Recent progress in studies on the health benefits of pyrroloquinoline quinone

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

Simple Summary

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

Abstract

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

Pyrroloquinoline quinone inhibits the production of inflammatory cytokines via the SIRT1/NF-κB signal pathway in weaned piglet jejunum

The small intestine is an important digestive organ and plays a vital role in the life of a pig. In this study, we explored the regulatory role and molecular mechanism of pyrroloquinoline quinone (PQQ) on intestinal health and to discussed the interaction between PQQ and vitamin C (VC). A total of 160 healthy piglets weaned at 21 d were randomly divided into four treatment groups according to 2 × 2 factoring. The results showed that dietary PQQ could significantly decrease the levels of plasma globulin, albumin/globulin (A/G), indirect bilirubin (IBIL), blood urea nitrogen (BUN), creatinine (CREA) (P < 0.05 for each), total bilirubin, (TBIL) (P < 0.01), diamine oxidase (DAO) (P < 0.01) and immunoglobulin G (IgG) (P < 0.0001) and increase the levels of immunoglobulin A (IgA) and immunoglobulin M (IgM) (P < 0.0001) in the plasma of weaned piglets. Similarly, dietary VC could significantly decrease the levels of plasma globulin, A/G, DAO (P < 0.05 for each) and IgG (P < 0.0001) and increase the levels of IgA and IgM (P < 0.0001) in the plasma of weaned piglets. In addition, dietary PQQ increased (P < 0.05) the mRNA levels of antioxidant genes (NQO1, UGT1A1, and EPHX1), thereby enhancing (oxidized) nicotinamide adenine dinucleotide (NAD+) concentration and sirtuin 1 (SIRT1) activity in tissues. However, the addition of 200 mg kg-1 VC to the diet containing PQQ reduced most of the effects of PQQ. We further show that PQQ reduced (P < 0.05) the expression of inflammation-related genes (IL-2, IL-6, TNF-α, and COX-2) via the SIRT1/NF-κB deacetylation signaling. In conclusion, our data reveals that PQQ exerts a certain protective effect on the intestines of piglets, but higher concentrations of VC react with PQQ, which inhibits the regulatory mechanism of PQQ.

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

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

Effects of dietary pyrroloquinoline quinone disodium supplementation on inflammatory responses, oxidative stress, and intestinal morphology in broiler chickens challenged with lipopolysaccharide

This study was conducted to investigate the effects of pyrroloquinoline quinone disodium (PQQ·Na2) on inflammatory responses, oxidative stress, and intestinal morphology of broiler chickens challenged with lipopolysaccharide (LPS). A 2 × 2 factorial arrangement in a complete randomized design experiment was used to study the effect of dietary PQQ·Na2 (0 or 1 mg/kg) on broiler chickens with or without a challenge with LPS. A total of two hundred eighty-eight 1-day-old Arbor Acre broiler chickens were randomly assigned to 4 treatments with 6 replicate cages of 12 birds per cage. All experimental broilers were injected intraperitoneally with 0.5 mg/kg body weight of either Escherichia coli LPS or sterile saline at 16, 18, and 20 d of age. Results showed that injecting LPS significantly increased the concentrations of interleukin-1beta (IL-1β) in serum of birds on day 20 and day 21. Meanwhile, LPS injection increased (P < 0.05) the relative mRNA expression of interleukin-6 (IL-6) in the duodenal mucosa of broilers on day 21. However, dietary supplementation with PQQ·Na2 decreased (P < 0.05) the concentration of IL-6 in serum of birds on day 20 and the levels of IL-1β, IL-6, and interleukin-10 (IL-10) in serum of broiler chickens on day 21. Besides, supplementation of PQQ·Na2 within diet decreased (P < 0.05) the mRNA expressions of IL-1β and IL-10 in the duodenal mucosa of birds on day 20. Relative to saline injection, the activity of glutathione peroxidase (GSH-Px) in serum and the activities of total superoxide dismutase (T-SOD) and catalase (CAT) in liver were found to be lower (P < 0.05) in broilers after LPS challenge on day 21. However, birds fed with PQQ·Na2 showed higher (P < 0.05) GSH-Px activity in serum and higher (P < 0.05) T-SOD activities in liver on day 21 and day 42. Pyrroloquinoline quinone disodium also significantly attenuated the LPS-induced decreases in villus height to crypt depth ratio in the duodenum of broilers. In conclusion, dietary PQQ·Na2 supplementation significantly exerted protective effects on inflammation damage and oxidant stress of broilers under LPS challenge by regulating the expression of inflammatory cytokines (IL-1β, IL-6, and IL-10) and activities of antioxidant enzymes (GSH-Px, T-SOD, and CAT). Moreover, dietary PQQ·Na2 supplementation significantly ameliorated the LPS-impaired intestinal morphology in broilers. Therefore, it has been considered that PQQ·Na2 can be used as a potential feed additive in broiler production.

