Perifusion of co-cultured hepatocytes: optimization of studies on drug metabolism and cytotoxicity in vitro

The combination of co-cultivation of hepatocytes and epithelial cell lines with a newly developed perifusion system was used for in vitro studies on drug metabolism and cytotoxicity. This approach improved the viability and enhanced the induction of the biotransforming capacity of the hepatocytes. As demonstrated for the induction of 7-ethoxyresorufin O-deethylase activity by 3-methylcholanthrene or benzanthracene, co-cultured hepatocytes in the perifusion system responded more sensitively to these inducers than without perifusion, most likely owing to stable (steady-state) concentrations of the inducers under the former conditions and rapidly declining concentrations under the latter conditions. The perifusion approach rendered it possible to determine the kinetics of drug metabolism during single or sequential incubations. After induction with 3-methylcholanthrene and phenobarbital, phase I metabolism of lonazolac to the monohydroxylated product in perifused co-cultures closely (87%) approached the values reported for the in vivo production, whereas in stationary co-cultures only 52% could be reached. Likewise, cytotoxic effects could be detected more precisely in the perifused co-cultures. If cells were pretreated with 0.2 mmol/L galactosamine for 3 h, perifusion with increasing concentrations of menadione differentially killed epithelial RL-ET-14 cells and hepatocytes at low and high concentrations, respectively, while in stationary co-cultures no differential effect was observed and only the higher concentrations were cytotoxic for both cells. Prevention by incubation with S-adenosylmethionine of menadione cytotoxicity up to a menadione concentration of 250 mol/L was seen only in the perifused co-cultures, whereas in stationary cultures only a slight shift of the cytotoxic concentration exerting 50% cell damage to higher values was noted. These results demonstrate the versatile application of perifused co-cultures for studies on drug metabolism including induction of cytochrome P450-dependent enzymes and steady-state kinetics of biotransformation, as well as cytotoxic and protective effects of different drugs.Abbreviations BA benzanthracene - CC₅₀ values cytotoxic concentration exerting 50% cell damage - EROD 7-ethoxyresorufin O-deethylase - LDH lactate dehydrogenase - LON lonazolac - MC 3-methylcholanthrene - PB phenobarbital     

Preventive effects of Cassia auriculata L. flowers on brain lipid peroxidation in rats treated with streptozotocin

The effect of aqueous extract of the flowers of Cassia auriculata were examined on antioxidants and lipid peroxidation in the brain of streptozotocin diabetic rats. Significant increase in the activities of superoxide dismutase, catalase, glutathione peroxidase, glutathione-S-transferase and reduced glutathione were observed in brain on treatment with Cassia auriculata flower extract (CFEt) and glibenclamide. Both the treated groups showed significant decrease in thiobarbituric reactive substances (TBARS) and hydroperoxide formation in brain, suggesting its role in protection against lipid peroxidation induced membrane damage. Since the study of induction of the antioxidant enzymes is considered to be a reliable marker for evaluating the antiperoxidative efficacy of medicinal plant, these findings are suggestions of possible antiperoxidative role played by Cassia auriculata flower extract.     

Protective effects of ginkgo biloba against acetaminophen-induced toxicity in mice

Background: The analgesic acetaminophen (AAP) causes a potentially fatal, hepatic centrilobular necrosis when taken in overdose. It was reported that these toxic effects of AAP are due to oxidative reactions that take place during its metabolism. Objective: In this study, we aimed to investigate the possible beneficial effect of Ginkgo biloba (EGb), an antioxidant agent, against AAP toxicity in mice. Methods: Balb/c mice were injected i.p. with: (1) vehicle, control (C) group; (2) a single dose of 50 mg/kg Ginkgo biloba extract, EGb group; (3) a single dose of 900 mg/kg i.p. acetaminophen, AAP group, and (4) EGb, in a dose of 50 mg/kg after AAP injection, AAP + EGb group. Serum ALT, AST, and tumor necrosis factor-alpha (TNF-α) levels in blood and glutathione (GSH), malondialdehyde (MDA) levels, myeloperoxidase (MPO) activity, and collagen contents in liver tissues were measured. Formation of reactive oxygen species in hepatic tissue samples was monitored by using chemiluminescence (CL) technique with luminol and lusigenin probe. Tissues were also examined microscopically. Results: ALT, AST levels, and TNF-α were increased significantly (p < 0.001) after AAP treatment, and reduced with EGb. Acetaminophen caused a significant (p < 0.05–0.001) decrease in GSH levels while MDA levels and MPO activity were increased (p < 0.001) in liver tissues. These changes were reversed by EGb treatment. Furthermore, luminol and lusigenin CL levels in the AAP group increased dramatically compared to control and reduced by EGb treatment (p < 0.01). Conclusion: Our results implicate that AAP causes oxidative damage in hepatic tissues and Ginkgo biloba extract, by its antioxidant effects protects the tissues. Therefore, its therapeutic role as a “tissue injury-limiting agent” must be further elucidated in drug-induced oxidative damage.     

