PQQ

Last Updated: September 28 2022

PQQ is a small molecule once thought to be a vitamin, although its actions in the human body are not related to this hypothesized vitamin-like mechanism. Via its actions as a REDOX agent in cells, it can modify signalling and is thought to support mitochondrial function.

PQQ is most often used for

Summary

Pyrroloquinoline quinone (henceforth PQQ) is a small quinone molecule which has the ability to be a REDOX agent, capable of reducing oxidants (an antioxidant effect) and then being recycled by glutathione back into an active form. It appears to be quite stable as it can undergo several thousand cycles before being used up, and it is novel since it associates with protein structures inside the cell (some antioxidants, mostly notably carotenoids like β-carotene and astaxanthin, are located at specific areas of a cell where they exert proportionally more antioxidant effects due to proximity; PQQ seems to do this near proteins like carotenoids do so at the cell membrane).

The aforementioned REDOX functions can alter protein function and signalling pathways, and while there is a lot of promising in vitro (outside of a living model) research on what it could do there are only a few promising results of PQQ supplementation, mostly related to either altering some signalling pathways or via its benefits to mitochondria (producing more of them and increasing their efficiency).

It is a coenzyme in bacteria (so, to bacteria, this would be something like a B-vitamin) but this role does not appear to extend to humans. Since this does not extend to humans, the designation of PQQ as a vitamin compound has fallen through and it is only considered 'vitamin-like' at best.

PQQ seems to modify oxidation in a cell after binding to some proteins, and this modulatory role it plays can alter the signalling processes that go on in a cell. Due to PQQ being a REDOX agent (capable of both reducing and oxidizing) it is not a pure antioxidant, but it is involved in a cyclical antioxidative cycle with an antioxidant enzyme known as glutathione

For human evidence, the limited evidence we have right now suggests a possible neuroprotective role in the aged (no research in clinical situations of neurodegeneration nor in youth) and it may have an antiinflammatory role. This limited evidence also suggests that the main claim of PQQ, an enhancement of mitochondrial function, occurs in otherwise healthy humans given PQQ supplementation.

The animal evidence that might apply to humans (using oral supplementation at doses similar to what humans use) include a radioprotective effect, possible benefits to insulin resistance, and being a growth factor when PQQ is added to the diet over a long period of time. Higher than normal oral doses in rodents seem to also enhance peripheral neurogenesis (nerve growth outside of the brain) but not necessarily in the brain.

A large amount of the evidence for a direct antioxidant role or the neurological actions related to NMDA signalling of PQQ seem to use very high concentrations in cells, due to possible transportation issues to the brain and low concentrations of PQQ found in the blood following oral ingestion.

It holds a potential to modify signalling in humans, and although the oxidation in the blood (easiest thing to measure) in mostly unaffected it also retains the potential to act as an intracellular antioxidant. The enhancement of mitochondrial function may also occur, but beyond some alterations in signalling and the mitochondrial biogenesis most other properties of PQQ are unlikely to extend to humans

What else is PQQ known as?
Note that PQQ is also known as:
  • PQQ
  • Methoxatin
  • Pyrroloquinoline Quinone
Dosage information

The optimal dosage of Pyrroloquinoline quinone (PQQ) to be taken daily is currently not known, but extrapolations from animal studies suggest that doses as low as 2mg are somewhat bioactive while most dietary supplements are sold in the 20-40mg range.

Join our supplement information course

Enter your email for a FREE five-day course on supplements. Get only the information that’s 100% backed by science. We take an independent and unbiased approach to figure out what works (and what’s a waste of time and money).

Examine is the only 100% independent company in the nutrition and supplement industry. While everyone else sells supplements and works with sponsors, we exclusively analyze research.

    The only 100% independent company. While everyone sells supplements, we only analyze research.

    Examine Database: PQQ
    What works and what doesn't?

