Prevention of lipopolysaccharide-induced apoptosis by (2S,3S,4R)-N"-cyano-N-(6-amino-3,4-dihydro-3-hydroxy-2-methyl-2-dimethoxymethyl-2H-benzopyran-4-yl)-N'-benzylguanidine, a benzopyran analog, in endothelial cells

KR-31831 improves survival and protects hematopoietic cells and radiosensitive tissues against radiation-induced injuries in mice

This study explored the radioprotective effects and possible underlying mechanisms of KR-31831 against radiation-induced injury in a mouse model. KR-31831 (30 and 50 mg/kg) was administered to mice 24 h and 30 min before exposure to a single lethal or sublethal dose of whole-body irradiation (WBI) (7 or 4 Gy, respectively). These animals were then evaluated for changes in mortality, various hematological and biochemical parameters, and histological features in response to these treatments. In addition, RNA sequencing was used to profile the radiation-induced transcriptomic response in the bone marrow cells. The results showed that KR-31831 dose-dependently prolonged the 30-day survival period and prevented damage to radiation-sensitive organs, such as the intestine and testis, in response to WBI. Damage to the hematopoietic system was also notably improved in the KR-31831-treated mice, as evidenced by an increase in bone marrow and peripheral blood cells, as well as recovery of the histopathological characteristics of the bone marrow. These protective effects were achieved, at least in part, via the suppression of radiation-induced increases in apoptotic cell death and erythropoietin levels in the plasma. Furthermore, the gene expression profiles of the bone marrow cells of the WBI-treated mice suggested that KR-31831 upregulates the expression of the genes involved in regulating apoptosis and modulating the immune response, both of which are required for protecting the bone marrow. These results suggest the potential therapeutic efficacy of KR-31831 for protection against radiation-induced injury.

Effect of endotoxin, dobutamine and dopamine on muscle mitochondrial respiration in vitro

Introduction: Mitochondrial respiration is impaired during endotoxemia. While catecholamines are frequently used in sepsis, their effects on mitochondrial function are controversial. We assessed effects of dobutamine and dopamine endotoxin on isolated muscle mitochondria.

Materials and Methods : Sternocleidomastoid muscle mitochondria were isolated from six anesthetized pigs. Each sample was divided into six different groups. Three groups were incubated with endotoxin, three with vehicle. After 1 h, dopamine and dobutamine at final concentrations of 100 µM were added to the vehicle and endotoxin groups. After 2 h, state 3 and 4 respiration rates were determined for all mitochondrial complexes. Oxygen consumption was determined with a Clark-type electrode.

Results: Endotoxin increased glutamate-dependent state 4 respiration from 9.3 ± 3.6 to 31.9 ± 9.1 ( P = 0.001) without affecting state 3 respiration. This reduced the efficiency of mitochondrial respiration (RCR; state 3/state 4, 9.9 ± 1.9 versus 3.6 ± 0.6; P < 0.001). The other complexes were unaffected. Catecholamine partially restored the endotoxin-induced increase in complex I state 4 respiration rate (31.9 ± 9.1 versus 17.1 ± 6.4 and 20.1 ± 12.2) after dopamine and dobutamine, respectively ( P = 0.007), and enhanced the ADP:O ratio ( P = 0.033).

Conclusions: Dopamine and dobutamine enhanced the efficiency of mitochondrial respiration after short-term endotoxin exposure.

Neuroprotective Effect of KR-31378, a Novel Potassium Channel Activator, on Spinal Cord Ischemic Injury in Rabbits

