Inhibition of Cu2+-induced LDL oxidation by nitric oxide: a study using donors with different half-time of NO release

The incubation of low density lipoproteins with Cu++ promotes oxidative modifications that make them atherogenic. Comparable alterations occur in vivo and are modulated by the generation of nitric oxide by endothelial cells or macrophages. Here we report that two donors (NOC-9 and NOC-18) with different half times of NO release (2.7 and >500 min, respectively) inhibit in vitro lipoprotein oxidation promoted by Cu++. Both donors increase the duration of the lag-phase and decrease the maximum rate of conjugated diene formation, prevent the loss of tryptophan in Apo B100, and decrease the formation of fluorescent adducts. The protective effect of NOC-9 was rapidly exhausted and its overall efficacy in preventing LDL oxidation was two orders of magnitude lower than that exhibited by NOC-18. These findings suggest that a continuous flux of NO generation, even at lower concentrations, is more efficient than considerably higher doses released as a burst in protecting both the lipid and the protein moiety of LDL from oxidation.

Disruption of actin microfilament organization by cholesterol oxides in 73/73 endothelial cells

Various cholesterol oxides generated during the oxidation of low-density lipoproteins have been reported to exert cytotoxic effects on cultured endothelial cells and to decrease their barrier function. The cytoskeleton, and in particular the actin microfilament meshwork, is one of the preferential targets in oxidative stress-and thiol-depleting agent-induced cell injury. The alterations occurring in the microfilament network were investigated using the endothelial cell line 73/73 treated with increasing concentrations (0.5-10 micrograms/ml) of cholestane-3 beta, 5 alpha, 6 beta-triol, CH, 5-cholesten-3beta-ol-7one, KC, and 25-OH-cholesterol, COH, for up to 6 h. The distribution of microfilaments was visualized using immunofluorescence and laser scanner confocal microscopy. All cholesterol oxides caused a progressive disruption of actin microfilaments that was characterized by the disappearance of the stress fibers within the cell body and, in selected cells, by a complete marginalization and clustering of the filaments to one edge of the cell. In addition, COH promoted F-actin fragmentation, as revealed by the presence of scattered fragments of F-actin in various cell regions. The redistribution of actin microfilaments was associated with a similar redistribution of alpha-actinin, an actin-binding protein involved in bundle formation and in the anchorage of actin filaments to the adhesion plaques. Concomitantly, cholesterol oxides promoted a loss of vinculin, another actin-binding protein, from the focal adhesion plaques located under the cell body and their marginalization and thinning. These alterations preceded cell detachment and cell death by apoptosis as revealed by the subsequent leakage of cytosolic enzymes and nuclear fragmentation. These results suggest that cytoskeletal (microfilament) alterations caused by cholesterol oxides may be one of the cytopathological events involved in the detachment of endothelial cells from the inner vascular surface promoted by cholesterol oxides.

Modifications of vimentin filament architecture and vimentin-nuclear interactions by cholesterol oxides in 73/73 endothelial cells

Among the different targets of the cytodamaging effects of cholesterol oxides in endothelial cells, cytoskeleton is one of the most relevant, due to the large variety of biological events controlled by this subcellular structure. The modifications of the intermediate filament network caused by three cholesterol oxides (cholestane-3beta,5alpha,6beta-triol, CH, 7-keto-cholesterol, KC, and 25-OH-cholesterol, COH) was investigated in the endothelial cell line 73/73 using immunofluorescence and laser scanner confocal microscopy. All three cholesterol oxides promoted a redistribution of vimentin filaments that took place well before cell detachment and the occurrence of any detectable sign of cell death. CH-induced alterations were characterized by the polarization of vimentin to the edges of the cell and a concomitant destruction of its interaction with the nucleus. In KC-treated cells, vimentin filaments appeared cross-linked and formed a sort of circular network ring between the nucleus and the cell periphery. COH promoted the aggregation of vimentin filaments in thick and irregular bundles that delimited apparently empty regions. All these changes occurred independently of gross modifications in microtubule organization, which was generally retained except for the appearance of immunoreactive tubulin spots throughout the cytoplasm. These results indicate that the organization of the intermediate-size filament protein vimentin is markedly affected by cholesterol oxides. The different rearrangements caused by CH, KC, and COH may derive from different pathobiochemical processes triggered by these compounds.

4-Hydroxynonenal triggers Ca2+ influx in isolated rat hepatocytes

Addition of micromolar concentrations of 4-hydroxynonenal (4-HNE), a reactive end-product of lipid peroxidation, to isolated rat hepatocytes was found to cause an early and transient increase in cytosolic Ca2+ concentration followed by a more pronounced and progressive elevation. Such a late effect of 4-HNE was prevented by chelation of extracellular Ca2+ with EGTA or by the addition of GdCl3, which is known to block the activity of store operated Ca2+ channels in the hepatocyte plasma membrane. Moreover, the preincubation of isolated hepatocytes with the phospholipase C inhibitor U73122 resulted in a complete inhibition of both the early increase of cytosolic Ca2+ and the subsequent Ca2+ inflow. When 4-HNE was added to the hepatocytes 5 min after the emptying of intracellular Ca2+ pools by thapsigargin, the aldehyde caused a further increase in the accumulation of Ca2+ which was prevented in the presence of GdCl3. Taken together these results indicate that in hepatocytes 4-HNE causes Ca2+ inflow across GdCl3-sensitive Ca2+ channels. The mechanism responsible for such an effect is triggered by the emptying of intracellular Ca2+ pools likely resulting from 4-HNE mediated stimulation of phospholypase C, but 4-HNE also appears to interfere with the channel protein(s) or with the mechanism(s) regulating capacitative Ca2+ inflow.

Low density lipoprotein oxidation is inhibited in vitro by olive oil constituents

Oxidation of low density lipoproteins maybe a factor in the development of atherosclerosis. The Mediterranean diet rich in vegetables, grains, legumes, fruits, and oils, mainly olive oil, has been suggested to reduce the incidence of coronary heart disease, because of its low saturated and high monounsaturated fatty acids content. It is also possible that the natural antioxidants in the oil help to prevent lipid oxidation, e.g. that of low density lipoproteins, thus retarding the formation of atherosclerotic plaques. First-pressed, extra-virgin olive oil contains appreciable amounts of polyphenolic compounds that prevent its autoxidation and are responsible for its high stability. We tested these compounds on low density lipoprotein oxidation and found an inhibitory effect, at low concentrations, on various indexes of lipid oxidation (vitamin E content, formation of thiobarbituric acid-reacting substances, lipid peroxides, levels of polyunsaturated fatty acids, protein modification, conjugated diene formation). Our data suggest that natural antioxidants could play a role in inhibiting the formation of cytotoxic products such as lipid peroxides thus retarding the onset of the atherosclerotic damage.

