Monitoring of Lactate in Interstitial Fluid, Saliva and Sweat by Electrochemical Biosensor: The Uncertainties of Biological Interpretation

Salzitsa Anastasova,Pankaj Vadgama,Anna-Maria Spehar-Délèze

doi:10.3390/chemosensors9080195

Salzitsa Anastasova, Pankaj Vadgama + Show 1 more

Open Access

https://doi.org/10.3390/chemosensors9080195

Copy DOI

Abstract

Lactate electrochemical biosensors were fabricated using Pediococcus sp lactate oxidase (E.C. 1.1.3.2), an external polyurethane membrane laminate diffusion barrier and an internal ionomeric polymer barrier (sulphonated polyether ether sulphone polyether sulphone, SPEES PES). In a needle embodiment, a Pt wire working electrode was retained within stainless steel tubing serving as pseudoreference. The construct gave linearity to at least 25 mM lactate with 0.17 nA/mM lactate sensitivity. A low permeability inner membrane was also unexpectedly able to increase linearity. Responses were oxygen dependent at pO2 < 70 mmHg, irrespective of the inclusion of an external diffusion barrier membrane. Subcutaneous tissue was monitored in Sprague Dawley rats, and saliva and sweat during exercise in human subjects. The tissue sensors registered no response to intravenous Na lactate, indicating a blood-tissue lactate barrier. Salivary lactate allowed tracking of blood lactate during exercise, but lactate levels were substantially lower than those in blood (0–3.5 mM vs. 1.6–12.1 mM), with variable degrees of lactate partitioning from blood, evident both between subjects and at different exercise time points. Sweat lactate during exercise measured up to 23 mM but showed highly inconsistent change as exercise progressed. We conclude that neither tissue interstitial fluid nor sweat are usable as surrogates for blood lactate, and that major reappraisal of lactate sensor use is indicated for any extravascular monitoring strategy for lactate.

Highlights

Lactate is a byproduct of glycolysis and accumulates when there is either an absolute or relative lack of tissue oxygen [1]
For the first time lactate sensor pO2 dependence was characterized, and we demonstrated an unusual effect on linearity through use of a lower permeability inner membrane
Silver coating of the needle is an attractive option for creating a formal electrochemical cell, so ultra-high vacuum (UHV) deposition of silver was undertaken as a simple, single step means for achieving this

Summary

Introduction

Lactate is a byproduct of glycolysis and accumulates when there is either an absolute or relative lack of tissue oxygen [1]. Whilst arterial pO2 provides a measure of the adequacy of central ventilatory and cardiac function [2], lactate serves as the ultimate marker of oxygen utilisation It serves as the benchmark indicator of a shift in energy utilization via the Krebs citric acid cycle and mitochondrial electron transport to that limited to the glycolytic pathway [3]. The latter provides for urgent short term energy needs, without the requirement for oxygen. It lies just a single redox equilibrium step from pyruvate at the end of the glycolytic pathway [6], and so is rapidly responsive to the oxygenation state

Methods

Results

Conclusion