Imbalance Glutathione Biosynthesis in Cingulated Cortices: ASD Kinetic Patterns In Vivo.

Background: Toxic effects defenses of reactive oxygen species are an essential task within the brain during a long human life, which indicates the presence of an effective antioxidant system. Markers of oxidative stress are strongly associated with severe mitochondrial dysfunction in autism spectrum disorders (ASD) pathology associated with deficits in the antioxidant defense of glutathione in selective regions of the brain, although the molecular pathway continue being unclear. Glutathione (GSH; γ-L-glutamyl-L-cysteinyl-glycine) is the most abundant endogenous antioxidant present in mammalian cells (0.1 to 15 mM) and plays a protective role for exogenous toxins and endogenous in the central nervous system. It biosynthesis pathway, have two consecutive reactions that consume ATP, including two enzymes; glutamate cysteine ligase (GCL), and glutathione synthetase (GSS), to generate GSH. Previously, we described the kinetic imbalance in tri-cellular metabolism of N-acetyl-aspartyl glutamate (NAAG), in anterior (ACC) and posterior (PCC) cingulated cortices relate to the executive control networks and the attention alert functions linked to pathogenesis of ASD, which lead the next step in our investigation to elucidate the multiple causes of imbalance neurochemistry linked to cingulated cortices.

Objectives: To study Kinetic imbalance of glutathione biosynthesis in the cingulated cortices as target of oxidative stress in individuals with ASD using ¹H-MRS.

Methods: Single voxel (¹H-MRS) in ACC and PCC, in adults with a clinical diagnosis of ASD (n=21) and controls (TD) typically development (n=46), matched for age, gender and Autism quotients (AQ) score were assessed. The affinity between enzyme and substrate (ES) associated with GSH biosyntethis was measured as Michaelis Menten constant (Km). Statistic one-way ANOVA and Bonferroni correction were applied.

Results: Km for glutathione biosynthesis in ASD group is significantly lower [1.1e^-012 (mM)]; R² = 0.001 in ACC and the dissociation constant (ki) reduced 67.22% compared to the TD group. Conversely, Vmax of the appearance of the product that depends on the slowest process of the reaction is significantly decreased [15.12 µM / min]; R² = 0.51 in PCC.

Conclusions: Imbalance enzymatic kinetic in ASD does not mean that the enzyme is not present. Our findings indicate that, at a small amount of substrate, the rate increases rapidly and linearly in ACC, suggesting that the active sites of the enzyme are saturated with the substrate. The enzyme-substrate complex is very tight and rarely dissociates without the substrate reacting to give the product. Imbalance enzymatic kinetic in glutathione biosynthesis in the autism cingulated cortices is a novel finding indicative of a chronic neuroinflamatory state in these regions. We further conclude that a better understanding of the enzymatic activity in the synthesis of glutathione in the cingulated cortices can lead us to a new therapeutic pathway in the treatment of individuals with ASD.