Metallothionein-overexpressing neonatal mouse cardiomyocytes are resistant to H2O2 toxicity

To study cellular and molecular events of cardiac protection by metallothionein (MT) from oxidative injury, a primary neonatal cardiomyocyte culture was established from a specific cardiac MT-overexpressing transgenic mouse model. Ventricular cardiomyocytes were isolated from 1- to 3-day-old neonatal mice and cultured in an Eagle's minimum essential medium supplemented with 20% fetal bovine serum under an atmosphere of 5% CO2-95% air at 37 degreesC. Forty-eight hours after plating was completed, the purity of such cultures was 95% myocytes, assessed by an immunocytochemical assay. Over 80% of the cardiomyocytes beat spontaneously on the first day of culture and synchronously in a confluent monolayer after the sixth day of culture. Cellular MT concentrations in the transgenic cardiomyocytes before culturing and on the sixth day postculturing were about seven- and twofold higher than nontransgenic controls, respectively. However, there were no significant differences in cell morphology, glutathione content, and antioxidant enzymatic activities between these two types of cardiomyocytes. When these cells were challenged by H2O2, the transgenic cardiomyocytes displayed a significant resistance to the toxic effect of this oxidant, as measured by cell viability, lactate dehydrogenase leakage, and morphological alterations. In addition, the transgenic cells were highly protected from H2O2-induced lipid peroxidation. These observations demonstrate that MT protects the cultured cardiomyocytes from H2O2 toxicity by preventing its interaction with macromolecules such as lipids, and this cultured primary neonatal mouse cardiomyocyte system provides a valuable tool to directly study cellular and molecular events of MT in cardiac protection against oxidative injury.

Surface ultrastructure of Metagonimus miyatai metacercariae and adults

A scanning electron microscopic study was performed to observe surface ultrastructures of excysted metacercariae and adults of Metagonimus miyatai. Metacercariae were collected from the scale of the pale chub (Zacco platypus), and adult flukes were harvested 1-4 weeks after infection to rats. In excysted metacercariae, the oral sucker was devoid of tegumental spines and had type I and type II sensory papillae. Anteriorly to the ventral sucker, spines were dense and digitated into 5-7 points, whereas near the posterior end of the body spines were sparse and digitated into 2-3 points. In one-week adults, 7 type II sensory papillae were arranged around the lip of the oral sucker, and at inner side of the lip one pair of small and two pairs of large type 1 sensory papillae were seen on each side. The distribution of tegumental spines was similar to that of metacercariae, but they were more differentiated with 9-11 pointed tips. In two- to four-week old adults, the surface ultrastructure was nearly the same as in one-week old adults, however, sperms were frequently seen entering into the Laurer's canal. Conclusively, the surface ultrastructure of M. miyatai was generally similar to that of M. yokogawai, however, differentiation of tegumental spines and distribution of sensory papillae around the oral sucker were different between the two species, which may be of taxonomic significance.

Inhibition of buthionine sulfoximine-enhanced doxorubicin toxicity in metallothionein overexpressing transgenic mouse heart

Cardiotoxicity and acquired drug resistance of tumor cells have been two impediments for the clinical use of doxorubicin (DOX). Trials are ongoing using buthionine sulfoximine (BSO) to deplete glutathione (GSH) content in tumors, whose elevation was found to contribute to the acquired drug resistance. However, BSO also decreases GSH content in the heart, enhancing DOX cardiotoxicity. Recent studies have shown that metallothionein (MT) is an important factor in cardiac protection against DOX. Our study was undertaken to determine whether MT can compensate for the loss of protection from GSH depletion in the heart. Transgenic mice with cardiac MT concentrations about 20-fold higher than normal, and nontransgenic controls were treated with BSO by i.p. injection at 5 mmol/kg, two times with a 12-hr interval, before treatment with DOX at a single dose of 15 mg/kg, lasting for 4 days. Cardiac GSH was depleted by 60% in both transgenic and non-transgenic mice. DOXinduced cardiotoxicity, as measured by blood levels of creatine kinase and malondialdehyde concentrations in the heart, was dramatically increased in the BSO-treated nontransgenic mice. This increase was completely inhibited in the BSO-treated transgenic mice. These results demonstrate that cardiac MT overexpressing transgenic mice are resistant to BSO-enhanced DOX cardiotoxicity. Selective modulations of decreasing DOX resistance in tumors by BSO and of increasing cardioprotection by MT induction may provide an alternative approach to improved DOX chemotherapeutic efficacy.