Twenty four-hour ambulatory blood pressure monitoring in women with pre-eclampsia

The aim of our study was to evaluate by means of ambulatory 24 h monitoring the diurnal systolic (SBP) and diastolic (DBP) blood pressure profiles in a group (n = 18) of gravid patients with pre-eclampsia compared with a group (n = 17) of healthy control subjects matched for age and week of gestation to assess whether: (i) ambulatory BP is also raised in pre-eclampsia; (ii) the increase of BP, if present, occurs to the same extent during both daytime and night; and (iii) a blunted BP pattern is consistently present in pre-eclampsia. BP was recorded at intervals of 15 min for 25 h using a TM2420 non-invasive pressurometer. The presence of a circadian rhythm of BP was assessed by cosinor analysis. SBP was higher in women with pre-eclampsia (24 h average 115 +/- 11 vs. 136 +/- 12, P = 6 x 10(-6); daytime 117 +/- 12 vs. 139 +/- 13, P = 6 x 10(-6); night 110 +/- 11 vs. 129 +/- 14, P = 5 x 10(-5) as well as DBP (24 h average 67 +/- 5 vs. 86 +/- 6, P = 8 x 10(-12); daytime 69 +/- 6 vs. 89 +/- 5, P = 2 x 10(-11); night 62 +/- 4 vs. 80 +/- 8, P = 5 x 10(-10).(ABSTRACT TRUNCATED AT 250 WORDS)

Alteration of Na+ homeostasis as a critical step in the development of irreversible hepatocyte injury after adenosine triphosphate depletion

The exposure of isolated hepatocytes to the redox-cycling quinone menadione caused an early loss of mitochondrial membrane potential, adenosine triphosphate (ATP) depletion, and decreased intracellular pH. These alterations were followed by an increase in intracellular Na+ and, ultimately, cell death. If HCO3- was omitted from the incubation buffer, or the hepatocytes were incubated in an acidic medium (pH 6.5) the accumulation of Na+ was markedly reduced. Inhibition of the Na+/H+ exchanger and of the Na+/HCO3- cotransporter by, respectively, amiloride and 4,4'-di-isothiocyano-2,2'-disulfonic acid stilbene (DIDS) suppressed the initial Na+ influx but did not prevent subsequent Na+ accumulation, because amiloride and DIDS inhibited the Na+/K+ pump. The omission of HCO3- from the extracellular medium or the incubation in acidic conditions also prevented menadione toxicity, without interfering with the loss of mitochondrial membrane potential and with ATP depletion. A similar protection was evident when hepatocytes were incubated with menadione in a medium without Na+. The preservation of adequate levels of ATP by supplementing hepatocytes with fructose allowed the initial Na+ load to be recovered and provided partial protection against menadione toxicity. These effects were suppressed if Na+/K(+)-ATPase was inhibited with ouabain. Taken together, these results indicated that the activation of the Na+/HCO3- cotransporter and of the Na+/H+ exchanger in response to the decrease of intracellular pH stimulated an enhanced influx of Na+. When the activity of the Na+/K+ pump was not able to control Na+ levels because of ATP depletion, such an uncontrolled Na+ influx precipitated irreversible injury and caused hepatocyte death.

The operation of Na+/Ca2+ exchanger prevents intracellular Ca2+ overload and hepatocyte killing following iron-induced lipid peroxidation

Stimulation of lipid peroxidation by incubating isolated rat hepatocytes with ADP/FeCl3 caused a time dependent increase in cytosolic free Ca2+ levels, without influencing cellular Na+ content. Omission of Na+ from the incubation medium greatly increased the accumulation of Ca2+, which was partially reverted upon transferring the cells in a Na+ containing medium. This suggested that a Na(+)-dependent Ca2+ transporter was activated upon the elevation of cytosolic Ca2+ and partially counteracted the influx of Ca2+ promoted by lipid peroxidation. In the presence of Na+ cell death was not associated with the increase of Ca2+ induced by peroxidative injury; however, decrease of mitochondrial membrane potential and loss of cell viability followed by massive accumulation of Ca2+ occurring in hepatocytes incubated with ADP/FeCl3 in a Na(+)-free medium. Both these effects were completely prevented by chelation of extracellular Ca2+ with EGTA. Thus, we conclude that Na(+)-dependent Ca2+ transporter is involved in controlling excessive accumulation of Ca2+ induced by stimulation of lipid peroxidation and can prevent hepatocyte death caused by Ca(2+)-dependent alterations of mitochondrial activity.

[Oxidation of low-density lipoproteins. Correlation between reduced resistance in vitro and increased oxidation in vivo]

OBJECTIVES

The oxidation of low-density lipoproteins has been recently proposed as one of the critical factors in promoting atherogenesis. This process results from the balance between the prooxidant stimuli and the endogenous antioxidants present in LDL and strictly depends on the concentration of oxidizable substrates, namely unsaturated fatty acids.

METHODS

Twelve male hypertriglyceridaemic patients were investigated before and after oral supplementation with omega-3 polyunsaturated fatty acids (PUFA) and compared with eighteen untreated healthy matched control subjects. The plasma lipid profile was measured in all patients. LDL oxidation was evaluated as both the susceptibility to in vitro oxidation and the presence of plasma anti-oxidized LDL antibodies (as a marker for in vivo oxidation).

RESULTS

Omega-3-fatty acid supplementation caused a significant reduction in plasma triglyceride level (267 +/- 38 vs 375 +/- 33 mg/dl, p < 0.01) and decreased the resistance of LDL to oxidation as revealed by an early and accelerated generation of conjugated dienes following exposure to CuSO4 (105.3 +/- 7 vs 133 +/- 9.3 min, p < 0.01). Moreover, the concentration of the antioxidant vitamin E in LDL was slightly but significantly decreased at the end of the treatment (2.59 +/- 0.19 vs 2.89 +/- 0.17 nmol/mg LDL, p < 0.05), but its efficiency in preventing LDL oxidation was unaltered. Furthermore, a marked increase of the plasma anti-oxidised LDL antibody titre was found in nearly all patients at the end of the treatment (2.08 +/- 0.48 vs 1.37 +/- 0.2 anti-oxidised/anti-native LDL antibody ratio, p < 0.001).

CONCLUSION

These results indicate that PUFA supplementation decreases the resistance of LDL to in vitro oxidation and that this decreased resistance is accompanied by an enhanced LDL oxidation in vivo.

Sodium-mediated cell swelling is associated with irreversible damage in isolated hepatocytes exposed to hypoxia or mitochondrial toxins

Incubation of isolated rat hepatocytes under hypoxic conditions or in the presence of inhibitors of mitochondrial functions such as KCN or carbonylcyanide m-chlorophenylhydrazone (CCCP) causes an increase of intracellular Na+ content and cell swelling. Both these effects precede the appearance of irreversible damage as measured by trypan blue staining of non-vital hepatocytes. When the increase of cellular Na+ is prevented by substitution of NaCl in the incubation medium with equimolar amount of choline chloride both cell swelling and loss of viability are greatly reduced. Thus, we propose that osmotic stress induced by an uncontrolled accumulation of Na+ might be associated with the ultimate events precipitating irreversible membrane lesions in hepatocyte undergoing metabolic inhibition.

