The Effect of Calcium and Vitamin B6 Supplementation on Oxalate Excretion in a Rodent Gastric Bypass Model of Enteric Hyperoxaluria.

OBJECTIVES: To test the effect of calcium and vitamin B6 therapies on urinary oxalate excretion in a rodent model of enteric hyperoxaluria (EH) after Roux-en Y gastric bypass (RYGB) surgery.

METHODS: Obese male Sprague-Dawley rats underwent sham (n=7) or RYGB (n=10). Animals were maintained on low oxalate (1.5%) and fat (10%; LOF), normal calcium (0.6 %; NC) diet for 8 weeks and then completed a 2-phase crossover metabolic study. In the first 2-week phase, animals were fed a LOF, high calcium (2.4%; HC) diet. After a 2-week washout, rats were fed a LOF/NC diet highly enriched with vitamin B6. Urine was collected before and after each intervention. Plasma pyridoxal 5'-phosphate (PLP) and metabolites were measured baseline and 11 weeks after sham or RYGB.

RESULTS: Compared to baseline, sham animals on LOF/HC diet doubled their urinary calcium excretion but not oxalate. RYGB animals on LOF/HC diet decreased urinary oxalate excretion 28% (p=0.001) without a significant rise in urinary calcium. Vitamin B6 supplementation decreased RYGB urinary oxalate by ∼15% (p=0.06), and serum PLP explained 63% of urinary oxalate variability.

CONCLUSIONS: Based on the findings in this model, calcium supplementation appears to be a reasonable therapy to decrease urinary oxalate in RYGB patients who maintain a low fat and oxalate diet. Serum PLP had a fair correlation to urinary oxalate excretion and may be a useful screening tool in hyperoxaluric RYGB patients. Further experimental human studies after RYGB are necessary to determine whether these commonly employed supplements truly provide a benefit in EH.