Effect of aging on zinc and histidine transport across rat intestinal brush-border membranes

Digestion and Postprandial Metabolism in the Elderly

The elderly are an increasing segment of the population. Despite the rapid gains in medical knowledge and treatments, older adults are more likely to experience chronic illnesses that decrease quality of life and accelerate mortality. Nutrition is a key modifiable lifestyle factor which greatly impacts chronic disease risk. Yet despite the importance of nutrition, relatively little is known of the impact of advancing age on the gastrointestinal function, the digestive responses, and the post-meal metabolic adaptations that occur in response to ingested food. Knowledge of the age-related differences in digestion and metabolism in the elderly is essential to the development of appropriate nutritional recommendations for the maintenance of optimal health and prevention of disease.

Maternal body mass index, dietary intake and socioeconomic status: differential effects on breast milk zinc, copper and iron content

BACKGROUND

As breast milk micronutrients content are essential for health and growth of the infants, this study was conducted to determine the breast milk zinc, copper and iron concen-trations and their possible correlations with maternal nutritional status, dietary intakes as well as socioeconomic status.

METHODS

Breast milk samples and information on maternal anthropometric characteristics and dietary intake were collected from 90 Iranian lactating women with 3 different socioeco-nomic status who exclusively breastfed their infants. Concentrations of trace elements were analyzed using atomic absorption spectrophotometry. Nutritionist III program, Multiple Re-gression and ANOVA test were used for data analyses.

RESULTS

The mean milk zinc, copper, and iron concentrations were 1.93 ± 0.71, 0.58 ± 0.32, and 0.81 ± 0.2 mg/l, respectively. In all three SES groups only zinc mean level was lower than the recommended range. A significant difference was observed in breast milk zinc, copper and iron concentration between high and low SES groups (Zn (P<0.001), Cu (P<0.001) and Fe (P<0.044)) and also moderate and low SES groups (Zn (P<0.03), Cu (P<0.001) and Fe (P<0.049)). After adjusting for maternal body mass index (BMI), socioeconomic status, mean dietary energy, zinc, copper, and iron intakes, there was a negative and significant association between maternal age and breast milk zinc (β=-0.28, P<0.034), copper (β=-0.18, P<0.048), and iron (β=-0.22, P<0.04) concentrations.

CONCLUSION

In low socioeconomic group with lower mean age, breast milk mineral levels were higher than others and there was no significant correlation between mineral levels and dietary intake. Hence it is supposed that maternal age may be better predictor of breast milk mineral levels.

Histidine absorption across apical surfaces of freshwater rainbow trout intestine: mechanistic characterization and the influence of copper

The essential amino acid histidine performs critical roles in health and disease. These functions are generally attributed to the amino acid itself, but could also be mediated by a positive effect on trace element bioavailability. Mechanistic information regarding the absorption of histidine across the gastrointestinal tract is essential for understanding the interplay between amino acid and mineral nutrients and the implications of these interactions for nutrition and toxicology. Using intestinal brush-border membrane vesicles obtained from freshwater rainbow trout, absorption of histidine over the range 0.78-780 microM: was found to be saturable, with a maximal transport rate (J (max)) of 9.1 +/- 0.8 nmol mg protein(-1) min(-1) and a K (m) (histidine concentration required to reach 50% of this level) of 339 +/- 68 microM: . Histidine uptake was highly specific as 10-fold elevated levels of a variety of amino acids with putative shared transporters failed to significantly inhibit uptake. Elevated levels of D: -histidine, however, impaired uptake of the natural L: -isomer. The presence of "luminal" copper (8.3 microM: ) significantly increased both the J (max) and K (m) of histidine transport. This suggests that chelated copper-histidine species cross the brush-border epithelium through transport pathways distinct from those used by histidine alone.

The effect of aging on intestinal absorption and status of calcium, magnesium, zinc, and copper in rats: a stable isotope study

Many investigators have reported changes in mineral status with age but conflicting observations were done concerning mineral absorption. This study was conducted to clarify the effect of aging on intestinal absorption and status of minerals, using a stable isotope approach. To do so, 40 rats of different ages: 9, 22, 44, and 88 weeks were fed with a semi-purified diet for a total of 30 days. At the beginning of the 4th week, the rats received a stable isotope solution containing (44)Ca, (25)Mg, (67)Zn, and (65)Cu. Individual feces and urine were then collected during 4 consecutive days in order to measure stable isotopes by inductively coupled plasma/mass spectrometry (ICP/MS) and blood and tissues were sampled for mineral status determination. Intestinal absorption of (44)Ca and (67)Zn considerably decreased with age, whereas intestinal (25)Mg absorption decreased only moderately and intestinal (65)Cu absorption was unaffected. Plasma and bone calcium (Ca) were not modified with age whereas urinary Ca excretion considerably increased. Plasma and erythrocyte magnesium (Mg) levels were unaffected with age whereas urinary Mg excretion and Mg bone level decreased. Plasma zinc (Zn) level decreased and bone Zn level increased with age whereas red blood cell and liver Zn level and urinary Zn excretion remained unchanged. Plasma Cu level increased with age whereas liver and bone Cu levels and urinary Cu excretion remained unchanged. These results show that the effect of aging on the intestinal mineral absorption and status differ largely according to the mineral considered. Further studies are required under different nutritional conditions to explore the underlying mechanisms during aging and to adjust a better nutrition of the elderly.