Autoantibodies against oxidatively modified low-density lipoproteins in NIDDM

Diabetes is an independent risk factor in the development of atherosclerosis, although the pathophysiological processes underlying this association are poorly understood. The oxidation of low-density lipoprotein (LDL) is considered a key event in the development and progression of atherosclerosis because it generates molecular epitopes that are more atherogenic than parent LDL. A total of 138 patients suffering from non-insulin-dependent diabetes mellitus (NIDDM) and 80 matched control subjects were investigated. LDL oxidation was evaluated as the presence of autoantibodies against oxidatively modified LDL, since they mirror the in vivo occurrence of oxidative processes. NIDDM patients had an antibody ratio (calculated as the ratio of antibodies against modified versus native LDL) significantly higher than control subjects for Cu(2+)-oxidized LDL (1.88 +/- 0.6 vs. 1.05 +/- 0.3, P < 0.01, for IgG), malondialdehyde-modified LDL (2.54 +/- 0.73 vs. 2.04 +/- 0.11, P < 0.01, for IgG and 3.96 +/- 1.51 vs. 2.90 +/- 0.15, P < 0.01, for IgM), and malondialdehyde-modified human serum albumin (1.79 +/- 0.54 vs. 1.46 +/- 0.1, P < 0.05 for IgG). The possible role played by glycation in sensitizing LDL to oxidation was investigated by measuring autoantibodies against both glycated LDL (glycLDL) and glycoxydated LDL (glycoxLDL). NIDDM patients had an antibody ratio significantly higher than control subjects for anti-glycLDL and anti-glycoxLDL IgG (1.79 +/- 0.38 vs. 1.12 +/- 0.23, P < 0.01 and 2.55 +/- 1.03 vs. 1.39 +/- 0.44, P < 0.01, respectively) but not anti-glycLDL and anti-glycox-LDL IgM.(ABSTRACT TRUNCATED AT 250 WORDS)

Presence of autoantibodies against oxidatively modified low-density lipoprotein in essential hypertension: a biochemical signature of an enhanced in vivo low-density lipoprotein oxidation

OBJECTIVE

We have previously reported that low-density lipoproteins (LDL) isolated from patients with essential hypertension are more susceptible to in vitro oxidation than lipoproteins isolated from normotensive control subjects. In the present study we investigated the occurrence of in vivo LDL oxidation in hypertensive patients.

DESIGN

The presence of antioxidatively modified LDL autoantibodies was taken as a suitable index of in vivo LDL oxidation because, after oxidative modifications, LDL express antigenic epitopes that elicit an immune response. The antibody titres were measured in plasma from untreated patients with newly diagnosed essential hypertension.

METHODS

An enzyme-linked immunosorbent assay method was employed, using native LDL, Cu(2+)-oxidized LDL and malondialdehyde-derivatized LDL (MDA-LDL) as antigens. Human serum albumin and MDA human serum albumin were also used to monitor cross-reactivity with other oxidized molecules. The antibody titre was expressed as the ratio between anti-modified and anti-native antigen absolute values.

RESULTS

The patients with essential hypertension had an antibody ratio significantly higher than control subjects with respect to anti-Cu(2+)-oxidized LDL immunoglobulins G and M, and with respect to anti-MDA-LDL immunoglobulins G and M. A significant positive correlation was found between anti-MDA-LDL and anti-Cu(2+)-oxidized LDL antibody titres. The anti-MDA human serum albumin antibody titre was not different in the two groups of patients. An inverse correlation was detected between the anti-MDA-LDL immunoglobulin M titre and the age of the patients.

CONCLUSIONS

The results obtained are consistent with the view that, during the early phases of hypertension development, LDL undergo in vivo oxidation that is mirrored by the generation of autoantibodies against epitopes of oxidized LDL. The oxidation process appears specific for LDL and might be relevant both for the progression of hypertension and for the development of the atherosclerosis that often complicates hypertension itself.

Detection of antibodies against proteins modified by hydroxyethyl free radicals in patients with alcoholic cirrhosis

BACKGROUND/AIMS

We have previously shown that hydroxyethyl free radicals produced during cytochrome P4502E1-mediated oxidation of ethanol covalently bind to microsomal proteins. The present study examined whether alkylation of proteins by hydroxyethyl radicals induces an immunologic response in alcoholic patients.

METHODS

A microplate enzyme-linked immunosorbent assay was developed using as antigen human serum albumin or bovine fibrinogen reacted with chemically produced hydroxyethyl radicals.

RESULTS

This assay showed that the sera of alcoholic cirrhotics contained both immunoglobulin (Ig) Gs and IgAs that recognized proteins modified by hydroxyethyl radicals, whereas practically no reaction was observed in the sera of healthy controls or cirrhotics without evidence of alcohol abuse. The reactivity of the sera from alcoholic patients was not influenced by the protein to which hydroxyethyl radicals were bound. The sera of alcoholic cirrhotics also contained antibodies directed against acetaldehyde-modified albumin. However, the reaction of alcoholic sera with hydroxyethyl radical epitopes was not inhibited by increasing concentrations of acetaldehyde-modified albumin produced under either reducing or nonreducing conditions.

CONCLUSIONS

The results indicate that a new group of antigens that do not cross-react with antibodies against acetaldehyde-derived epitopes is formed by the alkylation of protein by hydroxyethyl radicals and is involved in the development of immunologic reactions in alcoholic patients.

LDL oxidation in patients with severe carotid atherosclerosis. A study of in vitro and in vivo oxidation markers

Among the various risk factors involved in the development and progression of carotid atherosclerosis, the oxidation of LDL has been proposed to play a relevant role. LDL oxidation has been investigated in 94 patients with severe carotid atherosclerosis undergoing elective carotid artery endarterectomy and in 42 matched control subjects. LDL oxidation was evaluated in all patients as (1) the susceptibility to in vitro oxidation, (2) vitamin E concentration and its efficiency in LDL, and (3) the presence of autoantibodies against oxidatively modified lipoprotein to monitor the occurrence of the oxidative processes taking place in vivo. No difference was detected between control subjects and patients concerning vitamin E concentration and the kinetics of conjugated diene formation in isolated LDL exposed to CuSO4. However, vitamin E efficiency was lower (9.6 +/- 4.2 versus 30.2 +/- 7.6 min/nmol vitamin E) and the duration of the vitamin E-independent lag phase was longer (105.5 +/- 16.5 versus 58 +/- 11.8 minutes) in the patient group. Autoantibodies against oxidatively modified lipoproteins were measured with an ELISA method using native LDL, Cu(2+)-oxidized LDL (oxLDL), or malondialdehyde-derivatized LDL (MDA-LDL) as antigens. To monitor cross-reactivity of the antibodies detected with other oxidatively modified proteins, human serum albumin (HSA) and MDA-derivatized HSA (MDA-HSA) were also employed. The antibody titer was calculated as the ratio of antibodies against modified versus native proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Autoantibodies against oxidatively-modified LDL in uremic patients undergoing dialysis

