Science: The Best Neuronal Bioenergetic Substrate for Glaucoma - Pyruvate or BHB?
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Quick Summary

Current evidence suggests that supplying a neuronal energy substrate (such as the dietary supplement βHB) can help rescue optic nerves in glaucoma and may provide neuroprotection.

Pyruvate and βHB are both discussed in this article. βHB is deemed to be the superior choice of neuronal energy substrate. βHB is able to supercharge the mitochondrial energy generation process in a way that pyruvate cannot.

Other benefits of βHB are discussed in Part 2. A few of those include:

  • βHB is neuroprotective
  • βHB can boost mitochondrial biogenesis
  • βHB encourages the growth of new neurons
  • βHB can protect the brain from ischemia
  • βHB reduces neuro-inflammation
  • βHB may be an anti-aging metabolite

Part 1 is about pyruvate, which is not the recommended supplement. Therefore, if you do not wish to know the details behind that conclusion, you can skip Part 1.

Introduction

Optic nerve axons are metabolically stressed in glaucoma. Metabolic vulnerability appears to precede axon degeneration in glaucoma. Retinal ganglion cell (RGC) bodies survive for a time after the axons degenerate (Howell 2007; Buckingham 2008; Crish 2010). This survival of RGC bodies provides a fortuitous intervention window that suggests axon protection (even regeneration) could be a viable approach toward maintaining vision in glaucoma. Results suggest that supplying a neuronal energy substrate (such as pyruvate or βHB) can help rescue stressed optic nerves. Harun-Or-Rashid 2018-05

Mitochondrial dysfunction is thought to be a key part of the pathology of all forms of glaucoma. But there has been a question: is that dysfunction due to defective mitochondria or lack of neuronal bioenergetic substrates (pyruvate, lactate, ketones) and co-factors (NAD+)? There has been existing pre-clinical evidence supporting the lack of substrates and co-factors being involved, and providing further evidence that glaucomatous mitochondria are not defective. The new clinical study by De Moraes 2022 also supports this understanding.

Conclusions and relevance: A combination of nicotinamide and pyruvate yielded significant short-term improvement in visual function, supporting prior experimental research suggesting a role for these agents in neuroprotection for individuals with glaucoma and confirming the need for long-term studies to establish their usefulness in slowing progression.

This study combined an energy substrate (pyruvate) and NAD+ booster (nicotinamide) via dietary supplementation.

Recently we have had many discussions about the potential benefits of NAD+ boosters (such as niacinamide and nicotinamide riboside) in the treatment of glaucoma. However, even though we have been aware of the recent glaucoma research pairing pyruvate with NAD+ boosters, pyruvate has failed to generate as much excitement as NAD+ boosters. In fact, there seems to be little excitement regarding pyruvate at all. Why?

I've been thinking about a superior alternative because we cannot ignore the need to support neuronal energy metabolism. Dysregulation of glucose metabolism has been identified in optic nerve cells in glaucoma (and can be caused by elevated IOP, and is therefore independent of systemic glucose metabolism); this causes a reduction in energy availability to neurons and subsequent death of those optic nerve cells.

In the study above, pyruvate was proposed as a supplement to support neuronal energy metabolism. Let's understand why before we consider if we should supplement our diets with pyruvate or another supplement that serves the same purpose.

Part 1: Pyruvate

What Is Pyruvate?

The body produces pyruvate when it breaks down carbs and sugar (glucose). Pyruvate is available as a supplement in the form of calcium pyruvate.

The Rationale For Pyruvate Supplementation In Glaucoma

A mouse study shows an IOP-dependent decrease in retinal pyruvate levels:

Age-related bioenergetic insufficiency increases the vulnerability of retinal ganglion cells to intraocular pressure during glaucoma pathogenesis. We demonstrate an intraocular pressure-dependent decline in retinal pyruvate levels coupled to dysregulated glucose metabolism, and detected mTOR activation at the mechanistic nexus of neurodegeneration and metabolism. Harder 2020

There is further animal evidence as described in this study:

Pyruvate functions as a key molecule in energy production and as an antioxidant. The efficacy of pyruvate supplementation in diabetic retinopathy and nephropathy has been shown in animal models. Pyruvate likely plays a major role in maintaining glycolysis–TCA cycle flux and energy production in cultured cells under exposure to high-glucose insult. Yako 2021

In theory, pyruvate supports neuronal cell energy balance -- if you can get it to the neurons and supporting cells. Pyruvate is normally produced in cells by the breakdown of carbs (glucose) rather than being absorbed from the gastrointestinal tract. Once pyruvate is available, it can be further broken down into acetyl coA, a substrate for the core bioenergetic cycle in the mitochondria, the Kreb's cycle (a.k.a. citric acid cycle or TCA cycle).

The Krebs cycle takes place in mitochondria (in eukaryotes like us). Pyruvate's role is commonly described in biochemistry textbooks similarly to:

Pyruvate oxidation (by the pyruvate dehydrogenase complex) is the required step before the Kreb's cycle can begin. Two molecules of pyruvate generate two molecules of acetyl coA to enter the Kreb's cycle.

Our biochemistry education usually teaches us that pyruvate oxidation is the required step before the Kreb's cycle can begin. The Kreb's cycle produces the cell's energy currency (ATP). The need to support neuronal energy metabolism in glaucoma is well recognized now. Therefore, pyruvate supplementation seems like the obvious answer. But is it?

The Limitations Of The Pyruvate-Centric Perspective

Is pyruvate oxidation really the required step before the Kreb's cycle can begin? (Is pyruvate oxidation even part of the Kreb's cycle proper?)

