December 10, 2003
Multiple Sclerosis Society
Disease modifying drugs used for relapsing remitting MS are frequently effective in reducing the relapse rate. However, reducing the number of relapses often appears to have no effect on the progression of disability. Consequently, there is an urgent need for agents that can inhibit the progression of MS, both in relapsing remitting and progressive forms of the disease.
Studies have shown a beneficial effect of cannabinoids (the ?active? part of the cannabis plant) on spasticity and tremor in animal models of MS, and there is some subjective evidence from very small clinical trials. Cannabinoids are thought to cause these effects by acting on certain types of receptor present in the body, which cannabinoids ?recognise? and bind to, causing the effect.
Recent ?laboratory based? studies have shown that various cannabinoids can also reduce substances which have been shown to cause nerve cell loss in diseases like MS. This study aimed to definitively investigate whether the cannabinoid receptor system can protect nerves, by using mice genetically manipulated to be bred without cannabinoid receptors (i.e. in which cannabinoids don't cause an effect). Results were compared to ?normal? (control) mice i.e. with cannabinoid receptors, after an MS-like disease was induced in both types.
Results showed that mice bred without the cannabinoid receptors developed ?aggressive? relapsing remitting MS. This was characterised by periods of paralysis and sharply increasing disability, leading to permanent paralysis of the legs. This was a much more severe disease course than that observed in control mice. Mice bred without cannabinoid receptors also exhibited significantly more nerve fibre loss than in control mice and were found to have increased levels of substances which are toxic to nerve cells and cause nerve fibre loss.
These results suggest that in addition to symptom management, cannabinoids might offer the potential to slow the progression of MS. It is acknowledged that there are likely to be many events that cause nerve fibre loss and that these may change during the disease course. The level of disability experienced will be determined by the rate that nerve fibre loss accumulates, and the genetic background of the individual. Nerve fibre loss in MS correlates with disability levels and the authors suggest that any long-term trials of cannabis should include monitoring of nerve fibre loss and disease progression. Slowing the degeneration process early in the disease, before significant damage has accumulated, may help improve and extend a good quality of life.
This work received support from the Multiple Sclerosis Society of Great Britain and Northern Ireland.
This report was published in Brain, October 2003. Vol. 126, pages 2191-2202.
Copyright © 2003, Multiple Sclerosis Society