    Unlock the full potential of Examine

    Get started

    Don't miss out on the latest research

    Become an Examine Insider for FREE to stay on top of the latest nutrition research, supplement myths, and more

      References
      2.^Anthony CPyrroloquinoline quinone (PQQ) and quinoprotein enzymesAntioxid Redox Signal.(2001 Oct)
      3.^Kumazawa T1, Sato K, Seno H, Ishii A, Suzuki OLevels of pyrroloquinoline quinone in various foodsBiochem J.(1995 Apr 15)
      4.^Noji N, Nakamura T, Kitahata N, Taguchi K, Kudo T, Yoshida S, Tsujimoto M, Sugiyama T, Asami TSimple and sensitive method for pyrroloquinoline quinone (PQQ) analysis in various foods using liquid chromatography/electrospray-ionization tandem mass spectrometryJ Agric Food Chem.(2007 Sep 5)
      7.^Steinberg F, Stites TE, Anderson P, Storms D, Chan I, Eghbali S, Rucker RPyrroloquinoline quinone improves growth and reproductive performance in mice fed chemically defined dietsExp Biol Med (Maywood).(2003 Feb)
      8.^Ikemoto K, Sakamoto H, Nakano MCrystal structure and characterization of pyrroloquinoline quinone disodium trihydrateChem Cent J.(2012 Jun 19)
      10.^Rucker R, Chowanadisai W, Nakano MPotential physiological importance of pyrroloquinoline quinoneAltern Med Rev.(2009 Sep)
      11.^Kim J, Kobayashi M, Fukuda M, Ogasawara D, Kobayashi N, Han S, Nakamura C, Inada M, Miyaura C, Ikebukuro K, Sode KPyrroloquinoline quinone inhibits the fibrillation of amyloid proteinsPrion.(2010 Jan-Mar)
      16.^Felton LM, Anthony CBiochemistry: role of PQQ as a mammalian enzyme cofactorNature.(2005 Feb 3)
      17.^Rucker R, Storms D, Sheets A, Tchaparian E, Fascetti ABiochemistry: is pyrroloquinoline quinone a vitaminNature.(2005 Feb 3)
      18.^Wang L, Jil C, Xu Y, Xu J, Dai J, Wu Q, Wu M, Zou X, Sun L, Gu S, Xie Y, Mao YCloning and characterization of a novel human homolog* of mouse U26, a putative PQQ-dependent AAS dehydrogenaseMol Biol Rep.(2005 Mar)
      19.^Bauerly KA, Storms DH, Harris CB, Hajizadeh S, Sun MY, Cheung CP, Satre MA, Fascetti AJ, Tchaparian E, Rucker RBPyrroloquinoline quinone nutritional status alters lysine metabolism and modulates mitochondrial DNA content in the mouse and ratBiochim Biophys Acta.(2006 Nov)
      20.^Stites TE, Mitchell AE, Rucker RBPhysiological importance of quinoenzymes and the O-quinone family of cofactorsJ Nutr.(2000 Apr)
      22.^Puehringer S, Metlitzky M, Schwarzenbacher RThe pyrroloquinoline quinone biosynthesis pathway revisited: a structural approachBMC Biochem.(2008 Mar 27)
      24.^Flückiger R, Paz MA, Gallop PMRedox-cycling detection of dialyzable pyrroloquinoline quinone and quinoproteinsMethods Enzymol.(1995)
      25.^Stites T, Storms D, Bauerly K, Mah J, Harris C, Fascetti A, Rogers Q, Tchaparian E, Satre M, Rucker RBPyrroloquinoline quinone modulates mitochondrial quantity and function in miceJ Nutr.(2006 Feb)
      26.^Bauerly K, Harris C, Chowanadisai W, Graham J, Havel PJ, Tchaparian E, Satre M, Karliner JS, Rucker RBAltering pyrroloquinoline quinone nutritional status modulates mitochondrial, lipid, and energy metabolism in ratsPLoS One.(2011)
