Biology Reference
In-Depth Information
New Research Avenues
Edgar Pastene*
Laboratory of Pharmacognosy,
University of Concepción, Chile
2.1 Reactive Oxygen Species and
Antioxidants: so Far so Good
in
Science
(1954), published the manuscript
entitled: 'Oxygen poisoning and X-ray
irradiation: a mechanism in common'
(Gerschman
et al.
2005). Through the dec-
ades, the contribution of Gerschman and
pupils to the field of free radicals has been
recognized. Gerschman, in conjunction with
Gilbert, developed their theory, which could
be summarized in three points: (i) oxygen
free radicals are the common mechanism of
oxygen and irradiation toxicity; (ii) oxygen
toxicity appears equally when oxygen pres-
sure is increased or when there is a decrease
in the antioxidant defences; and (iii) oxygen
toxicity is a continuous phenomenon con-
tributing to determining lifespan.
Depending on concentration and physi-
cochemical features of the milieu, ROS can
be either 'friends' or 'foes'. In order to under-
stand how these species could act as cell sig-
nalling molecules (messengers), their
physiological functions are currently under
study. For many years, the Harman and
Gerschman hypothesis has prevailed and the
fact that ROS production is a central event in
the ageing process is still widely accepted.
So, in biological systems, an imbalance in
ROS generation might lead to cell death by
apoptosis and necrosis (Dypbukt
et al.
, 1994;
Free radicals are short-living and highly
reactive atoms or molecules with unpaired
electrons. In biological systems, the most
important radicals are derived from oxygen
(reactive oxygen species; ROS) and nitrogen
(reactive nitrogen species; RNS). These free
radicals are normally generated in cells as
products of metabolism and respiratory
activity. ROS comprise radical and non-radi-
cal oxygen-containing molecules that dis-
play high reactivity towards proteins, lipids
and nucleic acids. ROS exist in many differ-
ent inter-convertible forms (e.g. H
2
O
2
, O
2
•
−
,
hydroxyl radical, peroxynitrite, etc). Since
1956, when Harman stated that free radicals
are involved in cell ageing, a plethora of
studies has been carried out with the aim to
understand how such compounds cause del-
eterious effect on biological molecules
(Harman, 1956, 1988, 1992). Harman defined
the mitochondria as a biological clock and
his statements are the basis of the so called
'mitochondrial hypothesis of ageing'. Strictly
speaking so did the Argentinian researcher
Rebecca Gerschman who, on the basis of the
work of Michaelis simultaneously published
* E-mail: edgar.pastene@gmail.com
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