Pyrroloquinoline quinone nutritional status alters lysine metabolism and modulates mitochondrial DNA content in the mouse and rat

Effects of Pyrroloquinoline Quinone on Lipid Metabolism and Anti-Oxidative Capacity in a High-Fat-Diet Metabolic Dysfunction-Associated Fatty Liver Disease Chick Model

Metabolic dysfunction-associated fatty liver disease (MAFLD) and its interaction with many metabolic pathways raises global public health concerns. This study aimed to determine the therapeutic effects of Pyrroloquinoline quinone (PQQ, provided by PQQ.Na₂) on MAFLD in a chick model and primary chicken hepatocytes with a focus on lipid metabolism, anti-oxidative capacity, and mitochondrial biogenesis. The MAFLD chick model was established on laying hens by feeding them a high-energy low-protein (HELP) diet. Primary hepatocytes isolated from the liver of laying hens were induced for steatosis by free fatty acids (FFA) and for oxidative stress by hydrogen peroxide (H₂O₂). In the MAFLD chick model, the dietary supplementation of PQQ conspicuously ameliorated the negative effects of the HELP diet on liver biological functions, suppressed the progression of MAFLD mainly through enhanced lipid metabolism and protection of liver from oxidative injury. In the steatosis and oxidative stress cell models, PQQ functions in the improvement of the lipid metabolism and hepatocytes tolerance to fatty degradation and oxidative damage by enhancing mitochondrial biogenesis and then increasing the anti-oxidative activity and anti-apoptosis capacity. At both the cellular and individual levels, PQQ was demonstrated to exert protective effects of hepatocyte and liver from fat accumulation through the improvement of mitochondrial biogenesis and maintenance of redox homeostasis. The key findings of the present study provide an in-depth knowledge on the ameliorative effects of PQQ on the progression of fatty liver and its mechanism of action, thus providing a theoretical basis for the application of PQQ, as an effective nutrient, into the prevention of MAFLD.

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

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

Improving retinal mitochondrial function as a treatment for age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of blindness among the elderly. Currently, there are no treatments for dry AMD, which is characterized by the death of retinal pigment epithelium (RPE) and photoreceptors. Reports from human donors with AMD suggest that RPE mitochondrial defects are a key event in AMD pathology. Thus, the most effective strategy for treating dry AMD is to identify compounds that enhance mitochondrial function and subsequently, preserve the RPE. In this study, primary cultures of RPE from human donors with (n = 20) or without (n = 8) AMD were used to evaluate compounds that are designed to protect mitochondria from oxidative damage (N-acetyl-l-cysteine; NAC), remove damaged mitochondria (Rapamycin), increase mitochondrial biogenesis (Pyrroloquinoline quinone; PQQ), and improve oxidative phosphorylation (Nicotinamide mononucleotide, NMN). Mitochondrial function measured after drug treatments showed an AMD-dependent response; only RPE from donors with AMD showed improvements. All four drugs caused a significant increase in maximal respiration (p < 0.05) compared to untreated controls. Treatment with Rapamycin, PQQ, or NMN significantly increased ATP production (p < 0.05). Only Rapamycin increased basal respiration (p < 0.05). Notably, robust responses were observed in only about 50% of AMD donors, with attenuated responses observed in the remaining AMD donors. Further, within the responders, individual donors exhibited a distinct reaction to each drug. Our results suggest drugs targeting pathways involved in maintaining healthy mitochondria can improve mitochondrial function in a select population of RPE from AMD donors. The unique response of individual donors to specific drugs supports the need for personalized medicine when treating AMD.

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Human primary RPE cultures were used to test the efficacy of drugs on mitochondrial function.

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Drugs targeting mitochondrial homeostasis pathways improved mitochondrial function in AMD RPE.

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The donor-specific response to drugs suggests personalized medicine is needed to treat AMD.

Impaired autophagic and mitochondrial functions are partially restored by ERT in Gaucher and Fabry diseases

