By Vince Giuliano  

Minor update July 12, 2013

Pyrroloquinoline quinone (PQQ), a redox cofactor available as a dietary supplement, appears to have at least three central biological effects with powerful downstream health and longevity consequences: it stimulates the generation of PGC1-alpha, results in expression of SIRT3, and induces mitochondrial biogenesis.  After brief recapitulation of background, I review some of the key research literature involved. Of possible practical significance, supplementation with PQQ could possibly offer the benefits of exercise in a pill.

 Background on PGC-1alpha

In a June 2010 blog entry AMPK and longevity, I discussed how exercise activates the AMPK pathway and the role of PGC-1alpha (peroxisome-proliferator-activated receptor gamma co-activator-1alpha) as a co-transcriptional regulation factor that induces mitochondrial biogenesis by activating transcription factors.

The August 2010 blog entry PGC-1alpha and exercise provides a further and more general introduction to PGC1alpha.  I said “You can probably expect to hear a lot about PGC-1alpha as time goes on because this remarkable substance is turning out to have a lot to do with health and longevity. It appears to be the mediator of the health benefits produced by exercise. This blog post is about PGC-1alpha, about its relationship to exercise, and about efforts to stimulate it with various substances, in essence seeing if it is possible to provide “exercise in a pill.” 

In that blog entry I described how exercise generates PGC1alpha. Expression of PGC-1alpha can also come about as a consequence of cellular stress such as induced by cold.  I also discussed a number of physiological properties of PGC-1alpha affecting health and longevity including:

• PGC-1alpha regulates energy metabolism involving both white and brown fat. “PPARgamma coactivator-1alpha (PGC-1alpha), in cooperation with several transcription factors, has emerged as a key regulator of several aspects of mammalian energy metabolism including mitochondrial biogenesis, adaptive thermogenesis in brown adipose tissue, glucose uptake, fiber type-switching in skeletal muscle, gluconeogenesis in liver and insulin secretion from pancreas. Recent studies have shown a reduced expression of PGC-1alpha in skeletal muscle of diabetic and prediabetic humans. Moreover, expression of PGC-1alpha in white fat cells activates a broad program of adaptive thermogenesis characteristic of brown fat cells(ref).”
• “PGC-1alpha turns on the biogenesis of mitochondria primarily in brown fat, working through NRF1, NRF2 and ERRalpha. It promotes fatty acid oxidation working through the PPARs and RXRs, NRF1 and NRF2, combats ROS and promotes glucose utilization, promotes oxidative phosphorylation working via NRF2 and ERRalpha, promotes angiogenesis working through ERRalpha, and contributes to fiber-type switching.”
• “PGC-1alpha stimulates mitochondrial biogenesis and promotes the remodeling of muscle tissue to a fiber-type composition that is metabolically more oxidative and less glycolytic in nature, and it participates in the regulation of both carbohydrate and lipid metabolism(ref).”
• Exercise-induced expression of PGC-1alpha appears to enhance insulin sensitivity.  Thus, it is likely that maintenance of upregulated levels of PGC-1alpha is protective against diabetes.
• Muscle PGC-1alpha protects against oxidative damage in aging muscle and PGC1alpha prevents age-related loss of endurance running capacity.
• “It is highly likely that PGC-1alpha is intimately involved in disorders such as obesity, diabetes, and cardiomyopathy. In particular, its regulatory function in lipid metabolism makes it an inviting target for pharmacological intervention in the treatment of obesity and Type 2 diabetes(ref).”

