Increased risk of Parkinson disease with diabetes mellitus in a population-based study

Role of Insulin in Neurotrauma and Neurodegeneration: A Review

Insulin is a hormone typically associated with pancreatic release and blood sugar regulation. The brain was long thought to be “insulin-independent,” but research has shown that insulin receptors (IR) are expressed on neurons, microglia and astrocytes, among other cells. The effects of insulin on cells within the central nervous system are varied, and can include both metabolic and non-metabolic functions. Emerging data suggests that insulin can improve neuronal survival or recovery after trauma or during neurodegenerative diseases. Further, data suggests a strong anti-inflammatory component of insulin, which may also play a role in both neurotrauma and neurodegeneration. As a result, administration of exogenous insulin, either via systemic or intranasal routes, is an increasing area of focus in research in neurotrauma and neurodegenerative disorders. This review will explore the literature to date on the role of insulin in neurotrauma and neurodegeneration, with a focus on traumatic brain injury (TBI), spinal cord injury (SCI), Alzheimer’s disease (AD) and Parkinson’s disease (PD).

Diabetes Causes Dysfunctional Dopamine Neurotransmission Favoring Nigrostriatal Degeneration in Mice

BACKGROUND

Numerous studies indicate an association between neurodegenerative and metabolic diseases. Although still a matter of debate, growing evidence from epidemiological and animal studies indicate that preexisting diabetes increases the risk to develop Parkinson's disease. However, the mechanisms of such an association are unknown.

OBJECTIVES

We investigated whether diabetes alters striatal dopamine neurotransmission and assessed the vulnerability of nigrostriatal neurons to neurodegeneration.

METHODS

We used streptozotocin-treated and genetically diabetic db/db mice. Expression of oxidative stress and nigrostriatal neuronal markers and levels of dopamine and its metabolites were monitored. Dopamine release and uptake were assessed using fast-scan cyclic voltammetry. 6-Hydroxydopamine was unilaterally injected into the striatum using stereotaxic surgery. Motor performance was scored using specific tests.

RESULTS

Diabetes resulted in oxidative stress and decreased levels of dopamine and its metabolites in the striatum. Levels of proteins regulating dopamine release and uptake, including the dopamine transporter, the Girk2 potassium channel, the vesicular monoamine transporter 2, and the presynaptic vesicle protein synaptobrevin-2, were decreased in diabetic mice. Electrically evoked levels of extracellular dopamine in the striatum were enhanced, and altered dopamine uptake was observed. Striatal microinjections of a subthreshold dose of the neurotoxin 6-hydroxydopamine in diabetic mice, insufficient to cause motor alterations in nondiabetic animals, resulted in motor impairment, higher loss of striatal dopaminergic axons, and decreased neuronal cell bodies in the substantia nigra.

CONCLUSIONS

Our results indicate that diabetes promotes striatal oxidative stress, alters dopamine neurotransmission, and increases vulnerability to neurodegenerative damage leading to motor impairment. © 2020 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Association Between Glycemic Status and the Risk of Parkinson Disease: A Nationwide Population-Based Study

OBJECTIVE

Previous studies have suggested that diabetes increases the risk of Parkinson disease (PD); however, this has not been conclusively established. We analyzed the risk of PD based on baseline glucose tolerance status in a large-scale cohort representative of the general Korean population.

RESEARCH DESIGN AND METHODS

This analysis was performed in a cohort of 15,168,021 adults aged ≥40 years who underwent health checkups under the National Health Insurance Service between January 2009 and December 2010. The clinical course of subjects was monitored until December 2016. Subjects were classified into the following groups: no diabetes, impaired fasting glucose (IFG), diabetes duration <5 years, and diabetes duration ≥5 years. We analyzed the adjusted hazard ratio of PD for each group.

RESULTS

During the observation period of 49,076,148.74 person-years, PD occurred in 31,577 patients. Compared with the nondiabetes group, the adjusted hazard ratio was 1.038 (95% CI, 1.009-1.067) in the IFG group, 1.185 (95% CI, 1.143-1.229) in the diabetes duration <5 years group, and 1.618 (95% CI, 1.566-1.672) in the diabetes duration ≥5 years group. These results were consistent with those of the subgroup analysis, and the presence of diabetes further increased the risk of PD regardless of comorbidities such as cardiovascular, cerebrovascular, and chronic kidney diseases.

CONCLUSIONS

This population-based cohort study suggests that diabetes is an independent risk factor for PD.

Diabetes Mellitus and Parkinson's Disease: Shared Pathophysiological Links and Possible Therapeutic Implications

Diabetes mellitus (DM) is the most common chronic metabolic disease. Parkinson's disease (PD) is considered one of the most common neurodegenerative diseases. There are many similarities between both conditions. Both disorders are chronic diseases. Both diseases result from a decrease in a specific substance: dopamine in PD, and insulin in DM. Besides, both disorders arise due to the destruction of particular cells, dopaminergic cells in PD, and pancreatic beta-cell in DM. Recently, many epidemiological and experimental studies showed a connection between DM and PD. There are common underlying mechanisms in the pathophysiology of both diseases. These underlying mechanisms include mitochondrial dysfunction, oxidative stress, hyperglycemia, and inflammation. Insulin resistance is indeed the hallmark of DM, especially type 2 diabetes mellitus (T2DM), which plays a significant role in these pathophysiological and molecular mechanisms. Besides, many studies revealed that anti-diabetic drugs have a beneficial effect on PD. In this current literature review, we aim to explore the standard pathophysiological and molecular linkages between these two disorders as well as how DM could affect the incidence and progression of PD. We also review how anti-diabetic drugs impact PD. In the future, further experimental and expanded clinical studies are needed to fully understand the exact pathophysiological connections between the two disorders and the efficacy of insulin and other anti-diabetic drugs in the treatment of PD in diabetic patients. Fully understanding and targeting these pathophysiological and molecular links could result in de novo curative therapy for PD and DM.