Novel Pharmacological Targets for Combat PTSD-Metabolism, Inflammation, The Gut Microbiome, and Mitochondrial Dysfunction

INTRODUCTION

Current pharmacological treatments of post-traumatic stress disorder (PTSD) have limited efficacy. Although the diagnosis is based on psychopathological criteria, it is frequently accompanied by somatic comorbidities and perhaps "accelerated biological aging," suggesting widespread physical concomitants. Such physiological comorbidities may affect core PTSD symptoms but are rarely the focus of therapeutic trials.

METHODS

To elucidate the potential involvement of metabolism, inflammation, and mitochondrial function in PTSD, we integrate findings and mechanistic models from the DOD-sponsored "Systems Biology of PTSD Study" with previous data on these topics.

RESULTS

Data implicate inter-linked dysregulations in metabolism, inflammation, mitochondrial function, and perhaps the gut microbiome in PTSD. Several inadequately tested targets of pharmacological intervention are proposed, including insulin sensitizers, lipid regulators, anti-inflammatories, and mitochondrial biogenesis modulators.

CONCLUSIONS

Systemic pathologies that are intricately involved in brain functioning and behavior may not only contribute to somatic comorbidities in PTSD, but may represent novel targets for treating core psychiatric symptoms.

Pyrroloquinoline Quinone Alleviates Jejunal Mucosal Barrier Function Damage and Regulates Colonic Microbiota in Piglets Challenged With Enterotoxigenic Escherichia coli

This study aimed to evaluate the effect of dietary supplementation with pyrroloquinoline quinone (PQQ) on gut inflammation and microbiota dysbiosis induced by enterotoxigenic Escherichia coli (ETEC). Twenty Duroc × Landrace × Yorkshire crossbred barrows were assigned to four groups: two E. coli K88 challenge groups and two non-challenge groups, each provided a basal diet supplemented with 0 or 3 mg/kg PQQ. On day 14, piglets were challenged with 10 mL 1 × 10⁹ CFU/mL of E. coli K88 or PBS for 48 h. The villus height (VH) and villus height/crypt depth (VCR) ratio of the E. coli K88-challenged group supplemented with PQQ was significantly reduced than in the non-supplemented challenge group (P < 0.05), while levels of jejunal zonula occludens-3 (ZO-3), diamine oxidase, secretory immunoglobulin A (SIgA), interleukin-10 (IL-10), and IL-22 proteins were higher (P < 0.05), as were the activities of glutathione peroxidase, total superoxide dismutase, and total antioxidant capability (P < 0.05). Moreover, PQQ supplementation alleviated an increase in levels of mucosal inflammatory cytokines and reduced the activity of nuclear factor-kappa B (NF-κB) pathway by E. coli K88 (P < 0.05). Gene sequencing of 16S rRNA showed dietary supplementation with PQQ in E. coli K88-challenged piglets attenuated a decrease in Lactobacillus count and butyrate, isobutyrate level, and an increase in Ruminococcus and Intestinibacter counts, all of which were observed in non-supplemented, challenge-group piglets. These results suggest that dietary supplementation with PQQ can effectively alleviate jejunal mucosal inflammatory injury by inhibiting NF-κB pathways and regulating the imbalance of colonic microbiota in piglets challenged with E. coli K88.

Pyrroloquinoline Quinone Inhibits Oxidative Stress in Rats with Diabetic Nephropathy

Background

Diabetic nephropathy (DN) is one of the chronic microvascular complications of diabetes. This study focused on the protective effects of pyrroloquinoline quinone (PQQ) on oxidative stress (OS) in DN.

Material/Methods

Thirty Sprague Dawley rats were randomly selected for this study; 10 rats were randomly selected as the control group. The other 20 rats were established for the DN model. After establishment of the successful model, the DN model rats were randomly divided into a DN group and a PQQ group. The PQQ group was fed with a PQQ diet. Blood urea nitrogen (BUN), serum creatinine (SCr), and blood glucose levels were measured in each group, and OS-related protein expression and AMPK pathway were detected by western blot and quantitative real-time polymerase chain reaction (qRT-PCR). At the same time, we constructed a DN model by culturing NRK-52E cells with high glucose to detect the molecular mechanisms.