Interactions of betulinic acid with xenobiotic metabolizing and antioxidative enzymes in DMBA-treated Sprague Dawley female rats

Cancer chemoprevention is related to classical epidemiology and involves the use of agents that inhibit, delay, or reverse the carcinogenesis that occurs as a result of accumulation of mutations and increased proliferation. Betulinic acid is known for its cytotoxic effects against a panel of cancer cell lines. In the present study, interactions of betulinic acid (BA) with xenobiotic metabolizing enzymes including mixed function oxidases (cytochrome b5, P420, P450, NADPH cytochrome P450 reductase, and NADH cytochrome b5 reductase), phase II enzymes (GST, DT-diaphorase, γ-glutamyl transpeptidase), LDH, antioxidative enzymes (glutathione reductase, SOD, catalase, ascorbate peroxidase, and guaiacol peroxidase), and lipid peroxidation are studied alone as well as in the presence of 7,12 dimethylbenzanthracene (DMBA)—a potent carcinogen using Sprague Dawley female rats. The effect of BA on reduced glutathione content and protein content is also taken into consideration. It has been found that administration of BA decreased the level of mixed function oxidases that are involved in the conversion of carcinogen to electrophile, elevated the level of phase II enzymes which participated in the removal of electrophiles by sulfation, conjugation etc. It has been found that BA effectively removed or neutralized the reactive species by the action of phase II enzymes and such an effect was reflected from the specific activities of antioxidative enzymes which were found to be lower as compared to positive control (DMBA-treated group) and in some cases even that of untreated control. BA was also found to have a pronounced effect in protecting the animals from lipid peroxidation as evident from the reduced levels of TBARS, conjugated diene, and lipid hydroperoxide formation. This study highlights the role of BA in modulating the activities of xenobiotic and antioxidative enzymes that have putative roles in cancer initiation and proliferation.     

Effects of cypermethrin on monoamine transporters,xenobiotic metabolizing enzymes and lipid peroxidation in the rat nigrostriatal system

Abstract

Long-term exposure to cypermethrin induces the nigrostriatal dopaminergic neurodegeneration in adult rats and its pre-exposure in the critical periods of brain development enhances the susceptibility during adulthood. Monoamine transporters, xenobiotic metabolizing enzymes and oxidative stress play critical roles in the nigrostriatal dopaminergic neurodegeneration. The study was undertaken to investigate the effects of cypermethrin on DAT, VMAT 2, CYP2E1, GST Ya, GST Yc and GSTA4-4 expressions, CYP2E1 and GST activities and lipid peroxidation in the nigrostriatal system of adult rats with/without post-natal exposure to cypermethrin. Cypermethrin reduced VMAT 2 and increased CYP2E1 expressions without causing significant change in DAT. Although GSTA4-4 mRNA expression and lipid peroxidation were increased, no significant changes were observed in GST Ya and GST Yc expressions and total GST activity. The results obtained demonstrate that long-term exposure to cypermethrin modulates VMAT 2, CYP2E1, GSTA4-4 expressions and lipid peroxidation, which could contribute to the nigrostriatal dopaminergic neurodegeneration.     

