Saturday, September 05, 2015

Protons (36) Glycolysis to lactate

Before we can even begin to think about metformin and mtG3Pdh we have to re examine lactate and glycolysis. It's difficult to over emphasise how interesting this hypothesis is:

Schurr, A. Lactate: the ultimate cerebral oxidative energy substrate?

I've no idea who Avital Schurr is. But he appears to be an anaesthetist, always a plus point, and he has a view of glycolysis which I really like.

I've blogged before on the astrocyte-neuron lactate shuttle and why I, from my own personal viewpoint, consider lactate to be the ideal mitochondrial fuel when reverse electron transport through complex I is best avoided. It behaves like glucose but without easy access to mtG3Pdh. With the exclusion of fatty acids from neurons the only reduction in the CoQ couple other than complex I then comes from complex II, part of the TCA. There is no input from ETFdh or mtG3Pdh. Pure acetyl-CoA, driving mostly through complex I.

The lactate shuttle is controversial.

Many years ago I recall a sketch on a comedy program, probably on Radio 4, where two politicians of irreconcilable views were invited in to the studio to debate the finer points of some policy by throwing half-bricks at each other.

I never really realised this at the time but the lactate shuttle polarises people. Lactate is viewed by many as an utterly useless, rather toxic end product of anaerobic glycolysis. It is a surrogate for hypoxia, hypoperfusion or mitochondrial failure. It is remarkably unacceptable to almost all physiologists that lactate can be a super fuel or even a fuel of any sort at all. Schurr goes through the arguments and the people and the papers and the logical fallacies and how two groups can look at the same data and draw radically differing conclusions. Think LCer vs vegan vs potato head. You look at the same studies but see different explanations......... And you know, we can't all be correct. Lactophobia is an emotional response. Schurr's words are ‘glucoseniks’ vs ‘lactatians’. You really have to read the paper!

The basic argument is that glycolysis always goes to lactate through pyruvate via cytoplasmic LDH 5. Whatever the oxygen availability. It's energetically favourable.

Lactate is then transfered to the mitochondria via a monocarboxylate transporter and fuels the TCA via pyruvate generated from the intra mitochondrial LDH, putatively LDH 1.

Partly this is redox related. Traditionally, using pyruvate:

Glucose + 2 NAD+ + 2 ADP + 2 Pi → 2 Pyruvate + 2 NADH + 2 H+ + 2 ATP + 2 H2O

Obviously, when you run out of NAD+ glycolysis would grind to a halt. But just look at how neat things become if you take glycolysis through to lactate:










Glycolysis, if it runs to lactate, is self sustaining. There is no deficit of NAD+, just an NAD+:NADH cycle. There is no need for the glycerol-3-phosphate shuttle, not for NAD+ regeneration anyway. Obviously, once lactate enters the mitochondrion it gets converted back to pyruvate with the generation of NADH. But this NADH is where it's needed, in the mitochondrial matrix, well away from the nucleus, ready to be processed by complex I.

How neat is that? Edward Edmonds suggested "elegant" as the descriptor. Yes, some hypotheses are so elegant the really have to be correct.

If it is correct you can then start asking questions about what mtG3Pdh is doing (if it's not regenerating NAD+) and how this might fit in with metformin. We're also back to what controls insulin sensitivity and how a cell regulates energy throughput. And fructose. And hyperglycaemia. Lots to think about.

Peter

30 comments:

annlee said...

http://www.researchgate.net/profile/Avital_Schurr

Peter said...

Thanks Annlee, have put in minor correction

Peter

mommymd said...

I'm an anesthetist at a trauma hospital. At times, usually associated with major head trauma and disruption of the blood brain barrier, a patient's blood lactate will climb to the mid teens, where normally blood lactate is measured at less than one. There is nothing in our textbooks that discusses this. The acidosis doesn't get that bad. The patients survive. Other times, usually associated with gut ischemia, a patient's lactate will be around 10 and the metabolic acidosis is profound. These patients seem to do worse. Different mechanism of tissue injury and patient characteristics, but now I'm thinking that cerebral lactate does not equal body lactate. The molecule exists as two isomers. Is this a factor? I'll have to watch this clinically and see if I can find more.

George Henderson said...

Mommy MD, D-lactate from bacteria might be the isomer associated with gut ischaemia, not so easy to metabolise.

I was sent this Schurr paper by Catherine Crofts a while ago, elegant is right - how could evolution miss such economy? Lactate is an energetic molecule, no other such substrate needs conversion to glucose in the liver before it can be utilized. The Cori cycle is specific for when glucose is required (and lactate oxidation would need to shut down then - if it does decrease in starvation that would be an argument in favour of Schurr and the lactatians).
Tim Noakes remembers the lactatian idea being attributed to Brooks back in the day.

