Tritiated 2-deoxy-D-glucose as a probe for cell membrane permeability studies

High content drug screening of primary cardiomyocytes based on microfluidics and real-time ultra-large-scale high-resolution imaging

High content screening (HCS) plays an important role in biological applications and drug development. Existing techniques fail to simultaneously meet multiple needs of throughput, efficiency in sample and chemical consumption, and real-time imaging of a large view at high resolution. Leveraging advances in microfluidics and imaging technology, we setup a new paradigm of large-scale, high-content drug screening solutions for rapid biological processes, like cardiotoxicity. The designed microfluidic chips enable 10 types of drugs each with 5 concentrations to be assayed simultaneously. The imaging system has 30 Hz video rate for a centimeter filed-of-view at 0.8 μm resolution. Using the HCS system, we assayed 12 small molecules through their effects on the Ca²⁺ ion signal of cardiomyocytes. Experimental results demonstrated the unparalleled capability of the system in revealing the spatiotemporal patterns of Ca²⁺ imaging of cardiomyocytes, and validated the cardiotoxicity of certain molecules. We envision that this new HCS paradigm and cutting-edge platform offer the most advanced alternative to well-plate based methods.

Cell-penetrating peptide: a means of breaking through the physiological barriers of different tissues and organs

The selective infiltration of cell membranes and tissue barriers often blocks the entry of most active molecules. This natural defense mechanism prevents the invasion of exogenous substances and limits the therapeutic value of most available molecules. Therefore, it is particularly important to find appropriate ways of membrane translocation and therapeutic agent delivery to its target site. Cell penetrating peptides (CPPs) are a group of short peptides harnessed in this condition, possessing a significant capacity for membrane transduction and could be exploited to transfer various biologically active cargoes into the cells. Since their discovery, CPPs have been employed for delivery of a wide variety of therapeutic molecules to treat various disorders including cranial nerve involvement, ocular inflammation, myocardial ischemia, dermatosis and cancer. The promising results of CPPs-derived therapeutics in various tumor models demonstrated a potential and worthwhile scope of CPPs in chemotherapy. This review describes the detailed description of CPPs and CPPs-assisted molecular delivery against various tissues and organs disorders. An emphasis is focused on summarizing the novel insights and achievements of CPPs in surmounting the natural membrane barriers during the last 5 years.

Cellular effects of an anionic surfactant detected in V79 fibroblasts by different cytotoxicity tests

Several cytotoxicity tests were employed to detect the cellular effects of low concentrations of the anionic surfactant linear alkylbenzene sulphonate (LAS). When added to growth medium containing 5% foetal calf serum, LAS did not affect V79 cell growth, nor did it alter the permeability of cell membranes. The inactivity depended on the serum component of the medium. When treatments were carried out in serum-free saline, LAS inhibited cell proliferation, made the plasma membrane permeable to otherwise-undiffusible compounds, and reduced the uptake of tritiated thymidine. The alterations in membrane permeability were evaluated from the release of cytoplasmic molecules of different size (lactate dehydrogenase, adenine nucleotides, RNA) into the medium. The sensitivity of the spectrophotometric lactate dehydrogenase assay was inadequate for the conditions of treatment required to detect the cytotoxicity of LAS. In cultures pre-incubated with tritiated adenine instead, the release of labelled ATP pool components was time and dose dependent and allowed discrimination between levels of membrane damage causing the same degree of trypan blue staining. Also, macromolecular nucleic acids were detected outside the treated cells at doses of 4-6 mg LAS/litre, which indicated severe membrane damage.

Toxicity methods for CPPs

CPPs have for numerous years been utilized as delivery vectors of various pharmaceutically interesting cargoes, both in vitro and in vivo. As CPPs are gradually approaching the bedsides, investigating toxicity associated with these highly interesting peptides becomes increasingly important and thorough initial assessment of cytotoxicity in vitro is a first step towards advancing these delivery vehicles in to the clinics. The present chapter describes protocols for four cytotoxicity assays in order to provide a toolbox for toxicity assessment of CPPs. The foci lie on membrane integrity (deoxyglucose leakage and propidium iodide assays) and cell viability (the MTT assay), but the chapter also provides a protocol for assessing an important parameter for future clinical applications, namely the hemolytic properties of CPPs.

Cryoprotectant biosynthesis and the selective accumulation of threitol in the freeze-tolerant Alaskan beetle, Upis ceramboides

Adult Upis ceramboides do not survive freezing in the summer but tolerate freezing to -60 degrees C in midwinter. The accumulation of two cryoprotective polyols, sorbitol and threitol, is integral to the extraordinary cold-hardiness of this beetle. U. ceramboides are the only animals known to accumulate high concentrations of threitol; however, the biosynthetic pathway has not been studied. A series of (13)C-labeled compounds was employed to investigate this biosynthetic pathway using (13)C{(1)H} NMR spectroscopy. In vivo metabolism of (13)C-labeled glucose isotopomers demonstrates that C-3-C-6 of glucose become C-1-C-4 of threitol. This labeling pattern is expected for 4-carbon saccharides arising from the pentose phosphate pathway. In vitro experiments show that threitol is synthesized from erythrose 4-phosphate, a C(4) intermediate in the PPP. Erythrose 4-phosphate is epimerized and/or isomerized to threose 4-phosphate, which is subsequently reduced by a NADPH-dependent polyol dehydrogenase and dephosphorylated by a sugar phosphatase to form threitol. Threitol 4-phosphate appears to be the preferred substrate of the sugar phosphatase(s), promoting threitol synthesis over that of erythritol. In contrast, the NADPH-dependent polyol dehydrogenase exhibits broad substrate specificity. Efficient erythritol catabolism under conditions that promote threitol synthesis, coupled with preferential threitol biosynthesis, appear to be responsible for the accumulation of high concentrations of threitol (250 mm) without concomitant accumulation of erythritol.

Integrated Decision-tree Testing Strategies for Acute Systemic Toxicity and Toxicokinetics with Respect to the Requirements of the EU REACH Legislation

Liverpool John Moores University and FRAME conducted a joint research project, sponsored by Defra, on the status of alternatives to animal testing with regard to the European Union REACH (Registration, Evaluation and Authorisation of Chemicals) system for the safety testing and risk assessment of chemicals. The project covered all the main toxicity endpoints associated with REACH. This paper focuses on the use of alternative (non-animal) methods (both in vitro and in silico) for acute systemic toxicity and toxicokinetic testing. The paper reviews in vitro tests based on basal cytotoxicity and target organ toxicity, along with QSAR models and expert systems available for this endpoint. The use of PBPK modelling for the prediction of ADME properties is also discussed. These tests are then incorporated into a decision-tree style, integrated testing strategy, which also includes the use of refined in vivo acute toxicity tests, as a last resort. The implementation of the strategy is intended to minimise the use of animals in the testing of acute systemic toxicity and toxicokinetics, whilst satisfying the scientific and logistical demands of the EU REACH legislation.

