A Diet Containing Rutin Ameliorates Brain Intracellular Redox Homeostasis in a Mouse Model of Alzheimer’s Disease

**Background:** Alzheimer's disease (AD) is characterized by amyloid-β plaques and neurofibrillary tangles, with oxidative stress and glutathione (GSH) depletion occurring early in pathogenesis. Dietary flavonoids such as quercetin and its glycoside rutin have shown neuroprotective, anti-inflammatory, and antioxidant properties. This study aimed to determine whether a diet containing quercetin or rutin could ameliorate brain intracellular redox homeostasis and modulate AD-related molecular pathways in a transgenic mouse model of AD (TgAPP mice bearing the Swedish APP mutation).

**Methods:** TgAPP (Tg2576) mice and wild-type (WT) littermates, aged 6–7 weeks, were randomized into four groups (n=8/group): untreated TgAPP, quercetin-treated TgAPP, rutin-treated TgAPP, and untreated WT. Both male and female mice were studied. At 45 weeks of age, mice received a standard diet supplemented with quercetin or rutin at 200 ppm (≈30 mg/kg/day) for 4 weeks. After treatment, cortex and hippocampus were analyzed for: reduced (GSH) and oxidized (GSSG) glutathione levels (spectrofluorometric o-phthalaldehyde method); lipid peroxidation via thiobarbituric acid reactive substances (TBARs, expressed as MDA); enzymatic activities of SOD, CAT, GR, and GPx; BACE1 enzyme activity (fluorometric secretase assay); and gene expression of APP, BACE1, ADAM10, caspase-3, caspase-6, IL-1β, TNF-α, and IFN-γ by RT-PCR. Statistical analysis used one-way ANOVA with Newman–Keuls post-hoc test; p<0.05 was considered significant.

**Key Results:** TgAPP mice showed a significant decline in the GSH/GSSG ratio compared to WT, especially in the hippocampus, with males having a lower ratio than females. Both quercetin and rutin treatments significantly reversed this decline in the hippocampus (quercetin p<0.001; rutin p<0.05 vs. untreated TgAPP). In males, the ratio reached WT levels. Quercetin tended to increase GSH levels (p<0.05), while rutin tended to lower GSSG levels (p<0.05). MDA levels were significantly elevated in TgAPP vs. WT mice (p<0.001) in both brain regions and sexes; both flavonoids restored MDA to near WT levels. CAT activity was significantly decreased in TgAPP vs. WT mice (p<0.05); rutin increased CAT activity in the cortex and GR activity in the hippocampus in both sexes (p<0.05). BACE1 enzyme activity was approximately 10% higher in TgAPP vs. WT mice (p<0.05); both quercetin and rutin reduced this activity, with rutin showing a slightly greater effect in males. APP gene expression was >85% higher in TgAPP vs. WT mice (p<0.05); both flavonoids reduced expression by >45% (p<0.05), with more prominent effects in the hippocampus. No significant changes in BACE1 gene expression were observed. ADAM10 expression showed a non-significant increasing trend with rutin. Caspase-3 expression was >30% higher in TgAPP vs. WT hippocampi (p<0.05); quercetin and rutin significantly lowered hippocampal caspase-3 mRNA (p<0.05), with inhibition of ~17% in females and ~27% in males. IL-1β expression was ~20% higher in TgAPP vs. WT mice (p<0.05); both flavonoids reduced IL-1β to near WT levels (p<0.05). IFN-γ was ~30% higher in TgAPP males (p<0.05 in cortex); quercetin reduced cortical IFN-γ in males (p<0.05). No significant neurodegeneration or changes in glutamate receptor expression were observed.

**Clinical Implications:** This study demonstrates that dietary supplementation with quercetin or rutin, initiated at an asymptomatic stage in an AD mouse model, can restore brain glutathione redox homeostasis, reduce oxidative damage, lower BACE1 activity, and attenuate APP overexpression and neuroinflammation. The findings support the hypothesis that maintaining redox balance via flavonoid-rich diets may be a viable preventive strategy for early AD. Rutin showed slightly more consistent effects across multiple endpoints, making it a promising candidate for adjuvant dietary therapy. However, the authors caution that results from transgenic mouse models may not directly translate to human AD, and further studies are needed to determine optimal dosing and long-term safety.