High-performance liquid chromatographic analysis of retinal and retinol isomers

Simultaneous spectral illumination of microplates for high-throughput optogenetics and photobiology

The biophysical characterization and engineering of optogenetic tools and photobiological systems has been hampered by the lack of efficient methods for spectral illumination of microplates for high-throughput analysis of action spectra. Current methods to determine action spectra only allow the sequential spectral illumination of individual wells. Here we present the open-source RainbowCap-system, which combines LEDs and optical filters in a standard 96-well microplate format for simultaneous and spectrally defined illumination. The RainbowCap provides equal photon flux for each wavelength, with the output of the LEDs narrowed by optical bandpass filters. We validated the RainbowCap for photoactivatable G protein-coupled receptors (opto-GPCRs) and enzymes for the control of intracellular downstream signaling. The simultaneous, spectrally defined illumination provides minimal interruption during time-series measurements, while resolving 10 nm differences in the action spectra of optogenetic proteins under identical experimental conditions. The RainbowCap is also suitable for studying the spectral dependence of light-regulated gene expression in bacteria, which requires illumination over several hours. In summary, the RainbowCap provides high-throughput spectral illumination of microplates, while its modular, customizable design allows easy adaptation to a wide range of optogenetic and photobiological applications.

Analysis of the current vitamin A terminology and dietary regulations from vitamin A1 to vitamin A5

Dietary recommendations on vitamin intake for human food fortification concerning vitamin A in various countries, larger economic zones and international organizations are mainly based on the Food and Agriculture Organization of the United Nations (FAO)/World Health Organization (WHO) "Codex Alimentarius standards". The general vitamin A terminology is based on regulations of the International Union of Pure and Applied Chemistry (IUPAC) that are used to describe the involved derivatives. These regulations and terminology were set up in the middle of the last century. Starting with the decade of the 80ies in the 20th century a large improvement of molecular biological methodologies, background physiological mechanisms as well as analytical techniques contributed to a large diversification of this simply claimed vitamin A terminology. Unfortunately, the following terminology and governmental regulations for food fortification are imprecise and non-harmonized. In this article we tried to unravel this terminology for updating terminology, nutritional suggestions and governmental regulations for vitamin A, which are currently based on various uncertainties. According to the current regulations, the newly found vitamin A5/X can be included in the current vitamin A terminology as "vitamin A5" or alternatively or even in parallel as a new vitamin A-independent terminology as "vitamin X". Based on the detailed knowledge of research from the early beginning of general vitamin A pathway identification towards detailed research of the last decades the commonly used and simplified term vitamin A with relevance for governmental recommendations on vitamin intake and food fortification advice was now more correctly sub-categorized to further vitamin A1, and A5 sub-categories with vitamin A1-alcohol as retinol, vitamin A2-alcohol as 3,4-didehydroretinol and vitamin A5-alcohol as 9-cis-13,14-dihydroretinol as their mainly relevant vitamin forms present in the human organism. Here we suggest and advise how the vitamin A terminology and further governmental regulations should be organized depending on a successful unraveling of the organization of the current vitamin A terminology.

Differences in nutrient content of eggs and larvae as indicators for improvement of broodstock nutrition in walleye (Sander vitreus) production

The aim of this study was to increase our knowledge about the nutritional needs of walleye (Sander vitreus (Mitchill, 1818)) broodstock. Two dietary treatments were tested: the first consisted of frozen Atlantic mackerel (Scomber scombrus L., 1758) pieces with a supplement of experimental dry pellets and the second consisted of frozen Atlantic mackerel pieces with a supplement of commercial trout pellets. Hatching success was highest in eggs from the wild broodstock. Eggs and larvae from wild fish were characterized by the highest levels of linoleic (LOA; 18:2 n–6) and linolenic (LNA; 18:3 n–3) fatty acids in the neutral lipids. They had the lowest level of docosahexaenoic acid (DHA) in both neutral and polar lipids. The results suggest the importance of the amino acids leucine, lysine, methionine, and serine for better egg survival. Vitamin A1 content was similar in eggs from wild fish and the younger broodstock from both treatment groups, but was 10 times lower in eggs from older broodstock. Vitamin A2 was highest in eggs from wild fish. Our results showed that neither of the two diets really resulted in egg or larval quality that were comparable with that of wild fish.

