Insulin resistance 2.0

Insulin resistance is only an emergency.

Imagine that you are driving a car and you step on the gas (insulin). You expect an increase in engine speed, acceleration, but nothing. A red light on the dashboard lights up and the car goes into emergency mode (activates HIF-1α).

Why IR 2.0? Because this post is a loose follow-up to the post on insulin resistance, which quite knowingly and controversially states that we lack hydrogen peroxide. Well, it is not quite true, rather we lack oxygen in the tissues, CO2, nitrites, ground-level ozone or light, but it is correct to state that hydrogen peroxide works against insulin resistance. The controversial part is that you'll hear everywhere how ROS, free radicals, cause insulin resistance, and I say that hydrogen peroxide lets glucose into the cells. I am not alone. Recently, in a similar vein, the well-known blogger Petro Dobromylskyj published a series of articles entitled Insulin mimesis. There he shows how various components of the diet can trigger a series of reactions that result in an increase in the concentration of hydrogen peroxide on the outside of the cell membrane. This peroxide is carried inside and activates essentially the same pathway as insulin. If you add to that that hydrogen peroxide also prevents the release of fats from the fat droplets, then the substitute is almost perfect. From an evolutionary point of view, hydrogen peroxide was simply there first as the main regulatory agent for the regulation of metabolism and oxidation, only in higher organisms did insulin become involved.

Hydrogen peroxide generated on the outside of the cell membrane by the NOX enzyme is able to replace insulin and let glucose into the cell

EGF activates NOX and thus H2O2 and insulin signaling (pAKT), on the contrary, extracellular catalase, which is activated by the long-term presence of peroxide (lipid peroxides), removes H2O2 and suppresses signaling that takes place through the cell wall via aquaporin 3 (AQP3, column xAQP4).

Let's repeat that, the formed hydrogen peroxide carries the main information about how the oxidation of the fuel is going, if there is a problem to be solved. Under normal circumstances, all hydrogen peroxide is immediately eliminated at the point of formation by either catalase or glutathione peroxidase to water. The resulting O2 or NADP+ perform their other functions, primarily controlling respiration and oxygen availability. We talk about insulin resistance mainly in connection with the inability of cells to process glucose quickly after a carbohydrate meal. The scenario may be that first, more glucose increases oxygen demand through increased production of hydrogen peroxide. This requirement is not sufficiently converted to CO2 production, so the first rescue mechanism starts, letting more glucose into the cell and activating the anaerobic process of glycolysis, the result is enough energy without the need for oxygen supply and also lactate. Lactate can easily be converted back to pyruvate, so if the situation doesn't last very long, lactate is only used as a temporary storage for glucose and nothing else happens. It does not prevent the further entry of glucose. If lactate is produced persistently, MCT4 transporters open by activating the transcription factor HIF-1α and pseudohypoxia is initiated.

Insulin increases glycolysis in the cytosol, not oxidation in the mitochondria. Nitric oxide NO increases glycolysis less, but suppresses oxidation in mitochondria.

What happens if we simultaneously burn a fuel other than glucose itself, such as alcohol. According to the results of this study, it is clear that alcohol takes precedence over all other fuels. This is how poisons normally behave, namely they have priority, the body needs to get rid of them as quickly as possible. In the case of alcohol, both glucose oxidation and fat oxidation are reduced. This is very interesting because it is not very easy to stop the oxidation of fats. We know that fats are burned in mitochondria and peroxisomes. Mitochondria can be prevented from entering, but peroxisomes are the organ for poison metabolism and cannot be easily stopped. Only by taking cofactors for metabolism from them. Alcohol takes away the basic cofactor for beta oxidation, NAD+ molecules. With its high activity, it converts NAD+ to NADH so quickly that other fuels are out of luck and have to wait. This will cause not only the suppression of fat burning, but also the suppression of glucose burning and manifest as immediate insulin resistance. Glycolysis stops.

Effect of alcohol consumption in humans (0.75 g/kg body weight) on the oxidative metabolism of carbohydrates (CH), fats (FAT) and proteins (PROTEIN). Glucose administered intravenously, alcohol suppressed the burning of other fuels.

