TNF-alpha neutralizing antibody blocks thermal sensitivity induced by compound 48/80-provoked mast cell degranulation

BACKGROUND  Neuro-inflammatory circuits in the tissue regulate the complex pathophysiology of pain.  Protective nociceptive pain serves as an early warning system against noxious environmental stimuli.  Tissue-resident mast cells orchestrate the increased thermal sensitivity following injection of basic secretagogue compound 48/80 in the hind paw tissues of ND4 mice.  Here we investigated the effects of pre-treatment with TNF-α neutralizing antibody on compound 48/80-provoked thermal hyperalgesia.  METHODS  We treated ND4 Swiss male mice with intravenous anti-TNF-α antibody or vehicle 30 minutes prior to bilateral, intra-plantar compound 48/80 administration and measured changes in the timing of hind paw withdrawal observed subsequent to mice being placed on a 51 (o)C hotplate.  We also assessed changes in tissue swelling, TNF-α gene expression and protein abundance, mast cell degranulation, and neutrophil influx in the hind paw tissue.  FINDINGS  We found that TNF-α neutralization significantly blocked thermal hyperalgesia, and reduced early tissue swelling. TNF-α neutralization had no significant effect on mast cell degranulation or neutrophil influx into the tissue, however.  Moreover, no changes in TNF-α protein or mRNA levels were detected within 3 hours of administration of compound 48/80.  INTERPRETATION  The neutralizing antibodies likely target pre-formed TNF-α including that stored in the granules of tissue-resident mast cells. Pre-formed TNF-α, released upon degranulation, has immediate effects on nociceptive signaling prior to the induction of neutrophil influx.  These direct effects on nociceptors are abrogated by TNF-α blockade resulting in compromised nociceptive withdrawal responses to acute, harmful environmental stimuli.