Antioxidant and pro-oxidant properties of pyrroloquinoline quinone (PQQ): implications for its function in biological systems

Deep Learning-Driven Exploration of Pyrroloquinoline Quinone Neuroprotective Activity in Alzheimer's Disease

Alzheimer's disease (AD) is a pressing concern in neurodegenerative research. To address the challenges in AD drug development, especially those targeting Aβ, this study uses deep learning and a pharmacological approach to elucidate the potential of pyrroloquinoline quinone (PQQ) as a neuroprotective agent for AD. Using deep learning for a comprehensive molecular dataset, blood-brain barrier (BBB) permeability is predicted and the anti-inflammatory and antioxidative properties of compounds are evaluated. PQQ, identified in the Mediterranean-DASH intervention for a diet that delays neurodegeneration, shows notable BBB permeability and low toxicity. In vivo tests conducted on an Aβ₁₋₄₂-induced AD mouse model verify the effectiveness of PQQ in reducing cognitive deficits. PQQ modulates genes vital for synapse and anti-neuronal death, reduces reactive oxygen species production, and influences the SIRT1 and CREB pathways, suggesting key molecular mechanisms underlying its neuroprotective effects. This study can serve as a basis for future studies on integrating deep learning with pharmacological research and drug discovery.

Dietary pyrroloquinoline quinone hinders aging progression in male mice and D-galactose-induced cells

Background: Understanding and promoting healthy aging has become a necessity in the modern world, where life expectancy is rising. The prospective benefits of the antioxidant pyrroloquinoline quinone (PQQ) in healthy aging are promising. However, its role in aging remains unclear. Thus, this study aimed to investigate the effect of PQQ on preventing the progression of aging and to explore its underlying molecular mechanisms. Methods: Naturally aged C57BL/6J male mice were fed a normal diet with or without PQQ (20 mg/kg/day) for 10 weeks. Body composition was measured by bioimpedance at weeks 0 and 8. The integument conditions were evaluated at weeks 0, 4, and 8. Muscle strength and function were examined at week 8. At the ninth week, computed tomography images of the mice were captured, and blood and tissue samples were collected. The levels of inflammatory cytokines in the gastrocnemius muscle were measured, and the muscle fiber cross-sectional area in the soleus muscle was examined. Additionally, a D-galactose (D-gal)-induced cell aging model was used to study the effects of PQQ intervention on cell proliferation, senescence, differentiation, ROS levels, and mitochondrial function in myoblasts (C2C12). Cell proliferation and monolayer permeability of D-gal-induced intestinal epithelial cells (IEC6) were also examined. Results: Aged mice suffered from malnutrition; however, PQQ supplementation ameliorated this effect, possibly by improving metabolic dysfunction and small intestinal performance. PQQ prevented rapid loss of body fat and body fluid accumulation, attenuated muscle atrophy and weakening, reduced chronic inflammation in skeletal muscles, and improved skin and coating conditions in aged mice. Furthermore, PQQ intervention in D-gal-treated C2C12 cells improved mitochondrial function, reduced cellular reactive oxygen species (ROS) levels and senescence, and enhanced cell differentiation, consequently preventing age-related muscle atrophy. In addition, PQQ increased cell proliferation in D-gal-treated IEC6 cells and consequently improved intestinal barrier function. Conclusion: PQQ could hinder the aging process and particularly attenuate muscle atrophy, and muscle weakness by improving mitochondrial function, leading to reduced age-related oxidative stress and inflammation in muscles. PQQ may also ameliorate malnutrition caused by intestinal barrier dysfunction by enhancing IEC proliferation. This study provides evidence for the role of PQQ in aging and suggests that PQQ may be a potential nutritional supplementation that can be included in healthy aging strategies.

Microbial synthesis of pyrroloquinoline quinone

Pyrroloquinoline quinone (PQQ) is a peptide-modified natural product. PQQ has important physiological functions such as anti-oxidation, anti-aging, and immunity enhancement. However, due to the lack of in-depth understanding of PQQ biosynthesis and regulation, inefficient PQQ production level limits its wide application. Accordingly, there is still an urgent need to develop high-yielding strains for synthesis of PQQ. This paper reviewed the research and development trends on the PQQ biosynthetic pathways, catalytic reaction mechanism of key enzymes, and the selection of high-yielding strains, which also prospects for the future construction of PQQ biosynthetic microbial cell factories.

Protective effects of pyrroloquinoline quinone in brain folate deficiency

BACKGROUND

Folates (Vitamin B9) are critical for normal neurodevelopment and function, with transport mediated by three major pathways: folate receptor alpha (FRα), proton-coupled folate transporter (PCFT), and reduced folate carrier (RFC). Cerebral folate uptake primarily occurs at the blood-cerebrospinal fluid barrier (BCSFB) through concerted actions of FRα and PCFT, with impaired folate transport resulting in the neurological disorder cerebral folate deficiency (CFD). Increasing evidence suggests that disorders associated with CFD also present with neuroinflammation, oxidative stress, and mitochondrial dysfunction, however the role of brain folate deficiency in inducing these abnormalities is not well-understood. Our laboratory has identified the upregulation of RFC by nuclear respiratory factor 1 (NRF-1) at the blood-brain barrier (BBB) once indirectly activated by the natural compound pyrroloquinoline quinone (PQQ). PQQ is also of interest due to its anti-inflammatory, antioxidant, and mitochondrial biogenesis effects. In this study, we examined the effects of folate deficiency and PQQ treatment on inflammatory and oxidative stress responses, and changes in mitochondrial function.

METHODS

Primary cultures of mouse mixed glial cells exposed to folate-deficient (FD) conditions and treated with PQQ were analyzed for changes in gene expression of the folate transporters, inflammatory markers, oxidative stress markers, and mitochondrial DNA (mtDNA) content through qPCR analysis. Changes in cellular reactive oxygen species (ROS) levels were analyzed in vitro through a DCFDA assay. Wildtype (C57BL6/N) mice exposed to FD (0 mg/kg folate), or control (2 mg/kg folate) diets underwent a 10-day (20 mg/kg/day) PQQ treatment regimen and brain tissues were collected and analyzed.

