Hereditary alpha tryptasemia is not associated with specific clinical phenotypes.

BACKGROUND: Hereditary alpha tryptasemia (HαT) is found in approximately 7% of the population. Associations with a variety of clinical symptoms including gastric reflux, joint hypermobility, dysautonomia, flushing and pruritus, and hymenoptera allergy have variably been described in prior reports. However, our understanding of this genetic trait is limited by a paucity of published studies, referral bias, and conflicting findings at clinical presentation. OBJECTIVE: The purpose of this study was to assess the clinical phenotype of HαT in a random biorepository population and in patients with and without mastocytosis referred to the allergy clinic. METHODS: Tryptase copy number allele was assessed using digital droplet PCR. Participants with or without HαT were interviewed and examined by a clinician and surveyed regarding their medical history and symptomology. RESULTS: HαT was identified in 7.5% of the random biorepository samples and in 18% of patients with mastocytosis. There was no difference in the clinical symptomology or medical history of individuals with HαT compared to controls. Average baseline serum tryptase was higher in individuals with HαT compared to controls, but there was no difference in urinary mast cell activation products. CONCLUSIONS: Elevated baseline serum tryptase was the only consistent phenotypic marker for HαT in this study. There was a higher frequency of HαT in patients with mastocytosis than in the general population.

Genetic Regulation of Tryptase Production and Clinical Impact: Hereditary Alpha Tryptasemia, Mastocytosis and Beyond.

Tryptase is a serine protease that is predominantly produced by tissue mast cells (MCs) and stored in secretory granules together with other pre-formed mediators. MC activation, degranulation and mediator release contribute to various immunological processes, but also to several specific diseases, such as IgE-dependent allergies and clonal MC disorders. Biologically active tryptase tetramers primarily derive from the two genes TPSB2 (encoding ß-tryptase) and TPSAB1 (encoding either α- or ß-tryptase). Based on the most common gene copy numbers, three genotypes, 0α:4ß, 1α:3ß and 2α:2ß, were defined as "canonical". About 4-6% of the general population carry germline TPSAB1-α copy number gains (2α:3ß, 3α:2ß or more α-extra-copies), resulting in elevated basal serum tryptase levels. This condition has recently been termed hereditary alpha tryptasemia (HαT). Although many carriers of HαT appear to be asymptomatic, a number of more or less specific symptoms have been associated with HαT. Recent studies have revealed a significantly higher HαT prevalence in patients with systemic mastocytosis (SM) and an association with concomitant severe Hymenoptera venom-induced anaphylaxis. Moreover, HαT seems to be more common in idiopathic anaphylaxis and MC activation syndromes (MCAS). Therefore, TPSAB1 genotyping should be included in the diagnostic algorithm in patients with symptomatic SM, severe anaphylaxis or MCAS.

Altered Metabolism of Phospholipases, Diacylglycerols, Endocannabinoids, and N-Acylethanolamines in Patients with Mastocytosis.

BACKGROUND: Mastocytosis is a condition characterized by the expansion and accumulation of mast cells (MCs) in various organs. The symptoms are related to the increased release of MC-derived mediators that exert local and distant effects. MCs are a source and target of phospholipase enzymes (PLs), which catalyze the cleavage of membrane phospholipids releasing lipid mediators (e.g., diacylglycerols (DAGs) and the endocannabinoid (EC) 2-arachidonoylglycerol (2-AG)). To date, there are no data on the role of these lipid mediators in mastocytosis. Here, we analyzed plasma levels of PLA2, PLC, DAG, ECs, and EC-related N-acylethanolamines in patients with mastocytosis. METHODS: In 23 patients with mastocytosis and 23 healthy individuals, we measured plasma PLA2 and PLC activities, DAG, 2-AG, anandamide (AEA), palmitoylethanolamide (PEA), and oleoylethanolamide (OEA). RESULTS: Plasma PLA2 and PLC activities were increased in mastocytosis patients compared to controls. Concentrations of DAG (18:1 20:4 and 18:0 20:4), two second messengers produced by PLC, were higher in mastocytosis compared to controls, whereas the concentrations of their metabolite, 2-AG, were not altered. AEA was decreased in mastocytosis patients compared to controls; by contrast, AEA congener, PEA, was increased. PLA2 and PLC activities were increased only in patients with mediator-related symptoms. Moreover, PLC activity was positively correlated with disease severity and tryptase concentrations. By contrast, AEA was negatively correlated with tryptase concentrations. CONCLUSIONS: PLs and some lipid mediators are altered in patients with mastocytosis. Our results may pave the way for investigating the functions of these mediators in the pathophysiology of mastocytosis and provide new potential biomarkers and therapeutic targets.

