Arachidonate metabolites are potent biological mediators affecting multiple cellular functions. Although prostaglandins of the E series, which are products of the cyclooxygenase pathway, have been known as inhibitors or down-regulators of fibroblast proliferation and collagen synthesis, the more recently discovered products of the 5-lipoxygenase pathway have not been as extensively investigated with regard to fibroblast function. In this study, a sulfidopeptide product of the lipoxygenase pathway, leukotriene C4 (LTC4), was examined for its ability to modulate rat lung fibroblast collagen synthesis and proliferation in vitro. The data revealed the ability of LTC4 and to a lesser extent leukotriene D4 (LTD4) to stimulate collagen synthesis in a dose-dependent (10(-11)-10(-8) M) manner without affecting cellular proliferation as determined by radiolabeled thymidine incorporation; 1 nM LTC4 caused an 85% (p less than 0.02) increase above untreated controls in [3H]proline incorporation into collagenous protein in the media, which was blocked by the putative leukotriene receptor antagonist FPL55712 (10 microM) and inhibited by cycloheximide and actinomycin D. This LTC4 stimulatory effect was slightly more specific for collagen synthesis vs noncollagenous protein synthesis but was not accompanied with any change in the collagen type composition. Binding of [3H]LTC4 to these cells was specific, reversible, and saturable, with a Kd of 1.8 +/- 0.95 nM. Under equilibrium conditions, there was an estimated 2.39 X 10(4) receptors per cell. This binding was also inhibited by 10 microM FPL55712. Competitive binding studies show specificity of this binding for LTC4 relative to LTD4 and FPL55712. Furthermore, no significant conversion of LTC4 to LTD4 or leukotriene E4 was noted during the binding studies.(ABSTRACT TRUNCATED AT 250 WORDS)

Aspirin and nonsteroidal antiinflammatory drugs (NSAIDs) damage the gastroduodenal epithelium by two mechanisms: direct toxic effects and effects related to the depletion of endogenous prostaglandins. The prostaglandin-depleted mucosa has increased susceptibility to luminal aggressive factors, yet the role of acid in the pathogenesis of the NSAID ulcer is controversial. In humans, standard doses of H2-receptor antagonists prevent only duodenal injury and provide no protection for the gastric mucosa. It is not known whether more potent suppression of acid can prevent NSAID damage. Twenty healthy volunteers were randomized to a double-blind, placebo-controlled, crossover study to determine if omeprazole, 40 mg/day prevents gastroduodenal injury due to two weeks of aspirin administration (650 mg four times a day). The severity of mucosal injury was quantitated by endoscopy and stratified by a scale from 0 (normal) to 4 (ulcer). Fourteen of the 20 subjects had less gastric injury during cotherapy with omeprazole. All six with no difference received aspirin plus omeprazole in the first treatment period. Omeprazole significantly decreased aspirin-induced gastric mucosal injury (P < 0.001, Wilcoxon signed-rank test). Omeprazole protected 85% of subjects from extensive gastric erosions (often associated with evidence of intraluminal bleeding) or ulceration, whereas 70% of the subjects developed aspirin-induced grades 3 and 4 gastric injury on placebo (P < 0.01 by chi 2). No subject taking omeprazole developed duodenal injury of any grade, while 50% taking placebo developed erosions and 15% had ulcer (P < 0.001). Medication side effects were mild in the majority of subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

The macrophage is a source of many mediators with direct and indirect fibrogenic potential. In this study, release of macrophage-derived fibroblast growth factor (MDGF) activity by murine peritoneal macrophages is examined with regard to its regulation by arachidonate metabolites. Upon stimulation with 10 micrograms/ml lipopolysaccharide (LPS), resident peritoneal macrophages from CBA/J mice released MDGF activity into media rapidly, reaching maximal levels in approximately 1 h. Lysates of these stimulated cells also revealed significantly increased cell-associated MDGF activity, composing 45% of the total assayable activity. This activity, as assayed by radioactive thymidine incorporation by primary cultures of rat lung fibroblasts, was separable from interleukin-1 (IL-1) activity by reverse phase high performance liquid chromatography (HPLC). Furthermore, purified murine IL-1 had no MDGF activity in this assay system. This stimulated MDGF release was enhanced by the cyclooxygenase inhibitors indomethacin, ibuprofen, and aspirin at micromolar concentrations, but inhibited in a dose-dependent manner by prostaglandin E2 (PGE2). On the other hand, nordihydroguaiaretic acid (NDGA), a lipoxygenase inhibitor was inhibitory at 0.1 and 0.4 microM but not at 2.5 microM. Zymosan-stimulated macrophages also markedly increased MDGF release, albeit with a different time course which was characterized by a delay of approximately 7 h before peak levels were attained. Such stimulation, which is known to cause increased lipoxygenase activity, was also inhibited by 0.5 microM NDGA. In contrast, the lipoxygenase pathway products leukotrienes B4 (LTB4) and C4 (LTC4) stimulated MDGF release in a dose-dependent (10(-10)-10(-8) M) manner, with LTC4 being more potent on a per unit dose basis. Stimulation by LTC4 was inhibited by the putative leukotriene receptor antagonist, FPL55712, while LTD4 and LTE4 did not stimulate MDGF release, thus suggesting the mediation of this effect by specific LTC4 receptors. These data suggest also that products of the cyclooxygenase and lipoxygenase pathways are potentially important both as exogenous (ie, derived from cells other than the macrophage itself) and auto- or self-regulators of macrophage MDGF release. This, in turn, implies that cyclooxygenase products are antifibrogenic and important in maintaining or returning to the quiescent or normal state, whereas the lipoxygenase products are profibrogenic and important in induction of fibrosis or wound-healing and tissue repair. Any alteration in the balance between these two pathways may result in either a desirable or a harmful outcome.

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