Partial Mitigation of Oxidized Phospholipid-Mediated Mitochondrial Dysfunction in Neuronal Cells by Oxocarotenoids

Mitochondria are important (patho)physiological sources of reactive oxygen species (ROS) that mediate mitochondrial dysfunction and phospholipid oxidation; an increase in mitochondrial content of oxidized phospholipid (OxPL) associates with cell death. Previously we showed that the circulating OxPL 1-palmitoyl-2-(5’-oxo-valeroyl)-sn-glycero-3-phosphocholine (POVPC) increases in patients with Alzheimer’s disease (AD), and associates with lower plasma antioxidant oxocarotenoids, zeaxanthin, and lutein. Since oxocarotenoids are metabolized in mitochondria, we propose that during AD, lower concentrations of mitochondrial zeaxanthin and lutein may result in greater phospholipid oxidation and predispose to neurodegeneration. Here, we have investigated whether non-toxic POVPC concentrations impair mitochondrial metabolism in differentiated (d)SH-SY5Y neuronal cells and whether there is any protective role for oxocarotenoids against mitochondrial dysfunction. After 24 hours, glutathione (GSH) concentration was lower in neuronal cells exposed to POVPC (1–20μM) compared with vehicle control without loss of viability compared to control. However, mitochondrial ROS production (determined by MitoSOX oxidation) was increased by 50% only after 20μM POVPC. Following delivery of lutein (0.1-1μM) and zeaxanthin (0.5-5μM) over 24 hours in vitro, oxocarotenoid recovery from dSH-SY5Y cells was >  50%. Co-incubation with oxocarotenoids prevented loss of GSH after 1μM but not 20μM POVPC, whereas the increase in ROS production induced by 20μM POVPC was prevented by lutein and zeaxanthin. Mitochondrial uncoupling increases and ATP production is inhibited by 20μM but not 1μM POVPC; carotenoids protected against uncoupling although did not restore ATP production. In summary, 20μM POVPC induced loss of GSH and a mitochondrial bioenergetic deficit in neuronal cells that was not mitigated by oxocarotenoids

Effects of carotenoids on mitochondrial dysfunction

Oxidative stress, an imbalance between pro-oxidant and antioxidant status, favouring the pro-oxidant state is a result of increased production of reactive oxygen species (ROS) or inadequate antioxidant protection. ROS are produced through several mechanisms in cells including during mitochondrial oxidative phosphorylation. Increased mitochondrial-derived ROS are associated with mitochondrial dysfunction, an early event in age-related diseases such as Alzheimer's diseases (ADs) and in metabolic disorders including diabetes. AD post-mortem investigations of affected brain regions have shown the accumulation of oxidative damage to macromolecules, and oxidative stress has been considered an important contributor to disease pathology. An increase in oxidative stress, which leads to increased levels of superoxide, hydrogen peroxide and other ROS in a potentially vicious cycle is both causative and a consequence of mitochondrial dysfunction. Mitochondrial dysfunction may be ameliorated by molecules with antioxidant capacities that accumulate in mitochondria such as carotenoids. However, the role of carotenoids in mitigating mitochondrial dysfunction is not fully understood. A better understanding of the role of antioxidants in mitochondrial function is a promising lead towards the development of novel and effective treatment strategies for age-related diseases. This review evaluates and summarises some of the latest developments and insights into the effects of carotenoids on mitochondrial dysfunction with a focus on the antioxidant properties of carotenoids. The mitochondria-protective role of carotenoids may be key in therapeutic strategies and targeting the mitochondria ROS is emerging in drug development for age-related diseases

