Friday, 27 February 2015

Fat makes you ..... fat ?!

One of the reasons it is hard to dissociate calorie balance to weight is because your intestine secrets a large number of hormones upon food ingestion and the magnitude of the hormone response is proportional to the calorie intake.

I was doing some research on Orlistat which is one of the few drugs approved for obesity treatment. Its suppose to make you lose weight because you "absorb" less calories, and the unabsorbed fat comes out the other end, sometimes violently.  Orlistat produces only mild weight loss after 1 year of use, ~2.89kg, which essentially makes it useless, but its the mechanism of weight loss that im interested in.

This paper looks at the effect of orlistat on GIP secretion. Ive talked alot about GIP before, its an anabolic hormone secreted from the intestine in response to both fat and carbohydrate digestion, but remains almost unchanged in response to protein.  A look back at this post and you see a graph of GIP in response to nutrient ingestion.

Heres some quotes from the orlistat paper....

Our results demonstrate that in nonobese healthy subjects orlistat accelerates gastric emptying of an orally ingested ∼500 kcal solid-liquid mixed meal and attenuates plasma GIP response, while it does not appreciably alter the plasma responses of CCK, GLP-1, and PP compared with control. 
GIP is secreted from enteroendocrine cells of the K type in the upper gut in response to nutrients in a load-dependent manner, fat being the most potent secretagague in humans
There are functional GIP receptors on adipocytes, which have insulin mimetic properties such as uptake of glucose (37), fatty acid synthesis, upregulation of lipoprotein lipase synthesis, and reduction in glucagon-induced lipolysis
Thus GIP acting on its specific receptors and via insulin secretion promotes fat accumulation in adipocytes, obesity, and thus insulin resistance. GIP receptor knockout mice who are fed a high-fat diet are resistant to obesity



So im thinking, orlistat most likely causes weight loss because GIP secretion is reduced. The problem ofcourse is its hard to disentangle this from the idea that the weight loss is caused by reduced calorie absorption because GIP is secreted in response to free fatty acid absorption into the enterocyte.

Anyway, Im not trying to put forward the idea that "fat is fattening", I dont have data on how potent GIP is on adipocytes compared to insulin. But if you look at the data solely on GIP, its clearly a "fattening" hormone. and it *is* secreted primarily in response to fat.  ( GIP also is important for bone density, i.e. it increases bone mass, so blocking it completely might not be a good idea )

intriguingly it was also reported in the "accelerated glucose absorption" post that obese people exhibit enhanced GIP secretion in response to nutrients. A great example of how "a calorie is not a calorie".

I intend to experiment with orlistat on LC when I get the chance. Hopefully the Steatorrhea wont be too bad...





Friday, 6 February 2015

the "master" gene

I was reading through JJ's tweets other day and came across this




despite it being quite disturbing, something out of a horror movie, reading the ensuing discussion was fascinating. This article explains what is going on.

Basically, there is a gene they refer to as "eyeless" and when activated, this gene sets off cascade of signalling that results in the growth of an eye at that location.

The reason I found this so interesting is because we have also seen here on this blog another candidate for a "master" gene. PPAR-γ.    Just as activating "eyeless" caused eye growth in strange places of the body, substantial evidence indicates that activating PPAR-γ causes adipocyte appearance.

My guess is, it probably didn't how much the fly ate and exercised, once the eyeless gene was on, the eye WAS GOING TO GROW, regardless.

At this point im fairly sure that the cause of obesity is refined carbs promoting hyperglycemia and hyperinsulinemia.  These 2 in turn promote epigenetic changes to adipose tissue aswell as the recruitment of adipose tissue progenitor cells ( preadipocytes ) Once a preadipocyte turns into a mature adipocyte, its going to store (alot) fat, everything else is irrelevant.

I also found this interesting post on t-nation, where he explains that people who respond poorly to resistance training do so because of genetics and poor recruitment of muscle progenitors ( satellite cells ).  This could potentially be similar to the reason some people are resistant to obesity, i.e. failure to recruit progenitor cells in adipose tissue.











Tuesday, 9 December 2014

lipophilia and storage vs oxidation



You see this slide in most of Taubes's lectures, and I think what Julius was observing and trying to report can easily be explained by observing what happens when a pre-adipcoyte turns into an adipocyte.

