The association of renal tubular inflammatory and injury markers with uric acid excretion in chronic kidney disease patients

Association of urinary excretion rates of uric acid with biomarkers of kidney injury in patients with advanced chronic kidney disease

BACKGROUND

The potential influence of hyperuricemia on the genesis and progression of chronic kidney disease (CKD) remains controversial. In general, the correlation between blood levels of uric acid (UA) and the rate of progression of CKD is considered to be modest, if any, and the results of relevant trials oriented to disclose the effect of urate-lowering therapies on this outcome have been disappointing. Urinary excretion rates of UA could reflect more accurately the potential consequences of urate-related kidney injury.

METHOD

Using a cross-sectional design, we investigated the correlation between different estimators of the rates of urinary excretion of UA (total 24-hour excretion, mean urinary concentration, renal clearance and fractional excretion)(main study variables), on one side, and urinary levels of selected biomarkers of kidney injury and CKD progression (DKK3, KIM1, NGAL, interleukin 1b and MCP)(main outcome variables), in 120 patients with advanced CKD (mean glomerular filtration rate 21.5 mL/minute). We took into consideration essential demographic, clinical and analytic variables with a potential confounding effect on the explored correlations (control variables). Spearman's rho correlation and nonlinear generalized additive regression models (GAM) with p-splines smoothers were used for statistical analysis.

MAIN RESULTS

Multivariate analysis disclosed independent correlations between urinary UA concentrations, clearances and fractional excretion rates (but not plasma UA or total 24-hour excretion rates of UA), on one side, and the scrutinized markers. These correlations were more consistent for DKK3 and NGAL than for the other biomarkers. Glomerular filtration rate, proteinuria and treatment with statins or RAA axis antagonists were other independent correlates of the main outcome variables.

CONCLUSIONS

Our results support the hypothesis that urinary excretion rates of UA may represent a more accurate marker of UA-related kidney injury than plasma levels of this metabolite, in patients with advanced stages of CKD. Further, longitudinal studies will be necessary, to disclose the clinical significance of these findings.

Natural Xanthine Oxidase Inhibitor 5-O-Caffeoylshikimic Acid Ameliorates Kidney Injury Caused by Hyperuricemia in Mice

Xanthine oxidase (XOD) inhibition has long been considered an effective anti-hyperuricemia strategy. To identify effective natural XOD inhibitors with little side effects, we performed a XOD inhibitory assay-coupled isolation of compounds from Smilacis Glabrae Rhizoma (SGR), a traditional Chinese medicine frequently prescribed as anti-hyperuricemia agent for centuries. Through the in vitro XOD inhibitory assay, we obtained a novel XOD inhibitor, 5-O-caffeoylshikimic acid (#1, 5OCSA) with IC₅₀ of 13.96 μM, as well as two known XOD inhibitors, quercetin (#3) and astilbin (#6). Meanwhile, we performed in silico molecular docking and found 5OCSA could interact with the active sites of XOD (PDB ID: 3NVY) with a binding energy of −8.6 kcal/mol, suggesting 5OCSA inhibits XOD by binding with its active site. To evaluate the in vivo effects on XOD, we generated a hyperuricemia mice model by intraperitoneal injection of potassium oxonate (300 mg/kg) and oral gavage of hypoxanthine (500 mg/kg) for 7 days. 5OCSA could inhibit both hepatic and serum XOD in vivo, together with an improvement of histological and multiple serological parameters in kidney injury and HUA. Collectively, our results suggested that 5OCSA may be developed into a safe and effective XOD inhibitor based on in vitro, in silico and in vivo evidence.

Clinical classification of hyperuricemia in patients with chronic kidney disease

PURPOSE

Clinical classification of hyperuricemia (HUA) could help to guide therapy of HUA. Studies on the classification of HUA with chronic kidney disease (CKD) are rare. Therefore, we aimed to investigate the classification of HUA with CKD.

METHODS

A cross-sectional study of 428 CKD patients was conducted, including 218 HUA patients. By correlation analysis, the association of 24-h urinary uric acid (24-h Uur), uric acid clearance rate (Cur), the urinary uric acid excretion per kilogram of weight per hour (Eur) and fractional excretion of uric acid (FEur) with estimated glomerular filtration rate (eGFR) was analyzed in the HUA and non-HUA groups. According to Eur combined with Cur and the 24-h Uur combined with FEur, HUA with CKD was classified into underexcretion, renal overload, combined and 'normal' types, which were also stratified by CKD stages.

RESULTS

According to the Eur and Cur, in early CKD (eGFR ≥ 60 mL/min/1.73 m²), the underexcretion type accounted for 83.75%, and the renal overload type accounted for 2.5%. As the CKD stage increased, the proportion of the underexcretion type increased. According to the 24-h Uur and FEur, in early CKD, the underexcretion type accounted for 53.75%, and the renal overload type accounted for 15%. With increasing CKD stages, the proportion of the 'normal' type increased significantly.

CONCLUSION

Different uses of Eur with Cur or 24-h Uur with FEur varied significantly in classifying HUA patients with CKD. Eur + Cur may be more applicable to the classification of HUA patients with CKD, and further research is needed.