Caffeine and paracetamol co-purify with C-reactive protein from surgical patients

Abstract Background Cell damage caused by surgical trauma leads to the release of intracellular adenosine triphosphate (ATP), which activates purinergic P2X7 receptors and induces the maturation and secretion of the pro-inflammatory cytokine interleukin-1β (IL-1β). Excessive IL-1β production following major abdominal surgery can drive uncontrolled inflammation and increase the risk of postoperative complications and organ dysfunction. Our previous work demonstrated that binding of phosphocholine (PC) to pentameric C-reactive protein (pCRP) mediates an anti-inflammatory function by suppressing ATP-induced IL-1β release through activation of nicotinic acetylcholine receptors. The present study aimed to investigate the anti-inflammatory potential of circulating CRP in surgical patients and to identify endogenous compounds associated with CRP that could interact with its established PC-binding pocket. Methods Pre- and postoperative blood samples were collected from patients undergoing major abdominal surgery. Whole blood cells, peripheral blood mononuclear cells, and monocytic THP-1 cells were primed with lipopolysaccharide and subsequently stimulated with ATP in the presence or absence of autologous plasma or CRP-depleted plasma. Compounds co-purifying with circulating CRP were identified by immunoprecipitation followed by liquid chromatography and mass spectrometry (LC/MS). Complementary molecular docking analyses were performed to predict the potential binding of the identified compounds to the established PC-binding pocket of CRP. Results Patient plasma inhibited ATP-induced IL-1β release in a dose-dependent manner. However, depletion of CRP did not significantly alter the inhibitory effect of postoperative plasma. Immunoprecipitation followed by LC/MS identified caffeine and paracetamol as the predominant compounds co-purifying with circulating CRP. Complementary molecular docking predicted that both compounds could occupy the established PC-binding pocket of CRP. Conclusions Together, the LC/MS and computational findings link caffeine and paracetamol to the previously described PC-dependent immunomodulatory functions of CRP and suggest that small molecules other than PC may influence CRP biology. These observations raise the possibility that commonly used perioperative medications modulate CRP-dependent immune functions, with potential implications for postoperative immune regulation. Further studies are warranted to establish the relationship between caffeine, paracetamol, and CRP.