Partial purification and characterization of L-histidine decarboxylase from fetal rats

Histaminergic neurons in the tuberomammillary nucleus as a control centre for wakefulness

Histamine plays pleiotropic roles as a neurotransmitter in the physiology of brain function, this includes the maintenance of wakefulness, appetite regulation and memory retrieval. Since numerous studies have revealed an association between histaminergic dysfunction and diverse neuropsychiatric disorders, such as Alzheimer's disease and schizophrenia, a large number of compounds acting on the brain histamine system have been developed to treat neurological disorders. In 2016, pitolisant, which was developed as a histamine H₃ receptor inverse agonist by Schwartz and colleagues, was launched for the treatment of narcolepsy, emphasising the prominent role of brain histamine on wakefulness. Recent advances in neuroscientific techniques such as chemogenetic and optogenetic approaches have led to remarkable progress in the understanding of histaminergic neural circuits essential for the control of wakefulness. In this review article, we summarise the basic knowledge about the histaminergic nervous system and the mechanisms underlying sleep/wake regulation that are controlled by the brain histamine system. LINKED ARTICLES: This article is part of a themed issue on Neurochemistry in Japan. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.4/issuetoc.

The metabolism of histamine in rat hypothalamus and cortex after reserpine treatment

The effect of reserpine on histamine (HA) and tele-methylhistamine (N(τ)-MHA) in hypothalamus and cortex of rats was analyzed and compared to catecholamines. IP injection of reserpine (5 mg/kg) confirmed the effectiveness of reserpine treatment on noradrenaline and dopamine levels. Our in-vitro experiment with synaptosomal/crude mitochondrial fraction from hypothalamus and cortex confirmed that while mono amine oxidase (MAO) is an efficient metabolic enzyme for catecholamines, HA is not significantly affected by its enzymatic action. HMT activity after reserpine, pargyline and L-histidine treatment showed no differences compared to the control values. However HDC was significantly increased in both hypothalamus and cortex. In this study, Ws/Ws rats with deficiency of mast cells were used to clarify aspects of HA metabolism in HAergic neurons by eliminating the contribution of mast cells. The irreversible MAO-B inhibitor Pargyline (65 mg/kg) failed to accumulate N(τ)-MHA in the hypothalamus. However, when animals treated with reserpine and pargyline/reserpine were compared, the last group showed higher N(τ)-MHA values (p < 0.01). Moreover, the precursor of HA, L-histidine (1 g/kg), produced an increase of HA in the hypothalamus to 166% and the cortex to 348%. In conclusion, our results suggest that the effect of reserpine on the HA pools in the brain might be different. The neuronal HA pools are more resistant to reserpine as compared to those of catecholamine. Moreover, the HAergic pool appears to be more resistant to depletion than mast cells' pool, and thus HDC/HMT activity and its localization may play a key role in the understanding of HA metabolism in brain after reserpine treatment.

Progress in allergy signal research on mast cells: up-regulation of histamine signal-related gene expression in allergy model rats

Brown Norway allergy model rats sensitized to toluene 2,4-diisocyanate (TDI) were developed. Histamine H(1) receptor mRNA level was elevated in nasal mucosa of allergy model rats after the provocation with TDI, which was followed by H(1)-receptor up-regulation. Elevation of histamine H(1) receptor mRNA was partially suppressed by d-chlorpheniramine and olopatadine, antihistamines. Histamine induced increase in histamine H(1) receptor gene expression in vitro, and the protein kinase C-delta isoform was suggested to mediate the gene expression. On the other hand, elevation of histamine H(1) receptor mRNA was completely suppressed by dexamethasone in allergy model rats. Provocation with TDI also induced mRNA elevation of histidine decarboxylase, a sole histamine-forming enzyme, followed by the increase of both HDC activity and histamine content in nasal mucosa of allergy model rats. HDC mRNA elevation and increase in both HDC activity and histamine level were almost completely suppressed by dexamethasone. These observations suggest that histamine H(1) receptor up-regulation and increase in histamine level play an important role in allergy through the regulation of histamine signaling.

Food-deprived activity stress decreased the activity of the histaminergic neuron system in rats

The hypothalamus, which is rich in histaminergic neurons, is highly sensitive to aversive stimuli such as stress. Histamine H3 receptors, which regulate histamine release from the presynaptic site, are associated with stress-induced brain activity. In this study, we investigated the changes of histamine content and histamine H1 and H3 receptors in the brains of rats subjected to stress induced through food deprivation and physical activity on a running wheel (food-deprived activity stress). For purposes of comparison, we also examined the stressful effects of forced swimming on the histaminergic neuron system of rats. The H3 receptor density rapidly declined in the acute phase of stress but gradually returned to the control level in the chronic phase. On the other hand, the H1 receptor slowly decreased and remained at a low level during the chronic phase. These results reveal that there is a discrepancy between the levels of H1 and H3 receptors in the acute and chronic phases of stress. Brain histamine content gradually increased during the late phase of both food-deprived activity stress and forced swimming stress. These changes presumably resulted in the inhibition of histaminergic neuronal activity in the chronic stress condition. In accordance with this hypothesis, the intraventricular administration of histamine significantly reduced the hyperactivity caused by food-deprived activity stress. Since extensive exercise and restricted feeding are thought to be associated with anorexia nervosa, the abnormalities in the histaminergic neuron system might contribute to trait status in anorexia nervosa.

