PubMed Health⌕ Search

Biomedical subjects

B Lönnerdal

Publications and source records attributed to B Lönnerdal.

At least 109 records · Page 6Linked to original sources
PubMed1992

Solubility and digestibility of milk proteins in infant formulas exposed to different heat treatments.

There are presently several fundamentally different technologies to produce infant formulas (IF), such as sterilization, spray-drying, and treatment at ultrahigh temperature (UHT). The effects of heat treatment on milk proteins in IF were analyzed by column chromatography, gel electrophoresis, and Kjeldahl analysis, revealing strong protein-protein and protein-lipid interactions in processed milk. These interactions were more pronounced in conventionally (in-can) sterilized than in spray-dried (powdered) and UHT products confirming their temperature dependency. Analysis of raw materials, intermediate and end products of IF processing revealed that after homogenization the first indications of protein denaturation occurred, but that in-can sterilization as the final heat treatment caused irreversible denaturation of proteins and strong protein-lipid interactions. Lowering of the pH to 4-5, which is physiological for the stomach of young infants, enhanced the interactions. Support for an impairment of protein digestibility was given by in vitro analysis of protein digestibility, demonstrating significantly lower digestibility of in-can sterilized IF compared to their spray-dried and UHT counterparts. To investigate the effect of heat treatment on chemical reactions, i.e., occurrence of Maillard products, we showed by a fluorimetric assay that the amount of "available" lysine is lower in sterilized than in powdered IF. Our findings suggest that a more differentiated view regarding the protein quality of IF is needed.

Animals↗
PubMed1992

Re-evaluation of the whey protein/casein ratio of human milk.

Total casein subunits as well as whey proteins were quantitated in human milk samples during lactation. Two independent methods were used: precipitation at pH 4.3 in the presence of Ca2+ followed by Kjeldahl analysis and polyacrylamide gradient gel electrophoresis (PAGGE) followed by densitometric scanning. Both methods yielded similar results: casein synthesis is low or absent in early lactation, then increases rapidly and subsequently decreases. The concentration of whey proteins decreases from early lactation and continues to fall. These changes result in a whey protein/casein ratio of about 90:10 in early lactation, 60:40 in mature milk and 50:50 in late lactation. These observations indicate that the synthesis and/or secretion of caseins and whey proteins is regulated by different mechanisms. In addition, the relative proportion of the different beta- and kappa-casein subunits was found to vary throughout lactation.

Caseins↗
PubMed1992

Cloning and sequencing of human kappa-casein cDNA.

A cDNA encoding kappa-casein of human milk was cloned and sequenced. The kappa-casein cDNA was isolated from a lambda gt11 library generated from mRNA prepared from a mammary gland biopsy obtained from a lactating woman. The library was screened with polyclonal rabbit antibodies raised against purified native kappa-casein. The obtained nucleotide sequence contained an ORF sufficient to encode the entire amino acid sequence of a kappa-casein precursor protein consisting of 182 amino acids. This includes a tentative signal peptide of 20 amino acids and a processed protein of 162 amino acids.

Amino Acid Sequence↗
PubMed1992

Growth of breast-fed and formula-fed infants from 0 to 18 months: the DARLING Study.

Anthropometric data were collected monthly from birth to 18 months as part of the Davis Area Research on Lactation, Infant Nutrition and Growth study, which followed infants who were either breast-fed or formula-fed during the first 12 months. The two cohorts were matched for parental socioeconomic status, education, ethnic group, and anthropometric characteristics and for infant sex and birth weight, and neither group was given solid foods before 4 months. While mean weight of formula-fed infants remained at or above the National Center for Health Statistics median throughout the first 18 months, mean weight of breast-fed infants dropped below the median beginning at 6 to 8 months and was significantly lower than that of the formula-fed group between 6 and 18 months. In contrast, length and head circumference values were similar between groups. Weight-for-length z scores were significantly different between 4 and 18 months, suggesting that breast-fed infants were leaner. The groups had similar weight gain during the first 3 months, but breast-fed infants gained less rapidly during the remainder of the first year: cumulative weight gain in the first 12 months was 0.65 kg less in the breast-fed group. Length gain was similar between groups. These results indicate that weight patterns of breast-fed infants, even in a population of high socioeconomic status, differ from current reference data and from those of formula-fed infants. Thus, new growth charts based on breast-fed infants are needed.

Anthropometry↗
PubMed1991

Adequacy of energy intake among breast-fed infants in the DARLING study: relationships to growth velocity, morbidity, and activity levels. Davis Area Research on Lactation, Infant Nutrition and Growth.