Distribution of mast cell subtypes in interstitial cystitis: implications for novel diagnostic and therapeutic strategies?

AIMS: To identify the presence and geographical distribution of mast cell (MC) subtypes: MCT (tryptase positive-chymase negative) and MCTC (tryptase positive-chymase positive) in bladder tissue. METHODS: Bladder tissue was obtained from patients with painful bladder syndrome/interstitial cystitis (n=14) and normal histology from University Hospital Southampton tissue bank. Sequential tissue slices were immunohistochemically stained for MC subtypes using anti-MC tryptase (for MCT and MCTC) and anti-MC chymase (for MCTC). Stained sections were photographed, and positively stained MCs were quantified using ImageJ. Data were analysed using descriptive statistics and individual paired t-tests. RESULTS: There was a significant difference in the density of MCs between each layer of the disease bladder, with the greatest accumulation within the detrusor (p<0.001). There was a significant increase in MCTC subtype in the lamina (p=0.009) in painful bladder syndrome/interstitial cystitis. CONCLUSIONS: Our results suggest that mastocytosis is present within all layers of disease bladder, especially the muscle layer. The varying increase in MC subtypes in the lamina and mucosa may explain the variability in painful bladder syndrome/interstitial cystitis symptoms. A high influx of MCTC in the mucosa of individuals who also had ulceration noted within their diagnostic notes may be of the Hunner's ulcer subclassification. These findings suggest a relationship between the pathogenesis of MC subtypes and the clinical presentation of painful bladder syndrome/interstitial cystitis. A cohort study would further elucidate the diagnostic and/or therapeutic potential of MCs in patients with painful bladder syndrome/interstitial cystitis.

Kit receptor tyrosine kinase dysregulations in feline splenic mast cell tumours.

This study investigated Kit receptor dysregulations (cytoplasmic immunohistochemical expression and/or c-KIT mutations) in cats affected with splenic mast cell tumours. Twenty-two cats were included. Median survival time was 780 days (range: 1-1219). An exclusive splenic involvement was significantly (P = 0.042) associated with longer survival (807 versus 120 days). Eighteen tumours (85.7%) showed Kit cytoplasmic expression (Kit pattern 2, 3). Mutation analysis was successful in 20 cases. Fourteen missense mutations were detected in 13 out of 20 tumours (65%). Eleven (78.6%) were located in exon 8, and three (21.6%) in exon 9. No mutations were detected in exons 11 and 17. Seven mutations corresponded to the same internal tandem duplication in exon 8 (c.1245_1256dup). Although the association between Kit cytoplasmic expression and mutations was significant, immunohistochemistry cannot be considered a surrogate marker for mutation analysis. No correlation was observed between c-Kit mutations and tumour differentiation, mitotic activity or survival.

PKC potentiates tyrosine kinase inhibitors STI571 and dasatinib cytotoxic effect.