RESULTS

Folate deficiency resulted in increased expression of inflammatory and oxidative stress markers in vitro and in vivo, with increased cellular ROS levels observed in mixed glial cells as well as a reduction of mitochondrial DNA (mtDNA) content observed in FD mixed glial cells. PQQ treatment was able to reverse these changes, while increasing RFC expression through activation of the PGC-1α/NRF-1 signaling pathway.

CONCLUSION

These results demonstrate the effects of brain folate deficiency, which may contribute to the neurological deficits commonly seen in disorders of CFD. PQQ may represent a novel treatment strategy for disorders associated with CFD, as it can increase folate uptake, while in parallel reversing many abnormalities that arise with brain folate deficiency.

Pyrroloquinoline Quinone Administration Alleviates Allergic Airway Inflammation in Mice by Regulating the JAK-STAT Signaling Pathway

The current asthma therapies are inadequate for many patients with severe asthma. Pyrroloquinoline quinone (PQQ) is a naturally-occurring redox cofactor and nutrient that can exert a multitude of physiological effects, including anti-inflammatory and antioxidative effects. We sought to explore the effects of PQQ on allergic airway inflammation and reveal the underlying mechanisms. In vitro, the effects of PQQ on the secretion of epithelial-derived cytokines by house dust mite- (HDM-) incubated 16-HBE cells and on the differentiation potential of CD4+ T cells were investigated. In vivo, PQQ was administered to mice with ovalbumin- (OVA-) induced asthma, and lung pathology and inflammatory cell infiltration were assessed. The changes in T cell subsets and signal transducers and activators of transcription (STATs) were evaluated by flow cytometry. Pretreatment with PQQ significantly decreased HDM-stimulated thymic stromal lymphopoietin (TSLP) production in a dose-dependent manner in 16-HBE cells and inhibited Th2 cell differentiation in vitro. Treatment with PQQ significantly reduced bronchoalveolar lavage fluid (BALF) inflammatory cell counts in the OVA-induced mouse model. PQQ administration also changed the secretion of IFN-γ and IL-4 as well as the percentages of Th1, Th2, Th17, and Treg cells in the peripheral blood and lung tissues, along with inhibition the phosphorylation of STAT1, STAT3, and STAT6 while promoting that of STAT4 in allergic airway inflammation model mice. PQQ can alleviate allergic airway inflammation in mice by improving the immune microenvironment and regulating the JAK-STAT signaling pathway. Our findings suggest that PQQ has great potential as a novel therapeutic agent for inflammatory diseases, including asthma.

Pyrroloquinoline Quinone Chemistry, Biology, and Biosynthesis

The widely distributed, essential redox factor pyrroloquinoline quinone (PQQ, methoxatin) (1) was discovered in the mid-1960s. The breadth and depth of its biological effects are steadily being revealed, and understanding its biosynthesis at the genomic level is a continuing process. In this review, aspects of the chemistry, biology, biosynthesis, and commercial production of 1 at the gene level, and some applications, are presented from discovery through to mid-2021.

Pyrroloquinoline quinone alleviates oxidative damage induced by high glucose in HepG2 cells

Hyperglycemia as a common metabolic disorder in diabetes led to oxidative stress, inflammation and other complications. Natural and manufactured antioxidants alleviates the side effects of diabetes. The purpose of current study is to investigate the effect of pyrroloquinoline quinine (PQQ) as an antioxidant on the content of glucose-induced oxidative stress generation in the cells of the human hepatocellular liver carcinoma (HepG2) by inhibiting advanced glycation end products (AGEs) formation. The HepG2 cells were exposed to high dose (50 mM) of glucose (HG) only and with PQQ (HG + PQQ). Treatment with high dose increased AGEs formation, expression of receptor for advanced glycation endproducts (RAGE), reactive oxygen species ROS production, and oxidative stress markers in treated HepG2 cells. Interestingly, PQQ significantly reduced AGEs formation and (RAGE) expression, ROS formation, and inflammation induced by glucose. In conclusion, PQQ has a potentiail role as an antioxidant to reduce the oxidative damage during hyperglycemia by AGEs inhibition.

Targetable Pathways for Alleviating Mitochondrial Dysfunction in Neurodegeneration of Metabolic and Non-Metabolic Diseases

Many neurodegenerative and inherited metabolic diseases frequently compromise nervous system function, and mitochondrial dysfunction and oxidative stress have been implicated as key events leading to neurodegeneration. Mitochondria are essential for neuronal function; however, these organelles are major sources of endogenous reactive oxygen species and are vulnerable targets for oxidative stress-induced damage. The brain is very susceptible to oxidative damage due to its high metabolic demand and low antioxidant defence systems, therefore minimal imbalances in the redox state can result in an oxidative environment that favours tissue damage and activates neuroinflammatory processes. Mitochondrial-associated molecular pathways are often compromised in the pathophysiology of neurodegeneration, including the parkin/PINK1, Nrf2, PGC1α, and PPARγ pathways. Impairments to these signalling pathways consequently effect the removal of dysfunctional mitochondria, which has been suggested as contributing to the development of neurodegeneration. Mitochondrial dysfunction prevention has become an attractive therapeutic target, and there are several molecular pathways that can be pharmacologically targeted to remove damaged mitochondria by inducing mitochondrial biogenesis or mitophagy, as well as increasing the antioxidant capacity of the brain, in order to alleviate mitochondrial dysfunction and prevent the development and progression of neurodegeneration in these disorders. Compounds such as natural polyphenolic compounds, bioactive quinones, and Nrf2 activators have been reported in the literature as novel therapeutic candidates capable of targeting defective mitochondrial pathways in order to improve mitochondrial function and reduce the severity of neurodegeneration in these disorders.

