Issue |
OCL
Volume 23, Number 1, January-February 2016
|
|
---|---|---|
Article Number | D112 | |
Number of page(s) | 8 | |
Section | Dossier: Lipids and Brain / Lipides et cerveau | |
DOI | https://doi.org/10.1051/ocl/2015054 | |
Published online | 27 November 2015 |
Review Article
Phospholipid, arachidonate and eicosanoid signaling in schizophrenia
Signalisation des phospholipides, de l’arachidonate et de l’écosanoïde dans la schizophrénie
1
University of Cincinnati and Lindner Center for
Hope, Cincinnati,
OH,
USA
2
VA Pittsburgh Healthcare System, Pittsburgh, PA
15240,
USA
3
Department of Psychiatry, Western Psychiatric Institute Clinic,
University of Pittsburgh Medical Center, Pittsburgh, PA
15213,
USA
4
Department of Pharmaceutical Sciences, University of Pittsburgh
School of Pharmacy, Pittsburgh, PA
15213,
USA
* Correspondence: jkyao@pitt.edu
Received: 16 September 2015
Accepted: 21 September 2015
This paper reviews the potential role of arachidonic acid in the pathophysiology of schizophrenia. We discuss how abnormal levels of arachidonic acid may arise, and how dysregulation of signaling molecules derived from it have the potential to disrupt not only dopamine signaling, but numerous other physiological processes associated with the illness. Pharmacological doses of niacin stimulate the release of arachidonic acid; and arachidonic acid-derived molecules in turn dilate blood vessels in the skin. A blunted skin flush response to niacin is reliably observed among patients with schizophrenia. The niacin response abnormality may thus serve as a biomarker to identify a physiological subtype of schizophrenia associated with defective arachidonic acid-derived signaling.
Résumé
Cet article examine le rôle potentiel de l’acide arachidonique dans la physiopathologie de la schizophrénie. Il est discuté comment des niveaux anormaux d’acide arachidonique peuvent survenir, et comment la dérégulation des molécules de signalisation qui en découle est capable de perturber non seulement la signalisation de la dopamine, mais aussi de nombreux autres processus physiologiques associés avec cette maladie. Des doses pharmacologiques de niacine stimulent la libération d’acide arachidonique; des molécules dérivées de l’acide arachidonique dilatent à leur tour les vaisseaux sanguins dans la peau. Une brusque rougeur de la peau en réponse à la niacine est observée de manière constante parmi les patients atteints de schizophrénie. La réponse anormale à la niacine peut donc servir de biomarqueur afin d’identifier un sous-type physiologique de la schizophrénie, associé à un système défectueux de signalisation des dérivés de l’acide arachidonique.
Key words: Phospholipids / arachidonic acid / eicosanoids / niacin-induced flushing, endophenotype marker / schizophrenia
© E. Messamore and J.K. Yao, Published by EDP Sciences, 2015
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
1 Introduction
Schizophrenia (SZ) is a complex behavioral syndrome associated with diverse biochemical and physiological abnormalities. This paper will describe how arachidonic acid (AA) and abnormalities related to its metabolism may to some extent unify some seemingly unrelated biochemical findings in SZ (Horobin, 1998; Skosnik and Yao, 2003). We will also describe how a blunted skin flush response to niacin may serve as a biomarker for AA-related signaling defects, and suggest that AA-related abnormalities may represent a distinct physiological subtype within the SZ syndrome (Messamore, 2003; Messamore et al., 2010; Yao et al., 2015).
2 Heterogeneity of the Schizophrenias
Despite early acknowledgement of the likelihood that SZ is not a unitary illness (Bleuler, 1920), for most of the 20th century it was usually studied as if it were a single disease entity. The dominant view was that of a unitary illness with differing modes of expression. This view of SZ, however, is no longer tenable. The variable therapeutic response to antipsychotic medication provides strong evidence against a unitary cause of SZ (Garver et al., 2000). In fact, the preponderance of evidence is consistent with SZ having numerous, etiologically distinct causes (Jablensky, 2006). Efforts toward understanding its various causes, and toward developing improved, etiologically-focused treatments, may be more fruitful if the schizophrenias were deconstructed into physiologically-based intermediate phenotypes (Braff et al., 2007; Keshavan et al., 2008). We and others have observed evidence suggesting that one of these intermediate phenotypes may involve phospholipid signaling abnormalities that prominently involve dysregulation of AA levels or the actions of its physiologically active metabolites.
Fig. 1 An overview of phospholipids turnover, arachidonic acid, and eicosanoid signaling in schizophrenia symptomatology (adapted from Skosnik and Yao, 2003). Abbreviations: AODS, antioxidant defense system; NT, neurotransmitters; RO, reactive oxygen species; apoD, apolipoprotein D; PLA2, phospholipase A2; PLC, phospholipase C; LOX, lipooxygenase; AA, arachidonic acid; DAG, diacylglycerol; COX, cyclooxygenase; 2-AG, 2-arachidonoyl glycerol; GAP, growth-associated protein; PKC, phosphokinase C; PGG2. prostaglandin G2; PGH2, prostaglandin H2; PGD2, prostaglandin D2; CB, cannabinoid. |
3 Phospholipid, arachidonate and eicosanoid (PAE) signaling in SZ
A phospholipid turnover abnormality is present in many cases of SZ. Disordered phospholipid turnover with resulting changes in the levels and metabolic destinations of AA can unite seemingly unrelated neurochemical and clinical observations in SZ.
A model relating phospholipid signaling to SZ-relevant neurochemical abnormalities can be found in Figure 1. As shown, several factors – including oxidative stress and cytokine release – have the potential to lyse membrane phospholipids, resulting in the release of AA and, over time, reduce its cell membrane levels. Overactivity of phospholipase A2 (PLA2) or phospholipase C (PLC) enzymes would deplete the membrane-lysable pool of AA. In turn, changes in the availability of AA and AA-derived signaling molecules affect the release or circulating levels of several neuroactive molecules, including: GAP-43; the neurotransmitters dopamine and glutamate, and the endocannabinoids anandamide and 2-arachidonoylglycerol (2-AG). Alterations in AA may also affect the inflammatory response, which can then affect PLA2 release via cytokines, further exacerbating phospholipid turnover and AA release. These diverse disruptions have the potential to impact many neuronal signaling pathways relevant to psychosis (Horrobin, 1998; Peet et al., 1994; Skosnik & Yao, 2003).
