Dextromethorphan (3-methoxy-17-methylmorphinan) has complex pharmacologic effects on the central nervous system. Although some of these effects are neuropsychotoxic, this review focuses on the neuroprotective effects of dextromethorphan and its analogs. Some of these analogs, particularly dimemorfan (3-methyl-17-methylmorphinan) and 3-hydroxymorphinan, have promising neuroprotective properties with negligible neuropsychotoxic effects. Their neuroprotective effects, the mechanisms underlying these effects, and their therapeutic potential for the treatment of diverse neurodegenerative disorders are discussed.
Docosahexaenoic acid (DHA, C22:6 n-3), the most abundant n-3 polyunsaturated fatty acid in the brain, is essential for brain growth and development. Recent evidence has indicated the potential health benefits of DHA for managing Alzheimer’s disease (AD). For example, dietary administration of DHA considerably protects against and ameliorates the impairment of learning ability in amyloid-beta (Aβ)1–40-infused AD-model rats, with concurrent increases in DHA levels and decreases in the levels of lipid peroxide and reactive oxygen species in the cortico-hippocampal tissues. In addition, dietary DHA helps in eliminating the amyloid burden from the brains of AD-model rats. In vitro studies have revealed that DHA substantially inhibits Aβ fibrillation. Furthermore, DHA reduces amyloid-induced toxicity in cell culture. These in vitro data support the hypothesis that DHA can ameliorate the cognitive deficits of AD in vivo by limiting Aβ polymerization in the brains. Therefore, it might be a useful therapeutic agent to prevent and/or delay cognitive impairment in mild cases of AD.
Adult neurogenesis in the mammalian brain is well-known to occur in the subgranular zone of the hippocampus. As the hippocampus is related to learning, memory, and emotions, adult hippocampal neurogenesis possibly contributes to these functions. Adult neurogenesis is modulated by polyunsaturated fatty acids (PUFA) such as docosahexaenoic and arachidonic acids that are essential for normal brain development, maintenance, and function. They are reported to improve spatial learning and memory in rodents and cognitive functions in humans. However, detailed mechanisms of PUFA effects still remain obscure. PUFA are functionally linked with chaperons called fatty acid–binding proteins (FABP). FABP uptake and transport PUFA to different intracellular organelles. Intriguingly, PUFA were determined as ligands for G protein–coupled receptor 40 (GPR40), a cell membrane receptor abundantly expressed in the brain and the pancreas of primates. While the role of GPR40 in pancreatic β-cells is associated with insulin secretion, its role in the brain is not yet clarified presumably because of its absence in the rodent brain. The purpose of this review is to discuss the role of PUFA in adult neurogenesis, considering the role of GPR40 and FABP in the hippocampal neurogenic niche. Here, the authors would like to introduce a PUFA–GPR40 signaling pathway that is specific for the primate brain.
Oxidative stress is considered a major mediator of arteriosclerosis. In vascular smooth muscle cells, oxidative stress–induced cell death (including apoptosis) is probably related to arterial calcification in arteriosclerosis. Big mitogen-activated protein kinase-1 / extracellular signal–regulated kinase 5 (BMK1/ERK5) is a newly identified member of the mitogen-activated protein kinases family. Like Src tyrosine kinase, BMK1/ERK5 is known to be sensitive to oxidative stress; however, its pathophysiological significance is poorly understood. In this study, we investigated the involvement of BMK1 and Src in H2O2-induced cell death using cultured rat aortic smooth muscle cells (RASMCs). Cell apoptosis was evaluated by using the TdT-mediated dUTP nick end labeling (TUNEL) method, and BMK1 and Src activities were determined by Western blotting. The main results are as follows: 1) BMK1 and Src were activated by H2O2 in a time- and concentration-dependent manner in RASMCs; 2) BMK1 activation by H2O2 was attenuated both in Src-knockdown RASMCs and in RASMCs pretreated with 4-amino-5-(4-chloro-phenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2), a Src family kinases inhibitor; and 3) H2O2-induced cell death was increased in BMK1- and Src-knockdown RASMCs as well as in PP2-treated RASMCs. These findings suggested that Src and BMK1 may play defensive and resistive roles against oxidative stress–induced death in RASMCs.