      27.^Harris CB, Chowanadisai W, Mishchuk DO, Satre MA, Slupsky CM, Rucker RBDietary pyrroloquinoline quinone (PQQ) alters indicators of inflammation and mitochondrial-related metabolism in human subjectsJ Nutr Biochem.(2013 Dec)
      29.^Paz MA, Flückiger R, Boak A, Kagan HM, Gallop PMSpecific detection of quinoproteins by redox-cycling stainingJ Biol Chem.(1991 Jan 15)
      30.^Salisbury SA, Forrest HS, Cruse WBT, Kennard OA novel coenzyme from bacterial primary alcohol dehydrogenaseNature.(1979 Aug)
      31.^Dooley DM, McGuirl MA, Peisach J, McCracken JThe generation of an organic free radical in substrate-reduced pig kidney diamine oxidase-cyanideFEBS Lett.(1987 Apr 20)
      32.^van der Meer RA, van Wassenaar PD, van Brouwershaven JH, Duine JAPrimary structure of a pyrroloquinoline quinone (PQQ) containing peptide isolated from porcine kidney diamine oxidaseBiochem Biophys Res Commun.(1989 Mar 15)
      35.^Robertson JG, Kumar A, Mancewicz JA, Villafranca JJSpectral studies of bovine dopamine beta-hydroxylase. Absence of covalently bound pyrroloquinoline quinoneJ Biol Chem.(1989 Nov 25)
      36.^Duine JAPQQ in plants (and animals)Trends Biochem Sci.(1991 Jan)
      37.^Klinman JP, Dooley DM, Duine JA, Knowles PF, Mondovi B, Villafranca JJStatus of the cofactor identity in copper oxidative enzymesFEBS Lett.(1991 Apr 22)
      38.^Kamata H, Hirata HRedox regulation of cellular signallingCell Signal.(1999 Jan)
      42.^Arnér ES, Holmgren APhysiological functions of thioredoxin and thioredoxin reductaseEur J Biochem.(2000 Oct)
      45.^Brigelius-Flohé R, Müller M, Lippmann D, Kipp APThe yin and yang of nrf2-regulated selenoproteins in carcinogenesisInt J Cell Biol.(2012)
      46.^Locy ML, Rogers LK, Prigge JR, Schmidt EE, Arnér ES, Tipple TEThioredoxin reductase inhibition elicits nrf2-mediated responses in clara cells: implications for oxidant-induced lung injuryAntioxid Redox Signal.(2012 Nov 15)
      47.^Suvorova ES, Lucas O, Weisend CM, Rollins MF, Merrill GF, Capecchi MR, Schmidt EECytoprotective Nrf2 pathway is induced in chronically txnrd 1-deficient hepatocytesPLoS One.(2009 Jul 7)
      51.^Steinberg FM, Gershwin ME, Rucker RBDietary pyrroloquinoline quinone: growth and immune response in BALB/c miceJ Nutr.(1994 May)
      52.^Paul S Hwang, Steven B Machek, Thomas D Cardaci, Dylan T Wilburn, Caelin S Kim, Emiliya S Suezaki, Darryn S WilloughbyEffects of Pyrroloquinoline Quinone (PQQ) Supplementation on Aerobic Exercise Performance and Indices of Mitochondrial Biogenesis in Untrained MenJ Am Coll Nutr.(2020 Aug)
      53.^Wasserman K, Beaver WL, Davis JA, Pu JZ, Heber D, Whipp BJLactate, pyruvate, and lactate-to-pyruvate ratio during exercise and recoveryJ Appl Physiol (1985).(1985 Sep)
      54.^Guan M, Xie L, Diao C, Wang N, Hu W, Zheng Y, Jin L, Yan Z, Gao HSystemic perturbations of key metabolites in diabetic rats during the evolution of diabetes studied by urine metabonomicsPLoS One.(2013)
