Histamine N-methyltransferase Activity Research Articles

Histamine N-methyltransferase (HNMT) as a potential auxiliary biomarker for predicting adaptability to anti-HER2 drug treatment in breast cancer patients

BackgroundUp to 23% of breast cancer patients recurred within a decade after trastuzumab treatment. Conversely, one trial found that patients with low HER2 expression and metastatic breast cancer had a positive response to trastuzumab-deruxtecan (T-Dxd). This indicates that relying solely on HER2 as a single diagnostic marker to predict the efficacy of anti-HER2 drugs is insufficient. This study highlights the interaction between histamine N-methyltransferase (HNMT) and HER2 as an adjunct predictor for trastuzumab response. Furthermore, modulation of HER2 expression by HNMT may explain why those with low HER2 expression still respond to T-Dxd.MethodsWe investigated the impact of HNMT protein expression on the efficacy of anti-HER2 therapy in both in vivo and ex vivo models of patient-derived xenografts and cell line-derived xenografts. Our analysis included Förster resonance energy transfer (FRET) to assess the interaction strength between HNMT and HER2 proteins in trastuzumab-resistant and sensitive tumor tissues. Additionally, we used fluorescence lifetime imaging microscopy (FLIM), cleaved luciferase, and immunoprecipitation to study the interaction dynamics of HNMT and HER2. Furthermore, we evaluated the influence of HNMT activity on the binding of anti-HER2 antibodies to their targets through flow cytometry. We also observed the nuclear translocation of HNMT/HER2-ICD cells using fluorescent double staining and DeltaVision microscopy. Finally, ChIP sequencing was employed to identify target genes affected by the HNMT/HER2-ICD complex.ResultsThis study highlights HNMT as a potential auxiliary biomarker for diagnosing HER2 + breast cancer. FRET analysis demonstrated a significant interaction between HNMT and HER2 protein in trastuzumab-sensitive tumor tissue (n = 50), suggesting the potential of HNMT as a predictor of treatment response. Mechanistic studies revealed that the interaction between HNMT and HER2 contributes to increased HER2 protein expression at the transcriptional level, thereby impacting the efficacy of anti-HER2 therapy. Furthermore, a subset of triple-negative breast cancers characterized by HNMT overexpression was found to be sensitive to HER2 antibody–drug conjugates such as T-Dxd.ConclusionsThese findings offer crucial insights for clinicians evaluating candidates for anti-HER2 therapy, especially for HER2-low breast cancer patients who could gain from T-Dxd treatment. Identifying HNMT expression could help clinicians pinpoint patients who would benefit from anti-HER2 therapy.

Optically active iodohelicene derivatives exhibit histamine N-methyl transferase inhibitory activity.

Optically active helicene derivatives inhibit the activity on histamine N-methyl transferase (HNMT). Specifically, methyl (P)-1,12-dimethylbenzo[c]phenanthrene-8-carboxylate with 6-iodo and 5-trifluoromethanesulfonyloxy groups inhibits HNMT activity on the μM order of IC50. Chirality is important, and (M)-isomers exhibits substantially reduced activity. The 6-iodo group is also essential, which suggests the involvement of halogen bonds in protein binding. Substituents on the sulfonate moiety also affect the inhibitory activity.

Reduction of Motion Sickness Through Targeting Histamine N-Methyltransferase in the Dorsal Vagal Complex of the Brain.

