Autoimmune diseases, in which the body’s immune system begins to attack healthy tissue, have become much more common in recent decades. Some autoimmune problems are related to overproduction of TH17 cells, immune cells that produce a particular inflammatory protein (interleukin-17), but it is not clear why some people’s bodies start producing too many TH17 cells. Three studies published in the journal Nature in 2013 suggest that salt may play a role. They were recently summarized in Scientific American.
In the first study, researchers developed a model of how TH17 cells are controlled. In the second, they observed how immune cells are produced over a period of several days. The researchers noticed that a protein called serum glucocorticoid kinase 1 (SGK1), which is known to regulate salt in cells, seemed to act as a signal for TH17 production. Mouse cells in high-salt environments had more SGK1 and produced more TH17. The third study confirmed the connection with salt using both mouse cells and human cells.
While mice with multiple sclerosis (an autoimmune disease) worsen on a high-salt diet, it is not clear that salt in the diet is related to TH17 production. It is also not clear that slowing TH17 production is the answer to autoimmune diseases since autoimmunity differs across patients and disorders. However, in any event, low-salt diets are recommended for general health concerns, such as blood pressure.
Research has previously shown a link between stress, inflammation, and mood diorders. Anti-inflammatory treatments are now being explored for depression. In an abstract presented at the 2013 meeting of the Society of Biological Psychiatry, Nadia Alvi et al. reported that the commonly used anti-inflammatory COX-2 inhibitor celecoxib (Celebrex) showed better antidepressant effects than placebo when added to the selective serotonin reuptake inhibitor (SSRI) antidepressant escitalopram (Lexapro) in an 8-week study.
While this research has not yet been peer-reviewed, it can be found in the 2013 convention supplement (9S) to the journal Biological Psychiatry as abstract #661.
Editor’s Note: These data are consistent with an emerging literature that shows there are increases in signs of inflammation in both unipolar and bipolar depression. It remains to be determined whether those patients whose blood shows markers of inflammation (such as increases in C-reactive protein (CRP), interleukins 1 and 6, and TNF-alpha) are more likely to respond to anti-inflammatory treatment than patients in general.
At the 2013 meeting of the International Society for Bipolar Disorders, researcher Barbara Gracious presented evidence that increased levels of high sensitivity c-reactive protein (hsCRP), a marker of inflammation, were associated with an increased risk for developing a full-blown mood episode in 71 youth (average age 13.8) participating in a study called Longitudinal Assessment of Manic Symptoms (LAMS-2). The children were selected for the study because they had manic symptoms that were not severe enough to meet criteria for a diagnosis of bipolar I or II disorder. This research has not yet been published in a peer-reviewed journal, but the abstract can be found in first 2013 supplement of the journal Bipolar Disorders (page 67).
CRP levels are also known to predict cardiovascular disease and Type II diabetes.
Levels of 25-OH vitamin D, TNF?, and IL-6 did not predict a later mood disorder.
Editor’s Note: These data suggest the importance of assessing CRP and other markers in youth who are either prodromal (having early symptoms of a mood disorder) or at high risk because of a family history of a mood disorder.
The next step for clinical research would be to determine what treatment might decrease CRP and whether it would also prevent the development of mood episodes.
There appears to be a link between inflammation and depression. In the journal Neuropsychopharmacology, Cattanes et al. reported in 2013 that compared to controls, depressed patients had significantly higher baseline levels of inflammatory cytokines, less glucocorticoid receptor function, less neuroplasticity, and fewer neuroprotective factors. Certain variables predicted response to treatment, others were seen only in responders, and still others changed in everyone with antidepressant treatment.
Higher baseline levels of inflammatory markers interleukin IB, macrophage inhibitory factor (MIF), and tumor necrosis factor TNF? were each associated with nonresponse to antidepressant treatment, and the three combined accounted for 50% of the variance in response—that is, they were the major predictor of whether a patient responded to treatment.
Levels of other factors changed in only those patients who responded well to antidepressants. The biggest changes were the normalization in levels of the neurotrophic factors BDNF and VEGF.
Several other markers normalized with antidepressant treatment regardless of whether the patients responded to treatment, and these included decreases in cytokines interleukin-IB and MIF and improved glucocorticoid receptor function.
