Study On Pulmonary Toxicological Of Three Inorganic Lead Compounds

As a kind of metallic element with high concentration in air particulate matter(PM), lead (Pb) can cause severe adverse effects to human even at low level, in particular for children. Lead is a nonvolatile element, mainly exists in particulate matter in air. It was found that major sources of Pb in PM of Shanghai were coal combustion, vehicle exhaust emissions and metallurgic dusts. After the phasing out of leaded gasoline in 1997 in Shanghai, the Pb concentration in total suspended particles (TSP) decreased drastically from 3400 ng/m3 in 1995 to 400 ng/m3 in 2003. From 2003-2007, the Pb concentration in PM2.5 was range (213-176 ng/m3) in summer and (61-91 ng/m3) in winter. However, it was still higher than other cities in the world. For example, the Pb average concentration in PM2.5 was only 25 ng/m3 in USA from 2003-2005. One of main pathways of Pb ingestion is by respiration. Blood lead levels were closely correlated to aerosol lead concentrations. There are a lot of studies about lead toxicity in home and abroad. Many of these studies focused on its neurological effects and potential carcinogenesis through gastrointestinal exposure. Usually studies focused on one specific compound of lead. However, there are few studies about comparing toxicities in different lead compounds through respiratory tract exposure.In this study, PbSO4 and PbCl2 were used as surrogate of soluble lead component and PbO as surrogate of insoluable component in PM. Our study includes two parts: The first part was to study the acute respiratory toxic effects of three lead compounds. The second part was to assess the cytotoxicities of three lead compounds in cultured macrophage and cultured alveolar epithelium cell II.The first part of the study was to observe the pulmonary toxic effects of three lead compounds in rats, and compare to PM. Male Wistar rats were randomly divided into five groups including saline control group, fine particulate matter exposure group (low, medium and high exposure dose were 1.6,8.0,40.0 mg/kg b.w. respectively), lead sulfate exposure group, lead chloride exposure group and lead oxide exposure group. The dosages for low, medium and high lead exposure groups were 13.5,67.5,337.5μg/kg b.w. respectively. Rats were inoculated via trachea with lead compounds or PM2.5 or laine once a day for consecutive 3 days. Twenty four hours after last exposure, the rats were sacrificed and brochoalveolar lavage fluid (BALF) were collected and analyzed to determine lactate dehydrogenase (LDH), alkaline phosphatase (AKP), acid phosphatase (ACP), albumin (ALB), total protein (TP), maleic dialdehyde (MDA) and superoxide dismutase (SOD). Blood lead levels and activity of 8-ALAD were were analysed. Lung pathological change was also observed under optic microscope.Results showed that PM2.5 and three lead compounds all could increase the percentage of neutrophils and reduce the percentage of macrophages in BALF. The level of LDH,AKP,ACP,TP,ALB and MDA in exposure groups were higher, while SOD level were lower than control group with a significant dose-response relationship. The effects induced by PM2.5 with the same dose lead were more significant than lead compounds. When compared with two other lead compounds, lead sulfate was the most significant one. Twenty four hours after the last exposure, the blood lead level in both lead ang PM2.5 dasage groups was increased and theδ-ALAD activity was lowered. And the decrease was in does dependence. The same effects induced by PM2.5 was obsereved more significant compared with that by lead compounds. Theδ-ALAD activity reduced by lead sulfate was most significant compared with that by two other lead compounds. Pathological examination showed the lung injury degree induced by leads exposure was getting worse with the raise of administration dosage. The pathological changes (Epithelial hyperplasia, inflammatory cells infiltrating and hyperemia edema) induced by lead compounds were similar with PM2.5. It was indicated that three lead compounds could induce pulmonary inflammation, oxidative stress injury, and could enter blood circulation quickly after respiratory exposure. The lead compounds, as components of PM2.5, play a certain role on lung injury. Because of its soluble character, lead sulfate was more toxic than two other lead compounds.The second part of the study was to obsereved in vitro cytotoxicity by different inorganic lead compounds on A549 cells and RAW264.7 cells. Cells were exposed to lead sulfate, lead chloride and lead oxide respectively with different concentrations (Ommol/L,0.01mmol/L,O.1mmol/L,1.Ommol/L). The viability of cells was checked by methyl thiazolyl tetrazolium (MTT) after 24 h and 48h exposure. Meantime, the activity of LDH,MDA and IL-6 in cell culture supernatant and the concentration of SOD in cells were be determined to evaluate the in vitro cytotoxicity of the three lead compounds.Both RAW 264.7 cell and A549 cell were observed the morphology changes after 48h exposure. After 24h exposure, three lead compounds were showed obviously toxic effects to RAW 264.7 and A549. Lead oxide (PbO) in low doses induced A549 cell proliferation but inhibited cell proliferation in high doses. While lead compounds inhibited RAW264.7 cell proliferation in any doses. After 48h exposure, lead compounds produced further inhibition effects to cell proliferation. The levels of LDH, MDA and IL-6 in all lead exposed groups were higher, while SOD level were lower than control group and both had a dose-effect relationship. When exposed to the same dose, A549 cell had more severe cell membrane injury, oxidative stress and inflammatory injury than RAW264.7 cell whatever after 24h or 48h exposure. The comparison for toxic indecies among three lead compounds showed that at 1.0mmol/L dosage lead sulfate was the most toxic after 24h exposure. However, after 48h exposure, the three leads compounds showed the similar toxicity degree to A549 and RAW264.7cells. The results above demonstrated that exposed to lead compounds could increase the activity of oxygen free radical on the cells' surface and induce lipid peroxidation on membrane of the cells meantime decrease the antioxidant capacity and induce increase of membrane permeability and change the functions and structures of the cells. According to the results, oxidative stress may be an important route for damage on A549 and RAW264.7 cells by respiratory exposure to lead compounds.This study compared the-toxicities among different lead compounds by in vivo and in vitro experiments. As a component of particulate matter, lead compounds could induce pulmonary toxic effects in different degrees and played a certain role on lung toxicity of PM.