CSF levels in wild-type mice. NBP treatment also enhanced Hdc mRNA expression and erythropoiesis in the spleen and reduced erythropoiesis in bone marrow and the number of vascular adhesion molecule 1 (VCAM-1)-positive macrophages in wild-type mice, as well as increased the levels of hematopoietic progenitor cells and proliferating cells in the spleen and enhanced expression of bone morphogenetic protein 4 (Bmp4), CXC chemokine ligand 12 (Cxcl12), and hypoxia inducible factor 1 (Hif1) in the spleen. However, such changes were not observed in HDC-KO mice. These results suggest that histamine may affect hematopoietic microenvironments of the bone marrow and spleen by changing hematopoiesis-related factors in NBP-induced extramedullary hematopoiesis.

Impact of moderate prenatal alcohol exposure on histaminergic neurons, histidine decarboxylase levels and histamine H2 receptors in adult rat offspring.

We have reported that moderate prenatal alcohol exposure (PAE) elevates histamine H3 receptor-mediated inhibition of glutamatergic neurotransmission in dentate gyrus (DG), and that the H3 receptor antagonist ABT-239 ameliorates PAE-induced deficits in DG long-term potentiation. Here, we investigated whether PAE alters other markers of histaminergic neurotransmission. Long-Evans rat dams voluntarily consumed either a 0% or a 5% ethanol solution 4 h each day throughout gestation. Young adult female offspring from each prenatal treatment group were used in histidine decarboxylase (HDC) immunohistochemical studies of histamine neuron number in ventral hypothalamus, quantitative Western blotting studies of HDC expression in multiple brain regions, radiohistochemical studies of H2 receptor density in multiple brain regions, and in biochemical studies of H2 receptor-effector coupling in dentate gyrus. Rat dams consumed a mean of 1.90 g of ethanol/kg/day during pregnancy. This level of consumption did not affect maternal weight gain, offspring birth weight, or litter size. PAE did not affect the number of HDC-positive neurons in ventral hypothalamus. However, HDC expression was reduced in frontal cortex, dentate gyrus, and cerebellum of PAE rats compared to controls. Specific [125I]-iodoaminopotentidine binding to H2 receptors was not altered in any of the brain regions measured, nor was basal or H2 receptor agonist-stimulated cAMP accumulation in DG altered in PAE rats compared to controls. These results suggest that not all markers of histaminergic neurotransmission are altered by PAE. However, the observation that HDC levels were reduced in the same brain regions where elevated H3 receptor-effector coupling was observed previously raises the question of whether a cause-effect relationship exists between HDC expression and H3 receptor function in affected brain regions of PAE rats. This relationship, along with the question of why these effects occur in some, but not all brain regions, requires more-detailed investigation.

Lipopolysaccharide suppresses activation of the tuberomammillary histaminergic system concomitant with behavior: a novel target of immune-sensory pathways.

Infection and inflammation strongly inhibit a variety of behaviors, including exploration, social interaction, and food intake. The mechanisms that underlie sickness behavior remain elusive, but appear to involve fatigue and a state of hypo-arousal. Because histaminergic neurons in the ventral tuberomammillary nucleus of the hypothalamus (VTM) play a crucial role in the mediation of alertness and behavioral arousal, we investigated whether the histaminergic system represents a target for immune activation and, if so, whether modulation by ascending medullary immune-sensitive projections represents a possible mechanism. Rats were injected intraperitoneally with either the pro-inflammatory stimulus lipopolysaccharide (LPS) or saline, and exposed to one of various behavioral tests that would induce motivated behavior (exploration, play behavior, social interaction, sweetened milk consumption). Upon kill, brains were processed for c-Fos and histidine decarboxylase immunoreactivity. LPS treatment reduced behavioral activity and blocked behavioral test-associated c-Fos induction in histaminergic neurons of the VTM. These effects of LPS were prevented by prior inactivation of the caudal medullary dorsal vagal complex (DVC) with a local anesthetic. To determine whether LPS-responsive brainstem projection neurons might provide a link from the DVC to the VTM, the tracer Fluorogold was iontophoresed into the VTM a week prior to experiment. Retrogradely labeled neurons that expressed c-Fos in response to LPS treatment included catecholaminergic neurons within the nucleus of the solitary tract and ventrolateral medulla. These findings support the hypothesis that the histaminergic system represents an important component in the neurocircuitry relevant for sickness behavior that is linked to ascending pathways originating in the lower brainstem.

High frequency of histamine-producing bacteria in the enological environment and instability of the histidine decarboxylase production phenotype.

