目的
菸鹼酸紅腫減弱反應是思覺失調症的生物標記之一。菸鹼酸誘導之紅腫反應會藉由菸鹼酸受體傳導。一些研究指出異常的菸鹼酸反應路徑是由菸鹼酸受體訊號傳導異常，並影響其下游分子濃度改變。雖然多數思覺失調症患者對典型或非典型的抗精神病藥物有反應，但仍有約三分之一患者治療反應不佳，這類患者為難治型思覺失調症。難治型思覺失調症患者有更嚴重的負性及認知症狀。由菸鹼酸介導的信號傳導與難治型思覺失調症的分子機制仍不清楚。因此本研究將探討菸鹼酸紅腫減弱反應及菸鹼酸受體表現是否與難治型思覺失調症有關，並提供更多線索來探討難治型思覺失調症中菸鹼酸反應機轉。

方法
本研究目前共收案19位難治型思覺失調症患者與24位非難治型思覺失調症患者及其12位一等親家屬，和37位健康對照組。首先，我們在本研究的各組別進行菸鹼酸皮膚貼片測試及採集周邊血液並使用流式細胞儀進行GPR109A表現量分析。接著，我們會使用邏輯斯迴歸評估思覺失調症中菸鹼酸皮膚紅腫反應及GPR109A表現量與精神病症狀之關聯。最後，我們會建立鑑別模型分析菸鹼酸皮膚紅腫反應及GPR109A表現量是否能鑑別出難治型與非難治型的思覺失調症患者。鑑別模型利用接收者操作特徵曲線(ROC)並計算曲線下面積(AUC)與線性鑑別分析及機器學習演算法之支持向量機來進行分析。

結果
首先我們發現難治型患者相比非難治型患者及健康對照組，有減弱的菸鹼酸紅腫反應及較低的菸鹼酸受體(GPR109A)表現量。接著我們評估思覺失調症患者正性及負性症狀分數與菸鹼酸紅腫減弱反應及GPR109A表現量的差異，發現正性症狀較嚴重的思覺失調症患者，其菸鹼酸紅腫分數與GPR109A表現量可能較低。並且我們使用機器學習演算法之支持向量機分析菸鹼酸紅腫反應及GPR109A表現量的分類能力。結果顯示菸鹼酸紅腫分數在難治型患者與健康對照組中，其交叉驗證準確率為88%；在非難治型患者與健康對照組中，其交叉驗證準確率為85%。並且綜合菸鹼酸紅腫分數與GPR109A表現量，在難治型患者與非難治型患者中有較好的鑑別能力，其交叉驗證準確率為80%。

結論
上述結果顯示菸鹼酸紅腫反應與GPR109A表現量可能可以鑑別出難治型與非難治型思覺失調症患者。並且發現，GPR109A表現量可能與思覺失調症的精神病症狀有相關。本研究期待能利用菸鹼酸紅腫反應路徑的生物學機制能對難治型思覺失調症患者的診斷與治療有更多的臨床貢獻。

Purpose
Several studies showed that the abnormal niacin skin flush response is a biomarker in Schizophrenia. The niacin-induced skin flushing is mediated by a G-protein–coupled receptor 109A (GPR109A). Some studies described the association of abnormal niacin response pathway through signal transduction impairments of niacin receptors and its downstream molecules. While the majority of patients with schizophrenia respond to typical or atypical antipsychotics, approximately one-third of all patients with schizophrenia show a poor response to pharmacological treatment. This has been denoted as treatment-resistant schizophrenia (TRS). TRS patients tend to have prominent negative and cognitive symptoms and more severe psychopathology. The molecular mechanisms of niacin-mediated signaling with TRS patients remain unclear. Therefore, we aimed to determine whether the niacin flush response and GPR109A expression were associated with TRS patients and provided more clues for elucidating the etiology of treatment-resistant schizophrenia.

Methods
This study recruited 19 TRS patients, 24 non-TRS patients, 12 their first-degree relatives, and 37 healthy controls. First, we determined the niacin skin flush response and expression levels of GPR109A on monocytes by the FACSCalibur flow cytometer. Next, we used logistic regression to identify associations between niacin flush response and GPR109A expression for psychotic symptoms in schizophrenia. Final, we developed discriminative models for analyzing the discriminant abilities for TRS patients and non-TRS patients using the receiver operating characteristic (ROC), linear discriminant analysis, and support vector machine.

