P. Acnes Models Skin Response to UV-radiation

Non-melanoma skin cancer is known to affect more than 250,000 Americans each year, and is directly linked to exposure to ultraviolet (UV) radiation.¹ Although UV-mediated biomarkers indicating damage from UV radiation have been identified, detecting these biomarkers is time consuming and invasive. In their publication, Yanyan Wang et al. (2012)have hypothesized that a common bacteria present on the skin’s surface can show effects of UV radiation and may lead to the prediction of skin cancer before symptoms occur.²

The skin bacteria chosen for this study, Propionibacterium acnes (P. acnes), make up greater than 60% of bacteria present on the human face.³ When skin is exposed to UV radiation, P. acnes is also exposed and produces porphyrins, which absorb light and produce free radicals.⁴To measure porphyrins in P. acnes, cultured colonies were treated with 5-aminolevulinic acid (ALA) to further increase the amount of porohyrins produced⁵; these were visible via fluorescence. By increasing the amount of UV-B radiation from 0 to 100 mJ/cm², the production of porphyrins decreased over time, which suggests a change in chemical makeup in response to increased levels of radiation.

Mice treated with P. acnes and exposed to UV-B radiation exhibited a decrease in porphyrin production. The epidermis of the treated mice also developed cyclobutane pyrimidine dimers, which is evidence of DNA damage. Mass spectrometric analysis via a linear trap quadrupole (LTQ)-Orbitrap XL (Thermo Scientific) displayed five peptides oxidized by UV-B and seven peptides de-oxidized by UV-B exposure. To compare porphyrin production and protein oxidation/de-oxidation of P. acnes in response to non-UV radiation, P.acnes was exposed to gamma radiation (⁶⁰Co). Analysis using mass spectrometry on an LTQ-Orbitrap XL spectrometer (Thermo Scientific) revealed that five P. acnes proteins were oxidized after UV-B exposure and seven oxidized peptides derived from five P. acnes proteins were de-oxidized after UV-B exposure. Wang et al. plan to investigate dosage of UV-B radiation and establish UV-B-specific signatures based on the rate of UV-B-specific oxidation/de-oxidation of P. acnes over time. They hope this information will lead to further understanding of UV radiation and enhance diagnostics concerning skin cancer and exposure to radiation.

References

1. Talbott, E.O., and Craun, G.F. (1995) Introduction to Environmental Epidemiology, Boca Raton, FL: CRC Press.

2. Wang, Y., et al. (2012) “The response of human skin commensal bacteria as a reflection of UV radiation: UV-B decreases porphyrin production,” PLoS One, 7(10), e47798, doi: 10.1371/journal.pone.0047798.

3. Grice, E.A., and Segre, J.A. (2011) “The skin microbiome,” Nature Reviews: Microbiology, 9(4) (pp. 244–53).

4. Afonso, S.G., Enriquez de Salamanca, R., and Batlle, A.M. (1999) “The photodynamic and non-photodynamic actions of porphyrins,” The Brazillian Journal of Medical and Biological Research, 32(3) (pp. 255–66).

5. Ramstad, S., Le Anh-Vu, N., and Johnsson, A. (2006, January) “The temperature dependence of porphyrin production in Propionibacterium acnes after incubation with 5-aminolevulinic acid (ALA) and its methyl ester (m-ALA),” The Photochemical and Photobiological Sciences, 5(1) (pp. 66–72).