Altered metabolites of the rat hippocampus after mild and moderate traumatic brain injury - a combined in vivo and in vitro 1 H-MRS study

Metabolic Diaschisis in Mild Traumatic Brain Injury

Neurophysiological diaschisis presents in traumatic brain injury (TBI) as functional impairment distant to the lesion site caused by axonal neuroexcitation and deafferentation. Diaschisis studies in TBI models have evaluated acute phase functional and microstructural changes. Here, in vivo biochemical changes and cerebral blood flow (CBF) dynamics following TBI are studied with magnetic resonance. Behavioral assessments, magnetic resonance spectroscopy (MRS), and CBF measurements on rats followed cortical impact TBI. Data were acquired pre-TBI and 1-3 h, 2-days, 7-days, and 14-days post-TBI. MRS was performed on the ipsilateral and contralateral sides in the cortex, striatum, and thalamus. Metabolites measured by MRS included N-acetyl aspartate (NAA), aspartate (Asp), lactate (Lac), glutathione (GSH), and glutamate (Glu). Lesion volume expanded for 2 days post-TBI and then decreased. Ipsilateral CBF dropped acutely versus baseline on both sides (-62% ipsilateral, -48% contralateral, p < 0.05) but then recovered in cortex, with similar changes in ipsilateral striatum. Metabolic changes versus baseline included increased Asp (+640% by Day 7 post-TBI, p < 0.05) and Lac (+140% on Day 2 post-TBI, p < 0.05) in ipsilateral cortex, while GSH (-67% acutely, p < 0.05) and NAA decreased (-50% on Day 2, p < 0.05). In contralateral cortex Lac decreased (-73% acutely, p < 0.05). Analysis of variance showed significance for Side (p < 0.05), Time after TBI (p < 0.05), and interactions (p < 0.005) for Asp, GSH, Lac, and NAA. Transient decreases of GSH (-30%, p < 0.05, acutely) and NAA (-23% on Day 2, p < 0.05) occurred in ipsilateral striatum with reduced GSH (-42%, p < 0.005, acutely) in the contralateral striatum. GSH was decreased in ipsilateral thalamus (-59% ipsilateral on Day 2, p < 0.05). Delayed increases of total choline were seen in the contralateral thalamus were noted as well (+21% on Day 7 post-TBI, p < 0.05). Both CBF and neurometabolite concentration changes occurred remotely from the TBI site, both ipsilaterally and contralaterally. Decreased Lac levels on the contralateral cortex following TBI may be indicative of reduced anaerobic metabolism during the acute phase. The timing and locations of the changes suggest excitatory and inhibitory signaling processes are affecting post-TBI metabolic fluctuations.

Nontargeted metabolomics reveals sequential changes in amino acid and ferroptosis-related metabolism in Parkinson's disease

Parkinson's disease (PD) is inseparable from metabolic disorders but lacks assessment of specific metabolite alteration. To explore the sequential metabolic changes in PD progression, we evenly divided 78 C57BL/6 mice (10 weeks) into six groups (one control group and five experimental groups) and collected the hippocampus tissue of mice after treating with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, and probenecid (twice a week) at five periods (1, 2, 3, 4, and 5 weeks) for metabolome analysis. Our study identified 567 differentially abundant metabolites (DAMs) (total 4348 metabolites). Compared with controls, 145, 146, 171, 208, and 213 DAMs were obtained from the five experimental groups, respectively. Notably, 40 shared DAMs were present in five experimental groups, of which 22 shared DAMs formed a new metabolic network based on amino acid metabolism. Compared with group W3, 84 DAMs were identified in group W5, including 12 unique DAMs. DAMs in different stages of PD were significantly enriched in amino acid metabolism pathway, lipid metabolism pathway, and ferroptosis pathway. l-Glutamine, spermidine, and l-tryptophan were the key hubs in the whole metabolic process of PD. N-Formyl-l-methionine gradually increased in abundance with PD progression, whereas 5-methylcytosine gradually decreased. The study emphasized the sequential changes in DAMs in PD progression, stimulating subsequent studies.