Results

The kidney function of the DN group was significantly decreased, SCr and BUN levels were significantly increased, and the renal structure under the microscope was disordered, and interstitial edema was obvious. The expression of SOD1, SOD2, GPX1, and GPX3 were significantly decreased, and the level of reactive oxygen species (ROS) was significantly increased. PQQ treatment can effectively alleviate renal function, improve structural damage, and inhibit OS. In vivo, PQQ can effectively inhibit high glucose-induced OS damage and activate the AMPK/FOXO3a signaling pathway.

Conclusions

PQQ improves renal structural damage and functional damage, and protects kidney cells in DN by inhibiting OS, which may be related to activating the AMPK/FOXO3a pathway.

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

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

Supplementation of pyrroloquinoline quinone with atorvastatin augments mitochondrial biogenesis and attenuates low grade inflammation in obese rats

Mitochondrial dysfunction and Inflammation play a significant role in the manifestation of the co-morbidities of obesity. The study deciphered the impact of Pyrroloquinoline quinone (PQQ) per se and with Atorvastatin (ATS) on high fat, 10% fructose diet (HFFD) induced obese rats expressing low-grade inflammation, dyslipidemia, and mitochondrial dysfunction. HFFD was fed for 10 weeks followed by treatment for 5 weeks with ATS 10 or 20 mg/kg, PQQ 10 or 20 mg/kg, p.o. per se or their combinations. The impact on blood glucose, lipid profile and serum insulin, TNF-α, IL-1β, IL-18, IL-6 was estimated. Gene and protein expression of peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC 1α), Sirtuin 1 (SIRT1), Mitochondrial transcriptional factor A (TFAM) and augmented mitochondrial DNA (mtDNA), NOD like receptor protein 3 (NLRP3) and Caspase 1 was assessed. Rats receiving PQQ and ATS revealed significant decrease in body weights, anthropometric parameter, and adipose tissue vis-à-vis positive control. PQQ alone and with ATS improved glucose tolerance, lipid profile, insulin indices and lowered serum levels of inflammatory cytokines IL-18, IL-1β, TNF-α and IL-6 along with a rise in adiponectin. PQQ supplementation with ATS upregulated the mRNA expression of PGC 1α, SIRT1, TFAM and augmented mtDNA while downregulating inflammatory markers NLRP3 and Caspase 1. PQQ supplementation with atorvastatin holds therapeutic promise to effectively combat mitochondrial dysfunction and chronic low-grade inflammation in obesity.

Pyrroloquinoline quinone can prevent chronic heart failure by regulating mitochondrial function

Background

Myocardial mitochondrial dysfunction is the leading cause of chronic heart failure (CHF). Increased reactive oxygen species (ROS) levels, disruption of mitochondrial biogenesis and mitochondrial Ca²⁺([Ca²⁺]m) homeostasis and reduction of the mitochondrial membrane potential (ΔΨm) cause myocardial mitochondrial dysfunction. Therefore, treating CHF by targeting mitochondrial function is a focus of current research. For the first time, this study investigated the effects of the strong antioxidant pyrroloquinoline quinone (PQQ) on mitochondrial function in a cardiac pressure overload model, and the mechanism by which PQQ regulates [Ca²⁺]m homeostasis was explored in depth.

Methods

After transaortic constriction (TAC), normal saline and PQQ (0.4, 2 and 10 mg/kg) were administered intragastrically to Sprague Dawley (SD) rats for 12 weeks. In vitro, neonatal rat left ventricle myocytes (NRVMs) were pretreated with 200 nm angiotensin II (Ang II) with or without PQQ (1, 10 and 100 μM). Rat heart remodelling was verified by assessment of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) levels (qRT-PCR), cell surface area (wheat germ agglutinin (WGA) staining in vivo and α-actin in vitro) and echocardiography. Myocardial mitochondrial morphology was assessed by transmission electron microscopy. Western blotting was used to assess mitochondrial biogenesis [peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) and transcription factor A, mitochondrial (TFAM)]. The ΔΨm was determined by tetraethyl benzimidazolyl carbocyanine iodide (JC-1) staining and flow cytometry, and ROS levels were measured by dichloro-dihydro-fluorescein diacetate (DCFH-DA) and MitoSOX Red staining. [Ca²⁺]m was measured by isolating rat mitochondria, and mitochondrial Ca²⁺ channel proteins [the mitochondrial Na⁺/Ca²⁺ exchanger (NCLX) and mitochondrial Ca²⁺ uniporter (MCU)] were detected by Western blot.

