Age-related changes of antioxidant enzyme activities, glutathione status and lipid peroxidation in rat erythrocytes after heat stress

The aim of this study was to determine whether exposure to heat stress would lead to oxidative stress and whether this effect varied with different exposure periods. We kept 1-, 6- and 12-month-old male Wistar rats at an ambient temperature of either 22 degrees C or 40 degrees C for 3 and 7 days and measured glucose-6-phosphate dehydrogenase (G-6-PD), Cu,Zn-superoxide dismutase (Cu,Zn-SOD), catalase (CAT), selenium-dependent glutathione peroxidase (Se-GSH-Px) and glutathione-S-transferase (GST) activities and levels of thiobarbituric acid-reactive substances (TBARS), reduced glutathione (GSH) and oxidized glutathione (GSSG) in erythrocytes and determined GSH/GSSG ratio, total glutathione and the redox index. G-6-PD and CAT activities were found to be significantly increased in 1- and 6-month-old rats after 3 and 7 days of heat stress, but G-6-PD activities decreased in 12-month-old rats. Cu, Zn-SOD activity decreased in 1-month-old rats after heat stress, whereas it increased in 6- and 12-month-old rats. GST activity increased in all groups. GSH and total GSH levels and GSH/GSSG ratios decreased in 1- and 6-month-old rats but they increased in 12-month-old rats after heat stress. GSSG levels increased in 1- and 6-month-old rats but decreased in 12-month-old rats after heat stress. TBARS levels increased in all groups. Seven days of stress is more effective in altering enzyme activities and levels of GSH, GSSG and TBARS. When the effects of both heat stress and aging were examined together, it was interesting to note that they mostly influenced G-6-PD activity.     

Ameliorative action of melatonin on oxidative damage induced by atrazine toxicity in rat erythrocytes

Excessive generation of reactive oxygen species (ROS) can induce oxidative damage to vital cellular molecules and structures including DNA, lipids, proteins, and membranes. Recently, melatonin has attracted attention because of their free radical scavenging and antioxidant properties. The aim of this study was to evaluate the possible protective role of melatonin against atrazine-induced oxidative stress in rat erythrocytes in vivo. Adult male albino rats of Wistar strain were randomly divided into four groups. Control group received isotonic saline; melatonin (10 mg/kg bw/day) group; atrazine (300 mg/kg of bw/day) group; atrazine + melatonin group. Oral administration of atrazine and melatonin was given daily for 21 days. Oxidative stress was assessed by determining the glutathione (GSH) and malondialdehyde (MDA) level, and alteration in antioxidant enzymes such as superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT), glutathione-S-transferase (GST), and glucose-6-phosphate dehydrogenase (G-6-PD) in the erythrocytes of normal and experimental animals. A significant increase in the MDA levels and decrease in the GSH was observed in the atrazine treated animals (P < 0.05). Also, significant increase in the activities of SOD, CAT, GPx, and GST were observed in atrazine treated group compared to controls (P < 0.05). Moreover, significant decrease in protein, total lipids, cholesterol, and phospholipid content in erythrocyte membrane were demonstrated in atrazine treated rats. Administration of atrazine significantly inhibits the activities of G-6-PD and membrane ATPases such as Na(+)/K(+)-ATPase, Mg(2+)-ATPase, and Ca(2+)-ATPase (P < 0.05). Scanning electron microscopic (SEM) examination of erythrocytes revealed morphological alterations in the erythrocytes of atrazine treated rats. Furthermore, supplementation of melatonin significantly modulates the atrazine-induced changes in LPO level, total lipids, total ATPases, GSH, and antioxidant enzymes in erythrocytes. In conclusion, the increase in oxidative stress markers and the concomitant alterations in antioxidant defense system indicate the role of oxidative stress in erythrocytes of atrazine-induced damage. Moreover, melatonin shows a protective role against atrazine-induced oxidative damage in rat erythrocytes.     

