Neurotoxicity by synthetic androgen steroids: oxidative stress, apoptosis, and neuropathology: A review

Abstract

Anabolic-androgenic steroids (AAS) are synthetic substances derived from testosterone that are largely employed due to their trophic effect on muscle tissue of athletes at all levels. Since a great number of organs and systems are a target of AAS, their adverse effects are primarily on the following systems: reproductive, hepatic, musculoskeletal, endocrine, renal, immunological, infectious, cardiovascular, cerebrovascular, and hematological. Neuropsychiatric and behavioral effects as a result of AAS abuse are well known and described in the literature. Mounting evidence exists suggesting that in addition to psychiatric and behavioral effects, non-medical use of AAS carries neurodegenerative potential. Although, the nature of this association remains largely unexplored, recent animal studies have shown the recurrence of this AAS effect, ranging from neurotrophin unbalance to increased neuronal susceptibility to apoptotic stimuli. Experimental and animal studies strongly suggest that apoptotic mechanisms are at least in part involved in AAS-induced neurotoxicity. Furthermore, a great body of evidence is emerging suggesting that increased susceptibility to cellular oxidative stress could play a pivotal role in the pathogenesis of many neurodegenerative disorders and cognitive impairment. As in other drug-evoked encephalopathies, the key mechanisms involved in AAS - induced neuropathology could represent a target for future neuroprotective strategies. Progress in the understanding of these mechanisms will provide important insights into the complex pathophysiology of AAS-induced neurodegeneration, and will pave the way for forthcoming studies. Supplementary to abandoning the drug abuse that represents the first step in reducing the possibility of irreversible brain damage in AAS abusers, neuroprotective strategies have to be developed and implemented in future.

Keywords: Androgen-anabolic steroids; apoptosis; biochemical mechanisms; excitotoxic neuronal death; neuroprotective strategies; neurotoxicity; neurotrophin unbalance; oxidative-stress.

Fig. (1)

The three major classes of anabolic androgen steroids (modified from Oberlander, J.G.; Henderson, L.P, 2012, cited sub 51).

Fig. (2)

The different mechanisms of AAS neurotoxicity. In the classical pathway (1), the androgen freely passes through the membrane bilayer and binds cytoplasmic Androgen Receptor (AR); after translocation to the nucleus bound AR binds to Steroid-Response Elements (SRE), stimulating gene transcription. Bound AR also interacts with Src Homology Domain 3 (SH3) of the tyrosine kinase c-Src to activate the Mitogen-Activated Protein Kinase (MAPK) pathway and induces gene transcription via phosphorylation of coactivator/receptor complexes (2). The androgen binds to Steroid Hormone Binding Globulin (SHBG) activating the SHBG Receptor (SHBGR) and leading to an increase in Protein Kinase A (PKA) activity. PKA may influence AR-mediated transcription via alteration of phosphorylation status of AR and AR coregulators (3). AAS can be also metabolized to estrogens, interacting not only with AR but also with Estrogen Receptors (ERα and ERβ) to regulate gene transcription. These interaction can result in change in GABAA receptor subunit gene expression. AAS also induce directly changes in GABAergic signaling altering gene expression. On the right the non-genomic androgen action via changes in intracellular ion concentrations and membrane fluidity is represented. Androgen interacts with a membrane associated AR leading to the activation of Ltype calcium channels through some type of inhibitory g-protein (GP). This increase in intracellular calcium activates Protein Kinase C (PKC), and activates via calmodulin (CAM) PKA and MAPK pathway. The modulation of GP may also activate Phospholipase C (PLC) resulting in increases in inositol 1,4,5-thriphosphate (IP3) and consequently in release of intracellular calcium stores from the sarcoplasmic reticulum and in activation of the RAS/MEK/ERK pathway (MEK=MAPK/ERK kinase, ERK=extracellular-signal regulated kinase).

Fig. (3)

Mouse brain treated with nandrolone decanoate (A) Confocal laser scanning microscope. Increase of apoptosis (Tunel assay) with intense positive reaction (red). (B-C-D) TUNEL assay revealed neuronal and glial over-expression of apoptotic nuclei (arrows) with a brownish positive reaction.

Fig. (4)

A schematic illustration of the complex mechanisms leading to neuronal death. Extrinsic apoptosis is a caspase – dependent cell death subroutine that is initiated by the binding of lethal ligands, such as FAS/CD95 ligand (FASL/CD95L) to death receptor FAS/CD95; the complex recruit FAS-associated protein with a death domain (FADD), cellular inhibitor of apoptosis proteins (cIAPs), c-FLIPs and procaspase 8. This supramolecular platform controls the activation of caspase-8, that can directly trigger the caspase cascade by mediating the proteolytic maturation of caspase-3, or stimulate mitochondrial outer membrane permeabilization by cleaving the BH3 interacting-domain (BID). In the intrinsic apoptosis the multiple intracellular stress conditions lead to a mitochondrion-centered control mechanisms. When lethal signals prevail, mitochondrial outer membrane permeabilization occurs and leads to mitochondrial transmembrane potential dissipation and arrest of mitochondrial ATP synthesis. The respiratory chain gets uncoupled, leading to reactive oxygen species (ROS) and reactive nitrogen species (RNS) production. Cytochrome C (CytC), together with the cytoplasmic adaptor protein APAF1 and dATP, create the apoptosome, that triggers the caspase 9-caspase 3 proteolytic cascade. Direct IAP-binding protein with low pl (DIABLO, also known as second mitochondria-derived activator of caspases, SMAC) induces caspase activation

Fig. (5)

The multifaceted therapeutic approach to AAS abuse evoked neuropathy focuses on “traditional” and new treatment strategies. The first strategy would be to stop the subject from the abuse. Restore normal metabolism and correct nutritional deficiencies is a further fundamental step because drug abuse may cause nutritional insufficiencies. Psychological and family – based support also play and effective role. Another potential strategy is the potential of epigenetic modulation in reducing the risk of developing the drug abuse-evoked encephalopathy. Finally, new therapeutic strategies imply targeting the genomic, metabolic, and mitochondrial dysfunction resulting in increased excitotoxicity, reduced energy production, and lowered antioxidant potential.