Ki Yong Lee

Safety and Efficacy Evaluation of Carnosine, an Endogenous Neuroprotective Agent for Ischemic Stroke

Background and Purpose— An urgent need exists to develop therapies for stroke that have high efficacy, long therapeutic time windows, and acceptable toxicity. We undertook preclinical investigations of a novel therapeutic approach involving supplementation with carnosine, an endogenous pleiotropic dipeptide. Methods— Efficacy and safety of carnosine treatment was evaluated in rat models of permanent or transient middle cerebral artery occlusion. Mechanistic studies used primary neuronal/astrocytic cultures and ex vivo brain homogenates. Results— Intravenous treatment with carnosine exhibited robust cerebroprotection in a dose-dependent manner, with long clinically relevant therapeutic time windows of 6 hours and 9 hours in transient and permanent models, respectively. Histological outcomes and functional improvements including motor and sensory deficits were sustained on 14th day poststroke onset. In safety and tolerability assessments, carnosine did not exhibit any evidence of adverse effects or toxicity. Moreover, histological evaluation of organs, complete blood count, coagulation tests, and the serum chemistry did not reveal any abnormalities. In primary neuronal cell cultures and ex vivo brain homogenates, carnosine exhibited robust antiexcitotoxic, antioxidant, and mitochondria protecting activity. Conclusions— In both permanent and transient ischemic models, carnosine treatment exhibited significant cerebroprotection against histological and functional damage, with wide therapeutic and clinically relevant time windows. Carnosine was well tolerated and exhibited no toxicity. Mechanistic data show that it influences multiple deleterious processes. Taken together, our data suggest that this endogenous pleiotropic dipeptide is a strong candidate for further development as a stroke treatment.

Asiatic Acid Attenuates Infarct Volume, Mitochondrial Dysfunction, and Matrix Metalloproteinase-9 Induction After Focal Cerebral Ischemia

Background and Purpose— Asiatic acid (AA) has been shown to attenuate cerebral infarction in a mouse model of focal ischemia and shows promise as a neuroprotective stroke therapy. To facilitate translation of these findings to clinical studies, we determined pharmacokinetics, a dose–response relationship, the therapeutic time window, and efficacy using multiple stroke models. We also explored potential mechanisms of action. Methods— Escalating doses of intravenous AA were administered and serum concentrations were measured at multiple time points for the pharmacokinetic studies. Subsequently, a dose–response relationship was determined followed by administration at different intervals after the onset of ischemia to establish a therapeutic time window for neuroprotection. Outcome measurements included both histological and behavioral. Mitochondrial function and matrix metalloproteinase activity in controls and treated rats were also determined. Results— The pharmacokinetic studies showed that AA (75 mg/kg) has a half-life of 2.0 hours. AA significantly decreased infarct volume and improved neurological outcome even when administration was at time points up to 12 hours after the onset of ischemia. Infarct volume was also significantly decreased in female rats and spontaneously hypertensive rats. AA attenuated mitochondrial dysfunction and reduced matrix metalloproteinase-9 induction. Conclusions— Our study shows AA is effective against multiple models of focal ischemia, has a long therapeutic time window, and is also effective in females and hypertensive animals. AA may mediate neuroprotection by protecting mitochondria and inhibiting matrix metalloproteinase-9 induction and activation. Taken together these data suggest that AA is an excellent candidate for development as a stroke therapy.

Effects of geniposide on hepatocytes undergoing epithelial–mesenchymal transition in hepatic fibrosis by targeting TGFβ/Smad and ERK-MAPK signaling pathways

Liver fibrosis results from increased deposition of type-I collagen within the hepatic extracellular space and constitutes a common cardinal signature in all forms of liver injury, regardless of etiology. Transforming growth factor β1 (TGF-β1) plays a crucial role in the pathogenesis of liver fibrosis. Geniposide is recognized as being useful against hyperlipidemia and fatty liver. However, its cellular mechanism and anti-fibrotic effect in TGF-β1-induced hepatocytes have not been explored. In the present study, we investigated its anti-epithelial-mesenchymal transition (EMT) mechanism by examining the effect of geniposide on TGF-β1-induced hepatocytes. The effect of geniposide on TGF-β1-induced AML12 cells was assessed using Western blotting, quantitative real-time PCR, immunofluorescence staining and DNA binding activity. We found that geniposide significantly inhibited TGF-β1-induced mRNA and protein expression of type-I collagen. Cells treated concurrently with TGF-β1 and geniposide retained high levels of localized E-cadherin expression with no increase in vimentin. Treatment with geniposide almost completely blocked the phosphorylation of Smad2/3, extracellular signal-regulated kinase (ERK) and Akt in AML12 cells. Taken together, these results suggest that geniposide may suppress TGF-β1-induced EMT in hepatic fibrosis by inhibiting the TGFβ/Smad and ERK-mitogen-activated protein kinase (MAPK) signaling pathways. Our results may help researchers better understand the pathogenesis of liver fibrosis so they can develop novel therapeutic strategies for treatment of liver diseases.