Results
First, we found TRS patients tended to have attenuated niacin flush response and lower levels of GPR109A expression than non-TRS patients and healthy controls. Second, when comparing PANSS positive or negative subgroups in schizophrenia, it seems that patients with high positive symptoms might have a lower niacin flush response and GPR109A expression. Third, we further conducted the support vector machine to evaluate the discriminate accuracy of niacin flush response and expression of GPR109A. The results revealed that the cross-validation accuracy of niacin flush scores was 88% between TRS patients and healthy controls and 85% between non-TRS patients and healthy controls. Furthermore, the cross-validation accuracy of the combined with niacin flush scores and GPR109A expression was 80% between TRS patients and non-TRS patients through the support vector machine algorithm.

Conclusion
These findings might provide the discriminant validity of niacin flush response and GPR109A expression between TRS patients and non-TRS patients. Furthermore, evidence suggests that GPR109A expression might be associated with psychotic symptoms in schizophrenia. Through the investigation of biological mechanisms in the niacin skin flush pathway in TRS patients, we will expect to improve the clinical contribution and therapeutic direction for treatment-resistant schizophrenia.

Alacam H, Akgun S, Akca H, et al. miR-181b-5p, miR-195-5p and miR-301a-3p are related with treatment resistance in schizophrenia. Psychiatry Research, 2016;245:200-206.
Benyo Z, Gille A, Kero J, et al. GPR109A (PUMA-G/HM74A) mediates nicotinic acid-induced flushing. Journal of Clinical Investigation, 2005;115(12):3634-3640.
Beyer AC. Suggestions for Treatment of Schizophrenia. Brain Disorders & Therapy, 2019;08(01).
Bosveld-van Haandel L, Knegtering R, Kluiter H, et al. Niacin skin flushing in schizophrenic and depressed patients and healthy controls. Psychiatry Research, 2006;143(2-3):303-306.
Chai JT, Digby JE, and Choudhury RP. GPR109A and vascular inflammation. Curr Atheroscler Rep, 2013;15(5):325.
Chang SS, Liu CM, Lin SH, et al. Impaired flush response to niacin skin patch among schizophrenia patients and their nonpsychotic relatives: the effect of genetic loading. Schizophrenia Bulletin, 2009;35(1):213-221.
Correll CU, Brevig T, and Brain C. Patient characteristics, burden and pharmacotherapy of treatment-resistant schizophrenia: results from a survey of 204 US psychiatrists. BMC Psychiatry, 2019;19(1):362.
Covault J, Pettinati H, Moak D, et al. Association of a long-chain fatty acid-CoA ligase 4 gene polymorphism with depression and with enhanced niacin-induced dermal erythema. American Journal of Medical Genetics Part B: Neuropsychiatric Genetics, 2004;127B(1):42-47.
Dai P, Huan P, Wang H, et al. Characterization of a long-chain fatty acid-CoA ligase 1 gene and association between its SNPs and growth traits in the clam Meretrix meretrix. Gene, 2015;566(2):194-200.
de Bartolomeis A, Prinzivalli E, Callovini G, et al. Treatment resistant schizophrenia and neurological soft signs may converge on the same pathology: Evidence from explanatory analysis on clinical, psychopathological, and cognitive variables. Progress in Neuro-Psychopharmacology and Biological Psychiatry, 2018;81:356-366.
Digby JE, Martinez F, Jefferson A, et al. Anti-inflammatory effects of nicotinic acid in human monocytes are mediated by GPR109A dependent mechanisms. Arteriosclerosis, Thrombosis, and Vascular Biology, 2012;32(3):669-676.
Digby JE, McNeill E, Dyar OJ, et al. Anti-inflammatory effects of nicotinic acid in adipocytes demonstrated by suppression of fractalkine, RANTES, and MCP-1 and upregulation of adiponectin. Atherosclerosis, 2010;209(1):89-95.
