Continuous exposure to α-glycosyl isoquercitrin from developmental stages to adulthood is necessary for facilitating fear extinction learning in rats

Alpha-glycosyl isoquercitrin alleviates subchronic social defeat stress-induced depression symptoms by modulating the microbiota-gut-brain axis in mice

AIMS

Increasing evidence suggests a link between gut microbial dysbiosis and the pathogenesis of depression. Alpha-glycosyl isoquercitrin (AGIQ), consisting of isoquercitrin and its glycosylated quercetin, has beneficial effects on the gut microbiome and brain function. Here, we detected the potential antidepressant impact of a four-week administration of AGIQ and its underlying mechanisms using a mouse model of depression.

MAIN METHODS

Male C57BL/6 mice were orally administered AGIQ (0.05 % or 0.5 % in drinking water) for 28 days; subchronic social defeat stress was performed in the last 10 days. Behavior tests were conducted to assess anxiety and depressive-like behaviors. Additionally, evaluations encompassed 5-hydroxytryptamine (5-HT) levels, the gut microbiota composition, lipopolysaccharide (LPS) concentrations, short-chain fatty acids levels, and intestinal barrier integrity changes.

KEY FINDINGS

AGIQ significantly alleviated depression-like behaviors and increased hippocampal 5-HT levels. Further, AGIQ mitigated stress-induced gut microbial abnormalities and reduced the levels of LPS in the serum, which affected the relative gene expression levels of 5-HT biosynthesis enzymes in vitro. Furthermore, AGIQ reversed the reduced butyrate levels in cecal contents and improved the impaired intestinal barrier by increasing the expression of colonic zonula occluden-1 (ZO-1) and occludin, thereby decreasing LPS leakage.

SIGNIFICANCE

Our results suggest that AGIQ could improve stress-induced depression by regulating the gut microbiome, which inhibits LPS production and maintains the gut barrier. This is the first report on the potential effect of AGIQ on depression via the gut microbiota-brain axis, shedding new light on treatment options.

Potential Effects of Alpha-Glycosyl Isoquercitrin on Memory by Altering the Gut Microbiota-Blood-Brain Axis in Mice

Alpha-glycosyl isoquercitrin (AGIQ), composed of isoquercitrin and glycosylated quercetin, has multiple biological effects. Here, we further examined the influence of AGIQ on brain function and provided its potential mechanism. Male C57BL/6 mice were treated with 0, 0.005, and 0.05% AGIQ in drinking water for 4 weeks prior to behavioral testing. Behavior tests showed that 0.05% AGIQ treatment significantly improved learning and memory function without affecting emotion. In the hippocampus, the gene expression of antioxidative defense enzymes was upregulated after 0.05% AGIQ treatment. In contrast, AGIQ caused significant alterations in the microbial abundance of genera Akkermansia, Bifidobacterium, and Alistipes associated with memory function. Metabolomics analysis identified that taurine concentration was significantly increased in serum and hippocampus from AGIQ-treated mice. The correlation analysis suggested that elevated serum taurine levels were closely related to the abundance of Akkermansia, indicating the underlying crosstalk of gut microbiota and serum metabolites. In vitro fecal culture further demonstrated that AGIQ could increase the level of Akkermansia. Taurine could exert antioxidant activity in SH-SY5Y neuroblastoma cell lines in vitro. Finally, vancomycin-induced alterations of gut microbiota attenuated the taurine increases in the serum and the antioxidant gene level in the hippocampus by AGIQ. Taken together, it is likely that AGIQ could increase genus Akkermansia abundance and ultimately increase taurine levels in serum and hippocampus to improve learning and memory function, relying on the gut microbiota-blood-brain axis. Our results supply a new view for understanding effects of AGIQ on brain function.

Amelioration of lipopolysaccharides-induced impairment of fear memory acquisition by alpha-glycosyl isoquercitrin through suppression of neuroinflammation in rats

This study investigated the role of neuroinflammation in a lipopolysaccharides (LPS)-induced cognitive dysfunction model in rats using an antioxidant, α-glycosyl isoquercitrin (AGIQ). Six-week-old rats were dietary treated with 0.5% (w/w) AGIQ for 38 days, and LPS at 1 mg/kg body weight was administered intraperitoneally once daily on Days 8 and 10. On Day 11, LPS alone increased or tended to increase interleukin-1β and tumor necrosis factor-α in the hippocampus and cerebral cortex. Immunohistochemically, LPS alone increased the number of Iba1⁺ and CD68⁺ microglia, and GFAP⁺ astrocytes in the hilus of the hippocampal dentate gyrus (DG). AGIQ treatment decreased or tended to decrease brain proinflammatory cytokine levels and the number of CD68⁺ microglia in the DG hilus. In the contextual fear conditioning test during Day 34 and Day 38, LPS alone impaired fear memory acquisition, and AGIQ tended to recover this impairment. On Day 38, LPS alone decreased the number of DCX⁺ cells in the neurogenic niche, and AGIQ increased the numbers of PCNA⁺ cells in the subgranular zone and CALB2⁺ hilar interneurons. Additionally, LPS alone decreased or tended to decrease the number of synaptic plasticity-related FOS⁺ and COX2⁺ granule cells and AGIQ recovered them. The results suggest that LPS administration induced acute neuroinflammation and subsequent impairment of fear memory acquisition caused by suppressed synaptic plasticity of newborn granule cells following disruptive neurogenesis. In contrast, AGIQ exhibited anti-inflammatory effects and ameliorated LPS-induced adverse effects. These results suggest that neuroinflammation is a key factor in the development of LPS-induced impairment of fear memory acquisition.

