The effects of protease inhibitors on histidine decarboxylase activities and assay of enzyme in various rat tissues

Concurrent ozone and high temperature exacerbates nasal epithelial barrier damage in allergic rhinitis mice: Insights from the nasal transcriptome and nasal microbiota

The global ambient temperature has been rising in recent decades and high temperature is usually accompanied by ozone (O3) pollution. Environmental change is an underlying factor for the increased prevalence of respiratory allergic disease. However, the potential mechanisms are complex and remain elusive. This study was performed to reveal toxic effects and molecular mechanisms of O3 or/and high temperature induced allergic rhinitis (AR) deterioration. The results indicated that O3 and high temperature co-exposure exacerbated rhinitis symptoms, destroyed ultrastructure of nasal mucosa and down-regulated the expression of nasal epithelial barrier structural proteins ZO-1 and occludin. Moreover, the levels of total protein and lactate dehydrogenase (LDH) in nasal lavage fluid and the levels of IL-1β and TNF-α in serum also exhibited a significant upward trend. Transcriptomic analysis revealed that immune and inflammatory signaling pathways such as IL-17 signaling pathway was involved in the combined toxicity of O3 and high temperature. Microbiome examination showed that Prevotella and Elizabethkingia were linked to nasal injury. What's more, spearman correlation analysis revealed correlations among nasal microbiota dysbiosis, inflammation and injury. To sum up, the present study assessed the combined toxicity of O3 and high temperature and found potential mechanisms, which provided important experimental evidence for making preventive intervention strategies and protecting vulnerable populations.

Kujin suppresses histamine signaling at the transcriptional level in toluene 2,4-diisocyanate-sensitized rats

Kujin, the dried root of Sophorae flavescensis, has been used in Chinese folklore medicine against allergy. Evaluation of its anti-allergic potential as well as its mechanism of action has rarely been established. We investigated the effect of Kujin on toluene-2,4-diisocyanate (TDI)-induced allergic behavior and related histamine signaling including mRNA levels of histamine H(1) receptor (H1R) and histidine decarboxylase (HDC), H1R and HDC activities, and histamine content in rat nasal mucosa. We also investigated the effect of Kujin on the mRNA levels of helper T cell type 2 (Th2)-cytokine genes closely related to histamine signaling. TDI provocation caused acute allergic symptoms accompanied with up-regulations of H1R and HDC mRNAs and increases in HDC activity, histamine content, and [(3)H]mepyramine binding activity in the nasal mucosa, all of which were significantly suppressed by pretreatment with Kujin for 3 weeks. Kujin also suppressed the TDI-induced IL-4 and IL-5 mRNA elevations. These data suggest that oral administration of Kujin showed anti-allergic activity through suppression of histamine signaling by the inhibition of TDI-induced H1R and HDC mRNA elevations followed by decrease in H1R, HDC protein level, and histamine content in the nasal mucosa of TDI-sensitized rats. Suppression of Th2-cytokine signaling by Kujin also suggests that it could affect the histamine-cytokine network.

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.

Dexamethasone suppresses histamine synthesis by repressing both transcription and activity of HDC in allergic rats

BACKGROUND

Histamine synthesized by histidine decarboxylase (HDC) from L-histidine is a major chemical mediator in the development of nasal allergy which is characterized by nasal hypersensitivity. However the regulatory mechanism of histamine synthesis by HDC remains to be elucidated. The objectives of the present study were to examine the changes of histamine content, HDC activity and HDC mRNA expression in the nasal mucosa of allergy model rats sensitized by the exposure to toluene diisocyanate (TDI) and to investigate the effect of dexamethasone on the above mentioned allergic parameters.

METHODS

Rats were sensitized and provocated by TDI and the nasal allergy-like behaviors were scored during a 10 minute period after provocation. Histamine content and HDC activity in the nasal mucosa were determined using fluorometric high performance liquid chromatography. The expression of HDC mRNA in nasal mucosa was determined using real-time quantitative reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

In TDI-sensitized rats, nasal allergy-like behaviors such as sneezing and watery rhinorrhea were induced. Histamine content, HDC activity and HDC mRNA expression in nasal mucosa were also significantly increased after TDI provocation. Pretreatment with dexamethasone significantly suppressed nasal allergy-like behaviors, up-regulation of histamine content, HDC activity and HDC mRNA induced by TDI in TDI-sensitized rats.

