Reciprocal moderation by Toxoplasma gondii seropositivity and blood phenylalanine – tyrosine ratio of their associations with trait aggression
Mathai Ashwin Jacob,
Lowry Christopher A.,
Cook Thomas B.,
Brenner Lisa A.,
Brundin Lena,
Groer Maureen W.,
Peng Xiaoqing,
Giegling Ina,
Hartmann Annette M.,
Konte Bettina,
Friedl Marion,
Fuchs Dietmar,
Rujescu Dan,
Postolache Teodor T.
Affiliations
Mathai Ashwin Jacob
Mood and Anxiety Program, University of Maryland School of Medicine, 685 West Baltimore Street, MSTF Building, Baltimore, MD 21201, United States of America
Lowry Christopher A.
Department of Integrative Physiology and Center for Neuroscience, University of Colorado Boulder, Boulder, CO, United States of America
Cook Thomas B.
Department of Public Health and Mercyhurst Institute for Public Health, Mercyhurst University, Erie, PA, United States of America
Brenner Lisa A.
Rocky Mountain Mental Illness Research Education and Clinical Center (MIRECC), Denver, CO, United States of America
Brundin Lena
Van Andel Research Institute, Grand Rapids, MI, United States of America
Groer Maureen W.
University of South Florida, Tampa, FL, United States of America
Peng Xiaoqing
Mood and Anxiety Program, University of Maryland School of Medicine, 685 West Baltimore Street, MSTF Building, Baltimore, MD 21201, United States of America
Giegling Ina
Department of Psychiatry, Martin-Luther-University of Halle-Wittenberg, Halle, Germany
Hartmann Annette M.
Department of Psychiatry, Martin-Luther-University of Halle-Wittenberg, Halle, Germany
Konte Bettina
Department of Psychiatry, Martin-Luther-University of Halle-Wittenberg, Halle, Germany
Friedl Marion
Department of Psychiatry, Martin-Luther-University of Halle-Wittenberg, Halle, Germany
Fuchs Dietmar
Division of Biological Chemistry, Biocenter, Innsbruck Medical University, Innsbruck, Austria
Rujescu Dan
Department of Psychiatry, Martin-Luther-University of Halle-Wittenberg, Halle, Germany
Postolache Teodor T.
Mood and Anxiety Program, University of Maryland School of Medicine, 685 West Baltimore Street, MSTF Building, Baltimore, MD 21201, United States of America
We previously reported that trait aggression, proposed as an endophenotype for suicidal behavior, is positively associated with Toxoplasma gondii (T. gondii) seropositivity in females, but not in males. Additionally, older males seropositive for T. gondii had lower scores on measures of trait aggression, including self-aggression. Trait aggression may be influenced by dopaminergic signaling, which is known to be moderated by gender and age, and potentially enhanced in T. gondii positives through the intrinsic production of dopamine by the microorganism. Therefore, we investigated associations between trait aggression and interactions between T. gondii enzyme-linked immunoabsorbant assay (ELISA) IgG titer-determined seropositivity and high-performance liquid chromatography- (HPLC-) measured blood levels of dopamine precursors phenylalanine (Phe), tyrosine (Tyr), and their ratio in a sample of 1000 psychiatrically healthy participants. Aggressive traits were assessed using the questionnaire for measuring factors of aggression (FAF), the German version of the Buss-Durkee hostility questionnaire. We found that 1) the decrease in trait aggression scores in T. gondii-positive older males was only present in individuals with a low Phe:Tyr ratio, and 2) that there was a positive correlation between Phe:Tyr ratio and total aggression and selected subscales of aggression in T. gondii-positive males, but not in T. gondii-negative males. These findings point toward a gender-specific reciprocal moderation by Phe:Tyr ratio and T. gondii seropositivity of their associations with aggression scores, and lead to experimental interventions geared to manipulating levels of dopamine precursors in selected T. gondii positive individuals with increased propensity for aggression.
