Hyperphosphatemia in chronic kidney disease (CKD) patients is a risk factor for cardiovascular events, progressive kidney failure, and mortality. Improved therapeutic interventions to control hyperphosphatemia depend greatly on robust animal models that recapitulate the CKD disease process. Murine-based models of CKD as compared to rat models present significant advantages due to available genetic knockout lines that permit mechanistic dissection of CKD etiologies. The rat adenine model of renal failure has been extensively studied, and studies are now emerging describing adenine-induced renal failure in murine models. However, these newly developed murine models have not fully described the responses to calcitriol and phosphate binders, and the reported effects of adenine on serum phosphate is often lacking in murine models. Therefore, the objectives of this study were: 1) To induce hyperphosphatemia in mice using adenine with minimal mortality, and 2) Report the influence of calcitriol and phosphate binders on the disease process through measurement of serum phosphate and histology. In one approach, C57BL/6 male mice gavaged with 4 or 6 mg adenine/day, as compared to 0 mg adenine/day developed hyperphosphatemia, with low mortality. In a second approach, calcitriol exacerbated adenine-induced increases in serum phosphate at day 7 of adenine administration (p<0.05). Notably, adenine treated mice had 4-fold increased stomach weights vs. non-adenine treated mice (p<0.0001). The addition of a phosphate binder (experiment 3, sevelamer hydrochloride) was ineffective at preventing an adenine-induced increase in blood phosphate, a finding that likely resulted from adenine's inhibition of gastric emptying. We report the successful use of adenine to induce hyperphosphatemia, that the hyperphosphatemic status is exacerbated by calcitriol, and a limitation of the model for studying oral therapies for hyperphosphatemia.

Hyperimmunized hens are an effective means of generating large quantities of antigen specific egg antibodies that have use as oral supplements. In this study, we attempted to create a peptide specific antibody that produced outcomes similar to those of the human pharmaceutical, sevelamer HCl, used in the treatment of hyperphosphatemia (a sequela of chronic renal disease). Egg antibodies were generated against 8 different human intestinal sodium-dependent phosphate cotransporter 2b (NaPi2b) peptides, and hNaPi2b peptide egg antibodies were screened for their ability to inhibit phosphate transport in human intestinal Caco-2 cell line. Antibody produced against human peptide sequence TSPSLCWT (anti-h16) was specific for its peptide sequence, and significantly reduced phosphate transport in human Caco-2 cells to 25.3±11.5% of control nonspecific antibody, when compared to nicotinamide, a known inhibitor of phosphate transport (P≤0.05). Antibody was then produced against the mouse-specific peptide h16 counterpart (mouse sequence TSPSYCWT, anti-m16) for further analysis in a murine model. When anti-m16 was fed to mice (1% of diet as dried egg yolk powder), egg yolk immunoglobulin (IgY) was detected using immunohistochemical staining in mouse ileum, and egg anti-m16 IgY colocalized with a commercial goat anti-NaPi2b antibody. The effectiveness of anti-m16 egg antibody in reducing serum phosphate, when compared to sevelamer HCl, was determined in a mouse feeding study. Serum phosphate was reduced 18% (P<0.02) in mice fed anti-m16 (1% as dried egg yolk powder) and 30% (P<0.0001) in mice fed sevelamer HCl (1% of diet) when compared to mice fed nonspecific egg immunoglobulin. The methods described and the findings reported show that oral egg antibodies are useful and easy to prepare reagents for the study and possible treatment of select diseases.