Integrated decision-tree testing strategies for acute systemic toxicity and toxicokinetics with respect to the requirements of the EU REACH legislation

Liverpool John Moores University and FRAME conducted a joint research project, sponsored by Defra, on the status of alternatives to animal testing with regard to the European Union REACH (Registration, Evaluation and Authorisation of Chemicals) system for the safety testing and risk assessment of chemicals. The project covered all the main toxicity endpoints associated with REACH. This paper focuses on the use of alternative (non-animal) methods (both in vitro and in silico) for acute systemic toxicity and toxicokinetic testing. The paper reviews in vitro tests based on basal cytotoxicity and target organ toxicity, along with QSAR models and expert systems available for this endpoint. The use of PBPK modelling for the prediction of ADME properties is also discussed. These tests are then incorporated into a decision-tree style, integrated testing strategy, which also includes the use of refined in vivo acute toxicity tests, as a last resort. The implementation of the strategy is intended to minimise the use of animals in the testing of acute systemic toxicity and toxicokinetics, whilst satisfying the scientific and logistical demands of the EU REACH legislation.

Effects of vitamin E supplementation on plasma membrane permeabilization and fluidization induced by chlorpromazine in the rat brain

Neurotransmitter receptors play a key role in most research on antipsychotic drugs, but little is known about the effects of these drugs on the plasma membrane in the central nervous system. Therefore, we investigated whether chlorpromazine (CPZ), a typical phenothiazine antipsychotic drug, affects the plasma membrane integrity in the rat brain, and if so, whether these membrane alterations can be prevented by dietary supplementation with vitamin E, which has been shown to be an antioxidant and also a membrane-stabilizer. Leakage of [(18)F]2-fluoro-2-deoxy-D-glucose ([(18)F]FDG)-6-phosphate from rat striatal slices and decrease in 1,6-diphenyl-1,3,5-hexatriene fluorescence anisotropy were used as indexes for plasma membrane permeabilization and fluidization, respectively. CPZ induced leakage of [(18)F]FDG-6-phosphate from striatal slices, and the leakage was delayed in the vitamin E-supplemented group compared to that in the normal diet group. The decrease in plasma membrane anisotropy induced by CPZ was significantly attenuated by vitamin E supplementation. Chronic treatment with alpha-phenyl-N-tert-butyl nitrone, a free radical scavenger, had no effect on CPZ-induced plasma membrane permeabilization, and the treatment with CPZ did not induce lipid peroxidation. CPZ can reduce plasma membrane integrity in the brain, and this reduction can be prevented by vitamin E via its membrane-stabilizing properties, not via its antioxidant activity.

A comparative study of the plasma membrane permeabilization and fluidization induced by antipsychotic drugs in the rat brain

We compared the potency of the interaction of three antipsychotic drugs, i.e. chlorpromazine (CPZ), haloperidol (Hal) and sulpiride (Sul), with the plasma membrane in the rat brain. CPZ loading (> or = 100 microM) dose-dependently increased both membrane permeability (assessed as [18F]2-fluoro-2-deoxy-D-glucose-6-phosphate release from brain slices) and membrane fluidity (assessed as the reduction in the plasma membrane anisotropy of 1,6-diphenyl-1,3,5-hexatriene). On the other hand, a higher concentration of Hal (1 mM) was required to observe these effects. However, Sul failed to change membrane permeability and fluidity even at a high concentration (1 mM). These results indicated the following ranking of the potency to interact with the membrane: CPZ>Hal>Sul. The difference among antipsychotic drugs in the potency to interact with the plasma membrane as revealed in the present study may be partly responsible for the difference among the drugs in the probability of inducing extrapyramidal side-effects such as parkinsonism and tardive dyskinesia.

Effects of haloperidol and its pyridinium metabolite on plasma membrane permeability and fluidity in the rat brain

The use of antipsychotic drugs is limited by their tendency to produce extrapyramidal movement disorders such as tardive dyskinesia and parkinsonism. In previous reports it was speculated that extrapyramidal side effects associated with the butyrophenone neuroleptic agent haloperidol (HP) could be caused in part by the neurotoxic effect of its pyridinium metabolite (HPP(+)). Although both HPP(+) and HP have been shown to induce neurotoxic effects such as loss of cell membrane integrity, no information exists about the difference in the neurotoxic potency, especially in the potency to induce plasma membrane damage, between these two agents. In the present study, we compared the potency of the interaction of HPP(+) and HP with the plasma membrane integrity in the rat brain. Membrane permeabilization (assessed as [(18)F]2-fluoro-2-deoxy-d-glucose-6-phosphate release from brain slices) and fluidization (assessed as the reduction in the plasma membrane anisotropy of 1,6-diphenyl 1,3,5-hexatriene) were induced by HPP(+) loading (at >or=100 microM and >or=10 microM, respectively), while comparable changes were induced only at a higher concentration of HP (=1 mM). These results suggest that HPP(+) has a higher potency to induce plasma membrane damage than HP, and these actions of HPP(+) may partly underlie the pathogenesis of HP-induced extrapyramidal side effects.

Effects of chlorpromazine on plasma membrane permeability and fluidity in the rat brain: a dynamic positron autoradiography and fluorescence polarization study

Antipsychotic drugs have been widely used in psychiatry for the treatment of various mental disorders, but the underlying biochemical mechanisms of their actions still remain unclear. Although phenothiazine antipsychotic drugs have been reported to directly interact with the peripheral plasma membrane, it is not known whether these drugs actually affect plasma membrane integrity in the central nervous system. To clarify these issues, we investigated the effect of chlorpromazine (CPZ), a typical phenothiazine antipsychotic drug, on plasma membrane permeability in fresh rat brain slices using a dynamic positron autoradiography technique and [(18)F]2-fluoro-2-deoxy-D-glucose ([(18)F]FDG) as a tracer. Treatment with CPZ (> or =100 microM) resulted in the leakage of [(18)F]FDG-6-phosphate, but not [(18)F]FDG, suggesting that the [(18)F]FDG-6-phosphate efflux was not mediated by glucose transporters, but rather by plasma membrane permeabilization. The leakage of [(18)F]FDG-6-phosphate was followed by slower leakage of cytoplasmic lactate dehydrogenase, suggesting that CPZ could initially induce small membrane holes that enlarged with time. Furthermore, the addition of CPZ (> or =100 microM) caused a decrease in 1,6-diphenyl-1,3,5-hexatriene fluorescence anisotropy, which implies an increase in membrane fluidity. CPZ loading dose-dependently increased both membrane permeability and membrane fluidity, which suggested the involvement of a perturbation of membrane order in the mechanisms of membrane destabilization induced by antipsychotic drugs.