CONCLUSIONS

These findings indicate that increased synthesis of histamine through up-regulation of HDC gene expression and HDC activity in nasal mucosa plays an important role in the development of nasal hypersensitivity. Repression of HDC gene expression and HDC activity by dexamethasone may underlie its therapeutic effect in the treatment of allergy.

Simultaneous Determination of Histamine and Histidine by Liquid Chromatography Following Intramolecular Excimer-forming Fluorescence Derivatization with Pyrene-labeling Reagent

A highly sensitive and selective fluorometric method for the determination of histamine and histidine has been developed. This method is based on an intramolecular excimer-forming fluorescence derivatization with a pyrene reagent followed by reversed-phase liquid chromatography. The analytes, containing two amino moieties in a molecule, were converted to the corresponding dipyrene-labeled derivatives by derivatization. The derivatives afforded intramolecular excimer fluorescence (440 - 540 nm), which can clearly be discriminated from the normal fluorescence (360 - 420 nm) emitted from reagent blanks. The detection limits (signal-to-noise ratio = 3) were femto mole levels.

A sensitive and selective determination method of histamine by HPLC with intramolecular excimer-forming derivatization and ?uorescence detection

A highly sensitive, selective and simple method is described for the determination of histamine by high-performance liquid chromatography (HPLC) with fluorescence detection. The method is based on an intramolecular excimer-forming fluorescence derivatization of histamine with 4-(1-pyrene)butyric acid N-hydroxysuccinimide ester (PSE), followed by reversed-phase HPLC. Histamine, having two amino moieties in a molecule, was converted to the dipyrene-labeled derivative by reaction with PSE. The derivative afforded intramolecular excimer fluorescence (450-540 nm), which can clearly be discriminated from the monomer fluorescence (370-420 nm) emitted from PSE. Typically, a 10 micro L sample solution was mixed with 100 micro L of derivatization reagent solution, which was a mixture of 0.5 mm PSE in acetonitrile and 0.5 mm potassium carbonate in water (8:2, v/v). The derivatization was carried out at 100 degrees C for 90 min. The PSE derivative of histamine could be separated by reversed-phase ODS column with isocratic elution using acetonitrile:water (82:18, v/v) containing 0.03% triethylamine. The detection limit (singnal-to-noise ratio = 3) of histamine was 0.5 fmol for a 30 micro L injection. The method was successfully applied to the determination of histamine in human urine, and had enough selectivity and sensitivity for urinary histamine quantification.

Amine precursor therapy: manipulation of brain amine activity with precursor amino acid

Amine precursor therapies for the treatment of neuropsychiatric disorders and their neurochemical background are reviewed historically. Furthermore, peculiar or artificial amino acids, which are metabolized into the brain amines or their derivatives and promised their clinical application of treatment for morbid conditions, are also introduced.

Amine precursor amino acid therapy: from neurochemical basis to clinical aspects

The particulars regarding the amine precursor therapy for treatment of neuropsychiatric disorders and their neurochemical background are described historically. Furthermore, peculiar or artificial amino acids which are metabolized into the brain amine or their derivatives and promised their clinical application are also introduced.

Determination of histidine decarboxylase mRNA in various rat tissues by the polymerase chain reaction

Histidine decarboxylase (HDC) mRNA in various rat tissues were quantitated by using a reverse transcription-polymerase chain reaction (RT-PCR) in which a mouse mRNA was used as an internal standard. The stomach HDC mRNA level was the highest followed by the brain, skin, jejunum, spleen and liver. There was no measurable HDC mRNA in the kidney. The stomach HDC activity was also the highest followed by the brain, skin, spleen, jejunum, liver and kidney. A significant correlation (r = 0.940, p < 0.0001) was observed between the HDC mRNA levels and HDC activities in these tissues. We have also examined the HDC mRNA levels in fasting rats and found that HDC mRNA levels in the stomach were reduced after the 48-hr-fasting with the decrease in HDC activities. These observations indicate that there may exist a gene regulation, at least at the basal level, for the HDC activities in the rats.

