Changes in the hepatic glutathione peroxidase redox system produced by coplanar polychlorinated biphenyls in Ah-responsive and -less-responsive strains of mice: mechanism and implications for toxicity

Unveiling the potential of A. fabrum and γ-aminobutyric acid for mitigation of nickel toxicity in fenugreek

Nickel (Ni) is a heavy metal that adversely affects the growth of different crops by inducing oxidative stress and nutrient imbalance. The role of rhizobacteria (RB) is vital to resolve this issue. They can promote root growth and facilitate the uptake of water and nutrients, resulting in better crop growth. On the other hand, γ-aminobutyric acid (GABA) can maintain the osmotic balance and scavenge the reactive oxygen species under stress conditions. However, the combined effect of GABA and RB has not been thoroughly explored to alleviate Ni toxicity, especially in fenugreek plants. Therefore, in the current pot study, four treatments, i.e., control, A. fabrum (RB), 0.40 mM GABA, and 0.40 mM GABA + RB, were applied under 0Ni and 80 mg Ni/kg soil (80Ni) stress. Results showed that RB + 0.40 mM GABA caused significant improvements in shoot length (~ 13%), shoot fresh weight (~ 47%), shoot dry weight (~ 47%), root length (~ 13%), root fresh weight (~ 60%), and root dry weight (~ 15%) over control under 80 Ni toxicity. A significant enhancement in total chlorophyll (~ 14%), photosynthetic rate (~ 17%), stomatal CO2 concentration (~ 19%), leaves and roots N (~ 10 and ~ 37%), P (~ 18 and ~ 7%) and K (~ 11 and ~ 30%) concentrations, while a decrease in Ni (~ 83 and ~ 49%) concentration also confirmed the effectiveness of RB + 0.40 mM GABA than control under 80Ni. In conclusion, fabrum + 0.40 mM GABA can potentially alleviate the Ni toxicity in fenugreek plants. The implications of these findings extend to agricultural practices, environmental remediation efforts, nutritional security, and ecological impact. Further research is recommended to elucidate the underlying mechanisms, assess long-term effects, and determine the practical feasibility of using A. fabrum + 0.40GABA to improve growth in different crops under Ni toxicity.

Ameliorative effect of Ononis natrix against chronic lead poisoning in mice: neurobehavioral, biochemical, and histological study

Lead (Pb) is one of the most common heavy metals with toxicological effects on many tissues in humans as well as animals. In order to counteract the toxic effects of this metal, the administration of synthetic or natural antioxidants is thus required. The aim of this study was to examine the beneficial effect of the aqueous extract of Ononis natrix (AEON) against lead acetate-induced damage from a behavioral, biochemical, and histological point of view. Forty-eight male mice were divided into four equal groups: Ctr (control); Pb (lead acetate 1g/l); Pb + On 100 mg/kg (lead acetate 1 g/l + AEON 100 mg/kg); Pb + On 500 mg/kg (lead acetate 1 g/l + AEON 500 mg/kg). AEON was administered orally from day 21 after the start of lead exposure up to the end of the experiment. The results revealed that lead induced behavioral disorders, increased serum levels of liver markers (AST, ALT, and bilirubin), as well as kidney markers (urea and creatinine). At the same time, levels of thiobarbituric acid reactive substances (TBARS) and glutathione peroxidase (GPx) increased significantly. Moreover, Pb caused structural changes in the liver and kidneys of Pb-exposed mice. However, AEON administration significantly improved all lead-induced brain, liver, and kidney dysfunctions. Our results suggest that AEON could be a source of molecules with therapeutic potential against brain, liver, and kidney abnormalities caused by lead exposure.

Effect of carboxymethyl cellulose and gibberellic acid-enriched biochar on osmotic stress tolerance in cotton

The deleterious impact of osmotic stress, induced by water deficit in arid and semi-arid regions, poses a formidable challenge to cotton production. To protect cotton farming in dry areas, it's crucial to create strong plans to increase soil water and reduce stress on plants. The carboxymethyl cellulose (CMC), gibberellic acid (GA3) and biochar (BC) are individually found effective in mitigating osmotic stress. However, combine effect of CMC and GA3 with biochar on drought mitigation is still not studied in depth. The present study was carried out using a combination of GA3 and CMC with BC as amendments on cotton plants subjected to osmotic stress levels of 70 (70 OS) and 40 (40 OS). There were five treatment groups, namely: control (0% CMC-BC and 0% GA3-BC), 0.4%CMC-BC, 0.4%GA3-BC, 0.8%CMC-BC, and 0.8%GA3-BC. Each treatment was replicated five times with a completely randomized design (CRD). The results revealed that 0.8 GA3-BC led to increase in cotton shoot fresh weight (99.95%), shoot dry weight (95.70%), root fresh weight (73.13%), and root dry weight (95.74%) compared to the control group under osmotic stress. There was a significant enhancement in cotton chlorophyll a (23.77%), chlorophyll b (70.44%), and total chlorophyll (35.44%), the photosynthetic rate (90.77%), transpiration rate (174.44%), and internal CO2 concentration (57.99%) compared to the control group under the 40 OS stress. Thus 0.8GA3-BC can be potential amendment for reducing osmotic stress in cotton cultivation, enhancing agricultural resilience and productivity.

