Products Of Cyclooxygenase Pathway Research Articles

Intolerance to aspirin and the nonsteroidal anti-inflammatory drugs

A constant enigma has been the ability of aspirin and other structurally unrelated nonsteroidal anti-inflammatory drugs to induce non-IgE mediated allergic reactions. These reactions range from mild hypersensitivity to fatal anaphylaxis. Recent biochemical and pharmacologic studies involving the oxidative metabolism of arachidonic acid in different cells and tissues have provided insights into how this could conceivably occur. The products of cyclo-oxygenase and lipoxygenase pathways of arachidonic acid metabolism and their interactions may provide an approach, if not the solution, to the problem of aspirin intolerance.

Regulation of human B cell activation by prostaglandin E2. Suppression of the generation of immunoglobulin-secreting cells.

The role of prostaglandin E2 (PGE2) in the generation of immunoglobulin-secreting cells (ISC) from human peripheral blood B cells was examined. Initial studies demonstrated that monocyte (M phi)-mediated suppression of the generation of ISC in Staphylococcus aureus (SA)-stimulated cultures was mitigated by indomethacin, and thus suggested that the cyclooxygenase pathway products of arachidonic acid played a role in the regulation of B cell activation. The possibility that PGE2, one of the major products of this pathway generated by M phi-affected human B cell responses, was therefore investigated. PGE2 was found to cause concentration-dependent inhibition of the generation of ISC in pokeweed mitogen- or SA-stimulated B cell cultures supported by T cells. Studies were therefore carried out to determine whether PGE2 inhibited the production of necessary T cell factors or directly altered B cell responsiveness. Initially, the effect of PGE2 on the capacity of mitogen-stimulated cells to secrete a factor that supported the differentiation of B cells into ISC was investigated. Excessive numbers of M phi or PGE2 inhibited the production of B cell differentiation factor from mitogen-stimulated T cells. The effect of PGE2 on the capacity of B cells to differentiate into ISC was more complex. PGE2 inhibited the generation of ISC when B cells were stimulated with SA and B cell differentiation factor-containing T cell supernatants. PGE2-mediated inhibition of ISC generation was observed even when addition of PGE2 was delayed until after ISC first were detected in culture. By contrast, PGE2 caused only minimal inhibition of the generation of ISC cultures stimulated by T cell supernatants alone or protein A-free SA and T cell supernatants. These results suggested that SA-responsive B cells were particularly sensitive to inhibition by PGE2. Additional experiments supported the conclusion that B cell sensitivity to inhibition by PGE2 is augmented by the immunoglobulin cross-linking effects of protein A-containing SA. Overall, the results support the conclusion that PGE2 at physiologically relevant concentrations can influence human antibody responses by means of a direct inhibitory action on the responding B cell or an indirect one on the production of necessary T cell factors.

Direct and indirect effects of leukotriene D4 on the pulmonary and systemic circulations.

We investigated direct (vascular leukotriene receptor stimulation) and indirect (generation of cyclooxygenase metabolites) hemodynamic effects of leukotriene D4 (LTD4) in 6 conscious sheep. Pulmonary artery, pulmonary arterial wedge and systemic arterial pressures, and cardiac output were measured. From these parameters, pulmonary vascular resistance (PVR) and systemic vascular resistance (SVR) were calculated before and immediately after a rapid injection of LTD4 into the pulmonary artery. Injection of 0.1 micrograms/kg of LTD4 increased mean PVR to 421% of baseline (p less than 0.001). It produced a biphasic effect on SVR that, after an initial decrease of 18% (p less than 0.05), increased to 143% of baseline (p less than 0.05). Both PVR and SVR returned to baseline within 10 min. The same results were obtained when the dose of LTD4 was increased to 0.5 micrograms/kg. Dose-response curves with increasing doses of LTD4 )0.025 micrograms/kg to 0.5 micrograms/kg) revealed that the optimal dosage for maximal effect was 0.1 micrograms/kg. The effects of LTD4 (0.1 micrograms/kg) on the pulmonary circulation were completely blocked by the SRS-A antagonist, FPL-57231, as well as by indomethacin. In the systemic circulation, FPL-57231 blocked the biphasic effects of LTD4 on SVR, whereas indomethacin prevented the initial decrease without attenuating the subsequent increase in mean SVR (135% of baseline, p less than 0.05). We conclude that there are direct and indirect hemodynamic effects of LTD4: the systemic vasoconstrictor response is directly related to vascular leukotriene receptor stimulation, whereas activation of cyclooxygenase pathway products is responsible for the pulmonary vasoconstrictor and systemic depressor responses.