TP10, a delivery vector for decoy oligonucleotides targeting the Myc protein

One approach to investigate gene function, by silencing the activity of certain proteins, is the usage of double stranded decoy oligodeoxynucleotides (ds decoy ODNs). Decoy, in this sense, is ds ODNs bearing the consensus binding sequence for a DNA-binding protein. This can be used in clinical settings to attenuate the effect of overexpressed transcription factors in tumor cells. We here choose to target the oncogenic protein Myc. Since oligonucleotides are poorly internalized to cells, a cell-penetrating peptide, TP10, was coupled to the Myc decoy, using two different strategies. Either TP10 was simply mixed with ds decoy ODNs forming complexes through non-covalent electrostatic interactions, or by having a nona-nucleotide overhang in one of the decoy strands, and adding a complementary PNA sequence coupled to an NLS sequence and TP10, which could hybridize to the Myc decoy. By using these strategies, uptake was significantly enhanced, especially with the co-incubation approach. Interestingly, various endocytosis inhibitors had no effect on the uptake pattern, suggesting that uptake of these complexes is not mediated via endocytosis. Finally, a decreased proliferative capacity was observed when treating the neuroblastoma cell line N2a with TP10-PNA conjugate hybridized to Myc decoy compared to naked Myc decoy and untreated cells. A dose-dependent decrease in proliferation was also observed in MCF-7 cells, when using both strategies. These results suggest an alternative way to efficiently deliver ds ODNs into cells using the cell-penetrating peptide TP10 and prevent tumor growth by targeting the oncogenic protein Myc.

Cell-penetrating peptides: A comparative membrane toxicity study

Cell-penetrating peptides (CPPs) constitute a new class of delivery vectors with high pharmaceutical potential. However, the abilities of these peptides to translocate through cell membranes can be accompanied by toxic effects resulting from membrane perturbation at higher peptide concentrations. Therefore, we investigated membrane toxicity of five peptides with well-documented cell-penetrating properties, pAntp(43-58), pTAT(48-60), pVEC(615-632), model amphipathic peptide (MAP), and transportan 10, on two human cancer cell lines, K562 (erythroleukemia) and MDA-MB-231 (breast cancer), as well as on immortalized aortic endothelial cells. We studied the effects of these five peptides on the leakage of lactate dehydrogenase and on the fluorescence of plasma membrane potentiometric dye bis-oxonol. In all cell lines, pAntp(43-58), pTAT(48-60), and pVEC(615-632) induced either no leakage or low leakage of lactate dehydrogenase, accompanied by modest changes in bis-oxonol fluorescence. MAP and transportan 10 caused significant leakage; in K562 and MDA-MB-231 cells, 40% of total lactate dehydrogenase leaked out during 10 min exposure to 10 microM of transportan 10 and MAP, accompanied by a significant increase in bis-oxonol fluorescence. However, none of the CPPs tested had a hemolytic effect on bovine erythrocytes comparable to mastoparan 7. The toxicity profiles presented in the current study are of importance when selecting CPPs for different applications.

Cell-penetrating peptides: mechanism and kinetics of cargo delivery

Cell-penetrating peptides (CPPs) are short peptides of less than 30 amino acids that are able to penetrate cell membranes and translocate different cargoes into cells. The only common feature of these peptides appears to be that they are amphipathic and net positively charged. The mechanism of cell translocation is not known but it is apparently receptor and energy independent although, in certain cases, translocation can be partially mediated by endocytosis. Cargoes that are successfully internalized by CPPs range from small molecules to proteins and supramolecular particles. Most CPPs are inert or have very limited side effects. Their penetration into cells is rapid and initially first-order, with half-times from 5 to 20 min. The size of smaller cargoes does not affect the rate of internalization, but with larger cargoes, the rate is substantially decreased. CPPs are novel vehicles for the translocation of cargo into cells, whose properties make them potential drug delivery agents, of interest for future use.

Evaluation of transportan 10 in PEI mediated plasmid delivery assay

Cell-penetrating peptides (CPPs) are novel high-capacity delivery vectors for different bioactive cargoes. We have evaluated the CPP transportan 10 (TP10) as a delivery vector in different in vitro plasmid delivery assays. Tested methods include: TP10 crosslinked to a plasmid via a peptide nucleic acid (PNA) oligomer, TP10 conjugation with polyethyleneimine (PEI), and addition of unconjugated TP10 to standard PEI transfection assay. We found that without additional DNA condensing agents, TP10 has poor transfection abilities. However, the presence of TP10 increases the transfection efficiency several folds compared to PEI alone. At as low concentrations as 0.6 nM, TP10-PNA constructs were found to enhance plasmid delivery up to 3.7-fold in Neuro-2a cells. Interestingly, the transfection efficiency was most significant at low PEI concentrations, allowing reduced PEI concentration without loss of gene delivery. No increase in cytotoxicity due to TP10 was observed and the uptake mechanism was determined to be endocytosis, as previously reported for PEI mediated transfection. In conclusion, TP10 can enhance PEI mediated transfection at relatively low concentrations and may help to develop future gene delivery systems with reduced toxicity.

A brief introduction to cell-penetrating peptides

Cell membranes act as protective walls to exclude most molecules that are not actively imported by living cells. This is an efficient way for a cell to prevent uncontrolled influx or efflux of solutes, which otherwise would be harmful to it. Only compounds within a narrow range of molecular size, polarity and net charge are able to diffuse effectively through cell membranes. In order to overcome this barrier for effective delivery of membrane-impermeable molecules, several chemical and physical methods have been developed. These methods, e.g. electroporation, and more recent methods as cationic lipids/liposomes, have been shown to be effective for delivering hydrophobic macromolecules. The drawbacks of these harsh methods are, primarily, the unwanted cellular effects exerted by them, and, secondly, their limitation to in vitro applications. The last decade's discovery of cell-penetrating peptides translocating themselves across cell membranes of various cell lines, along with a cargo 100-fold their own size, via a seemingly energy-independent process, opens up the possibility for efficient delivery of DNA, antisense peptide nucleic acids, oligonucleotides, proteins and small molecules into cells both in vitro and in vivo.

