The urinary proteomic analysis and the vitamin d receptor polymorphisms in dogs with calcium oxalate urolithiasis

Abstract

Calcium oxalate (CaOx) urolithiasis is one of the most common stone components which frequently occurs in both humans and dogs. Hypercalciuria is one of the predisposing factors commonly found in both people and dogs with calcium urolithiasis. The genetic factors are also involved with the pathogenesis of stone formation, and the relationship between calcium handling and vitamin D receptor (VDR) polymorphisms has been demonstrated to be related to calcium urolithiasis in human populations. Moreover, some urinary proteins may be involved in the process of stone formation. The present study aimed firstly to evaluate the relationship between VDR polymorphism in dog with CaOx urolithiasis. Secondly, the urinary proteomic profile between hypercalciuric dogs with or without CaOx urolithiasis was investigated. The study was divided into two parts: part I and part II. The study in part I was divided into 2 groups, CaOx dogs (n=35) and stone-free control dogs (n=40). The blood sample was collected for determination of complete blood count, serum chemistry profiles, serum electrolytes, serum vitamin D, and DNA analysis for single nucleotide polymorphism (rs852900542 and rs851998024) of the VDR gene. The urine sample was collected for determination of electrolyte concentrations. In study part II, the urinary proteomic profiles were determined in CaOx stone dogs with hypercalciuria (n=7) compared with the breed, age-, and sex-matched hypercalciuric controls (n=7). The results from the study in part I showed that the genotypic distribution of rs852900542 was significantly different between CaOx stone and control dogs (P<0.05), and dogs with a CC or CT genotypes had an increased risk for CaOx stones than those with the TT genotype (OR = 3.82, 95% CI 1.04 – 13.98, P<0.05). Moreover, CaOx dogs with CC or CT had higher UCa/Cr and UMg/Cr than those with the TT (P<0.05). However, there was no difference in genotypic distribution of rs851998024 between CaOx dogs and control dogs in this study. In the study part II, 49 proteins were identified in urine from both hypercalciuric CaOx stone former and stone-free dogs. Thrombomodulin was significantly higher between the control and case groups (P<0.05). The vesicular integral-membrane protein (VIP) 36 and pantetheinase were higher in CaOx stone-former (P=0.16 and P=0.17, respectively), while intercellular adhesion molecule 1 was reduced (P=0.14). In conclusion, the rs852900542 VDR polymorphism is associated with CaOx susceptibility in dogs, which is related to urinary calcium excretion. In addition, the hypercalciuric CaOx dogs have an increased level of urinary proteins, including thrombomodulin, pantetheinase ,and VIP36 which indicate the urinary tract injury. This genetic finding might be useful for screening dogs that are at increased risk and prevention of CaOx urolithiasis, and the identification of urinary proteins may be useful for the urinary tract injury marker in dogs with CaOx urolithiasis.