Neurotoxicity and behavioral disorders induced in mice by acute exposure to the diamide insecticide chlorantraniliprole

Diamide insecticides activate ryanodine receptors expressed in lepidopteran skeletal muscle and promote Ca2+ release in the sarcoplasmic reticulum, causing abnormal contractions and paralysis, leading to death of the pest. Although they had been thought not to act on nontarget organisms, including mammals, adverse effects on vertebrates were recently reported, raising concerns about their safety in humans. We investigated the neurotoxicity of the acute no-observed-adverse-effect level of chlorantraniliprole (CAP), a diamide insecticide, in mice using clothianidin (CLO), a neonicotinoid insecticide, as a positive control. The CLO-administered group showed decreased locomotor activities, increased anxiety-like behaviors, and abnormal human-audible vocalizations, while the CAP-administered group showed anxiety-like behaviors but no change in locomotor activities. The CAP-administered group had greater numbers of c-fos-immunoreactive cells in the hippocampal dentate gyrus, and similar to the results in a CLO-administered group in our previous study. Blood corticosterone levels increased in the CLO-administered group but did not change in the CAP-administered group. Additionally, CAP was found to decreased 3-Methoxytyramine and histamine in mice at the time to maximum concentration. These results suggest that CAP-administered mice are less vulnerable to stress than CLO-administered mice, and the first evidence that CAP exposure increases neuronal activity and induces anxiety-like behavior as well as neurotransmitter disturbances in mammals.

Characterization of the ryanodine receptor gene in Encarsia formosa (Gahan) and its expression profile in response to diamide insecticides

Ryanodine receptors (RyRs) are the targets of diamide insecticides, which have been identified and characterized in a dozen insect pests of Lepidoptera, Hemiptera, Diptera and Coleoptera, but limited attention has been paid to the RyR in parasitoid natural enemies. Without this knowledge, it will hinder our effective and efficient application using both parasitoid natural enemies and diamide insecticides simultaneously in the integrated pest management (IPM). In this study, the full-length cDNA of RyR was cloned from Encarsia formosa (EfRyR), a parasitic wasp used worldwide for the biological control of whitefly. Its expression profile was examined in various tissues of E. formosa adults. The toxicities of four diamide insecticides to E. formosa were measured, and then the expression profile of EfRyR after 12 h and 24 h exposure to the LC₅₀ dosages of diamide insecticides was investigated. The results showed that the full-length cDNA of EfRyR was 16, 778 bp including a 15, 345 bp open reading frame, and two alternative splice (AS) sites. Comparing to its expression in the abdomen, EfRyR was highly expressed in the head (11.9-fold) and the thorax (3.7-fold). The toxicities of four dimide insecticides against E. formosa from low to high were chlorantraniliprole (LC₅₀ = 367.84 mg L^-1), cyantraniliprole (221.72 mg L^-1), cyclaniliprole (51.77 mg L^-1), and tetrachlorantraniliprole (8.35 mg L^-1). The expressions of EfRyR and its variants with AS were significantly increased after E. formosa adults were exposed to different diamide insecticides. This study improves our understanding of the RyR in parasitoid wasps and provides useful information on IPM by using E. formosa.

Ecotoxicity of neonicotinoids and diamides on population growth performance of Zygogramma bicolorata (Coleoptera: Chrysomelidae)

Relative ecotoxicity of approved neonicotinoids (i.e. imidacloprid, clothianidin, acetamiprid, thiacloprid, thiamethoxam and dinotefuran) and diamides (i.e. chlorantraniliprole, cyantraniliprole and flubendiamide) was examined on population growth parameters of Zygogramma bicolorata Pallister on parthenium under laboratory conditions at 27 ± 1 °C, 65 ± 5% relative humidity and 10 L : 14D photoperiod. The dose of all tested insecticides in the bioassay procedure was within a minimum range of their recommended field rate. In acute toxicity trial, imidacloprid caused highest rate of mortality in treated adults of Z. bicolorata, however, it was lowest in flubendiamide treatment followed by cyantraniliprole and chlorantraniliprole. Further, based on toxicity coefficient (E) value in acute toxicity trial, all were classified as harmful (H) and diamides were classified as moderately harmful (MH) as per IOBC classification. Moreover, chronic toxicity trials were carried out through life table response experiments (LTREs) in the F₁ progeny of acute toxicity experienced group. Prolonged development with the highest mortality was evident in as compared to diamides. Furthermore, population growth parameters i.e. potential fecundity (Pf), natality rate (m_x), intrinsic rate of increase (r_m), net reproductive rate (R₀) and finite rate of increase (λ) was greatly reduced in Z. bicolorata treated with neonicotinoids as compared with diamides. However, mean generation time (T_c), corrected generation time (τ) and the doubling time (DT) was prolonged in neonicotinoids followed by diamides. Furthermore, proportion of females was greatly reduced (0.43-0.48 females) in neonicotinoids as comparison to diamides (0.53-0.55 females) and control (0.67 females). On the basis of ecotoxicity trials, the tested neonicotinoids were highly toxic to Z. bicolorata than diamides. Therefore, diamide insecticides could be used with Z. bicolorata, however, for validation experimentation need to be done under natural field conditions.