Diffusive crack-healing behavior in polycrystalline alumina: A comparison between microwave annealing and conventional annealing

Abstract Crack-healing experiments via both conventional heating and microwave heating were performed on Vickers-indented specimens of polycrystalline alumina (Coors ADS-995). For the entire temperature range included in this experiment (1510–1742 K), the crack-healing rate was enhanced for microwave heating compared to conventional heating. The microwave crack-healing data were described well by a diffusive mass transport model given by Stevens and Dutton.

Neuroprotective biflavonoids of Chamaecyparis obtusa leaves against glutamate-induced oxidative stress in HT22 hippocampal cells

Four biflavonoids (1-4), five flavonoids glycosides (5-9), two catechins (10, 11), two lignans (12-13), neolignan glycoside (14) and phenylpropanoid glycoside (15) were isolated from the leaves of Chamaecyparis obtusa (Cupressaceae). Neuroprotective effects of the isolated compounds were evaluated employing HT22 mouse hippocampal cells, a model system to study glutamate-induced oxidative stress. The glutamate injured HT22 cells were protected significantly by amentoflavone (3), ginkgetin (4) and (-)-epitaxifolin 3-O-β-D-xylopyranoside (9). The reduced activities of antioxidant enzymes, superoxide dismutase (SOD), glutathione reductase (GR) in response to high concentration of glutamate were preserved by pre-treatment of 3, 4 or 9, while the activities of glutathione peroxidase (Gpx) and catalase (CAT) were little affected. The reduced content of GSH induced by glutamate was also recovered by 3, 4 or 9 in accommodation with the decrease in ROS production. In addition, the phosphorylation of ERK1/2 induced by glutamate insult was clearly prevented by 3, while little changed by 4. Taken together, amentoflavone (3), ginkgetin (4) and (-)-epitaxifolin 3-O-β-D-xylopyranoside (9) derived from C. obtusa could protect HT22 neuronal cells against glutamate-induced oxidative damage through preserving antioxidant enzymes activities and/or inhibiting ERK1/2 activation.

Sustained resistance to acute MPTP toxicity by hypothalamic dopamine neurons following chronic neurotoxicant exposure is associated with sustained up-regulation of parkin protein.

Hypothalamic tuberoinfundibular dopamine (TIDA) neurons remain unaffected in Parkinson disease (PD) while there is significant degeneration of midbrain nigrostriatal dopamine (NSDA) neurons. A similar pattern of susceptibility is observed following acute exposure to the neurotoxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and the resistance of TIDA neurons to MPTP is associated with increased expression of parkin and ubiquitin carboxy-terminal hydrolase L-1 (UCHL-1). In the present study, the response of TIDA and NSDA neurons to acute MPTP administration following chronic MPTP exposure was examined. Mice were treated with ten injections of either MPTP (20mg/kg; s.c.; every 3.5 days) or saline vehicle (10 ml/kg; s.c.; every 3.5 days). Following a 21 day recovery period, chronic saline- and MPTP-treated mice received an additional injection of either saline (10 ml/kg; s.c.) or MPTP (20mg/kg; s.c.) and were sacrificed 24h later. NSDA neurons displayed significant axon terminal degeneration (as reflected by decreases in DA, tyrosine hydroxylase (TH) and DA transporter concentrations in the striatum) as well as loss of TH-immunoreactive (IR) neurons in the substantia nigra (SN) following MPTP, whereas TIDA neurons revealed no overt axon terminal pathology or loss of TH-IR cell bodies. NSDA neuronal pathology was associated with transient decreases in concentrations of parkin and UCHL-1 protein in the SN, which returned to normal levels by 21 days following cessation of chronic neurotoxicant exposure. Resistance of TIDA neurons to MPTP toxicity was correlated with a transient increase in UCHL-1 and a sustained elevation in parkin in the arcuate nucleus. TIDA neurons represent a DA neuron population with a unique and inherent ability to adapt to acute and chronic toxicant administration with a sustained elevation of the neuroprotective protein parkin. The correlation between the ability to increase parkin and UCHL-1 expression and the resistance of DA neurons to neurotoxicant exposure is consistent with a functional link between these features and an underlying differential susceptibility to toxicant-associated neurodegeneration.