Quantitative radioisotopic determination of histidine decarboxylase using high-performance liquid chromatography

We have developed a procedure for the accurate measurement of histidine decarboxylase in tissues expressing low levels of enzymatic activity. Briefly, histamine is enzymatically synthesized from [3H]-labeled histidine, followed by purification using high-performance liquid chromatography (HPLC) and quantitation by liquid scintillation counting. This method presents three advantages over previous techniques. First, prior to HPLC purification, excess precursor [3H]histidine is removed on an anion-exchange resin. Second, purification by HPLC is considerably more selective than that of classical cation-exchange gravity columns or organic solvent extractions. Finally, the accuracy of this method is improved by including non-radiolabeled histamine as internal standard, which is quantified by ultraviolet detection. This simple procedure allows highly sensitive and accurate determinations of histamine synthesis.

Glucocorticoid hormones downregulate histidine decarboxylase mRNA and enzyme activity in rat lung

Histidine decarboxylase (HDC) is the primary enzyme regulating histamine biosynthesis. Histamine contributes to the pathogenesis of chronic inflammatory disorders such as asthma. Because glucocorticoids are effective in the treatment of asthma, we examined the effects of 6 h of exogenously administered dexamethasone (0.5-3,000 microg/kg ip), corticosterone (0.2-200 mg/kg ip), or endogenously elevated corticosterone (via exposure of rats to 10% oxygen) on HDC expression in the rat lung. HDC transcripts were decreased approximately 73% with dexamethasone treatment, 57% with corticosterone treatment, and 50% with exposure to 10% oxygen. Likewise, HDC enzyme activity was decreased 80% by treatment with dexamethasone and corticosterone and 60% by exposure to 10% oxygen. Adrenalectomy prevented the decreases in HDC mRNA and enzyme activity observed in rats exposed to 10% oxygen, suggesting that the adrenal gland is necessary for the mediation of hypoxic effects on HDC gene expression. These results demonstrate that corticosteroids initiate a process that leads to the decrease of HDC mRNA levels and enzyme activity in rat lung.

Recombinant expression of rat histidine decarboxylase: generation of antibodies useful for western blot analysis

Histidine decarboxylase catalyses the formation of histamine, an important biological messenger. In spite of the essential biological functions exerted by histamine the knowledge about the mechanisms involved in the regulation of histidine decarboxylase is rather limited. This is most likely due to the limited supply of suitable tools, including highly specific antibodies. In the present study we describe the production and characterisation of specific antisera against rat histidine decarboxylase using recombinant protein synthesised in a bacterial expression system. The antisera were shown to effectively immunoprecipitate histidine decarboxylase activity in extracts of fetal rat liver as well as to detect the histidine decarboxylase protein by Western blot analysis of COS-7 cells expressing recombinant rat histidine decarboxylase. The results demonstrate the successful production of highly specific antisera to histidine decarboxylase which may become valuable tools in future studies of the structure and function of this enzyme.

Ontogenetic development of histamine receptor subtypes in rat brain demonstrated by quantitative autoradiography

The postnatal ontogenetic development of the histamine receptor subtypes was studied in rat brain by quantitative receptor autoradiography with highly sensitive imaging plates. H1 receptor binding sites labeled with [3H]pyrilamine were detected on postnatal day 2 (P2) and increased very slowly until P9, and then rapidly reaching the adult levels in the hypothalamus, hippocampus, and amygdala by P16. The densities of H1 receptor binding sites in the cortex, striatum, thalamus, and substantia nigra were relatively low during development. H3 receptor binding sites labeled with [3H](R) alpha-methylhistamine were not detectable until P9. On P9, their density was higher in the substantia nigra than in other regions. Subsequently, H3 receptor binding increased, reaching the adult levels in the substantia nigra on P16 and in the other regions on P23. The histamine concentration was initially very high, but decreased to the adult level by P16. On the contrary, the activity of L-histidine decarboxylase of whole brain tissue was low on P5, and increased markedly from P16 to P23, to the adult level on P30. Administration of (S) alpha-fluoromethylhistidine (FMH), a specific inhibitor of L-histidine decarboxylase (HDC), significantly decreased both the HDC activity and histamine concentration during postnatal development. FMH treatment did not change H1 receptor binding in any brain region, but significantly increased H3 receptors in the substantia nigra and striatum on P23. Unilateral injection of 6-hydroxydopamine into the striatum on P2 resulted in up-regulation of H3 receptor binding sites in the dorsomedial (11%) and dorsolateral (18%) regions of the striatum and substantia nigra (31%) on P23, but no change in the H3 receptor density in the nucleus accumbens or frontal cortex on P11 and P23. These results demonstrate that the developmental patterns of H1 and H3 receptors are heterogeneous and independent of each other. There are marked mismatches of presynaptic and postsynaptic markers of the histaminergic neuron system as in other aminergic systems.

Histamine depletion in brain caused by treatment with (S)alpha-fluoromethylhistidine enhances ischemic damage of gerbil hippocampal CA2 neurons

The effect of (S)alpha-fluoromethylhistidine (FMH), a specific inhibitor of histamine synthesis from histidine, on ischemic damage was examined in gerbil brain after forebrain ischemia. Two h after subcutaneous FMH injection, the histamine content of the brain was significantly reduced. Neuronal loss in the CA2 region of the hippocampus 7 days after 3 min ischemia was enhanced by treatment with FMH. These results indicate that depletion of brain histamine aggravates neuronal death of hippocampal CA2 neurons after 3 min ischemia.