Induction of antioxidants by adriamycin in mouse heart

Cardiac oxidative injury is a major limiting factor for clinical application of Adriamycin (ADR) in cancer chemotherapy. ADR depresses some antioxidant systems, thereby further enhancing the cardiotoxicity. Previous studies have shown that ADR inhibits the overall synthesis of DNA, RNA, and protein. It was presumed that the depressed antioxidant activity resulted from the inhibited gene expression. However, there were no experimental data to demonstrate the relationship between the change in antioxidant activities and that in their gene expression. Therefore, the present study was undertaken to examine the effects of ADR on the activities and mRNA abundances of antioxidants in mouse heart. FVB mice (7 weeks old) were treated with ADR (15 mg/kg) by a single i.p. injection. Four days after the treatment, cardiac antioxidant activities and mRNA abundances were measured. The results showed that ADR increased the levels of mRNAs for Cu,Zn-superoxide dismutase (Cu,Zn-SOD), catalase, glutathione peroxidase (GSHpx), and gamma-glutamylcysteine synthetase (gamma-GCS). On the other hand, ADR increased the activities of catalase and gamma-GCS, and slightly decreased total glutathione concentrations in the heart. Cu,Zn-superoxide dismutase, Mn-superoxide dismutase, and glutathione peroxidase activities were not changed significantly. In addition, ADR increased both mRNA and protein levels of metallothionein in the heart. The data demonstrate that up-regulation of antioxidant gene expression occurred in response to ADR in the mouse heart, although the antioxidant activities were not all increased.

Comparison of relaxations evoked by photoactivation of NO-containing compounds and nitrergic nerve stimulation in 5-hydroxytryptamine- and potassium-contracted rat gastric fundus

1. The aim of the present study was to further investigate our earlier proposal of liberation of nitric oxide (NO) by photoactivation of molecules containing NO or NO2, which in turn relaxes gastric smooth muscle, and to determine whether presynaptic- and/or postsynaptic NO-mediated relaxation is affected differently by the degree of membrane depolarization in rat gastric fundus smooth muscle. 2. During contraction of rat gastric fundus with 5-hydroxytryptamine (5-HT, 10 microM), low (K+, 25 mM) and high potassium (K+, 65.4 mM), relaxation responses to nitrergic nerve stimulation, photo-activation of caged NO compounds (streptozotocin [STZ], N omega-nitro-L-arginine-methylacetate [L-NAME], N omega-nitro-D-arginine-methylacetate [D-NAME]), and sodium nitroprusside (SNP) were compared. 3. Nitrergic nerve (presynaptic) stimulation and photoactivation (postsynaptic) of all caged NO compounds produced rapid, transient and reversible relaxation of 5-HT and low-K(+)-contracted tissues. However, when contractions were induced by high K+, the relaxation induced by nerve stimulation was abolished, whereas relaxations induced by photoactivated NO compounds were significantly (P < 0.01) reduced. 4. The relaxation induced by sodium nitroprusside (SNP), but not papaverine, was also diminished in high-K(+)-contracted tissues. The magnitude of photoactivated NO-induced relaxation was related to the amount of NO release, light intensity and concentration of compounds. 5. The evidence that photoactivated NO-induced relaxation is mediated by cGMP comes from the observation that zaprinast, but not forskolin, potentiated the relaxation. 6. It is concluded that rat gastric smooth muscle relaxes to photoactivation of NO or NO2-carrying molecules via NO, and it appears that degree of membrane depolarization may be a critical factor in dissociating the response to presynaptic- and postsynaptic NO-mediated relaxation in this muscle.

Distribution and accumulation of storage protein-1 in ovary of Hyphantria cunea Drury

Storage protein-1 (SP-1) is a major storage protein found in the hemolymph and fat body of Hyphantria cunea. In this study, the uptake and accumulation of SP-1 into the ovary of H. cunea was investigated using biochemical and immunocytochemical methods. SP-1 in H. cunea has a high methionine content (4.6%) but is not female-specific, like other high methionine storage proteins. In the 6-day-old pupal ovary, SP-1 was detectable in trace amounts but accumulated to significant levels toward the end of the pupal stage. After adult emergence, SP-1 rapidly decreased in the ovarian follicles and remained low in the egg. This suggest that SP-1 is either extensively modified or degraded, causing a loss of its antigenic property in the ovary after adult emergence. During vitellogenesis, SP-1 is present in the hemolymph and penetrates through the tunica propria to reach the perioocytic space. From there, SP-1 is incorporated into yolk bodies. These results clearly show that SP-1 is taken up by the developing oocyte. Its disappearance suggests that SP-1 might be an amino acid reservoir for providing precursors for egg formation, in contrast to yolk proteins, which are utilized during postembryonic development.

