Thyroid status and cognitive function in euthyroid patients with early Parkinson's disease

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.

Shedding light on thyroid hormone disorders and Parkinson disease pathology: mechanisms and risk factors

Parkinson's disease (PD) is a neurodegenerative disorder characterized by loss of dopaminergic neurons. Dopaminergic system is interconnected with the hypothalamic-pituitary-thyroid axis. Dopamine (DA) upregulates thyrotropin releasing hormone (TRH) while downregulating thyroid stimulating hormone (TSH) and thyroid hormones. Moreover, TRH stimulates DA release. PD is associated with impaired regulation of TSH and thyroid hormones (TH) levels, which in turn associate with severity and different subtypes of PD, while levodopa and bromocriptine treatment can interfere with hypothalamic-pituitary-thyroid axis. Thyroid disturbances, including hypothyroidism, Hashimoto's thyroiditis (HT), hyperthyroidism and Graves' disease (GD) not only increase the risk of PD but also share some clinical signs with PD. Also, several genes including RASD2, WSB1, MAPT, GIRK2, LRRK2 and gene products like neurotensin and NOX/DUOX affect the risk for both PD and thyroid disease. Hypothyroidism is associated with obesity, hypercholesterolemia, anemia and altered cerebral blood flow which are associated with PD pathology. Herein we provide a comprehensive view on the association between PD and thyroid hormones regulation and dysregulations, hoping to provide new avenues towards targeted treatment of PD. We performed a comprehensive search in literature using Pubmed and Scopus, yielding to a total number of 36 original articles that had addressed the association between thyroid hormone disorders and PD.

Alterations of thyroidal status in brain regions and hypothalamo-pituitary-blood-thyroid-axis associated with dopaminergic depletion in substantia nigra and ROS formation in different brain regions after MPTP treatment in adult male mice

MPTP produces oxidative stress, damages niagrostriatal dopaminergic neurons and develops Parkinsonism in rodents. Due to paucity of information, the thyroidal status in brain regions and peripheral tissues during different post-treatment days in MPTP-induced mice had been executed in the present study. MPTP depleted tyrosine hydroxylase protein expressions that signify the dopaminergic neuronal damage in substantia nigra. MPTP elevated ROS formation differentially in brain regions (cerebral cortex, hippocampus, substantia nigra) with maximal elevation at hippocampus. The changes in thyroid hormone (T₄ and T₃) levels indicate that brain regions might combat the adverse situation by keeping the levels of thyroid hormones either unchanged or in the elevated conditions in the latter phases (day-3 and day-7), apart from the depletion of thyroid hormones in certain brain regions (T₄ in SN and hippocampus, T₃ in hippocampus) as the immediate (day-1) effects after MPTP treatment. MPTP caused alterations of cellular morphology, RNA:Protein ratio and TPO protein expression, concomitantly depleted TPO mRNA expression and elevated TSH levels in the thyroid gland. Although T₄ levels changed differentially, T₃ levels remained unaltered in thyroid gland throughout the post-treatment days. Results have been discussed mentioning the putative role of T₄ and TSH in apoptosis and/or proliferation/differentiation of thyrocytes. In blood, T₄ levels remained unchanged while the changes in T₃ and TSH levels did not signify the clinical feature of hypo/hyperthyroidism of animals. In the pituitary, both T₄ and T₃ levels remained elevated where TSH differentially altered (elevated followed by depletion) during post-treatment days. Notably, T₄, T₃ and TSH levels did not alter in hypothalamus except initial (day-1) depletion of the T₄ level. Therefore, the feedback control mechanism of hypothalamo-pituitary-blood-thyroid-axis failed to occur after MPTP treatment. Overall, MPTP altered thyroidal status in the brain and peripheral tissues while both events might occur in isolation as well.