Doncheva NT, Morris JH, Gorodkin J, et al. Cytoscape StringApp: Network Analysis and Visualization of Proteomics Data. Journal of Proteome Research, 2019;18(2):623-632.
E.Obiols J, Serrano F, Caparrós B, et al. Neurological soft signs in adolescents with poorperformance on the continuous performance test:markers of liability for schizophrenia spectrumdisorders? Psychiatry Research, 1999;86(3):217-228.
Elkis H, and Buckley PF. Treatment-Resistant Schizophrenia. Psychiatric Clinics of North America, 2016;39(2):239-265.
Fathi F, Oskouie AA, Tafazzoli M, et al. Metabonomics based NMR in Crohn's disease applying PLS-DA. Gastroenterol Hepatol Bed Bench, 2013;6(Suppl 1):S82-86.
Fernandez-Egea E, Vertes PE, Flint SM, et al. Peripheral Immune Cell Populations Associated with Cognitive Deficits and Negative Symptoms of Treatment-Resistant Schizophrenia. PloS One, 2016;11(5):e0155631.
Frydecka D, Beszlej JA, Goscimski P, et al. Profiling cognitive impairment in treatment-resistant schizophrenia patients. Psychiatry Research, 2016;235:133-138.
Gillespie AL, Samanaite R, Mill J, et al. Is treatment-resistant schizophrenia categorically distinct from treatment-responsive schizophrenia? a systematic review. BMC Psychiatry, 2017;17(1):12.
Glen AI, Cooper SJ, Rybakowski J, et al. Membrane fatty acids, niacin flushing and clinical parameters. Prostaglandins, Leukotrienes, and Essential Fatty Acids, 1996;55(1-2):9-15.
Guy W, Cleary P, and Switalski R. A comparison of drug-trial schizophrenics with their clinical counterparts. Psychopharmacology Bulletin, 1977;13(3):44-45.
Howes OD, McCutcheon R, Agid O, et al. Treatment-Resistant Schizophrenia: Treatment Response and Resistance in Psychosis (TRRIP) Working Group Consensus Guidelines on Diagnosis and Terminology. American Journal of Psychiatry, 2017;174(3):216-229.
Huang S, Cai N, Pacheco PP, et al. Applications of Support Vector Machine (SVM) Learning in Cancer Genomics. Cancer Genomics & Proteomics, 2018;15(1):41-51.
Hudson CJ, Lin A, Cogan S, et al. The niacin challenge test: clinical manifestation of altered transmembrane signal transduction in schizophrenia? Biological Psychiatry, 1997;41(5):507-513.
Iasevoli F, Giordano S, Balletta R, et al. Treatment resistant schizophrenia is associated with the worst community functioning among severely-ill highly-disabling psychiatric conditions and is the most relevant predictor of poorer achievements in functional milestones. Progress in Neuro-Psychopharmacology and Biological Psychiatry, 2016;65:34-48.
Jamali-Dolatabad M, Sadeghi-Bazargani H, and Sarbakhsh P. Predictors of fatal outcomes in pedestrian accidents in Tabriz Metropolis of Iran: Application of PLS-DA method. Traffic Inj Prev, 2019;20(8):873-879.
Kanehisa M, and Goto S. KEGG: Kyoto Encyclopedia of Genes and Genomes. Nucleic acids research, 2000;28(1):27-30.
Kay SR, Fiszbein A, and Opler LA. The positive and negative syndrome scale (PANSS) for schizophrenia. Schizophrenia Bulletin, 1987;13(2):261-276.
Langbein K, Schmidt U, Schack S, et al. State marker properties of niacin skin sensitivity in ultra-high risk groups for psychosis - An optical reflection spectroscopy study. Schizophrenia Research, 2018;192:377-384.
Law MH, Cotton RG, and Berger GE. The role of phospholipases A2 in schizophrenia. Molecular Psychiatry, 2006;11(6):547-556.
Leucht S, Kane JM, Kissling W, et al. What does the PANSS mean? Schizophrenia Research, 2005;79(2-3):231-238.
Lin AS, Chan HY, Peng YC, et al. Severity in sustained attention impairment and clozapine-resistant schizophrenia: a retrospective study. BMC Psychiatry, 2019;19(1):220.
