The 370-Da Inhibitor of the Sodium Pump in the Plasma of Haemodialysis Patients

Background: Previous studies have shown that a molecule of mass 370 Da that inhibits the sodium pump can be extracted from human placentas and from the concentrated plasma or ultrafiltrate of volume-expanded patients. Aim: This study aimed to study the abundance of the 370-Da molecule and its changes across dialysis in a population of patients with renal failure treated by haemodialysis. Methods: Four millilitres of pre- and post-dialysis blood samples (2 mL plasma) were taken from patients receiving intermittent haemodialysis and analysed by high-performance liquid chromatography coupled to high sensitivity mass spectrometry. Results: In over half of the study population, the 370-Da molecule was present in abundance that exceeded the limit of quantitation. Most patients experienced a marked fall in the abundance of the molecule over a haemodiafiltration session, though exceptions were seen in 2 individuals, both of whom showed clear evidence for the presence of 2 structural isomers of the 370-Da molecule. Conclusions: Advanced renal failure is frequently accompanied by an increased abundance of a 370-Da inhibitor of the sodium pump and that abundance is strongly impacted by haemodialysis. The technique described here could readily be applied to other clinical situations where sodium pump inhibition might be anticipated, such as hypertension, pregnancy, and foetal medicine, and thereby lead to a better understanding of the physiology and pathophysiology of these conditions.