Meta-analysis of cytokine and C-reactive protein levels in high-risk psychosis

SCHRES-08254; No of Pages 8 Schizophrenia Research xxx (xxxx) xxx

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Meta-analysis of cytokine and C-reactive protein levels in highrisk psychosis Sora Park a, Brian J. Miller b,⁎ a b

Medical College of Georgia at Augusta University, Augusta, GA, United States Department of Psychiatry and Health Behavior, Augusta University, Augusta, GA, United States

a r t i c l e

i n f o

Article history: Received 21 December 2018 Received in revised form 14 March 2019 Accepted 16 March 2019 Available online xxxx Keywords: High-risk psychosis Prodrome Schizophrenia Inflammation Cytokine Meta-analysis

a b s t r a c t Objective: Schizophrenia is associated with aberrant blood cytokine and C-reactive protein (CRP) levels. However, less is known about alterations in these markers prior to the onset of psychosis. We performed a meta-analysis of blood cytokines and CRP in subjects at high-risk for psychosis. Method: We identified articles by systematic searches of PubMed, PsycINFO, and Web of Science databases, and the reference lists of identified studies. Eight studies met the inclusion criteria, including seven studies of highrisk psychosis versus controls, and four studies of high-risk subjects who converted to a psychotic disorder versus non-converters. Results: Blood IL-6 levels were significantly higher (SMD = 0.31, 95% CI 0.02–0.59, p = 0.04) and blood IL-1β levels were significantly lower (SMD = −0.66, 95% CI −1.27 to −0.05, p = 0.05) in subjects at high-risk for psychosis versus controls. Between-study heterogeneity was not significant for either IL-1β or IL-6, and there was no evidence of publication bias. There was a non-significant trend for higher blood IL-12 levels in converters versus non-converters (SMD = 0.86, 95% CI −0.06–1.79, p = 0.07). Conclusion: We found limited evidence for blood cytokine and CRP alterations in subjects at high-risk for psychosis. Our findings should be interpreted with caution in light of a small number of studies, cumulative sample size, and heterogeneity of high-risk criteria, but warrant investigation in larger samples. This includes studies of subjects at high-risk of developing psychosis and controls, as well as the potential of inflammation as a predictor of conversion to psychosis. These findings have important potential implications for our understanding of the pathophysiology of schizophrenia. © 2019 Elsevier B.V. All rights reserved.

1. Introduction Psychotic disorders are commonly chronic and debilitating disorders with life-long consequences for affected individuals and families. Evidence for immune dysfunction in psychosis has been one of the more enduring findings in the field, although negative findings may reflect underlying heterogeneity of these disorders. Advances in molecular genetics have led to the identification of associations between genes involved in the regulation of the immune system and increased risk of psychosis (Psychiatric Genomics Consortium, 2014; Psychiatric Genomics Consortium, 2015). Infections requiring hospitalization (Köhler-Forsberg et al., 2018) and autoimmune disorders (Benros et al., 2014) are risk factors for incident schizophrenia. Psychotic disorders are also associated with abnormalities in immune cell numbers, inflammatory markers, and antibody titers (reviewed in Miller and Goldsmith, 2017). There is some evidence that adjunctive treatment ⁎ Corresponding author at: Department of Psychiatry and Health Behavior, Augusta University, 997 Saint Sebastian Way, Augusta, GA 30912, United States. E-mail address: [email protected] (B.J. Miller).