Results

In vivo and in vitro, PQQ pretreatment improved pressure overload-induced cardiac remodelling and cell hypertrophy, thus preventing the occurrence of CHF. PQQ also prevented mitochondrial morphology damage and reduced the PGC-1α and TFAM downregulation caused by TAC or Ang II. In addition, in NRVMs treated with Ang II + PQQ, PQQ regulated ROS levels and increased the ΔΨm. PQQ also regulated [Ca²⁺]m homeostasis and prohibited [Ca²⁺]m overloading by increasing NCLX expression.

Conclusions

These results show that PQQ can prevent [Ca²⁺]m overload by increasing NCLX expression and thereby reducing ROS production and protecting the ΔΨm. At the same time, PQQ can increase PGC-1α and TFAM expression to regulate mitochondrial biogenesis. These factors can prevent mitochondrial dysfunction, thereby reducing cardiac damage caused by pressure overload and preventing the occurrence of CHF.

PQQ-GDH - Structure, function and application in bioelectrochemistry

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

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

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

Riboflavin and pyrroloquinoline quinone generate carbon monoxide in the presence of tissue microsomes or recombinant human cytochrome P-450 oxidoreductase: implications for possible roles in gasotransmission

Carbon monoxide (CO), an endogenously produced gasotransmitter, regulates inflammation and vascular tone, suggesting that delivery of CO may be therapeutically useful for pathologies like preeclampsia where CO insufficiency is implicated. Our strategy is to identify chemicals that increase the activity of endogenous CO-producing enzymes, including cytochrome P-450 oxidoreductase (CPR). Realizing that both riboflavin and pyrroloquinoline quinone (PQQ) are relatively nontoxic, even at high doses, and that they share chemical properties with toxic CO activators that we previously identified, our goal was to determine whether riboflavin or PQQ could stimulate CO production. Riboflavin and PQQ were incubated in sealed vessels with rat and human tissue extracts and CO generation was measured with headspace-gas chromatography. Riboflavin and PQQ increased CO production ∼60% in rat spleen microsomes. In rat brain microsomes, riboflavin and PQQ increased respective CO production approximately fourfold and twofold compared to baseline. CO production by human placenta microsomes increased fourfold with riboflavin and fivefold with PQQ. In the presence of recombinant human CPR, CO production was threefold greater with PQQ than with riboflavin. These observations demonstrate for the first time that riboflavin and PQQ facilitate tissue-specific CO production with significant contributions from CPR. We propose a novel biochemical role for these nutrients in gastransmission.

Electron Paramagnetic Resonance Spectroscopic Identification of the Fe-S Clusters in the SPASM Domain-Containing Radical SAM Enzyme PqqE

Pyrroloquinoline quinone (PQQ) is an important redox active quinocofactor produced by a wide variety of bacteria. A key step in PQQ biosynthesis is a carbon-carbon cross-link reaction between glutamate and tyrosine side chains within the ribosomally synthesized peptide substrate PqqA. This reaction is catalyzed by the radical SAM enzyme PqqE. Previous X-ray crystallographic and spectroscopic studies suggested that PqqE, like the other members of the SPASM domain family, contains two auxiliary Fe-S clusters (AuxI and AuxII) in addition to the radical SAM [4Fe-4S] cluster. However, a clear assignment of the electron paramagnetic resonance (EPR) signal of each Fe-S cluster was hindered by the isolation of a His₆-tagged PqqE variant with an altered AuxI cluster. In this work, we are able to isolate soluble PqqE variants by using a less disruptive strep-tactin chromatographic approach. We have unambiguously identified the EPR signatures for four forms of Fe-S clusters present in PqqE through the use of multifrequency EPR spectroscopy: the RS [4Fe-4S] cluster, the AuxII [4Fe-4S] cluster, and two different clusters ([4Fe-4S] and [2Fe-2S]) bound in the AuxI site. The RS [4Fe-4S] cluster, the AuxII [4Fe-4S] cluster, and the [2Fe-2S] cluster form in the AuxI site can all be reduced by sodium dithionite, with g tensors of their reduced form determined as [2.040, 1.927, 1.897], [2.059, 1.940, 1.903], and [2.004, 1.958, 1.904], respectively. The AuxI [4Fe-4S] cluster that is determined on the basis of its relaxation profile can be reduced only by using low-potential reductants such as Ti(III) citrate or Eu(II)-DTPA to give rise to a g₁ = 2.104 signal. Identification of the EPR signature for each cluster paves the way for further investigations of SPASM domain radical SAM enzymes.

