Background:Fibroblast-to-myofibroblast transition is one of the fundamental steps involved in the fibrotic process that characterise systemic sclerosis (SSc) [1]. Myofibroblasts are α-smooth muscle actin (αSMA) positive cells that contribute to fibrosis through the excessive synthesis and deposition of extracellular matrix (ECM) proteins, primarily fibronectin (FN) and type I collagen (COL1) [2].Among the cells involved in the fibrotic process of SSc, circulating fibrocytes seem to have an emerging role as an important source of fibroblasts and myofibroblasts [3].Nintedanib is a tyrosine kinase inhibitor approved for the treatment of idiopathic pulmonary fibrosis that interferes with the signalling pathways involved in the pathogenesis of fibrosis (4). Nintedanib was recently demonstrated to have a beneficial effect in patients with interstitial lung disease (ILD) associated with SSc (5).Objectives:To investigate nintedanib effect in inhibiting the in vitro transition of circulating SSc fibrocytes into myofibroblasts and their pro-fibrotic activity.Methods:Circulating fibrocytes were obtained from 14 SSc patients (mean age 64±14 years), who fulfilled the 2013 ACR/EULAR criteria for SSc and that underwent complete disease staging in a day-hospital setting at the Rheumatology Division of Genoa University. Five age-matched healthy subjects (HSs) were also analysed. All SSc patients and HSs signed the informed consent and the local EC approved the study. Peripheral blood mononuclear cells were isolated by density gradient centrifugation and plated on FN-coated dishes. After overnight culture, non-adherent cells were removed, and adherent cells were maintained in growth medium for 8 days (T8) to obtain fibrocytes [6]. T8-cultured SSc fibrocytes were maintained in growth medium (untreated cells) or treated with nintedanib 0.1μM and 1μM for 3 and 24 hours. Fibroblast specific protein-1 (S100A4) and αSMA, as markers of fibroblast/myofibroblast phenotype, together with COL1 and FN, were investigated by qRT-PCR and Western blotting. Non-parametric Mann-Whitney and Wilcoxon tests were used for the statistical analysis.Results:Significantly elevated gene and protein expressions of αSMA, S100A4, COL1 and FN were observed in SSc fibrocytes compared to HS fibrocytes (gene: αSMA p<0.001; others p<0.0001; protein: all p<0.05). In accordance with the antibody positivity for Scl70 and the presence or absence of ILD at CT scan, SSc patients were grouped as either Scl70 positive patients with ILD (Scl70+ILD+) or Scl70 negative patients without ILD (Scl70-ILD-). Significant αSMA, S100A4, COL1 and FN gene expressions were found in fibrocytes from Scl70+ILD+ compared to HS fibrocytes (αSMA p<0.001; others p<0.0001). Moreover, fibrocytes from Scl70+ILD+patients showed a more significant gene expression of fibroblasts/myofibroblasts markers compared to Scl70-ILD-patients (p<0.01 for S100A4), whereas no differences were observed for ECM gene expression.Nintedanib reduced the gene and protein expression of αSMA, COL1 and FN in SSc fibrocytes compared to untreated ones with different statistical significance.Noteworthy, nintedanib significantly downregulated αSMA, S100A4, COL1 and FN gene expression (all p<0.05) in Scl70+ILD+fibrocytes, whereas only that of S100A4 and FN was significantly downregulated (p<0.05) in Scl70-ILD- fibrocytes compared to untreated cells.Conclusion:Nintedanib seems to downregulate in vitro the transition of fibrocytes into myofibroblasts and their pro-fibrotic activity, particularly in cells isolated from Scl70+ILD+SSc patients.References:[1]Cutolo M et al. Exp Rev Clin Immunol. 2019;15:753-64.[2]Van Caam A et al. Front. Immunol. 2018;9:2452.doi:10.3389/fimmu.2018.02452.[3]Distler JH et al. Arthritis Rheumatol. 2017;69:257-67.[4]Distler O et al. New Eng J Med. 2019; 380:2518-28.[5]Maher TB et al. Arthritis Rheumatol.2020.doi:10.1002/art.41576.[6]Cutolo M et al. Arthritis Res Ther. 2018;20:157.doi:10.1186/s13075-018-1652-6.Acknowledgements:We thank Stefano-Lutz Willing for the scientific support through the study.Disclosure of Interests:Stefano Soldano: None declared, Paola Montagna: None declared, Emanuele Gotelli: None declared, Samuele Tardito: None declared, Sabrina Paolino: None declared, Claudio Corallo: None declared, Carmen Pizzorni: None declared, Alberto Sulli: None declared, Carlotta Schenone: None declared, Greta Pacini: None declared, Vanessa Smith: None declared, Maurizio Cutolo Grant/research support from: I received grant/research support from Bristol-Myers Squibb, Boehringer, Celgene
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