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Biomedical subjects

B Lönnerdal

Publications and source records attributed to B Lönnerdal.

At least 145 records · Page 8Linked to original sources
PubMed1989

Manganese retention in man: a method for estimating manganese absorption in man.

Whole-body retention of 54Mn was studied in man by measurements in a sensitive whole-body counter after intake of an extrinsically labeled infant formula. Reproducible retention figures at day 10 were observed after repeated administrations to six subjects; 2.3 +/- 1.1, 3.3 +/- 3.1, and 2.4 +/- 1.4% (means +/- SD) for three separate occasions. Interindividual variation of manganese retention after intake of the same labeled diet was, however, shown to be substantial. Retention at day 10 was 2.9 +/- 1.8% (means +/- SD) and varied from 0.6 to 9.2% when measured in 14 healthy subjects. Large interindividual variations in rate of excretion were observed. The retention measurements for days 10-30, however, could be closely fitted to a single exponential function for each individual. The results regarding intraindividual and interindividual variation in Mn retention indicate that factors influencing Mn absorption can be identified only by repeated administrations using each subject as his/her own control.

Administration, Oral↗
PubMed1989

Human milk proteins: separation of whey proteins and their analysis by polyacrylamide gel electrophoresis, fast protein liquid chromatography (FPLC) gel filtration, and anion-exchange chromatography.

Human milk proteins are of nutritional and physiological significance to the newborn infant. To further study these proteins, a rapid procedure to separate and analyze human milk whey proteins was developed using fast protein liquid chromatography (FPLC). First, to separate whey proteins from casein, different variables such as low- or high-speed centrifugation at different temperatures with or without adjustment of pH to 4.6 or 4.3 and with or without addition of calcium to whole milk or skim milk were tested. Each variable was evaluated by gel filtration, anion-exchange chromatography, sodium dodecyl sulphate (SDS)-polyacrylamide gradient gel electrophoresis, immunoelectrophoresis, and immunodiffusion. The optimum method for a discrete separation of whey and casein is the adjustment of whole milk to pH 4.3 with addition of 60 mmol calcium/L, followed by ultracentrifugation. Rapid and sensitive separation and analysis of whey proteins was achieved by FPLC gel filtration and anion-exchange chromatography.

Chromatography, Gel↗
PubMed1989

Isolation of the nonprotein nitrogen fraction from human milk by gel-filtration chromatography and its separation by fast protein liquid chromatography.

Human milk (HM) is unique compared with the milk of other species in that nonprotein nitrogen (NPN) constitutes 20-25% of the total N. The NPN fraction consists of a diverse group of compounds with molecular masses less than 10,000 Da (in the picogram to microgram per milliliter range), which have only been partially characterized. We developed a methodology to separate and concentrate the NPN fraction for further analysis. NPN was initially separated from other milk components by Sephadex G-25 gel filtration. Further isolation and separation was carried out by fast protein liquid chromatography gel filtration and ion-exchange chromatography. Molecular masses of unknown peaks were determined by using known molecular mass markers and standards. The methodologies developed lead to the discrete separation of NPN from other milk compounds and can be particularly valuable for isolating peptides in HM.

Chromatography, Gel↗
PubMed1989

Identification of transferrin as the major plasma carrier protein for manganese introduced orally or intravenously or after in vitro addition in the rat.

It is known that the metabolic handling of manganese (Mn) introduced via the diet or by intravenous injection is quite different. We hypothesized that this difference could be due in part to different proteins carrying Mn in plasma that could affect tissue uptake and retention. To test this idea, 54Mn was administered orally or intravenously to rats, and blood samples were taken by cardiac puncture at various time points postdosing. Plasma proteins were separated using fast protein liquid chromatography with a combination of anion exchange and gel filtration columns. Using these methods, independent of the route of 54Mn administration, transferrin was identified as the major Mn-binding protein in plasma. The identity was further confirmed by SDS-polyacrylamide gradient gel electrophoresis and Western blotting. These results conclusively show that 54Mn in plasma is carried by transferrin, regardless of route of administration and time postdosing.

