Comparison of liquid chromatography-microchip/mass spectrometry to conventional liquid chromatography-mass spectrometry for the analysis of steroids

Bioconversion of Phytosterols into Androstenedione by Mycolicibacterium

The chapter describes the bioconversion of phytosterols into androstenedione (AD) by Mycolicibacterium spp. in shake flasks and fermenters, as well as LC-MS-based methods for analysis of phytosterols and steroid products. Phytosterols are derived as by-products of vegetable oil refining and manufacture of wood pulp. They contain the same four-ring nucleus as steroids and may be converted to high-value steroids by removing the sidechain at C17 and minor changes at other sites in the ring structure. Many bacteria, including Mycolicibacterium spp., can degrade phytosterols. Mutants of Mycolicibacterium spp. unable of ring cleavage can, when growing on phytosterols, accumulate the steroid intermediates androstenedione (AD) and androstadienedione (ADD). The practical challenge with microbial conversion of phytosterols to steroids is that both the substrate and the product are virtually insoluble in water. In addition, some steroids, notably ADD, may be toxic for the cells. Two main strategies have been employed to overcome this challenge: the use of two-phase systems and the addition of chemically modified cyclodextrins. The latter method is used here. Defined cultivation and bioconversion media for both shake flask and fermenter are given, as well as hints how to minimize the practical problems due to the water-insoluble phytosterol. Sampling, sample extraction, and quantification of substrates and products using LC-MS analysis are described.

Derivatization with 2-hydrazino-1-methylpyridine enhances sensitivity of analysis of 5α-dihydrotestosterone in human plasma by liquid chromatography tandem mass spectrometry

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Quantitative analysis of low abundance androgens in human plasma.

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Quantitation of androgens over physiological range in men and post-menopausal women.

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Use of hydrazine derivatives improves analytical sensitivity.

Liquid Chromatography tandem mass spectrometry (LC-MS/MS) is the gold-standard approach for androgen analysis in biological fluids, superseding immunoassays in selectivity, particularly at low concentrations. While LC-MS/MS is established for analysis of testosterone and androstenedione, 5α-dihydrotestosterone (DHT) presents greater analytical challenges. DHT circulates at low nanomolar concentrations in men and lower in women, ionizing inefficiently and suffering from isobaric interference from other androgens. Even using current LC-MS/MS technology, large plasma volumes (>0.5 mL) are required for detection, undesirable clinically and unsuitable for animals. This study investigated derivatization approaches using hydrazine-based reagents to enhance ionization efficiency and sensitivity of analysis of DHT by LC-MS/MS. Derivatization of DHT using 2-hydrazino-1-methylpyridine (HMP) and 2-hydrazino-4-(trifluoromethyl)-pyrimidine (HTP) were compared. A method was validated using an UHPLC interfaced by electrospray with a triple quadruple mass spectrometer , analyzing human plasma (male and post-menopausal women) following solid-phase extraction. HMP derivatives were selected for validation affording greater sensitivity than those formed with HTP. HMP derivatives were detected by selected reaction monitoring (DHT-HMP m/z 396→108; testosterone-HMP m/z 394→108; androstenedione-HMP m/z 392→108). Chromatographic separation of androgen derivatives was optimized, carefully separating isobaric interferents and acceptable outputs for precision and trueness achieved following injection of 0.4 pg on column (approximately 34 pmol/L). HMP derivatives of all androgens tested could be detected in low plasma volumes: male (100 µL) and post-menopausal female (200 µL), and derivatives were stable over 30 days at -20°C. In conclusion, HMP derivatization, in conjunction with LC-MS/MS, is suitable for quantitative analysis of DHT, testosterone and androstenedione in low plasma volumes, offering advantages in sensitivity over current methodologies.

Bioconversion of Phytosterols into Androstenedione by Mycobacterium

The chapter describes the bioconversion of phytosterols to androstenedione (AD) with Mycobacterium spp. in shake flasks and fermenters, as well as LC-MS based methods for analysis of phytosterols and steroid products.Phytosterols are derived as a by-product of vegetable oil refining and of manufacture of wood pulp. Phytosterols contain the same four-ring nucleus as steroids, and may be converted to high-value steroids by removing the side chain at C17 and minor changes at other sites in the ring structure.Many bacteria, including Mycobacterium spp., are able to degrade phytosterols. Mutants of Mycobacterium spp. unable of ring cleavage can, when growing on phytosterols, accumulate the steroid intermediates androstenedione (AD) and/or androstadienedione (ADD).The practical challenge with microbial conversion of phytosterols to steroids is that both the substrate and the product are virtually insoluble in water. In addition, some steroids, notably ADD, may be toxic to cells.Two main strategies have been employed to overcome this challenge: the use of two-phase systems, and the addition of chemically modified cyclodextrins. The latter method is used here.Defined cultivation and bioconversion media for both shake flask and fermenter are given, as well as suggestions to minimize the practical problems caused by the water-insoluble phytosterol. Sampling, sample extraction, and quantification of substrates and products using LC-MS analysis are described.