The core Kreb's cycle is a closed loop (the last part of the pathway reforms the molecule used in the first step) and pyruvate oxidation takes place outside of that loop (cycle). The direct prerequisite molecule is acetyl-CoA. Acetyl-CoA can be derived not just from carbohydrates (yielding pyruvate), but also from fats, proteins -- and ketone bodies, which will be significant in our analysis. Hence, the Kreb's cycle can begin without pyruvate if ketone bodies are available to be converted into acetyl coA.

However, when many of us studied biochemistry, ketone body metabolism was completely (or mostly) ignored. We may have been taught that the brain (and optic nerve) can only utilize glucose for energy. (Glucose is broken down into pyruvate.) In truth ketones are an important source of energy for the CNS (and they can cross the blood-brain-barrier), but many of us who are researching glaucoma (or other diseases) were not taught that in our biochemistry classes.

It seems that medical biochemistry continues to neglect ketone body metabolism -- or relegate this study to an entirely separate discussion carried out mostly by different researchers. I recall seeing a paper (published not too long ago) that called ketone body metabolism the fringe of biochemistry (or something very similar to that). Personally, in my graduate-level medical biochemistry classes (as well as in my undergrad biochemistry classes), the Kreb's cycle was a central focus (and had to be memorized) while ketone body metabolism was entirely neglected. I continue to read recently published peer-reviewed articles that describe key biochemical pathways as if ketone metabolism did not exist.

In vitro studies in cortical neurons showed that both pyruvate and the ketone body β-hydroxybutyrate (βHB) stimulated uncoupled respiration by equivalent amounts of up to 60%. (Lactate stimulation of respiratory capacity was approximately 45%.) Laird 2013

So there are alternatives, but why is an alternative to pyruvate needed?

Decreased Ability To Convert Pyruvate Into Energy As We Age

In normal conditions, the conversion of pyruvate into acetyl coA, the step required before pyruvate can be utilized in the Kreb's cycle to generate ATP, is the rate-limiting step. This step requires the pyruvate dehydrogenase complex (PDC). But elevated IOP can hinder that step Harder 2020.

Furthermore, relatively little attention has been accorded to the pyruvate dehydrogenase complex (PDC) relative to how we grow old and acquire age-related diseases. Stacpoole 2012 It generally declines as we age (suggesting that pyruvate may not be an ideal neuronal energy substrate for neurodegenerative diseases).

Aging and neurodegeneration are common outcomes of mitochondrial dysfunction, and are associated with a decrease in pyruvate dehydrogenase activity Jha 2012

While the basic biochemistry for pyruvate's central role appeared promising in theory, the dynamics of neurodegenerative diseases and aging cast doubt on its ultimate suitability. But that's not all.

Pyruvate vs. Lactate (optional section)

A 2007 paper emphasized a new hypothesis that lactate not pyruvate is indeed the principal end product of neuronal aerobic glycolysis. Schurr 2007 The paper is entitled, "Lactate, not pyruvate, is neuronal aerobic glycolysis end product."

Here's the rather satisfying 2022 follow-up describing in detail how lactate, not pyruvate, is the substrate for neuronal mitochondrial energy (oxidative phosphorylation) metabolism:

Provided here is a consideration of the ‘aerobic glycolysis’ phenomenon in light of published data that could prove the phenomenon to be a simple misconception at best, or a misleading concept at worst.

... [the old] hypothesis relies on the lingering old dogma, where there are two separate outcomes to glycolysis, aerobic, which ends with pyruvate, and anaerobic, which ends with lactate.

The time has arrived to drop the words ‘aerobic’ and ‘anaerobic’ when dealing with glycolysis. These are archaic terms that originated more than a century ago, when lactate was considered to be a waste product of glycolysis that the tissue must be rid of. Combining it with the erroneous claim that, in the presence of oxygen, glycolysis ends up with pyruvate, the presumed substrate of oxidative phosphorylation, led to the formulation of two distinct glycolytic pathways, aerobic and anaerobic.

Ample evidence is now available to show that glycolysis always ends with lactate, not with pyruvate. Therefore, the presence of oxygen does not change glycolysis’ end product from lactate to pyruvate, it only allows lactate to become the substrate of the mitochondrial oxidative phosphorylation. When oxygen is absent, lactate, the end-product of glycolysis, accumulates. Schurr 2022

I find the paper satisfying because it confronts a long-held dogma with new evidence. However, that's not central to our discussion and if I didn't find the paper so satisfying for these other reasons I might not even have mentioned it. Even this dogma-busting paper fails to mention ketone metabolism at all, thereby effectively allowing another dogma to survive (if it isn't pyruvate, it's lactate that is the most important energy substrate).

It would be nice to short-circuit a dogma wherein supplemental calcium pyruvate becomes the de facto neuronal energy substrate used in glaucoma clinical practice. The reasons to find a better solution are not limited to nuances of the biochemical pathways, as the next section discusses. However, I'm concerned that we're already headed toward a future where pyruvate becomes more recognized while a potentially superior alternative, βHB, remains obscure. Indeed clinical trials are already using pyruvate, but not βHB.

We need more clinical data with βHB (Kovács 2021), and I hope the FitEyes community can raise awareness of the evidence in favor of βHB ketone dietary supplements over pyruvate. In this article I show strong scientific evidence and practical examples in support of exogenous ketogenic supplements compared to calcium pyruvate.

Pyruvate's Lacklustre Performance As A Dietary Supplement

Clinicians, researchers and nutritionists often do not have the same views on healthy eating and the use of dietary supplements. To illustrate one side of this, I will share a quote:

Clinicians have little training in diet and nutrition, despite this being a great public health challenge and a key driver of disease. Robbins 2022

A biochemist might see pyruvate as an obvious answer (for the reasons given earlier above), see that it is available as a dietary supplement, and propose said supplement as something for glaucoma patients to try. Indeed, it is being tried in clinical trials now, as we know.

However, a nutritionist with experience recommending pyruvate might immediately recognize that it is not an ideal supplement (for glaucoma patients or anyone).

