A very interesting study, and one of the few that I have seen openly acknowledge the existence of the Randle Cycle and its importance to human health. Namely, the study demonstrated that increased FAO is sufficient to cause cellular dysfunction, senescence and ultimately diseases and the process known as “aging”. It is starting to look more and more plausible that aging/disease are nothing but symptoms of increasingly reduced glucose oxidation and increased FAO. As the study says, increased FAO “muscles out” glucose in competition for access to the Krebs/TCA Cycle. This increase in FAO leads to overabundance of acetyl-CoA and the abudance of acetyl group is what the study claims increases the activity of a gene called “p16”, implicated in many chronic conditions associated with aging. However, the study mentioned another mechanism that is mostly ignored by medicine and that mechanisms is the increased reactive oxygen species (ROS) generated by FAO compared to glucose. As discussed on many podcasts, ROS is actually a misnomer and is a symptom of “reductive” rather than “oxidative” stress. In addition, more than 98% of the ROS are generated when there is blockage at one (or more) of steps of the electron transport chain (ETC) and the accumulated electrons start flowing backwards through the chain – i.e. reverse electron flow (REF). REF itself further contributes to the already present reductive stress (low mitochondrial NAD+/NADH ratio) since the actual process of REF further lowers the mitochondrial NAD+/NADH ratio, this lower NAD+/NADH ratio further limits oxidation of glucose and promotes FAO, thus creating a vicious cycle. The buildup of electrons as a result of increased FAO is handled by the cell through an emergency mechanism by converting some of the superfluous acetyl-CoA into citrate and using that citrate to synthesize fat, which is then fed into the beta-oxidation cycle and ends up again as acetyl-CoA – again, a vicious cycle and it just so happens that this metabolic phenotype is the very hallmark of cancer. Medicine now recognizes such metabolic derangement in cancer, but claims that the ETC blocks are due to external agents, cancerous mutations, or just aging in general. But the study below makes it quite clear that the truth is actually backwards and that all that it takes for the “cancer” metabolism to occur is simply a sufficient shift from oxidation of glucose towards FAO, as per the Rande Cycle. This increased FAO results in lowering of the FAD/FADH ratio and thus a functional (co-factor deficiency) block at complex II of the ETC, which ultimately leads to the electron buildup, REF and thus drop in NAD+/NADH ratio as well. In contrast, oxidizing mostly glucose does not generate REF (since it does not lower the FAD/FADH ratio) and when the electrons flow forward it accounts for less than 2% of the total generated ROS during OXPHOS (the other 98% being generated as a result of REF). In other words, all that it takes for both function and structural pathological changes to occur, as well as senescence/aging, is increased FAO at the expense of glucose, which results in a shift of the redox balance in favor of reduction, forming a vicious metabolic cycle.
An interesting finding of the study is that saturated fats (SFA), despite being much preferable than PUFA for oxidation, are also capable of affecting the Randle Cycle and shifting the redox balance in favor of reduction. The specific lipid used in the study to increase FAO at the expense of glucose was octanoate (caprylic acid), and providing sufficiently high concentrations of that SFA was sufficient to trigger the increased FAO and cause senescence. Ray mentioned this on a few podcasts when people asked him if keto diets would be OK if one ate 100% saturated fat. His answer was that a diet which contains only saturated fats in its lipid fraction is preferable to a “standard” Western diet (i.e. 30%+ PUFA on average), however long term consumption of a keto diet with 100% SFA in its lipid fraction is also not optimal since it would generate less CO2, more ROS and ultimately cause the same metabolic derangements as a standard Western diet. Thus, he said, oxidizing primarily glucose is of paramount importance when it comes to systemic health.
In addition, the study contains an interesting finding that a widely used cancer drug known as doxorubicin can produce the exact same metabolic derangements and senescence as the increased FAO, which is another way of saying that the drug is harmful and ultimately (oh, the irony!) carcinogenic. One of the hallmark side effects of standard chemotherapy is that it visibly ages the patient, and the study below provides an explanation why – i.e. most chemotherapy drugs are likely metabolic blockers like doxorubicin and as such not only lead to accelerated aging, but are direct causes of secondary diseases (including cancer), further ruining the patient’s health already compromised by the cancer and its diagnosis. The study exposed another widely used drug – the lipid lowering agent fenofibrate – as also being a pro-senescent agent, and this should not be surprising considering fenofibrate increases FAO. To make matetrs worse, unlike doxorubicin, fenofibrate is used by a much larger group of people as prevention for heart disease (CVD) with (again) the irony being that the drug likely promotes the very disease it is supposed to prevent.
