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Schizophrenia Research Project

■ Hair zinc levels and psychosis risk among adolescents

Tabata K, Miyashita M, Yamasaki S, Toriumi K, Ando S, Suzuki K, Endo K, Morimoto Y, Tomita Y, Yamaguchi S, Usami S, Itokawa M, Hiraiwa-Hasegawa M, Takahashi H, Kasai K, Nishida A, Arai M. Hair zinc levels and psychosis risk among adolescents. Schizophrenia (Heidelb). 2022 Nov 25;8(1):107. doi: 10.1038/s41537-022-00307-y. PMID: 36433958.

Highlights

  • We have investigated the relationship of zinc and copper levels in hair with psychosis risk among healthy 252 drug-naïve adolescents, using data from population-based biomarker subsample study of the Tokyo Teen Cohort.
  • Zinc and copper levels were measured in hair, because hair sampling is less invasive than blood collection. The thought problems (TP) scale, a simple questionnaire tool, was used to evaluate psychosis risk.
  • Regression analysis showed that hair zinc levels were negatively correlated with a T-score of the TP scale. This finding suggests that lower zinc levels could be involved in the pathophysiology of psychosis.

Introduction

Recent meta-analyses have shown lower zinc and higher copper levels in the serum of people with schizophrenia than those in healthy controls. However, the relationship between trace elements and the pathophysiology of psychosis, including schizophrenia, remains unclear due to the possible effects of antipsychotic effects on mineral levels. In this study, we aimed to determine the relationship between zinc and copper levels in hair and psychosis risk among drug-naïve adolescents.

Results

Regression analysis showed that hair zinc levels were negatively correlated with the TP scale (T-score) (β = -0.176, P = 0.005). In contrast, hair copper levels were not associated with the TP scale (T-score) (β = 0.026, P = 0.687). Figure 1 shows the correlation of the TP scale (T-score) with hair zinc levels.

According to a previous study, a T-score of the TP scale > 68.5 is considered the cut-off for psychosis. As shown in Figure 2, the hair zinc levels of the participants with the TP scale (T-score) > 68.5 were significantly lower than those of the other participants with the TP scale (T-score) ≤ 68.5 (P < 0.01).

Fig 1. Correlation between hair zinc levels and the TP scale (T-score).
Fig 1. Correlation between hair zinc levels and the TP scale (T-score).
The regression line is shown on the graph.
Fig 2. Scatterplots of hair zinc levels in participants with TP scale (T-score) > 68.5 and TP scale (T-score) ≤ 68.5.
Fig 2. Scatterplots of hair zinc levels in participants with TP scale (T-score) > 68.5 and TP scale (T-score) ≤ 68.5.
** means P < 0.01. The data are presented as median with interquartile range.

Conclusion

In a population-based birth cohort study of adolescents, lower hair zinc levels could be associated with psychosis risk among drug-naïve adolescents, suggesting its involvement in the pathophysiology of psychosis, independent of antipsychotics. Further longitudinal studies are required to investigate hair zinc level as a new biomarker for assessing psychosis risk.



■ Carbonyl stress-sensitive brain regions in the patient with treatment-resistant schizophrenia with a glyoxalase 1 frameshift mutation: Autopsy study

Ishida.H, Miyashita M., Oshima K., Kawakami I., Sekiyama K., Kounoe M., Seki E., Arai N., Takizawa S., Nagata E., Itokawa M., Arai M. Psychiatry Res Case Rep. (in Press). doi: 10.1016/j.psycr.2022.100064.

Highlights

  • We have analyzed the postmortem brain of a patient with treatment-resistant schizophrenia with a glyoxalase 1 frameshift mutation.
  • Neuropathological research revealed that the neuropathological changes in his neurodegenerative disease were very mild.
  • Carbonyls stress-sensitive brain regions are cerebellum, basal ganglia, sensory and prefrontal cortices.
Fig 1. Overview: Neuropathological findings and pentosidine positive neurons in a schizophrenia patient with a GLO1 frameshift mutation (GLO1-FS).
Fig 1. Overview: Neuropathological findings and pentosidine positive neurons in a schizophrenia patient with a GLO1 frameshift mutation (GLO1-FS).