with immunomodulatory agents may be associated with improvement in psychopathology in psychosis (Nitta et al., 2013; Sommer et al., 2014). Taken together, these findings raise the possibility that immune dysfunction is relevant to disease etiopathophysiology in some patients with psychotic disorders. Aberrant blood levels of cytokines have been reported in patients with schizophrenia, including patients with first-episode psychosis, suggesting an association that may be independent of the effects of antipsychotic medication (Goldsmith et al., 2016; Miller et al., 2011; Upthegrove et al., 2014). Cytokines are key signaling molecules of the immune system that exert effects in the periphery and brain. They are produced by immune and non-immune cells, and exert their effects by binding specific receptors on a variety of target cells. Cytokine receptors exist in soluble forms, which can inhibit or enhance the biological activity of cytokines. There are also endogenous cytokine receptor antagonists, which compete with cytokines for membrane receptors. Cytokines are key regulators of acute and chronic inflammation, a complex but vital biological response that impacts all organ systems. Cytokines help coordinate the function of both the innate and adaptive components of the immune system as well as a host of other physiological

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Please cite this article as: S. Park and B.J. Miller, Meta-analysis of cytokine and C-reactive protein levels in high-risk psychosis, Schizophrenia Research, https://doi.org/10.1016/j.schres.2019.03.012

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processes throughout the body (Florencio-Silva et al., 2015; Ingman and Robertson, 2009). In contrast to evidence for blood cytokine alterations in first-episode psychosis, less is known about these markers prior to the onset of psychosis. Although several studies have reported significant cytokine alterations in subjects at high-risk for psychosis (Föcking et al., 2016; Karanikas et al., 2017; Stojanovic et al., 2014; Zeni-Graiff et al., 2016), there is between-study heterogeneity with respect to factors including markers studied, high-risk criteria utilized, and potential confounders (e.g., assay methodology, body mass index, fasting status, smoking). Meta-analysis is one approach that can bring increased clarity to an area of research with significant heterogeneity (Sullivan et al., 2003), and thus is well suited to the study of cytokines in subjects at highrisk for psychosis. Given the tremendous burden of psychotic disorders, there has been extensive research to identify subjects at high-risk for psychosis, and to investigate predictors of transition to psychotic disorders. This effort is critical, as early treatment of psychosis is associated with better outcomes (Larsen et al., 2011; Perkins et al., 2015), and approximately one-third of subjects at clinical high-risk will develop psychosis over a two year period (Fusar-Poli et al., 2012). Blood-based markers—in adjunct to other predictors—that could assist in the identification of high-risk subjects and the prediction of transition to a psychotic disorder would have extensive clinical utility and may help facilitate targeted intervention strategies. This paper presents meta-analyses comparing blood cytokine levels in subjects at high-risk psychosis versus controls, as well as high-risk subjects who converted to a psychotic disorder versus non-converters. In doing so, we investigate blood cytokines as a potential marker of high-risk for psychosis and the transition to psychotic disorder, identify important gaps in the literature, and discuss implications for the research agenda in this field. 2. Methods 2.1. Study selection Studies of blood cytokine and C-reactive protein (CRP) levels in subjects at high-risk for psychosis were identified by a systematic search using Medline (PubMed, National Center for Biotechnology Information, US National Library of Medicine, Bethesda, Maryland) and Thomson Reuters (formerly ISI), PsycInfo (via Ovid, American Psychological Association, Washington, DC), Web of Science (Science Citation Index and Social Sciences Citation Index, Thomson Reuters, Charlottesville, Virginia) in November 2018. The primary search strategy was: “(‘at-risk mental state’ OR ‘ultra high risk’ OR prodrome) AND (immune OR cytokine OR interferon OR tumor necrosis factor OR inflammation)”, limiting results to studies with abstracts in English. The initial search yielded 379 articles. After the removal of duplicates, 38 articles were screened. We also manually reviewed the reference lists of these screened articles for potentially relevant studies that did not appear in any of the database searches. The majority of initial matches were excluded because they were review articles, did not present cytokine data, or measured only in vitro cytokine production. We excluded studies of in vitro cytokine production because cytokine production in stimulated, separated mononuclear cells does not necessarily reflect endogenous immune system functioning. In addition to cytokines, we also included the acute phase reactant CRP, as cytokines, particularly interleukin-6 (IL6), are the primary inducers of acute phase proteins, including CRP. The inclusion criteria were: 1) studies assessing blood (plasma/ serum) cytokine levels and/or CRP in 1a) subjects at high-risk psychosis versus controls, 1b) high-risk subjects who converted to a psychotic disorder versus non-converters (sampled at study baseline), or 1c) subjects at high-risk psychosis versus first-episode psychosis, and 2) studies in English. Insufficient data were available for analyses of subjects at high-risk psychosis versus first-episode psychosis. The exclusion criteria were: 1) studies without a control group, and 2) studies that did

