Iron absorption by humans from hemosiderin and ferritin, further studies.

CARLOS MARTINEZ-TORRES, MARTHA RENZI ANDMIGUEL LAYRISSE Instituto Venezolano de Investigaciones CientÃ-ficas, Apartado 1827. Caracas, Venezuela ABSTRACT Iron absorption from hemosiderin and ferritin biosynthetically labeled with radioactive iron has been studied in 61 subjects. The geometrical mean iron absorption from hemosiderin in both normal and iron deficient subjects was 3.4%. Its mean absorption ranged from 1.9% in normal subjects to 4.7% in subjects with moderate iron deficiency and 7.3% in subjects with marked iron deficiency. The iron absorption from hemosiderin was markedly increased when it was administered with ascorbic acid or liver. The absorption of iron from hemosiderin when hemosiderin and wheat were consumed in a meal, was lower than the absorption from wheat. Iron from liver ferritin and liver hemosiderin were less absorbed in this study than that previously reported for liver hemo globin. The studies presented here support the possibility that ferritin and hemosiderin form an iron pool different from the non-heme pool formed by vegetal iron, egg iron and ferric and ferrous salts. J. Nutr. 106: 128135,1976. INDEXING KEY WORDS iron hemosiderin ferritin The iron absorption from animal foods such as meat, fish and liver represents the sum of the absorption of three main com pounds: heme, ferritin and hemosiderin (1, 2, 3). It is well known that the iron absorption from purified heme is very low (4) but it is several times greater when it is administered as hemoglobin and myoglobin (1, 2, 5-8). The iron ab sorption from purified ferritin is very low. Its mean absorption ranges from 0.9% in normal subjects to about 5.7% in subjects with marked iron deficiency. Its absorption is increased several times when it is ad ministered with either ascorbic acid, meat or liver (9, 10) and is decreased when it is administered with desferrioxamine (11). The study presented here provides in formation on the absorption of both hemo siderin and ferritin iron. The results show that the iron absorption from hemosiderin is very similar to that found from ferritin and it is distinctly lower than the absorp

tion from vegetal iron when they are ad ministered together. MATERIAL AND METHODS

Sixty one peasants from rural areas in Venezuela consented to collaborate in this study, 18 were males and 43 females.2 These subjects were in apparent good health. Only a few of them had moderate iron deficiency anemia. Each individual participated in several iron absorption tests. Hemoglobin concentration (12), serum iron concentration (13) and unsaturated iron binding capacity (14) were de termined. Purified ferritin and hemosiderin. Three month-old rabbits were injected intra muscularly with 10 mg of iron as iron dexReceived for publication July 7, 1975. 1 Supported In part by World Health Organization and William Waterman Fund. 'The study followed the guidelines of the Helsinki Doctrine.

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Iron Absorption by Humans from Hemosiderin and Ferritin, Further Studies1

HEMOSIDERIN AND FERRITIN IRON ABSORPTION

Ferrous ascorbate solution. Tracer doses of iron in the form of ferric chloride with specific activity of about 10-15 /Â¿Ci68Fe or 55Fe per /Â¿gFewere mixed with carrier ferrous sulfate. Two moles of ascorbic acid per mole of iron were added prior to oral administration. Preparation and mixing of labeled testing material The absorption test of hemosiderin given alone was made by suspending the radio active hemosiderin precipitate in about 200 ml of malfine 4 which contained 0.5 g of protein per 100 ml. In the other tests the hemosiderin precipitate was mixed with the foods. Radioactive ferritin solution was mixed with the foods. Radioactive and carrier whole-wheat was made into a dough, mixed thoroughly with hemosiderin precipitate and finally cooked in an aluminum pan in the form of pan cakes (8, 9).

