#41

Do we have any evidence that what matters is the change in O2 rather than the time spent in hypoxia?

If that were the case, we would find many papers showing the benefits of intermittent hyperoxic therapy. But I couldn’t find a single one. On the other hand, there are many papers on the benefits of intermittent hypoxic therapy or combined hypoxia–hyperoxia.

Also, this paper suggests that it’s just that at 30%, the body thinks it is in hypoxia: Oxygen Variations—Insights into Hypoxia, Hyperoxia and Hyperbaric Hyperoxia—Is the Dose the Clue? 2023

Fratantonio et al. [14] described the activation time trend of oxygen-sensitive transcription factors in human peripheral blood mononuclear cells (PBMCs) obtained from healthy subjects after one hour of exposure to mild (MH), high (HH), and very high (VHH) hyperoxia, corresponding to 30%, 100%, and 140% O2, respectively. They confirmed that MH is perceived as a hypoxic stress, characterized by the activation of HIF-1 α and nuclear factor (erythroid-derived 2)-like 2 (NRF2), but not of the Nuclear Factor kappa-light-chain-enhancer of activated B cells (NF-kB). Conversely, HH is associated with a progressive increase in oxidative stress leading to NRF2 and NF-kB activation, accompanied by the synthesis of glutathione (GSH). After VHH, HIF-1 α activation is totally absent and oxidative stress response, accompanied by NF-kB activation, is prevalent. Intracellular GSH and Matrix metallopeptidase 9 (MMP-9) plasma levels parallel the transcription factors’ activation patterns and remain elevated throughout the observation time (24 h). This confirms that, in vivo, the return to normoxia after MH is sensed as a hypoxic trigger characterized by HIF-1 α activation. On the contrary, HH and VHH induce a shift toward an oxidative stress response, characterized by NRF2 and NF-kB activation in the first 24 h post-exposure.

If I’m correct hen what matters is the time in hypoxia, not the degree of change: HIF1α/SLC7A11 signaling attenuates 6-hydroxydopamine-induced ferroptosis in animal and cell models of Parkinson’s disease 2025

Hypoxia-inducible factor-1α (HIF1α) is a transcription factor consisting of α and β subunits. In the presence of normal oxygen levels (normoxic state), HIF1α undergoes hydroxylation by prolinehydroxylase (PHD), leading to its degradation by the Von Hippel-Lindau (VHL) complex. However, in hypoxic conditions, this degradation process is inhibited, allowing HIF1α to accumulate and form a complex with HIF1β. Subsequently, HIF1α translocates from the cytoplasma to the nucleus,where it regulates the transcription of downstream genes by binding to the hypoxia response elements (HREs).9 Yang et al showed that HIF1α, but not HIF2α, played crucial roles in ferroptosis resistance of cancer cells under hypoxia via upregulation of the glutamate transporter SLC1A1.

(Also interesting from this paper: “Our findings shown a significant decrease in HIF1α expression in both animal and cell models of PD induced by 6-OHDA. Moreover, upregulation of HIF1α promoted ferroptosis, while downregulation of HIF1α inhibited this process. These findings indicate that HIF1α has diverse roles in diseases associated with ferroptosis.”)

I also trust the “Lindiness” of hypoxia: going in altitude for a retreat has been considered healthy for a long time. See also: Acute and cumulative effects of hypoxia exposure in people with Parkinson’s disease: A scoping review and evidence map 2024

#42

I haven’t read up on this recently, but when I read up on it in 2022 it was the change in partial pressure of O2. This is what is used in HBOT where really high partial pressures are used.

What we don’t really know is what the minimum change in partial pressure is and the periods that are required at the higher and lower partial pressures.

HBOT does not use any hypoxia.

I have not, however, read up on any more recent papers.

My blog post is I think unique in trying to analyse the distinction between HIF, NRF2 and NF kappa B activations.

Re reading your post where it says: " They confirmed that MH is perceived as a hypoxic stress,"

What they should have written is that the switch back to normal oxygen stimulates HIF1alpha. Strictly the name HIF should be changed to remove Hypoxia and replace it with a name implying a reduction in partial pressures.