Effect of Aloe vera gel extract on antioxidant enzymes and azoxymethane-induced oxidative stress in rats

The present work was undertaken with a view to study the effect of oral feeding of 2% Aloe vera gel extract (AGE) for 30 days on azoxymethane (AOM)-induced oxidative stress in rats. It was observed that AOM administration resulted in a significant increase in malondialdehyde and conjugated dienes, with reduction in hepatic glutathione (GSH), vitamin A and uric acid contents. AOM-induced reduction in hepatic GSH and uric acid was brought back to normal by AGE. There was a significant raise in hepatic catalase, superoxide dismutase and glucose-6-phosphate dehydrogenase (G-6-PD) activities as a result of feeding of the extract. Ingestion of the extract effected reduction in AOM-induced colonic GSH-peroxidase, G-6-PD and glutathione S-transferase and femur bone marrow micronuclei formation. Hence, it is suggested that Aloe vera gel extract possess the ability to reduce AOM- induced oxidative stress and toxicity in liver.     

Erythrocyte antioxidant enzymes in toxicological evaluation of commonly used organophosphate pesticides

Erythrocytes are excellent models for the study of interactions of xenobiotics with biomembranes. Present work is designed to study the in vitro effects of some organophosphates (ethion, chlorpyrifos, dimethoate and monocrotophos) on rat erythrocytes. Treatment of erythrocytes with organophosphates resulted in decreased erythrocyte glucose-6-phosphate dehydrogenase (G-6-PD) activity, whereas activities of glutathione-s-transferase (GST) and glutathione reductase (GR) were increased. Reduced Glutathione (GSH) content of RBCs was decreased after treatment with the pesticides. Increased activities of GST and GR were due to induction of natural defense mechanism of erythrocytes against the toxicity of the pesticides. Membrane bound enzymes like acetylcholinesterase (AChE), Na(+)-K(+)-ATPase and Ca(2+)-ATPase were also inhibited. Altered activities of these enzymes along with decreased GSH content indicate increased oxidative stress in erythrocytes after treatment with organophosphates.     

The effect of antimembrane testicular antibodies on Na+, K(+)-ATPase activity in the testicles of rats of different ages]

The effect of large and small doses of rabbit antibodies specific to plasma membranes of the rat testicle cells has been studied in the experiments on Wistar rats of three age groups (preadolescent--aged 20 days, puberal--aged 5-7 months and old--aged 24-26 months). It is stated that incubation of plasma membranes by IgG fraction isolated from antimembrane testicular serum (IgG-ATCSm) in a large dose (43 g of protein G per 125 g of protein of membrane fraction) caused statistically reliable inhibition of Na+, K(+)-ATPase activity in the membranes of testicle cells of puberal and old rats. Preadolescent rats exhibit only a tendency to decrease the activity of this enzyme. Incubation of plasma membranes of testicle cells in rats of different age by small doses of IgG-ATCSm (0.43 g of protein G per 125 g of membrane protein) induced a statistically reliable increase of Na+, K(+)-ATPase activity in puberal and old animals and its slight increase in preadolescent rats. The IgG fraction isolated from normal rabbit serum (IgG-NRS) exerted a less pronounced effect on Na+, K(+)-ATPase activity parallel with retention of a tendency to a decrease of activity under the influence of large doses of the drug and to an increase with introduction of small doses.     

Influences of different stress models on the antioxidant status and lipid peroxidation in rat erythrocytes

