Gas phase analytical methods for the study of steroids

A guide to understanding the steroid pathway: new insights and diagnostic implications

Steroid analysis has always been complicated requiring a clear understanding of both the clinical and analytical aspects in order to accurately interpret results. The literature relating to this specialised area spans many decades and the intricacies of the steroid pathway have evolved with time. A number of key changes, including discovery of the alternative androgen pathway, have occurred in the last decade, potentially changing our understanding and approach to investigating disorders of sexual development. Such investigation usually occurs in specialised paediatric centres and although preterm infants represent only a small percentage of the patient population, consideration of the persistence of the foetal adrenal zone is an additional important consideration when undertaking steroid hormone investigations. The recent expanded role of mass spectrometry and molecular diagnostic methods provides significant improvements for accurate steroid quantification and identification of enzyme deficiencies. However analysis of steroids and interpretation of results remain complicated. This review aims to provide an insight into the complexities of steroid measurement in children and offers an updated guide to interpretation, of serum and urine steroids through the presentation of a refined steroid pathway.

Proof-of-principle study to detect metabolic changes in peritoneal dialysis effluent in patients who develop encapsulating peritoneal sclerosis

BACKGROUND

Prolonged peritoneal dialysis (PD) therapy can result in the development of encapsulating peritoneal sclerosis (EPS), characterized by extensive sclerosis of the peritoneum with bowel adhesions often causing obstruction.

METHODS

As a proof-of-principle study, holistic profiling of endogenous metabolites has been applied in a prospective collection of PD effluent collected in multiple UK renal centres over 6 years in order to investigate metabolic differences in PD effluent between PD therapy patients who later developed clinically defined EPS (n = 11) and controls, who were matched for PD vintage, age and gender (n = 11).

RESULTS

'Fit-for-purpose' analytical methods employing gas chromatography-mass spectrometry (MS), direct injection MS and quality control samples were developed and validated. These methods were applied in a proof-of-principle study to define metabolic differences in PD effluent related to subsequent development of EPS. Changes in amino acids, amines and derivatives, short-chain fatty acids and derivatives and sugars were observed prior to EPS developing, and changes in the metabolomic profiles could be detected.

CONCLUSION

There is potential for applying metabolic profiles to identify patients at risk of developing EPS although long-term prospective studies with larger patient cohorts are required.

Charge inversion via concurrent cation and anion transfer: application to corticosteroids

A novel charge inversion process that involves the removal of an excess cation from an analyte ion and the transfer of an anion to the neutral analyte in a single ion/ion encounter is described. Polyamidoamine (PAMAM) half-generation dendrimer anions that contain small anions, such as the chloride ion, were used as charge inversion reagents. Several competing processes can occur that include removal of the cation to neutralize the analyte, the removal of the excess cation and an additional proton to yield the deprotonated molecule, or removal of the excess cation and transfer of a small anion to the analyte. For the latter process to dominate, several requirements for both the reagent anion and the analyte cation must be met. The reagent anion must form multiply charged anions and must be able to incorporate one or more small anions for transfer. The analyte must have no strongly acidic sites as well as a relatively high affinity for small anion attachment. The PAMAM dendrimer anions must meet the conditions for the reagent anions and the cations of the corticosteroids meet the conditions for the analyte. The estrogenic steroid estrone, on the other hand, does not meet the requirements and, as a result, is largely neutralized when reacted with the reagent anions. This reaction, therefore, is highly selective and might serve as a useful reaction for the screening of appropriate analytes.

Clinical steroid mass spectrometry: a 45-year history culminating in HPLC-MS/MS becoming an essential tool for patient diagnosis

Automated rapid HPLC tandem mass spectrometry has become the method of choice for clinical steroid analysis. It is replacing immunoassay techniques in most instances because it has high sensitivity, better reproducibility, greater specificity and can be used to analyze multiple steroids simultaneously. Modern multiplex instruments can analyze thousands of samples per month so even with high instrument costs the price of individual assays can be affordable. The mass spectrometry of steroids goes back decades; the first on-line chromatography/mass spectrometry methods for hormone analysis date to the 1960s. This paper reviews the evolution of mass spectrometric techniques applied to sterol and steroid measurement There have been three eras: (1) gas chromatography-mass spectrometry (GC/MS), (2) Fast Atom Bombardment (FAB) and (3) HPLC/MS. The first technique is only suitable for unconjugated steroids, the second for conjugated, and the third equally useful for free or conjugated. FAB transformed biological mass spectrometry in the 1980s but in the end was an interim technique; GC/MS retains unique qualities but is unsuited to commercial routine analysis, while LC-MS/MS is rightly stealing the show and has become the dominant method for steroid analysis in endocrinology.

