Yasushi Nagai

Mode of existence of cadmium in rat liver and kidney after prolonged subcutaneous administration

Abstract The relationship between the mode of existence of cadmium in cells and its concentration in the liver and kidney was studied. Male Wistar rats were injected with 0.3 mg of Cd (as CdCl 2 ) per kilogram sc for 6 days per week and sacrificed by bleeding at Weeks 1, 4, 9, 12, and 16. The cadmium concentration reached a near-maximum at 12 weeks. The 27,000 g supernatants of the liver and kidney homogenates were chromatographed on Sephadex G-75. At 1 week more than 97% of the cadmium was bound to metallothionein in both organs. At 9, 12, and 16 weeks, most of the increased cadmium was bound to metallothionein, but four additional fractions of bound cadmium newly appeared. The cadmium content in these four fractions increased in a dose-related fashion. The ratios of the cadmium concentration in the fraction at 4, 9, 12, and 16 weeks to that of the fraction at 1 week were greater in the additional fractions than in metallothionein. If present in sufficiently high concentration, the cadmium ions in the additional fractions may cause damage to cells. Cd-induced hepatic and renal metallothioneins contained not only cadmium but also zinc, and the ratio of cadmium to zinc increased with the cadmium concentration in both organs. Though the cadmium tissue concentration was smaller in the kidney, the Cd/Zn ratio of metallothionein was greater in that organ. In conclusion, the distribution pattern of cadmium in the cells changes as the tissue concentration increases and the hepatic and renal metallothioneins differ significantly in the ratio of the cadmium content to the zinc content.

Sex-related differences in cadmium-induced lipid peroxidation in the rat

Male and female rats were dosed once a day for 2 days injection with 1.5 mg of Cd/kg as CdCl2. 24 hr after administration of cadmium, lipid peroxidation determined by estimation of malondialdehyde (MDA) was greatly increased in male rat liver, but was not in female rats. Cadmium in a larger dose of 4.5 mg/kg, subcutaneous single injection, significantly increased content of MDA in female rat liver. These results suggest that sex-related differences exist in the ability of cadmium to induce MDA formation in rat liver, although administration of cadmium causes the enhancement of MDA formation in both male and female rats. The reason why sex-related differences exist in lipid peroxidation of rat liver is discussed.

Effect of zinc deficiency on the accumulation of metallothionein and cadmium in the rat liver and kidney.

The effects of zinc (Zn) deficiency and repeated exposure to cadmium (Cd) on the accumulation and distribution of metallothionein (MT), Cd and Zn in the liver and kidney were studied. Male Sprague-Dawley rats were fed either a Zn-deficient (1 ppm) or a Zn-adequate (40 ppm) diet during the experiment, and the rats were injected subcutaneously with a cadmium chloride solution (1.0 mg Cd/kg of body weight, 5 days a week) for 4 weeks. Cadmium, Zn, and Cd-induced MT concentrations in the liver and kidney were lower in the Zn-deficient rats (−Zn + Cd) than in the Zn-adequate rats (+ Zn + Cd), while the content of Cd bound to high molecular weight proteins (HMWP) was greater in the Zn-deficient rats (−Zn + Cd). The Zn bound to Cd-induced MT was reduced to 30% in the liver and to 60% in the kidney of the Zn-deficient rats (−Zn + Cd) as compared with that of the Zn-adequate rats (+ Zn + Cd). In the kidney of Zn-deficient rats, exposure to Cd caused a decrease in essential Zn associated with HMWP as compared with that of Zn-adequate rats (+ Zn + Cd). Thus, Zn-deficiency affected the distribution of Cd in tissues, MT and HMWP and accelerated substantially Cd-induced Zn-deficiency in the kidney. Although the renal Cd concentration was lower in the Zn-deficient rats (−Zn + Cd) than in the Zn-adequate rats (+ Zn + Cd), exposure to Cd for four weeks resulted in glucosuria and an increase in liver and kidney weights in the Zn-deficient rats (−Zn + Cd), but not in the Zn-adequate rats (+ Zn + Cd). These results suggest that development of Cd toxicity is related to the Zn status of the body, to the accumulation of Cd in HMWP and to the amount of essential Zn associated with HMWP.

