Hyperammonemia associated with liver cirrhosis plays a major role in the pathogenesis of hepatic encephalopathy (HE). The gut is a major source of ammonia (NH3) that contributes to systemic hyperammonemia in HE. Probiotic bacteria have shown benefits in the treatment of HE although the underlying mechanism is not completely understood. We engineered Escherichia coli Nissle 1917 bacterium (EcN) to consume NH3 and convert it to arginine in the gut (SYNARG). To enhance the beneficial effect of NH3 consumption, we further engineered the EcN to synthesize the short chain fatty acid butyrate in the gut (SYNARG+BUT). Both strains were tested in two experimental models of cirrhosis and HE: thioacetamide (TAA) or bile duct ligation (BDL). Methods: Cirrhosis was induced in BALB/c mice by treatment with TAA for 4 weeks, and in SD rats by BDL for 5 weeks (W). TAA-treated mice were gavaged with a daily dose of 1x1010 colony forming units (CFU) of SYNARG. BDL rats received 1x1012 CFU with SYNARG or SYNARG+BUT for 4 W. Plasma NH3 (mmol/L) was measured in both models at baseline (BL) and after treatment, with an additional measurement at 3 W post-BDL. Results: TAA mice developed hyperammonemia (BL: 22.4±3.3 to 4 W: 82.4±8.7, p<0.05) which was attenuated after SYNARG treatment (45.5±4.7, p<0.05). Longitudinal analysis in Veh-BDL rats developed hyperammonemia at 3 W (BL: 68.8±5.7 to 121.6±9.8, p<0.01) which was further increased after 5 W (158.8±22.0, p<0.001 vs BL and 3 W). At 3 W, SYNARG+BUT prevented a significant increase in blood NH3 in BDL rats (99.6±8.7, p<0.05 vs BL). Both SYNARG+BUT (115.9±17.2) and SYNARG (127.9±15.5) were protective in preventing further increase in blood NH3 from 3 to 5 W, as observed in Veh-BDL rats. Moreover, the analysis between groups at 5 W showed that SYNARG+BUT reduces NH3 compared to Vehicle-BDL rats (p<0.05). Conclusion: EcN, engineered to consume NH3 in the gut, is an effective approach to lower plasma NH3 in models of cirrhosis. Thus, the therapeutic potential of these engineered EcN strains should be further evaluated in patients with cirrhosis and HE.
