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

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.

Nicotinic acid promotes sleep through prostaglandin synthesis in mice

Nicotinic acid has been used for decades for its antiatherogenic properties in humans. Its actions on lipid metabolism intersect with multiple sleep regulatory mechanisms, but its effects on sleep have never been documented. For the first time, we investigated the effects of acute systemic administration of nicotinic acid on sleep in mice. Intraperitoneal and oral gavage administration of nicotinic acid elicited robust increases in non-rapid-eye movement sleep (NREMS) and decreases in body temperature, energy expenditure and food intake. Preventing hypothermia did not affect its sleep-inducing actions suggesting that altered sleep is not secondary to decreased body temperature. Systemic administration of nicotinamide, a conversion product of nicotinic acid, did not affect sleep amounts and body temperature, indicating that it is not nicotinamide that underlies these actions. Systemic administration of monomethyl fumarate, another agonist of the nicotinic acid receptor GPR109A, fully recapitulated the somnogenic and thermoregulatory effects of nicotinic acid suggesting that they are mediated by the GPR109A receptor. The cyclooxygenase inhibitor indomethacin completely abolished the effects of nicotinic acid indicating that prostaglandins play a key role in mediating the sleep and thermoregulatory responses of nicotinic acid.

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.

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.

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.

Acetylsalicylic acid reduces niacin extended-release-induced flushing in patients with dyslipidemia

BACKGROUND

Niacin extended-release (NER) is safe and effective for treatment of dyslipidemia. However, some patients discontinue NER treatment because of flushing, the most common adverse event associated with niacin therapy.

OBJECTIVE

To evaluate the effect of daily oral acetylsalicylic acid (ASA) on NER-induced flushing in patients with dyslipidemia.

METHODS

A randomized, double-blind, placebo-controlled, multicenter, 5-week study was conducted (ClinicalTrials.gov identifier: NCT00626392). Patients (n = 277) were randomly assigned to one of six treatment arms and received a 1-week run-in with ASA 325 mg or placebo followed by 4 weeks of ASA 325 mg or placebo 30 minutes before NER at a starting dose of 500 mg or 1000 mg; all patients were titrated to NER 2000 mg at week 3. The primary endpoint was the maximum severity of flushing events during week 1.

RESULTS

In week 1, ASA run-in, ASA pretreatment, and a lower starting dosage of NER (500 mg/day) resulted in reductions in mean maximum severity of flushing; 48% fewer patients who received ASA experienced flushing episodes of moderate or greater intensity relative to placebo (absolute rates 15% vs 29%; p = 0.01). Over 4 weeks, ASA reduced the number of flushing episodes/patient/week by 42% relative to placebo. The discontinuation rate due to flushing was lower in the ASA group compared with placebo (1.8% vs 9.4%; p = 0.007). Overall safety was not different between groups.

CONCLUSION

These data suggest that a clinically meaningful reduction in the severity and incidence of NER-induced flushing may be achieved with ASA use.

Impaired flush response to niacin skin patch among schizophrenia patients and their nonpsychotic relatives: the effect of genetic loading

We previously reported familial aggregation in flush response to niacin skin patch among schizophrenia patients and their nonpsychotic relatives. However, little is known about whether this abnormal skin response is associated with genetic loading for schizophrenia. This study compared the niacin flush response in subjects from families with only one member affected with schizophrenia (simplex families) with those from families having a sib-pair with schizophrenia (multiplex families). Subjects were patients with schizophrenia and their nonpsychotic first-degree relatives from simplex families (176 probands, 260 parents, and 80 siblings) and multiplex families (311 probands, 180 parents, and 52 siblings) as well as 94 healthy controls. Niacin patches of 3 concentrations (0.001M, 0.01M, and 0.1M) were applied to forearm skin, and the flush response was rated at 5, 10, and 15 minutes, respectively, with a 4-point scale. More attenuated flush response to topical niacin was shown in schizophrenia probands and their relatives from multiplex families than in their counterparts from simplex families, and the differentiation was better revealed using 0.1M concentration of niacin than 0.01M or 0.001M. For the highest concentration of 0.1M and the longest time lag of 15 minutes, a subgroup of probands (23%), parents (27%), and siblings (19%) still exhibited nonflush response. Flush response to niacin skin patch is more impaired in schizophrenia patients and their relatives from families with higher genetic loading for schizophrenia, and this finding has implications for future genetic dissection of schizophrenia.