Proteomic Analysis of Glutathione S-Transferases of Arabidopsis thaliana Reveals Differential Salicylic Acid-Induced Expression of the Plant-Specific Phi and Tau Classes

Plant glutathione S -transferases (GSTs) are a large group of multifunctional proteins that are induced by diverse stimuli. Using proteomic approaches we identified 20 GSTs at the protein level in Arabidopsis cell culture with a combination of GST antibody detection, LC-MS/MS analysis of 23-30 kDa proteins and glutathione-affinity chromatography. GSTs identified were from phi, tau, theta, zeta and DHAR sub-sections of the GST superfamily of 53 members. We have uncovered preliminary evidence for post-translational modifications of plant GSTs and show that phosphorylation is unlikely to be responsible. Detailed analysis of GST expression in response to treatment with 0.01-1 mM of the plant defence signal salicylic acid (SA) uncovered some interesting features. Firstly, GSTs appear to display class-specific concentration-dependent SA induction profiles highlighting differences between the large, plant specific phi and tau classes. Secondly, different members of the same class, while sharing similar SA dose responses, may display differences in terms of magnitude and timing of induction, further highlighting the breadth of GST gene regulation. Thirdly, closely related members of the same class ( GSTF6 and GSTF7 ), arising via tandem duplication, may be regulated differently in terms of basal expression levels and also magnitude of induction raising questions about the role of subfunctionalisation within this family. Our results reveal that GSTs exhibit class specific responses to SA treatment suggesting that several mechanisms are acting to induce GSTs upon SA treatment and hinting at class-specific functions for this large and important, yet still relatively elusive gene family.     

Influence of aqueous extract of Hibiscus sabdariffa L. petal on cadmium toxicity in rats

The effects of chronic exposure to cadmium (Cd) on some selected biochemical parameters, as well as the possible protective role of aqueous extracts of Hibiscus sabdariffa L petal were studied in 12-wk-old male Wistar albino rats. Exposure to Cd caused a significant increase in plasma l-alanine aminotransferases (ALT) only but with a corresponding decrease in liver l-alanine and l-aspartate aminotransferases (L-ALT, L-AST) when compared to the Cd-free control. Total superoxide dismutase activity was decreased in the liver, testis, and prostate of Cd-exposed rats, whereas malondialdehyde (MDA) concentrations were increased relative to the Cd-free control. The metal significantly increased prostatic acid phosphatase activity in the prostate, but decreased the body weight gain of the rats and organ/body weight ratio for prostate and testis compared to the Cd-free control. Pretreatment of rats with aqueous extract of H. sabdariffa resulted in significantly less hepatotoxicity than with Cd alone as measured by plasma ALT and liver ALT and AST activities. The extract also protected the rats against Cd-induced liver, prostate, and testis lipoperoxidation as evidenced by significantly reduced MDA values in these organs, as well as reduced prostatic acid phosphatase activity in the prostate, when compared to the Cd-only exposed rats. Also, when compared to the organ/body weight ratios obtained from rats exposed to Cd alone the prostate and testis were protected by the extract as shown by enhanced prostate/body weight and testis/body weight ratios of Cd- and extract-treated rats. These data suggest that H. sabdarrifa L might be protective in Cd toxicity.     

Relationship between glutathione S-transferase, catalase, oxygen consumption, lipid peroxidation and oxidative stress in eggs and larvae of Boophilus microplus (Acarina: Ixodidae)

Glutathione S-transferases (GSTs) are enzymes that act in excretion of physiologic and xenobiotic substances, protecting cells against chemical toxicity and stress. In this work, we characterized the enzymatic activity of GST in eggs and larvae of cattle tick Boophilus microplus, on different days after oviposition and eclosion. The results showed that the GST activity varied depending on the time elapsed after oviposition and eclosion. Molecules involved in mechanism of protection from oxidative stress are correlated with the increase in GST activity. The oxygen consumption kinetics showed a positive correlation with the increase in GST activity during embryogenesis. A high content of thiobarbituric acid reactive substances were observed in egg and larva extracts, indicating that ticks face high oxidative stress during embryogenesis and aging. In eggs and larvae, GST activity can be correlated to kinetic parameters of oxidative stress such as catalase and glutathione. In addition, GST activity showed strong positive correlation with lipid peroxidation, an indication that it plays a role in oxidant defences in eggs.     

