Clinical subtyping reveals significant differences in calcium-dependent phospholipase A2 activity in schizophrenia

Niacin Skin Flush Backs-From the Roots of the Test to Nowadays Hope

The niacin skin flush test (NSFT) is a simple method used to assess the content of fatty acids in cell membranes and is a possible indicator of factors hidden behind various outcomes in patients. The purpose of this paper is to determine the potential usefulness of NSFT in mental disorder diagnostics along with the determination of factors that may affect its results. The authors reviewed articles from 1977 onwards, focusing on the history, variety of methodologies, influencing factors, and proposed mechanisms underlying its performance. Research indicated that NSFT could be applicable in early intervention, staging in psychiatry, and the search for new therapeutic methods and drugs based on the mechanisms of NSFT action. The NSFT can contribute to defining an individualized diet for patients and prevent the development of damaging disease effects at an early stage. There is promising evidence for supplementation with polyunsaturated fatty acids, which have a beneficial influence on the metabolic profile and are effective even in the subclinical phase of the disease. NSFT can contribute to the new classification of diseases and a better understanding of certain mental disorders' pathophysiology. However, there is a need to establish a validated method for assessing the NSFT results.

Attenuated and delayed niacin skin flushing in schizophrenia and affective disorders: A potential clinical auxiliary diagnostic marker

AIM

Schizophrenia and affective disorders all show high heterogeneity in clinical manifestations. A lack of objective biomarkers has long been a challenge in the clinical diagnosis of these diseases. In this study, we aimed to investigate the performance of niacin skin flushing in schizophrenia and affective disorders and determine its clinical potential as an auxiliary diagnostic marker.

METHODS

In this case-control study, niacin skin-flushing tests were conducted in 613 patients (including 307 schizophrenia patients, 179 bipolar disorder patients, and 127 unipolar depression patients) and 148 healthy controls (HCs) with a modified method. Differences in niacin skin-flushing responses were compared with adjustment for gender, BMI, age, nicotine dependence, alcohol consumption and educational status. A diagnostic model was established based on a bivariate cut-off.

RESULTS

Schizophrenia and affective disorders showed similar performance of niacin bluntness, characterized by attenuated flushing extent and reduced flushing rate. An innovative bivariate cut-off was established according to these two features, by which we could identify -patients with either schizophrenia or affective disorders from HCs with a sensitivity of 55.28%, a specificity of 83.56% and a positive predictive value of 93.66%.

CONCLUSIONS

The niacin-induced skin flushing was prevalently blunted in patients with schizophrenia or affective disorders, indicating a promising potential as an auxiliary diagnostic marker in risk prediction and clinical management of these disorders. Additionally, the niacin-blunted subgroup implies a common biological basis in the investigated disorders, which provokes new thoughts in elucidating the pathological mechanisms.

Inflammation and JNK's Role in Niacin-GPR109A Diminished Flushed Effect in Microglial and Neuronal Cells With Relevance to Schizophrenia

Schizophrenia is a neuropsychiatric illness with no single definitive aetiology, making its treatment difficult. Antipsychotics are not fully effective because they treat psychosis rather than the cognitive or negative symptoms. Antipsychotics fail to alleviate symptoms when patients enter the chronic stage of illness. Topical application of niacin showed diminished skin flush in the majority of patients with schizophrenia compared to the general population who showed flushing. The niacin skin flush test is useful for identifying patients with schizophrenia at their ultra-high-risk stage, and understanding this pathology may introduce an effective treatment. This review aims to understand the pathology behind the diminished skin flush response, while linking it back to neurons and microglia. First, it suggests that there are altered proteins in the GPR109A-COX-prostaglandin pathway, inflammatory imbalance, and kinase signalling pathway, c-Jun N-terminal kinase (JNK), which are associated with diminished flush. Second, genes from the GPR109A-COX-prostaglandin pathway were matched against the 128-loci genome wide association study (GWAS) for schizophrenia using GeneCards, suggesting that G-coupled receptor-109A (GPR109A) may have a genetic mutation, resulting in diminished flush. This review also suggests that there may be increased pro-inflammatory mediators in the GPR109A-COX-prostaglandin pathway, which contributes to the diminished flush pathology. Increased levels of pro-inflammatory markers may induce microglial-activated neuronal death. Lastly, this review explores the role of JNK on pro-inflammatory mediators, proteins in the GPR109A-COX-prostaglandin pathway, microglial activation, and neuronal death. Inhibiting JNK may reverse the changes observed in the diminished flush response, which might make it a good therapeutic target.

[Membrane lipids in schizophrenia and early phases of psychosis: Potential biomarkers and therapeutic targets?]

