|PDB structures||RCSB PDB PDBe PDBsum|
NADPH oxidase (nicotinamide adenine dinucleotide phosphate oxidase) is a membrane-bound enzyme complex that faces the extracellular space. It can be found in the plasma membrane as well as in the membranes of phagosomes used by neutrophil white blood cells to engulf microorganisms. Human isoforms of the catalytic component of the complex include NOX1, NOX2, NOX3, NOX4, NOX5, DUOX1, and DUOX2.
NADPH oxidase catalyzes the production of a superoxide free radical by transferring one electron to oxygen from NADPH. During this process O2 is transported from the extracellular space to the cell interior and the H+ is exported.
- NADPH + 2O2 ↔ NADP+ + 2O2− + H+
NADPH oxidases (NOXes) are one of the major sources of cellular reactive oxygen species (ROS), and they still are the focus of extensive research interest due to their exclusive function in producing ROS under normal physiological conditions. The NADPH oxidase complex is dormant under normal circumstances, but is activated to assemble in the membranes during respiratory burst. The activated NADPH oxidase generates superoxide which has roles in animal immune response and plant signalling.
Superoxide can be produced in phagosomes which have ingested bacteria and fungi, or it can be produced outside of the cell. Superoxide kills bacteria and fungi by mechanisms that are not yet fully understood. It is presumed that superoxide kills bacteria directly, as the virulence of many pathogens is dramatically attenuated when their superoxide dismutase (SOD) genes are deleted. However, superoxide can also spontaneously form hydrogen peroxide that undergoes further reactions to generate other reactive oxygen species (ROS) like hypochlorous acid (the reactive agent in bleach). It may also inactivate critical metabolic enzymes, initiate lipid peroxidation, damage iron-sulphur clusters, and liberate redox-active iron, which allows the generation of indiscriminate oxidants such as the hydroxyl radical.
In insects, NOXes had some functions clarified. Arthropods have three NOX types (NOX4-art, an arthropod-specific p22-phox-independent NOX4, and two calcium-dependent enzymes, DUOX). In the gut, DUOX-dependent ROS production from bacteria-stimulated Drosophila melanogaster mucosa is an important pathogen-killing mechanism and can increase defecation as a defense response. In Aedes aegypti, DUOX is involved in the control of the gut indigenous microbiota. Rhodnius prolixus has calcium-activated DUOX, which is involved in eggshell hardening, and NOX5, which is involved in the control of gut motility and blood digestion.
Careful regulation of NADPH oxidase activity is crucial to maintain a healthy level of ROS in the body. The enzyme is dormant in resting cells but becomes rapidly activated by several stimuli, including bacterial products and cytokines. Vascular NADPH oxidases are regulated by a variety of hormones and factors known to be important players in vascular remodeling and disease. These include thrombin, platelet-derived growth factor (PDGF), tumor necrosis factor (TNFa), lactosylceramide, interleukin-1, and oxidized LDL. It is also stimulated by agonists and arachidonic acid. Conversely, assembly of the complex can be inhibited by apocynin and diphenylene iodonium. Apocynin decreases influenza-induced lung inflammation in mice in vivo and so may have clinical benefits in the treatment of influenza.
In mammals, NADPH oxidase is found in two types: one in white blood cells (neutrophilic) and the other in vascular cells, differing in biochemical structure and functions. Neutrophilic NADPH oxidase produces superoxide almost instantaneously, whereas the vascular enzyme produces superoxide in minutes to hours. Moreover, in white blood cells, superoxide has been found to transfer electrons across the membrane to extracellular oxygen, while in vascular cells, the radical anion appears to be released mainly intracellularly.
Superoxides are crucial in killing foreign bacteria in the human body. Consequently, under-activity can lead to an increased susceptibility to organisms such as catalase-positive microbes, and over-activity can lead to oxidative stress and cell damage.
Excessive production of ROS in vascular cells causes many forms of cardiovascular disease including hypertension, atherosclerosis, myocardial infarction, and ischemic stroke. Atherosclerosis is caused by the accumulation of macrophages containing cholesterol (foam cells) in artery walls (in the intima). ROS produced by NADPH oxidase activate an enzyme that makes the macrophages adhere to the artery wall (by polymerizing actin fibers). This process is counterbalanced by NADPH oxidase inhibitors, and by antioxidants. An imbalance in favor of ROS produces atherosclerosis. In vitro studies have found that the NADPH oxidase inhibitors apocynin and diphenyleneiodonium, along with the antioxidants N-acetyl-cysteine and resveratrol, depolymerized the actin, broke the adhesions, and allowed foam cells to migrate out of the intima.
