The Impact of Type 2 Diabetes in Parkinson's Disease

Understanding the link between type 2 diabetes mellitus and Parkinson's disease: role of brain insulin resistance

Type 2 diabetes mellitus and Parkinson's disease are chronic diseases linked to a growing pandemic that affects older adults and causes significant socio-economic burden. Epidemiological data supporting a close relationship between these two aging-related diseases have resulted in the investigation of shared pathophysiological molecular mechanisms. Impaired insulin signaling in the brain has gained increasing attention during the last decade and has been suggested to contribute to the development of Parkinson's disease through the dysregulation of several pathological processes. The contribution of type 2 diabetes mellitus and insulin resistance in neurodegeneration in Parkinson's disease, with emphasis on brain insulin resistance, is extensively discussed in this article and new therapeutic strategies targeting this pathological link are presented and reviewed.

Exploring the therapeutic potential of Chinese herbs on comorbid type 2 diabetes mellitus and Parkinson's disease: A mechanistic study

ETHNOPHARMACOLOGICAL RELEVANCE

Type 2 diabetes mellitus (T2DM) and Parkinson's disease (PD) are chronic conditions that affect the aging population, with increasing prevalence globally. The rising prevalence of comorbidity between these conditions, driven by demographic shifts, severely impacts the quality of life of patients, posing a significant burden on healthcare resources. Chinese herbal medicine has been used to treat T2DM and PD for millennia. Pharmacological studies have demonstrated that medicinal herbs effectively lower blood glucose levels and exert neuroprotective effects, suggesting their potential as adjunctive therapy for concurrent management of T2DM and PD.

AIM OF THE STUDY

To elucidate the shared mechanisms underlying T2DM and PD, particularly focusing on the potential mechanisms by which medicinal herbs (including herbal formulas, single herbs, and active compounds) may treat these diseases, to provide valuable insights for developing therapeutics targeting comorbid T2DM and PD.

MATERIALS AND METHODS

Studies exploring the mechanisms underlying T2DM and PD, as well as the treatment of these conditions with medicinal herbs, were extracted from several electronic databases, including PubMed, Web of Science, Google Scholar, and China National Knowledge Infrastructure (CNKI).

RESULTS

Numerous studies have shown that inflammation, oxidative stress, insulin resistance, impaired autophagy, gut microbiota dysbiosis, and ferroptosis are shared mechanisms underlying T2DM and PD mediated through the NLRP3 inflammasome, NF-κB, MAPK, Keap1/Nrf2/ARE, PI3K/AKT, AMPK/SIRT1, and System XC--GSH-GPX4 signaling pathways. Thirty-four medicinal herbs, including 2 herbal formulas, 4 single herbs, and 28 active compounds, have been reported to potentially exert anti-T2DM and anti-PD effects by targeting these shared mechanisms.

CONCLUSIONS

Traditional Chinese medicine effectively combats T2DM and PD through shared pathological mechanisms, highlighting their potential for application in treating these comorbid conditions.

Plasma fibronectin is a prognostic biomarker of disability in Parkinson's disease: a prospective, multicenter cohort study

In a prospective longitudinal study with 218 Parkinson's disease (PD) patients in the discovery cohort and 84 in the validation cohort, we aimed to identify novel blood biomarkers predicting disability milestones in PD. Through Least Absolute Shrinkage and Selection Operator-Cox (Lasso-Cox) regression, developed nomogram predictive model and Linear mixed-effects models, we identified low level of plasma fibronectin (pFN) as one of the best-performing risk markers in predicting disability milestones. A low level of pFN was associated with a short milestone-free survival period in PD. Longitudinal analysis showed an annual decline in the rate of pFN was significantly associated with the annual elevation rate in the Hoehn-Yahr stage. Moreover, pFN level was negatively correlated with phosphorylated α-synuclein, and a low level of pFN was associated with BBB disruption in the striatum on neuroimaging, providing evidence for pFN's role in PD progression. We finally identified pFN as a novel blood biomarker that predicted first-milestone disability in PD.

Exploring Cimetidine as a Potential Therapeutic Attenuator against Amyloid Formation in Parkinson's Disease: Spectroscopic and Microscopic Insights into Alpha-Synuclein and Human Insulin

Neurodegenerative diseases, notably Alzheimer's and Parkinson's, hallmark their progression through the formation of amyloid aggregates resulting from misfolding. While current therapeutics alleviate symptoms, they do not impede disease onset. In this context, repurposing existing drugs stands as a viable therapeutic strategy. Our study determines the antihistamine drug Cimetidine's potential as an inhibitor using diverse spectroscopic and microscopic methods on alpha-synuclein and human insulin amyloid formation, unveiling its efficacy. The thioflavin T (ThT) assay illustrated a dose-dependent reduction in amyloid formation with escalating concentrations of Cimetidine. Notably, the antihistamine drug maintained a helical structure and showed no significant conformational changes in the secondary structure. Confocal microscopy validated fewer fibrils in the Cimetidine-treated samples. Remarkably, Cimetidine interacted with pre-existing fibrils, leading to their disintegration. Further analyses (ThT, circular dichroism, and dynamic light scattering) showcased the conversion of fibrils into smaller aggregates upon Cimetidine addition. These findings signify the potential of this antihistamine drug as a plausible therapeutic option for Parkinson's disease. This study may open avenues for deeper investigations and possible therapeutic developments, emphasizing Cimetidine's promising role in mitigating neurodegenerative diseases like Parkinson's.

Sodium-glucose cotransporter 2 inhibitors and the risk of Parkinson disease in real-world patients with type 2 diabetes

IMPORTANCE

Diabetes increases the risk of Parkinson disease (PD). Sodium-glucose cotransporter 2 (SGLT2) inhibitors, a new glucose-lowering therapeutic class, have shown neuroprotective effects in mechanistic studies. However, the association between SGLT2 inhibitors and PD risk in real-world populations with type 2 diabetes (T2D) remains unclear.

OBJECTIVE

The aim was to assess the association between SGLT2 inhibitors and the risk of PD in older populations with T2D.

DESIGN, SETTING AND PARTICIPANTS

This retrospective cohort analysis used Medicare claims data from 2016 to 2020 to identify fee-for-service beneficiaries ≥65 years diagnosed with T2D and without pre-existing PD.

EXPOSURES

The initiation of an SGLT2 inhibitor was compared with that of a dipeptidyl peptidase-4 (DPP4) inhibitor.

