Biomarkers for nutrient intake with focus on alternative sampling techniques

Biomarkers of nutrient intake or nutrient status are important objective measures of foods/nutrients as one of the most important environmental factors people are exposed to. It is very difficult to obtain accurate data on individual food intake, and there is a large variation of nutrient composition of foods consumed in a population. Thus, it is difficult to obtain precise measures of exposure to different nutrients and thereby be able to understand the relationship between diet, health, and disease. This is the background for investing considerable resources in studying biomarkers of nutrients believed to be important in our foods. Modern technology with high sensitivity and specificity concerning many nutrient biomarkers has allowed an interesting development with analyses of very small amounts of blood or tissue material. In combination with non-professional collection of blood by finger-pricking and collection on filters or sticks, this may make collection of samples and analyses of biomarkers much more available for scientists as well as health professionals and even lay people in particular in relation to the marked trend of self-monitoring of body functions linked to mobile phone technology. Assuming standard operating procedures are used for collection, drying, transport, extraction, and analysis of samples, it turns out that many analytes of nutritional interest can be measured like metabolites, drugs, lipids, vitamins, minerals, and many types of peptides and proteins. The advantage of this alternative sampling technology is that non-professionals can collect, dry, and mail the samples; the samples can often be stored under room temperature in a dry atmosphere, requiring small amounts of blood. Another promising area is the potential relation between the microbiome and biomarkers that may be measured in feces as well as in blood.

Omega-3 polyunsaturated fatty acid profiling using fingertip-prick whole blood does not require overnight fasting before blood collection

Fatty acid profiling through the rapid analysis of capillary blood collected by fingertip prick could enable economical screening for omega-3 polyunsaturated fatty acid (PUFA) status, although the typical requirement of fasting prior to sample collection may limit application. We hypothesize that moderate changes in omega-3 biomarkers determined from fingertip-prick blood will occur and correspond to omega-3 PUFA content of the meals. Eight participants consumed a single breakfast with high fat, high fat with omega-3 functional foods, and low fat and low fat with fish oil capsules in a cross-over design. The fatty acid composition of fingertip-prick blood total lipid and venous blood erythrocyte total lipid, plasma total lipid, plasma triacylglycerol, and plasma phospholipids were analyzed at baseline and 1, 2, 3 and 4 hours after each single breakfast consumption. Omega-3 blood biomarkers; % of omega-3 highly unsaturated fatty acid (HUFA) in total HUFA, weight % of eicosapentaenoic acid+docosahexaenoic acid, weight % of eicosapentaenoic acid+omega-3 docosapentaenoic acid+docosahexaenoic acid, and the ratio of total omega-6 PUFA to total omega-3 PUFA in fingertip-prick blood, did not change from baseline during the postprandial period (P > .05). However, meal type yielded lower (P < .05) % omega-3 HUFA in total HUFA in the low fat meal (22.8 ± 3.9) as compared with the low fat with omega-3 (24.2 ± 3.9) and, the high fat (23.8 ± 4) meals. The ratio of total omega-6 PUFA to total omega-3 PUFA was generally higher in meals without omega-3 compared with omega-3. In conclusion, determinations of omega-3 status by fingertip-prick blood sampling may not require prior overnight fasting.

Use of dried blood for measurement of trans fatty acids

BACKGROUND

Fatty acid measurements especially trans fatty acid has gained interest in recent times. Among the various available biomarkers, adipose tissue is considered to be the best for the long term dietary intake but the invasive nature of tissue aspiration reduces its utility. Phlebotomy is a much less invasive method of sample collection when a large number of participants are involved in the study and therefore is an alternative, most suitable for large population based studies. In the present study fatty acid (with special emphasis on trans fatty acid) extraction from blood spotted and dried on filter paper was carried out to simplify the sample collection procedure and transportation.

METHODS

Blood samples were collected from 19 healthy volunteers. The blood was spotted (30 spots of 10 microl each) on filter paper, dried at room temperature and stored at 4 degrees C in zip-lock poly bags. For comparison whole blood stored at -70 degrees C was simultaneously analyzed.

RESULTS

A good agreement was seen between trans fatty acid values obtained in dried blood and whole blood as evident from the pearson correlation coefficients ('r' for monounsaturated (trans) 0.70 and for polyunsaturated (trans) 0.692 respectively). The intraclass correlation coefficient for monounsaturated trans was 0.805 and for polyunsarurated trans was 0.776.

CONCLUSION

Dried blood spots can be used for trans fatty acid analysis.

Direct microwave transesterification of fingertip prick blood samples for fatty acid determinations

Omega-3 polyunsaturated fatty acid (PUFA) dietary intakes and tissue levels are positively associated with various health benefits. The development of cost efficient, high throughput methodologies would enable research in large clinical and population studies, and clinical fatty acid profiling. Microwave heating for the transesterification of blood fatty acids was examined. Samples were collected by venous puncture and fingertip prick onto chromatography paper. Aliquots of serum, plasma, erythrocytes and whole blood were prepared from venous blood. Boron trifluoride in methanol was used for transesterification but sample preparation and heating varied. Fatty acid determinations and markers of omega-3 fatty acid status including the sum of eicosapentaenoic acid and docosahexaenoic acid, the ratio of total n-3 PUFA to n-6 PUFA, and the percentage of n-3 highly unsaturated fatty acids (HUFA, >or=20 carbons and >or=3 carbon-carbon double bonds) in total HUFA were compared. Quantitative determinations indicate that microwave transesterification results in significantly lower estimates of monounsaturates and polyunsaturates, possibly through incomplete transesterification of triacylglycerols. However, qualitative estimates of omega-3 fatty acid status were relatively similar. Fingertip prick blood collection combined with direct transesterification by microwave may be a very rapid method to estimate omega-3 fatty acid status for selected applications.

