No abstract

Peroxynitrite (ONOO-), an anion and a potent oxidant, generated by the interaction of nitric oxide (NO) and superoxide is able to induce apoptosis in HL-60 human leukemia cells in a time- and concentration-dependent manner. Characteristic morphology of apoptosis can be observed 3 h after HL-60 cells are exposed to 10 microM ONOO-. Treatment of HL-60 cells with increasing concentrations of ONOO- from 1 to 100 microM confirms the concentration dependence of apoptosis as evidenced by: 1) degradation of nuclear DNA of these cells into integer multiples of approximately 200 base pairs; 2) colorimetric DNA fragmentation assay; and 3) evidence of condensation of chromatin and nuclear fragmentation shown by propidium iodide staining. Under the same conditions, peroxynitrite causes apoptosis in another transformed cell line, U-937 cells, but is ineffective at inducing apoptosis in normal endothelial cells derived from human umbilical cord and normal human peripheral blood mononuclear cells. This direct evidence of peroxynitrite inducing apoptosis implicated a new function of this potent oxidant.

The effects of dietary fish-oil fatty acids on the function of the 5-lipoxygenase pathway of peripheral-blood polymorphonuclear leukocytes and monocytes were determined in seven normal subjects who supplemented their usual diet for six weeks with daily doses of triglycerides containing 3.2 g of eicosapentaenoic acid and 2.2 g of docosahexaenoic acid. The diet increased the eicosapentaenoic acid content in neutrophils and monocytes more than sevenfold, without changing the quantities of arachidonic acid and docosahexaenoic acid. When the neutrophils were activated, the release of [3H]arachidonic acid and its labeled metabolites was reduced by a mean of 37 per cent, and the maximum generation of three products of the 5-lipoxygenase pathway was reduced by more than 48 per cent. The ionophore-induced release of [3H]arachidonic acid and its labeled metabolites from monocytes in monolayers was reduced by a mean of 39 per cent, and the generation of leukotriene B4 by 58 per cent. The adherence of neutrophils to bovine endothelial-cell monolayers pretreated with leukotriene B4 was inhibited completely, and their average chemotactic response to leukotriene B4 was inhibited by 70 per cent, as compared with values determined before the diet was begun and six weeks after its discontinuation. We conclude that diets enriched with fish-oil-derived fatty acids may have antiinflammatory effects by inhibiting the 5-lipoxygenase pathway in neutrophils and monocytes and inhibiting the leukotriene B4-mediated functions of neutrophils.

1. Lipoxin A4 (LXA4) and lipoxin B4 (LXB4) have been evaluated for their capacities to modulate neutrophil (PMN) migration and endothelial cell adherence using compounds prepared by total chemical synthesis. 2. Increased PMN migration was seen with concentrations of LXA4 from 10(-9) mol/l to 10(-7) mol/l. LXA4 was 100-fold less potent than leukotriene B4 (LTB4) and it elicited only one-half of the maximal response of LTB4. 3. The (5S,6S,15S)-isomer of LXA4 induced only a weak migratory response and LXB4 was inactive, suggesting that the activity of LXA4 was stereospecific. 4. Modified chequerboard analysis indicated that LXA4 was a chemokinetic agent. 5. Preincubation of PMN with increasing concentrations of LXA4 induced a very similar dose- and time-dependent inhibition of the subsequent response to 10(-7) mol/l LTB4 or 10(-7) mol/l N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP). The inhibition was observed at 10(-10) mol/l LXA4; the concentration which produced 50% inhibition was 10(-8) mol/l and 100% inhibition of PMN locomotion occurred at 10(-6) mol/l LXA4. 6. The (5S,6S,15S)-isomers of LXA4 and LXB4 were 5- and 100-fold less potent than LXA4, respectively, in suppressing LTB4- or FMLP-induced PMN migration. 7. Preincubation of PMN with LXA4 led to a suppression of calcium mobilization, as assessed by Quin2-AM fluorescence, when the cells were subsequently stimulated under optimal conditions by LTB4 or FMLP. 8. These results suggest that the inhibitory activity of lipoxins may be related to the capacity of these molecules to regulate calcium ion mobilization.

This study was performed to determine whether lipoxin A4 (LXA4) inhalation in asthmatic subjects has an effect on airways response. Eight subjects (six asthmatic, two normal) attended for bronchial inhalation challenge with LXA4. In three of these subjects (two asthmatics, one normal) blood pressure, pulse, and symptoms before and after challenge were recorded. Subsequently five male patients with mild asthma (22 to 34 yr of age) reattended for bronchial inhalation challenge with either leukotriene C4 (LTC4) or the combination of LTC4 and 1 x 10(-4) M LXA4. After inhalation of each dose of agonist SGaw and V25 were measured. Airway responsiveness was determined by the concentration of agonist in the nebulizer required to induce a 35% fall in SGaw (PC35). There was no effect of LXA4 inhalation on SGaw, V25, blood pressure, pulse, or symptoms. There was a significant shift of the SGaw and V25 dose-response curve to the right after inhalation challenge with LTC4 combined with 1 x 10(-4) M LXA4 as compared with that after inhalation challenge with LTC4 alone (p less than 0.01 and p less than 0.025, respectively). Thus, LXA4 may modulate LTC4-induced airway obstruction and may act as an endogenous sulfidopeptide leukotriene receptor antagonist.