Menadione-induced cytotoxicity to rat osteoblasts

Menadione: a platform and a target to valuable compounds synthesis

Naphthoquinones are important natural or synthetic compounds belonging to the general class of quinones. Many compounds in this class have become drugs that are on the pharmaceutical market for the treatment of various diseases. A special naphthoquinone derivative is menadione, a synthetic naphthoquinone belonging to the vitamin K group. This compound can be synthesized by different methods and it has a broad range of biological and synthetic applications, which will be highlighted in this review.

Vitamin K: Redox-modulation, prevention of mitochondrial dysfunction and anticancer effect

This review is directed to the redox-modulating properties and anticancer effect of vitamin K. The concept is focused on two aspects: (i) redox-cycle of vitamin K and its effect on the calcium homeostasis, “oncogenic” and “onco-suppressive” reactive oxygen species and the specific induction of oxidative stress in cancer; (ii) vitamin K plus C as a powerful redox-system, which forms a bypass between mitochondrial complexes II and III and thus prevents mitochondrial dysfunction, restores oxidative phosphorylation and aerobic glycolysis, modulates the redox-state of endogenous redox-pairs, eliminates the hypoxic environment of cancer cells and induces cell death. The analyzed data suggest that vitamin C&K can sensitize cancer cells to conventional chemotherapy, which allows achievement of a lower effective dose of the drug and minimizing the harmful side-effects. The review is intended for a wide audience of readers - from students to specialists in the field.

Rapid generation of hydrogen peroxide contributes to the complex cell death induction by the angucycline antibiotic landomycin E

Landomycin E (LE) is an angucycline antibiotic produced by Streptomyces globisporus. Previously, we have shown a broad anticancer activity of LE which is, in contrast to the structurally related and clinically used anthracycline doxorubicin (Dx), only mildly affected by multidrug resistance-mediated drug efflux. In the present study, cellular and molecular mechanisms underlying the anticancer activity of landomycin E towards Jurkat T-cell leukemia cells were dissected focusing on the involvement of radical oxygen species (ROS). LE-induced apoptosis distinctly differed in several aspects from the one induced by Dx. Rapid generation of both extracellular and cell-derived hydrogen peroxide already at one hour drug exposure was observed in case of LE but not found before 24h for Dx. In contrast, Dx but not LE induced production of superoxide radicals. Mitochondrial damage, as revealed by JC-1 staining, was weakly enhanced already at 3h LE treatment and increased significantly with time. Accordingly, activation of the intrinsic apoptosis pathway initiator caspase-9 was not detectable before 12h exposure. In contrast, cleavage of the down-stream caspase substrate PARP-1 was clearly induced already at the three hour time point. Out of all caspases tested, only activation of effector caspase-7 was induced at this early time points paralleling the LE-induced oxidative burst. Accordingly, this massive cleavage of caspase-7 at early time points was inhibitable by the radical scavenger N-acetylcysteine (NAC). Additionally, only simultaneous inhibition of multiple caspases reduced LE-induced apoptosis. Specific scavengers of both H2O2 and OH• effectively decreased LE-induced ROS production, but only partially inhibited LE-induced apoptosis. In contrast, NAC efficiently blocked both parameters. Summarizing, rapid H2O2 generation and a complex caspase activation pattern contribute to the antileukemic effects of LE. As superoxide generation is considered as the main cardiotoxic mechanism of Dx, LE might represent a better tolerable drug candidate for further (pre)clinical development.

Cytotoxicity, hemolysis and in vivo acute toxicity of 2-hydroxy-3-anilino-1,4-naphthoquinone derivatives

The 1,4-naphthoquinones, important members of the family of quinones are used as both crude extracts and as compound manipulated by the pharmaceutical industry. They have gained great emphasis by presenting different pharmacological properties as antibacterial, antiviral, antiprotozoal and anthelmintic, and has antitumor activity. Our aim was to evaluate the cytotoxicity, hemolytic activity and in vivo acute toxicity of three derivatives of 2-hydroxy-1,4-naphthoquinones. The cell viability in vitro against RAW Cell Line displayed IC₅₀ ranging of 483.5–2044.8 μM, whereas in primary culture tests using murine macrophages, IC₅₀ were 315.8–1408.0 μM for naphthoquinones derivatives 4a and 4c respectively, besides no hemolysis was observed at the dose tested. The in vivo acute toxicity assays exhibited a significant safety margin indicated by a lack of systemic and behavioral toxicity up to 300 mg/kg, and at a dose of 1000 mg/kg the derivatives not triggering signs of toxicity although the compound 4a have promoted hepatic steatosis and hyperemia in kidney tissue. Thereby, these modifications decrease the toxicity of the tested derivatives naphthoquinones, providing a high potential for the development of news drugs.

