metallothionein and beta-hederin

Alpha-hederin, a triterpenoid saponin, has been reported to induce hepatic metallothionein (MT). However, the mechanism underlying its effects is unknown. This study investigated the effects of alpha-hederin on the regulation of MT expression in an in vitro model using the murine hepatoma cell line, Hepa-1c1c7, and the murine macrophage cell line, RAW 264.7. Alpha-hederin that was added directly to Hepa-1c1c7 cells had no effect on MT induction. However, MT and its mRNA levels increased markedly when the Hepa-1c1c7 cells were cultured with the alpha-hederin-treated, conditioned medium from the RAW 264.7 cells. Co-treating the RAW 264.7 cells with alpha-hederin and pentoxifylline, a TNF-alpha synthesis inhibitor, resulted in decreased effects of alpha-hederin on MT induction. In the alpha-hederin-exposed RAW 264.7 cell cultures, production and mRNA levels of TNF-alpha and IL-6 were increased. Accordingly, it was found that the MT induction activity was inhibited when antibodies to TNF-alpha and/or IL-6 were added to the alpha-hederin-treated, conditioned medium from the RAW 264.7 cells. These results suggest that the upregulation of MT expression by alpha-hederin is mediated by TNF-alpha and IL-6.

Topics: Animals; Cell Line, Tumor; Cell Survival; Cytokines; Dose-Response Relationship, Drug; Interleukin-6; Macrophages; Metallothionein; Mice; Oleanolic Acid; Phytotherapy; Plants, Medicinal; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Saponins; Tumor Necrosis Factor-alpha

The administration of alpha-hederin, an inducer of metallothionein, results in a secondary zinc deficiency that may be an important maternally mediated mechanism of developmental toxicity. Previous studies have shown adverse developmental outcome with a single administration of alpha-hederin to rats on gestation day (GD) 8 or 11. The objective of this study was to determine whether dosing of alpha-hederin throughout organogenesis would result in a sustained elevation of maternal hepatic metallothionein and subsequent developmental abnormalities. Rats were administered dosage levels of 0 (vehicle only), 20, or 30 mumol/kg from GD 6-15. Maternal hepatic metallothionein levels were 10-fold higher on GD 16 in the treatment groups than the controls. Consequently, liver zinc concentrations increased 60% and 54%, whereas plasma levels decreased 23% and 33% in the 20 and 30 mumol/kg treatment groups, respectively. At GD 20, mean fetal weights of the treatment litters were 11% less than control litters. The administration of alpha-hederin resulted in a threefold increase in the number of offspring that exhibited developmental abnormalities, including visceral and skeletal malformations. Following an oral pulse of 65Zn subsequent to treatment with 0 or 20 mumol/kg of alpha-hederin, the distribution of 65Zn to the liver of treated dams was twice that of controls, whereas the radiolabeled zinc apportioned to the decidua and uterus decreased by 44%. Furthermore, the 65Zn detected in the embryos from treated dams was 70% lower than in embryos from control dams. In conclusion, low doses of a metallothionein inducer administered to the dam from GD 6-15 resulted in a sustained elevation of hepatic metallothionein and a subsequent redistribution of zinc leading to a decrease in the zinc available to the embryo and ultimately to adverse development of the offspring. Repeated dosing throughout organogenesis, as required in regulated safety assessment testing, increased the severity of the effects previously observed with single large dosages of the toxicant administered during midgestation.

Topics: Animals; Dose-Response Relationship, Drug; Drug Administration Schedule; Embryonic and Fetal Development; Female; Maternal-Fetal Exchange; Metallothionein; Oleanolic Acid; Pregnancy; Pregnancy Outcome; Rats; Rats, Sprague-Dawley; Saponins; Zinc; Zinc Radioisotopes

To examine whether alpha-hederin (Hed) modulates hepatic detoxifying systems as a means of hepatoprotection.. Mice were injected Hed 10 and 30 mumol.kg-1 sc for 3 d, and liver cytosols were prepared 24 h after the last dose to study antioxidant enzymes and nonenzymatic defense components.. Hed increased liver glutathione (GSH) content (20%), but had no effect on GSH peroxidase, GSH reductase, and GSH S-transferase. The activities of superoxide dismutase and quinone reductase were unaffected by Hed treatment. At the high dose of Hed, catalase activity was decreased by 20%. Hepatic content of metallothionein was dramatically increased (50-fold), along with elevations of hepatic Zn and Cu concentrations (25%-80%). Hed also increased ascorbic acid concentration (20%), but no effect on alpha-tocopherol in liver.. Hed enhanced some nonenzymatic antioxidant components in liver, which play a partial role in Hed protection against hepatotoxicity produced by some chemicals.

