Determination of vitamins A, D and E in a small volume of human plasma by a high-throughput method based on liquid chromatography/tandem mass spectrometry

Most blood biomarkers related to vitamin status, one-carbon metabolism, and the kynurenine pathway show adequate preanalytical stability and within-person reproducibility to allow assessment of exposure or nutritional status in healthy women and cardiovascular patients

Knowledge of stability during sample transportation and changes in biomarker concentrations within person over time are paramount for proper design and interpretation of epidemiologic studies based on a single measurement of biomarker status. Therefore, we investigated stability and intraindividual vs. interindividual variation in blood concentrations of biomarkers related to vitamin status, one-carbon metabolism, and the kynurenine pathway. Whole blood (EDTA and heparin, n = 12) was stored with an icepack for 24 or 48 h, and plasma concentrations of 38 biomarkers were determined. Stability was calculated as change per hour, intraclass correlation coefficient (ICC), and simple Spearman correlation. Within-person reproducibility of biomarkers was expressed as ICC in samples collected 1-2 y apart from 40 postmenopausal women and in samples collected up to 3 y apart from 551 patients with stable angina pectoris. Biomarker stability was similar in EDTA and heparin blood. Most biomarkers were essentially stable, except for choline and total homocysteine (tHcy), which increased markedly. Within-person reproducibility in postmenopausal women was excellent (ICC > 0.75) for cotinine, all-trans retinol, cobalamin, riboflavin, α-tocopherol, Gly, pyridoxal, methylmalonic acid, creatinine, pyridoxal 5'-phosphate, and Ser; was good to fair (ICC of 0.74-0.40) for pyridoxic acid, kynurenine, tHcy, cholecalciferol, flavin mononucleotide, kynurenic acid, xanthurenic acid, 3-hydroxykynurenine, sarcosine, anthranilic acid, cystathionine, homoarginine, 3-hydroxyanthranilic acid, betaine, Arg, folate, total cysteine, dimethylglycine, asymmetric dimethylarginine, neopterin, symmetric dimethylarginine, and Trp; and poor (ICC of 0.39-0.15) for methionine sulfoxide, Met, choline, and trimethyllysine. Similar reproducibilities were observed in patients with coronary heart disease. Thus, most biomarkers investigated were essentially stable in cooled whole blood for up to 48 h and had a sufficient within-person reproducibility to allow one-exposure assessment of biomarker status in epidemiologic studies. The Western Norway B Vitamin Intervention Trial was registered at clinicaltrials.gov as NTC00354081.

Vitamin D status was not associated with 'one-year' progression of coronary artery disease, assessed by coronary angiography in statin-treated patients

BACKGROUND

Low vitamin D status is associated with increased risk of cardiovascular disease and may be involved in atherosclerosis. Our aim was to assess the association between vitamin D status and the progression of coronary artery disease (CAD).

METHODS AND RESULTS

We measured 25-hydroxyvitamin D3 (25OHD3) by liquid chromatography tandem mass spectrometry (LC-MS/MS) in plasma from 348 participants with established CAD (84% males, mean ± standard deviation (SD) age 60 ± 10 years) of the Western Norway B-vitamin Intervention Trial (WENBIT, 1999-2006). The patients underwent invasive coronary angiography (CA) and percutaneous coronary intervention at baseline and a second CA after 302 ± 79 days of follow-up. From the angiograms, minimal lumen diameter (MLD) and diameter stenosis (DS) of atherosclerotic lesions were obtained. Significant CAD in non-intervened vessels was found in 309 coronary arteries from 183 participants either at baseline and/or at follow-up. To assess the association between levels of 25OHD3 and CAD progression in non-intervened vessels, we applied a linear quantile fitted mixed effects model with MLD or DS measured at follow-up as a function of continuous 25OHD3 concentrations. There were no statistically significant associations between plasma 25OHD3 concentrations (median: 63.9, 95% confidence interval (CI): 48.1-78.5 nmol/l) measured at baseline and the follow-up measures of either MLD (estimated effect per 10 nmol/l increase of 25OHD3 and 95% CI: -0.015 (-0.032-0.002) mm, p = 0.088) or DS (0.225 (-0.354-0.804) percentage points, p = 0.444). Multivariate adjustment did not alter these results.

CONCLUSION

Plasma 25OHD3 levels were not associated with 'one-year' progression of CAD, assessed by CA in statin-treated patients.

Prospective study of maternal mid-pregnancy 25-hydroxyvitamin D level and early childhood respiratory disorders

BACKGROUND

Studies suggest that prenatal vitamin D status may be inversely associated with lower respiratory tract infections (LRTIs) early in life. Studies of prenatal vitamin D status and development of asthma have inconsistent findings.