A new label-free screen for steroid 5α-reductase inhibitors using LC-MS

Steroid 5α-reductase (S5αR) plays an important role in metabolizing testosterone into active androgen dihydrotestosterone (DHT) which is involved in many androgen dependent disorders, such as androgenic alopecia, benign prostatic hyperplasia and acne. The method for screening for S5αR inhibition is key in finding new antagonists. In this study, the label-free S5αR inhibitory assay using LC-MS was developed. S5αR type 1 enzyme was obtained from LNCaP prostate cancer cells. The enzymatic assay was optimised for enzyme-substrate (testosterone) concentration, NADPH-cofactor concentration, solvent tolerance, enzyme activity stability and incubation time. The developed assay was validated by measuring the signal to background ratio (S/B), the signal to noise ratio (S/N), the signal window (SW) and the zeta factor Z' in accordance with published bioassay guidelines. The enzymatic reaction was performed in 96-well plates and DHT formation was determined by LC-MS. S/B, S/N, SW and Z' factor were well above acceptable criteria and the reproducibility was good using Z' factor other 3days and further validated by dutasteride and finasteride inhibition. The method was successfully applied to quantify S5αR inhibitory activity of some Thai herbal extracts. Two plant extracts, Impatiens balsamina L. and Curcuma longa L. showed IC₅₀ at 5.4±0.2 and 9.0±1.2μgmL^-1 and are therefore promising sources of new S5αR inhibitors. The assay has high selectability and reproducibility and suited to medium throughput screening required by phytochemistry.

Advances in coupling microfluidic chips to mass spectrometry

Microfluidic technology has shown advantages of low sample consumption, reduced analysis time, high throughput, and potential for integration and automation. Coupling microfluidic chips to mass spectrometry (Chip-MS) can greatly improve the overall analytical performance of MS-based approaches and expand their potential applications. In this article, we review the advances of Chip-MS in the past decade, covering innovations in microchip fabrication, microchips coupled to electrospray ionization (ESI)-MS and matrix-assisted laser desorption/ionization (MALDI)-MS. Development of integrated microfluidic systems for automated MS analysis will be further documented, as well as recent applications of Chip-MS in proteomics, metabolomics, cell analysis, and clinical diagnosis.

Lab-on-a-Chip hyphenation with mass spectrometry: strategies for bioanalytical applications

The Lab-on-a-Chip concept aims at miniaturizing laboratory processes to enable automation and/or parallelization via microfluidic chips that are capable of handling minute sample volumes. Mass spectrometry is nowadays the detection method of choice, because of its selectivity, sensitivity and wide application range. We review the most interesting examples over the last two-and-a-half years where the two techniques were used for bioanalytical applications. Furthermore, we discuss the merits and limitations of such hyphenated systems. We inventorize the reported applications and approaches. We see an ongoing trend towards chip-based liquid chromatography-mass spectrometry usage and small volume analysis applications, particularly in the field of proteomics where bottom-up approaches profit from chip-based technologies and hyphenation with complex cell cultures.

A simple TLC and HPTLC method for separation of selected steroid drugs

Chromatographic properties of five steroid drugs: cortisone, hydrocortisone, methylprednisolone, prednisolone and norgestrel have been studied by normal-, reversed-phase and hydrophilic neutral cyano-bonded silica stationary phase with five binary mobile phases (acetonitrile-water, acetonitrile-DMSO, acetonitrile-methanol, acetone-petroleum ether, acetone-water) in which the concentration of organic modifier was varied from 0 to 100% (v/v). This study reports the optimization of steroid hormones separation. Chromatographic retention data and possible retention mechanisms are discussed. Separation abilities of mobile and stationary phases were studied using the principal component analysis method. The best separation of methylprednisolone and prednisolone is with a chromatographic system included silica gel as stationary phase and mixture of acetonitrile and DMSO (10:90 v/v). These two anti-inflammatory drugs can be fast separated from norgestrel when CN is used as stationary phase and acetone and water (40:60 v/v) as mobile phase. The highest values of the parameter Δ(ΔG°) and alfa for cortisone and hydrocortisone was observed in case of using CN as stationary phase and water-acetonitryle (40:60 v/v) as mobile phase.