Inflammation Tied to Increased Risk for Psychiatric Illness

New research provides more evidence that inflammation may contribute to the development of psychiatric disorders and suggests that measuring certain inflammatory biomarkers may aid in the early identification of individuals at high risk.

Using large-scale datasets, researchers found that elevated levels of certain inflammatory biomarkers, particularly leukocytes, haptoglobin, and C-reactive protein (CRP), and lower levels of anti-inflammatory immunoglobulin G (IgG) were associated with an increased risk for psychiatric disorders. 

Individuals with psychiatric disorders had persistently higher levels of leukocytes and haptoglobin, as well as persistently lower levels of IgG, than controls during the 30 years before diagnosis, which suggest “long-term processes and may aid in the identification of individuals at high risk,” the researchers wrote. 

In addition, a higher level of leukocytes was consistently associated with increased odds of depression across different methods of mendelian randomization (MR) analysis, “indicating a possible causal relationship between leukocytes and depression,” they said. 

The study, with first author Yu Zeng, MSc, with the Mental Health Center and West China Biomedical Big Data Center, West China Hospital, Sichuan University, Chengdu, China, was published online on August 21 in JAMA Psychiatry. 

Inflammatory Phenotype

Individuals with psychiatric disorders have been found to have elevated levels of inflammatory biomarkers, but prospective evidence is limited regarding the association between inflammatory biomarkers and subsequent psychiatric disorders risk. 

To investigate further, Zeng and colleagues employed a “triangulation” approach consisting of an exploration dataset of 585,279 adults in the Swedish AMORIS cohort with no prior psychiatric diagnoses and a measurement of at least one inflammatory biomarker, a validation dataset of 485,620 UK Biobank participants, and genetic and MR analyses using genome-wide association study summary statistics.

In the AMORIS cohort, individuals with a higher than median level of leukocytes (hazard ratio [HR], 1.11), haptoglobin (HR, 1.13), or CRP (HR, 1.02) had an elevated risk for any psychiatric disorder. In contrast, there was an inverse association for IgG level (HR, 0.92). 

“The estimates were comparable for depression, anxiety, and stress-related disorders, specifically, and these results were largely validated in the UK Biobank,” the authors reported. 

In trajectory analyses, compared with controls, individuals with psychiatric disorders had higher leukocyte and haptoglobin levels and lower IgG up to three decades before being diagnosed. 

The MR analysis suggested a possible causal relationship between leukocytes and depression. 

The underlying mechanisms for the associations of serum leukocytes, haptoglobin, CRP, and IgG with psychiatry disorders remain unclear.

“Possible explanations mainly include blood-brain barrier disruption, microglia activation, neurotransmission impairment, and other interactions between inflammations and neuropathology,” the researchers wrote. 

A related paper published online on August 21 in JAMA Psychiatry looked at trajectories of inflammation in childhood and risk for mental and cardiometabolic disorders in adulthood. 

This longitudinal cohort study found that having persistently raised levels of inflammation as measured by CRP throughout childhood and adolescence, peaking at age 9 years, were associated with an increased risk of developing psychosis disorder, severe depression, and higher levels of insulin resistance.

Support for Precision Psychiatry

This study is “another strong indication that inflammation plays a role in depression,” Andrew H. Miller, MD, professor of psychiatry and behavioral sciences and director of the behavioral immunology program, Emory University School of Medicine, Atlanta, Georgia, who wasn’t involved in the study, told Medscape Medical News. 

“The work adds to the mounting data that there exists an inflammatory phenotype of depression that may uniquely respond to treatment and may have a unique trajectory,” Miller said. 

“Eventually the field will want to embrace this novel phenotype and better understand how to recognize it and treat it. This is our entrée into precision psychiatry where we identify the right treatment for the right patient at the right time based on an understanding of the underlying cause of their illness,” Miller added. 

Also weighing in, Alexander B. Niculescu III, MD, PhD, professor of psychiatry and medical neuroscience, Indiana University School of Medicine, Indianapolis, cautioned that these biomarkers are “very nonspecific and are likely related to these subjects that go on to develop psychiatric disorders having more stressful, adverse life trajectories.”

“There are better, more specific blood biomarkers for psychiatric disorders already available,” Niculescu told Medscape Medical News.

His group recently reported that a panel of blood-based biomarkers can distinguish between depression and bipolar disorder, predict a person’s future risk for these disorders, and inform more tailored medication choices. 

Notably, they observed a strong circadian clock gene component to mood disorders, which helps explain why some patients’ conditions become worse with seasonal changes. It also explains the sleep alterations that occur among patients with mood disorders, they said.

This study had no commercial funding. Zeng and Miller had no relevant disclosures. Niculescu is a cofounder of MindX Sciences and is listed as inventor on a patent application filed by Indiana University.