Abstract

Neuronal lesions in Parkinson’s disease (PD) are commonly associated with α-synuclein (α-Syn)-induced cell damage that are present both in the central and peripheral nervous systems of patients, with the enteric nervous system also being especially vulnerable. Here, we bring together evidence that the development and presence of PD depends on specific sets of interlinking factors that include neuroinflammation, systemic inflammation, α-Syn-induced cell damage, vascular dysfunction, iron dysregulation, and gut and periodontal dysbiosis. We argue that there is significant evidence that bacterial inflammagens fuel this systemic inflammation, and might be central to the development of PD. We also discuss the processes whereby bacterial inflammagens may be involved in causing nucleation of proteins, including of α-Syn. Lastly, we review evidence that iron chelation, pre-and probiotics, as well as antibiotics and faecal transplant treatment might be valuable treatments in PD. A most important consideration, however, is that these therapeutic options need to be validated and tested in randomized controlled clinical trials. However, targeting underlying mechanisms of PD, including gut dysbiosis and iron toxicity, have potentially opened up possibilities of a wide variety of novel treatments, which may relieve the characteristic motor and nonmotor deficits of PD, and may even slow the progression and/or accompanying gut-related conditions of the disease.

Highlights

  • The global prevalence of Parkinson’s disease (PD) during 2016 reached 6.1 million [1].In the United States of America, Canada, and Europe the prevalence is projected to increase by approximately 92% by 2050 [2], involving an increased burden on global healthcare [3].α-Synuclein (α-Syn) is the principal component of Lewy bodies (LBs), which are the pathological hallmark of PD and other related conditions [4]

  • When gut dysbiosis is present in PD patients, gut-derived bacteria escape from the gastrointestinal tract into the blood

  • Gut dysbiosis is typically associated with an increase in Gram-negative bacteria such as E. coli and H. pylori, which are known to secrete a variety of pro-inflammatory molecules [135,144]

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Summary

Introduction

The global prevalence of Parkinson’s disease (PD) during 2016 reached 6.1 million [1]. The immune response in PD, which is proposed to occur early, involve peripheral and brain immune cells, eventually evolve as neuronal dysfunction progresses, and is likely to influence disease progression [40] Central to these immune changes in PD is the interplay between the microbiome–gut–brain axis [25,41,42,43]. High levels of iron and calcium in the substantia nigra, mitochondrial dysfunction and neuroinflammation directly contribute to the increased oxidative stress and dopaminergic neuronal loss in the brains of PD patients [78,81]. In a 2016 study, serum levels including that of iron, ferritin, transferrin, superoxide dismutase catalase, nitrosative stress marker, thiobarbituric acid reactive substances, and other similar oxidative stress markers were analysed in 40 PD patients and 46 controls [82].

An Integrated Physiological Systems Disease
A Continuum of Pathological Events or the Distinct Events Hypothesis?
Oral andisGut
Bacterial Inflammagens
LPS as a Potent Inflammagen
Formation of Nucleated Molecular Intermediates as Induced by LPS
Oral Microbiota Translocation in Parkinson’s Disease
Iron Chelation
Antibiotics and Probiotics
Faecal Microbiota Transplantation
Additional Therapeutic Options
Findings
Conclusions
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