Exposure of Aspergillus fumigatus to T-2 toxin results in a stress response associated with exacerbation of aspergillosis in poultry

Aspergillus fumigatus is a ubiquitous airborne pathogen. Saprophytic growth in the presence of environmental mycotoxins might affect its fitness and virulence. T-2 toxin (T-2) is a trichothecene mycotoxin produced by Fusarium spp. in various substrates. This study aimed to evaluate the effects of T-2 on the fitness of A. fumigatus in vitro and its virulence in experimentally inoculated chickens. We cultured A. fumigatus on agar media containing T-2, and examined the changes in viability, morphology, growth rate, proteome expression, and susceptibility to antimycotics and oxidative stress of this fungus. Results showed that exposure to 1000 ng/ml T-2 in the substrate did not reduce the viability of A. fumigatus, but its growth was inhibited, with wrinkling and depigmentation of the colonies. Proteomic analysis revealed 21 upregulated proteins and 33 downregulated proteins, including those involved in stress response, pathogenesis, metabolism, transcription. The proteome seems to have shifted to enhance the glycolysis, catabolism of lipids, and amino acid conversion. Assays on fungal susceptibility to antimycotics and oxidative stress showed that T-2 exposure did not affect the minimal inhibitory concentrations of amphotericin B, itraconazole, voriconazole and terbinafine against A. fumigatus, but increased the susceptibility of A. fumigatus to H2O2 and menadione. Experimental inoculation of chickens with A. fumigatus showed that exposure of A. fumigatus to T-2 significantly exacerbated aspergillosis in chickens exposed to dietary T-2. In conclusion, A. fumigatus is capable of surviving and growing on substrates containing levels of T-2 up to 1000 ng/ml. Growth in presence of T-2 induces a stress response in A. fumigatus, which is associated with exacerbation of aspergillosis in vivo.

Phosphanegold(I) dithiocarbamates, R3PAu[SC(=S)N((i)Pr)CH2CH2OH] for R = Ph, Cy and Et: role of phosphane-bound R substituents upon in vitro cytotoxicity against MCF-7R breast cancer cells and cell death pathways

The synthesis and characterisation of R3PAu[S2CN((i)Pr)CH2CH2OH], for R = Ph (1), Cy (2) and Et (3)4, is reported. Compounds 1-3 are cytotoxic against the doxorubicin-resistant breast cancer cell line, MCF-7R, with 1 exhibiting greater potency and cytotoxicity than either of doxorubicin and cisplatin. Based on human apoptosis PCR-array analysis, caspase activities, DNA fragmentation, cell apoptotic assays, intracellular reactive oxygen species (ROS) measurements and human topoisomerase I inhibition, induction of apoptosis by 1, and necrosis by 2 and 3, are demonstrated, by both extrinsic and intrinsic pathways. Compound 1 activates the p53 gene, 2 activates only the p73 gene, whereas 3 activates both the p53 and p73 genes. Compounds 1 and 3 activate NF-κB, and each inhibits topoisomerase I.

SATB2 participates in regulation of menadione-induced apoptotic insults to osteoblasts

Special AT-rich sequence binding protein 2 (SATB2), a nuclear matrix attachment region-binding protein, can regulate embryonic development, cell differentiation, and cell survival. Previous studies showed that SATB2 is involved in osteoblast differentiation and skeletal development. In this study, we evaluated the role of SATB2 in oxidative stress-induced apoptotic insults to human osteoblast-like MG63 cells and mouse MC3T3-E1 cells. Exposure of MG63 cells to menadione increased intracellular reactive oxygen species levels in a concentration- and time-dependent manner. Simultaneously, menadione-induced oxidative stress triggered cell shrinkage and decreased cell viability. In addition, treatment of MG63 cells with menadione time-dependently decreased the mitochondrial membrane potential but enhanced caspase-3 activity. As a result, menadione-induced DNA fragmentation and cell apoptosis. As to the mechanism, exposure of MG63 cells to menadione amplified SATB2 messenger (m)RNA and protein expression in a time-dependent manner. Knockdown of translation of SATB2 mRNA using RNA interference led to chromatin disruption and nuclear damage. When MG63 cells and MC3T3-E1 cells were treated with SATB2 small interfering RNA, menadione-induced cell apoptosis was increased. We conclude that menadione causes oxidative stress in human osteoblasts and induces cellular apoptosis via a mitochondrion-caspase protease pathway. In addition, SATB2 may play a crucial role in protecting against oxidative stress-induced osteoblast apoptosis.

