Adzuki bean ( Vigna angularis) extract reduces amyloid-β aggregation and delays cognitive impairment in Drosophila models of Alzheimer's disease

Abstract

Background/objectives: Alzheimer's disease is a neurodegenerative disease that induces symptoms such as a decrease in motor function and cognitive impairment. Increases in the aggregation and deposition of amyloid beta protein (Aβ) in the brain may be closely correlated with the development of Alzheimer's disease. In this study, the effects of an adzuki bean extract on the aggregation of Aβ were examined; moreover, the anti-Alzheimer's activity of the adzuki extract was examined.

Materials/methods: First, we undertook thioflavin T (ThT) fluorescence analysis and transmission electron microscopy (TEM) to evaluate the effect of an adzuki bean extract on Aβ₄₂ aggregation. To evaluate the effects of the adzuki extract on the symptoms of Alzheimer's disease in vivo, Aβ₄₂-overexpressing Drosophila were used. In these flies, overexpression of Aβ₄₂ induced the formation of Aβ₄₂ aggregates in the brain, decreased motor function, and resulted in cognitive impairment.

Results: Based on the results obtained by ThT fluorescence assays and TEM, the adzuki bean extract inhibited the formation of Aβ₄₂ aggregates in a concentration-dependent manner. When Aβ₄₂-overexpressing flies were fed regular medium containing adzuki extract, the Aβ₄₂ level in the brain was significantly lower than that in the group fed regular medium only. Furthermore, suppression of the decrease in motor function, suppression of cognitive impairment, and improvement in lifespan were observed in Aβ₄₂-overexpressing flies fed regular medium with adzuki extract.

Conclusions: The results reveal the delaying effects of an adzuki bean extract on the progression of Alzheimer's disease and provide useful information for identifying novel prevention treatments for Alzheimer's disease.

Keywords: Adzuki bean; alzheimer disease; amyloid beta; drosophila.

Fig. 1. Effect of adzuki bean extract on in vitro Aβ₄₂ aggregation.

(A) The Aβ₄₂ solution was incubated at 37℃ for 24 h in the absence (white bar) or presence (black bar) of various concentrations of the adzuki extract (0.01–1 mg/mL). The samples were evaluated by examining ThT fluorescence. Emission wavelength was monitored at 490 nm and excitation at 446 nm. The results are expressed as Means±SEM for three independent determinations. ^* P < 0.05, ^** P < 0.01 compared with the control, n = 3. (B) TEM results; the Aβ₄₂ solution was incubated at 37℃ for 24 h in the absence or presence of indicated concentrations of the adzuki extract. In each case, the scale bar represents 200 nm.

Fig. 2. Intake of adzuki bean extract reduces the Aβ₄₂ levels in the brain of Aβ₄₂-overexpressing flies.

Aβ₄₂-overexpressing flies were grown on regular medium (Aβ₄₂) or medium containing adzuki extract (Aβ₄₂+Adzuki). At 15 days old, Aβ₄₂ levels in fly head lysates were quantified by ELISA. Results are expressed as Means±SEM for three independent determinations. ^* P < 0.05 compared with Aβ₄₂ (grown on regular medium) n = 60.

Fig. 3. Intake of adzuki bean extract increases the locomotor activity of Aβ₄₂-overexpressing flies.

Control flies (carrying the Aβ₄₂ transgene but not expressing it) were grown on regular medium (control) or on medium containing adzuki extract (Control+Adzuki), and Aβ₄₂-overexpressing flies were grown on regular medium (Aβ₄₂) or medium containing adzuki extract (Aβ₄₂+Adzuki). All fly groups underwent climbing assays in the indicated days after eclosion. Results show the percentage of flies climbing to the top of the vial after 18 seconds. The results are expressed as Means±SEM for three independent determinations. Means with different letters are significantly different, P < 0.05, whereas means with similar letters are not different from each other; n > 90.

Fig. 4. Intake of adzuki bean extract increases the learning and memory abilities of Aβ₄₂-overexpressing flies.

Control flies (carrying the Aβ₄₂ transgene but not expressing it) grown on regular medium (Control) or medium containing adzuki extract (Control+Adzuki) and Aβ₄₂-overexpressing flies grown on regular medium (Aβ₄₂) or medium containing adzuki extract (Aβ₄₂+Adzuki) were tested using single-cycle olfactory training and memory assays in the indicated days after eclosion. The results are expressed as Means±SEM for three independent determinations. Means with different letters are significantly different, P < 0.05, whereas means with similar letters are not significantly different, n > 300.

Fig. 5. Intake of adzuki bean extract increases the lifespan of Aβ₄₂-overexpressing flies.

Survival rates of control flies (carrying the Aβ₄₂ transgene but not expressing it) grown on regular medium (Control) or medium containing adzuki extract (Control+Adzuki) and Aβ₄₂ flies grown on regular medium (Aβ₄₂) or medium containing adzuki extract (Aβ₄₂+Adzuki) were analyzed using survival assays. Kaplan-Meier and log-rank analyses revealed that median survival times for Aβ₄₂-overexpressing flies grown on regular medium and grown on medium containing adzuki extract were significantly different (32.8 days and 45.1 days, respectively, P < 0.001, n > 200).