Development of an on-animal separation-based sensor for monitoring drug metabolism in freely roaming sheep

Abstract

The development of an on-animal separation-based sensor that can be employed for monitoring drug metabolism in a freely roaming sheep is described. The system consists of microdialysis sampling coupled directly to microchip electrophoresis with electrochemical detection (MD-ME-EC). Separations were accomplished using an all-glass chip with integrated platinum working and reference electrodes. Discrete samples from the microdialysis flow were introduced into the electrophoresis chip using a flow-gated injection approach. Electrochemical detection was accomplished in-channel using a two-electrode isolated potentiostat. Nitrite was separated by microchip electrophoresis using reverse polarity and a run buffer consisting of 50 mM phosphate at pH 7.4. The entire system was under telemetry control. The system was first tested with rats to monitor the production of nitrite following introduction of nitroglycerin into the subdermal tissue using a linear probe. The data acquired using the on-line MD-ME-EC system was compared to that obtained off-line analysis by liquid chromatography with electrochemical detection (LC-EC), using a second microdialysis probe implanted parallel to the first probe in the same animal. The MD-ME-EC device was then used on-animal to monitor the subdermal metabolism of nitroglycerin in sheep. The ultimate goal is to use this device to simultaneously monitor drug metabolism and behavior in a freely roaming animal.

A review of microdialysis coupled to microchip electrophoresis for monitoring biological events

“…Therefore, it can sometimes be difficult to match this ionic strength in the separation buffer without substantial Joule heating. On the other hand, the composition of the perfusate can lead to isotachophoretic concentration enhancement of analyte as has been observed for the detection of nitrite using a phosphate-buffered saline as a perfusate [84]. …”

“…This device was used to monitor the production of hydrogen peroxide from the reaction of glucose with glucose oxidase using microdialysis sampling. Later, it was employed to monitor, subcutaneously on-animal, the production of nitrite from nitroglycerin administered using retrodialysis [84]. …”

“…Recently, our group has employed microdialysis-microchip electrophoresis with integrated electrochemical detection at platinum electrodes for on-animal monitoring [84]. To achieve on-animal sensing, all associated equipment was miniaturized and placed in a backpack on a sheep (Fig.…”

Separation-Based Methods Combined With Microdialysis Sampling for Monitoring Neurotransmitters and Drug Delivery to the Brain

“…The Susan Lunte group has pioneered this application in their labonasheep system. This device employs an allglass microchip with integrated electrochemical detection at a platinum electrode coupled online to microdialysis sampling (Scott et al, 2015). All the associated electronics (high voltage power supply, electrochemical detection) were also miniaturized, and the system was able to communicate wirelessly for data acquisition, as seen in Figure 1.10.…”

“…All the associated electronics (high voltage power supply, electrochemical detection) were also miniaturized, and the system was able to communicate wirelessly for data acquisition, as seen in Figure 1.10. The initial report demonstrated this system for monitoring subcuta neous nitrite after a nitroglycerin perfusion onanimal (sheep) and in nearreal time (Scott et al, 2015). While this was a substantial contribution to freely roam ing animal research, the ultimate goal is to monitor multiple neurotransmitters simultaneously in the brain and correlate their concentrations to behavior, a future direction discussed further in Section 1.6.1.…”