Quantitative determination of functional thiol groups on intact cell surfaces by resonance Raman spectroscopy

The sensitivity and selectivity of resonance Raman spectroscopy, combined with electronic spectroscopy, has been used to develop a method to quantify the membrane thiol population in situ in viable erythrocytes. This technique is based on the thiol-disulfide reaction of Ellman's reagent (5,5'-dithio-bis-2-nitrobenzoic acid). It has the advantage that continuous monitoring of lysis is simple and a correction can be made for any interference resulting from lysis. In addition, the extent of reaction can be expressed as a ratio of the reagent signal, providing an internal calibrant.

In vitro oxidation of vitamin E, vitamin C, thiols and cholesterol in rat brain mitochondria incubated with free radicals

The kinetics of oxidation of endogenous antioxidants such as vitamins C and E and thiols as well as membrane cholesterol in isolated rat brain mitochondria were studied. Oxidation was induced by incubating the mitochondria at 37 degrees C with the free radical generators 2,2' azobis (2'-amidinopropane) dihydrochloride (ABAPH) and 2,2' azobis (2,4-dimethyl) valeronitrile (ABDVN) which undergo thermal decomposition to yield free radicals. An approximate order for the in vitro ease of oxidation was: ascorbate >> alpha-tocopherol > sulfhydryls >> cholesterol. However, small amounts of ascorbate were present in the mitochondria when alpha-tocopherol and sulfhydryl compounds were getting oxidized. This observation is different from those with more homogeneous biological substrates like blood plasma or serum. The order of oxidation of the various compounds is a function of not only the redox potentials but also the (a) concentrations of the oxidized and reduced species, (b) compartmentation of the compounds and (c) enzymatic and nonenzymatic systems for the repair or regeneration of the individual antioxidants. Even though ascorbate levels are quite low within mitochondria this nutrient may play a major role as a first line of defense against oxidative stress. The lipid-soluble ABDVN was much more potent in oxidizing membrane alpha-tocopherol and thiols than the water-soluble ABAPH. With both free radical generators the rate of oxidation of the antioxidants consisted of two phases. The initial phase, that is more rapid, may represent a pool of antioxidant that is involved in immediate antioxidant protection of the organelle with the slower compartment being responsible for replenishing the faster pool whenever needed.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparative study of the interaction of Myocrisin with albumin and gamma-globulin

The reactions of Myocrisin with albumin and gamma-globulin have been investigated using atomic absorption spectrometry and gel filtration. Albumin rapidly binds gold up to the levels predicted from the concentration of free sulphydryl groups present in the protein. However, in the presence of glutathione, gold incorporation is increased, suggesting that in vivo, free thiols (glutathione, thiomalate) may facilitate gold uptake by the protein. In comparison, gamma-globulin is found to be capable of binding up to one atom of gold per molecule of protein in a slow reaction which requires high Myocrisin concentrations.

Out-of-plane motion compensation in multislice spin-echo MRI

In magnetic resonance imaging (MRI), it is well-known that patient motion plays a significant role in the degradation of image quality. Although the case of translational in-plane motion (x-y-motion) has been studied by several researchers, the effect of rigid, translational out-of-plane motion (z-motion) has not yet been completely analyzed due to its more complex nature. Out-of-plane motion introduces blurring along the slice-selection direction in addition to motion artifacts. Here, the authors present a model to represent the effect of out-of-plane motion on multislice MR data. The inversion of this model not only results in the correction of the artifacts due to out-of-plane motion, but also reduces blurring in the slice-selection direction, yielding higher resolution images. Because of the shift-varying nature of the authors' model, they propose to use a nonlinear postprocessing method, projection onto convex sets (POCS), for its inversion, provided that the motion kernel and the slice-selection profile are known. The proposed method has been tested on simulated data and then applied to actual MR data to demonstrate the feasibility of the technique in real imaging situations.

The interaction of colloidal metals with erythrocytes

The interactions of citrate reduced colloids (Ag, Au, and Bi) with intact erythrocytes and erythrocyte lysate have been studied by 1H spin echo NMR. Silver colloid is observed to induce cellular depletion of cytosolic glutathione and bismuth colloid induces cytosolic glutathione oxidation in the intact cell. In comparison, there is no detectable effect with gold colloid. With red cell lysate the three colloids all remove glutathione from the spectrum. The metal salts AgNO3 and NaAuCl4 both oxidize intracellular glutathione to diglutathione whereas BiO(NO3) has no effect. Thus colloidal preparations have a different reactivity to their parent metal salts. The differences observed between the three types of colloids (silver, gold, and bismuth) are unique to the colloids studied. None of the colloids studied were biologically inert in the erythrocyte model used.