Crystal structure of the N-terminal domain of ryanodine receptor from the honeybee, Apis mellifera

Ryanodine receptors (RyRs) are the molecular target of diamides, a new chemical class of insecticides. Diamide insecticides are used to control lepidopteran pests and were considered relatively safe for mammals and non-targeted beneficial insects, including honey bees. However, recent studies showed that exposure to diamides could cause long-lasting locomotor deficits of bees. Here we report the crystal structure of RyR N-terminal domain A (NTD-A) from the honeybee, Apis mellifera, at 2.5 Å resolution. It shows a similar overall fold as the RyR NTD-A from mammals and the diamondback moth (DBM), Plutella xylostella, and still several loops located at the inter-domain interfaces show insect-specific or bee-specific structural features. A potential insecticide-binding pocket formed by loop9 and loop13 is conserved in lepidopteran but different in both mammals and bees, making it a good candidate targeting site for the development of pest-selective insecticides. Furthermore, a conserved intra-domain disulfide bond was observed in both DBM and bee RyR NTD-A crystal structures, which explains their higher thermal stability compared to mammalian RyR NTD-A. This work provides a basis for the development of novel insecticides with better selectivity between pests and bees by targeting a distinct site on pest RyRs, which would be a promising strategy to overcome the current toxicity problem.

Temperature-dependent variations in toxicity of diamide insecticides against three lepidopteran insects

The effect of temperature on the toxicities of four diamide insecticides (chlorantraniliprole, cyantraniliprole, flubendiamide, tetraniliprole) against three lepidopteran insects (Helicoverpa armigera, Plutella xylostella, Athetis lepigone) were determined from 15 to 35 °C by exposing third-instar larvae to dip-treated cabbage leaf. The results indicated that increase in temperature led to an increase significantly and regularly in the toxicities of the four diamide insecticides against P. xylostella and H. armigera, but not for A. lepigone. The temperature coefficients (TCs) of the four diamide insecticides increased from 15 to 35 °C. Tetraniliprole for H. armigera (+825.83), chlorantraniliprole for P. xylostella (+315.65) and cyantraniliprole for H. armigera (+225.77) exhibited high positive TCs. For A. lepigone, temperature had a positively weak or no effect on the toxicities of most of the diamide insecticides from 20 to 30 °C, but a higher effect from 30 to 35 °C. In addition, the toxicities of chlorantraniliprole, cyantraniliprole and tetraniliprole all decreased from 15 to 20 °C. This study can guide pest managers in choosing suitable ambient field temperature when spraying diamide insecticides against lepidopteran insects.

Honey bees long-lasting locomotor deficits after exposure to the diamide chlorantraniliprole are accompanied by brain and muscular calcium channels alterations

Diamides belong to one of the newest insecticides class. We characterized cellular effects of the first commercialized diamide, chlorantraniliprole (ChlorAnt). ChlorAnt not only induces a dose-dependent calcium release from internal stores of honey bee muscle cells, but also a dose-dependent blockade of the voltage-gated calcium current involved in muscles and brain excitability. We measured a long lasting impairment in locomotion after exposure to a sublethal dose and despite an apparent remission, bees suffer a critical relapse seven days later. A dose that was sublethal when applied onto the thorax turned out to induce severe mortality when applied on other body parts. Our results may help in filling the gap in the toxicological evaluation of insecticides that has recently been pointed out by international instances due to the lack of suitable tests to measure sublethal toxicity. Intoxication symptoms in bees with ChlorAnt are consistent with a mode of action on intracellular calcium release channels (ryanodine receptors, RyR) and plasma membrane voltage-gated calcium channels (CaV). A better coupling of in vitro and behavioral tests may help in more efficiently anticipating the intoxication symptoms.

Diamide insecticide target site specificity in the Heliothis and Musca ryanodine receptors relative to toxicity

Anthranilic and phthalic diamides act on the ryanodine receptor (RyR), which constitutes the Ca(2+)-activated Ca(2+) channel and can be assayed as shown here in Heliothis thoracic muscle tissue with anthranilic diamide [(3)H]chlorantraniliprole ([(3)H]Chlo), phthalic diamide [(3)H]flubendiamide ([(3)H]Flu), and [(3)H]ryanodine ([(3)H]Ry). Using Heliothis with [(3)H]Chlo or [(3)H]Flu gives very similar anthranilic and phthalic diamide binding site structure-activity correlations, indicating a common binding site. The anthranilic and phthalic diamide stimulation of [(3)H]Ry binding in Heliothis generally parallels their inhibition of [(3)H]Chlo and [(3)H]Flu binding. In Musca adults [(3)H]Ry binding site stimulation is a good predictor of in vivo activity for anthranilic but not phthalic diamides, and no high-affinity [(3)H]Flu specific binding site is observed. These relationships establish species differences in diamide target site specificity important in structure optimization and target site-based resistance mechanisms.

