Pyrroloquinoline quinone: a novel vitamin?

Supplementation of PQQ from pregnancy prevents MK-801-induced schizophrenia-like behaviors in mice

RATIONALE

At present, the research on the prevention of schizophrenia is still in its infancy. Pyrroloquinoline quinone (PQQ) has potential to treat psychological and neurological diseases including schizophrenia. However, the preventive effect of PQQ on schizophrenia remains unclear.

OBJECTIVES

In this study, we aimed to examine the preventive effect of supplementation of dietary PQQ from pregnancy or after birth on dizocilpine (MK-801)-induced schizophrenia-like behaviors in mice.

RESULTS

Supplementation of dietary PQQ from pregnancy could effectively prevent MK-801-induced weight gain decrease, hyperlocomotion, stereotypical behavior, ataxia, exploratory activity decrease, social interaction disorder, memory deficit, and depression in mice. Supplementation of dietary PQQ after birth could effectively prevent MK-801-induced weight gain decrease, stereotypical behavior, ataxia, and memory deficit in mice. Female mice responded to a greater degree than males in preventing MK-801-induced weight gain decrease in both forms of PQQ supplementation. For mice that began PQQ supplementation after birth, females performed better than males in preventing MK-801-induced ataxia, memory deficit, and depression. For mice that began PQQ supplementation from pregnancy, males performed better than females in preventing MK-801-induced memory deficit. In vitro experiments indicated that PQQ supplementation in the earlier stage of life contributed to the growth of neurons and the development of neurites.

CONCLUSIONS

Our current study suggested that PQQ supplementation from pregnancy or postpartum could prevent some schizophrenia-like behaviors induced by MK-801 in mice. Our work supported the potential usage of dietary supplement of PQQ in preventing or alleviating symptoms associated with schizophrenia.

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 Disodium (PQQ2Na) Has an NLRP Inflammasome-Induced Caspase-1 Release Influence in UVB-Irradiated but Not ATP-Treated Human Keratinocytes but Has No Influence in Increasing Skin Cell Mitochondrial Biogenesis in Either Human Keratinocytes or Fibroblasts

Introduction

Pyrroloquinoline quinone is a bacterial-derived redox factor that has been shown to have numerous benefits in humans. Recently, a model for examining the ability of normal human epidermal keratinocytes (NHEKs) to demonstrate anti-inflammatory benefits via nod-like receptor protein (NLRP)-activated caspase-1 release was reported. The question of whether PQQ2Na might have anti-inflammatory benefits that function through NLRP-activated release of active caspase-1 has not been explored. In addition, it has been reported that PQQ2Na will induce mitochondrial biogenesis in humans when taken orally. Whether or not this effect occurs in skin cells is presently unknown.

Methods

The inflammation studies followed previously published methods that demonstrated both UVB and ATP were able to upregulate the NLRP-activated release of caspase-1 in NHEKs. In addition, NHEK and normal dermal human fibroblasts (NHDF) were treated with PQQ2Na to see if the molecule might stimulate mitochondrial biogenesis measured by increased expression of cyclooxygenase-1 (COX-1) and succinate dehydrogenase complex, subunit A (SDHA).

Results

At non-cytotoxic concentrations between 5 µg/mL and 100 µg/mL in NHEKs and between 0.1 µg/mL and 5 µg/mL in fibroblasts, the PQQ2Na had no influence on cellular mitochondrial biogenesis. In ATP-activated NHEKs at concentrations of PQQ2Na between 0.05 µg/mL and 50 µg/mL, there was no influence of PQQ2Na on release of active caspase-1. In NHEKs irradiated with 60mJ/cm² of UVB radiation as previously described and treated with 0.05 µg/mL to 50 µg/mL of PQQ2Na, the molecule showed a dose-dependent benefit at reducing the expression of active caspase-1 in the irradiated cells.