The major cellular clearance pathway for organelle and unwanted proteins is the autophagy-lysosome pathway (ALP). Lysosomes not only house proteolytic enzymes, but also traffic organelles, sense nutrients, and repair mitochondria. Mitophagy is initiated by damaged mitochondria, which is ultimately degraded by the ALP to compensate for ATP loss. While both systems are dynamic and respond to continuous cellular stressors, most studies are derived from animal models or cell based systems, which do not provide complete real time data about cellular processes involved in the progression of lysosomal storage diseases in patients. Gaucher and Fabry diseases are rare sphingolipid disorders due to the deficiency of the lysosomal enzymes; glucocerebrosidase and α-galactosidase A with resultant lysosomal dysfunction. Little is known about ALP pathology and mitochondrial function in patients with Gaucher and Fabry diseases, and the effects of enzyme replacement therapy (ERT). Studying blood mononuclear cells (PBMCs) from patients, we provide in vivo evidence, that regulation of ALP is defective. In PBMCs derived from Gaucher patients, we report a decreased number of autophagic vacuoles with increased cytoplasmic localization of LC3A/B, accompanied by lysosome accumulation. For both Gaucher and Fabry diseases, the level of the autophagy marker, Beclin1, was elevated and ubiquitin binding protein, SQSTM1/p62, was decreased. mTOR inhibition did not activate autophagy and led to ATP inhibition in PBMCs. Lysosomal abnormalities, independent of the type of the accumulated substrate suppress not only autophagy, but also mitochondrial function and mTOR signaling pathways. ERT partially restored ALP function, LC3-II accumulation and decreased LC3-I/LC3-II ratios. Levels of lysosomal (LAMP1), autophagy (LC3), and mitochondrial markers, (Tfam), normalized after ERT infusion. In conclusion, there is mTOR pathway dysfunction in sphingolipidoses, as observed in both PBMCs derived from patients with Gaucher and Fabry diseases, which leads to impaired autophagy and mitochondrial stress. ERT partially improves ALP function.

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.

Sensitivity of hiPSC-derived neural stem cells (NSC) to Pyrroloquinoline quinone depends on their developmental stage

Pyrroloquinoline quinone (PQQ) is a factor influencing on the mitochondrial biogenesis. In this study the PQQ effect on viability, total cell number, antioxidant capacity, mitochondrial biogenesis and differentiation potential was investigated in human induced Pluripotent Stem Cells (iPSC) - derived: neural stem cells (NSC), early neural progenitors (eNP) and neural progenitors (NP). Here we demonstrated that sensitivity to PQQ is dependent upon its dose and neural stage of development. Induction of the mitochondrial biogenesis by PQQ at three stages of neural differentiation was evaluated at mtDNA, mRNA and protein level. Changes in NRF1, TFAM and PPARGC1A gene expression were observed at all developmental stages, but only at eNP were correlated with the statistically significant increase in the mtDNA copy numbers and enhancement of SDHA, COX-1 protein level. Thus, the "developmental window" of eNP for PQQ-evoked mitochondrial biogenesis is proposed. This effect was independent of high antioxidant capacity of PQQ, which was confirmed in all tested cell populations, regardless of the stage of hiPSC neural differentiation. Furthermore, a strong induction of GFAP, with down regulation of MAP2 gene expression upon PQQ treatment was observed. This indicates a possibility of shifting the balance of cell differentiation in the favor of astroglia, but more research is needed at this point.

Nuclear Magnetic Resonance Structure and Binding Studies of PqqD, a Chaperone Required in the Biosynthesis of the Bacterial Dehydrogenase Cofactor Pyrroloquinoline Quinone

Biosynthesis of the ribosomally synthesized and post-translationally modified peptide (RiPP), pyrroloquinoline quinone (PQQ), is initiated when the precursor peptide, PqqA, is recognized and bound by the RiPP precursor peptide recognition element (RRE), PqqD, for presentation to the first enzyme in the pathway, PqqE. Unlike other RiPP-producing, postribosomal peptide synthesis (PRPS) pathways in which the RRE is a component domain of the first enzyme, PqqD is predominantly a separate scaffolding protein that forms a ternary complex with the precursor peptide and first tailoring enzyme. As PqqD is a stable, independent RRE, this makes the PQQ pathway an ideal PRPS model system for probing RRE interactions using nuclear magnetic resonance (NMR). Herein, we present both the solution NMR structure of Methylobacterium extorquens PqqD and results of ¹H-¹⁵N HSQC binding experiments that identify the PqqD residues involved in binding the precursor peptide, PqqA, and the enzyme, PqqE. The reported structural model for an independent RRE, along with the mapped binding surfaces, will inform future efforts both to understand and to manipulate PRPS pathways.