(a) Brain magnetic resonance (MR) image of the patient. (b) Neurofibrillary tangles (NFT) observed only in the transentorhinal cortex. Gallyas-Brrak stain. (c) The middle temporal gyrus only showed simple atrophy and neuronal ischemic changes. Hematoxylin and eosin (HE) stain. (d) positive pyramidal neurons for pentosidine in the middle temporal gyrus and (e) dorsal lateral prefrontal cortex. (f) The transentorhinal cortex did not show pentosidine positive neurons even though there were NFT positive cells. (g) The deposits of pentosidine were abundant in granule cells in the IV granular layer within the calcarine fissure, the primary visual cortex, (h) granule cells in the granular layer of the cerebellar cortex and (i) neurons in the external globus pallidus (GPe). (j) Examples of neural circuits in brain regions where pentosidine had accumulated; Thalamus (TH), DN (dentate neucleus), pontine (PN), and inferior olivary nuclei (ION).

Introduction

Carbonyl stress is an abnormal accumulation of reactive carbonyl species that leads to damage to proteins and increases their modification. In previous studies, we have shown that carbonyl stress increases in some patients with schizophrenia, even without complications of diabetes mellitus, a chronic kidney disease. In this subpopulation, plasma concentration of pentosidine, one of the biomarkers of advanced glycation end-products (AGEs) generated as a consequence of facilitated carbonyl stress, is correlated with a lower serum vitamin B6, a higher propensity to inpatient status, low educational status, a longer duration of hospitalization, higher doses of antipsychotic mediation, and lower processing speed scores on the Wechsler Adult Intelligence Scale. Although peripheral biomarkers have revealed an association with these clinical features, it is not yet clear whether pentosidine accumulates in the central nervous system and in which regions of the brain are sensitive to carbonyl stress. In this study, we microscopically examined the deposition of pentosidine throughout the brain of our first patient, which led to our hypothesis that carbonyl stress is enhanced in a subpopulation of schizophrenia.

Results

Pentosidine immunohistochemistry

Pentosidine immunoreactivities were found in both the nucleus and the cytoplasm of cells. As the previous study has shown, there is a weak pentosidine deposit in the pyramidal cells of the frontal and temporal cortices (Fig. 1d, e). However, in the hippocampal region including the transentorhinal cortex, pentosidine-positive pyramidal cells were not detected (Fig. 1f), where NFTs were deposited (Fig. 1b). Surprisingly, pentosidine deposits were abundant in granule cells in the IV granular layer within the calcarine fissure, the primary visual cortex, granule cells in the cerebellar cortex granular layer (Fig. 1g, h) and neurons in the external globus pallidus (GPe, Fig. 1i). The immunoreactivity of pentosidine in the entire brain region of the schizophrenia patient is summarized in Figure 2. In contrast, analysis of the primary visual cortex, cerebellar cortex, and globus pallidus in patients with diabetes nephropathy disease, and dementia matched for age and sex did not show accumulation of pentosidine in neurons (Figure 3).

Fig. 2. Pentosidine accumulates primarily in the cortico-basal ganglia-cerebellar cortex of the typical patient with GLO1-FS.
Fig. 2. Pentosidine accumulates primarily in the cortico-basal ganglia-cerebellar cortex of the typical patient with GLO1-FS.

Pentosidine deposits were prominent in the cerebellar cortex, pontine, and inferior olivary nuclei. Furthermore, pentosidine deposits were found in the dorsal lateral prefrontal cortex (middle prefrontal gyrus, area 9) and in the inferior parietal cortex (supramarginal gyrus, area 40) and the primary visual cortex. In other cortical regions, the anterior cingulate cortex and the primary motor cortex, there were no pentosidine positive neurons. In the basal ganglia and thalamus, pentosidine deposits were detected in neurons of the putamen, external globus pallidus (GPe), subthalamic nucleus (STN), and thalamus. In limbic structures, only neurons in the nucleus basalis of Meynert showed weak pentosidine deposits, but there were no pentosidine positive neurons in the amygdala, the nucleus accumbens, and the locus coeruleus.

Fig. 3. Control cases: No accumulation of pentosidine in patients with diabetic nephropathy and dementia
Fig. 3. Control cases: No accumulation of pentosidine in patients with diabetic nephropathy and dementia

No pentosidine accumulation in (a, d) granule cells in the IV granular layer within the calcarine fissure, the primary visual cortex, (b, e) granule cells in the granular layer of the cerebellar cortex, and (c, f) neurons in the external globus pallidus in age and sex matched patients with diabetic nephropathy and dementia.

