The role of membrane sulfhydryls in passive, mediated transport processes and for the barrier function of the erythrocyte membrane

Oxidative stress and damage to erythrocytes in patients with chronic obstructive pulmonary disease--changes in ATPase and acetylcholinesterase activity

The study indicates, for the first time, the changes in both ATPase and AChE activities in the membrane of red blood cells of patients diagnosed with COPD. Chronic obstructive pulmonary disease (COPD) is one of the most common and severe lung disorders. We examined the impact of COPD on redox balance and properties of the membrane of red blood cells. The study involved 30 patients with COPD and 18 healthy subjects. An increase in lipid peroxidation products and a decrease in the content of -SH groups in the membrane of red blood cells in patients with COPD were observed. Moreover, an increase in the activity of glutathione peroxidase and a decrease in superoxide dismutase, but not in catalase activity, were found as well. Significant changes in activities of erythrocyte membrane enzymes in COPD patients were also evident demonstrated by a considerably lowered ATPase activity and elevated AChE activity. Changes in the structure and function of red blood cells observed in COPD patients, together with changes in the activity of the key membrane enzymes (ATPases and AChE), can result from the imbalance of redox status of these cells due to extensive oxidative stress induced by COPD disease.

In vivo influence of extract from Aronia melanocarpa on the erythrocyte membranes in patients with hypercholesterolemia

Background

Hypercholesterolemia increases cholesterol concentration in erythrocyte membranes, which results in decrease of membrane fluidity and decreases the deformability of red blood cells. The fruits of Arona melanocarpa contains many of polyphenols and other compounds that have beneficial health effects.

Material/Methods

The aim of the study was to estimate the influence of 2-month supplementation of extract from Aronia melanocarpa (100 mg Aronox, three times per day) on cholesterol concentration, lipid peroxidation, membrane fluidity, level of thiol groups and activity of ATPase in erythrocytes from patients with hypercholesterolemia. The study involved 25 patients with hypercholesterolemia without pharmacological treatment and 20 healthy individuals as a control group. Blood samples were collected before, and after 1 and 2 months of Aronia administration.

Results

The 2-month Aronia supplementation resulted in a decrease of cholesterol concentration (by 22%) and a decrease of lipid peroxidation (by 40%), and an increase of membrane fluidity. No statistically significant increase of the concentration of thiol groups and of ATPase activity were observed.

Conclusions

Our study shows that supplementation of extract from Aronia melanocarpa has a beneficial effect on rheological properties of erythrocytes.

The effect of bone marrow transplantation on oxidative stress in X-linked adrenoleukodystrophy

Oxidative stress plays an important role in the pathophysiology of neurodegenerative diseases, including X-linked adrenoleukodystrophy (X-ALD). In the present work, we evaluated lipid (malondialdehyde [MDA] content) and protein (sulfhydryl and carbonyl contents) oxidative damage parameters in plasma from X-ALD patients before and after bone marrow transplant (BMT), in order to verify if this treatment is capable to alter the oxidative parameters studied. We also evaluated the plasma concentration of hexacosanoic acid (C26:0) from X-ALD patients and correlated it with the oxidative damage parameters investigated. We observed that MDA content was significantly increased in plasma of X-ALD patients before BMT and after BMT when compared to controls, and that it was significantly reduced in plasma of X-ALD after BMT when compared to the before BMT group. These results indicate that lipid peroxidation is stimulated in X-ALD patients but there is a significant reduction of lipid peroxidation after BMT. Next, we observed a significant reduction of sulfhydryl content in plasma of X-ALD patients before BMT compared to controls indicating protein oxidative damage and that this measurement was increased in these patients after BMT as compared to before BMT. We found no significant differences in plasma carbonyl content in X-ALD patients before and after BMT as compared to controls. However, we observed a significant reduction in this parameter in X-ALD patients after BMT compared to before BMT. Finally, C26:0 plasma concentration was significantly reduced in X-ALD patients after BMT when compared to before BMT. We found no significant correlations between MDA and carbonyl values with C26:0 levels of the patients before BMT and after BMT, but a significant inverse correlation between sulfhydryl content and C26:0 levels was detected. In conclusion, the present study reinforces the hypothesis that lipid peroxidation and protein damage are induced in plasma of X-ALD patients and, in addition, demonstrates that BMT treatment is capable to reduce this pathogenic process. Taken together, the data obtained from plasma of X-ALD patients before and after BMT showing induction and protection, respectively, of oxidative stress, allowed to suggest that BMT, when well succeeded and under the recommendations, is effective to reduce C26:0 plasma levels and the increased lipid and protein oxidative damage in X-ALD.

Oxidative stress in erythrocytes from patients with rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic inflammation. It has been suggested that the level of reactive oxygen species (ROS) in patients with RA is higher than in healthy subjects. The aim of the present study was to investigate the level of the lipid peroxidation, antioxidant enzyme activities (CAT, SOD, GSH-Px), level of the –SH groups and GSH and Na⁺K⁺ ATPase activity in erythrocytes from patients with RA. There are no significant differences in CAT and GSH-Px activities. SOD activity is lower in RA patients than in the control group. Increase in the lipid peroxidation is observed in RA patients. Levels of the GHS and –SH groups are significantly lower in RA patients than in the control groups. Total ATPase and Na⁺K⁺ ATPase activities decrease in RA patients.

Is the blood donated by habitual nut quid chewers suitable for use in transfusion?

BACKGROUND/PURPOSE

Betel quid (BQ) chewing is a popular oral masticatory activity, and there are approximately 600 million BQ chewers worldwide. Although chewing BQ has been linked to the patho-genesis of oral cancer, leukoplakia, and oral submucous fibrosis. The question whether the mixed constituents present in areca nut, which may exert cytotoxic effects on red blood cells (RBCs), has never been addressed.

METHODS

Heparinized blood specimens were obtained with informed consent from healthy laboratory personnel. RBCs were separated with the standard procedure and adjusted to 10% hematocrit with PBS. Various concentrations of areca nut extract (ANE; 100-800 microg/mL) were added to these RBC preparations and incubated at 37 degrees C for 4 hours. Two portions (0.4 mL each) of the incubated RBCs were then used for measuring osmotic deformability index and for observing RBC morphology with scanning electron microscopy. The remaining RBCs were used for determining membrane sulfhydryl groups and protein profiles by sodium dodecyl sulfate polyacrylamide gel electrophoresis.

