Metabolic effects of carbenoxolone in rat liver

Toluidine blue O directly and photodynamically impairs the bioenergetics of liver mitochondria: a potential mechanism of hepatotoxicity

Toluidine blue O (TBO) is a phenothiazine dye that, due to its photochemical characteristics and high affinity for biomembranes, has been revealed as a new photosensitizer (PS) option for antimicrobial photodynamic therapy (PDT). This points to a possible association with membranous organelles like mitochondrion. Therefore, here we investigated its effects on mitochondrial bioenergetic functions both in the dark and under photostimulation. Two experimental systems were utilized: (a) isolated rat liver mitochondria and (b) isolated perfused rat liver. Our data revealed that, independently of photostimulation, TBO presented affinity for mitochondria. Under photostimulation, TBO increased the protein carbonylation and lipid peroxidation levels (up to 109.40 and 119.87%, respectively) and decreased the reduced glutathione levels (59.72%) in mitochondria. TBO also uncoupled oxidative phosphorylation and photoinactivated the respiratory chain complexes I, II, and IV, as well as the F_oF₁-ATP synthase complex. Without photostimulation, TBO caused uncoupling of oxidative phosphorylation and loss of inner mitochondrial membrane integrity and inhibited very strongly succinate oxidase activity. TBO's uncoupling effect was clearly seen in intact livers where it stimulated oxygen consumption at concentrations of 20 and 40 μM. Additionally, TBO (40 μM) reduced cellular ATP levels (52.46%) and ATP/ADP (45.98%) and ATP/AMP (74.17%) ratios. Consequently, TBO inhibited gluconeogenesis and ureagenesis whereas it stimulated glycogenolysis and glycolysis. In conclusion, we have revealed for the first time that the efficiency of TBO as a PS may be linked to its ability to photodynamically inhibit oxidative phosphorylation. In contrast, TBO is harmful to mitochondrial energy metabolism even without photostimulation, which may lead to adverse effects when used in PDT.

The metabolic and toxic acute effects of phloretin in the rat liver

The current study sought to evaluate the acute effects of phloretin (PH) on metabolic pathways involved in the maintenance of glycemia, specifically gluconeogenesis and glycogenolysis, in the perfused rat liver. The acute effects of PH on energy metabolism and toxicity parameters in isolated hepatocytes and mitochondria, as well as its effects on the activity of a few key enzymes, were also evaluated. PH inhibited gluconeogenesis from different substrates, stimulated glycogenolysis and glycolysis, and altered oxygen consumption. The citric acid cycle activity was inhibited by PH under gluconeogenic conditions. Similarly, PH reduced the cellular ATP/ADP and ATP/AMP ratios under gluconeogenic and glycogenolytic conditions. In isolated mitochondria, PH inhibited the electron transport chain and the F_oF₁-ATP synthase complex as well as acted as an uncoupler of oxidative phosphorylation, inhibiting the synthesis of ATP. PH also decreased the activities of malate dehydrogenase, glutamate dehydrogenase, glucose 6-phosphatase, and glucose 6-phosphate dehydrogenase. Part of the bioenergetic effects observed in isolated mitochondria was shown in isolated hepatocytes, in which PH inhibited mitochondrial respiration and decreased ATP levels. An aggravating aspect might be the finding that PH promotes the net oxidation of NADH, which contradicts the conventional belief that the compound operates as an antioxidant. Although trypan blue hepatocyte viability tests revealed substantial losses in cell viability over 120 min of incubation, PH did not promote extensive enzyme leakage from injured cells. In line with this effect, only after a lengthy period of infusion did PH considerably stimulate the release of enzymes into the effluent perfusate of livers. In conclusion, the increased glucose release caused by enhanced glycogenolysis, along with suppression of gluconeogenesis, is the opposite of what is predicted for antihyperglycemic agents. These effects were caused in part by disruption of mitochondrial bioenergetics, a result that should be considered when using PH for therapeutic purposes, particularly over long periods and in large doses.

