Scleroderma-related lung disease: are adipokines involved pathogenically?

Linking Adiposity to Interstitial Lung Disease: The Role of the Dysfunctional Adipocyte and Inflammation

Adipose tissue has functions beyond its principal functions in energy storage, including endocrine and immune functions. When faced with a surplus of energy, the functions of adipose tissue expand by mechanisms that can be both adaptive and detrimental. These detrimental adipose tissue functions can alter normal hormonal signaling and promote local and systemic inflammation with wide-ranging consequences. Although the mechanisms by which adipose tissue triggers metabolic dysfunction and local inflammation have been well described, little is known about the relationship between adiposity and the pathogenesis of chronic lung conditions, such as interstitial lung disease (ILD). In this review, we detail the conditions and mechanisms by which adipose tissue becomes dysfunctional and relate this dysfunction to inflammatory changes observed in various forms of ILD. Finally, we review the existing basic and clinical science literature linking adiposity to ILD, highlighting the need for additional research on the mechanisms of adipocyte-mediated inflammation in ILD and its clinical implications.

An Increase in Plasma Adipsin Levels Is Associated With Higher Cumulative Dust Exposure and Airway Obstruction in Foundry Workers

OBJECTIVE

The aim of the study was to assess whether plasma adipokine levels (adipsin, adiponectin, leptin, and resistin) are associated with pulmonary function in foundry workers.

METHODS

We examined 65 dust-exposed foundry workers and 40 nonexposed controls and analyzed their lung function and plasma adipokine levels at baseline and after approximately 7 years of follow-up.

RESULTS

A higher increase in plasma adipsin was associated with the development of airway obstruction in exposed subjects during follow-up after adjusting for body mass index changes during the follow-up period. Furthermore, the increase in adipsin levels was positively associated with cumulative dust exposure even after adjusting for smoking and body mass index changes during follow-up ( P = 0.015).

CONCLUSION

The results suggest that plasma adipsin is involved in the pathogenesis of subclinical airway inflammation and the development of chronic obstruction and is induced by occupational dust exposure.

Diagnosis of Fibrotic Hypersensitivity Pneumonitis: Is There a Role for Biomarkers?

Hypersensitivity pneumonitis is a complex interstitial lung syndrome and is associated with significant morbimortality, particularly for fibrotic disease. This condition is characterized by sensitization to a specific antigen, whose early identification is associated with improved outcomes. Biomarkers measure objectively biologic processes and may support clinical decisions. These tools evolved to play a crucial role in the diagnosis and management of a wide range of human diseases. This is not the case, however, with hypersensitivity pneumonitis, where there is still great room for research in the path to find consensual diagnostic biomarkers. Gaps in the current evidence include lack of validation, validation against healthy controls alone, small sampling and heterogeneity in diagnostic and classification criteria. Furthermore, discriminatory accuracy is currently limited by overlapping mechanisms of inflammation, damage and fibrogenesis between ILDs. Still, biomarkers such as BAL lymphocyte counts and specific serum IgGs made their way into clinical guidelines, while others including KL-6, SP-D, YKL-40 and apolipoproteins have shown promising results in leading centers and have potential to translate into daily practice. As research proceeds, it is expected that the emergence of novel categories of biomarkers will offer new and thriving tools that could complement those currently available.

Role of adipokines in systemic sclerosis pathogenesis

Systemic sclerosis (SSc) is a chronic autoimmune connective tissue disease with manifestations in multiple organs, including the skin, lung, heart, joints, gastrointestinal tract, kidney, and liver. Its pathophysiology is characterized by inflammation, fibrosis, and vascular damage, with an increased expression of numerous cytokines, chemokines, and growth factors. However, besides these growth factors and cytokines, another group of molecules may be involved in the pathogenesis of SSc: the adipokines. Adipokines are proteins with metabolic and cytokine-like properties, which were originally found to be expressed by adipose tissue. However, their expression is not limited to this tissue, and they can also be found in other organs. Therefore, this review will describe the current knowledge regarding adipokines in the context of SSc and try to elucidate their potential role in the pathogenesis of SSc.

