Association between Early Neuroretinal Dysfunction and Peripheral Motor Unit Loss in Patients with Type 1 Diabetes Mellitus

Aberrant Neurovascular Coupling in Diabetic Retinopathy Using Arterial Spin Labeling (ASL) and Functional Magnetic Resonance Imaging (fMRI) methods

Background

Previous imaging studies have demonstrated that diabetic retinopathy (DR) is linked to structural and functional abnormalities in the brain. However, the extent to which DR patients exhibit abnormal neurovascular coupling remains largely unknown.

Methods

Thirty-one patients with DR and 31 sex- and age-matched healthy controls underwent resting-state functional magnetic resonance imaging (rs-fMRI) to calculate functional connectivity strength (FCS) and arterial spin-labeling imaging (ASL) to calculate cerebral blood flow (CBF). The study compared CBF-FCS coupling across the entire grey matter and CBF/FCS ratios (representing blood supply per unit of connectivity strength) per voxel between the two groups. Additionally, a support vector machine (SVM) method was employed to differentiate between diabetic retinopathy (DR) patients and healthy controls (HC).

Results

In DRpatients compared to healthy controls, there was a reduction in CBF-FCS coupling across the entire grey matter. Specifically, DR patients exhibited elevated CBF/FCS ratios primarily in the primary visual cortex, including the right calcarine fissure and surrounding cortex. On the other hand, reduced CBF/FCS ratios were mainly observed in premotor and supplementary motor areas, including the left middle frontal gyrus.

Conclusion

An elevated CBF/FCS ratio suggests that patients with DR may have a reduced volume of gray matter in the brain. A decrease in its ratio indicates a decrease in regional CBF in patients with DR. These findings suggest that neurovascular decoupling in the visual cortex, as well as in the supplementary motor and frontal gyrus, may represent a neuropathological mechanism in diabetic retinopathy.

The evaluation of tactile dysfunction in the hand in type 1 diabetes: a novel method based on haptics

AIMS

We present an innovative method based on haptics for the evaluation of the sense of touch in the hand, in people affected by type 1 diabetes.

METHODS

Forty individuals affected by diabetes and 20 healthy controls took part in the study; the diabetes group was further divided into two subgroups based on vibration sensitivity in the lower limb. By means of a novel haptic device, tactile sensitivity in the fingertip was measured as the ability of the participants to discriminate slip motion speed.

RESULTS

Tactile sensitivity was significantly lower in individuals affected by diabetes as compared to controls. Depending on the subgroup, the difference from the controls was equal to 0.11 (95% CI from 0.029 to 0.186) and to 0.267 (95% CI from 0.198 to 0.336). Within the diabetes group, tactile sensitivity correlated with vibration sensitivity in the upper (p = 0.001) and lower limb (p = 0.003). A significant relationship between nerve conduction parameters and tactile sensitivity was found (p = 0.03). Finally, we combined the different predictors (clinical, vibratory and electroneurography data) by using cluster analysis; tactile sensitivity was found to be significantly different between different clusters (p = 0.004).

CONCLUSIONS

Early signs of tactile dysfunction in the hand were found in individuals affected by diabetes, even in absence of diabetic neuropathy. The protocol presented in this study is a promising tool for the assessment of tactile dysfunction in the hand in people affected by type 1 diabetes.

Redefining distal symmetrical polyneuropathy features in type 1 diabetes: a systematic review

Diabetic neuropathy is among the most frequent complications of both type 1 (T1DM) and type 2 diabetes (T2DM) and commonly manifests as a distal symmetrical polyneuropathy (DSPN). Despite evidence that T1DM- and T2DM-related DSPN are separate entities, most of our knowledge on diabetic DSPN derives from studies focused on type 2 diabetes. This systematic review provides an overview of current evidence on DSPN in T1DM, including its epidemiological, pathophysiological and clinical features, along with principal diagnostic tests findings. This review included 182 clinical and preclinical studies. The results indicate that DSPN is a less frequent complication in T1DM compared with T2DM and that distinctive pathophysiological mechanisms underlie T1DM-related DSPN development, with hyperglycemia as a major determinant. T1DM-related DSPN more frequently manifests with non-painful than painful symptoms, with lower neuropathic pain prevalence compared with T2DM-associated DSPN. The overt clinical picture seems characterized by a higher prevalence of large fiber-related clinical signs (e.g., ankle reflexes reduction and vibration hypoesthesia) and to a lesser extent small fiber damage (e.g., thermal or pinprick hypoesthesia). These findings as a whole suggest that large fibers impairment plays a dominant role in the clinical picture of symptomatic T1DM-related DSPN. Nevertheless, small fiber diagnostic testing shows high diagnostic accuracy in detecting early nerve damage and may be an appropriate diagnostic tool for disease monitoring and screening.