Impacts of a neonicotinoid, neonicotinoid-pyrethroid premix, and anthranilic diamide insecticide on four species of turf-inhabiting beneficial insects

Many turf managers prefer to control foliage- and root-feeding pests with the same application, so-called multiple-targeting, using a single broad-spectrum insecticide or a premix product containing two or more active ingredients. We compared the impact of a neonicotinoid (clothianidin), a premix (clothianidin + bifenthrin), and an anthranilic diamide (chlorantraniliprole), the main insecticide classes used for multiple targeting, on four species of beneficial insects: Harpalus pennsylvanicus, an omnivorous ground beetle, Tiphia vernalis, an ectoparasitoid of scarab grubs, Copidosoma bakeri, a polyembryonic endoparasitoid of black cutworms, and Bombus impatiens, a native bumble bee. Ground beetles that ingested food treated with clothianidin or the premix suffered high mortality, as did C. bakeri wasps exposed to dry residues of those insecticides. Exposure to those insecticides on potted turf cores reduced parasitism by T. vernalis. Bumble bee colonies confined to forage on white clover (Trifolium repens L.) in weedy turf that had been treated with clothianidin or the premix had reduced numbers of workers, honey pots, and immature bees. Premix residues incapacitated H. pennsylvanicus and C. bakeri slightly faster than clothianidin alone, but otherwise we detected no synergistic or additive effects. Chlorantraniliprole had no apparent adverse effects on any of the beneficial species. Implications for controlling turf pests with least disruption of non-target invertebrates are discussed.

Effects of cyantraniliprole, a novel anthranilic diamide insecticide, against Asian citrus psyllid under laboratory and field conditions

BACKGROUND

The Asian citrus psyllid, Diaphorina citri (Hemiptera: Psyllidae), is the most destructive pest of citrus in Florida. The development of insecticide resistance in several populations of D. citri has been documented. There is an urgent need to develop and integrate novel tools for the successful management of D. citri and also to prevent the development of insecticide resistance.

RESULTS

The effects of a relatively newer chemistry, cyantraniliprole, against D. citri were investigated. The contact toxicity of cyantraniliprole was 297-fold higher against D. citri than its primary parasitoid, Tamarixia radiata (Hymenoptera: Eulophidae). D. citri settled and fed less on cyantraniliprole-treated plants than controls at concentrations as low as 0.025 and 0.125 µg AI mL⁻¹ respectively. D. citri egg production, first-instar emergence and adult emergence were significantly reduced on plants treated with 0.25, 0.02 and 0.25 µg AI mL⁻¹ of cyantraniliprole, respectively, when compared with control plants. Under field conditions, foliar and drench treatments with cyantraniliprole (1436.08 g ha⁻¹) reduced numbers of D. citri adults and nymphs, as well as of a secondary pest, citrus leafminer, Phyllocnistis citrella (Lepidoptera: Gracillariidae), more than a standard insecticide.

CONCLUSIONS

These results suggest that cyantraniliprole should be a valuable new tool for rotation into D. citri management programs. For insecticide resistance management, cyantraniliprole may be particularly useful for rotation with neonicotinoids. In addition, cyantraniliprole was much less toxic to T. radiata than to D. citri and thus may have less impact on biological control than other currently used broad-spectrum insecticides, such as organophosphates and pyrethroids.

Identification of a critical region in the Drosophila ryanodine receptor that confers sensitivity to diamide insecticides

Anthranilic diamides, which include the new commercial insecticide, chlorantraniliprole, are an exciting new class of chemistry that target insect ryanodine receptors. These receptors regulate release of stored intracellular calcium and play a critical role in muscle contraction. As with insects, nematodes express ryanodine receptors and are sensitive to the plant alkaloid, ryanodine. However the plant parasitic nematode, Meloidogyne incognita, is insensitive to anthranilic diamides. Expression of a full-length Drosophila melanogaster ryanodine receptor in an insect cell line confers sensitivity to the receptor agents, caffeine and ryanodine along with nanomolar sensitivity to anthranilic diamides. Replacement of a 46 amino acid segment in a highly divergent region of the Drosophila C-terminus with that from Meloidogyne results in a functional RyR which lack sensitivity to diamide insecticides. These findings indicate that this region is critical to diamide sensitivity in insect ryanodine receptors. Furthermore, this region may contribute to our understanding of the differential selectivity diamides exhibit for insect over mammalian ryanodine receptors.

Ineffective GSH regeneration enhances G6PD-knockdown Hep G2 cell sensitivity to diamide-induced oxidative damage

Glucose-6-phosphate dehydrogenase (G6PD) has been recently found to play growth-regulatory roles in nucleated cells. To identify any other physiologic roles of G6PD, we generated G6PD-knockdown Hep G2 cells and investigated their susceptibility to oxidants. Hep G2 cells expressing shRNA against G6PD (Gi) were more susceptible to diamide-induced cytotoxicity than control cells expressing scrambled control shRNA (Sc). The level of reactive oxygen species in the Gi cells substantially exceeded that in Sc cells. This was accompanied by increased membrane peroxidation and the appearance of high-molecular-weight aggregates of membrane-associated cytoskeletal proteins in Gi cells. G6PD knockdown was associated with an impaired ability to regenerate glutathione. Diamide caused a considerable decrease in cellular glutathione level and a concomitant increase in glutathione disulfide in Gi cells. Consistent with this finding, N-acetylcysteine mitigated diamide-induced oxidative stress and cell death. Our findings suggest that G6PD confers protection against oxidant-induced cytotoxicity through effective glutathione regeneration.

