Recirculation—a novel approach to quantify interstitial analytes in living tissue by combining a sensor with open-flow microperfusion

Abstract

We report a novel approach to quantify interstitial analytes in living tissue by combining open-flow microperfusion (OFM) with a sensor and the re-circulation method. OFM is based on the unrestricted exchange of molecules between the interstitial fluid (ISF) and a perfusion medium through macroscopic perforations that enables direct access to the ISF. By re-circulating the perfusate and monitoring the changes of the analytes' concentration with a sensor, the absolute analyte concentration in the ISF can be calculated. In order to validate the new concept, the absolute electrical conductivity of the ISF was identified in six subjects to be 1.33 ± 0.08 S/m (coefficient of variation CV = 6 %), showing the robustness of this approach. The most striking feature of this procedure is the possibility to monitor several compounds simultaneously by applying different sensors which will allow not only the determination of the concentration of a single substance in vivo but also the simultaneous dynamics of different analytes. This will open new fields in analytical chemistry, pharmacology, as well as clinical experimental research.

Estimation of human leptin concentration in the subcutaneous adipose and skeletal muscle tissues

“…adipose and muscle tissues. First, a zero flow rate experiment was conducted to evaluate the concentration in the ISF at different flow rates . Second, with the results of the zero flow rate experiment, the necessary leptin concentrations for the no‐net‐flux technique were given to determine sc.…”

“…The difference between concentrations in the perfusate entering and leaving the probe can be used to calculate the concentration in the ISF . Therefore, leptin above and below the expected interstitial concentration was used to determine absolute leptin concentration in the ISF .…”

“…The in vivo detection of molecules in the interstitial fluid (ISF) has received broad attention . Microdialysis, the most widespread technique for the evaluation of metabolic substrates in the ISF, with its large‐pore size dialysis membranes, allows not only for the measurement of low molecular weight substances such as glucose , lactate and glycerol but also for the sampling of large molecules such as insulin and neuropeptides.…”

“…Harvesting substances with microdialysis, however, is still limited by the pore size of the membrane. OFM allows pure ISF samples to be obtained, as there is no system membrane barrier as compared to techniques such as ultrafiltration or microdialysis .…”

OFM-recirculation and OFM-suction: advanced in-vivo open flow microperfusion (OFM) methods for direct and absolute quantification of albumin in interstitial fluid

“…Open flow microperfusion (OFM) can be used to collect ISF without membrane-related exclusion of substances, and can thus be used for relative and absolute quantification of large ISF compounds like proteins [24][25][26][27]. Absolute quantification of compounds from diluted ISF samples is possible by combining standard OFM with several available calibration methods [24][25][26]28]. However, direct and absolute albumin quantification in the ISF without additional calibration methods requires ISF samples, which are in equilibrium condition with the surrounding ISF, and the collection of such samples thus requires advanced OFM methods.…”