Acute effects of ketone monoester ingestion on monocyte phenotype and cytokine secretion in healthy humans

Beta-hydroxybutyrate (BHB) exerts anti-inflammatory effects in cell and animal models, but translational work in humans remains limited. We investigated how exogenous ketone monoester (KME) ingestion in vivo and BHB treatment of human whole blood and monocytes ex vivo influence cytokine secretion and phenotype. Healthy adults (N=13, age=28±7) consumed a KME supplement containing (R)-3-hydroxybutyl (R)-3-hydroxybutyrate (0.750g/kg of body mass). Venous blood samples were taken before and 2h post-ingestion. Cytokine secretion from lipopolysaccharide (LPS)-stimulated whole blood (4h) and monocyte (24h) cultures were used to determine BHB's anti-inflammatory effects, while flow cytometry assessed monocyte phenotype and polarization. Blood BHB concentration increased after KME consumption (P<0.0001), peaking after 2h (5.0±0.8 mmol/L). Total white blood cells increased 2h after KME consumption compared to baseline (P=0.006), mainly due to higher total neutrophils (P=0.0004). Tumour necrosis factor (TNF)-α secretion in LPS-stimulated (1 ng/mL) whole blood collected before and 2h after KME consumption was unaltered (P=0.616), suggesting that in vivo exposure to increased BHB did not alter blood leukocyte cytokine secretion. However, ex vivo BHB co-treatment of LPS-stimulated whole blood and monocyte cultures decreased TNF-α secretion in a dose-dependent manner (P≤0.0012). BHB co-treatment during 24-hour LPS stimulation also decreased monocyte CD80+ ("M1-like") expression. Lowering pH of whole blood cultures independent of BHB also reduced TNF-α secretion, albeit to a lesser extent than BHB (P=0.012). Collectively, BHB lowers pro-inflammatory monocyte marker expression ex vivo and dose-dependently reduces TNF-α production in LPS-stimulated whole blood and monocyte cultures. These effects appear to be partly mediated by acidification of the extracellular environment.