Lipid Metabolism is the common pathologic mechanism between Type 2 Diabetes Mellitus and Parkinson's disease

Although increasing evidence has suggested crosstalk between Parkinson's disease (PD) and type 2 diabetes mellitus (T2DM), the common mechanisms between the two diseases remain unclear. The aim of our study was to characterize the interconnection between T2DM and PD by exploring their shared biological pathways and convergent molecules. The intersections among the differentially expressed genes (DEGs) in the T2DM dataset GSE95849 and PD dataset GSE6613 from the Gene Expression Omnibus (GEO) database were identified as the communal DEGs between the two diseases. Then, an enrichment analysis, protein-protein interaction (PPI) network analysis, correlation analysis, and transcription factor-target regulatory network analysis were performed for the communal DEGs. As a result, 113 communal DEGs were found between PD and T2DM. They were enriched in lipid metabolism, including protein modifications that regulate metabolism, lipid synthesis and decomposition, and the biological effects of lipid products. All these pathways and their biological processes play important roles in both diseases. Fifteen hub genes identified from the PPI network could be core molecules. Their function annotations also focused on lipid metabolism. According to the correlation analysis and the regulatory network analysis based on the 15 hub genes, Sp1 transcription factor (SP1) could be a key molecule since it affected other hub genes that participate in the common mechanisms between PD and T2DM. In conclusion, our analyses reveal that changes in lipid metabolism could be a key intersection between PD and T2DM, and that SP1 could be a key molecule regulating these processes. Our findings provide novel points for the association between PD and T2DM.

β-Adrenoceptor Drugs and Parkinson's Disease: A Nationwide Nested Case-Control Study

BACKGROUND

Potential relationships between β-adrenergic drugs and α-synuclein synthesis in Parkinson's disease (PD) have been recently suggested.

OBJECTIVE

This study investigated the putative association between β-adrenoceptor drug exposure and PD occurrence.

METHODS

A nested case-control study was performed in the Echantillon Généraliste des Bénéficiaires (EGB) (a 1/97th random sample of affiliates to the French Insurance System). Incident PD patients diagnosed between 01/01/2008 and 31/12/2017 (index date) were matched 1:1 to controls by gender, birth year, and insurance scheme. Exposure to any β-agonist and to any β-antagonist was compared between cases and controls within 1-2 years before the index date, and exposure to salbutamol and to propranolol was individualized. The association between PD and β-adrenoceptor drugs was investigated through conditional logistic regression models adjusted for potential confounding factors. Because of a statistical interaction between β-agonists and diabetes, results were stratified according to the presence of diabetes.

RESULTS

Among the 2225 incident PD patients identified in the EGB (mean age 75.6 ± 10.2 years, sex ratio 1.04), no significant association was found between PD and β-antagonists (adjusted odds ratio [aOR] 1.05 [95% confidence interval 0.91-1.20]), except for propranolol (aOR 2.11 [1.38-3.23]). For β-agonists, a protective association in non-diabetic patients (aOR 0.75 [0.60-0.93]) and an opposite and significant association in diabetic patients (aOR 1.61 [1.02-2.55]) were observed. Similar results were found with salbutamol.

CONCLUSION

This study did not identify an increased risk of PD occurrence after β-antagonist exposure, except for propranolol (potential protopathic bias). The discordant results observed with β-agonists in patients with or without diabetes deserve further exploration of the influence of diabetic comorbidity on PD occurrence and evolution.

The Antioxidant, Anti-Inflammatory, and Neuroprotective Properties of the Synthetic Chalcone Derivative AN07

Chalcones belong to a class of biologically active polyphenolic natural products. As a result of their simple chemical nature, they are easily synthesized and show a variety of promising biological activities. 2-Hydroxy-4′-methoxychalcone (AN07) is a synthetic chalcone derivate with potential anti-atherosclerosis effects. In this study, we demonstrated the novel antioxidant, anti-inflammatory, and neuroprotective effects of AN07. In RAW 264.7 macrophages, AN07 attenuated lipopolysaccharide (LPS)-induced elevations in reactive oxygen species (ROS) level and oxidative stress via down-regulating gp91^phox expression and stimulating the antioxidant system of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) pathways, which were accompanied by increased glutathione (GSH) levels. Additionally, AN07 attenuated LPS-induced inflammatory factors, including NO, inducible NO synthase (iNOS), cyclooxygenase-2 (COX-2), and phosphorylated inhibitor of nuclear factor kappa B-alpha (p-IκBα) in RAW 264.7 macrophages. However, the effects of AN07 on promoting nuclear Nrf2 levels and decreasing COX-2 expressions were significantly abrogated by the peroxisome proliferator-activated receptor-γ (PPARγ) antagonist GW9662. In human dopaminergic SH-SY5Y cells treated with or without methylglyoxal (MG), a toxic endogenous by-product of glycolysis, AN07 up-regulated neurotrophic signals including insulin-like growth factor 1 receptor (IGF-1R), p-Akt, p-GSK3β, glucagon-like peptide 1 receptor (GLP-1R), and brain-derived neurotrophic factor (BDNF). AN07 attenuated MG-induced apoptosis by up-regulating the B-cell lymphoma 2 (Bcl-2) protein and down-regulating the cytosolic expression of cytochrome c. AN07 also attenuated MG-induced neurite damage via down-regulating the Rho-associated protein kinase 2 (ROCK2)/phosphorylated LIM kinase 1 (p-LIMK1) pathway. Moreover, AN07 ameliorated the MG-induced down-regulation of neuroprotective Parkinsonism-associated proteins parkin, pink1, and DJ-1. These findings suggest that AN07 possesses the potentials to be an anti-inflammatory, antioxidant, and neuroprotective agent

