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Serum leptin and its relationship with psychopathology in schizophrenia
Psychoneuroendocrinology (2014) 50, 149—154
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/psyneuen
Serum leptin and its relationship with psychopathology in schizophrenia Milawaty Nurjono a, Sasi Neelamekam a, Jimmy Lee a,b,c,∗ a
Research Division, Institute of Mental Health, Singapore, Singapore Department of General Psychiatry 1, Institute of Mental Health, Singapore, Singapore c Office of Clinical Sciences, Duke-NUS Graduate Medical School, Singapore, Singapore b
Received 29 April 2014; received in revised form 18 August 2014; accepted 25 August 2014
KEYWORDS Adipokines; Psychosis; Dopamine
Summary Leptin plays an important role in the modulation of the dopaminergic system and has recently been implicated in schizophrenia. There have been conflicting reports on leptin levels in schizophrenia; as well as on the association between leptin levels and clinical symptoms. Therefore, this study aims to examine (i) leptin levels in schizophrenia relative to control, and (ii) the relationship between leptin and symptoms in schizophrenia. One hundred participants with schizophrenia and 89 healthy controls were recruited from the Institute of Mental Health in Singapore. Demographic information and medical histories were collected. Schizophrenia symptoms were assessed using the positive and negative syndrome scale (PANSS) and serum leptin was measured using a commercially available bioplex leptin assay. Linear regressions were performed to examine the relationship between serum leptin and the positive, negative, general psychopathology subscales and total PANSS scores. Contrary to previously published literature, we did not find any significant difference in leptin level between participants with schizophrenia compared to controls, which might be the result of recruited controls being of comparable body mass index. Serum leptin was found to be positively associated with positive symptoms, general psychopathology and total PANSS score. This study provides evidence to suggest a positive association between serum leptin level and symptomatology in schizophrenia. However, since conflicting results in this area of research exist, it is important to understand better the mechanism behind this relationship and to examine temporal fluctuations in leptin levels in relation with changes in clinical symptomatology. © 2014 Elsevier Ltd. All rights reserved.
1. Introduction ∗
Corresponding author at: Department of General Psychiatry 1, Institute of Mental Health, 10 Buangkok View, Singapore 539747. Tel.: +1 65 63893600; fax: +1 65 63437962. E-mail address: jimmy [email protected] (J. Lee). http://dx.doi.org/10.1016/j.psyneuen.2014.08.017 0306-4530/© 2014 Elsevier Ltd. All rights reserved.
A complex interplay of physiologically important bioactive molecules has been implicated in the pathophysiology of schizophrenia. More recently, adipokines, in particular
150 leptin, have been of interest in schizophrenia. Leptin is a 16 KD protein hormone encoded by the obese (ob) gene and links nutritional status with neuroendocrine and immune functions (Otero et al., 2005). Leptin functions as a satiety factor, and is involved in obesity and insulin resistance (Faggioni et al., 2001; Otero et al., 2005; Panariello et al., 2012). A reduction in leptin was observed in starvation and malnutrition, and is reversible by caloric supplementation. Leptin also plays important roles in the central and peripheral nervous system (Monti et al., 2006). Its receptors were identified within non-hypothalamic neurons at the hippocampal, cortical, cerebellar and mesencephalon regions. Leptin has been postulated to be involved in brain development and maintenance, and contributes to cognitive and behavioral function. In the adult brain, leptin directs N-methyl-D-aspartate (NMDA) receptor dependent synaptic activity responsible for learning and memory, and regulates a variety of signaling pathways and synaptic activity within cortical and cerebellar regions in the brain. In both rodent and human studies, there exists evidence for an association between leptin, cognition and behavioral functions (Morrison, 2009; Warren et al., 2012). Furthermore, leptin has also been reported to modulate activity of mesolimbic dopaminergic neurons in the ventral tegmental area (VTA), which is implicated in schizophrenia (DiLeone, 2009). There have been conflicting studies in the literature, with reports of reduced (Atmaca et al., 2003; Kraus et al., 2001; Venkatasubramanian et al., 2010) and increased leptin level (Arranz et al., 2004; Wang et al., 2007) in antipsychoticnaive and antipsychotic-free patients with schizophrenia. A systematic review suggests that leptin was increased in individuals with schizophrenia who were treated with antipsychotics, with greater elevation in those treated with atypical antipsychotics (Sentissi et al., 2008). It was suggested that antipsychotics may alter the neuropeptide Y (NPY)-leptin relationship through interactions with multiple receptors and neurotransmitters to modulate the expression of NPY and leptin, resulting in weight gain (Raposo et al., 2011). The reported increase in leptin was observed to be associated with improvement in clinical symptoms and was proposed to be a useful objective predictor of clinical improvement (Kraus et al., 1999; Venkatasubramanian et al., 2010). Although, there are suggestions that leptin is altered in individuals with schizophrenia, it remains unclear whether the altered leptin expression is entirely due to the pathophysiology of schizophrenia or influenced by other factors. In healthy individuals, leptin has been reported to be influenced by age, gender (Al-Harithy, 2004), dietary intake (Jenkins et al., 1997), body mass index (BMI) and cigarette smoking (Jaleel et al., 2007). Older age, females, higher BMI, cigarette smoking and high carbohydrate diet were found to be associated with higher leptin level. In schizophrenia, studies have reported on the association between leptin and age of onset, duration of illness (Herran et al., 2001; Jow et al., 2006) and treatment with atypical antipsychotics (Sentissi et al., 2008). In spite of extensive research concerning the physiology of leptin, there are conflicting findings about the levels of leptin and its clinical relevance in schizophrenia. There exists a paucity of data that examine the relationship between leptin and psychopathology. Since most reports suggest that antipsychotic treatment increases leptin level
M. Nurjono et al. and our study population comprises of chronically ill patients with schizophrenia treated with antipsychotics, we would expect leptin levels to be higher compared to healthy controls. In addition, considering leptin’s role in upregulation of dopaminergic neurons in the mesolimbic cortex, it would seem plausible to hypothesize that leptin might play a role in the generation of psychotic symptoms. However, two studies reported increased leptin level to be associated with lower psychotic symptoms (Takayanagi et al., 2013; Venkatasubramanian et al., 2010). Therefore, the present study aims to investigate (i) serum leptin in patients diagnosed with schizophrenia in comparison to healthy individuals, and (ii) assess the relationship between serum leptin and psychopathology. We hypothesized that serum leptin is increased in participants with schizophrenia, and is positively associated with symptom severity in our study sample.
