Inhibition by cromoglycate and some flavonoids of nucleoside diphosphate kinase and of exocytosis from permeabilized mast cells

Identifying inhibitors of Trypanosoma cruzi nucleoside diphosphate kinase 1 as potential repurposed drugs for Chagas' disease

Trypanosoma cruzi is the causative agent of Chagas' disease, an endemic and neglected disease. The treatment is limited to only two drugs, benznidazole (BZL) and nifurtimox (NFX), introduced more than fifty years ago and no new advances have been made since then. Nucleoside diphosphate kinases (NDPK) are key metabolic enzymes which have gained interest as drug targets of pathogen organisms. Taking advantage of the computer-assisted drug repurposing approaches, in the present work we initiate a search of potential T. cruzi nucleoside diphosphate kinase 1 (TcNDPK1) inhibitors over an ∼ 12,000 compound structures database to find drugs targeted to this enzyme with trypanocidal activity. Four medicines were selected and evaluated in vitro, ketorolac (KET, an anti-inflamatory), dutasteride (DUT, used to treat benign prostatic hyperplasia), nebivolol and telmisartan (NEB and TEL, used to treat high blood pressure). The four compounds were weak inhibitors and presented different trypanocidal effect on epimastigotes, trypomastigotes and intracellular stages. NEB and TEL were the most active drugs with increased effect on intracellular stages, (IC50 = 2.25 µM and 13.21 µM respectively), and selectivity indexes of 13.01 and 8.59 respectively, showing comparable effect to BZL, the first line drug for Chagas' disease treatment. In addition, both presented positive interactions when combined with BZL. Finally, transgenic epimastigotes with increased expression of TcNDPK1 were more resistant to TEL and NEB, suggesting that TcNDPK1 is at least one of the molecular targets. In view of the results, NEB and TEL could be repurposed medicines for Chagas' disease therapy.

Mast cell-neural interactions contribute to pain and itch

Mast cells are best recognized for their role in allergy and anaphylaxis, but increasing evidence supports their role in neurogenic inflammation leading to pain and itch. Mast cells act as a "power house" by releasing algogenic and pruritogenic mediators, which initiate a reciprocal communication with specific nociceptors on sensory nerve fibers. Consequently, nerve fibers release inflammatory and vasoactive neuropeptides, which in turn activate mast cells in a feedback mechanism, thus promoting a vicious cycle of mast cell and nociceptor activation leading to neurogenic inflammation and pain/pruritus. Mechanisms underlying mast cell differentiation, activation, and intercellular interactions with inflammatory, vascular, and neural systems are deeply influenced by their microenvironment, imparting enormous heterogeneity and complexity in understanding their contribution to pain and pruritus. Neurogenic inflammation is central to both pain and pruritus, but specific mediators released by mast cells to promote this process may vary depending upon their location, stimuli, underlying pathology, gender, and species. Therefore, in this review, we present the contribution of mast cells in pathological conditions, including distressing pruritus exacerbated by psychologic stress and experienced by the majority of patients with psoriasis and atopic dermatitis and in different pain syndromes due to mastocytosis, sickle cell disease, and cancer.

Systemic mastocytosis with KIT V560G mutation presenting as recurrent episodes of vascular collapse: response to disodium cromoglycate and disease outcome

Background

Mastocytosis are rare diseases characterized by an accumulation of clonal mast cells (MCs) in one or multiple organs or tissues. Patients with systemic mastocytosis (SM), whose MCs frequently arbor the activating D816V KIT mutation, may have indolent to aggressive diseases, and they may experience MC mediator related symptoms. Indolent SM with recurrent anaphylaxis or vascular collapse in the absence of skin lesions, ISMs(−), is a specific subtype indolent SM (ISM), and this clonal MC activation disorder represents a significant fraction of all MC activation syndromes. The V560G KIT mutation is extremely rare in patients with SM and its biological and prognostic impact remains unknown.

Case presentation

A 15-year old boy was referred to our hospital because of repeated episodes of flushing, hypotension and syncope since the age of 3-years, preceded by skin lesions compatible with mastocytosis on histopathology that had disappeared in the late-early childhood. Diagnosis of ISM, more precisely the ISMs(−) variant, was confirmed based on the clinical manifestations together with increased baseline serum tryptase levels and the presence of morphologically atypical, mature appearing (CD117+high, FcεRI+) phenotypically aberrant (CD2+, CD25+) MCs, expressing activation-associated markers (CD63, CD69), in the bone marrow. Molecular genetic studies revealed the presence of the KIT V560G mutation in bone marrow MCs, but not in other bone marrow cells, whereas the screening for mutations in codon 816 of KIT was negative. The patient was treated with oral disodium cromoglycate and the disease had a favorable outcome after an eleven-year follow-up period, during which progressively lower serum tryptase levels together with the fully disappearance of all clinical manifestations was observed.