5-S-GAD, a novel radical scavenging compound, prevents lens opacity development

The ability of N-beta-alanyl-5-S-glutathionyl-3,4-dihydroxyphenylalanine (5-S-GAD)-a novel catechol derivative isolated from an insect as an antibacterial substance-to scavenge free radicals and prevent cataract progression was examined. 5-S-GAD scavenged 1,1-diphenylpicrylhydrazyl (DPPH) and superoxide anions (O(2)(*)(-)), and inhibited lipid peroxidation. It also significantly inhibited the onset of glucocorticoid-induced lens opacification in chick embryos. These effects of 5-S-GAD were stronger than those of N-acetylcarnosine and TEMPOL, which are reported to be effective radical scavengers in the prevention of cataract progression. 5-S-GAD clearly delayed the maturation of cataracts induced by diamide in cultured lenses of rats. Daily instillation of 5-S-GAD retarded the development of lens opacity in galactose-fed rats. Biochemical analysis of the lenses revealed that 20-kDa proteins, presumably consisting of alpha-crystallin, were the most susceptible to oxidative stress, which leads to the carbonylation of the side chains of these proteins. alpha-Crystallin carbonylation induced by diamide or galactose was notably inhibited by 5-S-GAD in a dose-dependent manner. Our results show that 5-S-GAD prevents acute lens opacification in these short-term experimental models, possibly in part by virtue of its antioxidative property, and 5-S-GAD is expected to have long-term pharmaceutical effects.

Diamide stress induces a metallothionein BmtA through a repressor BxmR and is modulated by Zn-inducible BmtA in the cyanobacterium Oscillatoria brevis

A cysteine-rich metal binding protein MT (metallothionein) (named BmtA) is induced upon exposure to multiple heavy metal ions in the freshwater cyanobacterium Oscillatoria brevis. The SmtB/ArsR family repressor BxmR from O. brevis represses the expression of an operon encoding bmtA and bxmR. In the present study, the expression of bmtA was induced in vivo by diamide, a specific thiol oxidant, in O. brevis cells. In vitro electrophoretic gel mobility shift experiments revealed that the incubation with diamide induces disassembly of the BxmR-bxmR/bmtA operator (O)/promoter (P) complex [multiple resolvable complexes of BxmR with oligonucleotide (named P5) containing a single 12-2-12 inverted repeat derived from the O/P region of bxmR/bmtA]. Thus, the exposure to diamide induces MT mRNA in O. brevis, and this induction is associated with diamide-mediated inhibition of BxmR-P5 complex. BxmR is more sensitive to diamide than to H(2)O(2). Furthermore, pretreatment of O. brevis with Zn decreased intracellular peroxidation products caused by diamide. Thus, these results imply that MT induced by Zn-pretreatment functions to protect O. brevis cells against diamide stress.

Sensitivities of the alternative respiratory components of potato tuber mitochondria to thiol reagents and Ca2+

Plant mitochondria differ from those of mammals, since they incorporate an alternative electron transport pathway, which branches at ubiquinol to an alternative oxidase (AOX), characteristically inhibited by salicylhydroxamic acid (SHAM). Another feature of plant mitochondria is that besides complex I (EC 1.6.5.3) they possess alternative NAD(P)H-dehydrogenases insensitive to rotenone. Many stress conditions are known to alter the expression of the alternative electron transport pathway in plant mitochondria. In the present study we investigated the effects of some thiol reagents and Ca(2+) on potato mitochondrial respiratory chain presenting different activities of the alternative respiratory components AOX and external NADH dehydrogenase, a condition induced by previous treatment of potato tubers (Solanum tuberosum L., cv. Bintje) to cold stress. The results showed that Ca(2+) presented an inhibitory effect on AOX pathway in potato mitochondria energized with NADH or succinate, which was only now observed when the cytochrome pathway was inhibited by cyanide. When the cytochrome pathway was functional, Ca(2+) stimulated the external NADH dehydrogenase. Diamide was a potent AOX inhibitor and this effect was only now observed when the cytochrome pathway was inactive, as was the case for the calcium ion. Mersalyl inhibited the externally located NADH dehydrogenase and had no effect on AOX activity. The results may represent an important function of Ca(2+) on the alternative mitochondrial enzymes NADH-DH(ext) and AOX.

Protective roles of mitochondrial manganese-containing superoxide dismutase against various stresses in Candida albicans

Candida albicans contains copper- and zinc-containing superoxide dismutase but also two manganese-containing superoxide dismutases (MnSODs), one in the cytosol and the other in the mitochondria. Among these, the SOD2 gene encoding mitochondrial MnSOD was disrupted and overexpressed to investigate its roles in C. albicans. The null mutant lacking mitochondrial MnSOD was more sensitive than wild-type cells to various stresses, such as redox-cycling agents, heating, ethanol, high concentration of sodium or potassium and 99.9% O2. Interestingly, the sod2/sod2 mutant was rather more resistant to lithium and diamide than the wild-type, whereas overexpression of SOD2 increased susceptibility of C. albicans to these compounds. The inverse effect of mitochondrial MnSOD on lithium toxicity was relieved when the sod2/sod2 and SOD2-overexpressing cells were grown on the synthetic dextrose medium containing sulphur compounds such as methionine, cysteine, glutathione or sulphite, indicating that mitochondrial MnSOD may affect lithium toxicity through sulphur metabolism. Moreover, disruption or overexpression of SOD2 increased or decreased glutathione reductase activity and cyanide-resistant respiration by alternative oxidase, respectively. Taken together, these findings suggest that mitochondrial MnSOD is important for stress responses, lithium toxicity and cyanide-resistant respiration of C. albicans.

