Plasma Dipeptidyl Peptidase-4 Activity, a Novel Biomarker or Even a Possible Therapeutic Target for Depression in Type 2 Diabetic Patients: Results from a Cross-Sectional Study in China

Prevalence and risk factors of depression in Chinese patients with type 2 diabetes mellitus: a protocol of systematic review and meta-analysis

BACKGROUND

The prevalence of type 2 diabetes mellitus (T2DM) is growing in China. Depression is a significant complication of T2DM, leading to poor management of T2DM. Thus, early detection and treatment of depression in patients with T2DM are essential and effective. Therefore, we plan to conduct a systematic review and meta-analysis to evaluate the prevalence of depression in Chinese patients with T2DM and explore potential risk factors of depression in T2DM.

METHODS

We will search literatures recorded in MEDLINE, EMBASE, the Cochrane Library, Chinese Biomedical Literature Database (CBM), China National Knowledge Infrastructure (CNKI), Chinese Science and Technology Periodical Database (VIP), and WanFang Database from their inception onwards. We will manually search gray literatures, reference lists of identified studies, relevant websites, and consult experts in this field. We will include population-based, cross-sectional surveys that investigated the prevalence of depression in Chinese patients with T2DM or/and the possible risk factors of depression in T2DM. Two reviewers will screen studies, extract data, and evaluate risk of bias independently. Agency for Healthcare Research and Quality methodology checklist will be used to assess the risk of bias. If feasible, we will conduct random effects meta-analysis of observational data to summarize the pooled prevalence, and use odds ratio for categorical data to explore potential risk factors. Prevalence estimates will be stratified according to age, gender, and other factors. Statistical heterogeneity will be estimated using Cochran's Q and I² index. We will conduct meta-regression to investigate the potential sources of heterogeneity, sensitivity analyses to assess robustness of the synthesized results, and funnel plots and Egger's test to assess publication bias.

DISCUSSION

This systematic review and meta-analysis will provide comprehensive evidence of the prevalence and potential risk factors of depression in Chinese patients with T2DM. We expect to provide evidence for healthcare practitioners and policy makers to pay attention to the mental health of patients with T2DM. Our data will highlight the need and importance of early detection and intervention for depression in patients with T2DM.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42020182979.

Association between plasma dipeptidyl peptidase-4 activity to brain-derived neurotrophic factor ratio and depressive symptoms in middle-aged and older adults with normal glucose tolerance: A cross-sectional study

Objectives: Attenuation of brain-derived neurotrophic factor (BDNF) availability and increased dipeptidyl peptidase-4 (DPP4) activity have both been reported to link to the pathogenesis of depression. The aim of this study was to test the correlation between depressive symptoms and plasma DPP4 activity to BDNF ratio (DBR).Methods: We evaluated DPP4 activity, BDNF, oxidative stress parameters and inflammatory markers and calculated DBR in a cross-sectional sample of 1640 non-diabetic participants.Results: DPP4 activity was negatively related to BDNF in participants with and without depressive symptoms (r= -0.351 and r= -0.404, p<.001). Nitrotyrosine and 8-iso-PGF2a mediated 18.4 and 12.6% of the total effect of DPP4 activity on BDNF, respectively. 8-iso-PGF2a, nitrotyrosine, C-reactive protein, interleukin-6 and PHQ-9 score progressively increased across DBR quartiles. Participants whose DBRs were in the highest quartile had 2.64-fold increased odds (OR = 3.03) of depressive symptoms. The depressive symptoms risk increased more with lower levels of BDNF and higher levels of DPP4 activity (p<.05).Conclusions: Our data suggested inverse correlation between DPP4 activity and BDNF through the oxidative stress mediator. The positive relationship between DBR and depressive symptoms risk raises feasibility of identifying DBR as a novel biological marker or even a possible therapeutic target for depression.

Association of Plasma DPP4 Activity and Brain-Derived Neurotrophic Factor With Moderate to Severe Depressive Symptoms in Patients With Type 2 Diabetes: Results From a Cross-Sectional Study

OBJECTIVE

The objective of this study was to assess the association of plasma dipeptidyl peptidase-4 (DPP4) activity, brain-derived neurotrophic factor (BDNF), and the DPP4/BDNF ratio (DBR) with moderate to severe depressive symptoms in patients with type 2 diabetes mellitus. Increased DPP4 activity and decreased BDNF in peripheral circulation have been implicated in the pathophysiology of depression.

METHODS

We performed a cross-sectional study using data from 1535 patients with type 2 diabetes mellitus. The main outcome measures were plasma DPP4 activity, BDNF levels, DBR, inflammation markers, and oxidative stress parameters. Depressive symptoms were assessed using the nine-item Patient Health Questionnaire.

RESULTS

DPP4 activity and BDNF were negatively correlated in patients with and without moderate to severe depressive symptoms (p < .001). Oxidative stress partially mediated the inverse correlation between DPP4 and BDNF. Nitrotyrosine, 8-iso-PGF2a, interleukin-6, C-reactive protein, and the nine-item Patient Health Questionnaire score increased significantly with rising quartiles of DBR. Patients in the highest quartile of DPP4 activity and DBR and lowest quartile of BDNF more often had moderate to severe depressive symptoms compared with those in the lowest quartile of DPP4 activity and DBR and the highest quartile of BDNF, respectively (p < .05). The likelihood of having moderate to severe depressive symptoms increased more with higher DPP4 activity and lower BDNF.

CONCLUSIONS

Our hypothesis-generating study demonstrates that oxidative stress might partially play a mediating role in the negative relationship between DPP4 activity and BDNF. DBR is positively related to moderate to severe depressive symptoms and thus might be used as a novel biological measure associated with depressive symptoms in patients with type 2 diabetes mellitus.