Effects of acute tryptophan depletion on negative symptoms and smoking topography in nicotine-dependent schizophrenics and nonpsychiatric controls

Kynurenic Acid in Schizophrenia: A Systematic Review and Meta-analysis

Kynurenic acid (KYNA) is an endogenous antagonist of N-methyl-D-aspartate and α7 nicotinic acetylcholine receptors that is derived from astrocytes as part of the kynurenine pathway of tryptophan degradation. Evidence suggests that abnormal KYNA levels are involved in the pathophysiology of schizophrenia. However, this has never been assessed through a meta-analysis. A literature search was conducted through Ovid using Embase, Medline, and PsycINFO databases (last search: December 2016) with the search terms: (kynuren* or KYNA) and (schizophreni* or psychosis). English language studies measuring KYNA levels using any method in patients with schizophrenia and healthy controls (HCs) were identified. Standardized mean differences (SMDs) were calculated to determine differences in KYNA levels between groups. Subgroup analyses were separately performed for nonoverlapping participant samples, KYNA measurement techniques, and KYNA sample source. The influences of patients' age, antipsychotic status (%medicated), and sex (%male) on study SMDs were assessed through a meta-regression. Thirteen studies were deemed eligible for inclusion in the meta-analysis. In the main analysis, KYNA levels were elevated in the patient group. Subgroup analyses demonstrated that KYNA levels were increased in nonoverlapping participant samples, and centrally (cerebrospinal fluid and brain tissue) but not peripherally. Patients' age, %medicated, and %male were each positively associated with study SMDs. Overall, KYNA levels are increased in patients with schizophrenia, specifically within the central nervous system. An improved understanding of KYNA in patients with schizophrenia may contribute to the development of novel diagnostic approaches and therapeutic strategies.

Socio-demographic and clinical characteristics of heavy and non-heavy smokers among schizophrenia inpatients in a Chinese Han population

OBJECTIVE

Despite higher smoking rates in schizophrenia, few studies have explored the clinical-demographic correlates of different amounts of smoking exposure. Little is known about the association between smoking severity and clinical phenotypes in Chinese patients with schizophrenia.

MATERIALS AND METHODS

We investigated differences between heavy (≥1 pack/day) and non-heavy (<1 pack/day) smoking in 550 male inpatients with schizophrenia using clinician-administered questionnaires and the Fagerstrom Test for Nicotine Dependence. They also were rated on the Positive and Negative Symptom Scale (PANSS), the Simpson and Angus Extrapyramidal Symptom Rating Scale (SAES), and the Abnormal Involuntary Movement Scale (AIMS), as well as were assayed with laboratory tests and an electrocardiogram.

RESULTS

Heavy smoking prevalence was approximately 31 %. Compared to the non-heavy smokers, the heavy smokers were younger, more with paranoid subtype but less with disorganized subtype schizophrenia, smoked at an earlier age, fewer getting clozapine or all atypical antipsychotics together, and were taking larger doses of antipsychotic drugs. The heavy smokers scored significantly lower on the PANSS negative symptom subscore and total score, and also on the SAES and AIMS scores than the non-heavy smokers. In addition, heavy smokers displayed longer rate-corrected electrocardiographic QT intervals, but without any significant differences in other laboratory tests.

CONCLUSION

Our results suggest several clinical or demographic differences between the heavy and non-heavy smoking patients with schizophrenia in a Chinese population. Heavy smoking remains a general health risk for schizophrenia.