Target-specific oxidation processes in LDL generate molecular epitopes that are more atherogenic than the native forms and are able to elicit an immunological reaction leading to the formation of anti-oxLDL autoantibodies (oxLDL-Ab) that may participate in the overall process of atherogenesis. Thus, the detection of oxLDLAb, in addition to mirroring the occurrence of in vivo LDL oxidation, will give valuable information on the occurrence of this immune response. Plasma oxLDLAb (IgG and IgM) were measured in 72 control subjects (CS) and in 80 patients with chronic renal failure (CRF), undergoing repetitive hemodialysis (N = 56) or peritoneal dialysis (N = 24), with an ELISA method using native LDL, CuSO4-oxidized LDL (oxLDL) or malondialdehyde-derivatized LDL (MDA-LDL) as antigens. To monitor cross reactivity of the antibodies detected with other oxidatively-modified proteins, human serum albumin (HSA) and MDA-derivatized HSA (MDA-HSA) were also employed as antigens. The antibody titer was calculated as the ratio of antibodies against modified versus native proteins. CRF patients had an antibody ratio significantly higher than CS as concerning anti-oxLDL IgG (1.39 +/- 0.36 vs. 1.05 +/- 0.3, P < 0.05) and IgM (2.15 +/- 0.75 vs. 1.43 +/- 0.43, P < 0.01), and anti-MDA-LDL IgG (3.05 +/- 0.74 vs. 2.04 +/- 0.42, P < 0.01) and IgM (5.55 +/- 1.79 vs. 2.9 +/- 0.85, P < 0.01). The anti-MDA-HSA antibody titer was also higher in CRF patients than in CS (2.49 +/- 0.5 vs. 1.46 +/- 0.39, P < 0.01 for IgG and 2.80 +/- 1.03 vs. 1.26 +/- 0.43, P < 0.01 for IgM).(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for a sodium-dependent calcium influx in isolated rat hepatocytes undergoing ATP depletion

ATP depletion caused by menadione and triethyllead in isolated hepatocytes is associated with intracellular acidosis and a sustained increase in intracellular Na+ and Ca2+ concentrations. Removal of Na+ from the incubation medium as well as the inclusion of EGTA largely prevented the increase in cytosolic Ca2+, thus indicating that Ca2+ was mobilized from the extracellular medium in response to Na+ load. To further validate these findings, hepatocytes were incubated with a combination of sodium propionate and ouabain in order to induce intracellular acidosis and inhibit Na+ extrusion. This treatment promoted a marked increase in intracellular Na+ and Ca2+ concentrations that was prevented by omission of Na+ from the incubation medium as well as by agents that inhibited cellular Na+ influx. These data indicate that following Na+ load, Ca2+ can be accumulated in hepatocytes via a Na+/Ca2+ antiporter operating on a reverse mode.

Enhanced LDL oxidation in uremic patients: an additional mechanism for accelerated atherosclerosis?

Since oxidized low-density lipoprotein (LDL) is more atherogenic than native LDL, LDL oxidation was investigated in uremic patients who often develop accelerated atherogenesis. Three groups of uremic patients were studied (10 on predialysis conservative therapy, 11 on repetitive hemodialysis, 13 on peritoneal dialysis) and compared with seventy matched controls. LDL oxidation was evaluated in all patients as: (i) the susceptibility to in vitro oxidation (by measuring the resistance to Cu(++)-induced formation of conjugated dienes), (ii) vitamin E concentration in LDL, and (iii) presence of plasma anti-oxidized LDL antibodies, expressed as the ratio anti-oxLDL/anti-nativeLDL antibodies. The lipid profile was studied in all patients. Vitamin E concentration did not differ between the various groups, although LDL from uremic patients appeared more susceptible to in vitro and in vivo oxidation (as demonstrated by an earlier generation of conjugated dienes and by the presence of an higher antibody ratio) compared to control subjects. Subclass analysis of the different patients revealed that peritoneal dialysis treatment ameliorated the oxidation markers. However, a prolonged dialytic treatment caused a decrease in vitamin E concentration in LDL and increased their susceptibility to oxidation.

Thyroxine pretreatment and halothane administration alter Ca2+ transport and transmembrane potential in rat liver mitochondria. An additional mechanism for halothane-induced liver damage in the hyperthyroid rat model

Male rats pretreated with thyroid hormones and exposed to halothane in non-hypoxic conditions develop acute liver damage. In order to investigate the mechanisms leading to liver damage in this animal model, the effects of thyroxine (T4) pretreatment and halothane administration on Ca2+ transport and transmembrane potential were studied in isolated rat liver mitochondria. Five-day T4-pretreatment reduced the mitochondrial Ca2+ loading capacity and increased the rate of Ca2+ cycling across the mitochondrial membrane. Halothane administration further increased Ca2+ cycling and produced a time- and dose-dependent loss of transmembrane potential which was more pronounced in mitochondria from T4-pretreated rats than in euthyroid animals. When mitochondria from T4-pretreated rats were incubated in the presence of the Ca2+ chelator EGTA, membrane potential was well preserved. In contrast, when Ca2+ concentration in the extramitochondrial medium was increased, mitochondria deenergization occurred earlier. These findings confirm that alterations in Ca2+ transport and mitochondrial function can be interrelated events and suggest that a Ca(2+)-dependent, halothane-induced loss of transmembrane potential could participate in generating acute liver damage in hyperthyroid rats exposed to halothane in non-hypoxic conditions.

Alterations of hepatocyte Ca2+ homeostasis by triethylated lead (Et3Pb+): are they correlated with cytotoxicity?

Isolated rat hepatocytes were used to investigate the biochemical mechanisms of toxicity of triethyllead (Et3Pb+), a highly neurotoxic degradation product of the antiknocking petrol additive tetraethyllead. As early as 5 min from the addition of 50 microM Et3Pb+ to hepatocyte suspensions a decrease of mitochondrial membrane potential and of the capacity of mitochondria and microsomes to retain Ca2+ occurred. A dose-dependent release of mitochondrial Ca2+ as well as an inhibition of microsomal Ca(2+)-ATPase activity were also evident when Et3Pb+ (from 2.5 microM up to 50 microM) was added to, respectively, isolated liver mitochondria and microsomes. Further experiments using hepatocytes loaded with the Ca2+ indicator Fura-2AM demonstrate that 1 min from addition of Et3Pb+ the cytosolic free Ca2+ levels increased by about 3-fold. High affinity plasma membrane Ca(2+)-ATPase activity was also significantly inhibited in hepatocytes treated with Et3Pb+, suggesting that an impairement of the mechanisms controlling the efflux of extracellular Ca2+ was concomitantly involved in the rise in cytosolic Ca2+ concentration. The increase in the cytosolic Ca2+ levels caused by Et3Pb+ was followed by a rapid decline of cell viability. However, the addition of EGTA or of the intracellular Ca2+ chelator BAPTA/AM did not affect either the time-course or the extent of cytotoxicity. Conversely, fructose, a glycolytic substrate that was able to support ATP production, prevented hepatocyte death. Thus, the depletion of cellular energy stores rather than the increase in cytosolic Ca2+ appears to be the mechanism by which Et3Pb+ causes irreversible injury in isolated hepatocytes.