Discussion

Benefits of PQQ2Na on various skin cell types which had not been investigated previously were addressed. Surprisingly, the PPQ2Na had no apparent influence on skin cell mitochondrial biogenesis. However, the molecule has a strong suppressing influence on UVB-induced active caspase-1 release in UVB-irradiated NHEKs.

Pyrroloquinoline quinone protects against exercise-induced fatigue and oxidative damage via improving mitochondrial function in mice

Pyrroloquinoline quinone (PQQ) has a variety of biological functions. However, rare attention has been paid to its effects on exercise-induced damage. Here, we assessed the potential protective effects of PQQ against the fatigue and oxidative damage caused by repeated exhaustive exercise, and studied the underlying mechanism. The models for exercise-induced fatigue were established, and the parameters were measured, including the time to exhaustion (TTE), biochemical indicators, the expression of nuclear factor kappa B (NF-κB) and inflammatory cytokines and so on. Besides, the mitochondrial function was evaluated by the morphology, membrane potential, respiratory function, adenosine triphosphate (ATP) levels, and the application of the mitochondrial complex I inhibitor. The results demonstrate that PQQ prolongs TTE, causes the decrease in the activity of serum creatine kinase and lactate dehydrogenase, increases the activity of antioxidant enzymes, inhibits the production of reactive oxygen species (ROS) and malondialdehyde (MDA), and diminishes the over expression of NF-κB (p65) and inflammatory mediators. Furthermore, PQQ preserves normal mitochondrial function. Particularly, PQQ reduces the accumulation of ROS triggered by the mitochondrial complex I inhibitor. These data suggest that PQQ can significantly protect mice from exercise-induced fatigue and oxidative damage by improving mitochondrial function. These data also suggest that PQQ controls mitochondrial activity through directly affecting the NADH dehydrogenase.

The Redox Biology of Excitotoxic Processes: The NMDA Receptor, TOPA Quinone, and the Oxidative Liberation of Intracellular Zinc

This special issue of Frontiers in Neuroscience-Neurodegeneration celebrates the 50th anniversary of John Olney's seminal work introducing the concept of excitotoxicity as a mechanism for neuronal cell death. Since that time, fundamental research on the pathophysiological activation of glutamate receptors has played a central role in our understanding of excitotoxic cellular signaling pathways, leading to the discovery of many potential therapeutic targets in the treatment of acute or chronic/progressive neurodegenerative disorders. Importantly, excitotoxic signaling processes have been found repeatedly to be closely intertwined with oxidative cellular cascades. With this in mind, this review looks back at long-standing collaborative efforts by the authors linking cellular redox status and glutamate neurotoxicity, focusing first on the discovery of the redox modulatory site of the N-methyl-D-aspartate (NMDA) receptor, followed by the study of the oxidative conversion of 3,4-dihydroxyphenylalanine (DOPA) to the non-NMDA receptor agonist and neurotoxin 2,4,5-trihydroxyphenylalanine (TOPA) quinone. Finally, we summarize our work linking oxidative injury to the liberation of zinc from intracellular metal binding proteins, leading to the uncovering of a signaling mechanism connecting excitotoxicity with zinc-activated cell death-signaling cascades.

Neurotoxicity and apoptosis induced by pyrroloquinoline quinone and its ester derivative on primary cortical neurons

Pyrroloquinoline quinone (PQQ) and its esterified derivative, PQQ ester (PQQE), have potential to treat or diagnose neurological and psychological disorders. However, their neurotoxicity remains unclear. To provide reference data for the brain targeting drug delivery techniques, the cytotoxic effects of PQQ and PQQE were examined in primary mouse cortical neurons. The results indicated that both PQQ and PQQE decreased neuron viability, reduced intracellular ATP level and disrupted the mitochondrial membrane potential in a concentration- and time-dependent manner, while PQQ was less potent than PQQE. PQQ and PQQE induced apoptosis involving increase of Bax, decrease of Bcl-2, release of mitochondrial cytochrome C into the cytosol, activation of caspase-3 and cleavage of PARP. A single mouse intracephalic injection of PQQ or PQQE showed similar results. Based on these findings, high-concentration PQQ or PQQE treatment could induce a wide range of neurotoxicity and apoptosis. The lowest observed adverse effect levels (LOAELs) of PQQ and PQQE were 10 μM and 2 μM respectively and the no observed adverse effect levels (NOAELs) were 5 μM and 1 μM respectively in mice cortical neurons.

