Chromatography of retinoids

One-Step, Low-Cost, Operator-Friendly, and Scalable Procedure to Synthetize Highly Pure N-(4-ethoxyphenyl)-retinamide in Quantitative Yield without Purification Work-Up

It is widely reported that N-(4-hydroxyphenyl)-retinamide or fenretinide (4-HPR), which is a synthetic amide of all-trans-retinoic acid (ATRA), inhibits in vitro several types of tumors, including cancer cell lines resistant to ATRA, at 1–10 µM concentrations. Additionally, studies in rats and mice have confirmed the potent anticancer effects of 4-HPR, without evidencing hemolytic toxicity, thus demonstrating its suitability for the development of a new chemo-preventive agent. To this end, the accurate determination of 4-HPR levels in tissues is essential for its pre-clinical training, and for the correct determination of 4-HPR and its metabolites by chromatography, N-(4-ethoxyphenyl)-retinamide (4-EPR) has been suggested as an indispensable internal standard. Unfortunately, only a consultable old patent reports the synthesis of 4-EPR, starting from dangerous and high-cost reagents and using long and tedious purification procedures. To the best of our knowledge, no article existed so far describing the specific synthesis of 4-EPR. Only two vendors worldwide supply 4-ERP, and its characterization was incomplete. Here, a scalable, operator-friendly, and one-step procedure to synthetize highly pure 4-EPR without purification work-up and in quantitative yield is reported. Additionally, a complete characterization of 4-EPR using all possible analytical techniques has been provided.

Nano-lipoidal carriers of isotretinoin with anti-aging potential: formulation, characterization and biochemical evaluation

BACKGROUND

Treatment of photoaging includes non-prescription cosmeceuticals and prescription products, retinoids. Isotretinoin, an established anti-acne retinoid, is also reported to delay the aging process. However, the drug is reported to be an irritant on skin.

PURPOSE

The present study endeavors to explore the potential of a novel set of biocompatible nano-structured systems of isotretinoin in the treatment of photoaging.

METHODS

Nano-lipoidal carriers (NLCs) of isotretinoin were developed, characterized and investigated in vivo for anti-aging potential in Laca mice vis-à-vis the marketed products of retinoids. The anti-aging efficacy of NLCs was measured in terms of visual and redox-biochemical parameters in ultraviolet (UV)-irradiated mice.

RESULTS

Visual observations revealed that there was no significant change (p < 0.05) w.r.t. erythema, skin sagging and wrinkles in the skin of the animals treated with NLCs formulation compared to the marketed product(s). The malondialdehyde levels were found to be significantly reduced, whereas glutathione levels were increased with the application of NLCs vis-à-vis control and test formulations. The NLCs were able to maintain the normal redox-balance of UV-irradiated skin, and were better tolerated by the animals.

CONCLUSION

The study ratifies enhancement in the efficacy of isotretinoin against photoaging and improved skin biocompatibility after its encasement in novel topical dosage forms.

Inhibition of metastatic lung cancer in C57BL/6 mice by liposome encapsulated all trans retinoic acid (ATRA)

The purpose of this study was to investigate whether all trans retinoic acid (ATRA) incorporated in liposome composed of distearoylphosphatidylcholine (DSPC/cholesterol) could inhibit the metastatic lung cancer in mice more efficiently than free ATRA. Metastatic lung cancer model was developed by intravenous injection of B16F10 cells and it is also referred as melanoma model. In this present study, C57BL/6 mice were divided into several groups as per experimental design and the free ATRA and liposome encapsulated ATRA were given for 21 days at a dose of 0.60 mg/kg body weight/day after cell line implantation. After 21 days, mice were sacrificed at different time interval for ATRA level analysis in serum and lung tissue by HPLC method and the remaining mice were kept for anticancer study. The ATRA level increased significantly in serum and lung tissue in liposome encapsulated ATRA treated mice. In cancer bearing mice, tumor nodule formation decreased and life span increased after receiving liposome encapsulated ATRA treatment than free ATRA treated mice. This result implies that the liposome encapsulated ATRA has maintained more ATRA concentration in lung tissue and showed more inhibition on the lung tumor nodule formation. The results indicate a possible use of liposome encapsulated ATRA in prevention of lung metastasis.