The various roles of membrane lipids in human health has urged researchers to study their impact in neuropsychiatric diseases, especially in schizophrenia spectrum disorders and more recently in early stages of psychosis. The progress in mass spectrometry technologies now allows a more comprehensive analysis of phospholipids (PL) and their fatty acid (FA) molecular species. FA are defined by a carbon chain of variable length and are said to be unsaturated when their chain has one or more carbon-carbon double bonds. The PL are composed of a hydrophilic polar head with a phosphoric acid group and an hydrophobic part with FAs; they encompass glycerophospholipids and sphingolipids. The plasma membrane is a complex and dynamic structure consisting of a lipid bilayer composed of an outer layer and an inner layer of specific lipid composition. The permanent remodeling of membrane lipids involves phospholipases especially the phospholipase A2. Seventy percent of the brain consists of lipids from different classes and molecular species. Most of the brain lipids are composed of polyunsaturated fatty acid (PUFA)-enriched diacyl classes where omega-3 and omega-6 molecular species predominate. The balance between omega-3 and omega-6 is important for the neurodevelopment. PUFA are also involved in neurogenesis and neurotransmission. Sphingomyelin (SM) is a sphingolipid that influences inflammation, cell proliferation and lipid rafts formation. It is an important component of myelin sheaths of white matter and therefore is involved in cerebral connectivity. In rat models, deficiency in omega-3 causes abnormalities in dopaminergic neurotransmission, impacts on the functioning of some receptors (including cannabinoids CB1, glutamatergic N-methyl-D-aspartate receptor, NMDA), and increases sensitivity to hallucinogens. In contrast, omega-3 supplementation improves cognitive function and prevents psychotic-like behavior in some animal models for schizophrenia. It also reduces oxidative stress and prevents demyelination. The historical membrane hypothesis of schizophrenia has led to explore the lipids abnormality in this disorder. This hypothesis was initially based on the observation of an abnormal membrane prostaglandin production in schizophrenia caused by a membrane arachidonic acid deficiency. It has evolved emphasizing the various PUFA membrane's roles in particular regarding oxidative stress, inflammation and regulation of the NMDA receptors. In patients with mental disorders, low omega-3 index is more frequent than in the general population. This lipid abnormality could lead to myelination abnormalities and cognitive deficits observed in patients. It could also participate in oxidative stress abnormalities and inflammation reported in schizophrenia. On the other hand, low omega-3 index deficit was reported to be associated with an increased cardiovascular risk, and omega-3 supplementation may also have a positive cardiovascular impact in psychiatric patients, even more than in the general population. The presence of membrane lipid abnormalities is also found in patients during the first psychotic episode (FEP). The omega-3 supplementation improved the recovery rate and prevented the loss of gray matter in FEP. In patients at ultra-high risk to develop a psychotic disorder (UHR), omega-3 supplementation has been associated with a reduction of the rate of conversion to psychosis and with metabolic changes, such as decreased activity of phospholipase A2. However, this study has not as yet been replicated. Not all patients exhibit lipid abnormalities. Several studies, including studies from our team, have found a bimodal distribution of lipids in patients with schizophrenia. But some studies have found differences (in PUFA) in the acute phase whereas our studies (on phospholipids) are in chronic phases. It will be interesting to study in more depth the links between these two parameters. Furthermore, we identified a subgroup which was identified with a deficit in sphingomyelin and PUFA whereas others have found an increase of sphingomyelin. Individuals with this abnormal lipid cluster had more cognitive impairments and more severe clinical symptoms. Because the niacin test is an indirect reflection of arachidonic acid levels, it has been proposed to identify a subset of patients with membrane lipids anomalies. Niacin test response is influenced by several factors related to lipid metabolism, including cannabis use and phospholipase A2 activity. Despite progress, the function and impact of membrane lipids are still poorly understood in schizophrenia. They could serve as biomarkers for identifying biological subgroups among patients with schizophrenia. In UHR patients, their predictive value on the conversion to psychosis should be tested. Omega-3 supplementation could be a promising treatment thanks to its good tolerance and acceptability. It could be more appropriate for patients with PUFA anomalies in a more personalized medical approach.

An investigation of calcium-independent phospholipase A2 (iPLA2) and cytosolic phospholipase A2 (cPLA2) in schizophrenia

Evidence indicates that abnormal phospholipase A2 (PLA2) levels and niacin insensitivity are present in individuals with schizophrenia. This study was designed to determine whether differences in plasma calcium-independent phospholipase A2 (iPLA2) and cytosolic phospholipase A2 (cPLA2) exist between those with schizophrenia and healthy controls, and to explore the correlation between PLA2s and the niacin skin reaction in schizophrenic patients. We performed ELISA experiments to measure the concentrations of plasma iPLA2 and cPLA2 and we conducted a series of niacin skin tests on schizophrenic patients from the Chinese Han population. In addition, a meta-analysis of the relationship between PLA2 and schizophrenia was conducted. The plasma concentration of iPLA2 in patients with schizophrenia was significantly higher than that in healthy controls while the plasma concentration of cPLA2 did not differ. The meta-analysis also revealed that the activity level of iPLA2 in individuals with schizophrenia was higher than that in healthy controls, whereas that of cPLA2 was not. Furthermore, a significant positive correlation was found between the concentration of iPLA2 and the score for the skin flushing response within 20 min. The abnormal plasma iPLA2 concentration and its relationship with the niacin skin test in schizophrenic patients has contributed to a deeper understanding of the pathology of schizophrenia, which may in turn provide new insights into the clinical diagnoses and treatment of schizophrenia.