Absorption studies Food biosynthetically labeled with radio active iron was administered in the morn Characteristics of the radioactive ing after an overnight fast. No food or hemosiderin and ferritin drink was allowed for 3 hours following The source of hemosiderin was the water the administration of radioactive material. The next day a dose of ferrous ascorbate insoluble material obtained after centrifu gation of the homogenized rabbit liver or another food labeled with a different (16, 17). Its specific activity was 0.12 Â¿tCi/ radioactive isotope of iron was admin istered. Blood was drawn 15 days after the mg Fe. The dose of this insoluble ma first administration of radioactive food to terial administered to each subject con determine hematological characteristics and tained 120 mg of non-hemosiderin protein, estimated from nitrogen content by Kjel- radioactivity. Some subjects were fed again on day 15 and 16 with another radioactive dahl procedure. and blood was taken on day 30. The electrophoretic pattern of ferritin material Approximately 0.6 /aCi of 59Fe and 2/Â¿Ci separated from other liver iron compounds 55Fe were used in each test. Duplicate by centrifugation and heat, showed small 10-ml blood samples were prepared for contamination with other proteins. It con radioactive counting following the tech tained about 80 mg of non-ferritin protein per dose administered to each subject. Its nique of Dern and Hart (18, 19). Radio specific activity was about 0.8-1.0 //.Ci/mg activity was measured in a liquid scintil lation spectrophotometer. Triplicate stan Fe. dards of the food administered were Other food. Wheat was biosynthetically labeled with radioactive iron by growing counted simultaneously with the blood plants in hydroponic culture with radio samples. The iron absorption from the active iron added to the medium (8, 9). foods was calculated from the S5Fe and Labeled veal liver iron was obtained from 59Fe activity in the subjects' blood using three month-old calves which had pre viously been injected intravenously with 3 Imferon, Sandoz, Venezuela, S.A. ' Food preparation of malt. radioactive iron (2).


tran complex 3 per kg body weight three times a week until a total dose of 100 mg of Fe/kg body weight was reached. Two days after the last injection a dose of 0.4 mg of mechlorethamine per kg body weight was injected intravenously to de press bone marrow function, and three days later 250 /xCi of 59Fe or 1500 /Â¿Ciof 55Fe was administered intravenously. A week later the animals were exanguinated by puncture the liver perfused "in cardiac situ" with saline and solution. Ferritin and hemosiderin were prepared by homogenizing rabbit liver in distilled water. The suspension was centrifuged at 3,000 X g for 30 minutes. The precipitate part was used as the hemosiderin prepara tion to test the iron absorption. The super natant was heated at 75Â°for 10 minutes according to the method of Laufberg ( 15 ) and modified by Cabrio et al. (16). The supernatant obtained after centrifugation of the heated supernatant was used as the ferritin preparation without further puri fication. The ferritin solution and hemo siderin precipitate were kept at 4Â°until used.

129

130

MARTINEZ-TORRES,

RENZI AND LAYRISSE

TABLE 1 Iron absorption from hemosiderin and iron ascorbate absorptionA Iron

ascorbate(SmgFe)Â«Fe%13.04.08.316.230.712.49.28.910.5 mg)saturation%4220451919182433163219272831293Â»30373146733391326301527Â»Fe%0 (3.7-4.7

fication1) /WO ml14.414.914.314.114.914.714.414.515. ml1616114366685082120549364849810393131921451031782995125481011186293Transferrin H.R.2) C.R.3) R.T.4) M.J.5) J.B.6) A.P.7) M.G.8) A.M.9) G.G.10) R.T.11) E.A.12)


HemosiderinIdenti

G13.714.015.914.913.813.812.314.115.614.313.613.113.312.914.113.113.113.214.314.1Serumironng/100

1.8.13)

J.B.14) N.G.15) R.M.16) G.G.17) R.G.18) O.A.B.19) B.M.20) A.R.A.21) D.S.22) F.J.23) R.G.24) R.G.25) M.C.26) M.H.27) C.G.28) M.I.G.MeanSEMHbg

an estimate of blood volume based on sex, weight and height ( 20 ). No correction was made to determine total iron utilization. Statistical analysis. The mean absorp tion and standard deviation were calcu lated from the logarithm of the percentage of absorption and the result was retransformed as antilogarithm to recover the original units. The comparison between the two absorption tests performed on dif ferent meals in tables 1 to 3 was calculated by the student's test in pair samples (21). The mean absorption ratio in tables 4 to 6 was calculated by the least square re gression analysis fitting the regression line through the origin.

