Pro-inflammatory and anti-inflammatory compounds exert similar effects on P-glycoprotein in blood-brain barrier endothelial cells

Objectives The effects of anti-inflammatory glucocorticoids dexamethasone (DX) and hydrocortisone (HC), pro-inflammatory cytokine interleukin-1 beta (IL-1 beta) and dietary long-chain polyunsaturated fatty acids (PUFAs) on expression and activity of the ATP-binding cassette transporter P-glycoprotein (P-GP) were studied in porcine brain endothelial cells (PBECs). Methods Primary PBECs were treated for 24 h with glucocorticoids, IL-1 beta and long-chain PUFAs. P-GP activity was determined by measuring intracellular calcein accumulation and P-GP expression by Western blotting. The effect of PUFAs on membrane fluidity was assessed by fluorescence recovery after photobleaching (FRAP). Key findings Dexamethasone, HC and IL-1 beta significantly increased P-GP expression and activity. The effect of IL-1 beta was attenuated by the IL-1 receptor antagonist (IL-1RA). This is the first report of the combined actions of IL-1 beta and IL-1RA on P-GP expression and the first evidence of glucocorticoid-mediated P-GP up-regulation in PBECs. Arachidonic acid (AA), docosahexaenoic acid (DHA) and eicosapentenoic acid (EPA) significantly decreased P-GP activity without affecting expression or membrane fluidity. AA, DHA and EPA counteracted IL-1 beta-mediated increases in P-GP activity, while AA and EPA, but not DHA, counteracted glucocorticoid-mediated increase in P-GP activity. Conclusions While glucocorticoids and IL-1 beta possess opposing actions in inflammation, they demonstrate functional consistency by increasing P-GP expression and activity in PBECs.