LC–ESI-MS/MS quantification of 4β-hydroxycholesterol and cholesterol in plasma samples of limited volume

A rapid quantitative UPLC-MS/MS method for analysis of key regulatory oxysterols in biological samples for liver cancer

An UPLC-APCI-MS/MS method was developed for the simultaneous determination of cholesterol, 7-dehydrocholesterol (7DHC) and eight oxysterols including 27-hydroxycholesterol (27OHC), 7α-hydroxycholesterol (7αOHC), 7β-hydroxycholesterol (7βOHC), 24S-hydroxycholesterol (24SOHC), 25-hydroxycholesterol (25OHC), 7α,24S-dihydroxycholesterol (7α,24SdiOHC), 7α,25-dihydroxycholesterol (7α,25diOHC), and 7α,27-dihydroxycholesterol (7α,27diOHC). It has been used for quantitative analysis of cholesterol, 7DHC and eight oxysterols in hepatocellular carcinoma (HCC) cells, plasma and tumor tissue samples. And the above compounds were extracted from the biological matrix (plasma and tissue) using liquid-liquid extraction with hexane/isopropanol after saponification to cleave the steroids from their esterified forms without further derivatization. Then cholesterol, 7DHC and oxysterols were separated on a reversed phase column (Agilent Zorbax Eclipse plus, C18) within 8 min using a gradient elution with 0.1 % formic acid in H2O and methanol and detected by an APCI triple quadrupole mass spectrometer. The lower limit of quantification (LLOQ) of the cholesterol, 7DHC and oxysterols ranged from 3.9 ng/mL to 31.25 ng/mL, and the recoveries ranged from 83.0 % to 113.9 %. Cholesterol, 7DHC and several oxysterols including 27OHC, 7αOHC and 7βOHC were successfully quantified in HCC cells, plasma, tissues and urine of HCC mice. Results showed that 27OHC was at high levels in three kind of HCC cells and tumor tissues as well as plasma samples from both HepG2 and Huh7 bearing mice model，and the high levels of 27OHC in tumors were associated with HCC development. Moreover, the levels of cholesterol in HCC cells and tumor issues varied in different HCC cells and mice model. Oxysterols profiling in biological samples might provide complementary information in cancer diagnosis.

LC-MS Approaches for Oxysterols in Various Biosamples

Oxysterols are involved in a plethora of biological processes, including a wide variety of diseases. Therefore, monitoring oxysterols is important for obtaining a deeper understanding of their biological roles and utilizing them as, for example, biomarkers. However, oxysterols can be challenging compounds to study, as they can be very similar in chemical structure but still have distinct biological roles. In addition, oxysterols may be difficult to detect, even with advanced analytical instrumentation. We here focus on the use of liquid chromatography-mass spectrometry (LC-MS) for the analysis of oxysterols, with an additional focus on the steps needed to prepare oxysterols for LC-MS. Steps can include chemical modification of the oxysterols for improving LC-MS sensitivity and adding chemicals that can reveal if the oxysterol levels have been perturbed during preparation. We then round off with descriptions and applications of various sample preparations for different biological matrices, from blood to cells, and biosamples with emerging attention, for example, exosomes and organoids. Taken together, oxysterol analysis is highly compatible with a wide variety of biosamples, allowing for a deeper understanding of these challenging analytes.

LC-MS/MS based quantification of steroidal biomarkers in polycystic ovary syndrome induced rats