      55.^Terán-García M, Ibarra I, Velázquez AUrinary organic acids in infant malnutritionPediatr Res.(1998 Sep)
      56.^Kumazawa T, Hiwasa T, Takiguchi M, Suzuki O, Sato KActivation of Ras signaling pathways by pyrroloquinoline quinone in NIH3T3 mouse fibroblastsInt J Mol Med.(2007 May)
      57.^Ishii T, Akagawa M, Naito Y, Handa O, Takagi T, Mori T, Kumazawa S, Yoshikawa T, Nakayama TPro-oxidant action of pyrroloquinoline quinone: characterization of protein oxidative modificationsBiosci Biotechnol Biochem.(2010)
      60.^Huyer G, Liu S, Kelly J, Moffat J, Payette P, Kennedy B, Tsaprailis G, Gresser MJ, Ramachandran CMechanism of inhibition of protein-tyrosine phosphatases by vanadate and pervanadateJ Biol Chem.(1997 Jan 10)
      62.^Cantó C, Auwerx JTargeting sirtuin 1 to improve metabolism: all you need is NAD(+)?Pharmacol Rev.(2012 Jan)
      64.^Li XSIRT1 and energy metabolismActa Biochim Biophys Sin (Shanghai).(2013 Jan)
      65.^Herranz D, Muñoz-Martin M, Cañamero M, Mulero F, Martinez-Pastor B, Fernandez-Capetillo O, Serrano MSirt1 improves healthy ageing and protects from metabolic syndrome-associated cancerNat Commun.(2010 Apr 12)
      66.^Banks AS, Kon N, Knight C, Matsumoto M, Gutiérrez-Juárez R, Rossetti L, Gu W, Accili DSirT1 gain of function increases energy efficiency and prevents diabetes in miceCell Metab.(2008 Oct)
      67.^Pfluger PT, Herranz D, Velasco-Miguel S, Serrano M, Tschöp MHSirt1 protects against high-fat diet-induced metabolic damageProc Natl Acad Sci U S A.(2008 Jul 15)
      68.^Kendrick AA, Choudhury M, Rahman SM, McCurdy CE, Friederich M, Van Hove JL, Watson PA, Birdsey N, Bao J, Gius D, Sack MN, Jing E, Kahn CR, Friedman JE, Jonscher KRFatty liver is associated with reduced SIRT3 activity and mitochondrial protein hyperacetylationBiochem J.(2011 Feb 1)
      69.^Brenmoehl J, Hoeflich ADual control of mitochondrial biogenesis by sirtuin 1 and sirtuin 3Mitochondrion.(2013 Nov)
      70.^Smidt CR, Unkefer CJ, Houck DR, Rucker RBIntestinal absorption and tissue distribution of {14C}pyrroloquinoline quinone in miceProc Soc Exp Biol Med.(1991 May)
      71.^VanEngelen MR, Szilagyi RK, Gerlach R, Lee BD, Apel WA, Peyton BMUranium exerts acute toxicity by binding to pyrroloquinoline quinone cofactorEnviron Sci Technol.(2011 Feb 1)
      74.^Aizenman E, Hartnett KA, Reynolds IJOxygen free radicals regulate NMDA receptor function via a redox modulatory siteNeuron.(1990 Dec)
      75.^Aizenman E, Lipton SA, Loring RHSelective modulation of NMDA responses by reduction and oxidationNeuron.(1989 Mar)
      81.^Zhang Q, Ding M, Cao Z, Zhang J, Ding F, Ke KPyrroloquinoline quinine protects rat brain cortex against acute glutamate-induced neurotoxicityNeurochem Res.(2013 Aug)
      83.^Panov A, Dikalov S, Shalbuyeva N, Taylor G, Sherer T, Greenamyre JTRotenone model of Parkinson disease: multiple brain mitochondria dysfunctions after short term systemic rotenone intoxicationJ Biol Chem.(2005 Dec 23)
