Thursday, March 23, 2017

Just a little on complex I and models

OK, just a brief summary of the parts I like most from the excellent

The CoQH2/CoQ Ratio Serves as a Sensor of Respiratory Chain Efficiency.

We should all have a picture of the ETC looking a bit like this, omitting mtG3Pdh and ignoring supercomplex formation:

Guarás et al set up a model, a proof of principle extreme. They blocked the ETC completely at either complex III, or at cytochrome C or at complex IV. They even discussed short term oxygen deprivation as a generator of ROS, equivalent of blocking the extreme end point of the ETC. If you completely block the ETC in this way then any input through FADH2 containing enzymes to CoQ will always generate a massively reduced CoQ pool, one prerequisite for reverse electron transport (RET),

leading to the near complete disassembly of complex I. It's a model, an extreme version of reality. Fascinating in its own right, as was the ability of the fungal CoQH2 oxidase (AOX) to protect complex I completely from any of the engineered ETC defects:

AOX may not pump any protons but it does preserve complex I by reducing the extreme levels of CoQH2 which drive RET.

They subsequently went on to look at more physiological ways to generate RET and came to the conclusion that, as the balance of inputs from NADH vs FADH2 shifted, then the amount of complex I relative to complex III would need to be altered. RET is the physiological signal to balance complexes I and III against NADH and FADH2 supply.

Elegant is not the word.

They even went on to ascertain which cysteine residues were preferentially oxidised to disassemble the complex. They group around the FMN and the CoQ docking area, surprise surprise... OK. If you insist, here is the ribbon diagram from fig 5:

There's a lot of explanation in the text of what the colours and the asterisks mean.

All I really wanted to lay down with this post is that there is a physiological process where FADH2 inputs control complex I abundance. That is how it should be.

When you want a pathological model of complex I destruction, pathological levels of FADH2 input will deliver.


Thursday, March 16, 2017

Protons: More from Dr Speijer

Mike Eades forwarded this paper to me, by Dr Speijer:

Being right on Q: shaping eukaryotic evolution

How good is it?

He covers a vast field including loads on

The CoQH2/CoQ Ratio Serves as a Sensor of Respiratory Chain Efficiency.


Supercomplex assembly determines electron flux in the mitochondrial electron transport chain

and even

Mitochondrial fatty acid oxidation and oxidative stress: lack of reverse electron transfer-associated production of reactive oxygen species (another gift from Mike Eades).

I've far from finished reading the paper, these are just some of the gems. At some point I really will get round to a bit more on complex I and RET to regulate susbstrate processing but there is rather a lot happening at home and there might be something of a delay. To say the least.


Stearic acid, FADH2, complex I and cancer

Just a quick aside:

George cited this study in the comments of the last but one post:

Metformin inhibits mitochondrial complex I of cancer cells to reduce tumorigenesis

While I think it is possible that metformin might inhibit mtG3Pdh at levels below those which inhibit complex I, the complex I effect may well still be equally real.

He goes on to say:

"Remodelling the ETC - I like that. The idea of the ETC as a modular assembly that will be reconfigured as the substrate balance shifts. Directly by the effects of the substrates on its outputs".

Remodelling the ETC using RET from FADH2 inputs might be antineoplastic too ie, less complex I would then be available for whatever ox phos the cancer is capable of…

Now: What normal food will generate the highest FADH2 input to the ETC per unit NADH? Correct, stearic acid will.

So what does stearic acid do to breast cancer cells in culture?

Stearate preferentially induces apoptosis in human breast cancer cells

Does it work in a rodent model?

Dietary stearate reduces human breast cancer metastasis burden in athymic nude mice

Do people with breast cancer have low stearate levels in their cell membranes?

Erythrocyte membrane fatty acid composition in cancer patients

Does stearate-driven RET down regulate complex I availability in cancer cells which are partially dependent of glucose derived NADH oxidation via said complex I? And so kill them?



