Synergistic Neuroprotective Effects of a Natural Product Mixture against AD Hallmarks and Cognitive Decline in Caenorhabditis elegans and an SAMP8 Mice Model

Abstract

The study of different natural products can provide a wealth of bioactive compounds, and more interestingly, their combination can exert a new strategy for several neurodegenerative diseases with major public health importance, such as Alzheimer's disease (AD). Here, we investigated the synergistic neuroprotective effects of a mixed extract composed of docosahexaenoic acid, Ginkgo biloba, D-pinitol, and ursolic acid in several transgenic Caenorhabditis elegans (C. elegans) and a senescence-accelerated prone mice 8 (SAMP8) model. First, we found a significantly higher survival percentage in the C. elegans group treated with the natural product mixture compared to the single extract-treated groups. Likewise, we found a significantly increased lifespan in group of C. elegans treated with the natural product mixture compared to the other groups, suggesting synergistic effects. Remarkably, we determined a significant reduction in Aβ plaque accumulation in the group of C. elegans treated with the natural product mixture compared to the other groups, confirming synergy. Finally, we demonstrated better cognitive performance in the group treated with the natural product mixture in both AD models (neuronal Aβ C. elegans strain CL2355 and the SAMP8 mice model), confirming the molecular results and unraveling the synergist effects of this combination. Therefore, our results proved the potential of this new natural product mixture for AD therapeutic strategies.

Keywords: AD hallmarks; Alzheimer’s disease; C. elegans; SAMP8; aging; natural extracts; nutritional intervention.

Figure 1

Representative experimental design with schematic behavioral and molecular studies. L: larval stage; SAMR1: Senescence-Accelerated Mouse Resistant 1; SAMP8: Senescence-accelerated mouse prone 8; OFT: Open field test; NORT: Novel object recognition test.

Figure 2

Summary of the OS response in different C. elegans N2 (WT) groups after treatment with each extract treatment, natural product mixture, or vitamin C (58 µM). Values represented are mean ± standard error of the mean (SEM); n = 3 with 120–150 worms in each group. * p < 0.05; **** p < 0.0001. DHA: docosahexaenoic acid; Gb: Ginkgo biloba; UA: ursolic acid.

Figure 3

Kaplan–Meier curve for the survival of C. elegans on different extracts (A). The lifespan means of the C. elegans treated and control groups with DMSO 1% (B). Values represented are mean ± standard error of the mean (SEM); n = 3 with 60–70 worms in each group. * p < 0.05. DHA: docosahexaenoic acid; Gb: Ginkgo biloba; UA: ursolic acid.

Figure 4

Chemotaxis assay results in the neuronal Aβ strain CL2355. Values represented are mean ± standard error of the mean (SEM); n = 3 with 120–150 worms in each group. *** p < 0.001; ns: non-significant. DHA: docosahexaenoic acid; Gb: Ginkgo biloba; UA: ursolic acid.

Figure 5

Quantification of ThS-positive particles in the head region of the CL2006 strain (A). Representative images from each group tested (B). Values represented are mean ± standard error of the mean (SEM); n = 4 with 50–60 worms in each group. **** p < 0.0001. DHA: docosahexaenoic acid; Gb: Ginkgo biloba; UA: ursolic acid.

Figure 6

Results of the discrimination index (DI) of short-term memory (A), and long-term memory (B), from novel object recognition tests (NORT) in all Senescence-accelerated mouse prone 8; (SAMP8) groups. Results of the DI from object location test (OLT) (C). Values represented are mean ± standard error of the mean (SEM); n = 36 (SAMR1 control n = 12; SAMP8 control n = 12; SAMP8 natural product mixture n = 12). * p < 0.05; ** p < 0.01; *** p < 0.001; **** p < 0.0001. SAMR1: Senescence-Accelerated Mouse Resistant 1.