Use of stable isotopes and mathematical modelling to investigate human mineral metabolism

The use of BeWo cells as an in vitro model for placental iron transport

BeWo cells are a placental cell line that has been widely used as an in vitro model for the placenta. The b30 subclone of these cells can be grown on permeable membranes in bicameral chambers to form confluent cell layers, enabling rates of both nutrient uptake into the cells from the apical surface and efflux from the basolateral membrane to be determined. The aim of this study was to evaluate structural and functional properties of confluent b30 BeWo cell layers grown in bicameral chambers, focusing on the potential application for studying receptor-mediated uptake and transport of transferrin (Tf)-bound iron (Fe-Tf). While it proved extremely difficult to establish and maintain an intact BeWo cell monolayer, it was possible to grow the cells to a confluent multilayer. Iron, applied as Fe-Tf, was rapidly transported across this cell layer; 9.3 +/- 0.5% of the total dose was transported after 8 h, equivalent to 38.8 +/- 2.1 pmol.cm(-2).h(-1). Transfer of Tf across the cell layer was much more limited; 2.4 +/- 0.2% of the total dose was transported after 8 h, equivalent to 5.0 +/- 0.4 pmol.cm(-2).h(-1). Compartmental modeling of these data suggested that iron was transported across the cell layer predominantly, if not exclusively, via a transcellular route, whereas Tf taken up into the cells was predominantly recycled back to the apical compartment. The results suggest that these cells are very efficient at transporting iron and, under carefully controlled conditions, can be a valuable tool for the study of iron transport in the placenta.

Assessment of the relationship between post-meal satiety, gastric volume and gastric emptying after swedish adjustable gastric banding. A pilot study using magnetic resonance imaging to assess postsurgery gastric function

BACKGROUND

Swedish adjustable gastric banding (SAGB) is a common weight loss procedure performed worldwide. The exact mechanism by which it achieves appetite suppression, and hence weight loss, is not clear. One possible mechanism is altered meal handling by the post-SAGB stomach.

METHODS

Five post SAGB patients and five age/sex-matched controls were recruited. Pre- and post-meal magnetic resonance imaging (MRI) was performed with two liquid test meals of differing viscosity-locust bean gum (3.0%) and water. Appetite was assessed using ten-point visual analogue scales.

RESULTS

There were significant relationships between hunger scores and esophageal, pouch and residual stomach fluid volume changes for the locust bean gum meal (p=0.033, 0.043 and 0.011, respectively). The rate constants for gastric emptying were similar in the two groups for both the gum (0.038+/-0.016 min(-1) for SAGB, 0.041+/-0.032 min(-1) for controls, p=0.44) and water meals (0.068+/-0.044 min(-1) for SAGB, 0.044+/-0.009 min(-1) for controls, p=0.35). An unexpected finding was asymptomatic esophageal meal retention with the locust bean gum meal in the post-SAGB arm (mean 16.9 ml at 15 min).

CONCLUSIONS

There is no evidence of differences in volume-dependent gastric emptying between the normal and post-SAGB stomach. Further investigation of the phenomenon of esophageal retention, and its role in post-SAGB satiety, is warranted.

Application of enriched stable isotopes as tracers in biological systems: a critical review

The application of enriched stable isotopes of minerals and trace elements as tracers in biological systems is a rapidly growing research field that benefits from the many new developments in inorganic mass spectrometric instrumentation, primarily within inductively coupled plasma mass spectrometry (ICP-MS) instrumentation, such as reaction/collision cell ICP-MS and multicollector ICP-MS with improved isotope ratio measurement and interference removal capabilities. Adaptation and refinement of radioisotope tracer experiment methodologies for enriched stable isotope experiments, and the development of new methodologies coupled with more advanced compartmental and mathematical models for the distribution of elements in living organisms has enabled a broader use of enriched stable isotope experiments in the biological sciences. This review discusses the current and future uses of enriched stable isotope experiments in biological systems.

Improving human micronutrient nutrition through biofortification in the soil-plant system: China as a case study

Micronutrient malnutrition is a major health problem in China. According to a national nutritional survey, approximately 24% of all Chinese children suffer from a serious deficiency of iron (Fe) (anemia), while over 50% show a sub-clinical level of zinc (Zn) deficiency. More than 374 million people in China suffer from goiter disease, which is related to iodine (I) deficiency, and approximately 20% of the Chinese population are affected by selenium (Se) deficiency. Micronutrient malnutrition in humans is derived from deficiencies of these elements in soils and foods. In China, approximately 40% of the total land area is deficient in Fe and Zn. Keshan and Kaschin-Beck diseases always appear in regions where the soil content of Se in low. The soil-plant system is instrumental to human nutrition and forms the basis of the "food chain" in which there is micronutrient cycling, resulting in an ecologically sound and sustainable flow of micronutrients. Soil-plant system strategies that have been adopted to improve human micronutrient nutrition mainly include: (1) exploiting micronutrient-dense crop genotypes by studying the physiology and genetics of micronutrient flow from soils to the edible parts of crops; (2) improving micronutrient bioavailability through a better knowledge of the mechanisms of the enhancers' production and accumulation in edible parts and its regulation through soil-plant system; (3) improving our knowledge of the relationship between the content and bioavailability of micronutrients in soils and those in edible crop products for better human nutrition; (4) developing special micronutrient fertilizers and integrated nutrient management technologies for increasing both the density of the micronutrients in the edible parts of plants and their bioavailability to humans.

A stable isotope method for the simultaneous measurement of vitamin K1 (phylloquinone) kinetics and absorption

OBJECTIVES

To measure uptake and disposal kinetics and absolute absorption of vitamin K(1) using two stable isotope-labelled forms of vitamin K(1).

