Neuroactive steroids and Parkinson's disease: Review of human and animal studies

The greater prevalence and incidence of Parkinson's disease (PD) in men suggest a beneficial effect of sex hormones. Neuroactive steroids have neuroprotective activities thus offering interesting option for disease-modifying therapy for PD. Neuroactive steroids are also neuromodulators of neurotransmitter systems and may thus help to control PD symptoms and side effect of dopamine medication. Here, we review the effect on sex hormones (estrogen, androgen, progesterone and its metabolites) as well as androstenediol, pregnenolone and dehydroepiandrosterone) in human studies and in animal models of PD. The effect of neuroactive steroids is reviewed by considering sex and hormonal status to help identify specifically for women and men with PD what might be a preventive approach or a symptomatic treatment. PD is a complex disease and the pathogenesis likely involves multiple cellular processes. Thus it might be useful to target different cellular mechanisms that contribute to neuronal loss and neuroactive steroids provide therapeutics options as they have multiple mechanisms of action.

[Androgens and Parkinson's disease: the role in humans and in experiment]

Parkinson's disease (PD) is the second most common neurodegenerative disease after Alzheimer's disease. There is evidence that PD has a wider prevalence among men, which indicates the existing role of sex hormones in the pathogenesis of the disease. The article presents an overview of studies devoted to the study of sex differences in the incidence and symptoms of PD. Drug therapy with androgens, androgen precursors, antiandrogens and drugs that modify androgen metabolism is available for the treatment of various endocrine conditions, having translational significance for PD, but none of these drugs has yet shown sufficient effectiveness. Although PD has now been proven to be more common in men than in women, androgens do not always have any effect on the symptoms or progression of the disease. 5α-reductase inhibitors have shown neuroprotective and anti-dyskinetic activity and need further investigation. Despite the fact that the neuroprotective effect of dutasteride was observed only before damage to DA neurons, the absence of a negative effect makes it an attractive drug for use in patients with PD due to its anti-dyskinetic properties.

Androgens and Parkinson's Disease: A Review of Human Studies and Animal Models

Parkinson's disease (PD) is the second most common neurodegenerative disorder after Alzheimer's disease. A greater prevalence and incidence of PD are reported in men than in women, suggesting a potential contribution of sex, genetic difference and/or sex hormones. This review presents an overview of epidemiological and clinical studies investigating sex differences in the incidence and symptoms of PD. This sex difference is replicated in animal models of PD showing an important neuroprotective role of sex steroids. Therefore, although gender and genetic factors likely contribute to the sex difference in PD, focus here will be on sex hormones because of their neuroprotective role. Androgens receive less attention than estrogen. It is well known that endogenous androgens are more abundant in healthy men than in women and decrease with aging; lower levels are reported in PD men than in healthy male subjects. Drug treatments with androgens, androgen precursors, antiandrogens, and drugs modifying androgen metabolism are available to treat various endocrine conditions, thus having translational value for PD but none have yet given sufficient positive effects for PD. Variability in the androgen receptor is reported in humans and is an additional factor in the response to androgens. In animal models of PD used to study neuroprotective activity, the androgens testosterone and dihydrotestosterone have given inconsistent results. 5α-Reductase inhibitors have shown neuroprotective activity in animal models of PD and antidyskinetic activity. Hence, androgens have not consistently shown beneficial or deleterious effects in PD but numerous androgen-related drugs are available that could be repurposed for PD.

Phenylglyoxal inhibition of the mitochondrial F1FO-ATPase activated by Mg2+ or by Ca2+ provides clues on the mitochondrial permeability transition pore

