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Published on: February 9, 2021
Dietary oxalate and calcium oxalate nephrolithiasis
Saeed R Khan1, Patricia A Glenton, Karen J Byer
1Department of Pathology and Laboratory Medicine, College of Medicine, University of Florida, Gainesville, Florida 32610-0275, USA. Khan@pathology.ufl.edu
Purpose:
Patients with calcium oxalate kidney stones are advised to decrease the consumption of foods that contain oxalate. We hypothesized that a cutback in dietary oxalate would lead to a decrease in the urinary excretion of oxalate and decreased stone recurrence. We tested the hypothesis in an animal model of calcium oxalate nephrolithiasis.
Materials And Methods:
Hydroxy-L-proline (5%), a precursor of oxalate found in collagenous foods, was given with rat chow to male Sprague-Dawley rats. After 42 days rats in group 1 continued on hydroxy-L-proline, while those in group 2 were given chow without added hydroxy-L-proline for the next 21 days. Food and water consumption as well as weight were monitored regularly. Once weekly urine was collected and analyzed for creatinine, calcium, oxalate, lactate dehydrogenase, 8-isoprostane and H(2)O(2). Urinary pH and crystalluria were monitored. Rats were sacrificed at 28, 42 and 63 days, respectively. Renal tissue was examined for crystal deposition by light microscopy.
Results:
Rats receiving hydroxy-L-proline showed hyperoxaluria, calcium oxalate crystalluria and nephrolithiasis, and by day 42 all contained renal calcium oxalate crystal deposits. Urinary excretion of lactate dehydrogenase, 8-isoprostane and H(2)O(2) increased significantly. After hydroxy-L-proline was discontinued in group 2 there was a significant decrease in urinary oxalate, 8-isoprostane and H(2)O(2). Half of the group 2 rats appeared to be crystal-free.
Conclusions:
Dietary sources of oxalate can induce hyperoxaluria and crystal deposition in the kidneys with associated degradation in renal biology. Eliminating oxalate from the diet decreases not only urinary oxalate, but also calcium oxalate crystal deposits in the kidneys and improves their function.
Insights
Reducing dietary oxalate intake lowers urinary oxalate levels and kidney stone formation. This study in rats demonstrates that decreasing oxalate consumption improves kidney health and reduces crystal deposits.
Area of Science:
- Nephrology
- Biochemistry
- Animal Studies
Background:
- Patients with calcium oxalate kidney stones are often advised to reduce dietary oxalate intake.
- The efficacy of dietary oxalate restriction in preventing stone recurrence requires further investigation.
Purpose of the Study:
- To test the hypothesis that reduced dietary oxalate intake decreases urinary oxalate excretion and kidney stone recurrence.
- To evaluate the impact of dietary oxalate on calcium oxalate nephrolithiasis in an animal model.
Main Methods:
- Male Sprague-Dawley rats were fed a diet supplemented with hydroxy-L-proline (a precursor of oxalate) for 42 days.
- Group 2 rats had hydroxy-L-proline discontinued for the final 21 days.
- Urinary and renal parameters, including oxalate excretion, crystalluria, and crystal deposition, were monitored.
Main Results:
- Rats fed hydroxy-L-proline developed hyperoxaluria, calcium oxalate crystalluria, and nephrolithiasis with renal crystal deposits.
- Discontinuing hydroxy-L-proline led to decreased urinary oxalate, reduced markers of renal injury, and clearance of crystals in some rats.
- Increased urinary levels of lactate dehydrogenase, 8-isoprostane, and H(2)O(2) were observed with hydroxy-L-proline, which decreased upon its removal.
Conclusions:
- Dietary oxalate can induce hyperoxaluria and kidney damage.
- Eliminating dietary oxalate sources effectively reduces urinary oxalate, kidney crystal deposition, and improves renal function.
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