Study on cytotoxicity and structure-activity relationship of HL-7702 cell exposed to naphthoquinones

The acute cytotoxicities of six naphthoquinone compounds, including Atovaquone, Buparvaquone, Menadione, 2-acetoxy-1,4-naphthoquinone and 2-ethoxy-1,4-naphthoquinone, to HL-7702 cells were determined. The results showed that the toxicities of these naphthoquinones were characterized by a steep response pattern except for 2-hydroxy-1,4-naphthoquinone. Meanwhile, the cellular injuries were unrecoverable. Several molecular descriptors, such as the octanol-water partition coefficients (LogP), diameter (Dia) and topological index (TIndx), played an important role in the toxicity of naphthoquinones to HL-7702 cell. Our results provide a foundation for further investigation using 3D-QSAR and HQSAR to evaluate the aquatic ecological risk and the possible mechanisms of toxicity of naphthoquinones.

Vitamin K3 attenuates lipopolysaccharide-induced acute lung injury through inhibition of nuclear factor-kappaB activation

Vitamin K is a family of fat-soluble compounds including phylloquinone (vitamin K1), menaquinone (vitamin K2) and menadione (vitamin K3). Recently, it was reported that vitamin K, especially vitamins K1 and K2, exerts a variety of biological effects, and these compounds are expected to be candidates for therapeutic agents against various diseases. In this study, we investigated the anti-inflammatory effects of vitamin K3 in in vitro cultured cell experiments and in vivo animal experiments. In human embryonic kidney (HEK)293 cells, vitamin K3 inhibited the tumour necrosis factor (TNF)-alpha-evoked translocation of nuclear factor (NF)-kappaB into the nucleus, although vitamins K1 and K2 did not. Vitamin K3 also suppressed the lipopolysaccharide (LPS)-induced nuclear translocation of NF-kappaB and production of TNF-alpha in mouse macrophage RAW264.7 cells. Moreover, the addition of vitamin K3 before and after LPS administration attenuated the severity of lung injury in an animal model of acute lung injury/acute respiratory distress syndrome (ARDS), which occurs in the setting of acute severe illness complicated by systemic inflammation. In the ARDS model, vitamin K3 also suppressed the LPS-induced increase in the serum TNF-alpha level and inhibited the LPS-evoked nuclear translocation of NF-kappaB in lung tissue. Despite marked efforts, little therapeutic progress has been made, and the mortality rate of ARDS remains high. Vitamin K3 may be an effective therapeutic strategy against acute lung injury including ARDS.

Partial attenuation of cytotoxicity and apoptosis by SOD1 in ischemic renal epithelial cells

Reactive oxygen species (ROS) contribute significantly to apoptosis in renal ischemia-reperfusion (IR) injury, however the exact mechanisms are not well understood. We used novel lentiviral vectors to over-express superoxide dismutase 1 (SOD1) in proximal tubular epithelial (LLC-PK(1)) cells and determined effects of SOD1 following ATP depletion-recovery, used as a model to simulate renal IR. SOD1 over-expression partially protected against cytotoxicity (P < 0.001) and decreased superoxide (O(2) (*-)) in ATP depleted cells. The ATP depletion-mediated increase in nuclear fragmentation, an index of apoptosis and activation of caspase-3 was also partially blocked by SOD1 (P < 0.05). However, SOD1 over-expression was insufficient to completely attenuate caspase-3, indicating that ROS other than cytoplasmic O(2) (*-) are involved in ATP depletion mediated injury. To test the contribution of hydrogen peroxide, a subset of enhanced green fluorescent protein (EGFP) and SOD1 (serum free and injured) cells were treated with polyethylene glycol-catalase (PEG-catalase). As expected there was 50% reduction in cytotoxicity and caspase-3 in SOD1 cells compared to EGFP cells; catalase treatment decreased both indices by an additional 28% following ATP depletion. To test the role of mitochondrial derived superoxide, we also treated a subset of LLC-PK(1) cells with the mitochondrial antioxidant, MitoTEMPO. Treatment with MitoTEMPO also decreased ATP depletion induced cytotoxicity in LLC-PK(1) cells in a dose dependant manner. These studies indicate that both SOD1 dependent and independent pathways are integral in protection against ATP depletion-recovery mediated cytotoxicity and apoptosis, however more studies are needed to delineate the signaling mechanisms involved.