Crystal Structure of the Catalytic and Cytochrome b Domains in a Eukaryotic Pyrroloquinoline Quinone-Dependent Dehydrogenase

Pyrroloquinoline quinone (PQQ) is known as the “third coenzyme” following nicotinamide and flavin. PQQ-dependent enzymes have previously been found only in prokaryotes, and the existence of a eukaryotic PQQ-dependent enzyme was in doubt. In 2014, we found an enzyme in mushrooms that catalyzes the oxidation of various sugars in a PQQ-dependent manner and that was a PQQ-dependent enzyme found in eukaryotes. This paper presents the X-ray crystal structures of this eukaryotic PQQ-dependent quinohemoprotein, which show the active site, and identifies the amino acid residues involved in the binding of the cofactor PQQ. The presented X-ray structures reveal that the AA12 domain is in a binary complex with the coenzyme, clearly proving that PQQ-dependent enzymes exist in eukaryotes as well as prokaryotes. Because no biosynthetic system for PQQ has been reported in eukaryotes, future research on the symbiotic systems is expected.

Pyrroloquinoline quinone (PQQ) was discovered as a redox cofactor of prokaryotic glucose dehydrogenases in the 1960s, and subsequent studies have demonstrated its importance not only in bacterial systems but also in higher organisms. We have previously reported a novel eukaryotic quinohemoprotein that exhibited PQQ-dependent catalytic activity in a eukaryote. The enzyme, pyranose dehydrogenase (PDH), from the filamentous fungus Coprinopsis cinerea (CcPDH) of the Basidiomycete division, is composed of a catalytic PQQ-dependent domain classified as a member of the novel auxiliary activity family 12 (AA12), an AA8 cytochrome b domain, and a family 1 carbohydrate-binding module (CBM1), as defined by the Carbohydrate-Active Enzymes (CAZy) database. Here, we present the crystal structures of the AA12 domain in its apo- and holo-forms and the AA8 domain of this enzyme. The crystal structures of the holo-AA12 domain bound to PQQ provide direct evidence that eukaryotes have PQQ-dependent enzymes. The AA12 domain exhibits a six-blade β-propeller fold that is also present in other known PQQ-dependent glucose dehydrogenases in bacteria. A loop structure around the active site and a calcium ion binding site are unique among the known structures of bacterial quinoproteins. The AA8 cytochrome domain has a positively charged area on its molecular surface, which is partly due to the propionate group of the heme interacting with Arg181; this feature differs from the characteristics of cytochrome b in the AA8 domain of the fungal cellobiose dehydrogenase and suggests that this difference may affect the pH dependence of electron transfer.

IMPORTANCE Pyrroloquinoline quinone (PQQ) is known as the “third coenzyme” following nicotinamide and flavin. PQQ-dependent enzymes have previously been found only in prokaryotes, and the existence of a eukaryotic PQQ-dependent enzyme was in doubt. In 2014, we found an enzyme in mushrooms that catalyzes the oxidation of various sugars in a PQQ-dependent manner and that was a PQQ-dependent enzyme found in eukaryotes. This paper presents the X-ray crystal structures of this eukaryotic PQQ-dependent quinohemoprotein, which show the active site, and identifies the amino acid residues involved in the binding of the cofactor PQQ. The presented X-ray structures reveal that the AA12 domain is in a binary complex with the coenzyme, clearly proving that PQQ-dependent enzymes exist in eukaryotes as well as prokaryotes. Because no biosynthetic system for PQQ has been reported in eukaryotes, future research on the symbiotic systems is expected.

Negative effects of ROS generated during linear sperm motility on gene expression and ATP generation in boar sperm mitochondria

Mitochondrial oxidative phosphorylation (OXPHOS) is essential for ATP production to maintain sperm linear motility during migration from the uterus to the oviduct. However, ROS are generated as by-products of OXPHOS, causing stress and damaging the sperm quality. This study aimed to clarify the ROS targets in sperm mitochondria that decrease linear motility and to investigate whether mitochondria-target antioxidants (PQQ and CoQ10) affect mitochondrial activity and sperm motility. Sperm linear motility pattern, ATP production, and mitochondrial activity were decreased with increasing ROS levels during incubation in the low-glucose medium. However, sperm motility patterns and ROS levels were not significantly changed in the high-glucose medium. Moreover, the gene expression system (mt-DNA, mitochondrial transcription factor-A (TFAM) and RNA polymerase (POLRMT)) in sperm mitochondria was damaged during incubation in the low-glucose medium. Interestingly, PQQ treatment increased the mt-DNA stability and decreased the damage to TFAM and POLRMT, which resulted in high expression of mitochondrial genes. Furthermore, the antioxidants increased mitochondrial activity and maintained sperm linear motility under the low glucose condition. These results revealed that both ATP production and the mitochondrial transcription system are damaged with increasing ROS levels in sperm that show a linear motility pattern. Treatment with antioxidants, such as PQQ and CoQ10, is beneficial tool to maintain sperm linear motility.