Conclusions

To the best of our knowledge this first report of a patient with ISM, whose bone marrow MCs carry the KIT V560G activating mutation, manifesting as recurrent spontaneous episodes of flushing and vascular collapse in the absence of skin lesions at the time of diagnosis, in whom disodium cromoglycate had led to long term clinical remission.

Advances in the understanding and clinical management of mastocytosis and clonal mast cell activation syndromes

Clonal mast cell activation syndromes and indolent systemic mastocytosis without skin involvement are two emerging entities that sometimes might be clinically difficult to distinguish, and they involve a great challenge for the physician from both a diagnostic and a therapeutic point of view. Furthermore, final diagnosis of both entities requires a bone marrow study; it is recommended that this be done in reference centers. In this article, we address the current consensus and guidelines for the suspicion, diagnosis, classification, treatment, and management of these two entities.

Pathophysiology of the Behçet's Disease

Behçet's disease (BD) is a multisystemic disease of unknown etiology characterized by chronic relapsing oral-genital ulcers and uveitis. Multiple systemic associations including articular, gastrointestinal, cardiopulmonary, neurologic, and vascular involvement are also observed in BD. Although the etiopathogenesis of the disease remains unknown, increased neutrophil functions such as chemotaxis, phagocytosis, and excessive production of reactive oxygen species (ROS), including superoxide anion, which may be responsible for oxidative tissue damage seen in BD, and also immunological alterations, T lymphocyte abnormalities in both subpopulation and function have been considered to be correlated with the etiopathogenesis of BD. There is some clinical evidence suggesting that emotional stress and hormonal alterations can influence the course and disease activity of BD.

Na+ and K+ regulate the phosphorylation state of nucleoside diphosphate kinase in human airway epithelium

We describe how cations, in the presence of ATP, regulate the phosphorylated form of 19- and 21-kDa nucleoside diphosphate kinase (NDPK; EC 2.7.4.6), a kinase controlling K+ channels, G proteins, cell secretion, cellular energy production, and UTP synthesis. In apically enriched human nasal epithelial membranes, 10 mM Na+ inhibits phosphorylation of NDPK relative to other cations. Dose response showed that, whereas K+ induces a fourfold greater phosphate incorporation (EC50 10 mM), Na+ is inhibitory (EC50 10 mM) compared with respective buffer controls. Cation discrimination is nucleotide selective (not seen with [gamma-32P]GTP) and NDPK specific (not seen with p37h, a previously characterized Cl--sensitive phosphoprotein). Na+ does not exert an inhibitory effect on NDPK phosphorylation directly but is likely to act via an okadaic acid-insensitive phosphatase. We speculate that the ability of NDPK to discriminate between physiologically relevant cation concentrations provides a novel example of cross talk within the apical membrane.

3'-Phosphorylated nucleotides are tight binding inhibitors of nucleoside diphosphate kinase activity

Nucleoside diphosphate (NDP) kinase catalyzes the phosphorylation of ribo- and deoxyribonucleosides diphosphates into triphosphates. NDP kinase is also involved in malignant tumors and was shown to activate in vitro transcription of the c-myc oncogene by binding to its NHE sequence. The structure of the complex of NDP kinase with bound ADP shows that the nucleotide adopts a different conformation from that observed in other phosphokinases with an internal H bond between the 3'-OH and the beta-O made free by the phosphate transfer. We use intrinsic protein fluorescence to investigate the inhibitory and binding potential of nucleotide analogues phosphorylated in 3'-OH position of the ribose to both wild type and F64W mutant NDP kinase from Dictyostelium discoideum. Due to their 3'-phosphate, 5'-phosphoadenosine 3'-phosphate (PAP) and adenosine 3'-phosphate 5'-phosphosulfate (PAPS) can be regarded as structural analogues of enzyme-bound ADP. The KD of PAPS (10 microM) is three times lower than the KD of ADP. PAPS also acts as a competitive inhibitor toward natural substrates during catalysis, with a KI in agreement with binding data. The crystal structure of the binary complex between Dictyostelium NDP kinase and PAPS was solved at 2.8-A resolution. It shows a new mode of nucleotide binding at the active site with the 3'-phosphate of PAPS located near the catalytic histidine, at the same position as the gamma-phosphate in the transition state. The sulfate group is directed toward the protein surface. PAPS will be useful for the design of high affinity drugs targeted to NDP kinases.