Acute and Chronic Neural and Glial Response to Mild Traumatic Brain Injury in the Hippocampus

Traumatic brain injury (TBI) is an established risk factor for developing neurodegenerative disease. However, how TBI leads from acute injury to chronic neurodegeneration is limited to post-mortem models. There is a lack of connections between in vitro and in vivo TBI models that can relate injury forces to both macroscale tissue damage and brain function at the cellular level. Needle-induced cavitation (NIC) is a technique that can produce small cavitation bubbles in soft tissues, which allows us to relate small strains and strain rates in living tissue to ensuing acute and chronic cell death, tissue damage, and tissue remodeling. Here, we applied NIC to mouse brain slices to create a new model of TBI with high spatial and temporal resolution. We specifically targeted the hippocampus, which is a brain region critical for learning and memory and an area in which injury causes cognitive pathologies in humans and rodent models. By combining NIC with patch-clamp electrophysiology, we demonstrate that NIC in the Cornu Ammonis (CA)3 region of the hippocampus dynamically alters synaptic release onto CA1 pyramidal neurons in a cannabinoid 1 receptor (CB1R)-dependent manner. Further, we show that NIC induces an increase in extracellular matrix proteins associated with neural repair that is mitigated by CB1R antagonism. Together, these data lay the groundwork for advanced approaches in understanding how TBI impacts neural function at the cellular level, and the development of treatments that promote neural repair in response to brain injury.

Spatial amine metabolomics and histopathology reveal localized brain alterations in subacute traumatic brain injury and the underlying mechanism of herbal treatment

INTRODUCTION

Spatial changes of amine metabolites and histopathology of the whole brain help to reveal the mechanism of traumatic brain injury (TBI) and treatment.

METHODS

A newly developed liquid microjunction surface sampling-tandem mass tag-ultra performance liquid chromatography-mass spectrometry technique is applied to profile brain amine metabolites in five brain regions after impact-induced TBI at the subacute stage. H&E, Nissl, and immunofluorescence staining are performed to spatially correlate microscopical changes to metabolic alterations. Then, bioinformatics, molecular docking, ELISA, western blot, and immunofluorescence are integrated to uncover the mechanism of Xuefu Zhuyu decoction (XFZYD) against TBI.

RESULTS

Besides the hippocampus and cortex, the thalamus, caudate-putamen, and fiber tracts also show differentiated metabolic changes between the Sham and TBI groups. Fourteen amine metabolites (including isomers such as L-leucine and L-isoleucine) are significantly altered in specific regions. The metabolic changes are well matched with the degree of neuronal damage, glia activation, and neurorestoration. XFZYD reverses the dysregulation of several amine metabolites, such as hippocampal Lys-Phe/Phe-Lys and dopamine. Also, XFZYD enhances post-TBI angiogenesis in the hippocampus and the thalamus.

CONCLUSION

This study reveals the local amine-metabolite and histological changes in the subacute stage of TBI. XFZYD may promote TBI recovery by normalizing amine metabolites and spatially promoting dopamine production and angiogenesis.

Comprehensive brain tissue metabolomics and biological network technology to decipher the mechanism of hydrogen-rich water on Radiation-induced cognitive impairment in rats

BACKGROUND

Hydrogen-rich water (HRW) has been shown to prevent cognitive impairment caused by ionizing radiation. This study aimed to investigate the pharmacological effects and mechanisms of HRW on ionizing radiation by coupling the brain metabolomics and biological target network methods.

METHODS AND RESULTS

HRW significantly improves the cognitive impairment in rats exposed to ionizing radiation. Based on metabolomics and biological network results, we identified 54 differential metabolites and 93 target genes. The KEGG pathway indicates that glutathione metabolism, ascorbic acid and aldehyde acid metabolism, pentose and glucuronic acid interconversion, and glycerophospholipid metabolism play important roles in ionizing radiation therapy.

