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.

Assessment of wild mint from Tunceli as source of bioactive compounds, and its antioxidant Activity

The types of wild mint (Mentha spicata L.) were sampled from different geographical regions in Tunceli (Turkey) in order to find out their vitamin, mineral, phenolic contents and their antioxidant properties. The total phenol varied from 77.7±0.242 to 52.34±0.351 mg of GAEs/g of dry mint. The highest radical effect of scavenging was observed in Mazgirt parting of the ways 7.5 km with 6.17±0.245 mg/mL. The highest reducing power and metal chelating were observed in the mint from Cicekli parting of the ways 6.5 km Demirkapı. Among the various macronutrients which were estimated in the plant samples, potassium was presented in the highest quantity followed by calcium and phosphate. Although rutin and resveratrol were not determined in any samples, kaempferol and catechin levels were found out in almost all samples. The concentrations of vitamin A ranged between 42,14±5.70 and 13.61±3.00 (mg/kg dry weight). These results show that plants of mint are quite rich in phenolic compounds, and these have been appeared to have antioxidant activity, which agrees with this work, since the extract showed a higher content of phenolic compounds and higher antioxidant activity and mint may be considered as a natural alternative source for food, pharmacology and medicine sectors.

Robust measurement of vitamin A status in plasma and blood dried on paper

Vitamin A deficiency is the leading cause of preventable blindness in children and increases the risk of disease and death from severe infections. In addition, fat soluble vitamin A and associated retinoids directly regulate the expression of genes involved in fatty acid metabolism. Conventional methods for measuring vitamin A involve venipuncture, centrifugation and refrigeration all of which make measuring vitamin A in nutritional surveys expensive. We aimed to develop a simple and robust system for measurement of retinol (biomarker for vitamin A) using dried blood spot (DBS) samples. Low recoveries and inconsistent results reported by others were found to be due to poor extraction efficiency rather than retinol instability. Maintaining acid conditions during extraction resulted in recoveries >95% with <6.5% of coefficient of variation. Using isocratic high performance liquid chromatography, separation was achieved in <3.5 min. Detector response was linear (R(2)=0.9939) within a range of 0.05-2 μg/mL, with a limit of quantification of 0.05 μg/mL. Retinol in DBS was shown to be stable (>95%) at room temperature for up to 10 weeks. DBS values for retinol were highly correlated with venous blood samples from 24 healthy subjects (r=0.9724) and were consistent with results from a commercial laboratory. This simple and reliable method for the determination of vitamin A status should prove particularly valuable for population studies and large clinical trials.

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.

Determination of vitamin A (retinol) in infant and medical nutritional formulas with AOAC method 992.06 using a modified extraction procedure: single-laboratory validation

The applicability of AOAC Official Method 992.06, vitamin A (retinol) in milk-based infant formula can be extended to specialty infant formulas, and medical and adult nutritional products with a few minor modifications to the sample preparation procedure. Currently, AOAC Official Method 992.06 is only applicable to milk-based infant formulas containing >500 IU vitamin A per reconstituted quart. When this method is used as written to test specialty infant formulas, vitamin A recoveries are low compared to results generated with alternate validated vitamin A methods. AOAC Method 992.06 vitamin A recoveries can be improved significantly in specialty infant formulas if the amount of potassium hydroxide used during the saponification step is doubled. With this one minor modification to the sample preparation procedure, AOAC Method 992.06 demonstrates acceptable precision and accuracy for the quantitation of vitamin A (retinol) in specialty infant formulas, milk- and soy-based infant formulas, and adult and medical nutritionals. Because increasing the amount of potassium hydroxide can cause emulsions to form, 2-4 mL aliquots of reagent alcohol may need to be added to some samples to separate the organic and aqueous layers during the extraction step. A single-laboratory validation of these modifications was completed. During validation, 15 different product matrixes were analyzed. The intermediate precision averaged 2.70% RSD, and spike recovery data averaged 96.3%.

Reverse-phase high-performance liquid chromatography (HPLC) analysis of retinol and retinyl esters in mouse serum and tissues

The ability to measure endogenous metabolites of retinoids (vitamin A and its derivatives) in biological samples is key to understanding the crucial physiological actions of vitamin A. Over the years, many assays and methods have been developed to analyze different retinoids in biological samples. Liquid chromatography is the best analytical technique for routine analysis of these compounds. However, due to their different chemical properties, different retinoid metabolites cannot be accurately separated and quantified in a single chromatographic run. Here, we will describe a reverse-phase HPLC isocratic method that enables extraction, separation, identification, and quantification of all-trans-retinol and different molecular species of retinyl ester with high accuracy, sensitivity, and reliability.

Molecular biology and analytical chemistry methods used to probe the retinoid cycle

The retinoid (visual) cycle is a complex enzymatic pathway essential for regeneration of the visual chromophore, 11-cis-retinal, a component of rhodopsin that undergoes activation by light in vertebrate eyes. Pathogenic mutations within genes encoding proteins involved in the retinoid cycle lead to abnormalities in retinoid homeostasis and numerous congenital blinding diseases of humans. Thus, elucidation of disease-specific changes in enzymatic activities and retinoid content of the retina can provide important insights into the mechanisms of disease initiation and progression. Here, we use the protein RPE65 as an example to describe generally applicable methods for determining the stability and enzymatic activity of proteins and their mutants involved in retinoid metabolism. Additionally, we introduce a range of analytical techniques involving high-performance liquid chromatography and mass spectrometry to detect and quantify retinoids and their derivatives in eye extracts. Biochemical protocols combined with advanced mass spectrometry should facilitate fundamental biological studies of vision.

