| With the benefits on absorption rate, growth, immunity and environment, iron amino acid chelate has been paid more attention in animal nutrition. Studies showed that chelated or proteinated sources of Fe have 125-185% relative availability compared with ferrous sulfate. The better bioavailability of iron amino acid chelate is maybe mainly due to its highly efficient absorption, but its absorption mechanism is still not clear. Iron glycine chelate (Fe-Gly) could be more easily absorbed compared with other Fe sources. In this study, research on manipulation of Fe-Gly uptake in iron-deficiency rat model, absorption mechanism of Fe-Gly in Caco-2 cell model and its application in weanling piglets and broilers were carried out to reveal the possible mechanism of absorption and biological effects of Fe-Gly.The main contents and results are as follows:1) Iron-deficiency SD rat model was established. The results showed that blood hemoglobin level fell to 107.67 g/L, serum iron and liver iron levels decreased significantly when 3-w old SD rats fed a low iron diet after 2 weeks. This indicated that SD rats with iron-deficiency model had been initially established. Compared with the control group, iron deficiency significantly reduce body weight of rat by18.03% (P＜0.01), serum TIBC increased by 29.37% (P＜0.01), SF content and CAT level decreased by 27.71% (P<0.01) and 12.40% (P<0.05). Iron deficiency greatly reduced relative expression of Hepcidin to 0.06-fold in liver; and increased duodenal DMT1 and FP1 relative expression level by 2.55-fold and 2.79-fold. There is no significant difference in relative expression of PepTl.2) Iron-deficiency rat model was conducted to determine the effects of Fe-Gly on growth, iron metabolism and iron regulation. Ninety iron-deficiency rats (initial weight of 66.43±6.86 g) were allotted to 3 treatments based on live weight and sex. Treatments consisted of:FeSO4 group (35mg Fe/kg diet from FeSO4, control group); glycine group (35 mg Fe/kg diet from FeSO4, and the molar ratio of Fe:glycine= 1:2); Fe-Gly group (35 mg Fe/kg diet from Fe-Gly). After 2-w feeding trial, the results showed that rat liver, spleen and kidney index was significantly increased (P<0.05) when rat was fed Fe-Gly. Supplemental Fe-Gly in diets increased serum, liver and spleen iron content by 26.76%(P<0.01),34.58% (P＜0.01) and 26.72% (P＜0.01). Addition with Fe-Gly enhanced serum SF and CAT levels by 22.72% and 81.00% (P＜0.01), and reduced TIBC, XOD levels by 20.42% and 23.05% (P＜0.05) compared with the control. Compared with the control, the relative expression levels of liver Hepcidin in glycine group and Fe-Gly group increased to 3.27-fold and 5.65-fold, duodenum PepTl enhanced to 2.55-fold and 6.27-fold, duodenum DMT1 decreased to 0.33-fold and 0.23-fold, duodenum FP1 reduced to 0.38-fold and 0.22-fold, respectively. The result indicated that Fe-Gly could improve the body iron status quickly and also found PepTl maybe play a key role in intestinel absorption of Fe-Gly.3) The Caco-2 cell transport model was established. After 21-days culture, the Caco-2 cell model has formed a tight monolayer, with a steady TEER value 466.75±50.48Ω·cm2 and a transportation percentage of fluorescein sodium at 0.85% in 150 min. The AKP activity in the apical side (AP) is greatly higher than the basolateral side (BL), which means the Caco-2 cell has polarity by 21-days differentiation. Therefore, the Caco-2 cell model established in this study can be used as an in vitro intestinal absorption model with accepted standards.4) The transports of Fe-Gly and FeSO4 in Caco-2 cell monolayers were conducted from AP to BL and BL to AP, respectively. The effects of concentration (0.5-20μmol/L of Fe), time (0-120 min) and temperature (37℃and 4℃) on transport Fe-Gly and FeSO4 were investigated. Transports of Fe-Gly and FeSO4 across Caco-2 monolayers both from AP to BL and BL to AP direction were concentration-and time-dependent. There are more amounts of Fe-Gly and FeSO4 transport under 37℃than those under 4℃from AP to BL direction. The apparent permeability coefficient (Papp) of Fe-Gly was between 0.15×10-6 cm/s and 10.40×10-6 cm/s, which decreased with the increased concentration. Papp of FeSO4 was between 0.18×10-6 cm/s and 4.70×10-6 cm/s. Fe-Gly transport across Caco-2 cell monolayers was significantly higher than FeSO4 (P＜0.05) when incubation temperature under 37℃. The transport rate of Fe-Gly decreased with increasing supplemental levels. Therefore, it can be deduced that the absorption of FeSO4 and Fe-Gly in Caco-2 cells is mainly through active transport. It is known that the intestinal absorption of FeSO4 is through DMT 1-mediated active transport, while the intestinal absorption of Fe-Gly may be through a specific or non-specific intestinal active transit system. The transport mounts of Fe-Gly accros Caco-2 cell monolayers were significantly higher than FeSO45) The study was carried out to determine the effects of