Ravinder D. Reddy

Oxidative Damage and Schizophrenia An Overview of the Evidence and Its Therapeutic Implications

Free radicals are highly reactive chemical species generated during normal metabolic processes, which in excess can lead to membrane damage. Elaborate anti-oxidant defence systems exist to protect against oxidative stress.There is accumulating evidence of altered antioxidant capacity in schizophrenia. Membrane dysfunction can be secondary to free radical-mediated pathology, and may contribute to specific aspects of schizophrenic symptomatology and complications of its treatment. Specifically, free radical-mediated abnormalities may contribute to the development of a number of clinically significant consequences, including prominent negative symptoms, tardive dyskinesia, neurological ‘soft’ signs and parkinsonian symptoms. Our previous results showing altered membrane dynamics and antioxidant enzyme activities in schizophrenia, and findings from other investigators, are consistent with the notion of free radical-mediated neurotoxicity in schizophrenia. These findings provide a theoretical basis from which the development of novel therapeutic strategies such as fatty acid and antioxidant supplementation can occur in the future.

Membrane phospholipid abnormalities in postmortem brains from schizophrenic patients.

Previous studies in schizophrenia have shown alterations in membrane phospholipids and polyunsaturated fatty acids. However, these studies have primarily examined peripheral (non-neuronal) cell types. The purpose of the present study was to examine whether the membrane deficits seen in peripheral tissues are also observed in the brain. The caudate was the primary region of interest for this study. Using high-pressure liquid chromatography in conjunction with an evaporative light-scattering detector, we first measured the level of various membrane phospholipids (PL) in schizophrenic (n=11) and control groups with (n=7) and without (n=14) other mental disorders. Polyunsaturated fatty acids (PUFAs) were then determined by capillary gas chromatography. Within groups, there are no significant correlations between membrane PL levels and other collection and demographic parameters including age, postmortem interval, storage time and brain weight. Significantly lower amounts of phosphatidylcholine and phosphatidylethanolamine were found in postmortem brain tissue from schizophrenic patients than in those from control groups, even after accounting for potential confounds. In addition, strong reductions of total PUFAs and saturated fatty acids were found in schizophrenic brains, relative to control brains. Specifically, the reduced PUFAs were largely attributable to decreases in arachidonic acid (AA) and, to a lesser extent, its precursors, linoleic and eicosadienoic acids. There are no significant differences between the control groups with and without other mental disorders. The present findings suggest that deficits identified in peripheral membranes may also be present in the brain from schizophrenic patients. Such a deficit in membrane AA may contribute to the many biological, physiological, and clinical phenomena observed in schizophrenia.

Free radical pathology in schizophrenia: a review

There is evidence that free radicals are involved in membrane pathology, and may play a role in schizophrenia. Free radicals are reactive chemical species generated during normal metabolic processes, and, in excess, can damage lipids, proteins, and DNA. Regions of high oxygen consumption, lipid content, and transition metals are at particular risk. Hence, neuronal membranes are uniquely vulnerable to radical-mediated damage. Elaborate antioxidant defense systems exist to protect against oxidative stress. In schizophrenia there is evidence for dysregulation of free radical metabolism, as detected by abnormal activities of critical antioxidant enzymes and other indices of lipid peroxidation in plasma, red blood cells, and cerebrospinal fluid. Such abnormalities have been associated with tardive dyskinesia, negative symptoms, neurological signs, poor premorbid function, and CT scan abnormalities. Studies to date have generally been exploratory. Further elucidation of the role of free radicals and antioxidants in schizophrenia and its treatment will require systematic investigation.

Correlations between peripheral polyunsaturated fatty acid content and in vivo membrane phospholipid metabolites

BACKGROUNDnThere is evidence for membrane abnormalities in schizophrenia. It is unclear whether the observed membrane deficits in peripheral cells parallel central membrane phospholipid metabolism. To address this question we examined the relations between red blood cell polyunsaturated fatty acids and brain phospholipid metabolites from different regions of interest in schizophrenia and healthy subjects.nnnMETHODSnRed blood cell membrane fatty acids were measured by capillary gas chromatography and in vivo brain phospholipid metabolite levels were measured using a multi-voxel (31)P Magnetic Resonance Spectroscopy technique on 11 first-episode, neuroleptic-naïve schizophrenic subjects and 11 normal control subjects.nnnRESULTSnBoth the total polyunsaturated fatty acids and the individual 20:4(n-6) contents were significantly correlated with the freely-mobile phosphomonoester [PME(s-tau(c))] levels (r =.5643, p =.0062 and r =.6729, p =.0006, respectively). The 18:2(n-6) polyunsaturated fatty acids content correlated positively with freely-mobile phosphodiester [PDE(s-tau(c))] levels (r =.5573, p =.0071). The above correlations were present in the combined right and left prefrontal region of the brain, while other regions including the basal ganglia, occipital, inferior parietal, superior temporal and centrum semiovale yielded no significant correlations.nnnCONCLUSIONSnOur preliminary data support the association between the decreased red blood cell membrane phospholipid polyunsaturated fatty acids content and the decreased building blocks [PME(s-tau(c))] and breakdown products [PDE(s-tau(c))] of membrane phospholipids in the prefrontal region of first-episode, neuroleptic-naïve schizophrenic subjects.

