Effects of a sustained release formulation of thyrotropin-releasing hormone (TRH-SR) on reduced a... more Effects of a sustained release formulation of thyrotropin-releasing hormone (TRH-SR) on reduced anxiety-like behavior and learning impairment in senescence-accelerated mice (SAM) were examined. SAMP8/Ta (SAMP8) mice showing age-related emotional changes as well as learning and memory impairments, and SAMR1TA (SAMR1) mice exhibiting normal aging were used at 8 months of age. Subcutaneous injection of TRH-SR (2.8 mg/kg as free TRH) produced a sustained increase in immunoreactive plasma TRH levels up to about 4 weeks after dosing in SAMP8. TRH-SR antagonized the reduced neophobia to novel food in SAMP8 in a dose-dependent manner when tested 10 days but not 3 days after the injection. In the elevated plus-maze test, the SAMP8 control group treated with vehicle had significant increases in the number of entries into open arms and the time spent in open arms in comparison to SAMR1 mice. TRH-SR showed dose-dependent decreases in the number of entries into open arms, and reduced the time spent in open arms in SAMP8 mice. Furthermore, TRH-SR significantly improved the impairment of water maze learning in SAMP8 mice. In contrast, bolus administration of TRH had no significant effects on behavioral abnormalities in SAMP8 even at high doses, implying that long-term and continuous infusion of TRH may be important for amelioration of the behavioral abnormalities. These results suggest that TRH-SR may be useful for treatment of age-related emotional disorders and memory disturbance in dementia.
Prolonged exposure to melatonin improves glycemic control in animals. Although glucose metabolism... more Prolonged exposure to melatonin improves glycemic control in animals. Although glucose metabolism is controlled by circadian clock genes, little is known about the role of melatonin signaling and its duration in the regulation of clock gene expression in pancreatic β-cells. Activation of MT1 and MT2 melatonin receptors inhibits cAMP signaling, which mediates clock gene expression. Therefore, this study investigated exposure duration-dependent alterations in cAMP element-binding protein (CREB) phosphorylation and clock gene expression that occur during and after exposure to ramelteon, a selective melatonin agonist used to treat insomnia. In rat INS-1 cells, a pancreatic β-cell line endogenously expressing melatonin receptors, ramelteon persistently decreased CREB phosphorylation during the treatment period (2-14 h), whereas the subsequent washout induced an enhancement of forskolin-stimulated CREB phosphorylation in a duration- and concentration-dependent manner. This augmentation wa...
Naunyn-Schmiedeberg's Archives of Pharmacology, 1998
The application of amyloid beta-peptide (Abeta) 1-40 (10 microM) caused neurodegeneration of hipp... more The application of amyloid beta-peptide (Abeta) 1-40 (10 microM) caused neurodegeneration of hippocampal neuronal cells, as indicated by the release of lactate dehydrogenase (LDH) into the culture medium. Treatment with idebenone (10-1000 nM), a potent antioxidant in mitochondria, protected the hippocampal neurons against the Abeta1-40(10 microM)-induced neurotoxicity. To determine the morphological change in neurons during the Abeta1-40-induced cytotoxicity, the cells were immunostained with anti-MAP2 antibodies. After 4-day exposure to 10 microM Abeta1-40, the number of neurons was reduced, and the surviving neurons had an apparently reduced number of neurites which were shorter than those of control neurons. When idebenone was added to the culture medium with Abeta1-40, the number of surviving neurons was significantly increased, and their neurites were as long as seen in control culture. These results suggest that reactive oxygen species mediate neurotoxicity of Abeta1-40, and idebenone protects neurons against the Abeta1-40-induced neurotoxicity.
The predictable chronological sequence of pathological events in Down syndrome (DS) provides the ... more The predictable chronological sequence of pathological events in Down syndrome (DS) provides the opportunity to rigorously investigate the relationship between oxidative stress and amyloid-beta (Abeta) deposition. In this study, we report a marked accumulation of oxidized nucleic acid, 8-hydroxyguanosine (8OHG), and oxidized protein, nitrotyrosine, in the cytoplasm of cerebral neurons in DS with the levels of nucleic acid and protein oxidation paralleling each other. Relative density measurements of neuronal 8OHG immunoreactivity showed that there was a significant increase (p < 0.02) in DS (n = 22, ages 0.3-65 yr) compared with age-matched controls (n = 10, ages 0.3-64 yr). As a function of age, 8OHG immunoreactivity increased significantly in the teens and twenties (p < 0.04), while Abeta burden only increased after age 30 (p < 0.0001). In 9 cases of DS bearing Abeta deposition, the extent of deposits of Abeta ending at amino acid 42 (Abeta42) was actually associated with a decrease in relative 8OHG (r = -0.79, p < 0.015) while Abeta40 was not. These findings suggest that in brains of patients with DS, increased levels of oxidative damage occur prior to the onset of Abeta deposition.
