Mass Spectrometry Technology Maps Chemicals as They Migrate Into Skin

A mass spectrometry technique gaining acceptance for medical applications such as imaging tumor surfaces can also be used to analyze the migration of small-molecule compounds applied to the skin. Because skin is such a complicated organ, the technology could be a helpful for developing transdermal drugs.

The study’s findings were published April 28, 2014, in the Journal of the American Chemical Society. Stanford University (Stanford, CA, USA) chemistry Profs. Richard N. Zare and Justin Du Bois, postdoc Livia S. Eberlin, graduate student John V. Mulcahy, and colleagues revealed that desorption electrospray ionization-mass spectrometry (DESI-MS) imaging has many advantages over other approaches that require complicated preparation of skin samples.

Moreover, DESI-MS imaging can be performed under ambient settings, instead of in a vacuum condition, as other MS methods require. Furthermore, test compounds do not have to be radioactively labeled or tagged with unwieldy dye molecules that could affect the compounds’ normal migration through skin. “That’s why this method is very appealing,” said Mark R. Prausnitz, a chemical and biomolecular engineering professor who heads the Laboratory for Drug Delivery at Georgia Institute of Technology (Atlanta, GA, USA).

DESI-MS was developed 10 years ago and involves spraying charged solvent droplets at a surface. Backsplash droplets containing dissolved molecules are then captured and examined using a mass spectrometer. The technology has been used for medical applications such as imaging drugs in tissue samples.

The Stanford scientists chose a number of small molecules that change sodium channels in skin cells, including lidocaine and a shellfish toxin. They applied them to the surface of skin samples and were able to track the compounds’ migration to a depth of 1.2 mm.

Such studies of drug migration are required to enlarge the limited selection of transdermal drugs, according to Prof. Prausnitz. Only approximately 30 agents, such as nicotine, have transdermal versions. The drugs must be small, lipophilic, and effective at a low dose. With this newly adapted tool, however, scientists could more readily study methods to enhance skin permeation, Prof. Prausnitz reported. “We’re very interested in the pathway--which part of the skin did the drug go through?”

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