Biguanides and thiazolidinediones inhibit stimulated lipolysis in human adipocytes through activation of AMP-activated protein kinase

Abstract

Aims/hypothesis In rodent adipocytes, activated AMPactivated protein kinase reduces the lipolytic rate. As the hypoglycaemic drugs metformin and thiazolidinediones activate this enzyme in rodents, we tested the hypothesis that in addition to their known actions they could have an anti-lipolytic effect in human adipocytes. Methods Adipose tissue was obtained from individuals undergoing plastic surgery. Adipocytes were isolated and incubated with lipolytic agents (isoprenaline, atrial natriuretic peptide) and biguanides or thiazolidinediones. Lipolysis was quantified by the glycerol released in the medium. AMPactivated protein kinase activity and phosphorylation state were determined using standard procedures. Results In human adipocytes, isoprenaline and atrial natriuretic peptide stimulated the lipolytic rate three-to fourfold. Biguanides and thiazolidinediones activated AMPactivated protein kinase and inhibited lipolysis by 30-40%, at least in part by inhibiting hormone-sensitive lipase translocation to the lipid droplet. Inhibition of AMPactivated protein kinase by compound C precluded this inhibitory effect on lipolysis. Stimulation of lipolysis also induced an activation of AMP-activated protein kinase concomitant with a drop in ATP concentration. Conclusions/interpretation We show for the first time in human adipocytes that biguanides and thiazolidinediones activate AMP-activated protein kinase, thus counteracting lipolysis induced by lipolytic agents. In addition, β-agonistor ANP-stimulated lipolysis increases AMP-activated protein kinase activity. This is because of an increase in the AMP/ATP ratio, linked to activation of some of the released fatty acids into acyl-CoA. AMP-activated protein kinase activation could represent a physiological means of avoiding a deleterious drain of energy during lipolysis but could be used to restrain pharmacological release of fatty acids.

AMP-activated protein kinase is activated in adipose tissue of individuals with type 2 diabetes treated with metformin: a randomised glycaemia-controlled crossover study

“…Gliclazide had no effect on AMPK activity in 3T3-L1 adipocytes and has been reported to increase plasma adiponectin concentrations in individuals with type 2 diabetes [33], whereas we have shown that metformin is capable of directly stimulating 3T3-L1 adipocyte AMPK activity. This latter observation is in agreement with previous reports in 3T3-L1 adipocytes [34] and isolated human subcutaneous adipocytes stimulated with metformin in vitro [35]. These data argue against the possibility that gliclazide Fig.…”

“…In contrast, incubation of 3T3-L1 adipocytes with metformin caused a robust stimulation of the equivalent phosphorylation site in mouse HSL (Ser565) and a recent study has demonstrated that ex vivo stimulation of isolated human adipocytes with metformin attenuated isoprenaline and atrial natriuretic peptide (ANP)-stimulated lipolysis without affecting basal lipolysis. Furthermore, metformin stimulated HSL Ser554 phosphorylation under ANPstimulated conditions, although the effect of metformin alone was not reported [35]. One explanation for the discrepancy between the effects observed in isolated or cultured cells and our in vivo study is likely to be the differing concentrations of metformin used in each case and the very different durations of exposure.…”

“…As AMPK activation in adipocytes has been associated with attenuated lipolysis [6][7][8]35], attenuated differentiation of pre-adipocytes into mature adipocytes [13,46] and reduced insulin-stimulated glucose transport in adipocytes [14][15][16], such effects may act to divert energy away from storage as lipid and stimulate glucose use by skeletal muscle. Furthermore, as stimulation of AMPK in vascular cells and macrophages has been demonstrated to elicit antiinflammatory effects that would also be beneficial in type 2 diabetes [28,45,47,48], stimulation of adipose AMPK in both the adipocyte and stromal/vascular cell fractions of adipose may explain some of the beneficial metabolic effects of metformin in patients with type 2 diabetes.…”

Anti-inflammatory Effects of Thiazolidinediones in Human Airway Smooth Muscle Cells

“…Both antagonists prevented the AICAR-induced activation of AMPK, as assessed by the Thr 172 phosphorylation of AMPK ( Figure 7A), indicating that they were active at the concentrations administered. Both compounds were also shown to inhibit the TZD-induced activation of AMPK in other cell types (72,73). However, they did not reverse the effects of TZDs on the release of inflammatory mediators from HASM cells (Figures 7B and 7C).…”

Augmenting energy expenditure by mitochondrial uncoupling: a role of AMP-activated protein kinase

“…It has been found in rodent adipocytes that lipolytic and cAMP-elevating stimuli increase AMPK activity, while its activation by AICAR or phenformin strongly reduces isoproterenol-induced lipolysis and fatty acid release (Daval et al 2005). In human adipocytes, b-adrenergic stimulation of lipolysis was found to be down-regulated by concomitant activation of AMPK through TZDs (Bourron et al 2010). Overall, acute AMPK activation in adipose tissue leads to an inhibition of both lipogenesis and lipolysis, whereas it increases fatty acid oxidation and glucose transport (Viollet et al 2009;Daval et al 2006).…”