A quercetin containing supplement reduces niacin-induced flush in humans

Coronary artery disease is associated with increased serum levels of cholesterol, triglycerides and LDL, but low levels of HDL. The most potent agent capable of reversing this trend is the vitamin nicotinic acid (niacin). However, compliance even with extended-release preparations and addition of acetylsalicylic acid (ASA) is hampered by the development of a feeling of erythema and burning ("flush"), especially on the face. We recently showed that the natural flavonoids quercetin and luteolin can eliminate "flush", as well as inhibit both niacin-induced plasma prostaglandin D2 (PGD2) and serotonin increase in an animal model. We conducted a pilot clinical study in humans. Four normal male subjects received (a) 1 g immediate release niacin either alone or after (b) the dietary formulation (Algonot-plus) containing 150 mg quercetin per capsule. Subjects completed a visual scale (1 = no, 5 = worst response) symptom assessment. Erythema and burning sensation scores were both 4.75+/-0.50 and lasted for 3.63+/-1.11 hours. After Algonot-plus administration, both scores were reduced to 2.5+/-0.58 and lasted only for 1.68+/-0.70 hours. Quercetin also inhibited methylnicotinate-induced human mast cell PGD2 release. These preliminary results suggest that quercetin could reduce niacin-induced "flush" in humans.

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

Niacin lowers serum cholesterol, low-density lipoprotein, and triglycerides, and it raises high-density lipoprotein. However, most patients experience cutaneous warmth and vasodilation (flush). Acetylsalicylic acid (ASA) can reduce this flush, presumably by decreasing prostaglandin D(2) (PGD(2)) release from macrophages. Here, we show that methylnicotinate induces significant PGD(2) release from human mast cells and serotonin from human platelets. Intradermal injection of methylnicotinate induces rat skin vasodilation and vascular permeability. Niacin increases plasma PGD(2) and serotonin in a rat model of flush. The phenothiazine prochlorperazine, the H(1), serotonin receptor antagonist cyproheptadine, and the specific serotonin receptor-2A antagonist ketanserin inhibit niacin-induced temperature increase by 90% (n = 5, p < 0.05), 90 and 50% (n = 3, p < 0.05), and 85% (n = 6, p = 0.0008), respectively, in this animal model. These results indicate that niacin-induced flush involves both PGD(2) and serotonin, suggesting that drugs other than ASA are required to effectively inhibit niacin-induced flush.

The high-affinity niacin receptor HM74A is decreased in the anterior cingulate cortex of individuals with schizophrenia

The pathway for de novo synthesis of the suite of niacin congeners, the kynurenine pathway, has been shown to be upregulated in prior studies of postmortem brain tissue from individuals with schizophrenia. The cause of the upregulation is unknown, but one factor may be a defect in feedback regulation via receptors responsive to niacin. A high-affinity and low-affinity receptor for niacin have been identified, HM74A and HM74, respectively. We used RT-QPCR and Western blots to quantify expression of HM74A and HM74 receptors in brain tissue obtained postmortem from patients with schizophrenia (N=12) or bipolar disorder (N=14) and from normal controls (N=14). Although the protein for the HM74 receptor was unchanged, the protein for HM74A was significantly decreased in the schizophrenia group, both when normalized to GAPDH protein or to HM74 as an internal control for degradation and gel-loading error (0.56-fold+/-0.36, p=0.016 and 0.58-fold+/-0.19 the mean control value, p=0.001, respectively). In contrast, the transcript for HM74A was significantly increased, revealing a striking dysregulation between gene transcription and final protein product. No significant differences in HM74A were found for the bipolar group relative to controls. These results are consistent with the blunted niacin flush response reported for individuals with schizophrenia and may be relevant to different rates of comorbid disease.

