The organism must confront and control the balance of both pro-oxidants and antioxidants
continuously. The balance between these is tightly regulated and extremely important for
maintaining vital cellular and biochemical functions. This balance often referred to as the
redox potential, is specific for each organelle and biological site, and any interference of the
balance in any direction might be deleterious for the cell and organism. Changing the
balance towards an increase in the pro-oxidant over the capacity of the antioxidant is
defined as oxidative stress and might lead to oxidative damage. Changing the balance
towards an increase in the reducing power, or the antioxidant, might also cause damage and
can be defined as reductive stress.Oxidative stress and damage have been implicated in numerous disease processes,
including inflammation, degenerative diseases, and tumor formation and involved in
physiological phenomena, such as aging and embryonic development. The dual nature of
these species with their beneficial and deleterious characteristics implies the complexities of
their effects at a biological site.
Lipid peroxidation has been pointed out as a key chemical event in the oxidative stress
associated with several inborn and acquired pathologies. Disruption of organelle and cell
membranes together with calcium homeostasis alterations are the main supramolecular
events linked to lipid peroxidation. However, it is not clear if lipid peroxidation process is a
cause, triggering step of the clinical manifestations of the disease, or a consequence of toxic
effects of lipid peroxidation products.
In pathological situations the reactive oxygen species are generated and as a consequence
lipid peroxidation occurs with -tocopherol deficiency. In addition to containing high
concentrations of polyunsaturated fatty acids and transitional metals, red blood cells are
constantly being subjected to various types of oxidative stress. Red blood cells however are
protected by a variety of antioxidant systems which are capable of preventing most of the
adverse effects under normal conditions. Among the antioxidant systems in the red cells, -
tocopherol possesses an important and unique role. -tocopherol may protect the red cells
from oxidative damage via a free radical scavenging mechanism and as a structural
component of the cell membrane (Chitra Shyamaladevi, 2011).
Levels of Met-Hb.
are regarded as an index of intracellular damage to the red cell and it is
increased when -tocopherol is consumed and the rate of lipid peroxidation is increased.
Scavenging of free radicals by -tocopherol is the first and the most critical step in
defending against oxidative damage to the red cells. When -tocopherol is adequate, GSH
and ascorbic acid may complement the antioxidant functions of -tocopherol by providing
reducing equivalents necessary for its recycling/regeneration.
On the other hand, when -tocopherol is absent, GSH and ascorbic acid release transitional
metals from the bound forms and/or maintain metal ions in a catalytic state. Free radical
generation catalysed by transition metal ions in turn initiates oxidative damage to cell
membranes. Membrane damage can lead to release of heme compounds from erythrocytes.
The heme compounds released may further promote oxidative damage especially when
reducing compounds are present (Boveris et al., 2008).