Clobenpropit (VUF-9153), a new histamine H3 receptor antagonist, inhibits electrically induced convulsions in mice

The effect of clobenpropit (VUF-9153), a new histamine H3 receptor antagonist, on electrically induced convulsions was studied in mice. Clobenpropit significantly and dose dependently decreased the duration of each convulsive phase. Its anticonvulsant effects were prevented by pretreatment with (R)-alpha-methylhistamine and imetit (VUF-8325), histamine H3 receptor agonists. These findings suggest that the effect of clobenpropit on electrically induced convulsions is due to an increase in endogenous histamine release in the brain, which is consistent with biochemical results that clobenpropit increased brain histidine decarboxylase activity dose dependently. The anticonvulsive effect of clobenpropit was antagonized by mepyramine, a histamine H1 receptor antagonist, but not by zolantidine, a histamine H2 receptor antagonist, indicating that histamine released by the anticonvulsant effect of clobenpropit interacts with histamine H1 receptors of postsynaptic neurons. The present findings of the effect of clobenpropit on electrically induced convulsions are fully consistent with those of thioperamide as described previously (Yokoyama et al., 1993, Eur. J. Pharmacol. 234, 129), supporting the hypothesis that the central histaminergic neuron system is involved in the inhibition of seizures.

Effects of the histamine H3 receptor ligands thioperamide and (R)-alpha-methylhistamine on histidine decarboxylase activity of mouse brain

The effects of the histamine H3 receptor ligands thioperamide and (R)-alpha-methylhistamine on the histidine decarboxylase (HDC) activity and histamine content of mouse brain were examined. Thioperamide, a histamine H3 antagonist, significantly increased the HDC activity in the brain of ddY, W/Wv and ICR mice 2-6 hr after its intraperitoneal (i.p.) injection. On the other hand, (R)-alpha-methylhistamine, a histamine H3-receptor agonist, caused no significant change in the HDC activity. The whole brain histamine content of ddY mice decreased significantly to 60-70% of the control level 2-8 hr after injection of thioperamide (25 mg/kg, i.p.), but then increased to 90% of the control level 10 hr after the injection. These in vivo results showed that blockade of the presynaptic histamine H3-receptor, which causes release of presynaptic histamine, increased the HDC activity.

Histidine decarboxylase measurement in brain by 14CO2 trapping

A method for measuring histidine decarboxylase (HDC) in crude rat brain homogenates was developed by modification of existing 14CO2-trapping methods. The addition of EDTA to tissue homogenates and assay buffer reduced non-enzymatic decarboxylation, and improved assay sensitivity and reliability. Addition of polyethylene glycol (molecular weight 300, PEG300) to the homogenizing buffer increased enzyme stability, permitting storage of crude homogenates. Studies of time course, tissue dilution and blanks showed that up to 8 mg of tissue could be assayed successfully with a 3.5-hr incubation. S-alpha-Fluoromethylhistidine (FMH) and alpha-hydrazinohistidine, specific inhibitors of HDC, induced concentration-dependent reductions of enzyme activity by up to 90%, whereas inhibitors of other decarboxylases had little or no effect. Kinetic studies of the enzyme in crude homogenates yielded Km and Vmax values similar to those found previously with other HDC methods, although a poor fit was found to a single enzyme model. When determined by the new method, the distribution of HDC in seven regions of the rat brain agreed well with previous results. The method is rapid, simple to perform, and requires no specialized equipment other than a scintillation counter.

Fluctuation of fetal rat hepatic histidine decarboxylase activity through the glucocorticoid-ACTH system

Our studies suggest that the fluctuation of HDC activity in fetal liver in late gestation is regulated by the plasma glucocorticoid level through the pituitary-adrenal system. Taken together, these results support the conclusion that glucocorticoid promotes a rapid increase in HDC synthesis in fetal liver histamine-forming cells, as well as in mouse mastocytoma P-815 cells and rat glandular stomachs.

Marked increase in gastric histidine decarboxylase activity in patients with hypergastrinemia

Histidine decarboxylase (HDC) activity and histamine content were measured in endoscopic gastric biopsy specimens of 19 control subjects with normogastrinemia and 6 patients with hypergastrinemia. In controls, the HDC activity was 3 fold higher in fundic mucosa (120 +/- 13 fmol/min/mg protein, mean +/- S.E.) than in antral mucosa (39 +/- 5 fmol/min/mg protein). In patients with hypergastrinemia, an extremely high HDC activity (713 +/- 181 fmol/min/mg protein) was observed in fundic mucosa, although the HDC activity in antral mucosa was not significantly different from that of controls. The histamine content in fundic mucosa was also significantly higher in patients with hypergastrinemia than in controls but no significant difference was seen in histamine content in antral mucosa between the two groups. These results are compatible with the hypothesis that in man, as well as in rat, histamine synthesis in fundic mucosa is enhanced by gastrin.