Background on sirt3 mitochondrial biogenesis

Besides the above references to mitochondrial biogenesis, the blog entry SIRT3 research – tying together knowledge of aging points out:

• ·        Systematic exercise up-regulates PGC-1alpha and increases SIRT3 expression as well as associated CREB phosphorylation. “CREB (cAMP response element-binding) is a cellular transcription factor. It binds to certain DNA sequences called cAMP response elements (CRE), thereby increasing or decreasing thetranscription of the downstream genes[1] (ref).”
• Cellular stress causes SIRT3 to translocate from the nucleus to the mitochondria and to be highly expressed in brown adipose tissue.  SIRT3 is a mitochondrial sirtuin protein that serves to deacetylate acetyllysine-modified proteins in mitochondria.  
• ·        “(PGC-1alpha) plays important roles in adaptive thermogenesis, gluconeogenesis, mitochondrial biogenesis and respiration. PGC-1alpha induces several key reactive oxygen species (ROS)-detoxifying enzymes, –Here we show that PGC-1alpha strongly stimulated mouse Sirt3 gene expression in muscle cells and hepatocytes. – Furthermore, Sirt3 was essential for PGC-1alpha-dependent induction of ROS-detoxifying enzymes and several components of the respiratory chain, including glutathione peroxidase-1, superoxide dismutase 2, ATP synthase 5c, and cytochrome c. —Our results indicate that Sirt3 functions as a downstream target gene of PGC-1alpha and mediates the PGC-1alpha effects on cellular ROS production and mitochondrial biogenesis. Thus, SIRT3 integrates cellular energy metabolism and ROS generation(ref).”

 Background on PQQ

PQQ is a quinone, a bacterial redox co-factor and antioxidant.  It is a natural dietary substance found in common foods, good sources being parsley, green tea, tofu, tomatoes green peppers, kiwi fruit and papaya(ref).The roots of the original discovery of PQQ goes back to 1964(ref) and the substance was first isolated in 1979(ref).  However, the biological significance of the substance has been discovered only through a chain of slowly-developing research.  Much of the original research on PQQ was concerned with its roles in bacteria.  PQQ was not known to be essential to human metabolism until 2003 and research on its central roles in stimulating PGC-1alpha and mitochondrial biogenesis was published until 2010.  TheWikipedia article on PQQ provides an excellent overview with an ample list of research citations. 

The basic relevance of PQQ in terms of the above discussion, put simply, is that it is an upstream activator of CREB which is an activator of PGC-1alpha which in turn activates SIRT3.  Therefore, PQQ is potentially an initiator of the chain of health and longevity benefits that devolve from expression of PGC-1alpha and SIRT3.  The substance could be the long sought-after “exercise in pill form.”

There appear to be some 200 publications on PQQ including a few books.  I will skip over the historical publications and start with a key 2010 publication and work selectively forwards from there.  That 2010 publication is Pyrroloquinoline quinone stimulates mitochondrial biogenesis through cAMP response element-binding protein phosphorylation and increased PGC-1alpha expression.  “Bioactive compounds reported to stimulate mitochondrial biogenesis are linked to many health benefits such increased longevity, improved energy utilization, and protection from reactive oxygen species. Previously studies have shown that mice and rats fed diets lacking in pyrroloquinoline quinone (PQQ) have reduced mitochondrial content. Therefore, we hypothesized that PQQ can induce mitochondrial biogenesis in mouse hepatocytes. Exposure of mouse Hepa1–6 cells to 10–30 μm PQQ for 24–48 h resulted in increased citrate synthase and cytochrome c oxidase activity, Mitotracker staining, mitochondrial DNA content, and cellular oxygen respiration. The induction of this process occurred through the activation of cAMP response element-binding protein (CREB) and peroxisome proliferator-activated receptor-gamma coactivator-alpha (PGC-1alpha), a pathway known to regulate mitochondrial biogenesis. PQQ exposure stimulated phosphorylation of CREB at serine 133, alpha mRNA and protein expression. PQQ did not stimulate mitochondrial biogenesis after small interfering RNA-mediated reduction in either PGC-1alpha or CREB expression. Consistent with activation of the PGC-1alpha pathway, PQQ increased nuclear respiratory factor activation (NRF-1 and NRF-2) and Tfam, TFB1M, and TFB2M mRNA expression. Moreover, PQQ protected cells from mitochondrial inhibition by rotenone, 3-nitropropionic acid, antimycin A, and sodium azide. The ability of PQQ to stimulate mitochondrial biogenesis accounts in part for action of this compound and suggests that PQQ may be beneficial in diseases associated with mitochondrial dysfunction.”

