Pyrroloquinoline quinone (PQQ) has potential to ameliorate streptozotocin-induced diabetes mellitus and oxidative stress in mice: A histopathological and biochemical study

Insights into the Sources, Structure, and Action Mechanisms of Quinones on Diabetes: A Review

Quinones, one of the oldest organic compounds, are of increasing interest due to their abundant presence in a wide range of natural sources and their remarkable biological activity. These compounds occur naturally in green leafy vegetables, fruits, herbs, animal and marine sources, and fermented products, and have demonstrated promising potential for use in health interventions, particularly in the prevention and management of type 2 diabetes (T2DM). This review aims to investigate the potential of quinones as a health intervention for T2DM from the multidimensional perspective of their sources, types, structure-activity relationship, glucose-lowering mechanism, toxicity reduction, and bioavailability enhancement. Emerging research highlights the hypoglycemic activities of quinones, mainly driven by their redox properties, which lead to covalent binding, and their structural substituent specificity, which leads to their non-covalent binding to biocomplexes. Quinones can improve insulin resistance and regulate glucose homeostasis by modulating mitochondrial function, inflammation, lipid profile, gastrointestinal absorption, and by acting as insulin mimetics. Meanwhile, increasing attention is being given to research focused on mitigating the toxicity of quinones during administration and enhancing their bioavailability. This review offers a critical foundation for the development of quinone-based health therapies and functional foods aimed at diabetes management.

Metabolic and Biochemical Effects of Pyrroloquinoline Quinone (PQQ) on Inflammation and Mitochondrial Dysfunction: Potential Health Benefits in Obesity and Future Perspectives

Obesity is defined as a complex, systemic disease characterized by excessive and dysfunctional adipose tissue, leading to adverse health effects. This condition is marked by low-grade inflammation, oxidative stress, and metabolic abnormalities, including mitochondrial dysfunction. These factors promote energy dysregulation and impact body composition not only by increasing body fat but also by promoting skeletal muscle mass atrophy. The decline in muscle mass is associated with an increased risk of all-cause mortality in individuals with this disease. The European Food Safety Authority approved pyrroloquinoline quinone (PQQ), a natural compound, as a dietary supplement in 2018. This narrative review aims to provide a comprehensive overview of the potential role of PQQ, based on its anti-inflammatory and antioxidant properties, in addressing dysfunctional adipose tissue metabolism and related disorders.

Novel Insights into the Antimicrobial and Antibiofilm Activity of Pyrroloquinoline Quinone (PQQ); In Vitro, In Silico, and Shotgun Proteomic Studies

Microbial infections pose a significant global health threat, affecting millions of individuals and leading to substantial mortality rates. The increasing resistance of microorganisms to conventional treatments requires the development of novel antimicrobial agents. Pyrroloquinoline quinone (PQQ), a natural medicinal drug involved in various cellular processes, holds promise as a potential antimicrobial agent. In the present study, our aim was, for the first time, to explore the antimicrobial activity of PQQ against 29 pathogenic microbes, including 13 fungal strains, 8 Gram-positive bacteria, and 8 Gram-negative bacteria. Our findings revealed potent antifungal properties of PQQ, particularly against Syncephalastrum racemosum, Talaromyces marneffei, Candida lipolytica, and Trichophyton rubrum. The MIC values varied between fungal strains, and T. marneffei exhibited a lower MIC, indicating a greater susceptibility to PQQ. In addition, PQQ exhibited notable antibacterial activity against Gram-positive and -negative bacteria, with a prominent inhibition observed against Staphylococcus epidermidis, Proteus vulgaris, and MRSA strains. Remarkably, PQQ demonstrated considerable biofilm inhibition against the MRSA, S. epidermidis, and P. vulgaris strains. Transmission electron microscopy (TEM) studies revealed that PQQ caused structural damage and disrupted cell metabolism in bacterial cells, leading to aberrant morphology, compromised cell membrane integrity, and leakage of cytoplasmic contents. These findings were further affirmed by shotgun proteomic analysis, which revealed that PQQ targets several important cellular processes in bacteria, including membrane proteins, ATP metabolic processes, DNA repair processes, metal-binding proteins, and stress response. Finally, detailed molecular modeling investigations indicated that PQQ exhibits a substantial binding affinity score for key microbial targets, including the mannoprotein Mp1P, the transcriptional regulator TcaR, and the endonuclease PvuRTs1I. Taken together, our study underscores the effectiveness of PQQ as a broad-spectrum antimicrobial agent capable of combating pathogenic fungi and bacteria, while also inhibiting biofilm formation and targeting several critical biological processes, making it a promising therapeutic option for biofilm-related infections.