O-GlcNAcylation as a Therapeutic Target for Alzheimer's Disease

Alzheimer's disease (AD) is the most common cause of dementia and the number of elderly patients suffering from AD has been steadily increasing. Despite worldwide efforts to cope with this disease, little progress has been achieved with regard to identification of effective therapeutics. Thus, active research focusing on identification of new therapeutic targets of AD is ongoing. Among the new targets, post-translational modifications which modify the properties of mature proteins have gained attention. O-GlcNAcylation, a type of PTM that attaches O-linked β-N-acetylglucosamine (O-GlcNAc) to a protein, is being sought as a new target to treat AD pathologies. O-GlcNAcylation has been known to modify the two important components of AD pathological hallmarks, amyloid precursor protein, and tau protein. In addition, elevating O-GlcNAcylation levels in AD animal models has been shown to be effective in alleviating AD-associated pathology. Although studies investigating the precise mechanism of reversal of AD pathologies by targeting O-GlcNAcylation are not yet complete, it is clearly important to examine O-GlcNAcylation regulation as a target of AD therapeutics. This review highlights the mechanisms of O-GlcNAcylation and its role as a potential therapeutic target under physiological and pathological AD conditions.

The Association Between Type 2 Diabetes Mellitus and Parkinson's Disease

In recent years, an emerging body of evidence has forged links between Parkinson's disease (PD) and type 2 diabetes mellitus (T2DM). In observational studies, those with T2DM appear to be at increased risk of developing PD, as well as experiencing faster progression and a more severe phenotype of PD, with the effects being potentially mediated by several common cellular pathways. The insulin signalling pathway, for example, may be responsible for neurodegeneration via insulin dysregulation, aggregation of amyloids, neuroinflammation, mitochondrial dysfunction and altered synaptic plasticity. In light of these potential shared disease mechanisms, clinical trials are now investigating the use of established diabetes drugs targeting insulin resistance in the management of PD. This review will discuss the epidemiological links between T2DM and PD, the potential shared cellular mechanisms, and assess the relevant treatment options for disease modification of PD.

Understanding the links between cardiovascular disease and Parkinson's disease

Studies investigating the associations between genetic or environmental factors and Parkinson's disease (PD) have uncovered a number of factors shared with cardiovascular disease, either as risk factors or manifestations of cardiovascular disease itself. Older age, male sex, and possibly type 2 diabetes are examples. On the other hand, coffee consumption and physical activity are each associated with a lower risk of both PD and cardiovascular disease. This observation raises questions about the underlying pathophysiological links between cardiovascular disease and PD. There is evidence for common mechanisms in the areas of glucose metabolism, cellular stress, lipid metabolism, and inflammation. On the other hand, smoking and total/low-density lipoprotein cholesterol appear to have opposite associations with cardiovascular disease and PD. Thus, it is uncertain whether the treatment of cardiovascular risk factors will impact on the onset or progression of PD. The available data suggest that a nuanced approach is necessary to manage risk factors such as cholesterol levels once the associations are better understood. Ultimately, the choice of therapy may be tailored to a patient's comorbidity profile. This review presents the epidemiological evidence for both concordant and discordant associations between cardiovascular disease and PD, discusses the cellular and metabolic processes that may underlie these links, and explores the implications this has for patient care and future research. © 2019 International Parkinson and Movement Disorder Society.

Causal association of type 2 diabetes with amyotrophic lateral sclerosis: new evidence from Mendelian randomization using GWAS summary statistics

BACKGROUND

Associations between type 2 diabetes (T2D) and amyotrophic lateral sclerosis (ALS) were discovered in observational studies in both European and East Asian populations. However, whether such associations are causal remains largely unknown.

METHODS

We employed a two-sample Mendelian randomization approach to evaluate the causal relationship of T2D with the risk of ALS in both European and East Asian populations. Our analysis was implemented using summary statistics obtained from large-scale genome-wide association studies with ~660,000 individuals for T2D and ~81,000 individuals for ALS in the European population, and ~191,000 individuals for T2D and ~4100 individuals for ALS in the East Asian population. The causal relationship between T2D and ALS in both populations was estimated using the inverse-variance-weighted methods and was further validated through extensive complementary and sensitivity analyses.

RESULTS

Using multiple instruments that were strongly associated with T2D, a negative association between T2D and ALS was identified in the European population with the odds ratio (OR) estimated to be 0.93 (95% CI 0.88-0.99, p = 0.023), while a positive association between T2D and ALS was observed in the East Asian population with OR = 1.28 (95% CI 0.99-1.62, p = 0.058). These results were robust against instrument selection, various modeling misspecifications, and estimation biases, with the Egger regression and MR-PRESSO ruling out the possibility of horizontal pleiotropic effects of instruments. However, no causal association was found between T2D-related exposures (including glycemic traits) and ALS in the European population.

CONCLUSION

Our results provide new evidence supporting the causal neuroprotective role of T2D on ALS in the European population and provide empirically suggestive evidence of increasing risk of T2D on ALS in the East Asian population. Our results have an important implication on ALS pathology, paving ways for developing therapeutic strategies across multiple populations.

