All tags Metabolism MitoNews, Volume 10, Issue 1

Metabolism

MitoNews, Volume 10, Issue 1

New players in the world of mitochondrial toxicity – the smoke clears!

Edited by Elisa Oquendo, PhD. and James Murray, PhD.

Thousands of researchers around the world are studying the connections between mitochondria, metabolism and disease. MitoNews summarizes a selection of the latest published findings and highlights how Abcam's MitoSciences Range of research tools has contributed to this effort. Read the full list of 71 original research papers published in the last two months.

In the mid-20th century, the international scientific community became aware of the negative health effects of tobacco thanks to the early epidemiological and pathology studies led by Richard Doll and Oscar Auerbach. This research led the American Surgeon General’s Advisory Committee exactly 50 years ago in January of 1964 and UK’s Royal College of Physicians in 1962 to issue reports warning the general public as well as public officials of the dangers of smoking. Today, 57% of countries around the world have put in place various smoking bans but only 10% have comprehensive national smoke-free laws despite almost 60 years of research showing the correlation/causation role of cigarette smoke in Cancer, Asthma, Chronic Obstructive Pulmonary Disease (COPD), Diabetes, Heart Disease and Stroke in users and second hand smokers. Since 1980 the proportion of smokers in the world has decreased to 31% in men and 6% in women however the total number of smokers has increased globally due to population increase and is approaching 1 billion.

In an article published by Respiratory Research, Hoffmann, et al. explored the molecular effects of chronic exposure to cigarette smoke extract (CSE) in the human bronchial epithelial cell line BEAS-2B and correlated their findings with results obtained from primary bronchial epithelial cells (PBEC’s) of COPD patients. After 6 months of exposure to various concentrations of CSE, researchers found significant changes in mitochondrial morphology (branching, cristae number and fragmentation) as well as density. All changes except fragmentation did not normalize after CSE withdrawal. In line with these observations, mRNA expression of OPA1, a critical regulator of morphology, was increased. Furthermore, the levels of OXPHOS proteins (CII-SDHB, CIII-UQCRC2 and CV-F1alpha) as well as markers of oxidative stress (Mn-SOD) were significantly increased. All these mitochondrial changes occurred in parallel with inflammatory activity as shown by increased production of cytokines IL-1B, IL-6 and IL-8. Similar mitochondrial changes were also observed in severe ex-smoking COPD patients in comparison to controls. The authors concluded that the observed mitochondrial changes in COPD epithelium are potentially the consequence of long-term exposure to cigarette smoke and proposed mitochondria dysfunction and ROS damage to be of pathophysiological importance in the development of COPD with probable future therapeutic implications.

Prolonged cigarette smoke exposure alters mitochondrial structure and function in airway epithelial cells. Respiratory Research. 2013. Hoffmann, R.F., Zarrintan, S., Brandenburg, S.M., Kol, A., de Bruin, H.G., Jafari S., Dijk, F., Kalicharan D., Kelders, M., Gosker, H.R., ten Hacken, N.H.T, van der Want, J.J., van Oosterhout, A.J.M. and Heijink, I.H.


The World Health Organization has declared that air pollution, an important determinant of human health, currently creates a disproportionate disease burden in the less affluent parts of the world.  One of these environmental pollutants affecting air quality is Dibenzofuran (DBF).  DBF has attracted the attention of the scientific community due to its persistence in the environment, bioaccumulation and toxicity to humans.  DBF is a dioxin-like compound generated as a consequence of fuel combustion (mainly gasoline, diesel and coal) as well as cigarette smoke.  Chronic exposure to DBF has been associated with the development of lung disease and cancer, both of which have been linked in the past to mitochondrial toxicity.  However the exact molecular mechanism had not been uncovered until recently.

In an article published by Toxicology In Vitro in December 2013, Duarte, et al. explored the effect of DBF in rat liver mitochondria and found that DBF inhibited carboxyatractyloside (CAT) induced mitochondrial permeability transition (MPT). The effect was of similar magnitude to the inhibition generated by classical compounds such as bongkrekic acid and Cyclosporin A.  Co-immunoprecipitation experiments of Adenine Nucleotide Translocator (ANT) with Cyclophilin D (CypD) showed that the immunoprecipitates from mitochondria exposed to CAT+DBF had a lower CyD/ANT ratio in comparison to mitochondria treated with CAT alone.  This was found to be associated with an increase in the lag phase preceding re-polarization during mitochondrial transmembrane potential measurements and a decrease in the activity of the ATP synthase enzyme.  The researchers hypothesized that DBF interferes with ANT and decreases mitochondria phosphorylative efficiency.