That poor old C57Bl/6 mouse

There is a is a link within the Guarás et al CoQ paper I put up in the last post (which I'll probably go back to in some detail in future posts). It's to a paper by Lapuente-Brun et al:

Supercomplex Assembly Determines Electron Flux in the Mitochondrial Electron Transport Chain

Here is my doodle, butchered from elsewhere, of the  Supercomplex (SC), also known as the Respirasome:

The things to note are the assembly of complexes I, III and IV in to one unit and that there are enclosed molecules of both CoQ and Cytochrome C within the SC. These electron transporters are isolated from their respective general membrane pools so as to ensure maximal efficiency of electron transfer within the integrated SC.

The SC doesn't just happen. It's glued together by specific assembly proteins. In particular C III and C IV are joined by a protein called Cox7A2l (to be renamed supercomplex assembly factor I, SCAFI).

Unless you are a C57Bl/6 mouse.

If you are a C57/Bl/6 mouse your SCAFI  is 4 amino acids too short. It doesn't work.

The whole, excellent, paper by Lapuente-Brun et al is really about supercomplex formation and preferential assembly of the basic complexes. But because it uses the broken C57Bl/6 as an example of defective respiration it does bring home how irrelevant this particular mouse might be to more humans with a more normal metabolism.

Quite how this defect of SC assembly might make that the C57Bl/6 mouse in to the strange metabolic item which it is is not clear.

But, at the core of normal respiratory supercomplex formation, the Bl/6 mouse broken. That's an awful lot of mouse research which is broken. You could almost feel sorry for obesity researchers. But not quite.

Just sayin'.


Thursday, March 09, 2017

Protons: The destruction of complex I

It is quite difficult to express how exciting this paper is to a Protons thread True Believer:

The CoQH2/CoQ Ratio Serves as a Sensor of Respiratory Chain Efficiency.

The paper covers essential everything I've worked at over the past few years about the ratio of NADH to FADH2 as inputs to the electron transport chain. They even give Dr Speijer an honourable mention. I like these people.

Look at the Graphical Abstract, it's pure Protons:

And these are their highlights:

But, as hinted in the highlights, they take it to another level, beyond where I've gotten to in Protons:

The destruction of complex I by eating saturated fat. Or by generating a few ketones.

Fantastic stuff.


Saturday, March 04, 2017

Trans fats vs linoleic acid

TLDR: Trans fats may not be as bad as they are made out to be.

This paper is comparing a high linoleate diet (using lard) to a soya oil derived (Primex) diet where much of the linoleate has been industrially hydrogenated in to trans fats and fully saturated fats.

A comparison of effects of lard and hydrogenated vegetable shortening on the development of high-fat diet-induced obesity in rats

The thing I like best about it is that, wait for it, they measured the fatty acid composition for their diets! HPLC and all that. Then, they put the results in the paper! On the down side their concepts about energy balance are pure CICO and rats have lingual receptors for fat which link to "hedonistic" centres in the brain. So they understand nothing, but we can forgive them for that.

Here are their results:

I think this might suggest that linoleic acid is obesogenic. Not that I've ever mentioned that before. Now obesity is obesity. What about health? Here are the numbers which matter, obviously insulin is the one we want to look at:

So, clearly, eating 11% of your calories as linoleic acid makes you fat and ill. The fat in the HVF (and the NF control) diet is made of:

"Diet compositions are presented in Supplementary Table 1. Primex pure vegetable shortening, a mixture of partially hydrogenated soybean and palm oil, was used by Dyets Inc. (Bethlehem, PA, USA) to formulate NF and HVF experimental diets".

Compositions panned out as :

Now these are measured, nothing is accepted from USDA food tables etc. So..... If we look at health outcomes (Table 3) in conjunction with diet composition (Table 1) it become pretty evident that, in these rats, trans fatty acid (TFA) feeding at 15% of total calories is positively health generating compared to linoleic acid feeding at 11% of calories. I did not expect this.