Body mass index, diabetes, and the risk of Parkinson's disease

BACKGROUND

There are conflicting findings in the literature regarding the association of body mass index and incidence of PD.

OBJECTIVES

This study aimed to investigate the association of body mass index with the risk of PD incidence while considering diabetes mellitus as a major confounding factor.

METHODS

We examined 6,800,601 individuals (aged ≥40 years) who were free of PD using the database of the Korean National Health Insurance Service. Cox proportional hazard regression was used to assess adjusted hazard ratios for PD with adjustment for potential confounders. Stratified analyses by diabetes status were also performed.

RESULTS

A total of 33,443 individuals were diagnosed with PD during the follow-up period (7.3 years). An increased risk of PD incidence was observed in the underweight group versus the normal group (adjusted hazard ratio: 1.28; 95% confidence interval: 1.21-1.36), whereas a decreased risk of PD incidence was observed (adjusted hazard ratio: 0.88; 95% confidence interval: 0.88-0.93) in the obese group and (adjusted hazard ratio: 0.77; 95% confidence interval: 0.72-0.82) in the severely obese group. This association consistently persisted after stratification by diabetes mellitus status, with the steepest downward slope for PD risk present with increasing body mass index in patients with severe diabetes mellitus (i.e., long duration or complication).

CONCLUSIONS

Being underweight and diabetes mellitus were associated with an increased risk of PD incidence, and effect of being underweight was more prominent in those with diabetes mellitus, with a dose-response relationship existing according to diabetes mellitus status. Further research is warranted to understand the clinical implications of the significant interaction between being underweight and diabetes mellitus status in the development of PD. © 2020 International Parkinson and Movement Disorder Society.

Analysis of the Relationship between Type II Diabetes Mellitus and Parkinson's Disease: A Systematic Review

In the early sixties, a discussion started regarding the association between Parkinson's disease (PD) and type II diabetes mellitus (T2DM). Today, this potential relationship is still a matter of debate. This review aims to analyze both diseases concerning causal relationships and treatments. A total of 104 articles were found, and studies on animal and “in vitro” models showed that T2DM causes neurological alterations that may be associated with PD, such as deregulation of the dopaminergic system, a decrease in the expression of peroxisome proliferator-activated receptor-gamma coactivator-1α (PGC-1α), an increase in the expression of phosphoprotein enriched in diabetes/phosphoprotein enriched in astrocytes 15 (PED/PEA-15), and neuroinflammation, as well as acceleration of the formation of alpha-synuclein amyloid fibrils. In addition, clinical studies described that Parkinson's symptoms were notably worse after the onset of T2DM, and seven deregulated genes were identified in the DNA of T2DM and PD patients. Regarding treatment, the action of antidiabetic drugs, especially incretin mimetic agents, seems to confer certain degree of neuroprotection to PD patients. In conclusion, the available evidence on the interaction between T2DM and PD justifies more robust clinical trials exploring this interaction especially the clinical management of patients with both conditions.

Using Medical Claims Analyses to Understand Interventions for Parkinson Patients

The scientific evidence to support the value of a range of non-pharmacological interventions for people with Parkinson’s disease (PD) is increasing. However, showing unequivocally that specific interventions are better than usual care is not straightforward because of generic drawbacks of clinical trials. Here, we address these challenges, specifically related to the context of evaluating complex non-pharmacological interventions for people with PD. Moreover, we discuss the potential merits of undertaking “real world” analyses using medical claims data. We illustrate this approach by discussing an interesting recent publication in The Lancet Neurology, which used such an approach to demonstrate the value of specialized physiotherapy for PD patients, over and above usual care physiotherapy.

Downregulated Dopamine Receptor 2 and Upregulated Corticotrophin Releasing Hormone in the Paraventricular Nucleus Are Correlated With Decreased Glucose Tolerance in Rats With Bilateral Substantia Nigra Lesions

Patients with Parkinson’s disease (PD) have a high prevalence of glucose metabolism abnormalities. However, the mechanism underlying these symptoms remains unclear. The hypothalamic-pituitary-adrenal (HPA) axis is the major neuroendocrine axis that regulates homeostasis in mammals, including glucose metabolism. Corticotrophin releasing hormone (CRH), which is synthesized in the paraventricular nucleus (PVN) of the hypothalamus, plays an important role in the regulation of blood glucose levels via the HPA axis. Our previous studies have reported that PVN neurons express numerous dopamine receptors (DRs) and accept direct projections from the substantia nigra (SN). We hypothesize that damage to dopaminergic neurons in the SN might influence the blood glucose level through the HPA system. Rats with bilateral SN lesions induced by 6-hydroxydopamine (6-OHDA) (referred to as 6-OHDA rats) were used to investigate alterations in the levels of blood glucose, CRH, and factors related to the HPA axis and to explore possible mechanisms. Blood glucose levels were detected at different time points after the glucose solution was intraperitoneally administered. CRH and DRs in the PVN were evaluated by immunofluorescence and western blot analysis. Adrenocorticotropic hormone (ACTH) in the pituitary and plasma corticosterone (CORT) was evaluated by radioimmunoassay (RIA). The results showed that 6-OHDA rats exhibited significantly decreased tyrosine hydroxylase (TH) in the SN and decreased glucose tolerance at 6 weeks, but not at 4 weeks. In the PVN, dopamine receptor 2 (D2) was expressed on CRH-positive neurons, and D2-positive neurons were surrounded by TH-positive fibers. Additionally, the expression of CRH was upregulated, whereas the expression of D2 and TH were downregulated in 6-OHDA rats compared with control rats. In D2 knock-out mice, the significantly enhanced expression of CRH and reduced expression of D2 were detected in the PVN. Furthermore, RIA revealed increased ACTH in the pituitary and elevated CORT in the blood. In summary, the present study suggests that the dopaminergic neurons in the SN are involved in the regulation of body glucose metabolism through CRH neurons that express D2 in the hypothalamic PVN. SN lesions decrease glucose tolerance mainly by downregulating D2 and upregulating CRH in the PVN through the HPA neuroendocrine system.