The aim of this study was to investigate the influences of different stress models on the antioxidant status and lipid peroxidation (LPO) in erythrocytes of rats. Swiss-Albino female rats (3 months old) were used in this study. Rats were randomly divided into the following four groups; control group (C), cold stress group (CS), immobilization stress group (IS) and cold+immobilization stress group (CS+IS). Control group was kept in an animal laboratory (22 ±2°C). Rats in CS group were placed in cold room (5°C) for 15 min/day for 15 days. Rats in IS group were immobilized for 180 min/day for 15 days. Rats in CS+IS group were exposed to both cold and immobilization stresses for 15 days. At the end of experimental periods, the activities of glucose-6-phosphate dehydrogenase (G-6-PD), Cu,Zn-superoxide dismutase (Cu,Zn-SOD), catalase (CAT) and glutathione peroxidase (GSH-Px), and concentration of reduced glutathione (GSH) were measured. LPO was determined by measuring the contents of thiobarbituric acid-reactive substances (TBARS). Cu,Zn-SOD activity and TBARS concentration were increased after cold and immobilization stresses, but CAT and GSH-Px activities and GSH levels were decreased. Immobilization stress decreased the activity of G-6-PD. The activities of G-6-PD, CAT and GSH-Px, and the level of GSH were lower in CS+IS group than in the control group. Cu,Zn-SOD activity and TBARS levels were increased in CS+IS group when compared with the control group. From these findings, three stress models are thought to cause oxidative stress.     

Influences of Different Stress Models on the Antioxidant Status and Lipid Peroxidation in Rat Erythrocytes

The aim of this study was to investigate the influences of different stress models on the antioxidant status and lipid peroxidation (LPO) in erythrocytes of rats. Swiss-Albino female rats (3 months old) were used in this study. Rats were randomly divided into the following four groups; control group (C), cold stress group (CS), immobilization stress group (IS) and cold+immobilization stress group (CS+IS). Control group was kept in an animal laboratory (22 &#45 2°C). Rats in CS group were placed in cold room (5°C) for 15 min/day for 15 days. Rats in IS group were immobilized for 180 min/day for 15 days. Rats in CS+IS group were exposed to both cold and immobilization stresses for 15 days. At the end of experimental periods, the activities of glucose-6-phosphate dehydrogenase (G-6-PD), Cu,Zn-superoxide dismutase (Cu,Zn-SOD), catalase (CAT) and glutathione peroxidase (GSH-Px), and concentration of reduced glutathione (GSH) were measured. LPO was determined by measuring the contents of thiobarbituric acid-reactive substances (TBARS). Cu,Zn-SOD activity and TBARS concentration were increased after cold and immobilization stresses, but CAT and GSH-Px activities and GSH levels were decreased. Immobilization stress decreased the activity of G-6-PD. The activities of G-6-PD, CAT and GSH-Px, and the level of GSH were lower in CS+IS group than in the control group. Cu,Zn-SOD activity and TBARS levels were increased in CS+IS group when compared with the control group. From these findings, three stress models are thought to cause oxidative stress.     

Adenosine triphosphatase activity in sciatic nerve tissue of streptozocin-induced diabetic rats with and without high dietary sucrose: effect of aldose reductase inhibitors.

The ability of aldose reductase inhibitors to prevent the decline in neural Na+,K(+)-ATPase activity in diabetic rats has not been confirmed by all laboratories. In this study, the efficacy of two structurally different aldose reductase inhibitors was evaluated under different experimental conditions. Na+,K(+)-ATPase activity was measured in sciatic nerves from streptozocin-induced diabetic rats fed normal rodent chow or a chow supplemented with 68% sucrose. Nerve homogenates from chow-fed rats were prepared with a Dounce tissue grinder, whereas homogenates from the sucrose-fed rats were prepared with an Ultra-Turrax disperser. In the chow-fed rats, 4 weeks of untreated diabetes resulted in an increase in neural sorbitol and fructose, a decrease in myoinositol, and a 54% decline in Na+,K(+)-ATPase activity. Sorbinil administration (20 mg/kg/day) completely prevented the rise in sorbitol and fructose and the depletion of myoinositol, but did not prevent the decline in Na+,K(+)-ATPase activity. In diabetic rats fed the sucrose diet for 4, 6, and 8 weeks, the neural sorbitol and fructose levels were elevated, the myoinositol concentration declined, and the Na+,K(+)-ATPase activity was 26 to 28% below the control. Prevention or intervention treatment with sorbinil (20 mg/kg/day) or tolrestat (50 mg/kg/day) for 4 to 6 weeks prevented the alterations in sorbitol, fructose, and myoinositol, and also prevented the decline in Na+,K(+)-ATPase activity. In conclusion, prevention and intervention therapy with aldose reductase inhibitors prevented the decline in Na+,K(+)-ATPase in sciatic nerves of sucrose-fed streptozocin-diabetic rats that were homogenized with an Ultra-Turrax disperser, but not in sciatic nerves from streptozocin-diabetic rats fed normal rodent chow that were homogenized with a Dounce tissue grinder. These findings indicate that the assessment of aldose reductase inhibitor efficacy is dramatically affected by the type of nerve preparation assayed and/or the diet.     

