Endogenous Oxalate Synthesis in Idiopathic Calcium Oxalate Kidney Stone Disease

In this study the investigators propose to measure the production of oxalate by the body (endogenous oxalate synthesis), after equilibration on a low oxalate diet (\<60 mg oxalate/day, 600-800 mg calcium/day) and estimate the importance of vitamin C and glycolate metabolism to oxalate production in both Calcium Oxalate Kidney Stone patients and matched controls by oral dosings of those two substances. Phase 1. Screening and low-oxalate diet 24-hr urinary excretions. Between the University of Alabama at Birmingham (UAB) and the University of Texas Southwestern Medical Center (UTSW), the study will enroll 40 subjects with idiopathic Calcium Oxalate Kidney Stone (20 Males/20 Females) and 40 non-kidney stone forming controls (20 Males/20 Females). Participants in the two groups will be matched for age (within 10 yrs) and gender. Screening will include blood complete metabolic profile and two 24-hour urine specimens collected at home on self-choice diets and anthropometric measurements. Participants will then ingest the controlled low-oxalate (\<60 mg/day) diet for 5 consecutive days and collect two 24-hour urines after 2 days of dietary equilibration. Phase 2. Oxalate production and 13C-glycolate dosing tests. On Day 5, participants will arrive after an overnight fast in the research unit to undergo the oral 13C-glycolate dosing test. After a 1-hour baseline urine collection, they will ingest an oral load containing 0.5 mg/kg body weight of 13C-glycolate, dissolved in bottled water. For the next 7 hours, blood and urine will be collected hourly, and breath as more time points. They will remain on the fixed diet for 24 hours with a meal 7 hours post-load, and dinner at home 12 hours post-load. They will collect the remainder of their 24-hour urine at home. Phase 3. Oxalate production and 13C-ascorbic acid dosing tests. After 1 day of equilibration on the same low-oxalate diet, participants will arrive after an overnight fast in the research unit to provid eone blood and one urine sample and then ingest an oral dose of 13C-ascorbic acid (0.75 mg/kg), return home and continue to ingest the low-oxalate diet. The next morning, participants will arrive after an overnight fast in the research unit. For the next 7 hours, blood and urine will be collected hourly. They will remain on the fixed diet for 24 hours with a meal at the end of the visit.