Carbenoxolon Is Capable to Regulate the Mitochondrial Permeability Transition Pore Opening in Chronic Alcohol Intoxication

Background: carbenoxolone, which is a derivative of glyceretic acid, is actively used in pharmacology for the treatment of diseases of various etiologies. In addition, we have shown carbenoxolone as an effective inducer of mitochondrial permeability transition pore in rat brain and liver mitochondria. Methods: in the course of this work, comparative studies were carried out on the effect of carbenoxolone on the parameters of mPTP functioning in mitochondria isolated from the liver of control and alcoholic rats. Results: within the framework of this work, it was found that carbenoxolone significantly increased its effect in the liver mitochondria of rats with chronic intoxication. In particular, this was expressed in a reduction in the lag phase, a decrease in the threshold calcium concentration required to open a pore, an acceleration of high-amplitude cyclosporin-sensitive swelling of mitochondria, as well as an increase in the effect of carbenoxolone on the level of mitochondrial membrane-bound proteins. Thus, as a result of the studies carried out, it was shown that carbenoxolone is involved in the development/modulation of alcohol tolerance and dependence in rats.

Astrocytic Connexin43 Channels as Candidate Targets in Epilepsy Treatment

In epilepsy research, emphasis is put on exploring non-neuronal targets such as astrocytic proteins, since many patients remain pharmacoresistant to current treatments, which almost all target neuronal mechanisms. This paper reviews available data on astrocytic connexin43 (Cx43) signaling in seizures and epilepsy. Cx43 is a widely expressed transmembrane protein and the constituent of gap junctions (GJs) and hemichannels (HCs), allowing intercellular and extracellular communication, respectively. A plethora of research papers show altered Cx43 mRNA levels, protein expression, phosphorylation state, distribution and/or functional coupling in human epileptic tissue and experimental models. Human Cx43 mutations are linked to seizures as well, as 30% of patients with oculodentodigital dysplasia (ODDD), a rare genetic condition caused by mutations in the GJA1 gene coding for Cx43 protein, exhibit neurological symptoms including seizures. Cx30/Cx43 double knock-out mice show increased susceptibility to evoked epileptiform events in brain slices due to impaired GJ-mediated redistribution of K⁺ and glutamate and display a higher frequency of spontaneous generalized chronic seizures in an epilepsy model. Contradictory, Cx30/Cx43 GJs can traffic nutrients to high-energy demanding neurons and initiate astrocytic Ca²⁺ waves and hyper synchronization, thereby supporting proconvulsant effects. The general connexin channel blocker carbenoxolone and blockers from the fenamate family diminish epileptiform activity in vitro and improve seizure outcome in vivo. In addition, interventions with more selective peptide inhibitors of HCs display anticonvulsant actions. To conclude, further studies aiming to disentangle distinct roles of HCs and GJs are necessary and tools specifically targeting Cx43 HCs may facilitate the search for novel epilepsy treatments.

Enhanced cytotoxicity of imidacloprid by biotransformation in isolated hepatocytes and perfused rat liver

Imidacloprid (IMD) is a neonicotinoid insecticide widely used in crops, pets, and on farm animals for pest control, which can cause hepatotoxicity in animals and humans. In a previous study using isolated rat liver mitochondria, we observed that IMD inhibited the activity of F_oF₁-ATP synthase. The aim of this study was to evaluate the effects of IMD on rat isolated hepatocytes and perfused rat liver, besides the influence of its biotransformation on the toxicological potential. For the latter goal, rats were pretreated with dexamethasone or phenobarbital, two classical cytochrome P-450 stimulators, before hepatocytes isolation or liver perfusion. IMD (150 and 200 μM) reduced state 3 mitochondrial respiration in digitonin-permeabilized cells that were energized with glutamate plus malate but did not dissipate the mitochondrial membrane potential. In intact (non-permeabilized) hepatocytes, the intracellular ATP concentration and cell viability were reduced when high IMD concentrations were used (1.5-3.0 mM), and only in cells isolated from dexamethasone-pretreated rats, revealing that IMD biotransformation increases its toxicity and that IMD itself affects isolated mitochondria or mitochondria in permeabilized hepatocytes in concentrations that do not affect mitochondrial function in intact hepatocytes. Coherently, in the prefused liver, IMD (150 and 250 μM) inhibited gluconeogenesis from alanine, but without affecting oxygen consumption and urea production, indicating that such effect was not of mitochondrial origin. The gluconeogenesis inhibition was incomplete and occurred only when the rats were pretreated with phenobarbital, signs that IMD biotransformation was involved in the observed effect. Our findings reveal that changes in hepatic energy metabolism may be acutely implicated in the hepatotoxicity of IMD only when animals and humans are exposed to high levels of this compound, and that IMD metabolites seem to be the main cause for its toxicity.