(1)H, (13)C, and (15)N resonance assignments and secondary structure information for Methylobacterium extorquens PqqD and the complex of PqqD with PqqA

The ribosomally synthesized and post-translationally modified peptide (RiPP), pyrroloquinoline quinone (PQQ), is a dehydrogenase cofactor synthesized by, but not exclusively used by, certain prokaryotes. RiPPs represent a rapidly expanding and diverse class of natural products-many of which have therapeutic potential-and the biosynthetic pathways for these are gaining attention. Five gene products from the pqq operon (PqqA, PqqB, PqqC, PqqD, and PqqE) are essential for PQQ biosynthesis. The substrate is the peptide PqqA, which is presented to the radical SAM enzyme PqqE by the small protein PqqD. PqqA is unstructured in solution, and only binds to PqqE when in complex with PqqD. PqqD is a member of a growing family of RiPP chaperone proteins (or domains in most cases) that present their associated peptide substrates to the initial RiPP biosynthesis enzymes. An X-ray crystal structure exists for dimeric Xanthomonas campestris PqqD (PDB ID: 3G2B), but PqqD is now known to act as a monomer under physiological conditions. In this study, the PqqD truncation from naturally fused Methylobacterium extorquens (Mex) PqqCD was overexpressed in Escherichia coli and MexPqqA was chemically synthesized. Solution NMR (1)H-,(15)N-HSQC chemical shift studies have identified the PqqD residues involved in binding PqqA, and (1)H, (13)C, and (15)N peak assignments for PqqD alone and for PqqD bound to PqqA are reported herein.

Catalysis of Heterocyclic Azadiene Cycloaddition Reactions by Solvent Hydrogen Bonding: Concise Total Synthesis of Methoxatin

Although it has been examined for decades, no general approach to catalysis of the inverse electron demand Diels-Alder reactions of heterocyclic azadienes has been introduced. Typically, additives such as Lewis acids lead to nonproductive consumption of the electron-rich dienophiles without productive activation of the electron-deficient heterocyclic azadienes. Herein, we report the first general method for catalysis of such cycloaddition reactions by using solvent hydrogen bonding of non-nucleophilic perfluoroalcohols, including hexafluoroisopropanol (HFIP) and trifluoroethanol (TFE), to activate the electron-deficient heterocyclic azadienes. Its use in promoting the cycloaddition of 1,2,3-triazine 4 with enamine 3 as the key step of a concise total synthesis of methoxatin is described.

Unified theory of Alzheimer's disease (UTAD): implications for prevention and curative therapy

The aim of this review is to propose a Unified Theory of Alzheimer's disease (UTAD) that integrates all key behavioural, genetic and environmental risk factors in a causal chain of etiological and pathogenetic events. It is based on three concepts that emanate from human's evolutionary history: (1) The grandmother-hypothesis (GMH), which explains human longevity due to an evolutionary advantage in reproduction by trans-generational transfer of acquired knowledge. Consequently it is argued that mental health at old-age must be the default pathway of humans' genetic program and not development of AD. (2) Therefore, mechanism like neuronal rejuvenation (NRJ) and adult hippocampal neurogenesis (AHN) that still function efficiently even at old age provide the required lifelong ability to memorize personal experiences important for survival. Cumulative evidence from a multitude of experimental and epidemiological studies indicate that behavioural and environmental risk factors, which impair productive AHN, result in reduced episodic memory performance and in reduced psychological resilience. This leads to avoidance of novelty, dysregulation of the hypothalamic-pituitary-adrenal (HPA)-axis and cortisol hypersecretion, which drives key pathogenic mechanisms of AD like the accumulation and oligomerization of synaptotoxic amyloid beta, chronic neuroinflammation and neuronal insulin resistance. (3) By applying to AHN the law of the minimum (LOM), which defines the basic requirements of biological growth processes, the UTAD explains why and how different lifestyle deficiencies initiate the AD process by impairing AHN and causing dysregulation of the HPA-axis, and how environmental and genetic risk factors such as toxins or ApoE4, respectively, turn into disease accelerators under these unnatural conditions. Consequently, the UTAD provides a rational strategy for the prevention of mental decline and a system-biological approach for the causal treatment of AD, which might even be curative if the systemic intervention is initiated early enough in the disease process. Hence an individualized system-biological treatment of patients with early AD is proposed as a test for the validity of UTAD and outlined in this review.

Identification of lactate dehydrogenase as a mammalian pyrroloquinoline quinone (PQQ)-binding protein

Pyrroloquinoline quinone (PQQ), a redox-active o-quinone, is an important nutrient involved in numerous physiological and biochemical processes in mammals. Despite such beneficial functions, the underlying molecular mechanisms remain to be established. In the present study, using PQQ-immobilized Sepharose beads as a probe, we examined the presence of protein(s) that are capable of binding PQQ in mouse NIH/3T3 fibroblasts and identified five cellular proteins, including l-lactate dehydrogenase (LDH) A chain, as potential mammalian PQQ-binding proteins. In vitro studies using a purified rabbit muscle LDH show that PQQ inhibits the formation of lactate from pyruvate in the presence of NADH (forward reaction), whereas it enhances the conversion of lactate to pyruvate in the presence of NAD⁺ (reverse reaction). The molecular mechanism underlying PQQ-mediated regulation of LDH activity is attributed to the oxidation of NADH to NAD⁺ by PQQ. Indeed, the PQQ-bound LDH oxidizes NADH, generating NAD⁺, and significantly catalyzes the conversion of lactate to pyruvate. Furthermore, PQQ attenuates cellular lactate release and increases intracellular ATP levels in the NIH/3T3 fibroblasts. Our results suggest that PQQ, modulating LDH activity to facilitate pyruvate formation through its redox-cycling activity, may be involved in the enhanced energy production via mitochondrial TCA cycle and oxidative phosphorylation.

