Plasma Nervonic Acid Is a Potential Biomarker for Major Depressive Disorder: A Pilot Study.

Background: Diagnostic biomarkers of major depressive disorder, bipolar disorder, and schizophrenia are urgently needed, because none are currently available. Methods: We performed a comprehensive metabolome analysis of plasma samples from drug-free patients with major depressive disorder (n=9), bipolar disorder (n=6), schizophrenia (n=17), and matched healthy controls (n=19) (cohort 1) using liquid chromatography time-of-flight mass spectrometry. A significant effect of diagnosis was found for 2 metabolites: nervonic acid and cortisone, with nervonic acid being the most significantly altered. The reproducibility of the results and effects of psychotropic medication on nervonic acid were verified in cohort 2, an independent sample set of medicated patients [major depressive disorder (n=45), bipolar disorder (n=71), schizophrenia (n=115)], and controls (n=90) using gas chromatography time-of-flight mass spectrometry. Results: The increased levels of nervonic acid in patients with major depressive disorder compared with controls and patients with bipolar disorder in cohort 1 were replicated in the independent sample set (cohort 2). In cohort 2, plasma nervonic acid levels were also increased in the patients with major depressive disorder compared with the patients with schizophrenia. In cohort 2, nervonic acid levels were increased in the depressive state in patients with major depressive disorder compared with the levels in the remission state in patients with major depressive disorder and the depressive state in patients with bipolar disorder. Conclusion: These results suggested that plasma nervonic acid is a good candidate biomarker for the depressive state of major depressive disorder.

Search for plasma biomarkers in drug-free patients with bipolar disorder and schizophrenia using metabolome analysis.

AIM: There is an urgent need for diagnostic biomarkers of bipolar disorder (BD) and schizophrenia (SZ); however, confounding effects of medication hamper biomarker discovery. In this study, we conducted metabolome analyses to identify novel plasma biomarkers in drug-free patients with BD and SZ. METHODS: We comprehensively analyzed plasma metabolites using capillary electrophoresis time-of-flight mass spectrometry in patients with SZ (n = 17), BD (n = 6), and major depressive disorder (n = 9) who had not received psychotropics for at least 2 weeks, and in matched healthy controls (n = 19). The results were compared with previous reports, or verified in an independent sample set using an alternative analytical approach. RESULTS: Lower creatine level and higher 2-hydroxybutyric acid level were observed in SZ than in controls (uncorrected P = 0.016 and 0.043, respectively), whereas they were unaltered in a previously reported dataset. Citrulline was nominally significantly decreased in BD compared to controls (uncorrected P = 0.043); however, this finding was not replicated in an independent sample set of medicated patients with BD. N-methyl-norsalsolinol, a metabolite of dopamine, was suggested as a candidate biomarker of BD; however, it was not detected by the other analytical method. Levels of betaine, a previously reported candidate biomarker of schizophrenia, were unchanged in the current dataset. CONCLUSION: Our preliminary findings suggest that the effect of confounding factors, such as duration of illness and medication, should be carefully controlled when searching for plasma biomarkers. Further studies are required to establish robust biomarkers for these disorders.

Intra-individual state-dependent comparison of plasma mitochondrial DNA copy number and IL-6 levels in patients with bipolar disorder.

BACKGROUND: Patients with bipolar disorder (BD) have increased plasma IL-6 levels, which are higher in depressed BD (dBD) than remitted BD (rBD). However, the mechanism that differentiates the cytokine levels between dBD and rBD is not understood. First, we determined whether brain-derived mtDNA can be detected in plasma using neuron-specific mutant Polg1 transgenic (Tg) mice. Second, we investigated whether the plasma circulating cell-free mitochondrial DNA (ccf-mtDNA) differentiate the cytokine levels between dBD and rBD. METHODS: Mouse plasma ccf-mtDNA levels were measured using real-time PCR targeting two regions of the mtDNA (CO1 and d-loop) in Tg mice and non-Tg littermates. Human plasma ccf-mtDNA levels were measured using real-time PCR targeting two regions of the mtDNA (ND1 and ND4) and IL-6 levels were evaluated in 10 patients in different states (depressed and remitted) of BD in a longitudinal manner and 10 healthy controls. RESULTS: The mouse plasma CO1/D-loop ratio was significantly lower in Tg than non-Tg mice (P = 0.0029). Human plasma ccf-mtDNA copy number, ND4/ND1 ratio, and IL-6 levels were not significantly different between dBD and rBD. Human plasma ccf-mtDNA levels showed a nominal significant correlation with delusional symptoms (P = 0.033, ρ = 0.68). LIMITATIONS: A larger sample size is required to generalize the results and to determine whether plasma ccf-mtDNA is associated with systemic inflammation. CONCLUSIONS: Tg mice revealed that brain-derived mtDNA could be present in peripheral blood. The present findings did not coincide with our hypothesis that plasma ccf-mtDNA differentiates the cytokine levels between dBD and rBD.

The relationship between circulating mitochondrial DNA and inflammatory cytokines in patients with major depression.

BACKGROUND: Although inflammatory cytokines are established biomarkers of mood disorders, their molecular mechanism is not known. We hypothesized that circulating mitochondrial DNA (mtDNA) contributes to inflammation and could be used as biomarkers. We investigated if circulating mtDNA level is associated with inflammatory cytokines and can be used as a biomarker of mood disorders. METHODS: Plasma mtDNA concentration was measured with real-time quantitative PCR targeting two regions of the mtDNA and plasma levels of four cytokines (GM-CSF, IL-2, IL-4, and IL-6) were measured with a multiplex immunoassay method in 109 patients with major depressive disorder (MDD). The most significantly correlated cytokine was verified with an enzyme-linked immunosorbent assay (ELISA). The data from 28 patients with bipolar disorder (BD), 17 patients with schizophrenia (SZ), and 29 healthy controls were compared. RESULTS: MtDNA levels showed a nominal positive correlation with GM-CSF, IL-2 and IL-4 in patients with MDD. The most significant correlation with IL-4 (ρ = 0.38, P < 0.00005) was verified with an ELISA (ρ = 0.19, P = 0.049). Unexpectedly, patients with MDD and BD showed significantly lower plasma mtDNA levels than controls. MtDNA levels were lower in the depressive state than in the euthymic state in patients with MDD. Patients with depression, bipolar disorder, and schizophrenia did not show significantly higher levels of these four cytokines than controls. LIMITATIONS: There is a possibility that the patients in this study are different from previous studies in which increased cytokine levels were reported. MtDNA levels should be measured in patients showing elevated plasma cytokine levels. A larger sample is required to generalize the results. CONCLUSIONS: The present findings coincide with our hypothesis that circulating mtDNA contributes to the inflammation in MDD. Further studies are needed to conclude whether plasma mtDNA would be a biomarker of mood disorders.