Tamoxifen inhibits nitrotyrosine formation after reversible middle cerebral artery occlusion in the rat
Article first published online: 20 DEC 2001
Journal of Neurochemistry
Volume 76, Issue 6, pages 1842–1850, March 2001
How to Cite
Osuka, K., Feustel, P. J., Mongin, A. A., Tranmer, B. I. and Kimelberg, H. K. (2001), Tamoxifen inhibits nitrotyrosine formation after reversible middle cerebral artery occlusion in the rat. Journal of Neurochemistry, 76: 1842–1850. doi: 10.1046/j.1471-4159.2001.00198.x
- Issue published online: 20 DEC 2001
- Article first published online: 20 DEC 2001
- Received August 18, 2000; revised manuscript received November 23, 2000; accepted November 24, 2000.
- cerebral ischemia;
- nitric oxide synthase;
Tamoxifen (TAM), a widely used non-steroidal anti-estrogen, has recently been shown to be neuroprotective in a rat model of reversible middle cerebral artery occlusion (rMCAo). Tamoxifen has several potential mechanisms of action including inhibition of the release of excitatory amino acids (EAA) and nitric oxide synthase (NOS) activity. The question addressed in this study was whether TAM reduces ischemia-induced production of nitrotyrosine, considered as a footprint of the product of nitric oxide and superoxide, peroxynitrite. In rat brain, 2 h rMCAo produced a time-dependent increase in nitrotyrosine content in the cerebral cortex, as measured by Western blot analysis. Compared with vehicle, TAM significantly reduced nitrotyrosine levels in the ischemic cortex at 24 h. The neuronal (n)NOS inhibitor, 7-nitroindazole also tended to reduce nitrotyrosine, but this reduction was not statistically significant. Immunostaining for nitrotyrosine was seen in cortical neurons in the MCA territory and this immunostaining was reduced by TAM. In vitro, TAM and the calmodulin inhibitor trifluoperazine inhibited, with similar EC50 values, the activity of recombinant nNOS as well as NOS activity in brain homogenates, measured by conversion of [3H]arginine to [3H]citrulline. There was marginal inhibition of recombinant inducible (i)NOS activity up to 100 µm TAM. These data suggest that TAM is an effective inhibitor of Ca2+/calmodulin-dependent NOS and the derived peroxynitrite production in transient focal cerebral ischemia and this may be one mechanism for its neuroprotective effect following rMCAo.