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Abstract
5-Oxoproline (L-pyroglutamic acid) accumulates in glutathione synthetase
deficiency, an autossomic recessive inherited disorder clinically characterized by hemolytic
anemia, metabolic acidosis and severe neurological symptoms. Considering that the
mechanisms of brain damage in this disease are poorly known, and that oxidative stress is
elicited by 5-oxoproline in vitro, we decided to study the in vivo effects of this metabolite
on oxidative stress parameters, in order to further clarify its role in 5-oxoproline
neurotoxicity and its participation on the neuropathological mechanisms of patients affected
by glutathione sintetase deficiency. The effects of acute subcutaneous administration of 5-
oxoproline were studied on a wide spectrum of oxidative stress parameters, such as total
radical-trapping antioxidant potential (TRAP); spontaneous chemiluminescence;
thiobarbituric acid-reactive substances (TBA-RS); and carbonyl, ascorbic acid, reduced
glutathione (GSH), hydrogen peroxide, thiol and disulfide contents (and SH/SS ratio), as
well as on the activities of the antioxidant enzymes catalase (CAT), superoxide dismutase
(SOD) and glutathione peroxidase (GPx), and on the activity of glucose 6-phosphate
dehydrogenase (G6PD) in cerebral cortex and cerebellum of 14-day-old rats. The results
indicated that in vivo 5-oxoproline causes lipid peroxidation and protein oxidation, impairs
brain antioxidant defenses and increases hydrogen peroxide content, indicating that 5-
oxoproline elicits oxidative stress in vivo in cerebral cortex and cerebellum of young rats, a
mechanism that may be involved in the neuropathology of gluthatione synthetase
deficiency, in which this metabolite accumulates.
N-acetylaspartic acid, on the other hand, accumulates in Canavan Disease, a severe
leukodystrophy characterized by swelling and spongy degeneration of the white matter of
the brain. This inherited metabolic disease, caused by deficiency of the enzyme
aspartoacylase, is clinically characterized by severe mental retardation, hypotonia and
macrocephaly, and also generalized tonic and clonic type seizures in about half of the
patients. N-acetylaspartic acid is an immediate precursor for the enzyme-mediated
biosynthesis of N-acetylaspartylglutamic acid, whose concentration is also increased in
urine and cerebrospinal fluid of patients affected by Canavan Disease. Considering that the
mechanisms of brain damage in this disease remain poorly understood, in the present study
we investigated whether oxidative stress is elicited by N-acetylaspartic acid or its
metabolite, N-acetylaspartylglutamic acid. The in vitro effects of N-acetylaspartic acid and
N-acetylaspartylglutamic acid, as well as the effect of the acute subcutaneous
administration of N-acetylaspartic acid, and the intracerebroventricular administration of N-
acetylaspartic acid or N-acetylaspartylglutamic acid, were studied on oxidative stress
parameters: TRAP, TAR, spontaneous chemiluminescence, TBA-RS, reduced glutathione
content, sufhydryl content, carbonyl content, and on enzyme activities of CAT, SOD and
GPx as well as on GSH and hydrogen peroxide contents and on G6PD activity, in the
cerebral cortex of rats. Our results indicated that only N-acetylaspartic acid promotes
oxidative stress by stimulating lipid peroxidation, protein oxidation and by impairing
antioxidant defenses and enhancing hydrogen peroxide content in rat brain. This could be
involved in the pathophysiological mechanisms responsible for the brain damage observed
in patients affected by Canavan Disease, in which N-acetylaspartic acid accumulation is the
biochemical hallmark.