Mechanisms of modulation of cytokine release by human cord blood monocytes exposed to high concentrations of caffeine

BACKGROUND: Serum caffeine concentrations >20 mu g/ml (100 mu mol/l) in infants treated for apnea of prematurity increases TNF-alpha and decreases IL-10, changes that perhaps are linked to comorbidities. We hypothesize that this proinflammatory cytokine profile may be linked to differential binding of caffeine to adenosine receptor subtypes (AR), inhibition of phosphodiesterases (PDEs), and modulation of toll-like receptors (TLR). METHODS: Lipopolysaccharide-activated cord blood monocytes (CBM) from 19 infants were exposed to caffeine (0-200 mu mol/l) with or without previous exposure to A(1)R, A(3)R, or PDE IV antagonists to determine changes in dose-response curves. Cytokines levels (enzyme-linked immunosorbent assay (ELISA)), intracellular cyclic adenosine monophosphate (cAMP) accumulation (enzyme immunoassay (EIA)), and TLR gene expression (real time qRT PCR) were measured. RESULTS: Caffeine at <= 100 mu mol/l decreased TNF-alpha levels (similar to 25%, P = 0.01) and cAMP. All caffeine concentrations decreased IL-10 levels (17-35%, P < 0.01). A(1)R, A(3)R, and PDE blockades decreased TNIF-alpha (31, 21, and 88%, P <= 0.01), but not IL-10. Caffeine further decreased TNF-alpha following A(3)R and PDE blockades. Caffeine concentrations directly correlated to TLR4 gene expression (r = 0.84; P < 0.001). CONCLUSION: Neither A(3)R, nor PDE blockades are involved in caffeine's modulation of cytokine release. by CBM at any concentration. Besides A(1)R blockade, caffeine's upregulation of TLR4 may promote inflammation at high concentrations.