Enhancing maize growth through the synergistic impact of potassium enrich biochar and spermidine

Maize cultivated for dry grain covers approximately 197 million hectares globally, securing its position as the second most widely grown crop worldwide after wheat. Although spermidine and biochar individually showed positive impacts on maize production in existing literature, their combined effects on maize growth, physiology, nutrient uptake remain unclear and require further in-depth investigation. That's why a pot experiment was conducted on maize with spermidine and potassium enriched biochar (KBC) as treatments in Multan, Pakistan, during the year 2022. Four levels of spermidine (0, 0.15, 0.30, and 0.45mM) and two levels of potassium KBC (0 and 0.50%) were applied in completely randomized design (CRD). Results showed that 0.45 mM spermidine under 0.50% KBC caused significant enhancement in maize shoot length (11.30%), shoot fresh weight (25.78%), shoot dry weight (17.45%), root length (27.95%), root fresh weight (26.80%), and root dry weight (20.86%) over control. A significant increase in maize chlorophyll a (50.00%), chlorophyll b (40.40%), total chlorophyll (47.00%), photosynthetic rate (34.91%), transpiration rate (6.51%), and stomatal conductance (15.99%) compared to control under 0.50%KBC validate the potential of 0.45 mM spermidine. An increase in N, P, and K concentration in the root and shoot while decrease in electrolyte leakage and antioxidants also confirmed that the 0.45 mM spermidine performed more effectively with 0.50%KBC. In conclusion, 0.45 mM spermidine with 0.50%KBC is recommended for enhancing maize growth.

Modulation of sunflower growth via regulation of antioxidants, oil content and gas exchange by arbuscular mycorrhizal fungi and quantum dot biochar under chromium stress

Chromium (Cr) toxicity significantly threatens sunflower growth and productivity by interfering with enzymatic activity and generating reactive oxygen species (ROS). Zinc quantum dot biochar (ZQDB) and arbuscular mycorrhizal fungi (AMF) have become popular to resolve this issue. AMF can facilitate root growth, while biochar tends to minimize Cr mobility in soil. The current study aimed to explore AMF and ZQDB combined effects on sunflower plants in response to Cr toxicity. Four treatments were applied, i.e. NoAMF + NoZQDB, AMF + 0.40%ZQDB, AMF + 0.80%ZQDB, and AMF + 1.20%ZQDB, under different stress levels of Cr, i.e. no Cr (control), 150 and 200 mg Cr/kg soil. Results showed that AMF + 1.20%ZQDB was the treatment that caused the greatest improvement in plant height, stem diameter, head diameter, number of leaves per plant, achenes per head, 1000 achenes weight, achene yield, biological yield, transpiration rate, stomatal conductance, chlorophyll content and oleic acid, relative to the condition NoAMF + No ZQDB at 200 mg Cr/kg soil. A significant decline in peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) while improvement in ascorbate peroxidase (APx), oil content, and protein content further supported the effectiveness of AMF + 1.20%ZQDB against Cr toxicity. Our results suggest that the treatment AMF + 1.20%ZQDB can efficiently alleviate Cr stress in sunflowers.

Evaluation of potassium-enriched biochar and GA3 effectiveness for Improving wheat growth under drought stress

Osmotic stress is a significant concern in agricultural crop production as it can harm crop growth, development, and productivity. Agriculture crops are particularly vulnerable to osmotic stress due to their reliance on water availability for various physiological processes. Organic amendments like activated carbon biochar and growth hormone gibberellic acid (GA3) can play a vital role. However, the time needed is to modify the established amendment to achieve better results. That's why the current study used potassium-enriched biochar (KBC = 0.75%) with and without GA3 (15 mg/L) as amendments under no osmotic stress and osmotic stress in wheat. Results showed that GA3 + KBC caused significant enhancement in germination (9.44%), shoot length (29.30%), root length (21.85%), shoot fresh weight (13.56%), shoot dry weight (68.38), root fresh weight (32.68%) and root dry weight (28.79%) of wheat over control under osmotic stress (OS). A significant enhancement in chlorophyll a, chlorophyll b and total chlorophyll, while the decline in electrolyte leakage of wheat, also validated the effectiveness of GA3 + KBC over control in OS. In conclusion, GA3 + KBC is the most effective among all applied treatments for improving wheat growth attributes under no osmotic and osmotic stress. Further research is needed at the field level, focusing on various cereal crops, to establish GA3 + KBC as the optimal treatment for effectively mitigating the impacts of osmotic stress.

Arbuscular mycorrhizal fungus Rhizophagus irregularis alleviates drought stress in soybean with overexpressing the GmSPL9d gene by promoting photosynthetic apparatus and regulating the antioxidant system

Drought is the most destructive abiotic stress and negatively affects crop growth and productivity. Modern breeding efforts have produced numerous cultivars with distinct genetic traits that improve crop growth and drought stress tolerance. Arbuscular mycorrhizal fungi (AMF) can enhance drought tolerance in soybean plants by directly providing nutrients to plants, promoting photosynthesis, or influencing interspecific plant interactions in natural communities. However, the interactions between AMF and wild and transgenic soybean genotypes remain unclear. Therefore, in the present study, we evaluated the effect of arbuscular mycorrhizal fungi on the growth performance of drought-stressed transgenic soybean lines (ZXOE-11 and ZXOE-13) overexpressing GmSPL9d gene and their wild soybean Tianlong 1 (TL1) at the seedling stage (45 d after sowing). The results showed that colonization of wild and transgenic soybean with Rhizophagus irregularis significantly decreased the adverse effects of drought on plant growth. AMF inoculation significantly increased plant biomass, root activity, chlorophyll metabolism, photosynthesis, and chlorophyll fluorescence in wild-type and transgenic plants under both control and drought stress conditions. Drought causes the production of ROS, such as hydrogen peroxide, which enhances MDA, thereby decreasing the membrane stability index (MSI). However, AMF-inoculated plants exhibited decreased ROS accumulation and increased MSI. Moreover, AMF treatment significantly improved osmolyte, nitrogen, and nitrate reductase activity under control and drought conditions, which increased the relative water content. Furthermore, AMF treatment enhanced the antioxidant systems of drought-stressed plants by increasing the activities of peroxidase, superoxide dismutase, catalase, and ascorbate peroxidase. AMF improved the growth performance, photosynthesis, and antioxidant activity of transgenic plants under drought stress conditions. The present findings indicate that the AMF contribution to soybean seedling drought tolerance was more significant for the transgenic plants than for the wild plants under drought conditions. The current findings emphasize the possibility of growth and photosynthetic variation in the degree of AMF-associated drought resistance in soybean plants. Our findings suggest that future crop breeding challenges include developing cultivars for sustainable production and maximizing crop cultivar and fungal species (AMF) combinations in drought-stressed regions.

