Zinc uptake by human placental microvillous membrane vesicles: effects of gestational age and maternal serum zinc levels.

Zinc uptake by syncytiotrophoblast microvillous membrane vesicles (SMMV) from human placentas was characterized and the effects of maternal serum zinc levels at term and of gestational age on kinetic parameters were evaluated. Zinc uptake at pH 7.2 was rapid for the first 2 min, followed by a slower increase, approaching equilibrium after 30 min. Uptake was saturable at a zinc concentration of 30 micromol/L, higher than the upper range of the physiological serum zinc level. Kinetic analysis of uptake at 1 min in SMMV from term placenta showed similar Km values (mean: 6.9+/-0.6 micromol/L) for different levels of maternal serum zinc. However, Vmax was higher (p < 0.05) in SMMV from mothers with serum zinc lower than 7.6 micromol/L compared to those with higher serum zinc levels (35.8+/-1.6 and 26.6+/-1.6 nmol 65Zn/mg protein/min, respectively). Km values were similar in term (>37 wk of gestation) and preterm (20-25 wk of gestation) placentas, whereas Vmax was higher (p < 0.05) in the preterm (34.3+/-1.6 nmol Zn/mg protein/min) compared to term placentas from mothers with serum zinc levels above 7.6 micromol/L. These results suggest that whereas afffinity for zinc was not altered with gestational age or maternal serum zinc levels, zinc-uptake capacity in human placenta is influenced both by gestational age and by low levels of maternal serum zinc in order to ensure an adequate maternal-fetal zinc transfer.

Effect of heat treatment on nutritional quality of germinated legume seeds.

The effect of heat treatment of germinated soybean, lupin, and black bean on chemical composition and protein utilization in rats was evaluated. Heat treatment caused complete inactivation of trypsin inhibitors whereas it did not affect phytic acid levels. Proximate components, minerals, and amino acids did not change, but low molecular weight sugars were affected by heat treatment differently for each germinated legume. The sugar digestibility ratio (total digestible sugars/total nondigestible sugars) in germinated black beans doubled after heat treatment. True protein digestibility (TD) increased with heat treatment only in germinated soybean. Net protein utilization was markedly improved (20%) with heat treatment in germinated soybean and lupin. Utilizable protein of heat-treated germinated legumes was 289, 236, and 132 g/kg of legume dry weight for soybean, lupin, and black bean, respectively. Supplementation with methionine did not alter TD but improved all other indices of protein utilization in the germinated legumes, particularly in black bean. All three germinated legumes become equivalent in protein quality when heating and supplementation with methionine are combined with germination. The use of germinated heat-treated soybean, lupin, and black bean on their own and/or as food ingredients is nutritionally advantageous due to the low content of nondigestible oligosaccharides and the high protein utilization.

Calcium and osteoporosis.

Osteoporosis is a crippling disease that emerges as an important public health problem both in developed and developing countries including Brazil. The clinical condition is characterized mainly by loss of bone mineral mass in later life as the net result of complex physiological and environmental interacting factors during lifetime. Calcium intake appears as an obvious nutritional factor in the prevention of osteoporosis but its contribution is still not well established particularly when populations with different habitual levels of calcium intake are compared. In this section, we examine the role of calcium intake as affecting bone mineral density at different stages of development and with aging, with special attention to the possible stress on bone mass due to pregnancy and lactation. Nutritional studies demonstrate that, in general, adequate calcium intake during lifetime contributes to decrease the risk of osteoporosis. However, the long term effects on bone health of sub-adequate, but not very low, habitual calcium intakes during highly demanding physiological periods such as adolescence, pregnancy and lactation, are still largely unknown. Sub-adequate calcium intakes are probably common in Brazil.

Erythrocyte metallothionein in relation to other biochemical zinc indices in pregnant and nonpregnant women.

Erythrocyte metallothionein (E-MT) is considered a promising index of zinc status in humans, since it may be more sensitive than other biochemical indices to changes in dietary zinc. However, conditions of high zinc demand with substantial redistribution of tissue zinc and specific changes in hormone profile, such as pregnancy, may have an influence on E-MT levels in addition to dietary zinc. In this study, we compared E-MT concentrations in relation to other biochemical zinc indices in healthy pregnant women at delivery (n = 40) and non-pregnant women (n = 22) with similar habitual dietary zinc intakes (average 13.3 mg/d). Pregnant women had lower serum zinc and albumin-bound serum zinc, but higher levels of alpha 2-macroglobulin-bound serum zinc than the nonpregnant women. Erythrocyte zinc (E-Zn) was similar in both groups, but E-MT (mean +/- SE) was slightly but significantly (p < 0.05) higher in the pregnant women (2.9 +/- 0.09 nmol/g protein) compared to nonpregnant women (2.6 +/- 0.06 nmol/g protein). A significant correlation was observed between E-MT and E-Zn in the nonpregnant women (r = 0.70; p < 0.001), consistent with the role of intracellular zinc in the regulation of metallothionein synthesis. However, such correlation was not observed in the pregnant women, suggesting that E-MT levels in pregnancy may be influenced by factors related to the pregnant state.

