Effects of organochlorine pesticides on human and rat 17ß-hydroxysteroid dehydrogenase 1 activity: Structure-activity relationship and in silico docking analysis.

The objective of this study was to examine the effect of 11 organochlorine pesticides on human and rat 17ß-Hydroxysteroid dehydrogenase 1 (17ß-HSD1) in human placental and rat ovarian microsome and on estradiol production in BeWo cells. The results showed that the IC50 values for endosulfan, fenhexamid, chlordecone, and rhothane on human 17ß-HSD1 were 21.37, 73.25, 92.80, and 117.69 µM. Kinetic analysis revealed that endosulfan acts as a competitive inhibitor, fenhexamid as a mixed/competitive inhibitor, chlordecone and rhothane as a mixed/uncompetitive inhibitor. In BeWo cells, all insecticides except endosulfan significantly decreased estradiol production at 100 µM. For rats, the IC50 values for dimethomorph, fenhexamid, and chlordecone were 11.98, 36.92, and 109.14 µM. Dimethomorph acts as a mixed inhibitor, while fenhexamid acts as a mixed/competitive inhibitor. Docking analysis revealed that endosulfan and fenhexamid bind to the steroid-binding site of human 17ß-HSD1. On the other hand, chlordecone and rhothane binds to a different site other than the steroid and NADPH-binding site. Dimethomorph binds to the steroid/NADPH binding site, and fenhexamid binds to the steroid binding site of rat 17ß-HSD1. Bivariate correlation analysis showed a positive correlation between IC50 values and LogP for human 17ß-HSD1, while a slight negative correlation was observed between IC50 values and the number of HBA. ADMET analysis provided insights into the toxicokinetics and toxicity of organochlorine pesticides. In conclusion, this study identified the inhibitory effects of 3-4 organochlorine pesticides and binding mechanisms on human and rat 17ß-HSD1, as well as their impact on hormone production.

Structural basis of lipid-droplet localization of 17-beta-hydroxysteroid dehydrogenase 13.

Hydroxysteroid 17-beta-dehydrogenase 13 (HSD17B13) is a hepatic lipid droplet-associated enzyme that is upregulated in patients with non-alcoholic fatty liver disease. Recently, there have been several reports that predicted loss of function variants in HSD17B13 protect against the progression of steatosis to non-alcoholic steatohepatitis with fibrosis and hepatocellular carcinoma. Here we report crystal structures of full length HSD17B13 in complex with its NAD+ cofactor, and with lipid/detergent molecules and small molecule inhibitors from two distinct series in the ligand binding pocket. These structures provide insights into a mechanism for lipid droplet-associated proteins anchoring to membranes as well as a basis for HSD17B13 variants disrupting function. Two series of inhibitors interact with the active site residues and the bound cofactor similarly, yet they occupy different paths leading to the active site. These structures provide ideas for structure-based design of inhibitors that may be used in the treatment of liver disease.

Substituted Aryl Benzylamines as Potent and Selective Inhibitors of 17ß-Hydroxysteroid Dehydrogenase Type 3.

17ß-Hydroxysteroid dehydrogenase type 3 (17ß-HSD3) is expressed at high levels in testes and seminal vesicles; it is also present in prostate tissue and involved in gonadal and non-gonadal testosterone biosynthesis. The enzyme is membrane-bound, and a crystal structure is not yet available. Selective aryl benzylamine-based inhibitors were designed and synthesised as potential agents for prostate cancer therapeutics through structure-based design, using a previously built homology model with docking studies. Potent, selective, low nanomolar IC50 17ß-HSD3 inhibitors were discovered using N-(2-([2-(4-chlorophenoxy)phenylamino]methyl)phenyl)acetamide (1). The most potent compounds have IC50 values of approximately 75 nM. Compound 29, N-[2-(1-Acetylpiperidin-4-ylamino)benzyl]-N-[2-(4-chlorophenoxy)phenyl]acetamide, has an IC50 of 76 nM, while compound 30, N-(2-(1-[2-(4-chlorophenoxy)-phenylamino]ethyl)phenyl)acetamide, has an IC50 of 74 nM. Racemic C-allyl derivative 26 (IC50 of 520 nM) was easily formed from 1 in good yield and, to determine binding directionality, its enantiomers were separated by chiral chromatography. Absolute configuration was determined using single crystal X-ray crystallography. Only the S-(+)-enantiomer (32) was active with an IC50 of 370 nM. Binding directionality was predictable through our in silico docking studies, giving confidence to our model. Importantly, all novel inhibitors are selective over the type 2 isozyme of 17ß-HSD2 and show <20% inhibition when tested at 10 µM. Lead compounds from this series are worthy of further optimisation and development as inhibitors of testosterone production by 17ß-HSD3 and as inhibitors of prostate cancer cell growth.

