Quantification of fat-soluble vitamins in human breast milk by liquid chromatography-tandem mass spectrometry

Mechanism of error caused by isotope-labeled internal standard: accurate method for simultaneous measurement of vitamin D and pre-vitamin D by liquid chromatography/tandem mass spectrometry

RATIONALE

Bias of up to 25% has been observed for vitamin D3 and D2 samples exposed to heating during sample preparation, even when isotope-labeled internal standards are used. The goals of this study were to identify the mechanism of the positive bias observed in measuring vitamin D3 and D2 by liquid chromatography/tandem mass spectrometry (LC/MS/MS) and determine a way to eliminate the error source.

METHODS

Several internal standards with varying locations of labeling were used for comparison in this study. Additionally, different temperatures (25, 37, 55, and 75 °C) and different treatment times were investigated for sample preparation and a LC/MS/MS method capable of simultaneously measuring vitamin D and pre-vitamin D was developed.

RESULTS

It was demonstrated that the different conversion behaviors of the analyte and the internal standard were the cause of the positive bias. This bias was eliminated when internal standards with labeling remote from the double-bond area of the molecules were used. Additionally, sample preparation was shortened from overnight saponification at room temperature to 0.5 h at 75 °C.

CONCLUSIONS

The use of an internal standard with labeling remote from the conjugated area eliminated the error source and gave accurate correction at all of the temperatures investigated. Heating may be used for rapid sample preparation as an alternative to overnight saponification at room temperature. This work not only describes the mechanism of an inaccurate internal standard correction, but also establishes a rapid LC/MS/MS method for simultaneous measurement of vitamin D and pre-vitamin D.

Sensitive method for the determination of paricalcitol by liquid chromatography and mass spectrometry and its application to a clinical pharmacokinetic study

A highly sensitive, specific and rapid LC-ESI-MS/MS method has been developed and validated for the quantification of paricalcitol (PAR) in human plasma (500 μL) using paricalcitol-d6 (PAR-d6 ) as an internal standard (IS) as per regulatory guidelines. A liquid-liquid extraction method was used to extract the analyte and IS from human plasma. Chromatography was achieved on Zorbax SB C18 column using an isocratic mobile phase in a gradient flow. The total chromatographic run time was 6.0 min and the elution of PAR and PAR-d6 occurred at ~2.6 min. A linear response function was established for the range of concentrations 10-500 pg/mL in human plasma. The intra- and inter-day accuracy and precision values for PAR met the acceptance criteria. The validated assay was applied to quantitate PAR concentrations in human plasma following oral administration of 4 µg capsules to humans.

Vitamin D in plants: a review of occurrence, analysis, and biosynthesis

The major function of vitamin D in vertebrates is maintenance of calcium homeostasis, but vitamin D insufficiency has also been linked to an increased risk of hypertension, autoimmune diseases, diabetes, and cancer. Therefore, there is a growing awareness about vitamin D as a requirement for optimal health. Vitamin D3 is synthesized in the skin by a photochemical conversion of provitamin D3, but the necessary rays are only emitted all year round in places that lie below a 35° latitude. Unfortunately, very few food sources naturally contain vitamin D and the general population as a results fail to meet the requirements. Fish have the highest natural content of vitamin D expected to derive from an accumulation in the food chain originating from microalgae. Microalgae contain both vitamin D3 and provitamin D3, which suggests that vitamin D3 exist in the plant kingdom and vitamin D3 has also been identified in several plant species as a surprise to many. The term vitamin D also includes vitamin D2 that is produced in fungi and yeasts by UVB-exposure of provitamin D2. Small amounts can be found in plants contaminated with fungi and traditionally only vitamin D2 has been considered present in plants. This review summarizes the current knowledge on sterol biosynthesis leading to provitamin D. It also addresses the occurrence of vitamin D and its hydroxylated metabolites in higher plants and in algae and discusses limitations and advantages of analytical methods used in studies of vitamin D and related compounds including recent advances in analytical technologies. Finally, perspectives for a future production of vitamin D biofortified fruits, vegetables, and fish will be presented.