Methylnicotinate stimulated prostaglandin synthesis in patients with schizophrenia: A preliminary investigation

Schizophrenia is a serious mental illness of unclear aetiology. The reduced ability of methylnicotinate to induce a topical vasodilatory response in patients with the disorder is well established. Methylnicotinate causes vasodilation via stimulating the release of prostaglandins (including prostaglandin D₂) in the skin which in turn leads to relaxation of vascular smooth muscle. To determine whether the abnormality is likely to be due to decreased prostaglandin production, or a decreased effect of prostaglandins upon the vessels, topical methylnicotinate was applied to the forearms of patients with schizophrenia or healthy controls, followed by rating of the resulting erythema. The concentration of prostaglandin D₂ and its metabolite 11β-prostaglandin F_2α in the blood draining the arm was also measured. Although erythema was reduced in the patient group, this was not correlated with plasma prostaglandin concentrations. This data suggests the abnormality underlying the reduced potency of methylnicotinate to produce vasodilation in the disorder occurs downstream of prostaglandin synthesis possibly within the vasculature itself.

Identification of the Niacin-Blunted Subgroup of Schizophrenia Patients from Mood Disorders and Healthy Individuals in Chinese Population

Schizophrenia (SZ) is a devastating mental disease caused by complex genetic and environmental factors. The pathological process and clinical manifestation of SZ are heterogeneous among patients, which hampers precise diagnosis and treatment of the disease. Since no objective marker for SZ has been established today, to identify a subgroup of the patients with homogeneous biochemical traits will provide a new angle for both researchers and clinicians to understand and manage the disease. In this study, we employed the niacin skin-flushing test in Chinese population and confirmed a niacin-blunted subgroup of SZ patients distinguishable from mood disorders (MD) and normal individuals. This subgroup accounted for 30.67% of the total SZ patients with a specificity of 88.37% in male subjects and 83.75% in female subjects. We support the notion that bluntness in niacin skin test might reflect abnormalities in membrane fatty acid composition, which could be induced by increased PLA2 enzyme activity, in vivo oxidative stress or lipid metabolism imbalance in SZ. Further studies are encouraged to clarify the molecular origins of niacin-bluntness in SZ, which would provide extra clues for etiological research in schizophrenia and for new targeted treatment.

Prevalence and Specificity of the Abnormal Niacin Response: A Potential Endophenotype Marker in Schizophrenia

The skin flush response to niacin is abnormally blunted among a subset of patients with schizophrenia (SZ), preferentially associates with SZ compared to other mental illnesses, occurs frequently in nonpsychotic members of SZ-affected families, appears heritable, and shows evidence of genetic association. The niacin response abnormality (NRA) may prove to be a useful SZ endophenotype. Using a laser Doppler flowmeter, we undertook this study to estimate the prevalence of NRA in SZ (n = 70), bipolar disorder (BP, n = 59), and healthy control (HC, n = 87) groups, and to estimate its specificity for the illness. From the dose-response curves, we calculated the concentration of methylnicotinate required to elicit a half-maximal blood flow (MBF) response (EC50 value) and MBF value for each subject. The median log10EC50 of the SZ was above the third quartile of log10EC50 of either the HC or BP groups, whereas the MBF was significantly lower in the SZ than in the HC or BP groups. With a definition of NRA of having both EC50 above the ninetieth percentile of the control samples and MBF response below the sixtieth percentile for the control range, the NRA predicted SZ with 31% sensitivity and 97% specificity. Moreover, the NRA was not influenced by age, gender, race, and cigarette smoking. In summary, the NRA may define a SZ subtype with a clinically significant phospholipid signaling defect. Understanding its molecular origins may shed light on the pathophysiology of SZ and suggest new tools for its early diagnosis and treatment.

Niacin subsensitivity is associated with functional impairment in schizophrenia

OBJECTIVE

Sensitivity to the skin flush effect of niacin is reduced in a portion of patients with schizophrenia. Though this peripheral physiological abnormality has been widely replicated, its relevance to neuropsychiatric manifestations of the illness has been unclear. The goal of this study was to determine if the niacin response abnormality in schizophrenia is associated with functional impairment.

METHODS

Following psychiatric assessment, a Global Assessment of Functioning (GAF) score was assigned to each of 40 volunteers with schizophrenia. For each subject, the blood flow responses to several concentrations of topical methylnicotinate were recorded. Blood flow was measured objectively, using laser Doppler flowmetry. From the dose-response data, EC(50) values were derived. GAF scores were assigned without knowledge of the participants' niacin response data.

RESULTS

There was a significant negative correlation between GAF scores and EC(50) values for methylnicotinate (Pearson r=-0.42; p=0.007).

CONCLUSIONS

Reduced niacin sensitivity is associated with greater functional impairment among patients with schizophrenia. These findings raise the possibility that a subset of schizophrenia patients possesses a biochemical abnormality that reduces niacin sensitivity in the skin and contributes to functional impairment from the disease.