Pyrroloquinoline Quinone Slows Down the Progression of Osteoarthritis by Inhibiting Nitric Oxide Production and Metalloproteinase Synthesis

Osteoarthritis (OA) is the most common arthritis and also one of the major causes of joint pain in elderly people. The aim of this study was to investigate the effects of pyrroloquinoline quinone (PQQ) on degenerated-related changes in osteoarthritis (OA). SW1353 cells were stimulated with IL-1β to establish the chondrocyte injury model in vitro. PQQ was administrated into SW1353 cultures 1 h before IL-1β treatment. Amounts of MMP-1, MMP-13, P65, IκBα, ERK, p-ERK, P38, and p-P38 were measured via western blot. The production of NO was determined by Griess reaction assay and reflected by the iNOS level. Meniscal-ligamentous injury (MLI) was performed on 8-week-old rats to establish the OA rat model. PQQ was injected intraperitoneally 3 days before MLI and consecutively until harvest, and the arthritis cartilage degeneration level was assessed. The expressions of MMP-1 and MMP-13 were significantly downregulated after PQQ treatment compared with that in IL-1β alone group. NO production and iNOS expression were decreased by PQQ treatment compared with control group. Amounts of nucleus P65 were upregulated in SW1353 after stimulated with IL-1β, while PQQ significantly inhibited the translocation. In rat OA model, treatment with PQQ markedly decelerated the degeneration of articular cartilage. These findings suggested that PQQ could inhibit OA-related catabolic proteins MMPs expression, NO production, and thus, slow down the articular cartilage degeneration and OA progression. Owing to its beneficial effects, PQQ is expected to be a novel pharmacological application in OA clinical prevention and treatment in the near future.

Bioenergetic differences between MCF-7 and T47D breast cancer cells and their regulation by oestradiol and tamoxifen

Oestrogen receptor α (ERα+) breast tumours rely on mitochondria (mt) to generate ATP. The goal of the present study was to determine how oestradiol (E2) and 4-hydroxytamoxifen (4-OHT) affect cellular bioenergetic function in MCF-7 and T47D ERα+ breast cancer cells in serum-replete compared with dextran-coated charcoal (DCC)-stripped foetal bovine serum (FBS)-containing medium ('serum-starved'). Serum-starvation reduced oxygen consumption rate (OCR), extracellular acidification rate (ECAR), ATP-linked OCR and maximum mt capacity, reflecting lower ATP demand and mt respiration. Cellular respiratory stateapparent was unchanged by serum deprivation. 4-OHT reduced OCR independent of serum status. Despite having a higher mt DNA/nuclear DNA ratio than MCF-7 cells, T47D cells have a lower OCR and ATP levels and higher proton leak. T47D express higher nuclear respiratory factor-1 (NRF-1) and NRF-1-regulated, nuclear-encoded mitochondrial transcription factor TFAM and cytochrome c, but lower levels of cytochrome c oxidase, subunit IV, isoform 1 (COX4, COX4I1). Mitochondrial reserve capacity, reflecting tolerance to cellular stress, was higher in serum-starved T47D cells and was increased by 4-OHT, but was decreased by 4-OHT in MCF-7 cells. These data demonstrate critical differences in cellular energetics and responses to 4-OHT in these two ERα+ cell lines, likely reflecting cancer cell avoidance of apoptosis.

Kinetic study of aroxyl radical scavenging and α-tocopheroxyl regeneration rates of pyrroloquinolinequinol (PQQH2, a reduced form of pyrroloquinolinequinone) in dimethyl sulfoxide solution: finding of synergistic effect on the reaction rate due to the coexistence of α-tocopherol and PQQH2

