The skin as an organ where interaction between the external and internal environments takes place is overcome by oxidative stress radicals (OSR) generated as a result of ongoing pro-oxidant and antioxidant imbalance 1. Psoriasis vulgaris (PsV) is a known OSR inducer that exhausts selenium (Se) of the body 2.
Oxidative stress and a weakened antioxidant defense in the skin result in increased OSR and lipid peroxidation, which play an important role in the inflammatory process of psoriasis 3. Se as one of the antioxidant enzymes contributes effectively toward the pathogenesis of psoriasis as a choric inflammatory disease besides other factors implicated in the etiopathogenesis of psoriasis 1.
Se is one of the essential trace elements that are necessary for an effective immune function as an antioxidant to maintain the balance between the oxidative products and endogenous antioxidant defense as a reduction of these natural antioxidants would enhance the toxic effects of the free radicals 4. It is also the principal component of cytoplasmic superoxide dismutase and glutathione peroxidase, respectively, which are important in the detoxification and scavenging of OSR. Being a transformation element, Se can also modulate the action of such enzymes and protect the skin from the deleterious effect of the OSR produced during the course of the disease 5.
Many studies have evaluated serum Se levels in psoriatic patients; most of these studies analyzed Se levels in serum specimens, aiming at highlighting its contribution toward the pathogenesis of psoriasis 6–9. Scalp hair has been reported to be a reliable tool for the assessment of various trace elements in systemic diseases such as respiratory tract infection, asthma, and rheumatic arthritis 10,11. Hair metal analysis is simple and pain free, and researches suggest its utility as a preliminary indicator of toxic exposure to metals or some nutrients 12. Hair samples are used to evaluate metal levels such as mercury 13.
The aim of this study was to determine the utility of hair Se level as a monitoring tool by assessing the levels of Se in hair and serum samples of patients with PsV and correlating these levels with PsV severity scores.
Patients and methods
This case–control study included 20 Egyptian patients with chronic plaque-type psoriasis who were diagnosed and recruited from the Dermatology Clinic, Ain Shams University Hospital, and 20 healthy sex-matched and age-matched individuals (control group) from December 2014 to December 2015. Informed written consents were obtained and approval from the research ethics committee of Ain Shams Faculty of Medicine was obtained. The participants included were nonsmokers, nondiabetic, and ranged in age from 20 to 65 years, with no sex predilection; the patients had total scaly scalp lesions (the occipital area was involved in all patients). Furthermore, no Se supplements before or throughout the study period were allowed. The exclusion criteria were as follows: presence of other scalp hair disease or systemic illness. Assessment of psoriasis severity was performed using the Psoriasis Area and Severity Index (PASI) score 14.
Estimation of selenium level in blood
Venous blood was withdrawn and separated sera were stored at 20°C. Se was measured in the serum by inductively coupled plasma spectroscopy (Perkin Elmer Optima 4300 DV; Norwalk, Connecticut, USA); two measurements for each sample and the average of the observations were recorded. Se solutions containing standard Se concentration were considered reference materials to verify the quality of the analysis.
Estimation of selenium level in scalp hair
Hair specimen collection
Hair samples were collected by cutting from the occipital area at 1.5–2 cm lengths, weighing ∼1.0 g. Hair samples were obtained from a scaly area in the head with clean stainless-steel scissors with vanadium blades and then placed in a tightly sealed plastic envelope.
The measurements of Se were performed by Electrothermal Atomic Absorption Spectrometer Zeenit 700 (Germany) equipped with Zeeman background correction and an automatic autosampler.
Before testing, samples were frequently washed with a metal-free detergent, rinsed with pure water, and dried before weighing. Metal-free acids were used for hair digestion in a microwave digestion system. The final water sample was diluted and then Se analysis was carried out by inductively coupled plasma mass spectrometry utilizing collision/reaction cell methods coupled with ion-molecule chemistry, a reliable new method for interference reduction 13 (7500 ICP-MS; Agilent Technologies, Santa Clara, California, USA).
Data analysis was carried out using the statistical package for social sciences software, version 18 (IBM Corporation, Armonk, New York, USA). Quantitative data were expressed as mean±SD. Qualitative data were expressed as frequency and percentage. The Student t-test was used to perform comparisons between normally distributed quantitative data. Differences between categorical variables were analyzed using χ2 with Fisher’s test applied when appropriate. Pearson’s correlation coefficient (r) test was used for correlation of data. Receiver operating characteristic curve analysis was used to determine the overall predictivity of parameters and the best cutoff value, with detection of sensitivity and specificity. Positive and negative predictive values were determined. A P-value less than 0.05 was considered statistically significant.
The age of the patients ranged from 30 to 55 years (38.3±8.3 years). There were 12 (60%) women and eight (40%) men. The age of onset of the disease ranged from 13 to 40 years (24.5±6 years). The disease duration ranged from 5 to 25 years (13.8±6.3 years).