Immuno-cross-reactivity of histidine and dopa decarboxylases

Immuno-cross-reactivity between histidine decarboxylase (HDC) and dopa decarboxylase (DDC) was investigated. By comparing the cDNA sequences of rat HDC with rat and guinea-pig DDCs, we found a region that may possibly be related to the cross-reactivity of anti-rat HDC antibody with guinea-pig DDC. The peptide encoded by this region was synthesized and anti-peptide antibody was prepared. We also purified HDC and DDC homogeniously from fetal rat liver and guinea-pig liver, respectively. On immunoblotting, anti-peptide antibody recognized both rat HDC and guinea-pig DDC. Anti-HDC polyclonal antibody which also recognizes both enzymes detected only rat HDC when it was absorbed by the peptide. This result indicates that this region is responsible for the immuno-cross-reactivity of anti-rat HDC antibody with guinea-pig DDC.

Histidine decarboxylase in human basophilic leukemia (KU-812-F) cells. Characterization and induction by phorbol myristate acetate

The human leukemic cell line KU-812-F is known to differentiate into mature basophil-like cells under serum-free culture conditions. In the present study, the activity of histidine decarboxylase (HDC), a histamine-forming enzyme, in KU-812-F cells was found to be high, ranging from 10 to 57 pmol/min/mg protein. The great variation in HDC activity appeared to be due to different percentages and degrees of maturity of basophil-like cells during differentiation of this cell line. The enzyme was inhibited by alpha-fluoromethylhistidine but not by carbidopa, was unable to form dopamine from L-3,4-dihydroxyphenylalanine, and had a Km value for histidine of 0.27 mM, indicating that it was HDC and not aromatic amino acid decarboxylase. The HDC activity increased 1.8-fold when the cells were stimulated by phorbol myristate acetate, which is known to activate protein kinase C, and this increase was blocked by staurosporine, a potent inhibitor of protein kinase C.

Histidine decarboxylase from rat and rabbit brain: partial purification and characterization

Histidine decarboxylase, the synthetic enzyme for histamine, was partially purified from regions of rat or rabbit brain rich in the enzyme. The enzyme was purified using ion exchange and hydrophobic column chromatography and chromatofocusing. Approximately 70-fold and 110-fold enrichments were attained from rat and rabbit brain, respectively. Rat and rabbit brain histidine decarboxylase had isoelectric points of pH 5.4 and 5.6, Km values of 80 microM and 120 microM histidine and Vmax values of 210 and 625 pmol histamine formed/hr-mg protein, respectively. The partially purified histidine decarboxylase from both sources was dependent on pyridoxal phosphate for maximal activity and was inhibited by alpha-fluoromethylhistidine, nickel chloride and cobaltous chloride but was not inhibited by impromidine, alpha-methyldopa, DTNB, zinc chloride or mercuric chloride. The enzyme had a broad pH optimum between pH 7.2 and 8.0. These studies provide further information on the characteristics of mammalian histidine decarboxylase from brain.

Effects of glycyrrhizin and glycyrrhetinic acid on dexamethasone-induced changes in histamine synthesis of mouse mastocytoma P-815 cells and in histamine release from rat peritoneal mast cells

The effects of glycyrrhizin and its aglycone, glycyrrhetinic acid, on dexamethasone-induced changes in the histamine synthesis of mastocytoma P-815 cells and in the histamine release from antigen-stimulated rat peritoneal mast cells were investigated. Glycyrrhetinic acid but not glycyrrhizin, at concentrations from 20 to 35 microM, almost completely inhibited the dexamethasone-induced increases in both the histamine content and histidine decarboxylase activity of cultured mastocytoma P-815 cells. Glycyrrhetinic acid, however, showed practically no inhibition of [3H]dexamethasone binding to the cytoplasmic receptor. On the other hand, glycyrrhetinic acid but not glycyrrhizin markedly inhibited the release of histamine from antigen-stimulated rat mast cells, and intensified the inhibitory activity induced by dexamethasone. Glycyrrhetinic acid inhibited the antigen-induced release and incorporation of [3H]arachidonic acid in immunized rat mast cells. The administration of glycyrrhizin into rats, in contrast to the in vitro treatment of the cells with glycyrrhizin, markedly inhibited histamine release from antigen-stimulated rat mast cells. These results suggest that glycyrrhetinic acid inhibited dexamethasone-induced changes in the histamine synthesis of mastocytoma P-815 cells, and in the histamine release from rat mast cells. On the other hand, glycyrrhizin may exert its effect after conversion to glycyrrhetinic acid in vivo.

Increase of histidine decarboxylase activity in murine myelomonocytic leukemia cells (WEHI-3B) in parallel to their differentiation into macrophages

When cells of mouse myelomonocytic leukemia cell line, WEHI-3B, were cultured in the presence of actinomycin D plus the serum which was obtained from mice injected with bacterial endotoxin, i.e., lipopolysaccharide, their histidine decarboxylase (L-histidine carboxy-lyase, EC 4.1.1.22) (HDC) activity increased about 100-fold with a peak at 48 h. According to the increase in HDC activity, the expression of surface antigens associated with macrophages, such as Mac II, Mac III and Iad, increased markedly on WEHI-3B cells as well as their morphological changes to macrophages. Histamine levels in the culture medium increased concomitantly with the increase in the HDC activity in WEHI-3B cells, whereas the histamine contents inside the cells did not increase remarkably. Furthermore, the addition of lipopolysaccharide to the culture medium caused an additional 2-fold increase in the HDC activity of WEHI-3B cells. These results indicate that the increase in HDC activity in WEHI-3B cells may represent an event in the process of the differentiation to macrophages.

