Serum level of total histone 3, H3K4me3, and H3K27ac after non-emergent cardiac surgery suggests the persistence of smoldering inflammation at 3 months in an adult population

BACKGROUND: Despite clinical relevance of immunological activation due to histone leakage into the serum following cardiac surgery, long-term data describing their longitudinal dynamic are lacking. Therefore, this study examines the serum levels of histone 3 (tH3) and its modifications (H3K4me3 and H3K27ac) alongside immune system activation during the acute and convalescence phases of cardiac surgery. METHODS: Blood samples from fifty-nine individuals were collected before non-emergent cardiac surgery (t(pre-op)) and 24 h (t(24hr)), seven days (t(7d)), and three months (t(3m)) post-procedure to examine serum levels of tH3, H3K4me3, and H3K27ac. Serum heat shock protein-60 (HSP-60) was a surrogate of the cellular damage marker. Serum C-reactive protein (CRP) and interleukin 6 (IL-6) assessed smoldering inflammation. TNFα and IL-6 production by whole blood in response to lipopolysaccharide (LPS) evaluated immunological activation. Electronic medical records provided demographic, peri-operative, and clinical information. Paired longitudinal analyses were employed with data expressed as mean and standard deviation (X ± SD) or median and interquartile range (Me[IQ25; 75%]. RESULTS: Compared to pre-operative levels (tH3(Pre-op) = 1.6[0.33;2.4]), post-operative serum tH3 significantly (p > 0.0001) increased after heart surgery (tH3(24hr) = 2.2[0.3;28]), remained elevated at 7 days (tH3(7d) = 2.4[0.37;5.3]), and at 3 months (tH3(3m) = 2.0[0.31;2.9]). Serum H3K27ac was elevated at 24 h (H3K27ac(24hr) = 0.66 ± 0.51; p = 0.025) and seven days (H3K27ac(7d) = 0.94 ± 0.95; p = 0.032) as compared to baseline hours (H3K27ac(Pre-op) = 0.55 ± 0.54). Serum H3K4me3 was significantly diminished at three months (H3K4me3(Pre-op) = 0.94 ± 0.54 vs. H3K27ac(3m) = 0.59 ± 0.89; p = 0.008). tH3 correlated significantly with the duration of anesthesia (r(2) = 0.38). In contrast, HSP-60 normalized seven days after surgery. Peri-operative intake of acetaminophen, but no acetylsalicylic acid (ASA), acid, ketorolac or steroids, resulted in the significant depression of serum H3K4me3 at 24 h (H3K4me3(acetom-) = 1.26[0.71; 3.21] vs H3K4me3(acetom+) = 0.54[0.07;1.01]; W[50] = 2.26; p = 0.021). CRP, but not IL-6, remained elevated at 3 months compared to pre-surgical levels and correlated with tH3(24hrs) (r(2) = 0.43), tH3(7d) (r(2) = 0.71; p < 0.05), H3K4me3(7d) (r(2) = 0.53), and H3K27ac(7d) (r(2) = 0.49). Production of TNFα by whole blood in response to LPS was associated with serum tH3(24hrs) (r(2) = 0.67). Diminished H3K4me3(24hrs,) H3K27ac(24hrs), and H3K27ac(3m), accompanied the emergence of liver failure. CONCLUSIONS: We demonstrated a prolonged elevation in serum histone 3 three months after cardiac surgery. Furthermore, histone 3 modifications had a discrete time evolution indicating differential immune activation.