Microdialysis as a method for biochemical and physiological studies of the porcine and human disc

Microdialysis for the Assessment of Intervertebral Disc and Vertebral Cancellous Bone Metabolism in a Large Porcine Model

BACKGROUND/AIM

It remains challenging to evaluate the in vivo pathophysiological biochemical characteristics in spine tissue, due to lack of an applicable model and feasible methods. The aim of this study was to apply microdialysis for the assessment of basic metabolites from the C3-C4 intervertebral disc, C3 vertebral cancellous bone and subcutaneous adipose tissue in a large porcine model.

MATERIALS AND METHODS

In 7 pigs, glucose, pyruvate, lactate and glycerol concentrations were evaluated in an 8-hour sampling period.

RESULTS

The mean lactate/pyruvate (L/P) ratios for the intervertebral disc and vertebral cancellous bone were comparable and exceeded the ischemic cut-off value of 25 for the entire sampling interval. For subcutaneous adipose tissue, the L/P ratio was below the ischemic cut-off.

CONCLUSION

This exploratory study confirms previous findings of ischemia in bone and the intervertebral disc. This encourages new microdialysis study designs in spine tissue employing large porcine models to create new knowledge and a greater understanding of the metabolism and pathogenesis in spine tissue.

Cytokine and Chemokine Recovery Is Increased by Colloid Perfusates during Dermal Microdialysis

Cytokines and chemokines play important roles in cell signalling, and microdialysis is a promising tool for monitoring these inflammation markers ex vivo. Therefore, the collecting of these mediators at the highest concentrations possible is crucial. Depending on the size of the mediator of interest, the collection of these high molecular mass molecules has thus far been difficult due to their low recovery, even when using high cut-off (100 kDa) microdialysis membranes. This study aimed to optimize the recovery of various cytokines and chemokines by validating the use of different perfusates in cutaneous microdialysis, and comparing intravenous (i.v.) colloids, crystalloids, and a lipid emulsion formulations that are approved for i.v. applications. Methods: In vitro and in vivo recovery experiments using six recombinant cytokines varying in molecular size (interleukin-2 (15 kDa), interleukin-6 (20.5 kDa), interleukin-8 (8 kDa), interleukin-12p70 (70 kDa), TNF-α (17.5 kDa), and vascular endothelial growth factor (VEGF) (38 kDa)) were performed in the presence of different perfusates for i.v. applications: Ringer’s lactate, dextran 60 kDa, hydroxyethyl starch 70 kDa, and hydroxyethyl starch 200 kDa solutions as well as a lipid emulsion formulation. Recovery was determined through (i) microdialysis of cytokines and chemokines in Ringer’s lactate solution or human serum in vitro, and (ii) retrodialysis of excised porcine and human skin cadavers in vitro and porcine skin in vivo. Furthermore, we used skin trauma (catheter insertion) and Ultraviolet B irradiation of 3 × 3 cm² skin areas to sample cytokines and chemokines in vivo and compared the amounts that were obtained using crystalloid and colloid perfusates. All the cytokines and chemokines within the dialysates were quantified through a flow cytometry-based bead array assay. Results: Overall, recovery was strongly increased by the colloids, particularly hydroxyethyl starch 70 kDa, in vitro, ex vivo, and in vivo. When compared with the recovery achieved using Ringer’s lactate, this increase was most effective for proteins ranging from 8 to 20.5 kDa. Hydroxyethyl starch 70 kDa significantly increased the recovery of interleukin (IL)-8 in human serum in vitro when compared with Ringer’s lactate. More cytokines and chemokines were recovered using colloids compared with crystalloids. However, the increase in recovery values was lower for IL-12p70 and VEGF. Conclusions: Regarding the dialysate volumes and final dialysate concentrations, colloid perfusates are overall superior to crystalloid perfusates, such as Ringer’s lactate, when sampling cytokines and chemokines, resulting in higher recoveries. However, the sampling of high-molecular-mass cytokines during microdialysis remains challenging, and experimental in vitro data are not completely comparable with data obtained ex vivo or in vivo.