Co-inoculation of Arbuscular Mycorrhizal Fungi and the Plant Growth-Promoting Rhizobacteria Improve Growth and Photosynthesis in Tobacco Under Drought Stress by Up-Regulating Antioxidant and Mineral Nutrition Metabolism

Drought stress is a major environmental concern that limits crop growth on a large scale around the world. Significant efforts are required to overcome this issue in order to improve crop production. Therefore, the exciting role of beneficial microorganisms under stress conditions needs to be deeply explored. In this study, the role of two biotic entities, i.e., Arbuscular mycorrhizal fungi (AMF, Glomus versiforme) and plant growth-promoting rhizobacteria (PGPR, Bacillus methylotrophicus) inoculation in drought tolerance of tobacco (Nicotiana tabacum L.), was investigated. The present results showed that drought stress considerably reduced tobacco plant's growth and their physiological attributes. However, the plants co-inoculated with AMF and PGPR showed higher drought tolerance by bringing up significant improvement in the growth and biomass of tobacco plants. Moreover, the co-inoculation of AMF and PGPR considerably increased chlorophyll a, b, total chlorophylls, carotenoids, photosynthesis, and PSII efficiency by 96.99%, 76.90%, and 67.96% and 56.88%, 53.22%, and 33.43% under drought stress conditions, respectively. Furthermore, it was observed that drought stress enhanced lipid peroxidation and electrolyte leakage. However, the co-inoculation of AMF and PGPR reduced the electrolyte leakage and lipid peroxidation and significantly enhanced the accumulation of phenols and flavonoids by 57.85% and 71.74%. Similarly, the antioxidant enzymatic activity and the plant nutrition status were also considerably improved in co-inoculated plants under drought stress. Additionally, the AMF and PGPR inoculation also enhanced abscisic acid (ABA) and indole-3-acetic acid (IAA) concentrations by 67.71% and 54.41% in the shoots of tobacco plants. The current findings depicted that inoculation of AMF and PGPR (alone or in combination) enhanced the growth and mitigated the photosynthetic alteration with the consequent up-regulation of secondary metabolism, osmolyte accumulation, and antioxidant system.

Seed Germination Behavior, Growth, Physiology and Antioxidant Metabolism of Four Contrasting Cultivars under Combined Drought and Salinity in Soybean

Drought and salinity stresses are persistent threat to field crops and are frequently mentioned as major constraints on worldwide agricultural productivity. Moreover, their severity and frequency are predicted to rise in the near future. Therefore, in the present study we investigated the mechanisms underlying plant responses to drought (5, 10 and 15% polyethylene glycol, PEG-6000), salinity (50, 100, and 150 mM NaCl), and their combination, particularly at the seed germination stage, in terms of photosynthesis and antioxidant activity, in four soybean cultivars, viz., PI408105A (PI5A), PI567731 (PI31), PI567690 (PI90), and PI416937 (PI37). Results showed that seed germination was enhanced by 10% PEG and decreased by 15% PEG treatments compared to the control, while seed germination was drastically decreased under all levels of NaCl treatment. Furthermore, combined drought and salinity treatment reduced plant height and root length, shoot and root total weights, and relative water content compared with that of control. However, the reductions were not similar among the varieties, and definite growth retardations were observed in cultivar PI5A under drought and in PI37 under salinity. In addition, all treatments resulted in substantially reduced contents of chlorophyll pigment, anthocyanin, and chlorophyll fluorescence; and increased lipid peroxidation, electrolyte leakage, and non-photochemical quenching in all varieties of soybean as compared to the control plants. However, proline, amino acids, sugars, and secondary metabolites were increased with the drought and salinity stresses alone. Moreover, the reactive oxygen species accumulation was accompanied by improved enzymatic antioxidant activity, such as that of superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase. However, the enhancement was most noticeable in PI31 and PI90 under both treatments. In conclusion, the cultivar PI31 has efficient drought and salinity stress tolerance mechanisms, as illustrated by its superior photosynthesis, osmolyte accumulation, antioxidative enzyme activity, and secondary metabolite regulation, compared to the other cultivars, when stressed.

Arbuscular mycorrhizal fungi improve growth, essential oil, secondary metabolism, and yield of tobacco (Nicotiana tabacum L.) under drought stress conditions

Drought is a major environmental threat limiting worldwide crop production. Drought stress affects the tobacco quality and yield; therefore, the current research studies were undertaken to investigate the effectiveness of arbuscular mycorrhizal fungi (AMF) under drought stress on morphological and biochemical attributes of tobacco (Nicotiana tabacum L. variety Yunyan 87). AMF-inoculated and AMF-non-inoculated plants were maintained in a greenhouse and irrigated with a half-strength Hoagland solution (100 mL pot-1) once a week. At harvesting, the plant height, number of leaves, fresh and dry weights, mycorrhizal colonization, and concentration of leaf photosynthetic pigments and photosynthetic rate were measured. Data were statistically analyzed by ANOVA and the principal component (PCA) analyses. The effect of root colonization significantly increased biomass production and essential oil accumulation. Results showed that drought at mild and severe stressed levels significantly affected tobacco growth by decreasing plant height, biomass, and a number of leaves. However, inoculation of AMF considerably increased plant height, fresh and dry weights, chlorophyll (a, b), total chlorophyll, and carotenoid content by 43.84, 40.87 and 49.76, 185.29, 325.60, 173.12, and 211.49%, respectively. Compared with non-inoculated plants, AMF inoculation significantly enhanced the essential oil yield and the uptake of nitrogen, phosphorus, and potassium with the increase of 257.36, 102.71, and 90.76, 62.32, and 84.51%, respectively, in mild drought + AMF-treated plants. Similarly, the antioxidant enzymatic activity, glomalin-related soil protein (GRSP), and accumulation of phenols and flavonoids and osmolytes content were also significantly improved in inoculated plants under drought stress. Additionally, AMF inoculation significantly upregulated the lipoxygenase (LOX) and phenylalanine ammonia-lyase (PAL) enzymes by 197 and 298.44% under drought conditions. These findings depicted that the symbiotic association of AMF improved the overall growth pattern and secondary metabolism in tobacco plants under severe drought stress conditions and may be used as an approaching source of important drugs in the field of pharmacology.