Maternal, placental and cord zinc components in healthy women with different levels of serum zinc.

Serum zinc is known to decrease during pregnancy, but the range of individual values at the end of normal gestation may be considerably large, with uncertain physiological significance in terms of maternal zinc status and maternal-fetal transfer of zinc. In this study we compared several maternal and cord blood indices of zinc status, placental zinc, placental metallothionein and the relationship between maternal, cord and placental components, in 40 healthy pregnant women at delivery with different levels of serum zinc. Subjects were divided into three groups according to serum zinc using as cutoff points the lower and upper quartile values [LZn, < 7.6 mumol/l (n = 10); MZn, 7.6-10.7 mumol/l (n = 20), and HZn, > 10.7 mumol/l (n = 10)]. Habitual zinc intakes were similar in all groups (average 11.5 mg/day). Considering all women, maternal serum and erythrocyte zinc correlated significantly (r = 0.40; p = 0.021). Maternal erythrocyte zinc was higher (p < 0.01) in HZn compared to the other groups. Maternal and cord values of serum zinc correlated significantly (r = 0.43; p = 0.006). Cord serum zinc values were very similar in LZn and MZn but were higher (p < 0.01) in HZn. Cord erythrocyte zinc levels were similar in all groups and about 20-25% of the maternal values. Cord erythrocyte metallothionein levels were also similar in all groups and similar to maternal values. Comparing the percentage distribution of zinc in maternal and cord serum fractions, major differences were observed in HZn, with zinc in albumin fraction being 70% in cord compared to 56% in maternal serum. There was a higher (p < 0.01) percentage of zinc bound to alpha 2-macroglobulin fraction in maternal serum of HZn compared to maternal serum of the other groups. Maternal and cord zinc in the albumin fractions correlated significantly (r = 0.48; p = 0.002) particularly in HZn (r = 0.71; p < 0.021). Placental zinc correlated negatively (r = -0.34; p = 0.035) with zinc in the maternal alpha 2-macroglobulin fraction, but did not relate to placental metallothionein, which had similar levels in all groups (average 0.28 nmol/g wet tissue). Placental zinc levels were lower (p < 0.01) in HZn. Our results indicate that high levels of maternal serum zinc in healthy women at delivery may be related to maternal tissue zinc redistribution that could favor diffusional components of maternal-fetal transfer of zinc.

Effect of subadequate maternal vitamin-A status on placental transfer of retinol and beta-carotene to the human fetus.

The placental transfer of retinol and beta-carotene was assessed based on maternal serum, cord serum and placental levels at term parturition in women with adequate (n = 15; serum retinol > 20 micrograms/dl) and subadequate (n = 16; serum retinol < or = 20 micrograms/dl) vitamin-A status. There was no difference in retinol and beta-carotene levels in placenta and cord serum between these groups. However, differences in the relation of maternal, placental and cord blood components were observed between women with adequate and subadequate vitamin-A status. In women with subadequate status, circulating fetal retinol levels correlated with placental retinol levels, and maternal serum beta-carotene correlated with placental retinol. Within this group, maternal serum beta-carotene and cord serum retinol correlated significantly in women with serum retinol levels lower than 15 micrograms/dl. These results suggest that beta-carotene may be a precursor of retinol in placenta and that this conversion may depend on the nutritional status of the mother, being particularly effective in a more depleted state.

Plasma zinc response to a breakfast meal or fasting in elderly women.

The aim of this study was to determine whether the postprandial decline in plasma zinc concentration is altered by aging. Eleven women, between the ages of 65 and 82 yr, participated in two separate experimental protocols: a high carbohydrate breakfast trial and a fasting trial. Plasma zinc concentrations were measured from blood samples obtained at 8:00 AM (baseline fasting) and at 30-min intervals until 1:00 PM during each trial. Following the breakfast meal, plasma zinc concentrations declined 14% from 75 +/- 1 to 65 +/- 2 micrograms/dL (p < 0.05), reaching a nadir 2.7 +/- 0.2 h after the meal. This decline was significantly (p < 0.0001) greater than the 3.6% fall observed during the fasting trial. Postprandial changes in the plasma zinc concentrations were correlated with postprandial changes in serum glucose (r = -0.43, p < 0.001), serum insulin (r = -0.17, p < 0.01), and serum phosphorus (r = 0.32, p < 0.005). These data show that plasma zinc concentrations decline following food intake in elderly women in the same manner as previously described for younger adult women.