Conclusion

This patient with GLO1-FS is the original case that leads to our hypothesis for the subpopulation of schizophrenia with enhanced carbonyl stress. Our findings suggested that the frontoparietal cortices, auditory cortex, primary visual cortex, cerebellum, and basal ganglia could be regions sensitive to carbonyl stress in the subpopulation. More research will be required to clarify the relationship between carbonyl stress and changes in brain tissue and mental function.



■ Role of advanced glycation end products in the longitudinal association between muscular strength and psychotic symptoms among adolescents.

Suzuki K, Yamasaki S, Miyashita M, Ando S, Toriumi K, Yoshikawa A, Nakanishi M, Morimoto Y, Kanata S, Fujikawa S, Endo K, Koike S, Usami S, Itokawa M, Washizuka S, Hiraiwa-Hasegawai M, Herbert Meltzer H, Kasai K, Nishida A, Arai M. Schizophr 8, 44 (2022).
https://doi.org/10.1038/s41537-022-00249-5

Research Summary

Muscular strength, assessed by handgrip, is a risk indicator for psychiatric disorders, including psychosis. However, the biological mechanisms underlying this association remain unclear.

Advanced glycation end products (AGEs) are derived from irreversible non-enzymatic modification of proteins and amino acids with reducing sugars. AGEs have been suggested to be responsible for the association between muscle strength and psychotic phenomena. Previous cross-sectional studies have reported an association between AGE accumulation and weak muscle strength. A recent longitudinal cohort study showed that AGEs can predict psychotic symptom trajectories among drug-naïve adolescents. Thus, there is a need to understand the role of AGEs in the association between muscle strength and psychosis to elucidate the biological mechanisms and early modifiable factors of psychosis.

In this study, we first evaluated the direction of the relationship between handgrip strength and urine levels of pentosidine, a representative AGEs in a population-based birth cohort of 1,542 adolescents at ages 12 and 14. Then, we examined the role of AGEs in the longitudinal association between handgrip strength and thought problems (TP), as a psychotic symptom indicator, in a subsample of 256 adolescents at ages 13 and 14.

As shown in Figure 1, an autoregressive cross-lagged model revealed that handgrip strength at age 12 negatively predicted pentosidine levels at age 14 (β=-0.20, p < 0.001), whereas pentosidine levels at age 12 did not predict handgrip strength at age 14 (β=0.04, p=0.062). Moreover, pentosidine levels had a significant indirect effect on the relationship between handgrip strength and TP (standard indirect effect=-0.051, p=0.012), which remained significant after adjusting for gender and preceded TP and pentosidine levels (Figure 2). Thus, adolescents with low muscular strength are at a high risk of developing psychotic symptoms, which could be mediated by AGEs.

In conclusion, our study shows the association between low muscular strength in adolescents and later psychotic symptoms, which could be mediated by AGEs. Future studies need to examine whether interventions focused on muscular strength prevent the accumulation of AGEs and the development of psychosis.

Figure 1: Cross-lagged panel model showing the direction of association between handgrip strength and pentosidine levels.
Figure 1: Cross-lagged panel model showing the direction of association between handgrip strength and pentosidine levels.

Note: Solid black line, path coefficient is statistically significant (p < 0.05); dotted line, path coefficient is not significant (p ≥ 0.05).

Figure 2: Path diagram describing the indirect effect between handgrip strength and thought problems via pentosidine.
Figure 2: Path diagram describing the indirect effect between handgrip strength and thought problems via pentosidine.

Note: solid black line, path coefficient is statistically significant (p < 0.05); dotted line, path coefficient is not significant (p ≥ 0.05). CFI: comparative fit index, RMSEA: root mean square error of approximation



AKR1A1 Variant Associated With Schizophrenia Causes Exon Skipping, Leading to Loss of Enzymatic Activity.

Iino K, Toriumi K, Agarie R, Miyashita M, Suzuki K, Horiuchi Y, Niizato K, Oshima K, Imai A, Nagase Y, Kushima I, Koike S, Ikegame T, Jinde S, Nagata E, Washizuka S, Miyata T, Takizawa S, Hashimoto R, Kasai K, Ozaki N, Itokawa M, Arai M. Front Genet. 2021 Dec 6;12:762999.
doi: 10.3389/fgene.2021.762999.