Lin SH, Liu CM, Chang SS, et al. Familial aggregation in skin flush response to niacin patch among schizophrenic patients and their nonpsychotic relatives. Schizophrenia Bulletin, 2007;33(1):174-182.
Liu CM, Chang SS, Liao SC, et al. Absent response to niacin skin patch is specific to schizophrenia and independent of smoking. Psychiatry Research, 2007;152(2-3):181-187.
Lorenzen A, Stannek C, Burmeister A, et al. G protein-coupled receptor for nicotinic acid in mouse macrophages. Biochemical Pharmacology, 2002;64(4):645-648.
Maciejewski-Lenoir D, Richman JG, Hakak Y, et al. Langerhans cells release prostaglandin D2 in response to nicotinic acid. Journal of Investigative Dermatology, 2006;126(12):2637-2646.
Messamore E. Niacin subsensitivity is associated with functional impairment in schizophrenia. Schizophrenia Research, 2012;137(1-3):180-184.
Messamore E. The niacin response biomarker as a schizophrenia endophenotype: A status update. Prostaglandins, Leukotrienes, and Essential Fatty Acids, 2018;136:95-97.
Messamore E, Hoffman WF, and Janowsky A. The niacin skin flush abnormality in schizophrenia: a quantitative dose-response study. Schizophrenia Research, 2003;62(3):251-258.
Miller CL, and Dulay JR. The high-affinity niacin receptor HM74A is decreased in the anterior cingulate cortex of individuals with schizophrenia. Brain Research Bulletin, 2008;77(1):33-41.
Muralidharan A, Finch A, Bowie CR, et al. Thought, language, and communication deficits and association with everyday functional outcomes among community-dwelling middle-aged and older adults with schizophrenia. Schizophrenia Research, 2018;196:29-34.
Mustafa A, Rienow A, Saadi I, et al. Comparing support vector machines with logistic regression for calibrating cellular automata land use change models. European Journal of Remote Sensing, 2018;51(1):391-401.
Nadalin S, Buretic-Tomljanovic A, Rubesa G, et al. Niacin skin flush test: a research tool for studying schizophrenia. Psychiatr Danub, 2010;22(1):14-27.
Nilsson BM, Holm G, Hultman CM, et al. Cognition and autonomic function in schizophrenia: inferior cognitive test performance in electrodermal and niacin skin flush non-responders. European Psychiatry, 2015;30(1):8-13.
Nucifora FC, Jr., Woznica E, Lee BJ, et al. Treatment resistant schizophrenia: Clinical, biological, and therapeutic perspectives. Neurobiology of Disease, 2019;131:104257.
Ozdin S, and Boke O. Neutrophil/lymphocyte, platelet/lymphocyte and monocyte/lymphocyte ratios in different stages of schizophrenia. Psychiatry Research, 2019;271:131-135.
Periyasamy S, John S, Padmavati R, et al. Association of Schizophrenia Risk With Disordered Niacin Metabolism in an Indian Genome-wide Association Study. JAMA Psychiatry, 2019.
Puri BK, Richardson AJ, Counsell SJ, et al. Negative correlation between cerebral inorganic phosphate and the volumetric niacin response in male patients with schizophrenia who have seriously and dangerously violently offended: a (31)P magnetic resonance spectroscopy study. Prostaglandins, Leukotrienes, and Essential Fatty Acids, 2007;77(2):97-99.
Quitadamo LR, Cavrini F, Sbernini L, et al. Support vector machines to detect physiological patterns for EEG and EMG-based human-computer interaction: a review. J Neural Eng, 2017;14(1):011001.
Reichert A, Kreiker S, Mehler-Wex C, et al. The psychopathological and psychosocial outcome of early-onset schizophrenia: preliminary data of a 13-year follow-up. Child Adolesc Psychiatry Ment Health, 2008;2(1):6.
Ross BM, Hughes B, Turenne S, et al. Reduced vasodilatory response to methylnicotinate in schizophrenia as assessed by laser Doppler flowmetry. European Neuropsychopharmacology, 2004;14(3):191-197.
Rybakowski J, and Weterle R. Niacin test in schizophrenia and affective illness. Biological Psychiatry, 1991;29(8):834-836.