2. Methods 2.1. Study participants This study was conducted at the Institute of Mental Health (IMH), Singapore, the only psychiatric hospital in the country. Cases — aged 21—50 years and fulfilling DSM-IV-TR diagnosis of schizophrenia — were recruited from the outpatient clinics between 2010 and 2011. Controls were healthy individuals from the community with no history of psychiatric disorders, and were recruited through referrals and advertisements. Cases and controls were matched according to age, gender and ethnicity at a group level. Individuals with a history of neurological disorders, current substance and alcohol use disorders were excluded from the study. Ethics approval for the study was provided by the domain specific review board of the national healthcare group, Singapore. Information related to the study was carefully explained to all study participants, and only participants who were able to provide informed consent were recruited into the study.
2.2. Data collection Demographic information and current smoking status were obtained from all study participants through clinical interviews by a trained investigator. Height and weight were measured and BMI was computed accordingly. Medical records were reviewed to collect medical histories of participants with schizophrenia. Age of onset (defined as the age at first onset of psychotic symptoms) and duration of illness (defined as the time from the first onset of psychotic symptoms to the date of recruitment) were collected. Current antipsychotic prescriptions were gathered from the medication administration records and daily dosages of antipsychotics were converted into chlorpromazine equivalents (Woods, 2003) for participants with schizophrenia. For healthy controls, details of their medical history, medications or supplements were self-reported during the research interview. If this information was not readily available, a follow-up phone call was made to verify the information obtained.
Serum leptin and its relationship with psychopathology in schizophrenia
2.3. Assessments For all participants with schizophrenia, the diagnosis of schizophrenia was ascertained with the Structured Clinical Interview for DSM-IV axis I disorders (SCID-I) patient edition. Clinical symptoms were assessed using the positive and negative syndrome scale (PANSS) by a single experienced psychiatrist at the time of interview. Controls were assessed on the SCID-I (non-patient edition) to ascertain that they had no psychiatric disorders prior to recruitment.
2.4. Measurement of serum leptin Venous blood was collected from all study participants into serum separating tubes (SST) after an overnight fast. Participants were reminded to fast one day before the study visit and fasting status was verified prior to sample collection. After collection, blood samples were allowed to coagulate at room temperature for approximately 30 min, centrifuged at 4◦ C using a clinical centrifuge (Hettich, Germany) and serum collected. Serum leptin was measured using a commercially available Bioplex leptin assays which utilize the xMAP technology (Biorad, USA). Briefly, serum samples were diluted 1:4 in sample diluents provided and run as duplicates according to the instruction’s manuals. The sensitivity of the kits was 3.1 pg/ml and the intra assay variations was less than 20%.
2.5. Data analysis Statistical analyses were performed using predictive analytics software statistics (PASW) version 18. Descriptive statistics were tabulated for cases and controls. Statistical significance was set at p < 0.05 and differences between cases and controls were examined using Fisher’s exact tests for categorical variables and Mann—Whitney U tests for continuous variables which were not normally distributed. Serum leptin was first compared between cases and controls using Mann—Whitney-U tests. Subsequently, unadjusted linear regressions were performed to examine the relationship between serum leptin and psychopathology among participants with schizophrenia. Another regression model, adjusted for age, gender, current smoking status, BMI, treatment with atypical antipsychotics and current antipsychotic dose was employed to examine the relationship between leptin and psychopathology. Crude and adjusted effect sizes (beta), 95% confidence intervals (CI) and p values were computed for the respective models.
3. Results One hundred cases with schizophrenia and 89 healthy controls were recruited for this study. One case and one control were excluded from the analysis as their serum leptin levels were considered to be outliers, i.e. their serum leptin did not fall within the range of mean ± 2 standard deviations. All analyses were performed on 99 cases and 88 controls. Table 1 summarizes the characteristics of the study participants. As displayed in Table 1, no significant differences in age, BMI, gender, and ethnic distribution were found between cases
151
and controls recruited into the study. Compared to controls, there were significantly (p = 0.007) more smokers among the cases. Although slightly higher, we did not find a significant difference in mean serum leptin between cases and controls. In the unadjusted linear regression models, there was a positive relationship between serum leptin and positive symptom score. For every 1 g/ml increase in serum leptin, positive symptom score was increased by 0.302. After adjusting for age, gender, current smoking status, BMI, duration of illness, exposure to atypical antipsychotics and antipsychotic dose, serum leptin was found to be positively associated with positive symptoms, general psychopathology and total PANSS score (Table 2).
4. Discussion Unlike previous reports that observed altered leptin level in patients with schizophrenia (Venkatasubramanian et al., 2010; Wang et al., 2007), this study did not find a significant difference in serum leptin level between participants with schizophrenia compared to controls. Leptin has been shown to be influenced by dietary intake (Jenkins et al., 1997) and the Southeast Asian diet differs from the diets of studies reported in the literature. It is possible that dietary differences could have contributed to the discrepancies in findings. Furthermore, as BMI has been reported to be associated with leptin level (Monti et al., 2006), it is likely that the similarly elevated BMI in both case and control groups observed in this study might have minimized the observed difference in the mean serum leptin between the two groups. In both cases and controls, serum leptin was observed to be moderately correlated with BMI with correlation coefficients of 0.644 and 0.434, respectively. After adjusting for variables that have previously been shown to affect leptin levels, we found a positive association between serum leptin and positive, general psychopathology and total PANSS scores. Differences in results observed in the unadjusted and adjusted models suggest that the covariates might have confounded the relationship between leptin and general psychopathology and total PANSS score. This could be due to the independent relationship between covariates and general psychopathology and total PANSS score, but the multivariate regression model used in this study was unable to explicitly demonstrate it. This finding is contrary to the previously reported studies. (Takayanagi et al., 2013; Venkatasubramanian et al., 2010). The differences observed could have been due to differences in methodologies and the nature of the study samples. Fluctuations in serum leptin levels have been demonstrated to follow a diurnal pattern with higher levels overnight as the body is fasting (Simon et al., 1998). Samples collected in this study were obtained after an overnight fast, unlike the study by Takayanagi et al. (2013) where there was heterogeneity in sample collection timings. In addition, participants in this study were exposed to various antipsychotics, both typical and atypical antipsychotics, which could have differential effects on serum leptin level. In our analyses, we took into account the effects of smoking, duration of illness, BMI, exposure to atypical antipsychotics and daily dose of antipsychotics, which might have resulted in different results from the published literature.
