Newer approaches to the isolation, identification, and quantitation of steroids in biological materials

Applications of chromatographic methods in metabolomics: A review

Chromatography is a robust and reliable separation method that can use various stationary phases to separate complex mixtures commonly seen in metabolomics. This review examines the types of chromatography and stationary phases that have been used in targeted or untargeted metabolomics with methods such as mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy. General considerations for sample pretreatment and separations in metabolomics are considered, along with the various supports and separation formats for chromatography that have been used in such work. The types of liquid chromatography (LC) that have been most extensively used in metabolomics will be examined, such as reversed-phase liquid chromatography and hydrophilic liquid interaction chromatography. In addition, other forms of LC that have been used in more limited applications for metabolomics (e.g., ion-exchange, size-exclusion, and affinity methods) will be discussed to illustrate how these techniques may be utilized for new and future research in this field. Multidimensional LC methods are also discussed, as well as the use of gas chromatography and supercritical fluid chromatography in metabolomics. In addition, the roles of chromatography in NMR- vs. MS-based metabolomics are considered. Applications are given within the field of metabolomics for each type of chromatography, along with potential advantages or limitations of these separation methods.

Sterolomics in biology, biochemistry, medicine

In mammalian systems "sterolomics" can be regarded as the quantitative or semi-quantitative profiling of all metabolites derived from cholesterol and its cyclic precursors. The system can be further complicated by metabolites derived from ingested phytosterols or pharmaceuticals, but this is beyond the scope of this article. "Sterolomics" can be performed on either an unbiased global format, or more usually, exploiting a targeted format. Here we discuss the different mass spectrometry-based analytical techniques used in "sterolomics" giving specific examples in the context of neurodegenerative disease and for the diagnosis of inborn errors of metabolism. We pay particular attention to the profiling of cholesterol metabolites in the bile acid biosynthesis pathways, although the analytical techniques discussed are also appropriate for analysis of hormonal steroids.

Analytical challenges for measuring steroid responses to stress, neurodegeneration and injury in the central nervous system

Levels of steroids in the adult central nervous system (CNS) show marked changes in response to stress, degenerative disorders and injury. However, their analysis in complex matrices such as fatty brain and spinal cord tissues, and even in plasma, requires accurate and precise analytical methods. Radioimmunoassays (RIA) and enzyme-linked immunosorbent assays, even with prepurification steps, do not provide sufficient specificity, and they are at the origin of many inconsistent results in the literature. The analysis of steroids by mass spectrometric methods has become the gold standard for accurate and sensitive steroid analysis. However, these technologies involve multiple purification steps prone to errors, and they only provide accurate reference values when combined with careful sample workup. In addition, the interpretation of changes in CNS steroid levels is not an easy task because of their multiple sources: the endocrine glands and the local synthesis by neural cells. In the CNS, decreased steroid levels may reflect alterations of their biosynthesis, as observed in the case of chronic stress, post-traumatic stress disorders or depressive episodes. In such cases, return to normalization by administering exogenous hormones or by stimulating their endogenous production may have beneficial effects. On the other hand, increases in CNS steroids in response to acute stress, degenerative processes or injury may be part of endogenous protective or rescue programs, contributing to the resistance of neural cells to stress and insults. The aim of this review is to encourage a more critical reading of the literature reporting steroid measures, and to draw attention to the absolute need for well-validated methods. We discuss reported findings concerning changing steroid levels in the nervous system by insisting on methodological issues. An important message is that even recent mass spectrometric methods have their limits, and they only become reliable tools if combined with careful sample preparation.

Steroids excreted in urine by neonates with 21-hydroxylase deficiency. 3. Characterization, using GC-MS and GC-MS/MS, of androstanes and androstenes

Urine from neonates with 21-hydroxylase deficiency contains a large range of androstane(ene)s, many of which have not been previously described. We present their characterization as the third part of a comprehensive study of urinary steroids, aiming to enhance the diagnosis of this disorder and to further elucidate steroid metabolism in neonates. Steroids were analyzed, after extraction and enzymatic conjugate hydrolysis, as methyloxime-trimethylsilyl ether derivatives on gas-chromatographs coupled to quadrupole and ion-trap mass-spectrometers. GC-MS and GC-MS/MS spectra were used together to determine the structure of hitherto undescribed androstane(ene)s. GC-MS/MS was pivotal for the structural characterization of 2-hydroxylated androstenediones but GC-MS was generally more informative for androstane(ene)s, in contrast to 17-hydroxylated pregnane(ene)s. Parallels were found between the GC-MS and GC-MS/MS characteristics of structurally similar androstenediones and progesterones without a substituent on the D-ring, but not with those of 17-hydroxylated progesterones. Assignment of 5α(β) orientation, based on GC-MS characteristics, was possible for 11-oxo-androstanes. The major endogenous 3β-hydroxy-5-enes in 21-hydroxylase deficiency did not differ from those in unaffected neonates. The key qualitative and quantitative differences encompassed 5α(β)-androstanes and 3-oxo-androst-4-enes. Major positions of hydroxylation in these were C(2), C(6), C(11), C(16) and C(18). Additional oxo-groups were common at C(6), C(11) and C(16). We conclude that the presence of multiple further oxygenated metabolites of androstenedione in urine from neonates with 21-hydroxylase deficiency and their pattern indicate a predominance of the classical pathway of androgen synthesis and reflect an increased demand for clearance. The positions of oxygenation in androstane(ene)s are dependent on the configuration at C(3)-C(5).