Quantification of retinoid concentrations in human serum and brain tumor tissues

Retinoic acid signaling is essential for central nervous system (CNS) differentiation and appears to be impaired in tumors. Thus far, there are no established methods to quantify relevant retinoids (all-trans-retinoic acid, 9-cis-retinoic acid, 13-cis retinoic acid, and retinol) in human brain tumors. We developed a single step extraction and quantification procedure for polar and apolar retinoids in normal tissue, lipid-rich brain tumor tissues, and serum. This quantification procedure is based on high performance liquid chromatography (HPLC) with diode-array detection (DAD) using all-trans-acitretin as an internal standard and extraction by liquid-liquid partition with ethyl acetate and borate buffer at pH 9. Recovery with this extraction procedure was higher than earlier (two-step) liquid-liquid extraction procedures based on hexane, NaOH, and HCl. The overall quantification procedure was validated according to Food and Drug Administration (FDA) guidelines and fulfilled all criteria of accuracy, precision, selectivity, recovery, and stability. The overall method accuracy varied between -5.6% and +5.4% for serum and -3.8% and +6.2% for tissues, and overall precision ranged from 3.1% to 6.9% for serum and 2.1% to 8.3% for tissues (%CV batch-to-batch). The lower limit of quantification for all compounds in tumor tissue (and serum) was 3.9 ng g(-1) (ng mL(-1)). Using this assay, photodegradation of the retinoids was evaluated and endogenous polar and apolar retinoids were quantified in sera and brain tumor tissues of patients and compared with serum and tonsil tissue concentrations of controls. It may thus serve as a suitable method for the characterization of retinoid uptake and metabolism in the respective compartments.

Quantitative high-throughput determination of endogenous retinoids in human plasma using triple-stage liquid chromatography/tandem mass spectrometry

A high-throughput ultrasensitive analytical method based on liquid chromatography with positive ion atmospheric pressure chemical ionization (APCI) coupled to tandem mass spectrometric detection (LC/MS/MS) was developed for the determination of all-trans-4-oxo-retinoic acid (at4oxoRA), 13-cis-4-oxo-retinoic acid (13c4oxoRA), 13-cis-retinoic acid (13cRA), all-trans-retinoic acid (atRA) and all-trans-retinol (atROH) in human plasma. A stable isotope of atRA was used as internal standard (IS). The analytes and IS were isolated from 100 microL plasma by acetonitrile mono-phase extraction (MPE) performed in black 96-well microtiterplates. A 100 microL injection was focused on-column and chromatographed on an Agilent ZORBAX SB-C18 rapid-resolution high-throughput (RRHT) column with 1.8-microm particles (4.6 mmx50 mm) maintained at 60 degrees C. The initial mobile phase composition was acetonitrile/water/formic acid (10:90:0.1, v/v/v) delivered at 1.8 mL/min. Elution was accomplished by a fast gradient to acetonitrile/methanol/formic acid (90:10:0.1, v/v/v). The method had a chromatographic total run time of 7 min. An Applied Biosystems 4000 Q TRAP linear tandem mass spectrometer equipped with a heated nebulizer (APCI) ionization source was operated in multiple reaction monitoring (MRM) mode with the precursor-to-product ion transitions m/z 315.4-->297 (4-oxo-retinoic acids), 301.2-->205 (retinoic acids), 305.0-->209 (IS) and 269.2-->93 (retinol) used for quantification. The assay was fully validated and found to have acceptable accuracy, precision, linearity, sensitivity and selectivity. The mean extraction recoveries from spiked plasma samples were 80-105% for the various retinoids at three different levels. The intra-day accuracy of the assay was within 8% of nominal and intra-day precision was better than 8% coefficient of variance (CV) for retinoic acids. Inter-day precision results for quality control samples run over a 12-day period alongside clinical samples showed mean precision better than 12.5% CV. The limit of quantification was in the range of 0.1-0.2 ng/mL and the mass limit of detection (mLOD) was in the range 1-4 pg on column for the retinoic acids. The assay has been successfully applied to the analysis of 1700 plasma samples.

Determination of plasma and brain levels of isotretinoin in mice following single oral dose by high-performance liquid chromatography

An isocratic reversed-phase high-performance liquid chromatographic method was established and validated according to FDA's Guidance for Industry, "Bioanalytical Method Validation", for the determination of isotretinoin in plasma and brain tissue from mice following single and multiple oral doses of Accutane. Plasma sample preparation included deproteination with acetonitrile-perchloric acid followed by centrifugation. Brain tissue was homogenized and extracted with acetonitrile-perchloric acid followed by centrifugation. The supernatants were analyzed by high-performance liquid chromatography (HPLC). Benz[alpha]anthrancene-7,12-dione was used as the internal standard. Chromatographic separation was achieved on a C18 column using an acetonitrile-aqueous 0.5% acetic acid (85:15, v/v) elution. The average extraction efficiency was >95% for plasma and >82% for brain. The lower limit of quantification was 30 ng/mL for plasma and was 30 ng/0.1g for brain tissue, respectively. The linear range for plasma was 30-600 ng/mL, and 15-300 ng/0.1g for brain. Maximum concentrations of isotretinoin in both plasma and brain were observed at 1h after single oral dosing (25 mg/kg). The maximum concentrations in plasma and brain were 2.36 microg/mL and 0.34 microg/g, respectively. The mean area under curve (AUC) in plasma was 6.13 microg h/mL. The mean eliminate half-life in plasma was estimated as 46 min.