16-Picolyl-androsterone derivative exhibits potent 17ß-HSD3 inhibitory activity, improved metabolic stability and cytotoxic effect on various cancer cells: Synthesis, homology modeling and docking studies.

A new androsterone derivative bearing a 16ß-picolyl group (compound 5; FCO-586-119) was synthetized in four steps from the lead compound 1 (RM-532-105). We measured its inhibitory activity on 17ß-HSD3 using microsomal fraction of rat testes as well as transfected LNCaP[17ß-HSD3] cells. We then assessed its metabolic stability as well as its cytotoxic effect against a panel of cancer cell lines. The addition of a picolyl moiety at C-16 of RM-532-105 steroid core improves the 17ß-HSD3 inhibitory activity in the microsomal fraction of rat testes, but not in whole LNCaP[17ß-HSD3] cells. Interestingly, this structural modification enhances 3-fold the metabolic stability in conjunction with a significant cytotoxic effect against pancreatic, ovarian, breast, lung, and prostate cancer cells. Because the inhibitory activity data against 17ß-HSD3 suggested that both steroid derivatives are non-competitive inhibitors, we performed docking and molecular dynamics simulations using a homology model of this membrane-associated enzyme. The results of these simulations revealed that both RM-532-105 (1) and FCO-586-119 (5) can compete for the cofactor-binding site displaying better binding energy than NADP+.

A Hybrid In Silico/In Vitro Target Fishing Study to Mine Novel Targets of Urolithin A and B: A Step Towards a Better Comprehension of Their Estrogenicity.

SCOPE: Urolithin A and B are gut metabolites of ellagic acid and ellagitannins associated with many beneficial effects. Evidence in vitro pointed to their potential as estrogenic modulators. However, both molecular mechanisms and biological targets involved in such activity are still poorly characterized, preventing a comprehensive understanding of their bioactivity in living organisms. This study aimed at rationally identifying novel biological targets underlying the estrogenic-modulatory activity of urolithins. METHODS AND RESULTS: The work relies on an in silico/in vitro target fishing study coupling molecular modeling with biochemical and cell-based assays. Estrogen sulfotransferase and 17ß-hydroxysteroid dehydrogenase are identified as potentially subject to inhibition by the investigated urolithins. The inhibition of the latter undergoes experimental confirmation either in a cell-free or cell-based assay, validating computational outcomes. CONCLUSIONS: The work describes target fishing as an effective tool to identify unexpected targets of food bioactives detailing the interaction at a molecular level. Specifically, it described, for the first time, 17ß-hydroxysteroid dehydrogenase as a target of urolithins and highlighted the need of further investigations to widen the understanding of urolithins as estrogen modulators in living organisms.

Characteristics and sex dimorphism of 17ß-hydroxysteroid dehydrogenase family genes in the olive flounder Paralichthys olivaceus.

Sex steroid hormones play important roles in fish sex differentiation, gonadal development and secondary sexual characteristics. Olive flounder Paralichthys olivaceus is a valuable commercial marine fish species and has marked sexual dimorphism. However, the mechanisms of action of sex hormones in flounder sex are still unclear. In this study, a total of ten Hsd17b family genes, including Hsd17b3, -4, -7, -8, -9, -10, -12a, -12b, -14 and -15, were identified in the flounder, which encoded critical enzymes acting on sex steroid synthesis and metabolism. Hsd17b genes were distributed on eight chromosomes. Hsd17b12a and -12b were located on chromosomes 19 and 7, respectively. It was speculated that these two genes were just highly similar rather than different transcripts derived from the same gene. According to the results of domain and motif analyses, they all belonged to the SDR superfamily and contained conserved Hsd17b motifs TGxxxGxG, PGxxxT, NNAG and YxxxK. Analysis of amino acid sequences predicted that Hsd17b1, -4, -7, -12a and -14 were hydrophilic proteins. The stability of Hsd17b1, -3 and -12b proteins was predicted to be low. The various Hsd17b family genes differed in tissue expression pattern, and Hsd17b10, -12a and -12b were highly expressed in the flounder ovary. Moreover, throughout gonadal development, Hsd17b3 was highly expressed in the testis, and Hsd17b1, -12a and -12b were highly expressed in the ovary, suggesting that they might play an important role in testosterone synthesis in the testis or estrogen synthesis in the ovary. Activities of Hsd17b3 at stages I-V were all significantly higher in the testis than in the ovary (P < 0.05, P < 0.01). Transfection analysis in HEK293T cells showed that Hsd17b1 and -3 were located in both the cytoplasm and nucleus. Additionally, after challenging fish with tamoxifen, Hsd17b3 expression level in the testis decreased significantly (P < 0.01), and in the ovary no significant change was observed. Moreover, the expression of Hsd17b1 in the ovary was significantly upregulated after injection with flutamide (P < 0.05). These findings introduce the characteristics of the flounder Hsd17b in subfamily, which contribute to our understanding of the regulation of sex steroid hormone synthesis in fish gonadal development.