Redox-Active Mn Porphyrin-based Potent SOD Mimic, MnTnBuOE-2-PyP(5+), Enhances Carbenoxolone-Mediated TRAIL-Induced Apoptosis in Glioblastoma Multiforme

Glioblastoma multiforme is the most malignant tumor of the brain and is challenging to treat due to its highly invasive nature and heterogeneity. Malignant brain tumor displays high metabolic activity which perturbs its redox environment and in turn translates to high oxidative stress. Thus, pushing the oxidative stress level to achieve the maximum tolerable threshold that induces cell death is a potential strategy for cancer therapy. Previously, we have shown that gap junction inhibitor, carbenoxolone (CBX), is capable of enhancing tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) -induced apoptosis in glioma cells. Since CBX is known to induce oxidative stress, we hypothesized that the addition of another potent mediator of oxidative stress, powerful SOD mimic MnTnBuOE-2-PyP(5+) (MnBuOE), could further enhance TRAIL-driven therapeutic efficacy in glioma cells. Our results showed that combining TRAIL + CBX with MnBuOE significantly enhances cell death of glioma cell lines and this enhancement could be further potentiated by CBX pretreatment. MnBuOE-driven cytotoxicity is due to its ability to take advantage of oxidative stress imposed by CBX + TRAIL system, and enhance it in the presence of endogenous reductants, ascorbate and thiol, thereby producing cytotoxic H2O2, and in turn inducing death of glioma cells but not normal astrocytes. Most importantly, combination treatment significantly reduces viability of TRAIL-resistant Asian patient-derived glioma cells, thus demonstrating the potential clinical use of our therapeutic system. It was reported that H2O2 is involved in membrane depolarization-based sensitization of cancer cells toward TRAIL. MnBuOE is entering Clinical Trials as a normal brain radioprotector in glioma patients at Duke University increasing Clinical relevance of our studies.

Solid-state supramolecular architecture of carbenoxolone – comparative studies with glycyrrhetinic and glycyrrhizic acids

Carbenoxolone (CBXH2), a pharmaceutically relevant derivative of glycyrrhetinic acid, was studied by X-ray crystallography. The crystal structures of its unsolvated form, propionic acid and dimethoxyethane solvates and a solvated cocrystal of the free acid with its monobasic sodium salt CBXH2·CBXHNa·(butan-2-one)2·2H2O reveal that the recurring motif of supramolecular architecture in all crystal forms is a one-dimensional ribbon with closely packed triterpene fragments. It does not result from strong specific interactions but solely from van der Waals interactions. The ribbons are further arranged into diverse layer-type aggregates with a hydrophobic interior (triterpene skeletons) and hydrophilic surfaces covered with carboxylic/carboxylate groups. Solvent molecules included at the interface between the layers influence hydrogen-bonding interactions between the carbenoxolone molecules and organization of the ribbons within the layer. Comparison of crystal structures of carbenoxolone, glycyrrhizic acid and its aglycone-glycyrrhetinic acid have shown the impact of the size and hydrophilic character of the substituent at the triterpene C3 atom on the supramolecular architecture of these three closely related molecules.

Hemolysis is a primary ATP-release mechanism in human erythrocytes

The hypothesis that regulated ATP release from red blood cells (RBCs) contributes to nitric oxide-dependent control of local blood flow has sparked much interest in underlying release mechanisms. Several stimuli, including shear stress and hypoxia, have been found to induce significant RBC ATP release attributed to activation of ATP-conducting channels. In the present study, we first evaluated different experimental approaches investigating stimulated RBC ATP release and quantifying hemolysis. We then measured ATP and free hemoglobin in each and every RBC supernatant sample to directly assess the contribution of hemolysis to ATP release. Hypotonic shock, shear stress, and hypoxia, but not cyclic adenosine monophosphate agonists, significantly enhanced ATP release. It tightly correlated, however, with free hemoglobin in RBC supernatants, indicating that lysis was responsible for most, if not all, ATP release. Luminescence ATP imaging combined with simultaneous infrared cell imaging showed that ATP was released exclusively from lysing cells with no contribution from intact cells. In summary, with all stimuli tested, we found no evidence of regulated ATP release from intact RBCs other than by cell lysis. Such a release mechanism might be physiologically relevant in vivo, eg, during exercise and hypoxia where intravascular hemolysis, predominantly of senescent cells, is augmented.

