Inflammatory Biomarkers, Cognitive Functioning, and Brain Imaging Abnormalities in Bipolar Disorder: A Systematic Review

Cerebrospinal Fluid Biomarkers of Central Nervous System Inflammation Predict Cortical Decline in Bipolar Disorder and Ventricular Enlargement in Healthy Controls

INTRODUCTION

Bipolar disorder has been associated with significant structural brain changes, potentially driven by central nervous system (CNS) inflammation. This study aimed to investigate the relationship between inflammation biomarkers in cerebrospinal fluid (CSF) and longitudinal structural brain changes.

METHODS

We included 29 individuals with bipolar disorder and 34 healthy controls, analyzing three selected inflammation-related biomarkers - interleukin-6 (IL-6), interleukin-8 (IL-8), and chitinase-3-like protein 1 (YKL-40) - in both blood serum and CSF. Structural brain changes were assessed through magnetic resonance imaging at two timepoints, focusing on cortical thickness of the middle temporal cortex and inferior frontal gyrus, as well as ventricular volume.

RESULTS

In healthy controls, baseline CSF levels of YKL-40 predicted ventricular enlargement in both hemispheres. Among individuals with bipolar disorder, higher baseline levels of IL-8 were associated with a decline in cortical thickness in the right and left middle temporal cortex, as well as the right inferior frontal gyrus. No significant associations were observed with serum biomarkers.

CONCLUSIONS

These findings suggest that CSF IL-8 may contribute to cortical decline in bipolar disorder. The lack of association between serum biomarkers and brain changes highlights the specificity of CNS inflammation in these processes. Additionally, the observed link between CSF YKL-40 and ventricular enlargement in healthy controls may indicate a role of CNS inflammation processes in normal brain aging.

INTRODUCTION

Bipolar disorder has been associated with significant structural brain changes, potentially driven by central nervous system (CNS) inflammation. This study aimed to investigate the relationship between inflammation biomarkers in cerebrospinal fluid (CSF) and longitudinal structural brain changes.

METHODS

We included 29 individuals with bipolar disorder and 34 healthy controls, analyzing three selected inflammation-related biomarkers - interleukin-6 (IL-6), interleukin-8 (IL-8), and chitinase-3-like protein 1 (YKL-40) - in both blood serum and CSF. Structural brain changes were assessed through magnetic resonance imaging at two timepoints, focusing on cortical thickness of the middle temporal cortex and inferior frontal gyrus, as well as ventricular volume.

RESULTS

In healthy controls, baseline CSF levels of YKL-40 predicted ventricular enlargement in both hemispheres. Among individuals with bipolar disorder, higher baseline levels of IL-8 were associated with a decline in cortical thickness in the right and left middle temporal cortex, as well as the right inferior frontal gyrus. No significant associations were observed with serum biomarkers.

CONCLUSIONS

These findings suggest that CSF IL-8 may contribute to cortical decline in bipolar disorder. The lack of association between serum biomarkers and brain changes highlights the specificity of CNS inflammation in these processes. Additionally, the observed link between CSF YKL-40 and ventricular enlargement in healthy controls may indicate a role of CNS inflammation processes in normal brain aging.

The role of predominant polarity on cognitive dysfunctions in patients with bipolar disorder

BACKGROUND

Cognitive impairment is frequently observed in bipolar disorder (BD). Previous findings indicated that predominant polarity could have an effect on cognitive deficits. This study aimed to examine the association between predominant polarity and cognitive impairments in BD.

MATERIALS AND METHODS

Euthymic BD patients with manic (MPP, n = 31), depressive (DPP, n = 25), undetermined predominant polarity (UPP, n = 28), and healthy controls (HC, n = 27) participated in the study. A battery of neurocognitive and social cognitive tests was implemented. Neurocognitive domains were identified via principal component analysis.

RESULTS

The MPP group performed worse in the Controlled Oral Word Association Test (COWAT), Reading the Mind in the Eyes Test (RMET), and Hinting Test (HT) compared to the DPP group and reasoning/problem-solving skills compared to the UPP group. Both MPP and UPP groups showed impairments in processing speed compared to HC. Among patient groups, there was no significant difference in working memory, attention, processing speed, verbal, and visual domain scores. The MPP group had poorer scores compared to controls in most of the social cognitive and neurocognitive domains in the study, while the overall cognitive impairment in the DPP group was relatively milder.

CONCLUSIONS

Although our sample size was relatively small, the MPP group yielded more severe cognitive impairment in verbal fluency and social cognition tests compared to DPP. Patients with MPP are particularly vulnerable to cognitive impairment, making them a priority for cognitive enhancement interventions. Future studies should focus on the outcomes of cognitive and pharmacological interventions in these polarity subgroups.

Mendelian randomisation analysis to explore the association between cathepsins and bipolar disorder

INTRODUCTION

Bipolar disorder is a psychiatric condition characterized by the coexistence of depression and mania. Diagnosis of this disorder can be challenging due to limited pathologic and experimental tools. Treatment compliance is often poor due to medication side effects. Although cathepsin is known to play a significant role in diseases such as tumors and osteoporosis, its role in psychiatric disorders is not yet fully understood.

OBJECTIVE

The aim of this study was to investigate the relationship between cathepsin in the blood circulation and bipolar disorder.

METHODS

The causal relationship between cathepsin and different subtypes of bipolar affective disorder was explored using bidirectional Mendelian randomization analysis and multivariate analysis.

RESULTS

It was found that cathepsin H level was a protective factor for type II bipolar disorder. No potential causal relationship was found between cathepsin H and type I bipolar disorder, but cathepsin B changes with the development of type I bipolar disorder. A causal relationship was found between cathepsin H and cerebral dopamine neurotrophic factor.

CONCLUSIONS

In conclusion, cathepsin H may be a diagnostic target for bipolar II disorder and may play a guiding role in clinical diagnosis. Cathepsin H may have an effect on BD through cerebral dopamine neurotrophic factor.