Even with the promising glaucoma studies that utilize pyruvate (such as De Moraes 2022), I have personally not wanted to take supplemental pyruvate because of past experience in a fitness community where many people tried it and had very poor results. My negative view on calcium pyruvate is echoed by Examine.com.

Key points from Examine.com's summary of pyruvate include:

  • Low doses of pyruvate (3-5 grams) tend to give no benefits. Yet, high dose pyruvate causes stomach distress and loose stools.

  • Pyruvate is not well absorbed and supplementation often fails to raise blood pyruvate, yet can still lead to gastrointestinal side effects.

Examine.com concludes:

The lowest effective range noted in the aforementioned studies is replacing 6-12 grams of carbohydrates with pyruvate, but even then the results seen with pyruvate are variable and lacklustre enough to warrant caution in buying this supplement.

That raises an important point, which seems to be neglected in the glaucoma studies -- if you choose to take pyruvate, you should probably reduce your carbs by an equal amount. But who would want to take a pyruvate supplement after learning about its lacklustre performance as a dietary supplement -- especially when a potentially superior alternative is now available?

Part 2: βHB

The Case For Beta-hydroxybutyrate (βHB) As A Superior Alternative To Pyruvate

βHB has potential disease-modifying activity that represents a novel therapeutic approach for neurodegenerative diseases. Dewsbury 2021

βHB is natural. Ketogenesis is an evolutionary survival mechanism whereby ketone bodies (primarily β-hydroxybutyrate (βHB)) are produced during periods of calorie restriction, fasting, exercise, or reduced carbohydrate availability (Puchalska 2017 citation). Puchalska 2017 To avoid over-complicating things, I'm going to refer to beta-hydroxybutyrate as a ketone body (as most researchers do).

During starvation, the body is heavily dependent on ketone bodies as energy fuel whereby two-fifth of fatty acid metabolism in the whole body occurs via hepatic ketogenesis, producing 140 to 280 grams of ketones per day. Yao et al., 2021, p. 6231

β-hydroxybutyrate (βHB) is the predominant ketone body in humans. As mentioned, the body's production of βHB is normally the result of fasting, but an extended low-carbohydrate (ketogenic) diet and prolonged exercise also stimulate the production of ketones.

Human studies using therapeutic ketosis have predominantly assessed the ketogenic diet in adults and children with treatment-resistant refractory epilepsy. An emerging body of literature is now exploring the application of therapeutic ketosis more broadly, especially in neurodegenerative diseases. Dewsbury 2021

However, as we now know, and as this 2021 paper emphasises, the therapeutic potential of βHB in glaucoma continues to be underappreciated.

Meanwhile, a class of endogenous functional metabolites, ketone bodies, which have properties seemingly suited to rescuing mitochondrial function, have been largely overlooked. Thickbroom 2021

The concept first introduced by Sir Philip Randle in 1964, and only recently demonstrated to hold true in the human brain, shows that CNS nerve cells prefer βHB over pyruvate.

A number of investigators have shown βHB displacing glucose utilization in brain preparations and the same has been shown to occur in man. This illustrates the concept introduced by Sir Philip Randle that fat and fat-derived products like acetate and βHB take precedent over carbohydrate and its products such as pyruvate. Cahill 2003

It has now been proven that ketogenic interventions lead to βHB becoming a primary energy source for the brain, alleviating cognitive dysfunction. Furthermore, cognitive enhancements have been seen in studies of young and healthy individuals (Ashton et al., 2021) as well as in the elderly or those suffering from cognitive dysfunction.

Importantly, supplemental βHB enables the body to utilize these metabolic pathways without a change in diet.

[Ketone] supplementation improves cognitive performance in healthy individuals after a minimum of 2-3 weeks with no change in their habitual diet. (Ashton et al., 2021)

Research shows that an increase in circulating βHB via dietary supplementation, without a change in diet, produces similar effects as a ketogenic diet, including enhanced cognitive performance and neuroprotection, without the difficulties or potential side effects of the more extreme dietary changes required to reach the same level of blood ketones.

Furthermore, increases in cognitive performance have been seen even with low intakes of supplemental ketones. (Ashton et al., 2021)

Beta-hydroxybutyrate (βHB) as a dietary supplement is relatively new, although βHB has been extensively studies for decades as part of research into the ketogenic diet.

Ketone bodies enter CNS (brain and optic nerve) cells (such as astrocytes, neurons, and oligodendrocytes) and are converted to acetyl-CoA in the mitochondria. That step (getting acetyl-CoA into the mitochondria) was the biochemical goal behind pyruvate, but as we learned, pyruvate supplements suffer many shortcomings (and those shortcomings are not evident from the biochemistry alone, but require understanding digestion and absorption issues). βHB as a dietary supplement (called "exogenous ketones") on the other hand is well-absorbed and highly efficient at supporting neuronal cell energy balance.

At low intakes, supplemental ketones are thought to increase cognitive performance due to an increased rate of mitochondrial biogenesis. This enhanced mitochondrial biogenesis has been observed in neuronal cells in several studies. Research also shows that ketone supplements (e.g., βHB) can improve performance in memory tests. (Ashton et al., 2021)

In addition, βHB offers many more benefits. I will briefly list some of them without going into details until later:

  • Ketogenic diets (which boost βHB) are proposed to be neuroprotective in glaucoma (Zarnowski et al., 2012)
  • Ketogenic diets protected retinal ganglion cell structure and function Harun-Or-Rashid 2018-11
  • Ketogenic diet was able to rescue optic nerves in a mouse model of glaucoma
  • βHB easily crosses the blood-brain-barrier and can provide the CNS (brain, optic nerve) with the majority of its energy needs, which is critical in a neurodegenerative disease like glaucoma where neuronal energy metabolism is compromised.
  • βHB is neuroprotective on the basis of being a neuronal energy substrate Laird 2013
  • βHB is neuroprotective on the basis of being an antioxidant
  • βHB can increase longevity gene SIRT1 expression Scheibye-Knudsen 2014
  • βHB can boost mitochondrial efficiency and biogenesis
  • βHB can improve the balance between inhibitory and excitatory neurotransmitters, which tend to be out of balance in neurodegenerative diseases like glaucoma.
  • βHB encourages the growth of new neurons
  • βHB can protect the brain from ischemia
  • βHB is a signalling molecule that activates epigenetic pathways leading to important gene expression (such as FOXO and MTL1)
    • FOXO regulates oxidative stress, apoptosis, cell cycles and more
      • FOXO3 is linked to longevity in humans
    • MTL1 helps reduce toxicity
  • βHB reduces neuro-inflammation by blocking the inflammatory protein NLRP3. Harun-Or-Rashid 2018-11 (Chronic NLRP3 stimulation is also related to Alzheimer's disease, some bone diseases, skin diseases, metabolic syndrome, type 2 diabetes, gout, etc.)
  • βHB reduces oxidative stress. Oxidative stress is one of the factors underlying glaucoma.
    • In the hippocampus βHB protect neuronal connections against oxidative stress. (The hippocampus is thought to regulate emotions, long term memory, and spatial navigation.)
    • βHB similarly protects against oxidative damage in the neocortex (the area of the brain associated with cognition, language and sensory perception).
  • βHB reduces insulin resistance (increases insulin sensitivity) and helps balance blood glucose
  • βHB (but not acetoacetate) suppresses gluconeogenesis (which is responsible for the hyperglycemia in diabetes) Pan 2022
  • βHB helps protect endothelial cells (lining blood vessels) from oxidative damage.
  • βHB blocks the insulin-like growth factor-1 (IGF-1) receptor gene. Lower IGF-1 is related to delayed aging and increased lifespan.
  • βHB can slow down the growth of some types of tumor cells (because cancerous cells have altered metabolism that prevents them from using ketones efficiently like normal cells do). This is why the ketogenic diet is popular with some cancer patients.
  • βHB is an alternative energy source for the heart, and can increase its mechanical efficiency up to 30% (boosting blood flow 75%) (The authors assume βHB metabolism in the brain is similar.)
  • βHB can reduce oxidative stress caused by demanding exercise in athletes.
  • βHB can lead to improved exercise performance and reduced fatigue
  • βHB can reduce cognitive fatigue during activity
  • βHB prevents bone loss by inhibiting the production of osteoclast cells which break down bone in those with osteoporosis.
  • βHB can help you lose body fat (by increasing fat-burning and decreasing your appetite).
  • βHB can enhance antioxidant mechanisms (Dewsbury #8)
  • βHB can increase mitochondrial respiration (Dewsbury #13) and mitochondrial biogenesis in the hippocampus (Dewsbury #14)
  • βHB can increase Aβ clearance (Dewsbury #15, Dewsbury #16)
  • βHB can protect against Aβ-induced neurotoxicity (Dewsbury #17)
  • βHB decreases proinflammatory cytokines (12, Dewsbury #18–20)
  • βHB decreases Aβ deposition (Dewsbury #21)
  • βHB reduces glutamate toxicity (excitotoxicity) (Dewsbury #18)

We'll look at the research supporting many of these observations below.

The Ketogenic Diet For Glaucoma

The goal of all ketogenic diets is to increase the levels of ketone bodies, primarily βHB, in the blood. Gough 2021 Calorie restriction, fasting and prolonged exercise similarly increase the levels of ketone bodies, again primarily βHB, in the blood.

The FitEyes group discussed ketogenic diets sporadically from 2006 to 2012, but the article "A Ketogenic Diet May Offer Neuroprotection in Glaucoma and Mitochondrial Diseases of the Optic Nerve" kicked interest up a notch. Zarnowski 2012

The ketogenic diet may be neuroprotective in certain diseases of the eye such as glaucoma, mitochondrial diseases of the optic nerve, or retinal ischaemic diseases (diabetic retinopathy and retinopathy of prematurity). Zarnowski 2012

Intermittent fasting can achieve neuroprotective effects, a result that corresponded to significant increases in the ketone body beta-hydroxybutyrate (βHB). These data indicate that metabolic syndromes may contribute to glaucoma incidence, and amelioration may be possible through management of mitochondrial efficiency or substrate complement (ketone bodies instead of glucose). Harun-Or-Rashid 2018-05

Controversies and Adverse Effects of the Ketogenic Diet

Adopting the ketogenic diet contradicts current dietary guidelines that recommend reduced intake of total fat. Although some of the negative effects of elevated dietary fat intake appear to be balanced by the beneficial effects of reduced carbohydrates and elevated ketones, real world experience informs us that some individuals suffer severe side effects on the ketogenic diet.

Traditional ketogenic diets are high in saturated fats including cream, butter, bacon, and other proteins high in saturated fats [160]. Hyperlipidemia is a common consequence of the traditional ketogenic diet. Mohammadifard 2022

Complicating the effect of the ketogenic diet on inflammation is the finding that acetoacetate activates inflammatory pathways through TNFα, which is in contrast to the anti-inflammatory properties of βHB (Gough 2021 #50). Additionally, some evidence suggests that moderate concentrations of βHB are preferred over high concentrations (Gough 2021 #51), suggesting an advantage of βHB supplementation with a standard diet. Gough 2021

Less common but more severe side effects [of the strict ketogenic diet] include specific nutrient deficiencies, kidney stones, bone fractures, increased infections, anemia and cardiomyopathy. Gough 2021

Some short-term side effects (such as hypercholesterolemia, dehydration, constipation, acidosis, lethargy, and gastrointestinal distress) [104,105] and long-term side effects (such as kidney problems, cardiomyopathy, hyperlipidemia, and bone mineral loss) following the administration of ketogenic diet in cancer patients were reported [68]. It is worth mentioning that ketogenic diet may cause deficiencies in some micronutrients in patients, and patients who are exposed to nutritional deficiencies may exacerbate their nutritional status if they adhere to such diets [106]. Mohammadifard 2022

My first exposure to the ketogenic diet was via the infamous Dr. Atkins diet. I did not have great success with it. Later when I began my biochemistry education, the Dr. Atkins diet was discredited (or so it seemed).

