Pyrroloquinoline quinone attenuates iNOS gene expression in the injured spinal cord

Effects of pyrroloquinoline quinone on noise-induced and age-related hearing loss in mice

We investigated whether the oxidoreductase cofactor pyrroloquinoline quinone (PQQ) prevents noise-induced and age-related hearing loss (NIHL and ARHL) in mice. To assess NIHL, 8 week-old mice with and without PQQ administration were exposed to noise for 4 h. PQQ was orally administered for one week before and after noise exposure and subcutaneously once before noise exposure. For ARHL evaluation, mice were given drinking water with or without PQQ starting at 2 months of age. In the NIHL model, PQQ-treated mice had auditory brainstem response (ABR) thresholds of significantly reduced elevation at 8 kHz, a significantly increased number of hair cells at the basal turn, and significantly better maintained synapses beneath the inner hair cells compared to controls. In the ARHL model, PQQ significantly attenuated the age-related increase in ABR thresholds at 8 and 32 kHz at 10 months of age compared to controls. In addition, the hair cells, spiral ganglion cells, ribbon synapses, stria vascularis and nerve fibers were all significantly better maintained in PQQ-treated animals compared to controls at 10 months of age. These physiological and histological results demonstrate that PQQ protects the auditory system from NIHL and ARHL in mice.

Pyrroloquinoline Quinone Chemistry, Biology, and Biosynthesis

The widely distributed, essential redox factor pyrroloquinoline quinone (PQQ, methoxatin) (1) was discovered in the mid-1960s. The breadth and depth of its biological effects are steadily being revealed, and understanding its biosynthesis at the genomic level is a continuing process. In this review, aspects of the chemistry, biology, biosynthesis, and commercial production of 1 at the gene level, and some applications, are presented from discovery through to mid-2021.

Inhibit inflammation and apoptosis of pyrroloquinoline on spinal cord injury in rat

Background

Pyrroloquinoline quinone (PQQ) is a redox cofactor that can participate in a variety of physiological and biochemical processes, such as anti-inflammatory, cytoprotection, anti-aging, and anti-apoptosis. PQQ plays an important protective role in the central nervous system (CNS). However, the effects of PQQ on astrocytes of the CNS and spinal cord injury (SCI) of rats is still unclear. The present study investigates the role of PQQ in inflammation, apoptosis, and autophagy after SCI in rats. And the effect of PQQ on lipopolysaccharide (LPS)-induced apoptosis and inflammation of astrocytes in vitro, to explore the neuroprotective mechanism of PQQ.

Methods

Sixty specific pathogen free (SPF) SD male rats (200–250 g) were randomly divided into Normal group, Sham group, SCI group, and SCI + PQQ group, with 15 rats in each group. BBB score, HE staining, Nissl staining, Western blot, immunofluorescence, and other methods were used for detection.

Results

Our results showed that PQQ could upregulate BBB score in SCI rats. In the second place, PQQ can increase the number and improve the morphology of neurons after SCI. The expression of IL-1β, TNF-α, IL-6 was significantly decreased after PQQ treatment. And then, the ratio of B-cell lymphoma-2 (Bcl-2)/Bcl-2 associated X protein (Bax) increased significantly, and the positive signal of NeuN increased obviously after PQQ treatment. There are a large number of co-localizations between Bcl-2 and NeuN. Meanwhile, PQQ could down-regulate the expression of Active-Caspase3, and PQQ treatment could reverse the transfer of Active-Caspase3/Caspase3 from the cytoplasm to the nucleus in neurons and astrocytes after SCI. At the same time, PQQ had no significant effect on the LC3b/a ratio. PQQ could decrease the LAMP2 expression in spinal cord after injury. The expression level of phospho-Akt (p-AKT) increased after SCI and decreased after PQQ treatment. In primary astrocytes, LPS could induce the expression levels of IL-1β, TNF-α, and IL-6, and which were inhibited by PQQ treatment at 12 hours. After treatment with LPS, the expression level of Active-Caspase3 increased, which could be reversed by PQQ treatment for 24 h.