not present either mean and standard deviations (SDs) or median and interquartile range (IQR) for cytokine and/or CRP levels (after attempting to contact the study authors). Due to the potential for low concentrations of some cytokines, the methods of the potential studies were reviewed to evaluate assay sensitivity. An assay result was excluded if: 1) the mean concentration was less than the lower limit of assay detection, 2) concentrations were not detectable in N50% of subjects, or 3) either the intra-assay coefficient of variation (CV) was N10% or the inter-assay CV was N15%. After independent searches, review of study methods by two authors (SP and BJM) and attempts to contact other authors, eight studies met the inclusion criteria (Delaney et al., 2018; Föcking et al., 2016; Karanikas et al., 2017; Labad et al., 2015; Lizano et al., 2016; Perkins et al., 2015; Stojanovic et al., 2014; Zeni-Graiff et al., 2016), including seven studies of high-risk psychosis versus controls, and three studies of high-risk subjects who converted to a psychotic disorder versus non-converters. If studies included data on both high-risk converters and non-converters, only the data for converters was used in the comparison versus healthy controls. There was universal agreement on the included studies. A flow chart summarizing the study selection process is presented in Fig. 1. 2.2. Data extraction and meta-analysis Data were extracted (sample size, mean/SD or median/IQR for patients), for every inflammatory marker assessed in each study. If necessary, we estimated the mean/SD from the median/IQR using the following formulas: (1) mean = (2 m + a + b) / 4, where m is the median and a and b are the 25th and 75th percentiles, respectively and (2) IQR = 1.35 × SD (Hernandez et al., 2014). One author (SP) extracted all data, which was independently verified by another author (BJM). We then calculated effect size (ES) estimates (Standardized Mean Difference [SMD]) for every marker in each study, and these data are included in Supplementary material. Random effects pooled ES estimates and 95% confidence intervals (95% CIs) were calculated using the method of Dersimion and Laird. Separate meta-analyses were performed for each individual marker in subjects at high-risk for psychosis versus controls, as well as for high-risk converters versus non-converters. The meta-analysis procedure also calculates a χ2 value for the heterogeneity in ES estimates, which is based on Cochran's Q-statistic (Cochran, 1950), and I2, the proportion of the variation in ES attributable to betweenstudy heterogeneity. χ2 was considered significant for p b 0.10 (Song et al., 2001). p-Values were considered statistically significant at the α = 0.05 level. Potential for publication bias was examined with Sterne's funnel plot analysis (Sterne and Egger, 2001). For blood IL-6 levels in highrisk subjects versus controls—the most frequently studied cytokine in the meta-analysis—we performed a series of meta-regression analyses to explore possible moderating variables of age, sex, body mass index (BMI), and year of publication. We were not able to perform metaregression analyses for other possible moderating variables (e.g., smoking) for IL-6, or perform meta-regression analyses for other markers, due to either the small number of studies (range 2–4) or the absence of adequate data. The statistical analyses were performed in Stata 10.0 (StataCorp LP, College Station, TX). 3. Results 3.1. Study and participant characteristics Table 1 presents details of the included studies. Three studies investigated subjects meeting criteria for the “at-risk mental state”, two studies used clinical high-risk criteria, two studies used ultra-high risk criteria, and one study identified subjects at familial high risk. Across the 7 studies of subjects at high-risk for psychosis versus controls, the number of high-risk subjects ranged from 14 to 76, and the number of

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Fig. 1. Flow chart of the study selection process.

controls ranged from 39 to 115, for each marker. Among the four studies of high-risk converters versus non-converters, the number of converters ranged from 14 to 56, and the number of non-converters ranged from 60 to 129, for each marker.

