Mechanism And Regulation Of The Crystallization Of Pathological Uric Acid Crystals

Uric acid,the end product of purine metabolism in human body,will crystallize to form monosodium urate monohydrate(MSUM)crystals deposited in the synovial fluid(p H 7.4)or uric acid crystals deposited in the kidneys(the p H 4.8～8.0 of urine)when its concentration exceeds a threshold caused by abnormal metabolism of uric acid in vivo,which further cause gout or urinary stone,respectively.Understanding the crystallization mechanism of the pathological crystals in vivo is the basis to pre-vent the lithiasis and develop effective therapeutic techniques.Therefore,the main goal of the thesis is to study the nucleation and growth of uric acid crystals(urate so-dium and uric acid hydrates)and the regulation mechanisms of physiological compo-nents on the deposition of uric acid crystals,which can propose some suggestions for the prevention and treatment of uric acid pathological crystals,leading to the follow-ing conclusions:Firstly,the crystallization mechanism of MSUM in a simulated biological envi-ronment was studied to understand the crystallization process of MSUM.It was found that the aggregation of sodium urate molecules first formed,further conglomerated to form amorphous form,finally transformed to crystal form accompanying molecular rearrangement.The structure of amorphous form was rather similar to that of MSUM crystal while amorphous form can reduce the inflammasome activation of the macro-phagocyte comparing with MSUM crystals.Furthermore,the ultrasound could de-struct the crystal structure of MSUM to transform to amorphous form,leading to crystals dissolving and inflammasome activation of the macrophagocyte inhibited.Secondly,the regulation of natural proteins in synovial fluid(albumin and chon-droitin sulfate)on the nucleation and crystal growth of MSUM were studied to clarify the mechanism of proteins modulating the crystallization of MSUM.The two proteins could hinder the aggregation of amorphous form by inhibiting the formation of pre-nucleation cluster while proteins could promote the growth of MSUM crystals wherein L-Arginine and L-Tyrosine in proteins bonded strongly to urate sodium.Therefore,we designed four peptides with different number and sequence of L-Arginine and L-Tyrosine based on the interaction between the two amino acids and urate,of which the inhibition on MSUM crystal growth reached 60%under a low concentration.Thirdly,the coexistence of uric acid dihydrate(UAD)and uric acid anhydrate(UAA)is common in urinary stone.We studied the crystallization of uric acid in acidic solution(simulated p H of urine)and found unusual phase transition mechanism between UAD and UAA through the core-shell structure.Uric acid molecules spon-taneously crystallized to form UAD crystal as the mother crystal under a certain su-persaturation.However,UAA would gradually nucleate and grow inside the mother crystal through the solid-state dehydration phase transition prior to its competitive transformation approach mediated by solvent,forming an unconventional core-shell structure.We revealed that the presence of crystal defects,imported by urate tautom-erism over the course of crystallization,elevated the metastability of mother crystal(UAD)crystal and triggered the UAD dehydration to the UAA phase in crystal core.Finally,the regulation of Na~+and K~+on the crystal growth of UAD crystals were studied to verify the roles of ions(in urine)in the crystallization of uric acid crystals.Na~+inhibited the crystal growth through blocking kinks on the surfaces.However,the presence of K~+could not only roughen the surfaces but also hinder the adsorption of solutes,leading to accelerated crystal growth along[100]direction while inhibited growth along[010]direction.The regulation mechanism of ions on the crystal growth of UAD along different directions depended on the chemical properties of different crystal planes,which provides a suggestion or a rational diet for patients with urinary stone.