The predictive effects of adiponectin and irisin hormones on diagnosis and clinical involvement of Sarcoidosis

Abstract

Background

Sarcoidosis is a chronic disease of unknown etiology characterised by systemic non-caseating granulomas that can affect any organ in the body, especially the lungs and in which genetic and environmental factors are thought to play a role in its pathophysiology.

Adipokines and myokines secreted from adipose and muscle tissue play a role in the pathogenesis or protection against many inflammatory and autoimmune diseases in which inflammation and immunity form the basis. In our study, we aimed to investigate the role of the irisin and adiponectin in sarcoidosis.

Methods

The study included 90 sarcoidosis patients and 86 healthy subjects. Adiponectin and irisin levels were analysed in addition to standard tests for diagnosis and follow-up of patients with sarcoidosis. The sensitivity and specificity of serum irisin levels for the diagnosis of sarcoidosis were evaluate dusing ROC analysis.

Results

Irisin levels were significantly lower in the patient group than in the control group (3.28–5.25, p < 0.001). There was no association between irisin levels and extrapulmonary involvement. The cut-off irisin value for the diagnosis of sarcoidosis was ≤ 4.2662 with 95% confidence interval, and the sensitivity and specificity were calculated as 84% and 55.8%, respectively.

Conclusions

To our knowledge, this is the first study to investigate irisin in sarcoidosis patients. Based on the available evidence, anti-inflammatory, anti-oxidant and anti-apoptocic effects of irisin may play a role in the pathophysiology of sarcoidosis.

Although no significant difference was found in our study, we believe that a comprehensive evaluation of adiponectin in sarcoidosis is important.

Introduction

Sarcoidosis is a chronic disease characterised by systemic non-caseating granulomas, the etiology and pathogenesis of which are not yet fully known, genetic and environmental factors are thought to play a role in its pathophysiology and it can involve any organ in the body, especially the lungs and lymphatic system [1]. The lungs and intrathoracic lymph nodes are affected in approximately 90% of patients. Peripheral lymph nodes, skin, eyes, liver, spleen, muscles, bones, upper respiratory tract, heart, nerves, urinary system and many other organs may be affected in 10–30% of patients [2].

Sarcoidosis is a systemic disease resulting from complex interactions between immunological, psychological, environmental, hormonal and genetic factors. The clinical presentation of patients can vary from asymptomatic to severe multi-organ involvement. The diagnosis is made by the combined evaluation of clinical, radiological, laboratory and/or histopathological findings. It is difficult to differentiate from other granulomatous diseases and to predict disease progression. Diagnosis can be made approximately 3 months after the onset of symptoms and repeated radiological examinations during this period cause significant radiation exposure.

Considering the radiation risk of radiological images used in the diagnosis and follow-up of sarcoidosis, the importance of peripheral blood biomarkers draws attention. To date, several biomarkers have been investigated to determine the diagnosis, activity and progression of the disease. Biomarkers that are specific and sensitive for sarcoidosis may reduce the number of radiological examinations used in disease management [3].

Several inflammatory cytokines are increased in sarcoidosis and the anti-inflammatory process is suppressed. In most patients, this cytokine release is controlled and spontaneous remission occurs. However, in some patients disease remains stable or progresses.

It is well known that adipose and muscle tissues are not only organs of storage and movement, but also play a role in various physiological or pathological processes through the hormones and cytokines they secrete. Immunological adipokines and myokines secreted by adipose and muscle tissues play a role in the development of many inflammatory and autoimmune systemic diseases in which inflammation and immunity are the basis, or in the prevention and progression of these diseases. Studies have shown that these hormones may play a role in lung diseases such as asthma, chronic obstructive pulmonary disease, lung cancer and sleep apnea, and may be effective in the severity of these diseases [4, 5].

Irisin is a hormone mainly secreted by muscle and adipose tissue and is thought to be primarily induced by exercise. Adiponectin is mainly secreted by adipose tissue and has several anti-inflammatory activities, interfering with macrophage function, inhibiting the production of IL-6 or TNF-α, reducing T-cell function, promoting the release of IL-10 and IL-1 receptor antagonist [6]. This study is the first to evaluate irisin in sarcoidosis and it is one of the few studies to evaluate adiponectin.

The aim of our study was to investigate the role of the hormones irisin and adiponectin in sarcoidosis and to evaluate their relationship in diagnosis, clinical involvement and prediction of disease progression.

Materials and methods

Between March 2022 and March 2023, patients diagnosed with sarcoidosis at the Department of Pulmonary Diseases, were prospectively evaluated.