The newer research on the ketogenic diet for glaucoma prompted me to try it again in 2017. However, I was forced to discontinue the ketogenic diet that same year and at the time (Dec 13, 2017) I wrote the following explanation to the FitEyes email list:

The first study concludes that "a ketogenic diet causes thyroid malfunction." (Kose 2017) That's a pretty strongly worded conclusion, but it exactly matches my test results and my experience. It is clear that the problem is not restricted to epileptic patients or to the most severe keto diets. [In my experience], it can happen to normal people on moderate keto diets.

The subsequent articles suggest the issue applies to low carb diets as well. For example, Anthony Colpo writes, "Adverse effects on thyroid hormone status: Carbohydrate restriction, to both ketogenic and non-ketogenic levels, has repeatedly been shown in controlled trials to impair the conversion of T4 into the all-important T3, a condition known as euthyroid sick syndrome." Source: Lies, Damned Lies, and Gutless Low-Carb Trolls – Anthony Colpo

NOTE: It has been mentioned to me that Anthony Colpo is not a reliable source. Nevertheless, this point is not central to the present discussion. We have made the point above that βHB supplementation is safe and effective without dietary changes. It is used by people on low carb diets as well as by those who do not restrict cabs.

My personal approach since 2018 has been to follow a healthy diet for my body and to consume a βHB supplement instead of eating breakfast, extending my fast from dinner the prior day to lunch the next day, while enjoying mild ketosis during that window, boosted by the supplemental βHB. (BTW, the βHB supplement is great for overcoming hunger on this program.) I consider this approach to be the best of both worlds, especially in the context of glaucoma.

The evidence presented herein suggests that supplemental βHB can play a role in glaucoma management regardless of the diet the individual chooses to follow. Intermittent fasting is also not required.

The recent research on pyruvate in glaucoma transformed my interest in supplemental βHB from a personal experiment I have been conducting in private to something that I feel needs serious attention by the glaucoma community, given the very favorable comparison of βHB to pyruvate as dietary supplements. Exogenous ketone supplements (especially βHB) are much more available and affordable compared to prior years.

Exogenous Ketones as a Solution -- Ketogenic Diet Optional, Not Required

To some extent, the harmful effects of the standard ketogenic diet can be overcome by modifying the diet to include less saturated fat and more healthier fats such as unsaturated fats, including omega-3 fatty acids.

However, because "β-Hydroxybutyrate (βHB) is the key element of ketogenic diet" (Huang 2021), and βHB by itself provides numerous documented health-promoting benefits without increasing dietary saturated fat intake, we suggest that one ideal approach is the addition of βHB (via dietary supplement) to a diet that meets widely accepted guidelines for total fat.

Of course, for those individuals who thrive on a ketogenic diet, supplementation with βHB can further improve results and overcome temporary compliance challenges.

In short, βHB may be used on a ketogenic diet or a non-ketogenic diet, and choice of diet is ultimately up to the individual and their healthcare professionals.

Administration of exogenous ketogenic supplements was proven to be an effective method to induce and maintain a healthy state of nutritional ketosis. Consequently, exogenous ketogenic supplements, such as ketone salts and ketone esters, may mitigate aging processes, delay the onset of age-associated diseases and extend lifespan through ketosis. Kovács 2021

The aim of this review (Kovács 2021) is to summarize the main hallmarks of aging processes and certain signaling pathways in association with (putative) beneficial influences of exogenous ketogenic supplements-evoked ketosis on lifespan, aging processes, the most common age-related neurodegenerative diseases (Alzheimer’s disease, Parkinson’s disease and amyotrophic lateral sclerosis), as well as impaired learning and memory functions.

Conclusions: A great deal of evidence suggests that exogenous ketone supplement-generated ketosis may improve healthspan, therefore can delay ageing and the onset of age-related neurodegenerative diseases, as well as learning and memory dysfunctions through neuroprotective effects. Kovács 2021

Neuroprotective Mechanisms of βHB

Various molecular mechanisms have been associated with neuroprotective effects of the ketogenic diet and ketone supplementation. Most studies report correlations between cellular pathways and neuroprotection, such as changes in oxidative stress or inflammatory proteins. Recently, several elegant studies using inhibitors and mouse knockout strains have helped resolve some of the questions and controversies by providing evidence for the direct contributions of specific keto-related cellular pathways in mediating neuroprotective effects. Gough 2021

βHB generates mitochondria, improves energy availability (by reversing monocarboxylate transporter decline), reduces glial hypertrophy, protects retinal ganglion cells and their axons from degeneration, and maintains physiological signaling from the retina to the brain. Harun-Or-Rashid 2018-05 (Monocarboxylate transporters are important membrane transporters for energy substrates (e.g., pyruvate, lactate, βHB).)

βHB Restores Neuronal Energy

The foundational mechanism for neuroprotection is that ketone bodies (primarily βHB) serve as alternative fuels for neuronal metabolism, which maintains mitochondrial function, ATP production and neuronal survival. Gough 2021

In one study, βHB induced neuroprotection by preventing the decline in mitochondrial respiration restoring ATP production. Tieu 2003

Here's an interesting paper and a new coined term to represent keto-focused bioenergetic medicine therapies: Neuroketotherapeutics

Abstract

Neuroketotherapeutics represent a class of bioenergetic medicine therapies that feature the induction of ketosis.

