Novel quercetin derivatives in treatment of peroxynitrite-oxidized SERCA1.

Sarco/endoplasmic reticulum calcium ATP-ase (SERCA) is regulated by low concentrations of peroxynitrite and inhibited by high levels, as indicated in human diseases. We studied quercetin (Q) and its novel derivatives monochloropivaloylquercetin (MPQ) and chloronaphthoquinonequercetin (CHQ) as agents with expected preventive properties against peroxynitrite-induced SERCA impairment. Q and MPQ protected the SERCA1 against peroxynitrite induced activity decrease, while CHQ potentiated the inhibitory effect of peroxynitrite. Quercetin derivatives were found to be weaker antioxidants compared with Q, as indicated by their ability to scavenge peroxynitrite and prevent of SERCA1 carbonylation, both decreasing in the order (Q > MPQ > CHQ). Quantum-chemical values of theoretical parameter E HOMO also indicated lower antioxidant capacities for MPQ and CHQ. Prooxidant properties estimated by calculations of frontier molecular orbitals (E LUMO) correlated with experimentally determined SH-group decrease induced by the compounds studied. Both methods showed a decrease of prooxidant properties as follows: CHQ > MPQ > Q. In addition, experimentally measured half-wave potentials indicated stronger prooxidant properties of quercetin derivatives as compared to Q. More expressive alterations of conformation in the transmembrane region of SERCA1 induced by quercetin derivatives, as compared with Q, may at least partially correlate with their higher lipophilicities. The protective effects of Q and MPQ on different isoforms of SERCA activity may be useful in prevention and treatment of inflammation or muscle diseases. The inhibitory effect of CHQ on SERCA isoforms may be beneficial in therapeutic approaches aimed at anti-tumor treatment.

Effect of some antioxidants on sarcoplasmic reticulum Ca2+-ATPase activity from rabbit skeletal muscle.

OBJECTIVES: Effects of phenolic antioxidants, synthetized (trolox, pyridoindole stobadine) and plant extracts (EGb 761 and Pycnogenol) were investigated on the activity of Ca(2+)-ATPase from sarcoplasmic reticulum (SR) of rabbit skeletal muscle to examine their potency to modulate the activity of this calcium level regulating enzyme. METHODS: SR vesicles and pure Ca(2+)-ATPase were isolated by ultracentrifugation. Ca(2+)-ATPase activity was measured spectrophotometrically by enzyme-coupled assay. RESULTS: Pycnogenol (Pyc) significantly decreased the activity of Ca(2+)-ATPase incorporated into SR vesicles as well as the activity of purified Ca(2+)-ATPase, the latter with respect to both enzyme substrates, Ca(2+) and ATP. Trolox, stobadine and EGb 761 did not influence significantly the activity SR- vesicle incorporated or pure Ca(2+)-ATPase, the latter with respect to either substrate, in spite of alterations of kinetic parameters in some cases. CONCLUSIONS: The decrease of SR Ca(2+)-ATPase activity induced by Pyc may be associated with its proapoptotic and anticancerogenic properties.

Oxidative damage to Ca2+-ATPase sarcoplasmic reticulum by HOCl and protective effect of some antioxidants.

Injury of rabbit skeletal sarcoplasmic reticulum (SR) induced by hypochlorous acid (HOCl) was studied. HOCl inhibited Ca2+-ATPase activity in a concentration-dependent manner (IC50=100 micromol/l). The concentration of 13.5 micromol/l HOCl reduced the level of sulfhydryl (SH) groups by 50%, yet it did not influence the enzyme activity. In comparison with SH group oxidation and enzyme activity inhibition, a significantly longer time was necessary for the generation of protein carbonyls in SR injured by HOCl. Protective effects of some antioxidants (stobadine, trolox, EGb 761, Pycnogenol) were studied in SR oxidatively injured by HOCl. Trolox and EGb 761 exerted a protective effect on ATPase activity and on SH groups of SR oxidatively modified by HOCl. Stobadine and Pycnogenol inhibited markedly protein carbonyl formation. Stobadine was the only antioxidant able to scavenge HOCl. In conclusion, the protective effects of antioxidants against decrease of Ca2+-ATPase activity induced by HOCl might be caused by protection of SH groups. The compounds with both antioxidant and Ca2+-ATPase protecting effect offer dual defense against tissue damage occurring, e.g. in aging process.

Pycnogenol and Ginkgo biloba extract: effect on peroxynitrite-oxidized sarcoplasmic reticulum Ca-ATPase.

The effect of two natural standardized plant extracts, Pycnogenol(®) and EGb 761, on sarcoplasmic reticulum Ca(2+)-ATPase (SERCA) activity and posttranslational modifications induced by peroxynitrite was investigated to assess their possible protective role. EGb 761 was found to have a protective effect on SERCA activity in the concentration range of 5-40 µg/ml. On the other hand, Pycnogenol(®) caused a decrease of SERCA activity at concentrations of 25 µg/ml. EGb 761 did not prevent protein carbonyl formation upon oxidation with peroxynitrite. On the contrary, Pycnogenol(®) at the concentrations of 5 and 10 µg/ml significantly decreased the level of protein carbonyls by 44% and 54%, respectively. Neither Pycnogenol(®) nor EGb 761 exerted a protective effect against thiol group oxidation.The plant extracts studied modulated peroxynitrite-injured SERCA activity by different ways and failed to correlate with posttranslational modifications. Their effect seems to be associated with their ability to change SERCA conformation rather than by their antioxidant capacity.

Natural and synthetic antioxidants: an updated overview.

Abstract The current understanding of the complex role of ROS in the organism and pathological sequelae of oxidative stress points to the necessity of comprehensive studies of antioxidant reactivities and interactions with cellular constituents. Studies of antioxidants performed within the COST B-35 action has concerned the search for new natural antioxidants, synthesis of new antioxidant compounds and evaluation and elucidation of mechanisms of action of both natural and synthetic antioxidants. Representative studies presented in the review concern antioxidant properties of various kinds of tea, the search for new antioxidants of herbal origin, modification of tocopherols and their use in combination with selenium and properties of two promising groups of synthetic antioxidants: derivatives of stobadine and derivatives of 1,4-dihydropyridine.

Markers of oxidative stress in children with Down syndrome.

BACKGROUND: Persons with Down syndrome have increased vulnerability to oxidative stress caused by overexpression of superoxide dismutase, an antioxidant enzyme coded on chromosome 21. Increased oxidative stress may lead to oxidative damage of important macromolecules. We monitored this damage by measuring levels of different biomarkers of oxidative stress (protein carbonyls and 4-hydroxy-2-nonenal), as well as plasma antioxidant capacity, in children with Down syndrome. A total of 20 children with Down syndrome and 18 healthy individuals were recruited for this purpose. METHODS: Plasma protein carbonyls were measured using an ELISA technique, 4-hydroxy-2-nonenal was monitored by HPLC and the antioxidant capacity was evaluated using a ferric reducing ability of plasma (FRAP) assay. RESULTS: We found that children with Down syndrome had significantly elevated levels of protein carbonyls compared to healthy controls (p < 0.01). Levels of 4-hydroxy-2-nonenal and antioxidant capacity were similar in both groups. CONCLUSION: Our results on oxidative damage to proteins confirm the assumption of increased oxidative stress in individuals with Down syndrome.