An inducible intestinal epithelial cell-specific NHE3 knockout mouse model mimicking congenital sodium diarrhea

Abstract The sodium–hydrogen exchanger isoform 3 (NHE3, SLC9A3) is abundantly expressed in the gastrointestinal tract and is proposed to play essential roles in Na+ and fluid absorption as well as acid–base homeostasis. Mutations in the SLC9A3 gene can cause congenital sodium diarrhea (CSD). However, understanding the precise role of intestinal NHE3 has been severely hampered due to the lack of a suitable animal model. To navigate this problem and better understand the role of intestinal NHE3, we generated a tamoxifen-inducible intestinal epithelial cell-specific NHE3 knockout mouse model (NHE3IEC-KO). Before tamoxifen administration, the phenotype and blood parameters of NHE3IEC-KO were unremarkable compared with control mice. After tamoxifen administration, NHE3IEC-KO mice have undetectable levels of NHE3 in the intestine. NHE3IEC-KO mice develop watery, alkaline diarrhea in combination with a swollen small intestine, cecum and colon. The persistent diarrhea results in higher fluid intake. After 3 weeks, NHE3IEC-KO mice show a ∼25% mortality rate. The contribution of intestinal NHE3 to acid–base and Na+ homeostasis under normal conditions becomes evident in NHE3IEC-KO mice that have metabolic acidosis, lower blood bicarbonate levels, hyponatremia and hyperkalemia associated with drastically elevated plasma aldosterone levels. These results demonstrate that intestinal NHE3 has a significant contribution to acid–base, Na+ and volume homeostasis, and lack of intestinal NHE3 has consequences on intestinal structural integrity. This mouse model mimics and explains the phenotype of individuals with CSD carrying SLC9A3 mutations.

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Absorption of Hemoglobin Iron: The Role of Xanthine Oxidase in the Intestinal Heme-Splitting Reaction

Blood ◽

10.1182/blood.v35.1.94.94 ◽

1970 ◽

Vol 35 (1) ◽

pp. 94-103 ◽

Cited By ~ 26

Author(s):

R. BEN DAWSON ◽

SHEILA RAFAL ◽

LEWIS R. WEINTRAUB

Keyword(s):

Epithelial Cell ◽

Xanthine Oxidase ◽

Intestinal Epithelial Cell ◽

Oxidase Inhibitor ◽

Small Intestinal Mucosa ◽

Intestinal Epithelial ◽

Sephadex Column ◽

Xanthine Oxidase Inhibitor

Abstract Heme from ingested hemoglobin—59Fe is taken into the epithelial cell of the small intestinal mucosa of the dog and the 59Fe subsequently appears in the plasma bound to transferrin. A substance was demonstrated in homogenates of the mucosa which releases iron from a hemoglobin substrate in vitro. Thus: (1) The addition of catalase to the mucosal homogenate reduces the "heme-splitting" reaction. In contrast, sodium azide, a catalase inhibitor, potentiates the reaction. This suggests that a peroxide generating system participates in the "heme-splitting" reaction. (2) Xanthine oxidase, an enzyme present in the intestinal epithelial cell, produces H2O2 by oxidation of its substrate. The addition of allopurinol, a xanthine oxidase inhibitor, to the intestinal mucosal homogenate diminishes the "heme-splitting" reaction. (3) Fractionation of the 50,000 Gm. supernatant of the mucosal homogenate on a G-200 Sephadex column shows the "heme-splitting" activity to have the same elution volume as xanthine oxidase, indicating a similar molecular weight. (4) The addition of a mucosal homogenate to a xanthine substrate results in the production of uric acid. These data suggest that xanthine oxidase in the intestinal epithelial cell is important in the release of iron from absorbed heme. The enzyme mediates the "heme-splitting" reaction by the generation of peroxides which, in turn, oxidize the alpha-methene bridge of the heme ring releasing iron and forming biliverdin.

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