The hair Se levels ranged between 182.2 and 311.7 ng/g (274.1±32). Serum Se levels ranged from 34 to 102 μmol/l (62.4±18.4). PASI scores ranged from 5.1 to 20.2 (10.9±5.1).
The age of the participants in the control group ranged from 33 to 55 years (37.1±7.2 years). There were 16 (80%) women and four (20%) men. The hair Se levels ranged from 289.6 to 430.5 ng/g (354.7±38.1). Serum Se levels ranged from 55 to 123 μmol/l (96.9±19.4).
There were no statistically significant differences between psoriasis patients and control individuals in age (P=0.642) or sex (P=0.168).
Psoriasis patients had significantly lower mean scalp hair Se levels compared with the healthy controls (P<0.001) (Fig. 1). Also, patients with psoriasis had significantly lower serum Se compared with the controls (P<0.001).
We found that hair Se levels were correlated positively with serum Se levels (r=0.426, P<0.001) in the patient group.
There was a significant negative correlation between scalp hair Se levels and serum Se levels with the PASI score (r=−0.638, P<0.002 and r=−0. 969, P<0.001, respectively) (Fig. 2).
No significant correlations were found between hair Se levels and the patients’ age (r=0.008, P=0.981), the age of onset of the disease (r=0.270, P=0.249), or the disease duration (r=−0.263, P=0.263). There were no statistically significant differences between women and men in the mean hair Se levels (280.33±19.89, 264.79±44.56, P=0.0299, t=−1.069, respectively) and also the mean serum Se level (262.41±37.20, 277.04±31.17, P=0.428, t=−0.811, respectively).
Receiver operating characteristics curve was used to define the best cutoff value of Se levels (ng/g), which was 311.65, with a sensitivity of 100%, a specificity of 95%, a positive predictive value of 95.2%, and a negative predictive value of 100%, with a diagnostic accuracy of 98.3% (Fig. 3).
In this case–control study, our results confirmed the usefulness of hair element analysis for the assessment of the Se status in chronic PsV. Participants with psoriasis had significantly lower means of hair and serum Se concentrations than healthy controls. We found an association of low hair and serum Se levels with PsV. Hair Se levels were correlated positively with serum Se concentrations. Lower hair and serum Se levels were associated with more severe disease. These findings might point to the influence of Se status on the pathogenesis of psoriasis; however, it may be a result of the disease. Differentiation of the severity of psoriasis using the level of the scalp hair Se as a tool can be reliable with 100% sensitivity, 95% specificity, and 98.3% diagnostic accuracy.
Our findings are in agreement with those of other colleagues who have established associations between low serum Se and psoriasis 6–8,15; they showed that low Se concentration could be a risk factor for a disease characterized by cell hyper-proliferation and suggested that decreased Se levels can also worsen psoriasis lesions. It was also indicated that a low plasma Se level is a predictable factor for the occurrence of psoriasis 9. In addition, it was shown that there was a negative correlation between severity of psoriasis and serum Se 7. To our knowledge, no previous studies on the estimation of hair Se in psoriasis have been carried out for comparisons.
An explanation for the link between Se and psoriasis could be that most probably an activation of antioxidative defenses occurs in the acute stage of this chronic disease, resulting in the depletion of these defenses during persistent inflammatory, hyper-proliferative, and excessive desquamation states with a reduction in the total body Se level. Se status may reflect the extent of induced oxidative stress and oxidative exhaustion. Thus, a vicious circle would result involving an increase in the severity of psoriasis and greater reductions of Se concentration.
Our study found no significant correlation between the scalp Se level and other parameters that may affect Se levels in psoriasis such as age, sex, family history and onset or duration of the disease; this may be attributed to the small sample size, which limited our findings. This also may be due to the great influence of psoriasis severity which masks the effect of these parameters on Se.
Serum Se concentration may not be the most perfect biomarker because it may show variations to physiologic or pathological reactions. Hair was recommended as a good alternative. It has been reported that hair Se levels are reliable for representing body concentrations 16. Hair trace element analysis is utilized as a means not only for the present evaluation but also previous biological events 17.
Testing for trace elements in hair is an interesting diagnostic method and provides an idea about mineral imbalances in the body 18 without being modified by external contamination 19,20.
The study indicates not only the possibility of assessing Se levels in scalp hair but that hair Se levels might also be suitable for representing the body concentrations in psoriasis. Se can be considered a suitable biomarker as it is affected by physiologic changes in the inflammatory process in psoriasis. Hair analysis may be a useful tool in identifying the links between factors leading to the development of PsV. Furthermore, assessment of the levels of Se in the hair of PsV patients may be more useful compared with serum and urine for treatment and prognosis.
The study recommends further studies on the use of hair Se as a monitoring aid for various chronic inflammatory skin diseases.
The authors thank the patients for participating in this study.
The kind participation of Dr Doaa Aly Hamed Hendy, MS, in data collection and analysis, is highly appreciated (Dar El-Sheffa Hospital).
Conflicts of interest
There are no conflicts of interest.
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