It is established that cAMP response element-binding protein (CREB) is an important regulator of PGC-1alpha that facilitates PGC-1alpha activation (ref).

NRF-2 is introduced in the blog entry Nrf2 and cancer chemoprevention by phytochemicals and I have mentioned its beneficial effects in a number of other blog postings.  ““Nuclear factor-erythroid-2-related factor 2 (Nrf2) plays a crucial role in the coordinated induction of those genes encoding many stress-responsive and cytoptotective enzymes and related proteins. These include NAD(P)H:quinone oxidoreductase-1, heme oxygenase-1, glutamate cysteine ligase, glutathione S-transferase, glutathione peroxidase, thioredoxin, etc.(ref).” (Several additional blog entries written after this one further characterize the health benefits of Nrf2.)

 “The function of PQQ in mammalian physiology remains controversial. PQQ has been proposed as a vitamin (19), but it has not been demonstrated that PQQ serves as an enzyme cofactor in mammalian tissues (20, 21). Upon appreciation that mitochondrial content can be influenced by PQQ nutritional status and that reported beneficial effects of PQQ may be directly related to mitochondrial function, we hypothesized that PQQ may induce mitochondrial biogenesis through a mitochondrial-related cell signaling mechanism. Given that many mitochondrial-related events are regulated by PGC-1alpha and nuclear respiratory factors (15), we hypothesized that PQQ may interact with a PGC-1alpha-related pathway. We used the mouse Hepa1–6 hepatocyte cell line as a model to investigate these hypotheses. We also explored whether PQQ may protect against the toxic effects of mitochondrial electron transport chain inhibition(ref).”

The aforementioned article goes on to describe experimental procedures that establish:

• PQQ induces mitochondrial biogenesis.
• PQQ induces nuclear respiratory factor (NRF) activation, both NRF-1 and NRF-2.  
• PQQ induces PGC-1alpha promoter activation and increases PGC-1alpha mRNA and protein expression.  Further, PGC-1alpha binding can directly regulate NRF-1 and NRF-2 activity.
• PGC-1alpha is required for the induction of mitochondrial biogenesis by PQQ.
• PQQ stimulates the phosphorylation of CREB at serine 133 and CREB is required for PQQ-induced mitochondrial biogenesis.
• PQQ-mediated mitochondrial biogenesis is not due to auto-oxidation or IPQ addition.  That is, “PQQ-induced mitochondrial biogenesis and nuclear respiratory factor activation is not caused by generation of either hydrogen peroxide, superoxide, or IPQ in the media by PQQ(ref).” 
• PQQ improves cell viability and preserves mitochondrial function due to mitochondrial inhibitors.
• The exact role of CREB in  PQQ stimulation of  PGC-1alpha is not clear. “CREB has been shown to regulate PGC-1alpha, and data shown here suggest that PQQ acts through CREB to regulate PGC-1alpha, but regulation of the PGC-1alpha and PGC-1-related co-activator by CREB has not yet been demonstrated. Also, it is recognized that the PGC-1 family of co-activators likely act and respond to differing physiological stimuli and processes (ref).”

PQQ and neuroprotectivity

 The 2011 publication The neuroprotective action of pyrroloquinoline quinone against glutamate-induced apoptosis in hippocampal neurons is mediated through the activation of PI3K/Akt pathwayreports “In this study, we investigated the effects of PQQ on glutamate-induced cell death in primary cultured hippocampal neurons and the possible underlying mechanisms. We found that glutamate-induced apoptosis in cultured hippocampal neurons was significantly attenuated by the ensuing PQQ treatment, which also inhibited the glutamate-induced increase in Ca2+ influx, caspase-3 activity, and ROS production, and reversed the glutamate-induced decrease in Bcl-2/Bax ratio. The examination of signaling pathways revealed that PQQ treatment activated the phosphorylation of Akt and suppressed the glutamate-induced phosphorylation of c-Jun N-terminal protein kinase (JNK). — Taken together, our results indicated that PQQ could protect primary cultured hippocampal neurons against glutamate-induced cell damage by scavenging ROS, reducing Ca2+ influx, and caspase-3 activity, and suggested that PQQ-activated PI3K/Akt signaling might be responsible for its neuroprotective action through modulation of glutamate-induced imbalance between Bcl-2 and Bax.”

