Gamma-glutamyl-transferase is associated with incident hip fractures in women and men ≥ 50 years: a large population-based cohort study

The association of serum gamma-glutamyl-transferase (GGT) with hip fracture risk has not been examined in women and men ≥ 50 years. We show that elevated GGT was associated with increased hip fracture risk, particularly in men. GGT could be a candidate serum marker of long-term hip fracture risk in the elderly.

INTRODUCTION

We herein examined a possible relation between serum levels of GGT and hip fracture risk in women and men aged ≥ 50 years, which has not been investigated before.

METHODS

In this population-based prospective cohort study, approximately 41,000 women and nearly 33,000 men ≥ 50 years participating in a medical prevention program 1985-2005 in western Austria were followed up for the occurrence of osteoporotic hip fractures during 2003-2013. ICD-10 based discharge diagnoses for hip fracture included S72.0, S72.1, and S72.2 available from all regional hospitals. GGT-related hip fracture risk was ascertained at each participant´s first and last examination during the prevention program. In a subset of 5445 participants, alcohol consumption could be included as a covariate.

RESULTS

In men, hip fracture risk rose significantly by 75% and 86% for every tenfold increase of GGT measured at the first and last examination, respectively, and in women, hip fracture risk rose by 22% from the last examination. Elevated GGT (≥ 36 U/l in women, ≥ 56 U/l in men) at the first examination was associated with increased hip fracture risk only in men (HR 1.51, 95% CI 1.25-1.82), and at the last examination in both women (HR 1.14, 95% CI 1.02-1.28) and men (HR 1.61, 95% CI 1.33-1.95). Alcohol consumption had no significant influence on GGT-mediated hip fracture risk in women and men.

CONCLUSIONS

Our findings identified an association of elevated GGT and hip fracture in women and men ≥ 50 years and suggest GGT as a candidate serum marker of long-term hip fracture risk in an elderly population.

Influence of unsaturated carbonic acids on hemocompatibility and cytotoxicity of poly-vinylacetate based co-polymers

The aim of this study was to investigate hemocompatibility and cytotoxicity properties of synthetic polymer coatings containing various unsaturated carbonic acids with vinylacetate. Co-polymers of vinylacetate and crotonic acid (CA), maleic acid (MA), and itaconic acid (IA) were made. The materials were characterized in terms of their adhesion to metal supports (titanium and stainless steel) as well as hemocompatibility (% hemolysis, wettability, erythrocyte aggregation, hemoglobin content, thrombocyte count and lipid peroxidation levels) and cytotoxicity (human endothelial cell activity in vitro and chromosome aberrations, bone marrow proliferation and cell ploidy in rats). Co-polymers of unsaturated carbonic acids with vinylacetate exhibited good hemocompatibility properties, as opposed to vinylacetate homopolymer for which substantial levels of hemolysis were observed. By coating the metal supports with co-polymers the cytotoxic effects associated with the bare metal samples were markedly reduced. MA samples showed excellent hemocompatibility and no cytotoxicity, yet they lacked good adhesion properties to metal substrate, probably due to high water content. CA samples, having the highest density of carboxylic groups among the samples under investigation, showed increased bone marrow proliferation activity and cell ploidy in rats, as compared to controls. The most promising results in the present study were obtained for the samples with IA, which showed good adhesion to metal substrates, good hemocompatibility and low cytotoxicity. Thus, co-polymers of vinylacetate and IA rich in carboxylic groups are promising materials for the design of novel drug-eluting stents.

Antioxidant capacity and protein oxidation in cerebrospinal fluid of amyotrophic lateral sclerosis

BACKGROUND

The causes of Amyotrophic Lateral Sclerosis (ALS) are unknown. A bulk of evidence supports the hypothesis that oxidative stress and mitochondrial dysfunction can be implicated in ALS pathogenesis. METHODS =: We assessed, in cerebrospinal fluid (CSF) and in plasma of 49 ALS patients and 8 controls, the amount of oxidized proteins (AOPP, advanced oxidation protein products), the total antioxidant capacity (FRA, the ferric reducing ability), and, in CSF, two oxidation products, the 4-hydroxynonenal and the sum of nitrites plus nitrates.

RESULTS

The FRA was decreased (p = 0.003) in CSF, and AOPP were increased in both CSF (p = 0.0039) and plasma (p = 0.001) of ALS patients. The content of AOPP was differently represented in CSF of ALS clinical subsets, resulting in increase in the common and pseudopolyneuropathic forms (p < 0.001) and nearly undetectable in the bulbar form, as in controls. The sum of nitrites plus nitrates and 4-hydroxynonenal were unchanged in ALS patients compared with controls.

CONCLUSION

Our results, while confirming the occurrence of oxidative stress in ALS, indicate how its effects can be stratified and therefore implicated differently in the pathogenesis of different clinical forms of ALS.

Expression of gamma-glutamyltransferase in cancer cells and its significance in drug resistance

The expression of gamma-glutamyltransferase (GGT), a cell surface enzyme involved in cellular glutathione homeostasis, is often significantly increased in human tumors, and its role in tumor progression, invasion and drug resistance has been repeatedly suggested. As GGT participates in the metabolism of cellular glutathione, its activity has been mostly regarded as a factor in reconsitution of cellular antioxidant/antitoxic defences. On this basis, an involvement of GGT expression in resistance of cancer cells to cytotoxic drugs (in particular, cisplatin and other electrophilic agents) has been envisaged. Mechanistic aspects of GGT involvement in antitumor pharmacology deserve however further investigations. Recent evidence points to a more complex role of GGT in modulation of redox equilibria, with effects acting both intracellularly and in the extracellular microenvironment. Indications exist that the protective effects of GGT may be independent of intracellular glutathione, and derive rather from processes taking place at extracellular level and involving reactions of electrophilic drugs with thiol metabolites originating from GGT-mediated cleavage of extracellular glutathione. Although expression of GGT cannot be regarded as a general mechanism of resistance, the involvement of this enzyme in modulation of redox metabolism is expected to have impact in cellular response to several cytotoxic agents. The present commentary is a survey of data concerning the role of GGT in tumor cell biology and the mechanisms of its potential involvement in tumor drug resistance.