RESULTS

Characteristics of iron absorption from hemosiderin Iron absorption from hemosiderin given alone was tested in 28 subjects, its mean geometrical absorption was 3.4%. The mean absorption ratio of hemosiderin to iron ascorbate was 0.16 (table 1). There was a highly significant correlation coeffi cient (r = 0.64 ) between the absorption of hemosiderin and iron ascorbate but a poor correlation was obtained when the ab sorption of hemosiderin was compared with the serum iron concentration ( r = 0.02) and the transferrin saturation (r = 0.07). According to these results the sub-

HEMOSIDERIN

AND FERRITIN

TABLE 2 Effect of ascorbic acid on the absorption of hemosiderin iron

131

IRON ABSORPTION

TABLE 3 Effect of liver on ike iron absorption from hemosiderin Iron absorptionHemosiderin

absorptionIdentification6)

Iron

Fe)+mg Fe)"Fe0.40.91.21.32.02.32.32.63.86.31.81.2BHemosiderin"Fe0.72.1 mg Fe)given mg ascorbicacid fication1)42j6)7)8)11)12)14)22)MeanSEMHemosiderin(3.7 alone (100 mg) "Fe1.62.84.34.76.76.38.011.012.06.31.7BHemosiderin(4 Â«Fe6.18.014.520.33.79.210.016.924.910.82.2B/A ratio3.812.863.374.320.651.461.261.642.082.040.81

A.P.11) E.A.16) G.G.17) R.G20) A.R.A.21) D.S.23) R.G.27) C.G.28) M.I.G.MeanSEMAHemosiderin(4


Fe)+ (3.7 mg Liver (8 mg

Fe)Identi

2.2:i.21.89.19.86.311.914.74.21.6CLiver"Fe2.6119.810.118.932.316.02 0.380.330.180.650.300.390.410.460.360.11

The absorption tests were performed 15 days apart.

jects were divided into three groups, namely, a) subjects with iron ascorbate absorption below 20%, representing most subjects with normal iron stores; b) sub jects with iron ascorbate absorption be tween 20% and 39%, representing normal subjects and those with moderate iron de-

ficiency and c ) subjects with iron ascorbate absorption above 40%, representing those with marked degree of reduction in iron stores. The mean absorption from hemo siderin in these three groups was 1.9%, 4.7% and 7.3 % respectively. Effect of ascorbic acid. Nine subjects were tested for iron absorption from hemo-

TABLE 4 The effect of interaction of hemosiderin and wheat on iron absorption absorptionHemosiderin Iron (3 mg Fe) + whole wheat (2 mg

Fe)Identi

siderinMFe%0.20.61.31.71.73.03.54.54.95.91.90.7BWheat"Fe%0.30.82.1 fication29) 1100 ml13.014.513.213.111.614.112.213.913.814.713.4Serumironng/100 ml11211272755911739117839488Transferrinsaturation%353020221428726192222AHemo I.M.30) A.L.31) L.E.32) E.G.33) B.V.34) J.R.C.35) J.P.36) E.P.37) A.C.38) B.C.MeanSEMHbg

1Calculated by the least square regression analysis.

