Blood and Brain Metabolites after Cerebral Ischemia

The study of an organism's response to cerebral ischemia at different levels is essential to understanding the mechanism of the injury and protection. A great interest is devoted to finding the links between quantitative metabolic changes and post-ischemic damage. This work aims to summarize the outcomes of the most studied metabolites in brain tissue-lactate, glutamine, GABA (4-aminobutyric acid), glutamate, and NAA (N-acetyl aspartate)-regarding their biological function in physiological conditions and their role after cerebral ischemia/reperfusion. We focused on ischemic damage and post-ischemic recovery in both experimental-including our results-as well as clinical studies. We discuss the role of blood glucose in view of the diverse impact of hyperglycemia, whether experimentally induced, caused by insulin resistance, or developed as a stress response to the cerebral ischemic event. Additionally, based on our and other studies, we analyze and critically discuss post-ischemic alterations in energy metabolites and the elevation of blood ketone bodies observed in the studies on rodents. To complete the schema, we discuss alterations in blood plasma circulating amino acids after cerebral ischemia. So far, no fundamental brain or blood metabolite(s) has been recognized as a relevant biological marker with the feasibility to determine the post-ischemic outcome or extent of ischemic damage. However, studies from our group on rats subjected to protective ischemic preconditioning showed that these animals did not develop post-ischemic hyperglycemia and manifested a decreased metabolic infringement and faster metabolomic recovery. The metabolomic approach is an additional tool for understanding damaging and/or restorative processes within the affected brain region reflected in the blood to uncover the response of the whole organism via interorgan metabolic communications to the stressful cerebral ischemic challenge.

Involvement of Proteasomal and Endoplasmic Reticulum Stress in Neurodegeneration After Global Brain Ischemia

A brief period of transient global brain ischemia leads to selective ischemic neurodegeneration associated with death of hippocampal CA1 pyramidal neurons days after reperfusion. The mechanism of such selective and delayed neurodegeneration is still uncertain. Our work aimed to study the involvement of proteasomal and endoplasmic reticulum (ER) stress in ischemic neurodegeneration. We have performed laser scanning confocal microscopy analysis of brain slices from control and experimental animals that underwent global brain ischemia for 15 min and varying times of reperfusion. We have focused on ubiquitin, PUMA, a proapoptotic protein of the Bcl-2 family overexpressed in response to both proteasomal and ER stress, and p53, which controls expression of PUMA. We have also examined the expression of HRD1, an E3 ubiquitin ligase that was shown to be overexpressed after ER stress. We have also examined potential crosstalk between proteasomal and ER stress using cellular models of both proteasomal and ER stress. We demonstrate that global brain ischemia is associated with an appearance of distinct immunoreactivity of ubiquitin, PUMA and p53 in pyramidal neurons of the CA1 layer of the hippocampus 72 h after ischemic insults. Such changes correlate with a delay and selectivity of ischemic neurodegeneration. Immunoreactivity of HRD1 observed in all investigated regions of rat brain was transiently absent in both CA1 and CA3 pyramidal neurones 24 h after ischemia in the hippocampus, which does not correlate with a delay and selectivity of ischemic neurodegeneration. We do not document significant crosstalk between proteasomal and ER stress. Our results favour dysfunction of the ubiquitin proteasome system and consequent p53-induced expression of PUMA as the main mechanisms responsible for selective and delayed degeneration of pyramidal neurons of the hippocampal CA1 layer in response to global brain ischemia.

Alzheimer's Disease-like Pathological Features in the Dorsal Hippocampus of Wild-Type Rats Subjected to Methionine-Diet-Evoked Mild Hyperhomocysteinaemia

