Treatment of neuroinflammation by soluble tumor necrosis factor receptor Type II fused to a thermally responsive carrier: Laboratory investigation

Object. Biochemical irritation of the dorsal root ganglion (DRG) after intervertebral disc herniation contributes to radiculopathy through tumor necrosis factor-α (TNFα)-mediated inflammation. Soluble TNF receptor Type II (sTNFRII) sequesters this cytokine, providing clinical benefit. Previous work involving conjugation of sTNFRII with thermally responsive elastin-like polypeptide (ELP) yielded a chimeric protein (ELP-sTNFRII) with in vitro anti-TNFα bioactivity. Furthermore, temperature-triggered ELP aggregation into a "depot" prolongs protein residence time following perineural injection. In this study the authors evaluated the inflammatory phenotype of DRG explants after TNFα stimulation, and assessed the abilities of sTNFRII or ELP-sTNFRII to attenuate these neuroinflammatory changes. Methods. Rat lumbar DRGs (35 animals) were treated in 6 groups, as follows: control; TNFα (25 ng/ml); TNFα with low- (0.2 μg/ml) or high-dose (1 μg/ml) sTNFRII; and TNFα with low- (52.5 μg/ml) or high-dose (262.5 μg/ml) ELP-sTNFRII. After 24 hours, supernatant was evaluated for inflammatory cytokines (interleukin [IL]-1, IL-6, and IL-10); prostaglandin E₂; and metabolites (glutamate, lactate, and pyruvate). Single-factor analysis of variance with post hoc Dunn analysis (α = 0.05) was used to assess treatment differences. Results. Incubation of explants with TNFα caused metabolic stress reflected by an increased lactate/pyruvate ratio (1.8 ± 0.5-fold) and extracellular glutamate (79 ± 8% increase). Inflammatory activation was observed with heightened IL-6 release (5.2 ± 1.4-fold) and prostaglandin E₂ production (14 ± 3-fold). An autoregulatory response occurred with an 11.8 ± 0.6-fold increase in sTNFRI shedding. Treatment with high doses of sTNFRII or ELP-sTNFRII reversed all changes. Values are expressed as the mean ± standard deviation. Conclusions. These results demonstrate that TNFα stimulation of DRG explants yields a phenotype of neurotoxic metabolite release and inflammatory mediator expression. Coincubation with either sTNFRII or ELP-sTNFRII antagonizes TNFα activity to abrogate these changes, suggesting potential for therapeutic intervention to treat peripheral nerve inflammatory disease.