Regulation of human B cell proliferation by prostaglandin E2.

The role of prostaglandin E2 (PGE2) in the regulation of human B cell proliferation in vitro was examined. Initial studies demonstrated that monocyte (M phi)-mediated suppression of B cell proliferation in Staphylococcus aureus (SA)-stimulated cultures was diminished by indomethacin, and thus it was suggested that cyclooxygenase pathway products of arachidonic acid played a role in the regulation of B cell activation. The possibility that PGE2, one of the major products of this pathway generated by M phi, affected human B cell responses was therefore investigated. PGE2 was found to suppress B cell DNA synthesis and proliferation stimulated by SA in the presence or absence of B cell growth factor (BCGF)-containing T cell supernatants. Suppression was concentration-dependent; significant inhibition was observed in indomethacin-blocked cultures with 10(-10) to 10(-9) M PGE2. In contrast to the effect of PGE2 on SA-induced B cell proliferation, it had minimal effect on pokeweed mitogen (PWM)-stimulated B cell or T cell DNA synthesis. The effect of PGE2 on the generation of BCGF activity from mitogen-stimulated T cells was also examined. PGE2 (10(-7) M) did not inhibit the production of BCGF activity from PWM-stimulated T cells, or from T cells stimulated with the combination of phytohemagglutinin and phorbol myristate acetate. Thus, PGE2 inhibits B cell proliferation in response to SA but not PWM, and has little effect on the production of BCGF by T cells. These results indicate that PGE2 at physiologically relevant concentrations exerts selective regulatory effects on human B cell responses.

Effects of inhibitors of eicosanoid synthesis on insulin release by neonatal pancreatic islets

In the pancreatic islet, eicosanoids may arise from both cyclooxygenase- and lipoxygenase-dependent metabolism of arachidonic acid. The inclusion of inhibitors of selective steps in these pathways indicated that in cultured neonatal rat islets, arachinodic acid may be metabolised through both pathways, concurrent with insulin release stimulated by D-glucose, D-glyceraldehyde and 2-ketoisocaproate. The effects of the inhibitors suggested that the products of the lipoxygenase pathway were necessary for the stimulatory effects of nutrients to be observed. In contrast to glucose, where insulin release was stimulated in the presence of inhibitors of cyclooxygenase, the stimulatory action of D-glyceraldehyde, 2-ketoisocaproate and melittin was only minimally affected by these inhibitors, although it was inhibited by lipoxygenase inhibition. These findings support a major stimulatory role for products of the lipoxygenase pathway of arachidonic acid metabolism in nutrient-induced insulin secretion, and a negative or modulatory role of cyclooxygenase pathway products on glucose-stimulated insulin release in the neonatal islet.

PULMONARY HYPERTENSION(P-HTN) FOLLOWING BOLUS INFUSIONS OF PNEUMOCOCCUS(PNEU), OTHER GRAM+(GM+) BACTERIA, AND ZYMOSAN

Group B Strep(GBS) infusions cause acute P-HTN in several animal models. This response includes increased pulmonary artery pressure (Ppa), and resistance (PVR), and decreased pulmonary flow; systemic flows are often decreased. We infused a bolus of PNEU in 2, <2-wk-old, acutely-operated, anesthetized lambs and found that P-HTN occurred. We then studied this effect in 2 unanesthetized, chronically-instrumented piglets, <1 mo. old. Infused bacteria were heat-killed, washed and resuspended in buffer. The pigs received 1 item/day at 3-4.5 × 109 particles/dose. Qualitatively similar severe P-HTN resulted from bolus infusions of all PNEU strains tested (P1, P14, and P23) also from Group E, Group G, and a nontypeable Group B Strep, Staph aureus, and zymosan. Agitation, cyanosis, systemic hypotension, bradycardia and seizures also occurred. Latex particles, similar size as bacteria, had no effect at this dose. A mild, transient rise in Ppa and PVR was noted after a double dose, suggesting that a quantity of particles alone doesn't produce the same P-HTN. Indomethacin blocked the P-HTN caused by PNEU. We conclude that P-HTN is a nonspecific host response that can be elicited by a variety of GM+ bacteria. Agent(s) that may trigger the response are not unique to GBS or endotoxin. Cyclooxygenase pathway products appear to mediate this P-HTN which may be clinically important in shock occurring with GM+ infections.

