Protons (77) Shulman PUFA and insulin sensitisation. Or not. Or so.

Over in the comments to the last post on metformin and Shulman's lab, Tucker pointed out that Shulman was an author (penultimate, so a senior author) on Nowotny et al's 2013 paper

Mechanisms Underlying the Onset of Oral Lipid–Induced Skeletal Muscle Insulin Resistance in Humans

which starts its discussion with the controversy about whether PUFA, particularly from soybean oil,  induce insulin resistance or insulin sensitivity. The most contradictory paper they cite is Xiao et al from 2006. In my head I think of this as the Hot Chocolate or the Cocoa study, which I discussed here as pure Protons in a cup of hot chocolate:

Differential effects of monounsaturated, polyunsaturated and saturated fat ingestion on glucose-stimulated insulin secretion, sensitivity and clearance in overweight and obese, non-diabetic humans

The two studies have diametrically opposite conclusions and this is an obvious opportunity for insight.

To me, it contradicts Protons, so let's go! Sadly, as Tucker points out, the chance for insight is completely missed by the Shulman group. They settled for PUFA -> insulin resistance. They lack the Protons perspective.

Equally sadly I have no handy mental label for the Nowotny/Shulman paper, probably because it produces no confirmation bias induced dopamine release in my head. My bad.

So let's compared the two.

The Cocoa study fasted obese subjects for 12 hours then fed them almost nothing but fat (with just a little carbohydrate) in small aliquots over 28-30 hours depending on how you read the methods. These subjects, by the time they started their hyperglycaemic clamp, had been either fully fasting or running their metabolism on the study fat, for approaching forty hours. In the control section of the study there were minimal calories supplied throughout, just a little carbohydrate in each drink. We can consider our control section to be, of necessity, in the functional insulin resistance of (very mild) starvation.

They are in a functional, very physiological, insulin resistance which is essential secondary to fasting or a fat based metabolism.

In Nowotny/Shulman their subjects were fasted for 10 hours in the aftermath of three days of a "high carbohydrate" eating period. By the start of the study period the subjects might have been ready for breakfast but they will have had absolutely no need (with a liver still full of glycogen) for the physiological insulin resistance adaptation to an absence of carbohydrate food intake such as would be necessitated by 40 hours of near fasting.

Subjects either drank 900kcal of soybean oil, started a 6h infusion of ~900kcal of intravenous soybean oil (Intralipid) or, for the control group, a 6h infusion containing approximately 54kcal of glycerol, ie mild fasting of 16h in total for the controls. Glycerol is primarily used by the liver for gluconeogensis so it will be a bit like the carbohydrate from the drink in the Cocoa study.

So Nowotny/Shulman  only looked at soybean oil vs nothing on a deliberately carbohydrate based metabolism of their mildly fasted control group. After carb loading to ensure a glucose based metabolism.

And soybean oil triggered insulin resistance. Glycerol didn't. QED, PUFA cause insulin resistance, directly. Diacylglycerols blah blah and all that crap as a mechanism, which is what the study seems to have been all about.

But the soybean oil was only being compared to a fully primed glucose based metabolism. Using an hyperinsulinaemic clamp and glucose supply to normoglycaemia.

In the Cocoa study the various fats were being compared to what was approaching a 40 hour fast. These subjects were already physiologically insulin resistant.

Adding more fat will (at approximately the correct 24h metabolic requirement for calories) either increase or decrease the degree of fasting insulin resistance based on Protons, the F:N ratio and reverse electron transport derived ROS.

Here PUFA cause a decrease in the physiological insulin resistance of 40 hours of fasting. Saturated fat augments it. MUFA is neutral:

You have to be very, very careful about what you are comparing to what.

Without thinking through the methods sections you could easily be forgiven for believing that the Nowotny/Shulman paper shows that PUFA cause insulin resistance. Possibly uniquely.