Polycystic ovary syndrome (PCOS) is a common endocrine disorder that causes reproductive hormones imbalance, missed periods, infertility and distributed steroidogenesis. Reportedly, during PCOS, the endogenous levels of P4 (Progesterone), 17OHP4 (17-α hydroxy progesterone), and T4 (Testosterone) were significantly altered. Thus, quantification of steroid biomarkers involved in the steroidogenesis pathway of PCOS, such as P4, 17OHP4, and T4, holds significant importance. One important drawback of current methods is steroid metabolome traceability. Without adequate traceability, the findings of these techniques will be less reliable for identifying P4, 17OHP4, and T4. These methods also need a high sample size, especially for the most important biomarker that initiates steroidogenesis. To address these challenges, we require a new liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for steroid biomarker analysis. Herein the present work, using validated LC-MS/MS, PCOS biomarkers were measured and compared between normal control rats and PCOS-induced rats before and after analyte administration. The experiment utilized an isocratic separation method employing an analytical C18 column. The mobile phase consisted of acetonitrile (ACN) and aqueous 0.1% formic acid (FA) in a ratio of 90:10 (v/v). The plasma samples were processed with protein precipitation (PPT) followed by the liquid-liquid extraction (LLE) method. The lower limit of quantification (LLOQ) was 0.5 ng/mL in plasma. According to USFDA criteria, the method's systematic validation took into account linearity (r2 > 0.99), accuracy and precision of intra- and inter-batch measurements, stability, biomarker recovery (60-85%) and matrix effect (<± 15%), all of which were determined to be within range ( ± 15%). The pharmacokinetic data showed that, as compared to normal rats, PCOS-induced animals had significantly higher Cmax values for 17OHP4 and T4 (∼2 fold), while lower Cmax values for P4 (∼2 fold). The present work is novel and provides scientific information to explore systematic processes involved in steroidogenesis and boost clinical applicability for PCOS therapy.

Clinical Evaluation Based on a New Approach to Improve the Accuracy of 4β-Hydroxycholesterol Measurement as a Biomarker of CYP3A4 Activity

This study examines 4β-Hydroxycholesterol (4β-HC), which is considered to be a potential marker for the CYP3A4 induction of new chemical entities (NCEs) in drug development. To ensure the use of 4β-HC as a practical biomarker, it is necessary to accurately measure 4β-HC and demonstrate that CYP3A4 induction can be appropriately assessed, even for weak inducers. In clinical trials of NCEs, plasma is often collected with various anticoagulants, in some cases, the plasma is acidified, then stored for an extended period. In this study, we examined the effects of these manipulations on the measurement of 4β-HC, and based on the results, we optimized the plasma collection and storage protocols. We also found that a cholesterol oxidation product is formed when plasma is stored, and by monitoring the compound, we were able to identify when plasma was stored inappropriately. After evaluating the above, clinical drug-drug interaction (DDI) studies were conducted using two NCEs (novel retinoid-related orphan receptor γ antagonists). The weak CYP3A4 induction by the NCEs (which were determined based on a slight decline in the systemic exposure of a probe substrate (midazolam)), was detected by the significant increase in 4β-HC levels (more specifically, 4β-HC/total cholesterol ratios). Our new approach, based on monitoring a cholesterol oxidation product to identify plasma that is stored inappropriately, allowed for the accurate measurement of 4β-HC, and thus, it enabled the evaluation of weak CYP3A4 inducers in clinical studies without using a probe substrate.

Sensitive UHPLC-MS/MS quantification method for 4β- and 4α-hydroxycholesterol in human plasma for accurate CYP3A phenotyping

4β-Hydroxycholesterol (4β-OHC) is formed by CYP3A4 and CYP3A5 and has drawn attention as an endogenous phenotyping probe for CYP3A activity. However, 4β-OHC is also increased by cholesterol autooxidation occurring in vitro due to dysregulated storage and in vivo by oxidative stress or inflammation, independent of CYP3A activity. 4α-hydroxycholesterol (4α-OHC), a stereoisomer of 4β-OHC, is also formed via autooxidation of cholesterol, not by CYP3A, and thus may have clinical potential in reflecting the state of cholesterol autooxidation. In this study, we establish a sensitive method for simultaneous quantification of 4β-OHC and 4α-OHC in human plasma using ultra-high performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). Plasma samples were prepared by saponification, two-step liquid-liquid extraction, and derivatization using picolinic acid. Intense [M+H]+ signals for 4β-OHC and 4α-OHC di-picolinyl esters were monitored using electrospray ionization. The assay fulfilled the requirements of the US Food and Drug Administration guidance for bioanalytical method validation, with a lower limit of quantification of 0.5 ng/mL for both 4β-OHC and 4α-OHC. Apparent recovery rates from human plasma ranged from 88.2% to 101.5% for 4β-OHC, and 91.8% to 114.9% for 4α-OHC. Additionally, matrix effects varied between 86.2% and 117.6% for 4β-OHC, and between 89.5% and 116.9% for 4α-OHC. Plasma 4β-OHC and 4α-OHC concentrations in healthy volunteers, stage 3-5 chronic kidney disease (CKD) patients, and stage 5D CKD patients as measured by the validated assay were within the calibration ranges in all samples. We propose this novel quantification method may contribute to accurate evaluation of in vivo CYP3A activity.