CoA and fatty acyl-CoA derivatives mobilize calcium from a liver reticular pool

The effect of CoA and fatty acyl-CoA esters on Ca2+ fluxes has been studied in isolated liver microsomes and in digitonin-permeabilized hepatocytes. When microsomes were loaded with increasing concentrations of Ca2+ (6-29 nmol/mg of protein), the extent to which CoA and palmitoyl-CoA released Ca2+ increased. At 23 nmol of Ca2+/mg of protein, half-maximal [CoA] and [palmitoyl-CoA] were 35 and 50 microM respectively. Under conditions of minimal Ca2+ loading, net release of Ca2+ was absent, but Ca2+ translocation from a CoA-sensitive to a CoA-insensitive pool took place. The effect of CoA required the presence of fatty acids, probably to form fatty acyl esters. In permeabilized hepatocytes, the pool(s) mobilized by CoA (or by palmitoyl-CoA) appeared to be different from that mobilized by Ins(1,4,5)P3.

Low-density lipoprotein oxidation in essential hypertension

OBJECTIVES

To investigate the occurrence of enhanced low-density lipoprotein (LDL) oxidation as an additional factor promoting atherosclerosis progression in hypertensive patients.

DESIGN

The oxidation of plasma LDL was investigated in a group of untreated patients with mild-to-moderate essential hypertension without clinically evident target organ damage and in a group of control subjects.

METHODS

LDL oxidation was evaluated as both the susceptibility to oxidation in vitro and the presence of plasma anti-oxidized LDL antibodies (as an index for oxidation in vivo).

RESULTS

LDL from hypertensive subjects exhibited enhanced susceptibility to oxidation in vitro as revealed by early and accelerated generation of conjugated dienes after exposure to CuSO4. Vitamin E concentration in LDL from hypertensive subjects was slightly but significantly decreased and its efficiency in protecting LDL from oxidation was impaired. Furthermore, a higher plasma anti-oxidized LDL titre was found in hypertensive patients. Subclass analysis revealed that the contemporary presence of hypercholesterolaemia did not significantly modify either the increased susceptibility of LDL to oxidation or the presence of plasma anti-oxidized LDL antibodies detected in hypertensive patients. Moreover, no correlation was found between LDL oxidation parameters and blood pressure values.

CONCLUSIONS

LDL from hypertensive patients is more susceptible to oxidation in vitro and is more promptly oxidized in vivo. These findings suggest a possible participation of LDL oxidation in promoting and accelerating the atherosclerosis that often develops in hypertensive patients.

Ca2+ and endonuclease activation in radiation-induced lymphoid cell death

Exposure of lymphoid cells to X-irradiation caused an increase in cytosolic Ca2+ ([Ca2+]i) in rat thymocytes but not in rat splenocytes. The Ca2+ elevation in rat thymocytes was transitory and by 2 h postirradiation, when the chromatin degradation began to be appreciable, the [Ca2+]i had returned to control level. Inhibitors of RNA and protein syntheses prevented the radiation-induced [Ca2+]i rise in thymocytes. Pretreatment of both cell types with Ca2+ chelators also prevented DNA fragmentation, chromatin condensation, and cell death caused by X-irradiation. These data suggest that Ca2+ plays an important role in the perpetuation of apoptosis in both thymocytes and splenocytes although a Ca2+ elevation, which may serve as a signal in thymocytes, does not appear to be required to initiate radiation-induced DNA fragmentation in splenocytes.

Intraluminal calcium of the liver endoplasmic reticulum stimulates the glucuronidation of p-nitrophenol

The relationship between the intraluminal Ca2+ content of endoplasmic reticulum and the rate of the glucuronidation of p-nitrophenol was investigated in isolated rat hepatocytes. Different agents which decrease the Ca2+ level in the endoplasmic reticulum [calcium ionophores (A23187, ionomycin) or Ca(2+)-ATPase inhibitors(thapsigargin,2,5-di-(t-butyl)-1,4-benzohydroquinone+ ++)] inhibited the conjugation of p-nitrophenol. Depletion of intracellular Ca2+ stores by preincubation of hepatocytes in the absence of free Ca2+ (in the presence of excess EGTA) also decreased the rate of glucuronidation; Ca2+ re-admission to EGTA-treated hepatocytes restored glucuronidation. In intact liver microsomes the p-nitrophenol UDP-glucuronosyl-transferase activity was not modified by varying the external free Ca2+ concentrations within a cytosol-like range. Emptying of the Ca2+ from the lumen of microsomal vesicles by A23187, after MgATP-stimulated Ca2+ sequestration, decreased the glucuronidation of p-nitrophenol. A similar effect was observed in filipin-permeabilized hepatocytes. In native and in detergent-treated microsomes, Ca2+ (1-10 mM) increased the p-nitrophenol UDP-glucuronosyltransferase activity. It is suggested that the physiological concentration of Ca2+ in the lumen of the endoplasmic reticulum is necessary for the optimal activity of p-nitrophenol UDP-glucuronosyltransferase; the depletion of Ca2+ decreases the activity of the enzyme.

Physiological concentrations of inorganic phosphate affect MgATP-dependent Ca2+ storage and inositol trisphosphate-induced Ca2+ efflux in microsomal vesicles from non-hepatic cells

1. MgATP-dependent 45Ca2+ uptake by microsomes obtained from various non-hepatic tissues, namely rat brain, rat solid Morris hepatoma 3924A and human platelets, was measured in the presence of P(i) at low, cytosol-like, concentrations. 2. Increasing P(i) concentrations (0.5-3 mM) caused a progressive enlargement of the 45Ca(2+)-storage capacity of all the microsomal fractions. 3. As a result of P(i) stimulation of Ca2+ uptake, 45Ca2+ and [32P]P(i) were co-accumulated by the three microsomal fractions. 4. The time course for 45Ca2+ and [32P]P(i) accumulation in brain microsomes revealed a biphasic 45Ca2+ uptake: a rapid phase was followed by a second, slower, phase, which depended on the presence of P(i). During the P(i)-dependent phase, the uptake of 45Ca2+ was paralleled by the uptake of [32P]Pi. 5. The passive efflux of Ca2+ was paralleled by the efflux of P(i) and vice versa. In fact, the inhibition of active Ca2+ uptake by excess EGTA, or lowering the P(i) concentration of the incubation system by dilution, caused the release of 45Ca2+ and [32P]P(i) from 45Ca2+ or [32P]P(i) pre-loaded brain microsomes. The Ca2+ ionophore A23187 also released 45Ca2+ and [32P]P(i). 6. Ca2+ efflux by A23187 was rapid (t 1/2 approx. 2 s) and independent of the extent of intravesicular Ca2+ loading, which indicates that Ca2+ and P(i) do not form intravesicular insoluble complexes. 7. The progressive increase in Ca2+ accumulation, depending on P(i) stimulation, resulted in a proportional increase in the amount of Ca2+ releasable by InsP3 in the three non-hepatic microsomal fractions and in digitonin-permeabilized platelets. 8. Concomitantly to Ca2+, microsomal P(i) was also released by InsP3.