The flavonoid luteolin inhibits niacin-induced flush

BACKGROUND AND PURPOSE

Sustained release niacin effectively lowers serum cholesterol, LDL and triglycerides, while raising HDL. However, 75% of patients experience cutaneous warmth and itching known as flush, leading to discontinuation. Acetylsalicylic acid (aspirin) reduces this flush only by about 30%, presumably through decreasing prostaglandin D2 (PGD2). We investigated whether niacin-induced flush in a rat model involves PGD2 and 5-HT, and the effect of certain flavonoids.

EXPERIMENTAL APPROACH

Three skin temperature measurements from each ear were recorded with an infrared pyrometer for each time point immediately before i.p. injection with either niacin or a flavonoid. The temperature was then measured every 10 min for 60 min.

KEY RESULTS

Niacin (7.5 mg per rat, equivalent to a human dose of 1750 mg per 80 kg) maximally increased ear temperature to 1.9+/-0.2 degrees C at 45 min. Quercetin and luteolin (4.3 mg per rat; 1000 mg per human), administered i.p. 45 min prior to niacin, inhibited the niacin effect by 96 and 88%, respectively. Aspirin (1.22 mg per rat; 325 mg per human) inhibited the niacin effect by only 30%. Niacin almost doubled plasma PGD2 and 5-HT, but aspirin reduced only PGD2 by 86%. In contrast, luteolin inhibited both plasma PGD2 and 5-HT levels by 100 and 67%, respectively. CONCLUSIONS AND IMPLICATIONS. Niacin-induced skin temperature increase is associated with PGD2 and 5-HT elevations in rats; luteolin may be a better inhibitor of niacin-induced flush because it blocks the rise in both mediators.

Comparison of rat and dog models of vasodilatation and lipolysis for the calculation of a therapeutic index for GPR109A agonists

INTRODUCTION

GPR109A is the receptor mediating both the antilipolytic and vasodilatory effects of nicotinic acid. In order to develop agonists for GPR109A with improved therapeutic indices we have sought to optimize animal models that evaluate both nicotinic acid-mediated inhibition of lipolysis and stimulation of vasodilatation. The rat and the dog have previously been used to study the antilipolytic effects of nicotinic acid, but no optimal vasodilatation model exits in either species.

METHODS

We have developed a vasodilatation model in the rat that measures changes in ear perfusion using laser Doppler flowmetry. In the dog, we have developed a model of vasodilatation measuring changes in red color values in the ear, using a spectrocolorimeter. Effects of GPR109A agonists on lipolysis were measured in both species after oral dosing of compounds, and measuring plasma levels of free fatty acids.

RESULTS

In both rat and dog, GPR109A agonists induce dose- and time-dependent vasodilatation, similar to that observed in humans. Vasodilatation is inhibited in both species with cyclooxygenase inhibitors or a specific DP1 receptor antagonist, indicating that, as in man, nicotinic acid-induced vasodilatation in rats and dogs is mainly mediated by the release of PGD(2).

DISCUSSION

Our results show that both rat and dog are useful models for the characterization of GPR109A agonists. A therapeutic index for GPR109A agonists can be calculated in either species.

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.

Urotensin-II induces ear flushing in rats

BACKGROUND AND PURPOSE

While investigating the effects of systemic urotensin II (U-II), a potent vasoactive peptide acting at the UT receptor, we observed ear pinna flushing after systemic administration to conscious rats. In the present study, U-II-induced ear flushing was quantified in terms of ear pinna temperature change and potential mechanisms were explored.

EXPERIMENTAL APPROACH

U-II-induced ear flushing was quantified by measuring lateral ear pinna temperature changes and compared to that of calcitonin gene-related peptide (CGRP), a known cutaneous vasodilator. Further, the effects of a variety of pharmacological agents on U-II-induced ear flushing were explored.