CONCLUSION

Our study has systematically elucidated the molecular mechanism of HRW against ionizing radiation, which can be mediated by modulating targets, pathways and metabolite levels. This provides a new perspective for identifying the underlying pharmacological mechanism of HRW.

Integrated metabolomics, network pharmacology, and molecular docking to reveal the mechanisms of Isodon excisoides against drug-induced liver injury

Isodon excisoides (Y.Z.Sun ex C.H.Hu) H. Hara has been often used to treat liver diseases in folk medicine. However, the potential hepatoprotective mechanism of I. excisoides remains unclear. In this study, the mechanism of I. excisoides in alleviating drug-induced liver injury (DILI) was explored using a strategy combining metabolomics with network pharmacology for the first time. First, serum metabolomics was applied to identify differential metabolites and enrich metabolic pathways. The potential targets of I. excisoides for the treatment of DILI were investigated by network pharmacology. Subsequently, a comprehensive network of network pharmacology and metabolomics was established to find the key genes. Finally, molecular docking technology was used to further verify the key targets. As a result, four key genes including TYMS, IMPDH2, DHODH, and ASAH1 were identified. The proteins produced by these genes had high affinity with the corresponding diterpenoids. These results indicate that the components of I. excisoides play a liver-protective role by affecting the aforesaid key genes and key proteins. Our results offer a novel strategy for determining the pharmacological effects and potential targets of natural compounds.

ILB®, a Low Molecular Weight Dextran Sulphate, Restores Glutamate Homeostasis, Amino Acid Metabolism and Neurocognitive Functions in a Rat Model of Severe Traumatic Brain Injury

In a previous study, we found that administration of ILB®, a new low molecular weight dextran sulphate, significantly improved mitochondrial functions and energy metabolism, as well as decreased oxidative/nitrosative stress, of brain tissue of rats exposed to severe traumatic brain injury (sTBI), induced by the closed-head weight-drop model of diffused TBI. Using aliquots of deproteinized brain tissue of the same animals of this former study, we here determined the concentrations of 24 amino acids of control rats, untreated sTBI rats (sacrificed at 2 and 7 days post-injury) and sTBI rats receiving a subcutaneous ILB® administration (at the dose levels of 1, 5 and 15 mg/kg b.w.) 30 min post-impact (sacrificed at 2 and 7 days post-injury). Additionally, in a different set of experiments, new groups of control rats, untreated sTBI rats and ILB®-treated rats (administered 30 min after sTBI at the dose levels of 1 or 5 mg/kg b.w.) were studied for their neurocognitive functions (anxiety, locomotor capacities, short- and long-term memory) at 7 days after the induction of sTBI. Compared to untreated sTBI animals, ILB® significantly decreased whole brain glutamate (normalizing the glutamate/glutamine ratio), glycine, serine and g-aminobutyric acid. Furthermore, ILB® administration restored arginine metabolism (preventing nitrosative stress), levels of amino acids involved in methylation reactions (methionine, L-cystathionine, S-adenosylhomocysteine), and N-acetylaspartate homeostasis. The macroscopic evidences of the beneficial effects on brain metabolism induced by ILB® were the relevant improvement in neurocognitive functions of the group of animals treated with ILB® 5 mg/kg b.w., compared to the marked cognitive decline measured in untreated sTBI animals. These results demonstrate that ILB® administration 30 min after sTBI prevents glutamate excitotoxicity and normalizes levels of amino acids involved in crucial brain metabolic functions. The ameliorations of amino acid metabolism, mitochondrial functions and energy metabolism in ILB®-treated rats exposed to sTBI produced significant improvement in neurocognitive functions, reinforcing the concept that ILB® is a new effective therapeutic tool for the treatment of sTBI, worth being tested in the clinical setting.