Chromatographic analysis of endogenous retinoids in tissues and serum

We present a reliable, highly sensitive, and versatile method for the simultaneous determination of endogenous polar (acidic) and apolar (retinol, retinal, and retinyl esters) retinoids in various biological matrices. Following a single liquid extraction of retinoids from tissues or plasma with isopropanol, polar retinoids are separated from apolar retinoids and neutral lipids via automated solid-phase extraction using an aminopropyl phase. After vacuum concentration to dryness and reconstitution of the residue in appropriate solvents, the obtained fractions are injected onto two different high-performance liquid chromatography (HPLC)-systems. Polar retinoids are analyzed on a RP18 column (2.1mm ID) using a buffered gradient composed of methanol and water and on-column-focusing large-volume injection. Apolar retinoids are separated on a normal-bore RP18 column using a nonaqueous gradient composed of acetonitrile, chloroform, and methanol. Both HPLC systems are coupled with UV detection, and retinoids are quantitated against appropriate internal standards. The method was validated with regard to recovery, precision, robustness, selectivity, and analyte stability. Using 400 microl serum or 200mg tissue, the limits of detection for all-trans-retinoic acid were 0.15ng/ml or 0.3ng/g, respectively. The corresponding values for retinol were 1.2ng/ml or 2.4ng/g, respectively. This method was successfully applied to mouse, rat, and human tissue and serum samples.

Formulation parameters determining the physicochemical characteristics of solid lipid nanoparticles loaded with all-trans retinoic acid

Solid lipid nanoparticles (SLNs) have gained attention as a colloidal drug carrier, particularly for drugs with limited solubility. The poor aqueous solubility of all-trans retinoic acid (ATRA) has been a limiting factor in its clinical use. This study was undertaken to overcome the solubility limitation of ATRA by loading in SLNs. The physicochemical characteristics of ATRA-loaded SLNs were investigated by particle size analysis, zeta potential measurement, thermal analysis and HPLC determination of ATRA content. The mean particle size of ATRA-loaded SLNs could be reduced (1) by mixing EggPC and Tween 80 as a surfactant and (2) by increasing the total surfactant amount. The smallest mean particle size of SLNs was obtained with 50 mg/g surfactant mixture composed of 54:46% (w/w) EggPC:Tween 80 (154.9 nm). The zeta potential of SLNs could be increased by mixing EggPC, Tween 80 and DSPE-PEG in the surfactant mixture. The zeta potential of SLNs prepared with 50 mg/g surfactant mixture composed of 48:6:46% (w/w) of EggPC:DSPE-PEG:Tween 80 was -38.18 mV. ATRA could be loaded at 2.4% (percentage of lipid matrix) on these SLNs without impairing their physical stability. After freeze-drying, the mean particle size and polydispersity index of ATRA-loaded SLNs were only slightly increased (181.8 vs. 265.2 nm, 0.173 vs. 0.200). Furthermore, no significant change was observed in the SLN-loaded concentration of ATRA and the zeta potential of SLNs after freeze-drying. Taken together, SLN formulation of ATRA with similar characteristics to those of parenteral emulsions could be obtained even after freeze-drying.

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.

Determination of 13-cis-3-hydroxyretinoic acid, all-trans-3-hydroxyretinoic acid and their 4-oxo metabolites in human and animal plasma by high-performance liquid chromatography with automated column switching and UV detection

A high-performance liquid chromatographic method with automated column switching was developed for the simultaneous determination of 13-cis-3-hydroxyretinoic acid, all-trans-3-hydroxyretinoic acid and their metabolites 13-cis-3-hydroxy-4-oxo-retinoic acid and all-trans-3-hydroxy-4-oxo-retinoic acid in plasma samples from man, rat, dog, rabbit and mouse. The method consists of deproteination of plasma (0.4 ml) with ethanol (1.5 ml), containing the internal standard Ro 12-7310. After centrifugation, 1.4 ml of the supernatant was directly injected onto the precolumn (PC) (4 x 4 mm) packed with LiChrospher 100 RP-18 (5 microm). Ammonium acetate (0.02%)-acetic acid-ethanol (100:3:4, v/v/v) was used as mobile phase M1A during injection, as well as to decrease the elution strength of the injection solution by on-line addition using a T-piece (M1B). After valve switching, the retained components were transferred to the analytical column (AC), separated by gradient elution and detected at 360 nm. Two coupled Purospher 100 RP-18 endcapped columns (both 250 x 4 mm) were used for the separation, together with a mobile phase consisting of acetonitrile-water-10% ammonium acetate-acetic acid, (A), 540:450:2:30 (v/v/v/v), (B), 600:350:2:30 (v/v/v/v), and (C), 950:40:2:30 (v/v/v/v). The method was linear in the range 1-500 ng ml(-1), at least, with a quantification limit of 1 ng ml(-1). The mean recoveries from human plasma were 100-107% and the mean inter-assay precision was 2.0-4.7% (range 1-500 ng ml(-1)). Similar results were obtained for animal plasma. The analytes were stable in the plasma of all investigated species stored at -20 degrees C for 3 months, at least. The method was successfully applied to clinical and toxicokinetic studies.