Oxidative stress resistance prompts pyrroloquinoline quinone biosynthesis in Hyphomicrobium denitrificans H4-45

Pyrroloquinoline quinone (PQQ) is a natural antioxidant with diverse applications in food and pharmaceutical industries. A lot of effort has been devoted toward the discovery of PQQ high-producing microbial species and characterization of biosynthesis, but it is still challenging to achieve a high PQQ yield. In this study, a combined strategy of random mutagenesis and adaptive laboratory evolution (ALE) with fermentation optimization was applied to improve PQQ production in Hyphomicrobium denitrificans H4-45. A mutant strain AE-9 was obtained after nearly 400 generations of UV-LiCl mutagenesis, followed by an ALE process, which was conducted with a consecutive increase of oxidative stress generated by kanamycin, sodium sulfide, and potassium tellurite. In the flask culture condition, the PQQ production in mutant strain AE-9 had an 80.4% increase, and the cell density increased by 14.9% when compared with that of the initial strain H4-45. Moreover, batch and fed-batch fermentation processes were optimized to further improve PQQ production by pH control strategy, methanol and H2O2 feed flow, and segmented fermentation process. Finally, the highest PQQ production and productivity of the mutant strain AE-9 reached 307 mg/L and 4.26 mg/L/h in a 3.7-L bioreactor, respectively. Whole genome sequencing analysis showed that genetic mutations in the ftfL gene and thiC gene might contribute to improving PQQ production by enhancing methanol consumption and cell growth in the AE-9 strain. Our study provided a systematic strategy to obtain a PQQ high-producing mutant strain and achieve high production of PQQ in fermentation. These practical methods could be applicable to improve the production of other antioxidant compounds with uncleared regulation mechanisms. KEY POINTS: • Improvement of PQQ production by UV-LiCl mutagenesis combined with adaptive laboratory evolution (ALE) and fermentation optimization. • A consecutive increase of oxidative stress could be used as the antagonistic factor for ALE to enhance PQQ production. • Mutations in the ftfL gene and thiC gene indicated that PQQ production might be increased by enhancing methanol consumption and cell growth.

Pyrroloquinoline-quinone to reduce fat accumulation and ameliorate obesity progression

Obesity is a major health concern worldwide, and its prevalence continues to increase in several countries. Pyrroloquinoline quinone (PQQ) is naturally found in some foods and is available as a dietary supplement in its disodium crystal form. The potential health benefits of PQQ have been studied, considering its antioxidant and anti-inflammatory properties. Furthermore, PQQ has been demonstrated to significantly influence the functions of mitochondria, the organelles responsible for energy production within cells, and their dysfunction is associated with various health conditions, including obesity complications. Here, we explore PQQ properties that can be exploited in obesity treatment and highlight the underlying molecular mechanisms. We review animal and cell culture studies demonstrating that PQQ is beneficial for reducing the accumulation of visceral and hepatic fat. In addition to inhibiting lipogenesis, PQQ can increase mitochondria number and function, leading to improved lipid metabolism. Besides diet-induced obesity, PQQ ameliorates programing obesity of the offspring through maternal supplementation and alters gut microbiota, which reduces obesity risk. In obesity progression, PQQ mitigates mitochondrial dysfunction and obesity-associated inflammation, resulting in the amelioration of the progression of obesity co-morbidities, including non-alcoholic fatty liver disease, chronic kidney disease, and Type 2 diabetes. Overall, PQQ has great potential as an anti-obesity and preventive agent for obesity-related complications. Although human studies are still lacking, further investigations to address obesity and associated disorders are still warranted.

