Modafinil exerts anti-inflammatory and anti-fibrotic effects by upregulating adenosine A_2A and A_2B receptors

Adenosine receptor (AR) suppresses inflammation and fibrosis by activating cyclic adenosine monophosphate (cAMP) signaling. We investigated whether altered AR expression contributes to the development of fibrotic diseases and whether A_2AAR and A_2BAR upregulation inhibits fibrotic responses. Primary human lung fibroblasts (HLFs) from normal (NHLFs) or patients with idiopathic pulmonary fibrosis (DHLF) were used for in vitro testing. Murine models of fibrotic liver or pulmonary disease were developed by injecting thioacetamide intraperitoneally, by feeding a high-fat diet, or by intratracheal instillation of bleomycin. Modafinil, which activates cAMP signaling via A_2AAR and A_2BAR, was administered orally. The protein amounts of A_2AAR, A_2BAR, and exchange protein directly activated by cAMP (Epac) were reduced, while collagen and α-smooth muscle actin (α-SMA) were elevated in DHLFs compared to NHLFs. In liver or lung tissue from murine models of fibrotic diseases, A_2AAR and A_2BAR were downregulated, but A₁AR and A₃AR were not. Epac amounts decreased, and amounts of collagen, α-SMA, K_Ca2.3, and K_Ca3.1 increased compared to the control. Modafinil restored the amounts of A_2AAR, A_2BAR, and Epac, and reduced collagen, α-SMA, K_Ca2.3, and K_Ca3.1 in murine models of fibrotic diseases. Transforming growth factor-β reduced the amounts of A_2AAR, A_2BAR, and Epac, and elevated collagen, α-SMA, K_Ca2.3, and K_Ca3.1 in NHLFs; however, these alterations were inhibited by modafinil. Our investigation revealed that A_2AAR and A_2BAR downregulation induced liver and lung fibrotic diseases while upregulation attenuated fibrotic responses, suggesting that A_2AAR and A_2BAR-upregulating agents, such as modafinil, may serve as novel therapies for fibrotic diseases.