Structure-Activity Relationship Studies of Coumarin-like Diacid Derivatives as Human G Protein-Coupled Receptor-35 (hGPR35) Agonists and a Consequent New Design Principle

A series of coumarin-like diacid derivatives were designed and synthesized as novel agonists of human G-protein-coupled receptor 35 (hGPR35). Active compounds were characterized to possess one acidic group on both sides of a fused tricyclic aromatic scaffold. Most of them functioned as full agonists selective to hGPR35 and exhibited excellent potency at low nanomolar concentrations. Substitution on the middle ring of the scaffold could effectively regulate compound potency. Structure-activity relationship studies and docking simulation indicated that compounds that carried two acidic groups with a proper special distance and attached to a rigid aromatic scaffold would most likely show a potent agonistic activity on hGPR35. Following this principle, we screened a list of known compounds and some were found to be potent GPR35 agonists, and compound 24 even had an EC₅₀ of 8 nM. Particularly, a dietary supplement pyrroloquinoline quinone (PQQ) was identified as a potent agonist (EC₅₀ = 71.4 nM). To some extent, this principle provides a general strategy to design and recognize GPR35 agonists.

Effects of Diet Supplemented with Excess Pyrroloquinoline Quinone Disodium on Growth Performance, Blood Parameters and Redox Status in Weaned Pigs

Simple Summary

Weaning is a vital process for weaned pigs since piglets are exposed to psychologic and environmental stresses. These stresses converge on the pig to cause low feed consumption and weight gain meanwhile increased risk of diarrhea and mortality during the early postweaning period. The use of antibiotic growth promoters to help prevent weaning stress in weaned pigs has been forbidden in the European Union, Korea, Japan and China. Pyrroloquinoline quinone disodium (PQQ·Na₂) is increasing interest in use of alternatives to in-feed antibiotics. In this study, we found PQQ·Na₂ can improve growth performance meanwhile improves antioxidant status of weaned pigs. A high oral dose of PQQ·Na₂ does not appear to have harmful effects on weaned pigs.

Abstract

The research was implemented to assess the safety of feeding excess of pyrroloquinoline quinone disodium (PQQ·Na₂) to 108 Duroc × Landrace × Large White weaned pigs (BW = 8.38 ± 0.47 kg). Pigs were weaned at 28 d and randomly distributed to one of three diets with six replicates and six pigs per replicate (three males and three females). Pigs in the control group were fed a corn-soybean meal-based diet (without growth promoter) while the two experimental diets were supplied with 7.5 and 75.0 mg/kg PQQ·Na₂, respectively. Average daily gain (ADG), average daily feed intake (ADFI), feed conversion (F:G), diarrhea incidence, hematology, serum biochemistry, organ index and general health were determined. Diets supplementation with 7.5 mg/kg PQQ·Na₂ in weaned pigs could increase ADG during the entire experimental period (p < 0.05). And there was a tendency to decrease F:G (p = 0.063). The F:G of weaned pigs fed 7.5 and 75.0 mg/kg PQQ·Na₂ supplemented diets was decreased by 9.83% and 8.67%, respectively, compared to the control group. Moreover, pigs had reduced diarrhea incidence (p < 0.01) when supplemented with PQQ·Na₂. No differences were observed between pigs supplemented with 0.0, 7.5 and 75.0 mg/kg PQQ·Na₂ diets on hematological and serum biochemical parameters as well as histological assessment of heart, liver, spleen, lung and kidney. At day 14, pigs had increased activity of glutathione peroxidase (GSH-Px) (p < 0.05), catalase (CAT) (p < 0.05) and total antioxidant capacity (T-AOC) (p < 0.05), and the serum concentration of malondialdehyde (MDA) was decreased (p < 0.01) with PQQ·Na₂ supplementation. At day 28, pigs had increased activities of total superoxide dismutase (T-SOD) (p < 0.01), GSH-Px (p < 0.01), CAT (p < 0.05) and T-AOC (p < 0.01), and serum concentration of MDA was lower (p < 0.01) with PQQ·Na₂ supplementation. In conclusion, PQQ·Na₂ can improve weaned pigs growth performance and serum antioxidant status. Meanwhile high PQQ·Na₂ inclusion of 75.0 mg/kg does not appear to result in harmful effects on growth performance of pigs.

Asphaltum Improves the Post-thaw Quality and Antioxidant Status of Nili Ravi Buffalo Bull Sperm

Asphaltum, a mineral exudate from the mountains, is an ayurvedic medicine believed to be a panacea for male reproductive health issues. The objective of the study was to evaluate asphaltum in terms of phytochemical components, radical scavenging activity (RSA), in vitro dose tolerability, and cryosurvivability of buffalo sperm. Asphaltum was procured from an authentic source and confirmed for the presence of flavonoids, terpenoids, saponins, tannins, alkaloids, steroids, and glycosides. It showed good RSA as confirmed by the DPPH (2,2-diphenyl-1-picrylhydrazyl) assay. In vitro dose tolerability of buffalo sperm (n = 3, replicate = 4, ejaculates = 24) for asphaltum was assessed at 0.75%, 1.5%, 2.25%, 3.0%, 3.75%, 4.5%, 5.25%, and 6.0% (w/v). Buffalo sperm showed good tolerance up to 3% of asphaltum in terms of sperm progressive motility and plasma membrane integrity. Buffalo semen (n = 3, replicates = 4, ejaculates = 24) was cryopreserved in extender supplemented with 0.0%, 0.75%, 1.5%, 2.25%, and 3.0% (w/v) asphaltum and sperm quality was assessed at post-dilution, post-cooling, and post-thaw. After dilution motility, viability and livability; post-cooling motility and plasma membrane integrity; and post-thaw motility, plasma membrane integrity, viability, livability, DNA integrity, sperm RSA, sperm total lipids, sperm mitochondrial activity, and total antioxidant activity of semen were improved by 3%. In conclusion, asphaltum supplementation in an extender at 3% improves the post-thaw quality and antioxidant activity of buffalo semen.

Free radical imaging of endogenous redox molecules using dynamic nuclear polarisation magnetic resonance imaging

Redox reactions accompanied by the oxidation-reduction of endogenous molecules play important roles in maintaining homeostasis in living organisms. In humans, numerous endogenous molecules that contribute towards maintaining physiological conditions form free radicals via electron transfer. A typical example of this is the mitochondrial electron transport chain, which is involved in energy production. If free radicals derived from endogenous molecules could be visualised and exploited as biological and functional probes, redox reactions mediated by endogenous molecules could be detected non-invasively. We succeeded in visualising the free radicals derived from endogenous molecules using an in vivo dynamic nuclear polarisation (DNP) magnetic resonance imaging (MRI) system. In this review, we describe the visualisation of endogenous redox molecules, such as flavins and ubiquinones, which are mitochondrial electron carriers, as well as vitamin E and vitamin C (ascorbate). In addition, we describe the application of melanin free radicals for the in vivo visualisation of metabola without using probes via in vivo DNP-MRI.