Highlights

  • Glucuronate (GlucA) levels were reported to be significantly higher in serum of patients with schizophrenia. The accumulation of GlucA is known to be related to treatment-resistant (TR) schizophrenia, since GlucA is known to promote drug excretion by forming conjugates with drugs.
  • Aldo-keto reductase family one member A1 (AKR1A1) is an oxidoreductase that catalyzes the reduction of GlucA. We identified 28 variants of the AKR1A1.
  • Among them, we found that c.753G > A variant induces exon skipping, leading to a loss of gene expression and enzymatic activity. AKR1A1 mRNA expression in the whole blood cells of individuals with the c.753G > A variant tended to be lower than that in those without the variants, leading to lower AKR activity.
  • Elevated GlucA may contribute to the pathophysiology of TR phenotype for these patients due to diminished enzymatic activity of AKR1A1 caused by mutation at c.753G > A.

Introduction

The accumulation of GlucA might be related to drug-resistant schizophrenia, since GlucA is known to promote drug excretion by forming conjugates with drugs. However, little is known about the molecular mechanisms underlying GlucA accumulation in patients with schizophrenia.

AKR1A1 is an approximately 40 kDa monomeric oxidoreductase, which is known to catalyze the reduction of GlucA. It can be assumed that AKR1A1 dysfunction leads accumulation of GlucA. Here, we aimed to explore genetic defects in AKR1A1 in patients with schizophrenia and identify the molecular mechanisms that cause the accumulation of GlucA.

Results

The AKR1A1 sequence was analyzed in patients with schizophrenia and control subjects, and 28 variants containing 4 novel variants were identified (Fig.1). Among them, four variants were found in the coding region. In particular, the c.753G>A variant was identified in 14 cases in the schizophrenia patient group and 5 subjects in the healthy group, and the c.264delC variant was observed in only one patient with schizophrenia.

Figure 1: DNA sequence chromatograms
Figure 1: DNA sequence chromatograms

Novel variants (blue arrows), variants in coding regions (V1–V4 variants: red arrows), and others (black arrows) are shown. Heterozygous sequence traces derived from individuals carrying (A) a cytosine deletion within exon 5 (V1 variant) and (B) a mutation from guanine to adenine at the first position of exon 8 (V3 variant).

A mutation at the first position of an exon has been reported to cause exon skipping by alternative splicing. To address whether the variant c.753G>A (V3 variant) located at the first position of exon 8 in the AKR1A1 gene results in exon skipping, a minigene assay was performed. The results showed that exon 8 skipping occurred in the A allele minigene (mutant [MT]) but not in the G allele (WT) in any cell type (Fig. 2A-C). In HEK293 and SH-SY5Y cells, MT considerably increased the frequency of exon skipping compared to WT (Fig.2C). The skipping of exon 8 causes a frameshift mutation and may result in the decreased enzymatic activity of AKR1A1 due to the c.753G>A variant, even though it is a silent mutation. To confirm this, we purified the AKR1A1 mutant recombinant protein produced by exon skipping and evaluated its activity. We found that AKR1A1 produced by the c.753G>A variant and c.264delC exhibited no activity, which was significantly lower than that of the WT AKR1A1 (Fig.2D, E).

Figure 2: Exon skipping induced by the c.753G>A variant in AKR1A1
Figure 2: Exon skipping induced by the c.753G>A variant in AKR1A1

(A) An outline of the splicing assay is shown. Exon 8 skipping was confirmed using cDNA generated from HEK293, SH-SY5Y, and 1321N1 cells expressing minigenes for WT or c.753G>A variant (mutant [MT]). (B) The results of the splicing assay are shown. The upper band indicates products including exons 7–9, whereas the lower band shows exon 8 skipping products, including only exons 7 and 9. (C) Data represent the mean of three independent experiments for the splicing assay. (D) GST and GST-AKR1A1s were purified and separated by sodium dodecyl sulfate polyacrylamide gel electrophoresis. (E) AKR1A1 activity of the purified GST-AKR1A1s was determined. AKR1A1 produced by the c.753G>A variant and c.264delC exhibited decreased enzymatic activity.

To investigate the effect of the c.753G>A variant on AKR1A1 enzymatic activity in patients with schizophrenia, AKR enzymatic activity in red blood cells from six patients with schizophrenia (SCZ#1~SCZ#6) and two control subjects (CON#1, CON#2) was measured. The enzymatic activity in four patients with GA (SCZ#1~SCZ#4) was slightly lower than that in four subjects with GG (SCZ#5, SCZ#6, CON#1, CON#2) (Fig.3A). Finally, we quantified mRNA level in the whole blood cells obtained from five subjects (CON#2 and SCZ#6 with c.753 GG alleles, and SCZ#1, SCZ#2, and SCZ#4 with c.753 GA alleles). We found that mRNA expression of AKR1A1 with c.753 GA alleles decreased to approximately 50% compared to that with c.753 GG (Fig.3B). These results suggest that the reduction of AKR activity in subjects with the variant may be caused from the reduction of gene expression.