METHODS

We examined the associations of maternal mid-pregnancy 25-hydroxyvitamin D [25(OH)D] level with the frequency of LRTIs by 36 months and with current asthma at 36 months using the Norwegian Mother and Child Cohort Study. Maternal plasma 25(OH)D level was measured using liquid chromatography-tandem mass spectrometry. Respiratory disorders were evaluated by maternal report through questionnaires. LRTIs were analysed in a random sample of 1248 children. Asthma was analysed using a case-control design, including 489 cases and 1183 controls. Multivariable generalised linear models calculated adjusted measures of association.

RESULTS

The median gestational week of sample collection was 18 weeks (range 9, 35). The mean 25(OH)D level was 73.7 nmol/L (standard deviation 23.7). Higher maternal mid-pregnancy 25(OH)D level was associated with a reduced risk of three or more LRTIs by 36 months vs. none, adjusted risk ratio 0.74 [95% confidence interval (CI): 0.58, 0.93] per 20 nmol/L increase. Associations were similar when examining the frequency of LRTIs by 18 months, and the frequency of LRTIs between 18 and 36 months. Maternal mid-pregnancy 25(OH)D level was not significantly associated with current asthma at 36 months, adjusted odds ratio 0.91 [95% CI 0.81, 1.02] per 20 nmol/L increase.

CONCLUSIONS

Higher maternal mid-pregnancy 25(OH)D level was associated with a modestly reduced risk of recurrent LRTIs by 36 months, but was not associated with current asthma at 36 months.

Ultra-performance liquid chromatographic determination of tocopherols and retinol in human plasma

A rapid, selective and sensitive ultra-performance liquid chromatography method has been developed for the detection and quantification of tocopherols and retinol in human plasma. Alpha-tocopherol, gamma-tocopherol and retinol are assayed using fluorescence detection. Excitation/emission wavelengths are 295/330 nm and 325/470 nm for the analysis of both tocopherols and retinol, respectively. Retinol acetate is employed as the internal standard. The reversed-phase method incorporates gradient elution with a mobile phase consisting of methanol and acetonitrile. Separation of vitamin compounds is achieved using a bridged ethyl hybrid C18 column. The retention times for retinol, retinol acetate, gamma-tocopherol and alpha-tocopherol are 1.6, 1.8, 3.9 and 4.3 min, respectively. The limits of quantification for retinol, gamma-tocopherol and alpha-tocopherol were 0.02, 0.02 and 0.1 µg/mL, respectively. The assay method is suitable for the analysis of tocopherols and retinol in human plasma. The method may be applied following the ingestion of foods fortified with these fat-soluble vitamins.

Simultaneous analysis of circulating 25-hydroxy-vitamin D3, 25-hydroxy-vitamin D2, retinol, tocopherols, carotenoids, and oxidized and reduced coenzyme Q10 by high performance liquid chromatography with photo diode-array detection using C18 and C30 columns alone or in combination

Circulating lipid-phase micronutrients (LPM) such as 25-hydroxylated D vitamers, retinol, tocopherols, carotenoids including their isomers, and coenzyme Q10 play important roles in health maintenance and disease prevention and can serve as useful biomarkers. We developed fast, affordable, and accurate HPLC assays that simultaneously measured all above LPM in a single run using UV/VIS detection at 265nm, 295nm, and 480nm with (1) a C18 column alone; (2) a C30 column alone; or (3) each of these columns connected in series. The C18 column alone could separate all major LPM of interest in less than 17min but insufficiently resolved the lycopene isomers, the 25-hydroxylated D vitamers, lutein from zeaxanthin and β- from γ-tocopherol. The C30 column alone separated all LPM of interest including many isomeric analytes but failed to resolve the Q10 compounds, which co-eluted with carotenoids. Connecting the C18 and C30 columns in series with a detector after the C30 column and a pressure resistant detector between the columns resulted in ideal resolution and accurate quantitation of all LPM of interest but required software capable of processing the acquired data from both detectors. Connecting the C18 and C30 columns in series with exclusively one detector after the C30 column resulted in carotenoid-Q10 interferences, however, this was remedied by heart-cutting 2D-LC with a 6-port valve between the columns, which resolved all analytes in 42min. Faster run times led to some analytes not being resolved. Many variations of these methods are possible to meet the needs of individual requirements while minimizing sample material and turn-around-times.

Analysis of circulating lipid-phase micronutrients in humans by HPLC: review and overview of new developments

Retinol, tocopherols, coenzyme Q10, carotenoids, and vitamin D are lipophilic compounds shown to function as important health-protective agents by mitigating the damaging effects of oxidative and other injury. Scientific interest in evaluating these compounds has resurfaced in recent years, particularly in the nutritional, clinical and epidemiologic fields, and has precipitated the development of a multitude of new analytical techniques. This review considers recent developments in HPLC-based assays since 2007 for the simultaneous determination of these lipid-phase compounds utilizing exclusively serum or plasma as these matrices are mostly used in clinical and epidemiological investigations. We also provide an overview of blood measurements for selected carotenoids, tocopherols, coenzyme Q10 and retinol from the last 15years of healthy umbilical cord blood, children, and adults.