Preliminary Study Of Effects Of Selenium On Renal Pathological Damage Induced By Cadmium And Their Toxic Mechanism In Rats

?Background? Cadmium(Cd)classified as a group I carcinogen for humans is a severe environmental toxicants.The widespread cadmium dispersion in the environment can be absorbed into the human body through diet and water that lead to chronic cadmium accumulation is a potential threat to human health.It has been reported that excessive accumulation of Cd content has the effect of inhibiting immunity,carcinogenicity,teratogenicity,mutagenicity and systemic damage.As the main organ of cadmium excretion and accumulation,kidney is easy firstly to suffer from pathological damage and dysfunction.Current studies have shown that cadmium poisoning can lead to renal tubular dysfunction and irreversible renal injury[1],but the specific mechanism has not fully elucidated yet.Therefore,the kidney damage mechanism caused by cadmium and relevant control strategies has become the current research hotspot [2,3].Selenium(Se),as one of the essential trace elements of the human body,is the main component of antioxidant enzyme to remove oxygen free radical.However,it is also rare in the past that the effect of Se on the renal toxicity induced by Cd [4],and their relevant mechanisms of injury.The aim of this research was to systematically study the effect of Cd on renal injury and the interaction of Se and Cd,and to study the possible mechanism of Se and Cd interactions leading to oxidative damage,and to provide basic experimental information to control the chronic toxicity of cadmium.?Objective? 1.To investigate the relationship between the different dose and time of Cd and the degree of renal injury by establishing a model of chronic Cd exposure in rats.2.To study the effect of different doses of selenium on cadmium-induced renal injury in rats.3.Preliminarily investigate the effect of selenium on cadmium nephrotoxicity.?Methods? Sprague Dawley(SD)male rats were randomly divided into eight groups according to body weight:(1)control(deionized water,Con)group;(2)low dose cadmium(1 mg /kg Cd Cl2,1Cd)group;(3)middle dose cadmium(3 mg/kg Cd Cl2,3Cd)group;(4)high dose cadmium(5 mg/kg Cd Cl2,5Cd)group;(5)low dose selenium(0.05 mg/kg Na2 Se O3,0.05Se)group;(6)high dose selenium(0.05 mg/kg Na2 Se O3,0.1Se)group;(7)low selenium + high cadmium group(0.05 mg/kg Na2 Se O3+5 mg/kg Cd Cl2,0.05Se+5Cd);(8)High selenium + high cadmium group(0.1 mg /kg Na2 Se O3 + 5 mg/kg Cd Cl2,0.1Se+5Cd).The mode of administration was intragastric and the dose was 10 ml/kg.The body weight was recorded and the growth curves were depicted.The dosage was determined according to the literature and combined with the preliminary work and pre-experimentation [6].The rats were intragastric adminstration one time every day for 3 months.And then the model of chronic Cd exposure in rats was established to investigate the relationship between the different dose and time of Cd and the degree of renal injury,also the interaction of Se andCd.Six rats of each group were sacrificed at the time of 1M,2M and 3M,and the blood samples were taken from the abdominal aorta.Kidneys of the rats were removed by autoclavable surgical instruments and weighted to calculate the renal index.The levels of Cd and Se in blood and renal cortex were detected by inductively coupled plasma mass spectrometry(ICP-MS).The levels of urea nitrogen(BUN)and creatinine(SCr)in serum were measured by Hitachi 7020 automatic biochemical analyzer to evaluate renal function.Kidney paraffin sections were made and stained with HE and observed by positive fluorescence microscopy.The frozen sections of kidney were stained with DHE and Mito SOX fluorescent probe,and the ROS levels were observed by laser confocal microscopy.The expression of SOD-1,SOD2,GPx-1,CAT,Bax,Bcl-2 and GRP78 were detected by Western Blot.?Results? 1?Exposure to cadmium can make the rats anorexia,rough-coated,emotional irritability,lower weight gain.Rats suffered with different doses of cadmium has no significant difference on kidney index(P>0.05),cadmium in the blood and renal cortex accumulated significantly.The content of cadmium in the blood increased with the dose rising at different time(r = 0.908,0.812,0827,and P<0.05),as same as the renal cortex(r = 0.849,0.821,0.944,P<0.05).With the prolongation of exposure time,the content of cadmium in blood of rats did not change significantly(P>0.05).The content of cadmium in the whole kidney increased gradually(P>0.05).2?After exposure to cadmium,the pathological changes of glomeruli and renal tubules were observed in rats,and with the increase of Cd Cl2 dose and time,the renal pathological damage was aggravated until the structure was completely destroyed.Ultrastructural observation showed that cadmium exposure could lead to the swelling of the mitochondria of glomerular mesangial cells.Renal tubular epithelial cell injury,especially mitochondrial damage,was seriously aggravated with the increase of Cd Cl2 dose and prolongation of exposure time.The renal function was evaluated by measuringthe