Fully automatic method for the determination of fat soluble vitamins and vitamin D metabolites in serum

Analysis of vitamin D and its metabolites in biological samples - Part II: Optimization of a sample preparation method for liver tissue

Extraction of vitamin D, including its hydroxylated and esterified metabolites, from soft tissues such as the liver is challenging due to the lipophilic character of matrix and analytes that are expected in very low concentration levels. In this study, we aimed at the optimization of two-step extraction using solid-liquid extraction as the first step, followed by solid-phase extraction. Various solvents, including ethanol, acetonitrile, methanol, acetone, heptane, and heptane with isopropanol, were investigated to isolate vitamin D compounds from liver tissue in the first step. Acetone was finally selected as the most suitable solvent for the solid-liquid extraction, with the highest recovery in the range of 67 - 98% for polar hydroxylated forms and 3 - 28% for lipophilic vitamin D and esters. Two solid phase extraction (SPE) based on the (i) "bind and elute strategy" and (ii) "removal strategy" using hydrophilic-lipophilic balanced SPE sorbent were optimized as a proceeding step for acetone extracts to increase the method selectivity. Finally, two optimized methods, combining solid-liquid extraction and individual SPE strategy, were examined in terms of sensitivity, recovery, matrix effect, accuracy, and precision. The limits of quantification were in the range of 1 - 10 ng/mL and 3 - 20 ng/mL analyzed by ultra-high performance supercritical fluid chromatography and ultra-high performance liquid chromatography hyphenated a with tandem mass spectrometer, respectively. The absolute recovery determined for the "bind and elute strategy" protocol was in the range of 3 - 24 %. Nevertheless, this method was free of matrix effects, which were determined to be in the 73 - 120 % range. On the contrary, the "removal strategy" approach provided higher recovery values for all compounds (47 - 123 %), but the results for nonpolar vitamin D and esters were strongly affected by signal suppression (matrix effects 3 - 51 %). Both methods fulfilled the criteria for accuracy and precision requested by the European Medicine Agency Guideline on Bioanalysis. "Removal strategy" SPE with decreased manual intervention and lower solvent consumption was finally applied to mouse liver tissue to determine vitamin D and its hydroxylated and esterified metabolites for the first time. The results, i.e., vitamin D esters detected in liver tissue, supported the notion that esters of vitamin D can be stored in lipophilic tissues to release vitamin D.

Vitamin D: sources, physiological role, biokinetics, deficiency, therapeutic use, toxicity, and overview of analytical methods for detection of vitamin D and its metabolites

Vitamin D has a well-known role in the calcium homeostasis associated with the maintenance of healthy bones. It increases the efficiency of the intestinal absorption of dietary calcium, reduces calcium losses in urine, and mobilizes calcium stored in the skeleton. However, vitamin D receptors are present ubiquitously in the human body and indeed, vitamin D has a plethora of non-calcemic functions. In contrast to most vitamins, sufficient vitamin D can be synthesized in human skin. However, its production can be markedly decreased due to factors such as clothing, sunscreens, intentional avoidance of the direct sunlight, or the high latitude of the residence. Indeed, more than one billion people worldwide are vitamin D deficient, and the deficiency is frequently undiagnosed. The chronic deficiency is not only associated with rickets/osteomalacia/osteoporosis but it is also linked to a higher risk of hypertension, type 1 diabetes, multiple sclerosis, or cancer. Supplementation of vitamin D may be hence beneficial, but the intake of vitamin D should be under the supervision of health professionals because overdosing leads to intoxication with severe health consequences. For monitoring vitamin D, several analytical methods are employed, and their advantages and disadvantages are discussed in detail in this review.

Nanoparticle-based polyacrylonitrile monolithic column for highly efficient micro solid-phase extraction of carotenoids and vitamins in human serum

In this work, a biocompatible monolithic column based micro-solid-phase extraction (µ-SPE) method was developed for biological fluid analysis. A novel nanoparticle-based polyacrylonitrile monolithic column (C30 NP-PMC) was fabricated by incorporating triacontyl (C30) modified silica nanoparticles (NPs) into the polyacrylonitrile monolithic matrix through thermally induced phase separation. With efficient mass transfer and sorption capacity, C30 NP-PMC exhibited outstanding performance for the extraction of carotenoids and fat-soluble vitamins (FSVs) from human serum samples, superior to commercial C18 cartridges as well as liquid-liquid extraction (LLE) method. Under optimal conditions, the proposed µ-SPE method coupled with high-performance liquid chromatography-diode array detection (HPLC-DAD) achieved satisfactory limits of detection (LODs) (1.5-75.0 ng/mL) and good recoveries (85.0-106.5 %) with relative standard deviations (RSDs) of less than 12.1% by consuming lower sorbent (35.0 mg) and organic solvent (0.8 mL). Successful application of the developed method demonstrated the great potential of such monolithic sorbents for efficient isolation and preconcentration of trace analytes from blood samples.

