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ORIGINAL ARTICLE
Ahead of print publication  

Serum Adipokine leptin levels in systemic lupus erythematosus patients and its correlation with clinical manifestations and disease activity – A cross-sectional study from a tertiary care center


1 Department of Rheumatology, Institute of Rheumatology, Madras Medical College; Department of Rheumatology, Sri Ramachandra Medical College and Research Institute, Chennai, Tamil Nadu, India
2 Department of Rheumatology, Institute of Rheumatology, Madras Medical College, Chennai, Tamil Nadu; Department of Rheumatology, Kerala Institute of Medical Sciences, Trivandrum, Kerala, India
3 Department of Rheumatology, Institute of Rheumatology, Madras Medical College, Chennai, Tamil Nadu, India
4 Department of Rheumatology, Institute of Rheumatology, Madras Medical College; Department of Rheumatology, Apollo Hospital, Chennai, Tamil Nadu, India

Correspondence Address:
Saranya Chinnadurai,
No: 1, 7th Cross Street, Near LIC Colony, Anna Nagar, Pammal, Chennai 70, Tamil Nadu
India
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/injr.injr_6_20

  Abstract 


Background: Leptin is an adipokine that has an important role in body weight regulation and endocrine function. Leptin also acts as a pro-inflammatory cytokine by inducing the production of Th1 cytokines. The aim of our study was to estimate the serum leptin levels in systemic lupus erythematosus (SLE) patients and analyze its associations with clinical manifestations of lupus and disease activity.
Materials and Methods: This study was conducted on 80 patients who satisfied Systemic Lupus International Collaborating Clinics 2012 criteria for SLE and 40 healthy controls. Demographic, clinical, and laboratory parameters were recorded. SLE disease activity index (SLEDAI) was scored for all SLE patients. Serum leptin levels (ng/dl) were estimated by enzyme-linked immunosorbent assay and the results were analyzed by SPSS.
Results: Baseline characteristics were comparable in both cases and controls. SLE patients had higher serum leptin levels as compared to controls (mean 16.01 vs. 5.86 ng/ml) which were statistically significant (P < 0.00001). Cutaneous lupus (85%) was the most common manifestation observed in patients with elevated leptin levels. Patients with lupus nephritis had high serum leptin levels (P = 0.04) in comparison to patients with nonrenal lupus. Serum leptin levels correlated positively with higher body mass index (BMI), higher uric acid levels, and lower high-density lipoproteins (HDL) cholesterol levels (P < 0.0001). Serum leptin levels showed no correlation with disease activity markers such as erythrocyte sedimentation rate, C-reactive protein, anti-double-stranded deoxyribonucleic acid titers, complements C3 and C4, and SLEDAI.
Conclusion: Patients with SLE had high serum leptin levels. High leptin levels were seen predominantly in mucocutaneous lupus and lupus nephritis. Serum leptin levels correlated positively with BMI and serum uric acid and negatively with serum HDL cholesterol levels but showed no correlation with disease activity markers.

Keywords: Adipokines, cutaneous lupus, cytokines, lupus, lupus nephritis



How to cite this URL:
Balaji C, Chinnadurai S, Bhuvanesh M, Ramesh R, Sriram S, Rajeswari S. Serum Adipokine leptin levels in systemic lupus erythematosus patients and its correlation with clinical manifestations and disease activity – A cross-sectional study from a tertiary care center. Indian J Rheumatol [Epub ahead of print] [cited 2020 Jun 2]. Available from: http://www.indianjrheumatol.com/preprintarticle.asp?id=282102




  Introduction Top


Adipose tissue which was once considered as inert is now being increasingly implicated as an organ that has an important role in immunity and inflammation.[1] Adipocytes in the adipose tissue secrete adipokines, cytokines, and chemokines. Adipokines such as leptin, resistin, visfatin, and adiponectin are a group of proteins released from adipocytes. These adipokines have various diverse physiological and pathological links with insulin sensitivity, appetite, satiety, atherosclerosis, bone metabolism, reproductive function, immunity, and inflammation.[2] Many studies have implicated the role of adipokines in rheumatological diseases.