Determination of endogenous levels of 13-cis-retinoic acid (isotretinoin), all-trans-retinoic acid (tretinoin) and their 4-oxo metabolites in human and animal plasma by high-performance liquid chromatography with automated column switching and ultraviolet detection

A highly sensitive HPLC method with automated column switching was developed for the simultaneous determination of endogenous levels of 13-cis-retinoic acid (isotretinoin), all-trans-retinoic acid (tretinoin) and their 4-oxo metabolites in plasma samples from man, Cynomolgus monkey, rabbit, rat and mouse. Plasma (0.4 ml) was deproteinated by adding ethanol (1.5 ml) containing the internal standard acitretin. After centrifugation, 1.4 ml of the supernatant were directly injected onto the precolumn packed with LiChrospher 100 RP-18 (5 microm). 1.25% ammonium acetate and acetic acid-ethanol (8:2, v/v) was used as mobile phase during injection and 1% ammonium acetate and 2% acetic acid-ethanol (102:4, v/v) was added, on-line, to decrease the elution strength of the injection solution. After backflush purging of the precolumn, the retained components were transferred to the analytical column in the backflush mode, separated by gradient elution and detected at 360 nm. Two coupled Superspher 100 RP-18 endcapped columns (both 250x4 mm) were used for the separation, together with a mobile phase consisting of acetonitrile-water-10% ammonium acetate-acetic acid: (A) 600:300:60:10 (v/v/v/v), (B) 950:20:5:20 (v/v/v/v), and (C) 990:5:0:5 (v/v/v/v). The method was linear in the range 0.3-100 ng/ml, at least, with a quantification limit of 0.3 ng/ml. The mean recoveries from human plasma were 93.2%-94.4% and the mean inter-assay precision was 2.8%-3.2% (range 0.3-100 ng/ml). Similar results were obtained for animal plasma. The analytes were found to be stable in the plasma of all investigated species stored at -20 degrees C for 4.3 months and at -80 degrees C for 9 months, at least. At this temperature, human plasma samples were even stable for 2 years. The method was successfully applied to more than 6000 human and 1000 animal plasma samples from clinical and toxicokinetic studies. Endogenous levels determined in control patients and pregnant women were similar to published data from volunteers.

Quantitative high-performance liquid chromatographic determination of retinoids in human serum using on-line solid-phase extraction and column switching. Determination of 9-cis-retinoic acid, 13-cis-retinoic acid, all-trans-retinoic acid, 4-oxo-all-trans-retinoicacid and 4-oxo-13-cis-retinoic acid

A fully automated isocratic high-performance liquid chromatographic method for the determination of 9-cis-retinoic acid, 13-cis-retinoic acid, all-trans-retinoic acid, 4-oxo-13-cis-retinoic acid and 4-oxo-all-trans-retinoic acid, has been developed using on-line solid-phase extraction and a column switching technique allowing clean-up and pre-concentration in a single step. A 500-microliter sample of serum was diluted with 750 microliters of a solution containing 20% acetonitrile and the internal standard 9,10-dimethylanthracene. About 1000 microliters of this mixture was injected on a 20 x 4.6 mm I.D. poly ether ether ketone (PEEK) pre-column with titanium frits packed with Bondapak C18, 37-53 microns, 300 A particles. Proteins and very polar compounds were washed out to waste, from the pre-column, with 0.05% trifluoroacetic acid (TFA)-acetonitrile (8.5:1.5, v/v). More than 200 aliquots of diluted serum could be injected on this pre-column before elevated back-pressure enforces replacement. Components retained on the pre-column were backflushed to the analytical column for separation and detection at 360 nm. Baseline separation was achieved using a single 250 x 4.6 mm I.D. Suplex pKb-100 column and a mobile phase containing 69:10:2:16:3 (v/v) of acetonitrile-methanol-n-butanol-2% ammonium acetate-glacial acetic acid. A total time of analysis of less than 30 min, including sample preparation, was achieved. Recoveries were in the range of 79-86%. The limit of detection was 1-7 ng/ml serum and the precision, in the concentration range 20-1000 ng/ml, was between 1.3 and 4.5% for all five compounds. The method was applied for the analysis of human serum after oral administration of 60 mg Roaccutan. The method is well suited for pharmacological studies, while the endogenous levels of some retinoic acid isomers are below the limit of quantitation.

