Monday, July 22, 2013

Physiological insulin resistance again

I started the Protons thread with the simple question: What is the difference, from the metabolic point of view, between the energy supplied by fat vs that supplied by glucose derivatives.

This gives a simple picture of insulin resistance as a metabolic technique to limit caloric entry in to an individual cell under conditions of excess availability. NADH, tending to come from glucose, drives complex I to generate a decent inner mitochondrial membrane potential (delta psi). Feeding substrate in at other access points to the electron transport chain's CoQ couple, be that electron transporting flavoprotein dehydrogenase, mtG3Pdehydrogease, NADPH dehydrogenase or others, reduces that CoQ couple and promotes reverse electron flow through complex I, superoxide generation and insulin resistance. This is the insulin resistance seen so clearly when you pay folks to over-eat, assuming you feed them crapinabag. The exact mechanism of this failure of insulin to act is not clear, but large amounts of H2O2 act at several points to inhibit the activation pathway. Of course an intramitochondrial mechanism would be really neat, or some sort of complexing of the insulin/receptor with ETC proteins. Hard to say what we will find here in future, but an interesting area.

What about the insulin resistance of starvation? Do we have the same phenomenon of reverse electron flow through complex I as the mechanism?

So now we have to think about ketones with normolglycaemia. Back in my early days of looking at mitochondria I spent many hours with Veech's seminal paper on mechanical work generated by isolated rat hearts, pumping fat-free fluids spiked with glucose, ketones, glucose/insulin or glucose/insulin/ketones.

Ketones alone do exactly what maximal glucose/insulin do in terms of mechanical work, but by a completely different mechanism. Ketones produce a DROP in delta psi. This reduces uncoupling because there is a much lower voltage pushing protons back in to the mitochondrial matrix. This means that even with a lower delta psi ATP production is maximised (plus a few other changes) and so is the ability of the muscle to pump.

Insulin/glucose together maintain a high delta psi but modify the ETC proteins to improve efficiency, probably involving covalent bonding. I would assume phosphorylation is key.

Mechanical work was perfectly well maintained on ketones vs glucose/insulin, no need for a high delta psi with the ketones. Of course, no one is going to generate superoxide from complex I when the mitochondrial matrix is at a mere -120mV. To generate reverse electron flow it is the high value of delta psi which, when there is enough NADH per unit NAD+, puts an electron on to oxygen via FeS N-1a in complex I.

But under conditions of ketosis, be that ketogenic isocaloric eating or simple starvation, it is axiomatic that somatic insulin resistance is essential to spare adequate molecules of glucose for that little bit of brain metabolism which cannot be met by ketones alone. You need insulin resistance exactly when ketones remove the key driving potential needed for insulin resistance...

The trick lies in insulin activation. Insulin's action both generates and requires a small burst of superoxide. The superoxide is generated intramitochndrially by reverse electron flow through complex I. The superoxide is converted to H2O2 which diffuses to the cytoplasm where it inhibits the enzyme which normally deactivates the insulin/insulin receptor complex. With the reduced delta psi induced by pure ketones this is not going to happen, the insulin receptor rapidly deactivates and we have a simple mechanism for the physiological insulin resistance of ketosis/starvation.

To summarise: Superoxide in large amounts from complex I signals excess calories in the cell and inhibits insulin's action for cellular protection.

Superoxide in nano molar concentrations is essential for insulin's activation and is not made when ketosis lowers the potential across the inner mitochondrial membrane.

The two phenomena are both utterly essential and quite separate.

That makes me happy

There is a mass of detail of this process laid out in this paper H2O2 Signalling Pathway: A Possible Bridge between Insulin Receptor and Mitochondria. It makes interesting reading. I love the stuff on antioxidants causing insulin resistance and Ian recently resurfaced the old paper about supplementing with Vitamins C and E blunting exercise induced improvement in insulin sensitivity.

Bear in mimd that an awful lot of this work comes from tissue culture, transgenic mice, isolated mitochondria, all the usual suspects, so accept with caution.

But it makes sense to me

Peter

15 comments:

George Henderson said...

That H2O2 paper is very lucid and enjoyable to read.
I remembered the other day that mitochondrial complexes are regulated spatially, by the cristae in which they are embedded expanding and contracting, as well as metabolically. Important if the products of metabolism accumulate to inhibit this movement (I'm looking at unesterified cholesterol's potential here). I'd forgotten all about this, need to re-read my textbooks.
Co-Q10 supplementation protects neurons from hypoxia and reperfussion injury...

Sondra Rose said...

Thank you so much for your blog, Peter!

Jane said...

Hi George
Do you remember a conversation we had about how insulin regulates the ETC? I talked garbage I think because I'd forgotten some interesting stuff about mTOR.

Peter says 'Insulin/glucose together maintain a high delta psi but modify the ETC proteins to improve efficiency, probably involving covalent bonding. I would assume phosphorylation is key.'

I think he's right, and it looks like it might be mTOR that's responsible for the phosphorylation. Have a look at this.

'...here we demonstrate that in mammalian cells the mammalian TOR (mTOR) pathway plays a significant
role in determining both resting
oxygen consumption and oxidative
capacity. In particular, we demonstrate that the level of complex formation between mTOR and one of its known protein partners, raptor, correlated with overall mitochondrial activity. Disruption of this complex ... lowered mitochondrial membrane potential, oxygen consumption, and ATP synthetic capacity ... we further demonstrated that inhibiting mTOR with rapamycin resulted in a dramatic alteration in the mitochondrial phosphoproteome ...'
http://www.ncbi.nlm.nih.gov/pubmed/16847060

Cool, huh? Peter I hope you like this. Your post is VERY interesting.

Jason Weekes said...

Thank you very much on your posts regarding high FBG on a VLC diet. I have been seeing elevated numbers and was concerned until I found your posts.

O Numnos said...

Nice summary Peter, will certainly save some future re-reading.

Came across this The Register article I thought you'd appreciate given your diet.

Gotta love how Switzerland sits top-right :-D

A bit tongue in cheek, but what the heck.

Jane said...

There's something else interesting about mTOR and mitochondria. Apparently mTOR inhibits PPAR alpha.
'... we find that the inhibition of mTORC1 is required for the fasting-induced activation of PPARĪ±, (peroxisome proliferator activated receptor alpha), the master transcriptional activator of ketogenic genes...' http://www.ncbi.nlm.nih.gov/pubmed/21179166

PPAR alpha activates transcription of fat burning genes as well as ketogenic genes, at least in liver. If it does it in adipocytes as well, this could provide a mechanism for insulin to cause obesity. Insulin --> mTOR --> inhibition of PPAR alpha --> no fat burning. So insulin makes fat AND makes new adipocytes AND stops them burning the fat. Taubes is right!

However, it looks like things are a bit more complicated. De novo lipogenesis makes an activating ligand for PPAR alpha.
'Identification of a physiologically relevant endogenous ligand for PPARalpha in liver' http://www.ncbi.nlm.nih.gov/pubmed/19646743
You have to make fat in order to burn it, apparently.

Ian said...

Hi Peter,

How do you dissociate the effects of beta-oxidation from ketone metabolism? Fat increases uncoupling and produces H2O2, and causes insulin resistance. Ketone production parallels eating lots of fat and decrease uncoupling as you say, and reduce H2O2 production and cause insulin resistance. I'm confused how the two work together. Is it that the fat metabolism uses the uncoupling to reduce delta psi? At the same time, though, metabolism of fat seems to produce superoxide through RET, is this is insulin resistance that you talk about when there is a large surge in ROS? If the tyrosine kinase that inhibits the insulin response is deactivated by ROS why wouldn't the RET H2O2 do the same thing?

Jane said...

Ian,

'..If the tyrosine kinase that inhibits the insulin response is deactivated by ROS why wouldn't the RET H2O2 do the same thing?' - do you mean the tyrosine phosphatase?

I would like to know the answers to your questions too. I hope Peter will write a new post to answer them.

Peter said...

Ian and Jane,

Fatty acids are both directly uncoupling and trigger uncoupling pathways in addition to their direct effect. This will give a low delta psi as per ketones and should maintain the starvation insulin resiatance.

Adding a spike of glucose, even without insulin, will get SOME glucose in to glycolysis, convert NAD+ to NADH and also increase the delta psi. You are then set for effective insulin signalling and a positive feedback. Insulin works, delivers more glycolysis products, maintains delta psi. Concurrent high levels of saturated fatty acid oxidation supply FADH2 through electron transporting flavoprotein dehydrogenase to reverse flow electrons to induce hypercaloric insulin resistance.

Excess calories in all cells summates a signal (elevated systemic insulin levels) which shuts down lipolysis (if it is on going) or diverts fat to adipocytes (if after a mixed meal). The lower the FFAs then lower the energy input to the hypercaloric cell.

I see the insulin resistance of high fructose feeding as working in the same way except that under hypercaloric conditions the insulin elevation can shut down lipolysis but not shut down fructose input to a given GLUT5-expressing cell. The fructose in excess (what ever that exactly means) probably provides high delta psi, high input through complex I, high input through mtG3Pdh and insulin resistance even when FFA levels are low.

Summary: Given enough glucose the insulin resistance of starvation automatically ends... Emphasis on enough.

Hope that's not too rambling, time to get kiddies to a party!

Peter

Cohen Ilan said...

Are there any more substances that we can be psychologically resistant to?

Jane said...

Thanks Peter, that's a great help. I need to do some homework on this. Your posts make homework fun.

Ian said...

Yeah you're really nice for responding to questions, it relieves a lot of frustration associated with lack of understanding.

William Eden said...

Thank you for this post, Peter. I've been reading you and trying to figure out metabolism for a long time, and this feels like you finally pulled it all together. Beautiful.

bellefire said...

The far more common form of diabetes is type 2, which affects 90 to 95 percent of diabetics. In this type, your body produces insulin but is unable to recognize and use it properly. It is considered an advanced stage of insulin resistance. Insulin resistance allows sugar to increase and cause of host of complications.

Craig Cousineau said...

Low carb high saturated/monounsaturated fat for 2 years- labs as of this morning (fasting)

A1c - 4.9
FBG - 99 mg/dl
Used to have FBG in the 80s prior to LCHF

Cholesterol - 163 mg/dl
HDL - 67
Trigs - 31
LDL - who cares
Chol/hdl - 2.4

I'll takes these numbers all day long. Not worried about the FBG which has increased on this 'diet' while A1c has slowly trended down.