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Levels of osteopontin in plasma and tissue in relation to metabolic status in patients with lichen planus

Sharaf, Amra; Zaki, Naglaa S.a; Kadry, Dinaa; Rashed, Lailab; Awad, Mohammad A.c

Journal of the Egyptian Women's Dermatologic Society: September 2017 - Volume 14 - Issue 3 - p 173–178
doi: 10.1097/01.EWX.0000526123.98579.b2
Original articles
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Background Chronic inflammation with lichen planus (LP) has been suggested as a component of the metabolic syndrome (MetS). LP is assumed to be related closely to dyslipidemia. Plasma osteopontin (OPN) has been reported to be a potential clinical marker for the prediction of atherosclerosis. Selenium (Se), an essential trace element, involved in the defense against oxidative stress, has been hypothesized to prevent cardiovascular disease (CVD). Se compounds are effective in the downregulation of OPN expression. Moreover, an inverse relation has been detected between the levels of plasma OPN and plasma Se in patients with psoriasis.

Objective To determine the possible role of OPN and Se in the pathogenesis of LP and their relation to the metabolic status in patients.

Patients and methods Thirty patients with LP and 30 controls were included. Participants were assessed for the presence of MetS and/or its components. In all participants, plasma and tissue OPN levels were assessed using an enzyme-linked immunosorbant assay, plasma Se levels were assessed by flame atomic absorption spectrophometry, and high-sensitivity C-reactive protein levels were assessed using a solid-phase enzyme-linked immunosorbant assay.

Results Patients with LP showed a significant association with MetS parameters than the controls. Plasma and tissue OPN were significantly higher in LP patients than those in the control group. Plasma Se levels were significantly lower in patients than those in the control group. In patients, plasma OPN levels were associated positively with the presence of diabetes mellitus, dyslipidemia, and MetS.

Conclusion The presence of LP in patients was associated strongly with MetS parameters, most probably because of long-standing inflammation. OPN may be a critical regulator of chronic inflammation in patients with LP and may explain its association with components of the MetS such as diabetes mellitus and dyslipidemia.

Departments of aDermatology

bBiochemistry and Molecular Biology, Faculty of Medicine, Cairo University

cDepartment of Dermatology, Atomic Energy Authority, Cairo 11728, Egypt

Correspondence to Dina Kadry, MD, 29 Street 13, Maadi, Cairo, Egypt Tel: +20 100 100 4741; fax: +20 233 468804; e-mail: dina.mkadry@gmail.com

Received June 23, 2016

Accepted March 30, 2017

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Introduction

Lichen planus (LP) is a chronic inflammatory disease that affects the skin, mucous membranes, and appendages 1. Although the exact pathogenesis is still unclear, some studies provide evidence that autoreactive cytotoxic T lymphocytes are the effector cells that cause degeneration and destruction of keratinocytes. Because of the predominant secretion of interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α), LP is characterized by a type 1 cytokine pattern 2.

Osteopontin (OPN) is an acidic glycoprotein that plays a role in various inflammatory disorders 3 and is expressed by many different cell types including activated immune cells such as macrophages, natural killer cells, and activated T lymphocytes 4. OPN gene expression is upregulated extensively upon obesity in adipose tissue and plasma OPN concentrations are elevated in morbidly obese patients 5. Moreover, plasma concentration of OPN was reported to be significantly increased in psoriasis patients compared with controls and this increase was associated significantly with the occurrence of psoriasis 3,6.

Selenium (Se) has been hypothesized to prevent cardiovascular disease (CVD) and Se compounds are effective in the downregulation of OPN expression 7. An inverse relation has been detected between the levels of plasma OPN and plasma Se in patients with psoriasis 8.

Serum C-reactive protein (CRP) is predominantly synthesized in the liver hepatocytes as an acute-phase reactant 9,10. Increased CRP, together with insulin resistance, dyslipidemia, obesity, and hypertension, plays an important role in the pathogenesis of atherosclerosis and CVD 11. Therefore, it is considered a marker for CVD risks 12.