A- and D-Ring Structural Modifications of an Androsterone Derivative Inhibiting 17ß-Hydroxysteroid Dehydrogenase Type 3: Chemical Synthesis and Structure-Activity Relationships.

Decreasing the intratumoral androgen biosynthesis by using an inhibitor of 17ß-hydroxysteroid dehydrogenase type 3 (17ß-HSD3) is a strategy to treat prostate cancer. The androsterone (ADT) derivative 1 (RM-532-105) has shown strong inhibitory activity on 17ß-HSD3, but needs to be improved. Herein, we describe the chemical synthesis and characterization of two series of analogues to address the impact of A- and D-ring modifications on 17ß-HSD3 inhibitory activity, androgenic effect, and metabolic stability. Structure-activity relationships were generated by adding different groups at C16/C17 (D-ring diversification) or replacing the ADT backbone by a nor-androstane or an estrane backbone (A-ring diversification). D-ring derivatives were less potent inhibitors than lead compound 1, whereas steroidal backbone (A-ring) change led to identifying promising novel estrane derivatives. This culminated with potent 17ß-HSD3 inhibitors 23, 27, 31, and 33 (IC50 = 0.10, 0.02, 0.13, and 0.17 µM, respectively), which did not stimulate LAPC-4 cell proliferation and displayed higher plasma concentration in mice than lead compound 1.

Crystal structures of human 17ß-hydroxysteroid dehydrogenase type 1 complexed with estrone and NADP+ reveal the mechanism of substrate inhibition.

Human 17ß-hydroxysteroid dehydrogenase type 1 (17ß-HSD1) catalyses the last step in estrogen activation and is thus involved in estrogen-dependent diseases (EDDs). Unlike other 17ß-HSD members, 17ß-HSD1 undergoes a significant substrate-induced inhibition that we have previously reported. Here we solved the binary and ternary crystal structures of 17ß-HSD1 in complex with estrone (E1) and cofactor analog NADP+ , demonstrating critical enzyme-substrate-cofactor interactions. These complexes revealed a reversely bound E1 in 17ß-HSD1 that provides the basis of the substrate inhibition, never demonstrated in estradiol complexes. Structural analysis showed that His221 is the key residue responsible for the reorganization and stabilization of the reversely bound E1, leading to the formation of a dead-end complex, which exists widely in NADP(H)-preferred enzymes for the regulation of their enzymatic activity. Further, a new inhibitor is proposed that may inhibit 17ß-HSD1 through the formation of a dead-end complex. This finding indicates a simple mechanism of enzyme regulation in the physiological background and introduces a pioneer inhibitor of 17ß-HSD1 based on the dead-end inhibition model for efficiently targeting EDDs. DATABASES: Coordinates and structure factors of 17ß-HSD1-E1 and 17ß-HSD1-E1-NADP+ have been deposited in the Protein Data Bank with accession code 6MNC and 6MNE respectively. ENZYMES: 17ß-hydroxysteroid dehydrogenase type 1 (17ß-HSD1) EC 1.1.1.62.

Role of HSD17B13 in the liver physiology and pathophysiology.