Aside: If any diet trial does not have its fatty acid composition measured you have no idea how much linoleic acid it contains. Usually more than you think. Also, joke of the century so far:

Question: If you are in a position of power over innocent folks who are trying to eat healthy food, which fat would you ban?

Answer: The wrong one!

End aside.

I was on a PubMed search looking for trans fat toxicity. In this current study trans fats not only fail to cause insulin resistance, they render insulin-glucose parameters identical to the NF fed rats, despite the TFA fed rats carrying an extra 100g of adipose tissue.

That is very interesting. You can't answer the whys and wherefores from this paper. The missing piece of information is probably FFAs.

Trans fats are very odd. On acute exposure to TFAs isolated adipocytes release stored FFAs. This is what Cromer et al have to say in their study:

Replacing Cis Octadecenoic [Oleic] Acid with Trans Isomers in Media Containing Rat Adipocytes Stimulates Lipolysis and Inhibits Glucose utilization

"Overall, results of this study clearly show that conversion of octadecenoic acid from the cis isomer [oleic acid] to the trans isomer [elaidic acid] in adipocyte media will substantially increase lipolysis and inhibit glucose oxidation and conversion to cell lipid".

Just to clarify: Acute exposure of freshly isolated adipocytes to trans-oleic acid causes fat release, decreased glucose uptake and decreased glucose incorporation in to lipids. Sounds like a weight loss drug to me.

I was expecting this lipolysis to show up as elevated fasting FFAs and elevated fasting insulin. But there isn't any insulin resistance under fasting conditions visible in Table 3 so I think it is reasonable to assume there is no elevation of FFAs at this time either......

The only explanation I can come up with is that the adipocytes of the TFA fed rats are not as "full" as they should be, due to trans fatty acid induced lipolysis. Giving some "space" within an adipocyte allows the insulin sensitising effect of PUFA oxidation to show, certainly while fasting and lipolysis is the correct state to be in. Hence the fasting insulin levels are normal despite the 100g of extra bodyweight.

Or you could theorise that excess lipolysis from the trans fats is being almost exactly matched by decreased lipolysis from the insulin sensitising effects of linoleic acid. The combination just happens to pan out close to normal, provided the rats carry 100g of excess adipose tissue.

Some degree of post prandial hyperinsulinaemia/insulin signalling seems essential just to maintain those extra 100g of accumulated fat, but it's clearly not visible in the post absorptive phase.

If anyone can come up with a better explanation, I'm all ears.

BTW, this obviously relates to Axen and Axen's work. Their hyper-obesogenic diet was based on something Crisco-ish from the 1990's:

"The hydrogenated vegetable fat contained ∼25% long-chain saturated, ∼44% monounsaturated and ∼28% PUFA, with ∼17% of total fat as trans fatty acids (manufacturer’s communication)".

With fat making up 60% of the calories in the diet, and that fat being 28% PUFA, this is somewhere around 17% of total calories as linoleic acid. That is a LOT of linoleic acid. At the time I thought that the trans fatty acids would be to blame. Nowadays I'm not so sure.

How much of the bad rap that trans fats have received is from the PUFA which travelled with them at the time? Without mentioning the amount of fructose in the biscuits. Modern Primex is much more hydrogenated, so lower in PUFA, than whatever Axen and Axen used. It's far less obesogenic too.


Other odd final thought: People who are obese and insulin sensitive: Are they the folks who eat most trans fats along with their hearthealthypolyunsaturated linoleic acid???????

Friday, March 03, 2017

Mitochondria in cancer cells

TLDR: This is just a speculative post about a paper which is interesting from the Protons point of view but is not really related to anything else.

This is the paper by Catalina-Rodriguez et al:

The mitochondrial citrate transporter, CIC, is essential for mitochondrial homeostasis

It is interesting on many levels. At the most basic, it gives you the actual concentration of glucose used to grow the cancer cells. This is pretty unusual.