Low levels of AA have been observed postmortem in the cerebral cortex of SZ patients (Horrobin et al., 1991; Yao et al., 2000). Low AA levels have been identified in red blood cell (RBC) membranes from patients with chronic SZ (Glen et al., 1994; Peet et al., 1994; Vaddadi et al., 1986; Yao et al., 1994a), as well as first-episode neuroleptic-naïve SZ (Avrindakshan et al., 2003; Reddy et al., 2004). Thus, abnormally low AA levels have been observed in brain as well as RBC membrane phospholipids from patients with SZ (further reviewed by Conklin et al., 2007; Peet, 2007; Skosnik and Yao, 2003; Yao, 2003). These changes could conceivably lead to decreased synthesis of eicosanoids. Collectively, these changes can account for numerous physiological and clinical observations in SZ.
Utilizing varying types of samples (e.g. plasma, RBC, platelets, postmortem brain, etc.) and methodologies (31P Magnetic resonance spectroscopy, platelet function, niacin-induced flushing, etc.), somewhat consistent patterns of decreased polyunsaturated fatty acids (PUFAs) and increased phospholipid turnover are apparent (Bentsen et al., 2011; Horrobin, 1998; Mahadik and Yao, 2006, Peet, 2007; Pettegrew et al., 1991; Skosnik and Yao, 2003; Yao et al., 1994a), particularly in relation to AA.
In addition to the formation of second messengers, AA released from membrane phospholipids can be converted to a variety of biologically active metabolites, collectively termed eicosanoids, through the concerted reactions of cyclooxygenase (COX), lipoxygenase (LOX) and cytochrome P-450 (CYP). Eicosanoids can modulate neural cell function, and can mediate several pathophysiological processes (Bazan, 2006). Since AA is the major C20 polyunsaturated fatty acid (PUFA) in mammalian tissues, the prostaglandin-2 (PG2) and thromboxanes-2 (TX2) series are the predominant classes of eicosanoids (Fig. 2). Inhibition of COX by nonsteroidal anti-inflammatory drugs has revealed the significance of PG2 in the regulation of nerve conduction, neurotransmitter release, inflammation, pain, fever, immune responses, apoptosis and psychosis (Akhondzadeh et al., 2007).
Fig. 2 Arachidonic acid cascade (adapted from Condray and Yao, 2011). EET, PGI2, PGD2, PGE2, PGF2, 12-HETE and 15-HETE are considered as potential vasodilators. |
4 Clinical and physiological effects of AA and eicosanoids
AA deficiency, or abnormal regulation of AA-derived signaling could explain several clinical and physiological findings in SZ. Association between low RBC membrane AA levels and the expression of the negative symptom syndrome (apathy, social withdrawal, affective flattening, etc.) has been reported (Glen et al., 1994). In other studies, low RBC membrane levels of dihomo-γ-linolenic acid, the immediate precursor of AA, were associated with increased psychosis ratings (Yao et al., 1994b) and disorganized symptoms (Doris et al., 1998). Among SZ patients receiving fatty acid supplementation therapy, increased RBC AA contents were associated with a reduction in the severity of symptoms (Peet et al., 2002).
Aspirin inhibits vascular dilation during electrical stimulation of cerebral cortex slices in vitro (Zonta et al., 2003); and pharmacological inhibition of COX-2, or COX-2 gene knockout, reduces by 40 to 50% the cerebral blood flow response of the sensory cortex to whisker stimulation in mice (Niwa et al., 2000). Thus, an eicosanoid signaling abnormality could potentially contribute to the cerebral neurovascular coupling defects that have been repeatedly observed in SZ (Berman et al., 1992; Liddle et al., 1992; Weinberger et al., 1992).
Many signs and symptoms of SZ are suggestive of excess dopamine activity (Snyder, 1981). Prostaglandin D2 (PGD2) and other PGs stimulate the production of cAMP and thereby exert functional antagonism of dopamine-D2 receptors, which modulate inhibition of cAMP synthesis (Ono et al., 1992; Wanibuchi and Usuda, 1990). PGD2 therefore counteracts the biochemical and behavioral effects of dopamine in vitro and in vivo. PGD2 administration blocks the behavioral effects of dopaminergic agents such as apomorphine, L-DOPA, and amphetamine; and induces catalepsy in a manner identical to dopamine-D2 receptor antagonists such as haloperidol (Ono et al., 1992; Wanibuchi and Usuda, 1990). Deficient PGD2 signaling would thus be expected to produce the signs of excessive dopamine activity that are seen in SZ. A role for PGs as endogenous anti-dopaminergic agents is supported by the findings that inhibitors of PG synthesis can cause psychotic symptoms in some people and can worsen psychotic symptoms in SZ patients (Hoppman et al., 1991; Sussman and Magid, 2000). The relationship between SZ and COX products is complex, however, as there are also reports suggesting that COX inhibitors may augment the efficacy of antipsychotic medications (Akhondzadeh et al., 2007; Laan et al., 2010; Müller et al., 2002). These seemingly contradictory findings nonetheless speak to the relevance of prostaglandins to the pathophysiology of the schizophrenias while also pointing toward their etiologic diversity.
A deficiency of prostaglandins has previously been related to SZ (Horrobin, 1977). It is likely that reduced AA availability may in part explain a variety of clinical observations that are usually ignored by the receptor-based etiological hypotheses (Horrobin, 1998). For example, in SZ, there appears to be a lower risk of arthritis and other inflammatory diseases (Eaton et al., 1992), greater resistance to pain (Davis et al., 1979, Horrobin, 1977), and remission of psychosis during fever has been observed (Horrobin, 1977). These effects could be secondary to reduced eicosanoid signaling.
5 Niacin Flush response as a test for eicosanoid abnormalities
Niacin (nicotinic acid), at sufficient doses, is well-known to dilate blood vessels in the skin resulting in a visible skin flush. The biochemical mechanism (Fig. 3) of this response has been studied over the course of several decades so many of the key steps have been well described. Niacin-induced skin flushing is prominently mediated by metabolites of AA. Thus, it may serve as a physiological marker of the integrity of phospholipid-arachidonate-eicosanoid (PAE) signaling. We will now describe how the niacin response abnormality might define a physiologically distinct subtype of SZ.
