Metabolism and cytotoxicity of menadione and its metabolite in rat platelets

A protocol for the cultivation and monitoring of ileal gut microbiota surrogates

AIMS

This research aimed to develop and validate a cultivation and monitoring protocol that is suitable for a surrogate microbial community that accounts for the gut microbiota of the ileum of the small intestine.

METHODS AND RESULTS

Five bacterial species have been selected as representatives of the ileal gut microbiota and a general anaerobic medium (MS-BHI, as minimally supplemented BHI) has been constructed and validated against BCCM/LGM recommended and commercial media. Moreover, appropriate selective/differential media have been investigated for monitoring each ileal gut microbiota surrogate. Results showed that MS-BHI was highly efficient in displaying individual and collective behavior of the ileal gut microbiota species, when compared with other types of media. Likewise, the selective/differential media managed to identify and describe the behavior of their targeted species.

CONCLUSIONS

MS-BHI renders a highly efficient, inexpensive and easy-to-prepare cultivation and enumeration alternative for the surrogate ileal microbiota species. Additionally, the selective/differential media can identify and quantify the bacteria of the surrogate ileal microbial community.

SIGNIFICANCE AND IMPACT OF STUDY

The selected gut microbiota species can represent an in vitro ileal community, forming the basis for future studies on small intestinal microbiota. MS-BHI and the proposed monitoring protocol can be used as a standard for gut microbiota studies that utilize conventional microbiological techniques.

The production of reactive oxygen species enhanced with the reduction of menadione by active thioredoxin reductase

Cytosolic thioredoxin reductase (TXNRD1) is an important selenoprotein that participates in the reduction of thioredoxin and many other redox-related substrates. The enhancement of ROS production to cause cancer cell death is an effective anticancer strategy. Herein, we found that menadione substantially increased ROS generation via interaction with TXNRD1. To elucidate the mechanism behind this, various TXNRD1 mutant proteins were used to investigate the relationship between ROS production and the reaction between enzymes and menadione. A mutation at the C-terminal active site -GCUG of TXNRD1 to -GSSG or -GC, or the N-terminal active site C59S, C64S, or the deletion of the C-terminal 16 amino acid residues caused the loss of TXNRD1 activity needed for the reduction of menadione and therefore resulted in the loss of the ROS production ability of menadione. In contrast, the mutation of -GCUG to -GCCG resulted in an increase in the TXNRD1 activity towards the reduction of menadione, thus leading to an increase in ROS production. The co-treatment of the TXNRD1 inhibitor aurothioglucose and menadione could significantly alleviate the efficiency of ROS generation in vitro and increase the viability of A549 cells. Moreover, menadione could be reduced by the glutathione system and caused ROS production with less efficiency. These results demonstrate that TXNRD1 can serve as an effective source to generate ROS, which may provide a novel anticancer method based on the use of menadione.

Age-related loss of mitochondrial glutathione exacerbates menadione-induced inhibition of Complex I

The role of mitochondrial GSH (mGSH) in the enhanced age-related susceptibility to xenobiotic toxicity is not well defined. We determined mGSH status and indices of mitochondrial bioenergetics in hepatocytes from young and old F344 rats treated with 300 μM menadione, a concentration that causes 50% cell death in old. At this concentration, mGSH was significantly lost only in hepatocytes from old rats, and with near total depletion due to lower basal mGSH in aged cells. In old hepatocytes, menadione caused mitochondrial membrane potential to collapse, as well as significant deficits in maximal O2 consumption and respiratory reserve capacity, indicators of cellular bioenergetic resiliency. Further examination revealed that the menadione-mediated loss of respiratory reserve capacity in aged hepatocytes was from significant inhibition of Complex I activity and increased proton leak, for which an increase in Complex II activity was not able to compensate. These data demonstrate an age-related increase in mitochondrial susceptibility to a redox-cycling challenge, particularly in regards to Complex I activity, and provide a plausible mechanism to link this vulnerability to mGSH perturbations.

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.

