Fucoxanthin is the most abundant carotenoid found in marine brown algae that exhibits several healthy properties. Dietary fucoxanthin is metabolized in the intestine, plasma, and other tissues to various metabolites, including fucoxanthinol. In this regard, the contribution of fucoxanthinol to the healthy properties of its precursor, fucoxanthin, against pathogenetic events associated with neurodegenerative diseases remains unexplored. Here, we evaluated and compared the antioxidant and neuroprotective effects of the carotenoids fucoxanthin and fucoxanthinol in in vitro models of Alzheimer’s (AD) and Parkinson’s (PD) disease. Neuronal SH-SY5Y cells were used to evaluate the antioxidant properties of the carotenoids against ABTS radical in the membrane and cytoplasm and oxidative stress elicited by tert-butyl hydroperoxide using the 2′,7′-dichlorodihydrofluorescein diacetate probe. We also assessed the ability of the carotenoids to increase the glutathione (GSH) and activate the Nrf2/Keap1/ARE pathway using the monochlorobimane probe and western blotting method, respectively. The neuroprotective effects of the carotenoids against the neurotoxicity generated by oligomers of Beta-Amyloid (1–42) peptide (OAβ) and 6-hydroxydopamine (6-OHDA), which are neurotoxins of AD and PD, respectively, were finally evaluated in the same neuronal cells using the thiazolyl blue tetrazolium bromide assay. Both carotenoids could reach the cytoplasm, which explains the mainly free radical scavenging activity at this level. Notably, fucoxanthinol had higher and lower antioxidant activity than fucoxanthin at extracellular and cellular levels. Although studied carotenoids exerted the ability to activate the Nrf2/Keap1/ARE pathway, leading to an increase of intracellular GSH, our results suggested that the antioxidant activity of the carotenoids could be mainly attributed to their radical scavenging activity in neuronal membrane and cytoplasm, where they accumulate. Fucoxanthinol also shared similar neuroprotective effects as fucoxanthin against the neurotoxicity generated by OAβ and 6-OHDA, suggesting a potential neuroprotective contribution to the action of fucoxanthin administered as a food supplement in in vivo experimental models. These results encourage further research to evaluate the bioavailability of fucoxanthinol and other metabolites of fucoxanthin at the brain level to elucidate the dietary neuroprotective potential of fucoxanthin.

Parkinson's disease (PD) is a neurodegenerative disease characterized by the degeneration of dopaminergic neurons in the substantia nigra and the presence of misfolded α-synuclein in the brain. Mitochondrial dysfunction and oxidative stress are factors contributing to the death of these neurons. Coenzyme Q10 (CoQ10) serve as an antioxidant and cofactor for mitochondrial enzymes, and its deficiency can exacerbate neurodegenerative processes in PD. However, the clinical efficacy of CoQ10 is limited by its low bioavailability and instability. Ubiquinol diacetate (CoQ10 Ac), an esterified form of CoQ10, shows improved pharmacokinetic properties and potential as a prodrug, converting into the reduced antioxidant form of CoQ10 by esterases in the body. This study aimed to investigate the antioxidant and neuroprotective effects of CoQ10 Ac compared to CoQ10 in SH-SY5Y cell line and Caenorhabditis elegans models of PD. CoQ10 Ac showed higher antioxidant activity than CoQ10 at both extracellular and intracellular levels, particularly in the membrane and cytosolic compartments. It exhibited superior neuroprotection against 6-hydroxydopamine toxicity, showing a greater ability to reduce the activation of caspase-3 and PARP1 compared to CoQ10. Both compounds decreased the increased ratio of mitochondrial fission protein, DRP1, to fusion protein, OPA1, induced by 6-hydroxydopamine in SH-SY5Y cells, enhancing OPA1 levels and promoting antiapoptotic death. However, CoQ10 Ac was more effective than CoQ10 in preserving mitochondrial structural integrity and mass. Additionally, both compounds significantly inhibited the aggregation of α-synuclein induced by 6-hydroxydopamine. Furthermore, CoQ10 Ac showed stronger neuroprotective effects than CoQ10 in C. elegans models of PD. It demonstrated greater anti-aggregant activity in C. elegans expressing human α-synuclein, suggesting higher bioavailability. These findings highlight CoQ10 Ac as a promising prodrug candidate and support further investigation in in vivo PD models.

Rising temperatures and the occurrence of heat waves due to climate change can increase the risk of various skin disorders. Moreover, elevated temperatures worsen oxidative damage and inflammation caused by other climate change stressors, such as UV exposure. Consequently, there is growing interest in innovative solutions to protect skin health from the effects of pollution and climate change stressors. Among natural cosmeceuticals, carotenoids are recognized for their antioxidant and anti-inflammatory properties. This study evaluated the thermoprotective effects of Hematococcus lacustris (the microalga formerly called Hematococcus pluvialis) extract (HLE), which is considered the richest natural source of carotenoid astaxanthin, against acute hyperthermia, which mimics the conditions of heat waves. In addition, we separately assessed the effects of HLE against UVA and hydrogen peroxide stress, complementing the antioxidant profile of the extract under study. The evaluation was conducted using in vitro tests on human HaCaT keratinocytes and the nematode Caenorhabditis elegans, which is a model organism sensitive to environmental stressors. The treatment of HaCaT keratinocytes with HLE counteracted the intracellular formation of reactive oxygen species and cytotoxicity induced by hyperthermia, UVA, and hydrogen peroxide exposure. Under the same experimental conditions, HLE also restored the impaired expression of stress-sensitive genes, such as matrix metalloproteinase-1, in HaCaT keratinocytes and promoted wound closure mimicking the process of re-epithelization. Lastly, experiments in C. elegans confirm that HLE reduces heat stress-induced oxidative damage and preserves motility, supporting a systemic protective effect consistent with dietary uptake of the extract. These findings suggest that HLE, rich in carotenoid astaxanthin, can protect keratinocytes against oxidative damage and cytotoxicity induced by thermal stress, indicating its potential role in mitigating thermal aging.