Acid-promoted tautomeric lactonization and oxidation-reduction of pyrroloquinoline quinone (PQQ)

Protective role of pyrroloquinoline quinone against gentamicin induced cochlear hair cell ototoxicity

Gentamicin (GM) is one of the commonly used antibiotics in the aminoglycoside class but is ototoxic, which constantly impacts the quality of human life. Pyrroloquinoline quinone (PQQ) as a redox cofactor produced by bacteria was found in soil and foods that exert an antioxidant and redox modulator. It is well documented that the PQQ can alleviate inflammatory responses and cytotoxicity. However, our understanding of PQQ in ototoxicity remains unclear. We reported that PQQ could protect against GM-induced ototoxicity in House Ear Institute-Organ of Corti 1 (HEI-OC1) cells in vitro. To evaluate reactive oxygen species (ROS) production and mitochondrial function, ROS and JC-1 staining, oxygen consumption rate (OCR), and extracellular acidification rate (ECAR) measurements in living cells, mitochondrial dynamics analysis was performed. GM-mediated damage was performed by reducing the production of ROS and inhibiting mitochondria biogenesis and dynamics. PQQ ameliorated the cellular oxidative stress and recovered mitochondrial membrane potential, facilitating the recovery of mitochondrial biogenesis and dynamics. Our in vitro findings improve our understanding of the GM-induced ototoxicity with therapeutic implications for PQQ.

Pyrroloquinoline quinone (PQQ) inhibits lipopolysaccharide induced inflammation in part via downregulated NF-κB and p38/JNK activation in microglial and attenuates microglia activation in lipopolysaccharide treatment mice

Therapeutic strategies designed to inhibit the activation of microglia may lead to significant advancement in the treatment of most neurodegenerative diseases. Pyrroloquinoline quinone (PQQ) is a naturally occurring redox cofactor that acts as an essential nutrient, antioxidant, and has been reported to exert potent immunosuppressive effects. In the present study, the anti-inflammatory effects of PQQ was investigated in LPS treated primary microglia cells. Our observations showed that pretreatment with PQQ significantly inhibited the production of NO and PGE2 and suppressed the expression of pro-inflammatory mediators such as iNOS, COX-2, TNF-a, IL-1b, IL-6, MCP-1 and MIP-1a in LPS treated primary microglia cells. The nuclear translocation of NF-κB and the phosphorylation level of p65, p38 and JNK MAP kinase pathways were also inhibited by PQQ in LPS stimulated primary microglia cells. Further a systemic LPS treatment acute inflammation murine brain model was used to study the suppressive effects of PQQ against neuroinflammation in vivo. Mice treated with PQQ demonstrated marked attenuation of neuroinflammation based on Western blotting and immunohistochemistry analysis of Iba1-against antibody in the brain tissue. Indicated that PQQ protected primary cortical neurons against microglia-mediated neurotoxicity. These results collectively suggested that PQQ might be a promising therapeutic agent for alleviating the progress of neurodegenerative diseases associated with microglia activation.

The neuroprotective effect of pyrroloquinoline quinone on traumatic brain injury

Pyrroloquinoline quinone (PQQ) is a water-soluble, anionic, quinonoid substance that has been established as an essential nutrient in animals. Owing to the inherent properties of PQQ as an antioxidant and redox modulator in various systems, PQQ is expected to be used in pharmacological applications in the near future. Although many recent studies have investigated its neuroprotective effects, the effect of PQQ on traumatic brain injury (TBI) has not been examined. In this study we employed Morris water maze (MWM) training, the results of which showed that PQQ led to improved behavioral performance in post-TBI animals. Considering that many experiments have suggested that β-1,4-galactosyltransferase I (β-1,4-GalT-I) and -V play significant roles in inflammation and the nervous system, in the present study we used Western blot analysis to study the effect of PQQ on the expression of β-1,4-GalT-I and -V. We found apparent expression upregulation of β-1,4-GalT-I and -V after PQQ was systemically administered. Lectin-fluorescent staining with RCA-I also revealed that PQQ contributed to expression upregulation of the galactosidase β-1 (Gal β-1), 4-galactosyltransferase N-acylsphingosine (4-GlcNAc) group in microglia and neurons of the cortex and hippocampal CA2 region. In summary, our experiment established that PQQ may play an important role in recovery post-TBI.