      84.^Sherer TB, Betarbet R, Testa CM, Seo BB, Richardson JR, Kim JH, Miller GW, Yagi T, Matsuno-Yagi A, Greenamyre JTMechanism of toxicity in rotenone models of Parkinson's diseaseJ Neurosci.(2003 Nov 26)
      85.^Qin J, Wu M, Yu S, Gao X, Zhang J, Dong X, Ji J, Zhang Y, Zhou L, Zhang Q, Ding FPyrroloquinoline quinone-conferred neuroprotection in rotenone models of Parkinson's diseaseToxicol Lett.(2015 Nov 4)
      86.^Yamaguchi K, Sasano A, Urakami T, Tsuji T, Kondo KStimulation of nerve growth factor production by pyrroloquinoline quinone and its derivatives in vitro and in vivoBiosci Biotechnol Biochem.(1993 Jul)
      87.^Urakami T, Tanaka A, Yamaguchi K, Tsuji T, Niki ESynthesis of esters of coenzyme PQQ and IPQ, and stimulation of nerve growth factor productionBiofactors.(1995-1996)
      88.^Yamaguchi K, Tsuji T, Uemura D, Kondo KCyclooxygenase induction is essential for NGF synthesis enhancement by NGF inducers in L-M cellsBiosci Biotechnol Biochem.(1996 Jan)
      91.^Bulló M, Peeraully MR, Trayhurn PStimulation of NGF expression and secretion in 3T3-L1 adipocytes by prostaglandins PGD2, PGJ2, and Delta12-PGJ2Am J Physiol Endocrinol Metab.(2005 Jul)
      92.^Toyomoto M, Ohta M, Okumura K, Yano H, Matsumoto K, Inoue S, Hayashi K, Ikeda KProstaglandins are powerful inducers of NGF and BDNF production in mouse astrocyte culturesFEBS Lett.(2004 Mar 26)
      93.^Satoh T, Furuta K, Suzuki M, Watanabe YProstaglandin J2 and its metabolites promote neurite outgrowth induced by nerve growth factor in PC12 cellsBiochem Biophys Res Commun.(1999 Apr 29)
      94.^Murase K, Hattori A, Kohno M, Hayashi KStimulation of nerve growth factor synthesis/secretion in mouse astroglial cells by coenzymesBiochem Mol Biol Int.(1993 Jul)
      95.^Liu S, Li H, Ou Yang J, Peng H, Wu K, Liu Y, Yang JEnhanced rat sciatic nerve regeneration through silicon tubes filled with pyrroloquinoline quinoneMicrosurgery.(2005)
      96.^Satake K, Matsuyama Y, Kamiya M, Kawakami H, Iwata H, Adachi K, Kiuchi KNitric oxide via macrophage iNOS induces apoptosis following traumatic spinal cord injuryBrain Res Mol Brain Res.(2000 Dec 28)
      97.^Xu J, Kim GM, Chen S, Yan P, Ahmed SH, Ku G, Beckman JS, Xu XM, Hsu CYiNOS and nitrotyrosine expression after spinal cord injuryJ Neurotrauma.(2001 May)
      98.^Hirakawa A, Shimizu K, Fukumitsu H, Furukawa SPyrroloquinoline quinone attenuates iNOS gene expression in the injured spinal cordBiochem Biophys Res Commun.(2009 Jan 9)
      99.^Gong D, Geng C, Jiang L, Aoki Y, Nakano M, Zhong LEffect of pyrroloquinoline quinone on neuropathic pain following chronic constriction injury of the sciatic nerve in ratsEur J Pharmacol.(2012 Dec 15)
      103.^Chapman AGGlutamate receptors in epilepsyProg Brain Res.(1998)
      104.^Bradford HFGlutamate, GABA and epilepsyProg Neurobiol.(1995 Dec)
      105.^Sanchez RM, Wang C, Gardner G, Orlando L, Tauck DL, Rosenberg PA, Aizenman E, Jensen FENovel role for the NMDA receptor redox modulatory site in the pathophysiology of seizuresJ Neurosci.(2000 Mar 15)
