Simultaneous profiles of sulfonated androgens, sulfonated estrogens and sulfonated progestogens in postpubertal boars (sus scrofa domestica) measured by LC-MS/MS

Quantification of glucocorticoid and progestogen metabolites in bovine plasma, skimmed milk and saliva by UHPLC-HR-MS with polarity switching

Steroid metabolites are increasingly in focus when searching for novel biomarkers in physiological mechanisms and their disorders. While major steroids such as progesterone and cortisol are well-researched and routinely determined to assess the health, particularly the reproductive status of mammals, the function of potentially biologically active progestogen and glucocorticoid metabolites is widely unexplored. One of the main reasons for this is the lack of comprehensive, sensitive, and specific analytical methods. This is particularly the case when analyzing matrices like milk or saliva obtained by non-invasive sampling with steroid concentrations often below those present in plasma. Therefore, a new UHPLC-HR-MS method based on an Ultimate UHPLC system equipped with an Acquity HSS T3 reversed-phase column and a Q Exactive™ mass spectrometer was developed, enabling the simultaneous chromatographic separation, detection and quantification of eleven isobaric glucocorticoids (11-dehydrocorticosterone (A), corticosterone (B), cortisol (F), cortisone (E), the tetrahydrocortisols (THF): 3α,5α-THF, 3α,5β-THF, 3β,5α-THF, 3β,5β-THF, and the tetrahydrocortisones (THE): 3α,5α-THE, 3α,5β-THE, 3β,5α-THE) and twelve progestogens (progesterone (P4), pregnenolone (P5), the dihydroprogesterones (DHP): 20α-DHP, 20β-DHP, 3α-DHP, 3β-DHP, 5α-DHP, 5β-DHP, and the tetrahydroprogesterones (THP): 3α,5α-THP, 3α,5β-THP, 3β,5α-THP, 3β,5β-THP) in bovine plasma, skimmed milk, and saliva. A simple liquid-liquid extraction (LLE) with MTBE (methyl tert-butyl ether) was used for sample preparation of 500 μL plasma, skimmed milk, and saliva. Heated electrospray ionization (HESI) with polarity switching was applied to analyze steroids in high-resolution full scan mode (HR-FS). The method validation covered the investigation of sensitivity, selectivity, curve fitting, carry-over, accuracy, precision, recovery, matrix effects and applicability. A high sensitivity in the range of pg mL-1 was achieved for all steroids suitable for the analysis of authentic samples.

Comparative Analysis of Epididymis Cauda of Yak before and after Sexual Maturity

Epididymis development is the basis of male reproduction and is a crucial site where sperm maturation occurs. In order to further understand the epididymal development of yak and how to regulate sperm maturation, we conducted a multi-omics analysis. We detected 2274 differential genes, 222 differential proteins and 117 co-expression genes in the cauda epididymis of yak before and after sexual maturity by RNA-seq and proteomics techniques, which included TGFBI, COL1A1, COL1A2, COL3A1, COL12A1, SULT2B1, KRT19, and NPC2. These high abundance genes are mainly related to cell growth, differentiation, adhesion and sperm maturation, and are mainly enriched via extracellular matrix receptor interaction, protein differentiation and absorption, and lysosome and estrogen signaling pathways. The abnormal expression of these genes may lead to the retardation of epididymal cauda development and abnormal sperm function in yak. In conclusion, through single and combined analysis, we provided a theoretical basis for the development of the yak epididymal cauda, sperm maturation, and screening of key genes involved in the regulation of male yak reproduction.

