Cannabinoids influence lipid-arachidonic acid pathways in schizophrenia

Deciphering the mechanisms of reciprocal regulation or interdependence at the cannabinoid CB1 receptors and cyclooxygenase-2 level: Effects on mood, cognitive implications, and synaptic signaling

The lipid endocannabinoid system refers to endogenous cannabinoids (eCBs), the enzymes involved in their synthesis and metabolism, and the G protein-coupled cannabinoid receptors (GPCRs), CB1, and CB2. CB1 receptors (CB1Rs) are distributed in the brain at presynaptic terminals. Their activation induces inhibition of neurotransmitter release, which are gamma-aminobutyric acid (GABA), glutamate (Glu), dopamine, norepinephrine, serotonin, and acetylcholine. Postsynaptically localized CB1Rs regulate the activity of selected ion channels and N-methyl-D-aspartate receptors (NMDARs). CB2Rs are mainly peripheral and will not be considered here. Anandamide metabolism, mediated by cyclooxygenase-2 (COX-2), generates anandamide-derived prostanoids. In addition, COX-2 regulates the formation of CB1 ligands, which reduce excitatory transmission in the hippocampus (HC). The role of CB1Rs and COX-2 has been described in anxiety, depression, and cognition, among other central nervous system (CNS) disorders, affecting neurotransmission and behavior of the synapses. This review will analyze common pathways, mechanisms, and behavioral effects of manipulation at the CB1Rs/COX-2 level.

Attenuated niacin response is associated with a subtype of first-episode drug-naïve psychosis characterized as serious negative symptoms

Although the phenomenon of attenuated niacin response (ANR) has been widely replicated in some patients with first-episode psychosis (FEP), its relevance to the negative symptoms (NS) of psychosis remains unclear. Total of 240 patients with drug-naïve FEP and 101 healthy controls (HCs) were recruited, and 209 were followed up for 1 year. Psychotic symptoms were assessed using the Positive and Negative Syndrome Scale (PANSS), and niacin-induced responses were measured using laser Doppler flowmetry. We calculated the log-transform EC50 [concentration of methyl nicotinate required to elicit a half-maximal blood flow (MBF) response] and MBF values. Core-NS was generated by factor analysis of the PANSS-NS subscale and cluster analysis to produce subtypes. Significant differences were found in the log10 (EC50) values between the FEP and HC groups (p < 0.001), supporting the ANR in patients with FEP. A higher NS severity was found in the ANR subgroup than that in other patients. Factor analysis determined that a two-dimensional model included core NS and rigidity of thinking. The log10 (EC50) value was significantly associated with only the core NS. Cluster analysis revealed three subtypes-36.7% (cluster-1, n = 88), 16.7% (cluster-2, n = 40), and 46.7% (cluster-3, n = 112). Cluster-2 characterized by extensive NS appeared to have a more remarkable ANR and less symptomatic improvement than those with other clusters during follow-up. No significant changes were found in the niacin response trajectories between the baseline and follow-up. Our findings indicate a significant correlation between ANR and core NS in patients with FEP. ANR may be a potential biomarker for certain subtypes with NS-dominated characteristics and poor symptomatic remission.

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.

[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.

State marker properties of niacin skin sensitivity in ultra-high risk groups for psychosis - An optical reflection spectroscopy study

Impaired niacin sensitivity (NS) is one of the most replicated findings in untreated schizophrenia, and reflects a disturbance of prostaglandin-mediated pathways in association with deregulated arachidonic acid metabolism, pro-inflammatory activation, and vasomotor function. In ultra-high risk individuals (UHR) increased NS was reported recently, pointing towards dynamic alterations of the underlying pathomechanisms in the period preceding psychosis. However, these characteristics are still unresolved in the diverse UHR groups. We tested the hypothesis that NS is attenuated in patients who have transitioned to psychosis and in the Brief Limited Intermittent Psychotic Symptoms (BLIPS, UHR-B) and/or the attenuated symptoms (UHR-A) groups, while it is unchanged or increased in the genetic risk group (UHR-G). Sensitivity to three concentrations (0.1-0.001M) of aqueous methylnicotinate was tested in 84 UHR patients, 105 first-episode psychosis patients (FEP) and 180 healthy individuals (HC), using optical reflection spectroscopy (ORS). The UHR subgroup and transition/non-transition outcomes were assessed according to PACE criteria using the CAARMS. Psychopathology was assessed using SANS, SAPS, and BPRS or SCL-90-R self-ratings. In 0.001M data, decreased NS was found in the UHR-B (n=12), UHR-A (n=45) and the transition groups (n=13), similar to the result in FEP. NS in the UHR-G (n=27) and HC groups did not differ. In the UHR-B and FEP groups, NS and positive symptom scores were inversely correlated. These state marker properties could be used to characterize the intensity of the underlying pathomechanisms during the onset of psychosis or to identify UHR individuals that might benefit from related indicated prevention strategies.