Schaeffer EL, Gattaz WF, and Eckert GP. Alterations of brain membranes in schizophrenia: impact of phospholipase A(2). Current Topics in Medicinal Chemistry, 2012;12(21):2314-2323.
Schennach R, Riedel M, Musil R, et al. Treatment Response in First-episode Schizophrenia. Clin Psychopharmacol Neurosci, 2012;10(2):78-87.
Shah SH, Vankar GK, Peet M, et al. Unmedicated schizophrenic patients have a reduced skin flush in response to topical niacin. Schizophrenia Research, 2000a;43(2-3):163-164.
Shah SH, Vankar GK, Peet M, et al. Unmedicated schizophrenic patients have a reduced skin flush in response to topical niacin. Schizophrenia Research, 2000b;43(2-3):163-164.
Singh N, Gurav A, Sivaprakasam S, et al. Activation of Gpr109a, receptor for niacin and the commensal metabolite butyrate, suppresses colonic inflammation and carcinogenesis. Immunity, 2014;40(1):128-139.
Smesny S, Berger G, Rosburg T, et al. Potential use of the topical niacin skin test in early psychosis—a combined approach using optical reflection spectroscopy and a descriptive rating scale. Journal of Psychiatric Research, 2003;37(3):237-247.
Smesny S, Klemm S, Stockebrand M, et al. Endophenotype properties of niacin sensitivity as marker of impaired prostaglandin signalling in schizophrenia. Prostaglandins, Leukotrienes, and Essential Fatty Acids, 2007;77(2):79-85.
Smesny S, Riemann S, Riehemann S, et al. [Quantitative measurement of induced skin reddening using optical reflection spectroscopy--methodology and clinical application]. Biomedizinische Technik, 2001;46(10):280-286.
Smesny S, Rosburg T, Klemm S, et al. The influence of age and gender on niacin skin test results - implications for the use as a biochemical marker in schizophrenia. Journal of Psychiatric Research, 2004;38(5):537-543.
Smesny S, Rosburg T, Riemann S, et al. Impaired niacin sensitivity in acute first-episode but not in multi-episode schizophrenia. Prostaglandins, Leukotrienes, and Essential Fatty Acids, 2005;72(6):393-402.
Sun L, Yang X, Jiang J, et al. Identification of the Niacin-Blunted Subgroup of Schizophrenia Patients from Mood Disorders and Healthy Individuals in Chinese Population. Schizophrenia Bulletin, 2018;44(4):896-907.
Szklarczyk D, Franceschini A, Wyder S, et al. STRING v10: protein–protein interaction networks, integrated over the tree of life. Nucleic acids research, 2015;43(Database issue):D447-D452.
Tang Y, Zhou L, Gunnet JW, et al. Enhancement of arachidonic acid signaling pathway by nicotinic acid receptor HM74A. Biochemical and Biophysical Research Communications, 2006;345(1):29-37.
Tavares H, Yacubian J, Talib LL, et al. Increased phospholipase A2 activity in schizophrenia with absent response to niacin. Schizophrenia Research, 2003;61(1):1-6.
Tunaru S, Lattig J, Kero J, et al. Characterization of determinants of ligand binding to the nicotinic acid receptor GPR109A (HM74A/PUMA-G). Molecular Pharmacology, 2005;68(5):1271-1280.
Ward PE, Sutherland J, Glen EM, et al. Niacin skin flush in schizophrenia: a preliminary report. Schizophrenia Research, 1998a;29(3):269-274.
Ward PE, Sutherland J, Glen EMT, et al. Niacin skin flush in schizophrenia: a preliminary report. Schizophrenia Research, 1998b;29(3):269-274.
Wimberley T, Støvring H, Sørensen HJ, et al. Predictors of treatment resistance in patients with schizophrenia: a population-based cohort study. The Lancet Psychiatry, 2016;3(4):358-366.
Yao JK, Dougherty GG, Jr., Gautier CH, et al. Prevalence and Specificity of the Abnormal Niacin Response: A Potential Endophenotype Marker in Schizophrenia. Schizophrenia Bulletin, 2016;42(2):369-376.