George Henderson said...

This is a very interesting experiment showing that lactate spares insulin (increases insulin sensitivity). How would this work?

https://www.dropbox.com/s/4zp7zvuuawusu2i/Lactate_Insulin.pdf?dl=0

George Henderson said...

P.S. Metformin inhibits the Cori cycle, not by much perhaps but it can cause the occasional case of lactic acidosis.

Peter said...

Oops, hit publish when I meant to hit edit, will re publish tidied version in a minute. George, I've for so much to work through on this front. I never no what I'll come up with before I do so but inhibiting mtG3Pdh might have a number of benefits but there's a lot more around metformin than ever meets the eye!

Peter

Peter said...

Hi mommymd,

That’s very interesting. My initial reaction is that the lactic acidosis in head injury patients might be adaptive. I did a little googling and picked up this paper which seems to suggest that lacate uptake by the brain, described as “abnormal brain lactate uptake” is associated with improved outcomes. My feeling is that this might be adaptive as lactate should generate less free radicals than glucose uptake per unit ATP produced

http://www.nature.com/jcbfm/journal/v23/n10/abs/9591472a.html

“Conclusions: During the first 6 days after moderate or severe TBI, CMRO2 and arterial lactate levels are the strongest predictors of neurologic outcome. However, the frequent occurrence of abnormal brain lactate uptake despite only moderate elevations in arterial lactate levels in the favorable outcome patients suggests the brain's ability to use lactate as a fuel may be another key outcome predictor. Future studies are needed to determine to what degree nonglycolytic energy production from alternative fuels such as lactate occurs after TBI and whether alternative fuel administration is a viable therapy for TBI patients”

I still tend to feel that the GI catastrophe patients (gastric dilation and volvulus for vets is the common one) are L-lactate via impaired perfusion. I think the assays are reasonably specific for the isomers though not full so, depending on sample processing and technique used.

Still, you have to wonder if the acidosis of head trauma is adaptive and evolutionarily conserved…

Peter

That's better!

Peter said...

George, the Sarajevo paper is very strange! Lactate as an insulin secretogogue (not what Protons ideas would expect) to the point of near fatality (and actual fatality in the pilot study). But only in the presence of exogenous insulin. How do they get a quadrupling of insulin levels by adding lactate to exogenous insulin? I wonder if it has been replicated? Lactate blocking insulin metabolism coupled with allowing catastrophic non insulin mediated glucose uptake? Or allowing insulin to act w/o being degraded? Insulin degradation is not totally tied to insulin action. Does lactate allow it to work w/o being degraded?

That one I'm thinking about!

I don't want to be too critical of what may be an important finding but the editing was very poor on the paper. I don't care about this provided the finding is real, and the paper seems quite honest in an innocent sort of way. Anyway, time to cook breakfast, the children want their bacon and eggs!

Hee hee, I keep adding edits to this comment and the children really are getting restless!

Peter

Passthecream said...

Excellent as usual. I can hardly contain my anticipation until we get to 'Protons 42 the answer to life the universe and everything'.

:)

I'm off to have a brainfood snack of double cream yoghurt.
C.

Peter said...

OMG it IS 42 next. How many roads must a man walk down??????

Peter

Peter said...

Oh, it's a few to go on that one!!!!

karl said...

BTW lactose and lactate/lactic acid are differnt things.

The name probably comes from 'lactic acid bacteria' that produce lactate from carbohydrates.

Lactate looks a bit like a rearranged beta-hydroxybutyric acid - a ketone body...

Any connection?

Ash Simmonds said...

https://www.youtube.com/watch?v=lThFQM503EU

https://en.wikipedia.org/wiki/Lactate_shuttle_hypothesis

Passthecream said...

@Peter, sorry I meant to cause no panic. The protons series is a fantastic resource and my anticipation is real.

@ Karl Wikip(yoghurt)'The bacteria used to make yogurt.....Fermentation of lactose by these bacteria produces lactic acid.'




C.

Simone Fleuren said...

Hi,

like the Schurr paper and it links nicely into other reading i have been doing over the summer, mainly to do with brain metabolism. I also love the Protons series and am glad it is picked up again!

There is conflicting evidence about the location of the mLDH, some research suggesting that all conversion from lactate to pyruvate is done in the inter-membrane space (see: Lactate is always the end product of glycolysis ) and some that the conversion takes place in the matrix (see: Transport and metabolism of l-lactate occur in mitochondria from cerebellar granule cells...

If mLDH works in the inter-membrane space, the NADH produced still has to enter the matrix (via mtG3Pdh), so no gain here in avoiding the reverse electron transport via Complex 1. I guess you are assuming that mLDH is active in the matrix then?

Best
Simone

Ilaine said...

Recently read a hypothesis, just a tweet by some gut bug guru, that metformin acts via gut bacteria. No idea, really, just sounded interesting.

Peter said...

Simone, yes, that seems logical. You wouldn't have thought that it would be so difficult to decide which side of a membrane a protein was on, would you? But life is never that simple when you are looking at single molecules...

Ilaine,

http://www.ncbi.nlm.nih.gov/pubmed/18154320
http://www.ncbi.nlm.nih.gov/pubmed/24847880
http://www.ncbi.nlm.nih.gov/pubmed/25603051
http://www.ncbi.nlm.nih.gov/pubmed/16478780

30-43% identical between bacterial and mitochondrial equivalents! Not homology, absolute sequence conservation. That is astounding as it goes back to the formation of the initial eukaryote symbiant. And mtG3Pdh is a very small protein, this well conserved. It is very important and the fact that metformin works on gut microbes as much as it works on mitochondria is no sort of a surprise... Obviously , there are a lot of follow ons from this, I just need the time to sort and blog some of them.

Peter

George Henderson said...

Metformin works like this (in the gut); it stimulates goblet cells to produce extra mucus in the gut lining. And it probably does this by diverting glucose into mucus (fibre) production, so a bit of a carb blocker. The mucus feeds akkermansia bacteria. These probably produce butyrate or acetate which acts on AMPK; so there's a carb for fat trade involved.
And this is presumably why there are GI upsets with metformin. You would need to have akkermansia present to take advantage of it, if not something else could flourish.
http://www.dailymail.co.uk/health/article-2323945/Good-gut-bacteria-provide-new-treatment-obesity-diabetes.html

Simone Fleuren said...

@George,

i am not sure which study the daily mail article is referring to, not the sort of publication that would supply a link to a scientific study. I guess it might have been this one:
Cross-talk between Akkermansia muciniphila and intestinal epithelium controls diet-induced obesity which shows that akkermansia is decreased in obese/T2D mice as compared to lean controls and that administration of the bacteria to the obese/T2D mice leads to an improvement in the metabolic disorder. No mention of metformin.

Another study around the same time is An increase in the Akkermansia spp. population induced by metformin treatment improves glucose homeostasis in diet-induced obese mice looks at metformins involvment ( i have access to the full paper if anybody is interested). Here, metformin increases the number of akkermansia in the HFD mice, but not in the NCD mice (who have a much higher population to start with anyway). It does increase the number of goblet cells in BOTH diet types though. when the HFD mice are just given a akkermansia probiotic, without metformin, the effects are similar, including the rise in goblet cells.

SO: i guess that metformin raises the number of any mucin-degrading bug and in HFD this happens to be akkermansia, in normal diet mice, this could be any other, not yet known mucin-degrading bacterium that is absent in the HFD mice. In both dietary types, the mucin-degrading bugs increase the number of goblet cells, to replace the used mucin. the increase in the goblet cells then exerts (how?) the effects, i.e. improved glucose tolerance. Just a theory, but will hunt around a bit to understand how goblet cells could improve glucose tolerance.

Another complication is that (as stated in the same paper) the administration of a antibiotic also improves the metabolic profile of the HFD mice. this might point to dysbiosis as an underlying cause of the disturbed glucose handling which can then be treated by either restoring some balance in the gut microbiota (metformin or akkermansia supplements) or by just getting rid of the whole lot.

sorry for the long comment, got carried away. Very interesting, but also still so speculative without enough data.

Best
Simone

Passthecream said...

A couple of references, looking at bug populations in people.


http://www.omicsonline.org/abundance-and-diversity-of-microbiota-in-type-2-diabetes-and-obesity-2155-6156.1000253.pdf


http://onlinelibrary.wiley.com/doi/10.1111/ped.12243/pdf


Which comes first, the bugs or the disease?


C.

raphi said...

great post & great discussions in the comments. i finished reading the paper and am glad i did - a great 'live' example of how textbooks are re-written.

Passthecream said...

I'm a pretty slow thinker & this topic continues to excercise my thoughts; the Avital Schurr papers are v. interesting reading + the links from Ash. Then reading about drunken lamb syndrome, seems to be related to a dysbiosis where the bugs involved are generating lots of D-lactic acid

http://www.ncbi.nlm.nih.gov/pubmed/23812111


so you'd probably want to select your yoghurt and sauerkraut organisms carefully. L. bulgaricus, L. helveticus, and L. delbrueckii produce L-lactic acid mostly and perhaps Streptococcus thermophilus does. Others?


