Utility of Neuronal-Derived Exosomes to Examine Molecular Mechanisms That Affect Motor Function in Patients With Parkinson Disease

Abstract

IMPORTANCE Exenatide, a glucagon-like peptide 1 agonist used in type 2 diabetes, was recently found to have beneficial effects on motor function in a randomized, placebo-controlled trial in Parkinson disease (PD). Accumulating evidence suggests that impaired brain insulin and protein kinase B (Akt) signaling play a role in PD pathogenesis; however, exploring the extent to which drugs engage with putative mechnisms in vivo remains a challenge.OBJECTIVE To assess whether participants in the Exenatide-PD trial have augmented activity in brain insulin and Akt signaling pathways. DESIGN, SETTING, AND PARTICIPANTS Serum samples were collected from 60 participants in the single-center Exenatide-PD trial (June 18, 2014, to June 16, 2016, which compared patients with moderate PD randomized to 2 mg of exenatide once weekly or placebo for 48 weeks followed by a 12-week washout period. Serum extracellular vesicles, including exosomes, were extracted, precipitated, and enriched for neuronal source by anti-L1 cell adhesion molecule antibody absorption, and proteins of interest were evaluated using electrochemiluminescence assays. Statistical analysis was performed from May 1, 2017, to August 31, 2017. MAIN OUTCOMES AND MEASURESThe main outcome was augmented brain insulin signaling that manifested as a change in tyrosine phosphorylated insulin receptor substrate 1 within neuronal extracellular vesicles at the end of 48 weeks of exenatide treatment. Additional outcome measures were changes in other insulin receptor substrate proteins and effects on protein expression in the Akt and mitogen-activated protein kinase pathways.RESULTS Sixty patients (mean [SD] age, 59.9 [8.4] years; 43 [72%] male) participated in the study: 31 in the exenatide group and 29 in the placebo group (data from 1 patient in the exenatide group were excluded). Patients treated with exenatide had augmented tyrosine phosphorylation of insulin receptor substrate 1 at 48 weeks (0.27 absorbance units [AU]; 95% CI, 0.09-0.44 AU; P = .003) and 60 weeks (0.23 AU; 95% CI, 0.05-0.41 AU; P = .01) compared with patients receiving placebo. Exenatide-treated patients had elevated expression of downstream substrates, including total Akt (0.35 U/mL; 95% CI, 0.16-0.53 U/mL; P < .001) and phosphorylated mechanistic target of rapamycin (mTOR) (0.22 AU; 95% CI, 0.04-0.40 AU; P = .02). Improvements in Movement Disorders Society Unified Parkinson's Disease Rating Scale part 3 off-medication scores were associated with levels of total mTOR (F 4,50 = 5.343, P = .001) and phosphorylated mTOR (F 4,50 = 4.384, P = .04). CONCLUSIONS AND RELEVANCEThe results of this study are consistent with target engagement of brain insulin, Akt, and mTOR signaling pathways by exenatide and provide a mechanistic context for the clinical findings of the Exenatide-PD trial. This study suggests the potential of using exosome-based biomarkers as objective measures of target engagement in clinical trials using drugs that target neuronal pathways.

The Association Between Type 2 Diabetes Mellitus and Parkinson’s Disease

“…Recently, a landmark double blind placebo-controlled trial also reported similar findings with patients treated with exenatide scoring on average 3.5 points less on the MDS-UPDRS than those not treated with exenatide, following a washout period to exclude a symptomatic effect [105]. In a novel approach to assessing target engagement using brain-derived exosomes purified from serum samples, the same group showed that patients treated with exenatide had an increase in levels of Akt and mTOR protein activation during the period of drug exposure in comparison with placebotreated patients [106].…”

Understanding the Links Between Cardiovascular Disease and Parkinson's Disease

“…If any of the CV drugs have “off target” (ie, independent of their effects on glucose, blood pressure, cholesterol, etc.) beneficial effects on PD neurodegeneration, then trials must focus on single agents and/or drug classes that may share a common mechanism(s) of “neuroprotection.” The GLP‐1 receptor agonists may be interesting because of their potential neuroprotective/neurorestorative properties in a range of animal models alongside data indicating potential mechanisms through antiinflammatory effects on microglia/astrocytic processes or antiapoptotic effects through the Akt/mechanistic target of rapamycin pathway . Whether these effects are distinct or if there is overlap between the neurodegenerative and microvascular disease processes is of clear interest but not yet known.…”

“…The GLP-1 receptor agonists may be interesting because of their potential neuroprotective/neurorestorative properties in a range of animal models [151][152][153][154] alongside data indicating potential mechanisms through antiinflammatory effects on microglia/astrocytic processes 154 or antiapoptotic effects through the Akt/mechanistic target of rapamycin pathway. 155 Whether these effects are distinct or if there is overlap between the neurodegenerative and microvascular disease processes is of clear interest but not yet known.…”

Extracellular Vesicle Biomarkers Reveal Inhibition of Neuroinflammation by Infliximab in Association with Antidepressant Response in Adults with Bipolar Depression

“…The majority of studies have used peripheral biomarkers to proxy brain processes, relying on the assumption that peripheral and brain immune activation are correlated (or that peripheral measures are reliable indicators of central processes), which has important limitations. A recent innovation is the use of blood extracellular vesicles (EVs) enriched for neuronal origin (NEVs) as a source of biomarkers that directly reflect neuronal-specific processes [19][20][21][22][23]. Extracellular vesicles (including exosomes) are membranous particles that are continuously released by virtually all cells, including neurons [24].…”