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Allergic Contact Dermatitis


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Allergic Contact Dermatitis — Another Medical Use for Marijuana?

 

Cannabinoids, endogenous and exogenous, suppressed contact dermatitis reactions in mouse ears.

Cannabinoid receptors (CB1 and CB2) are present on epidermal keratinocytes. These receptors are activated by the cannabinoid delta-9-tetrahydrocannabinol (THC), the psychoactive compound in marijuana, and by endogenous cannabinoids (endocannabinoids). Researchers noted that knockout mice lacking CB1 and CB2 developed dermatitis around their ear tags, which were made mostly of nickel. The mice could not bind molecules of endocannabinoids that normally suppress reactions, and the researchers theorized that cannabis might prevent or ameliorate allergic contact dermatitis.

 

The investigators found increased reactions to the topical sensitizer 2,4-dinitrofluorobenzene (DNFB) in the knockout mice compared with normal mice. Normal mice given cannabinoid receptor antagonists also displayed increased ear swelling compared to controls. In further study, endocannabinoid synthesis was found to be greater in knockout mice than in controls, and when contact allergy reactions were induced in normal mice, the inflamed skin was marked by increased endocannabinoid synthesis and cannabinoid receptor expression, compared with healthy skin. When the researchers injected THC into the ears of normal mice, followed by application of elicitation doses of DNFB to the injected areas, the degree of ear swelling and granulocyte infiltration in treated ears was significantly less than in control ears. Topical application of THC also suppressed reactions.

 

In separate experiments, mice that had higher levels of endocannabinoids also had milder elicitation responses. The researchers found large numbers of chemokines C-C and C-X-C motif ligands and receptors in the treated mice with upregulated genes. The monocyte-chemotactic protein 2/chemokines ligand 8 was the only chemokines gene upregulated in the knockout mice. Apparently, the endocannabinoid system regulates allergic contact dermatitis, at least partly, through this chemokine.

 

Comment: The ability of cannabinoids to suppress contact dermatitis reactions suggests that topical cannabinoid agonists or drugs that stimulate endocannabinoid synthesis could function as topical anti-inflammatory agents. However, allergic contact dermatitis is difficult to suppress, even with potent topical corticosteroids. Cannabinoids couldn’t suppress it completely, even in the thin skin of a mouse ear. It’s doubtful that topical marijuana will stop allergic reactions, but these beautifully controlled and thorough studies should spark both research and cocktail party conversation.

— Mark V. Dahl, MD

 

CITATION(S):

Karsak M et al. Attenuation of allergic contact dermatitis through the endocannabinoid system. Science Jun 8; 316:1494-7.

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