Specific histidine decarboxylases in the gastric mucosa of man and other mammals. Determination, location and properties

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.

Antisecretory effect of DS-4574, a mast cell stabilizer with peptidoleukotriene antagonism, on gastric acid secretion in the pig

The antisecretory effect of DS-4574, a mast cell stabilizer with peptidoleukotriene antagonism, on the hypersecretion of gastric acid stimulated by several secretagogues was examined in the pig. Goettingen miniature pigs with chronic gastric fistula were used. Intramuscular injection of carbachol (60 micrograms/kg), tetragastrin (50 micrograms/kg) or histamine (200 micrograms/kg)-induced gastric acid hypersecretion. Intraduodenal administration of DS-4574 (10 and 20 mg/kg) significantly inhibited both the hypersecretion induced by carbachol and that by tetragastrin. On the other hand, DS-4574 (50 mg/kg, intraduodenal) did not suppress histamine-induced hypersecretion. In the in vitro study, no effect on hog gastric K(+)-dependent ATPase activity was found at concentrations of DS-4574 from 10(-7) to 10(-4) M. These results were highly similar to those in the rat. The suppression of histamine release from histamine-containing cells in the gastric mucosa of the rat was concluded to be an antisecretory effect of DS-4574.

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.

Histamine metabolism of the human gastric mucosa--a study on the regional distribution of the amine and enzyme activities

Histamine content, histidine decarboxylase activity and histamine methyl transferase activity of the human gastric mucosa have been studied in healthy subjects. Histamine content was evenly distributed over the gastric mucosa and no significant difference could be observed between the oxyntic and pyloric gland area. A 'specific' histidine decarboxylase was found in the human gastric mucosa and the enzyme activity was significantly higher in the corpus compared to the antral mucosa. We found no difference in enzyme activity of the mucosa obtained from three defined areas of the corpus region of the stomach. Histamine methyl transferase activity was of the same magnitude in the corpus as in the antral mucosa. In addition, with regard to histamine methyl transferase activity, we were unable to demonstrate any difference in activity in the mucosal specimens obtained from the defined areas of the stomach. The presented technique to obtain gastric mucosal tissue specimens during routine fibreoptic endoscopy of the stomach, allows studies over gastric mucosal histamine metabolism in health as well as in disease states.

Induced histidine decarboxylase in endotoxic shock: identification of the enzyme in rat liver and influence of its inhibitors on survival parameters

The hypothesis of a causal relationship between a progressive and unrestrained increase of tissue histamine formation by activation of an inducible histidine decarboxylase (HDC) and lethality in endotoxic shock (Schayer's 'induced histamine concept') was tested in a standardized rat endotoxic shock model. Initial enzyme identification studies in the rat shock liver (8 hrs after endotoxin challenge) clearly demonstrate that the 'induced' histidine decarboxylase is an acid (specific) HDC. The succeeding randomized, controlled study with appropriate inhibitors of the enzyme, alpha-methyl-histidine (competitive inhibitor) and alpha-fluoromethyl-histidine (irreversible inhibitor) using doses of 2, 20 or 100 mg/kg showed no significant effect on the survival rate of rats in endotoxin shock. The survival rate of the non-treated endotoxin control group (NaCl) was 25%; all methylprednisolone treated rats (50 mg/kg) survived. Thus, the 'induced' histamine is not a predominant factor (necessary or sufficient determinant) for the lethal outcome in rat endotoxic shock. The protective effect of MP is not predominantly due to the inhibition of the 'induced' histidine decarboxylase. The use of HDC-inhibitors as the appropriate instruments for evaluation of the significance of this mechanism is discussed.