Zinc uptake and storage: the role of fundus pigmentation

BACKGROUND

Age-related macular degeneration (AMD) is associated with lower melanin pigmentation and is more prevalent among the elderly Caucasian population than among Africans. A correlation between light iris colour, fundus pigmentation and the incidence of AMD is reported. Moreover, melanin represents the main storage of zinc in the eye. Zinc enhances antioxidant capacity through its function as a cofactor of important enzymes or by influencing gene expression of regulatory elements in the eye. In this study, we investigated the uptake and storage of zinc in the human choroid/retinal pigment epithelium (RPE) complexes in dependence on the fundus pigmentation as judged by the iris colour.

MATERIAL AND METHODS

Choroid/RPE complexes of blue and brown human eyes were used. Tissues without any substitution served as controls. Specimens from choroid/RPE complexes were incubated with 100 microM zinc chloride for 24 h. After incubation, pieces of the complexes were stored to investigate the uptake of zinc. The rest of the tissues were kept for 3 and 7 days in culture medium (DMEM) for storage examination. The concentration of zinc was measured by inductively coupled plasma mass spectrometry.

RESULTS

After 24 h of zinc treatment the concentration of zinc in the choroid/RPE complexes of blue eyes was not significantly increased. The concentration of zinc in highly pigmented tissues (brown eyes) was increased by the factor 5.1 after 24 h and remained at high levels after 3 days (factor 4.4) and 7 days (factor 2.8).

CONCLUSIONS

Zinc uptake in the choroid/RPE complex correlates to the iris colour. Alterations of the degree of iris pigmentation result in differences of zinc uptake and storage in the choroids. A potential protective role of zinc may be more prominent in dark- than in light-coloured eyes.

Zinc uptake across the apical membrane of freshwater rainbow trout intestine is mediated by high affinity, low affinity, and histidine-facilitated pathways

Zinc is both a vital nutrient and an important toxicant to aquatic biota. In order to understand the interplay between nutrition and toxicity, it will be important to determine the mechanisms and the factors that regulate zinc uptake. The mechanism of apical intestinal Zn(II) uptake in freshwater rainbow trout and its potential modification by the complexing amino acid histidine was investigated using brush-border membrane vesicles (BBMVs). Following characterisation of the BBMV preparation, zinc uptake in the absence of histidine was both time- and concentration-dependent and consisted of two components. A saturable phase of uptake was described by an affinity constant of 57+/-17 microM and a transport capacity of 1867+/-296 nmol mg membrane protein(-1) min(-1). At higher zinc levels (>500 microM) a linear, diffusive component of uptake was evident. Zinc transport was also temperature-dependent, with Q10 values suggesting zinc uptake was a carrier-mediated process. Zinc uptake by vesicles in the presence of histidine was correlated to a mono-histidine species (Zn(His)+) at all Zn(II) concentrations examined.

Kinetics of zinc transport in vitro in rat small intestine and colon: interaction with copper

The present study was planned to investigate the kinetic transport of zinc, in the intact intestine of the rat, in order to establish if more than one transporter is involved as well as the existence of a preferent sector in the cation uptake. Using an in vitro technique, the influx of zinc across the brush border membrane in three sectors of the small intestine (proximal, mid and distal) and in the colon of the rat was measured at six different concentrations (from 0.0007 to 11 mM). The kinetic study showed that intestinal transport of zinc occurs by a saturable process in the small intestine. The K(m) value obtained in the proximal segment (10.78+/-4.40 mM) is clearly higher than those obtained in the mid and distal segments (1.94+/-0.39 and 3.04+/-0.44 mM, respectively). The same occurs with the J(max) values. These results seem to indicate that more than one transporter may be implicated in zinc transport. In colon the most probable mechanism is non-saturable diffusion, the diffusive permeability, P, being 2.95.10(-7)+/-0.43.10(-7) cm/h. The statistical comparison of the fluxes indicated that, on the whole, there is not a well defined preferent sector in zinc transport. Additionally, the influence of copper on zinc transport, in three sectors of the small intestine, has been evaluated quantifying the influx of zinc at 0.037 mM in the absence and presence of three different concentrations of copper. The results showed that copper significantly reduced the influx of zinc, in the three sectors studied, in a concentration-dependent manner.

Using wound fluid analyses to identify trace element requirements for efficient healing

A series of wound fluid and blood plasma samples from 20 patients with breast cancer were analysed by Potentiometric Stripping Analysis and computer-aided chemical speciation to quantify the concentrations of the trace elements of copper and zinc in the samples and to investigate the individual species of copper and zinc present. Comparisons were made between total concentrations of copper and zinc in wound fluid, pre-operative blood plasma levels and reference values. A wound fluid model constructed using JESS identified the main copper and zinc species present. It was also used to investigate the effects of a change in pH and changes in the total concentrations of certain components on their predominance. The clinical significance of the research is discussed, together with suggestions for a continuation in the research.

Analysis and chemical speciation of copper and zinc in wound fluid

A novel method for the analysis of trace element chemical speciation at parts per billion (ppb) levels in wound fluid samples both contributes to the fundamental inorganic biochemistry of the healing process and permits improved treatments. Potentiometric Stripping Analysis in combination with acid digestion has been used to quantify the total copper and zinc levels in a series of 0.5 ml samples of fluid obtained from surgical wounds. Further, the degree of blood contamination has been investigated using visible spectroscopy. The prevailing chemical speciation (chemical forms) of these total concentrations of copper and zinc amongst low molecular mass ligands in wound fluid has been investigated by computer modelling using JESS, the Joint Expert Speciation System. The model, involving 38 components, generates in the region of 3500 individual low molecular mass complexes including copper, zinc, iron, calcium and manganese species, and predicts that the majority of low molecular mass (lmm) copper complexes are electrically net-neutral, whilst those of zinc are predominantly charged. Further studies indicate that supplementing the concentrations of histidine and tryptophan may increase the net-neutral zinc fraction, the optimum effect being achieved at pH=7.4. This may be important in transporting zinc into healing cells.