6 Mediation of niacin flush by AA metabolites
The levels of PGD2 and 9α,11β-PGF2 (a stable metabolite of PGD2) rise markedly in skin exudate or venous blood following oral or topical administration of niacin in humans (Eklund et al., 1979; Kobza Black et al., 1982; Morrow et al., 1992). Evidence favors PGD2 as the predominant mediator of the flush response (Morrow et al., 1989). However PGE2 levels also increase in response to niacin (Eklund et al., 1979; Kobza Black et al., 1982). In man, the flush response to niacin can be completely abolished by COX inhibitors such as aspirin or indomethacin (Svedmyr et al., 1977; Wilkin et al., 1982). In mice, the flush response to niacin can be eliminated by knocking out genes for either the niacin receptor or COX-1, consistent with an exclusive and obligatory role for this pathway in niacin-evoked skin flushing (Benyó et al. 2005). Classical vasodilatory mediators, such as histamine, bradykinin, serotonin, and acetylcholine do undergo changes in their skin transudate levels after niacin challenge (Morrow et al., 1992; Plummer et al., 1977). However, Papaliodis et al. (2008) showed that niacin induced the release of serotonin from human platelets in vitro and elevated blood levels of serotonin after intraperitoneal injection of niacin in rats. Although further study will be needed to clarify the possible role of serotonin, the vast majority of evidence points to a strongly predominant role of AA metabolites as primary mediators of the flush response to niacin. Other eicosanoid vasodilators, however, have not been well studied in SZ.
Fig. 3 The mechanism of niacin-induced skin flushing (adapted from Messamore et al., 2010). Abbreviations: COX, cyclooxygenase; PLA2, phospholipase A2; IL, interleukin; INF, interferon; TNF, tumor necrosis factor; PGD2, prostaglandin D2; PGF2 prostaglandin F2. |
7 Mechanism of the niacin flush response
A model of our current understanding of the mechanism of niacin-induced skin flushing is illustrated in Figure 3. Niacin interacts with a specific G-protein coupled receptor, HM74a, located on dermal macrophages and adipocytes (Benyó et al., 2006; Urade et al., 1989); its activation by niacin stimulates PLA2mediated formation of AA (Tang et al., 2006). Formation of AA is the rate-limiting step in the biosynthesis of the vasodilatory PGD2 and E2 (PGE2) (Murakami and Kudo 2004) These prostaglandins bind to specific prostanoid receptors on vascular smooth muscle within the skin. Activation of prostanoid receptors dilates cutaneous blood vessels (Lai et al., 2007), and a visible skin flush arises from the ensuing increased blood flow (Benyó et al., 2005; Maciejewski-Lenoir et al., 2006; Morrow et al., 1989, 1992).
8 The abnormal niacin response in SZ
Abrams Hoffer first reported observations that a substantial portion of patients with SZ are unusually resistant to the skin flush effect of pharmacologically-dosed niacin (Hoffer, 1962). Citing this work, and supporting these observations with clinical evidence of prostaglandin defects in the illness, Horrobin (1980a, 1980b) proposed that the niacin response abnormality could be used to demonstrate a prostaglandin signaling abnormality in SZ Abnormally attenuated skin flushing in response to niacin has been very widely replicated in samples of patients with SZ (Messamore, 2003; Smesny et al., 2003; Yao et al., 2015). The niacin response abnormality is consistently over-represented in SZ compared to both healthy control groups (Messamore, 2003), or psychiatrically ill comparison groups with major depression (Bosveld-van Haandel et al., 2006) or bipolar disorder (Liu et al., 2007; Ross et al., 2004; Yao et al., 2015).
Consistent with the view that SZ is an etiologically heterogenous disorder, the niacin response abnormality is not present in all patients with SZ. The prevalence of the niacin abnormality was pegged at 80 to 90% in some studies (Puri et al., 2001; Ward et al., 1998). However, we have observed a prevalence of about 30% in SZ patients in two separate experiments, and 20% in first-degree relatives of patients with SZ (unpublished data). There has been very little consistency across reports with respect to the methods to stimulate or measure blood flow. This methodological variability accounts for the disparity of estimates of the prevalence of the niacin response abnormality in SZ. If, however, the same methods are used, there is remarkable consistency in the ability to find higher rates of abnormality among SZ patients versus other clinical or healthy comparison groups.
9 Biochemical correlates of abnormal niacin response
Lower RBC membrane AA levels are associated with decreased niacin sensitivity, but this expected correlation has only been described in a healthy control group (Messamore et al., 2010). Although lower AA levels were found in patients who did not flush in response to oral niacin (Glen et al., 1996), no correlation between AA levels and niacin response was observed in two different groups of patients with SZ (Maclean et al., 2003; Messamore et al., 2010). On the other hand, an unexpected correlation was observed between maximal niacin-induced blood flow and red blood cell membrane levels of adrenic acid (22:4 n-6), the elongation product of AA. Adrenic acid has vasodilatory actions in bovine coronary arteries and in arteries of the cortical layer of the adrenal gland (Kop et al., 2010). Lack of correlation between AA levels and niacin response may result from a homeostatic imbalance within the n-6 PUFAs pathway in SZ. The significance of adrenic acid levels as they relate to niacin-induced blood flow response deserves further attention.
RBC membrane levels AA are normally tightly correlated with its immediate elongation product adrenic acid (22:4 n-6). However, this expected correlation is abolished in SZ (Messamore et al., 2010). Similar precursor-product dysregulations have also shown in tryptophan (Yao et al., 2010b) and purine (Yao et al., 2010a) pathways. Although many of these correlated relationships persist across disease or medication status, others are lost among patients with SZ.
10 Clinical correlates of abnormal niacin response
The extent to which abnormal niacin-induced skin flushing associates with clinical manifestations of SZ has recently been reviewed (Messamore, 2012). Impaired niacin-induced flushing has been associated with greater severity of both positive and negative symptoms of SZ (Berger et al., 2002; Glen et al., 1996; Hudson et al., 1997; Smesny et al., 2003). Niacin response impairment was significantly linked to inorganic phosphate levels revealed by 31P magnetic resonance spectroscopy (Puri et al., 2007). This suggests that niacin-abnormal SZ patients may have higher levels of cerebral energy metabolism. Niacin response, as reflected in the ‘volumetric niacin response score’ appears much more impaired among SZ patients with a history of violence (Puri et al., 2007) compared to ordinary SZ patients (Puri et al., 2002). Niacin response impairment is associated with worsened global functioning among patients with SZ (Messamore, 2012). Additionally, the niacin response abnormality is associated with significant cognitive impairment in SZ (Nilsson et al., 2015).