17ß-Hydroxysteroid dehydrogenases (HSD17Bs) comprise a large family of 15 members that are mainly involved in sex hormone metabolism. Some HSD17Bs enzymes also play key roles in cholesterol and fatty acid metabolism. Recent study showed that hydroxysteroid 17ß-dehydrogenase 13 (HSD17B13), an enzyme with unknown biological function, is a novel liver-specific lipid droplet (LD)-associated protein in mouse and humans. HSD17B13 expression is markedly upregulated in patients and mice with non-alcoholic fatty liver disease (NAFLD). Hepatic overexpression of HSD17B13 promotes lipid accumulation in the liver. In this review, we summarize recent progress regarding the role of HSD17B13 in the regulation of hepatic lipid homeostasis and discuss genetic, genomic and proteomic evidence supporting the pathogenic role of HSD17B13 in NAFLD. We also emphasize its potential as a biomarker of advanced liver disease, such as non-alcoholic steatohepatitis (NASH) and liver cancer.

Chemical synthesis of C3-oxiranyl/oxiranylmethyl-estrane derivatives targeted by molecular modeling and tested as potential inhibitors of 17ß-hydroxysteroid dehydrogenase type 1.

17ß-Hydroxysteroid dehydrogenase type 1 (17ß-HSD1) is a promising therapeutic target known to play a pivotal role in the progression of estrogen-dependent diseases such as breast cancer, and endometriosis. This enzyme is responsible for the last step in the biosynthesis of the most potent estrogen, estradiol (E2) and its inhibition would prevent the growth of estrogen-sensitive tumors. Based on molecular modeling with docking experiments, we identified two promising C3-oxiranyl/oxiranylmethyl-estrane derivatives that would bind competitively and irreversibly in the catalytic site of 17ß-HSD1. They have been synthesized in a short and efficient route and their inhibitory activities over 17ß-HSD1 have been assessed by an enzymatic assay. Compound 15, with an oxiranylmethyl group at position C3, was more likely to bind the catalytic site and showed an interesting, but weak, inhibitory activity with an IC50 value of 1.3 µM (for the reduction of estrone into E2 in T-47D cells). Compound 11, with an oxiranyl at position C3, produced a lower inhibition rate, and the IC50 value cannot be determined. When tested in estrogen-sensitive T-47D cells, both compounds were also slightly estrogenic, although much less than the estrogenic hormone E2.

Interference of Paraben Compounds with Estrogen Metabolism by Inhibition of 17ß-Hydroxysteroid Dehydrogenases.

Parabens are effective preservatives widely used in cosmetic products and processed food, with high human exposure. Recent evidence suggests that parabens exert estrogenic effects. This work investigated the potential interference of parabens with the estrogen-activating enzyme 17ß-hydroxysteroid dehydrogenase (17ß-HSD) 1 and the estrogen-inactivating 17ß-HSD2. A ligand-based 17ß-HSD2 pharmacophore model was applied to screen a cosmetic chemicals database, followed by in vitro testing of selected paraben compounds for inhibition of 17ß-HSD1 and 17ß-HSD2 activities. All tested parabens and paraben-like compounds, except their common metabolite p-hydroxybenzoic acid, inhibited 17ß-HSD2. Ethylparaben and ethyl vanillate inhibited 17ß-HSD2 with IC50 values of 4.6 ± 0.8 and 1.3 ± 0.3 µM, respectively. Additionally, parabens size-dependently inhibited 17ß-HSD1, whereby hexyl- and heptylparaben were most active with IC50 values of 2.6 ± 0.6 and 1.8 ± 0.3 µM. Low micromolar concentrations of hexyl- and heptylparaben decreased 17ß-HSD1 activity, and ethylparaben and ethyl vanillate decreased 17ß-HSD2 activity. However, regarding the very rapid metabolism of these compounds to the inactive p-hydroxybenzoic acid by esterases, it needs to be determined under which conditions low micromolar concentrations of these parabens or their mixtures can occur in target cells to effectively disturb estrogen effects in vivo.

Secretory expression, purification and functional characterization of 17ß-hydroxysteroid dehydrogenase type 1 from mammalian HEK293T cells.

17ß-hydroxysteroid dehydrogenase type 1 (17ß-HSD1) mainly catalyzes the reduction of estrone into estradiol. The enzymatic conversion is a critical step in estradiol accumulation in breast tissue, which is a valuable prognosis index of breast cancer disease. However, the source of 17ß-HSD1 for inhibitor design is limited. In this study, the fragment encoding human 17ß-HSD1 was successfully cloned and expressed in human embryonic kidney (HEK) 293T mammalian cells. The recombinant protein was purified by immobilized metal ion affinity chromatography yielding above 17 mg of purified 17ß-HSD1 protein per liter of cell culture, with a specific activity of 8.54 µmoL/min/mg of protein for conversion of estradiol into estrone, with NAD+ as cofactor at pH 9.2. Enzyme characterization studies revealed that the protein has estrogenic activity and the Km value for estrone is about 20 nM. The recombinant protein purified from transfected HEK293T cells had higher specific activity compared to that of the enzyme purified directly from placenta. The present data show that the mammalian cell expression system can provide active 17ß-HSD1 which is functionally identical to its natural counterpart and easy to purify in qualities suitable for its structure-function study.