Conclusions

These results suggest that PQQ can ameliorate the motor function of hind limbs and the pathological changes of neurons and injured spinal cord after SCI, down-regulate the expressions of IL-1β, TNF-α, and IL-6, inhibit apoptosis after SCI, and inhibit LPS-induced apoptosis and inflammation of astrocytes.

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

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

Coaxial nanofibers outperform uniaxial nanofibers for the loading and release of pyrroloquinoline quinone (PQQ) for biomedical applications

Pyrroloquinoline quinone (PQQ), present in breast milk and various foods, is highly recommended as an antioxidant, anti-inflammatory agent, and a cofactor in redox reactions in several biomedical fields. Moreover, PQQ has neuroprotective effects on nervous system disorders and immunosuppressive effects on different diseases. Herein, we report on the optimum fabrication of electrospun CS/PVA coaxial, core/shell, and uniaxial nanofibers. The morphological, elemental, and chemical structure of the fabricated nanofibers were investigated and discussed. PQQ, as a drug, was loaded on the uniaxial nanofibers and in the core of the coaxial nanofibers and the sustained and controlled release of PQQ was compared and discussed. The results revealed the privilege of the coaxial over the uniaxial nanofibers in the sustained release and reduction of the initial burst of PQQ. Remarkably, the results revealed a higher degree of swelling for CS/PVA hollow nanofibers compared to that of the uniaxial and the coaxial nanofibers. The coaxial nanofibers showed a lower release rate than the uniaxial nanofibers. Moreover, the CS/PVA coaxial nanofibers loaded with PQQ were found to enhance cell viability and proliferation. Therefore, the CS/PVA coaxial nanofibers loaded with PQQ assembly is considered a superior drug delivery system for PQQ release.

Pyrroloquinoline quinone protected autophagy-dependent apoptosis induced by mono(2-ethylhexyl) phthalate in INS-1 cells

Mono(2-ethylhexyl) phthalate (MEHP) is the main metabolite of di(2-ethylhexyl) phthalate (DEHP) in organisms and is commonly used as a plasticizer. Exposure to DEHP impairs the function of islet beta cells (INS-1 cells), which is related to insulin resistance and type 2 diabetes. At present, some research data have also confirmed that MEHP has a certain damage effect on INS-1 cells. In our experiment, we found that MEHP would lead to the increase of reactive oxygen species (ROS) and the upregulation of autophagy. And downregulated ROS production by N-acetyl-L-cysteine could also reduce autophagy. In addition, MEHP-induced lysosomal membrane permeability (LMP) subsequently released cathepsin D. Additionally, MEHP induced the collapse of mitochondrial transmembrane potential and release of cytochrome c. Addition of autophagy inhibitor 3-methyladenine relieved MEHP-induced apoptosis as assessed by the expression of cleaved caspase 3, cleaved caspase 9, and terminal deoxynucleotidyl transferase dUTP nick end labeling assay, indicating that MEHP-induced apoptosis was autophagy dependent. Cathepsin D inhibitor, pepstatin A, suppressed MEHP-induced mitochondria release of cytochrome c and apoptosis as well. Meanwhile, pyrroloquinoline quinone (PQQ), a new B vitamin, improved the above phenomenon. Taken together, our results indicate that MEHP induces autophagy-dependent apoptosis in INS-1 cells by lysosomal-mitochondrial axis. PQQ improved this process by downregulating ROS and provided a degree of protection. Our study provides a new perspective for MEHP on the cytotoxic mechanism and PQQ protection in INS-1 cells.