Neuromuscular dysfunction and exercise training in people with diabetic peripheral neuropathy: A narrative review

Diabetic peripheral neuropathy (DPN) is a common condition that is associated with neuromuscular dysfunction and peripheral sensory impairment. These deficits predispose patients to sensory and motor system limitations, foot ulcers and a high risk of falls. Exercise training has been proposed as an effective tool to alleviate neural deficits and improve whole-body function. Here we review the effects of DPN on neuromuscular function, the mechanisms underlying this impairment, and the neural and muscular adaptations to exercise training. Muscle dysfunction is an early hallmark of DPN. Deficits in muscle strength, power, mass and a greater fatigability are particularly severe in the lower extremity muscles. Non-enzymatic glycation of motor proteins, impaired excitation-contraction coupling and loss of motor units have been indicated as the main factors underlying muscular dysfunction. Among the exercise-based solutions, aerobic training improves neural structure and function and ameliorates neuropathic signs and symptoms. Resistance training induces marked improvement of muscle performance and may alleviate neuropathic pain. A combination of aerobic and resistance training (i.e., combined training) restores small sensory nerve damage, reduces symptoms, and improves muscle function. The evidence so far suggests that exercise training is highly beneficial and should be included in the standard care for DPN patients.

Altered resting cerebral blood flow specific to patients with diabetic retinopathy revealed by arterial spin labeling perfusion magnetic resonance imaging

BACKGROUND

Previous neuroimaging studies have shown that patients with diabetic retinopathy (DR) were accompanied by abnormalities in cerebral functional and structural architecture, whereas the resting cerebral blood flow (CBF) alterations in patients with DR are not well understood.

PURPOSE

To explore CBF alterations in patients with DR using pseudo-continuous arterial spin labeling (pCASL) imaging.

MATERIAL AND METHODS

Thirty-one individuals with DR (15 men, 16 women; mean age = 53.38 ± 9.12 years) and 33 healthy controls (HC) (12 men, 21 women; mean age = 51.61 ± 9.84 years) closely matched for age, sex, and education, underwent pCASL imaging scans. Two-sample T test was conducted to compare different CBF values between two groups.

RESULTS

Patients with DR exhibited significantly increased CBF values in the left middle temporal gyrus (Brodmann's area, BA 22) and the bilateral supplementary motor area (BA3) and decreased CBF values in the bilateral calcarine (BA17,18) and bilateral caudate relative to HC group (two-tailed, voxel level at P < 0.01, Gaussian random field (GRF), cluster level at P < 0.05). Moreover, the HbA1c (%) level showed a positive correlation with CBF values in the bilateral caudate (r = 0.473, P = 0.007) in patients with DR.

CONCLUSION

Our results highlighted that patients with DR had abnormal CBF values in the visual cortices, caudate, middle temporal gyrus, and supplementary motor area, which might reflect vision and sensorimotor and cognition dysfunction in patients with DR. These findings might help us to understanding the neural mechanism of patients with DR.