The good news is that this vicious metabolic cycle caused by increased FAO can be broken through various methods that aim at either increasing glucose oxidation, reducing FAO or both. Aside from the increased supply of glucose, substances such as thiamine (vitamin B1), niacinamide (vitamin B3), biotin (vitamin B7), aspirin, oxidizing agents / quinones, thyroid, progesterone, DHEA, pregnenolone, testosterone, DHT, etc all work to increase glucose oxidation, while inhibiting FAO. It just so happens that the first four of the above mentioned substances are the cancer protocol I am using for the xenograft experiments that I have been running for the past 2+ years, and the results so far corroborate both the bioenergetic theory and the findings of the study below. Namely, everything in the body is controlled by metabolism/bioenergetics and oxidizing anything other than (primarily) glucose for an extended period of time ultimately leads to degeneration/disease, and is the primary driver of what we, perhaps mistakenly, call “aging”.
https://doi.org/10.1126/sciadv.ado5887
“…Recent studies have indicated that senescence contributes to aging and age-related diseases (1, 3). p16 expression increases in various tissues with age (7, 8). Increased p16 expression decreases the tissue-regenerative potential of pancreatic β cells and neuronal progenitor cells (2). Moreover, p16-expressing senescent cells that accumulate in the body impair heart and kidney function and shorten healthy lifespan (9). This impaired organ function may be due to the secretion of inflammatory cytokines and chemokines by senescent cells, a phenomenon termed the senescence-associated secretory phenotype (SASP) (10). The link between p16 and aging is further supported by the finding that the INK4/ARF locus, which encodes the senescence effectors p16, alternative reading frame (ARF), and p15, is a hotspot for susceptibility single-nucleotide polymorphisms associated with age-related diseases, such as atherosclerosis and diabetes (1). Therefore, elucidating the regulatory mechanisms of p16 expression may provide clues to understanding the mechanisms of aging. Numerous transcription factors and histone-modifying enzymes have been implicated in p16 expression (6).”
“…We found that upon DNA damage, BNIP3 is phosphorylated by ATM and contributes to an increase in the number of mitochondrial cristae. This increase in cristae enhances the oxidation of fatty acids to acetyl-CoA, an acetyl group donor, thereby promoting histone acetylation around the p16 transcription start site (TSS). Notably, pharmacological activation of FAO alone can induce senescence in fibroblasts, endothelial cells, and mouse liver.”
“…FAO activation decreases acetyl-CoA production from glucose (38). This effect, known as the Randle cycle, is primarily due to inhibitory phosphorylation of pyruvate dehydrogenase (PDH), the mitochondrial enzyme that converts pyruvate to acetyl-CoA (Fig. 4A). Isotope labeling with [U-13C]glucose indicated that the conversion of pyruvate to acetyl-CoA and then to citrate and acetylated amino acids decreased during doxorubicin-induced senescence (fig. S9A). In addition, doxorubicin treatment increased PDH phosphorylation (Fig. 4G and fig. S9, B to D). This increase was attenuated by the knockdown of CPT2, BNIP3, or ATM but not by knockdown of p16. In contrast to doxorubicin treatment, oncogenic RAS expression did not increase PDH phosphorylation (Fig. 4H), perhaps reflecting that PDH phosphorylation is not solely regulated by FAO (39). These results are consistent with FAO activation during DNA damage–induced senescence.”
“…To further investigate the importance of FAO in senescence induction, we used the medium-chain fatty acid octanoate. Unlike the more abundant long-chain fatty acids, octanoate freely crosses mitochondrial membranes (40). When added to cells, octanoate is readily oxidized to acetyl-CoA, an acetyl group donor, and promotes histone acetylation and the associated expression of lipid metabolism–related genes. Treatment of IMR-90 cells with octanoate increased p16, CPT2, and phosphorylated PDH levels and decreased lamin B1 levels (Fig. 5A). In contrast, the ATM-p53-p21 pathway and γH2AX foci were largely unaffected (Fig. 5, A and B). Octanoate treatment increased the percentage of SA-β-gal–positive cells (Fig. 5C). In addition, octanoate treatment decreased the percentage of EdU-positive proliferating cells and increased nuclear size (Fig. 5D and fig. S10A). These changes in cell proliferation and nuclear size were suppressed by p16 knockdown (Fig. 5D). Octanoate treatment increased the expression of inflammatory cytokines and chemokines (fig. S10B). Similar results were obtained with fenofibrate, a lipid-lowering drug that activates FAO through the transcription factor peroxisome proliferator–activated receptor α (PPARα) (Fig. 6, A to E, and fig. S10, C and D) (41). We confirmed that fenofibrate-induced p16 expression was attenuated by CPT2 knockdown (Fig. 6B). Treatment with octanoate or fenofibrate increased mitochondrial ROS levels, decreased mitochondrial membrane potential, and increased the number of cristae and mitochondrial length (fig. S10, E to I).”
“…In this study, we have shown that nuclear DNA damage signaling to mitochondria via BNIP3 induces senescence by activating FAO (Fig. 7L). Our results suggest that DNA damage–activated ATM translocates to mitochondria, where it phosphorylates BNIP3. BNIP3 increases the number of cristae and activates FAO. This activation may reflect an attempt to repair DNA damage through histone acetylation (44). If DNA damage persists, the resulting prolonged FAO activation appears to promote histone acetylation for p16 expression. However, histones are not the only proteins whose acetylation state is regulated by acetyl-CoA levels (45). In addition, FAO activation has effects other than increased acetyl-CoA levels (15, 38, 41). In particular, increased mitochondrial ROS production may contribute to the induction of senescence (12, 46). Further studies are needed to elucidate the mechanisms by which BNIP3 regulates cristae and by which FAO drives senescence. We used doxorubicin and oncogenic RAS, which cause DNA damage (1), to conclude that DNA damage–activated FAO drives senescence. However, we cannot completely exclude the possibility that doxorubicin activates FAO independently of DNA damage.”