Effects of azelnidipine were examined and compared with those of amlodipine on stunned myocardium in dogs. The left anterior descending (LAD) coronary artery was ligated for 20 min and subsequently released for 60 min. A vehicle, azelnidipine (0.3 mg/kg), or amlodipine (0.3 or 1 mg/kg) was injected intravenously 20 min before LAD ligation. The heart rate increased after a depressor response in the presence of amlodipine, while it decreased despite a decrease in arterial pressures in the presence of azelnidipine. After reperfusion, the coronary flow (CF) significantly increased in the presence of azelnidipine, but did not change with amlodipine after reperfusion. A positive inotropic effect was observed after treatment with both calcium antagonists. Ischemia significantly decreased the percentage of segment shortening (%SS) in all groups. Treatment with both calcium antagonists significantly increased %SS after reperfusion, although high-energy phosphate levels did not improve in the presence of calcium antagonists 60 min after reperfusion. Mortality with azelnidipine was significantly lower than that with 0.3 mg/kg amlodipine immediately after reperfusion. In conclusion, improvement in myocardial stunning after pretreatment with azelnidipine is associated with an increase in CF after reperfusion. The negative chronotropic action may have contributed to decreased mortality due to reperfusion arrhythmias. Azelnidipine is more beneficial than amlodipine and may provide an additional advantage to patients with angina and hypertension.
To investigate the effect of hypoxia or hypoxia/reoxygenation on vascular smooth muscle function, mechanical response of monkey coronary artery without endothelium was studied under normoxia, hypoxia, and hypoxia/reoxygenation. Hypoxia or hypoxia/reoxygenation impaired the relaxation by nitroglycerin or isosorbide dinitrate but not that by 8-bromoguanosine-3′,5′-cyclic monophosphate or isoproterenol. Tempol restored the impaired relaxation by nitroglycerin or isosorbide dinitrate, but superoxide dismutase had no effect. Apocynin, an NADPH oxidase inhibitor, improved the nitroglycerin-induced relaxation under hypoxia, but not under reoxygenation. Under combined treatment of apocynin with oxypurinol (xanthine oxidase inhibitor), rotenone (mitochondria electron transport inhibitor), or both, hypoxic impairment of vasorelaxation was restored more effectively. Similarly, impairment of the nitroglycerin-induced vasorelaxation under hypoxia/reoxygenation was restored by combined treatment with three inhibitors, apocynin, oxypurinol, and rotenone. Increase in superoxide production under hypoxia tended to be inhibited by apocynin and that under hypoxia/reoxygenation was abolished by combined treatment with three inhibitors. These findings suggest that increased intracellular superoxide production under hypoxia or hypoxia/reoxygenation attenuates vasodilation mediated with a nitric oxide/soluble guanylyl cyclase, but not adenylyl cyclase, signaling pathway. The main source of superoxide production under hypoxia seems to be different from that under reoxygenation: superoxide is produced by NADPH oxidase during hypoxia, whereas it is produced by xanthine oxidase, mitochondria, or both during reoxygenation. [Supplementary Figure: available only at http://dx.doi.org/10.1254/jphs.11031FP]
Increased intrahepatic resistance causes portal hypertension in cirrhosis. Liver myofibroblasts (MFs) are now regarded as the principle cells involved in sinusoidal blood flow regulation. Many other prostaglandin-receptor agonists have been reported to regulate liver MF contraction, but the role of the prostaglandin D2–receptor DP is unknown. In this study, we investigated the effect of a synthetic agonist of prostanoid DP receptor, BW245C, on contractile properties of primary rat liver MFs. Collagen gel contraction assay revealed that BW245C alone (1 and 10 μM) did not induce contraction but induced cell relaxation. Pretreatment with BW245C (10 μM, 30 min) attenuated bradykinin (100 nM)-induced liver MF contraction. Elevation of [Ca2+]i induced by bradykinin (100 nM) was partially suppressed by BW245C pretreatment (10 μM, 3 min). BW245C (1 and 10 μM) significantly increased intracellular cAMP level in a dose-dependent manner. Pretreatment with forskolin (30 – 300 nM, 30 min) and dibutyryl-cAMP (3 – 30 μM, 30 min) significantly reduced bradykinin-induced contraction. Furthermore, a protein kinase A (PKA) inhibitor KT5720 (10 nM to 1 μM, 30 min) blocked the relaxant effect of BW245C. These results suggest that prostanoid DP receptor agonism inhibits bradykinin-induced [Ca2+]i elevation and contraction through cAMP–PKA signal activation in rat liver MFs.