The effects of oxyresveratrol abrogates inflammation and oxidative stress in rat model of spinal cord injury

Oxyresveratrol and its glycoside are important natural active materials. As an effective tyrosine kinase inhibitor, oxyresveratrol may prevent herpes virus infection, inflammation and oxidative stress, as well as protect nerves. In addition, it is known to inhibit cell apoptosis following cerebral ischemia. In recent years, oxyresveratrol and its glycoside have been widely investigated, and their useful biological activities have been explored, indicating that they may be worthy of further comprehensive research. The aim of the present study was to evaluate the photoprotective effects of oxyresveratrol and its ability to abrogate inflammation and oxidative stress in a rat model of spinal cord injury (SCI). The authors identified that oxyresveratrol significantly reversed the SCI‑induced inhibition of Basso, Beattie, and Bresnahan scores, inhibited the SCI‑mediated increase in spinal cord water content, significantly suppressed SCI‑induced nuclear factor‑κB/p65, tumor necrosis factor‑α, interleukin (IL)‑1β and IL‑6 activities and reversed the malondialdehyde, superoxide dismutase, glutathione (GSH) and GSH peroxidase activities in SCI rats. SCI‑induced granulocyte‑macrophage colony‑stimulating factor (GM‑CSF), inducible nitric oxide synthase (iNOS) and cyclo‑oxygenase‑2 (COX‑2) protein expression was significantly suppressed by oxyresveratrol, and SCI‑mediated inhibition of nuclear factor (erythroid‑derived 2)‑like 2 (Nrf2) protein expression was significantly increased by oxyresveratrol. In conclusion, these results suggest that the effects of oxyresveratrol restores SCI, and abrogates inflammation and oxidative stress in rat model of SCI via the GM‑CSF, iNOS, COX‑2 and Nrf2 signaling pathway.

Beneficial effects of a pyrroloquinolinequinone-containing dietary formulation on motor deficiency, cognitive decline and mitochondrial dysfunction in a mouse model of Alzheimer's disease

Alzheimer’s disease (AD), a progressive neurodegenerative disorder, is linked to oxidative stress, altered amyloid precursor protein (APP) proteolysis, tau hyperphosphorylation and the accumulation of amyloid-β (Aβ) plaques and neurofibrillary tangles (NFT). A growing body of evidence suggests that mitochondrial dysfunction can be a key promoter of all of these pathologies and predicts that restoration of mitochondrial function might be a potential therapeutic strategy for AD. Therefore, in the present study, we tested the beneficial effect of a nutraceutical formulation Nutrastem II (Nutra II), containing NT020 (a mitochondrial restorative and antioxidant proprietary formulation) and pyrroloquinolinequinone (PQQ, a stimulator of mitochondria biogenesis) in 5XFAD transgenic mice. Animals were fed Nutra II for 12 weeks, starting at 3 months of age, after which behavioral and neuropathological endpoints were determined. The data from behavioral test batteries clearly revealed that dietary supplementation of Nutra II effectively ameliorated the motor deficiency and cognitive impairment of 5XFAD mice. In addition, Nutra II also protected mitochondrial function in 5XFAD mice brain, as evidenced by declined ROS levels and membrane hyperpolarization, together with elevated ATP levels and respiratory states. Interestingly, while Nutra II treatment only slightly reduced soluble Aβ₄₂ levels, this formulation significantly impacted tau metabolism, as shown by reduced total and phosphorylated tau levels of 5XFAD mouse brain. Taken together, these preclinical findings confirm that mitochondrial function may be a key treatment target for AD and that Nutra II should be further investigated as a potential candidate for AD therapy.

