In ancient times, physicians had a limited number of therapies to provide pain relief. Not surprisingly, plant extracts applied topically often served as the primary analgesic plan. With the discovery of the capsaicin receptor (TRPV1), the search for ‘new’ analgesics has returned to compounds used by physicians thousands of years ago. One such compound, capsaicin, couples the paradoxical action of nociceptor activation (burning pain) with subsequent analgesia following repeat or high-dose application. Investigating this ‘paradoxical’ action of capsaicin has revealed several overlapping and complementary mechanisms to achieve analgesia including receptor desensitization, nociceptor dysfunction, neuropeptide depletion and nerve terminal destruction. Moreover, the realization that TRPV1 is both sensitized and activated by endogenous products of inflammation including bradykinin, H+, ATP, fatty acid derivatives, NGF and trypsins, has renewed interest in TRPV1 as an important site of analgesia. Building on this foundation, a new series of preclinical and clinical studies targeting TRPV1 have been reported. These include trials using brief exposure to high-dose topical capsaicin in conjunction with prior application of a local anesthetic. Clinical use of resiniferatoxin (RTX), another ancient but potent TRPV1 agonist, is also being explored as a therapy for refractory pain. The development of orally-administered high affinity TRPV1 antagonists hold promise for pioneering a new generation of analgesics capable of blocking painful sensations at the site of inflammation and tissue injury. With the isolation of other members of the TRP channel family such as TRPA1, additional opportunities are emerging in the development of safe and effective analgesics.
Keywords: Analgesics, Non-Narcotic, Pain, Sensory Receptors, transient receptor potential cation channel, TRP channels, TRPV1, capsaicin receptor