Thymic stromal lymphopoietin controls prostaglandin D2 generation in patients with aspirin-exacerbated respiratory disease.

BACKGROUND: Prostaglandin (PG) D2 is the dominant COX product of mast cells and is an effector of aspirin-induced respiratory reactions in patients with aspirin-exacerbated respiratory disease (AERD). OBJECTIVE: We evaluated the role of the innate cytokine thymic stromal lymphopoietin (TSLP) acting on mast cells to generate PGD2 and facilitate tissue eosinophilia and nasal polyposis in patients with AERD. METHODS: Urinary eicosanoid levels were measured in aspirin-tolerant control subjects and patients with AERD. Nasal polyp specimens from patients with AERD and chronic rhinosinusitis were analyzed by using quantitative PCR, Western blotting, and immunohistochemistry. Human cord blood-and peripheral blood-derived mast cells were stimulated with TSLP in vitro to assess PGD2 generation. RESULTS: Urinary levels of a stable PGD2 metabolite (uPGD-M) were 2-fold higher in patients with AERD relative to those in control subjects and increased further during aspirin-induced reactions. Peak uPGD-M levels during aspirin reactions correlated with reductions in blood eosinophil counts and lung function and increases in nasal congestion. Mast cells sorted from nasal polyps expressed PGD2 synthase (hematopoietic PGD2 synthase) mRNA at higher levels than did eosinophils from the same tissue. Whole nasal polyp TSLP mRNA expression correlated strongly with mRNA encoding hematopoietic PGD2 synthase (r = .75), the mast cell-specific marker carboxypeptidase A3 (r = .74), and uPGD-M (r = 0.74). Levels of the cleaved active form of TSLP were increased in nasal polyps from patients with AERD relative to those in aspirin-tolerant control subjects. Recombinant TSLP induced PGD2 generation by cultured human mast cells. CONCLUSIONS: Our study demonstrates that mast cell-derived PGD2 is a major effector of type 2 immune responses driven by TSLP and suggests that dysregulation of this innate system contributes significantly to the pathophysiology of AERD.

Increased levels of prostaglandin D(2) suggest macrophage activation in patients with primary pulmonary hypertension.

STUDY OBJECTIVE: TXA(2) (thromboxane A(2)) is a lipid mediator believed to be produced primarily by platelets in normal subjects, although macrophages are capable of synthesis. There is increased production of TXA(2) in patients with primary pulmonary hypertension (PPH), which may reflect augmented production by macrophages. The objective of this study was to determine if macrophages are activated in PPH and whether they contribute to the increased production of TXA(2). STUDY TYPE: Case control. SETTING: University hospital. METHODS: We measured the urinary metabolites of three mediators that predominantly derive from different cell types in vivo: (1) TX-M (platelets and macrophages), a TXA(2) metabolite; (2) prostaglandin D(2) (PGD(2)) metabolite (PGD-M); and (3) N-methylhistamine (mast cells), a histamine metabolite, in 12 patients with PPH and 11 normal subjects. RESULTS: The mean (+/- SEM) excretion of both TX-M and PGD-M at baseline was increased in PPH patients, compared to normal subjects (460 +/- 50 pg/mg creatinine vs 236 +/- 16 pg/mg creatinine [p = 0.0006], and 1,390 +/- 221 pg/mg creatinine vs 637 +/- 65 pg/mg creatinine [p = 0.005], respectively). N-methylhistamine excretion was not increased compared to normal subjects. There was a poor correlation between excretion of TX-M and PGD-M (r = 0.36) and between excretion of PGD-M and methylhistamine (r = 0.09) in individual patients. CONCLUSION: In patients with PPH, increased levels of PGD-M, without increased synthesis of N-methylhistamine, suggest that macrophages are activated. The lack of correlation between urinary metabolite levels of TXA(2) and PGD(2) implies that macrophages do not contribute substantially to elevated TXA(2) production in patients with PPH. They may, however, have a role in the pathogenesis and/or maintenance of PPH, which warrants further investigation.

Increased formation of thromboxane in vivo in humans with mastocytosis.