Selective inhibition of nicotinamide adenine dinucleotide kinases by dinucleoside disulfide mimics of nicotinamide adenine dinucleotide analogues

Diadenosine disulfide (5) was reported to inhibit NAD kinase from Listeria monocytogenes and the crystal structure of the enzyme-inhibitor complex has been solved. We have synthesized tiazofurin adenosine disulfide (4) and the disulfide 5, and found that these compounds were moderate inhibitors of human NAD kinase (IC(50)=110 microM and IC(50)=87 microM, respectively) and Mycobacterium tuberculosis NAD kinase (IC(50)=80 microM and IC(50)=45 microM, respectively). We also found that NAD mimics with a short disulfide (-S-S-) moiety were able to bind in the folded (compact) conformation but not in the common extended conformation, which requires the presence of a longer pyrophosphate (-O-P-O-P-O-) linkage. Since majority of NAD-dependent enzymes bind NAD in the extended conformation, selective inhibition of NAD kinases by disulfide analogues has been observed. Introduction of bromine at the C8 of the adenine ring restricted the adenosine moiety of diadenosine disulfides to the syn conformation making it even more compact. The 8-bromoadenosine adenosine disulfide (14) and its di(8-bromoadenosine) analogue (15) were found to be the most potent inhibitors of human (IC(50)=6 microM) and mycobacterium NAD kinase (IC(50)=14-19 microM reported so far. None of the disulfide analogues showed inhibition of lactate-, and inosine monophosphate-dehydrogenase (IMPDH), enzymes that bind NAD in the extended conformation.

Oxidative stress evokes a metabolic adaptation that favors increased NADPH synthesis and decreased NADH production in Pseudomonas fluorescens

The fate of all aerobic organisms is dependent on the varying intracellular concentrations of NADH and NADPH. The former is the primary ingredient that fuels ATP production via oxidative phosphorylation, while the latter helps maintain the reductive environment necessary for this process and other cellular activities. In this study we demonstrate a metabolic network promoting NADPH production and limiting NADH synthesis as a consequence of an oxidative insult. The activity and expression of glucose-6-phosphate dehydrogenase, malic enzyme, and NADP(+)-isocitrate dehydrogenase, the main generators of NADPH, were markedly increased during oxidative challenge. On the other hand, numerous tricarboxylic acid cycle enzymes that supply the bulk of intracellular NADH were significantly downregulated. These metabolic pathways were further modulated by NAD(+) kinase (NADK) and NADP(+) phosphatase (NADPase), enzymes known to regulate the levels of NAD(+) and NADP(+). While in menadione-challenged cells, the former enzyme was upregulated, the phosphatase activity was markedly increased in control cells. Thus, NADK and NADPase play a pivotal role in controlling the cross talk between metabolic networks that produce NADH and NADPH and are integral components of the mechanism involved in fending off oxidative stress.

Indoxyl sulfate induces skeletal resistance to parathyroid hormone in cultured osteoblastic cells

Skeletal resistance to parathyroid hormone (PTH) is well known to the phenomenon in chronic renal failure patient, but the detailed mechanism has not been elucidated. In the process of analyzing an animal model of renal failure with low bone turnover, we demonstrated decreased expression of PTH receptor (PTHR) accompanying renal dysfunction in this model. In the present study, we focused on the accumulation of uremic toxins (UTx) in blood, and examined whether indoxyl sulfate (IS), a UTx, is associated with PTH resistance. We established primary osteoblast cultures from mouse calvariae and cultured the cells in the presence of IS. The intracellular cyclic adenosine 3',5' monophosphate (cAMP) production, PTHR expression, and free radical production in the primary osteoblast culture were studied. We found that the addition of IS suppressed PTH-stimulated intracellular cAMP production and decreased PTHR expression in this culture system. Free radical production in osteoblasts increased depending on the concentration of IS added. Furthermore, expression of organic anion transporter-3 (OAT-3) that is known to mediate cellular uptake of IS was identified in the primary osteoblast culture. These results suggest that IS taken up by osteoblasts via OAT-3 present in these cells augments oxidative stress to impair osteoblast function and downregulate PTHR expression. These finding strongly suggest that IS accumulated in blood due to renal dysfunction is at least one of the factors that induce skeletal resistance to PTH.

