Natural Products and Small Molecules Targeting Cellular Ceramide Metabolism to Enhance Apoptosis in Cancer Cells

Molecular targeting strategies have been used for years in order to control cancer progression and are often based on targeting various enzymes involved in metabolic pathways. Keeping this in mind, it is essential to determine the role of each enzyme in a particular metabolic pathway. In this review, we provide in-depth information on various enzymes such as ceramidase, sphingosine kinase, sphingomyelin synthase, dihydroceramide desaturase, and ceramide synthase which are associated with various types of cancers. We also discuss the physicochemical properties of well-studied inhibitors with natural product origins and their related structures in terms of these enzymes. Targeting ceramide metabolism exhibited promising mono- and combination therapies at preclinical stages in preventing cancer progression and cemented the significance of sphingolipid metabolism in cancer treatments. Targeting ceramide-metabolizing enzymes will help medicinal chemists design potent and selective small molecules for treating cancer progression at various levels.

Co-Culturing Rat Dorsal Root Ganglion Neurons With Rat Schwann Cells Protects Them Against the Cytotoxic Effects of Silver and Gold Nanoparticles

Previous studies using monotypic nerve cell cultures have shown that nanoparticles induced neurotoxic effects on nerve cells. Interactions between neurons and Schwann cells may protect against the neurotoxicity of nanoparticles. In this study, we developed a co-culture model consisting of immortalized rat dorsal root ganglion (DRG) neurons and rat Schwann cells and employed it to investigate our hypothesis that co-culturing DRG neurons with Schwann cells imparts protection on them against neurotoxicity induced by silver or gold nanoparticles. Our results indicated that neurons survived better in co-cultures when they were exposed to these nanoparticles at the higher concentrations compared to when they were exposed to these nanoparticles at the same concentrations in monotypic cultures. Synapsin I expression was increased in DRG neurons when they were co-cultured with Schwann cells and treated with or without nanoparticles. Glial fibrillary acidic protein (GFAP) expression was increased in Schwann cells when they were co-cultured with DRG neurons and treated with nanoparticles. Furthermore, we found co-culturing with Schwann cells stimulated neurofilament polymerization in DRG neurons and produced the morphological differentiation. Silver nanoparticles induced morphological disorganization in monotypic cultures. However, there were more cells displaying normal morphology in co-cultures than in monotypic cultures. All of these results suggested that co-culturing DRG neurons with Schwann cells imparted some protection on them against neurotoxicity induced by silver or gold nanoparticles, and altering the expression of neurofilament-L, synapsin I, and GFAP could account for the phenomenon of protection in co-cultures.

Pan HDACi Valproic Acid and Trichostatin A Show Apparently Contrasting Inflammatory Responses in Cultured J774A.1 Macrophages

This study was initiated as an attempt to clarify some of the apparent conflicting data regarding the so-called anti-inflammatory versus proinflammatory properties of histone deacetylase inhibitors (HDACis). In cell culture, typically, chronic pretreatment with the HDACi valproic acid (VPA) and trichostatin A (TSA) exhibits an anti-inflammatory effect. However, the effect of acute treatment with VPA and TSA on the levels of inflammatory cytokines in J774A.1 macrophage cell line is unknown. Therefore, this study investigated the effect of acute treatment with VPA and TSA on levels of key inflammatory cytokines in maximally stimulated J774A.1 cells. J774A.1 macrophages were treated with either VPA or TSA for 1 h (acute treatment), followed by maximal stimulation with LPS + IFNγ for 24 h. ELISA was used to measure the levels of proinflammatory cytokines TNFα, NO and IL-1β from the culture medium. Acute treatment with VPA showed a dose-dependent increase in levels of all three cytokines. Similar to VPA, TSA also showed a dose-dependent increase in levels of IL-1β alone. This study sheds new light on the conflicting data in the literature that may partly be explained by acute or short-term exposure versus chronic or long-term exposure to HDACi.

Combination of Biochanin A and Temozolomide Impairs Tumor Growth by Modulating Cell Metabolism in Glioblastoma Multiforme

BACKGROUND/AIM

Several epidemiological studies have reported the chemopreventive potential of biochanin A, in cancer development and progression. We investigated the anticancer potential of combination of biochanin A and temozolomide against U-87 MG and T98 G [glioblastoma multiforme (GBM)] cells.

MATERIALS AND METHODS

We evaluated the effect of biochanin A and temozolomide treatment on cell viability, expression of survival proteins, cell cycle, cell metabolism and mitochondrial function.

RESULTS

Enhanced inhibitory effects of the combination treatment were observed on cell viability, expression of cell survival proteins EGFR, p-ERK, p-AKT, c-myc and MT-MMP1, and increased expression of the tumor suppressor, p-p53. Combination treatment also induced arrest in the G₁ phase of the cell cycle. A shift in the metabolic phenotype of cells from glycolytic to oxidative phosphorylation was observed on combination treatment and the permeabilized cells showed a significant impairment in complex IV activity.

CONCLUSION

Biochanin A significantly enhanced the anticancer efficacy of temozolomide in GBM cells.

Abstract 4193: Biochanin A in pancreatic cancer

Pancreatic cancer, with its dismally low survival rate (<5%), is one of the most aggressive forms of cancer and is the fourth leading cause of cancer-related deaths in the U.S. Gemcitabine, the first-line drug approved by the FDA, has been marginally effective as it improves survival by only six months. Epidemiologic studies have implicated a role for dietary isoflavones in lowering the incidence of different cancers in the Asian population. Isoflavones such as genistein, biochanin A and daidzein have been tested for their anticancer potential in different cancers; however, the clastogenic effect associated with genistein limits its therapeutic potential. Primarily used in management of hyperlipidemia and cardiovascular diseases, statins have been documented to exert antiproliferative effects. We hypothesized that a combination treatment of biochanin A and atorvastatin exerts enhanced anticancer effects on pancreatic cancer cells viz. AsPC1, PANC-1 and MIAPaCa-2. Our studies showed a decrease in cell viability on combination drug treatment with differential effects on mitogenic and cell signaling pathways in the cell lines investigated. In PANC-1 cells, biochanin A and atorvastatin combination treatment decreased invasiveness, dampened the expression of activated STAT3, and critical mediators of cell cycle progression. We also observed the involvement of enhanced proapoptotic effect of the combination treatment in AsPC-1 cell line and potential cell cycle arrest phenomenon in PANC-1 cells. Cell metabolism studies using seahorse XFp analyzer showed an increase in mitochondrial respiration and a decrease in glycolytic activity on combination treatment. Further, the XF-Plasma Membrane Permeabilizer (XF-PMP) assay used to evaluate the mitochondrial ETC complex activity showed a complete impairment of complex I and II (prominently), with MIAPaCa-2 being more susceptible to the combination treatment than AsPC1 and PANC-1. Together, the combination treatment-induced effects on pancreatic cancer cell lines may have potential implications in developing novel and improved therapies for the treatment of pancreatic cancer.

Citation Format: Vilas Desai, Satya Murthy Tadinada, James C K Lai, Alok Bhushan. Biochanin A in pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4193.

