The revolution in microanalytic chemistry: a macro-opportunity for clinical nutrition

Lymphocyte metallothionein mRNA responds to marginal zinc intake in human volunteers

Marginal Zn deficiency is thought to be prevalent in both developed and developing countries. However, the extent of Zn deficiency is not known, due to the lack of a reliable diagnostic indicator. Blood plasma and erythrocyte concentrations of metallothionein (MT) reflect Zn status, but measurement of MT is dependent on the availability of sensitive immunoassays. Our aim was to show whether measurement of T lymphocyte MT-2A mRNA, using a competitive reverse transcriptase (RT)–polymerase chain reaction (PCR) assay, could indicate Zn status in human subjects in a residential Zn-depletion study. In the study, the Zn intake of seven volunteers was maintained at 13·7 mg/d for 5 weeks (baseline) followed by 4·6 mg/d for 10 weeks (marginal intake) and then 13·7 mg/d (repletion) for 5 weeks. The quantitative assay was developed using standard techniques and concentrations of MT-2A mRNA were normalized by reference to β-actin mRNA which was also measured by competitive RT–PCR assay. An alternative method of measuring the PCR product using capillary electrophoresis with laser-induced fluorescence detection was also evaluated. There was considerable inter-individual variation in MT-2A mRNA concentration and the mean level at the end of the baseline period was 10·3 (SE 3·7) fg MT-2A mRNA/pg β-actin mRNA, which then decreased by 64 % during the low Zn intake period. After repletion, MT-2A mRNA returned to baseline concentrations. In contrast, plasma Zn was unchanged by marginal Zn intake or repletion. The effect of low Zn in all individuals was consistent. We conclude that this assay is a sensitive method of evaluating marginal changes in dietary Zn intake.

Metabolomics in the opening decade of the 21st century: building the roads to individualized health

It is rapidly becoming possible to measure hundreds or thousands of metabolites in small samples of biological fluids or tissues. This makes it possible to assess the metabolic component of nutritional phenotypes and will allow individualized dietary recommendations. ASNS has to take action to ensure that appropriate technologies are developed and that metabolic databases are constructed with the right inputs and organization. The relations between diet and metabolomic profiles and between those profiles and health and disease must be established. ASNS also should consider the social implications of these advances and plan for their appropriate utilization.

Trace element biology: the knowledge base and its application for the nutrition of individuals and populations

Impressive strides are being made in the understanding of trace element metabolism and function. This is underscored by the many contributions in these proceedings. However, not so impressive are: i) the precise recognition of mild trace element deficiencies and how to establish their functional consequences, possibly confounded by concurrent trace element inadequacies, are difficult to assess, ii) approaches to the quantitative determination of requirements for trace elements remain unsatisfactory and archaic, in so many ways, iii) our understanding of the extent of the biological basis for the variation in requirements among apparently similar individuals is poor, and iv) much needs to be learned about the quantitative extent to which genetic, epigenetic and dietary factors interact to determine the nutritional phenotype. Some ideas are presented as to how we might embrace, in the context of a reconstructive approach, the exciting new knowledge and related techniques emerging during the postgenome era and develop new paradigms for assessing trace element needs and status, and for establishing effective nutrient intake under different conditions of complex genotype-environment interactions. Metabolites are functional cellular entities and I also urge a vigorous application of metabolomics and of metabolic profiling that is closely linked with genomics, proteomics, trace element kinetics and system analysis, as components of the new integrative paradigm. We need to understand the system and its strategy, not only the molecular details of its component parts and its individual controls. An interdisciplinary research and teaching enterprise will be necessary to best achieve this aim. All of this is related to our common goal to promote, through expanded biological knowledge and its effective application, the enhanced role of trace elements for human well-being.

DNA microarray analysis of genes differentially expressed in diet-induced (cafeteria) obese rats

OBJECTIVE

To better understand the molecular basis of dietary obesity, we examined adipose tissue genes differentially expressed in an obesity model using DNA microarray analysis.

RESEARCH METHODS AND PROCEDURES

We assessed the expression level of over 12,500 transcripts in epididymal fat pads from (cafeteria) obese and control rats with the aid of the array technology.

RESULTS

Cafeteria (obese) rats weighed 50% more and had 2.5-fold higher levels of epididymal fat and elevated levels of circulating leptin. Adipose genes differentially expressed in obese and control rats were categorized into five groups: macronutrient metabolism, transcription factors, hormone receptor and signal transduction, redox and stress proteins, and cellular cytoskeleton. Interestingly, the expression levels of a number of genes involved in lipid metabolism such as glycerol-3-phosphate dehydrogenase, stearoyl coenzyme A desaturase, together with the transcription factors implicated in adipocyte differentiation (CAAT/enhancer binding protein-alpha and peroxisome proliferator-activated receptor-gamma), were significantly increased in obese animals compared with control. The most up-regulated transcripts were the ob (49.2-fold change) and the fatty acid-binding protein genes (15.7- fold change). In contrast, genes related to redox and stress protein were generally down-regulated in obese animals compared with the control.

DISCUSSION

Our study showed that in diet-induced obesity, the expression levels of some important genes implicated in lipid metabolism were up-regulated, whereas those related to redox and stress protein were down-regulated in obese animals compared with control. This pattern of gene expression may occur in human obesity cases after high-fat intake.