Beneficial effects of selenium on some enzymes of diabetic rat heart

It is known that selenium compounds can restore some metabolic parameters in experimental diabetes. However, as there are no, clear data about their effects on the altered antioxidant defense system of the diabetic heart, we aimed to investigate whether these beneficial effects extend to the alterations of some enzyme activities, which play important roles in antioxidant defense system. Diabetes was induced by streptozotocin (50 mg/kg body weight) and rats were then treated with sodium selenite (5 μmol/kg/d) for 4 wk. Sodium selenite treatment of the diabetic rats significantly restored the altered activities of glutathione- S-transferase, glucose-6-phosphate dehydrogenase, and 6-phosphogluconate dehydrogenase, which are involved in the glutathione metabolism of the heart, but slightly but significantly decreased the high blood glucose level. In summary, the present study suggests that the beneficial effects of sodium selenite treatment appears to be the result of the restoration altered activities of the antioxidant enzymes in diabetic heart tissue.     

Inhibition of azoxymethane-induced aberrant crypt foci in rat by diphenylmethyl selenocyanate through downregulation of COX-2 and modulation of glutathione-S-transferase and lipid peroxidation

Preventive intervention of colorectal cancer has become essential, as a major portion of the population could develop the disease at some point during their lives. An inverse association between dietary intake of selenium, an important biological trace element, and colorectal cancer risk has been observed through epidemiological and experimental studies. Inhibitory activity of an organoselenocyanate, diphenylmethylseleno-cyanate, was tested on azoxymethane (15 mg/kg body wt) induced colon carcino genesis in Sprague-Dawley rats. Pretreatment and concomitant treatment, at a dose of 2 mg/kg body wt, was carried out and the effect was observed on aberrant crypt foci, the preneoplastic lesion. To investigate the mechanism of action of the compound, lipid peroxidation level and glutathione-S-transferase (GST) activities were assessed in the liver as well as in the colon. Expression of cyclooxygenase-2 protein, inducible during colon carcinogenesis, was also analyzed in the colon. Inhibitory activity of the compound was shown by the reduced incidences of aberrant crypt foci in the treated groups (by 63.3%, p=0.00044 in the pretreated group, and by 44%, p=0.0067 in the concomitant treatment group). Significant induction of GST activities and significant reduction in lipid peroxidation level both in the liver as well as in the colon and suppression of cyclooxygenase-2 expression in the colon of the treated groups suggest that the compound could exert its preventive effect at different levels of the carcinogenic process. The preventive effect was better in the pretreatment group than in the concomitant treatment group, suggesting some added protection to the target tissue resulting from preadministration of the compound.     

Identification and clarification of the role of key active site residues in bacterial glutathione S-transferase zeta/maleylpyruvate isomerase

The maleylpyruvate isomerase NagL from Ralstonia sp. strain U2, which has been structurally characterized previously, catalyzes the isomerization of maleylpyruvate to fumarylpyruvate. It belongs to the class zeta glutathione S-transferases (GSTZs), part of the cytosolic GST family (cGSTs). In this study, site-directed mutagenesis was conducted to probe the functions of 13 putative active site residues. Steady-state kinetic information for mutants in the reduced glutathione (GSH) binding site, suggested that (a) Gln64 and Asp102 interact directly with the glutamyl moiety of glutathione, (b) Gln49 and Gln64 are involved in a potential electron-sharing network that influences the ionization of the GSH thiol. The information also suggests that (c) His38, Asn108 and Arg109 interact with the GSH glycine moiety, (d) His104 has a role in the ionization of the GSH sulfur and the stabilization of the maleyl terminal carboxyl group in the reaction intermediate and (e) Arg110 influences the electron distribution in the active site and therefore the ionization of the GSH thiolate. Kinetic data for mutants altered in the substrate-binding site imply that (a) Arg8 and Arg176 are critical for maleylpyruvate orientation and enolization, and (b) Arg109 (exclusive to NagL) participates in k_cat regulation. Surprisingly, the T11A mutant had a decreased GSH K_m value, whereas little impact on maleylpyruvate kinetics was observed, suggesting that this residue plays an important role in GSH binding. An evolutionary trend in this residue appears to have developed not only in prokaryotic and eukaryotic GSTZs, but also among the wider class of cGSTs.     

