The fate of Cd, Cu, Ca, Zn, and Fe in rat during the recovery period following cessation of repeated exposure to Cd

Correlation of cadmium-induced nephropathy and the metabolism of endogenous copper and zinc in rats

Female Wistar rats were injected (sc) every second day for 8 weeks with Cd (0.25 mg/kg) as CdCl2. After only a 2-week exposure, when cadmium (Cd) concentration in liver was about 13 micrograms/g, ultrastructural examinations revealed some irregular ergastoplasm systems and significant proliferation of smooth endoplasmic reticulum in the hepatocyte ultrastructure. The increase in Zn content occurred simultaneously with the increase in Cd concentration in the liver (Zn to Cd ratio was 1:1). In the kidneys after a 3-week exposure, when Cd concentration was 7 micrograms/g, the concentration of endogenous Cu increased. At the same time the urinary excretion of that metal was considerably higher than that of the control group. In the kidneys after a 4-week exposure, when Cd concentration in this organ exceeded 10 micrograms/g tissue, injured brush border microvilli and swollen mitochondria in the proximal convoluted tubular cells were seen. In renal corpuscules, fusion between the podocyte pedicles was also found. The changes in renal cortex ultrastructure became more pronounced when Cd concentration in kidney was increasing. Necrotic changes in the examined organ were observed when Cd concentration increased to about 30 micrograms/g tissue. The critical concentration in renal cortex of about 200 micrograms/g tissue should be revised. The present margin of safety with regard to risk of renal effects is small.

New aspects on the distribution and metabolism of essential trace elements after dietary exposure to toxic metals

Under present environmental conditions, an increase in pollution owing to metals such as cadmium (Cd), lead (Pb), and methylmercury (MeHg) must be expected. The resulting effects would be seen particularly in the food chain. The daily intake of toxic metals in various parts of the world is different and depends on both the dietary habits and the concentration in foodstuffs. Oral ingestion of these toxic metals perturbs the metabolism of essential elements, especially zinc (Zn), copper (Cu), iron (Fe), and selenium (Se). The elemental composition of body tissues and fluids is an indicator of the nutritional and pathological status of humans. This review will describe the dietary intake and gut absorption of essential and toxic elements. Furthermore, it will discuss threshold values, toxic effects in relation to body burden of toxic metals, the biological indices of exposure, and the interaction between toxic and essential elements. The overall ratio of Cu, Zn, Fe, and Se concentration to Cd in the human kidney is the lowest in comparison to Hg and Pb. Increased kidney copper and urinary losses may be common denominators in the manifestation of renal toxicity induced by heavy metals. Factors affecting availability and loss of copper should be identified and measured. The critical kidney concentration for Cd, Pb, and MeHg should be revised in relation to essential elements.

The effect of cadmium pretreatment on the disposition and excretion of methylmercury and trace elements (zinc, copper) in rats

Cadmium chloride (Cd) was injected s.c. into male rats at a dose rate of 3 mg Cd/kg 3 times a week for 4 weeks. The animals were maintained for administration of methylmercury (203 Hg) chloride at a dose of 3 mg CH3Hg/kg given p.o. 3 times a week for 2 weeks, followed by 3 weeks of recovery period. Animals were sacrificed 24 h after the final dose of MeHg, or 5 weeks after cessation of Cd administration. Cd-pretreatment significantly decreased total Hg concentration in the kidney and RBC and almost completely inhibited demethylation of MeHg in the kidney (from 32% to 3% of inorganic Hg). Cd-pretreatment did not affect urinary excretion of total Hg, but significantly increased daily excretion of total Hg in feces. MeHg given alone significantly increased renal but not hepatic copper levels and decreased copper in the plasma and brain. In Cd-pretreated rats, both renal and hepatic copper concentration were in the normal ranges. Zinc levels in Cd-pretreated rats significantly increased in the kidney, liver and brain but decreased in plasma (compared to control and MeHg-alone treated animals). From these results it can be concluded that Cd-pretreatment may decrease MeHg toxicity by increasing the fecal mercury excretion and by inhibiting the formation of inorganic mercury in the kidney, which is a more potent renal toxin than MeHg.