3.2. Meta-analyses of blood cytokine levels and CRP in high-risk psychosis In subjects at high-risk for psychosis, blood IL-6 levels were significantly higher with a small-to-medium effect size (SMD = 0.31, 95% CI

Table 1 Studies of blood cytokines and C-reactive protein (CRP) in high-risk for psychosis. Study

Markers

High-risk psychosis versus controls Delaney et al., 2018 IL-6, CRP Föcking et al., 2016 IL-6, IL-8, IL-10, IL-12, IFN-γ, TNF-α, CRP Karanikas et al., 2017 IL-1β, IL-4, IL-5, IL-8, IL-10, IL-12, IFN-γ, TNF-α, TNF-β Labad et al., 2015 CRP Lizano et al., 2016 IL-1β, IL-6, IL-8, IL-10, IL-12, TNF-β Perkins et al., 2015 IL-1β, IL-4, IL-5, IL-6, IL-8, IL-12, TNF-α Stojanovic et al., 2014 IL-6 Zeni-Graiff et al., IL-6, IFN-γ 2016 High-risk converters versus non-converters Föcking et al., 2016 IL-6, IL-8, IL-10, IL-12, IFN-γ, TNF-α, CRP Labad et al., 2015 CRP Lizano et al., 2016 IL-1β, IL-6, IL-8, IL-10, IL-12, IFN-γ, CRP Perkins et al., 2015 IL-1β, IL-6, IL-8, IL-12, TNF-α, CRP

Assay

Location Mean age (years)

Sex (% male)

Mean BMI

ELISA Multiplex immunoassay Fluorescent Bead Immunoassay Immunoturbidimetry Multiplex immunoassay Multiplex immunoassay ELISA CBA

USA Ireland Greece

24.4 16.1 26.2

50 31 100

24.5 21.2 24.4

Spain USA USA Spain Brazil

22.68

63

22.2

19.62 24.9 18.14

51 57 41

Multiplex immunoassay Immunoturbidimetry Multiplex immunoassay Multiplex immunoassay

Ireland Spain USA USA

16.1 21.9

31 69

19.4

65

Smoking (% yes)

High-risk definition

62 40

A B C

– 21.8 22.3

25 31 –

B D A B C

21.2 21.9

62 29 36

B B D A

A. Clinical high risk. B. At-risk mental state. C. Ultra-high risk. D. Familial high-risk.

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number of studies, cumulative sample size, and heterogeneity of highrisk criteria. This limits our ability to make inferences regarding patterns and the utility of cytokine and CRP alterations in subjects at high-risk for psychosis. A second limitation is that we cannot account for either the type or the length of pharmacologic and/or psychosocial interventions employed in the studies included in our meta-analysis. Another limitation is the lack of agreement on which markers to study, which contributed to the small number of studies for some markers. Alternatively, it may be less important to measure individual markers, but instead measure overall patterns of immune activation, for example, flow cytometry of macrophages/monocytes versus TH1 versus TH2 versus TH17 cells. Although we were able to consider some potential moderating factors in the analyses of IL-6, other potential confounding and/or moderating factors such as smoking, level and type of psychopathology, genetic heterogeneity, sample issues (e.g., collection and processing, time of day, plasma versus serum, type of assay, and length of sample storage prior to assay) (Leng et al., 2008; O'Connor et al., 2009; De Berardis et al., 2010). Furthermore, although we did not find evidence for moderating effects of age, sex, BMI, and year of publication on IL-6 levels in high-risk subjects versus controls, this does not preclude moderating effects between such clinical and demographic factors and other cytokines and CRP. We found some evidence of concordance in the direction (but not necessarily statistical significance) of blood cytokine and CRP alterations between high-risk subjects and those with first-episode psychosis (FEP), although many discordant findings are noted (see Table 3). Notably, blood IL-6 levels are increased in both high-risk and FEP subjects compared to controls. This finding is broadly consistent with data on IL-6 from other population-based studies. In the Avon Longitudinal Study of Parents and Children (ALSPAC) birth cohort, higher blood IL6 levels at age 9 were associated with significant increased odds of depression, psychotic experiences, and fulminant psychotic disorder at