Passage of cell-penetrating peptides across a human epithelial cell layer in vitro

Cell barriers are essential for the maintenance and regulation of the microenvironments of the human body. Cell-penetrating peptides have simplified the delivery of bioactive cargoes across the plasma membrane. Here, the passage of three cell-penetrating peptides (transportan, the transportan analogue transportan 10, and penetratin) across a Caco-2 human colon cancer cell layer in vitro was investigated. The peptides were internalized into epithelial Caco-2 cells as visualized by indirect fluorescence microscopy and quantified by fluorimetry. Studies of peptide outflow from cells showed that the peptides were in equilibrium across the plasma membrane. The ability of the peptides to cross a Caco-2 cell layer was tested in a two-chambered model system. After 120 min, 7.0%, 2.8% and 0.6% of added transportan, transportan 10 and penetratin respectively was detected in the lower chamber. Both transportan and transportan 10 reversibly decreased the trans-epithelial electrical resistance of the barrier model, with minimum values after 60 min of 46% and 60% of control respectively. Penetratin did not affect the resistance of the cell layer to the same extent. Although transportan markedly increased the passage of ions, the paracellular flux of 4.4 kDa fluorescein-labelled dextran was limited. In conclusion, the results indicate that the transportan peptides pass the epithelial cell layer mainly by a mechanism involving a transcellular pathway.

Passage of cell-penetrating peptides across a human epithelial cell layer in vitro

Cell barriers are essential for the maintenance and regulation of the microenvironments of the human body. Cell-penetrating peptides have simplified the delivery of bioactive cargoes across the plasma membrane. Here, the passage of three cell-penetrating peptides (transportan, the transportan analogue transportan 10, and penetratin) across a Caco-2 human colon cancer cell layer in vitro was investigated. The peptides were internalized into epithelial Caco-2 cells as visualized by indirect fluorescence microscopy and quantified by fluorimetry. Studies of peptide outflow from cells showed that the peptides were in equilibrium across the plasma membrane. The ability of the peptides to cross a Caco-2 cell layer was tested in a two-chambered model system. After 120 min, 7.0%, 2.8% and 0.6% of added transportan, transportan 10 and penetratin respectively was detected in the lower chamber. Both transportan and transportan 10 reversibly decreased the trans-epithelial electrical resistance of the barrier model, with minimum values after 60 min of 46% and 60% of control respectively. Penetratin did not affect the resistance of the cell layer to the same extent. Although transportan markedly increased the passage of ions, the paracellular flux of 4.4 kDa fluorescein-labelled dextran was limited. In conclusion, the results indicate that the transportan peptides pass the epithelial cell layer mainly by a mechanism involving a transcellular pathway.

Cargo delivery kinetics of cell-penetrating peptides

A diversity of cell-penetrating peptides (CPPs), is known, but so far the only common denominator for these peptides is the ability to gain cell entry in an energy-independent manner. The mechanism used by CPPs for cell entry is largely unknown, and data comparing the different peptides are lacking. In order to gain more information about the cell-penetrating process, as well as to quantitatively compare the uptake efficiency of different CPPs, we have studied the cellular uptake and cargo delivery kinetics of penetratin, transportan, Tat (48-60) and MAP (KLAL). The respective CPPs (labelled with the fluorescence quencher, 3-nitrotyrosine) are coupled to small a pentapeptide cargo (labelled with the 2-amino benzoic acid fluorophore) via a disulfide bond. The cellular uptake of the cargo is registered as an increase in fluorescence intensity when the disulfide bond of the CPP-S-S-cargo construct is reduced in the intracellular milieu. Our data show that MAP has the fastest uptake, followed by transportan, Tat(48-60) and, last, penetratin. Similarly, MAP has the highest cargo delivery efficiency, followed by transportan, Tat (48-60) and, last, penetratin. Since some CPPs have been found to be toxic at high concentration, we characterized the influence of CPPs on cellular 2-[(3)H]deoxyglucose-6-phosphate leakage. Measurements on this system show that the membrane-disturbing potential appears to be correlated with the hydrophobic moment of the peptides. In summary, the yield and kinetics of cellular cargo delivery for four different CPPs has been quantitatively characterized.

VE-cadherin-derived cell-penetrating peptide, pVEC, with carrier functions

Cell-penetrating peptides, CPPs, have been shown to translocate into living cells by a receptor-independent mechanism and to carry macromolecules over the plasma membrane. This article reports studies of the internalization of pVEC, an 18-amino acid-long peptide derived from the murine sequence of the cell adhesion molecule vascular endothelial cadherin, amino acids 615-632. Fluorophore-labeled pVEC entered four different cell lines tested: human aortic endothelial cells, brain capillary endothelial cells, Bowes melanoma cells, and murine brain endothelial cells. In order to evaluate the translocation efficiency of pVEC, we performed a side-by-side comparison with penetratin, a well-characterized CPP. The cellular uptake of pVEC was highest for murine brain endothelial cells. All cell lines tested contained equal or slightly higher concentrations of pVEC than penetratin. pVEC mainly accumulated in nuclear structures but was also found throughout the cells. Furthermore, pVEC functioned as a transporter of both a hexameric peptide nucleic acid molecule of 1.7 kDa and a 67-kDa protein, streptavidin-FITC, and cellular uptake of fluorophore-labeled pVEC took place at 4 degrees C, suggesting a nonendocytotic mechanism of translocation. In conclusion, our results indicate that pVEC is efficiently and rapidly taken up into cells and functions as a potent carrier peptide.

Role of cytoplasmic membrane in the screening of potential tumour promoters

The functional changes of cytoplasmic membrane of mammalian cells as an alternative approach for evaluating the tumor promoter activity were investigated. The V79 metabolic cooperation assay, as the standard method for detection of tumor promoters in vitro was used. From three known tumor promoters only phenobarbital increased the efflux of [3H]2-deoxy-D-glucose-6-phosphate from the cells in the same concentration range where the inhibition of metabolic cooperation was estimated. Neither TPA, saccharin nor theophylline caused any functional changes of cytoplasmic membrane of V79 cells. On the basis of the results with known tumor promoters we suggest that following the functional changes of cytoplasmic membrane is not a convenient approach for screening potential tumor promoters.

