Biomedical subjects

A Roveri

Publications and source records attributed to A Roveri.

31 records · Page 2Linked to original sources

PubMed1993

Prooxidant role of vitamin E in copper induced lipid peroxidation.

When exposed to Cu2+, alpha-tocopherol, in detergent dispersion, is rapidly oxidised. Moreover, if phospholipids and traces of their hydroperoxide derivatives are included in these dispersions, Cu2+ initiates lipid peroxidation, the rate of which is dramatically stimulated by alpha-tocopherol. The observation that the rate of alpha-tocopherol consumption is identical in the absence and in the presence of lipids undergoing peroxidation, apparently rules out any antioxidant effect. These results are consistent with a prooxidant effect of vitamin E, mediated by its capability to reduce Cu2+ to Cu+ which, in turn, produces, from lipid hydroperoxides, the highly reactive alkoxyl radicals. Present data highlight the risk of misleading results in interpreting the significance of lags in peroxidation of LDL challenged with Cu2+.

Copper↗

PubMed1992

Phospholipid hydroperoxide glutathione peroxidase of rat testis. Gonadotropin dependence and immunocytochemical identification.

A high glutathione peroxidase activity toward phospholipid hydroperoxides is present in rat testis. The attribution of this activity to the selenoenzyme phospholipid hydroperoxide glutathione peroxidase (PHGPX) was supported by cross-reactivity with antibodies raised against pig heart PHGPX which had been purified and characterized. Rat testis PHGPX is partially cytosolic and partially linked to nuclei and mitochondria. The soluble and organelle-bound enzymes appear identical by Western blot analysis. PHGPX, but neither selenium-dependent nor non-selenium-dependent glutathione peroxidase activity, is expressed in testes only after puberty, disappears after hypophysectomy, and is partially restored by gonadotropin treatment. Specific immunostaining of testes by antiserum against PHGPX appears as a fine granular brown pattern localized throughout the cytoplasm in more immature cells but is confined to the peripheral part of the cytoplasm, the nuclear membrane, and mitochondria in maturating spermatogenic cells. As expected, immunostaining of spermatogenic cells in hypophysectomized animals was negative, but gonadotropin treatment only marginally increased the immunoreactivity. The expression of PHGPX in testes is consistent with the previously described specific requirement for selenium for synthesis of a 15-20-kDa selenoprotein which is related to the production of functional spermatozoa.

Animals↗

PubMed1992

Antioxidant effect of Ebselen (PZ 51): peroxidase mimetic activity on phospholipid and cholesterol hydroperoxides vs free radical scavenger activity.

The selenocompound Ebselen (PZ 51) is a potent inhibitor of lipid peroxidation. This antioxidant effect has been previously attributed both to a peroxidase mimetic activity and to a free radical scavenging capability. In the present paper the latter is ruled out by competition kinetic analysis based on the inhibition of carotenoid bleaching by hydroperoxyl radicals. Furthermore, evidence is reported indicating that Ebselen exhibits a peroxidase activity extended to cholesterol and cholesterol ester hydroperoxides, besides phospholipid hydroperoxides. According to this, we propose that the unique mechanism of the antioxidant capacity of Ebselen is the reduction of lipid hydroperoxides present in liposomes or lipoproteins, eventually leading to the prevention of hydroperoxide-dependent peroxidation.

Antioxidants↗

PubMed1992

Effect of hydrogen peroxide on calcium homeostasis in smooth muscle cells.

One of the major biological targets of free radical oxidations, prone, for anatomical reasons, to oxidative challenges, is the cardiovascular system. In the present paper the effect of hydrogen peroxide on intracellular ionized calcium ([Ca2+]i) homeostasis in smooth muscle cells (SMC) is studied, the major aim of the study being a better understanding of the protective effect of antioxidants and Ca2+ channel blockers. The exposure of SMC to 300 microM H2O2 induced a rapid increase of [Ca2+]i, followed by a decrease to a new constant level, higher than the basal before the oxidative challenge. When incubation medium was Ca2+ free, the pattern of [Ca2+]i change was different. The rapid increase was still observed, but it was followed by a rapid decrease to a level only slightly above the basal before the oxidative challenge. The involvement of intracellular Ca2+ stores was tested by using vasopressin, a hormone able to induce discharge of inositol 1,4,5-triphosphate-sensitive Ca2+ stores. When H2O2 was added after vasopressin no [Ca2+]i increase was observed. Treatment of cells, in which the stable increase of [Ca2+]i was induced by H2O2, with disulfide reducing compounds, induced a progressive decrease of [Ca2+]i toward the level observed before the oxidative challenge. Calcium channel blockers and antioxidants, on the other hand, effectively prevented the stabilization of [Ca2+]i at the high steady-state, after the internal Ca2+ release phase. Dihydropyridine Ca2+ channel blockers were by far more active than verapamil and among those the most active was lacidipine. Also the antioxidants trolox and N,N'-diphenyl-1,4-phenylenediamine both prevented the [Ca2+]i unbalance. These results suggest that Ca+ channel blockers and antioxidants, although inactive on oxidative stress-induced Ca2+ release from intracellular stores, prevent the increased influx apparently related to a membrane thiol oxidation.

