LOW SERUM BRAIN-DERIVED NEUROTROPHIC FACTOR BUT NOT BRAIN-DERIVED NEUROTROPHIC FACTOR GENE VAL66MET POLYMORPHISM IS ASSOCIATED WITH DIABETIC RETINOPATHY IN CHINESE TYPE 2 DIABETIC PATIENTS

Serum brain-derived neurotrophic factor levels in type 2 diabetes mellitus patients and its association with cognitive impairment: A meta-analysis

OBJECTIVE

To compare the serum levels of brain-derived neurotrophic factor (BDNF) in type 2 diabetes mellitus (T2DM) patients with healthy controls (HC) and evaluate the BDNF levels in T2DM patients with/without cognitive impairment.

METHODS

PubMed, EMBASE, and the Cochrane Library databases were searched for the published English literature on BDNF in T2DM patients from inception to December 2022. The BDNF data in the T2DM and HC groups were extracted, and the study quality was evaluated using the Agency for Healthcare Research and Quality. A meta-analysis of the pooled data was conducted using Review Manager 5.3 and Stata 12.0 software.

RESULTS

A total of 18 English articles fulfilled with inclusion criteria. The standard mean difference of the serum BDNF level was significantly lower in T2DM than that in the HC group (SMD: -2.04, z = 11.19, P <0.001). Besides, T2DM cognitive impairment group had a slightly lower serum BDNF level compared to the non-cognitive impairment group (SMD: -2.59, z = 1.87, P = 0.06).

CONCLUSION

BDNF might be involved in the neuropathophysiology of cerebral damage in T2DM, especially cognitive impairment in T2DM.

Elucidating glial responses to products of diabetes-associated systemic dyshomeostasis

Diabetic retinopathy (DR) is a leading cause of blindness in working age adults. DR has non-proliferative stages, characterized in part by retinal neuroinflammation and ischemia, and proliferative stages, characterized by retinal angiogenesis. Several systemic factors, including poor glycemic control, hypertension, and hyperlipidemia, increase the risk of DR progression to vision-threatening stages. Identification of cellular or molecular targets in early DR events could allow more prompt interventions pre-empting DR progression to vision-threatening stages. Glia mediate homeostasis and repair. They contribute to immune surveillance and defense, cytokine and growth factor production and secretion, ion and neurotransmitter balance, neuroprotection, and, potentially, regeneration. Therefore, it is likely that glia orchestrate events throughout the development and progression of retinopathy. Understanding glial responses to products of diabetes-associated systemic dyshomeostasis may reveal novel insights into the pathophysiology of DR and guide the development of novel therapies for this potentially blinding condition. In this article, first, we review normal glial functions and their putative roles in the development of DR. We then describe glial transcriptome alterations in response to systemic circulating factors that are upregulated in patients with diabetes and diabetes-related comorbidities; namely glucose in hyperglycemia, angiotensin II in hypertension, and the free fatty acid palmitic acid in hyperlipidemia. Finally, we discuss potential benefits and challenges associated with studying glia as targets of DR therapeutic interventions. In vitro stimulation of glia with glucose, angiotensin II and palmitic acid suggests that: 1) astrocytes may be more responsive than other glia to these products of systemic dyshomeostasis; 2) the effects of hyperglycemia on glia are likely to be largely osmotic; 3) fatty acid accumulation may compound DR pathophysiology by promoting predominantly proinflammatory and proangiogenic transcriptional alterations of macro and microglia; and 4) cell-targeted therapies may offer safer and more effective avenues for DR treatment as they may circumvent the complication of pleiotropism in retinal cell responses. Although several molecules previously implicated in DR pathophysiology are validated in this review, some less explored molecules emerge as potential therapeutic targets. Whereas much is known regarding glial cell activation, future studies characterizing the role of glia in DR and how their activation is regulated and sustained (independently or as part of retinal cell networks) may help elucidate mechanisms of DR pathogenesis and identify novel drug targets for this blinding disease.

Brain-derived neurotrophic factor in diabetes mellitus: A systematic review and meta-analysis

BACKGROUND

Brain-derived neurotrophic factor (BDNF) is a neurotrophic factor expressed in several tissues, including the brain, gut, and pancreas. Activation of the BDNF/TrkB/CREB reduces hepatic gluconeogenesis, induces hepatic insulin signal transduction, and protects against pancreatic beta-cell loss in diabetes mellitus (DM). Several studies have investigated the possible association between BDNF and DM and its complications, but the results have been conflicting.