These therapies include medium-chain triglyceride supplements, ketone esters, fasting, strenuous exercise, the modified Atkins diet, and the classic ketogenic diet.

Extended experience reveals persons with epilepsy, especially pediatric epilepsy, benefit from ketogenic diets although the mechanisms that underlie its effects remain unclear. Data indicate ketotherapeutics enhance mitochondrial respiration, promote neuronal long-term potentiation, increase BDNF expression, increase GPR signaling, attenuate oxidative stress, reduce inflammation, and alter protein post-translational modifications via lysine acetylation and β-hydroxybutyrylation.

These properties have further downstream implications involving Akt, PLCγ, CREB, Sirtuin, and mTORC pathways. Further studies of neuroketotherapeutics will enhance our understanding of ketone body molecular biology, and reveal novel central nervous system therapeutic applications. Koppel 2017

NAD+ Booster

The ketogenic diet, by restoring favorable neuronal bioenergetics, appears to foster positive changes in the NAD+/NADH ratio (and through this, lead to reduced inflammation -- further discussed below). Gough 2021

βHB was shown to provide NAD+ boosting functionality like the well-known NAD+ precursor nicotinamide riboside. "This study connects two emerging longevity metabolites, β-hydroxybutyrate and NAD+, through the deacetylase SIRT1." Scheibye-Knudsen 2014

A Deeper Dive Into Mitochondrial Energetics (background for next section)

We burn food with oxygen and extract energy in the form of ATP (the universal energy currency of life). This happens in our mitochondria in a process called aerobic respiration. It is called respiration because of the requirement for oxygen (O2). The final step of ATP generation is called oxidative phosphorylation and it involves one of the most unique molecular motors in all of nature as well as an energy gradient as powerful as a bolt of lightning.

There are hundreds to thousands of mitochondria in most cells -- more in those that require a lot of energy, such as nerve cells. When this mitochondrial energy process fails, the cells die. That's why mitochondrial well-being is so central to understanding neurodegeneration. Mitochondrial dysfunction is known to be involved in the pathogenesis of glaucoma.

ATP generation is powered by the respiratory electron transport chain (on the mitochondrial inner membrane), where electrons (derived from energy substrates) enter at different catalytic centers and travel up through various redox couples within the chain to ultimately combine with H+ and O2 to form H2O. Veech 2004

The total energy available from the movement of electron up the respiratory chain is therefore determined by the difference between the variable redox potential of the mitochondrial NAD couple and the O2 couple, and is given by delta G. Veech 2004

Sidebar - delta G defined

"Delta G" (∆G), known as the Gibbs free energy change, can be informally defined as the amount of "free" or "useful" energy available (or that can be extracted) from a system (such as mitochondrial ATP generation). This concept will become relevant when we discuss how βHB supercharges mitochondria in a way that pyruvate cannot.

The energy gained from mitochondrial electron transport is transferred to the pumping of protons across the mitochondrial membrane at sites I, III and IV creating an electrochemical proton gradient across the membrane. Veech 2004

This mitochondrial proton gradient has energy of 30 million volts per meter, which is equivalent to a bolt of lightning ~ Nick Lane, Professor of Evolutionary Biochemistry, University College London in Lane 2010

ATP is generated when protons return to the inner mitochondrial matrix via the ATP synthase complex (the fascinating molecular motor I mentioned above).

βHB Corrects Mitochondrial Dysfunction

βHB corrects mitochondrial dysfunction in multiple ways. First, βHB supplementation can generate new mitochondria.

Ketones are known to increase mitochondrial biogenesis and the expression of uncoupling proteins (UCPs). Scheibye-Knudsen 2014 #2; Scheibye-Knudsen 2014 #25

(UCPs belong to a family of mitochondrial carrier proteins that are present in the mitochondrial inner membrane.)

Even more importantly, βHB improves the energy generated by all mitochondria (even those that might not be in tip-top shape).

βHB has the potential to improve sub-optimally functioning mitochondrial complex I, as well as to bypass more severe complex I dysfunction. Thickbroom 2021 (This will be discussed in more detail below.)

Mitochondrial complex I is thought to potentially be the most critical source of free radicals in the body and the most important determinant of healthspan and lifespan. We have not found an effective way to target antioxidants at that location -- but βHB directly addresses that challenge (as will be discussed in more detail below). By this mechanism βHB reduces oxidative stress within the mitochondria. This result is far more promising for extending healthspan and lifespan than increasing the supply of exogenous antioxidants (which are largely ineffective for extending lifespan).

Mitochondrial dysfunction and glia-driven neuroinflammation are interdependent and reciprocal processes with widespread impacts in the glaucomatous retina and optic nerve. (Dysfunctional mitochondria stimulate inflammatory responses and proinflammatory mediators impair mitochondria -- a vicious cycle.) Tezel 2021

The following discussion contains a lot of details yet it still under-emphasizes how important βHB is to correcting mitochondrial function.

Although reactive oxygen species can be produced by cytoplasmic oxygenases as a result of increased intracellular calcium concentrations, mitochondria are the major source of reactive oxygen species, particularly complex I in neuronal mitochondria (Turrens 2003; Hunt 2006). Maalouf 2009

The evidence of βHB's ability to improve functioning (and reduce free radicals) at this critical location (complex I) is very strong and its importance cannot be over-emphasized. I do not know of any other dietary antioxidant that I would rank as more practical and more efficacious as an antioxidant at this location in the mitochondria.

βHB's role in both correcting mitochondrial dysfunction and activating anti-inflammatory pathways (next major section), suggests its actions are synergistic in the context of glaucoma and other neurodegenerative conditions.