Endogenous oxidative stress induces distinct redox forms of tumor necrosis factor receptor-1 in melanoma cells

Receptors of the TNFR superfamily possess abundant thiols in their extracellular domains, which makes them susceptible to redox modulation by prooxidant agents and processes. Previous studies from our laboratory have documented that membrane gamma-glutamyltransferase (GGT) activity can originate reactive oxygen species in the extracellular milieu, during the GGT-mediated metabolism of extracellular glutathione. The present study was aimed thus to verify a possible redox-modulating effect of GGT activity on TNFR1 receptors. The thiol-specific probe maleimide-polyethylene glycol was used to selectively label the reduced thiol groups in proteins of cell lysates; fractions corresponding to TNFR1 were then identified by immunoblot. In human melanoma Me665/2 cells, expressing varying GGT levels, at least five distinct forms of TNFR1 have been thus identified. The more oxidized forms appear to be prevalent in the 2/60 clone, expressing higher GGT levels, as compared to clone 2/21. Stimulation of GGT activity in the latter induced an increase of the oxidized TNFR1 forms. It is conceivable that different redox states of TNFR1 may correspond to different binding affinity and/or changes in the transducing function of the receptor. As GGT is frequently expressed by malignant tumors, the described phenomena might concur to alter the sensitivity of cancer cells to agents targeted on activation of TNF-alpha-dependent signaling pathways.

Gamma-glutamyltransferase in fine-needle liver biopsies of subjects with chronic hepatitis C

Serum gamma-glutamyltransferase (GGT) is considered as a sensitive but rather nonspecific marker of hepatobiliary disease, including chronic hepatitis C virus (HCV) infection. Although its increase in HCV infection is associated with poor response to interferon-alpha (IFN-alpha) and poor prognosis, there is little knowledge of the reasons of its increase during disease. Immunohistochemistry and enzyme histochemistry were performed on fine-needle biopsies of subjects with HCV infection. GGT was detected in the lumen of bile ducts and in bile canaliculi. Furthermore, in subjects with elevated serum GGT, immunoreactive and catalytically active GGT was also detected on the sinusoidal surface of hepatocytes and diffuse cytoplasmic positivity appeared in isolated hepatocytes and hepatocellular foci. Antigen unmasking procedures showed the presence of GGT in the cytoplasm of mature and immature bile cells and of inflammatory cells. These results suggest that during chronic HCV infection there is a general enhancement of GGT activity within the liver. As the activity of several inflammatory mediators, such as leukotrienes, nitric oxide, and interleukins is modulated by GGT activity, the present findings suggest a direct relationship between serum GGT, enhanced intrahepatic GGT activity and prognosis and therapeutic outcome of chronic HCV infection.

gamma-Glutamyl transpeptidase catalyses the extracellular detoxification of cisplatin in a human cell line derived from the proximal convoluted tubule of the kidney

Nephrotoxicity is a side-effect and the main factor limiting the clinical use of cisplatin. In vivo, the administration of the cysteine-containing tripeptide glutathione (GSH) has been found to reduce nephrotoxicity, but the biochemical mechanism of this protective action is not fully understood. The present study was designed to gain insights into the mechanism by which GSH prevents cisplatin nephrotoxicity. We also wanted to verify the hypothesis of whether the protective action of GSH is mediated by products of the extracellular breakdown of GSH catalysed by gamma-glutamyl transpeptidase (GGT), an enzyme that is highly expressed in kidney tubular cells. The study was performed in HK-2 cells, derived from the immortalisation of human kidney proximal tubule cells. We investigated the influence of modulators of GGT activity and/or thiols on the antiproliferative activity of cisplatin and on the intracellular GSH content. We determined the antiproliferative activity of cisplatin, platinum cellular accumulation and DNA platination following precomplexing of the drug with thiols. The antiproliferative effect of cisplatin was minimally affected by the addition of GSH. However, when the antiproliferative assay was performed in the presence of glycyl-glycine (GlyGly), to serve as a transpeptidation acceptor and thus to stimulate GGT-mediated GSH catabolism, cisplatin-induced growth inhibition was largely prevented. This effect was not mediated through an increase of intracellular GSH levels, which were not affected by the GlyGly supplementation. The thiol dipeptide cysteinyl-glycine, i.e. the GSH catabolite generated by GGT activity, showed a higher reactivity against cisplatin in vitro than GSH, as was shown by the more rapid oxidation of its -SH groups. The cisplatin/GSH or cisplatin/cysteinyl-glycine adducts did not display an antiproliferative effect. However, 2 h precomplexing with GSH in the presence of GGT, or directly with the GSH catabolite cysteinyl-glycine, decreased the antiproliferative effect of cisplatin and drug-induced DNA platination to a greater extent than precomplexing with GSH alone. The results of the present study show that, in HK-2 cells, extracellular GSH decreases the antiproliferative effects of cisplatin only upon its hydrolysis by GGT, thereby supporting the hypothesis that the extracellular metabolism of GSH by GGT plays a role in modulating cisplatin nephrotoxicity. A primary role in the protection of HK-2 cells appears to be played by cysteinyl-glycine, the proximal product of the GGT-mediated hydrolysis of GSH, which shows a high reactivity against CDDP resulting in the rapid inactivation of the drug.

Release of mercury from dental amalgam and its influence on salivary antioxidant activity

Dental amalgam fillings are known to release significant amounts of mercury (Hg) in saliva which could represent a continuous source of oxidative damage to mouth tissues. The present investigation was aimed at verifying this hypothesis by determining a possible correlation between salivary Hg levels and salivary total antioxidant activity (TAA), which is used as an index of oxidative stress. Samples of saliva from 34 healthy donors were analyzed for Hg content, by vapor atomic absorption spectrometry, and for TAA, by determining the ferric reducing ability ('FRAP' method). A significant correlation between Hg and the number of amalgam restorations or total amalgam surface was evident in both the male and female subjects. A significant negative correlation between TAA and Hg levels or number of amalgam restorations or amalgam surface was evident in females, indicating that small increases in salivary Hg were sufficient to produce a decrease in salivary TAA. On the other hand, no significant correlation was found in the males. The present study provides, for the first time, evidence of a pro-oxidant role of the amalgam Hg chronically released in saliva.

Prognostic value of serum gamma-glutamyl transferase activity after myocardial infarction

AIMS

Serum gamma-glutamyl transferase activity (gamma-GT) is able to catalyse low-density lipoprotein oxidation and has been detected in coronary atherosclerotic plaques. gamma-GT has been documented as an independent risk factor for cardiac mortality in middle-aged men. The purpose of this study is to determine the prognostic value of gamma-GT in patients with coronary artery disease.

