Tetsu Ono

Distribution and chromium-binding capacity of a low-molecular-weight, chromium-binding substance in mice

The distribution of low-molecular-weight, chromium-binding substance (LMWCr) and high-molecular-weight, chromium-binding substance (HMWCr) in the organ cytosol were analyzed by means of Sephadex G-25 gel filtration, after a single i.p. injection of K2Cr2O7 (280 mumol, Cr/Kg) to mice (male dd, 23 +/- 2 g). The amount of Cr in LMWCr per mouse was highest in the liver (83 micrograms), followed by those in the kidney (10 micrograms) and other organs (3-1 micrograms), with lesser amounts of Cr in HMWCr in all the organs. In these organs LMWCr was found to bind 3-28 times the amount of Cr to that in the in vivo binding after the in vitro incubation with K2Cr2O7 at 37 degrees C, showing a high Cr binding capacity of the substance. No inductive formation of LMWCr was observed in the liver even after daily repetitive administration of Cr (150 mumol/Kg, 4 days). Time course studies on the liver and the kidney of mice injected with K2Cr2O7 showed no difference in the accumulation of Cr in LMWCr and in the ratio of Cr in LMWCr to that in HMWCr between the organs at intervals of from 5 min to 24 hr after the injection. The comparative affinity of Cr(III) for LMWCr and for the serum proteins decreases in the order LMWCr, transferrin, albumin. The transfer of Cr from LMWCr to albumin and vice versa was almost negligible. However, significant amounts of the metal transfer was found from LMWCr to transferrin and vice versa, and from albumin to transferrin. These findings suggest that LMWCr is distributed widely in the body and it quickly binds invaded Cr in stable form at an organ site, especially in the liver, with participation of albumin or/then transferrin. This supports the hypothesis that LMWCr plays a large role in Cr detoxification.

Purification and chromium-excretory function of low-molecular-weight, chromium-binding substances from dog liver

From liver of dogs injected iv with potassium dichromate (38 mg/kg body wt), a low-molecular-weight chromium-binding substance (LMCr) was purified into two subfractions, LMCr I and LMCr II, which differ in physical and chemical properties. LMCr I was identified to be an anionic, organic chromium compound with a molecular weight of 1500. It contained glutamic acid, glycine, and cysteine as the predominant amino acids and firmly bound chromium in a ratio of one chromium(III) to one molecule of LMCr I. LMCr II was isolated in crystalline form and demonstrated to be a water-soluble, inorganic chromium(III) complex consisting of Na2HPO4 . 7H2O and Na2HPO4 . 2H2O. Although its crystallization reduced the chromium content, it had a maximum chromium-binding capacity as much as one chromium per one phosphorus in water. The mixture of LMCr I and LMCr II as approximated to be the natural composition showed a lower acute toxicity as measured by lethality in mice and had higher rates of urinary excretion and renal clearance in rabbits, accompanied by lower rates of renal tubular reabsorption and retention in kidney and liver than potassium dichromate(VI) and chromium(III) chloride. Pretreatment with chromium-free LMCr II remarkably reduced the mortality rates of mice acutely poisoned with chromium chloride. These results indicate that LMCr plays an important role in the detoxification and excretion of chromium in mammals.

A low-molecular-weight, chromium-binding substance in mammals.

Abstract Male mice (dd) were injected ip with a single dose of potassium dichromate (50 or 200 μmol Cr/kg). Assay of chromium (Cr) in organs and their soluble fractions showed that most of the Cr was found in the cytosol. Along with high-molecular-weight compounds of Cr, a low-molecular-weight chromium compound was identified by Sephadex chromatography of liver supernatants. Its content increased dramatically soon after injection and it persisted as long as 7 days, in contrast to the rapid disappearance of high-molecular-weight compounds. Examination of urine and feces by molecular sieve experiments revealed a similar low-molecular-weight chromium compound in the same fraction of the eluate as that of liver. Furthermore, a significant amount of Cr was found in the same elution fraction of plasma at 2 hr although it was not clearly evident at 15 min. The above results suggest that a low-molecular-weight, chromium-binding substance (LMCr) is formed in liver which participates in retention and excretion of Cr in the body. LMCr was partially purified from livers of rabbits injected iv with potassium dichromate (200 μmol Cr/kg) by a combination of ethanol extraction and DEAE-Sephadex, Sephadex gel, and thin-layer chromatography, followed by paper electrophoresis. Based on its demonstrated characteristics, LMCr appears to be an anionic organic complex which contains Cr (III), amino acids, and some other ultraviolet absorbable components. It has been separated into two subfractions with approximate molecular weights of 1600 and 2600.

