Leukotrienes and other products of the 5-lipoxygenase pathway. Biochemistry and relation to pathobiology in human diseases

Leukotriene B4 and Kawasaki disease

The role of LTB4 in Kawasaki disease as a chemo-attractant and immunomodulator is reviewed through our own experience and reports by other investigators. In our experiment using 19 patients, we measured calcium ionophore-stimulated LTB4 synthesis in PMNs obtained in three different stages of the illness (acute, convalescent and recovered phases). LTB4 synthesis was significantly increased in the convalescent phase of the illness. Other investigators showed increased serum-LTB4 concentration in acute as well as convalescent phases, suggesting that LTB4 participated in the inflammatory process of Kawasaki disease as an inflammatory mediator and immunomodulator. However, no difference was found in LTB4 synthetic activity in PMNs in any phases of the illness between the patients with and without coronary lesions, which indicated that LTB4 was not a parameter of coronary aneurysm formation. Therapeutic use of high-dose gamma-globulin showed a tendency to decreased LTB4 synthesis in PMNs, although it is not conclusive.

Improved in vitro antigen-specific antibody synthesis in two patients with common variable immunodeficiency taking an oral cyclooxygenase and lipoxygenase inhibitor (ketoprofen)

In the process of performing a previously published study examining B cell function in 16 patients with common variable immunodeficiency (CVI)(J Allergy Clin Immunol 1991; 87:1138-49), we noted improved in vitro antibody (Ab) synthesis in a patient, H. B., while he was taking a cyclooxygenase and lipoxygenase inhibitor, ketoprofen. Addition of ketoprofen in vitro to B cells from patients with CVI resulted in improved proliferation and differentiation in four of five additional patients with CVI studied. One patient, besides H. B., M. K. B., whose B cells secreted increased amounts of antigen (Ag)-specific Ab in response to in vitro ketoprofen, underwent a trial of oral ketoprofen M. K. B., like H. B., demonstrated improved in vitro Ag-specific Ab production while she was taking oral ketoprofen. No increase in serum Ab levels was noted in either patient taking ketoprofen, but both patients remained infection free during the time of their ketoprofen trials (H. B., 9 months, and M. K. B., 36 months). No improvement in in vitro Ag-specific Ab synthesis was noted when H. B. and M. K. B. took oral cyclooxygenase inhibitors (naproxen or ibuprofen). Thus, additional study is warranted to examine the role of lipoxygenase products of arachidonic acid in the B cell dysfunction of CVI.

Generation of leukotriene B4 by hemodialyzer membranes: a novel index of biocompatibility

Leukotriene B4 (LTB4) plays an important role in acute and chronic inflammatory and hypersensitive reactions. We studied the time course of LTB4 biosynthesis in whole blood in 18 patients with end-stage renal failure maintained on regular hemodialysis with two different membranes, cuprophane and polyacrylonitrile (AN 69). The basal levels of LTB4 from dialysis patients did not differ significantly from a normal control group. Compared to predialytic values, the cuprophane membrane caused a maximal release of LTB4 by a factor of about 4.5 (p less than 0.01) within the first 10 to 20 minutes. Thereafter the level fell and returned to baseline range at the end of the hemodialysis session. With the use of the AN 69 membrane no significant increase of LTB4 could be demonstrated. The changes in LTB4 concentration showed a close temporal correlation to the alterations in white blood cell count. We conclude that (1) LTB4 is a biologically important mediator of neutrophil activation during hemodialysis, and (2) LTB4 may be a sensitive marker of biocompatibility in vivo.

Inhibition of mammalian 5-lipoxygenase and cyclo-oxygenase by flavonoids and phenolic dietary additives. Relationship to antioxidant activity and to iron ion-reducing ability

We investigated the ability of various plant flavonoids (a) to inhibit 5-lipoxygenase and cyclooxygenase activities in rat peritoneal leukocytes, (b) to inhibit lipid peroxidation in rat liver microsomes, and (c) to stimulate DNA degradation caused by the antibiotic bleomycin in the presence of ferric ions. These compounds were compared with a range of synthetic phenolic substances including carnosol, vanillin, vitamin E and its analogue trolox c. The flavonoids were potent inhibitors of non-enzymatic peroxidation in membranes but this was not significantly correlated with their ability to inhibit either pathway of eicosanoid synthesis, suggesting that their mode of inhibition of 5-lipoxygenase/cyclooxygenase is not simply due to interception of peroxyl radicals generated at the active site of the enzymes. Many of the flavonoids and other compounds (including carnosol, vitamin E and trolox c) stimulated Fe3+/bleomycin-dependent DNA degradation. Those flavonoids which stimulated DNA degradation at low concentrations but which inhibited it at higher concentrations ("biphasic" effect, possibly caused by changing relative contributions of ability to reduce ferric-bleomycin or to chelate iron ions from the bleomycin) were selective inhibitors of 5-lipoxygenase compared to cyclo-oxygenase. In contrast, those flavonoids that did not stimulate DNA degradation at all proved to be cyclo-oxygenase selective inhibitors. Compounds that increased Fe3+/bleomycin-dependent DNA damage up to a maintained plateau were non-selective inhibitors of both 5-lipoxygenase and cyclo-oxygenase. Thus, a combination of iron-chelating and iron ion-reducing properties appears to be required for selective 5-lipoxygenase inhibition by phenolic compounds. Carnosol, vitamin E and trolox c were also found to be 5-lipoxygenase inhibitors of varying potency, and all were less active as cyclo-oxygenase inhibitors.