RESULTS

Blood incubated with various concentrations of ANE showed concentration-dependent decreases in osmotic deformability index and membrane sulfhydryl groups. Membrane protein profiles revealed a significant loss of the band 3 fraction, with the concomitant appearance of several new protein bands in the electropheretogram. Finally, drastic morphological changes of ANE-treated RBCs were observed.

CONCLUSION

We suggest that to assure the quality of transfusion, the blood donated by a habitual BQ chewer should be used with caution because of its possible contamination with areca nut ingredients that may be cytotoxic to RBCs.

Delta-ALA-D activity is a reliable marker for oxidative stress in bone marrow transplant patients

Background

Bone marrow transplantation (BMT) is often used in the treatment of various diseases. Before BMT, patients are submitted to a conditioning regimen (CR), which consists of the administration of high doses of chemotherapy. The action of many cytostatic drugs involves the overproduction of reactive oxygen species, which together with inadequate antioxidant protection can lead to oxidative stress and this has been implicated in the etiology of various diseases. The objectives of this study were to look for evidence of oxidative stress and also to analyze δ-Aminolevulinato dehydratase (δ-ALA-D) activity as a possible marker of oxidative stress in autologous and allogeneic BMT patients.

Methods

Lipid peroxidation, vitamin C and thiol group levels as well as catalase, superoxide dismutase and δ-ALA-D activity were determined in 37 healthy controls, 13 patients undergoing autologous peripheral blood stem cell transplantation and 24 patients undergoing allogeneic BMT.

Results

We found that patients presented signs of oxidative stress before they were submitted to BMT, during CR and up to 20 days after BMT. There was a decrease in enzymatic and non enzymatic antioxidant defenses, in δ-ALA-D activity, and an increase in lipoperoxidation in the blood of both patient groups.

Conclusion

This study has indicated that autologous and allogeneic BMT are associated with oxidative stress. Moreover, blood δ-ALA-D activity seems to be an additional biomarker of oxidative stress in BMT patients.

Oxidative stress and delta-ALA-D activity in different conditioning regimens in allogeneic bone marrow transplantation patients

OBJECTIVES

To compare different conditioning regimens (CR), in order to determine whether either of them could be less toxic to allogeneic bone marrow transplantation (BMT) patients in terms of oxidative stress and also analyze delta-ALA-D activity as a possible marker of oxidative stress.

DESIGN AND METHODS

Lipid peroxidation, vitamin C, thiol groups levels and catalase, superoxide dismutase and delta-ALA-D activity were determined in 21 healthy controls, 5 patients with fludarabine+cyclophosphamide (FluCy) CR, 12 with busulfan+cyclophosphamide (BuCy) and 4 with cyclophosphamide+total body irradiation (CyTBI).

RESULTS

There were a decrease in enzymatic and non enzymatic antioxidants, in delta-ALA-D activity, and in all CRs and an increase in lipid peroxidation more pronounced in CyTBI CR.

CONCLUSIONS

All CRs promoted oxidative stress in allogeneic BMT patients, but this was more pronounced with CyTBI and delta-ALA-D activity seemed to be an additional biomarker of oxidative stress in these patients.

The oxidative damage of butenolide to isolated erythrocyte membranes

Butenolide (CAS No. 16275-44-8), a mycotoxin produced by several Fusarium species, has been shown to be a potential risk factor for animal and human health. This study was undertaken to investigate the potential oxidative damage of butenolide to biomembranes in vitro using the erythrocyte membrane model. Following exposure of isolated rat erythrocyte membranes to butenolide, the extent of oxidative damage was assessed by measuring lipid peroxidation, -SH groups content, Ca2+/Mg2+-ATPase and Na+/K+-ATPase activities, and conformational changes in membrane proteins. It was observed that butenolide resulted in a significant lipid peroxidation, revealed by a concentration-dependent increase in the level of thiobarbituric acid reactive substances (TBARS). Similarly, this toxin induced a concentration-dependent decrease in the content of membrane total -SH groups, as well as free -SH groups. Membrane-bound enzymes were also impaired by the toxin, demonstrated by the marked inhibition of the activities of Na+/K+-ATPase and Ca2+/Mg2+-ATPase. Conformational changes in membrane proteins were determined using electron paramagnetic resonance (EPR) spin labeling. Butenolide caused an increase in the ratio of weakly to strongly immobilized components (W/S ratio) in a manner of concentration-dependent, indicating conformational changes in membrane proteins occurred. In conclusion, these findings indicate that butenolide is capable of inducing significant oxidative damage to membrane lipids and proteins.

Kinetic characterization of Zinc transport process and its inhibition by Cadmium in isolated rat renal basolateral membrane vesicles: In vitro and In vivo studies

We firstly characterized zinc uptake phenomenon across basolateral membrane vesicles (BLMVs) isolated from normal rat kidney. The process was found to be time, temperature, and substrate concentration dependent, and displayed saturability. Zn(2+) uptake was competitively inhibited in the presence of 2 mM Cd with Ki of 3.9 mM. Zinc uptake was also inhibited in the presence of sulfhydryl reacting compound suggesting involvement of [-]SH groups in the transport process. Further, to elucidate the effect of in vivo Cd on zinc transport in BLMVs, Cd nephrotoxicity was induced by subcutaneous administration of CdCl(2) at dose of 0.6 mg/kg/d for 5 days in a week for 12 weeks. An indolent renal failure developed in Cd exposed rats was accompanied with a significantly high urinary excretion of Cd(2+), Zn(2+) and proteins. The histopathology and electron microscopy of kidneys of Cd exposed rats documented changes of proximal tubular degeneration. Notably, Cd content in renal cortex of Cd exposed rats was 215 microg/g tissue that was higher than the critical concentration of Cd in kidneys which was associated with significantly higher Zn and metallothionein (MT) contents. Zinc uptake in BLMVs isolated from kidneys of Cd exposed rats was significantly reduced. Further, kinetic studies revealed that decrease in zinc uptake synchronized with decrease in maximal velocity (V(max)) and increase in affinity constant which is suggestive of decreased number of active zinc transporters. Furthermore, conformational modulation of Zn transporter in BLM was further supported by observed variation in transition temperature for zinc transport in BLMVs isolated from Cd-exposed kidney.