MAIN OUTCOMES AND MEASURES

The outcome was the first incident PD ever since the date initiating either an SGLT2 inhibitor or a DPP4 inhibitor. We employed a 1:1 propensity score matching to balance the baseline covariates between treatment groups, including sociodemographics, comorbidities and co-medications. We applied Cox regression models to assess the effect of SGLT2 inhibitors versus DPP4 inhibitors on incident PD.

RESULTS

Of 89 330 eligible Medicare beneficiaries (mean age: 75 ± 7 years, 52% women), 0.6% (n = 537) had incident PD over the follow-up. After 1:1 propensity matching, the PD incidence was 2.5 and 3.5 events per 1000 person-years in the SGLT2 inhibitor group and DPP4 inhibitor group, respectively. The SGLT2 inhibitor group was associated with a significantly lower risk of incident PD than the DPP4 inhibitor group (hazard ratio: 0.70 [95% confidence interval: 0.55-0.89]). There is a potential trend that the risk reduction in incident PD was profound in non-Hispanic Black individuals and insulin users.

CONCLUSION AND RELEVANCE

Compared to DPP4 inhibitors, SGLT2 inhibitors were associated with a significantly lower risk of incident PD in older populations with T2D.

The Interplay of Stress, Inflammation, and Metabolic Factors in the Course of Parkinson's Disease

Parkinson's disease (PD) is a prevalent neurodegenerative condition for which there are symptomatic treatments but no disease-modifying therapies (DMTs). Extensive research over the years has highlighted the need for a multi-target DMT approach in PD that recognizes the various risk factors and their intricate interplay in contributing to PD-related neurodegeneration. Widespread risk factors, such as emotional stress and metabolic factors, have increasingly become focal points of exploration. Our review aims to summarize interactions between emotional stress and selected key players in metabolism, such as insulin, as potential mechanisms underlying neurodegeneration in PD.

Type 2 diabetes mellitus and neurodegenerative disorders: The mitochondrial connection

The incidence of type 2 diabetes mellitus (T2DM) has increased in our society in recent decades as the population ages, and this trend is not expected to revert. This is the same for the incidence of the main neurodegenerative disorders, including the two most common ones, which are, Alzheimer's and Parkinson's disease. Currently, no pharmacological therapies have been developed to revert or cure any of these pathologies. Interestingly, in recent years, an increased number of studies have shown a high co-morbidity between T2DM and neurodegeneration, as well as some common molecular pathways that are affected in both types of diseases. For example, while the etiopathology of T2DM and neurodegenerative disorders is highly complex, mitochondrial dysfunction has been broadly described in the early steps of both diseases; accordingly, this dysfunction has emerged as a plausible molecular link between them. In fact, the prominent role played by mitochondria in the mammalian metabolism of glucose places the physiology of the organelle in a central position to regulate many cellular processes that are affected in both T2DM and neurodegenerative disorders. In this collaborative review, we critically describe the relationship between T2DM and neurodegeneration; making a special emphasis on the mitochondrial mechanisms that could link these diseases. A better understanding of the role of mitochondria on the etiopathology of T2DM and neurodegeneration could pave the way for the development of new pharmacological therapies focused on the regulation of the physiology of the organelle. These therapies could, ultimately, contribute to increase healthspan.

Corneal nerve fibre loss as a marker to identify the impact of diabetes on Parkinson's disease

BACKGROUND

Patients with Parkinson's disease (PD) suffer from serious quality of life problems. Diabetes has been demonstrated as an independent risk element for PD, aggravating its severity and accelerating its progression. There are currently no suitable biomarkers to reveal the impact of diabetes on PD. The purpose of our research was to study the impact of diabetes on PD using corneal confocal microscopy (CCM), a non-invasive and objective test.

METHODS

Fourteen PD patients with diabetes (PD-DM), 60 PD patients without diabetes (PD-NDM), and 30 healthy controls (HC) were included in the study. The clinical symptoms of patients with PD were assessed using the Unified Parkinson's Disease Rating Scale-3 (UPDRS-3) and the Parkinson's Disease Autonomic Symptom Prognosis Scale (SCOPA-AUT). Participants underwent CCM to quantify the corneal nerve fibres.

RESULTS

Corneal nerve fibre density (CNFD) and corneal nerve fibre length (CNFL) in patients with PD were lower than HC. Furthermore, CNFD in PD-DM was lower than in PD-NDM (P < 0.01). We also assessed the relationship between CCM parameters and clinical scores. CNFL and Hamilton anxiety (HAMA) have a negative correlation (r = -0.261, P = 0.032), but this study did not observe a significant correlation between CCM parameters and SCOPA-AUT. Additionally, CNFD could distinguish PD-DM from PD-NDM, achieving an area under the curve of 75.06% (95% CI, 61.76%-88.36%).

CONCLUSIONS

The CCM could be served as an objective and sensitive biomarker to investigate the impact of diabetes in PD.

Rate of motor progression in Parkinson's disease: a systematic review and meta-analysis

Background

The search for neuroprotective treatments for Parkinson's disease (PD) still relies largely on motor disability scales. A limitation of these tools is the strong influence of symptomatic dopaminergic treatment effects. Drawing on a wealth of published information, we conducted a systematic review and meta-analysis of motor progression in PD and its relationships with dopaminergic therapy.

Methods

We searched Medline, Embase, and Central to identify 84 publications with adequate serial motor scores to calculate progression, expressed as an increase in the percentage of maximum disability.

Results

A random-effects model showed motor progression at 2.0% p.a. (95% CI 1.7-2.4%). There were no significant differences by baseline age, sample size, or observation period. However, untreated patients, in 8 publications, progressed at 4.5% p.a. compared to 1.6% p.a. in 76 studies containing individuals on dopaminergic drugs (p = 0.0004, q = 0.003). This was supported by research on phenoconversion in prodromal PD, where motor progression exceeded 5% p.a. in the 2 years before diagnosis. Starting levodopa improved pre-treatment disability by 40.3 ± 15.2%. Practically defined off state measurements increase faster than on scores by a modest degree (p = 0.05).

Conclusion

This survey suggests that accurate long-term measurements of motor progression to assess disease-modifying therapies can be conducted despite the sequential commencement of dopaminergic drugs and sample attrition over time. While study designs involving prodromal or untreated PD avoid confounding effects of symptomatic treatment, different assumptions about motor progression may be needed. A defined off state with the levodopa test dose method maximizes information about the medication cycle once dopaminergic therapy has begun.

