The role of tryptophan degradation in the association between inflammatory markers and depressive symptoms in chronic dialysis patients

Biological, Psychological, and Social Determinants of Depression: A Review of Recent Literature

Depression is one of the leading causes of disability, and, if left unmanaged, it can increase the risk for suicide. The evidence base on the determinants of depression is fragmented, which makes the interpretation of the results across studies difficult. The objective of this study is to conduct a thorough synthesis of the literature assessing the biological, psychological, and social determinants of depression in order to piece together the puzzle of the key factors that are related to this condition. Titles and abstracts published between 2017 and 2020 were identified in PubMed, as well as Medline, Scopus, and PsycInfo. Key words relating to biological, social, and psychological determinants as well as depression were applied to the databases, and the screening and data charting of the documents took place. We included 470 documents in this literature review. The findings showed that there are a plethora of risk and protective factors (relating to biological, psychological, and social determinants) that are related to depression; these determinants are interlinked and influence depression outcomes through a web of causation. In this paper, we describe and present the vast, fragmented, and complex literature related to this topic. This review may be used to guide practice, public health efforts, policy, and research related to mental health and, specifically, depression.

Tryptophan levels associate with incident cardiovascular disease in chronic kidney disease

BACKGROUND

Non-traditional risk factors like inflammation and oxidative stress play an essential role in the increased cardiovascular disease (CVD) risk prevalent in chronic kidney disease (CKD). Tryptophan catabolism by the kynurenine pathway (KP) is linked to systemic inflammation and CVD in the general and dialysis population. However, the relationship of KP to incident CVD in the CKD population is unknown.

METHODS

We measured tryptophan metabolites using targeted mass spectrometry in 92 patients with a history of CVD (old CVD); 46 patients with no history of CVD and new CVD during follow-up (no CVD); and 46 patients with no CVD history who developed CVD in the median follow-up period of 2 years (incident CVD).

RESULTS

The three groups are well-matched in age, gender, race, diabetes status and CKD stage, and only differed in total cholesterol and proteinuria. Tryptophan and kynurenine levels significantly decreased in patients with 'Incident CVD' compared with the no CVD or old CVD groups (P = 5.2E-7; P = 0.003 respectively). Kynurenic acid, 3-hydroxykynurenine and kynurenine are all increased with worsening CKD stage (P < 0.05). An increase in tryptophan levels at baseline was associated with 0.32-fold lower odds of incident CVD (P = 0.000014) compared with the no CVD group even after adjustment for classic CVD risk factors. Addition of tryptophan and kynurenine levels to the receiver operating curve constructed from discriminant analysis predicting incident CVD using baseline clinical variables increased the area under the curve from 0.76 to 0.82 (P = 0.04).

CONCLUSIONS

In summary, our study demonstrates that low tryptophan levels are associated with incident CVD in CKD.

Interleukin-6 is associated with tryptophan metabolism and signs of depression in individuals with carbohydrate malabsorption

The aim of the present study was to investigate possible associations between interleukin-6 (IL-6), interferon-gamma (INF-γ), tumor necrosis factor-alpha (TNF-α), lactoferrin and lipopolysaccharide binding protein (LBP) with TRP metabolism and signs of depression in a large cohort of outpatients referred for carbohydrate malabsorption testing. Serum concentrations of IL-6, INF-γ, TNF-α, lactoferrin, LBP, tryptophan (TRP), kynurenine (KYN) and kynuric acid were determined in 250 adults referred for lactose and fructose malabsorption testing. All participants filled out the Beck Depression Inventory (BDI). Serum IL-6 levels were positively correlated with the BDI score (p = 0.001, ρ = 0.205) and indicators of TRP metabolism (KYN/TRP ratio, KYN) (P-values < 0.05, ρ = 0.176 and 0.136). Ninety-five individuals with a BDI score > 13 showed significantly higher IL-6 serum levels (1.7 [1.0 - 2.8] vs. 1.1 [0.8 - 1.7] pg/mL, p < 0.001) compared to 115 individuals with a BDI score ≤ 13. LBP showed a positive correlation with the KYN/TRP ratio (p = 0.005, ρ = 0.177). IL-6 and LBP were associated with indicators of TRP metabolism. IL-6 was found to be linked to signs of depression. Individuals with the presence of depressive symptoms showed higher serum IL-6 levels compared to individuals without depressive symptoms.

A Systematic Review and Meta-Analysis of Depression and Protein-Energy Wasting in Kidney Disease

Introduction

Depression comorbid with chronic disease may be mediated by inflammation. We sought to characterize relationships between inflammatory biomarkers and depressive symptoms in patients with chronic kidney disease and end-stage kidney disease.

Methods

A systematic literature search was conducted by 2 authors up to March 19, 2019, for studies of patients with chronic kidney disease or end-stage kidney disease evaluating circulating inflammatory biomarkers associated with depression of chronic disease: albumin, C-reactive protein (CRP), high-sensitivity CRP, interleukin-6 (IL-6), tumor necrosis factor-α, and interleukin-1. Standardized mean differences in biomarkers between individuals with and without depression were computed and analyzed using mixed effects models. Correlations between biomarkers and the severity of depressive symptoms were computed.

Results

Thirty-four studies (5652 participants) compared biomarkers between depressed and nondepressed individuals. Individuals with depression had lower albumin levels (standardized mean difference, −0.37; 95% confidence interval [CI], −0.61 to −0.13), higher CRP levels (standardized mean difference, 0.76; 95% CI, 0.16–1.37), and higher IL-6 levels (standardized mean difference, 0.42; 95% CI, 0.21–0.63). Studies were heterogeneous for albumin, CRP, high-sensitivity CRP, and tumor necrosis factor-α. Twenty-three studies (3047 participants) investigated correlations between biomarkers and depressive symptoms. The severity of depressive symptoms correlated with albumin (Z = −0.25; 95% CI, −0.36 to −0.14), high-sensitivity CRP (Z = 0.28; 95% CI, 0.13–0.43), and IL-6 (Z = 0.34; 95% CI, 0.18–0.49). There was heterogeneity across studies of IL-6. Only 6 studies (321 participants) investigated the effect of antidepressant treatment on inflammatory biomarkers, which was insufficient to combine in meta-analysis.

Conclusion

Lower albumin and higher IL-6 were associated with both the presence and severity of depression, CRP with the presence of depression, and high-sensitivity CRP with the severity of depressive symptoms. The effect of interventions to lower inflammation in patients with kidney disease and depression deserves investigation.