Introduction Ammonia reduces neutrophil phagocytic and bacteriocidal capacity. Neutrophils swell in response to ammonia exposure and activation of the p38-MAPK pathway has been implicated in protecting the neutrophil against osmotic shock and in normalising neutrophil phagocytic dysfunction. (Shawcross et al., Hepatology 2008) In patients with acute and chronic liver failure with elevated arterial ammonia, we hypothesised that treating neutrophils ex vivo with isoproterenol, a β adrenergic receptor and p38-MAPK agonist would improve neutrophil phagocytic capacity.
Aim Within the context of an ongoing longitudinal study of neutrophil function in 100 patients with acute (ALF) and chronic liver failure we investigated the role of ex vivo incubation of neutrophils with an exogenous ammonia load, a p38-MAPK agonist (isoproterenol) and the specific p38-MAPK antagonist SB203580 (Calbiochem) on neutrophil function in a cohort of 10 patients (5 ALF and 5 chronic) all with elevated arterial ammonia concentration.
Method Phagocytic capacity in heparinised whole blood was quantitatively determined by flow cytometry using FITC-labelled opsonised E. coli at baseline, and following incubation for 90 min with ammonium chloride (200 μmol/l), isoproterenol (2 μmol/l) or SB203580 (40 μmol/l) at 37°C.
Results The ALF patients (drug-induced n=3 and seronegative n=2) had a median SOFA score of 17 (IQR 16–18) and APACHE II score of 24 (22–28). The patients with cirrhosis (alcohol n=3; HCV; NASH) had a median MELD score of 10 (7–27). The median arterial ammonia level in the ALF group was 96 (49–158) and in the chronic group was 97 (63–122) μmol/l. Baseline bactericidal capacity was 49% (36–57) in the ALF group and 75% (67–84) in the chronic group compared to >85% in healthy controls and a median of 82% in a septic control group without liver disease. The exogenous ammonia load further reduced neutrophil phagocytic capacity by a median of 8% (3–16). The p38-MAPK agonist significantly abrogated the ammonia-induced phagocytic impairment and improved bacteriocidal capacity (p=0.003). The p38-MAPK antagonist however, exacerbated the ammonia-induced reduction in neutrophil phagocytic capacity by a median of 15% (4–24); p=0.0015.
Conclusion These data show that in patients with acute and chronic liver failure and elevated arterial ammonia that neutrophil bacteriocidal capacity is disabled. Activation of the p38-MAPK pathway serves as an important cellular protective mechanism against ammonia-induced impairment and further trials of p38-MAPK agonists in patients with liver failure are warranted.
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