The effects of diazinon on lipid peroxidation and antioxidant enzymes in rat heart and ameliorating role of vitamin E and vitamin C

Diazinon is one of the most widely used organophosphate insecticides (OPIs) in agriculture and public health programs. Reactive oxygen species (ROS) caused by OPIs may be involved in the toxicity of various pesticides. The aim of this study was to investigate how diazinon affects lipid peroxidation (LPO) and the antioxidant defense system in vivo and the possible ameliorating role of vitamins E and C. For this purpose, experiments were done to study the effects of DI on LPO and the activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT) in adult rat heart. Experimental groups were: (1) control group, (2) diazinon treated (DI) group, (3) DI+vitamins E and C-treated (DI+Vit) group. The levels of malondialdehyde (MDA) and the activities of SOD and CAT increased significantly in the DI group compared with the control group. The activity of SOD and the levels of MDA decreased significantly in the DI+Vit group compared with the DI group. The differences between the DI+Vit and control groups according to the MDA levels and the activities of both SOD and CAT were statistically significant. These results suggest that treating rats with a single dose of diazinon increases LPO and some antioxidant enzyme activities in the rat myocardium and, in addition, that single-dose treatment with a combination of vitamins E and C after the administration of diazinon can reduce LPO caused by diazinon, though this treatment was not sufficiently effective to reduce the values to those in control group.     

Interactive effects of cadmium and aluminum on growth and antioxidative enzymes in soybean

The effects of Al, Cd and pH on growth, photosynthesis, malondialdehyde (MDA) content, and some antioxidant enzyme activities of the two soybean cultivars with different Al tolerance were determined using a hydroponic culture. There were six treatments as follows: pH 6.5; pH 4.0; pH 6.5 + 1.0 μM Cd; pH 4.0 + 1.0 μM Cd; pH 4.0 + 150 μM Al; pH 4.0 + 1.0 μM Cd + 150 μM Al. The results showed that the low pH (4.0) and Al treatments caused marked reduction in the growth (root and shoot length and dry mass), chlorophyll content (SPAD value) and net photosynthetic rate. Higher malondialdehyde content, superoxide dismutase (SOD) and peroxidase (POD) activities were detected in the plants exposed to both Al and Cd than in those exposed to Al treatment alone. An expressive enhancement of SOD and POD was observed in the plants exposed to 150 μM Al in the comparison with the control plants, especially in Al-sensitive cv. Zhechun 2 which had also significantly higher Al and Cd content than Al tolerant cv. Liao-1. Cd addition increased Al content in the plants exposed to Al + Cd stress, and cv. Zhechun 2 had relatively lower Al content. The present research indicated that Al and Cd are synergistic in their effects on plant growth and some physiological traits.     

Expression of catalase and glutathione S-transferase genes in Chironomus riparius on exposure to cadmium and nonylphenol

Antioxidant enzymes play important roles in the protection against oxidative damage caused by environmental pollutants by scavenging high levels of reactive oxygen species and have been quantified as oxidative stress markers. However, combining mRNA expressions of genes coding for detoxification enzymes along with enzyme activities will be more useful biomarkers of stress. Therefore, in this study the cDNA of the catalase gene from the aquatic midge, Chironomus riparius (CrCAT) was sequenced using 454 pyrosequencing. The 2139 bp CrCAT cDNA included an open reading frame of 1503 bp encoding a putative protein of 500 amino acids with a predicted molecular mass of 56.72 kDa. There was an 18 bp 5’ and a long 618 bp 3' untranslated region with a polyadenylation signal site (AATAAA). The deduced amino acid sequence of CrCAT contained several highly conserved motifs including the proximal heme–ligand signature sequence RLFSYNDTX and the proximal active site signature FXRERIPERVVHAKGXGA. A comparative analysis showed the presence of conserved amino acid residues and all of the catalytic amino acids (His⁷⁰, Asn¹⁴³, and Tyr³⁵³) were conserved in all species. The CrCAT contained three potential glycosylation sites and a peroxisome targeting signal of ‘AKM’. The mRNA was detected using RT-PCR at all developmental stages. The time-course expression of CrCAT was measured using quantitative real-time PCR after exposure to different concentration and durations of Paraquat (PQ), cadmium chloride (Cd) and nonylphenol (NP). The expression of CrCAT was significantly up regulated on exposure to 50 and 100 mg/L PQ for 12 and 24 h. Among the different concentrations and durations of Cd tested, significantly highest level of expression for CrCAT mRNA and catalase enzyme activity was observed on exposure to 10 mg/L for 24 h. In the case of NP, the highest level of CrCAT expression was observed after exposure to 100 μg/L for 24 h. The expression profiles of three selected C. riparius glutathione S-transferase genes (CrGSTs) viz. CrGSTdelta3, CrGSTsigma4 and CrGSTepsilon1 was also studied on exposure to NP and were up or down regulated at different time points and concentrations. Significantly highest level of expression for CrGSTdelta3 was observed after 48 h and for CrGSTsigma4 and CrGSTepsilon1 after 24 h exposure to 100 μg/L of NP. The results show that CrGSTs and CrCAT could be used as potential biomarkers in C. riparius for aquatic ecotoxicological studies.     