KEY RESULTS

Subcutaneous injection of U-II (9 microg kg(-1))produced localized ear pinna flushing with an onset of approximately 15 min, a duration of approximately 30 min and a maximal temperature change of 9 degrees C. In contrast, CGRP caused cutaneous flushing within multiple cutaneous beds including the ear pinna with a shorter onset and greater duration than U-II. A potent UT receptor antagonist, urantide, blocked U-II-induced ear flushing but did not affect CGRP-induced ear flushing. Pretreatment with indomethacin or L-Nomega-nitroarginine methylester (L-NAME) abolished U-II-induced ear flushing. Mecamylamine or propranolol did not affect this response to U-II. Direct intracerebroventricular injection studies suggested that the ear flushing response to U-II was not mediated directly by the CNS.

CONCLUSION AND IMPLICATIONS

Our results suggest that U-II-induced ear flushing and temperature increase is mediated by peripheral activation of the UT receptor and involves prostaglandin- and nitric oxide-mediated vasodilation of small capillary beds in the rat ear pinna.

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.

Niacin skin flushing in schizophrenic and depressed patients and healthy controls

This study compares the skin reactions to the niacin flushing test of 16 schizophrenic patients with those of 17 depressed patients and 16 healthy controls. Methyl nicotinate (niacin) in a concentration of 0.1 M was applied to the forearm for 5 min. Significant differences could be observed between the group of schizophrenic patients (less flushing) in comparison to the other groups. There were no statistical differences in niacin flushing between patients with depression and healthy controls. Gender, age and the use of antipsychotic agents did not appear to be confounders. The differences in flushing within the group of schizophrenic patients were striking, however. Most patients showed little or no flushing, but some patients reacted strongly. Although the three groups could be differentiated by the niacin flushing test, to develop a reliable clinical application of this test, further research is necessary.

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.

Enhancement of arachidonic acid signaling pathway by nicotinic acid receptor HM74A

HM74A is a G protein-coupled receptor for nicotinic acid (niacin), which has been used clinically to treat dyslipidemia for decades. The molecular mechanisms whereby niacin exerts its pleiotropic effects on lipid metabolism remain largely unknown. In addition, the most common side effect in niacin therapy is skin flushing that is caused by prostaglandin release, suggesting that the phospholipase A(2) (PLA(2))/arachidonic acid (AA) pathway is involved. Various eicosanoids have been shown to activate peroxisome-proliferator activated receptors (PPAR) that play a diverse array of roles in lipid metabolism. To further elucidate the potential roles of HM74A in mediating the therapeutic effects and/or side effects of niacin, we sought to explore the signaling events upon HM74A activation. Here we demonstrated that HM74A synergistically enhanced UTP- and bradykinin-mediated AA release in a pertussis toxin-sensitive manner in A431 cells. Activation of HM74A also led to Ca(2+)-mobilization and enhanced bradykinin-promoted Ca(2+)-mobilization through Gi protein. While HM74A increased ERK1/2 activation by the bradykinin receptor, it had no effects on UTP-promoted ERK1/2 activation.Furthermore, UTP- and bradykinin-mediated AA release was significantly decreased in the presence of both MAPK kinase inhibitor PD 098059 and PKC inhibitor GF 109203X. However, the synergistic effects of HM74A were not dramatically affected by co-treatment with both inhibitors, indicating the cross-talk occurred at the receptor level. Finally, stimulation of A431 cells transiently transfected with PPRE-luciferase with AA significantly induced luciferase activity, mimicking the effects of PPARgamma agonist rosiglitazone, suggesting that alteration of AA signaling pathway can regulate gene expression via endogenous PPARs.

Antagonism of the prostaglandin D2 receptor 1 suppresses nicotinic acid-induced vasodilation in mice and humans