Pyrroloquinoline quinone attenuates isoproterenol hydrochloride‑induced cardiac hypertrophy in AC16 cells by inhibiting the NF‑κB signaling pathway

Pyrroloquinoline quinone (PQQ) is a naturally occurring redox co-factor that functions as an essential nutrient and antioxidant, and has been reported to exert potent anti-inflammatory effects. However, the therapeutic potential of PQQ for isoproterenol hydrochloride (Iso)-induced cardiac hypertrophy has not yet been explored, at least to the best of our knowledge. In the present study, the anti-inflammatory effects of PQQ were investigated in Iso-treated AC16 cells, a myocardial injury cellular model characterized by an increase in the apparent surface area of the cells and the activation of intracellular cardiac hypertrophy-associated proteins. The results revealed that pre-treatment with PQQ significantly inhibited the expression of cardiac hypertrophy marker proteins, such as atrial natriuretic peptide, brain natriuretic peptide and β-myosin heavy chain. PQQ also inhibited the activation of the nuclear factor (NF)-κB signaling pathway in Iso-treated AC16 cells, thus inhibiting the nuclear translocation of NF-κB and reducing the phosphorylation levels of p65. On the whole, the findings of this study suggest that PQQ may be a promising therapeutic agent for effectively reversing the progression of cardiac hypertrophy.

Effect of pyrroloquinoline quinone disodium in female rats during gestating and lactating on reproductive performance and the intestinal barrier functions in the progeny

The objective of this study was to investigate the effects of dietary pyrroloquinoline quinone disodium (PQQ·Na2) supplementation on the reproductive performance and intestinal barrier functions of gestating and lactating female Sprague–Dawley (SD) rats and their offspring. Dietary supplementation with PQQ·Na2increased the number of implanted embryos per litter during gestation and lactation at GD 20 and increased the number of viable fetuses per litter, and the weight of uterine horns with fetuses increased at 1 d of newborn. The mRNA expression levels of catalase (CAT), glutathione peroxidase (GPx2), superoxide dismutase (SOD1), solute carrier family 2 member 1 (Slc2a1) and solute carrier family 2 member 3 (Slc2a3) in the placenta were increased with dietary PQQ·Na2supplementation. Dietary supplementation with PQQ·Na2in gestating and lactating rats increased the CAT, SOD and GPx activities of the jejunal mucosa of weaned rats on PD 21. Dietary supplementation with PQQ·Na2in female rats affected the expression of tight junction proteins (claudin, zonula occludens-1(ZO-1) andoccludin) in the jejunal mucosa of their offspring by increasing the expression ofZO-1mRNA in the expression ofZO-1and claudin mRNA in the jejunal mucosa of weaned rats on PD 21. In conclusion, dietary supplementation with PQQ·Na2in gestating and lactating female rats had positive effects on their reproductive performance and on the intestinal barrier of weaned rats.

