High citrate diet delays progression of renal insufficiency in the ClC-5 knockout mouse model of Dent's disease.

BACKGROUND: Dent's disease, an X-linked renal tubular disorder, is characterized by low-molecular-weight proteinuria, hypercalciuria, nephrocalcinosis, nephrolithiasis, and progressive renal failure. Dent's disease results from mutations of the voltage-gated chloride channel CLC-5. METHODS: We studied the effect of zero and high citrate diet on renal function of ClC-5 knockout mice and wild-type mice. The mice were placed in metabolic cages from which the urine was collected. Mice were sacrificed to obtain serum and tissues for analysis. RESULTS: ClC-5 knockout mice fed zero or high citrate diet had significantly increased urinary calcium excretion compared with wild-type mice fed the same diets. Nine-month-old ClC-5 knockout mice on a zero citrate diet had significantly decreased glomerular filtration rate (GFR), whereas 9-month-old ClC-5 knockout mice on a high citrate diet had normal renal function. ClC-5 knockout mice fed a zero citrate diet had significantly increased tubular atrophy, interstitial fibrosis, cystic changes, and nephrocalcinosis compared to ClC-5 knockout mice fed a high citrate diet. Transforming growth factor-beta1 (TGF-beta1) was significantly increased in 9-month-old ClC-5 knockout mice on zero citrate diet compared to 9-month-old wild-type mice on the same diet. CONCLUSION: High citrate diet preserved renal function and delayed progression of renal disease in ClC-5 knockout mice even in the apparent absence of stone formation. We conclude from this that long-term control of hypercalciuria is an important factor in preventing renal failure in these mice

A QM/MM refinement of an experimental DNA structure with metal-mediated base pairs

A series of hybrid quantum mechanical/molecular mechanical (QM/MM) calculations was performed on models of a DNA duplex with artificial silver(I)-mediated imidazole base pairs. The optimized structures were compared to the original experimental NMR structure (Nat. Chem. 2 (2010) 229-234). The metal⋯metal distances are significantly shorter (~0.5Å) in the QM/MM model than in the original NMR structure. As a result, argentophilic interactions are feasible between the silver(I) ions of neighboring metal-mediated base pairs. Using the computationally determined metal⋯metal distances, a re-refined NMR solution structure of the DNA duplex was obtained. In this new NMR structure, all experimental constraints remain fulfilled. The new NMR structure shows less deviation from the regular B-type conformation than the original one. This investigation shows that the application of QM/MM models to generate additional constraints to be used during NMR structural refinements represents an elegant approach to obtaining high-resolution NMR structures