The same limitation of glycolysis occurs even without alcohol when burning fats, or in the presence of fats intended for burning, i.e. free fatty acids. However, we have very different free fatty acids. Some are processed only in mitochondria, some in peroxisomes, some in both. The difference is that peroxisomes produce malate and lactate into the cytosol. Mitochondria don't do that. For some processes, this malate replaces the missing NADH in the cytosol, i.e. outside the mitochondria, and also enables passage into the mitochondria via the so-called malate shuttle. It turns out that precisely the lack of NADH for material exchange with mitochondria could be one of the main factors affecting the willingness of cells to process glucose. Saturated fats are processed inside the mitochondria, and in the cytosol there will be a lack of NADH for the breakdown of glucose into lactate. This manifests outwardly as insulin resistance. Fats that are partially processed in peroxisomes allow partial preservation of glucose breakdown, but is this a good thing? Probably not, because it will cause more competition on the third mitochondrial complex and thus create more superoxide and hydrogen peroxide. If that would lead to a higher oxygen supply then nothing would happen, but if it doesn't then we have another problem.

If we let more different fuels into the cell for processing, this always leads to an increase in the formation of superoxide and hydrogen peroxide. This allows more glucose to enter the cell so that oxidation can be turned off and replaced by glucose fermentation to lactate. This is a normal defense mechanism to reduce the production of free radicals and hydrogen peroxide. It is the situation I have already described above. So far, insulin sensitivity has not been impaired, but if there is a lack of NADH, which I have already described, the cells will have a problem, there is no way to process glucose. The oxidation path is narrow and cannot be expanded, the fermentation path is also blocked. What will happen? The uptake of glucose into the cell will stop and lactate will not be produced either. I don't know exactly which enzyme it stops at, I would guess the phosphorylation of glucose due to the lack of ATP from fermentation in the cytosol. In any case, this condition manifests as insulin resistance, is caused by fuel competition, and is metabolically beneficial because it limits the generation of excessive superoxide and hydrogen peroxide concentrations in the cell. Beneficial! Remember it! Insulin resistance when burning fat is beneficial!

But only as long as there is enough oxygen. If it's not enough, we have a big problem.

A lack of oxygen (black bars) causes muscle cells to switch to anaerobic metabolism, insulin-resistant cells (i.e. in the presence of fat) retain oxidative metabolism and are destroyed.

The presence of free fats suppresses glycolysis and prevents the transition to anaerobic metabolism during hypoxia. Unlike normal metabolism, the SDH enzyme works in the opposite direction and produces succinate.

So everything has been right so far, so what's wrong? Well, nothing with this system. It is set so that in fat cells, fats turn off the glucose fermentation system, so the H2O2 level threshold to induce HIF-1α expression is quite high due to the lack of succinate in the presence of saturated and monounsaturated fats. In other cells, where free fat is only rare and in small amounts, it is easy to switch between oxidation and fermentation of glucose by means of HIF-1α expression, and it's bad when it is not possible, i.e. in the presence of fats.

It's bad when glucose fermentation is switched on in fat cells and oxygen is no longer used.

Example: Long polyunsaturated fatty acids stored in fat cells, which are processed in local peroxisomes, produce enough malate even in the presence of fat, thus providing malate for transfer to mitochondria and production of succinate, which causes activation of HIF-1α and switch to glucose fermentation with acetylated electron transport chain enzymes. This leads to anaerobic metabolism and continuous growth of cell size to extreme proportions. The fat cell then does not function properly.

Second example: Liver cells, which normally never process glucose by fermentation to lactate and should never activate HIF-1α, still do so when flooded with leptin and palmitate from adipose tissue with activated HIF-1. Among other things, this will cause a decrease in GLP-1 levels, obesity and fatty liver.

Third example: Cardiac muscle, which metabolizes mainly fats, but its own content of free fatty acids is normally low. In the case of diabetes, the protective anaerobic mechanism of HIF-1α expression does not trigger even in the absence of oxygen. Dysfunctional fat cells damaged by linoleic acid so that they produce lactate and free fatty acids permanently (activated HIF-1α), i.e. regardless of insulin levels, flood the body with an excess of free fatty acids and turn off the possibility of switching to anaerobic mode in tissues that vitally need it .

Vitamin E added to the diet eliminates the negative effect of linoleic acid.

A high-fat diet without omega-6 linoleic acid based on coconut oil will indeed cause obesity, but without disrupting metabolism. Fat cells remain fully functional and small.

