Effect of Ageing and Ischemia on Enzymatic Activities Linked to Krebs’ Cycle, Electron Transfer Chain, Glutamate and Aminoacids Metabolism of Free and Intrasynaptic Mitochondria of Cerebral Cortex

Abstract

The effect of ageing and the relationships between the catalytic properties of enzymes linked to Krebs' cycle, electron transfer chain, glutamate and aminoacid metabolism of cerebral cortex, a functional area very sensitive to both age and ischemia, were studied on mitochondria of adult and aged rats, after complete ischemia of 15 minutes duration. The maximum rate (Vmax) of the following enzyme activities: citrate synthase, malate dehydrogenase, succinate dehydrogenase for Krebs' cycle; NADH-cytochrome c reductase as total (integrated activity of Complex I-III), rotenone sensitive (Complex I) and cytochrome oxidase (Complex IV) for electron transfer chain; glutamate dehydrogenase, glutamate-oxaloacetate-and glutamate-pyruvate transaminases for glutamate metabolism were assayed in non-synaptic, perikaryal mitochondria and in two populations of intra-synaptic mitochondria, i.e., the light and heavy mitochondrial fraction. The results indicate that in normal, steady-state cerebral cortex, the value of the same enzyme activity markedly differs according (a) to the different populations of mitochondria, i.e., non-synaptic or intra-synaptic light and heavy, (b) and respect to ageing. After 15 min of complete ischemia, the enzyme activities of mitochondria located near the nucleus (perikaryal mitochondria) and in synaptic structures (intra-synaptic mitochondria) of the cerebral tissue were substantially modified by ischemia. Non-synaptic mitochondria seem to be more affected by ischemia in adult and particularly in aged animals than the intra-synaptic light and heavy mitochondria. The observed modifications in enzyme activities reflect the metabolic state of the tissue at each specific experimental condition, as shown by comparative evaluation with respect to the content of energy-linked metabolites and substrates. The derangements in enzyme activities due to ischemia is greater in aged than in adult animals and especially the non-synaptic and the intra-synaptic light mitochondria seems to be more affected in aged animals. These data allow the hypothesis that the observed modifications of catalytic activities in non-synaptic and intra-synaptic mitochondrial enzyme systems linked to energy metabolism, amino acids and glutamate metabolism are primary responsible for the physiopathological responses of cerebral tissue to complete cerebral ischemia for 15 min duration during ageing.

G-Protein–Coupled Receptor 91 and Succinate Are Key Contributors in Neonatal Postcerebral Hypoxia-Ischemia Recovery

“…[45][46][47] Accordingly, mechanisms that sense the early local HI would be critical to trigger a process of revascularization and repair. Because carbohydrate metabolites of the Krebs cycle, notably succinate, 48 accumulate under HI conditions, these metabolites have been proposed as preconditioning molecules. 49 The discovery of a specific receptor for succinate, namely GPR91, 23 led us to explore its role in post-HI brain vascularization.…”

Effect of In Vivo l-Acetylcarnitine Administration on ATP-ases Enzyme Systems of Synaptic Plasma Membranes from Rat Cerebral Cortex

“…As regards ATP-ases activities in relation to brain energy metabolism, in previous studies on L-acetylcarnitine in vivo administration [1][2][3], the inhibition of citrate synthase activity, key enzyme of the Krebs cycle (DG (kJ/ mol) = negative; DG0 0 (kJ/mol) = -31.5) [58,59], was observed in mitochondrial fractions from hippocampus, striatum and cerebral cortex. This event, together with an increased carnitine level, leads to an enhanced mitochondrial formation of acetylcarnitine or activates carnitine acetyl-tranferase reactions.…”

Energy Metabolism of Synaptosomes from Different Neuronal Systems of Rat Cerebellum During Aging: A Functional Proteomic Characterization

“…In addition, transamination reactions have been proposed to be favoured for glutamate catabolism in brain since a competition between GlDH and a-ketoglutarate dehydrogenase can not be ruled out [77] and since the catalytic efficiency of transaminases (DG°0 % 0 kJ/mol) is regulated by the in vivo varying biochemical situations [41]. Moreover, GlDH possesses a common regulatory mechanism during aging that is independent from the subcellular compartment and brain area [42,77], that is the cerebral availability of ATP, an allosteric modulator whose concentration does not change during steady-state aging [78].…”

“…enzyme activities, (2) identify potential pathogenic mechanisms, and (3) develop a suitable model to study pharmacological interventions. In fact, during aging, changes in energy-linked enzyme properties not only seem to predispose to some important physiopathological modifications in the in vivo brain [14,33,[37][38][39][40][41], but also may settle tissue responsiveness to drug treatments [30-32, 40, 42-46].…”