Neurologic deficits after the surgical repair of thoracic and thoracoabdominal aortic disease are devastating complications. Recently, pharmacologic preconditioning with potassium channel openers was reported to protect the spinal cord against neurologic injury in a model of spinal cord ischemia. A novel benzopyran derivative with an N-cyanoguanidine group, KR-31378, has been synthesized as a new therapeutic agent against ischemic injury. In the present study, we evaluated the protective effects of KR-31378 on spinal cord ischemic injury and compared its neuroprotective activities and hemodynamic stabilities with those of diazoxide. Thirty-four New Zealand white rabbits were randomly divided into four groups: ischemia group (n = 10, 25 min of aortic cross-clamping without any intervention), diazoxide group (n = 8, diazoxide [5 mg/kg] intravenously 15 min before the 25-min cross-clamping), KR20 group (n = 8, KR-31378 [20 mg/kg] intravenously 30 min before the 25-min cross-clamping), and the KR50 group (n = 8, KR-31378 [50 mg/kg] intravenously 30 min before the 25-min cross-clamping). Neurologic functions were evaluated for 72 h postoperatively using modified Tarlov's scores. All rabbits were sacrificed for histopathologic observations after finally scoring neurologic function. All rabbits but three survived. The rest were completely evaluated 72 h postoperatively. Unlike diazoxide-treated rabbits, KR-31378-treated rabbits showed relatively stable hemodynamics. Tarlov's score outcomes showed a marked improvement in the diazoxide group, in the KR20 group, and in the KR50 group compared to the ischemia group (p = .005, .002, and .001, respectively). However, Tarlov's scores in the KR50 group were not significantly different from those of the diazoxide group. Histopathologic data were not significantly different between the groups, but the degree of degenerative change in motor neurons showed a significant correlation with Tarlov's scores 3 days postoperatively (gamma = -.378, p = .036). Thus, the administration of KR-31378 before the aortic cross-clamping resulted in a significant improvement in neurologic outcome with stable hemodynamics in this rabbit model.

The intrinsic apoptotic pathway is required for lipopolysaccharide-induced lung endothelial cell death

LPS has been implicated in the pathogenesis of endothelial cell death associated with Gram-negative bacterial sepsis. The binding of LPS to the TLR-4 on the surface of endothelial cells initiates the formation of a death-inducing signaling complex at the cell surface. The subsequent signaling pathways that result in apoptotic cell death remain unclear and may differ among endothelial cells in different organs. We sought to determine whether LPS and cycloheximide-induced cell death in human lung microvascular endothelial cells (HmVECs) was dependent upon activation of the intrinsic apoptotic pathway and the generation of reactive oxygen species. We found that cells overexpressing the anti-apoptotic protein Bcl-X(L) were resistant to LPS and cycloheximide-induced death and that the proapoptotic Bcl-2 protein Bid was cleaved following treatment with LPS. The importance of Bid was confirmed by protection of Bid-deficient (bid(-/-)) mice from LPS-induced lung injury. Neither HmVECs treated with the combined superoxide dismutase/catalase mimetic EUK-134 nor HmVECs depleted of mitochondrial DNA (rho(0) cells) were protected against LPS and cycloheximide-induced death. We conclude that LPS and cycloheximide-induced death in HmVECs requires the intrinsic cell death pathway, but not the generation of reactive oxygen species.

Mechanisms of cell death in oxidative stress

Reactive oxygen or nitrogen species (ROS/RNS) generated endogenously or in response to environmental stress have long been implicated in tissue injury in the context of a variety of disease states. ROS/RNS can cause cell death by nonphysiological (necrotic) or regulated pathways (apoptotic). The mechanisms by which ROS/RNS cause or regulate apoptosis typically include receptor activation, caspase activation, Bcl-2 family proteins, and mitochondrial dysfunction. Various protein kinase activities, including mitogen-activated protein kinases, protein kinases-B/C, inhibitor-of-I-kappaB kinases, and their corresponding phosphatases modulate the apoptotic program depending on cellular context. Recently, lipid-derived mediators have emerged as potential intermediates in the apoptosis pathway triggered by oxidants. Cell death mechanisms have been studied across a broad spectrum of models of oxidative stress, including H2O2, nitric oxide and derivatives, endotoxin-induced inflammation, photodynamic therapy, ultraviolet-A and ionizing radiations, and cigarette smoke. Additionally ROS generated in the lung and other organs as the result of high oxygen therapy or ischemia/reperfusion can stimulate cell death pathways associated with tissue damage. Cells have evolved numerous survival pathways to counter proapoptotic stimuli, which include activation of stress-related protein responses. Among these, the heme oxygenase-1/carbon monoxide system has emerged as a major intracellular antiapoptotic mechanism.

