Biology subjects

Tyler, D. J.

Publications and source records attributed to Tyler, D. J..

7 recordsLinked to original sources

bioRxiv2026

Feasibility of multimodal metabolic analysis for detecting early changes in acute neuroinflammation

Given the prevalence of metabolic perturbations in a variety of neurological and neurodegenerative diseases, understanding and monitoring brain metabolism is a key step in our advancement of therapies. The details of the citric acid cycle were established at the beginning of the last century but only recently have its metabolic intermediates been observed in vivo in the brain. In this study, we employed orthogonal analyses to investigate metabolic alterations in response to acute neuroinflammation in vivo, demonstrating a multi-technique approach that could be used for future studies. Hyperpolarized 13C-pyruvate spectroscopy revealed an early decline in pyruvate metabolism via pyruvate dehydrogenase (PDH), leading to reduced 13C-bicarbonate formation. This metabolic disruption occurred despite the absence of structural or perfusion changes on conventional MRI. Further analysis of polar metabolites in the ipsilateral hemisphere confirmed ongoing inflammatory processes. These findings highlight the potential of this dual technique approach to inform upon metabolic changes due to neuroinflammation. Combining methods to probe metabolism in invasive (metabolomics) and non-invasive (hyperpolarized MRI) manners, this represents a promising translational approach for real-time metabolic assessments in an area of the body, the brain, where studying processes such as metabolism has traditionally been challenging. This study has demonstrated the approach to monitor changes in metabolism in response to inflammation in the brain.

neuroscience↗

bioRxiv2025

The effects of elevated serum lactate on measures of apparent cerebral metabolism and perfusion in the anesthetised rodent brain.

Cerebral metabolism is coupled to perfusion and can be probed using a combination of hyperpolarized carbon-13 MRI and perfusion weighted imaging. It is unknown how alterations in serum lactate affect apparent lactate exchange and pyruvate dehydrogenase flux using hyperpolarized 13C MRI, and so this pre-clinical study was designed to assess the sensitivity of MRI to detect changes in perfusion and apparent metabolism in the anesthetized rodent brain due to sodium lactate administration. Results demonstrated significant differences in cerebral blood flow between the saline and sodium L-lactate administered at 0.5 g/kg (112 {+/-} 5 vs 127 {+/-} 2 mL/100g/min), saline and sodium L-lactate administered at 1 g/kg (112 {+/-} 5 vs 90 {+/-} 5 mL/100g/min), and between sodium L-lactate at 0.5 g/kg and sodium L-lactate at 1 g/kg (127 {+/-} 2 vs 90 {+/-} 5 mL/100g/min). There was excellent reproducibility of cerebral perfusion measurements (ICC > 0.95) between observers, indicating high reliability in these results. There were significant differences in [1-13C] lactate:[1-13C] pyruvate between saline vs 0.5 g/kg (0.22 {+/-} 0.05 vs 0.59 {+/-} 0.15) and saline vs 1 g/kg (0.22 {+/-} 0.05 vs 0.62 {+/-} 0.04), but no significant differences in 13C bicarbonate:[1-13C] pyruvate (p = 0.1). In conclusion, perfusion and [1-13C] lactate:[1-13C] pyruvate are sensitive to changes in serum lactate, but 13C bicarbonate:[1-13C] pyruvate were not. This has implications for brain studies using [1-13C] pyruvate, and understanding the impact of serum lactate on clinical hyperpolarised imaging is needed.

neuroscience↗

bioRxiv2025

Micro-CT Analysis of a Needle to Nerve Approach for Interfascicular Peripheral Nerve Stimulation in Porcine Nerves