0.02–0.59, p = 0.04) and blood IL-1β levels were significantly lower with a medium-to-large effect size (SMD = −0.66, 95% CI −1.27 to −0.05, p = 0.05) versus controls (see Table 2a and Figs. 2 and 3). Between-study heterogeneity was not significant for either IL-1β or IL-6, and there was no evidence of publication bias. In meta-regression analyses, age, sex, BMI, and year of publication were all unrelated to the association between IL-6 and high-risk psychosis (p N 0.05 for each). There was also a non-significant trend for higher IL-4 levels (SMD = 1.10, 95% CI −0.14–2.35, p = 0.08) and lower IL-10 levels (SMD = −0.59, 95% CI −1.20–0.02, p = 0.06) in subjects at high-risk psychosis. There were no differences in levels of IL-5, IL-8, IL-12, IFNγ, TNF-α, TNF-β, or CRP in high-risk subjects versus controls. In high-risk converters versus non-converters, there was a nonsignificant trend for higher blood IL-12 levels in converters (SMD = 0.86, 95% CI -0.06-1.79, p = 0.07). There were no differences in levels of IL-1β, IL-6, IL-8, IL-10, IFN-γ, TNF-α, or CRP in high-risk converters versus non-converters (see Table 2b and Fig. 2). 4. Discussion We found that blood levels of IL-6 were significantly elevated, and levels of IL-1β were significantly decreased in subjects at high-risk for psychosis compared to controls. There was also a non-significant trend for higher IL-4 and lower IL-10 between these two groups. By contrast, there was a non-significant trend for higher blood IL-12 levels in high-risk converters versus non-converters. Otherwise, no markers high-risk converters versus non-converters/ The strengths of our study include comparisons of blood cytokines and CRP in subjects at high-risk for psychosis and controls, as well as high-risk converters versus non-converters, which has not been previously performed. There are several limitations to the present study. Our findings should be interpreted with caution in light of a small

Table 2 Meta-analyses of blood cytokine and C-reactive protein (CRP) alterations in subjects at high-risk for psychosis. 2a. High-risk versus controls Cytokine N High-risk Control SMD studies

95% CI

p-Value Heterogeneity 2

I2

References

Karanikas et al., 2017; Lizano et al., 2016 Karanikas et al., 2017; Perkins et al., 2015 Karanikas et al., 2017; Perkins et al., 2015 Delaney et al., 2018; Lizano et al., 2016; Perkins et al., 2015; Stojanovic et al., 2014; Zeni-Graiff et al., 2016 Karanikas et al., 2017; Lizano et al., 2016; Perkins et al., 2015 Karanikas et al., 2017; Lizano et al., 2016 Karanikas et al., 2017; Lizano et al., 2016; Perkins et al., 2015 Karanikas et al., 2017; Zeni-Graiff et al., 2016 Karanikas et al., 2017; Perkins et al., 2015 Karanikas et al., 2017; Lizano et al., 2016 Delaney et al., 2018; Labad et al., 2015; Perkins et al., 2015; Stojanovic et al., 2014

