Effects And Regulation Mechanism Of Different Zinc Sources On The Growth And Immunity Of Animals

Zinc is an essential trace-element required for growth, development and immunity ofanimals. Growth retardation and immunity defect are principal signs of zinc deficiency inhuman and animals, but the underlying mechanisms remain to be elucidated. Zinc methionine(Zn-Met) has been shown to have greater bioavailability than inorganic zinc sources in somesituations. The aim of our study was to evaluate the effects and its molecular mechanism ofzinc sulfate and zinc methionine on growth, and immunity in broilers and mice.1. Effect on production performance on early stage of broilers and differential display ofhepatic mRNAs regulated by different forms of zinc in dietsThis experiment was conducted to investigate the effect of different forms of zinc onproduction performance and to study the mechanism of different forms of zinc on animals bydifferential display reverse transcription PCR (DDRT-PCR). Seventy-five Avine broilers wereallotted at random into 3 treatments. The control was fed on corn-soybean basal diet.Treatments of ZnSO₄ and Zn-Met were supplemented with zinc sulfate and zinc-methionine at40 mg/kg zinc. The results showed that supplementing zinc in basal diet enhanced weight gainof 14, 21 day and improve feed conversion efficiency;Zn-Met showed more effectively thanZnSO₄. Zinc contents in tibia and pancreas were increased by zinc supplement;they wereincreased more by Zn-Met as compared to ZnSO₄. There were no significant difference ofserum zinc content and AKP activity among the three treatments (P>0.05). Twenty-sixdifferent bands were obtained from DDRT-PCR. Two of the differential fragments of cDNAswere sub-cloned;one positive clone was received successfully.2. Effect of zinc sulfate and zinc methionine on growth and their mechanism in miceNinety male KM mice were randomly divided into three treatments to investigate the effectof zinc sulfate and zinc methionine on growth and their possible regulating mechanism. Thecontrol was fed on the basal diet containing zinc of 11.67mg/kg. The treatments of ZnSO₄ andZn-Met were fed on the diets supplemented with ZnSO₄ or Zn-Met at 30mg/kg. Initial bodyweight and final body weight, serum and liver zinc contents, activity of serum AKP, plasmagrowth hormone concentration and the levels of GHR and IGF-I mRNA were determined.The results showed that, weight gain of the mice was enhanced by both forms of zinc, Zn-Metwas more efficient than ZnSO₄ (P<0.05) at the early growth stage. Serum, liver zinc contentsand serum alkaline phosphtase (AKP) activity were increased by both forms of zinc, thosetreated with Zn-Met were somewhat higher than with ZnSO₄ (P>0.05). The both forms ofzinc had no effect on GH concentration and the expression of GHR mRNA (P>0.05), whilethey markedly (P<0.05) up-regulated the expression of IGF-I mRNA. As compared to ZnSO₄,Zn-Met significantly increased the weight gain and the abundance of IGF-I mRNA (P<0.05).3. Transport and regulation mechanism of zinc sulfate and zinc methionine in miceNinety male KM mice were used to investigate the metabolism regulation of ZnSO4 andZn-Met in the intestine of mice. ZnT1 (zinc transporter), ZnT4, DCT1 (divalent cationtransporter) and MT-1 (metallothionein) mRNAs were determined using semi-quantificationreverse transcript polymerase chain reaction (RT-PCR). The results showed that ZnSO4 andZn-Met decreased the expression of ZnT1, ZnT4 and DCT1 mRNAs (P<0.05). Theexpression of ZnT1 and DCT1 mRNAs were down-regulated significantly by Zn-Met ascompared to ZnSO4 (P<0.05);ZnT4 mRNA abundance showed no difference between thetwo zinc sources (P>0.05). Both ZnSO4 and Zn-Met significantly increased MT-1 mRNA inliver and intestine (P<0.05). The expressions of DCT1 mRNA were down-regulated whileMT-1 mRNA expression was up-regulated more efficiently by Zn-Met as compared to ZnSO4(P<0.05). According to above results, the two forms of zinc might be transported or regulatedby different ways.4. Effect of zinc sulfate and zinc methionine on immunity of miceOne hundred and twenty weanling mice (KM) were allotted at random into 3 treatments,some immunology indexes were determined to investigate the effect of the two forms of zincon immunity of weanling mice. The results showed that zinc supplementation in basal dietenhanced immune response;indexes of thymus, ANAE+, IL-2, SI, IgA, IgG, and IgM were allincreased with supplementation of both forms of zinc (P<0.05);index of spleen, hemolysin,IL-1 in zinc treatment of ZnSO4 showed no difference (P>0.05) with the control, while intreatment of Zn-Met, it showed markedly difference (P<0.05);There were no significantdifference of indexes of liver and kidney, serum protein and albumin contents among the theretreatments (P>0.05). Based on all indexes except indexes of kidney and