Keeping in mind that LP is an inflammatory T-cell-mediated disease characterized by a type 1 cytokine pattern similar to psoriasis, this raised the question of whether, as in psoriasis, OPN could be involved in the pathogenesis of LP. We also aimed to investigate the metabolic status of patients with LP and to identify any possible link between the metabolic status and markers such as OPN, Se, and CRP.

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Patients and methods

Patients

Thirty patients with LP attending the Dermatology Outpatient Clinic of Kasr Al Ainy Hospital, Cairo University, between the period October 2012 and December 2013 were included in this study. Inclusion criteria included patients with cutaneous LP (not associated with oral LP lesions) older than 18 years of age, not receiving systemic treatment, and were off topical therapy for 6 weeks. Exclusion criteria included patients with hepatitis C virus (HCV) infection as OPN is upregulated in the plasma of patients with HCV 13. Exclusion criteria also included patients taking Se supplements or those with a history of associated disorders known to affect OPN levels including malignancy and autoimmune diseases. Thirty age-matched and sex-matched healthy controls without HCV were enrolled in the study. Participants provided informed written consent before enrollment and the study was approved by the Institutional Dermatology Research Ethical Committee (Derma Rec).

All participants were subjected to a full assessment of history including present and past medical history. The duration of disease, age of onset, and family history of LP were assessed in patients. On enrollment, age, weight, height, waist circumference (WC), smoking status, and blood pressure of all participants were recorded. WC was measured at the mid-point between the lower borders of the rib cage and the iliac crest. The BMI was calculated as weight/height (kg/m2) and participants were classified as normal weight (BMI 18.5–24.9 kg/m2), overweight (BMI 25–29.9 kg/m2), or obese (BMI>30 kg/m2). BMI over 40 suggests that the individual is morbidly obese 14. Lipid profile (total cholesterol and triglycerides), fasting blood sugar (FBS), homeostasis model assessment for insulin resistance (HOMA-IR), and the presence of metabolic syndrome (MetS) were assessed in both groups. For the definition of MetS, we adopted the New International Diabetes Federation MetS worldwide definition 15. Plasma and tissue OPN, plasma Se, and C-reactive protein were evaluated.

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Methods

After an overnight fasting, 5 ml of venous blood samples was collected from patient groups and immediately processed in EDTA tubes. After 15 min of centrifugation at 1000g, the plasma was rapidly pipetted off and kept frozen at −80°C till analysis. One skin biopsy (4 mm punch biopsy) from each patient (lesional skin) and one skin biopsy from the normal skin of controls were obtained. Plasma OPN was assessed using an enzyme-linked immunosorbent assay (ELISA) (Quantikine R&D System Inc., Minneapolis, Minnesota, USA). Tissue OPN was measured by homogenizing 20 mg of tissue specimen in 1 ml lysis buffer for protein extraction. This buffer contained 0.0625 mol/l Tris buffer (pH 6.8), 2% sodium dodecyl sulfate, 3% 2-mercaptoethanol, 10% glycerol, 10 lg/ml aprotinin, and 1 mol/l phenyl methyl sulfonyl fluoride (Sigma, St Louis, Missouri, USA). After cell lysis, the homogenate was centrifuged at 6654g for 20 min at 4°C. The supernatant was kept frozen at −70°C until analysis.

Plasma Se was estimated by flame atomic absorption spectrophometry. High-sensitivity C-reactive protein (hs-CRP) was measured using a solid-phase ELISA, which utilizes a unique monoclonal antibody directed against a distinct antigenic determinant on the CRP molecule. Enzymatic colorimetric determination methods were used to evaluate the FBS levels (glucose oxidase method), plasma cholesterol, triglycerides, and high-density lipoprotein levels. IR was calculated through HOMA-IR using the following equation: fasting insulin (µU/l)×fasting glucose (mg/dl)/405.

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Statistical analysis

Data were grouped as patients and controls, and analyzed using SPSS for Windows, version 16 (SPSS Inc., Chicago, Illinois, USA). Parametric (numeric) data were expressed as range (minimum, maximum) and mean±SD, and compared using Student’s t-test. Nonparametric data were expressed as frequency (number, percent) and compared using the Mann–Whitney U-test.