Effect of cadmium on lipid peroxidation and activities of antioxidant enzymes in growing pigs

Malondialdehyde (MDA), glutathione (GSH) content, total antioxidant capacity (T-AOC) levels, superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and glutathione transferase (GST) activities were studied in serum, liver, and kidney of growing pigs after graded doses of cadmium administration in diets. One hundred ninety-two barrows (Duroc x Landrace x Yorkshire), with similar initial body weight 27.67±1.33 kg, were randomly allotted into 4 different treatments with 3 replications (16 pigs per replication). The treatments received the same basal diet added with 0, 0.5, 5.0, and 10.0 mg/kg cadmium (as CdCl₂), respectively. The results showed pigs treated with 10 mg/kg cadmium significantly decreased average daily gain (ADG) (p<0.05) and increased feed/gain ratio (F/G) (p<0.05) compared to the control. In this treatment, the contents of MDA increased significantly (p<0.05), GSH concentrations, T-AOC levels, and the activities of SOD, GSH-PX, and GST decreased significantly (p<0.05). The results indicate 10 mg/kg cadmium could decrease pig antioxidant capacity after extended exposure and cadmium-induced increase lipid peroxidation might not be only the result of the possibility of lower level of GSH but could also be as a result of direct action of cadmium on peroxidation reaction.     

Effect of thymoquinone and Nigella sativa seeds oil on lipid peroxidation level during global cerebral ischemia-reperfusion injury in rat hippocampus

It has been previously reported that Nigella sativa oil (NSO) and thymoquinone (TQ), active constituent of N. sativa seeds oil, may prevent oxidative injury in various models. Therefore, we considered the possible effect of TQ and NSO on lipid peroxidation level following cerebral ischemia-reperfusion injury (IRI) in rat hippocampus. Male NMRI rats were divided into nine groups, namely, sham, control, ischemia and ischemia treated with NSO or TQ. TQ (2.5, 5 and 10 mg/kg), NSO (0.048, 0.192 and 0.384 mg/kg), phenytoin (50 mg/kg, as positive control) and saline (10 ml/kg, as negative control) were injected intraperitoneally immediately after reperfusion and the administration was continued every 24h for 72 h after induction of ischemia. The transient global cerebral ischemia was induced using four-vessel-occlusion method for 20 min. Lipid peroxidation level in hippocampus portion was measured as malondialdehyde (MDA) based on its reaction with thiobarbituric acid (TBA) following ischemic insult. The transient global cerebral ischemia induced a significant increase in TBA reactive substances (TBARS) level (p<0.001), in comparison with sham-operated animal. Pretreatment with TQ and NSO were resulted a significant decrease in MDA level as compared with ischemic group (66.9+/-1.5 vs. 297+/-2.5 nmol/g tissue for TQ, 10 mg/kg; p<0.001 and 153.5+/-1.3 nmol/g tissue for NSO, 0.384 mg/kg; p<0.001). Using a reversed-phase HPLC system, the amount of TQ in NSO was also quantified and was 0.58% w/w. These results suggest that TQ and NSO may have protective effects on lipid peroxidation process during IRI in rat hippocampus.     