Pyrroloquinoline Quinone Modifies Lipid Profile, but Not Insulin Sensitivity, of Palmitic Acid-Treated L6 Myotubes

Pyrroloquinoline quinone (PQQ) is a novel stimulator of mitochondrial biogenesis and cellular energy metabolism. This is the first study investigating regulatory mechanisms and metabolic responses underlying PQQ’s action in palmitate-exposed L6 myotubes. Particularly, we assessed alterations in lipid content and composition, expression of metabolic enzymes, and changes in glucose transport. The experiments were conducted using muscle cells subjected to short (2 h) and prolonged (24 h) incubation with PQQ in a sequence of pre- and post-palmitic acid (PA) exposure. We demonstrated the opposite effects of 2 and 24 h treatments with PQQ on lipid content, i.e., a decline in the level of free fatty acids and triacylglycerols in response to short-time PQQ incubation as compared to increases in diacylglycerol and triacylglycerol levels observed after 24 h. We did not demonstrate a significant impact of PQQ on fatty acid transport. The analysis of metabolic enzyme expression showed that the vast majority of PQQ-dependent alterations cumulated in the PA/PQQ 24 h group, including elevated protein amount of peroxisome proliferator activated receptor γ co-activator 1α (PGC-1α), sirtuin-1 (SIRT1), phosphorylated 5′AMP-activated protein kinase (pAMPK), carnitine palmitoyltransferase I (CPT1), citrate synthase (CS), fatty acid synthase (FAS), and serine palmitoyltransferase, long chain base subunit 1 (SPT1). In conclusion, the results mentioned above indicate PQQ-dependent activation of both fatty acid oxidation and lipid synthesis in order to adapt cells to palmitic acid-rich medium, although PQQ did not attenuate insulin resistance in muscle cells.

Two-stage oxygen supply strategy for enhancing fed-batch production of pyrroloquinoline quinone in Hyphomicrobium denitrificans FJNU-6

Oxygen is a vital parameter for pyrroloquinoline quinone (PQQ) biosynthesis. In this study, the effects of oxygen supply on the biosynthesis of PQQ were first investigated systematically with Hyphomicrobium denitrificans FJNU-6. Following a kinetic analysis of the specific cell growth rate (μ_x) and specific PQQ formation rate (μ_p) in 5 L benchtop fermentation systems at various oxygen supply levels ranging from 0 to 60%, a novel, two-stage oxygen supply strategy was developed for enhancing PQQ production and productivity. Moreover, the transcription of genes involved in methanol oxidation and PQQ biosynthesis was analyzed throughout the process to outline the effect of oxygen supply on cell metabolism. Furthermore, with constant feeding of methanol at 0-1 g/L after the initial methanol was consumed completely, the PQQ concentration and productivity reached 1070 mg/L and 7.64 mg/L/h, respectively, after 140 h in a 5-L fermenter. The two-stage oxygen supply strategy developed in this study provides an effective and economical strategy for the industrial production of PQQ.Key Points• A novel, two-stage oxygen supply strategy was developed for enhancing PQQ production and productivity.•The transcription of genes involved in methanol oxidation and PQQ biosynthesis was regulated by changes in oxygen supply.• This study offers an effective and economical strategy for industrial or large-scale production of PQQ.

PQQ-GDH - Structure, function and application in bioelectrochemistry

This review summarizes the basic features of the PQQ-GDH enzyme as one of the sugar converting biocatalysts. Focus is on the membrane -bound and the soluble form. Furthermore, the main principles of enzymatic catalysis as well as studies on the physiological importance are reviewed. A short overview is given on developments in protein engineering. The major part, however, deals with the different fields of application in bioelectrochemistry. This includes approaches for enzyme-electrode communication such as direct electron transfer, mediator-based systems, redox polymers or conducting polymers and holoenzyme reconstitution, and covers applied areas such as biosensing, biofuel cells, recycling schemes, enzyme competition, light-directed sensing, switchable detection schemes, logical operations by enzyme electrodes and immune sensing.

Effects of pyrroloquinoline quinone and imidazole pyrroloquinoline on biological activities and neural functions

Pyrroloquinoline quinone (PQQ) is contained in fruits and vegetables and in human breast milk. It has been reported that PQQ has high reactivity and changes to an imidazole structure (imidazole pyrroloquinoline) by a reaction with an amino acid at a high ratio in nature. A comparative study was conducted to clarify physiological effects including neuroprotective effects, growth-promoting effect, antioxidative effects and a stimulatory effect on mitochondriogensis of PQQ and imidazole pyrroloquinoline (IPQ) using a human neuroblastoma cell line and a hepatocellular carcinoma cell line. We also compared the expression levels of human cytochrome c oxidase subunit IV isoform Ⅰ (COX4/1), which is an index of the amount of mitochondria in the cells that had been exposed to PQQ, PQQH₂ and IPQ. The results of the comparison showed that IPQ had almost the same biological activities as those of PQQ except for anti-oxidative activity. It was also shown that PQQ and IPQ improve the memory learning ability of aged mice and that BioPQQ® improves brain function in the language field in humans.