Permeability of rat liver microsomal membrane to glucose 6-phosphate

Light-scattering measurements of osmotically induced changes in the size of rat liver microsomal vesicles pre-equilibrated in a low-osmolality buffer revealed the following. (1) The increase in extravesicular osmolality by addition of glucose 6-phosphate or mannose 6-phosphate (25 mM each) caused a rapid shrinking of microsomal vesicles. After shrinkage, a rapid swelling phase (t1/2 approx. 22 s) was present with glucose 6-phosphate but absent with mannose 6-phosphate, indicating that the former had entered microsomal vesicles, but the latter had not. (2) Almost identical results were obtained in the absence of any glucose 6-phosphate hydrolysis, i.e. with microsomes pre-treated with 100 microM-vanadate. (3) The anion-channel blocker 4,4'-di-isothiocyanostilbene-2,2'-disulphonic acid (DIDS) suppressed the glucose 6-phosphate-induced swelling phase. (4) The swelling phase was more prolonged as the glucose 6-phosphate concentration increased (t1/2 = 16 +/- 3, 22 +/- 3 and 35 +/- 4 s with 25 mM, 37.5 mM- and 50 mM-glucose 6-phosphate respectively). The behaviour of glucose-6-phosphatase activity of intact and disrupted microsomes measured in the presence of high concentrations (less than 30 mM) of substrate also indicated the saturation of the glucose 6-phosphate permeation system by extravesicular concentrations of glucose 6-phosphate higher than 20-30 mM. Additional experiments showed that vanadate-treated microsomes pre-equilibrated with 0.1 mM- and 1.0 mM-glucose 6-phosphate (and [1-14C]glucose 6-phosphate as a tracer) rapidly (t1/2 less than 20 s) released [1-14C]glucose 6-phosphate when diluted in a glucose 6-phosphate-free medium. The efflux of [1-14C]glucose 6-phosphate was largely prevented by DIDS, allowing an evaluation of the intravesicular space of glucose 6-phosphate of approx. 1.0 microliter/mg of microsomal protein.

Apoptosis--programmed cell death: a role in the aging process?

Cells continuously exposed to genotoxic agents, such as oxygen free radicals (OFRs), deeply involved in the aging process use a variety of cellular defense mechanisms. These defense mechanisms include DNA repair enzymes, antioxidants, poly(ADP-ribosyl)polymerase (pADPRP), and stress proteins and they constitute an integrated network. An age-related failure of the efficiency of this network can affect cell proliferation and cell death, two phenomena tightly linked and regulated. Recent data from our laboratory on the role of DNA damage and pADPRP activation and on the type of cell death induced by OFRs in human lymphocytes are reviewed. In vitro and in vivo data on possible strategies to reduce oxidative stress in lymphocytes from normal and Down syndrome subjects, by using natural compounds and trace elements, are presented. They indicate that nicotinamide and L-carnitine protect human cells from OFR-induced damage and suggest that they are possible candidates as antiaging substances.

Demonstration of nuclear compartmentalization of glutathione in hepatocytes

The intracellular distribution of glutathione (GSH) in cultured hepatocytes has been investigated by using the compound monochlorobimane (BmCl), which interacts specifically with GSH to form a highly fluorescent adduct. Image analysis of BmCl-labeled hepatocytes predominantly localized the fluorescence in the nucleus; the nuclear/cytoplasmic concentration gradient was approximately three. This concentration gradient was collapsed by treatment of the cells with ATP-depleting agents. The uneven distribution of BmCl fluorescence was not attributable to (i) nonspecific interaction of BmCl with protein sulfhydryl groups, (ii) any selective nuclear localization of the GSH transferase(s) catalyzing formation of the GSH-BmCl conjugate, or (iii) any apparent alterations in cell morphology from culture conditions, suggesting that this distribution did, indeed, reflect a nuclear compartmentalization of GSH. That the nuclear pool of GSH was found more resistant to depletion by several agents than the cytoplasmic pool supports the assumption that GSH is essential in protecting DNA and other nuclear structures from chemical injury.

Tumor necrosis factor alpha induces apoptosis in mammary adenocarcinoma cells by an increase in intranuclear free Ca2+ concentration and DNA fragmentation

The incubation of human mammary adenocarcinoma cells (BT-20) with tumor necrosis factor alpha in the absence or presence of cycloheximide resulted in progressive DNA fragmentation. This was preceded by a sustained increase in intracellular free Ca2+ concentration and was not detected in cells pretreated with intracellular Ca2+ chelators, calmodulin antagonists, or activators of protein kinase C. Image analysis of fura-2-loaded BT-20 cells treated with tumor necrosis factor alpha revealed that, in many cells, the initial increase in Ca2+ level occurred in a cellular region that corresponded to the localization of the nucleus. Our findings suggest that tumor necrosis factor alpha can promote an increase in intranuclear free Ca2+ which, in turn, may stimulate Ca(2+)-dependent endonuclease activity, resulting in DNA fragmentation and apoptosis.

Biological markers of oxidative stress in mitochondrial myopathies with progressive external ophthalmoplegia

According to experimental models suggesting that overproduction of oxygen free-radicals may occur when the electron transport in the respiratory chain is impaired, we searched for in vivo biological markers of oxidative stress in 11 patients affected by histologically proven mitochondrial myopathy with progressive external ophthalmoplegia (PEO) and partial cytochrome c oxidase deficiency in muscle fibres. Six of the patients carried large-scale deletions of mitochondrial DNA. Biochemical assays included the determination of plasma and erythrocyte reduced glutathione (GSH) concentration, plasma malondialdehyde, fluorescent adducts of aldehydes with plasma proteins, and serum level of lipid peroxides. In patients with PEO the mean values of lipid peroxides and of the fluorescent adducts of aldehydes with plasma proteins were significantly higher with respect to normal controls, while the mean values of plasma and erythrocyte GSH concentration were significantly lower. The reported data indicate an increase of lipid peroxidation indexes along with the reduction of one of the most important antioxidant systems and suggest the hypothesis that overproduction of reduced oxygen species might be an adjunctive cause of cell damage in mitochondrial myopathies and encephalomyopathies associated with defects of oxidative phosphorylation.

