Utilization of Deep Eutectic Solvents to Determine Indoxyl Sulfate in Plasma from Patients with Renal Disease

Abstract

Introduction: The uremic toxin, indoxyl sulfate (IS), has an important role in the development of various medical conditions notably cardiovascular, bone toxicity, and chronic kidney disease (CKD) progression. Hence, controlling the concentration of this biomarker in biological fluids may be a promising diagnostic tool that enables timely treatment to preserve renal system functionality. Therefore, several methods are available for quantification of IS in biological fluids and most of them require long laboratory run time.Aims: This study aimed to propose a rapid and efficient analytical method to identify IS in human plasma samples through extraction technique with deep eutectic solvent (DES) and spectrofluorimetric determination.Methods: Plasma samples of hemodialysis patients were deproteinized by trichloroacetic acid (TCA). Then, DES was added to extract IS. Subsequently, dipotassium hydrogen phosphate (K2HPO4) solution was added to form an aqueous two-phase system. The fluorescence intensity of IS which was first extracted to the DES-rich-phase and then back-extracted into the salt-rich-phase was measured by spectrofluorimetry method. Some crucial factors such as pH, centrifugation speed and time, DES/salt volume ratio, and salt concentration were optimized. Results: Under the optimized conditions, the suggested method had a linear range between 20-160 μg/mL with a coefficient of determination (R2) of 0.98. Precision (relative standard deviation) was less than 15% and accuracy (% error) was less than 15% at nominal concentration levels. In addition, the results showed that IS levels in real samples were higher than 40 μg/mL which was in accordance with reported IS levels in end-stage renal disease patients.Conclusions: IS is an important biomarker in evaluating the progress of CKD. A rapid and efficient analytical method was established for IS in plasma through extraction technique with DES and analytical quantification with spectrofluorimetricy. The results indicated that the presented analytical method can potentially be used for the determination of IS in real plasma samples.