Discovering inhibitor molecules for pathological crystallization of CaOx kidney stones from natural extracts of medical herbs

Ethnopharmacological relevance: Kidney stones is one of the common diseases of the urinary system. The primary cause of kidney stone formation is the thermodynamic supersaturation of lithogenic solutes in urine, which desaturates by nucleation, crystal growth and aggregation of minerals and salts, mainly Calcium oxalate (CaOx). One of the potential therapies is to develop drug molecules to inhibit or prevent CaOx crystallization in urine. Traditional Chinese medicines (TCMs) provided an efficient approach for the treatment of kidney stones with a specialized-designed recipe of medicinal herbs. But the action details of these herbs were poorly understood due to their complex components, and whether the effective constituents of herbs have an inhibitory effect on the process of stone formation has not been evaluated. Aim of the study: This study aims to develop and identify inhibitor substitutes from a library of kidney stone prescriptions in traditional Chinese medicines to prevent pathological kidney stone formation. Materials and methods: As many as twenty Chinese medicines were extracted and separated into five different polar extracts, the inhibition performance of which on CaOx crystallization was explored by recording and comparing crystallization kinetics. The potential inhibitor molecules in the inhibitory extracts were confirmed by HPLC and their retardation efficacy was evaluated by quantifying nucleation and growth kinetics using colorimetry. Then the inhibitor-COM crystal interactions and specificity were examined by morphology evolution and surface structure analysis. In vitro inhibition performance of inhibitors on crystal growth and attachment of CaOx crystals to human renal epithelial cells were further evaluated by recording the nucleation and adhesive crystal numbers. Results and conclusion: Water- and n-butanol- soluble extracts from 20 kinds of herbs show almost 100% inhibition percentage, and the n-butanol extracts was found better than commercial drug citrate. Twenty-one molecule substitutes were identified from these extracts, and among them polyphenols display the best inhibition efficacy to retard CaOx crystallization. The high-throughput colorimetric assay and morphology examinations reveals thirteen out of 21 molecules show inhibition potential and disrupt growth of CaOx monohydrate crystals by interacting with exposed Ca2+ and C2O42- on the (100) and (010) surfaces. Moreover, these inhibitors also display pronounced performance in protecting renal epithelial cells by inhibiting nucleation and adhesion of CaOx crystals to cells, thus reducing stone formation. The structure-performance correlation among 19 screened molecules that inhibitors having pKa<3.5, logD (pH = 6) <0, H-number>0.1 mmol are the best in suppressing CaOx crystallization. Our findings provide a novel solution to design and manufacture inhibitor drugs from Chinese medicines for preventing pathological kidney stones formation.

Automated summary

This study aimed to develop and identify inhibitor substitutes from a library of kidney stone prescriptions in traditional Chinese medicines to prevent pathological kidney stone formation. Water- and n-butanol-soluble extracts from 20 kinds of herbs showed almost 100% inhibition percentage, with n-butanol extracts found to be more effective than the commercial drug citrate.