Laser-induced oxidation of cholesterol observed during MALDI-TOF mass spectrometry

Conditions for the detection of three odd-electron cholesterol oxidation peaks were determined and these peaks were shown to be artifacts of the matrix-assisted laser desorption time of flight (MALDI-TOF) process. Matrix choice, solvent, laser intensity and cholesterol concentration were systematically varied to characterize the conditions leading to the highest signals of the radical cation peaks, and it was found that initial cholesterol solution concentration and resultant density of solid cholesterol on the MALDI target were important parameters in determining signal intensities. It is proposed that hydroxyl radicals, generated as a result of laser irradiation of the employed 2,5-dihydroxybenzoic acid (DHB) matrix, initiate cholesterol oxidation on the MALDI target. An attempt to induce the odd-electron oxidation peaks by means of adding an oxidizing agent succeeded using an acetonitrile solution of DHB, cholesterol, and cumene hydroperoxide. Moreover, addition of free radical scavengers reduced the abundances of some oxidation products under certain conditions. These results are consistent with the mechanism of oxidation proposed herein involving laser-induced hydroxyl radical production followed by attack on neutral cholesterol. Hydroxyl radical production upon irradiation of dithranol matrix may also be responsible for generation of the same radical peaks observed from cholesterol in dithranol by an analogous mechanism.

Analytical strategies for characterization of bile acid and oxysterol metabolomes

Cholesterol is the precursor of many compounds with functions in the physiology and metabolism of the organism. Methods for the multicomponent analysis of these compounds and their metabolites (metabolomics) are needed to improve our understanding of their roles in different species, organs, cells and metabolic situations and to clarify structure/activity relationships. This review discusses methods based on combinations of ion exchange and reversed-phase separations for sample preparation with derivatization and "charge-tagging" for chromatography-mass spectrometry in qualitative and quantitative characterizations of oxysterol, bile alcohol, bile acid, and steroid hormone metabolomes. Advantages, disadvantages and potential improvements for high-throughput applications are briefly discussed.

Molecular ions and protonated molecules observed in the atmospheric solids analysis probe analysis of steroids

Atmospheric pressure chemical ionisation (APCI) has often been used to ionise steroids in mass spectrometry, usually when interfaced to high-performance liquid chromatography (HPLC). However, in positive ion mode, a dehydrated protonated molecule is often observed with a loss of structural information. The recently introduced technique of atmospheric solids analysis probe (ASAP) has the advantage that the sample can be analysed directly and does not need to be interfaced to HPLC. Existing ionisation sources such as direct analysis in real time (DART) and desorption electrospray ionisation (DESI) have shown the advantage of direct analysis techniques in a variety of applications. ASAP can be performed on commercial atmospheric pressure ionisation (API) mass spectrometers with only simple modifications to API sources. The samples are vaporised by hot nitrogen gas from the electrospray desolvation heater and ionised by a corona discharge. A range of commercially available steroids were analysed by ASAP to investigate the mechanism of ionisation. ASAP analysis of steroids generally results in the formation of the parent molecular ion as either the radical cation M+* or the protonated molecule MH+. The formation of the protonated molecule is a result of proton transfer from ionised water clusters in the source. However, if the source is dry, then formation of the radical cation is the primary ionisation mechanism.

Steroids excreted in urine by neonates with 21-hydroxylase deficiency: characterization, using GC-MS and GC-MS/MS, of the D-ring and side chain structure of pregnanes and pregnenes

Steroid metabolites in urine from neonates with 21-hydroxylase deficiency are predominantly polyhydroxylated 17-hydroxyprogesterone and androgen metabolites, and most have incompletely defined structure. This study forms part of a comprehensive project to characterize and identify these in order to enhance diagnosis and to further elucidate neonatal types of steroid metabolism. Steroids were analyzed, after extraction and enzymatic conjugate hydrolysis, as methyloxime-trimethylsilyl ether derivatives on gas-chromatographs coupled to quadrupole and ion-trap mass-spectrometers. GC-MS and GC-MS/MS spectra, obtained with constant excitation conditions, were used together to determine the structure of the D-ring and the side chain of 20-oxo and 20-hydroxy pregnane(ene)s without oxo groups on the A-, B-, and C-ring. All possible combinations of D-ring and side chain configuration were considered. Most fragmentations could be interpreted as partial or complete D-ring cleavages with loss of the side chain, aided by comparison with spectra of deuterated derivatives and of borohydride reduced metabolites. Possible rearrangement ions are also discussed. More than 140 endogenous metabolites were characterized. GC-MS/MS was especially beneficial for characterization of compounds with 16,17-dihydroxy-20-oxo structure, interpreted as markers of intra-uterine enzyme induction. It also assisted the differentiation of 16-hydroxy-20-oxo metabolites, present in urine of non-affected neonates, from the diagnostic 17-hydroxy-20-oxosteroids and enabled the detection of 15,17-dihydroxy-20-oxo compounds in low concentrations. The presence of 17,21-dihydroxylated pregnane(ene)s despite the deficit in CYP21A2 is discussed. We conclude that GC-MS combined with GC-MS/MS allows reliable identification of the structure of the D-ring and side chain of pregnane(ene)s without prior isolation, even when in low concentrations in urine.

Analysis of neurosterols by GC-MS and LC-MS/MS

The term neurosteroid was coined by Baulieu and colleagues in Paris towards the end of the last century to describe steroids which are synthesised in the central or peripheral nervous system [E.E. Baulieu, Psychoneuroendocrinology 23 (1998) 963-87]. This definition was restricted to side-chain "shortened" steroids with 21 carbon atoms or less, and excluded sterols and their carboxylic acids with an intact side-chain. By analogy, we now use the term neurosterol to describe C(27) sterols synthesised in the nervous system. In this review we discuss the biological importance of neurosterols, and how they are extracted, isolated, and analysed by GC-MS and LC-MS/MS, from brain and relevant body fluids. We present applications of methodology employed for analysis of specific sterols and comment on the relative merits of the methods employed. Finally, the importance of future in-depth "sterolomic" investigations of brain is highlighted.