KR-31378 protects cardiac H9c2 cells from chemical hypoxia-induced cell death via inhibition of JNK/p38 MAPK activation

Using a metabolic inhibition buffer as an ischemic model, we show here that KR-31378, a cardioselective ATP-sensitive potassium channel opener, protects H9c2 cells from chemical hypoxia (CH)-induced cell death. Our previous study showed that CH downregulated caspase activities, but led to differential activation of mitogen-activated protein kinases (MAPKs) in H9c2 cells. The repression of CH-induced c-jun N-terminal kinase (JNK)/p38 MAPK activation resulted in partial protection against CH- induced cell death, implying JNK/p38 MAPK's causative role in CH-induced cell death. This study furthers that research and examines if KR-31378's protective effect came from modulating MAPK activity and/or caspase activity in H9c2 cells. Although KR-31378 did not restore downregulated caspase-3 activity, it did block the activation of JNK and p38 MAPK in a dose-dependent manner. Extracellular signal-regulated kinase activity was not recovered by KR-31378 treatment. CH-induced reactive oxygen species (ROS) generation was suppressed by KR-31378. Thus our results indicate that the cardioprotective effect of KR-31378 in CH is due, at least in part, to the differential inhibition of MAPKs.

Anti-apoptotic action of (2S,3S,4R)-N"-cyano-N-(6-amino-3,4-dihydro-3-hydroxy-2-methyl-2-dimethoxymethyl-2H-benzopyran-4-yl)-N'-benzylguanidine (KR-31378) by suppression of the phosphatase and tensin homolog deleted from chromosome 10 phosphorylation and increased phosphorylation of casein kinase2/Akt/ cyclic AMP response element binding protein via maxi-K channel opening in neuronal cells

This study shows the signaling pathway by which (2S,3S,4R)-N"-cyano-N-(6-amino-3,4-dihydro-3-hydroxy-2-methyl-2-dimethoxymethyl-2H-benzopyran-4-yl)-N'-benzylguanidine (KR-31378) prevents tumor necrosis factor (TNF)-alpha-induced neuronal cell death. KR-31378 restored TNF-alpha-induced decreased cell viability of SK-N-SH. U87-MG cells (PTEN-null glioblastoma cell line) transfected with expression vectors for sense PTEN (phosphatase and tensin homolog deleted from chromosome 10) showed significantly decreased cell viability, which was restored by KR-31378. TNF-alpha-induced increased PTEN phosphorylation and decreased phosphorylation of Akt/cyclic AMP response element-binding protein (CREB) in SK-N-SH cells were concentration-dependently reversed by KR-31378, those of which were antagonized by iberiotoxin, a maxi-K channel blocker. TNF-alpha and apigenin, a casein kinase2 (CK2) inhibitor, showed decreased CK2 phosphorylation and increased PTEN phosphorylation, which were reversed by KR-31378. KR-31378 increased K(+) currents by activating the maxi-K channels in SK-N-SH cells, with suppression of TNF-alpha-induced increase in cytosolic Ca(2+) and elevation of suppressed mitochondrial membrane potential, all of which were antagonized by iberiotoxin. It is suggested that increase in cell viability by KR-31378 is ascribed to the maxi-K channel opening-coupled upregulation of CK2/Akt/CREB phosphorylation and downregulation of PTEN phosphorylation in association with increased Bcl-2 and decreased Bax levels.

