Reactive oxygen species

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Reactive oxygen species ( English reactive oxygen species , ROS ) - also simply as "oxygen free radicals" means - are oxygen -containing molecules.

chemistry

Among the ROS on the one hand include radicals such as the superoxide - anion (old name: superoxide anion) O 2 · - , the highly reactive hydroxyl radical OH ·, that peroxyl ROO and the alkoxyl radical RO · of lipids, stable to other molecular oxidants such as hydrogen peroxide H 2 O 2 , hydroperoxide ROOH, ozone O 3 and the hypochlorite anion OCl - as well as excited oxygen molecules ( singlet oxygen 1 O 2 ). After the oxidation, reactive electrophilic species are formed .

The ROS at a glance:

Formula symbol designation annotation
O 2 · - Peroxide anion free radical, secondary messenger substance , old name: superoxide anion
HO · Hydroxyl radical free radical, highly reactive
HOO Hydroperoxyl radical free radical
ROO Peroxyl radical free radical, intermediate stage in sensitized photo-oxidation, see also autoxidation
RO Alkoxyl radical free radical, with lipids
H 2 O 2 Hydrogen peroxide Educt for the formation of other ROS, secondary messenger substance
ROOH Hydroperoxide
O 3 ozone
OCl - Hypochlorite anion
1 O 2 Singlet oxygen excited oxygen molecule

biology

In the organism, reactive oxygen species arise in the mitochondria as a by-product of cell respiration (through monoamine oxidases and in the respiratory chain at complex I and at complex III ), but also through inflammatory cells , in order to damage viruses and bacteria . ROS (especially hydrogen peroxide and nitrogen monoxide ) are also used in the plant's defense against pathogens . Environmental toxins and cigarette smoke are other major sources of reactive oxygen species.

The reaction of the hyperoxide anion O 2 · - with nitrogen monoxide NO · also produces peroxynitrite ONOO - which, together with nitrogen monoxide, is referred to as reactive nitrogen species (RNA) and is also a highly reactive compound (although it is not a free radical). ROS and RNS are therefore important oxidants that antioxidants counteract in the body .

In a biological context, ROS are important signaling molecules for the organism, but in high concentrations they have harmful effects in that they can lead to oxidative stress .

While ROS with various diseases such as B. cancer , diabetes and cardiovascular diseases have been associated, the causal involvement of ROS is worth discussing: In contrast to the above, it has been shown that ROS increase the life expectancy of model organisms, i.e. prevent aging . It is also known that antioxidants counteract the diabetes- preventive effect of sport in humans or prevent it completely by counteracting the formation of ROS.

According to today's view, ROS are in lower, i.e. H. physiological concentration beneficial to health, while in high, d. H. pathological concentration should contribute to the development of diseases. This non-linear dose-effect relationship (i.e. low-dose = healthy, but high-dose = disease-causing) is known as " mitohormesis ". Subsequent studies write ROS such as hyperoxide and hydrogen peroxide, in addition to generating oxidative stress, an important signal function, e.g. B. in the brain in signal transmission, synaptic plasticity and memory formation. They also have a strong vasodilator (vasodilator) effect there and therefore appear to be important for increasing cerebral blood flow and cerebrovascular tone . Furthermore, via the Wnt signaling pathway , they influence the growth and division of cells during the regeneration of severed tails of tadpoles and lizards.

Individual evidence

  1. ↑ a b S. G. Rhee: Redox signaling: hydrogen peroxide as intracellular messenger. In: Exp Mol Med. 31 (2), 1999, pp. 53-59.
  2. ^ A. Gilbert, J. Baggott: Essentials of molecular photochemistry. Blackwell Scientific, 1991, ISBN 0-632-02428-3 , p. 503.
  3. ↑ M. Ristow: Unraveling the truth about antioxidants: mitohormesis explains ROS-induced health benefits. In: Nature Medicine . 20, 2014, pp. 709-711. PMID 24999941
  4. ↑ GS Shadel, TL Horvath: Mitochondrial ROS signaling in organismal homeostasis. In: Cell . 163, 2015, pp. 560-569. PMID 26496603
  5. ↑ N. Panth, KR Paudel, K. Parajuli: Reactive Oxygen Species: A Key Hallmark of Cardiovascular Disease. In: Advances in medicine. Volume 2016, p. 9152732, doi: 10.1155 / 2016/9152732 . PMID 27774507 , PMC 5059509 (free full text).
  6. ↑ TJ Schulz et al .: Glucose restriction extends Caenorhabditis elegans life span by inducing mitochondrial respiration and increasing oxidative stress. In: Cell Metabolism . 6 (4), 2007, pp. 280-293. PMID 17908557
  7. ^ A. Sanz: Mitochondrial reactive oxygen species: Do they extend or shorten animal lifespan? In: Biochimica et Biophysica Acta . Volume 1857, number 8, August 2016, pp. 1116–1126, doi: 10.1016 / j.bbabio.2016.03.018 . PMID 26997500 .
  8. ^ M. Ristow et al.: Antioxidants prevent health-promoting effects of physical exercise in humans. In: Proc Natl Acad Sci. 106, 2009, pp. 8865-8870. PMID 19433800
  9. ^ Vitamins Found to Curb Exercise Benefits. In: The New York Times .
  10. ^ Vitamins "undo exercise efforts". In: BBC .
  11. ↑ Vitamin pills slow down the positive effects of sport. In: Der Spiegel .
  12. ↑ Why exercise only promotes health without vitamins. In: Deutsches Ärzteblatt .
  13. ↑ TJ Schulz et al .: Glucose restriction extends Caenorhabditis elegans life span by inducing mitochondrial respiration and increasing oxidative stress. In: Cell Metabolism . 6 (4), 2007, pp. 280-293. PMID 17908557
  14. ↑ J. Yun, T. Finkel: Mitohormesis. In: Cell Metabolism. 19, 2014, pp. 757-766. PMID 24561260
  15. ↑ M. Ristow: Unraveling the truth about antioxidants: mitohormesis explains ROS-induced health benefits. In: Nature Medicine . 20, 2014, pp. 709-711. PMID 24999941
  16. ↑ GS Shadel, TL Horvath: Mitochondrial ROS signaling in organismal homeostasis. In: Cell . 163, 2015, pp. 560-569. PMID 26496603
  17. ^ KT Kishida, E. Klann: Sources and targets of reactive oxygen species in synaptic plasticity and memory. In: Antioxidant Redox Signal . 9, 2007, pp. 233-244. PMID 17115936 .
  18. ↑ Researchers want to learn from tadpoles . In: Spiegel online . January 14, 2013.