Reactive oxygen species (ROS) and particularly free radical induced lipid peroxidative
tissue damage have been implicated in the pathogenesis of various diseases
1
including diabetes
2. Diabetes mellitus is a disorder with late complications including
cardiovascular diseases, nephropathy, neuropathy, retinopathy which affects severely
the quality of life
3. Although there are several reports on complications of diabetes,
pathopysiology of these complications are still needed to be deciphered
4. Recent
reports indicate that free radicals have important roles in pathogenesis of diabetes and
a relationship between oxidative stress and secondary complications of diabetes exists
5,6. Free radicals are produced as a result of glycosylation of several proteins
including hemoglobin (Hb) by non-enzymatic mechanisms
7,8.
Subsequently, free radicals change lipid/protein ratio of membranes by affecting poly
unsatured fatty acids and lipid peroxidation causes functional irregularities of several
cellular organelles 9,10.
Lipid peroxides are disintegrated quickly and form
reactive carbon compounds. Among these, MDA is an
important reactive carbon compound which is used
commonly as an indicator of lipid peroxidation 11. Since
free radical production is increased whereas capacity of
antioxidant systems is reduced in diabetes, it has been
proposed that diabetic patients may require more
antioxidants compared to healthy individuals 10,12.
Since effects of free radicals in diabetes are now
documented, it has been proposed to use antioxidant
vitamins to block formation of free radicals and hence
prevent development of diabetes 13,14. While
superoxide radicals are cleaned by enzymatic
dismutation, compounds known as antioxidants clean
free radicals in organism. Glutathione is a very important
non-enzymatic antioxidant together with antioxidant
vitamins. Vitamins A, E and C are among these
important nonenzymatic antioxidants 15,16.
It has been proposed that in diabetic patients several
abnormalities related with absorption develop in the
absence of antioxidant vitamins 17.
Vitamin A functions as catalyzer of removal of singlet
oxygen and as a result vitamin A inhibits singlet oxygendependent
reactions 15,18. Vitamin C is also has a role
in activating vitamin E when it loses its antioxidant
capacity by turning into tocopherol 19.
In addition, selenium has effect on preventing
decomposition, absorption and biological activity of α-
tocopherol 20,21. Selenium and vitamin E act as
complementing each others function against oxidative
stress 22,23.
Selenium, functioning as part of glutathione
peroxidase, has been recognized as a cellular
antioxidant in addition to its protecting function against
heavy metal toxicity 24,25. Selenium has important
role in vitamin E metabolism. Selenium is required for
normal pancreatic functions. It is needed for absorption
of lipids and vitamin E. In addition, selenium has roles to
keep vitamin E within lipids 20. There are intrinsic
enzymatic and non-enzymatic antioxidants detoxifying
mechanisms that decrease ROS concentrations in
human body. Vitamins A, C, E, selenium and glutathione
are some of the major non-enzymatic antioxidants in the
body 16. Therefore, the idea of using antioxidant
vitamins to prohibit development of diabetes as well as
its complications and/or to treat diabetic patients is
getting more attention than ever 13,26.
Although there are studies reporting serum or plasma
levels of antioxidant vitamins in diabetic patients, results
from different groups are rather contradictory. Studies
focusing on involvement of selenium in diabetic patients
are rather limited. Therefore, the present study was
designed to determine and evaluate changes in level of
selenium, antioxidant vitamins (A, E, C) and MDA in
patients with type 2 diabetes and healthy subjects.
Furthermore, we examined possible relationship among
four antioxidants (namely, selenium, Vitamin A, vitamin
E, vitamin C) and MDA.