Pathway analysis reveals common pro-survival mechanisms of metyrapone and carbenoxolone after traumatic brain injury

Developing new pharmacotherapies for traumatic brain injury (TBI) requires elucidation of the neuroprotective mechanisms of many structurally and functionally diverse compounds. To test our hypothesis that diverse neuroprotective drugs similarly affect common gene targets after TBI, we compared the effects of two drugs, metyrapone (MT) and carbenoxolone (CB), which, though used clinically for noncognitive conditions, improved learning and memory in rats and humans. Although structurally different, both MT and CB inhibit a common molecular target, 11β hydroxysteroid dehydrogenase type 1, which converts inactive cortisone to cortisol, thereby effectively reducing glucocorticoid levels. We examined injury-induced signaling pathways to determine how the effects of these two compounds correlate with pro-survival effects in surviving neurons of the injured rat hippocampus. We found that treatment of TBI rats with MT or CB acutely induced in hippocampal neurons transcriptional profiles that were remarkably similar (i.e., a coordinated attenuation of gene expression across multiple injury-induced cell signaling networks). We also found, to a lesser extent, a coordinated increase in cell survival signals. Analysis of injury-induced gene expression altered by MT and CB provided additional insight into the protective effects of each. Both drugs attenuated expression of genes in the apoptosis, death receptor and stress signaling pathways, as well as multiple genes in the oxidative phosphorylation pathway such as subunits of NADH dehydrogenase (Complex1), cytochrome c oxidase (Complex IV) and ATP synthase (Complex V). This suggests an overall inhibition of mitochondrial function. Complex 1 is the primary source of reactive oxygen species in the mitochondrial oxidative phosphorylation pathway, thus linking the protective effects of these drugs to a reduction in oxidative stress. The net effect of the drug-induced transcriptional changes observed here indicates that suppressing expression of potentially harmful genes, and also, surprisingly, reduced expression of pro-survival genes may be a hallmark of neuroprotective therapeutic effects.

Gap junctions: the claymore for cancerous cells

INTRODUCTION

Gap junctions play an important role in the cell proliferation in mammalian cells as well as carcinogenesis. However, there are controversial issues about their role in cancer pathogenesis. This study was designed to evaluate genotoxicity and cytotoxicity of Carbenoxolone (CBX) as a prototype of inter-cellular gap junction blocker in MCF7 and BT20 human breast cancer cells.

METHODS

The MCF7and BT20 human breast cancer cell lines were cultivated, and treated at designated confluency with different doses of CBX. Cellular cytotoxicity was examined using standard colorimetric assay associated with cell viability tests. Gene expression evaluation was carried out using real time polymerase chain reaction (PCR).

RESULTS

MCF7 and BT20 cells were significantly affected by CBX in a dose dependent manner in cell viability assays. Despite varying expression of genes, down regulation of pro- and anti-apoptotic genes was observed in these cells.

CONCLUSION

Based upon this investigation, it can be concluded that CBX could affect both low and high proliferative types of breast cancer cell lines and disproportionate down regulation of both pre- and anti-apoptotic genes may be related to interacting biomolecules, perhaps via gap junctions.

Pharmacological and genetic approaches to study connexin-mediated channels in glial cells of the central nervous system

This review gives an overview of connexin expression in glial cells of the central nervous system, the different modes of connexin action, including gap junctional channels and hemichannels, as well as the available methodologies to measure their activity. We summarize the strengths and limitations of current pharmacological and genetic approaches to interfere with connexin channel functions. We outline new avenues not only to study specific mechanisms by which connexins exert these functions but also to selectively investigate well-defined coupling compartments among glial networks.

Development and application of a simplified sample preparation method for determination of TEGDMA and related metabolites

Analysis of biological samples obtained from in vivo experiments can be often challenging. In general it is not possible to apply the commonly used matrices that are necessary for the experiments to the desired analysis systems without further conditioning or sample purification steps. Besides possible adverse effects for instruments, interference between analytes and matrices can affect the correct measurement of analytes. Different methods of sample preparation can be used to convert biological samples into samples suitable for analysis; SPE and HS-SPME are two well established methods. Research of in vivo metabolism of triethyleneglycoledimethacrylate (TEGDMA), one of the most frequently contained comonomer in dental restorative materials, demands sample preparation methods that offer separation of TEGDMA and its related metabolites from biological matrices. In the presented study two methods for sample preparation were developed in order to analyze TEGDMA as well as its metabolites triethyleneglycole (TEG), 2,3-epoxymethacrylicacid methylester (2,3-EMME), and methacrylacid methylester (MAME) in Krebs-Henseleit buffer samples to facilitate a subsequent analysis via GC-MS. An easy and time-saving separation protocol was developed. Recovery rates of TEGDMA and TEG after SPE were 21 +/- 3% and 105 +/- 12%, respectively, recovery rate after headspace extraction of 2,3-EMME and MAME was higher at 48 degrees C compared with 20 degrees C extraction temperature. The tested range for 2,3-EMME and MAME concentration after HS-SPME extraction was 0.1-100 mg/L and both analytes showed a good linearity.

