A phase II study repurposing atomoxetine for neuroprotection in mild cognitive impairment

Abstract

The locus coeruleus is the initial site of Alzheimer's disease neuropathology, with hyperphosphorylated Tau appearing in early adulthood followed by neurodegeneration in dementia. Locus coeruleus dysfunction contributes to Alzheimer's pathobiology in experimental models, which can be rescued by increasing norepinephrine transmission. To test norepinephrine augmentation as a potential disease-modifying therapy, we performed a biomarker-driven phase II trial of atomoxetine, a clinically-approved norepinephrine transporter inhibitor, in subjects with mild cognitive impairment due to Alzheimer's disease. The design was a single-centre, 12-month double-blind crossover trial. Thirty-nine participants with mild cognitive impairment and biomarker evidence of Alzheimer's disease were randomized to atomoxetine or placebo treatment. Assessments were collected at baseline, 6- (crossover) and 12-months (completer). Target engagement was assessed by CSF and plasma measures of norepinephrine and metabolites. Prespecified primary outcomes were CSF levels of IL1α and TECK. Secondary/exploratory outcomes included clinical measures, CSF analyses of amyloid-β42, Tau, and pTau181, mass spectrometry proteomics and immune-based targeted inflammation-related cytokines, as well as brain imaging with MRI and fluorodeoxyglucose-PET. Baseline demographic and clinical measures were similar across trial arms. Dropout rates were 5.1% for atomoxetine and 2.7% for placebo, with no significant differences in adverse events. Atomoxetine robustly increased plasma and CSF norepinephrine levels. IL-1α and TECK were not measurable in most samples. There were no significant treatment effects on cognition and clinical outcomes, as expected given the short trial duration. Atomoxetine was associated with a significant reduction in CSF Tau and pTau181 compared to placebo, but not associated with change in amyloid-β42. Atomoxetine treatment also significantly altered CSF abundances of protein panels linked to brain pathophysiologies, including synaptic, metabolism and glial immunity, as well as inflammation-related CDCP1, CD244, TWEAK and osteoprotegerin proteins. Treatment was also associated with significantly increased brain-derived neurotrophic factor and reduced triglycerides in plasma. Resting state functional MRI showed significantly increased inter-network connectivity due to atomoxetine between the insula and the hippocampus. Fluorodeoxyglucose-PET showed atomoxetine-associated increased uptake in hippocampus, parahippocampal gyrus, middle temporal pole, inferior temporal gyrus and fusiform gyrus, with carry-over effects 6 months after treatment. In summary, atomoxetine treatment was safe, well tolerated and achieved target engagement in prodromal Alzheimer's disease. Atomoxetine significantly reduced CSF Tau and pTau, normalized CSF protein biomarker panels linked to synaptic function, brain metabolism and glial immunity, and increased brain activity and metabolism in key temporal lobe circuits. Further study of atomoxetine is warranted for repurposing the drug to slow Alzheimer's disease progression.

Keywords: Alzheimer’s disease; atomoxetine; locus coeruleus; mild cognitive impairment; norepinephrine.

Figure 1

Atomoxetine study participant flow chart.

Figure 2

Adjusted effect of atomoxetine versus placebo on csf biomarkers of target engagement and Alzheimer’s disease. (A) Catecholamine biomarkers show target engagement with NE reuptake inhibition, increasing levels of NE and dopamine (DA), both substrates for the NE transporter. Values are estimated differences and corresponding 95% confidence (n = 36). (B) Alzheimer’s disease biomarkers amyloid-β₄₂, Tau, pTau₁₈₁ assays for were performed using the using Automated Lumipulse G System (Fujirebio) and analysed by logistic regression of change in Z-score after adjustment for baseline values. Atomoxetine treatment compared to placebo significantly reduced CSF levels of total tau (n = 33) and pTau₁₈₁ (n = 36) and had no effect on CSF amyloid-β₄₂ levels (n = 34). *P < 0.05; **P < 0.01; ****P < 0.0001

Figure 3

Atomoxetine therapy exerts normalizing effect on CSF Alzheimer’s disease biomarkers associated with synaptic, metabolic, and inflammatory pathophysiology. Longitudinal CSF samples collected from each of the 36 subjects at baseline, 6 months, and 12 months were analysed by tandem mass tagging-mass spectrometry and Alzheimer’s disease biomarker pathway panels were quantified. For each subject, abundance ratios before and after treatment with either placebo or atomoxetine therapy were calculated for each arm of the trial. The placebo effect measurements were derived from only the placebo/active arm of the trial due to concern that post-placebo responses in the active/placebo arm may be confounded by carryover effects from earlier atomoxetine (ATX) therapy. (A) Box plots demonstrating the log₂-transformed ratio of pre- and post-treatment panel abundance levels (Z-score) following 6 months of either placebo or ATX therapy. A t-test analysis was used to identify panels with significantly different (P < 0.05) post-treatment responses to placebo and ATX. (B) Volcano plot displaying the log₂-transformed difference in abundance ratio (x-axis) against the −log₁₀ statistical P-value (y-axis) for all proteins demonstrating differential responses following 6 months of ATX therapy compared to placebo. Proteins belonging to biomarker pathway panels are represented by coloured data-points.

Figure 4

Effect of atomoxetine versus placebo on PET and MRI imaging biomarkers. (A) 3D rendering of regions showing significantly increased (warm colours) and decreased (cold colours) FDG uptake. (B) Quantitative values of standard uptake value ratio in the hippocampus. (C) Resting state functional MRI shows brain networks of inferior frontal gyrus (IFG), insula, hippocampus (Hipp), and caudate. The inter-network connectivity increased significantly between insula and Hipp due to atomoxetine treatment, and decreased significantly between IFG and caudate networks.