different factors on Fe-Gly and FeSO4 transport across Caco-2 cell monolayers. Transport of 10μmol/L of Fe in the form of Fe-Gly or FeSO4 were conducted with 10μmol/L vitamin C (iron absorption enhancer) or sodium oxalate (iron absorption inhibitor), respectively. The studies shown that vitamin C had no great effect on transport of Fe-Gly (P>0.05). However, FeSO4 transport was significantly enhanced by supplemental vitamin C (P＜0.05). Sodium oxalate did not affect the transport of Fe-Gly (P>0.05), but greatly reduced FeSO4 transport (P＜0.05). These results indicated that FeSO4 was easily affected by dietary factors compared to Fe-Gly.6) The study was conducted to determine the effects of Fe-Gly on growth, immunological characteristics and meat color in weanling pigs. One hundred and eighty pigs (initial weight of 7.81±0.72 kg) were allotted to six treatments based on live weight and litter origin. Treatments consisted of 0,30,60,90, and 120 mg/kg Fe-Gly groups (calculated with Fe) and 120 mg/kg FeSO4 group (calculated with Fe). Compared with the control, ADG was enhanced (P＜0.05) when pigs fed diets containing 60,90 or 120 mg/kg Fe-Gly. Supplemental 60,90 or 120 mg/kg Fe-Gly or 120 mg/kg FeSO4 greatly increased thymus gland index (P＜0.05) compared with the control. Lymphocytes from whole blood of experimental pigs had a higher proliferative response to ConA (P<0.05) when diet supplemental 90,120 mg/kg Fe as Fe-Gly. The hemoglobin, RBC and PCV were increased by 13.08% (P＜0.05),14.31% (P＜0.05) and 20.53% (P＜0.05) when pigs fed 90 mg/kg Fe-Gly. Myoblobin concentrations of M. longissimus dorsi were enhanced with addition of Fe-Gly from 60 to 120 mg/kg. SOD and CAT activities were increased when pigs fed 90 mg/kg Fe-Gly.90,120 mg/kg Fe-Gly or 120 mg/kg FeSO4 also enhanced serum, heart, liver and spleen Fe concentration (P＜0.05 or P＜0.01) compared with the control.120 mg/kg Fe as Fe-Gly or FeSO4 enhanced Fe concentration in feces compared with the control. SUN and SUL contents increased and AKP activity decreased when pigs fed 60,90 or 120 mg/kg Fe-Gly. Those results indicated that 90 mg/kg Fe-Gly had benefits on improving growth, immulogical functions and meat color of weanling pigs.7) The study was carried out to determine the effects of Fe-Gly on growth performance, immunological characteristics and antioxidant index of broiler chickens. Three hundred and sixty 1-d old commercial broiler chicks (Ross×Ross) were randomly allotted to six dietary treatments. Treatments consisted of 0,40,80,120, and 160 mg/kg Fe-Gly groups (calculated with Fe) and 160 mg/kg FeSO4 group (calculated with Fe). Feeding trial included 0-21d and 22-42d period. The results showed that compared with the control,120 and 160 mg/kg Fe-Gly improved 6-w body weight and 22-42-d ADG of broiler chickens. Thymus gland index was increased (P＜0.05) when chicks fed 80,120 mg/kg Fe as Fe-Gly at d 21 and d 42. Lymphocytes from whole blood of experimental chickens had a higher proliferative response to LPS (P＜0.05) when diet supplemental 120,160 mg/kg Fe as Fe-Gly at d 21.80,120 mg/kg Fe-Gly enhanced IgM (P＜0.05) and IgG (P＜0.05) contents at d 21 and d 42. The concentration of Fe was significantly increased (P＜0.05) in serum, liver, breast muscle and feces of chicks fed diets supplemented with 120,160 mg/kg Fe as Fe-Gly or 160 mg/kg Fe as FeSO4 at d 21 and d 42. In addition, tibia Fe storage was improved (P＜0.05) when chicks were fed 80,120, 160 mg/kg Fe as Fe-Gly or 160 mg/kg Fe as FeSO4 at d 21 and d 42. Feeding 120,160 mg/kg Fe as Fe-Gly greatly enhanced serum SOD and CAT activities (P＜0.05), and decreased MDA activity of 21-d chicks. Serum CAT activity was increased when chicks fed 80,120,160 mg/kg Fe as Fe-Gly or 160 mg/kg Fe as FeSO4 at d 42. These results indicated that 120 mg/kg Fe as Fe-Gly has better effects on improving growth, increasing development of immune organs, enhancing serum IgM and IgG levels, promoting T lymphocyte proliferation, and enhancing antioxidant capacity of broiler chickens.In summary, the relative expression of liver hepcidin significantly reduced and relative expression of duodenal DMT1 and FP1 greatly improved when SD rat was in iron deficiency. Addition with iron glycine chelate could improve iron status of iron-deficiency rat quickly, and the relative expression of duodenal PepTl was significantly raised compared to FeSO4. PepTl may be played a key role in the intestine absorption of Fe-Gly. The transport mounts of Fe-Gly across Caco-2 cell monolayers were significantly higher than FeSO4, while FeSO4 was easily affected by dietary factors relative to Fe-Gly. Those indicated that there may be a specific or non-specific intestinal active transport system to transport Fe-Gly. In addition, dietary Fe-Gly was beneficial to growth, immune function and meat color of weanling pigs; also improve growth, immune function and antioxidation of broiler chickens. |
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