Pyrroloquinoline quinone (PQQ) is reduced to pyrroloquinoline quinol (PQQH2) by vitamin C, and PQQH2 produced is recycled to PQQ by air oxidation in buffer solution at pH 7.4

Measurements of the reaction of sodium salt of pyrroloquinoline quinone (PQQNa2) with vitamin C (Vit C) were performed in phosphate-buffered solution (pH 7.4) at 25 °C under nitrogen atmosphere, using UV–vis spectrophotometry. The absorption spectrum of PQQNa2 decreased in intensity due to the reaction with Vit C and was changed to that of pyrroloquinoline quinol (PQQH2, a reduced form of PQQ). One molecule of PQQ was reduced by two molecules of Vit C producing a molecule of PQQH2 in the buffer solution. PQQH2, thus produced, was recycled to PQQ due to air oxidation. PQQ and Vit C coexist in many biological systems, such as vegetables, fruits, as well as in human tissues. The results obtained suggest that PQQ is reduced by Vit C and functions as an antioxidant in biological systems, because it has been reported that PQQH2 shows very high free-radical scavenging and singlet-oxygen quenching activities in buffer solutions.

Protective Effect of Pyrroloquinoline Quinone (PQQ) in Rat Model of Intracerebral Hemorrhage

Pyrroloquinoline quinone (PQQ) has invoked considerable interest because of its presence in foods, antioxidant properties, cofactor of dehydrogenase, and amine oxidase. Protective roles of PQQ in central nervous system diseases, such as experimental stroke and spinal cord injury models have been emerged. However, it is unclear whether intracerebral hemorrhage (ICH), as an acute devastating disease, can also benefit from PQQ in experimental conditions. Herein, we examined the possible effect of PQQ on neuronal functions following ICH in the adult rats. The results showed that rats pretreated with PQQ at 10 mg/kg effectively improved the locomotor functions, alleviated the hematoma volumes, and reduced the expansion of brain edema after ICH. Also, pretreated rats with PQQ obviously reduced the production of reactive oxygen species after ICH, probably due to its antioxidant properties. Further, we found that, Bcl-2/Bax, the important indicator of oxidative stress insult in mitochondria after ICH, exhibited increasing ratio in PQQ-pretreated groups. Moreover, activated caspase-3, the apoptotic executor, showed coincident alleviation in PQQ groups after ICH. Collectively, we speculated that PQQ might be an effective and potential neuroprotectant in clinical therapy for ICH.

Say "no" to spinal cord injury: is nitric oxide an option for therapeutic strategies?

PURPOSE

a literature review was made to investigate the role of nitric oxide (NO) in spinal cord injury, a pathological condition that leads to motor, sensory, and autonomic deficit. Besides, we were interested in potential therapeutic strategies interfering with NO mechanism of secondary damage.

MATERIALS

A literature search using PubMed Medline database has been performed.

RESULTS

excessive NO production after spinal cord injury promotes oxidative damage perpetuating the injury causing neuronal loss at the injured site and in the surrounding area.

CONCLUSION

different therapeutic approaches for contrasting or avoiding NO secondary damage have been studied, these include nitric oxide synthase inhibitors, compounds that interfere with inducible NO synthase expression, and molecules working as antioxidant. Further studies are needed to explain the neuroprotective or cytotoxic role of the different isoforms of NO synthase and the other mediators that take part or influence the NO cascade. In this way, it would be possible to find new therapeutic targets and furthermore to extend the experimentation to humans.

Heterogeneous reconstitution of the PQQ-dependent glucose dehydrogenase immobilized on an electrode: a sensitive strategy for PQQ detection down to picomolar levels

A highly sensitive electroanalytical method for determination of PQQ in solution down to subpicomolar concentrations is proposed. It is based on the heterogeneous reconstitution of the PQQ-dependent glucose dehydrogenase (PQQ-GDH) through the specific binding of its pyrroloquinoline quinone (PQQ) cofactor to the apoenzyme anchored on an electrode surface. It is shown from kinetics analysis of both the enzyme catalytic responses and enzyme surface-reconstitution process (achieved by cyclic voltammetry under redox-mediated catalysis) that the selected immobilization strategy (i.e., through an avidin/biotin linkage) is well-suited to immobilize a nearly saturated apoenzyme monolayer on the electrode surface with an almost fully preserved PQQ binding properties and catalytic activity. From measurement of the overall rate constants controlling the steady-state catalytic current responses of the surface-reconstituted PQQ-GDH and determination of the PQQ equilibrium binding (Kb = 2.4 × 10(10) M(-1)) and association rate (kon = 2 × 10(6) M(-1) s(-1)) constants with the immobilized apoenzyme, the analytical performances of the method could be rationally evaluated, and the signal amplification for PQQ detection down to the picomolar levels is well-predicted. These performances outperform by several orders of magnitude the direct electrochemical detection of PQQ in solution and by 1 to 2 orders the detection limits previously achieved by UV-vis spectroscopic detection of the homogeneous PQQ-GDH reconstitution.