Improved Drought Tolerance by AMF Inoculation in Maize (Zea mays) Involves Physiological and Biochemical Implications

The role of arbuscular mycorrhizal fungus (AMF, Glomus versiforme) in amelioration of drought-induced effects on growth and physio-biochemical attributes in maize (Zea mays L.) was studied. Maize plants were exposed to two drought regimes, i.e., moderate drought (MD) and severe drought (SD), with and without AMF inoculation. Drought at both levels reduced plant height, and chlorophyll and carotenoid content, thereby impeding photosynthesis. In addition, drought stress enhanced the generation of toxic reactive oxygen species (ROS), including H2O2, resulting in membrane damage reflected as increased electrolyte leakage and lipid peroxidation. Such negative effects were much more apparent under SD conditions that those of MD and the control, however, AMF inoculation significantly ameliorated the deleterious effects of drought-induced oxidative damage. Under control conditions, inoculation of AMF increased growth and photosynthesis by significantly improving chlorophyll content, mineral uptake and assimilation. AMF inoculation increased the content of compatible solutes, such as proline, sugars and free amino acids, assisting in maintaining the relative water content. Up-regulation of the antioxidant system was obvious in AMF-inoculated plants, thereby mediating quick alleviation of oxidative effects of drought through elimination of ROS. In addition, AMF mediated up-regulation of the antioxidant system contributed to maintenance of redox homeostasis, leading to protection of major metabolic pathways, including photosynthesis, as observed in the present study. Total phenols increased due to AMF inoculation under both MD and SD conditions. The present study advocates the beneficial role of G. versiforme inoculation in maize against drought stress.

Learning and memory impairments associated to acetylcholinesterase inhibition and oxidative stress following glyphosate based-herbicide exposure in mice

Numerous clinical and epidemiological data have reported the deleterious effects of glyphosate on learning and memory. The ability of this herbicide to cross the blood-brain barrier may have adverse effects on the structure and various functions of the nervous system. This study was conducted to highlight the effects of Glyphosate-based herbicide (GBH) on these two functions in mice treated daily with 250 or 500 mg/kg following acute (unique administration), subchronic (6 weeks) and chronic (12 weeks) treatments. The integrity of learning and memory was assessed by using a specific behavioral test battery: Novel object recognition, Y-maze and passive avoidance tasks. The acetylcholinesterase (AChE) and anti-oxidant enzyme activities, especially superoxide dismutase (SOD) and peroxidase (PO) were evaluated. Our results indicated that unlike acute treatment, both subchronic and chronic exposure to GBH decreased discrimination index and the step-through-latency indicating recognition and retention memory impairments, respectively. In contrast, only chronic exposure affected working memory manifested by decreased spontaneous alternation. Furthermore, our results showed also a prominent decrease in AChE, SOD and PO specific activities within the brain of treated mice following repeated exposures. This study demonstrates that GBH induced numerous cognitive abnormalities referred to different forms of memory likely associated with a significant inhibition of AChE activity and oxidative stress induction.

Oxidative Stress and Apoptosis in Benzo[a]pyrene-Induced Neural Tube Defects

Neural tube defects (NTDs) are among the most common and severe congenital malformations and result from incomplete closure of the neural tube during early development. Maternal exposure to polycyclic aromatic hydrocarbons (PAHs) has been suggested to be a risk factor for NTDs and previous studies imply that the mechanism underlying the association between PAH exposure and NTDs may involve oxidative stress and apoptosis. The objectives of this study were to investigate whether there is a direct effect of maternal benzo[α] pyrene (BaP) exposure on the closure of the neural tube in mice, and to examine the underlying mechanisms by combining animal experiments and human subject studies. We found that intraperitoneal injection of BaP from embryonic day 7 at a dose of 250 mg kg^-1 induced NTDs (13.3% frequency) in ICR mice. BaP exposure significantly increased expression of genes associated with oxidative stress, Cyp1a1, Sod1 and Sod2, while repressing Gpx1. Elevated apoptosis and higher protein expression of cleaved caspase-3 in the neuroepithelium of treated embryos were observed. Pre-treatment with vitamin E, added to food, significantly protected against BaP-induced NTDs (1.4% frequency) (P < 0.05). Vitamin E also partly normalized oxidative stress related gene expression and excess apoptosis in BaP-treated embryos. Examination of human neural tissues revealed that increased levels of protein carbonyl and apoptosis were related with maternal exposure to PAHs and the risk of NTDs. Collectively, these results suggest that BaP exposure could induce NTDs and that this may involve increased oxidative stress and apoptosis, while vitamin E may have a protective effect.

