An environmentally regulated receptor for diamine oxidase modulates human endothelial cell/fibroblast histamine degradative uptake

Human diamine oxidase cellular binding and internalization in vitro and rapid clearance in vivo are not mediated by N-glycans but by heparan sulfate proteoglycan interactions

Human diamine oxidase (hDAO) rapidly inactivates histamine by deamination. No pharmacokinetic data are available to better understand its potential as a new therapeutic modality for diseases with excess local and systemic histamine, like anaphylaxis, urticaria or mastocytosis. After intravenous administration of recombinant hDAO to rats and mice, more than 90% of the dose disappeared from the plasma pool within 10 min. Human DAO did not only bind to various endothelial and epithelial cell lines in vitro, but was also unexpectedly internalized and visible in granule-like structures. The uptake of rhDAO into cells was dependent on neither the asialoglycoprotein-receptor (ASGP-R) nor the mannose receptor (MR) recognizing terminal galactose or mannose residues, respectively. Competition experiments with ASGP-R and MR ligands did not block internalization in vitro or rapid clearance in vivo. The lack of involvement of N-glycans was confirmed by testing various glycosylation mutants. High but not low molecular weight heparin strongly reduced the internalization of rhDAO in HepG2 cells and HUVECs. Human DAO was readily internalized by CHO-K1 cells, but not by the glycosaminoglycan- and heparan sulfate-deficient CHO cell lines pgsA-745 and pgsD-677, respectively. A docked heparin hexasaccharide interacted well with the predicted heparin binding site 568RFKRKLPK575. These results strongly imply that rhDAO clearance in vivo and cellular uptake in vitro is independent of N-glycan interactions with the classical clearance receptors ASGP-R and MR, but is mediated by binding to heparan sulfate proteoglycans followed by internalization via an unknown receptor.

Diamine oxidase levels in different chronic urticaria phenotypes

BACKGROUND

Diamine oxidase (DAO) is a polyamine-degrading enzyme also implicated in histamine metabolism. Chronic urticaria (CU) has a wide spectrum of clinical presentations and causes. Anisakis sensitisation associated chronic urticaria (CU+) has been characterised as a phenotype with different clinical and immunological characteristics and possibly associated with previous acute parasitism. We aimed to analyse serum DAO levels in different CU phenotypes. We further analysed the possible association of DAO with fish eating habits.

METHODS

We studied 35 CU+ patients and 39 non-sensitised CU patients (CU-) as well as 19 controls. We analysed fish-eating frequency as well as fish intake associated exacerbation of CU (FIAE) or gastro-intestinal complaints (GI). DAO levels were further analysed with respect to lymphoproliferative responses, cytokine and specific IgE production.

RESULTS

DAO levels were not different between CU and controls, but were significantly higher in CU+ than in CU-. CU+ patients with FIAE had lower DAO levels, but no differences were detected in patients with GI. DAO levels correlated positively with oily and canned fish consumption in CU-. In CU+, DAO levels correlated positively with specific Anisakis IgE, percentages of proliferation in Anisakis stimulated peripheral blood lymphocytes, serum IL-2 and IL-6, but correlated negatively with mitogen stimulated TGF-β in supernatants.

CONCLUSIONS

DAO levels in CU depend on fish-eating habits and in CU+ on the amount of specific IgE production. In the CU+ phenotype, lower levels of DAO predispose to urticaria exacerbation after fish intake, probably due to a relative insufficient enteric availability of this enzyme.

