Early Injury Effects Of Low Arsenic On Liver And Kidney And Their Mechanism In Mice

Objective:(1) To investigate the effects of low arsenic induce lipid peroxidation and ultrastructure changes of liver and kidney in mice.(2) To find out histological distribution of DNA incorporated-Brdu by testing expression of Brdu in liver and kidney and provide toxicological basis for the damage mechanism of liver and kidney on early stage.Methods: ninety-six male KM mice were randomly divided into four groups. Mice were treated with arsenite exposure at 0ppb,50ppb, 500ppb and 5 000ppb in the drinking water which were provided ad libitum for 4w,6w and 8w. Then the mice were killed and liver and kidney samples were collected. The following indices were observed and determined: body weight, water consumption, forage consumption, organ coefficient of liver, kidney, lung and spleen, and changes in malondialdehyde(MDA), activity of superoxide dismutase (SOD) and glutathione peroxidas(GSH-PX). The morphological changes of liver and kidney were observed by light microscopy and eletricmicroscopy. And 5-bromodeoxyUridine(5-Brdu) was detected by immunohistochemical method.Results:(1)The body weight gains of the animals in medium group were significantly higher compared to the control group on the fourth week and fifth week, The body weight gains of the low group were significantly higher than the control on the second, third, fourth and fifth week. After 5 weeks, body weight gains of arsenic-treated groups showed sluggish increase and body weight of the high arsenic-treated group even decreased. (2) The content of MDA significantly increases and the activity of GSH-PX significantly decreases in arsenite exposure groups compared to the control group. During the fourth weeks and sixth weeks, SOD activities in low and medium group were significantly higher than the control , but decrease with the extension of time, it showed that increase initially and following by a declining trend.(3)In high arsenic-treated group we observed swelling, cytoplasm vacuole degeneration and nuclear pyknosis, fragmentation or dissolution in hepatocytes by light microscope. Glomenrulus appeared mild swelling and hyperemia, there was slight swelling in proximal tubule epithelial cells, but the boundary between cells are clear and there was no pathological changes in cytoplasm and nuclear. By Transmission Electron Microscopy, we observed that the number of fenestrate decreased significantly or even disappeared in middle dose group at the end of 6 weeks, and kupffer cell appeared to have passed through the endothelial fenestrations and established direct contact with the underlying hepatocytes. At the end of 8 weeks, some cristae of mitochondria decreased or loss,swelling and degranulation of endoplasmic reticulum in middle dose group were observed. In the high dose group, it showed deformation and vacuolization of mitochondria, the formation of basement membrane from discontinuous fenestrated structure of the liver sieve. At the end of 6 weeks, the middle dose group showed that glomerular microcirculatary endothelial cell appeared to mild hyperplasia and swelling, cytoplasmic processes slightly arch, part of podocytic processes fusion and basement membrane didn't change significantly, the high dose group showed that swelling of glomerular microcirculatary endothelial cell, thickening of the filtration membrane and fusion of the podocyte processes were found at the end of 8 weeks. Renal tubular epithelial cell nuclear malformation,nuclear membrane unsmooth, heterochromatin stacking on the periphery of nuclear membrane, and swelling microvilli distorted, swelling, loss, and loose arrangement were also observed. (4) The result of immunohistochemistry showed that Brdu mainly expressed in liver sieve and renal glomerulus, the average of optical density value significantly higher compare to the control.Conclusions:(1) Low arsenic could induce lipid peroxidation, the significant increase of MDA and the significant decrease of activity of GSH-PX in liver and kidney, the activity of SOD showed increase initially and following by a declining trend.(2) Low level arsenic cause damage to hepatic sinusoidal endothelial cell,hepatocytes and glomerular filtration membrane to different extent, it may associate with lipid peroxidation.(3) Exposure to low arsenic, liver sieve and glomerular filtration membrane were the major target in liver and kidney earlier injury.