Liver reserves of iron, copper, and vitamin B12 in Brazilian fetuses and infants of different socioeconomic status.

The purpose of this study was to investigate the influence of the stage of fetal development and of maternal socioeconomic status on liver concentrations and total liver reserves of iron, copper, and vitamin B12 in Brazilian fetuses and infants. Eighty fetuses and infants ranging from 19 to 42 wk of gestational age were studied. Liver concentrations of nutrients did not vary significantly with the stage of fetal development. Therefore, increases in total liver reserves during development were caused mainly by increases in liver weight. There were significant correlations between total liver reserves of vitamin B12 and iron (r = 0.742, p < 0.001), vitamin B12 and copper (r = 0.444, p < 0.001), and iron and copper (r = 0.431, p < 0.001). Maternal socioeconomic status did not affect liver nutrient concentrations or total hepatic levels at any stage of fetal development.

Lactoferrin levels and unsaturated iron-binding capacity in colostrum of Brazilian women of two socioecomic levels

The objetive of this study was to compare lactoferrin (LF) levels and unsaturated iron-binding capacity (UIBC) of colostrum from Brazilian women aged 20-38 years of low (N = 28) and high (N = 15) socioeconomic level. Both groups received a similar amount of supplental iron (25-65 mg/day) during pregnancy. We also determined the relationship between LF levels and UIBC, and between these components and maternal iron status. Both groups (low and high socieconomic level) showed adequate and similar mean hematocrit (35.0 ñ 13% and 35.9 ñ 1.3%, respectively) and serum ferritin (64 ñ 12 µg/1 and 57 ñ 12 µg/1, respectively) levels. Furthermore, LF levels (5.7 ñ 0.9 mg/ml and 5.5 ñ 0.6 mg/ml) and UIBC (3.8 ñ 0.3 µg/ml and 3/1 ñ 0.3 µg/ml) were not significantly different in the two groups of women, nor were they related to maternal hematocrit or serum ferritin. UIBC was significantly (P = 0.009), although weakly positively correlated (r= 0.45) with LF levels, suggesting that other colostrum ligands may contribute substantially to the capacity of colostrum to bind exogenous iron

Lactoferrin levels and unsaturated iron-binding capacity in colostrum of Brazilian women of two socioeconomic levels.

The objective of this study was to compare lactoferrin (LF) levels and unsaturated iron-binding capacity (UIBC) of colostrum from Brazilian women aged 20-38 years of low (N = 28) and high (N = 15) socioeconomic level. Both groups received a similar amount of supplemental iron (25-65 mg/day) during pregnancy. We also determined the relationship between LF levels and UIBC, and between these components and maternal iron status. Both groups (low and high socioeconomic level) showed adequate and similar mean hematocrit (35.0 +/- 1.3% and 35.9 +/- 1.3%, respectively) and serum ferritin (64 +/- 12 micrograms/l and 57 +/- 12 micrograms/l, respectively) levels. Furthermore, LF levels (5.7 +/- 0.9 mg/ml and 5.5 +/- 0.6 mg/ml) and UIBC (3.8 +/- 0.3 micrograms/ml and 3.1 +/- 0.3 micrograms/ml) were not significantly different in the two groups of women, nor were they related to maternal hematocrit or serum ferritin. UIBC was significantly (P = 0.009), although weakly positively correlated (r = 0.45) with LF levels, suggesting that other colostrum ligands may contribute substantially to the capacity of colostrum to bind exogenous iron.

Estado Nutricional y composición de la leche materna en Hierro, Zinc, Folato y Vitamina B12 de madres de bajo nivel socioeconómico de Río de Janeiro / Nutritional status and iron, zinc, folate and vitamin B12 milk composition in mothers of low socioeconomic level in Río de Janeiro

