Metabolic consequences of cystinuria

Abstract

Background Cystinuria is an inherited disorder of renal amino acid transport that causes recurrent nephrolithiasis and significant morbidity in humans. It has an incidence of 1 in 7000 worldwide making it one of the most common genetic disorders in man. We phenotypically characterized a mouse model of cystinuria type A resultant from knockout of Slc3a1 . Methods Knockout of Slc3a1 at RNA and protein levels was evaluated using real-time quantitative PCR and immunofluorescence. Slc3a1 knockout mice were placed on normal or breeder chow diets and evaluated for cystine stone formation over time suing x-ray analysis, and the development of kidney injury by measuring injury biomarkers. Kidney injury was also evaluated via histologic analysis. Amino acid levels were measured in the blood of mice using high performance liquid chromatography. Liver glutathione levels were measured using a luminescent-based assay. Results We confirmed knockout of Slc3a1 at the RNA level, while Slc7a9 RNA representing the co-transporter was preserved. As expected, we observed bladder stone formation in Slc3a1 −/− mice. Male Slc3a1 −/− mice exhibited lower weights compared to Slc3a1 +/+ . Slc3a1 −/− mice on a regular diet demonstrated elevated blood urea nitrogen (BUN) without elevation of serum creatinine. However, placing the knockout animals on a breeder chow diet, containing a higher cystine concentration, resulted in the development of elevation of both BUN and creatinine indicative of more severe chronic kidney disease. Histological examination revealed that these dietary effects resulted in worsened kidney tubular obstruction and interstitial inflammation as well as worsened bladder inflammation. Cystine is a precursor for the antioxidant molecule glutathione, so we evaluated glutathione levels in the livers of Slc3a1 −/− mice. We found significantly lowered levels of both reduced and total glutathione in the knockout animals. Conclusions Our results suggest that that diet can affect the development and progression of chronic kidney disease in an animal model of cystinuria, which may have important implications for patients with this disease. Additionally, reduced glutathione may predispose those with cystinuria to injury caused by oxidative stress. Word count: 327. Electronic supplementary material The online version of this article (10.1186/s12882-019-1417-8) contains supplementary material, which is available to authorized users.

S-Methyl-L-Ergothioneine to L-Ergothioneine Ratio in Urine Is a Marker of Cystine Lithiasis in a Cystinuria Mouse Model

“…The results presented here also suggest that OCTN1 ( Slc22a4 ) might be a modulator of cystine lithiasis. The changes we observed in the levels of the antioxidant L-Erg together with the lower reduced and total glutathione levels described in cystinuric mice [ 36 ] and the reduction in cystine lithiasis when mice is treated with antioxidants [ 44 , 45 ], support the hypothesis of the involvement of redox mechanisms in cystinuria. Based on our results, it is also tempting to speculate that a lower activity or a defective OCTN1 might be behind those patients showing highly lithiasic phenotypes.…”

“…This hypothesis is supported by the correlation observed in the levels of hercynine or L-ergothioneine sulfonate and L-Erg in kidneys [ 35 ]. The reduce glutathione levels observed in the liver of cystinuric mice might predispose to injuries caused by oxidative stress [ 36 ] and can be speculated that ergothioneine, as an antioxidant, might be being used by tissues to compensate a reduced redox metabolism.…”

Single-cell profiling of healthy human kidney reveals features of sex-based transcriptional programs and tissue-specific immunity

“…2c, e ). Additional differentially expressed genes also relate to cysteine-glutathione availability and metabolism, including SLC3A1 33 , MGST3 , and HRASLS2 .…”

Gene therapy for kidney disease: targeting cystinuria

“…a-lipoic acid has been shown to improve cystine solubility in mice [35], but studies will reveal if it works in humans. It does not correct the transporter defect that can also affect amino acid levels in the blood and other tissues [36].…”