      107.^Fujikawa DG, Vannucci RC, Dwyer BE, Wasterlain CGGeneralized seizures deplete brain energy reserves in normoxemic newborn monkeysBrain Res.(1988 Jun 28)
      110.^Jensen FE, Gardner GJ, Williams AP, Gallop PM, Aizenman E, Rosenberg PAThe putative essential nutrient pyrroloquinoline quinone is neuroprotective in a rodent model of hypoxic/ischemic brain injuryNeuroscience.(1994 Sep)
      112.^Zhang L, Liu J, Cheng C, Yuan Y, Yu B, Shen A, Yan MThe neuroprotective effect of pyrroloquinoline quinone on traumatic brain injuryJ Neurotrauma.(2012 Mar 20)
      113.^Ohwada K, Takeda H, Yamazaki M, Isogai H, Nakano M, Shimomura M, Fukui K, Urano SPyrroloquinoline Quinone (PQQ) Prevents Cognitive Deficit Caused by Oxidative Stress in RatsJ Clin Biochem Nutr.(2008 Jan)
      115.^Zhang P, Xu Y, Li L, Jiang Q, Wang M, Jin LIn vitro protective effects of pyrroloquinoline quinone on methylmercury-induced neurotoxicityEnviron Toxicol Pharmacol.(2009 Jan)
      116.^Takatsu H, Owada K, Abe K, Nakano M, Urano SEffect of vitamin E on learning and memory deficit in aged ratsJ Nutr Sci Vitaminol (Tokyo).(2009)
      117.^Itoh Y, Hine K, Miura H, Uetake T, Nakano M, Takemura N, Sakatani KEffect of the Antioxidant Supplement Pyrroloquinoline Quinone Disodium Salt (BioPQQ™) on Cognitive FunctionsAdv Exp Med Biol.(2016)
      118.^Nakano M, Yamamoto T, Okamura H, Tsuda A, Kowatari YEffects of Oral Supplementation with Pyrroloquinoline Quinone on Stress, Fatigue, and SleepFunct Foods Health Dis.(2012 Aug 31)
      120.^Tao R, Karliner JS, Simonis U, Zheng J, Zhang J, Honbo N, Alano CCPyrroloquinoline quinone preserves mitochondrial function and prevents oxidative injury in adult rat cardiac myocytesBiochem Biophys Res Commun.(2007 Nov 16)
      121.^Zhu BQ, Simonis U, Cecchini G, Zhou HZ, Li L, Teerlink JR, Karliner JSComparison of pyrroloquinoline quinone and/or metoprolol on myocardial infarct size and mitochondrial damage in a rat model of ischemia/reperfusion injuryJ Cardiovasc Pharmacol Ther.(2006 Jun)
      122.^Singh SK, Suresh MV, Voleti B, Agrawal AThe connection between C-reactive protein and atherosclerosisAnn Med.(2008)
      123.^Stella C, Beckwith-Hall B, Cloarec O, Holmes E, Lindon JC, Powell J, van der Ouderaa F, Bingham S, Cross AJ, Nicholson JKSusceptibility of human metabolic phenotypes to dietary modulationJ Proteome Res.(2006 Oct)
      125.^Odkhuu E, Koide N, Haque A, Tsolmongyn B, Naiki Y, Hashimoto S, Komatsu T, Yoshida T, Yokochi TInhibition of receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclast formation by pyrroloquinoline quinine (PQQ)Immunol Lett.(2012 Feb 29)
      126.^Zhao Q, Wang X, Liu Y, He A, Jia RNFATc1: functions in osteoclastsInt J Biochem Cell Biol.(2010 May)
      127.^Takayanagi H, Kim S, Koga T, Nishina H, Isshiki M, Yoshida H, Saiura A, Isobe M, Yokochi T, Inoue J, Wagner EF, Mak TW, Kodama T, Taniguchi TInduction and activation of the transcription factor NFATc1 (NFAT2) integrate RANKL signaling in terminal differentiation of osteoclastsDev Cell.(2002 Dec)