The Relation Between Type 2 Diabetes Mellitus and Parkinson Disease Up to Date

Parkinson’s disease is defined nowadays as a neurodegenerative disease with prominent motor symptoms accompanied by a wide range of comorbidities, some of them, like type 2 diabetes mellitus, probably implicated in the pathogenesis and progression of the disease. In order to achieve this article, which aimed to realize an up to date synthesis of published dedicated papers, a PubMed search was performed; it revealed increasing evidence that these two morbid conditions share many pathogenic pathways and current studies are trying to finally transform the accumulated knowledge into curative therapy or effective prevention for these frequent and complex diseases.

Cardiovascular risk factors and Parkinson's disease in 500,000 Chinese adults

OBJECTIVE

The objectives of this study were to compare the risks of Parkinson's disease among those with versus those without prior stroke or heart disease at baseline in a prospective study of 0.5 million adults in China, and to examine associations of cardiovascular disease risk factors (cigarette smoking, hypertension, diabetes, obesity) with risk of Parkinson's disease.

METHODS

During an average of 11.5 years of follow-up of 503,497 middle-aged participants in the China Kadoorie Biobank study, 603 incident cases were hospitalized with a diagnosis of Parkinson's disease. Cox proportional hazards models were used to assess associations of history of heart disease or stroke with Parkinson's disease in all participants, and of cardiovascular disease risk factors with Parkinson's disease in a subset without prior cardiovascular disease.

RESULTS

In this population the incidence rate of Parkinson's disease (mean [SD] age of cases, 61 [10] years) was 13.3 (95% confidence interval: 12.3-14.4) per 100,000 person-years. Incidence increased with age, and was higher in men than in women, and in urban than in rural residents. Prior stroke was associated with about twofold higher risk of Parkinson's disease (hazard ratio 1.94; 1.39-2.69). After adjustment for confounders in those without prior cardiovascular disease, a 5 kg/m2 higher body mass index was associated with 17% (1.17; 1.03-1.34: P = 0.019) higher risk of Parkinson's disease, but neither hypertension, diabetes, nor current cigarette smoking was significantly associated with Parkinson's disease.

INTERPRETATION

Prior stroke and adiposity were each associated with higher risks of Parkinson's disease, but none of the other cardiovascular disease risk factors were significantly associated with Parkinson's disease in this population.

Neuroprotective Actions of Glucagon-Like Peptide-1 (GLP-1) Analogues in Alzheimer's and Parkinson's Diseases

The current absence of effective treatments for Alzheimer's disease (AD) and Parkinson's disease (PD) reflects an incomplete knowledge of the underlying disease processes. Considerable efforts have been made to investigate the central pathological features of these diseases, giving rise to numerous attempts to develop compounds that interfere with such features. However, further characterization of the molecular targets within the interconnected AD and PD pathways is still required. Impaired brain insulin signaling has emerged as a feature that contributes to neuronal dysfunction in both AD and PD, leading to strategies aiming at restoring this pathway in the brain. Long-acting glucagon-like peptide-1 (GLP-1) analogues marketed for treatment of type 2 diabetes mellitus have been tested and have shown encouraging protective actions in experimental models of AD and PD as well as in initial clinical trials. We review studies revealing the neuroprotective actions of GLP-1 analogues in pre-clinical models of AD and PD and promising results from recent clinical trials.

Association Between Diabetic Retinopathy and Parkinson Disease: The Korean National Health Insurance Service Database

CONTEXT

Studies have shown an association between diabetes and Parkinson disease (PD). The retina is a part of the central nervous system; it was proposed that diabetic retinopathy (DR) and PD share common pathophysiology of dopamine deficiency. However, no epidemiologic studies have investigated the relationship between these two diseases.

OBJECTIVE

We assessed the association between DR and incident PD using a population-based database.

DESIGN/SETTING/PARTICIPANTS

Using the Korean National Health Insurance Service database, 14,912,368 participants who underwent regular health checkup from 2005 to 2008 were included. Subjects were classified into non-diabetes, diabetes without DR, and diabetes with DR groups at baseline and followed up until the date of PD incidence, death, or 31 December 2013. Cox proportional hazards regression analysis was used to evaluate the association between DR and incident PD.

RESULTS

During the period, 34,834 subjects were newly diagnosed with PD. The incidence of PD was 2.74, 8.39, and 15.51 per 10,000 person-years for the non-diabetes, diabetes without DR, and diabetes with DR groups, respectively. In multivariate Cox proportional hazard models, DR groups were associated with significantly higher risk of PD than non-diabetes or diabetes without DR groups even after adjusting for age, sex, fasting plasma glucose level, insulin usage, and other possible risk factors.

CONCLUSION

Concurrent DR was associated with an increased risk of incident PD. Future studies are necessary to investigate the mechanism of increased risk of PD in DR including dopamine deficiency in the central nervous system and long-lasting poor glycemic control.

