Erik Årstad

Skeletal muscle undergoes rapid and dynamic changes in energy demand during exercise, limiting the physiological relevance of resting-state measurements. Here, we demonstrate the feasibility of combining hyperpolarised ¹³C magnetic resonance spectroscopy (¹³C-MRS) with ³¹P-MRS to non-invasively measure real-time metabolic responses in exercising human skeletal muscle. Sedentary and endurance-trained men perform plantar-flexion exercise inside a magnetic resonance scanner. Dynamic hyperpolarised [1-¹³C]pyruvate spectra from the medial gastrocnemius show that increasing exercise intensity escalates pyruvate-to-lactate conversion relative to mitochondrial pyruvate utilisation. Endurance training is associated with greater bicarbonate labelling, consistent with increased mitochondrial pyruvate utilisation, and reduced lactate production. These metabolic signatures are accompanied by intensity- and training-dependent differences in phosphocreatine degradation and intracellular pH decline measured by ³¹P-MRS. Together, these findings demonstrate the feasibility of combining hyperpolarised ¹³C- and ³¹P-MRS to phenotype skeletal muscle metabolism during exercise, providing a platform for investigating metabolic adaptations in ageing, disease and therapeutic intervention.

Microglial dysfunction and glutamatergic dysregulation are implicated in the neurobiology of schizophrenia. Microglia regulate brain glutamate levels through mechanisms including the cysteine-glutamate antiporter, raising the possibility that microglial dysfunction could underlie glutamatergic dysregulation in schizophrenia. We tested this using a combined cross-sectional/longitudinal study of individuals with first episode psychosis and healthy controls. We investigated two hypotheses: (1) increase in a positron emission tomography (PET) imaging marker of microglia is associated with increased anterior cingulate (ACC) glutamate levels; and (2) reducing immune trafficking into the CNS using the monoclonal antibody natalizumab would reduce ACC glutamate levels in people with first-episode psychosis. A total of 108 participants (68 patients and 40 healthy controls) underwent simultaneous proton magnetic resonance spectroscopy to quantify ACC glutamate and glutamate/glutamine (glx) levels and PET imaging with [18 F]DPA-714 to quantify translocator protein (TSPO) levels, a protein highly expressed by microglia in neuroinflammatory conditions. In the longitudinal arm, 50 first-episode psychosis patients were included and either randomised to receive natalizumab or placebo double-blind, or received open-label natalizumab. At baseline, there was no significant association between ACC glutamate concentration and ACC TSPO binding in the entire sample (β = -0.003, SE = 0.006, p = 0.55). In the longitudinal arm, natalizumab did not significantly alter ACC glutamate levels (mean difference = 0.227 i.u., t = 1.52, p = 0.139). These findings do not support the hypothesis that microglial dysfunction drives ACC glutamatergic dysregulation in early psychosis. Microglial dysfunction and glutamatergic dysregulation may therefore represent distinct mechanisms within the neurobiology of schizophrenia.

Skeletal muscle is defined by rapid and dynamic fluctuations in ATP demand during exercise, limiting the physiological relevance of resting-state measurements. Here, we show that hyperpolarised ¹³C magnetic resonance spectroscopy (¹³C-MRS), integrated with ³¹P-MRS, enables non-invasive, real-time resolution of mitochondrial and non-mitochondrial energy metabolism in human skeletal muscle during exercise. Sedentary or endurance-trained men performed plantar-flexion exercise inside a MR scanner. Dynamic hyperpolarised [1-¹³C]pyruvate spectra from the medial gastrocnemius revealed that increasing exercise intensity escalated pyruvate-to-lactate conversion relative to mitochondrial pyruvate utilisation. Moreover, endurance training status was associated with greater mitochondrial pyruvate flux and reduced lactate production. These metabolic signatures were mirrored by intensity- and training-dependent differences in muscle phosphocreatine degradation and intracellular pH decline measured by ³¹P-MRS. These findings establish the utility of combined hyperpolarised ¹³C- and ³¹P-MRS to phenotype human skeletal muscle during exercise and provide a platform for investigating altered metabolism in ageing, disease, and therapeutic intervention.

