Changes in plasma free and phospholipid-bound choline concentrations in chronic hemodialysis patients

Background: Choline deficiency may develop in malnourished patients, those with cirrhosis, and those who require total parenteral nutrition. Previous data has suggested an important role for the kidneys in the maintenance of choline homeostasis. Objective: This study was undertaken to determine the change in plasma choline during hemodialysis and to determine if it was lost in the dialysate. Design: Thirteen adult patients (10 men, 3 women) who had required hemodialysis for a mean of 10.8 years were studied. Dialysis was performed 3 times weekly for 4 hours using either a cellulose acetate or polysulfone dialyzer membrane. Venous and arterial blood, and dialysate samples were taken for measurement of plasma free and phospholipid-bound choline concentration before beginning dialysis and after each hour of dialysis. An in vitro system was devised to determine if choline could bind to a significant degree to the dialysis membrane. Results: Plasma free choline concentration was increased above normal (11.7 ± 3.7 nmol/mL) at baseline and declined progressively during dialysis. In contrast, plasma phospholipid-bound choline concentration increased progressively during dialysis. The decrease in plasma free choline (-1.8 ± 0.3 nmol/mL^-1/h^-1; P = 1.6 × 10^-6) was almost entirely related to that which was removed during dialysis, although the magnitude of the loss was not correlated with the increase in plasma phospholipid-bound choline concentration (125 ± 20.5 nmol/mL^-1/h^-1; P < 1.2 × 10^-6). Patients lost a mean of 246 μmol of free choline during hemodialysis. Choline did not bind to the dialysis membrane. Conclusion: Plasma free choline concentration is elevated before dialysis, and choline is lost to a significant degree in the dialysate. Further investigation is necessary to determine whether a transient, dialysis-induced choline deficiency develops, and whether there is a role for choline supplementation in these patients. The choline homeostatic mechanism requires further investigation in renal failure patients.