Ischemic Stroke Causes Disruptions in the Carnitine Shuttle System

Fatty acid β-oxidation in brain mitochondria: Insights from high-resolution respirometry in mouse, rat and Drosophila brain, ischemia and aging models

Glucose is the main energy source of the brain, yet recent studies demonstrate that fatty acid oxidation (FAO) plays a relevant role in the pathogenesis of central nervous system disorders. We evaluated FAO in brain mitochondria under physiological conditions, in the aging brain, and after stroke. Using high-resolution respirometry we compared medium-chain (MC, octanoylcarnitine) and long-chain (LC, palmitoylcarnitine) acylcarnitines as substrates of β-oxidation in the brain. The protocols developed avoid FAO overestimation by malate-linked anaplerotic activity in brain mitochondria. The capacity of FA oxidative phosphorylation (F-OXPHOS) with palmitoylcarnitine was up to 4 times higher than respiration with octanoylcarnitine. The optimal concentration of palmitoylcarnitine was 10 μM which corresponds to the total concentration of LC acylcarnitines in the brain. Maximal respiration with octanoylcarnitine was reached at 20 μM, however, this concentration exceeds MC acylcarnitine concentrations in the brain 15 times. F-OXPHOS capacity was highest in mouse cerebellum, intermediate in cortex, prefrontal cortex, and hypothalamus, and hardly detectable in hippocampus. F-OXPHOS capacity was 2-fold lower and concentrations of LC acylcarnitines were 2-fold higher in brain of aged rats. A similar trend was observed in the rat model of endothelin-1-induced stroke, but reduction of OXPHOS capacity was not limited to FAO. In conclusion, although FAO is not a dominant pathway in brain bioenergetics, it deserves specific attention in studies of brain metabolism.

Nanospray Desorption Electrospray Ionization Mass Spectrometry Imaging (nano-DESI MSI): A Tutorial Review

Nanospray desorption electrospray ionization (nano-DESI) is a liquid-based ambient mass spectrometry imaging (MSI) technique that enables visualization of analyte distributions in biological samples down to cellular-level spatial resolution. Since its inception, significant advancements have been made to the nano-DESI experimental platform to facilitate molecular imaging with high throughput, deep molecular coverage, and spatial resolution better than 10 μm. The molecular selectivity of nano-DESI MSI has been enhanced using new data acquisition strategies, the development of separation and online derivatization approaches for isobar separation and isomer-selective imaging, and the optimization of the working solvent composition to improve analyte extraction and ionization efficiency. Furthermore, nano-DESI MSI research has underscored the importance of matrix effects and established normalization methods for accurately measuring concentration gradients in complex biological samples. This tutorial offers a comprehensive guide to nano-DESI experiments, detailing fundamental principles and data acquisition and processing methods and discussing essential operational parameters.

The paradigm change from reactive medical services to 3PM in ischemic stroke: a holistic approach utilising tear fluid multi-omics, mitochondria as a vital biosensor and AI-based multi-professional data interpretation

Worldwide stroke is the second leading cause of death and the third leading cause of death and disability combined. The estimated global economic burden by stroke is over US$891 billion per year. Within three decades (1990-2019), the incidence increased by 70%, deaths by 43%, prevalence by 102%, and DALYs by 143%. Of over 100 million people affected by stroke, about 76% are ischemic stroke (IS) patients recorded worldwide. Contextually, ischemic stroke moves into particular focus of multi-professional groups including researchers, healthcare industry, economists, and policy-makers. Risk factors of ischemic stroke demonstrate sufficient space for cost-effective prevention interventions in primary (suboptimal health) and secondary (clinically manifested collateral disorders contributing to stroke risks) care. These risks are interrelated. For example, sedentary lifestyle and toxic environment both cause mitochondrial stress, systemic low-grade inflammation and accelerated ageing; inflammageing is a low-grade inflammation associated with accelerated ageing and poor stroke outcomes. Stress overload, decreased mitochondrial bioenergetics and hypomagnesaemia are associated with systemic vasospasm and ischemic lesions in heart and brain of all age groups including teenagers. Imbalanced dietary patterns poor in folate but rich in red and processed meat, refined grains, and sugary beverages are associated with hyperhomocysteinaemia, systemic inflammation, small vessel disease, and increased IS risks. Ongoing 3PM research towards vulnerable groups in the population promoted by the European Association for Predictive, Preventive and Personalised Medicine (EPMA) demonstrates promising results for the holistic patient-friendly non-invasive approach utilising tear fluid-based health risk assessment, mitochondria as a vital biosensor and AI-based multi-professional data interpretation as reported here by the EPMA expert group. Collected data demonstrate that IS-relevant risks and corresponding molecular pathways are interrelated. For examples, there is an evident overlap between molecular patterns involved in IS and diabetic retinopathy as an early indicator of IS risk in diabetic patients. Just to exemplify some of them such as the 5-aminolevulinic acid/pathway, which are also characteristic for an altered mitophagy patterns, insomnia, stress regulation and modulation of microbiota-gut-brain crosstalk. Further, ceramides are considered mediators of oxidative stress and inflammation in cardiometabolic disease, negatively affecting mitochondrial respiratory chain function and fission/fusion activity, altered sleep-wake behaviour, vascular stiffness and remodelling. Xanthine/pathway regulation is involved in mitochondrial homeostasis and stress-driven anxiety-like behaviour as well as molecular mechanisms of arterial stiffness. In order to assess individual health risks, an application of machine learning (AI tool) is essential for an accurate data interpretation performed by the multiparametric analysis. Aspects presented in the paper include the needs of young populations and elderly, personalised risk assessment in primary and secondary care, cost-efficacy, application of innovative technologies and screening programmes, advanced education measures for professionals and general population-all are essential pillars for the paradigm change from reactive medical services to 3PM in the overall IS management promoted by the EPMA.