152 Table 1
M. Nurjono et al. Demographic characteristic of study participants. Control (n = 88)
Age (years), mean (SD) Gender, n (%) Male Female Ethnicity, n (%) Chinese Malay Indian Others Non smoker/smoker, n (%) BMI (kg/m2 ), mean (SD) Leptin (g/ml), mean (SD) Age of onset (years), mean (SD) Duration of illness (years), mean (SD) Current antipsychotic treatment, n (%) Typical antipsychotics Atypical antipsychotics Combination of typical and atypical antipsychotics Dosage of antipsychotics (mg)a , mean (SD) Currently on an antidepressant, n (%) Selective serotonin reuptake inhibitors Tricyclic antidepressants PANSSb , mean (SD) Positive subscale Negative subscale General psychopathology subscale Total a b
Patients (n = 99)
26.2 (7.9)
36 (7.6)
57 (64.8%) 31 (35.2%)
69 (69.7%) 30 (30.3%)
73 (83%) 7 (8%) 8 (9.1%) 0 (0%) 77 (87.5%)/11 (12.5%) 24.8 (4.2) 3.86 (3.22)
83 (83.8%) 7 (7.1%) 8 (8.1%) 1 (1%) 64 (64.6%)/35 (35.4%) 25.5 (5.1) 4.11 (3.73) 24.1 (6.56) 11.9 (7.34)
P-value 0.875 0.533
0.802
0.001 0.375 0.812
39 (39.4%) 38 (38.4%) 22 (22.2%) 302.1 (305.2) 31 (31.3%) 26 (26.3%) 5 (5.1%) 10.4 (4.36) 9.58 (3.75) 19.64 (3.43) 39.72 (8.39)
Chlopromazine equivalent. Positive and negative syndrome scale.
Hyperstimulation of the dopaminergic D2 receptors is a hallmark feature of schizophrenia and the dopamine hypothesis had proposed that excess dopamine in the brain to be associated with positive symptoms (Abi-Dargham, 2004). Leptin plays a crucial role in modulation of the mesolimbic dopamine system that is disrupted in schizophrenia. This includes inhibition of dopamine neurons in the VTA and promotion of tryrosine hydroxylase (TH) expression for the production of dopamine within the VTA and NAc circuit (Opland et al., 2010). Under stressful conditions, leptin increases the production of dopamine (Burghardt
Table 2
et al., 2012). Therefore, it is highly probable that in stressful conditions commonly experienced by individuals with schizophrenia (Gispen-de Wied, 2000), leptin works to increase the production of dopamine, which in turn increases positive symptoms severity. Interestingly, antipsychotics and leptin have opposing effects on the dopaminergic system. Although the main role of antipsychotics is to treat psychotic symptoms, the effects of prolonged antipsychotic exposure on brain and behavior are less certain. Longitudinal imaging studies have reported reduced brain volumes with prolonged
Linear regressions of the associations between serum leptin and symptomatology. Model 1
PANSSa positive subscale score PANSSa negative subscale score PANSSa general psychopathology subscale score Total PANSSa score
Model 2
B
95% CI
p-value
B
95% CI
p-value
0.302 −0.116 0.175
0.074—0.530 −0.317—0.085 −0.007—0.357
0.010* 0.256 0.059
0.474 −0.192 0.461
0.086—0.863 −0.501—0.117 0.157—0.766
0.017* 0.220 0.003*
0.361
−0.087—0.809
0.113
0.73
0.009—1.450
0.047*
Model 2 is adjusted for age, gender, ethnicity, smoking status, duration of illness, BMI, exposure to atypical antipsychotics, daily dose of antipsychotics. * p-Value <0.05.
Serum leptin and its relationship with psychopathology in schizophrenia antipsychotic exposure (Ho et al., 2011). A recent 20-year longitudinal study found that antipsychotics, after the initial years, did not reduce the severity or frequency of psychosis in schizophrenia (Harrow et al., 2014). Previously, it was also suggested that prolonged exposure to antipsychotics might lead to tolerance and dopamine supersensitivity, a condition known as ‘‘supersensitivity psychosis’’ (Chouinard and Jones, 1980). When the above findings are evaluated in the context of leptin’s supposed roles in dopamine modulation and neuroplasticity, it would appear that leptin might be an interesting candidate to examine further. The strength of the present study lies in the reliability of the data collection and analysis. All participants with schizophrenia were recruited from a single site with control groups recruited from the same base population. The PANSS, a valid and reliable tool was used to assess subjects’ symptomatology and symptoms were assessed by single psychiatrist. In addition, blood samples were collected after an overnight fast; processed and analyzed using a commercially available assay that was optimized to measure serum leptin. This consistency minimized erroneous results due to variations. Furthermore, the evaluation of relationship between serum leptin and symptoms was adjusted for known confounders, giving rise to more precise estimates. However, due to the cross-sectional nature of the study, the temporal relationship between serum leptin and symptomatology in participants with schizophrenia could not be determined. Although we adjusted for current treatment with atypical antipsychotics, which was previously suggested to alter serum leptin level in patients with schizophrenia (Sentissi et al., 2008), we did not collect information of prior antipsychotic exposure which may have confounding effects on the relationship between serum leptin and symptomatology. In addition, as participants recruited in this study were mostly Chinese and were sufficiently stable to provide informed consent, the findings may not be generalizable to other ethnic groups and individuals with schizophrenia with more severe symptoms. This present study provided evidence to suggest a positive association between serum leptin and symptomatology in schizophrenia. However, since conflicting results in this area of research exist, it may be of benefit to understand the mechanism behind this relationship and to examine temporal fluctuations in leptin levels in relation with changes in clinical symptomatology. If leptin, through dopamine upregulation, exacerbates positive symptoms, the increased rate of obesity in schizophrenia is of concern as leptin is produced by adipocytes which are increased with weight gain. The positive relationship between leptin and positive symptoms also suggest that weight management might have beneficial effects on not only physical health and general mental health, but key aspects of schizophrenia symptomatology.
Contributors MN and JL were involved in the study design and data collection. MN analyzed the data and wrote up the first draft of the manuscript with SN. All authors were involved in interpretation of the results, provided intellectual input and approved the final manuscript for submission.
153
Role of funding sources This study was funded by the National Medical Research Council, Singapore (NMRC/NIG/1017/2010 and NMRC/TCR/003/2008). JL is further supported by the Singapore Ministry of Health’s National Medical Research Council under its Transition Award (Grant No.: NMRC/TA/002/2012). Both funding sources had no further role in the study design, in the collection, analysis, interpretation of data, in the writing of the report, and in the decision to submit the paper for publication.
Conflict of interests statement JL had served as a consultant and received an honorarium from Roche. All other authors have no conflicts of interests to declare.
Acknowledgements We would like to acknowledge all the study participants for participating in the study and laboratory technicians at Biorad, Singapore for assistance in the evaluation of serum leptin. We would also like to acknowledge Dr. Gwen-Li Sin and Ms. Virginia Wilson for their assistance in proofreading the manuscript.