Comprehensive profiling of carotenoids and fat-soluble vitamins in milk from different animal species by LC-DAD-MS/MS hyphenation

This paper describes a novel and efficient analytical method to define the profile of fat-soluble micronutrients in milk from different animal species. Overnight cold saponification was optimized as a simultaneous extraction procedure. Analytes were separated by nonaqueous reversed-phase (NARP) chromatography: carotenoids on a C(30) column and fat-soluble vitamins on a tandem C(18) column system. Besides 12 target analytes for which standards are available (all-trans-lutein, all-trans-zeaxanthin, all-trans-β-cryptoxanthin, all-trans-β-carotene, all-trans-retinol, α-tocopherol, γ-tocopherol, δ-tocopherol, ergocalciferol, cholecalciferol, phylloquinone, and menaquinone-4), the DAD-MS combined detection allowed the provisional identification of other carotenoids on the basis of the expected retention times, the absorbance spectra, and the mass spectrometric data. Retinol and α-tocopherol were the most abundant fat-soluble micronutrients and the only ones found in donkey's milk along with γ-tocopherol. Ewe's milk also proved to be a good source of vitamin K vitamers. Bovine milk showed a large variety of carotenoids that were absent in milk samples from other species with the only exception of all-trans-lutein and all-trans-zeaxanthin.

Quantitative measurement of vitamin K2 (menaquinones) in various fermented dairy products using a reliable high-performance liquid chromatography method

We evaluated menaquinone contents in a large set of 62 fermented dairy products samples by using a new liquid chromatography method for accurate quantification of lipo-soluble vitamin K(2), including distribution of individual menaquinones. The method used a simple and rapid purification step to remove matrix components in various fermented dairy products 3 times faster than a reference preparation step. Moreover, the chromatography elution time was significantly shortened and resolution and efficiency were optimized. We observed wide diversity of vitamin K(2) contents in the set of fermented dairy products, from undetectable to 1,100 ng/g of product, and a remarkable diversity of menaquinone forms among products. These observations relate to the main microorganism species currently in the different fermented product technologies. The major form in this large set of fermented dairy products was menaquinone (MK)-9, and contents of MK-9 and MK-8 forms were correlated, that of MK-9 being around 4 times that of MK-8, suggesting that microorganisms able to produce MK-9 also produce MK-8. This was not the case for the other menaquinones, which were produced independently of each other. Finally, no obvious link was established between MK-9 content and fat content or pH of the fermented dairy products.

The role of mass spectrometry in the analysis of vitamin D compounds

This review highlights the superseding role of mass spectrometry in the structural characterization and quantitation of vitamin D compounds in comparison to other analytical methods (e.g., UV, bioassays) that lack the sensitivity and specificity of mass spectrometry. After a short introduction to the biochemistry of vitamin D compounds, an overview of the current techniques to characterize and quantitate vitamin D compounds is given with emphasis on the contribution of mass spectrometry.

Quantification of vitamin D3 and its hydroxylated metabolites in waxy leaf nightshade (Solanum glaucophyllum Desf.), tomato (Solanum lycopersicum L.) and bell pepper (Capsicum annuum L.)

Changes in vitamin D(3) and its metabolites were investigated following UVB- and heat-treatment in the leaves of Solanum glaucophyllum Desf., Solanum lycopersicum L. and Capsicum annuum L. The analytical method used was a sensitive and selective liquid chromatography electrospray ionisation tandem mass spectrometry (LC-ESI-MS/MS) method including Diels-Alder derivatisation. Vitamin D(3) and 25-hydroxy vitamin D(3) were found in the leaves of all plants after UVB-treatment. S. glaucophyllum had the highest content, 200 ng vitamin D(3)/g dry weight and 31 ng 25-hydroxy vitamin D(3)/g dry weight, and was the only plant that also contained 1,25 dihydroxy vitamin D(3) in both free (32 ng/g dry weight) and glycosylated form (17 ng/g dry weight).

Vitamin D intake in young children with acute lower respiratory infection

OBJECTIVE

To determine if vitamin D intake is associated with acute lower respiratory infections (ALRI) in children.

METHODS

The vitamin D intakes of children younger than 5 years of age admitted to hospital with either bronchiolitis or pneumonia were compared to an unmatched control group of the same age without respiratory infection. Caregivers of 197 children completed a questionnaire collecting information on demographic variables, ALRI risk factors and diet. Associations of ALRI with vitamin D intake and other ALRI risk factors were determined.