Animals↗

PubMed1992

Lacidipine: a dihydropyridine calcium antagonist with antioxidant activity.

Lacidipine, a new, long-acting antihypertensive dihydropyridine calcium antagonist was tested for potential antioxidant effect in a series of tests that consider specific radical species. A direct quenching of several radical species could be measured. Moreover, in biological membranes deriving from rat brain tissue, lacidipine showed an activity comparable to reference antioxidant compounds like vitamin E.

Animals↗

PubMed1991

Phospholipid hydroperoxide glutathione peroxidase is a selenoenzyme distinct from the classical glutathione peroxidase as evident from cDNA and amino acid sequencing.

The primary structure of phospholipid hydroperoxide glutathione peroxidase (PHGPx) was partially elucidated by sequencing peptides obtained by cyanogen bromide cleavage and tryptic digestion and by isolating and sequencing corresponding cDNA fragments covering about 75% of the total sequence. Based on these data PHGPx can be rated as a selenoprotein homologous, but poorly related to classical glutathione peroxidase (GPx). Peptide loops constituting the active site in GPx are, however, strongly conserved in PHGPx. This suggests that the mechanism of action involving an oxidation/reduction cycle of a selenocysteine residue is essentially identical in PHGPx and GPx.

Amino Acid Sequence↗

PubMed1989

Phospholipid hydroperoxide glutathione peroxidase: specific activity in tissues of rats of different age and comparison with other glutathione peroxidases.

The tissue distribution of phospholipid hydroperoxide glutathione peroxidase (PHGPX) was studied in rats of different ages. In the same samples the activities of Se-dependent glutathione peroxidase (GPX), and non-Se-dependent glutathione peroxidase (non Se-GPX) were also determined using specific substrates for each enzyme. Enzymatically generated phospholipid hydroperoxides were used as substrate for PHGPX, hydrogen peroxide for GPX, and cumene hydroperoxide for non-Se-GPX (after correction for the activity of GPX on this substrate). PHGPX specific activity in different organs is as follows: liver = kidney greater than heart = lung = brain greater than muscle. Furthermore, this activity is reasonably constant in different age groups, with a lower specific activity observed only in kidney and liver of young animals. GPX activity is expressed as follows: liver greater than kidney greater than heart greater than lung greater than brain = muscle, and substantial age-dependent differences have been observed (adult greater than old greater than young). Non-Se-GPX activity was present in significant amount only in liver greater than lung greater than heart and only in adult animals. These results suggest a tissue- and age-specific expression of different peroxidases.

Aging↗

PubMed1989

Microsomal lipid peroxidation: effect of vitamin E and its functional interaction with phospholipid hydroperoxide glutathione peroxidase.

The role of vitamin E in the protection against iron dependent lipid peroxidation was studied in rat liver microsomes and Triton-dispersed microsomal lipid micelles. In these systems, an antioxidant effect of vitamin E at a physiological ratio to phospholipids could be observed only in the presence of phospholipid hydroperoxide glutathione peroxidase (PHGPX) and glutathione. The rationale of this cooperation is discussed on the basis of the hydroperoxyl radical scavenging capacity of vitamin E and the reduction of membrane hydroperoxides by PHGPX. The scavenging of lipid hydroperoxyl radicals by vitamin E, although inhibiting propagation of the peroxidative chain, produces lipid hydroperoxides from which ferrous iron generates alkoxyl radicals that react with vitamin E almost as fast as with fatty acids. Therefore, only if membrane hydroperoxides are continuously reduced by this specific peroxidase does the scavenging of hydroperoxyl radicals by vitamin E lead to an effective inhibition of lipid peroxidation.

Animals↗

PubMed1989

Antioxidant defences of rabbit alveolar lining fluid.

In the lower respiratory tract, alveolar cells are exposed to an oxidative challenge related to the exposure to both high levels of molecular oxygen and oxidants generated by activated phagocytes. The antioxidant defence system of alveolar cells has been thoroughly investigated, but some reports also suggest the presence of antioxidants in the layer of fluid lining the alveoli. In this report we present our studies on the antioxidant activities present in the bronchoalveolar lavage of adult rabbits. We studied total radical-trapping antioxidant capacity of surfactant and the activity of antiperoxidant enzymes. Although previous reports suggested the presence of radical scavengers, we did not find any antioxidant activity in purified surfactant. On the other hand the alveolar-lining fluid seems to contain superoxide dismutase, catalase and glutathione peroxidase, but not appreciable amounts of ferroxidase activity, as previously suggested. These enzymes could protect alveolar cells by catalyzing the dismutation of superoxide and hydrogen peroxide. The presence of glutathione peroxidase in the alveolar space seems to be physiologically relevant since the alveolar lining fluid also contains millimolar amounts of glutathione. Our studies support the concept that the alveolar lining fluid contains an active defence system against products of partial reduction of oxygen, but not chain-breaker antioxidants.