Repression of hypoxia-reoxygenation injury in the catalase-overexpressing heart of transgenic mice

Hypoxia-reoxygenation injury results at least in part from reactive oxygen free radicals. Catalase is a major enzyme involved in detoxification of hydrogen peroxide. The activity of catalase per gram of tissue in the heart is very low, being only about 2% that of liver in rodents and humans, which may be responsible for the high sensitivity of the heart to hypoxia-reoxygenation injury. The present study was undertaken to determine whether elevation of catalase specifically in the heart of transgenic mice could provide protection against hypoxia-reoxygenation injury. Transgenic mice with elevated cardiac catalase 60-fold higher than normal were selected, and the effects of catalase elevation on hypoxia-reoxygenation induced functional and morphological changes in isolated atria were determined. Catalase overexpression ameliorated reductions in contractile force and heart rate caused by hypoxia-reoxygenation, and eliminated reoxygenation-induced arrhythmia. The catalase-overexpressing transgenic atria were also highly resistant to hypoxia-reoxygenation-induced morphological alterations, as examined by electron microscopy. Use of cardiac catalase-overexpressing transgenic mice thus demonstrates that hydrogen peroxide is involved in hypoxia-reoxygenation cardiotoxicity, and that this mouse model provides a useful tool for study of free radical mechanism in the heart damage.

Cardiac troponin T is a sensitive, specific biomarker of cardiac injury in laboratory animals

A reliable serum assay that can discriminate between cardiac and skeletal muscle injury is not available for diagnostic use in laboratory animals. We tested and supported the hypotheses that serum cardiac troponin T (cTnT) was widely applicable in laboratory animals as a biomarker of cardiac injury arising from various causes; that it increased in proportion to severity of cardiac injury; and that it was more cardiospecific than creatine kinase (CK) or lactate dehydrogenase (LD) isozyme activities. In canine and rat models of myocardial infarction, cTnT concentration increased 1,000- to 10,000-fold and was highly correlated with infarct size within 3 h of injury. Serum CK and LD isozymes were substantially less effective biomarkers and, in contrast to cTnT, were ineffective markers in the presence of moderate skeletal muscle injury, with resulting serum CK activity > 5,000 U/L. Using these animal models, and mouse and ferret models, we also showed cTnT to be an effective biomarker in doxorubicin cardiotoxicosis, traumatic injury, ischemia, and cardiac puncture. Reference range serum concentrations for all species were at the detection limit of the assay, except those for mice, in which they were slightly increased, possibly because mice were used to generate assay monoclonal antibodies. We conclude that cTnT is a powerful biomarker in laboratory animals for the sensitive and specific detection of cardiac injury arising from various causes.

Overexpression of metallothionein in the heart of transgenic mice suppresses doxorubicin cardiotoxicity

Metallothionein (MT) may provide protection against doxorubicin-induced heart damage. To test this hypothesis, a heart-specific promoter was used to drive the expression of human MT-IIa gene in transgenic mice. Four healthy transgenic mouse lines were produced. Cardiac MT was constitutively overexpressed from 10- to 130-fold higher than normal. The MT concentration was not altered in liver, kidneys, lungs, or skeletal muscles. Other antioxidant components including glutathione, glutathione peroxidase, glutathione reductase, catalase, and superoxide dismutase were not altered in the MT-overexpressing heart. Mice (7-wk-old) from transgenic lines expressing MT activity 10- or 130-fold higher than normal and from nontransgenic controls were treated intraperitoneally with doxorubicin at a single dose of 20 mg/kg, and were killed on the 4th day after treatment. As compared to normal controls, transgenic mice exhibited a significant resistance to in vivo doxorubicin-induced cardiac morphological changes, and the increase in serum creatine phosphokinase activity. Atria isolated from transgenic mice and treated with doxorubicin in tissue bath was also more resistant to functional damage induced by this drug. The results provide direct evidence for the role of MT in cardioprotection against doxorubicin toxicity.