Mitochondrial Redox Energetics - Details

βHB Produces More Cellular Energy Than Pyruvate

Metabolizing βHB in a working heart creates a 28% increase in output compared to the metabolism of pyruvate. (The authors suggest similar results should be observed in the brain, but it is harder to experimentally quantify output, so they worked with the heart for practical reasons.) Veech 2004

The fundamental reason why the metabolism of βHB produces an increase of 28% in the pumping efficiency of the heart is an inherently higher level of energy (heat of combustion) in βHB than in pyruvate. Veech 2004

If pyruvate were burned in a calorimeter, it would liberate 185.7 kcal/mole of C2 units, whereas the combustion of βHB would liberate 243.6, or 31% more calories per C2 unit than pyruvate. Veech 2004

Aside: One may then ask, why would there not be even more energy released if the cells were to metabolize a fatty acid (e.g., palmitate), which has even more inherent energy available during combustion than a ketone body. There are two reasons this does not occur: the architecture of the pathway of fatty acid oxidation and the enzymatic changes induced by elevation of free fatty acids. Veech 2004

βHB Supercharges The Mitochondrial Energy-Generating Process

βHB accomplishes something special at mitochondrial complexes I and II. (Co-enzyme Q relays electrons from these two complexes to complex III. Stefely 2017)

The electrons liberated from NADH at complex I are carried within the mitochondria by co-enzyme Q, where they are transferred to cytochrome C by complex III. The difference between the redox potential of the mitochondrial NAD couple and the co-enzyme Q couple determines the energy of the proton gradient generated by mitochondria. This in turn determines the energy of hydrolysis of mitochondrial ATP (delta G). Veech 2004

The following quote was shared above, but I will unpack it a bit further in this section:

βHB has the potential to improve sub-optimally functioning mitochondrial complex I, as well as to bypass more severe complex I dysfunction. Thickbroom 2021

The conversion step of βHB modifies the redox state of complex I (and co-enzyme Q), increasing its drive and thus supercharging complex I.

When ketone bodies are metabolized in heart, the mitochondrial NAD couple is reduced while the mitochondrial Q couple is oxidized increasing the redox span between complex I and complex III, making more energy available for the synthesis of ATP, and hence an increase in the delta G of ATP hydrolysis. This in turn is observable in the 28% increase in the hydraulic efficiency of the working perfused rat heart. Veech 2004 (Note: the metabolic effects of βHB are of particular relevance to brain and optic nerve metabolism, but the study was conducted using the heart for practical reasons of being able to measure output.)

This up-regulation can potentially rescue neurons that are still partially functioning.

Furthermore, the Krebs cycle is substantially up-regulated because of an abundance of βHB-derived acetyl-CoA. This increases the production of other metabolic intermediates by the Krebs cycle, such as succinate, which increases the drive of complex II, in essence bypassing complex I to restart the electron transport chain. The combination of these factors would be expected increase ATP resynthesis and cellular bioenergetics. Thickbroom 2021

Pyruvate cannot "supercharge" the mitochondrial energy-generating process in the same way that βHB does, as described above. The properties of βHB described above are unique. Simply supplying an energy substrate will not replicate this unique redox effect.

βHB Boosts Anti-inflammatory Pathways

βHB itself functions as a signaling molecule in addition to serving as an energy source. Therefore, evidence is accumulating that ... βHB and its metabolites directly reduce pro-inflammatory responses leading to neuroprotection. Gough 2021

βHB inhibits NRLP3 inflammasome activation through a mechanism that involves blocking potassium efflux and preventing ATP-induced ASC oligomerization, which are both needed for inflammasome assembly. The other ketone bodies, acetoacetate, acetate and butyrate, did not inhibit inflammasome activity. Gough 2021

βHB binds directly to receptors on cells in the brain. Gough 2021

βHB is mechanistically synergistic with the anti-inflammatory effects of omega-3 fatty acids, which are already known to be of value in glaucoma (via "binding of βHB-HCA1 and fatty acids-GPR40, which leads to ARRB2-dependent suppression of NRLP3 inflammasome function"). Gough 2021

The ketogenic diet was also shown to increase anti-inflammatory responses in glaucomatous mice, evidenced by an increased marker of neuroprotective and anti-inflammatory microglia, as well as by increased expression of an anti-inflammatory in retinas and optic nerves. Harun-Or-Rashid 2018-11 Gough 2021

Induced ketosis may promote a transition towards predominantly anti-inflammatory microglial states/phenotypes by several mechanisms, including inhibition of glycolysis and increased NAD+ production; engagement of microglial GPR109A receptors; histone deacetylase inhibition; and elevated n-3 polyunsaturated fatty acids levels. Morris 2020

βHB Calms Hyperactivated Microglia Cells

Hyperactivated microglia are known to be involved in the pathogenesis of glaucoma. βHB modulates glial hyperactivation in the retina and optic nerve (Harun-Or-Rashid 2018-11).

βHB [was] demonstrated to have direct effects on microglia ramifications, causing microglia to polarize toward the M2-like neuro-reparative and protective phenotype. Gough 2021 Harun-Or-Rashid 2018-11. βHB appears to promote anti-inflammatory signaling by altering microglial morphology (Gough 2021), which would address a fundamental aspect of the glaucoma pathology.