Identification of vitamin A-free cells in a stellate cell-enriched fraction of normal rat liver as myofibroblasts

Myofibroblasts (MFs) as well as hepatic stellate cells (HSCs) are known to be involved in liver fibrogenesis. Quiescent HSCs (qHSCs) in culture have been thought to differentiate to replicative activated HSCs (aHSCs). In this study a qHSC-enriched fraction isolated by Nycodenz-isodensity centrifugation was separated with a fluorescence-activated cell sorter, which revealed the presence of a small fraction (occupancy rate=0.4%) of cells that did not show vitamin A-autofluorescence under ultraviolet (UV)-irradiation (UV- cells). The remaining vitamin A-containing cells were autofluorescent (UV+) and originally expressed markers of qHSCs, and, in culture, did not grow, lost vitamin A, and expressed markers of aHSCs. UV- cells showed morphology of MFs, and, in culture, grew to form colonies and expressed markers of MFs. These results indicated that UV+ and UV- cells represent qHSCs and MFs, respectively, and that aHSCs have no growth potential and are a cell-type distinct from proliferative MFs. Gene expression profiles of UV- cells (MFs) newly identified gremlin as one of MF-preferential genes and its proteins were localized around fibrotic septa in rat and human livers. In addition, we suggested that the qHSC-enriched fraction included approximately 6% of liver MFs.

Microemulsion electrokinetic chromatography for the separation of retinol, cholecalciferol, δ-tocopherol and α-tocopherol

A microemulsion electrokinetic chromatographic method was used to separate fat-soluble vitamins. The separation of retinol, cholecalciferol, and delta- and alpha-tocopherol was performed using a microemulsion containing 0.75% (v/v) n-heptane, 30 mM bis(2-ethylhexyl)sodium sulfosuccinate (AOT), 5% (v/v) 1-butanol, 15% (v/v) 1-propanol and 15% (v/v) methanol in 20mM boric acid-sodium borate buffer. The effect of the different microemulsion constituents was studied, including the type and concentration of surfactant, buffer, oil and co-surfactants. The presence of methanol in the microemulsion was found to be necessary to achieve the separation of the tocopherols. Detection was carried out at 200, 265 and 325 nm for the tocopherols, cholecalciferol and retinol, respectively. Calibration curves and precision data were obtained for each analyte. Good linear relationships were found between the analytical signal and the analytes concentration in the 25-500 mg L(-1) for retinol and cholecalciferol, and 25-300 mg L(-1) for tocopherols ranges. The precision of the method afforded relative standard deviations in the 4.0-10% range.

Simulation and optimization of a supercritical extraction process for recovering provitamin A

In this work, a simulation procedure of a supercritical extraction process was developed through the use of the commercial simulator HYSYS (Hyprotech Ltd.), adapting the existing units to the operating conditions typical of the supercritical extraction process. The objective is to recover provitamin A (beta-carotene) from palm oil (esterified) using carbon dioxide/ethanol as the supercritical mixed solvent. This example characterizes the problem for recovering high added value product from natural sources, as the palm oil, which is desired by the market. Owing to the fact that esterified palm oil is a complex mixture, made by several components, in order to characterize this system in the simulator, it was necessary to create hypothetical components using the UNIFAC (universal function-group activity coefficients model) group contribution, because they are not present in a conventional database and, then, their physical properties must be estimated and/or predicted before the simulation. The optimization was carried out in each simulation for each equipment, in terms of operating conditions (temperature and pressure), in order to obtain the maximum recovery of carotenes. According to the results, it was possible to concentrate carotenes through two cycles of supercritical extraction with high yield. Furthermore, ethyl esters (biodiesel) were also obtained, as a byproduct of the proposed process, which can also be used as an alternative fuel, with the important characteristic that it is renewable.

Hepatotoxicity of alcohol-induced polar retinol metabolites involves apoptosis via loss of mitochondrial membrane potential

Chronic alcohol consumption depletes hepatic vitamin A stores. However, vitamin A supplementation is hepatotoxic, which is further potentiated by concomitant alcohol consumption. It was suggested that polar retinol metabolites generated by alcohol-inducible cytochrome P4502E1 aggravate liver damage. However, experimental evidence supporting this hypothesis is lacking. To elucidate the effects of polar retinol metabolites on cultured HepG2 cells and primary rat hepatocytes, polar retinol metabolites were extracted from liver tissues of rats fed either an alcoholic or isocaloric control Lieber-DeCarli diet. Cell toxicity assays included morphology assessment, trypan blue exclusion test, and LDH/AST leakage. Staining for DAPI and acridine orange, FACS analysis, and Western blot for cleaved caspase-9 and -3 were used to detect apoptosis. Polar retinol metabolites caused marked cytotoxicity in a concentration- and time-dependent manner in both cell types reflected by morphological changes, a dramatic increase in trypan blue positive cells, and LDH/AST leakage. Toxicity was due to apoptosis, as demonstrated by a time-dependent increase of sub-G1 cellular events, a rapid loss of mitochondrial membrane potential, and a time-dependent activation of caspase-9 and -3. No toxicity was found with equivalent doses of the control extract from nonalcoholic rats. We demonstrate that polar retinol metabolites cause marked hepatocyte death through the induction of apoptosis.