Effects of a new neuroprotective agent KR-31378 on liver cytochrome P450s in male Sprague Dawley rats

The effects of KR-31378, a neuroprotective agent for ischemia-reperfusion damage, on liver microsomal cytochrome P450s (CYPs) were investigated in male Sprague Dawley rats. When rats were treated orally with KR-31378 for 7 consecutive days, CYP3A-selective erythromycin N-demethylase (ERDM) activity was significantly induced in a dose-dependent manner. In Western immunoblotting, CYP 3A proteins were clearly induced by treatment with KR-31378. Within 24 h after treatment with 80 mg/kg of KR-31378, ERDM activity was induced in liver microsomes in accompanied by induction of the level of CYP 3A proteins. The present results suggest that KR-31378 might modulate the expression of CYP 3A enzymes in humans.

Lipopolysaccharide initiates a TRAF6-mediated endothelial survival signal

Similar to tumor necrosis factor (TNF), bacterial lipopolysaccharide (LPS) elicits parallel apoptotic and antiapoptotic pathways in endothelial cells. The overall result is that there is minimal endothelial cell death in response to LPS without inhibition of the cytoprotective pathway. While the TNF-induced death and survival pathways have been relatively well elucidated, much remains to be learned about LPS signaling events in this regard. It is known that the transcription factor nuclear factor-κB (NF-κB) provides a critical cell survival signal in response to TNF, but is not an essential component of the LPS-induced survival pathway. The TNF receptor-associated factor 6 (TRAF6) is a major effector of multiple LPS-induced signals, including a c-Jun N-terminal kinase (JNK)-mediated apoptotic response. In this report we demonstrate that following LPS stimulation, TRAF6 also transmits an important endothelial cell survival signal in a situation of complete NF-κB blockade. In response to LPS, TRAF6 activates the phosphatidylinositol 3′-kinase (PI3K)/Akt pathway, but not ERK1/2 mitogen-activated protein kinases (MAPKs) in endothelial cells. Activation of PI3K signals a critical antiapoptotic pathway in response to LPS in endothelial cells, whereas ERK1/2 does not. Thus TRAF6 acts as a bifurcation point of the LPS-initiated death and survival signals in endothelial cells. (Blood. 2004;103:4520-4526)

KR-31378 protects neurons from ischemia–reperfusion brain injury by attenuating lipid peroxidation and glutathione loss

Neuronal hyperexcitability and oxidative stress play critical roles in neuronal cell death in stroke. Therefore, we studied the effects of (2S,3S,4R)-N?-cyano-N-(6-amino-3,4-dihydro-3-hydroxy-2-methyl-2-dimethoxymethyl-2H-benzopyran-4-yl)-N'-benzylguanidine (KR-31378), possessing both antioxidant and K(+) channel-modulating activities, on brain ischemia-reperfusion injury models. Treatment with KR-31378 (30 mg/kg, i.v.) significantly reduced infarct area and edema by 24% and 36%, respectively, in rats subjected to 2 h of middle cerebral artery occlusion and 22 h of reperfusion with significant attenuation of elevated lipid peroxidation (99% of normal) and glutathione loss (60% of normal) in ischemic hemisphere. We further studied its neuroprotective mechanism in fetal rat primary mixed cortical culture. Incubation of cortical neurons with KR-31378 protected FeSO(4)-induced cell death in a concentration-dependent manner (IC(50)=12 microM). Its neuroprotective effect was neither mimicked by other K(+) channel openers nor abolished in the presence of ATP-dependent K(+) channel (K(ATP)) blockers, indicating that its effect was not related to K(+) channel opening activity. The mechanism of protection is rather attributable to the antioxidant property of KR-31378 since it suppressed the intracellular accumulation of reactive oxygen species and ensured lipid peroxidation by 120% and 80%, respectively, caused by FeSO(4). We further studied its effect on antioxidant defense, enzymatic and nonenzymatic systems. Treatment of neurons with FeSO(4) resulted in decrease of catalase (8% of control) and glutathione peroxidase (14% of control) activities, which were restored by KR-31378 treatment (70% and 57% of control, respectively). In addition, it attenuated the depletion of glutathione contents (60% of control) caused by FeSO(4). These results suggest that KR-31378 exerts a beneficial effect in focal ischemia, which may be attributed to its antioxidant property.

