Partial Reversal of Tissue Calcification and Extension of Life Span following Ammonium Nitrate Treatment of Klotho-Deficient Mice

摘要

>Background/Aims: Klotho is required for the inhibitory effect of FGF23 on 1,25(OH)₂D₃ formation and Klotho-hypomorphic mice (kl/kl) suffer from severe tissue calcification due to excessive 1,25(OH)₂D₃ formation with subsequent increase of Ca2+ and phosphate concentrations and stimulation of osteogenic signaling. The excessive tissue calcification dramatically accelerates aging and leads to premature death of the animals. Osteogenic signaling in those mice is disrupted by treatment with NH₄Cl, which prevents tissue calcification and early death of kl/kl mice. The present study explored whether the beneficial effects of NH₄Cl treatment could be mimicked by NH₄NO₃ treatment. Methods: The kl/kl mice had free access to tap water either without or with addition of NH₄NO₃ (0.28 M) starting with the mating of the parental generation. Calcification of trachea, lung, kidney, stomach, heart and vessels was visualized by histology with von Kossa staining. Plasma phosphate concentration was determined utilizing photometry, blood gas and electrolytes utilizing a blood Gas and Chemistry Analysis System and plasma 1,25(OH)₂D₃ concentration with ELISA. Results: In untreated kl/kl mice plasma 1,25(OH)₂D₃ and phosphate concentrations were elevated, and the mice suffered from marked calcification of all tissues analyzed. Untreated kl/kl mice further suffered from respiratory acidosis due to marked lung emphysema. NH₄NO₃-treatment decreased both, blood pCO₂ and HCO₃-, decreased calcification of trachea, lung, kidney, stomach, heart and vessels and increased the life span of kl/kl mice more than 1.7-fold (♂) or 1.6-fold (♀) without significantly affecting extracellular pH or plasma concentrations of 1,25(OH)₂D₃, Ca2+, phosphate, Na+, and K+. Conclusions: NH₄NO₃-treatment turns respiratory acidosis into metabolic acidosis and mitigates calcification thus leading to a substantial extension of kl/kl mice survival.