Affinity-based microdialysis sampling using heparin for in vitro collection of human cytokines.

Microdialysis sampling is a widely used method to sample from complex biological matrices. Cytokines are important signaling proteins that are typically recovered with low relative recovery values during microdialysis sampling. Heparin was included in the microdialysis perfusion fluid as an affinity agent to increase in vitro recovery of different cytokines through polyethersulfone (PES) microdialysis membranes with 100 kDa molecular weight cutoff. No change in fluid volumes collected from the microdialysis probes occurred when heparin was included in the perfusion fluid up to concentrations of 10 microM. The loss of heparin (10 microM) across the dialysis membrane was minimal (2.7+/-0.9%, n=3). Additionally, heparin at these concentrations did not interfere with the cytokine immunoassays. The control and heparin-enhanced relative recoveries for five human cytokines using 0.1 microM heparin in the microdialysis perfusion fluid flowing at 0.5 microL min(-1) were (n=3): interleukin-4 (IL-4), 4.2+/-0.5% and 7.2+/-3.1%; interleukin-6 (IL-6), 1.4+/-0.8% and 3.6+/-1.3%; interleukin-7 (IL-7), 1.3+/-0.8% and 4.8+/-1.8%; monocyte chemoattractant protein-1 (MCP-1), 9.0+/-1.6% and 19.5+/-2.7%; and tumor necrosis factor-alpha (TNF-alpha), 7.4+/-1.3% and 16.9+/-1.6%, respectively. Heparin increased the microdialysis sampling relative recovery of several human cytokines in vitro.