Insulin Is an Anti-inflammatory and Anti-atherosclerotic Hormone

Insulin Is an Anti-inflammatory and Anti-atherosclerotic Hormone  (full text free until end of the month)

Fasting hyperinsulinemia is associated with an increased risk of atherosclerotic complications of heart attack and stroke. This has resulted in the concept that insulin may promote atherosclerosis in spite of the absence of any evidence that insulin is atherogenic either in the human or in experimental models. Recent evidence shows that insulin exerts vasodilatory, anti-platelet and anti-inflammatory effects at the cellular level in vitro and in the human in vivo. Since atherosclerosis is a chronic inflammatory process of the arterial wall, insulin may be potentially anti-atherosclerotic in the long term. More recent data on experimental atherosclerosis in the mouse shows that (1) insulin administration reduces the number and the size of atherosclerotic lesions in apo E null mice and (2) in IRS-2 null mice, the interruption in insulin signal transduction results in enhanced atherogenicity. Finally, the use of a low dose of insulin infusion in patients with acute myocardial infarction has been shown to markedly improve clinical outcomes, both in diabetic and nondiabetic patients. Our own most recent data show that a low dose infusion of insulin in patients with acute myocardial infarction induces a reduction in nflammation (C-reactive protein and serum amyloid A) and oxidative stress, and promotes fibrinolysis. We conclude that insulin is anti-inflammatory and potentially antiatherogenic and may be of use in the treatment of cardiovascular inflammatory conditions.
It seems that the demonization of insulin has followed much the same path as the correlation = causality logic of LDL and atherosclerosis.  Elevated LDL correlates with CVD, but there is not a whole lot of actual evidence demonstrating that the LDL itself directly causing atherosclerosis.   LDL remains a fairly reliable marker for determining risk (though it must be considered along with other factors), and whatever the flaws (and there are many) in cholesterol theories, this shouldn't be ignored out of hand.  If A causes B, and A causes C, then someone with B likely has C.

So with the insulin, we have hyperinsulinemia correlating with CVD, but as stated in the abstract above, there's little evidence that it causes it directly.  The "A" in this scenario seems to be elevated free fatty acids (NEFA/FFA) leading to "B" = hyperinsulinemia and "C" = atherosclerosis.  But in this case the correlation/causation connection may be even more convoluted.  Because there's an intermediate factor in all this -- the ever-increasingly apparent root of all evil: insulin resistance.  The way I see it is this:  Fat stores exceeding an individual's storage capacity lead to IR of the fat cells and/or excessive release of NEFA.  Elevated NEFA induces IR in peripheral tissues.  It is cellular resistance to insulin's inhibitory roles  in these cells that ultimately lead to metabolic dysfunction and/or cell damage/death.  In this regard, the relationship is not so much one of insulin not being the cause of atherosclerosis, etc., but the resistance masks the fact that it would appear that insulin is actually protective against it!  

Inflammation, shmimflamation!  :
Atherosclerosis is an inflammatory process.7 All the major classical risk factors for atherosclerosis, hypercholesterolemia, diabetes, hypertension, smoking, and menopause are associated with (and probably cause) inflammation. If high insulin levels are atherogenic, one would expect it also to exert part of its negative effect on the vessel wall through inflammatory processes. Recent evidence which we shall now review shows that just the opposite is the case, i.e., that insulin is anti-inflammatory.
The article goes on to summarize such research.  I'll let the more science minded read that for themselves (heck, I'm just too lazy at the moment to do a decent summary), but this section concludes with:
In view of the anti-inflammatory and vasodilatory effect of insulin, insulin resistance may be expected to be pro-inflammatory and a proconstrictor state. This indeed is the case.  Obesity,31 type 2 diabetes,32 and other insulin resistant states, such as polycystic ovary syndrome (PCOS),33 are pro-inflammatory and are associated with abnormal vascular reactivity and platelet hyperaggregability.  (clumping & clotting)
........... Insulin sensitizers have been shown to exert anti-inflammatory43–46 and anti-atherosclerotic effects.47,48  Thiazolidinediones (TZD) exert anti-inflammatory effects at the molecular and cellular levels. 
The article goes on to conclude as follows:

These facts, should encourage us to increase our understanding of these novel effects of insulin so that
(1) we have an improved conceptualization of inflammation in states of insulin resistance and the relationship of these states to atherogenesis;
(2) we explore the potential therapeutic role of insulin in inflammatory conditions, such as acute myocardial infarction; and
(3) we investigate novel potential therapeutic application of insulin sensitizers such as thiazolidinediones as anti-inflammatory agents.
I broke these out in more bullet form to address them.

