Freel, Robert W., Marguerite Hatch, Mike Green, and Manoocher Soleimani. Ileal oxalate absorption and urinary oxalate excretion are enhanced in Slc26a6 null mice. Am J Physiol Gastrointest Liver Physiol 290: G719 -G728, 2006; doi:10.1152/ajpgi.00481.2005.-Intestinal oxalate transport, mediated by anion exchange proteins, is important to oxalate homeostasis and consequently to calcium oxalate stone diseases. To assess the contribution of the putative anion transporter (PAT)1 (Slc26a6) to transepithelial oxalate transport, we compared the unidirectional and net fluxes of oxalate across isolated, short-circuited segments of the distal ileum of wild-type (WT) mice and Slc26a6 null mice [knockout (KO)]. Additionally, urinary oxalate excretion was measured in both groups. In WT mouse ileum, there was a small net secretion of putative anion transporter 1; hyperoxaluria; anion exchange; serum oxalate; 4,4Ј-diisothiocyanostilbene-2,2Ј-disulfonic acid THE MAMMALIAN INTESTINE plays a significant role in the homeostasis of the oxalate anion both as a site for dietary oxalate absorption and, together with renal mechanisms, as an avenue for the excretion of oxalate (11). Understanding the mechanisms and regulation of intestinal oxalate transport is thus an important component in the management of hyperoxaluria and calcium oxalate urolithiasis (11). From studies of isolated, short-circuited intestinal epithelia from rats and rabbits, it is clear that transepithelial oxalate transport occurs passively through paracellular pathways and actively (secondarily) through transcellular pathways in a vectorial manner that produces net absorption or net secretion of oxalate in a segment-specific fashion (6,12,13,15). The latter studies, and others employing membrane vesicles prepared from rabbit distal ileum (19,20), suggested that transmembrane oxalate transport across the apical and basolateral membrane is mediated by one or more distinct anion exchange systems (antiporters) that exhibit varying degrees of stilbene sensitivity. The apparent multiplicity of exchangers at a given membrane, the variety of possible cotransport partners (exchange modes), and the general inability to identify a single specific exchanger (beyond stilbene sensitivity or exchange modes) have hampered a completely satisfactory explanation of net oxalate absorption or secretion by intestinal or renal epithelia. The molecular identification of the individual pathways involved in transepithelial oxalate transport has become more promising with the recent characterization of a gene family (Slc26) encoding anion exchange proteins that accept a variety of monovalent and divalent substrates (4,17,27,35). At least one-half of the 10 functional genes in this family have the ability to transport oxalate when functionally characterized in heterologous expression systems (1,24,27,30,31,39), and several of these oxalate transporters are present in the intestine (1, 5, 8, 17, 18, 21, 27, 28, 30 -32, 35, 36, 38). For example, Slc26a3 (DRA) and Slc26a6 [putative anion transpor...

The primary goal of this study was to test the hypothesis that Oxalobacter colonization alters colonic oxalate transport thereby reducing urinary oxalate excretion. In addition, we examined the effects of intraluminal calcium on Oxalobacter colonization and tested the hypothesis that endogenously derived colonic oxalate could be degraded by lyophilized Oxalobacter enzymes targeted to this segment of the alimentary tract. Oxalate fluxes were measured across short-circuited, in vitro preparations of proximal and distal colon removed from Sprague-Dawley rats and placed in Ussing chambers. For these studies, rats were colonized with Oxalobacter either artificially or naturally, and urinary oxalate, creatinine and calcium excretions were determined. Colonized rats placed on various dietary treatment regimens were used to evaluate the impact of calcium on Oxalobacter colonization and whether exogenous or endogenous oxalate influenced colonization. Hyperoxaluric rats with some degree of renal insufficiency were also used to determine the effects of administering encapsulated Oxalobacter lysate on colonic oxalate transport and urinary oxalate excretion. We conclude that in addition to its intraluminal oxalate-degrading capacity, Oxalobacter interacts physiologically with colonic mucosa by inducing enteric oxalate secretion/excretion leading to reduced urinary excretion. Whether Oxalobacter, or products of Oxalobacter, can therapeutically reduce urinary oxalate excretion and influence stone disease warrants further investigation in long-term studies in various patient populations.

Hatch M, Gjymishka A, Salido EC, Allison MJ, Freel RW. Enteric oxalate elimination is induced and oxalate is normalized in a mouse model of primary hyperoxaluria following intestinal colonization with Oxalobacter. Am J Physiol Gastrointest Liver Physiol 300: G461-G469, 2011. First published December 16, 2010; doi:10.1152/ajpgi.00434.2010.-Oxalobacter colonization of rat intestine was previously shown to promote enteric oxalate secretion and elimination, leading to significant reductions in urinary oxalate excretion (Hatch et al. Kidney Int 69: 691-698, 2006). The main goal of the present study, using a mouse model of primary hyperoxaluria type 1 (PH1), was to test the hypothesis that colonization of the mouse gut by Oxalobacter formigenes could enhance enteric oxalate secretion and effectively reduce the hyperoxaluria associated with this genetic disease. Wild-type (WT) mice and mice deficient in liver alanine-glyoxylate aminotransferase (Agxt) exhibiting hyperoxalemia and hyperoxaluria were used in these studies. We compared the unidirectional and net fluxes of oxalate across isolated, short-circuited large intestine of artificially colonized and noncolonized mice. In addition, plasma and urinary oxalate was determined. Our results demonstrate that the cecum and distal colon contribute significantly to enteric oxalate excretion in Oxalobacter-colonized Agxt and WT mice. In colonized Agxt mice, urinary oxalate excretion was reduced 50% (to within the normal range observed for WT mice). Moreover, plasma oxalate concentrations in Agxt mice were also normalized (reduced 50%). Colonization of WT mice was also associated with marked (up to 95%) reductions in urinary oxalate excretion. We conclude that segment-specific effects of Oxalobacter on intestinal oxalate transport in the PH1 mouse model are associated with a normalization of plasma oxalate and urinary oxalate excretion in otherwise hyperoxalemic and hyperoxaluric animals. cecum; proximal colon; distal colon; slc26a6 CONSIDERABLE EVIDENCE HAS emerged from human and animal studies suggesting that colonization of the intestinal tract by the anaerobic bacterium Oxalobacter formigenes plays an important role in degrading dietary sources of oxalate in the intestine, leading to reduced intestinal oxalate absorption and, consequently, a lower urinary oxalate excretion (9, 10, 15, 18 -20, 22, 25-27, 29). Importantly, these bacteria, discovered by Allison et al.(1) in 1985, use oxalate as a sole carbon and energy source. In most of the studies involving human subjects, the approach has been to determine whether the lack of Oxalobacter colonization is associated with increased urinary oxalate excretion and stone formation (9, 10, 18 -20, 22, 26, 29). Clinical findings suggest a direct correlation between the complete absence or decreased activity of luminal Oxalobacter and the development of recurrent oxalate stone disease (18), as well as the hyperoxaluria associated with conditions such as inflammatory bowel disease, jejunoileal bypass, and cystic fibrosis (9,10,2...

In a genetically susceptible rodent model of diabetes, early increased intestinal permeability might allow unregulated passage of environmental antigens that could potentially trigger the autoimmune response leading to type 1 diabetes.