Crude Cell-Free Extract From Deinococcus radiodurans Exhibit Anticancer Activity by Inducing Apoptosis in Triple-Negative Breast Cancer Cells

Extremophilic organisms have the potential to tolerate extremely challenging environments of nature. This property can be accredited to its production of novel secondary metabolites that possess anticancer and other pharmaceutical values. The present study was aimed to investigate the anticancer activity of crude secondary metabolite extract (CSME) obtained from the radiation-tolerant bacterium Deinococcus radiodurans in triple-negative human breast carcinoma (MDA-MB-231) cells. The 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay showed the antiproliferative potential of CSME in MDA-MB-231 cells (IC₅₀ = 25 μg/ml) and MCF-7 cells (IC₅₀ = 10 μg/ml). Further, the CSME treatment led to the production of intracellular reactive oxygen species (ROS) and nuclear membrane alterations with the formation of apoptotic bodies in MDA-MB-231 cells. Considerable DNA damage and low antioxidant status were observed in CSME-treated MDA-MB-231 cells. The results also showed that the CSME treatment induced apoptotic markers expression in MDA-MB-231 cells. Western blot results illustrated significant upregulation of p53, caspase-3, and caspase-9 proteins expression. Then, we analyzed the presence of secondary metabolites which may be linked with antiproliferative potential of CSME by gas chromatography-mass spectrometry (GC-MS). The results illustrated the presence of 23 bioactive compounds some of which are already reported to possess anticancer properties. The study indicates that the CSME of D. radiodurans possess anticancer properties and exhibit the potential to be used as an anticancer agent.

Effects of pyrroloquinoline quinone supplementation on growth performance and small intestine characteristics in weaned pigs

This study was conducted to explore the effect of graded levels of pyrroloquinoline quinone disodium (PQQ·Na2) on the performance and intestinal development of weaned pigs. A total of 216 pigs weaned at 28 d were assigned in a randomized complete block design to 6 diets containing 0, 1.5, 3.0, 4.5, 6.0, or 7.5 mg/kg PQQ·Na2 for 28 d. Performance, diarrhea incidence, intestinal morphology, redox status, cytokines, and the expression of tight junction proteins were determined. Pigs had increased ADG (linear, P < 0.01), G:F (quadratic, P < 0.01), and lower diarrhea incidence (P < 0.01) with the increase of PQQ·Na2 supplementation. Villus height increased (quadratic, P < 0.01) in all segments of the small intestine, and crypt depth in the duodenum and jejunum was decreased (linear, P < 0.05) in pigs with the increase of PQQ·Na2 supplementation. Pigs fed PQQ·Na2-supplemented diets had higher (P < 0.05) activities of antioxidant enzymes including total superoxide dismutase in duodenum, jejunum, and ileum; glutathione peroxidase (GSH-Px) in jejunum and ileum; catalase (CAT) in duodenum and ileum; and lower (P < 0.05) malondialdehyde concentrations in the intestinal mucosa of all segments. In the intestinal mucosa, cytokines including interleukin (IL)-1β, IL-2, and interferon-γ were significantly decreased (P < 0.05) in pigs fed PQQ·Na2-supplemented diets. The protein expression of zonula occluden protein-1 (ZO-1) and occludin in the jejunum was significantly increased (P < 0.05) in pigs fed diets containing PQQ·Na2. In conclusion, these results have indicated that dietary PQQ·Na2 supplementation improves growth performance and gut health in weaned pigs. Moreover, pigs fed diet with as low as 1.5-mg/kg PQQ·Na2 have better performance compared with pigs fed no PQQ·Na2-supplemented diet; pigs fed diet with 4.5-mg/kg PQQ·Na2 have highest G:F among treatments during the whole period.

Discovery of Hydroxylase Activity for PqqB Provides a Missing Link in the Pyrroloquinoline Quinone Biosynthetic Pathway

Understanding the biosynthesis of cofactors is fundamental to the life sciences, yet to date a few important pathways remain unresolved. One example is the redox cofactor pyrroloquinoline quinone (PQQ), which is critical for C1 metabolism in many microorganisms, a disproportionate number of which are opportunistic human pathogens. While the initial and final steps of PQQ biosynthesis, involving PqqD/E and PqqC, have been elucidated, the precise nature and order of the remaining transformations in the pathway are unknown. Here we show evidence that the remaining essential biosynthetic enzyme PqqB is an iron-dependent hydroxylase catalyzing oxygen-insertion reactions that are proposed to produce the quinone moiety of the mature PQQ cofactor. The demonstrated reactions of PqqB are unprecedented within the metallo β-lactamase protein family and expand the catalytic repertoire of nonheme iron hydroxylases. These new findings also generate a nearly complete description of the PQQ biosynthetic pathway.

Cancer Prevention and Therapy of Two Types of Gap Junctional Intercellular Communication⁻Deficient "Cancer Stem Cell"

Early observations showed a lack of growth control and terminal differentiation with a lack of gap junctional intercellular communication (GJIC). Subsequent observations showed that epigenetic tumor promoters and activated oncogenes, which block gap junction function, provide insights into the multi-stage, multi-mechanism carcinogenic process. With the isolation of embryonic induced pluri-potent stem cells and organ-specific adult stem cells, gap junctions were linked to early development. While tumors and tumor cell lines are a heterogeneous mixture of "cancer stem cells" and "cancer non-stem cells", the cancer stem cells seem to be of two types, namely, they express (a) no connexin genes or (b) connexin genes, but do not have functional GJIC. These observations suggest that these "cancer stem cells" originate from normal adult stem cells or from the de-differentiation or re-programming of somatic differentiated cells. This "Concept Paper" provides a hypothesis that "cancer stem cells" either originate from (a) organ-specific adult stem cells before the expression of the connexin genes or (b) organ-specific adult stem cells that just express gap junction genes but that the connexin proteins are rendered dysfunctional by activated oncogenes. Therefore, cancer prevention and therapeutic strategies must account for these two different types of "cancer stem cell".

Dose- and time-dependent alterations in lipid metabolism after pharmacological PGC-1α activation in L6 myotubes

Pyrroloquinoline quinone (PQQ) acts as a powerful modulator of PGC‐1α activation and therefore regulates multiple pathways involved in cellular energy homeostasis. In the present study, we assessed the effects of L6 myotubes incubation with 0.5, 1, and 3 μM PQQ solution for 2 and 24 hr with respect to the cells' lipid metabolism. We demonstrated that PQQ significantly elevates PGC‐1α content in a dose‐ and time‐dependent manner with the highest efficiency for 0.5 and 1 µM. The level of free fatty acids was diminished (24 hr: −66%), while an increase in triacylglycerol (TAG) amount was most pronounced after 0.5 μM (2 hr: +93%, 24 hr: +139%) treatment. Ceramide (CER) content was elevated after 2 hr incubation with 0.5 µM and after prolonged exposure to all PQQ concentrations. The cells treated with PQQ for 2 hr exhibited decreased sphinganine (SFA) and sphinganine‐1‐phosphate (SFA1P) level, while 24 hr incubation resulted in an elevated sphingosine (SFO) amount. In summary, PGC‐1α activation promotes TAG and CER synthesis.