11 The niacin response abnormality is not an artifact of medication or smoking status
Evidence suggests that neither antipsychotic drugs nor smoking significantly affect the niacin skin flush response (Mills et al. 1997; Shah et al. 2000; Smesny et al. 2001; Turenne et al. 2001). The niacin skin flush is not affected by local anesthetics, suggesting that local neurotransmitter release is not involved in niacin-induced vasodilatation (Winklemann et al., 1965). There is no correlation between antipsychotic drug dose and niacin sensitivity in patients with SZ (Hudson et al., 1997; Messamore, 2003). Neither has a significant difference in niacin sensitivity been found between medicated versus unmedicated patients (Shah et al., 2000). In contrast, bipolar disorder patients who take antipsychotic medications have a normal or even enhanced flush response (Hudson et al., 1997) Moreover, niacin subsensitivity occurs in first-degree relatives of schizophrenics, which suggests that this is a heritable trait, independent of medication status (Shah et al., 1999; Waldo, 1999). On the other hand, Tavares et al. (2003) reported that 4 out of 13 SZ patients with niacin subsensitivity became sensitive to niacin after 8 weeks of atypical antipsychotic drug treatment. If such drugs do tend to normalize niacin sensitivity, then the potential bias in patient sample would be to underestimate the prevalence or magnitude of the niacin response abnormality in SZ. Taken together, comparing the niacin-induced flushing between medicated and unmedicated SZ patients, or unmedicated, non-psychotic relatives, suggests that the niacin response abnormality in SZ is not an artifact of antipsychotic medications (Chang et al., 2009; Lin et al., 2007; Maclean et al., 2003; Shah et al., 2000).
Similarly, it appears that nicotine use has no effect on the niacin-induced flushing response (Chang et al., 2009; Liu et al., 2007; Messamore, 2003, 2010; Ross et al., 2004; Shah et al., 2000; Smesny et al., 2003). Our recent findings (Yao et al., 2015) also support the notion that niacin sensitivity is not significantly affected by smoking.
12 Possible mechanisms for the niacin response abnormality in SZ
As depicted in Figure 3, there are several possible explanations for the finding of niacin subsensitivity in SZ. These include: abnormal signaling at the niacin receptor; abnormal presentation of free AA to COX; abnormal COX activity; abnormal conversion of initial COX products to vasodilatory end products; or abnormal signaling at prostanoid receptors in vascular smooth muscle. Support for abnormal niacin receptor signaling is provided by a report of decreased niacin receptor expression in postmortem brain from SZ patients (Miller and Dulay, 2008).
Presentation of free AA to COX is accomplished by the action of PLA2, which may be abnormally active in niacin-subsensitive SZ (Hudson et al., 1996; Tavares et al., 2003). Any process leading to diminished output of prostaglandins could potentially account for niacin subsensitivity. Abnormal COX activity in SZ was indirectly demonstrated by Das and Khan (1998).
Cyclooxygenase action on AA initially produces prostaglandin H2, which is subsequently converted by tissue-specific isomerases to vasodilatory end-products. Isomerase abnormalities have been detected in discrete brain regions from patients with a variety of mental illnesses (Maida et al., 2006).
It is intriguing to note that none of these pathways is specifically targeted by existing antipsychotic medications. Discovering the mechanisms responsible for the niacin response abnormality may inform the development of novel treatment strategies. Such treatments would likely involve targets outside the traditional monoamine receptors and thus would be expected to augment the efficacy of current medications. Elucidating the mechanism of the niacin response abnormality may also lead to physiologically-informed categorization of mental illness.
13 Conclusions
There is a compelling need to categorize the schizophrenias according to physiological criteria. Ideally such physiologically-defined categories would lead more easily than the older, traditional schema to insights about biochemical or genetic causes – and would suggest more tailored and effective treatments. Although this goal is desirable, there have been relatively few leads as to which physiological abnormalities may be more promising to follow.
We suggest that the niacin skin flush response abnormality is a viable candidate for the physiological subtyping of SZ In contrast to the incompletely-understood etiology of SZ, the mechanism of niacin-induced skin flushing in man is relatively well-characterized. This detailed knowledge, coupled with the accessibility of skin for scientific study, presents a technically feasible, straightforward, and economically attractive opportunity to broaden our understanding of the biochemical changes that accompany SZ.
It is intriguing to note that none of the biochemical pathways mediating the niacin response is specifically targeted by existing antipsychotic medications. Discovering the mechanisms responsible for the niacin response abnormality may inform the development of novel treatment strategies. Such treatments would likely involve targets outside the traditional monoamine receptors and thus would be expected to augment the efficacy of current medications. As the metabolic and genetic underpinnings of this biomarker are elucidated, it should yield valuable insights into the complex pathophysiology of schizophrenic illness.
Disclosure
The authors declare no conflict of interest
Acknowledgments
Supported in part by Department of Veterans Affairs [Merit Reviews 1I01CX000110 (JKY) and Senior Research Career Scientist Award (JKY)], and the VA Pittsburgh Healthcare System. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. The contents of this article do not represent the views of the Department of Veterans Affairs or the United States Government.