El objetivo del estudio fue verificar si el uso durante el embarazo de suplemento de hierro, folato y vitamina B12 por mujeres brasileñas de bajo nivel socioeconómico es suficiente para lograr un estado nutricional satisfactorio en estos nutrientes durante la amamantación y una composición adecuada de la leche. Como complemento del estudio fue analizado el estado nutricional de las madres y la composición de la leche en relación al zinc. Considerando los valores promedio, el estado nutricional de las madres en relación a los nutrientes estudiados fue adecuado. Sin embargo algunas madres tuvieron índices menores que los normales para mujeres no embarazadas. Estos bajos índices especialmente 30 días después del parto, sugieren que estas madres presentan un estado nutricional inadecuado. La composición de la leche en relación a los nutrientes estudiados fue comparable a la de mujeres bien nutridas de países desarrollados. Las madres que recibieron suplemento de folato durante el embarazo tuvieron niveles más altos en el suero inmediatamente después del parto, que las que no recibieron suplemento. Sin embargo, la composición de la leche no fue afectada. Se concluye que el suplemento recibido fue insuficiente para cubrir las demandas de este período y mantener reservas adecuadas

Iron, zinc, folate and vitamin B12 nutritional status and milk composition of low-income Brazilian mothers.

The purpose of this study was to assess the nutritional status of low-income Brazilian mothers, who were supplemented with iron and vitamin B12 during pregnancy, in terms of iron, zinc, folate and vitamin B12, in different stages of lactation and to determine the influence of the maternal nutritional status on milk composition. The effect of folate supplementation during pregnancy on folate status of the nursing mothers and milk composition was investigated. The effect of partial weaning on maternal status and milk composition was also studied. In general, the nutritional status of iron, zinc, folate and vitamin B12 of the mothers appears adequate. However, some of the mothers had indices of status lower than normal limits for non-pregnant women. These values, particularly after 30 d post-partum, indicate that these mothers might be at nutritional risk and that the nutrient supplementation received during pregnancy was insufficient to meet demands. There was an increase with the stage of lactation for haematocrit, serum vitamin B12, serum zinc, serum albumin, milk folate and saturation of its binding protein, but there was a decrease for milk protein, total and whey-bound iron and zinc, and lactoferrin. Mothers who took folate supplements during pregnancy had higher serum folate levels immediately after birth than those not taking the supplements but no differences were found at later stages of lactation. Milk composition was not affected. Partial weaning did not affect the maternal nutritional status or the milk composition except for iron which was higher in milk from mothers who were partially breastfeeding.(ABSTRACT TRUNCATED AT 250 WORDS)

Concentration and distribution pattern of selected micronutrients in preterm and term milk from urban Brazilian mothers during early lactation.

The purpose of this study was to assess the concentration and binding pattern of zinc, iron, folate and vitamin B12 in milk of Brazilian women of low socioeconomic status giving birth at term or preterm, during early lactation. Protein, fat, total solids and ash concentrations were also determined. Protein and zinc concentrations decreased significantly as lactation proceeded whereas milk fat and folate increased with the lactation period. Total solids, ash, iron and vitamin B12 remained unchanged. Zinc was present mainly in the whey fraction while less than half of the total iron was present in this fraction, with no significant change due to stage of lactation. Unsaturated folate and vitamin B12 binding capacities and percentage of saturation of the folate binding protein increased with the stage of lactation. The vitamin B12 binding protein was highly unsaturated in all samples. There was no significant difference between term and preterm samples in the parameters investigated. Correlation analysis between milk components indicated significant relationships between total solids and fat, total zinc and whey zinc, folate and total folate binding capacity, unsaturated and total folate binding capacity, and unsaturated and total B12 binding capacity. In general, the nutrient concentrations found in this study are in good agreement with published data on milk composition of women from developed countries, with the possible exceptions of folate, which was lower, and iron, which was higher. The correlation of folate concentration with its binding protein found in this work supports the hypothesis of a regulatory role for folate levels in milk exerted by the folate binding protein in the mammary gland.

Comparative effects of wheat bran and barley husk on nutrient utilization in rats. 2. Zinc, calcium and phosphorus.