One study suggests a role for NADPH oxidase in ketamine-induced loss of neuronal parvalbumin and GAD67 expression. Similar loss is observed in schizophrenia, and the results may point at the NADPH oxidase as a possible player in the pathophysiology of the disease. Nitro blue tetrazolium is used in a diagnostic test, in particular, for chronic granulomatous disease, a disease in which there is a defect in NADPH oxidase; therefore, the phagocyte is unable to make the reactive oxygen species or radicals required for bacterial killing, resulting in bacteria thriving within the phagocyte. The higher the blue score the better the cell is at producing reactive oxygen species.
It has also been shown that NADPH oxidase plays a role in the mechanism that induces the formation of sFlt-1, a protein that deactivates certain proangiogenic factors that play a role in the development of the placenta, by facilitating the formation of reactive oxygen species, which are suspected intermediaries in sFlt-1 formation. These effects are in part responsible for inducing pre-eclampsia in pregnant women
- X-linked chronic granulomatous disease (CGD)
- Autosomal recessive cytochrome b-negative CGD
- Autosomal recessive cytochrome b-positive CGD type I
- Autosomal recessive cytochrome b-positive CGD type II.
In these diseases, cells have a low capacity for phagocytosis, and persistent bacterial infections occur. Areas of infected cells are common, granulomas. A similar disorder called neutrophil immunodeficiency syndrome is linked to a mutation in the RAC2, also a part of the complex.
NADPH oxidase can be inhibited by apocynin, nitric oxide (NO), and diphenylene iodonium. Apocynin acts by preventing the assembly of the NADPH oxidase subunits. Apocynin decreases influenza-induced lung inflammation in mice in vivo and so may have clinical benefits in the treatment of influenza.
Inhibition of NADPH oxidase by NO blocks the source of oxidative stress in the vasculature. NO donor drugs (nitrovasodilators) have therefore been used for more than a century to treat coronary artery disease, hypertension, and heart failure by preventing excess superoxide from deteriorating healthy vascular cells.
More advanced NADPH oxidase inhibitors include GKT-831 (Formerly GKT137831), a dual Inhibitor of isoforms NOX4 and NOX1 which was patented in 2007. The compound was initially developed for Idiopathic pulmonary fibrosis and obtained orphan drug designation by the FDA and EMA at end of 2010.
The whole structure of the membrane-bound vascular enzyme is composed of five parts: two cytosolic subunits (p47phox and p67phox), a cytochrome b558 which consists of gp91phox, p22phox and a small G protein Rac. Generation of the superoxide in vascular NADPH occurs by a one-electron reduction of oxygen via the gp91phox subunit, using reduced NADPH as the electron donor. The small G protein carries an essential role in the activation of the oxidase by switching between a GDP-bound (inactive) and GTP-linked (active) forms.
The isoform found in neutrophils is made up of six subunits. These subunits are:
- a Rho GTPase, usually Rac1 or Rac2 (Rac stands for Rho-related C3 botulinum toxin substrate)
- Five phagocytic oxidase subunits:
There are several vascular isoforms of the complex which use paralogs the NOX2 subunit:
There are two further paralogs of NOX2 subunit in the thyroid:
- Sahoo S, Meijles DN, Pagano PJ (March 2016). "NADPH oxidases: key modulators in aging and age-related cardiovascular diseases?". Clinical Science. 130 (5): 317–35. doi:10.1042/CS20150087. PMC 4818578. PMID 26814203.
- Herb M, Gluschko A, Wiegmann K, Farid A, Wolf A, Utermöhlen O, et al. (February 2019). "Mitochondrial reactive oxygen species enable proinflammatory signaling through disulfide linkage of NEMO". Science Signaling. 12 (568): eaar5926. doi:10.1126/scisignal.aar5926. PMID 30755476.
- Herb M, Schramm M (February 2021). "Functions of ROS in Macrophages and Antimicrobial Immunity". Antioxidants. 10 (2): 313. doi:10.3390/antiox10020313. PMC 7923022. PMID 33669824.