Effects of snake venom phospholipase A2 toxins (beta-bungarotoxin, notexin) and enzymes (Naja naja atra, Naja nigricollis) on aminophospholipid asymmetry in rat cerebrocortical synaptosomes

The effects of snake venom phospholipase A2 (PLA2) toxins (beta-bungarotoxin, notexin) and PLA2 enzymes (Naja nigricollis, Naja naja atra) on aminophospholipid asymmetry in rat cerebrocortical synaptic plasma membranes (SPM) were examined. Incubation of intact synaptosomes with 2 mM 2,4,6-trinitrobenzene sulfonic acid (TNBS) for 40 min, under non-penetrating conditions, followed by SPM isolation, allowed us to calculate the percentage of phosphatidylethanolamine (PE) and phosphatidylserine (PS) in the outer leaflet of the SPM, while incubation with disrupted synaptosomes provided total labeling values with the difference representing labeling of the inner leaflet. We found that 30% of the PE and 2% of the PS were in the outer leaflet, with 54% of the PE and 80% of the PS in the inner leaflet; 16% of the PE and 18% of the PS was inaccessible to TNBS. PLA2 toxins and enzymes increased in a concentration-dependent manner the percentage of PS and, to a lesser extent, the percentage of PE in the outer leaflet of the SPM, due to a redistribution from the inner to the outer leaflet. There was no correlation between the PLA2 enzymatic activities and the increased percentage of PS in the outer leaflet of the SPM induced by the PLA2 toxins and enzymes. Alteration of aminophospholipid asymmetry does not explain the greater presynaptic specificity and potencies of the PLA2 toxins as compared to the PLA2 enzymes, but may be associated with the increased acetylcholine release from synaptosomes induced by both the toxins and enzymes.

The effect of six sesquiterpenoid unsaturated dialdehydes on cell membrane permeability in human neuroblastoma SH-SY5Y cells

The effect of six sesquiterpenes containing an unsaturated dialdehyde functionality, on cell membrane permeability in the human neuroblastoma cell line SH-SY5Y has been studied. The kinetics of the membrane leakage after addition of the sesquiterpenes were determined by measuring the efflux of radioactivity from cells preloaded with tritiated 2-deoxyglucose. The concentrations that gave 5% and 20% efflux of radioactivity as compared with control cells (EC5 and EC20) were determined for each compound. In spite of the structural similarities between the compounds, the effects on cell membrane permeability varied considerably. EC20 for polygodial, which is the most active compound, is 2.5 microM after 20-min incubation, but no leakage could be determined for merulidial even at concentrations as high as 4 mM. Rather, this compound seems to stabilize or fix the cell membrane and a lower efflux of radioactivity was observed as compared to the control cells. A quantitative structure-activity relationship analysis for the five active compounds showed a good correlation between the membrane leakage activity and certain chemical characteristics. Structural features strongly correlated with high activity were found to be: The geometry and the atomic charges of the unsaturated dialdehyde functionality, the dipole moment, the energy difference between the lowest unoccupied molecular orbital and the highest occupied molecular orbital and the lipophilicity.

Effects of Carbon Tetrachloride on Perfused Cultures of Hepatic and Neuronal Cells

Cultured hepatocytes and hemisphere neurons from chick embryos and mouse neuroblastoma cells were exposed to carbon tetrachloride (CC14; 0, 1, 2, 3 and 4mM) for 1 hour, using a perfusion system developed for studying the effects of volatile substances. In the perfused cultures, three parameters were compared: lipid peroxidation, membrane integrity and cellular respiration. In addition, cytochrome C oxidase activity was determined after incubation of cell homogenates with CC14. A concentration-dependent increase in lipid peroxidation and membrane permeability was found in the neuroblastoma cells. The hepatocytes responded to a lesser extent with respect to membrane permeability and their lipid peroxidation did not differ from that of controls. The hepatocytes responded with a 35% decrease in respiration when exposed to 3mM CC14, and a 20% decrease in cytochrome C oxidase activity after treatment with 1.5mM CCl4. In the neuronal cells, much smaller decreases in respiration were found and their cytochrome C oxidase activity remained unaffected. These results are very similar to those obtained after incubation in a closed chamber system. However, the perfused cells were found to be less sensitive to CCl4than cells exposed under static conditions.

Differential effects of triethyllead on synaptosomal [3H]dopamine vs. [3H]acetylcholine and [3H]gamma-aminobutyric acid release

In vitro exposure to tetraethyllead (Et4Pb, 10 microM) did not alter the release of [3H] dopamine (DA), [3H]acetylcholine (ACh), or [3H]gamma-aminobutyric acid (GABA) from superfused synaptosomes isolated from rat brain striatum, hippocampus, and cortex, respectively. On the other hand, a concentration-dependent increase in the spontaneous release of these transmitters was observed following exposure to triethyllead (Et3Pb, 0.1-10 microM). The magnitude of 1 microM Et3Pb-induced [3H]DA release was 5-fold greater than that observed for [3H]ACh or [3H]GABA release. Removal of [Ca2+]e did not alter the Et3Pb-induced increase in the release of these three transmitter substances, nor did Et3Pb alter synaptosomal 45Ca efflux. EtePb-induced [3H]ACh and [3H]GABA release, but not [3H]DA release, was blocked by lowering [Na+]e from 140 to 50 mM. Similarly, the release of [3H]ACh and [3H]GABA, but not [3H]DA, induced by either Na,K-ATPase inhibition or veratridine (a Na(+)-ionophore), was attenuated by lowering [Na+]e from 140 to 50 mM. However, Et3Pb did not inhibit isolated synaptic membrane Na,K-ATPase, nor did the magnitude or temporal patterns of Et3Pb-induced transmitter release resemble transmitter release induced by Na,K-ATPase inhibition. Et3Pb and veratridine, but not Na,K-ATPase inhibition, produced an increase in synaptosomal [3H] deoxyglucose phosphate (dGluP) efflux, suggesting that both compounds increase membrane permeability. A Et3Pb-induced increase in membrane permeability is further supported by electrophysiological studies using the frog neuromuscular junction in which Et3Pb was found to reduce both the input resistance and membrane potential of muscle cells. As with [3H]ACh and [3H]GABA release, the Et3Pb-induced increase in synaptosomal [3H]dGluP efflux was attenuated by lowering [Na+]e.(ABSTRACT TRUNCATED AT 250 WORDS)

Phospholipid hydrolysis and loss of membrane integrity following treatment of rat brain synaptosomes with beta-bungarotoxin, notexin, and Naja naja atra and Naja nigricollis phospholipase A2

The effects of the phospholipase A2 (PLA2) toxins, beta-bungarotoxin and notexin, and the PLA2 enzymes from Naja naja atra and Naja nigricollis snake venoms on the plasma membrane integrity of synaptosomes were examined. Synaptosomes were isolated from rat brain cerebral cortex, corpus striatum and hippocampus. Osmotic activity, lactate dehydrogenase leakage, and leakage of 2-deoxy-D-(1-3H)-glucose-6-phosphate were monitored (37 degrees C, 10-120 min) following incubation with 0.5, 5 and 50 nM concentrations of toxins and enzymes. Damage to the synaptosomal plasma membrane was time and concentration but not tissue dependent. The potencies of the treatments were as follows: N. n. atra PLA2 greater than or equal to N. nigricollis PLA2 greater than notexin greater than beta-bungarotoxin. Chelation of Ca2+ with 5 mM EDTA completely inhibited plasma membrane disruption caused by beta-bungarotoxin and N. n. atra PLA2. One mg/ml of bovine serum albumin also blocked the disruptive action of N. n. atra PLA2, while 8 mg/ml was required to antagonize beta-bungarotoxin. A correlation between phospholipid hydrolysis and loss of membrane integrity was also observed. The generation of phospholipid hydrolytic products may be critical in the permeabilization of synaptic plasma membranes by these toxins and enzymes, however, they do not explain the presynaptic specificity and potency of beta-bungarotoxin and notexin.