Two biochemically distinct populations of histaminocytes separated by isokinetic sedimentation of dispersed rat gastric cells

Two populations of histaminocytes, with different sedimentation rates (SR), were separated by a computer developed isokinetic gradient using dispersed rat gastric mucosal cells. Histamine content, histidine decarboxylase (HDC) activity and incorporation of radiolabelled histidine metabolites were used to assess the migration of specific cells throughout the gradients. One histaminocyte population, with cells of lower SR, contained high HDC activity and undetectable levels of histamine, whereas the other population, with cells of higher SR, contained lower HDC activity and high concentration of histamine. Both types of histaminocytes incorporated 3H-histidine metabolites. Electron microscopy showed that the fractions containing histaminocytes with lower SR had 3.5 times more endocrine ECL cells than the original population of dispersed fundic cells and lacked A and D cells, whereas the fractions with histaminocytes of higher SR were associated with a 2.7 times higher concentration of A and D cells and with a 7.7 times higher ratio of a variety of partial cells with a distinct mitochondrial morphology. These results are consistent with prior novel information regarding the separation of two populations of rat histaminocytes using different sedimentation techniques.

Separation and characteristics of two histaminocytes from rat gastric mucosa

To determine the properties of rat gastric cells involved in histamine metabolism (histaminocytes), fundic mucosa was enzymatically dispersed prior to separation by sedimentation methods. The distribution of histamine content, histidine decarboxylase (HDC) activity and incorporation of radioactive histidine metabolites were used to determine the characteristics of various populations of gastric cells. All activities measured, as well as most of the dispersed gastric cells, occurred in a narrow range of density between 1.083 and 1.091 g/ml. Velocity sedimentation showed that two populations of histaminocytes can be distinguished. One population has a higher sedimentation rate, suggesting a larger size, contains histamine, HDC activity and incorporates radioactive metabolites. Another population, in fractions with lower sedimentation rates, contains little histamine, has a higher HDC activity than the previous population and also incorporates radiolabelled histidine metabolites. For the first time, two populations of viable histaminocytes have been separated that differ in their biochemical properties.

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.

Properties of histidine decarboxylase from rat gastric mucosa

The properties of specific histidine decarboxylase from highly purified rat gastric mucosa preparations were studied. The kinetic parameters were pH dependent: the apparent Km value varied inversely with pH; the maximum reaction velocity was reached at pH 6.6; the optimum pH was related to substrate concentration. The enzyme was unstable below pH 5.5. The effect of temperature was investigated and the enzyme activity was optimum near 56 degrees C. The thermal inactivation of the enzyme showed the presence of several active forms displaying distinct thermostabilities. The effect of coenzyme and substrate on heat stability was established. A small amount of pyridoxal phosphate was required for maximum enzyme activity, and the Km was low. The cofactor appeared to be tightly bound to the apoenzyme; nevertheless there was a fraction more easily resolved by dialysis. With high pyridoxal phosphate concentrations non-competitive inhibition occurred. Histamine inhibited the enzyme at high concentrations, the inhibition being competitive with respect to the substrate. No metal ion was required for enzyme activity; the enzyme was inhibited by sulfhydryl reagents and heavy metal ions, and also by high concentrations of reducing agents. The tryptophan residue of the holoenzyme seemed to be essential for the catalytic process.

A modified Schayer procedure for the estimation of histidine decarboxylase activity: its application on tissue extracts from gastric mucosa of various mammals

The question of whether the gastric mucosa of mammals other than rats, mice and hamsters contains an acid (specific) histidine decarboxylase was re-investigated by using a modification of the classical isotope dilution method of Schayer. Its reliability was tested regarding sensitivity, specificity, precision and accuracy, applying criteria recommended by the International Federation of Clinical Chemistry. The assay is now suitable for measuring rather large series of samples. The suitability of several blanks for detecting histidine decarboxylase activity was investigated as a special problem of accuracy. The semicarbazide blank was found to be as reliable as the heating blank, the blank with tissue extract pretreated with perchloric acid or an incubation mixture without radio-labelled histidine. Reaction kinetics of histamine formation were linear over an incubation period of at least 3 h. Histidine decarboxylase activity as a rather low pH and substrate concentration, which is characteristic for the acid (specific) histidine decarboxylase, was demonstrated inthe gastric mucosa of human subjects, dogs, rabbits and guinea-pigs, always using the same incubation conditions for all species investigated. The highest enzymic activity was present in the oxyntic mucosa, but could be measured also in other parts of the stomach.

