Pyrroloquinoline quinone improves growth and reproductive performance in mice fed chemically defined diets

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.

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.

Can Drosophila melanogaster represent a model system for the detection of reproductive adverse drug reactions?

Once a molecule is identified as a potential drug, the detection of adverse drug reactions is one of the key components of its development and the FDA approval process. We propose using Drosophila melanogaster to screen for reproductive adverse drug reactions in the early stages of drug development. Compared with other non-mammalian models, D. melanogaster has many similarities to the mammalian reproductive system, including putative sex hormones and conserved proteins involved in genitourinary development. Furthermore, the D. melanogaster model would present significant advantages in time efficiency and cost-effectiveness compared with mammalian models. We present data on methotrexate (MTX) reproductive adverse events in multiple animal models, including fruit flies, as proof-of-concept for the use of the D. melanogaster model.

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.

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.

Knockout and overexpression of pyrroloquinoline quinone biosynthetic genes in Gluconobacter oxydans 621H

In Gluconobacter oxydans, pyrroloquinoline quinone (PQQ) serves as the cofactor for various membrane-bound dehydrogenases that oxidize sugars and alcohols in the periplasm. Proteins for the biosynthesis of PQQ are encoded by the pqqABCDE gene cluster. Our reverse transcription-PCR and promoter analysis data indicated that the pqqA promoter represents the only promoter within the pqqABCDE cluster of G. oxydans 621H. PQQ overproduction in G. oxydans was achieved by transformation with the plasmid-carried pqqA gene or the complete pqqABCDE cluster. A G. oxydans mutant unable to produce PQQ was obtained by site-directed disruption of the pqqA gene. In contrast to the wild-type strain, the pqqA mutant did not grow with d-mannitol, d-glucose, or glycerol as the sole energy source, showing that in G. oxydans 621H, PQQ is essential for growth with these substrates. Growth of the pqqA mutant, however, was found with d-gluconate as the energy source. The growth behavior of the pqqA mutant correlated with the presence or absence of the respective PQQ-dependent membrane-bound dehydrogenase activities, demonstrating the vital role of these enzymes in G. oxydans metabolism. A different PQQ-deficient mutant was generated by Tn5 transposon mutagenesis. This mutant showed a defect in a gene with high homology to the Escherichia coli tldD gene, which encodes a peptidase. Our results indicate that the tldD gene in G. oxydans 621H is involved in PQQ biosynthesis, possibly with a similar function to that of the pqqF genes found in other PQQ-synthesizing bacteria.

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

Pyrroloquinoline quinone (PQQ) added to purified diets devoid of PQQ improves indices of perinatal development in rats and mice. Herein, PQQ nutritional status and lysine metabolism are described, prompted by a report that PQQ functions as a vitamin-like enzymatic cofactor important in lysine metabolism (Nature 422 [2003] 832). Alternatively, we propose that PQQ influences lysine metabolism, but by mechanisms that more likely involve changes in mitochondrial content. PQQ deprivation in both rats and mice resulted in a decrease in mitochondrial content. In rats, alpha-aminoadipic acid (alphaAA), which is derived from alpha-aminoadipic semialdehyde (alphaAAS) and made from lysine in mitochondria, and the plasma levels of amino acids known to be oxidized in mitochondria (e.g., Thr, Ser, and Gly) were correlated with changes in the liver mitochondrial content of PQQ-deprived rats, but not PQQ-supplemented rats. In contrast, the levels of NAD dependent alpha-aminoadipate-delta-semialdehyde dehydrogenase (AASDH), a cytosolic enzyme important to alphaAA production from alphaAAS, was not influenced by PQQ dietary status. Moreover, the levels of U26 mRNA were not significantly changed even when diets differed markedly in PQQ and dietary lysine content. U26 mRNA levels were measured, because of U26's proposed, albeit questionable role as a PQQ-dependent enzyme involved in alphaAA formation.

Pyrroloquinoline quinone modulates mitochondrial quantity and function in mice

When pyrroloquinoline quinone (PQQ) is added to an amino acid-based, but otherwise nutritionally complete basal diet, it improves growth-related variables in young mice. We examined PQQ and mitochondrial function based on observations that PQQ deficiency results in elevated plasma glucose concentrations in young mice, and PQQ addition stimulates mitochondrial complex 1 activity in vitro. PQQ-deficient weanling mice had a 20-30% reduction in the relative amount of mitochondria in liver; lower respiratory control ratios, and lower respiratory quotients than PQQ-supplemented mice (2 mg PQQ/kg diet). In mice from dams fed a conventional laboratory diet, but switched at weaning to the basal diet, plasma glucose, Ala, Gly, and Ser concentrations were elevated at 4 wk (PQQ- vs. PQQ+), but not at 8 wk. The relative mitochondrial content (ratio of mtDNA to nuclear DNA) also tended (P<0.18) to be lower (PQQ- vs. PQQ+) at 4 wk, but not at 8 wk. PQQ also counters the mitochondrial complex 1 inhibitor, diphenylene iodonium (DPI). Mice were gavaged with 0, 0.4, or 4 microg PQQ/g body weight (BW) daily for 14 d. At each PQQ level, DPI was injected (i.p.) at 0, 0.4, 0.8, or 1.6 microg DPI/g BW. The PQQ-deficient mice exposed to 0.4 or 4.0 microg DPI/g lost weight and had lower plasma glucose levels than PQQ-supplemented mice (P<0.05). In addition, fibroblasts took up (3)H-PQQ added to cell cultures, and cultured hepatocytes maintained mitochondrial PQQ concentrations similar to those observed in vivo. Collectively, these results indicate that dietary PQQ can influence mitochondrial amount and function, particularly in perinatal and weanling mice.