Retinoid uptake, processing, and secretion in human iPS-RPE support the visual cycle

PURPOSE

Retinal pigmented epithelium derived from human induced pluripotent stem (iPS) cells (iPS-RPE) may be a source of cells for transplantation. For this reason, it is essential to determine the functional competence of iPS-RPE. One key role of the RPE is uptake and processing of retinoids via the visual cycle. The purpose of this study is to investigate the expression of visual cycle proteins and the functional ability of the visual cycle in iPS-RPE.

METHODS

iPS-RPE was derived from human iPS cells. Immunocytochemistry, RT-PCR, and Western blot analysis were used to detect expression of RPE genes lecithin-retinol acyl transferase (LRAT), RPE65, cellular retinaldehyde-binding protein (CRALBP), and pigment epithelium-derived factor (PEDF). All-trans retinol was delivered to cultured cells or whole cell homogenate to assess the ability of the iPS-RPE to process retinoids.

RESULTS

Cultured iPS-RPE expresses visual cycle genes LRAT, CRALBP, and RPE65. After incubation with all-trans retinol, iPS-RPE synthesized up to 2942 ± 551 pmol/mg protein all-trans retinyl esters. Inhibition of LRAT with N-ethylmaleimide (NEM) prevented retinyl ester synthesis. Significantly, after incubation with all-trans retinol, iPS-RPE released 188 ± 88 pmol/mg protein 11-cis retinaldehyde into the culture media.

CONCLUSIONS

iPS-RPE develops classic RPE characteristics and maintains expression of visual cycle proteins. The results of this study confirm that iPS-RPE possesses the machinery to process retinoids for support of visual pigment regeneration. Inhibition of all-trans retinyl ester accumulation by NEM confirms LRAT is active in iPS-RPE. Finally, the detection of 11-cis retinaldehyde in the culture medium demonstrates the cells' ability to process retinoids through the visual cycle. This study demonstrates expression of key visual cycle machinery and complete visual cycle activity in iPS-RPE.

Effects of refining and removal of persistent organic pollutants by short-path distillation on nutritional quality and oxidative stability of fish oil

Food and feed legislations are implemented to control the level of unwanted persistent organic pollutants (POPs) below health risk concerns. Short-path distillation is established as the most effective industrial process to remove POPs in fish oil. However, the technology involves heating of the oil to high temperature levels (>200 °C) that possibly give unwanted heat-induced side reactions and coevaporation of minor compounds of importance for the nutritional quality of the oil. The effects on retention of vitamins, cholesterol, and unsaponifiable compounds, geometrical isomerization, loss of polyunsaturated fatty acids (PUFA), oxidation level, and oxidative stability have been studied on the basis of experiments designed to optimize and model the effect of process conditions (i.e., evaporator temperature, feed rate, and addition of working fluid) on the reduction of POPs. Loss of volatile nutrients was observed, but the extent will depend on the process conditions needed to obtain target decontamination level, as well as the concentration ratio and difference in vapor pressure between free and esterified forms of the studied compounds. Some reduction in oxidation level was documented with preservation of PUFA level and quality. Oxidative stability was influenced both positively and negatively depending on the applied process conditions. Generally, no adverse negative effects on the nutritional quality of the fish oil could be documented. Optimal process conditions were modeled that ensure removal of POPs to within legislation levels while retaining most of the vitamin levels in fish oil. A 76% reduction of the WHO-PCDD/F-PCB-TEQ level in the used feedstock was needed to be in accordance with the voluntary industrial monograph of GOED. This could be achieved on the basis of operation conditions giving <20% loss of vitamins. A 90% decontamination rate gave vitamin retentions in the 60-90% range.

Duodenal administered seal oil for patients with subjective food hypersensitivity: an explorative open pilot study

Short-term duodenal administration of n-3 polyunsaturated fatty acid (PUFA)-rich seal oil may improve gastrointestinal complaints in patients with subjective food hypersensitivity, as well as joint pain in patients with inflammatory bowel disease (IBD). The aim of the present explorative pilot study was to investigate whether 10-day open treatment with seal oil, 10 mL self-administrated via a nasoduodenal tube 3 times daily, could also benefit nongastrointestinal complaints and quality of life (QoL) in patients with subjective food hypersensitivity. Twenty-six patients with subjective food hypersensitivity, of whom 25 had irritable bowel syndrome (IBS), were included in the present study. Before and after treatment and 1 month posttreatment, patients filled in the Ulcer Esophagitis Subjective Symptoms Scale (UESS) and the Gastrointestinal Symptom Rating Scale (GSRS) for gastrointestinal symptoms and subjective health complaints (SHC) inventory for nongastrointestinal symptoms in addition to short form of the Nepean dyspepsia index (SF-NDI) for evaluation of QoL. Compared with baseline, gastrointestinal, as well as nongastrointestinal, complaints and QoL improved significantly, both at end of treatment and 1 month posttreatment. The consistent improvements following seal oil administration warrant further placebo-controlled trials for confirmation of effect.