Background: We investigated imaging biomarkers of Aβ and neurodegeneration in relation to tau‐PET Braak stage in a preclinical birth cohort.Method: Cognitively normal individuals enrolled in Insight 46, the neuroimaging sub‐study of the MRC National Survey of Health and Development (1946 British birth cohort), were scanned on combined PET/MR with [18F]florbetapir Aβ‐PET at age ∼70 years and again at ∼73 years. A sub‐sample enriched for Aβ (Aβ+; Centiloid> = 13, hole cerebellum reference) is currently being assessed with [18F]MK‐6240 tau‐PET at age ∼76 years. For this interim analysis, tau‐PET images (90‐110 minutes post‐injection) were co‐registered with T1‐weighted MRI. Anatomical areas were parcellated on the T1 to form Braak regions. Standard uptake value ratios (SUVRs) were calculated using an inferior cerebellar grey reference without partial volume correction. Tau‐PET positivity (Tau+) was defined using Gaussian mixture modelling in each region. Participants were assigned to Tau‐, Braak I‐II, III‐IV or V‐VI groups based on the most advanced Tau+ region. Group differences in baseline Aβ (Centiloids), Aβ accumulation (Centiloids/year) and hippocampal atrophy rate (%/year) were investigated with Mann‐Whitney U tests.Result: Analysis included 80 individuals with tau‐PET data (Table 1), 45% of the sample were Aβ+ by age 73. Three individuals did not conform to the Braak stage hierarchy (orange triangles, Figure 1). No Aβ‐ individuals were Tau+ beyond Braak I. Figure 2 shows baseline Aβ, Aβ accumulation and hippocampal atrophy rates for Braak stage groups for participants who had data at all timepoints (N = 78). Tau+ individuals (in any Braak region) had significantly higher baseline Aβ than Tau‐ individuals. Rate of annual Aβ accumulation was higher for Braak III‐IV and Braak V‐VI compared to Tau‐ individuals. Hippocampal atrophy rate was elevated for Braak V‐VI compared to Tau‐, and Braak III‐IV was borderline significant.Conclusion: In this preliminary analysis, tau‐PET positivity beyond Braak I was restricted to individuals who were Aβ+ three years prior. Participants with elevated tau aged 76 had increased Aβ at age 70. Increased rates of hippocampal atrophy were occurring at least three years prior to tau scanning in individuals with advanced tau pathology. These findings will be updated as more data is acquired.

Background: In Alzheimer’s disease, early amyloid‐β and tau deposition may have differential downstream effects on synaptic function and neuronal loss in a stage‐dependent manner. Amyloid‐related synaptic changes are thought to precede tau accumulation, which starts in the medial temporal lobe before propagating and leading to neurodegeneration. We explored whether microstructural MRI measures can detect these different sequential cortical changes.Method: Seventy‐nine healthy, asymptomatic individuals, recruited from the Insight 46 study of the British 1946 birth cohort underwent combined PET/MR with [18F]florbetapir Aβ‐PET at ∼73yrs, and [18F]MK‐6240 tau‐PET at ∼76yrs. Standard uptake value ratios were calculated using a whole cerebellar reference for florbetapir and an inferior cerebellar reference for MK‐6240. Multi‐shell diffusion MRI was acquired; neurite orientation dispersion and density imaging was used to quantify neurite density (NDI) and orientation dispersion (ODI, a proxy measure of dendritic morphology/complexity), with DTI measuring mean diffusivity (MD), a less specific measure of degenerative change. PET and microstructural MRI biomarkers were assessed in a neocortical composite ROI and across Braak stages.Result: Thirty‐six participants were amyloid positive, 18 of whom were tau positive (eight Braak stage 1‐2, four Braak 3‐4, six Braak 5‐6). Across all participants, in the neocortical composite, significant differences between amyloid positive and amyloid negative individuals were found in both tau PET (p = 0.0092) and ODI (p = 0.030) but not for other measures. Within the amyloid positive group, in the cortical composite, significant differences in MD (p = 0.0093) but not ODI were seen when comparing those who were tau positive and negative. In the amyloid positive group, there was an association between tau PET and MD in the MTL (Braak 1‐2) (r = 0.34, p = 0.040) and Braak 3‐4 (r = 0.37, p = 0.025), with an association between tau and ODI (r = 0.48, p = 0.0031) in Braak 3‐4 only. After adjusting for volume, only the association between tau PET and ODI in Braak 3‐4 remained (p = 0.038).Conclusion: Our results are consistent with amyloid deposition causing dendritic/changes (as assessed by ODI) with consequent synaptic dysfunction. Later tau propogation is then associated with frank neuronal breakdown (as measured by MD). dMRI cortical imaging biomarkers have the potential to provide proxy measures of underlying AD stage/pathology prior to symptom onset.

