Table 4 Cited Properties of H₂S as a Medical Gas with Suggested Chemical/Biological Mechanisms.

radical scavenging antioxidant

• antioxidant inhibitor of peroxynitrite-mediated processes via activation of N-methly-D-aspartate (NMDA) receptors [82].

• shield cultured neurons from oxidative damage by increasing levels of glutathione [83].

• induce upregulation of HO-1, anti-inflammatory and cytoprotective genes [84, 85].

• inhibits myeloperoxidase and destroys H₂O₂ [86].

• mediates mitochondrial preservation in post hypoxic conditions that are ideal for mitochondrial permeability transition pore (MPTP) that would cause the mitochondria to break down and lead to cell death [56].

anti-apoptotic

• reduces IR induced apoptosis via reduction of cleaved caspase-3 and cleaved poly (ADP-ribose) polymerase (PARP) [87].

• protection of isolated mitochondria by decreasing Ca²⁺ loading via vascular smooth muscle K_ATP channel-mediated hyperpolarization [23, 38, 56] or inhibition of L-type Ca²⁺ channels.

• H₂S activated STAT3 and Protein Kinase C (PKC) inhibits the pro-apoptotic factor Bad and upregulated the prosurvival proteins Bcl-2 and Bcl-xl by altering phosphorylation [56].

• H₂S influences inactivation of pro-apoptotic pathways through survival pathway of extracellular-signal regulated kinase (ERK1/2)/mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI-3-kinase) [56].

anti-inflammatory

• inhibit leukocyte adherence in the rat mesenteric microcirculation during vascular inflammation [38].

decrease radiosensitivity

• transiently and reversibly inhibiting mitochondrial respiration [38].

metabolic alteration

• produces a "suspended animation-like" metabolic status with hypothermia and reduced oxygen demand in pigs (who received it intravenously) [88]. and mice (who received hydrogen sulfide via inhalation) [89, 90].

• mice breathing 80 ppm of H₂S for 6 hr reduced heart rate, core body temperature, respiratory rate and physical activity where as blood pressure remained unchanged [56].