A randomized double blind comparison of short-term duodenally administrated whale and seal blubber oils in patients with inflammatory bowel disease and joint pain

Compared with soy oil, 10 days treatment with seal oil (SO), 10mLx3 daily, self-administrated through a nasoduodenal feeding tube, relieves joint pain in patients with inflammatory bowel disease (IBD). This randomized, controlled, double blind pilot trial compares SO and whale oil (WO) administered similarly by duodenal tube, for 10 days in 18 patients with IBD-related joint pain (n=9 per group). Other long chain n-3 polyunsaturated fatty acids were prohibited 7-days prior to and during study. Significant changes from baseline to study end were observed in both groups: reduced plasma arachidonic acid to eicosapentaenoic acid ratio and prostaglandin E(2) (PGE(2)) levels (tendency in WO group), decreased IBD-related joint pain and IBD-disease activity, and improved quality of life. These changes were not significantly different between SO and WO groups. Inhibition of cyclooxygenase is consistent with amelioration of IBD-related joint pain, but, as active control was used, effects need confirmation.

Hepatic metabolism, phase I and II biotransformation enzymes in Atlantic salmon (Salmo Salar, L) during a 12 week feeding period with graded levels of the synthetic antioxidant, ethoxyquin

The synthetic antioxidant ethoxyquin (EQ) is a widely used additive in animal feeds, including farmed fish feed. The use of EQ as food additive is prohibited and it is also undesirable in farmed meat and fish products. The possible negative aspects of EQ in fish feeds, such as modulation of hepatic detoxifying enzymes and possible effects through "carry-over" to edible parts of fish are not known. In addition, the subsequent consequences for human consumers have not been previously studied. In the present work, the alteration in gene and protein expression patterns, and catalytic activities of phase I and II hepatic biotransformation enzymes due to prolonged exposure to graded levels of dietary EQ in the range of 11-1800 mg EQ/kg feed were studied. The kinetics of parent EQ and its major metabolite, ethoxyquin dimer (EQDM) was also studied. In general two weeks seem to be the critical point in the entire toxicological response of salmon to dietary consumed EQ. Biotransformation of EQ to EQDM is shown to be a rapid process. However, the decrease in biotransformation rate results in the accumulation of EQ metabolites, high concentration of which was postulated to alter translation and post-translational modification of CYP3A, GST and UDPGT at feeding day 14 and 42, with subsequent decreases in the biotransformation of consumed EQ. Decrease in the biotransformation of consumed EQ produced the retention of un-metabolized EQ rather than metabolites in salmon liver. This may be considered as undesirable effect, since it could lead to the transport and accumulation in other organs and edible tissues. It may also cause a new wave of biotransformation with formation of metabolites inhibiting detoxifying enzymes. In general, these processes may prolong the excretion of dietary EQ from the fish body and produce EQ-derived residues in the ready-to-consume salmon or fish products. These EQ residues may have higher toxicological effects for human consumers than the parent compound and therefore need to be studied in more detail.

Hepatic biotransformation and metabolite profile during a 2-week depuration period in Atlantic salmon fed graded levels of the synthetic antioxidant, ethoxyquin