The assessment of the HO. scavenging action of therapeutic agents

A new method is reported for the assessment of the HO. scavenging action of therapeutic agents. It is based on the photolysis of zinc oxide and has a detection limit of 3.3%. The scavenging order of the compounds tested was penicillamine > rentiapril > ascorbic acid > cysteine > glutathione > thiomalic acid > N-acetylcysteine > myocrysin > methionine. None were as effective as DMSO. It is argued that these compounds can have an in vivo protective effect where HO. is produced from oxidant producing cells, thus limiting radical induced damage.

Alteration of the erythrocyte glutathione redox balance by N-acetylcysteine, captopril and exogenous glutathione

The effect of the thiol containing compounds N-acetylcysteine and captopril on glutathione metabolism in human erythrocytes has been investigated non-invasively using 1H spin echo NMR. N-Acetylcysteine was found to increase the reduced form of glutathione while captopril increased the oxidized form, but no changes in the total glutathione concentration were observed. Incubation of the cells with buthionine sulphoximine to inhibit de novo glutathione synthesis did not affect the response. The results show that these compounds act by altering the redox balance of glutathione rather than by stimulating its synthesis, and that their mechanisms of action are different, and not simply due to the presence of the thiol group.

Increased susceptibility to oxidation of vitamin E in mitochondrial fractions compared with synaptosomal fractions from rat brains

The in vitro oxidation of vitamin E (alpha tocopherol) in rat brain synaptosomes and mitochondria by 2,2'-azo-bis-(2'-amidinopropane) dihydrochloride (ABAPH), a free radical generator, was studied. Subcellular fractions (300 micrograms total protein) were suspended in different buffers at pH 7.4 and incubated at 37 degrees C. In the presence of 0.5 mM ABAPH the mitochondrial alpha tocopherol began to get oxidized after a lag time or induction time of 15 min compared with a lag time of 30 min for the synaptosomal fraction. Thus the reserve of reducing compounds that are responsible for delaying tocopherol oxidation is less in mitochondria than in synaptosomes. More tocopherolquinone was produced during incubations without ABAPH compared with incubations in the presence of ABAPH suggesting that the mechanism of oxidation of tocopherol differs under these two conditions. When mitochondria were incubated in buffer without oxidants the production of tocopherolquinone preceded that of thiobarbituric acid reactive substances, an indicator of peroxidation of fatty acids. Therefore, alpha tocopherol is active as an anti-oxidant in mitochondrial membranes and the production of alpha tocopherolquinone could be a monitor of mild membrane oxidation under in vitro conditions. The ease of oxidation of mitochondrial tocopherol suggests a general vulnerability of the mitochondrial membranes to oxidation. Adding vitamin E or its water soluble analogs during in vitro experiments may improve the stability and viability of mitochondria. Furthermore, antioxidant protection by vitamin E may be crucial for the maintenance of tissues, such as brain, whose function is critically dependent upon the availability of high energy phosphates.(ABSTRACT TRUNCATED AT 250 WORDS)

Intracellular and extracellular antioxidant buffering levels in erythrocytes from pregnancy-induced hypertension

Both intracellular (lysate thiol, lysate glutathione and lysate superoxide dismutase) and extracellular (plasma thiol, plasma glutathione and membrane thiol) antioxidant buffering levels were measured in red blood cells from patients with pregnancy-induced hypertension (PIH). We found the following. (1) The levels of plasma thiol and plasma glutathione in PIH women with proteinuria were markedly lower than that in the normal pregnancy. (2) The concentrations of lysate glutathione and superoxide dismutase in PIH women with proteinuria were significantly decreased compared with that in the normal pregnancy. (3) With the exception of plasma and lysate glutathione, all the tested antioxidant markers were not significantly different between PIH women without proteinuria and normal pregnancy. (4) There was no statistical correlation between antioxidant buffering level and BP in patients with PIH. We concluded that both extracellular and intracellular antioxidant buffering levels were decreased in patients with PIH, especially in those with proteinuria. The reduction of the antioxidant buffering level could account for several important pathophysiological features of PIH, such as the elevation of intracellular calcium, decreased red blood cell deformability and endothelial damage.

Flow compensation in MRI using a phase-corrected real reconstruction

Flow- and motion-related artifacts are problematic in clinical MR imaging. In this paper we discuss the utility of a phase-corrected real reconstruction to reduce flow artifacts. This technique is particularly useful when flow-compensation pulse sequences may not be possible, such as when a very short echo delay or small field-of-view is desired. We will demonstrate that the phase-corrected real reconstruction provides superior results to the magnitude reconstruction either used alone or in conjunction with existing flow-compensation techniques.