Identification of neuroactive steroids and their precursors and metabolites in adult male rat brain

Steroids in the brain arise both from local synthesis and from peripheral sources and have a variety of effects on neuronal function. However, there is little direct chemical evidence for the range of steroids present in brain or of the pathways for their synthesis and inactivation. This information is a prerequisite for understanding the regulation and function of brain steroids. After extraction from adult male rat brain, we have fractionated free steroids and their sulfate esters and then converted them to heptafluorobutyrate or methyloxime-trimethylsilyl ether derivatives for unequivocal identification and assay by gas chromatography analysis and selected ion monitoring mass spectrometry. In the free steroid fraction, corticosterone, 3alpha,5alpha-tetrahydrodeoxycorticosterone, testosterone, and dehydroepiandrosterone were found in the absence of detectable precursors usually found in endocrine glands, indicating peripheral sources and/or alternative synthetic pathways in brain. Conversely, the potent neuroactive steroid 3alpha,5alpha-tetrahydroprogesterone (allopregnanolone) was found in the presence of its precursors pregnenolone, progesterone, and 5alpha-dihydroprogesterone. Furthermore, the presence of 3beta-, 11beta-, 17alpha-, and 20alpha-hydroxylated metabolites of 3alpha,5alpha-tetrahydroprogesterone implicated possible inactivation pathways for this steroid. The 20alpha-reduced metabolites could also be found for pregnenolone, progesterone, and 5alpha-dihydroprogesterone, introducing a possible regulatory diversion from the production of 3alpha,5alpha-tetrahydroprogesterone. In the steroid sulfate fraction, dehydroepiandrostrone sulfate was identified but not pregnenolone sulfate. Although pharmacologically active, identification of the latter appears to be an earlier methodological artifact, and the compound is thus of doubtful physiological significance in the adult brain. Our results provide a basis for elucidating the origins and regulation of brain steroids.

Matrix-assisted laser desorption/ionization high-energy collision-induced dissociation of steroids: analysis of oxysterols in rat brain

Neutral steroids have traditionally been analyzed by gas chromatography/mass spectrometry (GC/MS) after necessary derivatization reactions. However, GC/MS is unsuitable for the analysis of many conjugated steroids and those with unsuspected functional groups. Here we describe an alternative analytical method specifically designed for the analysis of oxosteroids and those with a 3beta-hydroxy-delta5 or 5alpha-hydrogen-3beta-hydroxy structure. Steroids were derivatized with Girard P (GP) hydrazine to give GP hydrazones, which are charged species and readily analyzed by matrix-assisted laser desorption/ionization mass spectrometry. The resulting [M]+ ions were then subjected to high-energy collision-induced dissociation on a tandem time-of-flight instrument. The product ion spectra give structurally informative fragment ion patterns. The sensitivity of the analytical method is such that steroid structures can be determined from low-picogram (low-femtomole) amounts of sample. The utility of the method has been demonstrated by the analysis of oxysterols extracted from rat brain.

HPLC–RIA analysis of steroid hormone profile in a virilizing stromal tumor of the ovary

The pathological steroid biosynthesis of a virilizing ovarian tumor was examined via high performance liquid chromatography-radioimmunoassay (HPLC-RIA) determination of the intratissular steroid concentrations. Sex cord-stromal tumor of the ovary was obtained surgically from an 18-year-old female patient with extremely high androst-4-ene-3,17-dione (4-en-dione) and testosterone (Test) blood serum levels. The tissue specimen was extracted with ethyl acetate and the extract was then purified on a C18 mini-column with methanol-water eluents. Steroids were isolated by reversed-phase HPLC on a C18 silica gel column with 51%, 55% and 64% v/v methanol-water eluents. Steroids in the collected eluent fractions were detected by the radioactivity of tritiated internal standards and then quantified by specific RIAs. In the tumor specimen, very high 17alpha-hydroxyprogesterone (17-OH-Prog; 6300 fmol/g), dehydro-epiandrosterone (2870 fmol/g), androst-4-ene-3,17-dione (3000 fmol/g), testosterone (5700 fmol/g) concentrations, and less progesterone (PROG; 320 fmol/g) and androst-5-ene-3beta,17beta-diol (5-en-diol; 320 fmol/g), were determined. Tissue levels of 5alpha-dihydrotestosterone (DHT), 5alpha-androstane-3alpha,17beta-diol (3alpha-diol), 5alpha-androstane-3beta,17beta-diol (3beta-diol), and 17beta-estradiol were found to be 71, 20, 28, and 12 fmol/g, respectively. Steroid profile analysis verified a pathological steroid biosynthesis in the ovarian tumor and suggested that the 17alpha-hydroxylase (17alpha-H), 17,20-lyase (17,20-L), and 3beta-hydroxysteroid dehydrogenase/Delta5-4-isomerase (Delta5-3beta-HSD) activities were particularly elevated in this tumorous tissue. Present data demonstrate that the analysis of intratissular steroid profile by a HPLC-RIA method may valuably contribute to the steroidal pathophysiology of endocrine tumors.

Novel lipoidal derivatives of pregnenolone and dehydroepiandrosterone and absence of their sulfated counterparts in rodent brain

A new sample preparation method coupled to GC-MS analysis was developed and validated for quantification of sulfate esters of pregnenolone (PREG-S) and dehydroepiandrosterone (DHEA-S) in rat brain. Using a solid-phase extraction recycling protocol, the results show that little or no PREG-S and DHEA-S (<1 pmol/g) is present in rat and mouse brain. These data are in agreement with studies in which steroid sulfates were analyzed without deconjugation. We suggest that the discrepancies between analyses with and without deconjugation are caused by internal contamination of brain extract fractions, supposed to contain steroid sulfates, by lipoidal forms of PREG and DHEA (L-PREG and L-DHEA, respectively). These derivatives can be acylated very efficiently with heptafluorobutyric anhydride and triethylamine, and their levels in rodent brain (approximately 1 nmol/g) are much higher than those of their unconjugated counterparts. They are distinct from fatty acid esters, and preliminary data do not favor structures such as sulfolipids or sterol peroxides. Noncovalent interactions between steroids and proteolipidic elements, such as lipoproteins, could account for some experimental data. Given their abundance in rodent brain, the structural characterization and biological functions of L-PREG and L-DHEA in the central nervous system merit considerable attention.