References Abi-Dargham, A., 2004. Do we still believe in the dopamine hypothesis? New data bring new evidence. Int. J. Neuropsychopharmacol. 7, S1—S5. Al-Harithy, R.N., 2004. Relationship of leptin concentration to gender, body mass index and age in Saudi adults. Saudi Med. J. 25, 1086—1090. Arranz, B., Rosel, P., Ramirez, N., Duenas, R., Fernandez, P., Sanchez, J.M., Navarro, M.A., San, L., 2004. Insulin resistance and increased leptin concentrations in noncompliant schizophrenia patients but not in antipsychotic-naive first-episode schizophrenia patients. J. Clin. Psychiatry 65, 1335—1342. Atmaca, M., Kuloglu, M., Tezcan, E., Ustundag, B., 2003. Serum leptin and cholesterol levels in schizophrenic patients with and without suicide attempts. Acta Psychiatr. Scand. 108, 208—214. Burghardt, P.R., Love, T.M., Stohler, C.S., Hodgkinson, C., Shen, P.H., Enoch, M.A., Goldman, D., Zubieta, J.K., 2012. Leptin regulates dopamine responses to sustained stress in humans. J. Neurosci. 32, 15369—15376. Chouinard, G., Jones, B.D., 1980. Neuroleptic-induced supersensitivity psychosis: clinical and pharmacologic characteristics. Am. J. Psychiatry 137, 16—21. DiLeone, R.J., 2009. The influence of leptin on the dopamine system and implications for ingestive behavior. Int. J. Obes. (Lond) 33 (Suppl 2), S25L S29. Faggioni, R., Feingold, K.R., Grunfeld, C., 2001. Leptin regulation of the immune response and the immunodeficiency of malnutrition. FASEB J. 15, 2565—2571. Gispen-de Wied, C.C., 2000. Stress in schizophrenia: an integrative view. Eur. J. Pharmacol. 405, 375—384. Harrow, M., Jobe, T.H., Faul, R.N., 2014. Does treatment of schizophrenia with antipsychotic medications eliminate or reduce psychosis? A 20-year multi-follow-up study. Psychol. Med. [Epub Mar 24, 1—10]-L.
154 Herran, A., Garcia-Unzueta, M.T., Amado, J.A., de La Maza, M.T., Alvarez, C., Vazquez-Barquero, J.L., 2001. Effects of long-term treatment with antipsychotics on serum leptin levels. Br. J. Psychiatry 179, 59—62. Ho, B.C., Andreasen, N.C., Ziebell, S., Pierson, R., Magnotta, V., 2011. Long-term antipsychotic treatment and brain volumes: a longitudinal study of first-episode schizophrenia. Arch. Gen. Psychiatry 68, 128—137. Jaleel, A., Jaleel, F., Majeed, R., Alam, E., 2007. Leptin and blood lipid levels in smokers and ex smokers. World Appl. Sci. J. 2, 348—352. Jenkins, A.B., Markovic, T.P., Fleury, A., Campbell, L.V., 1997. Carbohydrate intake and short-term regulation of leptin in humans. Diabetologia 40, 348—351. Jow, G.M., Yang, T.T., Chen, C.L., 2006. Leptin and cholesterol levels are low in major depressive disorder, but high in schizophrenia. J. Affect. Disord. 90, 21—27. Kraus, T., Haack, M., Schuld, A., Hinze-Selch, D., et al., 1999. Body weight and leptin plasma levels during treatment with antipsychotic drugs. Am. J. Psychiatry 156, 312—314. Kraus, T., Haack, M., Schuld, A., Hinze-Selch, D., Pollmacher, T., 2001. Low leptin levels but normal body mass indices in patients with depression or schizophrenia. Neuroendocrinology 73, 243—247. Monti, V., Carlson, J.J., Hunt, S.C., Adams, T.D., 2006. Relationship of ghrelin and leptin hormones with body mass index and waist circumference in a random sample of adults. J. Am. Diet. Assoc. 106, 822—828. Morrison, C.D., 2009. Leptin signaling in brain: a link between nutrition and cognition? Biochim. Biophys. Acta 1792, 401—408. Opland, D.M., Leinninger, G.M., Myers, J.M.G., 2010. Modulation of the mesolimbic dopamine system by leptin. Brain Res. 1350, 65—70.
M. Nurjono et al. Otero, M., Lago, R., Lago, F., Casanueva, F.F., Dieguez, C., GomezReino, J.J., Gualillo, O., 2005. Leptin, from fat to inflammation: old questions and new insights. FEBS Lett. 579, 295—301. Panariello, F., Polsinelli, G., Borlido, C., Monda, M., De Luca, V., 2012. The role of leptin in antipsychotic-induced weight gain: genetic and non-genetic factors. J. Obes. 2012, 572848. Raposo, N.R.B., Ferreira, A.S., Gattaz, W.F., 2011. Body mass index increase, serum leptin, Adiponectin, neuropeptide Y and lipid levels during treatment with olanzapine and haloperidol. Pharmacopsychiatry 44 (05), 169—172. Sentissi, O., Epelbaum, J., Olie, J.P., Poirier, M.F., 2008. Leptin and ghrelin levels in patients with schizophrenia during different antipsychotics treatment: a review. Schizophr. Bull. 34, 1189—1199. Simon, C., Gronfier, C., Schlienger, J.L., Brandenberger, G., 1998. Circadian and ultradian variations of leptin in normal man under continuous enteral nutrition: relationship to sleep and body temperature. J. Clin. Endocrinol. Metab. 83, 1893—1899. Takayanagi, Y., Cascella, N.G., Santora, D., Gregory, P.E., Sawa, A., Eaton, W.W., 2013. Relationships between serum leptin level and severity of positive symptoms in schizophrenia. Neurosci. Res. 77 (1—2), 97—101. Venkatasubramanian, G., Chittiprol, S., Neelakantachar, N., Shetty, T.K., Gangadhar, B.N., 2010. A longitudinal study on the impact of antipsychotic treatment on serum leptin in schizophrenia. Clin. Neuropharmacol. 33, 288—292. Wang, H.C., Yang, Y.K., Chen, P.S., Lee, I.H., Yeh, T.L., Lu, R.B., 2007. Increased plasma leptin in antipsychotic-naive females with schizophrenia, but not in males. Neuropsychobiology 56, 213—215. Warren, M.W., Hynan, L.S., Weiner, M.F., 2012. Leptin and cognition. Dement. Geriatr. Cogn. Disord. 33, 410—415. Woods, S., 2003. Chlorpromazine equivalent doses for the newer atypical antipsychotics. J. Clin. Psychiatry 64, 663—667.
