Comprehensive profiling of ceramides in human serum by liquid chromatography coupled to tandem mass spectrometry combining data independent/dependent acquisition modes

Ceramides are sphingolipids with a structural function in the cell membrane and are involved in cell differentiation, proliferation and apoptosis. Recently, these chemical species have been pointed out as potential biomarkers in different diseases, due to their abnormal levels in blood. In this research, we present an overall strategy combining data-independent and dependent acquisitions (DIA and DDA, respectively) for identification, confirmation, and quantitative determination of ceramides in human serum. By application of liquid chromatography-tandem mass spectrometry (LC-MS/MS) method in DIA mode we identified 49 ceramides including d18:1, d18:0, d18:2, d16:1, d17:1 and t18:0 species. Complementary, quantitative determination of ceramides was based on a high-throughput and fully automated method consisting of solid-phase extraction on-line coupled to LC-MS/MS in DDA to improve analytical features avoiding the errors associated to sample processing. Quantitation limits were at pg mL-1 level, the intra-day and between-days variability were below 20 and 25 %, respectively; and the accuracy, expressed as bias, was always within ±25 %. The proposed method was tested with the CORDIOPREV cohort in order to obtain a qualitative and quantitative profiling of ceramides in human serum. This characterization allowed identifying d18:1 ceramides as the most concentrated with 70.8% of total concentration followed by d18:2 and d18:0 with 13.0 % and 8.8 %, respectively. Less concentrated ceramides, d16:1, d17:1 and t18:0, reported a 7.1 % of the total content. Combination of DIA and DDA LC-MS/MS analysis enabled to profile qualitative and quantitatively ceramides in human serum.

Qualitative and quantitative determination of phenols and their metabolites in urine by in-syringe solid-phase extraction and LC-MS/MS analysis for evaluation of virgin olive oil metabolism

To know the bioavailability of virgin olive oil (VOO) phenols and its impact on health, it is necessary to determine the levels of phenols excreted in urine. We present here a novel strategy for in-syringe solid-phase extraction and analysis of the extract by liquid chromatography-tandem mass spectrometry (LC-MS/MS), using ammonium fluoride as ionization agent to enhance sensitivity. This approach allows avoiding additional steps such as solvent evaporation or analytes derivatization. The method can be used with a previous acid hydrolysis for quantitative determination of tyrosol and hydroxytyrosol to estimate metabolized phenols. We tested this application by analysis of a cohort of volunteers (n = 20) after a standardized intake of VOO. Additionally, the method can be used as such for metabolite profiling of phenolic derivatives in urine using LC-MS/MS in high-resolution data-independent acquisition (DIA). Information about the phenolic profile of the consumed VOO and the human metabolism is thus obtained. The proposed approach represents a simple and versatile tool for qualitative and quantitative characterization of VOO phenolic metabolism.

The Longitudinal Changes in Subcutaneous Abdominal Tissue and Visceral Adipose Tissue Volumetries Are Associated with Iron Status

Excess iron is known to trigger adipose tissue dysfunction and insulin resistance. Circulating markers of iron status have been associated with obesity and adipose tissue in cross-sectional studies. We aimed to evaluate whether iron status is linked to changes in abdominal adipose tissue longitudinally. Subcutaneous abdominal tissue (SAT) and visceral adipose tissue (VAT) and its quotient (pSAT) were assessed using magnetic resonance imaging (MRI), at baseline and after one year of follow-up, in 131 (79 in follow-up) apparently healthy subjects, with and without obesity. Insulin sensitivity (euglycemic- hyperinsulinemic clamp) and markers of iron status were also evaluated. Baseline serum hepcidin (p = 0.005 and p = 0.002) and ferritin (p = 0.02 and p = 0.01)) were associated with an increase in VAT and SAT over one year in all subjects, while serum transferrin (p = 0.01 and p = 0.03) and total iron-binding capacity (p = 0.02 and p = 0.04) were negatively associated. These associations were mainly observed in women and in subjects without obesity, and were independent of insulin sensitivity. After controlling for age and sex, serum hepcidin was significantly associated with changes in subcutaneous abdominal tissue index (iSAT) (β = 0.406, p = 0.007) and visceral adipose tissue index (iVAT) (β = 0.306, p = 0.04), while changes in insulin sensitivity (β = 0.287, p = 0.03) and fasting triglycerides (β = -0.285, p = 0.03) were associated with changes in pSAT. These data indicated that serum hepcidin are associated with longitudinal changes in SAT and VAT, independently of insulin sensitivity. This would be the first prospective study evaluating the redistribution of fat according to iron status and chronic inflammation.