There is a series of papers from the 1970's  looking at what changes are taking place in the conversion of pre to mature adipocyte.

When cells of the established preadipose line 3T3-L1 enter a resting state, they accumulate triglyceride and convert to adipose cells. The adipose conversion is brought about by a large increase in the rate of triglyceride synthesis,
 If 3T3-L1 cells incorporate bromodeoxyuridine during growth, triglyceride synthesis does not increase when the cells reach a stationary state, and triglycerides do not accumulate.
As would be expected from their known actions on tissue adipose cells, lipogenic and lipolytic hormones and drugs affect the rate of synthesis and accumulation of triglyceride by 3T3-L1 cells
Glycerophosphate acyltransferase activity rises sharply during the conversion and reaches a level of 80 times higher than that of another 3T3 subline in which practically no adipose conversion takes place (3T3-C2).(link)
There is alot revealing information here, remember this picture?



The underlying message here is that, a fat cell accumulates fat because there is a change in the internal mechanics and gene expression of that cell. If calorie availability itself was sufficient to drive increased triglyceride accumulation, how would you explain why pre-adipocytes store virtually no fat?

In the same sense, you have to ask yourself, is calorie availability sufficient to turn a small adipocyte ( thin person ) into a large adipocyte ( fat person ) ? Or does this change also require further increases in the trig synthesis rates of the adipocyte?

If you knockout the ASP receptor ( acylation-stimulating protein receptor ), this reduces trig synthesis in adipose tissue, the mice eat 60% more than controls, but weigh the same.  Also, they do not have increased energy expenditure because oxygen consumption was identical to controls, instead what happened was they had massively increased fat oxidation rates.

This seems to suggest that if you reduce the hormonal signals that drive the trig synthesis pathway's ( low-carb anyone? ), the increased FFA availability automatically drives increased fat oxidation. Further, it would appear fat oxidation is a slave to the driving force of storage. A reduced drive to store fat, promotes increased fat oxidation.

In this context, it appears wrong to say "if you dont burn it, you will store it"

but rather it looks like...  "if you dont store it, you will burn it"

Breaking down the Julius Bauer comment above, we have some explanations from what he was trying to describe...

The abnormal lipophilic tissue seizes on foodstuffs -  The foodstuffs flow into the adipocyte, but are seized/trapped due to the aggressive levels of trig synthesis inherent in adipocytes.

even in the case of undernutrition - the drive to store nutrients can override the need for fuel burning and sequester fuels away from oxidation.

it maintains its stock -  as we all know, adipocytes are extremely good at resisting size changes. decreases in adipocyte sizes encourage increased trig synthesis responses.

and may increase it independent of the needs of the organism - hormonal changes that drive increased trig synthesis pathways in adipocytes cause fat growth, whether that fat growth is needed or not is irrelevant.






Wednesday, 26 November 2014

Fucked up glucose digestion in obesity

very quickly...

Accelerated intestinal glucose absorption in morbidly obese humans – relationship to glucose transporters, incretin hormones and glycaemia

Another study showing that obese people have rapid and increased glucose absorption from the duodenum due to increased glucose transporters. This rapid glucose absorption facilitates hyperglycemia and hyperinsulinemia, because as we know, faster digesting carbs spike blood sugar and insulin more aggressively.



Although it has long been thought that the hyperglycemia and hyperinsulinemia in obese people is due to insulin resistance, the authors here question this, and speculate that rapid glucose absorption could instead easily account for this.

Further there is an imbalance of postprandial incretin hormones, obese people exhibit reduced GLP-1 secretion in response to carbs, ( which is also seen in the graphs here ), the authors here mention that reduced GLP-1 secretion allows glucagon secretion to be enhanced in the postprandial state, which is very inconvenient when combined with the hyperglycemia from the food ingested, because the job of glucagon is to raise blood sugar ( and its already raised from the food )  The combination of enhanced glucagon levels AND the carbs results in even HIGHER blood glucose, and you need even HIGHER insulin to deal with it. Something of a vicious cycle.