132

MARTINEZ-TORRES,

Effect of interaction of hemosiderin with animal and vegetal foods Table 3 shows the effect of liver on the absorption of iron from hemosiderin in 10 subjects. The geometrical mean absorp tion from hemosiderin given alone was 1.8%. It increased up to 4.2% when it was administered with liver, but this absorp tion still remained about 60% lower than the absorption from veal liver. Table 4 shows the effect of interaction of hemosiderin and whole wheat on iron absorption. The mean absorption from hemosiderin was 1.9%, from wheat was 2.9% and the mean ratio of hemosiderin to wheat iron absorption was 0.65. It can be

observed that the individual absorption ratio was very consistent, over a wide range of absorptions, from 0.2% to 5.9%. Effect of interaction of hemosiderin and ferritin on iron absorption Table 5 shows the iron absorption from hemosiderin and ferritin labeled with dif ferent isotopes when they were mixed and administered as a meal. The mean ab sorption ratio calculated by the least square regression analysis was 0.84 Â±0.08 (standard error). Although the mean ab sorption was close to unity, the individual ratios were rather diverse, especially those from individuals with low absorption. This is probably due to the difficulty in obtain ing an homogenous mixture of these sub stances and to the low radioactivity in the blood. When labeled hemosiderin and ferritin were mixed with nonradioactive liver, the absorption increased by about twice but

TABLE 5 The effect of interaction of hemosiderin and ferritin on iron absorption absorptionHemosiderin Iron

(2-3mgFe)Identi

fication39)

+ Ferritin

(3 mg Fe)

(3 mg Fe) + Ferritin (2-3 mg Fe) g)CHemo + carrier liver (40


siderin given alone and from hemosiderin administered with 100 mg of ascorbic acid (table 2). Ascorbic acid doubled the ab sorption of iron from hemosiderin, the mean absorption was 5.3% without ascor bic acid and it increased to 10.8% when the vitamin was added.

RENZI AND LAYRISSE

siderin"Fe%0.91.51.92.72.81.15.21.36.95.24.54.611.97.28.5 ritin"Fe%0.81.42.02.23.42.55.51.27.04.85.13.81 satu siderinMFe%0.70.81.01.01.01.21.72.22.32.73.44.15.45.55.62.01.2BFer ritin"Fe%0.90.60.60.90.91.12.32.22.83.04.33.75.37.37.42.11.2A/Bratio0.781.33 ration%102126432(>23372113242895241522AHemo

ml12.414.217.817.613.815.517.215.514.014.716.012.711.314.413.114.7Serumironlig/ ml38701141801071021596948107974624976788Transfer-rin 100 J.S.40) I.M.41) L.S.42) P.V.43) M.C.S.44) A.D.A.45) A.R.46) M.A.47) J.A.48) R.C.49) A.F.50) M.D.51) H.B.52) O.S.53) V.R.MeanSEMHbg/100


HEMOSIDERIN

the absorption unity.

ratio

remained

AND FERRITIN

close to

Effect of interaction of purified ferritin and non-heme liver iron on iron absorption

lower than the iron absorption from whole liver in which hemoglobin iron is also present. Although the iron absorption from whole liver was not tested in these subjects, one might expect an absorption to be above 20% since 6 out of the 8 sub jects tested had values for transferrin satu ration below 15% (2). DISCUSSION The data presented here have shown that the iron absorption from hemosiderin is in many aspects similar to that from ferritin (10). The absorption was low when it was given alone, but increased when administered with ascorbic acid or with liver. The iron absorption from hemo siderin given alone tended to be slightly higher than that from ferritin; the mean ratio of hemosiderin to iron ascorbate was 0.16 while the mean absorption ratio of ferritin to iron ascorbate was found pre viously to be 0.11 (10). However, the dif ference between the two ratios was not statistically significant. The absorption from hemosiderin and from ferritin was the same when they were mixed before in gestion. Iron absorption from liver is very close

TABLE 6 Effect of interaction of purified ferritin and non-hemoglobin liver iron on iron absorption absorptionFerritin Iron

(1 mÃ§Fe) + dehemoglobinized liver (50

g)Identi

fication54)