Figure 3: AKR enzymatic activity and AKR1A1 gene expression in human
Figure 3: AKR enzymatic activity and AKR1A1 gene expression in human

(A) The enzymatic activities of AKR in the red blood cells of six patients with schizophrenia (SCZ#1 to #4 with the c.753G>A variant and SCZ#5 and #6 without the variant) and two control subjects (CON#1 and #2 without the variant) were examined. The enzymatic activity in patients with GA was slightly lower than that in subjects with GG. (B) The AKR1A1 mRNA expression in five subjects (SCZ#1, SCZ#3, SCZ#4, SCZ#6, and CON#2) was quantified by qPCR. The mRNA expression of AKR1A1 with c.753 GA alleles was decreased to approximately 50% compared to that with c.753 GG.



■ Fingertip advanced glycation end products and psychotic symptoms among adolescents

Miyashita M, Yamasaki S, Ando S, Suzuki K, Toriumi K, Horiuchi Y, Yoshikawa A, Imai A, Nagase Y, Miyano Y, Inoue T, Endo K, Morimoto Y, Morita M, Kiyono T, Usami S, Okazaki Y, Furukawa TA, Hiraiwa-Hasegawa M, Itokawa M, Kasai K, Nishida A, Arai M. Fingertip advanced glycation end products and psychotic symptoms among adolescents. NPJ Schizophr. 2021 Aug 12;7(1):37.
doi: 10.1038/s41537-021-00167-y.

Research Summary

Advanced glycation end products (AGEs) play a key role in the pathophysiology of chronic schizophrenia. However, the association between AGEs and psychotic symptoms among drug-naïve adolescents remains unclear. A total of 277 community-dwelling adolescents aged 13 years were analyzed in a prospective cohort study. Multinomial logistic regression analysis adjusted for confounders revealed that baseline AGEs might predict the risk of persistent psychotic symptoms, which indicated its involvement in the pathophysiology of early psychosis.

Case control studies have suggested that advanced glycation end products play a key role in the pathophysiology of chronic schizophrenia. However, the longitudinal association between advanced glycation end products and psychotic symptoms among drug-naïve adolescents remains unclear.

This study examined whether advanced glycation end products could predict the trajectory of psychotic symptoms in drug-naïve adolescents using data from prospective population-based biomarker subsample study of the Tokyo Teen Cohort. A total of 277 community-dwelling adolescents aged 13 years without antipsychotic medication were analyzed. Fingertip advanced glycation end products were measured in adolescents using non-invasive technology that can be used quickly. The trajectory of psychotic symptoms in a 12-month follow-up was assessed by experienced psychiatrists using a semi-structured interview. Longitudinal profiles of psychotic symptoms across the two time points (baseline, follow-up) were defined as follows:

i. No experiences: Individuals without a psychotic symptom at any time point.

ii. Transient: Individuals with a psychotic symptom determined at only one time-point.

iii. Persistent: Individuals with a psychotic symptom at two time points.

Of the 277 participants, 13 (4.7%) experienced persistent psychotic symptoms (psychotic symptoms at baseline and follow-up), 65 (23.5%) experienced transient psychotic symptoms (psychotic symptoms at baseline or follow-up), and 199 (71.8%) did not have psychotic symptoms (Figure A). Multinomial logistic regression analysis adjusted for age and sex revealed that baseline fingertip advanced glycation end products might predict the risk of persistent psychotic symptoms (odds ratio = 1.68; 95% confidence interval, 1.05–2.69; P = 0.03, Figure B).

Altogether, fingertip advanced glycation end products potentially predicted the trajectory of psychotic symptoms among drug-naive adolescents, which indicated its involvement in the pathophysiology of early psychosis. Noninvasive and easy operation of the measurement may be widely accepted in clinical and community settings, and further studies are required to identify strategies to reduce adolescent advanced glycation end products, which may contribute to preventing the onset of psychosis.