Animals↗

PubMed1988

Kinetic mechanism and substrate specificity of glutathione peroxidase activity of ebselen (PZ51).

The glutathione peroxidase activity of ebselen (PZ51) was studied using different hydroperoxidic substrates. The single progression curves obtained in the spectrophotometric test were processed by a computer to fit the integrated rate equation that describes the ping pong reaction of the Se glutathione peroxidase. Ebselen catalyzes the GSH peroxidase reaction with a mechanism that appears kinetically identical to the mechanism of the enzymes. The inactivation of the catalytic properties of ebselen by iodoacetate suggests that a selenol moiety is involved. Among the substrates tested, the best hydroperoxidic substrates are the hydroperoxy derivatives of phosphatidyl choline. Ebselen is active also on membrane hydroperoxides as does phospholipid hydroperoxide glutathione peroxidase but not glutathione peroxidase.

Antioxidants↗

PubMed1986

Different effects of Triton X-100, deoxycholate, and fatty acids on the kinetics of glutathione peroxidase and phospholipid hydroperoxide glutathione peroxidase.

The effects of Triton X-100, deoxycholate, and fatty acids were studied on the two steps of the ping-pong reaction catalyzed by Se-dependent glutathione peroxidases. The study was carried out by analyzing the single progression curves where the specific glutathione oxidation was monitored using glutathione reductase and NADPH. While the "classic" glutathione peroxidase was inhibited only by Triton, the newly discovered "phospholipid hydroperoxide glutathione peroxidase" was inhibited by deoxycholate and by unsaturated fatty acids. The kinetic analysis showed that in the case of glutathione peroxidase only the interaction of the lipophilic peroxidic substrate was hampered by Triton, indicating that the enzyme is not active at the interface. Phospholipid hydroperoxide glutathione peroxidase activity measured with linoleic acid hydroperoxide as substrate, on the other hand, was not stimulated by the Triton concentrations which have been shown to stimulate the activity on phospholipid hydroperoxides. Furthermore a slight inhibition was apparent at high Triton concentrations and the effect could be attributed to a surface dilution of the substrate. Deoxycholate and unsaturated fatty acids were not inhibitory on glutathione peroxidase but inhibited both steps of the peroxidic reaction of phospholipid hydroperoxide glutathione peroxidase, in the presence of either amphiphilic or hydrophilic substrates. This inhibition pattern suggests an interaction of anionic detergents with the active site of this enzyme. These results are in agreement with the different roles played by these peroxidases in the control of lipid peroxide concentrations in the cells. While glutathione peroxidase reduces the peroxides in the water phase (mainly hydrogen peroxide), the new peroxidase reduces the amphyphilic peroxides, possibly at the water-lipid interface.

Binding Sites↗

PubMed1985

Enzymatic determination of membrane lipid peroxidation.

The recently purified "phospholipid hydroperoxide glutathione peroxidase" has been used to measure the membrane hydroperoxides formed during lipid peroxidation that are not substrates for the "classical" glutathione peroxidase. A spectrophotometric test in the presence of glutathione, glutathione reductase and NADPH has been used. The peroxidized membranes were added directly to the reaction mixture and the reaction was started by the addition of the enzyme. Triton X-100 exerted a stimulatory effect. Phospholipid hydroperoxide glutathione peroxidase allows a rapid, sensitive, accurate and specific determination of membrane hydroperoxides, the most quantitative index of lipid peroxidation. Glutathione peroxidase can be used in the same test to measure other hydroperoxides such as the cumene hydroperoxide used to induce the peroxidation.

Adenosine Diphosphate↗

PubMedDate not supplied

Phospholipid hydroperoxide glutathione peroxidase in the normal human kidney: a possible role in protecting cell membranes.

Reactive oxygen species have been implicated in the pathogenesis of tissue injury. It is generally accepted that selenium-glutathione peroxidases form an integrated system defending the living organism against oxidative damage. Phospholipid hydroperoxide glutathione peroxidase (PHGPX) is thought to play a prominent role in preventing lipid peroxidation. Indeed, the function of PHGPX is to reduce the lipophilic substrates in membranes. In the present study, we evaluated the expression of PHGPX in normal human kidney by immunohistochemistry. The enzyme in glomeruli is mainly expressed in podocytes and parietal epithelial cells. In addition, PHGPX antigen was detected in tubule epithelial cells. Therefore, these results suggest that renal epithelial cells possess an important antioxidizing activity related to the presence of PHGPX.

Cell Membrane↗