Biochemical interaction of arachidonic acid and vitamin e in human platelets

The effect of α-tocopherol on the oxidative transformation of arachidonic acid was investigated in human platelets. The major products of lipoxygenase and cyclo-oxygenase pathways were separated by high performance liquid chromatography (HPLC) and thin layer chromatoggaphy (TLC) evaluated by scanning the radiochromatograms. This study differs from others in the vitamin E field in important aspects of its experimental design: the prelabeling of platelets with non-aggregating concentrations of 14C-arachidonic acid, and the addition of α-tocopherol as a colloidal suspension rather than as an ethanolic solution. A moderately potent but consistent reduction of apparent cyclo-oxygenase activity by α-tocopherol could be demonstrated by TLC and HPLC. This effect was best shown by the change of the HETE/HHT ratio which increased significantly in vitamin E-treated platelets. It was found to be dosedependent up to 1 MM a-tocopherol, the maximal concentration tested in this study. Alpha-tocopherol quinone was equally effective in this action.

The effect of duodenal administration of fatty acids, triolein, liquid paraffin and lecithin on plasma neurotensin-like immunoreactivity (p-NTLI) in the rat.

The effect of intraduodenal administration of various types of lipids on the concentration of p-NTLI has been studied on anesthetized rats. Oleic acid, sodium oleate, triolein, linoleic acid, linolenic acid, arachidonic acid, butyric acid, liquid paraffin, phosphatidyl choline (lecithin) and saline were administered. Oleic acid, triolein, linoleic acid and linolenic acid significantly increased the integrated response of p-NTLI. The maximal concentration of p-NTLI was reached 40 min after administration of oleic acid. However after instillation of triolein, the maximal concentration was reached at 100 min which was significantly later. The results indicate that the response of p-NTLI following administration of fat into the duodenum of rats is a specific event caused by fatty acids rather than by lipophilic substances in general. Of the substances tested 18-carbon fatty acids were the most effective in increasing the concentration of p-NTLI. Shorter- or longer-chain fatty acids were less effective. The degree of unsaturation, i.e. the presence of one or more double bounds is also of importance. Triglycerides seem to be hydrolysed to fatty acids before they may bring about an increase in the concentration of p-NTLI. The charge of lipids seems to be critical since the sodium salt of oleic acid had limited effects. Arachidonic acid did not change the integrated response of p-NTLI indicating that products of cyclooxygenase and lipoxygenase pathways are not involved in the fatty acid induced release of NTLI.

Local Effects of Synthetic Leukotrienes (LTC4, LTD4, and LTB4) in Human Skin

The local effects of intracutaneous injections into humans of 1-3 nmol of five products of arachidonic acid metabolism, leukotrienes (LT) C4, D4, E4, and B4 from the 5-lipoxygenase pathways and prostaglandin (PG) D2 from the cyclooxygenase pathway, were assessed clinically and histologically. In equimolar concentrations, LTC4, LTD4, and LTE4, elicited erythema and wheal formation, in which a wheal with central pallor was present up to 2 hr, and the erythema persisted as long as 6 hr. PGD2 elicited a wheal that lasted up to 1 hr and erythema that lasted up to 2 hr. The dermal vascular sites affected by LTD4 and PGD2 included capillaries, superficial and deep venules, and arterioles. LTB4 elicited a transient wheal and flare, followed in 3-4 hr by induration that was characterized by a dermal infiltrate comprised predominantly of neutrophils. The combination of LTB4 and PGD2 elicited tenderness and increased induration associated with a more intense neutrophil infiltration. Thus, the products of the 5-lipoxygenase pathway of arachidonic acid metabolism in nanomole amounts can induce cutaneous vasodilation with edema formation and a neutrophil infiltrate, and these responses are enhanced by a cyclooxygenase pathway product, PGD2.