We know way back from the powdered carbs study that there is something about the digestibility of carbohydrates that can SERIOUSLY enhance how fattening they are. Indeed it seems to be refinement of carbs that makes them more easily and quickly digested that is the devil. The obesity epidemic has risen in parallel with refined carb consumption.

How hard would it be to believe that...

refined carbs -> morphological changes to intestine** -> hyperglycemia + hyperinsulinemia in response to carbs -> adipogenesis + histone acetylation in fat tissue -> elevated fat mass setpoint -> obesity + resistance to weight loss

There is already some evidence hyperglycemia can cause chromatin remodeling to DNA.

**to the best of my knowledge, this has never been investigated, so we dont know if its true, or false. I.E. if the refinement of dietary carbs can directly cause elevated glucose transporters in the duodenum.










Saturday, 22 November 2014

Why does glucose make fat?

I want to come back to this question at the end of the post, after we have examined some research results.

For those not aware a "pre-adipcoyte" is just a cell that has the potential to turn into a proper adipocyte, and is not really an "adipocyte" in the pure sense, it also does not store much fat.

Here's some pictures to do the talking, ( stolen from google )





Something we have to ask ourselves, is, why is the adipocyte storing large amounts of fat, and why is the "pre-adipocyte" not storing hardly any fat? Something to do with calories and energy balance? The adipocytes eat more than they burn, and are in positive energy balance, meanwhile the pre-adipocytes are in perfect energy balance,  they eat as much as they burn and stay slim. Calories in, calories out, second law of thermodynamics. Matter cannot be created or destroyed, only transferred.

Is any of this making any sense yet?

Dont dare ask WHY the adipocyte is eating more than it burns. Thats IRRELEVANT................or it might have something to do with its poor impulse control and lack of willpower when faced with tasty food. mmmmmmm cake.

Meanwhile, back in the lab, I came across this paper recently, which looks at epigenetics of the PPARγ gene. A question that has bugged me and should hopefully of bugged anyone else in obesity research is, why are obese people always drawn to regain weight after weight loss. Somehow it seems that the fat tissue is slowly and surely sucking up fat to regain its original mass. I think we've discussed to death on this blog the possible causes of this. Adipocyte hyperplasia and low leptin being the leading culprits. Aswell as catecholamine resistance, particularly in the subcutaneous depot.

However, I think the answer to the question of why fat tends to return to its original size lies in the answer to the question of how it got to that size in the first place.

1. What determines how much fat a fat cell stores?
2. What turns a pre-adipocyte into a mature adipocyte? ( Adipocyte hyperplasia )

Actually we have already seen the answer to the first question, back in this post. The idea put forward was that the histone H3 acetylation of the PPAR-gamma promoter region increased the transcriptional activity of this gene, and thus resulted in increased fat accumulation in the adipocyte.

I Advise you to watch this video which easily and quickly explains what all this histone H3 acetylation stuff is about



So in short, The histone H3 acetylation uncoils the DNA and allows the PPARγ gene to be read, with increasing permissiveness. The next question is,

Why would increased PPARγ lead to increased fat storage?

While I dont have hard conclusive evidence of this, my guess would be because PPARγ targets the gene transcription of proteins involved in the formation and maintenance of lipid droplets. If you want to build a huge single lipid droplet in the middle of the adipocyte ( which is the defining feature of the adipose ), you need proteins to do that. Fatty acids and triglycerides dont just magically like to clump together in large solid balls.

As an example, PPARγ targets and expresses perilipin1 , which is a lipid droplet protein involved in whole body energy balance. One of the crucial functions of perilipin1 is to coat the lipid droplet surface and stop hormone-sensitive lipase entering the droplet and chopping up triglycerides into fatty acids. (lipolysis )

Infact atleast one team are looking to make an inhibitor of perilipin1 to treat obesity. It has also been discovered that the weight loss associated with anti-retroviral drugs is due to their actions in degrading perilipin1. FSP27, is another lipid droplet protein controlled by PPARγ. The function of FSP27 is to make small lipid droplets fuse together into larger ones.

So, in essence, higher  PPARγ -> more lipid droplet proteins being manufactured and floating around -> increased ability to build large lipid droplets.

