Imbalance Glutathione Biosynthesis in ASD: A kinetic patterns “in vivo”

Abstract

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, especially in the central nervous system. Biochemistly knowns that biosynthesis pathway have two consecutive reactions that consume ATP, including two enzymes; glutamate cysteine ligase (GCL), [E-6.3.2.2], formerly known as ganma-glutamylcysteine synthetase (GCS) and glutathione synthetase (GSS), [E-6.3 .2.3] to generate GSH. The defense against the toxic effects of reactive oxygen species (ROS) is an essential task within the brain during a long human life, which indicates the presence of an effective antioxidant system. However, the balance between ROS generation and antioxidant processes can be altered, causing neurological disorders such as Alzheimer's and Parkinson's. The same way, markers of oxidative stress are strongly associated with severe mitochondrial dysfunction in autism pathology. Previous studies indicate that ASD is associated with deficits in the antioxidant defense of glutathione in selective regions of the brain, however, the molecular mechanisms of oxidative stress continue being unclear. In our previous studies 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 respectively, linked to ASD pathogenesis. In the present study, we use resonance magnetic spectroscopy (1H-MRS) to study the specie reduced of glutathione (GSH) biosynthesis in the cingulated cortices, as target of oxidative stress in individuals with ASD. The single voxel of 1H-MRS in bilateral anterior (ACC) and posterior (PCC) cingulated cortices, in adults with ASD and controls with typical development (n = 21 and n = 46 respectively) were assessed. Glutathione (GSH) concentration were significantly decreased in ACC (P = 0.05). The affinity between enzyme and substrate associated with the biosynthesis of reduced species at glutathione was calculate by Michaelis Menten constant (Km) showing that glutathione biosynthesis decreased significant (1.1e-12 mM; R2 = 0.001) in anterior cingulate cortex in autism and, the dissociation constant (ki) was reduced by 67.22% in consequence. On the other hand, maximum rate (Vmax) of the appearance of the product, which depends on the slowest pathway of the enzymatic reaction was significantly decreased (15.12 µM / min; R2 = 0.51) in PCC. Our findings indicate that, with 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, whereas 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.