Properties and ontogenic development of membrane-bound histidine decarboxylase from rat brain

Histidine decarboxylase (HD) activity was determined in high-speed fractions (100,000 g for 60 min) obtained from whole rat brain homogenates. Twenty-eight percent of the HD activity was associated with membranes, and the remaining was soluble. Several properties of the soluble and membrane-bound HD were compared. No significant differences in the values of Km for histidine and pyridoxal 5'-phosphate were observed. The solubilization of membrane-bound HD with Triton X-100 resulted in an increase of 60% over the nonsolubilized activity with no changes in the Km for substrate and cofactor. The proportion of free pyridoxal 5'-phosphate-independent activity was identical in both fractions. The soluble and membrane-bound forms of the enzyme differ slightly in their pH-activity profiles, although both enzymes showed an optimum pH near 6.5. The HD activities present in soluble and membrane fractions were determined at different postnatal ages. The soluble activity increased until day 90, whereas the membrane-bound activity became stabilized from day 20.

Long-term depletion of histamine in guinea-pigs by administration of alpha-fluoromethylhistidine, a specific inhibitor of histidine decarboxylase; effect on the sensitivity of histamine receptors

The effect of intraperitoneal administration of alpha-fluoromethylhistidine (alpha-FMH), a specific inhibitor of histidine decarboxylase, at a dose of 100 mg/kg twice a day for 6 weeks on the sensitivity of histamine receptors in the guinea-pigs was examined. The histamine contents in the ileum, heart and brain after the treatment decreased to about 54%, 83% and 9-62% (depending on the region), respectively, of those of controls. However, there were no significant difference in the histamine-induced contraction of the ileum and atrium, the maximal binding (Bmax) and the dissociation constant (Kd) of [3H]-mepyramine binding to membrane fractions of the ileum and brain (except the cortex) and the increase of cyclic AMP formation induced by histamine in membranes of the heart and brain (except the cortex) between alpha-FMH-treated- and untreated animals. These results suggest that long-term histamine depletion dose not significantly affect the sensitivity of histamine receptors of guinea-pig except in the brain cortex.

Induction of histidine decarboxylase of rat basophilic leukemia (2H3) cells stimulated by higher oligomeric IgE or phorbol myristate acetate

When rat basophilic leukemia (2H3) cells were stimulated by higher oligomer, the chemically cross-linked oligomers of IgE, in the presence of calcium the activity of histidine decarboxylase (HDC, L-histidine carboxylase, E.C.4.1.1.22), a histamine-forming enzyme, was increased by 1 hr, reaching maximum activity by 2 hr, and returning to the original level by 8 hr. A similar increase in enzyme activity was observed in cells treated with phorbol myristate acetate (PMA) or oleoyl-acetylglycerol (OAG), which are known activators of protein kinase C. Removal of calcium from medium abolished the increase in HDC activity in response to higher oligomer but not that induced by PMA or OAG, suggesting that the increase in HDC activity may be mediated by protein kinase C. The increase in the HDC activity probably required induction of enzyme synthesis, because it was prevented by cycloheximide.

Purification and properties of pyridoxal-5'-phosphate-dependent histidine decarboxylases from Klebsiella planticola and Enterobacter aerogenes

Histidine decarboxylases from Klebsiella planticola and Enterobacter aerogenes were purified to homogeneity and compared with the histidine decarboxylase from Morganella morganii. All three enzymes required pyridoxal 5'-phosphate as a coenzyme, showed optimal activity at pH 6.5, decarboxylated only histidine among the amino acids derived from protein, and were tetramers or dimers of identical subunits. Amino-terminal sequences of the three enzymes showed up to 81% homology through residue 33, but the enzymes differed sufficiently in amino acid composition and sequence so that no cross-reaction occurred between the K. planticola or E. aerogenes enzymes and antibodies to the decarboxylase from M. morganii. All three enzymes were inhibited by carbonyl reagents; by amino-, carboxyl-, and some methyl-substituted histidines; and by alpha-fluoromethylhistidine. These decarboxylases, all from gram-negative organisms, differed greatly in subunit structure, biogenesis, and other properties from the pyruvoyl-dependent histidine decarboxylases from gram-positive organisms described previously.

Demonstration of immunohistochemical and immunochemical cross-reactivity of L-histidine and L-dopa decarboxylases using antibodies against the two enzymes

Both rat L-histidine decarboxylase (HDC) and guinea-pig L-DOPA decarboxylase (DDC) were shown immunohistochemically and immunochemically to react with anti-rat HDC antibody. No cross-reaction was observed in immunoprecipitation experiments, but both anti-rat HDC antibody and anti-rat DDC antibody immunostained neurons in the substantia nigra, raphe nucleus and locus coeruleus of guinea-pig brain. Moreover, on immunoblotting, anti-rat HDC antibody recognized not only rat HDC but also guinea-pig DDC, but not rat DDC. However, anti-rat DDC antibody showed no immunohistochemical or immunochemical cross-reactivity with rat HDC.

Purification and characterization of histidine decarboxylase from mouse kidney

Histidine decarboxylase was purified 800-fold from the kidneys of thyroxine-treated mice. The purification procedure included precipitation of protein from a crude supernatant after heating it to 55 degrees C at pH 5.5, fractionation with (NH4)2SO4, phosphocellulose column chromatography, chromatofocusing, DEAE-Sepharose column chromatography, gel filtration on Sephacryl S-300 and preparative polyacrylamide-gel electrophoresis. The native enzyme had an estimated Mr of 113 000. The protein was analysed in SDS/10%-polyacrylamide gels and formed a single band corresponding to a subunit Mr of 55 000, indicating that it is a dimer. Three forms of the enzyme were resolved on isoelectrofocusing gels, with pI 5.3, 5.5 and 5.7.