High Serum Retinol as a Relevant Contributor to Low Bone Mineral Density in Postmenopausal Osteoporotic Women

There is controversial information about the impact of vitamin A on bone. Some epidemiological studies show that excessive intake of vitamin A, or an excess of serum vitamin A, has related with adverse impact on bone mass; however, other studies did not find these links, and some authors have proposed that this vitamin might promote a better bone health. The present work aims to contribute to clarify the real role of vitamin A in bone tissue. For this purpose, a cross-sectional study of 154 osteoporotic non-treated postmenopausal women (> 65 years old) was carried out. Bone mineral density (BMD) was measured by dual-energy X-ray absorptiometry. We assessed concentrations of serum retinol, osteocalcin, parathyroid hormone, alkaline phosphatase, calcium, and phosphorus. We also studied demographic and anthropometric parameters. Spearman's correlations between retinol levels and other variables found negative correlations with BMD in both lumbar spine (R = - 0.162, P < 0.01) and femoral neck (R = - 0.182, P < 0.01), as well as alkaline phosphatase (R = - 0.110; P < 0.05) and phosphorus (R = - 0.110; P < 0.05). A positive correlation between retinol and fertile window was observed (R = 0.158; P < 0.01). After multivariable adjustment, we still found a negative correlation between serum retinol and BMD, both at the lumbar spine (R = - 0.210; P < 0.01) and at the femoral neck (R = - 0.324, P < 0.001). It is concluded that elevated serum-retinol levels are associated with an increased risk of low bone mass and thus with osteoporotic fractures. Therefore, osteoporosis-risk assessment should include quantification of serum metabolite of vitamin A.

Vitamin D3 and calcidiol are not equipotent

Despite the discussion on the optimal threshold of 25-hydroxyvitamin D serum level continues, there is now consensus on the fact that post-menopausal and elderly populations have inadequate Vitamin D serum levels worldwide. The adjustment of these levels is necessary to improve both bone and general health, as it is to optimize bone response to antiresortive treatments. It is recommended, as endorsed by international clinical guides, to use Vitamin D₃, the physiological form of Vitamin D, in a dose range between 600-2000IU. It should be administered on a daily basis or on its weekly or monthly equivalents. In Spain, the use of calcidiol (25(OH)D₃) at the same dose than Vitamin D₃ is the most extended prescription, notwithstanding the available evidence stating that they are not equipotent. This may lead to over-dosage. In order to provide evidence on this circumstance, a convenience study was performed. Four groups of ten post-menopausal osteoporotic women each (average age 67), deficient in Vitamin D ((25(OH)D 37.5±10 nmol/L)) were enrolled. Each group followed a different treatment regimen: (G1) vitamin D₃ 20μg/day [800IU/day]; (G2) 25 (OH)D₃ 20μg/day; (G3) 25(OH)D₃ 266μg/week and (G4) 25(OH)D₃ 0.266mg every two weeks. 25(OH)D levels were measured for each group at 0, 6 and 12 months, with the following results: G1 (40.5±4.7;80.0±2; 86.2±23.7), G2 (37,2±4.2; 161±21.7;188.0±24.0), G3 (38±3.7;213.5±80.0; 233.0±81.2), G4 (39.5±4;164.5±41,7;210.5±22.2). These data reveal that both metabolites are not equipotent. Calcidiol is faster and 3-6 times more potent to obtain serum levels of 25(OH)D in the medium to long term. This circumstance must be assessed and included in the therapeutic prescription guides for Osteoporosis, since it should be of concern when planning and prescribing treatments to normalize serum levels of 25(OH)D₃ and avoid potential adverse impacts.

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.

Low calcium intake and inadequate vitamin D status in postmenopausal osteoporotic women

An observational cross-sectional study was conducted to assess calcium intake and vitamin D status by measurement of 25-hydroxyvitamin D (25(OH)D), in postmenopausal osteoporotic women (PMOW) treated and untreated for osteoporosis. To assess the influence of sunlight exposure on vitamin D status, the study group was categorized on the basis of sunlight exposure (above or below 2500 sunlight h/year). A group of 336 PMOW older than 65 years was identified (190 [56.5%] treated and 146 [43.5%] untreated for osteoporosis). The demographic and clinical data of the PMO women included history of prior fractures, pharmacological treatments and dietary calcium intake. BMD was measured by DEXA and 25(OH)D was determined by an HPLC method.

RESULTS

vitamin D serum levels were lower in the untreated group as compared with the treated group (58±27 vs. 67±27nmol/l; p=0.006). Prevalence of vitamin D deficiency (cut-off point set at <50nmol/l) was higher in the non-treated group (43.8% vs. 29.5%; p=0.009). Nearly all PMOW, whether treated or not for osteoporosis had a total calcium intake of less than 1200mg. Sunlight exposure did not influence the vitamin D status.

