C5a and pain development: An old molecule, a new target.

Pain is a distressing sensation, resulting from real or potential tissue damage. It is crucial to protect our body, but it can be so intense that it requires treatment. Furthermore, in some circumstances, pain can become persistent/chronic, such as that triggered by inflammatory disease or neuropathy. Treatments for pain are still a clinical challenge. An advance in the knowledge of the neurobiological mechanisms involved in the genesis of acute and chronic pain might be the fundamental approach for developing novel classes of analgesic drugs. In this context, there is emerging evidence indicating that C5a, a component of the complement system, and its cell membrane receptor, C5aR, play a critical role in the genesis of acute and chronic pain states. Thus, this review will describe the mechanisms by which C5a/C5aR signaling participates in the cascade of events involved in the pathophysiology of acute (postoperative), inflammatory and neuropathic pain states. Furthermore, it will also highlight the current possibilities for the development of a novel class of analgesic drugs that target C5a/C5aR signaling.