Natural inhibitors from earthworms for the crystallization of calcium oxalate monohydrate

The pathological mineralization of calcium oxalate monohydrate (COM) crystals in vivo inevitably brings renal injury wherein natural macromolecules play an indispensable role in regulating the process. However, the role of macromolecules in crystal growth is more complicated and less well understood. In this study, we innovatively propose two proteins extracted from earthworms, lumbrokinase (LRK) and earthworm protein (EP), as potent modifiers of calcium oxalate (CaOx) crystals. Our research shows that LRK and EP inhibit COM formation and initiate the calcium oxalate dihydrate (COD) phase, which is more easily excreted out of the body. Through a series of combined macroscopic and microscopic experimental techniques, we reveal the site-specific adsorption of inhibitors on the COM (121) and (021) surface, resulting in a reduction in the aspect ratio. In situ atomic force microscopy (AFM) measurements show that LRK and EP specifically inhibit the advancement of COM surface steps through more than one inhibition mode. In general, the discovery of natural macromolecules from earthworms as potent inhibitors of COM crystal formation provides some insights into the appropriate formulation of inhibitors, which could prevent the formation of undesired stones in the kidney. Our findings shed light on nature's remarkable mineralization capabilities and outline fabrication strategies for advanced materials.