Effects of methylmercury on neurotransmitter release from rat brain synaptosomes

Although the effects of methylmercury (MeHg) at the neuromuscular junction have been well characterized, similar studies employing CNS preparations and transmitters have been limited. We found that MeHg (0.5-5.0 microM) produced a concentration-dependent increase in the spontaneous release of [3H]dopamine. gamma-[3H]aminobutyric acid, and [3H]acetylcholine from synaptosomes isolated from rat brain striatum, cortex, and hippocampus, respectively. At these same concentrations MeHg did not attenuate calcium-dependent depolarization-evoked 3H-transmitter release. MeHg did not appear to induce calcium influx into the nerve terminal since the increase in release persists in the absence of extrasynaptosomal calcium. The increase in spontaneous transmitter release induced by MeHg persisted in the presence of low extrasynaptosomal sodium, suggesting that MeHg's effects on release are not mediated by either Na+, K+-ATPase inhibition or selective increases in membrane sodium permeability. MeHg produced only a very small increase in 45Ca efflux from synaptosomes preloaded with 45Ca, whereas these same MeHg concentrations produced large increases in 45Ca efflux from preloaded isolated mitochondria. MeHg did increase the efflux of [3H]deoxyglucose phosphate from synaptosomes. An increase in the efflux of [3H]deoxyglucose phosphate is believed to reflect an increase in neuronal membrane permeability. The quantitative and temporal aspects of the MeHg-induced [3H]-deoxyglucose phosphate efflux were similar to those observed for MeHg-induced neurotransmitter release. These data suggest that the increase in spontaneous transmitter release induced by MeHg is mainly the result of transmitter leakage that occurs subsequent to MeHg-induced increases in synaptosomal membrane permeability. However, these results cannot exclude possible effects of MeHg on intrasynaptosomal calcium homeostasis.

Selective oxidation of mitochondrial glutathione in cultured rat adrenal cells and its relation to polycyclic aromatic hydrocarbon-induced cytotoxicity

Primary cultures of rat adrenal cells, as well as rat adrenals in vivo, are sensitive to the potent carcinogen 7,12-dimethylbenz[a]anthracene and its liver metabolite 7-hydroxymethyl-12-methylbenz[a]anthracene, whereas unmethylated polycyclic aromatic hydrocarbons like benzo[a]pyrene or benzo[a]anthracene are ineffective. The adrenocorticolytic potencies of the hydrocarbons are affected by adrenocorticotrophic hormone and various steroids, cytochrome P450 inhibitors, and antioxidants. In the present investigation digitonin was used to fractionate cultured rat adrenal cells. It was found that the mitochondria and cytosol of the cells contained 3-5 nmol/10(6) cells (approximately 15%) and 20-30 nmol/10(6) cells (approximately 85%) of the total soluble cellular glutathione equivalents, respectively. After exposing the cells to 7-hydroxymethyl-12-methylbenz[a]anthracene in the culture medium, a time- and concentration-dependent selective oxidation of mitochondrial glutathione was observed, whereas the effect on the cytosolic glutathione was negligible. Under the same conditions, 7,12-dimethylbenz[a]anthracene and benzo[a]pyrene were unable to alter the redox levels of the subcellular pools of glutathione. Omission of adrenocorticotrophic hormone lowered the oxidation of mitochondrial glutathione induced by 7-hydroxymethyl-12-methylbenz[a]anthracene about twofold. The results suggest that rat adrenal cells contain two separate pools of glutathione, one cytosolic and one mitochondrial, of which the latter is selectively influenced by 7-hydroxymethyl-12-methylbenz[a]anthracene. Moreover, it is concluded that rat adrenal cells offer a unique model system for general studies of the effects of a selective oxidation of mitochondrial glutathione on various cell functions. These effects may constitute early changes in cytotoxicity, preceding, e.g., membrane damage and loss of cytosolic components.

Effects of divalent cations on snake venom cardiotoxin-induced hemolysis and 3H-deoxyglucose-6-phosphate release from human red blood cells

At a low concentration of Naja naja kaouthia cardiotoxin (3 microM) Ca2+, Sr2+ and Ba2+ (2 mM), had little to no effect on 3H-deoxyglucose-6-phosphate (3H-dGlu-6-p) or hemoglobin release. At higher concentrations of N. n. kaouthia cardiotoxin (greater than or equal to 10 microM), Ca2+ (2 mM), but not Sr2+ or Ba2+, significantly enhanced 3H-dGlu-6-p and hemoglobin release. Mn2+ (2 mM) almost completely inhibited 3H-dGlu-6-p release and hemolysis at both the 3 microM and 10 microM concentrations of cardiotoxin. At a fixed concentration of N. n. kaouthia cardiotoxin (3 microM). Ca2+ at low concentrations (0.5 mM) enhanced 3H-dGlu-6-p and hemoglobin release, but at higher concentrations caused a dose-dependent inhibition of cardiotoxin action. The cardiotoxin from N. n. kaouthia venom (3 microM) induced 3H-dGlu-6-p release and hemolysis release with similar time courses and to similar extents. 3H-dGlu-6-p release induced by cardiotoxin was greatly enhanced as the pH of the medium was increased from 7.0 to 8.5. Similarities between 3H-dGlu-6-p and hemoglobin release do not support opening of pores in the plasmalemma of all red blood cells as the mode of action of cardiotoxins, but suggests that complete lysis of a subpopulation of cells occurs. Cardiotoxins have two components of lysis, only one of which is Ca2+-dependent. The Ca2+-dependent lysis is only evident at higher cardiotoxin concentrations and is likely due to trace phospholipase A2 contamination in the toxin fraction. Mn2+ is an effective antagonist of cardiotoxin action.

