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

BACKGROUND: Serum caffeine concentrations >20µg/mL (100 µM) in infants treated for apnea of prematurity increases TNF-α and decreases IL-10, change that perhaps is linked to co-morbidities. We hypothesize that this pro-inflammatory 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: LPS-activated cord blood monocytes (CBM) from 19 infants were exposed to caffeine (0 to 200 µM) 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 (ELISA), intracellular cAMP accumulation (EIA) and TLR gene expression (real time qRT PCR) were measured. RESULTS: Caffeine at ≤100µM decreased TNF-α levels (~25%, p=0.01) and cAMP. All caffeine concentrations decreased IL-10 levels (17 to 35%, p<0.01). A(1)R, A(3)R and PDE blockades decreased TNF-α (31%, 21%, and 88%, p≤0.01), but not IL-10. Caffeine further decreased TNF-α 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 up-regulation of TLR4 may promote inflammation at high concentrations.