Assessment of Endogenous Oxalate Synthesis

Not Applicable

Completed

Interventions: Dietary Supplement: Low-oxalate controlled diet
Other: Primed, continuous intravenous infusion of 13C2-oxalate

Brief Summary: This study aims to determine the daily rate of endogenous synthesis of oxalate using carbon 13 oxalate isotope tracer technique and a low-oxalate controlled diet.

Detailed Description: Urinary oxalate excretion is derived from both dietary sources and endogenous synthesis. This study will use low-oxalate controlled diet and intravenous infusion of the isotope tracer carbon 13 oxalate, timed with blood and urine collections, to determine the daily rate of endogenous oxalate synthesis in non-stone forming volunteers and in subjects with calcium oxalate kidney stones. A DXA scan will be used to assess body composition.

Recruitment & Eligibility

Inclusion Criteria

Mentally competent adults, able to read and comprehend the consent form
Body Mass Index (BMI) between 18.5 and 50 kg/m2
Acceptable 24 hour urine collections (judged on screening)
good health as judged from a medical history, reported medications, and a complete blood metabolic profile
with or without history of calcium oxalate kidney stones

Exclusion Criteria

History of any hepatic, bowel, or endocrine disease or other condition that may influence the absorption, transport or urine excretion of ions
Abnormal urine chemistries or blood metabolic profiles
Poor 24 hour urine collections completed during screening, judged by 24 hour urine creatinine excretion (indicative of not collecting all urine in the 24 hour period)
Pregnancy, intention to become pregnant in the near future, or lactation
Aged lower than 18 or greater than 75 years
BMI lower than18.5 or greater than 50 kg/m2

Arm && Interventions

Group	Intervention	Description
Constant infusion of 13C2-oxalate	Low-oxalate controlled diet	Subjects who have passed screening, will consume a low-oxalate, normal calcium controlled diet for 5 days total. On Days 3 and 4, subjects will collect two 24-hour urines. On Day 5, they will receive a carbon 13 oxalate infusion which will occur at a constant rate for 6 hours, in the fasted state, following a priming dose. Hourly urine and twice hourly blood samples will be collected during the 6 hours. Meals will be resumed at the end of the infusion and timed urine collections will take place at home until the next day. A DXA scan will be performed to assess body composition at another date.
Constant infusion of 13C2-oxalate	Primed, continuous intravenous infusion of 13C2-oxalate	Subjects who have passed screening, will consume a low-oxalate, normal calcium controlled diet for 5 days total. On Days 3 and 4, subjects will collect two 24-hour urines. On Day 5, they will receive a carbon 13 oxalate infusion which will occur at a constant rate for 6 hours, in the fasted state, following a priming dose. Hourly urine and twice hourly blood samples will be collected during the 6 hours. Meals will be resumed at the end of the infusion and timed urine collections will take place at home until the next day. A DXA scan will be performed to assess body composition at another date.

Primary Outcome Measures

Name	Time	Method
Endogenous Oxalate Synthesis Rate	day 5	Daily oxalate synthesis rate (mg/day) determined by the 13c2-oxalate infusion method

Secondary Outcome Measures

Name	Time	Method
Urinary Oxalate Excretion	day 3-4	24-hr urinary oxalate excretion (mg/day) after equilibration on the low-oxalate controlled diet, measured by ion chromatography coupled with mass spectrometry.
Urinary Creatinine Excretion	day 3-4	24-hr urinary creatinine excretion (g/day) after equilibration on the low-oxalate controlled diet.