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.

Safety of pyrroloquinoline quinone disodium salt as a novel food pursuant to Regulation (EC) No 258/97

Following a request from the European Commission, the EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA) was asked to deliver an opinion on pyrroloquinoline quinone disodium salt (PQQ), trade name BioPQQ™, as a novel food pursuant to Regulation (EC) No 258/97. PQQ is produced by fermentation using Hyphomicrobium denitrificans CK-275 and purification process. PQQ has a minimum purity of 99.0%. The information provided on the composition, specifications, batch-to-batch variability, stability and production process of PQQ is sufficient and does not raise safety concerns. The applicant intends to market PQQ for use in food supplements for healthy adults, except pregnant and lactating women, at a maximum proposed level of consumption of 20 mg/day (corresponding to 0.29 mg/kg bw per day for a 70-kg person). The proposed level of consumption is at least 250 times higher than the estimated background intake of PQQ occurring naturally in foods. Information on the absorption, distribution, metabolism and excretion of PQQ in animals and humans is limited. Considering the no-observed-adverse-effect-level (NOAEL) of 100 mg/kg bw per day from a 90-day repeated dose oral toxicity study with BioPQQ™, and the maximum proposed level of consumption, the Panel concludes that the margin of exposure (of 344) is sufficient. The Panel concludes that the novel food, pyrroloquinoline quinone disodium salt (BioPQQ™), is safe under the intended conditions of use as specified by the applicant.

Microbe-mitochondrion crosstalk and health: An emerging paradigm

Human mitochondria are descendants of microbes and altered mitochondrial function has been implicated in processes ranging from ageing to diabetes. Recent work has highlighted the importance of gut microbial communities in human health and disease. While the spotlight has been on the influence of such communities on the human immune system and the extraction of calories from otherwise indigestible food, an important but less investigated link between the microbes and mitochondria remains unexplored. Microbial metabolites including short chain fatty acids as well as other molecules such as pyrroloquinoline quinone, fermentation gases, and modified fatty acids influence mitochondrial function. This review focuses on the known direct and indirect effects of microbes upon mitochondria and speculates regarding additional links for which there is circumstantial evidence. Overall, while there is compelling evidence that a microbiota-mitochondria link exists, explicit and holistic mechanistic studies are warranted to advance this nascent field.

The Effect of Pyrroloquinoline Quinone on the Expression of WISP1 in Traumatic Brain Injury

WISP1, as a member of the CCN4 protein family, has cell protective effects of promoting cell proliferation and inhibiting cell apoptosis. Although some studies have confirmed that WISP1 is concerned with colon cancer and lung cancer, there is little report about the influence of WISP1 in traumatic brain injury. Here, we found that the expression of WISP1 mRNA and protein decreased at 3 d and then increased at 5 d after traumatic brain injury (TBI). Meanwhile, immunofluorescence demonstrated that there was little colocation of WISP1 with GFAP, Iba1, and WISP1 colocalized with NeuN partly. WISP1 colocalized with LC3, but there was little of colocation about WISP1 with cleaved caspase-3. Subsequent study displayed that the expression of β-catenin protein was identical to that of WISP1 after TBI. WISP1 was mainly located in cytoplasm of PC12 or SHSY5Y cells. Compared with the negative control group, WISP1 expression reduced obviously in SHSY5Y cells transfected with WISP1 si-RNA. CCK-8 assay showed that pyrroloquinoline quinone (PQQ) had little influence on viability of PC12 and SHSY5Y cells. These results suggested that WISP1 played a protective role after traumatic brain injury in rats, and this effect might be relative to autophagy caused by traumatic brain injury.

Reflections on the use of 10 IARC carcinogenic characteristics for an objective approach to identifying and organizing results from certain mechanistic studies

To find a scientifically based method for evaluating mechanistic data related to risks to human beings, a new protocol for identifying, organizing, and summarizing mechanistic data for decision-making on cancer hazard identification was proposed by the International Agency for Research on Cancer and by an international working group of multidisciplinary experts. This Commentary examined the 10 key carcinogens’ characteristics proposed in the context of several paradigms assumed in the using of these 10 characteristics. These characteristics were assumed to represent a “carcinogen’s” mechanism of action but what was ignored were characteristics of the mechanisms of the “initiation,” “promotion,” and “progression” carcinogenic process. Challenges were made to the interpretation of genotoxicity data as well as from concepts and findings related to the promotion phase and the role of adult human stem cells. Reliance of interpretation of “genotoxicity” data (molecular-DNA lesions in DNA; induction of free radicals/oxidative stress markers; phenotypic surrogates of gene mutations), as well as from lesions in genomic versus mitochondrial DNA, or in the target cells for the carcinogenic process in either in vitro cultures or in vivo tissues, makes this “objective” use of the data questionable. A challenge to the “dedifferentiation” hypothesis of cancer was made. Because of an agent being misclassified as “genotoxic”—rather than an “epigenetic”—agent (which works by threshold levels; can be blocked; and must be present at critical times during development and at regular, sustained chronic exposures) could lead to unwise policy decisions.

Synthesis and crystal structure of pyrroloquinoline quinol (PQQH2) and pyrroloquinoline quinone (PQQ)

Pyrroloquinoline quinone (PQQ) is a water-soluble quinone compound first identified as a cofactor of alcohol- and glucose-dehydrogenases (ADH and GDH) in bacteria. For example, in the process of ADH reaction, alcohol is oxidized to the corresponding aldehyde, and inversely PQQ is reduced to pyrroloquinoline quinol (PQQH2). PQQ and PQQH2molecules play an important role as a cofactor in ADH and GDH reactions. However, crystal structure analysis has not been performed for PQQ and PQQH2. In the present study, the synthesis of PQQH2powder crystals was performed under air, by utilizing vitamin C as a reducing agent. By reacting a trihydrate of disodium salt of PQQ (PQQNa2·3H2O) with excess vitamin C in H2O at 293 and 343 K, yellowish brown and black powder crystals of PQQH2having different properties were obtained in high yield, respectively. The former was PQQH2trihydrate (PQQH2·3H2O) and the latter was PQQH2anhydrate (PQQH2). Furthermore, sodium-free red PQQ powder crystal (a monohydrate of PQQ, PQQ·H2O) was prepared by the reaction of PQQNa2·3H2O with HCl in H2O. Single crystals of PQQH2and PQQ were prepared from Me2SO/CH3CN mixed solvent, and we have succeeded in the crystal structure analyses of PQQH2and PQQ for the first time.