Inflammation, lipid (per)oxidation and redox regulation

Significance: Inflammation increases during the aging process. It is linked to mitochondrial dysfunction and increased reactive oxygen species (ROS) production. Mitochondrial macromolecules are critical targets of oxidative damage; they contribute to respiratory uncoupling with increased ROS production, redox stress, and a cycle of senescence, cytokine production, and impaired oxidative phosphorylation. Targeting the formation or accumulation of oxidized biomolecules, particularly oxidized lipids, in immune cells and mitochondria could be beneficial for age-related inflammation and comorbidities. Recent Advances: Inflammation is central to age-related decline in health and exhibits a complex relationship with mitochondrial redox state and metabolic function. Improvements in mass spectrometric methods have led to the identification of families of oxidized phospholipids (OxPLs), cholesterols, and fatty acids that increase during inflammation and which modulate nuclear factor erythroid 2-related factor 2 (Nrf2), peroxisome proliferator-activated receptor gamma (PPARγ), activator protein 1 (AP1), and NF-κB redox-sensitive transcription factor activity. Critical Issues: The kinetic and spatial resolution of the modified lipidome has profound and sometimes opposing effects on inflammation, promoting initiation at high concentration and resolution at low concentration of OxPLs. Future Directions: There is an emerging opportunity to prevent or delay age-related inflammation and vascular comorbidity through a resolving (oxy)lipidome that is dependent on improving mitochondrial quality control and restoring redox homeostasis

Distribution of plasma oxidised phosphatidylcholines in chronic kidney disease and periodontitis as a co-morbidity

Individuals with chronic kidney disease (CKD) and periodontitis as a co-morbidity have a higher mortality rate than individuals with CKD and no periodontitis. The inflammatory burden associated with both diseases contributes to an increased risk of cardiovascular and all-cause mortality. We previously demonstrated that periodontitis is associated with increasing circulating markers of inflammation and oxidative stress. We propose that inflammatory oxidised phosphocholines may contribute to the increased risk of cardiovascular disease in patients with CKD. However, the analysis of oxidised phospholipids has been limited by a lack of authentic standards for absolute quantification. Here, we have developed a comprehensive quantification liquid chromatography-mass spectrometry-based multiple reaction monitoring method for oxidised phospholipids (including some without available authentic species) that enables us to simultaneously measure twelve oxidised phosphatidylcholine species with high levels of sensitivity and specificity. The standard curves for commercial standards 1-palmitoyl-2-glutaroyl-sn-glycero-3-phosphatidylcholine (PGPC); 1-palmitoyl-2-(9′-oxo-nonanoyl)-sn-glycero-3-phosphatidylcholine (PONPC), 1-palmitoyl-2-azelaoyl-sn-glycero-3-phosphatidylcholine (PAzPC) and 1-palmitoyl-2-(5′-oxo-valeroyl)-sn-glycero-3-phosphatidylcholine (POVPC), were linear with a correlation coefficient greater than 0.99 for all analytes. The method is reproducible, with intra- and inter-day precision <15%, and accuracy within ±5% of nominal values for all analytes. This method has been successfully applied to investigate oxidised phosphatidylcholine in plasma from CKD patients with and without chronic periodontitis and the data that was obtained has been compared to plasma from healthy controls. Comparative analysis demonstrates altered chain fragmented phosphatidylcholine profiles in the plasma samples of patients with CKD and periodontitis as a co-morbidity compared to healthy controls

Circulating Oxysterols in Alzheimer’s disease: A Systematic Review and Meta-analysis

Despite decades of research, the cause and series of events underlying the advancement of Alzheimer’s disease (AD) has not yet been established. Lipids and especially cholesterol levels have been proposed to be implicated in AD. Several studies have been undertaken and many ongoing in different directions looking at the importance of circulating cholesterols and oxidised cholesterols in Alzheimer’s disease with inconsistent methods and results. This meta-analysis aims to systematically analyse available data describing the involvement of oxidised cholesterols in Mild cognitive impairment (MCI) and Alzheimer’s disease (AD). We conducted a systematic literature search of 6 databases MEDLINE (PubMed), BIOSIS (Web of Science), EMBASE (Elsevier), PsycNET, Scopus and Cochrane library for studies measuring oxysterols (24-hydroxycholesterol (24OHC); 26-hydroxycholesterol (26OHC) and 7-oxycholesterols) in serum or plasma from MCI / AD patients compared to age and gender matched cognitively normal controls. Data was analysed using the inverse variance and standard mean difference with random effect analysis model at 95% confidence interval for association between oxysterols and MCI / AD in Review Manager (RevMan) software version 5.4.1. 175 studies between January 2000 and April 2022 were identified by 2 independent researchers out of which 14 met the inclusion criteria and were analysed with a total of 957 controls, 469 MCI cases and 509 AD cases. The standard mean differences between MCI / AD participants and controls did not show any difference in the oxysterol levels except for 26OHC level which were higher in AD but not statistically significant