The synthetic antioxidant ethoxyquin (EQ) is increasingly used in animal feeds and has been candidate for carcinogenicity testing. EQ has the potential for toxicological and adverse health effects for both fish and fish consumers through "carryover" processes. The toxicological aspects of EQ have not been systematically investigated. The present study was performed to investigate the hepatic metabolism, metabolite characterization, and toxicological aspects of EQ in salmon during a 2-week depuration after a 12-week feeding period with 18 mg (low), 107 mg (medium), and 1800 mg/kg feed (high). The alteration in gene expressions and catalytic activities of hepatic biotransformation enzymes were studied using real-time polymerase chain reaction with specific primer pairs and by kinetics of two identified hepatic metabolites. Analysis of EQ metabolism was performed using high performance liquid chromatography (HPLC) method and showed the detection of four compounds of which two were quantified, parent EQ and EQ dimer (EQDM). Two metabolites were identified as de-ethylated EQ (DEQ) and quinone imine, but these were not quantified. The concentration of the quantified EQ-related compounds in the liver at day 0 showed a positive linear relationship with measured dietary EQ (R2= 0.86 and 0.92 for parent EQ and EQDM, respectively). While the low-EQ-feeding group showed a time-specific increase of aryl hydrocarbon receptor (AhR) mRNA expression, the medium-dose group showed decreased AhR mRNA at depuration day 7. Expression of CYP1A1 was decreased during the depuration period. Consumption of dietary EQ produced the expression of CYP3A, glutathione S-transferase (GST), and uridine diphosphate glucuronosyl-transferase (UDPGT) mRNA during the depuration period. A similar pattern of effect was observed for both CYP3A and phase II genes and supports our previous postulation of common regulation of these enzymes by the same inducer, namely EQ metabolites. The increase of CYP3A, UDPGT, and GST gene expressions at day 7 was in accordance with the low concentration of DEQ. The low concentration of putative DEQ may induce the CYP3A with subsequent increase in the biotransformation of EQ into DEQ. The increase in UDPGT may seem to be a synchronizing mechanism required for the excretion of DEQ. The biotransformation of dietary EQ is proven by simultaneous induction of both phase I and II detoxification system in the liver of Atlantic salmon. Therefore, the apparent low concentration of putative DEQ may account for the induced phase I and II detoxifying enzymes at least during depuration. This speculated hypothesis is currently a subject for systematic investigation in our laboratory using in vitro and genomic approaches.

The role of Drosophila ninaG oxidoreductase in visual pigment chromophore biogenesis

We previously reported (Sarfare, S., Ahmad, S. T., Joyce, M. V., Boggess, B., and O'Tousa, J. E. (2005) J. Biol. Chem. 280, 11895-11901) that the Drosophila ninaG gene encodes an oxidoreductase involved in the biosynthesis of the (3S)-3-hydroxyretinal serving as chromophore for Rh1 rhodopsin and that ninaG mutant flies expressing Rh4 as the major opsin accumulate large amounts of a different retinoid. Here, we show that this unknown retinoid is 11-cis-3-hydroxyretinol. Reversed phase high performance liquid chromatography coupled with a photodiode array UV-visible absorbance detector and mass spectrometer revealed a major product eluting at a retention time, t(r), of 3.5 min with a lambda(max) of approximately 324 nm and with a base peak in the mass spectrum at m/z 285. These observations are identical with those of the 3-hydroxyretinol standard. The base peak in the electrospray ionization mass spectrum arises from the loss of a water molecule from the protonated molecule at m/z 303 because of fragmentation in the ion source. These results suggest that 11-cis-3-hydroxyretinol is an intermediate required for chromophore biogenesis in Drosophila. We further show that ninaG mutants fed on retinal as the sole source of vitamin A are able to synthesize 3-hydroxyretinoids. Thus, the NinaG oxidoreductase is not responsible for the initial hydroxylation of the retinal ring but rather acts in a subsequent step in chromophore production. These data are used to review chromophore biosynthesis and propose that NinaG acts in the conversion of (3R)-3-hydroxyretinol to the 3S enantiomer.

Liquid chromatographic determination of geometrical retinol isomers and carotene in enteral feeding formulas

The objective of the present study was to evaluate a practical method for separation and determination of geometrical retinol isomers and carotene in enteral feeding formulas and to analyze 17 samples of commercial formulas. By using a normal-phase HPLC column and a mobile phase consisting of 1-octanol in n-hexane, seven isomers of retinol were separated and identified from the standard solution after photolysis. For evaluation of Vitamin A activity in these formulas, simultaneous determination of total carotene was performed. The data about linearity, recovery, accuracy and precision showed the reliability of analytical procedures. In the unsaponifiable portion of samples of commercial formulas, six retinol isomers were identified: (E)-retinol; (Z)-13; (Z)-9; (Z,Z)-9,13; (Z,Z)-11,13 and (Z)-7-retinol. (Z)-13/(E)-retinol ratios ranged between 3 and 37%. The range of total Z/(E)-retinol isomers fell between 5 and 42%. Despite the high concentration of Z-isomers observed in various commercial enteral feeding formulas, none of the samples presented Vitamin A activity below 90% of that specified on the label.