Characterization of the inhibition effect induced by nickel on glucose-6-phosphate dehydrogenase and glutathione reductase

Kinetic characterization of the inhibition effect of nickel on glucose-6-phosphate dehydrogenase (EC 1.1.1.49) (G-6-PD) and glutathione reductase (GR; EC 1.6.4.2) from Saccharomyces cerevisiae was made. The effect of nickel on G-6-PD activity is consistent with a mixed-type inhibition pattern, with a competitive character, since the inequality ki,int greater than ki,slope shows an inverse relation between varied substrate concentrations and fractional inhibition. An inhibition effect of nickel on GR activity, when NADPH is the varied substrate, is also consistent with a mixed-type inhibition pattern. However, pure competitive inhibition is found on GR reaction when oxidized glutathione is the varied substrate. This investigation shows the highest sensibility of GR before the inhibitory effect of nickel, in agreement with the experimental values of inhibition constants found in this study, where constants related to the GR system are lower than the ones of the G-6-PD system.     

Rat lung antioxidant enzyme activities and their specific proteins during hyperoxia

The hyperoxia-induced increases in the activity of lung glucose-6-phosphate dehydrogenase (G-6-P) and glutathione reductase (GR) after exposure of rats to greater than 97% O2 for 6 days were accompanied by equivalent increases in the amount of the respective immunoreactive proteins. Hyperoxia also increased lung glutathione (GSH) + oxidized glutathione (GSSG) content and the magnitude of this hyperoxic response of increased GSH + GSSG, G-6-P, and GR (maximal 1.3- to 1.8-fold) declined as a function of age during the first 3 wk of life. Fetal rat lung explants cultured 4 days in 95% O2 showed increased G-6-P and GR activity and increased levels of the specific proteins 1.5-fold those of explants at 2 days of culture. We conclude that the hyperoxic response of increased rat lung G-6-P and GR activity in vivo and in vitro involves not just alteration of enzyme activity but also specific increases in the proteins catalyzing the reactions.     

Effects of phenylhydrazine or recombinant human erythropoietin on deformability and activity of dehydrogenase glucose-6-phosphate and acetylcholinesterase in Wistar rats blood enriched in reticulocytes

Deformability and activity of the enzymes: acetylcholinesterase (AChE) and dehydrogenase glucose-6-phosphate (G-6-PD), were assayed for RBC enriched in immature reticulocytes. Reticulocytosis was evoked by administration of two different drugs: recombinant human erythropoietin (rHuEPO) and phenylhydrazine (PHZ) to two groups of Wistar rats. After treatment with the former compound, a group of animals exhibited 17.33% reticulocytes in blood whereas a group of rats treated with the latter drug reached 57.66% of these cells in blood. A marked decrease in RBC deformability was found in both groups of animals. AChE did not significantly change activity neither in PHZ-treated nor in rHuEPO-treated rats, whereas G-6-PD activity was significantly decreased in the PHZ-treated group.     

Impact of chromium on lipoperoxidative processes and subsequent operation of the glutathione cycle in rat renal system.

