Interleukin-6 collection through long-term implanted microdialysis sampling probes in rat subcutaneous space.

Microdialysis sampling is a method that has promise for collection of important signaling proteins such as cytokines that are involved in every aspect of the immune response. The objective of this study was to determine the role of membrane and tissue alterations on the reduction of interleukin-6 (IL-6) relative recovery of microdialysis probes implanted for 3 and 7 days versus probes implanted on day 0 (acute implant or control probe). Lipopolysaccharide (LPS), a bacterial endotoxin, was used to elicit IL-6 production in the animals. Within the same animal, the recovery of IL-6 through control probes implanted the day of sample collection was compared to the 3- or 7-day implanted probes. Two hours post-LPS administration, the IL-6 concentrations obtained from either the 3-day or 7-day implanted probe were reduced by more than 8-fold when compared to the control probe. The IL-6 concentrations obtained for the 3-day versus control probes 2-h post-LPS injection were 730 +/- 310 and 6440 +/- 1550 pg/mL (mean +/- SD, n = 3), respectively. For the 7-day implant, the IL-6 concentration in the dialysis probe obtained at 2-h post-LPS injection was 990 +/- 590 versus 5520 +/- 1430 pg/mL (mean +/- SD, n = 3) for the control. In vitro recovery experiments and scanning electron microscopy images combined with the in vivo data suggest that the decreased IL-6 content in the dialysate was caused principally by tissue alterations or tissue encapsulation rather than membrane blockage with biological components (membrane biofouling).