(1)  I take this to mean the lipid hypothesizers need to rethink as much as the carbohydrate hypothesizers do. Both need to re-think the role of dietary composition (and total intake) in terms of its impact on insulin SENSITIVITY, not insulin per se.

(2)  Insulin is, as Martha Stewart would say, a GOOD thing.  There's much promise in using it.  Insulin therapies have evolved from slow acting secretagogues (substances that enhance insulin secretion), to pumps delivering a more consistent, physiological basal level in T1's etc.

(3)  OK, I'm probably in agreement with many who disdain the whole "this gives us more reason to look into more drugs" angle, but we have to be pragmatic about it.  A Type 1 does not make insulin.  In that regard, whatever technology allows them to mimic insulin levels in a normal person, I would be grateful for it.  Type 2 is a far more varied diagnosis as the degree of irreversible damage (as opposed to suppressed function) cannot be assessed with mere fasting glucose levels or tolerance tests.   If you're hyperinsulinemic, you still have functional beta cells.  Temporarily giving them a rest with LC while you lose weight and reverse the IR that is causing the elevated insulin is a great strategy.  But if you cannot adhere to this, or if LC doesn't result in the desired weight loss, then it may well be worthwhile to at least temporarily look into pharmaceutical intervention that allows for insulin to "do its thing".  I wonder, even, if insulin might be helpful to the hyperinsulinemic T2 -- enough exogenous insulin may keep the pancreas from having to work overtime to produce the elevated levels that your body is telling it to anyway.  There's nothing about the hormone -- in and of itself -- that is deleterious!!!!!!!!


Melchior Meijer said…
Interesting! Thanks for creating some more confusion ;-). What do make of this?

In vivo studies in dogs [30], rabbits [31] and chickens
[32] provide further evidence that insulin promotes athero-
genesis. Non-diabetic chickens fed a high-cholesterol diet
develop severe atherosclerosis, which regresses when
switched to low-cholesterol diet [32]. Insulin administration
when the low-cholesterol diet was instituted prevented
regression of coronary atherosclerosis. Alloxan-induced
diabetic rabbits fed a high-cholesterol diet developed
marked hypercholesterolaemia, but their aorta remained
free of atherosclerotic plaque [31]. If rabbits are treated
with insulin, severe atherosclerosis develops. Dogs receiv-
ing a low-dose insulin infusion into a hindlimb artery (to
cause local, physiological hyperinsulinaemia) developed
severe femoral atherosclerosis, whereas all other arteries
remained free of atherosclerotic plaque [30]. Rats chroni-
cally (7–10 days) infused with insulin while maintaining
euglycaemia became markedly resistant to the stimulation
of glucose uptake and suppression of plasma NEFA by
insulin [23], and became hypertensive [33].
Melchior Meijer said…
Wow CarbSane, this smart thing was done just around my corner (Groningen, Netherlands). Havne’t seen the whole paper yet, so amount of exogenous insulin could reflect insulin resistance (impaired signaling).

High cumulative insulin exposure: a risk factor of atherosclerosis in type 1 diabetes?
(2005) Muis, M.J.; Bots, M.L.; Bilo, H.J.G.; Hoogma, R.P.L.M.; Hoekstra, J.B.L.; Grobbee, D.E.; Stolk, R.P.

