Divergent metabolic and immunoepigenetic responses in LPS-induced endotoxemia: a dose optimization study in male BALB/c mice

Lipopolysaccharide (LPS)-induced endotoxemia is widely used to model sepsis. This study aimed to identify the LPS dose that reliably induces hyperlactatemia, Murine Sepsis Score (MSS) ≥3 (clinically defined sepsis), dose-dependent differences in 48-hour survival, and optimal histone H3K18 lactylation in male BALB/c mice. Sixty-six male BALB/c mice (8–10 weeks) received intraperitoneal LPS at doses of 1, 2.5, 5, 10, 15, and 20 mg/kgBW (N = 11 per group). Blood lactate was measured at 6 h, MSS was used to assess disease severity, and survival was monitored for 48 h. Peritoneal macrophages were isolated, and histone H3K18 lactylation normalized to total H3 (H3K18la/H3) was quantified. All groups developed hyperlactatemia (>4 mmol/L) without dose-dependent differences (p = 0.289). Meanwhile, MSS increased proportionally with LPS dose (ρ = 0.785; p= <0.001) and negatively correlated with lactate (ρ=-0.527; p = 0.025). Survival showed a general dose-related downward trend that did not reach significance, with a non-monotonic exception at 5 mg/kgBW. Macrophage yield varied across groups, while H3K18la/H3 levels were markedly elevated at LPS 15 and 20 mg/kgBW. To conclude, lactate rises early and non-uniformly across LPS doses, limiting its value as severity marker in male BALB/c endotoxemia. MSS provides a more dose-responsive indicator of clinical severity. An LPS dose of 15 mg/kg provides an optimal model for studying immunometabolic and immunoepigenetic responses in sepsis.