Molecular profiling reveals diversity of stress signal transduction cascades in highly penetrant Alzheimer's disease human skin fibroblasts

The serious and growing impact of the neurodegenerative disorder Alzheimer's disease (AD) as an individual and societal burden raises a number of key questions: Can a blanket test for Alzheimer's disease be devised forecasting long-term risk for acquiring this disorder? Can a unified therapy be devised to forestall the development of AD as well as improve the lot of present sufferers? Inflammatory and oxidative stresses are associated with enhanced risk for AD. Can an AD molecular signature be identified in signaling pathways for communication within and among cells during inflammatory and oxidative stress, suggesting possible biomarkers and therapeutic avenues? We postulated a unique molecular signature of dysfunctional activity profiles in AD-relevant signaling pathways in peripheral tissues, based on a gain of function in G-protein-coupled bradykinin B2 receptor (BKB2R) inflammatory stress signaling in skin fibroblasts from AD patients that results in tau protein Ser hyperphosphorylation. Such a signaling profile, routed through both phosphorylation and proteolytic cascades activated by inflammatory and oxidative stresses in highly penetrant familial monogenic forms of AD, could be informative for pathogenesis of the complex multigenic sporadic form of AD. Comparing stimulus-specific cascades of signal transduction revealed a striking diversity of molecular signaling profiles in AD human skin fibroblasts that express endogenous levels of mutant presenilins PS-1 or PS-2 or the Trisomy 21 proteome. AD fibroblasts bearing the PS-1 M146L mutation associated with highly aggressive AD displayed persistent BKB2R signaling plus decreased ERK activation by BK, correctible by gamma-secretase inhibitor Compound E. Lack of these effects in the homologous PS-2 mutant cells indicates specificity of presenilin gamma-secretase catalytic components in BK signaling biology directed toward MAPK activation. Oxidative stress revealed a JNK-dependent survival pathway in normal fibroblasts lost in PS-1 M146L fibroblasts. Complex molecular profiles of signaling dysfunction in the most putatively straightforward human cellular models of AD suggest that risk ascertainment and therapeutic interventions in AD as a whole will likely demand complex solutions.

The dynamics of signaling at the histaminergic photoreceptor synapse of arthropods

Histamine, a ubiquitous aminergic messenger throughout the body, also serves as a neurotransmitter in both vertebrates and invertebrates. In particular, the photoreceptors of adult arthropods use histamine, modulating its release to signal increases and decreases in light intensity. Strong evidence from various arthropod species indicates that histamine is synthesized and stored in photoreceptors, undergoes Ca-dependent release, inhibits postsynaptic interneurons by gating Cl channels, and is then recycled. In Drosophila, the synthetic enzyme, histidine decarboxylase, and the subunits of the histamine-gated chloride channel have been cloned. Possible histamine transporters at synaptic vesicles and for reuptake remain elusive. Indeed, the mechanisms that remove histamine from the synaptic cleft, and that help terminate histamine's action, are unexpectedly complex, their details remaining unresolved. A major pathway in Drosophila, and possibly other arthropod species, is by conjugation of histamine to beta-alanine to form carcinine in adjacent glia. This conjugate then returns to the photoreceptors where it is hydrolysed to liberate histamine, which is then loaded into synaptic vesicles. Evidence from other species suggests that direct reuptake of histamine into the photoreceptors may also occur. Light depolarizes the photoreceptors, causing histamine release and postsynaptic inhibition; dimming hyperpolarizes the photoreceptors, causing a decrease in histamine release and an "off" response in the postsynaptic cell. Further pursuit of histamine's action at these highly specialized synapses should lead to an understanding of how they signal minute changes in presynaptic membrane potential, how they reliably extract signals from noise, and how they adapt to a wide range of presynaptic membrane potentials.

Vascular amine oxidases are needed for leukocyte extravasation into inflamed joints in vivo

OBJECTIVE

Leukocyte traffic from the blood to the joints is crucial in the pathogenesis of arthritis. A bifunctional endothelial cell-surface glycoprotein, AOC3 (amine oxidase, copper-containing 3; also known as vascular adhesion protein 1), has both adhesive and enzymatic properties. We undertook this study to determine the contribution of AOC3 and its oxidase activity to leukocyte trafficking into inflamed joints in vivo.

METHODS

We used gene-modified animals, molecular modeling, an AOC3 enzyme inhibitor, oxidase assays, and arthritis models (adjuvant-induced arthritis [AIA] in rats and anti-type II collagen antibody-induced arthritis in mice) to dissect the importance of AOC3 in vivo.

