Antioxidant and Cell-Signaling Functions of Hydrogen Sulfide in the Central Nervous System

Hydrogen sulfide (HS), a toxic gaseous molecule, plays a physiological role in regulating homeostasis and cell signaling. HS is produced from cysteine by enzymes, such as cystathionine -synthase (CBS), cystathionine -lyase (CSE), cysteine aminotransferase (CAT), and 3-mercaptopyruvate sulfurtransferase (3MST). These enzymes regulate the overall production of HS in the body. HS has a cell-signaling function in the CNS and plays important roles in combating oxidative species such as reactive oxygen species (ROS) and reactive nitrogen species (RNS) in the body. HS is crucial for maintaining balanced amounts of antioxidants to protect the body from oxidative stress, and appropriate amounts of HS are required to protect the CNS in particular. The body regulates CBS, 3MST, and CSE levels in the CNS, and higher or lower levels of these enzymes cause various neurodegenerative diseases. This review discusses how HS protects the CNS by acting as an antioxidant that reduces excessive amounts of ROS and RNS. Additionally, HS regulates cell signaling to combat neuroinflammation and protect against central neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS).