Thursday, December 04, 2014

ACCORD and musings on insulin

There are a couple of things I would just like to mention in passing. Jenny Ruhl has just posted a nice entry about ACCORD. This is very important. Lowering your blood glucose is significantly protective against CVD events. This is the exact opposite of the initial analysis of the results where a flawed interpretation of the data led to vociferous suggestions that lowering the HbA1c of diabetics might be actually dangerous. Hopefully this reanalysis will put an end to such stupid ideas which are still dangerously prevalent today.

Before Jenny posted the above I had been thinking about both metformin and insulin for the management of diabetes. I have posted on insulin, which is probably the ideal drug for diabetes management provided it is combined with low carbohydrate eating, in the past but it bears reiterating.

This is my opinion. If you can control your diabetes with metformin and wish to eat lots of carbohydrate, by all means get on with it, that's your choice. Not checking or not worrying about your blood glucose excursions might be a mistake. What you mean by good control might not involve HbA1c values in the 5% region or below.

If you need insulin to control your blood glucose, you have no choice. It's low carb. Live with it.


Some researchers (who write third rate papers using a rather inappropriate pancreatectomised dog model) are now starting to wake up to the fact that the pancreas secretes insulin in to the portal vein, not the subcutaneous tissues. In normal individuals insulin/glucose arrives at the liver via the portal vein and insulin facilitates transport of the glucose in to the liver, being metabolised in the process. Relatively little post pranial insulin or glucose penetrates to the peripheral circulation in a normal individual.

EDIT: Gretchen has kindly pointed out that the liver uptakes glucose through GLUT2, not GLUT4. The function of insulin, acting on its receptor (facilitating its degradation), is to suppress gluconeogenesis and hepatic glucose output. This is the correct function of the elevated portal insulin level. It makes no difference to the issues with peripheral vs portal insulin, but the correction is welcome. END EDIT

Once a person needs insulin to control their blood sugar levels they inject it subcutaneously. This will invariably elevate the systemic concentration of insulin. It will only modestly elevate the portal vein level. This is very important.

In the cited paper the dogs get a meal with 50% of calories from carbohydrate, 30% from fat and 20% from protein. In control dogs, instrumented but not pancreatectomised, the portal vein insulin after the meal is, at certain time points, ten times the peripheral systemic concentration. This is what is needed to allow the liver deal with the glucose load from the meal while simultaneously protecting the body from both hyperglycaemia and hyperinsulinaemia.

Subcutaneous insulin will make the rest of the body do the liver's job of clearing post prandial glucose, the liver can't manage because it never sees the requisite ten times the normal peripheral insulin concentration needed to deal effectively with the portal glucose load.

What happens when you use the rest of the body as a glucose sump? From the paper:

"Peripheral hyperinsulinemia is associated not only with increased risk of hypoglycemia, but also an increase in catechol and cortisol secretion and lipolysis [14], deleterious effects on vessel walls [6], ischemic heart disease, hypertension and hyperlipidemia [8], and abnormalities in hemostasis [10]"

As always, I would add that it's the obese, blind, legless person in the queue for dialysis who pays the bill for eating the carbohydrate.

This is the situation for all type I diabetics and the more advanced type 2 diabetics. The only route round it is to use intra peritoneal insulin which is, in part, absorbed through the mesenteric veins so is partially portal vein selective. There are, needless to say, a stack of complications to intra peritoneal insulin infusion. Tight control of glucose using subcutaneous insulin from a blood glucose controlled pump is no solution. Though glycaemia is better controlled it is still at the cost of too little insulin in the portal vein and too much in the periphery, using the body as a glucose sump. Over the years I have never been quite able to decide whether hyperinsulinaemia or hyperglycaemia is the primary factor which kills nerves and kidneys. It's a difficult call. And a fascinating discussion in its own right.

What happens if you eat a diet very low in starch?

Very little insulin is ever secreted by the pancreas, especially as glucokinase down regulates. Very little glucose ever needs to be taken up by the liver. Very little insulin will be metabolised by the liver. The insulin gradient between the portal vein and the systemic circulation will be as low as you can practically get it. If someone still needs to inject insulin alongside a very low carbohydrate diet, and many might not, injecting a very small amount subcutaneously will deliver an arterial concentration to the gut, pancreas and eventually to the portal vein and liver which is still quite close to what the portal vein might have supplied. If the body is not using insulin the tissues will not extract it, so portal and systemic concentrations will converge. Everything pans out at some near basal level.

A very low carbohydrate diet is not perfect for insulin dependent diabetics but it is streets ahead of anything else. What people do or do not consider a "normal" human diet will not get around this. Need exogenous insulin? You are not in a position to eat ancestral starch. It's a simple matter of anatomy, physiology and biochemistry.


Thursday, November 27, 2014

The P479L gene for CPT-1a and fatty acid oxidation

In order to work out what is happening with a given child having an episode of hypoglycaemia as a result of having the P479L version of CPT-1a, we need some information.

My thanks to Mike Eades for the full text of the paper on the Canadian Inuit, which does include a certain amount of useful clinical data.

Here is the snippet about a young girl having a hypoglycaemic episode while hospitalised:

“Plasma free fatty acid was 3.8 mmol/L and plasma 3-hydroxybutyrate was 0.5 mmol/L”

Blood glucose was 1.9 mmol/l at the time. An FFA level of 3,800 micromol/l is impressively high. She was generating a small amount of ketones.

No one would argue with intravenous glucose at this point, the question is about how she got here.

So. The problem here does not (as I'd initially thought) appear to insulin induced suppression of FFAs to a level at which beta oxidation fails to support metabolism. FFAs are very high, even for an P479L person after a short fast. With ketones starting to be produced (and low blood glucose) I feel it is reasonable to assume that her liver glycogen is depleted and, while some fatty acids are entering the hepatocytes, not enough of them are being oxidised to support ketogenesis. Glycogen is being depleted to keep liver cells functional. Gluconeogenesis from protein is unable to meet the hepatic (and whole body) demand for glucose calories in the situation of limited access to FFA calories.

However much glycogen derived glucose you consider that the ancestral diet contained I feel it is very, very unlikely to be greater than the glucose and fructose of a modern diet. I feel that getting enough glycogen in to the liver to fully fuel its metabolism in the absence of adequate fatty acid oxidation is a non starter. The P479L mutation was not "permitted" by high oral carb loading, it was permitted by conditions which facilitated fatty acid oxidation. You don't have to agree.

What starts to look much more interesting is what controls CPT-1a activity and how this might vary from the ancestral diet to the modern diet.

The paper makes the point that omega 3 fatty acids appear to up regulate fatty acid oxidation (in rats at least) by the liver. If this is true in humans then a high level of omega 3 fatty acids from marine fats might up regulate fatty acid oxidation to a level which no longer necessitates the depletion of hepatic glycogen derived form oral glucose intake or protein catabolism.

In support of this is that the distribution of P479L within Alaska is not uniform, it's significantly commoner in the coastal regions compared to the inland areas.

"The allele frequency and rate of homozygosity for the CPT-1a P479L variant were high in Inuit and Inuvialuit who reside in northern coastal regions. The variant is present at a low frequency in First Nations populations, who reside in areas less coastal than the Inuit or Inuvialuit in the two western territories"

I'm open to other explanations, there are papers suggesting that the mutation helps to preferentially dispose of omega 6 PUFA, with omega 3 fatty acids as the facilitator.

In summary: Maintaining adequate FFA oxidation to avoid glycogen depletion looks to be the core need in P479L. A high fat diet with a large proportion of omega 3 fats might be a plausible way of maintaining adequate hepatic fatty acid oxidation. Hyperglycaemia (via Crabtree effect) looks to be anathema. Glycogen loading with a normal starch/sugar based modern diet is clearly ineffective to prevent hypoglycaemia for some individuals. Resistant starch as a reliable nightly adjunct to infant feeding seems very unlikely in the ancestral diet. Repeated periods of fasting were probably routine when hunting was poor and does not appear to have selected against P479L in weaned children. Unweaned children are unlikely to be exposed to fasting, provided milk was available from lactation.

Well, there are some more thoughts on the biochemistry.

People clearly have very differing ideas of what the Inuit did or did not eat as an ancestral diet. The P479L gene eliminates the need for source of dietary glucose to explain very limited levels of ketosis recorded in the Inuit. While it is perfectly possible to invoke a high protein diet to explain a lack of ketosis in the fed state this goes nowhere towards explaining the limited ketosis of fasting. P479L fits perfectly well as an explanation.

I have some level of discomfort with using the Inuit as poster people for a ketogenic diet. That's fine. They may well have eaten what would be a ketogenic diet for many of us, but they certainly did not develop high levels of ketones when they carried the P479L gene.

However. Over the months Wooo and I seem to have come to some sort of conclusion that, while systemic ketones are a useful adjunct, a ketogenic diet is essentially a fatty acid based diet with minimal glucose excursions and maximal beta oxidation. Exactly how important the ketones themselves are is not quite so clear cut. From the Hyperlipid and Protons perspective I would be looking to maximise input to the electron transport chain as FADH2 at electron-transferring-flavoprotein dehydrogenase and minimise NADH input at complex I. Ketones do not do this. Ketones input at complex II, much as beta oxidation inputs at ETFdh, but ketones also generate large amounts of NADH in the process of turning the TCA from acetyl-CoA to get to complex II, which ETFdh does not. I'm not a great lover of increasing the ratio of NADH to NAD+. These are my biases.

Confirming that the Inuit are not poster boys for ketosis is a "so what?" moment for me. Using their P479L mutation to argue against ketogenic diets is more of a problem. It's a massive dis-service to any one of the many, many people out there who are eating their way in to metabolic syndrome to suggest that a ketogenic diet is a Bad Thing because no one has lived in ketosis before. Even the Inuit didn't! My own feeling is that everyone comes from stock who occasionally practiced and survived intermittent fasting so we are should be adapted to this. I'd guess that if you are of Siberian, Inuit or First Nations extraction you might benefit from Jay Wortman's oolichan oil as part of a ketogenic diet.

I'm always amazed by the concept that a ketogenic diet might be temporarily therapeutic but must be discontinued because it eventually becomes Bad For You. It reminds me so much of the converse concept that low fat diets, which might worsen every marker of health which people may care to look at, will deliver major benefits at some mythical future date.

Ultimately, point scoring on the internet about what the Inuit did or didn't eat shouldn't destroy people's chances of health. Destroying a circular argument about Inuit diets may may the destructor feel good. Destroying the feet, eyes and kidneys of a person with type 2 diabetes, who need a ketogenic diet, as a spin off from that victory must be difficult to live with. I don't know how anyone can do this.

I think that's probably all I have to say for now.


Sunday, November 16, 2014

Coconuts and Cornstarch in the Arctic?

EDIT There is a follow on post to this one including some clinical data on the hypoglycaemia episodes. I'll put a link in here now it's up. END EDIT

Remi and Ken both pointed me toward this paper:

A Selective Sweep on a Deleterious Mutation in CPT1A in Arctic Populations

The paper itself is largely an account of the detective work involved in pinning down a specific mutation which has been positively selected for in a Siberian population living in the Arctic. The same mutation is also present in non related groups inhabiting the Arctic areas of northern America. The mutated gene is very common and frequently homozygous. It puts a leucine in the place of a proline in CPT-1a, the core enzyme for getting long chain fatty acids in to mitochondria. Putting a leucine where there should be a proline means the protein is basically f*cked. The mutation is linked, not surprisingly, to failure to generate ketones in infancy and can be associated with profound hypoglycaemia, potentially causing sudden death.

From the evolutionary point of view we have here a mutation which is significantly lethal at well below reproductive age, so it should have been weeded out because affected individuals are less likely to live long enough to pass on the gene. But it has been highly positively selected for in several populations, the common factors being cold climate and minimal access to dietary carbohydrate. It's a paradox.

Following a link in the paper gives us this abstract, with this snippet:

"Investigation of seven patients from three families suspected of a fatty acid oxidation defect showed mean CPT-I enzyme activity of 5.9 ± 4.9 percent of normal controls"

A value 6% with an SD of 5% suggests to me that some of these people may well have a CPT-1a function very close to zero. How common is the mutation?

"We screened 422 consecutive newborns from the region of one of the Inuit families for this variant; 294 were homozygous, 103 heterozygous, and only 25 homozygous normal; thus the frequency of this variant allele is 0.81"

I think "very common" is a reasonable description.

How dangerous is it?

"Three of the seven patients and two cousins had hypoketotic hypoglycemia attributable to CPT-Ia deficiency"

Quite dangerous.

The next thing we can do is google CPT-1a deficiency and have a look what needs to be done to stay alive if you carry this gene.

Clearly, if you can't transport LCFAs in to your mitochondria, you should run your metabolism on glucose/pyruvate and avoid the dysfunctional fatty acid transporter. This means raw corn starch, as we have seen used (probably wrongly) for glycogen storage diseases. Properly cooked starches are too short acting to reliably keep a child alive all through the night. They aren't safe enough.

Of course MCT oils have a role too. A CPT-1a defect has no effect on MCT metabolism so these can be used either directly by tissues or indirectly via liver/glial produced ketones.

LCFAs, unable to be metabolised, accumulate in the tissues as a storage disease. The advice is to avoid them as far as possible.

So the archetypical CPT-1a defect tolerant environment would seem to be a person sitting on a South Seas Island beach by a pile of coconuts chewing on a raw yam, with copious flatus night and day.

But it's not.

The CPT-1a defect evolved in multiple non related populations where both starch and MCT were very notable by their near-complete absence. It's an Arctic selected gene. No starches. No coconuts.

Let's take a speculative look at what is going on.

Living on a very low carbohydrate diet is associated with chronically elevated free fatty acids, chronically low levels of insulin and an ignorance of glucose. i.e. the body ignores glucose. Synthesise what glucose is needed but, beyond that, who cares?

Living in a sea of free fatty acids, which are taken up in to cells in a largely concentration dependent manner, allows an increased gradient to push FFA-CoA at any residual function in CPT-1a. It would appear, from the evolutionary perspective of Arctic inhabitants, that near ketogenic levels of FFAs are adequate even if you have the proline to leucine substitution at amino acid 479 in CPT-1a. You can do enough beta oxidation to cope.

Of course, the minute you lower free fatty acids, perhaps to the level of a post prandial starchivore, beta oxidation is going to grind to a halt without the concentration gradient effect. This is pathological. The temporary fix of substrate level ATP synthesis and related pyruvate supply to the mitochondria is fine for a while, but any reactive hypoglycaemia is going to be potentially fatal, especially if you are asleep or food deprived at the time. We know that insulin suppresses lipolysis at levels which don't budge GLUT4s. When insulin has suppressed lipolysis and blood glucose is low, FFAs might be fatally limited.

If you have the mutation but you never do the starchivore thing your FFAs are high 24/7, whether you have just chewed on a lump of seal blubber or not. No paper in the reference list appears to have looked at the FFA levels of children with this mutation on a mixed diet, let alone on the ancestral fat based diet of the polar regions. Given sustained very high levels of FFAs, you might even make some ketones.

If free fatty acids are high and there is no insulin to divert them in to storage, all of the nasty storage diseases associated with CPT-1a dysfunction might well disappear. This is the situation where the mutation allows carriers to thrive.

I think elevated free fatty acids, without elevated insulin, is a recipe for the tolerance of this mutation.

But the mutation is not just tolerated. This is no neutral mutation, it is positively advantageous. The prevalence of the mutated gene is far from random. Why is it beneficial?

This is not quite so simple.

Uncoupling is one component. Uncoupling respiration generates heat. There might just be a positive advantage to running your metabolism fairly uncoupled in a very low temperature environment. Elevated FFAs are completely essential to uncoupling and heat generation. Limiting fatty acid removal from the cytoplasm to the mitochondria might be a facilitator of uncoupling. It's FFAs on the cytosolic side of UCPs which facilitate proton translocation. Having a higher level of cytoplasmic FFAs at a given level of plasma FFAs might give an advantage over the normal level of uncoupling seen under near ketogenic diet conditions.

The second possibility is that, once you have established high enough levels of FFAs to push through the CPT-1a bottle neck, you simply run at this level flat out, all the time. One of the features of the CPT-1a from the modified gene is that it fails to be inhibited by malonyl-CoA.  Even with limited CPT-1a activity there must be times at which ATP synthesis exceeds metabolic requirements and fatty acid transport ought to slow. There is no longer any brake to be applied to FFA transport if excess acetyl-CoA, exported to form malonyl-CoA in the cytoplasm, fails to inhibit CPT-1a . Oversupply of ATP within the matrix is likely to provide optimal uncoupling conditions, in excess of those from a ketogenic diet with regulated fatty acid uptake. That would be my guess. If it's cold enough, this might make the difference between survival or not. It keeps you warm, especially when you are asleep and the TCA should be quiescent.

Flicking through other references in the paper it does appear that indigenous Siberian people do have an elevated resting metabolic rate. In fat free mass it is 17% above calculated values i.e. they are uncoupled.

Finally, adults are not affected by the hypoglycaemia syndrome. My presumption is that, after puberty, they are sufficiently insulin resistant to have adequate FFAs present to maintain relatively normal mitochondrial function. It's the children who need their ancestral diet.

People with glycogen storage diseases die of hypoglycaemia (amongst other problems). We know that a deeply ketogenic diet both protects from hypoglycaemia and sets the body up to run perfectly well without any dietary glucose, which might be lost to glycogen stored permanently in the liver/muscles. There is every justification for giving the finger to cornstarch here and the folks suggesting a modification of ketogenic eating appear to be on fairly safe biochemical ground.

For the P497L mutation everything from the evolutionary perspective suggest that a very high FFA inducing diet may be equally efficacious. But the risks associated with failure, from the occasional safe starch meal or unsafe birthday cake at a party, carries the potential for catastrophe once insulin puts free fatty acids in to free fall.


BTW: You just have to wonder if any other CPT-1 mutations might behave in a similar manner to the P497L change in the Arctic... Could it be bye-bye time for cornstarch?

Tuesday, October 28, 2014

Are ketone esters dangerous?

Back in 1995 Veech was looking at a ketone mixture as physiologically equivalent to insulin/glucose. In order to limit his variables the isolated rat myocardia used in the study were perfused with Krebs-Henseleit buffer containing the metabolic milieu of interest. The buffer has no free fatty acids so takes the provision of acetyl CoA from beta oxidation right out of the equation. It also eliminates any uncoupling from free fatty acids in the perfusate. It took me a while to twig that this was potentially a very long way from the situation under fasting or ketogenic diet conditions where free fatty acids might well be at the maximal physiological levels whenever ketones hit 5.0mmol/l.

The idea was certainly in mind when the group published this, in 2004:

“Current ketogenic diets are all characterized by elevations of free fatty acids, which may lead to metabolic inefficiency by activation of the PPAR system and its associated uncoupling mitochondrial uncoupling proteins. New diets comprised of ketone bodies themselves or their esters may obviate this present difficulty.”

By 2012 the problem with ketogenic diets had been reduced to one of impossible compliance, rather than metabolic inefficiency of free fatty acid metabolism:

"Further, to achieve effective ketosis with KG diets, almost complete avoidance of carbohydrates is required to keep blood insulin levels low to maintain adipose tissue lipolysis. Such high-fat, no-carbohydrate diets are unpalatable, leading to poor patient compliance."

You notice the uncoupling, previously a potential problem, is now in the title of the paper. Ketones in real life, even from ketone esters, work in a milieu of free fatty acids. If you flood the mitochondria with ATP-generating ketones, which generate no ATP in the cytoplasm, you just might expect to open that uncoupling pore and allow a few FFAs to translocate some protons, to limit over production of ATP within the mitochondria.

Currently, in 2014, the delectable savour-the-flavour of ketone esters allows this:

“…the ester can be taken as an oral supplement without changing the habitual diet.”

I watch this stuff with some degree of amazement. There is a suspicion that AD incidence is increasing rather faster than an ageing population would explain. The suggestion is that it has  an environmental component. Now, many potential explanations are possible but I would like to think it is the saturophobic, cholesterophobic, fructophilic low fat based dietary advice from the American Heart Association which is the prime driver. Seems likely.

If AD (also known as type 3 diabetes) is a dietary disease, much as type 2 diabetes is largely a dietary disease, providing a crutch which will allow you to cling to the diet which got you in to AD in the first place strikes me as the biggest risk from ketone esters.

Excepting the stale urine/sweaty socks yummy aroma of course. Bring on the egg yolks fried in butter as an alternative, please.

A ketogenic diet features several things in addition to ketones. There is the chronic normoglycaemia which is anathema to the Crabtree effect. There is the physiological rock bottom basement insulin levels in a system where insulin signalling is f*cked. There are the elevated free fatty acids. These are the best.

Those free fatty acids are taken up by astroglial cells and used to generate in-situ ketone bodies. What sort of levels do they supply in vivo? That's an unknown (as far as I can tell), but I'm willing to bet that FFA supply under true ketogenic eating is both high and consistent, irrespective of fed/fasted state.

This is not quite the case if you are on the old MCT kick or mainlining sweaty socks while munching crapinabag.


A little background about Dr and Mr Newport and ketones which triggered this post off:

I have been unable to tease out, from Dr Newport's original article, that of Emily Deans or from the abstract of the case report above, quite what level of carbohydrate Mr Newport consumed in the original MCT phase, during the drug trial or while on ketone esters. I suspect it might have been more than a banana a day.

Oh, and another addendum. I, personally, clearly have issues with faking a ketogenic diet. This is true. But let me not decry ketones or their esters per se. If MCT oil or ketone esters get you out of bed and let you get dressed without needing assistance, that's great. They sure as hell knock spots off of anything which Big Pharma has to offer for AD management. The fact that I have yet to die as a direct result of eating less than one banana a day means that I hope never to need ketone esters. I feel a ketogenic diet should be high on the agenda for those with neurodegenerative diseases, with ketone esters or MCTs as a fall back. But then I would, wouldn't I...

Sunday, October 12, 2014

Where has the superoxide gone?

This is the first section of Fig 1 section C from the paper using dihydroethidium (DHE) to view in vivo superoxide production in control and diabetic kidneys, though not in the figure below.

It's a very important figure as it shows, very convincingly, that sudden onset hyperglycaemia has zero effect, none whatsoever, on superoxide production in their model of normal, non diabetic kidney tissue, that's the second column, identical to the first.

I have a lot of time for the failure to generate superoxide in diabetic kidneys, especially with pyruvate dehydrogenase complex down regulation limiting input to mitochondria from the end stage of glycolysis. But I have a concept that acute hyperglycaemia in normal, non Crabtree affected, tissues SHOULD generate superoxide, it should come from the respiratory chain and it should more particularly come from complex I in the region of the FAD moiety, preferably via the FeS cluster N1-a.

Now, if I had an in vivo tool for viewing superoxide generation, how would I do this? Well, I would use it in vivo. I would set up an iv glucose infusion, or perhaps a large intragastric glucose bolus, inject the DHE, wait a while, then look for superoxide/DHE derivative with my lovely optical scanner.

To keep the scrutineers happy I might have repeated the findings ex vivo, using the technique of paramagnetic detection of a superoxide/spin trap derivative, but the core finding, that superoxide generation on acute hyperglycaemia does NOT occur has to be shown in vivo. We already know it DOES occur ex vivo in multiple models, and the authors cite the studies to show this.

So, if hyperglycaemia triggers superoxide generation ex vivo in assorted non Crabtree adapted cells, why doesn't it do so in this study?

I don't know. There is a piece of core information which the scrutineers failed (miserably) to demand to be included in the study methods.

Figure 1C was not obtained in vivo. Column Ctrl was from a tissue homogenate of health kidney from non diabetic mice fed with pyruvate, malonate and ADP, subsequently flooded with 25mmol of glucose to produce the +HG column. That is not so bad. It's a model and it's clearly able to get GrantAid quality results.

But is it real?

Let's look at the equipment used. This is what they say:

"These studies were carried out in a MiniScope MS200 Benchtop EPR Spectrometer (Magnettech), which is designed to allow tight control of pO2 and temperature".

Why do they need tight control of pO2? You can obtain utterly rigid control control of pO2 by exposing your preparation to room air. Correct pressure to 760mmHG and pO2 is fixed at 21% of this.

To me the question is: What was the pO2 which failed to generate any superoxide when a mush of cytosol and mitochondria was exposed to 25mmol of glucose?

Was it 159.6mmHg, i.e. room air? Was it 40-50mmHg as other groups suspect mitochondria run at? Or was it 22mmHg?

This might matter. I got the 22mmHg value from the previous paper by the same authors which gave 3% oxygen as the likely conditions for normal mitochondrial function. This was a non referenced, throw away comment:

"Because the physiologic concentration of oxygen in mammals in vivo is less than 3% in most organs, we carried out a series of studies to determine whether ethidium or 2-hydroxyethidium was the specific oxidation product of DHE in vivo (i.e., in the intact animal, not cell culture/tissue slice) using several different validated animal models of increased or decreased superoxide".

Why it matters to me so much is that if an electron is thrown out of complex I due to hyperglycaemia triggered reverse electron flow through complex I, would it generate superoxide if the pO2 had been set to below physiological limits? Or if the guesstimate of 3% oxygen is correct and there is no superoxide generated, is there no reverse flow occurring? Or does the reverse flow occur, the electron is ejected, but it drops on to the surrounding protein structure rather than oxygen to be used as a distant signal via superoxide/H2O2/insulin receptor?

Using the in vivo technique would have told us exactly what was happening, at a true but non measured tissue pO2. I'm worried that the in vivo technique showed the anticipated (by me) hyperglycaemic superoxide and an ex vivo technique had to be developed and adjusted to maintain the fund generating core finding of no extra superoxide.

There was no reply to a simple polite email query as to the pO2 used.


Friday, October 10, 2014

The Crabtree Effect and superoxide in diabetes

I started with this paper about in vivo superoxide detection in the brain but, apart from the technique, there was no examination of the response to hyperglycaemia so I moved on. The next paper by the same group is looking at superoxide and mitochondrial function/health in the kidney under various models of diabetes. The general principles appear similar in neurons and kidney cells.

An in vivo technique to view superoxide is really useful. I have alluded to a certain discomfort in examining electron/oxygen interaction in mitochondria within cells/mitochondrial preparations under room air, with a partial pressure for oxygen of around 150mmHg (sorry for the non SI units, showing my age there!). There is no way that normal mitochondria are exposed to this much oxygen, a little browse around pubmed suggests that the best in vivo estimate is around 40-50mmHg, subject to some debate. That's without even thinking about what CO2 partial pressure you should use for cell culture... So observation in vivo takes care of a lot of this. If an electron is thrown out of the respiratory chain (I feel nothing in the ETC is accidental) the chances of it dropping on to an oxygen molecule seem somewhat higher if we have three times the oxygen partial pressure than the system was designed to work under. If the electron wasn't destined for an oxygen molecule, where else might it have been going?

The first point has to be that in two models of type one diabetes there is less superoxide production in the kidneys of diabetic mice in vivo than control mice, that's Figure 1 section C. Going ex vivo (I probably have a full post on the problems with this ex vivo section) we have the same effect demonstrated using a paramagnetic technique, that's Fig 2C. The reduced superoxide in diabetic kidneys was confirmed in the tissue homogenates under relatively normal metabolic substrate supply. Exposing the preparations to glucose at 25mmol/l has no effect on superoxide generation from the control kidney homogenate but actually reduces it, rather a lot, in the diabetic derived homogenate.


NOTE If you follow the text through about Fig 1C and their SOD2+/- mice you will find that the data is not very accurately described. So caution here. The SOD2+/- had a non significant increase in mitochondrial superoxide in Fig 1C, so it is hardly surprising this did not rescue the diabetic mice from renal disease in Fig 3A and F. I don't like their writing about this whole SOD2+/- section. Definite caution. END NOTE.

The paper has, amongst its problems, a lot of very perceptive points which make a great deal of sense. It's quite hard to know where to start. Let's begin with the failure of superoxide production.

So this paper flies in the face of the Protons concept of hyperglycaemia driving reverse electron flow from mtG3Pdh through complex I to generate insulin resistance. That too is probably another post, comparing the diabetic state with the non diabetic hyperglycaemic state. Anyhoo. The group rather like Crabtree. So do I. The Crabtree effect, the shutting down/mothballing of mitochondrial function, is an adaptation to oversupply of glycolysis derived substrates. It allows a limit to be set on the throughput of pyruvate to mitochondria and jettisons any excess as lactate. This situation, once it is established, is probably quite different to the situation which leads to its adoption.

Chronic hyperglycaemia induces the Crabtree effect and down regulates mitochondrial biogenesis, mitochondrial repair and electron transport chain function. It not only does this but it also phosphorylates the pyruvate dehydrogenase complex, very specifically, and this directly shuts down input to the TCA from glycolysis (or input from lactate itself, if we want to apply this concept to neurons, as we might). This is all in the paper. Of course I would add that it doesn't affect ketone derived acetyl-CoA input to the TCA, although the ketone derived acetyl-CoA will be processed by a degenerate electron transport chain...

Under sustained hyperglycaemia there is an excess of calories which leads to a failure to activate AMP kinase, a core sensor of energy abundance which is phosphorylated under hypo caloric conditions. AMPK regulates PGC 1 alpha, a messenger to trigger mitochondrial biogenesis. But the central link, the activation of AMKP, is mitochondrial derived superoxide. And, oddly enough, one of the functions of AMPK activation is the generation of mitochondrial superoxide. A self sustaining loop.

The group administered rotenone to control mice. Now, the effect of rotenone on superoxide generation appears (in general) to be rather dose rate related. In the present study the dose rate was chosen so that there was a near complete suppression of superoxide production from the ETC of the mice. Acute suppression of superoxide results in the reduced phosphorylation (reduced activation) of AMPK and increased phosphorylation of PDH, which shuts it down. This loss of superoxide is a short term mimic of the long term established Crabtree effect. No superoxide, no mitochondrial maintenance. Consider that chronic high dose rotenone poisoning is a standard model for Parkinsons Disease and you begin to see the importance of superoxide in the brain. Long term hyperglycaemic failure to generate superoxide is probably a more normal route to neurodegeneration than rotenone in most (but not all) neurodegenerate humans...

The fall in superoxide production in diabetic tissue homogenates again pulls me back to brain function. Crabtree suppresses hyperglycaemic superoxide production, i.e. the effect is antioxidant. Let's look at what glucose does to neurons from this paper which we've chatted about before. Here's the only bit I'm interested in today:

"Indeed, it has been shown that glucose is used by neurons to maintain their antioxidant status via the pentose phosphate pathway (PPP), which cannot be fueled by lactate (Magistretti, 2008; Herrero-Mendez et al., 2009)"

It's impossible over emphasise the importance of that sentence. It says it all about why neurons should run on lactate! To avoid upregulating antioxidant status.

What does increasing antioxidant status do to superoxide signalling? The term f*cked comes (unavoidably South Park-ishly) to mind. There are a swathe of papers showing that the antioxidant status in neurons of AD and PD patients is upregulated.

Once you go with Crabtree you can see that glucose and PPP driven antioxidant upregulation might be all that is needed to lose superoxide signalling and destroy mitochondrial function. Lactate does not do this. Lactate does not induce the Crabtree effect.

Let's be very specific: Glucose, under the Crabtree effect, triggers a cascade which ends up with failure to generate superoxide and this maintains mitochondrial shutdown. Up regulating antioxidant status may theoretically be helpful in dealing with non mitochondrial superoxide generation, but it's not going to help signal for mitochondrial biogenesis.

High glucose exposure generates glucose dependence. This is a recurring theme and is core to neurodegeneration. I look at safe starches and can see that, if you are living with the Crabtree effect in key neurons, some starch/glycolysis might make you feel better if you are ketogenically hypoglycaemic, but it's not going to help un-Crabtree your mitochondria. On the other hand I can't see that pushing starch to a level which produces hyperglycaemia is anything other than damaging, as opposed to merely neutral as it might be when your pancreas does its job effectively.

I'll take a break before going on to the sections on mitochondrial deletions and respiratory chain oxidative damage elsewhere in the paper. Or maybe I should talk about the bits I deeply dislike related to oxygen pressure and superoxide.


Thursday, September 25, 2014

Uncoupling control in defence of FFAs

I've been reading this review on beta hydroxybutyrate and am struck by the concerns expressed throughout about the potential damage caused by free fatty acids, due to uncoupling, a sentiment I have picked up in several of Veech's publications which are heavily cited in the review.

I was particularly struck by how two papers I've recently discussed were described, so it's topical for me. One was the puzzling toxicity of a LCKD diet as published by Wang et al. This is the one using vegetable shortening of indeterminate trans fat concentration, a point sadly un-noted (or considered unimportant?) by the review. And second is the Kuwait study, described as LCKD in the review, which was not exactly glycogen depleting for a rodent.

Aside: This cited study starved rats for three days before ischaemia/reperfusion. That should have depleted glycogen AND raised raised FFAs (neither of which was checked, but any lipophobe should expect uncoupling combined with backup anaerobic glycogen reserve loss to be disastrous in ischaemia/reperfusion) as well as predictably increasing B-OHB. Combined starvation changes in fact reduce the damage produced and improve recovery. End aside.

So I'm a little ambivalent about the review and how much of the rest of their ideas I might take at face value.

Ultimately, thinking about free fatty acids, we have to talk about the control of uncoupling.

Recall this image from this study in part 29 of the Protons thread:

Free fatty acids are essential for proton transport across the inner mitochondrial membrane to uncouple oxygen consumption from ATP synthesis and to maximise electron flow down the electron transport chain with minimal resistance and minimal non essential superoxide generation.

No free fatty acids, no uncoupling. Free fatty acids are core to uncoupling.

But they are far from the only factor. For protons to be transported through the channel of the UCP by free fatty acids the channel must undergo a conformational change, which is highly dependent on the ATP status of the cytoplasm and the mitochondrial matrix.

So we have this picture from this very impressive study:

ATP in the cytoplasm fits in to a specific binding site, with each phosphate moiety of ATP fitting up against a specific arginine, all three aligning results in closure of the channel and inhibition of uncoupling, whatever the FFA concentration. Here is what the authors say:

"Moreover, residues R79 and R279 correspond to the arginines involved in nucleotide binding and protein inhibition in UCP1. According to the three-step binding model proposed for UCP1, β-phosphate of PN [phospho-nucleotide] binds first to R182 (helix IV, loose binding). The second step is the binding of γ-phosphate to R83 after protonation of E190 (tight binding). After the subsequent binding of α-phosphate to R276 (helix VI) the protein switches to the inhibited conformation"

Cytoplasmic ATP (and GTP) inhibit uncoupling. But not all of the time, despite the fact that there is normally always enough cytoplasmic ATP to inhibit uncoupling. So yet another factor comes in to play.

It is quite possible to inhibit the inhibition of uncoupling produced by cytoplasmic ATP.

You do this with mitochondrial ATP. ATP binding from the mitochondrial side of the channel interferes with the binding of cytoplasmic ATP but cannot reach the R83 arginine itself to close the channel. So elevated mitochondrial ATP keeps the uncoupling channel open, even in the face of rather high cytoplasmic ATP levels.

The logic to this is that if there is plenty of ATP within the mitochondria there is no need to preserve delta psi and it's fine to uncouple. If there is ATP in the cytoplasm but very little in the mitochondria the implication appears to be that ATP synthase is not generating enough mitochondrial ATP, i.e. we are either hypoxic or over-uncoupled. Continued glycolysis generates ATP on the cytoplasmic side so allows the uncoupling channel to close using this cytoplasmic ATP.

It's pretty logical.

So. Under hypoxia, whatever the level of FFAs, what happens to uncoupling?

It stops due to a lack of mitochondrial ATP. Should you fear FFAs? Only if you think you will continue to uncouple respiration under hypoxia. The balance of mitochondrial to cytoplasmic ATP should shut down uncoupling very rapidly when needed.

Just say no to Crisco (if that's how Wang et al got their result).

It has long worried me that in Veech's seminal paper on glucose, insulin and ketone metabolism in an isolated heart preparation the group was very, very careful to run the study without any involvement of free fatty acids. For those of us living in a temperate latitudes, lounging on the beach under a coconut palm while waiting for lunch to drop on our heads is not an option. Have you ever been to Lowestoft beach? No ketones without elevated FFAs at latitude 52 deg N on the North Sea coast. Fasting, or living on meat for a while, seems more likely than eating MCTs outside the tropics. I fail to see how the body would manufacture the miracle of ketones at exactly the same time as it releases the devil incarnate of free fatty acids.

Some folks like free fatty acids. Me, for one.

Some of us like uncoupling too, in the right place, at the right time.