Complexity of NAC Action as an Antidiabetic Agent: Opposing Effects of Oxidative and Reductive Stress on Insulin Secretion and Insulin Signaling
Amongst the many, many things that this group did there is this section from Fig 9. They injected a set of mice with a dose of insulin typical for an insulin tolerance test. Fifteen minutes later they euthanised them and extracted muscle tissue for assessment of insulin signalling as represented by the phosphorylation of AKT. Half the mice had been on NAC in their drinking water, half hadn't. All were eating chow.
Here are the Western Blots
and here is the darkness of the blots converted to numerical form:
Both groups of mice received exactly the same dose of insulin, 0.75iu/kg, high enough to seriously kick the insulin signalling cascade but still with a fairly low incidence of serious hypoglycaemia. The intention is to get a near maximal insulin response *without* lethal hypoglycaemia.
If we go to the doodles from the last post this is what that dose is trying to achieve:
The 0.75iu/kg will produce *exactly* the same ROS signal in all of the mice, on or off of NAC. But in those mice on NAC a large proportion of the signalling ROS are simply mopped up by the NAC. So instead of getting the phosphorylation of AKT we expect we get much less:
The dose of insulin is identical, the ROS signal is identical but the NAC non specifically reduces those ROS which carry the onward signal.
The insulin effect is mediated through ROS, NAC limits it.
At low levels on insulin the small ROS signal would be completely wiped out.
At higher levels of exposure insulin will actually signal and should increase its downstream target activation, but not as effectively as it should. We're looking at the three points circled in red here if Fig 9B :
which are responsible for a significant increase in the AUC calculated for glucose.
The initial rise in glucose is unaffected by NAC, which might be surprising if you don't view it from the Protons perspective.
We are sightly stuck because we don't know the insulin exposure at times 15 and 30 minutes, which may not be comparable between the two groups.
We can guesstimate the insulin levels in the control group using the data from this paper for after a six hour fast. It looks like this, added on to the above. No units included for the insulin, it's the pattern I'm interested in:
Now, an OGTT is designed to elicit a maximal insulin response within the physiological range. A maximal physiological response will allow peak utilisation of glucose and, at some time point when combined with elevated plasma glucose, will produce insulin-induced insulin resistance as soon as the the mitochondrial delta psi rises high enough.
The signal to resist is, obviously, ROS.
A significant proportion of which disappears in to the soup of NAC so insulin-induced insulin resistance is blunted, so glucose continues to be disposed of at peak insulin. We're thinking about events somewhere within the time points circled in red:
If you choose your dose of NAC very carefully you can generate the above curves. This is NOT normality, this is balancing pharmacology against differing aspects of physiology.
How well this happens depends on your dose of NAC and probably on the metabolic state of your mice. Not all control groups are as free of metabolic disease as you might like.
Hence the results in JustPeachy's nice paper:
The Antioxidant N-Acetylcysteine Does Not Improve Glucose Tolerance or β-Cell Function in Type 2 Diabetes
I can't find a paper where NAC actually precipitated DMT2 but I had a vague recall that vitamin B3, a favourite of the orthomolecular practitioners, could occasionally precipitate glucose intolerance.
It turns out you need a massive study to pick up the small effect demonstrated in the second hour of the mouse OGTT above using the effective antioxidant B3 rather than NAC but I did find this bias-confirming meta-analysis (you know, one, two, skip a few, 99, 100):
Niacin therapy and the risk of new-onset diabetes: a meta-analysis of randomised controlled trials
Personally I avoid antioxidants. A few decent ROS is my preferred approach.
Niacin therapy and the risk of new-onset diabetes: a meta-analysis of randomised controlled trials
Personally I avoid antioxidants. A few decent ROS is my preferred approach.
Peter
13 comments:
That's a nice brain-bender. Thanks... Look at the time.
So pAkt upregulates glucose receptors, moving glucose into the cell and lowering blood gluccose.
NAC, by reducing pAkt should (and does, here) impair that process.
Is that correct?
In trying to figure out what you are talking about here, I can across two relevant papers
"NAC tended to decrease postexercise markers of the ROS/protein carbonylation ratio by −13.5% (P = 0.08) and increase the GSH/GSSG ratio twofold vs. CON (P < 0.05). Insulin sensitivity was reduced (−5.9%, P < 0.05) by NAC compared with CON without decreased phosphorylation of Akt or AS160.
"We conclude that NAC infusion attenuated muscle ROS and postexercise insulin sensitivity independent of Akt signaling. ROS also played a role in normal p70S6K phosphorylation in response to insulin stimulation in human skeletal muscle."