Simultaneous determination of all-trans-, 13-cis- and 9-cis-retinoic acid, their 4-oxo metabolites and all-trans-retinol in human plasma by high-performance liquid chromatography

All-trans-retinoic acid (all-trans-RA) and 13-cis-retinoic acid (13-cis-RA), due to their effects on cell differentiation, proliferation and angiogenesis, improved treatment results in some malignancies. Pharmacokinetic studies of all-trans-RA and 13-cis-RA along with monitoring of retinoic acid metabolites may help to optimize retinoic acid therapy and to develop new effective strategies for the use of retinoic acids in cancer treatment. Therefore, we developed a HPLC method for the simultaneous determination in human plasma of the physiologically important retinoic acid isomers, all-trans-, 13-cis- and 9-cis-retinoic acid, their 4-oxo metabolites, 13-cis-4-oxoretinoic acid (13-cis-4-oxo-RA) and all-trans-4-oxoretinoic acid (all-trans-4-oxo-RA), and Vitamin A (all-trans-retinol). Analysis was performed on a silica gel column with UV detection at 350 nm using a binary multistep gradient composed of n-hexane, 2-propanol and glacial acetic acid. For liquid-liquid extraction a mixture of n-hexane, dichloromethane and 2-propanol was used. The limits of detection were 0.5 ng/ml for retinoic acids and 10 ng/ml for all-trans-retinol. The method showed good reproducibility for all components (within-day C.V.: 3.02-11.70%; day-to-day C.V.: 0.01-11.34%). Furthermore, 9-cis-4-oxoretinoic acid (9-cis-4-oxo-RA) is separated from all-trans-4-oxo-RA and 13-cis-4-oxo-RA. In case of clinical use of 9-cis-retinoic acid (9-cis-RA) the pharmacokinetics and metabolism of this retinoic acid isomer can also be examined.

Fully automated determination of selective retinoic acid receptor ligands in mouse plasma and tissue by reversed-phase liquid chromatography coupled on-line with solid-phase extraction

A fully automated reversed-phase HPLC method was developed for the quantitative assay of three retinoids (Am-580, CD-2019 and CD-437) which selectively activate the retinoic acid receptors RAR alpha, RAR beta and RAR gamma, respectively. Mouse plasma, embryo and maternal tissues were prepared for injection by on-line solid-phase extraction (SPE) and valve-switching techniques. Following automatic injection, the sample was loaded on preconditioned disposable cartridges, cleaned-up and then transferred onto the analytical column to be eluted in the backflush mode, separated by gradient elution and detected by UV, while a new cartridge was concomitantly conditioned. The overall recovery was quantitative allowing for external standardization. The calibration curves were linear in all biological samples tested so far, with a correlation coefficient (r) >0.99. The intra-day precision was < or = 7.8% (n = 5-6) and the inter-day variability was < or = 9.4% (n = 3). The lower limit of detection was 2.5 ng/ml or ng/g for CD-2019 and CD-437, and 5 ng/ml for Am-580 with a S/N ratio of 5 using a sample weight of 25 microliters or mg. The method is now in routine use in our laboratory for the assessment of the pharmacokinetic profiles of these retinoids. The small sample size required, the simple sample preparation and the rapid analysis with high degree of automation make this method convenient for microanalysis of biological samples both in animal and human studies.

Determination of the arotinoid mofarotene in human, rat and dog plasma by high-performance liquid chromatography with automated column switching and ultraviolet detection

A sensitive and specific high-performance liquid chromatographic method was developed and validated for the determination of the third-generation retinoid (arotinoid) mofarotene (Ro 40-8757) in human, rat and dog plasma, using direct injection of deproteinated plasma samples, automated column switching (on-line solid-phase extraction) and ultraviolet detection. Plasma (0.5 ml) was deproteinated by adding ethanol (1 ml) containing the internal standard Ro 42-8659 (200 ng/ml). After centrifugation, 0.9 ml of the supernatant were directly injected onto a precolumn packed with C18 Corasil 37-50 microns. Polar plasma components were washed out from the precolumn using 1% ammonium acetate-acetic acid-acetonitrile (900:9:100, v/v/v). After valve switching, the pre-concentrated compounds were transferred to the analytical column (C18) in the backflush mode, separated by gradient elution and detected at 300 nm. The retention times (total run times) were approximately 15 and 20 min for the internal standard and mofarotene, respectively. The method was linear in the range 10-1000 ng/ml with a limit of quantification of 10 ng/ml. The mean recoveries were 80.4%, 81.7% and 77.8% (range 10-1000 ng/ml) and the inter-assay precision was 2.7% (range 20-1000 ng/ml), 1.5% and 2.0% (both range 100-1000 ng/ml) for human, rat and dog plasma, respectively. Mofarotene was found to be stable in human, rat and dog plasma stored at -20 degrees C for 3 months and 22 degrees C for 24 h. The method was successfully applied to clinical, pharmacokinetic and toxicokinetic studies.

