Studies on biotransformation of STS 557

Biotransformation of Current-Use Progestin Dienogest and Drospirenone in Laboratory-Scale Activated Sludge Systems Forms High-Yield Products with Altered Endocrine Activity

Dienogest (DIE) and drospirenone (DRO) are two fourth-generation synthetic progestins widely used as oral contraceptives. Despite their increasing detection in wastewaters and surface waters, their fate during biological wastewater treatment is unclear. Here, we investigated DIE and DRO biotransformation with representative activated sludge batch incubations and identified relevant transformation products (TPs) using high-resolution mass spectrometry. DIE exhibited slow biotransformation (16-30 h half-life) and proceeded through a quantitative aromatic dehydrogenation to form TP 309 (molar yields of ∼55%), an aromatic TP ∼30% estrogenic as 17β-estradiol. DRO experienced more rapid biotransformation (<0.5 h half-life), and 1,2-dehydrogenation formed the major TP 364 (molar yields of ∼40%), an antimineralocorticoid drug candidate named as spirorenone. Lactone ring hydrolysis was another important biotransformation pathway for DRO (molar yields of ∼20%) and generated pharmacologically inactive TP 384. Other minor pathways for DIE and DRO included hydroxylation, methoxylation, and 3-keto and C4(5) double-bond hydrogenation; distinct bioactivities are plausible for such TPs, including antigestagenic activity, antigonadotropic activity, and pregnancy inhibition effects. Thus, biotransformation products of DIE and DRO during wastewater treatment should be considered in environmental assessments of synthetic progestins, especially certain TPs such as the estrogenic TP 309 of DIE and the antimineralocorticoid spirorenone (TP 364) of DRO.

Environmental photochemistry of dienogest: phototransformation to estrogenic products and increased environmental persistence via reversible photohydration

Potent trienone and dienone steroid hormones undergo a coupled photohydration (in light)-thermal dehydration (in dark) cycle that ultimately increases their environmental persistence. Here, we studied the photolysis of dienogest, a dienone progestin prescribed as a next-generation oral contraceptive, and used high resolution mass spectrometry and both 1D and 2D nuclear magnetic resonance spectroscopy to identify its phototransformation products. Dienogest undergoes rapid direct photolysis (t_1/2 ∼ 1-10 min), forming complex photoproduct mixtures across the pH range examined (pH 2 to 7). Identified products include three photohydrates that account for ∼80% of the converted mass at pH 7 and revert back to parent dienogest in the absence of light. Notably, we also identified two estrogenic compounds produced via the A-ring aromatization of dienogest, evidence for a photochemically-induced increase in estrogenic activity in product mixtures. These results imply that dienogest will undergo complete and facile photolytic transformation in sunlit surface water, yet exhibit greater environmental persistence than might be anticipated by inspection of kinetic rates. Photoproduct mixtures also include transformation products with different nuclear receptor binding capabilities than the parent compound dienogest. These outcomes reveal a dynamic fate and biological risk profile for dienogest that must also take into account the composition and endocrine activity of its transformation products. Collectively, this study further illustrates the need for more holistic regulatory, risk assessment, and monitoring approaches for high potency synthetic pharmaceuticals and their bioactive transformation products.

Studies on the hydrogenation of the progestagen dienogest in vivo and in vitro in the female rabbit

The biotransformation of the progestagen dienogest (17 alpha-cyanomethyl-17 beta-hydroxy-4,9-estradien-3-one) was studied in vivo in female rabbits and in vitro by liver homogenates from female rabbits and rats. In vivo, in the female rabbit, 3H-dienogest was the subject of an extensive biotransformation. A significant difference between the composition of the urinary and biliary metabolite patterns of dienogest was found. While in the urinary metabolite pattern more polar metabolites dominated, in bile of animals with a bile fistula, a dienogest metabolite of medium polarity was prevalent. This main metabolite of dienogest was identified by MS, 1H- and 13C-NMR spectroscopy and CD measurement of an enzymatic dehydrogenation product as the tetrahydro metabolite 17 alpha-cyanomethyl-5 alpha-estr-9-en-3 beta,17 beta-diol. Thus, in vivo, the 4,9-dien-3-oxo-19-norsteroid dienogest is hydrogenated to a 5 alpha H-9-en metabolite. In vitro, however, 3H-dienogest was only poorly transformed by liver homogenates from both species, whereas 3H-levonorgestrel and 3H-3-keto-desogestrel were converted partially by liver homogenates from female rabbits and completely by liver homogenates from female rats. The principal biotransformation reactions of levonorgestrel and 3-ketodesogestrel were the reduction of the 3-oxo group to 3-OH and the 5 beta- and 5 alpha-hydrogenation of the 4-double bond by homogenates of female rabbit liver and female rat liver, respectively. A dihydro metabolite of dienogest, in which the 3-oxo group had been reduced to 3-OH, was isolated in small amounts from the incubation with rabbit liver homogenate. The data indicate that the enzymatic hydrogenation of the 4-double bond of the 4,9-dien-3-oxo steroid dienogest is inhibited in vitro. The hindered hydrogenation reaction in vitro has to be seen in association with the 9-double bond in the steroid molecule.