Topics: Animals; Antioxidants; Catalase; Copper; Drugs, Chinese Herbal; Glutathione; Liver; Male; Metallothionein; Mice; Oleanolic Acid; Saponins; Zinc

One mechanism by which chemicals cause cellular injury is the formation of reactive oxygen species. In vitro studies have shown that metallothionein (MT), a small metal-binding, sulfhydryl-rich, readily inducible protein, can scavenge reactive oxygen species, especially hydroxyl radicals. Nevertheless, whether or not MT protects against oxidative stress in the intact animal is not known. Experimental induction of MT could help to clarify this question, however, it is unclear whether agents that induce MT also influence known antioxidant systems. Therefore, the present study was designed to determine whether the well-known MT inducers are specific for induction of MT or whether they might also influence other hepatic systems that protect against oxidative stress. Male rats were administered cadmium chloride (Cd; 30 mumol/kg, s.c.), zinc chloride (Zn; 1000 mumol/kg, s.c.), alpha-hederin (alpha-H, 30 mumol/kg, s.c.) or lipopolysaccharide (LPS; 1 mg/kg, s.c.) 24 h prior to measurement of antioxidant systems. Zn and alpha-H increased hepatic GSH concentration 20% and 55%, respectively. Cd significantly increased, whereas LPS reduced, the activities of selenium-dependent glutathione peroxidase and glutathione reductase. Glutathione S-transferases were not altered by any of the inducers. Cd also increased DT-diaphorase activity. Cd, Zn and alpha-H all decreased catalase activity 20-35%, while the activity of superoxide dismutase was unaffected by the inducers. The amount of total cytochrome P450 enzymes and cytochrome b5 were decreased by LPS, Cd and alpha-H, while Zn appeared to have no effect. The activities of P450 enzymes towards testosterone oxidation were also decreased by LPS, Cd and alpha-H. In conclusion, all four MT inducers examined affect systems known to protect cells against oxidative stress. Therefore, using these chemicals to determine the in vivo role of MT in protecting against oxidative stress poses difficulties.

Topics: Analysis of Variance; Animals; Cadmium; Cadmium Chloride; Carcinogens; Catalase; Chlorides; Cytochrome P-450 Enzyme System; Cytochromes b5; Cytosol; Dihydrolipoamide Dehydrogenase; Glutathione; Glutathione Peroxidase; Glutathione Reductase; Glutathione Transferase; Lipopolysaccharides; Liver; Male; Metallothionein; Oleanolic Acid; Oxidative Stress; Rats; Rats, Sprague-Dawley; Saponins; Selenium; Superoxide Dismutase; Testosterone; Zinc Compounds

alpha-Hederin (alpha-Hed) is a triterpenoid saponin that has been shown to protect against some hepatotoxicants. This study examined the protective effect of alpha-Hed against cadmium (Cd) hepatotoxicity and the mechanism of protection. alpha-Hed pretreatment (100 mumol/kg, sc) dramatically decreased Cd (3.7 mg/kg, iv) hepatotoxicity as indicated by a reduction of serum alanine aminotransferase and sorbitol dehydrogenase, as well as by histopathological examination. alpha-Hed did not produce protection by decreasing the distribution of Cd to the liver, as higher amounts of Cd were found in the liver of alpha-Hed-pretreated mice. However, there was a marked alteration in subcellular distribution of Cd in the alpha-Hed-pretreated mice, with much less Cd distributing to nuclei, mitochondria, and microsomes and more in the cytosol. The increased cytosolic Cd was found primarily bound to a low-molecular-weight protein, metallothionein (MT). alpha-Hed (10-300 mumol/kg, sc) produced a dose-dependent increase in hepatic MT with a 100-fold increase over controls 24 hr after a single injection of 100 mumol/kg, as determined by the Cd/hemoglobin assay. The hepatic MT increase produced by alpha-Hed is relatively long lasting, in that it is still eight times control values 6 days after a single administration. The induction of MT was also relatively specific for the liver, as little or no increase in MT was observed in other tissues. Furthermore, alpha-Hed increased both hepatic MT-I and MT-II levels. Northern blot analysis revealed that alpha-Hed rapidly increased MT mRNA levels. In conclusion, alpha-Hed decreases the hepatotoxicity of Cd by inducing MT, which binds Cd in the cytosol, and thus reduces the amount of Cd in the critical cellular organelles. alpha-Hed is an effective inducer of both MT-I and MT-II in liver, and this effect is associated with an increase in MT mRNA.

Topics: Alanine Transaminase; Animals; Binding Sites; Blotting, Northern; Cadmium; Cadmium Chloride; Chlorides; Cytosol; Dose-Response Relationship, Drug; L-Iditol 2-Dehydrogenase; Liver; Male; Metallothionein; Mice; Microsomes, Liver; Mitochondria, Liver; Oleanolic Acid; RNA, Messenger; Saponins; Tissue Distribution