An Efficient UPLC-MS/MS Method for the Determination of Pyrroloquinoline Quinone in Rat Plasma and Its Application to a Toxicokinetic Study

Pyrroloquinoline quinone (PQQ) is a powerful antioxidant coenzyme existing in diet, benefiting growth, development, cognition function, and the repair of damaged organs. However, a method for detecting PQQ in vivo was rarely described, limiting the research on the bioanalysis and metabolic properties of PQQ. In this study, a novel, simple, and efficient ultra-high performance liquid chromatography/tandem mass spectrometry (UPLC-MS/MS) method was developed and validated to quantify the concentration of PQQ in rat plasma. Detection through mass spectrometry was operated by multiple reaction monitoring (MRM) in negative electrospray ionization mode with ion transitions m/z 328.99→197.05 for PQQ and m/z 280.04→195.04 for the internal standard. The calibration curves were linear up to 10,000 ng/mL, with a lower limit of quantitation of 10 ng/mL. Inter-run and intra-run precision ranged from 1.79% to 10.73% and accuracy ranged from -7.73% to 7.30%. The method was successfully applied to a toxicokinetic study in Sprague-Dawley rats after the oral administration of PQQ disodium salt at doses of 250 mg/kg, 500 mg/kg, and 1000 mg/kg. The toxicokinetic parameters were subsequently analyzed, which may provide valuable references for the toxicokinetic properties and safety evaluation of PQQ.

Hepatoprotective Effect of Actinidia deliciosa against Streptozotocin-Induced Oxidative Stress, Apoptosis, and Inflammations in Rats

The present research intended to assess the possible protective and hypoglycemic effect of Actinidia deliciosa fruit aqueous extract (ADAE) in diabetic rats. The scavenging antioxidant capabilities of ADAE were evaluated using GC-MS analysis. In addition, rats were divided into four groups: control, ADAE, streptozotocin-induced DM (STZ), and STZ-treated rats + ADAE in an in vivo investigation. GC-MS analysis of ADAE was shown to include major components with high total phenolic contents and high DPPH scavenging activity. In diabetic rats, significant elevation in blood glucose level, lipid peroxidation, bilirubin, and lactate dehydrogenase activity as well as a change in lipid profile was observed, while insulin, body and liver weights, enzymatic and nonenzymatic antioxidants, liver function biomarkers, and protein content were significantly decreased. Furthermore, changes in the expression of the peroxisome proliferator-activated receptor (PPAR-γ), apoptotic, and inflammation-related genes were found. In addition, histological differences in rat liver tissue architecture were discovered, corroborating the biochemical modifications. However, consuming ADAE alone reduced lipid peroxidation and improved antioxidant status. Furthermore, diabetic rats given ADAE showed significant reductions in oxidative stress indicators and biochemical parameters, as well as improved tissue structure, when compared to the diabetic rats' group. Also, ADAE supplementation protects diabetic rats' hepatic tissue by upregulating PPAR-γ and downregulating apoptotic and inflammatory-related gene expression. In conclusion, A. deliciosa has beneficial protective effects so, it might be used as a complementary therapy in diabetes mellitus.

