Targeting chronic pain with epigenetic drugs: Focus on mGlu2 receptors

Histone deacetylase (HDAC) enzymes regulate gene expression by affecting chromatin structure and/or the activity of transcription factors. We have recently demonstrated that histone deacetylase inhibitors (HDACIs) behave as epigenetic agents capable of inducing analgesia by up-regulating metabotropic glutamate type 2 (mGlu2) receptors. Specifically, the regulation of mGlu2 receptor expression appears to involve the acetylation of the NF-κB transcription factor. mGlu2 and mGlu3 receptors belong to class II metabotropic glutamate receptors. These receptors are coupled to Gi/o proteins and play an important role in mediating antinociception in a variety of inflammatory and chronic pain models. We have shown that the HDACI-mediated mGlu2 receptor up-regulation occurs in the dorsal horn of the spinal cord and in the dorsal root ganglia, supporting a predominant role for mGlu2 receptors as mediators of analgesia in experimental animal models of chronic pain. We suggest that drugs that increase the expression of mGlu2 receptors, such as HDACIs or acetylating drugs (e.g. L-acetylcarnitine), may be effective in patients with chronic pain that are refractory to conventional analgesics.