A two-component protease in Methylorubrum extorquens with high activity toward the peptide precursor of the redox cofactor pyrroloquinoline quinone

Pyrroloquinoline quinone is a prominent redox cofactor in many prokaryotes, produced from a ribosomally synthesized and post-translationally modified peptide PqqA via a pathway comprising four conserved proteins PqqB-E. These four proteins are now fairly well-characterized and span radical SAM activity (PqqE), aided by a peptide chaperone (PqqD), a dual hydroxylase (PqqB), and an eight-electron, eight-proton oxidase (PqqC). A full description of this pathway has been hampered by a lack of information regarding a protease/peptidase required for the excision of an early, cross-linked di-amino acid precursor to pyrroloquinoline quinone. Herein, we isolated and characterized a two-component heterodimer protein from the α-proteobacterium Methylobacterium (Methylorubrum) extorquens that can rapidly catalyze cleavage of PqqA into smaller peptides. Using pulldown assays, surface plasmon resonance, and isothermal calorimetry, we demonstrated the formation of a complex PqqF/PqqG, with a K_D of 300 nm We created a molecular model of the heterodimer by comparison with the Sphingomonas sp. A1 M16B Sph2681/Sph2682 protease. Analysis of time-dependent patterns for the appearance of proteolysis products indicates high specificity of PqqF/PqqG for serine side chains. We hypothesize that PqqF/PqqG initially cleaves between the PqqE/PqqD-generated cross-linked form of PqqA, with nonspecific cellular proteases completing the release of a suitable substrate for the downstream enzyme PqqB. The finding of a protease that specifically targets serine side chains is rare, and we propose that this activity may be useful in proteomic analyses of the large family of proteins that have undergone post-translational phosphorylation at serine.

Transcriptome analysis of the effect of pyrroloquinoline quinone disodium (PQQ·Na2) on reproductive performance in sows during gestation and lactation

Background

Pyrroloquinoline quinone (PQQ), which is a water soluble, thermo-stable triglyceride-quinone, is widely distributed in nature and characterized as a mammalian vitamin-like redox cofactor. The objective of this study was to investigate the effects of pyrroloquinoline quinone disodium (PQQ·Na₂) on reproductive performance in sows.

Results

Dietary supplementation with PQQ·Na₂ significantly increased the total number of piglets born, the number of piglets born alive and the born alive litter weight. It also increased the antioxidant status in the placenta, plasma and milk. The concentration of NO was significantly increased in the plasma and placenta. RNA-seq analysis showed that 462 unigenes were differentially expressed between the control (Con) treatment and PQQ treatment groups. Among these unigenes, 199 were upregulated, while 263 unigenes were downregulated. The assigned functions of the unigenes covered a broad range of GO categories. Reproduction (27, 7.03%) and the reproduction process (27, 7.03%) were assigned to the biological process category. By matching DEGs to the KEGG database, we identified 29 pathways.

Conclusions

In conclusion, dietary supplementation with PQQ·Na₂ in gestating and lactating sows had positive effects on their reproductive performance.

Electronic supplementary material

The online version of this article (10.1186/s40104-019-0369-y) contains supplementary material, which is available to authorized users.

Methods for Expression, Purification, and Characterization of PqqE, a Radical SAM Enzyme in the PQQ Biosynthetic Pathway

PqqE is the first enzyme in the biosynthetic pathway of the redox cofactor pyrroloquinoline quinone (PQQ), catalyzing the formation of a carbon-carbon bond in the precursor peptide PqqA. PqqE is a radical S-adenosyl-l-methionine (SAM) (RS) enzyme, a family of enzymes that use the reductive cleavage of a [4Fe-4S] cluster-bound SAM molecule to generate a 5'-deoxyadenosyl radical. This radical is then used to initiate an array of reactions that otherwise would be unlikely to occur. PqqE is a founding member of a subset family of RS enzymes that, additionally to the SAM [4Fe-4S] cluster, have a SPASM domain containing additional, auxiliary Fe-S clusters. Most radical SAM enzymes are highly sensitive to oxygen, which destroys their Fe-S clusters. This can pose several limitations when working with these enzymes, since most of the work has to be done under anaerobic conditions. Here, we summarize the methods developed in our lab for the expression and purification of PqqE. We also highlight the several methods we have used for the characterization of the enzyme.