The study included a total of 90 sarcoidosis patients and 86 healthy subjects. Voluntary patients aged 18 years and older with a diagnosis of sarcoidosis based on clinical, radiological, laboratory, bronchoscopic and/or histopathological findings were accepted into the study. Healthy subjects aged 18 years and older were included as controls. Exclusion criteria for the patient and control groups were: being younger than 18 years of age, having a chronic disease such as cardiovascular disease, diabetes, autoimmune disease and malignancy, being a professional athlete or exercising regularly and receiving treatment for sarcoidosis.

Both the individulas in patient and control groups were informed in detail about the study and their written informed consent was obtained. This study was approved by the Ethics Committee in accordance with the Declaration of Helsinki.

The routine diagnosis and follow-up of parameters of sarcoidosis patients including; demographic information such as age, gender, family history, smoking, physical examination, acute phase reactants (CRP, erythrocyte sedimentation rate), blood cell count, renal function tests (creatinine, urea, BUN), liver function tests (AST, ALT), alkaline phosphotase (ALP), gamma glutamyl transferase (GGT), serum calcium, 24-h urine calcium, vitamin D levels, BCG vaccination, tuberculin skin test (PPD), ACE level, FEV₁/FVC ratio, FEV₁ and FVC ml values, FEV₁ and FVC %, CO diffusion test %, postero-anterior chest radiograph (PA), computed tomography (CT) and bronchoscopic findings were recorded. Patients were assessed for common clinical complaints such as weight loss, weakness, fatigue, loss of appetite, fever and involvement of the respiratory system, skin, eyes and musculoskeletal system.

All patients were classically staged using postero anterior chest radiography. The presence of nodules, ground-glass opacities, parenchymal bands, interlobular septal thickening, subpleural interstitial thickening, traction bronchiectasis, bronchial distortion, cavitation, consolidation and lymphadenopathy on computed tomography were considered abnormal radiological findings.

Study specific non-routine laboratory tests were adiponectin and irisin hormones. For these laboratory tests, venous blood samples were taken from patients and controls. Venous blood samples were centrifuged at 3000 rpm for 10 min and separated into serum. Serum samples were then transferred to eppendorf tubes and stored at -80 °C.

Irisin hormone was analysed by ELISA (Enzyme-Linked Immunosorbent Assay) method using Mybiosource brand Human FGF-23 ELISA kit [MBS765419-96Wells] according to the manufacturer's catalogue.

Adiponectin hormone was analysed by ELISA method using Mybiosource brand Human alpha-klotho ELISA kit [MBS760772-96Wells] according to the manufacturer's catalogue.

IBM SPSS 20.0 (SPSS Inc., Chicago, IL, USA) was used for statistical analysis in this study. Normal distribution was assessed using the Kolmogorov–Smirnov test. Numerical variables with normal distribution were expressed as mean ± standard deviation, numerical variables without normal distribution were expressed as median (min–max), and categorical variables were expressed as frequency (percentage). When the number of groups was two, the difference between groups was determined using the independent groups t-test for numerical variables with normal distribution and the Mann–Whitney U test for numerical variables without normal distribution. When the number of groups was more than two, the difference between groups was determined using the Kruskal–Wallis test for non-normally distributed numerical variables. Associations between categorical variables were assessed using chi-squared analysis. ROC analysis was used to determine reference values for quantitative variables. When testing two-way hypotheses, p < 0.05 was considered sufficient for statistical significance.

Results

A total of 90 sarcoidosis patients and 86 healthy volunteers were included in the study. The mean age of the patient group was 49 ± 10 years and the mean age of the control group was 46 ± 8 years. In the patient group 71.1% (n = 64) and in the control group 83.7% (n = 72) were female. The mean BMI of the patient group was 28.97 ± 5.03 kg/m² and the mean BMI of the control group was 27.04 ± 4.78 kg/m². There was no statistically significant difference in age, gender and BMI between the patient and control groups.

At the diagnostic stage, bronchoscopic mucosa biopsy was performed in 48 (53.3%), excisional biopsy in 20 (22.2%), skin biopsy in 10 (11.1%), EBUS (Endobronchial ultrasound) in 8 (8.9%), open lung biopsy in 6 (6.7%), mediastinoscopy in 6 (6.7%), and other organ biopsies in 4 (6.7%).