Lactic acid bacteria contribute to wine transformation during malolactic fermentation. They generally improve the sensorial properties of wine, but some strains produce histamine, a toxic substance that causes health issues. Histamine-producing strains belong to species of the genera Oenococcus, Lactobacillus, and Pediococcus. All carry an hdcA gene coding for a histidine decarboxylase that converts histidine into histamine. For this study, a method based on quantitative PCR and targeting hdcA was developed to enumerate these bacteria in wine. This method was efficient for determining populations of 1 to 10(7) CFU per ml. An analysis of 264 samples collected from 116 wineries of the same region during malolactic fermentation revealed that these bacteria were present in almost all wines and at important levels, exceeding 10(3) CFU per ml in 70% of the samples. Histamine occurred at an often important level in wines containing populations of the above-mentioned bacteria. Fifty-four colonies of histamine producers isolated from four wines were characterized at the genetic level. All were strains of Oenococcus oeni that grouped into eight strain types by randomly amplified polymorphic DNA analysis. Some strains were isolated from wines collected in distant wineries. Moreover, hdcA was detected on a large and possibly unstable plasmid in these strains of O. oeni. Taken together, the results suggest that the risk of histamine production exists in almost all wines and is important when the population of histamine-producing bacteria exceeds 10(3) per ml. Strains of O. oeni producing histamine are frequent in wine during malolactic fermentation, but they may lose this capacity during subcultures in the laboratory.

Inductions of histidine decarboxylase in mouse tissues following systemic antigen challenge: contributions made by mast cells, non-mast cells and IL-1.

BACKGROUND: Previous findings suggest that antigen challenge (AC) may induce histidine decarboxylase (HDC) in cells other than mast cells (MCs) via MC-derived IL-1. We examined this hypothesis. METHODS: Mice were sensitized to ovalbumin. After the sensitization, an AC was delivered intravenously. RESULTS: In control mice, AC markedly induced HDC at a postanaphylactic time in the liver, lung, spleen, and ears. In MC-deficient W/W(v) mice, AC also induced HDC, although the effect was weaker than in control mice. AC increased IL-1 in the tissues, the pattern being similar in W/W(v) and control mice. AC induced HDC similarly in IL-1-deficient and control mice. In control mice, AC decreased histamine in the tissues (except the liver) for several hours. CONCLUSION: (1) AC induces HDC in both MC-dependent and MC-independent ways. (2) AC induces IL-1 mostly in non-MCs, but this IL-1 is not a prerequisite for the induction of HDC by AC. (3) HDC induction may contribute to the replenishment of the reduced pool of MC histamine in the anaphylactic period. (4) In the case of MC-dependent HDC induction, AC may stimulate MCs in such a way as to induce HDC within the MCs themselves, and/or AC-stimulated MCs may stimulate HDC induction in other cells, which will need to be directly identified in future studies.

Phenotypic profiling of engineered mouse melanomas with manipulated histamine production identifies histamine H2 receptor and rho-C as histamine-regulated melanoma progression markers.

In the present study, the impact of acquired neoplastic L-histidine decarboxylase (HDC) expression, and its direct consequence, the release of histamine in the tumor environment, was assessed on melanoma tumor progression. B16-F10 mouse melanoma cells were manipulated via stable transfection, and nine novel transgenic variants were generated in triplicates, constitutively expressing the full-length sense mouse HDC mRNA, a mock control, and an antisense HDC RNA segment, respectively. Establishing both primary skin tumors and lung metastases in C57BL/6 mice, the nine variants with different histamine-releasing capacities were subjected to a comprehensive comparative progression profiling in vivo. Our analyses showed trends of markedly accelerated tumor growth (P < 0.001), and moderately increased metastatic colony-forming potential (P = 0.010) along with rising levels of local histamine production. Using RNase protection assay for screening of the melanoma progression profile, and Western blotting for subsequent result validation, we looked for molecular progression markers affected by melanoma histamine secretion. Investigation of 21 functionally clustered markers associated with tumor proliferation, angiogenesis, invasivity, metastasis formation, local or systemic immunomodulation, and histamine signaling revealed positive correlations between histamine production, tumor histamine H2 receptor and rho-C expression (P < 0.001, P = 0.002, respectively). These observations confirm the involvement of histamine in the molecular machinery of melanoma progression.

Histidine decarboxylase, DOPA decarboxylase, and vesicular monoamine transporter 2 expression in neuroendocrine tumors: immunohistochemical study and gene expression analysis.