Fifty years with bile acids and steroids in health and disease

Cholesterol and its metabolites, e.g., steroid hormones and bile acids, constitute a class of compounds of great biological importance. Their chemistry, biochemistry, and regulation in the body have been intensely studied for more than two centuries. The author has studied aspects of the biochemistry and clinical chemistry of steroids and bile acids for more than 50 years, and this paper, which is an extended version of the Schroepfer Medal Award lecture, reviews and discusses part of this work. Development and application of analytical methods based on chromatography and mass spectrometry (MS) have been a central part of many projects, aiming at detailed characterization and quantification of metabolic profiles of steroids and bile acids under different conditions. In present terminology, much of the work may be termed steroidomics and cholanoidomics. Topics discussed are bile acids in human bile and feces, bile acid production, bacterial dehydroxylation of bile acids and steroids during the enterohepatic circulation, profiles of steroid sulfates in plasma of humans and other primates, development of neutral and ion-exchanging lipophilic derivatives of Sephadex for sample preparation and group separation of steroid and bile acid conjugates, profiles of steroids and bile acids in human urine under different conditions, hydroxylation of bile acids in liver disease, effects of alcohol-induced redox changes on steroid synthesis and metabolism, alcohol-induced changes of bile acid biosynthesis, compartmentation of bile acid synthesis studied with 3H-labeled ethanol, formation and metabolism of sulfated metabolites of progesterone in human pregnancy, abnormal patterns of these in patients with intrahepatic cholestasis of pregnancy corrected by ursodeoxycholic acid, inherited and acquired defects of bile acid biosynthesis and their treatment, conjugation of bile acids and steroids with N-acetylglucosamine, sulfate-glucuronide double conjugates of hydroxycholesterols, extrahepatic 7alpha-hydroxylation and 3-dehydrogenation of hydroxycholesterols, and extrahepatic formation of C27 bile acids. The final part discusses analysis of free and sulfated steroids in brain tissue by capillary liquid chromatography-electrospray MS and suggests a need for reevaluation of the function of steroid sulfates in rat brain.

Tandem mass spectrometry in the study of fatty acids, bile acids, and steroids

Over the last 50 years, the mass spectrometry of lipids has evolved to become one of the most mature techniques in biomolecule analysis. Many volatile and non-polar lipids are directly amenable to analysis by gas-chromatography-mass spectrometry (GC-MS), a technique that combines the unsurpassed separation properties of gas-chromatography with the sensitivity and selectivity of electron ionization mass spectrometry. Less volatile and/or thermally labile lipids can be analyzed by GC-MS, following appropriate sample derivatization. However, many complex lipids are not readily analyzed by GC-MS, and it is these molecules that are the subject of the current review. Since the early 1970s, there have been three outstanding developments in mass spectrometry that are particularly appropriate in lipid analysis; i.e., the introduction of (i) fast atom bombardment (FAB); (ii) electrospray (ES); and (iii) tandem mass spectrometry (MS/MS). The FAB and ES ionization techniques will be discussed in relation to MS/MS, and examples of their application in biochemical studies will be presented. The review will concentrate on the analysis of fatty acids, bile acids, steroid conjugates, and neutral steroids.

Transformation of steroids by Bacillus strains isolated from the foregut of water beetles (Coleoptera: Dytiscidae): II. Metabolism of 3 beta-hydroxypregn-5-en-20-one (pregnenolone)

The in vitro metabolism of pregnenolone by two Bacillus strains (HA-V6-3 and HA-V6-11) isolated from the foregut of the water beetle Agabus affinis (Payk.) was examined in the course of our studies about a possible participation of gut micro-organisms in the biosynthesis of prothoracic defensive steroids of dytiscids. The transformation products were identified by EI GC--MS of culture extracts after derivatization. The dominating reactions were hydroxylations, with 7 alpha-hydroxypregnenolone as the major product. With considerably lower yields, 7 beta- and 15xi-hydroxypregenolone were formed by both strains, while 11, 17 and 16 alpha-hydroxypregnenolone were produced only by HA-V6-3. The occurrence of 7, 11 alpha- and 7 beta, 11 alpha-dihydroxypregnenolone as well as several minor products containing a 17 alpha-OH group proved the capability of HA-V6-11 to hydroxylate pregenenolone at C(11) and C(17) as well. The monohydroxylated 7-OH-pregnenolones were partly oxidized to 7-oxopregnenolone by both strains. In trace amounts, HA-V6-3 performed 3 beta-acetylation of pregnenolone.

Stability indicating HPTLC method for the estimation of estradiol

Estradiol (ESD) is widely used in post climacteric replacement therapy. Most of the methods used for quantitation are expensive and time consuming. A rapid, selective and precise stability indicating high performance thin layer chromatography method was developed and validated for the estimation of ESD in bulk and pharmaceutical dosage forms. The method employed TLC aluminium plate precoated with silica gel 60F254 as the stationary phase. The solvent system employed consisted of chloroform-acetone-isopropyl alcohol-glacial acetic acid (9:1:0.4:0.1, v/v/v/v). Such a complex system was essential to obtain a dense and compact spot of the drug at an Rf value of 0.40 +/- 0.02. The drug on intentional degradation gave two products with Rf values of 0.52 +/- 0.01 and 0.58 +/- 0.01 respectively. Spectrodensitometric scanning-integration was performed on a Camag system using a wavelength of 286 nm. The polynomial regression data for the calibration plots exhibited good linear relationship (r = 0.9947) over a concentration range of 1-8 microg. Recovery studies were also performed at three experimental levels. The recovery data reveals that the RSD for intra-day and inter-day analysis was found to be 1.27% and 1.75%, respectively. The proposed method was found to be stability indicating. Statistical analysis proves that the method is precise, accurate and reproducible, hence can be employed for the routine analysis of the drug.