Detection of Emodin Derived Glutathione Adduct in Normal Rats Administered with Large Dosage of Polygoni Multiflori Radix

Polygoni Multiflori Radix (PMR) has been commonly used as a tonic in China for centuries. PMR-associated hepatotoxicity has been drawing increasingly more attention in recent years in parallel with its wide utilization. Anthraquinones (AQs) are recognized as the main hepatotoxic components in PMR. However, the exact underlying mechanism of AQs poisoning is still not fully understood. Herein, we proposed a hypothesis that metabolic activation of AQs such as emodin was involved in PMR-induced liver injury, AQs followed to generate the electrophilic reactive metabolites and subsequently formed covalent adduct with cellular nucleophiles in the liver to exert hepatotoxicity. In the present study, the link of cytotoxicity of PMR in primary human hepatocytes and the depletion of glutathione (GSH) was investigated by MTT assay and UHPLC-QqQ-MS/MS analysis. The results showed that PMR depleted GSH and therefore induced cytotoxicity. Then, emodin-GSH adduct was identified in bile of liver injured rats after intragastric administration of PMR or emodin with the aid of UHPLC-QTOF-MS/MS method. Our findings not only provided confirmative evidence that the mechanism of hepatotoxicity induced by AQs in PMR involved key metabolic steps, but also revealed that emodin-GSH adduct had potential to be further developed as a sensitive and traceable biomarker for the assessment of PMR-induced liver injury.

Glutathione maintenance mitigates age-related susceptibility to redox cycling agents

Isolated hepatocytes from young (4-6mo) and old (24-26mo) F344 rats were exposed to increasing concentrations of menadione, a vitamin K derivative and redox cycling agent, to determine whether the age-related decline in Nrf2-mediated detoxification defenses resulted in heightened susceptibility to xenobiotic insult. An LC50 for each age group was established, which showed that aging resulted in a nearly 2-fold increase in susceptibility to menadione (LC50 for young: 405μM; LC50 for old: 275μM). Examination of the known Nrf2-regulated pathways associated with menadione detoxification revealed, surprisingly, that NAD(P)H: quinone oxido-reductase 1 (NQO1) protein levels and activity were induced 9-fold and 4-fold with age, respectively (p=0.0019 and p=0.018; N=3), but glutathione peroxidase 4 (GPX4) declined by 70% (p=0.0043; N=3). These results indicate toxicity may stem from vulnerability to lipid peroxidation instead of inadequate reduction of menadione semi-quinone. Lipid peroxidation was 2-fold higher, and GSH declined by a 3-fold greater margin in old versus young rat cells given 300µM menadione (p<0.05 and p≤0.01 respectively; N=3). We therefore provided 400µMN-acetyl-cysteine (NAC) to hepatocytes from old rats before menadione exposure to alleviate limits in cysteine substrate availability for GSH synthesis during challenge. NAC pretreatment resulted in a >2-fold reduction in cell death, suggesting that the age-related increase in menadione susceptibility likely stems from attenuated GSH-dependent defenses. This data identifies cellular targets for intervention in order to limit age-related toxicological insults to menadione and potentially other redox cycling compounds.

Menadione

This chapter includes the aspects of Menadione (vitamin K). The drug is synthesized by the use of itaconic acid obtained through Friedel-Craft condensation or by direct oxidation of the 2-methyl-1,4-naphthquinone. Vitamin K generally maintains healthy blood clotting and prevents excessive bleeding and hemorrhage, it is also important for maintaining healthy bone structure and for carbohydrate storage in the body. In addition, it is given to newborn babies born in hospitals to prevent the development of life-threatening bleeding caused by low prothrombin levels. The chapter discusses the drug metabolism and pharmacokinetics and presents various method of analysis of this drug such as compendial tests, electrochemical analysis, spectroscopic analysis, and chromatographic techniques of separation. It also discusses its physical properties such as solubility characteristics, X-ray powder diffraction pattern, and thermal methods of analysis. The chapter is concluded with a discussion on its biological properties such as activity, toxicity, and safety.