Switching fat cells as the peaks of the histogram, the largest cells (right) enlarge the longest time, gradually more cells add in waves. After each wave, the environment of the surrounding cells changes, and the next one switches to anaerobic mode only after some time.

What I haven't mentioned yet, fat cells turn on HIF-1α expression individually, one by one. If one cell crosses the threshold of positive feedback H2O2+succinate -> HIF-1α, then it flips and no longer needs oxygen and does not produce H2O2. This will reduce the H2O2 level and signaling to other cells in the vicinity, it will last for a while. Only when the situation worsens again will they also switch to anaerobic metabolism. This is very bad for the fat cell, from this moment on, this still small cell will begin to grow, inflate with new fat and acquire enormous dimensions over time. How it goes can be seen on the graph of the size distribution of fat cells. The cells that switched first create a small peak on the far right, then a younger switch to the left creates another peak, then a gap and another peak, etc.

The threshold for turning on HIF-1α expression is variable, depending on the concentration and composition of free fatty acids in the cytosol. It also depends on the amount of ROS, i.e. H2O2. The amount of peroxide increases with a lack of oxygen. At the same time, the lack of oxygen also increases the production of nitric oxide, which, like H2O2, admits glucose into the cell, but reduces the activity of oxidation in the electron transport chain, saving oxygen. Thus, the lack of oxygen logically facilitates the expression of HIF-1α. In adipose tissue, it causes the activation of HIF-1α in fat cells and increases the amount of free fatty acids released throughout the body, thus burdening the liver, which in turn has to re-form triglycerides and VLDL particles. This will lead to an increase in the TG indicator in the blood and to an increase in the insulin level and later to an increase in glucose. It can even lead to type 2 diabetes. Advice? Limit omega-6 oils and breathe properly (less) to increase the CO2 content of the blood and thus facilitate the delivery of oxygen to the tissues. In mice, damage caused by omega-6 linoleic acid can be prevented by adding vitamin E or MCT oil to the diet. It probably works that way in humans too, studies with MCT oils show positive results, I don't know about vitamin E, I didn't search.

Supplement:

The question of succinate is very interesting because in hypoxia succinate dehydrogenase (SDH) works in the opposite direction, it is pushed by malate and FADH2 to form succinate. Thus, here succinate activates HIF-1α. During the normal course of the TCA cycle, succinate pushes against FADH2, and the more succinate, the greater the TCA cycle activity (supports thermogenesis). The function of succinate is different under different conditions. Therefore, coconut oil, which supports the activity of SDH by supporting omega-oxidation, can help when part of the saturated fats are converted into dicarboxylic acids, which are processed in peroxisomes. So thanks to the production of succinate, SDH is supported in the normal direction and thus counteracts the activation of HIF-1α (unlike unsaturated fats metabolized in perixosomes).

One more addition, such an outline of how glucose, peroxisome-metabolized unsaturated fats, and fructose interact (Per peroxisome, Mit mitochondrion, Glu glucose, Fru fructose, Pyr pyruvate, Lac lactate):

If we do not activate peroxisomes by unsaturated fats, then with a lack of NAD+ in the cytosol, the fermentation of glucose to lactate starts (green arrows) and the level of NAD+ is restored (insulin sensitivity). This does not apply if unsaturated fatty acids are also metabolized in peroxisomes (red arrows). The level of NAD+ in the cytosol is not replenished and glycolysis stops (metabolic insulin resistance as with alcohol). This could also stop fat metabolism in peroxisomes, but it does not if oxaloacetate is available. It enters peroxisomes, takes electrons and leaves them as malate. It then enters the mitochondrion and exits as citrate (and succinate, if TCA cycle is not running). Citrate serves to create new fats and oxaloacetate to continue the beta oxidation of fats in peroxisomes. Succinate can activate HIF-1α and starts rescue metabolism without the need for oxygen and without the production of CO2.

Omega-6 linoleic acid enters this process exclusively by producing NADP+ via the DECR enzyme, this allows malate to be processed into pyruvate via the ME1 enzyme and further into lactate, thus allowing the NAD+ level to be restored and glycolysis and insulin sensitivity to be preserved (mechanistically, this process may also occur as export of NADP+ from the peroxisome via the isocitrate α-ketoglutarate shuttle directly producing NAD+). But a higher level of lactate will further promote the activation of HIF-1α even in an environment where this transcription factor should not be activated.