Role of a nonmitochondrial Ca2+ pool in the synergistic stimulation by cyclic AMP and vasopressin of Ca2+ uptake in isolated rat hepatocytes

The subcellular distribution of 45Ca2+ accumulated by isolated rat hepatocytes exposed to dibutyryl cyclic AMP (dbcAMP) followed by vasopressin (Vp) was studied by means of a nondisruptive technique. When treated with dbcAMP followed by vasopressin, hepatocytes obtained from fed rats accumulated an amount of Ca2+ approximately fivefold higher than that attained under control conditions. Ca2+ released from the mitochondrial compartment by the uncoupler carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) accounted for only a minor portion of the accumulated Ca2+. The largest portion was released by the Ca2+ ionophore A23187 and was attributable to a nonmitochondrial compartment. DbcAMP + Vp-treatment also caused a maximal stimulation of glucose production and a twofold increase in cellular glucose 6-phosphate levels. In hepatocytes obtained from fasted rats, dbcAMP + Vp-stimulated Ca2+ accumulation was lower, although with the same subcellular distribution, and was associated with a minimal glucose production. In the presence of gluconeogenetic substrates (lactate plus pyruvate) hepatocytes from fasted rats were comparable to cells isolated from fed animals. However, Ca2+ accumulation and glucose 6-phosphate production could be dissociated in the absence of dbcAMP, in the presence of lactate/pyruvate alone. Under this condition in fact Vp induced only a minimal accumulation of Ca2+ in hepatocytes isolated from fasted rats, although glucose production was markedly increased. Moreover, treatment of fed rat hepatocytes with 1 mM ATP caused a maximal activation of glycogenolysis, but only a moderate stimulation of cellular Ca2+ accumulation. In this case, sequestration of Ca2+ occurred mainly in the mitochondrial compartment. By contrast, the addition of ATP to dbcAMP-pretreated hepatocytes induced a large accumulation of Ca2+ in a nonmitochondrial pool. Additional experiments using the fluorescent Ca2+ indicator Fura-2 showed that dbcAMP pretreatment can enlarge and prolong the elevation of cytosolic free Ca2+ caused by Vp. A nonmitochondrial Ca2+ pool thus appears mainly responsible for the Ca2+ accumulation stimulated by dbcAMP and Vp in isolated hepatocytes, and cyclic AMP seems able to activate Ca2+ uptake in such a nonmitochondrial pool.

Measurement of mitochondrial and non-mitochondrial Ca2+ in isolated intact hepatocytes: a critical re-evaluation of the use of mitochondrial inhibitors

Isolated rat hepatocytes treated with mitochondrial inhibitors FCCP or antimycin A release discrete amounts of Ca2+ in a Ca(2+)-free extracellular medium as revealed by changes in the absorbance of the Ca2+ indicator arsenazo III. The process is completed in 2 min and the amount of Ca2+ released is not affected by the type of the mitochondrial poison employed. The subsequent treatment with the cation ionophore A23187 causes a further release of Ca2+ that does not appear related to the specificity of the previous treatment with FCCP or antimycin A. Both FCCP and antimycin A cause a progressive loss of cellular ATP associated with a decrease in the ATP/ADP ratio from 6 to 2-1.5. However, this decrease does not significantly prevent 45Ca2+ accumulation in isolated liver microsomes. Moreover, the decrease of the ATP/ADP ratio to 1, does not promote a significant release of 45Ca2+ from 45Ca(2+)-preloaded microsomes. Finally, experiments with Fura-2-loaded hepatocytes reveal that agents specifically releasing Ca2+ from non-mitochondrial stores (vasopressin and 2,5-di-tert-butyl-1-4-benzohydroquinone) are still able to increase the cytosolic Ca2+ concentration in FCCP-treated cells. Taken together, these findings demonstrate that, in freshly isolated hepatocytes, FCCP specifically releases Ca2+ from mitochondrial stores without significantly affecting active Ca2+ sequestration in other cellular pools. For these reasons, FCCP can be used to release and quantitate mitochondrial Ca2+ in liver cells.

Liver glucose-6-phosphatase activity is not modulated by physiological intracellular Ca2+ concentrations

1. In the presence of MgATP and increasing amounts of added Ca2+, isolated liver microsomal vesicles accumulate approx. 10 nmol of Ca2+/mg of protein and buffer ambient free Ca2+ at increasing concentrations (0.22-10.9 microM). Under these experimental conditions, microsomal glucose-6-phosphatase activity is unaffected by the concentration of extravesicular free Ca2+. 2. Different levels of intravesicular Ca2+ were obtained by treating microsomes with the Ca2+ ionophore A23187 and by stimulating active microsomal Ca2+ accumulation with Pi (3 mM). In both instances, microsomal glucose-6-phosphatase activity is unaffected by the level of intravesicular Ca2+.

Ca(2+)-dependent and independent mitochondrial damage in hepatocellular injury

The alterations of mitochondrial membrane potential during the development of irreversible cell damage were investigated by measuring rhodamine-123 uptake and distribution in primary cultures as well as in suspensions of rat hepatocytes exposed to different toxic agents. Direct and indirect mechanisms of mitochondrial damage have been identified and a role for Ca2+ in the development of this type of injury by selected compounds was assessed by using extracellular as well as intracellular Ca2+ chelators. In addition, mitochondrial uncoupling by carbonylcyanide-m-chloro-phenylhydrazone (CCCP) resulted in a marked depletion of cellular ATP that was followed by an increase in cytosolic Ca2+ concentration, immediately preceding cell death. These results support the existence of a close relationship linking, in a sort of reverberating circuit, the occurrence of mitochondrial dysfunction and the alterations in cellular Ca2+ homeostasis during hepatocyte injury.

Plasma profiles of adrenocorticotropic hormone, cortisol, growth hormone and prolactin in patients with untreated Parkinson's disease

Plasma profiles of prolactin, growth hormone, adrenocorticotropic hormone (ACTH) and cortisol were evaluated in a group of untreated patients with idiopathic Parkinson's disease and a group of healthy age-matched controls. Plasma integrated concentrations of all hormones except prolactin were significantly lower in the patients as compared with the controls; however, prolactin nocturnal peak concentration was significantly elevated in the patients; nocturnal growth hormone levels were significantly reduced in the Parkinson group; ACTH and cortisol plasma concentrations were also consistently lower during most of the day in the patients with Parkinson's disease. These data confirm the presence of a hypothalamic disturbance in patients with idiopathic Parkinson's disease, which can affect pituitary function.

