| Trenbolone acetate (17β-hydroxyestra-4,9,11-trien-3-one17-acetate) is asynthetic anabolic steroid that has been used extensively since the1970s as a growthpromoter for livestocks in the USA. After being released, trenbolone acetate is rapidlyhydrolyzed to17β-trenbolone (17β-hydroxyestra-4,9,11-trien-3-one) in blood streamof the animals.17β-trenbolone shares similar molecular structure with endogenousandrogens. Humans are exposed to17β-trenbolone through several possible routes.(1)Humans contact trenbolone through deliberate injection. As an anabolic-androgenicsteroid, trenbolone is used by a large portion of recreational exercisers to increasemuscle size and strength. The exercisers often inject trenbolone in large doses for longtimes.(2)17β-trenbolone may remains in meat consumed by humans.(3)17β-trenbolone can be excreted by the animals and humans and the feedlot effluent,the river near the feedlot, and downstream discharges from urban wastewater can allbe contaminated by17β-trenbolone. Besides, manure from livestock feedlot iscommonly applied to agricultural fields as an alternative to commercial fertilizers.17β-trenbolone has long half-life (260d) and stable properties in the environment. Itmay be absorbed by aquatic animals as well as plants and can be incorporated intofood chains.(4)17β-trenbolone is regarded as a promising candidate in clinicalapplication. The properties that17β-trenbolone cannot be reduced or aromatized andis metabolized to less potent androgens and reduces serum testosterone anddihydrotestosterone levels make17β-trenbolone to be able to reduce incidence ofandrogenic and/or estrogenic side effects associated with androgen administration.Because17β-trenbolone is a synthetic androgen, its reproductive toxicity has beenthe research hotspot. Previous studies using different animal models reported that17β-trenbolone exposure altered the endogenous hormone level, disruptedhypothalamic-pituitary-gonadal axis, and influenced development of reproductiveorgan and reproductive capacity.17β-trenbolone could cause masculinization of females of different animal species and demasculinization developing maleindividuals. So far no literature has reported on the neurotoxicity of17β-trenbolone.Both genetic and environmental factors contribute to neurodegenerative disorders. Ina large number of neurodegenerative diseases, for example Alzheimer’s disease (AD),patients do not carry the mutant genes. Other risk factors, for example theenvironmental factors, should be evaluated. Brain is an androgen-sensitive tissue and17β-trenbolone is a synthetic androgen, thus17β-trenbolone might have effects onnervous system.In the present study, both animal experiment and cell culture experiment werecarried to evaluate the neurotoxicity of17β-trenbolone. In the animal experiment,17β-trenbolone was administered to adult and pregnant rats, with different doses (0.2,1, and5mg/kg body weight) and different treatment time (0.5,2,6,12,24, and48h).17β-trenbolone distribution in the adult rats and fetal rats were determined. Its effectson hormone levels and Aβ42accumulation in vivo were evaluated. In the in vitrostudies, effects of17β-trenbolone on primary cultured hippocampal neurons weretested.17β-trenbolone’s concentrations were from1-100nmol/L and the treatmenttime was48h. Cell viability and neuron apoptosis were assessed. Changes ofAD-related proteins β-amyloid (Aβ42) and presenilin-1(PS) were determined byELISA and western blot analysis, respectively. Underlying mechanisms were studied.The main results were listed below.1.17β-trenbolone could be detected in brain, hippocampus, cerebrospinal fluid,plasma, and muscle of male and female rats, and in fetus brain. It crossed the bloodbrain barrier and placental barrier.17β-trenbolone accumulated in adult rat brain,especially in hippocampus. When the injection doses were0.2,1, and5mg/kg bodyweight, as for male rats,17β-trenbolone concentrations in the hippocampus were5.42±0.27,6.12±0.21, and7.03±0.17ng/g, respectively.17β-trenbolone concentrationsin the rest of the brain were2.64±0.25,2.85±0.30, and4.44±0.24ng/g,respectively. As for female rats, when the injection doses were0.2,1, and5mg/kgbody weight,17β-trenbolone concentrations in the hippocampus were2.07±0.10,2.99±0.39, and6.43±0.55ng/g, respectively, while in the rest of the brain were1.55±0.20,1.89±0.22, and3.74±0.26ng/g, respectively. After being treated with17β-trenbolone at the dose of5mg/kg body weight for48h,17β-trenbolone concentration in fetus brain was2.59±0.21ng/g.17β-trenbolone administrationaltered the serum hormone levels, causing fluctuation of testosterone, estradiol, andprogesterone levels.17β-trenbolone administration led to Aβ42accumulation in thebrain (especially the hippocampus) of adult male rats. Increase of Aβ42was alsoobserved in fetus brain. Excessive Aβ42would influence the development and normalfunction of nervous system.2. To investigate the effects of17β-trenbolone on hippocampal neurons andunderlying mechanisms,17β-trenbolone was administered to primary culturedhippocampal neurons.17β-trenbolone exerted cytotoxicity on hippocampal neurons.Cell viability was reduced and17β-trenbolone induced neuron morphological changes,chromatin condensation, nuclear fragmentation, translocation of phosphatidylserine,and mitochondrial membrane potential decrease in primary hippocampal neurons,indicating induction of apoptosis of the neurons.17β-trenbolone resistedneuroprotective function of testosterone. Presenilin-1protein expression wasdown-regulated while Aβ42production and caspase-3activities were increased. Bothandrogen and estrogen receptors mediated the processes, so did the genomic andnon-genomic signaling pathways.In conclusion,17β-trenbolone had neurotoxicity. It can induce apoptosis ofhippocampal neurons and regulate the expression of AD-related proteins Aβ42andpresenilin-1.17β-trenbolone played roles in neurodegeneration.17β-trenbolone couldinfluence brain, especially the hippocampus, and the damage even occurs indevelopmental brains if the mother has been exposed to17β-trenbolone. As ananabolic-androgenic steroid, it is used widely in large doses for long times byexercisers. As an environmental androgen, common people may also be exposed to17β-trenbolone through various ways. Since damages of neurons may occur muchearlier than the clinical symptoms of neurodegenerative disorders, exposure to17β-trenbolone should be regarded as a high risk environmental factor in AD onset.Thus, the use of17β-trenbolone should be monitored. In addition, environmentalhormone may be at anywhere around us. Inspired by17β-trenbolone, when wepouring large amount of funds and efforts on research over genetic factors of AD, wecan spare some time to discover the environmental factors which may be influencingmore people. Innovations:1.17β-trenbolone distributed in the brain, especially in the hippocampus of theadult rats after intramuscular injection. It can also be detected in the fetus brain whenthe pregnant rats were exposed to17β-trenbolone. Nervous system is one of thetargets of17β-trenbolone.2.17β-trenbolone is neurotoxic. It induced apoptosis of the primary hippocampalneurons and changed the expression of two AD-related proteins, Aβ42andpresenilin-1. Production of Aβ42was promoted while the protein expression ofpresenilin-1was down-regulated. The processes were mediated by hormone receptors.3. As both an anabolic-androgenic steroid and an environment androgen,17β-trenbolone played roles in neurodegeneration. The results guided the use of17β-trenbolone. Moreover, they inspired the thinking of the relationship ofenvironmental hormones and neurodegenerative diseases. |
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