Researchers have come a long way in understanding the link between acute inflammation and treatment-resistant depression, but more work needs to be done, according to Mark Hyman Rapaport, MD.
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“Inflammation has been a hot topic in the past decade, both because of its impact in medical disorders and in psychiatric disorders,” Dr. Rapaport, CEO of the Huntsman Mental Health Institute in Salt Lake City, Utah, said during an annual psychopharmacology update held by the Nevada Psychiatric Association. “We run into difficulty with chronic inflammation, which we see with rheumatic disorders, and when we think of metabolic syndrome and obesity.”
The immune system helps to control energy regulation and neuroendocrine function in acute inflammation and chronic inflammatory diseases. “We see a variety of effects on the central nervous system or liver function or on homeostasis of the body,” said Dr. Rapaport, who also chairs the department of psychiatry at the University of Utah, also in Salt Lake City. “These are all normal and necessary to channel energy to the immune system in order to fight what’s necessary in acute inflammatory response.”
A chronic state of inflammation can result in prolonged allocation of fuels to the immune system, tissue inflammation, and a chronically aberrant immune reaction, he continued. This can cause depressive symptoms/fatigue, anorexia, malnutrition, muscle wasting, cachectic obesity, insulin resistance, dyslipidemia, increased adipose tissue in the proximity of inflammatory lesion, alterations of steroid hormone axes, elevated sympathetic tone, hypertension, decreased parasympathetic tone, inflammation-related anemia, and osteopenia. “So, chronic inflammation has a lot of long-term sequelae that are detrimental,” he said.
Both physical stress and psychological stress also cause an inflammatory state. After looking at the medical literature, Dr. Rapaport and colleagues began to wonder whether inflammation and immune activation associated with psychiatric disorders are attributable to the stress of acute illness. To find out, they performed a meta-analysis of blood cytokine network alterations in psychiatric patients and evaluated comparisons between schizophrenia, bipolar disorder, and depression. A total of three meta-analyses were performed: one of acute/inpatient studies, one on the impact of acute treatment, and one of outpatient studies. The researchers hypothesized that inflammatory and immune findings in psychiatric illnesses were tied to two distinct etiologies: the acute stress of illness and intrinsic immune dysfunction.
The meta-analyses included 68 studies: 40 involving patients with schizophrenia, 18 involving those with major depressive disorder (MDD) and 10 involving those with bipolar disorder. The researchers found that levels of four cytokines were significantly increased in acutely ill patients with schizophrenia, bipolar mania, and MDD, compared with controls: interleukin-6, tumor necrosis factor–alpha (TNF-alpha), soluble IL-2 receptor (sIL-2R), and IL-1 receptor antagonist (IL-1RA). “There has not been a consistent blood panel used across studies, be it within a disorder itself like depression, or across disorders,” Dr. Rapaport noted. “This is a challenge that we face in looking at these data.”
Following treatment of acute illness, IL-6 levels significantly decreased in schizophrenia and MDD, but no significant changes in TNF-alpha levels were observed in patients with schizophrenia or MDD. In addition, sIL-2R levels increase in schizophrenia but remained unchanged in bipolar and MDD, while IL-1RA levels in bipolar mania decreased but remained unchanged in MDD. Meanwhile, assessment of the study’s 24 outpatient studies revealed that levels of IL-6 were significantly increased in outpatients with schizophrenia, euthymic bipolar disorder, and MDD, compared with controls (P < .01 for each). In addition, levels of IL-1 beta and sIL-2R were significantly increased in outpatients with schizophrenia and bipolar disorder.
According to Dr. Rapaport, these meta-analyses suggest that there are likely inflammatory immune findings present in acutely ill patients with MDD, schizophrenia, and bipolar disorder.
“Some of this activation decreases with effective acute treatment of the disorder,” he said. “The data suggest that immune changes are present in a subset of patients with all three disorders.”
“We also need to understand the regulatory role that microglia and astroglia play within the brain,” he said. “We need to identify changes in brain circuitry and function associated with inflammation and other immune changes. We also need to carefully scrutinize publications, understand the assumptions behind the statistics, and carry out more research beyond the protein level.”
He concluded his presentation by calling for research to help clinicians differentiate acute from chronic inflammation. “The study of both is important,” he said. “We need to understand the pathophysiology of immune changes in psychiatric disorders. We need to study both the triggers and pathways to resolution.”
Dr. Rapaport disclosed that he has received research support from the National Institutes of Health, the National Institute of Mental Health, and the National Center for Complementary and Integrative Health.