A possible role of oxidative stress in the switch mechanism of the cell death mode from apoptosis to necrosis--studies on rho0 cells

Apoptosis is induced not only during morphogenesis and embryogenesis but also under various pathological conditions, especially related to oxidative stress. Apoptotic cells are phagocytized by neighboring cells while necrotic cells cause local and general reactions sometimes lethal to our bodies. Data have been accumulated to demonstrate that the switch of the cell death mode from apoptosis to necrosis does occur. However, detailed mechanisms involved in the switch mechanism remain unsolved although decreases in the intracellular level of ATP and a burst in the cellular level of reactive oxygen species (ROS) have been proposed. Recently, we have shown that the population of apoptotic cells reaches maximum in human osteosarcoma 143B cells treated for 6h with menadione (MEN) while necrotic cells become predominant at 9h of the treatment. In the present study we have attempted to clarify the role of cellular ATP in the switch mechanism using rho(0) cells derived from human osteosarcoma rho+ cells. Results are summarized as follows: (1) Apoptotic and necrotic changes in rho(0) cells are much faster than rho+ cells after the treatment with MEN. (2) Cellular level of ATP in rho(0) cells remains essentially in the same level before and after the MEN-treatment while intracellular levels of superoxide continuously increase after the MEN-treatment. (3) rho+ cells treated with MEN in the presence of antimycin A plus oligomycin show similar changes to those of MEN-treated rho(0) cells. (4) MEN-induced increases in the cellular level of superoxide are distinctly suppressed by inhibitors of NADPH oxidase. These results suggest that the intracellular level of superoxide may be a key factor directly related to the switch mechanism from apoptosis to necrosis, and that decreases in cellular level of ATP accelerate both apoptotic and necrotic changes of the cells.

Uremic toxin and bone metabolism

Patients with end-stage renal disease (ESRD) develop various kinds of abnormalities in bone and mineral metabolism, widely known as renal osteodystrophy (ROD). Although the pathogenesis of ESRD may be similar in many patients, the response of the bone varies widely, ranging from high to low turnover. ROD is classified into several types, depending on the status of bone turnover, by histomorphometric analysis using bone biopsy samples [1,2]. In the mild type, bone metabolism is closest to that of persons with normal renal function. In osteitis fibrosa, bone turnover is abnormally activated. This is a condition of high-turnover bone. A portion of the calcified bone loses its lamellar structure and appears as woven bone. In the cortical bone also, bone resorption by osteoclasts is active, and a general picture of bone marrow tissue infiltration and the formation of cancellous bone can be observed. In osteomalacia, the bone surface is covered with uncalcified osteoid. This condition is induced by aluminum accumulation or vitamin D deficiency. The mixed type possesses characteristics of both osteitis fibrosa and osteomalacia. The bone turnover is so markedly accelerated that calcification of the osteoid cannot keep pace. In the adynamic bone type, bone resorption and bone formation are both lowered. While bone turnover is decreased, there is little osteoid. The existence of these various types probably accounts for the diversity in degree of renal impairment, serum parathyroid hormone (PTH) level, and serum vitamin D level in patients with ROD. However, all patients share a common factor, i.e., the presence of a uremic condition.

Vulnerability to ROS-induced cell death in ageing articular cartilage: the role of antioxidant enzyme activity

OBJECTIVES

To test the hypothesis that age-related loss of chondrocytes in cartilage is associated with impaired reactive oxygen species (ROS) homeostasis resulting from reduced antioxidant defence.

METHODS

Cell numbers: The total number of chondrocytes in the articular cartilage of the femoral head of young, mature and old rats was estimated using an unbiased stereological method. ROS quantification: Fluorescence intensity in chondrocytes was quantified using the oxygen free radical sensing probe dihydrorhodamine 123 (DHR 123), confocal laser scanning microscopy and densitometric image analysis. In order to delineate the reactive species, explants were pre-treated with N-acetylcysteine (NAC) or N(G)-nitro-l-arginine methyl ester (l-NAME) prior to ROS quantification. Induction of intracellular ROS: Explants were incubated in the redox-cycling drug menadione after which they underwent ROS quantification and cell-viability assay. Antioxidant enzyme activity: The activity of catalase, superoxide dismutase (SOD) and glutathione peroxidase (GPX) was measured.

RESULTS

Chondrocyte numbers: A significant and progressive loss of chondrocytes was observed with ageing. Cellular ROS levels: A significant age-related increase in cellular ROS-induced fluorescence was demonstrated. NAC significantly reduced ROS levels in old chondrocytes only. Induction of intracellular ROS: Menadione increased cellular ROS levels dose-dependently in young and old chondrocytes, with a greater effect in the latter. Old chondrocytes were more vulnerable to menadione-induced cytotoxicity. Antioxidant enzymes: Catalase activity declined significantly in aged cartilage whilst SOD and GPX activities were unaltered.

CONCLUSIONS

Substantial loss of chondrocytes occurs in rat articular cartilage which may result from increased vulnerability to elevated intracellular ROS levels, consequent upon a decline in antioxidant defence.

