Biology subjects

Southworth, R.

Publications and source records attributed to Southworth, R..

3 recordsLinked to original sources

bioRxiv2024

Sarcolemmal and mitochondrial membrane potentials measured ex vivo and in vivo in the heart by pharmacokinetic modelling of sestamibi

We present a compartmental modelling approach to analyse radioactive time activity curves for first pass kinetics of [99mTc]sestamibi in the heart. Reparametrizing the kinetic equations using the Nernst membrane-potential equation provides a novel means of non-invasively estimating the sarcolemmal (Em) and mitochondrial ({Delta}{Psi}m) membrane potentials in the heart. A Markov Chain Monte Carlo (MCMC) fitting approach was applied to data derived from established interventions in Langendorff perfused rat hearts where the sarcolemmal membrane was depolarised using hyperkalaemic Krebs Henseleit buffers; the mitochondrial membrane was depolarised using carbonylcyanide-3-chlorophenylhydrazone (CCCP); or both membranes were depolarised using their combination. Translating this approach to single photon emission planar scintigraphy kinetics from healthy rats allowed an estimate of these membrane potentials (voltages) in vivo for the first time; the values were Em = -62 {+/-} 5 mV and {Delta}{Psi}m = -151 {+/-} 5 mV (n = 4, mean {+/-} SD).

biochemistry↗

bioRxiv2024

Perfusion-Independent Tissue Hypoxia in Cardiac Hypertrophy in Mice Measured by 64Cu-CTS PET Imaging

BackgroundHypoxia is central to many cardiac pathologies, but clinically its presence can only be inferred by indirect biomarkers including hypoperfusion and energetic compromise. Imaging hypoxia directly could offer new opportunities for the diagnosis and sub-stratification of cardiovascular diseases. ObjectivesTo determine whether [64Cu]CuCTS Positron Emission Tomography (PET) can identify hypoxia in a murine model of cardiac hypertrophy. MethodsMale C57BL/6 mice underwent abdominal aortic constriction (AAC) to induce cardiac hypertrophy, quantified by echocardiography over 4 weeks. Hypoxia and perfusion were quantified in vivo using [64Cu]CuCTS and [64Cu]CuGTSM PET, respectively, and radiotracer biodistribution was quantified post-mortem. Cardiac radiotracer retention was correlated with contractile function (measured by echocardiography), cardiac hypertrophy (measured by histology), HIF-1 stabilization and NMR-based metabolomics. The effect of anesthesia on [64Cu]CuCTS uptake was additionally investigated in a parallel cohort of mice injected with radiotracer while conscious. ResultsHearts showed increased LV wall thickness, reduced ejection fraction and fractional shortening following AAC. [64Cu]CuCTS retention was 317% higher in hypertrophic myocardium (p<0.001), despite there being no difference in perfusion measured by 64CuGTSM. Radiotracer retention correlated on an animal-by-animal basis with severity of hypertrophy, contractile dysfunction, HIF1 stabilization and metabolic signatures of hypoxia. [64Cu]CuCTS uptake in hypertrophic hearts was significantly higher when administered to conscious animals. Conclusions[64Cu]CuCTS PET can quantify cardiac hypoxia in hypertrophic myocardium, independent of perfusion, suggesting the hypoxia is caused by increased oxygen diffusion distances at the subcellular level. Alleviation of cardiac workload by anesthesia in preclinical models partially alleviates this effect.

bioengineering↗

bioRxiv2023

The Chicken Chorioallantoic Membrane as a Low-Cost, High-Throughput Model for Cancer Imaging

PurposeMouse models are invaluable tools for radiotracer development and validation. They are, however, expensive, low throughput, and are constrained by animal welfare considerations. Here, we assessed the chicken chorioallantoic membrane (CAM) as an alternative to mice for preclinical cancer imaging studies. MethodsGrowth of NCI-H460 Fluc tumors on the CAM was optimized using a range of physical and chemical supports. Tumor-bearing eggs were imaged by dynamic 18F-2-fluoro-2-deoxy-D-glucose (18F-FDG) or (4S)-4-(3-18F-fluoropropyl)-L-glutamate (18F-FSPG) PET/CT following intravenous injection, with mice bearing subcutaneous NCI-H460 Fluc xenografts imaged with 18F-FDG for comparison. The dependence of the transporter system xc- on in ovo 18F-FSPG tumor uptake was determined through treatment with imidazole ketone erastin. Additionally, 18F-FSPG PET/CT was used to monitor treatment response in ovo 24 h following external beam radiotherapy. ResultsNCI-H460 Fluc cells grown in Matrigel formed vascularized tumors of reproducible size without compromising embryo viability. By designing a simple method for cannulation it was possible to perform dynamic PET imaging in ovo, producing high tumor-to-background signal for both 18F-FDG and 18F-FSPG. 18F-FDG tumor uptake kinetics were similar in ovo and in vivo, with 18F-FSPG providing an early marker of both treatment response and target inhibition in CAM-grown tumors. ConclusionsThe CAM provides a low-cost alternative to tumor xenograft mouse models which may broaden access to PET and SPECT imaging. Rapid tumor growth and high-quality PET images that can be obtained with this model suggest its potential use for early radiotracer screening, pharmacological studies, and monitoring response to therapy.

cancer biology↗