Difference And Mechanism Of Iron Bioavailability In Grain Of Different Rice Genotypes

Iron is an important essential micronutrient that is involved in oxygen transport andenergy metabolism. Iron deficiency is a wide-spread major micronutrient malnutritionproblem for humans, affecting one-third of the world's population. Rice is the dominant staplefood in the world which provides calories consumed and energy intake of almost half theworld's population. Therefore, slightly increase of iron content and iron bioavailability in ricegrains can greatly improve human health. In this study, iron bioavailability of different ricegenotypes were studied, and effects of foliar irons, soils, field locations, and years on ironbioavailability in rice grains were valued by a vitro digestion/Caco-2 cell model. The mainresults are summarized as followings:The Caco-2 cells were seeded onto the polycarbonate microporal membranes in Transwellbichambers and cultured on 37℃and in an atmosphere of 5% carbon dioxide. After 21 daysof culture, the transepithelial electrical resistance was about 590 Ohms·cm², the transportrate of mannitol across Caco-2 cell monolayers was less than 0.07%·h^-1·cm^-2, and the activityof alkaline phosphatase in apical (AP) side was greatly higher than that in basolateral (BL)side. These results indicated that the Caco-2 cells cultured in our laboratory had similarity tointestinal epithelial cells in morphology, produced polarity, formed well tight junctionsbetween cells, and could be used as an in vitro model to investigate absorption mechanisms ofsubstances.Iron uptake of Caco-2 cells treated with different pH or iron levels were compared fromabsorption-transport model (modelâ… ) vs absorption- translation model (modelâ…¡). The resultsindicated that iron uptake of Caco-2 cells was decreased with increasing of pH from 5.5 to 7.5,but it was increased with added iron levels in the all both model. Moreover, the decrease trendwas more obvious for modelâ… than for modelâ…¡at exceed 25μmol/L of iron levels. The resultsindicated that preferable capability of iron uptake from modelâ… than modelâ…¡at higher ironlevels.The effects of inhibitors and/or exciters on iron uptake of ferrous and ferric in Caco-2cell monolayers were investigated. The results were as follows. Uptake of ferrous wassignificantly reduced than it of ferric with increased of oxalate levels. Moreover, maximalinhibition of iron uptake of ferrous by oxalate occurred at a 1: 5 ratio of Fe to oxalate. Onlyinhibition of ferric by oxalate occurred at a 1: 3 ratio of Fe to oxalate. Uptake of ferrouswas decreased with increased of silicate levels, and maximal inhibition of iron uptake bysilicate occurred at a 1: 3 ratio of Fe to silicate. But silicate did not affect the uptake of ferric.More inhibition of iron uptake by phytic acid were from ferrous than from ferric. Uptake offerrous was inhibited in different degree with Ca2+ or Zn2+ levels, Ca2+/Fe2+ and Zn2+/Fe2+ molar ratio at 1: 1 and 3: 1 was appeared maximal inhibition of ferrous,respectively. Iron uptake was enhanced by Cys, Cys-cys, and Vc as their concentrationincreased, respectively. Comparison of iron bioavailability from different iron compoundswere showed that maximal ferritin amount of Caco-2 cell was from treated with citrate ferrousor heine, respectively. Iron bioavailability of reduced iron powder is increased withdecreasing of power granularity and is much lower than other iron compounds when the sizeis above 43μm. In general, water soluble iron compounds have an acceptable bioavailabilitybut cause unacceptable organoleptic changes during the storage or preparation of grains. Incontrast, the reduced iron powder does not cause organoleptic changes during storage or foodpreparation of cereal flours.Fe (â…¡) at a concentration＞1.5 mM was found to be more effective in reducing cellularviability than Fe (â…¢). Lactate dehydrogenase (LDH) release investigation suggested that Fe(â…¡) can reduce the stability of cell membrane. The activities of superoxide dismutase (SOD)and the glutathione peroxidase (GSH-Px) of the cells treated with Fe (â…¡) were higher thanthose of Fe (â…¢), although both of them increased with raising iron supply levels. The resultsindicate that both Fe (â…¡) and Fe (â…¢) could reduce the cellular antioxidase gene expression athigh levels.Iron concentration of unpolished rice from nine hundred seventy two rice genotypes inYangtze River Delta Region (YRDR) were determined by Fast Screening methods andICP-MS methods. The results indicated that the lowest and highest of iron content was 15.74mg/kg and 54.68 mg/kg using Fast Screening methods, respectively. Means of Fast Screeningmethods was 35.01 mg/kg. The lowest and highest of iron content was 5.25 mg/kg and 20.55mg/kg using ICP-MS methods, respectively. Means of ICP-MS methods was 13.49 mg/kg.The Fast Screening methods were significantly correlation with ICP-MS methods as 0.7699of correlative coefficient. Iron content and iron bioavailability of polished rice of thirteen ricegenotypes selected from nine hundred seventy two rice genotypes in YRDR. Ironbioavailabilities from all rice genotypes were ranked as a percent relative to a control variety(IR68144) from the International Rice Research Institute (IRRI). Iron concentration in the ricesamples ranged from 3.7 mg/kg to 9.9 mg/kg. No correlation was observed between ironbioavailability and grain iron concentration. Iron bioavailabitity of polished rice from Gpei55,guangN66, HB075, and TN7189 genotypes were significantly higher than other ricegenotypes. Genotypes with high iron concentration (JiaXingZD, HESQ57, and GuangD50)have relatively low iron bioavailablity. In contrast, genotype of guangN66 with lowest ironconcentration has much high iron bioavailability. Cysteine and S levels showed positively andsignificantly correlation with iron bioavailability in polished rice. In contrast, P levels of polished rice showed negatively and significantly correlation with iron bioavailability. Theadded ascorbic