Prevalence of kidney stones has increased continously over several decades worldwide, the major causes of which are largely unknown. To explore the dietary causes of kidney stones, and reveal mechanisms underlying dietary risk factors inducing kidney stones, animal experiments using mice as the disease model were performed. Eight-week old male CD-1 mice were treated by ethylene glycol, cholesterol or/and apple tannins for 3 d, respectively. In the present study, the crystalline analysis in urine and kidney tissues, HE staining kidney sections as well as observation of micro-stones, tannins and cholesterol deposition in kidneys of mice in different groups were conducted. We found that gavage with ethylene glycol, cholesterol and tannins resulted in mice urine solute supersaturation in renal tubules and forming kidney stones. Significant cholesterol and tannin deposits in mouse kidney were observed by laser confocal microscopy and crystals were shown either adhered with or co-deposited with cholesterol and tannin deposits. The primary crystals were found in renal cortex, medullar, especially papilla in the kidney sections under polarized microscope. These findings demonstrate that interaction of cholesterol and tannins in kidney plays a critical role in the formation of kidney stones.

In this study, three representative pears ('Yali' Pear, 'Huangguan' Pear, and 'Xuehua' Pear) peel/flesh polyphenol extracts were characterized by their antioxidant activity, polyphenol composition, and in vitro cholesterol/cholates binding capacity. 'Yali' Pear polyphenol extracts were selected to further investigate the mechanism of in vitro cholesterol/cholates lowering capacity. Lagergren adsorption kinetic and Freundlich isotherm models confirmed the occurrence of this combination. Turbidity, average particle size, transmission electron microscopy, and zeta potential combined confirmed the existence of some interaction between polyphenols and cholesterol/cholates. Cholesterol/cholates quenched the exogenous fluorescence of polyphenols by static mechanism. The thermodynamic interaction results revealed that the interaction between polyphenols and cholesterol is a spontaneous process, primarily driven by hydrogen bonding and hydrophobic interactions. Overall, this study aimed to investigate the confirmation of the binding removal properties of pear polyphenols on cholesterol/cholates to mitigate the adverse health effects of a high-fat diet.