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Seasonal affective disorder (SAD) is a form of depression that is influenced by seasonal changes in weather and daylight. It commonly occurs in the dark, cool days of winter but can occur during other times of the year, as well. Approximately 10 percent of people worldwide experience SAD. A new study suggests that seasonal variation in the Nrf2 antioxidant pathway regulates winter depression-like behavior in fish.

Nrf2 (short for nuclear factor erythroid 2-related factor 2) is a cellular protein that regulates the expression of antioxidant and stress response proteins. Nrf2 functions within a biological pathway called Keap1-Nrf2-ARE, where it switches on the transcription of various cytoprotective proteins that protect against oxidative damage triggered by injury and inflammation.

The authors of the study exposed medaka, a type of fish that exhibits seasonal SAD-like differences in its behavior to either summer- or winter-like conditions. Then they examined the metabolites produced in their brains. They found evidence that winter-like conditions altered levels of 68 metabolites, some of which are associated with depression. In particular, winter-like conditions reduced levels of glutathione, a powerful antioxidant compound produced by the body’s cells. Glutathione helps prevent inflammation, a key driver in depression.

Then the study authors analyzed gene expression in the fish and found that winter-like conditions altered signaling pathways that are implicated in depression, including Nrf2. Results of a chemical screen indicated that celastrol, a plant-based compound commonly used in traditional Chinese medicine, activated Nrf2 signaling, which in turn induced the activity of Nrf2 target genes, including glutathione.

These findings demonstrate that celastrol could be beneficial in treating some of the symptoms associated with seasonal depression by switching on the activity of antioxidant pathways such as Nrf2. Interestingly, sulforaphane, an isothiocyanate compound derived from broccoli, is the most potent naturally occurring inducer of Nrf2 activity. Watch this clip featuring sulforaphane expert Dr. Jed Fahey in which he describes the importance of the Nrf2 pathway.

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