To investigate the role of histamine N-methyltransferase (HNMT) activity in the development of motion sickness (MS) in the dorsal vagal complex (DVC) to inform the development of new drugs for MS, Beagle dogs and Sprague-Dawley rats were rotated to simulate MS. HNMT expression in the brain stem and DVC was measured. The effects of systemic application of tacrine, an HNMT inhibitor, on the development of MS were observed. Moreover, we microinjected a histamine receptor H1 inhibitor, promethazine, into the DVC to verify the involvement of histaminergic neurotransmission in MS. Finally, lentiviral vectors were microinjected into the DVC to determine the effects of altered HNMT expression on MS. We found the following: 1) HNMT expression in the medulla oblongata of dogs and rats insusceptible to MS was higher than in susceptible animals; 2) tacrine dose-dependently promoted MS in both animals and raised histamine level in rat medulla oblongata; 3) blocking histaminergic neurotransmission in the DVC with promethazine inhibited MS; 4) rotatory stimulus induced an elevation in HNMT expression, and vestibular training elevated the basal level of HNMT in the DVC during habituation to MS; 5) in vivo transfection of a lentiviral vector packaged with the HNMT gene increased HNMT expression in the DVC and reduced MS; and 6) microinjection of a lentiviral vector driving the interference of HNMT gene expression in vivo significantly inhibited HNMT expression in the DVC and exacerbated MS. In conclusion, HNMT expression in the brain stem is inversely correlated with MS development. Increasing HNMT expression or stimulating its activity in the DVC could inhibit MS.

Analysis of brain histamine clearance using genetically engineered mice

Histamine acts as a neurotransmitter to regulate various physiological functions in CNS. Recent reports showed the involvement of histaminergic dysfunction in neurological disorders. Neurotransmitter clearance is essential to determine brain neurotransmitter concentration. However, molecular mechanism of brain histamine clearance remains largely unknown. First, we examined the molecular mechanism of histamine clearance in primary human astrocytes. We demonstrated that extracellular histamine was transported through organic cation transporter (OCT) 3 and plasma membrane monoamine transporter (PMAT), and subsequently intracellular histamine was inactivated by histamine N-methyltransferase (HNMT) in cytosol. Next, we generated HNMT knockout (HNMT KO) mice to investigate the role of HNMT in vivo. HNMT deficiency dramatically enhanced brain histamine concentration, indicating the important role of HNMT in histamine inactivation. HNMT KO mice showed high aggression via abnormal histamine H2 receptor (H2R) activation and the disrupted sleep-wake cycle via excessive H1R activation. These observations show that HNMT plays a pivotal role in regulating brain histamine concentration, and modulates aggression as well as the sleep-wake cycle. Although importance of OCT3 and PMAT in histaminergic nervous system remains still unknown, our preliminary data show the contribution of PMAT to brain histamine concentration. We also try to find novel inhibitors targeting brain histamine clearance. We hope our study could lead a better understanding of neuropsychiatric disorders and the development of new drugs inhibiting HNMT, OCT3 and PMAT activity.

Simultaneous electrochemical measurement method of histamine and Nτ-methylhistamine by high-performance liquid chromatography–amperometry with o-phthalaldehyde–sodium sulfite derivatization

An electrochemical detection (ECD) method for analyzing sub-micro amounts of histamine (HA) and N(τ)-methylhistamine (N(τ)-MHA) in biological samples by high-performance liquid chromatography (HPLC)-amperometry has been developed. The method consists of a precolumn derivatization of the amines with o-phthalaldehyde (OPA) and sodium sulfite (Na(2)SO(3)) to N-alkyl-1-isoindole sulfonate and posterior separation with the HPLC system. Biological samples were pretreated by using a Vivapure sulfonic acid minifilter in which the reaction of the reagent with the amines took place during filtering. HA and N(τ)-MHA retention times were 11.8 ± 0.02 and 18.3 ± 0.03 min, respectively (means ± standard deviations, n = 3). The lowest limit of amperometric detection at a signal-to-noise ratio of 3:1 was 0.125 pmol in both cases. HA and N(τ)-MHA contents in hypothalamus, cortex, skin, and fundic gland, as well as histamine N-methyltransferase (HMT) activities of mast cell-deficient (Ws/Ws) and Wistar rats, were measured and compared with an HPLC-fluorometry system, among other experiments, in order to validate and demonstrate the usefulness of this assay system. Hence, this consequently confirms not only the sensitivity and specificity of the assay but also the potential and convenience it offers to laboratory work, especially in the analysis of the regulation of histaminergic neurons as well as enzymatic investigation of HA metabolism.