CONCLUSIONS

vitamin D deficiency and an insufficient calcium intake are highly prevalent in both treated and untreated Spanish PMOW older than 65 years. This can be related to low therapeutic adherence and/or insufficient prescription. Therefore physician's and patient's knowledge regarding the optimization of vitamin D status and calcium intake should be improved and implemented. This article is part of a Special Issue entitled 'Vitamin D workshop'.

Lower vitamin E serum levels are associated with osteoporosis in early postmenopausal women: a cross-sectional study

The aim of this study was to evaluate the relationship between vitamin E status and osteoporosis in early postmenopausal women. Anthropometric data, osteoporosis risk factors, vitamin E serum levels, bone mineral density (BMD) and other serum parameters which may influence bone mineral density in postmenopausal women were analyzed in a cross-sectional study. The association between osteoporosis and age, age of menopause, body mass index, osteocalcin, calcium, vitamin D, vitamin E (measured as 25 hydroxyvitamin D and as α-tocopherol:lipids ratio, respectively), bone alkaline phosphatase, smoking status, leisure physical activity and alcohol intake were modeled by a multivariate logistic regression and multi-linear regression analysis in 232 early postmenopausal women. A lower vitamin E:lipid ratio was associated with osteoporosis in multivariate logistic regression. In a multivariate linear model with BMD of the lumbar spine as a dependent variable, the vitamin E:lipid ratio was clearly related with BMD of the lumbar spine (F ratio = 6.30, p = 0.002). BMD of the lumbar spine was significantly higher in the highest tertile of the vitamin E:lipid ratio than in the lowest tertile. The mean vitamin E:lipid ratio was significantly lower in osteoporotic postmenopausal women (T score ≤-2.5) (3.0 ± 0.6 μmol/mmol) than normal (neither osteoporotic nor osteopenic) postmenopausal women (T score >-1) (3.5 ± 0.7 μmol/mmol) using multivariable-adjusted BMD. These findings highlight that vitamin E may increase BMD in healthy postmenopausal women.

Vitamin D insufficiency together with high serum levels of vitamin A increases the risk for osteoporosis in postmenopausal women

Postmenopausal women who were vitamin D deficient and had high serum levels of retinol had an eight times higher risk of having osteoporosis. A high retinol level together with vitamin D deficiency/insufficiency is an additional risk factor for osteoporosis.

PURPOSE

The aim of this study was to evaluate the association between vitamin D deficiency/insufficiency and excess of vitamin A intake as an osteoporosis risk factor in healthy postmenopausal women

DESIGN

The design is a cross-sectional study of 232 healthy postmenopausal women.

METHODS

Bone mass was evaluated by dual energy X-ray absorptiometry. Serum calcium, albumin phosphorus, creatinine, total high-density lipoprotein (HDL) and low-density lipoprotein (LDL) cholesterol, and triglycerides analyzed by standard methods and retinol and 25-hydroxyvitamin D [25(OH)D] measured by an online solid-phase extraction coupled with high-pressure liquid chromatography-ultraviolet detection.

RESULTS

Prevalence of vitamin D deficiency [25(OH)D < 20 ng/mL] was 70.1 %; 14.3 % had a 25(OH)D < 10 ng/mL, and 23.6 % had insufficiency [25(OH)D 21-29 ng/mL]. Prevalence of high serum levels of retinol (>80 μg/dL) was 36.4 %. Among subjects with 25(OH)D <20 ng/mL (n = 152), 60.4 % (n = 92) had serum levels of retinol > 80 μg/dL. Bone density measurements revealed that the risk of osteoporosis was ~8 times higher in women with the highest retinol levels, as compared with women with the lowest retinol levels. In women with 25(OH)D < 20 ng/mL, the risk for osteoporosis increased substantially in women who had the highest blood levels of retinol compared to the women with lowest retinol levels.

CONCLUSIONS

Higher retinol levels together with vitamin D deficiency could be a significant additional risk factor for osteoporosis, underscoring the need for improved physician and public education regarding optimization of vitamin D status in postmenopausal women and developing policies to avoid high serum levels of vitamin A.

Optofluidic opportunities in global health, food, water and energy

Optofluidics is a rapidly advancing field that utilizes the integration of optics and microfluidics to provide a number of novel functionalities in microsystems. In this review, we discuss how this approach can potentially be applied to address some of the greatest challenges facing both the developing and developed world, including healthcare, food shortages, malnutrition, water purification, and energy. While medical diagnostics has received most of the attention to date, here we show that some other areas can also potentially benefit from optofluidic technology. Whenever possible we briefly describe how microsystems are currently used to address these problems and then explain why and how optofluidics can provide better solutions. The focus of the article is on the applications of optofluidic techniques in low-resource settings, but we also emphasize that some of these techniques, such as those related to food production, food safety assessment, nutrition monitoring, and energy production, could be very useful in well-developed areas as well.