AIM

In the present study, we aimed at systematically reviewing the literature on the serum and plasma levels of BDNF in DM and its subgroups such as T2DM, DM patients with depression, and patients with retinopathy.

METHODS

A comprehensive search was conducted in PubMed, Scopus, and Web of Science. We identified 28 eligible studies and calculated the standardized mean difference (SMD) of outcomes as an effect measure.

RESULTS

The meta-analysis included 2734 patients with DM and 6004 controls. Serum BDNF levels were significantly lower in patients with DM vs. controls (SMD = -1.00, P<0.001). Plasma BDNF levels were not different in patients with DM compared with controls. When conducting subgroup analysis, serum BDNF levels were lower among patients with T2DM (SMD = -1.26, P<0.001), DM and depression (SMD = -1.69, P<0.001), and patients with diabetic retinopathy (DR) vs. controls (SMD = -1.03, P = 0.01).

CONCLUSIONS

Serum BDNF levels were lower in patients with DM, T2DM, DM with depression, and DM and DR than the controls. Our findings are in line with the hypothesis that decreased BDNF levels might impair glucose metabolism and contribute to the pathogenesis of DM and its complications.

Comparison of brain-derived neurotrophic factor among subtypes of exudative age-related macular degeneration

PURPOSE

To compare the levels of brain-derived neurotrophic factor (BDNF) in serum and aqueous humor (AH) in eyes with typical neovascular age-related macular degeneration (tAMD), polypoidal choroidal vasculopathy (PCV), and retinal angiomatous proliferation (RAP).

METHODS

This prospective study included 20 patients with tAMD, 20 patients with PCV, 20 patients with RAP, and 20 healthy controls. BDNF levels in the serum and AH were assessed using enzyme-linked immunosorbent assay.

RESULTS

Serum and AH BDNF levels were significantly lower in the age-related macular degeneration groups (tAMD, PCV, and RAP) than in the control group (p < 0.05). There was no significant difference in the mean BDNF levels in the serum and AH among the different nAMD subtypes (p = 0.538).

CONCLUSIONS

We confirmed that serum and AH BDNF levels were independent of the nAMD subtype.

Serum and aqueous humor levels of brain-derived neurotrophic factor in patients with primary open-angle glaucoma and normal-tension glaucoma

PURPOSE

This study was designed to compare the levels of brain-derived neurotrophic factor (BDNF) in the serum and aqueous humor (AH) of patients with primary open-angle glaucoma (POAG) and normal-tension glaucoma (NTG).

METHODS

This prospective, observational study consists of 30 patients with POAG, 30 patients with NTG, and 30 healthy controls. The serum and AH BDNF levels were assessed using an enzyme-linked immunosorbent assay.

RESULTS

BDNF levels in serum and AH were markedly lower in the glaucoma groups (POAG and NTG) than in the control group (p < 0.05). When comparing the NTG and POAG groups, the average serum BDNF level was significantly lower in the NTG group than in the POAG group (p < 0.05). The difference in the mean BDNF levels in AH between the POAG and NTG groups was not statistically significant. (p = 0.538).

CONCLUSION

We confirmed that serum BDNF levels were lower in patients with NTG than in those with POAG. BDNF could be a causative systemic biomarker in NTG.

RELATIONSHIP BETWEEN STAGES OF DIABETIC RETINOPATHY AND LEVELS OF BRAIN-DERIVED NEUROTROPHIC FACTOR IN AQUEOUS HUMOR AND SERUM

PURPOSE

The aim of the study was to determine aqueous humor and serum levels of brain-derived neurotrophic factor (BDNF) in diabetic patients with and without retinopathy.

METHODS

The study included diabetic patients with or without retinopathy, who had an indication for cataract surgery. The study groups were diabetic patients without retinopathy (Group 2), with nonproliferative diabetic retinopathy (Group 3), and with proliferative retinopathy (Group 4). To quantitatively determine the amount of BDNF in samples, the RayBio Human BDNF ELISA kit (Norcross, GA), based on an enzyme-labeled immunosorbent assay was used.