Abstract 1097: Enhancing the efficacy of Temozolomide with Biochanin A: Mechanistic and metabolic effects

Enhancing the efficacy of Temozolomide with Biochanin A: Mechanistic and Metabolic effects

Glioblastoma multiforme (GBM) is the most frequent, primary malignant brain tumor prevalent in humans. GBM is characterized by aggressive cell proliferation and rapid invasion of normal brain tissue resulting in poor patient prognosis. Furthermore, the current standard therapy of surgical resection followed by radiotherapy and chemotherapy with Temozolomide is not very effective. The inefficacy of the currently available chemotherapeutic agents for GBM can be attributed to the challenges of drug delivery to the tumor. Our laboratory has previously reported the anticancer potential of isoflavones like Biochanin A against oral, pancreatic, breast and brain cancers. In this study, we tested our hypothesis that, Biochanin A sensitizes the GBM cells to Temozolomide, thereby increasing its efficacy in combination treatment. We used the MTT assay to determine the effects of Biochanin A alone and in combination with Temozolomide on survival of U-87 MG cells. Furthermore, two different nanoformulations of Single Walled Carbon Nanotubes (SWCNTs) functionalized with Biochanin A and Atorvastatin and SWCNTs functionalized with Temozolomide were synthesized and their effects on cell viability of U-87 MG glioblastoma cells tested. The cell viability results indicate a decrease in cell proliferation with the combination treatment as compared to the individual drug treatment. Similarly, the flow cytometry analysis showed an increased induction of apoptosis with combination treatment as compared to the drugs alone. Western-blot analysis and Immunofluorescence imaging methods were used to elucidate some of the cell survival/proliferation mechanisms involving EGFR, p-AKT, MMP-2, MT-MMP1. The effects of the drugs on U-87 MG cell metabolism (parameters like ECAR & OCR) studied using Seahorse XFp analyser, suggest an increase in the mitochondrial respiration. Our results provide support for our hypothesis and the data shows that it may have implications in increasing the efficacy of the conventional treatments for GBM. These results will potentially aid in designing new therapies that can improve the outcome of GBM.

Citation Format: Vilas Desai, Aditi Jain, Maryna Perepelyuk, Annie Chhun, Christopher Farrell, James C. K. Lai, Alok Bhushan. Enhancing the efficacy of Temozolomide with Biochanin A: Mechanistic and metabolic effects [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1097. doi:10.1158/1538-7445.AM2017-1097

Comparison of Glutamate Turnover in Nerve Terminals and Brain Tissue During [1,6-13C2]Glucose Metabolism in Anesthetized Rats

The ¹³C turnover of neurotransmitter amino acids (glutamate, GABA and aspartate) were determined from extracts of forebrain nerve terminals and brain homogenate, and fronto-parietal cortex from anesthetized rats undergoing timed infusions of [1,6-¹³C₂]glucose or [2-¹³C]acetate. Nerve terminal ¹³C fractional labeling of glutamate and aspartate was lower than those in whole cortical tissue at all times measured (up to 120 min), suggesting either the presence of a constant dilution flux from an unlabeled substrate or an unlabeled (effectively non-communicating on the measurement timescale) glutamate pool in the nerve terminals. Half times of ¹³C labeling from [1,6-¹³C₂]glucose, as estimated by least squares exponential fitting to the time course data, were longer for nerve terminals (Glu_C4, 21.8 min; GABA_C2 21.0 min) compared to cortical tissue (Glu_C4, 12.4 min; GABA_C2, 14.5 min), except for Asp_C3, which was similar (26.5 vs. 27.0 min). The slower turnover of glutamate in the nerve terminals (but not GABA) compared to the cortex may reflect selective effects of anesthesia on activity-dependent glucose use, which might be more pronounced in the terminals. The ¹³C labeling ratio for glutamate-C4 from [2-¹³C]acetate over that of ¹³C-glucose was twice as large in nerve terminals compared to cortex, suggesting that astroglial glutamine under the ¹³C glucose infusion was the likely source of much of the nerve terminal dilution. The net replenishment of most of the nerve terminal amino acid pools occurs directly via trafficking of astroglial glutamine.

Biochanin A inhibits endothelial cell functions and proangiogenic pathways: implications in glioma therapy

Malignant gliomas, such as glioblastoma multiforme, are highly vascularized tumors of the central nervous system. A rich network of angiogenic vessels supporting glioma growth is an important therapeutic target in glioma therapy. In the past few years, small molecules have gained interest as multitargeting therapies for cancer. Biochanin A is a small, natural dietary isoflavone known for its anticancer potential. Previously, we have found that biochanin A inhibits invasion in human glioblastoma cells. In this study, we elucidated the antiangiogenic mechanisms of biochanin A using rat brain tumor (C6) and murine brain endothelial (bEnd.3) cells and an ex-vivo chick chorioallantoic membrane model. Biochanin A inhibited endothelial cell functions such as cell viability, migration, and invasion, as analyzed using MTT, scratch wound, and gelatin zymography assays. Activation of proangiogenic proteins (ERK/AKT/mTOR) was inhibited. Biochanin A also inhibited chemical hypoxia-inducible factor-1α and vascular endothelial growth factor in C6 cells. Results of chick chorioallantoic membrane assay showed that biochanin A inhibited blood vessel formation ex vivo. As these results suggest that biochanin A directly targets different facets of angiogenesis in vitro and ex vivo, this study provides a rationale for future preclinical evaluation of its efficacy against angiogenic gliomas.

Tyrosine phosphorylation of HSC70 and its interaction with RFC mediates methotrexate resistance in murine L1210 leukemia cells

We previously identified and characterized a 66-68 kDa membrane-associated, tyrosine phosphorylated protein in murine leukemia L1210 cells as HSC70 which is a methotrexate (MTX)-binding protein. In order to further characterize the functional role of HSC70 in regulating MTX resistance in L1210 cells, we first showed that HSC70 colocalizes and interacts with reduced folate carrier (RFC) in L1210 cells by confocal laser scanning microscopy and Duolink in situ proximity ligation assay. The tyrosine phosphorylation status of HSC70 found in the membrane fraction was different from the parental L1210/0 and cisplatin (CDDP)-MTX cross resistant L1210/DDP cells. In MTX-binding assays, HSC70 from L1210/DDP cells showed less affinity for MTX-agarose beads than that of L1210/0 cells. In addition, genistein (a tyrosine phosphorylation inhibitor) significantly enhanced the resistance of L1210/0 cells to MTX. Moreover, site-directed mutation studies indicated the importance of tyrosine phosphorylation of HSC70 in regulating its binding to MTX. These findings suggest that tyrosine phosphorylation of HSC70 regulates the transportation of MTX into the cells via the HSC70-RFC system and contributes to MTX resistance in L1210 cells.

Interleukin-6 and JAK2/STAT3 signaling mediate the reversion of dexamethasone resistance after dexamethasone withdrawal in 7TD1 multiple myeloma cells

We previously reported the establishment and characteristics of a DXM-resistant cell line (7TD1-DXM) generated from the IL6-dependent mouse B cell hybridoma, 7TD1 cell line. After withdrawing DXM from 7TD1-DXM cells over 90 days, DXM significantly inhibited the cell growth and induced apoptosis in the cells (7TD1-WD) compared with 7TD1-DXM cells. Additionally, IL-6 reversed while IL-6 antibody and AG490 enhanced the effects of growth inhibition and apoptosis induced by DXM in 7TD1-WD cells. Our study demonstrates that 7TD1-DXM cells become resensitized to DXM after DXM withdrawal, and IL-6 and JAK2/STAT3 pathways may regulate the phenomenon.