Overview of extraction methods for analysis of vitamin D and its metabolites in biological samples

In the last decade the scientific and medical community was confronted with a renewed interest in vitamin D and its metabolites, interest prompted by new discoveries regarding the association between members of the vitamin D family and a great number of physiological functions and pathological states. An impressive number of research projects have helped clear the path towards a better understanding of the functions of vitamin D and have resulted in the development of numerous methods of analysis. This review focuses on the various extraction methods used for analysis of vitamin D in research or clinical settings. Two main extractive methods are usually employed: liquid–liquid extraction and solid-phase extraction. Some methods use no extraction step and direct analysis is performed at the cost of significantly increased matrix interference. On the other hand, other methods use combined extraction techniques, and even additional derivatization steps in order to increase the sensitivity and accuracy of the analysis. The method of choice ultimately depends on the research question and the purpose of the study.

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

We have developed an automated high-throughput assay for the determination of vitamin A (retinol), ergocalciferol (25-OH D2), cholecalciferol (25-OH D3) and vitamin E (α-tocopherol) in a small volume of human plasma. Sample preparation involved mixing 50 μL of plasma with 100 μL of ethanol containing isotope-labelled internal standards, followed by mixing with isooctane/chloroform (3:1, 300 μL). The organic phase was evaporated, and the sample reconstituted in 50 μL methanol. The analysis was performed using reversed-phase liquid chromatography with a gradient mobile phase containing water, methanol and ammonium formate. Chromatographic run-time was 5 min, and positive mode electrospray tandem mass spectrometry (MS/MS) was used for detection. The limits of detection were 0.10 μM for all-trans retinol and 3.3 nM for 25-OH D2 and 25-OH D3. Recoveries were 91.9-105.0%, and within- and between-day coefficients of variance (CVs) 2.4-5.3 and 3.1-8.2, respectively. The assay is presently being used in large-scale studies.

Measurement of 25-hydroxyvitamin D in the clinical laboratory: current procedures, performance characteristics and limitations

In this review we describe procedures, performance characteristics and limitations of methods available for the measurement of 25-hydroxyvitamin (25OHD) since the year 2000. The two main types of methods are competitive immunoassay and those based on chromatographic separation followed by non-immunological direct detection (HPLC, LC-MS/MS). Lack of a reference standard for 25OHD has, until recently, been a major issue resulting in poor between-method comparability. Fortunately this should soon improve due to the recent introduction of a standard reference material in human serum (SRM 972) from the National Institute of Standards and Technology (NIST). For immunoassay, specificity can be an issue especially in relation to the proportion of 25OHD2 that is quantified whereas HPLC and LC-MS/MS methods are able to measure the two major vitamin D metabolites 25OHD2 and 25OHD3 independently. HPLC and LC-MS/MS require more expensive equipment and expert staff but this can be offset against lower reagent costs. Increasingly procedures are being developed to semi-automate or automate HPLC and LC-MS/MS but run times remain considerably longer than for immunoassays especially if performed on automated platforms. For most HPLC and LC-MS/MS methods extraction and procedural losses are corrected for by the inclusion of an internal standard which, in part, may account for higher results compared to immunoassay. In general precision of immunoassay, HPLC and LC-MS/MS are comparable and all have the required sensitivity to identify severe vitamin D deficiency. Looking to the future it is hoped that the imminent introduction of a standard reference method (or methods) for 25OHD will further accelerate improvements in between method comparability.

Vitamin D deficiency and high serum levels of vitamin A increase the risk of osteoporosis evaluated by Quantitative Ultrasound Measurements (QUS) in postmenopausal Spanish women

OBJECTIVES

Association between vitamin D deficiency and excess of vitamin A as a potential risk factor of osteoporosis and fracture has been evaluated.

DESIGN AND METHODS

232 healthy postmenopausal women were studied. Serum parameters were analyzed by standard methods and fat-soluble vitamins by an own HPLC method. QUS measurement of the calcaneal bone was carried out by Sahara.

RESULTS

124 patients were considered non-osteoporotic and 101 (44.9%) were osteoporotic. The prevalence of high serum levels of retinol was 36.4% and vitamin D deficiency was 70.1%. 60.4% of women with vitamin D deficiency have high serum levels of retinol. In the whole population, the increased risk of osteoporosis was up to three times higher for the highest retinol quintile, as compared with the lowest retinol quintile. Whereas in women with vitamin D deficiency the risk of osteoporosis increased was up 5 times higher than women in the lowest quintile of retinol.

CONCLUSIONS

Our results show that high retinol levels together with vitamin D deficiency are hitherto an overlooked risk factor for osteoporosis.