The three different kinds of findings about these biomarkers were observed regardless of what type of antidepressant was used—SSRI versus tricyclic nortriptyline (which blocks norepinephrine reuptake).
Editor’s Note: This study replicates other studies in depression where signs of inflammation have been observed, including increases in inflammatory cytokines, decreases in glucocorticoid receptor function (needed to suppress high levels of the stress hormone cortisol) and lower levels of neuroplasticity and neuroprotection markers. This, however, is one of the first studies to show that levels of these markers at baseline may predict response to antidepressant treatment.
Also novel are the findings that while some high interleukin levels at baseline predicted antidepressant non-response, other ones normalized only in responders, and still others changed with treatment independent of whether the patients’ depression improved. These exciting findings require replication, but suggest the future possibility of personalized medicine, that is, choosing medications based on an individual biochemical marker profile. Eventually direct use of anti-inflammatory agents may be necessary in those with the highest levels of cytokines (predicting non-response to conventional antidepressant treatment). The same types of studies are needed in bipolar depression to determine the relationship between these inflammatory markers and treatment response.
Depression is often associated with increases in markers of inflammation in blood, which include IL-1, IL-6, TNF-alpha, and CRP. Risk factors for increased inflammation include stress, obesity, a diet high in omega-6 fatty acids, sedentary lifestyle, social isolation, low socio-economic status, smoking, and being female. Treatments such as lithium, other mood stabilizers, and antidepressants can all have anti-inflammatory effects.
At the International Congress of Neuropsychopharmacology in 2012, researcher Michael Berk reviewed data on inflammation in depression. Berk shared prospective data that in the general population, people whose levels of CRP fall within the highest third have the highest risk for a new onset of depression over the next 9 years, while those with CRP values in the lowest third (indicating low inflammation) had the least likelihood of becoming depressed.
Drugs with more direct anti-inflammatory properties are beginning to be studied in unipolar depression with some success. In a trial by Abbasi et al. published in the Journal of Affective Disorders in 2012, the anti-inflammatory COX-2 inhibitor celecoxib (Celebrex) when added to the selective serotonin reuptake inhibit (SSRI) sertraline (Zoloft) had better antidepressant effects than the addition of placebo.
Sepaujnia et al. reported in Neuropsychopharmacology in 2012 that an anti-diabetes drug that also has anti-inflammatory properties, pioglitazone (Actos), also beat placebo in depression.
Laan et al. reported in the Journal of Clinical Psychiatry that the same was true of acetylsalicylic acid (ASA or aspirin).
Finally, Berk summarized data that the class of cholesterol-lowering drugs called statins are also able to decrease CRP and improve or prevent depression. Epidemiological data by Pasco et al. published in Psychotherapy and Psychosomatics showed that subjects without depression were less likely to develop a new onset of depression if they were treated with statins compared to those who were not. Stafford et al. reported in the Journal of Clinical Psychiatry in 2010 that patients taking statins had a 79% decreased likelihood of depression at 9 months of follow-up. A third study in Sweden showed that simvastatin, a lipophilic (fat-soluble) drug that can readily enter the brain, decreases the incidence of depression more than some of the non-lipophilic statins.
Moreover, a meta-analysis by O’Neil et al. reported that overall, statins had positive effects on mood.
Editor’s Note: All these data come from studies of unipolar depression, so one must consider how relevant they are to bipolar depression. They may be pertinent, since elevated inflammatory markers have consistently been reported in bipolar depression. However, this cannot be assumed until appropriate studies are performed. (As usual, research in bipolar depression lags far behind that in unipolar depression.)
Preliminary uncontrolled retrospective data from one study did suggest that those treated with lithium plus aspirin did better than those on lithium and no anti-inflammatory.
Thus it may make sense for unipolar and bipolar depressed patients with risk factors for heart disease such as a positive family history of heart disease and elevated cholesterol and triglycerides to discuss with their doctors the possibility of starting statin treatment earlier rather than later. This is because depression itself is a major risk factor for heart disease, so statins might lower risk both by their approved indication of lowering cholesterol and by their apparent ability to help fend off new episodes of depression.