Regulation of astrocyte glutamine synthetase in epilepsy

Astrocytes play a crucial role in regulating and maintaining the extracellular chemical milieu of the central nervous system under physiological conditions. Moreover, proliferation of phenotypically altered astrocytes (a.k.a. reactive astrogliosis) has been associated with many neurologic and psychiatric disorders, including mesial temporal lobe epilepsy (MTLE). Glutamine synthetase (GS), which is found in astrocytes, is the only enzyme known to date that is capable of converting glutamate and ammonia to glutamine in the mammalian brain. This reaction is important, because a continuous supply of glutamine is necessary for the synthesis of glutamate and GABA in neurons. The known stoichiometry of glutamate transport across the astrocyte plasma membrane also suggests that rapid metabolism of intracellular glutamate via GS is a prerequisite for efficient glutamate clearance from the extracellular space. Several studies have indicated that the activity of GS in astrocytes is diminished in several brain disorders, including MTLE. It has been hypothesized that the loss of GS activity in MTLE leads to increased extracellular glutamate concentrations and epileptic seizures. Understanding the mechanisms by which GS is regulated may lead to novel therapeutic approaches to MTLE, which is frequently refractory to antiepileptic drugs. This review discusses several known mechanisms by which GS expression and function are influenced, from transcriptional control to enzyme modification.

Identification and characterization of a 66-68-kDa protein as a methotrexate-binding protein in murine leukemia L1210 cells

We previously observed an unidentified, tyrosine-phosphorylated, membrane-associated, 66-68-kDa protein which was present in the L1210 murine leukemia cells but not present, at least in the tyrosine-phosphorylated form, in cisplatin-methotrexate (CDDP-MTX) cross-resistant L1210/DDP cells. We purified and characterized this 66-68-kDa protein by affinity chromatography purification using its two identified properties, tyrosine phosphorylation and MTX-binding, and yielded a single band of 66-68 kDa. The purified protein was subjected to trypsin digestion and the isolated peptide fragments were sequenced and yielded two partial peptide sequences: VEIIANDQ and VTNAVVTVPAYFNDSQRQA. The two peptide sequences were used to search for the mouse genome at the national center for biotechnology information (NCBI) database for Open Reading Frame Sequence (ORFs) containing these peptides using the TBLASTN function. A single gene was identified containing both sequences, the HSPa8 gene, which codes for the heat shock family protein, HSC70. We further demonstrated that HSC70 is a MTX-binding protein using a binding assay with MTX-agarose beads followed by Western blotting. The HSC70 also existed in various cancer cell lines and showed binding to MTX. Additionally, the HSC70 protein, cloned from the L1210 murine leukemia cells, was expressed and purified from E. coli cells using a polyhistidine-tag purification system and it also showed the binding properties with MTX. DnaK, the HSC70 homologue in E. coli, also binds to MTX. By using the purified truncated HSC70 domains, we identified the adenosine triphosphatase (ATPase) domain of HSC70 that can bind to MTX. Thus, we have tentatively characterized a new, novel property of HSC70 as a MTX-binding protein.

Functional enhancement of chitosan and nanoparticles in cell culture, tissue engineering, and pharmaceutical applications

As a biomaterial, chitosan has been widely used in tissue engineering, wound healing, drug delivery, and other biomedical applications. It can be formulated in a variety of forms, such as powder, film, sphere, gel, and fiber. These features make chitosan an almost ideal biomaterial in cell culture applications, and cell cultures arguably constitute the most practical way to evaluate biocompatibility and biotoxicity. The advantages of cell cultures are that they can be performed under totally controlled environments, allow high throughput functional screening, and are less costly, as compared to other assessment methods. Chitosan can also be modified into multilayer composite by combining with other polymers and moieties to alter the properties of chitosan for particular biomedical applications. This review briefly depicts and discusses applications of chitosan and nanoparticles in cell culture, in particular, the effects of chitosan and nanoparticles on cell adhesion, cell survival, and the underlying molecular mechanisms: both stimulatory and inhibitory influences are discussed. Our aim is to update the current status of how nanoparticles can be utilized to modify the properties of chitosan to advance the art of tissue engineering by using cell cultures.

Abstract 1930: Inhibition of glioblastoma cell growth with the isoprenoids perillyl alcohol, farnesol, and geraniol

The naturally occurring isoprenoid perillyl alcohol has chemotherapeutic activity toward many solid tumor types. Early phase human clinical trials have shown low toxicity but only limited efficacy. In glioblastoma, perillyl alcohol has antitumor activity toward cultured cells and has shown some survival benefit in a Phase I/II clinical trial. More potent compounds are needed in order to make more significant impacts on patient survival from glioblastoma and other chemoresistant cancers. Isoprenoids may be especially useful in glioblastoma given their lipophilic nature and potential to cross the blood-brain barrier. Here, we compared the chemotherapeutic effects of perillyl alcohol with the related isoprenoids farnesol and geraniol on cell survival in cultured U87 human glioblastoma cells. Cells were treated for 72 h with isoprenoids, and cell survival was measured by the MTT assay. In U87 cells, each of the isoprenoids exhibited a dose-dependent effect on cell survival in the range of 0-2 mM. The relative potency was farnesol>perillyl alcohol>geraniol, with 52%, 38% and 23% inhibition at 1500 uM, respectively. We then tested the effects of isoprenoids on mitogenic signaling via ERK, phosphoERK, AKT and phosphAKT Western blots in U87 cells. Farnesol decreased phosphoERK at doses as low as 50 uM, whereas perillyl alcohol and geraniol had no effect. None of the isoprenoids affected phosphoAKT, total AKT, or total ERK. Together, these data suggest that farnesol may be a more effective agent than perillyl alcohol in the chemotherapy of glioblastoma, and its effects may be due in part to inhibition of ERK phosphorylation.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1930. doi:1538-7445.AM2012-1930

Treatment of human astrocytoma U87 cells with silicon dioxide nanoparticles lowers their survival and alters their expression of mitochondrial and cell signaling proteins

Recent evidence suggests silicon dioxide micro- and nanoparticles induce cytotoxic effects on lung cells. Thus, there is an increasing concern regarding their potential health hazard. Nevertheless, the putative toxicity of nanoparticles in mammalian cells has not yet been systematically investigated. We previously noted that several metallic oxide nanoparticles exert differential cytotoxic effects on human neural and nonneural cells. Therefore, we hypothesized that silicon dioxide nanoparticles induce cytotoxicity in U87 cells by lowering their survival by decreasing cell survival signaling and disturbing mitochondrial function. To investigate this hypothesis, we determined the activities of the key mitochondrial enzymes, citrate synthase and malate dehydrogenase, in astrocytoma U87 cells treated with silicon dioxide nanoparticles. In addition, we studied the expression of the mitochondrial DNA-encoded proteins, cytochrome C oxidase II and nicotinamide adenine dinucleotide (NADPH) dehydrogenase subunit 6, and cell signaling pathway protein extracellular signal-regulated kinase (ERK) and phosphorylated ERK in treated U87 cells. The activated form of ERK controls cell growth, differentiation, and proliferation. In parallel, we determined survival of U87 cells after treating them with various concentrations of silicon dioxide nanoparticles. Our results indicated that treatment with silicon dioxide nanoparticles induced decreases in U87 cell survival in a dose-related manner. The activities of citrate synthase and malate dehydrogenase in treated U87 cells were increased, possibly due to an energetic compensation in surviving cells. However, the expression of mitochondrial DNA-encoded cytochrome C oxidase subunit II and NADH dehydrogenase subunit 6 and the cell signaling protein ERK and phosphorylated ERK were altered in the treated U87 cells, suggesting that silicon dioxide nanoparticles induced disruption of mitochondrial DNA-encoded protein expression, leading to decreased mitochondrial energy production and decreased cell survival/proliferation signaling. Thus, our results strongly suggest that the cytotoxicity of silicon dioxide nanoparticles in human neural cells implicates altered mitochondrial function and cell survival/proliferation signaling.