Oral administration of K2Cr2O7 to male albino rats at an acute dose of 1500 mg/kg body wt/day for 3 days brought about sharp decrease in the activities of glucose-6-phosphate dehydrogenase and glutathione reductase of kidney epithelial cells. The scavenging system of kidney epithelium is also affected as evident by the highly significant fall in the activities of glutathione peroxidase, superoxide dismutase and catalase which ultimately leads to the increase in lipid peroxidation value in kidney cortical homogenate. However, glutathione-s-transferase activity in cytosol and glutathione and total thiol content in cortical homogenate were not altered. Chronic oral administration of K2Cr2O7 (300 mg/kg body wt/day) for 30 days to rats lead to elevation in the activities of glutathione peroxidase, glutathione reductase, glutathione-s-transferase, superoxide dismutase and catalase with no change in glucose-6-phosphate dehydrogenase activity in epithelial cells. This might lead to the increase in glutathione and total thiol status and decrease in lipid peroxidation value in whole homogenate system.     

Effect of partial hepatectomy on the invertor mechanism of regulation of the Na+,K+-ATPase activity in hepatocytes of rats of various ages]

Age peculiarities of partial hepatectomy effect on the hepatocytes plasma membrane Na+, K(+)-ATPase activity and its insulin-induced stimulation has been studied. It has been shown that partial hepatectomy does not change basal Na+, K(+)-ATPase activity in adult rats. In old partial hepatectomised rats Na+, K(+)-ATPase activity is slightly higher than in control old rats, although this increase is not statistically significant. At the same time, partial hepatectomy acts differently on the insulin-induced Na+, K(+)-ATPase activation in adult and old rats. Insulin activates Na+, K(+)-ATPase at the same extent both in control and partial hepatectomized adult animals. In old hepatectomized rats, but not in old control animals, insulin stimulates Na+, K(+)-ATPase activity as well as. Thus hepatectomy "rejuvenates" old hepatocytes and results in recovery of invertor mechanism of Na+, K(+)-ATPase activation.     

Regulation and rate of the hexose monophosphate shunt in Rana ridibunda erythrocytes

1. Resting rates of Rana ridibunda erythrocyte glucose consumption and 14CO2 production from 1-14C-glucose were found to be significantly lower than the respective values in human erythrocytes. 2. In the presence of 1-14C-glucose Methylene Blue stimulated 14CO2 production 7-fold, while in the presence of 6-14C-glucose Methylene Blue stimulated 14CO2 production 1.2-fold. 3. The Km of G-6-PD for G-6-P and NADP were 29 and 12 microM, respectively while the Km of 6-PGD for 6-PG and NADP were 83 and 32 microM, respectively. The Ki of G-6-PD and 6-PGD for NADPH were 80 and 12 microM, respectively. 4. Excess amounts of NADP resulted in a significant decrease of 14CO2 production from 1-14C-glucose in total haemolysates. 5. ATP, ADP and fructose diphosphate inhibited both G-6-PD and 6-PGD, the latter being more sensitive than G-6-PD to their inhibitory effect, 2,3-DPG and reduced and oxidized glutathione showed a marked inhibitory effect on 6-PGD, while the phosphorylated trioses inhibited only G-6-PD. 6. Physiological concentrations of oxidized glutathione decreased the inhibition exercised by NADPH on G-6-PD. 7. The possible role of the two dehydrogenases in the regulation of the HMS is discussed.     

Studies of enzymes connected with erythrocyte glutathione metabolism in a rural tropical population

Summary The activities of the erythrocyte enzymes hexokinase (HK), glucose-6-phosphate dehydrogenase (G-6-PD), 6-phosphogluconate dehydrogenase (6-PGD), glutathione reductase (GR) and glutathione peroxidase (GSH-PO) were determined in a group of 12 Europeans and in a group of 103 male Thai subjects in northern Thailand. In the Thai group there were 16 subjects with G-6-PD deficiency and 28 subjects with abnormally low levels of GR activity. A comparison of the enzyme activities in the different subgroups indicated that HK and 6-PGD are not influenced by G-6-PD deficiency whereas GR and GSH-PO activities are significantly higher in G-6-PD deficient subjects. In the group with low GR activity G-6-PD and GSH-PO showed a tendency to an elevation of activity when compared with the normal control group. Significant positive correlations exist between G-6-PD and 6-PGD in the normal group and between GR and GSH-PO in the G-6-PD deficient group. A negative correlation between GR and GSH-PO was present in the group with low GR activities. A study of the families of subjects with low activity of GR did not yield evidence for the existence of a deficiency polymorphism.