Nucleoside diphosphate kinase and Cl(-)-sensitive protein phosphorylation in apical membranes from ovine airway epithelium

We have previously shown that nucleotide species (adenosine triphosphate [ATP] or guanosine triphosphate [GTP]), [Cl-], and anion species determine the steady-state phosphorylation of apical membrane proteins within human airway epithelium in vitro. We found that a Cl(-)-regulated 37-kD protein (p37) principally phosphorylated with GTP but not ATP as substrate. Here we show that apical membranes from sheep tracheal epithelium also contain a Cl(-)-regulated 37-kD phosphoprotein (p37s) and characterize one of the kinases involved in the regulation of p37s. Analysis of phosphorylation of apical membrane proteins with gamma[32P]GTP in the presence of MgCl2 showed that two proteins circa 19 and 21 kD (p19s and p21s) were transiently phosphorylated before p37s. Renaturation of apical membrane proteins within polyacrylamide gels showed that p19s and p21s autophosphorylated with either gamma[32P]GTP or gamma[32P]ATP as substrates, suggesting that the two proteins were kinases. Immunoblotting and immunoprecipitation with a specific polyclonal antibody showed that p21s was a membrane-bound isoform of nucleoside diphosphate kinase (NDPK, EC 2.7.4.6), a protein kinase which catalyzes transfer of terminal phosphate from ATP to diphosphate nucleotides and is, among other functions, essential for cell secretion. Incubation of apical membrane proteins in the presence of gamma[32P]ATP and guanosine diphosphate (GDP) (but not GDPbetaS) resulted in enhancement of phosphorylation of p37s. Dephosphorylation of NDPK was stimulated by the addition of Mg2+, Mn2+, and Co2+ (but not Zn2+ or Ca2+). Our data show that ovine trachea is a good model for further characterization of the chloride-dependent cascade in airway epithelium.

A 16-kDa protein functions as a new regulatory protein for Hsc70 molecular chaperone and is identified as a member of the Nm23/nucleoside diphosphate kinase family

Cytoplasmic Hsc70 is a multifunctional molecular chaperone. It is hypothesized that accessory proteins are used to specify the diverse chaperone activities of Hsc70. A 16-kDa cytosolic protein (p16) co-purified with Hsc70 obtained from a fish hepatocyte cell line, PLHC-1. Hsc70 also co-immunoprecipitated with p16 from PLHC-1 cells and fish liver. p16 was identified as a member of the Nm23/nucleoside diphosphate (NDP) kinase family based on its amino acid sequence similarity, NDP kinase activity, and recognition by anti-human NDP kinase-A antibody. This antibody also co-immunoprecipitated Hsc70 and NDP kinase from human HepG2 cells. p16 monomerized Hsc70 and released Hsc70 from pigeon cytochrome c peptide (Pc) but not from FYQLALT, a peptide specifically designed for high affinity binding. Therefore, p16 may modulate Hsc70 function by maintaining Hsc70 in a monomeric state and by dissociating unfolded proteins from Hsc70 either through protein-protein interactions or by supplying ATP indirectly through phosphate transfer. p16 did not affect basal or unfolded protein-stimulated ATPase activity of bovine brain Hsc70 using in vitro assays. Interestingly, bovine liver NDP kinase did not dissociate the Hsc70.Pc complex. In addition, two nonconservative amino acid subsitutions were found near the amino terminus of p16. Therefore, p16 may be a unique Nm23/NDP kinase that functions as an accessory protein for cytosolic Hsc70 in eukaryotes.

Inhibition of rat peritoneal mast cell exocytosis by frusemide: a study with different secretagogues

It has been reported that the loop diuretic frusemide can prevent exercise induced asthma, and that this effect may be due to the inhibition of mast cells in the airway. By using various mast cell secretagogues which increase intracellular calcium via different routes, this study attempted to elucidate the mechanism of the mast cell stabilizing action of frusemide. As well as confirming that immunologically induced histamine release from rat peritoneal mast cells was dose dependently inhibited by frusemide (10(-3) - 10(-5) M), the present study has extended the observation to histamine release induced by compound 48/80. The inhibitory potency was however less in the case of compound 48/80 induced release. Frusemide induced inhibition by the two secretagogues was decreased by drug preincubation. In contrast, histamine release induced by ionophore A23187 and thapsigargin was not inhibited by frusemide. The prototype antiallergic compound disodium cromoglycate (DSCG) demonstrated a similar specificity pattern against the various secretagogues. Another loop diuretic, bumetanide, did not show the same results as frusemide on rat peritoneal mast cell degranulation. Hence it is concluded that frusemide does not inhibit immunological activation of mast cells via its diuretic Na+/K+/Cl- co-transporter capacity. Instead, it protects mast cells in a similar manner to DSCG.