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      Effect of bilirubin on cytochrome c oxidase activity of mitochondria from mouse brain and liver

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          Abstract

          Background

          The unbound, free concentration (B f) of unconjugated bilirubin (UCB), and not the total UCB level, has been shown to correlate with bilirubin cytotoxicity, but the key molecular mechanisms accounting for the toxic effects of UCB are largely unknown.

          Findings

          Mouse liver mitochondria increase unbound UCB oxidation, consequently increasing the apparent rate constant for unbound UCB oxidation by HRP (Kp), higher than in control and mouse brain mitochondria, emphasizing the importance of determining Kp in complete systems containing the organelles being studied. The in vitro effects of UCB on cytochrome c oxidase activity in mitochondria isolated from mouse brain and liver were studied at B f ranging from 22 to 150 nM. The results show that UCB at B f up to 60 nM did not alter mitochondrial cytochrome c oxidase activity, while the higher concentrations significantly inhibited the enzyme activity by 20% in both liver and brain mitochondria.

          Conclusions

          We conclude that it is essential to include the organelles being studied in the medium used in measuring both Kp and B f. A moderately elevated, pathophysiologically-relevant B f impaired the cytochrome c oxidase activity modestly in mitochondria from mouse brain and liver.

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          Most cited references34

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          Bilirubin is an antioxidant of possible physiological importance.

          A J G McDonagh, R Stocker, Yasuhiro Yamamoto … (1987)
          Bilirubin, the end product of heme catabolism in mammals, is generally regarded as a potentially cytotoxic, lipid-soluble waste product that needs to be excreted. However, it is here that bilirubin, at micromolar concentrations in vitro, efficiently scavenges peroxyl radicals generated chemically in either homogeneous solution or multilamellar liposomes. The antioxidant activity of bilirubin increases as the experimental concentration of oxygen is decreased from 20% (that of normal air) to 2% (physiologically relevant concentration). Furthermore, under 2% oxygen, in liposomes, bilirubin suppresses the oxidation more than alpha-tocopherol, which is regarded as the best antioxidant of lipid peroxidation. The data support the idea of a "beneficial" role for bilirubin as a physiological, chain-breaking antioxidant.
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            Bilirubin benefits: cellular protection by a biliverdin reductase antioxidant cycle.

            Solomon H. Snyder, Thomas Sedlak (2004)
            Article 0 comments Cited 85 times – based on 0 reviews     Review now
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              Peroxiredoxin III, a mitochondrion-specific peroxidase, regulates apoptotic signaling by mitochondria.

              Seok Cho, Sue Rhee, Shin-Tsu Chang … (2004)
              Various proapoptotic stimuli increase the production of superoxide and H(2)O(2) by mitochondria. Whereas superoxide impairs mitochondrial function and is removed by Mn(2+)-dependent superoxide dismutase, the role and metabolism of mitochondrial H(2)O(2) during apoptosis have remained unclear. The effects on apoptotic signaling of depletion of peroxiredoxin (Prx) III, a mitochondrion-specific H(2)O(2)-scavenging enzyme, have now been investigated by RNA interference in HeLa cells. Depletion of Prx III resulted in increased intracellular levels of H(2)O(2) and sensitized cells to induction of apoptosis by staurosporine or TNF-alpha. The rates of mitochondrial membrane potential collapse, cytochrome c release, and caspase activation were increased in Prx III-depleted cells, and these effects were reversed by ectopic expression of Prx III or mitochondrion-targeted catalase. Depletion of Prx III also exacerbated damage to mitochondrial macromolecules induced by the proapoptotic stimuli. Our results suggest that Prx III is a critical regulator of the abundance of mitochondrial H(2)O(2), which itself promotes apoptosis in cooperation with other mediators of apoptotic signaling.
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                Author and article information

                Journal
                Journal ID (nlm-ta): BMC Res Notes
                Title: BMC Research Notes
                Publisher: BioMed Central
                ISSN (Electronic): 1756-0500
                Publication date Collection: 2010
                Publication date (Electronic): 9 June 2010
                Volume: 3
                Page: 162
                Affiliations
                [1 ]Eijkman Institute for Molecular Biology, Jl. Diponegoro 69, Jakarta 10430, Indonesia
                [2 ]GI/Hepatology Division, Dept. Medicine, University of Washington, Seattle, WA, 98195, USA
                [3 ]CSF AREA Science Park and Dept. ACADEM, University of Trieste, 34012, Trieste, Italy
                Article
                Publisher ID: 1756-0500-3-162
                DOI: 10.1186/1756-0500-3-162
                PMC ID: 2901210
                PubMed ID: 20534120
                SO-VID: 645b5020-1205-4f40-9b9d-275eabb8d3bd
                Copyright © Copyright ©2010 Malik et al; licensee BioMed Central Ltd.
                License:

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                Date received : 13 April 2010
                Date accepted : 9 June 2010
                Categories
                Subject: Short Report

                ScienceOpen disciplines: Medicine
                Data availability:
                ScienceOpen disciplines: Medicine

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