Pyrroloquinoline Quinone Prevents Estrogen Deficiency-Induced Osteoporosis by Inhibiting Oxidative Stress and Osteocyte Senescence

Accumulating studies have shown that oxidative stress increases with aging, which is related to the pathophysiology of postmenopausal osteoporosis. Pyrroloquinoline quinone (PQQ) is a natural anti-oxidant with anti-oxidative and anti-aging effects. However, it is unclear whether PQQ has a protective role against estrogen deficiency-induced osteoporosis. Here, we evaluated the efficacy of PQQ on bone mineral density, bone microarchitecture, bone turnover and biomechanical strength in ovariectomy (OVX)-induced osteoporosis mouse model. Although dietary PQQ supplement did not affect serum E2 levels and uterine weight in OVX mice, it could prevent OVX-induced bone loss and improve bone strength by inhibiting oxidative stress, osteocyte senescence and senescence-associated secretory phenotype (SASP), subsequently promoting osteoblastic bone formation and inhibiting osteoclastic bone resorption, which was comparable to treatment with exogenous estrogen. The results from our study provide experimental evidence for the clinical use of PQQ to prevent estrogen deficiency-induced osteoporosis.

Fungal PQQ-dependent dehydrogenases and their potential in biocatalysis

In 2014, the first fungal pyrroloquinoline-quinone (PQQ)-dependent enzyme was discovered as a pyranose dehydrogenase from the basidiomycete Coprinopsis cinerea (CcPDH). This discovery laid the foundation for a new Auxiliary Activities (AA) family, AA12, in the Carbohydrate-Active enZymes (CAZy) database and revealed a novel enzymatic activity potentially involved in biomass conversion. This review summarizes recent progress made in research on this fungal oxidoreductase and related enzymes. CcPDH consists of the catalytic PQQ-binding AA12 domain, an N-terminal cytochrome b AA8 domain, and a C-terminal family 1 carbohydrate-binding module (CBM1). CcPDH oxidizes 2-keto-d-glucose (d-glucosone), l-fucose, and rare sugars such as d-arabinose and l-galactose, and can activate lytic polysaccharide monooxygenases (LPMOs). Bioinformatic studies suggest a widespread occurrence of quinoproteins in eukaryotes as well as prokaryotes.

Pyrroloquinoline quinone-dependent dehydrogenases of acetic acid bacteria

Pyrroloquinoline quinone (PQQ)-dependent dehydrogenases (quinoproteins) of acetic acid bacteria (AAB), such as the membrane-bound alcohol dehydrogenase (ADH) and the membrane-bound glucose dehydrogenase, contain PQQ as the prosthetic group. Most of them are located on the periplasmic surface of the cytoplasmic membrane, and function as primary dehydrogenases in cognate substance-oxidizing respiratory chains. Here, we have provided an overview on the function and molecular architecture of AAB quinoproteins, which can be categorized into six groups according to the primary amino acid sequences. Based on the genomic data, we discuss the types of quinoproteins found in AAB genome and how they are distributed. Our analyses indicate that a significant number of uncharacterized orphan quinoproteins are present in AAB. By reviewing recent experimental developments, we discuss how to characterize the as-yet-unknown enzymes. Moreover, our bioinformatics studies also provide insights on how quinoproteins have developed into intricate enzymes. ADH comprises at least two subunits: the quinoprotein dehydrogenase subunit encoded by adhA and the cytochrome subunit encoded by adhB, and the genes are located in a polycistronic transcriptional unit. Findings on stand-alone derivatives of adhA encourage us to speculate on a possible route for ADH development in the evolutional history of AAB. A combination of bioinformatics studies on big genome sequencing data and wet studies assisted with genetic engineering would unravel biochemical functions and physiological role of uncharacterized quinoproteins in AAB, or even in unculturable metagenome.

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.

