The incidence of AEs was higher than the IB reported.

The objective is to determine if acetohydroxamic acid (AHA) can prevent hydrolysis of urea by inhibiting the bacterial urease of gut flora of both healthy control adults as well as adults with urea cycle disorders

This project will study the efficacy and safety of the pharmacologic blockade of urease in the nitrogen salvage pathway of intestinal microbes in subjects with partial urea cycle disorders. Additional trapping of ammonia as excretable urea may result in improved nitrogen excretion and reduced ammonia levels.

Urea cycle disorders (UCDs) are a group of disorders resulting from a complete or partial deficiency of one of the 6 enzymes or 2 transporters that comprise the urea cycle, the essential biochemical pathway which converts toxic ammonia into urea. These disorders have as a common feature, a reduced or complete inability to convert ammonia into urea, thereby resulting in high ammonia levels, or hyperammonemia. If untreated, hyperammonemia may result acutely in lethargy and coma, and chronically in intellectual disability. Current treatment for hyperammonemia is suboptimal, thus the search for new treatments is critical.

The urease inhibitor, acetohydroxamic acid (AHA, Lithostat®, Mission Pharmacal), is an FDA-approved product for another indication- the treatment of struvite nephrolithiasis in chronic urinary tract infections in both adults and children.

It is known that many urea-splitting bacteria also exist in the gut, and that in healthy individuals, approximately 15-30% of blood urea is degraded via gut bacteria into ammonia3, which returns to the liver via the portal vein, only to be recycled into urea. This percentage of degraded urea may even be greater in patients with urea cycle disorders, who are on a low protein-diet4 and whose gastrointestinal contents thus likely have lower nitrogen content, promoting bacterial recycling of nitrogen from available urea. Additionally, urea hydrolysis has been shown to be greatest in infants5, precisely the age at which hyperammonemic episodes are the most frequent in UCD patients.

We intend to study if AHA can inhibit gut bacteria degradation of urea, thereby reducing the quantity of ammonia returning to the liver. We intend to investigate this by studying subjects on two occasions at least 3 days apart:

On the first occasion, subjects will receive an intravenous dose of 13C-urea. Following the intravenous bolus of 13C-urea, over the subsequent 4 hours, we will collect several sequential measurements of blood and urine biomarkers from an IV catheter placed in the other arm. The intent is to obtain baseline 13CO2 kinetics in the subject.

On the second occasion, subjects will first receive an oral dose of AHA approximately 1 hour prior to the intravenous 13C-urea dose. Similar sequential measurements of blood and urine biomarkers will be performed. The intent is to observe a reduction in 13CO2 when AHA is administered.

We intend to initially study a cohort of unaffected adult subjects. If successful, we will study adults with partial urea cycle disorders.

This study will be conducted in the Clinical Research Center (CRC) of the Clinical and Translational Research Institute (CTSI) of Children's National Medical Center (CNMC).

Inclusion Criteria:

• For Group 1 (healthy adults):
• Ages 18-60 years
• Compliant with receiving medications orally and intravenously
• Compliant with providing blood and urine samples

For Group 2 (adult UCD patients):

• Ages 18-60 years

• Compliant with receiving medications orally and intravenously

• Compliant with providing blood and urine samples

• Established diagnosis of CPSD, OTCD, ASSD or ASLD as follows:

  • Diagnosis of CPS I deficiency, defined as decreased (less than 20 % of control) CPS I enzyme activity in liver or an identified pathogenic mutation
  • Diagnosis of OTC deficiency, defined as the identification of a pathogenic mutation, linkage analysis in an affected family, less than 20% of control of OTC activity in the liver, or elevated urinary orotate (greater than 20 uM/mM) in a random sample or following allopurinol loading with absence of argininosuccinic acid
  • Diagnosis of AS deficiency (Citrullinemia), defined as a greater than or equal to 10-fold elevation of citrulline in plasma, decreased AS enzyme activity in cultured skin fibroblasts or other appropriate tissue, or identification of a pathogenic mutation in the AS gene
  • Diagnosis of AL deficiency (Argininosuccinic Aciduria, ASA), defined as the presence of argininosuccinic acid in the blood or urine, decreased AL enzyme activity in cultured skin fibroblasts or other appropriate tissue, or identification of a pathogenic mutation in the AL gene

Exclusion Criteria:

• For both Group 1 and Group 2:
• Current or prior Helicobacter pylori infection
• Chronic gastrointestinal illness (e.g., inflammatory bowel disease)
• Chronic renal failure
• Taking probiotic medications within a week of study start date
• Currently pregnant or lactating. Documentation of a negative pregnancy test within a week prior to testing is required, unless pre-menarchal or menopausal, experiencing menses that week, or other circumstances which preclude pregnancy (e.g. hysterectomy).
• Presence of acute infection at the time of inclusion
• Participation in any other clinical interventional trial or received experimental medication within the last 30 days
• Any clinical or laboratory abnormality or medical condition that, at the discretion of the investigator, may put the subject at an additional risk by participating in this study

All the enrolled participants have been healthy adults.

1 week