Biomedical subjects

Annalisa Biondi

Publications and source records attributed to Annalisa Biondi.

8 recordsLinked to original sources

PubMed2006

Defective oxidative phosphorylation in thyroid oncocytic carcinoma is associated with pathogenic mitochondrial DNA mutations affecting complexes I and III.

Oncocytic tumors are characterized by cells with an aberrant accumulation of mitochondria. To assess mitochondrial function in neoplastic oncocytic cells, we studied the thyroid oncocytic cell line XTC.UC1 and compared it with other thyroid non-oncocytic cell lines. Only XTC.UC1 cells were unable to survive in galactose, a condition forcing cells to rely solely on mitochondria for energy production. The rate of respiration and mitochondrial ATP synthesis driven by complex I substrates was severely reduced in XTC.UC1 cells. Furthermore, the enzymatic activity of complexes I and III was dramatically decreased in these cells compared with controls, in conjunction with a strongly enhanced production of reactive oxygen species. Osteosarcoma-derived transmitochondrial cell hybrids (cybrids) carrying XTC.UC1 mitochondrial DNA (mtDNA) were generated to discriminate whether the energetic failure depended on mitochondrial or nuclear DNA mutations. In galactose medium, XTC.UC1 cybrid clones showed reduced viability and ATP content, similarly to the parental XTC.UC1, clearly pointing to the existence of mtDNA alterations. Sequencing of XTC.UC1 mtDNA identified a frameshift mutation in ND1 and a nonconservative substitution in cytochrome b, two mutations with a clear pathogenic potential. In conclusion, this is the first demonstration that mitochondrial dysfunction of XTC.UC1 is due to a combined complex I/III defect associated with mtDNA mutations, as proven by the transfer of the defective energetic phenotype with the mitochondrial genome into the cybrids.

Adenoma, Oxyphilic↗

PubMed2006

Mitochondrial Complex I: structural and functional aspects.

This review examines two aspects of the structure and function of mitochondrial Complex I (NADH Coenzyme Q oxidoreductase) that have become matter of recent debate. The supramolecular organization of Complex I and its structural relation with the remainder of the respiratory chain are uncertain. Although the random diffusion model [C.R. Hackenbrock, B. Chazotte, S.S. Gupte, The random collision model and a critical assessment of diffusion and collision in mitochondrial electron transport, J. Bioenerg. Biomembranes 18 (1986) 331-368] has been widely accepted, recent evidence suggests the presence of supramolecular aggregates. In particular, evidence for a Complex I-Complex III supercomplex stems from both structural and kinetic studies. Electron transfer in the supercomplex may occur by electron channelling through bound Coenzyme Q in equilibrium with the pool in the membrane lipids. The amount and nature of the lipids modify the aggregation state and there is evidence that lipid peroxidation induces supercomplex disaggregation. Another important aspect in Complex I is its capacity to reduce oxygen with formation of superoxide anion. The site of escape of the single electron is debated and either FMN, iron-sulphur clusters, and ubisemiquinone have been suggested. The finding in our laboratory that two classes of hydrophobic inhibitors have opposite effects on superoxide production favours an iron-sulphur cluster (presumably N2) is the direct oxygen reductant. The implications in human pathology of better knowledge on these aspects of Complex I structure and function are briefly discussed.

Animals↗

PubMed2006

Mitochondrial activities of a cell line derived from thyroid Hürthle cell tumors.

OBJECTIVE: We conducted a study on the functional characteristics of mitochondria in an oxyphilic thyroid tumor cell line, which may provide useful clues about Hürthle cell tumors carcinogenesis. DESIGN: The functional study on thyroid tumors with cell oxyphilia (Hürthle cell tumors), characterized by mitochondrial hyperplasia, was carried out in XTC.UC1, and B-CPAP, an oxyphilic and nonoxyphilic thyroid tumor cell line, respectively. MAIN OUTCOME: XTC.UC1 cell line showed higher activity of mitochondrial respiratory complexes I and II and decreased activity of complex III. The increased activity of complex I was not matched by increased expression of complex I subunits. The XTC.UC1 cells relied mostly on oxidative phosphorylation for energy conservation, although their mitochondrial energetic function was less efficient when related to mitochondrial content of the cells. Finally, the oxyphilic cell line produced significantly higher amounts of reactive oxygen species (ROS) in comparison with B-CPAP cell line. CONCLUSION: The involvement of ROS in mitochondrial biogenesis and proliferation as well as in carcinogenesis and apoptosis indicate that differences in activity of respiratory chain components and their unbalance may be responsible for development of morphological and functional changes observed in thyroid tumors with cell oxyphilia.

Adenoma, Oxyphilic↗

PubMed2004

Plasma membrane oxidoreductase activity in cultured cells in relation to mitochondrial function and oxidative stress.