Decreased long-chain acylcarnitine content increases mitochondrial coupling efficiency and prevents ischemia-induced brain damage in rats

Long-chain acylcarnitines (LCACs) are intermediates of fatty acid oxidation and are known to exert detrimental effects on mitochondria. This study aimed to test whether lowering LCAC levels with the anti-ischemia compound 4-[ethyl(dimethyl)ammonio]butanoate (methyl-GBB) protects brain mitochondrial function and improves neurological outcomes after transient middle cerebral artery occlusion (MCAO). The effects of 14 days of pretreatment with methyl-GBB (5 mg/kg, p.o.) on brain acylcarnitine (short-, long- and medium-chain) concentrations and brain mitochondrial function were evaluated in Wistar rats. Additionally, the mitochondrial respiration and reactive oxygen species (ROS) production rates were determined using ex vivo high-resolution fluorespirometry under normal conditions, in models of ischemia-reperfusion injury (reverse electron transfer and anoxia-reoxygenation) and 24 h after MCAO. MCAO model rats underwent vibrissae-evoked forelimb-placing and limb-placing tests to assess neurological function. The infarct volume was measured on day 7 after MCAO using 2,3,5-triphenyltetrazolium chloride (TTC) staining. Treatment with methyl-GBB significantly reduced the LCAC content in brain tissue, which decreased the ROS production rate without affecting the respiration rate, indicating an increase in mitochondrial coupling. Furthermore, methyl-GBB treatment protected brain mitochondria against anoxia-reoxygenation injury. In addition, treatment with methyl-GBB significantly reduced the infarct size and improved neurological outcomes after MCAO. Increased mitochondrial coupling efficiency may be the basis for the neuroprotective effects of methyl-GBB. This study provides evidence that maintaining brain energy metabolism by lowering the levels of LCACs protects against ischemia-induced brain damage in experimental stroke models.

Glyceryl triacetate promotes blood-brain barrier recovery after ischemic stroke through lipogenesis-mediated IL-33 in mice

BACKGROUND

Lipid metabolism has a crucial role in neural repair in neurodegenerative diseases. We recently revealed that lipogenesis-mediated interleukin-33 (IL-33) upregulation lead to blood-brain barrier (BBB) repair after ischemic stroke. However, manipulating the key enzyme fatty acid synthase (FASN) to enhance lipogenesis was very challenging. Glyceryl triacetate (GTA) was used as a donor of acetate and precursor of acetyl coenzyme A, the key substrate for de novo lipogenesis catalyzed by FASN. Therefore, we hypothesized that GTA would promote lipogenesis the peri-infarct after ischemic stroke and contribute to the BBB repair through IL-33.

METHODS

Middle cerebral artery occlusion (MCAO) was performed on C57BL mice and GTA was gavage administrated (4 g/kg) on day 2 and 4 after MCAO. Lipogenesis was evaluated by assessment of the protein level of FASN, lipid droplets, and fatty acid products through liquid chromatography-mass spectrometry in the peri-infarct area on day 3 after MCAO, respectively. BBB permeability was determined by extravasation of Evans blue, IgG and dextran, and levels of tight junction proteins in the peri-infarct area on day 7 after MCAO, respectively. Infarct size and neurological defects were assessed on day 7 after MCAO. Brain atrophy on day 30 and long-term sensorimotor abilities after MCAO were analyzed as well. The inhibitor of FASN, C75 and the virus-delivered FASN shRNA were used to evaluate the role of FASN-driven lipogenesis in GTA-improved BBB repair. Finally, the therapeutic potential of recombinant IL-33 on BBB repair and neurological recovery was evaluated.

RESULTS

We found that treatment with GTA increased the lipogenesis as evidenced by lipid droplets level and lauric acid content, but not the FASN protein level. Treatment with GTA increased the IL-33 level in the peri-infarct area and decreased the BBB permeability after MCAO. However, infarct size and neurological defect score were unchanged on day 7 after MCAO, while the long-term recovery of sensorimotor function and brain atrophy were improved by GTA. Inhibition of lipogenesis using C75 or FASN shRNA reversed the beneficial effect of GTA. Finally, exogenous IL-33 improved BBB repair and long-term functional recovery after stroke.

CONCLUSION

Collectively, we concluded that treatment with GTA improved the BBB repair and functional recovery after ischemic stroke, probably by the enhancement of lipogenesis and IL-33 expression.

Global and Spatial Metabolomics of Individual Cells Using a Tapered Pneumatically Assisted nano-DESI Probe

Single-cell metabolomics has the potential to reveal unique insights into intracellular mechanisms and biological processes. However, the detection of metabolites from individual cells is challenging due to their versatile chemical properties and concentrations. Here, we demonstrate a tapered probe for pneumatically assisted nanospray desorption electrospray ionization (PA nano-DESI) mass spectrometry that enables both chemical imaging of larger cells and global metabolomics of smaller 15 μm cells. Additionally, by depositing cells in predefined arrays, we show successful metabolomics from three individual INS-1 cells per minute, which enabled the acquisition of data from 479 individual cells. Several cells were used to optimize analytical conditions, and 93 or 97 cells were used to monitor metabolome alterations in INS-1 cells after exposure to a low or high glucose concentration, respectively. Our analytical approach offers insights into cellular heterogeneity and provides valuable information about cellular processes and responses in individual cells.