Crystal Structure and Function of PqqF Protein in the Pyrroloquinoline Quinone Biosynthetic Pathway

Pyrroloquinoline quinone (PQQ) has received considerable attention due to its numerous important physiological functions. PqqA is a precursor peptide of PQQ with two conserved residues: glutamate and tyrosine. After linkage of the Cγ of glutamate and Cϵ of tyrosine by PqqE, these two residues are hypothesized to be cleaved from PqqA by PqqF. The linked glutamate and tyrosine residues are then used to synthesize PQQ. Here, we demonstrated that the pqqF gene is essential for PQQ biosynthesis as deletion of it eliminated the inhibition of prodigiosin production by glucose. We further determined the crystal structure of PqqF, which has a closed clamshell-like shape. The PqqF consists of two halves composed of an N- and a C-terminal lobe. The PqqF-N and PqqF-C lobes form a chamber with the volume of the cavity of ∼9400 Å(3) The PqqF structure conforms to the general structure of inverzincins. Compared with the most thoroughly characterized inverzincin insulin-degrading enzyme, the size of PqqF chamber is markedly smaller, which may define the specificity for its substrate PqqA. Furthermore, the 14-amino acid-residue-long tag formed by the N-terminal tag from expression vector precisely protrudes into the counterpart active site; this N-terminal tag occupies the active site and stabilizes the closed, inactive conformation. His-48, His-52, Glu-129 and His-14 from the N-terminal tag coordinate with the zinc ion. Glu-51 acts as a base catalyst. The observed histidine residue-mediated inhibition may be applicable for the design of a peptide for the inhibition of M16 metalloproteases.

Comparison of Pyrroloquinoline Quinone and/or Metoprolol on Myocardial Infarct Size and Mitochondrial Damage in a Rat Model of Ischemia/Reperfusion Injury

The cardioprotective effectiveness of low-dose pyrroloquinoline quinone (PQQ, 3 mg/kg) was compared with metoprolol, a β1-selective adrenoceptor antagonist. Rats underwent 30 minutes of left anterior descending coronary artery occlusion and 2 hours of reperfusion. Metoprolol and/or PQQ were given at the onset of reperfusion to mimic clinical treatment. Metoprolol and/or PQQ reduced infarct size and protected against ischemia-induced left ventricular dysfunction after 2 hours of reper-fusion. Combined therapy augmented left ventricular developed pressure at the end of reperfusion. Metoprolol or PQQ alone enhanced mitochondrial respiratory ratios in ischemic and nonischemic myocardium. Although the PQQ/metoprolol combination therapy increased respiratory ratio values, the effects were small when compared with PQQ alone. Only PQQ decreased lipid peroxidation. Metoprolol and/or PQQ given at the onset of reperfusion reduce infarct size and improve cardiac function. Combination therapy further reduces infarct size. PQQ is superior to metoprolol in protecting mitochondria from ischemia/reperfusion oxidative damage

Effects of Pyrroloquinoline Quinone Disodium Salt Intake on the Serum Cholesterol Levels of Healthy Japanese Adults

Pyrroloquinoline quinone (PQQ) is a water-soluble quinone compound that has a strong anti-oxidant capacity. A previous study in rats fed a PQQ-depleted diet showed that elevated levels of serum triglyceride (TG) decreased after PQQ supplementation. However, there is only one study reporting the effects of PQQ on serum lipid levels, such as those of TG and cholesterol, in humans. In this study, the effects of PQQ disodium salt (BioPQQ™) on serum TG and cholesterol levels in humans after 6 and 12 wk of treatment at an oral dosage of 20 mg/d were examined. This trial was conducted according to a randomized, placebo-controlled, double-blinded protocol. A total of 29 healthy Japanese adults, ranging from 40 to 57 y old, with normal to moderately high TG levels (110-300 mg/dL) as measured by a recent blood examination, were included in this study. In eleven volunteers out of 29, serum low-density lipoprotein cholesterol (LDL-chol) levels at baseline were high (≥140 mg/dL). After 12 wk, the mean serum TG levels had not changed; however, a marginally significant decrease in the mean LDL-chol (from 136.1 to 127.0 mg/dL) was observed in the PQQ group. In the stratification analysis of the high LDL-chol subgroup (baseline LDL-chol level ≥140 mg/dL), the mean LDL-chol levels decreased significantly from the baseline values in the PQQ group compared to the placebo group. Our study findings suggest that PQQ suppressed the LDL-chol level, which is an important finding, because a high level of this lipid is a risk factor for various lifestyle-related diseases.

Pyrroloquinoline quinone enhances the resistance to oxidative stress and extends lifespan upon DAF-16 and SKN-1 activities in C. elegans

Pyrroloquinoline quinone (PQQ) is linked to fundamental biological processes such as mitochondrial biogenesis and lipid metabolism. PQQ may also function as an essential micronutrient during animal development. Recent studies have shown the therapeutic potential of PQQ for several age-related diseases due to its antioxidant capacity. However, whether PQQ can promote longevity is unknown. Here, we investigate the effects of PQQ on oxidative stress resistance as well as lifespan modulation in Caenorhabditis elegans. We find that PQQ enhances resistance to oxidative stress and extends the lifespan of C. elegans at optimal doses. The underlying molecular mechanism involves the increased activities of the primary lifespan extension transcriptional factors DAF-16/FOXO, the conserved oxidative stress-responsive transcription factor SKN-1/Nrf2, and upregulation of daf-16, skn-1 downstream targets including sod-3, hsp16.2, gst-1 and gst-10. Our findings uncover a novel role of PQQ in longevity, supporting PQQ as a possible dietary supplement for overall health improvement.

