[Selenium methylation and toxicity mechanism of selenocystine].

Selenium is an essential trace element and a toxicant for animals. Selenocystine, a selenium-containing amino acid, is one of the chemical forms in which selenium exists in food. This review summarized recent studies on the toxicity mechanism of selenocystine in experimental animals. Hepatotoxicity is caused by repeated oral administration of selenocystine. Selenocystine is metabolized by reduced glutathione and/or glutathione reductase to hydrogen selenide via selenocysteine-glutathione selenenyl sulfide. The hydrogen selenide is a key intermediate in the selenium methylation metabolism of inorganic and organic selenium compounds. Accumulation of the hydrogen selenide resulting from inhibition of the selenium methylation metabolism, detoxification metabolic pathway of selenium, is found in animals following repeated administration of a toxic dose of selenocystine. The excess of the hydrogen selenide produced by inhibition of the selenium methylation metabolism contributes to the hepatotoxicity caused by selenocystine.

Mechanisms of selenium methylation and toxicity in mice treated with selenocystine.

Mechanisms of selenium methylation and toxicity were investigated in the liver of ICR male mice treated with selenocystine. To elucidate the selenium methylation mechanism, animals received a single oral administration of selenocystine (Se-Cys; 5, 10, 20, 30, 40, or 50 mg/kg). In the liver, both accumulation of total selenium and production of trimethylselenonium (TMSe) as the end-product of methylation were increased by the dose of Se-Cys. A negative correlation was found between production of TMSe and level of S-adenosylmethionine (SAM) as methyl donor. The relationship between Se-Cys toxicity and selenium methylation was determined by giving mice repeated oral administration of Se-Cys (10 or 20 mg/kg) for 10 days. The animals exposed only to the high dose showed a significant rise of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities in plasma. Urinary total selenium increased with Se-Cys dose. TMSe content in urine represented 85% of total selenium at the low dose and 25% at the high dose. The potential of Se-methylation and activity of methionine adenosyltransferase, the enzyme responsible for SAM synthesis, and the level of SAM in the liver were determined. The high dose resulted in inactivation of Se-methylation and decrease in SAM level due to the inhibition of methionine adenosyltransferase activity. To learn whether hepatic toxicity is induced by depressing selenium methylation ability, mice were injected intraperitoneally with periodate-oxidized adenosine (100 mumol/kg), a known potent inhibitor of the SAM-dependent methyltransferase, at 30 min before oral treatment of Se-Cys (10, 20, of 50 mg/kg). Liver toxicity induced by selenocystine was enhanced by inhibition of selenium methylation. These results suggest that TMSe was produced by SAM-dependent methyltransferases, which are identical with those involved in the methylation of inorganic selenium compounds such as selenite, in the liver of mice orally administered Se-Cys. Depression of selenium methylation ability resulting from inactivation of methionine adenosyltransferase and Se-methylation via enzymic reaction was also found in mice following repeated oral administration of a toxic dose of Se-Cys. The excess selenides accumulating during the depression of selenium methylation ability may be involved in the liver toxicity caused by Se-Cys.

Danazol concentrations in ovary, uterus, and serum and their effect on the hypothalamic-pituitary-ovarian axis during vaginal administration of a danazol suppository.

OBJECTIVE: To determine danazol concentrations in the ovary, uterus, and serum during daily vaginal administration of a danazol suppository and to examine its effect on the hypothalamic-pituitary-ovarian axis. DESIGN: Sampling of tissues after vaginal or oral administration of danazol and sampling of blood during control and danazol-administration menstrual cycles. SETTING: Outpatient volunteers and inpatients at a public hospital. PARTICIPANTS: Thirty patients who were to undergo hysterectomy and oophorectomy because of uterine leiomyoma and eight regularly menstruating volunteers. INTERVENTIONS: Danazol was administered as a vaginal suppository (100 mg) or orally (400 mg). MAIN OUTCOME MEASURE: Danazol concentrations in the ovary, uterus, and serum, and serum E2 and P levels. RESULTS: Danazol concentrations in the ovary and uterus after daily vaginal administration of a suppository containing 100 mg danazol were comparable to those after daily oral administration of 400 mg danazol, but the serum danazol concentration was much lower. Menstrual cycle patterns of serum E2 and P levels were normal during daily vaginal administration of a danazol suppository. CONCLUSION: Daily administration of a suppository containing 100 mg danazol produces high ovarian and uterine concentrations but low serum concentrations, and no effect was detected on the hypothalamic-pituitary-ovarian axis.

Chemical form of selenium-containing metabolite in small intestine and liver of mice following orally administered selenocystine.

The chemical form of a selenium-containing metabolite in the small intestine following a single oral administration of selenocystine was investigated with ICR male mice. Selenium content in the small intestine of animals treated with 50 mg/kg selenocystine significantly increased 15 min, 1 h and 6 h after treatment. In contrast, selenocystine significantly depressed the intestinal reduced glutathione (GSH) level at 1 h after administration. A significant negative correlation between the selenium level and the level of GSH in the small intestine was observed (r = -0.83, p < 0.001). Analysis of the intestinal metabolite of selenocystine showed that selenium-containing metabolites elute in two fractions from a Sephadex G-25 column: the low-molecular fraction (peak I) contained the selenocystine, while the high-molecular fraction (peak II) contained selenocysteine-containing metabolite. An in vitro experiment was performed to gain insight into the mechanism for selenocysteine-containing metabolite production in the intestinal cytosol. When selenocystine or selenocysteine reacted with excess GSH in the presence of intestinal homogenate, the peak II fraction which involved the selenocysteine-containing metabolite was recognized in the Sephadex G-25 chromatogram. From an examination of the distribution of the selenocysteine-containing metabolite, it was recognized that this metabolite exists in plasma and liver cytosol of mice after oral administration of selenocystine. These results suggested that the mice treated with selenocystine produce selenocysteine-containing metabolite by reaction of selenocystine with excess GSH in the small intestine, and the metabolite is then transported to the liver through blood plasma.

