Sulforaphane and Gut-Brain Axis: An Overview of Its Impact on Intestinal Inflammation, Microbiota Composition, and Neurodegeneration

Sulforaphane (or SFN), an isothiocyanate bioactive compound synthesized from methionine, is mostly found in cruciferous vegetables like cabbage, Brussels sprouts, broccoli, etc. Upon consumption, a spontaneous reaction of SFN with glutathione (GSH) triggers the mercapturic acid pathway through which SFN is metabolized primarily in the liver and gastrointestinal tract. Also, SFN is unstable and degradable, and its production is easily affected by temperature, pH, and enzyme activity, which limits its application. Hence, in recent years, several studies have focused on the extraction and purification of SFN using novel techniques to optimize an easy-to-scale protocol that can also prevent the degradation of SFN. SFN is sought after due to its high bioavailability and therapeutic effects as a chemopreventive agent. However, this study focuses on the lesser-known beneficial effects of SFN on the gut-brain axis through which it can alleviate inflammatory bowel diseases, gut dysbiosis, neuroinflammation, and neurodegenerative diseases. SFN reduces the transcription of nuclear factor kappa B, production of pro-inflammatory cytokines, and alleviates gut dysbiosis by reducing the Firmicutes/Bacteroidetes ratio and pathogenic gut microbes, along with increasing the production of anti-inflammatory cytokines, tight junction proteins, and neurotransmitters. Furthermore, SFN can activate nuclear factor erythroid-derived 2 and antioxidant response elements, producing phase II antioxidant enzymes and reducing the accumulation of α-synuclein, tau, etc. Hence, this review examines sulforaphane, its extraction, metabolism, mechanism of action, and importance in the gut-brain axis.