"Fatty Acid-Induced Insulin Resistance: Decreased Muscle PI3K Activation But Unchanged Akt Phosphorylation"
https://doi.org/10.1210/jcem.87.1.8187
And, in Intralipid-mediated insulin resistance:
"Despite the decrease in PI3K in the Intralipid study, no defect in Akt phosphorylation was found. In summary, NEFA-induced insulin resistance is associated with an impairment of IRS-1 tyrosine phosphorylation and IRS-1-associated PI3K activation. Down-regulation of IRS-1 levels is also impaired. The NEFA-induced defect in muscle glucose uptake appears to be a consequence of a defect in the insulin-signaling pathway leading to impaired PI3K activation. This in turn may lead to impaired glucose transport through an Akt-independent pathway because Akt phosphorylation was unaffected by elevated NEFA levels."
"Fatty Acid-Induced Insulin Resistance: Decreased Muscle PI3K Activation But Unchanged Akt Phosphorylation"
https://doi.org/10.1210/jcem.87.1.8187
Thoughts?
This is why metabolic research is getting nowhere:
“The NEFA-induced defect in muscle glucose uptake appears to be a consequence of a defect in the insulin-signaling”
There is no defect.
There is a precise, controlled regulation of glucose uptake by muscles cells, downward, by the exact amount *needed* to maintain energetic homeostasis. AKA the correct level of ROS. When AMKP is activated by exercise then fatty acid delivery and oxidation is increased. This *necessitates* an absolutely correct reduction of glucose entry in to the cells.
They can label this as “insulin resistance” or as a “defect” as much as they like but this merely reflects their total lack of understanding.
And, of course, palmitate or stearate would do the job of correctly controlling (downward) the ingress of glucose far better than the defective attempt made by linoleate.
Peter
So then what is T2DM? It's not just fat consumption.
My understanding is the central defect is insulin resistance in the liver, which results in excess glucose release leading to hyperglycemia.
With TPN it's a major issue:
"The increased risk of complications during TPN therapy can be related, among other factors, to the development of hyperglycemia, which occurs in 10–88% of hospitalized patients receiving TPN therapy (4,–6)." (Nice spread, right?).
https://doi.org/10.2337/dc09-1748
But, we can prevent it by changing the lipid infusion:
"Our conclusion was that Intralipid enhanced glucose production by increasing gluconeogenesis in preterm infants. This can be ascribed to the stimulatory effect of FFA in addition to any effect of glycerol alone. The lack of stimulation of gluconeogenesis in the Clinoleic vs. the Intralipid group suggests that different classes of fatty acids exert different effects on glucose kinetics in preterm infants."
"Stimulation of gluconeogenesis by intravenous lipids in preterm infants: response depends on fatty acid profile
https://doi.org/10.1152/ajpendo.00303.2005
Shouldn't Intralipid be producing less, not more, hyperglycemia?
So if you compare Intralipid to the higher-PUFA Omegaven (fish oil), it also produces worse outcomes.
" Intralipid treatment led to accumulation of acylcarnitines as a result of the released linoleic acid (C18:2-n6) and enhanced its integration into phospholipids, consistent with incomplete or impaired β-oxidation necessitating a compensatory increase in glucose oxidation. Accumulation of acylcarnitines was also associated with a higher nicotinamide adenine dinucleotide reduced/oxidized (NADH/NAD+) ratio, which inhibited pyruvate dehydrogenase (PDH), and resulted in excess lactate production. In contrast, Omegaven-treated hearts showed no acylcarnitine accumulation, low malonyl-CoA concentrations consistent with activated β-oxidation, and elevated PDH activity and glucose oxidation, together indicative of a higher metabolic rate possibly by substrate cycling."
10.1213/ANE.0000000000004838
Hi Tucker, for some reason Blogger keeps putting your comments in to spam and it's only when I get to reply and can't see them on the post that I realise. Duh. My bad.
Omegaven is simple. Mitochondria do not oxidise DHA. It goes to peroxisomes and they convert it to caprylic acid, extra-mitochondrial NADH and acetate. EPA is 50% diverted to peroxisomes so is only partly "seen" by mitochondria. Both are excellent uncouplers and do not need to be taken up to access UCPs to reduce insulin signalling. I would not expect them to cause hepatic insulin "resistance" unless it is via reduced ROS rather than increased ROS, ie EPA works on the lower left end of the NAC curves in the above posts.
The role of oleate vs linoleate for hepatic insulin resistance is exciting, explicable and will have to have its own post. But basically why does the liver become fatty? Obviously because it allows *excess* insulin signalling. ie we are talking inadequate ROS and lipid over distension. But, once the hepatocytes are over distended what happens next? This we don’t know directly. All we do know for certain is that they stop responding to insulin, so release glucose. Why do they stop responding to insulin?
Because they are oxidising fatty acids, of course. Why else should they resist insulin? You have, if you are me, to compare a lipid distended hepatocyte with a lipid distended adipocyte. You know, crown like structures, severe ROS generation and cell death. I strongly suspect that there is something resembling basal lipolysis in hepatocytes where distended lipid droplets release FFAs.
Oleate is far less effective at distending hepatocytes or adipocytes than linoleate, though of course neither resist this effect as well as palmitate or stearate would.