Development of chemosensitivity in neurons from the nucleus tractus solitarii (NTS) of neonatal rats

We studied the development of chemosensitivity during the neonatal period in rat nucleus tractus solitarii (NTS) neurons. We determined the percentage of neurons activated by hypercapnia (15% CO(2)) and assessed the magnitude of the response by calculating the chemosensitivity index (CI). There were no differences in the percentage of neurons that were inhibited (9%) or activated (44.8%) by hypercapnia or in the magnitude of the activated response (CI 164+/-4.9%) in NTS neurons from neonatal rats of all ages. To assess the degree of intrinsic chemosensitivity in these neurons we used chemical synaptic block medium and the gap junction blocker carbenoxolone. Chemical synaptic block medium slightly decreased basal firing rate but did not affect the percentage of NTS neurons that responded to hypercapnia at any neonatal age. However, in neonates aged Collapse

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MESH Headings

• Age Factors
• Analysis of Variance
• Animals
• Animals, Newborn
• Carbenoxolone/pharmacology
• Carbon Dioxide/pharmacology
• Chemoreceptor Cells/physiology
• Drug Interactions
• Electric Stimulation
• Hypercapnia/physiopathology
• In Vitro Techniques
• Membrane Potentials/drug effects
• Membrane Potentials/physiology
• Patch-Clamp Techniques/methods
• Rats
• Rats, Sprague-Dawley
• Solitary Nucleus/cytology
• Solitary Nucleus/growth & development

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Grants

• R01 HL056683-08 NHLBI NIH HHS
• HL-56683 NHLBI NIH HHS
• R01 HL056683-10 NHLBI NIH HHS
• R01 HL056683-09A1 NHLBI NIH HHS
• R01 HL056683-11 NHLBI NIH HHS
• R01 HL056683 NHLBI NIH HHS

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Affiliation(s)

Susan C. Conrad Department of Neuroscience, Cell Biology and Physiology, Wright State University School of Medicine, 3640 Colonel Glenn Highway, Dayton, OH 45435
Nicole L. Nichols Department of Neuroscience, Cell Biology and Physiology, Wright State University School of Medicine, 3640 Colonel Glenn Highway, Dayton, OH 45435
Nick A. Ritucci Department of Neuroscience, Cell Biology and Physiology, Wright State University School of Medicine, 3640 Colonel Glenn Highway, Dayton, OH 45435
Jay B. Dean Department of Molecular Pharmacology and Physiology, University of South Florida College of Medicine, 12901 Bruce B. Downs Boulevard, Tampa, FL 33612
Robert W. Putnam Department of Neuroscience, Cell Biology and Physiology, Wright State University School of Medicine, 3640 Colonel Glenn Highway, Dayton, OH 45435

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Characterization of the chemosensitive response of individual solitary complex neurons from adult rats

We studied the CO(2)/H(+)-chemosensitive responses of individual solitary complex (SC) neurons from adult rats by simultaneously measuring the intracellular pH (pH(i)) and electrical responses to hypercapnic acidosis (HA). SC neurons were recorded using the blind whole cell patch-clamp technique and loading the soma with the pH-sensitive dye pyranine through the patch pipette. We found that SC neurons from adult rats have a lower steady-state pH(i) than SC neurons from neonatal rats. In the presence of chemical and electrical synaptic blockade, adult SC neurons have firing rate responses to HA (percentage of neurons activated or inhibited and the magnitude of response as determined by the chemosensitivity index) that are similar to SC neurons from neonatal rats. They also have a typical response to isohydric hypercapnia, including decreased DeltapH(i), followed by pH(i) recovery, and increased firing rate. Thus, the chemosensitive response of SC neurons from adults is similar to the chemosensitive response of SC neurons from neonatal rats. Because our findings for adults are similar to previously reported values for neurons from neonatal rats, we conclude that intrinsic chemosensitivity is established early in development for SC neurons and is maintained throughout adulthood.