Niacin sensitivity and the arachidonic acid pathway in schizophrenia

OBJECTIVE

Schizophrenia is associated with a blunted flush response to niacin. Since niacin-induced skin flushing is mediated by vasodilators derived from arachidonic acid (AA), we tested whether the blunted flush response to niacin is a marker of AA deficiency.

METHODS

Eight concentrations of methylnicotinate were applied to the forearms of 20 adults with schizophrenia and 20 controls. Laser Doppler measurement of blood flow responses was used to derive values for niacin sensitivity (defined as the concentration eliciting half-maximal response, i.e., EC(50) value) and efficacy (defined as the maximal evoked blood flow response). RBC membrane fatty acids were analyzed by gas chromatography.

RESULTS

Niacin sensitivity and efficacy were reduced in schizophrenia. In the control group, there was significant correlation between AA levels and niacin sensitivity as well as a trend toward correlation between AA levels and niacin efficacy. In contrast, neither sensitivity nor efficacy of niacin correlated with AA levels in schizophrenia. An expected correlation between the levels of AA and its elongation product (adrenic acid) was absent in schizophrenia. Adrenic acid levels correlated with niacin efficacy in schizophrenia.

CONCLUSIONS

The schizophrenia-associated niacin response abnormality involves both diminished sensitivity and reduced efficacy. The lack of expected correlation between levels of AA and adrenic acid suggests homeostatic imbalance within the n-6 polyunsaturated fatty acid (PUFA) pathway in schizophrenia. Though AA levels were unrelated to measures of niacin response in schizophrenia, the correlation between adrenic acid and niacin efficacy in schizophrenia suggests relevance of the n-6 PUFA pathway to the blunted niacin response.

Test-retest stability of the oral niacin test and electrodermal activity in patients with schizophrenia

In schizophrenia, well-replicated findings support an attenuated niacin skin-flush response. We have previously reported a delayed skin-flush after niacin ingestion and also an association between niacin non-responding and electrodermal non-responding in schizophrenia. The stability of the niacin and electrodermal tests was now studied in a test-retest design. An additional aim was to assess the association previously found. Twenty-three patients with schizophrenia underwent two sessions 3 months apart during which an oral niacin test was conducted and electrodermal activity was measured. Despite similar values for niacin outcome variables at the group level, there was high intraindividual variation. Test-retest stability for the oral niacin test was thus low, although a trend toward correlation for the dichotomous response criterion was found. Most electrodermal measures correlated between baseline and retest. A significant association between the tests was again found; niacin non-responding implied electrodermal non-responding, providing further support for a common underlying aberration in schizophrenia.

Endophenotypes in schizophrenia: a selective review

BACKGROUND

Given the wealth of data in the literature on schizophrenia endophenotypes, it is useful to have one source to reference their frequency data. We reviewed the literature on disease-liability associated variants in structural and functional magnetic resonance images (MRI), sensory processing measures, neuromotor abilities, neuropsychological measures, and physical characteristics in schizophrenia patients (SCZ), their first-degree relatives (REL), and healthy controls (HC). The purpose of this review was to provide a summary of the existing data on the most extensively published endophenotypes for schizophrenia.

METHODS

We searched PubMed and MedLine for all studies on schizophrenia endophenotypes comparing SCZ to HC and/or REL to HC groups. Percent abnormal values, generally defined as >2 SD from the mean (in the direction of abnormality) and/or associated effect sizes (Cohen's d) were calculated for each study.

RESULTS

Combined, the articles reported an average 39.4% (SD=20.7%; range=2.2-100%) of abnormal values in SCZ, 28.1% (SD=16.6%; range=1.6-67.0%) abnormal values in REL, and 10.2% (SD=6.7%; range=0.0-34.6%) in HC groups.

CONCLUSIONS

These findings are reviewed in the context of emerging hypotheses on schizophrenia endophenotypes, as well as a discussion of clustering trends among the various intermediate phenotypes. In addition, programs for future research are discussed, as instantiated in a few recent large-scale studies on multiple endophenotypes across patients, relatives, and healthy controls.

The topical niacin sensitivity test: an inter- and intra-rater reliability study in healthy controls

Topical application of nicotinic acid results in erythema, and in some cases oedema of the skin, supporting a strong relationship between niacin sensitivity and prostaglandin D2. The aim of this study was to examine the inter-rater and intra-rater reliability of a 12-min niacin sensitivity test in healthy adults. Three raters assessed the skin reaction of 12 volunteers, over 3-min intervals across four niacin concentrations (0.1, 0.01, 0.001, and 0.0001), and over six sessions. Inter-rater reliability estimates ranged from 0.85 to 0.97 for the total niacin sensitivity score. Similar inter-rater reliability estimates were found for niacin sensitivity ratings by concentration and time. Intra-rater reliability estimates ranged from 0.63 to 0.93 for the total niacin sensitivity score. These data indicate that the 12-min topical niacin sensitivity test has excellent reliability.