Temporal profile of serum metabolites and inflammation following closed head injury in rats is associated with HPA axis hyperactivity

INTRODUCTION

Closed head injury (CHI) causes neurological disability along with systemic alterations that can activate neuro-endocrine response through hypothalamic-pituitary-adrenal (HPA) axis activation. A dysregulated HPA axis function can lead to relocation of energy substrates and alteration in metabolic pathways and inflammation at the systemic level.

OBJECTIVES

Assessment of time-dependent changes in serum metabolites and inflammation after both mild and moderate CHI. Along with this, serum corticosterone levels and hypothalamic microglial response were observed.

METHODS

Rats underwent mild and moderate weight-drop injury and their serum and hypothalamus were assessed at acute, sub-acute and chronic timepoints. Changes in serum metabolomics were determined using high resolution NMR spectroscopy. Serum inflammatory cytokine, corticosterone levels and hypothalamic microglia were assessed at all timepoints.

RESULTS

Metabolites including lactate, choline and branched chain amino acids were found as the classifiers that helped distinguish between control and injured rats during acute, sub-acute and chronic timepoints. While, increased αglucose: βglucose and TMAO: choline ratios after acute and sub-acute timepoints of mild injury differentiated from moderate injured rats. The injured rats also showed distinct inflammatory profile where IL-1β and TNF-α levels were upregulated in moderate injured rats while IL-10 levels were downregulated in mild injured rats. Furthermore, injury specific alterations in serum metabolic and immunologic profile were found to be associated with hyperactive HPA axis, with consistent increase in serum corticosterone concentration post injury. The hypothalamic microglia showed a characteristic activated de-ramified cellular morphology in both mild and moderate injured rats.

CONCLUSION

The study suggests that HPA axis hyperactivity along with hypothalamic microglial activation led to temporal changes in the systemic metabolism and inflammation. These time dependent changes in the metabolite profile of rats can further strengthen the knowledge of diagnostic markers and help distinguish injury related outcomes after TBI.

Branched-Chain Amino Acids Catabolism Pathway Regulation Plays a Critical Role in the Improvement of Leukopenia Induced by Cyclophosphamide in 4T1 Tumor-Bearing Mice Treated With Lvjiaobuxue Granule

Background: Cyclophosphamide is a common tumor chemotherapy drug used to treat various cancers. However, the resulting immunosuppression leads to leukopenia, which is a serious limiting factor in clinical application. Therefore, the introduction of immunomodulators as adjuvant therapy may help to reduce the hematological side effects of cyclophosphamide. Lvjiaobuxue granule has been widely used in the clinical treatment of gynecological diseases such as anemia and irregular menstruation. Recently, it has been found to increase the function of white blood cells, but its mechanism of action is still unclear. We aimed to reveal the mechanisms of Lvjiaobuxue granule against acute leukopenia by an integrated strategy combining metabolomics with network pharmacology. Methods: Subcutaneously inoculated 4T1 breast cancer cells to prepare tumor-bearing mice, intraperitoneal injection of cyclophosphamide to establish a 4T1 tumor-bearing mice leukopenia animal model, using pharmacodynamic indicators, metabolomics, network pharmacology and molecular biology and other technical methods. To comprehensively and systematically elucidate the effect and mechanism of Lvjiaobuxue granule in improving cyclophosphamide-induced leukopenia in 4T1 tumor-bearing mice. Results: Lvjiaobuxue granule can improve the blood routine parameters and organ index levels of the leukopenia model of 4T1 tumor-bearing mice. Metabolomics studies revealed that 15 endogenous metabolites in the spleen of mice were considered as potential biomarkers of Lvjiaobuxue granule for their protective effect. Metabonomics and network pharmacology integrated analysis indicated that Lvjiaobuxue granule exerted the leukocyte elevation activity by inhibiting the branched-chain amino acids (BCAAs) degradation pathway and increasing the levels of valine, leucine and isoleucine. The results of molecular biology also showed that Lvjiaobuxue granule can significantly regulate the key enzymes in the catabolism of BCAAs, which further illustrates the importance of BCAAs in improving leukopenia. Conclusion: Lvjiaobuxue granule exerts obvious pharmacological effects on the leukopenia model of 4T1 tumor-bearing mice induced by cyclophosphamide, which could be mediated by regulating the branched-chain amino acid degradation pathway and the levels of valine, leucine and isoleucine.