SUBJECTS

Ten subjects (nine women and one man) aged between 22 and 31 years, with a mean (+/-standard deviation) body mass index of 22.5+/-2.4 kg/m(2). Subjects took capsules containing 3 microg of methyl-(13)C vitamin K(1), three times a day for six days to reach a steady state for plasma vitamin K(1) isotopic enrichment. On day seven, subjects were given an intravenous dose of Konakion MM to measure disposal kinetics and at the same time, a capsule containing 4 microg of ring-D(4) vitamin K(1) to measure absorption. Plasma vitamin K(1) concentration was measured by high-performance liquid chromatography and isotopic composition by gas chromatography mass spectrometry.

RESULTS

The disposal kinetics of the intravenous dose of vitamin K(1) were resolved into two exponentials with half-times of 0.22 (+/-0.14) and 2.66 (+/-1.69) h. Absorption of oral, deuterated vitamin K(1) was 13 (+/-9)%.

CONCLUSIONS

Two-compartmental kinetic parameters observed in this study are similar to those obtained previously using radioactive tracers, but there may be additional slow-turnover body pools acting as stores of vitamin K(1). The kinetic parameters determined from the intravenous dose allowed determination of the absolute absorption of vitamin K(1) from a bolus oral dose.

Analysis of isotope ratios in vitamin K1 (phylloquinone) from human plasma by gas chromatography/mass spectrometry

Vitamin K(1) is a fat-soluble vitamin required for the gamma-carboxylation of vitamin K-dependent proteins. Recent work has suggested an important role for vitamin K(1) in bone health beyond its more established function in the control and regulation of blood coagulation. However, current UK recommended intakes do not reflect this recent evidence. The use of stable isotopes provides a powerful tool to investigate vitamin K kinetics, turnover and absorption in man, although published methods have reported difficulties in the extraction and analysis of isotope ratios of vitamin K in human plasma. In this paper, we report a new methodology for the extraction and measurement of isotope ratios in vitamin K(1). Sample clean-up is achieved with liquid-liquid extraction, enzyme hydrolysis with lipase and cholesterol esterase, and solid-phase extraction. Isotopic analysis of the pentafluoropropionyl derivative of vitamin K(1) is performed by gas chromatography/mass spectrometry (GC/MS). The limit of quantitation is equivalent to at least 0.3 nmol/L and the method is demonstrated to be linear over a range of enrichments. This method provides a robust alternative to previous work requiring the use of semi-preparative high-performance liquid chromatography (HPLC).

Species-Specific Isotope Dilution Analysis and Isotope Pattern Deconvolution for Butyltin Compounds Metabolism Investigations

A methodology for the study of the absorption and metabolism of butyltin compounds in laboratory animals using isotopically enriched species was developed. The method is based on the oral administration of 119Sn-labeled monobutyltin (MBT), 118Sn-labeled dibutyltin (DBT), and 117Sn-labeled tributyltin (TBT) to the animals and the measurement of both the concentration and isotopic composition of these compounds in the different tissues by GC-ICPMS. The degradation of butyltin compounds during their metabolism was computed using least-squares isotope pattern deconvolution, and their concentration was measured by reverse isotope dilution analysis using natural-abundance MBT, DBT, and TBT standards. Male Wistar rats were used as models to evaluate the proposed methodology. Preliminary toxicological results obtained with one rat indicate that TBT is highly absorbed (64.4%), and it is found in all organs with relatively high levels in stomach and intestines. The apparent absorption of DBT was 27.3% and was mainly found in liver, kidney, and intestines. However, a large proportion of the found DBT is formed from the degradation of TBT (approximately 40% of the found DBT in liver is degraded TBT). The apparent absorption of MBT was found to be 12.5%, and the originally administered MBT was mainly recovered in the feces. However, MBT was clearly detected in liver, kidney, stomach, intestines, and urine as degradation products of DBT and TBT. Although a significant variability from rat to rat is expected to be obtained, the analytical variability provided by this methodology is small enough to yield meaningful biological results. The results obtained demonstrate that the developed methodology is able to follow qualitatively, quantitatively, and simultaneously the specific metabolic pathways of different species of a given element.

Exchangeable magnesium pool masses in spontaneously hypertensive rats

We explored magnesium (Mg) metabolism by determination of exchangeable Mg pool masses and Mg kinetic parameters using stable Mg isotopes in spontaneously hypertensive rats (SHRs). Classical intracellular and extracellular Mg status biomarkers were also measured. Male SHRs and their male Wistar Kyoto (WKY) controls were fed a semipurified diet containing Mg 550 mg /kg for 2 weeks. Each rat received then an intravenous injection of 1.37 mg (25)Mg. The plasma (25)Mg disappearance curve over the next 7 days was used to measure the mass and fractional transport rate of 3 rapidly exchanging Mg metabolic pools, M1, M2, and M3. In the SHRs, plasma and erythrocyte Mg levels and urinary Mg excretion were not modified compared with their control WKYs, but tibia Mg level was significantly lower in the SHRs. Pool M3, the deep tissue pool, was significantly lower in SHRs compared with WKYs, but pools M1 and M2, the extracellular Mg pools, were statistically similar. The fractional transport rate of Mg from M1 to M2 and from M2 to M1 in the SHRs was higher than in the controls. The half-life of M1 was significantly decreased in SHRs compared with WKYs. In conclusion, this work demonstrates a decrease in intracellular Mg stores in SHRs compared with WKYs and disturbance of Mg exchanges in extracellular Mg, confirming a Mg metabolism disturbance in spontaneously hypertensive rats. Further work is now needed to elucidate the origin of the Mg depletion in SHRs and to explore Mg pools in hypertensive patients.