Catalase-overexpressing transgenic mouse heart is resistant to ischemia-reperfusion injury

Myocardial ischemia-reperfusion injury is at least partially mediated by oxygen-derived free radicals. Catalase is a major enzyme involved in the detoxification of hydrogen peroxide. The activity of catalase in the heart is very low, which may be a factor responsible for the high sensitivity of the heart to ischemia-reperfusion injury. The present study was undertaken to determine whether elevation of catalase specifically in the heart of transgenic mice can provide protection against ischemia-reperfusion injury. Hearts isolated from transgenic mice in which catalase in the heart was elevated approximately 60-fold higher than that in nontransgenic heart and from the non-transgenic littermates were subjected to 50 min of warm (37 degrees C) zero-flow ischemia followed by 90 min reflow. Compared with nontransgenic controls, transgenic hearts showed significantly improved recovery of contractile force (75 vs. 25% at the end of 90 min reperfusion, P < 0.01). Efflux of creatine kinase was reduced by approximately 50%, and the zone of myocardial infarction as demarcated by triphenyltetrazolium at the end of reperfusion was reduced by approximately 40% in transgenic hearts compared with nontransgenic controls. These findings support the view that hydrogen peroxide is an important cause of ischemia-reperfusion damage and suggest that protection may be provided by elevation of catalase activity.

Increased cystine uptake capability associated with malignant progression of Nb2 lymphoma cells

Analysis of rat, pre-T cell 'Nb2 lymphoma' sublines, manifesting different degrees of malignant progression, can indicate phenotypic changes potentially useful as therapeutic targets. In this study, the prolactin (cytokine)-dependent Nb2-11 and autonomous Nb2-SFJCD1 sublines were compared for in vitro thiol growth requirements. Whereas Nb2-11 culture growth depended on 2-mercaptoethanol (2-ME; 33-100 microM), Nb2-SFJCD1 cells were 2-ME-independent. This difference stemmed from differential uptake of exogenous L-cystine, critically required for proliferation. Uptake of 35S-L-cystine (10 microCi/ml; 40 microM) showed Nb2-11 cells had low cystine uptake capability; 2-ME enhanced cystine uptake to growth-sustaining levels. Nb2-SFJCD1 cells did not require 2-ME due to intrinsic, 11-fold higher cystine uptake via the x(c)- cystine/glutamate transport system. In absence of 2-ME, monosodium glutamate abrogated Nb2-SFJCD1 proliferation by specifically inhibiting cystine uptake (85% at 10 mM). Elevated glutathione (GSH) levels were not essential for growth of either line as shown with L-buthionine-(S,R)-sulfoximine (0.1-4 mM) treatment. The cyst(e)ine requirement therefore did not primarily involve maintenance of normal GSH levels, reported critical for T lymphocyte replication. These and other results suggest increased cystine uptake capability constitutes another potential step in progression of T cell cancers which is not coupled to cytokine autonomy or metastatic ability development. The x(c)- transport system apparently provides a novel target for T cell cancer therapy. Its inhibition would suppress cystine uptake by certain progressed cells, and also interfere with cystine uptake, and subsequent cysteine release, by eg macrophages, thought to have a role in cysteine delivery to lymphoid cells.

Decreased sensitivity to adriamycin in cadmium-resistant human lung carcinoma A549 cells

Cross-resistance presents an obstacle in cancer chemotherapy. Cadmium is a potential carcinogen whose exposure has been shown in epidemiological and laboratory experiments to cause lung cancer. Cadmium also induces various forms of resistance in human lung carcinoma cells. This resistance may be shared by antineoplastic agents, which should be a concern for chemotherapy of cadmium-induced lung cancer. In the present study, two subpopulations of human lung carcinoma A549 cells with a different magnitude of resistance to cadmium toxicity were shown to have a parallel resistance to the cytotoxic action of Adriamycin (ADR), an important anticancer drug. Several factors were examined to investigate the mechanism(s) for the cross-resistance, including cellular metallothionein and glutathione (GSH) concentrations, glutathione S-transferase activity, mdr1 expression, and antioxidant enzyme activities including superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase. Only cellular GSH content was elevated consistently in the cadmium/ADR-resistant cells relative to the cadmium/ADR-sensitive cells. Treatment with buthionine sulfoximine, a specific inhibitor of GSH synthesis sensitized both cell lines to ADR only when the cellular GSH levels were depleted to about 5% of control. This BSO treatment, however, did not affect cell viability. Further study revealed that the cadmium/ADR-resistant cells have a greater capacity in recovery of cellular GSH content following BSO treatment. The results demonstrate that cross-resistance to ADR exists in cadmium-resistant human lung carcinoma A549 cells, and enhanced GSH synthesis capacity, rather than elevated levels of cellular GSH, may be related to this resistance.

