HMOX1 and Cognitive impairment: Further studies have shown that pretreatment with quercetin and nano-quercetin could effectively regulate antioxidant levels, by down-regulating NF-κB, decreasing the levels of MDA and NO, as well as increasing brain serotonin levels in the rat brain and reducing neurodegeneration and cognitive deficits, and may protect against antioxidant stress cognitive deficits through modulating the Nrf2/HO-1/Keap-1 pathway (93) It was found that orally administered 100 mg/kg quercetin was detectable in the rat brain, suggesting that quercetin was able to cross the BBB (see Table 6) (94).