Chromatographic and electrophoretic analysis of biomedically important retinoids

The determination of retinol (vitamin A) and its metabolites, as well as synthetic retinoids, in biological samples is a challenging task due to the sensitivity of these compounds to light, heat and oxygen, high protein binding, separation of geometric isomers and determination of low endogenous levels. Numerous procedures for sample preparation have been published for biological fluids and tissues, consisting of solvent extraction, solid-phase extraction (off-line) and HPLC with column switching (on-line solid-phase extraction). The last-mentioned technique has several advantages, including a high degree of automation, no evaporation of extraction solvents, protection from light and higher sensitivity. Due to the favourable UV characteristics of most retinoids, HPLC with UV detection is most often employed, and photodiode array detection is becoming more and more popular. Fluorescence and electrochemical detection have found only a limited field of application, but the use of LC-MS resulted in a few highly sensitive methods. Reconsideration of GC through the use of better deactivated columns and cold on-column injection and evaluation of new promising separation methods, such as supercritical fluid chromatography and capillary electrophoresis, have shown preliminary encouraging results, but appear to reach the required sensitivity only by coupling to MS. Therefore, HPLC with UV detection is still the method of choice for highly sensitive and selective retinoid determination, as well as for high sample throughput and robustness.

Determination of the retinobenzoic acid derivative Am580 in rat plasma by high-performance liquid chromatography

A specific liquid chromatographic method for the determination of 4-[[(5,6,7,8,8-tetrahydro-5,5,8,8-tetramethyl-2- naphthalenyl)carbonyl]amino]benzoic acid (Am580) in rat plasma is described. The procedure includes one-step isolation of the compound and the internal standard (naphthol AS) from protein precipitated with acetonitrile, resolution on a reversed-phase column (Supelcosil LC18-DB, 5 microns) with water-acetonitrile-methanol-n-butanol (45:40:14:1, v/v) containing 65 mM ammonium acetate as elution system and UV absorbance detection at 280 nm. The assay was linear over a wide range (25-5000 ng ml-1) and the limit of quantitation was 25 ng ml-1 using 0.2 ml of plasma. It was precise and reproducible enough for pharmacokinetic studies. Application to a preliminary disposition study in the rat indicated that Am580 was characterized by a relatively large apparent volume of distribution (1.1-1.5 1 kg-1) and small clearance (8.8-9.7 ml min-1 kg-1). Its pharmacokinetic behaviour was linear within the dose range considered (2 and 10 mg kg-1, i.p.).

Determination of serum retinol by reversed-phase high-performance liquid chromatography

A rapid, sensitive and specific high-performance liquid chromatographic method was developed for the determination of serum levels of retinol in humans. A direct serum injection technique after deproteinisation was used to avoid lengthy pretreatment steps which can result in degradation of retinol during analysis. The column used was CLC-ODS, the mobile phase was acetonitrile-water and detection wavelength was 328 nm. Deterioration in column performance was not observed even after injection of 300 samples. The lower detection limit was 10 micrograms/l. On analyzing a serum pool six times, a C.V. of 0.7% was obtained. The method is quantitative, reproducible, rapid and highly accurate for routine analysis.

Simultaneous determination of all-trans and 13-cis retinoic acids and their 4-oxo metabolites by adsorption liquid chromatography after solid-phase extraction

All-trans retinoic acid (all-trans RA), the active metabolite of vitamin A, has been demonstrated to be an efficient alternative to chemotherapy in the treatment of acute promyelocytic leukemia (APL), the AML3 subtype of the FAB cytological classification. Complete remission is obtained by inducing terminal granulocytic differentiation of the leukemic cells. To study all-trans RA pharmacokinetics in patients with APL, a rapid, precise and selective high-performance liquid chromatographic (HPLC) assay was developed. This method is easy and shows good repeatability (C.V. = 8.41-12.44%), reproducibility (C.V. = 9.19-14.73%), accuracy (C.V. = 3.5-11%) and sensitivity with a detection limit of 5 pmol/ml. The analysis is performed using normal-phase HPLC in an isocratic mode with UV detection after solid-phase extraction on octadecyl (C18) columns. The mobile phase is hexane-dichloromethane-dioxane (78:18:4, v/v) containing 1% acetic acid.