Histamine N-methyltransferase Thr105Ile polymorphism is associated with Parkinson's disease

Histamine is a central neurotransmitter degraded by histamine-N-methyltransferase (HNMT). Several abnormalities in the histaminergic system were found in patients with Parkinson's disease (PD), thus we tested the possible association of a Thr105Ile functional polymorphism in HNMT with PD. A total of 913 patients with PD and 958 controls were genotyped using a TaqMan RT-PCR Genotyping Assay (Foster City, California, USA). Lower frequency of HNMT Ile105 allele that is associated with decreased enzymatic activity was found in patients compared with controls (χ(2) = 11.65; p = 0.0006). We performed meta-analysis to confirm the association of Thr105Ile functional polymorphism with PD. Our results indicate that lower HNMT activity plays a role in the pathogenesis of PD.

Inhibition of histamine N-methyltransferase activity in guinea-pig pulmonary alveolar macrophages by nicotine.

Both S-(-)- and R-(+)-nicotine enantiomers are inhibitors of histamine N tau-methylation activity in guinea-pig pulmonary alveolar macrophage cultures, exhibiting IC50 values of 7 and 8 microM, respectively. S-(-)-Nicotine is not biotransformed under the conditions of the experiment, however, R-(+)-nicotine undergoes significant N-methylation to produce N-methylnicotinium ion. S-(-)-Nicotine appears to inhibit the N-methylation of its optical antipode by the alveolar nicotine N-methyltransferase. The results indicate that a contributing factor in the toxicology of cigarette smoke inhalation may be due to the inhibition of pulmonary metabolism of histamine by nicotine.

Histamine N‐methyltransferase 939A>G polymorphism affects mRNA stability in patients with acetylsalicylic acid‐intolerant chronic urticaria

Histamine plays an important role in allergic inflammation. Histamine levels are regulated by histamine N-methyltransferase (HNMT). To investigate the functional variability of HNMT gene in relation to genetic polymorphisms in patients with aspirin intolerant chronic urticaria (AICU). Two single-nucleotide polymorphisms of the HNMT gene (314C>T, 939A>G) were genotyped in chronic urticaria patients. The functional variability of 3'-untranslated region polymorphism (3'-UTR) was assessed using the pEGFP-HNMT 3'-UTR reporter construct to examine mRNA stability and fluorescence-tagged protein expression. The HNMT enzymatic activities related to the 939A>G polymorphism were examined both in the human mast cells (HMC-1) transfected with the pHNMT CDS-3'-UTR construct and in the patients' red blood cells (RBCs). Histamine release from the basophils of AICU patients was examined. The 939A>G polymorphism was significantly associated with the AICU phenotype, while no association was found with the 314C>T polymorphism. An in vitro functional study using HMC-1 cells demonstrated that the 939A allele gave lower levels of HNMT mRNA stability, HNMT protein expression, and HNMT enzymatic activity and higher histamine release than the 939G allele. The in vivo functional study demonstrated that the AICU patients with the 939A allele had lower HNMT activity in RBC lysates and higher histamine release from their basophils. The HNMT 939A>G polymorphism lowers HNMT enzymatic activity by decreasing HNMT mRNA stability, which leads to an increase in the histamine level and contributes to the development of AICU.

Association of the HistamineN‐Methyltransferase C314T (Thr105Ile) Polymorphism with Atopic Dermatitis in Caucasian Children