Bile acids: analysis in biological fluids and tissues

The formation of bile acids/bile alcohols is of major importance for the maintenance of cholesterol homeostasis. Besides their functions in lipid absorption, bile acids/bile alcohols are regulatory molecules for a number of metabolic processes. Their effects are structure-dependent, and numerous metabolic conversions result in a complex mixture of biologically active and inactive forms. Advanced methods are required to characterize and quantify individual bile acids in these mixtures. A combination of such analyses with analyses of the proteome will be required for a better understanding of mechanisms of action and nature of endogenous ligands. Mass spectrometry is the basic detection technique for effluents from chromatographic columns. Capillary liquid chromatography-mass spectrometry with electrospray ionization provides the highest sensitivity in metabolome analysis. Classical gas chromatography-mass spectrometry is less sensitive but offers extensive structure-dependent fragmentation increasing the specificity in analyses of isobaric isomers of unconjugated bile acids. Depending on the nature of the bile acid/bile alcohol mixture and the range of concentration of individuals, different sample preparation sequences, from simple extractions to group separations and derivatizations, are applicable. We review the methods currently available for the analysis of bile acids in biological fluids and tissues, with emphasis on the combination of liquid and gas phase chromatography with mass spectrometry.

Steroid analysis and doping control 1960-1980: scientific developments and personal anecdotes

Definitive proof of anabolic steroid abuse in sports was not possible prior to the introduction of combined gas chromatography/mass spectrometry (GC/MS).This is a report of the early history (1960-1980) of GC/MS and radioimmunoassay, and how these techniques were utilized in the first years of steroid doping control in athletics. There were several key individuals and research groups involved in the early technical developments, and their essential contributions have been acknowledged. Our laboratory was the first IAAF (International Association of Athletic Federations) sanctioned site to do steroid GC/MS steroid analysis resulting in athletes being disqualified from competition. We had notable successes, including the only East German female competitor ever suspended during the tenure of the DDR (Deutsche Demokratische Republik). This paper not only covers scientific advances and milestones in the incorporation of steroid testing into international athletics, but also includes personal anecdotes of these early years before doping control became justifiably regimented. By the early 1980s, in anticipation of the Los Angeles Olympic games, dedicated year-round sports testing facilities had been established and part-time amateurs could step aside.

The corticosteroid metabolic profile of the mouse

Data are presented on the urinary corticosteroid metabolic profile of the mouse strain 129/svJ. Through the use of GC/MS we have characterized, or tentatively identified corticosterone (Kendall's compound B) metabolites of both the 11beta-hydroxy and 11-carbonyl (compound A) series in urine. Full mass spectra of the methyloxime-trimethylether derivatives of 15 metabolites are included in the paper as an aid to other researchers in the field. Metabolites ranged in polarity from tetrahydrocorticosterone (THB) to dihydroxy-corticosterone with dominance of highly polar steroids. We found that prior to excretion corticosterone can undergo oxidation at position 11beta, reduction at position 20 and A-ring reduction. Metabolites retaining the 3-oxo-4-ene structure can be hydroxylated at position 6beta- as well as at an unidentified position, probably 16alpha-. Saturated steroids can be hydroxylated at positions 1beta-, 6alpha-, 15alpha- and 16alpha. A pair of hydroxy-20-dihydro-corticosterone metabolites (OH-DHB) were the most important excretory products accounting for about 40% of the total. One metabolite of this type was identified as 6beta-hydroxy-DHB; the other, of similar quantitative importance was probably 16alpha-hydroxy-DHB. The ratio of metabolites of corticosterone (B) to those of 11-dehydro-corticosterone (A) was greater than 9:1, considerably higher than that for the equivalent "human" ratio of 1:1 for cortisol to cortisone metabolites. Results from this study allowed the evaluation of 11beta-hydroxysteroid dehydrogenase (11beta-HSD) activity in mice with deleted glucose-6-phosphate transporter (G6PT). These mice had attenuated back-conversion of A to B resulting in an increased ratio of A-metabolites to B-metabolites [Walker EA, Ahmed A, Lavery GG, Tomlinson JW, Kim SY, Cooper MS, Stewart PM, 11beta-Hydroxysteroid dehydrogenase type 1 regulation by intracellular glucose-6-phosphate, provides evidence for a novel link between glucose metabolism and HPA axis function. J Biol Chem 2007;282:27030-6]. We believe this study is currently the most comprehensive on the urinary steroid metabolic profile of the mouse. Quantitatively less steroid is excreted in urine than in feces by this species but urine analysis is more straightforward and the hepatic metabolites are less subject to microbial degradation than if feces was analyzed.