Effects of alpha-fluoromethylhistidine on increase in histidine decarboxylase activity of maternal mouse kidney observed during late pregnancy and evidence for its non-mast cell origin by using estrogen and W/WV mice

The increase of histidine decarboxylase (HDC) activity during late pregnancy in the whole bodies of fetal mice and the kidneys of their mothers were almost completely inhibited by i.p. administration of 25 mg/kg of alpha-fluoromethylhistidine (alpha-FMH), a suicide inhibitor of HDC, starting on day 13 of pregnancy. The increase of HDC in fetal mice was previously shown to be in mast cells [T. Watanabe et al., Proc. Natl. Acad. Sci. U.S.A. 78, 4209-4212 (1981)]. The increase of HDC in maternal kidneys was examined by using estrogen and W/WV mice, which were devoid of mast cells and infertile. Treatment of castrated mice with 17-beta-estradiol increased the HDC activity of the kidney, and this increase was antagonized by concomitant treatment with clomiphene, an antiestrogen, confirming that the increase is mediated through an estrogen receptor. HDC activity in the kidney of W/WV mice was also increased by estradiol treatment, indicating that HDC activity was associated with non-mast cells.

Effects of various compounds on histidine decarboxylase activity: active site mapping

The effect of about one hundred compounds on the activity of histidine decarboxylase partially purified from whole bodies of fetal rats was determined. Most of them at their 10 mM concentration had little effect on the enzyme activity; but 12 compounds inhibited the enzyme to a greater extent than 30%. Among these, except for alpha-methylhistidine that has been known to be a strong and specific inhibitor, DOPA, homocysteine, cysteine, methionine and urocanic acid were the best inhibitors; beta-phenyllactic acid, phenylpyruvic acid and carnosine were less strong inhibitors; valine, oxaloacetic acid and N tau-methylimidazole acetic acid were weak inhibitors. Histamine had no inhibitory action. Thus, the substrate binding site of histidine decarboxylase is very rigid and specific for L-histidine.

In vivo and in vitro inhibition of human histidine decarboxylase by (S)-alpha-fluoromethylhistidine

Histidine decarboxylase (HDC) activity in Ficoll-Hypaque purified human peripheral blood leukocytes (PBL) was determined by measuring the formation of [3H]histamine from L-[3H]histidine. HDC activity was inhibited in vitro to more than 90% by (S)-alpha-fluoromethylhistidine (alpha-FMH) at concentrations of 10(-5) M and above. Both polymorphonuclear and mononuclear cells possessed HDC activity, but on a per cell basis the former had several-fold higher enzyme activity than the latter. In safety and tolerability studies, alpha-FMH was administered orally to healthy human subjects twice daily for 7 days at doses of 2.5, 10, 50 and 100 mg per person. A dose-dependent inhibition of HDC activity was observed in PBL that were isolated both at 12 hr after administration of the first dose of alpha-FMH and after treatment for 1 week. At the 50 and 100 mg doses of alpha-FMH, there was complete inhibition of HDC activity and partial inhibition at the 10 mg dose. Twenty-four hours after the last dose, HDC activity had recovered to 64-100%, 44-46%, and 30-52% of control values in subjects that received 10, 50 and 100 mg alpha-FMH respectively.

Immunohistochemical analysis of the cross-reaction of anti-rat histidine decarboxylase antibody with guinea-pig DOPA decarboxylase

L-Histidine decarboxylase [L-histidine carboxylyase, HDC, EC 4.1.1.22] is an enzyme distinct from L-DOPA decarboxylase [L-aromatic amino acid carboxylyase, DDC, EC 4.1.1.28]: the two decarboxylases from fetal rat liver were completely separated from each other by DEAE-cellulose column chromatography and by affinity chromatography with L-carnosine as a ligand. The antibody raised against this HDC inhibited the HDC's from rat and guinea-pig brains very strongly, but their DDCs very weakly. However, in immunofluorescent histochemical studies, the antibody cross-reacted with DDC-like immunoreactive structures, such as chromaffin cells of the adrenal medulla, the raphe nucleus, the substantia nigra, and the locus coeruleus of the brain of guinea-pigs, but not of rats, suggesting that these two decarboxylases share some antigenic structures.

Induction of histidine decarboxylase activity in the spleen of mice treated with staphylococcal enterotoxin A and demonstration of its non-mast cell origin

Histidine decarboxylase (HDC) activity increased 13-, 7-, and 2-fold in the spleen, lung and liver, respectively, but not in other tissues of C57BL/6 mice injected i.v. with 50 micrograms/kg of Staphylococcal enterotoxin A (SEA). But even in the spleen, increase in the histamine level was only 1.5 times that of untreated mice. In genetically mast cell-deficient WBB6F1 - W/Wv mice HDC activity in the spleen increased to the same extent as in wild type WBB6F1 - +/+ mice on SEA treatment, but the histamine level in the spleen also increased 20-fold, whereas it increased only 1.4-fold in +/+ mice. These results suggest that the increases in HDC and histamine resulted from interaction of SEA with non-mast cells in tissues.