PQQ and uranium toxicity

The 2011 publication Uranium exerts acute toxicity by binding to pyrroloquinoline quinone cofactor provides at least one explanation of why uranium is so toxic – it binds to PQQ and prevents its biological actions.  “Uranium as an environmental contaminant has been shown to be toxic to eukaryotes and prokaryotes; however, no specific mechanisms of uranium toxicity have been proposed so far. Here a combination of in vivo, in vitro, and in silico studies are presented describing direct inhibition of pyrroloquinoline quinone (PQQ)-dependent growth and metabolism by uranyl cations. Electrospray-ionization mass spectroscopy, UV-vis optical spectroscopy, competitive Ca(2+)/uranyl binding studies, relevant crystal structures, and molecular modeling unequivocally indicate the preferred binding of uranyl simultaneously to the carboxyl oxygen, pyridine nitrogen, and quinone oxygen of the PQQ molecule. The observed toxicity patterns are consistent with the biotic ligand model of acute metal toxicity. In addition to the environmental implications, this work represents the first proposed molecular mechanism of uranium toxicity in bacteria, and has relevance for uranium toxicity in many living systems.”

Other health benefits of PPQ

Here is a sample of recent publications outlining other health benefits of PPQ, particularly as related to cancers and Alzheimer’s disease:

• Pyrroloquinoline quinone inhibits the fibrillation of amyloid proteins. (2010)
• Role of glutathione in augmenting the anticancer activity of pyrroloquinoline quinone (PQQ)  (2010)
• Protective effect of pyrroloquinoline quinone against Abeta-induced neurotoxicity in human neuroblastoma SH-SY5Y cells  (2009)
• Identification of transcriptional networks responding to pyrroloquinoline quinone dietary supplementation and their influence on thioredoxin expression, and the JAK/STAT and MAPK pathways  (2010)
• The inhibitory effect of pyrroloquinoline quinone on the amyloid formation and cytotoxicity of truncated alpha-synuclein (2010)

In addition, there have been many recent studies concerned with the chemistry and biochemistry of PQQ and its behavior in a number of bacteria.

The case for PQQ as a dietary supplement

 The first-mentioned publication goes on in its discussion to make what seems to be a possible case for PQQ supplementation: “The induction of mitochondrial biogenesis by PQQ has a number of health implications. PGC-1α elevation, particularly in muscle and adipose tissue, may also be helpful in that PGC-1alpha expression is decreased in obesity (56, 57). CREB null and PGC-1alpha null mice have hepatic steatosis and impaired gluconeogenesis and β-oxidation (38, 58, 59). PQQ-deficient mice have elevated serum triglycerides, which is reversed upon PQQ repletion (1). In addition, mice with deletion of all CREB isoforms have reduced commissural structure formation and impaired fetal T cell development (60), and other mouse models of CREB-targeted deletion show impaired memory and neurodegeneration (61, 62). Likewise, dietary PQQ deprivation results in immune dysfunction (63). PQQ is also neuroprotective when administered by intraperitoneal injection (64, 65) or diet supplementation (66).”

PQQ is not the only dietary supplement that can activate PGC-1alpha and therefore unleash its chain of beneficial results including enhanced SIRT3 expression and mitochondrial biogenesis.  Resveratrol and and other substances in my anti-aging firewalls dietary supplement regimen, can also do this.  And the drug rapamycin can also enhance PGC-1alpha expression(ref).

The basic arguments for PQQ supplementation relate to solubility and bioavailability.  Going on to quote additionally from the 2010 publication: “Although other phytochemicals are associated with the activation of cell signaling pathways important to mitochondrial function, PQQ has properties that set it apart from other compounds. As an example, resveratrol and genisten have been demonstrated to affect cell-signaling pathways, including those important for mitochondrial biogenesis. Resveratrol can induce deacetylation of PGC-1alpha (ref) and AMP-activated protein kinase activation (ref), which are potential mechanisms for PGC-1α activation. Both resveratrol and genistein are relatively insoluble in water, and increasing its water solubility does not increase resveratrol absorption (ref), although genistein bioavailability can be increased by complexing genistein with cyclodextrins (ref). In contrast, PQQ is relatively water-soluble (>1 g of PQQ/liter of water) and is easily absorbed at low dietary concentrations intakes (ref). Although genistein can induce PGC-1alpha protein expression and mitochondrial biogenesis (3), genistein may also have phytoestrogenic properties because of its ability to activate the estrogen receptor (ref).”

