| Microdialysis sampling has become a standard tool to collect small hydrophilic analytes from the extracellular fluid space of different tissues in animals and humans. Nowadays, researchers are interested in applying the technique to a wide variety of different analytes, e.g., hydrophobic molecules as well as peptides and proteins.; Hydrophobic analytes are usually recovered poorly by the microdialysis membrane. Combining chemical reactions inside the membrane with diffusion can facilitate the analyte mass transport through the membranes. Native cyclodextrins (CDs) have been used as trapping agents in the perfusion fluid to enhance the microdialysis relative recovery (RR) of hydrophobic analytes. However, native CDs diffuse through the microdialysis membrane and may cause accumulation in the sampling site. Cyclodextrin polymers were used as alternatives to native CDs inside the membrane to significantly enhance the microdialysis RR of amitryptiline, carbamazepine, hydroquinone, ibuprofen, and 4-nitrophenol. Different parameters including perfusion flow rates, polymer concentrations, membrane length, and membrane materials affecting the microdialysis RR enhancement were studied. beta-CD polymer has shown much lower loss through the polycarbonate microdialysis membrane than native cyclodextrins.; Cytokines are important mediators and modulators of many physiological systems. Low recovery combined with their pM or fM in vivo concentration presents significant challenges for microdialysis sampling. The low microdialysis recovery challenge has been overcome by adding cytokine antibody-coated microspheres as trapping agents in the perfusion fluid. Two to ten fold microdialysis RR enhancements were achieved for interferon (IFN)-gamma, interleukin (IL)-2, IL-4, IL-5, IL-6,11,-10, IL-12p70, monocyte chemoattractant protein (MCP)-1, and tumor necrosis factor (TNF)-alpha. A modified microdialysis mass transport model for cytokines was proposed by introducing a quantitative membrane diffusion hindrance factor into the well-accepted Bungay model. Experimental data using both quiescent and well-stirred systems were used to test the model and the experimental data gave a reasonable fit with the model predictions.; Coupling microdialysis sampling with microsphere-based flow cytometry immunoassay was successfully used to monitor the cytokine levels on-site from activated murine macrophages and mice in real time. Three inflammatory cytokines including TNF-alpha, MCP-1, and IL-6 were easily collected from bacterial lipopolysaccharide (LPS) stimulated macrophages in cell culture and in vivo mice using this approach. |