References
- Akhondzadeh S, Tabatabaee M, Amini H, et al. 2007. Celecoxib as adjunctive therapy in schizophrenia: a double-blind, randomized and placebo-controlled trial. Schizophr. Res. 90: 179–185. [CrossRef] [PubMed] [Google Scholar]
- Arvindakshan M, Sitasawad S, Debsikdar V, et al. 2003. Essential polyunsaturated fatty acid and lipid peroxide levels in never-medicated and medicated schizophrenia patients. Biol. Psychiatry 53: 56–64. [CrossRef] [PubMed] [Google Scholar]
- Bazan NG. 2006. Eicosanoids, docosanoids, platelet-activating factor and inflammation. In: Siegel GJ, Albers WR, Brady ST, Price DL, eds., Basic neurochemistry: Molecular, cellular, and medical aspects. 7th ed., Burlington, MA: Academic Press, pp. 575–591. [Google Scholar]
- Bentsen H, Solberg DK, Refsum H, et al. 2011. Bimodal distribution of polyunsaturated fatty acids in schizophrenia suggests two endophenotypes of the disorder. Biol. Psychiatry 70: 97–105 [CrossRef] [PubMed] [Google Scholar]
- Benyó Z, Gille Z, Kero J, Csiky M, et al. 2005. GPR109A (PUMA-G/HM74A) mediates nicotinic acid – induced flushing. J. Clin. Invest. 115: 3634–3640. [CrossRef] [PubMed] [Google Scholar]
- Benyó Z, Gille A, Bennett CL, Clausen BE, Offermanns S. 2006. Nicotinic acid-induced flushing is mediated by activation of epidermal langerhans cells. Mol. Pharmacol. 70: 1844–1849. [CrossRef] [PubMed] [Google Scholar]
- Berger G, Yuen H, McGorry P. 2002. The topical niacin flush test in early psychosis (Abstract). Schizophr. Res. 53: S38. [Google Scholar]
- Berman KF, Torrey EF, Daniel DG, Weinberger DR. 1992. Regional cerebral blood flow in monozygotic twins discordant and concordant for schizophrenia. Arch. Gen. Psychiatry. 49: 927–934. [CrossRef] [PubMed] [Google Scholar]
- Bleuler E. 1920. Lehrbuch der Psychiatrie, Berlin: Springer reprinted English translation (1976) Textbook of psychiatry. New York: Arno Press. [Google Scholar]
- Bosveld-van Haandel L, Knegtering R, Kluiter H, van den Bosch RJ 2006. Niacin skin flushing in schizophrenic and depressed patients and healthy controls. Psychiatry Res. 143: 303–306. [CrossRef] [PubMed] [Google Scholar]
- Braff DL, Freedman R, Schork NJ, Gottesman II. 2007. Deconstructing schizophrenia: an overview of the use of endophenotypes in order to understand a complex disorder. Schizophr. Bull. 33: 21–32. [CrossRef] [PubMed] [Google Scholar]
- Chang, S.S., Liu, C.M., Lin, S.H., et al. 2009. Impaired flush response to niacin skin patch among schizophrenia patients and their nonpsychotic relatives: the effect of genetic loading. Schizophr Bull 35: 213–221. [CrossRef] [PubMed] [Google Scholar]
- Condray R, Yao JK. 2011 Cognition, dopamine and bioactive lipids in schizophrenia. Front. Biosci. S3: 298–330. [Google Scholar]
- Conklin SM, Muldoon MF, Reddy RD, Yao JK. 2007. Fatty acids and psychiatric disorders. In: Chow C.K. ed., Fatty acids in foods and their health implications, 3rd ed. New York: Marcel Dekker, Inc., pp. 1229–1256. [Google Scholar]
- Das I, Khan NS. 1998. Increased arachidonic acid induced platelet chemiluminescence indicates cyclooxygenase overactivity in schizophrenic subjects. Prostagland. Leukot. Essent. Fatty Acids 58: 165–168. [CrossRef] [Google Scholar]
- Davis GC, Buchsbaum MS, van Kammen DP, Bunney WE Jr, 1979. Analgesia to pain stimuli in schizophrenics and its reversal by naltrexone. Psychiatry Res. 1: 61–69. [CrossRef] [PubMed] [Google Scholar]
- Doris AB, Wahle K, MacDonald A, et al. 1998. Red cell membrane fatty acids, cytosolic phospholipase A2 and schizophrenia. Schizophr. Res. 31: 185–196. [CrossRef] [PubMed] [Google Scholar]
- Eaton WW, Hayward C, Ram R. 1992. Schizophrenia and rheumatoid arthritis: a review. Schizophr. Res. 6: 181–192. [CrossRef] [PubMed] [Google Scholar]
- Eklund B, Kaijser L, Nowak J, Wennmalm A. 1979. Prostaglandins contribute to the vasodilation induced by nicotinic acid. Prostaglandins 17: 821–830. [CrossRef] [PubMed] [Google Scholar]
- Garver DL, Holcomb JA, Christensen JD. 2000. Heterogeneity of response to antipsychotics from multiple disorders in the schizophrenia spectrum. J. Clin. Psychiatry 61: 964–972. [Google Scholar]
- Glen AI, Glen EM, Horrobin DF, et al. 1994. A red cell membrane abnormality in a subgroup of schizophrenic patients: evidence for two diseases. Schizophr. Res. 12: 53–61. [CrossRef] [PubMed] [Google Scholar]
- Glen AI, Cooper SJ, Rybakowski J, Vaddadi K, Brayshaw N, Horrobin DF. 1996. Membrane fatty acids, niacin flushing and clinical parameters. Prostagland. Leukotr. Essent. Fatty Acids 55: 9–15. [CrossRef] [Google Scholar]
- Hoffer A. 1962. Niacin therapy in psychiatry. Springfield, IL: Charles Thomas. [Google Scholar]
- Hoppman RA, Peden JG, Over SK. 1991. Central nervous system side effects of nonsteroidal anti-inflammatory drugs. Arch. Intern. Med. 151: 1309–1313. [CrossRef] [PubMed] [Google Scholar]
- Horrobin DF. 1977. Schizophrenia as a prostaglandin deficiency disease. Lancet 1: 936–937. [CrossRef] [PubMed] [Google Scholar]
- Horrobin DF. 1980a. Niacin flushing, prostaglandin E and evening primrose oil: a possible objective test for monitoring therapy in schizophrenia. Orthomol. Psychiatry 91: 33–34 [Google Scholar]
- Horrobin DF. 1980b. Schizophrenia: a biochemical disorder? Biomedicine 32: 54–55. [PubMed] [Google Scholar]
