Antioxidant enzymes in blood of patients with Friedreich's ataxia

Abstract

Background and Aims: Increased generation of reactive oxygen species and mitochondrial dysfunction may underlie the pathophysiology of Friedreich's ataxia, the most common inherited ataxia, due to GAA expansion in a gene coding for a mitochondrial protein (frataxin), implicated in the regulation of iron metabolism. Because iron overload would cause oxidative stress in Friedreich's ataxia, we investigated the enzyme antioxidant system in the blood of 14 patients by determining superoxide dismutase, glutathione peroxidase, and glutathione trasferase catalytic activities. We also studied the glutathione S-transferase genotype polymorphism in order to evaluate its possible influence on enzyme activity. Methods: Blood samples were obtained from 14 unrelated patients with Friedreich's ataxia and 21 age matched healthy subjects. Antioxidant enzyme determinations were spectrophotometrically assayed using specific substrates; the glutathione S-transferase genotype polymorphism was analysed by endonuclease restriction mapping of exon 5 and 6 amplification products.Results: There was a significant elevation of the superoxide dismutase/glutathione peroxidase activity ratio (0.037 (0.01) v 0.025 (0.008) of controls) and an 83% rise of glutathione transferase specific activity (0.22 (0.1) v 0.12 (0.03) nmol/min/mg protein) in blood of patients with Friedreich's ataxia than in the controls. The genotype polymorphism of glutathione S-transferase enzyme did not show any relevant differences when compared to that of healthy subjects. Conclusions: Data show an impairment in vivo of antioxidant enzymes in patients with Friedreich's ataxia and provide evidence of an increased sensitivity to oxidative stress, supporting a consistent role of free radical cytotoxicity in the pathophysiology of the disease.

Friedreich's ataxia: Oxidative stress and cytoskeletal abnormalities

“…Reduced activities of mitochondrial holoproteins containing ironsulphur groups as well as an impairment of tissue energy metabolism have been demonstrated by biochemical and 31 P-MRS studies in cardiac and skeletal muscle from FRDA patients [9,[30][31][32][33]. Furthermore, the key role of oxidative stress in the pathophysiology of the disease has been supported by the finding of increased blood and urinary levels of oxidative stress markers in FRDA patients [13,16] as well as by in vivo evidence of impairment of antioxidant enzymes and of glutathione homeostasis [15,17].…”

“…Moreover, other studies have found increased plasma and urinary levels of oxidative stress markers in FRDA patients [13][14][15][16][17] and have demonstrated that some antioxidants, such as idebenone and vitamin E, might have a protective role [18,19].…”

Oxidative stress, mitochondrial dysfunction and cellular stress response in Friedreich's ataxia

“…In fact, a reduction of free glutathione levels in the blood of patients with Friedreich ataxia, a total glutathione concentration comparable to the controls and a significant increase of glutathione bound to haemoglobin in erythrocytes have been demonstrated in FRDA patients [128], also associated with a significant elevation in the superoxide dismutase/ glutathione peroxidase activity ratio and with an 83% rise of glutathione transferase activity in the blood [129].…”

The pathogenesis of Friedreich ataxia and the structure and function of frataxin

“…In turn, O 2 -is generated by the direct addition to oxygen of electrons prematurely leaking from the respiratory chain, a leakage that increases when the respiratory chain is defective. H 2 O 2 is eliminated by mitochondrial glutathione peroxidase, at the expense of the small-molecule anti-oxidant glutathione, which appears to be decreased in FRDA, possibly because of excess consumption [10]. Another iron-independent mechanism of oxidative stress has been identified recently in frataxin-deficient yeast, which was observed to show signs of oxidative stress even in iron-depleted media, provided that they are cultured aerobically [11].…”

“…In patients with FRDA, oxidative stress is revealed by increased plasma levels of malondialdehyde (a lipid peroxidation product) [16], increased urinary 8-hydroxy-2ʹ-deoxyguanosine (a marker of oxidative DNA damage) [17], decreased plasma free glutathione, and increased plasma glutathione-S-transferase activity [10]. It is intriguing that no evidence of oxidative stress was obtained in studies of conditional knockout mouse models [18], although results might have been confounded by various factors, including the admixture of cells having normal frataxin with progressively disappearing cells having no frataxin, and the almost complete shutdown of the respiratory chain in frataxindeficient cells (see the review in this supplement by Puccio).…”