Effect of combination treatment of rapamycin and isoflavones on mTOR pathway in human glioblastoma (U87) cells

Glioblastoma Multiforme (GBM) is a malignant primary brain tumor associated with poor survival rate. PI3K/Akt pathway is highly upregulated in gliomas due to deletion or mutation of PTEN and its activation is associated with tumor grade. mTOR is downstream from PI3K/Akt pathway and it initiates translation through its action on S6K and 4E-BP1. mTOR is an important therapeutic target in many cancers, including glioblastomas. Rapamycin and its analogues are known to inhibit mTOR pathway; however, they also show simultaneous upregulation of Akt and eIF4E survival pathways on inhibition of mTOR, rendering cells more resistant to rapamycin treatment. In this study we investigated the effect of combination treatment of rapamycin with isoflavones such as genistein and biochanin A on mTOR pathway and activation of Akt and eIF4E in human glioblastoma (U87) cells. Our results show that combination treatment of rapamycin with isoflavones, especially biochanin A at 50 muM, decreased the phosphorylation of Akt and eIF4E proteins and rendered U87 cells more sensitive to rapamycin treatment when compared to cells treated with rapamycin alone. These results suggest the importance of combining chemopreventive with chemotherapeutic agents in order to increase the efficacy of chemotherapeutic drugs.

Glycolytic enzyme inhibitors affect pancreatic cancer survival by modulating its signaling and energetics

BACKGROUND AND AIM

The importance of glycolysis in cancer cells is well documented. The effects of inhibiting glycolysis using metabolic inhibitors iodoacetate (IAA), an inhibitor of GAPDHase, and 3-bromopyruvate (3BP), an inhibitor of hexokinase-II, on survival and signaling of pancreatic cancer cells (Panc-1) were investigated.

MATERIALS AND METHODS

Cellular survival was evaluated using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Lactate dehydrogenase (LDH) assay was used to analyze the induced necrosis and protein levels were evaluated using Western blot analysis.

RESULTS

The results show that the inhibitors lowered cellular survival and increased cellular necrosis. Mitogenic signaling pathways were affected by 3BP but not by IAA.

CONCLUSION

We conclude that there may be a cross-talk between signaling pathways and glycolysis in regulating pancreatic cancer cell survival and signaling. Thus, a combination of agents that inhibit both energy production and cell signaling may provide a novel and effective approach to target pancreatic cancer effectively.

Reduced glutathione regenerating enzymes undergo developmental decline and sexual dimorphism in the rat cerebral cortex

Oxidative stress during development may predispose humans to neurodegenerative disorders in old age. Moreover, numerous ailments of brain disproportionately affect one of the genders. We therefore hypothesized that, activities of enzymes regenerating and utilizing glutathione (GSH) show sexual dimorphism and developmental differences in rat brain. To test this hypothesis, we collected cortex tissue from male and female Sprague-Dawley rats at post-natal day (PN) 5, PN 10, PN 20, PN 30, and PN 60. We measured tissue levels of NADP-linked isocitrate dehydrogenase (NADP-ICDH), glucose-6-phosphate dehydrogenase (G6PDH), and, glutathione reductase (GR) by UV spectrophotometry and determined glutathione peroxidase (GPx) expression therein by western blotting. Our results showed that sexual maturation had an impact on activities of enzymes that regenerate and utilize GSH and rat female cortex had more anti-oxidant capacity. Moreover, age-related decline in the activities of these key enzymes were observed. Reduced glutathione and NADPH protects the brain from oxidative stress. Thus, our results may have implications for neurodegenerative disorders like Parkinson's disease and developmental disorders of brain like autism in which oxidative stress plays a key role.

Exposure to titanium dioxide and other metallic oxide nanoparticles induces cytotoxicity on human neural cells and fibroblasts

The use of titanium dioxide (TiO₂) in various industrial applications (eg, production of paper, plastics, cosmetics, and paints) has been expanding thereby increasing the occupational and other environmental exposure of these nanoparticles to humans and other species. However, the health effects of exposure to TiO₂ nanoparticles have not been systematically assessed even though recent studies suggest that such exposure induces inflammatory responses in lung tissue and cells. Because the effects of such nanoparticles on human neural cells are unknown, we have determined the putative cytotoxic effects of these nanoparticles on human astrocytes-like astrocytoma U87 cells and compared their effects on normal human fibroblasts. We found that TiO₂ micro- and nanoparticles induced cell death on both human cell types in a concentration-related manner. We further noted that zinc oxide (ZnO) nanoparticles were the most effective, TiO₂ nanoparticles the second most effective, and magnesium oxide (MgO) nanoparticles the least effective in inducing cell death in U87 cells. The cell death mechanisms underlying the effects of TiO₂ micro- and nanoparticles on U87 cells include apoptosis, necrosis, and possibly apoptosis-like and necrosis-like cell death types. Thus, our findings may have toxicological and other pathophysiological implications on exposure of humans and other mammalian species to metallic oxide nanoparticles.

Apoptotic resistance exhibited by dexamethasone-resistant murine 7TD1 cells is controlled independently of interleukin-6 triggered signaling

Interleukin-6 (IL6)-mediated signaling is known to play a role in pathogenesis and resistance in several cancers like multiple myeloma (MM). In this report we used the IL6-dependent 7TD1 murine B-cell hybridoma as an in vitro model to study the interactions between IL6-signaling pathways and the development of dexamethasone resistance. Though in initial stages, 7TD1 cells grew IL6-dependent and were sensitive to dexamethasone-induced apoptosis, chronic exposure to dexamethasone led to a dexamethasone-resistant phenotype (7TD1-Dxm) that grew independent of exogenous IL6. While IL6-mediated JAK/STAT3 and PI3K/AKT signaling was important for proliferation of both cell lines, as shown in proliferation assays using the respective pathway inhibitors, AG490 and LY294002, the resistant cells were insensitive to induction of apoptosis using the same. STAT3 was constitutively phosphorylated in resistant cells and inhibition of its dimerization induced apoptosis but did not alter their insensitivity to dexamethasone. Our results suggest a role of entities downstream of IL6-mediated JAK/STAT3 signaling in development of dexamethasone resistance by 7TD1-Dxm cells.