Cystathionine pathway-dependent cytotoxicities of diethyl maleate and diamide in rat and human hepatoma-derived cell cultures

Glutathione (GSH) plays a role in many toxicologically important metabolic processes. It was previously established that L-buthionine S,R-sulphoximine (BSO), a specific inhibitor of (- glutamylcysteine synthetase, reduces the GSH content more efficiently in rat (Fa32) than in human (HEp-G2) hepatoma-derived cells. We therefore investigated whether the cystathionase inhibitor propargylglycine (PPG) could further decrease the BSO-induced GSH depletion in HEp-G2 cells. The influence of the cystathionine precursors N-acetylmethionine, methionine and homocysteine on the cytotoxicity of diethyl maleate (DEM) and diamide [1,1'-azobis(N,N-dimethylformamide)] was also investigated. PPG reduced the GSH content in both cell lines. A further GSH decrease in HEp-G2 was obtained when using a BSO + PPG combination containing relatively high concentrations of PPG. BSO diminished the toxicity of PPG. Homocysteine was the most efficacious of the tested cystathionine precursors in increasing the GSH content and reducing the cytotoxicity of DEM and diamide in Fa32 and HEp-G2 cells.

Glutathione protection against hydrogen peroxide, tert-butyl hydroperoxide and diamide cytotoxicity in rat hepatoma-derived Fa32 cells

1. Several ozonides, peroxides and aldehydes are formed during ozone therapy, recently introduced in medicine. tert-Butyl hydroperoxide (t-BHP), H2O2 and diamide were investigated as model substrate in rat hepatoma-derived Fa32 cells. 2. The cytotoxicity was measured by the neutral red uptake inhibition assay after 1 h or 24 h treatment. The relative toxicities were quantified by the determination of the NI50. This is the concentration of test compound required to induce an inhibition of 50% in neutral red uptake as compared to the control cells. All test chemicals were more toxic after 24 h than after 1 h. 3. The influence of the glutathione (GSH) alteration on the cytotoxicity was measured by treating the cells with 2-oxo-4-thiazolidine carboxylic acid (OTC) or L-buthionine sulfoximine (BSO). OTC increased the endogenous GSH content in the cells. BSO pretreatment strongly decreased the NI50 of the three chemicals. OTC pretreatment increased the NI50 of H2O2 but not of t-BHP and diamide. This can be explained by the strong GSH-depletion after 1 h by t-BHP and diamide, which contrasted with a weak GSH-depletion by H2O2 after the same time period. 4. The three test chemicals increased the endogenous GSH content after 24 h. t-BHP and H2O2, but not diamide, increased the total GSH transferase (GST) activity. Several alterations of the GST subunits were observed. Most striking was the increase of class alpha GST subunits, also for diamide. 5. Since H2O2 and t-BHP are ozone metabolites thought to be responsible for the therapeutic effects of well-dosed ozone, the results show that Fa32 cells can be used as a valuable alternative model system for studying the effects encountered in human ozone therapy.

Formation of protein-glutathione mixed disulfides in the developing rat conceptus following diamide treatment in vitro

Protein-glutathione mixed disulfide (protein-S-SG) formation was investigated in developing rat conceptuses during early organogenesis (gestational day 10, GD 10) using the whole embryo culture system. Low levels of protein-S-SG (25.0 +/- 6.6 pmoles resolved GSH/conceptus) were found in conceptuses under normal culture conditions. Incubation of the conceptuses with 75-500 microM diamide (a thiol oxidant) resulted in rapid increases in protein-S-SG (to 2- to 16-fold that of control values) in a dose-dependent manner during 30 min of the culture period. Approximately 20% of the observed cytosolic glutathione (GSH) depletion following diamide (500 microM) could be accounted for as mixed disulfides of protein sulfhydryls, when determined in whole conceptual tissues after 15 min. The most extensive S-thiolation of protein sulfhydryls by GSH was observed in visceral yolk sac (VYS) when compared to embryo proper and ectoplacental cone. This result indicates that the most abundant, sensitive, or accessible protein sulfhydryls were found in the VYS. Inhibition of glutathione disulfide reductase activity by pretreatment of the conceptuses with 25 microM BCNU for 2 hr potentiated protein-S-SG formation elicited by 75 microM diamide. Reincubation of the conceptuses in fresh media, following the 15-min treatment with 500 microM diamide, reversed both the GSH depletion and the protein-S-SG formation in conceptal tissues. The reduction of the protein-S-SG was dependent on adequate intracellular GSH levels and was inhibited when GSH was rapidly depleted by subsequent addition of N-ethylmaleimide (NEM, 100 microM). Under the same experimental conditions, addition of 1 mM dithiothreitol (DTT) did not significantly enhance the GSH restoration rate nor the protein-S-SG reduction rate. The results also indicated that low levels of intracellular cysteine do not play an important role in the reduction of protein-S-SG. Protein-S-SG formation may be important for cellular regulation and in mediating the embryotoxicity elicited by diamide or other oxidative stresses.

