Thursday, November 15, 2012

Protons: SCD1 and the bomb

Our daughter has taken to watching DVDs. When we are not being tortured by Postman Pat (Special Delivery Serrrrrrviccccce, you know the tune) or the Mickey Mouse Clubhousssse we do at least get some amusement when she requests that blistering LC comedy "A Matter of Loaf and Death", by Nick Park.

Just how funny you can make a story about an obese cereal killer (no typo, the subtitles specify cereal killer, I said Park is funny!), murdering bakers as revenge for her obesity ("Are you ballooning?") has to be seen to be appreciated. It's a lot more amusing than Postman Pat.

One of the funniest scenes is where Gromit cannot get rid of Paella's bomb. It's a direct tribute to the 1960s Batman scene where "Some days you just can't get rid of a bomb".

You know, with the ducks

and the nuns. Park has kitten-enhanced the nuns

and included Yorkshire as the preferred site for bomb disposal. The Wars of the Roses are, apparently, over but not forgotten.

This post is about how physiology uses SCD1 to dispose of the metabolic bomb of hyperglycaemia in the presence elevated levels of palmitic acid.

It was pancreatic beta cells in culture which produced this picture:

I love this group because not only do they tell you in the methods section EXACTLY what glucose concentration they used in culture (5mmol/l vs 11-25mmol/l) without making you go back through three layers of references (to bury the 25mmol/l most groups use, but never discuss), but they also describe 11mmol/l as hyperglycaemia. That is, pathology.

This is Figure 4 from the same paper showing markers of apoptosis, superb:

Note the increase from palmitate to stearate. Note the complete protective effect of oleic acid and very modest toxic effect of linoleic acid. Aside: Note also the complete and total protection provided by limiting glucose to 5mmol/l, with any fatty acid, at any concentration. You have adipocytes leaking FFAs? Your best hope of keeping a functional pancreas is to limit your glucose to 5mmol/l. How? Answers on a postage stamp to...

It's also worth noting that stearic acid had to be reduced from the original 0.4mmol/l to 0.25mmol/l because at the higher concentration with high glucose they found exactly the same thing as Dave Lister did in Red Dwarf when Holly brought him out of stasis. Everyone is dead Dave. Everyone. Is. Dead. Dave. You have to U-tube the clip. Stearic acid at 0.4mmol/l with glucose at 25mmol/l, in cell culture, is utterly lethal to beta cells. If you pharmacologically block apoptosis the cells simply undergo the rather messy collapse of necrosis. This is a non survival insult.

Okay, okay, here's the clip:

The group went on to do quite intersting things with blockade of acyl-CoA synthetase and also with inhibition of fatty acid oxidation, which leads to all sorts of other threads which are, in part, where I have been wandering for the last few weeks. Far too much for this post.

So let's look at SCD1 knockout mice which have been rendered obese by also knocking out their leptin gene. Here we have rapid onset obesity due to adipocyte fat storage, free fatty acid leakage due to adipocyte insulin resistance and a complete inability to place a double bond in to palmitic acid or stearic acid. They have elevated FFAs and these are almost all saturated. This paper describes the study. It has to be noted that to obtain the FFA levels you have to reverse engineer Fig4 part A:

A ruler and calculator gives FFAs for the normal ob/ob mice as 0.32mmol/l and for the SCD1 k/o ob/ob mice as 0.56mmol/l. Any group which makes you reverse engineer in this way to get something as simple as FFA levels is, in my book, highly suspect. Does anyone think that 0.32mmol/l is quite low? Despite the greater obesity. Partly due to maintained insulin sensitivity in adipocytes (that's why they distend) while ever de novo lipogenesis produces palmitoleate using SCD1 and partly due to the higher levels of insulin production (normal beta cell mass) working on those insulin sensitive adipocytes... These mice are still in a slightly privileged position, metabolically, as they have yet to become obese enough for their SD1 equipped adipocytes to become seriously insulin resistant, they are still only six weeks old.

And here is the % of types of FFAs.

The column on the left is the one which represents about 0.32mmol/l of total FFAs and the column on the right is around 0.56mmol/l, as above. Glucose varies but fasting levels can be as high a 700mg/dl. So what happens to beta cells?

They divide up in to two types. The health ones and the dying ones.

The basic finding is that young ob/ob mice need either oleic or palmitoleic acid to maintain a functional beta cell mass. Exposure to high levels of glucose combined with palmitic and/or stearic acids induces apoptosis plus some necrosis in beta cells. Most non pancreatic tissues in the SCD1 knock out mice appear to be able to upregulate beta oxidation, especially in peroxisomes, of fatty acids which minimises both obesity and insulin resistance.

The beta cells of the pancreas do not appear to have this luxury.

They need to lower that F:N ratio with palmitoleate or oleate, otherwise they are left holding the bomb.



karl said...

Here are the full papers:

From the second paper (emphasis mine):

Loss of SCD1 in leptinob/ob mice unexpectedly accelerated the progression to severe diabete...

Unexpected results are exciting - might be opening a door?

If loss of SCD1 prevents weight gain - is it at the expense of elevated glucose? which I would expect would produce elevated Trygly + elevated FFA which would have the recipe to kill beta cells and thus diabetes?

So they ended up with low insulin - like in T1D.

If I understand this correctly - SCD1 forms the double bond in MSFA - double bonds in FA I think increases insulin sensitivity? - not sure about MSFA.

