Application of Marine Natural Products against Alzheimer's Disease: Past, Present and Future

Structural Insights into the Marine Alkaloid Discorhabdin G as a Scaffold towards New Acetylcholinesterase Inhibitors

In this study, Antarctic Latrunculia sponge-derived discorhabdin G was considered a hit for developing potential lead compounds acting as cholinesterase inhibitors. The hypothesis on the pharmacophore moiety suggested through molecular docking allowed us to simplify the structure of the metabolite. ADME prediction and drug-likeness consideration provided valuable support in selecting 5-methyl-2H-benzo[h]imidazo[1,5,4-de]quinoxalin-7(3H)-one as a candidate molecule. It was synthesized in a four-step sequence starting from 2,3-dichloronaphthalene-1,4-dione and evaluated as an inhibitor of electric eel acetylcholinesterase (eeAChE), human recombinant AChE (hAChE), and horse serum butyrylcholinesterase (BChE), together with other analogs obtained by the same synthesis. The candidate molecule showed a slightly lower inhibitory potential against eeAChE but better inhibitory activity against hAChE than discorhabdin G, with a higher selectivity for AChEs than for BChE. It acted as a reversible competitive inhibitor, as previously observed for the natural alkaloid. The findings from the in vitro assay were relatively consistent with the data available from the AutoDock Vina and Protein-Ligand ANTSystem (PLANTS) calculations.

Unraveling the Anti-Aging Properties of Phycocyanin from the Cyanobacterium Spirulina (Arthrospira platensis)

In recent years, marine natural products have become one of the most important resources of novel lead compounds for critical diseases associated with age. Spirulina, a dietary supplement made from blue-green algae (cyanobacteria: scientific name Arthrospira platensis), is particularly rich in phycocyanin, a phycobiliprotein, which accounts for up to 20% of this cyanobacterium's dry weight and is considered responsible for its anti-cancer, anti-inflammatory and antioxidant activities. Although the anti-aging activity of phycocyanin has been investigated, how exactly this compound works against aging remains elusive. The aim of our research is to use the yeast Saccharomyces cerevisiae as a model organism to investigate the anti-aging properties of phycocyanin from A. platensis. Our results show that phycocyanin has a powerful anti-aging effect, greatly extending the chronological life span of yeast cells in a dose-dependent way, as the effect was also pronounced when cells were grown in SD medium under calorie restriction conditions (0.2% glucose). Both ROS and accumulation of dead cells were followed by staining chronologically aged cells with dihydrorhodamine 123 (DHR123) and propidium iodide (PI). Interestingly, we found that most of the aged phycocyanin-treated cells, which were unable to form colonies, were actually ROS+/PI-. Finally, we show that the moment in which phycocyanin is added to the culture does not substantially influence its effectiveness in counteracting chronological aging.

Arctigenin attenuated spatial memory impairment in pR5 mice by regulating mitochondrial energy metabolism

OBJECTIVES

Arctigenin (ATG) is a natural product with a variety of biological activity, which can improve the pathological changes of Alzheimer's disease (AD) model mice through multiple mechanisms. This study aims to further elucidate the potential mechanism by which ATG improves memory impairment in AD mice.

METHODS

Here, we used pR5 mice as an experimental model, and ATG was administered continuously for 90 days. Novel object recognition, Y-maze, and Morris water maze were used to evaluate the therapeutic effect of ATG on memory impairment in AD mice. Immunohistochemical and immunofluorescence analyses were used to evaluate the effects of ATG on tau hyperphosphorylation and neuroinflammation, respectively. Finally, proteomics techniques were used to explore the possible mechanism of ATG.

KEY FINDINGS

ATG significantly improved memory impairment in pR5 mice and inhibited tau phosphorylation in the hippocampus and neuroinflammation in the cortex. According to the proteomic analysis, the altered cognitive function of ATG was associated with the proteins of the tricarboxylic acid cycle and the electron transport chain.

CONCLUSION

These results suggest that ATG is a potential therapeutic agent for diseases related to aberrant energy metabolism that can treat AD by improving mitochondrial function.