Mitochondrial regulation by pyrroloquinoline quinone prevents rotenone-induced neurotoxicity in Parkinson's disease models

Pyrroloquinoline quinone (PQQ), a redox cofactor in the mitochondrial respiratory chain, has been reported to protect SH-SY5Y cells from cytotoxicity induced by rotenone, a mitochondrial complex I inhibitor. In this study, we aimed to investigate the mitochondrial mechanisms involved in the neuroprotection of PQQ both in vitro and in vivo. The cultured human SH-SY5Y neuroblastoma cells were exposed to different concentrations of PQQ after which the cells were treated with rotenone. Electron microscopy images showed that PQQ could prevent the mitochondrial morphology damage. The down-regulation of mitochondrial biogenesis related genes (PGC-1alpha and TFAM) and mitochondrial fission and fusion related genes (Drp1and Mfn2) in rotenone-injured SH-SY5Y cells could be inhibited by PQQ. PQQ could also promote the transposition of Drp1 and Mfn2 from cytosol to mitochondria. In addition, rotenone was injected into the left medial forebrain bundle of SD rats to establish a Parkinson's disease (PD) model in vivo, after which different doses of PQQ or Edaravone were given intraperitoneally once daily for 8 weeks. PQQ could up-regulate the mRNA levels of PGC-1alpha, TFAM, Drp-1 and Mfn2 in the midbrain of PD rats. Our findings indicated that PQQ could prevent mitochondrial dysfunction by promoting mitochondrial biogenesis and regulating mitochondrial fission and fusion, which might contribute to its neuroprotective effect in PD models.

Reconstruction and analysis of a genome-scale metabolic model of Methylovorus sp. MP688, a high-level pyrroloquinolone quinone producer

Methylovorus sp. MP688 is a methylotrophic bacterium that can be used as a pyrroloquinolone quinone (PQQ) producer. To obtain a comprehensive understanding of its metabolic capabilities, we constructed a genome-scale metabolic model (iWZ583) of Methylovorus sp. MP688, based on its genome annotations, data from public metabolic databases, and literature mining. The model includes 772 reactions, 764 metabolites, and 583 genes. Growth of Methylovorus sp. MP688 was simulated using different carbon and nitrogen sources, and the results were consistent with experimental data. A core metabolic essential gene set of 218 genes was predicted by gene essentiality analysis on minimal medium containing methanol. Based on in silico predictions, the addition of aspartate to the medium increased PQQ production by 4.6- fold. Deletion of three reactions associated with four genes (MPQ_1150, MPQ_1560, MPQ_1561, MPQ_1562) was predicted to yield a PQQ production rate of 0.123 mmol/gDW/h, while cell growth decreased by 2.5%. Here, model iWZ583 represents a useful platform for understanding the phenotype of Methylovorus sp. MP688 and improving PQQ production.

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.

Dietary supplementation of pyrroloquinoline quinone disodium protects against oxidative stress and liver damage in laying hens fed an oxidized sunflower oil-added diet

The protective effects of dietary pyrroloquinoline quinone disodium (PQQ.Na2) supplementation against oxidized sunflower oil-induced oxidative stress and liver injury in laying hens were examined. Three hundred and sixty 53-week-old Hy-Line Gray laying hens were randomly allocated into one of the five dietary treatments. The treatments included: (1) a diet containing 2% fresh sunflower oil; (2) a diet containing 2% thermally oxidized sunflower oil; (3) an oxidized sunflower oil diet with 100 mg/kg of added vitamin E; (4) an oxidized sunflower oil diet with 0.08 mg/kg of PQQ.Na2; and (5) an oxidized sunflower oil diet with 0.12 mg/kg of PQQ.Na2. Birds fed the oxidized sunflower oil diet showed a lower feed intake compared to birds fed the fresh oil diet or oxidized oil diet supplemented with vitamin E (P=0.009). Exposure to oxidized sunflower oil increased plasma malondialdehyde (P<0.001), hepatic reactive oxygen species (P<0.05) and carbonyl group levels (P<0.001), but decreased plasma glutathione levels (P=0.006) in laying hens. These unfavorable changes induced by the oxidized sunflower oil diet were modulated by dietary vitamin E or PQQ.Na2 supplementation to levels comparable to the fresh oil group. Dietary supplementation with PQQ.Na2 or vitamin E increased the activities of total superoxide dismutase and glutathione peroxidase in plasma and the liver, when compared with the oxidized sunflower oil group (P<0.05). PQQ.Na2 or vitamin E diminished the oxidized sunflower oil diet induced elevation of liver weight (P=0.026), liver to BW ratio (P=0.001) and plasma activities of alanine aminotransferase (P=0.001) and aspartate aminotransferase (P<0.001) and maintained these indices at the similar levels to the fresh oil diet. Furthermore, oxidized sunflower oil increased hepatic DNA tail length (P<0.05) and tail moment (P<0.05) compared with the fresh oil group. Dietary supplementation of PQQ.Na2 or vitamin E decreased the oxidized oil diet induced DNA tail length and tail moment to the basal levels in fresh oil diet. These results indicate that PQQ.Na2 is a potential antioxidant and is as effective against oxidized oil-related liver injury in laying hens as vitamin E. The protective effects of PQQ.Na2 against liver damage induced by oxidized oil may be partially due to its role in the scavenging of free radicals, inhibiting of lipid peroxidation and enhancing of antioxidant defense systems.