A family history of lung disease was present in 66.7% (n = 60) of the patients and 62.8% (n = 54) of the control group. Smoking was present in 22.2% (n = 20) of the patients and 34.9% (n = 30) of the controls. No significant difference was found between the patient and control groups with regard to family history and smoking.

The involvement of the skin was present in 30 (33.3%), eye in 14 (15.6%), musculoskeletal system in 16 (17.8%), cardiovascular system in 2 (2.2%) and gastrointestinal system in 2 (2.2%) patients.

Patients were staged according to chest radiographs. Of the patients, 14 (15.6%) were in stage 0, 30 (33.3%) in stage 1, 28 (31.1%) in stage 2, and 18 (20%) in stages 3 and 4 (Stages 3 and 4 were evaluated together due to the small number of patients at diagnosis).

The median irisin level was 3.28 (2.99–3-98) in the patient group and 5.25 (3.29–9.44) in the control group. The higher irisin level in the control group compared to the patient group was found to be statistically significant (p < 0.001).

The median adiponectin level was 7.57 (6.26–10.12) in the patient group and 10.53 (6.94–20.24) in the control group. There was no statistically significant difference in adiponectin levels between the patient and control groups (p = 0.094).

The distributions of age, gender, BMI, adiponectin and irisin levels, smoking and family history of the patient and control groups are shown in Table 1.

Table 1 Distributions of age, gender, BMI, adiponectin and irisin levels, smoking and family history in the patient and control groups

When irisin levels were compared between the patient and control groups, the median irisin levels were significantly lower in stages 1, 2, 3 and 4 than in the control group, whereas no statistically significant difference was found between stage 0 and the control group (Table 2).

Table 2 Comparison of irisin levels between stages and control group

There was no statistical significance in the comparison of adiponectin levels between the sarcoidosis stages and the control group and between the stages themselves.

Irisin, adiponectin, ACE, blood calcium, bronchoalveolar lavage lymphocyte percentage, CD4/CD8 ratio, FEV₁/FVC, FVC, FVC%, FEV₁, FEV₁%, DLCO% were compared between sarcoidosis stages (Table 3). It was found that there was a statistical difference between blood calcium and DLCO % between sarcoidosis stages. As expected, calcium increased with increasing stage, whereas DLCO percentage decreased with increasing stage. No statistically significant difference was found between sarcoidosis stages and other laboratory parameters such as CRP, haemogram and erythrocyte sedimentation rate.

Table 3 Comparison of laboratory, respiratory function test and BAL findings according to stages

Correlation analysis of irisin and adiponectin levels with age, BMI, ACE, calcium, 24-h urinary calcium, FEV₁/FVC, FVC, FVC%, FEV₁, FEV₁%, bronchoalveolar lavage lymphocyte percentage, CD4/CD8 ratio and DLCO% was performed. A statistically significant correlation was found between irisin and FVC (Table 4).

Table 4 Irisin and adiponectin correlation analysis

When irisin and adiponectin levels were compared according to the reference ranges of CRP, creatine, ACE, 24-h urine calcium, bronchoalveolar lavage lymphocyte percentage, CD4/CD8 ratio and blood calcium, no significant statistical difference was observed between these laboratory values.

When irisin and adiponectin levels were compared with gender, family history, smoking, physical examination, pulmonary function test (PFT) and FOB findings, irisin hormone was found to be significantly higher in females.

Irisin and adiponectin levels were compared with extrapulmonary skin, eye and musculoskeletal involvement and no statistically significant difference was found. Comparison with other extrapulmonary involvement was not possible due to the small number of patients.

The relationship between anergic PPD test and irisin and adiponectin levels was not significantly different.

The sensitivity and specificity of irisin and adiponectin levels in the diagnosis of sarcoidosis were evaluated using ROC analysis between patients and control group. The area under the curve was calculated. An irisin level of ≤ 4.2662 had a sensitivity of 84% and a specificity of 55.8% at 95% confidence interval (Table 5). The ROC curve is shown in Fig. 1. In the analysis of adiponectin, no statistically appropriate cut-off value was found for the diagnosis.

Table 5 ROC analysis data for serum irisin level

Fig. 1

Irisin level ROC analysis

Discussion

In the present study, lower irisin levels were observed in the patient group. In addition to clinical information, low irisin hormone levels may have a potential role in the diagnosis of sarcoidosis, although this requires further validation. To our knowledge, this is the first study to analyse irisin in sarcoidosis patients.