Peptide inhibition of mammalian histidine decarboxylase

The hypothesis that N-terminal histidine peptides might act as inhibitors to histidine decarboxylase was investigated. A murine mastocytoma was utilized as enzyme source. The crude extract of this tissue exhibits high rates of decarboxylation of both histidine and DOPA and was used to establish the specificity in the effect of the compounds tested. For kinetic analyses a highly purified histidine decarboxylase fraction was used. The effect of some representative peptides on both enzyme activities were recorded. Histidine decarboxylase exclusively was inhibited by N-terminal histidine peptides. None of the other peptides investigated interfered negatively with this enzyme. This inhibition was consistent in the purified preparation and appeared to be more pronounced with increasing hydrophobicity in the second amino acid. Histidyl-phenylalanine was found to be about 100-fold as potent as the commonly used specific histidine decarboxylase inhibitor alpha-methyl histidine. It is concluded that small peptides with histidine as the N-terminal amino acid might act as specific inhibitors for mammalian histidine decarboxylase. An analog effect of small tyrosyl or phenylalanyl peptides was not seen for the DOPA decarboxylase.

[Purification and detection of multiple forms of histidine decarboxylase in rat gastric mucosa (author's transl)]

A specific histidine decarboxylase from rat gastric mucosa has been obtained at high purity and good yield (purification about 600-fold). The purification procedure included double (NH4)2SO4 fractionation, ion-exchange chromatography, preparative isoelectric focusing in a granulated gel and gel filtration. Only the specific histidine enzyme was obtained by that procedure; DOPA decarboxylase, a non-specific enzyme, was absent in our final preparation. Each step of the purification was visualized by polyacrylamide gel electrophoresis and analytical isoelectric focusing. The purified enzyme was apparently homogenous by criteria of electrophoresis and gel filtration and has a molecular weight of 94 000. Several protein bands appeared after isoelectric focusing and the enzyme activity was localized in 3 distinct peaks. The gastric enzyme consists of 3 active forms which could be distinguished by their isoelectric points: 5.4, 5.75 and 6. Moleculare weights estimated by SDS polyacrylamide gel electrophoresis were 97 000, 93 000 and 90 000, and no subunits were observed. Pyridoxal phosphate was required as a coenzyme and resolution of the holoenzyme agreed with a portion of the coenzyme tightly bound to the apoenzyme. The purified enzyme was stable at low ionic strength, near neutral pH; concentrated reducing agents inhibit the enzyme.

Histamine and acute haemorrhagic lesions in rat gastric mucosa: prevention of stress ulcer formation by (+)-catechin, an inhibitor of specific histidine decarboxylase in vitro

Acute haemorrhagic lesions in the oesophagus, stomach and duodenum ('stress ulcers') occur relatively often under clinical conditions and are always dangerous to the patient (lethality rate about 70%). Since conservative and surgical treatment are without significant success up to now, prevention by adaptation to stressors or by administration of drugs seems mandatory. An improved technique for producing acute gastric lesions in rats by immobilization and a new method for assessing this disease in the animals is presented in this communication. High precision is obtained within a single experimental series especially from day to day. Since histamine was suggested to be involved in the pathogenesis of stress ulcer disease, (+)-catechin, a rather specific inhibitor of specific histidine decarboxylase from rat stomach, was tested in immobilized rats. It prevented the formation of acute gastric lesions by 80% in seven series of experiments lasting for half a year. Since the drug has low toxicity in man, it is recommended for clinical trials.

Effect of amodiaquine on gastric histamine methyltransferase and on histamine-stimulated gastric secretion

1 Amodiaquine was found to be a potent inhibitor in vitro of gastric histamine methyltransferase from human and canine corpus and from pig antrum. The ID50 for the enzyme, purified from pig antrum mucosa by ultracentrifugation and chromatography on DEAE-cellulose, was 2.5 muM. 2 In six dogs with Heidenhanin pouches the maximum secretory response to histamine (40 mug/kg i.m.) was augmented by i.m. injection of amodiaquine. The augmentation depended on the dose of amodiaquine, the optimum effect (40% increase in volume of gastric juice, 80% in acid output) being achieved with 2 mg/kg. The maximum secretory response to betazole was also enhanced by amodiaquine. 3 It was suggested that amodiaquine may enhance the histamine and betazole stimulated gastric secretion by an inhibition of gastric histamine methyltransferase in vivo.