Histamine content, synthesis and degradation in nasal mucosa and lung of guinea-pigs treated with toluene diisocyanate (TDI)

We have reported the presence of a histamine synthesizing enzyme, histidine decarboxylase (HDC), and histamine degrading enzymes, histamine N-methyltransferase (HMT) and histaminase (diamine oxidase, DAO) in human nasal mucosa and the histamine content of the mucosa. In this study, we demonstrate the influences of the toluene diisocyanate (TDI) treatment on the histamine content and these enzyme activities in guinea-pigs as an animal model of respiratory hypersensitivity. Application of TDI to the nasal vestibuli induced intense nasal allergy-like and mild asthma-like responses in TDI-sensitized guinea pigs. Increases in the histamine content and HDC and HMT activities were observed in the nasal mucosa and lung of TDI-sensitized guinea pigs. No apparent changes in the histaminase activities were observed in either the nasal mucosa or the lung. These data suggest that the turnover rate of histamine is increased in the nasal mucosa and the lung of guinea pigs with respiratory hypersensitivity.

Histamine metabolism in nasal polyps

We attempted to determine the relationship of nasal polyps to histamine (HA) metabolism. Compared to that in allergy-related nasal polyps and infection-related nasal polyps, the level of HA in aspirin-induced asthma-related polyps was significantly lower. Large differences between the groups were not observed in HA-synthesizing enzyme activity, but degradative enzyme activity was much higher in aspirin-induced asthma-related polyps than in other types of nasal polyps tested. These findings suggest the possibility that the amount of HA in polyps associated with aspirin-induced asthma was less because of greatly enhanced degradation. We found, in addition, that in nasal tissues such as polyps, histamine-N-methyl transferase, rather than histaminase, was the principal degradative enzyme.

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.

Histamine synthesis and catabolism in various tissues in diabetic rats

In view of the observations that (1) plasma histamine concentrations are significantly higher in diabetic patients and diabetic rats than those in controls, and (2) tissue concentrations of histamine are elevated in rats with experimental diabetes, we have investigated histamine synthesis, as reflected by histidine decarboxylase (HDC) activity, and histamine catabolism, as reflected by histaminase activity, in various tissues of the diabetic rat. Rats with streptozotocin-induced diabetes mellitus (DM) showed an increase in histamine synthesis in various tissues; this was most marked in the aorta and to a lesser, but significant, extent in the kidneys, lungs, and heart, but not in the brain, stomach, or skin. Tissue content of histamine was significantly increased in all tissues except the stomach and skin. We conclude that tissue histamine synthesis is significantly increased in diabetic animals and that this increase is most marked in the aorta. The elevation in HDC activity in these tissues probably accounts for the increase in tissue and plasma concentrations of histamine in diabetic animals, since there is no change in histamine catabolism. This increase in histamine synthesis and release may contribute to the pathogenesis of endothelial damage in diabetic microangiopathy and macroangiopathy.

Characterization and expression of the complementary DNA encoding rat histidine decarboxylase

Histamine is a neurotransmitter in the central nervous system and an important modulator of gastric acid secretion, vasomotor control, inflammation, and allergic reactions. In biological systems the formation of histamine from its precursor histidine is catalyzed by the enzyme L-histidine decarboxylase (HDC; L-histidine carboxy-lyase, EC 4.1.1.22). We have cloned HDC-encoding cDNA from a fetal rat liver cDNA library (phage lambda gt11) have deduced the amino acid sequence from the nucleotide sequence. The clone was proven to be HDC cDNA by expression of active recombinant enzyme in COS cells and by chromosomal mapping. The cDNA encodes a protein of Mr 73,450 (655 amino acid residues). The discrepancy between this molecular weight and the size of the purified fetal liver protein subunits [Taguchi, Y., Watanabe, T., Kubota, H., Hayashi, H. & Wada, H. (1984) J. Biol. Chem. 259, 5214-5221] (Mr = 54,000) suggests that HDC may be posttranslationally processed. The 469 amino acid residues from the amino-terminal portion of the protein share 50% identity with rat and Drosophila L-dopa decarboxylases and much less homology with other characterized amino acid decarboxylases.