DNA Product Formation in Female Sprague-Dawley Rats Following Polyhalogenated Aromatic Hydrocarbon (PHAH) Exposure

DNA oxidation damage has been regarded as one of the possible mechanisms for the hepatic carcinogenesis of dioxin-like compounds (DLCs). In this study, we evaluated the toxic equivalency factor (TEF) from the standpoint of induced DNA oxidation products and their relationship to toxicity and carcinogenicity. Nine DNA oxidation products were analyzed in the liver of female Sprague–Dawley rats exposed to 2,3,7,8-tetrachlorodibenzo-pdioxin (TCDD) alone or the tertiary mixture of TCDD, 3,3′,4,4′,5-pentachlorobiphenyl (PCB 126), and 2,3,4,7,8-pentachlorodibenzofuran (PeCDF) by gavage for 14, 31, and 53 weeks (5 days/week) by LC–MS/MS: 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxo-dGuo); 1,N⁶-etheno-2′-deoxyadenosine (1,N⁶-εdAdo); N²,3-ethenoguanine (N²,3-εG); 7-(2-oxoethly)guanine (7-OEG); 1,N²-etheno-2′-deoxyguanosine (1,N²-εdGuo); malondialdehyde (M₁dGuo); acrolein (AcrdGuo); crotonaldehyde (CrdGuo); and 4-hydroxynonenal (HNEdGuo) derived 2′-deoxyguanosine adducts. Exposure to TCDD (100 ng/kg/day) significantly induced 1,N⁶-εdAdo at 31 and 53 weeks, while no increase of 8-oxo-dGuo was observed. Significant increases were observed for 8-oxo-dGuo and 1,N⁶-εdAdo at all time points following exposure to the tertiary mixture (TEQ 100 ng/kg/day). Exposure to TCDD for 53 weeks only significantly increased 1,N⁶-εdAdo, while increases of N²,3-εG and 7-OEG were only found in the highest dose group (100 ng/kg/day). Exposure to the tertiary mixture for 53 weeks had no effect on N²,3-εG in any exposure group (TEQ 0, 22, 46, or 100 ng/kg/day), while significant increases were observed for 1,N⁶-εdAdo (all dose groups), 8-oxo-dGuo (46 and 100 ng/kg/day), and 7-OEG (100 ng/kg/day). While no significant increase was observed at 53 weeks for 1,N²-εdGuo, M₁dGuo, AcrdGuo, or CrdGuo following exposure to TCDD (100 ng/kg/day), all of them were significantly induced in animals exposed to the tertiary mixture (TEQ 100 ng/kg/day). This oxidation DNA product data suggest that the simple TEF methodology cannot be applied to evaluate the diverse patterns of toxic effects induced by DLCs.

Polychlorinated Biphenyls Induce Oxidative DNA Adducts in Female Sprague-Dawley Rats

Polychlorinated biphenyls (PCBs) are organic chemicals that were traditionally produced and widely used in industry as mixtures and are presently formed as byproducts of pigment and dye manufacturing. They are known to persist and bioaccumulate in the environment. Some have been shown to induce liver cancer in rodents. Although the mechanism of the toxicity of PCBs is unknown, it has been shown that they increase oxidative stress, including lipid peroxidation. We hypothesized that oxidative stress-induced DNA damage could be a contributor for PCB carcinogenesis and analyzed several DNA adducts in female Sprague-Dawley rats exposed to 3,3',4,4',5-pentachlorobiphenyl (PCB 126), 2,2',4,4',5,5'-hexachlorobiphenyl (PCB 153), and a binary mixture (PCB 126 + 153) for 14, 31, and 53 wks. Eight adducts were measured to profile oxidative DNA lesions, including 8-oxo-deoxyguanosine (8-oxo-dG), 1,N(6)-ethenodeoxyadenosine (1,N(6)-εdA), N(2),3-ethenoguanine (N(2),3-εG), 1,N(2)-ethenodeoxyguanosine (1,N(2)-εdG), as well as malondialdehyde (M1dG), acrolein (AcrdG), crotonaldehyde (CrdG), and 4-hydroxynonenal-derived dG adducts (HNEdG) by LC-MS/MS analysis. Statistically significant increases were observed for 8-oxo-dG and 1,N(6)-εdA concentrations in hepatic DNA of female rats exposed to the binary mixture (1000 ng/kg/day + 1000 μg/kg/day) but not in rats exposed to PCB 126 (1000 ng/kg/day) or PCB 153 (1000 μg/kg/day) for 14 and 31 wks. However, exposure to PCB 126 (1000 ng/kg/day) for 53 wks significantly increased 8-oxo-dG, 1,N(6)-εdA, AcrdG, and M1dG. Exposure to PCB 153 (1000 μg/kg/day) for 53 wks increased 8-oxo-dG, and 1,N(6)-εdA. Exposure to the binary mixture for 53 wks increased 8-oxo-dG, 1,N(6)-εdA, AcrdG, 1,N(2)-εdG, and N(2),3-εG significantly above control groups. Increased hepatic oxidative DNA adducts following exposure to PCB 126, PCB 153, or the binary mixture shows that an increase in DNA damage may play an important role in hepatic toxicity and carcinogenesis in female Sprague-Dawley rats.

Selenium-binding protein 1: its physiological function, dependence on aryl hydrocarbon receptors, and role in wasting syndrome by 2,3,7,8-tetrachlorodibenzo-p-dioxin

BACKGROUND

Selenium-binding protein 1 (Selenbp1) is suggested to play a role in tumor suppression, and may be involved in the toxicity produced by dioxin, an activator of aryl hydrocarbon receptors (AhR). However, the mechanism or likelihood is largely unknown because of the limited information available about the physiological role of Selenbp1.

METHODS

To address this issue, we generated Selenbp1-null [Selenbp1 (-/-)] mice, and examined the toxic effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in this mouse model.

RESULTS

Selenbp1 (-/-) mice exhibited only a few differences from wild-type mice in their apparent phenotypes. However, a DNA microarray experiment showed that many genes including Notch1 and Cdk1, which are known to be enhanced in ovarian carcinoma, are also increased in the ovaries of Selenbp1 (-/-) mice. Based on the different responses to TCDD between C57BL/6J and DBA/2J strains of mice, the expression of Selenbp1 is suggested to be under the control of AhR. However, wasting syndrome by TCDD occurred equally in Selenbp1 (-/-) and (+/+) mice.

