Regular ArticlePostischemic infusion of adrenomedullin protects against ischemic stroke by inhibiting apoptosis and promoting angiogenesis
Introduction
Adrenomedullin (AM) is a peptide hormone with multifunctional biological properties (Nagaya et al., 2005, Bunton et al., 2004). AM immunoreactivity is widely distributed in the central nervous system (CNS) (Serrano et al., 2002b). In the rat, AM is present in many neurons throughout the brain and spinal cord, as well as in vascular endothelial cells and perivascular glial cells (Serrano et al., 2000). AM expression is elevated after an ischemic insult and is believed to be part of the mechanism in response to hypoxic injury in the CNS (Serrano et al., 2002a). Over-expression of AM and changes in its intracellular location may be involved in neuronal responses to brain ischemia with a potential neuroprotective role (Encinas et al., 2002). AM has an important autocrine and paracrine role by regulating cerebral circulation and blood–brain barrier functions (Kis et al., 2001a, Kis et al., 2001b, Kis et al., 2003). Endothelial cells in the cerebrum are a potential source of AM, where AM can also be involved in the regulation of neuroendocrine functions (Kis et al., 2002). Previous studies suggest that AM and calcitonin gene-related peptide (CGRP) act via a common CGRP-like receptor, and antagonism of this receptor by CGRP (8–37) can inhibit the vasodilator action of AM (Eguchi et al., 1994, Baskaya et al., 1995). Taken together, these findings indicate that AM may play an important role in ischemic stroke via CGRP-like receptor.
By employing a rat model of focal cerebral ischemia by middle cerebral artery occlusion (MCAO) for 60 min, we previously demonstrated that delayed AM gene transfer 3 days after cerebral ischemia/reperfusion (I/R) promoted neuroprotection by enhancing glial cell survival and migration (Xia et al., 2004). In the present study, we optimized AM delivery and investigated whether a stable supply of AM peptide via subcutaneous osmotic minipump infusion at 1 day after MCAO has neuroprotective effects on cerebral I/R. Our results demonstrate that AM exerts neuroprotection, characterized by significant reduction in neurological deficits scores, cerebral infarction, and oxidative stress. The protective effect of AM was associated with decreased neuronal and glial cell apoptosis and increased blood vessel growth. AM’s effects were blocked by CGRP (8–37), suggesting that these actions of AM were mediated by a CGRP-like receptor.
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Animals and treatments
Male Sprague–Dawley rats (Harlan Sprague–Dawley, Indianapolis, IN) (220–220 g body weight) were used in this experiment. All procedures complied with the standards for care and use of animal subjects as stated in the Guide for the Care and Use of Laboratory Animals (Institute of Laboratory Resources, National Academy of Sciences, Bethesda, MD).
Cerebral I/R was generated by MCAO for 60 min followed by reperfusion as previously described (Borlongan et al., 2000). Briefly, rats were anesthetized
Results
Effect of AM Peptide Infusion on Neurological Function and Cerebral Infarction Behavioral tests were performed at days 2, 4, and 8 after MCAO. AM infusion significantly decreased neurological deficit scores at day 2 (1.2 ± 0.32 vs. 2.7 ± 0.41, n = 9, P < 0.01), day 4 (0.8 ± 0.27 vs. 2.0 ± 0.33, n = 9, P < 0.01), and day 8 (0.1 ± 0.08 vs. 1.33 ± 0.42, n = 9, P < 0.01) compared with saline infusion group after cerebral I/R. CGRP (8–37), an AM receptor antagonist, partially abolished the effect of
Discussion
Stroke-induced neurological deficits and mortality are associated with the timing of treatment after the onset of stroke. In this study, we showed that delayed AM peptide infusion via osmotic pump at 24 h after focal cerebral ischemic injury significantly reduced I/R-induced neurological deficit scores, cerebral infarction, and apoptosis of both neuronal and glial cells in the cerebral brain injury. Moreover, the protective effect of AM on ischemic brain injury was associated with increased
Acknowledgments
This work was supported by National Institutes of Health grants HL29397 and DK 066350, and American Heart Association grant-in-aid 025603U.
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