I picked the paper up while looking at what Lisanti has published recently on the fuelling of cancer growth using ketones derived from glucose via cancer associated fibroblasts. He appears to have been asked to write a commentary on the Catalina-Rodriguez paper. Here it is:

Genetic Induction of the Warburg Effect Inhibits Tumor Growth

The basic idea of the commentary, partly agreed with by Catalina-Rodriguez, is that genetically inducing the Warburg Effect in cancer cells kills them. This is obviously very compatible with Lisanti's ideas, that cancer cells generate ATP via ox phos, and is the diametric opposite of the Warburg Effect.

But the paper by Catalina-Rodriguez, while it does discuss the Warburg Effect, also provides enough information that other explanations are tenable beyond those supported by Lisanti. Anyone looking at Lisanti's work without considering other explanations needs to be more circumspect. The paper is all about the mitochondrial citrate transporter, CIC.

We had better put CIC in to context first. It exports citrate from the mitochondria to liberate mitochondrial derived acetyl-CoA to the cytoplasm for anabolic processes.

It's an antiporter, it exchanges citric acid for malate. Citrate out, acetyl-CoA released, residual oxaloacetate reduced to malate via NADH, malate re enters the TCA.

We can add this to the TCA like this:

So CIC exports citrate and imports malate. Because citrate carries 3 negative charges and malate only two, a proton is carried out with the citrate which maintains electrical neutrality but generates a pH gradient. It's also clear that a cytoplasmic NADH is consumed converting oxaloacetate to malate and this is regenerated within the mitochondria by the TCA as malate reconverts back to oxaloacetate.

So we can look at this as a cycle:

It bypasses all of the energetic processes in the rest of the TCA so delivers very little to the ETC. The normal function of this pathway appears to be a safety valve for the cell when the mitochondria are presented with far too much acetyl-CoA.

In some cancer cells things go very awry.

Two hallmarks of cancer cells appear to be abnormal electron transport function and free radical leakage from the ETC. The free radical leakage is at levels which cause proliferation rather than apoptosis.

Complex I primarily reduces NADH to NAD+. If we have a dysfunctional complex I (either directly or by poor function downstream in the ETC) there is going to be a great deal of NADH per unit NAD+ within the matrix. High levels of NADH inhibit isocitrate dehydrogenase and so drive citrate export in to the aberrant CIC cycle. The cost is limited to one imported cytoplasmic NADH, the benefits are reduced generation of TCA derived NADH and FADH2... Plus cytosolic citrate is an inhibitor of glycolysis, so works as a brake on the excessive supply of pyruvate derived acetyl-CoA.

So some degree of poor ETC function can be accommodated by exporting acetyl-CoA rather than turning the TCA. The red cycle in the above doodle predominates and the TCA is almost inactive.

Under these conditions the mitochondria are largely protected from their dysfunctional electron transport chains. There are ROS (mostly superoxide) being generated but at levels which are not fatal to the cell although they can drive mutagenesis, in both mitochondrial and nuclear genomes.

What happens if you inhibit CIC in a cancer cell which is using CIC to both limit ROS production and to deliver cytoplasmic acetyl-CoA for anabolism? The whole extra-mitochondrial cycle should shut down, meaning acetyl-CoA has nowhere to go other than around the TCA. Less citrate can be exported, so cytosolic citrate levels fall. Falling cytoplasmic citrate allows increased glycolysis and this can feed even more acetyl-CoA in to the TCA. Complex I is still dysfunctional so we are then in to a massively elevated NADH:NAD+ ratio. We will also increase FADH2 driven CoQ reduction via complex II as the TCA turns. A high NADH:NAD+ is the prerequisite to getting an electron on to an oxygen atom to generate superoxide in complex I, back in Protons (22) I speculated this might be at FeS N-1a. A reduced CoQ couple also drives this via reverse electron transport.

Putting an electron on to oxygen aborts all of its downstream proton pumping. What might happen if a very high percentage of electrons jumped ship at complex I due to a grossly elevated NADH:NAD ratio and a reduced CoQ couple?