CONCLUSIONS

The above pieces of evidence suggest that 1) Selenbp1 suppresses the expression of tumor-promoting genes although a reduction in Selenbp1 alone is not very serious as far as the animals are concerned; and 2) Selenbp1 induction by TCDD is neither a pre-requisite for toxicity nor a protective response for combating TCDD toxicity.

GENERAL SIGNIFICANCE

Selenbp1 (-/-) mice exhibit little difference in their apparent phenotype and responsiveness to dioxin compared with the wild-type. This may be due to the compensation of Selenbp1 function by a closely-related protein, Selenbp2.

Acute toxicity of 3,3',4,4',5-pentachlorobiphenyl (PCB 126) in male Sprague-Dawley rats: effects on hepatic oxidative stress, glutathione and metals status

Although polychlorinated biphenyl (PCBs) production, and new uses for PCBs, was halted in the 1970s in the United States, PCBs continue to be used in closed systems and persist in the environment, accumulating in fatty tissues. PCBs are efficacious inducers of drug metabolism and may increase oxidative events and alter many other biochemical and morphologic parameters within cells and tissues. The goal of the present study was to evaluate the effects of a single, very low dose of PCB 126 (3,3',4,4',5-pentachlorobiphenyl), a coplanar, dioxin-like PCB congener and aryl hydrocarbon receptor (AhR) agonist, on redox status, metals homeostasis, antioxidant enzymes, and cellular morphology. To examine these parameters, male Sprague-Dawley rats were fed a purified AIN-93 basal diet containing 0.2 ppm selenium for two weeks, then administered a single i.p. injection of corn oil (5 ml/kg body weight) or 1µmol PCB 126/kg body weight (326µg/kg body weight) in corn oil. Rats were maintained on the diet for an additional two weeks before being euthanized. This dose of PCB 126 did not alter feed intake or growth, but significantly increased liver weight (42%) and hepatic microsomal cytochrome P-450 (CYP1A) enzyme activities (10-40-fold increase). Hepatic zinc, selenium, and glutathione levels were significantly decreased 15%, 30%, and 20%, respectively, by PCB 126. These changes were accompanied by a 60% decrease in selenium-dependent glutathione peroxidase activity. In contrast, hepatic copper levels were increased 40% by PCB 126. PCB 126-induced pathology was characterized by hepatocellular hypertrophy and mild steatosis in the liver and a mild decrease in cortical T-cells in the thymus. This controlled study in rats fed a purified diet shows that even a single, very low dose of PCB 126 that did not alter feed intake or growth, significantly perturbed redox and metals homeostasis and antioxidant and enzyme levels in rodent liver.

Precision-Cut Liver Slices of Salmo salar as a tool to investigate the oxidative impact of CYP1A-mediated PCB 126 and 3-methylcholanthrene metabolism

Fish isolated cell systems have long been used to predict in vivo toxicity of man-made chemicals. In present study, we tested the suitability of Precision-Cut Liver Slices (PCLS) as an alternative to these models that allows the evaluation of a global tissue response to toxicants, to investigate oxidative stress response to cytochrome P450 1A (CYP1A) induction in fish liver. PCLS of Salmo salar were exposed for 21 h to increasing doses of 3-methylcholanthrene (3-MC) and Polychlorobiphenyl 126 (PCB 126). 3-MC (25 μM) strongly induced CYP1A transcription. In dose-response analysis (25-100 μM), EROD activity was strongly increased at intermediate 3-MC concentrations. We found the counter-intuitive decline of EROD at the highest 3-MC doses to result from reversible competition with ethoxyresorufin. No increases of H(2)O(2) production, antioxidant enzymes activities or oxidative damage to lipids were found with 3-MC treatments. PCLS subjected to PCB 126 (2-200 nM) showed increased contamination levels and a parallel increased CYP1A mRNA synthesis and EROD activity. H(2)O(2) production tended to increase but no oxidative damage to lipids was found. As antioxidant enzymes activities declined at the highest PCB 126 dose, it is suggested that longer incubation periods could be required to generate oxidative stress in PCLS.

Effects of acute exposure to heavy fuel oil from the Prestige spill on a seabird

Large quantities of petroleum products are released into the marine environment as result of tanker wrecks. Such catastrophic events have a dramatic impact on marine ecosystems, affecting a broad range of species. Seabirds are placed at the uppermost trophic level of the marine food chain. Therefore, important toxic effects are expected in these organisms. The recent Prestige oil spill gave the opportunity to test this. A previous study reported that yellow-legged gulls (Larus michahellis) breeding in the oiled area (17 months after the spill) showed differences both in plasma biochemistry and in the total circulating levels of polycyclic aromatic hydrocarbons (TPAHs) in blood regard to gulls sampled in clean areas. In the present study, wild yellow-legged gulls were fed with heavy fuel oil from the Prestige oil spill (P-gulls) and compared with control gulls (C-gulls) fed only with the vehicle (vegetable oil). Consistent with the cited previous findings, gulls fed with fuel oil showed reduced glucose and inorganic phosphorus levels in plasma, as well as a trend to significantly reduced creatinine values. In addition, glucose concentration was negatively related to TPAH levels. Males but not females fed with fuel oil showed higher plasma activity of asparatate aminotransferase (AST) than controls. With regard to plasma activity of gamma-glutamyl transferase (GGT), the results were opposite to the previous study. The GGT activity increased in C-females, apparently to meet with increased liver metabolism due to egg laying demands, but not in P-females. Differences to the previous study possibly reflect different adaptive responses of these enzymes to an acute short-term exposure to heavy fuel oil. Since the yellow-legged gull belongs to a complex of species widely distributed throughout the Northern hemisphere, the results as a whole might provide a tool for future evaluations of short- and long-term effects of oil spills on seabirds. Decreased glucose and inorganic phosphorus levels in plasma are expected in both short- and long-lasting exposures to fuel oil, whereas responses of AST and GGT enzymes would depend on both the sex of individuals and the temporal pattern of exposure.