NPJ Schizophr. 2021 Aug 12;7(1):37.,Overviews of the results
Figure: Overviews of the results

The results of this study are summarized (A-B). Among 277 drug-naïve adolescents, 13 (4.7%) were assessed as persistent psychotic symptoms. Among the rest of the sample, 199 (71.8 %) and 65 (23.5 %) participants had no psychotic symptoms and transient psychotic symptoms, respectively (A). Multinomial logistic regression analysis adjusted for age and sex demonstrated that ORs for persistent and transient psychotic symptoms compared with those for no psychotic symptoms were 1.78 (95% CI, 1.14–2.76, P = 0.011) and 1.05 (95% CI, 0.79–1.40, P = 0.73), respectively, for a 1 SD increase in fingertip AGEs. The significance and magnitude of effect size for persistent psychotic symptoms remained even after excluding five participants who were using antipsychotic medications (OR, 1.68; 95% CI, 1.05–2.69; P = 0.03) (B). Error bars indicate the 95% confidence interval.



■ Combined glyoxalase 1 dysfunction and vitamin B6 deficiency in a schizophrenia model system causes mitochondrial dysfunction in the prefrontal cortex.

Toriumi K, Berto S, Koike S, Usui N, Dan T, Suzuki K, Miyashita M, Horiuchi Y, Yoshikawa A, Asakura M, Nagahama K, Lin H-C, Sugaya Y, Watanabe T, Kano M, Ogasawara Y, Miyata T, Itokawa M, Konopka G, Arai M. Redox Biology (2021) 45: 102057.
DOI : 10.1016/j.redox.2021.102057

Highlights

  • We generated a novel mouse model for this subgroup of schizophrenia patients by feeding Glo1 knockout mice VB6-deficent diets (KO/VB6(-)), and we found that the KO/VB6(-) mice showed schizophrenia-like behavioral impairments such as prepulse inhibition (PPI) deficit.
  • Methylglyoxal (MG) accumulation is detected in the prefrontal cortex (PFC), hippocampus and striatum in KO/VB6(-) mice.
  • KO/VB6(-) mice exhibit schizophrenia-like behavioral deficits.
  • Gene expression related to mitochondria is impaired in the PFC of KO/VB6(-) mice.
  • Mitochondria in the PFC of KO/VB6(-) mice show respiratory dysfunction, leading to an enhanced oxidative stress.
Overviews of the results
Figure: Overviews of the results

Introduction

SMethylglyoxal (MG) is a highly reactive α-ketoaldehyde formed endogenously as a byproduct of the glycolytic pathway. MG accumulates under conditions of hyperglycemia, impaired glucose metabolism, or oxidative stress. An excess of MG formation causes mitochondrial impairment and reactive oxygen species (ROS) production that further increases oxidative stress. It also leads to the formation of advanced glycation end products (AGEs) due to MG reacting with proteins, DNA, and other biomolecules, which can induce aberrant inflammation via binding to receptors for AGEs (RAGE). To remove the toxic MG, various detoxification systems work together in vivo, including the glyoxalase system which enzymatically degrades MG using glyoxalase 1 (GLO1) and GLO2, and the MG scavenging system by vitamin B6 (VB6).

Schizophrenia is a heterogeneous psychiatric disorder characterized by positive symptoms, such as hallucinations and delusions, negative symptoms, such as anhedonia and flat affect, and cognitive impairment. We have reported that several patients with schizophrenia have a novel heterozygous frameshift and a single nucleotide variation (SNV) in GLO1 that results in reductions of enzymatic activity. Furthermore, we have reported that VB6 (pyridoxal) levels in peripheral blood of patients with schizophrenia are significantly lower than that of healthy controls. More than 35% of patients with schizophrenia have low levels of VB6 (clinically defined as male: < 6 ng/ml, female: < 4 ng/ml). However, the effects of MG detoxification deficits on the pathophysiology of schizophrenia in vivo remain unclear.

Results

In this study, we created a novel mouse model for MG detoxification deficits by feeding Glo1 knockout mice VB6-deficent diets (KO/VB6(-)) and evaluated the effects of impaired MG detoxification systems on brain function. KO/VB6(-) mice accumulated MG in the PFC, hippocampus, and striatum, and displayed behavioral deficits, such as impairments of social interaction and cognitive memory and a sensorimotor deficit in the PPI test. Furthermore, we found aberrant gene expression related to mitochondria function in the PFC of the KO/VB6(-) mice by RNA-sequencing and weighted gene co-expression network analysis (WGCNA). Finally, we demonstrated abnormal mitochondrial respiratory function and subsequently enhanced oxidative stress in the PFC of KO/VB6(-) mice in the PFC. These findings suggest that MG detoxification deficits may cause the observed behavioral deficits via mitochondrial dysfunction and oxidative stress in the PFC.