A case of carpal tunnel syndrome due to dialysis-related amyloidosis in a patient undergoing long-term hemodialysis

Carpal tunnel syndrome (CTS) is characterized by burning pain, numbness and tingling sensation in the thumb, index and middle fingers and the lateral half of the palm and progressive atrophy of the thenar muscles by compression of the median nerve within the carpal tunnel due to a variety of etiologic factors. Surgical intervention usually successfully relieves symptoms of CTS. Recently CTS has been regarded as one of the major clinical manifestations of dialysis-related amyloidosis due to beta 2-microglobulin deposition and recognized with increasing frequency in patients undergoing long-term hemodialysis. We report a case of carpal tunnel syndrome due to dialysis-related amyloidosis in patients undergoing long-term hemodialysis, confirmed by electromyography and biopsy in transverse carpal ligament and median nerve.

Attenuated central pressor response to nitric oxide synthesis inhibition in chronic renal failure rats

OBJECTIVES

Central and peripheral roles of nitric oxide (NO) in blood pressure regulation have been suggested. The present study was aimed at examining if the role of NO in blood pressure regulation is altered in chronic renal failure.

METHODS

Blood pressure responses to acute inhibition of NO were examined in 5/6 nephrectomized rats. Three weeks after the renal ablation, under thiopental (50 mg/kg, i.p.) anesthesia, an intracerebroventricular cannula was placed in the left lateral ventricle and the femoral vein was cannulated to serve as an infusion route. The arterial blood pressure was measured in the right femoral artery. NG-nito-L-arginine methyl ester (L-NAME) was infused (100 microgram/kg per min for 60 min either intracerebroventricularly or intravenously.

RESULTS

Chronic renal failure rats showed a significantly higher arterial pressure than the control rats (147 +/- 14 mmHg vs. 122 +/- 13 mmHg). Intracerebroventricular L-NAME did not affect the arterial pressure in chronic renal failure rats (0.5 +/- 4 mmHg increase from the basal), while it significantly increased the arterial pressure in normal rats (22 +/- 3 mmHg increases from the basal). Intravenous L-NAME increased the arterial pressure, the magnitude of which did not differ between the normal and chronic renal failure rats (24 +/- 3 vs. 16 +/- 3 mmHg increases from the basal).

CONCLUSION

These results indicate that the central role of NO in the regulation of blood pressure is altered in chronic renal failure.

Tuberous sclerosis and polycystic kidney disease. A case report

Polycystic kidney disease is a relatively uncommon finding of tuberous sclerosis. Furthermore, the renal insufficiency by the severe polycystic kidney disease is extremely rare in tuberous sclerosis. The patient was a 27-year-old man, complaining of generalized seizure and progressive abdominal distension. His clinical features were chracterized by epilepsy, mental retardation, skin abnormalities including adenoma sebaceum, shagreen patch and ash-leaf spots. Abdominal computed tomography demonstrated numerous variable sized cysts throughout both kidneys. Clinical and laboratory findings revealed chronic renal failure due to severe polycystic kidneys. On reviewing the literature, the present case is the first report of polycystic kidneys associated with tuberous sclerosis in Korea.

Suppression of doxorubicin cardiotoxicity by overexpression of catalase in the heart of transgenic mice

Weak antioxidant capacity, particularly low catalase activity in the heart, may be a factor responsible for the high sensitivity of this organ to doxorubicin-induced oxidative damage. To test this hypothesis, a heart-specific promoter was used to drive the expression of murine catalase cDNA in transgenic mice. Fifteen healthy transgenic mouse lines were produced. Cardiac catalase activity was constitutively overexpressed in both atrium and ventricule, ranging from 2- to 630-fold higher than normal. This enzyme activity was not altered in liver, kidneys, lungs, and skeletal muscles. Other antioxidant components, including glutathione, glutathione peroxidase, glutathione reductase, metallothionein, and superoxide dismutase, were not altered in the catalase-overexpressing heart. Mice (7 weeks old) from several transgenic lines and from nontransgenic controls were treated intraperitoneally with doxorubicin at a single dose of 20 mg/kg and sacrificed on the 4th day after treatment. As compared to normal controls, transgenic lines expressing catalase activity 60- or 100-fold higher than normal exhibited a significant resistance to doxorubicin-induced cardiac lipid peroxidation, elevation of serum creatine phosphokinase, and functional changes in the isolated atrium. Interestingly, 200-fold or greater elevation of catalase activity did not provide protection. The results provide direct evidence for the role of catalase in doxorubicin cardiotoxic responses.