liver, SI and IgM, theimmunity was improved more efficiently by Zn-Met than ZnSO4.5. Effect of different zinc sources on the ability of antioxidation of miceThis experiment was conducted to investigate the effect of zinc sulfate and zinc methionineon the redox of weanling mice (KM). One hundred and twenty weanling mice (KM) wereallotted at random into 3 treatments. Nitric oxide synthase (NOS), glutathione peroxidase(GSH-Px), total superoxide dismutase (T-SOD) and CuZn-SOD, the content of nitric oxide(NO) and total antioxidation capacity (T-AOC) were determined. The result indicated that,oxidation damage was induced by zinc deficiency based on the increased plasma MDAconcentration;the activity of GSH-Px was enhanced significantly with zinc supplementation(P<0.05);while the two zinc sources showed no difference. T-AOC, T-SOD and CuZn-SODwere increased by zinc supplementation (P<0.05), and zinc methionine exerted effectivelythan zinc sulfate (P<0.05). The content of NO was decreased with zinc supplementation(P<0.05), Zn-Met did more effectively than ZnSO4 (P<0.05). The activity of NOS wasincrease slightly by zinc supplementation (P>0.05). Based on above results, it was concludedthat Zn-Met improved the ability of antioxidation more effectively than ZnSO4.6. Effects and mechanism of zinc sources and levels on apoptosis of thymocytes culturedin vitroThis experiment was conducted to investigate the effects of different zinc sources andlevels on apoptosis and their mechanism. Dexamethasone was used to make the apoptosismodel of thymocytes;zinc sulfate and zinc methionine were added to the medium with thelevels of 0, 50, 100, 500, 1000μM. The activities of AKP, GSH-Px, CuZn-SOD andintracellular calcium concentration, the percentage of apoptosis nuclei were determined. Theresults showed that, both ZnSO4 and Zn-Met increased the activities of cells which weredrceased by dexamethasone;Zn-Met was more efficient than ZnSO4. Both forms of zincinhibited apoptosis, the modulation relied on the dose of zinc. With 50, 100, 1000μM, theability of Zn-Met inhibiting apoptosis was less efficient than ZnSO4 (P<0.05), and theyshowed no difference on modulating apoptosis with 500μM (P>0.05). Intracellular calciumconcentrations of cells cultured with Zn-Met were higher than those cultured with ZnSO4 ofthe same level. Zinc supplementation decreased the concentration of intracellular calciumsignificantly (P<0.05), but increased the activities of GSH-Px and CuZn-SOD (P<0.05) inboth the extract and the supernatant of the cells cultured, the AKP activity in the supernatantof the culture fluids was also increased by zinc supplementation (P>0.05). Zn-Met did moreefficiently than ZnSO4 in improving the ability of antioxdiation of the cells. It was concludedthat both forms of zinc inhibited apoptosis of thymocytes induced by glucocorticoid;themechanism involved the exchange of intracellular calcium and the redox of cells;and the twoforms of zinc inhibited apoptosis by different ways.7. The regulation mechanism of different zinc sources on apoptosisDexamethasone was used to make the apoptosis model of thymocytes. ZnSO4 and Zn-Metwas added to the medium at 1000μM, the percentage of apoptosis nuclei were determined byflow cytometric analysis, bcl-2, bax and caspase-3 mRNAs abundance were measured byRT-PCR. The results showed that both ZnSO4 and Zn-Met inhibited apoptosis induced bydexamethasone (P<0.05);no difference was shown between the two forms of zinc (P>0.05).Both forms of zinc decreased the up-regulation of bcl-2, bax and caspase-3 mRNAsexpression by dexamethasone (P<0.05). Cell availability and caspase-3 mRNA expression ofcells cultured with Zn-Met were higher than those cultured with ZnSO4 (P<0.05). Thepercentage of apoptosis nuclei, bcl-2 and bax mRNAs expression were similar within the twotreatments (P>0.05). It was concluded that both forms of zinc could inhibit apoptosis ofthymocytes induced by glucocorticoid;the mechanism involved the regulating ability of zincon genes expression, and the two forms of zinc regulated apoptosis by different ways.From above results, it was concluded that, both ZnSO4 and Zn-Met improved the growth ofanimals by up-regulating the expression of IGF-I mRNA. Zn-Met enhanced the weight gain,up-regulated IGF-I mRNA expression and was transported more efficiently than ZnSO4.DDRT-PCR was an effective way to identify unknown genes regulated by different zincsources. Both forms of zinc improved the immunity and ability of antioxidation in mice, whileZn-Met showed more effectively than ZnSO4. In inhibiting apoptosis, Zn-Met was moreefficiently in increasing the ability of antioxidation and the ratio of bcl-2 and bax mRNAs,and less efficient in decreasing apoptosis happening, the increment of intracellular calciumand caspase-3 mRNA expression. In addition, Zn-Met was less harmful to cells cultured.