Oxidative stress in Rett syndrome

Reactive oxygen species and related haem pathway components as possible epigenetic modifiers in neurobehavioural pathology

The neuroendocrine response to stress utilizes several bio-communicative pathways which also play a role in neurodevelopmental plasticity. The mechanism of action of steroidal compounds includes DNA alteration by reactive oxygen species (ROS) arising through redox cycling of reactive hormone derivatives. ROS and reactive nitrogen species play a significant role in signaling networks affecting gene transcriptional regulation during normal as well as stress-induced responses. ROS-associated synaptic and regulatory region plasticity may have been important for normal brain evolution, but probably simultaneously lowered the threshold for inducing neuropathology. A shift from 'plasticity' to 'instability' is likely to be associated with the emergence of complex effects depending on the timing, duration and intensity of the ROS insult, and is suggested to include heritable epigenetic chromatin/regulatory region remodeling differentially influencing expression levels of significant neuropsychiatric genes and their variant alleles. Neurobehavioural disorder clinical manifestations have been linked with ROS effects. The concepts discussed here relate to ROS-associated instability of DNA regulatory region sequences and a proposal that it may play an important modifying role in brain and neuro-behaviourally related gene expression. Genes encoding key steps in mitochondrial, haem, iron and bilirubin ROS metabolic pathways have been used as examples to illustrate how ROS-modified regulatory networks could possibly alter the context within which (even ostensibly unrelated) neuropsychiatric gene candidates may sometimes be recruited. Furthermore, reactions of certain radicals release sufficient energy to generate UV-photons. DNA conformational changes accompanied by changes in photon emission suggest that functional neuroimaging findings probably reflect interaction on the level of ROS/biophoton/genome regulatory region domains rather than the signatures of individual neurobehavioural disorder candidate genes.

Evaluation of oxidative stress measurements in obstructive sleep apnea syndrome

Assessment of reactive oxygen species (ROS) is highly important in neurodegenerative disorders and neuroleptic treatment. However, conflicting results have been reported, which may arise from methodological difficulties. Obstructive sleep apnea (OSA) syndrome with episodic hypoxia-reoxygenation is proposed as a human model for the investigation of ROS measurements. Despite a broad analytical approach comprising lipid peroxidation and amino acid oxidation products, oxidative DNA damage, and activity of the antioxidant defense, only plasma malondialdehyde (MDA) and urinary o,o'-dityrosine seemed to be appropriate, robust biomarkers of oxidative stress, which are also simple enough for routine clinical use. MDA concentrations correlated with a duration of nocturnal desaturation below 85% (r = 0.77, p<0.0005), and o,o'-dityrosine levels decreased after therapy (p<0.05) as a function of baseline concentrations (r = -0.61, p<0.05). Gender effects in ROS generation also have to be considered. At present, we recommend the application of several oxidative stress measurements at different time points, preferably involving plasma MDA and urinary o,o'-dityrosine.

The role of oxidative damage in the neuropathology of organic acidurias: insights from animal studies

Organic acidurias represent a group of inherited disorders resulting from deficient activity of specific enzymes of the catabolism of amino acids, carbohydrates or lipids, leading to tissue accumulation of one or more carboxylic (organic) acids. Patients affected by organic acidurias predominantly present neurological symptoms and structural brain abnormalities, of which the aetiopathogenesis is poorly understood. However, in recent years increasing evidence has emerged suggesting that oxidative stress is possibly involved in the pathology of some organic acidurias and other inborn errors of metabolism. This review addresses some of the recent developments obtained mainly from animal studies indicating oxidative damage as an important determinant of the neuropathophysiology of some organic acidurias. Recent data showing that various organic acids are capable of inducing free radical generation and decreasing brain antioxidant defences is presented. The discussion focuses on the relatively low antioxidant defences of the brain and the vulnerability of this tissue to reactive species. This offers new perspectives for potential therapeutic strategies for these disorders, which may include the early use of appropriate antioxidants as a novel adjuvant therapy, besides the usual treatment based on removing toxic compounds and using special diets and pharmacological agents, such as cofactors and L-carnitine.