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PubMed2002

Bivalent inhibition of beta-tryptase: distance scan of neighboring subunits by dibasic inhibitors.

Based on bifunctional diketopiperazines as templates and m-aminomethyl-phenylalanine as arginine mimetic, we have synthesized a new class of structurally related dibasic tryptase inhibitors with systematically increasing spacer length. These compounds were used to scan the distance between the active sites of two neighboring subunits of the beta-tryptase tetramer. The K(i)-values obtained are a function of the distance between the terminal amino groups and indicate optimal binding of inhibitors with 29-31 bonds between the amino groups. These experimental data are in full agreement with predictions derived from a novel modeling program that allows the docking of bivalent ligands.

Algorithms↗

PubMed2002

Synthesis and SAR of 4-carboxy-2-azetidinone mechanism-based tryptase inhibitors.

A series of N1-activated C4-carboxy azetidinones was prepared and tested as inhibitors of human tryptase. The key stereochemical and functional features required for potency, serine protease specificity and aqueous stability were determined. From these studies compound 2, BMS-262084, was identified as a potent and selective tryptase inhibitor which, when dosed intratracheally in ovalbumin-sensitized guinea pigs, reduced allergen-induced bronchoconstriction and inflammatory cell infiltration into the lung.

Animals↗

PubMed2001

Bivalent inhibition of human beta-tryptase.

BACKGROUND: Human beta-tryptase is a mast cell specific trypsin-like serine protease that is thought to play a key role in the pathogenesis of diverse allergic and inflammatory disorders like asthma and psoriasis. The recently resolved crystal structure revealed that the enzymatically active tetramer consists of four quasi-identical monomers. The spatial display of the four identical active sites represents an ideal basis for the rational design of bivalent inhibitors. RESULTS: Based on modeling experiments homobivalent inhibitors were constructed using (i) 6A,6D-dideoxy-6A,6D-diamino-beta-cyclodextrin as a rigid template to bridge the space between the two pairs of identical active sites and (ii) 3-(aminomethyl)benzene as a headgroup to occupy the arginine/lysine specific S1 subsites. A comparative analysis of the inhibitory potencies of synthetic constructs that differ in size and type of the spacer between headgroup and template revealed that the construct contained two 3-(aminomethyl)benzenesulfonyl-glycine groups linked to the 6A,6D-diamino groups of beta-cyclodextrin as an almost ideal bivalent inhibitor with a cooperativity factor of 1.9 vs. the ideal value of 2. The bivalent binding mode is supported by the inhibitor/tetramer ratio of 2:1 required for inactivation of tryptase and by X-ray analysis of the inhibitor/tryptase complex. CONCLUSION: The results obtained with the rigid cyclodextrin template underlined the importance of a minimal loss of conformational entropy in bivalent binding, but also showed the limitations imposed by such rigid core molecules in terms of optimal occupancy of binding sites and thus of enthalpic strains in bidentate binding modes. The main advantage of bivalent inhibitors is their high selectivity for the target enzyme that can be achieved utilizing the principle of multivalency.

Binding Sites↗

PubMed2003

Tryptase, a novel link between allergic inflammation and fibrosis.

Allergy is a complex inflammatory disease, the etiology of which is well defined. It has recently been proposed that eosinophil, mast-cell and fibroblast interactions contribute to allergy perpetuation. Moreover, mast-cell-derived tryptase might act as a link among these cells. This hypothesis is supported by two recent papers that show that tryptase, seemingly through the protease-activated receptor-2, mediates eosinophil infiltration in the airways and fibroblast proliferation that depends on both cyclooxygenase and prostaglandin synthesis.

Animals↗

PubMed2002

Diverse stability and catalytic properties of human tryptase alpha and beta isoforms are mediated by residue differences at the S1 pocket.

