An Engineered Nissle Improves Hyperammonemia and Survival in Mice and Shows Dose-dependent Exposure in Healthy Humans

The intestine is a major source of systemic ammonia (NH); thus, capturing part of gut NH may mitigate disease symptoms in conditions of hyperammonemia such as urea cycle disorders and hepatic encephalopathy. As an approach to the lowering of blood ammonia arising from the intestine, we engineered the orally delivered probiotic Nissle 1917 to create strain SYNB1020 that converts NH to l-arginine (l-arg). We up-regulated arginine biosynthesis in SYNB1020 by deleting a negative regulator of l-arg biosynthesis and inserting a feedback-resistant l-arg biosynthetic enzyme. SYNB1020 produced l-arg and consumed NH in an in vitro system. SYNB1020 reduced systemic hyperammonemia, improved survival in ornithine transcarbamylase-deficient mice, and decreased hyperammonemia in the thioacetamide-induced liver injury mouse model. A phase 1 clinical study was conducted including 52 male and female healthy adult volunteers. SYNB1020 was well tolerated at daily doses of up to 1.5 × 10 colony-forming units administered for up to 14 days. A statistically significant dose-dependent increase in urinary nitrate, plasma N-nitrate (highest dose versus placebo, = 0.0015), and urinary N-nitrate was demonstrated, indicating in vivo SYNB1020 activity. SYNB1020 concentrations reached steady state by the second day of dosing, and excreted cells were alive and metabolically active as evidenced by fecal arginine production in response to added ammonium chloride. SYNB1020 was no longer detectable in feces 2 weeks after the last dose. These results support further clinical development of SYNB1020 for hyperammonemia disorders including urea cycle disorders and hepatic encephalopathy.