Reactive oxygen species especially on H2O2 in physiological and pathological conditions mainly in vascular diseases

Mazen SAEEDM.A student at Pharmacology Department, Ege University 2015

REACTIVE OXYGEN SPECIES

• Radicals are species containing one or more unpaired electrons.

Two types:

1. Free radical such as the oxygen radicalsuperoxide (O 2

-)

2. The non-radical oxidants such as hydrogenperoxide (H2O2) and hypochlorous acid(HOCl) are produced during normal metabolism and perform several usefulfunctions.

Types of ROS

ROS in physiological state

• Intracellular ROS is primarily produced by NADPH oxidase enzymes (NOXs), the mitochondria, theendoplasmic reticulum, and the peroxisome.

ROS in physiological state

• Cytosolic superoxide (O2 _) is rapidly converted intohydrogen peroxide (H2O2) by superoxide dismutase 1 (SOD1).

• H2O2 can either act as a signaling molecule by oxidizingcritical thiols within proteins to regulate numerousbiological processes, including metabolic adaptation, differentiation, and proliferation or be detoxified towater (H2O) by the scavenging enzymes peroxiredoxin(PRX), glutathione peroxidase (GPX), and catalase (CAT).

ROS in physiological state

• In addition, H2O2 can react with metal cations (Fe2+ or Cu+) to generate the hydroxyl radical (OH _), which causes irreversible oxidative damage to lipids, proteins, and DNA

HYDEROGEN PEROXIDE IN PHYSIOLOGIC STATE

HYDEROGEN PEROXIDE

• H2O2 is produced as a by-product of protein oxidation in the endoplasmic reticulum (ER), as an end product in numerous peroxisomal oxidationpathways such as in the beta-oxidation of very long-chain fatty acids, and by a wide range of enzymesincluding cytochrome P450.

HYDEROGEN PEROXIDE

• H2O2 act as signaling molecules is through theoxidation of critical cysteine residues within redox-sensitive proteins.

H2O2-mediated cysteine oxidation of redox-sensitive proteins mechanism

• Susceptible cysteine residues have a low pKa andexist as a thiolate anion (S _) at physiological pH, making them more reactive than the protonatedcysteine thiol group (SH) and providing a level of selectivity and specificity .

H2O2-mediated cysteine oxidation of redox-sensitive proteins mechanism

• H2O2 oxidization of the thiolate anion to the sulfenicform (SO _) impinges on cellular signaling by alteringprotein conformation and activity. In the presence of high concentrations of H2O2, SO _ is further oxidizedto form sulfinic (SO2 _) and sulfonic (SO3 _) acids(i.e. hyperoxidation), where SO3 _ generallyrepresents an irreversible oxidative modification.

H2O2-mediated cysteine oxidation of redox-sensitive proteins mechanism

• To prevent irreversible cysteine oxidation, the SO _ intermediate is com-monly incorporated into a disulfide (S–S) or sulfenic- amide (S–N) bond. Thesemodifications are reversible by the actions of glutaredoxin (GRX) and thioredoxin (TRX), whichrestore protein function; the oxidized protein is returned to its reduced state.

H2O2-mediated cysteine oxidation of redox-sensitive proteins

Possible mechanisms for H2O2-dependent signal transduction

• H2O2 can oxidize critical cysteine thiol groups of phosphatases including PTEN, PTP1B, and MAPK opened up the possibility that H2O2 serve as signaling molecules

• There are many mechanisms explined that includingredox relay, floodgate model and others.

Redox relay

• The redox relay mechanism uses a scavengingenzyme such as glutathione peroxidase (GPX) orperoxiredoxin (PRX) to transduce the H2O2 signaland oxidize the target protein

Floodgate model

• H2O2 inactivates the scavenger, perhaps throughhyperoxidation to sulfinic (SO2 _) acid or through a posttranslational modification (PTM), to allow forH2O2-mediated oxidation of the target protein.

Other mechanisms

• The scavenging enzyme accepts H2O2 oxidation andtransfers the oxidation to an intermediate redoxprotein such as thioredoxin (TRX), whichsubsequently oxidizes the target protein.

Other mechanisms

• Dissociation of the target protein from the oxidizedscavenging enzyme results in target protein activation.

Oxidative stress

• A condition of imbalance between pro-oxidant (ROS) and anti-oxidant as definedby Sies in 1985

Hydrogen peroxide-induced oxidativestress

• Hydrogen peroxide (H2O2) is a cell-permeant and highlystable reactive oxygen species (ROS)

• H2O2 produced mainly by the dismutation of superoxide anion (O2 .-) by superoxide dismutase andalso directly by the NOX-4 isoform of the NAD(P)H oxidase .

• H2O2 levels are regulated by intracellular andextracellular enzymes including catalase, glutathioneperoxidase, thioredoxin and other peroxyredoxins, which convert H2O2 to water and O2(1)

The vascular functional effects of H2O2

• Are very complex and depend among other factors, of the specific vascular bed studied and the nature of the precontractile agent.(1)

• H2O2 can either contract or relax arteries from different species (in resting state or after preconstriction with stimuli(1)

• According to an other studies that indicated the samethings “H2O2 can act as a vasodilator and/or vasoconstrictor depending on the vascular bed, species, and experimental conditions”.(2)

Mechanisms whereby H2O2 get itseffects on vessels

H2O2 induces vasoconstriction by :-

• Stimulation of cyclooxygenase and release of TXA2 orTXA2 analogue U46619

• Activation of c-Src(c-Src mediates H2O2 contractile responses by increase of TP activation, H2O2-induced TXA2 production)

Mechanisms whereby H2O2 get itseffects on vessels

• Activation of ERK1/2 mitogen activated protein kinases (MAPK)

• Activation of Rho kinase(1)

• Activation of phospholipase A2 and phospholipase C ,pathways (2).