Gynura divaricata Water Extract Presented the Possibility to Enhance Neuronal Regeneration

Gynura divaricata (GD) is an Asian herb widely used as an alternative medicine and functional food for type 2 diabetes. Diabetic neuropathy is considered as an important complication of diabetic patients. This study focused on neuroregenerative effects of GD for use in the prevention of diabetic neuropathy. GD leaves were cut and boiled in water to mimic real-life cooking. The boiled content was filtered through white gauze and lyophilized to preserve as dried powder. Antioxidant assay was performed using DPPH assays. UHPLC-QTOF-MS/MS was employed to test for important compounds in the extract of these herbs. MTT assay was used to test for cell viability. The extracts at concentration of 250 μg/mL were tested with human gingival cell to observe the change of gene expression. The DPPH assay showed that GD water extract at the concentration of 5000 μg/mL could inhibit DPPH radical for 39.2%. The results showed that 5000 µg of GD water extract contained total phenolic content equivalent to 310.9 µg standard gallic acid. UHPLC-QTOF-MS/MS result found phenolic acids and flavonoids as the main components. Human gingival cells treated with 250 μg/mL of GD water extract for 10 days showed upregulation of some neuronal differentiation markers. Staining with Cdr3 dye confirmed the presentation of neuronal progenitors. The extract at the concentration of 250 μg/mL was also tested with apical papilla cells to screen for change of gene expression by RNA sequencing. The result also showed significant upregulation of alpha-internexin (INA). These results indicated that GD water extract might have an inductive effect for neural regeneration and could be used as functional food and supplementation for the prevention or treatment of diabetic neuropathy. This work provided the basic knowledge for further investigations into the benefits of GD for diabetic neuropathy.

Cutaneous and muscular afferents from the foot and sensory fusion processing: Physiology and pathology in neuropathies

The foot-sole cutaneous receptors (section 2), their function in stance control (sway minimisation, exploratory role) (2.1), and the modulation of their effects by gait pattern and intended behaviour (2.2) are reviewed. Experimental manipulations (anaesthesia, temperature) (2.3 and 2.4) have shown that information from foot sole has widespread influence on balance. Foot-sole stimulation (2.5) appears to be a promising approach for rehabilitation. Proprioceptive information (3) has a pre-eminent role in balance and gait. Reflex responses to balance perturbations are produced by both leg and foot muscle stretch (3.1) and show complex interactions with skin input at both spinal and supra-spinal levels (3.2), where sensory feedback is modulated by posture, locomotion and vision. Other muscles, notably of neck and trunk, contribute to kinaesthesia and sense of orientation in space (3.3). The effects of age-related decline of afferent input are variable under different foot-contact and visual conditions (3.4). Muscle force diminishes with age and sarcopenia, affecting intrinsic foot muscles relaying relevant feedback (3.5). In neuropathy (4), reduction in cutaneous sensation accompanies the diminished density of viable receptors (4.1). Loss of foot-sole input goes along with large-fibre dysfunction in intrinsic foot muscles. Diabetic patients have an elevated risk of falling, and vision and vestibular compensation strategies may be inadequate (4.2). From Charcot-Marie-Tooth 1A disease (4.3) we have become aware of the role of spindle group II fibres and of the anatomical feet conditions in balance control. Lastly (5) we touch on the effects of nerve stimulation onto cortical and spinal excitability, which may participate in plasticity processes, and on exercise interventions to reduce the impact of neuropathy.

Diabetes Mellitus-Related Dysfunction of the Motor System

Although motor deficits in humans with diabetic neuropathy have been extensively researched, its effect on the motor system is thought to be lesser than that on the sensory system. Therefore, motor deficits are considered to be only due to sensory and muscle impairment. However, recent clinical and experimental studies have revealed that the brain and spinal cord, which are involved in the motor control of voluntary movement, are also affected by diabetes. This review focuses on the most important systems for voluntary motor control, mainly the cortico-muscular pathways, such as corticospinal tract and spinal motor neuron abnormalities. Specifically, axonal damage characterized by the proximodistal phenotype occurs in the corticospinal tract and motor neurons with long axons, and the transmission of motor commands from the brain to the muscles is impaired. These findings provide a new perspective to explain motor deficits in humans with diabetes. Finally, pharmacological and non-pharmacological treatment strategies for these disorders are presented.