Background: Since insulin therapy might have an atherogenic effect, we studied the relationship between cumulative insulin dose and atherosclerosis in type 1 diabetes. We have focused on patients with type 1 diabetes instead of type 2 diabetes to minimise the effect of insulin resistance as a potential confounder. Methods: An observational study was performed in 215 subjects with type 1 diabetes treated with multiple insulin injection therapy. Atherosclerosis was assessed by measurement of carotid intima-media thickness (CIMT). Results: The cumulative dose of regular insulin showed a positive and significant relation with CIMT: increase of 21 mu m in CIMT per S.D. of insulin use (95% CI: 8-35 adjusted for gender and age), which remained unchanged after adjustment for duration of diabetes, HbA1c, BMI, pulse pressure. physical activity and carotid lumen diameter. A similar relation was found for intermediate-acting insulin: 15.5 mu m per S.D. (2-29), which was no longer present after further adjustment. Conclusions: These findings provide evidence that a high cumulative dose of regular insulin is a risk factor for atherosclerosis. (c) 2005 Elsevier Ireland Ltd. All rights reserved
Melchior Meijer said…
An MI is a massive trauma, creating a massive stress response and huge insulin resistance. In cases of trauma, overcoming the resistance by jacking in a large bolus of insulin can be life saving. In all other cases hyperinsulinaemia might be not so good...
CarbSane said…
Lots of food for thought there Melchior and I'll get back to you with some thoughts when I get a chance.

But that last comment you made stuck out at me: "hyperinsulinaemia might be not so good", and I wanted to respond to that. I most certainly don't believe it is good. The article just questions whether it is the insulin itself that is "bad" when elevated chronically through normal physiological means (however dysfunctional, still obtainable w/o outside influence in a living human).
Melchior Meijer said…
Yes CarbSane, I understand that. Your very important question is if the bad things associated with chronic hyperinsulinaemia are due to insulin resistance, the hyperinsulinaemia per se or both. You suggest (or mention the possibility of) treating hyperinsuliaemic type 2's with insulin, right? This just flies so strongly into the face of what I think to know, that I reacted a bit strong ;-). But I don't say you're wrong! I don't know. I do know that tight control (with insulin) worsens outcome, despite improved HbA1c's. Have to dig around for the ref.

I wonder how the authors of 'your' paper can state this:

" spite of the absence of any evidence that insulin is atherogenic either in the human or in experimental models..."

Regarding inflammation: Vioxx is anti inflammatory, but increases the risk of MI. I don't think inflammation is ever causal. Inflammation is a normal response to injury or infection. Something makes the process to overshoot in some situations. What?

My highly uneducated guess:

HPA axis dysfunction
Fructose overload
PUFA overload
Large amounts of grass seed lectins (you may shoot!)
Persistent infections
Iron overload

That's why I personaly still go for a 'paleo' WOE, without paying any attention to carbs (I mean, I don't restrict them purposely). And I'm not bleeding enough ;-).
LynMarie Daye said…
"Regarding inflammation: Vioxx is anti inflammatory, but increases the risk of MI. I don't think inflammation is ever causal. Inflammation is a normal response to injury or infection."

I must admit, that's a very good point! Now you have me wondering about aspirin. Does aspirin help prevent MI because of it's anti-inflammatory effects or it's anti-clotting effects? In an acute situation, it's most likely the anti-clotting effects that are at play, but over the long-term? I would have said the anti-inflammatory effects, but now I'm not so sure. Something to mull over... :)
Melchior Meijer said…
I must admit that Vioxx is not an entirely honest expample. The reason it induces MI’s is because it greatly increases clotting. A hugely increased clotting tendency could probably ‘outperform’ the best anti inflammatory effect, even if inflammation was a root cause.

Maybe statins are a better example. If you assume that the etiology of diabetes is mainly inflammatory, you would expect statins to protect against it. Statins have powerful anti inflammatory pleiotropic effects. Yet especially rosuvastatin (Crestor) nicely destroys beta cell function. Statins also complicate (and maybe increase) atherosclerotic plaques. They make them less vulnerable though, less prone to rupture.
CarbSane said…
Melchior. First, please don't every worry over any "strong" response! This is SUCH a critical issue and I am so very glad that you are contributing in this manner to make me think! I'm going to respond to these seeming contradictions in a separate post in the next day or so addressing your links and including some other stuff I've come across. The more I read, the more I believe we do a disservice even calling these two different diseases both diabetes (meaning Type 1 & Type 2). Even within the T2 population there seems to be a great variety in physiology that can produce the same symptoms and yet should be treated differently.