- Horrobin DF. 1998. The membrane phospholipid hypothesis as a biochemical basis for the neuro-developmental concept of schizophrenia. Schizophr. Res. 30: 193–208. [CrossRef] [PubMed] [Google Scholar]
- Horrobin DF, Manku MS, Hillman H, Iain A, Glen M. 1991. Fatty acid levels in the brains of schizophrenics and normal controls. Biol. Psychiatry 30: 795–805. [CrossRef] [PubMed] [Google Scholar]
- Hudson CJ, Kennedy JL, Gotowiec A, et al. 1996. Genetic variant near cytosolic phospholipase A2 associated with schizophrenia. Schizophr. Res. 21: 111–116. [CrossRef] [PubMed] [Google Scholar]
- Hudson CJ, Lin A, Cogan S, Cashman F, Warsh JJ. 1997. The niacin challenge test: clinical manifestation of altered transmembrane signal transduction in schizophrenia. Biol. Psychiatry 41: 507–513. [CrossRef] [PubMed] [Google Scholar]
- Jablensky A. 2006 Subtyping schizophrenia: implications for genetic research. Mol. Psychiatry 11: 815–836. [CrossRef] [PubMed] [Google Scholar]
- Keshavan MS, Tandon R, Boutros NN, Nasrallah HA. 2008. Schizophrenia, just the facts: what we know in 2008 Part 3: neurobiology. Schizophr. Res. 106: 89–107. [CrossRef] [PubMed] [Google Scholar]
- Khanna N, Altmeyer W Zhuo J, Steven A. 2015 Functional neuroimaging: Fundamental principles and clinical applications. Neuroradiol. J. 28: 87–96. [CrossRef] [PubMed] [Google Scholar]
- KobzaBlack A, Greaves MW, Hensby CN. 1982. The effect of systemic prednisolone on arachidonic acid, and prostaglandin E2 and F2 alpha levels in human cutaneous inflammation. Br. J. Clin. Pharmacol. 14: 391–394. [CrossRef] [PubMed] [Google Scholar]
- Kop PG, Zhang D.,Gauthier KM, et al. 2010. Adrenic acid metabolites as endogenous endothelium-derived and zona glomerulosa-derived hyperpolarizing factors. Hypertension 55: 547–554. [Google Scholar]
- Laan W, Grobbee, D, Selten JP, Heijnen CJ, Kahn RS, Burger H. 2010. Adjuvant asprin therapy reduces symptoms of schizophrenia spectrum disorders: results from a randomized, double-blind, placebo controlled trial. J. Clin. Psychiatry 71, 520–527. [Google Scholar]
- Lai E, De Lepeleire I, Crumley TM, et al. 2007. Suppression of niacin-induced vasodilation with an antagonist to prostaglandin D2 receptor subtype 1. Clin. Pharmacol. Ther. 81: 849–857. [CrossRef] [PubMed] [Google Scholar]
- Liddle PF, Friston KJ, Frith CD, Hirsch SR, Jones T, Frackowiak RS. 1992. Patterns of cerebral blood flow in schizophrenia Brit. J. Psychiatry 160: 179–186. [CrossRef] [Google Scholar]
- Lin SH, Liu CM, Chang SS, et al. 2007. Familial aggregation in skin flush response to niacin patch among schizophrenic patients and their nonpsychotic relatives. Schizophr. Bull. 33: 174–182. [CrossRef] [PubMed] [Google Scholar]
- Liu CM, Chang SS, Liao SC, et al. 2007. Absent response to niacin skin patch is specific to schizophrenia and independent of smoking. Psychiatr. Res. 152: 181–187. [CrossRef] [Google Scholar]
- Maciejewski-Lenoir D.,Richman JG, Hakak Y, Gaidarov I, Behan DP, Connolly DT. 2006. Langerhans cells release prostaglandin D2 in response to nicotinic acid. J. Invest. Dermatol. 126: 2637–2646. [CrossRef] [PubMed] [Google Scholar]
- Maclean R, Ward PE, Glen I, Roberts SJ, Ross BM, 2003. On the relationship between methylnicotinate-induced skin flush and fatty acids levels in acute psychosis. Prog. Neuropsychopharmacol. Biol. Psychiatry. 27: 927–933. [Google Scholar]
- Mahadik SP, Yao JK. 2006. Phospholipids in schizophrenia. In: Lieberman, J.A., Stroup, T.S., and Perkins, D.O. eds. Textbook of schizophrenia. Washington, DC: The American Psychiatric Publishing, Inc., pp. 117–135. [Google Scholar]
- Maida ME, Hurley SD, Daeschner JA, Moore AH, O’Banion MK. 2006. Cytosolic prostaglandin E2 synthase (cPGES) expression is decreased in discrete cortical regions in psychiatric disease. Brain Res. 1103: 164–172. [CrossRef] [PubMed] [Google Scholar]
- Messamore E. 2003. Relationship between the niacin skin flush response and essential fatty acids in schizophrenia. Prostagland. Leukot. Essent. Fatty Acids 69: 413–419. [CrossRef] [Google Scholar]
- Messamore E. 2012. Niacin subsensitivity is associated with functional impairment in schizophrenia. Schizophr. Res. 137: 180–184 [CrossRef] [PubMed] [Google Scholar]
- Messamore E, Hoffman WF, Yao JK. 2010. Niacin sensitivity and the arachidonic acid pathway in schizophrenia. Schizophr. Res. 122: 248–256. [CrossRef] [PubMed] [Google Scholar]
- Miller C.L., Dulay J.R. 2008. The high-affinity niacin receptor HM74A is decreased in the anterior cingulate cortex of individuals with schizophrenia. Brain Res. Bull. 77: 33–41. [CrossRef] [PubMed] [Google Scholar]
- Mills CM, Hill SA, Marks R. 1997. Transdermal nicotine suppresses cutaneous inflammation. Arch. Dermatol. 133: 823–902 [CrossRef] [PubMed] [Google Scholar]
- Morrow JD, Parsons WG, Roberts LJ. 1989. Release of markedly increased quantities of prostaglandin D2 in vivo in humans following the administration of nicotinic acid. Prostaglandins 38: 263–274. [CrossRef] [PubMed] [Google Scholar]
- Morrow JD, Awad JA, Oates JA, Roberts LJ. 1992. Identification of skin as a major site of prostaglandin D2 release following oral administration of niacin in humans. J. Invest. Dermatol. 98: 812–815. [CrossRef] [PubMed] [Google Scholar]
- Müller N, Riedel M, Scheppach C, et al. 2002. Beneficial antipsychotic effects of celecoxib add-on therapy compared to risperidone alone in schizophrenia. Am. J. Psychiatry 159: 1029–1034. [CrossRef] [PubMed] [Google Scholar]
