Localized delivery of dexamethasone-21-phosphate via microdialysis implants in rat induces M(GC) macrophage polarization and alters CCL2 concentrations

Abstract

Microdialysis sampling probes were implanted into the subcutaneous space on the dorsal side of male Sprague Dawley rats to locally deliver dexamethasone-21-phosphate (Dex) with the aim of altering in vivo macrophage polarization. Macrophage polarization is of significant interest in the field of biomaterials since wound healing macrophages are a possible means to extend implant life as well as improve tissue remodeling to an implant. Quantitative analysis of CCL2 in collected dialysates, gene expression and immunohistochemistry performed on the tissue surrounding the microdialysis implant were used to evaluate if Dex polarized macrophages. Dex infusion down regulated IL-6 and CCL2 gene expression and decreased CCL2 concentrations in dialysates collected at the implant site. Dex appeared to have no significant effect on the gene regulation of CD163, a commonly used M2c macrophage surface marker; Arg2; and iNOS2. However, Dex infusion was effective at increasing the number of CD 163+ cells surrounding the implanted microdialysis probe. This work demonstrates the use of microdialysis sampling to deliver agents such as Dex to alter macrophage polarization in vivo while allowing the ability to collect cytokines in the surrounding microenvironment.

Effects of delayed delivery of dexamethasone-21-phosphate via subcutaneous microdialysis implants on macrophage activation in rats

“…Most work with Dex-releasing biomaterials uses standard histological, rather than molecular assessments, of implant/tissue outcomes. Our previous work has shown that Dex delivered immediately after microdialysis probe insertion is capable of shifting macrophages to a more CD163+ state, the former M2c designation [37]. This is consistent with other macrophage studies in rats with dexamethasone that have also targeted CD163+ cells [38].…”

“…Similarly, we showed in a previous study that immediate and daily infusion of Dex to a subcutaneous wound site in rats, resulted in the significant decrease in IL-6 gene transcription [37]. It should also be noted that IL-6 is known to exhibit either pro- and anti-inflammatory properties [55].…”

“…In the cases of TNF-α and TGF-β1, these results are not surprising as TNF-α levels have been shown to immediately rise following Dex administration [56] and the effects of Dex on TGF-β1 have been shown to be highly variable [57–59]. These results were unexpected in the case of CCL2 which has been shown to be decreased in response to Dex in a rat pancreatitis model [60], and in response to locally delivered Dex to the subcutaneous space [37]. The inability of Dex to down-regulate CCL2 gene transcription may be due to the delayed delivery of the Dex, the concentration of the Dex delivered being insufficient to reduce CCL2, or a combination of the two.…”

“…The techniques for implanting microdialysis probes into the rats have been previously described [37, 40]. Two probes were implanted on opposite sides of the spine with approximately 2.5 cm separation between them.…”

Drug delivery strategies to control macrophages for tissue repair and regeneration

“…For example, microdialysis tubing might be used to control the timing of cytokine infusion into the site of a wound. Keeler et al 72 have used this strategy to deliver dexamethasone, which promotes M2c polarization and reduces fibrous encapsulation. Similarly, osmotic pumps have also been used to deliver IL4 to modulate M2a polarization and mitigate orthopedic implant wear particle-associated inflammation.…”