Breast-fed infants grow less rapidly after the first 2 to 3 months of age than current standards. The DARLING study (Davis Area Research on Lactation, Infant Nutrition and Growth) was designed to evaluate whether this pattern should be considered "faltering" or is a normal outcome even under optimal conditions. Data on intake, growth, morbidity, activity, and motor development were collected longitudinally from infants who were breast fed for at least 12 months. Gross energy intake, calculated from 4-day records of milk and food intake at 3, 6, 9, and 12 months, averaged 91.4, 84.1, 86.7, and 91.8 kcal/kg per day, respectively, well below recommended amounts of metabolizable energy. Nevertheless, infants usually left some food unconsumed. Growth velocity was also below current reference data and was weakly correlated with energy intake. There were no significant negative associations between energy intake at any time and incidence, prevalence, or duration of any category of morbidity during the subsequent 3 months. There were no consistent associations between energy intake and activity level, time spent sleeping, or achievement of key developmental milestones. Similarly, infants with slower growth velocity were just as active and were ill no more often in subsequent months than infants who were growing more rapidly. Thus the deviation from current recommendations for energy intake and growth can be considered a normal pattern with no apparent deleterious consequences in our population of breast-fed infants.

Body Weight↗
PubMed1991

Determinants of energy, protein, lipid, and lactose concentrations in human milk during the first 12 mo of lactation: the DARLING Study.

Factors associated with concentrations of energy-yielding nutrients in human milk were examined at 3, 6, 9, and 12 mo postpartum in the DARLING (Davis Area Research on Lactation, Infant Nutrition and Growth) Study. Samples were obtained by complete expression of alternate breasts over 24 h. Milk energy density was highly correlated with lipid concentration; both were positively related to maternal percent of ideal body weight (%IBW) at 6, 9, and 12 mo and negatively related to milk volume at 3 mo and to parity at 12 mo. Milk protein concentration was negatively related to milk volume at 6 and 9 mo and positively related to nursing frequency at 6 mo and %IBW at 9 mo. Milk lactose concentration was positively related to milk volume at 6 and 9 mo and to continued amenorrhea at 9 mo. In a subsample who completed dietary records, protein intake was positively associated with lipid concentration after 16 wk postpartum but not before. These findings suggest that milk composition is more sensitive to maternal factors such as body composition, diet, and parity during later lactation than during the first few months.

Diet↗
PubMed1991

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

Zinc and manganese may interfere with iron absorption because of similar physicochemical properties and shared absorptive pathways. The effects of zinc and manganese on iron absorption were studied in human subjects by using paired observations and a dual-radioisotope method (55Fe and 49Fe). Manganese inhibited iron absorption both in solutions and in a hamburger meal. Fractional iron absorption is strongly dose dependent. Adding 2.99 mg Mn to 0.01 mg Fe reduced iron absorption to the same extent as increasing the iron dose 300-fold to 3 mg, strongly indicating a direct competitive inhibition of manganese on iron absorption. In the same experiment with zinc, no inhibitory effect was observed, suggesting different pathways for the absorption of zinc and iron. An intraluminal interaction may occur, because a fivefold excess of zinc to iron (15 mgZn/3 mg Fe) reduced iron absorption by 56% when given in a water solution but not when given with a hamburger meal.

Absorption↗
PubMed1991

Postprandial changes in the content and composition of nonprotein nitrogen in human milk.

The effect of a meal on human milk (HM) total nitrogen (TN) and nonprotein nitrogen (NPN) content and composition was examined. Two studies were performed in which milk and blood samples were collected 2-3 h after subjects consumed either a test breakfast or lunch. To monitor the rate of transfer of plasma urea into milk, two women were given [15N]2-urea with the meal. Milk TN concentrations were not significantly different from premeal values. However, concentrations of milk NPN, urea nitrogen, and alanine were increased by greater than or equal to 20% over premeal values. [15N]2-Urea appeared in plasma and milk within 15 min and reached maximum enrichments of 10% and 5.5% in plasma and milk, respectively. Several HM NPN components increase in concentration postprandially; however, these concentrations were not always correlated with changes in plasma concentrations, suggesting that milk NPN may also reflect metabolic activities within the mammary gland.

Adult↗
PubMed1991

The effect of individual dietary components on manganese absorption in humans.

Our knowledge of dietary factors affecting manganese absorption in man is very limited. In this study we used a recently developed radionuclide technique to measure manganese absorption in human adults. Using paired observations, we explored the effects of adding calcium and manganese to human milk on manganese absorption. Furthermore, the effects of adding phytate, phosphate, and ascorbic acid to infant formula as well as iron and magnesium to wheat bread were evaluated. Addition of calcium to human milk resulted in a significant decrease in manganese absorption whereas no significant differences in manganese absorption were observed as a result of the other test meals administered with and without the evaluated dietary component, respectively. Thus, manganese absorption was not significantly affected by most dietary factors evaluated in this study, except for the addition of calcium to human milk.

