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

Object. Biochemical irritation of the dorsal root ganglion (DRG) after intervertebral disc herniation contributes to radiculopathy through tumor necrosis factor-alpha (TNF alpha)-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-TNF alpha 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 TNF alpha 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; TNFa (25 ng/ml); TNFa with low- (0.2 mu g/ml) or high-dose (1 mu g/ml) sTNFRII; and TNFa with low- (52.5 mu g/ml) or high-dose (262.5 mu g/ml) ELP-sTNFRII. After 24 hours, supernatant was evaluated for inflammatory cytokines (interleukin [IL]-1, IL-6, and IL-10); prostaglandin E(2); and metabolites (glutamate, lactate, and pyruvate). Single-factor analysis of variance with post hoc Dunn analysis (alpha = 0.05) was used to assess treatment differences. Results. Incubation of explants with TNFa 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 E(2) 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 TNFa stimulation of DRG explants yields a phenotype of neurotoxic metabolite release and inflammatory mediator expression. Coincubation with either sTNFRII or ELP-sTNFRII antagonizes TNFa activity to abrogate these changes, suggesting potential for therapeutic intervention to treat peripheral nerve inflammatory disease.