Metabolomic Recovery as a Result of Ischemic Preconditioning Was More Pronounced in Hippocampus than in Cortex That Appeared More Sensitive to Metabolomic Blood Components

Abstract

The study of an organism's response to ischemia at different levels is essential to understand the mechanism of the injury as well as protection. We used the occlusion of four vessels as an animal model of global cerebral ischemia to investigate metabolic alterations in cerebral cortex, hippocampus, blood plasma, as well as in a remote organ, the heart, in rats undergoing 24 h postischemic reperfusion. By inducing sublethal ischemic stimuli, we focused on endogenous phenomena known as ischemic tolerance that is currently the best known and most effective way of protecting against ischemic injury. NMR spectroscopy was used to analyze relative metabolite levels in homogenates from rats' cerebral cortex, hippocampus, and heart together with deproteinized blood plasma. In individual animals subjected to global cerebral ischemia, relative concentrations of the essential amino acids isoleucine, valine, phenylalanine, and tyrosine in cerebral cortex correlated with those in blood plasma (p < 0.05, or boundary significant p < 0.09). This did not apply for the hippocampus, suggesting a closer relation between ischemic cortex and metabolomic blood components. Hippocampal non-participation on correlation with blood components may emphasize the observed partial or full normalization the post-ischemically altered levels of a number of metabolites in the preconditioned animals. Remarkably, that was observed for cortex to a lesser extent. As a response to the global cerebral ischemia in heart tissue, we observed decreased glutamate and increased 3-hydroxybutyrate. Ischemically induced semi-ketotic state and other changes found in blood plasma partially normalized when ischemic preconditioning was introduced. Some metabolomic changes were so strong that even individual metabolites were able to differentiate between ischemic, ischemically preconditioned, and control brain tissues.

Keywords: NMR metabolomics; blood plasma; cerebral cortex; heart; hippocampus; ischemia; ischemic preconditioning; rat.

Figure 1

PCA analyses of system control-IR-IPC for cortex, hippocampus, heart and blood plasma in rats, as variables were used relative concentrations of metabolites determined by NMR.

Figure 2

Metabolomic response of cortex (left) and hippocampus (right) to 24 h reperfusion after global cerebral ischemia, with and without ischemic preconditioning. Relative amounts of metabolites in tissue extracts were determined by 1H NMR, scaled to median of controls set = 1, IR—ischemia reperfusion, IPC—ischemic preconditioning.

Figure 3

Relative changes in metabolites levels in heart tissue extracts and blood plasma, determined by 1H NMR, scaled to median of controls set = 1, IR—ischemia reperfusion, IPC—ischemic preconditioning.

Figure 4

Schematic representation of operating steps in rats, IR—rats with 24 h postischemic reperfusion, IPC—ischemically preconditioned rats with 24 h postischemic reperfusion.