Absent response to niacin skin patch is specific to schizophrenia and independent of smoking

This study investigated the differences in niacin skin flush responses between patients with schizophrenia, bipolar mania, and normal controls. We applied niacin patches of three concentrations (0.001 M, 0.01 M, and 0.1 M) to the skin of 61 patients with schizophrenia, 18 patients with bipolar mania, and 40 normal controls for 5 min. Flush responses were rated at 5, 10 and 15 min after application. Flush responses were significantly different among three groups at the concentrations of 0.1 M and 0.01 M at all of the three rating time points. The use of nicotine did not have significant influences on the flush responses. Absent response was significantly more prevalent in the schizophrenia group than in the other two groups, but was not significantly different between the bipolar and the control group. The greatest degree of differentiation in flush responses among groups occurred at the 0.01 M concentration, and the rating time point of 10 min with 49.2% of schizophrenic patients but only 7.5% of controls and 11.1% of bipolar patients not showing a flush response. The niacin skin test for schizophrenia had 49.2% sensitivity and 92.5% specificity compared with controls. This study found that absent response to niacin skin patch was specific to schizophrenia and independent of smoking status.

Familial aggregation in skin flush response to niacin patch among schizophrenic patients and their nonpsychotic relatives

Though a reduced flush response to niacin has been found in schizophrenic patients, whether it is a vulnerability indicator to schizophrenia remains little known. We aimed to examine the familial aggregation in niacin flush response among schizophrenic patients and their nonpsychotic relatives. In a sample of 153 schizophrenia probands, 217 parents, 70 siblings, and 94 normal subjects, 3 concentrations (0.001 M, 0.01 M, and 0.1 M) of niacin were applied to the forearm skin and the flush response was rated at 5, 10, and 15 minutes, respectively, with a 4-point scale. Both the heritability for continuous flush scores and the recurrence risk ratios for binary non-flush response in the nonpsychotic relatives of schizophrenic patients were estimated, and ordinal logistic regression analyses of relatives' niacin response on probands' were further conducted to adjust for potential confounders. The greatest heritabilities ranged from 47% (0.01 M at 10 minutes) to 54% (0.1 M at 5 minutes). The risk ratios of 0.01 M at 10 minutes (ranging from 2.60 for using score 1 or less to 5.06 for using score 0 as non-flush) and 5 minutes (1.66 for using score 0 as non-flush) were significantly greater than one. Multiple ordinal logistic regression analyses further revealed that the association between probands and relatives in niacin flush response remained after adjustment for potential confounders, including age, sex, allergy, tobacco smoking, and coffee drinking. These findings provide support for the potential of niacin flush response as a vulnerability indicator to schizophrenia.

The role of phospholipases A2 in schizophrenia

A range of neurotransmitter systems have been implicated in the pathogenesis of schizophrenia based on the antidopaminergic activities of antipsychotic medications, and chemicals that can induce psychotic-like symptoms, such as ketamine or PCP. Such neurotransmitter systems often mediate their cellular response via G-protein-coupled release of arachidonic acid (AA) via the activation of phospholipases A2 (PLA2s). The interaction of three PLA2s are important for the regulation of the release of AA--phospholipase A2 Group 2 A, phospholipase A2 Group 4A and phospholipase A2 Group 6A. Gene variations of these three key enzymes have been associated with schizophrenia with conflicting results. Preclinical data suggest that the activity of these three enzymes are associated with monoaminergic neurotransmission, and may contribute to the differential efficacy of antipsychotic medications, as well as other biological changes thought to underlie schizophrenia, such as altered neurodevelopment and synaptic remodelling. We review the evidence and discuss the potential roles of these three key enzymes for schizophrenia with particular emphasis on published association studies.

Niacin skin-flush response and electrodermal activity in patients with schizophrenia and healthy controls

Patients with schizophrenia have in different studies shown reduced niacin sensitivity and lower electrodermal activity (EDA) after auditory stimulation. Peripheral mediation of prostaglandins may have a physiological role in both responses. This motivates study of both niacin response and electrodermal responding in the same patients with schizophrenia. Thirty patients with schizophrenia and 17 controls were investigated with EDA and thereafter given 200mg niacin orally with continuous assessment of skin temperature. The patients showed a delayed temperature increase after niacin ingestion (P=0.002) and a higher frequency of electrodermal non-responding (P<0.05). Response/non-response for niacin correlated with EDA response/non-response in the patient group (P=0.009). The niacin test revealed a slower vasodilation reaction in the patients. The association between response patterns for the niacin test and EDA suggests that a common aberration in skin physiology may be of importance for both reactions in schizophrenia.

Bioactive lipids in schizophrenia

Bioactive lipids, in particular arachidonic acid (AA), are vital for monoaminergic neurotransmission, brain development and synaptic plasticity. Phospholipases A2 (PLA2) are key-enzymes in AA metabolism and are activated during monoaminergic neurotransmission. Reduced membrane AA levels, and an altered activity of PLA2 have been found in peripheral membranes of drug-naïve patients with schizophrenia with some conflicting results in more chronic patient populations. Furthermore, in vivo brain phosphorus-31 magnetic resonance spectroscopy suggests reduced lipid membrane precursors (phosphomonoesters) and increased membrane breakdown products (phosphodiesters) in drug-naïve or early treated first-episode schizophrenia patients compared to age-matched controls or chronic populations and these changes were correlated with peripheral red blood cell membrane AA levels. We postulate that processes modulating membrane lipid metabolism are associated with psychotic illnesses and might partially explain the mechanism of action of antipsychotic agents, as well as experimental agents such as purified ethyl-eicosapentaenoic acid (E-EPA). Recent supplementation trials suggest that E-EPA is a modestly effective augmentation treatment resulting in reduced doses of antipsychotic medication in acutely ill patients with schizophrenia (but not in residual-type schizophrenia). This review investigates the role of bioactive lipids in schizophrenia and its treatment, as well as its potential use in prevention.

