Urinary Cystatin C as a Marker of Tubular Dysfunction

Combining Neprilysin Inhibitor With AT2R Agonist Is Superior to Combination With AT1R Blocker in Providing Reno-Protection in Obese Rats

Clinical use of the combination therapy of the neprilysin inhibitor sacubitril and angiotensin II type 1 receptor blocker valsartan is known to be associated with albuminuria. Albuminuria is both a risk factor for and an indicator of kidney injury. Earlier work from our laboratory reported that the agonist of angiotensin II type 2 receptor Compound 21 (C21) prevents proteinuria, albuminuria, and is reno-protective in obese Zucker rats fed high salt diet (HSD). Thus, we hypothesized that sacubitril/C21 combination provides superior reno-protection compared to sacubitril/valsartan. Male obese Zucker rats 10–11 weeks old were treated daily with vehicle, sacubitril + C21, or sacubitril + valsartan while fed HSD for 16 days. HSD-feeding caused kidney dysfunction, evident by significant increases in urinary protein, osteopontin, and cystatin C. HSD-feeding lowered plasma cystatin C and creatinine concentrations suggestive of hyperfiltration, which was not affected by either treatment. Unlike sacubitril/valsartan, sacubitril/C21 treatment significantly decreases proteinuria, albuminuria, the expression of nephrin, and kidney weight, independent of hyperfiltration, compared with HSD alone. Moreover, sacubitril/valsartan therapy increased plasma renin and did not prevent HSD-induced increases in renal angiotensin II, while sacubitril/C21 completely prevented these changes. Together, this study suggests that sacubitril/C21 afforded superior reno-protection compared to sacubitril/valsartan therapy in high salt-fed obese Zucker rats.

Soluble Expression of Recombinant Human Cystatin C and Comparison of the Ni Column and Magnetic Bead Purification

Cystatin C, also known as γ-trace or post-γ-globulin, is a cysteine protease inhibitor from the cystatin superfamily. It is usually used as a marker of the glomerular filtration rate owing to its low molecular weight and constant secretion. The recently available methods for cystatin C preparation have low outputs. Hence, a productive preparation system is urgently required. In this study, a 6 × His-tag coupled with a thrombin cleavage site was fused to the C-terminus of cystatin C, and the protein was well expressed in Escherichia coli after optimization. Then, two different systems were used to obtain no-tag cystatin C: a traditional nickel (Ni)-column system and a subtly Ni magnetic bead system. The column system was more commonly used, and the magnetic bead system was more convenient. Cystatin C (purity > 97%) was successfully obtained, and the yields in both the systems were higher than those in previous studies. Further, the proper folding status and bioactivity of recombinant cystatin C were confirmed using the papain inhibition assay, dynamic light scattering, and circular dichroism spectroscopy.

Novel automated immune turbidimetric assay for routine urinary cystatin-C determinations

AIM

There is no commercially available urinary cystatin-C (u-CYSC) test in the market. Therefore, we optimized and validated an automated immune turbidimetric test for u-CYSC measurements and investigated u-CYSC concentrations in acute and chronic diseases which might lead to renal tubular disorders.

MATERIALS & METHODS

A particle-enhanced immune turbidimetric assay was adapted and validated on a Cobas 8000/c502 analyzer. Urine samples of different patient groups were also analyzed.

RESULTS

Our method showed excellent analytical performance. U-CYSC/u-creatinine (u-CREAT) was higher in sepsis-related acute kidney injury group (p < 0.001) compared with controls and to patients with chronic hypertension and Type 2 diabetes.

CONCLUSION

We validated a fast, sensitive, fully automated u-CYSC assay which is ideal for routine use and might be a potential complementary laboratory test to evaluate renal tubular function.

Cystatin C, Renal Function and Cardiovascular Risk

Cystatin C is a novel serum marker of the glomerular filtration rate (GFR), a critical measure of normal kidney function. Unlike serum creatinine, cystatin C concentrations are independent of gender, age and muscle mass. As cystatin C shown no tubular secretion, it is a much earlier indicator of decreased GFR and allows the detection of mild reductions in GFR, which are not detected by creatinine. Cystatin C has been shown to be associated with future cardiovascular disease and deaths in a dose-dependent relationship that possibly reflects a very early stage of chronic ranal dysfunction. In addition, >sub-clinically< elevated cystatin C concentrations in individuals without chronic kidney disease indicated by creatinine are an independent predictor of progression to chronic kidney disease, heart failure and all-cause mortality.