Lessons from rodent gastric bypass model of enteric hyperoxaluria

Beneficial roles of gastrointestinal and urinary microbiomes in kidney stone prevention via their oxalate-degrading ability and beyond

Formation of calcium oxalate (CaOx) crystal, the most common composition in kidney stones, occurs following supersaturation of calcium and oxalate ions in the urine. In addition to endogenous source, another main source of calcium and oxalate ions is dietary intake. In the intestinal lumen, calcium can bind with oxalate to form precipitates to be eliminated with feces. High intake of oxalate-rich foods, inappropriate amount of daily calcium intake, defective intestinal transporters for oxalate secretion and absorption, and gastrointestinal (GI) malabsorption (i.e., from gastric bypass surgery) can enhance intestinal oxalate absorption, thereby increasing urinary oxalate level and risk of kidney stone disease (KSD). The GI microbiome rich with oxalate-degrading bacteria can reduce intestinal oxalate absorption and urinary oxalate level. In addition to the oxalate-degrading ability, the GI microbiome also affects expression of oxalate transporters and net intestinal oxalate transport, cholesterol level, and short-chain fatty acids (SCFAs) production, leading to lower KSD risk. Recent evidence also shows beneficial effects of urinary microbiome in KSD prevention. This review summarizes the current knowledge on the aforementioned aspects. Potential benefits of the GI and urinary microbiomes as probiotics for KSD prevention are emphasized. Finally, challenges and future perspectives of probiotic treatment in KSD are discussed.

Roux-en-Y gastric bypass surgery induced oxalosis and acute kidney injury: A case report

Introduction and importance

Diabetes mellitus and hypertension are two conditions that can coexist in obese individuals. Roux-en-Y gastric bypass (RYGB) surgery, are used to control obesity. Complications such as steatorrhea, hyperoxaluria, and decreased bone mineral density, may occur after RYGB.

Case presentation

A 58-year-old woman referred to the emergency department complaining of pain on the right side of her lower abdomen. Her past medical history was RYGB surgery, COVID-19 with 40% pulmonary involvement, and Chronic Kidney Disease (CKD). Rapid progressive glomerulonephritis (RPGN) was predicted based on extensive laboratory test results. A kidney biopsy demonstrated oxalate nephropathy. Along with the findings from the kidney biopsy, acute tubulointerstitial nephritis with tubular injury secondary oxalosis was diagnosed.

Clinical discussion

RYGB surgery and chronic kidney disease, can increase the risk of secondary oxalosis. Recent studies introduce enteric hyperoxaluria as an important marker for diagnosing end-stage kidney disease. Renal biopsy is often prescribed for absolute recognition of oxalosis. On the other hand, our patient has a recent history of COVID-19 infection. The use of anti-Covid-19 drugs in patients with renal insufficiency should be considered with caution.

Conclusion

It is important to monitor kidney function following RYGB surgery, particularly in patients with underlying diseases such as diabetes or hypertension.

Urolithiasis and sleeve gastrectomy: a prospective assessment of urinary biochemical variables

INTRODUCTION

to evaluate urinary biochemical alterations related to urolithogenesis processes after sleeve gastrectomy (SG).

MATERIALS AND METHODS

: prospective study with 32 individuals without previous diagnosis of urolithiasis who underwent SG. A 24-h urine test was collected seven days prior to surgery and at 6-month follow-up. The studied variables were urine volume, urinary pH, oxalate, calcium, citrate, and magnesium and calcium oxalate super saturation (CaOx SS).

RESULTS

patients were mainly women (81.2%), with mean age of 40.6 years. Mean pre- and postoperative BMI were 47.1 ± 8.3 Kg/m2 and 35.5 ± 6.1 Kg/m2, respectively (p<0.001). Urine volume was significantly lower at the postoperative evaluation in absolute values (2,242.50 ± 798.26 mL x 1,240.94 ± 352.39 mL, p<0.001) and adjusted to body weight (18.58 ± 6.92 mL/kg x 13.92 ± 4.65 mL/kg, p<0.001). CaOx SS increased significantly after SG (0.11 ± 0.10 x 0.24 ± 0.18, p<0.001). Moreover, uric acid levels were significantly lower at the postoperative evaluation (482.34 ± 195.80 mg x 434.75 ± 158.38 mg, p=0.027). Urinary pH, oxalate, calcium, citrate, and magnesium did not present significant variations between the pre- and postoperative periods.

CONCLUSION

SG may lead to important alterations in the urinary profile. However, it occurs in a much milder way than that of RYGB.