Increased superoxide, more oxygen consumption (though not necessarily at complex IV), much more ROS. Might the ROS release cytochrome C by oxidation of its cardiolipins, so giving collapse of the mitochondrial membrane potential and triggering apoptosis?

This is not the "genetic induction of the Warburg Effect", however Lisanti describes it. This is over driving a dysfunctional electron transport chain to the point of mitochondrial destruction. The most telling results section graph is this one:

These are the death rates for cancer cell cultures. On the left are three control cultures with functional CIC, on the right are those treated with BTA, a CIC inhibitor. NAC is n-acetyl cysteine. Which is the most lethal treatment? I think we must all agree with the devastating effect of pyruvate alone as being the most lethal treatment. Which gets zero mention in the text anywhere that I can find...

My idea would be that pyruvate is toxic because it bypasses glycolysis so cannot be shut down by the glycolytic inhibitory effect of raised cytoplasmic citrate. There is a spike of acetyl-CoA which cannot be avoided and which CIC levels are not set up to deal with. More acetyl-CoA enters the TCA, more NADH, more superoxide from complex I... The authors focus instead on the fifth column where pyruvate rescues cells from BTA toxicity. I can see no logic to this and have no explanation for that particular result. At least I do actually mention the results which don't fit my hypothesis!

The next very interesting result is the effect of uncoupling. CCCP is an uncoupler which reduces the MMP. This leads to mitophagy +/- apoptosis. A functional CIC cycle saves cells from CCCP damage. You could argue that CIC is just a Saviour of Distressed Cells. But on a more interesting level: Uncoupling normally markedly increases electron flow down the ETC. In normal mitochondria this reduces ROS generation. But if the ETC is leaking electrons to generate ROS under even normal flow it's easy to see why uncoupling can allow massive ROS generation. CIC is protective because it keeps electrons out of the ETC.

They also found that CCCP induces CIC production. My assumption would be that CIC is induced by ROS and CCCP generates ROS. The same thing happens with rotenone by the opposite process. Rotenone does not uncouple, it blocks the ETC at the exit of complex I. This gives reduced conversion of NADH to NAD+, markedly increase the NADH:NAD+ ratio, electrons jump to O2 to N-1a to form superoxide... CIC induction is the solution to limit this.

There are some very interesting results here.

I have absolutely nothing against looking at CIC inhibition as a management for certain subgroups of cancers. It may well help, but thinking about what is actually happening might give more insight.


Wednesday, February 15, 2017

Linoleic acid and Tuberous Sclerosis

TLDR: I don't like linoleic acid much.

Tuberous Sclerosis (TS) is a genetic disease which affects mTOR signalling and predisposes to many problems, one of which is early onset kidney tumours. People with TS also have a tendency to suffer from intractable epilepsy so, almost by accident, a number of them have had their tumours closely monitored while eating a deeply ketogenic diet for the epilepsy. Does the KD help slow tumour growth?


To look at this in more detail a group in Poland has used a TS rat model and tried to manage the disease with a KD. This is the study:

Long-term High Fat Ketogenic Diet Promotes Renal Tumor Growth in a Rat Model of Tuberous Sclerosis

It is a very interesting paper. All rats were euthanased at 14 months of age, having spent differing periods of time eating a close derivative of the F3666 ketogenic diet. The longer the rats had spent on this diet, the more aggressive the renal tumour progression was found to be, especially in the rats which ate it for eight months (the longest duration).

Other than this there were some additional interesting findings. Insulin and glucose did (almost) exactly what you would expect:


What is more interesting is that growth hormone increased progressively with duration of time spent on the KD:

This was noted by the authors and was considered as one of the potential explanations of the increase in tumour burden after 8 months on KD:

"Likewise, it has been shown that the growth hormone activates the MAPK pathway, thus its overproduction in the ketogenic groups may also boost ERK1/2 phosphorylation. We believe that HFKD induced the ERK1/2 activation results as a cumulative effect of the renal oleic acid accumulation and the systemic growth hormone overproduction".

