Leukotrienes activation

Spector SL. Leukotriene activity modulation in asthma. Drugs 1997 54(3) 369-384. Determinants of bronchial responsiveness in the European Community Respiratory Health Survey in Italy evidence of an independent role of atopy, total serum IgE levels, and asthma symptoms. Allergy 1998 53(7) 673-681. 

Leukotrienes and Prostanoids. Arachidonic acid (AA) (213) and its metabohtes are iavolved ia cellular regulatory processes ia all three principal chemical signaling systems endocrine (see Hormones), immune, and neuronal (62). FoUowiag receptor activation or iacreased iatraceUular... 

Endotoxin and Muramyl Dipeptide Derivatives. Bacterial cell wall constituents such as the Hpopolysaccharide endotoxin and muramyl dipeptide, which stimulate host defense systems, show radioprotective activity in animals (204). Although endotoxin is most effective when given - 24 h before irradiation, it provides some protection when adrninistered shortiy before and even after radiation exposure. Endotoxin s radioprotective activity is probably related to its Hpid component, and some of its properties may result from PG and leukotriene induction (204). 

The organization of Part Two is according to structural type. The first section, Chapter Seven, is concerned with the synthesis of macrocyclic compounds. Syntheses of a number of heterocyclic target structures appear in Chapter Eight. Sesquiterpenoids and polycyclic higher isoprenoids are dealt with in Chapters Nine and Ten, respectively. The remainder of Part Two describes syntheses of prostanoids (Chapter Eleven) and biologically active acyclic polyenes including leukotrienes and other eicosanoids (Chapter Twelve). 

Leukotriene B5 can be biosynthesized in the body from eicosapentaenoic acid, which is ingested in the form of dietary fish lipid. Synthetic LTB5 was synthesized as outlined below and found to have only 20% of the neutrophil chemotactic activity of LTB4, a fact which may be relevant to the antiinflammatory effect of dietary marine lipid. 

Mammals can add additional double bonds to unsaturated fatty acids in their diets. Their ability to make arachidonic acid from linoleic acid is one example (Figure 25.15). This fatty acid is the precursor for prostaglandins and other biologically active derivatives such as leukotrienes. Synthesis involves formation of a linoleoyl ester of CoA from dietary linoleic acid, followed by introduction of a double bond at the 6-position. The triply unsaturated product is then elongated (by malonyl-CoA with a decarboxylation step) to yield a 20-carbon fatty acid with double bonds at the 8-, 11-, and 14-positions. A second desaturation reaction at the 5-position followed by an acyl-CoA synthetase reaction (Chapter 24) liberates the product, a 20-carbon fatty acid with double bonds at the 5-, 8-, IT, and ITpositions. 

Horie and coworkers synthesized a series of flavones that showed promising inhibitory activity against archidonate 5-lipooxygenase. This enzyme is responsible for the initiation of bioactive leukotrienes that are chemical mediators of anaphylaxis and inflammation. Under standard K-R conditions o-hydroxyarylketone 66 and anhydride 67 in presence of the corresponding anhydride 68 delivered flavones 69 in yields of 42-65%. Subsequent hydrogenation of 69 afforded the flavone inhibitors 70. 

Oxo-4//-pyrido[],2-n]pyrimidin-2-yl]oxymethylsaccharin derivatives 418 exhibited human leukocyta elastase inhibitory activities (94EUP626378, 95USP5378720). 2-Substituted 4//-pyrido[l, 2-n]pyrimidin-4-one (419) is a potent human leukocyta elastase inhibitors (A", 1.79/xM) (96USP5512576). The 4//-pyrido[l,2-n]pyrimidin-4-one moiety was included in leukotriene antagonist 2-ethynylthiazole derivatives (98JAP(K) 98/195063)... 

While the obvious value of in vivo animal models is clear, there also are instances—especially in cases of inflammatory arthritis, behavior, and tumor growth—where they have failed to be predictive of useful clinical activity in humans [51], For example, leukotriene (LTB4) antagonists showed activity in animal models of inflammatory arthritis yet failed to be useful in rheumatoid arthritis [52]. Similarly, dopamine D4 antagonists showed activity in animal behavior models previously predictive of dopamine D2 antagonists in schizophrenia. However, testing of dopamine D4 antagonists showed no efficacy in humans [53]. 

FIGURE 9.20 Design of multiple ligancl activity, (a) Dual histamine HI receptor and leukotriene receptor antagonist incorporating known antihistaminic properties of cyproheptadine and LTD4. (b) Joint ACE/NEP inhibitor formed from incorporating similarities in substrate structures for both enzymes. From [57],... 

Polmar, S., Diaz-Gonzalez, F., Dougados, M., Ortiz, P., and del-Miguel, G. (2004). Limited clinical efficacy of a leukotriene B4 receptor (LTBQ antagonist in patients with active rheumatoid arthritis (RA). Arthritis Rheum. 50 S239. 

These cells respond to a number of different chemoattractants which have specific and distinct receptors on the membrane surface (for recent reviews see Refs. 3 and 4). Such chemoattractants include N-formylpeptides, which are bacterial peptides, and mediators of inflammation such as leukotriene B4, C5a, and platelet activating factor. 

Lie WJ, Homburg CH, Kuijpers TW, Knol EF, Mul FR Roos D, Tool AT Regulation and kinetics of platelet-activating factor and leukotriene C4 synthesis by activated human basophils. Clin Exp Allergy 2003 33 1125-1134. 

In a third study the time course of the effects of intravenous and intracoronary injections of cysteinyl leukotrienes on metabolic parameters and systemic and coronary hemodynamics was examined in patients with normal coronary arteries [32]. LTD4 (3 nmol, injected into the left coronary artery) induced an early (20 s), transient fall in mean arterial pressure paralleled by rises in heart rate and plasma levels of epinephrine and norepinephrine, all of which had returned to baseline by 10 min. CVR rose at 10 and 15 min and myocardial oxygen extraction at 15 min. Thus, small doses of cysteinyl leukotrienes may induce both an early, transient fall in mean arterial pressure, with secondary sympathoadrenergic activation, and a later increase in small coronary arteriolar resistance. 

Cysteinyl leukotrienes can induce an early, transient fall in arterial pressure associated with sympathoadrenergic activation, plus a late rise in small coronary arteriolar resistance [32]. Using specific antagonists of CysFTi and CysFT2 [63] it will be possible to assess the each receptor s contribution to the cardiovascular effects of these vasoactive mediators. 

The detection of reactions mediated by specific IgE to agents triggering anaphylaxis may be achieved by means of serological methods serum-specific IgE, or by means of cellular tests which determine the release of basophil mediators (leukotrienes and histamine) or by means of the analysis of basophil expression markers, a technique known as the basophil activation test (BAT). 

The principle underlying the BAT is that the attachment of the antigen to the IgE present on the surface of the basophil leads to the activation of the basophil and the release of its mediators (histamine, leukotrienes, prostaglandins, etc.) and the expression on its membrane of molecules such as CD63, CD203c or others which are markers of basophil activation. The basophils are identified with monoclonal antibodies marked with fluorochromes and anti-IgE and anti-CD63 receptors [for a complete review, we suggest readers read references 19-22]. 

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