Leukotriene D4 and E4 formation by plasma membrane bound enzymes

Effect of leukotriene C4 exposure on ciliated cells of the nasal mucosa

To clarify the effects of leukotriene C4 (LTC4) on human ciliated epithelium, ciliary activity of the ethmoid sinus mucosa was measured photoelectrically in tissue culture. At concentrations ranging from 10(-6)M to 10(-9)M, LTC4 showed minimal effects on the ciliated epithelium during the initial 30 minutes of exposure; thereafter, ciliary inhibition was observed in a concentration- and time-dependent manner. Irrigation of the mucosa with culture medium 15 minutes after exposure prevented the LTC4-induced ciliary inhibition. However, irrigation 60 minutes after exposure failed to inhibit 10(-8)M LTC4-induced ciliary dysfunction and mucosal damage. The LTC4-induced ciliary inhibition was blocked in the presence of FPL-55712 and/or Ly-171883, both leukotriene receptor antagonists. L-serine and sodium tetraborate complex (SBC), a gamma-glutamyl transpeptidase (gamma-GTP) inhibitor, also inhibited the LTC4-induced ciliary inhibition. These findings indicate that LTC4 is converted to LTD4 by gamma-GTP during 60 minutes of exposure, and LTC4 itself has minimal direct effects on the ciliated cells.

Inhibition of mucociliary clearance of the eustachian tube by leukotrienes C4 and D4

The effect of leukotrienes C4 (LTC4) and D4 (LTD4) and prostaglandin E2 (PGE2) on mucociliary clearance of the eustachian tube was investigated in vitro and in vivo. Normal ciliated epithelium was obtained from the eustachian tube of guinea pigs and incubated separately with LTC4, LTD4, and PGE2 at concentrations of 10(-8) mol/L and 10(-6) mol/L. Ciliary activity was measured photoelectrically. Leukotriene D4 progressively inhibited ciliary activity, while PGE2 promoted it. Leukotriene C4 also induced ciliary inhibition. One milliliter each of 10(-5) mol/L LTC4, LTD4, and PGE2 was directly injected into the tympanic bullae of chinchillas under anesthesia. The middle ears were examined by otomicroscopy, tympanometry, and auditory brain stem response over time. Clearance of middle ear effusion was delayed by LTC4 and LTD4, as compared with PGE2 and the control. These findings indicate that LTC4 and LTD4 inhibit mucociliary clearance of the eustachian tube.

Inactivation of leukotriene C4 in the airways and subsequent urinary leukotriene E4 excretion in normal and asthmatic subjects

Leukotrienes (LT) are synthesized in the lung during asthmatic reactions and mediate certain inflammatory symptoms. Pulmonary metabolism and clearance of exogenously added peptidoleukotrienes were studied in nonasthmatics, asthmatics, and asthmatics challenged with allergen. [3H]LTC4 and [14C]dextran were instilled into the airways, and bronchoalveolar lavage fluid (BALF) was obtained 15 min later. After comparing the [3H]/[14C] ratio of the instilled solution with that in BALF, 77% of LT were found to have been removed from the airways of nonasthmatics, and 72% of unchallenged asthmatics. Allergen administration to asthmatics 1 min before LT instillation inhibited LT transfer out of the airways by 26%, compared with asthmatics not challenged with allergen. This decrease in the removal of LT from the airways during allergic reactions could potentiate the physiologic effects of LT produced in the airways. The predominant LT in BALF was LTE4, constituting 56% of the LT in asthmatics and 61% in nonasthmatics. The percentage of LTE4 in BALF increased to 87% in allergen-stimulated asthmatics (p < 0.05 compared with the two other groups), this again reflecting decreased transfer of LT out of the lung rather than an increase in metabolism. Urinary excretion of LT metabolites occurred rapidly, the majority being excreted excreted within 6 h after instillation. LTE4, the major urinary LT metabolite identified by high-performance liquid chromatography, was a similar percentage concentration in the three groups and, thus, can be accurately used as an index of LT synthesis.

Metabolism of leukotriene D4 by rat peritoneal mast cells

Metabolism of sulfidopeptide leukotrienes, leukotrienes (LT) C4 and D4 by rat peritoneal mast cells was studied. Rat peritoneal mast cells converted LTD4 to LTE4 but not LTC4 to LTD4. The LTD4-metabolizing activity was equally distributed on the cell surface and inside cells, but not released to the extracellular milieu even when a considerable portion of histamine and the secretory granule enzymes were released. Among various enzyme inhibitors examined, o-phenanthroline, a metal chelator, and dithiothreitol significantly suppressed the LTD4-metabolizing activity of mast cell. These results would suggest that some metalloenzyme located on the cell surface is involved in the conversion of LTD4 to LTE4 by rat peritoneal mast cells.