Omega – 3 fatty acids in schizophrenia – part I: importance in the pathophysiology of schizophrenia

Despite the increasing offer of antipsychotic drugs, the effectiveness of pharmacotherapy in schizophrenia is still unsatisfactory. Drug resistance, lack of complete remission and the increasing risk of metabolic complications are the reasons why the new forms of therapy in schizophrenia among which unsaturated essential fatty acids omega 3 (EFAs ω-3) affecting the proper functioning of nervous system, are mentioned, are being looked for.

Fatty acids represent 50-60% of the dry weight of the brain and diet is one of the factors that influence the value of each of the fat fractions in the neuron membranes. Patients with schizophrenia tend to have irregular nutritional status concerning essential fatty acids ω-3, which might result from metabolic disorders or irregular consumption of fatty acids.

Apart from being a review of the literature on this subject, this very paper characterizes essential fatty acids ω-3, their metabolism, the most important sources in the diet and the opinions of experts in the field about the recommended intake. It pays attention to the role of essential fatty acids in both the structure and functioning of the central nervous system is, as well as their role in the pathophysiology of schizophrenia, with particular emphasis on the membrane concept by David Horrobin. The assessment of the errors in consumption and metabolism of essential fatty acids are described as well.

The evidence was found both in epidemiological and modeling studies. It supports the participation of EFAs in etiopathogenesis and pathophysiology of schizophrenia. Further research is needed, both observational and interventional, as to the role of essential fatty acids ω-3 in the functioning of the CNS as well as the development and course of schizophrenia.

Niacin Skin Sensitivity Is Increased in Adolescents at Ultra-High Risk for Psychosis

Background

Most studies provide evidence that the skin flush response to nicotinic acid (niacin) stimulation is impaired in schizophrenia. However, only little is known about niacin sensitivity in the ultra-high risk (UHR) phase of psychotic disorders.

Methods

We compared visual ratings of niacin sensitivity between adolescents at UHR for psychosis according to the one year transition outcome (UHR-T n = 11; UHR-NT n = 55) with healthy controls (HC n = 25) and first episode schizophrenia patients (FEP n = 25) treated with atypical antipsychotics.

Results

Contrary to our hypothesis niacin sensitivity of the entire UHR group was not attenuated, but significantly increased compared to the HC group, whereas no difference could be found between the UHR-T and UHR-NT groups. As expected, niacin sensitivity of FEP was attenuated compared to HC group. In UHR individuals niacin sensitivity was inversely correlated with omega-6 and -9 fatty acids (FA), but positively correlated with phospholipase A₂ (inPLA₂) activity, a marker of membrane lipid repair/remodelling.

Conclusions

Increased niacin sensitivity in UHR states likely indicates an impaired balance of eicosanoids and omega-6/-9 FA at a membrane level. Our findings suggest that the emergence of psychosis is associated with an increased mobilisation of eicosanoids prior to the transition to psychosis possibly reflecting a “pro-inflammatory state”, whereas thereafter eicosanoid mobilisation seems to be attenuated. Potential treatment implications for the UHR state should be further investigated.

Polyunsaturated fatty acid concentration predicts myelin integrity in early-phase psychosis

BACKGROUND

White matter (WM) abnormalities have been implicated in schizophrenia, yet the mechanisms underlying these abnormalities are not fully understood. Several lines of evidence suggest that polyunsaturated fatty acids (PUFAs) play a role in myelination, and there is substantial evidence documenting decreased PUFA concentrations in schizophrenia. We therefore hypothesized that lower membrane PUFA concentrations may be related to reduced WM integrity in schizophrenia and related disorders.

METHODS

In 30 male patients with a recent-onset psychotic disorder, erythrocyte membrane PUFA concentrations were assessed and diffusion tensor imaging was performed with voxelwise analysis.

RESULTS

Lower total PUFA concentration was associated with lower fractional anisotropy (FA) throughout the corpus callosum and bilateral parietal, occipital, temporal and frontal WM (P < .05, corrected). Of the individual PUFAs, lower arachidonic acid concentration, and to a lesser extent, lower nervonic acid, linoleic acid, and docosapentaenoic acid concentration were significantly associated with lower FA. PUFA concentrations were inversely associated with radial diffusivity but showed little association with axial diffusivity. Greater severity of negative symptoms was associated with lower nervonic acid concentration and lower FA values.