levels of serum urea(BUN)and creatinine(SCr)in serum [5].The results showed that Cd Cl2 could impair renal function in rats,but there was no obvious trend.3?Low selenium dose(0.05 mg/kg Na2 Se O3)and high selenium dose(0.1mg/kg Na2 Se O3)were co-exposed with cadmium respectively.After 3M cadmium exposure the kidney index was decreased,selenium co-treatment group has a tendency of increasing but there was no significant difference between the two groups(P>0.05).Pathological results showed that compared with the control group,the 0.05 Se group could increase the severity of the renal tubular dilatation with the prolongation of exposure time,and 0.1Se group appeared early glomerular injury,then the damage is reduced but the renal tubular dilatation aggravated.After co-treatment with selenium and cadmium,the glomerular swelling in the 0.05Se+5Cd group was relieved and the interstitial hyperemia was alleviated.Over time,glomerular conditions continue to improve,but the expansion of the renal tubular gradually deteriorated.And 0.1Se+5Cd group not only failed to improve renal tissue damage but also increased renal tubular injury.Ultrastructural observation showed that 0.05 Se + 5Cd group had a limited protection on pathological changes of renal tissue,but it could significantly improve the ultrastructure damage of renal tissue,especially mitochondria,due to cadmium exposure.Despite in 0.1Se+5Cd group the glomerular ultrastructural damage caused by cadmium exposure had improved,for renal tubular epithelial cells,mitochondrial damage had no attenuation,and myeloid-like structure and endoplasmic reticulum expansion appeared.4?With the prolongation of exposure time and the dose of Cd Cl2 increased,the ROS levels of renal tissue gradually increased.When exposed to Cd Cl2 for 1M,the expression of SOD2,GPx-1 and CAT in renal tissue increased(r=0.854,0.975,0.918,P<0.05),which was positively correlated with the dose.The expression of SOD-1 was negatively correlated with the dose(r=-0.987,P<0.05).The expression of Bax/Bcl-2 in kidney tissue was increased in a dose-dependent manner.Meanwhile,the expression of GRP78 was also increased with the increase of Cd Cl2 dose.The contents of cadmium in blood and renal cortex of 5Cd group,0.05Se+5Cd group and 0.1Se+5Cd group were significantly increased compared with Con group after Cd co-treated with low selenium and highselenium(P<0.05).There was no significant change of the blood cadmium content in the 0.05 Se + 5Cd group and the 0.1Se+5Cd group compared with the 5Cd group(P>0.05).In renal cortex,the cadmium content in the 0.05Se+5Cd group was significantly higher than that in the 5Cd group(P<0.05 in 1M group and 3M,P>0.05 in 2M group),but there was no significant difference between the 0.1Se+5Cd group and the 5Cd group(P>0.05).Compared with the control group,the levels of ROS in the 0.05 Se group were not significantly changed,but the ROS in the 0.1Se group was significantly increased.Low selenium can inhibit intracellular ROS increasing(1M)caused by cadmium(5Cd group),but has no significant effect on the mitochondrial ROS levels increasing.High selenium had no significant effect on intracellular and mitochondrial ROS increasing caused by cadmium(5Cd group).?Conclusion? 1?Establishment of rat model of renal injury induced by chronic cadmium exposure A relative ideal model of renal injury induced by chronic cadmium exposure can be established after giving 5 mg/kg Cd Cl2 for 3 months.The damage of rat kidney caused by Cd exposure is dose-and time-dependent,and the degree of damage was related to Cd content in renal tissue.2?Low selenium intervention can protect cadmium-induced renal injury in rats,high selenium dry intervention aggravated the kidney damage The effect of selenium on renal injury induced by cadmium was related to selenium dose.The intervention of low selenium(0.05 mg/kg Na2 Se O3)can significantly improve the cadmium-induced renal injury in rats.However,the use of high dose selenium(0.1 mg/kg Na2 Se O3)can significantly aggravate renal pathological damage and renal tubular ultrastructural damage,and the mitochondria of renal tubular epithelial cells were the main target.3?Oxidative stress,mitochondrial damage and endoplasmic reticulum stress may be the mechanisms of renal injury induced by cadmium exposure After exposure to cadmium,the level of ROS in renal tissue was significantlyincreased,the redox balance was broken,the mitochondria of renal tubular epithelial cells were significantly damaged,and the changes were dose and time-dependent.In addition,the expression of endoplasmic reticulum stress marker protein GRP78 increased.4?Redox disorders may be the mechanism of that high selenium intervention aggravates cadmium-induced renal injury in rats.High selenium intervention can significantly increase kidney cadmium accumulation,can not significantly improve the cadmium-induced renal tissue ROS levels increasing,and pure selenium exposure can also promote ROS production,which suggests that selenium and cadmium co-treatment may lead to redox disorders,resulting in renal tissue damage.