(1 mg Fe) + dehemoglobinized liver (50 g) + nonradioactive maize Fe)CFer (1 mg


In order to determine whether the ab sorption of iron from purified ferritin was similar to the absorption from ferritin and hemosiderin retained in the liver, labeled and unlabeled rabbit livers were exanguinated carefully, reducing heme iron to less than 10% of the total liver iron. Fer ritin labeled with a different radioactive isotope of iron was then mixed with the dehemoglobinized liver and administered to subjects as a meal. The absorption from ferritin and from iron non heme liver was about 5% and the mean absorption ratio close to one. Both absorption values were reduced to 3% when the mixture of labeled ferritin and dehemoglobinized liver was administered with 1 mg of non-radioactive maize iron. These results indicate that absorption of iron from purified ferritin mixed with liver reflects the iron absorption from both the ferritin and the hemosiderin present in the liver. They also indicate that the iron ab sorption of these iron compounds is much

133

IRON ABSORPTION

satu ritinHFe%1.41.42.97.07.210.511.915.05.01.8BLiverÂ»Fe%1.51.42.76.55.98.711.214.04.8 ritin"Fe%1.45.31.01.04.94.97.55.13.01.5DLiver"Fe%1.14 ration%243711510fi81014AFer

1100 ml12.115.313.411.510.98.711.012.211.9Serumironpg/100 ml10215039212826313854Transfer-rin E.H.55) J.L.R.56) R.P.57) G.T.58) C.V.59) O.G.60) D.H.61) H.R.S.MeanSEMHbg


134

MARTINEZ-TORRES,

whether or not their absorption is similar when they are administered together. Ac cording to this concept vegetal iron, ferric and ferrous salts, egg iron, ferritin, hemo siderin and possibly dust iron could form this pool. If this concept is restricted only to those iron compounds which have sim ilar absorptions when they are adminis tered together, ferritin and hemosiderin should be placed apart as a third iron pool or at least as a sub-group of the nonheme iron pool. Studies on the iron absorption from a meal determined by the extrinsic label method have demonstrated that a small amount of labeled ferric or ferrous salt mixed with the foods measured with ac curacy the iron absorption of vegetal, egg and iron salts present in the meal (24-27). Similarly, a small amount of labeled rabbit hemoglobin determined the absorption of both hemoglobin and myoglobin present in the meal (26). Neither iron salt nor hemoglobin could with accuracy detect the iron absorption from ferritin and hemo siderin, but labeled purified ferritin could be used to measure the absorption of these iron compounds present in liver and other animal foods. ACKNOWLEDGMENTS The authors are indebted to Mr. Gui llermo LÃ³pez-CalzÃ³n, Irene Leets and Hamilton Bello for their technical as sistance. LITERATURE CITED 1. Martinez-Torres, C. & Layrisse, M. (1971) Iron absorption from veal muscle. Am. J. Clin. Ntitr. 24, 521-540. 2. Martinez-Torres, C., Leets, I., Renzi, M. & Layrisse, M. ( 1974 ) Iron absorption from veal liver. J. Nutr. 104, 983-993. 3. Martinez-Torres, C., Leets, I. & Layrisse, M. (in press) Iron absorption from Fish. Arch. Latinoamericanos Nutr. 4. Conrad, M. E., Cortei], S., Williams, H. L. & Foy, A. L. ( 1968 ) Polymerization and intraliiminal factors in the absorption of hemoglobinâ€”iron. J. Lab. Clin. Med. 68, 659-668. 5. Callender, S. T., Mallett, B. J. & Smith, M. D. ( 1957 ) Absorption of hemoglobin iron. Brit. J. Haemat. 3, 186-192. 6. Turnbull, A., Cleton, F. & Finch, C. A. ( 1962 ) Iron absorption IV. The absorption of hemoglobin iron. J. Clin. Invest. 41, 18971907.