METHODS AND RESULTS

In a prospective study, gamma-GT and other cardiac risk factors were evaluated in 469 consecutive subjects with angiographically documented coronary artery disease, using mortality and mortality plus non-fatal myocardial infarction as end-points. gamma-GT showed an independent prognostic value beyond known established risk factors in the subgroup of 262 patients with previous myocardial infarction. At a 6-year follow-up, cardiac mortality was 25.2% in patients with gamma-GT >40 U x l(-1)vs 13.9% in those with gamma-GT <40 U x l(-1)(P=0.038). When both cardiac mortality and non-fatal myocardial infarction were considered as end-points, these events were recorded in 32.7% of patients with gamma-GT >40 U x l(-1)and in 20.4% of those with levels <40 U x l(-1)(P=0.031). Excess mortality and non-fatal infarction in patients with high gamma-GT levels were concentrated in the first 2 years of follow-up (P=0.014). The association of gamma-GT values >40 U x l(-1), previous myocardial infarction, and multiple vessel disease identified a subgroup of 168 patients with the highest risk of cardiac events at 6 years (P=0.024). The relationship between gamma-GT levels and cardiac events remained significant after adjustment for cardiac risk factors, and possible confounders, including alcohol consumption. gamma-GT did not show significant prognostic value in the 207 patients without previous myocardial infarction.

CONCLUSION

gamma-GT is an independent cardiac risk factor in ischaemic patients with established coronary atherosclerosis and previous myocardial infarction.

Restoration of nitric oxide availability after calcium antagonist treatment in essential hypertension

Essential hypertension is associated with impaired endothelium-dependent vasodilation caused by oxygen free radical-induced nitric oxide (NO) breakdown. Because calcium antagonists can improve endothelial function in patients with essential hypertension, in this study we tested the hypothesis that this beneficial effect could be related to restoration of NO availability by antioxidant properties. In 15 healthy subjects and 15 hypertensive patients, we studied forearm blood flow (strain-gauge plethysmography) modifications induced by intrabrachial acetylcholine (ACh; 0.15, 0.45, 1.5, 4.5, and 15 microg/100 mL per minute), an endothelium-dependent vasodilator in basal conditions, during infusion of N:(G)-monomethyl-L-arginine (L-NMMA, 100 microg/100 mL forearm tissue per minute), an NO-synthase inhibitor, vitamin C (8 mg/100 mL forearm tissue per minute), and finally, simultaneous infusion of L-NMMA and vitamin C. The response to sodium nitroprusside (SNP; 1, 2, and 4 microg/100 mL forearm tissue per minute) was also evaluated. In control subjects, vasodilation to ACh was inhibited by L-NMMA and not changed by vitamin C. In hypertensive patients, vasodilation to ACh was blunted as compared with control subjects and resistant to L-NMMA. Vitamin C, which decreased plasma isoprostanes and increased plasma antioxidant capacity, increased the response to ACh and restored the inhibiting effect of L-NMMA. In hypertensive patients, the study was repeated after 3-month treatment with nifedipine gastrointestinal therapeutic system (30 to 60 mg/daily). Nifedipine treatment decreased circulating plasma lipoperoxides and isoprostanes and increased plasma antioxidant capacity. Moreover, nifedipine increased the vasodilation to ACh but not to SNP and restored the inhibiting effect of L-NMMA on ACh-induced vasodilation, whereas vitamin C no longer exerted its facilitating activity. These results indicate that nifedipine increases endothelium-dependent vasodilation by restoring NO availability, an effect probably determined by antioxidant activity.

Histochemical visualization of oxidant stress

Free radicals induce oxidative modification in distinct components of the living matter (lipid, proteins, and DNA). For qualitative and quantitative determination of free radical-induced modifications, different, more or less sensitive biochemical methods are available. Because of the high reactivity and short life of free radicals, ongoing oxidative damage is generally analyzed by measurement of secondary products-such as H(2)O(2), oxidized proteins, peroxidized lipids, and their breakdown products, oxidized DNA-or by fluorographic analysis in combination with fluorescent dyes such as dichlorofluorescin (DCFH). In addition, the determination of free radical-related oxidation products is usually carried out in plasma, urine, or, less frequently, in bioptic material. Consequently, biochemical data seldom reflect the effects of free radical insults in situ. The histochemical visualization of selected molecular markers of oxidative damage can often provide more valuable information concerning the in vivo distribution of oxidative processes. This review summarizes the methods currently available for histochemical detection and indirect visualization of free radical-induced alterations in tissues and isolated cells.

Determination of a redox compensation index and its relationships to glycaemic control in type 2 diabetes mellitus

The measurement of single parameters of oxidative stress in biological fluids can often give results difficult to interpret as to the real involvement of oxidative processes in a given disease condition. In the present study we propose a novel integrated parameter, called "redox compensation index", obtained by combining the results of two established and convenient procedures, i.e. the Fox-2 assay for plasma lipid hydroperoxides and the ferric reducing/antioxidant power (FRAP) assay for total antioxidant potential of plasma. These procedures were employed for the evaluation of oxidative stress in a group of patients with type 2 diabetes mellitus, a condition in which oxidative processes are implicated in the development of complications. In type 2 diabetic patients, plasma lipid hydroperoxides were directly correlated with levels of glycated hemoglobin. On the other hand, a significant inverse correlation was observed between levels of glycated hemoglobin and redox compensation values. The data reported suggest that the redox compensation index could represent a convenient parameter for the direct appraisal of oxidative status in clinical subjects, and are in support of the proposed role of protein glycation in production of oxidative alterations during type 2 diabetes mellitus.

Membrane gamma-glutamyl transpeptidase activity of melanoma cells: effects on cellular H(2)O(2) production, cell surface protein thiol oxidation and NF-kappa B activation status

The metabolism of glutathione by membrane-bound γ-glutamyl transpeptidase (GGT) has been recently recognized as a basal source of hydrogen peroxide in the extracellular space. Significant levels of GGT activity are expressed by malignant tumours, and in melanoma cell lines they were found to correlate with the malignant behaviour. As hydrogen peroxide and other oxidants can affect signal transduction pathways at several levels, the present study was aimed to verify: (i) the occurrence of GGT-dependent production of hydrogen peroxide in melanoma cells; (ii) the effects of GGT-dependent prooxidant reactions on known redox-sensitive cellular targets, i.e. protein thiols, the nuclear transcription factor NF-kappa B and p53. Two melanoma Me665/2 cell clones, exhibiting traces of (clone 2/21) or high (clone 2/60) GGT activity, were studied. The occurrence of GGT-dependent production of hydrogen peroxide was apparent in 2/60 cells, in which it was accompanied by lower levels of cell surface protein thiols. In 2/60 cells, GGT expression was also associated with higher levels of NF-kappa B activation, as compared to GGT-poor 2/21 cell clone. Indeed, stimulation or inhibition of GGT activity in 2/60 cells resulted in progressive activation or inactivation of NF-kappa B, respectively. An analysis of the p53 gene product indicated lack of protein expression in 2/60 cells, whereas a mutant protein was highly expressed in 2/21 cells. Taken together, these results indicate that the expression of GGT activity can provide melanoma cells with an additional source of hydrogen peroxide, and that such prooxidant reactions are capable to modify protein thiols at the cell surface level. In addition, GGT expression results in an up-regulation of the transcription factor NF-kappa B, which could explain the higher metastatic behaviour reported for GGT-rich melanoma cells as compared to their GGT-poor counterparts.