Absorption↗
PubMed1991

Longitudinal changes in the mineral composition of mouse milk and the relationship to zinc metabolism of the suckling neonate.

We studied changes in the mineral composition of milk of lactating Swiss-Webster mice and the relationship of those changes to mineral metabolism of suckling mouse pups. Concentrations of Zn, Cu, Mg and Ca were analyzed in maternal and neonatal tissues and in milk; Zn metabolism was studied using 65Zn. Although Cu, Ca and Mg concentrations in milk declined during the first 2 d of lactation, only the concentration of Zn decreased progressively throughout 30 d. Various pup tissues were characterized by developmental changes in concentrations of some elements. Turnover of Zn in neonatal tissues was studied by radiolabeling litters in utero and fostering them at birth to nonradiolabeled lactating dams. The turnover of whole-body 65Zn in suckling mice decreased during development, and, at 20 d of age, the biological half-life of 65Zn in the neonate was approximately the same as for a nonpregnant, nonlactating adult female (20 d). The decreased turnover of 65Zn in lactating dams that characterized progressive lactation and was reflected in the Zn concentration of milk is in agreement with changes in whole-body 65Zn turnover observed for the suckling mouse. These findings demonstrate that the metabolism of the suckling neonate is directly related to longitudinal changes in the composition of maternal milk.

Animals↗
PubMed1991

Mineral status of mice suckling early-, mid- and late-lactating foster dams.

We have demonstrated that the zinc (Zn) concentration of mouse milk declines significantly over the lactation period. Pups radiolabeled in utero with 65Zn were forward-fostered (FF) to nonradiolabeled dams at a later stage of lactation to study the effects of early milk deprivation. Other groups of radiolabeled pups were back-fostered at 5, 10 and 15 days of age to a nonradiolabeled dam who had just given birth; this provided additional colostrum during the suckling period. Litters fostered at birth to an unlabeled dam at d 0 of lactation were used as controls. Weight gain of FF litters decreased and signs of Zn deficiency increased as the foster dam's days of lactation increased. The Zn concentration of kidney, brain and plasma tended to decrease with increasing lactation days of the foster dam. Tibia Zn concentration declined progressively as the lactation days of the foster dam increased, and the concentration of calcium also was lower in all three groups of FF litters than in controls, indicating that bone calcification may have been impaired. Kinetic data proved to be a more sensitive index of Zn status than tissue Zn concentration. The biological half-life of whole-body 65Zn for FF suckling mice increased in a linear fashion with increasing lactation days of the foster dam; whole-body retention of 65Zn for back-fostered litters did not differ from that for controls. Brain, small intestine, kidney muscle, plasma and tibia of pups FF to late-lactating dams seemed to have greater retention of Zn than did controls. Thus, deprivation of early milk impaired growth and development of the mouse neonate despite some ability to conserve Zn.

Animals↗
PubMed1991

Isolation and function of a receptor for human lactoferrin in human fetal intestinal brush-border membranes.

Iron absorption is known to be higher from human milk than from infant formula or bovine milk. The high bioavailability of human milk iron suggests that lactoferrin (Lf), the major iron-binding protein in human milk, may be a factor contributing to iron absorption in infants. We have isolated a human Lf receptor from solubilized human fetal intestinal brush-border membranes by affinity chromatography using immobilized human Lf. We also investigated the interaction of 125I-labeled human Lf and bovine Lf with brush-border membrane vesicles (BBMVs) from human small intestine using a rapid filtration technique. The molecular weight of the receptor was 110,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under nonreducing conditions and 37,000 under reducing conditions. Competitive binding studies demonstrated specific binding of human Lf. The binding was pH dependent, with an optimum between pH 6.5 and 7.5. Scatchard plot analysis indicated 4.3 x 10(14) binding sites/mg membrane protein with an affinity constant of 0.3 x 10(6) M-1 for human Lf. Both half-Lf and deglycosylated Lf bound to the receptor with an affinity similar to intact Lf. In contrast, little binding of bovine Lf or human transferrin to human BBMVs occurred. These results suggest that the brush-border membrane receptor for human Lf may be responsible for the high iron absorption from human milk.

Animals↗
PubMed1990

Cloning and sequencing of a cDNA encoding human milk beta-casein.