Dibenzofuran-induced: mitochondrial dystunction:Interaction with ANT carrier. Toxicology In Vitro. 2013. Duarte F.V., Gomes A.P., Teodoro J.S., Varela A.T., Moreno A.J.M., Rolo A.P.


The pharmaceutical industry has come to recognize that drug–induced mitochondrial toxicity is an important factor in the drug attrition pipeline as well as in the post-market withdrawal due to safety concerns.  Recently, one of such compounds creating increased concern is the immunosuppressive medication FK506, also known as Tacrolimus.  FK506 is a macrolide first introduced in 1989 as a human immunosuppressive medication to prevent graft rejection following organ transplantation.  FK506 binds to FK-binding protein 12 (FKB12), leading to inhibition of calcineurin, dephosphorylation of nuclear factor of activated T cell (NFATc) and therefore prevention of T cell-mediated immune response, characterized by the production of Th1/Th2 cytokines.  However adverse side effects such as neurotoxicity, nephrotoxicity and diabetes are the main reasons for long term protocol failure.  Because some in-vitro models have shown decreased oxygen consumption rate after FK506 treatment, it has been suggested that this compound may target the oxidative phosphorylation system via inhibition of mitochondrial protein synthesis as many other macrolide molecules do.

In an article published ahead of print by Cell Biology and Toxicology,  Palacίn, et al. explored the hypothesized effect of FK506 on mitochondrial protein synthesis and its consequence on the activity of the complexes of the electron transport chain (ETC).  Experiments were carried out on six cybrid human osteosarcoma 143B cell lines from two different mtDNA genotypes grown in galactose and treated with 50 ng/mL of FK506 for 72 hours. They found that FK506 decreased in a reproducible manner the endogenous and uncoupled oxygen consumption rate as well as the levels of the mitochondrial encoded cytochrome c oxidase subunit I (MT-CO1) in comparison to the nuclear encoded  succinate dehydrogenase subunit A (SDHA).  Furthermore, this finding correlated with a decrease in the amount of mitochondrial translation products.  In contrast, these effects were not mirrored by a parallel decrease in the endogenous activity of complex I+III or complex IV.  The lack of correlation between  mtDNA encoded proteins and activity of ETC complexes has been explained in other models, due to the higher expression of subunits from what it is necessary for complex assembly.  Further research into the direct inhibition of FK506 on all the complexes of the ETC as well as into other pathways affecting mitochondrial function, such as mTOR, are yet to be fully investigated.

FK506 affects mitochondrial protein synthesis and oxygen consumption in human cells. Cell Biology and Toxicology. 2013. Palacίn M., Coto E., Llobet L., Paceu-Graw D., Montoya J., Ruiz-Pesini E.

References

17β-Estradiol protects cerebellar granule cells against β-amyloid-induced toxicity via the apoptotic mitochondrial pathway. Neuroscience Letters. 2013. Napolitano M., Costa L., Piacentini R., Grassi C., Lanzone A., Gulino A.

Changes in Fat Mitochondrial DNA and Function in Subjects Randomized to Abacavir-Lamivudine or Tenofovir DF–Emtricitabine With Atazanavir-Ritonavir or Efavirenz: AIDS Clinical Trials Group Study A5224s, Substudy of A5202. Journal of Infections Diseases. 2013. McComsey G.A., Daar E.S., O’Riordan M., Collier A. C., Kosmiski L., Santana J.L., Fichtenbaum C.J., Fink H., Sax P.E., Libutti D. E., Gerschenson M

Cisplatin Induces a Mitochondrial-ROS Response That Contributes to Cytotoxicity Depending on Mitochondrial Redox Status and Bioenergetic Functions. PLOS ONE. 2013. Marullo R., Werner E., Degtyareva N., Moore B., Altavilla G., Ramalingam S.S., Doetsch P.W

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