Abstract
Urolithiasis is a complex genetic traits disease that the formation is regarded as a process of biomineralization. The exact mechanism of the stone formation is still unclear. However, biomolecules are proposed to play a role in the biomineralization. In this study, we aimed to investigate the mechanism of stone formation through biochemistry and molecular genetics.Effects of nephrocalcin, Tamm-Horsfall protein, and albumin on calcium oxalate crystallization were tested through crystal nucleation, crystal growth, and crystal aggregation which were determined by spectrophotometry. Albumin and Tamm-Horsfall proteins exerted a promoting effect of nucleation in this study. Inhibitory effects of these proteins on crystal growth and crystal aggregation were found in this study. Nephrocalcin showed an inhibitory effect on the crystal growth but lost its effect when nephrocalcin was fragmented into two short peptides by the interaction with added ascorbic acid and copper ions in the solution.Being able to promote the nucleation of calcium oxalate crystal and then reduce the concentration of calcium and oxalate ions, Tamm-Horsfall protein and albumin showed an overall effect of inhibition in the calcium oxalate crystallization. Nephrocalcin is also an inhibitor in the crystallization of calcium oxalate. The influence of ascorbic acid and copper ions in calcium oxalate stone formation should be further studied clinically.Genetic polymorphisms were used in the identification of associated genes with complex disease. To our knowledge, fewer studies were done on the urolithiasis. Case-control studies comparing the allele frequencies of candidate genes between affected individuals and unaffected individuals were performed. Vitamin D receptor gene (start codon and intron 8), calcitonin receptor gene (the 1377th nucleotide), p21 gene (codon 31), osteocalcin gene, interleukin 1β gene (start codon and intorn 5), interleukin 1 receptor antagonist gene (intron 2), androgen receptor gene (CAG repeats), and estrogen receptor gene (TA repeats) polymorphisms were tested for the association with urolithiasis.Polymerase chain reaction based restriction analyses were used for the association study. The results indicated that vitamin D receptor gene, calcitonin receptor gene, p21 gene, interleukin 1 receptor antagonist gene, and androgen receptor gene (only for male patients) polymorphisms are associated with urolithiasis. The odds ratios for the risk of disease were 1.672, 5.634, 1.39, 6.041, and 0.328 (for low risk), respectively. No statistically significant difference were found in vitamin D receptor gene intron 8, osteocalcin, interleukin 1β gene start codon and intorn 5, and androgen receptor gene (for female patients) polymorphisms.Although positive association does not necessarily imply carrying the genes will develop clinical disease, it worth to be further studied for the interaction of genes and some risk factors. Documenting gene-environmental interactions may identify groups at highest risk for the stone formation. In conclusion, it is helpful to understand the candidate genes through studies of genetic polymorphisms. Studies effects of proteins on crystallizations are also helpful to understand the inhibitor roles of nephrocalcin, Tamm-Horsfall protein and albumin. The approach through biochemistry and molecular genetics can get further information on the biomineralized processes of urolithiasis.