Mechanisms underlying hypoxia tolerance in Drosophila melanogaster: hairy as a metabolic switch

Hypoxia-induced cell injury has been related to multiple pathological conditions. In order to render hypoxia-sensitive cells and tissues resistant to low O₂ environment, in this current study, we used Drosophila melanogaster as a model to dissect the mechanisms underlying hypoxia-tolerance. A D. melanogaster strain that lives perpetually in an extremely low-oxygen environment (4% O₂, an oxygen level that is equivalent to that over about 4,000 m above Mt. Everest) was generated through laboratory selection pressure using a continuing reduction of O₂ over many generations. This phenotype is genetically stable since selected flies, after several generations in room air, survive at this low O₂ level. Gene expression profiling showed striking differences between tolerant and naïve flies, in larvae and adults, both quantitatively and qualitatively. Up-regulated genes in the tolerant flies included signal transduction pathways (e.g., Notch and Toll/Imd pathways), but metabolic genes were remarkably down-regulated in the larvae. Furthermore, a different allelic frequency and enzymatic activity of the triose phosphate isomerase (TPI) was present in the tolerant versus naïve flies. The transcriptional suppressor, hairy, was up-regulated in the microarrays and its binding elements were present in the regulatory region of the specifically down-regulated metabolic genes but not others, and mutations in hairy significantly reduced hypoxia tolerance. We conclude that, the hypoxia-selected flies: (a) altered their gene expression and genetic code, and (b) coordinated their metabolic suppression, especially during development, with hairy acting as a metabolic switch, thus playing a crucial role in hypoxia-tolerance.

Hypoxia-induced injury has been related to multiple pathological conditions. In order to render mammalian cells and tissues resistant to low O₂ environment, we wished to first understand the mechanisms underlying hypoxia-tolerance in resistant animals. Therefore, we generated a D. melanogaster strain that is tolerant to severe hypoxic conditions through long-term experimental selection. Several adaptive changes were identified in the hypoxia-selected flies that included up-regulation of multiple signal transduction pathways (such as Notch pathway, Insulin pathway, EGF receptor pathway, and Toll/Imd pathway), modulation of cellular respiration enzymes, and polymorphic differences in metabolic enzymes (such as TPI). While we believe that multiple pathways contribute to the hypoxia-tolerant trait in this Drosophila strain, we demonstrate that hairy-mediated metabolic suppression is a critical mechanism for reducing the mismatch between supply and demand of O₂.

Recurrent seizures and brain pathology after inhibition of glutamine synthetase in the hippocampus in rats

An excess of extracellular glutamate in the hippocampus has been linked to the generation of recurrent seizures and brain pathology in patients with medically intractable mesial temporal lobe epilepsy (MTLE). However, the mechanism which results in glutamate excess in MTLE remains unknown. We recently reported that the glutamate-metabolizing enzyme glutamine synthetase is deficient in the hippocampus in patients with MTLE, and we postulated that this deficiency is critically involved in the pathophysiology of the disease. To further explore the role of glutamine synthetase in MTLE we created a novel animal model of hippocampal glutamine synthetase deficiency by continuous (approximately 28 days) microinfusion of methionine sulfoximine (MSO: 0.625 to 2.5 microg/h) unilaterally into the hippocampus in rats. This treatment led to a deficiency in hippocampal glutamine synthetase activity by 82-97% versus saline. The majority (>95%) of the MSO-treated animals exhibited recurrent seizures that continued for several weeks. Some of the MSO-treated animals exhibited neuropathological features that were similar to mesial temporal sclerosis, such as hippocampal atrophy and patterned loss of hippocampal neurons. However, many MSO-treated animals displayed only minimal injury to the hippocampus, with no clear evidence of mesial temporal sclerosis. These findings support the hypothesis that a deficiency in hippocampal glutamine synthetase causes recurrent seizures, even in the absence of classical mesial temporal sclerosis, and that restoration of glutamine synthetase may represent a novel approach to therapeutic intervention in this disease.

Effects of continuous hypoxia on energy metabolism in cultured cerebro-cortical neurons

Mechanisms underlying hypoxia-induced neuronal adaptation have not been fully elucidated. In the present study we investigated glucose metabolism and the activities of glycolytic and TCA cycle enzymes in cerebro-cortical neurons exposed to hypoxia (3 days in 1% of O2) or normoxia (room air). Hypoxia led to increased activities of LDH (194%), PK (90%), and HK (24%) and decreased activities of CS (15%) and GDH (34%). Neurons were incubated with [1-(13)C]glucose for 45 and 120 min under normoxic or hypoxic (120 min only) conditions and 13C enrichment determined in the medium and cell extract using 1H-{13C}-NMR. In hypoxia-treated neurons [3-(13)C]lactate release into the medium was 428% greater than in normoxia-treated controls (45-min normoxic incubation) and total flux through lactate was increased by 425%. In contrast glucose oxidation was reduced significantly in hypoxia-treated neurons, even when expressed relative to total cellular protein, which correlated with the reduced activities of the measured mitochondrial enzymes. The results suggest that surviving neurons adapt to prolonged hypoxia by up-regulation of glycolysis and down-regulation of oxidative energy metabolism, similar to certain other cell types. The factors leading to adaptation and survival for some neurons but not others remain to be determined.

Inhibition of Cell Proliferation and MAP Kinase and Akt Pathways in Oral Squamous cell Carcinoma by Genistein and Biochanin A

High morbidity and mortality associated with oral squamous cell carcinoma (OSCC) are largely attributable to late stage diagnosis. Despite significant advances in therapeutic strategies, the five-year survival rate for oral cancer remains at about 50%. A chemopreventive approach may be an effective alternative or adjunct to current therapies. Previous studies have shown anti-tumor effects of isoflavones in several cancers, including oral cancer. However, their mechanisms of action are still unclear. We hypothesized that isoflavones inhibit multiple signaling pathways implicated in oral carcinogenesis. To address our hypothesis, we investigated the effects of three isoflavone derivatives, genistein, biochanin A and daidzein, on SCC15 and SCC25 squamous cell carcinoma cell lines. In cell proliferation experiments, we found that genistein and biochanin A inhibited SCC15 and SCC25 cell growth with an IC50 of 50 μM. We also investigated the effect of isoflavones on ERK and Akt pathways. Our results, from western blot analysis, suggest that both genistein and biochanin A induced decreases in phosphorylation of ERK and Akt at treatment concentrations of 20, 50 and 100 μM. Taken together, our results clearly demonstrate a differential regulation of signaling pathways by various isoflavones in OSCC cell lines. Thus, tumor progression models can be utilized to study the preventive and therapeutic roles of isoflavones in oral cancer cell lines.

Metabolic and antioxidant system alterations in an astrocytoma cell line challenged with mitochondrial DNA deletion

Oxidative stress can induce mitochondrial dysfunction, mitochondrial DNA (mtDNA) depletion, and neurodegeneration, although the underlying mechanisms are poorly understood. The major mitochondrial antioxidant system that protects cells consists of manganese superoxide dismutase (MnSOD), glutathione peroxidase (GPx) and glutathione (GSH). To investigate the putative adaptive changes in antioxidant enzyme protein expression and targeting to mitochondria as mtDNA depletion occurs, we progressively depleted U87 astrocytoma cells of mtDNA by chronic treatment with ethidium bromide (EB, 50 ng/ml). Cellular MnSOD protein expression was markedly increased in a time-related manner while that of GPx showed time-related decreases. The mtDNA depletion also altered targeting or subcellular distribution of GPx, suggesting the importance of intact mtDNA in mitochondrial genome-nuclear genome signaling/communication. Cellular NADP(+)-ICDH activity also showed marked, time-related increases while their GSH content decreased. Thus, our findings suggest that interventions to elevate MnSOD, GPx, NADP(+)-ICDH, and GSH levels may protect brain cells from oxidative stress.