A cytochemical study on the effects of energy deprivation on autophagocytosis in Ehrlich ascites tumor cells

The effect of energy deprivation on autophagocytosis in Ehrlich ascites tumor cells was studied using cytochemical techniques. Autophagocytosis was induced with vinblastine incubation (0.1 mM) and the cellular ATP-level was lowered with 2-deoxy-D-glucose (0.35 mM). Acid phosphatase was used as a marker for lysosomal enzymes and imidazole-buffered osmium tetroxide impregnation in order to study the effects of energy deprivation on the maturation of autophagic vacuole (AV) membranes. Control and vinblastine treated cells maintained their ATP-levels throughout the incubation period tested (120 min). 2-Deoxy-D-glucose alone and with vinblastine decreased the intracellular ATP-level significantly after only 3 min incubation. Most of the AV's in control and vinblastine treated cells contained degraded material and acid phosphatase activity. Their membranes were stained only slightly or not at all with imidazole-buffered osmium tetroxide. 2-Deoxy-D-glucose alone as well as with vinblastine induced in particular an accumulation of early stages of AV's. These vacuoles contained undegraded cytoplasmic material and no acid phosphatase activity and their membranes were stained usually partly with imidazole-buffered osmium tetroxide. The membranes of some early AV's resembled endoplasmic reticulum and still had attached ribosomes. It was concluded that the inhibition of cellular energy production used in the present study did not inhibit autophagic sequestration but retarded the maturation of AV membranes and impaired the functioning of lysosomal hydrolases.

Differential effects of Clostridium difficile toxins A and B on rabbit ileum

The pathogenesis of Clostridium difficile enterocolitis appears to involve colonization of the bowel followed by release of toxin A, an enterotoxin, and toxin B, a cytotoxin. The purpose of this study was to determine the effect of purified toxins A and B on intestinal secretion, epithelial permeability, and morphology in perfused rabbit ileal loops. Intestinal permeability after toxin exposure was assessed by blood-to-lumen clearance of [3H]mannitol. Toxin A at doses of 5-100 micrograms/10 cm ileal loop caused a threefold to fivefold increase in [3H]mannitol permeability (p less than 0.001) vs. equal concentrations of toxin B or buffer control. In addition, perfusate from toxin A-exposed loops contained significantly more neutrophils (p less than 0.001) than toxin B or control loops. Toxin A caused severe epithelial cell necrosis with destruction of villi and polymorphonuclear infiltration. Electron microscopy of mucosa subjected to a low dose of toxin revealed widespread nonspecific dilatation of endoplasmic reticulum and mitochondrial swelling. In contrast to these effects of toxin A in ileal loops, in vitro experiments with ileal explants in short-term organ culture revealed that toxin A had no effect on epithelial cell permeability, protein synthesis, release of alkaline phosphatase, or morphology. Our results show that purified toxin A but not toxin B causes severe inflammatory enteritis in rabbit ileal loops, but has no discernable effect on rabbit ileum in vitro. We speculate that toxin A may contribute significantly to intestinal damage in C. difficile-associated colitis and diarrhea.

Some biochemical characteristics and cell membrane actions of a toxic phospholipase A2 isolated from the venom of the pit viper Agkistrodon halys (Pallas)

A toxic component (AgTx) from the venom of Agkistrodon halys (Pallas) was isolated using DEAE-cellulose DE11 and CM-Sephadex C50 column chromatography and finally purified to homogeneity by FPLC on a MonoQ column. The toxin is a neutral (pI 6.9) single chain polypeptide with a mol. wt of 14,000 and an amino acid composition (123 residues) roughly similar to that of notexin. AgTx was found to have phospholipase A2 activity which was dependent on calcium and stimulated by sodium deoxycholate. The toxin caused efflux of 2-deoxy-(1-3H)-glucose-6-phosphate (a cell membrane integrity probe) as well as of [3H]acetylcholine from rat brain synaptosomes. No cell membrane damage was induced by AgTx on cultured N1E 115 neuroblastoma cells and chick myotube cultures. The LD50 ws 150 micrograms/kg (i.p.) in mice. The main symptom observed was respiratory paralysis. The results obtained show that AgTx can be classified as a toxic phospholipase A2 with a presynaptic site of action.

Use of a perfusion technique for measurements of respiratory activity in cultured cells

A method for measuring respiratory activity in anchorage-dependent cultured cells has been developed. This method is based on a technique that permits the perfusion of standard plastic culture dishes with attached cells. Basal respiratory activities were studied in two continuous cell lines of neural origin, neuroblastoma C1300 clone 41A3 and glioma 138MG. As compared to traditional measurements on detached cells, a fourfold increase in value was obtained. Investigations on membrane permeability suggested that the observed difference could be attributed to alterations in cell membrane integrity. Pretreatment with dibutyryl cyclic AMP, known to induce a morphological and biochemical differentiation in C1300 and 138MG cells, caused in both cell lines an enhanced respiration.

Photometric recording of cell viability using trypan blue in perfused cell cultures

A perfusion system was developed to increase the reliability of cell viability estimations by continuous measurement of the uptake of trypan blue dye. Monolayer cell cultures were perfused with buffer containing toxic substances and trypan blue, and the staining of cells was continuously recorded at 591 nm in a spectrophotometer. Using mercuric chloride and methylmercuric chloride as test substances with C6 rat glioma cells, time- and dose-dependent increases in light absorbance were obtained over a 12h recording period. Methylmercuric chloride at 10(-6) M caused a half-maximal increase in relative absorbance in 4.5 h, whereas the corresponding time for mercuric chloride was 10.5 h.

On the application of cultured neuroblastoma cells in chemical toxicity screening

The acute toxic action of a number of common chemicals was tested by their ability to cause detachment of cultured mouse neuroblastoma C1300 cells. A TD25 value was obtained by graphic estimation of the concentration needed to cause 25% of the total cell number to detach. These TD25 values were compared with LD50 values obtained from the literature, and they were found to correlate with a coefficient of 0.86. For six of the tested substances-diuron, butylated hydroxytoluene, benzidine, cyclophosphamide, Na2SeO3, and KCN-a very poor correlation was obtained. These diverging results could be ascribed to deficiencies in the neuroblastoma cell detachment test and emphasize the necessity for combined in vitro test procedures.

Uridine uptake inhibition as a cytotoxicity test: correlations with the Draize test

The effects of 25 xenobiotic chemicals on the uptake of [3H]-uridine by Balb/c 3T3 cells were assessed. The test compounds, which included alcohols, ethers, esters, ketones, amides, acids and a detergent, inhibited uridine uptake at concentrations lower than those required to kill the cells; thus uridine uptake inhibition is a more sensitive indicator of toxic action than is cell lethality. The concentration of agent required to induce a 50% inhibition in uridine uptake rates after 4 h of treatment was determined for each agent, and this value (UI-50) was used to rank the potency of the test agents. This ranking correlated well with published data on the chemicals' capacity to induce ocular irritation in rabbits (the Draize test). Combinations of agents with differing functional groups produced additive uridine uptake inhibitory effects, suggesting the utility of this approach for the analysis of mixtures. Cells treated with levels of agents that reduced uridine uptake by 60-80% were able to recover most of their uridine uptake capacity after refeeding, indicating that the test shares with in vivo tests the ability to demonstrate recovery from toxic insult. This uridine uptake assay system provides a quantitative and rapid method for assessing toxicity that correlates well with Draize test results.