Histidine decarboxylase from rat mast cells. Enhanced recovery in cell-free extracts and isotopic labelling

A procedure for obtaining rat mast-cell histidine decarboxylase in greater than 50% yield in cell-free extracts was developed. The enzyme was found in the supernatant fractions from a 3,500 g and a 105,000 g centrifugation step and was demonstrated to be sensitive to inhibition by alpha-fluoromethylhistidine but not by phenylalanine. Although the enzyme shows a half-life of only 3 h in cell-free extract, the initial high recovery of activity allowed for active-site labelling of the enzyme by [3H]histidine and NaBH4. Labelled protein migrated on non-denaturing polyacrylamide-gradient-gel electrophoresis as a 55,000 Da species.

Significance of increased secretion of glucocorticoids in mice and rats injected with bacterial endotoxin

Injection of mice or rats with lipopolysaccharide (LPS) is associated with an increased secretion of glucocorticoids. The high level of mortality following injection of LPS that is noted in adrenalectomized rats can be reversed by dexamethasone or corticosterone. That histamine may be an endogenous mediator of the release of corticosterone caused by LPS is suggested by an attenuation of this corticosterone response by promethazine, an H1 antihistamine. Additional support that LPS-dependent glucocorticoid secretion is mediated, in part, by histamine, is suggested by spleen cell transfer studies revealing differences in the induction of histidine decarboxylase (HDC) synthesis and corticosterone release by the C3H/HeN and C3H/HeJ strains of mice that are differentially sensitive to LPS effects. These and other data on increased levels of histamine and HDC during mitogen-induced lymphocyte blastogenesis, as well as experiments revealing immunomodulatory effects of histamine and histamine agonists and antagonists on lymphocyte blastogenesis, are consistent with the hypothesis that following infection with gram-negative bacteria, the histamine-induced increase in glucocorticoid secretion results in inhibition of HDC in splenocytes, a concomitant attenuation of histamine production, and a resulting return to immune homeostasis.

Possible role of endogenous histamine in mediation of LPS-induced secretion of corticosterone in mice

Escherichia coli lipopolysaccharide (LPS) induced a strong secretion of corticosterone in C3H/HeN mice with a concomitant increase in the splenic histidine decarboxylase activity. Treatment of the mice with alpha-fluoromethyl histidine, a suicide substrate for the enzyme, markedly attenuated both the secretion and the increase. In C3H/HeJ mice, LPS provoked little corticosterone release and induction of the enzyme. However, these mice responded to tetradecanoyl phorbol acetate with a large increase in both this secretion and enzyme activity. Injection of LPS produced a comparable increase in the serum histamine and corticosterone level and activity of histidine decarboxylase in various tissues of genetically mast-cell-deficient W/WV mice and in closely related +/+ mice. These results suggest that secretion of corticosterone caused by LPS is mediated by histamine produced through induction of histidine decarboxylase in non-mast cells.

Sex difference of pinnal hyperemia in magnesium-deficient rats: effects of castration and administration of sex hormone

In the course of studies on the effects of magnesium (Mg) depletion in the diet (0.001% Mg) on mature rats (10 week-old), it became apparent that females developed less hyperemia than males. In the females, the time of onset and severity of hyperemia were enhanced by castration, but not in the males. These data suggest that the development of hyperemia in Mg-deficient adult rats depends on the female sex hormone. The effects of administration of estradiol were examined, using immature rats (3 week-old), in relation to hyperemia and histamine metabolism. Two to 3 days after feeding young male and female rats a Mg-deficient diet, the pinnal hyperemia appeared in the same degree. The hyperemia was reduced by the administration of estradiol benzoate (0.04-0.08 mg/100 g body wt. per day, s.c.) every day. The increments in urinary histamine excretion, splenic histamine content and histidine decarboxylase activity during Mg-deficiency were markedly reduced by the administration of estradiol. The sex difference in the hyperemia which appeared upon Mg-depletion depends on the effects of the female hormone, estradiol, on histamine metabolism.

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.