Measurements of aroxyl radical (ArO•)-scavenging rate constants (ks AOH) of antioxidants (AOHs: pyrroloquinolinequinol (PQQH2), α-tocopherol (α-TocH), ubiquinol-10 (UQ10H2), epicatechin, epigallocatechin, epigallocatechin gallate, and caffeic acid) were performed in dimethyl sulfoxide (DMSO) solution, using stopped-flow spectrophotometry. The ks AOH values were measured not only for each AOH but also for the mixtures of two AOHs ((i) α-TocH and PQQH2 and (ii) α-TocH and UQ10H2). A notable synergistic effect that the ks AOH values increase 1.72, 2.42, and 2.50 times for α-TocH, PQQH2, and UQ10H2, respectively, was observed for the solutions including two kinds of AOHs. Measurements of the regeneration rates of α-tocopheroxyl radical (α-Toc•) to α-TocH by PQQH2 and UQ10H2 were performed in DMSO, using double-mixing stopped-flow spectrophotometry. Second-order rate constants (kr) obtained for PQQH2 and UQ10H2 were 1.08 × 105 and 3.57 × 104 M−1 s−1, respectively, indicating that the kr value of PQQH2 is 3.0 times larger than that of UQ10H2. It has been clarified that PQQH2 and UQ10H2 having two HO groups within a molecule may rapidly regenerate two molecules of α-Toc• to α-TocH. The result indicates that the prooxidant effect of α-Toc• is suppressed by the coexistence of PQQH2 or UQ10H2.

Estradiol and tamoxifen regulate NRF-1 and mitochondrial function in mouse mammary gland and uterus

Nuclear respiratory factor-1 (NRF-1) stimulates the transcription of nuclear-encoded genes that regulate mitochondrial (mt) genome transcription and biogenesis. We reported that estradiol (E2) and 4-hydroxytamoxifen (4-OHT) stimulate NRF-1 transcription in an estrogen receptor α (ERα)- and ERβ-dependent manner in human breast cancer cells. The aim of this study was to determine whether E2 and 4-OHT increase NRF-1 in vivo. Here, we report that E2 and 4-OHT increase NRF-1 expression in mammary gland (MG) and uterus of ovariectomized C57BL/6 mice in a time-dependent manner. E2 increased NRF-1 protein in the uterus and MG; however, in MG, 4-OHT increased Nrf1 mRNA but not protein. Chromatin immunoprecipitation assays revealed increased in vivo recruitment of ERα to the Nrf1 promoter and intron 3 in MG and uterus 6 h after E2 and 4-OHT treatment, commensurate with increased NRF-1 expression. E2- and 4-OHT-induced increases in NRF-1 and its target genes Tfam, Tfb1m, and Tfb2m were coordinated in MG but not in uterus due to uterine-selective inhibition of the expression of the NRF-1 coactivators Ppargc1a and Ppargc1b by E2 and 4-OHT. E2 transiently increased NRF-1 and PGC-1α nuclear staining while reducing PGC-1α in uterus. E2, not 4-OHT, activates mt biogenesis in MG and uterus in a time-dependent manner. E2 increased mt outer membrane Tomm40 protein levels in MG and uterus whereas 4-OHT increased Tomm40 only in uterus. These data support the hypothesis of tissue-selective regulation of NRF-1 and its downstream targets by E2 and 4-OHT in vivo.

Genotoxicity of pyrroloquinoline quinone (PQQ) disodium salt (BioPQQ™)

The genotoxic potential of pyrroloquinoline quinone (PQQ) disodium salt (BioPQQ™) was evaluated in a battery of genotoxicity tests. The results of the bacterial mutation assay (Ames test) were negative. Weak positive results were obtained in 2 separate in vitro chromosomal aberration test in Chinese hamster lung (CHL) fibroblasts. Upon testing in an in vitro chromosomal aberration test in human peripheral blood lymphocytes, no genotoxic activity of PQQ was noted. In the in vivo micronucleus assay in mice, PQQ at doses up to 2,000 mg/kg body weight demonstrated that no genotoxic effects are expressed in vivo in bone marrow erythrocytes. The weak responses in the in vitro test CHL cells were considered of little relevance under conditions of likely human exposure. PQQ disodium was concluded to have no genotoxic activity in vivo.

Pyrroloquinoline quinine protects rat brain cortex against acute glutamate-induced neurotoxicity

To investigate possible protective effects of pyrroloquinoline quinone (PQQ) on the rat cortex with glutamate injection and to understand the mechanisms linking the in vivo neuroprotection of PQQ. Adult Sprague-Dawley rats received glutamate injection into the rat cortex. Terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling assay was performed to observe influences of co-treatment with PQQ (simultaneous injection with PQQ and glutamate) on neural cell apoptosis in the rat cortex. The production of reactive oxygen species (ROS) in the rat cortex was detected by flow cytometry using 2',7'-dichlorofluorescin diacetate labeling, and the activity of superoxide dismutase, glutathione and malondialdehyde was respectively determined. Real time quantitative RT-PCR and Western blot were applied to measure the mRNA and protein expressions of Nrf1, Nrf2, HO-1 and GCLC in the rat cortex. Western blot was used to detect the phosphorylation of Akt and GSK3β in the rat cortex. Co-treatment with PQQ protected neural cells in the rat cortex from glutamate-induced apoptosis. PQQ decreased the ROS production induced by glutamate injection. PQQ increased the mRNA and protein expressions of Nrf2, HO-1 and GCLC and the phosphorylation of Akt and GSK3β in the cortex of glutamate-injected rats. PQQ could produce neuroprotective effects on the rat cortex. The antioxidant properties of PQQ and PQQ-induced activation of Akt/GSK3β signal pathway might be responsible for the in vivo neuroprotection of PQQ.