To investigate potential associations between the histamine N-methyltransferase (HNMT) gene, HNMT, C314T (Thr105Ile) polymorphism and atopic dermatitis in a cohort of Caucasian children. Prospective, multicenter, genotype-association study. Four academic, tertiary care medical centers within the Pediatric Pharmacology Research Unit network. Two hundred forty-nine Caucasian children aged 6 months-5 years with atopic dermatitis (127 patients) or without (122 control subjects). Buccal swabs (one swab/cheek) were performed to obtain epithelial cells for extraction of genomic DNA. Data were collected on severity of atopic dermatitis, oral antihistamine treatment, and treatment response through parental report. The HNMT genotypes were successfully obtained in 116 control subjects and 122 patients with atopic dermatitis. Frequencies of the T314 variant allele (0.12 vs 0.06, p=0.04) and combined CT/TT genotype (0.24 vs 0.12, p=0.02) were significantly higher in children with atopic dermatitis compared with control subjects. Children with genotypes conferring reduced HNMT activity were 2 times more likely to have atopic dermatitis than those who were homozygous for the C314 reference allele. Increased histamine levels in patients with atopic dermatitis may result, at least in part, from reduced enzymatic inactivation via HNMT. Genetically associated reduction in histamine biotransformation may therefore contribute to the pathogenesis, persistence, and progression of atopic dermatitis. If confirmed, these data indicate that HNMT genotype might represent a common risk factor for development of atopic dermatitis, asthma, and allergic rhinitis and may be useful in identifying individuals who are candidates for early preventive pharmacotherapeutic intervention. Additional longitudinal studies will be required to assess the relationship between genotype, disease severity, and antihistamine response.

Decreased Histamine Catabolism in the Colonic Mucosa of Patients with Colonic Adenoma

Alterations in mucosal histamine degradation play an important role in various gastrotinestinal diseases including colonic adenoma. In humans, histamine can be catabolized either by oxidative deamination by diamine oxidase (DAO) or by ring methylation by histamine N-methyltransferase (HNMT). The significance of HNMT in this context was investigated for the first time in this project. About 94 colonic biopsies were endoscopically obtained from 23 patients suffering from colonic adenoma and 26 biopsies from six healthy individuals. Each sample was mechanically homogenized, homogenates were cleared by centrifugation and used for determination of protein and histamine concentrations and enzyme activities of DAO and HNMT by radiometric assay. In adenoma patients DAO activities were slightly and HNMT activities were significantly decreased in normal mucosa compared to controls. Activities of both enzymes were significantly lower in adenoma tissue than in healthy mucosa in the same patients. A significant correlation was found between HNMT and DAO in all investigated samples. Histamine concentrations were elevated in adenoma patients. Histamine catabolism is decreased in the colonic mucosa of patients with colonic adenoma.

The Hemolymph of the Ascidian Styela plicata (Chordata-Tunicata) Contains Heparin inside Basophil-like Cells and a Unique Sulfated Galactoglucan in the Plasma

The hemolymph of ascidians (Chordata-Tunicata) contains different types of hemocytes embedded in a liquid plasma. In the present study, heparin and a sulfated heteropolysaccharide were purified from the hemolymph of the ascidian Styela plicata. The heteropolysaccharide occurs free in the plasma, is composed of glucose ( approximately 60%) and galactose ( approximately 40%), and is highly sulfated. Heparin, on the other hand, occurs in the hemocytes, and high performance liquid chromatography of the products formed by degradation with specific lyases revealed that it is composed mainly by the disaccharides DeltaUA(2SO(4))-1-->4-beta-d-GlcN(SO(4)) (39.7%) and DeltaUA(2SO(4))-1-->4-beta-d-GlcN(SO(4))(6SO(4)) (38.2%). Small amounts of the 3-O-sulfated disaccharides DeltaUA(2SO(4))-1-->4-beta-d-GlcN(SO(4))(3SO(4)) (9.8%) and DeltaUA(2SO(4))-1-->4-beta-d-GlcN(SO(4))(3SO(4))(6SO(4)) (3.8%) were also detected. These 3-O-sulfated disaccharides were demonstrated to be essential for the binding of the hemocyte heparin to antithrombin III. Electron microscopy techniques were used to characterize the ultrastructure of the hemocytes and to localize heparin and histamine in these cells. At least five cell types were recognized and classified as univacuolated and multivacuolated cells, amebocytes, hemoblasts, and granulocytes. Immunocytochemistry showed that heparin and histamine co-localize in intracellular granules of only one type of hemocyte, the granulocyte. These results show for the first time that in ascidians, a sulfated galactoglucan circulates free in the plasma, and heparin occurs as an intracellular product of a circulating basophil-like cell.