Clair D, Batinic-Haberle I. Manganese superoxide dismutase, MnSOD and its mimics

Increased understanding of the role of mitochondria under physiological and pathological conditions parallels increased exploration of synthetic and natural compounds able to mimic MnSOD - endogenous mitochondrial antioxidant defense essential for the existence of virtually all aerobic organisms from bacteria to humans. This review describes most successful mitochondrially-targeted redox-active compounds, Mn porphyrins and MitoQ(10) in detail, and briefly addresses several other compounds that are either catalysts of O(2)(-) dismutation, or its non-catalytic scavengers, and that reportedly attenuate mitochondrial dysfunction. While not a true catalyst (SOD mimic) of O(2)(-) dismutation, MitoQ(10) oxidizes O(2)(-) to O(2) with a high rate constant. In vivo it is readily reduced to quinol, MitoQH(2), which in turn reduces ONOO(-) to NO(2), producing semiquinone radical that subsequently dismutes to MitoQ(10) and MitoQH(2), completing the "catalytic" cycle. In MitoQ(10), the redox-active unit was coupled via 10-carbon atom alkyl chain to monocationic triphenylphosphonium ion in order to reach the mitochondria. Mn porphyrin-based SOD mimics, however, were designed so that their multiple cationic charge and alkyl chains determine both their remarkable SOD potency and carry them into the mitochondria. Several animal efficacy studies such as skin carcinogenesis and UVB-mediated mtDNA damage, and subcellular distribution studies of Saccharomyces cerevisiae and mouse heart provided unambiguous evidence that Mn porphyrins mimic the site and action of MnSOD, which in turn contributes to their efficacy in numerous in vitro and in vivo models of oxidative stress. Within a class of Mn porphyrins, lipophilic analogs are particularly effective for treating central nervous system injuries where mitochondria play key role. This article is part of a Special Issue entitled: Antioxidants and Antioxidant Treatment in Disease.

Expression of UDP-glucuronosyltransferase 1A6 isoform in Caco-2 cells stimulated with lipopolysaccharide

Glucuronidation is an important metabolic process of detoxification in all vertebrates. The reaction is catalyzed by a multigene family of UDP-glucuronosyltransferases (UGTs) able to convert many xenobiotics and endobiotics (hydrophobic substances) to inactive, water-soluble glucuronides. The UGTs play a protective role, facilitating the elimination of potentially toxic metabolites via urine, bile and feces; therefore, impairment of UGTs may have important toxicological consequences. The regulation of UGTs during bacterial infection or inflammation is not well described. In this study, we investigated the in vitro effect of lipopolysaccharide (LPS) on the expression of the UGT1A6 isoform in human colon carcinoma Caco-2 cells. Results demonstrated a significant down-regulation of UGT1A6 expression, both in terms of mRNA and protein levels, and a reduced UGT activity after LPS exposure of cell cultures, suggesting a role for endotoxins on UGT regulation mechanisms.