Origins of histamine-containing fibers in the cerebral cortex of rats studied by immunohistochemistry with histidine decarboxylase as a marker and transection

The origins of histamine-containing fibers in the cerebral cortex were examined by means of the retrograde tracer technique of horseradish peroxidase (HRP)-immunohistochemistry with histidine decarboxylase (HDC) as a marker for the histamine neuron system. Total transection of the brain rostral to the posterior hypothalamus resulted in disappearance of HDC-like immunoreactive (HDCI) fibers in the cerebral cortex, but total transection caudal to the posterior hypothalamus did not decrease the number of HDCI fibers in the cortex, suggesting that HDCI fibers in the cerebral cortex originate in the posterior hypothalamus. The projection of HDCI neurons from the posterior hypothalamus to the cerebral cortex seemed to be bilateral because hemi-transection of the brain rostral to the posterior hypothalamus resulted in a bilateral decrease of HDCI fibers in the cerebral cortex with ipsilateral predominance. After injection of HRP into the cerebral cortex, numerous cells containing both HRP granules and HDCI structures were found bilaterally in the tuberal, caudal and postmamillary magnocellular nuclei, with ipsilateral predominance. These findings indicate that HDCI cells in the above nuclei give rise to axons extending bilaterally to the cerebral cortex.

Fine structure of histaminergic neurons in the caudal magnocellular nucleus of the rat as demonstrated by immunocytochemistry using histidine decarboxylase as a marker

The morphology of histamine-containing neurons in the caudal magnocellular nucleus was light and electron microscopically examined by means of peroxidase-antiperoxidase (PAP) immunocytochemistry with histidine decarboxylase (HDC) as a marker. HDC-like immunoreactive (HDCI) neurons had large (25-30 microns in diameter) perikarya from which two to four primary dendrites arose. The perikarya had a nearly round nucleus and well-developed Golgi apparatus in addition to a large number of mitochondria and rough endoplasmic reticulum. Immunoreactive endproducts were found diffusely throughout the perikarya, dendrites, and axons. HDCI neurons made synaptic contact with nonreactive axon terminals on the perikarya and dendrites. In addition, the HDCI neurons very frequently formed puncta adherentia with neuronal elements, either HDCI or nonreactive, or glial cells. Most of the HDCI axon terminals serially observed under electron microscopy did not exhibit typical synaptic contact in the caudal magnocellular nucleus. These findings suggest the nonsynaptic release of histamine in the caudal magnocellular nucleus.

Histidine decarboxylase: isolation and molecular characteristics

High levels of histidine decarboxylase activity were measured in rat basophilic leukemia cells grown in ascitic form in 4 week old WKY/N rats. The potent inhibition of this enzyme by brocresine and alpha-methylhistidine but not by alpha-methyl DOPA identified it as a specific histidine decarboxylase. Gel filtration and polyacrylamide gel electrophoresis revealed a molecular weight of 125,000 for the native enzyme, similar to that of fetal rat liver histidine decarboxylase. Using rat basophilic leukemia cells as starting material, histidine decarboxylase was purified extensively in a seven step procedure. Electrophoresis under denaturing conditions revealed that histidine decarboxylase is a dimeric protein consisting of two identical subunits with a molecular weight of 62,000. The results indicate that rat basophilic leukemia cells provide a new and rich source for the purification of histidine decarboxylase.

Mechanism of inactivation of mammalian L-histidine decarboxylase by (S)-alpha-fluoromethylhistidine

The mechanism of inactivation by (S)-alpha-fluoromethylhistidine (FMH) of L-histidine decarboxylase (HDC, L-histidine carboxy-lyase, EC 4.1.1.22) purified from whole bodies of fetal rats was studied. FMH inhibited the activities of HDC purified from fetal HDC as well as HDCs from the brain and stomach of adult rats. The activity was not restored by extensive dialysis, indicating that the inhibition was irreversible. The inactivation of HDC was time and concentration dependent and followed pseudo first-order kinetics. L-Histidine, a substrate, protected HDC against inactivation, but D-histidine did not. Apo-HDC was not inactivated by FMH. On labeling of HDC with [3H]FMH, a correlation was found between the extent of incorporation of radioactivity into the enzyme and the degree of inactivation. Two moles of the inhibitor were incorporated into one mole of HDC (108,000 daltons). Experiments with [carboxyl-14C]FMH and [ring 2-14C]FMH showed that decarboxylation was necessary for the inactivation and that one molecule of FMH moiety was incorporated into an HDC monomer during every three decarboxylations of FMH.

Histidine decarboxylase phenotypes of inbred mouse strains: a regulatory locus (Hdc) determines kidney enzyme concentration

Mouse kidney histidine decarboxylase (HDC) provides a model system to study genetic control of a hormone-regulated enzyme (inducible by estrogen and thyroxine; repressible by testosterone). Five major HDC phenotypes scored on the basis of (i) enzyme activity and (ii) the difference in activity between the sexes (females usually higher than males) have been discovered by screening 38 strains of mice. One genetic difference between high-activity strains (DBA/2 and C3H/He) and low-activity strains (C57BL/6 and C57BL/10) has been examined in detail. The phenotypic difference segregates as a single gene in both conventional crosses and between recombinant inbred (RI) strains. Immunoprecipitation has shown that the activity difference is due to an alteration in the number of enzyme molecules. The phenotypic difference between high and low strains can therefore be attributed to different alleles of a single regulatory locus, Hdc; the allele Hdcb determines low HDC concentration, and the allele Hdcd high concentration. Hdc has been mapped to chromosome 2 using data from both comparisons of strain distribution patterns of previously mapped loci within RI strains and a conventional three-point cross. The probable gene order is B2m-pa-Hdc, with map distances of 3.1 +/- 1.7 and 2.0 +/- 1.4 cM, respectively.

