Therapeutic Approach to Neurodegenerative Diseases by Medical Gases: Focusing on Redox Signaling and Related Antioxidant Enzymes

Table 1

Reducing ROS by medical gases, hydrogen (H₂), carbon monoxide (CO), and hydrogen sulphide (H₂S). These gases can increase endogenous antioxidant enzymes and stress response protein such as HO-1, SOD, and Hsp72. Hydrogen and hydrogen sulphide can directly react with ROS and show radical scavenging effects.

Medical gases	Direct reaction to ROS	Reference	Endogenous cytoprotective protein induction	Reference
Hydrogen (H2)	Radical scavenging; HO^•+H2→H2O+H^•	[67]	Increase superoxide dismutase (SOD)	[81]
			Increase bilirubin; ≒ induction of HO-1	[81]
			Activation of p38 MAPK signaling; p38→HSF1→Hsp72	[59]
Carbon monoxide (CO)			Activation of Nrf2 pathway; Nrf-2→HO-1	[61]
			Induce superoxide dismutase (SOD2) and HO-1	[62]
Hydrogen sulphide (H2S)	Radical scavenging	[64]	Upregulation of cytoprotective genes including HO-1	[65]
	2O2^•−+H2S→HS−SH+O2+2OH^−	[63]		[66]