Role of glutathione in augmenting the anticancer activity of pyrroloquinoline quinone (PQQ)

Mini-review: Functions and Action Mechanisms of PQQ in Osteoporosis and Neuro Injury

Pyrroloquinoline Quinone (PQQ) is the third coenzyme found after niacinamide and flavone nucleotides and is widely present in microorganisms, plants, animals, and humans. PQQ can stimulate the growth of organisms and is very important for the growth, development and reproduction of animals. Owing to the inherent properties of PQQ as an antioxidant and redox modulator in various systems. In recent years, the role of PQQ in the field of osteoporosis and neuro injury has become a research hotspot. This article mainly discusses the derivatives, distribution of PQQ, in vitro models of osteoporosis and neuro injury, and the research progress of its mechanism of action. It provides new ideas in the study of osteoporosis and neuro injury.

Pyrroloquinoline quinine protects HK-2 cells against high glucose-induced oxidative stress and apoptosis through Sirt3 and PI3K/Akt/FoxO3a signaling pathway

High glucose(HG)-induced oxidative stress and apoptosis in renal tubular epithelial cells play an important role in the pathogenesis of diabetic nephropathy. Pyrroloquinoline quinine (PQQ), a new B vitamin, has been demonstrated to be important in antioxidant and anti-apoptotic effects. However, its effect on HK-2 cells and the potential mechanism are rarely investigated. In this study, we investigated that PPQ had protective effects against HG-induced oxidative stress damage and apoptosis in vitro model of diabetic nephropathy. PPQ at 10, 100, 500, 1000 and 10000 nM could protect HK-2 cell from HG-induced inhibition. The protective effects of PQQ were associated with increasing the level of antioxidants(SOD2, CAT), inhibition of reactive oxygen species(ROS) production, and dependent modulation of Bcl-2 family proteins. PPQ significantly upregulated the protein and mRNA expression of Sirtuin3(Sirt3) in HG-induced HK-2 cells. PPQ also reduced apoptosis in HG-induced HK-2 cells by the PI3K/Akt/FoxO3a signal pathway. As down-regulated sirt3 or inhibitory the activity of PI3K/Akt/FoxO3a pathway, the protective effects of PPQ were weakened. In conclusion, our data suggest that PPQ achieves the protective effects through PI3K/Akt/FoxO3a pathway and dependent modulation of Sirt3.

Pyrroloquinoline quinone induces chondrosarcoma cell apoptosis by increasing intracellular reactive oxygen species

Pyrroloquinoline quinone (PQQ) has been reported to contribute to cancer cell apoptosis and death; however, little is known of its underlying mechanisms. The present study was designed to investigate the role of PQQ in chondrosarcoma cell apoptosis and the underlying mechanism. A cell cytotoxicity assay was used to detect cell death; flow cytometry analysis was also performed to determine cell apoptosis and intracellular reactive oxygen species (ROS). Biochemical methods were employed to detect the activity and the expression of superoxide dismutase (SOD)1, SOD2 and glutathione. The present study also examined the effect on tumorigenesis in vivo. The results demonstrated that the apoptosis of SW1353 cells induced by PQQ increased in a concentration- and time-dependent manner, which may be attributable to the accumulation of intracellular ROS. In the in vivo experiments, PQQ inhibited proliferation and promoted apoptosis, increased ROS levels and caused DNA damage in transplanted cells. Taken together, the findings of the present study confirmed that PQQ induced apoptosis in human chondrosarcoma SW1353 cells and transplanted cells, by increasing intracellular ROS and reducing the ability of scavenging oxygen free radicals.