acid significantly promoted iron bioavailability relative to experimentswithout added ascorbic acid.Iron concentration of unpolished rice from grown in Silt Loam Soil (SLS)(P＞0.05) andPurplish Clayey Soil (PCS)(P＞0.05) were reversely higher than grown in Yellowish red Soil(YRS). Different soil had no effect on Calcium, Copper, Zinc, protein and Amylose (P＞0.05).Phytic acid (P＜0.05) and P(P＞0.05) concentration of unpolished rice from YRC werelower than from SLS and PCS, respectively. S concentration of unpolished rice from SLS wassignificantly lower than PCS (P＜0.05) and YRS (P＜0.05). moreover, maximal Sconcentration of unpolished rice from YRS. Cysteine content of unpolished rice was showedthat rice grown in YRS was significantly higher than it grown in SLS (P＜0.05) or PCS (P＜0.05). Dialyzable iron amount and ferritin formation of unpolished rice from YRS weresignificantly higher than from SLS (P＜0.05) or PCS (P＜0.05), and no significant differencebetween SLS and PCS. Transport iron of Caco-2 cells treated with unpolished rice from YRSwas significantly lower than SLS (P＜0.05) and PCS (P＜0.05), respectively. Comparison ofiron bioavailability among different rice genotypes were indicated that genotype of IR64 hadthe lowest dialyzable iron and ferritin formation amount than other genotypes (P＜0.05), andthose were highest in genotypes of TN7189 and IR68144. Transport iron amount of Caco-2cells treated with genotype of IR64 (P＜0.05) and TN7189 (P＜0.05) was significantly lowerthan treated with IR68144 and HB075 genotypes, respectively. Obvious genotypic differencesin nutrient compositions were observed among the tested genotypes, such as protein, amylase,phytic acid, P, S, Ca, Cu, Zn, and 17 amino acids, however, only dialyzable iron levelsshowed positively and significantly correlation with iron bioavailability in unpolished rice. Incontrast, phytic acid and P levels of unpolished rice showed negatively and significantlycorrelation with iron bioavailability. Noticeable, iron bioavailability was no significantlycorrelation with grain iron in unpolished rice.Four rice genotypes from IRRI were grown in Hangzhou, Donghui, and Haining at twoyears, respectively. The effects of variety, location, and variety×location (G×E) onnutrient compositions and iron bioavailability of polished rice were investigated. The resultswere as follows. The varieties (P＜0.01; P＜0.01; P＜0.01), and variety×location (P＜0.01; P＜0.05; P＜0.01) interaction effects were highly significant for grain-Fe, -Caconcentration and iron bioavailability. Grain-Cu and-Mn concentration were significantlyaffected by varieties (P＜0.05; P＜0.01) and locations (P＜0.05; P＜0.01). The varietieseffects was higher than locations and variety×location (P＞0.05) for grain Znconcentration. Grain protein content of polished rice from area of Hangzhou was higher thanareas of Donghui and Haining. Different plant areas did not affect the amylose concentration in polished rice. Grain phytic acid and P content of rice from area of Donghui were higherthan areas of Hangzhou and Haining, but grain S was lower than Hangzhou and Haining.Relative content of 17 amino acids in polished rice from area of Hangzhou were higher than itfrom areas of Donghui and Haining. Iron bioavailability of polished rice was determinedusing an in vitro digestion/Caco-2 cell model. The results indicated that genotype IR68144had the highest iron bioavailability, and genotype IR72 had the lowest iron bioavailabilityamong all the rice genotypes. Grain phytic acid and P levels showed negatively andsignificantly correlation with iron bioavailability in polished rice. In contrast, grain cysteineand S levels showed positively and significantly correlation with iron bioavailability. But nosignificantly correlation between grain iron content and iron bioavailability. The ironbioavailability of four rice varieties from second year was significantly higher than it fromfirst year.The effects of different foliar irons on nutrient compositions and iron bioavailability in ricegrain were investigated. The results were as follows. The total Fe amount of polished rice wasadvanced as two genotypes rice applied foliar irons. Cysteine concentration of rice grain wassignificantly increased as HB075 genotype treated with FeSO₄ and EDTAFeNa, but nosignificant difference between without and with foliar irons in TN7189 genotype. Phytic acidconcentration of polished rice was significantly decreased as treated with foliar irons inHB075 genotype. Except HEDTAFe, other foliar irons significantly decrease phytic acidlevels in grain of TN7189 genotype. P concentration of rice grain was decreased as appliedfoliar irons in two genotypes. S content of polished rice was significantly increased by foliarirons in HB075 genotype, but no significant difference in TN7189 genotype. DTPAFe offoliar iron significantly increase calcium concentration in grain of HB075 genotype.HEDTAFe of foliar iron significantly increase calcium concentration in grain of TN7189genotype. The concentration of iron and zinc in the HB075 genotype increased as treated withfoliar irons, and peaked treated with DTPAFe. Copper concentration of grain was significantlyincreased with HEDTFe, however, concentration of zinc was significantly decreased byEDTAFeNa in TN7189 genotype. Iron bioavailability of polished rice from HB075 genotypesignificantly higher than TH7189 genotype. Dialyzable iron amount of grain no significantlyincreased as treated with different foliar irons in two rice genotypes. The ferritin formation ofCaco-2 cell treated with polished rice from applied foliar irons was increased in HB075genotype, and hardly increased in TN7189 genotype. Transport iron amount of HB075genotype significantly increased by FeSO₄ and DTPAFe, and it significantly increased byFeSO₄, EDTAFe and HEDTAFe in grain of TN7189 genotype. This result suggested that ironbioavailability of grain significantly controlled with genotypes, and it can be increased withdifferent genotypes as applied appropriate foliar iron.