Irisin is a hormone mainly secreted by muscles and is thought to be induced primarily by exercise. Bostrom et al. reported that the expression of FNDC5 mRNA, a precursor of irisin, increased in skeletal muscle after exercise in humans and mice [7]. Some subsequent studies on this topic have reported different results. It is thought that these different results may be due to reasons such as the duration, intensity and type of exercise performed, or the body mass index and gender differences of the people included in the study, whether they were athletes or not [8]. For this reason, we did not include athletes or active exercisers in our patient and control groups and we made sure that there were no differences, such as gender, age or BMI, between our patient and control groups.

Ijiri et al. compared irisin levels between patients with COPD and healthy volunteers. This study showed that COPD patients had lower serum irisin levels before and after exercise compared with healthy controls [9]. Similarly, a study published in 2017 by Sugiyama et al. found that the amount of emphysema in COPD patients was associated with lower irisin levels [10]. Kubo et al. reported that irisin secreted into muscle after exercise can improve cigarette smoke-induced emphysema and may be used as a new treatment [11]. The basic pathogenesis of COPD involves an oxidant-antioxidant and protease-antiprotease imbalance. Studies have reported that irisin may have both anti-inflammatory effects against inflammation underlying COPD and protective effects against inflammation-induced apoptosis [12,13,14].

In the study by Sun et al. irisin was shown to improve the overall condition of mice with induced asthma and suppressed inflammatory cells in serum and bronchial lavage fluid. This study stated that irisin, with its current anti-inflammatory effect, may be a potential agent to be used in the treatment of asthmatic patients [15].

There are several studies showing the relationship between irisin, which has been shown to have a protective effect against many diseases including various malignancies and lung cancer. In a study by Shao et al. irisin was shown to reduce proliferation, invasion and migration of lung cancer cells [16]. In a study published in 2020 by Fan et al., FNDC5, a precursor of irisin, was found to downregulate multidrug resistant protein 1 (MDR1) and increase paclitaxel sensitivity by blocking NF-KB activation [17].

Uncontrolled inflammation is an important pathological mechanism in the development of lung fibrosis. Irisin is thought to protect patients with ALI (Acute lung injury) and ARDS (Acute respiratory distress syndrome) from excessive inflammation and subsequent fibrosis [18].

Irisin is essentially a myokine that is secreted by exercise induction. Several studies have shown that regular exercise reduces mortality, improves symptoms and reduces acute exacerbations in diseases where fibrosis is predominant, such as idiopathic pulmonary fibrosis (IPF). During our review of the literature, we found only one study that assessed irisin levels in patients with IPF and analysed irisin, omentin and visfatin before and after lung transplantation [19,20,21,22].

During COVID-19 infection, excessive cytokine release is the main cause of mortality. There are studies showing that exercise protects against COVID-19 infection and is associated with a good prognosis In addition, studies have shown that exercise may be useful as a treatment for COVID-19 infection [23, 24]. This positive association between COVID-19 and exercise may be due to irisin. A study by Alves et al. found that irisin may be a potential agent in the prevention of complications related to COVID-19 [25].

Díaz et al. reported that myokines, which enter the bloodstream during exercise and muscle contraction by an unknown mechanism, may be beneficial in autoimmune diseases [26]. Similarly, there are studies suggesting that exercise is beneficial for patients with diseases with immunopathology partially similar to sarcoidosis, such as idiopathic inflammatory myopathy, rheumatoid arthritis, systemic lupus erythematosus [23, 24]. In our study, as in other diseases where inflammation is the main pathology, irisin was found to be lower in the patient group.

In the study by Ochman et al., which included 23 patients, no statistically significant difference was found between irisin levels and lung function parameters [27]. Similarly, in our study, no significant difference was found with other parameters except for the correlation between FVC and irisin.

One of the aims of our study was to investigate the role of irisin hormone in predicting clinical involvement and progression. In patients with sarcoidosis, it is known that remission rates decrease with increasing stage and that clinical progression worsens with increasing stage. In our study, we compared stage and irisin hormone at the time of diagnosis in previously untreated patients, but we found no correlation between stages and irisin hormone. Similarly, there was no statistically significant difference between extrapulmonary involvement and irisin.

Adipokines are thought to have two different functions. The first is the local regulation of metabolic activities such as energy storage in adipose tissue, lipolysis, lipogenesis and glycolysis, the second is the systemic regulation of appetite, levels of immune response and inflammation [28, 29].