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Zusammenfassung Bei 12 Europäern und einer Gruppe von 103 männlichen thailändischen Versuchspersonen wurden die Aktivitäten der Erythrocytenenzyme Hexokinase (HK), Glucose-6-Phosphat-Dehydrogenase (G-6-PD), 6-Phosphogluconat-Dehydrogenase (6-PGD), Glutathion-Reduktase (GR) und Glutathion-Peroxidase (GSH-PO) bestimmt. In der Thai-Gruppe waren 16 Personen mit G-6-PD-Mangel und 28 Personen mit abnormal niedrigen Aktivitäten der GR. Ein Vergleich der Enzymaktivitäten in verschiedenen Untergruppen zeigte, daß HK und 6-PGD durch G-6-PD-Mangel nicht beeinflußt werden. Im Gegensatz hierzu sind die Aktivitäten der GR und der GSH-PO bei G-6-PD-Mangel signifikant erhöht. In der Gruppe mit erniedrigter GR-Aktivität bestand eine Tendenz zu erhöhten Werten für G-6-PD und GSH-PO. Die Korrelationen zwischen G-6-PD und 6-PGD in der Gruppe mit normaler G-6-PD und die zwischen GR und GSH-PO in der Gruppe mit G-6-PD-Mangel waren signifikant. In der Gruppe mit erniedrigter GR-Aktivität fand sich eine negative Korrelation zwischen GR und GSH-PO. Die Untersuchungen in Familien von Personen mit niedriger GR-Aktivität ergaben keinen sicheren Hinweis auf das Vorliegen eines GR-Mangel-Polymorphismus in der untersuchten Bevölkerung.

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Established and supported by Stiftung Volkswagenwerk, Hannover.     

Glutathione system adaptation to acute stress in the heart of rats during different regimes of hypoxia training

The intensity of lipid peroxidation (LPO), reduced and oxidized glutathione (GSH and GSSG) contents, glutathione reductase, glutathione peroxidase, glutathione-S-transferase, glucose-6-phosphate dehydrogenase (G-6-PDH), and NADP-isocitrate dehydrogenase (NADP-IDH) activities were studied in the heart of male rats exposed to two modes of intermittent hypoxic training (IHT): I-breathing in normobaric chamber with 7% O2 gas mixture for 5 min with 15 min normoxic intervals 4 times daily during 3 weeks; II-breathing by 12% O2 gas mixture in the same manner). After adaptation to hypoxia, the rats were subjected to 6h-immobilization stress. It has been shown that stress action after IHT (regime I) caused the increase in LPO and the shift of GSH/GSSG to disulfides. A disbalance in antioxidative defense system was determined by the decrease in glutatione peroxidase, G-6-PDH activities, and GSH content. The support of glutathione reductase activity under stress in this group with simultaneous decrease of enzyme activity in the pentose phosphate pathway was realized through the participation of NADP-IDH. Hypoxic training in regime II induced LPO decrease in the heart tissue after stress. The increase in the heart GSH content, optimal balance of glutathione-related enzymes in this group evidences for the dependence of adaptation effects on the vigor of hypoxic exposition. Our results suggest the active participation of glutathione system in the formation of adaptation reactions under the extreme factor influences through the action on intracellular red/ox potential as well as effectiveness of antioxidant defense.     

Effect of mercury, lead and acetylphenylhydrazine (APHZ) on erythrocyte and bone marrow glucose-6-phosphate dehydrogenase (E.C. 1.1.1.49). an electrophoretic study

Male and female rats of Wistar strain have been injected with 0.2% HgCl2, 203HgCl2, PbNO3 and 2% APHZ, in the volume of 0.5 ml saline for 4 days. Subbands of G-6-PD enzyme from erythrocytes and bone marrow cells, were separated by disc polyacrylamide electrophoresis. Four subbands of the enzyme resulted electrophoretic separation. In erythrocytes increase of activity of fraction I. and decrease of fraction II were observed, while in bone marrow opposite reaction was visible. In both tissue following administration of Hg and Pb, fractions III and IV disappeared. In the place of disappeared bands increased radioactivity of 203Hg was detected.     