Chemically imaging living cells by scanning electrochemical microscopy

Scanning electrochemical microscopy (SECM) is useful in probing and characterizing interfaces at high resolution. In this paper, the general principles of this technique are described and several applications of SECM to biological systems, particularly to living cells, is discussed, along with several example systems. Thiodione was detected and monitored electrochemically during the treatment of hepatocytes with cytotoxic menadione. The antimicrobial effects of silver(I) was followed by SECM through bacterial respiration. Living HeLa cells were shown to accumulate ferrocencemethanol (FcMeOH) and generated positive feedback for FcMeOH oxidation that can be further used to monitor the cell viability. Finally, individual giant liposomes, as cell models, with encapsulated redox compounds were successfully probed by SECM. In general SECM has the advantage of very high spatial resolution and versatility, especially for the detection of electroactive substances.

Vitamin K1 (phylloquinone) induces vascular endothelial dysfunction: Role of oxidative stress

We aimed to investigate the mechanisms underlying the vascular effects induced by phylloquinone (Vitamin K1; VK1). Vascular reactivity experiments, using standard muscle bath procedures, showed that VK1 (5 and 50 microM) enhances the contractile response of endothelium-intact, but not denuded, rat carotid rings to phenylephrine. Similarly, maximal contraction induced by phenylephrine was enhanced in the presence of the nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME). The combination of L-NAME and VK1 did not produce any further additional effect. Pre-incubation of intact-rings with VK1 reduced both acetylcholine- and bradykinin-induced relaxation. VK1 induced an increment in tension on carotid rings submaximally pre-contracted with phenylephrine. VK1-induced increment in tension was completely abolished by endothelial removal or incubation of intact rings with L-NAME and L-NNA. Conversely, 7-nitroindazole, 1400 W, or indomethacin did not affect VK1-induced contraction. Moreover, VK1 reduced L-arginine-induced relaxation in endothelium-intact rings. Lucigenin-amplified chemiluminescence assays showed that VK1 induced an increase in the level of superoxide anions in endothelium-intact but not denuded rings. Measurement of nitrite and nitrate generation showed that VK1 did not alter nitrate formation but strongly inhibited the generation of nitrite. Finally, the superoxide anions scavenger tiron prevented the endothelial vasomotor dysfunction caused by VK1 on phenyleprine-induced contraction and acetylcholine or bradykinin-induced relaxation. In conclusion, our data show that VK1 disrupts the vasomotor function of rat carotid. Our results suggest that VK1-induced oxidative stress through production of superoxide anion is interfering with the NO pathway, which in turn is responsible for the altered vascular reactivity induced by VK1.

Menadione metabolism to thiodione in hepatoblastoma by scanning electrochemical microscopy

The cytotoxicity of menadione on hepatocytes was studied by using the substrate generation/tip collection mode of scanning electrochemical microscopy by exposing the cells to menadione and detecting the menadione-S-glutathione conjugate (thiodione) that is formed during the cellular detoxication process and is exported from the cell by an ATP-dependent pump. This efflux was electrochemically detected and allowed scanning electrochemical microscopy monitoring and imaging of single cells and groups of highly confluent live cells. Based on a constant flux model, approximately 6 x 10(6) molecules of thiodione per cell per second are exported from monolayer cultures of Hep G2 cells.

Scanning electrochemical microscopy of menadione-glutathione conjugate export from yeast cells

The uptake of menadione (2-methyl-1,4-naphthoquinone), which is toxic to yeast cells, and its expulsion as a glutathione complex were studied by scanning electrochemical microscopy. The progression of the in vitro reaction between menadione and glutathione was monitored electrochemically by cyclic voltammetry and correlated with the spectroscopic (UV-visible) behavior. By observing the scanning electrochemical microscope tip current of yeast cells suspended in a menadione-containing solution, the export of the conjugate from the cells with time could be measured. Similar experiments were performed on immobilized yeast cell aggregates stressed by a menadione solution. From the export of the menadione-glutathione conjugate detected at a 1-microm-diameter electrode situated 10 microm from the cells, a flux of about 30,000 thiodione molecules per second per cell was extracted. Numerical simulations based on an explicit finite difference method further revealed that the observation of a constant efflux of thiodione from the cells suggested the rate was limited by the uptake of menadione and that the efflux through the glutathione-conjugate pump was at least an order of magnitude faster.

