A simultaneous quantitative method for vitamins A, D and E in human serum using liquid chromatography-tandem mass spectrometry

Non-classical roles of fat-soluble vitamins (FSVs) in many pathologies including cancer have been identified. There is also evidence of hormonal interactions between two of these vitamins, A and D. As a result of this enhanced clinical association with disease, translational clinical research and laboratory requests for FSV measurement has significantly increased. However there are still gaps in the analytical methods available for the measurement of these vitamins. This study aimed to develop a method for simultaneous quantification of 25-hydroxyvitamin-D2 (25-OHD2), 25-hydroxyvitamin-D3 (25-OHD3) and its 3-epimer (epi-25-OHD3), retinol and α-tocopherol in human serum using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The procedure was developed and validated across two LC-MS/MS platforms, using commercial calibrators referenced to certified reference materials, controls, and deuterated internal standards. The samples were prepared by liquid-liquid extraction prior to injection and LC separation (using a Pursuit-PFP column) on two Agilent MS/MS systems (6410 and 6490) in electrospray ionisation positive mode with multiple reaction monitoring. Identification and quantification of 25-OHD3 from its 3-epimer as well as 25-OHD2, retinol and α-tocopherol were achieved. The dynamic ranges were 4-160 nmol/L for 25-OHD2 and epi-25-OHD3, 4-200 nmol/L for 25-OHD3, 0.1-4.0μmol/L for retinol and 4-70μmol/L for α-tocopherol with correlation (r(2)) of 0.997-0.998. Based on participation in an external quality assurance program, the overall performance of the simultaneous methods were: imprecision (CV%) and inaccuracy (average bias) 3.0% and 3.2 nmol/L, respectively, for 25-OHD3; 5.0% and 0.04μmol/L, respectively, for retinol; and 4.7% and 0.2μmol/L, respectively, for α-tocopherol. In summary, two simple LC-MS/MS methods were successfully developed and validated for the simultaneous quantification of the three vitamin D metabolites (25-OHD2, 25-OHD3 and 3-epimer of 25-OHD3), vitamin A (retinol) and vitamin E (α-tocopherol) in serum.

Neonatal aortic dilatation secondary to vitamin A deficiency

We report on a term neonate with unexplained respiratory distress, dilatation of the descending aorta, and low serum retinol concentration. The respiratory distress did not respond to conventional medical management and persisted for 22 days requiring an inspired oxygen fraction of 0.4 to 0.5 to maintain adequate arterial oxygen saturation. One week after intramuscular vitamin A therapy, the respiratory distress and requirement for supplementary oxygen resolved. Dilatation of the distal aorta resolved at 7 weeks of age. An association between vitamin A deficiency and aortic dilatation has previously been described in rats, but the association in humans has rarely been reported. We suggest that unexplained neonatal respiratory distress and a dilated aorta should prompt suspicion of vitamin A deficiency. An underlying infective or inflammatory process may give rise to a falsely low serum retinol concentration. Serum retinol and retinol binding protein concentrations in both the mother and infant should be used to guide vitamin A status, treatment, and subsequent response.

The CDC VITAL-EQA program, external quality assurance for serum retinol, 2003-2006

BACKGROUND

With approximately 127 million preschool children currently suffering from vitamin A deficiency globally, it is important for affected countries to have the capacity to determine the prevalence of vitamin A deficiency and to monitor the progress being made to eradicate this problem through supplementation and fortification programs. The VITamin A Laboratory-External Quality Assurance program (VITAL-EQA) administered by the US Centers for Disease Control and Prevention was developed in 2003 to help predominantly less developed countries to assess and improve their ability to accurately and precisely measure serum retinol, and more recently other nutritional indicators.

METHODS

Twice each year, laboratories test serum samples in duplicate over the course of 3 days. Results are returned and troubleshooting is performed if needed.

RESULTS

Measurement accuracy improved for 2 laboratories and declined for 2 laboratories, whereas the remainder of laboratories participating in >1 round showed consistently acceptable performance. Precision improved for 7 laboratories, declined for 4 laboratories, and remained at <or=5% coefficient of variation for the rest of the participants.

CONCLUSIONS

This program is a valuable tool for the assessment and improvement of retinol testing in laboratories throughout the world.

Feasibility of using retinol-binding protein from capillary blood specimens to estimate serum retinol concentrations and the prevalence of vitamin A deficiency in low-resource settings

Vitamin A deficiency (VAD) is a significant public health problem in many countries. While cost-effective interventions are available to control VAD, reliable information is needed to the track progress of control programmes. However, assessment of VAD is uncommon because current approaches are expensive and not feasible in low-resource settings. The present study explores the utility of retinol-binding protein (RBP), analysed by enzyme-linked immunosorbent assay from capillary blood, as an alternative measure of serum retinol concentrations in populations. The study collected matched panels of venous and capillary blood from pre-school children in Chiang Mai, Thailand. Of a total sample of 195 children, there were no differences between RBP from venous blood, RBP from capillary blood or retinol from capillary blood relative to retinol from venous blood. Receiver-operating characteristic curve analysis suggested a cut-off of RBP < 0.825 μmol l−1had optimal screening proficiency relative to retinol <0.70 μmol l−1. For the purpose of population assessment, all three parameters performed well in screening for VAD relative to retinol from venous blood. There were no differences in the estimates of VAD between children stratified by inflammation status. Lower RBP concentrations were found in children in the early convalescent stage of infection than in children with no infection or in the late convalescent stage. This study provided evidence of the biological comparability between retinol and RBP estimated from venous blood and capillary blood. This is a critical observation as it provides empirical evidence that RBP from capillary blood is a surrogate measure of serum retinol concentrations.