The switch mechanism of the cell death mode from apoptosis to necrosis in menadione-treated human osteosarcoma cell line 143B cells

Time-dependent changes in the cell death mode from apoptosis to necrosis were studied in cultured 143B cells treated with menadione, an anti-cancerous drug, excluding a possible involvement of "secondary necrosis." The population of apoptotic cells judged by FITC-Annexin V and propidium iodide (PI) double staining reached its maximum at 6 hours after 100 microM menadione treatment followed by an abrupt decrease thereafter, while that of necrotic cells continuously increased reaching 90% at 24 hours. Electron microscopically, cells attached to the culture dish at 6 hours after the treatment consisted of two different types of cells: cells with typical apoptotic features occupying the major population and those with condensed nuclei and swollen cytoplasm. Cells attached to the culture dish at 8 hours after the treatment consisted exclusively of those with condensed nuclei and swollen cytoplasm. Mitochondria in these cells showed various structural changes: those swollen to various degrees with deposition of flocculent densities, or those with highly condensed matrix. Distinct decreases both in intracellular levels of ATP and caspase-3-like activities and remarkable elevations of intracellular levels of superoxide, which were partly suppressed by NAD(P)H oxidase inhibitors, occurred at 6 hours after the treatment. These results may suggest that distinct increases of the intracellular level of superoxide derived from plasma membrane NAD(P)H oxidase besides that from mitochondria have triggered the transition of cell death mode from apoptosis to necrosis. Transition of highly condensed mitochondria to extremely swollen ones may reflect necrotic processes in menadione-treated cells. The present study strongly suggests that time-dependent study is essential using the electron microscopic technique to analyze detailed processes in the changes of the cell death mode.

Superoxide mediates shock wave induction of ERK-dependent osteogenic transcription factor (CBFA1) and mesenchymal cell differentiation toward osteoprogenitors

Extracorporeal shock wave (ESW) is an alternative non-invasive method for the promotion of bone growth and tendon repair. In an animal model, we have reported that ESW promoted bone marrow osteoprogenitor growth through transforming growth factor-beta1 induction. We have further explored the mechanism for the ESW promotion of osteogenesis. Results showed that an optimal ESW treatment at 0.16 mJ/mm(2) for 500 impulses rapidly induced a higher O(2)(-) and ONOO(-) production associated with a decrease of nitric oxide level in 1 h, and induced a higher transforming growth factor-beta1 production in 24 h, and a higher colony-forming units-osteoprogenitor formation in 12 days. The colony-forming units-osteoprogenitor colonies revealed positive staining of bone alkaline phosphatase and turned into bone nodules in 21 days. Early scavenging of O(2)(-) but not Ca(2+), H(2)O(2), or prostaglandin E(2) suppressed osteoprogenitor cell growth and maturation. Scavenging of O(2)(-) by superoxide dismutase raised the nitric oxide level back to the basal level and suppressed ESW-promoted osteoprogenitor cell growth, whereas inhibition of ONOO(-) by urate or NO by N-nitro-l-arginine methyl ester did not affect ESW promotion of osteogenesis, indicating that O(2)(-) acted as an early signal for ESW-induced cell growth. Further studies demonstrated that ESW induced ERK activation, and blockage of O(2)(-) production or inhibition of tyrosine kinase, but not protein kinase A and C inhibitors, suppressed ESW-induced ERK activation. In support that O(2)(-) mediated the ESW-induced ERK activation and osteogenic differentiation, we further demonstrated that scavenging of O(2)(-) by superoxide dismutase and inhibition of ERK activation by PD98059 decreased specific osteogenic transcription factor, core binding factor A1 activation, and decreased osteocalcin expression. Taken together, we showed that ESW-induced O(2)(-) production followed by tyrosine kinase-mediated ERK activation and core binding factor A1 activation resulted in osteogenic cell growth and maturation. Thus, an appropriate modulation of redox reaction by ESW may have some positive effect on the bone regeneration.