Pyrroloquinoline quinone ameliorates diabetic cardiomyopathy by inhibiting the pyroptosis signaling pathway in C57BL/6 mice and AC16 cells

Purpose

Diabetic cardiomyopathy (DCM), a common complication of diabetes mellitus and is characterized by myocardial hypertrophy and myocardial fibrosis. Pyrroloquinoline quinone (PQQ), a natural nutrient, exerts strong protection against various myocardial diseases. Pyroptosis, a type of inflammation-related programmed cell death, is vital to the development of DCM. However, the protective effects of PQQ against DCM and the associated mechanisms are not clear. This study aimed to investigate whether PQQ protected against DCM and to determine the underlying molecular mechanism.

Methods

Diabetes was induced in mice by intraperitoneal injection of streptozotocin, after which the mice were administered PQQ orally (10, 20, or 40 mg/kg body weight/day) for 12 weeks. AC16 human myocardial cells were divided into the following groups and treated accordingly: control (5.5 mmol/L glucose), high glucose (35 mmol/L glucose), and HG + PQQ groups (1 and 10 nmol/L PQQ). Cells were treated for 24 h.

Results

PQQ reduced myocardial hypertrophy and the area of myocardial fibrosis, which was accompanied by an increase in antioxidant function and a decrease in inflammatory cytokine levels. Moreover, myocardial hypertrophy—(ANP and BNP), myocardial fibrosis—(collagen I and TGF-β1), and pyroptosis-related protein levels decreased in the PQQ treatment groups. Furthermore, PQQ abolished mitochondrial dysfunction and the activation of NF-κB/IκB, and decreased NLRP3 inflammation-mediated pyroptosis in AC16 cells under high-glucose conditions.

Conclusion

PQQ improved DCM in diabetic mice by inhibiting NF-κB/NLRP3 inflammasome-mediated cell pyroptosis. Long-term dietary supplementation with PQQ may be greatly beneficial for the treatment of DCM.

Graphical abstract

Diagram of the underlying mechanism of the effects of PQQ on DCM. PQQ inhibits ROS generation and NF-κB activation, which stimulates activation of the NLRP3 inflammasome and regulates the expression of caspase-1, IL-1β, and IL-18. The up-regulated inflammatory cytokines trigger myocardial hypertrophy and cardiac fibrosis and promote the pathological process of DCM.

PQQ Dietary Supplementation Prevents Alkylating Agent-Induced Ovarian Dysfunction in Mice

Alkylating agents (AAs) that are commonly used for cancer therapy cause great damage to the ovary. Pyrroloquinoline-quinine (PQQ), which was initially identified as a redox cofactor for bacterial dehydrogenases, has been demonstrated to benefit the fertility of females. The aim of this study was to investigate whether PQQ dietary supplementation plays a protective role against alkylating agent-induced ovarian dysfunction. A single dose of busulphan (20 mg/kg) and cyclophosphamide (CTX, 120 mg/kg) were used to establish a mouse model of ovarian dysfunction. Feed containing PQQNa₂ (5 mg/kg) was provided starting 1 week before the establishment of the mouse model until the date of sacrifice. One month later, estrous cycle period of mice were examined and recorded for consecutive 30 days. Three months later, some mice were mated with fertile male mice for fertility test. The remaining mice were sacrificed to collect serum samples and ovaries. One day before sacrifice, some mice received a single injection of BrdU to label proliferating cells. Serum samples were used for test hormonal levels. Ovaries were weighted and used to detect follicle counts, cell proliferation, cell apoptosis and cell senescence. In addition, the levels of inflammation, oxidative damage and Pgc1α expression were detected in ovaries. Results showed that PQQ treatment increased the ovarian weight and size, partially normalized the disrupted estrous cycle period and prevented the loss of follicles of mice treated with AAs. More importantly, we found that PQQ treatment significantly increased the pregnancy rate and litter size per delivery of mice treated with AAs. The protective effects of PQQ appeared to be directly mediated by promoting cell proliferation of granulosa, and inhibiting cell apoptosis of granulosa and cell senescence of ovarian stromal cells. The underlying mechanisms may attribute to the anti-oxidative stress, anti-inflammation and pro-mitochondria biogenesis effects of PQQ.Our study highlights the therapeutic potential of PQQ against ovarian dysfunction caused by alkylating agents.