to that from meat (1, 2, 22, 23). However, in each instance the absorption from heme and non-heme iron compounds pres ent in these foods was not determined separately. Previous studies ( 10) demon strated that the iron absorption from puri fied ferritin is always lower than the iron absorption from liver when both foods are administered together. Similar results were also found in this paper when hemosiderin was administered with liver. The results in table 6 confirm these previous studies and provide evidence that ferritin and hemosiderin iron in liver are about one third less absorbed than liver hemoglobin iron. According to the transferrin satura tion in the serum of subjects tested in table 6, one would expect a mean absorp tion over 20% if they were tested for the absorption of iron from hemoglobin or from veal liver in which more than 80% of the iron content is in the form of hemo globin iron (2, 8). Previous studies have identified, in terms of iron absorption, two iron pools; namely a) a non-heme pool formed by vegetal iron, egg iron and ferric and ferrous salt and b) a heme pool formed by hemo globin and myoglobin (24, 25, 26). Iron compounds belonging to the same pool show the same percentage of absorption when they are administered together. Most of the experiments on the iron ab sorption from ferritin ( 10 ) and those per formed here with hemosiderin were con ducted to determine whether these iron compounds could be identified in these pools, especially in the non-heme pool. The administration of ferritin with vegetÃ¡is in a meal showed that its iron absorption was distinctly lower than the absorption from either maize, wheat or soybean (10). The absorption from hemosiderin was also distinctly lower than the absorption from whole wheat when they were administered together. According to these results, the concept of the non-heme iron pool should be reviewed. Considering this pool as a broad spectrum, it would be possible to in clude in it all the iron compounds behaving in their absorptions differently from the heme iron pool; that is, their absorption is increased by the administration of as corbic acid, meat, liver or fish and is de creased by desferrioxamine regardless of

RENZI AND LAYRISSE

HEMOSIDERIN

AND FERRITIN

19.

20.

21. 22.

23.

24.

25.

26.

27.

135

and Fe68 as ferrous perchlorate. J. Lab. Clin. Med. 57, 322-330. Dem, J. R. & Hart, W. L. (1961) Studies with doubly labelled iron. II. Separation of iron from blood samples and preparation of ferrous perchlorate for liquid scintillation counting. J. Lab. Clin. Med. 57, 460-467. Nadler, S. B., Hidalgo, J. U. & Bloch, T. (1962) The Tulane table of blood volume in normal men. Surgery (St. Luis) 51, 224232 Snedecor, G. W. & Cochran, W. G. (1967) Statistical methods. The Iowa State Univer sity Press. Sixth Edition, p. 91. Heinrich, H. C., Barteies, H., Gabbe, E. E., Meineke, B., Nass, W. P., Whang, D. H. (1969) Die intestinale Resorption des Nahrungs-Eisens aus dem HÃ¤moglobin, der Leber und Muskulatur bei Menschen mit normalen Eisenreserven und Personen mit pralatentem/latentem Eisenmangel. Klin. Wschr. 47, 309-317. Heinrich, H. C., Gabbe, E. E. & Kugler, G. ( 1971 ) Nahrungs Eisenresorption aus Schweine-Fleisch-Leber und Haemoglobin bei Menschen mit normalen und erschÃ¶pften Eisenreserven. Klin. Wschr. 49, 819-825. Cook, J., Layrisse, M., Martinez-Torres, C., Walker, R., Monsen, E. & Finch, C. A. ( 1972 ) Food iron absorption measured by an extrinsic tag. J. Clin. Invest. 51, 805-815. Bjorn-Rasmussen, E., Hallberg, L. & Walker, R. B. (1972) Food iron absorption in man. I. Isotopie exchange between food iron and inorganic iron salt added to food: Studies on maize, wheat and eggs. Am. J. Clin. Nutr. 25, 317â€”323 Layrisse, M. & Martinez-Torres, C. (1972) Model for measuring dietary absorption of heme iron: test with a complete meal. Am. J. Clin. Nutr. 25, 401-411. Layrisse, M., Martinez-Torres, C., Gonzalez, M. ( 1974 ) Measurement of the total daily dietary absorption by the extrinsic tag model. Amer. J. Clin. Nutr. 27, 152-162.