Since lactate and glucose (and pyruvate) are so closely coupled, what is the relation between lactate and insulin?


This is an interesting paper:

http://www.ncbi.nlm.nih.gov/pubmed/9920088

figure 3 is fascinating, even for the insulin/glucose dynamics alone and eg:

"During nighttime, the frequency and amplitude of glucose oscillations were lower. The daytime profiles showed significant temporal coupling and pattern synchrony among insulin, lactate, and glucose. Only the close temporal relationship between insulin and lactate release persisted during nighttime. The temporal coupling and pattern synchrony between insulin and lactate were correlated inversely with insulin sensitivity, and positively with the degree of abdominal obesity.During nighttime, the frequency and amplitude of glucose oscillations were lower. The daytime profiles showed significant temporal coupling and pattern synchrony among insulin, lactate, and glucose. Only the close temporal relationship between insulin and lactate release persisted during nighttime. The temporal coupling and pattern synchrony between insulin and lactate were correlated inversely with insulin sensitivity, and positively with the degree of abdominal obesity."



Phew!

C.

Chris said...

I'm probably splashing around in the shallows here but this discussion reminds me of this talk with Dr George Brooks at Berkeley on lactate as brain fuel https://www.youtube.com/watch?t=2&v=lThFQM503EU. He also has an energy drink called Cytomax with lactate in it.

Passthecream said...

The people seem to be towards the glucosenik camp (see mct1 para re:lsh p3-p4) but it's still an interesting overview of MCT's.

http://www.bris.ac.uk/biochemistry/halestrap/mctpart2.pdf


C.

George Henderson said...

This is quite a brilliant ketogenic diet case-study.

http://www.ojrd.com/content/10/1/120

Ketogenic diet in a patient with congenital hyperinsulinism: a novel approach to prevent brain damage.
Maiorana, A, Manganozzi, L, Barbetti, F, Bernabei, S, Gallo, G, Cusmai, R, Caviglia, S, Dionisi-Vici, C. Orphanet Journal of Rare Diseases 2015, 10:120 doi:10.1186/s13023-015-0342-6

The neurologists who wrote it up have no doubt that lactate is a cerebral substrate.

"Although glucose is the main energy source for neurons, human brain can also utilize ketone bodies from FFA, lactate, pyruvate, glycerol and some aminoacids, as alternative substrate."

I thought this case study relevant to Type 1 diabetes and wrote about the link here.

http://hopefulgeranium.blogspot.co.nz/2015/10/do-moderate-ketone-levels-from-low-carb.html

George Henderson said...

Thanks Simone,

I think the goblet cells make mucin from glucose (as per Perfect Health Diet "mucus deficiency will kill low carbers"). This means metformin mimics acarbose or lower carb. Ultimately glucose is being traded for short-chain fat. Win-win.

Passthecream said...

Dang, this gets more and more interesting George, somehow I hadn't been aware of acarbose before but since it "inhibits alpha glucosidase, an intestinal enzyme that releases glucose from larger carbohydrates " and it is a widely known and effective diabetes medication reducing the impact of carb inputs, how amazing that the (Au) DA and the (US) ADA still have the blatant stupidity to promote high carb eating for diabetics? ( perhaps it is a glucose induced non-sequitur?)


The drunken lamb syndrome I mentioned earlier is probably a type of lactic acidosis - lactate MCTx's only transport L-Lactate ,leaving the D-lactate floating around. Hence the success of the bicarb plus antibiotic treatment. Since lactate is an energy substrate, it raises the question of what leads to lactic acidosis in humans? Is it a manifestation of some form of lactate resistance? Perhaps the MCTx's 'pull their heads in' when cells are replete in the same way that physiological insulin resistance occurs?

Hyperglycaemia plus lactic acidosis - sounds like real fun.


C.


Passthecream said...

Here's a link that comes late to the party. There is no doubt in this bloggers mind about the nature of lactate, acidosis, &etc

https://theendurancerunner.wordpress.com/tag/lactate/


C.

Peter said...

Nice find. Makes sense. I came across a technical paper years ago saying the same thing but didn't follow it up as I'd not started the Protons train of thought, was (and still am) not interested in exercise to exhaustion and will probably never find the paper. But clearly, thinking about exhaustion is the current follow on in Protons. And what glycogen depletion means. And why this is associated with lactate rise and exhaustion. But other things want to be written too and......

Peter