This is the first report to show that MG detoxification deficits are involved in the development of schizophrenia. Considering the molecular mechanism revealed in this study, antioxidants to prevent oxidative stress and VB6 supplementation may be effective as a new therapeutic strategy for patients with MG detoxification deficits, GLO1 dysfunction and VB6 deficiency.



■ Vitamin B6 deficiency hyperactivates the noradrenergic system, leading to social deficits and cognitive impairment.

Toriumi K, Miyashita M, Suzuki K, Yamasaki N, Yasumura M, Horiuchi Y, Yoshikawa A, Asakura M, Usui N, Itokawa M, Arai M. Transl Psychiatry. 2021 May 3;11(1):262. doi: 10.1038/s41398-021-01381-z.PMID: 33941768

Highlights

  • A mouse model was generated to mimic the condition of vitamin B6 (VB6) deficiency observed in a subtype of patients with schizophrenia by feeding with a VB6-lacking diet.
  • The noradrenergic system in the brain of VB6-deficient (VB6(-)) mice was enhanced, leading to social deficits and cognitive impairment.
  • Inhibiting the excessive noradrenaline (NA) release by VB6 supplementation into the brain or treatment with α2A adrenoreceptor agonist guanfacine suppressed the increased NA metabolism and ameliorated the behavioral deficits.
Fig. 1: Overviews of the results

(A) VB6(-) mice showed hyperactivate noradrenergic (NAergic) signaling, resulting in behavioral deficits comparable to schizophrenia. (B) These are ameliorated by VB6 supplementation into the brain or treatment with the α2A adrenoreceptor agonist guanfacine (GFC), which suppresses NA release.

Introduction

Schizophrenia is a heterogeneous psychiatric disorder characterized by positive symptoms such as hallucinations and delusions, negative symptoms such as apathy and lack of emotion, and cognitive impairment. We have reported that VB6 (pyridoxal) levels in peripheral blood of a subpopulation of patients with schizophrenia is significantly lower than that of healthy controls. More than 35% of patients with schizophrenia have low levels of VB6 (clinically defined as male: < 6 ng/ml, female: < 4 ng/ml). VB6 level is inversely proportional to severity score on the positive and negative symptom scale (PANSS), suggesting that VB6 deficiency might contribute to the development of schizophrenia symptoms. In fact, a recent review has shown the decreased VB6 in patients with schizophrenia as the most convincing evidence in peripheral biomarkers for major mental disorders. Additionally, we recently reported that high-dose VB6 (pyridoxamine) was effective in alleviating psychotic symptoms, particularly the PANSS negative and general subscales, in a subset of patients with schizophrenia. Although a link between lower VB6 level and schizophrenia is widely hypothesized, the mechanism behind this remains poorly understood.

Results

VB6 is not synthesized de novo in humans, but is primarily obtained from foods. In the present study, to clarify the relationship between VB6 deficiency and schizophrenia, we generated VB6-deficient (VB6(-)) mice through feeding with a VB6-lacking diet as a mouse model for the subpopulation of schizophrenia patients with VB6 deficiency.

After feeding for 4 weeks, plasma VB6 level in VB6(-) mice decreased to 3% of that in control mice. The VB6(-) mice showed social deficits and cognitive impairment. Furthermore, the VB6(-) mice showed a marked increase in 3-methoxy-4-hydroxyphenylglycol (MHPG) in the brain, suggesting enhanced NA metabolism in VB6(-) mice (Fig. 2A-C). We confirmed the increased NA release in the prefrontal cortex and the striatum of VB6(-) mice through in vivo microdialysis (Fig. 2D). These findings suggest that the activities of NAergic neuronal systems are enhanced in VB6(-) mice.

Fig. 2: Enhanced noradrenergic system in VB6(-) mice

(A) NA, (B) MHPG, and (C) NA turnover in each brain region of VB6(-) mice were measured. (D) NA release in the prefrontal cortex was measured. High K+ stimulation was performed at the time point of 0 min. VB6(-) mice showed hyperactivate NAergic signaling.