Suppression of plasma estradiol and progesterone concentrations by buthionine sulfoximine in female rats

Glutathione (GSH) is an important factor involved in the resistance of tumor cells to anticancer agents. Buthionine sulfoximine (BSO), a specific inhibitor of GSH synthesis, effectively decreases cellular GSH concentrations both in vitro and in vivo. Depletion of GSH by BSO sensitizes a variety of cancer cells to chemotherapeutic agents. Therefore, BSO has been on clinical trial as an anticancer adjuvant. For this purpose, it is important to understand the effect of BSO treatment not only on the sensitivity of tumor cells to anticancer agents, but also on the metabolism and function of normal tissues. The present study was undertaken to determine the effect of BSO treatment on GSH concentrations in the blood, liver, and ovary, and changes in concentrations of ovarian hormones and other important components in plasma. Female Sprague-Dawley rats, 90 days of age, were treated with 2.0 mmol/kg BSO in saline by intraperitoneal injection, twice daily for 7 days. This treatment depressed GSH concentrations in the blood, liver and ovary by 95, 75, and 85%, respectively. Several blood components were measured. These included red blood cells, hemoglobin, ceruloplasmin, hematocrit, mean corpuscular volume and hemoglobin concentration, alkaline phosphatase, urea nitrogen, creatine and creatinine, glucose, cholesterol, triglycerides, triiodothyronine (T3), thyroxine (T4), and hormones including estradiol, progesterone, and prolactin. BSO treatment significantly (P < 0.05) elevated and lowered plasma concentrations of ceruloplasmin and urea nitrogen, respectively, More importantly, plasma concentrations of estradiol and progesterone were decreased markedly (P < 0.05) in the BSO-treated animals. The hormonal results suggest that investigations on the role of BSO-induced GSH depletion in the treatment of malignancies both with and without hormone dependence in women should be undertaken.

Alterations of the glutathione redox cycle status in fumonisin B1-treated pig kidney cells

Fumonisin B1 (FB1) causes equine leukoencephalomalacia, porcine pulmonary edema, and liver tumors and chronic nephritis in rats. To investigate mechanisms by which FB1 induces toxicity, effects of FB1 on cellular glutathione (GSH) redox status and GSH depletion on FB1 toxicity in pig kidney (LLC-PK1) cells were studied. Treatment of LLC-PK1 cells with 50 microM FB1 for 24 hours significantly decreased cellular GSH contents from 56 +/- 3.2 to 42.7 +/- 4.4 nmol/mg protein (p < 0.05) and increased the activities of glutathione reductase (GR) from 25.7 +/- 2.4 to 35.7 +/- 5.0 mumol NADPH/mg protein (p < 0.05). The activities of glutathione peroxidase (GSHpx), catalase, and Cu,Zn-superoxide dismutase (SOD) were not changed by this treatment. Treatment of LLC-PK1 cells for 12 hours with 0.1 mM buthionine sulfoximine (BSO), a selective inhibitor of the enzyme gamma-glutamylcysteine synthetase that catalyzes the rate-limiting reaction in de novo GSH synthesis, decreased cellular GSH levels to about 20% of that found in the control cells. The cells pretreated with 0.1 mM BSO for 12 hours were significantly sensitized to the FB1 cytotoxicity as determined by a long-term survival assay (p < 0.05). The results demonstrate that FB1 changes GSH redox cycle status in LLC-PK1 cells, and GSH may play a role in cytoprotection against FB1 toxicity.

Cadmium resistance in A549 cells correlates with elevated glutathione content but not antioxidant enzymatic activities

Glutathione has been implicated to function in cytoprotection against cadmium toxicity. The mechanism by which glutathione plays this role has not been well understood. Because glutathione is an important antioxidant and several studies have shown that cadmium induces oxidative stress, this study was undertaken to determine whether development of cadmium resistance is linked to enhanced antioxidant activities. A cadmium-resistant subpopulation of human lung carcinoma A549 cells, which was developed by repeatedly exposing the cells to step-wise increased cadmium concentrations, was compared to a cadmium-sensitive one. The acquired cadmium resistance resulted from neither decreased cadmium uptake nor enhanced cellular metallothionein synthesis. Glutathione content, however, was markedly elevated in the cadmium-resistant cells. In contrast, the activities of the glutathione redox cycle related enzymes, glutathione peroxidase and reductase, were unchanged. Two other antioxidant enzymes, superoxide dismutase and catalase, were also not altered. The results suggest that the development of cadmium resistance in A549 cells unlikely results from enhanced antioxidant enzyme activities, although it is associated with elevated cellular glutathione levels. In addition, measurement of the mRNA and DNA levels for gamma-glutamylcysteine synthetase, the rate-limiting enzyme for glutathione biosynthesis, revealed that enhanced expression of the enzyme but not gene amplification is likely responsible for the elevation of cellular glutathione levels.