Dental Scaling Decreases the Risk of Parkinson's Disease: A Nationwide Population-Based Nested Case-Control Study

The protective effect of dental scaling in Parkinson’s disease (PD) remains inconclusive. The aim of this study was to analyze the association between dental scaling and the development of PD. A retrospective nested case-control study was performed using the National Health Insurance Research Database of Taiwan. The authors identified 4765 patients with newly diagnosed PD from 2005 to 2013 and 19,060 individuals without PD by matching sex, age, and index year. In subgroup 1, with individuals aged 40–69 years, individuals without periodontal inflammatory disease (PID) showed a protective effect of dental scaling against PD development, especially for dental scaling over five consecutive years (adjusted odds ratio = 0.204, 95% CI = 0.047–0.886, p = 0.0399). In general, the protective effect of dental scaling showed greater benefit for individuals with PID than for those without PID, regardless of whether dental scaling was performed for five consecutive years. In subgroup 2, with patients aged ≥70 years, the discontinued (not five consecutive years) scaling showed increased risk of PD. This was the first study to show that patients without PID who underwent dental scaling over five consecutive years had a significantly lower risk of developing PD. These findings emphasize the value of early and consecutive dental scaling to prevent the development of PD.

Cardiac abnormalities in Parkinson's disease and Parkinsonism

OBJECTIVES

Though there is increasing evidence for primary cardiac disease in Parkinson's disease (PD) and Parkinsonism (PS), this evidence is hardly included in the general management of these patients.

METHODS

Literature review.

RESULTS

PD is one of the most common age-related neurodegenerative disorders. Epidemiological studies have shown that PD is accompanied by high rates of premature death compared with the general population. In general, death in PD/PS is usually caused by determinant factors such as pneumonia, cerebrovascular, and cardiovascular disease. There is a significant body of literature demonstrating involvement of the heart in PD/PS. Cardiac involvement in PD/PS includes cardiac autonomic dysfunction, cardiomyopathy, coronary heart disease, arrhythmias, conduction defects, and sudden cardiac death (SCD), and sudden unexpected death in Parkinson's disease (SUDPAR).

CONCLUSIONS

Cardiac abnormalities found in PD/PS are manifold but the most prominent is cardiac autonomic dysfunction. The frequency of coronary heart disease in PD is a matter of debate. Only rarely reported in PD/PS are cardiomyopathies, arrhythmias, and sudden cardiac death, and SUDPAR. It is particularly recommended that PD/PS patients are more intensively investigated cardiologically as soon as the diagnosis is established. Early recognition of cardiac involvement is important for preventing SCD and SUDPAR.

Old wines in new bottles: Repurposing opportunities for Parkinson's disease

Parkinson's disease (PD) is a chronic progressive neurological disorder characterized by accumulation of Lewy bodies and profound loss of substantia nigra dopaminergic neurons. PD symptomatology is now recognized to include both cardinal motor as well as clinically significant non-motor symptoms. Despite intensive research, the current understanding of molecular mechanisms underlying neurodegeneration in PD is limited and has hampered the development of novel symptomatic and disease modifying therapies. The currently available treatment options are only partially or transiently effective and fail to restore the lost dopaminergic neurons or retard disease progression. Given the escalating drug development costs, lengthening timelines and declining R&D efficiency, industry and academia are increasingly focusing on ways to repurpose existing molecules as an accelerated route for drug discovery. The field of PD therapeutics is witnessing vigorous repurposing activity supported by big data analytics, computational models, and high-throughput drug screening systems. Here we review the mechanisms, efficacy, and safety of several emerging drugs currently aspiring to be repositioned for PD pharmacotherapy.

Diabetes Mellitus as a Risk Factor for Parkinson's Disease: a Molecular Point of View

Type 2 diabetes mellitus (T2DM) is a metabolic disorder characterized by elevated concentrations of glucose in the blood. The chronic hyperglycemic state accounts for most of the vascular complications associated to the disease and the prevalent mechanism proposed is related to the glycating chemistry mediated by methylglyoxal (MG), which accumulates in T2DM. In recent years, a higher risk of Parkinson's disease (PD) onset in people affected by T2DM has become evident, but the molecular mechanisms underlying the interplay between T2DM and PD are still unknown. The oxidative chemistry of dopamine and its reactivity towards the protein α-Synuclein (aS) has been associated to the pathogenesis of PD. Recently, aS has also been described to interact with MG. Interestingly, MG and the dopamine oxidation products share both structural similarity and chemical reactivity. The ability of MG to spread over the site of its production and react with aS could represent the rationale to explain the higher incidence of PD in T2DM-affected people and may open opportunities for the development of novel strategies to antagonize the raise of PD.

Alpha-Synuclein Glycation and the Action of Anti-Diabetic Agents in Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder with complex etiology and variable pathology. While a subset of cases is associated with single-gene mutations, the majority originates from a combination of factors we do not fully understand. Thus, understanding the underlying causes of PD is indispensable for the development of novel therapeutics. Glycation, the non-enzymatic reaction between reactive dicarbonyls and amino groups, gives rise to a variety of different reaction products known as advanced glycation end products (AGEs). AGEs accumulate over a proteins life-time, and increased levels of glycation reaction products play a role in diabetic complications. It is now also becoming evident that PD patients also display perturbed sugar metabolism and protein glycation, including that of alpha-synuclein, a key player in PD. Here, we hypothesize that anti-diabetic drugs targeting the levels of glycation precursors, or promoting the clearance of glycated proteins may also prove beneficial for PD patients.