Endogenous Histamine and Cortisol Levels in Subjects with Different Histamine N-Methyltransferase C314T Genotypes

Histamine N-methyltransferase (HNMT) catalyzes the methylation of histamine and plays an important role in histamine biotransformation in bronchial epithelium. Enzymatic activity of HNMT has been shown to be regulated by genetic factors, including polymorphisms in the HNMT gene. In this pilot study we determined endogenous levels of histamine and cortisol in plasma and whole blood samples from subjects with different genotypes for the HNMT C314T polymorphism, and investigated whether these parameters differed between individuals with the HNMT CC genotype and those with the CT genotype. Blood samples were collected from 48 unrelated volunteers (36 males, 12 females), aged 21-40 years, who participated in the study. PCR-restriction fragment length polymorphism analysis was used to determine HNMT C314T genotypes. Erythrocyte HNMT activity was determined as well as plasma and whole blood levels of histamine and cortisol. Two-group comparisons of the various parameters were analyzed by Blocked Wilcoxon test and Wilcoxon Rank Sum test as appropriate. Thirty-seven subjects (24 Caucasians, three African Americans, one Middle Eastern, five Indians, three Chinese, and one Filipino) were found to have the homozygous CC genotype. Ten subjects (eight Caucasians, one Middle Eastern, and one Chinese) were heterozygous and one individual (Pakistani) was homozygous for the variant 314T allele. The frequency of HNMT CT heterozygotes in the small Caucasian cohort was 0.125. Median enzyme activity was significantly lower in subjects with the heterozygous CT genotype than in those with the homozygous CC genotype (485 vs 631 U/mL of red blood cells; p=0.023). A broad range of histamine levels in plasma and whole blood was observed for all subjects. Whereas the median plasma histamine level was found to be higher in heterozygotes for the wild-type 314C allele than homozygotes (3.32 vs 2.30 nmol/L; p=0.021), there was no difference between the two groups in histamine levels in whole blood. Cortisol levels were similar between individuals with the homozygous CC genotype and those with the heterozygous CT genotype. Wide variability of plasma and whole-blood histamine levels was observed in subjects with different HNMT C314T genotypes. Endogenous levels of histamine are likely to be affected by various genes and polymorphisms.

Histamine inactivation in the colon of pigs in relationship to abundance of catabolic enzymes

Objective. Catabolism of histamine plays a crucial role in the intestine in preventing intoxication by luminal histamine. Two enzymes are involved, namely histamine N-methyltransferase (HMT) and diamine oxidase (DAO). The purpose of this study was to find a link between histamine catabolism and the activities of HMT and DAO.Material and methods. Epithelia of porcine proximal colon were mounted in Ussing chambers. After mucosal addition of 3H-histamine (100 µmol·l−1) and 14C-mannitol, the appearance of non-catabolized histamine, 3H-histamine label (hist-rad) and 14C-mannitol label were measured in parallel on the serosal side. Activities of HMT and DAO were determined in the proximal colon and proximal jejunum.Results. Differences between the fluxes of histamine and hist-rad indicated catabolic conversion of 81.4±1.6% histamine during epithelial transit. Fluxes of hist-rad and histamine increased linearly with increasing mannitol fluxes but the percentage of catabolized histamine was not related to either mannitol or hist-rad fluxes. However, the percentage of catabolized histamine rose with increasing DAO activity. Given a negative correlation between DAO and HMT activities, the fraction of catabolized histamine decreased with increasing HMT activity. HMT activity was comparable in the colon and jejunum, but DAO activity was approximately nine times higher in the jejunum.Conclusions. Permeation, but not the relative efficiency of catabolism, of histamine depends on epithelial/paracellular tightness. While previous studies have shown that colonic HMT essentially catabolizes the bulk of histamine during permeation, DAO activity seems to be more variable and limiting for the overall efficiency of the catabolic process.