Simultaneous determination of 13-cis- and all-trans-retinoic acids and retinol in human serum by high-performance liquid chromatography

A simple and accurate method was developed for the simultaneous determination of 13-cis- and all-trans-retinoic acid (13cRA, tRA), and retinol (ROH) in human serum using isocratic high-performance liquid chromatography (HPLC). The serum sample (0.2 ml) was diluted with 2 ml of acetonitrile-100 mM ammonium acetate (1:3, v/v), pH 5.5, and extracted with 5 ml of n-hexane. The extract was analyzed on an ODS column with a mobile phase consisting of 70 vols. of acetonitrile-methanol (2:1) and 30 vols. of 100 mM ammonium acetate, pH 7.0, at 50 degrees C. The retinoids were detected at 340 nm. Average recoveries were 88.4% for 13cRA, 82.5% for tRA at fortification levels of 5, 10 and 25 ng/ml, and 84.8% for ROH at 550 ng/ml. Within-day precision for normal human serum samples was 4.7% for 13cRA, 11.9% for tRA and 3.7% for ROH, and between-day precision was 10.4%, 14.2% and 4.7%, respectively. The limit of determination was 0.5 ng/ml in serum for the RAs. Mean concentration in 20 human sera was found to be 1.80 ng/ml for 13cRA, 1.77 ng/ml for tRA, and 487 ng/ml for ROH.

Determination of acitretin in the skin, in the suction blister, and in plasma of human volunteers after multiple oral dosing

Several HPLC methods for quantification of acitretin and its 13-cis isomer in biological fluids have been described. Only limited data are available on determination of this drug in skin samples. Our objective was to improve the sensitivity and selectivity of existing methods to measure drug in small skin samples from humans treated with acitretin. With a new optimized mobile phase [methanol: acetonitrile (7:3, v/v), purified water with 1.5% (v/v) acetic acid, mixed in a 85:15 ratio (v/v)] and a new internal standard (arotinoid ethyl sulfone), a limit of quantification of 1 ng/g tissue was reached. Nine male volunteers were given an oral daily dose of 50 mg acitretin for up to 28 days. Blood and skin samples (punch and shave biopsies, suction blister skin, and fluid) were taken at various time points during and after treatment. Drug concentration and metabolism in plasma and skin samples appeared to be linked in that the trans-isomer concentration was always higher than the cis-isomer concentration during dosing and 3 h after the last dose. However, 7 and 14 days after the last dose in plasma and in all tissue samples (except the shave biopsy), the all-trans-acitretin concentration rapidly decreased and approached the detection limit. In the shave biopsy, the all-trans-acitretin concentration remained higher than the 13-cis-acitretin concentration. Furthermore, the elimination of two isomers from the shave biopsy was delayed.(ABSTRACT TRUNCATED AT 250 WORDS)

Solid-phase extraction technique for the analysis of biological samples

This article reviews the literature on solid-phase extraction published in the last 10 years. Emphasis has been placed on dealing with samples of biological origin. The sections consist of introduction, history and development, types of columns, selection of a suitable column, types of samples, advantages and applications.

Micro liquid chromatography-mass spectrometry with direct liquid introduction used for separation and quantitation of all-trans- and 13-cis-retinoic acids and their 4-oxo metabolites in human plasma

The separation and quantitation of the pentafluorobenzyl derivatives of all-trans- and 13-cis-retinoic acids and their 4-oxo metabolites in human plasma on micro high-performance liquid chromatographic columns (0.32 mm I.D.) is described. The column outlet was directly coupled to the source of a quadrupole mass spectrometer via a simple SFC-frit interface. Negative ion chemical ionization conditions were obtained by coaxial introduction of ammonia as a reagent gas. A signal-to-noise ratio well above 3 was obtained for 1 pg of each analyte injected. The limit of quantitation calculated from spiked biological plasma extracts was 0.3 ng/ml.

Pharmacokinetics and drug interactions of etretinate and acitretin

Acitretin, the metabolite of etretinate, is eliminated far more rapidly from the human body than is etretinate. It had therefore been suggested that only a short period of contraception would be required after the cessation of long-term therapy with acitretin. However, recent studies have demonstrated the presence of etretinate in the plasma of patients who were treated with acitretin. In this article we provide results from a study in our center and discuss earlier data in light of the recently discovered metabolic pathways for acitretin. Reesterification of acitretin to etretinate, however, results in a loss of the metabolic advantages of acitretin. Because of this situation the recommended contraception period after acitretin therapy has been lengthened to 2 years.