Ribosomal peptide natural products: bridging the ribosomal and nonribosomal worlds

Ribosomally synthesized bacterial natural products rival the nonribosomal peptides in their structural and functional diversity. The last decade has seen substantial progress in the identification and characterization of biosynthetic pathways leading to ribosomal peptide natural products with new and unusual structural motifs. In some of these cases, the motifs are similar to those found in nonribosomal peptides, and many are constructed by convergent or even paralogous enzymes. Here, we summarize the major structural and biosynthetic categories of ribosomally synthesized bacterial natural products and, where applicable, compare them to their homologs from nonribosomal biosynthesis.

Pyrroloquinoline quinone prevents oxidative stress-induced neuronal death probably through changes in oxidative status of DJ-1

Pyrroloquinoline quinone (PQQ) has been shown to play a role as an anti-oxidant in neuronal cells and prevent neuronal cell death in a rodent stroke model. DJ-1, a causative gene product for a familial form of Parkinson's disease, plays a role in anti-oxidative stress function by self-oxidation of DJ-1. In this study, the expression level and oxidation status of DJ-1 were examined in SHSY-5Y cells and primary cultured neurons treated with 6-hydroxydopamine (6-OHDA) or H(2)O(2) in the presence or absence of PQQ. The pI shift of DJ-1 to an acidic point, which was observed in SHSY-5Y cells treated with 6-OHDA, was inhibited by PQQ. TOF-MS analyses showed that while the level of a reduced form of DJ-1, one of the active forms of DJ-1, was decreased in SHSY-5Y cells treated with 6-OHDA or H(2)O(2), PQQ increased the level of the reduced form of DJ-1. These results suggest that PQQ prevents oxidative stress-induced changes in oxidative status of DJ-1. Therefore, the neuroprotective effects of PQQ on oxidative stress-induced neuronal death may be at least in part involved in increased level of an active form of DJ-1.

Singlet oxygen potentiates thrombolysis

Activated polymorphonuclear neutrophils (PMN) participate in physiologic thrombolysis. PMN produce large amounts of urokinase (u-PA) and oxidants of the hypochlorite/chloramine-type that generate nonradical excited singlet oxygen ((1)O(2)). The u-PA/(1)O(2)-mediated thrombolysis was imitated in vitro. One hundred microliters microclots of normal human plasma were oxidized with 25 microL 0 to 5.0 micromoles of chloramine-T in physiol. NaCl in the absence or presence of 100 microL 6% bovine serum albumin or 100 microL normal plasma. Twenty-five microliters 0 to 167 IU/mL (related to 150 microL added supernatant) u-PA or 0 to 2.08 microg/mL t-PA were added. The absorbance at 405 nm was determined after 0 to 27 hours (37 degrees C). The specific clot turbidity was calculated, subtracting the 100% lysis absorbance from the respective measured absorbance. The chloramine-effective dose 50% (ED(50)) after 27 hours was determined in the presence of 2.6 IU/mL u-PA. The plasminogen activator-ED(25) was determined after 2 hours (37 degrees C), and the ET(25); i.e., the time needed to lyse a microclot by 25%, was determined for each respective clot-oxidation. The ED(25) of u-PA depends on the oxidation of the microclots: 1.25 micromoles chloramine/100 microL clot enhances thrombolysis approximately 20-fold; here, 25% of clot lysis is achieved within 50 minutes (using approximately 20 IU/mL u-PA), whereas approximately 5 hours are needed to lyse an unoxidized microclot by 25%. The present global assay technique imitates the u-PA/(1)O(2) aspects of physiologic thrombolysis by PMN.