They clearly do, compared to to glucose. But they are *less* effective than saturated fats in performing the essential metabolic function of resisting insulin when glucose is in short supply. Shulman missed this, despite having Xiao point it out (*sarcasm warning*) in words of one syllable. PUFA are insulin sensitising when compared to whatever FFAs an obese person has available after nearly 40 hours of fasting.

Peter

Afterthought: The Cocoa SFA group required just under 40μmol/kg/min of glucose to maintain 20mmol/l in their plasma. The PUFA group needed about 55μmol/kg/min of glucose.

Given an infinite supply of donuts, which state would result in you eating the most?

Mmmmmm PUFA. The fat that makes you fat. By limiting insulin resistance.

Metformin (16) The LaMoia Shulman review

I first came across Gerard Shulman and his research group at Yale here:

Metformin suppresses gluconeogenesis by inhibiting mitochondrial glycerophosphate dehydrogenase

and, although they are now looking at other targets for metformin's action, mitochondrial glycerol-3-phosphate dehydrogenase inhibition appears to be adequate to explain most of its clinical features.

I finally looked up who he is because, while looking for papers about certain aspects of metformin, I found this comprehensive review paper:

Cellular and Molecular Mechanisms of Metformin Action

which contains the bias confirming lines:

"Taken together, these studies indicate that metformin’s effect to increase insulin-stimulated peripheral glucose uptake is secondary to improved glycemic control and reversal of glucose toxicity, which can mostly be attributed to metformin’s ability to directly inhibit hepatic gluconeogenesis and HGP."

My own turn of phrase was:

"It [metformin] *appears* to improve insulin sensitivity, lowering the plasma level of insulin and glucose, but this is because it inhibits hepatic gluconeogenesis via inhibiting mtG3Pdh. That drops hepatic glucose output and that is what lowers the insulin level." I'm slightly cautions about the glucotoxicity aspect.

If you want more of an idea about how Shulman works there is a relatively short interview here which gives the flavour.

https://www.youtube.com/watch?v=qXxZ-I9N7Kc

Obviously he needs to take about four more steps backwards up the course of insulin resistance before he reaches perilipins and basal lipolysis. Whether he will ever go a step further beyond that and realise how linoleic acid controls the adipocyte size which controls the perilipins is possibly another order of magnitude further away. He also has zero concept that insulin resistance, which he notes is utterly preserved across all of those metazoan species which use insulin (which is most of us), is a functionally protective mechanism. As in here:

Insulin resistance is a cellular antioxidant defense mechanism

Until you realise insulin resistance is an antioxidant defence mechanism you will keep trying to "cure" it.

Never the less, he's a bright guy.

Tracy LaMoia, who is first author on the above two author review, seems to be a recent addition to the Shulman lab and is deeply steeped in metformin function. To the point where she is first author of this paper in addition to the review:

Metformin, phenformin, and galegine inhibit complex IV activity and reduce glycerol-derived gluconeogenesis

I've yet to examine how convincing the complex IV part of the study might be, there's a lot to read, but it does pretty convincingly destroy any residual notion that metformin acts clinically by inhibiting complex I.

Or that a one millimolar or higher concentration of metformin is in any way related to clinical usage/efficacy. In fact actually measuring plasma metformin and reporting it in your research appears to be unusual.

This has consequences.

If you read any paper where they are using metformin at 1mM, 5mM or even 20mM to blockade complex I, crash ATP supply and thus activate AMPK, you can absolutely bin all of the cell culture sections of the paper. On diabetes, cancer, ageing etc. All of them. It is always the first thing I check.

Any section of such studies describing in-vivo work, be that mouse, rat or human, will give results that are likely to be believable. Though interpretation of the findings will be unreliable when swathes of the research population still mistakenly believe that metformin is an insulin sensitiser which works by blockade of complex I after being concentrated within mitochondria to 1000 times plasma level.

Which is preposterous. See piericidin A in LaMoia's paper above.

Peter