AIM: The aim of the present study was to determine the relationship between the tyrosine kinase inhibitors, STI571 and dasatinib effects and protein kinase C (PKC) status in HMC-1(560) and HMC-1(560,816) cell lines. MATERIAL AND METHODS: Viability results were obtained by two different methods: MTT and a flow cytometry with Annexin V-FITC/PI double-staining protocol. The lipid-based transfection method was used to silence PKC. RESULTS: Long-term PKC activation induces apoptosis in both HMC-1 cell lines. Moreover, PKC activation potentiates STI571 and dasatinib cytotoxic effects in HMC-1(560) and HMC-1(560,816) cells, respectively, by increasing necrotic populations. To investigate this PKC effect, the role of PKCδ, an isoform intimately related with apoptotic cell death, was studied. The results obtained evidence that either STI571 or dasatinib apoptotic cell death are PKCδ-dependent. Particularly, STI571 showed less dependence to PKCδ than dasatinib. CONCLUSION: PKCδ modulation is essential and determines mastocytosis treatment effectiveness, since STI571 and dasatinib effects are PKCδ-dependent.

Epidemiology, prognosis, and risk factors in mastocytosis.

This article updates current knowledge about epidemiology, prognosis, and risk factors for major complications in mastocytosis. A prevalence of mastocytosis of 1 in 10000 inhabitants has been reported, but underdiagnosis is assumed. The prognosis for cutaneous and indolent systemic mastocytosis is excellent. For more advanced forms of disease, prognostic parameters have been identified. A high extent of skin involvement, increased basal serum tryptase values, and extensive blistering are risk factors for severe mast cell activation episodes in children, whereas these associations seem to be less strong or nonexistent for anaphylaxis and osteoporosis in adult patients with indolent systemic mastocytosis.

Drug allergy in mastocytosis.

Drugs are known triggers of anaphylaxis in patients with mastocytosis even to the association between drug anaphylaxis and mastocytosis does not appear frequently appear. Nevertheless, mast cell disorders might be ruled out in cases of severe systemic reactions. Careful examination of the skin should accompany measurement of basal serum tryptase levels. The data published about drug anaphylaxis in patients with mast cell disorders are scarce, and it is not currently possible to provide clear recommendations. Most papers report cases of anaphylaxis during surgical procedures or radiocontrast media exposure. There are no specific recommendations to prevent severe reactions during such procedures, although some specialists suggest performing premedication with antihistamines and corticosteroids before anesthesia or radiocontrast media administration.

Neuropsychological features of adult mastocytosis.

In approximately one-third of cases, patients with mastocytosis can display various disabling general and neuropsychological symptoms. General signs may have a major impact on quality of life. Neurologic symptoms are less frequent. In a majority of cases, the pathophysiology of these symptoms is not known but could be linked to tissular mast cell infiltration, mast cell mediator release, or both. Treatments aiming at reducing mast cell number and/or stabilizating mast cells may be useful. Preliminary results suggest that treatment with kinase inhibitors may improve symptoms of depression and cognitive impairment.

Sensitive KIT D816V mutation analysis of blood as a diagnostic test in mastocytosis.

The recent progress in sensitive KIT D816V mutation analysis suggests that mutation analysis of peripheral blood (PB) represents a promising diagnostic test in mastocytosis. However, there is a need for systematic assessment of the analytical sensitivity and specificity of the approach in order to establish its value in clinical use. We therefore evaluated sensitive KIT D816V mutation analysis of PB as a diagnostic test in an entire case-series of adults with mastocytosis. We demonstrate for the first time that by using a sufficiently sensitive KIT D816V mutation analysis, it is possible to detect the mutation in PB in nearly all adult mastocytosis patients. The mutation was detected in PB in 78 of 83 systemic mastocytosis (94%) and 3 of 4 cutaneous mastocytosis patients (75%). The test was 100% specific as determined by analysis of clinically relevant control patients who all tested negative. Mutation analysis of PB was significantly more sensitive than serum tryptase >20 ng/mL. Of 27 patients with low tryptase, 26 tested mutation positive (96%). The test is furthermore readily available and we consider the results to serve as a foundation of experimental evidence to support the inclusion of the test in diagnostic algorithms and clinical practice in mastocytosis.

Targeting c-kit in the therapy of mast cell disorders: current update.