      128.^Ikeda F, Nishimura R, Matsubara T, Tanaka S, Inoue J, Reddy SV, Hata K, Yamashita K, Hiraga T, Watanabe T, Kukita T, Yoshioka K, Rao A, Yoneda TCritical roles of c-Jun signaling in regulation of NFAT family and RANKL-regulated osteoclast differentiationJ Clin Invest.(2004 Aug)
      129.^Wagner EF, Eferl RFos/AP-1 proteins in bone and the immune systemImmunol Rev.(2005 Dec)
      130.^Abraham AK, Ramanathan M, Weinstock-Guttman B, Mager DEMechanisms of interferon-beta effects on bone homeostasisBiochem Pharmacol.(2009 Jun 15)
      131.^Takayanagi H, Kim S, Matsuo K, Suzuki H, Suzuki T, Sato K, Yokochi T, Oda H, Nakamura K, Ida N, Wagner EF, Taniguchi TRANKL maintains bone homeostasis through c-Fos-dependent induction of interferon-betaNature.(2002 Apr 18)
      132.^Takayanagi H, Sato K, Takaoka A, Taniguchi TInterplay between interferon and other cytokine systems in bone metabolismImmunol Rev.(2005 Dec)
      133.^Tremblay F, Lavigne C, Jacques H, Marette ARole of dietary proteins and amino acids in the pathogenesis of insulin resistanceAnnu Rev Nutr.(2007)
      134.^Omata J, Fukatsu K, Murakoshi S, Moriya T, Ueno C, Maeshima Y, Okamoto K, Saitoh D, Yamamoto J, Hase KInfluence of adding pyrroloquinoline quinone to parenteral nutrition on gut-associated lymphoid tissueJPEN J Parenter Enteral Nutr.(2011 Sep)
      135.^Hogg N1, Darley-Usmar VM, Wilson MT, Moncada SProduction of hydroxyl radicals from the simultaneous generation of superoxide and nitric oxideBiochem J.(1992 Jan 15)
      136.^Rein D, Lotito S, Holt RR, Keen CL, Schmitz HH, Fraga CGEpicatechin in human plasma: in vivo determination and effect of chocolate consumption on plasma oxidation statusJ Nutr.(2000 Aug)
      137.^Xiong XH, Zhao Y, Ge X, Yuan SJ, Wang JH, Zhi JJ, Yang YX, Du BH, Guo WJ, Wang SS, Yang DX, Zhang WCProduction and radioprotective effects of pyrroloquinoline quinoneInt J Mol Sci.(2011)
      138.^Tsuchida T, Yasuyama T, Higuchi K, Watanabe A, Urakami T, Akaike T, Sato K, Maeda HThe protective effect of pyrroloquinoline quinone and its derivatives against carbon tetrachloride-induced liver injury of ratsJ Gastroenterol Hepatol.(1993 Jul-Aug)
      139.^Adachi O, Moonmangmee D, Toyama H, Yamada M, Shinagawa E, Matsushita KNew developments in oxidative fermentationAppl Microbiol Biotechnol.(2003 Feb)
      140.^Matsushita K, Arents JC, Bader R, Yamada M, Adachi O, Postma PWEscherichia coli is unable to produce pyrroloquinoline quinone (PQQ)Microbiology.(1997 Oct)
      141.^Smidt CR, Bean-Knudsen D, Kirsch DG, Rucker RBDoes the intestinal microflora synthesize pyrroloquinoline quinoneBiofactors.(1991 Jan)
      142.^Shankar BS, Pandey R, Amin P, Misra HS, Sainis KBRole of glutathione in augmenting the anticancer activity of pyrroloquinoline quinone (PQQ)Redox Rep.(2010)
      146.^Irizarry MC, Growdon W, Gomez-Isla T, Newell K, George JM, Clayton DF, Hyman BTNigral and cortical Lewy bodies and dystrophic nigral neurites in Parkinson's disease and cortical Lewy body disease contain alpha-synuclein immunoreactivityJ Neuropathol Exp Neurol.(1998 Apr)