Although other adipokines synthesised from adipose tissue are generally known to be pro-inflammatory, adiponectin has several anti-inflammatory activities, mainly by interfering with macrophage functions, inhibiting IL-6 or TNFα production, reducing T-cell functions, promoting IL-10 and IL-1 receptor antagonist release. Adiponectin, like irisin, is thought to exert some of its anti-inflammatory effects through this pathway by inhibiting NF-KB [30].

Adiponectin levels have been shown to be increased in diseases in which chronic inflammation and autoimmunity play a role in the pathogenesis, such as systemic lupus erythematosus, sjögren disease and scleroderma [6, 31].

In a study by Toussirot et al., adiponectin was analysed along with other adipokines in female patients with systemic autoimmune disease and adiponectin was found to be higher in the patient group than in the control group [4]. In a study by Neumann et al., it was shown that in systemic sclerosis and idiopathic pulmonary fibrosis, adiponectin levels increased at the onset of the disease, fibrosis occurred and inflammation decreased and adiponectin decreased in the last periods [32]. A study by Enomo et al. reported that adiponectin increased in acute exacerbation of idiopathic pulmonary fibrosis and correlated with inflammatory markers. It has also been reported that adipokines may play a role in the regulation of inflammation and fibrosis via the PPARγ pathway [33, 34].

In the studies conducted between adiponectin and systemic autoimmune diseases, there was no difference between the patient and control groups in terms of BMI, gender and age, as in our study [35].

In a study by Zielinski et al., adipokines were analysed in patients with sarcoidosis and idiopathic interstitial pneumonia [35]. In a study conducted in 44 patients with sarcoidosis, higher adiponectin levels were found in patients with sarcoidosis, similar to the study by Zielinski et al. In this study, elevated adiponectin levels were found to be associated with arthralgia and ankle swelling, whereas in our study no association was found between clinical involvement and adiponectin levels [5]. Contrary to these studies, there are also studies showing that adiponectin levels are similar in connective tissue diseases and control groups [36]. In our study, there was no statistical difference in adiponectin levels between the patient and control groups.

Adiponectin hormone has been shown to inhibit many cytokines involved in inflammation underlying sarcoidosis in several autoimmune and inflammatory diseases. It is also involved in the regulation of fibrosis and inflammation.

The fact that adiponectin was found at similar levels to the control group in our study may be due to the fact that it has a strong anti-inflammatory effect and is inhibited by pro-inflammatory cytokines in sarcoidosis. Although no significant difference was found in our study, we believe that a thorough evaluation of adiponectin in sarcoidosis is important.

Biomarkers such as angiotensin-converting enzyme (ACE), chitotriosidase (CTO), lysozyme, neopterin, and serum soluble interleukin-2 receptor (SIL-2R) have been most frequently studied in patients with sarcoidosis. Among these, ACE is the most widely used biomarker. It plays a crucial role in the diagnosis and assessment of activity in sarcoidosis patients. ACE levels are elevated in 30–80% of untreated sarcoidosis patients. Sensitivity from 22 to 86% and specificity between 54 and 95% [37, 38]. In our study, the sensitivity of irisin was determined to be 84%, with a specificity of 55.8%; however, an appropriate cut-off value for adiponectin could not be established. Most studies have reported that high ACE levels correlate with systemic involvement, disease activity, and stage; conversely, our study found no significant associations between ACE, irisin, or adiponectin levels and extrapulmonary involvement or disease stages.

This study has several limitations. First, it is a single-centre study with a relatively small sample size. As a single-centre study, it focuses on a specific patient population, making it challenging to generalize the results to other geographical or demographic groups. This may limit the applicability of the findings to a broader population. To ensure wider generalizability, it is important to validate these findings in larger, multicentre studies across different populations. This approach would not only enhance the generalizability of the results but also provide a more comprehensive understanding of the role of adiponectin and irisin across various region different patient populations. In addition, due to the limited number of patients, the number of patients with some extrapulmonary involvement was found to be very low and meaningful statistical analysis could not be performed. The second and most significant limitation is that adiponectin and irisin hormone levels were not analyzed during and after follow-up. Studying these hormones in relation to clinical status, spontaneous remission, the need for treatment, and post-treatment periods could provide a better understanding of the underlying pathophysiology and mechanisms.

Despite these limitations, a notable strength of this study is that it is the first in the literature to evaluate the relationship between irisin and sarcoidosis.

Conclusion

It is suggested that irisin and adiponectin hormones play a significant role in diseases characterized by oxidative stress and inflammation, and they may serve as potential biomarkers for diagnosis, treatment, and possibly prevention. In addition to the studies already conducted, more long-term studies with a high level of evidence are needed.