MotivationPeripheral nerve interfaces typically have a tradeoff between selectivity and invasiveness. Interfascicular interfaces placed within the peripheral nerve, but outside of the fascicles preserving the perineurium are a promising avenue in balancing this tradeoff. This study quantifies electrode placement using novel tools designed to deliver flexible microwires interfascicularly in a porcine model. MethodsSeven Yorkshire pigs were implanted with Minimally invasive interfascicular Nerve Stimulation (MiiNS) arrays in the nerves of the brachial plexus resulting in a total of ten implanted nerve samples. High-resolution micro-computed tomography (micro-CT) of implanted nerves stained with phosphotungistic acid (PTA) showed contact placement relative to fascicular anatomy and all other contacts. The analysis also examined the relationship between microwire trajectory angle and fascicle traversal. Further, in a subset of samples (n=4), hematoxylin and eosin (H&E) histological analysis was performed after micro-CT imaging. These histological images were coregistered with the micro-CT to validate the positional information of the micro-CT. ResultsAcross the 56 total MiiNS microwire placements, 84% were interfascicular, while 16% were intrafascicular, characterized by traversal through a fascicle. Contacts were broadly distributed throughout the nerves cross section and the majority (79%) were in the central half of the nerves cross section (R>0.707), with no evidence of angular clustering in any single direction. On average, nearest neighbor distances between contacts measured 2256.26{+/-}1760.28 {micro}m in 3D and 730.71 {+/-}564.83 {micro}m transversely, with implants spanning 10.3 {+/-} 4.3 mm along length of nerve. The angle of wire trajectory into the nerve was correlated with fascicle traversal, with steeper angles of insertion associated with more instances of fascicle traversal. Histological analysis corroborated the fascicular borders and wire placements found on micro-CT and demonstrated perineurium integrity. SignificanceInterfascicular implantation can reliably access both central and distributed regions of the nerve, while not being confined to a single plane, enabling access to regions which have been historically challenging to stimulate effectively. The observed nearest-neighbor transverse spacing between contacts is within the range of reported ideal values for selective activation. The MiiNS placement characteristics show its potential as an effective peripheral nerve interface alternative which achieves distributed contact placement, including in the center of the nerve volume, while remaining predominantly outside of the perineurium.

bioengineering↗

bioRxiv2024

Modulating Cardiac Energetics in Cardio-Metabolic Syndromes: A mechanistic, hyperpolarized MR Trial of Ninerafaxstat Treatment

BackgroundType 2 diabetes (T2D) and obesity are key contributors for heart failure (HF)- development, especially for HF with a preserved ejection fraction (HFpEF). On a molecular basis, excessive use of fatty acids (FA) induces lipotoxicity which in turn promotes inflammation, reduces mitochondrial pyruvate dehydrogenase (PDH) activity and impairs myocardial energetics and -function. Harnessing in-vivo, real time measurement of cellular metabolism via hyperpolarized pyruvate MR, we aimed to assess the effects of ninerafaxstat, a selective FA oxidation inhibitor, on cardiac energetics, metabolism & diastolic function in patients with cardio-metabolic syndromes. MethodsIMPROVE-DiCE was an open-label, mechanistic phase 2a trial. 21 participants received 200mg ninerafaxstat twice daily for four (n=5) or eight weeks (n=16). Myocardial energetics (phosphocreatine to adenosine triphosphate ratio, PCr/ATP), metabolism and function were assessed pre-& post-treatment using magnetic resonance imaging (MRI), 31P- and 1H-MR spectroscopy (MRS). We utilised hyperpolarized [1-13C]pyruvate MRS to assess in-vivo PDH-flux (n=9) and plasma metabolomics and proteomics to assess whole body metabolism. ResultsPatients presented with impaired PCr/ATP, (median 1.6 [IQR 1.4, 2.1]), myocardial steatosis (2.2 % [IQR 1.5, 3.2]) and LV diastolic dysfunction (peak circumferential diastolic strain rate 0.86/s [IQR 0.82, 1.06]) at baseline. Ninerafaxstat treatment improved myocardial energetics by 32% (p<0.01), reduced myocardial triglyceride content by 34% (p=0.03) and showed a trend towards improved PDH-flux (mean 45% increase, p=0.08). Diastolic function was significantly improved post-treatment (peak diastolic strain rate by 10%, peak LV filling rate by 11%, both p<0.05). ConclusionsMetabolic modulation with ninerafaxstat significantly improved myocardial energetics, reduced myocardial steatosis and improved LV diastolic filling. Combining hyperpolarized MRS and metabolomics, is a powerful approach to examine the mechanism of action of novel metabolic modulators. REGISTRATIONURL: https://clinicaltrials.gov; Unique identifier: NCT04826159 O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=121 SRC="FIGDIR/small/591019v1_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@86fae1org.highwire.dtl.DTLVardef@1c1037eorg.highwire.dtl.DTLVardef@cc5ca9org.highwire.dtl.DTLVardef@d789d1_HPS_FORMAT_FIGEXP M_FIG C_FIG

molecular biology↗

bioRxiv2022

AICAR prevents doxorubicin-induced heart failure in rats by ameliorating cardiac atrophy and improving fatty acid oxidation