Histidine decarboxylase (HDC) and vesicular monoamine transporter 2 (v-MAT2) are involved in the biosynthesis and storage of histamine. DOPA decarboxylase (DDC) is involved in the biosynthesis of a variety of amines and shares a high degree of homology with HDC. HDC and v-MAT2 immunoreactivities (IR) have recently been detected in well-differentiated neuroendocrine tumors (WDNETs) and poorly differentiated neuroendocrine carcinomas (PDNECs) of various sites and have been proposed as general endocrine markers. We evaluated HDC and v-MAT2 IR in a series of 117 WDNETs and PDNECs from different sites. Western blotting analysis was performed to verify the specificity of anti-DDC and anti-HDC antibodies. Real-time RT-PCR was performed using specific probes for HDC and DDC on 42 cases, examined also for DDC IR. HDC and v-MAT2 IR were observed in the majority of WDNETs and PDNECs of all sites and HDC-IR cases were always also DDC-IR. In contrast, high levels of HDC mRNA were detected only in the gastroenteropancreatic WDNETs, which did not show increased DDC mRNA levels. On the other hand, bronchial carcinoids and lung PDNECs showed high DDC mRNA levels, but nearly undetectable HDC mRNA levels. Western blotting analysis showed a cross-reaction between anti-HDC and anti-DDC antibodies. HDC should not be considered as a general endocrine marker and HDC IR in bronchial carcinoids and PDNECs of the lung can probably be attributed to a cross-reaction with DDC.

Granulocyte macrophage-colony stimulating factor increases the expression of histamine and histamine receptors in monocytes/macrophages in relation to arteriosclerosis.

OBJECTIVE: To study the effect of granulocyte macrophage-colony-stimulating factor (GM-CSF) on histamine metabolism in arteriosclerosis, the expression of histidine decarboxylase (HDC; histamine-producing enzyme), histamine receptors 1 and 2 (HH1R and HH2R), and GM-CSF was investigated in human and mouse arteriosclerotic carotid arteries. Furthermore, the molecular mechanisms of GM-CSF-induced HDC and HH1R expression in monocytic U937 cells were investigated. METHODS AND RESULTS: Immunohistochemistry showed that atherosclerotic human coronary and mouse ligated carotid arteries contained HDC-expressing macrophages. Gene expression of HDC, HH1R, HH2R, and GM-CSF was also detected in the lesions. In U937 cells, GM-CSF enhanced histamine secretion and gene expression of HDC and HH1R. A promoter assay showed that GM-CSF enhanced gene transcription of HDC and HH1R but not HH2R. CONCLUSIONS: The present results indicate that HDC and HHR are expressed in arteriosclerotic lesion, and that GM-CSF induces HDC and HH1R expression in monocytes. Locally produced histamine might participate in atherogenesis by affecting the expression of atherosclerosis-related genes in monocytes and smooth muscle cells. The presence of histamine-producing macrophages and gene expression of histamine receptors and GM-CSF was demonstrated in arteriosclerotic lesions. In monocytic U937 cells, GM-CSF upregulated the expression of histamine and HH1R. Coordinated expression of histamine and its receptors by GM-CSF would participate in atherogenesis by affecting monocytic and SMC gene expression.

Inhibitory effect of quercetin on tryptase and interleukin-6 release, and histidine decarboxylase mRNA transcription by human mast cell-1 cell line.

Mast cells are involved in inflammatory processes and in allergic reactions where immunologic stimulation leads to degranulation and generation of numerous cytokines and inflammatory mediators. Mast cells have been proposed as an immune gate to the brain, as well as sensors of environmental and emotional stress, and are likely involved in neuropathologic processes such as multiple sclerosis. Among mast cell products, the protease tryptase could be associated with neurodegenerative processes through the activation of specific receptors (PARs) expressed in the brain, while interleukin (IL)-6 likely causes neurodegeneration and exacerbates dysfunction induced by other cytokines; or it could have a protective effect against demyelinisation. In this report we show that quercetin, a natural compound able to act as an inhibitor of mast cell secretion, causes a decrease in the release of tryptase and IL-6 and the down-regulation of histidine decarboxylase (HDC) mRNA from human mast cell (HMC)-1 cells. As quercetin dramatically inhibits mast cell tryptase and IL-6 release and HDC mRNA transcription by HMC-1 cell line, these results nominate quercetin as a therapeutical compound in association with other therapeutical molecules for neurological diseases mediated by mast cell degranulation.

Strain difference of murine bone marrow-derived mast cell functions.

