Background and purpose:

Matrix metalloproteinases (MMPs) have been implicated in joint tissue destruction in arthritis. However, MMPs have not been assigned a role in joint pain. We investigated the ability of BaP1, a metalloproteinase from Bothrops asper snake venom, with structural homology to MMPs, to induce joint hypernociception.

Experimental approach:

Animals received intra-articular (i.art.) BaP1. Hypernociception was assessed using the rat-knee joint articular incapacitation test. Cell influx, prostaglandin E₂ (PGE₂), and TNF-α levels were assessed in joint exudates following BaP1 injection.

Key results:

BaP1 (5 μg per joint) provoked hypernociception between 1 and 6 h after i.art. injection. Cell influx, mostly neutrophils, was maximal 3 h after BaP1 i.art. injection. BaP1 also led to increase in PGE₂ and TNF-α levels in the joint exudates. Pretreatment with either indomethacin (4 mg.kg⁻¹ i.p.) or with an anti-TNF-α antiserum (i.art.) significantly inhibited both BaP1-induced joint hypernociception and cell influx. In isolated rat peritoneal macrophages, BaP1 increased cyclooxygenase (COX)-2 expression, while not altering that of COX-1.

Conclusions and implications:

This is the first demonstration that a metalloproteinase promotes joint hypernociception. This effect involves local release of PGE₂ and TNF-α. BaP1-induced increase in PGE₂ is associated to increased COX-2 expression in macrophages. Blocking PGE₂ or TNF-α inhibits BaP1-induced hypernociception. In addition to unravelling a hitherto unknown mechanism whereby TNF blockade provides analgesia in arthritis, the data show, for the first time that MMPs are involved in inflammatory joint hypernociception and induce COX-2 expression.