Crystal structure and characterization of pyrroloquinoline quinone disodium trihydrate

Background

Pyrroloquinoline quinone (PQQ), a tricarboxylic acid, has attracted attention as a growth factor, and its application to supplements and cosmetics is underway. The product used for these purposes is a water-soluble salt of PQQ disodium. Although in the past, PQQ disodiumpentahydrates with a high water concentration were used, currently, low hydration crystals of PQQ disodiumpentahydrates are preferred.

Results

We prepared a crystal of PQQ disodium trihydrate in a solution of ethanol and water, studied its structure, and analyzed its properties. In the prepared crystal, the sodium atom interacted with the oxygen atom of two carboxylic acids as well as two quinones of the PQQ disodium trihydrate. In addition, the hydration water of the prepared crystal was less than that of the conventional PQQ disodium crystal. From the results of this study, it was found that the color and the near-infrared (NIR) spectrum of the prepared crystal changed depending on the water content in the dried samples.

Conclusions

The water content in the dried samples was restored to that in the trihydrate crystal by placing the samples in a humid environment. In addition, the results of X-ray diffraction (XRD) and X-ray diffraction-differential calorimetry (XRD-DSC) analyses show that the phase of the trihydrate crystal changed when the crystallization water was eliminated. The dried crystal has two crystalline forms that are restored to the original trihydrate crystals in 20% relative humidity (RH). This crystalline (PQQ disodium trihydrate) is stable under normal environment.

Altering pyrroloquinoline quinone nutritional status modulates mitochondrial, lipid, and energy metabolism in rats

We have reported that pyrroloquinoline quinone (PQQ) improves reproduction, neonatal development, and mitochondrial function in animals by mechanisms that involve mitochondrial related cell signaling pathways. To extend these observations, the influence of PQQ on energy and lipid relationships and apparent protection against ischemia reperfusion injury are described herein. Sprague-Dawley rats were fed a nutritionally complete diet with PQQ added at either 0 (PQQ−) or 2 mg PQQ/Kg diet (PQQ+). Measurements included: 1) serum glucose and insulin, 2) total energy expenditure per metabolic body size (Wt^3/4), 3) respiratory quotients (in the fed and fasted states), 4) changes in plasma lipids, 5) the relative mitochondrial amount in liver and heart, and 6) indices related to cardiac ischemia. For the latter, rats (PQQ− or PQQ+) were subjected to left anterior descending occlusions followed by 2 h of reperfusion to determine PQQ's influence on infarct size and myocardial tissue levels of malondialdehyde, an indicator of lipid peroxidation. Although no striking differences in serum glucose, insulin, and free fatty acid levels were observed, energy expenditure was lower in PQQ− vs. PQQ+ rats and energy expenditure (fed state) was correlated with the hepatic mitochondrial content. Elevations in plasma di- and triacylglyceride and β-hydroxybutryic acid concentrations were also observed in PQQ− rats vs. PQQ+ rats. Moreover, PQQ administration (i.p. at 4.5 mg/kg BW for 3 days) resulted in a greater than 2-fold decrease in plasma triglycerides during a 6-hour fast than saline administration in a rat model of type 2 diabetes. Cardiac injury resulting from ischemia/reperfusion was more pronounced in PQQ− rats than in PQQ+ rats. Collectively, these data demonstrate that PQQ deficiency impacts a number of parameters related to normal mitochondrial function.