Separation and determination of Vitamins E and A in multivitamin syrup using micellar liquid chromatography and simplex optimization

A rapid method has been described for separation and determination of Vitamins A and E using micellar liquid chromatography (MLC). Influence of temperature of column and addition of organic modifiers on separation efficiency was investigated. A temperature of 30 degrees C and 1-butanol modifier was selected. Optimization of the parameters affecting the separation including percent of organic modifier, pH of the mobile phase, concentration of surfactant, and flow rate of the mobile phase was performed simultaneously using the super-modified simplex (SMS) procedure. Results showed that 11.7% 1-butanol, 76.9 mM sodium dodecyl sulphate (SDS), pH of 6.73 and a flow rate of 1.35 ml min(-1) are the best conditions for separation of these compounds. The analytical parameters including linearity, r>0.9990; limit of detection 1.71 and 4.52 microg ml(-1) for A and E, respectively; precision of the method, R.S.D.<2.85%; and recovery, more than 90%, show that the method is useful for measuring these compounds in pharmaceutical preparations.

Identification of all-trans-retinol:all-trans-13,14-dihydroretinol saturase

Retinoids carry out essential functions in vertebrate development and vision. Many of the retinoid processing enzymes remain to be identified at the molecular level. To expand the knowledge of retinoid biochemistry in vertebrates, we studied the enzymes involved in plant metabolism of carotenoids, a related group of compounds. We identified a family of vertebrate enzymes that share significant similarity and a putative phytoene desaturase domain with a recently described plant carotenoid isomerase (CRTISO), which isomerizes prolycopene to all-trans-lycopene. Comparison of heterologously expressed mouse and plant enzymes indicates that unlike plant CRTISO, the CRTISO-related mouse enzyme is inactive toward prolycopene. Instead, the CRTISO-related mouse enzyme is a retinol saturase carrying out the saturation of the 13-14 double bond of all-trans-retinol to produce all-trans-13,14-dihydroretinol. The product of mouse retinol saturase (RetSat) has a shifted UV absorbance maximum, lambda(max) = 290 nm, compared with the parent compound, all-trans-retinol (lambda(max) = 325 nm), and its MS analysis (m/z = 288) indicates saturation of a double bond. The product was further identified as all-trans-13,14-dihydroretinol, since its characteristics were identical to those of a synthetic standard. Mouse RetSat is membrane-associated and expressed in many tissues, with the highest levels in liver, kidney, and intestine. All-trans-13,14-dihydroretinol was also detected in several tissues of animals maintained on a normal diet. Thus, saturation of all-trans-retinol to all-trans-13,14-dihydroretinol by RetSat produces a new metabolite of yet unknown biological function.

Identification of 3,4-didehydroretinal isomers in the Xenopus tadpole tail fin containing photosensitive melanophores

It is well characterized that melanophores in the tail fin of Xenopus laevis tadpoles are directly photosensitive. In order to better understand the mechanism underlying this direct photosensitivity, we performed a retinal analysis of the tail fins and eyes of Xenopus tadpoles at stages 51-56 using high performance liquid chromatography (HPLC). Following the extraction of retinoids by the formaldehyde method, a fraction containing retinal and/or 3,4-didehydroretinal isomers from the first HPLC analysis were collected. These isomers were then reduced by sodium borohydride to convert retinal and/or 3,4-didehydroretinal isomers into the corresponding retinol isomers to prepare for a second HPLC analysis. Peaks of 11-cis and all-trans 3,4-didehydroretinol were detected in the eyes and tail fins containing melanophores, but they were not detected in the tail fins without melanophores. The amounts of 11-cis and all-trans 3,4-didehydroretinol were 27.5 and 5.7 fmol/fin, respectively, and the total quantity of 3,4-didehydroretinal was calculated at approximately 5 x 10(6) molecules/melanophore. These results strongly suggest the presence of 11-cis and all-trans 3,4-didehydroretinal in melanophores of the tadpole tail fin, which probably function as the chromophore of photoreceptive molecules.

