Testosterone level and the effect of levodopa and agonists in early Parkinson disease: results from the INSPECT cohort

Understanding the dopaminergic pathway relative to men's sexual dysfunction in patients with Parkinson's disease: a narrative review with implications for future research

Parkinson's disease (PD) is often most recognized for motor symptoms but associated non-motor symptoms such as sexual dysfunction can significantly impact quality of life. This condition involves a hormonal disruption and has a predilection for male patients, yet there are no formal guidelines for screening or management of sexual health pathology in these patients. While prior publications have addressed the presence of sexual dysfunction (SD) among men with PD, there has been a paucity of work examining the hypothalamic-pituitary-gonadal (HPG) axis and the interplay between dopamine, prolactin (PRL), and testosterone. This review provides an overview of data extracted from the existing peer-reviewed literature regarding hormonal and sexual health changes in men with PD and the impact of dopaminergic and/or androgen replacement therapy. Furthermore, while some research suggests that PD patients are at higher risk for prolactin elevation and testosterone deficiency, heterogeneity of the data limits extrapolation. Additionally, data related to pharmacologic optimization of the HPG axis in this patient population is similarly limited. Prospective studies are needed to better characterize the hormonal pathophysiology of PD as it relates to sexual dysfunction such that men at risk can be effectively identified so as to offer interventions that may improve quality of life.

[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.

Sex, Pramipexole and Tiagabine Affect Behavioral and Hormonal Response to Traumatic Stress in a Mouse Model of PTSD

Posttraumatic stress disorder (PTSD) has been associated with abnormal regulation of the hypothalamic-pituitary-adrenal gland axis (HPA). Women demonstrate a more robust HPA response and are twice as likely to develop PTSD than men. The role of sex hormones in PTSD remains unclear. We investigated whether post-trauma chronic treatment with the GABA-ergic agent tiagabine and dopamine-mimetic pramipexole affected the behavioral outcome and plasma levels of corticosterone, testosterone, or 17β-estradiol in female and male mice. These medications were investigated due to their potential capacity to restore GABA-ergic and dopaminergic deficits in PTSD. Animals were exposed to a single prolonged stress procedure (mSPS). Following 13 days treatment with tiagabine (10 mg/kg) or pramipexole (1 mg/kg) once daily, the PTSD-like phenotype was examined in the fear conditioning paradigm. Plasma hormones were measured almost immediately following the conditioned fear assessment. We report that the exposure to mSPS equally enhanced conditioned fear in both sexes. However, while males demonstrated decreased plasma corticosterone, its increase was observed in females. Trauma elevated plasma testosterone in both sexes, but it had no significant effects on 17β-estradiol. Behavioral manifestation of trauma was reduced by pramipexole in both sexes and by tiagabine in females only. While neither compound affected corticosterone in stressed animals, testosterone levels were further enhanced by tiagabine in females. This study shows sex-dependent efficacy of tiagabine but not pramipexole in a mouse model of PTSD-like symptoms and a failure of steroid hormones’ levels to predict PTSD treatment efficacy.

Expanding sexual and gender minority research in movement disorders: More than awareness and acceptance

Culturally competent and inclusive care is slowly becoming the standard throughout healthcare institutions. Awareness, acceptance, and inclusion of the sexual and gender minority (SGM) groups in medicine and neurology are progressing. Research in SGM health, although increasing, remains remarkably scant in parkinsonism and other movement disorders, a community whose patient population is on the rise. Most SGM health research in movement disorders only focuses on the symptoms associated with infection by the human immunodeficiency virus and the acquired immunodeficiency syndrome. Multiple clinical and epidemiological research questions remain unaddressed when considering the intersection of movement disorders and SGM health. In this article, we highlight gaps in the care of SGM individuals with movement disorders. First, the prevalence and phenomenology of movement disorders could be different, considering the different rates of risk factors and the use of gender-affirming hormones. Also, the effect of creating a safe environment in healthcare institutions to disclose sexual orientation and gender identity on seeking care, access to resources, and quality of services remains unknown. Moreover, many individuals with movement disorders would require services from multidisciplinary teams or long-term care facilities, which might not consider the needs of SGM patients in their models of care. Last, the effect of social isolation and self-perception (or misperceptions) in the SGM populations on the non-motor and motor symptoms of movement disorders and the treatment plans is not understood.

Parkinson's disease in women: Mechanisms underlying sex differences

Parkinson's disease is a neurodegenerative disease which is associated with different motor, cognitive and mood-related problems. Though it has been established that Parkinson's disease is less prevalent in women in comparison to men, the differences tend to diminish with the advancing age. Different genetic, hormonal, neuroendocrinal and molecular players contribute towards the differences in the Parkinson's disease pathogenesis. Furthermore, data available with respect to the therapeutic management of Parkinson's disease in females is limited; women often tend to suffer more from the side effects of the currently available drugs. The present review highlights the sex-specific differences which play a role in the manifestation of these symptoms and side effects of the currently available therapeutic strategies. We have also discussed the current and upcoming therapeutic strategies which are in the clinical trials such as adenosine 2A (A2A) receptor antagonists, estrogen replacement therapy, α-synuclein targeting vaccines and antibodies, Botulinum toxin A, Fas-associated factor-1 (FAF-1) inhibitors, thiazolidinediones, 5-HT1_A receptor agonists, dopamine D1/D5 receptor agonists, Glucagon-like peptide 1 (GLP-1) analogues and certain plant based principles for the treatment of Parkinson's disease in women.