Pyrroloquinoline quinone attenuated benzyl butyl phthalate induced metabolic aberration and a hepatic metabolomic analysis

Benzyl butyl phthalate (BBP) has recently been implicated as an obesogen. Our recent study demonstrated that BBP can exacerbate high fat diet (HFD) induced diabesity in male mice. Here, we explored if pyrroloquinoline quinone (PQQ), a natural antioxidant andphytochemical, can attenuate metabolic aberrations induced by HFD or HFD-BBPcombination. C57Bl/6 male and female mice were fed either a chow diet (CD) or HFD with or without BBP (3 mg/kg body weight/day)and/or PQQ (20 mg/kg/day)for 16 weeks. The mice's body and tissue weight, fasting blood glucose, glucose and insulin tolerance test, and liver metabolites level weremeasured. In HFD-fed male mice, PQQ significantly attenuated the increased body weight, liver weight, fasting blood glucose, and insulin intolerance under BBP exposure.Even though female mice did show some reversal of metabolic characteristics by PQQ, the response was not similar nor consistent with the male population. Amongthe 14 hepatic metabolites that were significantly altered by HFD compared to CD, only three major metabolites (acetyl-L-carnitine, DL-stachytine, and propionylcarnitine) were decreased. These three were shown to have more reduction under BBP exposure in the presence of HFD whereas with addition of PQQ, these metabolites were restored. Pathway analysis and literature search revealed that these metabolites were negatively associated with obesity and were involved in several pathways including beta-oxidation, oxidative stress, and mitochondrial function. Overall,this finding indicated the potential use of PQQ to restore thewide range of aberrant metabolic effectinduced by an obesogen in the presence of a western diet.

Pyrroloquinoline quinone (PQQ) alleviated sepsis-induced acute liver injury, inflammation, oxidative stress and cell apoptosis by downregulating CUL3 expression

PQQ has anti-inflammatory and anti-oxidant effects. PQQ can relieve high glucose-induced renal cell damage by suppressing Keap1 expression. Keap1 can interact with CUL3. Upregulation of CUL3 facilitates the apoptosis of LPS-induced podocytes. Based on knowledge above, this current work was designed to explore the role of PQQ in sepsis and determine the molecular function of CUL3 in the pathogenesis of sepsis. Rats received CLP surgery to establish sepsis models in vivo. Kupffer cells were pretreated with PQQ (10, 50 and 100 nmol/L) for 2 h and then treated with 100 ng/mL LPS for 24 h, simulating sepsis-induced acute liver injury in vitro. H&E staining was performed to evaluate liver injury of SD rats. Levels of inflammatory factors and oxidative stress markers were detected to assess inflammatory response and oxidative stress. Moreover, TUNEL staining, flow cytometric analysis and western blot were applied to determine cell apoptosis. It was confirmed that PQQ treatment relieved acute liver injury, inflammatory and oxidative stress damage and apoptosis of liver tissue cells in sepsis rats. In addition, PQQ therapy could alleviate inflammation, oxidative stress and apoptosis in LPS-induced Kupffer cells. Notably, LPS stimulation enhanced CUL3 expression and PQQ repressed CUL3 expression in Kupffer cells suffered from LPS. Overall, CUL3 overexpression weakened the remission effects of PQQ on LPS-induced inflammatory and oxidative damage and apoptosis of Kupffer cells. Mechanistically, PQQ treatment may mitigate sepsis-induced acute liver injury through downregulating CUL3 expression.

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.

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.