Carotenoid composition and vitamin A value of an Argentinian squash (Cucurbita moschata)

The carotenoid composition of butternut squash (Cucurbita moschata) cultivated in the province of Santiago del Estero, Argentina, was determined. The main carotenoids isolated were identified as beta-carotene (beta,beta-carotene), alpha-carotene (beta,epsilon-carotene), and lutein (beta,epsilon-carotene-3,3'-diol) and the minor carotenoids, as phytofluene (7,8,11,12,7',8'-hexahydro-psi,psi-carotene), zeta-carotene (7,8,7',8'-tetrahydro-psi,psi-carotene), neurosporene (7,8-dihydro-psi,psi-carotene), violaxanthin (5,6,5',6'- diepoxy-5,6,5',6'-tetrahydro-beta,beta-carotene-3,3'-diol) and neoxanthin (5,6-epoxy-6,7-didehydro-5,6,5',6'-tetrahydro-beta,beta- carotene-3,5,3'-triol). In some samples, 5,6,5',6'-beta-carotene diepoxide, (5,6,5',6'-diepoxy-5,6,5',6'-tetrahydro-beta,beta-carotene) and flavoxanthin (5,8-epoxy-5,8-dihydro-beta,epsilon-carotene-3,3'-diol) were detected. The presence of cis-isomers of beta,beta-carotene was also detected by HPLC. The vitamin A value obtained was 432 micrograms RE/100 g fresh sample, which indicates that this vegetable is an important source of provitamin A.

Nonaqueous electrochromatography on continuous bed columns of sol-gel bonded large-pore C18 material: separation of retinyl esters

A nonaqueous electrochromatographic reversed-phase separation method for retinyl esters using continuous bed columns has been developed. The packing material 7 microm Nucleosil 4,000 angstroms C18 was sol-gel bonded in 180 microm I.D. capillaries. The mobile phase used was 2.5 mM lithium acetate in N,N-dimethylformamide-acetonitrile-methanol (2+7+1, v/v). At 350 V/cm and 30 degrees C, this mobile phase composition gave rise to an electroosmotic flow of 1 mm/s. No Joule heating nor bubble formation were observed even at 625 V/cm (17 microA). With a 36 cm L(eff) column complete separation of the commercially available and synthesized standards (all-trans-retinyl acetate, palmitate, heptadecanoate, stearate, oleoate, and linoleoate) was obtained within 10 min. The within-day and between-day variations of retention times of all-trans-retinyl palmitate were <0.3% relative standard deviation (RSD) (n=3) and <2% RSD (n=6), respectively. The within-day and between-day variations of peak areas were both <2% (both n=3). The columns were used for more than 1 month without degradation. Liver extracts from arctic seal were analyzed.

Thermometric sensing of peroxide in organic media. Application to monitor the stability of RBP-retinol-HRP complex

The stability of horseradish peroxidase (HRP) in aqueous and organic solvents is applied to develop a simple thermometric procedure to detect the binding of retinoic acid-HRP conjugate to retinol binding protein (RBP). Butanone peroxide (BP) in organic phase and hydrogen peroxide in aqueous phase is detected thermometrically on a HRP column, immobilized by cross-linking with glutaraldehyde on controlled pore glass (CPG). Acetone, acetonitrile, methanol, and 2-butanol are used for detection of BP, in the flow injection analysis (FIA) mode. A linear range between 1 and 50 mM BP is obtained in all the organic solvents with a precision of 5-7% (CV%). The magnitude and nature of the thermometric response is significantly different in each organic solvent. The stability of HRP in the organic phase is used to study the stability of a retinoic acid-HRP conjugate bound to immobilized RBP. The response of HRP (to 20 mM BP) in the retinoic acid-HRP conjugate is used as an indicator of the stability of the RBP-retinoic acid-HRP complex, after challenges with various organic/aqueous solvents. Both immobilized HRP and RBP are stable at least for 6 months. The effect of o-phenylene diamine on the thermometric response of HRP is also investigated. A scheme for the design of a thermometric retinol (vitamin A) biosensor is proposed.

Determination of food constituents based on SFE: applications to vitamins A and E in meat and milk

A method has been developed for the determination of vitamins A and E in food using supercritical fluid extraction (SFE), applying liquid or solid trapping, with an accuracy equal to conventional solvent extraction methods. Under optimal conditions, using methanol modified carbon dioxide as a supercritical fluid, Hydromatrix as a water adsorbent, and with a small amount of ascorbic acid and methanol added to the sample, the extraction time is reduced to 80 min. This time is considerably shorter than in conventional methods. Other advantages are the reduction of manual manipulations leading to lower labour costs and reduced consumption of organic solvents in the sample preparation step.

Microemulsion electrokinetic chromatography in suppressed electroosmotic flow environment. Separation of fat-soluble vitamins

Microemulsion electrokinetic chromatography (MEEKC) was carried out in a pH 2.5 phosphate buffer to effectively suppress the electroosmotic flow (EOF). With 66.6% (w/w) 25 mM phosphate buffer pH 2.5, 20.0% (w/w) 2-propanol, 6.6% (w/w) 1-butanol, 6.0% (w/w) sodium lauryl sulphate (SDS), and 0.8% (w/w) n-octane as the separation medium, the fat-soluble vitamins A palmitate, E acetate, and D3 were baseline separated within 11 min. With strongly suppressed EOF, the polarity of the separation voltage was reversed (positive electrode at the outlet); the n-octane micro droplets surrounded by negatively charged SDS molecules migrated towards the detector. The aqueous part of the microemulsion was modified with 20% (w/w) 2-propanol to improve partition between the n-octane phase and the surrounding aqueous medium. The fat-soluble vitamins were separated in order of decreasing hydrophobicity with a high migration time stability (repeatable within 0.1% RSD). Excellent accuracy and precision were obtained when the system was applied for the determination of vitamin E acetate in commercial vitamin tablets; quantitative data corresponded to 97.0% of label claim, intra-day results varied within 1.72% RSD (n=6), and inter-day results varied within 3.22% RSD (n=5).