Effect and mechanism of pyrroloquinoline quinone on anti-osteoporosis in Bmi-1 knockout mice-Anti-oxidant effect of pyrroloquinoline quinone

Pyrroloquinoline quinone (PQQ), considered as an ROS scavenger,could protect mitochondrial activity from damage of oxidative stress. To determine the role of PQQ supplement in rescuing long bone osteoporosis in Bmi-1^-/- mice. We fed Bmi-1 knockout mice a diet supplemented with PQQ (BKO+PQQ), BKO mice with normal diet (BKO) and wild type mice with normal diet (WT) as controls. We compared the differences of skeletal phenotype by means of imaging, histopathological and molecular biology methods in three groups of animals. Results showed that BKO+PQQ mice increased morphology of tibia, decreased X-ray transmittance, and increased bone density, thickness of cortical bone, width of growth plate and trabecular bone mass compared with BKO mice. Our study also investigated that, compared mice BKO, PCNA positive cells percentage of tibial growth plate areas significantly increased in BKO+PQQ mice, and TUNEL positive cells percentage was significantly decreased. To detect the effect of PQQ on osteoblast formation of tibiae. Our results showed, compared with BKO mice, osteogenic cell, osteoblast number areas, ALP, Col I and OCN positive areas significantly increased in tibia of BKO+PQQ mice. Further studies showed that supplemental PQQ played a role in anti-osteoporosis by up-regulating antioxidant capacity, inhibiting oxidative stress and reducing DNA damage, down-regulating CDKI proteins levels, and decreasing cell apoptosis. This study not only reveals the mechanism of PQQ supplementation in anti-osteoporosis, but also provides the experimental and theoretical basis for the clinical application of PQQ in osteoporosis.

Flavoenzyme-mediated reduction reactions and antitumor activity of nitrogen-containing tetracyclic ortho-quinone compounds and their nitrated derivatives

Nitrogen-based tetracyclic ortho-quinones (naphtho[1'2':4.5]imidazo[1,2-a]pyridine-5,6-diones, NPDOs) and their nitro-substituted derivatives (nitro-(P)NPDOs) were obtained by condensation of substituted 2,3-dichloro-1,4-naphthoquinones with 2-amino-pyridine and -pyrimidine and nitration at an elevated temperature. The structural features of the compounds as well as their global and regional electrophilic potency were characterized by means of DFT computation. The compounds were highly reactive substrates of single- and two-electron (hydride) - transferring P-450R (CPR; EC 1.6.2.4) and NQO-1 (DTD; EC 1.6.99.2), respectively, concomitantly producing reactive oxygen species. Their catalytic efficiency defined in terms of the apparent second-order rate constant (k_cat/K_{M (Q)}) values in P-450R- and NQO-1-mediated reactions varied in the range of 3-6 × 10⁷ M^-1 s^-1 and 1.6-7.4 × 10⁸ M^-1 s^-1, respectively. The cytotoxic activities of the compounds on tumor cell lines followed the concentration-dependent manner exhibiting relatively high cytotoxic potency against breast cancer MCF-7, with CL₅₀ values of 0.08-2.02 µM L^-1 and lower potency against lung cancer A-549 (CL₅₀ = 0.28-7.66 µM L^-1). 3-nitro-pyrimidino-NPDO quinone was the most active compound against MCF-7 with CL₅₀ of 0.08 ± 0.01 µM L^-1 (0.02 µg mL^-1)) which was followed by 3-nitro-NPDO with CL₅₀ of 0.12 ± 0.03 µM L^-1 (0.035 µg mL^-1)) and 0.28 ± 0.08 µM L^-1 (0.08 µg mL^-1) on A-549 and MCF-7 cells, respectively, while 1- and 4-nitro-quinoidals produced the least cytotoxic effects. Tumor cells quantified by AO/EB staining showed that the cell death induced by the compounds occurs primarily through apoptosis.