Increased calcium-independent phospholipase A2 activity in first but not in multiepisode chronic schizophrenia

BACKGROUND

Increased activity of calcium independent phospholipase A2 (iPLA2) has repeatedly been found in the serum of unmedicated first-episode schizophrenia patients and assumed to reflect a pertubation of phospholipid metabolism. Previous studies in chronic schizophrenia were less conclusive. To explore whether iPLA2 changes are stage dependent, we investigated serum iPLA2 activity in various stages of schizophrenia.

METHODS

iPLA2 activity was assessed in the serum of 30 first-episode and 23 multiepisode schizophrenia patients and 53 healthy control subjects matched for age and gender. A fluorimetric assay was applied using the PLA2 specific substrate NBDC6-HPC, thin-layer chromatography of reaction products, and digital image scanning for signal detection.

RESULTS

Group comparison between first-episode and multiepisode patients and corresponding control groups revealed significantly increased iPLA2 activity only in first-episode patients. Enzyme activity in first-episode patients was also markedly increased, compared with chronic patients. iPLA2 changes observed were irrespective of neuroleptic medication, age, or gender.

CONCLUSIONS

Our results suggest increased lipid turnover in the acute early phase of schizophrenia that is less obvious in chronic stages. Future longitudinal studies involving iPLA2 activity and phosphorous magnetic resonance spectroscopy need to address the relation between perturbed brain lipid metabolism and iPLA2 increment in the course of schizophrenia.

Layer upon layer: thermoregulation in schizophrenia

A review of the relevant published literature regarding disorders of thermoregulation in people with schizophrenia was undertaken. This entailed a search of the Medline and PsychINFO databases to 28th May 2003 using the search terms "schizophrenia and thermoregulation" and "schizophrenia and temperature". The relevant articles as well as secondary references were reviewed. It has generally been shown that, when compared with controls, people with schizophrenia exhibit dysregulation of body temperature including different baseline temperatures; abnormal daily range of temperatures and diurnal variation showing an earlier peak; an impaired ability to compensate to heat stress; and compensating more effectively to cold stress. This may be intrinsic to the syndrome of schizophrenia but is potentially confounded by the administration of neuroleptic medication. The underlying cause is likely to be a combination of "peripheral" and "central" mechanisms of thermoregulation. Further study is required to delineate clearly the quality and magnitude of the temperature dysregulation as well as elucidating its mechanism(s). This could further our understanding of the mechanism underlying the syndrome of schizophrenia.

Calcium signaling dysfunction in schizophrenia: a unifying approach

The present paper demonstrates a remarkable pervasiveness of underlying Ca(2+) signaling motifs among the available biochemical findings in schizophrenic patients and among the major molecular hypotheses of this disease. In addition, the paper reviews the findings suggesting that Ca(2+) is capable of inducing structural and cognitive deficits seen in schizophrenia. The evidence of the ability of antipsychotic drugs to affect Ca(2+) signaling is also presented. Based on these data, it is proposed that altered Ca(2+) signaling may constitute the central unifying molecular pathology in schizophrenia. According to this hypothesis schizophrenia can result from alterations in multiple proteins and other molecules as long as these alterations lead to abnormalities in certain key aspects of intracellular Ca(2+) signaling cascades.

Relationship between the niacin skin flush response and essential fatty acids in schizophrenia

The skin flush response to niacin is selectively mediated by the release of vasodilatory prostaglandins from the skin. The normal skin flush response to niacin is attenuated in many individuals with schizophrenia (SCZ). This finding suggests abnormal prostaglandin signaling in SCZ. Since prostaglandins are derived from arachidonic acid (AA), the finding of an abnormal skin flush response is consistent with biochemical data suggesting relative depletion of AA, and other essential fatty acids (EFAs), in a substantial portion of people with SCZ. This paper will describe the mechanism of the skin flush response to niacin, and will review evidence that the response to niacin is abnormal in SCZ, that this abnormality is not related to psychotropic medications, and that it may be a marker of the EFA deficiency which has been documented to be present in many patients with SCZ.

Phospholipid and eicosanoid signaling disturbances in schizophrenia

A variety of biochemical, clinical and genetic evidence suggests that phospholipid metabolism may play an aetiological role in schizophrenia. A key piece of evidence is the reduced vasodilatory response of patients with schizophrenia to nicotinic acid (NA). NA causes vasodilation via the activation of phospholipase A2 (PLA2) leading to the release of free fatty acids from membrane phospholipids and the subsequent production of prostaglandins. Insensitivity to NA may be due to a 'block' in the downstream signaling pathway used by the drug to evoke its response. It can be argued that if such an abnormality occurs in neurons, impaired PLA2-dependent signaling could result in altered glutamateric and dopaminergic transmission in such a way as to produce or exacerbate psychotic symptoms. The complimentary finding of increased PLA2 activity in schizophrenia may be an attempt to overcome the signaling block. It is suggested that intervention aimed at increasing the activity of PLA2-dependent signaling systems may be therapeutically useful in the treatment of the illness.