Classically, mast cells have been widely associated with allergic reactions and parasite infections, but recent studies have elucidated the important role of these cells in innate and acquired immunity, wound healing, fibrosis, and chronic inflammatory diseases. Mast cells release an impressive array of proinflammatory and immunoregulatory mediators after activation induced by either immunoglobulin-E (IgE)-dependent or IgE-independent mechanisms. Proliferation, differentiation, survival and activation of mast cells are regulated by stem cell factor (SCF), the ligand for the c-kit tyrosine kinase receptor which is expressed on the mast cell surface. Inappropriate c-kit activation causes accumulation of mast cells in tissues resulting in mastocytosis. A number of activating mutations in c-kit have recently been identified and these mutations results in aberrant mast cell growth. Thus, c-kit inhibitors may have potential application in multiple conditions associated with mast cell disorders including systemic mastocytosis, anaphylaxis, and asthma. The present perspective aims to summarize recent findings in mast cell biology and the role of c-kit tyrosine kinase inhibitors in the treatment of different mast cell associated disorders.

Impact of age and heterophilic interference on the basal serum tryptase, a risk indication for anaphylaxis, in 1,092 dermatology patients.

A raised baseline serum tryptase is a risk indicator for anaphylactic reactions, especially in patients with hymenoptera venom allergy. Borderline elevations (> 11.4 µg/l) occur frequently and may necessitate invasive diagnostic procedures to rule out systemic mastocytosis. We retrospectively analysed 1,092 non-mastocytotic patients from our general dermatology clinic with respect to age- and gender-associated effects and investigated the impact of heterophilic antibody interference on the tryptase assay. The results were stratified by gender and five age classes. Sera with raised tryptase (n = 106) were re-tested after pre-incubation with Heterophilic Blocking Tubes (HBT(®), Scantibodies Laboratory; Santee, CA, USA). A significant increase in baseline tryptase was observed with increasing age. Incubation with HBT(®) caused a decline of more than 50% in only one case. In conclusion, older patients showed significantly higher serum tryptase levels and heterophilic interference was of subordinate relevance.

PIP3 regulation as promising targeted therapy of mast-cell-mediated diseases.

It is well established that mast cells play a key regulatory role in allergy and inflammation involving engagement of antigen with IgE bound to high-affinity IgE receptors (FcεRI). The most aggressive efforts in regulating mast cell function have focused on selectively inhibiting cell activation and subsequent mediator synthesis and release, or alternatively, blocking the action of proinflammatory mediators in order to prevent or reduce disease severity. More recently, the goal for rationally designed pharmacotherapy has shifted focus to targeting and disrupting signaling pathways leading to inhibition of specific cell function(s). In this context, the PI-3K/PIP3/Akt pathway represents a potent target for pharmacologic intervention in mast cell-mediated inflammatory disorders. A pivotal component of this cascade is the activation of phosphatidylinositol-3-kinase (PI-3K) leading to a rise in intracellular levels of phosphatidylinositol 3,4,5-trisphosphate (PIP3). PIP3 has broad effects on mast cell signaling and function as well as on proliferation and survival. We propose that PIP3 represents a potent target for developing therapeutic approaches to down regulate mast cell function and, in turn, reduce the severity of mast cell dependent disease. In this article we review approaches that have been taken to regulate the PI-3K pathway in mast cells. Moreover, we review a novel approach to target the signaling lipid, PIP3, and deplete intracellular levels of this phosphoinositol using a chimeric toxin composed of the FcεRI binding region of IgE and the active subunit of the cytolethal distending toxin, CdtB, which we have recently demonstrated to function as a PIP3 phosphatase.

Clinical and laboratory parameters of mast cell activation as basis for the formulation of diagnostic criteria.

