Suppressive effects of three diketopiperazines from marine-derived bacteria on TGFBIp-mediated septic responses in human endothelial cells and mice

Diketopiperazine is a naturally occurring cyclic dipeptide found from diverse living organisms. The compounds in this structure class have been known with a broad spectrum of bioactivities including anti-inflammatory activities. Transforming growth factor β-induced protein (TGFBIp) is an extracellular matrix protein whose expression in several cell types is greatly increased by TGF-β. TGFBIp is released by human umbilical vein endothelial cells and functions as a mediator of experimental sepsis. Here, three (1–3) of diketopiperazines were isolated from two strains of marine-derived bacteria and we hypothesized that 1–3 could reduce TGFBIp-mediated severe inflammatory responses in human endothelial cells and mice. Here, we investigated the anti-septic effects and underlying mechanisms of 1–3 against TGFBIp-mediated septic responses. 1–3 effectively inhibited lipopolysaccharide-induced release of TGFBIp and suppressed TGFBIp-mediated septic responses. In addition, 1–3 suppressed cecal ligation and puncture (CLP)-induced sepsis lethality and pulmonary injury. In conclusion, 1–3 suppressed TGFBIp-mediated and CLP-induced septic responses. Therefore, 1–3 could be a potential therapeutic agent for treatment of various severe vascular inflammatory diseases via inhibition of the TGFBIp signaling pathway.