Acetylation: a novel method for modulation of the immune response following trauma/hemorrhage and inflammatory second hit in animals and humans

Background: Hemorrhage induces an imbalance in histone acetyl transferase/histone deacetylase (HAT/HDAC) ratio. Correction of this imbalance with histone deacetylase inhibitors (HDACI) improves survival. We aimed to identify whether this was due to modulation of the post-shock immune response. Methods: We established a "two-hit" model in which rats (n=11; 5-6/group) and humans (n=10; 5/group) sustained trauma/hemorrhage, followed by exposure of splenic leukocytes to lipopolysaccharide (LPS, 10ng/mL) for 8 or 24 hours. The leukocytes were treated with: No treatment, SAHA (suberoylanilide hydroxamic acid, HDACI, 400nM), or Garcinol (HAT inhibitor, 20μM). Results: Hemorrhage in the animals produced severe shock and a pro-inflammatory state. SAHA reduced TNFa secretion in the hemorrhaged leukocytes after LPS "second-hit" (34.0%, P = .003), whereas it increased transcript levels of TNFa and IL-1b (2.1±0.3 and 5.1± 2.2 fold respectively, P < .05). Leukocytes from trauma patients displayed 2 distinct responses to SAHA after LPS "second-hit," with markedly increased or decreased cytokine levels. Conclusions: SAHA normalizes TNFa levels following hemorrhage and LPS "second hit" in the rats, whereas trauma patients respond to SAHA in 2 distinct patterns, with either marked attenuation or exaggeration of inflammatory cytokines. Cytokine levels were independent of gene expression, implicating acetylation of non-nuclear proteins as the dominant regulatory mechanism.