Neuropathic pain is chronic pain that can arise from nerve damage resulting from inflammation in the central nervous system (CNS). People worldwide suffer from neuropathic pain, which can include hyperalgesia (heightened pain sensation, such that mildly uncomfortable stimuli are perceived as severely painful) and allodynia ('misplaced' pain, such that nonpainful stimuli are perceived as painful). The few available treatments for neuropathic pain are relatively ineffective and have potentially dangerous side effects; safe, effective options are badly needed.

Credit: Piero Malaer

Zhi-Hong Wen, Yen-Hsuan Jean and colleagues (Department of Marine Biotechnology and Resources, National Sun Yat-Sen University, Taiwan) may be close to providing one. They have discovered that a compound called capnellene (named after the soft coral from which it is isolated, Capnella imbricata) has pain-relieving effects in a rat model of neuropathic pain.

Wen's group tested two capnellene compounds in male Wistar rats with chronic constriction injury, an experimental model of neuropathic pain. The compounds were administered intrathecally and intraperitoneally, and researchers assessed the rats' thermal hyperalgesia response by measuring the time they took to withdraw a hind paw from a low-intensity heat source (Br. J. Pharmacol. published online 5 August 2009; doi:10.1111/j.1476-5381.2009.00323.x). After intrathecal administration, both compounds acted quickly to relieve pain. Pain relief was dose-dependent, reached a maximum about 30 min after compounds were administered and lasted 30–180 min. One of the compounds was also tested as a single intraperitoneal dose; this route was also effective for pain relief, taking effect within 1–3 h and lasting for at least 6 h. Administration of capnellene did not cause any neurological problems in normal rats.

Capnellene's analgesic effects may stem from its inhibition of the expression of COX-2 protein in the spinal cord. COX-2 is a pro-inflammatory protein that can excite the nerves that carry pain signals. It is released by cells surrounding nerve cells, such as microglia, when they are activated by some disturbance to the CNS. In Wen's study, both capnellene compounds inhibited expression of COX-2 in activated microglial cells in vitro.

The research results suggest that capnellene could have clinical application as a treatment for neuropathic pain. “Today there are few pharmacological agents that can help people suffering from neuropathic pain, but we believe that these marine-derived compounds could lead to the development of a new range of drugs of great potential,” stated Wen.