Recent Advances in Molecular Pharmacology of the Histamine Systems: Organic Cation Transporters as a Histamine Transporter and Histamine Metabolism

Histamine is inactivated by the histamine-metabolizing enzyme histamine N-methyltransferase (HNMT) in bronchus, kidney, and the central nervous system. HNMT seems to be localized in the cytoplasm, but histamine is unable to easily enter the intracellular space. Therefore, two hypotheses can be elicited: one is the plasma membrane hypothesis that HNMT can be translocated to the plasma membrane and function at the cell surface under growth factor stimulation and the other is the transporter hypothesis that organic cation transporter (OCT)-2 and -3 can function as a histamine transporter as well. To investigate the involvement of OCT2, HEK293 cells stably double transfected with C-terminal hemagglutinin (HA)-tagged HNMT cDNA and/or C-terminal myc-tagged rat OCT2 were prepared for analysis of HNMT activity associated with OCT2 function. After 60-min incubation of these cells with PBS including HA (100 microM), N(tau)-methylhistamine (MHA) concentration of the supernatants was determined by the HPLC-fluorometry method. MHA from cells with HNMT plus OCT-2 was produced at about 3-fold higher level than that from cells with HNMT alone, suggesting that OCT-2 could function as a histamine transporter as well and that HNMT function could partly depend on OCT-2 transporter activity. Using OCT-3 knockout (OCT-3-/-) mice, histamine content and survival rates were investigated in lipopolysaccharide (LPS)-induced endotoxemia model. Without LPS stimulation, histamine content was compared between OCT-3-/- and wild mice. Histamine content in the spleen of OCT-3-/- mice was higher than that f wild mice. With LPS stimulation, the survival rate of OCT-3-/- mice was significantly decreased 12 h after LPS (20 mg/kg) stimulation, suggesting that before immunological stimulation, a higher content of histamine in spleen could stimulate histamine receptors in mast cells, macrophages, dendritic cells, as well as T lymphocytes and explaining the decreased survival rate in OCT-3-/- mice possibly due to the functional changes of immunological cells.

Actions of tacrine and galanthamine on histamine-N-methytransferase

Histamine-synthesizing neurons in the brain may play an important role in cognition, and a histaminergic deficit has been found in Alzheimer's disease (AD). The AD medication tacrine was previously shown to inhibit some forms of rodent histamine-N-methyltransferase (HNMT), but the effects of AD drugs have not been investigated on human HNMT activity. Presently, the effects of tacrine and galanthamine (another AD medication) were studied on the activity of several forms of human and rat HNMT. Tacrine (0.01-10 microM) inhibited both human and rat HNMT activity in a concentration-dependent manner, but was less potent on both human embryonic kidney and recombinant human brain HNMT than on rat kidney HNMT (IC50 values were 0.46 and 0.70 microM vs. 0.29 microM, respectively). Galanthamine (up to 10 microM) did not influence the activity of rat kidney or human HNMT. Tacrine, but not galanthamine, may achieve brain levels sufficient to influence histamine metabolism in some patients treated for AD.

Involvement of arginine vasopressin in endogenous central histamine-induced reversal of critical haemorrhagic hypotension in rats.