Going on: “The observed effects of PQQ are also observed at concentrations lower than those for resveratrol and genistein, particularly in vivo. In cell cultures in vitro, PQQ causes changes in mitochondriogenesis and function at concentrations similar to those reported recently for small molecule activators of SIRT1 (ref), which are being explored for their therapeutic potential (ref). These observations suggest that further study related to PQQ is warranted. One important note is that PQQ can increase PGC-11alpha mRNA transcription, which is different from the post-translation regulation of PGC-1alpha by resveratrol and raises the likelihood that a combination of various compounds, such as are often present in fruits and vegetables, can stimulate mitochondrial biogenesis through different modes of action. Because mitochondria function as the principal energy source of the cell, compromised function of this key organelle is linked to numerous diseases and metabolic disorders (ref)(ref). In this regard, PQQ would appear to have therapeutic potential similar to resveratrol, genistein, hydroxytyrosol, quercetin, or other compounds that can induce mitochondrial biogenesis(ref).”

Does PGG supplementation make sense?

My impression is that the PQQ supplementation phenomenon is new and just taking off. A few of the supplement companies have picked up on the 2010 findings outlined above and are starting to offer PQQ supplements, Life Extension Foundation having been a leader in this regard.  Most supplement vendors offer PQQ only in proprietary combinations with other substances.   I have found this discussion of PPG supplementation dosage on a site providing practicalPyrroloquinoline Quinone & Methoxatin information. My impression is that the information on that site is responsible and informative although not completely documented.  For example, that site contains an  interesting table for the PQQ content that researchers have found in food.  That discussion points out that there are many imponderable factors that could affect what is the optimum amount for a healthy adult to take as a daily PQQ supplement. “This question has not been fully resolved and is complicated by the inability to measure all forms of PQQ (pyrroloquinoline quinone | methoxatin). However, it is possible to make several good inferences from current animal studies and data–.”  The discussion argues that, all things considered, 10-20mg of PQQ a day is probably a reasonable dose. The supplement-makers apparently concur and the PQQ supplement products I have seen range from having 5 to 20 mg of PQQ per pill. 

In considering PQQ supplementation, I hasten to point out that a number of other dietary supplements offer positive benefits for mitochondrial health including r-alpha-lipoic acid, acetyl-l-carnitine, resveratrol, quercetin and co-enzyme Q10.  For a discussion of the supplements I have been  taking related to mitochondrial health, you can have a look at the Mitochondrial Damage Firewall in my treatise.

Some supplement marketers are representing PQQ as being a new vitamin, although whether it satisfies the criteria for being a vitamin has been disputed(ref).

Given that I exercise at least 45 minutes a day, eat a reasonable diet, and take all the supplements in my anti-aging firewalls dietary supplement regimen, do I think additional enhancement of PGC-1alpha and all of the associated health benefits would come about for me if I added PQQ as a supplement?  Or would adding PQQ to my dietary regimen be simply redundant?  Or could I increase the effectiveness or reduce the cost of the regimen by substituting PQQ for other supplements?  I simply did not know when I first drafted this blog in April 2011.  Because of the importance of SIRT3 expression, however, in 2012 I started regular supplementation with PQQ and have continued that pattern since (July 2013).

Since drafting the above over two years ago,  another 50 research publications relating to PQQ have appeared in pubmed.org, further elucidating its mechanisms of action and health benefits. In the interim I have developed an increased appreciation of the importance of SIRT3 expression for controlling mitochondrial ROS and general health maintenance during aging.  At some point I will generate a new blog entry covering the new research and updating this one.