That is what the normobaric oxygen paradox is.

This has been cited quite recently

#43

I will try to be simple: if I hyperventilate my oxygenometer will say 100%. What does this mean? I thought it meant that my red blood cells cannot carry more oxygen.

If I take an oxygenometer into an HBOT will it show 300%? Or get stucked in 100%?

#44

This is what they wrote: “This confirms that, in vivo, the return to normoxia after MH is sensed as a hypoxic trigger characterized by HIF-1 α activation. On the contrary, HH and VHH induce a shift toward an oxidative stress response, characterized by NRF2 and NF-kB activation in the first 24 h post-exposure.” (They cite the “normobaric oxygen paradox”)

But why would 30% to 21% activate HIF-1 α but not 100% to 21%? So it’s not only the Δ(ppO2) that matters.

#45

More on this: Pulsed Hyperoxia Acts on Plasmatic Advanced Glycation End Products and Advanced Oxidation Protein Products and Modulates Mitochondrial Biogenesis in Human Peripheral Blood Mononuclear Cells: A Pilot Study on the “Normobaric Oxygen Paradox” 2024

We have previously characterized the time trend of oxygen-sensitive transcription factors in human PBMCs, in which the return to normoxia after 30% oxygen is sensed as a hypoxic trigger, characterized by hypoxia-induced factor (HIF-1) activation. On the contrary, 100% and 140% oxygen induce a shift toward an oxidative stress response, characterized by NRF2 and NF-kB activation in the first 24 h post exposure.
Our results show that AGEs and AOPPs increase in a different manner according to oxygen dose. Mitochondrial levels of peroxiredoxin (PRX3) supported the cellular response to oxidative stress and increased at 24 h after mild hyperoxia, MH (30% O2), and high hyperoxia, HH (100% O2), while during very high hyperoxia, VHH (140% O2), the activation was significantly high only at 3 h after oxygen exposure. Mitochondrial biogenesis was activated through nuclear translocation of PGC-1α in all the experimental conditions. However, the consequent release of nuclear Mitochondrial Transcription Factor A (TFAM) was observed only after MH exposure. Conversely, HH and VHH are associated with a progressive loss of NOP response in the ability to induce TFAM expression despite a nuclear translocation of PGC-1α also occurring in these conditions. This study confirms that pulsed high oxygen treatment elicits specific cellular responses, according to its partial pressure and time of administration, and further emphasizes the importance of targeting the use of oxygen to activate specific effects on the whole organism.
Our results show that this “linearity” on reduced risk is not only present on the toxicity side, but also on the elicited response. In fact, it seems that in the first 24 h following a session, lower oxygen concentrations act more positively than higher levels of hyperoxia on mitochondrial biogenesis factors.

So I wouldn’t go above 30% O2. But should we also go to 15%?

#46

Its also the exposure to high oxygen. That is a time and quantity issue and I do some detailed analysis in my blog post.

Basically you need to avoid long exposures at higher partial pressures of oxygen otherwise you kick off NF kappa B. Interestingly also very low oxygen levels also kick off NF kappa B and that is part of the function of the stem cell niches.

#47

They had an exposure of an hour. HBOT uses 20 mins.

#48

Looking at my post I find

https://www.sciencedirect.com/science/article/abs/pii/S0952818012004175

This is 100% oxygen for 30 mins which increases reticulocytes (an indicator of HIF).

#49

Yes, that is SPO2 it is a different thing to the percentage of oxygen in the air. The “partial pressure” of oxygen is the key issue. That is that proportion of air pressure caused by oxygen and it affects how much oxygen is dissolved in water. In the end this drives the partial pressure of oxygen next to the mitochondrial membrane. This is lower than that in blood serum, but it directly affects how the mitochondria behave. It is also driven by the serum partial pressure.