Mass spectrometry in metabolome analysis

In the post-genomic era, increasing efforts have been made to describe the relationship between the genome and the phenotype in cells and organisms. It has become clear that even a complete understanding of the state of the genes, messages, and proteins in a living system does not reveal its phenotype. Therefore, researchers have started to study the metabolome (or the metabolic complement of functional genomics). Within this context, mass spectrometry (MS) has increasingly occupied a central position in the methodologies developed for determination of the metabolic state. This review is mainly focused on the status of MS in the metabolome field, trying to direct the reader to the main approaches for analysis of metabolites, reviewing basic methodologies in sample preparation, and the most recent MS techniques introduced. Apart from the description of the different methods, this review will try to state a general comparison between the several different techniques that involve MS and metabolite analysis, and will highlight their limitations and preferred applicability.

An HPLC-MS approach for analysis of very long chain fatty acids and other apolar compounds on octadecyl-silica phase using partly miscible solvents

A novel approach for analyzing underivatized very long chain fatty acids (C16-C26) and other apolar compounds such as triacylglycerols is described. It is based on reversed-phase HPLC separation followed by mass spectrometric detection. Partly miscible solvents are used for stepwise gradient elution starting with a methanol/water and ending with a methanol/n-hexane binary mixture. The developed technique does not need derivatization, and analysis is fast (fatty acids were separated in 2-min-long chromatograms) and robust. The developed method is also very sensitive; a quantitation limit in the low-picogram range was achieved for fatty acids. The separation mechanism and advantages of the suggested technique are discussed and illustrated in the case of blood analysis and plant oil characterization.

Diagnostic patterns of very-long-chain fatty acids in plasma of patients with X-linked adrenoleukodystrophy

Pattern recognition analysis on the levels of the very-long-chain fatty acids (VLCFAs) in plasma is described for the visual discrimination of X-linked adrenoleukodystrophy (X-ALD) patients from normal healthy group. Plasma VLCFA compositions of 58 normal subjects and 16 X-ALD patients were examined by gas chromatography as their methyl esters to determine the area percentages of behenic acid (C22:0), lignoceric acid (C24:0) and hexacosanoic acid (C26:0) in the total fatty acids, and the concentration (microg/ml) of C26:0. When star symbol plotting was applied to the VLCFA values of C22:0 (%), C24:0 (%), C26:0 (%), C24:0/C22:0, C26:0/C22:0 and C26:0 (microg/ml) after normalization to the corresponding median values in normal group, the resulting deformed hexagonal star pattern was characteristic of each patient. Therefore, simple visual comparison with the equilateral hexagon of normal group average as the control pattern enabled one readily to discriminate X-ALD patients from the normal group. Additionally, canonical discriminant analysis performed on the six unnormalized VLCFA values correctly classified 74 plasma specimens into two separate clusters according to normal subject or X-ALD patient in the canonical plot.

Urinary organic acids in peroxisomal disorders: a simple screening method

Using GC-MS, we studied urinary organic acids in 20 Japanese patients with peroxisomal disorders, including Zellweger syndrome (ZS), neonatal adrenoleukodystrophy, and single deficiency of peroxisomal beta-oxidation enzymes. Non-ketotic dicarboxylic aciduria with elevated sebacate/adipate molar ratio was observed in 19 of the 20 patients. Elevation of 2-hydroxysebacate and epoxydicarboxylic acids were seen in 13 and 18, respectively. Tyrosyluria was remarkable in all patients. In two ZS patients, we tracked the time course from birth to infancy, and all the above stated findings were detected, except for one sample. Urinary organic acid analysis is indeed useful for screening subjects with peroxisomal disorders.

A rapid screening procedure for the diagnosis of peroxisomal disorders: quantification of very long-chain fatty acids, as dimethylaminoethyl esters, in plasma and blood spots, by electrospray tandem mass spectrometry

A rapid method with potential to screen for many of the peroxisomal disorders using 5 microl of plasma or a 3-mm blood spot (3.6 microl blood impregnated on filter paper) is described. Fatty acids are liberated from plasma or blood spots and converted to dimethylaminoethyl esters. Trideuterated fatty acids, added as internal standards, are used to quantify eicosanoic (C20:0), docosanoic (C22:0), tetracosanoic (C24:0) and hexacosanoic (C26:0) acids by electrospray tandem mass spectrometry. The C26:0/C22:0 and C24:0/C22:0 ratios are significantly greater in the plasma of patients with peroxisomal disorders compared to controls. The C20:0/C22:0 ratio is elevated in the plasma of peroxisomal patients who accumulate phytanic acid. Blood spots collected from four peroxisomal patients between 2 and 10 days after birth and stored for up to 17 years, were shown to give between 33% and 233% higher C26:0/C22:0 ratios compared to age-matched controls.