Monday, August 20, 2012

Protons: FADH2:NADH ratios and MUFA

A few more thoughts building on F:N ratios of differing metabolic substrates:

Each cycle of beta oxidation (assuming an even numbered carbon chain fully saturated fatty acid) produces one FADH2, one NADH and one acetyl-CoA. This gives a total of 2FADH2 inputs and 4 NADHs per cycle of beta oxidation. But the very last pair of carbon atoms in a saturated fat do not need to go through beta oxidation as they already comprise acetate attached to CoA, so they can simply enter the TCA as acetyl-CoA. This last step only produces 1 FADH2 and 3 NADHs, with no extras.

So the shorter the fatty acid, the less FADH2 per unit NADH it produces. Short chain fatty acids like C4 butyric acid have an F:N ratio of 0.43 while very long chain fatty acids, up at 26 carbons, have an F:N ratio of about 0.49.

As Dr Speijer points out, differing length fatty acids are dealt with differently. Very short chain fatty acids head straight for the liver and get metabolised by hepatic mitochondria immediately. Any excess acetyl-CoA gets off-loaded as ketones.

Very long chain fatty acids end up in peroxisomes for shortening, usually to C8, which is then shunted to mitochondria for routine beta oxidation. Of course peroxisomal beta oxidation generates zero FADH2, except that from acetyl-CoA, because peroxisomal FADH2 is reacted directly with oxygen to give H2O2. And heat, of course.

Bear in mind that the ratio of F:N generated by a metabolic fuel sets the ability to generate reverse electron flow through complex I and subsequent superoxide production, macroscopically described as insulin resistance.

So fatty acids up to C8 are cool, dump them to the liver and make a few ketones. Very long chain fatty acids over C18, shorten to C8 in peroxisomes, shift them to mitochondria and make some ketones if needs must. The F:N ratio of C8 is about 0.47, a value chosen by metabolism as the end product of peroxisomal shortening. The number is important. Actually the number is even lower as peroxisomal beta oxidation generates the NADHs of beta oxidation, just not the FADH2s, but why allow facts like this to spoil a great argument. C8 from breast milk and/or coconuts seems fine and has that F:N ratio of 0.47.

Now the area of interest is, of course, C16, palmitic acid. This has an F:N ratio of about 0.48, almost as superoxide generating as a C26 fatty acid up at 0.49. And palmitic acid does, without any shadow of a doubt, produce macroscopic insulin resistance. That's 15 FADH2s and 31 NADHs.

So an F:N of 0.47 is not a serious generator of superoxide and an F:N of 0.48 is.

What happens when we drop a double bond in to palmitic acid? Mitochondrial beta oxidation generates FADH2 as it drops a double bond in to the saturated fat chain. If the double bond is already there, hey, no FADH2!

Palmitoleate has one double bond. This of course gives 14 FADH2s and 31 NADHs, an F:N ratio of 0.45.

Palmitate 0.48
C8 caprylic 0.47, chosen by peroxisomes to hand to mitochondria
Palmitoleic 0.45

Adding a single double bond to palmitic acid drops its F:N ratio from significantly superoxide generating to minimally superoxide generating. It looks like a switch to me.

I just love the way the numbers pan out. Of course we can now go on to what these number signify and what determines unsaturation. And uncoupling too, I guess. We are then back to insulin and stearoyl-CoA desaturase and also de novo lipogenesis. It might be worth an aside to PUFA and how these behave too, especially in adipocytes.

Peter


21 comments:

CharlesVegas said...

Doesn't the mitochondria have a feedback response to the generation of superoxide, regardless of F:N, in the form of uncoupling proteins?

Excess proton gradient -> H2O2 -> deploy UCP2 -> relax gradient

CharlesVegas said...

"By targeting [i.e., disabling. My edit] the UCP2-gene there was no effect on whole body energy metabolism, but instead, a reduced ability to protect against free-radical oxygen species. UCP2 has also been shown to act as a negative regulator for insulin secretion."

http://www.ncbi.nlm.nih.gov/pubmed/12864746

Peter said...

Not only do LCFAs induce uncoupling proetin production/usage but they are themselves uncouplers, but what they do is dependent on the direction of electron flow.

UCPs came early but fatty acids probably came first as self regulators is the way I'm thinking.

Charles, succinic acid ester, a pure complex II driver, was/is looked at primarily as an insulinotropic agent for diabetes management. Fascinating.

Peter

CharlesVegas said...

Well, I'm just concerned that my LCHF diet is making a bunch of ROS.

It's good to see there's a more immediate feedback to throttle respiration than inducing insulin resistance.

Peter said...

Charles, well that gave me a giggle. I think I'd draw a parallel with moderate exercise. Free radicals mediate the benefits, ascorbate negates them (ok, blunts rather than negates, still hate those antioxidants!). The benefits from exercise are probably more mitochondria, ditto LCHF eating. We'll have to get to mitochondrial biogenesis at some stage.

Peter

CharlesVegas said...

Wait, you're going to tell me the ROS generated from over-driven mitochondrial membranes provides a signal to make more mitochondria?

And sure enough I quickly encounter: Peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1alpha).

Every day I study this stuff another wonderful and fascinating aspect of life is revealed.

dr j said...

Charles,
any value for you re this thesis re PGC-1?
http://edoc.unibas.ch/1422/1/Dissertation_AnnaEgger051211.pdf

Brian H said...

My guess is what Peter meant by getting to biogenesis is that we will not get a final solution to mitochondrial shortcomings until we can induce (thru drugs, etc) the production of new mitochondria (hopefully youthful & dewy). Anything short of that is limited patch. The current responses to ailing mitochondria, especially in light of the Western high sugar diet, reminds me of Apocalypse Now: "We shoot these people in half, and then we put band-aids on them."