RESULTS

The median serum BDNF levels were significantly lower in all the study groups than in the control group (P values: 0.038 Group 2, 0.02 Group 3, and 0.002 Group 4). Serum BDNF was lower in Group 4 than in Group 3 (P = 0.030), and in Group 3 than in Group 2 (P = 0.04). The median aqueous humor BDNF levels were significantly decreased in all groups (P values: 0.047 Group 2, 0.021 Group 3, and 0.007 Group 4). There was no significant difference between Groups 2, 3, and 4 (P = 0.214).

CONCLUSION

The serum and aqueous humor BDNF levels decreased in patients with diabetes mellitus (DM) before the emergence of clinical signs of retinopathy.

Brain-derived neurotrophic factor in non-proliferative diabetic retinopathy with diabetic macular edema

PURPOSE

To investigate aqueous humor (AH) and serum levels of brain-derived neurotrophic factor (BDNF) in non-proliferative diabetic retinopathy (NPDR) patients with diabetic macular edema (DME).

METHODS

The prospective study consists of 20 patients with DME NPDR, 20 patients with no-DME NPDR, and 20 healthy control subjects. Serum and AH samples were obtained during cataract surgery and intravitreal injection. Serum and AH levels of BDNF were measured by enzyme-linked immunosorbent assay.

RESULTS

The mean serum levels of BDNF were lower in both NPDR groups compared to the control group (DME NPDR group, p = 0.015; no-DME NPDR group, p = 0.024). Furthermore, the mean serum level of BDNF was lower in the DME NPDR group compared to the no-DME NPDR group (p = 0.041). The mean AH levels of BDNF were significantly reduced in both NPDR groups compared to the control group (DME NPDR group, p < 0.001; no-DME NPDR group, p = 0.006). Further, the mean AH level of BDNF was significantly lower in the DME NPDR group compared to the no-DME NPDR group (p = 0.037).

CONCLUSION

Serum and AH levels of BDNF were reduced in NPDR patients with DME than without DME.

Placental CpG Methylation of Inflammation, Angiogenic, and Neurotrophic Genes and Retinopathy of Prematurity

Purpose

Extremely preterm infants are at increased risk for retinopathy of prematurity (ROP). We previously identified several inflammatory proteins that were expressed early in life and are associated with an increased risk of ROP and several angiogenic and neurotrophic growth factors in the neonatal systemic circulation that are associated with a lower risk of ROP. In this paper, we report the results of a set of analyses designed to test the hypothesis that placental CpG methylation levels of 12 inflammation-, angiogenic-, and neurotrophic-associated genes predict the occurrence of prethreshold ROP in extremely preterm newborns.

Methods

We used placental CpG methylation data from 395 newborns from the Extremely Low Gestational Age Newborns study.

Results

Multivariable regression models revealed that placental DNA methylation of 16 CpG sites representing 8 genes were associated with prethreshold ROP. Specifically, CpG methylation in the serum amyloid A SAA1 and SAA2, brain-derived neurotrophic factor (BDNF), myeloperoxidase (MPO), C-reactive protein (CRP), angiopoietin 1 (ANGPT1), and tumor necrosis factor receptor superfamily member 1B (TNFRSF1B) genes was associated with a lower risk of prethreshold ROP. Conversely, CpG methylation at three probes within tumor necrosis factor receptor superfamily member 1A (TNFRSF1A) and in two alternative probes within the BDNF and ANGPT1 genes was associated with an increased risk of ROP.

Conclusions

CpG methylation may be a useful marker for improving ROP prediction, opening the opportunity for early intervention to lessen disease severity.

Brain-Derived Neurotrophic Factor in Patients With Age-Related Macular Degeneration and Its Correlation With Retinal Layer Thicknesses

Purpose

To determine brain-derived neurotrophic factor (BDNF) levels in serum and aqueous humor (AH) and to assess the relationship between BDNF levels and retinal layer thicknesses in age-related macular degeneration (AMD).

Methods

A total of 48 AMD patients (AMD group) that was composed of twenty-three nonexudative and 25 exudative patients and 26 control subjects (control group) were included in the study. Serum and AH BDNF levels were assessed by ELISA method. Retinal layer thicknesses were calculated by segmentation analysis of optical coherence tomography.