- Murakami M, Kudo I. 2004. Recent advances in molecular biology and physiology of the prostaglandin E2-biosynthetic pathway. Prog. Lipid Res. 43: 3–35. [CrossRef] [PubMed] [Google Scholar]
- Nilsson BM, Holm G, Hultman CM, Ekselius L. 2015 Cognition and autonomic function in schizophrenia: inferior cognitive test performance in electrodermal and niacin skin flush non-responders Eur. Psychiatry 30: 8–13. [CrossRef] [PubMed] [Google Scholar]
- Niwa K, Araki E, Morham SG, Ross ME, Iadecola C. 2000. Cyclooxygenase-2 contributes to functional hyperemia in whisker-barrel cortex. J. Neurosci. 20: 763–770. [PubMed] [Google Scholar]
- Ono N, Abiru T, Kamiya H. 1992. Influences of cyclooxygenase inhibitors on the cataleptic behavior induced by haloperidol in mice. Prostagland. Leukotr. Essent. Fatty Acids 46: 59–63. [CrossRef] [Google Scholar]
- Papaliodis D, Boucher W, Kempuraj D, et al. 2008. Niacin-induced “flush” involves release of prostaglandin D2 from mast cells and serotonin from platelets: Evidence from human cells in vitro and an animal model. J. Pharmacol. Exp. Ther. 327: 665–672. [CrossRef] [PubMed] [Google Scholar]
- Peet M. 2007. Membrane fatty acid deficit in schizophrenia and mood disorders. In: Reddy R and Yao JK eds. Fatty acids and oxidative stress in neuropsychiatric disorders. New York: Nova Science Publishers, Inc., pp. 101–114. [Google Scholar]
- Peet M, Laugharne JDE, Horrobin DF, Reynolds GP. 1994. Arachidonic acid: A common link in the biology of schizophrenia? Arch. Gen. Psychiatry 51: 665–666. [CrossRef] [PubMed] [Google Scholar]
- Peet M, Horrobin DF, Group EEMS. 2002. A dose ranging exploratory study of the effects of ethyleicosapentaenoate in patients with persistent schizophrenic symptoms. J. Psychiatr. Res. 36: 7–18. [CrossRef] [PubMed] [Google Scholar]
- Pettegrew JW, Keshavan MS, Panchalingam K, et al. 1991. Alterations in brain high-energy phosphate and membrane phospholipid metabolism in first-episode, drug-naive schizophrenics. A pilot study of the dorsal prefrontal cortex by in vivo phosphorus 31 nuclear magnetic resonance spectroscopy. Arch. Gen. Psychiatry. 48: 563–568. [CrossRef] [PubMed] [Google Scholar]
- Plummer NA, Hensby CN, Black AK, Greaves MW. 1977. Prostaglandin activity in sustained inflammation of human skin before and after aspirin. Clin. Sci. Mol. Med. 52: 615–620. [PubMed] [Google Scholar]
- Puri BK, Easton T, Das I, Kidane L, Richardson AJ. 2001. The niacin skin flush test in schizophrenia: a replication study. Int. J. Clin. Pract. 55: 368–370. [PubMed] [Google Scholar]
- Puri BK, Hirsch SR, Easton T, Richardson AJ. 2002. A volumetric biochemical niacin flush based index that noninvasively detects fatty acid deficiency in schizophrenia. Prog. Neuropsychopharmacol. Biol. Psychiatry 26: 49–52. [CrossRef] [PubMed] [Google Scholar]
- Puri BK, Richardson AJ, Counsell SJ, et al. 2007. Negative correlation between cerebral inorganic phosphate and the volumetric niacin response in male patients with schizophrenia who have seriously and dangerously violently offended: a (31)P magnetic resonance spectroscopy study. Prostagland. Leukot. Essent. Fatty Acids 77: 97–99. [CrossRef] [Google Scholar]
- Reddy RD, Keshavan MS, Yao JK. 2004. Reduced red blood cell membrane polyunsaturated fatty acids in first-episode schizophrenia at neuroleptic-naïve baseline. Schizophr. Bull. 30: 901–911. [CrossRef] [PubMed] [Google Scholar]
- Ross BM, Hughes B, Turenne S, Seeman M, Warsh JJ. 2004. Reduced vasodilatory response to methyl-nicotinate in schizophrenia as assessed by laser doppler flowmetry. Eur. Neuropsychopharma 14: 191–197. [CrossRef] [Google Scholar]
- Shah SH, Ramchand CN, Peet M. 1999. The niacin skin flush test: first-degree relatives show responses intermediate between patients and controls. Schizophr. Res. 36: 314. [Google Scholar]
- Shah SH, Vankar GK, Peet M, Ramchand CN. 2000. Unmedicated schizophrenic patients have a reduced skin flush in response to topical niacin. Schizophr. Res. 43: 163–164. [PubMed] [Google Scholar]
- Skosnik PD, Yao JK. 2003. From phospholipid and fatty acid defects to altered neurotransmission: Is arachidonic acid a nexus in the pathophysiology of schizophrenia? Prostagland. Leukot. Essent. Fatty Acids 69: 367–384 [CrossRef] [Google Scholar]
- Smesny S, Riemann S, Riehemann S, Bellemann ME, Sauer H. 2001. Quantitative measurement of induced skin reddening using optical reflection spectroscopy–methodology and clinical application. Biomed. Tech. (Berl). 46: 280–286. [CrossRef] [PubMed] [Google Scholar]
- Smesny S, Berger G, Rosburg T, et al. 2003. Potential use of the topical niacin skin test in early psychosis a combined approach using optical reflection spectroscopy and a descriptive rating scale. J. Psychiatr. Res. 37: 237–247. [CrossRef] [PubMed] [Google Scholar]
- Snyder SH. 1981. Dopamine receptors, neuroleptics, and schizophrenia. Am. J. Psychiatry. 138: 460–464. [CrossRef] [PubMed] [Google Scholar]
- Sussman N, Magid S. 2000. Psychiatric manifestations of nonsteroidal antiinflammatory drugs. Primary Psychiatry 7: 26–30. [Google Scholar]
- Svedmyr N, Heggelund A, Aberg G, 1977. Influence of indomethacin on flush induced by nicotinic acid in man. Acta. Pharmacol. Toxicol. 41: 397–400. [CrossRef] [Google Scholar]