Leptin is derived from the Greek word “Leptos” which means thin.[3] Leptin is a 167-amino acid peptide with a four-helix bundle motif similar to interleukin (IL)-12 which is cleaved to give mature human leptin. Leptin is a 16 kDa nonglycosylated polypeptide present predominantly in adipocytes.[4] It is also detected at lower levels in the chondrocytes, placenta, cartilage and bone cells, immune cells, pituitary, hypothalamus, stomach, intestine, muscle, and mammary epithelium.[5],[6],[7],[8],[9],[10],[11] Leptin deficiency has been associated with an increased susceptibility to infection. Leptin has an important role in both innate and acquired immune systems. Leptin promotes chemotaxis and activates neutrophils and natural killer cells. Leptin activates monocytes and macrophages to produce pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha) and IL-6. Leptin also induces phagocytosis and also plays a role in the expression of Type 2 cyclooxygenase. Leptin induces activation and proliferation of naive T-cells, by the production of IL-2. Leptin activates T-lymphocytes and induces the production of Th1 cytokines.[12],[13],[14] The leptin levels in adipose tissue and serum have found to be elevated after the administration of inflammatory stimuli such as lipopolysaccharide.[15],[16] In animal models of lupus, genetic deficiency of leptin protected mice from systemic lupus erythematosus (SLE) and also reduced the production of autoantibodies and renal disease. Exogenous administration of leptin promoted an acceleration of the autoimmune disease and leptin blockade protected from autoimmunity in animal studies.[17] Leptin as a proinflammatory cytokine is being associated with inflammation in SLE. Several studies have reported increased leptin levels in SLE patients.[18],[19],[20]

The aim of our study was to evaluate the serum leptin levels in SLE patients and compare them with healthy controls and also analyze its possible correlation with clinical manifestations, laboratory parameters, and disease activity in SLE patients.


  Materials and Methods Top


Study design

This was a cross-sectional study done between December 2014 and February 2015. Patients who satisfied Systemic Lupus International Collaborating Clinics 2012 classification criteria for SLE were included in this study. Patients with overlap syndrome, mixed connective tissue disease, undifferentiated connective tissue disease with lupus-like features, age <18 years, pregnant women, and body mass index (BMI) >30 kg/m2 were excluded from this study. Healthy controls were age and sex matched, recruited from among healthy individuals attending the outpatient master health checkup clinics. All of the controls recruited had no previous history of medical illness or surgical illness or any autoimmune illness and were not related to the patients.

A detailed history was obtained. A complete clinical examination was done for all the patients. BMI = weight in kg/height in m2 was recorded for all patients and controls enrolled in this study. Routine laboratory investigations included erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), quantitative determination of anti-double-stranded deoxyribonucleic acid (anti-dsDNA) antibodies, quantitative determination of serum complements C3 and C4, serum creatinine, serum uric acid, serum fasting lipids–total cholesterol, serum triglycerides (TGLs), and high-density lipoproteins (HDLs) cholesterol. Disease activity was assessed using the SLE disease activity index (SLEDAI) 2K. SLEDAI was scored based on the presence or absence of manifestations within the past 30 days of the evaluation.[21]

Five milliliter of fasting venous blood sample was collected from all patients and controls. Sera were separated and the sample was stored at −80°C till the analysis. Serum Leptin levels were estimated by indirect enzyme-linked immunosorbent assay (ELISA) using commercial ELISA kit-DIAsource Leptin-ELISA Kit, Belgium-KAP2281, in all cases and controls. Serum leptin levels were estimated in ng/ml.

Normal or elevated levels were determined as per the BMI chart as per the instructions given in the DIAsource Leptin-ELISA Kit KAP2281 as mentioned below in [Table 1] and [Table 2].
Table 1: Normal range of serum leptin levels as per BMI (DIAsource Leptin-ELISA Kit)

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Table 2: Normal range of serum leptin levels as per BMI (DIAsource Leptin-ELISA Kit)

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Ethical approval

Informed consent was obtained from all the SLE patients and controls after the explanation of the purpose of the study. Our study protocol was approved by the institutional ethical board.

Statistical analysis

All statistical analyses were performed using the Statistical Package for the Social Sciences (SPSS) version 23 (Armonk, NY, USA, IBM Corp). Proportions were computed for discrete data. Mean and standard deviation were used for continuous data. The student's t-test was used for independent samples. For comparing categorical data, Chi-square test was performed. Linear correlations were calculated by Pearson's correlation coefficient. For all statistical evaluations, P < 0.05 was considered statistically significant.