Aerobic-Strength Exercise Improves Metabolism and Clinical State in Parkinson's Disease Patients

Regular exercise ameliorates motor symptoms in Parkinson’s disease (PD). Here, we aimed to provide evidence that exercise brings additional benefits to the whole-body metabolism and skeletal muscle molecular and functional characteristics, which might help to explain exercise-induced improvements in the clinical state. 3-months supervised endurance/strength training was performed in early/mid-stage PD patients and age/gender-matched individuals (n = 11/11). The effects of exercise on resting energy expenditure (REE), glucose metabolism, adiposity, and muscle energy metabolism (³¹P-MRS) were evaluated and compared to non-exercising PD patients. Two muscle biopsies were taken to determine intervention-induced changes in fiber type, mitochondrial content, and expression of genes related to muscle energy metabolism, as well as proliferative and regenerative capacity. Exercise improved the clinical disability score (MDS-UPDRS), bradykinesia, balance, walking speed, REE, and glucose metabolism and increased muscle expression of energy sensors (AMPK). However, the exercise-induced increase in muscle mass/strength, mitochondrial content, type II fiber size, and postexercise phosphocreatine (PCr) recovery (³¹P-MRS) were found only in controls. Nevertheless, MDS-UPDRS was associated with muscle AMPK and mechano-growth factor (MGF) expression. Improvements in fasting glycemia were positively associated with muscle function and the expression of Sirt1 and Cox7a1, and the parameters of fitness/strength were positively associated with the expression of MyHC2, MyHC7, and MGF. Moreover, reduced bradykinesia was associated with better muscle metabolism (maximal oxidative capacity and postexercise PCr recovery; ³¹P-MRS). Exercise training improved the clinical state in early/mid-stage Parkinson’s disease patients, including motor functions and whole-body metabolism. Although the adaptive response to exercise in PD was different from that of controls, exercise-induced improvements in the PD clinical state were associated with specific adaptive changes in muscle functional, metabolic, and molecular characteristics.

Biological and Clinical Implications of Comorbidities in Parkinson's Disease

A wide spectrum of comorbidities has been associated with Parkinson's disease (PD), a progressive neurodegenerative disease that affects more than seven million people worldwide. Emerging evidence indicates that chronic diseases including diabetes, depression, anemia and cancer may be implicated in the pathogenesis and progression of PD. Recent epidemiological studies suggest that some of these comorbidities may increase the risk of PD and precede the onset of motor symptoms. Further, drugs to treat diabetes and cancer have elicited neuroprotective effects in PD models. Nonetheless, the mechanisms underlying the occurrence of these comorbidities remain elusive. Herein, we discuss the biological and clinical implications of comorbidities in the pathogenesis, progression, and clinical management, with an emphasis on personalized medicine applications for PD.

Role of Diet and Nutritional Supplements in Parkinson's Disease Progression

OBJECTIVES

The goal of this study is to describe modifiable lifestyle variables associated with reduced rate of Parkinson's disease (PD) progression.

METHODS

The patient-reported outcomes in PD (PRO-PD) were used as the primary outcome measure, and a food frequency questionnaire (FFQ) was used to assess dietary intake. In this cross-sectional analysis, regression analysis was performed on baseline data to identify the nutritional and pharmacological interventions associated with the rate of PD progression. All analyses were adjusted for age, gender, and years since diagnosis.

RESULTS

1053 individuals with self-reported idiopathic PD were available for analysis. Foods associated with the reduced rate of PD progression included fresh vegetables, fresh fruit, nuts and seeds, nonfried fish, olive oil, wine, coconut oil, fresh herbs, and spices (P < 0.05). Foods associated with more rapid PD progression include canned fruits and vegetables, diet and nondiet soda, fried foods, beef, ice cream, yogurt, and cheese (P < 0.05). Nutritional supplements coenzyme Q10 and fish oil were associated with reduced PD progression (P = 0.026 and P = 0.019, resp.), and iron supplementation was associated with faster progression (P = 0.022).

DISCUSSION

These are the first data to provide evidence that targeted nutrition is associated with the rate of PD progression.

Diabetes in a Large Dementia Cohort: Clinical Characteristics and Treatment From the Swedish Dementia Registry

OBJECTIVE

We aimed to investigate the differences in clinical characteristics and pharmacological treatment associated with the presence of diabetes in a large cohort of patients with dementia.

RESEARCH DESIGN AND METHODS

A cross-sectional registry-based study was conducted using data from the Swedish Dementia Registry (SveDem). Data on dementia diagnosis, dementia type, and demographic determinants were extracted from SveDem. Data from the Swedish Patient Register and Prescribed Drug Register were combined for the diagnosis of diabetes. Data on antidiabetic, dementia, cardiovascular, and psychotropic medications were extracted from the Swedish Prescribed Drug Register. Logistic regression was used to determine whether the variables were associated with diabetes after adjustment for confounders. In total, 29,630 patients were included in the study, and 4,881 (16.5%) of them received a diagnosis of diabetes.

RESULTS

In the fully adjusted model, diabetes was associated with lower age at dementia diagnosis (odds ratio [OR] 0.97 [99% CI 0.97-0.98]), male sex (1.41 [1.27-1.55]), vascular dementia (1.17 [1.01-1.36]), and mixed dementia (1.21 [1.06-1.39]). Dementia with Lewy bodies (0.64 [0.44-0.94]), Parkinson disease dementia (0.46 [0.28-0.75]), and treatment with antidepressants (0.85 [0.77-0.95]) were less common among patients with diabetes. Patients with diabetes who had Alzheimer disease obtained significantly less treatment with cholinesterase inhibitors (0.78 [0.63-0.95]) and memantine (0.68 [0.54-0.85]).