Damage to the structure of erythrocyte plasma membranes in patients with type-2 hypercholesterolemia

BACKGROUND

Hypercholesterolemia may decrease the deformability of red blood cells which impairs their hemorheological behavior and promotes atherosclerosis. The study involved 60 hypercholesterolemic patients and 30 healthy individuals as the control group.

METHODS

The membrane fluidity of erythrocytes was estimated by a spin-label method (5-doxylstearic acid (5-DSA)). The ratio of weakly to strongly (W/S) immobilized residues of erythrocyte membrane-bond maleimide-tempo spin label was studied in oxidative damage to membrane protein. Damage to erythrocyte proteins was also indicated by means of Na(+) K(+) ATPase activity.

RESULTS

The membranes of hyperlipidemia (hlp) patients contain larger concentrations of cholesterol 2.16+/-0.24 than do those of the normolipemic individuals 0.31+/-0.24 (P<0.001). The level of Na(+) K(+) ATPase in the erythrocyte membrane from the control group was higher 103.4+/-1.3 (nmolPi/(mgproteinsh)) than in the patient group 93.6+/-3.2 (nmolPi/(mgproteinsh)) (P<0.001). The order parameter S 5-DSA in the control group was 0.745+/-0.009 and in hlp patients was 0.755+/-0.009 (P<0.001). The W/S ratio in the control group amounted to 2.00+/-0.09 and in the hlp patient group was 2.50+/-0.11 (P<0.001).

CONCLUSION

Type-2 hypercholesterolemia causes changes in the structure and fluidity of erythrocyte plasma membranes since the excess of cholesterol affects the normal rheology of blood through its interaction with erythrocytes. It also impairs the function and structure of plasma membrane proteins.

Towards an understanding of organic anion transporters: Structure-function relationships

Organic anion transporters (OAT) play essential roles in the body disposition of clinically important anionic drugs, including anti-viral drugs, anti-tumor drugs, antibiotics, anti-hypertensives, and anti-inflammatories. The activities of OATs are directly linked to drug toxicity and drug-drug interactions. So far, four members of the OAT family have been identified: OAT1, OAT2, OAT3, and OAT4. These transporters share several common structural features including 12 transmembrane domains, multiple glycosylation sites localized in the first extracellular loop between transmembrane domains 1 and 2, and multiple phosphorylation sites present in the intracellular loop between transmembrane domains 6 and 7, and in the carboxyl terminus. The impact of these structural features on the function of these transporters has just begun to be explored. In the present review, the author will summarize recent progress made from her laboratory as well as from others, on the molecular characterization of the structure-function relationships of OATs, including particular amino acid residues/regions of the transporter protein ("molecular domains") that potentially determine transport characteristics.

The mycotoxin patulin alters the barrier function of the intestinal epithelium: mechanism of action of the toxin and protective effects of glutathione

Patulin is a mycotoxin mainly found in apple and apple products. In addition to being toxic for animals, mutagenic, carcinogenic and teratogenic, patulin induces intestinal injuries, including epithelial cell degeneration, inflammation, ulceration, and hemorrhages. In a study of the cellular mechanisms associated with the intestinal toxicity of patulin, two human epithelial intestinal cell lines (HT-29-D4 and Caco-2-14) were exposed to the mycotoxin. Micromolar concentrations of patulin were found to induce a rapid and dramatic decrease of transepithelial resistance (TER) in both cell lines without major signs of toxicity as assessed by the LDH release assay. Since TER reflects the organization of tight junctions, these data indicate that patulin affected the barrier function of the intestinal epithelium. The inhibitory effect of patulin on TER was closely associated with its reactivity for SH groups: (i) cysteine and glutathione prevented the cells from patulin injury; (ii) patulin toxicity was potentiated by buthionine sulfoximine, a specific glutathione-depleting agent; (iii) treatment of the cells with N-ethylmaleimide, a compound known to react with SH groups, resulted in a marked decrease of TER. Moreover, the inhibitory effect of patulin on TER was mimicked and potentiated by phenylarsine oxide, a specific inhibitor of protein tyrosine phosphatase (PTP). This cellular enzyme is a key regulator of intestinal epithelial barrier function. The active site of PTP contains a cysteine residue (Cys215) that is essential for phosphatase activity. Sulfhydryl-reacting compounds such as acetaldehyde decrease TER through covalent modification of Cys215 of PTP. We propose that the toxicity of patulin for intestinal cells involves, among other potential mechanisms, an inactivation of the active site of PTP.

Enhancement of lysosomal proton permeability induced by photooxidation of membrane thiol groups

Effects of photooxidation of membrane thiol groups on lysosomal proton permeability were studied by measuring intralysosomal pH with fluorescein isothiocyanate-dextran and monitoring proton leakage with p-nitrophenol. Methylene blue-mediated photooxidation of lysosomes decreased their membrane thiol groups and produced cross-linking of the membrane proteins, which was established by the measurement of residual membrane thiol groups with 5,5'-dithio-bis(2-nitrobenzoic acid) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, respectively. The cross-linking of proteins could be abolished by subsequent treatment of the photodamaged lysosomes with dithiothreitol, indicating that the proteins were linked via disulfide bonds. In addition, the photodamage of lysosomes raised the intralysosomal pH and caused leakage of the lysosomal protons, which could also be reversed by subsequent dithiothreitol treatment. This indicates that lysosomal proton permeability can be increased by photooxidation of the membrane thiol groups and recovered to the normal level by reduction of the groups.

Enhancement of lysosomal osmotic sensitivity induced by the photooxidation of membrane thiol groups

The osmotic lysis of photodamaged lysosomes is a critical event for killing tumor cells. How the photodamage increases lysosomal osmotic sensitivity is still unclear. In this work, the effect of the photooxidation of membrane thiol groups on the lysosomal osmotic sensitivity was studied by measuring the thiol groups with 5,5'-dithiobis(2-nitrobenzoic acid) and examining the lysosomal beta-hexosaminidase latency loss in a hypotonic sucrose medium. The results show that methylene blue-mediated photooxidation of lysosomes decreased their membrane thiol groups and produced cross-linkage of membrane proteins (molecular weight ranging from 75000 to 125000), which was visualized by sodium dodecyl sulfatepolyacrylamide gel electrophoresis. Simultaneously, the lysosomal osmotic sensitivity increased. These photoinduced alterations of the lysosomes could be recovered by reducing the oxidized thiol groups with dithiothreitol. It indicates that the photooxidation of membrane thiol groups can increase the lysosomal osmotic sensitivity and therefore provides a new explanation for the photoinduced lysosomal lysis.