- Slauch JM (May 2011). "How does the oxidative burst of macrophages kill bacteria? Still an open question". Molecular Microbiology. 80 (3): 580–3. doi:10.1111/j.1365-2958.2011.07612.x. PMC 3109634. PMID 21375590.
- Djaman O, Outten FW, Imlay JA (October 2004). "Repair of oxidized iron-sulfur clusters in Escherichia coli". The Journal of Biological Chemistry. 279 (43): 44590–9. doi:10.1074/jbc.M406487200. PMID 15308657.
- Gandara AC, Torres A, Bahia AC, Oliveira PL, Schama R (March 2017). "Evolutionary origin and function of NOX4-art, an arthropod specific NADPH oxidase". BMC Evolutionary Biology. 17 (1): 92. doi:10.1186/s12862-017-0940-0. PMC 5372347. PMID 28356077.
- Kawahara T, Quinn MT, Lambeth JD (July 2007). "Molecular evolution of the reactive oxygen-generating NADPH oxidase (Nox/Duox) family of enzymes". BMC Evolutionary Biology. 7 (1): 109. doi:10.1186/1471-2148-7-109. PMC 1940245. PMID 17612411.
- Ha EM, Oh CT, Bae YS, Lee WJ (November 2005). "A direct role for dual oxidase in Drosophila gut immunity". Science. 310 (5749): 847–50. Bibcode:2005Sci...310..847H. doi:10.1126/science.1117311. PMID 16272120. S2CID 12476863.
- Du EJ, Ahn TJ, Kwon I, Lee JH, Park JH, Park SH, et al. (January 2016). Miguel-Aliaga I (ed.). "TrpA1 Regulates Defecation of Food-Borne Pathogens under the Control of the Duox Pathway". PLOS Genetics. 12 (1): e1005773. doi:10.1371/journal.pgen.1005773. PMC 4699737. PMID 26726767.
- Oliveira JH, Gonçalves RL, Lara FA, Dias FA, Gandara AC, Menna-Barreto RF, et al. (March 2011). Schneider DS (ed.). "Blood meal-derived heme decreases ROS levels in the midgut of Aedes aegypti and allows proliferation of intestinal microbiota". PLOS Pathogens. 7 (3): e1001320. doi:10.1371/journal.ppat.1001320. PMC 3060171. PMID 21445237.
- Dias FA, Gandara AC, Queiroz-Barros FG, Oliveira RL, Sorgine MH, Braz GR, Oliveira PL (December 2013). "Ovarian dual oxidase (Duox) activity is essential for insect eggshell hardening and waterproofing". The Journal of Biological Chemistry. 288 (49): 35058–67. doi:10.1074/jbc.M113.522201. PMC 3853258. PMID 24174530.
- Montezano AC, De Lucca Camargo L, Persson P, Rios FJ, Harvey AP, Anagnostopoulou A, et al. (June 2018). "NADPH Oxidase 5 Is a Pro-Contractile Nox Isoform and a Point of Cross-Talk for Calcium and Redox Signaling-Implications in Vascular Function". Journal of the American Heart Association. 7 (12). doi:10.1161/JAHA.118.009388. PMC 6220544. PMID 29907654.
- Gandara AC, Dias FA, de Lemos PC, Stiebler R, Bombaça AC, Menna-Barreto R, Oliveira PL (2021-02-25). ""Urate and NOX5 Control Blood Digestion in the Hematophagous Insect Rhodnius prolixus"". Frontiers in Physiology. 12: 633093. doi:10.3389/fphys.2021.633093. PMC 7947236. PMID 33716782.
- Geiszt M (July 2006). "NADPH oxidases: new kids on the block". Cardiovascular Research. 71 (2): 289–99. doi:10.1016/j.cardiores.2006.05.004. PMID 16765921.
- Griendling KK, Sorescu D, Ushio-Fukai M (March 2000). "NAD(P)H oxidase: role in cardiovascular biology and disease". Circulation Research. 86 (5): 494–501. doi:10.1161/01.res.86.5.494. PMID 10720409.
- Vlahos R, Stambas J, Bozinovski S, Broughton BR, Drummond GR, Selemidis S (February 2011). "Inhibition of Nox2 oxidase activity ameliorates influenza A virus-induced lung inflammation". PLOS Pathogens. 7 (2): e1001271. doi:10.1371/journal.ppat.1001271. PMC 3033375. PMID 21304882.