I'm not convinced by the oleic acid idea but no one would argue against identifying elevated growth hormone as a stimulant for tumour growth.

Overall we have progressively falling levels of both glucose and insulin, with a progressively rising growth hormone concentration, over the eight months of a ketogenic diet. I asked myself if there might be an explanation for the nature of these reciprocal changes, before thinking about the tumour growth.

Looking at the insulin-glucose levels we can say that insulin sensitivity increased with time on the ketogenic diet, using the surrogate HOMA score based on the product of insulin and glucose. That's despite a concurrent tripling of GH levels, which should induce insulin resistance.

The obvious concept is that GH was being used to maintain normoglycaemia in a set of rats which were developing progressively increasing (pathological) insulin sensitivity and might, theoretically, have become hypoglycaemic on a very low carbohydrate, very low protein diet. That is, despite having been on a high fat diet, they failed to maintain adequate (ie physiological) insulin resistance to spare glucose for the brain.

Does GH sound like a metabolic solution for the problem of pathologically increasing insulin sensitivity? Pathological insulin sensitivity: Is anyone thinking linoleic acid? Well, I am (now there's a surprise).

The rats were raised on a standard chow of un-stated composition before switching to their KD. It seems a reasonable assumption that the chow was relatively low in fat. Exactly how much linoleic acid was supplied is unknown but other rodent chows I've seen described or analysed tend to provide about 2% of calories as linoleic acid.

The F3666 derived diet looks, depending on the lard composition, to be in the region of 18% omega 6 PUFA. That's high (yes, another rodent study has shown that mice develop NASH on this diet, no surprise there).

The rats were raised initially on a starch based diet so their juvenile adipose tissue would probably be composed of DNL derived saturated and monounsaturated fats, supplemented by a little PUFA from the diet. Transition to F3666, which provides approximately 18% of calories in the form of linoleic acid, generates a metabolism much more dependent on linoleic acid. The younger the rats were when they switched to F3666, the less "normal" adipose tissue they would have had available and the more rapidly they would end up with adipose tissue (and plasma) high in linoleic acid.

Rats on true ketogenic diets do not become obese, even on F3666. So we have slim, omega 6 fed rats. Small adipocytes, no excess FFA release, no insulin sensitivity differential between adipocytes and the rest of the body. There is nothing to over-ride the insulin sensitising effect of linoleic acid. Both adipocytes and the rest of the body become progressively more insulin sensitive mediated through linoleic acid. They don't become obese because insulin stays so low due to the lack of carbohydrate and protein. The excess insulin sensitivity only kicks in gradually because their pre-stored, chow derived adipose tissue provides a supply of physiological FFAs which can act as a buffer to the sensitising effect of 18% linoleic acid for a while.

Glucose falls progressively due to the development of progressively increasing pathological insulin sensitivity, linoleic acid induced. GH may well be a stress response to maintain normoglycaemia under these conditions. The GH may or may not be acting as a tumour promoter, but we cannot ignore the role of linoleic acid in its elevation.

Now the tumours.

We all remember Sauer's rats with their xenografts which grew like wildfire as soon as he starved them? Yes. The tumours grew because they were exposed to linoleic acid released from their adipocytes under starvation. Linoleic acid is a precursor for 13-hydroxyoctadecadienoic acid, better known as 13-HODE. Sauer demonstrated that this was the problem very neatly, at the cost of extensive vivisection. I doubt anyone would be allowed to replicate his work today.

We have no idea of either the linoleic acid or the 13-HODE concentration in the plasma of the F3666 fed TS rats. It would be interesting to know. It might matter...

I particularly think it might matter because F3666 is going to be the "off the shelf" KD that a lot of researchers are going to use.....