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/psyneuen
Serum leptin and its relationship with psychopathology in schizophrenia Milawaty Nurjono a, Sasi Neelamekam a, Jimmy Lee a,b,c,∗ a
Research Division, Institute of Mental Health, Singapore, Singapore Department of General Psychiatry 1, Institute of Mental Health, Singapore, Singapore c Office of Clinical Sciences, Duke-NUS Graduate Medical School, Singapore, Singapore b
Received 29 April 2014; received in revised form 18 August 2014; accepted 25 August 2014
KEYWORDS Adipokines; Psychosis; Dopamine
Summary Leptin plays an important role in the modulation of the dopaminergic system and has recently been implicated in schizophrenia. There have been conflicting reports on leptin levels in schizophrenia; as well as on the association between leptin levels and clinical symptoms. Therefore, this study aims to examine (i) leptin levels in schizophrenia relative to control, and (ii) the relationship between leptin and symptoms in schizophrenia. One hundred participants with schizophrenia and 89 healthy controls were recruited from the Institute of Mental Health in Singapore. Demographic information and medical histories were collected. Schizophrenia symptoms were assessed using the positive and negative syndrome scale (PANSS) and serum leptin was measured using a commercially available bioplex leptin assay. Linear regressions were performed to examine the relationship between serum leptin and the positive, negative, general psychopathology subscales and total PANSS scores. Contrary to previously published literature, we did not find any significant difference in leptin level between participants with schizophrenia compared to controls, which might be the result of recruited controls being of comparable body mass index. Serum leptin was found to be positively associated with positive symptoms, general psychopathology and total PANSS score. This study provides evidence to suggest a positive association between serum leptin level and symptomatology in schizophrenia. However, since conflicting results in this area of research exist, it is important to understand better the mechanism behind this relationship and to examine temporal fluctuations in leptin levels in relation with changes in clinical symptomatology. © 2014 Elsevier Ltd. All rights reserved.
1. Introduction ∗
Corresponding author at: Department of General Psychiatry 1, Institute of Mental Health, 10 Buangkok View, Singapore 539747. Tel.: +1 65 63893600; fax: +1 65 63437962. E-mail address: jimmy [email protected] (J. Lee). http://dx.doi.org/10.1016/j.psyneuen.2014.08.017 0306-4530/© 2014 Elsevier Ltd. All rights reserved.
A complex interplay of physiologically important bioactive molecules has been implicated in the pathophysiology of schizophrenia. More recently, adipokines, in particular
150 leptin, have been of interest in schizophrenia. Leptin is a 16 KD protein hormone encoded by the obese (ob) gene and links nutritional status with neuroendocrine and immune functions (Otero et al., 2005). Leptin functions as a satiety factor, and is involved in obesity and insulin resistance (Faggioni et al., 2001; Otero et al., 2005; Panariello et al., 2012). A reduction in leptin was observed in starvation and malnutrition, and is reversible by caloric supplementation. Leptin also plays important roles in the central and peripheral nervous system (Monti et al., 2006). Its receptors were identified within non-hypothalamic neurons at the hippocampal, cortical, cerebellar and mesencephalon regions. Leptin has been postulated to be involved in brain development and maintenance, and contributes to cognitive and behavioral function. In the adult brain, leptin directs N-methyl-D-aspartate (NMDA) receptor dependent synaptic activity responsible for learning and memory, and regulates a variety of signaling pathways and synaptic activity within cortical and cerebellar regions in the brain. In both rodent and human studies, there exists evidence for an association between leptin, cognition and behavioral functions (Morrison, 2009; Warren et al., 2012). Furthermore, leptin has also been reported to modulate activity of mesolimbic dopaminergic neurons in the ventral tegmental area (VTA), which is implicated in schizophrenia (DiLeone, 2009). There have been conflicting studies in the literature, with reports of reduced (Atmaca et al., 2003; Kraus et al., 2001; Venkatasubramanian et al., 2010) and increased leptin level (Arranz et al., 2004; Wang et al., 2007) in antipsychoticnaive and antipsychotic-free patients with schizophrenia. A systematic review suggests that leptin was increased in individuals with schizophrenia who were treated with antipsychotics, with greater elevation in those treated with atypical antipsychotics (Sentissi et al., 2008). It was suggested that antipsychotics may alter the neuropeptide Y (NPY)-leptin relationship through interactions with multiple receptors and neurotransmitters to modulate the expression of NPY and leptin, resulting in weight gain (Raposo et al., 2011). The reported increase in leptin was observed to be associated with improvement in clinical symptoms and was proposed to be a useful objective predictor of clinical improvement (Kraus et al., 1999; Venkatasubramanian et al., 2010). Although, there are suggestions that leptin is altered in individuals with schizophrenia, it remains unclear whether the altered leptin expression is entirely due to the pathophysiology of schizophrenia or influenced by other factors. In healthy individuals, leptin has been reported to be influenced by age, gender (Al-Harithy, 2004), dietary intake (Jenkins et al., 1997), body mass index (BMI) and cigarette smoking (Jaleel et al., 2007). Older age, females, higher BMI, cigarette smoking and high carbohydrate diet were found to be associated with higher leptin level. In schizophrenia, studies have reported on the association between leptin and age of onset, duration of illness (Herran et al., 2001; Jow et al., 2006) and treatment with atypical antipsychotics (Sentissi et al., 2008). In spite of extensive research concerning the physiology of leptin, there are conflicting findings about the levels of leptin and its clinical relevance in schizophrenia. There exists a paucity of data that examine the relationship between leptin and psychopathology. Since most reports suggest that antipsychotic treatment increases leptin level
M. Nurjono et al. and our study population comprises of chronically ill patients with schizophrenia treated with antipsychotics, we would expect leptin levels to be higher compared to healthy controls. In addition, considering leptin’s role in upregulation of dopaminergic neurons in the mesolimbic cortex, it would seem plausible to hypothesize that leptin might play a role in the generation of psychotic symptoms. However, two studies reported increased leptin level to be associated with lower psychotic symptoms (Takayanagi et al., 2013; Venkatasubramanian et al., 2010). Therefore, the present study aims to investigate (i) serum leptin in patients diagnosed with schizophrenia in comparison to healthy individuals, and (ii) assess the relationship between serum leptin and psychopathology. We hypothesized that serum leptin is increased in participants with schizophrenia, and is positively associated with symptom severity in our study sample.