Combining data acquisition modes in liquid-chromatography-tandem mass spectrometry for comprehensive determination of acylcarnitines in human serum

Acylcarnitines (ACs) are metabolites involved in fatty acid β-oxidation and organic acid metabolism. Metabolic disorders associated to these two processes can be evaluated by determining the complete profile of ACs. In this research, we present an overall strategy for identification, confirmation, and quantitative determination of acylcarnitines in human serum. By this strategy we identified the presence of 47 ACs from C2 to C24 with detection of the unsaturation degree by application of a data-independent acquisition (DIA) liquid chromatography-tandem mass spectrometry (LC-MS/MS) method. Complementary, quantitative determination of ACs is based on a high-throughput and fully automated method consisting of solid-phase extraction on-line coupled to LC-MS/MS in data-dependent acquisition (DDA) to improve analytical features avoiding the errors associated to sample processing. Quantitation limits were at pg mL^-1 level, the intra-day and between-day variability were below 15-20%, respectively; and the accuracy, expressed as bias, was always within ± 25%. The proposed method was tested with 40 human volunteers to determine the relative concentration of ACs in serum and identify predominant forms. Significant differences were detected by comparing the ACs profile of obese versus non-obese individuals.

Fully automated method for quantitative determination of steroids in serum: An approach to evaluate steroidogenesis

Steroidogenesis is a set of metabolic reactions where the enzymes play a key role to control the physiological levels of steroids. A deficiency in steroidogenesis induces an accumulation and/or insufficiency of steroids in human blood and can lead to different pathologies. This issue added to the low levels of steroids (pg mL^-1 to ng mL^-1) in this biofluid make of their determination an analytical challenge. In this research, we present a high-throughtput and fully automated method based on solid-phase extraction on-line coupled to liquid chromatography with tandem mass spectrometry detection (SPE-LC-MS/MS) to quantify estrogens (estrone and estradiol), androgens (testosterone, androstenedione, dihydrotestosterone and dehydroepiandrosterone), progestogens (progesterone, pregnenolone, 17-hydroxyprogesterone and 17-hydroxypregnenolone), glucocorticoids (21-hydroxyprogesterone, 11-deoxycortisol, cortisone, corticosterone and cortisol) and one mineralocorticoid (aldosterone) in human serum. The performance of the SPE step and the multiple reaction monitoring (MRM) mode allowed reaching a high sensitivity and selectivity levels without any derivatization reaction. The fragmentation mechanisms of the steroids were complementary studied by LC-MS/MS in high-resolution mode to confirm the MRM transitions. The method was characterized with two SPE sorbents with similar physico-chemical properties. Thus, limits of quantification were at pg mL^-1 levels, the variability was below 25% (except for pregnenolone and cortisone), and the accuracy, expressed as bias, was always within ±25%. The proposed method was tested in human serum from ten volunteers, who reported levels for the sixteen target steroids that were satisfactorily in agreement with the physiological ranges reported in the literature.

Gut microbiota steroid sexual dimorphism and its impact on gonadal steroids: influences of obesity and menopausal status

BACKGROUND

Gonadal steroid hormones have been suggested as the underlying mechanism responsible for the sexual dimorphism observed in metabolic diseases. Animal studies have also evidenced a causal role of the gut microbiome and metabolic health. However, the role of sexual dimorphism in the gut microbiota and the potential role of the microbiome in influencing sex steroid hormones and shaping sexually dimorphic susceptibility to disease have been largely overlooked. Although there is some evidence of sex-specific differences in the gut microbiota diversity, composition, and functionality, the results are inconsistent. Importantly, most of these studies have not taken into account the gonadal steroid status. Therefore, we investigated the gut microbiome composition and functionality in relation to sex, menopausal status, and circulating sex steroids.