Lysosomal sulphate transport is dependent upon sulphydryl groups

Using thiol blocking agents, we examined the role of sulphydryl groups for function of the lysosomal sulphate transport system. Monothiol binding reagents, p-hydroxymercuribenzoic acid (p-HMB) and p-chloromercuribenzene sulphonic acid (p-CMBS), dithiol binding reagents such as CuCl2, the alkylating agent, N-ethylmaleimide (NEM), and NADH all inhibited lysosomal sulphate transport. The inhibitory effects of NEM and Cu2+ were not additive, suggesting that they both act upon the same critical sulphydryl group(s). Unlike the case for NEM, the inhibitory effects of Cu2+ were reversed by the reducing agent, dithiothreitol. Exposure to NEM resulted in a seven-fold increase in Km to 867 microM versus a control value of 126 microM and a modest decrease in Vmax to 99 pmolperunit beta-hexosaminidase per 30 s versus a control value of 129 pmolperunit beta-hexosaminidase per 30 s. Similar although somewhat less dramatic results were obtained using Cu2+ with an increase of Km to 448 microM and a Vmax of 77 pmolperunit beta-hexosaminidase per 30 s. The sulphate transport activity of detergent solubilized lysosomal membranes could be bound to a p-chloromercuribenzoic acid (p-CMB)-Sepharose sulphydryl affinity resin and eluted with mercaptoethanol. Sulphydryl groups thus appear to play a role in sulphate transport through effects on substrate affinity. Sulphydryl-binding appears to be a strategy that may be useful for purification of the transporter.

Kinetic characterization of zinc binding to brush border membranes from rat kidney cortex: interaction with cadmium

Extravesicular and intravesicular zinc bindings were evaluated in brush border membrane vesicles isolated from rat kidney cortex. The process was found to be time-, temperature- and substrate concentration-dependent and displayed saturability. Zn2+ influx measurements revealed a progressive uptake and massive accumulation at equilibrium which was 50 times higher than the amount that could have been accommodated by the intravesicular space calculated from the equilibrium uptake of D-glucose. Initial (5 s) and equilibrium uptakes (2 h) were found not to be osmotically sensitive as modified by adding mannitol to the medium. It was concluded from these results that the uptake involved massive binding of the Zn2+ to the brush border membranes components. The ionophore A23187 enhanced the rates of uptake and efflux of Zn2+ without affecting equilibrium values, suggesting binding of Zn2+ to interior sites of the membranes. Zn2+ flux measurements led to the conclusion that two vesicular pools of Zn2+ bindings existed: a small external pool, accessible to cation chelator (EGTA) or competitive cation cadmium and large intravesicular pool. Accumulated 65Zn was quickly removed from its internal sites only after the membrane had been permeabilized by the cation ionophore A23187 in association with exchangeable ions like zinc and cadmium. Scatchard plot analysis revealed two distinct types of extravesicular binding sites. High affinity extravesicular zinc binding sites reached saturation at 1.6 mM zinc, had a Kd of 137 microM and the number of binding sites were 12 nmol/mg protein. Low affinity extravesicular zinc binding sites could not be saturated under experimental conditions up to 3.2 mM zinc. It had a Kd of 526 microM and the number of binding sites 28 nmol/mg protein. Interestingly intravesicular binding of zinc revealed only one type of high affinity binding sites (Kd of 104 microM and number of maximal binding sites 400 nmol/mg protein). Furthermore, kinetic analysis of inhibitory effect of Cd2+ on extravesicular zinc bindings showed an increase in Kd of both types of binding sites but there was no significant change in number of maximal binding sites. Extravesicular zinc binding was temperature-sensitive. Arrhenius plot showed the break point at 30 degrees C. The apparent energies of activation were 13.36 Kcal/mol and 3.1 Kcal/mol below and above the break points respectively. The inhibitory effect of sulfhydryl blocking agents on extravesicular zinc binding suggest the involvement of -SH groups in zinc translocation. An increase in initial zinc uptake was observed in the presence of outwardly directed proton gradient. Intravesicular pool of 65Zn was displaced by unlabelled 2 mM Zn2+ or 2 mM Cd2+ but not by calcium present in the bathing medium. It is inferred that intravesicular binding sites have a high affinity and are specific for zinc. It is concluded from the present study that in the first instance the binding of zinc to the exofacial zinc binding component and concomitantly its translocation across the membrane, and subsequently massive binding of zinc to interior sites of brush border membranes occurs.

Intracellular accumulation of cytosine arabinoside in murine normal and neoplastic lymphocytes following their exposure to sodium 2-mercaptoethanesulphonate

The effect of mesna on intracellular accumulation of cytosine arabinoside (Ara-C) in murine normal and neoplastic lymphocytes was studied. Simultaneous exposure of cells to mesna at concentrations ranging from 0.25 to 1.0 mM and 3H-Ara-C (40.0 nM) resulted in a strong inhibition of Ara-C uptake in normal lymphocytes. Under the same experimental conditions, mesna did not affect the Ara-C uptake in neoplastic cells (cultured L5178Y mouse leukaemia cells and neoplastically transformed thymus cells). It was found that the inhibitory effect of mesna was not cell cycle-dependent, since mesna reduced the Ara-C uptake in both normal quiescent and PHA-stimulated cells. We therefore concluded that mesna may selectively reduce Ara-C uptake by normal cells in vitro.

