Synthesis of a hemin-containing copolymer as a novel immunostimulator that induces IFN-gamma production

Abstract

Kazuaki Hoshi,1 Tomohiko Yamazaki,2 Chiaki Yoshikawa,3 Wakako Tsugawa,1 Kazunori Ikebukuro,1 Koji Sode1,4 1Department of Biotechnology and Life Science, Graduate School of Engineering, Tokyo University of Agriculture & Technology, Koganei, Tokyo, Japan; 2Research Center for Functional Materials, National Institute for Materials Science (NIMS), Tsukuba, Ibaraki, Japan; 3International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), Tsukuba, Ibaraki, Japan; 4Joint Department of Biomedical Engineering, The University of North Carolina at Chapel Hill and North Carolina State University, Chapel Hill, NC, USA Background: Hemozoin, a chemical analog of a malarial pigment, is a crystal composed of heme dimers that can act as a potent Th1-type adjuvant, which strongly induces antibody production. However, the clinical applications of malarial hemozoin have limitations due to biosafety concerns and difficulties in the manufacturing process. Based on the premise that an analog of the heme polymer might display immunostimulatory effects, a hemin-containing polymer was developed as a novel immunostimulator. Materials and methods: To synthesize the copolymer containing hemin and N-isopropylacrylamide (NIPAM), this study employed a conventional radical polymerization method using 2,2'-azodiisobutyronitrile as the radical initiator; the synthesized copolymer was designated as NIPAM-hemin. Results: NIPAM-hemin was soluble and showed no cytotoxicity in vitro. The NIPAM-hemin copolymer induced the production of interferon (IFN)-γ and interleukin (IL)-6 from peripheral blood mononuclear cells, although hemin and the NIPAM monomer individually did not induce the production of any cytokines. The production of IFN-γ induced by NIPAM-hemin was independent of toll-like receptor 9 and the NLRP3 inflammasome pathway. Conclusion: Given that NIPAM-hemin induced IL-6 and IFN-γ production in immune cells without any cytotoxic effects, NIPAM-hemin has potential therapeutic applications as a Th1-type adjuvant. Keywords: hemin copolymer, immunostimulator, adjuvant, radical polymerization, NIPAM, toll-like receptor 9, T-helper 1, inflammasome

Keywords

• hemin copolymer
• immunostimulator
• adjuvant
• radical polymerization
• NIPAM