Fluorometric assays of phospholipase A2 activity with three different substrates in biological samples of patients with schizophrenia

The rationale of this study was to understand the complexity of kinetics of fluorogenic phospholipid substrates as well as contradictory findings of clinical papers measuring phospholipase A2 (PLA2) activity using different methodologies. The aim was to recommend to clinicians and researchers what substrate in conjunction with what assay should be used. Two methods, (i) continuous fluorometric assay and (ii) high performance thin layer chromatography (HPTLC) on microplates combined with quantitative image scanning, were studied with three different substrates (bis-BODIPY FL C11-PC, NBDC6-HPC, PED6). The study demonstrates that NBD-PC is not a suitable substrate to measure PLA2 activity using a spectrofluorometer. On the other hand, NBD-PC gives the highest and most reproducible integrated light intensities (ILls) in HPTLC studies. Slow time-dependent increases in fluorescence intensities recorded with biological samples in fluorometers, but not caused by substrate splitting, had to be classified as "perturbation kinetics". PLA2 activities in blood samples of 26 unmedicated schizophrenia patients and 26 age-matched healthy controls were measured by the spectrofluorometric method and then compared with the activity data obtained with the HPTLC method. A significant group difference was found only with the HPTLC. In order to get more reliable results, we recommend that clinicians and researchers use NBD-phosphatidylcholines as PLA2 substrates in biological samples and start with an analytical separation of reaction products followed by image analysis of the fluorescent spots.

Brain incorporation of [11C]arachidonic acid in young healthy humans measured with positron emission tomography

Arachidonic acid (AA) is an important second messenger involved in signal transduction mediated by phospholipase A2. The goal of this study was to establish an in vivo quantitative method to examine the role of AA in this signaling process in the human brain. A simple irreversible uptake model was derived from rat studies and modified for positron emission tomography (PET) to quantify the incorporation rate K* of [11C]AA into brain. Dynamic 60-minute three-dimensional scans and arterial input functions were acquired in 8 young healthy adults studied at rest. Brain radioactivity was corrected for uptake of the metabolite [11C]CO2. K* and cerebral blood volume (Vb) were estimated pixel-by-pixel and were calculated in regions of interest. K* equaled 5.6+/-1.2 and 2.6+/-0.5 microL x min(-1) x mL(-1) in gray and white matter, respectively. K* and Vb values were found to be unchanged with data analysis periods from 20 to 60 minutes. Thus, PET can be used to obtain quantitative images of the incorporation rate K* of [11C]AA in the human brain. As brain incorporation of labeled AA has been shown in awake rats to be increased by pharmacological activation associated with phospholipase A2-signaling, PET and [11C]AA may be useful to measure signal transduction in the human brain.

Implications of lipid biology for the pathogenesis of schizophrenia

OBJECTIVE

Preclinical and clinical data suggest that lipid biology is integral to brain development and neurodegeneration. Both aspects are proposed as being important in the pathogenesis of schizophrenia. The purpose of this paper is to examine the implications of lipid biology, in particular the role of essential fatty acids (EFA), for schizophrenia.

METHODS

Medline databases were searched from 1966 to 2001 followed by the cross-checking of references.

RESULTS

Most studies investigating lipids in schizophrenia described reduced EFA, altered glycerophospholipids and an increased activity of a calcium-independent phospholipase A2 in blood cells and in post-mortem brain tissue. Additionally, in vivo brain phosphorus-31 Magnetic Resonance Spectroscopy (31P-MRS) demonstrated lower phosphomonoesters (implying reduced membrane precursors) in first- and multi-episode patients. In contrast, phosphodiesters were elevated mainly in first-episode patients (implying increased membrane breakdown products), whereas inconclusive results were found in chronic patients. EFA supplementation trials in chronic patient populations with residual symptoms have demonstrated conflicting results. More consistent results were observed in the early and symptomatic stages of illness, especially if EFA with a high proportion of eicosapentaenoic acid was used.

CONCLUSION

Peripheral blood cell, brain necropsy and 31P-MRS analysis reveal a disturbed lipid biology, suggesting generalized membrane alterations in schizophrenia. 31P-MRS data suggest increased membrane turnover at illness onset and persisting membrane abnormalities in established schizophrenia. Cellular processes regulating membrane lipid metabolism are potential new targets for antipsychotic drugs and might explain the mechanism of action of treatments such as eicosapentaenoic acid.