Results

The mean BDNF levels in AH were found to be significantly lower in both the nonexudative and exudative AMD groups than in the control group (P = 0.003 and P < 0.001, respectively). Optical coherence tomography segmentation analysis revealed that the total average retina pigment epithelium thickness was statistically significantly thinner in the nonexudative AMD group compared with the exudative AMD and control groups (P = 0.001 and P = 0.040, respectively). The total average outer nuclear layer (ONL) thicknesses of nonexudative and exudative AMD cases were reduced compared to control group; however, the decrement was statistically significant only in the nonexudative AMD group (P = 0.009). In the correlation analysis of BDNF levels with retinal layer thicknesses, statistically significant correlations exist between BDNF levels of AH with ONL thicknesses in cases of AMD and with retina pigment epithelium thicknesses in the nonexudative AMD group.

Conclusions

BDNF concentrations in AH decreased in the AMD group and this decrease correlates with outer retinal layer thicknesses. Low BDNF levels detected in the AMD group may be insufficient to protect the photoreceptors, resulting in thinning of ONL.

Molecular Mechanisms Mediating Diabetic Retinal Neurodegeneration: Potential Research Avenues and Therapeutic Targets

Diabetic retinopathy (DR) is a devastating complication of diabetes with a prevalence rate of 35%, and no effective treatment options. Since the most visible clinical features of DR are microvascular irregularities, therapeutic interventions often attempt to reduce microvascular injury, but only after permanent retinal damage has ensued. However, recent data suggests that diabetes initially affects retinal neurons, leading to neurodegeneration as an early occurrence in DR, before onset of the more noticeable vascular abnormalities. In this review, we delineate the sequence of initiating events leading to retinal degeneration in DR, considering neuronal dysfunction as a primary event. Key molecular mechanisms and potential biomarkers associated with retinal neuronal degeneration in diabetes are discussed. In addition to glial reactivity and inflammation in the diabetic retina, the contribution of neurotrophic factors, cell adhesion molecules, apoptosis markers, and G protein signaling to neurodegenerative pathways warrants further investigation. These studies could complement recent developments in innovative treatment strategies for diabetic retinopathy, such as targeting retinal neuroprotection, promoting neuronal regeneration, and attempts to re-program other retinal cell types into functional neurons. Indeed, several ongoing clinical trials are currently attempting treatment of retinal neurodegeneration by means of such novel therapeutic avenues. The aim of this article is to highlight the crucial role of neurodegeneration in early retinopathy progression, and to review the molecular basis of neuronal dysfunction as a first step toward developing early therapeutic interventions that can prevent permanent retinal damage in diabetes. ClinicalTrials.gov: NCT02471651, NCT01492400.

Prognostic Utility of Fatty Acid-Binding Protein 4 in Patients with Type 2 Diabetes and Acute Ischemic Stroke

The role of fatty acid-binding proteins (FABPs) in atherosclerosis has been investigated. The aim of this study was to verify the hypothesis that higher levels of serum fatty acid-binding protein 4 (FABP4) could be a prognostic factor in Chinese patients with type 2 diabetes (T2DM) and acute ischemic stroke (AIS). From September 2015 to August 2016, consecutive first-ever AIS patients combined with T2DM were included in this study. FABP4, NIH stroke scale (NIHSS), and conventional risk factors were evaluated to determine their value to predict functional outcomes within 3 months. Multivariate analyses were performed using logistic regression models. We measured FABP4 in 329 patients. The median age of patients included in this study was 63 (IQR, 56-72) years and 45.9% were women. FABP4 serum levels were obtained at a median of 8.5 h (IQR, 4.0-14.0 h) after the stroke onset with a median value of 21.4 ng/ml (IQR, 15.6-28.2 ng/ml). In multivariable models, FABP4 remained an independent stroke severity predictor with an adjusted OR of 1.05 (95% CI, 1.02-1.09). In multivariate models comparing the third (odd ratio (OR), 2.25; 95% confidence interval (CI), 1.59-3.54) and fourth quartiles (OR, 3.75; 95% CI, 2.48-5.03) against the first quartile of the FABP4, levels of FABP4 were associated with poor functional outcome. At 3 months, 38 patients (11.6%; 95%CI, 8.1-15.0%) had died. The mortality distribution across the FABP4 quartiles ranged between 3.7% (first quartile) and 20.7% (fourth quartile). Elevation of FABP4 is associated with an increased risk of death and poor functional outcome events in patients with type 2 diabetes and acute ischemic stroke and is independent of other established clinical risk predictors and biomarkers.