The correlation of variables was performed using the Pearson correlation coefficient test for parametric variables, and a cross-table (Pearson’s r – Pearson’s χ2) and the Fisher Exact test for nonparametric variables. The analysis of variance test and η2 association were used to assess differences within groups of single variables. Two-tailed significant values were considered when P value of less than 0.05. All statistical calculations were carried out using the computer programs Microsoft Excel 2010 (Microsoft Corporation, New York, New York, USA) and statistical package for the social science (SPSS; SPSS Inc.), version 16 for Microsoft Windows.

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Results

This case–control study included 30 (24 men and six women) patients with cutaneous LP. Thirty (24 men and six women) apparently healthy volunteers served as controls. The demographic and clinical data of the groups studied are shown in Table 1.

Table 1

Table 1

Patients with LP showed a significant association with increased BMI (P=0.01), presence of MetS (P=0.002), diabetes mellitus (P=0.000), and dyslipidemia (P=0.03) compared with the controls (Table 1).

Plasma and tissue OPN levels showed a significant increase in LP patients compared with those of the controls (P<0.001 for each), whereas plasma Se levels showed a significant decrease in the patients compared with those in the controls (P<0.001). Plasma hs-CRP levels showed a significant increase in the patients compared with those of the controls (P<0.001) (Table 2).

Table 2

Table 2

A statistically significant positive correlation was found between levels of plasma OPN and tissue OPN in patients, but not in controls (r=0.366, P=0.04). Significant positive correlations were detected between plasma levels of OPN and FBS (r=0.42, P=0.02) (Fig. 1), insulin levels (r=0.58, P=0.001), and HOMA-IR (r=0.53, P=0.002) in patients, but not in controls. Moreover, plasma OPN showed a significant positive relation with the presence of diabetes mellitus (P=0.01), dyslipidemia (P=0.002) (Fig. 2), and MetS (P=0.008) in patients, but not in controls.

Figure 1

Figure 1

Figure 2

Figure 2

No relation was detected between tissue OPN and demographic data, measured clinical or laboratory parameters, except for a positive correlation with WC (r=0.49, P=0.006), and insulin levels (r=0.39, P=0.02) in patients. Moreover, plasma Se showed a negative correlation only with FBS (r=−0.38, P=0.03). No correlation was detected between plasma OPN and plasma Se in patients or controls.

In patients with LP, we assessed the impact of diabetes, hypertension, dyslipidemia, smoking, obesity, and MetS on the levels of plasma and tissue OPN and plasma Se. The presence of diabetes, dyslipidemia, MetS, and obesity in patients was associated with significantly higher values of OPN in plasma and tissue (Table 3).

Table 3

Table 3

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Discussion

In the present work, we found that plasma and lesional skin levels of OPN were significantly higher in cutaneous LP patients compared with the controls. This is in agreement with the results of previous reports 16,17 that showed significantly increased OPN expression in lesions of oral lichen planus (OLP) patients compared with the control group. They suggested that the production of OPN was associated with the inflammatory process of OLP development, and that it may serve as a potential disease marker of OLP. Moreover, we found a significant positive correlation between the levels of plasma OPN and tissue OPN in patients, but not in controls.

Parallel to our results, previous reports found that patients with psoriasis had higher plasma and tissue concentrations of OPN compared with controls and that elevated plasma OPN was associated significantly with the occurrence of psoriasis 3,6,18. OPN appears to be critical for the maturation and recruitment of dendritic cells (DC), and OPN-activated DCs produce interleukin (IL)-12 and TNF-α, which promote T cells to differentiate toward the T helper (Th)1 type, producing Th1 cytokines (IL-12, IFN-γ). Also, OPN inhibits the production of the Th2 cytokine IL-10, which leads to an enhanced Th1 response 19. This may explain the elevated levels of plasma and tissue OPN in this Th1-mediated disease and may also explain the similar findings of OPN in previous reports in psoriasis.