A direct, sensitive microassay for mammalian histidine decarboxylase

A microassay procedure for mammalian histidine decarboxylase based on the conversion of L-[3H]histidine to [3H]histamine, which were separated by an alkaline butanol extraction followed by thin-layer chromatography, is described. This assay is direct and simple to perform, in addition to being very sensitive and reproducible. It is useful for tissues containing high levels of endogenous histamine, because only newly formed radiolabeled histamine is measured. This report includes information on histidine decarboxylase activity at various pH levels, in different buffers, and in the presence of selected histamine active drugs. In addition, it describes histidine decarboxylase activity in several fetal rat tissues.

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.

Histamine content and histidine decarboxylase activity in the spleen of the magnesium-deficient rat: comparison with the skin and peritoneal mast cells

In young rats, some effects of magnesium (Mg) depletion in the diet on histamine content and histidine decarboxylase (HDC) activity in spleen were studied in comparison with those in the skin and peritoneal mast cells. In the case of the young rats fed a Mg-deficient diet (0.001% Mg), the splenic histamine contents increased to levels about 1.3, 2.8 and 23 times as high as those in the rats fed a control diet (0.07% Mg) on the 4th, 6th and 8th day, respectively; histamine contents in the peritoneal mast cells also increased to about 1.2 and 1.8 times the control levels on the 6th and 8th day, respectively; no change was observed in histamine contents in the skin during 8 days of Mg depletion. HDC activities in the spleen of Mg-deficient rats on the 4th, 6th and 8th day increased to levels about 5.5, 15.5 and 35 times as high as the respective control values; the activities in the skin increased to about 37, 7 and 10 times the control values on the 4th, 6th and 8th day, respectively; while in the peritoneal mast cells, the activities increased to about 1.2 and 2.2 times the control values on the 6th and 8th day, respectively. On the 8th day of the Mg deficiency, some studies were made on the effects of histamine releasers on histamine contents in the spleen and peritoneal mast cells. Compound 48/80 (0.5 microgram/ml) or polymyxin B (5 micrograms/ml) induced a release of histamine from the peritoneal mast cells, but not from the spleen cells isolated from the Mg-deficient rat in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Enhanced carnosine (beta-alanyl-L-histidine) breakdown and histamine metabolism following treatment with compound 48/80

We have previously suggested that carnosine may serve as a reservoir for histidine to be used as a source of histamine in the trauma response of rats. In this study we report the effect of stimulation of histamine-forming capacity by compound 48/80 on muscle carnosinase (C'ASE) and histidine decarboxylase (HDC) activities as well as on muscle carnosine and histamine concentrations. Male rats (180 g) were injected i.p. with 5 mg/kg bw of compound 48/80 and C'ASE and HDC activities as well as carnosine, histidine and histamine concentrations were monitored over a 72 h period post-injection. This treatment resulted in an 120% increase in muscle HDC activity and an 110% increase in muscle histamine concentration at 15 min post-injection, followed by an 80% increase in muscle C'ASE activity at 1 h and a 100% reduction in muscle carnosine concentration at 24 h post-injection when compared to control animals injected with 0.9% saline. Histidine concentration was not affected by treatment. The time frame of response, a rapid increase in muscle HDC activity and in muscle histamine concentration followed by an increase in muscle C'ASE activity and a later decrease in muscle carnosine concentration, suggests that carnosine is hydrolysed to liberate histidine and that carnosine, as a reservoir for histidine, is mobilized to maintain a constant muscle concentration of histidine for histamine synthesis.

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.

Transport of histidine into synaptosomes of the rat central nervous system

Histidine transport into synaptosomes was studied in order to characterize this aspect of histamine synthesis in neurons. Histidine transport was found to be independent of sodium, calcium, and magnesium ions and dependent upon potassium and chloride ions. Histidine transport was also found to be energy dependent, and fractionation studies suggested it was highly localized to nerve terminals. Kinetic analysis of histidine transport in several brain regions indicated the presence of two uptake sites, a high-affinity site with a Km of approximately 35 microM and a low-affinity site with a Km in the millimolar range. Density of the high-affinity site, as reflected by Vmax, correlates well with density of proposed histaminergic innervation. Rate of histidine transport was not altered by prior depolarization of the synaptosomes, indicating that histidine transport probably does not play a regulatory role in histamine synthesis.