Advantages and Challenges of Platform Trials for Disease Modifying Therapies in Parkinson's Disease

Traditional drug development in Parkinson's disease (PD) faces significant challenges because of its protracted timeline and high costs. In response, innovative master protocols are emerging and designed to address multiple research questions within a single overarching protocol. These trials may offer advantages such as increased efficiency, agility in adding new treatment arms, and potential cost savings. However, they also present organizational, methodological, funding, regulatory, and sponsorship challenges. We review the potential of master protocols, focusing on platform trials, for disease modifying therapies in PD. These trials share a common control group and allow for the termination or addition of treatment arms during a trial with non-predetermined end. Specific issues exist for a platform trial in the PD field considering the heterogeneity of patients in terms of phenotype, genotype and staging, the confounding effects of symptomatic treatments, and the choice of outcome measures with no consensus on a non-clinical biomarker to serve as a surrogate and the slowness of PD progression. We illustrate these aspects using the examples of the main PD platform trials currently in development with each one targeting distinct goals, populations, and outcomes. Overall, platform trials hold promise in expediting the evaluation of potential therapies for PD. However, it remains to be proven whether these theoretical benefits will translate into increased production of high-quality trial data. Success also depends on the willingness of pharmaceutical companies to engage in such trials and whether this approach will ultimately hasten the identification and licensing of effective disease-modifying drugs. © 2024 International Parkinson and Movement Disorder Society.

Update: Protective and risk factors for Parkinson disease

We review the epidemiologic literature on potential protective and risk factors in Parkinson's Disease (PD). Prior research identified numerous possible protective and risk factors. Potential protective factors include tobacco abuse, physical activity, urate levels, NSAID use, calcium channel blocker use, statin use, and use of some α1-adrenergic antagonists. Some potential protective factors could be products of reverse causation, including increased serum urate, tobacco abuse, and coffee-tea-caffeine consumption. Potential risk factors include traumatic brain injury, pesticide exposure, organic solvent exposure, lead exposure, air pollution, Type 2 Diabetes, some dairy products, cardiovascular disease, and some infections including Hepatitis C, H. pylori, and COVID-19. Potential non-environmental risk factors include bipolar disorder, essential tremor, bullous pemphigoid, and inflammatory bowel disease. There is an inverse relationship with PD and risk of most cancers. Though many potential protective and risk factors for PD were identified, research has not yet led to unique, rigorous prevention trials or successful disease-modifying interventions. While efforts to reduce exposure to some industrial toxicants are well justified, PD incidence might be most effectively reduced by mitigation of risks, such as Type 2 Diabetes, air pollution, traumatic brain injury, or physical inactivity, that are general public health intervention targets.

Glucagon-like peptide-1 class drugs show clear protective effects in Parkinson's and Alzheimer's disease clinical trials: A revolution in the making?

Parkinson's disease (PD) is a complex syndrome for which there is no disease-modifying treatment on the market. However, a group of drugs from the Glucagon-like peptide-1 (GLP-1) class have shown impressive improvements in clinical phase II trials. Exendin-4 (Bydureon), Liraglutide (Victoza, Saxenda) and Lixisenatide (Adlyxin), drugs that are on the market as treatments for diabetes, have shown clear effects in improving motor activity in patients with PD in phase II clinical trials. In addition, Liraglutide has shown improvement in cognition and brain shrinkage in a phase II trial in patients with Alzheimer disease (AD). Two phase III trials testing the GLP-1 drug semaglutide (Wegovy, Ozempic, Rybelsus) are ongoing. This perspective article will summarize the clinical results obtained so far in this novel research area. We are at a crossroads where GLP-1 class drugs are emerging as a new treatment strategy for PD and for AD. Newer drugs that have been designed to enter the brain easier are being developed already show improved effects in preclinical studies compared with the older GLP-1 class drugs that had been developed to treat diabetes. The future looks bright for new treatments for AD and PD.

Epidemiology of Parkinson's Disease: An Update

PURPOSE OF REVIEW

In recent decades, epidemiological understanding of Parkinson disease (PD) has evolved significantly. Major discoveries in genetics and large epidemiological investigations have provided a better understanding of the genetic, behavioral, and environmental factors that play a role in the pathogenesis and progression of PD. In this review, we provide an epidemiological update of PD with a particular focus on advances in the last five years of published literature.

RECENT FINDINGS

We include an overview of PD pathophysiology, followed by a detailed discussion of the known distribution of disease and varied determinants of disease. We describe investigations of risk factors for PD, and provide a critical summary of current knowledge, knowledge gaps, and both clinical and research implications. We emphasize the need to characterize the epidemiology of the disease in diverse populations. Despite increasing understanding of PD epidemiology, recent paradigm shifts in the conceptualization of PD as a biological entity will also impact epidemiological research moving forward and guide further work in this field.

Toxic interactions between dopamine, α-synuclein, monoamine oxidase, and genes in mitochondria of Parkinson's disease

Parkinson's disease is characterized by its distinct pathological features; loss of dopamine neurons in the substantia nigra pars compacta and accumulation of Lewy bodies and Lewy neurites containing modified α-synuclein. Beneficial effects of L-DOPA and dopamine replacement therapy indicate dopamine deficit as one of the main pathogenic factors. Dopamine and its oxidation products are proposed to induce selective vulnerability in dopamine neurons. However, Parkinson's disease is now considered as a generalized disease with dysfunction of several neurotransmitter systems caused by multiple genetic and environmental factors. The pathogenic factors include oxidative stress, mitochondrial dysfunction, α-synuclein accumulation, programmed cell death, impaired proteolytic systems, neuroinflammation, and decline of neurotrophic factors. This paper presents interactions among dopamine, α-synuclein, monoamine oxidase, its inhibitors, and related genes in mitochondria. α-Synuclein inhibits dopamine synthesis and function. Vice versa, dopamine oxidation by monoamine oxidase produces toxic aldehydes, reactive oxygen species, and quinones, which modify α-synuclein, and promote its fibril production and accumulation in mitochondria. Excessive dopamine in experimental models modifies proteins in the mitochondrial electron transport chain and inhibits the function. α-Synuclein and familiar Parkinson's disease-related gene products modify the expression and activity of monoamine oxidase. Type A monoamine oxidase is associated with neuroprotection by an unspecific dose of inhibitors of type B monoamine oxidase, rasagiline and selegiline. Rasagiline and selegiline prevent α-synuclein fibrillization, modulate this toxic collaboration, and exert neuroprotection in experimental studies. Complex interactions between these pathogenic factors play a decisive role in neurodegeneration in PD and should be further defined to develop new therapies for Parkinson's disease.

Hyperglycemia affects axial signs in patients with Parkinson's disease through mechanisms of insulin resistance or non-insulin resistance

OBJECTIVE

To investigate the influence of hyperglycemia on motor symptoms, especially axial signs, and potential mechanisms related to insulin resistance (IR) in patients with Parkinson's disease (PWP).

