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.

中文翻译：

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胃肠道和泌尿微生物组通过其草酸盐降解能力等在预防肾结石中发挥有益作用

草酸钙 (CaOx) 晶体是肾结石中最常见的成分，它的形成是在尿液中的钙离子和草酸根离子过饱和之后发生的。除了内源性来源外，钙和草酸根离子的另一个主要来源是饮食摄入。在肠腔中，钙可以与草酸盐结合形成沉淀，并随粪便排出体外。大量摄入富含草酸盐的食物、每日钙摄入量不适当、草酸盐分泌和吸收的肠道转运蛋白有缺陷以及胃肠道（GI）吸收不良（即胃绕道手术）会增强肠道对草酸盐的吸收，从而增加尿草酸盐水平和肾结石病（KSD）的风险。富含草酸降解菌的胃肠道微生物组可以降低肠道草酸吸收和尿草酸水平。除了草酸盐降解能力外，胃肠道微生物组还影响草酸盐转运蛋白的表达和肠道草酸盐净转运、胆固醇水平和短链脂肪酸 (SCFA) 的产生，从而降低 KSD 风险。最近的证据还表明，尿液微生物组对预防 KSD 具有有益作用。本综述总结了当前关于上述方面的知识。强调了胃肠道和尿液微生物组作为益生菌预防 KSD 的潜在益处。最后，讨论了益生菌治疗 KSD 的挑战和未来前景。