Is vitamin A consumption a risk factor for osteoporotic fracture?

Severe vitamin A toxicity is known to have adverse effects on skeletal health. Studies involving animal models and case reports have documented that hypervitaminosis A is associated with bone resorption, hypercalcaemia and bone abnormalities. More recently, some epidemiological studies have suggested that high habitual intake of vitamin A could contribute to low bone mineral content and fracture risk. The evidence relating to the possible deleterious role of vitamin A in bone health is of variable quality and is potentially confounded by collinearity of nutrient intake and difficulties in assessing vitamin A exposure. Furthermore, because intake of vitamin A varies between studies it is not possible to define an intake threshold associated with harm.

Serum retinoids and beta-carotene as predictors of hip and other fractures in elderly women

There is debate about the possible deleterious effect of excessive vitamin A exposure on fracture risk. In this nested case control study in older women (312 cases and 934 controls), serum retinol, retinyl palmitate, and beta-carotene were not associated with fracture risk, and there was no evidence of excess risk with multivitamin or cod liver oil supplementation.

INTRODUCTION

Recent studies have suggested that higher vitamin A intake may account for a component of fracture risk within the general population and that supplemental vitamin A may be harmful even within recommended limits. No studies have examined the relationship between biochemical retinol status and fracture in older women.

MATERIALS AND METHODS

We examined serum retinol, retinyl palmitate, and beta-carotene as predictors of incident hip and other fractures in a large prospective study of British women over the age of 75 years (n = 2606, 312 incident osteoporotic fractures, 92 incident hip fractures; mean follow-up duration, 3.7 years). Fasting blood samples (9:00-11:00 a.m.) were collected at baseline. Using a case-control design (three controls per case), serum retinol, retinyl palmitate, and beta-carotene were assessed as univariate predictors of incident osteoporotic fracture or hip fracture. Baseline BMD at the total hip, age, 25(OH)D, serum beta Crosslaps, bone-specific alkaline phosphatase, weight, height, and smoking were considered as covariates in a multivariate model.

RESULTS

Serum retinol, retinyl palmitate, and beta-carotene were not significant univariate predictors of either hip fracture or any fracture (all p > 0.05; Cox proportional hazards regression). For all osteoporotic fractures, the hazard ratio (HR) was 0.92 (95% CI, 0.81-1.05) per 1 SD increase in serum retinol. Risk of any osteoporotic fracture was slightly less in the highest quartile of serum retinol compared with the lowest quartile (HR, 0.85; 95% CI, 0.69-1.05; p = 0.132) There was a tendency for increased serum retinol to predict benefit rather than harm in terms of BMD (r = 0.09, p = 0.002). Multivitamin or cod liver oil supplementation was associated with a significantly lower risk of any fracture (HR, 0.76; 95% CI, 0.60-0.96; p = 0.021). In multivariate analysis, only age, total hip BMD, and weight were associated with fracture risk (p < 0.05).

CONCLUSIONS

We found no evidence to support any skeletal harm associated with increased serum indices of retinol exposure or modest retinol supplementation in this population.

Development of a rapid enzyme immunoassay for the detection of retinol-binding protein

BACKGROUND

Retinol-binding protein (RBP) was chosen as a surrogate marker for retinol because of the close correspondence between retinol and RBP.

OBJECTIVE

To meet the need for rapid, cost-effective determination of vitamin A status in populations, a quantitative enzyme immunoassay (EIA) for detection of RBP was developed.

DESIGN

The resulting RBP EIA, a competitive assay, uses RBP adsorbed to microtest strip wells to compete with RBP in serum. The assay takes approximately 40 min.

RESULTS

With a reference panel of sera, test accuracy was found to be within 4% of expected values through the calibrated range of 0.48-1.92 micro mol RBP/L (10-40 micro g RBP/mL). Intraassay and interassay variability averaged 6.7% and 8.9%, respectively. Specificity testing showed no interference from other serum proteins, prealbumin, rheumatoid factor, bilirubin, estrogen, or C-reactive protein. The RBP EIA provided linear results between 0.43 and 1.80 micro mol RBP/L (9 and 38 micro g RBP/mL). Preliminary laboratory evaluations indicated that the RBP EIA correlates well with radial immunodiffusion for RBP and with HPLC for retinol, the current reference standard. A field evaluation in a population at risk for vitamin A deficiency (VAD) resulted in close correlation between RBP EIA measures and retinol measures by HPLC (R(2) = 0.82).

CONCLUSIONS

The RBP EIA is as reliable in estimating VAD as is HPLC retinol. After successful validations, the test should enable public health authorities to rapidly monitor VAD and track vitamin A status in populations.