Smoking topography and outcome expectancies among individuals with schizotypy

Compared to smokers in the general population, smokers with schizophrenia smoke more cigarettes per day and have higher nicotine dependence and biochemical indicators of nicotine intake. They also have more intense smoking topography and greater positive smoking expectancies. Little is known about the relationship between smoking and schizotypy, defined as the personality organization reflecting a vulnerability to schizophrenia-spectrum pathology. This study assessed schizotypy symptoms, smoking characteristics and behaviors, and smoking expectancies in young adults with psychometrically defined schizotypy and demographically matched controls without schizotypy. Smokers with schizotypy had higher nicotine dependence and smoked more cigarettes per week compared to control smokers. They were also more likely to endorse greater positive consequences (i.e., improved state enhancement, stimulation, social facilitation, taste/sensorimotor manipulation, reduced negative affect and boredom) and fewer negative consequences of smoking. Smokers with schizotypy and control smokers did not differ on smoking topography or carbon monoxide levels. This is the first known study to investigate relationships between these smoking-related variables in smokers with schizotypy. Individuals with schizotypy possessed certain smoking-related characteristics and smoking expectancies similar to those with schizophrenia. This offers preliminary insight into unique smoking-related factors among individuals with schizotypy and highlights the importance of continued research in this area.

Clinical characteristics of heavy and non-heavy smokers with schizophrenia

Up to 50-90% of persons with schizophrenia smoke cigarettes. Limited data and theories suggest persons with schizophrenia may smoke for different reasons than persons without schizophrenia, making smoking cessation interventions particularly challenging in this population. Although health consequences of smoking are widely known, less information is available regarding characteristics of different amounts of smoking exposure in this population. This study was performed to investigate differences between heavy (≥ 1 pack per day) and non-heavy (<1 pack per day) smoking in patients with schizophrenia. Data from 745 patients, mean age 41.3+/-12.6 years, were drawn from a population of smokers admitted to State of Maryland inpatient mental health facilities (1994-2000). Records were reviewed to obtain demographic information, diagnosis, medication, smoking and substance use. 43% of patients were characterized as heavy smokers. Heavy and non-heavy groups did not differ in age, GAF, weight, or BMI. No differences were found in race, gender or antipsychotic treatments. However, patients smoking ≥ 1 packs per day were more likely to use other substances such as alcohol (χ(2)=6.67, df=1, p=0.01), cocaine (χ(2)=6.66, df=1, p=0.01), and other substances (χ(2)=9.95, df=1, p=0.003) compared to non-heavy smokers. No differences in cannabis or heroin use were found by smoking category. Controlling for age, race, sex and BMI, heavy smokers had higher total cholesterol (190.7(51.6)mg/dL) compared to non-heavy smokers (178.2 (43.0)mg/dL, p=0.03), but no differences were found in glucose or blood pressure. Heavy smoking may be a particular health risk in schizophrenia and significant efforts for smoking cessation or reduction are needed.

Neural expression of nicotine's antidepressant properties during tryptophan depletion: an EEG study in healthy volunteers at risk for depression

Nicotine amelioration of serotonergically mediated mood dysregulation may contribute to the comorbidity between cigarette smoking and depression, a disorder which is associated with aberrant activation and hemispheric asymmetry in frontal and posterior cortical regions. This randomized, double-blind study in 20 healthy volunteers with a positive family history of depression examined the effects of transdermal nicotine on mood and EEG changes accompanying transient reductions in serotonin induced by acute tryptophan depletion (ATD). Increased self-ratings of depressed mood and elevation in left frontal high alpha power (decreased activation) were evidenced with ATD (vs. balanced mixture) in participants treated with the placebo but not the nicotine treated group. Nicotine alone increased vigor and posterior high alpha bilaterally, and during ATD it prevented the reduction in left frontal high alpha that was evident in the placebo patch group. These findings indicate that in depression prone individuals, nicotine acts to stabilize the mood lowering and associated frontal functional asymmetry elicited by an acute decrease in brain serotonin.