A liquid chromatographic method for the simultaneous determination of alpha-tocopherol and tocopherolquinone in human red blood cells and other biological samples where tocopherol is easily oxidized during sample treatment

A liquid chromatographic method for the simultaneous determination of alpha-tocopherol and tocopherolquinone in human red blood cells is described. Tocopherols in the red cell membrane are very susceptible to oxidation during sample processing. Red cell samples are saponified in the presence of a mixture of butylated hydroxytoluene, ascorbic acid, and pyrogallol and then extracted with hexane. The tocopherol compounds are separated on a C-18 column using a mobile phase containing 12% acetonitrile, 83% methanol, and 5% buffer (NaH2PO4.H2O, 7.5 mM final concentration) and are detected electrochemically. The mixture of antioxidants is essential to avoid loss of the tocopherol compounds during processing of samples. The use of acetonitrile in the mobile phase results in the separation of tocopherolquinone from delta-tocopherol. The proposed method may be generally suitable for the analysis of biological samples where tocopherols are especially vulnerable to oxidation. The levels of tocopherolquinone and delta-tocopherol in normal red cells are quite small (less than 1% of alpha-tocopherol). The ratio of tocopherol and tocopherolquinone concentrations might serve as a useful index of the redox status of red cell membranes, particularly under in vitro conditions.

Evidence of oxidative stress in chronic heart failure in humans

Chronic heart failure (CHF) due to coronary artery disease (CAD) has been shown to be associated with increased plasma thiobarbituric reactive substances (TBARS) and reduced plasma thiol (PSH) concentrations, suggesting oxidative stress (OS). The aims of the present studies were (a) to determine whether OS is due to CAD or CHF per se and (b) to determine if a wider range of more specific markers of OS are abnormal in CHF. In the first study, two groups of patients (n = 15 each) were compared. Group 1 (11 male, mean age 56 years) had CHF due to CAD and group 2 (12 male, mean age 53 years) had non-CAD CHF. Median plasma TBARS in controls was 7.6 nmol.ml-1, 10.0 nmol.ml-1 in group 1 and 9.3 nmol.ml-1 in group 2 (P < 0.01 both groups vs control). Median PSH was 505 384 and 364 nmol.ml-1 (P < 0.05 and P < 0.01 vs control) respectively. Fifty-three patients with CHF were recruited in the second study. Malondialdehyde and PSH were 10.3 and 409 nmol.ml-1 respectively, compared to control values of 7.9 and 560 nmol.ml-1 (both P < 0.001). The median values for the following additional measures of OS in controls and patients were: erythrocyte superoxide dismutase 131 vs 114 U.l-1 (P = 0.005); caeruloplasmin oxidase 97 vs 197 U.l-1 (P < 0.01); erythrocyte glutathione 1.56 nmol.ml-1 vs 1.77 nmol.ml-1 (P < 0.02); plasma conjugated dienes 0.28 vs 0.33 optical density units (P = ns).(ABSTRACT TRUNCATED AT 250 WORDS)

Prostacyclin, thromboxane and antioxidant levels in pregnancy-induced hypertension

1. Plasma 6-keto-prostaglandin F1 alpha (6-keto-PGF 1 alpha, a major metabolite of prostacyclin), plasma thromboxane B2 (TXB2, a major metabolite of thromboxane A2) and five antioxidants (indirect markers of reactive oxygen species) namely, plasma thiol, erythrocyte lysate thiol, erythrocyte superoxide dismutase, plasma total glutathione and erythrocyte membrane thiol, were measured in 25 healthy non-pregnant women, 36 normotensive pregnant women and 35 women with pregnancy-induced hypertension (PIH). 2. The levels of TXB2 were significantly increased in normal pregnant women and PIH women with or without proteinuria compared with non-pregnant women. The concentrations of TXB2 in PIH women with proteinuria were higher than those without proteinuria (P < 0.05). 3. The levels of 6-keto-PGF1 alpha in healthy non-pregnant women and PIH women with or without proteinuria were significantly lower than that in normotensive pregnant women (all of three P < 0.01). There were no significant differences between healthy non-pregnant women and PIH women with and without proteinuria. 4. The ratio of TXB2 to 6-keto-PGF1 alpha was markedly elevated in PIH women with or without proteinuria compared with normotensive pregnant women and healthy non-pregnant women. The difference between PIH women with proteinuria and those without proteinuria was not significant (P > 0.05). 5. The levels of plasma thiol, superoxide dismutase and glutathione were significantly decreased in PIH women compared with normotensive pregnant women. 6. There were significant positive correlations between the levels of prostaglandins and antioxidant activity.(ABSTRACT TRUNCATED AT 250 WORDS)