Diamide-induced alterations of intracellular thiol status and the regulation of glucose metabolism in the developing rat conceptus in vitro

Direct oxidation of embryonic reduced glutathione (GSH) by a thiol oxidant, diamide, has been demonstrated to result in increased glutathione disulfide (GSSG) and protein-glutathione mixed disulfide (protein-S-SG) formation, which is accompanied by embryotoxicity and reductions in amniotic fluid volume. The altered functions of critical proteins or enzymes caused by the formation of protein-S-SG perturb cellular metabolism and may be involved in the embryotoxicity produced by GSH oxidation. The present study investigates changes in the metabolism of glucose through glycolysis and the pentose phosphate shunt pathways (PPP) and their related enzymes under the oxidative conditions produced by diamide exposure in organogenesis-stage rat conceptus (gestational day 10) in vitro. The metabolism of glucose via the PPP, measured as amounts of CO2 production from D-[1-14C]-glucose, was significantly increased in the conceptus exposed to 100-500 microM diamide to levels 2.5-3-fold those of controls. It was found that these substantial increases in the PPP activity did not correlate well with a moderate activation of glucose 6-phosphate dehydrogenase (G6PD) activity, the key enzyme in the PPP pathway. Changes in glycolysis due to diamide treatment were also determined by measurements of lactate production from D-[U-14C]-glucose. Production of lactate by the conceptus exposed to 250-500 microM diamide for 60 min was reduced (to approximately 54% of control values) concomitantly with a significant inhibition of the glycolytic enzymes, glyceraldehyde 3-phosphate dehydrogenase (GPD) and phosphofructokinase (PFK), indicating an overall decrease in glycolysis. Diamide was found to produce a differential effect on the enzymatic activities determined in this study, with greater degrees of inhibition seen in the tissue supernatants from the visceral yolk sac (VYS) compared to those from the embryo. Activities of GPD and PFK were decreased to approximately 22% and 43% control values, respectively, when determined in the supernatants from the VYS of the conceptus exposed to 500 microM diamide for 60 min. In addition, more than 90% of the GPD activity in the VYS, but not the embryo, was rapidly inhibited by the thiol alkylating agent N-ethylmaleimide (NEM, 100 microM) within 15 min of the exposure. In contrast to diamide and NEM, no alterations in lactate production were seen in the conceptus treated with the GSH depletor L-buthionine-S,R-sulfoximine (1 mM) for 5 hr in the culture media. Further experiments demonstrated that the activity of the GPD, inhibited by a 30-min incubation with 500 microM diamide, can be reversed after removal of diamide and that this effect was potentiated by subsequent treatment with dithiothreitol (30 mM), a thiol reducing agent. These results indicated the involvement of thiol/disulfide status in regulation of the metabolism of glucose in the developing conceptus and support the hypothesis that GSH oxidation and protein-S-SG formation could be a critical event associated with mechanisms of embryotoxicity elicited by oxidative stress. It was suggested in this study that, under these experimental conditions, embryotoxicity induced by diamide is primarily mediated via altered VYS functions, including disrupted energy production (glycolysis).

Mechanism for the changes in levels of glutathione upon exposure of cultured mammalian cells to tertiary-butylhydroperoxide and diamide

Qualitative and quantitative changes associated with cellular glutatione (GSH) in response to oxidants were investigated in cultured Chinese hamster V79 cells. Incubation of cells with benzoylperoxide (BZP), tert-butylhydroperoxide (t-BuOOH), hydrogen peroxide or diamide for 1 h reduced the level of total GSH (GSH + GSSG). Among the oxidants, t-BuOOH and diamide caused an increase in levels of glutathione disulfide (GSSG) and a resultant increase in the ratio of the level of GSSG to the level of total GSH, suggestive of the induction within the cells of a pro-oxidant state by the oxidants. o-Phenanthroline, a chelator of divalent ion, almost completely suppressed the decrease in levels of total GSH caused by t-BuOOH while it did not suppressed either increases in levels of GSSG or increases in the ratio of the levels of GSSG to that of total GSH caused by the hydroperoxide. These results suggest that reactive oxygen radicals are involved in the decrease in levels of GSH by treatment with t-BuOOH but not in the increase in the level of GSSG. After treatment with either t-BuOOH or diamide for 1 h, the level of GSH rapidly increased to more than twice the control level during 15-45 min of post-treatment incubation. o-Phenanthroline almost completely suppressed the increase in levels of GSH caused by t-BuOOH, while it did not affect the changes caused by diamide, suggesting a difference between the mechanisms by which t-BuOOH and diamide cause increases in levels of GSH. It seems likely that reactive oxygen radicals participate not only in the decrease in levels of GSH caused by t-BuOOH but also in the rapid increase that occurs after such treatment. Hence, the first decrease in levels of GSH by the hydroperoxide may be causally related to the latter increase. The amount of [35S]-cysteine taken up by cells after treatment with t-BuOOH was about one half of that taken up by control cells. By contrast, the rate of incorporation of radioactive cysteine into acid-soluble material increased to more than twice that of the controls after treatment with t-BuOOH. The increase in the rate of incorporation of [35S]cysteine into acid-soluble material caused by t-BuOOH was not a consequence of inhibition by the hydroperoxide of utilization of cysteine for protein synthesis. Inhibition of protein synthesis by cycloheximide caused neither an increase in the incorporation of cysteine into acid-soluble material nor an increase in rate of biosynthesis of GSH.(ABSTRACT TRUNCATED AT 400 WORDS)