Validation of an analytical procedure to measure trace amounts of neurosteroids in brain tissue by gas chromatography-mass spectrometry

A selective and extremely sensitive procedure has been developed and optimized, using high-performance liquid chromatography (HPLC), specific derivatization and gas chromatography-mass spectrometry (GC-MS), to simultaneously quantify very small amounts of different neurosteroids from rat brain. Unconjugated and sulfated steroids in brain extracts were separated by solid-phase extraction. The unconjugated fraction was further purified by HPLC, the steroids being collected in a single fraction, and the sulfated fraction was solvolyzed. All steroids were derivatized with heptafluorobutyric acid anhydride and analyzed by GC-MS (electron impact ionization) using selected-ion monitoring. High sensitivity and accuracy were obtained for all steroids. The detection limits were 1 pg for pregnenolone (PREG), dehydroepiandrosterone (DHEA) and their sulfate esters PREG-S and DHEA-S, 2 pg for progesterone (PROG) and 5 pg for 3alpha,5alpha-tetrahydroprogesterone (3alpha,5alpha-THP). In a pilot study on a rat brain, the concentrations of PREG-S and DHEA-S were 8.26+/-0.80 and 2.47+/-0.27 ng/g, respectively. Those of PREG, DHEA and PROG were 4.17+/-0.22, 0.45+/-0.02 and 1.95+/-0.10 ng/g, respectively. Good linearity and accuracy were observed for each steroid. The methodology validated here, allows femtomoles of neurosteroids, including the sulfates, found in small brain samples (at least equal to 10 mg) to be quantified simultaneously.

Analysis of oxosteroids by nano-electrospray mass spectrometry of their oximes

A method for the analysis of neutral oxosteroids by electrospray mass spectrometry is described. The oxosteroids are converted into their oximes by treatment with hydroxyammonium chloride in aqueous methanol. Intense peaks corresponding to protonated oxime molecules are observed in nano-electrospray mass spectra. The detection limits for the oximes of progesterone, pregnenolone and dehydroepiandrosterone were 2.5, 5 and 25 pg/microL, respectively, approximately 20 times lower than for the underivatised steroids. The signal intensities were proportional to the concentration of the steroids in the range of 500 to 2.5 pg/microL. Fragmentation by collision-induced dissociation (CID) was studied using oximes of 28 model steroids carrying an oxo group at C-3, C-17 or C-20. Some of the steroid oximes were labelled with deuterium or (15)N. Fragment ions were observed which yielded useful structural information. Upon CID, protonated oximes of 3-oxo-Delta(4)-steroids produced abundant ions by cleavage through the B-ring and by loss of the side chain, while protonated oximes of saturated 3-oxosteroids did not give abundant ions by cleavage through the B-ring. Protonated oximes of 20-oxosteroids unsubstituted at C-21, C-17 or C-16 produced a characteristic ion at m/z 86 containing the side chain, C-16 and C-17. Protonated oximes of steroids containing only a 17-oxo group gave fewer ions of diagnostic value. Coupled with the selective isolation of steroid oximes from a biological matrix this method of derivatisation and CID may be used for the analysis of neutral oxosteroids in biological samples.

Clinical applications of gas chromatography and gas chromatography-mass spectrometry of steroids

This review article underlines the importance of gas chromatography-mass spectrometry (GC-MS) for determination of steroids in man. The use of steroids labelled with stable isotopes as internal standard and subsequent analysis by GC-MS yields up to now the only reliable measurement of steroids in serum. Isotope dilution GC-MS is the reference method for evaluation of routine analysis of serum steroid hormones. GC-MS is an important tool for detection of steroid hormone doping and combined with a combustion furnace and an isotope ratio mass spectrometer the misuse of testosterone by athletes can be discovered. Finally the so called urinary steroid profile by GC and GC-MS is the method of choice for detection of steroid metabolites in health and disease.

Transformation of steroids by Bacillus strains isolated from the foregut of water beetles (Coleoptera:Dytiscidae): I. Metabolism of androst-4-en-3,17-dione (AD)

Two Bacillus strains were isolated from the foregut of the water beetle Agabus affinis (Payk.) and tested for their steroid transforming ability. After incubation with androst-4-en-3,17-dione (AD), 13 different transformation products were detected. AD was hydroxylated at C6, C7, C11 and C14, resulting in formation of 6beta-, 7alpha-, 11alpha- and 14alpha-hydroxy-AD. One strain also produced small amounts of 6beta,14alpha-dihydroxy-AD. Partly, the 6beta-hydroxy group was further oxidized to the corresponding 6-oxo steroids. In addition, a specific reduction of the delta4-double bond was observed, leading to the formation of 5alpha-androstane derivatives. In minor yields the carbonyl functions at C3 and C17 were reduced leading to the formation of 3zeta-OH or 17beta-OH steroids. EI mass spectra of the trimethylsilyl and O-methyloxime trimethylsilyl ether derivatives of some transformation products are presented for the first time.

The identification of novel steroid N-acetylglucosaminides in the urine of pregnant women