Kinetic study of the quenching reaction of singlet oxygen by Pyrroloquinolinequinol (PQQH(2), a reduced form of Pyrroloquinolinequinone) in micellar solution

A kinetic study of the quenching reaction of singlet oxygen ((1)O(2)) with pyrroloquinolinequinol (PQQH(2), a reduced form of pyrroloquinolinequinone (PQQ)), PQQNa(2) (disodium salt of PQQ), and seven kinds of natural antioxidants (vitamin C (Vit C), uric acid (UA), epicatechin (EC), epigallocatechin (EGC), α-tocopherol (α-Toc), ubiquinol-10 (UQ(10)H(2)), and β-carotene (β-Car)) has been performed. The second-order rate constants k(Q) (k(Q) = k(q) + k(r), physical quenching and chemical reaction) for the reaction of (1)O(2) with PQQH(2), PQQNa(2), and seven kinds of antioxidants were measured in 5.0 wt % Triton X-100 micellar solution (pH 7.4), using UV-visible spectrophotometry. The k(Q) values decreased in the order of β-Car > PQQH(2) > α-Toc > UA > UQ(10)H(2) > Vit C ∼ EGC > EC ≫ PQQNa(2). PQQH(2) is a water-soluble antioxidant. The singlet oxygen-quenching activity of PQQH(2) was found to be 6.3, 2.2, 6.1, and 22 times as large as the corresponding those of water-soluble antioxidants (Vit C, UA, EGC, and EC). Further, the activity of PQQH(2) was found to be 2.2 and 3.1 times as large as the corresponding activity of lipid-soluble antioxidants (α-Toc and UQ(10)H(2)). On the other hand, the activity of PQQH(2) is 6.4 times as small as that of β-Car. It was observed that the chemical reaction (k(r)) is almost negligible in the quenching reaction of (1)O(2) by PQQH(2). The result suggests that PQQH(2) may contribute to the protection of oxidative damage in biological systems, by quenching (1)O(2).

Identification of transcriptional networks responding to pyrroloquinoline quinone dietary supplementation and their influence on thioredoxin expression, and the JAK/STAT and MAPK pathways

PQQ (pyrroloquinoline quinone) improves energy utilization and reproductive performance when added to rodent diets devoid of PQQ. In the present paper we describe changes in gene expression patterns and transcriptional networks that respond to dietary PQQ restriction or pharmacological administration. Rats were fed diets either deficient in PQQ (PQQ−) or supplemented with PQQ (approx. 6 nmol of PQQ/g of food; PQQ+). In addition, groups of rats were either repleted by administering PQQ to PQQ− rats (1.5 mg of PQQ intraperitoneal/kg of body weight at 12 h intervals for 36 h; PQQ−/+) or partially depleted by feeding the PQQ− diet to PQQ+ rats for 48 h (PQQ+/−). RNA extracted from liver and a Codelink® UniSet Rat I Bioarray system were used to assess gene transcript expression. Of the approx. 10000 rat sequences and control probes analysed, 238 were altered at the P<0.01 level by feeding on the PQQ− diet for 10 weeks. Short-term PQQ depletion resulted in changes in 438 transcripts (P<0.01). PQQ repletion reversed the changes in transcript expression caused by PQQ deficiency and resulted in an alteration of 847 of the total transcripts examined (P<0.01). Genes important for cellular stress (e.g. thioredoxin), mitochondriogenesis, cell signalling [JAK (Janus kinase)/STAT (signal transducer and activator of transcription) and MAPK (mitogen-activated protein kinase) pathways] and transport were most affected. qRT-PCR (quantitative real-time PCR) and functional assays aided in validating such processes as principal targets. Collectively, the results provide a mechanistic basis for previous functional observations associated with PQQ deficiency or PQQ administered in pharmacological amounts.

Pyrroloquinoline quinone stimulates mitochondrial biogenesis through cAMP response element-binding protein phosphorylation and increased PGC-1alpha expression

Bioactive compounds reported to stimulate mitochondrial biogenesis are linked to many health benefits such increased longevity, improved energy utilization, and protection from reactive oxygen species. Previously studies have shown that mice and rats fed diets lacking in pyrroloquinoline quinone (PQQ) have reduced mitochondrial content. Therefore, we hypothesized that PQQ can induce mitochondrial biogenesis in mouse hepatocytes. Exposure of mouse Hepa1-6 cells to 10-30 microm PQQ for 24-48 h resulted in increased citrate synthase and cytochrome c oxidase activity, Mitotracker staining, mitochondrial DNA content, and cellular oxygen respiration. The induction of this process occurred through the activation of cAMP response element-binding protein (CREB) and peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha), a pathway known to regulate mitochondrial biogenesis. PQQ exposure stimulated phosphorylation of CREB at serine 133, activated the promoter of PGC-1alpha, and increased PGC-1alpha mRNA and protein expression. PQQ did not stimulate mitochondrial biogenesis after small interfering RNA-mediated reduction in either PGC-1alpha or CREB expression. Consistent with activation of the PGC-1alpha pathway, PQQ increased nuclear respiratory factor activation (NRF-1 and NRF-2) and Tfam, TFB1M, and TFB2M mRNA expression. Moreover, PQQ protected cells from mitochondrial inhibition by rotenone, 3-nitropropionic acid, antimycin A, and sodium azide. The ability of PQQ to stimulate mitochondrial biogenesis accounts in part for action of this compound and suggests that PQQ may be beneficial in diseases associated with mitochondrial dysfunction.

