Vienna: Papain is an important industrial protein-degrading enzyme that is
used, for example, in the food and cosmetic industries. When humans or
animals come in contact with papain, strong allergic reactions of the
skin can be the result, as scientists from the Messerli Research
Institute of the University of Veterinary Medicine Vienna, the Medical
University of Vienna, and the University of Vienna have found out. Their
study was published in the Journal of Investigative Dermatology.
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 3.4.22.2) as
much as possible and observe the ingredients declaration for consumer
products as regulated by EU Directive 2000/13/EC,” says Jensen-Jarolim.