Objective: Attenuated niacin responses and changes in cytokine levels have been reported in schizophrenia. However, prior studies have typically focused on schizophrenia, and little is known about the association between niacin response and inflammatory imbalance in clinically high-risk psychosis (CHR). This study aimed to assess the niacin response to inflammatory imbalance for association with conversion to psychosis within 2 years.
Methods: A prospective case-control study was performed to assess the niacin response and interleukin (IL)-1β, IL-2, IL-6, IL-8, IL-10, and tumor necrosis factor-α levels in 60 CHR individuals and 60 age- and sex-matched healthy controls (HC) from May 2019 to December 2021. Participants with CHR were identified using the Structured Interview for Prodromal Syndromes. The niacin-induced responses were measured using laser Doppler flowmetry. From the dose-response curves, the log-transferred concentration of methylnicotinate required to elicit a half-maximal blood flow response (LogEC50) and maximal minus minimal blood flow response (Span) values were calculated for each subject. Serum cytokine levels were measured using enzyme-linked immunosorbent assay. Individuals with CHR were then divided into converters (CHR-C, n = 15) and non-converters (CHR-NC, n = 45) to psychosis based on their 2-year follow-up clinical status.
Results: The CHR group exhibited significantly higher LogEC50 (t = 3.650, P < .001) and Span (t = 2.657, P = .009) values than the HC group. The CHR-C group exhibited a significantly shorter Span (t = 4.027, P < .001) than the CHR-NC group. The LogEC50 showed a trend toward significance (t = 1.875, P = .066). None of the cytokine levels were significant. The conversion outcome can therefore be predicted by applying LogEC50 (P = .049) and Span (P < .001). The regression model with variables of LogEC50, Span, family history, and scores of positive symptoms showed good discrimination of subsequent conversion to psychosis and achieved a classification accuracy of 91.7%. The decreased LogEC50 in the CHR-C group was significantly correlated with the increased IL-1β/IL-10 ratio (Spearman ρ = -0.600, P = .018), but this correlation was nonsignificant in the CHR-NC group.
Conclusions: Our findings indicate a significant association between niacin response and psychosis conversion outcomes in individuals with CHR. Compared with peripheral inflammatory cytokines, the niacin response can better predict conversion, although there may be an intersection between the two in biological mechanisms.
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