Carotenoid and retinoid--two pigments in a gecko eye lens

The eye lenses of the Moroccan day gecko Quedenfeldtia trachyblepharus contain two different pigments: a retinoid (minor pigment) and a carotenoid (major pigment). The retinoid, all-trans 3, 4-didehydroretinol, is bound to iota-crystallin, which comprises only 2% of the total amount of crystallins. The carotenoid is associated to gammas-crystallin - comprising about 10% of total amount of crystallins--and causes the dark yellow colour of the lens. The absorption spectrum of the isolated carotenoid shows a major, triple-peaked band at 372, 392, and 416 nm and two minor peaks at 284 and 294 nm. This spectrum reminds of that of galloxanthin, a carotenoid found in oil droplets of some avian retinae. The absorption spectrum of the carotenoid-gammas-crystallin complex is shifted 6-8 nm bathochromically. In the lens, this complex absorbs ultraviolet and shortwave blue radiation, supposedly improving the optical quality of the dioptric apparatus and protecting the retina against photodamage. Both the retinoid and the carotenoid are present in eye cups. The lenticular carotenoid of Quedenfeldtia is the first example of a carotenoid in the lens of a terrestrial vertebrate with a sufficiently high concentration to be physiologically effective as a UV-filter. Additionally, it is unique in being the first example of a carotenoid associated with gammas-crystallin.

Nonaqueous electrochromatography on C30 columns: separation of retinyl esters

A nonaqueous packed capillary electrochromatographic reversed-phase method for separation of retinyl esters has been developed. The retinyl esters all-trans-retinyl acetate, palmitate, heptadecanoate, stearate, oleoate, and linoleoate were separated on a 180 microm ID column packed with 5 microm C30 particles with a mobile phase consisting of 2.5 mM lithium acetate in N,N-dimethylformamide-methanol (99:1, v/v). With this mobile phase, the electroosmotic flow was 0.8 mm/s at 650 V/cm and 40 degrees C, and the separation was completed in less than 30 min on 30 cm columns. To obtain electrostable frits of the hydrophobic C30 material both the preparation of the frits and the conditioning of the column prior to electroconditioning were of importance. Selectivity changes were introduced by replacing up to 70% v/v of the N,N-dimethylformamide by acetonitrile. The increase in the amount of acetonitrile was, however, accompanied by a significant increase in analysis time. Liver extracts obtained from arctic seal were analyzed.

Determination of retinol, alpha-tocopherol, alpha- and beta-carotene by direct extraction of human serum using high performance liquid chromatography

In this report we describe a modified reverse phase HPLC method that avoids the solvent evaporation step and allows simple and rapid determination of retinol, alpha-tocopherol, alpha-carotene and beta-carotene and achieves complete separation of alpha- and beta-carotene. Retinyl acetate, alpha-tocopheryl acetate and retinyl palmitate in ethanol were added to serum as internal standards. Serum was then deproteinized with an equal volume of ethanol, and the lipid was extracted with ethyl acetate-butanol (1:1 v/v). A portion of this solution was injected into a C18 reverse phase chromatographic column and absorbencies of the vitamins and internal standards were measured at 292 nm for tocopherols, 325 nm for retinoids and 450 nm for carotenoids; peak-height ratios were used to quantify each vitamin. The analytical recoveries for retinol, alpha-tocopherol alpha- and beta-carotene at various concentrations tested were 95-103, 90-98, 92-99 and 94-96%, respectively. The intra- and interassay variations for low and high concentrations of retinol, alpha-tocopherol, alpha- and beta-carotene ranged from 2.4 to 6.7 for intraassay and from 4.3 to 8.5 for interassay replication. The detection limits were 1.25 (0.04), 19 (0.44), 0.35 (0.006) and 0.94 (0.017) micrograms/dL (delta mol/L) for retinol, alpha-tocopherol, alpha- and beta-carotene, respectively.

Separation of representative lipid compounds of biological membranes and lipid derivatives from peroxidized polyunsaturated fatty acids by reversed phase high-performance liquid chromatography

A complex mixture of different lipid compounds, including phosphatidylcholine, phosphatidylserine, all trans-retinol, 15(S)-hydroperoxyeicosatetraenoic acid, D-alpha-tocopherol, saturated and unsaturated fatty acids can be separated by reversed phase HPLC by using a C-18, 120 mm x 4 mm, 3 microns particle size column and a step gradient from acetonitrile/water (1:1; v:v) to 100% acetonitrile at a flow rate of 0.8 ml/min. By applying this elution condition, separation of various groups of lipid hydroperoxides and lipid derivatives, each one originating from a different in vitro peroxidized polyunsaturated fatty acid, can be obtained. Simultaneous detection is carried out by a diode array detector at a wavelength accumulation range set up between 195 and 400 nm. The possibility of simultaneously having such a large number of measurements renders this chromatographic method particularly suitable in studies concerning lipid peroxidation where, in addition to the detection of free radical-induced lipid hydroperoxides, data on some key antioxidant molecules, i.e. vitamin A and E, as well as that of structural compounds of biological membranes, i.e. phosphatidylcholine and phosphatidylserine, can be achieved.