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

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

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

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

Injury-induced accumulation of glial cell line-derived neurotrophic factor in the rostral part of the injured rat spinal cord

The spinal cord of a 7-week-old female Wistar rat was hemi-transected at thoracic position 10 with a razor blade, and changes in glial cell line-derived neurotrophic factor (GDNF) protein and mRNA expression levels in the spinal cord were examined. GDNF protein and mRNA expression levels were evaluated by enzyme immunoassay and reverse transcription polymerase chain reaction, respectively. Although GDNF is distributed in the healthy spinal cord from 150 to 400 pg/g tissue in a regionally dependent manner, hemi-transection (left side) of the spinal cord caused a rapid increase in GDNF content in the ipsilateral rostral but not in the caudal part of the spinal cord. On the other hand, injury-induced GDNF mRNA was distributed limitedly in both rostral and caudal stumps. These observations suggest the possibility that increased GDNF in the rostral part is responsible for the accumulation of GDNF that may be constitutively transported from the rostral to caudal side within the spinal cord. Although such local increase of endogenous GDNF protein may not be sufficient for nerve regeneration and locomotor improvement, it may play a physiological role in supporting spinal neurons including motoneurons.

Crystal structure and characterization of pyrroloquinoline quinone disodium trihydrate

Background

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

Results

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

Conclusions

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

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

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

Caffeic acid phenethyl ester reduces spinal cord injury-evoked locomotor dysfunction

Caffeic acid phenethyl ester (CAPE) is a component of propolis, which is a substance taken from the hives of honeybees, and is known to exhibit an anti-inflammatory activity. Such activity has been thought to be partly based on its potential and specific inhibitory activities toward nuclear factor-κB, a transcription factor. Therefore, in the present study, we evaluated the effect of CAPE on functional locomotor recovery after spinal cord injury (SCI) caused by hemi-transection, because inflammatory responses are a major cause of the secondary injury observed following SCI and play a pivotal role in regulating the pathogenesis of acute and chronic SCI. When CAPE was i.p.-administered at a dosage of 10 µmol/kg, it enhanced the recovery of locomotor function and reduced the lesion size while suppressing the expression of the mRNAs for a pro-inflammatory cytokine interleukin-1β and the inflammatory enzymes, inducible nitric oxide synthase and cyclooxygenase-2. These results suggest CAPE to be a promising therapeutic tool for reducing the secondary neuronal damage following primary physical injury to the spinal cord.

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

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

Role of glutathione in augmenting the anticancer activity of pyrroloquinoline quinone (PQQ)

Pyrroloquinoline quinone (PQQ), a bacterial redox co-factor and antioxidant, is highly reactive with nucleophilic compounds present in biological fluids. PQQ induced apoptosis in human promonocytic leukemia U937 cells and this was accompanied by depletion of the major cellular antioxidant glutathione and increase in intracellular reactive oxygen species (ROS). Treatment with glutathione (GSH) or N-acetyl-L-cysteine (NAC) did not spare PQQ toxicity but resulted in a 2-5-fold increase in PQQ-induced apoptosis in U937 cells. Cellular GSH levels increased following treatment by NAC alone but were severely depleted by co-treatment with NAC and PQQ. This was accompanied by an increase in intracellular ROS. Alternatively, depletion of glutathione also resulted in increased PQQ cytotoxicity. However, the cells underwent necrosis as evidenced by dual labeling with annexin V and propidium iodide. PQQ-induced cytotoxicity is thus critically regulated by the cellular redox status. An increase in GSH can augment apoptosis and its depletion can switch the mode of cell death to necrosis in the presence of PQQ. Our data suggest that modulation of intracellular GSH can be used as an effective strategy to potentiate cytotoxicity of quinones like PQQ.

