Neurochemical evidence that 3‐methylglutaric acid inhibits synaptic Na⁺,K⁺‐ATPase activity probably through oxidative damage in brain cortex of young rats

Abstract

3-Methylglutaconic aciduria (MGTA) comprehends a group of disorders biochemically characterized by accumulation of 3-methylglutaric acid (MGA), 3-methylglutaconic acid (MGT) and occasionally 3-hydroxyisovaleric acid (OHIVA). Although neurological symptoms are common in the affected individuals, the mechanisms of brain damage are poorly known. In the present study we investigated the in vitro effect MGA, MGT and OHIVA, at concentrations ranging from 0.1 to 5.0mM, on bioenergetics and oxidative stress in synaptosomal preparations isolated from cerebral cortex of young rats. MGA significantly reduced mitochondrial redox potential (25%), as determined by resazurin reduction, and inhibited the activity of Na(+),K(+)-ATPase (30%), whereas MGT and OHIVA did not modify these parameters. Moreover, the inhibitory effect elicited by MGA on Na(+),K(+)-ATPase activity was totally prevented by co-incubation with the scavenging antioxidants creatine and melatonin, implying a role for reactive species in this effect. MGA also increased 2',7'-dichlorofluorescein (DCFH) oxidation (30%), reinforcing that this organic acid induces reactive species production. The present data indicate that MGA compromises mitochondrial function, elicits reactive species production and inhibits the activity of a crucial enzyme implicated in neurotransmission. It is therefore presumed that these deleterious effects may play a role in the pathophysiology of the brain damage observed in patients affected by disorders in which MGA accumulates.

Experimental Evidence that 3-Methylglutaric Acid Disturbs Mitochondrial Function and Induced Oxidative Stress in Rat Brain Synaptosomes: New Converging Mechanisms

“…In this study, using synaptosomes of cerebral cortex from young rats, the authors found reduced mitochondrial function, increased ROS formation and inhibition of the Na + ,K + -ATPase enzyme activity, but no changes in lipid peroxidation were observed. Thus, our present study represents a logic extension of the one from Ribeiro et al [20] and confirms part of the effects previously described for the toxic pattern of 3MGA. Interestingly, in contrast to that study we found changes in the levels of TBARS at concentrations of 1 and 5 mM.…”

“…5b) and MTT reduction (Fig. 5c) were estimated as endpoints of the toxicity exerted by the synergic action of 3MGA and QUIN The toxic model induced by 3MGA and used in the present work was previously validated in synaptosomes by Ribeiro et al [20]. In this study, using synaptosomes of cerebral cortex from young rats, the authors found reduced mitochondrial function, increased ROS formation and inhibition of the Na + ,K + -ATPase enzyme activity, but no changes in lipid peroxidation were observed.…”

Increased oxidative stress in patients with 3-hydroxy-3-methylglutaric aciduria

“…,K ? -ATPase in rat brain and this effect was associated with an increased free radical generation [35]. So, in this work, we aimed to investigate oxidative stress parameters in biological fluids from HMGA patients and verify if the therapy with protein restriction and L-carnitine could exert some influence on this process.…”

Biochemical Characterisation and Whole Genome Expression Profiling of Cultured Skin Fibroblasts from Two South African Adults with Urinary 3-Hydroxyisovaleric Acid and 3-Methylcrotonylglycine

“…Similar to the transcriptome of symptomatic, clinically severe MCC deficiency and neurological studies on the cerebral cortex of young rats [55][56][57][60][61][62][63][64][65], this marginal MCC deficiency skin fibroblast transcriptome also had a genetic footprint suggestive of partial mitochondrial dysfunction, oxidative stress and disruption of energy homeostasis. Transcripts of mitochondrial respiratory chain complexes I, II and IV were significantly differentially expressed (Table 4) affecting the OXPHOS system (NDUFS2, SDHD, MT-CO1/COX1, COX6 and COX17).…”

“…Imbalances in eicosanoid metabolism signalling have been detected in individuals with a weak tolerance to environmental factors and susceptibility to environmental stressors that often result in asthma [94][95][96][97], allergy, eczema [98][99][100], arthritis [81] as well as the development of cancer [73] and might also play a role in the development of non-specific symptoms of marginal MCC deficiency. Therefore, life-long monitoring of ROS levels of individuals with MCC deficiency along with the administration of anti-oxidants to prevent and manage deleterious secondary signalling responses may be beneficial as previously proposed (Figure 3) [55,56,60,64,65,101].…”