Our study aims at developing knowledge-based strategies minimizing chronic changes in the brain after severe spinal cord injury (SCI). The SCI-induced long-term metabolic alterations and their reactivity to treatments shortly after the injury are characterized in rats. Eight weeks after severe SCI, significant mitochondrial lesions outside the injured area are demonstrated in the spinal cord and cerebral cortex. Among the six tested enzymes essential for the TCA cycle and amino acid metabolism, mitochondrial 2-oxoglutarate dehydrogenase complex (OGDHC) is the most affected one. SCI downregulates this complex by 90% in the spinal cord and 30% in the cerebral cortex. This is associated with the tissue-specific changes in other enzymes of the OGDHC network. Single administrations of a pro-activator (thiamine, or vitamin B1, 1.2 mmol/kg) or a synthetic pro-inhibitor (triethyl glutaryl phosphonate, TEGP, 0.02 mmol/kg) of OGDHC within 15–20 h after SCI are tested as protective strategies. The biochemical and physiological assessments 8 weeks after SCI reveal that thiamine, but not TEGP, alleviates the SCI-induced perturbations in the rat brain metabolism, accompanied by the decreased expression of (acetyl)p53, increased expression of sirtuin 5 and an 18% improvement in the locomotor recovery. Treatment of the non-operated rats with the OGDHC pro-inhibitor TEGP increases the p53 acetylation in the brain, approaching the brain metabolic profiles to those after SCI. Our data testify to an important contribution of the OGDHC regulation to the chronic consequences of SCI and their control by p53 and sirtuin 5.

The disturbed metabolism of vitamins B1 or B6, which are essential for neurotransmitters homeostasis, may cause seizures. Our study aims at revealing therapeutic potential of vitamins B1 and B6 by estimating the short- and long-term effects of their combined administration with the seizure inductor pentylenetetrazole (PTZ). The PTZ dose dependence of a seizure and its parameters according to modified Racine’s scale, along with delayed physiological and biochemical consequences the next day after the seizure are assessed regarding sexual dimorphism in epilepsy. PTZ sensitivity is stronger in the female than the male rats. The next day after a seizure, sex differences in behavior and brain biochemistry arise. The induced sex differences in anxiety and locomotor activity correspond to the disappearance of sex differences in the brain aspartate and alanine, with appearance of those in glutamate and glutamine. PTZ decreases the brain malate dehydrogenase activity and urea in the males and the phenylalanine in the females. The administration of vitamins B1 and B6 24 h before PTZ delays a seizure in female rats only. This desensitization is not observed at short intervals (0.5–2 h) between the administration of the vitamins and PTZ. With the increasing interval, the pyridoxal kinase (PLK) activity in the female brain decreases, suggesting that the PLK downregulation by vitamins contributes to the desensitization. The delayed effects of vitamins and/or PTZ are mostly sex-specific and interacting. Our findings on the sex differences in sensitivity to epileptogenic factors, action of vitamins B1/B6 and associated biochemical events have medical implications.

Specific inhibitors of mitochondrial 2-oxoglutarate dehydrogenase (OGDH) are administered to animals to model the downregulation of the enzyme as observed in neurodegenerative diseases. Comparison of the effects of succinyl phosphonate (SP, 0.02 mmol/kg) and its uncharged precursor, triethyl succinyl phosphonate (TESP, 0.02 and 0.1 mmol/kg) reveals a biphasic response of the rat brain metabolism and physiology to increasing perturbation of OGDH function. At the low (TE)SP dose, glutamate, NAD⁺, and the activities of dehydrogenases of 2-oxoglutarate and malate increase, followed by their decreases at the high TESP dose. The complementary changes, i.e., an initial decrease followed by growth, are demonstrated by activities of pyruvate dehydrogenase and glutamine synthetase, and levels of oxidized glutathione and citrulline. While most of these indicators return to control levels at the high TESP dose, OGDH activity decreases and oxidized glutathione increases, compared to their control values. The first phase of metabolic perturbations does not cause significant physiological changes, but in the second phase, the ECG parameters and behavior reveal decreased adaptability and increased anxiety. Thus, lower levels of OGDH inhibition are compensated by the rearranged metabolic network, while the increased levels induce a metabolic switch to a lower redox state of the brain, associated with elevated stress of the animals.

α-oxoacid dehydrogenase complexes are large, tripartite enzymatic machineries carrying out key reactions in central metabolism. Extremely conserved across the tree of life, they have been, so far, all considered to be structured around a high–molecular weight hollow core, consisting of up to 60 subunits of the acyltransferase component. We provide here evidence that Actinobacteria break the rule by possessing an acetyltranferase component reduced to its minimally active, trimeric unit, characterized by a unique C-terminal helix bearing an actinobacterial specific insertion that precludes larger protein oligomerization. This particular feature, together with the presence of an odhA gene coding for both the decarboxylase and the acyltransferase domains on the same polypetide, is spread over Actinobacteria and reflects the association of PDH and ODH into a single physical complex. Considering the central role of the pyruvate and 2-oxoglutarate nodes in central metabolism, our findings pave the way to both therapeutic and metabolic engineering applications. Significance α-oxoacid dehydrogenase are large, evolutionary-conserved multienzymatic complexes that carry out key oxidative reactions in central metabolism. For decades, these complexes were thought to share a similar organization in all aerobic organisms, structured around a hollow core resulting from the high oligomeric arrangement of the acyltransferase component. Here, we show that Actinobacteria, one of the largest eubacterial phyla, break this “dogma” owing to a distinct trimeric acyltransferase core. We provide a structural explanation to this different oligomeric architecture and show how this feature, related to a fusion of two genes coding for 2-oxoglutarate dehydrogenase, constitutes a trait of Actinobacteria providing a different perspective on the evolution of these metabolic complexes.

Unlike the OGDH-encoded 2-oxoglutarate dehydrogenase (OGDH), which is an essential enzyme present in all animal tissues, expression of the DHTKD1-encoded isoenzyme, 2-oxoadipate dehydrogenase (OADH), depends on a number of factors, and mutant DHTKD1 phenotypes are rarely manifested. Physiological significance of OADH is also obscured by the fact that both isoenzymes transform 2-oxoglutarate and 2-oxoadipate. By analogy with other members of the 2-oxo acid dehydrogenases family, OADH is assumed to be a component of the multienzyme complex that catalyzes oxidative decarboxylation of 2-oxoadipate. This study aims at molecular characterization of OADH from animal tissues. Phylogenetic analysis of 2-oxo acid dehydrogenases reveals OADH only in animals and Dictyostelium discoideum slime mold, within a common branch with bacterial OGDH. Examination of partially purified animal OADH by immunoblotting and mass spectrometry identifies two OADH isoforms with molecular weights of about 130 and 70 kDa. These isoforms are not observed upon the expression of human DHTKD1 protein in either bacterial or yeast system, where the synthesized OADH is of expected molecular weight (about 100 kDa). Thus, the OADH isoforms present in animal tissues, may result from the animal-specific regulation of the DHTKD1 expression and/or posttranslational modifications of the encoded protein. Mapping of the peptides identified in the OADH preparations, onto the protein structure suggests that the 70-kDa isoform is truncated at the N-terminus, but retains the active site. Since the N-terminal domain of OGDH is required for the formation of the multienzyme complex, it is possible that the 70-kDa isoform catalyzes non-oxidative transformation of dicarboxylic 2-oxo acids that does not require the multienzyme structure. In this case, the ratio of the OADH isoforms in animal tissues may correspond to the ratio between the oxidative and non-oxidative decarboxylation of 2-oxoadipate.