Nicotinic acid (NA) is commonly used to treat dyslipidemia, but it elicits an adverse effect, termed flushing, which consists of cutaneous vasodilation with associated discomfort. An animal model of NA-induced flushing has been established in mice. As in humans, NA stimulated vasodilation in a dose-dependent manner, was associated with an increase of the vasodilatory prostaglandin (PG) D2 in plasma and could be blocked by pretreatment with aspirin. Two PGD2 receptors have been identified: PGD2 receptor 1 (DP1, also called DP) and PGD2 receptor 2 (DP2, sometimes termed CRTH2). DP2 does not mediate NA-induced vasodilation; the DP2-specific agonist DK-PGD2 (13,14-dihydro-15-keto-PGD2) did not induce cutaneous vasodilation, and DP2-/- mice had a normal vasodilatory response to NA. By contrast, BW245C, a DP1-selective agonist, induced vasodilation in mice, and MK-0524, a DP1-selective antagonist, blocked both PGD2- and NA-induced vasodilation. NA-induced vasodilation was also studied in DP1+/+, DP1+/-, and DP1-/- mice; although NA-induced vasodilation depended almost completely on DP1 in female mice, it depended only partially on DP1 in male mice. The residual NA-induced vasodilation in male DP-/- mice was aspirin-sensitive. Thus, in the mouse, DP1 appears to be an important component involved in NA-induced vasodilation, but other cyclooxygenase-dependent mechanisms also may be involved. A clinical study in healthy men and women demonstrated that treatment with MK-0524 reduced the symptoms of flushing and the increase in skin perfusion after the administration of NA. These studies suggest that DP1 receptor antagonism may be an effective means to suppress NA-induced flushing in humans.

Methodological and Conceptual Issues in Functional Magnetic Resonance Imaging: Applications to Schizophrenia Research

Functional magnetic resonance imaging (MRI) is a noninvasive, highly repeatable, and increasingly available method to study disordered brain activity among patients with psychological or neurological disorders. In this chapter the biophysical principles underlying functional MRI are presented, and methodological limitations of the method are discussed. Artifacts related to the biophysical basis of the functional MRI signal or associated with image acquisition methods are presented, as are artifacts related to baseline effects-especially those associated with medication, caffeine, and nicotine use. The difficulties associated with the comparison of groups of subjects differing in performance receive special attention. The limitations of cognitive subtraction designs for functional MRI are also discussed. Functional MRI studies of schizophrenia patients are used to illustrate these points.

Impaired niacin sensitivity in acute first-episode but not in multi-episode schizophrenia

Niacin (vitamin B3) flushing--a marker of altered prostaglandin signaling--is indirectly linked to the phospholipid-prostaglandin metabolism. Diminished skin flushing was repeatedly found in schizophrenia, but has not been systematically investigated at different stages of disorder as yet. We compared niacin sensitivity of 32 first-episode and 32 multi-episode patients (mainly on stable medication) with age and gender matched healthy controls. Methylnicotinate was applied in three concentrations onto the inner forearm skin. Flush response was assessed in 3 min intervals over 15 min using optical reflection spectroscopy. Whereas first-episode patients showed significantly diminished flush response as compared to controls, comparable differences were not found between multi-episode patients and controls. Comparison of niacin sensitivity at different stages of schizophrenia support the notion of altered prostaglandin signaling primarily at the onset of disorder. Longitudinal studies have to rule out possible long-term effects of neuroleptic medication.

Delayed vasodilatory response to methylnicotinate in patients with unipolar depressive disorder

BACKGROUND

Recent evidence has suggested an important role for lipids in the etiology and treatment of depression. Methylnicotinate-induced vasodilation can be used to investigate lipid-dependent signalling mechanisms involving the phospholipase A2 (PLA2)/cyclooxygenase pathway, an important signalling system involved in the action of several neurotransmitters including serotonin. To investigate whether abnormalities in this signalling system may occur in depressive illness, we undertook a study of methylnicotinate response in unipolar depression (UD).

METHODS

Methylnicotinate was applied to the forearm of 20 patients with depression and 38 age and sex-matched healthy volunteers (HV). The resulting erythema was assessed over a 15-min period.

RESULTS

Methylnicotinate-induced erythema was reduced in subjects with depression compared to HV at 5 min after application, it returned to normal after 15 min. Thus, although the maximal response to methylnicotinate appears normal, patients with UD exhibit an apparently delayed response.

LIMITATIONS

The major limitation is that all unipolar patients were medicated at the time of testing.

CONCLUSIONS

Our results support the hypothesis that UD may be associated with abnormalities in lipid-associated signalling systems, and may provide insight into how lipid intake may modulate depressive symptoms.