7. Hallberg, L. & SÃ¶lvell,L. (1967) Absorp tion of hemoglobin iron in man. Acta Med. Scand. 181, 335-354. 8. Layrisse, M., Cook, J. D., Martinez-Torres, C., Roche, M., KÃ¼hn,I. N. & Finch, C. A. ( 19R9) Food iron absorption: A comparison of vege table and animal foods. Blood 33, 430-443. 9. Hussain, R., Walker, R. B., Layrisse, M., Clark, P. & Finch, C. A. (1965) Nutritive value of food iron. Am. J. Clin. Nutr. 16, 464-471. 10. Layrisse, M., Martinez-Torres, C., Renzi, M. & Leets, I. ( 1975 ) Ferritin Iron Absorp tion in Man. Blood 45 (5), 689-698. 11. KÃ¼hn,I. N., Layrisse, M., Roche, M., Mar tinez, C. & Walker, R. B. (1968) Observa tions on the mechanism of iron absorption. Am. J. Clin. Nutr. 21, (10), 1184-1188. 12. Crosby, W. H., Munn, J. L. & Furth, F. W. ( 1954 ) Standardizing a method for clinical hemoglobinometry. U.S. Armed Forces M.J. 5, 693-703. 13. International Committee for Standardization in Heniatology ( 1971 ) Proposed Recom mendations for measurement of serum iron in human blood. J. of Clin. Path. 56, 543545. 14. Izak, G. & Lewis, S. M. (1972) Studies on the Standardization of serum iron and ironbinding capacity assays. In: Modern Con cepts in Hematology, p. 69, Academic Press. 15. Laufberger, M. V. (1937) Sur la cristalli sation de la ferritine. Bull. Soc. Chini. Biol. 19, 1575-1582. 16. Cabrio, B. W., Shoden, A., and Finch, C. A. ( 1953 ) A quantitative fractionation of tissue ferritin and hemosiderin. J. Biol. Chem. 24, 815-821. 17. Sturgeon, P. & Shoden, A. (1964) Mecha nism of iron storage. Iron Metabolism, Springer-Verlag, Berlin 121. 18. Dem, J. R. & Hart, W. L. (1961) Studies with doubly labelled iron. I. Simultaneous liquid scintillation counting isotopes of Fe56

IRON ABSORPTION

Increasing and decreasing phases of ferritin and hemosiderin iron determined by serum ferritin kinetics.

Transformation rate between ferritin and hemosiderin assayed by serum ferritin kinetics in patients with normal iron stores and iron overload.

Ferritin and intestinal iron absorption: pancreatic enzymes and free iron.

Serum-ferritin concentration and diagnostic 59Fe2+ absorption in humans with iron deficiency.

Iron absorption and serum ferritin in chronic inflammatory bowel disease.

The relationship between marrow iron stores, plasma ferritin concentrations and iron absorption.

Ferroportin mediates the intestinal absorption of iron from a nanoparticulate ferritin core mimetic in mice.

Iron absorption by rats from nonprescription dietary iron supplements.

Soy protein, phytate, and iron absorption in humans.

Superoxide-mediated release of iron from ferritin by some flavoenzymes.

Ferritin and iron overload.

Ferritin and iron overload.

Nitric oxide mediates iron release from ferritin.

The binding of ferric iron by ferritin.

Competitive inhibition of iron absorption by manganese and zinc in humans.

Mobilisation of iron from ferritin fractions of defined iron content by biological reductants.

Iron absorption in normal subjects and patients with idiopathic haemochromatosis: relationship with serum ferritin concentration.

Reevaluation of iron absorption and serum ferritin in beta-thalassemia intermedia.

Iron K-edge absorption spectroscopic investigations of the cores of ferritin and haemosiderins.

Normal and abnormal intestinal absorption by humans.

Further studies on the action of prolactin on fluid and ion absorption by the rat jejunum.

Haem binding to ferritin and possible mechanisms of physiological iron uptake and release by ferritin.

Sugar as a vehicle for iron fortification: further studies.

Mechanism and kinetics of iron release from ferritin by dihydroflavins and dihydroflavin analogues.