Enhancement of platelet aggregation and thrombus formation by arsenic in drinking water: a contributing factor to cardiovascular disease

Arsenic in drinking water is a worldwide health problem that is associated with cardiovascular disease, but the cause is currently unknown. Arsenic effects on platelets, which are important in development of cardiovascular disease, were examined in vitro and in a drinking water study using a rat animal model. Trivalent inorganic arsenic (arsenite) induced in vitro aggregation when platelets were exposed to subthreshold challenge by thrombin and several other agonists in a concentration-dependent manner, with arsenite being the most potent form tested. Arsenite also induced significant increases in serotonin secretion, thromboxane A(2) formation, and adhesion protein expression in platelets. Consistent with the in vitro studies, 4-week ingestion of arsenite-contaminated drinking water resulted in enhanced arterial thrombosis. Human platelets showed similar responses, suggesting that the effects seen in animal experiments are applicable to humans. These results will provide new insights into the mechanism of arsenic-induced cardiovascular disease. They will also allow regulatory agencies to estimate risk from arsenic-induced cardiovascular disease and to determine if drinking water regulatory levels based on human cancer studies will protect against noncancer effects associated with cardiovascular disease.

Schisandrin B protects against menadione-induced hepatotoxicity by enhancing DT-diaphorase activity

Pretreating mice with schisandrin B (Sch B), a dibenzocyclooctadiene derivative isolated from the fruit of Schisandra chinensis, at a daily dose of 1 mmol/kg for 3 days protected against menadione-induced hepatic oxidative damage in mice, as evidenced by decreases in plasma alanine aminotransferase activity (78%) and hepatic malondialdehyde level (70%), when compared with the menadione intoxicated control. In order to define the biochemical mechanism involved in the hepatoprotection afforded by Sch B pretreatment, we examined the activity of DT-diaphorase (DTD) in hepatocytes isolated from Sch B pretreated rats. Hepatocytes isolated from Sch B pretreated (a daily dose of 1 mmol/kg for 3 days) rats showed a significant increase (25%) in DTD activity. The increase in DTD activity was associated with the enhanced rate of menadione elimination in the hepatocyte culture. The ensemble of results suggests that the ability of Sch B pretreatment to enhance hepatocellular DTD activity may at least in part be attributed to the protection against menadione hepatotoxicity.

Pharmacological effects of novel quinone compounds, 6-(fluorinated-phenyl)amino-5,8-quinolinediones, on inhibition of drug-induced relaxation of rat aorta and their putative action mechanism

Two 6-(fluorinated-phenyl)amino-5,8-quinolinedione derivatives, OQ21 and OQ1, were newly synthesized as potent inhibitors of endothelial-dependent vasorelaxation. The purpose of the present study was to investigate the effects of OQ21 and OQ1 on different types of vasorelaxation and to pursue their action mechanisms. For acetylcholine both compounds, at a low concentration (0.1 microM), reduced the maximal response with increase of EC(50) values. OQ21 is a novel quinone compound and showed a more potent and efficacious inhibitory effect on acetylcholine-induced relaxation of rat aorta than that of LY83583 (6-anilino-5,8-quinolinedione). Relatively high concentrations (1 microM) of OQ21 and OQ1 inhibited the sodium nitroprusside-induced relaxation of endothelium-denuded ring, producing rightward shifts of the curve for sodium nitroprusside without altering the maximal response. They also prevented acetylcholine and sodium nitroprusside-induced elevations of cyclic GMP. In addition, OQ21 and OQ1 (1 microM) significantly decreased (52-72%) the sensitivity of L-arginine-induced relaxation of precontracted endothelium-denuded aortic rings from lipopolysaccaride-treated (20 mg/kg, i.p.) rats. The inhibitory effect of OQ21 on endothelium-dependent vasodilation was enhanced by N(G)-nitro-L-arginine, which inhibits nitric oxide synthase (NOS) by binding the oxygenase domain of the enzyme, but not by diphenylendiodonium, which inhibits NOS by binding to the reductase domain of the enzyme. Treatment of blood vessels with OQ21 or OQ1 showed a significant increase in chemiluminescence output, which was prevented by adding superoxide dismutase, suggesting that superoxide generation is involved in the action mechanism for OQ21. Present results indicate that a novel naphthoquinone compound, OQ21, potently inhibits endothelial NOS, possibly by interacting with the reductase domain of the enzyme, which leads to induce superoxide formation. The new benzoquinone compounds, OQ21 and OQ1, inhibit not only endothelium-dependent vasorelaxation but also endothelium-independent relaxation induced by exogenous NO generated from a nitrovasodilator via the reduction of cyclic GMP. They also reduced L-arginine-induced vasorelaxation in endotoxin-treated rats, indicating their possession of inhibitory effect on inducible NOS.