Effects of thiol compounds on methotrexate uptake by murine lymphocytes from thymus and thymic lymphosarcoma

The characteristics of methotrexate (MTX) uptake and the effects of exogenous sulfhydryl compounds (i.e. reduced glutathione and cysteine) on MTX accumulation in thymocytes and thymic lymphosarcoma cells has been studied. Significant differences in the rate and the extent of MTX uptake between normal and neoplastic cells were demonstrated. MTX accumulation was found to be more efficient in thymic lymphosarcoma cells as compared with parental cells. In the cells examined, MTX uptake was not affected by membrane impermeable GSH. In contrast, short-term exposure to cysteine revealed heterogeneity in MTX uptake systems between normal and neoplastic thymocytes. Thus, cysteine was demonstrated to enhance the rate and extent of MTX accumulation exclusively in thymic lymphosarcoma cells. The results obtained indicate that in neoplastic thymocytes biochemical changes had developed in the membrane redox state around the MTX uptake system. These alterations are chemically distinguishable by their characteristic response to cysteine. The findings suggest that the plasma membrane changes could be exploited for preferential enhancement of MTX uptake by neoplastic thymocytes.

Involvement of cytoskeletal proteins in the barrier function of the human erythrocyte membrane. II. Formation of membrane leaks in ghost membranes after limited proteolysis of skeletal proteins by trypsin

Limited proteolysis of human erythrocyte ghost membranes by low levels of trypsin (10-240 ng/ml) added bilaterally at 0 degrees C together with the proteinase inhibitor, phenylmethylsulfonyl fluoride (PMSF) before resealing at 37 degrees C leads to a graded digestion of spectrin and ankyrin and the disappearance of band 4.1 protein, while band 3 is cleaved only to a very low extent. These alterations are accompanied by an increase of membrane permeability of the resealed ghosts to hydrophilic nonelectrolytes (erythritol to sucrose), taken to reflect impaired resealing. Moreover, the membrane begins to vesiculate. Shedding of vesicles during the efflux measurements can not be responsible for the increased release of test solutes, since the ghosts do not loose hemoglobin and discriminate the nonelectrolytes according to their size. Moreover, the vesiculation site itself does not seem to act as the leak site, since ghosts prepared from erythrocytes pretreated with a carbodiimide which induces membrane rigidification still exhibit a pronounced protein degradation and vesiculation while the permeability enhancement induced by trypsination is markedly suppressed. The trypsin-induced leak has the properties of an aqueous pore as indicated, besides size selectivity, by its inhibition by phloretin and the very low activation energy. In analogy with concepts developed in the preceding paper (Klonk, S. and Deuticke, B. (1992) Biochim. Biophys. Acta 1106, 126-136 (Part I in this series)) the impaired resealing after limited proteolysis is assumed to be related to a perturbation of interactions of membrane skeletal elements with themselves and/or with the bilayer domain constituting the permeability barrier.

Involvement of cytoskeletal proteins in the barrier function of the human erythrocyte membrane. I. Impairment of resealing and formation of aqueous pores in the ghost membrane after modification of SH groups

Resealed human erythrocyte ghosts prepared by a two-step procedure were shown to have small residual barrier defects with the properties of aqueous pores, such as size discrimination of hydrophilic nonelectrolytes (erythritol to sucrose), indicative of an apparent pore radius of about 0.7 nm, and a low activation energy (about 12-20 kJ/mol (mannitol, sucrose)) of the leak fluxes. As in other cases (Deuticke et al. (1991) Biochim. Biophys. Acta 1067, 111-122) these leak fluxes can be inhibited by phloretin. Treatment of such resealed ghosts with the mild SH oxidizing agent, diamide, induces additional membrane leaks to the same extent and with the same properties as in native erythrocytes (Deuticke et al. (1983) Biochim. Biophys. Acta 731, 196-210), including reversibility of the leak by SH reducing agents, inhibition by phloretin and stimulation by alkanols. In contrast, resealed ghosts prepared either from diamide-treated erythrocytes or by adding diamide to the 'open' membranes prior to reconstitution of high ionic strength and raising the temperature, exhibit a state of greater leakiness. This leakiness is somewhat different in its origin from the former class of leaks, since it can also be produced by N-ethylmaleimide, which is essentially ineffective when added to the membrane in its 'tight' state. The leaks induced in the 'open' state of the membrane, which can be regarded as a consequence of an impaired resealing, are nevertheless reversible by reducing agents added after resealing and are comparable in many, but not all their characteristics to leaks induced in the 'tight' state of the membrane. Resealing in the presence of the isothiocyanostilbenes DIDS or SITS mimicks the leak forming effect of diamide by modifying a small population of SH groups, while amino groups seem not to be involved. The findings indicate and substantiate an important role of the redox state of membrane skeletal protein sulfhydryls in the maintenance and the re-establishment of the barrier function of the erythrocyte membrane.

Hormonal effects on the sulfhydryl groups associated with intestinal brush border membrane proteins

Previous studies demonstrated that the administration of 1,25-dihydroxycholecalciferol (1,25(OH)2D3) to cholecalciferol-deficient chicks rapidly increases the reactivity and amount of the sulfhydryl (HS-) groups in intestinal brush border membranes (BBM). In the present study, the tissue and hormonal specificity of this effect was investigated. The HS- groups of intestinal and renal BBM were enhanced by vitamin D-3 and/or 1,25(OH)2D3, but no change was noted in isolated intestinal mitochondria and purified intestinal basolateral membranes, cardiac sarcolemma and erythrocyte membranes. Other steroid hormones including estradiol, testosterone, aldosterone, cortisol, dexamethasone and progesterone, yielded a response similar to 1,25(OH)2D3 on BBM HS- groups. Triiodothyronine and retinoic acid also resulted in an increase in intestinal BBM HS- groups. In a kinetic approach, using a specific sulfhydryl fluorescent probe (N-7-dimethylamino-4-coumarin-3-yl-maleimide, DACM), the reactivity of the BBM HS- groups was increased by estrogen and testosterone, as was previously shown for 1,25(OH)2D3. Intestinal BBM proteins, labeled with DACM, were separated by gel electrophoresis. Fluorescence scans of the gel showed two heavily labeled bands, one of 110 kDa, putatively brush border myosin I, and one of 43 kDa, putatively actin. Labeling of the 110 kDa protein was increased by 1,25(OH)2D3 and estradiol. Further studies are required to elucidate the physiological meaning of these hormone-mediated increases in reactivity and amount of the BBM sulfhydryl groups, as well as the nature of the intermediate biochemical reactions involved in this response.