Glutamate Metabolism in Mitochondria is Closely Related to Alzheimer's Disease

Glutamate is the main excitatory neurotransmitter in the brain, and its excitatory neurotoxicity is closely related to the occurrence and development of Alzheimer's disease. However, increasing evidence shows that in the process of Alzheimer's disease, glutamate is not only limited to its excitotoxicity as a neurotransmitter but also related to the disorder of its metabolic balance. The balance of glutamate metabolism in the brain is an important determinant of central nervous system health, and the maintenance of this balance is closely related to glutamate uptake, glutamate circulation, intracellular mitochondrial transport, and mitochondrial metabolism. In this paper, we intend to elaborate the key role of mitochondrial glutamate metabolism in the pathogenesis of Alzheimer's disease and review glutamate metabolism in mitochondria as a potential target in the treatment of Alzheimer's disease.

Increased biological antioxidant potential in the cerebrospinal fluid of transient global amnesia patients

Oxidative stress may accompany the pathological process in transient global amnesia (TGA). We measured the biological antioxidant potential (BAP) in the cerebrospinal fluid (CSF) of TGA patients. We enrolled 13 TGA patients (7 men, 6 women; mean age 65.0 years [48–70 years]) and 24 control subjects (12 men, 12 women; mean age 38.2 years [17–65 years]; age did not correlate with csfBAP in this group). We performed brain MRI in all TGA patients, and CA1 lesions were noted by MRI in 5 subjects. We measured csfBAP, total antioxidant properties, in all TGA patients and controls. csfBAP levels were higher in TGA patients than in controls (p = 0.024, 0.028). csfBAP levels in TGA patients did not differ between MRI-positive and -negative subgroups. Elevated csfBAP levels were observed in TGA patients, suggesting that oxidative stress may have a role in the pathogenesis of TGA.

Contribution of macromolecules to brain 1 H MR spectra: Experts' consensus recommendations

Proton MR spectra of the brain, especially those measured at short and intermediate echo times, contain signals from mobile macromolecules (MM). A description of the main MM is provided in this consensus paper. These broad peaks of MM underlie the narrower peaks of metabolites and often complicate their quantification but they also may have potential importance as biomarkers in specific diseases. Thus, separation of broad MM signals from low molecular weight metabolites enables accurate determination of metabolite concentrations and is of primary interest in many studies. Other studies attempt to understand the origin of the MM spectrum, to decompose it into individual spectral regions or peaks and to use the components of the MM spectrum as markers of various physiological or pathological conditions in biomedical research or clinical practice. The aim of this consensus paper is to provide an overview and some recommendations on how to handle the MM signals in different types of studies together with a list of open issues in the field, which are all summarized at the end of the paper.

18F-FDG PET Combined With MR Spectroscopy Elucidates the Progressive Metabolic Cerebral Alterations After Blast-Induced Mild Traumatic Brain Injury in Rats