Protective Effect of Selenium on Aflatoxin B1-Induced Testicular Toxicity in Mice.

Aflatoxins have been considered as one of the major risk factors of male infertility, and aflatoxin B1 (AFB1) is the most highly toxic and prevalent member of the aflatoxins family. Selenium (Se), an essential nutritional trace mineral for normal testicular development and male fertility, has received extensive intensive on protective effects of male reproductive system due to its potential antioxidant and activating testosterone synthesis. To investigate the protective effect of Se on AFB1-induced testicular toxicity, the mice were orally administered with AFB1 (0.75 mg/kg) and Se (0.2 mg/kg or 0.4 mg/kg) for 45 days. We found that that Se elevated testes index, sperm functional parameters (concentration, malformation, and motility), and the level of serum testosterone in AFB1-exposed mice. Moreover, our results showed that Se attenuated the AFB1-induced oxidative stress and the reduction of testicular testosterone synthesis enzyme protein expression such as steroidogenic acute regulatory protein (StAR), P450 side-chain cleavage (P450scc), and 17ß-hydroxysteroid dehydrogenase (17ß-HSD) in AFB1-exposed mice. These results demonstrated that Se conferred protection against AFB1-induced testicular toxicity and can be attributed to its antioxidant and increased testosterone level by stimulating protein expression of StAR and testosterone synthetic enzymes.

A chemical genomics approach to drug reprofiling in oncology: Antipsychotic drug risperidone as a potential adenocarcinoma treatment.

Drug reprofiling is emerging as an effective paradigm for discovery of cancer treatments. Herein, an antipsychotic drug is immobilised using the Magic Tag® chemical genomics tool and screened against a T7 bacteriophage displayed library of polypeptides from Drosophila melanogaster, as a whole genome model, to uncover an interaction with a section of 17-ß-HSD10, a proposed prostate cancer target. A computational study and enzyme inhibition assay with full length human 17-ß-HSD10 identifies risperidone as a drug reprofiling candidate. When formulated with rumenic acid, risperidone slows proliferation of PC3 prostate cancer cells in vitro and retards PC3 prostate cancer tumour growth in vivo in xenografts in mice, presenting an opportunity to reprofile risperidone as a cancer treatment.

Covalent Immobilization of Human Placental 17ß-Hydroxysteroid Dehydrogenase Type 1 onto Glutaraldehyde Activated Silica Coupled with LC-TOF/MS for Anti-Cancer Drug Screening Applications.

Human 17ß-hydroxysteroid dehydrogenase type 1 (17ß-HSD1), a potential target in breast cancer prevention and therapy, was extracted from human placenta and immobilized on nonporous silica (∼5 µm) with a covalent method for the first time. The optimum initial enzyme concentration and immobilization time during the immobilization process were 0.42 mg mL-1 and 12 h, repectively. The binding was confirmed by scanning electron microscope (SEM) and infrared spectroscopy (FT-IR). It could improve the pH, thermal and storage stability compared to free enzyme. Moreover, the immobilized enzyme could be reused at least four times. A screening method based on it coupled with liquid chromatography-time-of-flight mass spectrometer (LC-TOF/MS) was established, and the half-maximal inhibitory concentration (IC 50) of apigenin for the immobilized enzyme was 291 nM. Subsequently, 10 natural products were evaluated leading to inhibition of the activity of 17ß-HSD1 at the concentration of 25 µM, and six of them inhibit the activity over 50%.

Androgen-metabolizing enzymes: A structural perspective.

Androgen-metabolizing enzymes convert cholesterol, a relatively inert molecule, into some of the most potent chemical messengers in vertebrates. This conversion involves thermodynamically challenging reactions catalyzed by P450 enzymes and redox reactions catalyzed by Aldo-Keto Reductases (AKRs). This review covers the structures of these enzymes with a focus on active site interactions and proposed mechanisms. Due to their role in a number of diseases, particularly in cancer, androgen-metabolizing enzymes have been targets of drug design. Hence we will also highlight how existing knowledge of structure is being used to this end.

