Neuropharmacology and AnalgesiaNatural and synthetic retinoids afford therapeutic effects on intracerebral hemorrhage in mice
Introduction
Intracerebral hemorrhage (ICH) refers to devastating pathological conditions triggered by extravasation of blood constituents into brain parenchyma. Brain pathology involves substantial tissue damage associated with neuron loss, pro-inflammatory activation of microglia/macrophages, and infiltration of neutrophils (Qureshi et al., 2009). ICH frequently results in poor prognosis characterized by enduring disabilities in sensorimotor performance. Effective drug therapies for ICH are yet unavailable, although pathogenic mechanisms of ICH are increasingly revealed by recent progress in basic research using animal models of ICH (Katsuki, 2010, Xi et al., 2006).
In a recent study, we have proposed that retinoids may serve as neuroprotective drugs for ICH (Matsushita et al., 2011). Retinoids produce their biological actions through binding to their receptors, namely, retinoic acid receptors (NR1Bs) and retinoid X receptors (NR2Bs). NR1Bs and NR2Bs both include three subtypes designated as NR1B1-3 and NR2B1-3, which are widely distributed in the adult central nervous system (Krezel et al., 1999). Increasing lines of evidence suggest that the physiological actions of retinoids in the central nervous system range from regulation of dopamine receptor expression to modulation of hippocampal synaptic functions (Aoto et al., 2008, Maden, 2007). Besides, under pathological conditions such as Alzheimer disease, multiple sclerosis and spinal cord injury, retinoids may provide beneficial influences to ameliorate disease pathology (Malaspina and Michael-Titus, 2008, Mey, 2006). These beneficial actions may be attributable in part to inhibitory effects on inflammatory reactions involving microglia/macrophages and neutrophils (Mey, 2006), but also may involve neurotrophic effects via up-regulation of neurotrophic factors (Katsuki et al., 2009, Kurauchi et al., 2011).
Our previous investigations revealed that an NR1B1/NR1B2 agonist Am80 (tamibarotene) ameliorated several pathological and neurological parameters in mouse ICH model based on collagenase injection (Matsushita et al., 2011). That is, daily oral administration of Am80 starting from 1 day before ICH induction inhibited the decrease in the number of surviving striatal neurons, suppressed the increase in the number of activated microglia/macrophages, and promoted recovery from neurological deficits. With regard to neuroprotection, Am80 was effective even when the first administration was performed 6 h after induction of ICH (Matsushita et al., 2011). However, whether the post-treatment regimen is also effective on other pathological parameters has not been investigated. Another interesting point to be addressed is whether all-trans retinoic acid (ATRA), a naturally occurring NR1B agonist, provides beneficial effects on ICH, since ATRA has been demonstrated to modify pathogenic events in several models of central nervous system disorders (Choi et al., 2009, Ding et al., 2008). Notably, ATRA as well as Am80 is already available clinically as a therapeutic drug for acute promyelocytic leukemia (Ohnishi, 2007).
We firstly examined the effect of ATRA in a pretreatment regimen to reveal whether ATRA mimics the effect of Am80 in ameliorating ICH pathology. Secondly, we evaluated the effects of ATRA and Am80 in a post-treatment regimen, to reveal whether NR1B could be a therapeutic target for ICH.
Section snippets
Induction of intracerebral hemorrhage
All procedures in the present study were approved by Kumamoto University ethical committee concerning animal experiments, and animals were treated in accordance with the Guidelines of the United States National Institutes of Health regarding the care and use of animals for experimental procedures. Male C57BL/6J mice at 8 to 10 weeks of age weighing 21 to 28 g were used. Animals were maintained at constant ambient temperature (22 ± 1 °C) under a 12-h light/dark cycle. Under anesthesia with
Pretreatment with ATRA inhibits neuron loss and accumulation of activated microglia/macrophages associated with ICH
We examined the effect of ATRA, a naturally occurring agonist acting on NR1Bs. ATRA at 5 or 15 mg/kg was administered orally for 4 consecutive days, starting from the day before ICH induction by collagenase injection. This protocol was based on our previous report that demonstrated neuroprotective effect of Am80 (Matsushita et al., 2011). Results of NeuN immunostaining of brain sections obtained 3 days after induction of ICH showed that ATRA prevented ICH-induced decrease in the number of
Discussion
We demonstrated here that, when the pretreatment regimen was employed, ATRA exerted qualitatively similar effects as those of Am80 described previously (Matsushita et al., 2011). That is, ATRA prevented the decrease in the number of surviving neurons and suppressed accumulation of activated microglia/macrophages, but had no significant effect on lesion volume that reflects the extent of bleeding. ATRA is the major, naturally occurring agonist at NR1Bs, and the present results are consistent
Acknowledgments
This work was supported by Takeda Science Foundation, The Smoking Research Foundation, and Grants-in-Aid for Scientific Research from The Ministry of Education, Culture, Sports, Science and Technology, Japan (20390026, 23117714).
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