Multifactorial interactions, including nutritional state, likely participate in neurodegeneration's pathogenesis and evolution. Dysregulation in methionine (Met) metabolism could lead to the development of hyperhomocysteinaemia (hHcy), playing an important role in neuronal dysfunction, which could potentially lead to the development of Alzheimer's disease (AD)-like pathological features. This study combines proton magnetic resonance spectroscopy (1H MRS) with immunohistochemical analysis to examine changes in the metabolic ratio and histomorphological alterations in the dorsal rat hippocampus (dentate gyrus-DG) subjected to a high Met diet. Male Wistar rats (420-480 g) underwent hHcy evoked by a Met-enriched diet (2 g/kg of weight/day) lasting four weeks. Changes in the metabolic ratio profile and significant histomorphological alterations have been found in the DG of hHcy rats. We have detected increased morphologically changed neurons and glial cells with increased neurogenic markers and apolipoprotein E positivity parallel with a diminished immunosignal for the N-Methyl-D-Aspartate receptor 1 in hHcy animals. A Met diet induced hHcy, likely via direct Hcy neurotoxicity, an interference with one carbon unit metabolism, and/or epigenetic regulation. These conditions lead to the progression of neurodegeneration and the promotion of AD-like pathological features in the less vulnerable hippocampal DG, which presents a plausible therapeutic target.

Hippocampal metabolic recovery as a manifestation of the protective effect of ischemic preconditioning in rats

The ever-present risk of brain ischemic events in humans and its full prevention make the detailed studies of an organism's response to ischemia at different levels essential to understanding the mechanism of the injury as well as protection. We used the four-vessel occlusion as an animal model of forebrain ischemia to investigate its impact on the metabolic alterations in both the hippocampus and the blood plasma to see changes on the systemic level. By inducing sublethal ischemic stimuli, we focused on the endogenous phenomena known as ischemic tolerance. NMR spectroscopy was used to analyze relative metabolite levels in tissue extracts from rats' hippocampus and blood plasma in three various ischemic/reperfusion times: 3 h, 24 h, and 72 h. Hippocampal tissues were characterized by postischemically decreased glutamate and GABA (4-aminobutyrate) tissue content balanced with increased glutamine level, with most pronounced changes at 3 h reperfusion time. Glutamate (as well as glutamine) levels recovered towards the control levels on the third day, as if the glutamate re-synthesis would be firstly preferred before GABA. These results are indicating the higher feasibility of re-establishing of glutamatergic transmission three days after an ischemic event, in contrast to GABA-ergic. Tissue levels of N-acetylaspartate (NAA), as well as choline, were decreased without the tendency to recover three days after the ischemic event. Metabolomic analysis of blood plasma revealed that ischemically preconditioned rats, contrary to the non-preconditioned animals, did not show hyperglycemic conditions. Ischemically induced semi-ketotic state, manifested in increased plasma ketone bodies 3-hydroxybutyrate and acetoacetate, seems to be programmed to support the brain tissue revitalization after the ischemic event. These and other metabolites changes found in blood plasma as well as in the hippocampus were observed to a lower extent or recovered faster in preconditioned animals. Some metabolomic changes in hippocampal tissue extract were so strong that even single metabolites were able to differentiate between ischemic, ischemically preconditioned, and control brain tissues.

Metabolic Changes Induced by Cerebral Ischemia, the Effect of Ischemic Preconditioning, and Hyperhomocysteinemia

¹H Nuclear Magnetic Resonance (NMR) metabolomics is one of the fundamental tools in the fast-developing metabolomics field. It identifies and quantifies the most abundant metabolites, alterations of which can describe energy metabolism, activated immune response, protein synthesis and catabolism, neurotransmission, and many other factors. This paper summarizes our results of the ¹H NMR metabolomics approach to characterize the distribution of relevant metabolites and their alterations induced by cerebral ischemic injury or its combination with hyperhomocysteinemia in the affected tissue and blood plasma in rodents. A decrease in the neurotransmitter pool in the brain tissue likely follows the disordered feasibility of post-ischemic neurotransmission. This decline is balanced by the increased tissue glutamine level with the detected impact on neuronal health. The ischemic injury was also manifested in the metabolomic alterations in blood plasma with the decreased levels of glycolytic intermediates, as well as a post-ischemically induced ketosis-like state with increased plasma ketone bodies. As the 3-hydroxybutyrate can act as a likely neuroprotectant, its post-ischemic increase can suggest its supporting role in balancing ischemic metabolic dysregulation. Furthermore, the ¹H NMR approach revealed post-ischemically increased 3-hydroxybutyrate in the remote organs, such as the liver and heart, as well as decreased myocardial glutamate. Ischemic preconditioning, as a proposed protective strategy, was manifested in a lower extent of metabolomic changes and/or their faster recovery in a longitudinal study. The paper also summarizes the pre- and post-ischemic metabolomic changes in the rat hyperhomocysteinemic models. Animals are challenged with hyperglycemia and ketosis-like state. A decrease in several amino acids in plasma follows the onset and progression of hippocampal neuropathology when combined with ischemic injury. The ¹H NMR metabolomics approach also offers a high potential for metabolites in discriminatory analysis in the search for potential biomarkers of ischemic injury. Based on our results and the literature data, this paper presents valuable findings applicable in clinical studies and suggests the precaution of a high protein diet, especially foods which are high in Met content and low in B vitamins, in the possible risk of human cerebrovascular neuropathology.