Administration, Oral↗
PubMed1989

Inhibitory effects of phytic acid and other inositol phosphates on zinc and calcium absorption in suckling rats.

While it is known that phytic acid, inositol hexaphosphate, has a negative effect on zinc and calcium absorption, the effects of inositol which is phosphorylated to a lesser extent are less known. We have prepared inositol triphosphate (IP-3), tetraphosphate (IP-4), pentaphosphate (IP-5) and hexaphosphate (IP-6) by hydrolysis of sodium phytate and separation by ion-exchange chromatography and have studied their effect on zinc and calcium absorption. Using a suckling rat pup model, we found that liver uptake of 65Zn after 6 h was 5% of the total dose from solutions of IP-6, 19% from IP-5, 28% from IP-4, 29% from IP-3 and 31% from ZnCl2 (control). Non-absorbed calcium was 17%, 1.4%, 0.5%, 0.5% and 0.5% of the given dose of 45Ca, respectively. Thus, at a high degree of phosphorylation (IP-6, IP-5), zinc and calcium uptake was inhibited, while no effect was observed for the other phosphates. Consequently, total "phytate" analysis, which includes inositol phosphates with varying degrees of phosphorylation, can give misleading information with regard to mineral availability. In addition, even limited dephosphorylation of inositol hexaphosphate can have a positive effect on mineral absorption.

Animals↗
PubMed1989

Selenium content and glutathione peroxidase activity of milk from vegetarian and nonvegetarian women.

The concentration of selenium (Se) in milk samples obtained from 26 lacto-ovo-vegetarian (vegetarian) women was significantly greater (22.2 +/- 0.8 ng/ml) than from 12 nonvegetarian women (16.8 +/- 1.3). Mean GSH-Px activity (EC 1.11.1.9) in milk from vegetarians was 146% of that in milk from nonvegetarians. A significant correlation between GSH-Px activity and Se concentration was observed (r = 0.76). Likewise a significant correlation was observed between milk linoleic acid content and GSH-Px activity (r = 0.68). In undialyzed samples from vegetarian women, most of the increased content of Se was found in fractions containing proteins of 100 kdaltons (kD) or more. The high glutathione peroxidase activity in milk from vegetarians was associated with selenoproteins in the 90 to 100 kD range. A distinct 40 kD Se peak was also detected in milk from vegetarians. There was no difference in Se intake between the two groups of women. Therefore, although data from the present study show that both the quantity and distribution of Se in human milk can be modified by the maternal diet, the increased Se content and GSH-Px activity in milk from vegetarians cannot be explained by an increased Se intake.

Adult↗
PubMed1989

Trace element absorption in infants as a foundation to setting upper limits for trace elements in infant formulas.

The bioavailability of the trace elements iron, zinc, copper and manganese from human milk is high compared to cow's milk and infant formulas. This high bioavailability may be explained by the presence of lactoferrin in human milk, which may facilitate iron and manganese uptake via an intestinal receptor for this protein. High concentrations of ascorbate and citrate may also facilitate uptake of trace elements from human milk and milk formulas, while a high concentration of casein in cow's milk and cow's milk formulas may limit trace element absorption from these diets. Trace element absorption from soy formula is low, mostly due to the presence of phytate but possibly also due to some protein fraction. Trace elements sharing absorptive pathways compete for uptake, and imbalances in the ratios between trace elements (Fe/Zn, Zn/Cu, Fe/Mn) in formulas may impair trace element absorption. These factors need to be taken into consideration when setting upper limits for trace elements in formulas. With our present knowledge, an upper limit for iron of 14 mg/l, for zinc, 12 mg/l, copper, 1.2 mg/l, and manganese, 0.6 mg/l are suggested. The capacity of infants to homeostatically adapt to varying intakes of trace elements needs to be further evaluated.

Female↗
PubMed1989

Development of a human milk protein standard.