- Dusting GJ, Selemidis S, Jiang F (March 2005). "Mechanisms for suppressing NADPH oxidase in the vascular wall". Memórias do Instituto Oswaldo Cruz. 100 Suppl 1: 97–103. doi:10.1590/S0074-02762005000900016. PMID 15962105.
- Pagano PJ, Chanock SJ, Siwik DA, Colucci WS, Clark JK (August 1998). "Angiotensin II induces p67phox mRNA expression and NADPH oxidase superoxide generation in rabbit aortic adventitial fibroblasts". Hypertension. 32 (2): 331–7. doi:10.1161/01.hyp.32.2.331. PMID 9719063.
- Griendling KK, Minieri CA, Ollerenshaw JD, Alexander RW (June 1994). "Angiotensin II stimulates NADH and NADPH oxidase activity in cultured vascular smooth muscle cells". Circulation Research. 74 (6): 1141–8. doi:10.1161/01.res.74.6.1141. PMID 8187280.
- Zafari AM, Ushio-Fukai M, Akers M, Yin Q, Shah A, Harrison DG, et al. (September 1998). "Role of NADH/NADPH oxidase-derived H2O2 in angiotensin II-induced vascular hypertrophy". Hypertension. 32 (3): 488–95. doi:10.1161/01.hyp.32.3.488. PMID 9740615.
- Wattanapitayakul SK, Bauer JA (February 2001). "Oxidative pathways in cardiovascular disease: roles, mechanisms, and therapeutic implications". Pharmacology & Therapeutics. 89 (2): 187–206. doi:10.1016/S0163-7258(00)00114-5. PMID 11316520.
- Park YM, Febbraio M, Silverstein RL (January 2009). "CD36 modulates migration of mouse and human macrophages in response to oxidized LDL and may contribute to macrophage trapping in the arterial intima". The Journal of Clinical Investigation. 119 (1): 136–45. doi:10.1172/JCI35535. PMC 2613464. PMID 19065049.
- Curtiss LK (March 2009). "Reversing atherosclerosis?". The New England Journal of Medicine. 360 (11): 1144–6. doi:10.1056/NEJMcibr0810383. PMID 19279347.
- Behrens MM, Ali SS, Dao DN, Lucero J, Shekhtman G, Quick KL, Dugan LL (December 2007). "Ketamine-induced loss of phenotype of fast-spiking interneurons is mediated by NADPH-oxidase". Science. 318 (5856): 1645–7. Bibcode:2007Sci...318.1645B. doi:10.1126/science.1148045. PMID 18063801. S2CID 41932041.
- Tom Fagan. Does Oxidative Stress Link NMDA and GABA Hypotheses of Schizophrenia? Archived 2007-12-30 at the Wayback Machine Schizophrenia Research Forum. December 09, 2007.
- Huang QT, Zhang M, Zhong M, Yu YH, Liang WZ, Hang LL, et al. (December 2013). "Advanced glycation end products as an upstream molecule triggers ROS-induced sFlt-1 production in extravillous trophoblasts: a novel bridge between oxidative stress and preeclampsia". Placenta. 34 (12): 1177–82. doi:10.1016/j.placenta.2013.09.017. PMID 24144948.
- Aoyama T, Paik YH, Watanabe S, Laleu B, Gaggini F, Fioraso-Cartier L, et al. (December 2012). "Nicotinamide adenine dinucleotide phosphate oxidase in experimental liver fibrosis: GKT137831 as a novel potential therapeutic agent". Hepatology. 56 (6): 2316–27. doi:10.1002/hep.25938. PMC 3493679. PMID 22806357.
- "Espacenet - Bibliographic data". worldwide.espacenet.com. Retrieved 2017-05-04.
- "FDA granting Genkyotex Orphan Drug Designation of GKT137831 for IPF - Genkyotex S.A." pauahosting.co.nz. Retrieved 2017-05-04.[permanent dead link]
- Heyworth PG, Knaus UG, Settleman J, Curnutte JT, Bokoch GM (November 1993). "Regulation of NADPH oxidase activity by Rac GTPase activating protein(s)". Molecular Biology of the Cell. 4 (11): 1217–23. doi:10.1091/mbc.4.11.1217. PMC 275755. PMID 8305740.