These are just my 24h thoughts but, experience tells me, that when the answers are as straight s forward as this, Pubmed tends to confirm them. You have to separate underlying cause from down stream effects.
No one, ever, gets fat from resisting insulin. The very idea is preposterous.
Peter
Then, again, what is T2DM?
What is the insulin resistance that we see in that condition?
It's clearly not just fat consumption.
Wanted to ask about this one. Why would iron chelation get rid of insulin resistance, and could this cause problems related to excessive insulin sensitivity down the line?
https://pubmed.ncbi.nlm.nih.gov/38173374/
@Tucker. Insulin resistance is the rejection of insulin facilitated caloric substrate ingress in to a cell when non insulin controlled caloric substrate is meeting a cell's substrate needs.
That's physiology.
It’s usually FFAs but can equally be ethanol or fructose.
What we call “insulin resistance” is a pathology of adipocytes which have been damaged by failing to resist insulin’s distention signal through LA’s failure to *adequately* resist insulin’s signal, ie too few ROS through too little FADH2.
This “leakage” (in reality this is a tightly controlled system to limit adipocyte distension to destruction, see crown-like structures) of FFAs from adipocytes continues to supply FFAs under circumstances where they *should* be suppressed by insulin. Insulin can’t suppress the process (though it can, given a pancreas of steel, force FFAs back in to adipocytes as a temporary patch on the problem).
This is adipocyte pathology causing the *necessity* (see paragraph one) of the utilisation of “resisting insulin” to maintain cellular energy homeostasis. ie correct ROS generation.
“Insulin resistance” in these terms is the correct physiological response to the supply of FFAs which should not be there, they are only there because adipocytes are leaking FFAs that cannot be suppressed by insulin.
The above “insulin resistance”, ie adipocyte pathology, converts to DMT2 when the pancreatic beta cells die through the excess ROS from FFA and glucose supply which cannot be correctly controlled in plasma.
With failing beta cell function glucose rises.
With glucose above 21mmol/l insulin is not needed for enough glucose to enter cells to meet all of their metabolic needs. With hypoinsulinaemia from beta cell dysfunction then FFAs really cannot be suppressed so every cell gets all of its needs from glucose (independent of insulin) plus a surfeit of FFAs and the mitochondrial delta psi will generate sufficient ROS to damage everything and keep producing those ROS until apoptosis is called in for a merciful end or necrosis happens for a painful end. Or a mix.
The problem stems from adipocytes. Protons explains the adipocyte problem. All else is downstream.
Peter
@Lev, later. Gotta go run now.
Is there a path from starch consumption to osteoarthritis in general population ie without any special genetics such as HLA subtype?
Dr Eades is writing again on how visceral fat is attacked by immune system as a foreign body and thereby promotes inflammation through the body. Is it all nonsense?
Probably nonsense in as far as he's missing the point. The immune cell doesn't "attack" visceral fat, it appropriately contains dying fat cells and tries to mitigate the damage done by runaway pyroptosis and whatnot, caused by distention, hypoxia, linoleic acid and whatever. See Peter's "size matters" post.
No specific information on that. Ebringer suggests that even HLAB27 -ve people may benefit from a low sartch, ie low carbohydrate (in most cases) diet. You could go on to anti inflammatory effects of ketones etc but that's switching the question around. So dunno...
Gyan & Lev. Yes and no. Dying visceral adipocytes produce the same signal as dying bacteria or dying virally infected cells. All you need to add is the explanation of *why* adipocytes are dying and you have the answer. He is correct. What he may or may not realise is that the reason that visceral adipocytes are particularly affected is that they are the most insulin *sensitive* adipocytes. So they get bigger faster and hit pyroptosis (or whatever you want to call it) more easily than sc adipocytes.
https://high-fat-nutrition.blogspot.com/2023/07/insulin-sensitivity-makes-you-fat.html
https://pubmed.ncbi.nlm.nih.gov/16567516/
People make the *massive* mistake of seeing the insulin resistance caused by the cytokine soup of crown cells and thinking this insulin resistance is *causal* of visceral obesity.
That's a boo boo. I may have mentioned this before but the concept that insulin resistance makes you fat is preposterous.
This is very, very complicated and has been on the periphery of my thinking for many years. It's not just iron. In chronic hepatopathies Cu builds up as a secondary change. You have to also consider the aluminium which accumulates in Alzheimers. Are they there to generate ROS?
It's almost as if physiology is trying to instigate insulin resistance when all else has failed. And the desperation attempt turns in to pathology when the poorly controlled ROS which the metal ions generate turn in to a serious boo boo when surrounded by tissues saturated with linoleic acid.
Just a vague feeling. But we know, and it's well articulated by Tucker, that ferroptosis is just a code word for linoleate intoxication. Are the metal ions harmless without the PUFA? Are they even needed, if we countenance that they are a functional part of physiology while physiology is functioning correctly?????
Hmmmmm
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