Mechanisms whereby H2O2 get itseffects on vessels

Vasorelaxation Effects of H202

• The vasoactive role of H2O2 in endothelium-dependent vasorelaxation was recently recognized to involve a multiplicity of responses.

• H2O2 is considered as a primar EDHF, because it is produced by endothelial cells and causes vascular smooth muscle relaxation through activation of Ca2+-dependent K+ (KCa) channels

Mechanisms whereby H2O2 get its effects on vessels

1. Activation of potassium channelspathway

H2O2 can activates different potassiumchannels in vascular smooth muscle cells byproduce membrane hyperpolarization . (3)

Activation of potassium channels pathway

• There are also conflicting results about the types of potassium channels involved in relaxant effect of H2O2 in different vascular tissues

Type of vessels References Subtypes of Ca+2 channel involved

in H2O2 vessel relaxation

Cat cerebral arteries Wei EP, Kontos HA, Beckman JS. Mechanisms

of cerebral

vasodilation by superoxide, hydrogen

peroxide, and peroxynitrite.

Am J Physiol 1996;271:H1262–6.

ATPdependent

potassium channels

Rat cerebral arteries Sobey CG, Heistad DD, Faraci FM. Mechanisms

of bradykinininduced

cerebral vasodilatation in rats: evidence that

reactive

oxygen species activate K+ channels. Stroke

1997;28:2290–5.

Ca2+-activated potassium channels

Canine cerebral arteries Iida Y, Katusic ZS. Mechanisms of cerebral

arterial relaxations to

hydrogen peroxide. Stroke 2000;31:2224–

3220.

Ca2+-activated potassium channels

and voltage-dependent potassium

Channel

Mouse mesenteric Matoba T, Shimokawa H, Nakashima M,

Hirakawa Y, Mukai Y,

Hirano K, et al. Hydrogen peroxide is an

endothelium-derived

hyperpolarizing factor in mice. J Clin Invest

2000;106:1521–30.

Ca2+-activated potassium channels

Porcine coronary arteries Barlow RS, White RE. Hydrogen peroxide

relaxes porcine

coronary arteries by stimulating BKCa channel

activity. Am J

Physiol 1998;275:H1283–9.

Ca2+-activated potassium channels

Human atrial Miura H, Bosnjak JJ, Ning G, Saito T, Miura M.

Gutterman DD.

Role of hydrogen peroxide in flow-induced

dilation of human

coronary arterioles. Circ Res 2003;92:e31–40.

Ca2+-activated potassium

channels

Pig coronary arterioles. Thengchaisri N, Kuo L. Hydrogen peroxide

induces endotheliumdependent

and -independent coronary arteriolar dilation:

role of

cyclooxygenase and potassium channels. Am J

Physiol 2003;285:

H2255–63.

Ca2+-activated potassium

channels

Human ITA voltage-dependent potassium

channel

Canine coronary arteries Rogers PA, Dick GM, Knudson JD, Focardi M,

Bratz IN,

Swafford AN, et al. H2O2-induced redox-

sensitive coronary

vasodilation is mediated by 4-aminopyridine-

sensitive K+ channels.

Am J Physiol 2006;291:H2473–82.

voltage-dependent potassium

channel

Rat coronary arteries Rogers PA, Dick GM, Knudson JD, Focardi M,

Bratz IN,

Swafford AN, et al. H2O2-induced redox-

sensitive coronary

vasodilation is mediated by 4-aminopyridine-

sensitive K+ channels.

Am J Physiol 2006;291:H2473–82.

voltage-dependent potassium

channel

2. Activation of COX pathway

H2O2 activate COX pathway starting with the activatesphospholipase A2 to release arachidonic acid fromvascular smooth muscle cells and produces COX products .This products may have role in the relaxationeffect of H2O2.(3)

3. Producation of nitric oxide (NO):

• It have been reported that H2O2 improve release of manyreporte endothelial nitric oxide (NO) and accumulate of cyclic GMP in smooth muscle resulting in relaxation effectof H2O2.(4)

1. GARCÍA-REDONDO, Ana B., et al. c-Src, ERK1/2 and Rho kinase mediate hydrogenperoxide-induced vascular contraction in hypertension: role of TXA2, NAD (P) H oxidase and mitochondria. Journal of hypertension, 2015, 33.1: 77-87.

2. HATOUM, Ossama A., et al. Role of hydrogen peroxide in ACh-induced dilation of human submucosal intestinal microvessels. American Journal of Physiology-Heart andCirculatory Physiology, 2005, 288.1: H48-H54.

3. NACITARHAN, Cahit, et al. The effect of hydrogen peroxide in human internal thoracicarteries: role of potassium channels, nitric oxide and cyclooxygenaseproducts. Cardiovascular Drugs and Therapy, 2007, 21.4: 257-262.

4. YANG, Zhi-wei, et al. Endothelium-dependent relaxation to hydrogen peroxide in canine basilar artery: a potential new cerebral dilator mechanism. Brain researchbulletin, 1998, 47.3: 257-263.

5. Reczek, Colleen R., and Navdeep S. Chandel. "ROS-dependent signaltransduction." Current opinion in cell biology 33 (2015): 8-13.

REFERENECES