RESULTS

No significant differences were found in alpha diversity indices among pre- and post-menopausal women and men, but beta diversity differed among groups. The gut microbiota from post-menopausal women was more similar to men than to pre-menopausal women. Metagenome functional analyses revealed no significant differences between post-menopausal women and men. Gonadal steroids were specifically associated with these differences. Hence, the gut microbiota of pre-menopausal women was more enriched in genes from the steroid biosynthesis and degradation pathways, with the former having the strongest fold change among all associated pathways. Microbial steroid pathways also had significant associations with the plasma levels of testosterone and progesterone. In addition, a specific microbiome signature was able to predict the circulating testosterone levels at baseline and after 1-year follow-up. In addition, this microbiome signature could be transmitted from humans to antibiotic-induced microbiome-depleted male mice, being able to predict donor's testosterone levels 4 weeks later, implying that the microbiota profile of the recipient mouse was influenced by the donor's gender. Finally, obesity eliminated most of the differences observed among non-obese pre-menopausal women, post-menopausal women, and men in the gut microbiota composition (Bray-Curtis and weighted unifrac beta diversity), functionality, and the gonadal steroid status.

CONCLUSIONS

The present findings evidence clear differences in the gut microbial composition and functionality between men and women, which is eliminated by both menopausal and obesity status. We also reveal a tight link between the gut microbiota composition and the circulating levels of gonadal steroids, particularly testosterone. Video Abstract.

Development of a quantitative method for determination of steroids in human plasma by gas chromatography-negative chemical ionization-tandem mass spectrometry

Sex steroids are involved in biological functions that encompass from the complete sexual development of individuals up to the deregulation of metabolic pathways leading to some pathologies. Steroids are present in blood at low concentration levels from pg mL^-1 to ng mL^-1. For this reason, a high sensitive and selective method based on gas chromatography-negative chemical ionization-tandem mass spectrometry (GC-NCI-MS/MS) is here proposed to quantify either androgens (androstenedione, dehydroepiandrosterone, dihydrotestosterone and testosterone), estrogens (estrone and estradiol) and a progestogen (progesterone) in human plasma. The sample preparation steps, protein precipitation and solid phase extraction, were optimized to ensure the sample matrix removal and to extract steroids with high efficiency. The NCI-MS/MS detection approach was compared with that based on electron impact to evaluate the incidence of the ionization source in the determination of steroids. The quantification limits for determination of these analytes were in a range from 10 pg mL^-1 to 5 ng mL^-1, with a high sensitivity for estrogens, typically found at low concentrations. The proposed method was tested for the determination of steroids in male blood samples, in which 6 out of 7 steroids were detected and quantified to report concentration values in agreement with those described in the literature.

Study of sample preparation for determination of endocannabinoids and analogous compounds in human serum by LC-MS/MS in MRM mode

Endocannabinoids are lipids with a key role in physiological processes such as the immune response or the metabolism. This involvement explains their association to pathologies such as cancer, obesity or multiple sclerosis. The determination of endocannabinoids constitutes a challenge for clinical laboratories due to the variety of biological matrices and the wide range of concentrations at which they can be found. This research deals with the comparison of three sample preparation strategies (viz., on-line SPE, off-line SPE for interferents removal, and protein precipitation) for subsequent LC-MS/MS analysis of 14 endocannabinoids and analogous compounds in serum. As a result, the on-line coupling between SPE and LC-MS/MS is proposed as the best approach for this determination. The proposed method allows full automation of the overall process, shortening of the analysis time, and avoidance of errors associated with sample preparation steps. The improvement in sensitivity and selectivity thus achieved allows obtaining quantification limits at the pg mL^-1 level, which makes possible the application of the method for clinical studies.

Metabolomics: A potential way to know the role of vitamin D on multiple sclerosis

The literature about the influence of vitamin D on multiple sclerosis (MS) is very controversial, possibly as a result of the way through which the research on the subject has been conducted. The studies developed so far have been focused exclusively on gene expression: the effect of a given vitamin D metabolite on target receptors. The influence of the vitamin D status (either natural or after supplementation) on MS has been studied by measurement of the 25 monohydroxylated metabolite (also known as circulating form), despite the 1,25 dihydroxylated metabolite is considered the active form. In the light of the multiple metabolic pathways in which both forms of vitamin D (D₂ and D₃) are involved, monitoring of the metabolites is crucial to know the activity of the target enzymes as a function of both the state of the MS patient and the clinical treatment applied. The study of metabolomics aspects is here proposed to clarify the present controversy. In "omics" terms, our proposal is to take profit from up-stream information-thus is, from metabolomics to genomics-with a potential subsequent step to systems biology, if required.