Recombinant human tryptases (rHTs) corresponding to alpha and beta isoforms were characterized. rHTbeta was similar to tryptase isolated from skin (HST); it was a tetramer, hydrolyzed model substrates efficiently, and was functionally unstable when incubated under physiological conditions. Activity was lost rapidly (t(1/2) approximately 1 min) by a reversible process similar to that observed for the spontaneous inactivation of HST. Circular dichroism (CD) and intrinsic fluorescence emission (IFE) spectra of active rHTbeta corresponded to those of active HST and upon spontaneous inactivation IFE decreased in parallel to activity loss. rHTalpha differed from HST in catalytic ability and stability. rHTalpha did not react with model substrates, an active site titrant, or a competitive inhibitor of HST/rHTbeta. IFE and CD spectra were similar to those of the active and not the spontaneously inactivated form of HST. Under physiological conditions, rHTalpha IFE decreased at a rate 900-fold slower than that observed for HST, and rHTalpha remained tetrameric when examined by size exclusion chromatography at physiological salt concentration. Thus, rHTalpha is a stable "inactive" form of HT. Three active site variants of rHTalpha, K192Q, D216G, and K192Q-D216G were characterized. Residues 192 and 216 (chymotrypsinogen numbers for residues 191 and 215 of rHTalpha) lie at the entrance to the primary specificity (S1) pocket, and the mutations converted them to the residues of HTbeta. While K192Q displayed the same properties as rHTalpha, the catalytic and stability characteristics of D216G and K192Q-D216G progressively approached those of HST. Thus, the contrasting stability/activity properties of rHTalpha and rHTbeta are largely related to differences at the S1 pocket. On the basis of the properties of the variants, we suggest that the side chain of Asp216 is blocking and stabilizing the S1 pocket and that this stabilization is sufficient to prevent spontaneous inactivation.

Amino Acid Sequence↗

PubMed1998

1,2-Benzisothiazol-3-one 1,1-dioxide inhibitors of human mast cell tryptase.

A library of compounds were prepared by reacting 2-(bromomethyl)-1, 2-benzisothiazol-3(2H)-one 1,1-dioxide (5) with commercially available carboxylic acids in the presence of potassium carbonate or a tertiary amine base. From this library, (1,1-dioxido-3-oxo-1, 2-benzisothiazol-2(3H)-yl)methyl N-[(phenylmethoxy)carbonyl]-beta-alanate (7b) emerged as a potent inhibitor of human mast cell tryptase (IC50 = 0.85 microM). Extension of the side chain of 7b by two carbons gave (1, 1-dioxido-3-oxo-1,2-benzisothiazol-2(3H)-yl)methyl 5-[[(phenylmethoxy)carbonyl]amino]pentanoate (7d) which was an 8-fold more potent inhibitor (IC50 = 0.1 microM). Further modification of this series produced benzoic acid derivative (1, 1-dioxido-3-oxo-1,2-benzisothiazol-2(3H)-yl)methyl 4-[[(phenylmethoxy)carbonyl]amino]benzoate (7n) which is the most potent inhibitor identified in this series (IC50 = 0.064 microM). These compounds exhibit time-dependent inhibition consistent with mechanism-based inhibition. For 7b, the initial enzyme velocity is not a saturable function of the inhibitor concentration and the initial Ki could not be determined (Ki > 10 microM). The steady-state rate constant, Ki, was determined to be 396 nM. On the other hand, compounds 7d and 7n are time-dependent inhibitors with a saturable initial complex. From these studies, an initial rate constant, Ki, for 7d and 7n was found to be 345 and 465 nM, respectively. The steady-state inhibition constants, Ki, for 7d and 7n were calculated to be 60 and 52 nM, respectively. Compound 7n is a 13-fold more potent inhibitor than 7b, and these kinetic studies indicate that the increase in inhibitory activity is due to an increase in initial affinity toward the enzyme and not an increase in chemical reactivity. These inhibitors generally show high selectivity for tryptase, being 40-fold weaker inhibitors of elastase, being 100-fold weaker against trypsin, and showing no inhibition against thrombin. These compounds are not inhibitors of thrombin, plasmin t-PA, urokinase, and factor Xa (IC50 > 33 microM). In the delayed-type hypersensitivity (DTH) mouse model, a model of skin inflammation, a 5% solution of 7d reduced edema by 69% compared to control animals.

Animals↗

PubMed2003

Retinoic acid inhibits in vitro development of mast cells but has no marked effect on mature human skin tryptase- and chymase-positive mast cells.

Stem cell factor plays a key role in the development of human mast cells via interaction with Kit receptor. We and other groups have previously shown that a number of cytokines can regulate the stem-cell-factor-dependent development of mast cells in vitro. In this study we investigated the effect of retinoic acid on human mast cells in vitro and in vivo. Retinoids are known to have strong modulatory effects on hematopoietic differentiation. We found that all-trans-retinoic acid, at concentrations as low as 1 nM, inhibits the stem-cell-factor-dependent differentiation of mast cells in vitro. This effect of retinoic acid was found to be on progenitor cells, whereas more mature mast cells were less affected. The use of specific agonists binding either to the RAR or the RXR nuclear receptors indicated involvement of both the RAR/RXR and RXR/RXR pathways in inhibiting mast cell differentiation. In contrast to the effects on mast cell progenitors, retinoic acid had no effect on the number of mature mast cells in skin organ cultures. Furthermore, topical treatment of normal skin with a retinoic-acid-containing cream caused an increase in the number of tryptase-positive mast cells, whereas the numbers of the major cutaneous mast cell type, tryptase- and chymase-positive mast cells, remained unaffected. Our results suggest that retinoic acid suppresses commitment of progenitor cells into the mast cell lineage and/or acts on early mast cell progenitors, whereas mature cutaneous mast cells are less susceptible to retinoic acid.