CONCLUSIONS

Membrane PUFA concentrations appear to be robustly related to brain WM integrity in early phase psychosis. These findings may provide a basis for studies to investigate the effects of PUFA supplementation on WM integrity and associated symptomatology in early psychosis.

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.

Alterations of niacin skin sensitivity in recurrent unipolar depressive disorder

INTRODUCTION

Skin flushing after niacin (methylnicotinate, vitamin B(3)) stimulation is a biological marker of availability of polyunsaturated fatty acids (PUFA). Decreased PUFA levels have been reported in depressive disorder, while add-on supplementation of omega-3 PUFA has been suggested to improve depressive symptoms. This study aimed to clarify whether a disturbance of niacin skin flushing occurs also in depression, and to identify patient characteristics for those who might benefit from PUFA supplementation.

METHOD

We studied 30 patients with recurrent unipolar depressive disorder during a major depressive episode (treated with antidepressants), and 30 healthy volunteers matched for age and gender. Aqueous methylnicotinate was applied in three dilution steps (0.001M, 0.01M, and 0.1M) onto the inner forearm skin. Skin flushing was assessed in three-minute intervals over 15min using optical reflection spectroscopy.

RESULTS

While there was no overall difference in skin flushing between patients and controls, niacin sensitivity was inversely correlated with severity of symptoms, and flush deficits were significantly associated with depressed mood, feelings of anxiety and somatic symptoms (loss of appetite and weight loss).

CONCLUSION

Results are suggestive of a subgroup of depressive patients characterised by a specific symptom cluster and disturbed niacin skin flushing.

Arachidonic acid drives postnatal neurogenesis and elicits a beneficial effect on prepulse inhibition, a biological trait of psychiatric illnesses

Prepulse inhibition (PPI) is a compelling endophenotype (biological markers) for mental disorders including schizophrenia. In a previous study, we identified Fabp7, a fatty acid binding protein 7 as one of the genes controlling PPI in mice and showed that this gene was associated with schizophrenia. We also demonstrated that disrupting Fabp7 dampened hippocampal neurogenesis. In this study, we examined a link between neurogenesis and PPI using different animal models and exploring the possibility of postnatal manipulation of neurogenesis affecting PPI, since gene-deficient mice show biological disturbances from prenatal stages. In parallel, we tested the potential for dietary polyunsaturated fatty acids (PUFAs), arachidonic acid (ARA) and/or docosahexaenoic acid (DHA), to promote neurogenesis and improve PPI. PUFAs are ligands for Fabp members and are abundantly expressed in neural stem/progenitor cells in the hippocampus. Our results are: (1) an independent model animal, Pax6 (+/−) rats, exhibited PPI deficits along with impaired postnatal neurogenesis; (2) methylazoxymethanol acetate (an anti-proliferative drug) elicited decreased neurogenesis even in postnatal period, and PPI defects in young adult rats (10 weeks) when the drug was given at the juvenile stage (4–5 weeks); (3) administering ARA for 4 weeks after birth promoted neurogenesis in wild type rats; (4) raising Pax6 (+/−) pups on an ARA-containing diet enhanced neurogenesis and partially improved PPI in adult animals. These results suggest the potential benefit of ARA in ameliorating PPI deficits relevant to psychiatric disorders and suggest that the effect may be correlated with augmented postnatal neurogenesis.

Endophenotype properties of niacin sensitivity as marker of impaired prostaglandin signalling in schizophrenia

BACKGROUND

Disruption of arachidonic acid pathways and prostaglandin signalling has been implicated in the pathophysiology of schizophrenia.

AIMS

We intended to study prostaglandin signalling in groups of young schizophrenia patients, first-degree relatives, and healthy controls in order to assess effects of heritability on this biological marker-one important endophenotype criterion.

METHOD

Namely, we assessed intensity of methylnicotinate skin flushing using optical reflection spectroscopy. Tests were applied to 19 adolescent first-episode schizophrenia patients, 21 first-degree relatives, and groups of age and gender matched healthy controls.

RESULTS

Compared to healthy controls, attenuation of skin flushing at low niacin concentrations was found only in schizophrenia patients, but not in first-degree relatives.

CONCLUSION

While our results indicate niacin hyposensitivity as reliable biological marker in schizophrenia, they do not provide clear evidence for its heritability. Particularly, the results in adolescent schizophrenia patients are suggestive for the perception of attenuated niacin flushing as secondary to the pathophysiology at the onset of schizophrenic illness, namely increased oxidative stress, alterations of unspecific immune-response or inflammation-like processes.