REGULATION OF RAT PULMONARY ENDOTHELIAL-CELL INTERLEUKIN-6 PRODUCTION BY BLEOMYCIN - EFFECTS OF CELLULAR FATTY-ACID COMPOSITION

Previous studies have shown upregulation of lung cell interleukin-6 (IL-6) production in bleomyc-ininduced pulmonary fibrosis. To further elucidate the regulatory mechanisms governing this disease, the effects of bleomycin on the production of the pleiotropic cytokine, IL-6, were investigated in lung endothelial cells. Rat pulmonary artery endothelial cells were treated with bleomycin at doses previously shown to be effective in upregulating cytokine production in these cells, and the conditioned media was collected and assayed for IL-6 activity. The results show that these endothelial cells constitutively produced IL-6 and that bleomycin increased the production in a time- and dose-dependent manner. Feeding rats diets deficient in n-6 fatty acids is known to ameliorate bleomycin-induced lung fibrosis. In order to examine if fatty acids could modulate IL-6 production in vitro, cells were lipid depleted and then supplemented with 18:1n-9, 18:2n-6, or 18:3n-3 fatty acids, and the effects of bleomycin on IL-6 production reexamined. This regimen resulted in significant depletion of arachidonate in the 18:1n-9 and 18:3n-3 supplemented cells, which was associated with significantly reduced IL-6 production relative to the 18:2n-6-supplemented cells, both constitutively and when stimulated with bleomycin. Preincubation with indomethacin did not significantly inhibit the production of IL-6 by all three groups of cells, nor did supplementation with a stable prostacyclin analog increase n-6 production. These results suggest that endothelial cell IL-6 production is not directly dependent on prostacylin or other cyclooxygenase metabolites but may require or be upregulated by 18:2n-6 and/or metabolites derived from it. This conclusion would be consistent with the previous in vivo observation that diets low in 18:2n-6 have a protective effect on bleomycin-induced pulmonary fibrosis.