Rubber Additive Forms Potent Skin Allergens

Enzymes in human skin convert the common synthetic rubber additive diphenylthiourea into metabolites that can cause contact dermatitis, a finding that helps solve the chemical mystery behind the skin allergy triggered when some people are exposed to neoprene (Chem. Res. Toxicol., DOI: 10.1021/tx100241z). Diphenylthiourea is used as an accelerator to speed up vulcanization of rubber, for example, in the production of neoprene, which is a stretchable, waterproof, and chemical- and abrasion-resistant polymer used to make wet suits, running shoes, computer mouse pads, iPod holders, and other products. Most contact allergens, known as haptens, are small molecules that form protein adducts, which trigger an immune system response. A team led by Ann-Therese Karlberg of the University of Gothenburg, in Sweden, activated ¹⁴C-labeled diphenylthiourea by using a cocktail of the primary P450 enzymes found in human skin and subsequently analyzed the metabolites via mass spectrometry. Karlberg and coworkers then tested the three major metabolites for their ability to bind to proteins and assayed them in mice. Although diphenylthiourea itself does not cause an allergic reaction, two of the three metabolites are strong skin sensitizers. The researchers believe their results could lead to better allergy-screening tests.