Reversible and irreversible inhibition, by stilbenedisulphonates, of lactate transport into rat erythrocytes. Identification of some new high-affinity inhibitors

1. Inhibition of L-lactate transport into rat erythrocytes by stilbenedisulphonates was studied under conditions which allowed the contribution of reversible and irreversible inhibition to be assessed. 2. At low temperatures (7 degrees C), 4,4'-di-isothiocyanostilbene-2,2'-disulphonate (DIDS) and other stilbenedisulphonates were found to inhibit lactate transport instantaneously, in a manner which was fully reversible. The most potent reversible inhibitors were 4,4'-dibenzamidostilbene-2,2'-disulphonate (DBDS), DIDS and 4-acetamido-4'isothiocyanostilbene-2,2'-disulphonate (SITS), for which apparent Ki values at 0.5 mM-L-lactate were approx. 36, 53 and 130 microM respectively. 3. DIDS and DBDS were competitive inhibitors with respect to L-lactate, with Ki values of approx 40 microM and 22 microM respectively. 4. After incubation for 1 h at 37 degrees C with DIDS or its dihydro derivative (H2DIDS), which contain the amino-reactive isothiocyanate group, most of the inhibition observed was irreversible. Under these conditions the IC50 value (concn. causing 50% inhibition) for irreversible inhibition by both compounds was approx 100 microM. SITS was much less potent as an irreversible inhibitor of L-lactate transport, approx. 20% inhibition being obtained at 100 microM. 5. The reversible inhibitor DBDS (1 mM) afforded protection against irreversible inhibition by DIDS and H2DIDS (100 microM); protection was 60 and 65% respectively after a 60 min incubation. This indicates that specific binding of the irreversible inhibitors is required before covalent modification can take place. 6. These compounds may be useful high-affinity probes for lactate transport in other tissues and might act as affinity labels for the transport protein(s).

Effect of diamide on nucleoside and glucose transport in Plasmodium falciparum and Babesia bovis infected erythrocytes

Normal human erythrocytes, preincubated with the oxidizing agent diamide, did not demonstrate any increased permeability, but showed a significant decrease in their ability to transport the nucleoside adenosine. Diamide appeared to have little effect on glucose permeation in uninfected and Plasmodium falciparum infected cells. The inhibition of adenosine transport in human erythrocytes by diamide pretreatment appeared to be unrelated to the inhibition by the established nucleoside transport inhibitor, nitrobenzylthioinosine (NBMPR). An ID50 for diamide of 0.3 mM was determined for 1 microM adenosine transport in human erythrocytes after preincubation for 45 min at 37 degrees C. However, preincubation of diamide (20 mM, 60 min at 37 degrees C) with Babesia bovis-infected bovine erythrocytes resulted in complete inhibition of the capacity of the parasitised cell to transport adenosine and partial inhibition of glucose permeation. By contrast, diamide was shown to have little or no effect on the new or induced nucleoside permeation site in P. falciparum (trophozoite) infected erythrocytes nor on the glucose transporter in these cells. The results further indicate the differences between the normal human erythrocyte nucleoside and glucose transporters and those new or altered transporters in the membrane of P. falciparum or B. bovis-infected red blood cells.

The mitochondrial aspartate/glutamate and ADP/ATP carrier switch from obligate counterexchange to unidirectional transport after modification by SH-reagents

The influence of various SH-reagents on the aspartate/glutamate carrier was investigated in the reconstituted system. When liposomes carrying partially purified carrier protein were treated with 5,5'-dithiobis(2-nitrobenzoic acid) or N-ethylmaleimide, antiport activity was strongly reduced. Several mercury compounds exerted a dual effect. They completely blocked the antiport and, in addition, induced an efflux pathway for internal aspartate. The maximum rate of this unidirectional flux was comparable to the original antiport activity. Induction of efflux always was coupled to inhibition of antiport. Efflux was neither due to unspecific leakage of proteoliposomes nor to a possible contamination by porin, but depended on active carrier protein, as elucidated by the sensitivity to proteinases and protein-modifying reagents. Besides efflux of aspartate, HgCl2 and mersalyl also induced a slow efflux of ATP from liposomes carrying coreconstituted aspartate/glutamate and ADP/ATP carrier. The two efflux activities could be discriminated taking advantage of the differential effectiveness of several inhibitors and proteinases. Although basic carrier properties were changed by the applied mercurials (Dierks, T., Salentin, A. and Krämer, R. (1990) Biochim. Biophys. Acta 1028, 281), aspartate and ATP efflux could clearly be correlated with the aspartate/glutamate and the ADP/ATP carrier, respectively. When purifying these two translocators the respective efflux activity copurified with the antiporter, thus elucidating that the two different transport functions are mediated by the same protein. These results argue for a participation of the aspartate/glutamate and the ADP/ATP carrier in the generally observed increase of mitochondrial permeability after treatment with SH-reagents.

Erythrocyte pathology and mechanisms of Heinz body-mediated hemolysis in cats

Despite the frequency of both oxidant drug-induced and spontaneous Heinz body formation in cats, the cellular and biochemical mechanisms by which Heinz bodies result in red blood cell (RBC) destruction and hemolytic anemia in this species remain unknown. Feline spleens are non-sinusoidal and inefficient at removing Heinz body-containing RBC from the circulation; therefore, alternative mechanisms must be involved in accelerated RBC destruction. Propylene glycol (PG) ingestion causes dose-dependent Heinz body formation and decreased RBC survival in cats. We investigated several aspects of Heinz body-containing RBC from three cats ingesting diets that provided 8.0 g PG/kg body weight for up to 3 weeks, in order to characterize cellular lesions that are associated with the presence of Heinz bodies and that might contribute to chronic, accelerated RBC destruction, as well as to gain insight into the mechanism by which PG induces Heinz body formation. Erythrocytes with PG-induced Heinz bodies had decreased levels of reduced glutathione and adenosine triphosphate and reduced deformability. There was no change in hemoglobin isoelectric focusing or membrane lipid peroxidation. Electrophoretic patterns of Heinz body-containing RBC membranes were significantly altered, and membrane surface charge distribution was disturbed. Progressively protruding Heinz bodies suggested that extrusion of Heinz bodies may be a means of cell healing and/or destruction in the absence of splenic pitting. When compared to results obtained using RBC from cats treated with the oxidant drug phenylhydrazine, significant differences were noted in packed cell volume, turbidity index, membrane heme, and morphologic appearance of Heinz bodies. Our results indicate that multiple cellular abnormalities develop in RBC with PG-induced Heinz bodies that do not cause acute hemolysis but that may shorten RBC survival. Propylene glycol-induced Heinz bodies provide an ideal model for studying the chronic effects of Heinz bodies on RBC structure and function and may be useful in understanding the mechanisms of formation and the consequences of endogenous Heinz bodies in cats.