Supercritical fluid extraction and reversed-phase liquid chromatography methods for vitamin A and beta-carotene heterogeneous distribution of vitamin A in the liver

We developed supercritical fluid procedures for extracting vitamin A and beta-carotene from vitamin supplements and calf liver tissue. The SF extracts could be injected onto an HPLC column without further pretreatment. Samples were analysed by RP-HPLC using diode array detection or by spectrophotometry. Recoveries were very good. SF extracts from a vitamin preparation of uniform composition had an R.S.D. of 4%. Extracts from calf liver supplements were predictably more heterogeneous. The SF extraction method is less labor intensive then traditional liquid-liquid procedures for extracting vitamin A and carotenoids from tissues.

Micellar electrokinetic capillary chromatography of three natural vitamin A derivatives

Micellar electrokinetic chromatography (MEKC) using bile salts has been employed to separate retinoids differing in structure and charge; bile salts in MEKC allows the separation of liposoluble molecules but, to the best of our knowledge, there are only few data on the above-mentioned technique for the separation of highly hydrophobic compounds. The three natural vitamin A derivatives, retinal, retinol and retinoic acid, were successfully separated by MEKC using sodium cholate within a relatively short time (ca. 25 min), whereas the separation of these compounds was not successful using sodium dodecyl sulfate or sodium deoxycholate. Several parameters (pH and organic modifiers, in addition to bile salts concentration) have been tested to provide a system that can be extended to synthetic retinoids, which are often used in treating several diseases, including cancer prevention and therapy.

High-performance liquid chromatography-electrospray mass spectrometry of retinoids

High-performance liquid chromatography (HPLC)-electrospray mass spectrometry (LC-MS) was used to analyze vitamin A-active retinoids including retinoic acid, retinol, retinal, and retinyl acetate. Unlike previous LC-MS methods such as negative ion electron capture chemical ionization, no derivatization of retinoic acid was required. HPLC separations were carried out on a C30 reversed phase column with gradient elution using mobile phases containing water, methanol, and methyl-tert-butyl ether. Ammonium acetate (5 mM) was added to the mobile phase to facilitate ion pair formation during reversed phase HPLC of retinoic acid, and acetic acid (0.5% v/v) was added to the mobile phase to enhance protonation during LC-MS analysis of nonacidic retinoids. During negative ion electrospray, retinoic acid formed abundant deprotonated molecules, [M-H]-, of m/z 299 without significant fragmentation. Although retinol, retinal, and retinyl acetate did not ionize during negative ion electrospray, the positive ion electrospray mass spectra of these retinoids showed an abundant protonated molecule of m/z 285 for retinal and base peaks of m/z 269 corresponding to elimination of water or acetic acid from the protonated molecules of retinol or retinyl acetate, respectively. No ions from retinoic acid were detected during positive ion electrospray. Limits of detection for retinoic acid, retinal, retinol, and retinyl acetate were 23 pg, 1.0 ng, 0.5 ng, and 10 ng, respectively.

Vitamin E, retinyl palmitate, and protein in rhesus monkey retina and retinal pigment epithelium-choroid

PURPOSE

To measure the amounts of vitamin E, retinyl palmitate, and protein in the primate retina and its supporting tissues-the retinal pigment epithelium and choroid. To compare the amounts and concentrations of these materials in the central retina with those in the peripheral retina and to compare the concentration of vitamin E in the retina with that in plasma. Finally, to compare these results in rhesus monkey with existing measurements in humans.

METHODS

Ocular tissues from rhesus monkeys (Macaca mulatta) were extracted with a two-phase solvent system. Components in the extract were separated by reverse-phase high-pressure liquid chromatography. Two detectors in series monitored the effluent: Vitamin E was quantified with an internal standard and fluorescence detection, whereas retinyl palmitate was quantified with an external standard and ultraviolet light detection.

RESULTS

Amounts of vitamin E, retinyl palmitate, and protein in tissues from rhesus monkey compared reasonably well with those reported for humans. The content of vitamin E in the peripheral neural retina was moderately correlated with its protein content and, to a greater extent, with the concentration of vitamin E in the plasma; however, the content of vitamin E in the central neural retina correlated only with the amount of protein in the central neural retina.

CONCLUSIONS

These results are consistent with rhesus monkey as a model for the use of vitamin E by human ocular tissues. The amount of vitamin E in the central neural retina appears to be more closely regulated than the amount of vitamin E in the peripheral neural retina.

