Nootropic effect of Indian Royal Jelly against okadaic acid induced rat model of Alzheimer's disease: Inhibition of neuroinflammation and acetylcholineesterase

Abstract

Background: Royal jelly is an anti-inflammatory, antioxidant, and neuroprotective bee product. There are several sources for royal jelly and one of them is Indian Royal Jelly (IRJ). However, the neuroprotective actions of IRJ and the underlying molecular mechanisms involved are not well known.

Objective: To evaluate the neuroprotective effect of IRJ in the okadaic acid (OKA)-induced Alzheimer's disease (AD) model in rats.

Methods: In male Wistar rats, OKA was intracerebroventricularly (ICV) administered, and from day 7, they were treated orally with IRJ or memantine for 21 days. Spatial and recognition learning and memory were evaluated from days 27-34; employing the Morris water maze (MWM) and the novel object recognition tests (NORT), respectively. In vitro biochemical measurements were taken of the cholinergic system and oxidative stress markers. In silico docking was used to find the role of tau protein kinase and phosphatase in the pharmacological action.

Results: In OKA-induced rats, IRJ decreased the escape latency and path length in MWM and increased the exploration time for novel objects and the discrimination index in NORT. ICV-OKA rats had higher free radicals and cytokines that caused inflammation and their level of free radical scavengers was back to normal with IRJ treatment. IRJ increased the level of acetylcholine and inhibited acetylcholinesterase. Moreover, the in silico docking study revealed the strong binding affinity of 10-hydroxy-2-decenoic acid (10-HDA), a bioactive constituent of IR, to the tau protein kinases and phosphatases.

Conclusion: IRJ may serve as a nootropic agent in the treatment of dementia, and owing to its capacity to prevent oxidative stress and neuroinflammation, and increase cholinergic tone; it has the potential to be explored as a novel strategy for the treatment of dementia and AD. More studies may be needed to develop 10-HDA as a novel drug entity for AD.

Keywords: 10-Hydroxy-2-decenoic acid; Alzheimer's disease; Indian royal jelly; Neuroinflammation; Okadaic acid; Tau protein kinases.

Graphical abstract

Fig. 1

Representative high-performance liquid chromatography profile of standard 10-HDA (A) and Indian royal jelly (IRJ, B). Alpha-naphthol was used as internal standard (IS). Peak was obtained at same time after 10-HDA or IRJ sampling at 6.03 min and for IS at 14.02 min. Quantification assay showed the highest concentration of 10-HDA in IRJ II (Inset).

Fig. 2

Effects of memantine and IRJ on recognition (A,B) and spatial (C–E) learning and memory in okadaic acid (OKA) induced rat model of neurodegeneration. A. Exploration time of rats to familiar and novel objects during choice trial and Mean (Sec) ± SEM was statistically compared for significance using Student's t-test (**p < 0.01, ***p < 0.001). B. Discrimination index by employing One-way ANOVA followed by Dunnett's multiple comparison test (^###p < 0.001 vs Sham-operated group; **P < 0.01 and ***P < 0.001 vs OKA). C. Escape latency (Sec) effect was statistically compared by employing Two-way ANOVA followed by Tukey's multiple comparison post hoc test (^@p < 0.05, ^@@@p < 0.001 vs day 1 within the same group; ^#p < 0.05, ^##p < 0.01 vs Sham-operated group; *p < 0.05, **p < 0.01, ***p < 0.001 vs respective days in OKA group). D. Represents the mean time spend in each target quadrant (^###p < 0.001 vs Sham-operated group; **p < 0.01 and ***p < 0.001 vs OKA. E. Path length of rats on day 4 of acquisition trial. Analysis of path length was descriptive.

Fig. 3

Effect of oral treatment with memantine (10 mg/kg) and IRJ (100, 200 and 400 mg/kg) on acetylcholinesterase (AChE) inhibition (A), acetylcholine level (B) and AChE activity (C) in the brain. Values were expressed as mean ± SEM. ^##p < 0.01 and ^###p < 0.001 vs Sham-operated group; *p < 0.05, **p < 0.01 and ***p < 0.001 vs OKA group. (One-way analysis of variance followed by Dunnett's multiple comparison post hoc test).

Fig. 4

Effect of oral memantine (10 mg/kg) and IRJ (100, 200 and 400 mg/kg) treatment on nitric oxide (A), malondialdehyde (B), reduced glutathione (C), superoxide dismutase (D) and catalase (E) activity in brain. Values were expressed as mean ± SEM. ^#p < 0.05, ^##p < 0.01 and ^###p < 0.001 vs Sham-operated group; *p < 0.05, **p < 0.01 and ***p < 0.001 vs OKA group. (One-way analysis of variance followed by Dunnett's multiple comparison post hoc test).

Fig. 5

Effect of oral treatment with memantine (10 mg/kg) and IRJ (100, 200 and 400 mg/kg) on interleukin (IL)-1β (A), IL-6 (B) and tumor necrotic factor-α (TNF-α, C) level in the brain. Values were expressed as mean ± SEM. ^###p < 0.001 vs Sham-operated group; *p < 0.05, **p < 0.01 and ***p < 0.001 vs OKA group.

Fig. 6

Brain sections through hippocampus regions processed for hematoxylin and eosin staining. A. Normal control group, B. OKA control group, C. OKA-memantine (10 mg/kg) and D. OKA-IRJ (400 mg/kg). Small arrows are pointed at normal and degenerated neurons. Images were captured at 40X magnification.

Fig. 7

The figure represents docking zone of ligands aloisine A (a, d and g), memantine (b, e and h) and 10-HDA (c, f, and i) bonded with enzyme glycogen synthase kinase-3 (GSK-3β, 4ACC), cycline-dependent kinase-5 (Cdk5, 3O0G) and tau protein phosphatase-2A (PP2A, 2IAE) in 2D and 3D.