Phenylglyoxal (PGO), known to cause post-translational modifications of Arg residues, was used to highlight the role of arginine residues of the F₁F_O-ATPase, which may be crucial to yield the mitochondrial permeability transition pore (mPTP). In swine heart mitochondria PGO inhibits ATP hydrolysis by the F₁F_O-ATPase either sustained by the natural cofactor Mg²⁺ or by Ca²⁺ by a similar uncompetitive inhibition mechanism, namely the tertiary complex (ESI) only forms when the ATP substrate is already bound to the enzyme, and with similar strength, as shown by the similar K'i values (0.82 ± 0.07 mM in presence of Mg²⁺ and 0.64 ± 0.05 mM in the presence of Ca²⁺). Multiple inhibitor analysis indicates that features of the F₁ catalytic sites and/or the F_O proton binding sites are apparently unaffected by PGO. However, PGO and F₁ or F_O inhibitors can bind the enzyme combine simultaneously. However they mutually hinder to bind the Mg²⁺-activated F₁F_O-ATPase, whereas they do not mutually exclude to bind the Ca²⁺-activated F₁F_O-ATPase. The putative formation of PGO-arginine adducts, and the consequent spatial rearrangement in the enzyme structure, inhibits the F₁F_O-ATPase activity but, as shown by the calcium retention capacity evaluation in intact mitochondria, apparently favours the mPTP formation.

Divergent Expression Patterns of Drp1 and HSD10 in the Nigro-Striatum of Two Mice Strains Based on their MPTP Susceptibility

Alterations in the basal ganglia circuitry are critical events in the pathophysiology of Parkinson's disease (PD). We earlier compared MPTP-susceptible C57BL/6J and MPTP-resistant CD-1 mice to understand the differential prevalence of PD in different ethnic populations like Caucasians and Asian-Indians. The MPTP-resistant CD-1 mice had 33% more nigral neurons and lost only 15-17% of them following MPTP administration. In addition to other cytomorphological features, their basal ganglia neurons had higher calcium-buffering protein levels. During disease pathogenesis as well as in MPTP-induced parkinsonian models, the loss of nigral neurons is associated with reduction in mitochondrial complex-1. Under these conditions, mitochondria respond by undergoing fusion or fission. 17β-hydroxysteroid type 10, i.e., hydroxysteroid dehydrogenase10 (HSD10) and dynamin-related peptide1 (Drp1) are proteins involved in mitochondrial hyperfusion and fission, respectively. Each plays an important role in mitochondrial structure and homeostasis. Their role in determining susceptibility to the neurotoxin MPTP in basal ganglia is however unclear. We studied their expression using immunohistochemistry and Western blotting in the dorsolateral striatum, ventral tegmental area, and substantia nigra pars compacta (SNpc) of C57BL/6J and CD-1 mice. In the SNpc, which exhibits more neuron loss following MPTP, C57BL/6J had higher baseline Drp1 levels; suggesting persistence of fission under normal conditions. Whereas, HSD10 levels increased in CD-1 following MPTP administration. This suggests mitochondrial hyperfusion, as an attempt towards neuroprotection. Thus, the baseline differences in HSD10 and DRP1 levels as well as their contrasting MPTP-responses may be critical determinants of the magnitude of neuronal loss/survival. Similar differences may determine the variable susceptibility to PD in humans.

From the Ca2+-activated F1FO-ATPase to the mitochondrial permeability transition pore: an overview

Based on recent advances on the Ca²⁺-activated F₁F_O-ATPase features, a novel multistep mechanism involving the mitochondrial F₁F_O complex in the formation and opening of the still enigmatic mitochondrial permeability transition pore (MPTP), is proposed. MPTP opening makes the inner mitochondrial membrane (IMM) permeable to ions and solutes and, through cascade events, addresses cell fate to death. Since MPTP forms when matrix Ca²⁺ concentration rises and ATP is hydrolyzed by the F₁F_O-ATPase, conformational changes, triggered by Ca²⁺ insertion in F₁, may be transmitted to F_O and locally modify the IMM curvature. These events would cause F₁F_O-ATPase dimer dissociation and MPTP opening.

