Hisayoshi Ohta

Age-dependent changes in metallothionein levels in liver and kidney of the Japanese.

Samples of liver, renal cortex, and medulla were obtained from 55 forensic autopsies (0- to 95-yr-old Japanese). Metallothionein (MT) was determined by the Ag-hem or Cd-hem method. Zinc (Zn), copper (Cu), and cadmium (Cd) were determined by atomic absorption spectrophotometry. The mean levels of MT were 250 μg/g in the liver, and 394 μg/g (cortex) and 191 μg/g (medulla) in the kidney. Age-dependent changes were observed in both the liver and kidney. In the liver, MT level decreased during infancy and increased thereafter with age. Similar age-dependent changes in the levels of Zn and Cu were observed. In the kidney cortex, MT level increased with age, although no correlation was found after middle age. The levels of Cd and Zn also increased with age until middle age; however, they decreased thereafter. These results suggest that age-dependent changes in renal MT levels are associated with accumulation of Cd.

Metallothionein-like cadmium binding protein in rat testes administered with cadmium and selenium.

It is well known that the testicular damage caused by acute cadmium toxicity are protected by simultaneous selenium administration with cadmium, and that the cadmium concentration in the testis increases remarkably as compared with that of only cadmium administration. The increased cadmium in the testis was found in the high molecular weight fraction containing selenium, and it has been thought that the shift of cadmium from the low molecular weight fraction to the high molecular weight fraction containing selenium is an important protection mechanism. However, the cadmium concentration in this high molecular weight fraction decreased with time, then re-shifted to the fraction of metallothionein, a low molecular weight protein having a protective effect against cadmium toxicity. While recently studying the cadmium binding protein, like metallothionein, in testes, it has been reported that the amino acid composition of cadmium binding protein in testis is not similar to that of the hepatic metallothionein. The present study was undertaken to clarify the properties of the increased cadmium binding protein in the testis protected by simultaneous selenium administration with cadmium.

Induction of metallothionein-like cadmium binding protein in testis and its protective role against cadmium toxicity

Despite the numerous studies conducted on the testicular Cadmium (Cd) binding protein (Cd-BP) or metallothionein (MT), there is still no consensus on whether the testicular Cd-BP is the same as MT. Moreover, it is unclear whether the testicular Cd-BP is inducible. Therefore, the possible induction of MT-like Cd-BP was investigated in rat testis after oral Cd administration and Cd injection.