Lifespan extension by peroxidase and dual oxidase-mediated ROS signaling through pyrroloquinoline quinone in C. elegans

Reactive oxygen species (ROS), originally characterized based on their harmful effects on cells or organisms, are now recognized as important signal molecules regulating various biological processes. In particular, low levels of ROS released from mitochondria extend lifespan. Here, we identified a novel mechanism of generating appropriate levels of ROS at the plasma membrane through a peroxidase and dual oxidase (DUOX) system, which could extend lifespan in Caenorhabditis elegans A redox co-factor, pyrroloquinoline quinone (PQQ), activates the C. elegans DUOX protein BLI-3 to produce the ROS H₂O₂ at the plasma membrane, which is subsequently degraded by peroxidase (MLT-7), eventually ensuring adequate levels of ROS. These ROS signals are transduced mainly by the oxidative stress transcriptional factors SKN-1 (Nrf2 or NFE2L2 in mammals) and JUN-1, and partially by DAF-16 (a FOXO protein homolog). Cell biology experiments demonstrated a similarity between the mechanisms of PQQ-induced activation of human DUOX1 and DUOX2 and that of C. elegans BLI-3, suggesting that DUOXs are potential targets of intervention for lifespan extension. We propose that low levels of ROS, fine-tuned by the peroxidase and dual oxidase system at the plasma membrane, act as second messengers to extend lifespan by the effect of hormesis.

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

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

Early PQQ supplementation has persistent long-term protective effects on developmental programming of hepatic lipotoxicity and inflammation in obese mice

Nonalcoholic fatty liver disease (NAFLD) is widespread in adults and children. Early exposure to maternal obesity or Western-style diet (WD) increases steatosis and oxidative stress in fetal liver and is associated with lifetime disease risk in the offspring. Pyrroloquinoline quinone (PQQ) is a natural antioxidant found in soil, enriched in human breast milk, and essential for development in mammals. We investigated whether a supplemental dose of PQQ, provided prenatally in a mouse model of diet-induced obesity during pregnancy, could protect obese offspring from progression of NAFLD. PQQ treatment given pre- and postnatally in WD-fed offspring had no effect on weight gain but increased metabolic flexibility while reducing body fat and liver lipids, compared with untreated obese offspring. Indices of NAFLD, including hepatic ceramide levels, oxidative stress, and expression of proinflammatory genes (Nos2, Nlrp3, Il6, and Ptgs2), were decreased in WD PQQ-fed mice, concomitant with increased expression of fatty acid oxidation genes and decreased Pparg expression. Notably, these changes persisted even after PQQ withdrawal at weaning. Our results suggest that supplementation with PQQ, particularly during pregnancy and lactation, protects offspring from WD-induced developmental programming of hepatic lipotoxicity and may help slow the advancing epidemic of NAFLD in the next generation.-Jonscher, K. R., Stewart, M. S., Alfonso-Garcia, A., DeFelice, B. C., Wang, X. X., Luo, Y., Levi, M., Heerwagen, M. J. R., Janssen, R. C., de la Houssaye, B. A., Wiitala, E., Florey, G., Jonscher, R. L., Potma, E. O., Fiehn, O. Friedman, J. E. Early PQQ supplementation has persistent long-term protective effects on developmental programming of hepatic lipotoxicity and inflammation in obese mice.

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.

NAD(P)H-dependent quinone oxidoreductase 1 (NQO1) and cytochrome P450 oxidoreductase (CYP450OR) differentially regulate menadione-mediated alterations in redox status, survival and metabolism in pancreatic β-cells

NQO1 (NAD(P)H-quinone oxidoreductase 1) reduces quinones and xenobiotics to less-reactive compounds via 2-electron reduction, one feature responsible for the role of NQO1 in antioxidant defense in several tissues. In contrast, NADPH cytochrome P450 oxidoreductase (CYP450OR), catalyzes the 1-electron reduction of quinones and xenobiotics, resulting in enhanced superoxide formation. However, to date, the roles of NQO1 and CYP450OR in pancreatic β-cell metabolism under basal conditions and oxidant challenge have not been characterized. Using NQO1 inhibition, over-expression and knock out, we have demonstrated that, in addition to protection of β-cells from toxic concentrations of the redox cycling quinone menadione, NQO1 also regulates the basal level of reduced-to-oxidized nucleotides, suggesting other role(s) beside that of an antioxidant enzyme. In contrast, over-expression of NADPH cytochrome P450 oxidoreductase (CYP450OR) resulted in enhanced redox cycling activity and decreased cellular viability, consistent with the enhanced generation of superoxide and H₂O₂. Basal expression of NQO1 and CYP450OR was comparable in isolated islets and liver. However, NQO1, but not CYP450OR, was strongly induced in β-cells exposed to menadione. NQO1 and CYP450OR exhibited a reciprocal preference for reducing equivalents in β-cells: while CYP450OR preferentially utilized NADPH, NQO1 primarily utilized NADH. Together, these results demonstrate that NQO1 and CYP450OR reciprocally regulate oxidant metabolism in pancreatic β-cells.

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

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

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

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