Protection of erythrocytes against oxidative damage and autologous immunoglobulin G (IgG) binding by iron chelator fluor-benzoil-pyridoxal hydrazone

Iron is released in a free desferrioxamine-chelatable form when erythrocytes are challenged by an oxidative stress. The release of iron is believed to play an important role in inducing destructive damage (lipid peroxidation and hemolysis) or in producing membrane protein oxidation and generation of senescent cell antigens (SCA). In this report, we further tested the hypothesis that intracellular chelation of iron released under conditions of oxidative stress prevents erythrocyte damage or SCA formation. Fluor-benzoil-pyridoxal hydrazone (FBPH), an iron-chelating molecule of the family of aromatic hydrazones, was prepared by synthesis and used for the above purpose after the capacity of the product to enter cells had been ascertained. GSH-depleted mouse erythrocytes were incubated with the oxidant drug phenylhydrazine in order to produce iron release, lipid peroxidation, and hemolysis. FBPH at a concentration of 200 microM prevented lipid peroxidation and hemolysis in spite of equal values of iron release. FBPH was active even at a lower concentration (100 microM) when the erythrocytes were preincubated with it for 15 min. No preventive effect was seen when FBPH saturated with iron was used. Prolonged aerobic incubation (60 hr) of erythrocytes produced iron release and formation of SCA as determined by autologous immunoglobulin G (IgG) binding. The IgG binding was detected by using an anti-IgG antibody labeled with fluorescein and by examining the cells for fluorescence by confocal microscopy. FBPH prevented SCA formation in a dose-related manner. These results lend further support to the hypothesis that iron release is a key factor in erythrocyte ageing.

Iron release and oxidant damage in human myoblasts by divicine

Divicine is an aglycone derived from vicine, a glucosidic compound contained in fava beans (Vicia faba major or broad beans). In this study, we investigated the effect of divicine on cultured human myoblasts from normal subjects, in order to see if the drug may induce signs of oxidant stress in these cells. Myoblasts incubated 24 hours in the presence of 1 mM divicine, showed an increase of carbonyl groups and 4-hydroxynonenal (4-HNE) bound to cell proteins, as well as a significant release of iron and lactate dehydrogenase in the culture medium. Desferrioxamine (DFO), an iron chelator, significantly prevented protein oxidation and formation 4-HNE adducts. Our results can be interpreted as indicating that divicine autooxidizes both at extracellular level and into myoblasts thus inducing the release of free iron, which initiates oxidation of cellular proteins and lipids. DFO protects the cells by subtracting the free iron both at intracellular and extracellular level.

Release of mercury from dental amalgam and its influence on salivary antioxidant activity

Dental amalgam fillings are known to release significant levels of mercury (Hg) in saliva which could represent a continuous source of oxidative damage to tissues. The present investigation was aimed at verifying this hypothesis by determining a possible correlation between salivary Hg levels and salivary total antioxidant activity (TAA), used as an index of oxidative stress. Samples of saliva from 34 healthy donors were analyzed for Hg content, through vapor atomic absorption spectrometry, and for TAA, by determining the ferric reducing ability ('FRAP' method). A significant correlation between Hg and the number of amalgam restorations or total amalgam surface was evident in both the male and female subjects. A significant negative correlation between TAA and Hg levels or number of amalgam restorations or amalgam surface was evident in females, indicating that small increases in salivary Hg were sufficient to produce a decrease in salivary TAA. On the other hand, no significant correlation was found in the males. The present study provides, for the first time, evidence of a pro-oxidant role of the amalgam Hg chronically released in saliva.

Contribution of gamma glutamyl transpeptidase to oxidative damage of ischemic rat kidney

BACKGROUND

A variety of mechanisms have been considered in the pathogenesis of the cell damage occurring in the kidney that is undergoing transient ischemia. However, little information is available about the role of oxidative stress in building up the tissue injury in the hypoxic organ during short-term ischemia.

METHODS

After a standard brief period (25 min) of unilateral kidney ischemia in rats, pretreated or not with acivicin (60 micromol/L/kg i.v.), tissue samples from both ischemic and not ischemic kidneys were obtained to measure malondialdehyde (MDA) and glutathione (GSH) content, gamma glutamyl transpeptidase (GGT) activity by spectrophotometry, localization and intensity of enzyme activity, and tissue damage by histochemistry.

RESULTS

GGT activity was found to be increased in both cortical and medullar zones of the ischemic kidneys, where the GSH level was only slightly decreased and the MDA level, in contrast, was markedly increased; in parallel, the cytosolic volume of the proximal tubular (PT) cells showed a significant increment. The animal pretreatment with acivicin, a specific inhibitor of GGT, besides preventing the up-regulation of the enzyme during ischemia, afforded good protection against the observed changes of MDA and GSH tissue levels, as well as of tubular cell volume.

CONCLUSIONS

Ex vivo data supporting a net pro-oxidant effect of up-regulated GGT during short-term ischemia of rat kidney have been obtained. The enzyme stimulation appears to contribute to the renal morphological damage exerted by a brief hypoxic condition at the level of PT cells. The actual impact on kidney function by GGT-dependent oxidative damage during transient ischemia and the potential protective action of GGT inhibitors require subsequent investigation.

The visualization of oxidant stress in tissues and isolated cells

Many studies have implicated the role of oxidant stress in a wide range of human diseases and have led to the rapid expansion of research in this area. With many experimental approaches a direct detection of the production of reactive oxygen species (ROS) and free radicals is not possible. Free radicals are very reactive, short-lived and react in a non-specific way, so that ongoing oxidative damage is generally analyzed by measurement of secondary products e.g. H2O2, "oxidized" proteins, peroxidized lipids and their break-down products, "oxidized" DNA or by fluorographic analysis in combination with fluorescent dyes e.g. dichlorofluorescin (DCFH). The histochemical visualization of selected molecular markers for oxidative phenomena can often provide valuable information concerning the distribution of oxidative processes in vivo. A number of biochemical methods are available for the monitoring of almost all oxidant stress-related processes, although their applicability in vivo is limited. This review summarizes the biochemical methods currently available for histochemical detection and indirect visualization of an excess of free radicals and ROS. The cited methods are discussed and the results obtained from their application are critically evaluated.