1. The present work was undertaken to study comparatively the effect on mineral availability in rats of wheat bran and barley husk when supplying the same amount of dietary fibre (DF). The experiment involved a total of nine dietary treatments including a control group and two series of four groups with increasing amounts of fibre from the two sources (total DF ranging from 42 to 117 g/kg dry matter (DM]. Dietary nitrogen concentration was kept constant at 15 g N/kg DM. Zinc concentration of the diets was adjusted to the level provided by the diet with the highest wheat-bran content (21 mg/kg DM) using zinc sulphate. Other minerals were not adjusted. 2. Two experiments were performed. In Expt 1 the diets were given to 5-week-old rats during 9 d and apparent absorptions of Zn, calcium and phosphorus and the femur concentrations of Zn, Ca and P were measured. In Expt 2 the diets were given to 9-week-old rats during 12 d. Mineral concentration in femur and total and albumin-bound plasma Zn and availability of plasma Zn for enzyme reactivation were measured. 3. In the younger animals, wheat bran depressed significantly the absorption of Zn when providing 40 g DF/kg DM and absorbtion of Ca when providing 80 g DF/kg DM. Barley husk depressed significantly both the absorption of Zn and Ca already at 20 g DF/kg DM. Both fibre sources had a more negative effect on Zn than on Ca absorption. Only barley husk had a small negative effect on absorption of P. Phytate did not appear as a major factor affecting mineral absorption in barley husk. All diets containing barley husk had a very low molar ratio, phytate:Zn. 4. The age of the animals influenced the utilization of dietary minerals using femur concentration as a criterion, particularly in the case of Zn. In the younger animals the decrease in femur Zn with fibre correlated with apparent Zn absorption both with wheat bran (R2 0.986, P less than 0.01) and with barley husk (R2 0.996, P less than 0.01). In the older animals femur Zn did not change significantly with fibre. 5. In the older animals, plasma Zn, albumin-bound plasma Zn and availability of plasma Zn for enzyme reactivation were lowest with the highest addition of wheat bran.

Comparative effects of wheat bran and barley husk on nutrient utilization in rats. 1. Protein and energy.

1. The present work with growing rats was undertaken to compare the effect of wheat bran and barley husk on nutrient bioavailability. The experiment involved a total of nine dietary treatments consisting of a control group, without wheat bran or barley husk, and two series of four groups with increasing amounts of fibre from 50 to 117 g/kg dry matter (DM) from the two fibre sources. Dietary nitrogen concentration was kept constant at 15 gN/kg DM by adjusting the diets with an N-free mixture. Protein sources were casein, fortified with methionine and white wheat flour. True protein digestibility (TD), biological value (BV), net protein utilization (NPU) and digestible energy (DE) were estimated. 2. TD decreased when total dietary fibre (TDF) increased, the effect being greater in the case of wheat bran. The difference in response can be explained by the larger N contribution from bran than from barley husk. N from barley husk was actually digested less than N from wheat bran. 3. Changes in TD due to fibre were small, both for wheat and barley husk. It was concluded that decreased TD with fibre at moderate levels was due to poor digestibility of the N associated with the fibre source rather than decreased digestibility of N from other dietary components. 4. BV was only marginally affected by the fibre levels, indicating that the relatively high lysine content in both wheat bran and barley husk had a low availability. 5. Wheat bran and barley husk showed almost the same negative effect on DE and DM digestibility (DMD). DMD correlated significantly with DE, demonstrating that DMD is a simple and convenient means of monitoring DE.

[Serum zinc in Brazilian children of families of low income]. / Zinco sérico em criancas brasileiras de famílias de baixa renda.

Serum zinc was measured in 103 Brazilian children from low income families, 3 months to 6 years of age, with the purpose of characterizing their zinc nutritional status. Serum albumin was determined in some of the children studied. They were grouped in three categories according to the adequacy of height for age and weight for height indices related to the growth curves determined for Brazilian children. There were 30 normal, 18 acutely malnourished and five chronically malnourished children. This criteria was complemented by the Gomez criteria. Thirty healthy adults of both sexes served as a reference group for the analytical procedures. In the adults, serum zinc was 107.5 +/- 14.5 micrograms/dl, similar to values observed by other investigators, and significantly higher than in all of the children studied. Serum zinc of normal children was 98.3 +/- 15.7 micrograms/dl. It decreased with the degree of malnutrition, being significant for second degree acutely malnourished (87.8 +/- 9.2 micrograms/dl; p less than 0.05) and chronically malnourished children (68.7 +/- 8.9 micrograms/dl; p less than 0.001). Serum zinc and albumin correlated significantly (r = 0.51; n = 37; p less than 0.01), particularly in the severely malnourished children (r = 0.63; n = 8; p less than 0.05).

An enzymatic assay for available zinc in plasma and serum.

A convenient enzymatic assay for available zinc in plasma and serum was developed. The assay is based upon the reactivation of the zinc metalloenzyme alkaline phosphatase which had been previously inactivated by nitrilotriacetic acid. The enzymatic assay was applied to serum samples from human subjects in a study of zinc utilization in pregnancy and to plasma samples from rats in a zinc deficiency study. Most plasma samples with low zinc levels (less than 70 microgram/dl) reactivated the enzyme to less than 30% of control activity. Most samples with normal zinc levels (70-120 microgram/dl) reactivated the enzyme 30-65%. Samples with elevated zinc levels (greater than 120 microgram/dl) reactivated the enzyme over 70%. The assay is quick, convenient, and in principle measures functionally available zinc.