Suppression of oxidative neuronal damage after transient middle cerebral artery occlusion in mice lacking interleukin-1 Hirokazu Ohtaki a,b , Hisayuki Funahashi a , Kenji Dohi a , Takiko Oguro c , Reiko Horai d , Masahide Asano d , Yoichiro Iwakura d , Li Yin a , Masaji Matsunaga a , Noboru Goto a , Seiji Shioda a,b, * a Department of Anatomy, Showa University School of Medicine, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan b The Core Research for Evolutional Science and Technology (CREST) of Japan Science and Technology Corporation (JST), Tokyo, Japan c Pharmaceutical Sciences, Showa University, Shinagawa-ku, Tokyo 142-8555, Japan d The Institute of Medical Science, Laboratory of Animal Research Center, The University of Tokyo, Minato-ku, Tokyo 108-8639, Japan Received 11 September 2002; accepted 19 November 2002 Abstract Interleukin-1 (IL-1) contributes to ischemic neurodegeneration. However, the mechanisms regulating action of IL-1 are still poorly understood. In order to clear this central issue, mice that were gene deficient in IL-1a and b (IL-1 KO) and wild-type mice were subjected to 1-h transient middle cerebral artery occlusion (tMCAO). Expression levels of IL-1b and IL-1 receptor I (IL-1RI) were then examined. Generation of peroxynitrite and the expression of mRNAs for nitric oxide synthase (NOS) subtypes were also determined. Immunostaining for IL-1b was increased from 6 h and peaked at 24 h after tMCAO in the microglia and macrophage. The immunoreactivities of IL-1RI were increased progressively in the microvasculature and neuron-like cells of the ipsilateral hemisphere. Infarct volumes were significantly lower in IL-1 KO mice compared with wild-type mice 48 h after tMCAO (P B/0.01). The immunoreactivities of 3-nitro-L-tyrosine were determined in the neurons and microvasculature 24 h after tMCAO and were significantly decreased in the IL-1 KO mice compared to wild-type mice. In addition, expression levels of NOS mRNA in IL-1 KO mice were lower than that measured in wild-type mice. These results indicate that IL-1 is up-regulated and may play a role in neurodegeneration by peroxynitrite production during ischemia. # 2003 Elsevier Science Ireland Ltd. and the Japan Neuroscience Society. All rights reserved. Keywords: Interleukin-1 (IL-1); Interleukin-1 receptor I (IL-1RI); Focal brain ischemia; Brain infarction; Microglia; Peroxynitrite (ONOO); Nitric oxide synthase (NOS) 1. Introduction Interleukin-1 (IL-1) is a proinflammatory cytokine, which plays a crucial role in the host’s response to inflammation, infection, injury, and immunological challenge (Durum and Oppenheim, 1993; Van Dam et al., 1995; Dinarello, 1996; Tocci and Schmidt, 1997). IL- 1 consists of two molecular species, IL-1a and b, which are derived from two distinct genes located 50 kb apart on chromosome 2 of the mouse genome (D’Eutachio et al., 1987; Silver et al., 1990). IL-1, especially IL-1b has diverse actions in the brain and there is considerable evidence implicating it in neurodegeneration. Injection of IL-1b has been shown to exacerbate ischemic brain damage (Yamasaki et al., 1995; Rothwell, 1999; Touzani et al., 1999) and injection of IL-1 receptor antagonist leads to a decrease in infarct volumes (Relton and Rothwell, 1992; Betz et al., 1995; Garcia et al., 1995; Loddick and Rothwell, 1996; Sanderson et al., 1999; Yang et al., 1999a). However, the mechanisms regulat- ing the action of IL-1 are poorly understood. There is increasing evidence available to indicate that nitric oxide (NO) may be an important mediator of ischemic brain injury (Hara et al., 1996; Homma et al., 1997; Kamii et al., 1996; Iadecola, 1997). NO is produced by nitric oxide synthase (NOS), and reacts * Corresponding author. Tel.:  /81-3-3784-8103; fax:  /81-3-3784- 6815. E-mail address: shioda@med.showa-u.ac.jp (S. Shioda). Neuroscience Research 45 (2003) 313  /324 www.elsevier.com/locate/neures 0168-0102/02/$ - see front matter # 2003 Elsevier Science Ireland Ltd. and the Japan Neuroscience Society. All rights reserved. doi:10.1016/S0168-0102(02)00238-9