METHODS

According to glycated hemoglobin (HbA1c) level, PWP were divided into the low-HbA1c and the high-HbA1c groups. Demographic information, glucose metabolism-related variables, Hoehn-Yahr stage, and motor function were compared between the two groups. Correlations between levels of HbA1c and the homeostatic model assessment (HOMA)-IR and motor function in PWP were further analyzed.

RESULTS

HbA1c level was significantly and positively correlated with the Movement Disorder Society Unified Parkinson's Disease Rating Scale Part III score, axial signs subscore, the Timed Get Up and Go test time, the center of pressure displacement of standing with eyes open and closed, and significantly and negatively correlated with the 10-m walk test comfortable gait speed. HOMA-IR level was significantly and negatively correlated with 10-m walk test comfortable gait speed, but not with others.

CONCLUSIONS

PWP with high HbA1c showed worse axial symptoms, including dysfunction of automatic walking, dynamic balance, and postural control than those with low HbA1c. In PWP, the effects of hyperglycemia on automatic walking speed may be associated with the IR-related mechanisms, and the effects on dynamic balance and postural control may be related to mechanisms other than IR.

The Contribution of Type 2 Diabetes to Parkinson's Disease Aetiology

Type 2 diabetes (T2D) and Parkinson's disease (PD) are chronic disorders that have a significant health impact on a global scale. Epidemiological, preclinical, and clinical research underpins the assumption that insulin resistance and chronic inflammation contribute to the overlapping aetiologies of T2D and PD. This narrative review summarises the recent evidence on the contribution of T2D to the initiation and progression of PD brain pathology. It also briefly discusses the rationale and potential of alternative pharmacological interventions for PD treatment.

Fasting Plasma Glucose Levels and Longitudinal Motor and Cognitive Outcomes in Parkinson's Disease Patients

OBJECTIVE

Hyperglycemia and diabetes mellitus have been identified as poor prognostic factors for motor and nonmotor outcomes in patients with Parkinson's disease (PD), although there is some controversy with this finding. In the present study, we investigated the effects of fasting plasma glucose (FPG) levels on longitudinal motor and cognitive outcomes in PD patients.

METHODS

We included a total of 201 patients who were diagnosed with PD between January 2015 and January 2020. The patients were categorized based on FPG level into euglycemia (70 mg/dL < FPG < 100 mg/dL), intermediate glycemia (100 mg/dL ≤ FPG < 126 mg/dL), and hyperglycemia (FPG ≥ 126 mg/dL), and longitudinal FPG trajectories were analyzed using group-based trajectory modeling. Survival analysis was conducted to determine the time until motor outcome (Hoehn and Yahr stage ≥ 2) and the conversion from normal cognition to mild cognitive impairment.

RESULTS

Among the patient cohort, 82 had euglycemia, 93 had intermediate glycemia, and 26 had hyperglycemia. Intermediate glycemia (hazard ratio 1.747, 95% confidence interval [CI] 1.083-2.816, p = 0.0221) and hyperglycemia (hazard ratio 3.864, 95% CI 1.996-7.481, p < 0.0001) were found to be significant predictors of worsening motor symptoms. However, neither intermediate glycemia (hazard ratio 1.183, 95% CI 0.697-2.009, p = 0.5339) nor hyperglycemia (hazard ratio 1.297, 95% CI 0.601-2.800, p = 0.5078) demonstrated associations with the longitudinal progression of cognitive impairment. Diabetes mellitus, defined by self-reported medical history, was not related to poor motor or cognitive impairment outcomes.

CONCLUSION

Our.

RESULTS

suggest that both impaired glucose tolerance and hyperglycemia could be associated with motor progression in PD patients.

Cholecystokinin (CCK): a neuromodulator with therapeutic potential in Alzheimer's and Parkinson's disease

Cholecystokinin (CCK) is a neuropeptide modulating digestion, glucose levels, neurotransmitters and memory. Recent studies suggest that CCK exhibits neuroprotective effects in Alzheimer's disease (AD) and Parkinson's disease (PD). Thus, we review the physiological function and therapeutic potential of CCK. The neuropeptide facilitates hippocampal glutamate release and gates GABAergic basket cell activity, which improves declarative memory acquisition, but inhibits consolidation. Cortical CCK alters recognition memory and enhances audio-visual processing. By stimulating CCK-1 receptors (CCK-1Rs), sulphated CCK-8 elicits dopamine release in the substantia nigra and striatum. In the mesolimbic pathway, CCK release is triggered by dopamine and terminates reward responses via CCK-2Rs. Importantly, activation of hippocampal and nigral CCK-2Rs is neuroprotective by evoking AMPK activation, expression of mitochondrial fusion modulators and autophagy. Other benefits include vagus nerve/CCK-1R-mediated expression of brain-derived neurotrophic factor, intestinal protection and suppression of inflammation. We also discuss caveats and the therapeutic combination of CCK with other peptide hormones.

Racial disparities in hospitalization characteristics among Native Hawaiians, Pacific Islanders and Asian American subgroups with Parkinson's disease

BACKGROUND

Differences among Native Hawaiians/Pacific Islanders (NHPI) and Asian American (AA) subgroups have not been adequately studied in Parkinson's disease (PD).

OBJECTIVE

To determine differences in demographics, comorbidities, and healthcare utilization among NHPI, AA subgroups, and White hospitalized PD patients.

METHODS

We conducted a retrospective cross-sectional analysis of Hawai'is statewide registry (2016-2020). Patients with PD were identified using ICD10 code G20 and categorized as White, Japanese, Filipino, Chinese, NHPI, or Other. Variables collected included: age, sex, residence (county), primary source of payment, discharge status, length of stay, in-hospital expiration, Charlson Comorbidity Index (CCI) and Deep Brain Stimulation (DBS) utilization. Bivariate analyses were performed: differences in age and CCI were further examined by multivariable linear regression and proportional odds models.

RESULTS

Of 229,238 hospitalizations, 2428 had PD (Japanese: 31.3 %, White: 30.4 %, Filipino: 11.3 %, NHPI: 9.6 %, Chinese: 8.0 %). NHPI were younger compared to rest of the subgroups [estimate in years (95 % CI): Whites: 4.4 (3.0-5.8), Filipinos: 4.3 (2.7-5.9), Japanese: 7.7 (6.4-9.1), Chinese: 7.9 (6.1-9.7), p < 0.001)]. NHPI had a higher CCI compared to White, Japanese, and Chinese (p < 0.001). Among AA subgroups, Filipinos were younger and had a higher CCI compared to Japanese and Chinese (p < 0.001). There were no significant differences in DBS utilization among subgroups.

