Elsevier

Brain Research

Volume 1369, 19 January 2011, Pages 235-244
Brain Research

Research Report
Dual mechanism of brain damage induced in vivo by the major metabolites accumulating in hyperornithinemia–hyperammonemia–homocitrullinuria syndrome

https://doi.org/10.1016/j.brainres.2010.10.112Get rights and content
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Abstract

Hyperornithinemia–hyperammonemia–homocitrullinuria (HHH) syndrome is an autosomal recessive disorder caused by a defect in the mitochondrial ornithine transporter, leading to accumulation of ornithine (Orn), homocitrulline (Hcit) and ammonia. Progressive neurological regression whose pathogenesis is not well established is common in this disease. The present work investigated the in vivo effects of intracerebroventricular administration of Orn and Hcit on important parameters of oxidative stress and energy metabolism in cerebral cortex from young rats. Orn and Hcit significantly increased thiobarbituric acid-reactive substances values and carbonyl formation, indicators of lipid and protein oxidative damage, respectively. Furthermore, N-acetylcysteine and the combination of the free radical scavengers ascorbic acid plus α-tocopherol attenuated the lipid oxidation and totally prevented the protein oxidative damage provoked by Orn and Hcit, suggesting that reactive species were involved in these effects. Hcit, but not Orn administration, also decreased glutathione concentrations, as well as the activity of catalase and glutathione peroxidase, indicating that Hcit provokes a reduction of brain antioxidant defenses. As regards to the parameters of energy metabolism, we verified that Orn and Hcit significantly inhibited the citric acid cycle function (inhibition of CO2 synthesis from [1-14C] acetate), the aerobic glycolytic pathway (reduced CO2 production from [U-14C] glucose) and complex I–III activity of the respiratory chain. Hcit also inhibited the activity of aconitase, an enzyme very susceptible to free radical attack. Taken together, our data indicate that mitochondrial homeostasis is disturbed by Orn and especially by Hcit. It is presumed that the impairment of brain bioenergetics and the oxidative damage induced by these metabolites may possibly contribute to the brain deterioration and neurological symptoms affecting patients with HHH syndrome.

Research highlights

►Ornithine (Orn) and homocitrulline (Hcit) accumulate in HHH syndrome. ►Affected patients present neurological symptoms whose pathogenesis is poorly known. ►Orn and Hcit provoke oxidative damage and reduce antioxidant defenses in the brain. ►Orn and Hcit inhibit major pathways of energy production in the brain. ►These pathomechanisms may be involved with the neuropathology of HHH syndrome.

Abbreviations

HHH
hyperornithinemia–hyperammonemia–homocitrullinuria
Orn
ornithine
Hcit
homocitrulline
ICV
intracerebroventricular

Keywords

Ornithine
Homocitrulline
Hyperornithinemia–hyperammonemia–homocitrullinuria syndrome
Oxidative stress
Energy metabolism
Cerebral cortex

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