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

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.

Methionine Diet Evoked Hyperhomocysteinemia Causes Hippocampal Alterations, Metabolomics Plasma Changes and Behavioral Pattern in Wild Type Rats

L-methionine, an essential amino acid, plays a critical role in cell physiology. High intake and/or dysregulation in methionine (Met) metabolism results in accumulation of its intermediate(s) or breakdown products in plasma, including homocysteine (Hcy). High level of Hcy in plasma, hyperhomocysteinemia (hHcy), is considered to be an independent risk factor for cerebrovascular diseases, stroke and dementias. To evoke a mild hHcy in adult male Wistar rats we used an enriched Met diet at a dose of 2 g/kg of animal weight/day in duration of 4 weeks. The study contributes to the exploration of the impact of Met enriched diet inducing mild hHcy on nervous tissue by detecting the histo-morphological, metabolomic and behavioural alterations. We found an altered plasma metabolomic profile, modified spatial and learning memory acquisition as well as remarkable histo-morphological changes such as a decrease in neurons' vitality, alterations in the morphology of neurons in the selective vulnerable hippocampal CA 1 area of animals treated with Met enriched diet. Results of these approaches suggest that the mild hHcy alters plasma metabolome and behavioural and histo-morphological patterns in rats, likely due to the potential Met induced changes in "methylation index" of hippocampal brain area, which eventually aggravates the noxious effect of high methionine intake.

Metabolomic profiling of blood plasma of patients with lung cancer and malignant tumors with metastasis in the lungs showed similar features and promising statistical discrimination against controls

Targeting metabolomic pathways is a promising strategy for cancer treatment. Alterations in the metabolomic state have also an epigenetic impact, making the metabolomic studies even more interesting. We explored metabolomic changes in the blood plasma of patients with primary and secondary lung cancer and tried to explore their origin. We also applied a discrimination algorithm to the data. In the study, blood samples from 132 patients with primary lung cancer, 47 with secondary lung cancer, and 77 subjectively healthy subjects without any cancer history were used. The samples were measured by NMR spectroscopy. PCA and PLS-DA analyses did not distinguish between patients with primary and secondary lung tumors. Accordingly, no significantly changed levels of plasmatic metabolites were found between these groups. When comparing with healthy controls, significantly increased glucose, citrate, acetate, 3-hydroxybutyrate, and creatinine balanced with decreased pyruvate, lactate, alanine, tyrosine, and tryptophan were found as a common feature of both groups. Metabolomic analysis of blood plasma showed considerable proximity of patients with primary and secondary lung cancer. The changes observed can be partially explained as cancer-derived and also as changes showing ischemic nature. Random Forrest discrimination based on the relative concentration of metabolites in blood plasma performed very promising with AUC of 0.95 against controls; however noticeable parts of differencing metabolites are overlapping with those observed after ischemic injury in other studies.