CONCLUSIONS

NHPI and Filipinos with PD were hospitalized at a younger age and had a greater comorbidity burden compared to other AAs and Whites. Further research, ideally prospective studies, are needed to understand these racial disparities.

Increasing incidence of Parkinson's disease in patients with epilepsy: A Nationwide cohort study

BACKGROUND

Although epilepsy is an uncommon comorbidity of Parkinson's disease (PD), the exact incidence of PD among the patients with epilepsy is not clarified yet.

OBJECTIVES

We aimed to estimate the incidence of PD in patients with epilepsy and explore the association between epilepsy and PD.

METHODS

Epilepsy patients enrolled in the National Health Insurance Service Health Screening Cohort (NHIS-HealS) (2002-2013) between 2003 and 2007 were set up as the experimental group. The major outcome was the occurrence of PD. Non-epilepsy patients were obtained through Propensity Score Matching of 'greedy nearest neighbor' algorithm in 1:1 ratio. The Cox Proportional Hazards model was used to calculate PD incidence and hazard ratio (HR).

RESULTS

A total of 10,510 patients were finally included in the study, which contained 5255 patients in epilepsy and non-epilepsy groups, respectively. During the follow-up period, 85 patients with Parkinson's disease among 5255 patients with epilepsy and 57 patients with Parkinson's disease among 5255 patients without epilepsy occurred. The 10,000 Person-Year (PY), representing the number of PD patients per 10,000 per year, was 21.38 in the epilepsy group and 11.18 in the non-epilepsy group. When all variables were adjusted, it was found that the epilepsy group had a 2.19 times significantly higher risk of developing Parkinson's disease than the control group (The adjusted HR: 2.19 (95% CI, 1.55-3.12)).

CONCLUSION

This study indicates an increased risk of PD in patients with epilepsy. However, further research is needed to prove an exact causal relationship between these two brain disorders.

Microbiota-gut-brain axis and its therapeutic applications in neurodegenerative diseases

The human gastrointestinal tract is populated with a diverse microbial community. The vast genetic and metabolic potential of the gut microbiome underpins its ubiquity in nearly every aspect of human biology, including health maintenance, development, aging, and disease. The advent of new sequencing technologies and culture-independent methods has allowed researchers to move beyond correlative studies toward mechanistic explorations to shed light on microbiome-host interactions. Evidence has unveiled the bidirectional communication between the gut microbiome and the central nervous system, referred to as the "microbiota-gut-brain axis". The microbiota-gut-brain axis represents an important regulator of glial functions, making it an actionable target to ameliorate the development and progression of neurodegenerative diseases. In this review, we discuss the mechanisms of the microbiota-gut-brain axis in neurodegenerative diseases. As the gut microbiome provides essential cues to microglia, astrocytes, and oligodendrocytes, we examine the communications between gut microbiota and these glial cells during healthy states and neurodegenerative diseases. Subsequently, we discuss the mechanisms of the microbiota-gut-brain axis in neurodegenerative diseases using a metabolite-centric approach, while also examining the role of gut microbiota-related neurotransmitters and gut hormones. Next, we examine the potential of targeting the intestinal barrier, blood-brain barrier, meninges, and peripheral immune system to counteract glial dysfunction in neurodegeneration. Finally, we conclude by assessing the pre-clinical and clinical evidence of probiotics, prebiotics, and fecal microbiota transplantation in neurodegenerative diseases. A thorough comprehension of the microbiota-gut-brain axis will foster the development of effective therapeutic interventions for the management of neurodegenerative diseases.

The comorbidity and co-medication profile of patients with progressive supranuclear palsy

BACKGROUND

Progressive supranuclear palsy (PSP) is usually diagnosed in elderly. Currently, little is known about comorbidities and the co-medication in these patients.

OBJECTIVES

To explore the pattern of comorbidities and co-medication in PSP patients according to the known different phenotypes and in comparison with patients without neurodegenerative disease.

METHODS

Cross-sectional data of PSP and patients without neurodegenerative diseases (non-ND) were collected from three German multicenter observational studies (DescribePSP, ProPSP and DANCER). The prevalence of comorbidities according to WHO ICD-10 classification and the prevalence of drugs administered according to WHO ATC system were analyzed. Potential drug-drug interactions were evaluated using AiDKlinik®.

RESULTS

In total, 335 PSP and 275 non-ND patients were included in this analysis. The prevalence of diseases of the circulatory and the nervous system was higher in PSP at first level of ICD-10. Dorsopathies, diabetes mellitus, other nutritional deficiencies and polyneuropathies were more frequent in PSP at second level of ICD-10. In particular, the summed prevalence of cardiovascular and cerebrovascular diseases was higher in PSP patients. More drugs were administered in the PSP group leading to a greater percentage of patients with polypharmacy. Accordingly, the prevalence of potential drug-drug interactions was higher in PSP patients, especially severe and moderate interactions.

CONCLUSIONS

PSP patients possess a characteristic profile of comorbidities, particularly diabetes and cardiovascular diseases. The eminent burden of comorbidities and resulting polypharmacy should be carefully considered when treating PSP patients.

Association between Type 1 Diabetes Mellitus and Parkinson's Disease: A Mendelian Randomization Study

While much evidence suggests that type 2 diabetes mellitus increases the risk of Parkinson's disease (PD), the relationship between type 1 diabetes mellitus (T1DM) and PD is unclear. To study their association, we performed a two-sample Mendelian randomization (MR) using the following statistical methods: inverse variance weighting (IVW), MR-Egger, weight median, and weighted mode. Independent datasets with no sample overlap were retrieved from the IEU GWAS platform. All the MR methods found a lower risk of PD in T1DM (IVW-OR 0.93, 95% CI 0.91-0.96, p = 3.12 × 10-5; MR-Egger-OR 0.93, 95% CI 0.88-0.98, p = 1.45 × 10-2; weighted median-OR 0.93, 95% CI 0.89-0.98, p = 2.76 × 10-3; and weighted mode-OR 0.94, 95% CI 0.9-0.98, p = 1.58 × 10-2). The findings were then replicated with another independent GWAS dataset on T1DM (IVW-OR 0.97, 95% CI 0.95-0.99, p = 3.10 × 10-3; MR-Egger-OR 0.96, 95% CI 0.93-0.99, p = 1.08 × 10-2; weighted median-OR 0.97, 95% CI 0.94-0.99, p = 1.88 × 10-2; weighted mode-OR 0.97, 95% CI 0.94-0.99, p = 1.43 × 10-2). Thus, our study provides evidence that T1DM may have a protective effect on PD risk, though further studies are needed to clarify the underlying mechanisms.