Biochemistry of asthma

Asthma is a chronic condition of the airways that involves many types of inflammatory cell and the release of many mediators and neurotransmitters that have multiple effects on the various target cells in the airway. There have been important advances in understanding the biochemical events involved in signal transduction in inflammatory cells, in mediator synthesis and release, in contraction and relaxation of airway smooth muscle and in neural mechanisms. This may lead to more effective and specific therapies for this common but complex disease.

Inflammatory bowel disease. Part I: Nature and pathogenesis

Once regarded as medical curiosities, ulcerative colitis and Crohn's disease have achieved a remarkable change in status recently and today are among the more compelling of all human illnesses. The cause(s) of inflammatory bowel disease (IBD) are not known. Genetic, environmental, microbial, and immunologic factors are involved, but the precise mechanisms are obscure. The incidence of ulcerative colitis is relatively stable, while Crohn's disease continues to increase in frequency. In 10% to 15% of patients, it is hard to differentiate between ulcerative colitis and Crohn's colitis; however, problems with diagnosis usually resolve with time and repeated examinations. In part I of his two-part monograph on IBD, Dr. Kirsner addresses the nature and pathogenesis of the disease. Increased study of ulcerative colitis and Crohn's disease in recent years has generated new knowledge regarding their etiology. Part I focuses on microbial, immunologic, and genetic mechanisms and the inflammatory processes involved in the disease. In part II, which will be presented in next month's issue of Disease-a-Month, Dr. Kirsner deals with the clinical features, course, and management of IBD, based on the author's 55 years of experience with these problems and supplemented by critical examination of the recent (1988-1990) literature. Particular attention is directed to the symptoms and physical findings of ulcerative colitis and Crohn's disease, the laboratory, radiologic, endoscopic, and pathologic features, and the many systemic complications. The IBDs are mimicked by several enterocolonic infections and other conditions, making differential diagnosis necessary. Inflammatory bowel disease in children and the elderly conforms to conventional clinical patterns modified by the health circumstances of the respective age groups. Because the cause of IBD has not been established, current medical therapy is facilitative and supportive rather than curative. The principles of medical treatment are approximately the same for ulcerative colitis and Crohn's disease. Treatment emphasizes a program rather than a drug and also considers the individuality of the therapeutic response. A clearer understanding of dietary and nutritional needs, including hyperalimentation and electrolyte and fluid balance, aids treatment. Antidiarrheal and antispasmodic preparations and sedatives are prescribed for symptom relief. The bowel inflammation is controlled with sulfasalazine or the newer 5-amino salicylic acid (5-ASA) compounds, antibacterial drugs for complications of Crohn's disease and IBD, adrenocortical steroids, and the immunosuppressive compounds 6-mercaptopurine (6-MP), azathioprine, and cyclosporine, as determined in each patient. The surgical procedures available for treatment of ulcerative colitis include total proctocolectomy and ileostomy or ileoanal anastomosis.(ABSTRACT TRUNCATED AT 400 WORDS)

Antibody enhancement of respiratory syncytial virus stimulation of leukotriene production by a macrophagelike cell line

The clinical and epidemiologic features of respiratory syncytial virus (RSV) infections suggest that RSV-specific antibody may sometimes contribute to the disease process. Recently, it has been demonstrated that virus-specific antibody can enhance RSV infection of macrophagelike cells in vitro. We evaluated the possibility that antibody might also enhance RSV stimulation of the bronchoactive mediator of inflammation leukotriene C-4 (LTC4)in a macrophagelike cell line, U937. The addition of RSV led to little increase in LTC4 production, but addition of RSV plus anti-RSV antibody increased production to a level similar to that achieved with calcium ionophore, a known stimulator of LTC4 production. The antibody-enhanced increase in LTC4 production occurred rapidly (within 15 min), peaked at 60 min, and achieved levels 1.5- to 3.0-fold above that for cells or cells plus virus. RSV plus anti-RSV antibodies in the form of polyclonal serum, monoclonal antibodies, or F(ab')2 fragments and parainfluenza virus types 1 and 3 plus their respective antibodies all increased LTC4 levels over that for the virus alone. These results demonstrate that antibody plus the corresponding virus or protein can increase leukotriene production. This phenomenon could contribute to diseases, such as RSV bronchiolitis, that appear to be caused by an interaction between the virus (or antigen) and host immunity.

