title: Non-invasive monitoring of oxidative skin stress by ultraweak photon emission (UPE)-measurement. I: mechanisms of UPE of biological materials.
abstract: OBJECTIVE
  Oxidation of proteins and amino acids is associated with generation of ultraweak photon emission (UPE), which may be used to assess oxidative processes in the skin in a non-invasive way. This first part of a series of reports addresses the physicochemical basis of oxidation-induced UPE in the skin, with a special focus on the contribution of amino acid oxidation.
  
  
  METHODS
  UPE of biological samples and protein/amino acid solutions following oxidation with H(2)O(2) in the presence of Fe(2+) was recorded using a sensitive photomultiplier system. Signals were analyzed with regard to overall signal intensity and spectral distribution.
  
  
  RESULTS
  Increasing concentrations of H(2)O(2) in aqueous bovine serum albumin solutions induced linearly correlated UPE and protein carbonyl compounds, with a substantially higher sensitivity for the measurement of UPE. In single amino acid solutions, strong UPE signals were generated by oxidation from Phe, Trp, His, and Cys, and weak signals from Lys and Thr. Analysis of reaction products by MS revealed high oxidative material turnover for Cys and His, whereas barely detectable oxidative material turnover seems to be sufficient to generate a UPE signal of similar strength from Trp and Phe. Combination of different amino acids did not result in a simple addition of individual oxidation-induced UPE signals, but in interactions ranging from antagonism to clear synergism. Synergism was evident between Trp- and UPE-generating amino acids such as Thr, Cys, and His, with the strongest synergism by far observed between Trp and His. The strikingly different individual UPE spectra of His and Trp, despite being of comparable overall strength, were congruent with a pure Trp UPE spectrum after combining His with Trp in solution, indicating energy transfer between both amino acids. Combination of Trp and DNA, which also gives UPE signals following oxidation, did not result in a synergistically enhanced or antagonized overall UPE signal, but in a simple addition of individual UPE signals.
  
  
  CONCLUSIONS
  Measurement of UPE could be proven to be a highly sensitive method to assess oxidative processes in biological molecules. The reported data indicate that UPE generated by oxidation stressed skin is mainly due to non-fluorescent photon emission via Trp, whereby Trp acts as an energy receptor from other excited species of oxidation-modified amino acids.
authors.affiliation: F&E cosmed, Beiersdorf AG, Hamburg, Germany.
authors.forename: Faryar
authors.initials: F
authors.lastname: Khabiri
authors.forename: Ralf
authors.initials: R
authors.lastname: Hagens
authors.forename: Christoph
authors.initials: C
authors.lastname: Smuda
authors.forename: Andreas
authors.initials: A
authors.lastname: Soltau
authors.forename: Volker
authors.initials: V
authors.lastname: Schreiner
authors.forename: Horst
authors.initials: H
authors.lastname: Wenck
authors.forename: Klaus-Peter
authors.initials: KP
authors.lastname: Wittern
authors.forename: Hans-Jürgen
authors.initials: HJ
authors.lastname: Duchstein
authors.forename: Weiping
authors.initials: W
authors.lastname: Mei
mesh_terms: D000596:Amino Acids / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D001585:Benzoyl Peroxide / Q000494:pharmacology; D001703:Biophysics / Q000379:methods*; D004247:DNA / Q000737:chemistry; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D066298:In Vitro Techniques; D007501:Iron; D007700:Kinetics; D013058:Mass Spectrometry; D009841:Oligonucleotides / Q000737:chemistry; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D017785:Photons; D050050:Protein Carbonylation; D011506:Proteins / Q000737:chemistry / Q000378:metabolism*; D012710:Serum Albumin, Bovine / Q000737:chemistry / Q000378:metabolism*; D012867:Skin / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects; D013552:Swine; D014466:Ultraviolet Rays
chemical_list: D000596:Amino Acids; D009841:Oligonucleotides; D011506:Proteins; D012710:Serum Albumin, Bovine; D004247:DNA; D006861:Hydrogen Peroxide; D007501:Iron; D001585:Benzoyl Peroxide