Isolation and properties of cadmium-binding protein induced in rat small intestine by oral administration of cadmium

Inhibition of L-threonine intestinal absorption in rabbits by cadmium

Cadmium compounds are widely spread in the environment. Animal exposure to cadmium compounds occurs mainly through foods or drinks contaminated by this metal. Cadmium has been shown to produce several negative effects on the gastrointestinal tract such as inhibition on sugars and amino acids absorption. The aim of the present work was to study the inhibitory characteristics of cadmium on L-threonine intestinal absorption in rabbits in order to understand about this malabsorption of nutrients. Our results show that L-threonine tissue accumulation as well as mucosal to serosal transepithelial fluxes are decreased in a dose-dependent manner in rabbit jejunum. Amino acid diffusion across the intestinal epithelium was not affected by cadmium. A noncompetitive mechanism and a partial reversion by dithioerythritol (thiol groups protector) is described for this inhibition.

Oncogenicity of rat prostate cells transformed in vitro with cadmium chloride

Three rat ventral prostate (RVP) cell lines transformed after in vitro treatment with cadmium chloride (CdCl2) and one control untreated cell line were tested for tumorigenicity in newborn rats. All three cadmium-transformed RVP cell lines induced tumors at the site of inoculation in 95-100% of animals. The fibroblastoid RVP56Cd cell line induced sarcomas, whereas the epithelial cell lines RVP47-3G and RVP47-3F produced highly differentiated squamous cell carcinomas. About 20% of animals injected with RVP47-3G developed lung and splenic metastases. The tumors could be further passaged into young rats. The sarcomas had a hyperdiploid modal chromosome number similar to that of the RVP56Cd cell line. Carcinomas induced by the RVP47-3G cell line had a large proportion of stromal metaphases. The modal chromosome number of these carcinomas was in the hypertriploid-hypotetraploid range, similar to that of the parental cell line. These results demonstrate that treatment of RVP cells with CdCl2 in vitro results in neoplastic transformation. Since both fibroblastoid and epithelial prostate cells have undergone transformation, it seems possible that cadmium acted as a carcinogen without cell specificity. The susceptibility of these cells to the carcinogenic effect may be related to their resistance to cadmium. In the process of neoplastic transformation induced by CdCl2 in RVP epithelial cells changes of squamous metaplasia occur, and probably precede acquisition of tumorigenicity.

Intestinal absorption of cadmium and inorganic mercury in the rat: no major involvement of metallothionein

The intestinal absorption of cadmium and inorganic mercury was studied in adult rats, administered the metal salts intragastrically or parenterally in repeated or single doses. The intestines contained only small proportion of the body burden; no major change was found in the intestinal level of metallothionein, copper and zinc. Therefore, no major role can be ascribed to intestinal metallothionein in limiting absorption of high oral doses of cadmium and mercury.

Physiological zinc-binding proteins of medium molecular weight in the rat gut

1. Gel filtration on Sephadex G 75 was used to separate the medium-molecular-weight zinc-binding proteins from the soluble fractions from the duodenal and jejuno-ileal segments of the rat gut at 30 min after the intragastric administration of a tracer dose of 65Zn. These proteins were resolved by ion-exchange chromatography on DEAE cellulose. 2. In both the duodenum and jejuno-ileal segment an appreciable fraction of the total soluble Zn was bound in a protein fraction that resembled metallothionein (MT) in its behaviour on gel filtration. These fractions, however, were not homogeneous, but contained several medium-molecular-weight Zn-binding proteins. In the duodenum, but not in the jejuno-ileal segment, two of these proteins appeared to be the isometallothioneins, ZnMT-I and ZnMT-II. 3. These results suggest a possible role for MT in the binding of newly-absorbed Zn in the duodenal mucosal cells. They also show that gel filtration alone is insufficient for the identification of MT in the intestine.

Observations on the distribution and movement of cadmium in epithelial cells of rat small intestine by light- and electron-microscope radioautography

The localization of cadmium in the absorptive cells of the small intestine has been studied by light- and electron-microscope radioautography at intervals in the first 27 h after intubation of radiocadmium into the stomach of rats. Light-microscope autoradiographic studies showed that cadmium was taken up very quickly by the absorptive cells, and radioactivity in the absorptive layer was disseminated over the entire area of the absorptive cells. Electron-microscope autoradiography showed that there was no concentration of radioactive cadmium in any particular site in the epithelial cells or in the lamina propria. It suggests that the transport mechanism of cadmium through the intestine may be nonspecific. Radioautographic investigation using radiocadmium may provide useful information for cadmium distribution and movement in rat small intestine.