5-Lipoxygenase is not essential in macrophage-mediated oxidation of low-density lipoprotein

The concentration-dependent effects of a series of lipoxygenase inhibitors and antioxidants on the macrophage-mediated oxidative modification of low-density lipoprotein (LDL) were measured. Their influence on macrophage 5-lipoxygenase pathway activity was also studied over the same concentration range. No correlation between inhibition of 5-lipoxygenase and of macrophage-mediated oxidation of LDL was observed. The capacity of the compounds to prevent cell-mediated modification of LDL could be explained in terms of their activity as either aqueous- or lipid-peroxyl radical scavengers. Two potent 5-lipoxygenase inhibitors (MK 886 and Revlon 5901), which had no radical-scavenging properties, were unable to block LDL modification. It is concluded that 5-lipoxygenase is not essential for LDL oxidation by macrophages.

The role of leukotrienes in allergic rhinitis: a review

Leukotrienes are potent proinflammatory mediators. Our understanding of their role in allergic rhinitis has increased, but further, extensive investigation is required. The sulfidopeptide LTs are generated during the immediate response to antigen provocation and are probably increased during the late inflammatory phase and during seasonal exposure. The source of LTC4 in the early allergic reaction includes the mast cell, but other cell types may also contribute. LTD4 causes nasal congestion and increased blood flow, but not sneezing or significant rhinorrhea. Studies in which LT generation was pharmacologically reduced support a role for these mediators in allergic rhinitis. There is now a need to evaluate the more potent, recently developed, LT antagonists in rhinitis. These agents should help establish the relative importance of LTs to the many other inflammatory mediators that are implicated in the pathogenesis of allergic rhinitis. Such knowledge will broaden and improve our choice of therapeutic modalities for this disease.

Glutathione and inflammatory disorders of the lung

Glutathione (GSH) is an essential tripeptide present in most eukaryotic cells. Because of its sulfhydryl group, GSH is a versatile molecule capable of protecting cells against oxidants and toxic xenobiotics. However, it also plays key roles in multiple metabolic pathways, such as the synthesis of certain leukotrienes, proteins, and DNA precursors as well as the activation of enzymes, the regulation of immune responses and others. Not only is GSH synthesized by cells for local use but it also participates in an elaborate intercellular exchange process regulated by the gamma-glutamyl cycle. Extracellular GSH in plasma and in alveolar epithelial lining fluid is thus subject to variations according to the degree of expression of gamma-glutamyl cycle enzymes and the rate of consumption of GSH by electrophilic molecules. Bronchoalveolar lavage has allowed us to observe many of these variations of GSH within the extracellular environment of the normal and diseased human lung. Studies of lung GSH have lead to a better understanding of pathogenic processes and have stimulated investigations of novel therapeutic approaches in lung inflammatory disorders.

Reduced allergen-induced nasal congestion and leukotriene synthesis with an orally active 5-lipoxygenase inhibitor

BACKGROUND AND METHODS

The clinical importance of leukotrienes in human allergy has not been defined, in part because there have been no selective 5-lipoxygenase inhibitors that have been effective and safe for use in humans. To address the hypothesis that stimulated leukotriene synthesis causes symptoms of immediate-hypersensitivity reactions in vivo, I investigated the effects of a new 5-lipoxygenase inhibitor, A-64077, on provoked allergic nasal symptoms and mediator release in a double-blind, randomized, placebo-controlled study. Eight subjects with allergic rhinitis underwent nasal challenge on two occasions after an oral dose of 800 mg of A-64077 or an identical-appearing placebo.

RESULTS

Allergen-induced nasal congestion was significantly attenuated (P less than 0.02) by A-64077; peak levels of leukotriene B4 (median, 684 pg per milliliter) and 5-hydroxyeicosatetraenoic acid (median, 704 pg per milliliter) in nasal-rinse fluids were markedly reduced (to 67 and 185 pg per milliliter, respectively; P less than 0.01), whereas levels of prostaglandin D2 were not. Histamine release and sneezing were not reduced significantly by A-64077, but there was a significant correlation (P less than 0.01) between the changes in these variables within subjects. The mean (+/- SEM) stimulated synthesis of leukotriene B4 in whole blood ex vivo was markedly reduced by A-64077 (from 153 +/- 19 to 20 +/- 9 ng per milliliter, P less than 0.01), and the specificity of A-64077 for 5-lipoxygenase inhibition was verified by its lack of effect on the synthesis of serum thromboxane B2 or 12-hydroxyeicosatetraenoic acid.

CONCLUSIONS

These results provide direct evidence of an important role for the 5-lipoxygenase products of arachidonic acid in allergic rhinitis and support the notion that further experiments in this area may lead to new therapeutic approaches to allergic disorders.

Leukotriene A4 hydrolase is a zinc-containing aminopeptidase

A comparison of amino acid sequences revealed that leukotriene A4 (LTA4) hydrolase is homologous to various types of aminopeptidases. Consistently with the finding, the purified LTA4 hydrolases from both human and guinea pig sources contained equimolar zinc ion, as determined by atomic absorption spectrometry. The enzyme had a significant amount of aminopeptidase activity toward synthetic peptide substrates. Both LTA4 hydrolase and aminopeptidase activities were inhibited by o-phenanthroline, p-chloromercuribenzoic acid, and Leu-thiol with similar IC50 values. Co-purification as well as co-immunoprecipitation of both enzyme activities with an affinity-purified antibody against LTA4 hydrolase strongly suggest that the two enzyme activities reside in a single protein.