  Results Top


During the study period, we recruited 80 consecutive patients of SLE who satisfied the inclusion criteria. [Table 3] compares demographics and BMI of SLE patients and healthy controls.
Table 3: Comparison of demographics and body mass index in systemic lupus erythematosus patients and healthy controls

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Comparison between SLE patients (n = 80) and controls (n = 40) showed that the mean ages of SLE patients (33.4 ± 7.6 years) and controls (34.3 ± 6.9 years) were similar. Furthermore, the male-to-female ratios in SLE patients (1:12) and controls (1:12) were similar. The mean disease duration in patients with SLE in this study was <5 years. The mean BMIs of SLE patients (20.6 ± 2.4 kg/m2) and controls (19.9 ± 2.3 kg/m2) were also similar and within the normal range.

[Table 4] and [Figure 1] show a comparison of serum leptin levels in patients with SLE and healthy controls. Serum leptin levels were significantly higher in SLE patients compared to healthy controls (mean 16.01 ± 10.74 versus 5.86 ± 3.17 ng/ml., P < 0.00001). [Figure 2] shows that 61 (76%) of 80 SLE patients had elevated serum leptin levels in comparison to 1 (2.5%) of 40 healthy controls.
Table 4: Comparison of serum leptin levels in systemic lupus erythematosus patients and healthy controls

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Figure 1: Comparison of serum leptin levels in systemic lupus erythematosus patients and healthy controls

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Figure 2: Comparison of number of patients with elevated leptin levels in systemic lupus erythematosus patients and healthy controls

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In our study, patients with SLE had one or more of the following manifestations: mucocutaneous, musculoskeletal, hematological, lupus nephritis, neuropsychiatric, and secondary antiphospholipid antibody syndrome. [Figure 3] shows clinical manifestations in SLE patients with elevated serum leptin levels. Mucocutaneous manifestation (n = 68, 85%) was the most common clinical manifestation in SLE patients with elevated serum leptin levels in this study. This was followed by musculoskeletal manifestations (n = 48, 55%), lupus nephritis (n = 25, 32%), and hematological manifestations (n = 23, 28%). The least common clinical manifestations were neuropsychiatric manifestations (n = 16, 20%) and secondary antiphospholipid antibody syndrome (n = 1, <1%).
Figure 3: Clinical manifestations in systemic lupus erythematosus patients with elevated leptin levels

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[Figure 4] compares serum leptin levels in renal and nonrenal lupus patients. Twenty-five (89%) of 28 patients with lupus nephritis had elevated serum leptin levels in comparison to 36 (69%) of 52 patients with nonrenal manifestations of lupus which was statistically significant (P = 0.04).
Figure 4: Comparison of serum leptin levels in renal and nonrenal lupus

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[Table 5] shows correlation of serum leptin levels with BMI, laboratory parameters and SLEDAI using Pearson correlation coefficient. Significant statistical correlations were found between serum leptin levels, BMI, serum uric acid, and serum HDL cholesterol. However, no significant statistical differences were found regarding serum total cholesterol (P = 0.041), serum TGL (P = 0.159), ESR (P = 0.902), CRP (P = 0.399), anti-dsDNA titres (P = 0.155), serum complements C3 (P = 0.262) and C4 (P = 0.724), and SLEDAI (P = 0.427).
Table 5: Correlation of serum leptin levels with body mass index, laboratory parameters and systemic lupus eythematosus disease activity index

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  Discussion Top


SLE is an autoimmune multisystem connective tissue disease characterized by systemic inflammation. Several cytokines including IL-2, IL-4, IL-6, interferon gamma, and TNF-alpha and adipokines such as leptin, adiponectin, resistin, and visfatin have been found to be elevated in SLE. Leptin is a pro-inflammatory adipokine that could contribute to inflammation in rheumatological diseases such as SLE. Leptin promotes SLE by increasing autoantibody production and inhibiting immune regulation. Leptin has also been linked with the promotion of metabolic syndrome and accelerated atherosclerosis in SLE patients.[22]

In our study, serum leptin levels in 80 patients with SLE were compared to those of 40 healthy age-, sex-, and BMI-matched controls, and we found that the serum leptin levels were significantly higher in SLE patients in comparison to the healthy controls (mean: 16.01 vs. 5.86 ng/ml., P < 0.00001).

