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Background information

Schizophrenia is a complex multi-factorial mental disorder that causes psychiatric morbidity worldwide. It affects 1% of the world population and each individual has 0.7% risk of developing the disorder over one's lifetime. In 2002, World Health Organisation (WHO) estimated that Malaysia has estimated one death per a thousand populations due to schizophrenia (2004). There are variations in the incidence of schizophrenia, where family history, urban-living and oxidative stress are linked to a higher risk for developing the disorder.

Free radicals are reported to play a major role in the aetiology of many diseases such as neuropsychiatric disorder and schizophrenia. They are usually produced as the body immune response to exogenous oxidants for instance, bacteria, polluted air, cigarette smoke, inappropriate diet, and radiation. Examples of free radicals are superoxide anion radical, hydrogen peroxide, singlet oxygen, and hydroxyl radical, which have highly reactive unpaired electrons that seek to damage cellular components. Such oxidative damage in lipid, which is essential in nerve cell membrane function, would affect signal transmissions and might degenerate brain functions.

Antioxidants are the antidotes to counteract oxidative stress, functioning to improve immune functions and prevent diseases. They scavenge the reactive species by reducing and neutralising them to a stable form in a reduction-oxidation reaction. Used antioxidant would then become inert and need to be replenished often. Examples of antioxidants in human plasma and tissue are vitamins A, C, and E and the carotenoids. Important sources of carotenoid include red, orange, yellow, and green vegetable and fruits. Research reported skin carotenoid as a reliable indicator of overall antioxidant level in human that provide evidence of oxidative stress which is often related to diseases.

Individual antioxidant level varies on lifestyle, dietary habit, and smoking habit. Lifestyle factors such as excessive emotional stress, lack of exercise, and alcohol and drug abuse induce free radicals production in human brain.

In the present study, total antioxidant level was determined by a simple, quick, non-invasive technique using Raman spectroscopy which utilises laser spectroscopic technique to detect characteristic vibration energy of carotenoids on human skin. Research demonstrated a significant correlation between serum carotenoid and skin carotenoid levels.  

This study examined possible differences of skin carotenoid level in relation to demographic and clinical characteristics of healthy and schizophrenic population.

Methodology

 ( a )   Subject selection 

The sample population consisted of 524 schizophrenic subjects recruited from Ulu Kinta Mental Hospital (HBUK), Perak, Malaysia. The subjects were grouped into their respective subtype: catatonic, disorganised, paranoid, residual, and undifferentiated. The diagnoses of schizophrenic subjects were done according to the Mini International Neuropsychiatric Interview (M.I.N.I.), English Version 5.0.0. This study also enrolled 289 normal control subjects. All of the subjects and controls are residents of Malaysia, with age range from 16 to 80 years. Written consents were obtained from subjects before participation in the study. This study was approved by the National Institute of Health (NIH), Ministry of Health, Malaysia.

Carotenoid levels of subjects were measured using Pharmanex® BioPhotonic Scanner S2 (Pharmanex, U.S.A.). Subjects were required to clean their palms and hold them to the scanner for two minutes. Individual skin carotenoid score was compiled.

( b )   Statistical analysis 

Data analyses were perform using Statistical Package for Social Sciences (SPSS) version 16.0 for Windows (SPSS Inc, Chicago, USA). Carotenoid score difference between schizophrenic and control subjects were evaluated using independent sample T-test. Variables tested using analysis of variance (ANOVA) including gender, age, schizophrenia subtypes, patient medication, depot injection and duration of illness. In the analysis of schizophrenia subtype, subjects with catatonic and residual subtype were excluded from the analysis due to low sample size. Both control and schizophrenia subjects were grouped into four age ranges: 16 to 30 years, 31 to 40 years, 41 to 50 years and more than 50 years of age. Patients were divided into three categories depending on their medication: typical antipsychotics such as haloperidol and chlorpromazine; atypical antipsychotics such as olanzapine and clozapine; and other antipsychotics that are not in the above two categories, such as diazepam, fluvoxamine and sulpiride. Following that, analysis of depot injection compared patients that received intramuscular injection of antipsychotics with patients that did not received any injections, regardless of type of antipsychotics. Patients were grouped into four duration periods: ill for less than 5 years, between 5 to 10 years, between 10 to 20 years, and above 20 years. For each studied population, Levene?s homogeneity test was used to test for equality variances. Descriptive statistics were calculated for all variables and mean carotenoid score was reported separately for each variable.

( c )   Result 

A total of 84% schizophrenic patients obtained carotenoid score less than 30,000. In contrast, 33% control subjects scored higher than 30,000. Statistical analysis showed that carotenoid score of schizophrenic patients was significantly lower than controls, where the mean score of controls is 27,372, while mean score of schizophrenic subjects is 22,213, with approximately 19% difference from the controls. On average, female obtained significantly higher mean carotenoid score compared to male. Individual analysis control and patient group showed that mean score for female were higher than male by 15% and 10% respectively.

The mean carotenoid score of control and schizophrenic subjects vary with different age ranges. Among controls, those aged between 16 to 30 years have the lowest mean score; with 11% lower than the average controls' mean score. On the other hand, patients in the same age range scored slightly higher by 3% than the average patients' mean score. When comparing mean score between control and patient in this age range, controls obtained 8% higher mean score than patients, but statistical analysis showed no significant difference. In the age ranges of 31 to 40 years old, 41 to 50 years old, and above 50 years old, controls showed higher mean score compared to patients by 21 %, 18%, and 24% respectively. With the exclusion of age range 16 to 30 years, controls in the other three age ranges marked significant higher mean score than patients. When comparing mean score between control and patient in different age range, younger patients were found to have significant lower antioxidant score compared to older controls. Controls that lies in age range above 50 years obtained significantly higher score compared to patients in the other three lower age ranges.

In subtype analysis, carotenoid levels for disorganised, paranoid, and undifferentiated  subtypes were not significantly different from each other, but were found significantly  lower compared to controls. The mean carotenoid score of patients that received atypical antipsychotics were found to be higher compared to those that received typical and other antipsychotic medications. Despite that, statistical analysis of carotenoid score between patient with different type of medication received showed no significant difference. However, when compared to controls, patients' score were found significantly lower. Similarly, carotenoid score of depot injection recipients did not differ significantly with non-recipient, but both recipient and non-recipient showed significant lower score compared to controls. The carotenoid score of patient with different duration of illness did not showed significant difference with each other, but showed significant lower score when compared to controls. 

Conclusion 

Schizophrenia subjects scored significant lower carotenoid level compared to healthy control, indicating higher level of oxidative stress in schizophrenia. Factors contributing to oxidative stress such as subtype, age, antipsychotic drug treatment, and duration of illness showed significant difference between control and schizophrenic but showed no difference in antioxidant among patients. Results showed that carotenoid scores were not affected by type of medication, depot injection, nor patient duration of illness. Antipsychotics treatment and schizophrenia illness itself were suggested to be the possible reasons to the reduced antioxidant level in schizophrenic patients. Further work is needed to cross-validate the relationship between antioxidant level and schizophrenia in terms of ethnic, stages of disease progression, and antipsychotic drug dosage.