Dynamic change of hydrogen sulfide during global cerebral ischemia–reperfusion and its effect in rats

Abstract

Hydrogen sulfide (H₂S) is a gaseous messenger and serves as an important neuromodulator in central nervous system. In the current study, we investigated the change of H₂S and cystathionine β-synthase (CBS), an H₂S-synthesizing enzyme at different time points of reperfusion following global cerebral ischemia in rats, and the effect of exogenous H₂S on global cerebral ischemia–reperfusion injury. First, we used global cerebral ischemia–reperfusion model by occlusion of bilateral common carotid arteries and vertebral arteries. Next, we measured H₂S levels in the hippocampus, cortex and plasma, the activity of H₂S-synthesizing enzymes and expression of CBS mRNA and protein in the hippocampus and cortex at 12 h, 24 h, 48 h, 72 h and 7 days of reperfusion following 15 min cerebral ischemia. Second, we pretreated rats with different doses of sodium hydrogen sulfide (NaHS), an H₂S donor and observed its effect on neuronal injury induced by 7 days of reperfusion after 15 min global cerebral ischemia. We found that when compared to sham group the amount of H₂S in the hippocampus was increased significantly at 12 h of reperfusion after cerebral ischemia, markedly decreased at 24 h, restored to the same level as that in sham group at 48 h and maintained at 72 h and 7 days. The same change tendency in the levels of H₂S was found in the cortex as described for the hippocampus. We found a similar change tendency in the activity of H₂S-synthesizing enzymes, CBS mRNA and protein expression to that in the H₂S level at different time points of reperfusion. Furthermore, while 180 μmol/kg NaHS pretreatment deteriorated the neuronal injury after global cerebral ischemia, 25 μmol/kg NaHS attenuated the neuronal injury. We suggest that a decrease of H₂S level at 24 h of reperfusion after global cerebral ischemia may be involved in neuronal injury after cerebral ischemia and lower concentration rather than higher concentration of exogenous H₂S may offer a protection against the neuronal injury induced by global cerebral ischemia–reperfusion.

Introduction

Hydrogen sulfide (H₂S) has been known as a toxic gas and environment pollutant. However, in recent years, there has been growing interest in the potential role of H₂S as an endogenous signaling molecule (Li and Moore, 2008, Wang, 2002). Endogenous H₂S is mainly formed from cysteine by cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE). CBS is mainly expressed in the brain, peripheral nervous system, liver and kidney, whereas CSE is mostly found in the liver, vascular smooth muscle and endothelial cells (Lowicka and Beltowski, 2007). Recently, Kimura group reported that endogenous H₂S could also be produced by 3-mercaptopyruvate along with cysteine aminotransferase along with cysteine aminotransferase in the brain (Shibuya et al., 2009). Physiological concentrations of H₂S potentiate the activity of the N-methyl-d-aspartate receptor and enhance the induction of hippocampal long-term potentiation, a synaptic model of learning and memory (Abe and Kimura, 1996). Mutant mice lacking CSE display pronounced hypertension indicating that H₂S is a physiologic vasorelaxant and regulator of blood pressure (Yang et al., 2008). These findings suggest that H₂S may play an important physiological function in the central nervous system as an endogenous neuromodulator (Abe and Kimura, 1996).

In some pathological states, H₂S-synthesizing enzymes are changed, and thereby H₂S is changed, which may regulate the pathological state. There are some controversial effects of H₂S in different pathological states. Exogenous H₂S is of benefit in animal models of hypertensive diseases (Qingyou et al., 2004), while the inhibition of the endogenous synthesis of H₂S is beneficial in various etiologies of shock (Hui et al., 2003, Mok et al., 2004). In ischemic conditions, inhibitors of H₂S synthesis reduce the infarct volume caused by middle cerebral artery occlusion (Qu et al., 2006). However, H₂S is produced by myocardial ischemia in sufficient amounts to limit myocardial injury (Geng et al., 2004, Sivarajah et al., 2006). Thus, H₂S may have both beneficial and/or detrimental effects depending on what pathological state and/or what phase in a certain pathological state. However, changes of H₂S in different phase during pathological state such as cerebral ischemia–reperfusion are not known. We therefore investigated the change of H₂S and H₂S-synthesizing enzymes at different time points of reperfusion following global cerebral ischemia in rats. Second, we determined the effect of different concentrations of exogenous H₂S on neuronal injury induced by global cerebral ischemia–reperfusion.