Reactivity of sulfhydryl groups in the brush-border membranes of chick duodena is increased by 1,25-dihydroxycholecalciferol

The total amount and reactivity of SH-groups were determined in isolated duodenal brush-border membranes from rachitic chicks given 1,25-dihydroxyvitamin D-3 (1,25(OH)2D3) before isolation of the membranes. 1,25(OH)2D3 treatment significantly increased the total amount of SH groups (9.7 +/- 2.3 vs. 23.9 +/- 2.1, P less than 0.001, n = 6) in brush-border membranes solubilized in 1% sodium dodecyl sulfate. The rate of reaction (reactivity) of membrane-bound SH-groups, determined with the fluorescent thiol reagent, N-(7-dimethylamino-4-methylcoumarin-3-yl)maleimide (DACM), was also significantly enhanced by the intravenous injection of various doses (0.005-0.10 microgram) of 1,25(OH)2D3 into vitamin D-deficient chicks. An increase in reactivity occurred as early as 10 min after dosing of the chicks with 1,25(OH)2D3. Fluorescence scanning of the membrane proteins labeled with DACM and separated by polyacrylamide gel electrophoresis revealed three major peaks of fluorescence and a generally higher degree of fluorescent labeling of these and many other proteins in the membranes isolated from the 1,25(OH)2D3-treated chicks. The physiological significance of the 1,25(OH)2D3-mediated increase in the reactivity and total amount of membrane-bound SH-groups in terms of vitamin-D-dependent epithelial transport and epithelial membrane properties needs to be further explored.

Chronology of patulin-induced alterations in membrane function of cultured renal cells, LLC-PK

In a previous study we compared the effects of patulin (PAT) and ouabain, a specific inhibitor of the Na(+)-K+ ATPase, and found significant differences with regard to the kinetics of Na+ influx and K+ efflux, and sulfhydryl reactivity in LLC-PK1 cells. The purpose of the present study was to determine the relationship between Na+ influx, K+ efflux, membrane potential ([3H]tetraphenylphosphonium accumulation), cellular viability [lactate dehydrogenase (LDH) release], and changes in cell morphology (blebs). The effects of PAT are concentration and time dependent. At concentrations of PAT above 10 microM there is a transient increase in intracellular electronegativity (less than 1 hr) followed by a sustained depolarization (greater than 1 hr) which is correlated with complete Na+ influx, K+ efflux, total LDH release, and bleb formation. However, at PAT concentrations of 5-10 microM there is a sustained increased intracellular electronegativity (4-8 hr) which is associated with partial Na+ influx and K+ efflux, no significant LDH release, and relatively few blebs. The hyperpolarizing effect may be a result of increased permeability to K+ relative to Na+. At times and concentrations which result in increased intracellular electronegativity, PAT has no effect on [3H]ouabain binding and thus increased Na+/K+ pump turnover does not seem to be the cause of the transient hyperpolarizing effect of PAT. These results are consistent with the hypothesis that PAT causes alterations in plasma membrane permeability which favor K+ efflux relative to Na+ influx. The toxic effects of PAT are irreversible in LLC-PK1 cells after even short pretreatment with PAT. The primary toxic lesion appears to be at some level other than that involving inhibition of macromolecular synthesis, perhaps the plasma membrane itself.

Involvement of ATP-dependent aminophospholipid translocation in maintaining phospholipid asymmetry in diamide-treated human erythrocytes

Crosslinking of membrane skeletal proteins such as spectrin by oxidation of their SH-groups can be provoked by treatment of intact erythrocytes with diamide. Shortly after exposure of human erythrocytes to diamide and despite the transverse destabilization of the lipid bilayer that was observed in these cells (Franck, P.F.H., Op den Kamp, J.A.F., Roelofsen, B. and Van Deenen, L.L.M. (1986) Biochim. Biophys. Acta 857, 127-130), no abnormalities could be detected regarding the asymmetric distribution of the phospholipids when probed by either the prothrombinase assay or brief exposure of the cells to a modified phospholipase A2 with enhanced membrane penetrating capacity. This asymmetry appeared to undergo dramatic changes however, when the ATP content of the cytosol had decreased to less than 10% of its original level during prolonged incubation of the treated cells. These observations indicate that the initial maintenance of phospholipid asymmetry in diamide-treated erythrocytes can be solely ascribed to the action of the ATP-dependent aminophospholipid translocase. This view is supported by experiments involving radiolabeled phospholipids of which trace amounts had been inserted into the outer membrane leaflet of diamide-treated red cells and which still showed a preferential translocation of both aminophospholipids in favour of the inner monolayer, be it that the efficiency of the translocase was found to be impaired when compared to control cells.

Patulin-induced ion flux in cultured renal cells and reversal by dithiothreitol and glutathione: a scanning electron microscopy (SEM) X-ray microanalysis study

Patulin (PAT), a compound produced by certain species of Aspergillus, Penicillium, and Byssochlamys, is frequently found associated with agricultural commodities. PAT has many effects on membrane function, including the inhibition of the isolated Na+-K+ ATPase. In this study, a scanning electron microscope equipped with an energy dispersive spectroscopy X-ray microanalysis system was used to examine individual cultured renal epithelial cells (LLC-PK1) in order to determine the effects of PAT on the relative intracellular ion concentrations. The estimated EC50 (60 min) for both sodium influx and potassium efflux was between 10 and 50 microns for ouabain. For PAT, the EC50 (60 min) was 250 microns for sodium influx and 100 microns for potassium efflux. However, 1 mM patulin at 240 min caused complete reversal of the sodium and potassium content of cells, and 1 mM ouabain at 240 min did not. The effect of patulin on sodium and potassium flux was both concentration and time dependent and was reversed by dithiothreitol and glutathione. PAT (250 microM) but not ouabain (250 microM) induced massive blebbing of LLC-PK1 cells. Thus, the interaction of PAT with cellular membranes involves both alterations in the regulation of intracellular ion content and the cytoskeleton. We hypothesize that patulin alters intracellular ion content via Na+-K+ ATPase and non-Na+-K+ ATPase mechanisms.