Genetic variation in the serotonin pathway and smoking cessation with nicotine replacement therapy: new data from the Patch in Practice trial and pooled analyses

The serotonin pathway has been implicated in nicotine dependence and may influence smoking cessation. Therefore, 792 cigarette smokers from the Patch in Practice trial were genotyped for the tryptophan hydroxylase (TPH1 A779C), serotonin transporter (SLC6A45-HTTLPR), and 5-HT1A (HTR1A C-1019G) polymorphisms. Cox regression analysis did not demonstrate significant effects of any of the three genotypes on relapse to smoking: TPH1 (Reference AA; AC: hazard ratio (HR) 0.99, 95% confidence interval (CI) 0.78, 1.24, p=0.90; CC: HR 0.93, 95% CI 0.73, 1.18, p=0.55); 5-HTTLPR (Reference LL; SL: HR 1.01, 95% CI 0.85, 1.20, p=0.90; SS: HR 1.13, 95% CI 0.91, 1.39, p=0.27); HTR1A (Reference CC; CG: HR 1.04, 95% CI 0.86, 1.25, p=0.70; GG: HR 1.01, 95% CI 0.82, 1.24, p=0.93). Moreover, pooled analyses of data from all three extant pharmacogenetic NRT trials (N=1398) found no significant effect of 5-HTTLPR genotype on continuous abstinence at 12-week (Reference LL; SL: odds ratio (OR)=1.25, 95% CI 0.89, 1.74, p=0.19; SS: OR=1.31, 95% CI 0.86, 1.98, p=0.21) or 26-week follow-up (Reference LL; SL: OR=0.93, 95% CI 0.64, 1.33, p=0.68; SS: OR=1.00, 95% CI 0.63, 1.58, p=1.00). These data do not support a statistically or clinically significant moderating effect of these specific 5-HT pathway genetic variants on smoking cessation. However, the possibility remains that other variants in these or other 5-HT genes may influence NRT efficacy for smoking cessation in treatment seeking smokers.

Effect of tryptophan depletion on the attentional salience of smoking cues

RATIONALE

There is increasing evidence linking cigarette craving and smoking behavior to serotonergic neurotransmission.

OBJECTIVES

The purpose of the current study was to examine the effects of a serotonergic challenge on the attentional salience of various cues associated with cigarettes. We hypothesized that cigarette-related word cues would be more distracting after acute tryptophan depletion than after a placebo challenge. We also hypothesized that smokers vulnerable to recurrent depression would show greater attentional bias towards these cues than smokers without a history of depression.

METHODS

Thirty-four smokers diagnosed as having (n = 15) or lacking (n = 19) a history of DSM-IV major depressive disorder (MDD) underwent acute tryptophan depletion (ATD) and placebo challenges in double-blind and counterbalanced order 1 week apart. Five hours after consumption of each mixture, subjects completed a modified Stroop task to measure attentional bias to smoking-related, positive affect, and negative affect word cues. Stroop interference was calculated as a difference score between latencies for the motivationally salient and the neutral (furniture) word lists.

RESULTS

Controlling for change in dysphoric mood from baseline to 5 h, repeated measures MANOVAs showed that ATD, as compared to placebo challenge, produced greater interference for smoking word cues [F(1,29)=4.15, p = 0.05], but not for negative [F(1,29)=2.78, p = 0.11] or positive [F(1,29)=1.60, p = 0.22] affect word cues.

CONCLUSIONS

Acutely compromising central serotonergic neurotransmission via ATD heightens the attentional salience of cigarette-related cues, perhaps by triggering reward and motivational deficits underlying nicotine dependence.

Acute psychomotor, subjective and physiological responses to smoking in depressed outpatient smokers and matched controls

RATIONALE

Cigarette smoking is highly prevalent in people diagnosed with depression, and depressed smokers are less likely to quit. Examining depressed smokers' responses to smoking will help determine the role of depression in maintaining cigarette smoking.

OBJECTIVES

To determine the psychomotor, subjective and physiological effects of cigarette smoking in currently depressed smokers versus matched controls.

MATERIALS AND METHODS

Fourteen currently depressed smokers and 14 never-depressed smokers, matched in age, gender, nicotine dependence and daily cigarette consumption, smoked three cigarettes at half-hourly intervals. All smokers were non-deprived. Self-reported mood and craving for cigarettes, performance on a simple reaction time task, expired-air carbon monoxide, heart rate and blood pressure were assessed before and after smoking each cigarette. Smoking topography was also assessed.