How should we be using biomarkers in trials of disease modification in Parkinson's disease?

The recent validation of the α-synuclein seed amplification assay as a biomarker with high sensitivity and specificity for the diagnosis of Parkinson's disease has formed the backbone for a proposed staging system for incorporation in Parkinson's disease clinical studies and trials. The routine use of this biomarker should greatly aid in the accuracy of diagnosis during recruitment of Parkinson's disease patients into trials (as distinct from patients with non-Parkinson's disease parkinsonism or non-Parkinson's disease tremors). There remain, however, further challenges in the pursuit of biomarkers for clinical trials of disease modifying agents in Parkinson's disease, namely: optimizing the distinction between different α-synucleinopathies; the selection of subgroups most likely to benefit from a candidate disease modifying agent; a sensitive means of confirming target engagement; and the early prediction of longer-term clinical benefit. For example, levels of CSF proteins such as the lysosomal enzyme β-glucocerebrosidase may assist in prognostication or allow enrichment of appropriate patients into disease modifying trials of agents with this enzyme as the target; the presence of coexisting Alzheimer's disease-like pathology (detectable through CSF levels of amyloid-β42 and tau) can predict subsequent cognitive decline; imaging techniques such as free-water or neuromelanin MRI may objectively track decline in Parkinson's disease even in its later stages. The exploitation of additional biomarkers to the α-synuclein seed amplification assay will, therefore, greatly add to our ability to plan trials and assess the disease modifying properties of interventions. The choice of which biomarker(s) to use in the context of disease modifying clinical trials will depend on the intervention, the stage (at risk, premotor, motor, complex) of the population recruited and the aims of the trial. The progress already made lends hope that panels of fluid biomarkers in tandem with structural or functional imaging may provide sensitive and objective methods of confirming that an intervention is modifying a key pathophysiological process of Parkinson's disease. However, correlation with clinical progression does not necessarily equate to causation, and the ongoing validation of quantitative biomarkers will depend on insightful clinical-genetic-pathophysiological comparisons incorporating longitudinal biomarker changes from those at genetic risk with evidence of onset of the pathophysiology and those at each stage of manifest clinical Parkinson's disease.

Diabetes: a tipping point in neurodegenerative diseases

Diabetes is associated with an increased risk and progression of Alzheimer's (AD) and Parkinson's (PD) diseases. Conversely, diabetes may confer neuroprotection against amyotrophic lateral sclerosis (ALS). It has been posited that perturbations in glucose and insulin regulation, cholesterol metabolism, and mitochondrial bioenergetics defects may underlie the molecular underpinnings of diabetes effects on the brain. Nevertheless, the precise molecular mechanisms remain elusive. Here, we discuss the evidence from molecular, epidemiological, and clinical studies investigating the impact of diabetes on neurodegeneration and highlight shared dysregulated pathways between these complex comorbidities. We also discuss promising antidiabetic drugs, molecular diagnostics currently in clinical trials, and outstanding questions and challenges for future pursuit.

Impact of diabetes and glycated hemoglobin level on the clinical manifestations of Parkinson's disease

BACKGROUND

The coexistence of diabetes mellitus (DM) has been suggested to accelerate the progression of Parkinson's disease (PD) and make the phenotype more severe. In this study, we investigated whether DM or glycated hemoglobin (HbA1c) levels affect the differences in motor and nonmotor symptoms.

METHODS

We conducted a cross-sectional study including 140 consecutive Japanese patients with PD for whom medical history and serum HbA1c records were available. The PD patients with a DM diagnosis were classified into the diabetes-complicated group (PD-DM) and the nondiabetes-complicated group (PD-no DM). Next, patients were classified based on a median HbA1c value of 5.7, and clinical parameters were compared. The correlations between HbA1c levels and other clinical variables were analyzed.

RESULTS

Of 140 patients, 23 patients (16%) had DM. Compared to PD-no DM patients, PD-DM patients showed lower MMSE scores. Compared to the lower HbA1c group, the higher HbA1c group showed a higher MDS-UPDRS part III score and a lower metaiodobenzylguanidine (MIBG) scintigraphy heart-to-mediastinum (H/M) ratio. HbA1c levels were positively correlated with age and the MDS-UPDRS part III score and negatively correlated with the MMSE score and H/M ratio on cardiac MIBG scintigraphy. Binary logistic regression analysis, which included age, sex, disease duration, and MMSE and MDS-UPDRS part III scores as independent variables, revealed that a lower MMSE score was an independent contributor to PD-DM and PD with high HbA1c levels.

CONCLUSIONS

DM complications and high HbA1c levels may affect cognitive function in patients with PD.

Mortality and causes of death in patients with Parkinson's disease: a nationwide population-based cohort study

Objective

Parkinson's disease (PD) is a neurodegenerative disease involving multiple systems that can affect mortality. This study aimed to compare all-cause and cause-specific mortality between people with PD and without PD.

Methods

This population-based prospective cohort study is based on Korean National Health Insurance Service data. The primary outcome was the hazard ratio (HR) of all-cause and cause-specific mortality for PD from 2010 to 2019. Cox proportional hazards regression was applied to calculate HRs under crude and three adjusted models with epidemiologic variables.

Results

A total of 8,220 PD patients and 41,100 age- and sex-matched controls without PD were registered. Ten-year mortality was 47.9% in PD patients and 20.3% in non-PD controls. The mortality rate was higher among older and male participants. The leading cause of death in PD was nervous system diseases (38.73%), and 97.1% of those were extrapyramidal and movement disorders, followed by circulatory diseases (15.33%), respiratory diseases (12.56%), and neoplasms (9.7%). PD contributed to an increased risk of all-cause death with an HR of 2.96 (95% CI = 2.84-3.08). HRs of death for PD were 3.07 (95% CI = 2.74-3.45) from respiratory diseases, 1.93 (95% CI = 1.75-2.13) from circulatory diseases, 2.35 (95% CI = 2.00-2.77) from external causes, and 2.69 (95% CI = 2.10-3.43) from infectious diseases.

Conclusion

These results showed that PD was related to a higher risk of mortality in all ages and sexes. The leading causes of death in PD were nervous, circulatory, respiratory, infectious diseases, and external causes.