Kinetic study of the antioxidant activity of pyrroloquinolinequinol (PQQH(2), a reduced form of pyrroloquinolinequinone) in micellar solution

Kinetic study of the aroxyl radical-scavenging action of pyrroloquinolinequinol [PQQH(2), a reduced form of pyrroloquinolinequinone (PQQ)] and water-soluble antioxidants (vitamin C, cysteine, glutathione, and uric acid) has been performed. The second-order rate constants (k(s)) for the reaction of aroxyl radical with PQQH(2) and water-soluble antioxidants were measured in Triton X-100 micellar solution (5.0 wt %) (pH 7.4), using stopped-flow and UV-visible spectrophotometers. The k(s) values decreased in the order PQQH(2) > vitamin C >> cysteine > uric acid > glutathione. The aroxyl radical-scavenging activity of PQQH(2) was 7.4 times higher than that of vitamin C, which is well-known as the most active water-soluble antioxidant. Furthermore, PQQNa(2) (disodium salt of PQQ) was easily reduced to PQQH(2) by reaction of PQQNa(2) with glutathione and cysteine in buffer solution (pH 7.4) under nitrogen atmosphere. The result suggests that PQQ exists as a reduced form throughout the cell and plays a role as antioxidant.

Neuroprotection by pyrroloquinoline quinone (PQQ) in reversible middle cerebral artery occlusion in the adult rat

Pyrroloquinoline quinone (PQQ) is a naturally occurring redox cofactor that acts as an essential nutrient, antioxidant, and redox modulator. It has previously been reported to reduce infarct size in 7-day-old rat pups with an in vivo cerebral hypoxia/ischemia model (Jensen et al., 1994). In this study, we tested whether improvement is found in both behavioral measures of protection and by histological measures of infarcted tissue at 72 h after reversible middle cerebral artery occlusion (rMCAo) in adult rats. Two-hour rMCAo was induced in adult rats using the intraluminal suture technique. PQQ (10, 3, and 1 mg/kg) was given once by intravenous injection at the initiation, or 3 h after the initiation, of 2 h rMCAo. Neurobehavioral deficits were evaluated daily for 3 days followed by infarct volumes measurements by 2,3,5-triphenyltetrazolium chloride (TTC) staining. PQQ at 10 mg/kg infused at the initiation, or 3 h after the initiation, of rMCAo was effective in reducing cerebral infarct volumes measured 72 h later. At 3 h after ischemia, a dose of 3 mg/kg significantly reduced infarct volume compared to vehicle-treated animals, but 1 mg/kg was ineffective. Neurobehavioral scores were also significantly better in the PQQ-treated group compared to the vehicle controls when PQQ was given at 10 and 3 mg/kg, but not at 1 mg/kg. Thus, PQQ is neuroprotective when given as a single administration at least 3 h after initiation of rMCAo. These data indicate that PQQ may be a useful neuroprotectant in stroke therapy.

Newly discovered redox cofactors: possible nutritional, medical, and pharmacological relevance to higher animals

Research spurred by the discovery of pyrroloquinoline quinone (PPQ) in 1979 led to the discovery of four additional oxidation-reduction (redox) cofactors, all of which result from transmogrification of amino acyl side chains in respective enzymes. These cofactors are (a) topa quinone in copper-containing amine oxidases, enzymes found in nearly all forms of life, including human; (b) lysyl topa quinone of the copper protein lysyl oxidase, an enzyme required for proper cross-linking of collagen and elastin; (c) tryptophan tryptophylquinone of alkylamine dehydrogenases from gram-negative soil bacteria; and (d) the copper-complexed cysteinyltyrosyl radical of fungal galactose oxidase. Originally, PQQ was thought to be a covalently bound cofactor in numerous enzymes from eukaryotes and prokaryotes. Today, PQQ is only found as a noncovalent cofactor in bacterial enzymes. The ubiquity of PQQ in the environment and its steady accessibility in the human diet has raised questions concerning its role as a vitamin, or an essential or helpful nutrient. The relevance to nutrition, medicine, and pharmacology of PQQ, topa quinone, lysyl topa quinone, tryptophan trytophylquinone, the galactose oxidase cofactor, and the enzymes harboring these cofactors are discussed in this review.