1. An inositol monophosphatase was purified to homogeneity from bovine brain. 2. The enzyme is a dimer of subunit Mr 29,000. 3. The enzyme hydrolyses both enantiomers of myo-inositol 1-phosphate and both enantiomers of myo-inositol 4-phosphate, but has no activity towards inositol bisphosphates, inositol trisphosphates or inositol 1,3,4,5-tetrakisphosphate. 4. Several non-inositol-containing monophosphates are also substrates. 5. The enzyme requires Mg2+ for activity, and Zn2+ supports activity to a small extent. 6. Other bivalent cations (including Zn2+) are inhibitors, competitive with Mg2+. 7. Phosphate, but not inositol, is an inhibitor competitive with substrate. 8. Li+ inhibits hydrolysis of inositol 1-phosphate and inositol 4-phosphate uncompetitively with different apparent Ki values (1.0 mM and 0.26 mM respectively).

Lithium-sensitive inositol monophosphatase from bovine brain was purified from brain and from a recombinant strain of Escherichia coli BL21-DE3. The natural and recombinant enzymes displayed identical physical and kinetic properties. At low [Li'], Li' inhibited the hydrolysis of racemic myo-inositol 1 -phosphate, myo-inositol4-phosphate and adenosine 2'-phosphate in a linear uncompetitive manner with apparent K, values of 1.1, 0.11 and 1.52mM, respectively. At Li' concentrations higher than 4 mM, Li' acted as a non-linear noncompetitive inhibitor for myo-inositol 1-phosphate, K, greater than 1.5 mM.The enzyme was unable to catalyze the transesterification of ['4C]inositol in the presence of inositol 1-phosphate or adenosine 2'-phosphate and attempts to trap a phosphorylated enzyme intermediate directly, were unsuccessful. In the presence of Li+, the enzyme was able to release inositol from inositol 1-phosphate, in a burst, faster than the rate of steady-state substrate turnover suggesting that Li' binds after P-0 bond cleavage in the substrate has occurred. The possibility that a free phosphorylated enzyme intermediate might exist was discounted when the exchange of "0 from water into phosphate was shown to be completely dependent upon inositol. The K, for inositol for "0 exchange was 190 mM and in the presence of saturating phosphate, VEX was at least 60% of V,, for the hydrolysis reaction. Thus, the enzyme operates via a ternary-complex mechanism, and Li' exerts its action by binding to enzyme/product complexes. At low concentration, Li' inhibition with respect to the cofactor, Mg2+ was non-competitive. Mg2+ acted as a non-competitive activator for substrate hydrolysis at pH 8.0, but as the second substrate in an equilibrium-ordered mechanism at pH 6.5. Cooperativity effects were observed for Mg2+ with inositol I-phosphate and 2'AMP as the substrate but not with inositol4-phosphate. The combined results indicate that Mgz' and substrate binding is ordered with substrate adding first. Inositol, the first product off, was a poor non-competitive inhibitor for inositol 1-phosphate whereas the other product, phosphate, was a competitive inhibitor. Phosphate inhibition was markedly pH dependent (K, = 8 mM at pH 6.5 and 0.32 mM at pH 8.0). In the presence of Li' and phosphate, increasing [Li'] caused the K, for phosphate to decrease by a factor of (1 + [Li+]/K,,). The K, for the first product off (inositol) was, however, unaltered by Li'. The results indicate that Li' can bind to the species E.Ins.P, and E.P,, but not to enzyme/substrate complexes. Further examination of the burst-phase release of [14C]inositol and its rate relative to that of the steady-state reaction under a variety of conditions revealed that Li' acts as a retarder rather than as a dead-end inhibitor and that the burst was due to hysteresis.Evidence is provided to suggest that Mg2+ is required for the catalysis only and that Li' occupies the site vacated by Mg2+ in its action as an inhibitor. The mechanisms of the reactions, the modes of inhibition...

Nitrogen dioxide (NO2) is a free radical and a common oxidant in polluted air. Here we present data on the time course of inflammation after NO2 exposure, as reflected in bronchial biopsy and airway lavage specimens. Healthy, nonsmoking subjects were exposed to air or 2 ppm NO2 for 4 h in random order on separate occasions. Endobronchial biopsies, bronchial washing (BW), and bronchoalveolar lavage (BAL) were done at 1.5 h (n = 15) or 6 h (n = 15) after exposure. In BW, exposure to NO2 induced a 1.5-fold increase in interleukin-8 (IL-8) (p < 0.05) at 1.5 h and a 2.5-fold increase in neutrophils (p < 0.01) at 6 h. In BAL fluid (BALF), small increases were observed in CD45RO+ lymphocytes, B-cells, and natural killer (NK) cells only. Immunohistologic examination of bronchial biopsy specimens showed no signs of upregulation of adhesion molecules, and failed to reveal any significant changes in inflammatory cells at either time point after NO2 exposure. In summary, NO2 induced a neutrophilic inflammation in the airways that was detectable in BW at 6 h after NO2 exposure. The increase in neutrophils could be related to the enhanced IL-8 secretion observed at 1.5 h after exposure. The absence of adhesion-molecule upregulation or cellular inflammation in mucosal biopsy specimens indicates that the major site of inflammation following exposure to NO2 may be in the smaller airways and not in the alveoli.

