Substrate concentration affects the in vitro metabolism of 17-hydroxyprogesterone by ovaries of the carp, Cyprinus carpio

The in vitro interference of synthetic progestogens with carp steroidogenic enzymes

Synthetic progestogens represent a class of pharmaceuticals widely used in oral contraceptives and in hormone replacement therapies. They reach the aquatic environment through wastewater effluents; however, environmental concentrations and effects on non-target organisms are poorly known. Given the important role of progestogens regulating fish spawning processes, this study aimed at assessing the in vitro interference of four currently used progestogens-drospirenone (DRO), levonorgestrel (LNG), norethindrone (NOR) and cyproterone acetate (CPA) - with key enzymatic activities involved in the synthesis of active steroids in carp (Cyprinus carpio). The enzymatic pathways investigated were (a) CYP17 (C17,20-lyase) and CYP11β involved in the synthesis of androgens, (b) CYP19 that catalyses the aromatization of androgens to estrogens, and (c) 20β-hydroxysteroid dehydrogenase (20β-HSD) responsible for the synthesis of maturation-inducing hormones. All tested progestogens significantly inhibited the synthesis of androgens: DRO (IC50: 3.8 μM) was the strongest inhibitor of CYP17 followed by CPA (IC50s: 183 μM). Moreover, NOR (IC50: 0.4 μM), DRO (IC50: 1.8 μM) and CPA (IC50s: 87 μM) inhibited CYP11β. An inhibition by NOR of ovarian CYP19 activity, and by DRO and CPA of 20β-HSD was also observed, but at rather high concentrations (500 μM). Overall, this study highlights the potential of synthetic progestogens, and particularly DRO and NOR, to interfere with the biosynthesis of androgens in carp gonads.

The role of the maturation-inducing steroid, 17,20beta-dihydroxypregn-4-en-3-one, in male fishes: a review

The major progestin in teleosts is not progesterone, as in tetrapods, but 17,20beta-dihydroxypregn-4-en-3-one (17,20beta-P) or, in certain species, 17,20beta,21-trihydroxy-pregn-4-en-3-one (17,20beta,21-P). Several functions for 17,20beta-P and 17,20beta,21-P have been proposed (and in some cases proved). These include induction of oocyte final maturation and spermiation (milt production), enhancement of sperm motility (by alteration of the pH and fluidity of the seminal fluid) and acting as a pheromone in male cyprinids. Another important function, initiation of meiosis (the first step in both spermatogenesis and oogenesis), has only very recently been proposed. This is a process that takes place at puberty in all fishes and once a year in repeat spawners. The present review critically examines the evidence to support the proposed functions of 17,20beta-P in males, including listing of the evidence for the presence of 17,20beta-P in the blood plasma of male fishes and discussion of why, in many species, it appears to be absent (or present at low and, in some cases, unvarying concentrations); consideration of the evidence, obtained mainly from in vitro studies, for this steroid being predominantly produced by the testis, for its production being under the control of luteinizing hormone (gonadotrophin II) and, at least in salmonids, for two cell types (Leydig cells and sperm cells) being involved in its synthesis; discussion of the factors involved in the regulation of the switch from androgen to 17,20beta-P production that seems to occur in many species just at the time of spermiation; discussion of the effects of in vivo injection and application of 17,20beta-P (and closely related compounds) in males; a listing of previously published evidence that supports the proposed new function of 17,20beta-P as an initiator of meiosis; finally, discussion of the evidence for environmental endocrine disruption by progestins in fishes.

Evidence for 15α- and 7α-hydroxylase activity in gonadal tissue of the early-life stages of sea lampreys, Petromyzon marinus