Prosthetic devices: Challenges and implications of robotic implants and biological interfaces

Although among designs of prosthetics there have been some successes in the design of functional robotic implants, there remain many issues and challenges concerned with the failure to meet the ‘ideal’ requirements of a satisfactory prosthetic. These ‘ideals’ require the device to be easy to control, comfortable to wear, and cosmetically pleasing. Because the literature on prosthetics and robotic implants are voluminous, this review focuses on four topics to determine key challenges and opportunities underlying these interdisciplinary research areas: firstly, an artificial hand as a biomimetic; secondly, prosthetic implants (electromyography signals and control); thirdly, prosthetic implants and tissue reactions to the material(s) of implants; fourthly, how inflammatory responses of cells and tissues surrounding implanted sensors interfere with the signal transmission of such sensors. This review also notes the importance of the biological interfaces that robotic implants and other prosthetic devices are in contact with and how an improved knowledge of pathophysiological changes at such biological interfaces will lead to improved and more biocompatible designs of prosthetics. This review concludes with the vision that, to develop a design that satisfies the above ‘ideals’, an interdisciplinary team of biomedical and tissue engineers, and biomaterial and biomedical scientists is needed to work together holistically and synergistically.

Cationic surfactants and other factors that affect enzymatic activities and transport

Surfactants influence functions of proteins in cell signalling. Because molecular mechanisms of surfactants are poorly understood, the cationic surfactant effect on three metabolically important enzymes - L-glutamate dehydrogenase, L-lactate dehydrogenase, and L-malate dehydrogenase - were investigated at a physiologically relevant pH range (6.5-7.4). How a cationic, a non-ionic, and an anionic surfactant could differentially influence these enzymes, and how these surfactants could influence the interfacial mass transport of these enzymes across a polycarbonate membrane in a separation cell were also investigated. Provided the charge density was the same, cationic surfactants affected enzymatic activities similarly, regardless of their molecular masses. Hence, a cationic surfactant behaved similarly to a hydrophilic anionic surfactant; however, the cationic surfactant also enhanced enzymatic activity at pH 6.5 and a moderately high concentration (150 ppm). The hydrophilic surfactant enhanced enzymatic activity and the hydrophobic surfactant depressed enzymatic activity. Addition of 0.1 ppm of the hydrophilic anionic surfactant decreased the amount of enzyme permeation through the membrane, but 0.1 ppm of the non-ionic surfactant had no effect, whereas 0.1 ppm of the hydrophobic surfactant increased enzyme permeation. These results have physiological and signalling implications in nanobiotechnology.

Manganese-induced neurotoxicity is differentially enhanced by glutathione depletion in astrocytoma and neuroblastoma cells

Manganese (Mn) is neurotoxic: the underlying mechanisms have not been fully elucidated. L: -Buthionine-(S,R)-sulfoximine (BSO) is an irreversible inhibitor of gamma-glutamylcysteine synthetase, an important enzyme in glutathione (GSH) synthesis. To test the hypothesis that BSO modulates Mn toxicity, we investigated the effects of treatment of U-87 or SK-N-SH cells with MnCl(2), BSO, or MnCl(2) plus BSO. We monitored cell viability using MTT assay, staining with HO-33342 to assess live and/or apoptotic cells, and staining with propidium iodide (PI) to assess necrotic cells; we also measured cellular glutathione. Our results indicate decreased viability in both cell types when treated with MnCl(2) or BSO: Mn was more toxic to SK-N-SH cells, whereas BSO was more toxic to U-87 cells. Because BSO treatment accentuated Mn toxicity in both cell lines, GSH may act to combat Mn toxicity. Thus, further investigation in oxidative stress mediated by glutathione depletion will unravel new Mn toxicity mechanism(s).

Manganese treatment modulates the expression of peroxisome proliferator-activated receptors in astrocytoma and neuroblastoma cells

Peroxisome proliferator-activated receptors (PPARs) play roles in neural cells by regulating energy balance, cell proliferation and anti-oxidant responses although the molecular mechanisms underlying such roles are unclear. Chronic exposure to excess manganese (Mn) leads to neurotoxicity, although Mn-induced neurotoxic mechanisms have not been fully elucidated. We hypothesized Mn neurotoxicity differentially alters the expression of PPARs. We investigated the effects of manganese chloride treatment (0.01-4 mM) on protein expression of PPAR isoforms (alpha, beta, and gamma) in human astrocytoma (U87) and neuroblastoma (SK-N-SH) cells. The two cell types expressed the 3 PPAR isoforms differentially: their expression of the PPARs was altered by Mn-treatment. Furthermore, nuclear and cytosolic fractions derived from the 2 cell types, with and without Mn-treatment, exhibited marked differences in the protein content of PPARs. Our results constitute the first demonstration that the PPAR signaling pathway may assume pathophysiological importance in Mn neurotoxicity.

Signaling Pathways Mediating Manganese-Induced Toxicity in Human Glioblastoma Cells (U87)

Although essential, manganese (Mn) intake in excess leads to neurotoxicity. Mn neurotoxicity induces impairment of energy metabolism and ultimately cell death. Nevertheless, the signaling mechanisms underlying Mn toxicity are unknown. Employing human glioblastoma (U87) cells, we investigated several signaling pathways (ones promoting cellular proliferation and invasion) underlying Mn toxicity. Mn-treatment of U87 cells induced a down-regulation of MAPK pathway but the AKT pathway was not markedly affected. Mn-treatment of these cells induced decreases in their levels of c-Jun and c-Fos transcription factors and extracellular matrix degrading enzymes like MMP-2, which are associated with glioblastoma invasiveness. Mn-treatment also induced apoptosis in U87 cells. Thus, our results indicate that other than inducing apoptosis in U87 cells, Mn exerts differential effects on several signaling pathways promoting glioblastoma proliferation and invasion. Consequently, Mn may have pathophysiological roles in inducing apoptosis and in blocking glioblastoma invasion. Our results may thus have therapeutic implications.

Differential glutamate dehydrogenase (GDH) activity profile in patients with temporal lobe epilepsy

PURPOSE

Pathophysiologic mechanisms underlying temporal lobe epilepsy (TLE) are still poorly understood. One major hypothesis links alterations in energy metabolism to glutamate excitotoxicity associated with seizures in TLE. The purpose of this study was to determine whether changes in the activities of enzymes critical in energy and neurotransmitter metabolism contributed to the alterations in metabolic status leading to the excitotoxic effects of glutamate.

METHODS

Activities of four key enzymes involved in energy metabolism and glutamate cycling in the brain [aspartate aminotransferase (AAT), citrate synthase (CS), glutamate dehydrogenase (GDH), and lactate dehydrogenase (LDH)] were measured in anterolateral temporal neocortical and hippocampal tissues obtained from three different groups of medically intractable epilepsy patients having either mesial, paradoxical, or mass lesion-associated temporal lobe epilepsy (MTLE, PTLE, MaTLE), respectively.

RESULTS

We found that GDH activity was significantly decreased in the temporal cortex mainly in the MTLE group. A similar trend was recognized in the hippocampus of the MTLE. In all three patient groups, GDH activity was considerably lower, and AAT and LDH activities were higher in cortex of MTLE as compared with the corresponding activities in hippocampus (p<0.05). In the MTLE cortex and hippocampus, GDH activities were negatively correlated with the duration since the first intractable seizure.

CONCLUSIONS

Our results support the hypothesis suggesting major alteration in GDH activity mainly in the MTLE group. It is proposed that significant alterations in the enzyme activities may be contributing to decreased metabolism of glutamate, leading to its accumulation.