At the end of the last post I mentioned that fact that any person who is currently obese through following conventional advice to replace healthy saturated fats with 13-HODE generating linoleic acid is probably carting around kilos of a tumour growth-promoting precursor. In Sauer's study all that was needed to release the linoleic acid was starvation. I would suggest that ketogenic eating might do the same, especially if it is based around saturophobic stupidity (think of kids in the USA with tuberous sclerosis on a "medical" ketogenic diet, or the rats in the above study). There is also anecdote on tinternet that patients of Dr Atkins did fine if they had CVD but those with cancer did badly. I find this plausible. They were obese because they were loaded with linoleic acid and they may well have followed an Atkins diet high in hearthealthypolyunsaturates. That's a good way to grow a cancer.

Sauer found a solution in the form of fish oil to limit tumour growth in his rats, most especially EPA. The very long chain omega 3 PUFAs activate g-protein coupled receptors to reduce lipolysis from adipocytes and activate fatty acid oxidation from the diet. VLC omega-3 fatty acids do not promote excessive insulin sensitivity via the Protons based FADH2:NADH ratio concept because they are specifically oxidised in peroxisomes, not mitochonria. The peroxisomes shorten them to C8 length and then pass this to mitochondria as caprylic acid which has a "palmitate-like" FADH2:NADH ratio of 0.47 which is fine for maintaining physiological insulin resistance.

You do have to wonder whether the benefits of fish/oil in a population loaded with linoleic acid might stem largely from this effect of limiting adipocyte release of that linoleic acid. An interesting idea.

I still find it breathtaking how much the lipid hypothesis of heart disease might have done to injure individual people exposed to its recommendations. Which includes much of the world.


Thursday, February 09, 2017

Musing about linoleic acid

TLDR: I have long wanted to know how you could have differential insulin resistance between adipocytes and the rest of the body. Linoleic acid appears to be the answer

This is a set of thoughts, jotted down without references, that have been of interest to me over the last six months while I have neglected poor old Hyperlipid.

Linoleic acid produces excessive whole body insulin sensitivity.

Adipocytes distend under this effect.

Distended adipocytes release unregulated FFAs.

FFAs cause insulin resistance which eventually overcomes the excess systemic insulin sensitivity.

Hyperinsulinaemia results.

Here we go.

I have nothing against the role of both sucrose and refined starch in the pathogenesis of both obesity and insulin resistance. Anyone who has read Weston Price or Vilhjalmur Stefansson will be only too aware that the substances most easily transported over long distances to affect unacculturated peoples were sugar and flour. No one was carting margarine or corn oil to the Arctic in the early part of the last century. Both fructose and alcohol, both of which deliver largely uncontrolled calories in to cells, can clearly generate aspects of metabolic syndrome. However I am interested in linoleic acid and free fatty acid release from adipocytes at the moment, so I'll leave the case against sugar for the time being. So, linoleic acid:

One of the core ideas which came out of the Protons thread was that palmitic acid is a generator of physiological insulin resistance. The complementary fatty acid is palmitoleate and this generates less insulin resistance for when insulin action is desirable.

The function of physiological insulin resistance is to limit ingress of calories in to a cell when there is a surfeit of calories available. Or to limit the ingress of glucose when glucose is in short supply and it's best not to waste it on non-glucose dependent tissues.

In to this well balanced system comes linoleic acid as a bulk nutrient. The oxidation of linoleic acid, by the Protons hypothesis, produces even less insulin resistance than palmitoleate and so undermines the ability of a given cell to refuse caloric ingress in excess of its needs. Failure to develop insulin resistance means that insulin continues to act.

Continued action of insulin in a calorie replete cell results in diversion of excess calories to intracellular triglycerides (+/- glycogen). This is very reasonable in adipocytes, at the cost of obesity, but less acceptable in tissues such as muscle, liver and pancreas.

The underlying pathology is continued inappropriate insulin sensitivity.

But obesity is a condition more normally associated with insulin resistance.