A series of pregnanediols and pregnanetriols doubly conjugated with N-acetylglucosamine and glucuronic or sulfuric acid has been identified in urine from pregnant women. Steroid conjugates were separated by ion-exchange chromatography and the glucuronide and monosulfate fractions were analysed by fast atom bombardment mass spectrometry. After removal of the acid moiety, the neutral steroids were isolated, derivatized, and analysed by gas chromatography-mass spectrometry (GC-MS). The analyses revealed the presence of steroids conjugated with N-acetylhexosamine both in the glucuronide and the monosulfate fractions. Following enzyme hydrolysis, the sugar was identified by GC-MS as N-acetylglucosamine (GlcNAc). The major steroid conjugated with GlcNAc both in the glucuronide and monosulfate fractions was identified as 5alpha-pregnane-3alpha,20alpha-diol. 5beta-Pregnane-3alpha,2Oalpha-diol was also present as a GlcNAc conjugate in both fractions whereas a GlcNAc conjugate of 5alpha-pregnane-3beta,20alpha-diol was only found in the sulfate fraction. 5alpha-Pregnane-3alpha,20alpha,21-triol was a double conjugate with GlcNAc in the sulfate fraction whereas a pregnane-2,3,20-triol was a double conjugate in the glucuronide fraction. The positions of conjugation were determined by collision-induced dissociation of the pseudomolecular anions produced by fast atom bombardment ionization. The sulfate and glucuronic acid moieties were located at C-3 and N-acetylglucosamine at C-20. An alternative localization of GlcNAc at C-21 of 5alpha-pregnane-3alpha,20alpha,21-triol cannot be excluded. Judging from the enzymatic hydrolysis of the conjugates, the sugar was attached in beta-glycosidic linkage. The mean excretion of N-acetylglucosaminides of the pregnanediols and pregnanetriols was 32.2 micromol/g creatinine (range 17.9-49.1 micromol) in five healthy women in the 38th-39th week of pregnancy. The mean excretion of 5beta-pregnane-3alpha,20alpha-diol glucuronide in the same women was 71 micromol/g creatinine, (range 27-127 micromol). This indicates that conjugation with N-acetylglucosamine constitutes a quantitatively important pathway of progesterone metabolism in human pregnancy.

Urinary steroids from a newborn human infant. Identification of 2 alpha-hydroxy-4-pregnene-3,20-dione, 3 beta,15 beta-dihydroxy-5-pregnen-20-one and 3 beta,15 alpha-dihydroxy-5-pregnen-20-one

Urinary steroids from healthy newborn human infants were analyzed by gas-liquid chromatography and gas-liquid chromatography-mass spectrometry. The identification of 2 alpha-hydroxy-4-pregnene-3,20-dione and the characterization of its 2 beta-isomer is recorded here for the first time. Mass spectrometric evidence supporting the identification of 3 beta,15 beta-dihydroxy-5-pregnen-20-one and 3 beta,15 alpha-dihydroxy-5-pregnen-20-one is also presented. Furthermore, the following 15-hydroxylated steroids were also found and identified: 3 beta,15 epsilon,16 epsilon-trihydroxy-5-androsten-17-one, 5-androstene-3 beta,15 alpha,16 alpha,17 beta-tetrol, 3 beta,15 beta,17-trihydroxy-5-pregnen-20-one and 5-pregnene-3 beta,15 epsilon,17,20 epsilon-tetrol. The origin of these 2- and 15-hydroxylated urinary steroids is discussed in relation to current knowledge of 4-pregnene-3,20-dione and 3 beta-hydroxy-5-pregnen-20-one metabolism during the human perinatal period.

Synthesis and characterization of the 6 alpha- and 6 beta-hydroxylated derivatives of corticosterone, 11-dehydrocorticosterone, and 11-deoxycortisol

This report describes the synthesis of 6 alpha, 17,21- and 6 beta, 17,21-trihydroxypregn-4-ene-3,20-dione, 6 alpha, 7,21- and 6 beta, 11 beta, 21-trihydroxypregn-4-ene-3,20-dione, and--for the first time--that of 6 alpha, 21- and 6 beta, 21-dihydroxypregn-4-ene-3,11,20-trione. The former four compounds were prepared by 6-hydroxylation of 17,21-trihydroxypregn-4-ene-3,20-dione and 11 beta, 21-dihydroxypregn-4-ene-3,20-dione, respectively. This was achieved by autoxidation or by oxidation with 3-chloroperbenzoic acid, of the 3-methoxy-pregna-3,5-dienes of the latter two steroids. The yield of the 6 beta-hydroxylated steroids, but not of their corresponding 6 alpha-epimers, was higher using autoxidation than the peracid. The two 6-hydroxylated pregnenetriones were prepared from 6 alpha, 21-diacetoxy-11 beta-hydroxypregn-4-ene-3,20-dione and 6 beta, 21-diacetoxy-11 beta-hydroxypregn-4-ene-3,20-dione, respectively, by oxidation with pyridinium chlorochromate. The above-mentioned six steroids were identified and characterized by nuclear magnetic resonance, infrared, ultraviolet, high performance liquid chromatography, gas chromatography, and mass spectrometry.

Steroids and their conjugates in the mammalian brain

Five steroids--3 beta-hydroxypregn-5-en-20-one (pregnenolone; P), 3 beta-hydroxy-5 alpha-pregnan-20-one (3 beta-AP), 3 alpha-hydroxy-5 alpha-pregnan-20-one (3 alpha-AP), 3 beta-hydroxyandrost-5-en-17-one (dehydroepiandrosterone; D), and 3 beta-hydroxy-5 alpha-androstan-17-one (EpiA)--were extracted from the brains of adult male rats, rabbits, and dogs. The steroids exist in this organ as unconjugated compounds and as sulfates, lipoidal esters, and sulfolipids. The techniques for separating these four classes of steroids from each other and for separating the five steroids from each other are described. In all cases, the steroids were identified by their retention time (Rt) on HPLC, their Rt by gas chromatography, and by selected ion monitoring of their mass spectra. The latter were also used for quantification. In their reaction toward organic bases, the sulfolipid conjugates resemble previously described sulfolipids of cholesterol and sitosterol. These conjugates are relatively abundant in brain, particularly those of P and D, and this suggests that, in the search for the physiological significance of these brain constituents, these conjugates warrant attention.

A method for characterization of endogenous ligands to orphan receptors belonging to the steroid hormone receptor superfamily--isolation of progesterone from pregnancy plasma using progesterone receptor ligand-binding domain

An analytical method is described whereby progesterone is isolated from pregnancy plasma on the basis of the high affinity and specificity of the progesterone receptor for its ligand. Partially purified progesterone receptor ligand-binding domain, expressed as a protein A fusion protein in Escherichia coli, is incubated with a neutral steroid fraction obtained by extraction and ion-exchange chromatography of human late-pregnancy plasma. The incubated sample is passed through two Lipidex 1000 (lipophilic gel) beds. The first, at 4 degrees C, separates the specific ligand-fusion protein complex from nonspecifically bound and unbound compounds, and the second, at 40 degrees C, separates the specific ligand from the protein. Elution of the second bed with methanol yields a fraction containing specific ligand that can be characterized by gas chromatography-mass spectrometry. This methodology may be valuable for identification of endogenous ligands to orphan receptors of the steroid hormone receptor superfamily.

