Role of hydrogen sulfide in cognitive deficits: Evidences and mechanisms.

Hydrogen sulfide (H2S) is a gaseous molecule and is endogenously produced in the brain by cystathionine beta-synthase, 3-mercaptopyruvate-sulfurtransferase, cysteine aminotransferase and cystathionine γ-lyase. Physiologically, H2S acts as a neuromodulator and regulates synaptic activity of neurons and glia to promote the development of long-term potentiation. A decrease in H2S levels in the brain and plasma has been directly correlated with the degree of severity of Alzheimer disease in patients. A large number of studies have shown a decrease in the H2S levels in experimental models of cognitive dysfunction and exogenous administration of sodium hydrosulfide (NaHS), a H2S donor, has been shown to prevent the development of memory deficits. The beneficial effects of H2S in different models has been ascribed to decrease in neuroinflammation, up-regulation of antioxidant defense, decrease in endoplasmic reticulum (ER) stress, inhibition of phosphatidylinositol 3-kinase (PI3-K)/Akt signaling, inhibition of mitogen activated protein (MAP) kinases, decrease in glutamate and normalization of NMDA receptors, inhibition of matrix metalloproteinases (MMPs), up-regulation of silent information regulator 1 (Sirt 1) and preservation of mitochondrial function. The present review describes the role of H2S in different models of cognitive deficits and human subjects along with possible mechanisms.