Growth and morphology of neuronal cell lines cultured in perfusion

To optimize culture conditions and gain a more reliable culturing system for studies of metabolic properties of neuronal cells, a simplified perfusion chamber was developed. It consists of two parts: a perfusion block and a standard plastic culture dish. To confirm the suitability of this chamber for continuous culturing of anchorage-dependent cells, the growth and morphology of the four neuronal cell lines, glioma C6 and glioma 138MG, neuroblastoma C1300, clones N1E115 and N18 were followed for 4 d using both traditional and perfusion techniques. A marked increase in growth and a decrease in the degree of morphological differentiation were obtained with the latter technique compared to the former.

Assessment of membrane damage in continuous cultures of mammalian cells

The present studies were aimed at evaluating procedures for assessing the effect of chemicals on the integrity of the plasma membrane in continuous cell cultures. The degree of membrane damage was monitored by determining the 'leakage' of alpha-[3H]aminoisobutyric acid ([3H]AIB) and [14C]deoxy-2-fluoro-D-glucose ([14C]FdG) from the prelabelled cells. These parameters were compared to the loss of lactate dehydrogenase (LDH) from the cells and the decrease in the intracellular level of K+. Triton X-100, sodium dodecylsulfate (SDS), phospholipase C and nystatin which are known to affect membranes by different mechanisms served as test agents. In parallel, we monitored the effects of the chemicals on the viability of the cells. The following results were obtained: (1) The two radioactive markers [3H]AIB and [14C]FdG were found to be suitable to probe for damages of the plasma membrane in a variety of continuous cell lines which differ widely in their phenotype, rate of growth and degree of differentiation. (2) The leakage of the two markers could conveniently be monitored by double labelling techniques. (3) The loss from the cells of the 3 markers of smaller molecular size, K+, [3H]AIB, [14C]FdG, differed considerably depending on the test agent used. (4) Intracellular K+ level and [3H]AIB leakage generally appeared to follow a similar pattern, whereas [14C]FdG leakage may have shown a distinctly different response. (5) The leakage of LDH was an insensitive indicator for membrane damage. (6) No clear relationship was detectable between a particular leakage pattern of the markers and the loss of cellular viability.

On the Application of Cultured Neuronal Cell Lines in Neurotoxicological Studies: Implications of Acrylamide-induced Neurite Disintegration

Summary

Cultures of the mouse neuroblastoma cell line C1300, clone N1E115 were exposed to acrylamide at 3.5 x 10-4M for 14 days (subacute situation) or at 2.8 x 10-3 M for 24 hr (acute situation).

In the subacute situation the total uptake of 2-deoxy-D-glucose was stimulated. This could be explained by an increase in both the non-specific diffusion and the specific transport. The activity of the glycolytic enzyme, enolase (EC4.2.1.11), was unaffected by exposure to acrylamide, whereas the activity of glyceraldehyde-3-phosphate-dehydrogenase (EC1.2.1.12) was inhibited. Acrylamide had a marked stimulating effect on the respiratory activity of the cells, whereas the incorporation of tritiated leucine remained unchanged. Furthermore, membrane integrity was maintained throughout the acrylamide exposure as judged by an unchanged rate of 2-deoxy-D-glucose-6-phosphate efflux. Corresponding results were obtained in the acute situation. In N1E115 cultures and under the experimental conditions used in this work acrylamide caused neurite degeneration resembling distal axonopathy in vivo. It is suggested that these degenerative changes are not due to a general intoxication of the cells, but rather to a specific effect. Consequently, the N1E115 cell line might be useful in studies of chemically-induced axonopathies.

The male antifertility agents alpha chlorohydrin, 5-thio-D-glucose, and 6-chloro-6-deoxy-D-glucose interfere with sugar transport across the epithelium of the rat caput epididymidis

The effects of the male antifertility agents alpha-chlorohydrin, 5-thio-D-glucose, and 6-chloro-6-deoxy-D-glucose on sugar transport (3H-3-O-methyl-D-glucose and 3H-2-deoxy-D-glucose) across the rat caput epithelium was studied in vivo and in vitro. The compound alpha-chlorohydrin reduced sugar transport uptake in vivo but not in vitro, whereas 5-thio-D-glucose and 6-chloro-6-deoxy-D-glucose were both effective in vivo and in vitro. The mechanism of action of these compounds on sugar movement across the caput epithelium is probably complex. Direct competition for the glucose carrier situated on the basolateral membrane and intratubular effects are suggested. Thirty-day injections of 5-thio-D-glucose or alpha-chlorohydrin did not have adverse effects on sugar transport or the permeability of the blood-testis and blood-epididymis barriers as assessed by an in vitro technique.

Membrane lesions in cultured mouse neuroblastoma cells exposed to metal compounds

Tritiated 2-deoxy-D-glucose (dGlc) was rapidly taken up into cultured mouse neuroblastoma C1300 cells (clone 41A3). Upon perfusion the preloaded cultures slowly released radioactivity as [3H] 2-deoxy-D-glucose-6-phosphate ([3H]dGlc-6-P) (rate const. = 0.017 min-1) from a pool corresponding to 74% (t1/2 = 41 min) of the total radioactivity incorporated. Destruction of the plasma membrane of the cells by means of Triton X-100 (1.0%) resulted in a rapid and total release of the radioactivity. CH3HgCl, HgCl2, (C2H5)3SnCl and K2Cr2O7 all caused an increase in the passive cell membrane permeability to [3H]dGlc-6-P. A membrane toxic concentration (MTC) was defined as the concentration of the tested metal compound giving rise to an increase in the relative efflux from 1.0 to 1.2 during 60 min perfusion. Using this MTC-value, the membrane toxicity of the compounds could be ranked in the following order: CH3HgCl (MTC = 9 x 10(-7) M) greater than HgCl2 (MTC = 6 x 10(-6) M) greater than (C2H5)3SnCl (MTC = 3 x 10(-4) M) greater than K2Cr2O7 (MTC = 7 x 10(-4) M). Since this differential toxicity is in accordance with other reports it is concluded that 2-deoxy-D-glucose (dGlc) may be used together with 41A3 cells to screen metal compounds for their membrane toxicity.