Chromatographic determination of vitamins in foods

Chromatographic methods for the determination of water- and fat-soluble vitamins in foods are reviewed. For each vitamin, sample preparation, detection problems and chromatographic conditions are presented and discussed. High-performance liquid chromatography (HPLC) is becoming a standard method in vitamin assay, especially for routine work. HPLC systems can be automated using in-line solid-phase extraction and column switchings, resulting in very sensitive methods, even when simple UV detection is employed.

High-performance liquid chromatographic method for routine determination of vitamins A and E and beta-carotene in plasma

A simple and reliable reversed-phase high-performance liquid chromatographic (HPLC) method for the routine determination of vitamins A and E and beta-carotene in plasma (or serum) with wavelength-programmed ultraviolet-visible absorbance detection is described. A 200-microliters aliquot of serum or plasma sample, after deproteinization with ethanol, and containing tocopherol acetate as internal standard, was extracted with butanol-ethyl acetate. Sodium sulphate was added for dehydration. Analytes of extracted samples were found to be stable for at least four days. A 10-microliters aliquot of this organic extract was used for HPLC analysis. The mobile phase was methanol-butanol-water (89.5:5:5.5, v/v) and the flow-rate was set at 1.5 ml/min. The analytes of interest were well separated from other plasma constituents within 22 min at 45 degrees C. The lowest detection limits of vitamins A and E and beta-carotene were 0.02, 0.5 and 0.1 microgram/ml, respectively. The recovery and reproducibility of the present method were around 90%. The method is sensitive, specific and can be used for epidemiological studies and for routine determination of vitamin deficiency. Several important factors that may affect the analysis are also discussed in this paper.

Quantitative analysis of retinoids in biological fluids by high-performance liquid chromatography using column switching. III. Determination of the arotinoid sumarotene and its Z-isomer in human and animal plasma

A fully automated and sensitive high-performance liquid chromatographic method, using on-line solid-phase extraction, automated column switching and ultraviolet detection, was developed for the third-generation retinoid (arotinoid) sumarotene (methyl p-[(E)-2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthyl)propenyl]phe nyl sulphone; Ro 14-9706) and its Z-isomer. Nearly quantitative recoveries for human, rat and dog plasma were obtained by addition of acetonitrile (final content ca. 17%) to the plasma sample prior to injection. No isomerization was observed when the samples were stored in the autosampler for more than 20 h. The injection volume was 0.5 ml, resulting in quantification limits of 1 ng/ml for sumarotene and 2 ng/ml for the Z-isomer. More than 40 injections could be made on to one precolumn, allowing routine overnight injections. Using a 1-ml injection volume, the limit of quantification for sumarotene could be improved to 0.5 ng/ml. The method was applied to toxicokinetic studies in rats and dogs, and was used to monitor human plasma samples after repeated topical application. The method could also be adapted to etarotene (Ro 15-1570), which was used as an internal standard, and which is at present in clinical development.

Simple reversed-phase high-performance liquid chromatographic method for 13-cis-retinoic acid in serum

An isocratic reversed-phase high-performance liquid chromatographic method for the analysis of 13-cis-retinoic acid in serum is developed. Sample preparation includes deproteination with acetonitrile-perchloric acid-acetic acid followed by centrifugation. 9-Methylanthracene is used as the internal standard. Chromatographic separation is achieved on a C18 column (Zorbax) using an acetonitrile-aqueous 0.5% acetic acid (85:15, v/v) eluent containing 0.05% (w/v) sodium hexanesulfonate. The limit of detection is 12 ng/ml in serum, using 0.5 ml samples. Quantitative recoveries and excellent intra-day and inter-day precision are reported.

Use of direct injection precolumn techniques for the high-performance liquid chromatographic determination of the retinoids acitretin and 13-cis-acitretin in plasma

A previously developed highly sensitive high-performance liquid chromatographic method for the determination of retinoids, using direct injection of large plasma volumes, on-line solid-phase extraction and ultraviolet detection, was improved and fully validated for the determination of acitretin and 13-cis-acitretin in plasma samples. The addition of acetonitrile to improve the recovery was performed on-line by a T-piece, avoiding any cis-trans isomerization which could occur when acetonitrile was added prior to storage in the autosampler. About 30 injections could be made onto one precolumn despite the large injection volume (1 ml of plasma containing the internal standard). Full automation was attained by the use of automated precolumn replacement. In addition, forward- and back-flush purging of the precolumn enhanced the longevity of the analytical column. This consisted of three coupled C18 columns of 125 mm length each. The quantification limit was 0.3 ng/ml, using ultraviolet detection at 360 nm, and the mean inter-assay precision was 3.8% for the two compounds.