Redox modulation of cell surface protein thiols in U937 lymphoma cells: the role of gamma-glutamyl transpeptidase-dependent H2O2 production and S-thiolation

The expression of gamma-glutamyl transpeptidase (GGT), a plasma membrane ectoenzyme involved in the metabolism of extracellular reduced glutathione (GSH), is a marker of neoplastic progression in several experimental models, and occurs in a number of human malignant neoplasms and their metastases. Because it favors the supply of precursors for the synthesis of GSH, GGT expression has been interpreted as a member in cellular antioxidant defense systems. However, thiol metabolites generated at the cell surface during GGT activity can induce prooxidant reactions, leading to production of free radical oxidant species. The present study was designed to characterize the prooxidant reactions occurring during GGT ectoactivity, and their possible effects on the thiol redox status of proteins of the cell surface. Results indicate that: (i) in U937 cells, expressing significant amounts of membrane-bound GGT, GGT-mediated metabolism of GSH is coupled with the extracellular production of hydrogen peroxide; (ii) GGT activity also results in decreased levels of protein thiols at the cell surface; (iii) GGT-dependent decrease in protein thiols is due to sulfhydryl oxidation and protein S-thiolation reactions; and (iv) GGT irreversible inhibition by acivicin is sufficient to produce an increase of protein thiols at the cell surface. Membrane receptors and transcription factors have been shown to possess critical thiols involved in the transduction of proliferative signals. Furthermore, it was suggested that S-thiolation of cellular proteins may represent a mechanism for protection of vulnerable thiols against irreversible damage by prooxidant agents. Thus, the findings reported here provide additional explanations for the envisaged role played by membrane-bound GGT activity in the proliferative attitude of malignant cells and their resistance to prooxidant drugs and radiation therapy.

Gamma-glutamyl transpeptidase-dependent iron reduction and LDL oxidation--a potential mechanism in atherosclerosis

BACKGROUND

gamma-Glutamyl transpeptidase (gamma-GT) is found in serum and in the plasma membranes of virtually all cell types. Its physiologic role is to initiate the hydrolysis of extracellular glutathione (GSH), a tripeptide in which cysteine lies between alpha-glycine and gamma-glutamate residues. Cysteine and other thiol compounds are known to promote LDL oxidation by reducing Fe(III) to redox active Fe(II); therefore, we sought to determine whether similar reactions can be sustained by GSH and influenced by gamma-GT.

METHODS

Fe(III) reduction and LDL oxidation were studied by monitoring the formation bathophenanthroline-chelatable Fe(II) and the accumulation of thiobarbituric acid-reactive substances, respectively. Human atheromatous tissues were examined by histochemical techniques for the presence of oxidized LDL and their colocalization with cells expressing gamma-GT activity.

RESULTS

A series of experiments showed that the gamma-glutamate residue of GSH affected interactions of the juxtaposed cysteine thiol with iron, precluding Fe(III) reduction and hence LDL oxidation. Both processes increased remarkably after addition of purified gamma-GT, which acts by removing the gamma-glutamate residue. GSH-dependent LDL oxidation was similarly promoted by gamma-GT associated with the plasma membrane of human monoblastoid cells, and this process required iron traces that can be found in advanced or late stage atheromas. Collectively, these findings suggested a possible role for gamma-GT in the cellular processes of LDL oxidation and atherogenesis. Histochemical analyses confirmed that this may be the case, showing that gamma-GT activity is expressed by macrophage-derived foam cells within human atheromas, and that these cells colocalize with oxidized LDL.

CONCLUSIONS

Biochemical and histochemical correlates indicate that gamma-GT can promote LDL oxidation by hydrolyzing GSH into more potent iron reductants. These findings may provide mechanistic clues to the epidemiologic evidence for a possible correlation between persistent elevation of gamma-GT and the risk of fatal reinfarction in patients with ischemic heart disease.

Hydrogen peroxide produced during gamma-glutamyl transpeptidase activity is involved in prevention of apoptosis and maintainance of proliferation in U937 cells

It has been reported in several cell lines that exposure to low levels of reactive oxygen species can exert a stimulatory effect on their proliferation. We have previously shown that mild oxidative conditions can also counteract apoptotic stimuli. A constitutive cellular production of low levels of superoxide and hydrogen peroxide originates from various sources; among these, gamma-glutamyl transpeptidase (GGT), the plasma membrane-bound activity in charge of metabolizing extracellular reduced glutathione, has recently been included. Since the inhibition of GGT is a sufficient stimulus for the induction of apoptosis in selected cell lines, we investigated whether this effect might result from the suppression of the mentioned GGT-dependent prooxidant reactions, on the theory that the latter may represent a basal antiapoptotic and proliferative signal for the cell. Experiments showed that: 1) GGT activity in U937 monoblastoid cells is associated with the production of low levels of hydrogen peroxide, and two independent GGT inhibitors cause a dose-dependent decrease of such GGT-dependent production of H2O2; 2) GGT inhibition with acivicin results in cell growth arrest, and induces cell death and DNA fragmentation with the ladder appearance of apoptosis; 3) treatment of cells with catalase--and even more with Trolox C--is able to decrease their proliferative rate; 4) GGT inhibition (with suppression of H2O2 production) results in a down-regulation of poly(ADP-ribose) polimerase (PARP) activity, which precedes the proteolytic cleavage of PARP molecule, such as that typically induced by caspases. The reported data suggest that the low H2O2 levels originating as a by-product during GGT activity are able to act as sort of a 'life signal' in U937 cells, insofar as they can maintain cell proliferation and protect against apoptosis, possibly through an up-regulation of PARP activity.

Postnatal expression of glucose-6-phosphate dehydrogenase in different brain areas

The activity of glucose-6-phosphate dehydrogenase (G6PD) was studied in five brain areas of rats aged 5 to 90 days. The areas studied were: the olfactory bulb (OB), cortex, hippocampus, striatum and septum. The G6PD activity increased more than 2-fold from 5 to 90 days in the OB, while it was almost constant in the other areas. At every stage of development, the G6PD activity was significantly higher in the OB than in the other areas. The G6PD pattern was compared with 6-phosphogluconate dehydrogenase (6PGD), glutathione reductase (GR); glutathione peroxidase (GPX), catalase (CAT) and superoxide dismutase (SOD) in order to find synergistic interactions among activities of these enzymes during development. Over the considered period, the activity of 6PGD increased significantly in the OB, while no significant difference in activity was detected in the other areas. GR increased significantly and progressively at each developmental stage in all areas. GPX showed a progressive increase in the OB, while in other areas a significant increase was detected at 90 days only. CAT and SOD showed a different and independent pattern which differed from the G6PD pattern. CAT showed the highest level of activity at 5 days then progressively decreased or was constant until 90 days; SOD had the highest value at 5 days, than it decreased at 10 days and increased from 10 to 90 days. In all areas, G6PD activity showed three electrophoretic bands, whose relative activity changed with development. At histochemical level, we found a marked G6PD activity in the periglomerular zone of the OB, which increased with age, while other areas showed a homogeneous staining. The present results demonstrate that G6PD activity increases in the OB during the developmental stages and there is a coordinated simultaneous activation of 6PGD, GPX and GR. It is likely that this enzyme induction increases the antioxidant defense of periglomerular cells that are subject to a rapid renewal and thus much more exposed to oxidant stress.