Oxidative stress induced in PCB 126-exposed northern leopard frogs, Rana pipiens

Northern leopard frogs Rana pipiens exposed to PCB 126 (3,3',4,4',5-pentachlorobiphenyl) were examined for hepatic oxidative stress. In a dose-response study, northern leopard frogs were injected intraperitoneally with either PCB 126 in corn oil (0.2, 0.7, 2.3, or 7.8 mg/kg body weight) or corn oil alone. In a time-course study, frogs received 7.8 mg/kg or corn oil alone, and were examined at 1, 2, 3, and 4 wk after dosing. Hepatic concentrations of reduced glutathione (GSH), thiobarbituric acid-reactive substances (TBARS), and total sulfhydryls (total SH), as well as activities of glutathione peroxidase (GSH-P), GSSG reductase (GSSG-R), glucose-6-phosphate dehydrogenase (G-6-PDH), and glutathione S-transferase (GSH-S-T) were measured. In the dose-response experiment, few effects were apparent 1 wk after dosing. In the time-course experiment, significant changes were observed in the 7.8-mg/kg group at 2 wk or more posttreatment. Hepatic concentrations of GSH and TBARS were higher than in corresponding controls at wk 3 and 4; the activities of GSSG-R and GSH-S-T were higher than in controls at wk 2 and 4; and the activity of G-6-PDH was increased at wk 2 and 4. These data collectively indicate that altered glutathione metabolism and oxidative stress occurred and were indicative of both toxicity and induction of protective mechanisms in frogs exposed to PCB. A similar delay in response was reported in fish and may relate to lower metabolic rate and physiological reactions in ectothermic vertebrates.

Suppression of carbonic anhydrase III mRNA level by an aryl hydrocarbon receptor ligand in primary cultured hepatocytes of rat

The effect of an aryl hydrocarbon receptor (AhR) ligand on the carbonic anhydrase III (CAIII) mRNA level was studied using primary cultured hepatocytes of rats. CAIII gene which is highly suppressible by dioxins in vivo, was also suppressible in primary cultured hepatocytes of rats by an AhR ligand, 3-methylchlanthrene (3MC). The suppression of CAIII by 3MC was observed in a dose-dependent fashion. The suppression was marked at 10 microM MC. It is likely that AhR is involved in the suppression of the CAIII gene. The transcriptional regulation region of rat CAIII gene was cloned by polymerase chain reaction on the basis of the similarity to the mouse and human CAIII genes. A 1.5 kb section upstream of rat CAIII was sequenced and the transcription initiation site of this gene was mapped to 58 bases upstream of the initiation codon. A xenobiotic responsive element (XRE)-like sequence was found at -555 to -549 bp of the transcription initiation site. The location of XRE-like element was conserved between rats and mice those CAIIIs in liver were shown as dioxins-suppressible. Although the roles of the XRE have not been clarified, these results suggest that the AhR ligands could elicit the suppressive effect on hepatic CAIII and the effect on the factors from extrahepatic tissues is not required for the suppression.

Changes in antioxidant defense systems by 2,2',5,5'-tetrachlorobiphenyl exposure in neuronal SK-N-MC cells

Polychlorinated biphenyls (PCBs) are known to alter the mammalian antioxidant defense system. To determine whether similar detoxification processes are activated in human neuronal cells, we investigated activities of antioxidant enzymes and the glutathione status (i.e., the levels of reduced and oxidized glutathione, GSH and GSSG) in human neuronal SK-N-MC cells exposed to 2,2',5,5'-tetrachlorobiphenyl (PCB 52). Upon PCB 52 treatment, time- and concentration-dependent inhibitions of cell viability were observed. PCB 52 did not affect GSH contents upon increasing the concentration up to 15 microg/ml, but significant depletions in GSH were observed at the concentrations of 20 and 25 microg/ml. PCB 52 exposure increased GSSG levels in the SK-N-MC cells, while GSH levels were decreased, and these changes naturally modified the GSSG/GSH ratios. Cytosolic glutathione S-transferase (GST) activity with 1-chloro-2,4-dinitrobenzene as substrate was enhanced by two-fold in neuronal cells after exposure to PCB 52 versus controls. In contrast, neuronal cells showed a sustained decrease in glutathione peroxidase activity with increasing concentrations of PCB 52, and a sustained decrease in Cu/Zn-superoxide dismutase (SOD) activity with increasing concentrations of PCB 52. Catalase activity was increased until 12 h after exposure to PCB 52, but was decreased 24 h after exposure. Overall, these results imply a major effect of PCB 52 on GSH status and upon the activities of antioxidant enzymes in human neuronal SK-N-MC cells, and upon the overall process of detoxification in human neuronal cells.

Effects of selected polychlorinated biphenyl (PCB) congeners on hepatic glutathione, glutathione-related enzymes, and selenium status: implications for oxidative stress

