Parkinson's Disease and Type 2 Diabetes: HbA1c Is Associated with Motor and Cognitive Severity

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.

Use of dipeptidyl peptidase-4 inhibitors was associated with a lower risk of Parkinson's disease in diabetic patients

Diabetes mellitus is a risk factor for Parkinson's disease (PD). While animal studies have supported the benefits of incretin-based therapies, including dipeptidyl peptidase-4 (DPP4) inhibitors, in PD, clinical research has yielded controversial results. This cohort study aimed to assess the relationship between PD incidence and the utilization of DPP4 inhibitor in diabetic patients. Using Taiwan's National Health Insurance Research Database from 2009 to 2018, diabetic patients receiving metformin plus at least one second-line oral antidiabetic (OAD) were enrolled. The patients were categorized as DPP4 inhibitor users and non-users. Propensity score matching was employed to establish a 1:1 ratio between DPP4 inhibitor users and non-users. Among the 205,910 patients enrolled, 149 were diagnosed with PD during follow-up. The incidence rate was 0.29 per 1000 person-years for DPP4 inhibitor users and 0.55 per 1000 person-years for the non-users. DPP4 inhibitor users exhibited a significantly lower risk of PD (adjusted hazard ratio, 0.51; 95% CI 0.39-0.68). Among DPP4 inhibitor users, vildagliptin showed the strongest correlation with a reduction in the risk of PD. This study demonstrates that the use of DPP4 inhibitors along with metformin in diabetic patients is associated with a lower risk of PD compared to those using other OADs.

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.

Glycated hemoglobin A1c, cerebral small vessel disease burden, and disease severity in Parkinson's disease

OBJECTIVE

Our study aimed to investigate the glucose levels in PD and controls. We also examine whether glucose control is associated with PD severity regardless of diabetic status, and test whether the correlation is mediated by cerebral small vessel disease (CSVD) burden.

METHODS

A total of 100 patients with idiopathic PD and 100 age- and sex-matched controls who underwent brain magnetic resonance imaging (MRI) were enrolled in this study. We collected the clinical data and blood parameters, including fasting blood glucose (FBG), glycated hemoglobin A1c (HbA1c), and blood lipid. Patients with PD were divided into early (n = 61) and advanced (n = 39) subgroups, based on Hoehn and Yahr (H&Y) stages. Differences between the PD and controls, PD with and without diabetes, and between two PD subgroups were compared. CSVD markers were assessed, including lacunes, white matter hyperintensities, enlarged perivascular spaces, and cerebral microbleeds. Multivariable logistic regressions were used to test the association between HbA1c and H&Y stages. Interaction between HbA1c and CSVD burden in relation to H&Y stages was also analyzed.

RESULTS

PD group exhibited higher HbA1c (p < 0.001), lower high-density lipoprotein cholesterol (p < 0.001) and triglyceride (p = 0.049) than controls. Advanced PD patients showed higher HbA1c than early PD group (p = 0.022). Increasing HbA1c (OR = 1.54, 95% CI 1.03-2.32, p = 0.036) along with longer disease duration (OR = 1.14, 95% CI 1.01-1.27, p = 0.028) and higher UPDRS III score (OR = 1.07, 95% CI 1.02-1.11, p = 0.002) increased the risk of belonging to the higher H&Y stage. However, interaction between HbA1c and CSVD burden in relation to H&Y stages was not significant.

INTERPRETATION

HbA1c is independently associated with H&Y stages in PD, and this correlation may not be mediated by CSVD burden.

Chaudhuri's Dashboard of Vitals in Parkinson's syndrome: an unmet need underpinned by real life clinical tests

We have recently published the notion of the "vitals" of Parkinson's, a conglomeration of signs and symptoms, largely nonmotor, that must not be missed and yet often not considered in neurological consultations, with considerable societal and personal detrimental consequences. This "dashboard," termed the Chaudhuri's vitals of Parkinson's, are summarized as 5 key vital symptoms or signs and comprise of (a) motor, (b) nonmotor, (c) visual, gut, and oral health, (d) bone health and falls, and finally (e) comorbidities, comedication, and dopamine agonist side effects, such as impulse control disorders. Additionally, not addressing the vitals also may reflect inadequate management strategies, leading to worsening quality of life and diminished wellness, a new concept for people with Parkinson's. In this paper, we discuss possible, simple to use, and clinically relevant tests that can be used to monitor the status of these vitals, so that these can be incorporated into clinical practice. We also use the term Parkinson's syndrome to describe Parkinson's disease, as the term "disease" is now abandoned in many countries, such as the U.K., reflecting the heterogeneity of Parkinson's, which is now considered by many as a syndrome.

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.

Diabetes, Glycated Hemoglobin (HbA1c), and Neuroaxonal Damage in Parkinson's Disease (MARK-PD Study)

BACKGROUND

Diabetes is associated with incidence and prevalence of Parkinson's disease (PD). Furthermore, glycated hemoglobin (HbA1c) levels have been linked with motor function and progression.

OBJECTIVES

We evaluated the relationship between prevalent diabetes and HbA1c levels with serum neurofilament light chain (NfL) levels as marker of neuroaxonal damage.

METHODS

NfL concentrations were analyzed with Simoa in serum of 195 PD patients with available HbA1c values. Motor (MDS-UPDRS III, Hoehn & Yahr [H&Y]) and cognitive (Montreal Cognitive Assessment [MoCA]) function was assessed and vascular comorbidities were documented from medical records.

RESULTS

PD patients with prevalent diabetes had higher serum NfL levels and lower MoCA scores independent of age, body mass index (BMI), and vascular risk factors. Furthermore, diabetes was associated with higher H&Y stages in unadjusted and age/BMI-adjusted models. Higher HbA1c levels were associated with increased NfL in unadjusted and age/BMI-adjusted models.

CONCLUSIONS

In PD patients, diabetes and high HbA1c are associated with increased neuroaxonal damage and cognitive impairment. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson Movement Disorder Society.