I would propose that  PPARγ IS the "vacuum" that is sucking up fat from the blood and causing it to be stored and maintained in the large central lipid droplets of adipocytes.

There is *some* evidence for this, because forced expression of PPAR gamma in fibroblasts and myoblasts  is sufficient to differentiate these cells into adipocytes. Its almost as if PPARγ is itself entirely responsible the adipocyte phenotype. Basically, once PPARγ becomes active in a cell, that cell BECOMES an adipocyte. And with that, this is a good time to move on to the second question....




What turns a pre-adipocyte into a mature adipocyte?

Again you can read pubmed[22991504]  for an in depth description of the very complex multi-step process that is adipocyte differentiation,  But basically....

the transcriptional activation of PPARγ during adipogenesis correlates with an epigenetic switch at the PPARγ gene. For instance, adipocyte differentiation is associated with a strong increase in levels of histone activation marks at the two PPARγ promoters.

in essence, PPARγ is not expressed in pre-adipocytes, then, modifications to the chromatin and promoter regions causes the DNA that codes for PPARγ to unwind from the nucleosome, this allows access by RNA polymerase II to start transcribing PPARγ.   PPARγ itself then starts off a cascade that involves unwinding the DNA in its gene target regions. 

An important ingredient in adipogenic differentiation media is high glucose and insulin.  For some reason, ( and this is what the title of the post refers to ) pre-adipocytes regard high glucose and high insulin levels as a signal to epigenetically modify the DNA to expose the PPARγ promoter region, to start transcribing this gene, and ultimately become an adipocyte.  There are other key ingredients in adipogenic media, indeed glucose and insulin exclusively may not be sufficient. (shrug, glucose and insulin appears to be enough to make me fat in vivo )

Whats the real reason sugary drinks make you fat? It may because,  the hyperglycemia and insulin these drinks promote causes epigenetic changes to DNA in cells that ultimately result in increased and sustained expression of PPARγ.  There is already evidence out there that diet and hyperglycemia cause chromatin remodeling to DNA. 

Is histone acetylation of PPARγ the reason obese people have elevated fat mass set point?

Its important to point out PPARγ is regulated both at the nutritional and hormonal level, aswell as at the genetic level by chromatin modelling acetylation/methylation. The ligands for PPARγ are fatty acids and prostaglandins. Further, PPARγ is strongly upregulated by insulin. 

A curious study from 1997 found increased mRNA of PPARγ in adipose tissue of obese people ( 14.25 obese vs 9.9 lean ), whats more, the increased mRNA of  PPARγ  positively correlated with the BMI of the subject. The fatter you are, the more likely your  PPARγ is to be higher. Given what we have learned above, that would be expected.

But the most curious part of the the study was that they made the obese people lose 10% bodyweight on a 800 calorie diet, and  PPARγ decreased by 25%. This was then followed by a 4 week intervention of weight maintenance, during this time, PPARγ increased back to pre-treatment levels! Isnt that funny? Suddenly my brain is flooded with images and notions of weight regain following weight loss. Its entirely possible these obese people, like pretty much the vast majority of obese people, have chromatin modifications to their  PPARγ promoter regions thus encouraging increased basal levels of PPARγ.

Going on a diet temporarily suppresses PPARγ, because as discussed, PPARγ is also regulated by nutrition and insulin. But returning to normal eating patterns would see metabolic hormones return to normal. The PPARγ levels return to normal, and their weight will probably return to normal. ( normal being the pre-treatment obese state ).

Adipocyte dedifferentiation.

As eluded to in the fat cell size regulation post.... it would appear adipocytes are actually capable of de-differentiating back into pre-cursor cells, losing their lipid content in the process. Indeed they appear to take on stem cell properties.

As such it may not be necessary  to cause any kind of apoptosis to reduce obesity, instead it may only be necessary to silence the PPARγ gene in the adipocyte. Through either DNA methylation or de-acetylation of the histone H3, , or some other complex restructuring of the chromatin, . Once the PPAR gene is silenced, lipid droplet proteins will no longer be manufactured, the adipocyte will have no way to build the large lipid droplet and lipid stores should exhibit a net flow out of the cell.