Distribution of the histaminergic neuron system in the central nervous system of rats; a fluorescent immunohistochemical analysis with histidine decarboxylase as a marker

The distribution of histidine decarboxylase-like immunoreactivity (HDCI) in the rat central nervous system was studied by the indirect immunofluorescence technique. HDCI cell bodies were concentrated in the posterior hypothalamic area, such as in the tuberal magnocellular nucleus, caudal magnocellular nucleus, posterior hypothalamic nucleus and lateral hypothalamus just lateral to the fasciculus mammillothalamicus at the level of the posterior hypothalamic nucleus. Extensive networks of HDCI fibers of various densities were found in many areas of the brain; they were particularly dense in the hypothalamus but were also found in the following areas: rostrally in the cerebral cortex, olfactory nuclei, medial amygdaloid nucleus, n. tractus diagonalis, and bed nucleus of the stria terminalis, and caudally in the central gray matter of the midbrain and pons, auditory system, n. vestibularis medialis, n. originis nervi facialis, n. parabrachialis, n. commissuralis, n. tractus solitarii, and n. raphe dorsalis.

Comparison of histidine decarboxylases from rat stomach and brain with that from whole bodies of rat fetus

Histidine decarboxylases from the stomach and brain of adult rats were purified 380- and 160-fold, respectively, and their properties compared with those of the enzyme from whole bodies of fetal rats (7600-fold purification). The molecular weights (about 90,000) and the apparent Km values for L-histidine (3 X 10(-4) M) of the three enzymes were similar. The pI value of the fetal enzyme was 5.0, and that of the brain enzyme was 5.4. Histidine decarboxylase of the stomach showed two peaks of activity corresponding to those of the fetal and brain enzymes (pI's of 5.0 and 5.4) on isoelectric focusing. Anti-fetal-histidine decarboxylase antiserum inhibited the stomach and fetal enzymes extensively, but the brain enzyme only slightly. These results indicate that there are at least two types of histidine decarboxylase in rat tissue.

Evidence for the presence of a histaminergic neuron system in the rat brain: an immunohistochemical analysis

Histamine-containing cells in rats were identified by indirect immunofluorescent histochemistry using an antibody raised against histidine decarboxylase (HDC), the enzyme forming histamine, which was purified from fetal rat liver. HDC-like immunoreactive (HDCI) structures could be detected in the brain as well as in peritoneal mast cells and basal-granulated cells in deep crypts of the gastric mucosa of rats. Numerous HDCI neurons were found in the posterior hypothalamic area and HDCI nerve fibers with a varicose appearance of fluorescence were widely distributed in various regions of the brain.

Effect of alpha-fluoromethylhistidine on the histamine content of the brain of W/Wv mice devoid of mast cells: turnover of brain histamine

In the brains of W/Wv mutant mice that have no mast cells, the histidine decarboxylase (HDC) level is as high as in the brain of congenic normal mice (+/+), but the histamine content is 53% of that of +/+ mice. The effects of alpha-fluoromethylhistidine (alpha-FMH) on the HDC activity and histamine content of the brain of W/Wv and +/+ mice were examined. In both strains, 30 min after i.p. injection of alpha-FMH the HDC activity of the brain had decreased to 10% of that in untreated mice. The histamine content decreased more gradually, and after 6 h about half of the control level remained in +/+ mice, whereas histamine had disappeared almost completely in W/Wv mice. It is concluded that the portion of the histamine content that was depleted by HDC inhibitor in a short time is derived from non-mast cells, probably neural cells. The half-life of histamine in the brain of W/Wv mice was estimated from the time-dependent decrease in the histamine content of the brain after administration of alpha-FMH: 48 min in the forebrain, 103 min in the midbrain, and 66 min in the hindbrain.

Increase in histidine decarboxylase activity in skin of genetically mast-cell-deficient W/Wv mice after application of phorbol 12-myristate 13-acetate: evidence for the presence of histamine-producing cells without basophilic granules

Histidine decarboxylase (HisDCase, EC 4.1.1.22) activity in mouse skin increased by a factor of more than 10 after a single application of phorbol 12-myristate 13-acetate. The cell type that was responsible for the increase in HisDCase activity was examined by using (WB X C57BL/6)F1-W/Wv mice, which are genetically deficient in tissue mast cells. In contrast to a report that increase of ornithine decarboxylase (EC 4.1.1.17) activity occurs in the epidermis [O'Brien, T. G., Simisiman, R. C. & Boutwell, R. K. (1975) Cancer Res. 35, 2426-2433], the HisDCase activity was found to increase in the dermis. Although most of the histamine in the dermis was present in mast cells, the increase in HisDCase activity in the skin in W/Wv mice was comparable with that in congeneic +/+ mice. This increase of HisDCase activity in the skin of W/Wv mice was abolished by prior x-ray irradiation (800 rads; 1 rad = 0.01 gray) but was restored by subsequent bone marrow transplantation. Because mice, in general, are known to lack basophilic leukocytes, the present results suggest the existence of histamine-producing cells without basophilic granules that are derived from the bone marrow.