Preparation of 99mTc-PQQ and preliminary biological evaluation for the NMDA receptor

Pyrroloquinoline quinone (PQQ), an essential nutrient, antioxidant, redox modulator and nerve growth factor found in a class of enzymes called quinoproteins, was labeled with ^99mTc by using stannous fluoride (SnF₂) method. Radiolabeling qualification, quality control and characterization of ^99mTc-PQQ and its biodistribution studies in mice were performed and discussed. Effects of pH values, temperature, time and reducing agents concentration on the radiolabeling yield were investigated. The quality control procedure of ^99mTc-PQQ was determined by thin layer chromatography (TLC), radio high-performance liquid chromatography (RHPLC) and paper electrophoresis methods. The average radiolabeling yield was 94 ± 1% under optimum conditions of 0.99 mg of PQQ, 30 μg of SnF₂, 0.5 mg of ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) and 18.5 MBq of Na^99mTcO₄ at pH 6 and 25 °C with a response volume of 1 ± 0.1 mL. ^99mTc-PQQ was stable and anionic. Lipid–water partition coefficient of ^99mTc-PQQ was −1.49 ± 0.16. The pharmacokinetics parameters of ^99mTc-PQQ were t_1/2α = 18.16 min, t_1/2β = 100.45 min, K₁₂ = 0.013 min⁻¹, K₂₁ = 0.017 min⁻¹, K_e = 0.016 min⁻¹, AUC (area under the curve) = 1040.78 ID% g⁻¹ min and CL (plasma clearance) = 0.096 mL min⁻¹. The dual-exponential equation was Y = 10.88e^−0.038t + 5.21e^−0.0069t. The biodistribution of ^99mTc-PQQ was studied in ICR (Institute for Cancer Research 7701 Burhelme Are., Fox Chase, Philadelphia, PA 1911 USA) mice. In vitro autoradiographic studies clearly showed that the ^99mTc-PQQ radioactivity accumulated predominantly in the hippocampus and cortex, which had a high density of N-methyl-d-aspartate Receptor (NMDAR). The enrichment can be blocked by NMDAR redox modulatory site antagonists-ebselen (EB) and ^99mTc-PQQ is therefore a promising candidate for the molecular imaging of NMDAR. To date, however, there have been no studies characterizing ^99mTc-PQQ.

Ethanol extract of chinese propolis facilitates functional recovery of locomotor activity after spinal cord injury

An ethanol extract of Chinese propolis (EECP) was given intraperitoneally to rats suffering from hemitransection of half of their spinal cord (left side) at the level of the 10th thoracic vertebra to examine the effects of the EECP on the functional recovery of locomotor activity and expression of mRNAs of inducible nitric oxide (NO) synthase (iNOS) and neurotrophic factors in the injury site. Daily administration of EECP after the spinal cord injury ameliorated the locomotor function, which effect was accompanied by a reduced lesion size. Furthermore, the EECP suppressed iNOS gene expression, thus reducing NO generation, and also increased the expression level of brain-derived neurotrophic factor and neurotrophin-3 mRNAs in the lesion site, suggesting that the EECP reduced the inflammatory and apoptotic circumstances through attenuation of iNOS mRNA expression and facilitation of mRNA expression of neurotrophins in the injured spinal cord. These results suggest that Chinese propolis may become a promising tool for wide use in the nervous system for reducing the secondary neuronal damage following primary physical injury.

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

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