      147.^Wakabayashi K, Matsumoto K, Takayama K, Yoshimoto M, Takahashi HNACP, a presynaptic protein, immunoreactivity in Lewy bodies in Parkinson's diseaseNeurosci Lett.(1997 Dec 12)
      148.^Spillantini MG, Schmidt ML, Lee VM, Trojanowski JQ, Jakes R, Goedert MAlpha-synuclein in Lewy bodiesNature.(1997 Aug 28)
      149.^Sode K, Usuzaka E, Kobayashi N, Ochiai SEngineered alpha-synuclein prevents wild type and familial Parkin variant fibril formationBiochem Biophys Res Commun.(2005 Sep 23)
      151.^Kim TD, Paik SR, Yang CHStructural and functional implications of C-terminal regions of alpha-synucleinBiochemistry.(2002 Nov 19)
      152.^Zhu M, Rajamani S, Kaylor J, Han S, Zhou F, Fink ALThe flavonoid baicalein inhibits fibrillation of alpha-synuclein and disaggregates existing fibrilsJ Biol Chem.(2004 Jun 25)
      153.^Kim J, Harada R, Kobayashi M, Kobayashi N, Sode KThe inhibitory effect of pyrroloquinoline quinone on the amyloid formation and cytotoxicity of truncated alpha-synucleinMol Neurodegener.(2010 May 20)
      155.^Andrew R, Watson DG, Best SA, Midgley JM, Wenlong H, Petty RKThe determination of hydroxydopamines and other trace amines in the urine of parkinsonian patients and normal controlsNeurochem Res.(1993 Nov)
      157.^Yokota T, Sugawara K, Ito K, Takahashi R, Ariga H, Mizusawa HDown regulation of DJ-1 enhances cell death by oxidative stress, ER stress, and proteasome inhibitionBiochem Biophys Res Commun.(2003 Dec 26)
      158.^Lev N, Ickowicz D, Melamed E, Offen DOxidative insults induce DJ-1 upregulation and redistribution: implications for neuroprotectionNeurotoxicology.(2008 May)
      159.^Bonifati V, Rizzu P, van Baren MJ, Schaap O, Breedveld GJ, Krieger E, Dekker MC, Squitieri F, Ibanez P, Joosse M, van Dongen JW, Vanacore N, van Swieten JC, Brice A, Meco G, van Duijn CM, Oostra BA, Heutink PMutations in the DJ-1 gene associated with autosomal recessive early-onset parkinsonismScience.(2003 Jan 10)
      160.^Nunome K, Miyazaki S, Nakano M, Iguchi-Ariga S, Ariga HPyrroloquinoline quinone prevents oxidative stress-induced neuronal death probably through changes in oxidative status of DJ-1Biol Pharm Bull.(2008 Jul)
      161.^Zhou W, Zhu M, Wilson MA, Petsko GA, Fink ALThe oxidation state of DJ-1 regulates its chaperone activity toward alpha-synucleinJ Mol Biol.(2006 Mar 3)
      162.^Kobayashi M, Kim J, Kobayashi N, Han S, Nakamura C, Ikebukuro K, Sode KPyrroloquinoline quinone (PQQ) prevents fibril formation of alpha-synucleinBiochem Biophys Res Commun.(2006 Oct 27)
      164.^Watanabe A, Hobara N, Ohsawa T, Higashi T, Tsuji TNephrotoxicity of pyrroloquinoline quinone in ratsHiroshima J Med Sci.(1989 Mar)
      165.^Nakano M, Ubukata K, Yamamoto T, Yamaguchi HEffect of Pyrroloquinoline Quinone (PQQ) on mental status of Middle-Aged and Elderly PersonsFood Style.(2009)
      166.^Nakano M, Suzuki H, Imamura T, Lau A, Lynch BGenotoxicity of pyrroloquinoline quinone (PQQ) disodium salt (BioPQQ™)Regul Toxicol Pharmacol.(2013 Nov)