Acute ketone monoester ingestion increases monocyte lysine β-hydroxybutyrylation and plasma β-hydroxybutyrate amino acid conjugates in humans

Endogenous ketosis during fasting can induce β-hydroxybutyrylation of lysine residues on proteins (known as Kbhb) in human immune cells and increase circulating β-hydroxybutyrate (BHB) amino acid conjugates, both of which are hypothesized to have functional physiological consequences. It remains unknown if similar modifications occur with acute consumption of an exogenous ketone monoester (KME) supplement [(<i>R</i>)-3-hydroxybutyl (<i>R</i>)-3-hydroxybutyrate], which robustly increases circulating BHB. Thirteen healthy adults (7 females; 6 males, age: 28 ± 7 yr) consumed 0.750 g/kg body mass KME with blood samples collected before and after 2 h, coinciding with peak plasma BHB concentration. Monocytes (CD14⁺) were isolated by negative immunomagnetic selection for Kbhb assessment by immunoblotting. Plasma BHB-amino acid conjugates were quantified by mass spectrometry. Blood BHB concentration significantly increased after KME consumption (<i>P</i> < 0.0001), peaking at 2 h (5.0 ± 0.8 mmol/L). Compared with baseline, monocyte Kbhb was significantly increased after 2 h (∼70% increase; <i>P</i> = 0.004). Plasma BHB-amino acid conjugates, including BHB-phenylalanine, -leucine, -valine, and -methionine were also increased at 2 h (<i>P</i> < 0.0001). Changes in capillary blood BHB and BHB-amino acid concentrations were positively correlated (<i>r</i> ≥ 0.58; <i>P</i> ≤ 0.046), suggesting a dose-dependent increase. Acute high-dose KME ingestion increases monocyte lysine Kbhb and plasma BHB amino acid conjugates in healthy humans, highlighting the possible immunomodulatory and systemic signaling effects of raising BHB through exogenous ketone supplementation.<b>NEW & NOTEWORTHY</b> This study provides the first in vivo evidence that exogenous ketone supplementation elevates lysine Kbhb in monocytes of healthy humans. Exogenous ketone supplementation also increased recently discovered BHB-amino acid conjugates, including BHB-phenylalanine, -leucine, -valine, and -methionine. These results highlight the potential immunomodulatory and systemic signaling effects of exogenous ketones.