The mitochondrial pool of free amino acids reflects the composition of mitochondrial DNA-encoded proteins: indication of a post- translational quality control for protein synthesis

Mitochondria can synthesize a limited number of proteins encoded by mtDNA (mitochondrial DNA) by using their own biosynthetic machinery, whereas most of the proteins in mitochondria are imported from the cytosol. It could be hypothesized that the mitochondrial pool of amino acids follows the frequency of amino acids in mtDNA-encoded proteins or, alternatively, that the profile is the result of the participation of amino acids in pathways other than protein synthesis (e.g. haem biosynthesis and aminotransferase reactions). These hypotheses were tested by evaluating the pool of free amino acids and derivatives in highly-coupled purified liver mitochondria obtained from rats fed on a nutritionally adequate diet for growth. Our results indicated that the pool mainly reflects the amino acid composition of mtDNA-encoded proteins, suggesting that there is a post-translational control of protein synthesis. This conclusion was supported by the following findings: (i) correlation between the concentration of free amino acids in the matrix and the frequency of abundance of amino acids in mtDNA-encoded proteins; (ii) the similar ratios of essential-to-non-essential amino acids in mtDNA-encoded proteins and the mitochondrial pool of amino acids; and (iii), lack of a correlation between codon usage or tRNA levels and amino-acid concentrations. Quantitative information on the mammalian mitochondrial content of amino acids, such as that presented in the present study, along with functional studies, will help us to better understand the pathogenesis of mitochondrial diseases or the biochemical implications in mitochondrial metabolism.

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

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

In vitro protective effects of pyrroloquinoline quinone on methylmercury-induced neurotoxicity

Methylmercury (MeHg), as a well-known neurotoxicant, has been implicated to induce massive neurodegeneration. Pyrroloquinoline quinone (PQQ) is a novel redox cofactor and also exists in various plants and animal tissues. In vivo as well as in vitro experimental studies have shown that PQQ functions as an essential nutrient or antioxidant. In this study, we demonstrated the protective effects of PQQ on MeHg-induced neurotoxicity in PC12 cells. The results showed that after pretreatment of PC12 cells with PQQ prior to MeHg exposure, the MeHg-induced cytotoxicity was significantly attenuated, and then DNA fragmentation was correspondingly reduced. PQQ prevented the disruption of mitochondrial membrane potential, up-regulated the level of Bcl-2, and consequently inhibited the activation of caspase-3. Moreover, PQQ also decreased the production of ROS and maintained the GSH levels in PC12 cells exposed to MeHg. Thus, these data indicate that PQQ can protect neurons against MeHg-induced apoptosis and oxidative stress via ameliorating the mitochondrial dysfunction. Data from this study provide a new useful strategy for the treatment of neuronal toxicity induced by mercury toxins.

Glial cell regulation of neurotransmission and behavior in Drosophila

Mounting evidence demonstrates that glial cells might have important roles in regulating the physiology and behavior of adult animals. We summarize some of this evidence here, with an emphasis on the roles of glia of the differentiated nervous system in controlling neuronal excitability, behavior and plasticity. In the review we highlight studies in Drosophila and discuss results from the analysis of mammalian astrocytes that demonstrate roles for glia in the adult nervous system.

The pyrroloquinoline quinone biosynthesis pathway revisited: a structural approach

BACKGROUND

The biosynthesis pathway of Pyrroloquinoline quinone, a bacterial redox active cofactor for numerous alcohol and aldose dehydrogenases, is largely unknown, but it is proven that at least six genes in Klebsiella pneumoniae (PqqA-F) are required, all of which are located in the PQQ-operon.

RESULTS

New structural data of some PQQ biosynthesis proteins and their homologues provide new insights and functional assignments of the proteins in the pathway. Based on sequence analysis and homology models we propose the role and catalytic function for each enzyme involved in this intriguing biosynthesis pathway.

CONCLUSION

PQQ is derived from the two amino acids glutamate and tyrosine encoded in the precursor peptide PqqA. Five reactions are necessary to form this quinone cofactor. The PqqA peptide is recognised by PqqE, which links the C9 and C9a, afterwards it is accepted by PqqF which cuts out the linked amino acids. The next reaction (Schiff base) is spontaneous, the following dioxygenation is catalysed by an unknown enzyme. The last cyclization and oxidation steps are catalysed by PqqC. Taken together the known facts of the different proteins we assign a putative function to all six proteins in PQQ biosynthesis pathway.