Enhancement of oxidative cell injury and antitumor effects of localized 44 degrees C hyperthermia upon combination with respiratory hyperoxia and xanthine oxidase

The effects of respiratory hyperoxia (RH) and xanthine oxidase (XO) during localized hyperthermia (HT) were investigated by determining markers of oxidative damage to lipids and proteins and tumor growth. Anesthetized rats with s.c. DS-sarcomas underwent one of the following treatments: (a) localized saline-bath HT (60 min, 44 degrees C); (b) HT + RH (100% O2); and (c) HT + RH + XO (15 units/kg i.v.). Sham-treated animals served as controls. Tumors were investigated for: (a) thiobarbituric acid-reactive substance formation and protein-bound 4-hydroxynonenal, as indicators of lipid peroxidation; (b) reactive oxygen-mediated protein modifications; (c) apoptosis; and (d) tumor volume growth. Upon treatment, increases in thiobarbituric acid-reactive substances, protein-bound 4-hydroxynonenal, protein-associated carbonyl functions, and number of cells undergoing apoptosis were found in tumor tissue, together with an inhibition of tumor growth. When treatment groups were compared, effects in the group HT + RH + XO were generally most pronounced. These findings indicate that the antitumor effect of HT is at least partially mediated through the selective induction of lipid peroxidation and oxidative injury in tumor cells, leading to apoptosis. This effect was enhanced by adding RH or RH + XO, presumably due to enhanced tissue damage following an increased formation of reactive oxygen species, with higher levels of lipid peroxidation and protein oxidation.

Biochemistry and histochemistry of oxidant stress and lipid peroxidation

Oxidant stress--i.e. the prevalence within the cell of oxidizing species over the cellular antioxidant potential--is recognized as a primary factor in the pathogenesis of a series of important human pathologies. The possibility of a preventive or therapeutic intervention by means of antioxidant factors, including those naturally contained in diet, increases the importance of a correct understanding of the molecular mechanisms involved in such pathologies. A number of sophisticated biochemical methods are available, for the monitoring of nearly all oxidant stress-related processes; their applicability to in vivo conditions is however limited. In these conditions, the histochemical visualization in tissue sections and isolated cells of selected molecular markers for oxidative phenomena can often provide valuable information about the distribution of processes in vivo. This paper includes an overview of the basic biochemical reactions occurring during oxidant stress and lipid peroxidation, as well as of the main histochemical studies published in the field.

Methods for studying the glucose-6-phosphate dehydrogenase activity in brain areas

This paper reports on the protocols for the spectrophotometric determination of the enzymatic activity, the electrophoretic pattern and the cytochemical assay of glucose-6-phosphate dehydrogenase (G6PD) in different areas of rat brain. For the spectrophotometric assay we used the method of Glock and McLean. Non-denaturing polyacrylamide gel electrophoresis was performed using 1.5 mm thick slab-gel, with a 7.5% acrylamide separating gel and a 4% acrylamide stacking gel. NADP (0.01 mM) was included at the cathode buffer. The cytochemical assay was performed on unfixed cryostat sections, by incubating the slides for 5 min at 37 degrees C in the staining medium. A combination of these techniques offers a means for the study of the effect of age, drugs, oxidizing or reducing agents on the G6PD activity in different brain areas.

Release of free, redox-active iron in the liver and DNA oxidative damage following phenylhydrazine intoxication

Following the subchronic intoxication of rats with phenylhydrazine, resulting in marked anemia, reticulocytosis, methemoglobinemia and increased hemocatheresis, the hepatic content of total iron was increased, as was hepatic ferritin and its saturation by iron. A striking increase (approximately 7-fold) was also observed in free iron which appeared to be redox-active. The increase in liver free iron involved the hepatocellular component of the liver. Since DNA is one of the cellular targets of redox active iron, liver DNA from phenylhydrazine-treated rats was analyzed by electrophoresis and found to be markedly fragmented. Experiments with isolated hepatocytes in culture or in suspension challenged with phenylhydrazine or Fe-nitrilotriacetate strongly suggested that the DNA damage was due to reactive iron rather than to the hepatic metabolism of phenylhydrazine. The levels of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo), a specific marker of oxidative DNA damage, were significantly higher in phenylhydrazine-treated rats as compared to untreated controls. The prolongation of phenylhydrazine treatment over a period of 6 weeks resulted in a persistent damage to DNA and in phenotypic changes such as an increase in hepatocyte gamma-glutamyl transpeptidase (gamma-GT, EC 2.3.2.2) activity. Possible relationships between iron overload, iron release, DNA damage and tumor initiation are discussed.

The cell-specific anti-proliferative effect of reduced glutathione is mediated by gamma-glutamyl transpeptidase-dependent extracellular pro-oxidant reactions

We have shown earlier that extracellular GSH can exert a cell-specific growth-inhibitory effect on human tumor cells. In the present study, 2 human ovarian carcinoma cell lines (A2780 and IGROV-1) were used to investigate the biochemical basis of the GSH growth-inhibitory effect. Whereas cells were resistant, A2780 cells were sensitive to a 1 hr exposure to GSH, as assessed by the growth inhibition assay. Analysis of relevant GSH-dependent enzymes indicated that A2780 cells had low level of GSH S-transferase, glutathione reductase and gamma-glutamyl transpeptidase (gamma-GT) activities in comparison with those of IGROV-1 cells, and GSH peroxidase activity was undetectable in A2780 cells. The GSH effect was reversed by catalase and by dithiothreitol, indicating the occurrence of oxidative phenomena resulting in the impairment of critical cellular thiols. Indeed treatment of cells with H(2)O(2) also resulted in growth inhibition, which was more marked in A2780 cells. The gamma-glutamyl acceptor glycylglycine, a co-substrate for gamma-GT, potentiated the growth-inhibitory effect of GSH, which in contrast was decreased by the gamma-GT inhibitors, serine-borate complex and acivicin, suggesting that the production of reactive forms of oxygen (probably H(2)O(2)) was mediated by cysteinyl-glycine after GSH hydrolysis. The results support that the growth-inhibitory effect of low GSH concentration is the result of oxidative damage related to extracellular GSH metabolism.

