Hemodialysis Decreases the Concentration of Accumulated Plant Phenols in the Plasma of Patients on Maintenance Dialysis: Influence of Residual Renal Function

Plant phenols may accumulate in end‐stage kidney disease. The effect of hemodialysis on their plasma concentration remains poorly determined. Contingent on concentration, health‐promoting or noxious effects occur; therefore, we assessed plasma concentration in hemodialyzed patients. In total, 21 maintenance hemodialyzed patients with diuresis < 500 mL per day (with oliguria), nine hemodialyzed patients with diuresis ≥ 500 mL per day (without oliguria) and 31 healthy volunteers were included. Nine phenolic acids were identified with high‐performance liquid chromatography and total polyphenol concentration was determined with the Folin–Ciocalteu method in pre‐ or post‐hemodialysis plasma and pre‐ or intra‐hemodialysis dialysate. The concentration of total polyphenols was 27% higher in pre‐hemodialysis plasma than in that of controls (0.95 ± 0.18 mmol/L [ P < 0.0001]). The concentration of total polyphenols was higher in patients with oliguria (1.01 ± 0.17) than in those without (0.84 ± 0.13 mmol/L), despite the former having more intense hemodialysis (Kt/V 1.29 ± 0.31 and 0.77 ± 0.25, respectively). Pre‐hemodialysis phenolic acid concentration in patients undergoing dialysis exceeded reference values by 3 to 34 times (3‐hydroxyphenylacetic acid and vanillic acid, respectively), from 0.69 (dihydrocaffeic acid) to 169.3 μmol/L (hippuric acid). The concentration of six phenolic acids (3‐hydroxyhippuric, caffeic, dihydrocaffeic, hippuric, homovanillic, and vanillic acid) was 1.1 (homovanillic) to 11.3 (3‐hydroxyhippuric) times higher in patients with oliguria than in those without. 4‐hydroxyhippuric acid occurred more in the plasma of patients with oliguria than in those without oliguria. A single hemodialysis session decreased total polyphenol concentration by 16% and phenolic acids from 30% (caffeic) to 58% (vanillic and 3‐hydroxyphenylacetic acid) and these compounds appeared in the dialysate. The percentage decrease (Δ%) of creatinine concentration correlated with the Δ% of total polyphenols and five phenolic acids (3‐hydroxyphenylacetic, dihydrocaffeic, hippuric, homovanillic, and vanillic acid). Urea Δ% and Kt/V correlated only with the Δ% of homovanilic acid. The results demonstrate that phenols accumulate variably in hemodialyzed patients and are differently eliminated during hemodialysis. Residual renal function ensures a lower concentration of plasma phenols.