Inhibition of matrix degrading enzymes and invasion in human glioblastoma (U87MG) cells by isoflavones

Glioblastoma multiforme is a primary brain tumor associated with extensive invasion into surrounding brain tissue. Matrix metalloproteinases (MMPs) and urokinase plasminogen activation (uPA) system are shown to be involved in tumor invasion as they help in degradation of extracellular matrix (ECM) proteins and thus assist in the movement of cells. MMP-2 and 9 were shown to be upregulated in gliomas, suggesting their involvement in invasion. Genistein and biochanin A are isoflavones commonly known as phytoestrogens and have some anticancer properties. We hypothesize that these two isoflavones can induce a lowering of tumor invasion by decreasing the activity of matrix degrading enzymes. In this study we investigated the effects of genistein and biochanin A on invasive activity of U87MG cells using the Calbiochem in vitro invasion assay system. Our results suggest that genistein and biochanin A induced a decrease in invasive activity of U87MG cells in a dose-related manner. Genistein also induced a decrease in EGF-stimulated invasion thereby implicating an involvement of EGF-mediated signaling in invasion. Our results also show that treatment of U87MG cells with the two isoflavones induced decreases in the enzymatic activity of MMP-9 and the protein levels of MT1-MMP and uPAR.

The calcium-sensitive large-conductance potassium channel (BK/MAXI K) is present in the inner mitochondrial membrane of rat brain

Large-conductance voltage- and calcium-sensitive channels are known to be expressed in the plasmalemma of central neurons; however, recent data suggest that large-conductance voltage- and calcium-sensitive channels may also be present in mitochondrial membranes. To determine the subcellular localization and distribution of large-conductance voltage- and calcium-sensitive channels, rat brain fractions obtained by Ficoll-sucrose density gradient centrifugation were examined by Western blotting, immunocytochemistry and immuno-gold electron microscopy. Immunoblotting studies demonstrated the presence of a consistent signal for the alpha subunit of the large-conductance voltage- and calcium-sensitive channel in the mitochondrial fraction. Double-labeling immunofluorescence also demonstrated that large-conductance voltage- and calcium-sensitive channels are present in mitochondria and co-localize with mitochondrial-specific proteins such as the translocase of the inner membrane 23, adenine nucleotide translocator, cytochrome c oxidase or complex IV-subunit 1 and the inner mitochondrial membrane protein but do not co-localize with calnexin, an endoplasmic reticulum marker. Western blotting of discrete subcellular fractions demonstrated that cytochrome c oxidase or complex IV-subunit 1 was only expressed in the mitochondrial fraction whereas actin, acetylcholinesterase, cadherins, calnexin, 58 kDa Golgi protein, lactate dehydrogenase and microtubule-associated protein 1 were not, demonstrating the purity of the mitochondrial fraction. Electron microscopic examination of the mitochondrial pellet demonstrated gold particle labeling within mitochondria, indicative of the presence of large-conductance voltage- and calcium-sensitive channels in the inner mitochondrial membrane. These studies provide concrete morphological evidence for the existence of large-conductance voltage- and calcium-sensitive channels in mitochondria: our findings corroborate the recent electrophysiological evidence of mitochondrial large-conductance voltage- and calcium-sensitive channels in glioma and cardiac cells.

The effects of 17beta-estradiol and ethanol on zinc- or manganese-induced toxicity in SK-N-SH cells

Serious neurodegenerative disorders are increasingly prevalent in our society and excessive oxidative stress may be a key mediator of neuronal cell death in many of these conditions. A variety of metals, such as manganese and zinc, are essential trace elements but can reach localized toxic concentrations through various disease processes or environmental exposures and have been implicated as having a role in neurodegeneration. Both manganese and zinc exist as bivalent cations and are essential cofactors/activators for numerous enzymes. Evidence suggests one action of these metals, when concentrated beyond physiological levels, may be to inhibit cellular energy production, ultimately leading to increased radical formation. Our studies were undertaken to directly investigate the toxic effects of manganese and zinc in an immortalized neuronal-like cell line (SK-N-SH) by testing interactions with the antioxidant, 17beta-estradiol, and the neurotoxin, ethanol. Employing undifferentiated SK-N-SH cells, we found that these metals caused biphasic effects, enhancing cell proliferation at low doses and inducing cell death at higher doses. Zinc was both more efficacious and more potent than manganese in enhancing growth and in causing cell death. 17beta-Estradiol and ethanol enhanced the proliferative actions of zinc and manganese across a wide concentration range. Furthermore, co-treatment with either 17beta-estradiol or ethanol afforded protection against manganese-, but not zinc-induced toxicity. Finally, combined administration of 17beta-estradiol and ethanol to SK-N-SH cells resulted in both a loss of growth enhancement and protective properties that were observed when these substances were administered individually. We also noted that the toxic effects occurred more rapidly from zinc than manganese exposure. Taken together, these data suggest that oxidative stress likely has a role in cell death resulting from toxic exposure to either zinc or manganese, but there is a difference in the precise mechanism of their effects.

Alterations in metabolism and gap junction expression may determine the role of astrocytes as ?good samaritans? or executioners

Our knowledge of astroglia and their physiological and pathophysiological role(s) in the central nervous system (CNS) has grown during the past decade, revealing a complex picture. It is becoming increasingly clear that glia play a significant role in the homeostasis and function of the CNS and that neurons should no longer be considered the only cell type that responds, both rapidly and slowly, to electrochemical activity. We discuss recent advances in the field with an emphasis on the impact of hypoxia and ischemia on astrocytic metabolism and the functional relationship between glucose metabolism and gap junctions in astrocytes. We also address the controversy over whether astrocytic gap junctions mediate protection or killing of neurons during or after hypoxic or ischemic insults.

Iron uncouples oxidative phosphorylation in brain mitochondria isolated from vitamin E-deficient rats

Few, if any, studies have examined the effect of vitamin E deficiency on brain mitochondrial oxidative phosphorylation. The latter was studied using brain mitochondria isolated from control and vitamin E-deficient rats (13 months of deficiency) after exposure to iron, an inducer of oxidative stress. Mitochondria were treated with iron (2 to 50 microM) added as ferrous ammonium sulfate. Rates of state 3 and state 4 respiration, respiratory control ratios, and ADP/O ratios were not affected by vitamin E deficiency alone. However, iron uncoupled oxidative phosphorylation in vitamin E-deficient mitochondria, but not in controls. In vitamin E-deficient mitochondria, iron decreased ADP/O ratios and markedly stimulated state 4 respiration; iron had only a modest effect on these parameters in control mitochondria. Thus, vitamin E may have an important role in sustaining oxidative phosphorylation. Low concentrations of iron (2 to 5 microM) oxidized mitochondrial tocopherol that exists in two pools. The release of iron in brain may impair oxidative phosphorylation, which would be exacerbated by vitamin E deficiency. The results are important for understanding the pathogenesis of human brain disorders known to be associated with abnormalities in mitochondrial function as well as iron homeostasis (e.g., Parkinson's disease).