Lower

Upper

χ

p-Value

IL-1β IL-4 IL-5 IL-6

2 2 2 5

14 44 44 81

60 58 58 148

−0.66 1.10 −0.19 0.31

−1.27 −0.14 −0.59 0.02

−0.05 2.35 0.20 0.59

0.04 0.08 0.34 0.04

0.08 6.86 0.66 3.69

0.78 b0.01 0.42 0.45

0.0 85.40 0.0 0.0

IL-8 IL-10 IL-12 IFN-γ TNF-α TNF-β CRP

3 2 3 2 2 2 4

47 15 47 24 44 15 76

97 62 97 39 58 62 136

0.23 −0.59 0.51 −0.31 0.00 0.03 −0.06

−0.36 −1.20 −0.76 −0.82 −0.62 −0.58 −0.36

0.82 0.02 1.78 0.21 0.17 0.63 0.24

0.44 0.06 0.43 0.24 0.26 0.94 0.69

2.90 0.30 16.58 0.09 0.37 0.02 3.22

0.14 0.58 b0.01 0.77 0.54 0.89 0.36

48.7 0.0 87.9 0.0 0.0 0.0 6.7

2b. High risk converter versus non-converter p-Value Heterogeneity I2

95% CI

References

Cytokine N studies

Converter Non-converter SMD

IL-1β IL-4 IL-5 IL-6 IL-8 IL-10 IL-12 IFN-γ TNF-α TNF-β CRP

2

15

62

−0.31 −0.92 0.29

0.39

0.49 0.49

0.0

Föcking et al., 2016; Lizano et al., 2016

3 3 2 3 2 2

46 46 14 46 14 43

100 100 60 100 60 68

−0.10 0.25 0.54 0.86 −0.12 0.07

0.29 0.62 1.55 1.79 0.48 0.46

0.61 0.18 0.29 0.07 0.70 0.71

2.15 1.24 2.18 8.55 0.44 0.06

6.9 0.0 76.6 76.6 0.0 0.0

Föcking et Föcking et Föcking et Föcking et Föcking et Föcking et

4

56

129

−0.19 −0.51 0.14

0.27

1.91 0.59

0.0

Föcking et al., 2016; Labad et al., 2015; Lizano et al., 2016; Perkins et al., 2015

Lower

−0.50 −0.12 −0.47 −0.06 −0.72 −0.31

χ2

Upper

p-Value

0.34 0.54 0.14 0.01 0.51 0.80

al., 2016; Lizano et al., 2016; Perkins et al., 2015 al., 2016; Lizano et al., 2016; Perkins et al., 2015 al., 2016; Lizano et al., 2016 al., 2016; Lizano et al., 2016; Perkins et al., 2015 al., 2016; Lizano et al., 2016 al., 2016; Perkins et al., 2015

Bolded, italicized p-values are statistically significant at the 0.05 level.

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Converter vs Non-Converter

-0.19

CRP

-0.06 High-Risk vs Control

TNF-β

0.03 0.07 0.00

TNF-α

-0.12

IFN-γ

-0.31 0.86

Cytokine

IL-12

IL-10

0.51 0.54 -0.59 0.25 0.23

IL-8

-0.10

IL-6

0.31

IL-5

-0.19

IL-4

IL-1β

-1.50

1.10 -0.31 -0.66

-0.50

0.50

1.50

2.50

Effect Size (SMD)

Fig. 2. Blood cytokine alterations in patients at high-risk for psychosis.