Effect of garden cress in reducing blood glucose, improving blood lipids, and reducing oxidative stress in a mouse model of diabetes induced by a high-fat diet and streptozotocin

BACKGROUND

A mouse model in which diabetes mellitus was induced by low-dose streptozotocin (STZ) injection combined with a high-fat diet was used to study the effect of two water cress (Lepidium savitum) preparations. Diabetic mice were treated with dried cress powder or with water-soluble extracts (tested at two doses), together with proper control groups. The mice were evaluated after 4 weeks of continuous intervention for type 2 diabetic and associated markers. We determined blood glucose, body weight, total cholesterol (TC), triglyceride (TG), low-density lipoprotein (LDL), high-density lipoprotein (HDL), serum insulin levels, and DNA integrity of hepatic cells. The concentrations of malondialdehyde (MDA) and lipid peroxide (LPO) and the activities of four enzymes that are part of the antioxidant defense system were determined in liver samples, as well as gene expression (by semi-quantitative reverse transcription polymerase chain reaction) and enzyme activity of IRS-1, IRS-2, PI3K, AKT-2, and GLUT4.

RESULTS

After 4 weeks of intervention, the levels of TC, TG, and LDL cholesterol were significantly (P < 0.5) decreased and HDL cholesterol was significantly increased. Enzyme activities of liver superoxide dismutase, glutathione, glutathione peroxidase, and catalase were significantly increased, whereas MDA and LPO concentrations were significantly reduced. The transcription level of the five genes assessed was increased, with corresponding increases in protein expression.

CONCLUSION

Oral uptake of garden cress can significantly reduce the blood glucose and improve the blood lipid metabolism of diabetic mice. Considerable improvements in the activity of antioxidant defense enzymes were observed in type 2 diabetic mice that improved the body's antioxidant emergency response. © 2019 Society of Chemical Industry.

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.

Adiponectin deficiency induces mitochondrial dysfunction and promotes endothelial activation and pulmonary vascular injury

Adiponectin (APN), an adipocyte-derived adipokine, has been shown to limit lung injury originating from endothelial cell (EC) damage. Previously we reported that obese mice with low circulatory APN levels exhibited pulmonary vascular endothelial dysfunction. This study was designed to investigate the cellular and molecular mechanisms underlying the pulmonary endothelium-dependent protective effects of APN. Our results demonstrated that in APN-/- mice, there was an inherent state of endothelium mitochondrial dysfunction that could contribute to endothelial activation and increased susceptibility to LPS-induced acute lung injury (ALI). We noted that APN-/- mice showed decreased expression of mitochondrial biogenesis regulatory protein peroxisome proliferator-activated receptor γ coactivator 1-α (PGC-1α) and its downstream proteins nuclear respiratory factor 1, transcription factor A, mitochondrial, and Sirtuin (Sirt)3 and Sirt1 expression in whole lungs and in freshly isolated lung ECs from these mice at baseline and subjected to LPS-induced ALI. We further showed that treating APN-/- mice with PGC-1α activator pyrroloquinoline quinone enhances mitochondrial biogenesis and function in lung endothelium and attenuation of ALI. These results suggest that the pulmonary endothelium-protective properties of APN are mediated, at least in part, by an enhancement of mitochondrial biogenesis through a mechanism involving PGC-1α activation.-Shah, D., Torres, C., Bhandari, V. Adiponectin deficiency induces mitochondrial dysfunction and promotes endothelial activation and pulmonary vascular injury.

The Improvement Effects of Gordonia bronchialis on Male Fertility of Rats with Diabetes Mellitus Induced by Streptozotocin