Glucose-6-phosphate dehydrogenase activity is higher in the olfactory bulb than in other brain areas

The activity of antioxidant enzymes was measured in the olfactory bulb (OB) of rat and compared with cortex, hippocampus, striatum and septum. Glutathione reductase, glutathione peroxidase, catalase and superoxide dismutase were not significantly different in the five brain areas, while glucose-6-phosphate dehydrogenase (G6PD) and 6-phosphogluconate dehydrogenase activities were four times higher in the OB than in the other areas. This picture prompted us to explore the reasons of the marked increase of G6PD, since it is the enzyme that regulates the operation of the hexose monophosphate shunt. A first approach was to analyze the G6PD electrophoretic pattern. The analysis revealed that the high G6PD activity of the bulb was neither due to new isoenzymes nor to a modification of the equilibrium between the G6PD dimers. We secondly hypothesized an induction of G6PD activity in the OB by oxidant stress. The assay of markers of the oxidant stress, such as thiobarbituric acid reactive substances, oxidized and reduced glutathione, did not confirm this hypothesis. A third approach was the cytochemical analysis of cryostat sections of OB. By this method we identified a particular cell type which was very rich in G6PD and located at the border of the glomerular layer. Thus, we attributed the high G6PD activity of the OB to the consistent presence of periglomerular cells, that probably need a high G6PD activity for their regulatory function in the neurochemical transmission.

gamma-Glutamyl transpeptidase-dependent lipid peroxidation in isolated hepatocytes and HepG2 hepatoma cells

Gamma-glutamyltranspeptidase (GGT), a plasma membrane-bound enzyme, provides the only activity capable to effect the hydrolysis of extracellular glutathione (GSH), thus favoring the cellular utilization of its constituent amino acids. Recent studies have shown however that in the presence of chelated iron prooxidant species can be originated during GGT-mediated metabolism of GSH, and that a process of lipid peroxidation can be started eventually in suitable lipid substrates. The present study was undertaken to verify if a GGT-dependent lipid peroxidation process can be induced in the lipids of biological membranes, including living cells, and if this effect can be sustained by the GGT highly expressed at the surface of HepG2 human hepatoma cells. In rat liver microsomes (chosen as model membrane lipid substrate) exposed to GSH and ADP-chelated iron, the addition of GGT caused a marked stimulation of lipid peroxidation, which was further enhanced by the addition of the GGT co-substrate glycyl-glycine. The same was observed in primary cultures of isolated rat hepatocytes, where the lipid peroxidation process did not induce acute toxic effects. GGT-stimulation of lipid peroxidation was dependent both on the concentration of GSH and of ADP-chelated iron. In GGT-rich HepG2 human hepatoma cells, the exposure to GSH, glycyl-glycine, and ADP-chelated iron resulted in a nontoxic lipid peroxidation process, which could be prevented by means of GGT inhibitors such as acivicin and the serine-boric acid complex. In addition, by co-incubation of HepG2 cells with rat liver microsomes, it was observed that the GGT owned by HepG2 cells can act extracellularly, as a stimulant on the GSH- and iron-dependent lipid peroxidation of microsomes. The data reported indicate that the lipid peroxidation of liver microsomes and of living cells can be stimulated by the GGT-mediated metabolism of GSH. Due to the well established interactions of lipid peroxidation products with cell proliferation, the phenomenon may bear particular significance in the carcinogenic process, where a relationship between the expression of GGT and tumor progression has been envisaged.

Microspectrophotometric evaluation of digestibility of pollen grains

Digestibility of pollen grains of poppy (Papaver rhoeas) and hazelnut (Corylus avellana) subjected to a human-like in vitro digestion with pancreatic enzymes was evaluated. Pollens showed different types of walls. Digestibility was determined for total protein and insoluble carbohydrate contents by means of a new application of microspectrophotometry. Results demonstrated that pollen grains of both species were only partly digested; after 24 h treatment, only 26% of carbohydrates and 48% of proteins were digested in poppy and only 3% and 59% in hazelnut. This is probably due to the difficulty of enzymes to penetrate the intine of pollen grains. The degree of digestion of insoluble carbohydrates varied in the studied species according to their chemical nature and their storage sites.

Modulation of human T lymphocyte proliferation by 4-hydroxynonenal, the bioactive product of neutrophil-dependent lipid peroxidation

The proliferative capacity of immune cells is known to be sensitive to conditions of oxidative stress and lipid peroxidation. We tested the hypothesis that activated neutrophils can induce peroxidation in extracellular lipid substrates, and evaluated the effects of 4-hydroxy-2,3-trans-nonenal (4-HNE)--the most reactive aldehydic product of lipid peroxidation--on mitogen-induced proliferation of human T lymphocytes. Neutrophils activated in the presence of extracellular lipid substrates (liposomes, cellular membranes) induced lipid peroxidation. By means of cytoimmunofluorescent labeling and confocal microscopy, the binding of 4-HNE to surface and cytoplasmic proteins of activated neutrophils was observed. Short (20 min) pre-treatment of cells with low concentrations of 4-HNE were able to dose-dependently decrease the proliferation of human peripheral blood lymphocytes challenged with PHA or anti-CD3 monoclonal antibody OKT3, as well as the proliferation of a tetanus specific human T-cell line challenged with tetanus toxoid. In these conditions, the binding of 4-HNE to surface and cytoplasmic proteins of lymphocytes was also observed. When the proliferative capacity of peripheral blood lymphocytes was monitored over several days after 4-HNE treatment and PHA challenge, a recovery and a rebound in cell proliferation was observed. Data reported indicate that the lipid peroxidation promoted by activated neutrophils can exert modulatory effects on the responsivity of human T cells, through the action of its most reactive product, 4-HNE.

Gamma-glutamyltranspeptidase activity in human ovarian carcinoma

Gamma-glutamyltranspeptidase (GGT) is a cell membrane enzyme involved in the hydrolysis and uptake of extracellular glutathione. Histochemically detectable GGT has been shown in several human neoplasms. However, few studies have addressed the quantitative biochemical assessment of GGT activity in human tumors, and the importance of GGT activity in human tumor biology remains to be elucidated. The aim of the present study was to assess biochemically GGT enzyme activity in human ovarian surgical biopsies. GGT activity was assayed in homogenates of surgical samples of ovarian tumors and compared with the clinical data of the patients in order to establish: a) the level of tumor GGT activity, b) its correlation with other clinical parameters of the neoplasms, c) the possibility of the induction in vivo of GGT after anticancer platinum-based therapy, since some of the patients were pretreated. The results indicated that ovarian tumor expresses biochemically relevant GGT activity. The sensitive method used in this study allowed the quantitative evaluation of enzyme activity in all samples examined, showing that GGT activity values in ovarian carcinoma samples were extremely variable among the different subjects, both in untreated neoplasms (6.2 +/- 5.4 mU/mg protein) and in second-look laparotomy biopsies following platinum-based therapy (4.7 +/- 3.8 mU/mg protein). The mean GGT activity in benign ovarian tumors was lower than that in malignant tumors. No significant correlation was found between GGT activity and patient characteristics (tumor stage, age of patients, serum CA125, TAG-72, and GGT levels). However, the biological and pharmacological relevance of GGT expression remain to be elucidated in a large series of tumors.