A more complicated issue would be the question of when, if at all, to use primary anti-inflammatory drugs in the adjunctive treatment of unipolar or bipolar depression. Read more
At a recent scientific meeting, researcher Georgia E. Hodes presented evidence that in mice, the immune system may play a role in behaviors that resemble human depression. Repeated social defeat stress (when an intruder mouse is threatened by a larger mouse defending its territory) is often used as a model to study human depression. Animals repeatedly exposed to social defeat stress start to exhibit social avoidance and lose interest in sucrose. Hodes et al. determined that interleukin 6 (IL-6), an inflammatory cytokine, or signaling molecule, secreted into the blood was crucial to these behaviors. When the researchers injected mice with antibodies that block the effects of IL-6, or when they irradiated the mice’s peripheral immune system to prevent the formation of IL-6, the depressive behaviors did not emerge following defeat stress.
Editor’s Note: There are increasing data that immunological and inflammatory mechanisms play a role in human affective disorders, and these preliminary data raise the possibility that blocking some immune mechanisms more directly in humans could be a novel therapeutic approach to explore in the future.
Most drugs used to treat schizophrenia target dopamine and serotonin receptors in the brain. While these are effective in many patients, relapse is common and side effects can be severe. Researchers are looking for ways to target other mechanisms that cause schizophrenia, and inflammation seems to be one of these. There is evidence that a treatment as simple as aspirin, when added to regular treatment with antipsychotics, can improve schizophrenia by targeting inflammation.
In a 2010 study by Laan et al. published in the Journal of Clinical Psychiatry, patients with moderate or severe schizophrenia were given either placebo or aspirin (acetylsalicylic acid, 1000mg) in addition to their regular treatments every day for three months. The patients who received aspirin showed a significant reduction in the positive symptoms of schizophrenia, and to a lesser extent the negative symptoms, compared to those who received placebo. Cognitive function was not improved. The effect size (Cohen d) for the total scale score was 0.5, which is considered a “medium” effect and one that is clinically relevant.
The reductions in symptoms were greater in those patients who had more altered immune function.
Physical activity and light to moderate drinking (as is often associated with the Mediterranean diet) are recommended as ways to reduce risk for heart disease and type 2 diabetes. New research shows that among healthy people, symptoms of depression can counteract the anti-inflammatory benefits of both exercise and light to moderate alcohol consumption.
C-reactive protein (CRP) is a cardiometabolic risk marker. High measures of CRP are a sign of inflammation. Leisure-time physical activity and light to moderate alcohol intake (defined as about half a drink per day for women and one drink per day for men) are associated with lower levels of CRP. Depression is associated with higher levels.
A study by Edward C. Suarez et al. published recently in the journal Brain, Behavior, and Immunity examined 222 nonsmoking men and women aged 18-65 years. These participants were physically healthy and had no history or diagnosis of psychiatric conditions. Participants recorded the amount of alcohol they consumed and the amount of physical activity in which they participated. CRP levels in their fasting blood samples were measured, and they also completed an inventory of depressive symptoms.
Those people who were physically active had lower levels of CRP, but the 4.5% of participants with depressive symptoms did not see any anti-inflammatory benefits from physical activity. Similarly, light to moderate drinking was associated with lower levels of CRP only in men who were not depressed.
Depression did not seem to affect other markers of physical health in this study, such as levels of triglycerides or cholesterol.
Editor’s Note: This study suggests that treating depressive symptoms should be a part of any plan to reduce cardiovascular risk. It seems that depression has effects that go beyond psychological distress and may prevent patients from reaping the benefits of their healthy behaviors. The effect of depression in preventing heart healthy changes in CRP could be one of many factors mediating the high levels of cardiovascular risk in depression. People with depression are twice as likely to have a heart attack than those without depression.
This editor (RM Post) in collaboration with Jacqueline Fleming and Flavio Kapczinski published the article “Neurobiological mechanisms of illness progression in the recurrent affective disorders” in the Journal of Psychiatric Research this year. The article built on several themes about the progression of bipolar illness that had been explored in previous research.
These themes include:
- The likely acceleration of repeated episodes as a function of the number of prior episodes (episode sensitization)
- The increased responsivity of the illness to repeated stressors (stress sensitization)
- The increased behavioral reactivity to repeated use of psychomotor stimulants such as cocaine (stimulant-induced behavioral sensitization)
Not only are these observations well documented in the scientific literature, but recent observations also suggest that each type of sensitization can show cross-sensitization to the other two types. That is, individuals exposed to repeated stressors are more likely both to experience affective illness episodes and to adopt comorbid substance abuse. In a similar way, episodes of an affective disorder and stressors may also be associated with the relapse into drug administration in those who have been abstinent.