Highly sensitive and selective detection of cytochrome P450 46A1 activity by a ultra-high-performance liquid chromatography-tandem mass spectrometry method

Cytochrome P450 46A1 (CYP46A1) is a key enzyme responsible for metabolizing cholesterol to 24-hydroxycholesterol in the brain, and thus might serve as a therapeutic target for several neurodegenerative disorders including Parkinson's disease, Alzheimer's disease and Huntington's disease. However, an applicable, sensitive and reliable method for the precise measurement of CYP46A1 activities in complex biological samples remains limited. In this study, a novel ultra-high-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for highly sensitive and selective determination of 24-hydroxycholesterol was developed to characterize CYP46A1 activity. The mass spectrometric detection was performed using multiple reaction monitoring for 24-hydroxcholesterol at m/z 385.2 → 367.2. The limit of quantification for 24-hydroxycholesterol using this UPLC-MS/MS method was as low as 10 nM, which is lower than those reported previously. The method also showed favorable accuracy and precision. Meanwhile, the short- and long-term stability of this method was fully validated. In addition, the method was successfully applied to investigate the kinetic properties of 24-hydroxycholesterol formation by CYP46A1.

Options of the Main Derivatization Approaches for Analytical ESI and MALDI Mass Spectrometry

The inclusion of preliminary chemical labeling (derivatization) in the analysis process by such powerful and widespread methods as electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) is a popular and widely used methodological approach. This is due to the need to remove some fundamental limitations inherent in these powerful analytic methods. Although a number of special reviews has been published discussing the utilization of derivatization approaches, the purpose of the present critical review is to comprehensively summarize, characterize and evaluate most of the previously developed and practically applied, as well as recently proposed representative derivatization reagents for ESI-MS and MALDI-MS platforms in their mostly sensitive positive ion mode and frequently hyphenated with separation techniques. The review is focused on the use of preliminary chemical labeling to facilitate the detection, identification, structure elucidation, quantification, profiling or MS imaging of compounds within complex matrices. Two main derivatization approaches, namely the introduction of permanent charge-fixed or highly proton affinitive residues into analytes are critically evaluated. In situ charge-generation, charge-switch and charge-transfer derivatizations are considered separately. The potential of using reactive matrices in MALDI-MS and chemical labeling in MS-based omics sciences is given.

Hybrid 213 nm photodissociation of cationized Sterol lipid ions yield [M]+. Radical products for improved structural characterization using multistage tandem mass spectrometry