Antineoplastic Agents↗

PubMed2005

Pyrrole carboxamidine tryptase inhibitors from Leptonychia pubescens.

The root and stem bark extracts of a Nigerian sample of Leptonychia pubescens Keay (Sterculiaceae) were found to inhibit the serine protease tryptase, a potential therapeutic target for the treatment of asthma and chronic obstructive pulmonary disease (COPD). Bioassay-guided isolation led to the identification of 1-beta-ribofuranosylbrunfelsamidine as the active component with a tryptase IC (50) of 3 microM. Brunfelsamidine was also isolated, but was only weakly active.

Humans↗

PubMed2001

Inhibition of mast cell tryptase by inhaled APC 366 attenuates allergen-induced late-phase airway obstruction in asthma.

BACKGROUND: APC 366, a selective inhibitor of mast cell tryptase, has been shown to inhibit antigen-induced early asthmatic response (EAR), late asthmatic response (LAR), and bronchial hyperresponsiveness (BHR) in a sheep model of allergic asthma. OBJECTIVE: The purpose of this study was to investigate the effects of APC 366 on antigen-induced EAR, LAR, and BHR in mild atopic asthmatics not on any anti-inflammatory therapy. METHODS: Sixteen mild atopic asthmatics, each with a demonstrable antigen-induced EAR, LAR, and BHR to histamine, were recruited into this randomized, double-blinded, crossover study. APC 366 (5 mg)/placebo was administered by aerosol inhalation 3 times per day on treatment days 1 through 4. Allergen challenge was carried out on day 4. Histamine challenge was performed the following morning, 1 hour after final dosing. RESULTS: Subjects were shown to have a significantly smaller overall mean area under the curve for the LAR (P =.012) and mean maximum fall in FEV(1) for the LAR (P =.007) after pretreatment with APC 366 in comparison with placebo. No significant effects on BHR were demonstrable. Although the EAR was reduced by 18% after treatment with APC 366 in comparison with placebo, this was not statistically significant. CONCLUSION: Short-term repeated administration of APC 366 significantly reduced the magnitude of antigen-induced LAR in atopic asthmatics, which supports the role of mast cell tryptase in the pathophysiology of the LAR.

Administration, Inhalation↗

PubMed2003

Assessment of the extent of cutaneous involvement in children and adults with mastocytosis: relationship to symptomatology, tryptase levels, and bone marrow pathology.

BACKGROUND: Cutaneous involvement occurs in most patients with systemic mastocytosis. OBJECTIVE: We sought to determine whether the extent of cutaneous involvement is predictive of systemic disease. METHODS: In a prospective survey of 48 adults and 19 children, the extent and density of cutaneous lesions were compared with patient history, symptoms, internal organ involvement, serum total mast cell tryptase level, and bone marrow pathology. RESULTS: Cutaneous lesions in children were of a greater mean and maximum diameter, but similar in extent and density compared with lesions in adults. In adults with skin lesions, the extent of lesions correlated to disease duration. Adults with extensive cutaneous disease experienced more pruritus and flushing. Fatigue, splenomegaly, and hepatomegaly were more frequent in adults without cutaneous involvement; and in those with a greater density of lesions and disease duration. Increased tryptase levels were found in children and adults with systemic disease and correlated to skin lesion density and bone marrow pathology. CONCLUSION: An examination of the extent and density of cutaneous lesions in adults helps identify those with more extensive extracutaneous disease and, thus, requiring a more thorough evaluation.

Adolescent↗

PubMed1999

Potent selective nonpeptidic inhibitors of human lung tryptase.

Human lung tryptase, a homotetrameric serine protease unique to mast cell secretory granules, has been implicated in the pathogenesis of asthma. A hypothesis that tethered symmetrical inhibitors might bridge two adjacent active sites was explored via a rationally designed series of bisbenzamidines. These compounds demonstrated a remarkable distanced-defined structure-activity relationship against human tryptase with one series possessing subnanomolar potencies. Additional evidence supporting the concept of active-site bridging is also presented.

Asthma↗

PubMed1995

Purification and characterization of dog mast cell protease-3, an oligomeric relative of tryptases.