Furthermore, VB6 supplementation directly into the brain using an osmotic pump ameliorated the hyperactivation of the NAergic system and behavioral abnormalities (Fig.3A-C). indicating that the enhanced NA turnover and the behavioral deficits shown in the VB6(-) mice are attributed to VB6 deficiency in the central nervous system. In addition, the α2A adrenergic receptor agonist guanfacine also improved the hyperactivated NAergic system in the frontal cortex and behavioral disorders (Fig. 3D-F). These results show that the behavioral deficits in VB6(-) mice may be caused by an enhancement of NAergic signaling.

Fig. 2: Improvement of NAergic hyperactivation and behavioral deficits in VB6(-) mice by VB6 supplementation into the brain and α2A adrenergic receptor agonist guanfacine
Fig. 3: Improvement of NAergic hyperactivation and behavioral deficits in VB6(-) mice by VB6 supplementation into the brain and α2A adrenergic receptor agonist guanfacine

(A)(D) The NA turnover in the PFC were assessed. The results in (B)(E) social interaction test and (C)(F) novel object recognition test were shown. The VB6 supplementation into the brain and guanfacine ameliorated the enhanced NAergic system and the behavioral deficits observed in VB6(-) mice.

Schizophrenic patients with VB6 deficiency, who account for more than 35% of all patients, present with relatively severe clinical symptoms and treatment resistance. Our findings suggest that a new therapeutic strategy targeting the NAergic system might be effective for these patients. They will also provide evidence based on pathophysiology for a new therapeutic strategy called "VB6 treatment for schizophrenia," which we are currently conducting clinical research on.



■ Research interest

Metabolic profiles in carbonyl stress, oxidative stress, and advanced glycation end products

The profiling of the peripheral metabolic system is a viable schizophrenia research strategy that can lead to earlier diagnostic methods, elucidation of its molecular mechanisms, and novel strategies for the prevention and treatment. We focus on 1) developing individualized medicine for treating schizophrenia, 2) investigating factors involved in disease onset, and 3) understanding the molecular pathology by using biomarkers to overcome the barrier of heterogeneity. Our research outcomes will be applied to drug development by establishing a new biomarker-based field of research in molecular psychiatry. Data obtained from metabolomics, genomics, induced pluripotent stem (iPS) cell models, animal models, post-mortem brain analyses, neuropsychology, and genetic counseling research will be consolidated to elucidate the genetic and environmental factors relevant to psychiatric disorders such as schizophrenia.


Masanari Itokawa
Makoto Arai

“The correlations between the clinical features of patients exhibiting biomarkers and cell biology/animal model data could create new ways to improve patients’ quality of life.”

This biomarker-based approach is anticipated to become an innovative and creative strategy for elucidating the metabolic system of schizophrenia disease expression independently of conventional pathological hypotheses. Verification in cellular and animal models can shed light on the molecular mechanisms underlying the utility of naturally-derived substances, and is expected to lead to the future development of much safer treatments and prophylactic methods.

Schizophrenia Research Project,
Project Leader
Makoto ARAI Ph.D.


Characterization of the Etiology of Schizophrenia and Development of Treatments and Preventative Measures

(https://www.igakuken.or.jp/english/project/detail/schizo-dep.html)

  • To reveal biomarkers that will help diagnose the treatment of schizophrenia
  • To work with metropolitan hospitals to develop methods for early diagnosis
  • To elucidate the cause of schizophrenia and develop new methods of prevention and treatment



Members of the project

■ Project Leader

  • Makoto Arai Ph.D. / Project Leader

■ Researcher

  • Masanari Itokawa M.D., Ph.D. / Vice Director General
  • Yasue Horiuchi Ph.D. / Chief Researcher
  • Kazuya Toriumi Ph.D. / Chief Researcher
  • Hiroaki Ishida Ph.D. / Senior Researcher

■ Staff

  • Nanako Obata / Technician
  • Izumi Nohara / Technician
  • Mai Hatakenaka / Technician
  • Tomoko Inoue / Yoga Therapist

■ Secretary

  • Ikuyo Kito / B.S.

■ Student

  • Wang Tianran / The University of Tokyo
  • Asakura Mai / Tokyo Medical and Dental University
  • Miyano Yasuhiro / Niigata University
  • Iino Kyoka/ Tokyo Medical and Dental University
  • Ozawa Azuna/ Niigata University
  • Tomita Yasufumi/ The University of Tokyo
  • Masada Mayuko/ The University of Tokyo