Analysis of serum adiponectin and leptin in patients with acute exacerbation of idiopathic pulmonary fibrosis

Weight loss progresses with the progression of idiopathic pulmonary fibrosis (IPF), and acute exacerbation of IPF (AE-IPF) frequently occurs in its advanced stage. Adiponectin and leptin are adipokines produced from adipose tissue, and are related to thinness and obesity, respectively. Additionally, these adipokines are implicated in the regulation of inflammation and fibrosis centering on peroxisome proliferator-activated receptor γ (PPARγ). However, the relationship between adiponectin/leptin and AE-IPF remains poorly known. We conducted this study to evaluate levels of serum adiponectin/leptin, and to elucidate the clinical importance of adiponectin and leptin in patients with AE-IPF. Thirty-two patients (39 episodes) who were diagnosed with AE-IPF at our hospital from 1997 to 2016 were retrospectively studied. Serum adiponectin and leptin concentrations were measured with enzyme-linked immunosorbent assay. Patients with AE-IPF showed higher levels of serum adiponectin and leptin than those at initial diagnosis of IPF (p = 0.007 and p = 0.027, respectively). Serum adiponectin/leptin (A/L) ratio was negatively correlated with body mass index at AE-IPF (r = -0.456, p = 0.003) and PaO₂ before AE-IPF (r = -0.498, p = 0.034), and positively correlated with C-reactive protein at AE-IPF (r = 0.316, p = 0.049). Patients with higher A/L ratios had worse survival than those with lower A/L ratios (log-rank, p = 0.026). Further, in multivariate analysis, serum A/L ratio was a significant prognostic factor in patients with AE-IPF (HR 2.60, p = 0.042). In conclusion, the higher adiponectin/leptin ratio may be associated with a poor prognosis in patients with AE-IPF.

Adipokine expression in systemic sclerosis lung and gastrointestinal organ involvement

OBJECTIVES

The immunomodulatory properties of adipokines have previously been reported in autoimmune disorders. Less is known about the role of adipokines in systemic sclerosis (SSc). Lung and gastrointestinal tract are frequently involved in SSc; therefore, these organs were analyzed for adipokine expression as well as pulmonary samples of patients suffering from idiopathic pulmonary fibrosis (IPF) as comparison.

METHODS

Gastric samples (antrum, corpus) of SSc were analyzed immunohistochemically for adiponectin, resistin and visfatin compared with non-SSc related gastritis. Inflammatory cells were quantified in gastric samples and correlated with adipokine expression. Lung samples of SSc, IPF and healthy controls were also analyzed. Protein levels of lung tissue lysates and bronchoalveolar lavages (BAL) in minor fibrotic stages were measured by ELISA.

RESULTS

Lung sections of donor parenchyma showed significantly stronger adiponectin signals as IPF and SSc (donor vs. IPF: p < 0.0001). In SSc and IPF, resistin and visfatin were increased within immune cell infiltrates, but overall no difference in expression for resistin or visfatin compared to controls was observed. In BAL and lung protein lysates of early stages of fibrosis, adiponectin and visfatin were not reduced in IPF and SSc compared to controls. In gastric samples collected by standard endoscopic gastric biopsy, adiponectin was also significantly reduced in SSc- compared to non-SSc gastritis (p = 0.049) while resistin and visfatin were comparable although deeper fibrotic layers were not included in the respective samples. Adiponectin-positive tissues showed higher amounts of CD4⁺ but not CD8⁺ T cells. Controls showed no correlation between CD4⁺ T cells and resistin, whereas SSc showed significantly more CD4⁺ T cells in resistin-negative tissues.

CONCLUSION

Adipokines are expressed in gastric and lung samples of patients with SSc and in lung samples affected by IPF. Prominently, adiponectin levels were reduced in fibrotic SSc gastritic tissue as well as in IPF and SSc lung tissue. Consequently, adiponectin expression seems to be associated with fibrotic progression in the context of SSc and IPF.