#50

Interesting here: ClinicalTrials.gov

The Nobel Prize in Physiology was recently awarded to scientists who established the basis for our understanding of how varying oxygen levels affect cellular metabolism, which paved the way for promising new strategies to fight diseases. Breathing low levels of oxygen, or hypoxia, stimulates glucose uptake in skeletal muscle via 5’ adenosine monophosphate-activated protein kinase (AMPK), the same signaling pathway as muscle contraction, which acts independently from the actions of insulin. Thus, patients with type 2 diabetes were exposed to either normoxia or 60 min of continuous hypoxia (fraction of inspired oxygen of ~0.15, arterial oxygen saturation of 92%) immediately before performing a 4-hour intravenous glucose tolerance test. Hypoxia lowered blood glucose levels and did not affect insulin concentrations, therefore, it was suggested that the improved glycemic control was caused by the activation of the AMPK pathway in combination with an improved insulin sensitivity. Similarly, a single exposure to intermittent hypoxia, consisting of 6 min at a fraction of inspired oxygen of 0.13 alternated with 6 min of normoxia for 1 hour, improved glycemic control in patients with type 2 diabetes. Specifically, there was a greater decrease in glucose levels measured immediately after intermittent hypoxia, and the increase in glucose levels following a meal was attenuated following intermittent hypoxia when compared to a placebo condition. A decrease in glucose levels was also observed following a single session of intermittent hypoxia, consisting of brief desaturation and resaturation cycles to maintain an arterial oxygen saturation of 80% for approximately 70 min, in overweight and obese individuals with normal baseline glucose levels.

#51

https://www.sciencedirect.com/science/article/pii/S0021925820698672

The toxicity of high levels of oxygen is caused by increased ROS. At a point the cells defences are overwhelmed and NRF2 and NF kappa B start being initiated.

It is important to avoid this. Hence if you start with high levels of oxygen then the period should be short. It has to be long enough to stablise.

I use 8 minutes.

#52

According to Dr Dallam, adaptation to lower oxygen partial pressure for RBC boosting (live high; train low) only comes from being in lower O2 “almost all of the time”. Sleeping in a low O2 tent wouldn’t being enough.

I was asking him if I could get benefit from shallow breathing …. keeping my spo2 at 90% for 10 minutes would be helpful for signaling RBC increase. He said no. He said it might help with co2 tolerance which is good enough.

I do it 1x/week. I hope also to get additional epigenetic signaling.

Dr Nelson said to use nasal breathing during exercise and breath holds to stress the body on lower O2 and higher CO2. I do 5 sets of 30 second exhale holds plus 10 seconds breathing (5x 40 seconds = 200 seconds or almost 3.5 minutes) every morning. Subjectivity I get an energy/ alertness boost from it. I think my spleen releases extra RBC so it’s also useful for accelerating my cardio warmup, I think.

Any thought?

#53

There is an interesting question if there is a difference between people who live at a high altitude and never visit sea level or other lower altitudes and those that shift between altitudes.

I don’t know the answer.

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#54

I put all the other ongoing trials here: Hypoxia–Hyperoxia trials - Google Sheets

Most use 10% O2, 1.5 min hypoxia, 1 min normoxia, 15 cycles, once daily, 3 days per week.

@John_Hemming did you notice the same impact on glycemic control with your protocol? Discussion about Oxygen, Hypoxia and Hyperoxia 2024 03 30 AntiAging Reading Group - #50 by adssx

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#55

One of my difficulties is separating out individual interventions and their effects. Hence although I can say in the round that I am doing reasonably well on glycemic control (HbA1c below 5 lowest was 4.18) I cannot say precisely why.

From a process perspective I think a middling to short period at a higher oxygen level followed by an extended period at a lower oxygen level would get the best results.

I think the cells need a period of time to get HIF functioning properly and if you take the oxygen back up too quickly then that will undermine the activation of HIF.

I have no evidence base to justify this, however.