Clinical manifestations of mastocytosis are mediated, at least in part, by release of the mast cell mediators histamine and prostaglandin D2. It has been previously reported that in addition to prostaglandin D2, mast cells produce other eicosanoids, including thromboxane. Nonetheless, little information exists regarding the formation of other prostanoids in vivo. The most accurate method to examine the systemic production of eicosanoids in vivo is the quantitation of urinary metabolites. We previously developed a highly accurate assay employing mass spectrometry to measure a major urinary metabolite of thromboxane, 11-dehydro-thromboxane B2, in humans. We utilized this assay to quantitate thromboxane production in 17 patients with histologically proven mastocytosis. We report that thromboxane formation was significantly increased (>2 SD above the mean) in at least one urine sample from 65% of patients studied. Of these, 91% of patients with documented systemic involvement had elevated thromboxane generation. In addition, endogenous formation of thromboxane was highly correlated with the urinary excretion of the major urinary metabolite of prostaglandin D2 (r = 0.98) and Ntau-methylhistamine (r = 0.91), suggesting that the cellular source of increased thromboxane in vivo could be the mastocyte. Enhanced thromboxane formation in patients with this disorder is unlikely to be of platelet origin as other markers of platelet activation, platelet factor 4 and beta-thromboglobulin, were not increased in three patients with marked overproduction of thromboxane. Furthermore, the recovery of 11-dehydro-thromboxane B2 excretion in two patients after the administration of aspirin occurred significantly more rapidly than the recovery of platelet thromboxane generation. These studies, therefore, report that thromboxane production is significantly increased in the majority of patients with mastocytosis that we examined and provide the basis to elucidate the role of this eicosanoid in disorders of mast cell activation.

Improved diagnosis of mastocytosis by measurement of the major urinary metabolite of prostaglandin D2.

Symptoms of mastocytosis have been attributed to the overproduction of both histamine and prostaglandin (PG) D2. Recently, we developed an assay for the major urinary metabolite of PGD2 (PGD-M), 9 alpha,11 beta-dihydroxy-15-oxo-2,3,18,19-tetranorprost-5-ene-1,20-dioic acid, and demonstrated that urinary excretion of this compound is markedly increased in patients with mastocytosis. It had been shown previously that measurement of the urinary excretion of histamine metabolites provides a more sensitive biochemical diagnostic indicator of systemic mastocytosis than does measurement of unmetabolized histamine. Therefore, we examined the correlation between the urinary excretion of the histamine metabolite, NT-methylhistamine, and PGD-M in urine samples from patients with mastocytosis. Urinary excretion of NT-methylhistamine and PGD-M was measured in 46 urine samples from 17 patients with histologically documented mastocytosis. Both compounds were quantified by mass spectrometry. In all urine collections showing an increase above normal (2 SD above the mean) in the excretion of NT-methylhistamine, the fold increase above normal in the urinary excretion of PGD-M was substantially greater. Further, in some urine samples from four patients whose excretion of NT-methylhistamine was consistently normal, the excretion of PGD-M was increased above normal by as much as 300%. These data indicate that quantification of the urinary excretion of PGD-M is a more sensitive biochemical diagnostic indicator of mastocytosis than is the quantification of NT-methylhistamine.

Detection of the major urinary metabolite of prostaglandin D2 in the circulation: demonstration of elevated levels in patients with disorders of systemic mast cell activation.

The symptoms and hemodynamic alterations that accompany episodes of systemic mast cell activation have been largely attributed to excessive prostaglandin (PG)D2 release. Quantification of the major urinary metabolite of PGD2 has been invaluable in elucidating a role for PGD2 in these clinical entities and in the biochemical evaluation of systemic mastocytosis. With the use of a modified mass spectrometric assay for the major urinary metabolite of PGD2, this metabolite was detected in plasma from 10 normal volunteers (3.5 +/- 1.4 pg/ml). Ingestion of niacin, which induces endogenous release of PGD2, increased plasma levels of this metabolite 6.3 to 33 times above the upper limit of normal by 2 hours. Thereafter, levels declined gradually but remained elevated for up to 6 to 8 hours. In contrast, circulating levels of 9 alpha, 11 beta-PGF2, the initial metabolite of PGD2, peaked by 30 minutes and returned to baseline by 2 hours. The clinical utility of measuring the major urinary metabolite in the circulation was demonstrated by detection of markedly increased levels in plasma and serum from patients with systemic mastocytosis and a patient with a severe type I allergic reaction. Thus in the biochemical evaluation of episodes of systemic mast cell activation and endeavors to further elucidate the role of PGD2 in human disease, there are kinetic advantages of measuring the major urinary metabolite of PGD2 in the circulation. One particular advantage is the evaluation of clinical events, which only in retrospect are suspected to be associated with excessive release of PGD2, yet plasma or serum was obtained proximate to the event.

