A human strain of Oxalobacter (HC-1) promotes enteric oxalate secretion in the small intestine of mice and reduces urinary oxalate excretion

Abstract

Enteric oxalate secretion that correlated with reductions in urinary oxalate excretion was previously reported in a mouse model of primary hyperoxaluria, and in wild type (WT) mice colonized with a wild rat strain (OXWR) of Oxalobacter (Am J Physiol 300:G461–G469, 2010). Since a human strain of the bacterium is more likely to be clinically used as a probiotic therapeutic, we tested the effects of HC-1 in WT. Following artificial colonization of WT mice with HC-1, the bacteria were confirmed to be present in the large intestine and, unexpectedly, detected in the small intestine for varying periods of time. The main objective of the present study was to determine whether the presence of HC-1 promoted intestinal secretion in the more proximal segments of the gastrointestinal tract. In addition, we determined whether HC-1 colonization led to reductions in urinary oxalate excretion in these mice. The results show that the human Oxalobacter strain promotes a robust net secretion of oxalate in the distal ileum as well as in the caecum and distal colon and these changes in transport correlate with the beneficial effect of reducing renal excretion of oxalate. We conclude that OXWR effects on intestinal oxalate transport and oxalate homeostasis are not unique to the wild rat strain and that, mechanistically, HC-1 has significant potential for use as a probiotic treatment for hyperoxaluria especially if it is also targeted to the upper and lower gastrointestinal tract.

Figure 1

Distribution of HC-1 along the length of the WT mouse intestine between 7 and 9 days after gavage (G+7 to G+9, n=8, in Figure 1A) and between G+40 to G+56, n=8, in Figure 1B). PJ = Proximal jejunum; MI = Mid-ileum; DI = Distal ileum; CE = Caecum; DC = Distal colon.

Figure 2

Comparison of 24-h urinary oxalate excretion in WT mice (n=18 pools) before and after gavage (G) with HC-1. HC-1, is a human strain of Oxalobacter. Urinary oxalate excretion is significantly increased from basal levels (Control-no Oxalate) before the mice are fed a diet supplemented with 1.5% oxalate (Control+Oxalate, *p < 0.05, n=18). Following colonization, at G+7 days, there is a significant reduction in oxalate excretion, in a sub-group of n=11 mice, compared to the Control+Oxalate group (†, p ≤ 0.05). At G+12 days after gavage, the standard chow replaced the oxalate-supplemented diet and at G+40 urinary oxalate excretion (n=18) is significantly lower compared to both the Control-no Oxalate group (*, p ≤ 0.05) and the Control+Oxalate group values (†, p ≤ 0.05).

Figure 3

Unidirectional and net transepithelial fluxes of oxalate across isolated, short-circuited segments of distal ileum (n=13 vs 7), mid-ileum (n=6 vs 7), and proximal jejunum (n=15 vs 5) of WT mice not colonized vs mice artificially colonized with HC-1. An asterisk indicates a significant difference between the two groups, p ≤ 0.05. Transepithelial conductance (G_T) was not significantly affected by colonization in any segment (G_T = 34.2 ± 3.4 vs 36.9 ± 1.5 mS/cm², across distal ileum, G_T = 35.3 ± 1.9 vs 40.3 ± 4.9 mS/cm² mid-ileum, and G_T = 27.9 ± 1.7 vs 39.0 ± 7.7 mS/cm² in proximal jejunum of non-colonized vs colonized mice, respectively). With the exception of the distal ileum, I_sc was not affected by colonization (I_sc = 2.9 ± 0.5 vs 6.9 ± 0.8* μEq/cm² in distal ileum, I_sc = 5.6 ±0.5 vs 4.8 ±0.7 μEq/cm² in mid-ileum, and I_sc = 2.5 ± 0.3 vs 2.9 ± 0.7 μEq/cm² in the proximal jejunum of non-colonized mice vs colonized mice, respectively).

Figure 4

Unidirectional and net transepithelial fluxes of oxalate across isolated, short-circuited segments of caecum (n=11 vs 7) and distal colon (n=8 vs 10) of WT mice (not colonized vs mice artificially colonized with HC-1. An asterisk indicates a significant difference between the two groups p ≤ 0.05. Transepithelial conductance (G_T) was not significantly affected by colonization in any segment (G_T = 19.5 ± 1.7 vs 20.8 ± 1.2 mS/cm², across caecum, G_T = 15.5 ± 2.0 vs 16.5 ± 1.3 mS/cm² in distal colon of non-colonized mice vs colonized mice, respectively). I_sc was not affected by colonization (I_sc = 0.5 ± 0.1 vs 0.5 ± 0.1 μEq/cm² in caecum and I_sc = 0.7 ± 0.1 vs 1.3 ±0.1 μEq/cm² in distal colon of non-colonized mice vs colonized mice, respectively).