Mineral bioavailability and metabolism determined by using stable isotope tracers1

The art of establishing mineral tolerances of dogs and cats

For over six decades, nutritional science has provided well-developed, peer-reviewed nutrient recommendations to support the health of dogs and cats. These guidelines are updated based on new scientifically valid research and appropriate peer-review. Recent regulatory and scientific positions around health issues have resulted in strong opinions and desires for rapid regulatory action surrounding mineral nutrition, but with limited and conflicting scientific evidence. Pet Food Institute nutrition experts have come together to jointly author an article on the complexities of establishing mineral tolerances of dogs and cats to illustrate the limitations in defining mineral tolerances. This discussion covers how mineral requirements were determined, including the opportunities and pitfalls encountered. Scientific councils must review and clarify any proposed changes in conducting mineral nutrition research that might impact complete and balanced foods and surrounding regulations. It is important to clarify the multiple issues in mineral nutrition research and the necessity for thorough evaluation of data while avoiding arbitrary and potentially harmful guidelines.

Human biokinetic data and a new compartmental model of zirconium--a tracer study with enriched stable isotopes

Biokinetic models describing the uptake, distribution and excretion of trace elements are an essential tool in nutrition, toxicology, or internal dosimetry of radionuclides. Zirconium, especially its radioisotope (95)Zr, is relevant to radiation protection due to its production in uranium fission and neutron activation of nuclear fuel cladding material. We present a comprehensive set of human data from a tracer study with stable isotopes of zirconium. The data are used to refine a biokinetic model of zirconium. Six female and seven male healthy adult volunteers participated in the study. It includes 16 complete double tracer investigations with oral ingestion and intravenous injection, and seven supplemental investigations. Tracer concentrations were measured in blood plasma and urine collected up to 100 d after tracer administration. The four data sets (two chemical tracer forms in plasma and urine) each encompass 105-240 measured concentration values above detection limits. Total fractional absorption of ingested zirconium was found to be 0.001 for zirconium in citrate-buffered drinking solution and 0.007 for zirconium oxalate solution. Biokinetic models were developed based on the linear first-order kinetic compartmental model approach used by the International Commission on Radiological Protection (ICRP). The main differences of the optimized systemic model of zirconium to the current ICRP model are (1) recycling into the transfer compartment made necessary by the observed tracer clearance from plasma, (2) different parameters related to fractional absorption for each form of the ingested tracer, and (3) a physiologically based excretion pathway to urine. The study considerably expands the knowledge on the biokinetics of zirconium, which was until now dominated by data from animal studies. The proposed systemic model improves the existing ICRP model, yet is based on the same principles and fits well into the ICRP radiation protection approach.

Symposium 2: Modern approaches to nutritional research challenges: Targeted and non-targeted approaches for metabolite profiling in nutritional research

The present report discusses targeted and non-targeted approaches to monitor single nutrients and global metabolite profiles in nutritional research. Non-targeted approaches such as metabolomics allow for the global description of metabolites in a biological sample and combine an analytical platform with multivariate data analysis to visualise patterns between sample groups. In nutritional research metabolomics has generated much interest as it has the potential to identify changes to metabolic pathways induced by diet or single nutrients, to explore relationships between diet and disease and to discover biomarkers of diet and disease. Although still in its infancy, a number of studies applying this technology have been performed; for example, the first study in 2003 investigated isoflavone metabolism in females, while the most recent study has demonstrated changes to various metabolic pathways during a glucose tolerance test. As a relatively new technology metabolomics is faced with a number of limitations and challenges including the standardisation of study design and methodology and the need for careful consideration of data analysis, interpretation and identification. Targeted approaches are used to monitor single or multiple nutrient and/or metabolite status to obtain information on concentration, absorption, distribution, metabolism and elimination. Such applications are currently widespread in nutritional research and one example, using stable isotopes to monitor nutrient status, is discussed in more detail. These applications represent innovative approaches in nutritional research to investigate the role of both single nutrients and diet in health and disease.

Recent progress in stable isotope methods for assessing vitamin metabolism

PURPOSE OF REVIEW

Recent developments in mass spectrometric methodology, in particular the widespread adoption of liquid chromatography/mass spectrometry, have presented investigators with new opportunities to investigate micronutrient absorption and metabolism. This review focuses on recent reports of the use of stable isotope techniques to facilitate research into vitamin uptake and utilization in humans.

RECENT FINDINGS

Stable isotopes are used principally in two ways, as analytical standards in isotope dilution assays and as tracers in studies of physiology. There have been a number of advances in both fields recently for almost all of the vitamins. In particular, the effects of food preparation and meal composition on vitamin bioavailability are being probed more widely than before.

SUMMARY

A considerable amount of method development has been reported. We now have the opportunity to consolidate our understanding of vitamin metabolism to better inform the dietary recommendations for optimal health.