Gonads of premetamorphosing larval (PML), transforming (TL) and newly metamorphosed (juvenile) sea lampreys (JL) (Petromyzon marinus) were incubated in vitro with tritiated pregnenolone ([(3)H]P(5)), progesterone ([(3)H]P(4)), and androstenedione ([(3)H]A(4)) to identify the major products of steroidogenesis in early developmental stages. Reverse-phase high-performance liquid chromatography, using two mobile phase gradients, was used to separate the radioactive steroid metabolites. 7alpha-Hydroxylase activity was evident, based on the loss of radioactivity from [(3)H]P(5) labelled at position 7, appearing as tritiated water, and on the appearance of radiolabelled 7alpha-hydroxypregnenolone in the incubation medium. In addition, there was evidence of the synthesis of 15alpha-hydroxylated steroids from the three steroid precursors used. For the progestogen precursors, one of the major 15alpha -hydroxylated metabolites synthesized by both testis and ovarian tissue co-eluted with authentic 15alpha-hydroxyprogesterone, and for [(3)H]A(4), the product was predominantly [(3)H]15alpha-hydroxyandrostenedione. Additional polar steroids were produced, some of which co-eluted with authentic 15alpha-hydroxytestosterone and 15alpha-hydroxyestradiol, whereas others could not be correlated with the authentic 15alpha- or 15beta-hydroxylated steroids available. Ovarian tissues from PML and TL developmental stages synthesized several very non-polar compounds, some of which were present as unconjugated compounds, and others only in the conjugated fraction. These molecules had retention times consistent with pregnanes, and their presence in the incubation medium was therefore indicative of the presence of 5alpha-reductase. These metabolites were not present in the incubation medium from testis, or the JL ovary, suggesting that there is no expression of 5alpha-reductase activity in these tissues. Traces of 17beta-estradiol were found in the incubation medium from ovarian tissue incubated with P(5), but not following incubation with P(4) or A(4). Testosterone was not present in the incubation medium from either ovarian or testis fragments incubated with any of the substrates used.

In vitro metabolism of pregnenolone to 7alpha-hydroxypregnenolone by rainbow trout embryos

Tissues taken from rainbow trout embryos at several developmental stages, were incubated in the presence of radioactively-labelled pregnenolone in order to determine the capability of salmonid embryos to metabolize steroids, such as pregnenolone, that are incorporated into the oocyte during gonadal growth and maturation. High performance liquid chromatography was used to separate the steroid products, and gas chromatography-mass spectrometry was applied for the chemical identification of the product. 7alpha-Hydroxypregnenolone, previously known to be produced only by ovarian tissues, was found to be the sole metabolite of pregnenolone metabolism by rainbow trout embryos. Sulfate and glucuronide conjugated forms of 7alpha-hydroxypregnenolone were also produced. We hypothesize that this metabolite provides a pathway for excretion of pregnenolone, enabling the embryo to maintain its own steroid milieu, although the possibility of 7alpha-hydroxypregnenolone also playing a physiological role cannot be excluded.

Synthesis of 17,20alpha/beta-dihydroxy-4-pregnen-3-one and 5beta-pregnanes in spermatozoa of primary and 17alpha-methyltestosterone-induced secondary male grouper (Epinephelus coioides)

The in vitro metabolism of [3H]17-hydroxyprogesterone by spermatozoa of primary and 17alpha-methyltestosterone (MT)-induced secondary male grouper (Epinephelus coioides) has been examined. With only the labeled precursor, the four predominant 5beta-pregnanes (17, 20alpha-dihydroxy-5beta-pregnan-3-one; 5beta-pregnan-3alpha,17, 20alpha-triol; 3alpha,17-dihydroxy-5beta-pregnan-20-one; and 17hydroxy-5beta-pregnan-3,20-dione) accounted for 75% of the total product yield, with the remainder comprising 17, 20alpha-dihydroxy-4-pregnen-3-one (17,20alphaP) and traces (3%) of 17,20beta-dihydroxy-4-pregnen-3-one. This is the first report of the synthesis of these 5beta-pregnanes by teleost spermatozoa. The addition of excess unlabeled precursor caused a marked shift to the synthesis of only 17,20alphaP. The steroidogenic profile in spermatozoa of the primary and secondary males appears similar in both cases. The shift to 17,20alphaP synthesis at high substrate concentration may suggest a gonadotropin (GtH) control of 17, 20alphaP synthesis, involving the competition for 17P between the high-activity, low-capacity 5beta-reductases and the low-activity, high-capacity 20alpha-HSD. Poor spermiation in MT-induced males may thus be due to the lack of 17P arising from low GtH secretion in vivo in the secondary males.