Steroid sulfates in domestic mammals and laboratory rodents

Historically steroid sulfates have been considered predominantly as inactive metabolites. It was later discovered that by cleavage of the sulfate residue by steroid sulfatase (STS), they can be (re-)converted into active forms or into precursors for the local production of active steroids. This sulfatase pathway is now a very active field of research, which has gained considerable interest particularly in connection with the steroid metabolism of human steroid hormone-dependent cancer tissue. In comparison, there is much less information available on the occurrence of the sulfatase pathway in physiological settings, where the targeted uptake of steroid sulfates by specific transporters and their hydrolysis could serve to limit steroid effects to a subgroup of potentially steroid responsive cells. In humans, steroid sulfates of adrenal origin circulate in intriguingly high concentrations throughout most of life. Thus, ample substrate is available for the sulfatase pathway regardless of sex. However, the abundant adrenal output of steroid sulfates is a specific feature of select primates. Compared to humans, in our domestic mammals (dogs, cats, domestic ungulates) and laboratory rodents (mouse, rat) research into the biology of steroid sulfates is still in its infancy and information on the subject has so far been largely limited to punctual observations, which indicate considerable species-specific peculiarities. The aim of this overview is to provide a summary of the relevant information available in the above-mentioned species, predominantly taking into account data on concentrations of steroid sulfates in blood as well as the expression patterns and activities of relevant sulfotransferases and STS.

Concentrations of sulphated estrone, estradiol and dehydroepiandrosterone measured by mass spectrometry in pregnant mares

BACKGROUND

Few studies have provided a longitudinal analysis of systemic concentrations of conjugated oestrogens (and androgens) throughout pregnancy in mares, and those only using immunoassay. The use of liquid chromatography tandem mass spectrometry (LC-MS/MS) will provide more accurate concentrations of circulating conjugated steroids.

OBJECTIVES

To characterise circulating concentrations of individual conjugated steroids throughout equine gestation by using LC-MS/MS.

STUDY DESIGN

Longitudinal study and comparison of pregnant mares treated with vehicle or letrozole in late gestation.

METHODS

Sulphated oestrogens and androgens were measured in mares throughout gestation and mares in late gestation (8-11 months) treated with vehicle or letrozole to inhibit oestrogen synthesis in late gestation. An analytical method was developed using LC-MS/MS to evaluate sulphated estrone, estradiol, testosterone and dehydroepiandrosterone (DHEAS) during equine gestation.

RESULTS

Estrone sulphate concentrations peaked by week 26 at almost 60 μg/mL, 50-fold higher than have been reported in studies using immunoassays. An increase in DHEAS was detected from 7 to 9 weeks of gestation, but concentrations remained consistently low (if detected) for the remainder of gestation and testosterone sulphate was undetectable at any stage. Estradiol sulphate concentrations were highly correlated with estrone sulphate but were a fraction of their level. Concentrations of both oestrogen sulphates decreased from their peak to parturition. Letrozole inhibited estrone and estradiol sulphate concentrations at 9.25 and 10.5 months of gestation but, no increase in DHEAS was observed.

MAIN LIMITATIONS

Limited number of mares sampled and available for analysis, lack of analysis of 5α-reduced and B-ring unsaturated steroids due to lack of available standards.

CONCLUSIONS

Dependent on methods of extraction and chromatography, and the specificity of primary antisera, immunoassays may underestimate oestrogen conjugate concentrations in blood from pregnant mares and may detect androgen conjugates (neither testosterone sulphate nor DHEAS were detected here by LC-MS/MS) that probably peak coincident with oestrogen conjugates between 6 and 7 months of equine gestation.

SULFATION PATHWAYS: Formation and hydrolysis of sulfonated estrogens in the porcine testis and epididymis

Boars exhibit high concentrations of sulfonated estrogens (SE) mainly originating from the testicular-epididymal compartment. Intriguingly, in porcine Leydig cells, sulfonation of estrogens is colocalized with aromatase and steroid sulfatase (STS), indicating that de novo synthesis of unconjugated estrogens (UE), their sulfonation and hydrolysis of SE occur within the same cell type. So far in boars no plausible concept concerning the role of SE has been put forward. To obtain new information on SE formation and hydrolysis, the porcine testicular-epididymal compartment was screened for the expression of the estrogen-specific sulfotransferase SULT1E1 and STS applying real-time RT-qPCR, Western blot and immunohistochemistry. The epididymal head was identified as the major site of SULT1E1 expression, whereas in the testis, it was virtually undetectable. However, SE tissue concentrations are clearly consistent with the testis as the predominant site of estrogen sulfonation. Results from measurements of estrogen sulfotransferase activity indicate that in the epididymis, SULT1E1 is the relevant enzyme, whereas in the testis, estrogens are sulfonated by a different sulfotransferase with a considerably lower affinity. STS expression and activity was high in the testis (Leydig cells, rete testis epithelium) but also present throughout the epididymis. In the epididymis, SULT1E1 and STS were colocalized in the ductal epithelium, and there was evidence for their apocrine secretion into the ductal lumen. The results suggest that in porcine Leydig cells, SE may be produced as a reservoir to support the levels of bioactive UE via the sulfatase pathway during periods of low activity of the pulsatile testicular steroidogenesis.