The interaction of sodium nitroprusside with peripheral white blood cells in vitro: a rationale for cyanide release in vivo

Isolated monocytes and polymorphonuclear leukocytes release the cyanide anion from the hypotensive agent, sodium nitroprusside. The proposed mechanism involves the production of hydrogen peroxide which oxidizes the substitution inert d6 iron(II) transition metal complex to a labile d5 iron(III) complex. Consequently, the release of cyanide becomes more favoured. This mechanism is supported by the chemical release of the cyanide anion from sodium nitroprusside in vitro by hydrogen peroxide and the demonstrated ability of monocytes and polymorphonuclear leukocytes to generate hydrogen peroxide ex vivo when chemically stimulated by the nitroprusside anion. The results suggest that within a clinical environment white cell counts and cell activation induced as a consequence of disease processes may be important for predicting the toxicity of sodium nitroprusside.

Site of action for the inhibition by gold sodium thiomalate of rabbit platelet activation

The inhibitory action of the gold-based drug gold sodium thiomalate was investigated in rabbit platelets. Gold sodium thiomalate at concentrations of 0.25-13 x 10(-4) M inhibits collagen-, ADP-, and 9,11,dideoxy-11 alpha,9 alpha-epoxymethanoprostaglandin F2 alpha (U46619)-induced aggregation as well as collagen- and U46619-induced serotonin release. This inhibition occurs in both Tyrodes-albumin or Tyrodes-gelatin buffer systems. Preincubation of gold sodium thiomalate with platelets resulted in less inhibition as the time of preincubation increased. The inhibitory effect of gold sodium thiomalate could be removed by washing the platelets. Other sulfhydryl-reacting compounds, such as D-penicillamine, thiomalic acid, 5,5'-dithiobis-2-nitrobenzoic acid, and 6,6'-dithiodinicotinic acid, were all capable of inhibiting collagen-induced aggregation and serotonin release. Evidence is presented that gold sodium thiomalate interferes with the activation of rabbit platelets by several activators, that this action of gold sodium thiomalate is similar to the action of other sulfhydryl-reacting agents, that this inhibition is likely occurring at the membrane, and that the action of the drug is not dependent on the presence of albumin.

Studies of oxidative stress in cellular systems. The interaction of monocytes and erythrocytes

1H spin echo NMR spectroscopy is used to follow the interaction of intact and viable erythrocytes and monocytes obtained from different sources in mixed cultures. After a lag time (270 min) erythrocyte glutathione is observed to become more oxidised. This result is believed to occur as a consequence of monocyte activation generating hydrogen peroxide or hypochlorous acid, which is targeted at the erythrocyte. The red cell in turn employs its sulphydryl system as an anti-oxidant defence.

Domains of the catalytically self-sufficient cytochrome P-450 BM-3. Genetic construction, overexpression, purification and spectroscopic characterization

1. The gene CYP102 encoding cytochrome P-450 BM-3 and subgenes encoding the cytochrome P-450 and cytochrome P-450 reductase domains have been cloned in Escherichia coli. 2. The protein products of these genes have been overexpressed and purified to homogeneity. 3. The cytochrome P-450 domain is purified in the ferric low-spin state, but is readily converted into the high-spin state by addition of the substrate palmitate (Ks = 1 microM). The cytochrome P-450 reductase domain readily reduces cytochrome c. Mixing the two domains reconstitutes only about one-thousandth of the fatty acid hydroxylase activity associated with the intact cytochrome P-450 BM-3. 4. The X-band e.p.r. spectra of both the cytochrome P-450 domain and intact cytochrome P-450 BM-3 give g-values indicating low-spin ferric haem. The spectra are virtually identical with those of the equivalent form of cytochrome P-450 cam indicating that the haem ligation in cytochrome P-450 BM-3 is identical with that of cytochrome P-450 cam. 5. Resonance Raman spectra of the substrate-free and substrate-bound forms of the cytochrome P-450 domain are given. Spectral differences in comparison with cytochrome P-450 cam may reflect subtle electronic differences between the respective haem environments.

Evidence for oxidative stress in unstable angina

OBJECTIVE

To determine whether unstable angina, which is characterised by recurring episodes of myocardial ischaemia and reperfusion, is associated with oxidative stress (that is, where there is an imbalance between oxidants, such as free radicals, which are in excess and antioxidants).

DESIGN

Between group comparison of patients with unstable angina, stable angina, and healthy controls.

SETTING

The coronary care unit and cardiac investigation ward of a regional cardiology centre.