RESULTS

The AOC3 inhibitor fitted well with a covalent binding mode into the active site of the AOC3 crystal structure. It selectively blocked the oxidase activity of AOC3 in enzyme assays. Intraperitoneal and oral administration of the AOC3 inhibitor significantly ameliorated rat AIA. In anti-type II collagen antibody-induced arthritis in mice, the AOC3 inhibitor also improved the outcome of the joint inflammation. The acute semicarbazide-sensitive amine oxidase blockade by the inhibitor had even more pronounced effects than genetic deletion of AOC3. Enzymatic analyses showed that the inhibitor also blocked 2 other structurally very closely related AOCs, but not any of more than 100 other enzymes tested.

CONCLUSION

These are the first data to demonstrate that the enzymatic activity of the atypical endothelial adhesion molecule AOC3, and possibly that of other closely related ecto-oxidases, is crucial for leukocyte exit from the vessels in inflamed joints in vivo.

Alzheimer's disease skin fibroblasts selectively express a bradykinin signaling pathway mediatingtauprotein Ser phosphorylation

Increased Ser phosphorylation of tau microtubule-associated protein in the brain is an early feature of Alzheimer's disease (AD) that precedes progression of the disease to frank neuronal disruption. We demonstrate that bradykinin (BK) B2 receptor activation leads to selective Ser phosphorylation of tau in skin fibroblasts from persons who have or will develop AD due to Presenilin 1 mutations or Trisomy 21, but not in skin fibroblasts from normal individuals at any age. The increased signal transduction in AD fibroblasts that culminates in tau Ser phosphorylation reflects modification of the G protein-coupled BK B2 receptors themselves. Both the BK B2 receptor modification and BK-mediated tau Ser phosphorylation are dependent on activation of protein kinase C and can be detected in fibroblasts from persons with Trisomy 21 two decades before the characteristic onset of AD. This dysregulated signaling cascade in AD may thus be expressed throughout life as an aberrant pathway in peripheral tissues more accessible than brain for molecular analysis. The sites of greatest BK B2 receptor expression in brain overlap with those areas displaying the earliest pathology in the course of AD, suggesting that BK receptor pathway dysfunction may be a molecular signature yielding information about the pathogenesis of AD.

Membrane-bound histamine N-methyltransferase in mouse brain: possible role in the synaptic inactivation of neuronal histamine

In the CNS, histamine is a neurotransmitter that is inactivated by histamine N-methyltransferase (HNMT), a soluble enzyme localized to the cytosol of neurons and endothelial cells. However, it has not been established how extracellular histamine, a charged molecule at physiological pH, reaches intracellular HNMT. Present studies investigated two potential routes of histamine inactivation in mouse brain nerve terminal fractions (synaptosomes): (i) histamine uptake and (ii) histamine metabolism by HNMT. Intact synaptosomes demonstrated a weak temperature-dependent histamine uptake (0.098 pmol/min-mg protein), but contained a much greater capacity to metabolize histamine by HNMT (1.4 pmol/min-mg protein). Determination of the distribution of HNMT within synaptosomes revealed that synaptosomal membranes (devoid of soluble HNMT) contribute HNMT activity equivalent to intact synaptosomes (14.3 +/- 2.2 and 18.2 +/- 4.3 pmol/min-tube, respectively) and suggested that histamine-methylating activity is associated with the membrane fraction. Additional experimental findings that support this hypothesis include: (i) the histamine metabolite tele-methylhistamine (tMH) was found exclusively in the supernatant fraction following an HNMT assay with intact synaptosomes; (ii) the membrane-bound HNMT activity was shown to increase 6.5-fold upon the solubilization of the membranes with 0.1% Triton X-100; and (iii) HNMT activity from the S2 fraction, ruptured synaptosomes, and synaptosomal membranes displayed different stability profiles when stored over 23 days at - 20 degrees C. Taken together, these studies demonstrate functional evidence for the existence of membrane-bound HNMT. Although molecular studies have not yet identified the nature of this activity, the present work suggests that levels of biologically active histamine may be controlled by an extracellular process.