Dichlorophenol indophenol (DCIP) reduction by intracellualr pyridine nucleotides was investigated in two different lines of cultured cells characterized by enhanced production of reacive oxygen species (ROS) with respect to suitable controls. The first line denominated XTC-UC1 was derived from a metastasis of an oxyphilic thyroid tumor characterized by mitochondrial hyperplasia and compared with a line (B-CPAP) derived from a papillary thyroid carcinoma with normal mitochondrial mass. The second line (170 MN) was a cybrid line derived from rho0 cells from an osteosarcoma line (143B) fused with platelets from a patient with a nucleotide 9957 mutation in mitochondrial DNA (encoding for cytochrome c oxidase subunit III) in comparison with the parent 143B line. The experimental lines had no major decreases of electron transfer activities with respect to the controls; both of them, however, exhibited an increased peroxide production. The XTC-UC1 cell line exhibited enhanced activity with respect to control of dicoumarol-sensitive DCIP reduction, identified with membrane bound DT-diaphorase, whereas dicoumarol insensitive DCIP reduction was not significantly changed. On the other hand the mtDNA mutated cybrids exhibited a strong increase of both dicoumarol sensitive and insensitive DCIP reduction. The results suggest that enhanced oxidative stress and not deficient respiratory activity per se is the stimulus triggering over-expression of plasma membrane oxidative enzymes.

Breast Neoplasms↗

PubMed2004

The mitochondrial production of reactive oxygen species in relation to aging and pathology.

Mitochondria are known to be strong producers of reactive oxygen species (ROS) and, at the same time, particularly susceptible to the oxidative damage produced by their action on lipids, proteins, and DNA. In particular, damage to mtDNA induces alterations to the polypeptides encoded by mtDNA in the respiratory complexes, with consequent decrease of electron transfer, leading to further production of ROS and thus establishing a vicious circle of oxidative stress and energetic decline. This deficiency in mitochondrial energetic capacity is considered the cause of aging and age-related degenerative diseases. Complex I would be the enzyme most affected by ROS, since it contains seven of the 13 subunits encoded by mtDNA. Accordingly, we found that complex I activity is significantly affected by aging in rat brain and liver mitochondria as well as in human platelets. Moreover, due to its rate control over aerobic respiration, such alterations are reflected on the entire oxidative phosphorylation system. We also investigated the role of mitochondrial complex I in superoxide production and found that the one-electron donor to oxygen is most probably the Fe-S cluster N2. Short chain coenzyme Q (CoQ) analogues enhance ROS formation, presumably by mediating electron transfer from N2 to oxygen, both in bovine heart SMP and in cultured HL60 cells. Nevertheless, we have accumulated much evidence of the antioxidant role of reduced CoQ(10) in several cellular systems and demonstrated the importance of DT-diaphorase and other internal cellular reductases to reduce exogenous CoQ(10) after incorporation.

Aging↗

PubMed2004

Methods to detect mitochondrial function.

The bioenergetic function of mitochondria can be investigated in intact cells by a variety of methods. A simple biochemical method to compare mitochondrial oxidative phosphorylation with glycolytic ATP synthesis takes advantage of the Pasteur effect, since the amount of lactate produced under basal conditions is an indication of glycolytic ATP, while the Delta-lactate (the difference between excess lactate produced after inhibition of respiration and basal lactate) represents ATP produced anaerobically in order to compensate for decreased oxidative phosphorylation after respiratory chain inhibition. The system has been validated in a series of cells, including human platelets and lymphocytes and lines cultured in vitro. Measurement of KCN-sensitive oxygen consumption by the cells and its sensitivity to uncouplers can be good supplementary indication of mitochondrial phosphorylative capacity.

Adenosine Triphosphate↗

PubMed2003

Mitochondrial production of oxygen radical species and the role of Coenzyme Q as an antioxidant.

The mitochondrial respiratory chain is a powerful source of reactive oxygen species (ROS), which is considered as the pathogenic agent of many diseases and of aging. We have investigated the role of complex I in superoxide radical production and found by the combined use of specific inhibitors of complex I that the one-electron donor to oxygen in the complex is a redox center located prior to the sites where three different types of Coenzyme Q (CoQ) competitors bind, to be identified with an Fe-S cluster, most probably N2, or possibly an ubisemiquinone intermediate insensitive to all the above inhibitors. Short-chain Coenzyme Q analogs enhance superoxide formation, presumably by mediating electron transfer from N2 to oxygen. The clinically used CoQ analog, idebenone, is particularly effective, raising doubts on its safety as a drug. Cells counteract oxidative stress by antioxidants. CoQ is the only lipophilic antioxidant to be biosynthesized. Exogenous CoQ, however, protects cells from oxidative stress by conversion into its reduced antioxidant form by cellular reductases. The plasma membrane oxidoreductase and DT-diaphorase are two such systems, likewise, they are overexpressed under oxidative stress conditions.

Animals↗

PubMed2002

Ubiquinol and a coenzyme Q reducing system protect platelet mitochondrial function of transfusional buffy coats from oxidative stress.

The conditions under which Coenzyme Q (CoQ) may protect platelet mitochondrial function of transfusional buffy coats from aging and from induced oxidative stress were investigated. The Pasteur effect, i.e. the enhancement of lactate production after inhibition of mitochondrial respiratory chain, was exploited as a marker of mitochondrial function as it allows to calculate the ratio of mitochondrial ATP to glycolytic ATP. Reduced CoQ10 improves platelet mitochondrial function of transfusional buffy coats and protects the cells from induced oxidative stress. Oxidized CoQ is usually less effective, despite the presence, shown for the first time in this study, of quinone reductase activities in the platelet plasma membranes. The addition of a CoQ reducing system to platelets is effective in enhancing the protection of platelet mitochondrial function from the oxidative stress. The results support on one hand a possibility of protection of mitochondrial function in aging by exogenous CoQ intake, on the other a possible application in protection of transfusional buffy coats from storage conditions and oxidative deterioration.

Aging↗