Jane said...

Peter, don't you find it odd that C8 from breast milk and/or coconuts is fine with an F:N ratio of 0.47 but palmitate with an almost identical F:N ratio of 0.48 is very much not fine?

Here's a paper about palmitate-induced insulin resistance in hepatocytes, which seems to show an important contribution of NADPH oxidase (NOX3) derived superoxide.

'..In conclusion, our data demonstrate a critical role of NOX3-derived ROS in palmitate-induced insulin resistance in hepatocytes, indicating that NOX3 is the predominant source of palmitate-induced ROS generation and that NOX3-derived ROS may drive palmitate-induced hepatic insulin resistance through JNK and p38MAPK pathways. ..'
http://www.jbc.org/content/285/39/29965




Jack Kruse said...

Wait, you're going to tell me the ROS generated from over-driven mitochondrial membranes provides a signal to make more mitochondria? Sounds like Nick Lane's work to me......Peter another fantastic blog.

Brian H said...

OK, I think I get it now. Since F:N ratios, ROS production, etc have so many countervailing effects, then ultimately, to explain the benefits of walking/LCHF, we just have to drag in the mitochondrial biogenesis they induce to be able to account for their benefit. Right? (he queries, hopefully)

Peter said...

Jane, not really, the switch has to be set somewhere and is probably not all or nothing. I have a side thread about exactly why the liver summons iron when overloaded with fructose or PUFA. Both overload hepatocyte energy supply (after the initial depletion of ATP with fructose) but don't generate superoxide by F:N ratio standards. You have to resist caloric overload somehow, summoning iron is a logical way to do this, but is pathological under the SAD HFCS and corn oil conditions... End result is cirrhosis. I like self consistent ideas. Must go chase that paper you posted along those lines.

Brian, probably yes.

Peter

Peter said...

Jack, thanks...

Jane said...

Peter, I don't understand a word you said, but it sounds very intriguing. This is why I read Hyperlipid. I don't understand what you say at first, but if I work at it eventually very interesting things emerge.

Peter said...

Jane,

http://www.ncbi.nlm.nih.gov/pubmed/22854109

Why why why???? C57BL/6 mice are in to severe insulin resistance, but fructose has a F:N ration of 0.2, same as glucose. Or even lower if it diverts to lactate. Not sure the liver can do this!!!! But fructose has a low F:N ratio and the liver cannot resist fructose. There is no reason for the liver to want to accept fructose but the best it can do is reject glucose. How do you reject glucose? Superoxide. How much superoxide is generated by fructose? Diddly squat in the mitochondria. So you need some other way of generating superoxide. Like iron. So the liver summons iron by a hepcidin-independent mechanism. I found the same on the PUFA cirrhosis series, which I'll go back to.

But with oversupply of fructose or PUFA at F:Ns at or under 3.5 you can't make superoxide easily in mitochondria. Making superoxide in the cytoplasm is the first step to cirrhosis. Cirrhosis seem preferable to caloric overload of hepatocytes.

I'm not sure this will all hold up, but I think it might...

Peter

Peter said...

Or maybe they hepatocytes throw iron in to their mitochondria to make superoxide where it's needed, but it's not exactly a controlled process like reverse electron transport. Some fructose is fine, some PUFA is fine. Basing your metabolism on them is a mistake.

Peter

Jane said...

I see what you mean. This is very interesting indeed. Dammit, the library is shut for the next 3 days, I won't be able to find out anything until Tuesday. Don't go away.

Jane said...

Peter, I have never heard of iron producing superoxide, are you sure it can do this? It does produce hydroxyl radicals.

Iron does generate superoxide indirectly via NADPH oxidase, which is a haem enzyme. If you treat endothelial cells with iron, you get increased NADPH oxidase activity.

'.. Iron chelation by DFO effectively suppresses endothelial NADPH oxidase activity...'
http://atvb.ahajournals.org/content/29/5/732.full







Jane said...

Oh, I've just remembered. There's another way iron can produce superoxide. It can prevent access of manganese to mitochondria so MnSOD has no Mn and doesn't work. Ha!
'Iron-mediated inhibition of mitochondrial manganese uptake mediates mitochondrial dysfunction in a mouse model of hemochromatosis'
http://www.ncbi.nlm.nih.gov/pubmed/18317567

I think I remember posting this link before. Sorry I forgot it.

Wittrockiana said...

Could this be why nuts are known to cause weight-loss stalls on LCHF diets? The fat in pecans, for instance, are 8.5% SFA (mostly palmitic), 56% MUFA (nearly all palmitoleic), and 30% PUFA (nearly all linoleic). And just 1 oz (19 halves) has 20g of fat.

I would guess that the palmitoleic and linoleic acid would lower the F:N ratio, causing cells to lose insulin resistance and take up glucose from the blood. This would increase hunger in someone on a LCHF diet because there would be less glucose available for the brain.

Wittrockiana said...

Could this be why nuts are known to cause weight-loss stalls on LCHF diets? The fat in pecans, for instance, are 8.5% SFA (mostly palmitic), 56% MUFA (nearly all palmitoleic), and 30% PUFA (nearly all linoleic). And just 1 oz (19 halves) has 20g of fat.

I would guess that the palmitoleic and linoleic acid would lower the F:N ratio, causing cells to lose insulin resistance and take up glucose from the blood. This would increase hunger in someone on a LCHF diet because there would be less glucose available for the brain.