Abstract
Increased blood ammonium concentrations cause neurological complications. Existing drugs are not always sufficiently effective. Alternatively, erythrocytes-bioreactors (EBRs) loaded with enzymes utilizing ammonium, were suggested for ammonium removal from blood. However all they worked only for a short period of time. The reasons for this were not investigated. In this study, EBR mathematical models were developed and analysed based on the reactions of glycolysis and different enzymes utilizing ammonium, which showed that the efficiency and duration of EBRs’ functioning could be limited due to low permeability of the cell membrane for some key substrates and products. A new enzyme system including glutamate dehydrogenase and alanine aminotransferase was proposed and realised experimentally, which was not limited by cell membrane permeability for glutamate and α-ketoglutarate due to creating metabolic pathway where these metabolites were produced and consumed cyclically. New bioreactors removed ammonium in vitro at the rate of 1.5 mmol/h × lRBCs (for human bioreactors) and in vivo in a model of hyperammoniemia in mice at the rate of 2.0 mmol/h × lRBCs (for mouse bioreactors), which correlated with model calculations. Experimental studies proved the proposed mathematical models are correct. Mathematical simulation of erythrocyte-bioreactors opens new opportunities for analysing the efficiency of any enzyme included in erythrocytes.
Highlights
The aim of this study was to develop a new bioreactor based on human erythrocytes (EBR), to provide an effective ammonium removal from the blood of patients with hyperammonaemia
We developed mathematical models for human EBRs based on the following enzymes: EBR #1: glutamine synthetase (GS, reaction [1]): glutamic acid (GLU) + NH+4 + ATP ↔ GLN + ADP + PO−4 3 [1]
Given that cellular bioreactors should function in the body for many tens of hours and that the characteristic times of most metabolic processes in erythrocytes do not exceed several tens of minutes, it must be assumed that the created bioreactor will function under physiological conditions in a quasi-steady state, i.e., the concentrations of all intracellular metabolites of glycolysis such as glucose, LAC and PYR, will remain constant for many hours, despite the fact that the bioreactor produces or consumes these substances
Summary
The aim of this study was to develop a new bioreactor based on human erythrocytes (EBR), to provide an effective ammonium removal from the blood of patients with hyperammonaemia. Bioreactors for ammonium removal based on mouse, sheep and human erythrocytes were investigated by various groups They used only two enzymes: glutamine synthetase (GS) catalysing the formation of L-glutamine from L-glutamic acid and ammonium in the presence of ATP (reaction 1) or L-glutamate dehydrogenase (GDH) which catalyses the formation of L-glutamic acid from α-ketoglutarate and ammonium in the presence www.nature.com/scientificreports/. In vivo these EBRs effectively removed ammonium from the mice circulation only in the first 0.5–1 h23,25 After this time, the blood ammonium concentration decreased approximately at the same rate in both the experimental and the control animals, which received dialysed erythrocytes but without enzymes. Bioreactors might remove ammonium from the blood for a short period of time, until the reaction equilibrium completely shifts towards ammonium production. This approach can be used to analyse the effect of any enzyme included in erythrocytes
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call