珙桐幼苗生理生化指标对重金属铅、镉胁迫的响应

铅和镉在土壤中表现出很强的毒性,严重危害植物的生长发育.该研究着眼于中国特有濒危珍稀植物珙桐,探究盆栽实验条件下其抗氧化酶活性、丙二醛(MDA)以及游离脯氨酸、可溶性蛋白对不同浓度重金属铅、镉胁迫的响应规律.结果表明:(1)不同浓度铅处理下,珙桐幼苗MDA浓度均显著高于对照组,而镉胁迫条件下除10 mg·kg-1浓度外...     

Region specific increase in the antioxidant enzymes and lipid peroxidation products in the brain of rats exposed to lead

The objective of this study is to determine the effect of lead (pb) on antioxidant enzymes and lipid peroxidation products in different regions of rat brain. Wistar male rats were treated with lead acetate (500 ppm) through drinking water for a period of 8 weeks. Control animals were maintained on sodium acetate. Treated and control rats were sacrificed at intervals of 1st, 4th and 8th week and the whole brains were dissected on ice into four regions namely the cerebellum, the hippocampus, the frontal cortex and the brain stem. Antioxidant enzymes namely catalase and superoxide dismutase in all the four regions of brain were determined. In addition, lipid peroxidation products were also estimated. The results indicated a gradual increase in the activity of antioxidant enzymes in different regions of the brain and this response was time-dependent. However, the increase was more in the cerebellum and the hippocampus compared to other regions of the brain. The lipid peroxidation products also showed a similar trend suggesting increased effect of lead in these two regions of the brain. The data indicated a region-specific oxidative stress in the brain exposed to lead.     

Effect of cadmium on growth and the activity of H2O2 scavenging enzymes in Colocassia esculentum

Cadmium is a non-essential heavy metal that can be harmful even at low concentrations to plants. Colocassia esculentum (Araceae) plant was studied to know its tolerance capability to cadmium. Colocassia esculentum plants grown in pots containing different concentrations of cadmium (Cd) were analyzed for dry matter, fresh weight and total metal content. Cadmium depressed dry matter production of the plant up to 33%. Plant accumulated larger portion of the heavy metal in the roots followed by stem and leaf. Chlorophyll content of the plant declined on treatment with heavy metal while the activity of antioxidative enzymes catalase and peroxidase increased. Colocassia esculentum also showed an increase in total protein along with greater A₂₅₀/A₂₈₀ value suggesting an increase in metal protein complexes. Cadmium elicited anatomical changes in the root of C. esculentum. These changes under heavy metal stress indicate the adaptive properties of this plant species.     

Glycerol and dihydroxyacetone metabolizing enzymes in fission yeasts of the genus Schizosaccharomyces

The only species of fission yeasts capable of growing on glycerol or dihydroxyacetone were Schizosaccharomyces pombe and S. malidevorans. When growing on glycerol or grown on glucose until it was exhausted, these species contained glycerol:NAD⁺ 2-oxidoreductase and dihydroxyacetone kinase but no glycerol kinase, consistent with utilization of glycerol via dihydroxyacetone. When grown to exhaustion of glucose, S. octosporus, S. slooffiae and S. japonicus contained dihydroxyacetone kinase but no glycerol:NAD⁺ 2-oxidoreductase or glycerol kinase. Prior to exhaustion of glucose in the medium, all species contained dihydroxyacetone kinase, all species except S. japonicus contained glycerol:NADP⁺ 2-oxidoreductase, and only S. pombe and S. malidevorans contained glycerol:NAD⁺ 2-oxidoreductase. Possible roles for the glycerol:NAD⁺ 2-oxidoreductase, glycerol:NADP⁺ 2-oxidoreductase and dihydroxyacetone kinase in metabolism of glycerol and dihydroxyacetone are discussed.Non-standard abbreviations DHA dihydroxyacetone - DHAK dihydroxyacetone kinase - DHAP dihydroxyacetone phosphate - GK glycerol kinase - G2DH-NAD glycerol - NAD⁺ 2-oxidoreductase - G2DH-NADP glycerol - NADP⁺ 2-oxidoreductase - MEA malt extract agar - YEP yeast extract phosphate medium