Pyrroloquinoline quinone (PQQ) decreases myocardial infarct size and improves cardiac function in rat models of ischemia and ischemia/reperfusion

As pyrroloquinoline quinone (PQQ) is a redox cofactor in mammals, we asked if it is cardioprotective. Rats were subjected to 2 h of left anterior descending (LAD) coronary artery ligation without reperfusion (model 1, ischemia). In model 2 (ischemia/reperfusion), rats were subjected to 17 or 30 min of LAD occlusion and 2 h of reperfusion. PQQ (15-20 mg/kg) was given i.p., either 30 min before LAD occlusion (Pretreatment) or i.v. at the onset of reperfusion (Treatment). In model 1, PQQ reduced infarct size (10.0 +/- 1.5 vs 19.1 +/- 2.1%, P < 0.01). In model 2, either PQQ Pretreatment or Treatment also reduced infarct size (18.4 +/- 2.3 and 25.6 +/- 3.5% vs 38.1 +/- 2.6%, P < 0.01). PQQ resulted in higher LV developed pressure and LV (+)dP/dt after 1-2 h of reperfusion (P < 0.05), and fewer ventricular fibrillation episodes. PQQ dose (5-20 mg/kg) was inversely related to infarct size. PQQ reduced myocardial tissue levels of malondialdehyde (MDA), an indicator of lipid peroxidation (316 +/- 88 vs 99 +/- 14 nmol/g, P < 0.01). PQQ given either as Pretreatment or as Treatment at the onset of reperfusion is highly effective in reducing infarct size and improving cardiac function in a dose-related manner in rat models of ischemia and ischemia/reperfusion. The optimal dose in this study, which exhibited neither renal nor hepatic toxicity, was 15 mg/kg, but lower doses may also be efficacious. We conclude that PQQ, which appears to act as a free radical scavenger in ischemic myocardium, is a highly effective cardioprotective agent.

Biochemistry: role of PQQ as a mammalian enzyme cofactor?

The announcement by Kasahara and Kato of a new redox-cofactor vitamin for mammals, pyrroloquinoline quinone (PQQ), was based on their claim that an enzyme, predicted to be involved in mouse lysine metabolism, is a PQQ-dependent dehydrogenase. However, this claim was dependent on a sequence analysis using databases that inappropriately label beta-propeller sequences as PQQ-binding motifs. What the evidence actually suggests is that the enzyme is an interesting novel protein that has a seven-bladed beta-propeller structure, but there is nothing to indicate that it is a PQQ-dependent dehydrogenase.

Quinone biogenesis: Structure and mechanism of PqqC, the final catalyst in the production of pyrroloquinoline quinone

The biosynthesis of pyrroloquinoline quinone (PQQ), a vitamin and redox cofactor of quinoprotein dehydrogenases, is facilitated by an unknown pathway that requires the expression of six genes, pqqA to -F. PqqC, the protein encoded by pqqC, catalyzes the final step in the pathway in a reaction that involves ring cyclization and eight-electron oxidation of 3a-(2-amino-2-carboxyethyl)-4,5-dioxo-4,5,6,7,8,9-hexahydroquinoline-7,9-dicarboxylic-acid to PQQ. Herein, we describe the crystal structures of PqqC and its complex with PQQ and determine the stoichiometry of H2O2 formation and O2 uptake during the reaction. The PqqC structure(s) reveals a compact seven-helix bundle that provides the scaffold for a positively charged active site cavity. Product binding induces a large conformational change, which results in the active site recruitment of amino acid side chains proposed to play key roles in the catalytic mechanism. PqqC is unusual in that it transfers redox equivalents to molecular oxygen without the assistance of a redox active metal or cofactor. The structure of the enzyme-product complex shows additional electron density next to R179 and C5 of PQQ, which can be modeled as O2 or H2O2, indicating a site for oxygen binding. We propose a reaction sequence that involves base-catalyzed cyclization and a series of quinone-quinol tautomerizations that are followed by cycles of O2/H2O2-mediated oxidations.