Millions of people suffer from Alzheimer's disease (AD) and Parkinson's disease (PD) worldwide. Due to their complex pathology, no effective pharmacological treatment has been found to date, despite extensive research. Developing new, effective therapeutic agents to cure these disease remains a major challenge. Although the cause of AD and PD remains illusive, numerous studies indicates that oxidative stress and neuro-inflammation lead to neurodegeneration in the central nervous system and play vital role in AD and PD morbidity and progression. Flavonoids, which are found widely in nature, exhibit anti-oxidative, anti-inflammatory, anti-mutative, anti-microbial, and neuroprotective properties, so have potential to treat these two kinds of diseases. In this review, we focus on the anti-oxidative and neuroprotective action of flavonoids in attenuating Alzheimer's and Parkinson's disease, and how they might be harnessed in the development of new pharmacological agents to treat these two diseases. Some flavonoid compounds, like hesperidin, naringin, naringenin, tangeretin, nobiletin, silibinin, Epigallocatechin-3-gallate, displayed to be effective in both AD and PD. Considerable studies have demonstrated the anti-AD and anti-PD effects of flavonoids through various in vitro and in vivo models. However, more rigorous studies are needed to be done for flavonoids to develop into effective drugs and apply them to clinical practice.

Major depressive disorder (MDD) is one of the most common mental health conditions, characterized by pervasive and persistent low mood, low self-esteem, and a loss of interest or pleasure in activities that are typically enjoyable. Despite decades of research into the etiology and pathophysiological mechanisms of depression, the therapeutic outcomes for many individuals remain less than expected. A promising new area of research focuses on stress-induced neuroinflammatory processes, such as the excessive activation and crosstalk of microglia and astrocytes in the central nervous system under stress, as well as elevated levels of pro-inflammatory cytokines, which are closely linked to the onset and progression of depression. This review summarizes the mechanisms through which neuroinflammation induces or promotes the development of depression, and also highlights the effective roles of small molecules with anti-inflammatory activity in the treatment of MDD. Understanding the specific mechanisms through which stress-induced neuroinflammation further impacts depression, and using technologies such as single-cell RNA sequencing to elucidate the specific subtypes and interactions of microglia and astrocytes in depression, is of great importance for developing more effective therapeutic strategies for MDD.