Simplification of the mass spectrometric assay for the major urinary metabolite of prostaglandin D2.

The symptoms and hemodynamic alterations that accompany systemic mast cell activation have been attributed in large part to an excessive release of prostaglandin D2 (PGD2). Further, PGD2 has been implicated in the adverse effects of some pharmacologic agents (e.g. nicotinic acid). Quantitation of the major urinary metabolite of PGD2 has been invaluable in elucidating a role for PGD2 in these clinical entities and in the biochemical diagnosis of the disease systemic mastocytosis. However, the stable-isotope mass spectrometric assay originally developed for quantification of this metabolite has been too cumbersome for routine use. We now report improvements in the assay that greatly increase its utility by shortening sample processing and eliminating the need for purification using thin-layer chromatography. The precision and accuracy of the modified assay was evaluated and found to be comparable with the previously described assay. These modifications potentially allow wider use of the assay to explore the role of PGD2 in human disease and in the routine biochemical diagnosis of systemic mastocytosis and other disorders of mast cell activation.

Metabolic fate of radiolabeled prostaglandin D2 in a normal human male volunteer.

50 microCi of [3H]prostaglandin D2 tracer (100 Ci/mmol) was infused intravenously into a normal human male volunteer. 75% of the infused radioactivity was excreted into the urine within 5 h. This urine was added to urine obtained from two mastocytosis patients with marked overproduction of prostaglandin D2. Radiolabeled prostaglandin D2 urinary metabolites were chromatographically isolated and purified and subsequently identified by gas chromatography-mass spectrometry. 25 metabolites were identified. 23 of these compounds comprising 37% of the recovered radioactivity had prostaglandin F-ring structures, and only two metabolites comprising 2.7% of the recovered radioactivity retained the prostaglandin D-ring structure. The single most abundant metabolite identified was 9,11-dihydroxy-15-oxo-2,3,18,19-tetranorprost-5-ene-1,20-dioic acid which was isolated in a tricyclic form as a result of formation of a lower side chain hemiketal followed by lactonization of the terminal carboxyl and the hemiketal hydroxyl. Different isomeric forms of several prostaglandin F-ring metabolites were identified. An isomer of prostaglandin F2 alpha was also excreted intact into the urine as a metabolite of prostaglandin D2. 15 PGF-ring compounds were treated with n-butylboronic acid and 13 failed to form a boronate derivative, suggesting that the orientation of the hydroxyl group at C-11 in these 13 metabolites is beta. This study documents that prostaglandin D2 is metabolized to prostaglandin F-ring metabolites in vivo in humans. These results also bring into question the accuracy of quantifying prostaglandin F2 alpha metabolites as a specific index of endogenous prostaglandin F2 alpha biosynthesis, as well as quantifying urinary prostaglandin F2 alpha as an accurate index of renal production of prostaglandin F2 alpha.

Metabolic fate of endogenously synthesized prostaglandin D2 in a human female with mastocytosis.

Increased production of prostaglandin D2 was recently demonstrated in patients with systemic mastocytosis. One female patient investigated with mastocytosis was found to have overproduction of prostaglandin D2 of such magnitude (150-fold above normal) that it provided the unique opportunity to delineate the metabolic fate of endogenously synthesized prostaglandin D2. A five percent aliquot of a twenty-four hour urine collection from this patient was extracted, purified by silicic acid chromatography, methylated, and finally subjected to high pressure liquid chromatography. Column fractions collected were derivatized and analyzed by gas chromatography-mass spectrometry. Increased quantities of sixteen urinary metabolites were identified and included a series of metabolites retaining the PGD-ring as well as a series of metabolites with a PGF-ring. PGF-ring metabolites were excreted in approximately 4-fold greater relative abundance than PGD-ring metabolites. More than one apparent isomeric form of some PGF-ring metabolites were found. The predominant urinary metabolite was 2,3-dinor-prostaglandin F2. This study provides evidence that endogenously synthesized prostaglandin D2 is converted in substantial part to prostaglandin F2 metabolites in vivo in humans.

Intervention with epinephrine in hypotension associated with mastocytosis.

The occurrence of the episodes of vasodilatory hypotension can be a life-threatening manifestation of systemic mastocytosis. This article describes the reversal by epinephrine of episodes of severe hypotension in two hospitalized patients with mastocytosis. Recognition of the efficacy of epinephrine in hypotension associated with mastocytosis can be important when other methods fail to restore hemodynamic stability.