In vitro testing of the potential for orthopedic bone cements to cause apoptosis of osteoblast-like cells

The purpose of this study was to investigate in vitro the apoptosis- and/or necrosis-inducing potential of polymethylmethacrylate (PMMA)-based bone cements for prosthetic surgery. Four bone cements widely used in orthopedics were tested as extracts onto osteoblast-like MG-63 cells and for comparison, HL-60 cells, which are remarkably sensitive to apoptotic stimuli. Neutral red uptake (NRU) was used to measure cell viability while Hoechst 33258 staining was used to detect DNA content. Apoptosis was characterized using a BrdU-based ELISA assay for DNA fragmentation and examined by fluorescence microscopy using acridine orange and propidium iodide staining of nuclei. The generation of reactive oxygen species (ROS), which could mediate apoptosis, was verified using dichlorofluorescein-diacetate (DCFH-DA) oxidation to DCF. After 24 h of challenge of the cells with the four cement extracts, the viability of either MG-63 or HL-60 cells was found to be unaltered, as recorded by NRU. Apoptotic cell death was induced by three cements in HL-60, whereas MG-63 cells were significantly affected by the four cements tested: the finding of DNA fragments both in the cytoplasm and supernatants of MG-63 after 24 h demonstrated that these cells underwent late-apoptosis secondary necrosis. Fluorescent staining of the nuclei confirmed the results obtained with the ELISA test. Oxygen free radicals were elicited by two cements in HL-60 cells, while MG-63 did not generate ROS in response to cements. This study helps to gain more insight into the mechanism of cell death induced by PMMA-based cements and suggests apoptosis of osteoblasts as a part of the tissue reaction around cemented prostheses.

Evidence that oxidative stress-induced apoptosis by menadione involves Fas-dependent and Fas-independent pathways

Menadione (vitamin K3) a redox cycling quinone, is a clinically important chemotherapeutic agent. The objective of this study was to clarify the cytotoxic mechanisms by which menadione induces cell death in a lymphoblastoid cell line. Our results show that while the Jun kinase cascade and FasL expression may contribute to cell death at lower drug concentrations, a mitochondrial pathway dominates the cytotoxic effect at higher menadione concentrations. Menadione treatment clearly affected the mitochondrial function of Jurkat T cells by inducing a collapse of the inner transmembrane potential (DeltaPsi(m)) and a decrease in inner membrane mass, which could be completely reversed by N-acetylcysteine. Importantly, while a broad range of fmk-derived caspase inhibitors had potent effects on Fas-induced apoptosis, they failed to interfere in menadione cytotoxicity, indicating that menadione-induced cell death is predominantly Fas-independent. In addition, the mitochondrial changes coincided with ATP depletion. The failure in ATP production explains the occurrence of Fas-independent death events.

Reactive oxygen species and substance P in monocrotaline-induced pulmonary hypertension

We attempted to evaluate whether the antioxidants 1,3-dimethyl-2-thiourea (DMTU) and hexa(sulfobutyl)fullerenes (FC(4)S) attenuate monocrotaline (MCT)-induced pulmonary hypertension (PH) by lowering lung substance P (SP) in Wistar rats. Sixty-three rats weighing 297 +/- 8 g were divided into six groups: control; MCT; capsaicin + MCT; MCT + DMTU-1; MCT + DMTU-2; and MCT + FC(4)S. Three weeks before the functional study, saline was injected into each control rat, whereas each MCT rat received 60 mg/kg sc MCT. Rats in the third group received capsaicin pretreatment followed by MCT. A 3-day injection of DMTU was performed during the early (DMTU-1) or the late (DMTU-2) post-MCT period. For the last group, each MCT-treated rat received a daily FC(4)S injection until the commencement of the functional study. Compared to the control group, MCT caused significant increases in pulmonary arterial pressure (Ppa), right ventricular hypertropy, pulmonary arterial medial thickness, lung SP level, and luminol-enhanced chemiluminescence counts in bronchoalveolar lavage. Both capsaicin and antioxidants significantly attenuated the above MCT-induced alterations. SP-induced acute increase in Ppa was exaggerated in MCT-treated rats. These results suggest that oxygen radicals play an important role in MCT-induced PH via elevating lung SP level.

Inhibition of apoptosis: a potential mechanism for syndromic craniosynostosis

The biologic pathogenesis of syndromic craniosynostosis remains unknown. The purpose of this investigation was to determine whether specific biologic differences exist between normal calvarial osteoblasts and osteoblasts derived from patients with syndromic craniosynostosis. This study (1) examined the apoptotic rate and cell cycle of osteoblasts derived from patients with syndromic craniosynostosis, and (2) investigated for the presence of soluble factors released from syndrome-derived osteoblasts. Osteoblast cell lines were established from calvarial specimens of patients with clinically diagnosed syndromic synostosis and from normal controls. A co-culture technique was used to investigate for the presence of elaborated soluble factors. Apoptotic rate and cell cycle analyses were performed by using flow cytometry after staining with annexin V-fluorescein isothiocyanate and propidiumiodide, respectively. The apoptotic rate was significantly reduced in syndrome-derived osteoblasts as compared with control osteoblasts. Control osteoblasts co-cultured with syndromic osteoblasts demonstrated a dramatic reduction in their apoptotic rate as compared with those co-cultured with control osteoblasts. These results indicate that osteoblasts derived from patients with syndromic craniosynostosis display a lower apoptotic rate, a normal DNA synthetic rate, and the capability to reduce the apoptotic rate in normal calvarial osteoblasts through the elaboration of soluble factors.