PATIENTS

Twenty five consecutive patients admitted to the coronary care unit with unstable angina. Twenty five consecutive patients admitted to the cardiac investigation ward (patients with stable angina undergoing coronary angiography) were used as controls for the presence of atherosclerosis, drug treatment, and smoking habit. Thirty eight healthy controls (hospital staff and patients admitted for minor surgical procedures who were otherwise healthy) were also studied.

MAIN OUTCOME MEASURES

Thiobarbituric acid related substances (TBARS) in plasma and plasma reduced thiol (PSH) as indicators of oxidative damage to lipids and proteins respectively were measured. Coronary angiography was performed in all patients with stable angina and roughly half of those with unstable angina.

RESULTS

Mean (SEM) plasma TBARS in unstable angina and stable angina were 9.95 (0.36) nmol/ml and 9.14 (0.28) nmol/ml respectively (p = 0.08). Mean plasma TBARS in healthy controls were 8.09 (0.21) nmol/ml (p < 0.05 compared with both angina groups). Mean (SEM) PSH concentration in unstable angina was 4.21 (9) nmol/ml and in stable angina was 4.85 (9) nmol/ml (p < 0.05). Mean PSH in healthy controls was 5.64 (8) nmol/ml (p < 0.001 compared with both angina groups). The extent of coronary artery disease, use of medication, and smoking habit were not significantly different between the angina groups.

CONCLUSIONS

Biochemical indicators of oxidative stress are more abnormal in unstable than stable angina. This is in keeping with experimental evidence that episodes of ischaemia and reperfusion lead to generation of free radicals and toxic oxygen species and depression of endogenous antioxidant activity. The clinical significance of this finding remains to be determined, although, experimentally, free radicals and toxic oxygen species have adverse effects on myocardial contractile function, myocardial electrical stability, endothelial mediated vasodilatation, and coagulation.

Spin echo nuclear magnetic resonance studies on intact erythrocytes: changes in cellular metabolism as a consequence of carbimazole therapy

OBJECTIVE

Because the exact mechanism of action of carbimazole is uncertain, nuclear magnetic resonance (NMR) spectroscopy was used to investigate cellular changes in erythrocytes from Graves' patients following a course of carbimazole therapy.

DESIGN

NMR spectroscopy was carried out using intact erythrocytes obtained from Graves' patients prior to and at 2 and 12 months after carbimazole treatment. The data were correlated with thyroid hormone and antibody levels.

PATIENTS

Twenty patients (four males; 16 females) with newly diagnosed and previously untreated Graves' disease were enrolled into the study. Assessments were made prior to the commencement of therapy and after 2 and 12 months on treatment. Of the 20 patients assessed at 0 and 2 months only 12 completed the study.

MEASUREMENTS

The oxidation-reduction balance of erythrocyte glutathione was measured directly using 1H spin echo NMR spectroscopy of intact cells. Thyroid hormone and antibody levels were measured using reported methods.

RESULTS

At 2 and 12 months a significant (P < 0.01) oxidation of the erythrocyte glutathione was observed. Of the four thyroid related markers (T3, T4, TRAb and TSH) assessed in this study both T3 (P < 0.001) and TRAb (P < 0.001) were observed to correlate with the NMR observed changes in glutathione. However, in-vitro experiments indicated that carbimazole does not affect red cell glutathione directly.

CONCLUSIONS

A model is presented which uses the hydrated iodium cation (I+), the natural product of T4 conversion to T3, as a chemical oxidant which can produce the observed clinical alteration in intracellular glutathione in ex-vivo erythrocytes. It is suggested that a major factor in the action of carbimazole in Graves' disease may be to stimulate the function of the deiodinase enzymes.

Estimation of the spatio-temporal correlations of biological electrical sources from their magnetic fields

Quasi-static electromagnetic systems, such as those found in biological systems, produce electric and magnetic fields whose temporal and spatial correlations reflect the source correlations in a straightforward manner. These fields can be noninvasively measured, providing information about the coherence properties of the source, which may directly represent ordered physiological processes of the organism. The description "biocoherence" will be adopted here to refer to the manifestation of the coherence in the magnetic measurements of these sources due solely to physiological processes. In this paper a general formulation linking the spatial and temporal coherence of measurable magnetic fields with the corresponding spatial and temporal coherence of the inaccessible current sources is derived in the quasi-static model. A method for reconstructing the spatial and temporal coherence of the source distribution is then presented. Such coherence maps would be useful descriptors of physiological processes occurring over time and space, and would represent more information than an image of the current sources frozen in time, or even a temporal sequence of such images.