To clarify the relation of essential metals to cadmium (Cd) toxicity, we evaluated metallothionein expression and analyzed the subcellular distribution of essential metals using in-air micro-Particle-Induced X-ray Emission (PIXE). Four mice were dosed orally with 100 mg/L of Cd in drinking water for 1.5 or 2 years. Frozen samples of organs were used for micro-PIXE analysis and formalin-fixed samples were used for metallothionein staining. Immunohistochemically, metallothionein induction by 1.5y-Cd exposure was higher in the renal cortex than in the liver. Metallothionein expression was reduced after 2y-Cd administration compared to the 1.5y-Cd-exposed mice. Cd-induced tissue damage became marked in the 2y-Cd-exposed mice compared to the 1.5y-Cd-exposed mice, in which nephrotoxicity was more prominent than hepatotoxicity. Cd yield was higher in the renal cortex of the 2y-Cd-exposed mouse than in that of the 1.5y-Cd-exposed mouse, whereas no such increasing tendency was found in the liver. Compared to the control, the Cd-exposed mice markedly accumulated zinc in the liver and renal cortex. In the Cd-exposed mice, iron was mildly accumulated in the renal cortex and was slightly deprived in the liver. Elemental maps showed that a large amount of Cd was spatially combined with zinc in the 1.5y-Cd mouse. Free Cd became abundant in the 2y-Cd-exposed mouse. In addition, a small amount of Cd was colocalized with iron. The data suggest that zinc may contribute to protect against oral-administrated Cd toxicity, and impaired induction of MT may participate in hepato-nephrotoxicity of the 2y-Cd-exposed mouse.

lthough metals are minor constituents in the body, some are essential in the normal functioning body and others are highly tox i c, i n d i c ating their cri t i c a l b i o l ogical actions, i rre s p e c t ive of their being beneficial or a dve rs e. As a re s u l t , the biological effects of metals on health have been of concern from the viewpoints of nu t rie n t s , their biological and phy s i o l ogical functions, their tox ic o l ogical actions and also the biochemical mechanisms of their functions. The detection and ch a ra c t e ri z ation of biol ogical trace metals is the fi rst step to add ress these conc e rns. Howeve r, detection itself has been a ch a l l e n ging pro blem in terms of trace analysis with accura cy and pre c i s i o n. B i o l ogical and env i ronmental trace metals have been analy zed for a long time only at the concentration leve l , i. e. it has been a ch a l l e n ge in elemental analysis to elevate the sens i t ivity from % to the ppm, ppb and ppt leve l s , but there has been no focus on their chemical fo rm s , i. e. it has been not extended to the level of elemental speciation.