Investigating metabolomics and the effects of oxyresveratrol in experimental Parkinson's disease

Abstract

Parkinson’s disease (PD) is the second most common neurodegenerative disorder, with risk factors such as aging and genetic predisposition. The cardinal symptoms of PD are movement related—rigidity of the limbs, resting tremors, and bradykinesia. Brain pathologies in PD include the death of dopaminergic neurons in the substantia nigra pars compacta (SNpc) resulting in diminished striatal dopamine, and the presence of intracytoplasmic spherical inclusions, known as Lewy bodies (LB). LBs comprise aggregates of the amyloid protein, α-synuclein (α-syn). Current therapeutic strategies for PD aim to replenish dopamine levels thereby providing symptomatic relief only. Compounds that can delay and slow down disease progression are an alternative strategy. Several nutraceuticals with antioxidant properties are under investigation in this regard. Stilbenoids are a class of polyphenolics including resveratrol (RES) and its hydroxylated analogue, oxyresveratrol (OXY). Oxyresveratrol, found in the mulberry bark, is a very potent antioxidant with a wider therapeutic window than RES. It exerts several therapeutic effects, including neuroprotection. The aim of this study was to investigate in detail the protective effects of OXY in experimental PD. In the first part of the study, the effects of OXY on endoplasmic reticulum (ER) stress, a prime pathological pathway in PD, were studied. To induce ER stress, neurons were treated with the dopaminergic toxin 6-hydroxydopamine (6-OHDA), or transfected with familial mutants of α-syn, which form toxic oligomers. OXY mitigated ER stress in both these models, by modulating distinct pathways. The effects of OXY exposure on rats unilaterally lesioned with 6-OHDA in the medial forebrain bundle (MFB), were then assessed. At lower doses OXY successfully rescued these rats from severe motor impairment, with a mild effect on dopaminergic loss. Subsequently, mass spectrometry-based metabolomics was employed to investigate small molecules altered in this model. The plasma was used for its translational potential, and midbrain to uncover metabolites disturbed at the site of damage. Saturated free fatty acids were significantly upregulated in the plasma of 6-OHDA-treated rats, while monoglycerides, myo-inositol and one unidentified metabolite were decreased in their midbrain. The fatty acids showed a very high correlation with motor symptoms (r > 0.6) while the unidentified metabolite showed a high prediction ability, with an area under the curve (AUC) value of 100% (sensitivity = 1, specificity = 1), as seen by receiver operating curve (ROC) analysis. Moreover, phosphatidylinositol (PI 40:6 and PI 38:4) and diglycerides, lipids associated with cellular signalling, were also disrupted in the midbrain. OXY, but not RES, partially protected the metabolite imbalance in the lesioned rats. Metabolomics also uncovered molecular targets of OXY. Levels of lactic acid, alanine and gamma-Aminobutyric acid (GABA) in the midbrain were significantly decreased in the OXY-treated rats. These metabolites are intermediates of energy metabolism in neurons, suggesting that maintaining energy homeostasis is a protective mechanism of OXY. In summary, this study elucidated the protective effects of OXY against symptomatic and metabolic disturbances associated with experimental PD, which make it a promising prophylactic candidate for neurodegeneration.