Expression of gamma-glutamylcysteine synthetase in the liver of copper-deficient rats

Copper deficiency in rats increases hepatic glutathione concentration. The present study was undertaken to determine the biochemical and molecular basis for the glutathione elevation. Weanling Sprague-Dawley rats were fed a purified diet deficient in copper (0.4 micrograms/g diet) or one containing adequate copper (5.7 micrograms/g diet) for 4 weeks. Hepatic glutathione concentration, the activity of the rate-limiting enzyme in glutathione biosynthesis, gamma-glutamylcysteine synthetase (gamma-GCS) and the relative amount of mRNA for the enzyme were determined. Hepatic glutathione concentration in copper-deficient rats was significantly elevated (6.6 vs 5.6 mumol/g). The activity of hepatic gamma-GCS was 1.6 times higher in the copper-deficient than in the copper-adequate rats (58.0 vs 35.9 nmol NADH/min.mg protein). The steady-state amount of mRNA for gamma-GCS was increased 5-fold in the copper-deficient rat liver. The findings demonstrate that the elevated hepatic glutathione concentration in copper-deficient rats results from upregulation of gamma-GCS activity. This study provides further understanding of changes in hepatic glutathione metabolism induced by copper deficiency.

A case of adult-onset Bartter's syndrome

Bartter's Syndrome is characterized by renal potassium wasting with hypokalemia, metabolic alkalosis, increased renin-angiotensin-aldosterone system, normal blood pressure, resistance to the pressor effects of angiotensin II and juxtaglomerular cell hyperplasia. Most of the cases have been noted in the pediatric age group and adult-onset cases are very rare. We report a case of adult-onset Bartter's syndrome.

Glutathione stimulates A549 cell proliferation in glutamine-deficient culture: the effect of glutamate supplementation

Extracellular glutathione (GSH) is degraded by an external cell-surface enzyme, gamma-glutamyltranspeptidase (gamma-GT). The products are transported into cells to participate in important cellular processes. In the present study, we tested the hypothesis that extracellular GSH is a source of glutamic acid for cells that express gamma-GT. Under a glutamine-deficient culture condition, the extracellular GSH-supplemented glutamic acid would enhance intracellular glutamine synthesis, thereby stimulating cell proliferation. Human lung carcinoma A549 cells were cultured in glutamine-deficient Dulbecco's modified Eagle medium, and they did not proliferate unless glutamine was supplemented. Extracellular GSH, however, provoked a partial proliferation. The GSH effect correlated with a high level of gamma-GT activity and an increased intracellular level of glutamic acid. A constituent amino acid of GSH, glutamic acid but not cysteine, produced the same growth-stimulatory effect as GSH. Furthermore, neither oxothiazolidine-4-carboxylate (OTC), a cellular cysteine-delivery compound, nor cysteinylglycine, a dipeptide released from the gamma-GT reaction, stimulated cell proliferation. Moreover, buthionine sulfoximine (BSO), a selective inhibitor of gamma-glutamylcysteine synthetase, enhanced the GSH growth stimulatory effect, suggesting that increased cellular GSH synthesis does not correlate with cell growth stimulation. The results obtained demonstrated that glutamine is required for A549 cell proliferation and exogenous GSH partially substitutes for the growth stimulatory action of glutamine. It also suggests that the glutamic acid rather than the cysteine released from the GSH is responsible for the cell proliferation.