KR‐31378 ameliorates atherosclerosis by blocking monocyte recruitment in hypercholestrolemic mice

The recruitment of monocytes into the artery wall is a crucial early step in atherogenesis. A novel compound, KR-31378, has been shown to be a neuroprotective agent for ischemia-reperfusion damage in rat brain via its potent antioxidant and antiapoptotic actions. Here, we report the effects of this compound on atherogenesis and possible mechanisms of action. In Ldlr knockout mice fed with a high-fat, high-cholesterol diet, treatment with KR-31378 significantly inhibited fatty streak formation and macrophage accumulation. To address the possibility that KR-31378 may influence the initial stages of atherogenesis, we examined its effect on the adhesion and migration of monocytes to endothelial cells stimulated with tumor necrosis factor-alpha. KR-31378 decreased the adhesion in a dose-dependent manner. The observed decreases in cell adhesion and migration correlated with KR-31378-mediated down-regulation of vascular cell adhesion molecule-1 (VCAM-1) and interleukin (IL)-8. Nuclear factor-kappaB (NF-kappaB) is known to regulate the expression of adhesive and chemotactic molecules including VCAM-1 and IL-8. Indeed, transient transfection experiments, electrophoretic mobility shift assay, and IkappaB degradation assay showed that KR-31378 decreased NF-kappaB activation. These results indicate that KR-31378 potently reduces fatty streak formation by inhibiting NF-kappaB-dependent cellular adhesion and chemotactic molecule expression, which are crucial to monocyte infiltration into the arterial wall during the early stages of atherogenesis.

Reactive oxygen and nitrogen intermediates contribute to Haemophilus somnus lipooligosaccharide-mediated apoptosis of bovine endothelial cells

Although Haemophilus somnus causes septicemia and vasculitis in cattle, relatively little is known about how H. somnus affects endothelial cells in vitro. We previously reported that H. somnus lipooligosaccharide (LOS)-induced activation of caspases-3, -8 and -9, and apoptosis of bovine pulmonary artery endothelial cells (BPAEC) in vitro. Previous reports indicate that the generation of reactive oxygen species (ROS) or reactive nitrogen intermediates (RNI) can contribute to the induction of apoptosis. In the present study, we sought to determine whether ROS and RNI are involved in LOS-mediated apoptosis of BPAEC. We found that H. somnus LOS induced the generation of ROS in BPAEC, which was blocked by pretreatment with membrane permeable ROS scavengers, such as dimethylsulfoxide (DMSO) and allopurinol (AP). Addition of DMSO or AP significantly reduced H. somnus LOS-mediated caspase-3 activation. Addition of membrane impermeable ROS scavengers (e.g. catalase and superoxide dismutase), failed to block LOS-mediated caspase-3 activation, suggesting a role for intracellular generation of ROS in LOS-induced apoptosis of BPAEC. Addition of N(G)-nitro-L-arginine methyl ester (L-NAME) or aminoguanidine, which are selective inhibitors of nitric oxide synthase, blocked NO release and significantly reduced caspase-3 activation in LOS treated BPAEC. These data suggest H. somnus LOS triggers endogenous ROS and RNI production by endothelial cells, which contributes to apoptosis.

Evidence that lipopolysaccharide-induced cell death is mediated by accumulation of reactive oxygen species and activation of p38 in rat cortex and hippocampus

Lipopolysaccharide (LPS) administration stimulates immune activation, inflammation and deterioration in cell function. Neuronal tissue in cortex and hippocampus are particularly susceptible. In this study, we report that LPS induces cell death as measured by caspase-3 activation and DNA fragmentation and that this is coupled with stimulation of the mitogen-activated protein kinase, p38. We provide evidence of co-localization of activated p38 and caspase-3 in cells prepared from cortical and hippocampal tissue after LPS treatment. Furthermore, administration of the p38 inhibitor, SB203580, abolished the LPS-induced increase in caspase-3 activation. We observed that LPS treatment provoked accumulation of reactive oxygen species (ROS) while in vitro incubation of cortical and hippocampal tissue with H(2)O(2) increased p38 activity. In addition, H(2)O(2)-induced activation of caspase-3 was abrogated by SB203580. We propose, based on the data presented, that the action of LPS to induce cell death in cortex and hippocampus may be mediated by ROS accumulation and activation of p38.