The abnormal proliferation of vascular smooth muscle cells (VSMCs) in arterial wall is an important pathogenic factor for vascular disorders such as atherosclerosis and restenosis after angioplasty. The present study was designed to investigate the inhibitory effects of docetaxel on VSMC proliferation, as well as the molecular mechanism of this inhibition. Docetaxel at 10, 20 and 40 μM significantly inhibited both the proliferation and the DNA synthesis of fetal bovine serum (FBS)- and platelet-derived growth factor (PDGF)-BB–stimulated VSMCs in a concentration-dependent manner. In accordance with these findings, docetaxel blocked the FBS- and PDGF-BB–induced progression of synchronized cells through the G0/G1 phase of the cell cycle. Docetaxel also decreased the expressions of cell cycle-related proteins, including cyclin-dependent kinase (CDK) 2, cyclin E, CDK4, cyclin D1, retinoblastoma protein, and proliferative cell nuclear antigen in PDGF-BB–stimulated VSMCs. Docetaxel significantly inhibited the phosphorylation of extracellular signal-regulated kinase 1/2, Akt, and phospholipase C-γ1, downstream molecule in the PDGF-BB signaling pathway. Docetaxel suppressed the phosphorylation of PDGF receptor (PDGF-R) β, the upstream molecule in PDGF-BB signaling cascade, suggesting that the inhibitory effect of docetaxel on the proliferation of VSMCs may occur by blocking PDGF-Rβ phosphorylation. Thus, docetaxel may be a potential antiproliferative agent for the treatment of atherosclerosis and angioplasty restenosis. [Supplementary Figures: available only at http://dx.doi.org/10.1254/jphs.10276FP]
The benzo[b]furan derivative MU314 inhibits in vitro bone resorption as potently as β-estradiol (E2). Here, we examined the point of action on the anti-osteoporotic effects of MU314. MU314 (10 nM) suppressed lacunae formation by osteoclastic cells and ICI-182,780, a pure E2 antagonist, inhibited this effect. Specifically, we ovariectomized (OVX) Wistar female rats and subcutaneously injected them with either MU314 (30 or 100 μg/kg) or E2 (100 μg/kg) over an 8-week period. Bone mineral content (BMC) in the proximal end of the tibia was significantly decreased (14%) in OVX rats, and MU314 (100 μg/kg) and E2 significantly suppressed the decline in BMC. OVX rats exhibited decreased cancellous bone in the proximal end of the tibia and induced destruction of its trabecular structure. MU314 suppressed these changes. OVX also reduced the mechanical strength of the femoral neck, which was also recovered by MU314 and E2. E2 completely protected against OVX-induced uterine atrophy, but MU314 had no effect. These results strongly indicate that MU314 acts as a selective estrogen receptor modulator.
To identify the therapeutic potential for cartilage degradation and its action mechanisms, the effects of naturally-occurring flavonoids on matrix metalloproteinase-13 (MMP-13) induction were examined in the human chondrocyte cell line SW1353. Flavones including apigenin and wogonin strongly inhibited MMP-13 induction in interleukin (IL)-1β–treated SW1353 cells, while flavonols such as kaempferol, quercetin, and flavanone (naringenin) did not at 5 – 25 μM. Apigenin and wogonin primarily inhibit MMP-13 by blocking the c-Fos / activator protein-1 (AP-1) and Janus kinase 2 (JAK2) / signal transducer and activator of transcription 1/2 (STAT1/2) pathways, but not nuclear factor-κB (NF-κB) signaling. Apigenin was also shown to inhibit extracellular matrix degradation in rabbit cartilage culture. The following study using some synthetic flavones demonstrated that A-ring C-5,7-dihydroxyl and B-ring dihydroxyl substitution at C-2,3, C-2,4, or C-3,4 are important for the suppression of MMP-13 expression. Among these flavones, 2′,3′,5,7-tetrahydroxyflavone also inhibited both the c-Fos/AP-1 and STAT1/2 pathways. Taken together, these results indicate that certain flavonoids, especially flavones, inhibit MMP-13 expression in IL-1β–treated chondrocytes, at least in part, by suppressing the c-Fos/AP-1 and JAK2/STAT1/2 pathways. Furthermore, these findings suggest that some flavonoids have the potential for protecting against collagen matrix breakdown in the cartilage of diseased tissues such as those found in arthritic disorders.
Citidine-5-diphosphocholine or citicoline (CDP-choline) is used as a neuroprotective and memory-enhancing drug in cerebral stroke, Alzheimer’s disease, and other neurovascular diseases. Non-clinical studies have demonstrated the neuroprotective effects of CDP-choline in ischemic animal models. However, the relationship between the neuroprotective effect and the memory enhancing effect of CDP-choline is still unknown. No studies have demonstrated the ameliorative effect on impaired spatial memory and the suppressive effect on neuronal cell death of CDP-choline in the same model. In this study, we examined the effect of CDP-choline on impaired spatial memory and hippocampal CA1 neuronal death in rats subjected to repeated cerebral ischemia, and we compared the mechanism of CDP-choline to that of donepezil. Seven days post administration of CDP-choline (100, 300, 1000 mg/kg per day, p.o.) or donepezil increased correct choices and reduced error choices in an eight-arm radial maze task in a dose-dependent manner. Neuronal cell death of caspase-3 protein–positive neurons in the hippocampus were reduced by repeated administration of CDP-choline at the highest dose. These results suggest that CDP-choline has ameliorative effects on the impairment of spatial memory via hippocampal neuronal cell death in a rat model of cerebral ischemia.