Commentary: Adenosine A2A Receptor Blockade Prevents Rotenone-Induced Motor Impairment in a Rat Model of Parkinsonism

Quantitative Structure-Neurotoxicity Assessment and In Vitro Evaluation of Neuroprotective and MAO-B Inhibitory Activities of Series N'-substituted 3-(1,3,7-trimethyl-xanthin-8-ylthio)propanehydrazides

The neurotoxic, neuroprotective and MAO-B inhibitory effects of series N'-substituted 3-(1,3,7-trimethyl-xanthin-8-ylthio)propanehydrazides are evaluated. The results indicate compounds N'-(2,3-dimethoxybenzylidene)-3-(1,3,7-trimethyl-2,6-dioxo-2,3,6,7-tetrahydro-1H-purin-8-ylthio)propanehydrazide (6k) and N'-(2-hydroxybenzylidene)-3-(1,3,7-trimethyl-2,6-dioxo-2,3,6,7-tetrahydro-1H-purin-8-ylthio)propanehydrazide (6l) as most perspective. The performed QSTR analysis identified that the decreased lipophilicity and smaller dipole moments of the molecules are the structural features ensuring lower neurotoxicity. The obtained results may be used as initial information in the further design of (xanthinyl-8-ylthio)propanhydrazides with potential hMAOB inhibitory effect and pronounced neuroprotection.

The Pharmacological Potential of Adenosine A2A Receptor Antagonists for Treating Parkinson's Disease

The adenosine A_2A receptor subtype is recognized as a non-dopaminergic pharmacological target for the treatment of neurodegenerative disorders, notably Parkinson’s disease (PD). The selective A_2A receptor antagonist istradefylline is approved in the US and Japan as an adjunctive treatment to levodopa/decarboxylase inhibitors in adults with PD experiencing OFF episodes or a wearing-off phenomenon; however, the full potential of this drug class remains to be explored. In this article, we review the pharmacology of adenosine A_2A receptor antagonists from the perspective of the treatment of both motor and non-motor symptoms of PD and their potential for disease modification.

A2A Adenosine Receptor Antagonists and their Potential in Neurological Disorders

Endogenous nucleoside adenosine modulates a number of physiological effects through interaction with P1 purinergic receptors. All of them are G protein coupled receptors and, to date, four subtypes have been characterized and named A1, A2A, A2B, and A3. In recent years adenosine receptors, particularly the A2A subtype, have become attractive targets for the treatment of several neurodegenerative disorders, known to involve neuroinflammation, like Parkinson's and Alzheimer's diseases, multiple sclerosis and neuropsychiatric conditions. In fact, it has been demonstrated that inhibition of A2A adenosine receptors exerts neuroprotective effects counteracting neuroinflammatory processes and astroglial and microglial activation. The A2A adenosine receptor antagonist istradefylline, developed by Kyowa Hakko Kirin Inc., was approved in Japan as adjunctive therapy for the treatment of Parkinson's disease and very recently it was approved also by the US Food and Drug Administration. These findings pave the way for new therapeutic opportunities, so, in this review, a summary of the most relevant and promising A2A adenosine receptor antagonists will be presented along with their preclinical and clinical studies in neuroinflammation related diseases.

Xanthine Derivatives as Agents Affecting Non-dopaminergic Neuroprotection in Parkinson`s Disease

Parkinson's Disease (PD) is a neurodegenerative and debilitating disease that affects 1% of the elderly population. Patient's motor disability results in extreme difficulty to deal with daily activities. Conventional treatment is limited to dopamine replacement therapy, which fails to delay disease's progression and is often associated with a number of adverse reactions. Recent progress in understanding the mechanisms involved in PD has revealed new molecular targets for therapeutic approaches. Among them, caffeine and xanthine derivatives are promising drug candidates, because of the possible symptomatic benefits in PD. In fact, consumption of coffee correlates with a reduced risk of PD. Over the last decades, a lot of efforts have been made to uncover the therapeutic potential of xanthine structures. The substituted xanthine molecule is used as a scaffold for the synthesis of new compounds with protective effects in neurodegenerative diseases, including PD, asthma, cancer and others. The administration of the xanthines has been proposed as a non-dopaminergic strategy for neuroprotection in PD and the mechanisms of protection have been associated with antagonism of adenosine A2A receptors and Monoamine Oxidase type B (MAO-B) inhibition. The current review summarizes frequently suspected non-dopaminergic neuroprotective mechanisms and the possible beneficial effects of the xanthine derivatives in PD, along with some synthetic approaches to produce perspective xanthine derivatives as non-dopaminergic agents in PD treatment.

The Protective Effect of Korean Red Ginseng Against Rotenone-Induced Parkinson's Disease in Rat Model: Modulation of Nuclear Factor-κβ and Caspase-3

OBJECTIVE

Korean red ginseng was reported to have many biological effects like the antioxidant and the anti-inflammatory activities. Oxidative stress and neuro-inflammation play major roles in the pathogenesis of Parkinson's disease (PD). The current study aimed to investigate the protective effects of ginseng on rotenone-induced PD in rats.

METHODS

Rats were randomly allocated into 4 groups: normal rats, rotenone control, ginseng+rotenone and ginseng only treated rats. The severity of PD was evaluated through locomotor activity perceived in the open field test, histological examination and immunohistochemical detection of amyloid-β in brain tissues, in addition to the biochemical assessment of tyrosine hydroxylase activity in brain tissues. Moreover, the following parameters were investigated for studying the possible mechanisms of ginseng neuroprotective effect: nuclear factor-κβ (NF-κβ), tumor necrosis factor-alpha (TNF-α), caspase- 3, lipid peroxides and reduced glutathione (GSH).

RESULTS

Ginseng exhibited potent neuroprotective effect that was reflected upon the histopathological examination, marked improvement in the locomotor activity and through its ability to suppress the amyloid- β deposition in the cortex and striatum along with significant increase in the tyrosine hydroxylase activity. Ginseng successfully inhibited the NF-κβ inflammatory pathway in brain tissues beside the inhibition of other oxidative stress and inflammatory mediators. Furthermore, it exhibited antiapoptotic effect via the inhibition of caspase-3 expression.

CONCLUSION

Ginseng could be a promising treatment in PD. It can suppress dopaminergic neuron degeneration through variable mechanisms mainly via inhibition of NF-κβ pathway in addition to inhibition of oxidative stress and apoptosis.