A cDNA of 1065 bp encoding the human milk beta-casein was cloned and sequenced using a synthetic oligodeoxyribonucleotide probe and a human mammary gland library. The nucleotide (nt) sequence contained an open reading frame sufficient to encode the entire amino-acid (aa) sequence of a beta-casein precursor protein consisting of 210 aa and a signal peptide of 15 aa. The nt sequence shows 45-62% homology to those of bovine, ovine, rat, and mouse beta-caseins. The highly phosphorylated site, which is responsible for the calcium-binding capacity of beta-casein, the signal peptide, and a sequence encoding for an inhibitor to the angiotensin-converting enzyme seem highly conserved among the beta-caseins with known sequences.

Amino Acid Sequence↗
PubMed1990

Calcium retention from milk-based infant formulas, whey-hydrolysate formula, and human milk in weanling rhesus monkeys.

An adequate supply of calcium is important for normal bone mineralization in infants. Special infant formulas have been developed to treat infants with a high risk of developing allergy. Similar to other diets, it is important that these products are nutritionally adequate. We have measured calcium retention from a new formula based on whey hydrolysate and compared it with conventional formulas, using extrinsic labeling with calcium 47 and the weanling rhesus monkey as an animal model. Retention of calcium was similar for all formulas studied: 45% +/- 4% (mean +/- SEM) from whey-hydrolysate, 47% +/- 2% from whey-predominant, and 53% +/- 7% from casein-predominant formula. Calcium retention from human milk, 72% +/- 3%, was significantly higher than from formula. Using these retention values and the calcium concentrations of the diets, infant formula and human milk deliver approximately equal amounts of calcium to the infant.

Animals↗
PubMed1990

Effect of marginal maternal zinc intake on zinc absorption and growth of 3-month-old infant rhesus monkeys.

One compensatory mechanism for marginal zinc intake may be through an enhanced absorption of zinc. Such a compensatory mechanism could be of value to the neonate, as poor zinc nutriture during early life has severe consequences on growth and development. We studied the uptake of zinc by 3-month-old infant rhesus monkeys born to dams fed control diets (100 micrograms of zinc per gram of diet or zinc-restricted diets (4 micrograms of zinc per gram of diet). Zinc uptake/retention was studied by feeding 3-month-old infant monkeys that had fasted an infant formula containing zinc 65 by gavage. Whole body radioactivity was counted immediately after intubation and on days 10 and 17 after intubation. Regardless of dietary group, 65 zinc retention was high, ranging from 33% to 71% of the dose fed to the monkeys. There were no significant differences between the two dietary groups in the percentage of zinc retention at days 10 and 17. Independent of the dietary group, there was no correlation between plasma zinc and zinc absorption. A positive correlation was found between weight gain and zinc retention in the marginal zinc infants, while a negative correlation between weight gain and zinc retention was observed in the control infants. These observations suggest that the mechanisms underlying growth may be different in infants born to dams fed control vs marginal zinc diets.

Animals↗
PubMed1990

Influence of maternal dietary zinc intake on in vitro tubulin polymerization in fetal rat brain.

The hypothesis that one of the biochemical lesions underlying zinc deficiency-induced teratogenicity is altered microtubule formation was tested. Day 19 fetuses from zinc-deficient Sprague-Dawley dams were characterized by low brain supernate zinc concentrations and slow brain tubulin polymerization rates compared to controls. Brain supernate tubulin and protein concentrations were similar in zinc-deficient and control fetuses. In vitro brain tubulin polymerization rates were increased following addition of zinc to either control or zinc-deficient brain supernates; however, the stimulatory effect of added zinc on polymerization was significantly higher in brain supernates obtained from zinc-deficient fetuses compared to controls. These results support the idea that one effect of fetal zinc deficiency is a reduction in tubulin polymerization, which in turn may result in altered microtubule function.

Animals↗
PubMed1990

Effects of marginal zinc deficiency on microtubule polymerization in the developing rat brain.

One of the possible mechanisms that has been proposed to underlie the deleterious effects of zinc deficiency on brain development is an impairment in the normal formation of the cytoskeletal network. In the current study, in vivo microtubule polymerization was characterized in brain supernatant fluids, from 20-d-old pups whose dams were fed diets containing control (50 micrograms zinc/g) or marginal levels of zinc (10 micrograms zinc/g) throughout pregnancy and lactation. Pup brain and body weights were similar between the groups; however, plasma zinc concentrations were lower (27%) in pups fed the marginal zinc diet than in controls. Tubulin concentrations in 100,000 g brain supernates were similar between the groups; however, tubulin polymerization in the brain supernates was significantly lower in pups fed the marginal zinc diet compared to controls. Primarily, the early events of polymerization were affected; the lag period of the reaction was doubled, and the initial velocity was slower (26%) in supernates from pups fed the marginal zinc diet than in controls. These findings support the idea that some of the negative effects of marginal zinc deficiency on brain development and function may be mediated by an alteration in microtubule formation.

Animals↗