The Protective Effect Of Hydrogen Sulfide On Uranium-induced Hepatic And Renal Toxicities In Rat

Background and Object: Uranium(U) is a potentially environmental hazardous metal,which has radioactive and heavy metal toxicities. The liver and kidney are the main target organ of U toxicities. It has been recognized that oxidative stress is responsible for U-induced hepatic and renal toxicities in mammalians. Hydrogen sulfide(H2S) has been recognized as the third physiological gasotransmitter(after NO and CO) with a variety of biology functions. H2 S has also been shown to have powerful anti-oxidative, anti-inflammatory, cytoprotective, as well as organ-protective properties. Accumulating evidences suggest that H2 S presents protective effect in many liver and kidney diseases.The current study was designed to investigate the effects of acute U intoxication in rats on endogenous H2 S production level and upstream events of oxidative stress in the liver and kidney of rats. Treatment with exogenous H2 S was used to determine the protective effect of H2 S and the specific molecular pathways in retarding U-induced deterioration of hepat and renal structure and function in order to provide a novel approach and theoretical basis for the prevention and treatment of uranium poisoning.Methods: In chapter 1, healthy adult Sprague Dawley rats were exposed to the different doses of U(2.5, 5 or 10mg/kg). After 2 d exposure to U, hepatic and renal function, histopathology and antioxidant levels in both tissues were explored in rats. The methylene blue spectrophotometric method was used to determine the levels of endogenous H2 S in serum, liver and kidney. The protein expression of Nrf2, CBS and CSE were detected by Western blotting analysis. In chapter 2, NaHS solution(28, or 56μmol/kg) was injected intraperitoneally 30 min after U(5mg/kg) injection. Then, the rats were treated with NaHS solution again on the second day. Rats were killed on 2 days after U injection. Assessments of histopathology, renal function, oxidative stress indicators were performed to investigate the effect of H2 S on U-induced nephrotoxicity. Western blotting analyses was used to investigate the protein expression of Nrf2 and its downstream target genes HO-l,NQO-1,GCLC,TXNRD-1, Nf-KB and its downstream target genes TNF-α, iNOS, COX-2, which were used to explore the mechanism of protective role of H2 S against uranium-induced nephrotoxicity. In chapter 3, the method of rat exposed to U and NaHS administration were the same with that in chapter 2. Rats were killed at 2days after U injection. Assessments of liver histopathology, hepatic function, Oxidative stress indicators were performed to investigate the effect of H2 S on U-induced hepatotoxicity.Results: In chapter 1, U expsure significantly increasing uranium content, the hepatic and renal functions injury, as well as serious pathological damage were observed in the liver and kidney of rats. The toxicity became more severe with higher U dose. In addition, U intoxication caused oxidative stress injuries in both liver and kidney tissues, led to the decrease of the antioxidant capacity and lipid peroxidation degree rise, may be one of the mechanism of U-induced toxicity. U administration in rats significantly reduced endogenous H2 S generation levels as well as expression levels of H2S-producing enzymes including CBS and CSE in the hepatic and renal tissues. Finally, U treatment of middle and high concentrations significantly decreased the expression, nuclear translocation and accumulation of Nrf2 in the liver and kidney tissues. In chapter 2, treatment with NaHS(28umol/kg or 56umol/kg) significantly has obvious detoxification for acute poisoning of uranium(5 mg/kg). The serum BUN and Cr levels significantly increased but UA decreased remarkably. The urine BUN, Cr and NAG concentrations were significantly raised. Compared to rats only exposed to U. NaHS administration in U-intoxicated rats decreased MDA content, increased GSH level and anti-oxidative enzymes activities like SOD, CAT, GPx, and produced amelioration in renal pathological damage induced by U. NaHS treatment in U-intoxicated rats activated U-inhibited protein expression and nuclear translocation of nuclear factor Nrf2, which increased protein expression of downstream target-Nrf2 genes HO-1, NQO-1, GCLC and TXNRD-1. NaHS administration in U-intoxicated rats inhibited U-induced nuclear translocation and phosphorylation of nuclear factorκB/p65, which decreased protein expression of target-p65 inflammatory genes TNF-α, iNOS and COX-2. In chapter 3, H2 S significantly decreased serum ALT and AST, increased the activity of SOD, CAT and GPX, increase the GSH content and decrease MDA level, and reduced the liver pathological damage.Conclusion: Decreasing of endogenous H2 S production by down-regulating protein expression of CBS and CSE through reducing Nrf2 level is involved in hepatotoxicity and nephrotoxicity in acute U-intoxicated rats. H2 S afforded protection to rat kidneys against U-induced adverse effects through induction of antioxidant defense by activating Nrf2 pathway and reduction of inflammatory response by suppressing Nf-κB pathway. H2 S prevented oxidative stress injury induced by U through improving the antioxidant capacity and decreasing the degree of lipid peroxidation.