Chromatography as a reference technique for the determination of clinically important steroids

Chromatographic methods (paper chromatography, thin layer chromatography, high performance liquid chromatography, gas chromatography and gas chromatography-mass spectrometry) for the determination of clinically important steroids in biological specimens are reviewed. The emphasis is on the use of gas chromatography, gas chromatography-mass spectrometry and high performance liquid chromatography as reference rather than routine techniques. Chromatographic methods are compared with colorimetric, fluorimetric and radioimmunoassay procedures in terms of simplicity of operation, cost and ability to analyse large numbers of specimens. The importance of correct specimen collection and storage are discussed. Sample preparation techniques for the various analytical methods are described. These include extraction of free and conjugated steroids from serum, plasma, urine and saliva by solvent partition, with polymer-based resins such as Amberlite XAD-2, DEAE-Sephadex and Sephadex resins bonded with various other function groups and, more recently, with chemically bonded reversed-phase silicas.

Manual and automated enrichment procedures for biological samples using lipophilic gels

Aspects of the use of lipophilic gels in manual sample preparation procedures are reviewed. Neutral gels with a controlled hydrophobicity are used for sorbent extraction of non-polar and medium polarity compounds from biological fluids. Acidic amphiphilic compounds can be extracted as ion-pairs with decyltrimethylammonium ions. Solvent or detergent extracts of tissues or faeces can be mixed with hydrophobic gels for transfer of analytes from a solvent to a gel phase, permitting subsequent sample preparation in gel bed systems. Hydrophobic gels, alkyl-bonded silica and polystyrene matrices can be used in series for extraction of compounds with a wide range of polarities. Group fractionations are performed on neutral and ion-exchanging lipophilic gels to yield fractions of neutral, basic and acidic metabolites within selected polarity ranges. Selective isolation of phenolic acids on a strong anion exchanger, of ethynylic steroids on a strong cation exchanger in silver form and of oximes of ketonic steroids on a strong cation exchanger in hydrogen form is possible. A computerized system for automatic sample preparation is also described. It consists of an extraction bed, a cation-exchange column and an anion-exchange column. The pumps and switching valves are arranged so that the columns can operate in series or parallel for isolation of neutral, basic and acidic metabolites of amphiphilic compounds and for regeneration of the column beds. Fractions can be collected, or the effluent from the column beds can be diluted with water to permit sorption on a solid phase. The applicability of the automated method to the analysis of bile acids and metabolites of mono(2-ethylhexyl) phthalate is demonstrated.

Studies on rat liver microsomal steroid metabolism using 18O-labelled testosterone and progesterone

In order to investigate the possible involvement of oxygen functions in the rat liver microsomal metabolism of progesterone and testosterone these steroids were specifically labelled with 18O in their oxo-functions and incubated with NADPH supplemented 105,000 g sediments. Gas chromatography-mass spectrometry was used to identify the metabolites formed as well as to quantitate the losses of 18O-label. With 18O-labelled testosterone as substrate two of the major monohydroxylated metabolites, i.e. 2 beta- and 6 beta-hydroxytestosterone were shown to have lost about 25 and 50% of their 18O respectively. A complete retention of label was found in 7 alpha- and 16 alpha-hydroxytestosterone. None of the monohydroxylated progesterone metabolites, i.e. the 2 alpha-, 6 beta- and 16 alpha-hydroxyprogesterone had lost any 18O following incubation with 3,20-18O-labelled progesterone. Control incubation (30', 37 degrees C) with buffer and 18O-labelled progesterone and testosterone revealed no exchange of 18O. Thus the partial loss of 3-18O-label during 2 beta- and 6 beta-hydroxylation of testosterone may indicate a covalent interaction between the steroid 3-oxo-group and one or more cytochrome P-450 species in the rat liver microsomes. In view of the potentiating effect of a 3-imine group in spontaneous 6 beta-hydroxylation the present in vitro data suggest that a steroid protein-interaction may occur via a 3-imine group during 6 beta-hydroxylation of testosterone in rat liver microsomes. Analysis of 5 alpha-reduced metabolites of both progesterone and testosterone showed significant losses of 3-18O, but due to the ease with which 3-oxo-5 alpha-steroids exchange their 3-18O with aqueous media an enzymatically induced loss of 3-18O could not be safely established. The 20-oxido-reductase which converted progesterone did not induce a loss of 20- or 3-18O thus indicating that the oxofunctions were not covalently engaged in the enzymatic binding of the steroid.

On the homogeneity of stools with respect to bile acid composition and normal day-to-day variations: a detailed qualitative and quantitative study using capillary column gas chromatography-mass spectrometry

Fecal bile acid excretion was determined using recently developed techniques in order to investigate: the extent of the homogeneity in composition and concentration of individual bile acids in a single stool sample, the detailed qualitative and quantitative day-to-day variations in total and individual bile acids in the typical healthy adult, information on the relative proportions of conjugated bile acids in healthy stools, and inter-individual variations in fecal bile acid excretion. Bile acids were extracted from feces and separated into groups based upon their mode of conjugation using lipophilic gel chromatography, prior to analysis by capillary column gas chromatography-mass spectrometry. The majority of bile acids were excreted in the unconjugated form, while in all samples, conjugated bile acids accounted for less than 6% of the total fecal bile acids excreted, of which sulphated bile acids represented less than 3% of the total. Quantitative total and individual bile acid excretion, determined from single daily collections exhibited wide variations in values from day-to-day, and in accordance with early findings, indicates the need to use a minimum of 3- to 5-day collections for a more reliable index of bile acid excretion in feces. Examination of frozen and sectioned single stools revealed wide variations in water content and in quantitative bile acid concentration and composition within the stool. These data indicate random stool samples, which are commonly used in clinical studies, and data expressed as concentrations to be unsatisfactory for the accurate determination of fecal bile acid excretion.