Nutrients regulate diamine oxidase release from intestinal mucosa

Diamine oxidase is continuously released from the intestinal mucosa and carried to the circulation by the lymphatics. The effect of nutrients on this release was examined. Rats were prepared with duodenal and intestinal lymph cannulas. Test mixtures of lipid emulsions containing triolein, oleic acid, or tricaprylin and solutions of carbohydrate and protein were infused into the duodenum. The enzyme release and triglyceride transport were determined and in some experiments were done in the presence and absence of Pluronic L-81, an inhibitor of chylomicron formation, and aminoguanidine, an inhibitor of diamine oxidase activity. The data indicate that nonlipid nutrients did not increase diamine oxidase activity in the intestinal lymph, but the mucosal tissue content was significantly reduced in the distal small intestine, particularly after protein infusion. Triglycerides and fatty acids increased diamine oxidase in the intestinal lymph, and the longer-chain triglyceride was more effective. Inhibition of triglyceride transport did not interfere with the enzyme release, and the inhibition of diamine oxidase activity had no significant effect on lipid absorption. According to our observations, only lipids increase intestinal lymph diamine oxidase. Nonfat nutrients appear to increase diamine oxidase in the intestinal lumen. Diamine oxidase is not directly required for lipid absorption.

Newly discovered redox cofactors: possible nutritional, medical, and pharmacological relevance to higher animals

Research spurred by the discovery of pyrroloquinoline quinone (PPQ) in 1979 led to the discovery of four additional oxidation-reduction (redox) cofactors, all of which result from transmogrification of amino acyl side chains in respective enzymes. These cofactors are (a) topa quinone in copper-containing amine oxidases, enzymes found in nearly all forms of life, including human; (b) lysyl topa quinone of the copper protein lysyl oxidase, an enzyme required for proper cross-linking of collagen and elastin; (c) tryptophan tryptophylquinone of alkylamine dehydrogenases from gram-negative soil bacteria; and (d) the copper-complexed cysteinyltyrosyl radical of fungal galactose oxidase. Originally, PQQ was thought to be a covalently bound cofactor in numerous enzymes from eukaryotes and prokaryotes. Today, PQQ is only found as a noncovalent cofactor in bacterial enzymes. The ubiquity of PQQ in the environment and its steady accessibility in the human diet has raised questions concerning its role as a vitamin, or an essential or helpful nutrient. The relevance to nutrition, medicine, and pharmacology of PQQ, topa quinone, lysyl topa quinone, tryptophan trytophylquinone, the galactose oxidase cofactor, and the enzymes harboring these cofactors are discussed in this review.

Human lung fibroblasts express multiple means for enhanced activity of bradykinin receptor pathways

Human lung fibroblasts represent important targets for the biologic activities of bradykinin (BK). We have identified multiple mechanisms in these cells which may extend their potential for BK receptor responsiveness, particularly with regard to generation of arachidonate metabolites. These fibroblasts can constitutively express B2 and B1 BK receptors concurrently, both coupled to the pathway for arachidonate metabolism resulting in generation of PGE2 and the potent vasoactive lipid mediator Thromboxane A2. Although expression patterns for B2 and B1 receptors have classically been regarded as 'constitutive' and 'inducible', respectively, we demonstrate that in human lung fibroblasts both can be expressed spontaneously at equivalent biologic activity levels without selective induction by other mediators. Concurrent B2/B1 receptor expression extends the scope of fibroblast response potential to both BK and des-Arg9-BK in the same time frame. We have identified additional short-term and long-term cellular events, involving both protein kinase pathways through which BK receptors act and those which act upon BK receptors, that result in enhanced BK receptor response potential. These properties of BK receptors may affect whether fibroblast behaviors maintain controlled activities of normal homeostasis or foster escalating cellular responses which may influence the progression of certain human disease states.