Reduction of the synaptophysin level but normal levels of glycerophospholipids in the gyrus cinguli in schizophrenia

The 'membrane hypothesis' of schizophrenia postulates a disturbance in the metabolism and structure of membrane phospholipids resulting in a disturbance in the function of neuronal membrane proteins. Most studies exploring this hypothesis have examined components of peripheral blood. Since it may be questioned if these peripheral measurements reflect changes in the brain, we studied the fatty acid composition of glycerophospholipids in brain tissue. As a marker for synaptic density, we also measured the synaptic vesicle protein synaptophysin. Brain tissue (gyrus cinguli) from 11 schizophrenic patients (mean age 80 +/- 10 years) and 13 controls (mean age 75 +/- 14 years) was examined. The glycerophospholipid fatty acids were determined by gas chromatography. Synaptophysin protein level was determined using quantitative immunoblotting followed by Western blotting. There were no significant differences between the groups in the total or in any individual level of fatty acids, either in the n - 6 or n - 3 series. The level of synaptophysin was significantly p = (0.002) decreased in the schizophrenic group(0.73 + 0.18) as compared with the control group (1.02 + 0.21). The normal pattern and concentration of glycerophospholipids fatty acids found in the present study do not support the membrane hypothesis of schizophrenia. The possibility of a type II error should, however. be considered. On the other hand, the reduced synaptophysin' levels in the gyrus cinguli demonstrate that biological differences can be revealed in this relatively small sample. This also lends further support to the notion that a synaptic disturbance or loss is of importance in the pathogenesis of schizophrenia.

Hippocampal expression of the calcium sensor protein visinin-like protein-1 in schizophrenia

Hippocampal cytoarchitectural abnormalities may be part of the cerebral substrate of schizophrenia. Amongst the chemical components being abnormal in brains of schizophrenics are altered calcium concentrations and reduced expression of the neurotrophin receptor, trkB. We studied by immunohistochemical methods the distribution of visinin-like protein-1 (VILIP-1), which is a calcium sensor protein and at the same time a trkB mRNA binding protein, in hippocampi of nine schizophrenic patients and nine matched control subjects. In normal hippocampi VILIP-1 immunoreactivity was found in multiple pyramidal cells and interneurons. A portion of VILIP-1 immunoreactive interneurons co-express calretinin (60%) and parvalbumin (<10%). In schizophrenics fewer pyramidal cells but more interneurons were immunostained. Our data point to an involvement of the protein in the altered hippocampal circuitry in schizophrenia.

An animal model of nicotinic-acid-induced vasodilation: effect of haloperidol, caffeine and nicotine upon nicotinic acid response

BACKGROUND

The normal vasodilatory response to ingestion of nicotinic acid (NA) is impaired in some patients with schizophrenia. It is unclear whether the impairment is a feature of the disorder itself or to a confounding factor such as neuroleptics, caffeine or nicotine use.

METHODS

To address this question in a controlled manner, we have developed an animal (rat) model of NA-induced vasodilation, in which response is monitored by measuring change in skin temperature.

RESULTS

We observed that (i) acute administration of acetylsalicylic acid (100mg/kg), caffeine (2.5mg/kg) and haloperidol (0.1 or 0.5mg/kg) and (ii) chronic administration of haloperidol (0.2mg/kg/day) significantly inhibited NA (30 mg/kg) response, whereas neither acute (0.25mg/kg) or chronic (0.5mg/kg/day for 14 days) administration of nicotine, or chronic administration of caffeine (5mg/kg/day for 14 days) had any significant effect upon NA response.

CONCLUSIONS

Our data suggest that at least one drug commonly used to treat schizophrenia (haloperidol) can interfere with the vasodilatory response to NA. Studies using non-medicated patients with schizophrenia are required to determine whether reduced vasodilatory response to NA in schizophrenia is a feature of the disorder or a consequence of treatment.

Molecular characterization of schizophrenia viewed by microarray analysis of gene expression in prefrontal cortex

Microarray expression profiling of prefrontal cortex from matched pairs of schizophrenic and control subjects and hierarchical data analysis revealed that transcripts encoding proteins involved in the regulation of presynaptic function (PSYN) were decreased in all subjects with schizophrenia. Genes of the PSYN group showed a different combination of decreased expression across subjects. Over 250 other gene groups did not show altered expression. Selected PSYN microarray observations were verified by in situ hybridization. Two of the most consistently changed transcripts in the PSYN functional gene group, N-ethylmaleimide sensitive factor and synapsin II, were decreased in ten of ten and nine of ten subjects with schizophrenia, respectively. The combined data suggest that subjects with schizophrenia share a common abnormality in presynaptic function. We set forth a predictive, testable model.

Gene targets related to phospholipid and fatty acid metabolism in schizophrenia and other psychiatric disorders: an update

Phospholipids make up about 60% of the brain's dry weight and play key roles in many brain signal tranduction mechanisms. A recent review(1)identified the increasing evidence that abnormal phospholipid and related fatty acid metabolism may contribute to illnesses such as schizophrenia, bipolar disorder, depression and attention deficit hyperactivity disorder. This current paper reviews the main pathways of phospholipid metabolism, emphasizing the role of phospholipases of the A2 in signal tranduction processes. It also updates the chromosomal locations of regions likely to be involved in these disorders, and relates these to the known locations of genes directly or indirectly involved in phospholipid and fatty acid metabolism.