Histidine uptake by isolated rat peritoneal mast cells. Effect of inhibition of histidine decarboxylase by alpha-fluoromethylhistidine

Preincubation with (S)-alpha-fluoromethylhistidine, an irreversible inhibitor of histidine decarboxylase, was found to markedly reduce, but not eliminate, the uptake of [3H]histidine by rat peritoneal mast cells. The Vmax for histidine transport for cells in which decarboxylation of histidine had been completely inhibited was 11.9 pmoles per min per 10(6) cells, compared to a Vmax of 18.9 pmoles per min per 10(6) cells in the presence of active mast cell histidine decarboxylase. The Km of uptake was 139 microM in the presence of alpha-fluoromethylhistidine, several times higher than the Km of 44.0 microM in the uninhibited cell. alpha-Fluoromethylhistidine did not inhibit mast cell uptake of phenylalanine, a competitive inhibitor of histidine uptake but not a substrate for histidine decarboxylase; nor did it inhibit the uptake of histidine by non-mast cells, which lack histidine decarboxylase. Levels of intracellular [3H]histidine in mast cells were similar in the presence and absence of the decarboxylase inhibitor. Based on these observations, we propose that intracellular decarboxylation of histidine in the mast cell serves to specifically enhance the uptake of histidine by the relatively non-specific amino acid transporter present in the plasma membrane of the cell.

Isolation and properties of multiple forms of histidine decarboxylase from rat gastric mucosa

The heterogeneity of histidine decarboxylase from rat gastric mucosa was studied. The partially purified enzyme was fractionated by preparative isoelectric focusing on a flat-gel bed by using narrow pH-range carrier ampholytes and a short focusing time. The activity was resolved, with about 95% recovery, into three forms, designated I, II and III, with pI values of 5.90, 5.60 and 5.35 respectively. These three forms exhibited similar molecular weights, indicating that the forms were not the result of different degrees of polymerization. By preparative refocusing each form refocused as a single peak of enzyme activity with reproducible pI, but a high loss of activity occurred with repeated focusing. Forms I, II and III were purified by the combined use of preparative isoelectric focusing and gel chromatography and other fractionation methods. The active forms could be distinguished by electrophoresis and isoelectric focusing on polyacrylamide gels and displayed protein heterogeneity. These forms were found in the crude extract and in the partially purified preparations in the presence or absence of proteinase inhibitors. Form II had the highest specific activity, but all three forms had the same optimum pH and Km value for histidine.

Histamine synthesis in intact and disrupted rat mast cells

Histamine production by purified intact rat peritoneal mast cells, as measured by formation of [beta-3H]histamine from [beta-3H]L-histidine or by release of 14CO2 from 14C-carboxyl-labeled histidine, was ten to thirty times greater than that of disrupted cells of soluble extracts of these cells. Loss of activity was evident whether cells were disrupted by sonification, freezing and thawing, or lysis, both in the absence and presence of inhibitors of proteolytic enzymes and agents known to preserve enzyme responsible for histamine formation in both the intact cells and cell extracts. In the presence of subsaturating concentrations of histidine, various histidine analogs and glutamine inhibited histidine data indicate that, at physiological concentrations of histidine, blockade of histidine transport (through system N) may limit histamine synthesis in the intact cell and that measurement of histidine decarboxylase activity in tissue homogenates or cell extracts may not reflect actual histidine decarboxylase activity in vivo.

Absence of increase of histidine decarboxylase activity in mast cell-deficient W/W mouse embryos before parturition

The histidine decarboxylase (L-histidine carboxylase, EC 4.1.1.22) activity of whole W/W mouse embryos, which are devoid of mast cells, remained very low and did not show the rapid increase before birth (17-20 days of gestation) seen in wild-type +/+ embryos. During the same period, the histamine content also remained very low and no mast cells were detected in the W/W embryos, in the contrast to the large increase in both histamine content and number of mast cells in wild-type embryos. These findings imply that the histamine in embryos is largely derived from mast cells. In +/+ mice, histidine decarboxylase activity decreased rapidly soon after birth without concomitant decrease in histamine content or number of mast cells, suggesting that the enzyme activity in mast cells is regulated by some unknown mechanism.