CONCLUSIONS

Patients with diabetes were younger at dementia diagnosis and obtained less dementia medication for Alzheimer disease, suggesting less optimal dementia treatment. Future research should evaluate survival and differences in metabolic profile in patients with diabetes and different dementia disorders.

Long-term exposure to air pollution and the incidence of Parkinson's disease: A nested case-control study

BACKGROUND

Previous studies revealed that chronic exposure to air pollution can significantly increase the risk of the development of Parkinson's disease (PD), but this relationship is inconclusive as large-scale prospective studies are limited and the results are inconsistent. Therefore, the purpose of this study was to ascertain the adverse health effects of air pollution exposure in a nationwide population using a longitudinal approach.

MATERIALS AND METHODS

We conducted a nested case-control study using the National Health Insurance Research Dataset (NHIRD), which consisted of 1,000,000 beneficiaries in the National Health Insurance Program (NHI) in the year 2000 and their medical records from 1995 to 2013 and using public data on air pollution concentrations from monitoring stations across Taiwan released from the Environmental Protection Administration to identify people with ages ≥ 40 years living in areas with monitoring stations during 1995-1999 as study subjects. Then, we excluded subjects with PD, dementia, stroke and diabetes diagnosed before Jan. 1, 2000 and obtained 54,524 subjects to follow until Dec. 31, 2013. In this observational period, 1060 newly diagnosed PD cases were identified. 4240 controls were randomly selected from those without PD using a matching strategy for age, sex, the year of PD diagnosis and the year of entering the NHI program at a ratio of 1:4. Ten elements of air pollution were examined, and multiple logistic regression models were used to measure their risks in subsequent PD development.

RESULTS

The incidence of PD in adults aged ≥ 40 years was 1.9%, and the median duration for disease onset was 8.45 years. None of the chemical compounds (SO2, O3, CO, NOx, NO, NO2, THC, CH4, or NMHC) significantly affected the incidence of PD except for particulate matter. PM10 exposure showed significant effects on the likelihood of PD development (T3 level: > 65μg/m3 versus T1 level: ≤ 54μg/m3; OR = 1.35, 95% CI = 1.12-1.62, 0.001 ≤ P < 0.01). In addition, comorbid conditions such as dementia (ORs = 3.53-3.93, Ps < 0.001), stroke (ORs = 2.99-3.01, Ps < 0.001), depression (ORs = 2.51-2.64, Ps < 0.001), head injury (ORs = 1.24-1.29, 0.001 ≤ Ps < 0.01 or 0.01 ≤ Ps < 0.05), sleep disorder (OR = 1.23-1.26, 0.001 ≤ Ps < 0.01), and hypertension (ORs = 1.18-1.19, 0.01 ≤ Ps < 0.05) also significantly increased the risk for PD development.

CONCLUSIONS

Although PM10 plays a significant role in PD development, the associated chemical/metal compounds that are capable of inducing adverse biological mechanisms still warrant further exploration. Because of a link between comorbid conditions and PM exposure, research on the causal relationship between long-term exposure to PM and the development of PD should be considered with caution because other possible modifiers or mediators, comorbid diseases in particular, may be involved.

Periodontal inflammatory disease is associated with the risk of Parkinson's disease: a population-based retrospective matched-cohort study

Background

The cause−effect relation between periodontal inflammatory disease (PID) and Parkinson’s disease (PD) remains uncertain. The purpose of our study was to investigate the association between PID and PD.

Methods

We conducted a retrospective matched-cohort study by using Taiwan’s National Health Insurance Research Database. We identified 5,396 patients with newly diagnosed PID during 1997–2004 and 10,792 cases without PID by matching sex, age, index of year (occurrence of PID), and comorbidity. Cox proportional hazard regression was used to evaluate the risk of subsequent PD.

Results

At the final follow-up, a total of 176 (3.26%) and 275 (2.55%) individuals developed PD in the case and control groups, respectively. Patients with PID have a higher risk of developing PD (adjusted hazard ratio = 1.431, 95% CI [1.141–1.794], p = 0.002).

Discussion

Our results show that PID is associated with an increased risk of developing PD. Whilst these findings suggest that reducing PID may modify the risk of developing PD, further study will be needed.

Epidemiology of pharmaceutically treated depression and treatment resistant depression in Taiwan

Epidemiologic data on treatment resistant depression (TRD) in Asia-Pacific countries are limited. We estimated the incidence of TRD in Taiwan using a cohort of 704,265 adults randomly sampled from Taiwan's National Health Insurance Research database for 2005. TRD was defined as a patient having pharmaceutically treated depression (PTD) not adequately responding to 2 antidepressant (AD) regimens, i.e., AD regimens that were followed by other AD regimens. Among 2751 PTD subjects, 576 (20.94%, 95% CI: 19.46, 22.49) developed TRD, a proportion similar to that in North American studies. TRD incidence was 0.82 (95% CI: 0.75, 0.89) cases /1000 population in 2005, increased with age, and was higher in females than in males. SSRI's were the most frequently used ADs. Augmentation with antipsychotics was common. The median time from PTD onset (first AD medication) to TRD onset was 416 days but psychiatrists practicing in Taiwan indicated they would switch within <=3 months if an AD medication was not effective. We therefore repeated the analysis with a 6 months cap on time from onset of PTD to TRD. In this supplemental, post-hoc, analysis, 68 PTD subjects, 2.47%, (95% CI: 1.94, 3.10) developed TRD; i.e., 0.10 (95% CI: 0.08, 0.12) incident cases/1000 population.