Differential Lowering by Manganese Treatment of Activities of Glycolytic and Tricarboxylic Acid (TCA) Cycle Enzymes Investigated in Neuroblastoma and Astrocytoma Cells Is Associated with Manganese-Induced Cell Death

Manganese (Mn) is a trace metal required for normal growth and development. Manganese neurotoxicity is rare and usually associated with occupational exposures. However, the cellular and molecular mechanisms underlying Mn toxicity are still elusive. In rats chronically exposed to Mn, their brain regional Mn levels increase in a dose-related manner. Brain Mn preferentially accumulates in mitochondria; this accumulation is further enhanced with Mn treatment in vivo. Exposure of mitochondria to Mn in vitro leads to uncoupling of oxidative phosphorylation. These observations prompted us to investigate the hypothesis that Mn induces alterations in energy metabolism in neural cells by interfering with the activities of various glycolytic and TCA cycle enzymes using human neuroblastoma (SK-N-SH) and astrocytoma (U87) cells. Treatments of SK-N-SH and U87 cells with MnCl2 induced cell death in these cells, in a concentration- and time-dependent manner, as determined by MTT assays. In parallel with the Mn-induced, dose-dependent decrease in cell survival, treatment of these cells with 0.01 to 4.0 mM MnCl2 for 48 h also induced dose-related decreases in their activities of hexokinase, pyruvate kinase, lactate dehydrogenase, citrate synthase, and malate dehydrogenase. Hexokinase in SK-N-SH cells was the most affected by Mn treatments, even at the lower range of concentrations. Mn treatment of SK-N-SH cells affected pyruvate kinase and citrate synthase to a lesser extent as compared to its effect on other enzymes investigated. However, citrate synthase and pyruvate kinase in U87 cells were more vulnerable than other enzymes investigated to the effects of Mn. The results suggest the two cell types exhibited differential susceptibility toward the Mn-induced effects. Additionally, the results may have significant implications in flux control because HK is the first and highly regulated enzyme in brain glycolysis. Thus these results are consistent with our hypothesis and may have pathophysiological implications in the mechanisms underlying Mn neurotoxicity.

Loss of glutamine synthetase in the human epileptogenic hippocampus: possible mechanism for raised extracellular glutamate in mesial temporal lobe epilepsy

BACKGROUND

High extracellular glutamate concentrations have been identified as a likely trigger of epileptic seizures in mesial temporal lobe epilepsy (MTLE), but the underlying mechanism remains unclear. We investigated whether a deficiency in glutamine synthetase, a key enzyme in catabolism of extracellular glutamate in the brain, could explain the perturbed glutamate homoeostasis in MTLE.

METHODS

The anteromedial temporal lobe is the focus of the seizures in MTLE, and surgical resection of this structure, including the hippocampus, leads to resolution of seizures in many cases. By means of immunohistochemistry, western blotting, and functional enzyme assays, we assessed the distribution, quantity, and activity of glutamine synthetase in the MTLE hippocampus.

FINDINGS

In western blots, the expression of glutamine synthetase in the hippocampus was 40% lower in MTLE than in non-MTLE samples (median 44 [IQR 30-58] vs 69 [56-87]% of maximum concentration in standard curve; p=0.043; n=8 and n=6, respectively). The enzyme activity was lower by 38% in MTLE vs non-MTLE (mean 0.0060 [SD 0.0031] vs 0.0097 [0.0042] U/mg protein; p=0.045; n=6 and n=9, respectively). Loss of glutamine synthetase was particularly pronounced in areas of the MTLE hippocampus with astroglial proliferation, even though astrocytes normally have high content of the enzyme. Quantitative immunoblotting showed no significant change in the amount of EAAT2, the predominant glial glutamate transporter in the hippocampus.

INTERPRETATION

A deficiency in glutamine synthetase in astrocytes is a possible molecular basis for extracellular glutamate accumulation and seizure generation in MTLE. Further studies are needed to define the cause, but the loss of glutamine synthetase may provide a new focus for therapeutic interventions in MTLE.

Oxidation of vitamin E and vitamin C and inhibition of brain mitochondrial oxidative phosphorylation by peroxynitrite

The effects of peroxynitrite (PN; product of the reaction between nitric oxide and superoxide) on mitochondrial respiration as well as oxidation of alpha-tocopherol and ascorbic acid were studied. Mitochondria were isolated from brain hemispheres of 4-month-old male Fisher rats by standard centrifugation procedures utilizing Ficoll gradients. Treatment of brain mitochondria with PN caused a concentration-dependent impairment of oxidative phosphorylation and depletion of the endogenous antioxidants alpha-tocopherol and ascorbic acid. PN-induced mitochondrial dysfunction was characterized by 1) decreases in state 3 respiration and oxidative phosphorylation, 2) loss of respiratory control [ratio of ADP-stimulated (state 3) to basal (state 4) respiration], and 3) uncoupling of oxidative phosphorylation. PN did not function as a pure uncoupler, insofar as the increase in state 4 respiration was accompanied by a larger decrease in state 3 respiration. This contrasts with the uncoupling action of the protonophore carbonyl cyanide m-chlorophenylhydrozone, which increases both state 3 and state 4 respiration. PN-induced reduction in respiratory control and oxidative phosphorylation closely paralleled the oxidation of membrane tocopherol and were preceded by loss of ascorbate. alpha-Tocopherol (the most potent biological lipid antioxidant) may have a unique role in protecting mitochondrial membranes from oxidative stress. The two antioxidant nutrients alpha-tocopherol and ascorbate (which interact with each other and glutathione) may be intimately involved in protecting mitochondria in situations in which excessive release of superoxide and nitric oxide occurs under normal and/or pathological conditions.

Chronic hypoxia in development selectively alters the activities of key enzymes of glucose oxidative metabolism in brain regions

The immature brain is more resistant to hypoxia/ischemia than the mature brain. Although chronic hypoxia can induce adaptive-changes on the developing brain, the mechanisms underlying such adaptive changes are poorly understood. To further elucidate some of the adaptive changes during postnatal hypoxia, we determined the activities of four enzymes of glucose oxidative metabolism in eight brain regions of hypoxic and normoxic rats. Litters of Sprague-Dawley rats were put into the hypoxic chamber (oxygen level maintained at 9.5%) with their dams starting on day 3 postnatal (P3). Age-matched normoxic rats were use as control animals. In P10 hypoxic rats, lactate dehydrogenase (LDH) activity in cerebral cortex, striatum, olfactory bulb, hippocampus, hypothalamus, pons and medulla, and cerebellum was significantly increased (by 100%-370%) compared to those in P10 normoxic rats. In P10 hypoxic rats, hexokinase (HK) activity in hypothalamus, hippocampus, olfactory bulb, midbrain, and cerebral cortex was significantly decreased (by 15%-30%). Neither alpha-ketoglutarate dehydrogenase complex (KGDHC, which is believed to have an important role in the regulation of the tricarboxylic acid [TCA] cycle flux) nor citrate synthase (CS) activity was significantly decreased in the eight regions of P10 hypoxic rats compared to those in P10 normoxic rats. In P30 hypoxic rats, LDH activity was only increased in striatum (by 19%), whereas HK activity was only significantly decreased (by 30%) in this region. However, KGDHC activity was significantly decreased in olfactory bulb, hippocampus, hypothalamus, cerebral cortex, and cerebellum (by 20%-40%) in P30 hypoxic rats compared to those in P30 normoxic rats. Similarly, CS activity was decreased, but only in olfactory bulb, hypothalamus, and midbrain (by 9%-21%) in P30 hypoxic rats. Our results suggest that at least some of the mechanisms underlying the hypoxia-induced changes in activities of glycolytic enzymes implicate the upregulation of HIF-1. Moreover, our observation that chronic postnatal hypoxia induces differential effects on brain glycolytic and TCA cycle enzymes may have pathophysiological implications (e.g., decreased in energy metabolism) in childhood diseases (e.g., sudden infant death syndrome) in which hypoxia plays a role.