Polychlorinated biphenyls (PCBs) induce drug metabolism that may lead to the bioactivation of PCBs themselves or alternatively may lead to oxidative events within the cell. The goal of the present study was to determine the influence of congeneric PCBs, selected as substrates for or inducers of drug metabolism, upon hepatic glutathione, glutathione-related enzymes, and selenium status. Male and female Sprague-Dawley rats received two i.p. injections per week of PCB 3 (4-chlorobiphenyl), PCB 28 (2,4,4'-trichlorobiphenyl), PCB 38 (3,4,5-trichlorobiphenyl), PCB 77 (3,3',4,4'-tetrachlorobiphenyl), PCB 153 (2,2',4,4',5,5'-hexachlorobiphenyl), or both PCBs 77 and 153 (100 micromol/kg/injection) and were killed at the end of 1, 2, or 3 weeks. Whole liver homogenates, hepatic cytosol, and microsomes were prepared. Both glutathione reductase and glutathione transferase activities were increased significantly in both male and female rats receiving PCB 77, an aryl hydrocarbon receptor agonist, as well as in those receiving both PCBs 77 and 153. No significant trend was observed in the levels of hepatic total glutathione. PCB 77 treatment decreased hepatic selenium-dependent glutathione peroxidase (SeGPX) activity in both male and female rats significantly. This decrease in activity following PCB 77 treatment was accompanied by a decrease in the cytosolic selenium-dependent glutathione peroxidase gene (GSPx1) transcript, as well as a decrease in hepatic total selenium levels. These data support the concept that exposure to the coplanar PCB 77 suppresses, via gene regulatory mechanisms, the cellular antioxidant enzyme SeGPX and that this decrease involves selenium. Lower halogenated PCBs that may be bioactivated to reactive oxygen species (ROS)-producing metabolites, and higher halogenated PCBs that are not Ah receptor agonists, were inactive.

Role of oxidative stress and antioxidant defense in 3,3',4,4',5-pentachlorobiphenyl-induced toxicity and species-differential sensitivity in chicken and duck embryos

The role of oxidative stress and antioxidant defense in 3,3',4,4',5-pentachlorobiphenyl (PCB 126)-induced toxicity and species-specific sensitivity was examined in White Leghorn chicken (Gallus domesticus) and Pekin duck (Anas platyrhynchos) embryos. Eggs were injected into the air cell with 0.4-1.6 microgram PCB 126/kg egg in corn oil prior to incubation. Lipid peroxidation measured by thiobarbituric acid reactive substances (TBARS), the GSSG:GSH ratio, and glutathione peroxidase (GPox) activities were determined in liver and adipose tissue of day 19 chicken and day 26 duck embryos. In chicken embryos, PCB 126 increased mortality and the incidence of edema and liver lesions, decreased embryo size, increased eye and head malformations, and markedly reduced fat storage. In contrast, no effects on the endpoints were observed in duck embryos even at the highest dose used in chicken embryos. PCB 126 increased hepatic 7-ethoxyresorufin-O-deethylase (EROD) activity in a dose-dependent manner in chicken but not duck embryos. PCB 126 significantly increased TBARS levels in liver and to a greater degree in adipose tissue of chicken embryos, indicating that adipose tissue is a sensitive target for this compound. Increases in lipid peroxidation by PCB 126 were associated with significant decreases in GPox activity in these tissues. These biochemical changes support oxidative stress playing a role in PCB 126-induced embryo toxicity while antioxidant defenses provided protection against oxidative damage induced by this compound. Ducks, the less-sensitive species, showed higher basal levels of hepatic GPox than chickens, suggesting that this antioxidant enzyme may contribute to the differences in sensitivity to this compound between the two species.

Polychlorinated biphenyl-induced effects on metabolic enzymes, AP-1 binding, vitamin E, and oxidative stress in the rat liver

Environmental pollutants, such as polychlorinated biphenyls (PCBs), may induce drug metabolism and may be substrates for the induced metabolic enzymes. Both processes may lead to oxidative stress. The goal of this study was to determine the influence of polychlorinated biphenyls, selected as inducers and substrates of drug metabolism, on oxidative events within the liver over a 3-week time course. Male and female Sprague-Dawley rats received two ip injections per week of 4-chlorobiphenyl, 2,4,4'-trichlorobiphenyl, 3,4,5-trichlorobiphenyl, 3,3',4,4'-tetrachlorobiphenyl (PCB 77), 2,2',4,4',5,5'-hexachlorobiphenyl (PCB 153), or both PCB 77 and 153 (100 micromol/kg/injection) and were euthanized at the end of 1, 2, or 3 weeks. Hepatic cytochrome P450 1A1 (EROD) activity, DT-diaphorase activity, AP-1 DNA-binding activity, conjugated dienes, and alpha-tocopherol (vitamin E) as well as alpha-tocopheryl quinone (oxidized vitamin E) were determined. While the lower chlorinated biphenyls (at these doses and times) showed little or no effect on these oxidative stress parameters, both CYP 1A1 and DT-diaphorase activities were significantly increased in both male and female rats receiving PCB 77, a ligand for the aryl hydrocarbon receptor. In addition, the DNA-binding activity of the transcription factor AP-1 was increased in rats treated with PCB 77 or PCB 153. Within the lipid fraction there was no significant increase observed in conjugated diene concentrations, but there was a significant increase in alpha-tocopheryl quinone upon treatment with all PCBs tested. These data indicate that alpha-tocopheryl quinone may be a sensitive marker for PCB exposure and is possibly increased by a wide range of PCBs.

Suppression of carbonic anhydrase III in rat liver by a dioxin-related toxic compound, coplanar polychlorinated biphenyl, 3, 3',4,4',5-pentachlorobiphenyl

A coplanar polychlorinated biphenyl, 3,3',4,4',5-pentachlorobiphenyl (PenCB), significantly suppresses the expression of rat liver carbonic anhydrase III (CAIII), an enzyme which has recently been suggested to prevent from H(2)O(2)-inducible apoptosis. Marked changes in the CAIII levels of liver cytosol were observed in rats following doses of PenCB ranging from 0.5 to 25 mg/kg body weight and maximum suppression was observed at a dose of 10 mg/kg. Northern analysis revealed that the level of CAIII mRNA in rat liver was dramatically reduced by PenCB treatment while only weak suppression was observed in pair-fed controls. Two AU-rich elements, considered as a destabilizing signal of mRNA, were found in the 3'-untranslated region of CAIII sequenced after reverse transcription-PCR and 3'-rapid amplification of the cDNA end. Dramatic decrease of CAIII in rat liver by PenCB could account for the suppression of the defense system for oxidative stress.