Mast cell (MC) activation occurs in a number of different pathologic conditions. Acute activation is commonly seen in patients with allergic reactions, with consecutive massive release of vasoactive and proinflammatory mediator substances from MCs, leading to the clinical signs and symptoms of anaphylaxis. In these patients, serum tryptase concentrations usually increase subtantially above baseline levels. Chronic MC activation is more difficult to diagnose, especially when symptoms are mild or atypical, and no underlying disease is found. In these patients, serum tryptase levels usually are normal. In a smaller group of patients, tryptase levels are constantly elevated and may point to an occult form of mastocytosis. These patients have to be examined for MC monoclonality, other criteria of a primary MC disease, non-MC hematopoietic neoplasms, and reactive disorders producing chronic MC activation or MC accumulation. In most patients in whom MC activation is found, histamine-induced symptoms can be documented and usually respond to treatment with histamine receptor antagonists or MC stabilizers. If this is not the case, alternative explanations for symptoms and differential diagnoses have to be considered.

Expulsion of secondary Trichinella spiralis infection in rats occurs independently of mucosal mast cell release of mast cell protease II.

Our aim was to elucidate the contribution of mucosal mast cells to the effector phase of a secondary immune response to Trichinella spiralis. During secondary infection, rats expel 90-99% of T. spiralis first-stage larvae from the intestine in a matter of hours. This phenomenon appears to be unique to rats and has been called rapid expulsion. Primary intestinal infection by T. spiralis induces mastocytosis, and mast cell degranulation occurs when challenged rats exhibit rapid expulsion. These observations have engendered the view that mast cells mediate rapid expulsion. In this study, we report that immunization of adult Albino Oxford rats by an infection limited to the muscle phase did not induce intestinal mastocytosis, yet such rats exhibited rapid expulsion when challenged orally. Although mastocytosis was absent, the protease unique to mucosal mast cells, rat mast cell protease II (RMCPII), was detected in sera at the time of expulsion. We further evaluated mast cell activity in neonatal rats that display rapid expulsion. Pups born to infected dams displayed rapid expulsion, and RMCPII was detected in their sera. By feeding pups parasite-specific mAbs or polyclonal Abs before challenge infection, it was possible to dissociate mast cell degranulation from parasite expulsion. These results indicate that rapid expulsion can occur in the absence of either intestinal mastocytosis or RMCPII release. Furthermore, release of RMCPII is not sufficient to cause expulsion. The data argue against a role for mast cells in the mechanism underlying the effector phase of protective immunity against T. spiralis in rats.

Alpha 2-macroglobulin capture allows detection of mast cell chymase in serum and creates a reservoir of angiotensin II-generating activity.

Human chymase is a highly efficient angiotensin II-generating serine peptidase expressed by mast cells. When secreted from degranulating cells, it can interact with a variety of circulating antipeptidases, but is mostly captured by alpha(2)-macroglobulin, which sequesters peptidases in a cage-like structure that precludes interactions with large protein substrates and inhibitors, like serpins. The present work shows that alpha(2)-macroglobulin-bound chymase remains accessible to small substrates, including angiotensin I, with activity in serum that is stable with prolonged incubation. We used alpha(2)-macroglobulin capture to develop a sensitive, microtiter plate-based assay for serum chymase, assisted by a novel substrate synthesized based on results of combinatorial screening of peptide substrates. The substrate has low background hydrolysis in serum and is chymase-selective, with minimal cleavage by the chymotryptic peptidases cathepsin G and chymotrypsin. The assay detects activity in chymase-spiked serum with a threshold of approximately 1 pM (30 pg/ml), and reveals native chymase activity in serum of most subjects with systemic mastocytosis. alpha(2)-Macroglobulin-bound chymase generates angiotensin II in chymase-spiked serum, and it appears in native serum as chymostatin-inhibited activity, which can exceed activity of captopril-sensitive angiotensin-converting enzyme. These findings suggest that chymase bound to alpha(2)-macroglobulin is active, that the complex is an angiotensin-converting enzyme inhibitor-resistant reservoir of angiotensin II-generating activity, and that alpha(2)-macroglobulin capture may be exploited in assessing systemic release of secreted peptidases.

Clonal mast cell disorders in patients with systemic reactions to Hymenoptera stings and increased serum tryptase levels.