RESULTS

Depressives and controls did not differ in terms of dependence on cigarettes or expired-air carbon monoxide. Topographic and cardiovascular measures were similar in depressed and control participants, suggesting that they smoke cigarettes in a similar manner. However, depressives displayed enhanced reaction time performance after the first cigarette. Positively reinforced craving was reduced after smoking each cigarette but returned to baseline levels within 30 min in depressed but not in control smokers. Depressed smokers also displayed higher levels of negatively reinforced craving. Both depressives and controls reported improved positive mood after smoking.

CONCLUSIONS

Cigarette smoking in non-deprived depressed smokers enhances psychomotor performance and the reduction of positively reinforced craving in depressed smokers after smoking is transient, suggesting that enhanced craving may play a role in the maintenance of smoking in depression.

Effect of tryptophan depletion on smokers and nonsmokers with and without history of major depression

BACKGROUND

Serotonergic dysregulation is posited to contribute to comorbidity between nicotine dependence and depression. We tested whether acute tryptophan depletion (ATD) triggers depressive symptoms in euthymic, unmedicated smokers and nonsmokers with and without history of major depressive disorder (MDD).

METHODS

Acute tryptophan depletion and taste-matched placebo challenges were administered double-blind in counter-balanced order. Participants were four groups of volunteers hypothesized to be of increasing affective vulnerability as follows: nonsmokers lacking recurrent personal and familial history of MDD (n = 20), smokers lacking recurrent personal and familial history of MDD (n = 21), nonsmokers with history of recurrent personal and familial MDD (n = 16), and smokers with recurrent personal and familial history of MDD (n = 16). Depression, dysphoric mood, and plasma amino acids were measured at baseline and around the time of peak depletion.

RESULTS

Depressive symptom response to ATD was heightened significantly by history of MDD (p < .001) and marginally by smoking (p = .09). Smoking seemed to magnify the ATD response of those with a history of MDD (effect size = .63) but had no effect on those without MDD history (effect size = .06).

CONCLUSIONS

Depressive symptom response to serotonergic challenge is exaggerated in unmedicated, euthymic adults with recurrent personal and familial vulnerability to MDD, perhaps especially if they also smoke.

Upregulation of the initiating step of the kynurenine pathway in postmortem anterior cingulate cortex from individuals with schizophrenia and bipolar disorder

Upregulation of the kynurenine pathway has been associated with several etiologies of psychosis, an indication that increased levels of pathway intermediates might be involved in eliciting some psychotic features. In schizophrenia, tryptophan 2,3-dioxygenase (TDO2) was previously identified in postmortem frontal cortex as the enzyme likely responsible for the reported increase in pathway activity in the brain. For this follow-up study of postmortem anterior cingulate gyrus, we have found evidence of increased TDO2 activity in schizophrenia at three different levels of regulation: mRNA, protein, and metabolic product. The results were unaffected by neuroleptic status or smoking history. To make the distinction between mental disorders with psychosis and those without, this study included patients with bipolar disorder and major depression. Compared to the control group, the HPLC, RT-PCR, and immunohistochemistry results show significant elevation of (1) kynurenine in schizophrenia (1.9-fold, P = 0.02), and in bipolar disorder (1.8-fold, P = 0.04), primarily in the bipolar subgroup with psychosis (2.1-fold, P = 0.03); (2) TDO2 mRNA in schizophrenia (1.7-fold; P = 0.049); and (3) the immunohistochemistry values for the density of TDO2-positive white matter glial cells in schizophrenia (P = 0.01) and in major depression (P = 0.03) as well as the density and intensity of glial cells (in both gray and white matter) stained for TDO2 in bipolar disorder (P = 0.02). Unlike the results for schizophrenia and bipolar disorder, the increase in TDO2 protein in the major depression group was not associated with an increase in kynurenine concentration.