Plasma oxylipin profiles reflect Parkinson's disease stage

Highlights

• UPLC-MS/MS analysis of plasma oxylipins: 73 samples from patient with Parkinson's disease (PD) and 36 healthy volunteers (HC).

• The concentration of plasma AA, AEA and LTE4 decreased while 19-HETE and 12-HETE increased in PD vs HC.

• Plasma oxylipin profiles differ in patients with early and advanced Parkinson's disease.

Abstract

Derivatives of polyunsaturated fatty acids (PUFAs), also known as oxylipins, are key participants in regulating inflammation. Neuroinflammation is involved in many neurodegenerative diseases, including Parkinson's disease. The development of ultra-high-performance liquid chromatography-mass spectrometry (UPLC-MS/MS) facilitated the study of oxylipins on a system level, i.e., the analysis of oxylipin profiles. We analyzed oxylipin profiles in the blood plasma of 36 healthy volunteers (HC) and 73 patients with Parkinson’s disease (PD), divided into early (L\M, 29 patients) or advanced (H, 44 patients) stages based on the Hoehn and Yahr scale. Among the 40 oxylipins detected, we observed a decrease in the concentration of arachidonic acid (AA) and AA derivatives, including anandamide (AEA) and Leukotriene E4 (LTE4), and an increase in the concentration of hydroxyeicosatetraenoic acids 19-HETE and 12-HETE (PD vs HC). Correlation analysis of gender, age of PD onset, and disease stages revealed 20 compounds the concentration of which changed depending on disease stage. Comparison of the acquired oxylipin profiles to openly available PD patient brain transcriptome datasets showed that plasma oxylipins do not appear to directly reflect changes in brain metabolism at different disease stages. However, both the L\M and H stages are characterized by their own oxylipin profiles – in patients with the H stage oxylipin synthesis is increased, while in patients with L\M stages oxylipin synthesis decreases compared to HC. This suggests that different therapeutic approaches may be more effective for patients at early versus late stages of PD.

Introduction

Neuroinflammation is involved in the pathogenesis of a number of neurodegenerative diseases [1], [2]. Oxylipins, as well as their precursors, polyunsaturated fatty acids (PUFAs), are signaling mediators involved in innate immune responses, the regulation of inflammatory responses (including acute and chronic inflammation), and are related to systemic diseases [3], [4], [5], [6]. Individual oxylipins have been studied for a long time in the context of neurodegenerative diseases [7], [8]. However, due to the complex interrelationships between individual oxylipin species, and the lack of appropriate detection methods which would allow these relationships to be captured, our understanding of their role in neurodegeneration is lacking.

There are several PUFAs, of which the main representatives include arachidonic (AA) and docosahexaenoic (DHA) acids [3], [4]. Oxylipins are synthesized from PUFAs via three major pathways, named in accordance with the key enzymes in respective pathways: the cyclooxygenase (COX), lipoxygenase (LOX), and cytochrome P450 monooxygenase (CYP450) branches, as well as via anandamide (AEA) pathways and non-enzymatic conversions of PUFAs [3], [4], [5].

During stimulation, a wide range of oxylipins are synthesized simultaneously, all of which have different functions at the cellular level, due to the fact that their targets are various surface and intracellular proteins. [5], [9]. Recently, mass spectrometric approaches have made it possible to simultaneously determine the concentrations of a large number of oxylipins, which facilitates the analysis of the oxylipin profile in a sample [3], [10]. Such approaches enable the study of oxylipins in the context of pathological processes, and open up the possibility of using them as potential biomarkers in a wide range of diseases, including various brain pathologies [4], [6], [11], [12]. Currently, oxylipin profiles can be evaluated in a wide range of biological materials, including blood, various tissues, tears, and intraocular fluid [10], [13], [14], [15]. The possibility of analyzing oxylipin profiles in blood plasma is of particular interest. The results obtained provide new information about the pathogenesis of the investigated disease, and improve their applicability as biomarkers for early diagnosis, the search for new drugs targets, or the evaluation of therapy effectiveness [11], [16], [17], [18].

Although some studies have shown a correlation between blood oxylipin profiles and changes in brain function [17], it remains unclear whether changes in oxylipin profiles reflect general changes in organism responses, or specific changes in oxylipin metabolism in brain tissue. In this case, an approach combining measurements of oxylipins in the blood and analysis of transcriptome changes in tissue can be applied, as done previously in a breast cancer study [13]. In this paper, we used this approach to study oxylipin profile changes in Parkinson's disease.

Parkinson’s disease (PD) is a degenerative disorder of the central nervous system which affects 4 million people worldwide [19], [20], characterized by a broad spectrum of motor and non-motor features. The etiology of PD is still poorly understood [21], and although a large number of molecular mechanisms involved in PD pathogenesis are known, such as α-synuclein aggregation, oxidative stress, genetic mutations, mitochondrial dysfunction and neuroinflammation [22], [23], the relationships between them remain vague. Several stages are delineated in accordance with clinical manifestations, which are characterized by varying degrees of disease severity [24]. The relationship of individual lipids, including oxylipins, with various processes that manifest themselves in Parkinson's disease has been shown in a number of works (reviewed recently [6]). Extensive evidence from human samples and animal models also supports the involvement of inflammation in PD onset and progression (rev. in [25]). It remains unclear to what extent oxylipin profiles could reflect different disease stages; therefore, the blood plasma of 73 patients and 36 healthy volunteers was examined to characterize oxylipin profiles in Parkinson's disease. We also assessed the extent to which these profiles can correlate with changes in the brain transcriptome of patients with PD, previously published in open databases. This made it possible to assess whether changes in oxylipin concentrations reflect changes in the expression of the corresponding genes in brain tissue, or if oxylipin profiles are an independent characteristic of the disease and its stages.