Altered interactions of tryptophan metabolites in first-episode neuroleptic-naive patients with schizophrenia.

Schizophrenia is characterized by complex and dynamically interacting perturbations in multiple neurochemical systems. In the past, evidence for these alterations has been collected piecemeal, limiting our understanding of the interactions among relevant biological systems. Earlier, both hyper- and hyposerotonemia were variously associated with the longitudinal course of schizophrenia, suggesting a disturbance in the central serotonin (5-hydroxytryptamine (5-HT)) function. Using a targeted electrochemistry-based metabolomics platform, we compared metabolic signatures consisting of 13 plasma tryptophan (Trp) metabolites simultaneously between first-episode neuroleptic-naive patients with schizophrenia (FENNS, n=25) and healthy controls (HC, n=30). We also compared these metabolites between FENNS at baseline (BL) and 4 weeks (4w) after antipsychotic treatment. N-acetylserotonin was increased in FENNS-BL compared with HC (P=0.0077, which remained nearly significant after Bonferroni correction). N-acetylserotonin/Trp and melatonin (Mel)/serotonin ratios were higher, and Mel/N-acetylserotonin ratio was lower in FENNS-BL (all P-values<0.0029), but not after treatment, compared with HC volunteers. All three groups had highly significant correlations between Trp and its metabolites, Mel, kynurenine, 3-hydroxykynurenine and tryptamine. However, in the HC, but in neither of the FENNS groups, serotonin was highly correlated with Trp, Mel, kynurenine or tryptamine, and 5-hydroxyindoleacetic acid (5HIAA) was highly correlated with Trp, Mel, kynurenine or 3-hydroxykynurenine. A significant difference between HC and FENNS-BL was further shown only for the Trp–5HIAA correlation. Thus, some metabolite interactions within the Trp pathway seem to be altered in the FENNS-BL patients. Conversion of serotonin to N-acetylserotonin by serotonin N-acetyltransferase may be upregulated in FENNS patients, possibly related to the observed alteration in Trp–5HIAA correlation. Considering N-acetylserotonin as a potent antioxidant, such increases in N-acetylserotonin might be a compensatory response to increased oxidative stress, implicated in the pathogenesis of schizophrenia.

Human plasma glutathione peroxidase and symptom severity in schizophrenia

BACKGROUNDnPrevious studies have shown impaired antioxidant defense system in schizophrenia, including alterations in glutathione peroxidase (GSH-Px) activity in erythrocytes. There exists a related enzyme, human plasma GSH-Px (hpGSH-Px), that has not been previously examined in schizophrenia.nnnMETHODSnAn enzyme-linked immunoassay was used to determine hpGSH-Px levels in male schizophrenic patients (n = 39), using a within-subject, on-off haloperidol (HD) treatment design, compared with age- and gender-matched normal control subjects (n = 37).nnnRESULTSnhpGSH-Px was not significantly different between normal control subjects and patients, consistent with our previous findings in erythrocyte GSH-Px. There were no significant treatment effects. hpGSH-Px was significantly and positively correlated with psychosis rating scores in patients both on and off HD treatment.nnnCONCLUSIONSnAlthough not different from normal controls, hpGSH-Px levels in patients may reflect oxidative stress associated with greater psychosis severity. The present findings thus suggest that schizophrenic patients, without obvious increase of endogenous antioxidant enzymes (e.g., hpGSH-Px), may be at risk for oxidative damage.

3-Hydroxykynurenine and clinical symptoms in first-episode neuroleptic-naive patients with schizophrenia

One branch of the tryptophan catabolic cascade is the kynurenine pathway, which produces neurotoxic [3-hydroxykynurenine (3-OHKY), quinolinic acid] and neuroinhibitory (kynurenic acid) compounds. Kynurenic acid acts as a competitive antagonist at the glycine site of N-methyl-d-asparate receptors at high concentrations and as a non-competitive antagonist on the α7-nicotinic acetylcholine receptor at low concentrations. Kynurenine compounds also influence cognitive functions known to be disrupted in schizophrenia. Alterations in tryptophan metabolism are therefore of potential significance for the pathophysiology of this disorder. In this paper, tryptophan metabolites were measured from plasma using high-pressure liquid chromatography coupled with electrochemical coulometric array detection, and relationships were tested between these metabolic signatures and clinical symptoms for 25 first-episode neuroleptic-naive schizophrenia patients. Blood samples were collected and clinical and neurological symptoms were rated at baseline and again at 4 wk following initiation of treatment. Level of 3-OHKY and total clinical symptom scores were correlated when patients were unmedicated and neuroleptic-naive, and this relationship differed significantly from the correlation observed for patients 4 wk after beginning treatment. Baseline psychosis symptoms were predicted only by neurological symptoms. Moreover, baseline 3-OHKY predicted clinical change at 4 wk, with the lowest concentrations of 3-OHKY being associated with the greatest improvement in symptoms. Taken together, our findings suggest a neurotoxic product of tryptophan metabolism, 3-OHKY, predicts severity of clinical symptoms during the early phase of illness and before exposure to antipsychotic drugs. Baseline level of 3-OHKY may also predict the degree of clinical improvement following brief treatment with antipsychotics.