A majority of blast-induced mild traumatic brain injury (mTBI) patients experience persistent neurological dysfunction with no findings on conventional structural MR imaging. It is urgent to develop advanced imaging modalities to detect and understand the pathophysiology of blast-induced mTBI. Fluorine-18 fluorodeoxyglucose positron emission tomography (¹⁸F-FDG PET) could detect neuronal function and activity of the injured brain, while MR spectroscopy provides complementary information and assesses metabolic irregularities following injury. This study aims to investigate the effectiveness of combining ¹⁸F-FDG PET with MR spectroscopy to evaluate acute and subacute metabolic cerebral alterations caused by blast-induced mTBI. Thirty-two adult male Sprague–Dawley rats were exposed to a single blast (mTBI group) and 32 rats were not exposed to the blast (sham group), followed by ¹⁸F-FDG PET, MRI, and histological evaluation at baseline, 1–3 h, 1 day, and 7 days post-injury in three separate cohorts. ¹⁸F-FDG uptake showed a transient increase in the amygdala and somatosensory cortex, followed by a gradual return to baseline from day 1 to 7 days post-injury and a continuous rise in the motor cortex. In contrast, decreased ¹⁸F-FDG uptake was seen in the midbrain structures (inferior and superior colliculus). Analysis of MR spectroscopy showed that inflammation marker myo-inositol (Ins), oxidative stress marker glutamine + glutamate (Glx), and hypoxia marker lactate (Lac) levels markedly elevated over time in the somatosensory cortex, while the major osmolyte taurine (Tau) level immediately increased at 1–3 h and 1 day, and then returned to sham level on 7 days post-injury, which could be due to the disruption of the blood–brain barrier. Increased ¹⁸F-FDG uptake and elevated Ins and Glx levels over time were confirmed by histology analysis which showed increased microglial activation and gliosis in the frontal cortex. These results suggest that ¹⁸F-FDG PET and MR spectroscopy can be used together to reflect more comprehensive neuropathological alterations in vivo, which could improve our understanding of the complex alterations in the brain after blast-induced mTBI.

Integrated metabolomics and network pharmacology to reveal the mechanisms of hydroxysafflor yellow A against acute traumatic brain injury

Traumatic brain injury (TBI) has become a leading cause of mortality, morbidity and disability worldwide. Hydroxysafflor yellow A (HSYA) is effective in treating TBI, but the potential mechanisms require further exploration. We aimed to reveal the mechanisms of HSYA against acute TBI by an integrated strategy combining metabolomics with network pharmacology. A controlled cortical impact (CCI) rat model was established, and neurological functions were evaluated. Metabolomics of brain tissues was used to identify differential metabolites, and the metabolic pathways were enriched by MetaboAnalyst. Then, network pharmacology was applied to dig out the potential targets against TBI induced by HSYA. The integrated network of metabolomics and network pharmacology was constructed based on Cytoscape. Finally, the obtained key targets were verified by molecular docking. HSYA alleviated the neurological deficits of TBI. Fifteen potentially significant metabolites were found to be involved in the therapeutic effects of HSYA against acute TBI. Most of these metabolites were regulated to recover after HSYA treatment. We found 10 hub genes according to network pharmacology, which was partly consistent with the metabolomics findings. Further integrated analysis focused on 4 key targets, including NOS1, ACHE, PTGS2 and XDH, as well as their related core metabolites and pathways. Molecular docking showed high affinities between key targets and HSYA. Region-specific metabolic alterations in the cortex and hippocampus were illuminated. This study reveals the complicated mechanisms of HSYA against acute TBI. Our work provides a novel paradigm to identify the potential mechanisms of pharmacological effects derived from a natural compound.

L-lactate preconditioning promotes plasticity-related proteins expression and reduces neurological deficits by potentiating GPR81 signaling in rat traumatic brain injury model

Currently, there is no efficacious pharmacological treatment for traumatic brain injury (TBI). Previous studies revealed that L-lactate preconditioning has shown rich neuroprotective effects against cerebral ischemia, and therefore has the potential to improve neurological outcomes after TBI. L-lactate played a neuroprotective role by activating GPR81 in diseases of the central nervous system (CNS) such as TBI and cerebral ischemia. In this study we investigated the effects of L-lactate preconditioning on TBI and explored the underlying mechanisms. In this study, the mNSS test revealed that L-lactate preconditioning alleviates the neurological deficit caused by TBI in rats. L-lactate preconditioning significantly increased the expression of GPR81, PSD95, GAP43, BDNF, and MCT2 24 h after TBI in the cortex and hippocampus compared with the sham group. Taken together, these data suggested that L-lactate preconditioning is an effective method with which to recover neurological function after TBI. This reveals the mechanism of L-lactate preconditioning on TBI and provides a potential therapeutic method for TBI in humans.