SULFATION PATHWAYS: Expression of SULT2A1, SULT2B1 and HSD3B1 in the porcine testis and epididymis

In the porcine testis, in addition to estrogen sulfates, the formation of numerous sulfonated neutral hydroxysteroids has been observed. However, their functions and the underlying synthetic pathways are still widely unclear. To obtain further information on their formation in postpubertal boars, the expression of sulfotransferases considered relevant for neutral hydroxysteroids (SULT2A1, SULT2B1) was investigated in the testis and defined segments of the epididymis applying real-time RT-qPCR, Western blot and immunohistochemistry (IHC). Sulfotransferase activities were assessed in tissue homogenates or cytosolic preparations applying dehydroepiandrosterone and pregnenolone as substrates. A high SULT2A1 expression was confirmed in the testis and localized in Leydig cells by IHC. In the epididymis, SULT2A1 expression was virtually confined to the body. SULT2B1 expression was absent or low in the testis but increased significantly along the epididymis. Immunohistochemical observations indicate that both enzymes are secreted into the ductal lumen via an apocrine mechanism. The results from the characterization of expression patterns and activity measurements suggest that SULT2A1 is the prevailing enzyme for the sulfonation of hydroxysteroids in the testis, whereas SULT2B1 may catalyze the formation of sterol sulfates in the epididymis. In order to obtain information on the overall steroidogenic capacity of the porcine epididymis, the expression of important steroidogenic enzymes (CYP11A1, CYP17A1, CYP19, HSD3B1, HSD17B3, SRD5A2) was monitored in the defined epididymal segments applying real-time RT-qPCR. Surprisingly, in addition to a high expression of SRD5A2 in the epididymal head, a substantial expression of HSD3B1 was detected, which increased along the organ.

Human DHEA sulfation requires direct interaction between PAPS synthase 2 and DHEA sulfotransferase SULT2A1

The high-energy sulfate donor 3′-phosphoadenosine-5′-phosphosulfate (PAPS), generated by human PAPS synthase isoforms PAPSS1 and PAPSS2, is required for all human sulfation pathways. Sulfotransferase SULT2A1 uses PAPS for sulfation of the androgen precursor dehydroepiandrosterone (DHEA), thereby reducing downstream activation of DHEA to active androgens. Human PAPSS2 mutations manifest with undetectable DHEA sulfate, androgen excess, and metabolic disease, suggesting that ubiquitous PAPSS1 cannot compensate for deficient PAPSS2 in supporting DHEA sulfation. In knockdown studies in human adrenocortical NCI-H295R1 cells, we found that PAPSS2, but not PAPSS1, is required for efficient DHEA sulfation. Specific APS kinase activity, the rate-limiting step in PAPS biosynthesis, did not differ between PAPSS1 and PAPSS2. Co-expression of cytoplasmic SULT2A1 with a cytoplasmic PAPSS2 variant supported DHEA sulfation more efficiently than co-expression with nuclear PAPSS2 or nuclear/cytosolic PAPSS1. Proximity ligation assays revealed protein–protein interactions between SULT2A1 and PAPSS2 and, to a lesser extent, PAPSS1. Molecular docking studies showed a putative binding site for SULT2A1 within the PAPSS2 APS kinase domain. Energy-dependent scoring of docking solutions identified the interaction as specific for the PAPSS2 and SULT2A1 isoforms. These findings elucidate the mechanistic basis for the selective requirement for PAPSS2 in human DHEA sulfation.