Age-related changes of n-3 and n-6 polyunsaturated fatty acids in the anterior cingulate cortex of individuals with major depressive disorder.

Accumulating evidence finds a relative deficiency of peripheral membrane fatty acids in persons with affective disorders such as unipolar and bipolar depression. Here we sought to investigate whether postmortem brain fatty acids within the anterior cingulate cortex (BA-24) varied according to the presence of major depression at the time of death. Using capillary gas chromatography we measured fatty acids in a depressed group (n=12), and in a control group without lifetime history of psychiatric diagnosis (n=14). Compared to the control group, the depressed group showed significantly lower concentrations of numerous saturated and polyunsaturated fatty acids including both the n-3 and n-6 fatty acids. Additionally, significant correlations between age at death and precursor (or metabolites) in the n-3 fatty acid pathway were demonstrated in the depressed group but not in control subjects. In the n-6 fatty acid family, the ratio of 20:3(n-6)/18:2(n-6) was higher in patients than in control groups, whereas the ratio of 20:4(n-6)/20:3(n-6) was relatively decreased in patients. Lastly, a significant negative correlation between age and the ratio of 20:4(n-6) to 22:6(n-3) was found in patients, but not in controls. Taken together, decreases in 22:6(n-3) may be caused, at least in part, by the diminished formation of 20:5(n-3), which is derived from 20:4(n-3) through a Delta5 desaturase reaction. The present findings from postmortem brain tissue raise the possibility that an increased ratio of 20:4(n-6) to 22:6(n-3) may provide us with a biomarker for depression. Future research should further investigate these relationships.

Homeostatic imbalance of purine catabolism in first-episode neuroleptic-naïve patients with schizophrenia.

Background Purine catabolism may be an unappreciated, but important component of the homeostatic response of mitochondria to oxidant stress. Accumulating evidence suggests a pivotal role of oxidative stress in schizophrenia pathology. Methodology/Principal Findings Using high-pressure liquid chromatography coupled with a coulometric multi-electrode array system, we compared 6 purine metabolites simultaneously in plasma between first-episode neuroleptic-naïve patients with schizophrenia (FENNS, nu200a=u200a25) and healthy controls (HC, nu200a=u200a30), as well as between FENNS at baseline (BL) and 4 weeks (4w) after antipsychotic treatment. Significantly higher levels of xanthosine (Xant) and lower levels of guanine (G) were seen in both patient groups compared to HC subjects. Moreover, the ratios of G/guanosine (Gr), uric acid (UA)/Gr, and UA/Xant were significantly lower, whereas the ratio of Xant/G was significantly higher in FENNS-BL than in HC. Such changes remained in FENNS-4w with exception that the ratio of UA/Gr was normalized. All 3 groups had significant correlations between G and UA, and Xan and hypoxanthine (Hx). By contrast, correlations of UA with each of Xan and Hx, and the correlation of Xan with Gr were all quite significant for the HC but not for the FENNS. Finally, correlations of Gr with each of UA and G were significant for both HC and FENNS-BL but not for the FENNS-4w. Conclusions/Significance During purine catabolism, both conversions of Gr to G and of Xant to Xan are reversible. Decreased ratios of product to precursor suggested a shift favorable to Xant production from Xan, resulting in decreased UA levels in the FENNS. Specifically, the reduced UA/Gr ratio was nearly normalized after 4 weeks of antipsychotic treatment. In addition, there are tightly correlated precursor and product relationships within purine pathways; although some of these correlations persist across disease or medication status, others appear to be lost among FENNS. Taken together, these results suggest that the potential for steady formation of antioxidant UA from purine catabolism is altered early in the course of illness.

Metabolic investigation in psychiatric disorders.

A multiplicity of theories have been proposed over the years that aim to conceptualize the pathophysiology of neuropsychiatric disorders, including impaired neurotransmission, viral infections, genetic mutation, energy metabolism deficiency, excitotoxicity, oxidative stress, and others. It is likely that complex disorders such as schizophrenia, bipolar disorder, and major depression are associated with multiple etiologies and pathogenetic mechanisms. In light of the interwoven biochemistry of human organs, identifying a network of multiple interacting biochemical pathways that account for the constellation of clinical and biological features would advance our understanding of these disorders. One such approach is to evaluate simultaneously the multiple metabolites in order to uncover the dynamic relations in the relevant biochemical systems. These metabolites are a group of low-molecular-weight, redox-active compounds, such as antioxidants, amino acids, catecholamines vitamins, lipids, and nucleotides, which reflect the metabolic processes, including anabolism and catabolism as well as other related cellular processes (e.g., signal transduction, regulation, detoxification, etc.). Such an analytic approach has the potential to yield valuable insights into the likely complex pathophysiological mechanisms that affect multiple metabolic pathways and thereby offer multiple windows of therapeutic opportunities.