Doxorubicin (DOX) is a widely used chemotherapeutic agent that can cause serious cardiotoxic side effects, leading to functional cardiac decline and ultimately, congestive heart failure (HF). Impaired mitochondrial function and energetics are thought to be key factors driving progression into HF. We have previously shown in a rat model of chronic intravenous DOX-administration that heart failure with reduced ejection fraction correlates with mitochondrial loss and dysfunction. Adenosine monophosphate-dependent kinase (AMPK) is a cellular energy sensor, regulating mitochondrial biogenesis and oxidative metabolism, including fatty acid oxidation. We hypothesized that AMPK activation could restore mitochondrial number and function and therefore be a novel cardioprotective strategy for the prevention of DOX-HF. We therefore set out to assess whether 5-aminoimidazole-4-carboxamide 1-{beta}-D-ribofuranoside (AICAR), an activator of AMPK, could prevent cardiac functional decline in this clinically relevant rat model of DOX-HF. In line with our hypothesis, AICAR improved cardiac systolic function. We show that this could be due to normalisation of substrate supply to the heart, as AICAR prevented DOX-induced dyslipidaemia. AICAR furthermore improved cardiac mitochondrial fatty acid oxidation, despite no increase in mitochondrial number. In addition, we found that AICAR prevented excessive myocardial atrophy, and RNAseq analysis showed that this may be due to normalisation of protein synthesis pathways, which are impaired in DOX-treated rat hearts. Taken together, these results show promise for use of AICAR as a cardioprotective agent in DOX-HF to both preserve cardiac mass and improve cardiac function.

biochemistry↗

bioRxiv2020

Frequency shapes the quality of tactile percepts evoked through electrical stimulation of the nerves

AO_SCPLOWBSTRACTC_SCPLOWTouch is critical for our ability to manipulate objects, as evidenced by the deficits incurred when touch is absent. To restore the sense of touch via electrical stimulation of the peripheral nerves requires that we understand how the parameters of stimulation shape the evoked sensation. To this end, we investigated the sensory consequences of changing the frequency of pulse trains (PF) delivered to the peripheral nerves of humans chronically implanted with multi-channel nerve cuff electrodes. We found that increases in PF led to systematic increases in perceived frequency, up to about 50 Hz, at which point further changes in PF had little to no impact on sensory quality. Above this transition frequency, ratings of perceived frequency levelled off, the ability to discriminate changes in PF was abolished, and verbal descriptors selected to characterize the sensation changed abruptly. We conclude that the quality of electrically evoked tactile sensations can be shaped by imposing temporal patterns on a fixed neural population, but this temporal patterning can only be resolved up to about 50 Hz. These findings highlight the importance of spike timing in shaping the quality of a sensation and will contribute to the development of encoding strategies for conveying touch feedback through bionic hands and feet.

bioengineering↗

bioRxiv2018

Assessing the effect of hypoxia on cardiac metabolism using hyperpolarized 13C magnetic resonance spectroscopy

Abstract summaryHypoxia plays a role in many diseases and can have a wide range of effects on cardiac metabolism depending on the extent of the hypoxic insult. Non-invasive imaging methods could shed valuable light on the metabolic effects of hypoxia on the heart in vivo. Hyperpolarized carbon-13 magnetic resonance spectroscopy (HP 13C MRS) in particular is an exciting technique for imaging metabolism that could provide such information.\n\nThe aim of our work was, therefore, to establish whether hyperpolarized 13C MRS can be used to assess the in vivo response of cardiac metabolism to systemic acute and chronic hypoxic exposure. Groups of healthy male Wistar rats were exposed to either acute (30 minutes), one week or three weeks of hypoxia. In vivo MRS of hyperpolarized [1-13C]pyruvate was carried out along with assessments of physiological parameters and ejection fraction. No significant changes in heart rate, respiration rate, or ejection fraction were observed at any timepoint. Haematocrit was elevated after one week and three weeks of hypoxia.\n\nThirty minutes of hypoxia resulted in a significant reduction in pyruvate dehydrogenase (PDH) flux, whereas one or three weeks of hypoxia resulted in a PDH flux that was not different to normoxic animals. Conversion of hyperpolarized [1-13C]pyruvate into [1-13C]lactate was elevated following acute hypoxia, suggestive of enhanced anaerobic glycolysis. Elevated HP pyruvate to lactate conversion was also seen at the one-week timepoint, in concert with an increase in lactate dehydrogenase (LDH) expression. Following three weeks of hypoxic exposure, cardiac metabolism was comparable to that observed in normoxia.\n\nWe have successfully visualized of the effects of systemic hypoxia on cardiac metabolism using hyperpolarized 13C MRS, with differences observed following 30 minutes and 1 week of hypoxia. This demonstrates the potential of in vivo hyperpolarized 13C MRS data for assessing the cardiometabolic effects of hypoxia in disease.

physiology↗