Development of a procedure for the assay of an experimental steroid drug in dog plasma

Studies of the estimation of 16alpha-cyano-3beta-cyclopentyloxypregn-5-en-20-one (an experimental drug) in dog plasma are described. Extraction using a salt/solvent pair (ammonium carbonate/ethyl acetate) is followed by a rapid chromatographic procedure employing Lipidex 5000, which affords a substantially purified fraction. After preparation of the t-butyldimethylsilyloxime, quantification of the drug is performed by selected ion monitoring. The [2H9]cyclopentyloxyl analogue is used as an internal standard. In a preliminary experiment, the advantages (in terms of both sensitivity and selectivity) of the use of an open tubular GLC column are demonstrated.

Fatty acid compositions of lipid fractions from vegetative cells and mature sorocarps of the cellular slime mold Dictyostelium discoideum

A wild-type strain of Dictyostelium discoideum was grown upon Aerobacter aerogenes. Fatty acid compositions of lipid fractions and of total lipids obtained from vegetative amoebae and mature sorocarps were compared. Fatty acids isolated from vegetative cells were found to include large quantities of 17- and 19-carbon cyclopropane fatty acids while straight-chain, saturated fatty acids represented only 10% (w/w) of total fatty acids. These cyclopropane fatty acids appear to be derived from ingested bacteria and are preferentially incorporated into neutral lipids of the slime mold. Development of amoebae to mature sorocarps is accompanied by a substantial decrease in cyclopropane fatty acid content and a concomitant increase in unsaturated fatty acids, mostly as octadeca-5,11-dienoic acid. The delta-22 stigmastenyl ester fraction is the richest source of this acid. Fully 65% of the fatty acids in this fraction are the octadecadienoate.

Mass spectra of delta 4- and 5 alpha-3-ketosteroids formed during the oxidation of some 3 beta-hydroxysteroids by cholesterol oxidase

Thirty-six delta5- and 5'alpha-3beta-hydroxysteroids have been oxidized with cholesterol oxidase to give the corresponding delta4- and 5alpha-3-ketosteroids, respectively. The mass spectral characteristics of the products (or their trimethylsilyl ether derivatives, in the case of 3-keto-hydroxysteroids) varied considerably, depending especially on the nature of the C-17 sidechain. The ion of m/e 124 (or its equivalent) from cleavage of ring B was frequently a major fragment from delta4-3-ketosteroids, but in some instances was of insignificant abundance. Trimethylsilylation of the product of the oxidation of neoergosterol gave neoergosterone enol-trimethylsilyl ether. Fragmentations of the sidechain predominated in the mass spectra of the 5alpha-3-ketosteroids.

GLC analysis of hydrochlorothiazide in blood and plasma

GLC with electron-capture detection was successfully applied to the analysis of hydrochlorothiazide in human blood and plasma with a sensitivity (0.05 mug/ml) suitable for use with persons on therapeutic dosage levels. On-column methylation with trimethylanilinium hydroxide in methanol was employed to convert hydrochlorothiazide and its bromo analog, which served as the internal standard, to their tetramethyl derivatives.

Mass spectrometry in the analysis of steroid drugs and their metabolites: electron-impact-induced fragmentation of ring D

Certain steroid drugs, their metabolites, and related model compounds which possess a 17-hydroxy group can be converted to trimethylsilyl ethers which give characteristic ions of type [128 + R]+in their mass spectra, where R is the mass of the other 17-substituent. Extensive deuterium labelling studies are carried out to verify the modes of formation of these and related ions which are of diagnostic value in analytical work.