I first went looking for papers on Acipimox in 2014. I had read that it was an inhibitor of lipolysis and I was interested in how much weight gain it caused. Back in those days I was still fairly attached to the most basic of carbohydrate-insulin-models of obesity. If you consider that insulin causes weight gain by the inhibition of lipolysis, giving a non-insulin inhibitor of lipolysis should do the same... Shouldn't it?
Well, no, it doesn't. Acipimox produces a profound fall in free fatty acids and a marked improvement in glucose tolerance. Very, very occasionally I found snippets in discussion fora that it could increase hunger but this was not by any means routine. These give the flavour:
Effect of the Antilipolytic Nicotinic Acid Analogue Acipimox on Whole-Body and Skeletal Muscle Glucose Metabolism in Patients with Non-insulin-dependent Diabetes Mellitus
Effect of a Sustained Reduction in Plasma Free Fatty Acid Concentration on Intramuscular Long-Chain Fatty Acyl-CoAs and Insulin Action in Type 2 Diabetic Patients
All of which sounds very good (unless you are into the CIM of obesity!) and you have to wonder quite why Acipimox has not become standard of care and have largely reversed the current global diabetes pandemic. In fact, a recent 2020 meta-analysis of niacin (the parent compound from which Acipimox is derived) trials suggests we might be remiss in failing to do so:
But then you could go on to ask why giving niacin itself might actually make people with impaired glucose tolerance flip in to frank type two diabetes (amongst other medical catastrophes) with worrying regularity
Effects of extended-release niacin with laropiprant in high-risk patients
Of course you could blame the laropiprant, given to suppress the niacin flushing. Or you could more usefully think about the metabolic consequences of dropping plasma FFAs by using a potent inhibitor of lipolysis.
If we work on the basis that DMT2 is essentially the down stream consequence of the inability of distended adipocytes to limit basal lipolysis, it comes as no surprise that artificially shutting down release of FFAs might improve markers of metabolic health.
The cost would be larger adipocytes.
But this doesn't happen, at least not much. The explanation is contained in this paper from 1992, largely looking at the reasons for the long term failure of Acipimox to control FFA levels:
It's simple. Making adipocytes retain their lipids increases their size. There is no suggestion that tolerance develops to this. All that happens is that there is a rebound increase in basal lipolysis as the Acipimox wears off. The drug-induced transient fall in FFAs produces a transient decrease in the oversupply of calories from FFAs, so cells should and must adapt to by reducing insulin resistance. Numbers improve at the cost of bigger adipocytes. As soon as the drug wears off the adipocytes, now bigger, reinstate basal lipolysis at their previous high rate plus some extra due to the extra distending effect of Acipimox. As they off-load their extra size by releasing FFAs, the physiological need of other cells in the body to resist insulin is both restored and augmented.
There is no net benefit and all the drug might do, if it does produce any increase in adipocyte size, is to convert IGT people, with some reserve function remaining in their adipocytes, in to very sightly heavier diabetics who have less ability to suppress adipocyte size-induced increased basal lipolysis.
If you are pre diabetic but not glycosuric and you become glycosuric in the periods between Acipimox/niacin doses you will convert from pre-diabetic to diabetic, assuming you use glycosuria as your marker for diabetes.
Peter