LC/ESI-MS analysis of two elastin cross-links, desmosine and
isodesmosine, and their radiation-induced degradation products
Melkamu Getie, Klaus Raith, Reinhard H.H. Neubert
Institute of Pharmaceutics and Biopharmaceutics, Martin Luther University Halle-Wittenberg, Wolfgang-Langenbeck Str. 4, D-06120, Halle(Saale), Germany
Received 27 May 2003; received in revised form 24 September 2003; accepted 26 September 2003
In this work, the effect of Fenton reaction on two elastin cross-linked amino acids, desmosine (DES) and isodesmosine (IDE), in the
absence or presence of different wavelength radiations generated from artificial sources has been evaluated using LC/ESI-MS. Irradiation as
well as incubation of DES or IDE solutions in the presence of Fe
resulted in products with m/z 497.1 and 481.1 for [M + H]
strongly dose-dependent degradation of both amino acids was observed upon exposure to UVB at doses ranging from 0 to 3 J/cm
moderate dose-dependent degradation upon exposure to UVA at doses 10 times higher than that of UVB. A significant time-dependent
degradation of DES and IDE was also observed upon exposure of these amino acids to a lamp emitting visible light similar to sunlight.
Exposure of both amino acids to IR radiation (520 W) for 8 h did not cause significant degradation.
D 2003 Elsevier B.V. All rights reserved.
Keywords: Desmosine; Isodesmosine; Skin; Elastin; LC/MS; Radiation
Due to its function as a barrier between the organism and
its environment, the skin is directly exposed to exogenous
oxidative stress such as solar and artificial radiation, chem-
ical oxidants and air pollutants, which are potent inducers of
reactive oxygen species (ROS) [1,2]. Ultraviolet (UV)
radiation represents the most deleterious part of solar light
to cells and has been associated with the incidence of skin
cancer . In addition, fractions of UVB (290–320 nm) and
UVA (320–400 nm) radiations that reach the earth surface
are of paramount importance in causing several other skin
health complications such as wrinkling, sagging, and pig-
mentary alterations; collectively referred to as photoaging
[4,5]. The major histopathologic alteration in the dermis of
photoaged skin underlying wrinkling, sagging, and yellow
discolouration is the accumulation of large amount of
abnormal elastin, termed solar elastosis, replacing the nor-
mally collagen-rich dermis .
Elastin is a highly hydrophobic fibrous protein that
comprises the main part of elastic fibres, which are respon-
sible for the elastic properties of several vertebrate tissues
such as skin, lung and large blood vessels. It is secreted
from cells as a soluble precursor protein, tropoelastin. Then,
the tropoelastin molecules are highly cross-linked into a
rubber-like network in the extracellular matrix [7,8]. The
principal step in the biosynthesis of elastin is well charac-
terized; first, the lysine residues of the tropoelastin react
with lysyl oxidase to form a-amino adipic acid y-semi-
aldehyde (allysine). Then, allysine molecules react with
lysine and/or another allysine to form polyfunctional
cross-links such as desmosine (DES), isodesmosine (IDE),
lysinonorleucine, merodesmosine and cyclopentenone [7–
10]. Since they are specifically present in elastin, DES and
IDE are used as markers to study the role of elastic fibre in
the pathology of skin diseases. They were first isolated from
elastin hydrolysate by Thomas et al. .
Biochemical studies report a decrease of elastin content
and particularly of its cross-links in the tissue with aging,
which is proposed to be due to oxidative stress [12– 15].
The reduction of cross-links appears to be of key impor-
tance, because the elasticity and strength of elastin are
maintained by the existence of these cross-links. The
mechanism and causes are still not well defined. However,
it is assumed that ROS are causal factors in aging [16,17].
More recently, Umeda et al.  reported that hydroxyl
radicals derived from Fenton reaction between transition
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* Corresponding author. Tel.: +49-345-5525000; fax: +49-345-
E-mail address: firstname.lastname@example.org (R.H.H. Neubert).
Biochimica et Biophysica Acta 1624 (2003) 81 – 87