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#56

Among all these trials, two are especially interesting as they’re done by the VA Office of Research and Development:

  • Mild Intermittent Hypoxia: A Prophylactic for Autonomic Dysfunction in Individuals With Spinal Cord Injuries (MIH and AD) (NCT05351827): “The overall goal of the present proposal is to investigate if daily exposure to mild intermittent hypoxia (MIH) can ameliorate autonomic dysfunction in persons with SCI as well as improve mitochondrial and microvascular function.”
  • Intermittent Hypoxia-initiated Plasticity in Humans: A Multi-pronged Therapeutic Approach to Treat Sleep Apnea and Overlapping Co-morbidities (NCT05558501): “The investigators propose that exposure to MIH has a multipart effect. MIH directly targets heart and blood vessel associated conditions, while simultaneously increasing upper airway stability and improving sleep quality. These modifications may serve to directly decrease breathing episodes and may also serve to improve usage of CPAP. Independent of its effect, MIH may serve as an adjunctive therapy which provides another path to reducing heart and blood vessel abnormalities that might ultimately result in improvements in exercise capacity and reverse performance fatigue in individuals with OSA. […] In the recent funding cycle, the investigators established that repeated daily exposure to mild intermittent hypoxia (MIH) coupled with CPAP modifies autonomic nervous system activity and dramatically decreases blood pressure compared to CPAP treatment alone. […] Although the investigators obtained some indirect evidence that modifications in autonomic nervous system activity were coupled to the reduction in blood pressure, the investigators did not establish if modifications in microvascular function were evident. Microvascular dysfunction together with sympatho-vagal imbalance may have consequences not only for peripheral vascular resistance and blood pressure but also for muscle perfusion and metabolism, thereby limiting exercise performance and increasing fatigability in patients with OSA. Thus, reductions in blood pressure and improvement in microvascular function following treatment with MIH might serve to improve exercise capacity and reverse performance fatigue in individuals with OSA. Besides its potential effect on autonomic and cardiovascular function, the investigators and others previously established that acute exposure to MIH initiates sustained increases in upper airway muscle activity in humans. This sustained increase is a form of respiratory plasticity known as long-term facilitation. However, in the absence of CPAP the investigators have shown that acute MIH immediately prior to or during sleep leads to increases in apnea severity. This might occur because the manifestation of long-term facilitation is absent in the presence of hypocapnia. Hypocapnia can be induced during sleep by the initiation of another form of plasticity known as progressive augmentation. However, it is possible that the combination of daily exposure to MIH administered many hours before the sleep period may mitigate the effects of progressive augmentation leading to increased upper airway stability. Independent of this possibility, the investigators showed in the previous funding cycle that increased upper airway stability following treatment with MIH was coupled to a reduction in therapeutic CPAP and improved adherence. However, improved adherence to CPAP might also be linked to an increase in the arousal threshold to both respiratory and non-respiratory stimuli. All the uncertainties outlined above will be addressed in the present proposal.”

Sleep apnea causes intermittent hypoxia but intermittent hypoxia could also be a treatment for sleep apnea?! What if sleep apnea was a reactive mechanism of the body to induce hypoxia and improve mitochondrial function (at the detriment of other functions) @John_Hemming ?

To understand this paradox, this 2024 paper suggests that the the dose makes the poison when it comes to hypoxia:

Researchers have sought to enhance the therapeutic benefits of IHE, but they have encountered challenges. Increasing the number of IHE sessions tends to diminish its effectiveness, while reducing the oxygen levels below 10-11% is poorly tolerated by patients and can lead to adverse side effects.
As a response to these challenges, a novel approach has emerged in recent decades, intermittent hypoxia-hyperoxia exposure (IHHE), which involves combining hypoxic and hyperoxic periods (FiO2 = 0.30–0.40) within the IHE regimen.
These methods may be of major interest in the fight against cognitive decline since they improve many of the physiological mechanisms currently responsible for early cognitive decline and the onset of neurodegenerative diseases such as high blood pressure, hyperglycemia, and inflammation.
Extended IHE exposure for 22 days enhanced blood lipid profiles in seniors with severe coronary artery disease. Additionally, IHT reduced fasting glucose levels in prediabetes
Importantly, IHE and IHT also improved cognitive functions in both healthy and cognitively impaired older adults.
This systematic review reveals that both IHT and IHE show improvements in cognitive functions and cerebral health-related outcomes, including ScO2, VMCA and CVC. Additionally, IHE showed an increase in ScO2 only when used with cognitively impaired populations. However, IHT and IHHT had no significant effect on BDNF levels. IHHT demonstrated benefits in improving cognitive function, but this was only investigated in cognitively impaired populations; future studies need to test these effects on healthy older adults. Notably, there are no studies on IHHE in both cognitively and non-cognitively impaired older adults.
These enhancements can be attributed to cellular responses that promote neuroprotection and neuroplasticity, mechanisms that are crucial in countering age-related cognitive decline.
These responses include enhanced antioxidant defenses, anti-inflammatory mechanisms, improved mitochondrial function, and effective autophagy. Enhanced mitochondrial biogenesis and function improve neuronal survival, and ensure protein homeostasis, preventing the accumulation of misfolded proteins that can lead to neuronal death. Neural connections are reorganized and new ones are formed, which is essential for learning, memory, and recovery from injury. This process is supported by neurotrophic factors, which are upregulated through exercise, enhancing synaptic plasticity and cognitive function. Furthermore, myokines and exerkines, released during physical activity, play significant roles in these processes by crossing the blood-brain barrier and stimulating in their turn neurotrophic factors, highlighting the systemic benefits of regular exercise on brain health.

:thinking:

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#57

In this paper, they found that “The lifespan extension observed in IHT does not require HIF-1 but is partially blocked by loss of DAF-16/FOXO.”

And in this paper from last month, a team at Harvard created “hypoxia in a pill” by combining two drugs:

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GBT440 (Voxelotor) is “an allosteric activator of oxygen affinity recently approved for sickle cell anemia”. PT2399 is an analogue of belzutifan (“a member of a new class of HIF-2α inhibitors approved for renal cell cancer”).

Preclinical studies have demonstrated the therapeutic potential of hypoxia for treating mitochondrial disorders. In the Ndufs4-KO mouse model of Leigh syndrome and the shFxn model of Friedreich’s ataxia, continuous breathing of 11% oxygen can prevent and reverse neurological disease, while 55% oxygen accelerates disease. Multiple mechanisms likely underlie the benefits of hypoxia, including attenuation of oxygen toxicity from brain hyperoxia, restoration of Fe-S clusters, and normalization of oxygen sensing. Alternative means of reducing oxygen delivery, including sublethal carbon monoxide and severe anemia, also reverse brain disease in Ndufs4-KO mice. Intermittent regimens of inhaled hypoxic air — 16 hours of 11% and 8 hours of 21% — have proven ineffective — probably due to a compensatory, HIF-2α–dependent increase in hemoglobin (Hb) that, combined with periods of 21% oxygen, may be detrimental. Collectively, these studies highlight the potential of hypoxia therapy but also underscore the need for more practical modalities that are safe and effective.
our drug combination could safely achieve tissue hypoxia
Brain MRI revealed characteristic T2-intense, Leigh-like lesions and/or hemorrhages in vestibular or cerebellar nuclei that were attenuated or even absent with the combination
Although neither drug individually affected lifespan, the combination extended median lifespan by 30% from approximately 70 to 98 days and maximum lifespan from 80 to 144 days (P < 0.0001)
Our results provide preclinical proof of concept that simultaneously enhancing Hb oxygen affinity while antagonizing HIF-2α can mimic the effects of continuous hypoxic breathing for therapeutic benefit. The regimen did not confer as impressive a lifespan rescue as continuous breathing of 11% oxygen, probably because GBT440 has a short half-life (6), and for practical reasons, we treated the mice five weekdays per week. Future studies in humans are required to evaluate the safety of this combination, given that hypoxia can be associated with acute and long-term side effects. Such safety studies could pave the path for first-in-human “hypoxia-in-a-pill” trials in patients with mitochondrial disease.

Do these two papers update your views @John_Hemming? Interesting mention of anemia, which is a protective factor in PD, together with another source of hypoxia… asthma!