Glutathione oxidation and embryotoxicity elicited by diamide in the developing rat conceptus in vitro

This study was performed in the rat whole-embryo culture system to investigate the effects of glutathione oxidation by diamide, a thiol oxidant, in developing rat conceptuses during early organogenesis. The effects of diamide on reduced glutathione (GSH), glutathione disulfide (GSSG), and embryotoxicity were found to be concentration and time dependent. Diamide at concentrations of 75 and 100 microM produced abnormal axial rotation (62-89%), decreased viability (to 69% by 100 microM diamide), and reduced protein and DNA content in the embryo and visceral yolk sac (VYS) when evaluated on Day 11. High concentrations of diamide (250-500 microM) resulted in 100% mortality. GSH and GSSG levels in the conceptuses were not significantly affected during 2 hr following diamide addition at concentrations of 50 to 100 microM. At concentrations of 250 and 500 microM, rapid GSH depletion (50% of control) was seen within 5 min of exposure and was followed at 5-30 min by a significant increase in GSSG relative to control values. Diamide (500 microM) exposure for only 15 min on Gestational Day 10 was sufficient to elicit malformations (53% of exposed conceptuses with abnormal axial rotation) without significant loss of viability. After 30 min of exposure to the high concentration (500 microM), viability was decreased to 71% and defects of axial rotation increased to 87% in surviving conceptuses. This indicates that events associated with initial exposure are critical for expression of toxicity. Inhibition of glutathione disulfide reductase (GSSG reductase) activities in embryo and VYS with 1,3-bis(2-chloroethyl)-1-nitro-sourea prior to diamide addition potentiated the embryotoxicity of diamide (75 microM) and resulted in corresponding reductions in GSH/GSSG ratios as determined during the first 2 hr of exposure. Inhibition of new GSH synthesis with L-buthionine-[S,R]-sulfoximine during diamide (75 microM) exposure also exacerbated toxicity compared to diamide treatment alone. These results implicate the involvement of GSH synthesis and GSSG reductase activity in mediating the embryotoxicity of diamide.

Differential cytotoxicity of buthionine sulfoximine to "normal" and transformed human lung fibroblast cells

Glutathione (GSH) depletion has been studied extensively as a possible means to sensitive tumor cells to radiation treatment and chemotherapy. The present study was undertaken to compare the cytotoxicity of GSH depletion in normal and transformed cells. The results showed that specific inhibition of GSH synthesis by L-buthionine sulfoximine (BSO) caused significantly higher cytotoxicity in "normal" human-lung fibroblast cells than in their transformed counterparts. This finding suggests a possibility that depletion of GSH could be more harmful to normal cells than to transformed and/or tumor cells and that the selective cytotoxicity of BSO to normal cells could limit its potential as an effective sensitizer for cancer treatment.

Diamide-induced cross-linking of the lens water-soluble proteins as a model of the early oxidative changes during senile cataract formation

This study deals with the effects of the SH oxidizing agent diamide (diazene dicarboxylic acid bis-(N,N-dimethyl-amide)) on the water-soluble proteins from rabbit lenses. The dialyzed protein extracts were incubated for 0.5-1.5 h with various concentrations of diamide. Alterations in sulphydryl contents, gel filtration and gel electrophoresis profiles of proteins were recorded. The response to 2 mM diamide treatment for 1 h consists of rapid oxidation (up to 40%) of protein-bound sulphydryl groups accompanied by appearance of polypeptides with apparent molecular weights in excess of 68,000. A protein with a molecular weight of 29 kDa was shown to be specially involved in cross-linking. The linkages in the dialyzed water-soluble lens protein fraction induced by diamide may be reduced by GSH (10 mM) treatment of the protein extract. The main target of oxidative insult induced by diamide in the water-soluble proteins of the lens is probably the superficially localized sulphydryl groups of crystallins. Our observations suggest that this oxidative system of proteins may be a useful tool for cataract research.

Modulation of diamide toxicity in thermotolerant cells by inhibition of protein synthesis

Chinese hamster ovary cells were exposed in vitro to various concentrations of diamide for 1 h at 37 degrees C. This treatment resulted in a dose dependent increase in cytotoxicity. Cells were also heated at 43 degrees C for 15 min, incubated at 37 degrees C for 3 h, and then exposed to various concentrations of diamide. This heat shock has been shown previously to trigger the synthesis of heat shock proteins and the development of thermotolerance. Further, under these experimental conditions both were inhibited if protein synthesis was inhibited by exposure to cycloheximide (M. L. Freeman et al., Radiat. Res., 112: 195-203, 1987). Diamide toxicity was diminished in cells made thermotolerant by the 43 degrees C/15-min heat shock. For example, at the highest dose used, 0.8 mM, survival increased from 0.93% to 6.1%. However, diamide toxicity was unaffected if the cells were exposed to diamide 3 h after a 43 degrees C/60 min heat shock. This latter heat shock produced significant inhibition of protein synthesis whereas the 15-min heat shock did not (M. L. Freeman et al., Cancer Res., 48: 7033-7037, 1988). Further, a 43 degrees C/15-min heat shock did not confer protection against diamide toxicity if the cells were simultaneously exposed to cycloheximide. Exposure to 0.8 mM diamide was shown to oxidize specific cellular proteins as measured by 2-dimensional thiol blotting. However, the degree of protein thiol modification was not affected by a prior heat shock. Nor did the heat shock increase the intracellular concentration of glutathione or the activity of glutathione reductase. The diamide treatment caused specific, as opposed to general, protein thiol oxidation and heat shock did not prevent this. It is hypothesized that it was the oxidation of protein thiols which led to cellular toxicity. Protein synthesis, triggered by heat shock, protected cells from the diamide toxicity without preventing protein thiol modification. These results suggest that the proteins synthesized after heat shock can provide protection against the consequences of aberrant proteins produced by thiol oxidation.