In the present study, a statistically significant positive correlation was observed between plasma levels of OPN and FBS, insulin, and HOMA-IR in patients, but not in controls, together with a statistically significant positive correlation between tissue levels of OPN and WC and insulin in patients, but not in controls. Moreover, the presence of diabetes, dyslipidemia, and obesity in patients was associated with significantly higher values of OPN in plasma and tissue. OPN was shown to be present in human omental adipose tissue by immunohistochemistry together with increased plasma OPN levels in overweight and obese patients 20. Moreover, OPN may play a key role in linking obesity to the development of insulin resistance by promoting inflammation and the accumulation of macrophages, which are important mediators of insulin resistance, and their recruitment from circulation into adipose tissue during inflammation is dependent on the expression of OPN 4,21. Furthermore, OPN expression in adipose tissue macrophages is enhanced by high glucose and OPN itself activates several inflammatory signaling pathways leading to adipose tissue insulin resistance and type 2 diabetes mellitus; several studies have described OPN as a critical regulator of adipose tissue inflammation, insulin resistance, and diabetes mellitus 22. This may explain the statistically significant positive correlation between OPN and FBS, insulin, and HOMA-IR in these patients.

In the present study, the prevalence of MetS was higher in patients with LP in relation to controls, and LP patients with MetS tended to have significantly higher levels of plasma and tissue OPN compared with patients without MetS. Analysis of MetS parameters showed a higher significant prevalence of dyslipidemia and diabetes mellitus in patients with LP. There were differences in WC and blood pressure between patients and controls, but these were not statistically significant.

Moreover, inflammation plays a very important role in the development of dyslipidemia. Patients with chronic diseases (e.g. systemic lupus erythematous and rheumatoid arthritis) show decreased levels of high density lipoprotein cholesterol and hypertriglyceridemia, with a positive correlation with cytokine levels 23. In agreement with previous reports 24,25, LP was found to be associated with a higher prevalence of dyslipidemia.

Both LP and the MetS are characterized by increases in the immunological activity of type 1 helper T cells. Cytokines such as TNF-α and IL-6 seem to play a central role. TNF-α may lead to insulin resistance by inhibiting insulin-mediated tyrosine phosphorylation of the insulin receptor 26. LP is characterized by the upregulation of inflammatory CXCR3 ligands associated with the recruitment of effector cytotoxic T cells and plasmacytoid DCs 27. Various cytokines including IL-2, IL-4, IL-6, IL-10, TNF-α, IFN-γ, IFN-c, and transforming growth factor-β1 are involved in LP 27,28. These inflammatory processes could potentially explain the link between LP and dyslipidemia, and possibly other components of the MetS, because chronic inflammation has been suggested as a component of the MetS.

Reduced antioxidant levels as a result of extended release of reactive oxygen species such as in chronic inflammation lead to increased oxidative damage 29. In contrast to the results of a previous work 30, we found that plasma Se levels were significantly lower in patients than in the controls. Reduced plasma levels of Se in our patients suggest that free radicals and the resulting oxidative damage might be important in the pathogenesis of LP lesions.

Moreover, plasma hs-CRP levels were significantly higher in patients than in controls, and this is in agreement with previous results 25,31. CRP has been shown to predict CVD events. It is predominantly synthesized in the liver hepatocytes as an acute-phase reactant and is transcriptionally driven by IL-6, with synergistic enhancement by IL-1 and TNF-α, which are key factors in the activation of DCs and T cells, and are also produced in adipose tissue hereby linking inflammation of the skin with obesity 9,10. This may explain the elevated levels of hs-CRP in our patients.

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Conclusion

On the basis of the above, we conclude that OPN might play a role in the pathogenesis of cutaneous LP. OPN may be a critical regulator of chronic inflammation in patients with LP and may explain its association with components of the MetS such as diabetes mellitus and dyslipidemia. We, therefore, recommend screening of plasma OPN, CRP, glucose, and lipids levels in LP patients. This might be useful to detect individuals at risk for CVD and to initiate preventive measures.

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Conflicts of interest

There are no conflicts of interest.

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Keywords:

lichen planus; metabolic syndrome; osteopontin; selenium

© 2017 Egyptian Women's Dermatologic Society