The influence of age and gender on niacin skin test results - implications for the use as a biochemical marker in schizophrenia

Investigation of abnormal skin response to niacin (vitamin B3) stimulation has gained increasing interest in schizophrenia research during last years. However, current efforts to implement niacin tests in routine diagnostics are jeopardised by wide inter-individual variations of skin response. We investigated age and gender as potential factors of influence on niacin sensitivity in 117 healthy subjects (63 male, 54 female). Niacin was applied in three dilution steps (0.1, 0.01, 0.001 M) onto the inner forearm skin. Skin reaction was assessed in three minute intervals over 15 min using optical reflection spectroscopy. Males displayed a significantly weaker flush response than females. The rate of non-responders at the lowest concentration was about twice as high in men than women. Significant negative correlations between age and niacin sensitivity were revealed for both sexes. Age and gender considerably influence niacin sensitivity, possibly due to the effects of sex hormones on vasomotor function and prostaglandin metabolism. Consideration of gender and age is strongly recommended for further clinical niacin studies.

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.

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.

Methyl nicotinate-induced vasodilation in generalized social phobia

Elevated vasodilatory response (blushing) to social situations is characteristic of social phobia (SP). A relatively unexplored basis for this phenomenon is alteration in underlying vasodilatory mechanisms. To investigate this possibility, we evaluated the vasodilatory response induced by methyl nicotinate (niacin ester derivative) in 31 generalized SP patients and 41 matched healthy volunteers (HV). A patch impregnated with 0, 0.1, 0.5, 1, and 10 mM methyl nicotinate was applied to the forearm or face of subjects for 1 min, followed by 20-min laser Doppler spectroscopy blood flow monitoring. Blood flow stimulation with 1 and 10 mM methyl nicotinate was significantly reduced in SP patients by 35 and 17%, respectively. Induced blood flow was negatively correlated with patients' Leibowitz Social Phobia Scale (LSAS) at 1 and 10 mM doses. Furthermore, the maximal rate of change of vasodilatory reaction was correlated with symptom scores at 1 and 10 mM doses. Induced increases in the arm and face blood flow measurements correlated, supporting the external validity of the former location. Generalized SP patients vasodilate less to topical methyl nicotinate challenges, with effect amplification in severely ill patients. Although the mechanism for this is unclear, we propose desensitization of the prostaglandin-mediated vasodilating system as an explanation. Neuropsychopharmacology (2003) 28, 1846-1851, advance online publication, 23 July 2003; doi:10.1038/sj.npp.1300227

Potential use of the topical niacin skin test in early psychosis -- a combined approach using optical reflection spectroscopy and a descriptive rating scale

The niacin skin phenomenon reflects a prostaglandin (PG) mediated flush and oedema reaction. As PG metabolism is linked to breakdown of membrane lipids, diminished sensitivity to niacin application suggests potential disturbance in membrane phospholipid-arachidonic acid-PG pathways. We aimed to evaluate and quantify topical niacin skin reaction in early psychosis using optical reflection spectroscopy (ORS) and a new descriptive assessment scale integrating time course, redness, and oedema. Niacin skin tests were performed on 25 medicated first-episode psychosis patients fulfilling DSM-IV criteria for schizophreniform psychosis or schizophrenia and on 25 healthy controls. Nicotinic acid was applied in four dilution steps to the subjects inner forearm skin and skin reaction was consecutively assessed using ORS and a seven point rating scale. Both descriptive ratings and spectroscopic measures revealed significant group differences at the lower niacin concentrations (0.001 and 0.0001 M). At higher concentrations (0.01 and 0.1 M) only descriptive ratings were capable to show significant group effects. Data of both methods showed moderate to strong correlation (r=0.605) as long as the erythema was not affected by the oedema. The data suggest that niacin sensitivity is inversely correlated with negative symptoms. Both methods demonstrate that niacin sensitivity is impaired in a group of first episode psychosis patients and are therefore able to distinguish a subgroup of patients with metabolic impairment. Niacin sensitivity in high risk populations and the specificity of impaired skin response are subjects of further investigation.