Sexual Disorders and Quality of Life in Parkinson's Disease

Introduction

Sexual disorders are the most neglected nonmotor symptoms in Parkinson's disease (PD). Although doctors seek greater priority to motor manifestations, which are the basis for the diagnosis of PD, the nonmotor symptoms deserve to be highlighted as much as the motor problems because of their strong presence and discomfort in the patients, causing the important impairment in the quality of life (QoL) of the individual with PD.

Aim

Provide the prevalence of sexual disorders among patients with PD and alert the medical profession to investigate and be familiar with problems related to QoL and sexual disorders in PD.

Methods

This is a large literature review on sexual disorders in PD and impaired QoL.

Main Outcome Measures

Sexual disorders in PD and prevalence between genders have been described in epidemiological studies. Neuroanatomy, pathophysiology, risk factors, QoL, and etiologies were reviewed.

Results

The estimate of the prevalence of sexual dysfunction in the form of compulsive sexual behavior in PD is higher in men by 5.2% than in women by 0.5%. This diagnosis is a determinant of intense and persistent suffering and is related to several health problems of a social, economic, personal, family, psychological, and occupational nature, which can even culminate in sexual abuse. It is most commonly associated with the use of drugs commonly used in PD therapy in 98.1% of cases. In addition to this serious public health problem, another common condition of sexual dysfunction occur with the decreased libido by loss of the neurotransmitter dopamine proper of the pathophysiology of PD.

Conclusion

The presence of sexual disorders in PD should be tracked and monitored because of its harmful consequences, whether due to increased sexual behavior or associated psychological distress, as well as the impacts on QoL. Early recognition and adequate treatment of PD in its fullness and richness of associated symptoms are essential for improving QoL.

Santa Rosa Malcher CM, Roberto da Silva Gonçalves Oliveira K, Fernandes Caldato MC, et al. Sexual Disorders and Quality of Life in Parkinson's Disease. Sex Med 2021;9:100280.

Sex-related differences in oxidative stress and neurodegeneration

Oxidative stress has been implicated in a number of neurodegenerative diseases spanning various fields of research. Reactive oxygen species can be beneficial or harmful, depending on their concentration. High levels of reactive oxygen species can lead to oxidative stress, which is an imbalance between free radicals and antioxidants. Increased oxidative stress can result in cell loss. Interestingly, sex differences have been observed in oxidative stress generation, which may underlie sex differences observed in neurodegenerative disorders. An enhanced knowledge of the role of sex hormones on oxidative stress signaling and cell loss can yield valuable information, leading to sex-based mechanistic approaches to neurodegeneration.

Effect of the 5α-reductase enzyme inhibitor dutasteride in the brain of intact and parkinsonian mice

Dutasteride is a 5alpha-reductase inhibitor in clinical use to treat endocrine conditions. The present study investigated the neuroprotective mechanisms of action of dutasteride in intact and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned mice using a low dose of MPTP not affecting motor activity modeling early stages of Parkinson's disease (PD). We hypothesized that dutasteride neuroprotection is due to altered steroids levels. Dutasteride pre-treatment prevented loss of striatal dopamine (DA) and its metabolite DOPAC. Dutasteride decreased effects of MPTP on striatal dopamine transporter (DAT), vesicular monoamine transporter 2 (VMAT2) and D2 DA receptor specific binding while D1 receptor specific binding remained unchanged. Dutasteride enhanced DAT specific binding and the glycosylated form of DAT in intact mice. MPTP-lesioned mice had plasma and brain testosterone and dihydrotestosterone levels lower than control mice whereas progesterone and its metabolites (dihydroprogesterone, isopregnanolone and tetrahydroprogesterone) pathway showed increases. Dutasteride treatment by inhibiting transformation of progesterone and testosterone to its metabolites elevated plasma and brain concentrations of testosterone compared to MPTP mice and decreased DHT levels in intact mice. Plasma and brain estradiol levels were low and remained unchanged by MPTP and/or dutasteride treatment. Dutasteride treatment did not affect striatal phosphorylation of Akt and its downstream substrate GSK3β as well as phosphorylation of ERK1/2 in intact and MPTP lesioned MPTP mice. Striatal glial fibrillary acidic protein (GFAP) levels were markedly elevated in MPTP compared to control mice and dutasteride reduced GFAP levels in MPTP mice. Treatment with dutasteride post-lesion left unchanged striatal DA levels. These results suggest dutasteride as promising drug for PD neuroprotection.