Sterols are a class of lipid molecules that include cholesterol, oxysterols, and sterol esters. Sterol lipids play critical functional roles in mammalian biology, including the dynamic regulation of cell membrane fluidity, as precursors for the synthesis of bile acids, steroid hormones and vitamin D, as regulators of gene expression in lipid metabolism, and for cholesterol transport and storage. The most common method employed for sterol analysis is high performance liquid chromatography coupled with tandem mass spectrometry (MS/MS). However, conventional collision induced dissociation (CID) methods used for ion activation during MS/MS typically fail to provide sufficient structural information for unambiguous assignment of sterol species based on their fragmentation behaviour alone. This places a significant burden on the efficiency of the chromatographic separation methods for the effective separation of isomeric sterols. Here, toward developing an improved analysis strategy for sterol lipids, we have explored the novel use of 213 nm photodissociation MS/MS and hybrid multistage-MS/MS (i.e., MSⁿ) data acquisition approaches for the improved structural characterization of cholesterol, representative isomeric oxysterols, and cholesteryl esters. Most notably, UVPD-MS/MS of ammoniated, lithiated and sodiated adducts of cholesterol, several representative oxysterol species, and an oxosterol lipid, are shown to give rise to abundant [M]^+. radical cation products, that subsequently fragment during collision induced MS³ to yield extensive structurally informative product ions, similar to those observed by Electron Ionization, and that enable their unambiguously assignment, including isomeric differentiation of oxysterols. For cholesterol esters, a reversed hybrid collision induced-MS/MS and UVPD-MS³ approach is shown to enable assignment of the sterol backbone, and localization of the site(s) of unsaturation within esterified fatty acyl chains.

Cholesterol and oxysterol sulfates: Pathophysiological roles and analytical challenges

Cholesterol and oxysterol sulfates are important regulators of lipid metabolism, inflammation, cell apoptosis, and cell survival. Among the sulfate-based lipids, cholesterol sulfate (CS) is the most studied lipid both quantitatively and functionally. Despite the importance, very few studies have analysed and linked the actions of oxysterol sulfates to their physiological and pathophysiological roles. Overexpression of sulfotransferases confirmed the formation of a range of oxysterol sulfates and their antagonistic effects on liver X receptors (LXRs) prompting further investigations how are the changes to oxysterol/oxysterol sulfate homeostasis can contribute to LXR activity in the physiological milieu. Here, we aim to bring together for novel roles of oxysterol sulfates, the available techniques and the challenges associated with their analysis. Understanding the oxysterol/oxysterol sulfate levels and their pathophysiological mechanisms could lead to new therapeutic targets for metabolic diseases. LINKED ARTICLES: This article is part of a themed issue on Oxysterols, Lifelong Health and Therapeutics. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.16/issuetoc.

LC-MS/MS quantification of 7α-hydroxy-4-cholesten-3-one (C4) in rat and monkey plasma

7α-hydroxy-4-cholesten-3-one (C4) is an oxidative enzymatic product of cholesterol metabolism via cholesterol 7α-hydroxylase, an enzyme also known as cholesterol 7-alpha-monooxygenase or cytochrome P450 7A1 (CYP7A1). C4 is a stable intermediate in the rate limiting pathway of bile acid biosynthesis. Previous studies showed that plasma C4 levels correlated with CYP7A1 enzymatic activity and could serve as a biomarker for bile acid synthesis. Here we developed and qualified a simple and robust high-throughput method using liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) to quantify C4 in rat and monkey plasma. As C4 being an endogenous compound, this method used calibration standards in 50/50: acetonitrile/water (v/v). In order to mimic the incurred samples, quality control samples were prepared in the authentic plasma. Stable isotope labeled C4 (C4-d₇) was used as the internal standard. The sample volume for analysis was 20μL and the sample preparation method was protein precipitation with acetonitrile. The average endogenous C4 concentrations, from 10 different lots of rat and monkey plasma, were 53.0±16.5ng/mL and 6.8±5.6ng/mL, respectively. Based on these observed endogenous C4 levels, the calibration curve ranges were established at 1-200ng/mL and 0.5-100ng/mL for rat assay and monkey assay, respectively. The method was qualified with acceptable accuracy, precision, linearity, and specificity. Matrix effect, recovery, and plasma stability of bench-top, freeze-thaw, and long-term frozen storage were also evaluated. The method has been successfully applied to pre-clinical studies.