Lymphocyte Cell Kinase Activation Mediates Neuroprotection during Ischemic Preconditioning

The molecular mechanisms underlying preconditioning (PC), a powerful endogenous neuroprotective phenomenon, remain to be fully elucidated. Once identified, these endogenous mechanisms could be manipulated for therapeutic gain. We investigated whether lymphocyte cell kinase (Lck), a member of the Src kinases family, mediates PC. We used both in vitro primary cortical neurons and in vivo mouse cerebral focal ischemia models of preconditioning, cellular injury, and neuroprotection. Genetically engineered mice deficient in Lck, gene silencing using siRNA, and pharmacological approaches were used. Cortical neurons preconditioned with sublethal exposure to NMDA or oxygen glucose deprivation (OGD) exhibited enhanced Lck kinase activity, and were resistant to injury on subsequent exposure to lethal levels of NMDA or OGD. Lck gene silencing using siRNA abolished tolerance against both stimuli. Lck−/− mice or neurons isolated from Lck−/− mice did not exhibit PC-induced tolerance. An Lck antagonist administered to wild-type mice significantly attenuated the neuroprotective effect of PC in the mouse focal ischemia model. Using pharmacological and gene silencing strategies, we also showed that PKCε is an upstream regulator of Lck, and Fyn is a downstream target of Lck. We have discovered that Lck plays an essential role in PC in both cellular and animal models of stroke. Our data also show that the PKCε-Lck-Fyn axis is a key mediator of PC. These findings provide new opportunities for stroke therapy development.

Pancreatic lipase inhibitory constituents from Morus alba leaves and optimization for extraction conditions.

The leaves of Morus alba (Moraceae) have been traditionally used for the treatment of metabolic diseases including diabetes and hyperlipidemia. Thus, inhibitory effect of M. alba leaves on pancreatic lipase and their active constituents were investigated in this study. Twenty phenolic compounds including ten flavonoids, eight benzofurans, one stilbene and one chalcones were isolated from the leaves of M. alba. Among the isolated compounds, morachalcone A (20) exerted strong pancreatic lipase inhibition with IC50 value of 6.2 μM. Other phenolic compounds containing a prenyl group showed moderate pancreatic lipase inhibition with IC50 value of <50 μM. Next, extraction conditions with maximum pancreatic lipase inhibition and phenolic content were optimized using response surface methodology with three-level-three-factor Box-Behnken design. Our results suggested the optimized extraction condition for maximum pancreatic lipase inhibition and phenolic content as ethanol concentration of 74.9%; temperature 57.4 °C and sample/solvent ratio, 1/10. The pancreatic lipase inhibition and total phenolic content under optimized condition were found to be 58.5% and 26.2 μg GAE (gallic acid equivalent)/mg extract, respectively, which were well matched with the predicted value.

Antiproliferative prenylated xanthones and benzophenones from the roots of Cudrania tricuspidata in HSC-T6 cells.

Four new prenylated xanthones, cudracuspixanthones A-D (1-4), two new prenylated benzophenones, cudracuspiphenones A (5) and B (6), and 11 known xanthones (7-17) were isolated from the roots of Cudrania tricuspidata. The absolute configurations of compounds 2-4 were deduced by the comparison of the calculated optical rotation values with the measured data. Compounds 1, 5, and 6 showed moderate antiproliferative activity on HSC-T6 cells with IC50 values of 9.7, 3.3, and 7.1 μM, respectively. Compounds 2-4, 10, and 14-16 had weaker activity. Flow cytometric analysis suggested that compounds 1 and 5 inhibited HSC-T6 cell proliferation in part by inducing apoptosis.

Suppression of Th2 chemokines by crocin via blocking of ERK‐MAPK/NF‐κB/STAT1 signalling pathways in TNF‐α/IFN‐γ‐stimulated human epidermal keratinocytes

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