2. Methods 2.1. Study participants This study was conducted at the Institute of Mental Health (IMH), Singapore, the only psychiatric hospital in the country. Cases — aged 21—50 years and fulfilling DSM-IV-TR diagnosis of schizophrenia — were recruited from the outpatient clinics between 2010 and 2011. Controls were healthy individuals from the community with no history of psychiatric disorders, and were recruited through referrals and advertisements. Cases and controls were matched according to age, gender and ethnicity at a group level. Individuals with a history of neurological disorders, current substance and alcohol use disorders were excluded from the study. Ethics approval for the study was provided by the domain specific review board of the national healthcare group, Singapore. Information related to the study was carefully explained to all study participants, and only participants who were able to provide informed consent were recruited into the study.
2.2. Data collection Demographic information and current smoking status were obtained from all study participants through clinical interviews by a trained investigator. Height and weight were measured and BMI was computed accordingly. Medical records were reviewed to collect medical histories of participants with schizophrenia. Age of onset (defined as the age at first onset of psychotic symptoms) and duration of illness (defined as the time from the first onset of psychotic symptoms to the date of recruitment) were collected. Current antipsychotic prescriptions were gathered from the medication administration records and daily dosages of antipsychotics were converted into chlorpromazine equivalents (Woods, 2003) for participants with schizophrenia. For healthy controls, details of their medical history, medications or supplements were self-reported during the research interview. If this information was not readily available, a follow-up phone call was made to verify the information obtained.
Serum leptin and its relationship with psychopathology in schizophrenia
2.3. Assessments For all participants with schizophrenia, the diagnosis of schizophrenia was ascertained with the Structured Clinical Interview for DSM-IV axis I disorders (SCID-I) patient edition. Clinical symptoms were assessed using the positive and negative syndrome scale (PANSS) by a single experienced psychiatrist at the time of interview. Controls were assessed on the SCID-I (non-patient edition) to ascertain that they had no psychiatric disorders prior to recruitment.
2.4. Measurement of serum leptin Venous blood was collected from all study participants into serum separating tubes (SST) after an overnight fast. Participants were reminded to fast one day before the study visit and fasting status was verified prior to sample collection. After collection, blood samples were allowed to coagulate at room temperature for approximately 30 min, centrifuged at 4◦ C using a clinical centrifuge (Hettich, Germany) and serum collected. Serum leptin was measured using a commercially available Bioplex leptin assays which utilize the xMAP technology (Biorad, USA). Briefly, serum samples were diluted 1:4 in sample diluents provided and run as duplicates according to the instruction’s manuals. The sensitivity of the kits was 3.1 pg/ml and the intra assay variations was less than 20%.
2.5. Data analysis Statistical analyses were performed using predictive analytics software statistics (PASW) version 18. Descriptive statistics were tabulated for cases and controls. Statistical significance was set at p < 0.05 and differences between cases and controls were examined using Fisher’s exact tests for categorical variables and Mann—Whitney U tests for continuous variables which were not normally distributed. Serum leptin was first compared between cases and controls using Mann—Whitney-U tests. Subsequently, unadjusted linear regressions were performed to examine the relationship between serum leptin and psychopathology among participants with schizophrenia. Another regression model, adjusted for age, gender, current smoking status, BMI, treatment with atypical antipsychotics and current antipsychotic dose was employed to examine the relationship between leptin and psychopathology. Crude and adjusted effect sizes (beta), 95% confidence intervals (CI) and p values were computed for the respective models.
3. Results One hundred cases with schizophrenia and 89 healthy controls were recruited for this study. One case and one control were excluded from the analysis as their serum leptin levels were considered to be outliers, i.e. their serum leptin did not fall within the range of mean ± 2 standard deviations. All analyses were performed on 99 cases and 88 controls. Table 1 summarizes the characteristics of the study participants. As displayed in Table 1, no significant differences in age, BMI, gender, and ethnic distribution were found between cases
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and controls recruited into the study. Compared to controls, there were significantly (p = 0.007) more smokers among the cases. Although slightly higher, we did not find a significant difference in mean serum leptin between cases and controls. In the unadjusted linear regression models, there was a positive relationship between serum leptin and positive symptom score. For every 1 g/ml increase in serum leptin, positive symptom score was increased by 0.302. After adjusting for age, gender, current smoking status, BMI, duration of illness, exposure to atypical antipsychotics and antipsychotic dose, serum leptin was found to be positively associated with positive symptoms, general psychopathology and total PANSS score (Table 2).
4. Discussion Unlike previous reports that observed altered leptin level in patients with schizophrenia (Venkatasubramanian et al., 2010; Wang et al., 2007), this study did not find a significant difference in serum leptin level between participants with schizophrenia compared to controls. Leptin has been shown to be influenced by dietary intake (Jenkins et al., 1997) and the Southeast Asian diet differs from the diets of studies reported in the literature. It is possible that dietary differences could have contributed to the discrepancies in findings. Furthermore, as BMI has been reported to be associated with leptin level (Monti et al., 2006), it is likely that the similarly elevated BMI in both case and control groups observed in this study might have minimized the observed difference in the mean serum leptin between the two groups. In both cases and controls, serum leptin was observed to be moderately correlated with BMI with correlation coefficients of 0.644 and 0.434, respectively. After adjusting for variables that have previously been shown to affect leptin levels, we found a positive association between serum leptin and positive, general psychopathology and total PANSS scores. Differences in results observed in the unadjusted and adjusted models suggest that the covariates might have confounded the relationship between leptin and general psychopathology and total PANSS score. This could be due to the independent relationship between covariates and general psychopathology and total PANSS score, but the multivariate regression model used in this study was unable to explicitly demonstrate it. This finding is contrary to the previously reported studies. (Takayanagi et al., 2013; Venkatasubramanian et al., 2010). The differences observed could have been due to differences in methodologies and the nature of the study samples. Fluctuations in serum leptin levels have been demonstrated to follow a diurnal pattern with higher levels overnight as the body is fasting (Simon et al., 1998). Samples collected in this study were obtained after an overnight fast, unlike the study by Takayanagi et al. (2013) where there was heterogeneity in sample collection timings. In addition, participants in this study were exposed to various antipsychotics, both typical and atypical antipsychotics, which could have differential effects on serum leptin level. In our analyses, we took into account the effects of smoking, duration of illness, BMI, exposure to atypical antipsychotics and daily dose of antipsychotics, which might have resulted in different results from the published literature.