Background: This study evaluated the possible protective effects of Gordonia bronchialis (Gb) on oxidative stress and some subsequent alterations on testis from rats undergoing an experimentally induced type 1 diabetes. Methods: A total of 40 male rats were randomly divided into four groups of ten. Diabetes was induced by injection of 55 mg/kg streptozotocin in 30 rats. Oral administration of Gb at dose of 105 (low dose) and 107 (high dose) CFU/rat was performed in two groups continuously for 14 days. The third and fourth groups received normal saline as the diabetic and healthy control groups, respectively. The blood and testicular tissue samples were taken on the 14th and 21st days post treatment for biochemical and histopathological evaluations. Results: Significant differences were found in blood glucose level, insulin, IL-6 and TNF-α values together with catalase and superoxide dismutase activities and malondialdehyde level in the diabetic group in comparison with healthy and Gb recipient groups. Moreover, the histopathological lesions observed in the diabetic rats mainly included basement membrane thickening, decreased number of Sertoli cells, and severe reduction of spermatogenesis markedly attenuated in Gb-treated rats. Conclusion: Taken together, it seems that oral administration of Gb could ameliorate testicular damage associated with some related parameters in the diabetic animal model.

Current Models of Fatty Liver Disease; New Insights, Therapeutic Targets and Interventions

Non-alcoholic fatty liver disease (NAFLD) encompasses a spectrum of disorders ranging from simple steatosis to steatosis with inflammation and fibrosis. NAFLD is currently the most prevalent chronic liver disease worldwide, with a global prevalence of 25%, and is soon projected to be the leading cause for liver transplantation in the US. Alarmingly, few effective pharmacotherapeutic approaches are currently available to block or attenuate development and progression of NAFLD. Preclinical models are critical for unraveling the complex and multi-factorial etiology of NAFLD and for testing potential therapeutics. Here we review preclinical models that have been instrumental in highlighting molecular and cellular mechanisms underlying the pathogenesis of NAFLD and in facilitating early proof-of-concept investigations into novel intervention strategies.

Determination of pyrroloquinoline quinone by enzymatic and LC-MS/MS methods to clarify its levels in foods

Pyrroloquinoline quinone (PQQ) is believed to be a new B vitamin-like compound, and PQQ supplementation has received attention as a possible treatment for diseases including dementia and diabetes. However, the distribution of PQQ in foods is unclear, due to the difficulty in analyzing the compound. Therefore, in this study, enzymatic and LC-MS/MS methods were optimized to enable an accurate analysis of PQQ in foods. The optimized methods were applied to the screening of foods, in which PQQ contents were identified in ng/g or ng/mL levels. Furthermore, we newly found that some foods related to acetic acid bacteria contain PQQ at 1.94~5.59 ng/mL higher than beer, which is known to contain relatively high amounts of PQQ. These results suggest that the optimized methods are effective for the screening of foods containing PQQ. Such foods with high PQQ content may be valuable as functional foods effective towards the treatment of certain diseases.

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

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

Pyrroloquinoline quinone attenuates cachexia-induced muscle atrophy via suppression of reactive oxygen species

BACKGROUND

Cachexia, a wasting syndrome, is most commonly observed in individuals with advanced cancer including lung cancer, esophageal cancer, liver cancer, etc. The characteristic sign of cachexia is muscle atrophy. To date, effective countermeasures have been still deficiency to alleviate muscle atrophy. Reactive oxygen species (ROS) are important regulators of muscle atrophy. Therefore, the effects of a naturally antioxidant, pyrroloquinoline quinone (PQQ), were explored on muscle atrophy induced by cachexia in the present study.

METHODS

Tumor necrosis factor-α (TNF-α) induced C2C12 myotubes atrophy model was constructed. The atrophied C2C12 myotubes were dealt with the presence or absence of N-acetyl-L-cysteine (NAC, an antioxidant for ROS abolition) (5 mM) or PQQ (80 µM) for 24 hours. ROS content was determined by dichlorodihydrofluorescein diacetate (DCFH-DA) staining. The diameter of myotubes was analyzed by myosin heavy chain (MHC) staining. The protein levels of MHC, muscle atrophy F-box (MAFbx) and muscle RING finger-1 (MuRF-1) in each group were observed by Western blotting.