Radioprotective effects of pyrroloquinoline quinone on parotid glands in C57BL/6J mice

The aim of the present study was to investigate whether pyrroloquinoline quinine (PQQ) serve a radioprotective role in parotid gland damage induced by total body irradiation (TBI) in C57BL/6J mice. A total of 15 female 8-week-old C57BL/6J mice were randomly assigned into three treatment groups: i) Untreated control (no irradiation); ii) 4 gray (Gy) X-ray irradiation; iii) 4 Gy X-ray irradiation with additional dietary PQQ (4 mg PQQ/kg in normal diet). Each group included five mice. After 4 weeks, all animals were collected for evaluating the phenotype, body weight, pathological and biochemical parameters. The results indicated that PQQ had biological effects on total body phenotype. PQQ could partially rescue TBI-induced damage to parotid glands. In addition, PQQ served radioprotective effects on parotid glands via multiple mechanisms, such as promoting proliferation, inhibiting apoptosis and senescence, upregulating antioxidant ability, scavenging reactive oxygen species and reducing DNA damage. The results of the present study demonstrate that PQQ serves a radioprotective role in parotid gland damage induced by TBI, possibly via inhibiting oxidative stress and participating in DNA damage repair. The study provides experimental and theoretical knowledge for the development of radioprotective clinical drugs.

Biological effects of pyrroloquinoline quinone on liver damage in Bmi-1 knockout mice

Pyrroloquinoline quinone (PQQ) has been demonstrated to function as an antioxidant by scavenging free radicals and subsequently protecting the mitochondria from oxidative stress-induced damage. The aim of the present study was to investigate whether PQQ is able to rescue premature senescence in the liver, induced by the deletion of B cell-specific Moloney MLV insertion site-1 (Bmi-1), by inhibiting oxidative stress. In vivo, the mice were allocated into three groups that underwent the following treatment protocols. WT mice received a normal diet, while BKO mice also received a normal diet. An additional group of BKO mice were fed a PQQ-supplemented diet (BKO + PQQ; 4 mg PQQ/kg in the normal diet). The results indicated that PQQ partially rescued the liver damage induced by the deletion of Bmi-1. PQQ was demonstrated to exhibit these therapeutic effects on liver damage through multiple aspects, including the promotion of proliferation, antiapoptotic effects, the inhibition of senescence, the upregulation of antioxidant ability, the downregulation of cell cycle protein expression, the scavenging of reactive oxygen species and the reduction of DNA damage. The results of these experiments indicated that treatment of BKO mice with a moderate dose of PQQ significantly protected the liver from deleterious effects by inhibiting oxidative stress and participating in DNA damage repair. Therefore, PQQ has great potential as a therapeutic agent against oxidative stress during liver damage.

Pyrroloquinoline quinone protects nucleus pulposus cells from hydrogen peroxide-induced apoptosis by inhibiting the mitochondria-mediated pathway

PURPOSE

Intervertebral disc cell apoptosis has been suggested to play a key role in promoting disc degeneration, and many studies have shown that the mechanism may be related to oxidative stress. Pyrroloquinoline quinone (PQQ), a redox cofactor for bacterial dehydrogenases, possesses the potential to scavenge reactive oxygen species (ROS) and inhibit cell apoptosis. The objective of this study was to evaluate the effects of PQQ on cultured rat nucleus pulposus (NP) cells under conditions of oxidative injury induced by hydrogen peroxide (H2O2) and to investigate the underlying mechanisms in vitro.

METHODS

Cell viability was determined by CCK8 assay. Changes in the apoptosis rate, intracellular ROS levels and the mitochondrial membrane potential were measured by flow cytometry. Extracellular matrix (ECM)-related proteins (collagen-2 and aggrecan) and apoptosis-related proteins (Bcl-2, Bax, cytochrome c, and caspase-3) were investigated by western blotting.

RESULTS

The results show that NP cells pretreated with PQQ before H2O2 exposure exhibited increased cell viability, decreased ROS formation, maintained mitochondrial membrane potential, and reduced apoptosis. In the presence of PQQ, ECM production was maintained by the cells despite being in an apoptotic environment. In addition, pretreatment with PQQ increased the expression of Bcl-2, inhibited the release of mitochondrial cytochrome c, and decreased the expressions of Bax and cleaved caspase-3.