Whether this can happen in vivo in humans to produce practical weight loss is anyones guess however, and this subject would require another post.










Friday, 17 October 2014

Increased glucose transport in the duodenum of diabetics

From a 2002 paper, the researchers found in the biopsies taken from the duodenum of diabetic patients greatly increased glucose transport, when compared to healthy controls.





They also found much higher protein levels of the glucose transporters SGLT1 and GLUT5 and GLUT2. Not only that, they found increased activity levels of the enzymes sucrase and lactase that break down sucrose and lactose respectively.

Jeez, so it looks like the intestine of diabetic people has undergone some serious morphological changes to make carbohydrate digestion faster, and not surprisingly this is probably what contributes to excessive hyperglycemia in diabetics when they try to eat carbs.

The reason this should be so concerning is because of the huge body of literature which suggests that it is the fast digesting and processed carbs that cause diabesity. High GI foods and in particular powdered carbs are reported to be the worst offenders.

To what degree does eating high GI foods/powdered/processed carbs mimic having elevated glucose transporters in the duodenum, I can only speculate.

People are not born diabetic, ( although thats been changing in recent years ), they become so after exposure to the "western diet". So I think it would be fair to say these morphological changes to the intestine are a biological adaption to a carb heavy processed diet.

Whats more intriguing are the results from gastric bypass surgery, which typically resolve diabetes before significant weight loss, and also how duodenal bypass exclusively has been reported to cure diabetes in atleast 1 person. Also I remember from this paper the author suggesting that a diabetic signal originating from the gut, caused fasting hyperinsulinemia. If excessive transport of glucose in the duodenum "causes" diabetes/hyperinsulinemia, then it would make sense that completely bypassing the duodenum with surgery would fix it.

It should also become apparent now one of the reasons Low-Carb is so effective is because it side-steps excessive glucose absorption in the duodenum, simply because there is no glucose to absorb. It also makes me wonder if the cause of "permanent" glucose intolerance people seems to inherit from diabesity is largely due to increased glucose transporters in the duodenum. Infact I would say that if you have increased glucose transporters in your duodenum, you have no CHOICE but to go low-carb. ( or surgically re-arrange your insides, up to you )

Theres still many "if's", and we must be careful with direction of causality.

I mean, it could be the high levels of fat and calorie intake and insulin resistance that spontaneously appears that makes these morphological changes happen................  who knows??

To me, it seems that *somehow* a carb heavy processed diet simultaneously changes the duodenum to facilitate increased glucose transport, aswell as morphological changes to the pancreas which make it hyperplasia/hypertrophy and secrete huge amounts of insulin, which makes you fat. With genetics helping to explain precise individual responses.

Artificial Sweeteners.

I really dont want to be against AS's, I have an incredible diet soda addiction, ( ive been known to drink 3 liters of diet soda at work in a single 12 hour shift ) However there is some evidence that AS's may facilitate diabetes, but also that they may promote increased glucose transporters in the duodenum by means of the sweet taste receptors they bind to.

In 2010 one team found piglets with AS's added to their diet unregulated SGLT1 and glucose transport in the intestine.

Indeed, this paper also speculates that increased sweet taste receptor activation elevates SGLT1 and contributes to hyperglycemia ( in diabetics )

Lastly, this paper says that sweet taste receptors on the pancreas regulate basal insulin secretion, such that islets deprived of sweet taste receptor signalling hypersecrete insulin. Intestinal sweet receptors are rapidly downgraded in response to glucose or AS's, so downgrading your sweet taste receptors on your pancreas through AS's probably = insulin hypersecretion

However im not sure if ingested AS's even hit sweet taste receptors on the pancreas, my guess is they probably dont make it that far during the digestion process, so that last study may not be at all relevant. However AS's certainly hit the sweet taste receptors in your gut.










Tuesday, 2 September 2014

Fat cell size regulation

Thanks to Bill for sending me this paper....

The premise of the paper is this......

Since individual cells from freshly isolated white adipose tissue (WAT) exhibit variable levels of fat accumulation, we attempted to determine which factor(s) cause this variation.

