Oxalobacter formigenes-derived bioactive factors stimulate oxalate transport by intestinal epithelial cells

Hyperoxaluria is a major risk factor for kidney stones and has no specific therapy, although Oxalobacter formigenes colonization is associated with reduced stone risk. O. formigenes interacts with colonic epithelium and induces colonic oxalate secretion, thereby reducingurinary oxalate excretion, via an unknownsecretagogue. The difficulties in sustaining O. formigenes colonization underscore the need to identify the derived factors inducing colonicoxalate secretion.We therefore evaluatedthe effects of O. formigenes culture conditionedmedium(CM) on apical ¹⁴C-oxalate uptake by human intestinal Caco-2-BBE cells. Compared with control medium, O. formigenes CM significantly stimulated oxalate uptake (.2.4-fold), whereas CM from Lactobacillus acidophilus did not. Treating the O. formigenes CM with heat or pepsin completely abolished this bioactivity, and selective ultrafiltration of the CMrevealed that the O. formigenes-derived factors have molecular masses of 10-30 kDa. Treatment with the protein kinase A inhibitor H89 or the anion exchange inhibitor 4,4'-diisothiocyano-2,2'- stilbenedisulfonic acid completely blocked the CM-induced oxalate transport. Knockdown of the oxalate transporter SLC26A6 also significantly restricted the induction of oxalate transport byCM. In amousemodel of primary hyperoxaluria type 1, rectal administration of O. formigenes CM significantly reduced (.32.5%) urinary oxalate excretion and stimulated (.42%) distal colonic oxalate secretion. We conclude that O. formigenes-derived bioactive factors stimulate oxalate transport in intestinal cells through mechanisms including PKA activation. The reduction in urinary oxalate excretion in hyperoxaluric mice treated with O. formigenesCMreflects the in vivo retention of biologic activity and the therapeutic potential of these factors.