Background: We investigated imaging biomarkers of Aß and neurodegeneration in relation to tau‐PET Braak stage in a preclinical birth cohort.Method: Cognitively normal individuals enrolled in Insight 46, the neuroimaging sub‐study of the MRC National Survey of Health and Development (1946 British birth cohort), were scanned on combined PET/MR with [18F]florbetapir Aß‐PET at age ∼70 years and again at ∼73 years. A sub‐sample enriched for Aß (Aß+; Centiloid> = 13, hole cerebellum reference) is currently being assessed with [18F]MK‐6240 tau‐PET at age ∼76 years. For this interim analysis, tau‐PET images (90‐110 minutes post‐injection) were co‐registered with T1‐weighted MRI. Anatomical areas were parcellated on the T1 to form Braak regions. Standard uptake value ratios (SUVRs) were calculated using an inferior cerebellar grey reference without partial volume correction. Tau‐PET positivity (Tau+) was defined using Gaussian mixture modelling in each region. Participants were assigned to Tau‐, Braak I‐II, III‐IV or V‐VI groups based on the most advanced Tau+ region. Group differences in baseline Aß (Centiloids), Aß accumulation (Centiloids/year) and hippocampal atrophy rate (%/year) were investigated with Mann‐Whitney U tests.Result: Analysis included 80 individuals with tau‐PET data (Table 1), 45% of the sample were Aß+ by age 73. Three individuals did not conform to the Braak stage hierarchy (orange triangles, Figure 1). No Aß‐ individuals were Tau+ beyond Braak I. Figure 2 shows baseline Aß, Aß accumulation and hippocampal atrophy rates for Braak stage groups for participants who had data at all timepoints (N = 78). Tau+ individuals (in any Braak region) had significantly higher baseline Aß than Tau‐ individuals. Rate of annual Aß accumulation was higher for Braak III‐IV and Braak V‐VI compared to Tau‐ individuals. Hippocampal atrophy rate was elevated for Braak V‐VI compared to Tau‐, and Braak III‐IV was borderline significant.Conclusion: In this preliminary analysis, tau‐PET positivity beyond Braak I was restricted to individuals who were Aß+ three years prior. Participants with elevated tau aged 76 had increased Aß at age 70. Increased rates of hippocampal atrophy were occurring at least three years prior to tau scanning in individuals with advanced tau pathology. These findings will be updated as more data is acquired.

Background: Primary aldosteronism (PA) is the most common potentially curable cause of secondary hypertension and is a risk factor for cardiovascular morbidity and mortality. For patients with unilateral disease adrenalectomy can be curative. However, PA remains substantially underdiagnosed due the complex diagnostic pathway required to identify patients with unilateral disease, and the difficulties in accurate lateralization of the affected adrenal gland. Specific and selective imaging of aldosterone synthase with PET-CT could provide a non-invasive readout of aldosterone production from both adrenals and allow patients with suspected PA to be better stratified for surgery or medical intervention. To achieve this, we have developed [¹⁸F]AldoView – the first highly selective aldosterone synthase PET tracer. Here we report the results of the first-in-human imaging with [¹⁸F]AldoView. Methods: The PET ligand is a highly selective antagonist of aldosterone synthase with fluoride in its primary structure which enables labelling without structural modifications. [¹⁸F]AldoView was synthesized in accordance with Good Manufacturing Practice. Four patients (1F,3M) diagnosed with PA (RAA, saline infusion confirmatory test) with unilateral excessive aldosterone secretion confirmed by cross sectional imaging and Adrenal Venous Sampling were imaged with [¹⁸F]AldoView PET-CT prior to adrenalectomy. Results: [¹⁸F]AldoView showed rapid clearance from background tissues and substantial uptake in the abnormal adrenal gland. The adrenal lateralisation index, measured as the SUVmax ratio between the two adrenals 35-45 min post-injection, was 6:1, 11:1, 4:1, and 7:1, suggesting it is markedly more selective relative to results reported with alternative PET tracers. Patients tolerated [¹⁸F]AldoView well and had no side effects. Conclusion: PET/CT imaging with [¹⁸F]AldoView in this preliminary report of the first four patients has provided highly promising results and suggests that this highly selective tracer has potential to improve the stratification of patients with unilateral PA.

Supplementary Figures 1 - 6. Fig. S1 shows the ability of PEO1, PEO4 and PEO6 cells to form colonies following cisplatin treatment; Fig. S2 demonstrates that [18F]FDG uptake in A2780 cells is unrelated to drug resistance; Fig. S3 examines the expression of key ABC transporters; Fig. S4 provides representative PET images of mice bearing A2780 WT and A2780 DoxR tumors; Fig. S5 quantifies the [18F]FSPG tumor-to-background ratio in WT and DoxR tumor-bearing mice; and Fig. S6 illustrates [18F]FSPG DoxR tumor retention after doxil treatment of mice.