Accurate quantitation of the protein content of human milk (HM) is clinically important for both determining protein and energy intakes of HM-fed infants. Protein can be determined by Kjeldahl analysis or colorimetric assays. Colorimetric assays are rapid and convenient, but usually overestimate the protein content when compared to Kjeldahl protein (KP). In this study a protein standard based on human milk protein (HMPS) was isolated by size exclusion column chromatography. Purity and composition of the standard was determined by gel electrophoresis, Kjeldahl and amino acid analyses. The protein content of 20 mature milk samples was determined by the Lowry, BCA and BioRad colorimetric assays, using bovine serum albumin, human serum albumin/IgG, and HMPS as standards. These results were compared with KP results using Student's t-test. All colorimetric assays overestimated milk protein content; however, the Lowry assay gave the lowest protein levels, with our protein standard yielding values closest to the KP value.

Amino Acids↗
PubMed1989

Non-protein nitrogen and true protein in infant formulas.

Protein and nitrogen (N) requirements of infants and the optimum protein level of infant formulas are still under debate. Human milk (HM) N is considered adequate although 25% of the N is provided as non-protein nitrogen (NPN), half in the form of urea. Soluble N, insoluble N, NPN and urea N were determined in HM and cow's milk (CM), 5 CM-based infant formulas, 4 soy protein-based formulas (SF), and manufacturers' skim milk and whey protein sources. Total, peptide and free amino acids were also determined in all samples. Levels of NPN and urea N in formulas were highly dependent on the type of whey used, with ion-exchange whey being highest, followed by electrodialyzed and ultrafiltered whey, respectively. SF contained very little NPN with the exception of Soyalac. Consequently, true protein [(Total N-NPN) x 6.38] was lower than the reported levels in several formulas. Levels of peptide and free amino acids were also affected by the method of whey preparation. While it has been recognized that "casein-predominant" CM formulas will have different effects on metabolic indices than "whey-predominant" formulas, this study demonstrates that there are also pronounced differences among "whey-predominant" formulas.

Amino Acids↗
PubMed1989

Fe-saturation and proteolysis of human lactoferrin: effect on brush-border receptor-mediated uptake of Fe and Mn.

We have previously characterized a brush-border membrane receptor that facilitates iron uptake from human lactoferrin. The receptor is specific for human and monkey lactoferrin and does not recognize human transferrin or bovine lactoferrin. In this study, iron uptake from lactoferrin fragments was studied, as well as from lactoferrin partially saturated with iron. Brush-border membrane vesicles (BBMV) prepared from infant rhesus monkey small intestine efficiently accumulated iron from lactoferrin half-molecules, although competition experiments showed that intact lactoferrin has a higher affinity toward the receptor. Lactoferrin partially saturated with iron also effectively delivered iron to the receptor, whereas the affinity was lower than for lactoferrin saturated with iron. Lactoferrin also carries a large proportion of human milk manganese, and receptor-mediated uptake of lactoferrin-bound manganese into BBMV was demonstrated, although this complex had lower affinity than that found for iron-lactoferrin. Thus, although the receptor has a preference for intact iron-saturated lactoferrin, partially digested lactoferrin and partially iron-saturated lactoferrin can also deliver iron to the receptor. Therefore, these molecular species, which are likely to occur in the gastrointestinal tract of the infant, may contribute to the high degree of iron absorption from human milk lactoferrin.

Animals↗
PubMed1989

Influence of marginal maternal zinc deficiency on pregnancy outcome and infant zinc status in rhesus monkeys.

To investigate the effects of marginal zinc deficiency on early development, rhesus monkeys were fed a diet marginally deficient in zinc (M; 4 micrograms/g) throughout pregnancy and during the first month of lactation. Despite the low concentration of zinc in the diet. M dams did not develop overt signs of zinc deficiency. However, compared to control dams fed diets adequate in zinc (C; 100 micrograms Zn/g), M dams showed a low response to the mitogens concanavalin A and phytohemagglutinin. Pregnancy outcome was similar in the two groups and all of the neonates were judged to be healthy at delivery. From birth until d 30 of age, the infants were closely monitored for signs of zinc deficiency, and at d 30, they were killed and tissues were removed and analyzed for a number of parameters reported to be affected by zinc status. At birth, M infants had low plasma zinc concentrations compared to controls; however, this difference was not observed at d 30. D 30 M infants showed a normal response to the mitogens concanavalin A and phytohemagglutinin, but showed a low response to pokeweed mitogen. Tissue (liver, brain, spleen, kidney, and heart) trace element concentrations were similar in the two groups of infants, as were liver metallothionein concentrations and 65Zn uptake/retention by isolated hepatocytes. Infant wt gain was inversely correlated with plasma zinc, liver zinc, and liver metallothionein concentrations in both the M and C groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Effect of the antihypertensive drug hydralazine on mineral metabolism in the rat.