- Tang Y, Zhou L, Gunnet JW, Wines PG, Cryan EV, Demarest KT. 2006. Enhancement of arachidonic acid signaling pathway by nicotinic acid receptor HM74A. Biochem. Biophys. Res. Commun. 345: 29–37. [CrossRef] [PubMed] [Google Scholar]
- Tavares H, Yacubian J, Talib LL, Barbosa NR, Gattaz WF. 2003. Increased phospholipase A2 activity in schizophrenia with absent response to niacin. Schizophr. Res. 61: 1–6. [CrossRef] [PubMed] [Google Scholar]
- Turenne SD, Seeman M, Ross BM. 2001. An animal model of nicotinic-acid-induced vasodilation: effect of haloperidol, caffeine, and nicotine upon nicotinic acid response Schizophr. Res. 50: 191–197 [CrossRef] [PubMed] [Google Scholar]
- Urade Y, Ujihara M, Horiguchi Y, Ikai K, Hayaishi O. 1989. The major source of endogenous prostaglandin D2 production is likely antigen-presenting cells. Localization of glutathione-requiring prostaglandin D synthetase in histiocytes, dendritic, and Kupffer cells in various rat tissues. J. Immunol. 143: 2982–2989. [PubMed] [Google Scholar]
- Vaddadi KS, Gilleard CJ, Mindham RHButler R. 1986. A controlled trial of prostaglandin E1 precursor in chronic neuroleptic resistant schizophrenic patients. Psychopharmacol. 88: 362–367. [CrossRef] [Google Scholar]
- Waldo MC. 1999. Co-distribution of sensory gating and impaired niacin flush response in the parents of schizophrenics. Schizophr. Res. 40: 49–53. [CrossRef] [PubMed] [Google Scholar]
- Wanibuchi F, Usuda S. 1990. Synergistic effects between D-I and D-2 dopamine antagonists on catalepsy in rats. Psychopharmacology 102: 339–342. [CrossRef] [PubMed] [Google Scholar]
- Ward PE, Sutherland J, Glen EM, Glen AI. 1998. Niacin skin flush in schizophrenia: a preliminary report. Schizophr. Res. 29: 269–274. [CrossRef] [PubMed] [Google Scholar]
- Weinberger DR, Berman KF, Suddath R, Torrey EF. 1992. Evidence of dysfunction of a prefrontal-limbic network in schizophrenia: a magnetic resonance imaging and regional cerebral blood flow study of discordant monozygotic twins. Am J. Psychiatry. 149: 890–897. [CrossRef] [PubMed] [Google Scholar]
- Wilkin JK, Wilkin O, Kapp R, Donachie R, Chernosky ME, Buckner J. 1982. Aspirin blocks nicotinic acid-induced flushing. Clin. Pharmacol. Ther. 31: 478–482. [CrossRef] [PubMed] [Google Scholar]
- Winklemann RK, Wilhelmj CM, Horner FA. 1965. Experimental studies on dermographism. Arch. Dermatol. 92: 436–442. [CrossRef] [PubMed] [Google Scholar]
- Yao JK. 2003. Abnormalities of fatty acid metabolism in red cells, platelets and brain in schizophrenia. In: Peet M, Glen I, Horrobin DF, eds., Phospholipid spectrum disorders in psychiatry and neurology, 2nd ed. Lancashire, UK: Marius Press, pp. 193–212. [Google Scholar]
- Yao JK, van Kammen DP, Welker JA. 1994a. Red blood cell membrane dynamics in schizophrenia. II. Fatty acid composition. Schizophr. Res. 13: 217–226. [CrossRef] [PubMed] [Google Scholar]
- Yao JK, van Kammen DP, Gurklis J. 1994b. Red blood cell membrane dynamics in schizophrenia. III. Correlation of fatty acid abnormalities with clinical measures. Schizophr. Res. 13: 227–232. [CrossRef] [PubMed] [Google Scholar]
- Yao JK, Leonard S, Reddy R. 2000. Membrane phospholipid abnormalities in postmortem brains from schizophrenic patients. Schizophr. Res. 42: 7–17. [CrossRef] [PubMed] [Google Scholar]
- Yao JK, Dougherty GG, Reddy RD, et al. 2010a. Homeostatic imbalance of purine catabolism in first-episode neuroleptic-naïve patients with schizophrenia. PLoS One 5: e9508. [CrossRef] [PubMed] [Google Scholar]
- Yao JK, Dougherty GG, Reddy RD, et al. 2010b. Altered interactions of tryptophan metabolites in first-episode neuroleptic-naïve patients with schizophrenia. Mol. Psychiatry. 15: 938–953. [CrossRef] [PubMed] [Google Scholar]
- Yao JK, Dougherty Jr GG, Gautier CH, et al. 2015. Prevalence and specificity of the abnormal niacin response: A potential endophenotype marker in schizophrenia. Schizophr. Bull. DOI: 10.1093/schbul/sbv130. [Google Scholar]
- Zonta M, Angulo MC, Gobbo S, Rosengarten B, Hossmann KA, Pozzan T, Carmignot G. 2003. Neuron-to-astrocyte signaling is central to the dynamic control of brain microcirculation. Nat. Neurosci. 6: 43–50. [CrossRef] [PubMed] [Google Scholar]
Cite this article as: Erik Messamore, Jeffrey K. Yao. Phospholipid, arachidonate and eicosanoid signaling in schizophrenia. OCL 2016, 23(1) D112.
All Figures
Fig. 1 An overview of phospholipids turnover, arachidonic acid, and eicosanoid signaling in schizophrenia symptomatology (adapted from Skosnik and Yao, 2003). Abbreviations: AODS, antioxidant defense system; NT, neurotransmitters; RO, reactive oxygen species; apoD, apolipoprotein D; PLA2, phospholipase A2; PLC, phospholipase C; LOX, lipooxygenase; AA, arachidonic acid; DAG, diacylglycerol; COX, cyclooxygenase; 2-AG, 2-arachidonoyl glycerol; GAP, growth-associated protein; PKC, phosphokinase C; PGG2. prostaglandin G2; PGH2, prostaglandin H2; PGD2, prostaglandin D2; CB, cannabinoid. |
|
In the text |
Fig. 2 Arachidonic acid cascade (adapted from Condray and Yao, 2011). EET, PGI2, PGD2, PGE2, PGF2, 12-HETE and 15-HETE are considered as potential vasodilators. |
|
In the text |
Fig. 3 The mechanism of niacin-induced skin flushing (adapted from Messamore et al., 2010). Abbreviations: COX, cyclooxygenase; PLA2, phospholipase A2; IL, interleukin; INF, interferon; TNF, tumor necrosis factor; PGD2, prostaglandin D2; PGF2 prostaglandin F2. |
|
In the text |
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.