In addition to these mechanisms of illness progression in the recurrent affective disorders, the new article reviews the literature showing that the number of affective episodes or the duration of the illness appear to be associated with a variety of other clinical and neurobiological variables.
The number of affective episodes a patient experiences is associated with the degree of cognitive dysfunction present in their bipolar illness, and experiencing more than 4 episodes of unipolar or bipolar depression is a risk factor for dementia in late life. A relative lack of response to most treatments is also correlated with the number of prior episodes, and this holds true for response to naturalistic treatment in general. While most of these data are correlational and the direction of causality cannot be ascertained for certain, it is likely that the number of affective episodes and/or their duration could account for and drive difficulties with treatment and with cognitive function.
If this were the case, one would expect to see a variety of neurobiological correlates with the number of prior episodes or duration of illness, and in the article we summarize those that have been found in unipolar and bipolar disorder. Considerable data indicate that cortical volume and degrees of prefrontal cortical dysfunction can vary as a function of number of prior episodes. There is evidence that increased activity of the amygdala and the nucleus accumbens are also related to episodes or duration of illness. In those with unipolar depression, the volume of the hippocampus is decreased with longer duration of illness. Read more
A Genetic Risk Factor For Bipolar Disorder: The CACNA1C Gene
In an abstract presented at the 5th Biennial Conference of the International Society for Bipolar Disorders, Sophia Frangou reported on the CACNA1C polymorphism, a genetic variation that has been associated with the risk of developing bipolar disorder in several genome-wide association studies that search for links between genes and illnesses. Frangou found that those people with the genetic variation had increased volume in some parts of the brain, including the right hypothalamus and the right amygdala, and decreased volume in others, including the putamen, as well as alterations in the functional connectivity of different cortical areas.
These data may be related to findings that calcium influx may play a role in bipolar disorder. In people with the genetic variation, the risk allele binds to a subunit of the voltage-dependent calcium channel, which modulates the influx of calcium from the outside to the inside the neuron.
Increased amounts of calcium are consistently found in the white cells and platelets of patients with bipolar disorder compared to controls. Moreover, the drug nimodipine, a dihydropyridine L-type calcium channel blocker, is effective in the prevention of manic and depressive episodes in a subgroup of patients, particularly those with cycling patterns that are ultra-rapid (4+ episodes per month) or ultradian (including a mood switch within a 24-hour period 4+ times per month). A large randomized study of patients with bipolar disorder presented by H.R. Chaudhry at the 2010 meeting of the Society of Biological Psychiatry also found that while lithium was associated with a 50% response rate, the combination of lithium and nimodipine was associated with a 73% response rate, again suggesting the additional efficacy of blocking L-type calcium channels.
Immune Abnormalities May Predict Onset of Bipolar Disorder in Children at High Risk
At the 5th Biennial Conference of the International Society for Bipolar Disorders E. Mesman discussed connections between immunity and bipolar disorder. Mesman and colleagues followed offspring of parents with confirmed bipolar disorder for 12 years and compared them to children in the general population. In the children of bipolar parents they found higher levels of immune markers called cytokines (PTX3 and sCD25) in circulating monocytes, a type of white blood cell. In the children of bipolar parents they also found a high inflammatory setpoint in the monocytes. T-effector and T-regulatory cells were also different in the offspring of bipolar parents.
While these findings were present in children who had already become ill with bipolar disorder, they were also present in those who had yet to experience a mood disorder, suggesting that these immune and inflammatory markers may ultimately be an important risk marker for the onset of bipolar disorder.
Editor’s Note: These are among the first studies suggesting that immune and inflammatory abnormalities may precede the onset of bipolar disorder. Many studies have shown that patients with active bipolar disorder show more inflammation, including increases in inflammatory markers interleukin 1 (IL-1), interleukin 6 (IL-6), C reactive protein (CRP), and tumor necrosis factor alpha (TNFa). The new data are of considerable importance not only because inflammation could serve as a marker of illness onset, but also because inflammation could become a potential target for therapeutics (i.e. using anti-inflammatory and immune-suppressing agents to treat bipolar disorder).