Novel tricyclic dihydrofuran derivatives were designed, synthesized, and evaluated as melatonin r... more Novel tricyclic dihydrofuran derivatives were designed, synthesized, and evaluated as melatonin receptor (MT(1)/MT(2)) ligands based on the previously reported 1,6-dihydro-2H-indeno[5,4-b]furan 1a. By screening the central tricyclic cores, we identified 8,9-dihydrofuro[3,2-c]pyrazolo[1,5-a]pyridine as a potent scaffold with a high ligand-lipophilicity efficiency (LLE) value. Subsequent optimization of the side chains led to identification of the potent MT(1)/MT(2) agonist 4d (MT(1), K(i) = 0.062 nM; MT(2), K(i) = 0.420 nM) with good oral absorption and blood-brain barrier (BBB) penetration in rats. The oral administration of compound 4d exhibited a sleep-promoting action in freely moving cats at 0.1 mg/kg.
Abstract: Increased awareness for a role of oxidative stress in the pathogenesis of Alzheimer&... more Abstract: Increased awareness for a role of oxidative stress in the pathogenesis of Alzheimer's disease has highlighted the issue of whether oxidative damage is a fundamental step in the pathogenesis or instead results from disease-associated pathology. In vitro experiments support both possibilities: Oxidative stress increases amyloid-β production, and, conversely, amyloid-β increases oxidative damage. To address the relationship between amyloid-β and oxidative stress in vivo, we examined, using an array of oxidative markers, transgenic mice that overexpress amyloid-β precursor protein and, as in Alzheimer's disease, develop characteristic amyloid-β deposits within the brain parenchyma. Transgenic animals show the same type of oxidative damage that is found in Alzheimer's disease, and it is important that this damage directly correlates with the presence of amyloid-β deposits. The significance of these studies is twofold. First, they provide evidence that amyloid-β and oxidative damage are inextricably linked in vivo. Second, they support the use of transgenic animals for the development of antioxidant therapeutic strategies.
During our efforts to identify a series of potent, selective, orally active human Orexin-2 Recept... more During our efforts to identify a series of potent, selective, orally active human Orexin-2 Receptor (OX2R) antagonists, we elucidated structure-activity relationship (SAR) on the 7-position of a benzoxazepine scaffold by utilizing Hammett σ(p) and Hansch-Fujita π value as aromatic substituent constants. The attempts led to the discovery of compound 1m, possessing good in vitro potency with over 100-fold selectivity against OX1R, good metabolic stability in human and rat liver microsome, good oral bioavailability in rats, and in vivo antagonistic activity in rats by oral administration.
Effects of a sustained release formulation of thyrotropin-releasing hormone (TRH-SR) on reduced a... more Effects of a sustained release formulation of thyrotropin-releasing hormone (TRH-SR) on reduced anxiety-like behavior and learning impairment in senescence-accelerated mice (SAM) were examined. SAMP8/Ta (SAMP8) mice showing age-related emotional changes as well as learning and memory impairments, and SAMR1TA (SAMR1) mice exhibiting normal aging were used at 8 months of age. Subcutaneous injection of TRH-SR (2.8 mg/kg as free TRH) produced a sustained increase in immunoreactive plasma TRH levels up to about 4 weeks after dosing in SAMP8. TRH-SR antagonized the reduced neophobia to novel food in SAMP8 in a dose-dependent manner when tested 10 days but not 3 days after the injection. In the elevated plus-maze test, the SAMP8 control group treated with vehicle had significant increases in the number of entries into open arms and the time spent in open arms in comparison to SAMR1 mice. TRH-SR showed dose-dependent decreases in the number of entries into open arms, and reduced the time spent in open arms in SAMP8 mice. Furthermore, TRH-SR significantly improved the impairment of water maze learning in SAMP8 mice. In contrast, bolus administration of TRH had no significant effects on behavioral abnormalities in SAMP8 even at high doses, implying that long-term and continuous infusion of TRH may be important for amelioration of the behavioral abnormalities. These results suggest that TRH-SR may be useful for treatment of age-related emotional disorders and memory disturbance in dementia.
Prolonged exposure to melatonin improves glycemic control in animals. Although glucose metabolism... more Prolonged exposure to melatonin improves glycemic control in animals. Although glucose metabolism is controlled by circadian clock genes, little is known about the role of melatonin signaling and its duration in the regulation of clock gene expression in pancreatic β-cells. Activation of MT1 and MT2 melatonin receptors inhibits cAMP signaling, which mediates clock gene expression. Therefore, this study investigated exposure duration-dependent alterations in cAMP element-binding protein (CREB) phosphorylation and clock gene expression that occur during and after exposure to ramelteon, a selective melatonin agonist used to treat insomnia. In rat INS-1 cells, a pancreatic β-cell line endogenously expressing melatonin receptors, ramelteon persistently decreased CREB phosphorylation during the treatment period (2-14 h), whereas the subsequent washout induced an enhancement of forskolin-stimulated CREB phosphorylation in a duration- and concentration-dependent manner. This augmentation wa...