From the Protons point of view the question is: How can linoleic acid acid, which results in pathological insulin sensitivity whole body, eventually result in insulin resistance, also whole body?

Insulin activates lipoprotein lipase and inhibits hormone sensitive lipase. Combined, these effects facilitate fat storage in adipocytes. But there is another lipase which controls both basal and stimulated lipolysis known as Adipocyte Triglyceride Lipase (ATGL). One, amongst the several, factors which control ATGL is perilipin A, a protein which surrounds the lipid droplet in adipocytes. It is probably an interaction between ATGL and perilipin A which determines the increase in basal lipolysis as adipocyte lipid droplet size increases.

So there is a balance. Linoleic acid is allowing increased insulin action and so causing fat accumulation with a suppression of both FFA release and adipocyte lipid turnover. ATGL is looking to limit adipocyte distension by allowing lipolysis, so raising FFAs, outside of the control of insulin. But will only act on basal lipolysis in response to progressive lipid droplet expansion.

For as long as the pathological sensitivity to insulin exceeds the FFA release driven by ATGL we can have worsening obesity but metabolic syndrome is delayed.

Once ATGL mediated lipolysis raises systemic FFA levels enough, despite insulin continuing to act on adipocytes, we can then have systemic insulin resistance with insulin sensitive adipocytes. Insulin resistance when combined with a carbohydrate based diet requires elevated insulin levels which will continue to act on the insulin sensitive adipocytes. Which will increase ATGL driven lipolysis...

This is metabolic syndrome.

Once the elevated glucose from insulin resistance kills off enough beta cells then insulin levels drop, glucose levels rise, HSL is disinhibited so FFAs rise. You might even get ketoacidosis. This is type 2 diabetes. ATGL might even take a break.

The first approach to correcting it is carbohydrate restriction, so dropping hyperinsulinaemia and minimising the vicious cycle. Doing something about the kilos of linoleic acid stored in an obese person's adipocytes is an altogether longer term project.


Can linoleic acid keep you slim?

TLDR This is a weird study which might show the insulin sensitising effect of linoleic acid in obesity resistant rats.

Saturated, but not n-6 polyunsaturated, fatty acids induce insulin resistance: role of intramuscular accumulation of lipid metabolites

I deeply dislike this paper on so many levels. I'm not going to go through everything which is wrong with it, I'll just highlight a few aspects which strike me as interesting.

The first (unexpected) finding is that none of the groups of rats on high fat diets were significantly heavier than the chow fed rats. The PUFA fed rats were slightly lighter (you read that correctly) and the SAT fed rats were slightly heavier, but all ns at eight weeks of feeding. Who can buy rats which can eat coconut/lard and not gain weight? Korean rats? Korean lard? Who knows. But neither the safflower oil nor the lard fed rats become obese. I find this very, very odd in a set of "we bought them off the shelf" Wistar rats. But well, maybe. Just seems odd.

Second point (expected) is that not only did the SAT fed rats develop insulin resistance, but the PUFA fed rats did not, in fact they showed enhanced insulin sensitivity when compared to either chow or SAT fed rats. This is compatible with the Protons view of PUFA oxidation in non-adipocyte distended rats.

Third (expected) is that as insulin acted on muscles under PUFA those muscles developed the highest levels of stored triglycerides. This is exactly what you would expect, insulin diverts excess calories to be safely sequestered as triglycerides.

The fourth point (very unexpected) is that while triglycerides were being happily sequestered in to muscle, they weren't being sequestered in to adipocytes. Adipocyte sequestration of triglycerides (obesity) happens routinely in a huge swathe of linoleic acid feeding trials in many different species.

Sooo, can you extract anything from this mass of contradictions? I'm just wondering whether if you happened upon a generally obesity resistant rat strain you might be left viewing the insulin sensitising effect of PUFA oxidation without the insulin resistance generating effect of adipocyte distension.

Maybe it separates out the the opposing drives on the adipocyte under PUFA exposure...