152 Table 1
M. Nurjono et al. Demographic characteristic of study participants. Control (n = 88)
Age (years), mean (SD) Gender, n (%) Male Female Ethnicity, n (%) Chinese Malay Indian Others Non smoker/smoker, n (%) BMI (kg/m2 ), mean (SD) Leptin (g/ml), mean (SD) Age of onset (years), mean (SD) Duration of illness (years), mean (SD) Current antipsychotic treatment, n (%) Typical antipsychotics Atypical antipsychotics Combination of typical and atypical antipsychotics Dosage of antipsychotics (mg)a , mean (SD) Currently on an antidepressant, n (%) Selective serotonin reuptake inhibitors Tricyclic antidepressants PANSSb , mean (SD) Positive subscale Negative subscale General psychopathology subscale Total a b
Patients (n = 99)
26.2 (7.9)
36 (7.6)
57 (64.8%) 31 (35.2%)
69 (69.7%) 30 (30.3%)
73 (83%) 7 (8%) 8 (9.1%) 0 (0%) 77 (87.5%)/11 (12.5%) 24.8 (4.2) 3.86 (3.22)
83 (83.8%) 7 (7.1%) 8 (8.1%) 1 (1%) 64 (64.6%)/35 (35.4%) 25.5 (5.1) 4.11 (3.73) 24.1 (6.56) 11.9 (7.34)
P-value 0.875 0.533
0.802
0.001 0.375 0.812
39 (39.4%) 38 (38.4%) 22 (22.2%) 302.1 (305.2) 31 (31.3%) 26 (26.3%) 5 (5.1%) 10.4 (4.36) 9.58 (3.75) 19.64 (3.43) 39.72 (8.39)
Chlopromazine equivalent. Positive and negative syndrome scale.
Hyperstimulation of the dopaminergic D2 receptors is a hallmark feature of schizophrenia and the dopamine hypothesis had proposed that excess dopamine in the brain to be associated with positive symptoms (Abi-Dargham, 2004). Leptin plays a crucial role in modulation of the mesolimbic dopamine system that is disrupted in schizophrenia. This includes inhibition of dopamine neurons in the VTA and promotion of tryrosine hydroxylase (TH) expression for the production of dopamine within the VTA and NAc circuit (Opland et al., 2010). Under stressful conditions, leptin increases the production of dopamine (Burghardt
Table 2
et al., 2012). Therefore, it is highly probable that in stressful conditions commonly experienced by individuals with schizophrenia (Gispen-de Wied, 2000), leptin works to increase the production of dopamine, which in turn increases positive symptoms severity. Interestingly, antipsychotics and leptin have opposing effects on the dopaminergic system. Although the main role of antipsychotics is to treat psychotic symptoms, the effects of prolonged antipsychotic exposure on brain and behavior are less certain. Longitudinal imaging studies have reported reduced brain volumes with prolonged
Linear regressions of the associations between serum leptin and symptomatology. Model 1
PANSSa positive subscale score PANSSa negative subscale score PANSSa general psychopathology subscale score Total PANSSa score
Model 2
B
95% CI
p-value
B
95% CI
p-value
0.302 −0.116 0.175
0.074—0.530 −0.317—0.085 −0.007—0.357
0.010* 0.256 0.059
0.474 −0.192 0.461
0.086—0.863 −0.501—0.117 0.157—0.766
0.017* 0.220 0.003*
0.361
−0.087—0.809
0.113
0.73
0.009—1.450
0.047*
Model 2 is adjusted for age, gender, ethnicity, smoking status, duration of illness, BMI, exposure to atypical antipsychotics, daily dose of antipsychotics. * p-Value <0.05.
Serum leptin and its relationship with psychopathology in schizophrenia antipsychotic exposure (Ho et al., 2011). A recent 20-year longitudinal study found that antipsychotics, after the initial years, did not reduce the severity or frequency of psychosis in schizophrenia (Harrow et al., 2014). Previously, it was also suggested that prolonged exposure to antipsychotics might lead to tolerance and dopamine supersensitivity, a condition known as ‘‘supersensitivity psychosis’’ (Chouinard and Jones, 1980). When the above findings are evaluated in the context of leptin’s supposed roles in dopamine modulation and neuroplasticity, it would appear that leptin might be an interesting candidate to examine further. The strength of the present study lies in the reliability of the data collection and analysis. All participants with schizophrenia were recruited from a single site with control groups recruited from the same base population. The PANSS, a valid and reliable tool was used to assess subjects’ symptomatology and symptoms were assessed by single psychiatrist. In addition, blood samples were collected after an overnight fast; processed and analyzed using a commercially available assay that was optimized to measure serum leptin. This consistency minimized erroneous results due to variations. Furthermore, the evaluation of relationship between serum leptin and symptoms was adjusted for known confounders, giving rise to more precise estimates. However, due to the cross-sectional nature of the study, the temporal relationship between serum leptin and symptomatology in participants with schizophrenia could not be determined. Although we adjusted for current treatment with atypical antipsychotics, which was previously suggested to alter serum leptin level in patients with schizophrenia (Sentissi et al., 2008), we did not collect information of prior antipsychotic exposure which may have confounding effects on the relationship between serum leptin and symptomatology. In addition, as participants recruited in this study were mostly Chinese and were sufficiently stable to provide informed consent, the findings may not be generalizable to other ethnic groups and individuals with schizophrenia with more severe symptoms. This present study provided evidence to suggest a positive association between serum leptin and symptomatology in schizophrenia. However, since conflicting results in this area of research exist, it may be of benefit to understand the mechanism behind this relationship and to examine temporal fluctuations in leptin levels in relation with changes in clinical symptomatology. If leptin, through dopamine upregulation, exacerbates positive symptoms, the increased rate of obesity in schizophrenia is of concern as leptin is produced by adipocytes which are increased with weight gain. The positive relationship between leptin and positive symptoms also suggest that weight management might have beneficial effects on not only physical health and general mental health, but key aspects of schizophrenia symptomatology.
Contributors MN and JL were involved in the study design and data collection. MN analyzed the data and wrote up the first draft of the manuscript with SN. All authors were involved in interpretation of the results, provided intellectual input and approved the final manuscript for submission.
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Role of funding sources This study was funded by the National Medical Research Council, Singapore (NMRC/NIG/1017/2010 and NMRC/TCR/003/2008). JL is further supported by the Singapore Ministry of Health’s National Medical Research Council under its Transition Award (Grant No.: NMRC/TA/002/2012). Both funding sources had no further role in the study design, in the collection, analysis, interpretation of data, in the writing of the report, and in the decision to submit the paper for publication.
Conflict of interests statement JL had served as a consultant and received an honorarium from Roche. All other authors have no conflicts of interests to declare.
Acknowledgements We would like to acknowledge all the study participants for participating in the study and laboratory technicians at Biorad, Singapore for assistance in the evaluation of serum leptin. We would also like to acknowledge Dr. Gwen-Li Sin and Ms. Virginia Wilson for their assistance in proofreading the manuscript.
