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Stress, Bacteria, and Barriers

Mice subjected to psychological stress had reduced levels of antimicrobial peptides in the stratum corneum and developed larger infections than unstressed mice.

Stress adversely affects skin barrier function; it disturbs permeability, barrier homeostasis, and wound healing. This disruption may be partially due to physiologic changes wrought by nerves that end in the epidermis. Recently, Aberg and co-workers suggested that barrier disruption might also be due to increased endogenous cortisol levels induced by stress. Basically, psychological stress increases circulating levels of glucocorticoids, which inhibits lipid synthesis and decreases production of lamellar bodies. The lamellar bodies normally contribute lipids, enzymes of desquamation, and antimicrobial peptides to the stratum corneum. It follows that inhibited lipid synthesis might adversely affect barrier function and stratum corneum levels of the antimicrobial peptides cathelicidin and β-defensin.

To test this mechanism of skin barrier disturbance, mice were subjected to psychological stress (exposure to crowding, visible light, and radio noise for 72 hours). The stressed mice produced fewer antimicrobial peptides (a decrease that was reversible by glucocorticoid blockade). Abscesses induced by injected group A streptococcus were nearly twice as large in stressed animals as in controls. When the authors applied the superpotent topical glucocorticosteroid clobetasol to normal mouse skin, the protein levels for antimicrobial peptides also declined.

Comment: Glucocorticoids can interfere with barrier homeostasis and decrease production of antimicrobial peptides. Startling! We use topical corticosteroids to treat all sorts of eczemas teeming with bacteria, and these findings indicate that this practice can damage the barrier and decrease resistance to bacterial infection. Nevertheless, treating eczemas with topical corticosteroids remains appropriate. As the eczema resolves, barrier effectiveness improves despite the countereffect of the glucocorticoid. Also, surface bacterial counts drop as the weeping and spongiosis resolve, even if the level of antimicrobial peptides declines. One does wonder, though, about marginal eczemas, like those nearly healed. For such eczemas, the beneficial effects of steroid creams in reducing inflammation may be outstripped by persisting disruption to barrier homeostasis. Is the skin really healed in this situation?

— Mark V. Dahl, MD

Published in Journal Watch Dermatology December 7, 2007

Citation(s):

Aberg KM et al. Psychological stress downregulates epidermal antimicrobial peptide expression and increases severity of cutaneous infections in mice. J Clin Invest 2007 Nov 1; 117:3339.

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