RESULTS

First, ROS generation was enhanced in C2C12 myotubes treated with TNF-α. NAC treatments significantly avoided the reduction in the diameter of C2C12 myotubes, and concomitantly increased MHC levels, and decreased ROS contents, MuRF1 and MAFbx levels. These data suggested that the increased ROS induced by TNF-α might play a central role in muscle wasting. PQQ (a naturally occurring antioxidant) administration inhibited C2C12 myotubes atrophy induced by TNF-α, as evidenced by the increase of the diameter of C2C12 myotubes, together with increased MHC levels and decreased ROS, MAFbx and MuRF-1 levels.

CONCLUSIONS

PQQ resists atrophic effect dependent on, at least in part, decreased ROS in skeletal muscle treated with TNF-α.

Oleanolic acid derivative DKS26 exerts antidiabetic and hepatoprotective effects in diabetic mice and promotes glucagon-like peptide-1 secretion and expression in intestinal cells

BACKGROUND AND PURPOSE

Glucagon-like peptide-1 (GLP-1) is an important target for diabetes therapy based on its key role in maintaining glucose and lipid homeostasis. This study was designed to investigate antidiabetic and hepatoprotective effects of a novel oleanolic acid derivative DKS26 in diabetic mice and elucidate its underlying GLP-1 related antidiabetic mechanisms in vitro and in vivo.

EXPERIMENTAL APPROACH

The therapeutic effects of DKS26 were investigated in streptozotocin (STZ)-induced and db/db diabetic mouse models. Levels of plasma glucose, glycosylated serum protein (GSP), lipid profiles, insulin, alanine aminotransferase (ALT) and aspartate aminotransferase (AST), oral glucose tolerance (OGT), pancreatic islets and hepatic histopathological morphology, liver lipid levels and expression of pro-inflammatory cytokines were assessed. Intestinal NCI-H716 cells and diabetic models were used to further validate its potential GLP-1-related antidiabetic mechanisms.

KEY RESULTS

DKS26 treatment (100 mg·kg^-1 ·day^-1 ) decreased plasma levels of glucose, GSP, ALT and AST; ameliorated OGT and plasma lipid profiles; augmented plasma insulin levels; alleviated islets and hepatic pathological morphology; and reduced liver lipid accumulation, inflammation and necrosis in vivo. Furthermore, DKS26 enhanced GLP-1 release and expression, accompanied by elevated levels of cAMP and phosphorylated PKA in vitro and in vivo.

CONCLUSION AND IMPLICATIONS

DKS26 exerted hypoglycaemic, hypolipidaemic and islets protective effects, which were associated with an enhanced release and expression of GLP-1 mediated by the activation of the cAMP/PKA signalling pathway, and alleviated hepatic damage by reducing liver lipid levels and inflammation. These findings firmly identified DKS26 as a new viable therapeutic option for diabetes control.

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.

Synergistic effect of pyrroloquinoline quinone and graphene nano-interface for facile fabrication of sensitive NADH biosensor

A self-assembly composite of graphene-pyrroloquinoline quinone (PQQ) was fabricated and modified on glassy carbon electrode (GCE) for sensitive detection of nicotinamide adenine dinucleotide (NADH). Chitosan (CTS) was applied to disperse graphene to form a stable robust film on GCE. A synergistic effect between PQQ and graphene was observed during the electrocatalytic oxidation of NADH, with about 260mV reduction in the oxidation potential and 2.5-fold increase in the oxidation current compared with those on the bare GCE. The electrochemical sensors based on the modified electrodes allowed the detection of NADH with a good linear dependence from 0.32 to 220µM with a high sensitivity of 0.421µAµM^-1cm^-2 and a low detection limit of 0.16µM (S/N=3). It could also eliminate the interference of electroactive substances like ascorbic acid (AA), uric acid, and dopamine and its derivatives. The outstanding performances of graphene-PQQ/CTS composite capable of improving the electrical conductivity and accelerating the electron transport suggested its promising applications for design of different graphene based composites used in electrochemical sensing and energy fields.