Quantitative analysis of vitamin A degradation by Raman spectroscopy

Vitamin A is known to support cell growth promotion, maintenance, and differentiation of epithelial tissues. Retinol is currently used in cosmetic formulations and products to deliver these and other benefits to the skin. However, retinol is known to be unstable and, therefore, remains of great concern to the cosmetic industry. The decomposition pathways of the retinoids in general have been previously postulated and investigated mostly by high-performance liquid chromatography (HPLC) with UV/Vis spectroscopy. In our studies, we examined specific conditions at which retinol degrades and subsequently identified and quantified the products of retinol decomposition by Raman spectroscopy. We reveal which experimental settings and computational tools allow monitoring of in situ evolution of an all-trans retinol solution when submitted to UV light in the presence of oxygen.

A high retinol dietary intake increases its apical absorption by the proximal small intestine of juvenile sunshine bass (Morone chrysops x M. saxatilis)

The relationship between dietary intake and systemic availability of retinol is likely to be complex because although retinol is an essential nutrient, it is toxic at high levels. The present study determined whether rates of transapical retinol absorption are modulated so that availability is increased at low dietary levels, but decreased when dietary intake is excessive. Juvenile hybrid striped bass were fed for 6 wk diets with 568 (below), 1657 (approximating the requirement) and 40,244 (excessive) micro g/kg dry diet of trans retinol. Proximal small intestine segments were used to measure rates of retinol absorption and tissue concentrations. Initial and final body mass did not differ among groups; deficiency and toxicity symptoms were not observed. Uptake of tracer retinol was inhibited by unlabeled retinol, indicating the presence of saturable, carrier-mediated absorption. Increasing dietary levels of retinol increased the rates of absorption measured at 0.05 mmol/L [8.04 +/- 0.65; 15.2 +/- 1.53; 25.1 +/- 3.4 pmol/(mg. min) for below, approximating and exceeding the retinol requirement; P < 0.0001]; this resulted in higher tissue concentrations of all-trans retinol (0.21 +/- 0.03, 0.49 +/- 0.21 and 338 +/- 89 pmol/g; P < 0.0001) and dehydro-retinol (0.11 +/- 0.04, 0.91 +/- 0.04, and 454 +/- 109 pmol/g; P < 0.001). These findings suggest that the systemic availability of various dietary levels of retinol is modulated after transapical absorption.

Qualitative and quantitative liquid chromatographic determination of natural retinoids in biological samples

Liquid chromatography continues to be the preferred method for determining retinoids in biological samples. The highly unstable nature of retinoids and the real possibility of artifacts or erroneous results have led to the development of rapid and highly automated protocols for retinoid extraction, separation and detection. Due to strong light absorbance in the ultraviolet region, UV detectors still predominate although mass spectrometric detection is gaining increased popularity. This paper reviews recent advances and provides major guidelines for using liquid chromatography to identify and quantify retinoids in biological samples.

High-performance liquid chromatography of non-polar retinoid isomers

Normal-phase high-performance liquid chromatograms of retinal, retinol and retinyl palmitate isomers using n-heptane-tert.-butyl methyl ether as mobile phase are presented. Methods for the synthesis of various isomers of these retinoids are described. This enables one to produce standard chromatograms and to select various isomers for cochromatography and the identification of the various peaks under study. Assignment of the peaks is based on chromatograms published previously in this journal. For the main isomers it is possible to get baseline separation of the commonly occurring isomeric forms in a reasonably short analysis time.

A reversed-phase high-performance liquid chromatographic method to analyze retinal isomers

A high-performance liquid chromatographic (HPLC) procedure was developed to separate all-trans-, 13-cis-, 11-cis- and 9-cis-retinal isomers. Two reversed-phase Vydac C18 columns in series were used with an isocratic solvent system of 0.1 M ammonium acetate-acetonitrile (40:60, v/v) as mobile phase and all-trans-9-(4-methoxy-2,3,6-trimethylphenyl)-3,7-dimethyl-2,4,6,8-no natetraene-1-ol (TMMP) as internal standard. Prior to HPLC, the retinal isomers were efficiently extracted in their original isomeric conformation using dichloromethane-n-hexane in the presence of formaldehyde. This technique is suitable for the assay of 11-cis- and all-trans-retinal isomers in retina.