The biological significance of non-enzymatic reaction of menadione with plasma thiols: enhancement of menadione-induced cytotoxicity to platelets by the presence of blood plasma

To test the hypothesis that the non-enzymatic reaction of quinones with thiols in plasma can generate reactive oxygens (ROS), thereby leading to potentiated cellular toxicity, we have studied the effect of a representative quinone compound, menadione, on plasma isolated from rats. The experimental results are as follows: (1) menadione generated ROS via non-enzymatic reaction with protein thiols in plasma; (2) the presence of plasma increased menadione-induced cytotoxicity to platelets; (3) pretreatment of plasma with a thiol-depleting agent significantly suppressed menadione-induced ROS and cytotoxicity. These results suggest that the non-enzymatic reaction of menadione with plasma thiols could be an important process in quinone-induced cellular toxicity.

The relative importance of oxidative stress versus arylation in the mechanism of quinone-induced cytotoxicity to platelets

Our previous studies demonstrated that menadione is cytotoxic to rat platelets. In an attempt to assess the relative contributions of enzymatic redox cycling versus arylation in menadione-induced cytotoxicity, we have studied three quinones with different mechanisms of action: 2,3-dimethoxy-1,4-naphthoquinone (DMNQ; pure redox cycler), menadione (both redox cycler and arylator), and 1,4-benzoquinone (BQ; pure arylator). BQ was more toxic to rat platelets than menadione, while DMNQ did not cause LDH leakage at all. Cellular uptake kinetics revealed that DMNQ concentration taken up by the cells was equivalent to that decreased in incubation medium. On the other hand, the concentrations of BQ and menadione taken into the cells were significantly lower than the decreases in concentrations seen in the incubation medium. This suggests indirectly that BQ and menadione may have undergone arylation, binding to glutathione (GSH) or protein thiols. The difference in arylation capacity between BQ and menadione was well correlated with their relative cytotoxicity (LDH leakage) observed in platelets. All three quinones caused a rapid, extensive depletion of intracellular GSH in platelets. Treatments with BQ and menadione did not result in formation of oxidized glutathione (GSSG), whereas DMNQ showed a time-dependent increase in GSSG. Altogether, these results suggest that enzymatic redox cycling does not play a critical role in quinone-induced cytotoxicity in rat platelets, while arylation is likely to be quinone's primary mechanism of action.

Chemically induced platelet lysis causes vasoconstriction by release of serotonin

Our previous studies have shown that menadione is cytotoxic to platelets, leading to substantial release of vasoactive substances. To test whether platelet lysis induced by menadione could cause vasoconstriction, we investigated the effect of platelet lysate induced by menadione on rat aorta in organ bath system. We showed that menadione-induced platelet lysate caused vasoconstriction in a dose- and time-dependent manner. These effects were seen in aortic rings both with and without endothelium, but it was much greater in rings without intact endothelium. The time course of vasoconstriction was well correlated with the time courses of platelet lysis (assessed by lactate dehydrogenase release) as well as serotonin release. The vasoconstriction by platelet lysate was blocked by serotonin antagonists, ketanserin, and LY53,857, but not by thromboxane A2 (TXA2) receptor antagonist, SQ29,548, suggesting that vasoconstriction mainly occurred secondary to the release of serotonin in our in vitro system. However, potentiation of vasoconstriction by combined treatment of serotonin and a stable TXA2 mimic, U46619, suggests the possibility of the increased risk for vasoconstriction in vivo. In addition, the serotonin-induced vasoconstriction was potentiated by residual menadione present in the organ bath. These results suggest that chemically induced platelet cytotoxicity can provoke alteration in vasomotor tone by release of serotonin.