BACKGROUND: Anaphylaxis after Hymenoptera stings has been reported in subjects with mastocytosis, but few data exist regarding disease prevalence in populations allergic to these insects. OBJECTIVE: The incidence of clonal mast cell (MC) disorders in subjects with both systemic reactions to Hymenoptera stings and increased serum baseline tryptase (sBT) levels was assessed by using bone marrow (BM) aspirates and biopsy specimens. METHODS: Subjects with a history of a systemic reaction caused by a Hymenoptera sting underwent the standard diagnostic work-up for Hymenoptera allergy, and sBT levels were measured. Subjects with an increased sBT level had BM evaluation that included histology/cytology, flow cytometry, and detection of KIT mutations. RESULTS: Forty-four (11.6%) of 379 subjects with systemic reactions had increased sBT levels (>11.4 ng/mL), and 31 (70.5%) of these had a history of anaphylaxis. Thirty-four subjects with increased sBT levels underwent a BM analysis. Histology detected diagnostic or subdiagnostic MC infiltrates in 22 (65%) of 34 patients. Abnormal MCs were identified by means of flow cytometry and cytology in 26 (78.8%) of 33 and 20 (58.8%) of 34 subjects, respectively. A KIT mutation was detected in 17 (54.8%) of 31 subjects. The diagnosis was indolent systemic mastocytosis in 21 (61.7%) of 34 subjects and monoclonal MC activation syndrome in 9 (26.5%) of 34 subjects. All subjects with anaphylaxis had one of those 2 disorders. CONCLUSION: The concomitant presence of systemic reactions (especially anaphylaxis) after Hymenoptera stings and increased sBT levels strongly suggests that a BM examination is indicated for the diagnosis of clonal MC disease.

KIT and mastocytosis.

KIT is a receptor tyrosine kinase that is functionally relevant for hematopoiesis, mast cell development and function, gametogenesis and melanogenesis. Normal KIT signaling requires binding to stem cell factor, and PI3K-Akt is one of the putative effector pathways. In humans, germline loss-of-function KIT mutations have been associated with piebaldism - an autosomal dominant condition characterized by depigmented patches of skin and hair. Gain-of-function KIT mutations are usually acquired and have been associated with myeloid malignancies including core binding factor acute myeloid leukemia and systemic mastocytosis (SM), germ cell tumors, gastrointestinal stromal tumors and sinonasal T cell lymphomas. KITD816V is the most prevalent KIT mutation in mast cell disease and occurs in more than 90% of the cases that fulfill the World Health Organization diagnostic criteria for SM. However, its precise pathogenetic contribution is not well understood. In clinical practice, SM is considered either indolent or aggressive depending on the respective absence or presence of symptomatic target organ dysfunction aside from skin disease. In general, conventional therapy for SM is suboptimal, and efforts are under way to develop and employ small molecule drugs that target mutant KIT.

Kit: molecule of interest for the diagnosis and treatment of mastocytosis and other neoplastic disorders.

Kit a type III receptor tyrosine kinase, along with its ligand the stem cell factor, play a critical role in normal cell growth, differentiation, development and survival. Ligand independent activation of kit (dysregulated kit function) has been found to be an important component of oncogenesis in a large number of neoplastic disorders such as systemic mastocytosis, gastro intestinal stromal tumors, germ cell tumors, acute myelogenous leukemia with the disruption of the core binding factor, amongst others. The identification of small molecule inhibitors with activity against Kit, has offered a wider and more effective range of therapeutic options in the treatment of these neoplastic processes. Novel tyrosine kinase inhibitors such as imatinib, nilotinib and dasatinib, have been found to be effective in the management of various subtypes of systemic mastocytosis and gastrointestinal stromal tumors. Non-tyrosine kinase inhibitors like rapamycin, 17-AAG and IMD- 0354 have been added to the therapeutic armamentarium, with the hope that combination therapy might have a synergistic effect, or prevent/delay the development of drug resistance.