Identification of fused 16ß,17ß-oxazinone-estradiol derivatives as a new family of non-estrogenic 17ß-hydroxysteroid dehydrogenase type 1 inhibitors.

A new family of cyclic carbamate-estradiol derivatives has been designed to remove the intrinsic estrogenic activity of a parent acyclic compound reported as a potent inhibitor of 17ß-hydroxysteroid dehydrogenase type 1 (17ß-HSD1). The synthesis of two series of fused 16ß,17ß-oxazinone-estradiol derivatives, saturated compounds 7a-d and unsaturated compounds 10a-d, led to the identification of 10b, a 17ß-HSD1 inhibitor (IC50 = 1.4 µM) without estrogenic activity in estrogen-sensitive T-47D cells. Interestingly, this compound was found selective over 17ß-HSD2 and 17ß-HSD12. A computational analysis of inhibitors into 17ß-HSD1 by molecular docking also revealed interesting structure-activity relationships that could be helpful in the design of new generation of 16ß,17ß-oxazinone-estradiol analogs.

Pitfalls in hormonal diagnosis of 17-beta hydroxysteroid dehydrogenase III deficiency.

Steroid 17ß-hydroxysteroid dehydrogenase III (17ß-HSD3) deficiency is a rare autosomal recessive disorder that usually presents in patients with a 46,XY karyotype with ambiguous genitalia at birth. The 17ß-HSD3 enzyme, which is encoded by the HSD17B3 gene, converts gonadal delta-4 androstenedione (Δ4) to testosterone (T). Such 17ß-HSD3 enzyme deficiency is expected to lead to an increased ratio of D4 to T when the patient undergoes a human chorionic gonadotropin stimulation (hCG) test. Two patients with 46,XY disorders of sexual differentiation were studied. Serum D4 and T levels were measured by HPLC tandem mass spectrometry. As one of the patients was born to consanguineous parents, we performed single nucleotide polymorphism (SNP) microarray to analyze regions of homozygosity (ROH). The HSD17B3 gene was sequenced using the Sanger method. Contrary to expectations, both patients demonstrated decreased D4/T ratio after hCG stimulation. Initial sequencing results for the androgen receptor or 5α-reductase were negative for mutations. ROH analysis identified HSD17B3 as a candidate gene that might cause the disease. Sanger sequencing of the HSD17B3 gene confirmed 17ß-HSD3 deficiency in both patients. Serum D4/T ratios are not reliable parameters for the diagnosis of 17ß-HSD3 deficiency. Molecular genetic analysis provides accurate diagnosis.

Characteristics of 17ß-hydroxysteroid dehydrogenase 8 and its potential role in gonad of Zhikong scallop Chlamys farreri.

17ß-Hydroxysteroid dehydrogenases (17ß-HSDs) are important enzymes catalyzing steroids biosynthesis and metabolism in vertebrates. Although studies indicate steroids play a potential role in reproduction of molluscs, little is known about the presence and function of 17ß-HSDs in molluscs. In the present study, a full-length cDNA encoding 17ß-HSD type 8 (17ß-HSD8) was identified in the Zhikong scallop Chlamys farreri, which is 1104bp in length with an open reading frame of 759bp encoding a protein of 252 amino acids. Phylogenetic analysis revealed that the C. farreri 17ß-HSD8 (Cf-17ß-HSD8) belongs to the short chain dehydrogenase/reductase family (SDR) and shares high homology with other 17ß-HSD8 homologues. Catalytic activity assay in vitro demonstrated that the refolded Cf-17ß-HSD8 expressed in Escherichia coli could effectively convert estradiol-17ß (E2) to estrone (E1), and weakly catalyze the conversion of testosterone (T) to androstenedione (A) in the presence of NAD(+). The Cf-17ß-HSD8 mRNA was ubiquitously expressed in all tissues analyzed, including gonads. The expression levels of Cf-17ß-HSD8 mRNA and protein increased with gametogenesis in both ovary and testis, and were significantly higher in testis than in ovary at growing stage and mature stage. Moreover, results of in situ hybridization and immunohistochemistry revealed that the mRNA and protein of Cf-17ß-HSD8 were expressed in follicle cells and gametes at all stages except spermatozoa. Our findings suggest that Cf-17ß-HSD8 may play an important role in regulating gametogenesis through modulating E2 levels in gonad of C. farreri.