Oxidative stress and muscular dystrophy

Oxidative stress may be the fundamental basis of many of the structural, functional and biochemical changes characteristic of the inherited muscular dystrophies in animals and humans. The presence of by-products of oxidative damage, and the compensatory increases in cellular antioxidants, both indicate oxidative stress may be occurring in dystrophic muscle. Changes in the proportions and metabolism of cellular lipids, abnormal functions of cellular membranes, altered activity of membrane-bound enzymes such as the SR Ca2+-ATPase, disturbances in cellular protein turnover and energy production and a variety of other changes all indicate that these inherited muscular dystrophies appear more like the results of oxidative stress to muscle than any other type of underlying muscle disturbance. Particular details of these altered characteristics of dystrophic muscle, in combination with current knowledge on the processes of oxidative damage to cells, may provide some insight into the underlying biochemical defect responsible for the disease, as well as direct research towards the ultimate goal of an effective treatment.

Thiol-dependent K:Cl transport in sheep red cells: VIII. Activation through metabolically and chemically reversible oxidation by diamide

The sulfhydryl (SH) oxidant diamide activated in a concentration-dependent manner ouabain-resistant (OR), Cl-dependent K flux in both low potassium (LK) and high potassium (HK) sheep red cells as determined from the rate of zero-trans K efflux into media with Cl or Cl replaced by NO3 or methane sulfonate (CH3SO3). Diamide did not alter the OR Na efflux into choline Cl. The diamide effect on K efflux appeared after 80% of cellular glutathione (GSH) was oxidized to GSSG, its disulfide. The stimulation of K efflux was completely reversed during metabolic restitution of GSH, a process that depended on the length of exposure to and the concentration of diamide. The action of diamide on both the K:Cl transporter and GSH was also fully reversed by the reducing agent dithiothreitol (DTT). Diamide apparently oxidized the same SH groups alkylated by N-ethylmaleimide (NEM) (Lauf, P.K. 1983. J. Membrane Biol. 73:237-246). Like NEM, diamide activated K:Cl transport several-fold more in LK cells than in HK cells, and the effect on LK cells was partially inhibited by anti-L1, the allo-antibody known to inhibit OR K fluxes.

Kinetic comparison of ouabain-resistant K:Cl fluxes (K:Cl [Co]-transport) stimulated in sheep erythrocytes by membrane thiol oxidation and alkylation

The stimulatory effects of two thiol (SH) group oxidants, methylmethane thiosulfonate (MMTS) and diazene dicarboxylic acid bis [N,N-dimethylamide] (diamide), on the kinetics of ouabain-resistant (OR) K:Cl [co]-transport in low K (LK) sheep red blood cells were compared with the effects of alkylating agents, notably N-ethylmaleimide (NEM). At low concentrations, both MMTS and diamide stimulated K:Cl [co]-transport, and with a latency period, as measured by OR zero-trans K efflux and OR uptake of external Rb, Rbo, as K congener in Cl and NO3 media. At high concentrations the effect of diamide saturated, and that of MMTS disappeared. The stimulatory effect of MMTS was partially reversed by the reducing agent dithiothreitol (DTT) known to fully restore the diamide-activated K flux (Lauf, J. Memb. Biol. 101:179-188, 1988). In diamide preequilibrated LK sheep red cells, the Km of K:Cl [co]-transport for external Cl, Clo, was 84.3 mM, and 18.7 mM for Rbo, with nearly identical Vmax values around 4 mmol Rb/L cells x h for K (Rb) fluxes in Cl and after correction for the small Cl-independent component. Zero net K (Rb) flux existed at Kc (cell K)/Rbo concentration ratios, [K]c/[Rb]c, of 0.8 i.e. when the electrochemical driving forces across the membrane were about equal. The measured K efflux/Rb influx ratios were almost twice those predicted from [K]c/[Rb]o and the Cl equilibrium potential suggesting that the diamide-stimulated K (Rb) flux may occur through non-diffusional, carrier-mediated transport.(ABSTRACT TRUNCATED AT 250 WORDS)

The Wellcome Trust lecture. Mechanisms of molecular trafficking in malaria

The asexual stages of Plasmodium living within the erythrocyte result in growth-related changes in the permeability properties of the red cell for substances such as glucose, amino acids, purine nucleosides, sodium, potassium, calcium, zinc, iron and several antimalarial drugs such as chloroquine, amodiaquine and mefloquine. In most cases such changes do not appear to be due to a modification in the affinity or specificity of red cell transporters; indeed, for most substances the membrane-associated transporters are either unaffected or are partially inactivated. In malaria-infected erythrocytes, where a striking increase in influx has been observed, it has been attributed to the insertion of parasite-encoded transporters into the red cell membrane or the formation of aqueous leaks and/or pores. Leak formation, in the vast majority of cases, does not appear to be dependent on the insertion of plasmodial proteins into the red cell membrane. However, since the data presently available are less than satisfactory for discriminating amongst the various possible transport mechanisms future studies will require painstaking efforts and carefully controlled conditions to discriminate amongst the various transport systems which are operational in the malaria-infected red cell and the parasite.

New permeability pathways induced by the malarial parasite in the membrane of its host erythrocyte: potential routes for targeting of drugs into infected cells

Malarial parasites propagate asexually inside the erythrocytes of their vertebrate host. Six hours after invasion, the permeability of the host cell membrane to anions and small nonelectrolytes starts to increase and reaches its peak as the parasite matures. This increased permeability differs from the native transport systems of the normal erythrocyte in its solute selectivity pattern, its enthalpy of activation and its susceptibility to inhibitors, suggesting the appearance of new transport pathways. A biophysical analysis of the permeability data indicates that the selectivity barrier discriminates between permeants according to their hydrogen bonding capacity and has solubilization properties compared to those of iso-butanol. The new permeability pathways could result from structural defects caused in the host cell membrane by the insertion of parasite-derived polypeptides. It is suggested that the unique transport properties of the new pathways be used to target drugs into infected cells, to affect the parasite either directly or through the modulation of the intraerythrocytic environment. The feasibility of drug targeting is demonstrated in in vitro cultures of the human malarial parasite Plasmodium falciparum.