Chemotactic activity in inflammatory bowel disease. Role of leukotriene B4

An important histologic feature of inflammatory bowel disease (IBD) is infiltration of the colonic mucosa with neutrophils. To investigate the nature of the chemotactic agents responsible for this infiltration, colonic mucosa from three normals and nine patients with inflammatory bowel disease (seven ulcerative colitis, two Crohn's colitis) was assayed for chemotactic activity for human neutrophils in vitro in a Boyden chamber. There was more (greater than 10-fold more) chemotactic activity in homogenates of inflammatory bowel disease mucosa than in homogenates of normal colonic mucosa. Analysis of the chemotactic activity in the inflammatory bowel disease mucosa revealed that most was lipid extractable. Moreover, when the lipid extract was fractionated by reverse-phase high-pressure liquid chromatography, the only fraction with significant chemotactic activity was the fraction that coeluted with leukotriene B4. The chemotactic response to IBD mucosa was blocked by anti-LTB4 antisera. The amount of chemotactic activity in lipid extracts of different inflammatory bowel disease specimens correlated well with the concentration of leukotriene B4 measured by UV absorbance (250 ng/g of mucosa). These data suggest that leukotriene B4 is an important stimulus to neutrophil chemotaxis in inflammatory bowel disease and, thus, may play a major role in the amplification of the inflammatory response in this condition.

Leukotrienes and other lipoxygenase products of arachidonic acid synthesized in the kidney

Lipoxygenase products are synthesized in the kidney. Rabbit medulla and murine and human glomeruli produce 12- and 15-hydroxy-5,8,10,14-eicosatetraenoic acid (HETE). Minor amounts of leukotrienes are formed under normal conditions, but it is likely that the resident renal cells are capable of synthesizing these metabolites. Rat glomeruli and papillae possess the enzymes necessary to process leukotriene C4 into leukotrienes D4 and E4. However, the enzyme activity of the papillae is masked due to the presence of an inhibitor detected in the 10,000 g supernate of the papillary homogenate. 12-HETE synthesis is markedly increased in glomeruli from rats with nephrotoxic serum nephritis and leukotriene B4 synthesis in glomeruli from rats with cationic bovine gamma-globulin-induced glomerulonephritis. In vivo consequences of the association between the resident glomerular cells and the bone marrow-derived cells have been studied in vitro in co-incubation experiments. Glomeruli release factors that stimulate the cyclo-oxygenase and lipoxygenase pathways in macrophages. Co-incubation of glomeruli, platelets, and polymorphonuclear leukocytes results in the formation of 12,20-diHETE and an excess of 12-HETE. Lipoxygenase products, regardless of their origin, modify the renal functions. Leukotriene C4 binds specifically to rat glomeruli and human cultured glomerular epithelial cells. Leukotrienes C4 or D4 administered in vivo cause renal vasoconstriction and a decline in the glomerular filtration rate. In vitro, these two sulfidopeptide leukotrienes promote epithelial cell proliferation and produce mesangial cell contraction. The lipoxygenase pathway is also implicated in the attachment of macrophages to glomeruli and in the oxidative burst of glomerular mesangial cells during phagocytosis. The future use of specific inhibitors of the synthesis or antagonists of the lipoxygenase products, particularly the leukotrienes, should provide a tool for evaluating the role of these metabolites in renal diseases.

Bioconversion of leukotriene C4 by rat glomeruli and papilla

Since leukotriene C4 (LTC4) may be locally synthesized by bone marrow-derived cells infiltrating the kidney in inflammatory renal diseases we examined the in vitro metabolism of exogenously added [3H] LTC4 by rat glomeruli and papilla using radiometric HPLC. Homogenized as well as intact glomeruli converted [3H] LTC4 mainly into [3H] LTE4 (83%) and, at a smaller extent, into [3H] LTD4 (4%). Intact [3H] LTC4 represented 13% of the sum of radioactive leukotrienes. Addition of L-cysteine resulted in accumulation of LTD4. In contrast, there was nearly no conversion of [3H] LTC4 (87% intact) in the presence of homogenized papilla. The metabolism of [3H] LTC4 by the glomeruli was time- and temperature-dependent. The 10,000 g supernatant and pellet of homogenized glomeruli both retained the ability to metabolize [3H] LTC4. The papillary 10,000 g supernatant was inactive, as found for the total homogenate, whereas the papillary 10,000 g pellet separated from its supernatant could transform [3H] LTC4 into its metabolites, LTD4 and LTE4. Addition of increasing amounts of papillary 10,000 g supernatant to homogenized glomeruli progressively protected [3H] LTC4 from its bioconversion. These results demonstrate that both glomeruli and papilla possess the gamma-glutamyl transpeptidase and dipeptidase necessary to process LTC4. However, the enzyme activity of the papilla is unmasked only when the inhibitor present in the 10,000 g supernatant is separated from the enzyme present in the pellet.