Sex-related differences in NADPH-dependent lipid peroxidation induced by cadmium

Male and female rats were dosed once a day for 2 days with injections of 1.5 mg Cd/kg. Formation of thiobarbituric acid reactive substances (TBA-RS) was significantly increased in male rat liver but not in the females. NADPH-dependent lipid peroxidation in vitro in microsomes derived from untreated rat liver was greater in males than in females. Furthermore, addition of cadmium (Cd) to microsomes isolated from male rat liver produced a dose-dependent potentiation of NADPH-dependent lipid peroxidation from low concentrations of Cd. In microsomes derived from females a significant increase in lipid peroxidation was observed only at high Cd concentrations. NADPH-dependent lipid peroxidation enhanced by Cd was greater in the males than in the females. These data suggest that a sex-related difference in the ability of Cd to induce lipid peroxidation in vivo in rat liver appears to be mediated partly through differences in hepatic microsomal NADPH-dependent lipid peroxidation.

Effect of cadmium administration upon urinary excretion of hydroxylysine and hydroxyproline in the rat

Abstract To investigate the effect of cadmium upon collagen metabolism, urinary excretion of hydroxylysine (Hyl) and its glycosides, glucosyl-galactosyl-hydroxylysine (Glc-Gal-Hyl) and galactosyl-hydroxylysine (Gal-Hyl), and also hydroxyproline (Hyp) was determined in rats treated with cadmium. Female Wistar rats were injected sc with 0.4 mg of cadmium/kg/day for 5 days per week. The 24-hr urine specimens were collected at 2, 8, and 13 weeks. At 2 weeks there were no distinguishable changes in urine between the control and the cadmium-treated groups. But at 8 and 13 weeks renal lesions appeared in the form of proteinuria and aminoaciduria. At these stages, the excretions of total Hyl and Hyp were significantly increased; excretions of Glc-Gal-Hyl, Gal-Hyl, and free Hyl were also increased. These results suggested that cadmium exposure caused an increase of collagen catabolism. Moreover, the molar ratio of Glc-Gal-Hyl Gal-Hyl of urine approached that of bone, so that the degradation of collagen might occur preferentially in bone.

Urinary excretion of metallothionein-I and its degradation product in rats treated with cadmium, copper, zinc or mercury

The metallothionein-I (MT-I) content of urine following administration of cadmium (Cd), copper (Cu), mercury (Hg) or zinc (Zn) to rats was determined by radioimmunoassay. Urinary excretion of MT-I was increased significantly after injection of each of these metals. Fractionation of urine from Cd-treated rats on Sephadex G-50 showed a single immunoreactive component corresponding to native MT-I, whereas in urine from Cu, Zn or Hg-treated rats 2 immunoreactive components corresponding to MT-I and a possible degradation production were observed. Since a comparable low molecular weight component corresponding to this degradation product was not detected to the same extent on fractionation of plasma from Cu-exposed rat, it seemed to be derived from degradation of MT in the kidney.

Increased urinary excretion of collagen metabolites in cadmium-metallothionein nephropathy

In order to investigate the effect of cadmium-metallothionein (Cd-MT) on renal reabsorption of collagen metabolites, urinary excretion of hydroxylysine (Hyl), glucosyl-galactosyl-Hyl (Glc-Gal-Hyl), galactosyl-Hyl (Gal-Hyl), and hydroxyproline (Hyp), which are unique collagen metabolites, was determined in rats. Administration of Cd-MT resulted in acute renal failure in the form of proteinuria, aminoaciduria and glycosuria. Protein content in urine was greatly increased 1 day after injection of Cd-MT and decreased from 5 days, while the maximum levels of excretion of amino acids and glucose were observed at 6 days post-injection. The urinary excretion of total Hyp and Hyl, including Glc-Gal-Hyl, Gal-Hyl and free Hyl, were significantly increased at 3, 6 and 8 days after injection of Cd-MT with the maximum level at 6 days. Moreover, the molar ratio of Glc-Gal-Hyl/Gal-Hyl of urine in the Cd-MT-treated group was almost the same as that in the controls. These results suggest that a portion of Hyp, Hyl and its glycosides is normally reabsorbed from the renal tubule in the controls, and Cd-MT exposure caused an increase in urinary excretions of Hyp and Hyl, including its glycosides, through a renal tubular defect in reabsorption of Hyl in the same manner as with common amino acids.