NMR plasma metabolomics study of patients overcoming acute myocardial infarction: in the first 12 h after onset of chest pain with statistical discrimination towards metabolomic biomarkers

Acute myocardial infarction (AMI) is one of the leading causes of death among adults in older age. Understanding mechanisms how organism responds to ischemia is essential for the ischemic patient's prevention and treatment. Despite the great prevalence and incidence only a small number of studies utilize a metabolomic approach to describe AMI condition. Recent studies have shown the impact of metabolites on epigenetic changes, in these studies plasma metabolites were related to neurological outcome of the patients making metabolomic studies increasingly interesting. The aim of this study was to describe metabolomic response of an organism to ischemic stress through the changes in energetic metabolites and aminoacids in blood plasma in patients overcoming acute myocardial infarction. Blood plasma from patients in the first 12 h after onset of chest pain was collected and compared with volunteers without any history of ischemic diseases via NMR spectroscopy. Lowered plasma levels of pyruvate, alanine, glutamine and neurotransmitter precursors tyrosine and tryptophan were found. Further, we observed increased plasma levels of 3-hydroxybutyrate and acetoacetate in balance with decreased level of lipoproteins fraction, suggesting the ongoing ketonic state of an organism. Discriminatory analysis showed very promising performance where compounds: lipoproteins, alanine, pyruvate, glutamine, tryptophan and 3-hydroxybutyrate were of the highest discriminatory power with feasibility of successful statistical discrimination.

Time-related metabolomics study in the rat plasma after global cerebral ischemia and reperfusion: Effect of ischemic preconditioning

Cardiac arrest is one of the major causes of death and disability. The aim of the study was to identify dynamic time-dependent metabolomic changes reflected in rat plasma induced by cerebral ischemia and reperfusion with the focus on the protective effect of ischemic preconditionig. Global cerebral ischemia in rats was induced by the four-vessel occlusion. Blood plasma was collected in three reperfusion times: an early post-acute 3 hr, then 24 hr, as an incipient time for delayed neuronal death induction and 72 hr as prolonged reperfusion period. The metabolomic measurements were conducted via untargeted nuclear magnetic resonance spectroscopy. Plasma of ischemized rats manifested dynamic metabolomic changes over the reperfusion time, such as increased levels of ketone bodies, decreased levels of pyruvate, alanine, and citrate. All three branched chain amino acids showed common pattern during reperfusion time: a decrease in 3 hr compared to sham, then a highest level in 24 hr and decrease in 72 hr reperfusion time, similar to their corresponding ketoacids. The protective effect of ischemic preconditioning was demonstrated by a faster tendency of plasma metabolites to normalize. Results also proved the remarkable metabolomic differences between the control (naïve) and sham-operated anesthetized animals, what warrants for critical evaluation of surgery/anaesthesy in the algorithm of metabolomic animal studies.

Effect of Methionine Diet on Metabolic and Histopathological Changes of Rat Hippocampus

Hyperhomocysteinemia (hHcy) is regarded as an independent and strong risk factor for cerebrovascular diseases, stroke, and dementias. The hippocampus has a crucial role in spatial navigation and memory processes and is being constantly studied for neurodegenerative disorders. We used a moderate methionine (Met) diet at a dose of 2 g/kg of animal weight/day in duration of four weeks to induce mild hHcy in adult male Wistar rats. A novel approach has been used to explore the hippocampal metabolic changes using proton magnetic resonance spectroscopy (1H MRS), involving a 7T MR scanner in combination with histochemical and immunofluorescence analysis. We found alterations in the metabolic profile, as well as remarkable histo-morphological changes such as an increase of hippocampal volume, alterations in number and morphology of astrocytes, neurons, and their processes in the selective vulnerable brain area of animals treated with a Met-enriched diet. Results of both methodologies suggest that the mild hHcy induced by Met-enriched diet alters volume, histo-morphological pattern, and metabolic profile of hippocampal brain area, which might eventually endorse the neurodegenerative processes.