Naunyn-Schmiedeberg's Archives of Pharmacology, 1998
The application of amyloid beta-peptide (Abeta) 1-40 (10 microM) caused neurodegeneration of hipp... more The application of amyloid beta-peptide (Abeta) 1-40 (10 microM) caused neurodegeneration of hippocampal neuronal cells, as indicated by the release of lactate dehydrogenase (LDH) into the culture medium. Treatment with idebenone (10-1000 nM), a potent antioxidant in mitochondria, protected the hippocampal neurons against the Abeta1-40(10 microM)-induced neurotoxicity. To determine the morphological change in neurons during the Abeta1-40-induced cytotoxicity, the cells were immunostained with anti-MAP2 antibodies. After 4-day exposure to 10 microM Abeta1-40, the number of neurons was reduced, and the surviving neurons had an apparently reduced number of neurites which were shorter than those of control neurons. When idebenone was added to the culture medium with Abeta1-40, the number of surviving neurons was significantly increased, and their neurites were as long as seen in control culture. These results suggest that reactive oxygen species mediate neurotoxicity of Abeta1-40, and idebenone protects neurons against the Abeta1-40-induced neurotoxicity.
The predictable chronological sequence of pathological events in Down syndrome (DS) provides the ... more The predictable chronological sequence of pathological events in Down syndrome (DS) provides the opportunity to rigorously investigate the relationship between oxidative stress and amyloid-beta (Abeta) deposition. In this study, we report a marked accumulation of oxidized nucleic acid, 8-hydroxyguanosine (8OHG), and oxidized protein, nitrotyrosine, in the cytoplasm of cerebral neurons in DS with the levels of nucleic acid and protein oxidation paralleling each other. Relative density measurements of neuronal 8OHG immunoreactivity showed that there was a significant increase (p < 0.02) in DS (n = 22, ages 0.3-65 yr) compared with age-matched controls (n = 10, ages 0.3-64 yr). As a function of age, 8OHG immunoreactivity increased significantly in the teens and twenties (p < 0.04), while Abeta burden only increased after age 30 (p < 0.0001). In 9 cases of DS bearing Abeta deposition, the extent of deposits of Abeta ending at amino acid 42 (Abeta42) was actually associated with a decrease in relative 8OHG (r = -0.79, p < 0.015) while Abeta40 was not. These findings suggest that in brains of patients with DS, increased levels of oxidative damage occur prior to the onset of Abeta deposition.
Novel tricyclic dihydrofuran derivatives were designed, synthesized, and evaluated as melatonin r... more Novel tricyclic dihydrofuran derivatives were designed, synthesized, and evaluated as melatonin receptor (MT(1)/MT(2)) ligands based on the previously reported 1,6-dihydro-2H-indeno[5,4-b]furan 1a. By screening the central tricyclic cores, we identified 8,9-dihydrofuro[3,2-c]pyrazolo[1,5-a]pyridine as a potent scaffold with a high ligand-lipophilicity efficiency (LLE) value. Subsequent optimization of the side chains led to identification of the potent MT(1)/MT(2) agonist 4d (MT(1), K(i) = 0.062 nM; MT(2), K(i) = 0.420 nM) with good oral absorption and blood-brain barrier (BBB) penetration in rats. The oral administration of compound 4d exhibited a sleep-promoting action in freely moving cats at 0.1 mg/kg.
Abstract: Increased awareness for a role of oxidative stress in the pathogenesis of Alzheimer&... more Abstract: Increased awareness for a role of oxidative stress in the pathogenesis of Alzheimer's disease has highlighted the issue of whether oxidative damage is a fundamental step in the pathogenesis or instead results from disease-associated pathology. In vitro experiments support both possibilities: Oxidative stress increases amyloid-β production, and, conversely, amyloid-β increases oxidative damage. To address the relationship between amyloid-β and oxidative stress in vivo, we examined, using an array of oxidative markers, transgenic mice that overexpress amyloid-β precursor protein and, as in Alzheimer's disease, develop characteristic amyloid-β deposits within the brain parenchyma. Transgenic animals show the same type of oxidative damage that is found in Alzheimer's disease, and it is important that this damage directly correlates with the presence of amyloid-β deposits. The significance of these studies is twofold. First, they provide evidence that amyloid-β and oxidative damage are inextricably linked in vivo. Second, they support the use of transgenic animals for the development of antioxidant therapeutic strategies.
During our efforts to identify a series of potent, selective, orally active human Orexin-2 Recept... more During our efforts to identify a series of potent, selective, orally active human Orexin-2 Receptor (OX2R) antagonists, we elucidated structure-activity relationship (SAR) on the 7-position of a benzoxazepine scaffold by utilizing Hammett σ(p) and Hansch-Fujita π value as aromatic substituent constants. The attempts led to the discovery of compound 1m, possessing good in vitro potency with over 100-fold selectivity against OX1R, good metabolic stability in human and rat liver microsome, good oral bioavailability in rats, and in vivo antagonistic activity in rats by oral administration.
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Papers by Keisuke Hirai