age 18, with evidence for a dose-dependent association (Khandaker et al., 2014). In this cohort, blood IL-6 levels at age 9 were significantly associated with diurnal mood variation, impaired concentration, fatigue, and sleep disturbances at age 18 (Chu et al., 2018). Furthermore, in the ALSPAC birth cohort, a common functional variant of the IL-6 receptor (IL6R) gene was associated with decreased risk of depression and/or psychosis and decreased blood CRP levels, but increased blood IL-6, independent of potential confounding factors. Interestingly, a recent study from the North American Prodromal Longitudinal Study (NAPLS; Goldsmith et al., 2018) found that baseline IL-6 levels negatively predicted the trajectory of negative symptoms, as measured by the Positive and Negative Syndrome Scale (PANSS), over the first year of follow-up in clinically high-risk subjects (that is, higher baseline IL6 levels were associated with a greater decrease in negative symptoms between baseline and follow-up). One potential explanation for this finding is the IL6R gene, which may confer both decreased risk of psychosis and increased blood IL-6 levels. One study in the present meta-analysis (Stojanovic et al., 2014) found in subjects with at-risk mental state (ARMS), blood IL-6 levels were positively associated with both positive and negative symptoms, as measured by the Positive and Negative Syndrome Scale. However, another included study (Zeni-Graiff et al., 2016) did not find any correlations between IL-6 and ratings of depression, mania, or global functioning. These studies underscore the need to consider genetics and associations with psychopathology in the longitudinal assessment of cytokines and CRP as potential biomarkers in high-risk psychosis. However, in the present study, we found non-significantly lower blood IL-6 levels in high-risk converters versus non-converters. Small cumulative sample size and genetic heterogeneity may have contributed to this and other negative or discordant findings. Another potential explanation of discordant findings is that alterations in cytokines and CRP are not specific to psychosis. For example, there is meta-analytic

evidence that blood IL-6 levels are increased in patients with major depression (Dowlati et al., 2010) and bipolar disorder (Modabbernia et al., 2013) compared to controls, with similar magnitude across mood and psychotic disorders (Goldsmith et al., 2016). Therefore, increased IL-6 in high-risk non-converters may reflect an inherent increased vulnerability to mood and other psychiatric disorders. Interestingly, a previous study of cerebrospinal fluid (CSF) samples found significantly decreased soluble IL-6 receptor levels in subjects with ARMS compared to controls, and decreased IL-6 levels in subjects with ARMS compared to patients with FEP (Hayes et al., 2014). To our knowledge, this is the only published study of CSF cytokines in high-risk subjects. Future studies of blood and CSF cytokines are needed to provide valuable clues regarding potential mechanisms of the association between inflammation and psychosis, and whether alterations observed in the periphery are mirrored in the central nervous system. Another notable concordant finding is that there was a trend for higher blood IL-12 levels in high-risk converters versus nonconverters. In a previous meta-analysis, we found evidence that blood IL-12 levels may be a trait marker for psychosis (Goldsmith et al., 2016). That is, blood IL-12 levels are elevated in acutely ill subjects with psychosis compared to controls, and that IL-12 levels increase following antipsychotic treatment for acute psychosis. Indeed, in one of the studies from the present meta-analysis (Föcking et al., 2016), blood IL-12 levels did not change following 12 weeks administration of omega-3 fatty acid supplementation in subjects with ARMS, including those who transitioned to a psychotic disorder. Therefore, IL-12 appears to be another important cytokine for future study in this area. Many important questions about cytokines and CRP in patients with psychosis are also relevant to high-risk subjects (Goldsmith et al., 2016): What are the most useful markers to measure? Should future studies preferentially measure markers with more robust evidence (in order to replicate findings), or those that have not been thoroughly

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a. Forest plot of blood IL-6 alterations in patients at high-risk for psychosis versus controls

IL-6 in High-Risk vs Control Study

%

ID

SMD (95% CI)

Weight

Delaney 2018

0.00 (-0.59, 0.59)

23.98

Lizano 2016

0.76 (-0.43, 1.94)

5.84

Perkins 2015

0.32 (-0.17, 0.80)

35.27

Stojanovic 2014

0.16 (-0.45, 0.78)

21.55

Zeni-Graiff 2016

0.85 (0.07, 1.64)

13.37

Overall (I-squared = 0.0%, p = 0.450)

0.31 (0.02, 0.59)

100.00

NOTE: Weights are from random effects analysis

-1

-.5

0

.5

1

1.5

2

b. Forest plot of blood IL-1β alterations in patients at high-risk for psychosis versus controls

IL-1b in High-Risk vs Control %

Study

ID

SMD (95% CI)

Weight

Focking 2016

-0.71 (-1.43, 0.00)

73.41

Lizano 2016

-0.51 (-1.70, 0.68)

26.59

Overall (I-squared = 0.0%, p = 0.779)

-0.66 (-1.27, -0.05)

100.00

NOTE: Weights are from random effects analysis

-1.5

-1

-.5

0

.5

1

1.5

Fig. 3. Blood cytokine alterations in patients at high-risk for psychosis.