Similar to our study, elevated serum leptin levels in SLE patients in comparison to healthy controls have been observed in studies done by Kim et al.[23] in 70 SLE patients and 39 healthy controls, Garcia-Gonzalez et al.[24] in 41 SLE patients and 23 healthy controls, Chung et al.[25] in 109 SLE patients and 78 healthy controls, Barbosa et al.[26] in 52 SLE patients and 33 healthy controls, and Mohammeda et al.[27] in 40 SLE patients and 20 healthy controls.

However, a study done by Wisłowska et al.[28] found no difference in serum leptin levels between 60 SLE patients and 30 healthy controls. Reagan et al.[29] studied 35 SLE and 35 non-SLE patients and found that serum leptin levels in the SLE group were higher than the non-SLE group but showed no statistical significance.Contrary to the above studies, De Sanctis et al.[30] observed significantly lower serum leptin levels in patients with SLE than healthy controls.

Meta-analysis done by Olazagasti et al.[31] and Lee and Song[32] concluded that in various studies, serum leptin levels were elevated in SLE patients. However, in a meta-analysis done by Li et al.,[33] they concluded that the various studies related to serum leptin levels in SLE patients did not show significant differences compared with healthy controls.

The clinical manifestations and disease activity markers in patients with SLE are usually associated with the change in cytokine mileu. Hence, we investigated the possible association between clinical manifestations and disease activity and serum leptin levels in our study. In our study, we observed that mucocutaneous manifestations such as malar rash, discoid rash, and alopecia were the most common clinical manifestations in patients with elevated serum leptin levels followed by musculoskeletal manifestation such as polyarthritis and hematological manifestations such as autoimmune hemolytic anemia, leucopenia, and thrombocytopenia. We also observed that patients with renal lupus frequently had higher serum leptin levels than those without renal involvement. Neuropsychiatric manifestations and secondary antiphospholipid antibody syndrome were the least common manifestations associated with elevated serum leptin levels in our study. Kim et al.[23] observed higher serum leptin levels in SLE patients with mucocutaneous, musculoskeletal, and renal lupus which was very similar to the observations made by in our study. Wisłowska et al.[28] found significantly lower serum levels of leptin in patients with arthritis (contrary to our study) and central nervous system involvement (similar to our study). Barbosa et al.[26] observed a significant correlation between renal lupus and leptin levels similar to our study and concluded that renal involvement was the only clinical manifestation associated with increased serum leptin levels in their study.

SLE patients in our study had a mean BMI of 20.6 kg/m2. Patients with higher BMI had elevated serum leptin levels. We also observed that SLE patients with elevated serum leptin levels had lower HDL cholesterol levels. However, there was no correlation between serum leptin levels and serum TGL and serum total cholesterol levels in our study. Similar observations were made in a study by Barbosa et al.[26] where they concluded that serum leptin levels correlated with BMI and HDL cholesterol but not low-density lipoproteins (LDLs) cholesterol or TGL in their SLE patients. On the contrary, Chung et al.[25] observed that serum leptin levels correlated significantly with BMI, total cholesterol, LDL cholesterol, and TGL. Wisłowska et al.[28] also found no correlation between serum leptin levels, total cholesterol, TGL, HDL, and LDL cholesterol. We also observed a correlation between elevated leptin levels and serum uric acid levels which was not observed in any of the above studies.

There was no correlation observed between serum leptin levels and disease duration of our patients. In our study, we did not find any significant correlation between serum leptin levels and ESR, CRP, anti-ds DNA titers, complements C3 and C4, and SLEDAI 2K which are the usual disease activity markers in SLE patients. This lack of correlation between disease activity markers and serum leptin levels was also observed in many other studies.[34] Barbosa et al.[26] and Gordeladze et al.[35] also observed no correlation between serum leptin levels and anti-dsDNA levels, which was similar to our study. However Vadacca et al.[18] observed a correlation between leptin levels and SLEDAI in SLE patients.

The limitations of our study were the paucity of a larger cohort of SLE patients and comparison with patients with other rheumatic diseases to make a stronger conclusion. We could not assess the role of leptin in both steroid naïve and immunosuppressant naïve and active and inactive groups of SLE patients.


  Conclusion Top


Patients with SLE had elevated serum leptin levels in comparison to healthy controls. Mucocutaneous lupus was the most common manifestation associated with elevated leptin levels. Patients with renal lupus had elevated leptin levels in comparison to patients with nonrenal lupus. Elevated leptin levels correlated significantly with BMI, HDL cholesterol, and uric acid. Serum leptin levels showed no correlation with disease activity markers.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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