Renal Metabolism of Glycolate to Oxalate

Study Overview
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Brief Summary
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This study will determine the contribution of glycolate metabolism to urinary oxalate excretion in healthy subjects, using carbon 13 isotope glycolate tracer technique and a low-oxalate controlled diet.

Detailed Description
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It is known that glycolate, an intermediary molecule in normal metabolism, can be converted into oxalate. The origin of urinary oxalate is of interest as calcium oxalate is a main component of kidney stones. In the rare disease primary hyperoxaluria, excessive production of oxalate by the body results in frequent kidney stones and can cause loss of kidney function. Primary hyperoxaluria is caused by deficiencies in one of several enzymes involved in the glycolate pathway. This study will seek to determine how much oxalate is formed from glycolate in normal subjects. After consuming a controlled diet, subjects will either ingest or have an intravenous infusion of carbon 13 glycolate, a stable isotope of glycolate that can be tracked and will also label downstream metabolic products. Blood and urine samples will be assessed for their amounts of labeled glycolate and labeled oxalate to provide an accurate measure of how much oxalate is made from normal glycolate breakdown in healthy human subjects.

Official Title
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Renal Metabolism of Glycolate to Oxalate

Conditions
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Healthy

Intervention / Treatment
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* Dietary Supplement: Low oxalate controlled Diet
* Other: Primed, continuous intravenous infusion of 13C2-Glycolate
* Other: Bolus intravenous infusion of 13C2-Glycolate
* Other: Oral bolus administration of 13C2-Glycolate


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Mentally competent adults, able to read and comprehend the consent form 18-75 years of age Body Mass Index (BMI) between 19 and 40 In good health as judged from a medical history, reported medications, and a complete blood metabolic profile Acceptable 24 hour urine collections (performed twice for screening) Exclusion Criteria: History of any hepatic, renal, bowel, or endocrine disease or any 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 <18 or >75 BMI <19 or >40

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 75 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Non-Randomized
Intervention Model: Sequential Assignment
Interventional Model Description: Subject will undergo the gold-standard technique of steady-state intravenous infusion of 13-glycolate administration. Selected subjects will also undergo other modified modalities of 13-glycolate administration.
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Constant Infusion of 13C2-Glycolate<br>Subjects will consume a controlled diet for 5 days total. On Days 3 and 4, subjects will collect 24 hour urines. On Day 5, they will come to the Clinical Research Unit (CRU) in the fasted state for a visit lasting from 7:00 am to 5:30 pm. An intravenous (IV) catheter will be placed in a vein on the back of the hand at 7:30 am for the carbon 13 glycolate infusion which will occur at a constant rate for 10 hours, following a priming dose. From 7:30 am to 5:30 pm, urine collections will occur hourly, and from 8:30 am to 5:30 pm, IV blood collections will occur every half hour. Subjects will receive a meal at 5:30 pm, thus concluding the CRU visit. At home, subjects will collect timed urine until the next morning to be returned to the CRU. | Dietary Supplement: Low oxalate controlled Diet<br>* Participants will consume a diet that is controlled in its contents of protein, carbohydrates, fat, calcium, oxalate, vitamin C and sodium. Participants will be asked not to take any dietary supplements, exercise strenuously, or consume food or drink that is not provided to them.<br>Other: Primed, continuous intravenous infusion of 13C2-Glycolate<br>* Participants will receive a continuous intravenous administration of carbon-13 glycolate, a naturally occurring form of glycolate, over the course of several hours until steady-state is achieved, using an IV catheter.<br>* Other names: Constant infusion of 13C2-Glycolate;|
| Experimental: Single Intravenous Dose of 13C2-Glycolate<br>Subjects will consume a controlled diet for 5 days total. On Days 3 and 4, subjects will collect 24 hour urines. On Day 5, they will come to the Clinical Research Unit (CRU) in the fasted state for a visit lasting from 7:00 am to 2:30 pm. An intravenous (IV) catheter will be placed in a vein on the back of the hand at 8:30 am for a single dose of carbon-13 glycolate to be administered. From 7:30 am to 2:30 pm, urine collections will occur hourly. At 8:30 am, IV blood samples will be taken every fifteen minutes until 9:30 am, every half hour from 9:30 am to 10:30 am, and then finally hourly from 10:30 am to 2:30 pm . Subjects will receive a meal at 2:30 pm, thus concluding the CRU visit. At home, subjects will collect timed urine until the next morning to be returned to the CRU. | Dietary Supplement: Low oxalate controlled Diet<br>* Participants will consume a diet that is controlled in its contents of protein, carbohydrates, fat, calcium, oxalate, vitamin C and sodium. Participants will be asked not to take any dietary supplements, exercise strenuously, or consume food or drink that is not provided to them.<br>Other: Bolus intravenous infusion of 13C2-Glycolate<br>* Participants will receive a bolus intravenous administration of carbon-13 glycolate, a naturally occurring form of glycolate, using an IV catheter.<br>* Other names: Single intravenous dose of 13C2-Glycolate;|
| Experimental: Single Oral Dose of 13C2-Glycolate<br>Subjects will consume a controlled diet for 5 days total. On Days 3 and 4, subjects will collect 24 hour urines. On Day 5, they will come to the Clinical Research Unit (CRU) in the fasted state for a visit lasting from 7:00 am to 2:30 pm. At 8:30 am, subjects will ingest the carbon-13 glycolate, dissolved in to 50 ml (about 1/4 cup) of water. From 7:30 am to 2:30 pm, urine collections will occur hourly. At 8:30 am, intravenous (IV) blood samples will be taken every fifteen minutes until 9:30 am, every half hour from 9:30 am to 10:30 am, and then finally hourly from 10:30 am to 2:30 pm . Subjects will receive a meal at 2:30 pm, thus concluding the CRU visit. At home, subjects will collect timed urine until the next morning to be returned to the CRU. | Dietary Supplement: Low oxalate controlled Diet<br>* Participants will consume a diet that is controlled in its contents of protein, carbohydrates, fat, calcium, oxalate, vitamin C and sodium. Participants will be asked not to take any dietary supplements, exercise strenuously, or consume food or drink that is not provided to them.<br>Other: Oral bolus administration of 13C2-Glycolate<br>* Participants will orally ingest a single dose of carbon-13 glycolate, a naturally occurring form of glycolate.<br>* Other names: Single oral dose of 13C2-Glycolate;|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Urinary oxalate measured by ion chromatography coupled with mass spectrometry | Measurement of carbon 13 labeled and unlabeled urinary oxalate following carbon 13 glycolate administration, after equilibration under a low-oxalate diet. | day 5 of dietary control | 
| Plasma glycolate measured by ion chromatography coupled with mass spectrometry | Measurement of carbon 13 labeled and unlabeled plasma glycolate following carbon 13 glycolate administration, after equilibration under a low-oxalate diet. | day 5 of dietary control | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Urinary creatinine | Baseline assessment of 24hr urinary creatinine under controlled low-oxalate diet. | day 5 of dietary control | 
| Urinary glycolate measured by ion chromatography coupled with mass spectrometry | Measurement of carbon 13 labeled and unlabeled urinary glycolate following carbon 13 glycolate administration, after equilibration under a low-oxalate diet. | day 5 of dietary control | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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oxalate metabolism, kidney stones, glycolate, isotope tracer study, urolithiasis, oxalate