The existence of a protein approximately 48% identical with mast cell tryptases was predicted previously from a dog mastocytoma cDNA. Antibodies raised against a peptide based on the deduced sequence suggested that the protein (dog mast cell protease-3, dMCP-3) is expressed in mast cells. In this report, characterization of the protein purified from mastocytomas reveals an N-glycosylated, high molecular weight, tryptic serine protease, which appears to be a tetramer of catalytic subunits, approximately half of which are linked by disulfide bonds. The oligomeric complex yields a single NH2-terminal sequence, which is identical with that predicted by dMCP-3 cDNA. This finding, and the lack of closely related genes on blots of genomic DNA, predict that each subunit is the product of one gene. Although dMCP-3 binds to heparin, it is active and stable at low ionic strength in heparin's absence. It resists inactivation by inhibitors in plasma but is sensitive to small inhibitors, e.g. leupeptin and bis(5-amidino-2-benzimidazolyl)methane (BABIM). dMCP-3 hydrolyzes extended peptidyl p-nitroanilides ending in basic residues, with P1 arginine preferred to lysine; it hydrolyzes the Arg18-Ser19 bond of calcitonin gene-related peptide but cleaves neither vasoactive intestinal peptide nor casein. These data suggest that dMCP-3 is a unique serine protease whose stability, formation of intersubunit disulfide bonds, inhibitor susceptibilities and substrate preferences differ from those of its closest relatives, the mast cell tryptases.

Amino Acid Sequence↗

PubMed1999

Mast cells in developing subepidermal bullous diseases: emphasis on tryptase, chymase and protease inhibitors.

The possible involvement of mast cell tryptase and chymase in subepidermal bullous diseases was studied enzyme-histochemically in specimens from erythematous and vesicular skin and from non-involved skin of patients with dermatitis herpetiformis, bullous pemphigoid, erythema multiforme, infective bullous eruption and linear IgA dermatosis. Patients with pemphigus were biopsied for comparison. The immunoreactivity of chymase inhibitors, alpha1-proteinase inhibitor (alpha1-PI) and alpha1-antichymotrypsin (alpha1-AC), in mast cells was demonstrated using the sequential double staining method. Tryptase-positive mast cells were unchanged or only slightly increased in number in erythematous lesions and slightly decreased in blistering skin compared with healthy-looking skin. Only occasionally were mast cells seen in apparent contact with the basement membrane zone. Chymase-positive mast cells and the chymase/tryptase ratio steadily decreased during the development of the lesions in each subepidermal bullous disease. The percentage of alpha1-PI+ and/or alpha1-AC+ mast cells increased simultaneously, which could explain the disappearance of chymase activity. Similar results were obtained regardless of the bullous disease. The results were also similar in pemphigus, which is an intraepidermal bullous disease. In conclusion, these results show significant alterations in mast cell chymase and protease inhibitors in a range of different bullous diseases, suggesting mast cell involvement. The apparent inactivation of chymase could be due to the action of chymase inhibitors detected in numerous mast cells. However, these alterations probably reflect general inflammation rather than a specific reaction in a certain bullous disease.

Adolescent↗

PubMed1993

Postmortem diagnosis of acute anaphylaxis by serum tryptase analysis. A case report.

Systemic anaphylaxis is an acute allergic emergency resulting from generalized mast cell degranulation. In the United States, it is estimated that anaphylaxis accounts for about 500 deaths each year. Hymenoptera-sting hypersensitivity is one of the most common causes of systemic anaphylaxis. The authors report a case of a healthy 26-year-old man who developed acute anaphylaxis after a bee sting, could not be resuscitated, and died within 1 hour. At autopsy, performed 14 hours after the event, the only pathologic findings were laryngeal edema and congestion of lung. Postmortem tryptase levels in the blood were obtained and were instrumental in confirming a diagnosis of acute anaphylaxis. This case is reported to discuss the difficulties associated with using traditional histamine levels in making a diagnosis of anaphylaxis and to validate the value of using tryptase levels to document acute anaphylaxis as a cause of death, even when serum is not obtained until many hours after death.

Adult↗

PubMed2001

Co-localization of matrix metalloproteinase-1 and mast cell tryptase in the human uterus.

The endometrium displays characteristic cyclical changes involving proliferation and differentiation. The differentiation that takes place requires major tissue remodelling involving the matrix metalloproteinase (MMP) family as key enzymes in this process. Mast cells, containing the tryptase and chymase enzymes that are capable of stimulating the MMP cascade, have been identified in the endometrium, but their role is still unclear. In this study, we observed that the majority of mast cells in the uterus reside in the myometrium and that they co-express mast cell tryptase and MMP-1 in the same intracellular granules. In endometrium exposed to synthetic progestogen via an intrauterine levonorgestrel system a significant increase in mast cells numbers was observed in women experiencing breakthrough bleeding compared to those in women with no reported bleeding. We conclude that mast cells contain MMP-1 and we postulate a potential role for mast cells in breakthrough bleeding.