Mechanisms of bacterial lipopolysaccharide-induced endothelial apoptosis

Gram-negative bacterial sepsis remains a common, life-threatening event. The prognosis for patients who develop sepsis-related complications, including the development of acute respiratory distress syndrome (ARDS), remains poor. A common finding among patients and experimental animals with sepsis and ARDS is endothelial injury and/or dysfunction. A component of the outer membrane of gram-negative bacteria, lipopolysaccharide (LPS) or endotoxin, has been implicated in the pathogenesis of much of the endothelial cell injury and/or dysfunction associated with these disease states. LPS is a highly proinflammatory molecule that elicits a wide array of endothelial responses, including the upregulation of cytokines, adhesion molecules, and tissue factor. In addition to activation, LPS induces endothelial cell death that is apoptotic in nature. This review summarizes the evidence for LPS-induced vascular endothelial injury and examines the molecular signaling pathways that activate and inhibit LPS-induced endothelial apoptosis. Furthermore, the role of apoptotic signaling molecules in mediating LPS-induced activation of endothelial cells will be considered.

Simultaneous determination of the novel neuroprotective agent KR-31378 and its metabolite KR-31612 using high performance liquid chromatography with tandem mass spectrometry in human plasma

An LC/MS/MS method for the simultaneous determination of a neuroprotective agent for ischemia-reperfusion damage, KR-31378 and its N-acetyl metabolite KR-31612 in human plasma was developed. KR-31378, KR-31612 and the internal standard, KR-31543 were extracted from human plasma by liquid-liquid extraction. A reverse-phase HPLC separation was performed on Luna phenylhexyl column with the mixture of acetonitrile-5 mM ammonium formate (55:45, v/v) as mobile phase. The detection of analytes was performed using an electrospray ionization tandem mass spectrometry in the multiple reaction monitoring mode. The lower limits of quantification for KR-31378 and KR-31612 were 2.0 ng/ml. The method showed a satisfactory sensitivity, precision, accuracy, recovery and selectivity.

Neuroprotective effect of (2S,3S,4R)-N"-cyano-N-(6-amino-3, 4-dihydro-3-hydroxy-2-methyl-2-dimethoxymethyl-2H-benzopyran-4-yl)-N'-benzylguanidine (KR-31378), a benzopyran analog, against focal ischemic brain damage in rats

This study shows the preventive effect of KR-31378 [(2S,3S,4R)-N"-cyano-N-(6-amino-3,4-dihydro-3-hydroxy-2-methyl-2-dimethoxymethyl-2H-benzopyran-4-yl)-N'-benzylguanidine] against cerebral infarct via antioxidant and antiapoptotic actions evoked by subjecting rats to 2 h of occlusion of the left middle cerebral artery followed by 24 h of reperfusion. The brain infarct zone in the cortex and striatum of the left hemisphere was consistently identified in the cortex and striatum of the left hemisphere. The infarct area was significantly reduced after three intraperitoneal administrations of 10, 30, or 50 mg/kg KR-31378 at 5 min, 4 h, and 8 h after the completion of 2 h of ischemia. Treatment with KR-31378 (30 or 50 mg/kg) significantly reduced the increase in the number of terminal deoxynucleotidyl transferase dUTP nick-end labeling positive cells as well as strongly suppressed the laddered feature of DNA fragmentation in the lateral cortical tissue corresponding to the penumbra. The findings of samples from penumbral zone, which showed markedly reduced Bcl-2 protein level and increased Bax protein and cytochrome c release, were wholly reversed by treatment with KR-31378. In conclusion, postischemic treatment with KR-31378 provided significant levels of cortical neuroprotection in association with inhibition of apoptotic cell death through the up-regulation of Bcl-2 expression, and the down-regulation of Bax protein and cytochrome c release.