βHB Reduces Oxidative Stress

As reported in this study, βHB substantially protects against oxidative stress:

Concentrations of acetyl-coenzyme A and NAD+ affect histone acetylation and thereby couple cellular metabolic status and transcriptional regulation. We report that the ketone body d-β-hydroxybutyrate (βHB) is an endogenous and specific inhibitor of class I histone deacetylases (HDACs). Administration of exogenous βHB, or fasting or calorie restriction, two conditions associated with increased βHB abundance, all increased global histone acetylation in mouse tissues. Inhibition of HDAC by βHB was correlated with global changes in transcription, including that of the genes encoding oxidative stress resistance factors FOXO3A and MT2. Treatment of cells with βHB increased histone acetylation at the Foxo3a and Mt2 promoters, and both genes were activated by selective depletion of HDAC1 and HDAC2. Consistent with increased FOXO3A and MT2 activity, treatment of mice with βHB conferred substantial protection against oxidative stress. Shimazu 2013

This study supports that result:

Ketones decrease oxidative stress, increase antioxidants and scavenge free radicals.Greco 2016

These results strongly suggest that ketones improve post-TBI (traumatic brain injury) cerebral metabolism by providing alternative substrates and through antioxidant properties, preventing oxidative stress-mediated mitochondrial dysfunction. Greco 2016

As discussed above (see Mitochondrial dysfunction section), βHB increases the expression of mitochondrial uncoupling proteins, which is thought to be an important method of reducing oxidative stress within the mitochondria. Mitochondrial dysfunction, inflammation and oxidative stress are all interdependent and reciprocal processes.

βHB and Gut Microbiome Alterations

The gut microbiome has been associated with several neurological disorders, such as Alzheimer's disease, epilepsy, Parkinson's disease and multiple sclerosis. Gough 2021

βHB (with or without the context of a ketogenic diet) has been shown to positively influence each of these mechanisms:

  • increasing cerebral metabolism
  • increasing glucose transport (including glucose transporter 1 deficiency)
  • increasing mitochondrial functioning
  • reducing cerebral excitability
  • decreasing cortical spreading depressions (CSD) incidence
  • reducing oxidative stress (reactive oxygen species (ROS))
  • decreasing inflammation
  • improving the microbiome and increasing digestive health Gross 2019

The following results show that at least some of the benefits of the the ketogenic diet come from the gut microbial composition it confers:

Enrichment of and co-colonization with the ketogenic diet-associated Akkermansia and Parabacteroides was shown to restore seizure protection [in epilepsy]. Even in mice fed a control diet, transplantation of the ketogenic diet gut microbiota and treatment with Akkermansia and Parabacteroides each conferred seizure protection. Gross 2019

The rationale for a direct role of βHB (rather than solely the ketogenic diet) comes from this:

Given the close structural and functional similarity between butyrate (known to be beneficial to gut health) and βHB (which is β-hydroxy-butyrate), it could be hypothesized that higher systemic concentrations of βHB could substitute for microbial butyrate production [221]. Gross 2019 Gross 2019

Diet-induced changes in gut microbiome and fecal organic acids are associated with changes in cerebral spinal fluid (CSF) biomarkers of Alzheimer's disease (AD) in subjects clinically diagnosed with mild cognitive impairment.

The data suggest that the Mediterranean-ketogenic diet can modulate the gut microbiome and metabolites in association with improved Alzheimer's disease biomarkers in cerebrospinal fluid. Fecal butyrate was significantly increased on this diet. Nagpal 2019

βHB's Epigenetic Mechanisms

In addition to serving as an energy source and metabolic intermediate, a metabolite can exert a signaling function by binding to a protein. βHB's function as a signaling molecule was only discovered recently. It is now known that βHB can regulate gene expression Huang 2021

βHB increased SIRT1 expression. Scheibye-Knudsen 2014

Similar to what we reported in the "Reducing Oxidative Stress" section above,

βHB regulates the epigenome by modifying histone acetylation by inhibiting HDAC or activating Sirtuin 1. Gough 2021 Shimazu 2013

The following two studies reveal details of how βHB functions in previously unknown epigenetic roles:

Metabolism-mediated epigenetic changes represent an adapted mechanism for cellular signaling, in which lysine acetylation and methylation have been the historical focus of interest. We recently discovered a β-hydroxybutyrate-mediated epigenetic pathway that couples metabolism to gene expression. Huang 2021

Histone β-hydroxybutyrylation thus represents a new epigenetic regulatory mark that couples metabolism to gene expression, offering a new avenue to study chromatin regulation and diverse functions of β-hydroxybutyrate in the context of important human pathophysiological states, including diabetes, epilepsy, and neoplasia. Xie 2016

Further details in the same 2021 abstract quoted above reveal a substantial role for βHB in epigenetic regulation.

We report that the acyltransferase p300 can catalyze the enzymatic addition of β-hydroxybutyrate to lysine (Kbhb), while histone deacetylase 1 (HDAC1) and HDAC2 enzymatically remove Kbhb. We demonstrate that p300-dependent histone Kbhb can directly mediate in vitro transcription. Moreover, a comprehensive analysis of Kbhb substrates in mammalian cells has identified 3248 Kbhb sites on 1397 substrate proteins. The dependence of histone Kbhb on p300 argues that enzyme-catalyzed acylation is the major mechanism for nuclear Kbhb. Our study thus reveals key regulatory elements for the Kbhb pathway, laying a foundation for studying its roles in diverse cellular processes. Huang 2021

FOXO transcription factors are regulators of longevity that maintain cellular quality control and appear to be critical in processes and pathologies where damaged proteins and organelles accumulate in cells, including aging and neurodegenerative diseases. Webb 2014

βHB is a natural "enhancer"* of FOXO transcription factors. βHB results in transcription of the enzymes of antioxidant pathways (Veech 2017), as well as factors supporting neuroprotection and anti-aging.

Recently, it was shown that administration of βHB to a nematode species (C. elegans) extended its life span by approximately 20%, providing more evidence that βHB could be “an anti-aging ketone body.” In this work, βHB's life extension property was shown to involve two longevity pathways (DAF-16/FOXO and SKN-1/Nrf), a sirtuin, and an AMP kinase. Edwards 2014

dietary-supplements glaucoma neuroprotection bhb:beta-hydroxybutyrate • 2.2k views
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