Weak antioxidant defenses make the heart a target for damage in copper-deficient rats

Copper deficiency causes more salient pathologic changes in the heart than in the liver of rats. Although oxidative stress has been implicated in copper deficiency-induced pathogenesis, little is known about the selective toxicity to the heart. Therefore, we examined the relationship between the severity of copper deficiency-induced oxidative damage and the capacity of antioxidant defense in heart and liver to investigate a possible mechanism for the selective cardiotoxicity. Weanling rats were fed a purified diet deficient in copper (0.4 microgram/g diet) or one containing adequate copper (6.0 microgram/g diet) for 4 weeks. Copper deficiency induced a 2-fold increase in lipid peroxidation in the heart (thiobarbituric assay) but did not alter peroxidation in the liver. The antioxidant enzymatic activities of superoxide dismutase, catalase, and glutathione peroxidase were, respectively, 3-, 50- and 1.5-fold lower in the heart than in the liver, although these enzymatic activities were depressed in both organs by copper deficiency. In addition, the activity of glutathione reductase was 4 times lower in the heart than in the liver. The data suggest that a weak antioxidant defense system in the heart is responsible for the relatively high degree of oxidative damage in copper-deficient hearts.

Impairement of endothelium-dependent relaxation in chronic two-kidney, one clip hypertensive rats

OBJECTIVES

Hypertension is commonly associated with an endothelial dysfunction that may contribute to the rise in blood pressure. Little information has been available so far on the role of endothelium-derived nitric oxide(EDNO) in renin-dependent, 2-kidney, 1 clip(2KIC) hypertension. The present study was aimed to determine a role for EDNO in the development and maintenance of 2KIC hypertension.

METHODS

The effects of blocking synthesis or supplementation with precursor of EDNO on the development of hypertension were determined in 2KIC rats. Vascular responses to acetylcholine, nitroprusside, atrial natriuretic peptide and nifedipine were examined in 7- and 12-week hypertensive 2KIC rats.

RESULTS

NG-nitro-L-arginine-methyl ester caused a sustained increase of blood pressure in normal rats, while it was only partially associated with a more pronounced increase of blood pressure in the developmental phase of hypertension in 2KIC rats. In 7-week and 12-week hypertensive rats, phenylephrine-induced contraction of the isolated thoracic aortic rings was more sensitive compared with control. Their acetylcholine-induced relaxation was attenuated while the responses to nitroprusside or atrial natriuretic peptide were unaltered. Although their blood pressure did not differ between 7-week and 12-week hypertensive groups, the attenuation in the acetylcholine-induced relaxation was more prominent in the latter with a longer duration of hypertension. Indomethacin did not affect the attenuated relaxation to acetylcholine. The relaxation response to nifedipine was more pronounced in 2KIC rats.

CONCLUSION

These results indicate that ENDO has little influence of the 2KIC hypertension, at least during its developmental phase, which is associated with an activated reninangiotensin system. The chronic stage of 2KIC hypertension, however, is associated with an endothelial dysfunction which may contribute to the enhanced vasoconstriction and sustained high blood pressure.

Exogenous glutathione attenuates the antiproliferative effect of buthionine sulfoximine

Buthionine sulfoximine (BSO) inhibits proliferation of human lung carcinoma A549 cells in a manner that does not correlate with intracellular glutathione (GSH) depletion, nor does it reflect overt toxic effects of BSO. However, BSO inhibits uptake by A549 cells of cystine, which is an essential amino acid for cell growth in culture. Thus, it is hypothesized that inhibition of cellular cystine uptake is, or is partially, responsible for the antiproliferative effect of BSO. It has been shown that the gamma-glutamyl amino acid transport system plays a role in cystine transport across cell membranes. This transport system requires extracellular GSH for its operation. BSO, by inhibiting intracellular GSH synthesis, would reduce GSH export and decrease extracellular GSH levels. Therefore, the present study was undertaken to examine the effect of exogenously added GSH on BSO inhibition of cellular cystine uptake and its relationship to the antagonistic effect of GSH on BSO antiproliferation. A549 cells were treated with 10 mM BSO and exogenous GSH was added to these BSO-treated cultures. Effects of exogenous GSH on BSO antiproliferation and cellular GSH depletion were determined simultaneously as a function of time. The effect of GSH on BSO inhibition of cystine accumulation was measured using [35S]cystine. The results obtained demonstrate that exogenously added GSH partially overcame BSO antiproliferation. The GSH antagonistic effect did not correlate with repletion of intracellular GSH, but it did correlate with recovery of BSO-inhibited cystine accumulation. Exogenous GSH also enhanced proliferation of non-BSO treated cells at concentrations below 1.0 mM. The results of this study suggest that BSO inhibition of cystine uptake may represent one mechanism by which BSO exerts its antiproliferative effect. The antagonistic effect of exogenous GSH on BSO antiproliferation may result from recovery of BSO-inhibited cystine uptake, although other mechanisms responsible for the GSH antagonistic effect may also exist.