Background Parkinson's disease (PD) is the most common movement disorder among adults, affecting 2% of the world population older than 65 years of age. No diagnostic biomarker for routine use in clinical settings currently exists. Dysregulation of microRNAs (miRNAs) has been implicated in various neurodegenerative conditions, including PD. Distinct miRNAs have been demonstrated to be involved in the regulation of α‐synuclein, a key player in PD pathogenesis; miR‐153 and miR‐223 are downregulated in the brain and serum of parkinsonian GFAP.HMOX1 transgenic mice where they directly regulate α‐synuclein. Objective To ascertain whether salivary miR‐153 and miR‐223 are similarly downmodulated in, and may serve as diagnostic biomarkers of, idiopathic PD. Methods Using reverse transcriptase quantitative polymerase chain reaction, miR‐153 and miR‐223 levels were evaluated in the saliva of 77 non‐neurological controls and 83 PD patients. Levels of heme oxygenase‐1 and α‐synuclein were measured using enzyme‐linked immunosorbent assay. Analyses were adjusted by age, sex, medication exposure, disease duration, and relevant comorbidities. Results Log‐transformed expression levels of miR‐153 and miR‐223 were significantly decreased in the saliva of human PD patients in comparison with nonneurological controls. The miRNA expression levels did not change as a function of disease progression (Hoehn and Yahr staging). The area under the receiver operating characteristic curve separating controls from PD patients was 79% (95% confidence interval, 61%–96%) for miR‐153 and 77% (95% confidence interval, 59%–95%) for miR‐223. The ratios of miRNAs to oligomeric α‐synuclein, total α‐synuclein, or heme oxygenase‐1 protein did not improve accuracy of the test. Conclusion Salivary miR‐153 and miR‐223 levels may serve as useful, noninvasive, and relatively inexpensive diagnostic biomarkers of idiopathic PD. © 2019 International Parkinson and Movement Disorder Society

Heme oxygenase‐1 (HO‐1), a highly inducible stress protein that degrades heme to biliverdin, carbon monoxide, and free ferrous iron, is increased in blood and other biofluids of subjects with various systemic and neurological disorders. HO‐1 does not contain an N‐terminal signal peptide and the mechanism responsible for its secretion remains unknown. Extracellular vesicles (EVs) are membrane‐bound inclusions that transport microRNAs, messenger RNAs, lipids, and proteins among diverse cellular and extracellular compartments. The objective of the current study was to determine whether EVs in human biofluids contain HO‐1, and whether the latter may be transported in EVs from brain to periphery. Total, L1 cell adhesion molecule protein (L1CAM)‐enriched (neuron‐derived), and glutamate aspartate transporter 1 (GLAST)‐enriched (astrocyte‐derived) EVs were purified from five different human biofluids (saliva [n = 40], plasma [n = 14], serum [n = 10], urine [n = 10], and cerebrospinal fluid [n = 11]) using polymer precipitation and immuno‐affinity‐based capture methods. L1CAM‐enriched, GLAST‐enriched, and L1CAM/GLAST‐depleted (LGD) EV, along with EV‐depleted (EVD), fractions were validated by nanoparticle tracking analysis, enzyme‐linked immunosorbent assay (ELISA), and western blot. HO‐1 was assayed in all fractions using ELISA and western blot. The majority of HO‐1 protein was localized to LGD, L1CAM‐enriched, and GLAST‐enriched EVs of all human biofluids surveyed after adjusting for age and sex, with little HO‐1 protein detected in EVD fractions. HO‐1 protein in human biofluids is predominantly localized to EV compartments. A substantial proportion of EV HO‐1 in peripheral human biofluids is derived from the central nervous system and may contribute to the systemic manifestations of various neurological conditions.

Background: Parkinson disease (PD) is the second most common neurodegenerative disease, affecting 2% of the population over 65 years of age. PD diagnosis is based on clinical examination and can only be confirmed during autopsy. In 2018, we reported that heme oxygenase-1 (HO-1), an inducible stress response protein important for heme catabolism and implicated in PD pathology, was higher in PD saliva relative to healthy controls, suggesting that salivary HO-1 may serve as a potential biomarker of PD. Objectives: To ascertain whether HO-1 protein levels are elevated in PD saliva relative to degenerative neurological, non-degenerative neurological and healthy controls. Methodology: The study included 307 participants comprising 75 participants with idiopathic PD and 3 control groups: 162 non-neurological, 37 non-PD degenerative neurological, and 33 non-degenerative neurological participants. Salivary HO-1 and total protein concentrations were measured using ELISA and BCA assay, respectively. Receiver operating characteristic (ROC) curves were used to estimate model discrimination. Analyses were adjusted by age, sex, total protein, and relevant comorbidities. Results: Elevated HO-1 concentrations were observed in the PD group and other neurodegenerative conditions compared to subjects with no neurological or non-degenerative neurological conditions. ROC curves using HO-1 levels and covariates yielded areas under the curve above 85% in models for PD or neurodegenerative conditions versus controls. Conclusions: Salivary HO-1 concentrations in combination with covariates may provide a biomarker signature that distinguishes patients with neurodegenerative conditions from persons without. Classification of evidence: This study provides Class III evidence that salivary HO-1 multivariable models can distinguish neurodegenerative conditions.

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