Styrene-maleic acid copolymer-encapsulated CORM2, a water-soluble carbon monoxide (CO) donor with a constant CO-releasing property, exhibits therapeutic potential for inflammatory bowel disease

Carbon monoxide (CO), the physiological product of heme oxygenase during catabolic breakdown of heme, has versatile functions and fulfills major anti-oxidative and anti-apoptotic roles in cell systems. Administration of CO is thus thought to be a reasonable therapeutic approach in diseases-such as inflammatory bowel disease-that are induced by reactive oxygen species (ROS). Tricarbonyldichlororuthenium(II) dimer (CORM2) is a commonly used CO donor, but it has poor aqueous solubility and a very short CO-releasing half-life (t(1/2)). In the present study, we prepared micelles consisting of water-soluble styrene-maleic acid copolymer (SMA) encapsulating CORM2 (SMA/CORM2) that had a hydrodynamic size of 165.3 nm. Compared with free CORM2, SMA/CORM2 demonstrated betterwater solubility (>50 mg/ml in a physiological water solution). Moreover, because of micelle formation in an aqueous environment, the CO release ratewas slow and sustained. These properties resulted in much longer in vivo bioactivity of SMA/CORM2 compared with that of free CORM2, i.e. the t(1/2) in blood of SMA/CORM2 in mice after intravenous (i.v.) injection was about 35 times longer than that of free CORM2. We then evaluated the therapeutic potential of SMA/CORM2 in a murine model of inflammatory colitis induced by dextran sulfate sodium (DSS). Administration (either i.v. or oral) of SMA/CORM2 once at the beginning of colitis, 3 days after DSS treatment, significantly improved colitis symptoms-loss of body weight, diarrhea, and hematochezia-as well as histopathological colonic changes-shortening of the colon and necrosis or ulcers in the colonic mucosa. Up-regulation of inflammatory cytokines including monocyte chemotactic protein-1, tumor necrosis factor-alpha, and interleukin-6 in this DSS-induced colitis was significantly suppressed in SMA/CORM2-treatedmice. SMA/CORM2may thus be a superior CO donor and may be a candidate drug, which involves cytokine suppression, for ROS-related diseases including inflammatory bowel disease. (C) 2014 Elsevier B. V. All rights reserved.