Cannabis suggests treatment for chronic pain

By Yun Xie

Cannabinoids, chemical compounds found in cannabis, are drawing the interest of medical scientists, as they contain compounds that may lead to treatments for ailments ranging from bacterial infections to nausea from chemotherapy. In a report from the journal Pain, British scientists attempted to figure out how cannabinoids affected (surprise!) pain and determine if they are effective against chronic pain.

Many of the biological effects of cannabinoids like the psychoactive THC (Δ9-tetrahydrocannibinol) occur when they bind to one or both of two cannabinoid receptor subtypes: CB1 and CB2. The neurons of the central nervous system express CB1, while CB2 is mostly located in the periphery, in systems such as lymphoid tissues.

Since most pain occurs in the periphery, cannabinoids that can selectively bind CB2 are more interesting than those that are inclined to target CB1. CB1 is associated with the central nervous system, which means that targeting its activities can produce many negative side-effects.

Although past studies have examined the processes that occur when CB2 agonists (drugs that activate it) suppress acute and chronic pain in animals, not much work has been done on humans. In order to design optimal clinical trials, it is important to know where drugs interact with CB2 and how pain suppression occurs in humans. In performing the new functional studies on CB2, the British scientists examined human tissues from a large variety of sources, including people who have experienced no injuries, suffered traffic accidents, undergone upper limb amputations, and went through various surgical procedures.

For the first time, the scientists were able to show that both uninjured and injured people had CB2 receptors in their dorsal root ganglion neurons, which are located along the vertebral column at the spine. In addition, CB2 protein was found in the same location as TRPV1, which is responsible for transmitting various painful stimuli. Their close proximity allows CB2 drug binding to regulate the sensitivity of TRPV1, causing the analgesic effect. The authors mention that CB2 agonists have other modes of action in human bodies that reduce pain, such as inducing the release of β–endorphins and inhibiting inflammation.

The scientists conclude that "CB2 agonists may produce new therapy for chronic pain." They also write that "CB2 agonists deserve clinical trials for nociceptive, inflammatory and neuropathic chronic pain." For any such clinical trials, the results of their study will be valuable, as they have located active populations of CB2 neurons and added to the knowledge of how they function.

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