Physical activity and lifestyle modifications in the treatment of neurodegenerative diseases

Neurodegenerative diseases have reached alarming numbers in the past decade. Unfortunately, clinical trials testing potential therapeutics have proven futile. In the absence of disease-modifying therapies, physical activity has emerged as the single most accessible lifestyle modification with the potential to fight off cognitive decline and neurodegeneration. In this review, we discuss findings from epidemiological, clinical, and molecular studies investigating the potential of lifestyle modifications in promoting brain health. We propose an evidence-based multidomain approach that includes physical activity, diet, cognitive training, and sleep hygiene to treat and prevent neurodegenerative diseases.

Association between metabolic syndrome components and impulse control disorders in Parkinson's disease

Background

Current evidence on management of impulse control disorders (ICDs) in Parkinson's disease (PD) remains scarce, and exploring modifiable risk factors is crucial.

Objective

We evaluated the profiles of ICDs in PD patients and aimed to determine the associations between ICDs, metabolic syndrome components and other clinical features.

Methods

We enrolled patients diagnosed with PD in this study and conducted comprehensive clinical assessments.

Results

We recruited 39 PD patients with ICDs and 66 PD patients without ICDs. Out of the 39 patients with ICDs, 19 (48.7%) had one impulse control disorder, while 20 (51.3%) had two or more. The most commonly reported symptom of ICDs was compulsive eating (48.7%). Significant differences were observed between the PD patients with and without ICDs in terms of their HbA1c levels, history of diabetes mellitus, dopamine agonist use, levodopa equivalent dose of dopamine agonists (LED DA), and Hamilton Depression Rating Scale (HAMD) scores. HbA1c levels were significantly higher in the PD patients with compulsive eating. Stepwise logistic regression analyses were performed with the dependent variables of ICDs (yes/no) and compulsive eating (yes/no). Among the 105 PD patients, those with ICDs exhibited higher levels of HbA1c, HAMD score and LED DA than those without ICDs (p < 0.01). Among 39 PD patients with ICDs, those with compulsive eating exhibited higher levels of HbA1c (OR = 2.148, 95% CI = 1.004-4.594, p < 0.05). Among 105 PD patients, those with compulsive eating exhibited higher levels of HbA1c, LED DA and HAMD score (p < 0.05).

Conclusion

This study provides insights into the profiles of ICDs in PD patients and their associations with various clinical features. Compulsive eating was the most common ICDs symptom reported. Notably, HbA1c levels were found to be higher in patients with compulsive eating, indicating that poor blood glucose control may be a potential risk factor for ICDs in PD. However, it should be noted that the higher HbA1c levels could also be a consequence of compulsive eating rather than a causal factor for ICDs in PD. Further research is needed to confirm the modifiable risk factors for ICDs in PD.

Parkinson's Disease and Diabetes Mellitus: Individual and Combined Effects on Motor, Cognitive, and Psychosocial Functions

BACKGROUND/OBJECTIVE

Understanding the effects of multimorbidity on motor and cognitive function is important for tailoring therapies. Individuals with diabetes mellitus (DM) have a greater risk of developing Parkinson's disease (PD). This study investigated if individuals with comorbid PD and DM experienced poorer functional ability compared to individuals with only PD or DM.

METHODS

A cross-sectional analysis of 424 individuals: healthy older adults (HOA), n = 170; PD without DM (PD-only), n = 162; DM without PD (DM-only), n = 56; and comorbid PD and DM (PD+DM), n = 36. Motor, motor-cognitive, cognitive, and psychosocial functions and PD motor symptoms were compared among groups using a two-way analyses of covariance with PD and DM as factors.

RESULTS

The PD-only and DM-only participants exhibited slower gait, worse balance, reduced strength, and less endurance. Motor-cognitive function was impaired in individuals with PD but not DM. DM-only participants exhibited impaired inhibition. Individuals with comorbid PD+DM had worse PD motor symptoms and exhibited impaired attention compared to the PD-only group.

CONCLUSIONS

Having PD or DM was independently associated with poorer physical and mental quality of life, depression, and greater risk for loss of function. Both PD and DM have independent adverse effects on motor function. Comorbid PD+DM further impairs attention compared to the effect of PD-only, suggesting the importance of therapies focusing on attention. Understanding the functional ability levels for motor and cognitive domains will enhance the clinical care for PD, DM, and PD+DM.

Parkinson's Disease and Diabetes Mellitus: Synergistic Effects on Pathophysiology and GI Motility

PURPOSE OF REVIEW

Parkinson's disease and diabetes affect an increasing proportion of the aging global population. Both conditions extensively affect gastrointestinal (GI) motility with similar and differing clinical symptoms. Nonetheless, GI symptoms in Parkinson's disease and diabetes pose significant morbidity and impairment of quality of life. Their pathophysiology is poorly understood, and therefore, effective treatment options are lacking.

RECENT FINDINGS

Parkinson's disease patients have oropharyngeal dysphagia and constipation. They also have mild or absent upper GI symptoms associated with delayed gastric emptying, which is prevalent in 70% of patients. Delayed gastric emptying in Parkinson's disease leads to erratic medication absorption and fluctuating motor symptoms. Half of diabetics have upper GI symptoms, which correlate to gastric emptying and changes in brain activity of the insular cortex. The majority of diabetics also have constipation. Diabetics have an increased risk for developing Parkinson's disease and anti-diabetic medications are associated with risk reduction of developing Parkinson's disease. Hyperglycemia is associated with advanced glycated end products formation and acceleration of α-synuclein aggregation. GLP-1 receptor agonists have also demonstrated efficacy in improving motor symptoms and cognition in Parkinson's disease patients with diabetes. Parkinson's disease and diabetes are pan-enteric disorders with significant GI symptoms and impairment of gut motility. Both conditions have synergistic pathophysiologies that propagate neurodegenerative changes. Treatment options for GI symptoms in diabetic and Parkinson's disease patients are lacking. Anti-diabetic treatment improves motor symptoms in Parkinson's disease, however, its effect on GI symptoms is unclear.

Association between diabetes mellitus, prediabetes and risk, disease progression of Parkinson's disease: A systematic review and meta-analysis

Background

Previous studies reported inconsistent results regarding association between diabetes mellitus (DM), prediabetes and risk, disease progression of Parkinson's disease (PD). The meta-analysis was made to investigate association between DM, prediabetes and risk, disease progression of PD.

Methods

Literatures investigating association between DM, prediabetes and risk, disease progression of PD were searched in these databases: PubMed and Web of Science. Included literatures were published before October 2022. STATA 12.0 software was used to compute odds ratios (ORs)/relative risks (RRs) or standard mean differences (SMDs).