Pyrroloquinoline quinone preserves mitochondrial function and prevents oxidative injury in adult rat cardiac myocytes

We investigated the ability of pyrroloquinoline quinone (PQQ) to confer resistance to acute oxidative stress in freshly isolated adult male rat cardiomyocytes. Fluorescence microscopy was used to detect generation of reactive oxygen species (ROS) and mitochondrial membrane potential (Deltapsi(m)) depolarization induced by hydrogen peroxide. H(2)O(2) caused substantial cell death, which was significantly reduced by preincubation with PQQ. H(2)O(2) also caused an increase in cellular ROS levels as detected by the fluorescent indicators CM-H2XRos and dihydroethidium. ROS levels were significantly reduced by a superoxide dismutase mimetic Mn (III) tetrakis (4-benzoic acid) porphyrin chloride (MnTBAP) or by PQQ treatment. Cyclosporine-A, which inhibits mitochondrial permeability transition, prevented H(2)O(2)-induced Deltapsi(m) depolarization, as did PQQ and MnTBAP. Our results provide direct evidence that PQQ reduces oxidative stress, mitochondrial dysfunction, and cell death in isolated adult rat cardiomyocytes. These findings provide new insight into the mechanisms of PQQ action in the heart.

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.

Enhanced rat sciatic nerve regeneration through silicon tubes filled with pyrroloquinoline quinone

Pyrroloquinoline quinone (PQQ) is an antioxidant that also stimulates nerve growth factor (NGF) synthesis and secretion. In an earlier pilot study in our laboratory, Schwann cell growth was accelerated, and NGF mRNA expression and NGF secretion were promoted. The present study was designed to explore the possible nerve-inducing effect of PQQ on a nerve tube model over a 1-cm segmental deficit. An 8-mm sciatic nerve deficit was created in a rat model and bridged by a 1-cm silicone tube. Then,10 mul of 0.03 mmol/l PQQ were perfused into the silicone chamber in the PQQ group. The same volume of normal saline was delivered in the control group. Each animal underwent functional observation (SFI) at 2-week intervals and electrophysiological studies at 4-week intervals for 12 weeks. Histological and morphometrical analyses were performed at the end of the experiment, 12 weeks after tube implantation. Using a digital image-analysis system, thickness of the myelin sheath was measured, and total numbers of regenerated axons were counted. There was a significant difference in SFI, electrophysiological index (motor-nerve conduct velocity and amplitude of activity potential), and morphometrical results (regenerated axon number and thickness of myelin sheath) in nerve regeneration between the PQQ group and controls (P < 0.05). More mature, high-density, newly regenerated nerve was observed in the PQQ group. We conclude that PQQ is a potent enhancer for the regeneration of peripheral nerves.

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

Pyrroloquinoline quinone (PQQ) is a novel redox cofactor recently found in human milk. It has been reported to function as an essential nutrient, antioxidant and redox modulator in cell culture experiments and in animal models of human diseases. As mitochondria are particularly susceptible to oxidative damage we studied the antioxidant properties of PQQ in isolated rat liver mitochondria. PQQ was an effective antioxidant protecting mitochondria against oxidative stress-induced lipid peroxidation, protein carbonyl formation and inactivation of the mitochondrial respiratory chain. In contrast, PQQ caused extensive cell death to cells in culture. This surprising effect was inhibited by catalase, and was shown to be due to the generation of hydrogen peroxide during the autoxidation of PQQ in culture medium. We conclude that the reactivities of PQQ are dependent on its environment and that it can act as an antioxidant or a pro-oxidant in different biological systems.

The essential nutrient pyrroloquinoline quinone may act as a neuroprotectant by suppressing peroxynitrite formation

