Reduction in oxidative stress and cell death explains hypothyroidism induced neuroprotection subsequent to ischemia/reperfusion insult Leena Rastogi a , Madan M. Godbole a, ⁎ , Madhur Ray d , Priyanka Rathore d , Sunil Pradhan b , Sushil K. Gupta a , Chandra M. Pandey c a Department of Endocrinology, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Raebareli Road, Lucknow-226014, India b Department of Neurology, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Raebareli Road, Lucknow-226014, India c Department of Biostatistics, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Raebareli Road, Lucknow-226014, India d Division of Pharmacology, Central Drug Research Institute, Mahatma Gandhi Marg, Lucknow-226001, India Received 21 September 2005; revised 4 February 2006; accepted 10 February 2006 Available online 17 April 2006 Abstract Hypometabolic state following hypothermia is known to protect tissues from ischemic injury. Hypothyroidism produces a hypometabolic state. The present study was undertaken to investigate the protective effects of hypothyroidism following cerebral ischemia and to ascertain the underlying mechanism. Euthyroid (E) and hypothyroid (H) animals were exposed to a 2 h of middle cerebral artery occlusion followed by 24 h of reperfusion (I/R). Specific enzymatic methods and flowcytometry were used to assess the quantitative changes of molecules involved in neuronal damage as well as in protection. As compared to euthyroid ischemic reperfused (E + I/R) rats, H + I/R rats had insignificant neurological deficit, and smaller area of infarct. H + I/R rats had significantly lower markers of oxidative stress, and lactate dehydrogenase (LDH) activity (a marker for necrosis). Natural antioxidant activity (particularly superoxide dismutase) and integrity of mitochondria (membrane potential) were maintained in H + I/R group but not in E + I/R group. The number of neurons undergoing apoptosis significantly lower in hypothyroid ischemic rats as compared to euthyroid ones. These results suggest that hypothyroid animals face ischemia and reperfusion much better compared to euthyroid animals. A possible explanation could be the decreased oxidative stress and maintained antioxidant activity that finally leads to a decrease in necrosis and apoptosis. These observations may suggest strategies to induce brain-specific downregulation of metabolism that may have implications in the management of strokes in human beings. © 2006 Elsevier Inc. All rights reserved. Keywords: Stroke; Hypothyroidism; Oxidative stress; Necrosis; Apoptosis Introduction Stroke is the third leading cause of death in developed countries. About 25% of sufferers die due to stroke or its complications while 50% have moderate to severe long-term neurological disabilities. Only 26% recover most or all normal health and function (Reed et al., 1999). Though there have been several efforts focussing on the vascular front to reduce infract size or neurological disabilities in human beings in the initial 3–6 h after stroke modalities to render brain tissue less prone for ischemic damage (i.e., neuroprotection) are still in the experimental stage. Several mechanisms of neuronal injury in stroke have been proposed. These include release of excitatory amino acids, calcium overload, protein inhibition and Experimental Neurology 200 (2006) 290 – 300 www.elsevier.com/locate/yexnr Abbreviations: E, euthyroid; H, hypothyroid; I/R, ischemia/reperfusion; E + I/R, euthyroid plus ischemia/reperfusion; H + I/R, hypothyroid plus ischemia/ reperfusion; LDH, lactate dehydrogenase; TH, thyroid hormone; BMR, basal metabolic rate; T 3 , triiodothyronine; MMZ, 2-mercapto-1-methylimidazole; MCA, middle cerebral artery; TTC, 2,3,5-triphenyltetrazolium chloride; H&E, haematoxylin and eosin; TUNEL, transferase dUTP nick end labeling; NADPH, reduced pyridine nucleaotide; ROS, reactive oxygen species; Ca 2+ , intracellular calcium; SOD, superoxide dismutase; MPO, myeloperoxidase; MDA, melon- dialdehyde; H 2 O 2 , hydrogen peroxide; FITC, fluorescien isothiocynate; PI, propidium iodide. ⁎ Corresponding author. Fax: +91 522 2668017, 2668973. E-mail addresses: madangodbole@yahoo.co.in, godbole@sgpgi.ac.in (M.M. Godbole). 0014-4886/$ - see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.expneurol.2006.02.013