Brain Mitochondria, Aging, and Parkinson's Disease

This paper reconsiders the role of mitochondria in aging and in Parkinson’s Disease (PD). The most important risk factor for PD is aging. Alterations in mitochondrial activity are typical of aging. Mitochondrial aging is characterized by decreased oxidative phosphorylation, proteasome activity decrease, altered autophagy, and mitochondrial dysfunction. Beyond declined oxidative phosphorylation, mitochondrial dysfunction consists of a decline of beta-oxidation as well as of the Krebs cycle. Not inherited mitochondrial DNA (mtDNA) mutations are acquired over time and parallel the decrease in oxidative phosphorylation. Many of these mitochondrial alterations are also found in the PD brain specifically in the substantia nigra (SN). mtDNA deletions and development of respiratory chain deficiency in SN neurons of aged individuals as well as of individuals with PD converge towards a shared pathway, which leads to neuronal dysfunction and death. Finally, several nuclear genes that are mutated in hereditary PD are usually implicated in mitochondrial functioning to a various extent and their mutation may cause mitochondrial impairment. In conclusion, a tight link exists between mitochondria, aging, and PD.

Repurposing sex steroids and related drugs as potential treatment for Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder for which a greater prevalence and incidence is described in men. This suggests a protective effect of sex hormones in the brain. Therefore, steroids and drugs to treat endocrine conditions could have additional application for PD. Here, we review the protective effect of sex hormones, particularly estrogens, progesterone, androgens and dehydroepiandrosterone, in animal models of PD and also in human studies. Data also support that drugs affecting estrogen neurotransmission such as selective estrogen receptor modulators or affecting steroid metabolism with 5α-reductase inhibitors could be repositioned for treatment of PD. Sex steroids are also modulator of neurotransmission, thus they could repurposed to treat PD motor symptoms and to modulate the response to PD medication. No drug is yet available to limit PD progression. PD is a complex disease implicating multiple pathological processes and a therapeutic strategy using drugs with several mechanisms of action, such as sex steroids and endocrine drugs are interesting repositioning options for symptomatic treatment and disease-modifying activity for PD. This article is part of the Special Issue entitled 'Drug Repurposing: old molecules, new ways to fast track drug discovery and development for CNS disorders'.

1-Trichloromethyl-1,2,3,4-tetrahydro-beta-carboline (TaClo) Alters Cell Cycle Progression in Human Neuroblastoma Cell Lines

1-Trichloromethyl-1,2,3,4-tetrahydro-β-carboline, abbreviated as TaClo, is an endogenous neurotoxin capable of formation in the brain through the condensation of neuronal tryptamine with ingested exogenous toxins such as trichloroethylene or chloral hydrate. Due to its structural resemblance to 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP), and similar ability to inhibit mitochondrial complex I, TaClo has been implicated in the etiology of Parkinson's disease. Previous studies have shown the cytotoxicity of TaClo in various cell culture models. In this study, we were interested in identifying the early molecular events within the cell upon exposure to TaClo, a potent mitochondrial toxin. We found increased phosphorylation of 5'-adenosine monophosphate-activated protein kinase (AMPK), induction of autophagy, and a dependence on glycolysis as some of the downstream events to TaClo treatment. Furthermore, TaClo-treated cells undergo accelerated late proliferation but form daughter cells containing fewer neurites, leading to their eventual apoptosis. We also found that TaClo inhibits neuronal prostaglandin E₂ synthesis which may play an important role in synaptic plasticity. These results show that TaClo-mediated inhibition of mitochondrial complex I have multiple effects on cellular physiology which are in line with other mitochondrial effectors of Parkinson's disease.

Resveratrol Regulates Mitochondrial Biogenesis and Fission/Fusion to Attenuate Rotenone-Induced Neurotoxicity

It has been confirmed that mitochondrial impairment may underlie both sporadic and familial Parkinson's disease (PD). Mitochondrial fission/fusion and biogenesis are key processes in regulating mitochondrial homeostasis. Therefore, we explored whether the protective effect of resveratrol in rotenone-induced neurotoxicity was associated with mitochondrial fission/fusion and biogenesis. The results showed that resveratrol could not only promote mitochondrial mass and DNA copy number but also improve mitochondrial homeostasis and neuron function in rats and PC12 cells damaged by rotenone. We also observed effects with alterations in proteins known to regulate mitochondrial fission/fusion and biogenesis in rotenone-induced neurotoxicity. Therefore, our findings suggest that resveratrol may prevent rotenone-induced neurotoxicity through regulating mitochondrial fission/fusion and biogenesis.