Genetically engineered E. coli Nissle attenuates hyperammonemia and prevents memory impairment in bile-duct ligated rats

Abstract

Hyperammonemia associated with chronic liver disease (CLD) is implicated in the pathogenesis of hepatic encephalopathy (HE). The gut is a major source of ammonia production that contributes to hyperammonemia in CLD and HE and remains the primary therapeutic target for lowering hyperammonemia. As an ammonia-lowering strategy, Escherichia coli Nissle 1917 bacterium was genetically modified to consume and convert ammonia to arginine (S-ARG). S-ARG was further modified to additionally synthesize butyrate (S-ARG + BUT). Both strains were evaluated in bile-duct ligated (BDL) rats; experimental model of CLD and HE.

Methods: One-week post-surgery, BDLs received non-modified EcN (EcN), S-ARG, S-ARG + BUT (3x10¹¹ CFU/day) or vehicle until sacrifice at 3 or 5 weeks. Plasma (ammonia/pro-inflammatory/liver function), liver fibrosis (hydroxyproline), liver mRNA (pro-inflammatory/fibrogenic/anti-apoptotic) and colon mRNA (pro-inflammatory) biomarkers were measured post-sacrifice. Memory, motor-coordination, muscle-strength and locomotion were assessed at 5 weeks.

Results: In BDL-Veh rats, hyperammonemia developed at 3 and further increased at 5 weeks. This rise was prevented by S-ARG and S-ARG + BUT, whereas EcN was ineffective. Memory impairment was prevented only in S-ARG + BUT vs BDL-Veh. Systemic inflammation (IL-10/MCP-1/endotoxin) increased at 3 and 5 weeks in BDL-Veh. S-ARG + BUT attenuated inflammation at both timepoints (except 5-week endotoxin) vs BDL-Veh, whereas S-ARG only attenuated IP-10 and MCP-1 at 3 weeks. Circulating ALT/AST/ALP/GGT/albumin/bilirubin and gene expression of liver function markers (IL-10/IL-6/IL-1β/TGF-β/α-SMA/collagen-1α1/Bcl-2) were not normalized by either strain. Colonic mRNA (TNF-α/IL-1β/occludin) markers were attenuated by synthetic strains at both timepoints vs BDL-Veh.

Conclusion: S-ARG and S-ARG + BUT attenuated hyperammonemia, with S-ARG + BUT additional memory protection likely due to greater anti-inflammatory effect. These innovative strategies, particularly S-ARG + BUT, have potential to prevent HE.

Keywords: E. coli Nissle; Hepatic encephalopathy; ammonia; arginine; bile-duct ligature; butyrate; cirrhosis; inflammation; memory; probiotics.