References Abi-Dargham, A., 2004. Do we still believe in the dopamine hypothesis? New data bring new evidence. Int. J. Neuropsychopharmacol. 7, S1—S5. Al-Harithy, R.N., 2004. Relationship of leptin concentration to gender, body mass index and age in Saudi adults. Saudi Med. J. 25, 1086—1090. Arranz, B., Rosel, P., Ramirez, N., Duenas, R., Fernandez, P., Sanchez, J.M., Navarro, M.A., San, L., 2004. Insulin resistance and increased leptin concentrations in noncompliant schizophrenia patients but not in antipsychotic-naive first-episode schizophrenia patients. J. Clin. Psychiatry 65, 1335—1342. Atmaca, M., Kuloglu, M., Tezcan, E., Ustundag, B., 2003. Serum leptin and cholesterol levels in schizophrenic patients with and without suicide attempts. Acta Psychiatr. Scand. 108, 208—214. Burghardt, P.R., Love, T.M., Stohler, C.S., Hodgkinson, C., Shen, P.H., Enoch, M.A., Goldman, D., Zubieta, J.K., 2012. Leptin regulates dopamine responses to sustained stress in humans. J. Neurosci. 32, 15369—15376. Chouinard, G., Jones, B.D., 1980. Neuroleptic-induced supersensitivity psychosis: clinical and pharmacologic characteristics. Am. J. Psychiatry 137, 16—21. DiLeone, R.J., 2009. The influence of leptin on the dopamine system and implications for ingestive behavior. Int. J. Obes. (Lond) 33 (Suppl 2), S25L S29. Faggioni, R., Feingold, K.R., Grunfeld, C., 2001. Leptin regulation of the immune response and the immunodeficiency of malnutrition. FASEB J. 15, 2565—2571. Gispen-de Wied, C.C., 2000. Stress in schizophrenia: an integrative view. Eur. J. Pharmacol. 405, 375—384. Harrow, M., Jobe, T.H., Faul, R.N., 2014. Does treatment of schizophrenia with antipsychotic medications eliminate or reduce psychosis? A 20-year multi-follow-up study. Psychol. Med. [Epub Mar 24, 1—10]-L.
154 Herran, A., Garcia-Unzueta, M.T., Amado, J.A., de La Maza, M.T., Alvarez, C., Vazquez-Barquero, J.L., 2001. Effects of long-term treatment with antipsychotics on serum leptin levels. Br. J. Psychiatry 179, 59—62. Ho, B.C., Andreasen, N.C., Ziebell, S., Pierson, R., Magnotta, V., 2011. Long-term antipsychotic treatment and brain volumes: a longitudinal study of first-episode schizophrenia. Arch. Gen. Psychiatry 68, 128—137. Jaleel, A., Jaleel, F., Majeed, R., Alam, E., 2007. Leptin and blood lipid levels in smokers and ex smokers. World Appl. Sci. J. 2, 348—352. Jenkins, A.B., Markovic, T.P., Fleury, A., Campbell, L.V., 1997. Carbohydrate intake and short-term regulation of leptin in humans. Diabetologia 40, 348—351. Jow, G.M., Yang, T.T., Chen, C.L., 2006. Leptin and cholesterol levels are low in major depressive disorder, but high in schizophrenia. J. Affect. Disord. 90, 21—27. Kraus, T., Haack, M., Schuld, A., Hinze-Selch, D., et al., 1999. Body weight and leptin plasma levels during treatment with antipsychotic drugs. Am. J. Psychiatry 156, 312—314. Kraus, T., Haack, M., Schuld, A., Hinze-Selch, D., Pollmacher, T., 2001. Low leptin levels but normal body mass indices in patients with depression or schizophrenia. Neuroendocrinology 73, 243—247. Monti, V., Carlson, J.J., Hunt, S.C., Adams, T.D., 2006. Relationship of ghrelin and leptin hormones with body mass index and waist circumference in a random sample of adults. J. Am. Diet. Assoc. 106, 822—828. Morrison, C.D., 2009. Leptin signaling in brain: a link between nutrition and cognition? Biochim. Biophys. Acta 1792, 401—408. Opland, D.M., Leinninger, G.M., Myers, J.M.G., 2010. Modulation of the mesolimbic dopamine system by leptin. Brain Res. 1350, 65—70.
M. Nurjono et al. Otero, M., Lago, R., Lago, F., Casanueva, F.F., Dieguez, C., GomezReino, J.J., Gualillo, O., 2005. Leptin, from fat to inflammation: old questions and new insights. FEBS Lett. 579, 295—301. Panariello, F., Polsinelli, G., Borlido, C., Monda, M., De Luca, V., 2012. The role of leptin in antipsychotic-induced weight gain: genetic and non-genetic factors. J. Obes. 2012, 572848. Raposo, N.R.B., Ferreira, A.S., Gattaz, W.F., 2011. Body mass index increase, serum leptin, Adiponectin, neuropeptide Y and lipid levels during treatment with olanzapine and haloperidol. Pharmacopsychiatry 44 (05), 169—172. Sentissi, O., Epelbaum, J., Olie, J.P., Poirier, M.F., 2008. Leptin and ghrelin levels in patients with schizophrenia during different antipsychotics treatment: a review. Schizophr. Bull. 34, 1189—1199. Simon, C., Gronfier, C., Schlienger, J.L., Brandenberger, G., 1998. Circadian and ultradian variations of leptin in normal man under continuous enteral nutrition: relationship to sleep and body temperature. J. Clin. Endocrinol. Metab. 83, 1893—1899. Takayanagi, Y., Cascella, N.G., Santora, D., Gregory, P.E., Sawa, A., Eaton, W.W., 2013. Relationships between serum leptin level and severity of positive symptoms in schizophrenia. Neurosci. Res. 77 (1—2), 97—101. Venkatasubramanian, G., Chittiprol, S., Neelakantachar, N., Shetty, T.K., Gangadhar, B.N., 2010. A longitudinal study on the impact of antipsychotic treatment on serum leptin in schizophrenia. Clin. Neuropharmacol. 33, 288—292. Wang, H.C., Yang, Y.K., Chen, P.S., Lee, I.H., Yeh, T.L., Lu, R.B., 2007. Increased plasma leptin in antipsychotic-naive females with schizophrenia, but not in males. Neuropsychobiology 56, 213—215. Warren, M.W., Hynan, L.S., Weiner, M.F., 2012. Leptin and cognition. Dement. Geriatr. Cogn. Disord. 33, 410—415. Woods, S., 2003. Chlorpromazine equivalent doses for the newer atypical antipsychotics. J. Clin. Psychiatry 64, 663—667.