The mechanism of the inhibitory effect of protease inhibitors on platelet aggregation

The inhibitory effect of protease inhibitors on platelet aggregation was investigated. The inhibitors tested were SBTI, leupeptin, aprotinin and FOY (a synthetic protease inhibitor).They completely inhibited the secondary aggregation of platelets induced by ADP or epinephrine. They also completely inhibited the platelet aggregation induced by collagen, thrombin or sodium arachidonate. The mechanism of their inhibitory effect was investigated, utilizing radioactive arachidonic acid and prostaglandin H2. All the protease inhibitors tested blocked the release of arachidonic acid from platelet phospholipids. SBTI and aprotinin inhibited the cellular synthesis of thromboxane B2 from arachidonic acid but not from prostaglandin H2, suggesting their inhibitory effect on cyclooxygenase. Leupeptin did not possess any effect on thromboxane synthesis either from arachidonic acid or from prostaglandin H2. FOY exhibited selective inhibition on the formation of thromboxane B2 both from arachidonic acid and from prostaglandin H2, yielding higher amount of other stable end products of cyclooxygenase pathway. Therefore, FOY seemed to possess an inhibitory effect on thromboxane synthetase and this drug could be an ideal antiplatelet without suppressing the formation of a natural inhibitor of platelet aggregation; prostaglandin I2.

Observations upon the pressor substance causing the rise in blood pressure following the termination of temporary, complete renal ischemia: Leo, Sidney D., Prinzmetal, Myron, and Lewis, Harvey A.: Am. J. Physiol. 131: 18, 1940

Background: Acetaldehyde, a main factor in alcohol-induced asthma, causes bronchoconstriction indirectly through histamine release; and tachyphylaxis in response to repeated inhalation of acetaldehyde is observed in patients with asthma. Objective: The study was designed to clarify the mechanism of tachyphylaxis in response to acetaldehyde-induced bronchoconstriction. Methods: We investigated the bronchial response to inhaled acetaldehyde in 10 patients with asthma who were treated with indomethacin in a double-blind, randomized, placebo-controlled, crossover fashion. Results: The mean acetaldehyde concentration causing a 20% fall in FEV1 with placebo increased significantly from 13.0 mg/ml (geometric SEM = 0.115) to 31.1 mg/ml (geometric SEM = 0.069) over a period of 1 hour (p < 0.01), whereas there was a slight but not significant tachyphylaxis during indomethacin treatment. The tachyphylactic effect, expressed as logarithmic value of the second PC20 minus logarithmic value of the first PC 20, was significantly (p < 0.05) reduced from 0.380 (0.066) with placebo treatment to 0.148 (0.094) with indomethacin treatment. Conclusion: These results suggest an important role of cyclooxygenase pathway products in decreased response to repeated inhalation of acetaldehyde in patients with asthma. (J Allergy Clin Immunol 1997;99:620-3.)

The cardiac output in rest and work in humid heart: Asmussen, Erling: Am. J. Physiol. 131: 54, 1940

Background: Acetaldehyde, a main factor in alcohol-induced asthma, causes bronchoconstriction indirectly through histamine release; and tachyphylaxis in response to repeated inhalation of acetaldehyde is observed in patients with asthma. Objective: The study was designed to clarify the mechanism of tachyphylaxis in response to acetaldehyde-induced bronchoconstriction. Methods: We investigated the bronchial response to inhaled acetaldehyde in 10 patients with asthma who were treated with indomethacin in a double-blind, randomized, placebo-controlled, crossover fashion. Results: The mean acetaldehyde concentration causing a 20% fall in FEV1 with placebo increased significantly from 13.0 mg/ml (geometric SEM = 0.115) to 31.1 mg/ml (geometric SEM = 0.069) over a period of 1 hour (p < 0.01), whereas there was a slight but not significant tachyphylaxis during indomethacin treatment. The tachyphylactic effect, expressed as logarithmic value of the second PC20 minus logarithmic value of the first PC 20, was significantly (p < 0.05) reduced from 0.380 (0.066) with placebo treatment to 0.148 (0.094) with indomethacin treatment. Conclusion: These results suggest an important role of cyclooxygenase pathway products in decreased response to repeated inhalation of acetaldehyde in patients with asthma. (J Allergy Clin Immunol 1997;99:620-3.)