Histamine is a potent stimulator of arginine vasopressin (AVP) release and therefore, the role of AVP was studied in the reversal of critical haemorrhagic hypotension induced by endogenous central histamine after inhibition of histamine N-methyltransferase (HNMT) activity in rats. In 48 ethylurethane-anaesthetised male Wistar rats cardiovascular parameters and plasma hormone concentrations were measured. Haemorrhage-shocked rats with mean arterial pressure (MAP) 20-25 mmHg were injected intracerebroventricularly (icv) with HNMT inhibitor metoprine (20 microg) after pre-treatment with V(1a), V(1b) and V(2) receptor antagonists - [beta-mercapto-beta,betacyclopentamethylenepropionyl(1), O-me-Tyr(2),Arg(8)]AVP (10 microg/kg; iv), SSR149415 (10 mg/kg; ip) and [adamantaneacetyl(1),O-Et-D-Tyr(2),Val(4), aminobutyryl(6),Arg(8,9)]AVP (10 microg/kg; iv), respectively, or saline. MAP, heart rate (HR) and regional haemodynamics were monitored within 2 h after treatment or to death if it occurred earlier. Plasma hormone concentrations were measured using enzyme immunoassays. ANOVA followed by Neuman-Keules test, and Fisher's exact test were used to compare the results. Metoprine produced a long-lasting increase in MAP, HR, renal, hindquarters and mesenteric blood flows, and a 100% survival at 2 h (P < 0.05 vs. the control group). The action was associated with increased plasma AVP concentration (587.5 +/- 98.9 vs. 387.3 +/- 125.2 pg/ml; P < 0.05) in comparison to the control group as measured at 20 min after treatment. V(1a), but not V(1b) and V(2), receptor antagonist inhibited metoprine-induced haemodynamic effects, with no influence on survival at 2 h. SSR149415 did not influence ACTH and adrenaline plasma concentrations in the metoprine-treated group. AVP, acting via V(1a) receptors, is involved in endogenous central histamine-induced reversal of critical haemorrhagic hypotension in rats.

Cardiac and regional haemodynamic effects of histamine N-methyltransferase inhibitor metoprine in haemorrhage-shocked rats.

The increase in central histamine concentrations after inhibition of histamine N-methyltransferase (HNMT) activity is associated with the reversal of critical haemorrhagic hypotension, therefore the present study examines cardiac and regional haemodynamic effects of HNMT inhibitor metoprine in haemorrhage-shocked rats. Cardiovascular parameters were measured in 72 and central histamine concentrations in 12 male Wistar rats anaesthetised with ketamine/xylazine. Metoprine (5, 15 mg/kg) was administered intraperitoneally to normotensive and critically-hypotensive rats with mean arterial pressure (MAP) 20-25 mmHg. Haemorrhage-shocked rats were pre-treated intracerebroventricularly with histamine H(3) receptor agonist R(-)-alpha-methylhistamine (10 microg) or saline. MAP, heart rate (HR) and cardiac and regional haemodynamics were monitored within 2 h after treatment, or to death if it occurred earlier. Histamine concentrations were measured using enzyme immunoassay. ANOVA followed by Neuman-Keules test, and Fisher's exact test were used to compare the results. Bleeding resulted in an extreme decrease in cardiac index (CI), an increase in total peripheral resistance index (TPRI) and the death of control animals within 30 min. Metoprine induced increases in MAP and HR which were significantly higher in hypotensive than in normotensive animals. The resuscitating effect of metoprine (15 mg/kg) was associated with a rise in CI, a decrease in TPRI, and a 100% survival at 2 h. TPRI changes resulted from decreased renal, hindquarters and mesenteric vascular resistance. R(-)-alpha-methylhistamine inhibited metoprine-induced increases in endogenous histamine concentrations in the cerebral cortex (0.89 +/- 0.12 vs. 1.25 +/- 0.29 nmol/g of wet tissue; P < 0.05), hypothalamus (4.37 +/- 0.42 vs. 5.74 +/- 0.47 nmol/g of wet tissue; P < 0.01) and medulla oblongata (0.39 +/- 0.07 vs. 0.65 +/- 0.28 nmol/g of wet tissue; P < 0.05), diminished haemodynamic effects and decreased the survival rate at 2 h to 33% (P < 0.05 vs. the saline-pre-treated group). The results support the hypothesis that histaminergic system activation leads to mobilisation of compensatory mechanisms in haemorrhagic hypotension.

