Combined Effect Of Lead And Cadmium On Liver And Kidney Of Rats

Pb and Cd are widespread occupational and environmental toxicants and are recognized to be the most hazardous pollutants to various ecosystems and human health. Inhalation and ingestion are the two main routes of exposure to Pb and Cd, of which ingestion is the primary route of environmentally exposed people. They have been implicated as the cause of renal disturbances, lung insufficiency, bone lesions, cancer, and hypertension. Considering the wide distribution in potential health risk and the lack of co-exposure toxicological properties, the toxicological profiles of combined Pb and Cd must be clarified. In this study, we present a comprehensive toxicological evaluation on Pb and Cd co-exposure by performing acute and 90 day sub-chronic oral toxicity studies in SD rats. 1. Acute toxicity test In order to study the acute oral toxicity of lead nitrate[Pb(NO3)2] and cadmium chloride [CdCl2·2.5H2O] combined to Sprague-Dawley(SD) rats, lead nitrate and cadmium chloride were mixed according the method of equitoxic ratio mixing, and the effect of combinative toxicity were tested by Bliss method. The results were evaluated with Keplinger evaluation system; also the optical and electron microscopic were used to display the lesions differences between the groups that administrated orally with or without different dose of lead nitrate and cadmium chloride. The results showed that absolutely lethal dose (LD100) of combined exposure of lead and cadmium was 5062.00 mg/kg; the maximum tolerance concentration (MTD) was 1436.00 mg/kg; median lethal dose (LD50) is 2696.54 mg/kg, with the 95% confidence interval 2162.00-3362.89 mg/kg. Histopathological test and electron microscope results showed that the target organs of combined acute toxicity of lead nitrate and cadmium chloride were liver, kidney and spleen. Different degree of congestion and hemolysis of blood vessel, different degree of degeneration of parenchyma cell (such as blister degeneration and particle degeneration) and necrosis was observed in these target organs. Cell structure damages of the target organs were also observed in the electron micrographs. In conclusion, the acute toxicity oral of lead and cadmium had an additive effect and the liver, kidney and spleen of test rats showed the different level of acute toxicity injuries; the three organs may be the potential target organs for toxicity.2.Sub-chronic toxicity test 80 SD rats were randomly divided into three experiment groups and one control group. The rats in the three experiment groups were orally administrated with lead nitrate [Pb(NO3)2] and cadmium chloride[CdCl2·2.5H2O] combined solution at the doses of 29.96,89.88 and 269.65 mg/kg for 90 days respectively, and the rats in control group were orally administrated with water. A series of tests were carried out:① Blood were collected every 30 days to determine physiological and biochemical indexes.② at the end of 30,60 and 90 day of treatment, the levels of malondialdehyde (MDA), glutathione(GSH) and activities of total superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px) in the serum, liver and kidney were measured. ③ Changes in histopathology and ultrastructure of liver and kidney were detected by optical microscope and transmission electron microscope (TEM), respectively. ④ The expressions of metallothionein submits (MT-1, MT-2) in the liver and kidney were detected by immunohistochemistry method and RT-PCR, respectively. The results are as follows: ① The results showed in each poisoning groups that WBC, RBC and HGB was increased during early experiment period and then decreased; ALT, AST and BU was increased all the experiment time:GLU was decreased in the experiment time. Compared with control grcup, it showed the increase of TC at high-dose poisoning group and the decrease of TG at low-dose poisoning group The TP, ALB, GLO and CRE in the poisoning groups were not significantly different from those in the control group. And the hepatic cells and renal tubule epithelial cells showed granular degeneration, vacuolar degeneration and necrosis in poisoning groups. ② The activities of SOD, GSH-Px and CAT, the contents of reduced GSH in liver and renal cortex of rats in poisoning groups were significantly lower than those in control group (P<0.01). Meanwhile, contents of MDA in these poisoning groups increased remarkably (P<0.01). At the same time, changes of the above mentioned enzymes activities and MDA contents in serum were consistent with those of liver and renal cortex. ③ Compared with those of control group, the hepatic cells and renal tubule epithelial cells showed granular degeneration, vacuolar degeneration and necrosis in poisoning groups. Under electron microscopy, a serial of ultrastructural changes were observed:mitochondria swelling, cristae vague, partial cavity changes, endoplasmie reticulum expansion and fracture, chromatin margination and perinuclear space broadening in hepatocyte and renal tubule epithelial cells.④ MT mRNA and protein significantly increased (P< 0.01) in the liver and kidney of rats. Furthermore, the expression levels of MT-1 mRNA and MT-2 mRNA differed between theliver and kidney. Based on these results, the conclusions are as following:① Low-dose Pb-Cd combined exposure can significantly change physiological and biochemical indexes of blood to cause hepatic and renal pathological injury of SD rats.;② Exposure to lead and cadmium can induce the decrease of the anti-oxidative function in the livers and kidneys of rats, then made the hepatic and renal damage induced by oxidative stress worse. ③Obvious pathological changes and damage of many organelles in the liver and kidney were medicated by Pb-Cd combined. Among these organelles, mitochondria underwent the greatest changes:④ The increased expression level of MT-1 and MT-2 gene played an important role in the hepatotoxicity and nephrotoxicity induced by Pb-Cd combined.