Rapid LC-MS/MS method for the determination of 4-hydroxycholesterol/cholesterol ratio in serum as endogenous biomarker for CYP3A activity in human and foals

Cytochrome P450 3A (CYP) enzymes are involved in the elimination of many drugs and are known to be regulated by several environmental factors. Thus, it was the aim of this study to develop and validate an analytical method allowing estimation of the hepatic CYP3A enzyme activity using the 4-hydroxycholesterol to cholesterol ratio as an endogenous biomarker in serum. Both compounds were isolated from the biological matrix by liquid-liquid extraction using n-hexane after saponification with ethanolic sodium methoxide solution (2M) to cleave the steroids from their esterified forms without any kind of further derivatization. Chromatographic separation was achieved on a reversed-phase column (SupelcoAcsentis(®), C8) within 7min using an isocratic elution with ammonium acetate 5mM (pH=3.8, 10%) and acetonitrile (90%) at a flow rate of 300μl/min. d6-cholesterol and d7-4β-hydroxycholesterol were used as internal standards. Detection was done on a triple quadrupole mass spectrometer using the following mass transitions: 369.3/161.5, 369.3/147.1 and 369.3/95.2 for cholesterol; 385.2/367.4, 385.2/109.1 for 4-hydroxycholesterol; 374.4/152.7 and 392.2/108.9 for d6-cholesterol and d7-4-hydroxycholesterol, respectively as the internal standards. The method was validated according to current bioanalytical guidelines considering selectivity, linearity, accuracy, precision, recovery, stability. The analytical range was 5-250 and 50-1000ng/ml, for 4-hydroxycholesterol and cholesterol, respectively. The method was shown to be selective for both compounds with good linearity over the selected range (r>0.99) as well as good within- and between day accuracy (error: -1.2-3.7% for 4-hydroxycholesterol and -7.7-9.5% for cholesterol) and within- and between day precision (2.1-14.6% for 4-hydroxycholesterol and 1.1-14.9% for cholesterol). Recovery was found to be over 80% for both analytes while significant stability issues could not be observed. Finally, the validated assay was applied to measure 4-hydroxycholesterol and cholesterol in serum samples of clinical studies in humans and foals that could verify induction of hepatic CYP3A4 (human) and CYP3A89 (foals) after premedication with the known enzyme inducer rifampicin.

Determination of 7α-OH cholesterol by LC-MS/MS: Application in assessing the activity of CYP7A1 in cholestatic minipigs

An LC-MS/MS method was developed and validated to determine 7α-OH cholesterol in liver microsome. This method was convenient and fast with high specificity and sensitivity. Briefly, a gradient elution was performed on a Synergi polar-C18 column (50×4.6mm i.d., 3μm). The mobile phase (consisting of 0.1% HCOOH solution and acetonitrile) eluted in gradient at a flow rate of 1ml/min. MS detection was operated on APCI (+) mode; the MRM transitions for 7α-OH cholesterol and D7-cholesterol (I.S.) were 385.1≥159.1 and 376.4≥266.3, respectively. The linear response range of 7α-OH cholesterol was covered from 1.563 to 100.0ng/ml. All of the validation items meet the requirement of FDA guidance for bioanalytical method validation. This method was applied to enzymatic studies for determination of cholesterol 7alpha-hydroxylation activity catalyzed by CYP7A1 in the cholestatic minipigs liver microsomes.

Use of 4β-hydroxycholesterol in animal and human plasma samples as a biomarker for CYP3A induction

Background: 4β-hydroxycholesterol (4βHC) has recently been proposed as a potential endogenous biomarker for CYP3A activity. Developing bioanalytical assays for 4βHC is challenging for several reasons, including endogenous background levels in plasma; the presence of free and ester forms; the inherent lack of MS sensitivity; and the presence of multiple positional isomers. Results: Bioanalytical assays in mouse, rat, dog and human plasma were adapted and modified from a previous published human plasma assay for 4βHC by using alkaline de-esterification, picolinic derivatization, a surrogate analyte (d7-4βHC) in authentic matrices and chromatographic conditions that showed good separation from isobaric, positional isomers. Conclusion: These assays were applied to multiple studies and demonstrated potential applications of 4βHC as a CYP3A biomarker across preclinical and clinical settings.