Inappropriate insulin resistance is the hall-mark of T2D - here we have loss of insulin generation - like in T1D.


I could see where T2D could progress until there isn't enough beta cells, thus worse diabetes, but I'm still obsessed with my quest, wanting to find a definitive answer of what changed that is causing the pandemic of T2D.

If consumption of O-6 FA causes inappropriate fasting insulin sensitivity in adipose tissue, I can see that leading to obesity - once fat there is leakage of FFA, and insulin resistance, thus elevated BG there is a toxic combination. But is this what is causing the T2D pandemic? ( I'm also perplexed about insulin sensitivity - it is often talked about as if it is the same in muscles and adipose tissure - I don't think I should follow that assumption. )

I'm also looking at what I know about the Philippines - when I was first there, I just didn't see people with T2D - yet, poor kids would eat rice with sugar if they couldn't afford vegetables and meat.

Now the Philippines has plenty of T2D so I ask, "what changed there that matches the earlier time of what changed in the US?" One thing is refrigerated foods - when I was first there in 1986, we would get meat at the market that was slaughtered the same day. Today, most of it is refrigerated. There is also lots of packaged foods with various food-like-substances. I don't know how to figgure out the change in O-6 or transfats.

John said...

This connects even more dots. Is there a practical application regarding fat sources? ...Avoiding PUFA is easy, but what happens as someone goes from macadamia fat to beef to butter to coconut? Living on coconut does not of course give us the fat profile of a coconut.

Puddleg said...

This is a nice illustration of the Feinman doctrine: dietary carbohydrate is a control element that determines the fate of dietary fats.

bert hubert said...

karl, perhaps those poor kids are t2d now? But, if I'd had to guess at the really big changes, I'd point my finger at fructose and especially fructose consumed outside of fruit or with a different glucose:fructose ratio than we were used to.

cavenewt said...

Two of my favorite things, Red Dwarf and Wallace and Gromit, in one post.

No wonder Hyperlipid is one of my favorite blogs, despite being over my head much of the time.

Scott Russell said...

This makes a lot of sense to me: add lots of easily oxidized PUFA and our bodies lower blood sugar as much as possible.

I've been wondering the same thing. I am particularly interested in how short and medium chain fats fit into this picture. My gut feeling is that coconut oil will be fundamentally different as its MCTs are going to be shuttled into ketone development, which seems to do some wonky things at the mitochondrial level.

I am also interested in the site specific nature of this. Obviously the ideal scenario would be insulin resistant fat cells and insulin sensitive muscles, but I doubt this will be attainable through diet alone. Just more motivation to go to the gym for some additional Glut4 activation. Clearly proof of the validity of ELMM.

Peter said...

IcedCoffee, ketones lower the inner mitochondrial membrane potential, glucose + insulin doesn't. This comes back to Veech and mitochondria, something I have yet to get to, despite the wish to. Nick Lane has a throw away comment that insulin phosphorylates ETC proteins. Veech, back in the 1990s, came to the conclusion that the effect of insulin on metabolic work was a due to modification of the ETC. I like convergence. Ketones don't. They appear to decrease uncoupling to maximise ATP production at a lower membrane potential. This is very interesting...


Scott Russell said...

Yea ketones are certainly a different animal. Seems a little counter-intuitive that something that increases mitochondrial efficiency would be promoted for weight loss; but then again, it would be useful to convert fat into fuel that has to be spent.

I've parsed through some of Veech's work, even though some of the specifics went a bit over my pay-grade. I always found myself distracted by him ending an article on ketones by bemoaning the need for a high-fat diet. Cant tell if its just a perfunctory point to appease the sponsors, or if he really doesn't see the disconnect.

Peter said...

The problem Veech seems to have with high fat diets is that he doesn't seem to like FFAs.

There is absolutely no doubt that blocking the entry of activated FFAs in to mitochondria is utterly catastrophic for cells through the ceramide pathway to apoptosis. This appears to be what hyperglycaemia does, probably acting within the mitochondria to leave mitochondria-ready fatty acids in the cytoplasm. I wonder if the cell considers the ceramide derivatives to indicate all mitochondria are either dead or utterly non functiona (hypoxia mimetic???). There is also the concept of pseudohypoxia too. Defunct mitochondria suggest that it's time to die. There is, apparently, no issue with ketones. The drop in inner mt membrane voltage is highly protective against reverse electron transport.

This per se is challenging as MCTs spike insulin in the absence of hyper or hypoglycaemia. What's going on there? Do the MCTs or the ketones trigger this????

I'm wanting to go back to this ground. Veech is very, very perceptive but none of us has to agree on all points or on all subtleties.


Scott Russell said...

I had always assumed the insulin response people saw with MCTs was from the ketones, but MCTs seem to do a lot of things differently.

MCTs tend to induce physiological insulin resistance without the IMTG accumulation seen with LCTs. Which makes sense, as MCTs like to be oxidized rather than stored. But this seems to do some wonky things with insulin sensitivity. Might be that MCTs make our muscles less insulin resistant. And MCTs increase serum adiponectin, which seems to play a role in insulin sensitivity, possibly mediated through the mitochondrial oxidation of other fatty acids.

I also wonder how the liver-oriented nature of shorter fatty acids plays in. I seem to recall the F:N ratio of lauric acid being right in between palmitic and oleic, but would they even get to the adipocyte, or would this only be seen in the liver?

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