Selective colocalization of lipid peroxidation and protein thiol loss in chemically induced hepatic preneoplastic lesions: the role of gamma-glutamyltranspeptidase activity

A number of studies indicate that cell proliferation can be modulated by changes in the redox balance of (soluble and protein) cellular thiols. Free radical processes, including lipid peroxidation (LPO), can affect such a balance, and a role for LPO in multistage carcinogenesis has been envisaged. The present study was aimed to assess the relationships between the protein thiol redox status and the LPO process in chemically induced preneoplastic tissue. The Solt-Farber's initiation-promotion model of chemical carcinogenesis in the rat liver was used. In fresh cryostat sections, preneoplastic lesions were identified by the reexpression of gamma-glutamyltranspeptidase (GGT) activity. In serial sections, different classes of protein thiols were stained; in additional sections, LPO was elicited by various prooxidant mixtures and determined thereafter by the hydroxynaphthoic hydrazide-Fast Blue B procedure. The incubation of sections in the presence of chelated iron plus substrates for GGT activity leads to the development of LPO in selected section areas closely corresponding to GGT-positive lesions, indicating the ability of GGT activity to initiate LPO. Protein-reactive thiols, as well as total protein sulfur, were decreased by 20-25% in cells belonging to GGT-positive preneoplastic nodules, suggesting the occurrence of oxidative conditions in vivo. The incubation of additional adjacent sections with the prooxidant mixture H2O2 plus iron(II), in order to induce the complete oxidation of lipid present in the section, showed a decreased basal concentration of oxidizable lipid substrate in GGT-rich areas. The decreased levels of both protein thiols and lipid-oxidizable substrate in GGT-positive nodules suggest that the observed GGT-dependent pathway of LPO initiation can be chronically operative in vivo during early stages of chemical carcinogenesis, in cells expressing GGT as part of their transformed phenotype.

Single-cell investigation by laser scanning confocal microscopy of cytochemical alterations resulting from extracellular oxidant challenge

Confocal laser scanning fluorescence microscopy coupled to image analysis was employed in order to develop and evaluate procedures for the appraisal at the single-cell level of: (1) protein-bound 4-hydroxynonenal, the specific product of membrane peroxidation (by means of immunocytochemistry with biotin-avidin revelation); (2) protein oxidation (by reaction of protein carbonyls with 2, 4-dinitrophenyl-hydrazine followed by immunocytochemistry of dinitrophenyl moieties); and (3) cellular protein thiols (by direct alkylation of sulfhydryl groups with thiol-specific fluorescent reagents possessing different cell permeabilities). The procedures proved able to reveal the subcellular distribution of cytochemical parameters useful as indices of oxidative stress conditions, and may allow "redox phenotyping" of isolated cells, which would provide an efficient tool in selected experimental models.

Protection by ascorbic acid against oxidative injury of isolated hepatocytes

1. The ability of ascorbic acid to protect from prooxidant-induced toxic injury was investigated in isolated, intact rat hepatocytes, whose ascorbic acid content had been restored by means of exogenous supplementation. 2. Ascorbate-supplemented and ascorbate-non-supplemented cells in suspension were treated with a series of different prooxidants (allyl alcohol, diethyl maleate, carbon tetrachloride, menadione), and the development of lipid peroxidation and cell injury was evaluated. 3. With allyl alcohol and diethyl maleate, ascorbic acid was able to protect cells from both lipid peroxidation and cell injury. The same protection was offered by ascorbate also in hepatocytes obtained from vitamin E-deficient animals. 4. With carbon tetrachloride, ascorbate supplementation did not affect the initial steps of lipid peroxidation, but nevertheless provided a marked protection against lipid peroxidation and cell injury at later times of incubation. The protection was unaffected by the vitamin E content of cells. 5. With menadione, a toxin which does not induce lipid peroxidation, ascorbic acid did not protect cells against injury. 6. It is concluded that ascorbic acid can act as an efficient antioxidant in isolated rat liver cells, with protection against cell injury. The antioxidant effect appears primarily to involve membrane lipids, and can be independent from the cellular content of vitamin E, thus suggesting that ascorbic acid can play a direct and independent role in the intact cell, in addition to its synergistic interaction with vitamin E described in other models.

NADPH-dependent lipid peroxidation capacity in unfixed tissue sections: characterization of the pro-oxidizing conditions and optimization of the histochemical detection

Factors which influence the iron-stimulated lipid peroxidation in rat liver have been studied by incubating unfixed cryostat sections with a pro-oxidant system and using an optimized histochemical detection method for lipid peroxidation products with 3-hydroxy-2-naphthoic acid hydrazide and Fast Blue B. We used a method that was slightly different from the one described previously. The final reaction product was exclusively localized in the cytoplasm of liver parenchymal cells with a homogeneous distribution within the liver lobule. The absorbance maximum, as measured cytophotometrically, was found to be 550 nm. Maximum lipid peroxidation was observed when the pro-oxidant system contained 0.2 mM NADPH, 1 mM ADP and 15 microM FeCl2. Some reaction product was found when NADPH was omitted. Iron concentrations higher than 180 microM prevented the formation of lipid peroxidation products in certain areas of the sections, whereas ADP concentrations higher than 1 mM inhibited the reaction in the whole section. A pH dependency was also observed, with the highest lipid peroxidation at pH 7.2. Optimum lipid peroxidation was induced by incubating for 30 min at 37 degrees C with the pro-oxidant system. A linear relationship was found between the thickness of the sections (up to 20 microns) and the amount of lipid peroxidation products. The addition of scavengers of O2-. (superoxide dismutase), hydrogen peroxide (catalase) and OH. (mannitol) to the first step medium did not affect the amount of final reaction product. These findings appear to confirm the hypothesis proposed for events occurring in isolated microsomes, leading to the formation of hydroperoxides and ultimately lipid peroxidation-derived carbonyls.(ABSTRACT TRUNCATED AT 250 WORDS)