Mast cells play an important role for the induction and the expression of allergic responses. In this report, we studied the strain difference of bone marrow-derived murine mast cell (BMMC) functions in vitro. BMMC were induced by in vitro culture of bone marrow cells from BALB/c and C57BL/6 mice with interleukin (IL)-3 for 4 weeks, stimulated with immunoglobulin E antibody and antigen, and mediators and cytokines released in the culture supernatant were assayed. BMMC from C57BL/6 mice released a higher amount of granule-associated mediators, beta-hexosaminidase, and histamine than that from BALB/c mice. The expression of mRNA of histidine decarboxylase was higher in C57BL/6 mice. Conversely, the productions of newly synthesized mediators, prostaglandin D2 (PGD2), IL-6, and monocyte chemoattractant protein-1, and the mRNA expression of IL-5 were higher in BALB/c BMMC than C57BL/6 BMMC. Although mRNA and protein expression levels of cyclooxygenase-2 were equal in two strains, both expression levels of hematopoietic PGD synthase (hPGDS) were higher in BALB/c BMMC. Mast cells, freshly obtained from mice, also showed the same strain difference concerning the mediator release. These results indicate that the strain difference exists in mast cell functions in mice, and this difference can be considered to induce the susceptibility difference to allergic reactions in mouse strains.

Tumor-promoting activity of staurosporine, a protein kinase inhibitor on mouse skin.

Staurosporine, which is a potent inhibitor of protein kinases, such as protein kinase C, inhibited both inductions of adhesion of human promyelocytic leukemia cells (50% effective dose = 9.0 nM) and Epstein-Barr virus early antigen in Raji cells (50% effective dose = 3.4 nM) by teleocidin. However, staurosporine induced irritation on mouse ear and histidine decarboxylase activity in mouse skin. It did not induce ornithine decarboxylase activity in mouse epidermis. The two-stage carcinogenesis experiments of staurosporine were carried out at two different doses. Experiment 1 revealed that the group treatment with a single application of 100 micrograms of 7,12-dimethylbenz(a)anthracene, followed by repeated applications of 50 micrograms of staurosporine, resulted in 85.7% of tumor-bearing mice at Wk 30, whereas group treatment with staurosporine alone or 7,12-dimethylbenz(a)anthracene alone gave 6.7% and 0%, respectively. Experiment 2 showed that group treatment with 7,12-dimethylbenz(a)anthracene followed by applications of 10 micrograms of staurosporine resulted in 33% of tumor-bearing mice at Wk 30. In addition, staurosporine treatment reduced the percentages of tumor-bearing mice treated with teleocidin from 100% to 67% in Wk 15. These results demonstrated that staurosporine is a weak tumor promoter of mouse skin compared with teleocidin, but staurosporine has some potency to inhibit tumor promotion by teleocidin.

Hypothalamic L-Histidine Decarboxylase Is Up-Regulated During Chronic REM Sleep Deprivation of Rats.

A competition of neurobehavioral drives of sleep and wakefulness occurs during sleep deprivation. When enforced chronically, subjects must remain awake. This study examines histaminergic neurons of the tuberomammillary nucleus of the posterior hypothalamus in response to enforced wakefulness in rats. We tested the hypothesis that the rate-limiting enzyme for histamine biosynthesis, L-histidine decarboxylase (HDC), would be up-regulated during chronic rapid eye movement sleep deprivation (REM-SD) because histamine plays a major role in maintaining wakefulness. Archived brain tissues of male Sprague Dawley rats from a previous study were used. Rats had been subjected to REM-SD by the flowerpot paradigm for 5, 10, or 15 days. For immunocytochemistry, rats were transcardially perfused with acrolein-paraformaldehyde for immunodetection of L-HDC; separate controls used carbodiimide-paraformaldehyde for immunodetection of histamine. Immunolocalization of histamine within the tuberomammillary nucleus was validated using carbodiimide. Because HDC antiserum has cross-reactivity with other decarboxylases at high antibody concentrations, titrations localized L-HDC to only tuberomammillary nucleus at a dilution of ≥ 1:300,000. REM-SD increased immunoreactive HDC by day 5 and it remained elevated in both dorsal and ventral aspects of the tuberomammillary complex. Our results suggest that up-regulation of L-HDC within the tuberomammillary complex during chronic REM-SD may be responsible for maintaining wakefulness.

Wnt-ß-Catenin Signaling Promotes the Maturation of Mast Cells.