Neuropathic damage in the diabetic eye: clinical implications

In recent years, emerging evidence support that the eye is target of diabetes neuropathy. There are two components of the eye that are mainly involved in the neurodegenerative process induced by diabetes: the retina and the cornea. The study of functional and structural changes in these components of the eye will provide useful information to identify subjects with diabetes at risk of diabetic peripheral neuropathy and dementia. In this review the state of the art regarding the evidence and clinical implications of this emerging concept will be provided. In addition, the relationship between retinal and corneal neurodegeneration with peripheral neuropathy and cognitive decline will be analyzed. Finally, the scientific gaps than need to be covered and will be critically examined.

The proteasome as a druggable target with multiple therapeutic potentialities: Cutting and non-cutting edges

Ubiquitin Proteasome System (UPS) is an adaptable and finely tuned system that sustains proteostasis network under a large variety of physiopathological conditions. Its dysregulation is often associated with the onset and progression of human diseases; hence, UPS modulation has emerged as a promising new avenue for the development of treatments of several relevant pathologies, such as cancer and neurodegeneration. The clinical interest in proteasome inhibition has considerably increased after the FDA approval in 2003 of bortezomib for relapsed/refractory multiple myeloma, which is now used in the front-line setting. Thereafter, two other proteasome inhibitors (carfilzomib and ixazomib), designed to overcome resistance to bortezomib, have been approved for treatment-experienced patients, and a variety of novel inhibitors are currently under preclinical and clinical investigation not only for haematological malignancies but also for solid tumours. However, since UPS collapse leads to toxic misfolded proteins accumulation, proteasome is attracting even more interest as a target for the care of neurodegenerative diseases, which are sustained by UPS impairment. Thus, conceptually, proteasome activation represents an innovative and largely unexplored target for drug development. According to a multidisciplinary approach, spanning from chemistry, biochemistry, molecular biology to pharmacology, this review will summarize the most recent available literature regarding different aspects of proteasome biology, focusing on structure, function and regulation of proteasome in physiological and pathological processes, mostly cancer and neurodegenerative diseases, connecting biochemical features and clinical studies of proteasome targeting drugs.

Thinning of Macular Neuroretinal Layers Contributes to Sleep Disorder in Patients With Type 2 Diabetes Without Clinical Evidences of Neuropathy and Retinopathy

Aims: To investigate the impact of thinning at individual grids of macular neuroretinal layers, clinical factors, and inadequate light exposure on the specific components of sleep disorder in patients with type 2 diabetes. Methods: One hundred twenty-four patients with type 2 diabetes without clinical evidences of diabetic retinopathy and neuropathy (HbA1c: 8.3%, diabetes duration; 8.7 years) and 54 age- and sex-matched control subjects (HbA1c: 5.6%) underwent detailed clinical, neurological, and ophthalmological examinations. The sleep disorder was assessed by the Pittsburgh Sleep Quality Index Japanese Version (PSQI-J). The temporal structures of daily life were assessed by the Munich Chronotype Questionnaire Japanese Version. The thickness at nine grids defined by the Early Treatment Diabetic Retinopathy Study of nine macular neuroretinal layers was determined by swept-source optical coherence tomography and OCT-Explorer. The associations between the individual components of sleep disorders and the thickness at each grid of macular neuroretinal layers, clinical factors, or the temporal structures of daily life were examined. Results: The prevalence of the sleep disorder, global score, and four individual PSQI-J scores in patients with type 2 diabetes were higher than control subjects. The thickness of two and five grids of two inner retinal layers and four to seven grids of four outer retinal layers in patients with type 2 diabetes was thinner than those in control subjects. The thickness at one to eight grids of four outer retinal layers in type 2 diabetic patients was inversely associated with global score and five individual scores of sleep disorder. The thinning at one to two grids of the inner plexiform layer was related to three high individual scores of sleep disorder. The inappropriate light exposure was associated with the sleep disorder and altered macular neuroretinal layers. The high HbA1c and LDL-cholesterol levels were related to the high global score and two individual scores of sleep disorder, respectively. Conclusion: In patients with type 2 diabetes, the thinning at grids of the inner plexiform layer and outer retinal layers was associated with the high scores of specific components of the sleep disorder. The sleep disorder was also related to hyperglycemia, dyslipidemia, and inappropriate light exposure.