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

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-deoxyglucose (2-DG) relative recovery at 1.0 microL/min were observed between resting (74 +/- 7%, n = 18) and lipopolysaccharide (LPS) (1 microg/mL)-activated (56 +/- 6%, n = 18) macrophages in culture that 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-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 Sprague-Dawley rats for either 3, 5, or 7 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.