Microdialysis Sampling Extraction Efficiency of 2-Deoxyglucose:  Role of Macrophages in Vitro and in Vivo

Abstract

Macrophages are a class of inflammatory cells believed to direct the outcome of device biocompatibility. Despite their relevance to implanted in vivo devices, particularly implanted glucose sensors, few studies have attempted to elucidate how these cells affect device performance. Microdialysis sampling probes were used to determine glucose uptake alterations in the presence of resting and activated macrophages in vitro. Significant differences for 2-DG relative recovery at 1.0 μL/min were observed between resting (74 ± 7%, n=18) and lipopolysaccharide (LPS) (1 μg/mL) activated (56 ± 6%, n=18) macrophages in culture which had 2-DG spiked into the media (p<0.005). To establish if in vitro characterization could be correlated to in vivo studies, microdialysis probes were implanted into the dorsal subcutis of male Sprague-Dawley rats for 0,3,5 and 7 days. An internal standard, 2-deoxyglucose (2-DG), was passed through the microdialysis probe during in vivo studies. No significant differences in 2-DG extraction efficiency from the probe into the tissue site were observed in vivo among microdialysis probes implanted into the subcutaneous space of SpragueDawley rats for either three, five or seven days vs. probes implanted the day of sample collection. These results suggest that macrophage activation in vivo at implant sites is much lower than highly activated macrophages in vitro. It is important to note that these results do not rule out the potential for increased glucose metabolism at sensor implant sites.

Long-term calibration considerations during subcutaneous microdialysis sampling in mobile rats

“…The lack of change in the EE values for 2-DG is consistent with our previously reported preliminary studies in anesthetized rats [29]. If there were a significantly higher uptake of 2-DG into the metabolically active immune cells surrounding the implanted probe it could be reflected as an increase in the EE values for 2-DG.…”

“…To determine how calibration may be affected by potential alterations in metabolism and capillary permeability during the long-term implantation, three internal standards were perfused through the implanted microdialysis probes. The compound 2-deoxyglucose (2-DG) is widely used in studies for glucose metabolism and has been used to determine the variation of glucose in the presence of active macrophages [28,29]. Antipyrine rapidly equilibrates in the extracellular fluid of tissues and has been widely used as a marker for capillary permeability and has been used as an internal standard during microdialysis sampling [30,31].…”

Hypoxia But Not Inflammation Augments Glucose Uptake in Human Macrophages

“…Lederman et al (3) reported that the 3 H-2dG signal from rabbit plaques on autoradiography originates not only from macrophagerich areas, but also from smooth muscle cell (SMC) rich areas. Mou et al (21) showed that inflammatory cells in the focus of microdialysis probe implantation in rats consumed relatively small amounts of 2dG infused through the probe. This discrepancy is not surprising, as many studies performed in untransformed and cancer cell lines (17,22,23) have shown that numerous factors can affect glucose uptake, but those factors do not apply universally to all cell types.…”

Analyte Flux at a Biomaterial-Tissue Interface over Time: Implications for Sensors for Type 1 and 2 Diabetes Mellitus

“…[7][8][9] Microdialysis is an in vivo diffusion-based sampling technique for studying metabolism in different tissues, 10 and it is a simple analogue to in vivo analyte sensors. 11,12 It permits concurrent study of numerous small molecules that diffuse from the tissue through a semipermeable membrane, similar to the semipermeable membrane of sensors, but without the complexities of detection enzymes, electronics, and other components of implanted sensors. Figure 1 describes the relation of various metabolites of interest for continuous monitoring in the subcutaneous (sc) tissue.…”