Studies on the chromatographic fractionation of metabolites of benzo[a]pyrene in faeces and urine from germfree and conventional rats

Rats, germfree and conventional, were dosed with 14C-labelled benzo[a]pyrene. Faeces and urine were collected. Metabolites in faeces were effectively extracted with a new method using a combination of solvents and solid sorbents. Metabolites in urine were extracted with octadecylsilane-bonded silica. The metabolites were fractionated into groups by chromatography on a cation exchanger (SP-LH-20 or SP-Sephadex C-25) and an anion exchanger (TEAP-LH-20). Some of the groups were further purified by column chromatography and analysed by HPLC and TLC. The analyses show a complex pattern of metabolism. A large part of the metabolites (9-24% depending on animal type and route of excretion) had amphoteric properties, e.g. like glutathione and cysteine conjugates. The abundance of conjugates sensitive to beta-glucuronidase and sulphatase was low. The relative amount of acidic conjugates in faeces was much higher in the germfree than in the conventional rats indicating the influence of the intestinal flora on the metabolism. The results support the view that the mercapturic acid pathway is a quantitatively important metabolic route for benzo[a]pyrene in rats. The methods of extraction and group fractionation were designed to be generally applicable to the analysis of lipophilic xenobiotics and their metabolites.

Profiling steroid hormones and urinary steroids

This paper reviews techniques utilized in the profiling of steroids in body fluids and tissues. Methods for profiling plasma unconjugated steroids and urinary steroid metabolites are focused on. Concentrations or levels of excretion of a variety of steroids have been documented and reviewed. The importance of profiling techniques in the study of normal and pathophysiology of hormonal steroids is discussed.

Analysis of profiles of unconjugated steroids in rat testicular tissue by gas chromatography-mass spectrometry

A gas chromatographic-mass spectrometric (GC-MS) method for analysis of unconjugated steroids in a rat testis is described. A combined solvent-solid extraction procedure, utilizing Lipidex 1000 and Sep-Pak C18, gives a 25-fold purified extract. Steroids in this extract are fractionated by straight phase high-performance liquid chromatography (HPLC) on a LiChrosorb DIOL column in n-hexane-2-propanol, 92:8 (v/v). Four fractions are collected and the steroids are converted to tert-butyldimethylsilyl (TBDMS), 3-enol-TBDMS, and mixed TBDMS-trimethylsilyl (TMS) derivatives using TBDMS- and TMS-imidazole with sodium formate as catalyst under conditions suitable for the steroids present in the respective fractions. The derivatives are purified by reversed phase HPLC in 100% methanol and are analyzed by GC-MS, using selected ion monitoring of the major ions of high mass. For quantification, a mixture of known amounts of ten 14C-labelled steroids, [3H]estradiol and [2H3]estradiol are added to the testis homogenate. The mean concentrations (ng/g wet wt) of the twelve steroids determined were: 4-androstene-3, 17-dione, 4.0; testosterone, 127; 17 beta-hydroxy-5 alpha-androstan-3-one, 4.5; 5 alpha-androstane-3 alpha, 17 beta-diol, 5.7; 5 alpha-androstane-3 beta, 17 beta-diol, 1.5; progesterone, 5.5; 17 alpha-hydroxyprogesterone, 14.4; 3 beta-hydroxy-5-androsten-17-one, 0.07; 5-androstene-3 beta, 17 beta-diol, 0.25; 3 beta-hydroxy-5-pregnen-20-one, 10.3; 3 beta, 17 beta-dihydroxy-5-pregnen-20-one, 0.95; and estradiol, 0.025. Variations between animals were large whereas testes from the same animal in most cases had similar steroid concentrations.

Formation of imine derivatives between biologically occurring amines and oxo-steroids

Various biologically occurring amines have been shown to react with 3-oxo-17-oxo and 20-oxo-steroids during solvent evaporation at room temperature to form a complex pattern of products in each case. Using aliphatic monoamines it was shown that imine derivatives are first formed which rapidly rearrange into yet unidentified compounds. The extent of the overall transformation of the oxo-steroid varied with the amine investigated. Thus histamine gave rise to a 95% conversion of 17 beta-hydroxy-4-androsten-3-one (testosterone), whereas epinephrine caused 5% transformation under the same conditions. Imine formation as an experimental error in studies on the biochemistry of steroids is suggested.

Sample work-up by column techniques

A review is given of the extraction and purification of biological samples by filtration through lipophilic neutral and ion-exchange dextran gels and their derivatives. Liquid-gel extraction, reversed-phase liquid chromatography and ligand-exchange chromatography are also discussed. The applications of Sephadex and Lipidex gels are reviewed, with special reference to extractions from biological fluids and solid samples and the extraction of metabolites. A number of selective isolation procedures are reviewed for estrogens, lignans, isoflavanes, isoflavones, catechol estrogens, ketonic compounds and ethynyl steroids.

A method combining solvent and gel extraction for isolation and preliminary purification of steroids in tissues

A method for the combined extraction and purification of steroids from testicular tissue is described. The tissue is homogenized and extracted with n-hexane/isopropyl alcohol, and the column to which a Sep-Pak C18 cartridge is attached. Following a wash of the Lipidex/Sep-Pak beds with water to remove inorganic and polar organic substances, steroids are eluted with 85% aqueous methanol. Most of the nonpolar lipids and phospholipids remain on the Lipidex/Sep-Pak. The steroid fraction is acidified with acetic acid, diluted to 70% methanol, and passed through a small bed of Lipidex 5000 to remove cholesterol. Recoveries of testosterone and progesterone are about 90%.