Mast cells play an important role in the pathogenesis of allergic diseases. Immature mast cells migrate into peripheral tissues from the bone marrow and undergo complete maturation. Interestingly, mast cells have characteristics similar to hematopoietic stem cells (HSCs), such as self-renewal and c-kit expression. In HSCs, Wnt signaling is involved in their maintenance and differentiation. On the other hand, the relation between Wnt signaling and mast cell differentiation is poorly understood. To study whether Wnt signals play a role in the maturation of mast cells, we studied the effect of Wnt proteins on mast cell maturation of bone marrow-derived mast cells (BMMCs). The expression levels of CD81 protein and histidine decarboxylase mRNA and activity of mast cell-specific protease were all elevated in BMMCs treated with Wnt5a. In addition, Wnt5a induced the expression of Axin2 and TCF mRNA in BMMCs. These results showed that Wnt5a could promote the maturation of mast cells via the canonical Wnt signaling pathway and provide important insights into the molecular mechanisms underlying the differentiation of mast cells.

Augmented lipopolysaccharide-induction of the histamine-forming enzyme in streptozotocin-induced diabetic mice.

Disorders of the microcirculation and reduced resistance to infection are major complications in diabetes. Histamine enhances capillary permeability, and may also reduce cellular immunity. Here we demonstrate that streptozotocin (STZ)-induced diabetes in mice not only enhances the activity of the histamine-forming enzyme, histidine decarboxylase (HDC), but also augments the lipopolysaccharide (LPS)-induced elevation of HDC activity in various tissues, resulting in a production of histamine. The augmentation of HDC activity occurred as early as 2 days after STZ injection, but was not seen in nondiabetic mice. When given to STZ-treated mice, nicotinamide, an inhibitor of poly(ADP-ribose) synthetase, reduced both the elevation of blood glucose and the elevations of HDC activity and histamine production. These results suggest that hyperglycemia may initiate a sequence of events leading not only to an enhancement of basal HDC activity, but also to a sensitization of mice to the HDC-inducing action of LPS. We hypothesize that bacterial infections and diabetic complications may mutually exacerbate one another because both involved an induction of HDC.

Induction of histidine decarboxylase by dexamethasone in mastocytoma P-815 cells.

Dexamethasone at a concentration as low as 10 nM significantly increased both the histamine content and histidine decarboxylase activity of cultured mastocytoma P-815 cells. Both effects were clearly seen using several glucocorticoids, which were as effective as dexamethasone. In contrast to that of histamine, the serotonin level of mastocytoma P-815 cells was decreased by treatment with dexamethasone. The dexamethasone-induced increases in histamine content and histidine decarboxylase activity were completely suppressed by the addition of cycloheximide and actinomycin D. Mastocytoma P-815 cells were found to possess binding sites for [3H]dexamethasone in the cytosol (Kd = 15.7 nM) and the nuclei (Kd = 1.26 nM). These results show that glucocorticoids significantly stimulate de novo synthesis of histidine decarboxylase.

Expression and characterization of recombinant mouse mastocytoma histidine decarboxylase.

The possibility of post-translational processing of mouse mastocytoma histidine decarboxylase (HDC; EC 4.1.1.22) was investigated. The molecular mass of the recombinant HDC expressed in Sf9 cells using HDC cDNA from mouse mastocytoma cells was determined to be 74 kDa by SDS-PAGE. In contrast to the native HDC from mastocytoma cells, the recombinant 74 kDa HDC was essentially inactive and precipitable in Sf9 cells. On the other hand, deletion mutants of the recombinant HDC lacking a C-terminal region equivalent to 10 (64 kDa) or 20 kDa (54 kDa) in size were present as active forms in the soluble fraction of Sf9 cells. To examine the C-terminal deletion of the 74 kDa species yielding the 53 kDa species by means of the immunoblotting analysis, two peptides (corresponding to residues 323-337 and 572-586 of the recombinant 74 kDa HDC peptide) were synthesized, and rabbit antiserum specific for each peptide was prepared. On immunoblotting analysis, anti-peptide 323-337 antiserum recognized both the recombinant 74 kDa and native enzyme subunit peptides, but anti-peptide 572-586 antiserum recognized only the recombinant 74 kDa peptide, i.e., not the native enzyme subunit peptide. Furthermore, HDC activity in the crude extract from Sf9 cells was not precipitable with antipeptide 572-585 antiserum. These results strongly suggest that the 53 kDa subunit peptide of native mastocytoma HDC is derived from the unidentified inactive 74 kDa HDC peptide, probably by post-translational processing of HDC in its C-terminal region.