Study On The Effect Of Yeast - Derived Metallothionein Lead And The Damage To Lead Oxidation Damage

Metallothionein(MT) is a kind of metal binding protein with low molecular weight that isrich in cysteine protease. Because of its strong biological functions such as anti-oxidation,chelating heavy metal ions and heavy-metal detoxification, metallothionein has gradually beenapplied to the areas of deleading drugs, functional food, feed additives and cosmetics, etc.In our research group’s previous work, we had obtained the induced metallothioneins fromyeast by inducer,which were beneficial to industrial production and promoted application for ashorter cycle time, simpler technologies, lower prices and higher security. In this paper, theeffects of metallothioneins from yeast on lead expelling and oxidative damage protecting in vitroand vivo were studied in the following four aspects:First, compared with control group(Vc and Zn-MT), the free radical clearance rate and totalreducing power of metallothioneins were measured by UV. Overall, in terms of antioxidantactivity in vitro, the antioxidant activities of metallothioneins from yeast were stronger than VCunder the same concentration, and the antioxidant activity of MT-Ⅰ wasstronger than MT-Ⅱ.Compared with control group(Zn-MT), the Pb2+-chelating activities of two monomericforms of metallothionein from yeast in simulated gastrointestinal environment were measured bygraphite furnace atomic absorption spectrometry and SDS-PAGE. The results showed thatmetallothioneins exhibited excellent activities to chelate Pb2+in simulated gastrointestinalenvironment, and the Pb2+-chelating activity increased with the increasing of the concentration ofmetallothioneins. In simulated gastric environment, the Pb2+-chelating rates of MT-Ⅰ andMT-Ⅱ w ere significantly higher than those of Zn-MT. Pepsin had weakening effects onPb2+-chelating rates MT-Ⅰ a nd Zn-MT,which were not obvious on MT-Ⅱ. In simulated intestinalenvironment, the Pb2+-chelating activities of metallothioneins were Zn-MT＞MT-Ⅰ＞MT-Ⅱ.Furthermore, trypsin had little effects on Pb2+-chelating activities of metallothioneins. The resultsindicated that the simulated gastrointestinal environment had a destructive impact on themercapto group, but MT-Ⅰ a nd MT-Ⅱ had the excellent activities to chelate Pb2+in simulatedgastrointestinal environment,and keep Pb2+-chelating activities through resisting the digestion ofsimulated gastrointestinal environment.The acute lead poisoning models were builded with lead acetate by intraperitoneal injection, and then the drugs were chronically administrated to mice for14days. As compared with thecontrol group(DMSA and Zn-MT), the levels of blood lead, MDA, SOD and GSH-Px weremeasured after14days. The morphological characteristics and weights of mice in14days werealso noted. Compared with model group,the blood lead levels of metallothioneins group weredecreased significantly(P <0.05), and showed a significant dose-response relationship(P<0.05).The lead expelling effects of MT-Ⅰg roup and Zn-MT group were sample(P>0.05),buthigher than that of MT-Ⅱ group significantly(P<0.05). The MDA, SOD and GSH-Px levelstended to be normal(P>0.05), and the MDA levels of MT-Ⅰ group and MT-Ⅱ group weresignificantly lower than Zn-MT(P<0.05), but SOD and GSH-Px levels had no significantdifference(P>0.05). And the MDA levels of DMSA were significantly higher than high dose MTgroups. The results indicated that the two monomeric forms of metallothionein from yeast hadsignificant effect on lead expelling in acute lead-treated mice, which were similar to themetallothionein from animal origin.They also could renovate oxidative damage induced by leadthrough increasing the activities of antioxidant enzyme and reducing the lipid peroxidationproducts.The MT were chronically administrated to chronic lead poisoning mice by lead acetatesolution for35days. As compared with the control group(DMSA and Zn-MT), the levels ofweight, blood lead, some routine blood examination and liver function indexes were measuredafter35days. Histopathological examinations were carried out to supplement the biochemicalresults. Compared with model group,the weight of metallothioneins group had no significantchange. The levels of WBC, WCV and HGB in high-dose MT treatment groups were increasedsignificantly(P<0.05), but the levels of GR in all lead poisoning groups had no significantdifferences(P＞0.05). The levels of GPT in all drug groups were decreased significantly(P<0.05). The levels of GOT in high-dose MT treatment groups were decreased significantly(P<0.05), and degrees of liver and kidney tissue pathological changes were ameliorated byhigh-dose MT, which were better than DMSA groups. The results indicated that two monomericforms of metallothionein from yeast had the obvious effecs on lead expelling and hepatorenalfunctions protecting in chronic lead poisoning mice, and the effects were similar tometallothioneins from animals.