Role of brain lysosomes in the development of manganese toxicity in mice

To study the mechanism of development of manganese toxicity, the manganese content in blood, brain, liver, and subcellular fractions of brain was measured at several intervals following ip injection of a single dose of manganese (245 mg Mn(CH3COO)2 X 4H2O/kg body wt) in mice. The ultrastructural alterations in neurons were correlated with the data for manganese content. Peak concentrations of manganese in blood and liver occurred and disappeared in less than 24 hr. In brain, however, manganese concentration was maintained for 4 days and decreased very little during the 10-day postdose interval studied. Most of the absorbed manganese in brain was recovered in mitochondria and lysosome-rich fractions separated by density gradient centrifugation. Lysosomes took up manganese to a greater extent than mitochondria when compared to controls. Electron microscopy revealed that by 24-hr postdose the number of lysosomes in neurons increased in corpus striatum and midbrain in mice given manganese by ip injection. These results suggested that brain lysosomes play an important role in the cellular metabolism of manganese and in the development of manganese toxicity.

Intestinal uptake site, enterohepatic circulation, and excretion of tetra‐and trialkyltin compounds in mammals

The intestinal uptake site, enterohepatic circulation, and excretion into bile, feces, and urine of alkyltins (tetra and trialkyltin) were investigated after oral, sc, or intestinal administration of the compounds to rats and rabbits. Assays of tetra- and trialkyltins in biological materials were carried out by gas chromatography. The main uptake sites in the small intestine were the jejunum and duodenum for tetraalkyltins and the ileum and jejunum for trialkyltins. Tetra- and trialkyltins were detected in the small intestine and contents of the intestinal lumen after sc injection of these compounds in rats. These facts suggest that tetra- and trialkyltins are transported in the body through enterohepatic circulation. The route, rate, and amount of excretion of tetra and trialkyltins seem to depend on the velocity of dealkylation, doses, physical and chemical properties, and route of administration of the compounds.

Distribution of trace metals in nuclei and nucleoli of normal and regenerating rat liver with special reference to the different behavior of nickel and chromium

The distribution of some metals in nuclei and nucleoli of normal and regenerating rat liver was determined. The contents of Ca, Zn, Cu, and Mn in nuclei were less than 3% of those in whole cells. Cr and Ni, which are known carcinogens, were present in cells in much smaller amounts than the metals above, but their contents in nuclei were more than 20% of those in cells. All of these metals were retained in nucleoli; the contents in nucleoli, per milligram of protein, were 3 (Zn) to 18 (Ni) times those in nuclei. Binding of Cr and Ni to nucleoli was more resistant than that of the other metals to treatment with nucleases. The concentrations of Ca, Zn, Cu, and Mn in nuclei and nucleoli changed synchronously with changes in the amounts of nucleic acids and protein in the corresponding fraction of the regenerating liver after partial hepatectomy. The Cr concentration showed no such synchronization.

Cadmium stimulates glucose metabolism in rat adipocytes

Cd2+ caused an increase in CO2 formation from glucose in rat adipocytes. The apparent Km value for glucose was 2.02 mM for control condition, with Cd2+, and with insulin. Cd2+ stimulates glucose metabolism even though specific diffusion of glucose is blocked. A possible site effected by Cd2+ is discussed.

Effect of acute administration of cadmium on distribution of zinc in the hamster

Acute administration of sc doses of Cd (1mg/kg . d, 3 or 6 d) to male golden hamsters resulted in a remarkable dose-dependent increase of Zn in the liver and kidney. In contrast, Zn contents in the heart and testes showed a significant dose-dependent decrease. No change was found in Zn contents of the bone. The correlation coefficients between contents of Cd and Zn in the liver and kidney were much higher in metallothionein fractions than in the corresponding whole organs. These results suggest that Cd induces the synthesis of metallothionein in the liver and kidney, leading to simultaneous accumulation of Cd and Zn in the organs; this in turn decreases the Zn contents in other organs, where weak or no induction of metallothionein synthesis takes place. Therefore Cd might induce Zn deficiency in humans or animals whose pool size and intake of Zn are marginal.

Pathogenesis of hyperlipidemia induced in rabbits by methyl iodide

Abstract The metabolism of lipids and genesis of hyperlipidemia in methyl iodide-treated rabbits were investigated. Methyl iodide (57 mg/kg body weight/day) was administered sc to male Japan white rabbits on two successive days. The treatment induced a marked hyperlipidemia characterized by approximately elevenfold increase in very low-density lipoproteins (VLDL) and threefold increase in low-density lipoproteins (LDL) compared to control animals. A significant enhancement of triglyceride production in methyl iodide-treated animals by Triton methodology was demonstrated. In contrast, no change was observed in lipolytic activity in postheparin plasma of these animals. Thus hyperlipidemia induced by methyl iodide seems to be primarily due to an increased lipid synthesis. An increased insulin resistance and hyperinsulinemia were also observed in methyl iodide-treated rabbits. This change suggests that the enhancement of triglyceride production in methyl iodide-treated animals may be predominantly mediated by hyperinsulinemia due to the increased insulin resistance provoked in the animals by methyl iodide.