Pyrroloquinoline quinone (PQQ) is a redox active essential nutrient that can generate or scavenge superoxide depending on its microenvironment. PQQ has been shown previously to be neuroprotective in a rodent stroke model. Here we test whether PQQ interacts with reactive nitrogen species, known to be involved in the pathogenesis of stroke. Using rat forebrain neurons in culture, we determined that the toxicity of SIN-1 was mediated by peroxynitrite and that PQQ could block this toxic action. However, PQQ could not block the toxicity of peroxynitrite itself. Both SIN-1 and peroxynitrite caused ATP depletion, but only SIN-1 evoked ATP depletion was blocked by PQQ. In a cell-free system, PQQ blocked nitration of bovine serum albumin produced by SIN-1, but potentiated peroxynitrite-induced nitration. PQQ was unable to block ATP depletion and cell death induced by NO. donors (DEA/NO, DPT/NO and DETA/NO), indicating that it does not directly interact with nitric oxide, and suggesting that it acts as a superoxide scavenger. PQQ significantly potentiated cGMP accumulation evoked by SIN-1, similar to the effect of superoxide dismutase (SOD). However, unlike SOD, which potentiated neurotoxicity induced by SIN-1, PQQ blocked its toxicity, arguing against the possibility that PQQ functions simply as a SOD mimetic. Indeed, substantially less H2O2 was produced by the incubation of SIN-1 with PQQ, when compared to SOD. These results suggest that PQQ scavenges superoxide without forming toxic levels of H2O2. Therefore, the protective effect of PQQ on stroke might be due, at least in part, to the suppression of peroxynitrite formation.

Chemoprotection by phenolic antioxidants. Inhibition of tumor necrosis factor alpha induction in macrophages

Phenolic antioxidants exhibit anti-inflammatory activity in protection against chemical toxicity and cancer. To investigate the molecular mechanism of anti-inflammation, we analyzed the regulation of tumor necrosis factor alpha (TNF-alpha) expression in macrophages, a key step in inflammation, by the antioxidants. Whereas lipopolysaccharide (LPS), an inflammatory inducer, stimulates rapid synthesis of TNF-alpha protein, phenolic antioxidants, exemplified by tert-butyl hydroquinone and 1,4-dihydroquinone, block LPS-induced production of TNF-alpha protein in a time- and dose-dependent manner. Inhibition of TNF-alpha induction correlates with the capacity of the antioxidants to undergo oxidation-reduction cycling, implicating oxidative signaling in the inhibition. The antioxidants blocked LPS-induced increase of the steady-state mRNA of TNF-alpha but did not affect the half-life of the mRNA. Electrophoretic mobility shift assay reveals a total inhibition of LPS-induced formation of nuclear factor kappaB.DNA binding complexes by phenolic antioxidants. Finally, 1,4-dihydroquinone blocks the induction of TNF-alpha target genes interleukin 1beta and interleukin 6 at both mRNA and protein levels. Our findings demonstrate that phenolic antioxidants potently inhibit signal-induced TNF-alpha transcription and suggest a mechanism of anti-inflammation by the antioxidants through control of cytokine induction during inflammation.

Pyrroloquinoline quinone (PQQ) and quinoprotein enzymes

This review summarises the characteristics, identification, and measurement of pyrroloquinoline quinone, the prosthetic group of bacterial quinoprotein dehydrogenases whose structures, mechanisms, and electron transport functions are described in detail. Type I alcohol dehydrogenase includes the "classic" methanol dehydrogenase; its x-ray structure and mechanism are discussed in detail. It is likely that its mechanism involves a direct hydride transfer rather than a mechanism involving a covalent adduct. The x-ray structure of a closely related ethanol dehydrogenase is also described. The type II alcohol dehydrogenase is a soluble quinohaemoprotein, having a C-terminal extension containing haem C, which provides an excellent opportunity for the study of intraprotein electron transfer processes. The type III alcohol dehydrogenase is similar but it has two additional subunits (one of which is a multihaem cytochrome c) bound in an unusual way to the periplasmic membrane. One type of glucose dehydrogenase is a soluble quinoprotein whose role in energy transduction is uncertain. Its x-ray structure (in the presence and absence of substrate) is described together with the detailed mechanism, which also involves a direct hydride transfer. The more widely distributed glucose dehydrogenases are integral membrane proteins, bound to the membrane by transmembrane helices at the N-terminus.