Histamine-degrading enzymes as cellular markers of acute small bowel allograft rejection

Abstract Intestinal histaminedegrading enzymes diamine oxidase (DAO) and histamine N-methyltransferase (HNMT) activities are relatively constant per individual and bowel segment, and they reflect the functional integrity of the intestinal mucosa. It was, therefore, hypothesised that a decrease in these enzymes could be indicative of acute rejection of an intestinal allograft. Enzymatic activities of DAO and HNMT were determined in mucosal biopsies of isogeneic (Lewis-to-Lewis, n=48) and allogeneic (Brown Norway-to-Lewis, n=48) heterotopic small bowel transplants in a rat model at various time periods. Allograft recipients were not given any immunosuppression. While no changes in enzyme activities were observed in isografts up to day 8 following transplantation, significantly reduced activities of both enzymes were found in all allografts 6–8 days after transplantation. Activities of both DAO and HNMT exhibited a strong negative correlation with the histological rejection score (P<0.01). We can conclude that DAO and HNMT activities in gut mucosa are reliable quantitative markers of acute intestinal allograft rejection in the rat that support histopathological analysis.

Effects of amphotericin B and caspofungin on histamine expression.

To determine the effects of amphotericin B deoxycholate and caspofungin on the release of histamine from human peripheral blood cells, mononuclear cells, and mast cells. In vitro cell culture experiments. University medical center. Cultured human mononuclear (THP-1) and mast (HMC-1) cells from five healthy volunteers. The cultured cells were incubated with increasing concentrations of amphotericin B deoxycholate, diphenhydramine, amphotericin B deoxycholate plus diphenhydramine, caspofungin, caspofungin plus diphenhydramine, and the calcium ionophore A23187 for up to 24 hours. Histamine concentrations and histamine N-methyltransferase activity were determined at various time points throughout exposure. Cell viability was assessed by exclusion of erythrocin B. The A23187 increased histamine concentrations from baseline in peripheral blood and HMC-1 cells. No change in histamine concentrations was observed in response to amphotericin B deoxycholate, whereas caspofungin induced a significant increase in histamine release in peripheral blood cells and HMC-1 cells. No change in histamine concentrations was observed in THP-1 cells in response to any pharmacologic agent tested. Similarly, histamine N-methyltransferase activity in peripheral blood was not affected by amphotericin B deoxycholate, but was significantly decreased by caspofungin. Amphotericin B deoxycholate does not affect histamine concentrations or histamine N-methyltransferase activity in whole blood or HMC-1 cells, suggesting that the amphotericin B-induced infusion-related reaction is not a histamine-mediated event. Conversely, caspofungin increased histamine concentrations in whole blood and HMC-1 cells and inhibited histamine N-methyltransferase activity. These data suggest that infusion-related reactions associated with caspofungin may be mediated by histamine release secondary to caspofungin.

Histamine-degrading enzymes as cellular markers of acute small bowel allograft rejection.

Intestinal histamine-degrading enzymes diamine oxidase (DAO) and histamine N-methyltransferase (HNMT) activities are relatively constant per individual and bowel segment, and they reflect the functional integrity of the intestinal mucosa. It was, therefore, hypothesised that a decrease in these enzymes could be indicative of acute rejection of an intestinal allograft. Enzymatic activities of DAO and HNMT were determined in mucosal biopsies of isogeneic (Lewis-to-Lewis, n=48) and allogeneic (Brown Norway-to-Lewis, n=48) heterotopic small bowel transplants in a rat model at various time periods. Allograft recipients were not given any immunosuppression. While no changes in enzyme activities were observed in isografts up to day 8 following transplantation, significantly reduced activities of both enzymes were found in all allografts 6-8 days after transplantation. Activities of both DAO and HNMT exhibited a strong negative correlation with the histological rejection score ( P<0.01). We can conclude that DAO and HNMT activities in gut mucosa are reliable quantitative markers of acute intestinal allograft rejection in the rat that support histopathological analysis.