Pyruvate Dehydrogenase and Tricarboxylic Acid Cycle Enzymes Are Sensitive Targets of Traumatic Brain Injury Induced Metabolic Derangement

Using a closed-head impact acceleration model of mild or severe traumatic brain injury (mTBI or sTBI, respectively) in rats, we evaluated the effects of graded head impacts on the gene and protein expressions of pyruvate dehydrogenase (PDH), as well as major enzymes of mitochondrial tricarboxylic acid cycle (TCA). TBI was induced in anaesthetized rats by dropping 450 g from 1 (mTBI) or 2 m height (sTBI). After 6 h, 12 h, 24 h, 48 h, and 120 h gene expressions of enzymes and subunits of PDH. PDH kinases and phosphatases (PDK1-4 and PDP1-2, respectively), citrate synthase (CS), isocitrate dehydrogenase (IDH), oxoglutarate dehydrogenase (OGDH), succinate dehydrogenase (SDH), succinyl-CoA synthase (SUCLG), and malate dehydrogenase (MDH) were determined in whole brain extracts (n = 6 rats at each time for both TBI levels). In the same samples, the high performance liquid chromatographic (HPLC) determination of acetyl-coenzyme A (acetyl-CoA) and free coenzyme A (CoA-SH) was performed. Sham-operated animals (n = 6) were used as controls. After mTBI, the results indicated a general transient decrease, followed by significant increases, in PDH and TCA gene expressions. Conversely, permanent PDH and TCA downregulation occurred following sTBI. The inhibitory conditions of PDH (caused by PDP1-2 downregulations and PDK1-4 overexpression) and SDH appeared to operate only after sTBI. This produced almost no change in acetyl-CoA and free CoA-SH following mTBI and a remarkable depletion of both compounds after sTBI. These results again demonstrated temporary or steady mitochondrial malfunctioning, causing minimal or profound modifications to energy-related metabolites, following mTBI or sTBI, respectively. Additionally, PDH and SDH appeared to be highly sensitive to traumatic insults and are deeply involved in mitochondrial-related energy metabolism imbalance.

Acute Mitochondrial Impairment Underlies Prolonged Cellular Dysfunction after Repeated Mild Traumatic Brain Injuries

Mild traumatic brain injuries (mTBI), accounting for more than 80% of TBIs, can cause cognitive and behavioral impairments, the severity and duration of which increase after additional mTBIs. While mTBI does not cause widespread neuronal death, the mechanisms underlying increased cellular susceptibility to subsequent head impacts remain unknown. To investigate the hypothesis that altered mitochondrial bioenergetics underlie cellular vulnerability to repeated insults, we employed a mouse model of mild closed head injury (CHI) to examine mitochondrial function and oxidative stress, because these mechanisms are often intertwined. Mitochondrial respiration was assayed (Seahorse XFe24 Flux Analyzer) from cortex and hippocampus collected at 6 h, 24 h, 48 h, and 96 h post-injury. State III (adenosine diphosphate [ADP]-mediated) respiration was significantly decreased in the hippocampal mitochondria of the CHI group compared with sham at 48 h post-injury. Further, cortex-derived mitochondria exhibited a decrease in State III respiration at 24 h and 48 h post-injury. No significant differences were observed at 6 h or 96 h post-injury in either region of interest. A second CHI repeated either 48 h or 96 h after the first did not worsen State III respiration at 48 h after the final injury compared with a single CHI, but CHI repeated at a 48 h interval prolonged cortical mitochondrial dysfunction to 96 h after the final injury. Markers of oxidative stress were significantly elevated after two CHIs delivered 48 h apart, but not after single CHI or two CHI delivered 96 h apart. This study establishes that mTBI results in early mitochondrial dysfunction, which may be a determinant for cellular vulnerability to repeated head impacts. Thus, therapies targeting mitochondrial impairment could improve outcomes after repeated mTBI.