The effects of hydralazine (HZ) on mineral metabolism was investigated in rats. Sprague-Dawley rats were fed HZ (0.1-4%, w/w) in three separate experiments: (1) a 2-week dose-response study; (2) a 2-month long-term feeding study; and (3) a pregnancy study. At the end of each experiment, tissues were removed and concentrations of Mn, Cu, Zn and Fe were measured. Results from the three experiments were similar. HZ had no effect on tissue Mn and Zn concentrations, while tissue Fe concentrations were lower and kidney Cu concentrations were higher in HZ-treated groups compared to controls. The effect of HZ on mineral metabolism may be, in part, responsible for some of its negative side effects.

Animals↗
PubMed1988

Studies of marginal zinc deprivation in rhesus monkeys. III. Use of liver biopsy in the assessment of zinc status.

Studies of marginal zinc deficiency in rhesus monkeys have demonstrated that plasma Zn levels are often a poor indication of Zn status. To better assess the Zn status of these animals, we examined their liver concentration of Zn as well as of other minerals, metallothionein (MT), and superoxide dismutase (SOD). Liver-wedge biopsies were obtained from adult rhesus monkeys fed for 15 mo, either a control (100 micrograms Zn/g) or a marginally Zn deficient diet (4 micrograms/g; ZD). Liver Zn and MT concentrations were lower in ZD monkeys than in controls whereas iron concentration was higher in ZD monkeys than in controls. Liver copper, manganese, and magnesium concentrations and activities of CuZnSOD and MnSOD were similar in the two groups. Data from the groups were pooled for regression analysis. Measurement of liver Zn and MT concentrations are useful in the assessment of the effects of long-term Zn deprivation in primates.

Animals↗
PubMed1988

Coffee consumption as a factor in iron deficiency anemia among pregnant women and their infants in Costa Rica.

The influence of coffee consumption on hematological and trace element status was studied in two groups of pregnant, low-income Costa Rican women: coffee drinkers (greater than or equal to 450 mL/d, n = 22) and coffee nondrinkers (0 mL/d, n = 26). Groups had similar income, education, prenatal care, age, parity, weight, height, pregnancy weight gain, prenatal iron supplementation, energy, protein, Fe, and vitamin C intake and infant sex and gestational age. Maternal hemoglobin (Hb) and hematocrit (Hct) at 8 mo gestation, cord blood Hb and Hct, infant birth weight and Hb and Hct at 1 mo of age, and breast-milk Fe concentration were significantly lower in the coffee group than in the noncoffee group. The association of coffee with infant Hb and Hct was independent of maternal Fe status and birth weight. These results are consistent with our previously reported data in rats and indicate that maternal coffee intake may contribute to maternal and infant anemia.

Adult↗
PubMed1988

Effect of phytate removal on zinc absorption from soy formula.

Low zinc bioavailability from soy formula may be the result of the formula's phytate content. We assessed the effect of phytate removal from soy formula on Zn absorption using infant rhesus monkeys and suckling rat pups as animal models. Zn absorption in monkeys, as determined by whole-body counting, was 65% from human milk, 54% from monkey milk, 60% from whey-predominant formula, 46% from casein-predominant formula, and only 27% from conventional soy formula (0.621 mmol phytate/L). In contrast, Zn absorption from dephytinized soy formula (0.067 mmol phytate/L) was 45%. In suckling rats, Zn absorption from conventional soy formula was only 16% vs 47% from dephytinized soy formula. Phytate concentration in a variety of experimental soy formulas was inversely correlated to Zn absorption. These results suggest that the low bioavailability of Zn from soy formula is a function of its phytate concentration and can be overcome by the removal of phytate.

Animals↗