CONCLUSIONS

Our results suggest that PQQ can protect rat NP cells against oxidative stress via a mitochondria-mediated pathway. PQQ might be useful as a potential pharmaceutical agent in the prevention of intervertebral disc degeneration.

Pyrroloquinoline Quinone Induces Cancer Cell Apoptosis via Mitochondrial-Dependent Pathway and Down-Regulating Cellular Bcl-2 Protein Expression

Pyrroloquinoline quinone (PQQ) has been reported as a promising agent that might contribute to tumor cell apoptosis and death, yet little is known on its mechanisms. In current study, the effect of PQQ on cell proliferation and mitochondrial-dependent apoptosis were examined in 3 solid tumor cell lines (A549, Neuro-2A and HCC-LM3). PQQ treatment at low to medium dosage exhibited potent anti-tumor activity on A549 and Neuro-2A cells, while had comparably minimal impact on the viabilities of 2 human normal cell lines (HRPTEpiC and HUVEC). The apoptosis of the 3 tumor cell lines induced by PQQ were increased in a concentration-dependent manner, which might be attributed to the accumulation of intracellular reactive oxygen species (ROS), decline in ATP levels and dissipation of mitochondrial membrane potential (MMP), in conjunction with down-regulation of Bcl-2 protein expression, up-regulation of activated caspase-3, and disturbed phosphorylated MAPK protein levels. PQQ induced tumor cells apoptosis was significantly alleviated by pan-caspase inhibitor Z-VAD-FMK. The present work highlights the potential capability of PQQ as an anti-tumor agent with low toxicity towards normal cells through activating mitochondrial-dependent apoptosis pathways, and warrants its development for cancer therapy.

Combinatorial synthesis of pyrrolo[3,2-f]quinoline and pyrrolo[3,2-a]acridine derivatives via a three-component reaction under catalyst-free conditions

A combinatorial synthesis of pyrrolo[3,2-f]quinoline and pyrrolo[3,2-a]acridine derivatives is described as a three-component reaction of aromatic aldehyde, 1H-indol-5-amine, and 1,3-dicarbonyl compounds under catalyst-free conditions. The 1,3-dicarbonyl compounds include 5,5-dimethylcyclohexane-1,3-dione, cyclopentane-1,3-dione, and 2H-indene-1,3-dione. It is interesting that the designed reactions gave aromatized or unaromatized products, which depend on the reaction temperature and reactants of 1,3-dicarbonyl compounds.

Pyrroloquinoline quinone stimulates epithelial cell proliferation by activating epidermal growth factor receptor through redox cycling

Pyrroloquinoline quinone (PQQ), a redox cofactor for bacterial dehydrogenases, has been implicated to be an important nutrient in mammals functioning as a potent growth factor. However, the underlying molecular mechanisms have not been elucidated. The present study revealed that PQQ induces the activation (tyrosine autophosphorylation) of epidermal growth factor receptor (EGFR) and its downstream signaling in a ligand-independent manner, leading to increased cellular proliferation in an epithelial cell line A431. PQQ inhibited protein tyrosine phosphatase 1B (PTP1B), which negatively regulates the EGFR signaling by tyrosine dephosphorylation, to oxidatively modify the catalytic cysteine through its redox cycling activity to generate H(2)O(2). PQQ-inducible intracellular ROS production and EGFR activation were significantly suppressed by the pre-treatment with antioxidants. The intracellular redox state regulates the EGFR signaling through the redox-sensitive catalytic cysteine of PTP1B and modulates cell proliferation. Our data suggest that PQQ may stimulate epithelial cell proliferation by activating EGFR by oxidation and subsequent inactivation of PTP1B via its redox cycling. Our results provide novel insight into the mechanisms by which PQQ may function as a growth factor to contribute to mammalian growth.