Papain is found naturally in papaya and is often referred to as a “plant-based pepsin” in reference to the digestive enzyme pepsin that is present in the stomach. Erika Jensen-Jarolim, Head of the Department of Comparative Medicine at the Messerli Research Institute, and her team researched the effect of papain directly on the skin of mice as well as on skin cells in the petri dish. The cosmetic industry uses papain in exfoliating treatments to remove dead surface skin. There even are enzyme-based shampoos for house pets to clean the fur and make it easier to brush.
How papain induces allergic reactions
Skin consists of several layers joined via cellular connections called “tight junctions”. First authors Caroline Stremnitzer and Krisztina Manzano-Szalai and the project team showed that papain induces a breakdown of these cell-cell junctions. On the skin, papain results in a loss of the barrier function. “After just a short period of time, papain increased vascular permeability and inflammatory cells infiltrated the skin,” Jensen-Jarolim explains. Around two weeks after being exposed to papain, the researchers found antibodies to papain in the mice. These immunoglobulins are the cause of the allergic reaction toward the enzyme. “Exposed mice not only experienced a loss of the barrier function of the skin, but also had a specific allergic sensitization toward papain. The animals developed an allergy,” says allergy expert Jensen-Jarolim.
Caution is called for with papain-containing products
But the permeation of the skin barrier does not appear to be a prerequisite for sensitization toward papain. “The enzyme remains allergenic even when its enzymatic function has been blocked,” explains Jensen-Jarolim. The disruption to the skin barrier, she says, is essential for the infiltration of other allergens and bacteria. In humans and in animals, diseases of the skin such as atopic dermatitis, commonly referred to as eczema, involve an increased permeability of the skin with a heightened risk for bacterial, fungal, or viral colonisation. Besides genetic factors, allergenic enzymes from external sources may also contribute to the symptoms. It is striking that papain has an enormous structural similarity with one of the most important house dust mite allergens. The authors conclude that sensitization toward these house dust mite allergens follows the same principle. “People with sensitive skin as well as small children should avoid the enzyme (EC Number 22.214.171.124) as much as possible and observe the ingredients declaration for consumer products as regulated by EU Directive 2000/13/EC,” says Jensen-Jarolim.
The article “Papain Degrades Tight Junction Proteins of Human Keratinocytes In Vitro and Sensitizes C57BL/6 Mice via the Skin Independent of its Enzymatic Activity or TLR4 Activation” by Caroline Stremnitzer, Krisztina Manzano-Szalai, Anna Willensdorfer, Philipp Starkl, Mario Pieper, Peter König, Michael Mildner, Erwin Tschachler, Ursula Reichart and Erika Jensen-Jarolim was published in the Journal of Investigative Dermatology. http://www.ncbi.nlm.nih.gov/pubmed/25705851
About the Messerli Research Institute
The Messerli Research Institute was founded in 2010 with support from the Messerli Foundation (Switzerland) under management of the University of Veterinary Medicine, Vienna and in cooperation with the Medical University of Vienna and the University of Vienna. The research is devoted to the interaction between humans and animals, as well as its theoretical principles in animal cognition and behaviour, comparative medicine and ethology. The institute’s work is characterized by its broad interdisciplinary approach (biology, human medicine, veterinary medicine, philosophy, psychology, law) and strong international focus. www.vetmeduni.ac.at/messerli