Human platelet glucose-6-phosphate dehydrogenase. Total purification, kinetic studies and relationship with enzyme from other blood cells.

Human platelet G-6-PD has been highly purified, to homogeneity, and its kinetic, electrophoretic and immunological characteristics have been studied. Platelet G-6-PD differs from erythrocyte or leukocyte enzymes by an increased Michaelis constant for G-6-P and a slow activity at the acid pHs. By electrofocusing only a main active band (band a) of platelet G-6-PD was found. The incubation at 37 degrees C in the presence of NADP+ and dithiothreitol normalize Km-G-6-P of platelet G-6-PD; the incubation with boiled and ultrafiltered leukemic granulocyte extracts led to an anodisation of G-6-PD active forms, a decrease of the molecular specific activity and a further increase of Km-G-6-P; these last modifications are the same as those undergone by G-6-PD incubated in crude extracts of normal or leukemic granulocytes.     

Hymenolepis diminuta: Activity of anti-oxidant enzymes in different parts of rat gastrointestinal tract

The aim of this study was to assess the intensity of oxidative stress by measuring levels of lipid peroxidation products in the duodenum, jejunum and colon of rats infected with Hymenolepis diminuta and evaluate the effectiveness of protection against oxidative stress by measuring the glutathione levels and activity of anti-oxidant enzymes: superoxide dismutase, catalase, glutathione reductase and glutathione peroxidase.In exposed rats we observed a significant increase of lipid peroxidation products in the duodenum and jejunum. A significant decrease in superoxide dismutase activity in all the examined parts of the digestive tract was observed. Additionally, rats from 16 to 40 days post H. diminuta infection (dpi) had a decreased catalase activity in the colon, while at 60 dpi it increased. The glutathione peroxidase activity increased significantly in the colon at 60 dpi. The increase in glutathione reductase activity was observed in the colon in rats 60 dpi. There was a lack of changes in the levels of glutathione in the duodenum and a significant increase in its concentration in the jejunum and colon from 40 to 60 dpi and from 16 to 40 dpi, respectively. In this study we observed altered activity of anti-oxidant enzymes and glutathione level in experimental hymenolepidosis, as a consequence of oxidative stress. It may indicate a decrease in the efficiency of intestinal protection against oxidative stress induced by the presence of the parasite. The imbalance between oxidant and anti-oxidant processes may play a major role in pathology associated with hymenolepidosis.     

Evidence contrary to the protein error hypothesis for in vitro senescence.

A strain of diploid fibroblasts, obtained from the skin of a male infant, was cultured in vitro and cells were tested throughout their lifespan for the appearance of altered glucose-6-phosphate dehydrogenase (G-6-PD) detected either by thermostability studies or by immunotitration. No significant difference was found in the proportion of thermolabile enzyme in 31 young cultures (4.8 +/- 1%, S.E.), in comparison with that in 19 old cultures (4.9 +/- 1%, S.E.). Old cultures had ceased active cell division (49-60 doublings); DNA replication, measured by [3H]thymidine uptake over a period of 24 hours, was limited to less than 5% of these cells. Young cells (5-22 doublings) had a [3H]thymidine labeling index of 75-85%. Titration of G-6-PD activity in extracts of young and old cells with neutralizing antibody directes specifically against G-6-PD failed to detect an increment of enzymatically defective G-6-PD in old cells. The thermostability studies were capable of detecting altered G-6-PD in skin fibroblasts from a female heterozygous for a thermolabile mutant of G-6-PD, and in fibroblasts treated with a proline analogue, azetidine carboxylic acid. The immunotitration technique was also capable of detecting catalytically altered G-6-PD from the thermolabile mutant and G-6-PD inactivated with N-ethylameimide. These findings argue against a protein error catastrophe as the cause of in vitro clonal senescence.