Stable isotope methods for the study of beta-carotene-d8 metabolism in humans utilizing tandem mass spectrometry and high-performance liquid chromatography

This report presents analytical methods for the isolation and quantification of all-trans-beta-carotene-d8 in human plasma following a 73 mumol oral dose. Retinol-d4 derived from beta-carotene-d8 was also determined in the same plasma. Plasma samples drawn over a 24 day period were analyzed. beta-Carotene and retinol were isolated and purified for analysis using a solid phase extraction protocol with aminopropyl-bonded silica sorbent. Ratios of beta-carotene-d8/beta-carotene were determined using reversed-phase HPLC with spectrophotometric detection, which fully resolved the isotopomers, and by tandem mass spectrometry (MS/MS) with electron ionization. Results obtained from MS/MS and HPLC analysis showed close agreement and demonstrated improved selectivity relative to analysis using a single mass analyzer. Retinol-d4 was converted to its tert-butyldimethylsilyl ether and analyzed by gas chromatography/mass spectrometry using selected ion monitoring. The ability to resolve the beta-carotene isotopomers by HPLC makes it feasible for investigators without mass spectrometers to investigate the dynamics of absorption and metabolism of beta-carotene-d8 in humans.

The retinoids of seven species of mantis shrimp

Eyes of stomatopod crustaceans, or mantis shrimps, contain the greatest diversity of visual pigments yet described in any species, with as many as ten or more spectral classes present in a single retina. In this study, the eyes of seven species of mantis shrimp from three superfamilies of stomatopods were examined for their content of retinoids. Only retinal and retinol were found; neither hydroxyretinoids nor dehydroretinoids were detected. The principal isomers were 11-cis and all-trans. The eyes of most of these species contain stores of 11-cis retinol, principally as retinyl esters, and in amounts in excess of retinal. Squilla empusa is particularly noteworthy, with over 5000 pmoles of retinol per eye.

Crystal structure of liganded and unliganded forms of bovine plasma retinol-binding protein

The three-dimensional structures of bovine plasma retinol-binding protein (bRBP) complexed with retinol (space group P2(1)2(1)2(1), a = 46.08, b = 49.12, c = 76.10 A) and of the unliganded protein prepared in vitro by extracting retinol with ethyl ether (space group P2(1)2(1)2(1), a = 46.55, b = 48.97, c = 76.87 A) have been solved at 1.9 and 1.7 A resolution, respectively. The final crystallographic R factors are 0.190 for holobRBP and 0.196 for the unliganded bRBP. The model for the bovine holoprotein is quite similar to that of the human protein, with which it exhibits 92% sequence similarity. The root mean square deviation between the alpha-carbons in the two proteins is 0.31 A. The retinol binding site is almost completely preserved. The loops that surround the opening of the beta-barrel are also particularly conserved, in contrast with the presence of several substitutions in parts of the RBP molecule opposite the opening of the calyx that binds retinol. Despite the fact that unliganded bovine RBP was prepared and crystallized using procedures completely different from those used to obtain the unliganded human RBP, the conformational differences between unliganded and liganded forms of bRBP are almost identical to those found previously between the same forms of human RBP. They mainly involve a few residues in the region extending from amino acid residues 32 to 37. Therefore, similar differences are very likely to exist between holoRBP and the physiologically occurring apoprotein. A not yet identified electron density, different in shape and orientation from retinol, also occupies the central cavity of the beta-barrel in the unliganded bRBP, as found for unliganded human RBP. The functional consequences of the conformational change induced by the removal of retinol on the interaction between RBP and transthyretin, coupled with the conservation of the entrance loops of the beta-barrel in mammalian RBPs, are consistent with their participation in molecular interactions.

A method for determining concentrations of retinol, tocopherol, and five carotenoids in human plasma and tissue samples

To explore the relation between plasma and tissue concentrations of seven fat-soluble micronutrients (retinol, alpha-tocopherol, lutein, cryptoxanthin, lycopene, alpha-carotene, and beta-carotene), we developed methods for clarifying plasma and tissue samples and quantitating these seven analytes simultaneously by using HPLC with ultraviolet detection. Clarification of tissue samples was performed by using enzymatic digestion followed by mechanical homogenization; saponification was avoided and tocopherol nicotinate was used as an internal standard. Precision and sensitivity for small samples of plasma and solid tissues were determined. Accuracy for plasma samples was assessed by comparing results obtained by using this method with those obtained by using older, standardized methods. Results from application of this method to patient samples of plasma and various tissues are presented. This method will be of interest to investigators seeking to quantitate these seven micronutrients in solid tissue samples, but desiring to avoid the usual saponification step required in most other reported techniques.

[Use of high performance liquid chromatography for analysis of vitamin A in food products]

High-performance liquid chromatography (HPLC) was used for vitamin A assay in foods and raw materials. Metrological characteristics of this method have been estimated: relative standard deviation was 0.06-0.08, average recovery of vitamin A was 97.3 +/- 2.6 with n = 6, P = 0.95). The statistical analysis of the results obtained with HPLC has shown that it could be successfully used for vitamin A assay in varying foods containing no less than 0.01 mg of vitamin A per 100 g.