The endothelium is the primary barrier to leukocyte recruitment at sites of inflammation. Neutrophil recruitment is directed by transendothelial gradients of IL-8 that, in vivo, are bound to the endothelial cell surface. We have investigated the identity and function of the binding site(s) in an in vitro model of neutrophil transendothelial migration. In endothelial culture supernatants, IL-8 was detected in a trimolecular complex with heparan sulfate and syndecan-1. Constitutive shedding of IL-8 in this form was increased in the presence of a neutralizing Ab to plasminogen activator inhibitor-1 (PAI-1), indicating a role for endothelial plasminogen activator in the shedding of IL-8. Increased shedding of IL-8/heparan sulfate/syndecan-1 complexes was accompanied by inhibition of neutrophil transendothelial migration, and aprotinin, a potent plasmin inhibitor, reversed this inhibition. Platelets, added as an exogenous source of PAI-1, had no effect on shedding of the complexes or neutrophil migration. Our results indicate that IL-8 is immobilized on the endothelial cell surface through binding to syndecan-1 ectodomains, and that plasmin, generated by endothelial plasminogen activator, induces the shedding of this form of IL-8. PAI-1 appears to stabilize the chemoattractant form of IL-8 at the cell surface and may represent a therapeutic target for novel anti-inflammatory strategies.

The presence of cytokines and the toxic eosinophil granule product major basic protein (MBP) was investigated in nasal aspirates from children with naturally occurring virus-induced asthma exacerbations and compared with levels in nasal aspirates taken from the same children when asymptomatic. Increased levels of MBP accompanied by increased levels of the chemokines RANTES and macrophage-inhibitory protein 1alpha were observed in nasal aspirates from children during the virus-induced exacerbations. Granulocyte-macrophage colony-stimulating factor was mostly undetectable in samples obtained during both symptomatic and asymptomatic periods. Interleukin-5 levels were low, but tended to increase in samples from symptomatic children. These data confirm that the eosinophil product MBP and the eosinophil chemoattractant chemokines RANTES and macrophage-inhibitory protein 1alpha are increased in upper respiratory viral infections associated with asthma exacerbations and suggest an important role for these chemokines in regulating eosinophil influx and activation. These chemokines may represent targets for therapeutic intervention in virus-induced asthma exacerbations.

ObjectivesUlcerative colitis (UC) is a relapsing inflammatory disorder of unconfirmed aetiology, variable severity and clinical course, characterised by progressive histological inflammation and with elevation of eicosanoids which have a known pathophysiological role in inflammation. Therapeutic interventions targetting eicosanoids (5-aminosalicylates (ASA)) are effective first line and adjunctive treatments in mild-moderate UC for achieving and sustaining clinical remission. However, the variable clinical response to 5-ASA and frequent deterioration in response to cyclo-oxygenase (COX) inhibitors, has prompted an in depth simultaneous evaluation of multiple lipid mediators (including eicosanoids) within the inflammatory milieu in UC. We hypothesised that severity of inflammation is associated with alteration of lipid mediators, in relapsing UC.DesignStudy was case-control design. Mucosal lipid mediators were determined by LC-MS/MS lipidomics analysis on mucosal biopsies taken from patients attending outpatients with relapsing UC. Univariate and multivariate statistical analyses were used to investigate the association of mucosal lipid mediators, with the disease state and severity graded histologically.ResultsLevels of PGE2, PGD2, TXB2, 5-HETE, 11-HETE, 12-HETE and 15-HETE are significantly elevated in inflamed mucosa and correlate with severity of inflammation, determined using validated histological scoring systems.ConclusionsOur approach of capturing inflammatory mediator signature at different stages of UC by combining comprehensive lipidomics analysis and computational modelling could be used to classify and predict mild-moderate inflammation; however, predictive index is diminished in severe inflammation. This new technical approach could be developed to tailor drug treatments to patients with active UC, based on the mucosal lipid mediator profile.

Heparin and glycosaminoglycans (GAGs) related structurally to heparin, notably heparan sulphate, bind to most, if not all, chemokines and many growth factors. The chemokine and growth factor interactions with GAGs localise the peptide mediators to specific sites in tissues and influence their stability and function. This chapter discusses the nature of these interactions and the effect on the function of a number of chemokines (PF-4, interleukin-8, RANTES and SDF-1) and growth factors (FGF, HGF, VEGF) in normal physiology and the disease setting. Novel therapeutic interventions that target chemokine and growth factor interactions with GAGs are also discussed.

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