Progressive disruption of neurodevelopment by mid-gestation exposure to lipopolysaccharides and the ameliorating effect of continuous alpha-glycosyl isoquercitrin treatment

We investigated the effect of lipopolysaccharide (LPS)-induced maternal immune activation used as a model for producing neurodevelopmental disorders on hippocampal neurogenesis and behaviors in rat offspring by exploring the antioxidant effects of alpha-glycosyl isoquercitrin (AGIQ). Pregnant Sprague-Dawley rats were intraperitoneally injected with LPS (50 μg/kg body weight) at gestational days 15 and 16. AGIQ was administered in the diet to dams at 0.5% (w/w) from gestational day 10 until weaning at postnatal day 21 and then to offspring until adulthood at postnatal day 77. During postnatal life, offspring of LPS-injected animals did not show neuroinflammation or oxidative stress in the brain. At weaning, LPS decreased the numbers of type-2b neural progenitor cells (NPCs) and PCNA⁺ proliferating cells in the subgranular zone, FOS-expressing granule cells, and GAD67⁺ hilar interneurons in the dentate gyrus. In adulthood, LPS decreased type-1 neural stem cells, type-2a NPCs, and GAD67⁺ hilar interneurons, and downregulated Dpysl3, Sst, Fos, Mapk1, Mapk3, Grin2a, Grin2b, Bdnf, and Ntrk2. In adults, LPS suppressed locomotor activity in the open field test and suppressed fear memory acquisition and fear extinction learning in the contextual fear conditioning test. These results indicate that mid-gestation LPS injections disrupt programming of normal neurodevelopment resulting in progressive suppression of hippocampal neurogenesis and synaptic plasticity of newborn granule cells by suppressing GABAergic and glutamatergic neurotransmitter signals and BDNF/TrkB signaling to result in adult-stage behavioral deficits. AGIQ ameliorated most aberrations in hippocampal neurogenesis and synaptic plasticity, as well as behavioral deficits. Effective amelioration by continuous AGIQ treatment starting before LPS injections may reflect both anti-inflammatory and anti-oxidative stress effects during gestation and neuroprotective effects of continuous exposure through adulthood.

Enzymatically Modified Isoquercitrin: Production, Metabolism, Bioavailability, Toxicity, Pharmacology, and Related Molecular Mechanisms

Quercetin and its glycosides, such as isoquercitrin or rutin, are among the most ubiquitous flavonoids present in plants. They possess numerous health-promoting properties, whose applicability is, however, limited by poor water solubility and absorption issues. Enzymatically modified isoquercitrin (EMIQ) is an isoquercitrin derivative obtained from rutin via enzymatic transformations that greatly enhance its bioavailability. Due to advantageous reports on its safety and bioactivity, EMIQ is currently gaining importance as a food additive and a constituent of dietary supplements. This review summarizes the thus-far-conducted investigations into the metabolism, toxicity, biological properties, and molecular mechanisms of EMIQ and presents a comprehensive characterization of this valuable substance, which might represent the future of flavonoid supplementation.

Ameliorating effect of continuous alpha-glycosyl isoquercitrin treatment starting from late gestation in a rat autism model induced by postnatal injection of lipopolysaccharides

The present study investigated the role of neuroinflammation and brain oxidative stress induced by neonatal treatment with lipopolysaccharides (LPS) on the development of autism spectrum disorder (ASD)-like behaviors and disruptive hippocampal neurogenesis in rats by exploring the chemopreventive effects of alpha-glycosyl isoquercitrin (AGIQ) as an antioxidant. AGIQ was dietary administered to dams at 0.25% or 0.5% (w/w) from gestational day 18 until postnatal day (PND) 21 on weaning and then to pups until the adult stage on PND 77. The pups were intraperitoneally injected with LPS (1 mg/kg body weight) on PND 3. At PND 6, LPS alone increased Iba1+ and CD68+ cell numbers without changing the CD163+ cell number and strongly upregulated pro-inflammatory cytokine gene expression (Il1a, Il1b, Il6, Nfkb1, and Tnf) in the hippocampus, and increased brain malondialdehyde levels. At PND 10, pups decreased ultrasonic vocalization (USV), suggesting the induction of pro-inflammatory responses and oxidative stress to trigger communicative deficits. By contrast, LPS alone upregulated Nfe2l2 expression at PND 6, increased Iba1+, CD68+, and CD163+ cell numbers, and upregulated Tgfb1 at PND 21, suggesting anti-inflammatory responses until the weaning period. However, LPS alone disrupted hippocampal neurogenesis at weaning and suppressed social interaction parameters and rate of freezing time at fear acquisition and extinction during the adolescent stage. On PND 77, neuroinflammatory responses had mostly disappeared; however, disruptive neurogenesis and fear memory deficits were sustained. AGIQ ameliorated most changes on acute pro-inflammatory responses and oxidative stress at PND 6, and the effects on USVs at PND 10 and neurogenesis and behavioral parameters throughout the adult stage. These results suggested that neonatal LPS treatment induced acute but transient neuroinflammation, triggering the progressive disruption of hippocampal neurogenesis leading to abnormal behaviors in later life. AGIQ treatment was effective for ameliorating LPS-induced progressive changes by critically suppressing initial pro-inflammatory responses and oxidative stress.