A comparison of albumin removal procedures for proteomic analysis of blood plasma

Blood biomarkers are usually present in low concentration and can be masked by the high-abundance proteins, of which albumin is the predominant one. The purpose of this study was to compare four different albumin removal methods compatible with in-gel based proteomics, applicable for plasma, without requiring specific techniques and high financial input. Plasma underwent albumin depletion with ultrafiltration device Amicon Ultra, commercial ProteoPrep Blue Albumin and IgG Depletion Kit, acetonitrile precipitation method and precipitation with acetonitrile-methanol protocol. All samples were evaluated by 1-D and 2-D gel electrophoresis with subsequent mass spectrometry protein identification. Two of the tested methods (ProteoPrep BlueKit and acetonitrile-methanol precipitation) maintained sufficient protein content for further in-gel analyses. Their 2-D protein profiles were distinctively separated and overlapped with protein profile of crude plasma. Protein spot count showed significant increase in protein spots, compared to crude plasma, only with acetonitrile-methanol precipitation method. Precipitation with acetonitrile-methanol method significantly increased number of protein spots on 2-D protein profile and improved score of mass spectrometry identification. However, albumin was still present and found in number of protein spots.

Metabolomic study of altered energy metabolism during global forebrain ischemia and ischemic precoditioning in blood plasma in homocysteine treated rats

Elevated homocysteine (Hcy) level is a well known risk factor for cardiovascular and neuropsychiatric diseases. In this study, we investigated metabolic changes in blood plasma in Hcy-treated rats. In combination with Hcy injections to induce hyperhomocysteinemia-like state, we used an animal model of global cerebral ischemia to investigate metabolic changes after 24 h reperfusion in rats. We also focused on the endogenous phenomenon known as ischemic tolerance induced by the preischemic treatment. The experiments were carried out on blood plasma samples as they are easily available and metabolically reflect the overall changes in injured organism. We observed significant changes in plasma metabolite levels of: pyruvate, citrate, acetate implicating alterations in energy metabolism, and increase in triacylglycerols, arginine and lysine, in Hcy-treated rats compared with naive animals. Ischemic insult with 24 reperfusion in Hcy-treated rats led to increase in plasma lactate, and decrease in plasma glucose, pyruvate, citrate and acetate. Complementary, an increase in ketone body 3-hydroxybutyrate was observed. The plasma metabolites: alanine, lactate, valine, glucose, leucine, isoleucine, acetate, citrate and 3-hydroxybutyrate were considered to reflect the response induced by ischemic preconditioning in Hcy rats, where the extent of postischemic damage was not as high as in the non-preconditioned rats. Our results provide evidence that nuclear magnetic resonance (NMR) spectra analysis can identify a specific group of metabolites present in plasma with the capability of discriminating between individual groups of animals. Regarding the effect of elevated Hcy level on plasma metabolome, we showed, that acetate, pyruvate and glucose had the excellent discriminatory power between Hcy-treated and naive rats plasma. Concerning ischemic insult in Hcy-treated animals, we also document the ideal discrimination of ischemic from non-ischemic rats by various groups of metabolites, that can be considered as a potential plasma biomarkers.

Thalamic paramagnetic iron by T2* relaxometry correlates with severity of multiple sclerosis

Iron can contribute to the pathogenesis and progression of multiple sclerosis (MS) due to its accumulation in the human brain. We focus on the thalamus as an information transmitter between various subcortical and cortical areas. Thalamic iron seems to follow different rules than iron in other deep gray matter structures and its relation to the clinical outcomes of MS is still indistinct. In our study, we investigated a connection between thalamic iron and patients' disability and course of the disease. The presence of paramagnetic substances in the tissues was tracked by T2* quantification. Twenty-eight subjects with definite MS and 15 age-matched healthy controls underwent MRI examination with a focus on gradient echo sequence. We observed a non-monotonous course of T2* values with age in healthy controls. Furthermore, T2* distribution in MS patients was significantly wider than that of age matched healthy volunteers (P<0.001). A strong significant correlation was demonstrated between T2* distribution spread and the expanded disability status scale (EDSS) (left thalamus:P<0.00005; right thalamus: P<0.005), and multiple sclerosis severity scale (MSSS) (left thalamus: P<0.05; right thalamus: P<0.005). The paramagnetic iron distribution in the thalamus in MS was not uniform and this inhomogeneity may be considered as an indicator of thalamic neurodegeneration in MS.