Abnormal proteins as the trigger for the induction of stress responses: heat, diamide, and sodium arsenite

Thermotolerance and synthesis of heat shock proteins are induced in cells in response to a variety of environmental stresses. We examined the suggestion of Hightower (1980) that modifications of intracellular proteins may be the triggering event that induces heat shock protein synthesis and thermotolerance. We did so by modifying cellular proteins, using diamide, a sulfhydryl oxidizing agent, and dithio-bis (succinimidyl propionate), an agent that cross-links bifunctional amino groups. Both of these agents induced heat shock proteins and thermotolerance in CHO (HA-1) cells. Furthermore, we observed cross-resistance and self-tolerance with three seemingly unrelated stimuli (diamide, heat, and sodium arsenite). This observation suggests that the induction of protective responses to these stimuli is mediated by a common mechanism. The results support the hypothesis that production of abnormal proteins by various stresses induces the stress responses as well as tolerance.

Effects of inhibitors of DNA strand break repair on HeLa cell radiosensitivity

The effects of three drugs (hydroxyurea, 1-beta-arabinofuranosylcytosine, and diamide) known to inhibit DNA synthesis on the repair of ionizing radiation-induced DNA single-strand breaks measured by alkaline elution and on cellular radiosensitivity were examined. Inhibition of repair was observed at 10(-2) M hydroxyurea, 10(-4) M 1-beta-D-arabinofuranosylcytosine, and 5 X 10(-5) M diamide, levels causing only 10% cell kill. While the mechanisms by which the drugs inhibit DNA synthesis differ, they are equally effective at inhibiting repair; without drug, cells, after a dose of 10 grays, repair 35% of DNA strand breaks in 3 min and a further 35% in 1 hr; with drug, only 10% is repaired in 3 min, and the deficiency in repair amount remains, even after 60 min. The effect of similar drug treatment on radiation-induced cell killing shows that radiosensitivity is increased; the major effect is reduction in D0 from 1.3 grays to approximately 0.8 grays with smaller effects on Dq. The data are consistent with the hypothesis that radiation produces potential double-strand breaks in DNA which, if not rapidly repaired, are converted into lethal actual double-strand breaks.

Spindle disturbances in mammalian cells. I. Changes in the quantity of free sulfhydryl groups in relation to survival and C-mitosis in V79 Chinese hamster cells after treatment with colcemid, diamide, carbaryl and methyl mercury

Asynchronously growing V79 Chinese hamster cells were treated with colcemid, diamide, carbaryl and methyl mercury, which are all known to be spindle disturbing agents. For each compound the dose response for c-mitosis, survival and level of free sulfhydryl groups was investigated under comparable conditions. Diamide, carbaryl and methyl were all found to give a significant increase of c-mitosis at a dose giving a decrease of non-protein sulfhydryl groups (NPSH, mainly glutathione) of 30-40% suggesting that a decrease of this magnitude may have a predictive value for spindle disturbances. Despite this similarity at concentrations close to the respective thresholds it was found that the c-mitotic activity at higher concentrations was not a simple function of average NPSH decrease. Diamide, which rapidly oxidizes glutathione to glutathione disulfide, was a less efficient c-mitotic agent than carbaryl and methyl mercury in relation to average NPSH decrease at higher concentrations. Protein bound sulfhydryl groups (PSH) were not significantly affected with diamide and carbaryl at their lowest c-mitotic concentrations while methyl mercury caused a significant decrease already at concentrations below the lowest c-mitotic concentration. With colcemid a significant decrease of average NPSH (14%) and PSH (12%) was observed only with concentrations giving close to 100% c-mitotic cells. Concentrations giving more than 20% c-mitosis gave a pronounced decrease of survival with carbaryl, diamide and methyl mercury while no toxic effects were obtained with colcemid, not even with concentrations giving close to 100% c-mitosis. Carbaryl, diamide and methyl mercury caused increased glutathione peroxidase activity indicating that these compounds cause increased lipid peroxidation. The possible connection between peroxidative damage of membranes and c-mitosis is discussed.

Modification of the action of misonidazole. III. The effect of diamide on toxicity and radiosensitization

Diamide, a compound which depletes cells of reduced glutathione, decreases toxicity of misonidazole to hypoxic cells, as measured by single-strand break (SSB) production, cell inactivation, and uptake of radioactive misonidazole. As a radiosensitizer, the effect of diamide in cell pellets is additive to that of misonidazole. Individually, both misonidazole and diamide enhance SSB production in DNA of cells irradiated under hypoxia in dilute suspension, but a combination of the two drugs does not appear to produce a greater number of SSB than misonidazole alone.