Apoptosis provoked by the oxidative stress inducer menadione (Vitamin K(3)) is mediated by the Fas/Fas ligand system

Menadione, or vitamin K(3) (VK(3)), a potent oxidative stress inducer, has been recently used as an effective and remarkably safe cytotoxic drug for treatment of several human tumors. VK(3) induces apoptotic cell death through a poorly understood mechanism. Here we show for the first time that VK(3)-induced apoptosis requires the Fas/FasL system. Spleen cells from both Fas- and FasL-deficient mice (C57BL/6-lpr and C57BL/6-gld, respectively) had much lower levels of VK(3) apoptosis in vitro compared to cells from control C57BL/6 mice. VK(3) cytotoxicity toward mouse splenocytes was also blocked with a Fas-Fc fusion protein. VK(3) induced apoptosis in Jurkat cells, coincident with an increase in both Fas and FasL expression. A FasL-resistant variant of these Jurkat cells was also resistant to VK(3)-induced apoptosis. Furthermore, because VK(3) effects were inhibited by glutathione, a potent antioxidant, oxidative stress was linked to the Fas/FasL system. Moreover, since the Jurkat cell lines were p53 null, the activation of Fas/FasL system after oxidative stress apparently acted through a p53-independent pathway. The therapeutic relevance of the K vitamins has been growing in recent years; our findings offer new insight for improving and expanding their applications.

Scavenging effect of benzophenones on the oxidative stress of skeletal muscle cells

Benzophenone is an ultraviolet (UV)-absorbing agent that has been used in industry and medicine for more than 30 years. Consumers of cosmetics and sunscreens containing UV-absorbers are exposed to benzophenones on a daily basis, owing to the widespread use of these compounds. However, the efficacy of these compounds as scavengers of oxidative stress is still not well established. In the present study, we investigate the antioxidative capacity of six sunscreen benzophenone compounds. A primary myoblast culture was mixed in vitro with 100 microM menadione. The cytotoxic effect by menadione-induced oxidative stress was monitored by the lucigenin- or luminol-amplified chemiluminescence, methylthiotetrazole (MTT) assay, and the antioxidative effects of various benzophenone compounds were evaluated. The results showed that the addition of menadione can induce oxidative stress on myoblasts by superoxide and hydrogen peroxide production, which can be eradicated by superoxide dismutase (SOD) and catalase, respectively, in a dose-dependent mode. The catalase has a protective effect on the cytotoxicity induced by menadione as measured by the MTT assay, while the SOD does not. The selected benzophenones also have a significant scavenging effect on the menadione-induced cell death on the myoblasts. The ortho-dihydroxyl structure and other hydroxy groups in the same ring have a stronger scavenging effect on the superoxide anion on myoblasts; thus, a stable penoxy radical may be formed. The mechanism of this effect remains to be clarified.

A comparative study of apoptosis and necrosis in HepG2 cells: oxidant-induced caspase inactivation leads to necrosis

Apoptosis and necrosis are two distinct forms of cell death that can occur in response to various agents. In the present study the HepG2 cell line was used for a comparative study of CD95-mediated apoptosis and menadione-induced necrosis. Apoptosis coincided with the release of cytochrome c from mitochondria, activation of caspases, cleavage of cellular proteins, and also involved nuclear condensation and DNA fragmentation. Necrosis was not accompanied by DNA fragmentation, caspase activation or cleavage of caspase target proteins, despite cytochrome c release from mitochondria. In fact, the addition of menadione to cells undergoing CD95-mediated apoptosis blocked their caspase activity. Inhibition of caspases coincided with an accumulation of reactive oxygen species (ROS) and ATP depletion. In order to determine the predominance of either of these events in the inhibition of caspase, cells were either co-incubated with antioxidant enzymes or their ATP level was manipulated to maintain it at a relatively high level during the experiments. Co-incubation with catalase, but not Cu/Zn superoxide dismutase, substantially reduced the levels of ROS and reversed the inhibitory effect of menadione on caspase activity. In contrast, increasing cellular ATP level had little effect on restoring caspase activity. These data suggest that menadione inhibits caspase activity by the generation of hydrogen peroxide through redox cycling and that caspase inactivation by this mechanism may prevent cell death by apoptosis in this oxidative-stress model.