Female↗

PubMed2003

Tryptase-stimulated human airway smooth muscle cells induce cytokine synthesis and mast cell chemotaxis.

Asthmatic patients have higher numbers of mast cells in the smooth muscle layer of airways than normal subjects. Human airway smooth muscle cells (HASMCs) are a source of various cytokines including transforming growth factor beta1 (TGF-beta1), which is chemotactic for mast cells. We have thus examined the potential for interaction between HASMCs and mast cells and have investigated, in particular, the hypothesis that after stimulation, HASMCs can induce mast cell chemotaxis through the production of cytokines. Supernatants of HASMCs treated with the major mast cell product tryptase had increased chemotactic activity for the HMC-1 mast cell line. The effect depended on an intact catalytic site for tryptase and could be induced by a peptide agonist for protease activated receptor 2. Chemotactic activity was related to the synthesis of TGF-beta1 by HASMCs and, to a lesser extent, to stem cell factor. The number of mast cells within the smooth muscle layer of asthmatic patients was closely related to TGF-beta1 expression by smooth muscle. HASMCs may thus be able to stimulate the accumulation of mast cells, and these cells may, in turn, stimulate the secretion of chemotactic factors by HASMCs.

Asthma↗

PubMed1994

Eosinophil cationic protein (ECP), histamine and tryptase in peripheral blood before and during inhalation challenge with toluene diisocyanate (TDI) in sensitized subjects.

To determine whether the measurement of specific markers of inflammatory cells in peripheral blood might be used to detect the inflammatory activity in the airways in asthma induced by toluene diisocyanate (TDI), we measured the levels of eosinophil cationic protein (ECP), histamine and tryptase in peripheral blood before and during inhalation challenge with TDI or methacholine in two groups of subjects who exhibited or did not exhibit an asthmatic reaction after exposure to toluene diisocyanate in the laboratory. When the subjects developed a late asthmatic reaction after exposure to TDI, they showed an increase in their ECP serum levels. By contrast, there were no significant changes in serum ECP levels after exposure to TDI in the control group or after methacholine challenge in either group. Tryptase levels in serum were not detectable before or during inhalation challenge with TDI or methacholine. There was no significant increase in plasma histamine levels during inhalation challenge with TDI or methacholine. These results suggest that eosinophils are 'activated' in subjects who develop a late asthmatic reaction after exposure to TDI and that the measurement of ECP levels in peripheral blood may be a useful marker to monitor airway inflammation.

Administration, Inhalation↗

PubMed1995

Tryptase and histamine release due to a sting challenge in bee venom allergic patients treated successfully or unsuccessfully with hyposensitization.

BACKGROUND: Hyposensitization with been venom leads to full protection in most, but not all patients with IgE-mediated systemic reactions to bee stings. OBJECTIVE: To determine the relationship of clinical reactivity to the release of mediators and to changes of antibody concentrations in the peripheral circulation at a bee sting challenge test. METHODS: Blood was sampled before (1 min) and at 15, 60 and 180 min after a sting challenge from 19 patients on hyposensitization. Of these six still reacted and 13 were protected. Histamine, mast cell tryptase, bee venom-specific IgE and IgG in the serum, and histamine release from peripheral blood leucocytes (PBL) upon exposure to bee venom were determined. RESULTS: Tryptase above the detection level was found only at 15 (60) min in 4/6 (1/6) patients who reacted. After the sting challenge there was a significant increase of the histamine levels in patients who reacted at 15 min (P < 0.05) and in patients who did react at 60 and 180 min (P < 0.01). The total histamine content of PBL was significantly decreased after 15 and 60 min in patients who reacted (P < 0.01) and in those that did not (P < 0.05). Bee venom-induced histamine release was significantly reduced in patients reacting and those that did not at 15 min (P < 0.05), and was significantly decreased in reactors also at 60 and 180 min (P < 0.05/0.01). Specific IgG antibodies showed a minor decrease (P < 0.05) after the sting challenge in both groups, whereas specific IgE did not change significantly. CONCLUSION: These results indicate that bee venom anaphylaxis is associated with the release of mediators from both mast cells as well as basophils. Successful hyposensitization does not induce a state of immunological non-reactivity, but rather alters the magnitude and the pattern of mediator release.

Adult↗