Results

DM was associated with a higher risk of PD, compared to non-diabetic participants with a random effects model (OR/RR = 1.23, 95% CI 1.12-1.35, I 2 = 90.4%, p < 0.001). PD with DM (PD-DM) was associated with a faster motor progression compared to PD without DM (PD-noDM) with a fixed effects model (RR = 1.85, 95% CI 1.47-2.34, I 2 = 47.3%, p = 0.091). However, meta-analysis for comparison in change rate of United Rating Scale (UPDRS) III scores from baseline to follow-up time between PD-DM and PD-noDM reported no difference in motor progression between PD-DM and PD-noDM with a random effects model (SMD = 2.58, 95% CI = -3.11 to 8.27, I 2 = 99.9%, p < 0.001). PD-DM was associated with a faster cognitive decline compared to PD-noDM with a fixed effects model (OR/RR = 1.92, 95% CI 1.45-2.55, I 2 = 50.3%, p = 0.110).

Conclusions

In conclusion, DM was associated with a higher risk and faster disease decline of PD. More large-scale cohort studies should be adopted to evaluate the association between DM, prediabetes and PD.

Type 2 Diabetes and Parkinson's Disease: A Focused Review of Current Concepts

Highly reproducible epidemiological evidence shows that type 2 diabetes (T2D) increases the risk and rate of progression of Parkinson's disease (PD), and crucially, the repurposing of certain antidiabetic medications for the treatment of PD has shown early promise in clinical trials, suggesting that the effects of T2D on PD pathogenesis may be modifiable. The high prevalence of T2D means that a significant proportion of patients with PD may benefit from personalized antidiabetic treatment approaches that also confer neuroprotective benefits. Therefore, there is an immediate need to better understand the mechanistic relation between these conditions and the specific molecular pathways affected by T2D in the brain. Although there is considerable evidence that processes such as insulin signaling, mitochondrial function, autophagy, and inflammation are involved in the pathogenesis of both PD and T2D, the primary aim of this review is to highlight the evidence showing that T2D-associated dysregulation of these pathways occurs not only in the periphery but also in the brain and how this may facilitate neurodegeneration in PD. We also discuss the challenges involved in disentangling the complex relationship between T2D, insulin resistance, and PD, as well as important questions for further research. © 2022 International Parkinson and Movement Disorder Society.

Predictors of cognitive impairment in newly diagnosed Parkinson's disease with normal cognition at baseline: A 5-year cohort study

Background and objective

Cognitive impairment (CI) is a substantial contributor to the disability associated with Parkinson's disease (PD). We aimed to assess the clinical features and explore the underlying biomarkers as predictors of CI in patients with newly diagnosed PD (NDPD; less than 2 years).

Methods

We evaluated the cognitive function status using the Montreal Cognitive Assessment (MoCA) and a battery of neuropsychological tests at baseline and subsequent annual follow-up for 5 years from the Parkinson's Progression Markers Initiative (PPMI) database. We assessed the baseline clinical features, apolipoprotein (APO) E status, β-glucocerebrosidase (GBA) mutation status, cerebrospinal fluid findings, and dopamine transporter imaging results. Using a diagnosis of CI (combined mild cognitive impairment and dementia) developed during the 5-year follow-up as outcome measures, we assessed the predictive values of baseline clinical variables and biomarkers. We also constructed a predictive model for the diagnosis of CI using logistic regression analysis.

Results

A total of 409 patients with NDPD with 5-year follow-up were enrolled, 232 with normal cognitive function at baseline, and 94 patients developed CI during the 5-year follow-up. In multivariate analyses, age, current diagnosis of hypertension, baseline MoCA scores, Movement disorder society Unified PD Rating Scale part III (MDS-UPDRS III) scores, and APOE status were associated with the development of CI. Predictive accuracy of CI using age alone improved by the addition of clinical variables and biomarkers (current diagnosis of hypertension, baseline MoCA scores, and MDS-UPDRS III scores, APOE status; AUC 0.80 [95% CI 0.74-0.86] vs. 0.71 [0.64-0.77], p = 0.008). Cognitive domains that had higher frequencies of impairment were found in verbal memory (12.6 vs. 16.8%) and attention/processing speed (12.7 vs. 16.9%), however, no significant difference in the prevalence of CI at annual follow-up was found during the 5-year follow-up in NDPD patients.

Conclusion

In NDPD, the development of CI during the 5-year follow-up can be predicted with good accuracy using a model combining age, current diagnosis of hypertension, baseline MoCA scores, MDS-UPDRS III scores, and APOE status. Our study underscores the need for the earlier identification of CI in NDPD patients in our clinical practice.

Type 2 diabetes mellitus augments Parkinson's disease risk or the other way around: Facts, challenges and future possibilities

About 10% of the adult population is living with type 2 diabetes mellitus (T2DM) and 1% of the population over 60 years of age is suffering from Parkinson's disease (PD). A school of thought firmly believes that T2DM, an age-related disease, augments PD risk. Such relationship is reflected from the severity of PD symptoms in drug naive subjects possessing T2DM. Onset of Parkinsonian feature in case controls possessing T2DM corroborates the role of hyperglycemia in PD. A few cohort, meta-analysis and animal studies have shown an increased PD risk owing to insulin resistance. High fat diet and role of insulin signaling in the regulation of sugar metabolism, oxidative stress, α-synuclein aggregation and accumulation, inflammatory response and mitochondrial function in PD models and sporadic PD further connect the two. Although little is reported about the implication of PD in hyperglycemia and T2DM, a few studies have also contradicted. Ameliorative effect of anti-diabetic drugs on Parkinsonian symptoms and vague outcome of anti-PD medications in T2DM patients also suggest a link. The article reviews the literature supporting augmented risk of one by the other, analysis of proof of the concept, facts, challenges, future possibilities and standpoint on the subject.

Actions of Metformin in the Brain: A New Perspective of Metformin Treatments in Related Neurological Disorders

Metformin is a first-line drug for treating type 2 diabetes mellitus (T2DM) and one of the most commonly prescribed drugs in the world. Besides its hypoglycemic effects, metformin also can improve cognitive or mood functions in some T2DM patients; moreover, it has been reported that metformin exerts beneficial effects on many neurological disorders, including major depressive disorder (MDD), Alzheimer’s disease (AD) and Fragile X syndrome (FXS); however, the mechanism underlying metformin in the brain is not fully understood. Neurotransmission between neurons is fundamental for brain functions, and its defects have been implicated in many neurological disorders. Recent studies suggest that metformin appears not only to regulate synaptic transmission or plasticity in pathological conditions but also to regulate the balance of excitation and inhibition (E/I balance) in neural networks. In this review, we focused on and reviewed the roles of metformin in brain functions and related neurological disorders, which would give us a deeper understanding of the actions of metformin in the brain.