Distribution and chemical form of selenium in mice after administration of selenocystine.

To elucidate the relationship between chemical forms of selenium in tissues and subacute liver damage induced by selenocystine (T. Hasegawa et al., Arch. Toxicol., 68, 91 (1994)), the distribution and chemical form of selenium were investigated in ICR male mice treated with the chemical orally (50 mg/kg) and intravenously (5 mg/kg). The time-distribution of selenium in plasma, erythrocytes and liver after separate administration varied. However, Sephadex G-150 chromatograms of plasma, and stroma-free hemolysate from mice treated orally or intravenously with selenocystine, revealed that selenium exists mainly in the albumin and hemoglobin fractions, respectively, and is neither route- or time-dependent. Sephadex G-150 chromatograms of liver cytosol of the animals 1 h after oral administration or 1 and 6 h after intravenous administration showed two selenium-containing fractions, void volume and a low-molecular fraction (Kav = 0.85); 6 h after oral treatment, however, animals had an additional high-molecular fraction (Kav = 0.45). Levels of acid-volatile selenium and dialyzable selenium in the fraction with a Kav value of 0.45 were similar, being 31.2% and 30.3%, respectively. No acid-volatile selenium was recognized in the non-dialyzable high-molecular fraction. The present study demonstrated that when selenocystine is administered orally to mice, the selenium which produces acid-volatile selenium by acidification may bind to protein sulfhydryl groups in the liver cytosol; this was not seen in the case of intravenous administration.

Toxicity and chemical form of selenium in the liver of mice orally administered selenocystine for 90 days.

The subacute oral toxicity of selenocystine and chemical form of selenium in the liver following exposure to this compound were assessed in ICR male mice. Animals were dosed 6 days/week for 30, 60 or 90 days with 0, 5, 10 or 15 mg/kg per day. Body weight gain decreased with dosage. The activities of aspartate aminotransferase and alanine aminotransferase in plasma were significantly elevated at the highest dose level after 60 days and at the two higher dose levels after 90 days of exposure. However, the level of selenium content in the liver was the same at the two higher dosages at both 60 and 90 days of exposure. The subcellular distribution of selenium in the liver from mice treated with selenocystine showed that the major part of the total selenium content, 68.3-72.1%, existed in the cytosolic fraction. Sephadex G-150 chromatograms of liver cytosol of the animals administered selenocystine revealed three selenium-containing fractions which involve glutathione peroxidase (molecular weight 80,000) high molecular (molecular weight 55,000-60,000) and low molecular (molecular weight < 10,000) substances. Selenium content and acid-volatile selenium content in the high molecular weight fraction increased with exposure time to selenocystine. Thus, in a subacute toxicity study selenocystine given for 90 days caused hepatic damage in mice, depending on the acid-volatile selenium content in the liver cytosol.

Subchronic oral toxicity of glyoxal via drinking water in rats.

The subchronic oral toxicity of glyoxal via drinking water and the effect on in vivo protein synthesis in tissues following a single treatment with this substance were assessed in Sprague-Dawley male rats. Animals received drinking water containing glyoxal levels of 2000, 4000, and 6000 mg/liter ad libitum for 30, 60, and 90 days in Phase I. In Phase II, the high-dose and control-1 groups fed the diet ad libitum, and a diet-limited control-2 group given the same amount of diet as consumed by the high-dose group were maintained for 90 and 180 days. The study designs included observations of clinical signs, body weights, major organ weights, gross and histopathological examinations, serum clinical chemistry, and biochemical examinations such as glyoxalase activity and glutathione content in selected tissues. Body weight gain and organ weights significantly decreased with dosage. Although consumption of food and water was also depressed in the exposed group, the reduction of body weight gain was greater in the high-dose group than in the diet-limited control 2 group. Histopathological examinations revealed only a slight papillary change in the kidneys from the high-dose group at both 90 and 180 days terminations in Phase II. The induction of both glyoxalase I and II was observed in liver and erythrocytes at 30-day termination of the exposed groups. Serum enzyme and protein levels were significantly reduced by the mid- and/or high-dose exposures. With a single oral high-dose treatment of glyoxal, a great decline in the incorporation of L-[3H]leucine was shown particularly in the liver, and this probably led in part to a reduction in the serum protein levels in rats following subchronic exposure to glyoxal. These data indicated an overall low degree of systemic toxicity to rats exposed subchronically to glyoxal via drinking water.

Studies on selenium-related compounds. V. Cytogenetic effect and reactivity with DNA.

Five selenium compounds, Na2Se04, H2Se04, Na2Se03, H2Se03 and Se02, were tested for their capacity to induce chromosome aberrations in cultured human leukocytes and for their reactivity with DNA by a rec-assay system and inactivation of transforming activity in Bacillus subtilis. Chromosome-breaking activity was significantly higher for the compounds with four-valent than with six-valent selenium, the efficiency being in the decreasing order H2S03 greater than Na2Se03 greater than Se02 greater than H2Se04 greater than Na2Se04. Rec assay using B. subtilis with different recombination capacities suggested that damage to DNA was produced by selenites but not by selenates. The reactivity of selenites with DNA was also indicated by a significant loss of transformation of the tryptophan marker of B. subtilis DNA treated with H2Se03 and Se02.