RESULTS

The mean vitamin D intake of children with ALRI was 48 IU/kg/d compared to 60 IU/kg/d in the control group. When controlling for age, ethnicity, socio-economic status, northern residence, breastfeeding, immunizations and smoking contact, children with a vitamin D intake of less than 80 IU/kg/d were greater than 4 times more likely to have ALRI compared to children with a vitamin D intake exceeding 80 IU/kg/day (OR 4.9, 95% CI: 1.5, 16.4).

CONCLUSIONS

A higher vitamin D intake than currently recommended might be needed to offer protection against diseases such as ALRI. Increased vitamin D supplementation could have important public health consequences, as bronchiolitis and pneumonia are the most common reasons for hospitalization in young children.

Derivatization methods for quantitative bioanalysis by LC–MS/MS

LC with atmospheric pressure ionization MS is essential to a large number of quantitative bioanalyses for a variety of compounds, especially nonvolatile or highly polar compounds. However, in many instances, weak ionization, poor LC retention and instability of certain analytes hinder the development of the LC–MS/MS method. Chemical derivatization has been used for different classes of analytes to improve their ionization efficiency, chromatographic separation and chemical stability. This work presents an overview of chemical derivatization methods that have been applied to the quantitative LC–MS/MS analyses of nine classes of molecules, including aldehydes, amino acids, bisphosphonate drugs, carbohydrates, carboxylic acids, nucleosides and their associated analogs, steroids, thiol-containing compounds and vitamin D metabolites, in biological matrices.

Vitamin D in pregnancy and lactation in humans

Concerns exist about the adequacy of vitamin D in pregnant and lactating women. This review assesses the evidence that maternal vitamin D status influences maternal, fetal, and breast-fed infant bone health; maternal adverse outcomes (preeclampsia, gestational diabetes, obstructed labor, and infectious disease); fetal adverse outcomes (growth, gestational age, and developmental programming); and infant adverse outcomes. The evidence for all of these outcomes is contradictory (except for maternal infectious disease) and lacking causality; thus, it is inconclusive. The 2011 Dietary Reference Intakes for vitamin D and their implications for assessing vitamin D status are discussed. An estimated 5% to 29% of American pregnant women may have inadequate vitamin D status, with the higher prevalence in African Americans. Little is known about the prevalence of inadequacy in American lactating women. Research needs are also identified, especially the need for rigorous and well-designed randomized clinical trials to determine the role of vitamin D in nonbone health outcomes in pregnancy and lactation.

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.

Application of stable isotope-labeled compounds in metabolism and in metabolism-mediated toxicity studies

Stable isotope-labeled compounds have been synthesized and utilized by scientists from various areas of biomedical research during the last several decades. Compounds labeled with stable isotopes, such as deuterium and carbon-13, have been used effectively by drug metabolism scientists and toxicologists to gain better understanding of drugs' disposition and their potential role in target organ toxicities. The combination of stable isotope-labeling techniques with mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy, which allows rapid acquisition and interpretation of data, has promoted greater use of these stable isotope-labeled compounds in absorption, distribution, metabolism, and excretion (ADME) studies. Examples of the use of stable isotope-labeled compounds in elucidating structures of metabolites and delineating complex metabolic pathways are presented in this review. The application of labeled compounds in mechanistic toxicity studies will be discussed by providing an example of how strategic placement of a deuterium atom in a drug molecule mitigated specific-specific renal toxicity. Other examples from the literature demonstrating the application of stable isotope-labeled compounds in understanding metabolism-mediated toxicities are presented. Furthermore, an example of how a stable isotope-labeled compound was utilized to better understand some of the gene changes in toxicogenomic studies is discussed. The interpretation of large sets of data produced from toxicogenomics studies can be a challenge. One approach that could be used to simplify interpretation of the data, especially from studies designed to link gene changes with the formation of reactive metabolites thought to be responsible for toxicities, is through the use of stable isotope-labeled compounds. This is a relatively unexplored territory and needs to be further investigated. The employment of analytical techniques, especially mass spectrometry and NMR, used in conjunction with stable isotope-labeled compounds to establish and understand mechanistic link between reactive metabolite formation, genomic, and proteomic changes and onset of toxicity is proposed. The use of stable isotope-labeled compounds in early human ADME studies as a way of identifying and possibly quantifying all drug-related components present in systemic circulation is suggested.