In Vitro Permeability Study of Homotaurine Using a High-Performance Liquid Chromatography with Fluorescence Detection Pre-Column Derivatization Method

Homotaurine (HOM) is considered a promising drug for the treatment of Alzheimer's and other neurodegenerative diseases. In the present work, a new high-performance liquid chromatography with fluorescence detection (HPLC-FLD) (λex. = 340 nm and λem. = 455 nm) method was developed and validated for the study of substance permeability in the central nervous system (CNS). Analysis was performed on a RP-C18 column with a binary gradient elution system consisting of methanol-potassium phosphate buffer solution (pH = 7.0, 0.02 M) as mobile phase. Samples of homotaurine and histidine (internal standard) were initially derivatized with ortho-phthalaldehyde (OPA) (0.01 M), N-acetylcysteine (0.01 M) and borate buffer (pH = 10.5; 0.05 M). To ensure the stability and efficiency of the reaction, the presence of different nucleophilic reagents, namely (a) 2-mercaptoethanol (2-ME), (b) N-acetylcysteine (NAC), (c) tiopronin (Thiola), (d) 3-mercaptopropionic acid (3-MPA) and (e) captopril, was investigated. The method was validated (R2 = 0.9999, intra-day repeatability %RSD < 3.22%, inter-day precision %RSD = 1.83%, limits of detection 5.75 ng/mL and limits of quantification 17.43 ng/mL, recovery of five different concentrations 99.75-101.58%) and successfully applied to investigate the in vitro permeability of homotaurine using Franz diffusion cells. The apparent permeability (Papp) of HOM was compared with that of memantine, which is considered a potential therapeutic drug for various CNSs. Our study demonstrates that homotaurine exhibits superior permeability through the simulated blood-brain barrier compared to memantine, offering promising insights for enhanced drug delivery strategies targeting neurological conditions.

In vitro and in silico cholinesterase inhibitory potential of metabolites from Laurencia snackeyi (Weber-van Bosse) M. Masuda

Alzheimer's disease (AD) is a neurodegenerative disease that causes deterioration in intelligence and psychological activities. Yet, till today, no cure is available for AD. The marine environment is an important sink of bioactive compounds with neuroprotective potential with reduced adverse effects. Recently, we collected the red algae Laurencia snackeyi from Terumbu Island, Malaysia which is known to be rich in halogenated metabolites making it the most sought-after red algae for pharmaceutical studies. The red alga was identified based on basic morphological characteristics, microscopic observation and chemical data from literature. The purplish-brown algae was confirmed a new record. In Malaysia, this species is poorly documented in Peninsular Malaysia as compared to its eastern continent Borneo. Thus, this study intended to investigate the diversity of secondary metabolites present in the alga and its cholinesterase inhibiting potential for AD. The extract inhibited both acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) with IC50 values of  14.45 ± 0.34 μ g mL-1 and 39.59 ± 0.24 μ g mL-1, respectively. Subsequently, we isolated the synderanes, palisadin A (1), aplysistatin (2) and 5-acetoxypalisadin B (3) that was not exhibit potential. Mass spectrometry analysis detected at total of 33 additional metabolites. The computational aided molecular docking using the AChE and BChE receptors on all metabolites shortlisted 5,8,11,14-eicosatetraynoic acid (31) and 15-hydroxy-1-[2-(hydroxymethyl)-1-piperidinyl]prost-13-ene-1,9-dione (42) with best inhibitory properties, respectively with the lowest optimal combination of S-score and RMSD values. This study shows the unexplored potential of marine natural resources, however, obtaining sufficient biomass for detailed investigation is an uphill task. Regardless, there is a lot of potential for future prospects with a wide range of marine natural resources to study and the incorporation of synthetic chemistry, in vivo studies in experimental design.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03725-6.

Astaxanthin ameliorates dopaminergic neuron damage in paraquat-induced SH-SY5Y cells and mouse models of Parkinson's disease

Parkinson's disease (PD) is the second largest neurodegenerative disorder caused by the decreased number of dopaminergic (DAc) neurons in the substantia nigra pars compacta (SNpc). There is evidence that oxidative stress can contribute degeneration of DAc neurons in SNpc which is mainly caused by apoptotic cell death. Thus, suppressing oxidative stress and apoptosis of DAc neurons is an effective strategy to mitigate the progress of PD. Astaxanthin (AST) is a carotenoid, which mainly exists in marine organisms and is a powerful biological antioxidant. In this study, we aimed to determine the neuroprotective effect of AST on paraquat (PQ) -induced models of PD in vitro and in vivo. Here, we showed that AST significantly enhanced cell survival of SH-SY5Y cells against PQ toxicity by suppressing apoptotic cell death and oxidative stress. Moreover, we found that AST significantly ameliorated PQ-induced behavioral disorders associated with PD in C57BL/6 J mice and the damage to DAc neurons in the SNpc of mice. Lastly, we found that the neuroprotective effects of AST were conducted through inhibiting PQ-induced activation of MAPK signaling. In conclusion, our study indicates that AST had a strong protective effect on PQ-induced oxidative stress and antagonized apoptotic cell death in SH-SY5Y cells and PQ-induced mice PD model, which might provide new insights of AST for PD treatment.