Anti-inflammatory effects of octadecylamine-functionalized nanodiamond on primary human macrophages

Abstract

Chronic inflammatory disorders such as rheumatoid arthritis are characterized by excessive pro-inflammatory or “M1” activation of macrophages, the primary cells of the innate immune system. Current treatments include delivery of glucocorticoids (e.g. dexamethasone – Dex), which reduce pro-inflammatory M1 behaviour in macrophages. However, these treatments have many off-target effects on cells other than macrophages, resulting in broad immunosuppression. To limit such side effects, drug-incorporated nano- and microparticles may be used to selectively target macrophages via phagocytosis, because of their roles as highly effective phagocytes in the body. In this study, surface-modified nanodiamond (ND) was explored as a platform for the delivery of dexamethasone to macrophages because of ND’s rich surface chemistry, which contributes to ND’s high potential as a versatile drug delivery platform. After finding that octadecylamine-functionalized nanodiamond (ND-ODA) enhanced adsorption of Dex compared to carboxylated ND, the effects of Dex, ND-ODA, and Dex-adsorbed ND-ODA on primary human macrophage gene expression were characterized. Surprisingly, even in the absence of Dex, ND-ODA had strong anti-inflammatory effects, as determined by multiplex gene expression via NanoString and by protein secretion analysis via ELISA. ND-ODA also inhibited expression of M2a markers yet increased the expression of M2c markers and phagocytic receptors. Interestingly, the adsorption of Dex to ND-ODA further increased some anti-inflammatory effects, but abrogated the effect on phagocytic receptors, compared to its individual components. Overall, the ability of ND-ODA to promote anti-inflammatory and pro-phagocytic behaviour in macrophages, even in the absence of loaded drugs, suggests its potential for use as an anti-inflammatory therapeutic to directly target macrophages through phagocytosis.

Modulation of macrophage phenotype via phagocytosis of drug‐loaded microparticles

“…Again, we observed that cells treated with high Dex microparticles acted similarly to the positive control cells treated with continuous Dex, even 7 days after microparticle administration. CD163 , a gene associated with hemoglobin and haptoglobin scavenging, and MERTK , a gene associated with apoptotic cell clearance, were differentially expressed across treatment conditions in macrophages on day 7. As expected, free Dex treatment increased the expression of CD163 and MERTK .…”

“…Many researchers have attempted to harness the immune system through administration of immunomodulatory drugs or through biomaterial applications . Several landmark studies showed the possibility of using biomaterials to modulate macrophage phenotype and behavior for therapeutic applications . Here, we describe a novel strategy to use intracellular drug‐loaded microparticles to modulate macrophage gene expression for up to 7 days after microparticle administration.…”

“…9,[33][34][35][36] Several landmark studies showed the possibility of using biomaterials to modulate macrophage phenotype and behavior for therapeutic applications. 18,[37][38][39][40] Here, we describe a novel strategy to use intracellular drug-loaded microparticles to modulate macrophage gene expression for up to 7 days after microparticle administration. Importantly, we found that gene expression related to inflammation can be mitigated when human primary monocytes are loaded with Dex-loaded microparticles.…”

“…Administration of the corticosteroid dexamethasone (Dex) affects macrophage phenotype by inhibiting the expression of genes related to inflammation and promoting genes related to homing, phagocytosis, and iron metabolism, functions that promote tissue regeneration. However, systemic Dex administration has failed in a number of clinical trials and cannot be tolerated by patients over long treatment regimens because of adverse side effects .…”

“…However, attempts to overcome chronic inflammation by locally administering anti-inflammatory macrophages into the damaged tissue have been unsuccessful because macrophages rapidly respond to their environment and quickly revert to a detrimental, inflammatory state. 9,10 Administration of the corticosteroid dexamethasone (Dex) affects macrophage phenotype by inhibiting the expression of genes related to inflammation [11][12][13] and promoting genes related to homing, 14 phagocytosis, [15][16][17][18][19][20] and iron metabolism, 21 functions that promote tissue regeneration. However, systemic Dex administration has failed in a number of clinical trials and cannot be tolerated by patients over long treatment regimens because of adverse side effects.…”