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c. Funnel plot of blood IL-6 alterations in patients at high-risk for psychosis

IL-6 in High-Risk vs Controls

.6

.4

SE of ES

.2

0

Funnel plot with pseudo 95% confidence limits

-1

-.5

0

.5

1

1.5

ES

Fig. 3 (continued).

investigated, or some combination of both? There is need for an agreed upon standard for assay methodology: should we be using a multiplex system or an ELISA-based system? What are the most reasonable statistical approaches to employ with data that are frequently highly skewed? Is measurement of blood cytokine and CRP levels are sufficient? For example, coupling peripheral findings with CSF markers and/or brain imaging may be more informative. We need to better characterize which, if any, clinical and demographic features are associated with cytokine and CRP alterations. Furthermore, rigorously designed longitudinal studies are needed to assess whether baseline or changes in cytokine and CRP levels distinguish high-risk subjects from controls, as well as converters from non-converters. It is also important to consider that moderate effect sizes observed for cytokine alterations in psychosis most likely reflects that fact that immune system involvement occurs in only a subset of patients with these syndromes. Therefore, focusing on the trajectories of high-risk subjects with comorbid inflammation may also be informative.

Table 3 Comparison of blood and cytokine and C-reactive protein (CRP) alterations in patients with high-risk and first-episode psychosis controls.

Marker

IL-1β IL-4 IL-6 IL-8 IL-10 IL-12 IFN-γ TNF-α CRP

Subjects Converter vs non-converter  (NS)  (NS)  (NS)  (NS)  (trend)  (NS)  (NS)  (NS)

High-risk vs control   (trend)   (NS)  (trend)  (NS)  (NS)  (NS)  (NS)

First-episode vs control         

5. Conclusions We found limited evidence for blood cytokine and CRP alterations in subjects at high-risk for psychosis. Although our findings should be interpreted with caution, further investigation in larger samples is warranted. This includes studies of subjects at high-risk of developing psychosis and controls, the potential of inflammation as a predictor of conversion to psychosis, and comparisons between high-risk and firstepisode psychosis subjects. These findings have important potential implications for our understanding of the pathophysiology of psychosis. Supplementary data to this article can be found online at https://doi. org/10.1016/j.schres.2019.03.012. Role of funding source Not applicable.

Contributors Dr. Miller designed the study. Ms. Park and managed the literature searches and data extraction, which was verified by Dr. Miller. Dr. Miller managed the analyses. Ms. Park and Dr. Miller wrote the first draft of the manuscript. All authors contributed to and have approved the final manuscript. Conflict of interest Ms. Park has nothing to disclose relevant to the present work. Dr. Miller has nothing to disclose for the work under consideration. In the past 12 months, Dr. Miller received research support from the National Institute of Mental Health, NARSAD, the Stanley Medical Research Institute, and Augusta University, and Honoraria from Psychiatric Times.

Acknowledgements The authors thank Dr. David Cotter and Dr. Shannon Delaney for sharing data. This manuscript is dedicated to the memory of Dr. Jeffrey Yao.

References NS = Not significant

 = increased in patients versus controls  = decreased in patients versus controls

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Please cite this article as: S. Park and B.J. Miller, Meta-analysis of cytokine and C-reactive protein levels in high-risk psychosis, Schizophrenia Research, https://doi.org/10.1016/j.schres.2019.03.012