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#58

I haven’t spent a lot of time looking at HIF 2 alpha. For now I have concluded that activating HIF 1 alpha is a good thing and hence I look for tools to do that.

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#59

I’m not sure that HIF 1 alpha is the key to benefits.

See also: Hypoxia extends lifespan and neurological function in a mouse model of aging 2023

We report that chronic continuous 11% oxygen commenced at 4 weeks of age extends lifespan by 50% and delays the onset of neurological debility in Ercc1 Δ/- mice. Chronic continuous hypoxia did not impact food intake and did not significantly affect markers of DNA damage or senescence, suggesting that hypoxia did not simply alleviate the proximal effects of the Ercc1 mutation, but rather acted downstream via unknown mechanisms.
Hypoxia significantly delays the onset of replicative senescence in cultured mammalian cells. Compared to standard atmospheric conditions (21% oxygen at sea level), hypoxia extends the number of population doublings until replicative senescence in mouse embryonic fibroblasts, primary human lung fibroblasts, and even in the presence of specific senescence-inducers such as etoposide and nutlin-3a.
While the above studies come from cell culture and invertebrate models, 2 observations raise the possibility that hypoxia could slow mammalian aging. First, the naked mole rat (H. glaber), whose lifespan far exceeds that which would be predicted by phylogeny or body mass, experiences significant durations of relative ambient hypoxia because of extreme crowding in their burrows (though the precise oxygen tension has not been measured in their natural environment). Second, in genetically heterogenous HET3 mice, a hypoxia transcriptomic signature appears to be shared among myriad interventions shown to extend lifespan in both the NIA Interventions Testing Program and long-lived mutants.
An important future goal is to define the mechanism by which chronic continuous hypoxia is extending lifespan in this model, and the extent to which this mechanism overlaps with that of pathways known to be involved in aging, such as mTOR and insulin signaling. Three plausible mechanisms are the following: (i) activation of the HIF pathway; (ii) diminution of oxidative stress; and (iii) interruption of the vicious cycle of neurodegeneration and neuroinflammation. With respect to HIF pathway activation, in our prior work in the Ndufs4 KO model, we showed that HIF activation was not sufficient to recapitulate the benefits of hypoxia, and in the current work, we did not detect a signature of HIF activation in the brain based on RNA-seq.
In multiple contexts, hypoxia has been demonstrated to increased lifespan (yeast, C. elegans) or time to replicative senescence (primary human lung fibroblasts), via an increase in ROS production which then activates life-extending pathways, a form of hormesis.
At present, we do not know where in this vicious cycle between neuronal damage and inflammation hypoxia exerts its effect—through dampening the inflammatory response to neuronal injury, or conferring neuronal resilience to the stress of DNA damage and inflammation, or some combination of the two. In either case, the vicious cycle appears to be blunted.
Epidemiologic evidence suggests that lifelong oxygen restriction might slow the aging process in humans. Though there are many potential confounders to this finding, recent cross-sectional studies in Bolivia have demonstrated significant enrichment for nonagenarians and centenarians at very high altitudes. There is also intriguing data that suggests there are potential benefits of moving to altitude in adulthood. In a longitudinal study of over 20,000 soldiers of the Indian Army assigned to serve at 2 to 3 mile elevations above sea level for 3 years between 1965 and 1972, their risk of developing the major sources of age-related morbidity in modern societies—diabetes mellitus, hypertension, and ischemic heart disease—was a fraction of the risk of their comrades serving at sea level

The interplay of NAD and hypoxic stress and its relevance for ageing 2025

In conclusion, NAD metabolism and cellular hypoxia responses are strongly intertwined and together mediate protective processes against hypoxic insults. Their interactions likely contribute to age-related changes and vulnerabilities. Targeting NAD homeostasis presents a promising avenue to prevent/treat hypoxic insults and – conversely – controlled hypoxia is a potential tool to regulate NAD homeostasis.

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#60

There is an issue about ROS being higher with higher O2.

However, I think there is plenty of evidence for HIF 1 alpha being useful.

It may be that people would do better at 15% O2 than 21%.