Co-precipitating calcium phosphate as oral detoxification of cadmium

Abstract

Bone-eating (also known as osteophagia), found in wild animals, is primarily recognized as a means to supplement phosphorus and calcium intake. Herein, we describe a novel function of bone-eating in detoxifying heavy metal ions through the dissolution and co-precipitation of bone minerals as they travel through the gastrointestinal (GI) tract. In this study, cadmium (Cd), a heavy metal ion, served as a toxic model. We demonstrated that hydroxyapatite (HAp), the major calcium phosphate (CaP) in bone, dissolves in the stomach and acts as a co-precipitant in the intestine for Cd detoxification. We compared HAp to a common antidote, activated charcoal (AC), which did not precipitate within the GI tract. In vitro experiments showed that HAp dissolves under acidic conditions and, upon return to a neutral environment, efficiently re-sequesters Cd. Similarly, oral administration of HAp effectively prevented Cd absorption and accumulation, resulting in enhanced Cd excretion in the feces when compared to AC. A co-precipitating CaP in the GI tract could serve as an excellent detoxification system, as it helps prevent the accumulation of toxic substances and aids in developing appropriate strategies to reduce tissue toxicity. Moreover, understanding this detoxification system would be a valuable indicator for designing efficient detoxification materials.