[Retinol Acetate Reference Standard for Thin-layer Chromatography (Control 901) and Retinol Palmitate Reference Standard for Thin-layer Chromatography (Control 901) of National Institute of Hygienic Sciences]

The raw materials of retinol acetate and retinol palmitate were examined for the preparation of the "Retinol Acetate Reference Standard for Thin-layer Chromatography" and "Retinol Palmitate Reference Standard for Thin-layer Chromatography", respectively. Analytical data obtained were as follows: thin-layer chromatography, no impurities were detected in retinol acetate and one impurities was detected in retinol palmitate; The Rf values of retinol acetate and retinol palmitate were consistent with those of Reference Standards (Control 713), respectively; ultraviolet spectrum, lambda max = 326 approximately 327 nm; relative extinction, within the range reported in JPXI; weight variation of capsules, retinol acetate 224.0 +/- 15.5 mg (RSD 6.9%), retinol palmitate 222.0 +/- 13.8 mg (RSD 6.2%); assay, retinol acetate 57000 I.U./g, retinol palmitate 57000 I.U./g. Based on the above results, these raw materials were authorized to be the Reference Standards of the National Institute of Hygienic Sciences.

Interaction of fatty acid binding protein with microsomes: removal of palmitic acid and retinyl esters

[14C] palmitic acid or [3H] retinyl esters incorporated in microsomal membranes were removed by a cytosolic fraction enriched in fatty acid binding protein. When mouse liver cytosol was fractionated by 70% ammonium sulphate, a precipitate and a soluble fraction were obtained. The soluble fraction containing the fatty acid binding protein was able to remove from microsomal membranes, [14C] palmitic acid or [3H] retinyl esters, whereas the precipitate fraction had no removal capacity. Retinoid analysis indicated that 70% ammonium sulphate soluble fraction was enriched in endogenous retinyl esters with regard to cytosol or 70% ammonium sulphate precipitate fraction.

Carotenoid composition and vitamin A value of a squash and a pumpkin from northeastern Brazil

The carotenoid composition of a squash and a pumpkin from Northeastern Brazil was determined. Nineteen carotenoids were detected in Cucurbita moschata variety "Baianinha"; beta-carotene was the principal carotenoid, contributing about 74% of an average total carotenoid content of 317.8 micrograms/g. In C. maxima variety "Jerimum Caboclo", 11 carotenoids were found with lutein, and beta-carotene as the major pigments accounting for about 60% and 27%, respectively, of an average total carotenoid content of 78.4 micrograms/g. The abundance of beta-carotene in the C. moschata variety "Baianinha" makes this squash one of the richest sources of provitamin A. The average vitamin A value was 43,175 IU (International Units) per 100 g or 4,317 RE (retinol equivalents) per 100 g. Its vitamin A values is more than 11 times that of C. maxima variety "Jerimum Caboclo" and five times that of C. moschata cultivar "Menina Verde", the squash found previously to be highest in provitamin A among the Cucurbita vegetables most commercialized in São Paulo (Southeastern Brazil).

Effect of tetrachlorodibenzo-p-dioxin (TCDD) on the glucuronidation of retinoic acid in the rat

Administration of a single oral dose (10 micrograms/kg) of tetrachlorodibenzo-p-dioxin (TCDD) caused a 33% decrease in retinyl esters in the livers of male rats, but a 13-fold increase in retinyl esters in the kidney and a 3-fold increase in serum retinol. Liver and kidney microsomal uridine diphosphoglucuronosyltransferase (UDPGT) activity toward all-trans-retinoic acid was increased 3.7- and 2.6-fold, respectively, ten days following exposure to TCDD. Verification of the in vitro formation of [3H]retinoyl beta-glucuronide (RG) was by cochromatography with authenic RG on reversed phase high pressure liquid chromatography (HPLC), identification of retinoic acid as the hydrolysis product after beta-glucuronidase treatment, and the characterization of the all-trans-retinoyl glucuronide by negative fragment mass spectroscopy, fast atom bobardment. We conclude that increased retinoic acid glucuronidation may be a contributing factor to the hepatic depletion of vitamin A and the increased excretion of vitamin A metabolites following TCDD exposure.

A rapid and sensitive separation of retinol and retinyl palmitate using a small, disposable bonded-phase column: kinetic applications

A method utilizing small disposable C18 bonded-phase columns has been developed to separate retinol and retinyl palmitate mixtures into their individual components in high yield and purity. Up to ten mixtures can be processed in 1 hr and the columns are reusable after suitable washing. Although the method was developed with standard retinoid mixtures, it was shown that it is also applicable to the assay of the kinetics of both a bile salt-stimulated human milk lipase-catalyzed hydrolysis reaction and acyl transfer reaction. This rapid, accurate, and inexpensive method is complementary to other chromatographic techniques, especially in kinetic investigations, and enables one to detect these fluorescent retinoids in quantities as small as 2 picomoles. --O'Connor, C. J., and B. Yaghi. A rapid and sensitive separation of retinol and retinyl palmitate using a small, disposable bonded-phase column: kinetic applications.

Identification of 3-dehydroretinol (vitamin A2) in mouse liver

3-Dehydroretinol (vitamin A2) and its long-chain fatty acyl esters have been isolated from hairless mouse liver by high-performance liquid chromatography (HPLC). In adult animals, these compounds amount to 1-2 micrograms/g liver, corresponding to 1-2% of the retinol (vitamin A1) concentration. Studies on the regulation of 3-dehydroretinol levels in liver showed that the age and vitamin A status of the animal affect the levels, but the relative proportions of retinol and 3-dehydroretinol are constant.