Screening of dietary antioxidants against mitochondria-mediated oxidative stress by visualization of intracellular redox state

Mitochondrial impairment and the resulting generation of reactive oxygen species (ROS) have been associated with aging and its related pathological conditions. Recently, dietary antioxidants have gained significant attention as potential preventive and therapeutic agents against ROS-generated aging and pathological conditions. We previously demonstrated that food-derived antioxidants prevented intracellular oxidative stress under proteasome inhibition conditions, which was attributed to mitochondrial dysfunction and ROS generation, followed by cell death. Here, we further screened dietary antioxidants for their activity as redox modulators by visualization of the redox state using Redoxfluor, a fluorescent protein redox probe. Direct alleviation of ROS by antioxidants, but not induction of antioxidative enzymes, prevented mitochondria-mediated intracellular oxidation. The effective antioxidants scavenged mitochondrial ROS and suppressed cell death. Our study indicates that redox visualization under mitochondria-mediated oxidative stress is useful for screening potential antioxidants to counteract mitochondrial dysfunction, which has been implicated in aging and the pathogenesis of aging-related diseases.

Dynamic nuclear polarization-magnetic resonance imaging at low ESR irradiation frequency for ascorbyl free radicals

Highly water-soluble ubiquinone-0 (CoQ₀) reacts with ascorbate monoanion (Asc) to mediate the production of ascorbyl free radicals (AFR). Using aqueous reaction mixture of CoQ₀ and Asc, we obtained positively enhanced dynamic nuclear polarization (DNP)-magnetic resonance (MR) images of the AFR at low frequency (ranging from 515 to 530 MHz) of electron spin resonance (ESR) irradiation. The shape of the determined DNP spectrum was similar to ESR absorption spectra with doublet spectral peaks. The relative locational relationship of spectral peaks in the DNP spectra between the AFR (520 and 525 MHz), ¹⁴N-labeled carbamoyl-PROXYL (¹⁴N-CmP) (526.5 MHz), and Oxo63 (522 MHz) was different from that in the X-band ESR spectra, but were similar to that in the 300-MHz ESR spectra. The ratio of DNP enhancement to radical concentration for the AFR was higher than those for ¹⁴N-CmP, Oxo63, and flavin semiquinone radicals. The spectroscopic DNP properties observed for the AFR were essentially the same as those for AFR mediated by pyrroloquinoline quinone. Moreover, we made a success of in vivo DNP-MR imaging of the CoQ₀-mediated AFR which was administered by the subcutaneous and oral injections as an imaging probe.

Recent progress in studies on the health benefits of pyrroloquinoline quinone

Pyrroloquinoline quinone (PQQ), an aromatic tricyclic o-quinone, was identified initially as a redox cofactor for bacterial dehydrogenases. Although PQQ is not biosynthesized in mammals, trace amounts of PQQ have been found in human and rat tissues because of its wide distribution in dietary sources. Importantly, nutritional studies in rodents have revealed that PQQ deficiency exhibits diverse systemic responses, including growth impairment, immune dysfunction, and abnormal reproductive performance. Although PQQ is not currently classified as a vitamin, PQQ has been implicated as an important nutrient in mammals. In recent years, PQQ has been receiving much attention owing to its physiological importance and pharmacological effects. In this article, we review the potential health benefits of PQQ with a focus on its growth-promoting activity, anti-diabetic effect, anti-oxidative action, and neuroprotective function. Additionally, we provide an update of its basic pharmacokinetics and safety information in oral ingestion.

Pyrroloquinoline quinone (PQQ) is reduced to pyrroloquinoline quinol (PQQH2) by vitamin C, and PQQH2 produced is recycled to PQQ by air oxidation in buffer solution at pH 7.4

Measurements of the reaction of sodium salt of pyrroloquinoline quinone (PQQNa2) with vitamin C (Vit C) were performed in phosphate-buffered solution (pH 7.4) at 25 °C under nitrogen atmosphere, using UV–vis spectrophotometry. The absorption spectrum of PQQNa2 decreased in intensity due to the reaction with Vit C and was changed to that of pyrroloquinoline quinol (PQQH2, a reduced form of PQQ). One molecule of PQQ was reduced by two molecules of Vit C producing a molecule of PQQH2 in the buffer solution. PQQH2, thus produced, was recycled to PQQ due to air oxidation. PQQ and Vit C coexist in many biological systems, such as vegetables, fruits, as well as in human tissues. The results obtained suggest that PQQ is reduced by Vit C and functions as an antioxidant in biological systems, because it has been reported that PQQH2 shows very high free-radical scavenging and singlet-oxygen quenching activities in buffer solutions.

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 ameliorates oxidative stress and lipid peroxidation in the brain of streptozotocin-induced diabetic mice

Diabetes, characterized by hyperglycemia, leads to several complications through the generation of reactive oxygen species and initiates tissue damage. Pyrroloquinoline quinone (PQQ) is believed to be a strong antioxidant, as it protects cells from oxidative damage. In this study, we elucidated the hitherto unknown potential of PQQ to ameliorate the brain damage caused by diabetes mellitus and the associated hyperglycemia-induced oxidative damage. Administration of a single dose of streptozotocin (STZ), i.e., 150 mg·(kg body mass)−1significantly enhanced the brain tissue levels of lipid peroxidation and hydroperoxidation and decreased the levels of antioxidants. It also increased the serum levels of glucose, cholesterol, and triglycerides. However, when STZ-treated animals received PQQ (20 mg·(kg body mass)−1·d−1, for 15 days), this significantly decreased the serum levels of glucose and lipid peroxidation products, and increased the activities of antioxidants in the diabetic mouse brain. These findings suggest that PQQ has the potential to ameliorate STZ-induced oxidative damage in the brain, as well as the STZ-induced diabetes.

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.

Unusual post-translational protein modifications: the benefits of sophistication

This review summarizes the “seemingly bizarre”, yet naturally occurring, covalent non-disulphide cross-links in enzymatic and scaffolding proteins and their functions.