Cytoskeleton as a target in menadione-induced oxidative stress in cultured mammalian cells: alterations underlying surface bleb formation

Several in vitro and in vivo studies have suggested that surface bleb formation during oxidative cell injury is related to alteration in cytoskeleton organization. Various cell lines different in origin and growth characteristics were exposed to 2-methyl-1,4-naphthoquinone (menadione) which is known to induce bleb formation and cytotoxicity by generating considerable amounts of oxygen-reactive species. Treated cells were analyzed by means of immunocytochemistry and electron microscopy in order to investigate the morphological and molecular features underlying bleb generation. The results obtained indicate that menadione-induced bleb formation is a widely observed phenomenon present mainly in round or mitotic cells. Surface blebs appear free of organelles and contain only few ribosomes and amorphous material. Occasionally, they undergo detachment from the cell surface as large cytoplasmic vesicles. Bleb surfaces with protein clusters as well as bald blisters with an almost exclusive localization of intramembrane particles on their narrow base were detected using freeze-fracture techniques. Immunocytochemical investigations performed on menadione-exposed cells revealed that some surface proteins (collagen IV, sialo-proteins, beta 2 microglobulin and fibronectin) and adhesion molecules (vinculin) underwent changes in their expression over the bleb surface. Moreover, different behavioural characteristics of actin microfilaments, vimentin and keratin intermediate filaments and microtubules was observed. Alpha-actinin, vimentin and microtubular proteins (tubulin, MAPs and tau) were detected within the blebs. On the other hand, actin and keratin filaments appeared to be absent. The results presented here demonstrate that cytoskeletal structures and the microfilament system in particular, represent important targets in menadione-induced morphological changes in cultured cells. These changes appear to lead to the redistribution of several cytoskeletal and membrane proteins as well as dissociation of the cytoskeleton network from its anchoring domains in the plasma membrane thus generating sites of structural weakness where blebs would arise and progressively grow. Experimental evidence supporting a crucial role of thiol oxidation and elevation of cytoplasmic calcium concentration in bleb formation is also provided.

Sympathetic vascular function in patients with central dysautonomia

This study used digital photoplethysmography (d-FPG) to investigate alterations in skin blood flow after exposure to cold as well as the post-prandial blood pressure pattern to assess how the sympathetic branch of autonomic nervous system (ANS) functioned in 31 patients with cerebral dysautonomia and in 27 healthy controls. d-FPG was carried out on all ten fingers in basal conditions and after exposure to ice-cold water (4-5 degrees C). Amplitude, crest time and inclination time were used to calculate the alterations induced by the cold pressor test. After a standard lunch blood pressure was monitored every 20 minutes using a fully automatic non-invasive sphygmanometer. Unlike the controls the amplitude of the photoplethysmographic wave increased in all patients except 2; crest time and inclination time decreased in all except 3; post-prandial diastolic and systolic blood pressure levels fell markedly in all but 3. Blood vessel smooth muscle tone is disturbed in patients with ANS failure because dysautonomia may permit the action of vasodilating substances to predominate. The post-prandial blood pressure pattern and the d-FPG used in conjunction with a cold pressor test are useful tools in the non-invasive investigation of ANS function.

MgATP-dependent accumulation of calcium ions and inorganic phosphate in a liver reticular pool

1. MgATP-dependent Ca2+ uptake by rat liver microsomal preparations and permeabilized hepatocytes was measured in the presence or absence of Pi. 2. Monitoring of free Ca2+ in incubation systems with a Ca2+ electrode in the presence of Pi (2-7 mM) revealed a biphasic Ca2+ uptake, with the onset of a second, Pi-dependent, Ca2+ accumulation. 3. Increasing Pi concentrations (up to 10 mM) caused a progressive enlargement of 45Ca2(+)-loading capacity of microsomal fractions. 4. As a result of Pi stimulation of active Ca2+ uptake, [32P]Pi and 45Ca2+ were co-accumulated. 5. Experiments with permeabilized hepatocytes revealed that the amount of Ca2+ releasable by myo-inositol 1,4,5-trisphosphate is unaffected by Pi.

Relationships between the mitochondrial transmembrane potential, ATP concentration, and cytotoxicity in isolated rat hepatocytes

The relationships between mitochondrial transmembrane potential, ATP concentration, and cytotoxicity were evaluated after exposure of isolated rat hepatocytes to different mitochondrial poisons. Both the neurotoxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and its fully oxidized metabolite, the 1-methyl-4-phenylpyridinium (MPP+) ion, caused a concentration- and time-dependent depolarization of mitochondrial membranes which followed ATP depletion and preceded cytotoxicity. The effect of MPTP, but not that of MPP+, was prevented by deprenyl, an inhibitor of MPTP conversion to MPP+ via monoamine oxidase type B. Addition of fructose to the hepatocyte incubations treated with either MPTP or MPP+ counteracted the loss of mitochondrial transmembrane potential. Fructose was also effective in protecting against the mitochondrial membrane depolarization as well as ATP depletion and cytotoxicity induced by antimycin. A, carbonyl cyanide p-trifluoromethoxyphenyl hydrazone, and valinomycin. Data confirm the key role played by MPP(+)-induced mitochondrial damage in MPTP toxicity and indicate that (i) ATP produced via the glycolytic pathway can be utilized by hepatocytes to maintain mitochondrial electrochemical gradient, and (ii) a loss of mitochondrial membrane potential may occur only when supplies of ATP are depleted.

Cytoskeleton as a target in menadione-induced oxidative stress in cultured mammalian cells. I. Biochemical and immunocytochemical features

Cytoskeletal abnormalities occurring during oxidative stress generated by the metabolism of the redox cycling compound 2-methyl-1,4-naphtoquinone (menadione) have been investigated in different mammalian cells in culture. Extraction of the whole cytoskeleton as well as the intermediate filament- and the microtubule-enriched fractions from menadione-treated cells revealed a marked depletion of protein sulfhydryl groups. The analysis of the whole cytoskeletal fraction by PAGE showed a menadione-dependent and thiol-sensitive oxidation of actin, leading to the formation of high-molecular-weight aggregates. In addition, the extraction of this fraction with high concentrations of KCl entailed only a partial solubilization of actin. The comparative cytochemical analysis performed on treated cells showed a menadione-dependent clustering of actin microfilaments. The metabolism of menadione induced microtubule depolymerization and inhibition of GTP-induced microtubule assembly from soluble cytosolic components. The latter phenomenon was prevented by previously treating the cytosolic fraction with thiol reductants such as dithiothreitol. Menadione increased the protein content of the intermediate-size filament fraction, partially purified by one or more cycles of disassembly/assembly, and particularly enriched in polypeptides reacting with antikeratin antibodies. Furthermore, a reversible and oxidation-dependent change of the electrophoretic mobility of some polypeptides in this fraction was detected. The immunocytochemical investigation of intermediate-size filament distribution in menadione-treated cells, however, revealed only minor modifications mainly consisting of perinuclear condensation of cytokeratin structures. These findings suggest that cytoskeletal structures (actin microfilaments, microtubules, and intermediate-size filaments) are actually significant targets in quinone-induced oxidative stress.