If you look at those micro-scope pictures of adipocytes from adipose tissue, youll notice that they are not all exactly the same size.  ( see here for ex ). Below is a distribution count of rodent adipocytes isolated and exposed to growth  + adipogenic media....

Cells were divided into a "high" and "low" category according to their BODIPY staining which was closely related to their size and therefore how much fat they stored.

As you can see from the top graph, you get an approximate normal distribution. But the question is why? Why arent adipocytes all the same size?

In general adipocytes from the same localized region of the body are exposed to the same concentrations of nutrients in the blood ( or there abouts ) and therefore CICO should predict for them to be roughly the same size. But they arent.....   therefore this can only mean there is a property intrinsic to the adipocyte that determines its size......

Now... if you want the TL:DR point of this post... it is this......

The extent of fat accumulation is correlated with histone acetylation of the Ppar promoter that is heritable and maintained even in dedifferentiated adipocytes.

What this means in plain english is, that if you take a bunch of adipocytes and expose them to growth media and adipogenic media, leave them to incubate for a few weeks, then examine them under a microscope, they are NOT all exactly the same size, even though they were all exposed to the exact same conditions. 

If you snoop around a bit more, youll find the thing that determines how "fat" an adipocyte gets is correlated with the histone acetylation of the PPAR-gamma gene. "histone acetylation" is how biology does gene regulation, I.E. how strongly a gene is expressed. As the paper says....

Histone acetylation is generally correlated with transcriptional activation

So a gene with a high histone acetylation will have a high transcriptional activity and be expressed strongly within the cell. Overall this is just a fancy way of saying, a fat cell has a "set point" for the amount of fat it will store that is dependent on the genetics of that cell.

To understand how I can make that statement, you need to go back all the way to this post...in which we learned that PPAR-gamma plays a huge role in determining how much fat you store.  Now we can understand a bit better why there is *some* truth to the idea of a fat/weight "set point", .

Each individual fat cell in your body has a fat/weight set point, that is determined by the histone acetylation of the PPAR-gamma gene. And your total body fat mass is just the sum of the fat mass of all your individual adipocytes...... therefore YOUR fat mass has a "set point".....unless you grow new adipocytes, in which case your fat mass "set point" goes up

This helps explain why people with more fat cells are generally fatter.

The following graphs show some of the characteristics of the fat cells before and after exposure to growth media....



Interestingly, the insulin receptor expression was not different between fat cells that ended up being small or large.....

This would suggest that it is post-receptor signalling that is involved in the "insulin sensitivity" of a fat cell.  Indeed you could say that large fat cells achieve their inflated sizes by having elevated expression levels of PPAR/GLUT4/SREBP1c.

I was especially interested in the GLUT4 graph, because I have seen previous evidence that GLUT4 is very anabolic for fat tissue. GLUT4 over-expression on adipocytes results in gross adipocyte hyperplasia, and that hyperinsulinemia selectively increases GLUT4 on adipocytes and reduces it on muscles.

Anyway, im not sure what controls GLUT4 gene transcription in adipocytes, I think PPAR-gamma is involved since Thiazolidinediones, which are PPAR-gamma agonists, increase GLUT4 on adipocytes. 

This study demonstrates that subpopulations reside within WAT and 3T3-L1 cells that vary in their capability to accumulate fat and that these differences are heritable. We have shown that the extent of the cell’s ability to accumulate fat correlated positively with expression levels of Ppar , a master regulator of adipogenesis, and with other markers of differentiated adipocytes, including Lep, Tshr, InsR, Glut4, Fasn, Srebp1c, aP2, and Pref1; exogenous expression of Ppar in 3T3-L1 cells increased fat accumulation; and the levels of histone H3 acetylation of the Ppar promoter in preadipocytes was a predictor of the extent of fat accumulation upon induction of adipogenesis.  
We thus suggest that epigenetic modification of the Ppar promoter is, in part, the mediator of the heritability of adipocyte differentiation.

With respect to the bolded sentence, "exogenous expression of Ppar in 3T3-L1 cells increased fat accumulation", do you remember how to increase Ppar in vivo?......... Insulin.

I do also wonder about the implications of the epigenetic modifcation of the histone acetylation of Ppar and the coincidence of fat mothers ( parents ) giving birth to fat babies.